ASPEN PLUS Unit Operation Models 11-1

Part Number: Aspen Plus® 11.1 September 2001 Copyright (c) 1981-2001 by Aspen Technology, Inc. All rights reserved. Aspen Plus®, Aspen Properties®, Aspen Engineering Suite™, AspenTech®, ModelManager™, the aspen leaf logo and Plantelligence are trademarks or registered trademarks of Aspen Technology, Inc., Cambridge, MA. ™

™

BATCHFRAC and RATEFRAC are trademarks of Koch Engineering Company, Inc. All other brand and product names are trademarks or registered trademarks of their respective companies. This manual is intended as a guide to using AspenTech's software. This documentation contains AspenTech proprietary and confidential information and may not be disclosed, used, or copied without the prior consent of AspenTech or as set forth in the applicable license agreement. Users are solely responsible for the proper use of the software and the application of the results obtained. Although AspenTech has tested the software and reviewed the documentation, the sole warranty for the software may be found in the applicable license agreement between AspenTech and the user. ASPENTECH MAKES NO WARRANTY OR REPRESENTATION, EITHER EXPRESSED OR IMPLIED, WITH RESPECT TO THIS DOCUMENTATION, ITS QUALITY, PERFORMANCE, MERCHANTABILITY, OR FITNESS FOR A PARTICULAR PURPOSE.

Corporate Aspen Technology, Inc. Ten Canal Park Cambridge, MA 02141-2201 USA Phone: (1) (617) 949-1021 Toll Free: (1) (888) 996-7001 Fax: (1) (617) 949-1724 URL: http://www.aspentech.com

Division Design, Simulation and Optimization Systems Aspen Technology, Inc. Ten Canal Park Cambridge, MA 02141-2201 USA Phone: (617) 949-1000 Fax: (617) 949-1030

Contents For More Information......................................................................................................... xi Technical Support ............................................................................................................xiii Contacting Customer Support .............................................................................. xiii Hours ....................................................................................................................xiii Phone.................................................................................................................... xiv Fax......................................................................................................................... xv E-mail .................................................................................................................... xv

Mixearn sSdplitters

1-1

Mixer Reference...............................................................................................................1-2 Flowsheet Connectivity for Mixer ....................................................................... 1-2 Specifying Mixer..................................................................................................1-3 EO Usage Notes for Mixer...................................................................................1-4 FSplit Reference...............................................................................................................1-5 Flowsheet Connectivity for FSplit ....................................................................... 1-5 Specifying FSplit..................................................................................................1-6 EO Usage Notes for FSplit...................................................................................1-7 SSplit Reference...............................................................................................................1-8 Flowsheet Connectivity for SSplit ....................................................................... 1-8 Specifying SSplit..................................................................................................1-8

Separators

2-1

Flash2 Reference .............................................................................................................. 2-2 Flowsheet Connectivity for Flash2 ......................................................................2-2 Specifying Flash2.................................................................................................2-3 EO Usage Notes for Flash2..................................................................................2-3 Flash3 Reference .............................................................................................................. 2-4 Flowsheet Connectivity for Flash3 ......................................................................2-4 Specifying Flash3.................................................................................................2-5 Decanter Reference .......................................................................................................... 2-6 Flowsheet Connectivity for Decanter...................................................................2-6 Specifying Decanter 2-7 EO Usage Notes for ............................................................................................. Decanter ..............................................................................2-9 Sep Reference.................................................................................................................2-10 Flowsheet Connectivity for Sep ......................................................................... 2-10

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Specifying Sep....................................................................................................2-10 EO Usage Notes for Sep.....................................................................................2-11 Sep2 Reference...............................................................................................................2-12 Flowsheet Connectivity for Sep2 ....................................................................... 2-12 Specifying Sep2..................................................................................................2-12 EO Usage Notes for Sep2...................................................................................2-13

HE ea xc t hangers

3-1

Heater Reference .............................................................................................................. 3-2 Flowsheet Connectivity for Heater ......................................................................3-2 Specifying Heater.................................................................................................3-3 EO Usage Notes for Heater..................................................................................3-3 HeatX Reference .............................................................................................................. 3-4 Flowsheet Connectivity for HeatX.......................................................................3-5 Specifying HeatX ................................................................................................. 3-6 EO Usage Notes for HeatX ................................................................................ 3-18 MHeatX Reference.........................................................................................................3-19 Flowsheet Connectivity for MHeatX .................................................................3-19 Specifying MHeatX............................................................................................3-20 Hetran Reference............................................................................................................3-23 Flowsheet Connectivity for Hetran ....................................................................3-23 Specifying Hetran...............................................................................................3-24 Aerotran Reference ........................................................................................................3-25 Flowsheet Connectivity for Aerotran.................................................................3-25 Specifying Aerotran ...........................................................................................3-26 HxFlux Reference ..........................................................................................................3-27 Flowsheet Connectivity for HxFlux...................................................................3-27 Specifying HxFlux ............................................................................................. 3-27 Convective Heat Transfer...................................................................................3-28 Log-Mean Temperature Difference ...................................................................3-28 EO Usage Notes for HXFlux .............................................................................3-28 HTRI-Xist Reference ..................................................................................................... 3-29 Flowsheet Connectivity for HTRI-Xist..............................................................3-29 Specifying HTRI-Xist ........................................................................................ 3-30

Columns

4-1

DSTWU Reference ..........................................................................................................4-3 Flowsheet Connectivity for DSTWU...................................................................4-4 Specifying DSTWU ............................................................................................. 4-4 Distl Reference.................................................................................................................4-5 Flowsheet Connectivity for Distl ......................................................................... 4-5 Specifying Distl....................................................................................................4-6 SCFrac Reference.............................................................................................................4-7 Flowsheet Connectivity for SCFrac ..................................................................... 4-7 Specifying SCFrac................................................................................................4-8 RadFrac Reference ........................................................................................................... 4-9

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C on t en ts

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Flowsheet Connectivity for RadFrac..................................................................4-11 Specifying RadFrac ............................................................................................ 4-12 EO Usage Notes for RadFrac ............................................................................. 4-17 Free-Water and Rigorous Three-Phase Calculations ......................................... 4-18 Efficiencies.........................................................................................................4-19 Algorithms..........................................................................................................4-20 Rating Mode.......................................................................................................4-21 Design Mode ...................................................................................................... 4-22 Reactive Distillation...........................................................................................4-23 Solution Strategies..............................................................................................4-24 Physical Properties ............................................................................................. 4-26 Solids Handling..................................................................................................4-26 Sizing and Rating of Trays and Packings...........................................................4-27 MultiFrac Reference.......................................................................................................4-28 Flowsheet Connectivity for MultiFrac ...............................................................4-30 Specifying MultiFrac..........................................................................................4-31 Efficiencies.........................................................................................................4-38 Algorithms..........................................................................................................4-39 Rating Mode.......................................................................................................4-39 Design Mode ...................................................................................................... 4-39 Column Convergence.........................................................................................4-40 Physical Properties ............................................................................................. 4-42 Free Water Handling .......................................................................................... 4-43 Solids Handling..................................................................................................4-43 Sizing and Rating of Trays and Packings...........................................................4-43 PetroFrac Reference ....................................................................................................... 4-44 Flowsheet Connectivity for PetroFrac................................................................4-46 Specifying PetroFrac .......................................................................................... 4-48 Efficiencies.........................................................................................................4-52 Convergence.......................................................................................................4-53 Rating Mode.......................................................................................................4-54 Design Mode ...................................................................................................... 4-54 Physical Properties ............................................................................................. 4-55 Free Water Handling .......................................................................................... 4-55 Solids Handling..................................................................................................4-55 Sizing and Rating of Trays and Packings...........................................................4-56 EO Usage Notes for PetroFrac...........................................................................4-56 RateFrac Reference ........................................................................................................ 4-57 Flowsheet Connectivity for RateFrac.................................................................4-59 The Rate-Based Modeling Concept ...................................................................4-60 Specifying RateFrac ........................................................................................... 4-62 Mass and Heat Transfer Correlations.................................................................4-71 References .......................................................................................................... 4-77 BatchFrac Reference ...................................................................................................... 4-78 Flowsheet Connectivity for BatchFrac...............................................................4-80 Specifying BatchFrac ......................................................................................... 4-80


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Column Setup.....................................................................................................4-80 Column Operation..............................................................................................4-81 Free-Water and Rigorous Three-Phase Calculations ......................................... 4-81 Reactive Distillation...........................................................................................4-82 Physical Property Specifications........................................................................4-82 Feed Conventions...............................................................................................4-83 Extract Reference ........................................................................................................... 4-84 Flowsheet Connectivity for Extract....................................................................4-85 Specifying Extract..............................................................................................4-85 EO Usage Notes for Extract ............................................................................... 4-86

Reactors

5-1

RStoic Reference..............................................................................................................5-3 Flowsheet Connectivity for RStoic ...................................................................... 5-3 Specifying RStoic.................................................................................................5-4 EO Usage Notes for RStoic..................................................................................5-6 RYield Reference ............................................................................................................. 5-7 Flowsheet Connectivity for RYield......................................................................5-7 Specifying RYield ................................................................................................ 5-8 EO Usage Notes for RYield ................................................................................. 5-8 REquil Reference ............................................................................................................. 5-9 Flowsheet Connectivity for REquil......................................................................5-9 Specifying REquil .............................................................................................. 5-10 RGibbs Reference ..........................................................................................................5-11 Flowsheet Connectivity for RGibbs...................................................................5-11 Specifying RGibbs .............................................................................................5-12 References .......................................................................................................... 5-15 RCSTR Reference .......................................................................................................... 5-16 Flowsheet Connectivity for RCSTR ..................................................................5-16 Specifying RCSTR.............................................................................................5-17 RPlug Reference.............................................................................................................5-20 Flowsheet Connectivity for RPlug ..................................................................... 5-20 Specifying RPlug................................................................................................5-22 RBatch Reference...........................................................................................................5-24 Flowsheet Connectivity for RBatch ...................................................................5-24 Specifying RBatch..............................................................................................5-25

PressuCrh e angers

6-1

Pump Reference ............................................................................................................... 6-2 Flowsheet Connectivity for Pump........................................................................6-3 Specifying Pump .................................................................................................. 6-3 EO Usage Notes for Pump ................................................................................... 6-7 Compr Reference..............................................................................................................6-8 Flowsheet Connectivity for Compr......................................................................6-9 Specifying Compr ................................................................................................6-9 EO Usage Notes for Compr ...............................................................................6-12

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MCompr Reference........................................................................................................6-13 Flowsheet Connectivity for MCompr ................................................................6-14 Specifying MCompr...........................................................................................6-15 References .......................................................................................................... 6-18 Valve Reference ............................................................................................................. 6-19 Flowsheet Connectivity for Valve......................................................................6-19 Specifying Valve................................................................................................6-19 Reference............................................................................................................6-27 Pipe Reference................................................................................................................6-28 Flowsheet Connectivity for Pipe ........................................................................ 6-29 Specifying ..................................................................................................6-29 Two-Phase Pipe Correlations ..................................................................................... 6-32 Pipeline Reference..........................................................................................................6-33 Flowsheet Connectivity for Pipeline .................................................................. 6-34 Specifying Pipeline ............................................................................................6-35 Two-Phase Correlations ..................................................................................... 6-39 Closed-Form Methods........................................................................................6-41 References .......................................................................................................... 6-42

Manipulators

7-1

Mult Reference.................................................................................................................7-2 Flowsheet Connectivity for Mult .........................................................................7-2 Specifying Mult....................................................................................................7-2 EO Usage Notes for Mult.....................................................................................7-3 Dupl Reference.................................................................................................................7-4 Flowsheet Connectivity for Dupl ......................................................................... 7-4 Specifying Dupl....................................................................................................7-5 EO Usage Notes for Dupl.....................................................................................7-5 ClChng Reference ............................................................................................................ 7-6 Flowsheet Connectivity for ClChng.....................................................................7-6 Specifying ClChng ............................................................................................... 7-6 Analyzer Reference..........................................................................................................7-7 Flowsheet Connectivity for Analyzer ..................................................................7-8 Specifying Analyzer.............................................................................................7-8 EO Usage Notes for Analyzer..............................................................................7-8 Feedbl Reference..............................................................................................................7-9 Selector Reference..........................................................................................................7-10 Flowsheet Connectivity for Selector..................................................................7-10 Specifying Selector ............................................................................................7-10 EO Usage Notes for Selector .............................................................................7-11 Qtvec Reference ............................................................................................................. 7-12 Flowsheet Connectivity for Qtvec......................................................................7-12 Specifying Qtvec................................................................................................7-12 Measurement Reference.................................................................................................7-14


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Solids

8-1

Crystallizer Reference ...................................................................................................... 8-3 Flowsheet Connectivity for Crystallizer ..............................................................8-3 Specifying Crystallizer.........................................................................................8-4 References ............................................................................................................ 8-9 Crusher Reference..........................................................................................................8-10 Flowsheet Connectivity for Crusher ..................................................................8-10 Specifying Crusher.............................................................................................8-11 References .......................................................................................................... 8-14 Screen Reference............................................................................................................8-15 Flowsheet Connectivity for Screen ....................................................................8-15 Specifying Screen...............................................................................................8-15 Reference............................................................................................................8-17 FabFl Reference ............................................................................................................. 8-18 Flowsheet Connectivity for FabFl......................................................................8-18 Specifying FabFl ................................................................................................ 8-18 References .......................................................................................................... 8-21 Cyclone Reference ......................................................................................................... 8-22 Flowsheet Connectivity for Cyclone..................................................................8-22 Specifying Cyclone ............................................................................................ 8-23 References .......................................................................................................... 8-28 VScrub Reference ..........................................................................................................8-29 Flowsheet Connectivity for VScrub...................................................................8-29 Specifying VScrub .............................................................................................8-30 References .......................................................................................................... 8-31 ESP Reference................................................................................................................8-32 Flowsheet Connectivity for ESP ........................................................................ 8-32 Specifying ESP...................................................................................................8-33 References .......................................................................................................... 8-35 HyCyc Reference ........................................................................................................... 8-36 Flowsheet Connectivity for HyCyc....................................................................8-36 Specifying HyCyc .............................................................................................. 8-37 References .......................................................................................................... 8-40 CFuge Reference ............................................................................................................ 8-42 Flowsheet Connectivity for CFuge ....................................................................8-42 Specifying CFuge...............................................................................................8-43 References .......................................................................................................... 8-44 Filter Reference .............................................................................................................. 8-45 Flowsheet Connectivity for Filter ......................................................................8-45 Specifying Filter.................................................................................................8-45 References .......................................................................................................... 8-47 SWash Reference ........................................................................................................... 8-48 Flowsheet Connectivity for SWash....................................................................8-48 Specifying SWash .............................................................................................. 8-49 CCD Reference ..............................................................................................................8-50 Flowsheet Connectivity for CCD.......................................................................8-50

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Specifying CCD .................................................................................................8-51

M Uo se drels

9-1

User Reference ................................................................................................................. 9-2 Flowsheet Connectivity for User..........................................................................9-2 Specifying User....................................................................................................9-3 User2 Reference ............................................................................................................... 9-4 Flowsheet Connectivity for User2........................................................................9-4 Specifying User2 .................................................................................................. 9-5 User3 Reference ............................................................................................................... 9-6 Flowsheet Connectivity for User3........................................................................9-6 Specifying User3 .................................................................................................. 9-7 EO Usage Notes for User3...................................................................................9-7 ACMUser3 Reference ...................................................................................................... 9-8 Flowsheet Connectivity for ACMUser3 ..............................................................9-8 Specifying ACMUser3.........................................................................................9-8 Hierarchy Reference.......................................................................................................9-10 Flowsheet Connectivity for Hierarchy ............................................................... 9-11 Specifying Hierarchy..........................................................................................9-11

Pressu Rreelief

10-1

Pres-Relief Reference.....................................................................................................10-2 Specifying Pres-Relief........................................................................................10-2 Scenarios ............................................................................................................10-3 Compliance with Codes .....................................................................................10-6 Stream and Vessel Compositions and Conditions .............................................10-6 Rules to Size the Relief Valve Piping ................................................................ 10-7 Reactions ............................................................................................................ 10-9 Relief System .....................................................................................................10-9 Data Tables for Pipes and Relief Devices........................................................10-12 Valve Cycling...................................................................................................10-15 Vessel Types ....................................................................................................10-16 Disengagement Models .................................................................................... 10-17 Stop Criteria ..................................................................................................... 10-17 Solution Procedure for Dynamic Scenarios ..................................................... 10-18 Flow Equations.................................................................................................10-19 Calculation and Convergence Methods............................................................10-22 Vessel Insulation Credit Factor ........................................................................ 10-22 Additional Reading ..........................................................................................10-23

Advanced Distillation Features

A-1

Sizing and Rating for Trays and Packings: Overview .................................................... A-2 Single-Pass and Multi-Pass Trays ....................................................................... A-3 Modes of Operation for Trays............................................................................. A-7 Flooding Calculations for Trays.......................................................................... A-8 Bubble Cap Tray Layout ..................................................................................... A-9


Con t en t s

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Pressure Drop Calculations for Trays ............................................................... A-10 Foaming Calculations for Trays ........................................................................ A-10 Packed Columns................................................................................................ A-11 Packing Types and Packing Factors..................................................................A-11 Modes of Operation for Packing ....................................................................... A-12 Maximum Capacity Calculations for Packing .................................................. A-12 Pressure Drop Calculations for Packing............................................................ A-14 Liquid Holdup Calculations for Packing........................................................... A-15 Pressure Profile Update ..................................................................................... A-15 Physical Property Data Requirements............................................................... A-16 ......................................................................................................... A-16 ColumnReferences Targeting ......................................................................................................... A-18 Column Targeting Thermal Analysis................................................................ A-18 Column Targeting Hydraulic Analysis .............................................................A-19 Specifications for Column Targeting and Hydraulic Analysis .........................A-19 Selection of Key Components...........................................................................A-20 Using Column Targeting Results ...................................................................... A-23

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Cont ents

A s p e nP l u s1 1 . 1U n i tO p e r a t ionM o d e ls

About This Manual This manual includes detailed technical reference information for all Aspen Plus unit operation models and the Pres-Relief model. The information in this manual is also available in online help and prompts. Models are grouped in chapters according to unit operation type. The reference information for each model includes a description of the model and its typical usage, a diagram of its flowsheet connectivity, a discussion of the specifications you must provide for the model, important equations and correlations, and other relevant information. An overview of all Aspen Plus unit operation models, and general information about the steps and procedures in using them is in the Aspen Plus User Guide as well as in the online help and prompts in Aspen Plus.

For More Information Aspen Plus has a complete system of online help and context-sensitive prompts. The help system contains both context-sensitive help and reference information. For more information about using Aspen Plus help, see the Aspen Plus User Guide, Chapter 3. Online Help

A suite of sample online Aspen Plus simulations illustrating specific processes is delivered with Aspen Plus.

Aspen Plus application examples

This guide provides instructions on installation of Aspen Plus and other AES products.

Aspen Engineering Suite Installation Guide

Aspen Plus Getting Started Guides This set of tutorials includes

several hands-on sessions to familiarize you with Aspen Plus. The guides take you step-by-step to learn the full power and scope of Aspen Plus.

A s p e nP l u s1 1 . 1U n i tO pe ra t i o nM o d e l s

A b o u tT h i sM a n u a l

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Aspen Plus User Guide The three-volume Aspen Plus User Guide provides step-by-step procedures for developing and using an Aspen Plus process simulation model. The guide is task-oriented to help you accomplish the engineering work you need to do, using the powerful capabilities of Aspen Plus.

Aspen Plus reference manuals provide detailed technical reference information. These manuals include background information about the unit operation models available in Aspen Plus, and a wide range of other reference information. The set comprises: Aspen Plus reference manual series

•

Unit Operation Models

•

User Models

•

System Management

•

Summary File Toolkit

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Input Language Guide

Aspen Physical Property System reference manual series

Aspen Physical Property System reference manuals provide detailed technical reference information. These manuals include background information about the physical properties methods and models available in Aspen Plus, tables of Aspen Plus databank parameters, group contribution method functional groups, and other reference information. The set comprises: •

Physical Property Methods and Models

•

Physical Property Data

The Aspen Plus manuals are delivered in Adobe portable document format (PDF) on the Aspen Plus Documentation CD.

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Technical Support For additional information about AspenTech products and services, check the AspenTech World Wide Web home page on the Internet at: http://www.aspentech.com/ World Wide Web

AspenTech customers with a valid license and software maintenance agreement can register to access the Online Technical Support Center at Technical resources

http://support.aspentech.com/ This web support site allows you to: •

Access current product documentation

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Search for tech tips, solutions and frequently asked questions (FAQs)

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Search for and download application examples

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Submit and track technical issues

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Send suggestions

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Report product defects

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Review lists of known deficiencies and defects

Registered users can also subscribe to our Technical Support eBulletins. These e-Bulletins are used to proactively alert users to important technical support information such as: • •

Contacting Customer Support

Technical advisories Product updates and Service Pack announcements

Customer support is also available by phone, fax, and email for customers with a current support contract for this product. For the most up-to-date phone listings, please see the Online Technical Support Center at http://support.aspentech.com . The following contact information was current when this product was released:

Hours Support Centers

Operating Hours

North America

8:00 – 20:00 Eastern Time

South America

9:00 – 17:00 Local time

Europe

8:30 – 18:00 Central European time

Asia and Pacific Region

9:00 – 17:30 Local time



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Phone

Support Centers

Phone Numbers

North America

1-888-996-7100

Toll-free from U.S., Canada, Mexico

1-281-584-4357

North America Support Center

(52) (5) 536-2809

Mexico Support Center

(54) (11) 4361-7220

Argentina Support Center

South America

Europe

(55) (11) 5012-0321

Brazil Support Center

(0800) 333-0125

Toll-free to U.S. from Argentina

(000) (814) 550-4084

Toll-free to U.S. from Brazil

8001-2410

Toll-free to U.S. from Venezuela

(32) (2) 701-95-55

European Support Center

Country specific toll-free numbers:


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Belgium

(0800) 40-687

Denmark

8088-3652

Finland

(0) (800) 1-19127

France

(0805) 11-0054

Ireland

(1) (800) 930-024

Netherlands

(0800) 023-2511

Norway

(800) 13817

Spain

(900)951846

Sweden

(0200) 895-284

Switzerland

(0800) 111-470

UK (65) 395-39-00

(0800)376-7903 Singapore

(81) (3) 3262-1743

Tokyo

As pe nP l u s1 1 . 1U n i tO p e r a t i onM o d e ls

Fax

E-mail

Support Ce nters

Fax Nu mbers

North America

1-617-949-1724 (Cambridge, MA) 1-281-584-1807 (Houston, TX: both Engineering and Manufacturing Suite) 1-281-584-5442 (Houston, TX: eSupply Chain Suite) 1-281-584-4329 (Houston, TX: Advanced Control Suite) 1-301-424-4647 (Rockville, MD) 1-908-516-9550 (New Providence, NJ) 1-425-492-2388 (Seattle, WA)

South America

(54) (11) 4361-7220 (Argentina)

Europe

(55) (11) 5012-4442 (Brazil) (32) (2) 701-94-45


(65) 395-39-50 (Singapore) (81) (3) 3262-1744 (Tokyo)

Support Centers

E-mail

North America

[email protected] (Engineering Suite) [email protected] (Aspen ICARUS products) [email protected] (Aspen MIMI products) [email protected] (Aspen PIMS products) [email protected] (Aspen Retail products) [email protected] (Advanced Control products) [email protected] (Manufacturing Suite) [email protected] (Mexico)

South America

[email protected] (Argentina) [email protected] (Brazil)

Europe

[email protected] (Engineering Suite) [email protected] (All other suites) [email protected] (CIMVIEW products)


[email protected] (Singapore: Engineering Suite) [email protected] (Singapore: All other suites) [email protected] (Tokyo: Engineering Suite) [email protected] (Tokyo: All other suites)



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C HA P TE R 1

Mixers and Splitters

This chapter describes the unit operation models for mixing and splitting streams. The models are: M odel

Description

Purpose

UseFor

Mixer

Stream mixer

Combines multiple streams into one stream

Mixing tees. Stream mixing operations. Adding heat streams. Adding work streams

FSplit

Stream splitter

Divides feed based on splits specified for outlet streams

Stream splitters. Bleed valves

SSplit

Substream splitter

Divides feed based on splits specified for each substream

Stream splitters. Perfect fluid-solid separators

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M i x e r sa n dS pl i t t e r s

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Mixer Reference Use Mixer to combine streams into one stream. Mixer models mixing tees or other types of mixing operations. Mixer combines material streams (or heat streams or work streams) into one stream. Select the Heat (Q) and Work (W) Mixer icons from the Model Library for heat and work streams respectively. A single Mixer block cannot mix streams of different types (material, heat, work). Use the following forms to enter specifications and view results for Mixer: Use this form

Flowsheet Connectivity for Mixer

To do this

Input

Enter operating conditions and flash convergence parameters

Block Options

Override global values for physical properties, simulation options, diagnostic message levels, and report options for this block

Results

View Mixer simulation results

Dynamic

Specify parameters for dynamic simulations

Material (2 or more)

Material Water (optional)

Flowsheet for Mixing Material Streams Material Streams

inlet

At least two material streams

outlet One material stream One water decant stream (optional)

Heat (2 or more)

Heat

Flowsheet for Adding Heat Streams

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Heat Streams

inlet

At least two heat streams

outlet One heat stream

Work (2 or more)

Work

Flowsheet for Adding Work Streams Work Streams

inlet

At least two work streams

outlet One work stream

Specifying Mixer

Use the Mixer Input Flash Options sheet to specify operating conditions. When mixing heat or work streams, Mixer does not require any specifications. When mixing material streams, you can specify either the outlet pressure or pressure drop. If you specify pressure drop, Mixer determines the minimum of the inlet stream pressures, and applies the pressure drop to the minimum inlet stream pressure to compute the outlet pressure. If you do not specify the outlet pressure or pressure drop, Mixer uses the minimum pressure from the inlet streams for the outlet pressure. You can select the following valid phases: ValidPhase

Solids?

Vapor-Only

Yes or no

1

No

V

Liquid-Only

Yesorno

1

No

L

Vapor-Liquid

Yesorno

2

No

–

Vapor-Liquid-Liquid

Yesorno

LiquidFree-Water†

Yesorno

Vapor-LiquidFree-Water† Yesorno Solid-Only

Yes

Numberof phases?

3

Free Phase? Water?

No

1

Yes 2

Yes 1

– –

No

– S

† Check the Use Free Water Calculations checkbox on the Setup

Specifications Global sheet. An optional water decant stream can be used when free-water calculations are performed.



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Mixer performs an adiabatic calculation on the product to determine the outlet temperature, unless Mass Balance Only Calculations is specified on the Mixer BlockOptions SimulationOptions sheet or the Setup SimulationOptions Calculations sheet.

EO Usage Notes for Mixer

1-4

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All features of Mixer are available in the EO formulation, except the features which are globally unsupported.


FSplit Reference FSplit combines streams of the same type (material, heat, or work streams) and divides the resulting stream into two or more streams of the same type. All outlet streams have the same composition and conditions as the mixed inlet. Select the Heat (Q) and Work (W) FSplit icons from the Model Library for heat and work streams respectively. Use FSplit to model flow splitters, such as bleed valves. FSplit cannot split a stream into different types. For example, FSplit cannot split a material stream into a heat stream and a material stream. To model a splitter where the amount of each substream sent to each outlet can differ, use an SSplit block. To model a splitter where the composition and properties of the output streams can differ, use a Sep block or a Sep2 block. Use the following forms to enter specifications and view results for FSplit: Usethisform

T odot hi s

Input

Enter split specifications, flash conditions and calculation options, and key components associated with split specifications

Block Options


Results

Flowsheet Connectivity for FSplit

View split fractions for outlet streams, and material and energy balance results

Material (any number)


Flowsheet for Splitting Material Streams Material Streams

inlet

At least one material stream

outlet At least two material streams



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Heat (2 or more)

Heat (any number) Flowsheet for Splitting Heat Streams Heat Streams

inlet

At least one heat stream

outlet At least two heat streams Work (2 or more)

Work (any number)

Flowsheet for Splitting Work Streams Work Streams

inlet

At least one work stream

outlet At least two work streams

Specifying FSplit

To split material streams Give one of the following specifications for each outlet stream except one:

• • •

Fraction of the combined inlet flow

• • •

Standard liquid volume flow rate Actual volume flow rate

Mole flow rate Mass flow rate

Fraction of the residue remaining after all other specifications are satisfied

FSplit puts any remaining flow in the unspecified outlet stream to satisfy material balance. You can specify mole, mass, or standard liquid volume flow rate for one of the following:

• •

The entire stream A subset of key components in the stream

To specify the flow rate of a component or group of components in an outlet stream, specify a group of key components and the total flow rate for the group (the sum of the component flow rates) on the Input Specifications sheet, and define the key components in the group on the Input KeyComponents sheet. Outlet streams have the same composition as the mixed inlet stream. For this reason, when you specify the flow rate of a key component, the total flow rate of the outlet stream is greater than the flow rate you specify.

1-6

•



When FSplit has more than one inlet, you can do one of the following:

• •

Enter the outlet pressure on the FSplit Input FlashOptions sheet Let the outlet pressure default to the minimum pressure of the inlet streams

To split heat streams or work streams Specify the fraction of the combined inlet heat or work for each outlet stream except one. FSplit puts any remaining heat or work in the unspecified outlet stream to satisfy energy balance.

EO Usage Notes for FSplit

The features listed below are not supported in equation-oriented formulation. However, the capabilities are still available for the EO solution strategy via the Perturbation Layer.

•

Specifications which result in renormalized split fractions during sequential-modular calculations

•

Features which are globally unsupported



•

1-7

SSplit Reference SSplit combines material streams and divides the resulting stream into two or more streams. Use SSplit to model a splitter where the split of each substream among the outlet streams can differ. Substreams in the outlet streams have the same composition, temperature, and pressure as the corresponding substreams in the mixed inlet stream. Only the substream flow rates differ. To model a splitter in which the composition and properties of the substreams in the output streams can differ, use a Sep block or a Sep2 block. Use the following forms to enter specifications and view results for SSplit: Use this form

To do this

Input

Enter split specifications, flash conditions, calculation options, and key components associated with split specifications

BlockOptions


Results

View split fractions of each substream in each outlet stream, and material and energy balance results

Flowsheet Connectivity for SSplit


Material (any number) Material Streams

inlet


outlet At least two material streams

Specifying SSplit

For each substream, specify one of the following for all but one outlet stream:

• • • •

Fraction of the inlet substream Mole flow rate Mass flow rate Standard liquid volume flow rate

SSplit puts any remaining flow for each substream in the unspecified stream. You cannot specify standard liquid volume flow rate when the substream is of type CISOLID, and mole and standard liquid volume flow rates when the substream is of type NC.

1-8

•



You can specify mole or mass flow rate for one of the following:

• •

The entire substream A subset of components in the substream

You can specify the flow rate of a component in a substream of an outlet stream. To do this, define a key component and specify the flow rate for the key component. Similarly, you can specify the flow rate for a group of components in a substream of an outlet stream. To do this, define a key group of components and specify the total flow rate for the group (the sum of the component flow rates). Substreams in outlet streams have the same composition as the corresponding substream in the mixed inlet stream. For this reason, when you specify the flow rate of a key, the total flow rate of the substream in the outlet stream is greater than the flow rate you specify. When SSplit has more than one inlet, you can do one of the following:

• •

Enter the outlet pressure on the Input FlashOptions sheet. Let the outlet pressure default to the minimum pressure of the inlet streams.

The composition, temperature, pressure, and other substream variables for all outlet streams have the same values as the mixed inlet. Only the substream flow rates differ.



•

1-9

1-10

•


A s p e nP l u s1 1 .1U ni tO p e r a t i onM o d e ls

C HA P TE R 2

Separators

This chapter describes the unit operation models for component separators, flash drums, and liquid-liquid separators. The models are: M odel

Description

Purpose

Flash2

Two-outlet flash

Separates feed into two Flash drums, evaporators, knock-out drums, outlet streams, using single stage separators rigorous vapor-liquid or vapor-liquid-liquid equilibrium

UseFor

Flash3

Three-outlet flash

Separates feed into three Decanters, single-stage separators with two outlet streams, using liquid phases rigorous vapor-liquidliquid equilibrium

Decanter

Liquid-liquid decanter Separates feed into two liquid outlet streams

Decanters, single-stage separators with two liquid phases and no vapor phase

Sep

Component separator Separates inlet stream components into multiple outlet streams, based on specified flows or split frractions

Component separation operations, such as distillation and absorption, when the details of the separation are unknown or unimportant

Sep2

Two-outlet component Separates inlet stream separator components into two outlet streams, based on specified flows, split fractions, or purities

Component separation operations, such as distillation and absorption, when the details of the separation are unknown or unimportant

You can generate heating or cooling curve tables for Flash2, Flash3, and Decanter models.


Sepa r a t or s

•

2-1

Flash2 Reference Use Flash2 to model flashes, evaporators, knock-out drums, and other single-stage separators. Flash2 performs vapor-liquid or vapor-liquid-liquid equilibrium calculations. When you specify the outlet conditions, Flash2 determines the thermal and phase conditions of a mixture of one or more inlet streams. Use the following forms to enter specifications and view results for Flash2. Use this form

To do this

Input

Enter flash specifications, flash convergence parameters, and entrainment specifications

Hcurves

Specify heating or cooling curve tables and view tabular results

Block Options


Results

View Flash2 simulation results

Dynamic

Specify parameters for dynamic simulations Vapor Heat (optional)

Flowsheet Connectivity for Flash2


Water (optional) Heat (optional)

Liquid

Material Streams

inlet


outlet One material stream for the vapor phase One material stream for the liquid phase. (If three phases exist, the liquid outlet contains both liquid phases.)

One water decant stream (optional) You can specify liquid and/or solid entrainment in the vapor stream.

2-2

•

S e p a ra t or s


Heat Streams

inlet

Any number of heat streams (optional)

outlet One heat stream (optional)

If you give only one specification (temperature or pressure) on the Input Specifications Sheet, Flash2 uses the sum of the inlet heat streams as a duty specification. Otherwise, Flash2 uses the inlet heat stream only to calculate the net heat duty. The net heat duty is the sum of the inlet heat streams minus the actual (calculated) heat duty. You can use an optional outlet heat stream for the net heat duty.

Specifying Flash2

Use the Input Specifications sheet for all required specifications and valid phases. For valid phases you can choose the following options: You can choose the following options

Solids?

Number o f phases?

Vapor-Liquid

Yesorno

Vapor-Liquid-Liquid

Yesorno

3

No

Vapor-Liquid-FreeWater

Yesorno

2

Yes

2

Free Water?

No

Use the Input FlashOptions sheet to specify temperature and pressure estimates and flash convergence parameters. Use the Input Entrainment sheet to specify liquid and solid entrainment in the vapor phase. Use the Hcurves form to specify optional heating or cooling curves.

Solids

All phases are in thermal equilibrium. Solids leave at the same temperature as the fluid phases. Flash2 can simulate fluid phases with solids when the stream contains solid substreams or when you request electrolytes chemistry calculations.

Solid Substreams: Materials in solid substreams do not participate in phase equilibrium calculations. Electrolyte Chemistry Calculations: You can request these on the Properties Specifications Global sheet or the BlockOptions Properties sheet. Solid salts do participate in liquid-solid phase equilibrium and thermal equilibrium calculations. The salts are in the MIXED substream.

EO Usage Notes for Flash2

All features which of Flash2 available in the EO formulation, except the features are are globally unsupported.


Sepa r a t or s

•

2-3

Flash3 Reference Use Flash3 to model flashes, evaporators, knock-out drums, decanters, and other single-stage separators in which two liquid outlet streams are produced. Flash3 performs vapor-liquid-liquid equilibrium calculations. When you specify outlet conditions, Flash3 determines the thermal and phase conditions of a mixture of one or more inlet streams. Use the following forms to enter specifications and view results for Flash3: Use this form

To do this

Input

Enter flash specifications, key components, flash convergence parameters, and entrainment specifications

Hcurves


Block Options


Results

View Flash3 simulation results

Dynamic

Specify parameters for dynamic simulations Vapor Heat (optional)

Flowsheet Connectivity for Flash3


1st Liquid Heat (optional)

2nd Liquid

Material Streams

inlet


outlet One material stream for the vapor phase One material stream for the first liquid phase One material stream for the second liquid phase

2-4

•

S e p a ra t or s


You can specify liquid entrainment of each liquid phase in the vapor stream. You can also specify entrainment for each solid substream in the vapor and first liquid phase. Heat Streams

inlet



If you give only one specification on the Input Specifications Sheet (temperature or pressure), Flash3 uses the sum of the inlet heat streams as a duty specification. Otherwise, Flash3 uses the inlet heat stream only to calculate the net heat duty. The net heat duty is the sum of the inlet heat streams minus the actual (calculated) heat duty. You can use an optional outlet heat stream for the net heat duty.

Specifying Flash3

Use the Input Specifications sheet for all required specifications. Use the Input Entrainment sheet to specify solid entrainment. To specify optional heating or cooling curves, use the Hcurves form.

Solids

All phases are in thermal equilibrium. Solids leave at the same temperature as the fluid phases. Flash3 can simulate fluid phases with solids when the stream contains solid substreams, or when you request electrolyte chemistry calculations.

Solid Substreams: Materials in solid substreams do not participate in phase equilibrium calculations. Electrolyte Chemistry Calculations: You can request these on the Properties Specifications Global sheet or on the Input BlockOptions Properties sheet. Solid salts do participate in liquidsolid phase equilibrium and thermal equilibrium calculations. You can only specify apparent component calculations (Select Simulation Approach=Apparent Components on the BlockOptions Properties sheet). The salts will not appear in the MIXED substream.


Sepa r a t or s

•

2-5

Decanter Reference Decanter simulates decanters and other single stage separators without a vapor phase. Decanter can perform:

• •

Liquid-liquid equilibrium calculations Liquid-free-water calculations

Use Decanter to model knock-out drums, decanters, and other single-stage separators without a vapor phase. When you specify outlet conditions, Decanter determines the thermal and phase conditions of a mixture of one or more inlet streams. Decanter can calculate liquid-liquid distribution coefficients using:

• • • •

An activity coefficient model An equation of state capable of representing two liquid phases A user-specified Fortran subroutine A built-in correlation with user-specified coefficients

You can enter component separation efficiencies, assuming equilibrium stage is present. Use Flash3 if you suspect any vapor phase formation. Use the following forms to enter specifications and view results for Decanter: Use this form

Flowsheet Connectivity for Decanter

2-6

•

S e p a ra t or s

To do this

Input

Specify operating conditions, key components, calculation options, valid phases, efficiency, and entrainment

Properties

Specify and/or override property methods, KLL equation parameters, and/or user subroutine for phase split calculations

Hcurves


Block Options


Results

Display simulation results

Dynamic



1st Liquid

Heat (optional)

Heat (optional)

2nd Liquid


Material Streams

inlet


outlet One material stream for the first liquid phase One material stream for the second liquid phase

You can specify entrainment for each solid substream in the first liquid phase. Heat Streams

inlet



If you specify only pressure on the Input Specifications sheet, Decanter uses the sum of the inlet heat streams as a duty specification. Otherwise, Decanter uses the inlet heat stream only to calculate the net heat duty. The net heat duty is the sum of the inlet heat streams minus the actual (calculated) heat duty. You can use an optional outlet heat stream for the net heat duty.

Specifying Decanter

You can operate Decanter in one of the following ways:

• • •

Adiabatically With specified duty At a specified temperature

Use the Input Specifications sheet to enter:

• • Defining the Second Liquid Phase

Pressure Temperature or duty

If two liquid phases are present at the decanter operating condition, Decanter treats the phase with higher density as the second phase, by default. When only one liquid phase exists and you want to avoid ambiguities, you can override the default by:

•

Specifying key components for identifying the second liquid phase on the Input Specifications sheet

•

Optionally specifying the threshold key component mole fraction on the Input Specifications sheet

When

Decantertreatsthe

Two liquid phases are present

Phase with the higher mole fraction of key components as the second liquid phase

One liquid phase is present

Liquid phase as the first liquid phase, unless the mole fraction of key components exceeds the threshold value


Sepa r a t or s

•

2-7

Methods for Calculating the Liquid-Liquid Distribution Coefficients (KLL)

When calculating liquid-liquid distribution coefficients (KLL), by default Decanter uses the physical property method specified for the block on the Properties PhaseProperty sheet or BlockOptions Properties sheet. On the Input CalculationOptions sheet, you can override the default by doing one of the following:

•

Specify separate property methods for the two liquid phases using the Properties PhaseProperty sheet

•

Use a built-in KLL correlation. Enter correlation coefficients

•

on the Properties KLLCorrelation sheet. Use a Fortran subroutine that you specify on the Properties KLLSubroutine sheet

See Aspen Plus User Models for more information about writing Fortran subroutines.

Phase Splitting

Decanter has two methods for solving liquid-liquid phase split calculations:

• •

Equating fugacities of two liquid phases Minimizing Gibbs free energy of the system

You can select a method on the Input CalculationOptions sheet. If you select Minimizing Gibbs free energy of the system, the following must be thermodynamically consistent:

•

Physical property models

•

Block property method You cannot use the Minimizing Gibbs free energy of the system method when: Youspecify

Onthissheet

Separate property methods for the two liquid phases

Properties PhaseProperty

The built-in correlation for liquid-liquid distribution coefficient ( KLL) calculations

Input CalculationOptions

A user subroutine for liquidliquid distribution coefficient (KLL) calculations

Input Calculation Options

Equating fugacities of two liquid phases is not restricted by physical property specifications. However, Decanter can calculate solutions that do not minimize Gibbs free energy.

Efficiency

2-8

•

S e p a ra t or s

Decanter outlet streams are normally at equilibrium. However, you can specify separation efficiencies on the Input Efficiency sheet to account for departure from equilibrium. If you select Liquid-


FreeWater for Valid Phases on the Input CalculationOptions sheet, you cannot specify separation efficiencies.

Solids Entrainment

If solids substreams are present, they do not participate in phase equilibrium calculations, but they do participate in enthalpy balance. You can use the Input Entrainment sheet to specify solids entrainment in the first liquid outlet stream. Decanter places any remaining solids in the second liquid outlet stream.

EO Usage Notes for Decanter

The features listed below are not supported in equation-oriented formulation. However, the capabilities are still available for the EO solution strategy via the Perturbation Layer. • User KLL subroutine

• •


KLL correlation Features which are globally unsupported

Sepa r a t or s

•

2-9

Sep Reference Sep combines streams and separates the result into two or more streams according to splits specified for each component. When the details of the separation are unknown or unimportant, but the splits for each component are known, you can use Sep in place of a rigorous separation model to save computation time . If the composition and conditions of all outlet streams of the block you are modeling are identical, you can use an FSplit block instead of Sep. Use the following forms to enter specifications and view results for Sep: Use this form

To do this

Input

Enter split specifications, flash specifications, and convergence parameters for the mixed inlet and each outlet stream

Block Options


Results

View Sep simulation results

Flowsheet Connectivity for Sep



Heat (optional)

Material Streams

inlet


outlet At least two material streams Heat Streams

inlet

No inlet heat streams

outlet One stream for the enthalpy difference between inlet and outlet material streams (optional)

Specifying Sep

2-10

•

S e pa r a t o r s

For each substream of each outlet stream except one, use the Sep Input Specifications sheet to specify one of the following for each component present:

•

Fraction of the component in the corresponding inlet substream

• • •

Mole flow rate of the component Mass flow rate of the component Standard liquid volume flow rate of the component

As pe nP l u s1 1 .1U n i tO p e r a t i onM o d e ls

Sep puts any remaining flow in the corresponding substream of the unspecified outlet stream.

Inlet Pressure

Use the Sep Input Feed Flash sheet to specify either the pressure drop or the pressure at the inlet. This is useful when Sep has more than one inlet stream. The inlet pressure defaults to the minimum inlet stream pressure.

Outlet Stream Conditions Use the Sep Input Outlet Flash sheet to specify the conditions of the outlet streams. If you do not specify the conditions for a stream, Sep uses the inlet temperature and pressure.

EO Usage Notes for Sep


•


•



Sepa r a t or s

•

2-11

Sep2 Reference Sep2 separates inlet stream components into two outlet streams. Sep2 is similar to Sep, but offers a wider variety of specifications. Sep2 allows purity (mole-fraction) specifications for components. You can use Sep2 in place of a rigorous separation model, such as distillation or absorption. Sep2 saves computation time when details of the separation are unknown or unimportant. If the composition and conditions of all outlet streams of the block you are modeling are identical, you can use FSplit instead of Sep2. Use the following forms to enter specifications and view results for Sep2: Use this form

Flowsheet Connectivity for Sep2

To do this

Input

Enter split specifications, flash specifications, and convergence parameters for the mixed inlet and each outlet stream

Block Options


Results

View Sep2 simulation results Material


Material Heat (optional)

Material Streams

inlet


outlet Two material streams Heat Streams

inlet


outlet One stream for the enthalpy difference between inlet and outlet material streams (optional)

Specifying Sep2

2-12

•

S e pa r a t o r s

Use the Input Specifications sheet to specify stream and/or component fractions and flows. The number of specifications for each substream must equal the number of components in that substream.


You can enter these stream specifications:

• • •

Fraction of the total inlet stream going to either outlet stream

•

Total standard liquid volume flow rate of an outlet stream (for substreams of type MIXED)

Total mass flow rate of an outlet stream Total molar flow rate of an outlet stream (for substreams of type MIXED or CISOLID)

You can enter these component specifications:

•

Fraction of a component in the feed going to either outlet stream

• •

Mass flow rate of a component in an outlet stream

•

Standard liquid volume flow rate of a component in an outlet stream (for substreams of type MIXED)

• •

Mass fraction of a component in an outlet stream

Molar flow rate of a component in an outlet stream (for substreams of type MIXED or CISOLID)

Mole fraction of a component in an outlet stream (for substreams of type MIXED or CISOLID)

Sep2 treats each substream separately. Do not:

Inlet Pressure

• •

Specify the total flow of both outlet streams

•

Enter both a mole-frac and a mass-frac specification for a component in a stream

Enter more than one flow or frac specification for each component

Use the Input Feed Flash sheet to specify either the pressure drop or pressure at the inlet. This information is useful when Sep2 has more than one inlet stream. The inlet pressure defaults to the minimum of the inlet stream pressures.

Outlet Stream Conditions Use the Input Outlet Flash sheet to specify the conditions of the outlet streams. If you do not specify the conditions for a stream, Sep2 uses the inlet temperature and pressure.

EO Usage Notes for Sep2


•


•



Sepa r a t or s

•

2-13

2-14

•

S e pa r a t o r s


C HA P TE R 3

Heat Exchangers

This chapter describes the unit operation models for heat exchangers and heaters (and coolers), and for interfacing to the BJAC heat exchanger programs. The models are: M odel

Description

Heater

Heater or cooler

Determines thermal and phase conditions of outlet stream

HeatX

Two-stream heat exchanger

Exchanges heat between Two-stream heat exchangers. Rating shell two streams and tube heat exchangers when geometry is known.

MHeatX

Multistream heat exchanger

Exchanges heat between Multiple hot and cold stream heat any number of streams exchangers. Two-stream heat exchangers. LNG exchangers.

Hetran

Shell and tube heat exchanger

Provides interface to the Shell and tube heat exchangers, including B-JAC Hetran shell and kettle reboilers tube heat exchanger program

Aerotran

Air-cooled heat exchanger

Provides interface to the Crossflow heat exchangers, including air B-JAC Aerotran aircoolers cooled heat exchanger program

HxFlux

Heat transfer calculation

Perform heat transfer Two single-sided heat exchangers calculations between a heat sink and a heat source, using convective heat transfer

HTRI-Xist Shell and tube heat exchanger

Purpose

Provides interface to HTRI’s Xist shell and tube heat exchanger

UseFor

Heaters, coolers, condensers, and so on

Shell and tube heat exchangers, including kettle reboilers

program

A s pe nP l u s1 1 . 1Un i tO p e r a t io nM od e l s

H e a tE x c ha n g e r s

•

3-1

Heater Reference You can use Heater to represent:

• • • •

Heaters Coolers Valves Pumps (whenever work-related results are not needed)

•

Compressors (whenever work-related results are not needed) You also can use Heater to set the thermodynamic condition of a stream. When you specify the outlet conditions, Heater determines the thermal and phase conditions of a mixture with one or more inlet streams. Use the following forms to enter specifications and view results for Heater: Use this form

To do this

Input

Enter operating conditions and flash convergence parameters

Hcurves


Block Options

Override global values for physical properties, simulation options,for diagnostic message levels, and report options this block

Results

ViewHeaterresults Heat (optional)

Flowsheet Connectivity for Heater Material (any number)

Heat (optional)

Material

Water (optional)

Material Streams

inlet


outlet One material stream One water decant stream (optional) Heat Streams

inlet



3-2

•

H e a tE x c ha ng e r s

A s p e nP l u s1 1 .1U ni tO p e r a t ionM o d e ls

If you give only one specification (temperature or pressure) on the Specifications sheet, Heater uses the sum of the inlet heat streams as a duty specification. Otherwise, Heater uses the inlet heat stream only to calculate the net heat duty. The net heat duty is the sum of the inlet heat streams minus the actual (calculated) heat duty. You can use an optional outlet heat stream for the net heat duty.

Specifying Heater

Use the Heater Input Specifications sheet for all required specifications and valid phases. Dew point calculations are two- or three-phase flashes with a vapor fraction of unity. Bubble point calculations are two- or three-phase flashes with a vapor fraction of zero. Use the Heater Input FlashOptions sheet to specify temperature and pressure estimates and flash convergence parameters. Use the Hcurves form to specify optional heating or cooling curves. This model has no dynamic features. The pressure drop is fixed at the steady state value. The outlet flow is determined by the mass balance.

Solids

Heater can simulate fluid phases with solids when the stream contains solid substreams or when you request electrolyte chemistry calculations. All phases are in thermal equilibrium. Solids leave at the same temperature as fluid phases. Solid Substreams Materials in solid substreams do not participate in phase equilibrium calculations. Electrolyte Chemistry Calculations You can request these on the Properties Specifications Global sheet or the Heater BlockOptions Properties sheet. Solid salts participate in liquid-solid phase equilibrium and thermal equilibrium calculations. The salts are in the MIXED substream.

EO Usage Notes for Heater

All features of Heater are available in the EO formulation, except the features which are globally unsupported.



•

3-3

HeatX Reference HeatX can model a wide variety of shell and tube heat exchanger types including:

• • • •

Countercurrent and co-current Segmental baffle TEMA E, F, G, H, J, and X shells Rod baffle TEMA E and F shells Bare and low-finned tubes

HeatX can perform a full zone analysis with heat transfer coefficient and pressure drop estimation for single- and two-phase streams. For rigorous heat transfer and pressure drop calculations, you must supply the exchanger geometry. If exchanger geometry is unknown or unimportant, HeatX can perform simplified shortcut rating calculations. For example, you may want to perform only heat and material balance calculations. HeatX has correlations to estimate sensible heat, nucleate boiling, and condensation film coefficients. HeatX can

• • •

Perform design calculations Perform mechanical vibration analysis Estimate fouling factors

Use the following forms to enter specifications and view results for HeatX: Use this form

3-4

•


To do this

Setup

Specify shortcut, detailed or Hetran-rigorous calculations, flow direction, exchanger pressure drops, heat transfer coefficient calculation methods, and film coefficients

Options

Specify different flash convergence parameters and valid phases for the hot and cold sides, HeatX convergence parameters, and block-specific report option

Hetran Options

Specify the name of the Hetran input file, parameters for calculating the property curves, optional Hetran program inputs.

Hetran Browser

Specify data when using the Hetran-Rigorous

Geometry

calculation type. Specify the shell and tube configuration and indicate any tube fins, baffles, or nozzles


Use this form

To do this

Hot-Hcurves

Specify hot stream heating or cooling curve tables and view tabular results

Cold-Hcurves

Specify cold stream heating or cooling curve tables and view tabular results

User Subroutines

Specify parameters for user-defined Fortran subroutines to calculate overall heat transfer coefficient, LMTD correction factor, tube-side liquid holdup, or tube-side pressure drop

Dynamic


Block Options


Thermal Results

View a summary of results, mass and energy balances, pressure drops, velocities, and zone analysis profiles

Geometry Results

View detailed shell and tube results, and information about tube fins, baffles, and nozzles

Hetran Thermal Results

View overall results and detailed results for the shell side and tube side when using the Hetran-Rigorous calculation type. Cold Outlet

Flowsheet Connectivity for HeatX

Water (optional)

Hot Inlet

Hot Outlet Water (optional)

Cold Inlet Material Streams

inlet

One hot inlet One cold inlet

outlet One One One One


hot outlet cold outlet water decant stream on the hot side (optional) water decant stream on the cold side (optional)


•

3-5

Specifying HeatX

Consider these questions when specifying HeatX:

• • •

Should rating calculations be simple (shortcut) or rigorous?

• • •

How should the heat transfer coefficient be calculated?

What specification should the block have? How should the log-mean temperature difference correction factor be calculated? How should the pressure drops be calculated? What equipment specifications and geometry information are available?

The answers to these questions determine the amount of information required to complete the block input. You must provide one of the following specifications:

• • • • • • •

Heat exchanger area or geometry Exchanger heat duty Outlet temperature of the hot or cold stream Temperature approach at either end of the exchanger Degrees of superheating/subcooling for the hot or cold stream Vapor fraction of the hot or cold stream Temperature change of the hot or cold stream

Shortcut Versus Rigorous HeatX has three calculation methods:shortcut, detailed, and Rating Calculations Hetran-rigorous. Use the Calculation field on the Setup Specifications sheet to specify the appropriate calculation method. With the shortcut calculation method you can simulate a heat exchanger block with the minimum amount of required input. The shortcut calculation does not require exchanger configuration or geometry data. With the detailed calculation method, you can use exchanger geometry to estimate:

• • •

Film coefficients Pressure drops Log-mean temperature difference correction factor

The detailed calculation method provides more specification options for HeatX, but it also requires more input. The detailed calculation method provides defaults for many options. You canThe change the defaults to gain complete over the calculations. following table lists these optionscontrol with valid values. The values are described in the following sections.

3-6

•



The Hetran-rigorous method allows you to design new equipment, and to rate or simulate the performance of existing equipment. In addition to the more rigorous heat transfer and hydraulic analyses, the program will also determine possible operational problems such as vibration or excessive velocities. You can use the Hetran-rigorous method to estimate the cost for the equipment. The modules used in theHetran-rigorous method are the same as those used in the Aspen Hetran standalone product for shell and tube heat exchanger analysis. Available in

Available in

Variable LMTD Correction Factor

Calculation M ethod Constant Geometry User subroutine Calculated

Shortcut Mode Single tube pass † No No Multiple tube pass †

Detailed Mode Hetran-rigorous mode Yes No Default No Yes No No No

Heat Transfer Coefficient

Constant value Phase-specific values Power law expression Film coefficients Exchanger geometry User subroutine

Yes Default Yes No No No

Yes Yes Yes Yes Default Yes

No No No No No No

Film Coefficient

Constant value Phase-specific values Power law expression Calculate from geometry

No No No No

Yes Yes Yes Default

No No No No

Yes Default

No No

Pressure Drop Outlet pressure Default Calculate from geometry No

Available in

† In shortcut mode, a constant LMTD must be supplied for exchangers with a single tube pass. For exchangers with multiple tube passes, the LMTD correction factor will be calculated.

Calculating the Log-Mean The standard equation for a heat exchanger is: Temperature Difference ⋅ Q = U ⋅A LMTD Correction Factor where LMTD is the log-mean temperature difference. This equation applies for exchangers with pure countercurrent flow. The more general equation is:

Q = U⋅ A ⋅ F⋅ L MTD where the LMTD correction factor, F, accounts for deviation from countercurrent flow. Use the LMTD Correction Factor field on the Setup Specifications sheet to enter the LMTD correction factor. In shortcut rating mode, the LMTD correction factor is constant for a cocurrent or countercurrent exchanger. For a multipass



•

3-7

exchanger, HeatX will calculate the correction factor. See Shortcut Model of a System of Multiple Tube Pass Exchangers in Series, for more information. In rigorous rating mode, use the LMTD Correction Method field on the Setup Specifications sheet to specify how HeatX calculates the LMTD correction factor. You can choose from the following calculation options:

Calculating the Heat Transfer Coefficient

If LMTD Correction Method is

Then

Constant

The LMTD correction factor you enter is constant.

Geometry

HeatX calculates the LMTD correction factor using the exchanger specification and stream properties

User subroutine

You supply a user subroutine to calculate the LMTD correction factor.

To determine how the heat transfer coefficient is calculated, set the Calculation Method on the Setup U Methods sheet. You can use these options in shortcut or rigorous rating mode: If Calculation Method is

HeatX uses

And you specify

Constant value

A constant value for the heat transfer coefficient

Phase-specific values

A different heat transfer coefficient A constant for each heat transfer zone of the value for each exchanger, indexed by the phase for zone the hot and cold streams

Power law expression

A power law expression for the heat Constants for transfer coefficient as a function of the power law one of the stream flow rates expression

The constant value

In rigorous rating mode, three additional values are allowed:

3-8

•


If Calculation Method is

Then

Exchanger geometry

HeatX calculates the heat transfer coefficient using exchanger geometry and stream properties to estimate film coefficients.

Film coefficients

HeatX calculates the heat transfer coefficients using the film coefficients. You can use any option on the Setup Film Coefficients sheet to calculate the film coefficients.

User subroutine

You supply a user subroutine to calculate the heat transfer coefficient.


Film Coefficients

HeatX does not calculate film coefficients in shortcut rating mode. In rigorous rating mode, if you use film coefficients or exchanger geometry for the heat transfer coefficient calculation method, HeatX calculates the heat transfer coefficient using: 1 U

=

1 hc

+

1 hh

Where:

hc

=

Cold stream film coefficient

hh

=

Hot stream film coefficient

To choose an option for calculating film coefficients, set the Calculation Method on the Setup Film Coefficients sheet. The following are available: If Calculation Method is

HeatX uses

And you specify

Constant value

A constant value for the film coefficient

A constant value to be used throughout the exchanger

Phase-specific values

A different film coefficient A constant for each heat transfer zone value for each (phase) of the exchanger, phase indexed by the phase of the stream

Power law expression

A power law expression for Constants for the film coefficient as a the power law function of the stream flow expression rate

Calculate from geometry

The exchanger geometry and stream properties to calculate the film coefficient

The hot stream and cold stream film coefficient calculation methods are independent of each other. You can use any combination that is appropriate for your exchanger.

Pressure Drop Calculations

To enter exchanger pressure or pressure drop for the hot and cold sides, use the Outlet Pressure fields on the Setup Pressure Drop sheet. In shortcut rating mode the pressure drop is constant. In rigorous rating mode, you can choose how pressure drops are calculated by setting the pressure on drop the Setup PressureDrop sheet. The followingoptions pressure options are available:



•

3-9

If P ressure Option is

T hen

Outlet Pressure

You must enter the outlet pressure or pressure drop for the stream.

Calculate from geometry HeatX calculates the pressure drop using the exchanger geometry and stream properties

HeatX calls the Pipeline model to calculate tube-side pressure drop. You can set the correlations for pressure drop and liquid holdup that the Pipeline model uses on the Setup PressureDrop sheet.

Exchanger Configuration Exchanger configuration refers to the overall patterns of flow in the heat exchanger. If you choose Calculate From Geometry for any of the heat transfer coefficients, film coefficients, or pressure drop calculation methods, you may be required to enter some information about the exchanger configuration on the Geometry Shell sheet. This sheet includes fields for:

• • • • • •

3-10

•

He a tE x c ha ng e r s

TEMA shell type (see the next figure, TEMA Shell Types) Number of tube passes Exchanger orientation Tubes in baffle window Number of sealing strips Tube flow for vertical exchangers


E Shell One Pass Shell

F Shell Two Pass Shell with Longitudinal Baffle

G Shell

Split Flow

H Shell

Double Split Flow

J Shell

Divided Flow

X Shell

Cross Flow TEMA Shell Types



•

3-11

The Geometry Shell sheet also contains two important dimensions for the shell:

• •

Inside shell diameter Shell to bundle clearance

The next figure shows the shell dimensions. Outer Tube Limit

Shell Diameter

Shell to Bundle Clearance Shell Dimensions

Baffle Geometry

Calculation of shell-side film coefficient and pressure drop require information about the baffle geometry within the shell. Enter baffle geometry on the Geometry Baffles sheet. HeatX can calculate shell-side values for both segmental baffle shells and rod baffle shells. Other required information depends on the baffle type. For segmental baffles, required information includes:

• • •

Baffle cut Baffle spacing Baffle clearances

For rod baffles, required information includes:

• •

Ring dimensions Support rod geometry

The next two figures show the baffle dimensions. The Baffle Cut in the Dimensions for Segmental Baffles figure is a fraction of the shell diameter. All clearances are diametric.

3-12

•



Baffle Cut

Tube Hole

Shell to Baffle Clearance

Dimensions for Segmental Baffles

Rod Diameter

Ring Outside Diameter

Ring Inside Diameter

Dimensions for Rod Baffles

Tube Geometry

Calculation of the tube-side film coefficient and pressure drop require information about the geometry of the tubebank. HeatX also uses this information to calculate the heat transfer coefficient from the film coefficients. Enter tube geometry on the Geometry Tubes sheet. You can select a heat exchanger with either bare or low-finned tubes. The sheet also includes fields for:

• • • • •

Total number of tubes Tube length Tube diameters Tube layout Tube material of construction

The next two figures show tube layout patterns and fin dimensions.



•

3-13

30

o

o

o

45 Tube Pitch

Triangle

o

60 Tube Pitch

90 Tube Pitch

Rotated Square

Rotated Triangle

Tube Pitch Square

Direction of Flow Tube Layout Patterns

Fin Thickness Outside Diameter

Root Mean Diameter Fin Height

Fin Dimensions

Nozzle Geometry

Calculations for pressure drop include the calculation of pressure drop in the exchanger nozzles. Enter nozzle geometry on the Geometry Nozzles sheet.

Model Correlations

HeatX uses open literature correlations for calculating film coefficients and pressure drops. The next four tables list the model correlations. Tube-side Heat Transfer Coefficient Correlations

3-14

•


Mechanism

Flow Regime

Correlation

References

Single-phase

Laminar Turbulent

Schlunder Gnielinski

[1] [1]

Boiling vertical tubes

Steiner/Taborek

[2]

Boiling horizontal tubes

Shah

[3, 4]

Condensation - Laminar vertical tubes Laminar wavy Turbulent Shear-dominated

Nusselt Kutateladze Labuntsov Rohsenow

[5] [6] [7] [8]

Condensation - Annular horizontal tubes Stratifying

Rohsenow [8] Jaster/Kosky method [9]


Shell-side Heat Transfer Coefficient Correlations

Mechanism

Correlation

References

Single-phase segmental

Flow Regime

Bell-Delaware

[10, 11]

Single-phase ROD

Gentry

[12]

Boiling

Jensen

[13]

Condensation - Laminar vertical Laminar wavy

Nusselt Kutateladze

[5] [6]

Labuntsov Rohsenow

[7] [8]

Kern

[9]

Turbulent Shear-dominated Condensation horizontal

Tube-side Pressure Drop Correlations

Mechanism

Correlation

Single-phase

Darcy’s Law

Two-phase

SeePipeline

Shell-side Pressure Drop Correlations

Mechanism

Correlation

References

Single-phase segmental

Bell-Delaware

[10, 11]

Single-phaseROD Two-phase segmental

Two-phaseROD

Gentry

[12]

Bell-Delaware method with [10, 11], [14] Grant’s correction for two-phase flow Gentry

[12]

References

1

Gnielinski, V., "Forced Convection in Ducts." In: Heat Exchanger Design Handbook. New York:Hemisphere Publishing Corporation, 1983.

2

Steiner, D. and Taborek, J., "Flow Boiling Heat Transfer in Vertical Tubes Correlated by an Asymptotic Model." In: Heat Transfer Engineering, 13(2):43-69, 1992.

3

Shah, M.M., "A New Correlation for Heat Transfer During Boiling Flow Through Pipes." In: ASHRAE Transactions, 82(2):66-86, 1976.

4

Shah, M.M., "Chart Correlation for Saturated Boiling Heat Transfer: Equations and Further Study." In: ASHRAE Transactions, 87(1):185-196, 1981.

5

Nusselt, W., "Surface Condensation of Water Vapor." Z. Ver. Dtsch, Ing., 60(27):541-546, 1916.

6

Kutateladze, S.S., Fundamentals of Heat Transfer. New York: Academic Press, 1963.



•

3-15

7

Labuntsov, D.A., "Heat Transfer in Film Condensation of Pure Steam on Vertical Surfaces and Horizontal Tubes." In: Teploenergetika, 4(7):72-80, 1957.

8

Rohsenow, W.M., Webber, J.H., and Ling, A.T., "Effect of Vapor Velocity on Laminar and Turbulent Film Condensation." In: Transactions of the ASME, 78:1637-1643, 1956.

9

Jaster, H. and Kosky, P.G., "Condensation Heat Transfer in a Mixed Flow Regime." In: International Journal of Heat and Mass Transfer, 19:95-99, 1976.

10 Taborek, J., "Shell-and-Tube Heat Exchangers: Single Phase Flow." In: Heat Exchanger Design Handbook. New York: Hemisphere Publishing Corporation, 1983. 11 Bell, K.J., "Delaware Method for Shell Side Design." In: Kakac, S., Bergles, A.E., and Mayinger, F., editors, Heat Exchangers: Thermal-Hydraulic Fundamentals and Design. New York: Hemisphere Publishing Corporation, 1981. 12 Gentry, C.C., "RODBaffle Heat Exchanger Technology." In: Chemical Engineering Progress 86(7):48-57, July 1990. 13 Jensen, M.K. and Hsu, J.T., "A Parametric Study of Boiling Heat Transfer in a Tube Bundle." In: 1987 ASME-JSME Thermal Engineering Joint Conference, pages 133-140, Honolulu, Hawaii, 1987. 14 Grant, I.D.R. and Chisholm, D., "Two-Phase Flow on the Shell

Side of a Segmentally Heat Exchanger." In: JournalBaffled of HeatShell-and-Tube Transfer, 101(1):38-42, 1979.

Flash Specifications

Use the Options Flash Options sheet to enter flash specifications. If you want to perform these calculations

Solids?

Vaporphase

Yesorno

Vapor-only

Liquidphase

Yesorno

Liquid-only

2-fluid flash phase

Yes or no

Vapor-Liquid

3-fluid flash phase

Yes or no

Vapor-Liquid-Liquid

3-fluid phase free-water flash Yes or no Solidsonly

Physical Properties

Yes

Set Valid Phases to

Vapor-Liquid-FreeWater Solid-only

To override global or flowsheet section property specifications, use the BlockOptions Properties sheet. You can use different physical property options for the hot side and cold side of the heat exchanger. yousetsupply only of property specifications, HeatX uses Ifthat for both hotone andsetcold side calculations.

Solids

3-16

•


All phases are in thermal equilibrium. Solids leave at the same temperature as the fluid phases.


HeatX can simulate fluid phases with solids when the stream contains solid substreams, or when you request electrolyte chemistry calculations.

Solid Substreams: Materials in solid substreams do not participate in phase equilibrium calculations. Electrolyte Chemistry Calculations: You can request these on the Properties Specifications Global sheet or HeatX BlockOptions Properties sheet. Solid salts participate in liquid-solid phase equilibrium and thermal equilibrium calculations. The salts are in Shortcut Model of a System of Multiple Tube Pass Exchangers in Series

the MIXED substream. HeatX can perform a shortcut calculation of a system of multiple tube pass heat exchangers in series. The following restrictions apply:

• •

All units in series are identical

•

The overall heat transfer coefficient is the same for each unit

Each unit in series has one shell pass and an even number of tube passes

To do this, on the Setup Specifications sheet: 1

Select the Shortcut calculation type

2

Select Multiple tube passes for flow direction.

3

In the No. shells in series field, enter the number of units in series.

When this option is chosen, Aspen Plus will calculate the LMTD correction factor. You can also choose to specify a minimum value for the calculated LMTD correction factor. HeatX will issue a warning if the calculated value is less than this value. The LMTD correction factor is calculated as follows: If R, the ratio of heat capacities, is not equal to 1, then:

1 − P ∗ R  ∗  R +1  1− P  F= 1− R  2 − P ∗ ( R + 1 − R 2 + 1)  ln    2 − P ∗ ( R + 1 + R 2 + 1)  ln 

2

If R = 1, then:

F

P∗ 2

= (1 − P


∗

 2 − P ∗ (2 − ) ln  ∗  2 − P (2 +

2) 



2)


•

3-17

Where:

F

=

R

=

P∗

=

LMTD correction factor Ratio of heat capacities:

(WC p ) cold /(WC p ) hot

Thermal effectiveness of each unit, calculated by the Bowman transformation

The Bowman transformation gives the thermal effectiveness of each unit based on the overall thermal effectiveness. IfR ≠1, then: 1N

11−−PR  −1 P  P∗ =  1N 1 − PR  − R  1 − P  If R=1, then:

P∗

=

P P − NP + N

Where:

P

=

Thermal effectiveness for the overall heat exchanger: (temp. increase of cold fluid)/(inlet T hot fluid – inlet T cold fluid)

N

=

Number of shells in series

Reference

Dodd, R., "Mean Temperature Difference and Temperature Efficiency for Shell and Tube Heat Exchangers Connected in Series with Two Tube Passes per Shell Pass." In: Trans. IChemE, Vol. 58, 1980.

EO Usage Notes for HeatX


• • •

3-18

•


Rigorous method (with geometry) Phase-specific heat transfer coefficients and zone analysis Features which are globally unsupported


MHeatX Reference Use MHeatX to represent heat transfer between multiple hot and cold streams, such as in an LNG exchanger. You can also use MHeatX for two-stream heat exchangers. Free water can be decanted from any outlet stream. MHeatX ensures an overall energy balance but does not account for the exchanger geometry. MHeatX can perform a detailed, rigorous internal zone analysis to determine the internal pinch points and heating and cooling curves for all streams in the heat exchanger. MHeatX can also calculate the overall UA for the exchanger and model heat leak to or from an exchanger. MHeatX uses multiple Heater blocks and heat streams to enhance flowsheet convergence. Aspen Plus automatically sequences block and stream convergence unless you specify a sequence or tear stream. Use the following forms to enter specifications and view results for MHeatX: Use this form

To do this

Input

Specify operating conditions, flash convergence parameters, parameters for zone analysis, flash table, MHeatX convergence parameters, and blockspecific report options

Hcurves


Block Options

Override global values for physical properties, simulation options, diagnostic message levels and report options for this block

Results

View stream results, exchanger results, zone profiles, stream profiles, flash profiles, and material and energy balance results o ne ts (any number)

Flowsheet Connectivity for MHeatX

Hot Outlets Hot Inlets (any number)

Water (optional) Hot Outlets

Water (optional) Cold Outlets


Water (optional)


•

3-19

Material Streams

inlet

At least one material stream on the hot side, unless a load stream is used. At least one material stream on the cold side, unless a load stream is used.

outlet One outlet stream for each inlet stream. One water decant stream for each outlet stream (optional). Load Streams

inlet

Any number of load streams on either or both sides.

outlet One outlet load stream for each inlet load stream.

The inlet stream sides are non-contacting.

Specifying MHeatX

You must give outlet specifications for each stream on one side of the heat exchanger. On the other side you can specify any of the outlet streams, but you must leave at least one unspecified stream. Different streams can have different types of specifications. MHeatX assumes that all unspecified streams have the same outlet temperature. An overall energy balance determines the temperature of any unspecified stream(s). You can use a different property method for each stream in MHeatX. Specify the property methods on the BlockOptions Properties sheet.

Zone Analysis

MHeatX can perform a detailed, rigorous internal zone analysis to determine:

• • • •

Internal pinch points UA and LMTD of each zone Total UA of the exchanger Overall average LMTD

To obtain a zone analysis, specify Number of zones greater than 0 on the MHeatX Input Zone Analysis sheet. During zone analysis MHeatX can add:

•

Stream entry points (if all feed streams are not at the same temperature)

•

Stream exit points (if all product streams are not at the same temperature)

•

Phase change points (if a phase change occurs internally)

MHeatX can also account for the nonlinearities of zone profiles by adding zones adaptively. MHeatX can perform zone analysis for both countercurrent and co-current heat exchangers.

3-20

•



Using Flash Tables in Zone Analysis

Use Flash Tables to estimate zone profiles and pinch points quickly. These tables are most useful for heat exchangers that have many streams, for which zone analysis calculations can take a long time. To use a Flash Table for a stream, specify the number of flash points for the stream on the MHeatX Input Flash Table sheet. When you specify a flash table for a stream, MHeatX generates a temperature-enthalpy profile of that stream before zone analysis, and interpolates that profile during zone analysis, rather than flashing the stream. You can also specify the fraction of total pressure drop in each phase region of a stream on the MHeatX Input Flash Table sheet. Aspen Plus uses these fractions to determine the pressure profile during Flash Table generation.

Computational Structure for MHeatX

The computational structure of MHeatX may affect your specifications. Unlike other unit operation blocks, MHeatX is not simulated by a single computation module. Instead, Aspen Plus generates heaters and heat streams to represent the multistream heat exchanger. A Heater block represents streams with outlet specifications. A multistream heater block represents streams with no outlet specifications. The next figure shows the computational structure generated for a sample exchanger. $LNGH02 S3

HEATER

$LNGH03 S4S

5

$LNGH04 S6S

HEATER

7

S8

HEATER

$LNGQ03 $LNGQ02

$LNGQ04 $LNGHTR S1

LNGIN

S2 MHEATER LNGOUT

Example of MHeatX Computational Structure

This computational sequence converges much more rapidly than simulation of MHeatX as a single block. Block results are given for the entire MHeatX sequence. In most cases, you do not need to know about the individual blocks generated in the sequence. The following paragraphs describe the exceptions. Simulation history and control panel messages are given for the generated Heater blocks and heat streams.



•

3-21

You can provide an estimate for duty of the internally generated heat stream. If the heat stream is a tear stream in the flowsheet, Aspen Plus uses this estimate as an initial value. You can give convergence specifications for the flowsheet resulting when MHeatX blocks are replaced by their generated networks. The generated Heater block and heat stream IDs must be used on the Convergence SequenceSpecifications and Convergence TearSpecifications sheets. Automatic flowsheet analysis is based on the flowsheet resulting when MHeatX Heater blocks blocks, are replaced byof generated Heater blocks. The generated instead the MHeatX block, appear in the calculation sequence. You can select generated heat streams as tear streams.

Solids

MHeatX can simulate fluid phases with solids when the stream contains solid substreams, or when you request electrolyte chemistry calculations. All phases are in thermal equilibrium. Solids leave at the same temperature as the fluid phases.

Solid Substreams: Materials in solid substreams do not participate in phase equilibrium calculations. Electrolyte Chemistry Calculations: You can request these on the Properties Specifications Global sheet or the MHeatX BlockOptions Properties sheet. Solid salts participate in liquidsolid phase equilibrium and thermal equilibrium calculations. The salts are in the MIXED substream.

3-22

•



Hetran Reference Hetran is the interface to the B-JAC Hetran program for designing and simulating shell and tube heat exchangers. Hetran can be used to simulate shell and tube heat exchangers with a wide variety of configurations. To use Hetran, place the block in the flowsheet, connect inlet and outlet streams, and specify a small number of block inputs, including the name of the B-JAC input file for that exchanger. You enter information related to the heat exchanger configuration and geometry through the Hetran standalone program interface. The exchanger specification is saved as a B-JAC input file. You do not have to enter information about the exchanger ’s physical characteristics through the Aspen Plus user interface or through input language. Use the following forms to enter specifications and view results for Hetran: Use this form

To do this

Input

Specify the name of the B-JAC input file, parameters for calculating the property curves, optional Hetran program inputs, flash convergence parameters, and valid phases

Block Options

Override global values for physical properties, simulation options,for diagnostic message levels, and report options this block

Flowsheet Connectivity for Hetran

Results

View inlet and outlet stream conditions and material and energy balance results

Detailed Results

View overall results and detailed results for the shell side and tube side

Cold Inlet Hot Inlet Hot Water (optional)

Hot Outlet Cold Outlet Cold Water (optional) Material Streams

inlet




•

3-23


Specifying Hetran



Enter the input for the shell and tube heat exchanger through the Hetran program’s graphical user interface. The input for Hetran in Aspen Plus is limited to:

•

The B-JAC input file name that contains the heat exchanger specification

• •

A set of parameters to control how property curves are generated A set of Hetran program inputs that you can change from within Aspen Plus (for example, fouling factors and film coefficients)

Use the Flash Options sheet to enter flash specifications. If you want to perform these calculations

Solids?

Set Valid Phases to

Vaporphase

Yesorno

Vapor-only

Liquidphase

Yesorno

Liquid-only

2-fluid flash phase

Yes or no

Vapor-Liquid

3-fluid flash phase

Yes or no

Vapor-Liquid-Liquid

3-fluid phase free-water flash

Yes or no

Solidsonly

Yes


Physical Properties

To override global or flowsheet section property specifications, use the Flash Options sheet. You can use different physical property methods for the hot side and cold side of the heat exchanger. If you supply only one set of property specifications, Hetran uses that set for both hot- and cold-side calculations.

Solids

Hetran cannot currently handle streams with solids substreams.

3-24

•



Aerotran Reference Aerotran is the interface to the B-JAC Aerotran program for designing and simulating air-cooled heat exchangers. Aerotran can be used to simulate air-cooled heat exchangers with a wide variety of configurations. It can also be used to model economizers and the convection section of fired heaters. To use Aerotran, place the block in the flowsheet, connect inlet and outlet streams, and specify a small number of block inputs, including the name of the B-JAC input file for that exchanger. You enter information related to the air cooler configuration and geometry through the Aerotran standalone program interface. The air cooler specification is saved as a B-JAC input file. You do not have to enter information about the air cooler’s physical characteristics through the Aspen Plus user interface or through input language. Use the following forms to enter specifications and view results for Aerotran: Use this form

Flowsheet Connectivity for Aerotran

To do this

Input

Specify the name of the B-JAC input file, parameters for calculating the property curves, optional Aerotran program inputs, flash convergence parameters, and valid phases

Block Options


Results


Detailed Results

View overall results, detailed results for the outside and tube side, and fan results Cold Water (optional)

Hot Inlet

Cold (Air) Outlet

Hot Water (optional)

Hot Outlet

Cold (Air) Inlet



•

3-25

Material Streams

inlet

One hot inlet One cold (air) inlet


Specifying Aerotran

hot outlet cold (air) outlet water decant stream on the hot side (optional) water decant stream on the cold side (optional)

Enter the input for the air-cooled heat exchanger through the Aerotran program’s graphical user interface. The input for Aerotran in Aspen Plus is limited to: • The B-JAC input file name that contains the heat exchanger specification


•

A set of parameters to control how property curves are generated

•

A set of Aerotran program inputs that you can change from within Aspen Plus (for example, fouling factors and film coefficients)

Use the FlashOptions sheet to enter flash specifications. If you want to perform these calculations

Solids?

Set Valid Phases to

Vaporphase

Yesorno

Vapor-only

Liquidphase

Yesorno

Liquid-only

2-fluid flash phase

Yes or no

Vapor-Liquid

3-fluid flash phase 3-fluid phase free-water flash

Yes or no Vapor-Liquid-Liquid Yes or no Vapor-Liquid-FreeWater

Solidsonly

Yes

Solid-only

Physical Properties

To override global or flowsheet section property specifications, use the FlashOptions sheet. You can use different physical property methods for the hot side and cold side of the air cooler. If you supply only one set of property specifications, Aerotran uses that set for both hot- and cold-side calculations.

Solids

Aerotran blocks cannot currently handle streams with solids substreams.

3-26

•



HxFlux Reference HxFlux is used to perform heat transfer calculations between a heat sink and a heat source, using convective heat transfer. The driving force for the convective heat transfer is calculated as a function of log-mean temperature difference (LMTD). Specify variables among inlet and outlet stream temperatures, duty, heat transfer coefficient, and heat transfer area. HxFlux calculates the unknown variable and determines the log-mean temperature difference, using either the rigorous or the approximate method. Use the following forms to enter specifications and view results for HxFlux: Use this fo rm To d o th is

Input

Specify required and optional variables for heat transfer calculations

Results

View a summary of results and mass and energy balances. Heat (optional)

Flowsheet Connectivity for HxFlux

Heat (optional)

inlet

Inlet heat stream (optional)

outlet Outlet heat stream (optional)

Specifying HxFlux

You have to specify inlet hot stream temperature or temperature from a reference stream, and inlet cold stream temperature or temperature from a reference stream. You also have to specify four of the following variables:

•

Outlet hot stream (temperature or temperature from a reference stream)

•

Outlet cold stream (temperature or temperature from a reference stream)

• • •

Duty, duty from a reference heat stream, or inlet heat stream Overall heat transfer coefficient Heat transfer area

You can select the flow direction for either counter-current or cocurrent flow. When there is an inlet heat stream or when the duty is



•

3-27

from a reference heat stream, you can select the heat stream direction to indicate whether the duty value is positive or negative. You can also select the calculation method in determining the logmean temperature difference.

Convective Heat Transfer

The standard equation for convective heat transfer is:

Q

= UA ⋅ LMTD

Where: Q

=

Heatduty

U

=

Overall heat transfer coefficient

A

=

Heattransferarea

LMTD

=

Log-mean temperature difference

This equation applies for heat transfer with either counter-current or co-current flow.

Log-Mean Temperature Difference

Two methods are used in determining log-mean temperature difference (LMTD). For the rigorous method:

LMTD =

∆T1 − ∆T2  ∆T  ln  1   ∆T2 

For the approximate method: 1

LMTD =  ∆



where

T1

1

3

2+ ∆

∆T1 and ∆T2

T2

3

3



are the approach temperatures.

The approximate method is used even if the rigorous method is specified when:

• • EO Usage Notes for HXFlux

3-28

•


Either of the approach temperatures is zero. There is no difference in the approach temperatures.

All features of HXFlux are available in the EO formulation, except the features which are globally unsupported.


HTRI-Xist Reference HTRI-Xist is the interface to HTRI’s Xist program for designing and simulating shell and tube heat exchangers. HTRI-Xist can be used to simulate shell and tube heat exchangers with a wide variety of configurations. To use HTRI-Xist, place the block in the flowsheet, connect inlet and outlet streams, and specify a small number of block inputs, including the name of the Xist input file for that exchanger. You can enter information related to the heat exchanger configuration and geometry through the Xist standalone program interface. The exchanger specification is saved as an Xist input file. You do not have to enter information about the exchanger ’s physical characteristics through the Aspen Plus user interface or through input language. Use the following forms to enter specifications and view results for HTRI-Xist: Use this form

To do this

Input

Specify the name of the Xist input file, parameters for calculating the property curves, optional Xist program inputs, flash convergence parameters, and valid phases

Block Options

Override global values for physical properties, simulation options, diagnostic report options for this block message levels, and

Flowsheet Connectivity for HTRI-Xist

Results


Detailed Results


Cold Inlet Hot Inlet Hot Water (optional)

Hot Outlet Cold Outlet Cold Water (optional) Material Streams

inlet




•

3-29


Specifying HTRI-Xist



Enter the input for the shell and tube heat exchanger through the Xist program’s graphical user interface. The input for HTRI-Xist in Aspen Plus is limited to:

•

The Xist input file name that contains the heat exchanger specification

• •

A set of parameters to control how property curves are generated A set of Xist program inputs that you can change from within Aspen Plus (for example, fouling factors and film coefficients)

Use the FlashOptions sheet to enter flash specifications. If you want to perform these calculations

Set V alid P hases to

Vaporphase

Yesorno

Vapor-only

Liquidphase

Yesorno

Liquid-only

2-fluid flashphase

Yes orno

Vapor-Liquid

3-fluid flash phase

Yes or no

Vapor-Liquid-Liquid

3-fluid phase free-water flash

Yes or no

Solidsonly

Physical Properties

Solids?

Yes


To override global or flowsheet section property specifications, use the FlashOptions sheet. You can use different physical property methods for the hot side and cold side of the heat exchanger. If you supply only one set of property specifications, HTRI-Xist uses that set for both hot- and cold-side calculations.

Solids

3-30

•


HTRI-Xist cannot currently handle streams with solids substreams.


C HA P TE R 4

Columns

This chapter describes the unit operation models for distillation columns using shortcut and rigorous calculations, and for liquidliquid extraction. The models are: M odel

Description

DSTWU

Shortcut Determines minimum Columns with one feed and two product distillation design reflux ratio, minimum streams using the Winn- number of stages, and Underwoodeither actual reflux ratio or Gilliland method actual number of stages

Purpose

UseFor

Distl

Shortcut distillation rating using the Edmister method

Determines separation based on reflux ratio, number of stages, and distillate-to-feed ratio

SCFrac

Shortcut distillation for complex petroleum fractionation units

Determines product Complex columns, such as crude units and composition and flow, vacuum towers number of stages per section, and heat duty using fractionation indices

RadFrac

Rigorous fractionation

Performs rigorous rating Ordinary distillation, absorbers, strippers, and design calculations for extractive and azeotropic distillation, threesingle columns phase distillation, reactive distillation

Columns with one feed and two product streams

MultiFrac Rigorous Performs rigorous rating fractionation for and design calculations for complex columns multiple columns of any complexity

Heat integrated columns, air separation columns, absorber/stripper combinations ethylene plant primary fractionator quench tower combinations, petroleum refining applications

PetroFrac

Preflash tower, atmospheric crude unit, vacuum unit, catalytic cracker main fractionator, delayed coker main fractionator, vacuum lube fractionator, ethylene plant primary fractionator and quench tower combinations

Petroleum refining fractionation

Performs rigorous rating and design calculations for complex columns in petroleum refining applications

A s pe nP l u s1 1 . 1U n i tO p e r a t i onM o de l s

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M odel

Description

Purpose

UseFor

RateFrac†

Rate-based distillation

Performs rigorous rating and design for single and multiple columns. Based on nonequilibrium calculations. Does not require efficiencies and HETPs.

Distillation columns, absorbers, strippers, reactive systems, heat integrated units, petroleum applications, such as crude and vacuum units, absorber-stripper combination

BatchFrac† Batch distillation Performs rigorous calculations for batch Extract

distillation Rigorous liquid- Models countercurrent liquid extraction extraction of a liquid stream using a solvent

Batch distillation

Liquid-liquid extractors

†

RateFrac and BatchFrac require a separate license and can be used only by customers who have purchased it through a specific license agreement with Aspen Technology, Inc. This chapter is organized into the following sections: Section

Models

Shortcut Distillation

DSTWU, Distl, SCFrac

Rigorous Distillation

RadFrac, MultiFrac, PetroFrac, RateFrac, BatchFrac

Liquid-Liquid Extraction Extract

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DSTWU Reference DSTWU performs shortcut design calculations for single-feed, two-product distillation columns with a partial or total condenser. DSTWU assumes constant molal overflow and constant relative volatilities. DSTWU uses this method/correlation

To estimate

Winn

Minimumnumberofstages

Underwood

Minimumrefluxratio

Gilliland

Requiredrefluxratioforaspecified number of stages or the required number of stages for a specified reflux ratio

For the specified recovery of light and heavy key components, DSTWU estimates:

• •

Minimum reflux ratio Minimum number of theoretical stages

DSTWU then estimates one of the following:

•

Required reflux ratio for the specified number of theoretical stages

•

Required number of theoretical stages for the specified reflux ratio

DSTWU also estimates the optimum feed stage location and the condenser and reboiler duties. DSTWU can produce tables and plots of reflux ratio versus number of stages. Use the following forms to enter specifications and view results for DSTWU: Use this form

To do this

Input

Specify configuration and calculation options, block-specific report options, flash convergence parameters, valid phases, and DSTWU convergence parameters

BlockOptions


Results

View summary results, material and energy balance results, and reflux ratio profile


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Flowsheet Connectivity for DSTWU

Heat (optional)

Heat (optional) Distillate

1

Water (optional)

2

Feed N-1

N

Heat (optional)

Bottoms Heat (optional)

Material Streams

inlet

One material feed stream

outlet One distillate stream One bottoms stream One water decant stream from condenser (optional) Heat Streams

inlet

One stream for condenser cooling (optional) One stream for reboiler heating (optional)

outlet One stream for condenser cooling (optional) One stream for reboiler heating (optional)

Each outlet heat stream contains the net heat duty for either the condenser or the reboiler. The net heat duty is the inlet heat stream minus the actual (calculated) heat duty. If you use heat streams for the reboiler, you must also use them for the condenser.

Specifying DSTWU

Use the Input Specifications sheet to enter column specifications. The following table shows the specifications and what is calculated based on them: Specification

Result

Recovery of light and heavy key components

Minimum reflux ratio and minimum number of theoretical stages

Number of theoretical stages

Required reflux ratio

Refluxratio

Requirednumberoftheoretical stages

DSTWU also estimates the optimum feed stage location, and the condenser and reboiler duties. DSTWU can generate an optional table of reflux ratio versus number of stages. Use the Input CalculationOptions sheet to enter specifications for the table.

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Distl Reference Distl simulates multistage multicomponent columns with a feed stream and two product streams. Distl performs shortcut distillation rating calculations for a singlefeed, two-product distillation column. The column can have either a partial or total condenser. Distl calculates product composition using the Edmister approach. Distl assumes constant mole overflow and constant relative volatilities. Use the following forms to enter specifications and view results for Distl: Use this form

Flowsheet Connectivity for Distl

To do this

Input

Specify basic column configuration, operating conditions, Distl convergence parameters, and flash convergence parameters

BlockOptions


Results

View summary of column results and material and energy balance results

Dynamic

Specify parameters for dynamic simulation

Heat (optional)

Heat (optional) 1

Distillate Water (optional)

2

Feed N-1

N

Heat (optional)

Bottoms Heat (optional)

Material Streams

inlet


outlet One distillate stream One bottoms stream One water decant stream from condenser (optional) Heat Streams

inlet


One stream for condenser cooling (optional) One stream for reboiler heating (optional)

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outlet One stream for condenser cooling (optional) One stream for reboiler heating (optional)

Each outlet heat stream contains the net heat duty for either the condenser or the reboiler. The net heat duty is the inlet heat stream minus the actual (calculated) heat duty. If you use heat streams for the reboiler, you must also use them for the condenser.

Specifying Distl

Use the Input Specifications sheet to enter the number of stages, reflux ratio, distillate to feed ratio, and other column specifications. Use the Input Convergence sheet to override default valid phases for condenser, convergence parameters for flash calculations, and model convergence parameters.

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SCFrac Reference Use SCFrac to simulate complex distillation columns with a single feed, optional stripping steam, and any number of products. SCFrac also estimates the number of theoretical stages and the heating/cooling duty for each section. SCFrac can model complex columns, such as crude units and vacuum towers. SCFrac performs shortcut distillation calculations for columns with a single feed, one optional stripping steam stream, and any number of products. SCFrac divides a column with n products into n – 1 sections. These sections are numbered from the top down. SCFrac assumes:

• •

Relative volatilities are constant for each section The flow of liquid from section to section is negligible

SCFrac does not handle solids. SCFrac can perform free-water calculations in the condenser. Use the following forms to enter specifications and view results for SCFrac: Use this form

Flowsheet Connectivity for SCFrac

To do this

Input

Specify operating parameters, valid phases, SCFrac convergence parameters, and flash convergence parameters

Block Options


Results

View condenser results, material and energy balance results, design specification results, section profiles, and product summary Distillate Side Products (any number)

Steam (optional)

Feed

Material Streams

inlet


Bottoms

One material feed stream One optional stripping steam stream (used for all sections)

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outlet One distillate stream One bottoms stream At least one side product stream

Specifying SCFrac

SCFrac divides an n–product column into n – 1 sections (see the next figure, SCFrac Multidraw Column). SCFrac numbers the column sections from the top down. For each section, you must specify:

• •

Product pressure Estimate of product flow or flow fraction based on feed flow

You must specify the ratio of steam to product flow rate for all product streams except the distillate. You must also enter 2( n – 1) specifications from the following:

•

Fractionation index (number of theoretical stages at total reflux) of a section

•

Total flow, flow rate, or recovery of any group of components for a product stream

•

Value of a property set property for a product stream (see Aspen Plus User Guide, Chapter 28)

•

Difference of any pair of property set properties for one or a pair of product stream(s)

•

Ratio of any pair of property set properties for one or a pair of product stream(s)

Because SCFrac performs steam calculations, water must always be present. All water flow leaves with the top product stream. A Multidraw Column P1

P1

P2 Stream-1 P3 Stream-2 P4 Feed

Feed

Stream-3 P5

Stream-1 P2 Stream-2 P3 Stream-3 P4 Stream-4 P5

Stream-4

SCFrac Multidraw Column

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RadFrac Reference RadFrac is a rigorous model for simulating all types of multistage vapor-liquid fractionation operations. These operations include:

• • • • • •

Ordinary distillation Absorption Reboiled absorption Stripping Reboiled stripping Extractive and azeotropic distillation

RadFrac is suitable for:

• • • •

Two-phase systems Three-phase systems Narrow and wide-boiling systems Systems exhibiting strong liquid phase nonideality

RadFrac can detect and handle a free-water phase or other second liquid phase anywhere in the column. RadFrac can handle solids on every stage. RadFrac can handle pumparounds leaving any stage and returning to the same stage or to a different stage. RadFrac can model columns in which chemical reactions are occurring. Reactions can have fixed conversions, or they can be:

• • •

Equilibrium Rate-controlled Electrolytic

RadFrac can also model columns in which two liquid phases and chemical reactions occur simultaneously, using different reaction kinetics for the two liquid phases. In addition, RadFrac can model salt precipitation. Although RadFrac assumes equilibrium stages, you can specify either Murphree or vaporization efficiencies. You can manipulate Murphree efficiencies to match plant performance. You can use RadFrac to size and rate columns consisting of trays and/or packings. RadFrac can model both random and structured packings.


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Use the following forms to enter specifications and view results for RadFrac: Use this form

Setup

To do this

Specify basic column configuration and operating conditions

DesignSpecs

Specify design specifications and view convergence results

Vary

Specify manipulated variables to satisfy design specifications and view final values

HeatersCoolers

Specify stage heating or cooling

Pumparounds

Specify pumparounds and view pumparound results

Pumparounds Hcurves

Specify pumparound heating or cooling curve tables and view tabular results

Decanters

Specify decanters and view decanter results

Efficiencies

Specify stage, component or sectional efficiencies

Reactions

Specify equilibrium, kinetic, and conversion reaction parameters

CondenserHcurves Specify condenser heating or cooling curve tables and view tabular results ReboilerHcurves

Specify reboiler heating or cooling curve tables and view tabular results

TraySizing

Specify sizing parameters for tray column sections, and view results

TrayRating

Specify rating parameters for tray column sections, and view results

PackSizing

Specify sizing parameters for packed column sections, and view results

PackRating

Specify rating parameters for packed column sections, and view results

Properties

Specify physical property parameters for column sections

Estimates

Specify initial estimates for stage temperatures, and vapor and liquid flows and compositions

Convergence

Specify convergence parameters for the column and feed flash calculations, and

Report

block-specific diagnostic message levels Specify block-specific report options and pseudostreams

BlockOptions


UserSubroutines

Specify user subroutines for reaction kinetics, KLL calculations, tray sizing and rating, and packing sizing and rating

ResultsSummary

View key column results for the overall RadFrac column

Profiles

View and specify column profiles

Dynamic


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Flowsheet Connectivity for RadFrac

RadFrac can have any number of:

• • • •

Stages Interstage heaters/coolers Decanters Pumparounds

Material Streams

inlet

At least one inlet material stream

outlet One vapor or liquid distillate product stream, or both One water distillate product stream (optional) One bottoms liquid product stream Up to three side product streams per stage (optional)

Any number of pseudo-product streams (optional) Each stage can have:

• •

Any number of inlet streams Up to three outlet streams (one vapor and two liquid)

Outlet streams can be partial or total drawoffs of the stage flows. Decanter outlet streams can return to the stage immediately below. Or they can be split into any number of streams, each returning to a different user-specified stage. Pumparounds can go between any two stages, or to the same stage. Any number of pseudoproduct streams can represent column internal flows, pumparound flows, and thermosyphon reboiler flows. A pseudoproduct stream does not affect column results. Heat Streams

inlet

One heat inlet stream heat stream per stage (optional) One per pumparound (optional)

outlet One outlet heat stream per stage (optional) One heat stream per pumparound (optional)


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RadFrac uses an inlet heat stream as a duty specification for all stages except the condenser, reboiler, and pumparounds. If you do not give two column operating specifications on the Setup Configuration sheet, RadFrac uses a heat stream as a specification for the condenser and reboiler. If you do not give two specifications on the Pumparounds Specifications sheet, RadFrac uses a heat stream as a specification for pumparounds. If you give two specifications on the Setup Configuration sheet or Pumparounds Specifications sheet, RadFrac does not use the inlet heat stream as a specification. The inlet heat stream supplies the required heating or cooling. Use optional outlet streams for the net heat duty of the condenser, reboiler, and pumparounds. The value of the outlet heat stream equals the value of the inlet heat stream (if any) minus the actual (calculated) heat duty.

Specifying RadFrac

This section describes the following topics on RadFrac column configuration:

• • • • • • Stage Numbering Feed Stream Conventions

Stage Numbering Feed Stream Conventions Columns Without Condensers or Reboilers Reboiler Handling Heater and Cooler Specifications Decanters

•

Pumparounds RadFrac numbers stages from the top down, starting with the condenser (or starting with the top stage if there is no condenser). Use the Setup Streams sheet to specify the feed and product stages. RadFrac provides three conventions for handling feed streams:

• • •

Above-Stage On-Stage Decanter (for three phase calculations only)

(See the following figures, RadFrac Feed Convention Above-Stage and RadFrac Feed Convention On-Stage.) When the feed convention is Above-Stage, RadFrac introduces a material stream between adjacent stages. The liquid portion flows to the stage you specify. The vapor portion flows to the stage above. You can introduce a liquid feed to the top stage (or condenser) by specifying Stage=1. You can introduce a vapor feed to the bottom stage (or reboiler) by specifying Stage= the number of equilibrium stages + 1. Feed convention Decanter is used only

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in three-phase calculations (Valid Phases=Vapor-Liquid-Liquid on the Setup Configuration sheet) involving decanters. You can introduce a feed directly to a decanter attached to a stage using this convention. n-1 Vapor Mixed feed to stage n Liquid n RadFrac Feed Convention Above-Stage

n-1

Mixed feed to stage n

n

RadFrac Feed Convention On-Stage

When the Feed Convention is On-Stage, both the liquid and vapor portions of a feed flow to the stage you specify.

Columns Without You can specify the column configuration on the Setup Condensers or Reboilers Configuration sheet. If t he column has no

Reboiler Handling

Then specify

On s heet

Condenser

Nonefor Condenser

Setup Configuration

Reboiler

Nonefor Reboiler

Setup Configuration

RadFrac can model two reboiler types:

• •

Kettle Thermosyphon

A kettle reboiler is modeled as the last stage in the column on the Setup Configuration sheet. Select Kettle for reboiler. By default, RadFrac uses a kettle reboiler. To specify the reboiler duty, enter


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Reboiler Duty as one of the operating specifications on the Setup Configuration sheet or leave it as a calculated value. A thermosyphon reboiler is modeled as a pumparound with a heater, from and to the bottom stage. Select Thermosyphon for Reboiler on the Setup Configuration sheet. Enter all other thermosyphon reboiler specifications on the Setup Reboiler sheet. The next figure shows the thermosyphon reboiler configuration. By default, RadFrac returns the reboiler outlet to the last stage using the On-Stage feed convention. You can also use the Reboiler Return Feeddirects Convention on the Reboiler sheet to specify Stage. This the vapor portion of the reboiler outletAboveto Stage= the number of equilibrium stages - 1.

Nstage - 1

Reboiler

Bottoms (B) Thermosyphon Reboiler

The thermosyphon reboiler model has five related variables:

• • • • •

Pressure Flow rate Temperature Temperature change Vapor fraction

You must specify one of the following:

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• • •

Temperature

•• • •

Flow rate Flow rate and temperature

Temperature change Vapor fraction

Flow rate and temperature change Flow rate and vapor fraction


If you choose an option consisting of two variables, you must specify the reboiler heat duty on the Setup Configuration sheet. RadFrac treats the value you enter for the reboiler heat duty as an initial estimate. The reboiler pressure is optional. If you do not enter a value, RadFrac uses the bottom stage pressure.

Heater and Cooler Specifications

You can specify interstage heaters and coolers in one of two ways:

•

Specifying the duty directly on the HeatersCoolers SideDuties sheet

•

Requesting UA calculations on the HeatersCoolers UtilityExchangers sheet

If you specify the duty directly on the HeatersCoolers SideDuties sheet, enter a positive duty for heating and a negative duty for cooling. If you request UA calculations on the HeatersCoolers UtilityExchangers sheet, RadFrac calculates the duty and outlet temperature of the heating/cooling fluid simultaneously with the column. The UA calculations:

• • •

Assume the stage temperature is constant Use an arithmetic average temperature difference Assume the heating or cooling fluid does not experience any phase change

To request UA calculations, specify the:

• • •

UA Heating or cooling fluid component Flow and inlet temperature of the fluid

You can specify the heat capacity of the fluid directly on the HeatersCoolers UtilityExchangers sheet or RadFrac can compute it from a property method. If RadFrac computes the heat capacity, you must also enter the pressure and phase of the heating or cooling fluid. By default, RadFrac calculates the heat capacity using the block property method. But you can also use a different property method. You can also specify the heat loss for sections of the column on the HeatersCoolers HeatLoss sheet.

Decanters

For three-phase calculations (Valid Phases=Vapor-Liquid-Liquid on the Setup Configuration sheet), you can define any number of decanters. Enter decanter specifications on the Decanters form. For the decanter on the top stage, you must enter the return fraction of at least one of the two liquid phases (Fraction of 1st Liquid


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Returned, Fraction of 2nd Liquid Returned on the Decanters Specifications sheet). For decanters on other stages, you must always specify both Fraction of 1st Liquid Returned and Fraction of 2nd Liquid Returned. You can enter Temperature and Degrees Subcooling on the Decanters Options sheet to model subcooled decanters. If you do not specify Temperature and Degrees Subcooling, the decanter is operated at the temperature of the stage to which the decanter is attached. If side product streams are decanter products, you cannot specify their flow rates. RadFrac calculates their flow rates from the Fraction of 1st Liquid Returned and Fraction of 2nd Liquid Returned. By default RadFrac returns decanter streams to the stage immediately below. You can return the decanter streams to any other stage by entering a different Return Stage number on the Decanters Specifications sheet. You can split a return stream into any number of streams by giving a split fraction (Split Fraction of Total Return for the 1st Liquid and 2nd Liquid). Each resulting stream may go to a different return stage. When return streams do not go to the next stage, a feed or pumparound must go to the next stage. This prevents dry stages.

Pumparounds

RadFrac can handle pumparounds from any stage to the same or any other stage. Use the Pumparounds form to enter all pumparound specifications. You must enter the source and destination stage locations for pumparounds. A pumparound can be either a partial or total drawoff of the:

• • • •

Stage liquid First liquid phase Second liquid phase Vapor phase

You can associate a heater or cooler with a pumparound. If the pumparound is a partial drawoff of the stage flow, you must enter two of the following specifications:

• • • • •

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Flow rate Temperature Temperature change Vapor fraction Heat Duty


If the pumparound is a total drawoff, you must enter one of the following specifications:

• • • •

Temperature Temperature change Vapor fraction Heat Duty

Vapor fraction is allowed only when Valid Phases=Vapor-Liquid or Vapor-Liquid-Liquid. Use the Pumparounds Specifications sheet to enter these operating specifications. Pressure specification is optional. The default pumparound pressure is the same as the source stage pressure. RadFrac assumes that the pumparound at the heater/cooler outlet has the same phase condition as the pumparound at the inlet. You can override the phase condition using the Valid phases field on Pumparound Specifications sheet. RadFrac can return the pumparound to a stage using either the:

• •

On-stage option Above-stage option (returns the pumparound to the column between two stages)

In three-phase columns, RadFrac can also return the pumparound to a decanter associated with a stage. You can select above-stage using the Return option field. RadFrac assumes the pumparound at the heater/cooler outlet has the same phase condition as the inlet. You can use Return-Phase on the Pumparounds Specifications sheet to assign a different phase at the heater/cooler outlet. Or you can specify Valid Phases=VaporLiquid or Vapor-Liquid-Liquid and let RadFrac determine the return phase condition from the heater/cooler specifications.

EO Usage Notes for RadFrac


• • •

Thermosyphon Reboiler * TPSAR with pressure update Features which are globally unsupported

* Thermosyphon reboiler is supported in the EO formulation when vfrac is one of the specifications.


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RadFrac is capable of performing three-phase calculations in the equation-oriented formulation. By default, the EO formulation assumes the same stages will have three-phase separation as in the sequential-modular solution. You can force the EO formulation to check for three-phase separation on all stages specified on the RadFrac | Setup | 3-Phase sheet by selecting the checkbox for the Phase splitting on all specified trays option on the RadFrac | Block Options | EO Options | Additional Variables dialog box.. When three-phase calculations are specified, RadFrac checks the final EO solution for missed three-phase separation (on stages modeled as two-phase) using Gibbs free energy minimization. If such three-phase separation is found, RadFrac issues an error. You can either reconcile results with SM and run again, or use the Phase splitting on all specified trays option to specify the stages where RadFrac should look for three-phase separation.

Free-Water and Rigorous ThreePhase Calculations

RadFrac can perform both free-water and rigorous three-phase calculations. (See Aspen Plus Physical Property Methods and Models, Chapter 6.) These calculations are controlled by options you specify on the Setup Configuration sheet. You can select from three types of calculations:

• • •

Free water in the condenser only Free water on any or all stages Rigorous three-phase calculations

When you choose free-water calculations in the condenser, only free water can be decanted from the condenser. You cannot use nonideal for the Overall Loop convergence method. Specify one of the following on the Setup Configuration sheet: ValidPhases=

OnSheet

For

Vapor-LiquidFreeWaterCondenser

Setup Configuration

Free water in the condenser only

Vapor-LiquidFreeWaterAnyStage

Setup Configuration

Free water on all stages

Vapor-Liquid-Liquid

Setup Configuration

Rigorous three-phase calculations

For RadFrac calculations, you must also specify which stages to test for two liquid phases on the Setup 3-Phase sheet. When you choose completely rigorous three-phase calculations on all stages selected, RadFrac makes no assumptions about the nature of the two liquid phases. You can associate a decanter with any stage. You cannot use Sum-Rates for the Overall Loop convergence method.

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Efficiencies

You can specify one of two types of efficiencies:

• •

Vaporization Murphree

Vaporization efficiency is defined as:

=

Effi v

yi , j K i,j xi j,

Murphree efficiency is defined as: iy j ,

Effi ,Mj

=

−ij y , 1 −i jy+, +1

K i,j ixj ,

Where:

K

=

Equilibrium K value

x

=

Liquid mole fraction

y

=

Vapor mole fraction

Eff

v

=

Vaporization efficiency

Eff

M

=

Murphree efficiency

i

=

Component index

j

=

Stage index

To specify vaporization or Murphree efficiencies, enter the number of actual stages on the Setup Configuration sheet. Then use the Efficiencies form to enter the efficiencies. For three-phase calculations, the vaporization and Murphree efficiencies you enter apply equally to the following equilibrium by default:

• •

Vapor-liquid1 (VL1E) Vapor-liquid2 (VL2E)

You can use the Efficiencies form to enter separate efficiencies for VL1E and VL2E. You cannot enter separate efficiencies for VL1E and VL2E when you specify equilibrium reactions or when using Murphree efficiencies. You can use any of these efficiencies to account for departure from equilibrium. But you cannot convert from one efficiency to the other. Magnitudes of the efficiencies can be quite different. You should manipulate the Murphree efficiency to match the operating data when: • Efficiency is unknown

•


Actual column operating data are available

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When manipulating the Murphree efficiency, use design specifications on the DesignSpecs and Vary forms. Details on using and estimating efficiencies are described by Holland, Fundamentals of Multi-Component Distillation , McGraw-Hill Book Company, 1981.

Algorithms

You can select an algorithm and/or initialization option for column simulation on the Convergence Basic sheet. The default standard algorithm and standard initialization option are appropriate for most applications. You can improve convergence behavior for the following applications using the guidelines described in this section: • Petroleum and Petrochemical Applications

• • • •

Highly Nonideal Systems Azeotropic Distillation Absorbers and Strippers Cryogenic Applications

In order to change the algorithm and initialization option on the Convergence Basic sheet, you must first choose Custom as the option in the Convergence field on the Setup Configuration sheet.

Petroleum and Petrochemical Applications

In petroleum and petrochemical applications involving extremely wide-boiling mixtures and/or many components and design specifications, you can improve the convergence efficiency and reliability by choosing Sum-Rates in the Algorithm field on the Convergence Basic sheet.

Highly Nonideal Systems When liquid phase nonidealities are exceptionally strong, choose Nonideal in the Algorithm field on the Convergence Basic sheet to improve the convergence behavior. Use this algorithm only when the number of outside loop iterations (using the standard algorithm) exceeds 25. You can also use the Newton algorithm for highly nonideal systems. Newton is better for columns with highly sensitive specifications. But it is usually slower, especially for columns with many stages and components.

Azeotropic Distillation

For azeotropic distillation applications where an entraining agent separates an azeotropic mixture, specify the following on the Convergence Basic sheet:

• •

Algorithm, Newton Initialization method, Azeotropic

A classic example of azeotropic distillation is ethanol dehydration using benzene.

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Absorbers and Strippers

To model absorbers and strippers specify Condenser=None and Reboiler=None on the Setup Configuration sheet. The heat duty is zero for adiabatic operation. For extremely wide-boiling mixtures, specify one of the following:

• • Cryogenic Applications

Algorithm=Sum-Rates on the Convergence Basic sheet Convergence=Standard on the Setup Configuration sheet and choose Absorber=Yes on the Convergence Basic sheet

For cryogenic applications such as air separation, the standard algorithm is recommended. To invoke a special initialization procedure designed cryogenic Basic systems, specify Cryogenic for Initialization on the for Convergence sheet.

Rating Mode

RadFrac allows the column to be operated in a rating mode or a design mode. Rating mode requires different column specifications for two- and three-phase calculations. For two-phase calculations, you must enter the following on the Setup Form:

•

Valid Phases=Vapor-Liquid or Vapor-LiquidFreeWaterCondenser for handling free water in condenser

• •

A Total, Subcooled, or Partial-Vapor condenser Two additional column operating variables

If the condenser or reflux is subcooled, you can also specify the degrees subcooling or the subcooled temperature. For three-phase calculations, you must specify Valid Phases= Vapor-Liquid-Liquid or Vapor-Liquid-FreeWaterAnyStage (for free water calculations) on the Setup Configuration sheet. The required specifications depend on what you specify for the return fractions of the two liquid phases (Fraction of 1st Liquid Returned and Fraction of 2nd Liquid Returned) in the top stage decanter. The following table lists the three specification options: If you specified this on Decanters Specifications

Enter on Setup Configuration

Fraction of 1st Liquid Returned A Total, Subcooled, or Partial-Vapor or Fraction of 2nd Liquid condenser and two operating Returned, or no top decanter specifications Fraction of 1st Liquid Returned A Total, Subcooled, or Partial-Vapor and Fraction of 2nd Liquid condenser and one operating Returned specification Fraction of 1st Liquid Returned Two operating specifications, and an and Fraction of 2nd Liquid estimate for the amount of vapor in the Returned distillate on the Estimates Vapor Composition sheet. RadFrac assumes a partial condenser with both vapor and liquid distillates.


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Design Mode

RadFrac allows the column to be operated in rating mode or design mode. In design mode, use the DesignSpecs form to specify column performance parameters (such as purity or recovery). You must indicate which variables to manipulate to achieve these specifications. You can manipulate any variables that are allowed in rating mode, except:

• • •

Number of stages

•• • •

Subcooled reflux temperature Degrees of subcooling

• •

Pressures of thermosyphon reboiler and pumparounds

Pressure profile Vaporization efficiency

Decanter temperature and pressure Locations of feeds, products, heaters, pumparounds, and decanters UA specifications for heaters

The flow rates of inlet material streams and the duties of inlet heat streams can also be manipulated variables. These are the design specifications. Youcanspecify

Forany

Purity

Streamincludinginternalstreams

Recovery of any components

Set of product streams, including

groups Flow rate of any components groups

sidestreams †† Internal stream or set of product streams

†

Temperature

Stage

Value of an y Prop-Set property

Internal or product stream †††

Ratio or difference of any pair of Prop-Set properties

Single or paired internal or product streams

Flow ratio of any components groups to any other component groups

Internal streams to any other internal streams, or to any set of feed or product streams

† Express the purity as the sum of mole, mass, or standard liquid volume fractions of any group of components relative to any other group of components. †† Express recovery as a fraction of the same components in any set of feed streams. ††† See Aspen Plus User Guide, chapter 28.

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Reactive Distillation

RadFrac can handle chemical reactions. These reactions can occur in the liquid and/or vapor phase. The details about the reactions are entered on a generic Reactions form outside RadFrac. RadFrac allows two different reaction model types: REAC-DIST or USER. RadFrac can model the following types of reactions:

• • • •

Equilibrium-controlled Rate-controlled Conversion Electrolytic

RadFrac can also model salt precipitation, especially in the case of electrolytic systems. You can request reaction calculations for the entire column, or you can restrict reactions to a certain column segment (for example, to model the presence of catalyst). For three-phase calculations, you can restrict reactions to one of the two liquid phases, or use separate reaction kinetics for the two liquid phases. To include reactions in RadFrac you must enter the following information on the Reactions Specifications sheet:

• •

Reaction type and Reaction/Chemistry ID Column section in which the reactions occur

Depending on the reaction type, you must enter equilibrium constant, kinetic, or conversion parameters on the generic Reactions form outside RadFrac. For electrolytic reactions, you can alsoRadFrac. enter the To reaction datasalt on precipitation, the Reactionsenter Chemistry outside consider the saltform precipitation parameters on the Reactions Salt sheet or the Reactions Chemistry form outside RadFrac. To associate reactions and salt precipitation with a column segment, enter the corresponding Reactions ID (or Chemistry ID) on the Reactions Specifications sheet. For rate-controlled reactions, you must enter holdup or residence time data in the phase where the reactions occur. Use the Reactions Holdups or Residence Times sheets. For conversion reactions, use the Reactions Conversion sheet to override the conversion parameters specified on the Reactions Conversion form. RadFrac also supports User Reaction Subroutine. The name and other details of the reaction subroutine are entered on the UserSubroutines form.


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Solution Strategies

RadFrac uses two general approaches for column convergence:

• •

Inside-out Napthali-Sandholm

The standard, sum-rates, and nonideal algorithms are variants of the inside-out approach. The MultiFrac, PetroFrac, and Extract models also use this approach. The Newton algorithm uses the classical Napthali-Sandholm approach. Use the Convergence form to select the algorithm and specify the associated parameters.

Inside-Out Algorithms

The inside-out algorithms consist of two nested iteration loops. The K-value and enthalpy models you specify are evaluated only in the outside loop to determine parameters of simplified local models. When using nonideal, algorithm RadFrac introduces a composition dependence into the local models. The local model parameters are the outside loop iteration variables. The outside loop is converged when the changes of the outside loop iteration variables are sufficiently small from one iteration to the next. Convergence uses a combination of the bounded Wegstein method and the Broyden quasi-Newton method for selected variables. In the inside loop, the basic describing equations (component mass balances, total mass balance, enthalpy balance, and phase equilibrium) are expressed in terms of the local physical property models. RadFrac solves these equations to obtain updated temperature and composition profiles. Convergence uses one of the following methods:

• • • •

Bounded Wegstein Broyden quasi-Newton Schubert quasi-Newton Newton

RadFrac adjusts the inside loop convergence tolerance with each outside loop iteration. The tolerance becomes tighter as the outside loop converges.

Newton Algorithm

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The Newton algorithm solves column-describing equations simultaneously, using Newton’s method. The convergence is stabilized using the dogleg strategy of Powell. Design specifications may be solved either simultaneously with the column-describing equations or in an outer loop.


Design Mode Convergence

Nested Design Spec Convergence (for all algorithms except SUMRATES)

RadFrac provides two methods for handling design specification convergence:

• •

Nested convergence Simultaneous convergence

The Nested Middle Loop convergence method attempts to satisfy the design specifications by determining the values of the manipulated variables (within their bounds) that minimize the weighted sum of squares function:

Φ=

∑ m

 ∧ Gm −GM Wm *  Gm 

   

2

Where:

m

=

Design specification number

∧

G

=

Calculated value

G

=

Desired value

G*

=

Scaling factor

w

=

Weighting factor

Φ does The algorithm that manipulates the variables to minimize not depend on matching particular variables with corresponding design specifications. You should carefully select the manipulated variables and design specifications. Make sure that each manipulated variable has a significant effect on at least one design specification. The number of design specifications must be equal to or greater than the number of manipulated variables. If there are more design specifications than manipulated variables, assign weighting factors to reflect the relative importance of the specifications. The larger the weighting factor, the more nearly a specification will be satisfied. Scale factors normalize the errors, so that different specification types are compared on a consistent basis. When a value of a manipulated variable reaches a bound, that bound is active. If a problem has no active bounds and the same Φ number of manipulated variables as design specifications, then will approach zero (within some tolerance) when all specifications are satisfied. If there are active bounds or more design specifications than manipulated variables, RadFrac minimizesΦ . The weighting factors determine the relative degree to which the design specifications are satisfied.


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Simultaneous Design Spec Convergence (for Algorithm=SUM-RATES, NEWTON)

The Simultaneous Middle Loop convergence method algorithm solves the design specification functions simultaneously with the column-describing equations:



∧

Gm G− M Fm =  *  Gm 

  =0  

Because the Simultaneous Middle Loop convergence method uses an equation-solving approach, there must be an equal number of design and manipulated variables. the nested and method,specifications no coupling is assumed between design In specifications manipulated variables. However, each design specification must be significantly affected by at least one manipulated variable. Bounds and weighting factors are not used. In general, the Simultaneous method gives better performance if all the specifications are feasible.

Physical Properties

To override the global physical property method, use the Properties PropertySections sheet. You can specify different physical properties for different parts of the column. For three-phase calculations, you can specify separate calculation methods for Vapor-Liquid1 Equilibrium (VL1E) and Liquid1Liquid2 Equilibrium (LLE). Use one of the following methods:

•

Associate separate property methods with VL1E and LLE using the Phase Equilibrium list box

•

Calculate VL1E using a property method. Specify LLE using liquid-liquid distribution (KLL) coefficients

You can use the Properties KLLSections sheet to enter the KLL coefficients using a built-in temperature polynomial, and associate the coefficients with one or more column segments. Or you can use the Properties KLLCorrelations sheet to associate a user-KLL subroutine with one or more column segments.

Solids Handling

RadFrac has two methods for handling inert solids:

• •

Overall-balance Stage-by-stage

Use the Solids handling option on the Convergence Basic sheet to select either an overall balance or stage-by-stage. The two methods differ in how they treat solids in the mass and energy balances. Neither method considers inert solids in the phase equilibrium calculations. However, salts formed by salt precipitation reactions (see Reactive Distillation) are considered in phase equilibrium calculations.

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C o l um ns


The overall-balance method:

• • •

Temporarily removes all solids from inlet streams Performs column calculations without solids Adiabatically mixes solids removed from inlet streams with liquid product from the bottom stage

The overall-balance method maintains an overall mass and energy balance around the column. But it does not satisfy individual stage balances. This is the default method. The stage-by-stage method treats solids rigorously in all stage mass and energy balances. The ratio of liquids to solids on a stage is maintained in the product streams withdrawn from that stage. The specified product flow is the total flow rate of the stream, including the solids. If a nonconventional (NC) solids substream is present in the column feeds, you must give all column flow and flow ratio specifications on a mass basis. When you specify a decanter, RadFrac can decant the solids partially or totally. By default, RadFrac decants the solids partially along with the second liquid phase. RadFrac uses the return fraction you specify for the second liquid phase (Fraction of 2nd Liquid Returned on the Decanters Specifications sheet) to decant the solids. If there is no second liquid phase in the decanter, RadFrac decants the solids partially along with the first liquid phase. RadFrac uses the return fraction you specify for the first liquid phase (Fraction of 2nd Liquid Returned on the Decanters Specifications sheet) in this case. You can request complete decanting of the solids by selecting Decant Solids Totally on the Decanters Options sheet.

Sizing and Rating of Trays and Packings

RadFrac has extensive capability to size, rate and perform pressure drop calculations for trayed and packed columns. Use the following forms to enter specifications:

• • • •

TraySizing TrayRating PackSizing PackRating

See Appendix A of the Unit Operation Models Reference Manual for details on tray and packing types and correlations.


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MultiFrac Reference MultiFrac is a rigorous model for simulating general systems of interlinked multistage fractionation units. MultiFrac models can handle a complex configuration consisting of:

• •

Any number of columns, each with any number of stages

•

Arbitrary flow splitting and mixing of connecting streams

Any number of connections between columns or within each column

MultiFrac can handle operations with:

• • • • •

Side strippers Pumparounds External heat exchangers Single-stage flashes Feed furnace

Typical MultiFrac applications include:

• • • •

Heat-interstaged columns, such as Petlyuk towers Air separation column systems Absorber/stripper combinations Ethylene plant primary fractionator/quench tower combinations

You can also use MultiFrac for petroleum refining fractionation units such as atmospheric crude units and vacuum units. But for these applications, PetroFrac is more convenient to use. Use MultiFrac only when the configuration is beyond the capabilities of PetroFrac. MultiFrac can detect a free-water phase in the condenser or anywhere in the column. It can decant the free-water phase on any stage. Although MultiFrac assumes equilibrium stage calculations, you can specify either Murphree or vaporization efficiencies. You can use MultiFrac for both sizing and rating trays and packings. MultiFrac can model both random and structured packings.

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C o l um ns


Use the following forms to enter specifications and view results for MultiFrac: Use this form

T o do t hi s

Columns

Specify parameters and view results for columns

Inlets Outlets

Specify inlet and outlet material and heat stream locations

ConnectStreams

Specify sources and destinations of connecting material and heat streams, view connecting stream results

FlowRatios DesignSpecs

Specify stream flow ratios Specify design specifications, and view convergence results

Vary


Condenser Hcurves

Specify condenser heating or cooling curve tables and view tabular results

Reboiler HCurves


Connect Stream HCurves

Specify connecting stream heating or cooling curve tables and view tabular results

Tray Sizing

Specify sizing parameters for tray column sections, and view results

Tray Rating

Specify rating parameters for tray column sections, and view results

Pack Sizing

Specify sizing parameters for packed column sections, and view results Specify rating parameters for packed column sections, and view results

Pack Rating Convergence

Specify convergence parameters for column calculations, and block-specific diagnostic message levels

Report

Specify block-specific report options and pseudostream information

UserSubroutines

Specify user subroutine parameters for tray sizing and rating, and packing sizing and rating

BlockOptions


ResultsSummary

View results of balances and splits


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Top Stage or Condenser Heat Duty (optional)

Flowsheet Connectivity for MultiFrac

Vapor Distillate 1 Reflux

Heat Liquid Distillate (optional) Water Distillate (optional)

Feeds

Side Products (optional)

Heat

Interconnecting Streams (Heater Optional)

Pumparounds and Bypasses (Heater Optional)

Interconnecting Streams (Heater Optional) Heat (optional)

Bottom Stage or Reboiler Heat Duty (optional)

Top Stage or Condenser Heat Duty (optional)

Nstage Nstage

Heat (optional) Bottoms (or Interconnecting Stream)

Vapor Distilate 1

Heat Liquid Distillate (optional) Water Distillate (optional) Side Products (optional)

Feeds

Heat

Interconnecting Streams (Heater Optional)

Pumparounds and Bypasses (Heater Optional)

Interconnecting Streams (Heater Optional) Heat (optional)

Bottom Stage or Reboiler Heat Duty (optional)

Nstage

Heat (optional) Bottoms (or Interconnecting Stream)

Material Streams

inlet

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outlet Any number of optional pseudo-product streams Up to three optional outlet material streams per stage (one vapor, one liquid, and one free water)

You can connect any number of columns by any number of connecting streams. For each column, any number of connecting streams can represent pumparounds and bypasses. These streams can flow between any two stages, or to the same stage. Each connecting stream can have an associated heater. Each column must have one liquid product or connecting stream leaving stage. The topstream, stage of the main column (columnthe 1) bottom must have a product which cannot be a connecting stream. The top stage of the other columns (column 2, 3, ...) must have a vapor product or a vapor connecting stream. The pseudoproduct streams represent column internal flows and connecting stream flows. Heat Streams

inlet

One inlet heat stream per stage (optional) One inlet heat stream per connecting stream (optional)

outlet One outlet heat stream per connecting stream (optional)

MultiFrac uses an inlet heat stream as a duty specification for all stages except the condenser, reboiler, and connecting streams. If you do not provide two column operating specifications on the Columns Setup Configuration sheet, MultiFrac uses a heat stream as a specification for the condenser and reboiler. If you do not provide two specifications on the ConnectStreams form, MultiFrac uses a heat stream as a specification for connecting streams. If you provide two specifications on the Columns Setup Configuration sheet or ConnectStreams form, MultiFrac does not use the inlet heat stream as a specification. The inlet heat stream supplies the required heating or cooling. You can use optional outlet heat streams for the net heat duty of the condenser, reboiler, and connecting streams. The value of the outlet heat stream equals the value of the inlet heat stream (if any), minus the actual (calculated) heat duty.

Specifying MultiFrac

Individual columns are identified by column numbers. The numbering order does not affect algorithm performance. Column 1 has different specifications from the other columns. Within each column, the stages are numbered from the top down, starting with the condenser.


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Stream Definitions

MultiFrac uses four types of streams:

• • • •

External streams Connecting streams Internal streams Pseudostreams

External streams are standard MultiFrac inlet and outlet streams. They are identified by stream IDs. Connecting streams are within MultiFrac but external to individual columns. They canand connect two columns, stages of theasame column (bypasses pumparounds). Youorcan associate heater with any connecting stream. Connecting stream heaters are identified by connecting stream numbers. Internal streams are liquid or vapor flows between adjacent stages of the same column. An internal stream is identified by a source stage number and a column number. Pseudostreams store the results of internal and connecting streams. They are a subset of external outlet streams. Unlike normal outlet streams, pseudostreams do not participate in block mass balance calculations.

Required Specifications

Follow these guidelines when entering specifications for column 1:

• •

The number of stages must be greater than 1 Two additional operating specifications are required

•

The distillate flow may not be a connecting stream You must specify:

•

Bottoms rate or distillate rate. The distillate rate includes both the vapor and liquid distillate flows

• •

Either condenser duty, reboiler duty, reflux ratio or reflux rate Distillate vapor fraction or condenser temperature

If you specify the condenser stage temperature:

•

Both liquid and vapor distillate products must be present (distillate vapor fraction is greater than 0 or less than 1)

•

You must also specify an estimate for the distillate vapor fraction

Follow these guidelines when entering specifications for other columns:

• • • 4-32

•

C o l um ns

The stages can be 1 (for example, to model a singlestagenumber flash oroffeed furnace) The distillate can be a connecting stream MultiFrac calculates the distillate vapor fraction


•

The distillate rate includes only the vapor distillate flow and must be greater than zero. If a liquid distillate is present, specify flow on the InletsOutlets form.

For columns with more than one stage, you may specify condenser duty, reboiler duty, bottoms rate, distillate rate, and reflux rate. For columns with one stage, you must specify either:

• • • Feed Stream Conventions

Bottoms rate Distillate rate (includes only the vapor distillate) Condenser duty

MultiFrac provides two conventions for handling feed streams (see MultiFrac Feed Convention Above-Stage and MultiFrac Feed Convention On-Stage in the following figures):

• •

Above-Stage On-Stage

When Feed-Convention is Above-Stage, MultiFrac introduces a material stream between adjacent stages. The liquid portion flows to the stage (n) you specify. The vapor portion flows to the stage above (n – 1). You can introduce a liquid feed to the top stage (or condenser) by specifying Stage=1. You can introduce a vapor feed to the bottom stage (or reboiler) by specifying Stage=Number of stages + 1. n-1

Vapor Mixed feed to stage n Liquid

MultiFrac Feed Convention Above-Stage


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•

4-33

n-1


n

n+1 MultiFrac Feed Convention On-Stage

When Feed-Convention is On-Stage, both the liquid and vapor portions of a feed flow to the stage n( ) you specify.

Connecting Streams

MultiFrac allows any number of connecting streams. Any number of these streams can have the same:

• •

Source column, stage, and phase Destination column and stage

MultiFrac introduces connecting streams on the destination stage regardless of their phase (that is, Feed Convention=On-Stage). All connecting streams can have a heater with heat duty, temperature, or temperature change specified. Use the ConnectStreams form to enter all specifications for connecting streams. Each terminal stream can be the source of a product stream and any number of connecting If there is no product stream, at least one connecting streamstreams. must have an unspecified flow. For a connecting stream, required specifications depend on whether the stream:

•

Has a flow rate that is fixed indirectly on the FlowRatios or Columns FlowSpecs form

• •

Is a terminal stream Is a pumparound to the top stage of column 1

For this type of connecting stream

You must specify

One that does not satisfy the above conditions

Two of the following: flow, temperature (or temperature change), and duty †

One whose flow is fixed Either temperature (or temperature indirectly on the FlowRatios or change), or duty † Columns FlowSpecs form A terminal stream (vapor distillate or liquid bottoms)

Either temperature (or temperature change) or duty †

† Duty can default to 0 if necessary.

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C o l um ns


You can enter a second specification. If this specification is missing, MultiFrac uses the net flow from the stage excluding any other connecting stream with flow specifications. For a connecting stream that is the liquid pumparound to the top stage of column 1, enter two of the following:

• • •

Flow Temperature (or temperature change) Duty (specify 0 if there is no associated heater or cooler)

If you enter only one of flow, temperature, or temperature change, MultiFrac uses the top stage duty for the missing requirement. When a stage is the destination of a connecting stream, MultiFrac uses the heat duty associated with the stage to determine the temperature of the connecting stream. When you enter the duty, temperature, or temperature change of the connecting stream, the stage duty does not affect the connecting stream temperature. Stage duty is properly accounted for in the stage enthalpy calculations. When a pumparound, bypass, or other connecting stream has a specified temperature change or outlet temperature, MultiFrac assumes that the specific value does not result in a phase change of any fraction of the stream. When you specify heat duty, a phase change may occur. Connecting streams can be either a total or partial drawoff of the stage flow. MultiFrac determines the drawoff type based on the number of specifications you give. If the drawoff type is

You enter

Partial

Two of the following: flow, temperature, temperature change, and heat duty †

Total

One of the following: temperature, temperature change, and heat duty ††

† Enter zero for heat duty if heater is absent. †† Enter zero for heat duty if heater is absent. Flow rate is taken as the net flow of the stage, excluding any product flow and any other connecting stream flow.

MultiFrac allows total drawoff only for the top vapor stream and bottom liquid stream. For partial drawoffs you can specify the flow rate. Or MultiFrac can determine the flow rate based on one of the following:

••


Another flow specification (Columns FlowSpecs form) A flow ratio specification (FlowRatios form)

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•

4-35

If you enter only one specification for pumparounds to the top stage of the main column, MultiFrac uses the top stage heat duty as the second specification. When a connecting stream has a specified temperature or temperature change, MultiFrac assumes the specified value does not result in a phase change of any fraction of the stream. When you specify the heat duty, a phase change can occur.

Heaters

Use the Columns HeatersCoolers form to enter heater stage locations and duties. You can specify heaters indirectly by choosing heater duty as the adjusted variable in one of the followingaforms:

Flow Rate Specifications

Form

Usedtospecify

Columns FlowSpecs

Stage liquid or vapor flow rate

FlowRatios

Vapor-to-liquid flow ratio

You can use the Columns FlowSpecs form to specify any stage liquid and vapor flow rates. The value you specify refers to the net flow of the stage liquid or vapor flow. This value excludes any portions withdrawn by side products and other connecting streams with flow specifications. This feature is typically used for specifying:

• • •

Internal reflux rate or total internal drawoff Overflash in refining applications Boilup rate

For a terminal stream, flow specifications refer to the net flow of the stream excluding any portion withdrawn by connecting streams with flow specifications. Flow specifications include:

• • •

Specifications provided on the ConnectStreams form Specifications fixed by the associated heater specifications Another FlowSpecs or FlowRatios specification

For an internal stream, flow specifications refer to the net flow of the stream excluding any portions withdrawn as products or connecting streams. When you enter a flow specification, MultiFrac adjusts the flow rate of a connecting stream or the duty of a heater. If the adjusted variable You enter the is

A connecting stream flowConnecting stream number in the IC-Stream A heater duty

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C o l um ns

field Heater column and stage numbers


You can place the calculated heat duty in an outlet heat stream using the InletsOutlets form. Initial estimates for adjusted variables are not required. If a product or connecting stream of the same phase is leaving the stage, a specified value may be zero to model a total drawoff . MultiFrac will vary the heat duty associated with the heater of the same stage or another stage or the flow rate of an associated connecting stream to satisfy enthalpy and mass balances. If this w ill be varied

You must specify

Heatduty Flow rate of a connecting stream

Q-ColumnandStage Stream number (IC-Stream)

Be cautious when selecting the:

• •

Associated stage with varied heat duty Connecting stream with varied flow rate

An initial guess for the associated heat duty is not required.

Flow Ratio Specifications Use the FlowRatios form to specify the ratio of two flow rates. The flows can be of different phases, and come from any stage of any column. This feature is typically used for specifying the:

• • •

Internal reflux ratio Overflash in refining applications Boilup ratio

For a terminal stream, the flows refer to the net flow of a stream, excluding any portion withdrawn by connecting streams with flow specifications. Flow specifications include those:

• •

Specified on the ConnectStreams form Fixed by either the associated heater specification, another Columns FlowSpecs sheet, or a FlowRatios Specifications sheet)

For an internal stream, the flows refer to the net flow of the stream, excluding any portion withdrawn as products or connecting streams. When you specify a flow ratio, these will be varied to satisfy enthalpy and mass balances:

• •


Heat duty of the same stage or another stage Flow rate of an associated connecting stream

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•

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When you enter a flow ratio specification, MultiFrac adjusts the flow rate of a connecting stream or the duty of a heater. If the adjusted variable You enter the is

A connecting stream flowConnecting stream number in the IC-Stream field A heater duty

Heater column and stage numbers

You can place the calculated heat duty in an outlet heat stream using the InletsOutlets form. Initial estimates for these adjusted variables are not required. Be cautious when selecting the:

• • Efficiencies

Associated stage with varied heat duty Connecting stream with varied flow rate

You can specify one of two types of efficiencies:

• •


Vaporization efficiency is defined as: Effi v

=

yi , j K i,j xi j,

Murphree efficiency is defined as: iy j ,

M

Effi , j

=

−ij y , +1 −i jy , +1

K i,j ixj ,

Where:

K

=

Equilibrium K value

x

=


y

=

Vapor mole fraction

Eff

v

=


Eff

M

=

Murphree efficiency

i

=

Component index

j

=

Stage index

To specify vaporization or Murphree efficiencies, enter the number of actual stages on the Columns Setup Configuration sheet. Then use the Columns Efficiencies form to enter the efficiencies. You can use any of these efficiencies to account for departure from equilibrium. But you cannot convert from one efficiency to the other. Magnitudes of the efficiencies can be quite different. Details

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C o l um ns


on using and estimating these efficiencies are described by Holland, Fundamentals of Multi-Component Distillation , McGraw-Hill Book Company, 1981.

Algorithms

MultiFrac has three convergence algorithms. Use the Overall field on the Convergence Methods sheet to select the algorithm. The default standard algorithm is appropriate for most applications. Your choice of algorithm depends on the types of systems you are modeling: Application

Algorithm

Airseparation Close-boiling, e.g., C3 splitter

Standard Standard

Wide-boiling, e.g., absorbers

Sum-Rates

Petroleum refining, e.g., crude unit

Sum-Rates

Ethylene plant primary fractionator

Sum-Rates

Highly-nonideal, e.g., azeotropic

Newton

Highly-coupled design specifications

Sum-rates or Newton

Rating Mode

In rating mode, MultiFrac calculates column profiles and product compositions based on specified values of column parameters. Examples of column parameters are reflux ratio, reboiler duties, and feed flow rates.

Design Mode

In design mode, use the DesignSpecs form to specify column performance parameters (such as purity or recovery). You must indicate which variables to manipulate to achieve these specifications using the Vary form. You can specify any variables that are allowed in rating mode, except:

• • • • • •


Number of stages Pressure profile Efficiencies Subcooled reflux temperature Degrees of subcooling Locations of feeds, products, heaters, and connecting streams

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•

4-39

The flow rates of inlet material streams and the duties of inlet heat streams can also be manipulated variables. Youcanspecify

Forany

Purity

Stream,includinganinternal stream †

Recovery of any component groups

Set of product streams ††

Flow rate of any component groups

Internal stream or set of product streams

Temperature

Stage

Heatduty Heatdutyratio

Stageorconnectingstream Stageorconnectingstreamtoany other stage or connecting stream

Value of any Prop-Set property


Ratio or difference of any pair of properties in a Prop-Set

Single or paired internal or product stream

Flow ratio of any component groups to any other component groups

First group can be in any internal streams ‡

† Express the purity as the sum of mole, mass, or standard liquid volume fractions of any group of components, relative to any other group of components. †† You can express recovery as a fraction of the same components in a subset of the feed stream. ††† See Aspen Plus User Guide, chapter 28. ‡ The second group can be in any other internal streams, or set of feed or product streams.

Column Convergence MultiFrac uses the inside-out approach for column convergence. You can choose from two algorithm variants of this approach:

• •

Standard Sum-rates

To select an algorithm, use the Overall field on the Convergence Methods sheet. The standard algorithm uses the standard inside-out formulation for the inside loop. It uses either the nested or simultaneous approach (specified as the Middle loop method on the Convergence Methods sheet) to converge the design specifications. This algorithm is appropriate for most systems. The sum-rates algorithm uses:

• •

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•

C o l um ns

A sum-rates variant formulation for the inside loop The simultaneous approach to converge the design specifications


Sum-rates is well suited for:

• •

Wide-boiling systems Columns with steep flow gradients

MultiFrac also has the Newton algorithm, which uses a NapthaliSandholm formulation. It solves the column-describing equations and design specifications simultaneously, using Newton ’s method. This method can enhance convergence for highly-nonideal systems, such as azeotropic distillation. The Newton algorithm is generally slower than the other algorithms.

Design Specification Convergence

MultiFrac provides two methods for handling design specification convergence:

• •

Nested middle loop Simult middle loop

When you use the nested middle loop method, the algorithm attempts to satisfy the design specifications by determining the values of the manipulated variables (within their bounds) that minimize the weighted sum of squares function:

 ^−  Φ = ∑wm  G G   G **  m

2

Where:

m

=


G

=

Calculated value

G

=

Desired value

G **

=

Scaling factor

w

=

Weighting factor



For purity and recovery, G and G are transformed by taking the ** logarithm, and G is taken as unity. 

When you use the simult middle loop method, the following algorithm solves the design specification functions simultaneously with the column describing equations:

(

)

Fm =Gm Gm−Gm / 

**

=0

The weighting factor is not available for this method. You can handle design specification convergence by using either scaling factors or weighting factors. The following algorithm attempts to satisfy design specifications by determining the values


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•

4-41

of the manipulated variables (within their bounds) that minimize the weighted sum of squares function:

 −  Φ = ∑wm  G **G   G  m

2



Where:

m

=


G

=

Calculated value

= =

Desired value Scaling factor

=

Weighting factor



G G

**

w Initialization

Use Initialization Method on the Convergence Methods sheet to choose the initialization method. MultiFrac has two initialization procedures:

• •

Standard Crude

Standard is appropriate for most systems. You must enter at least the top and bottom temperature estimates for each column. Crude invokes a special initialization procedure designed for petroleum refining and ethylene plant primary fractionator/quench tower applications. This procedure is designed for systems consisting of a main column connected to any number of sidestrippers. If you specify the following information on the Columns Setup and/or Columns FlowSpecs forms, you do not need to provide estimates:

• •

All stripper bottoms flow rates Either the distillate or bottoms flow rate of the main column

Otherwise, you must enter at least the top and bottom temperature estimates for each column. You may enter profile estimates on the Columns Estimates form to enhance convergence. Temperature estimates are usually adequate. Highly nonideal systems may require composition estimates.

Physical Properties

Use the BlockOptions form to override the global physical property method. You can specify a single property method on the BlockOptions form. MultiFrac uses this property method for all stages in all columns. Use the Columns Properties form to specify physical property methods when you use a separate property method for an

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C o l um ns


individual column. You can also split a column into any number of segments, each using a different property methods.

Free Water Handling

MultiFrac can perform free-water calculations. By default, MultiFrac performs free-water calculations for the main column condenser. The free-water phase, if present, is decanted. Use the Columns Properties form to request free-water calculations for additional stages in any column. You can define additional water decant product streams on the InletsOutlets form. You can use this capability to simulate the primary fractionator/quench

Solids Handling

tower combination of an ethylene plant. MultiFrac handles solids by:

• • •

Temporarily removing all solids from inlet streams Performing calculations without solids Adiabatically mixing solids removed from inlet streams with main column liquid bottoms

This calculation approach maintains an overall mass and energy balance around the MultiFrac block. But the bottom stage liquid product will not be in exact thermal or phase equilibrium with other bottom stage flows (for example, the bottom stage vapor flow).


MultiFrac has extensive capability to size, rate and perform pressure drop calculations for trayed and packed columns. Use the following forms to enter specifications:

• • • •




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PetroFrac Reference PetroFrac is a rigorous model designed for simulating all types of complex vapor-liquid fractionation operations in the petroleum refining industry. Typical operations include:

• • • • • •

Preflash tower Atmospheric crude unit Vacuum unit Catalytic cracker main fractionator Delayed coker main fractionator Vacuum lube fractionator

You also can use PetroFrac to model the primary fractionator/quench tower combination in the quench section of an ethylene plant. PetroFrac can detect a free-water phase in the condenser or anywhere in the column. It can decant the free-water phase on any stage. Although PetroFrac assumes equilibrium stage calculations, you can specify either Murphree or vaporization efficiencies. You can use PetroFrac to size and rate columns consisting of trays and/or packings. PetroFrac can model both random and structured packings. Use the following forms to enter specifications and view results of PetroFrac: Use this form

To do this

Setup


Pumparounds

Specify pumparound specifications and view results

Pumparounds Hcurves Specify pumparound heating or cooling curve tables and view tabular results

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C o l um ns

Strippers

Specify parameters and view results of side strippers

HeatersCoolers

Specify stage heating or cooling specifications

RunbackSpecs

Specify runback specification parameters

Efficiencies

Specify stage or component efficiencies

DesignSpecs

Specify design specifications, manipulated variables, and view convergence results

CondenserHcurves

Specify condenser heating or cooling curve

ReboilerHcurves

tables and view tabular results Specify reboiler heating or cooling curve tables and view tabular results


Use this form

To do this

TraySizing

Specify sizing calculation parameters for tray column sections, and view results

TrayRating

Specify rating calculation parameters for tray column sections, and view results

PackSizing

Specify sizing calculation parameters for packed column sections, and view results

PackRating

Specify rating calculation parameters for packed column sections, and view results

Properties


Estimates

Specify estimates for column temperatures and flows

Convergence

Specify convergence parameters

Report

Specify block-specific report options and pseudostreams

BlockOptions


UserSubroutines

Specify user subroutines for tray and packing rating and sizing

Connectivity

View stream connectivity for the PetroFrac block

ResultsSummary

View key column results for the overall PetroFrac column

Profiles

Viewcolumnprofiles


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Flowsheet Connectivity for PetroFrac

PetroFrac models column configurations consisting of a main column with any number of pumparounds and side strippers. You can specify a feed furnace. For single columns without pumparounds and side strippers, use RadFrac. For other multicolumn systems such as air separation systems, Petlyuk towers, and complex primary fractionators, use MultiFrac. Material Streams

inlet

At least one inlet material stream One steam feed per stripper (optional)

outlet One vapor or liquid distillate, or both One free water distillate stream (optional) One bottoms product from the main column Any number of side products from main column (optional) Any number of water decant products from main column (optional) One bottoms product per side stripper Any number of pseudoproduct streams (optional)

You can use any number of pseudoproduct streams to represent:

• • •

Column internal streams Pumparound streams Column connecting streams

A pseudoproduct stream does not affect column results.

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Heat Streams

inlet

One One One One

heat stream per stage for the main column (optional) heat stream per pumparound heater/cooler (optional) heat stream per stripper reboiler (optional) heat stream per stripper bottom liquid return (optional)


heat stream per stage for the main column (optional) heat stream per pumparound heaters/cooler (optional) heat stream per stripper reboiler (optional) heat stream per stripper bottom liquid return (optional)

PetroFrac usesthe an condenser, inlet heat stream as pumparounds, a duty specification for all stages except reboiler, and stripper bottom liquid return. If you do not give sufficient operating column specifications on the Setup Configuration sheet, PetroFrac uses a heat stream as a specification for the condenser and reboiler. If you do not give two specifications on the Pumparounds Specifications sheet, PetroFrac uses a heat stream as a specification for pumparounds. If you do not give two specifications for the bottom liquid return on the Strippers Setup LiquidReturn sheet, PetroFrac uses a heat stream as a specification. If you give two specifications on the Setup Configuration sheet or Pumparounds Specifications sheet, PetroFrac does not use the inlet heat stream as a specification. The heat stream supplies the required heating or cooling. Use optional outlet streams for the net heat duty of the condenser, reboiler, and pumparounds. The value of the outlet heat stream equals the value of the inlet heat stream (if any) minus the actual (calculated) heat duty.

Main Column

The main column can have any number of inlet streams. It can also have up to three product streams per stage (one vapor, one hydrocarbon liquid, and one free water).

Side Strippers

The side strippers can have a steam feed. They must have a liquid bottoms product. You can use a heat stream as the heat source for the reboiler. If you do not specify the reboiler duty, bottoms flow rate, and steam feed, PetroFrac uses the heat stream as a duty specification. Optionally, the stripper liquid bottoms may be partially returned to the main column. To specify a bottom liquid return, you must enter two specifications on the Strippers Setup LiquidReturn sheet.


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Feed Furnace

You can specify a feed furnace. Afeed furnace can have any number of feeds. The vapor and liquid streams from the furnace are fed to the stage where the furnace is attached.

Specifying PetroFrac

Within each column or stripper, stages are numbered from the top down. If present, the main column condenser is stage 1.

Main Column

You define the main column configuration using Condenser and Reboiler on the Setup Configuration sheet. PetroFrac allows six condenser types:

•

Subcooled

• • • • •

Total Partial with vapor distillate product only Partial with both vapor and liquid distillate products No condenser, with pumparound to top stage No condenser, with external feed to top stage

You can specify one of three reboiler types:

• • •

Kettle reboiler No reboiler, with pumparound to bottom stage No reboiler, with external feed to bottom stage

The types and number of required operating specifications depend on the column configuration. Normally, you must enter two column operating specifications. If either a condenser or a reboiler is absent, you must enter one specification. If both the condenser

Feed Stream Handling

and reboiler are absent, do not enter any specification. Use the Setup Streams sheet to specify the feed and product stage locations. You may also identify a feed as the stripping steam, and override its flow by specifying a steam-to-product ratio. PetroFrac provides three conventions for handling feed streams (see PetroFrac Feed Convention Above-Stage and PetroFrac Feed Convention On-Stage in the following figures):

• • •

Above-Stage On-Stage Furnace

When Feed-Convention is Above-Stage, PetroFrac introduces a material stream between adjacent stages. The liquid portion flows to the stage (n) you specify. The vapor portion flows to the stage above (n – 1). You can introduce a liquid feed to the top stage (or condenser) by specifying Stage=1. You can introduce a vapor feed to the bottom stage (or reboiler) by specifying Stage=Number of stages+1.

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When Feed-Convention is On-Stage, both the liquid and vapor portions of a feed flow to the stage (n) you specify. n-1

Vapor Mixed feed to stage n Liquid

PetroFrac Feed Convention Above-Stage

n-1


n

n+1 PetroFrac Feed Convention On-Stage

When Feed-Convention is Furnace, a furnace is attached to the stage (n) you specify. The feed enters the furnace before being introduced to the specified stage.

Feed Furnace

PetroFrac can simulate a feed furnace simultaneously with the column/strippers. You can simulate the feed furnace as a simple heater or as a single stage flash with or without feed overflash bypass to the furnace. You can specify one of the following:

• • •

Heat Duty Temperature Fractional overflash

To do this

Use this heet

Define a feed to the feed furnace Enter a furnace model type and associated

Setup Streams (Feed Convention) Setup Furnace

specifications

You can select from three furnace model types, as shown in the next three figures.


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Main Column

Heat Feed Furnace Modeled as a Stage Heat Duty

Main Column

Feed

Furnace

Furnace Modeled as a Single Stage Flash

Main Column

Feed Furnace

Furnace Modeled as a Single Stage Flash with Overflash Bypass

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Liquid Runbacks

If M odel=

PetroFrac models the And calculates furnace as

Heater

Stage heat duty on the feed stage

—

Flash

Single-stage flash

Furnace temperature, degree of vaporization, vapor/liquid compositions

Flash-Bypass

Single-stage flash with Furnace temperature, degree of the overflash bypassed vaporization, vapor/liquid back to the furnace compositions

Use the RunbackSpecs form to specify the flow rate of liquid runback from any stage. When you enter a liquid runback specification, you must allow PetroFrac to adjust one of the following:

• • Pumparounds

Flow rate of a pumparound Duty of an interstage heater/cooler

Use the following sheets to enter specifications for pumparounds. Use this sheet

Pumparounds Specifications

To enter

Pumparound connectivity and cooler/heater specifications

Report PseudoStreams Pseudostream assignment for the pumparound Hcurves Specifications Heating/cooling curve specifications

Pumparounds are associated with the maincolumn. They can be total or partial drawoffs of the stage liquid flow. You must specify the draw and return stage locations for each pumparound. For partial drawoffs, you must specify two of the following:

• • • •

Flow rate Temperature Temperature change Heat Duty

For total drawoffs, you must specify one of the following:

• • • Side Strippers

Temperature Temperature change Heat Duty

Use the Stripper forms and sheets to enter specifications for side strippers. Side strippers may be either steam-stripped or reboiled. For steam strippers, you must enter a steam stream. You can override its flow


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rate by specifying a steam-to-product ratio. For reboiled strippers, you must specify a reboiler duty. PetroFrac assumes:

•

A liquid draw goes from the main column to the top of the stripper.

•

The stripper overhead is returned to the main column.

You must specify the draw and return stage locations. You can also:

• • Efficiencies

Return a fraction of the stripper bottoms to the main column Specify additional liquid draws from other stages of the main column as feeds to the strippers

PetroFrac supports two kinds of efficiencies: vapor-liquidequilibrium efficiencies and thermal efficiencies. Vapor-Liquid-Equilibrium Efficiencies

You can specify one of two types of vapor-liquid-equilibrium efficiencies:

• •


Vaporization efficiency is defined as: Effi v

=

yi , j K i,j xi j,

Murphree efficiency is defined as: Effi ,Mj

=

iyj ,

−ij y , +1 −i jy , +1

ki,j ixj ,

Where:

K

=

Equilibrium K value

x

=


y

=

Vapor mole fraction

Eff v

=


Eff M

=

Murphree efficiency

i

=

Component index

j

=

Stage index

To specify vaporization or Murphree efficiencies, enter the number of actual stages on the Setup Configuration sheet and Strippers Setup Configuration sheet as Number of stages. Then use the

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Efficiencies and Strippers Efficiencies forms to enter the efficiencies. You can use any of these efficiencies to account for departure from equilibrium. But you cannot convert from one efficiency to the other. Magnitudes of the efficiencies can be quite different. Details on using and estimating these efficiencies are described by Holland, Fundamentals of Multi-Component Distillation , McGraw-Hill Book Company, 1981. Thermal efficiencies

Thermal efficiencies are thermal an AspenTech proprietary type of efficiencytray used to model the non-equilibrium effects found in large refinery columns such as crude columns and main fractionators. Vapor thermal efficiencies are designed for columns that have high vapor loads such as crude columns, cat cracker, and coker main fractionators. These columns typically have superheated vapor feeds and are characterized by high vapor-to-liquid ratios, especially near the bottom of the column. The thermal tray efficiency allows the vapor and liquid temperatures to be different (not at equilibrium), thus allowing for the calculation of both a compositional and a thermal deviation from equilibrium. In contrast, Murphree tray efficiencies assume thermal equilibrium between the vapor and liquid phases. Thermal tray efficiencies are definedstrictly over the range 0.0 to 1.0 with 1.0 corresponding to an ideal stage atthermal equilibrium. Vapor thermal tray efficiencies should be used where high and/or superheated vapor flows dominate the column profile. Liquid thermal tray efficiencies should be used in the opposite situation where high and/or sub-cooled liquid flows dominate the column profile. Only one of these two types of thermal efficiency may be used on any given section of the column. Thermal tray efficiencies are defined analogously to Murphree tray efficiencies. Murphree tray efficiencies can be used with vapor of liquid tray efficiencies, but care must be taken to understand the relative effects of the two efficiencies and to ensure that independent measurements are used to tune them.

Convergence

For convergence PetroFrac uses:

• •


The sum-rates variant of the inside-out algorithm A special initialization procedure designed for petroleum refining applications

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PetroFrac generally does not need initial estimates. For ethylene plant primary fractionator/quench tower combinations, you should provide temperature estimates. To enhance convergence, you may enter profile estimates on the following PetroFrac forms:

• •

Estimates Strippers Estimates

Temperature estimates are usually adequate. You can increase convergence stability by selecting varying degrees of damping on

Rating Mode

the Convergence Basic sheet. In rating mode, PetroFrac calculates the column profiles and product compositions based on specified values of column parameters. Examples of column parameters are:

• • • • • Design Mode

Reflux ratio Reboiler duties Feed flow rates Furnace temperature Pumparound loads

In design mode you can manipulate subsets of the column parameters to achieve certain specifications on column performance. Youcanspecify

Purity

Stream,includinginternal streams †

Recovery of any components group


Flow rate of any components group

Internal stream or set of product streams

Flow rates of any components groups to any other component groups

Internal streams to any other internal streams, or set of feed or product streams

Temperature

Stage

Heat duty Fractionaloverflash

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Forany

Stage Stage

TBP and D86 temperature gaps

Pair of product streams

TBPtemperature

Productstream

D86temperature

Productstream

D1160temperature

Productstream

Vacuum distillation temperature APIgravity

Product stream Productstream

Standard liquid density

Product stream

Specificgravity

Productstream


Youcanspecify

Forany

Flashpoint

Productstream

Pourpoint

Productstream

Refractiveindex

Productstream

Reidvaporpressure

Productstream

Value of any Prop-Set property


Difference of any pair of Prop-Set properties

Pair of product streams

WatsonUOPKfactor

Productstream

† Express the purity as the sum of mole, mass, or standard liquid volume fraction of any group of components relative to any other group of components. †† Express recovery as a fraction of the same components in a subset of feed streams. ††† See Aspen Plus User Guide, Chapter 28.

You can also specify overflash for a furnace feed stream.

Physical Properties

Use the BlockOptions form to override the global physical property method. You can specify one method on this form, which PetroFrac uses for all stages in the main column and strippers. You can also split the main column or a stripper into any number of segments, each using a different property method.

Free Water Handling

Use this sheet

When you use different properties for

Properties Property Sections Strippers Properties Property Sections

The main column A stripper

PetroFrac can perform free-water calculations in the main column and side strippers. By default, PetroFrac performs free-water calculations for the main column condenser. The free-water phase, if present, is decanted. Todothis

Usethesesheets

Request free-water calculations Properties Freewater Stages for additional stages in the main Strippers Properties Freewater Stages columns and strippers Define additional water decant Setup Streams product streams for the main column

Solids Handling

PetroFrac handles solids by:

• •


Temporarily removing all solids from inlet streams Performing calculations without solids

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•

Adiabatically mixing solids removed from inlet streams with main column liquid bottoms

This calculation approach maintains an overall mass and energy balance around the PetroFrac block. But the bottom stage liquid product will not be in exact thermal or phase equilibrium with other bottom stage flows (for example, the bottom stage vapor flow).


PetroFrac has extensive capabilities to size, rate, and perform pressure drop calculations for trayed and packed columns. Use the following PetroFrac forms to enter specifications: • TraySizing, TrayRating, PackSizing, PackRating

•

Strippers TraySizing, Strippers TrayRating, Strippers PackSizing, Strippers PackRating


EO Usage Notes for PetroFrac


• • • • • •

Feed conventions FURNACE and ABOVE-STAGE

• • • • •

Liquid return from strippers to main column

Multiple feeds to trays All Furnace specifications Ratio of steam to products specifications Additional feed from main column to strippers Stage pseudostreams for main shell and strippers with total liquid/total vapor phase Free-water stage specifications in the main column or strippers TPSAR with pressure update Prop-sections Features which are globally unsupported

Some features in Petrofrac are not supported in the EO formulation. When these features appear in Petrofrac blocks running in EO mode, they are dropped from the problem specifications with a warning.

• •

Design specs involving property differences Design specs and manipulated variables spanning different columns

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RateFrac Reference RateFrac is a rate-based nonequilibrium model for simulating all types of multistage vapor-liquid fractionation operations. RateFrac simulates actual tray and packed columns, rather than the idealized representation of equilibrium stages. RateFrac explicitly accounts for the underlying interphase mass and heat transfer processes to determine the degree of separation. RateFrac does not use empirical factors such as efficiencies and the Height Equivalent to a Theoretical Plate (HETP). RateFrac is applicable for:

• • • • • •

Ordinary distillation Absorption Reboiled absorption Stripping Reboiled stripping Extractive and azeotropic distillation

RateFrac is suitable for:

• • •

Two-phase systems Narrow and wide-boiling systems Systems exhibiting strong liquid phase nonideality

RateFrac can also detect and handle a free water phase in the condenser. RateFrac can model columns with chemical reactions. Reactions include:

• • •

Equilibrium Rate-controlled Electrolytic

RateFrac models a complex configuration consisting of a single column or interlinked columns. The configuration may have:

•

Any number of columns, each with any number of RateFrac Segments

•

Any number of connections between columns or within each column

Arbitrary flow splitting and mixing of connecting streams •RateFrac can handle operations with:

•


Side strippers

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• • •

Pumparounds Bypasses External heat exchangers

RateFrac can be used to

• •

Rate existing columns Design new columns

You can define pseudoproduct streams to represent column internal flows or connecting streams in RateFrac. You can use Fortran Blocks, Sensitivity Analysis, and Case Study blocks to vary configuration parameters, such as feed location or number of segments. RateFrac can produce segmentwise column profile plots. RateFrac can be used with other Aspen Plus features and capabilities much in the same way as the equilibrium-based models, RadFrac, PetroFrac, and MultiFrac. Use the following forms to enter specifications and view results for RateFrac: Usethisform

BlockParameters

Todothis

Specify overall block parameters, convergence and initialization parameters, block-specific diagnostic message levels, and feed flash convergence parameters

Columns

Enter specifications and view results for individual columns

Inlets Outlets

Specify feed and product stream locations and conventions, inlet and outlet heat streams

Connect Streams

Specify connecting stream sources and destinations and view results

Design Specs

Specify design specifications and view convergence results

Vary


Flow Ratios

Specify the flow ratio and view results

Condenser Hcurves

Specify condenser heating or cooling curve tables and view tabular results

Reboiler Hcurves


Connect Stream Hcurves

Specify connecting stream heating or cooling curve tables and view tabular results

Reports

Specify block-specific report options, and pseudostream information

User Subroutines

Specify user subroutine parameters for mass and heat transfer coefficients, interfacial area, pressure drop, and kinetics

Block Options

Override global values for physical properties, simulation options, diagnostic

Results Summary

message levels, and report options for this block View material and energy balance results and overall split fractions

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Flowsheet Connectivity for RateFrac

Vapor Distillate or Interconnecting Stream

Top Segment or Condenser Heat Duty (optional)

Feeds

1

Reflux

Heat (optional)

Heat (optional) Liquid Distillate (optional) Water Distillate (optional) Side Products Interconnecting Streams (Heater optional)

Pumparounds and Bypasses (Heater optional)

Interconnecting Streams

(Heater optional) Heat (optional) Bottom Segment or Reboiler Heat Duty (optional)

N

Heat (optional) Bottoms or Interconnecting Streams

RateFrac models single and interlinked columns. Any number of columns can be connected by any number of connecting streams. Each connecting stream can have an associated heater. Each column may have:

• • •

Any combination of packed and tray segments Any number of connecting streams Any number of side product streams

Material Streams

inlet


outlet Up to two product streams (one vapor, one liquid) per segment One water distillate product stream (optional) Any number of pseudoproduct streams (optional)

Each column must have:

• •

At least one vapor or liquid stream leaving the top segment One liquid stream leaving the bottom segment

When you model interlinked columns, the top and bottom streams can be connecting streams. However, the free-water stream from the condenser cannot be a connecting stream. Heat Streams

inlet

One heat stream per segment (optional) One heat stream per connecting stream (optional)

outlet One heat stream per connecting stream (optional)


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RateFrac uses an inlet heat stream as a duty specification for all segments except the condenser, reboiler, and connecting streams. If you do not provide two column operating specifications on the Columns Setup Configuration sheet, RateFrac uses a heat stream as a specification for the condenser and reboiler. If you do not provide two specifications on the ConnectStreams Input sheet, RateFrac uses a heat stream as a specification for connecting streams. If you provide two specifications on the Columns Setup Configuration sheet ConnectStreams Input sheet, RateFrac not use the inlet heatorstream as a specification. The inlet heat does stream supplies the required heating or cooling. You can use optional outlet heat streams for the net heat duty of the condenser, reboiler, and connecting streams. The value of the outlet heat stream equals the value of the inlet heat stream (if any), minus the actual (calculated) heat duty.

The Rate-Based Modeling Concept

Most models available for simulating and designing multicomponent, multistage separation processes are based on the idealized concept of equilibrium or theoretical stages. This approach assumes that the liquid and vapor phases leaving any stage are in thermodynamic equilibrium with each other. The phase compositions, temperature, and vapor and liquid flow profiles are calculated by solving the governing material balances, energy balances, and equilibrium relations for each stage. In practice, columns rarely operate under thermodynamic equilibrium conditions. Vapor-liquid equilibrium prevails only at the interface separating vapor and liquid phases. The separation achieved in a multistage column depends on the interphase mass and heat transfer rate processes. Multicomponent mass transfer interactions can also have pronounced effects on the separation. When the equilibrium approach is used to model a tray column, a correction factor (referred to as an efficiency) attempts to account for the departure from equilibrium. Many definitions for efficiency exist, with wide variations in complexity and accuracy. In general, efficiencies depend on:

•

Physical characteristics of the equipment, such as column configuration

• •

Hydrodynamics of the column Fluid properties of the system

Murphree vapor efficiencies are the most widely used. These efficiencies generally vary from stage to stage within a column, and from component to component. For multicomponent systems,

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there are no theoretical limitations on Murphree efficiencies. Experimental evidence shows that component efficiencies:

• •

May vary strongly from component to component Can take any value including negative values

Methods used to calculate component efficiencies generally do not include the effect of the departure from thermal equilibrium. Packed columns are also designed using the equilibrium stage concept. However, HETP is commonly used in place of efficiencies. HETP varies with:

• • •

Type and size of the packing Hydrodynamics of the column Fluid properties of the system

Like efficiencies, HETPs may vary strongly from point to point within a column and from system to system. RateFrac is based on a fundamental and rigorous approach. This approach avoids uncertainties that result when the equilibrium approach is used with estimated efficiencies or HETP. RateFrac directly includes mass and heat transfer rate processes in the system of equations representing the operation of separation process units. RateFrac:

•

Describes the simultaneous mass and heat transfer rate phenomena

•

Accounts for the multicomponent interactions between simultaneously diffusing species

For nonreactive systems, RateFrac comprises:

• •

Mass and heat balances around vapor and liquid phases

•

Vapor-liquid equilibrium relations applied at interfacial conditions

•

Correlations to estimate mass and heat transfer coefficients and interfacial areas

Mass and heat transfer rate models to determine interphase transfer rates

For chemically reactive systems, RateFrac includes equations to account for the influence of chemical reactions on heat and mass transfer rate processes. For systems involving equilibrium reactions, RateFrac includes equations to represent the chemical equilibrium conditions. RateFrac completely avoids the need for efficiencies in tray columns or HETPs in packed columns. RateFrac has far greater predictive capabilities than the conventional equilibrium model.


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Specifying RateFrac

RateFrac numbers segments from the top down, starting with the condenser (or starting with the top segment if there is no condenser).

Column Numbering

Individual columns are identified by a column number. The numbering order does not affect algorithm performance. Within each column, segments are numbered from top to bottom, starting with the condenser (when present).

Stream Definition

RateFrac uses four types of streams:

•

External streams

• • •

Connecting streams Internal streams Pseudostreams

External streams are the standard RateFrac inlet and outlet streams. They are identified by stream IDs. Connecting streams are streams within RateFrac but external to individual columns. These streams are identified by connecting stream numbers. Connecting streams may connect two columns or segments of the same column (such as bypasses and pumparounds). You can associate a heater with any connecting stream. Heaters are identified by the connecting stream number. Internal streams are the liquid or vapor flows between adjacent segments of the same column. These streams are identified by a segment number and a column number. Pseudostreams store the results of internal and connecting streams. They are a subset of external outlet streams. Unlike normal outlet streams, pseudostreams do not participate in the block material balance calculations.

Material Feed Streams

RateFrac uses two conventions for handling material feed streams (see RateFrac Feed Conventions in the following figures):

• •

Above segment On segment Segment n-1

Mixed Feed to

Vapor Liquid

Segment n Segment n RateFrac Feed Convention Above Segment

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Segment n-1

Liquid

Mixed Feed to Segment n Segment n Vapor

Segment n + 1 RateFrac Feed Convention On Segment

When the feed convention is defined as Above segment, RateFrac introduces a material stream between adjacent segments. The liquid portion flows to segment n, specified as the feed segment. The vapor portion flows to the segment above (segment n-1 in the figure RateFrac Feed Convention Above segment). You can introduce a liquid to the top segment (or condenser) by specifying Segment=1. You can introduce a vapor feed to the bottom segment (or reboiler), by specifying the segment equal to the last segment in the column +1. When a two-phase feed stream is fed to segment 1, the vapor phase is combined directly with the vapor distillate. Similarly, when a two-phase feed stream is fed to the last segment of that column + 1, the liquid phase is combined directly with the liquid bottoms product. When the feed convention is defined as On segment, both the liquid and vapor portions of the feed flow to segment specified (segment n in the previous figure RateFrac Feed Convention On segment). RateFrac assumes that a vapor feed (or the vapor portion of a mixed feed) combines with the vapor phase in the segment it enters. RateFrac also assumes that a liquid feed (or the liquid portion of a mixed feed) combines with the liquid phase in the segment it enters.

Column Configuration

Specify the column configuration by indicating the following on the Columns Configuration sheet:

• • • A s pe nP l u s1 1 . 1U n i tO p e r a t i onM o de l s

Number of segments Presence or absence of condensers and reboilers Equilibrium and nonequilibrium segments

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Connecting Streams

RateFrac allows any number of connecting streams. Any number of these streams can have the same:

• •

Source column, segment, and phase Destination column and segment

RateFrac introduces connecting streams on the destination segment regardless of their phase (Convention = On Segment). All connecting streams can have a heater. Enter all specifications for connecting streams on the ConnectStreams Input sheet. RateFrac does not allow phase change for connecting streams. Connecting streams can be either a total or a partial drawoff of the segment flow. Enter the required specifications as follows: If th e drawoff type is You enter

Partial

Two of the following: flow, temperature or temperature change and heat duty †

Total

One of the following: temperature or temperature change and heat duty ††

† Enter zero for heat duty if heater is absent. †† Enter zero for heat duty if heater is absent. Flow is taken as the net flow of the segment, excluding any product flow and any other connecting stream flow.

Required Specifications

You must specify the total number of columns and connecting streams. Usethisform

Toenter

Suchas

Columns TraySpecs

Tray specifications

Number of trays or Number of trays per segment Tray type Tray characteristics

Columns PackSpecs

Packing specifications

Total height of packing or Height of packing per segment Packing type Packing characteristics

You must also specify:

• • • • • •

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C o l um ns

Inlet stream locations Heat stream locations, heat duty, and phase Pressure profile for each column Condenser type Two operating specifications for multisegment columns and one for single-segment columns Source and destination of any connecting stream and associated heater specifications


•

Outlet stream locations and phases. If the outlet stream is a side drawoff stream from a segment, you must specify its flow.

A segment refers to one of the following:

•

A slice (or portion) of packing in a packed column (see the preceding figure, Nonequilibrium Segment in a Packed Column)

•

One (or more) tray(s) in a tray column (see the preceding figure, Nonequilibrium Segment in a Tray Column)

A column consists of segments. To evaluate mass and heat transfer rates between contacting phases, RateFrac uses one of the following:

• •

Height of packing in a packed segment Number of trays in a tray segment

Nonequilibrium Segment in a Packed Column


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Nonequilibrium Segment in a Tray Column

Equilibrium Stages

RateFrac can model both equilibrium stages and nonequilibrium segments in the same column. Use the Columns EquilibriumSegments form to specify the location of equilibrium stages. When all stages are equilibrium, you can obtain the same results using RateFrac as you can using RadFrac, MultiFrac, or PetroFrac with ideal stages.

Reactive Systems

RateFrac can handle kinetically controlled reactions and equilibrium reactions in both liquid and vapor phases. Chemical reactions can be of any type, including:

• • • • •

Simultaneous Consecutive Parallel Forward Reverse

For kinetically controlled reactions, the kinetics can be defined by one of the following:

• •

Built-in power law expressions User-supplied Fortran subroutines

For equilibrium reactions, the chemical reaction equilibrium constant can be defined either in terms of user-supplied coefficients for a temperature-dependent polynomial, or can be computed from the reference state free energies of participating components. RateFrac can model electrolyte systems using both the apparent and the true component approaches.

4-66

•

C o l um ns


Enter the following information on the Reactions form:

• • •

Reaction stoichiometry Reaction type Phase in which reactions occur

Depending on the reaction type, you must enter either the equilibrium constant or kinetic parameters. For electrolytic reactions, you can also enter the reaction data on the Chemistry form. To associate reactions with a column segment, enter the corresponding Reactions ID (or Chemistry ID or User Reactions ID) on the Columns Reactions Specifications sheet. For rate-controlled reactions, you must enter holdup data for the phase where reactions occur.

Heaters and Coolers

For these segments

Use this form to enter holdup information

Equilibrium

Columns Reactions

Tray

ColumnsTraySpecs

Packed

ColumnsPackSpecs

Use the Columns HeatersCoolers Side Duties sheet to specify:

• • •

Heat duty for a segment Heater segment location (column and segment) Phase

Use the Columns HeatersCoolers Utility Exchangers sheet to specify cooling (or heating) of any segment using a coolant (or heating fluid). You can use a heat stream to provide heat integration. Heat integration occurs when the duty recovered from another block is used as the heat source of heaters and coolers. Enter heat stream data on the InletsOutlets Heat Streams sheet.

Physical Property Specifications

Use the RateFrac BlockOptions form to override the global physical property property method. You can specify only one property method on the BlockOptions form. RateFrac uses this property method for the whole column. RateFrac does not allow multiple physical property methods.

Handling Free Water

RateFrac can perform free-water calculations only in condensers.

Rating Mode

In rating mode, RateFrac calculates temperatures, flows, and mole fraction profiles based on specified values of column parameters such as:

• • A s pe nP l u s1 1 . 1U n i tO p e r a t i onM o de l s

Reflux ratio Product flows

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•

4-67

• Design Mode

Heat duties

In design mode, use the DesignSpecs form to specify column performance parameters (such as purity or recovery). You must indicate which variables to manipulate to achieve these specifications using the Vary form. You can specify any variables that are allowed in rating mode, except:

• • • •

Number of columns, segments, and connecting streams Pressure profile Locations of feeds, products, heaters, and connecting streams Column configurations, including the number of trays, tray characteristics, height of packing, packing specifications

The flows of inlet material streams and the duties of inlet heat streams can also be manipulated variables. Youcanspecify

Forany

Purity

Stream,includinganinternalstream

Recovery of any component groups


†

Flow of any component groups Internal stream or set of product streams Component ratio

Internal stream and a second internal stream or feed streams and product streams

Temperature of va por stream

Segment

Temperature of liquid stream

Segment

Heat duty

Condenser,reboiler, or aconnecting stream

Value of any Prop-Set property Internal or product stream ††† Ratio or difference of any pair Single or paired internal or product of properties in a Prop-Set stream

† Express the purity as the sum of mole, mass, or standard liquid volume fractions of any group of components, relative to any other group of components. †† You can express recovery as a fraction of the same components in a subset of the feed stream. ††† See Aspen Plus User Guide, Chapter 28.

Calculating Efficiency and From converged vapor and liquid composition profiles, RateFrac HETP back-calculates the component Murphree vapor efficiencies. These efficiencies are defined for each component as the fractional approach to equilibrium of the the vapor stream leaving any segment, with the liquid stream leaving same segment. Eff ij

4-68

•

C o l um ns

=

y ij

− yij +1 − Yij +1

K ij xij


Where:

Eff

=

Murphree vapor efficiency

K

=

Vapor-liquid equilibrium K value

x

=


y

=

Vapor mole fraction

i

=

Component index

j

=

Segment index

For each segment columns, RateFrac calculates theas fractional approachoftopacked equilibrium using the same definition used for Murphree vapor efficiency. RateFrac reports the height of packing required to achieve equilibrium as the HETP for that segment.

Convergence and Computing Time

RateFrac must solve many more equations for a given column than an equilibrium model. Computing times for RateFrac are greater than they are for equilibrium models, particularly for problems containing many components. The solution algorithm RateFrac uses is an efficient, Newton-based simultaneous correction approach. RateFrac solution times increase with the square of the number of components. Solution times can be an order of magnitude greater than RadFrac, MultiFrac, or PetroFrac solution times for the same problems.

References for Built-In Correlations

RateFrac uses well-known and accepted correlations to calculate:

••

Binary mass transfer coefficients for the vapor and liquid phase Interfacial areas

In general, these quantities depend on column diameter and operating parameters such as:

• • • • •

Vapor and liquid flow Densities Viscosities Surface tension of liquid Vapor and liquid phase binary diffusion coefficients

Mass transfer coefficients and interfacial areas depend on: Packing characteristics

Tray characteristics

Type (random or structured)

Type (sieve, valve, or bubble-cap)

Size Specific surface area Material of construction


Weirandflowpathlength Downcomer area Weir height

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•

4-69

The correlations involve well-defined dimensionless groups, such as the Reynolds, Froude, Weber, Schmidt, and Sherwood numbers. The correlations have been fitted to experimental measurements from laboratory and pilot plant absorption and distillation columns. The correlations RateFrac uses for mass transfer coefficients and interfacial areas are: Columntype

Correlationused

Packed Columns (random packing)

Onda et al. (1968)

Packed Columns (structured)

Bravo et al. (1985, 1992)

Sieve Trays † ValveTrays

Chan and Fair (1984) ScheffeandWeiland(1987)

Bubble-Cap Trays †

Grester et al. (1958)

† These correlations do not provide the mass transfer coefficients and interfacial areas separately.

RateFrac allows you to write Fortran subroutines to calculate:

• • •

Binary mass transfer coefficients Heat transfer coefficients Interfacial areas

The subroutines are described in theAspen Plus User Models reference manual. By applying a rigorous multicomponent mass transfer theory (Krishna and Standart, 1976), RateFrac uses binary mass transfer coefficients to evaluate: • Multicomponent binary mass transfer coefficients

•

Component mass transfer rates between vapor and liquid phases

RateFrac calculates the vapor phase and liquid phase heat transfer coefficients using the Chilton-Colburn analogy (King, 1980). This analogy relates:

• • • •

4-70

•

C o l um ns

Mass transfer coefficients Heat transfer coefficients Schmidt number Prandtl number


Mass and Heat Transfer Correlations

Packed Column

RateFrac uses several mass and heat transfer correlations:

• • • • •

Packed column mass transfer coefficients Valve Tray column mass transfer coefficients Bubble-Cap Tray column mass transfer coefficients Sieve Tray column mass transfer coefficients Heat transfer coefficients

RateFrac calculates the mass transfer coefficients and the interfacial area available for mass transfer using the correlations developed by Onda et al., 1968. The correlation for the liquid phase binary mass transfer coefficients is: 2/ 3  L  ρ L  1/ 3   L  −1/ 2 k in   ( ScinL ) a( dp   = 0.0051  aω µ L    gµ L  

p

)

0 .4

The correlation for the gas phase binary mass transfer coefficient is: 0 .7  g  RT g       = 5.23 G  ( Scing ) 1/ 3 a( dp k in   a pug    a p Din  

p

)

−2

The interfacial area available for mass transfer is given by the correlation: 0.1

aω = a

p

Where:

Re L

=

L [ − 1Re.45 Fr

{

L a pµ L

FrL ,

=

a ρ L2 gρ 2L

We L ,

L

=

−0.75

0 .2

− 0.05

WeL

1 − exp

L

(σ σ c )

]}

2

a p σρ L

and: =

Binary mass transfer coefficient for the binary pair i and n in the liquid phase (m/sec)

ρL

=

Density of liquid (kg/m )

g

=

Acceleration due to gravity (m/sec )

µL

=

Viscosity of liquid (Newton-sec/m )

L aw

= =

Liquid superficial mass velocity (kg/m /sec)

L

k in

3

2

2

2


2

Wetted interfacial area (m interfacial area/m packing volume)

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•

3

4-71

L

Sc in

Schmidt number for the binary pair i and n in

=

the liquid phase = L

D in

=

µ L ( ρ L DinL )

Binary Maxwell-Stefan diffusion coefficient 2

for the binary pair i and n (m /sec)

ap

=

Specific surface area of the packing

dp

=

Nominal diameter of packing or packing size (m)

g

=

Binary mass transfer coefficient for the binary pair i and n in the vapor phase (kg

k in

2

mole/atm/m /sec) 3

=

Universal gas constant (m atm/kg mole/K)

=

Gas phase temperature (K)

G

=

Gas superficial mass velocity (kg/m /sec)

µg

=

Viscosity of gas mixture (Newton-sec/m )

=

Gas phase Schmidt number for the binary pair

R

T

g

g

Sc in

2

2

µ g ( ρg

i and n =

Valve Tray Column

Dg

in

)

ρg

=

Density of gas mixture (kg/m )

D ing

=

Gas-phase binary Maxwell-Stefan diffusion 2 coefficient for the binary pairi and n (m /sec)

σ σc

=

Surface tension (Newton/m)

=

Critical surface tension of the packing material (Newton/m)

3

RateFrac calculates the mass transfer coefficients and the interfacial area available for mass transfer using the correlations developed by Scheffe and Weiland, 1987. The correlation for the liquid phase binary mass transfer coefficient is:

ShinL

0.68

= 1254. Re (

g

) Re(

0.09

)v

L

(Sc)in0.05 (

L 0.5

)

The correlation for the gas phase binary mass transfer coefficients is:

Shing

4-72

•

C o l um ns

= 9.93Re (

0.87

g

) Re(

L

)

0.13

( ϖSc )in0.39 (

g

)

0.5


The interfacial area available for mass transfer is given by the correlation:

a

= 0.27( Reg )

0.37

( Re L )

0.25

( ϖ) 0.52

Where: L

ShinL

Re L

= =

g

k in ad

Shing

L

ρ L D in Ld

µL ,

,

Re g

=

=

k in ad

ρ g D in

Gd

ScinL

g

,

µg , ϖ =

=

µL

Scing

L

ρ L D in

=

,

µg ρ g D ing

,

W d

and: 2

L

=

Liquid mass velocity (kg/m /sec) (Velocity is based on tower active area.)

d

=

Geometric parameter of unit length (m)

µL

=

Viscosity of liquid mixture (Newton-sec/m )

G

=

Gas mass velocity (kg/m /sec) (Velocity is based on tower active area.)

µg

=


L

=

Binary mass transfer coefficient for the binary

k in

2

2

2

2

pair i and n in the liquid phase (kg mole/m /sec) 2

2

a

=

Interfacial area (m interfacial area/m tower active area)

ρL

=

Molar density of liquid (kg mole/m )

=

Binary Maxwell-Stefan diffusion coefficient

L

D in g

k in

ρg g

2

for the binary pair i and n (m /sec) =


Binary mass transfer coefficient for the binary 2

pair i and n in the vapor phase (kg mole/m /sec) 3

=

Molar density of gas mixture (kg mole/m )

=

Gas-phase binary Maxwell-Stefan diffusion

D in

ρL

3

2

coefficient for the binary pairi and n (m /sec) =

3

Density of liquid mixture (kg/m )

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•

4-73

ρg

=


W

=

Weir height (m)

3

Bubble-Cap Tray Column RateFrac calculates the product of the binary mass transfer coefficients and interfacial areas using the correlations developed by Grester et al., 1958. The product of liquid phase binary mass transfer coefficients and interfacial area is given by the correlation: L

ak in

8

= ( 4.127D× 10

L 0.5 in

Lt . ) + 015 ) F(0.21313

L

The product of gas phase binary mass transfer coefficient and interfacial area is given by the correlation: g

k in a

=

( 0.776 + 4.567hw − 0.2377 F + 104.85QL ) G ( Scing ) 0.5

Where: L

k in

a

L

=



2

=


=


D in

2


F

=

µg

=

F-Factor =

µ g ρ1g/ 2

 1/ 2 k g

/s ec/ m

1/ 2 

 3

Gas volumetric flow per unit active area (m 2

/sec/m )

ρg

=


L

=

Liquid molar velocity (kg mole/m /sec) (Velocity is based on active area.)

tL

=

Liquid residence time = 0.9998hL Z L / QL (sec)

hL

=

Liquid holdup =

ZL QL

4-74

•

C o l um ns

= =

3

2

0.04191 + 0.19hw

+ 2.4545 Q

L

−m0F.0135

( )

Liquid flow path length (m) 3

Liquid flow per average path width (m /sec/m)


hw

=

Outlet weir height (m)

g

=

Binary mass transfer coefficient for the binary

k in

2

pair i and n in the vapor phase (kg mole/m /sec)

G

g

Sc in

2

=

Gas molar velocity (kg mole/m /sec) (Velocity is based on active area.)

=

Gas-phase Schmidt number for the binary pair

µ g ρg i and n =

µg g

D in Sieve Tray Column

Dg

in

(

)

2

=


=

Gas-phase binary Maxwell-Stefan diffusion 2

coefficient for the binary pairi and n (m /sec)

RateFrac calculates the product of mass transfer coefficients and interfacial areas using the correlations developed by Chan and Fair, 1984. The product of liquid phase binary mass transfer coefficient and interfacial area is given by the correlation: L

kain

= ( 4x.127 D

10 8

L 0.5 in

+ 0.15) Lt ) F ( 0.21313

L

The product of the gas phase binary mass transfer coefficient and interfacial area is given by the correlation: 0.5

g

k in a

=

( Ding ) (1030 F − 867 F ) 2

hL

0.5

Where: L

k in

a

L

D in

=



2

=


=

Binary Maxwell-Stefan diffusion coefficient 2


F

=

µg

=

F-Factor =

µ g ρ g 1/ 2 ( kg 1/ 2 / sec / m1/ 2 ) 3

Gas volumetric flow per unit active area (m 2

/sec/m )


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•

4-75

ρg

=


L

=

Liquid molar velocity (kg mole/m /sec) (Velocity is based on active area.)

tL

=

Liquid residence time = 0.9998hL Z L / QL (sec)

hL

=

0.04191 + 0.19hw

ZL

=

Liquid flow path length (m)

Q

=

Liquid flow per average path width

3

2

L

+ 2.4545 Q

−m0F.0135

( )

3

(m /sec/m)

hw

=

Outlet weir height (m)

g

=

Binary mass transfer coefficient for the binary pair i and n in the vapor phase (m/sec)

=


k in g

D in

2


F

=

Fractional approach to flooding gas velocity = µg / µgF

µgF

=

Gas velocity through active area at flooding (m/sec)

hL

=

Liquid height =

Γwe h + 1533 eL Γ B e (Q

Heat Transfer Coefficients

L

/Γ

)

2/ 3

( m)

Γe

=

exp( − 1255 . Ks

B

=

0.0327 + 0.0286 exp( − 137.8hω )

Ks

=

µ gρ (g ρL( g ρ−

ρL

=

Density of liquid mixture (kg/m )

0.91

)

)

) 0.5

( m / sec) 3

RateFrac calculates the heat transfer coefficients, using the Chilton-Colburn analogy (King, 1980). The heat transfer coefficient is given by: 2/ 3 k av ( Sc)

4-76

•

C o l um ns

=

htc Cpmix

Where: k av

=

Average binary mass transfer coefficients (kg mole/sec)

Sc

=

Schmidt number


References

htc

=

Heat transfer coefficient (Watts/K)

Cpmix

=

Molar heat capacity (Joules/kg mole/K)

Pr

=

Prandtl number

Bravo, J.L., Rocha, J.A., and Fair, J.R., "Mass Transfer in Gauze Packings", Hydrocarbon Processing, January, 91 (1985). Bravo, J.L., Rocha, J.A., and Fair, J.R., "A Comprehensive Model for the Performance of Columns Containing Structured Packings", ICHEME Symposium Series, 128, A439 (1992). Chan, H. and Fair, J.R., "Prediction of Point Efficiencies in Sieve Trays: 1. Binary Systems, 2. Multicomponent Systems," Ind. Eng. Chem. Process Des. Dev., 23, (1984) p. 814. Grester, J.A., Hill, A.B., Hochgraf, N.N., and Robinson, D.G., "Tray Efficiencies in Distillation Columns," AIChE Report, (1958). King, C.J., Separation Processes, Second Edition, McGraw-Hill Company, (1980). Krishna, R. and Standart, G.L., "A Multicomponent Film Model Incorporating a General Matrix Method of Solution to the Maxwell-Stefan Equations," AIChE J., 22, (1976) p. 383. Onda, K., Takeuchi, H., and Okumoto, Y., "Mass Transfer Coefficients between Gas and Liquid Phases in Packed Columns," J. Chem. Eng., Japan, 1, (1968) p. 56. ’ Handbook," Perry, R.H. and Chilton, C.H., "Chemical Engineers Fifth Edition, McGraw-Hill Book Company, Section 18 (1973).

Scheffe, R.D. and Weiland, R.H., "Mass Transfer Characteristics of Valve Trays," Ind. Eng. Chem. Res., 26, (1987) p. 228.


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•

4-77

BatchFrac Reference BatchFrac is a batch distillation model that solves unsteady-state heat and material balance equations. These equations describe the behavior of a multi-stage batch distillation column. BatchFrac applies rigorous heat balances, material balances, and equilibrium relationships at each stage. BatchFrac calculates the profiles of column composition, temperature, pressure, and vapor and liquid flows as a function of time. BatchFrac can model the following systems:

• • • • •

Narrow-boiling Wide-boiling Strong liquid phase nonideality Three-phase Reactive

BatchFrac assumes:

• •

Equilibrium stages Constant liquid holdup and zero vapor holdup

BatchFrac can handle:

• • • • •

Continuous feeds to the column Continuous sideproduct withdrawal Nonadiabatic column operation Interstage heaters and coolers Vaporization efficiencies for modeling nonequilibrium stages

BatchFrac can also handle the presence of:

• •

A free-water phase in the condenser Two liquid phases in the condenser

BatchFrac does not model column hydraulics.

4-78

•

C o l um ns


Use these forms to enter specifications and view results for BatchFrac: Use this form

T o do t hi s

Setup


Operation Steps

Specify column operating conditions and view results for different operation steps

Heaters Coolers

Specify stage heating or cooling

Efficiencies

Specify stage, component, or sectional

Reactions

efficiencies Specify equilibrium, kinetic, and conversion reaction parameters

Properties


Estimates

Specify initial estimates for stage temperatures, and vapor and liquid flows and compositions

Convergence

Specify convergence parameters for column calculations, and block-specific diagnostic message levels

Records

Specify stage variables to be tracked during the simulation

Report

Specify block-specific report options

User Subroutines

Specify user subroutines for pressure drop and reboiler duties

Block Options


ResultsSummary

View overall key column results

SnapshotResults

View configurational and operating specification results

Profiles

Viewstageprofiles

TimeProfiles

View columnn profiles as a function of time

RecordProfiles

View specific stage profiles recorded

RecordTimeProfiles

View specific column profiles recorded as a function of time


Colu mns

•

4-79

Flowsheet Connectivity for BatchFrac

inlet

One material stream for the initial charge; any number of optional material streams for intermediate charges; any number of optional material streams for continuous feeds

outlet One material stream for final column contents; one material stream for final main accumulator contents; one material stream for the final contents of optional additional accumulators; any number of optional streams for intermediate dump products; any number of optional pseudo-product streams.

Specifying BatchFrac BatchFrac numbers stages from the top down, starting with the condenser. The distillation operation is represented by a series of sequential operation steps. BatchFrac performs a total reflux calculation at the beginning of the first operation step. BatchFrac has two types of data specifications:

•• Column Setup

4-80

•

C o l um ns

Column setup Column operation

Setup specifications define the column you are modeling, but they do not define its operation. These specifications include:


• • • • •

Number of stages Column holdup profile Pressure profile Initial charge Final product specifications

You can choose to specify these on the BatchFrac Setup Form:

• •

Interstage heaters and coolers

• • •

Three-phase distillation and decanters Vaporization efficiency

Heat-loss profile

Reactions and property options for column segments

All Column Setup specifications, except for the initial feed and final charge, can be overridden during any subsequent operation step. You can also request the simulation to record result profiles other than the default at the Setup level. You can set specific block options, algorithm convergence parameters, and diagnostic levels. You can specify user subroutines for pressure profile calculation and reboiler heat duty calculation. You must specify

On this sheet

Total number of stages

Setup Configuration

Column holdup profile

Setup Holdup

Column pressure profile

Setup Pressure

Initital charge stream and final outlet streams

Setup Charge/Products

Column Operation

Column operation specifications define the operating conditions of the column during an operation step. They include operating specifications such as reflux ratio and distillate rate, and stopcriterion information. You can choose to specify intermediate charges to the reboiler, continuous feeds, sidedraws, and intermediate dumps at the operation step level. You can override some global specifications at the operation step level. Other specifications depend on the column configuration and algorithm being used.

Free-Water and Rigorous ThreePhase Calculations

BatchFrac can perform

• •

Free-water calculations Rigorous three-phase calculations

BatchFrac can perform free-water calculations for the condenser only. To specify free water calculations:


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•

4-81

Onsheet

Specify

Block Options

Free-Water=Yes

BatchFrac Setup Configuration

Valid phases=Vapor -liquid -free water condenser

To specify the fraction of free-water phase returned to the column, use the Retfrac2 field on the OperationSteps Setup ColumnSpecifications sheet. BatchFrac can perform rigorous three-phase calculations for: Any stage

•• •

Any column segments The entire column

To specify rigorous three-phase calculations Onsheet

Reactive Distillation

Specify

BatchFrac Setup Configuration

Valid phases=Vapor-liquid -liquid

BatchFrac Setup 3Phase

Key components in the second liquid phase,column segments tested for two liquid phase,decanter locations

BatchFrac can handle chemical reactions. Reactions can be equilibrium and/or rate-controlled. These reactions

Can occur in these phases

Equilibrium Rate-controlled

Liquid and/or vapor Liquid

Reactions may not occur in accumulators or on stages with zero holdup. Usethisform

Todothis

Reactions ReactiveDistillation

Enter reaction chemistry and associated equilibrium and/or kinetic data.

Batchfrac Reactions

Associate a set of reactions with one or more segments of the column.

BatchFrac cannot perform reactive distillation calculations for three-phase distillation.

Physical Property Specifications

Normally, you enter physical property specifications on the Properties Specification Form. When column calculations require more than one property option specification, you can use the BatchFrac Properties PropertySection sheet to specify property options for a segment of the column or a decanter. You can also override property specifications for an individual operation step using the OperationSteps Properties PropertySection sheet.

4-82

•

C o l um ns


Feed Conventions

When Feed-Convention=Above-Stage, a material stream is introduced between adjacent stages. The liquid portion of the stream flows to the stage specified in the feed location Stage field. The vapor portion of the stream goes to the stage above (Stage 1). Youcanintroducea

Byspecifying

Liquid feed to the top stage (or condenser

Stage=1

Vapor feed to the bottom stage (or reboiler)

Stage=Number Of Stages (Setup Configuration sheet) + 1

When Feed-Convention=On-Stage, both the liquid portions of a feed flow to the stage specified in the and feedvapor location Stage field.


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•

4-83

Extract Reference Extract is a rigorous model for simulating liquid-liquid extractors. It can have multiple feeds, heater/coolers, and side streams. Extract can calculate distribution coefficients using:

•

An activity coefficient model or equation of state capable of representing two liquid phases

•

A built-in temperature-dependent correlation (KLL Correlation

•

sheet) A Fortran subroutine (KLL Subroutine sheet)

Although equilibrium stages are assumed, you can specify component or stage separation efficiencies. Extract can be used only for rating calculations. You can define pseudoproduct streams (Report PseudoStreams sheet) to represent extractor internal flows. You can use Fortran and sensitivity blocks to vary configuration parameters, such as feed location or number of stages. Use the following forms to enter specifications and view results for Extract: Use this form

4-84

•

C o l um ns

To do this

Setup


Efficiencies Properties

Specify stage or component efficiencies Specify parameters for KLL correlations and KLL subroutines

Estimates

Specify initial estimates for stage temperatures and compositions

Convergence

Specify convergence parameters and blockspecific diagnostic message levels

Report

Specify block-specific report options and pseudostream information

Block Options


Results

View column performance summary, material and energy balance results, and split fractions

Profiles

View extractor profiles

Dynamic



Flowsheet Connectivity for Extract

L1 Phase

L2 Phase 1

Side feeds (any number)

Side products (any number)

Nstage L1 Phase

L2 Phase

Material Streams

inlet

One material stream to the first (top) stage, rich in the first liquid phase (L1) One material stream to the last (bottom) stage, rich in the second liquid phase (L2) One material stream per intermediate stage (optional)

outlet One material stream for L1 from the last stage One material stream for L2 from the first stage Up to two side product streams per stage, one for L1 and one for L2 (optional)

Specifying Extract

Extract can operate in one of the following ways:

• • •

Adiabatically (default) At a specified temperature With specified stage heater or cooler duties

You must specify:

• • • •

Number of stages Feed and product stream stage locations Side product stream phase and mole flow rate Pressure profile

The first liquid phase (L1) flows from the first stage to the last stage. The second (L2) flows in the opposite direction. You must identify the key components in each phase using L1-Comps and L2-Comps on the Setup form. Extract can treat phase L1 as the solvent/extract phase or the feed/raffinate phase.


Colu mns

•

4-85

Liquid-liquid distribution coefficients are required to represent the liquid-liquid equilibrium. Extract calculates these coefficients using one of the following methods: Youcanuse

Youenter

Any physical property method that can represent two liquid phases

Onsheet

A global property method or a property method name to override the global physical property method

A built-in temperature- Polynomial coefficients dependent polynomial A Fortran subroutine

Subroutine name

BlockOptions Properties

Properties KLL Correlation Properties KLL Subroutine

See Aspen Plus User Models for more information about Fortran subroutines.

EO Usage Notes for Extract


• • • •

4-86

•

C o l um ns

User KLL subroutine KLL correlation Pseudo streams Features which are globally unsupported


C HA P TE R 5

Reactors

This chapter describes the unit operation models for reactors. The models are: M odel

Description

Purpose

RStoic

Stoichiometric reactor

Models stoichiometric Reactors where reaction kinetics are unknown or reactor with specified unimportant but stoichiometry and extent of reaction reaction extent or are known conversion

RYield

Yield reactor

Models reactor with specified yield

Reactors where stoichiometry and kinetics are unknown or unimportant but a yield distribution is known

REquil

Equilibrium reactor

Reactors with simultaneous chemical equilibrium and phase equilibrium

RGibbs

Equilibrium reactor with Gibbs energy minimization

Performs chemical and phase equilibrium by stoichiometric calculations Performs chemical and phase equilibrium by Gibbs energy minimization

RCSTR

Continuous stirred tank reactor

Models continuous stirred tank reactor

One-, two, or three-phase stirred tank reactors with rate-controlled and equilibrium reactions in any phase based on known stoichiometry and kinetics

RPlug

Plug flow reactor Models plug flow reactor

One-, two-, or three-phase plug flow reactors with rate-controlled reactions in any phase based on known stoichiometry and kinetics

RBatch

Batch reactor

One-, two-, or three-phase batch and semi-batch reactors with rate-controlled reactions in any phase based on known stoichiometry and kinetics

Models batch or semibatch reactor

UseFor

Reactors with phase equilibrium or simultaneous phase and chemical equilibrium. Calculating phase equilibrium for solid solutions and vapor-liquidsolid systems.

RCSTR, RPlug, and RBatch are kinetic reactor models. Use the Reactions Reactions form to define the reaction stoichiometry and data for these models. You do not need to specify heats of reaction, because Aspen Plus uses the elemental enthalpy reference state for the definition of the

A s pe nP l u s1 1 . 1Un i tO p e r a t io nM o de l s

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component heat of formation. Therefore, heats of reaction are accounted for in the mixture enthalpy calculations for the reactants versus the products.

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A s p e nP l u s1 1 . 1U ni tO p e r a t ionM o de ls

RStoic Reference Use RStoic to model a reactor when:

• •

Reaction kinetics are unknown or unimportant and Stoichiometry and the molar extent or conversion is known for each reaction

RStoic can model reactions occurring simultaneously or sequentially. In addition, RStoic can perform product selectivity and heat of reaction calculations. Use the following forms to enter specifications and view results for RStoic: Use this form

To do this

Setup

Specify operating conditions, reactions, reference conditions for heat of reaction calculations, product and reactant components for selectivity calculations, particle size distribution, and component attributes

Convergence

Specify estimates and convergence parameters for flash calculations

BlockOptions


Results

View summary of operating results, mass and energy balances, heats of reaction, product selectivities, reaction extents, and phase equilibrium results for the outlet stream

Dynamic

Flowsheet Connectivity for RStoic



Heat (optional)

Heat (optional)

Water (optional) Material Material Streams

inlet At least one material stream outlet One product stream One water decant stream (optional)


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Heat Stream

inlet


RStoic uses the sum of the inlet heat streams as the heat duty specification, if you do not specify an outlet heat stream. outlet One heat stream (optional)

The value of the outlet heat stream is the net heat duty (sum of the inlet heat streams minus the calculated heat duty) for the reactor.

Specifying RStoic

Use the Setup Specifications sheet to specify the reactor operating conditions and to select the phases to consider in flash calculations in the reactor. Use the Setup Reactions sheet to define the reactions occurring in the reactor. You must specify the stoichiometry for each reaction. In addition, you must specify either the molar extent or the fractional conversion for all reactions. Alternatively, you can use the Setup Combustion sheet to have RStoic generate combustion reactions. When solids are created or changed by the reactions, you may specify the component attributes and the particle size distribution in the outlet stream using the Setup Component Attr. sheet and the Setup PSD sheet respectively. If you wish to calculate the heats of reaction, use the Setup Heat of Reaction sheet to specify the reference component for each reaction defined in the Setup Reactions sheet. You may also choose to specify the heats of reaction, and RStoic adjusts the calculated reactor duty, if needed. If you wish to calculate product selectivities use the Setup Selectivity sheet to specify the selected product component and the reference reactant component.

Heat of Reaction

RStoic calculates the heat of reaction from the heats of formation in the databanks when you select the Calculate Heat of Reaction option on the Setup Heat of Reaction sheet. The heats of reaction are calculated at the specified reference conditions based on consumption of a unit mole or mass of the reference reactant selected for each reaction. The following reference conditions are used by default: Specification

Default

Reference temperature

25 degrees C

Referencepressure

1atm

Reference fluid phase

Vapor phase

You can also use the Setup Heat of Reaction sheet to specify the heats of reaction. The specified heat of reaction may differ from

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the heat of reaction that Aspen Plus computes from the heats of formation at reference conditions. If this occurs, RStoic adjusts the calculated reactor heat duty to reflect the differences. Under these circumstances, the calculated reactor heat duty will not be consistent with the inlet and outlet stream enthalpies.

Selectivity

The selectivity of the selected componentP to the reference component A is defined as:

SP,A

 ∆P   ∆A  =   Real  ∆∆PA  Ideal

Where:

∆P

=

Change in number of moles of component P due to reaction

∆A

=

Change in number of moles of component A due to reaction

In the numerator, real represents changes that actually occur in the reactor. Aspen Plus obtains this value from the mass balance between the inlet and outlet. In the denominator, ideal represents changes according to an idealized reaction scheme. This scheme assumes that no reactions are present, except for the reaction that produces the selected component from the reference component. Therefore, the denominator indicates how many moles ofP are produced per mole of A consumed in an ideal stoichiometric equation, or: υP  ∆P   ∆A  Ideal = υ A

where υ P and υ A are stoichiometric coefficients. This example shows how RStoic calculates selectivity:

a1 A + b1 B → c1 C + d1 D c2 C + e2 E → p2 P a3 A + f3 F → q3 Q The selectivity of P to A is:

S P, A

 Moles of P produced   c1∗ p2  = /   Moles of A consumed   a1∗ c2 

In most cases, selectivity ranges between 0 and 1. However, if the selected component is also produced from components other than the reference component, selectivity may be greater than 1. If the


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selected component is consumed in other reactions, selectivity may be less than 0.

EO Usage Notes for RStoic

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• •

Reactions in series

•


Specifications which result in modified conversions during sequential-modular calculations


RYield Reference Use RYield to model a reactor when:

• • •

Reaction stoichiometry is unknown or unimportant Reaction kinetics are unknown or unimportant Yield distribution is known

You must specify the yields (per mass of total feed, excluding any inert components) for the products calculate them in a usersupplied Fortran subroutine. RYieldornormalizes the yields to maintain a mass balance. RYield can model one-, two-, and threephase reactors. Use the following forms to enter specifications and view results for RYield: Use this form

Flowsheet Connectivity for RYield

To do this

Setup

Specify reactor operating conditions, component yields, inert components, flash convergence parameters, and PSD and component attributes for the outlet stream

Assay Analysis

Specify distillation, gravity, molecular weight, petroleum properties, and viscosity data for petroleum characterization and petroleum properties calculation

UserSubroutine

Specify subroutine name and p arameters for the user-supplied yield subroutine

Dynamic


BlockOptions


Results

View summary of operating results, mass and energy balances for the reactor and phase equilibrium results for the outlet stream


Heat (optional)

Heat (optional)

Water (optional) Material


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Material Streams

inlet


outlet One product stream One water decant stream (optional) Heat Streams

inlet



If you give only one specification on the Setup Specifications sheet (temperature or pressure), RYield uses the sum of the inlet heat streams as a duty specification. Otherwise, RYield uses the inlet heat stream(s) only to calculate the net heat duty. The net heat duty is the sum of the inlet heat streams minus the actual (calculated) heat duty. You can use an outlet heat stream for the net heat duty.

Specifying RYield

Use the Setup Specifications and Setup Yield sheets to specify the reactor conditions and the component yields. For each reaction product, specify the yield as either moles or mass of a component per unit mass of feed. If you specify inert components on the Setup Yield sheet, the yields will be based on unit mass of non-inert feed. Calculated yields are normalized to maintain an overall material balance. For this reason, yield specifications establish a yield distribution, rather than absolute yields. RYield does not maintain atom balances because you enter the fixed yield distribution. You can also use Ryield to re-characterize an assay or a blend defined on the Components Assay/Blend Form. You can request one-, two-, or three-phase calculation. When solids are created or changed by the reactions, you can specify their component attributes and/or particle size distribution in the outlet stream using the Setup Component Attr. and Setup PSD sheets, respectively.

EO Usage Notes for RYield


• •

User yield subroutines Specifications which result in renormalized yields during sequential-modular calculations Petroleum characterization option for specifying yield

••

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REquil Reference Use REquil to model a reactor when:

• •

Reaction stoichiometry is known and Some or all reactions reach chemical equilibrium

REquil calculates simultaneous phase and chemical equilibrium. REquil allows restricted chemical equilibrium specifications for reactions that do not reach equilibrium. REquil can model one- and two-phase reactors. Use the following forms to enter specifications and view results for REquil: Use this form

Flowsheet Connectivity for REquil

To do this

Input

Specify r eactor operating conditions, valid phases, reactions, convergence parameters, and solid and liquid entrainment in the vapor stream

Block Options


Results

View summary of operating results, mass and energy balances, and calculated chemical equilibrium constants


Material (vapor phase) Material (liquid phase)

Heat (optional)

Heat (optional)

Material Streams

inlet


outlet One material stream for the vapor phase One material stream for the liquid phase Heat Streams

inlet



If you give only one specification on the REquil Input Specifications sheet (temperature or pressure), REquil uses the sum of the inlet heat streams as a duty specification. Otherwise, REquil uses the inlet heat stream(s) only to calculate the net heat


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duty. The net heat duty is the sum of the inlet heat streams minus the actual (calculated) heat duty. You can use an outlet heat stream for the net heat duty.

Specifying REquil

You must specify the reaction stoichiometry and the reactor conditions. If no additional specifications are given, REquil assumes that the reactions will reach equilibrium. REquil calculates equilibrium constants from the Gibbs energy. You can restrict the equilibrium by specifying one of the following:

• •

The molar extent for any reaction A temperature approach to chemical equilibrium (for any reaction)

If you specify temperature approach,∆T, REquil evaluates the chemical equilibrium constant at T +∆T, where T is the reactor temperature (specified or calculated). REquil performs single-phase property calculations or two-phase flash calculations nested inside a chemical equilibrium loop. REquil cannot perform three-phase calculations.

Solids

Reactions can include conventional solids. REquil treats each participating solid component as a separate pure solid phase, not as a component in a solid solution. Any participating solids must have a free energy formation (DGSFRM) and enthalpy of formation (DHSFRM), or heat capacity parameters (CPSXP1). Solids not participating in reactions, including any nonconventional components, are treated as inert. These solids have no effect on the equilibrium calculations except on the energy balance.

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RGibbs Reference RGibbs uses Gibbs free energy minimization with phase splitting to calculate equilibrium. RGibbs does not require that you specify the reaction stoichiometry. Use RGibbs to model reactors with:

• •

Single phase (vapor or liquid) chemical equilibrium

• •

Phase and/or chemical equilibrium with solid solution phases Simultaneous phase and chemical equilibrium

Phase equilibrium (an optional vapor and any number of liquid phases) with no chemical reactions

RGibbs can also calculate the chemical equilibria between any number of conventional solid components and the fluid phases. RGibbs also allows restricted equilibrium specifications for systems that do not reach complete equilibrium. Use the following forms to enter specifications and view results for RGibbs:

Flowsheet Connectivity for RGibbs

Use this form

To do this

Setup

Specify reactor operating conditions and phases to consider in equilibrium calculations, identify possible products, assign phases to outlet streams, specify inert components and specify equilibrium restrictions

Advanced

Specify atomic of components, estimates for temperature andformula component flows, and convergence parameters

Block Options

Override global values for physical properties, simulation options, diagnostic message levels and report options for this block

Results

View summary of operating results, mass and energy balances, molar compositions of fluid and solid phases present, the atomic formula of components, and calculated reaction equilibrium constants

Dynamic



Heat (optional)


Heat (optional)

Material Streams

inlet



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outlet At least one material stream

If you specify as many outlet streams as the number of phases that RGibbs calculates, RGibbs assigns each phase to an outlet stream. If you specify fewer outlet streams, RGibbs assigns the additional phases to the last outlet stream. Heat Streams

inlet



If you specify only pressure on the Setup Specifications RGibbs uses the sum of the inlet heat streams as a duty sheet, specification. Otherwise, RGibbs uses the inlet heat stream(s) only to calculate the net heat duty. The net heat duty is the sum of the inlet heat streams minus the actual (calculated) heat duty. You can use an outlet heat stream for the net heat duty.

Specifying RGibbs

This section describes how to specify:

• • • • •

Phase equilibrium only Phase and chemical equilibrium Restricted chemical equilibrium Reactions Solids

Phase Equilibrium Only Tospecify

Usethisoption

On

Phase equilibrium calculations Phase Equilibrium Only only

Setup Specifications sheet

Maximum number of fluid phases that RGibbs should consider

Maximum Number of Fluid Phases


Maximum number of solid solution phases

Maximum Number of Solid Solution Phases

Solid Phases dialog box from the Setup Specifications sheet

RGibbs distributes all species among all solution phases by default. You can use the Setup Products sheet to assign different sets of species to each solution phase. You can also assign different thermodynamic property methods to each phase. If there is a possibility that a solid solution phase may exist, use the Setup Products sheet to identify the species that will exist in that phase.

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Phase Equilibrium and Chemical Equilibrium Tospecify

Usethisoption

On

Chemical equilibrium calculations (with or without phase equilibrium)

Phase Equilibrium and Chemical Equilibrium


Maximum number of fluid phases that RGibbs should consider

Maximum Number of Fluid Phases


Maximum number of solid solution phases

Maximum Number of Solid Solution Phases

Solid Phases dialog Specifications sheet box from the Setup

By default, RGibbs considers all components entered on the Components Specifications Selection sheet as possible fluid phase or solid products. You can specify an alternate list of products on the Setup Products sheet. RGibbs distributes all solution species among all solution phases by default. You can use the Setup Products sheet to assign different sets of species to each solution phase. You can also assign different thermodynamic property methods to each phase. RGibbs needs the molecular formula for each component that is present in a feed or product stream. RGibbs retrieves this information from the component databanks. For non-databank components, use the Properties Molec-Struct Formula sheet to enter:

• •

Atom (the atom type) Number of occurrences (the number of atoms of each type)

Alternatively, you can enter the atom matrix on the Advanced Atom Matrix sheet. The atom matrix defines the number of each atom in each component. If you enter the atom matrix, you must enter it for all components and atoms, including databank components. If there is a possibility that a solid solution phase may exist, use the Setup Products sheet to identify the species which will exist in that phase.


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Restricted Chemical Equilibrium

To restrict chemical equilibrium: Specify

On

The molar extent of the reaction Edit Reactions dialog box (from the Setup RestrictedEquilibrium sheet) A temperature approach to equilibrium for individual reactions

Edit Reactions dialog box (from the Setup RestrictedEquilibrium sheet)

A temperature approach to chemical equilibrium for the entire system

Edit Reactions dialog box (from the Setup RestrictedEquilibrium sheet)

The outlet amount of any Setup Inerts sheet † component as total mole flow or as a fraction of the feed of that component

† You can specify inert components by setting the fraction to 1.

For temperature approach specifications, RGibbs evaluates the chemical equilibrium constant atT + ∆T, where T is the actual reactor temperature (specified or calculated) and∆T is the desired temperature approach. You can enter one of the following restricted equilibrium specifications for individual reactions:

• •

The molar extent of a reaction The temperature approach for an individual reaction

Use the Setup RestrictedEquilibrium sheet to supply the reaction stoichiometry. If you enter one of the preceding specifications, you must also supply the stoichiometry for a set of linearly independent reactions involving all components in the system.

Reactions

You can have RGibbs consider only a specific set of reactions. You can restrict the chemical equilibrium by specifying temperature approach or molar extent for the reactions. You must specify the stoichiometric coefficients for a complete set of linearly independent chemical reactions, even if only one reaction is restricted. The number of linearly independent reactions required equals the total number of products in the product list, including solids (see the Setup Products sheet), minus the number of atoms present in the system. The reactions must involve all participating components. A component is participating if it satisfies these criteria:

•

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It is in the product list.


Solids

•

It is not inert. A component is inert if it consists entirely of atoms not present in any other product components.

•

It has not been dropped. A component listed on the Setup Products sheet is dropped if it contains an atom not present in the feed.

RGibbs can calculate the chemical equilibria between any number of conventional solid components and the fluid phases. RGibbs detects whether the solid is present at equilibrium, and if so, calculates the amount. RGibbs treats each solid component as a pure solid phase, unless it is specified as a component in a solid solution. Any solid that RGibbs considers a product must have both:

• •

Free energy of formation (DGSFRM or CPSXP1) Heat of formation (DHSFRM or CPSXP1)

Nonconventional solids are treated as inert and have no effect on equilibrium calculations. If chemical equilibrium is not considered, RGibbs treats all solids as inert. RGibbs cannot perform solidsphase-only calculations. RGibbs places all pure solids in the last outlet stream unless you specify otherwise on the Setup AssignStreams sheet. RGibbs can handle only a single CISOLID substream, which contains all conventional solids products defined as pure solid phases. RGibbs places the solid solution phases in the MIXED substream of the outlet stream(s). RGibbs cannot directly handle phase equilibrium between solids and fluid phases (for example, water-ice equilibrium). To work around this, you can list the same component twice on the Components Specifications Selection sheet, with different component IDs. If you want RGibbs to calculate the chemical equilibrium between these components:

• • References

Specify both component IDs on the Setup Products sheet. Designate one ID as a solids phase component, the other as a fluid phase component.

Gautam, R. and Seider, W.D., "Computation of Phase and Chemical Equilibrium," Parts I, II, and III, AIChE J. 25, 6, November, 1979, pp. 991-1015. White, C.W. and Seider, W.D., "Computation of Phase and Chemical Equilibrium: Approach to Chemical Equilibrium," AIChE J., 27, 3, May, 1981, pp.446-471. Schott, G. L., "Computation of Restricted Equilibria by General Methods," J. Chem. Phys., 40, 1964.


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RCSTR Reference RCSTR rigorously models continuous stirred tank reactors. RCSTR can model one-, two-, or three-phase reactors. RCSTR assumes perfect mixing in the reactor, that is, the reactor contents have the same properties and composition as the outlet stream. RCSTR handles kinetic and equilibrium reactions as well as reactions involving solids. You can provide the reaction kinetics through the built-in Reactions models or through a user-defined Fortran subroutine. Use the following forms to enter specifications and view results for RCSTR: Use this form

To do this

Setup

Specify reactor operating conditions and holdup, select the reaction sets to be included, and specify PSD and component attributes in the outlet stream

Convergence

Provide estimates for component flow rates, reactor temperature and volume, and specify flash convergence parameters, RCSTR convergence methods and parameters, and initialization options

UserSubroutine

Specify parameters for the user-supplied kinetics subroutine and block-specific report option for the kinetics subroutine

BlockOptions


Results

View summary of operating results and mass and energy balances for the block

Dynamic

Specify parameters for dynamic simulations Heat (optional)

Flowsheet Connectivity for RCSTR Material (any number)

Material

Heat (optional)

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Material Streams

inlet


outlet One material stream Heat Streams

inlet



If you specify only pressure on the Setup Specifications sheet, RCSTR uses the sum of the inlet heat streams as a duty specification. Otherwise, RCSTR uses the inlet heat stream only to calculate the net heat duty. The net heat duty is the sum of the inlet heat streams minus the actual (calculated) heat duty. You can use an outlet heat stream for the net heat duty.

Specifying RCSTR

You must specify the reactor operating conditions, which are pressure and either temperature or heat duty. You must also enter the reactor volume or residence time (overall or phase).

Reactions

You must specify reaction kinetics on the Reactions Reactions forms and select the Reaction Set ID on the Setup Reactions sheet. You can specify one-, two-, or three-phase calculations. You can specify the phase for each reaction on the Reactions Reactions forms. RCSTR can handle the kinetic and equilibrium type reactions.

Phase Volume

In a multi-phase reactor, by default, Aspen Plus calculates the volume of each phase, using phase equilibrium results, as: Vi f i V Pi = VR ΣV j f j Where: VPi

=

Volume of phase i

VR

=

Reactor volume

Vi

=

Molar volume of phase i

fi

=

Molar fraction of phase i

You can override the default calculation by specifying the volume of a phase directly (Phase Volume) or as a fraction of the reactor volume (Phase Volume Frac) on the Setup Specifications sheet. Alternatively, when you specify the residence time of a phase in the reactor, Aspen Plus calculates the phase volume iteratively.


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Residence Time

Aspen Plus calculates the residence time (overall and phase) in the CSTR as:

RT = RTi

=

VR F * Σf iVi V Pi F * f iVi

Where:

RT

=

Overall residence time

RTi

=

Residence time of phase i

VR

=

Reactor volume

F

=

Total molar flow rate (outlet)

Vi

=

Molar volume of phase i

fi

=

Molar fraction of phase i

VPi

=

Volume of phase i

When the default calculation for phase volume, based on phase equilibrium results, is used, the phase residence time is equal for all phases. If you specify Phase Volume or Phase Volume Frac on the Setup Specifications sheet, the residence time for the phase specified in the Holdup Phase is calculated with the specified phase volume rather than the default phase volume.

Solids

RCSTR can handle reactions involving solids. RCSTR assumes that solids are at the same temperature as the fluid phase. RCSTR cannot perform solids-phase-only calculations.

Scaling of Variables

Four types of variables are predicted by RCSTR: component flow rates, stream enthalpy, component attributes and PSD (if present). RCSTR normalizes these variables, for faster convergence, by dividing each one by a scale factor. Two types of scaling are available in RCSTR: component-based scaling and substream-based scaling. Component-based scaling weighs each variable against its previous or estimated value. Substream-based scaling weighs each variable in a substream against the substream flow rate. For component-based scaling, minimum scale values are set by the Trace Scaling Factor in the Advanced Parameters dialog box (from the Convergence Parameters sheet). You may reduce the trace scaling threshold to increase the prediction accuracy of trace components.

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Component-based scaling generally provides more accuracy than substream-based scaling, especially for trace components. Use component-based scaling when:

• •

The reaction network involves trace intermediates The reaction rates are very sensitive to trace reactants (such as catalysts and initiators which participate in degradation reactions)

The following tables summarize the scale factors used by each method. Substream-based Scaling Method

VariableT ype

Variable

InitialScaleFactor

Component Flows Component mole flow in outlet stream

Estimated outlet substream mole flow rate

Stream Enthalpy

Net enthalpy flow of inlet stream

Net enthalpy flow of outlet stream

Component Product of component mass flow (with Default attribute scale factor Attributes (attr/kg) attributes) and attribute value in outlet stream PSD

Product of substream mass flow rate (with PSD) and PSD value in outlet stream

Default attribute scale factor

Note: If any substream-based scaling factor is equal to zero, the default scaling factor is used instead (the default factor is 1.0 for component flow rates and 1.0E5 for stream enthalpy). Component-based Scaling Method

VariableT ype Variable Component Flows Component mole flow in outlet stream

InitialScaleFactor Larger of:

- Estimated component mole flow in outlet stream - Product of Trace threshold and estimated outlet substream mole flow

Stream Enthalpy

Net enthalpy flow of outlet stream

Net enthalpy flow of inlet stream

Component Product of component mass flow Larger of: Attributes (attr/kg) with attributes and attribute value in - Product of estimated attributed component outlet stream mass flow and estimated attribute value in outlet stream - Product of Trace threshold and estimated outlet substream mole flow PSD

Product of substream mass flow rate and PSD value in outlet stream

Larger of: - Product of estimated substream mass flow with PSDs and estimated PSD value in outlet stream - Product of Trace threshold and default attribute scale factor


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RPlug Reference RPlug is a rigorous model for plug flow reactors. RPlug assumes that perfect mixing occurs in the radial direction and that no mixing occurs in the axial direction. RPlug can model one-, two-, or three-phase reactors. You can also use RPlug to model reactors with coolant streams (co-current or counter-current). RPlug handles kinetic reactions, including reactions involving solids. You must know the reaction kinetics when you use RPlug to model a reactor. You can provide the reaction kinetics through the built-in Reactions models or through a user-defined Fortran subroutine. Use the following forms to enter specifications and view results for RPlug: Use this form

To do this

Setup

Specify operating conditions and reactor configuration, select reaction sets to be included, and specify pressure drops

Convergence

Specify flash convergence parameters, calculation options and parameters for the integrator

Report

Specify block-specific report options

UserSubroutine

Specify user subroutine parameters for kinetics, heat transfer, pressure drop, and list user variables to be included in the profile report

BlockOptions

Override global values for property methods, simulation options, diagnostic levels, and report options for this block

Results

View summary of operating results and mass and energy balances for the block

Profiles

View profiles versus reactor length for process stream conditions, coolant stream conditions, properties, component attributes, PSD, and user variables

Dynamic

Specify parameters for dynamic simulations Heat (optional)

Flowsheet Connectivity for RPlug Material

Material

Flowsheet Reactor without Coolant Stream

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Material Coolant (optional)

Material

Material

Material Coolant (optional) Flowsheet Reactor with Coolant Stream Material Streams

inlet

One material feed stream One coolant stream (optional)

outlet One material product stream One coolant stream (optional) Heat Streams

inlet


outlet One heat stream (optional) for the reactor heat duty. Use the heat outlet stream only for reactors without a coolant stream.


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Use the Setup Configuration sheet to specify reactor tube length and diameter. If the reactor consists of multiple tubes, you can also specify the number of tubes. You can specify the pressure drop across the reactor on the Setup Pressure sheet. Additional required input for RPlug depends on the reactor type.

Specifying RPlug

When you use this Reactor Type

And solid phase is

And fluid and solid phase temperatures are

Specify

Reactor with specified temperature

-

-

Reactortemperature,ortemperature profile

Adiabatic reactor

Not present

-

Norequiredspecifications

Present

Same

Norequiredspecifications

Present

Different

U (fluid phase - solids phase)

Not present

-

Coolanttemperature,and U (coolant - process stream)

Present

Same

Coolanttemperature,and U (coolant - process stream)

Present

Different

Coolanttemperature, U (coolant - fluid phase), U (coolant - solids phase), and U (fluid phase - solids phase)

Not present

-

U(coolant-processstream)

Present

Same

U(coolant-processstream)

Present

Different

U (coolant -fluid phase), U (coolant - solids phase), and U (fluid phase - solids phase)

Not present

-

Coolantoutlettemperatureormolar vapor fraction, and U (coolant - process stream)

Present

Same

Coolant outlettemperature or molar vapor fraction, and U (coolant - process stream)

Present

Different

Coolant outlet temperature or molar vapor fraction, U (coolant - fluid phase), U (coolant - solids phase), and U (fluid phase - solids phase)

Reactor with constant coolant temperature

Reactor with cocurrent coolant

Reactor with countercurrent coolant

For reactors with countercurrent external coolant, RPlug calculates the coolant inlet temperature. The result overrides your specified inlet coolant temperature. You can use a design specification that manipulates the coolant exit temperature or vapor fraction to achieve a specified coolant inlet temperature.

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For reactors with an external coolant stream, you can use different physical property methods and options (BlockOptions Properties sheet) for the process stream and the coolant stream.

Reactions

You must specify reaction kinetics on the Setup Reactions sheet, by referring to Reaction IDs that you select. You can specify one-, two-, or three-phase calculations. Specify the reaction phases on the Reactions Reactions forms. RPlug can handle only kinetic type reactions.

Solids

Reactions can involve solids. Solids can be:

• •

At the same temperature as the fluid phases At a different temperature from the fluid phases (only for Reactor Types other than the reactor with specified temperature)

In the latter case, you must specify the heat transfer coefficients on the Setup Specifications sheet.


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RBatch Reference RBatch is a rigorous model for batch or semi-batch reactors. Use RBatch when you know the kinetics of the reactions taking place. You can specify any number of continuous feed streams. A continuous vent is optional. The reaction runs until it reaches a stop criterion that you specify. Batch operations are unsteady-state processes. RBatch uses holding tanks and your specified cycle times to provide an interface between the discrete operations of the batch reactor and the continuous streams used by other models. RBatch can model one-, two-, or three-phase reactors. Use the following forms to enter specifications and view results for RBatch:

Flowsheet Connectivity for RBatch

Use this form

To do this

Setup

Specify operating conditions, select reaction sets to be included, specify operation stop criteria, operation times, continuous feeds, and controller parameters

Convergence

Specify convergence parameters for flash calculations, integration, and pressure calculations

Report

Specify block-specific report options for profiles and reactor, vent, and vent accumulator property profiles

UserSubroutine

Specify parameters for the user kinetics subroutine, name and parameters for the user heat transfer subroutine, and user variables for the profile report

Block Options


Results

View summary of block operating results and mass and energy balances

Profiles

View time profiles of reactor conditions, compositions, continuous feed stream flows, properties, component attributes, and user variables

Batch charge

Heat (optional) Vent (optional)

Continuous feeds (optional)

Product

5-24

•

R eact or s


Material Streams

inlet

One batch charge stream (required) One or more continuous feed streams for semi-batch reactors (optional)

outlet One product stream (required) One vent stream for semi-batch reactors (optional) Heat Streams

inlet



Specifying RBatch

Use the Setup Specifications sheet to specify the reactor conditions. Use the Setup Operations sheet to specify:

• •

One or more stop criteria Either a feed time or a batch cycle time

Other required input for RBatch depends on reactor type. To establish the pressure of the vessel, enter one of the following specifications on the Setup Specifications sheet:

• • •

Constant pressure Pressure profile Reactor volume

Use the Setup ContinuousFeeds sheet to enter mass flow rates for the continuous feeds at any number of points in time. You can thus simulate delayed feeds and step changes in feeds. For specified duty reactors, you can specify either a constant heat duty or a heat duty profile. For a reactor with constant duty, RBatch assumes adiabatic operation if you do not specify a heat duty. For reactors with specified coolant temperature, you must specify:

• • •

Coolant temperature An over-all heat transfer coefficient Total heat transfer area

For constant temperature and specified temperature reactors, RBatch handles the temperature specification in one of the following ways:

• •


By assuming perfect control By interpreting the specified temperature(s) as the setpoint(s) of a PID controller

R ea ct or s

•

5-25

Controller

RBatch assumes perfect control when one of these conditions exists:

•

Pressure in the reactor is converged upon (that is, reactor volume is specified)

•

A single-phase batch reactor is used with no continuous feed streams

If RBatch cannot assume perfect control, it interprets the specified temperature(s) as the setpoint(s) of a PID controller. This interpretation occurs when:

• •

A two-phase reactor is used. RBatch does not calculate reactor pressure (that is, pressure or pressure profile is specified).

•

Continuous feeds are present during semi-batch operation.

Use the Setup Controllers sheet to specify the controller tuning parameters. The controller equation is:



t

Q = M cK T−(T+



s

∫

s K ) I−( T/+T) (dt K D) 0

d (T − T s )   dt 

Where:

Q

=

Reactor heat duty (J/sec)

Mc

=

Reactor charge (kg)

K

=

Proportional gain (J/kg/K)

=

Reactor temperature (K)

=

Temperature set point (K)

I

=

Integral time (sec)

D

=

Derivative time (sec)

t

=

Time (sec)

T T

s

The gain factor is a specific gain per unit mass.

Reactions

5-26

•

R eact or s

Reactions may or may not be present in RBatch. If they are, you must include the Reaction Set IDs on the Setup Reactions sheet. You can specify one-, two-, or three-phase calculations. You specify the reaction phases on the Reactions Reactions forms. RBatch can only handle kinetic type reactions.


Specifying Stop Criteria

A reaction runs until one of your specified stop criteria reached. A stop criterion can be one of the following:

• • • • • •

Reaction time

•• •

Temperature in the reactor Vapor fraction in the reactor

Reactor composition Vent accumulator or continuous vent composition Conversion of a component Amount of material in the reactor or vent accumulator Vent flow rate

Any property specified on the Properties Prop-Sets Properties sheet

As the stop criterion variable approaches its cut-off from above or below, you can specify whether or not RBatch should halt the reaction. If you specify more than one stop criterion, RBatch halts the reaction as soon as one of the criteria is reached. In addition, you must specify a halt time for the reaction. If the reaction does not reach the specified stop criteria by this time, RBatch halts the reaction.

Cycle Time

You can specify a reactor cycle time. Or, you can let RBatch calculate it from your specified reaction and down times for draining, cleaning, and charging the reactor. If you do not specify reactor cycle time, then specify a feed cycle time. RBatch uses this time to determine the batch charge, because the reaction time is not known at the beginning of block execution. Note: If the reactor batch charge stream is ina recycle loop, you must specify the reactor cycle time.

Mass Balances

Because RBatch uses different cycle times to calculate timeaveraged flows, RBatch may not maintain a mass balance around the block. For example, suppose you specify a feed time of 30 minutes, but the down time plus the calculated value reaction time equals 45 minutes. The resulting net mass flow from the reactor is less than the charge flow by a factor of 45/30=1.5. Remember that the mass balance pertains to the time-averaged inlet and outlet continuous streams. RBatch always satisfies a mass balance for its own internal batch computations. If there is no continuous feed stream, the mass balance around RBatch closes only if the cycle time is specified. This ensures that the same time is used for averaging the batch change and product streams. If there is a continuous feed stream, and it is not time-varying, the mass balance closes only if the cycle time is specified, and the specified value is equal to the calculated reaction time. In all other


R ea ct or s

•

5-27

cases, the mass balance around RBatch does not close, although the compositions, temperature, and so on are correct.

Batch Operation

RBatch can operate in a batch or in semi-batch mode. The reactor mode is determined by the streams you enter on the flowsheet. A semi-batch reactor can have a vent product stream, one or more continuous feed streams, or both. The vent product stream exits a vent accumulator. It does not exit the reactor itself. The vent accumulator is for the continuous (but time-varying) vapor vent leaving the reactor. The composition and temperature of each continuous feed stream remain constant throughout the reaction. The flow rate also remains constant, unless you specify a time profile for the flow rate of a continuous stream. Batch operations are unsteady-state processes. Variables like temperature, composition, and flow rate change with time, in contrast to steady-state processes. To interface RBatch with a steady-state flowsheet, it is necessary to use time-averaged streams. Four types of streams are associated with RBatch, as follows: Batch Charge: The material transferred to the reactor at the start of the reactor cycle. The mass of the batch charge equals the flow rate of the batch charge stream, multiplied by the feed cycle time. The mass of the batch charge is equivalent to accumulating the batch charge stream in a holding tank during a reactor cycle. The contents of the holding tank are transferred to the reactor at the beginning of the next cycle . (See figure RBatch Reactor Configuration - No Vent Case.) To compute the amount of the batch charge, RBatch multiplies the flowsheet stream representing the batch charge by a cycle time you enter (either Cycle Time or Batch Feed Time). Batch Feed Time is not the time required to charge the reactor; it is a total cycle time used only to compute the amount of the charge. Batch Feed Time is required when Cycle Time is unknown. If Batch Feed Time differs from the actual computed cycle time, the RBatch flowsheet inlet and outlet streams are not in mass balance. However, all internal RBatch calculations and reports will be correct for the computed batch charge.

Continuous Feed: A steady-state flowsheet stream fed continuously to the reactor during reaction. Its composition and temperature remain constant throughout the reaction. Its flow rate either remains constant or follows a specified time profile. Reactor Product: The material left in the reactor at the end of the reactor cycle. The flow rate of the reactor product stream equals the total mass in the reactor, divided by the reactor cycle time. You

5-28

•

R eact or s


can think of this process as analogous to transferring the reactor product to a product holding tank. This tank is drawn down during the next reactor cycle to feed the continuous blocks downstream (see figure RBatch Reactor Configuration - No Vent Case ). Vent Product: The contents of the vent accumulator at the end of the reactor cycle. During the reactor cycle, the time-varying vent stream accumulates in the vent accumulator (see figure RBatch Reactor Configuration - Vent Case). The flow rate of the vent product stream is the total mass in the vent accumulator, divided by the reactor cycle time. Feed Holding Tank Flowsheet Stream for Batch Charge Batch charge transferred once each cycle

Product Holding Tank

Reactor

Reactor product transferred once each cycle

Optional Flowsheet Stream for Continuous Feed

Flowsheet Stream for Reactor Product

RBatch Reactor Configuration—No Vent Case

Feed Holding Tank

Vent Accumulator

Flowsheet Stream for Batch Charge Batch charge transferred once each Reactor cycle Optional Flowsheet Stream for Continuous Feed

Vent Holding Tank

Vent Product transferred once per cycle

Flowsheet Stream for Vent Product

Product Holding Tank

Reactor product transferred once each cycle

Flowsheet Stream for Reactor Product

RBatch Reactor Configuration—Vent Case


R ea ct or s

•

5-29

5-30

•

R eact or s


C HA P TE R 6

Pressure Changers

This chapter describes the unit operation models for pumps and compressors, and models for calculating pressure change through pipes and valves. The models are: M odel

Description

Purpose

UseFor

Pump

Pump or hydraulic turbine

Changes stream pressure when the power requirement is needed or known

Pumps and hydraulic turbines

Compr

Compressor or turbine Changes stream pressure when power requirement is needed or known

MCompr

Multistage co mpressor Changes stream Multistage polytropic compressors, or turbine pressure across multiple polytropic positive displacement stages with intercoolers. compressors, isentropic compressors, Allows for liquid isentropic turbines knockout streams from intercoolers

Valve

Valve pressure drop

Models pressure drop through a valve

Control valves and pressure changers

Pipe

Single segment pipe

Models pressure drop through a single segment of pipe

Pipe with constant diameter (may include fittings)

Pipeline

Multiple se gment pipeline

Models pressure drop through a pipe or annular space

Pipeline with multiple lengths of different diameter or elevation

Polytropic compressors, polytropic positive displacement compressors, isentropic compressors, isentropic turbines

Use Pump, Compr, and MCompr models when energy-related information such as power requirement is needed or known.

A s pe nP l u s1 1 . 1Un i tO pe r a t i o nM od e l s

P r e s s u r eC h a n g e r s

•

6-1

Pump Reference Use Pump to model a pump or a hydraulic turbine. Pump is designed to handle a single liquid phase. For special cases, you can specify two- or three-phase calculations to determine the outlet stream conditions and to compute the fluid density used in the pump equations. The accuracy of the results depends on a number of factors, such as the relative amounts of the phases present, the compressibility of the fluid, and the efficiency specified. Use Pump to change pressure when the power requirement is needed or known. For pressure change only, you can use other models such as Heater. Pump can model pumps and hydraulic turbines. Use the Pump block to rate a pump or a turbine by specifying scalar parameters or by specifying the related performance curves. To use the performance curves, you can specify either:

•

Dimensional curves such as head versus flow or power versus flow

•

Dimensionless curves such as head coefficient versus flow coefficient

Use the following forms to enter specifications and view results for Pump: Use this form

6-2

•

P r e s s u r eC ha n g e r s

To do this

Setup

Specify operating conditions, efficiencies, net positive suction head parameters, specific speed parameters, valid phases, and flash convergence parameters

PerformanceCurve s

Specify parameters and enter data for the performance curves

UserSubroutine

Specify name and parameters for the user performance curve subroutine

BlockOptions


Results

View summary of Pump results, material and energy balance results, and performance curve summary


Work (optional)

Flowsheet Connectivity for Pump

Material Material (any number) Water (optional)

Work (optional) Material Streams

inlet


outlet One material stream One water decant stream (optional) Work Streams

inlet

Any number of work streams (optional)

outlet One work stream for the net work load (optional)

If you do not specify either power or pressure on the Setup Specifications sheet, Pump uses the sum of the inlet work streams as a power specification. Otherwise, Pump uses the inlet work stream(s) only to calculate the net work load. The net work load is the sum of the inlet work streams minus the actual (calculated) work load. You can use an optional outlet work stream for the net work load.

Specifying Pump

Use the Setup Specifications sheet for Pump specifications. Ifyouspecify

Pumpcalculates

Dischargepressure

Powerrequiredorproduced

Pressure increase (for a pump) or decrease (for a turbine)

Power required or produced

Pressure ratio (outlet pressure to inlet pressure)

Power required or produced

Power required (for a pump) or produced (for a turbine)

Discharge pressure

Curves of head, discharge pressure, pressure Power required or produced ratio, pressure change, or head coefficient Powercurve

Dischargepressure

You can supply a Fortran subroutine to calculate performance curves in Pump. See Aspen Plus User Models for more information.



•

6-3

NPSH Available

The Net Positive Suction Head (NPSH) available for a pump is defined as:

NPSHA = P− in

Pvapor +

+

H v

H

s

Where:

NPSHA

=

Net Positive Suction Head Available

Pin

=

Inlet pressure

Pvapor

=

Vapor pressure of the liquid at inlet conditions

Hv

=

Velocity head = u 2 / 2 g where u is the velocity and g is gravitation constant

Hs

=

Hydraulic static head corrected to the pump centerline

The NPSH available has to be greater than the NPSH required (NPSHR) to avoid cavitation. NPSH required is a function of pump design.

NPSH Required

The Net Positive Suction Head (NPSH) required can be considered the suction pressure required by the pump for safe, reliable operation. The NPSHR can be specified using the performance curves on the PerformanceCurves NPSHR sheet, or calculated from the following empirical equation by specifying suction specific speed (N ss ) on the Setup CalculationOptions sheet.

NPSHR =

 N Q 0.5   N   ss 

4

3

Where:

NPSHR

=

Net Positive Suction Head Required

N

=

Pump shaft speed (rpm)

Q

=

Volumetric flow rate at the suction conditions

N ss

=

Suction specific speed

The units for Q and NPSHR are:

Specific Speed

6-4

•


US:

Q in gal/min and NPSHR in feet

Metric:

Q in cum/hr and NPSHR in meters

Specific speed and suction specific speed are two important parameters that define the suitability of a pump design for its intended conditions. The pump specific speed is defined as:


Ns

=

N Q 0.5 Head 0.75

Where:

Head

=

Head developed across the pump

Ns

=

Specific speed

N

=


Q

=


The units for Q and Head are: US:

Headinfeet

Metric:

Head in meters

In general, pumps with a low specific speed are termed low capacity and those with a high specific speed are termed high capacity. For a turbine, the specific speed is defined as follows:

Ns

=

N BHP Head

0.5

1.25

Where:

Suction Specific Speed

Ns

=

Specific speed

BHP

=

Developed horsepower

Head

=

Total dynamic head across turbine

Suction specific speed (N ss ) is an index number for a centrifugal pump and is used to define its suction characteristic. It is defined as follows:

N ss

=

N Q 0.5 NPSHR 0.75

Where:

NPSHR

=

Net positive suction head required for a pump or net positive discharge head required for a turbine

N ss

=

Suction specific speed

N

=


Q

=


The units for Q and NPSHR are: US: Q in gal/min and NPSHR in feet Metric:


Q in cum/hr and NPSHR in meters


•

6-5

Suction specific speed is a criterion of a pump’s performance with regard to cavitation. For a pump of normal design, values ofN ss vary from 6,000 to 12,000 in US units. A typical value is 8,500.

Head Coefficient

Head coefficient is defined as follows:

Headc =

Head u2

Where:

Flow Coefficient

Headc

=

Head coefficient

Head

=

Head developed across the pump

u

=

Impeller tip speed

Flow coefficient is the ratio of discharge throat velocity to impeller tip speed. It is defined as:

Flowc = A1

Q A1 u

= π × d12 / 4

Where:

Flowc

=

Flow coefficient

Q

=

Volumetric flow rate

A1

=

Cross-sectional area of discharge throat

d1

=

Diameter of discharge throat

u

=

Impeller tip speed

The diameter of throat and diameter of impeller are related by the following empirical equation:

Ns

= 5500

d1 Diam

Where:

Ns

=

Specific speed at the best efficiency point

Diam

=

Diameter of impeller

You can specify Specific Speed (N s ) on the Setup CalculationOptions sheet.

6-6

•



Performance Curves

The performance curves can be entered in one of the following curve formats:

• • •

Tabular data Polynomials User subroutine

You can select one of the following performance curves (the dependent variable) for the pump type you specified on the Pump Setup Specifications sheet: Performance Curve Type

Data for a pump

Data for a turbine

Head

Headrequired

Headproduced

Head-Coeff

Head coefficient

Head coefficient

Power

Powerrequired

Powerproduced

Dis-Pressure

Outlet pressure

Outlet pressure

Pres-Ratio

Pressureratio

Pressureratio

Pres-Change

Pressure increase

Pressure decrease

The flow variable (the independent variable) can be one of the following:

• • • •

Volume flow rate at suction conditions Mass flow rate at suction conditions Specific volumetric flow rate (for head coefficient only) Flow coefficient (for head coefficient only)

You can select one of the following options for specifying curves: • A single curve at the operating shaft speed

EO Usage Notes for Pump

•

A single curve; use affinity laws to scale the performance from a reference speed

•

Multiple curves at multiple shaft speeds


•

Power, discharge pressure, and pressure-ratio performance curves

• •

Multiple performance curves of other types Features which are globally unsupported

Single performance curves for head, head coefficient, and pressure change are supported.



•

6-7

Compr Reference Use Compr to model:

• • • •

A polytropic centrifugal compressor A polytropic positive displacement compressor An isentropic compressor An isentropic turbine

Use Compr to change stream pressure when energy-related information, such as power requirement, is needed or known. Compr can handle single-phase as well as two- and three-phase calculations. You can use Compr to rate a single stage of a compressor or a single wheel of a compressor, by specifying the related performance curves. Compr allows you to specify either:

•

Dimensional curves, such as head versus flow or power versus flow

•

Dimensionless curves, such as head coefficient versus flow coefficient

Compr can also calculate compressor shaft speed. Compr cannot handle performance curves for a turbine. Use the following forms to enter specifications and view results for Compr: Use this form

6-8

•


To do this

Setup

Identify compressor specifications, calculation options, convergence parameters, and valid phases

Performance Curves


User Subroutine

Enter performance curve subroutine parameters and name

Block Options


Results

View summary of Compr results, material and energy balance results, and performance curve summary

Dynamic



Flowsheet Connectivity for Compr


Work (optional)

Work (optional)

Water (optional Material Material Streams

inlet


outlet One material stream One water decant stream (optional) Work Streams

inlet

Any number of work streams (optional)

outlet One work stream for net work load (optional)

If you do not specify either power or pressure on the Compr Setup Specifications sheet, Compr uses the sum of the inlet work streams as a power specification. Otherwise, Compr uses the inlet work stream(s) only to calculate the net work load. The net work load is the sum of the inlet work streams minus the actual (calculated) work load. You can use an optional outlet work stream for the net work load.

Specifying Compr

Ifyouspecify

Comprcalculates

Discharge pressure

Powerrequiredor produced

Power required (for a compressor) or produced (for a turbine)

Discharge pressure

Curves of head, power, discharge pressure, pressure ratio, pressure change, or head coefficient

Power required and discharge pressure

Discharge pressure and curves of head or power or head coefficient

Power required, discharge pressure, and shaft speed

Power required and curves of discharge Discharge pressure, and shaft pressure, pressure ratio, or pressure speed change

When you use performance curves, you can specify either a scalar value of efficiency or efficiency curves. You can supply a Fortran subroutine to calculate performance curves in Compr. See Aspen Plus User Models for more information.



•

6-9

Some required specifications depend on the compressor type. Specify the compressor type on the Setup Specifications sheet. You can model a polytropic compressor using either the GPSA or ASME method. You can model an isentropic compressor using either the GPSA, ASME, or Mollier-based methods. To model a turbine, you must use the Mollier-based method. The GPSA method can be based on either:

• •

Suction conditions Average of suction and discharge conditions

The ASME method is more rigorous than the GPSA method for polytropic or isentropic compressor calculations. The Mollier method is the most rigorous for isentropic calculations.

Polytropic Efficiency

η

The polytropic efficiency p is used in the equation for the polytropic compression ratio:

n − 1  k − 1 =  ηp n  k  The basic compressor relation is:



P PV ∆h = in in  out n − 1   Pin  ηp   n 

  

n −1 n

 − 1 

Where:

Isentropic Efficiency

n

=

Polytropic coefficient

k

=

Heat capacity ratio Cp/Cv

ηp

=

Polytropic efficiency

∆h

=

Enthalpy change per mole

P

=

Pressure

V

=

Molar volume

ηs

There are two equations for the isentropic efficiency For compression:

ηs

=

s hout

h out

6-10

•


− hin −h in

A s pe nP l u s1 1 . 1U n i tO p e r a t i onM o d e ls

For expansion:

ηs

=

hout s hout

− hin − hin

Where :

h s out

h

Mechanical Efficiency

=

Molar enthalpy

=

Outlet molar enthalpy assuming isentropic compression or expansion to the specified outlet pressure

Mechanical efficiency horsepower:

ηm

is used to calculate the brake

IHP = F∆h

BHP = IHP / η m Where:

Integration Method

IHP

=

Indicated horsepower

F

=

Mole flow rate

∆h

=


BHP

=

Brake horsepower

ηm

=

Mechanical efficiency

The head developed for a compressor to change the pressure of a stream from the inlet pressureP1 to the outlet pressure P2 is given by:

HEAD =

∫

p2

p1

VdP

where V is the molar volume and subscripts 1 and 2 refer to inlet and outlet conditions, respectively. Two integration methods are provided for the polytropic and positive displacement model calculations using piecewise integration: Direct method

Applying the gas law PV = ZRT and using the average point for each interval, given the number of intervals betweenP1 and P2, subpath i for head developed can be written as: i

HEAD


= R( ZT )

av

 P2i  ln P1i 


•

6-11

The total polytropic head is the sum of the subpath heads:

HEAD =

∑ H EAD

i

i

n-Method

In a polytropic compression process, the relation of pressureP to volume V is expressed by the following equation:

PV n

= C = constant

where n is the polytropic exponent. The n-method is to integrate head equation, betweenP1 and P2, over a small interval such that a constant n is assumed. For subpathi, the head developed can be written as:



HEAD

Power Loss

i

=

P1iV1i  P2i   n − 1   P1i     n 

  

n −1 n

 − 1 

Power loss can be used to calculate the brake horsepower, in place of the mechanical efficiency specification on theSetup Specifications sheet. For compression process:

BHP = (IHP) + PLOSS and for expansion process:

BHP = (IHP) – PLOSS Where:

EO Usage Notes for Compr

BHP

=

Brake horsepower

IHP

=


PLOSS

=

Power loss


• • •

6-12

•


Suction nozzle parameters Multiple performance curves at different speeds Features which are globally unsupported


MCompr Reference Use MCompr to model:

• • • •

A multi-stage polytropic compressor A multi-stage polytropic positive displacement compressor A multi-stage isentropic compressor A multi-stage isentropic turbine

For polytropic compressors, MCompr can handle a single, compressible phase. For special cases you can specify two- or three-phase calculations. These calculations determine the outlet stream conditions and the properties used in the compressor equations. The accuracy of results depends primarily on the relative amounts of the phases present and the efficiency specified. The rigorous polytropic compressor uses real fluid properties calculated from the property method you specify. It does not assume ideal gas behavior. MCompr handles single-phase isentropic compressors and turbines. MCompr can also handle two- and three-phase mixtures. You can use MCompr to rate a multi-stage compressor, by using either:

•

Stage-by-stage dimensional performance curves, such as head versus flow or power versus flow

•

Wheel-by-wheel dimensionless performance curves, such as head coefficient versus flow coefficient

MCompr can also calculate shaft speed. MCompr cannot handle performance curves for a turbine.



•

6-13

Use the following forms to enter specifications and view results for MCompr: Use this form

To do this

Setup

Identify multi-stage compressor specifications, stage specifications, cooler specifications, convergence parameters, and valid phases

Performance Curves


User Subroutine

Specify performance curve user subroutine

Hcurves

parameters and name Specify heating or cooling curve tables and view tabular results

Block Options


Results

View summary of operating results, material and energy balance results, compressor and cooler profiles, and performance profiles

Dynamic

Flowsheet Connectivity for MCompr


Work (any number) From Stage K-1

Feed to Heat (any number) Stage K+1 (any number)

Cooler Compressor Stage K

Stage K

To Stage K+1 Heat (optional)

Work (optional) Stage K

Knockout Water (optional)

Material Streams

inlet

At least one material stream for the first compressor stage One or more material streams for stages after the first (optional). These streams enter the intercooler before the stages you specify.

outlet One material stream leaving the last compressor stage Either one optional knockout material stream for each intercooler for the liquid formed, or one optional global knockout for the liquid formed in all intercoolers Either one optional water decant stream for each intercooler, or one optional global water decant stream

6-14

•



If you use liquid knockout outlet streams from one stage, you must use them for all stages. The last stage cannot have a liquid knockout material stream or a water decant stream. Heat Streams

inlet

Any number of heat streams to each intercooler (optional)

outlet Either one optional heat stream for the net heat load of each intercooler, or one global heat outlet stream for the net heat duty for all intercoolers

If you do not specify cooler conditions on the Setup Cooler sheet, MCompr adds the heat streams together and uses the total as a duty specification for the cooler. The net heat load equals the heat in the inlet heat streams minus the actual (calculated) heat duty. If you use a heat outlet from one stage, you must use one for all stages. Work Streams

inlet

Any number of work streams to each compressor stage (optional)

outlet Either one optional work stream for net work load, or one global work stream for the net power for all compressor stages

MCompr adds all work inlet streams together to provide the power requirement. If you do not specify power or pressure on the Setup Specs sheet, MCompr uses the total power as a power specification for the stage. The power in the outlet work stream equals the power in the inlet work streams minus the actual (calculated) power required. If you use a work outlet from one stage, you must use one for all stages.

Specifying MCompr

Ifyouspecify

M Comprcalculates

Discharge pressure

Powerrequiredor produced

Power required (for a compressor) or produced (for a turbine)

Discharge pressure

Curves of head, power, discharge pressure, pressure ratio, pressure change, or head coefficient

Power required and discharge pressure

Discharge pressure and curves of head

Power required, and shaft speed

or power or head coefficient

When you use performance curves, you can specify either a scalar value for efficiency or efficiency curves.



•

6-15

You can supply a Fortran subroutine to calculate performance curves in MCompr. See Aspen Plus User Models for more information. MCompr can have an intercooler between each compression (or expansion) stage, and an aftercooler after the last stage. You can perform one-, two-, or three-phase flash calculations in the intercoolers. Each cooler can have a liquid knockout stream, except the cooler after the last stage. You can model a polytropic compressor using either the GPSA or ASME method. You canASME, model or an Mollier-based isentropic compressor/turbine using either the GPSA, methods. The GPSA method can be based on either:

• •

Suction conditions Average of suction and discharge conditions

The ASME method is more rigorous than the GPSA method for polytropic or isentropic compressor calculations. The Mollier method is the most rigorous for isentropic calculations.

Polytropic Efficiency

η

The polytropic efficiency p is used in the equation for the polytropic compression ratio:

n −1  k −1 =  ηp n  k  The basic compressor relation is:



P PV ∆h = in in  out − n 1    Pin ηp   n  

  

n −1 n

 − 1 

Where:

Isentropic Efficiency

n

=

Polytropic coefficient

k

=

Heat capacity ratio Cp/Cv

ηp

=

Polytropic efficiency

∆h

=


P

=

Pressure

V

=

Molar volume

There are two equations for the isentropic efficiencyη s . For compression:

6-16

•



ηs

=

− hin − hin

s hout

hout

For expansion:

ηs

=

− hin − hin

hout s out

h

Where :

Mechanical Efficiency

h

=

Molar enthalpy

s hout

=

Outlet molar enthalpy assuming isentropic compression or expansion to the specified outlet pressure

Mechanical efficiency horsepower:

ηm

is used to calculate the brake

IHP = F∆h

BHP = IHP / η m Where:

Parasitic Pressure Loss

IHP

=


F

=

Mole flow rate

∆h

=


BHP

=

Brake horsepower

ηm

=

Mechanical efficiency

The parasitic pressure loss at the suction of a stage is calculated using the equation:

∆P = Kρ

V2 2

Where:

Specific Speed

∆P

=

Parasitic pressure loss

K

=

Velocity head multiplier

ρ

=

Density

V

=

Linear velocity of process gas at suction conditions

The specific speed is defined as: SpSpd =


ShSpd (VflIn) 0.5 (Head)0.75


•

6-17

Where:

Specific Diameter

ShSpd

=

Shaft speed

VflIn

=

Suction volumetric flow rate

Head

=

Head developed

The specific diameter is defined as: SpDiam =

ImpDiam (Head) 0.25 (VflIn)0.5

Where:

Head Coefficient

ImpDiam

=

Impeller diameter of compressor wheel

Head

=

Headdeveloped

VflIn

=

Volumetric flow rate at suction conditions

The head coefficient is defined as: Hc =

Head ( π ShSpd ImpDiam) 2

Where:

Flow Coefficient

Head

=

Headdeveloped

π

=

3.1416

ShSpd

=

Shaftspeed

ImpDiam = Impeller diameter of compressor wheel The flow coefficient is defined as: Fc =

VflIn ShSpd (ImpDiam) 3

Where:

References

VflIn

=

Volumetric flow rate at suction conditions

ShSpd

=

Shaftspeed

ImpDiam

=

Impeller diameter of compressor wheel

GPSA Engineering Data Book, 1979, Chapter 4, pp. 5-6 to 5-10. ASME Power Test Code 10, 1965, pp. 31-32.

6-18

•



Valve Reference Valve models control valves and pressure changers. Valve relates the pressure drop across a valve to the valve flow coefficient. Valve assumes the flow is adiabatic, and determines the thermal and phase condition of the stream at the valve outlet. Valve can perform one-, two-, or three-phase calculations. Use the following forms to enter specifications and view results for Valve: Use this form

Flowsheet Connectivity for Valve

To do this

Input

Specify valve operating conditions, flash convergence parameters, valid phases, valve parameters, sizes for pipe fittings, calculation options, and Valve convergence parameters

Block Options


Results

View summary of operating results and mass and energy balances

Material

Material

Material Streams

inlet

One material stream

outlet One material stream

Specifying Valve

Use the Input Operation sheet to select the calculation type. If you select the Pressure changer option or the Design option for the calculation type, you must specify, on the same sheet, one of the following:

• •

Outlet pressure Pressure drop

If you select the Pressure changer option, the specification is complete and Valve performs an adiabatic flash to calculate the thermal and phase condition of the outlet stream.



•

6-19

If you select the Rating option for the calculation type, you must specify, on the same sheet, one of the following:

• •

Flow coefficient at operating valve position Valve operating position (% Opening)

If you specify the valve operating position, you must also specify one of the following on the Input ValveParameters sheet:

•

Characteristic equation type and flow coefficient at maximum valve opening

• •

Data flow coefficient Valvefor Parameters Table (Cv) versus valve opening in the A valve from the built-in library based on valve type, manufacturer, series/style, and size

On the Input CalculationOptions sheet, you can specify that Valve:

• •

Check for choked flow Calculate cavitation index

For vapor-containing streams, you must specify the pressure drop ratio factor (Xt) for the valve. For liquid-containing streams, if you specify that Valve check for choked flow, you must also specify the pressure recovery factor (Fl) for the valve. You can specify the pressure drop ratio factor and the pressure recovery factor for the valve in one of the following ways on the Input ValveParameters sheet: Specify

•

Value at the operating valve position (Pres Drop Ratio Factor, Pres Recovery Factor)

•

Data for pressure drop ratio factor (Xt) and for pressure recovery factor (Fl) versus valve opening (% Opening) in the Valve Parameters Table

•

A valve from the built-in library based on Valve Type, Manufacturer, Series/Style, and Size

If you want to include the effect of head loss from pipe fittings on the valve flow capacity, you must specify the diameters of the valve and pipe fittings on the Input PipeFittings sheet. Valve uses the valve and pipe diameters, and estimates the piping geometry factor to account for the reduction in flow capacity.

Pressure Drop Ratio Factor

The pressure drop ratio factor (X t ) accounts for the effect of the internal geometry of the valve on the change in fluid density as it passes through the valve. The pressure drop ratio factor is the limiting value (under choked conditions) of the pressure drop ratio and is given by:

6-20

•



Xt

=

1

Fk

 dPch     Pin 

(1)

Where:

dPch

=

Pressure drop for choked vapor flow

Fk

=

Ratio of specific heats factor

Pin

=

Inlet pressure

You can specify the pressure drop ratio factor on the Input ValveParameters sheet in one of the following ways: • Choose a Library Valve

•

Enter data for Xt and % Opening in the Valve Parameters Table

•

Specify the value at the operating valve position in Valve Factors

(C ) If you know the ratio of the gas sizing coefficient g to the liquid ( C ) sizing coefficient v , as defined in Fisher Controls Company

Control Valve Handbook, you can calculate the pressure drop ratio factor (with the assumption Fk = 1) by either:

 dPch    • Using valve manufacturer’s data for  Pin  versus •

Cg Cv

in

equation (1) Using the expression

Xt

=

6.31 × 10 − 4  C g 

Fk

2

   Cv 

This relationship is based on equating the choked flow calculated (in US units of measure) with: Universal Gas Sizing Equation

Wch

= 106 . C g rPin

ISA Standard Valve Sizing Equation

Wch

=N C 6 vY

Fk X rP t in

Where:

Wch

=

Mass flow rate (choked flow)

r

=

Mass density of inlet stream

Y N6

= =

Expansion factor (= 0.667 for choked flow) Numerical constant (= 63.3 for US units of measure)



•

6-21

If you specify the pressure drop ratio factor by choosing a valve from the built-in library or by entering data in the Valve Parameters Table on the Input ValveParameters sheet, Valve uses cubic splines to interpolate the value of the pressure drop ratio factor at the operating valve position. Valve uses the pressure drop ratio factor only when both of the following are true:

• • Pressure Recovery Factor

Vapor is present in the inlet stream The Design or Rating option is selected for Calculation Type

on the Input Operation sheet (F ) The pressure recovery factor l accounts for the effect of the internal geometry of the valve on its liquid flow capacity under choked conditions. The pressure recovery factor is defined as:

Fl

 dPch  =   Pin − Pvc 

1/ 2

Where:

dPch

=

Pressure drop for choked liquid flow

Pin

=

Inlet pressure

Pvc

=

Pressure at the vena contracta in the valve

and Pvc

=

F f Pv

Pv

=

Vapor pressure of inlet liquid stream

Ff

=

Liquid critical pressure ratio factor

with

You can specify the pressure recovery factor on the Input ValveParameters sheet in one of the following ways:

• • •

Choose a Library Valve Enter data for Fl and % Opening in the Valve Parameters Table Specify the value at the operating valve position in Valve Factors

The pressure recovery factor is equivalent to the valve recovery coefficient K m , as defined in Fisher Controls CompanyControl Valve Handbook.

6-22

•



You can use the valve recovery coefficient to calculate the pressure recovery factor as:

Fl

=

Km

If you specify the pressure recovery factor by choosing a valve from the built-in library or by entering tabular data in the Valve Parameters Table on the Input ValveParameters sheet, Valve uses cubic splines to interpolate the value of the pressure recovery factor at the operating valve position. The pressure recovery factor is used in the Valve model calculations only when all of the following are true:

Valve Flow Coefficient

• •

Liquid is present in the inlet stream

•

The Design or Rating option is selected for Calculation Type on the Input Operation sheet.

The Check for Choked Flow box is checked or the Set Equal to Choked Outlet Pressure option is selected on the Input CalculationOptions sheet

The valve flow coefficient (Cv ) measures the flow capacity of the valve. The flow coefficient is defined as the number of US gallons per minute of water (at 60°F) that will pass through the valve with a pressure drop of 1 psi. The valve flow coefficient relates the pressure drop across the valve to the flow rate as (Instrument Society of America, 1985):

W

Liquid Gas/Vapor with

= N F6 Cp rv P ( Pin − out ) W =N F P − out ) 6 Yp r P ( in Y

= 1−

Pin

− Pout

3 Fk Xt iPn

Where:

W

=

Mass flow rate

N6

=

Numerical constant (based on the units of measure)

Fp

=

Piping geometry factor

Cv

=

Valve flow coefficient

Y

=

Expansion factor

Pin Pout

= =

Inlet pressure Outlet pressure

r

=

Mass density of inlet stream



•

6-23

Fk

=


Xt

=

Pressure drop ratio factor

You can specify the flow coefficient in one of the following ways:

•

Use Flow Coef on the Input Operation sheet to specify the value at the operating valve position

• •

Choose a Library Valve on the Input ValveParameters sheet

•

Specify Valve Characteristics in the Input ValveParameters sheet

Enter data for Cv and % Opening in the Valve Parameters Table on the Input ValveParameters sheet

If you specify the flow coefficient by choosing a valve from the built-in library or by entering data in the Valve Parameters Table, Valve uses cubic splines to interpolate the value of the flow coefficient at the operating valve position.

Characteristic Equation Type

The characteristic equation for the valve relates the flow coefficient to the valve opening. Use the Input ValveParameters sheet to specify the characteristic equation type. The six built-in characteristic equations are: Type

Equation

Linear

V

=P

Parabolic

V

= 0.01P 2

Square Root

V

= 10.0

V

=

V

=

V

=

Quick Opening

Equal Percentage

Hyperbolic

P 10.0 P

(1.0 + 9.9 × 10 −3 P 2 ) 0.01P 2 2.0 − 1.0 × 10 −8 P 4

01 . P

(1.0 − 9.9 × 10 −5 P 2 )

Where: P = Valve opening as a percentage of maximum opening V = Flow coefficient as a percentage of flow coefficient at maximum opening

Piping Geometry Factor

The piping geometry factor is defined as: Fp

6-24

•


=

Cυp Cυ


Where: Cυp

=

Flow coefficient of the valve with attached fittings

Cυ

=

Flow coefficient of the valve installed in a straight pipe of the same size

The piping geometry factor accounts for the reduction in the flow capacity of a valve due to the head loss from the pipe fittings. The piping geometry factor has a default value of 1.0 if the valve and pipe fittings have the same diameter. Aspen calculates1985): the piping geometry factor as (Instrument SocietyPlus of America,

Fp

 ΣKC 2    υ = 4 + 1 N d  2 

with

−0.5

ΣK =K +1K K+ 2 −KB1

B2

Where:

K1

 d2  = 0.51 − 2   D1 

K B2

d = 1−    D2 

2

K2 ,

 d2  = 10 . 1 − 2   D2 

2

K B1 ,

d = 1−    D1 

4

,

4

and: Fp

=

Piping geometry factor

Cυ

=

Valve flow coefficient

N2

=

Numerical constant (based on the units of measure)

d

=

Valve diameter

K1 , K 2

=

Resistance coefficients of the inlet and outlet fittings

K B1 , K B2

=

Bernoulli coefficients for the inlet and outlet fittings

D1

=

Inlet pipe diameter

D2

=

Outlet pipe diameter

If the valve and pipe fittings diameters are different and you wish to include the effect of the additional head loss on the valve flow



•

6-25

capacity, you must specify the valve and pipe diameters on the Input PipeFittings sheet.

Choked Flow

Aspen Plus calculates the limiting pressure drop for choked flow conditions using (Instrument Society of America, 1985): Liquid

(

dPlc =F LP 2

dP

Vapor with

Ff

υc

F= Xk PT

in

F−P

f

υ

)

in

 Pv  0 . 96 0 . 28 = −  Pc 

0.5

Where: FL

=

Pressure recovery factor

Ff

=

Liquid critical pressure ratio factor

Fk

=


XT

=

Pressure drop ratio factor

Pin

=

Inlet pressure

Pυ

=

Vapor pressure at inlet

Pc

=

Critical pressure at inlet

dPlc

=

Limiting pressure drop, liquid phase

dP

vc = Limiting pressure drop, vapor phase For multi-phase streams, Valve takes the limiting pressure drop for

choked flow to be the smaller of dPlc and dPvc . Flow in the valve is choked when the pressure drop exceeds this limiting pressure drop. Valve displays the choking status of the valve if you check the Check for Choking box on the Input CalculationOptions sheet.

Cavitation Index

The likelihood of cavitation in a valve is measured by the cavitation index. Aspen Plus calculates the cavitation index as (Instrument Society of America, 1985):

Kc

P −P  =  in out   Pin − Pv 

Where:

6-26

•


Kc

=

Cavitation index

Pin

=

Inlet pressure

Pout

=

Outlet pressure


Pv

=

Vapor pressure at inlet

The cavitation index definition is valid only for all-liquid streams. Valve calculates the cavitation index if you check the Calculate Cavitation Index box on the Input CalculationOptions sheet.

Reference

Flow Equations for Sizing Control Valves, ISA-S75.01-1985, Instrument Society of America, 1985.



•

6-27

Pipe Reference Pipe calculates the pressure drop and heat transfer in a single segment pipe. You can also use Pipe to model the pressure drop due to fittings. Pipe handles a single inlet and outlet material stream. Pipe assumes the flow is one-dimensional, steady-state, and fully developed (that is, no entrance effects are modeled). Pipe can perform one-, two-, or three-phase calculations. Flow direction and elevation angle are arbitrary. To model multiple pipe segments of different diameters or elevations, use Pipeline instead of Pipe. If the inlet pressure is known, Pipe calculates the outlet pressure. If the outlet pressure is known, Pipe calculates the inlet pressure and updates the state variables of the inlet stream. Use Pipe to:

• •

Calculate inlet or discharge conditions Calculate pressure drops for one-, two-, or three-phase vapor and liquid flows

Use the following forms to enter specifications and view results for Pipe: Use this form

6-28

•


To do this

Setup

Specify pipe parameters, thermal specifications, fittings, flash convergence parameters and property profiles to be reported

Advanced

Specify calculation options, solution methods, property grid, integration parameters and Beggs and Brill coefficients

UserSubroutine

Specify pressure drop and/or holdup and/or diameter calculation user subroutine name and parameters

Dynamic


BlockOptions


Results

View summary of Pipe results, inlet and outlet stream results, material and energy balance results, and profiles


Flowsheet Connectivity for Pipe

Material

Material Material Streams

inlet

One material stream


Specifying Pipe

You must specify the following for Pipe:

•

Pipe length, diameter, roughness, and angle on the Setup PipeParameters sheet

•

Thermal specification type on the Setup ThermalSpecification sheet to determine whether Pipe operates with a temperature profile or temperature is calculated

•

Whether to integrate, assume constant dP/dL, or use a closed form equation on the Advanced Methods sheet

•

Frictional and holdup correlation when a closed form equation is not used on the Advanced Methods sheet

•

Pressure and temperature grid for fluid property calculations on the Advanced PropertyGrid sheet, if you request a pressuretemperature grid on the AdvancedCalculation Options sheet

•

Integration direction in which calculations proceed with respect to flow on the Advanced CalculationOptions sheet

If the option selected is

Pipe needs the

And the integration direction is

Calculate pipe outlet pressure(default)

Inlet pressure

Downstream

Calculate pipe inlet pressure

Outlet pressure

Upstream

Pipe uses the inlet or outlet stream pressure to start the calculations. If the stream is an external feed to your flowsheet, or the outlet of a block that will execute after Pipe, use the Stream Specifications sheet to specify the stream pressure. If the integration direction is upstream, you can also specify the initial pressure for Pipe on the Advanced CalculationOptions sheet, by entering the outlet pressure. This pressure value will override the stream pressure entered on the Stream Specifications sheet.



•

6-29

Select the flow calculation option on the Advanced CalculationOptions sheet to specify whether Pipe is to calculate the outlet or inlet stream flow and composition. If the option selected is

Reference inlet stream (default) Use outlet stream flow

Stream Specification

Pipe needs the

Inlet flow and composition Outlet flow and composition

You must initialize the inlet stream to Pipe whenever the option to reference inlet stream is selected, even if the inlet pressure is being calculated. Similarly, you must initialize the outlet stream whenever the option to use the outlet stream flow is selected. The initialized stream must be one of the following:

Physical Property Calculations

• •

Entered on a Stream Specifications sheet

•

Transferred from another part of a flowsheet using a Transfer block

An outlet stream from part of the flowsheet executed (if option to use outlet stream flow is selected)

You can specify that a rigorous flash is to be performed each time properties are calculated, by selecting the option to do Flash at Each Integration Step on the Advanced CalculationOptions sheet. If you select the option to Interpolate from Property Grid, Pipe will determine properties by interpolating in a table of property values at various temperatures and pressures. Specify one of the following if you use the Property Grid:

•

A range of temperatures and pressures on the Advanced Property Grid sheet. Pipe will calculate properties at these conditions and interpolate

•

The block ID of a Pipe block for which the option to interpolate from property grid was also selected, and which will be executed before the current block in the flowsheet

Pressure Drop Calculations

Pipe can calculate pressure drop for either one-, two-, or threephase vapor and liquid flows. If vapor-liquid flow exists, Pipe also calculates liquid holdup and flow regime (pattern). You may specify a flowing fluid temperature profile, or Pipe can determine it from heat transfer calculations. Pipe treats multiple liquid phases (for example, oil and water) as a single homogeneous liquid phase for pressure-drop and holdup calculations. Pipe automatically detects the special case of a single component fluid (for example, steam) and treats it appropriately.

Downstream and Upstream Integration

For downstream and upstream integration, the combination of options selected for pressure and flow calculation on the Advanced CalculationOptions sheet determine which stream Pipe will update. The following table describes the available combinations. The next

6-30

•



figure, Downstream and Upstream Integration, defines the inlet and outlet stream and pressure variables: If the pressure And the flow Then Pipe updates the calculation option is calculation option is

Calculate pipe outlet Calculate outlet pressure stream flow

Outlet stream only

Calculate pipe outlet Calculate inlet stream Outlet stream pressure flow thermodynamic conditions Inlet stream composition and flow Calculate pipe inlet pressure

Calculate inlet stream Inlet stream only flow

Calculate pipe inlet pressure

Calculate outlet stream flow

Inlet stream thermodynamic conditions Outlet stream composition and flow

Inlet Stream

InletPressure

Outlet Stream

OutletPress ure


Design-Spec Convergence Loop

Use caution when using Pipe inside a Design-Spec convergence loop. For example, you can manipulate the flow rate to a pipe to achieve a desired pipe outlet pressure. During the design specification convergence, the flow rate variables may become unreasonable in an intermediate iteration, causing Pipe to predict a negative pressure. Convergence difficulties occur as a result. You can avoid this situation by doing one of the following:

Erosional Velocity

•

Keep the upper limit of the flow rate sufficiently low in Design-Spec

•

Perform an upstream integration from the known outlet pressure. Select option to calculate pipe inlet pressure on the Advanced CalculationOptions sheet for this purpose. Define a Design-Spec to manipulate the flow rate to achieve the specified inlet pressure.

Erosional velocity is the velocity of the fluid in the pipe, above which the pipe material will start to break off. The fluid is traveling so fast that it starts to strip material from the walls of the pipe. In general use, the flow rate should be below this value. You can specify the erosional velocity coefficient on the Setup Pipe Parameters sheet.



•

6-31

The erosional velocity is related to the erosional velocity coefficient by the following equation:

υc

=

c

ρ

Where:

Methane Gas Systems

υc

=

Erosional velocity in ft/second

c

=

Erosional velocity coefficient (default=100)

ρ

=

Density in lbs/cubic ft

Gas systems consisting mostly of methane occur frequently in the dense-phase region of wellbores and flowlines. In the dense-phase region, definable vapor and liquid phases do not exist. Equationof-state methods classify the dense-phase material as either all vapor or all liquid. Significant differences in the predicted fluid transport properties may occur, depending on whether you choose the vapor or liquid state. Experience has shown that gas system flow in the dense-phase region is best modeled by using vapor-phase properties. For systems consisting of mostly methane, where the pipe conditions lie above the cricondenbar of the phase envelope, specify vaporonly valid phase on the Setup FlashOptions sheet.

Modeling Valves and

Pipe assumes that the pressure drop due to valves and fittings is

Fittings

distributed evenly along the specified length of the pipe. The total length Pipe uses in calculations corresponds to the specified pipe length, plus any equivalent pipe length due to valves, fittings, and miscellaneous L/D. If the pipe is not horizontal, Pipe adjusts the angle from the horizontal to achieve the same vertical rise or fall for the total length used in the calculations. This adjustment ensures the correct pressure drop due to elevation. If the order and position of the valves and fittings are important, you need to model each valve and fitting separately with a Pipe model, specifying zero length of pipe.

Two-Phase Correlations

6-32

•


See Pipeline reference for information on Two-Phase FrictionFactor and Liquid-Holdup Correlations and Closed Form Methods.


Pipeline Reference Use Pipeline to calculate the pressure drop in a straight pipe or annular space. Pipeline can:

•

Simulate a piping network with successive blocks, including wellbores and flowlines

•

Contain any number of segments within each block to describe pipe geometry

• •

Calculate inlet or discharge conditions Calculate pressure drops for one-, two-, or three-phase vapor and liquid flows. Pipeline treats multiple liquid phases (for example, oil and water) as a single homogeneous liquid phase for pressure-drop and holdup calculations. If vapor-liquid flow exists, Pipeline calculates liquid holdup and flow regime (pattern).

You may specify a flowing fluid temperature profile, or Pipeline can calculate it from heat transfer calculations. Flow is assumed to be one-dimensional, steady-state, and fully developed (no entrance effects are modeled). Flow direction and elevation angle are arbitrary. To model a single pipe segment with constant diameter and elevation, you can also use Pipe. Use the following forms to enter specifications and view results for Pipeline: Use this form

To do this

Setup

Specify pipeline configuration, segment connectivity and characteristics, calculation methods, property grid parameters, flash convergence parameters, valid phases, and block-specific diagnostic message level

Convergence

Override default values for integration parameters, downhill flow options, correlation parameters and Beggs and Brill coefficients (optional input)

BlockOptions


UserSubroutines

Specify name and parameters for pressure drop and liquid holdup user subroutines

Results

View summary of Pipeline results, inlet and outlet stream results, profiles, and material and energy balance results



•

6-33

For Pipeline you must specify:

•

Integration direction in which calculations proceed with respect to flow

•

Thermal calculation option to specify whether pipeline node temperatures are calculated or specified

• •

Specifications for at least one pipeline segment Pressure and Temperature grid for the fluid property calculations, if you request a pressure-temperature grid

When using a Pipeline block an inside a Design-Spec convergence loop (for example, obtaining outlet pressure by varying the inlet flow rate) it is possible that the flow rate variable could cause Pipeline to predict negative pressures or fail to converge, which will result in convergence problems. Avoid this by keeping the upper limit of the flow rate low in the Design-Spec block, or by performing an upstream integration from the known outlet pressure (Select Calculate Inlet Pressure for Calculation Direction on the Setup Configuration sheet for this purpose. Your Design-Spec will then need to manipulate the flow rate to achieve the specified inlet pressure). Pipeline handles a single inlet and outlet material stream. If the inlet pressure is known, Pipeline calculates the outlet pressure. If the outlet pressure is known, Pipeline calculates the inlet pressure and updates the state variables of the inlet stream.

Flowsheet Connectivity for Pipeline

Material

Material Pipeline Streams Material Streams

inlet

One material stream


6-34

•



Specifying Pipeline

Use the Calculation Direction option on the Setup Configuration sheet to specify whether Pipeline is to calculate the outlet or inlet pressure. If Ca lculation Direction = Pipeline will need And the integration the direction is

Calculate outlet pressure (default)

Inlet pressure

Downstream

Calculate inlet pressure

Outlet pressure

Upstream

Pipeline uses the inlet or outlet stream pressure to start the calculations. the stream is an external feed to youruse flowsheet, or the outlet of aIfblock that will execute after Pipeline, the Streams Specifications sheet to specify the stream pressure. You can also specify the initial pressure for Pipeline on the Setup Configuration sheet by entering the pressure value at the inlet or outlet. This pressure value overrides the stream pressure. Use the Pipeline flow basis option on the Setup Configuration sheet to specify whether Pipeline is to calculate the outlet or inlet stream flow and composition. If Pipeline flow basis=

Pipeline will need the

Use inlet stream flow (default)

Inlet flow and composition

Reference outlet stream flow

Outlet flow and composition

Use Thermal Options on the Setup Configuration sheet to specify whether or not the node temperatures are to be calculated by Pipeline using an energy balance. When you select the Specify Temperature Profile option, the temperature at each node can be specified. When you choose the Constant Temperature option, the temperature will be same at every node. You can define this temperature by specifying the inlet temperature (for downstream integrations) or the outlet temperature (for upstream integrations). If neither the inlet nor the outlet temperatures are specified, the temperature of the referenced stream will be used. When you choose the linear temperature profile option, you can specify the temperature at one or more nodes. Pipeline will do a linear interpolation between the temperatures specified to calculate the fluid temperature in each segment.



•

6-35

Stream Specification

Nodes and Segments

You must initialize the inlet stream to Pipeline whenever the Use Inlet Flow option is selected for Pipeline Flow Basis, even if the inlet pressure is being calculated. Similarly, you must initialize the outlet stream whenever you select the Reference Outlet Stream Flow option. The initialized stream must be one of the following:

• •

On a stream form

•

Transferred from another part of a flowsheet using a Transfer block

An outlet stream from part of the flowsheet executed previously

Create at least one segment using the New button on the Pipeline Setup Connectivity sheet. Enter specifications for each segment on the Setup Connectivity Segment Data dialog box . For each segment, enter the inlet and outlet node names (maximum 4 characters). The required data depends on the options selected on the Setup Configuration sheet. If you select Do Energy Balance with Surroundings, you must specify a heat transfer coefficient (U-Value) and the ambient temperature. If you select the Linear Temperature Profile option, Pipeline uses the temperatures specified for the nodes to override the stream values. If specifications are not made for the nodes, then Pipeline uses the stream values. If you select Enter Node Coordinate, you must enter node coordinates (X, Y, and Elevation) for each segment node. You must enter Length and Angle for each segment if you select Enter Segment Length and Angle.

Physical Property Calculations

You can specify a rigorous flash each time properties are calculated by selecting Do Flash at Each Step on the Setup Configuration sheet. If Interpolate from Property Grid is selected, Pipeline will determine properties by interpolating in a table of property values at various temperatures and pressures. Specify one of the following if you use the Property Grid:

•

A range of temperatures and pressures grid on the Setup PropertyGrid sheet. Pipeline calculates properties under these conditions and interpolates them.

•

The block ID of a Pipeline block for which you selected Interpolate from the Property Grid, and which will be executed before the current block in the flowsheet.

Pressure Drop

Pipeline can calculate pressure drop for either one-, two-, or three-

Calculations

phase vapor and liquid flows. If vapor-liquid flow exists, Pipeline also calculates liquid holdup and flow regime (pattern). You may specify a flowing fluid temperature profile, or Pipeline can calculate it from heat transfer calculations. Pipeline treats multiple

6-36

•



liquid phases (for example, oil and water) as a single homogeneous liquid phase for pressure-drop and holdup calculations. Pipeline automatically detects the special case of a single component fluid (for example, steam) and treats it appropriately.


For downstream and upstream integration, the combination of the selections made for Calculation Direction and Pipeline Flow Basis on the Setup Configuration sheet determine which stream Pipeline will update. The following table describes the available combinations. The next figure, Downstream and Upstream Integration, defines the inlet and outlet stream and pressure variables. If you specify And Pipeline Flow Then Pipeline updates the Calculation Direction= Basis=

Calculate Outlet Pressure

Reference inlet stream flow

Outlet stream only

Calculate Outlet Pressure

Use outlet stream flow

Outlet stream thermodynamic conditions Inlet stream composition and flow

Calculate Inlet Pressu re Reference outlet stream flow

Inlet stream only

Calculate Inlet Pressure Use inlet stream flow

Inlet stream thermodynamic conditions Outlet stream composition and flow

Inlet Stream

InletPressure

Outlet Stream

OutletPress ure


Design Spec Convergence Loop

Use caution when using Pipeline inside a Design-Spec convergence loop. For example, suppose you achieve a desired pipeline outlet pressure by varying the flow rate to the pipeline. In this case, the flow rate variable might cause Pipeline to predict negative pressures, resulting in convergence problems. You can avoid this situation by doing one of the following:

•

Keep the upper limit of the flow rate sufficiently low in the Design-Spec

•

Perform an upstream integration from the known outlet pressure. Use Calculate Inlet Pressure on the Setup Configuration sheet for this purpose. Your Design-Spec will then need to manipulate the flow rate to achieve the specified inlet pressure.



•

6-37

Erosional Velocity

Erosional velocity is the velocity of the fluid in the pipe over which the pipe material will start to break off. The fluid is traveling so fast that it starts to strip material from the walls of the pipe. In general usage, the flow rate should be below this value. You can specify the erosional velocity coefficient in the C-Erosion field on the Segment Data dialog box on the Setup Connectivity sheet. The erosional velocity is related to the erosional velocity coefficient by the following equation:

υc

=

c ρ

Where:

Methane Gas Systems

υc

=

Erosional velocity in ft/sec

c

=

Erosional velocity coefficient (default=100)

ρ

=

Density in lb/cubic ft

Gas systems consisting mostly of methane occur frequently in the dense-phase region of wellbores and flowlines. In the dense-phase region, definable vapor and liquid phases do not exist. Equationof-state methods classify the dense-phase material as either all vapor or all liquid. Significant differences in the predicted fluid transport properties may occur, depending on whether you choose the vapor or liquid state. Experience has shown that gas system flow in the dense-phase region is best modeled by using vapor-phase properties. For systems consisting of mostly methane, where the pipeline conditions lie above the cricondenbar of the phase envelope, specify Valid Phases = Vapor only on the Setup FlashOptions sheet.

6-38

•



The following tables list the two-phase frictional pressure drop and holdup correlations available.

Two-Phase Correlations

Two-Phase Friction Factor Correlations

Pipe orientation

Inclination

Horizontal

-2 deg to +2 deg

Friction factor correlations

Vertical

+45 deg to +90 deg Beggs and Brill (BEGGS-BRILL) Orkiszewski (ORKI) Angel-Welchon-Ros (AWR) Hagedorn-Brown (H-BROWN) Darcy (DARCY) User subroutine (USER-SUBR)

Downhill

-2 deg to -90 deg

Inclined

+2 deg to +45 deg Beggs and Brill (BEGGS-BRILL) Dukler (DUKLER) Orkiszewski (ORKI) Angel-Welchon-Ros (AWR) Hagedorn-Brown (H-BROWN) Darcy (DARCY) User subroutine (USER-SUBR)

Pipe orientation

Inclination

Horizontal

-2 deg to +2 deg

Vertical

+45 deg to +90 deg Beggs and Brill (BEGGS-BRILL) Orkiszewski (ORKI) Angel-Welchon-Ros (AWR) Hagedorn-Brown (H-BROWN) User subroutine (USER-SUBR)

Downhill

-2 deg to -90 deg

Beggs and Brill (BEGGS-BRILL) Dukler (DUKLER) Lockhart-Martinelli (LOCK-MART) Darcy (DARCY) User subroutine (USER-SUBR) †

Beggs and Brill (BEGGS-BRILL) Slack (SLACK) Darcy (DARCY) User subroutine (USER-SUBR)

Two-Phase Liquid Holdup Correlations


Liquid holdup correlations

Beggs and Brill (BEGGS-BRILL) Eaton (EATON) Lockhart-Martinelli (LOCK-MART) Hoogendorn (HOOG) Hughmark (HUGH) User subroutine (USER-SUBR) †

Beggs and Brill (BEGGS-BRILL) Slack (SLACK) User subroutine (USER-SUBR)


•

6-39

Pipe orientation

Inclination

Inclined

+2 deg to +45 deg Beggs and Brill (BEGGS-BRILL) Flanigan (FLANIGAN) Orkiszewski (ORKI) Angel-Welchon-Ros (AWR) Hagedorn-Brown (H-BROWN) User subroutine (USER-SUBR)

Liquid holdup correlations

† See Aspen Plus User Models. Note: Some of the related information for the two-phase friction

factor and liquid holdup correlations was taken from "Two-Phase Flow in Pipes" by James P. Brill and H. Dale Beggs, Sixth Edition, Third Printing, January, 1991.

Beggs and Brill Correlation

Slip and flow regimes are considered with this method. Friction factor and holdup correlations depend upon flow regime and pipe inclination. It is suitable for all inclinations, including vertical flow downward.

Dukler Correlation

The Hughmark holdup method should be used with this pressure drop method. The Dukler method was developed from field data using air-water mixtures in 1-inch pipes. It tends to over-predict frictional pressure drop. It is recommended in a design manual published jointly by the AGA and API.

Hagedorn-Brown Correlation

The Hagedorn-Brown correlation considers slip between phases, but flow regime is not considered. It uses the same correlations for liquid holdup and friction factor for all flow regimes. It is an old method that works well for conventional oil wells. It is suitable for vertical upward flow, but not downward. It is generally recommended for gas wells, and is based on data obtained from U.S. Gulf Coast oil wells with 2-3/8 inch and 2-7/8 inch tubing.

Lockhart-Martinelli Correlation

The Lockhart-Martinelli correlation is one of the oldest pressure drop correlations. It does not consider pressure drop due to acceleration. The method treats the vapor and liquid phases separately and uses a correction factor to find the 2-phase pressure gradient. Our implementation assumes turbulent gas and liquid phase flow.

Orkiszewski Correlation

The Orkiszewski correlation considers slip and flow regimes. The friction factor and holdup correlation depend on the flow regime. It is suitable for vertical flow upward, but not downward. It is generally reliable for oil wells. It may exhibit problems for oil wells with high water cuts or high total gas to liquid ratios. It can significantly underpredict pressure drop for higher rate and higher pressure wells (Beggs and Brill/1984).

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•



Angel-Welchon-Ros Correlation

This Angel-Welchon-Ros method was developed for low gas-toliquid ratio water wells. It assumes no slip between the vapor and liquid phases when calculating liquid holdup.

Slack Correlation

This method assumes a stratified flow regime, and should be used only for downhill flow.

Eaton Correlation

The Eaton correlation holdup method was developed from data on 2- and 4-inch pipes with a gas-water-crude mixture, and a 17-inch pipe with a gas-oil mixture. It is often used with the Dukler frictional pressure drop correlation.

Flanigan Correlation

The Flanigan correlation holdup method was developed from data taken in a 16-inch pipe. It calculates liquid holdup as a function of superficial gas velocity. It is suitable for inclined flow.

Beggs and Brill Correlation Parameters

The following table lists the Beggs and Brill liquid holdup correlation parameters.

Flow Regime

Name Description

Segregated

BB1 BB2 BB3

Leading coefficient, A (default = 0.98) Liquid volume fraction exponent, alpha (default = 0.4846) Froude no. exp., beta (default = 0.0868)

Intermittent

BB4 BB5 BB6


Distributed

BB7 BB8 BB9


In addition, you can change the Beggs and Brill two-phase Friction Factor modifier, BB10 (default = 1.0).

Closed-Form Methods

Smith

The following are closed-form methods:

• • • • • • •

Smith Weymouth AGA Oliphant Panhandle A Panhandle B Hazen-Williams

The Smith method may be used for vertical dry gas flow. It should be considered for gas wells with condensate-gas ratios less than 50 bbls/mcf, water-gas ratios less than 3.5 bbls/mcf, and flow rates above the Turner predicted critical rate. Smith does not model gas well loadup, and will significantly underpredict wellbore pressure drop if loadup is actually occurring. Smith results must be crosschecked against the Turner predicted critical rates to verify that the



•

6-41

well is unloaded. Smith also does not model condensation of water vapor in the wellbore.

Weymouth

The Weymouth horizontal gas flow equation was first published in 1912. It is based on data taken on pipes with diameters from 0.8 inches to 11.8 inches. As a result, it is most accurate for smaller pipes having a diameter less than 12 inches.

AGA

The AGA method may be used for horizontal gas applications.

Oliphant

The Oliphant method may be used for horizontal gas applications with pressures between vacuum and 100 PSI.

Panhandle A

The Panhandle A method was developed by Panhandle Eastern for horizontal gas flow in large diameter cross country gas transmission lines. As a result, it is best used on lines having diameters larger than 12 inches. However, it does not account for gas compressibility (Z-factor), and assumes completely turbulent flow.

Panhandle B

The Panhandle B method is a revised version of the Panhandle A method for horizontal gas flow and was developed by Panhandle Eastern. It is also called the "Panhandle Eastern Revised Equation". It accounts for the gas compressibility factor, and has revised exponents. This equation is not quite so Reynolds-Number dependent as the Panhandle A equation, although it, too, is best for pipe diameters of 12 inches or more.

Hazen-Williams

The Hazen-Williams method was developed for the horizontal flow of water. When this method is used, the Hazen-Williams Coefficient must be specified in place of the Segment Efficiency on the Connectivity Edit Dialog Box.

References

Beggs, H.D., and Brill, J.P., "A Study of Two-Phase Flow in Inclined Pipes," Journal of Petroleum Technology, May 1973, pp. 607-617. Dukler, A.E., Wicks, M., and Cleveland, R.G, "Frictional Pressure Drop in Two-Phase Flow: An Approach Through Similarity Analysis," AIChE Journal, Vol. 10, No. 1, January 1964, pp. 4451. Lockhart, R.W. and Martinelli, R.C. "Proposed Correlation of Data for Isothermal Two-Phase, Two-Component Flow in Pipes," Chemical Engineering Progress, Vol. 45, 1949, pp. 39-48. Orkiszewski, J., "Predicting Two-Phase Pressure Drops in Vertical Pipe," Journal of Petroleum Technology, June 1967, pp. 829-838. Beggs, H.D., and Brill, J.P., "Two-Phase Flow in Pipes," University of Tulsa Short Course Notes, Third Printing, February 1984.

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•



Angel, R.R., and Welchon, J.K., "Low-Ratio Gas-Lift Correlation for Casing-Tubing Annuli and Large Diameter Tubing," API Drilling and Production Practice, 1964, pp. 100-114. Ros, N.C.J., "Simultaneous Flow of Gas and Liquid as Encountered in Well Tubing," Journal of Petroleum Technology, October 1961, pp. 1037-1049. Eaton, B.A. et al., "The Prediction of Flow Patterns, Liquid Holdup, and Pressure Losses Occurring During Continuous TwoPhase Flow in Horizontal Pipelines," "Trans. AIME, June 1967, pp. 815-828. Flanigan, Orin, "Effect of Uphill Flow on Pressure Drop in Design of Two-Phase Gathering Systems," Oil and Gas Journal, March 10, 1958, pp. 132-141. Smith, R.V., "Determining Friction Factors for Measuring Productivity of Gas Wells," AIME Petroleum Transactions, Volume 189, 1950, pp. 73-82. Weymouth, T.R., Transactions of the American Society of Mechanical Engineers, Vol. 34, 1912. "Steady Flow in Gas Pipes," American Gas Association, IGT Technical Report 10, Chicago, 1965. Oliphant, F.N., "Production of Natural Gas," Report of USGS, 1902. Engineering Data Book, Volume II, Gas Processors Suppliers Association, Tulsa, Oklahoma, Revised Tenth Edition, 1994.



•

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6-44

•



C HA P TE R 7

Manipulators

This chapter describes the models for stream manipulators. The models are: M odel

Description

Purpose

Mult

Streammultiplier

Multipliesc omponent Scaling streams by a factor and total flow rates by a factor

Dupl

Stream duplicator

Copies inlet stream into Duplicating feed or internal streams any number of duplicate outlet streams

ClChng

Stream class changer

Changes stream class between blocks and flowsheet sections

Analyzer

EO stream property Calculates values of Calculating stream properties in equationcalculator material stream oriented (EO) simulations and component fractions and optimizations. stream properties.

Feedbl

Feed stream

Holds data for feed streams.

Selector

Stream selector

Copies one selected input Selecting one stream from any number of stream to the outlet inlet streams. stream.

Qtvec

Load stream manipulator

Creates and modifies load streams.

Measurement Plant measurement Incorporates measu red plant data into a

UseFor

Adding or deleting empty solid substreams between flowsheet sections

Feedbl is provided for compatibility with RT-OPT version 10 simulations. Do not use it in new simulations. Aspen Plus creates new feed blocks automatically as needed.

Combining multiple heat streams into a single load stream or adding an additional temperature and duty point to an existing load stream. Defining plant measurements for data reconciliation purposes.

simulation.


M a n i pu l a t o r s

•

7-1

Mult Reference Mult multiplies the component flow rates and the total flow rate of a material stream by a factor you supply on the Mult Input Specifications sheet. For heat or work streams, Mult multiplies the heat or work flow. Select the Heat (Q) and Work (W) Mult icons from the Model Library for heat and work streams respectively. Mult is useful when other conditions during the simulation determine the flow rate of the stream. Mult does not maintain heat or material balances. For material streams, the outlet stream has the same composition and intensive properties as the inlet stream. Use the Mult form to specify the stream multiplication factor and diagnostics message levels.

Flowsheet Connectivity for Mult

Material

Material

or

or

Heat

Heat

or

or

Work

Work

Material Streams

inlet

One material stream

outlet One material stream Heat Streams

inlet

One heat stream

outlet One heat stream Work Streams

inlet

One work stream


The outlet stream must be the same type (material, heat, or work) as the inlet stream.

Specifying Mult

The stream multiplication factor, specified on the Input Specifications sheet, is the only input required for Mult. This factor has to be positive for material streams. You can specify either a positive or negative factor for heat or work streams, thus allowing a change in direction for the heat or work flow. Use the Input Diagnostics sheet to override global values for the stream and simulation message levels specified on the Setup Specifications Diagnostics sheet.

7-2

•



This model has no dynamic features. For material stream multipliers the pressure of each outlet stream is equal to the pressure of the inlet stream. The flow rate of each outlet stream is equal to the flow rate of the inlet stream multiplied by the factor as specified in the steady-state simulation.

EO Usage Notes for Mult

All features of Mult are available in the EO formulation, except the features which are globally unsupported.



•

7-3

Dupl Reference Dupl copies an inlet stream (material, heat, or work) to any number of duplicate outlet streams. It is useful for simultaneously processing a stream in different types of units. Select the Heat (Q) and Work (W) Dupl icons from the Model Library for heat and work streams respectively. Dupl does not maintain heat or material balances. Use the Dupl form to specify diagnostics message levels.

Flowsheet Connectivity for Dupl Material (any number)

Material

Flowsheet for Duplicating Material Streams Material Streams

inlet

One material stream

outlet At least one material stream, which is a copy of the inlet stream

Heat (any number)

Heat

Flowsheet for Duplicating Heat Streams Heat Streams

inlet

One heat stream

outlet At least one heat stream, which is a copy of the inlet stream

Work (any number)

Work

Flowsheet for Duplicating Work Streams

7-4

•



Work Streams

inlet

One work stream

outlet At least one work stream, which is a copy of the inlet stream

Specifying Dupl

Dupl requires no input parameters. Use the Input Diagnostics sheet to override global values for the stream and simulation message levels specified on the Setup Specifications Diagnostics sheet. This model has no dynamic features. For material stream duplicators the pressure of each outlet stream is equal to the pressure of the inlet stream. The flow rate of each outlet stream is equal to the flow rate of the inlet stream.

EO Usage Notes for Dupl

All features of Dupl are available in the EO formulation, except the features which are globally unsupported.



•

7-5

ClChng Reference ClChng changes the stream class between blocks and flowsheet sections. You can use ClChng to add or delete empty solid substreams between flowsheet sections. ClChng does not represent a real unit operation. Use the ClChng Input Form to specify diagnostics message levels.

Flowsheet Connectivity for ClChng Feed

Product

Material Streams

inlet


outlet One material product stream

Specifying ClChng

ClChng does not require input. It copies substreams from the inlet stream to the corresponding substreams of the outlet stream. If a substream is

Then ClChng

In the outlet but not in the Initializes the substream to zero flow inlet In the inlet but not in the Drops the substream outlet

ClChng does not maintain mass and energy balances if any dropped substream contains material flow or heat/work information.

7-6

•



Analyzer Reference The Analyzer block is a mole flow based model that allows you to calculate values of material stream component fractions and stream properties for use in the equation-oriented (EO) simulation and optimization phases of a flowsheet. You can specify one inlet and one outlet material stream, or specify a stream to analyze on the Input form. Analyzer performs selected analyses on a connected or referenced stream.You refer an existing stream in the flowsheet or specify the connectivity by identifying an inlet and an outlet stream. This model calculates requested stream properties at specified conditions. The default conditions are the same as the inlet or referenced stream conditions. You can also specify a temperature or vapor fraction, in addition to a pressure. In cases where inlet and outlet streams are given, the outlet stream is a copy of the inlet stream. When using sequential-modular (SM) strategy to solve the problem, Analyzer has no effect on the stream. Use the following forms to enter specifications and view results for Analyzer: Use this form

To do this

Input

Specify the Analyzer conditions and referenced stream specifications

Prop Set

Specify the property specifications and perturbation data

Block Options

Override global values for physical properties, simulation options, diagnostic message levels, EO options, EO variable/vector, and report options for this block

Results

View the Analyzer results

EO Variables

Specify equation-oriented variable attribute changes for this block, for the current run only

EO Input

Specify the equation-oriented variables for this block

Spec Groups

Specify the specification groups for this block

Ports

Specify the EO variables collected to form ports for this block



•

7-7

Flowsheet Connectivity for Analyzer

Material (optional)

Material (optional)

Material Streams inlet

One inlet material stream (optional)

outlet One outlet material stream (optional)

If Analyzer is not connected to streams, you must specify a stream to analyze on the Input form.

Specifying Analyzer

Specify a material stream for Analyzer to analyze by either connecting inlet and outlet material streams to the analyzer block on the flowsheet or specifying a stream on the Input Specifications sheet. Also on the Input Specifications sheet, you can specify conditions for the analysis. Each property you want Analyzer to calculate must be specified in a property set on the top-level Properties Prop-Sets form. Specify properties for Analyzer to calculate by choosing these property sets on the Analyzer Prop-Set form.

EO Usage Notes for Analyzer

7-8

•


All features of Analyzer are available in the EO formulation, except the features which are globally unsupported.


Feedbl Reference Use Feedbl to maintain compatibility with Feedbl blocks in RTOPT version 10.0 projects. If you are creating a new simulation in Aspen Plus, do not use Feedbl. Aspen Plus automatically creates the necessary feed specifications. Feedbl is a mole-flow model which is used to define material feed streams for the RT-Opt flowsheet. Containing one inlet and one outlet material stream, it calculates stream flows, composition, and properties. Feedbl includes an extra equation to compute the total molar flow for the inlet stream. This ensures that the inlet stream component and total molar flows are consistent. When using sequentialmodular (SM) strategy to solve the problem, Feedbl has no effect on the stream, except for an optional pressure drop. Use the following forms to enter specifications and view results for Feedbl: Use this form

To do this

Input

Specify the Feedbl conditions and referenced stream specifications

Prop Set

Specify the property specifications and perturbation data

Block Options

Override global values for physical properties, simulation options, diagnostic message levels, EO options, EO variable/vector, and report options for this block

Results

View the results for this block

EO Variables

Specify equation-oriented variable attribute changes for this block, for the current run only

EO Input


Spec Groups

Specify the specification groups for this block

Ports

Specify the EO variables collected to form ports for this block



•

7-9

Selector Reference The Selector block is a switch between different inlet streams. Any number of streams may enter the block, and one designated stream from among these is copied to the outlet stream. The Selector block can be used with material, heat, or work streams. Use the Selector Input Form to specify which stream is copied to the outlet stream.

Flowsheet Connectivity for Selector

Material, Heat, or Work

Material, Heat, or Work (any number of one type) For Material Streams

inlet

One or more material streams

outlet One material stream For Heat Streams

inlet

One or more heat streams

outlet One heat stream For Work Streams

inlet

One or more work streams


Specifying Selector

The only input needed for Selector is the ID of the inlet stream which is to be copied to the outlet stream. Selector may be used with material, heat, or work streams. When you place the selector block on the flowsheet, click the arrow to the right of the Selector icon in the model library to choose the selector for heat streams (labeled with a Q), for work streams (labeled with a W), or for material streams (unlabeled).

7-10

•

M a n i pu l a t or s

A s p e nP l u s1 1 . 1U ni tO p e r a t i onM o de ls

You can use Selector when modeling alternate simulation trains or analyzing different feedstock options for a process. For example, copy the feed streams into each alternate train with a Dupl block. Connect the products of the alternate trains to a Selector block. On the Selector Input Specifications sheet, select the product stream from the desired simulation train.

Train 1 Dupl

Selector Train 2

Example of modeling alternate simulation trains with a Selector block

EO Usage Notes for Selector

All features of Selector are available in the EO formulation, except the features which are globally unsupported.



•

7-11

Qtvec Reference Qtvec is a load stream manipulator which can be used to combine multiple heat streams into a single load stream or to add an additional temperature and duty point to an existing load stream.

Flowsheet Connectivity for Qtvec

Inlet

Two or more heat streams or one load stream

Outlet One load stream

Specifying Qtvec

To combine multiple heat streams into a single load stream:

For heat streams to be combined into a load stream, the following conditions must be true:

•

Each heat stream must have a corresponding ending temperature. Heat streams produced by RadFrac, MultiFrac, Heater, Flash2, and Flash3 have starting and ending temperatures.

•

The duty associated with each heat stream must have the same sign.

Suppose there are 4 heat streams H1, H2, H3, and H4 with duties Q1, Q2, Q3, and Q4 and ending temperatures Tend1, Tend2, Tend3, and Tend4. The combined load stream will then consist of: Q1 + Q2 + Q3 + Q4 Tbegin Q2 + Q3 + Q4 Q3 + Q4 Q4 0

}H1 } H2 Tend2 } H3 Tend3 }H4 Tend4 Tend1

Tbegin is either specified by the user or taken from the hottest or coldest starting temperature, depending on the sign of the duty.

7-12

•



To add an additional temperature and duty point to a load stream:

Cumulative load streams coming from a Radfrac block do not contain a 0 duty point. Consider a RadFrac block in which Q1, Q2, Q3, and Q4 represent the duties of stages 1 through 4, and T1, T2, T3, and T4 represent the duties of these stages. The cumulative load stream leaving this block will have the following values: Q1 + Q2 + Q3 + Q4 T4 Q2 + Q3 + Q4

T3

Q3 + Q4

T2

Q4

T1

To convert this to a load stream usable by MHeatX, it needs to be manipulated by Qtvec to give it a 0 duty point and a Tbegin. This will transform it into: Q1 + Q2 + Q3 + Q4 Tbegin Q2 + Q3 + Q4

T1

Q3 + Q4

T2

Q4

T3

0

T4

Tbegin must be specified on the Qtvec Input Specifications sheet.



•

7-13

Measurement Reference The measurement model is used to define plant measurements for data reconciliation purposes. It provides a:

• •

Way of relating plant measurements to model predictions Mechanism for entering values for plant measurements

It also provides a convenient method for supplying a data reconciliation objective, by allowing you to specify the objective function in terms of measurement offsets and standard deviations. Use the following forms to enter specifications and view results for Measurement: Usethisform

Input

7-14

•


Todothis

Specifythemeasurementandflowsheet variables for this block.

Results

ViewtheMeasurementresults

EO Variables

Specify equation-oriented variable attribute changes related to this block for the current run only

EO Input



C HA P TE R 8

Solids

This chapter describes the unit operation models for solids processing such as crystallizers, solid crushers and separators, gassolid separators, liquid-solid separators, and solids washers. The models are: M odel

Description

Crystallizer Crystallizer

Purpose

UseFor

Produces crystals from solution based on Mixed suspension, mixed product solubility removal (MSMPR) crystallizer

Crusher

Solids crusher Breaks solid particles to reduce particle size

Wet and dry crushers, primary and secondary crushers

Screen

Solids separator

Separates solid particles based on particle size

Upper and lower dry and wet screens

FabFl

Fabric filter

Separates solids from gas using fabric

Rating and sizing baghouses

Cyclone

Cyclone separator

filter baghouses Separates solids from gas using gas vortex in a cyclone

Rating and sizing cyclones

VScrub

Venturi scrubber

Separates solids from gas by direct contact with an atomized liquid

Rating and sizing venturi scrubbers

ESP

Electrostatic precipitator

Separates solids from gas using an electric charge between two plates

Rating and sizing dry electrostatic precipitators

HyCyc

Hydrocyclone Separates solids from liquid using liquid Rating or sizing hydrocyclones vortex in a hydrocyclone

CFuge

Centrifuge filter

Filter

Rotary vacuum Separates solids from liquid using a filter continuous rotary vacuum filter

SWash

Single-stage Models recovery of dissolved Single -stage solids washer solids washer components from an entrained liquid of a solids stream using a washing liquid

CCD

Countercurrent decanter

Separates solids from liquid using a rotating basket

Rating or sizing centrifuges Rating or sizing rotary vacuum filters

Models multi-stage recovery of dissolved Multi-stage solids washers components from an entrained liquid of a solids stream using a washing liquid

A s pe nP l u s1 1 . 1U n i O t pe r a t io nM o de l s

Sol ids

•

8-1

This chapter is organized into the following sections: Section

8-2

•

S o l i ds

Models

Crystallizer

Crystallizer

Crushers and Screens

Crusher, Screen

Gas-Solid Separators

FabFl, Cyclone, VScrub, ESP

Liquid-Solid Separators

HyCyc, CFuge, Filter

Solids Washers

SWash, CCD

A s p e nP l u s1 1 . 1U n iO t p e r a t i onM o d e ls

Crystallizer Reference Crystallizer models a mixed suspension, mixed product removal (MSMPR) crystallizer. It performs mass and energy balance calculations and optionally determines the crystal size distribution. Crystallizer assumes that the product magma leaves the crystallizer in equilibrium, so the mother liquor in the product magma is saturated. The feed to Crystallizer mixes with recirculated magma and passes through a heat exchanger before it enters the crystallizer. The product stream from Crystallizer contains liquids and solids. You can pass this stream through a hydrocyclone, filter, or other fluid-solid separator to separate the phases. Crystallizer can have an outlet vapor stream. Use the following forms to enter specifications and view results for Crystallizer:

Flowsheet Connectivity for Crystallizer

Use this form

To do this

Setup

Specify operating parameters, crystal product and solubility parameters, recirculation options, and flash convergence parameters

PSD

Specify PSD and crystal growth calculation parameters

Advanced

Specify component attributes, convergence parameters, and name and parameters for user solubility subroutine

Block Options


Results

View summary of Crystallizer results, material and energy balance results, and crystal size distribution results Vapor (optional)


Liquid and Solid Heat (optional)

Heat (optional)


Sol ids

•

8-3

Material Streams

inlet


outlet One material stream for liquid and solid One optional vapor stream

The outlet material stream should normally have at least one solid substream for the crystals formed. If you select Calculate PSD from Growth Kinetics or User-Specified Values on the PSD PSD sheet, each substream must have a particle size distribution (PSD) attribute. If electrolyte salts are formed based on electrolyte chemistry calculations, a solid substream is not required when you select Copy from Inlet Stream on the PSD PSD sheet. If you do not use the vapor outlet stream, vapor products will be placed in the liquid/solid product stream. Heat Streams

inlet

Any number of optional inlet heat streams

outlet One optional outlet heat stream

If you give only one specification on the Setup Specifications sheet (temperature or pressure), Crystallizer uses the sum of the inlet heat streams as a duty specification. Otherwise, Crystallizer uses the inlet heat streams only to calculate the net heat duty. The net heat duty is the sum of the inlet heat streams minus the actual (calculated) heat duty. You can use an optional outlet heat stream for the net heat duty.

Specifying Crystallizer

Crystallizer calculates crystal product flow rate and/or vapor flow, based on solubility data you supply. Or you can specify the chemistry for electrolyte systems instead of specifying solubility data. You must specify two of the following:

• • • • •

8-4

•

S o l i ds

Crystallizer temperature Pressure or pressure drop Heat duty for the heat exchanger Crystal product flow rate Vapor flow


Ifyouspecify

Crystallizercalculates

Temperature and Pressure

Heat duty, crystal product flow rate, vapor flow rate

Pressure and Heat Duty

Temperature, crystal product flow rate, vapor flow rate

Temperature and Heat Duty

Pressure, crystal product flow rate, vapor flow rate

Pressure and Crystal Product Flow Temperature, heat duty, vapor flow Rate Temperature and Crystal Product Flow Rate

rate Pressure, heat duty, vapor flow rate

Pressure and Vapor Flow Rate

Temperature, heat duty, crystal product flow rate

Temperature and Vapor Flow Rat e Pressure, heat duty, crystal product flow rate

Recirculation Specifications

You can model crystallizer with or without magma recirculation. To activate recirculation, specify one of the following on the Setup Recirculation sheet:

• • •

Recirculation fraction Recirculation flow rate Temperature change across heat exchanger

If you want to model a different crystallization process flowsheet, youthe can use Crystallizer recirculation, and use other blocks in flowsheet to modelwithout the recirculation.

Solubility

Crystallizer calculates the amount of crystal produced at its saturation (class II crystallization). You can provide solubility data in one of these ways:

• •

Enter solubility data on the Setup Solubility sheet

•

Supply a subroutine to provide the saturation concentration or to calculate crystal product flow rate directly


Reference an electrolyte chemistry (defined in the Reactions Chemistry forms) in which the crystallizing component has been declared as a "salt"

Sol ids

•

8-5

Saturation Calculation Method

Choose the saturation calculation method from these options:

•

Solubility method: Identify the crystallizing component as solid product on the Setup Crystallization sheet. Enter solubility data on the Setup Solubility sheet. This data applies to the reactant species in the mixed substream.

•

Chemistry method: Create a new Chemistry on the Reactions Chemistry object manager. Enter the crystallization as a salt reaction on the Reactions Chemistry Stoichiometry sheet. On the BlockOptions Properties sheet of the crystallizer, enter the Chemistry ID and select True Species for Simulation Approach. You must specify the crystallizing component as a Salt Component ID on the Setup Specifications sheet.

•

User Subroutine method: Identify the crystallizing component on the Setup Crystallization sheet and the solubility data basis and solvent ID on the Setup Solubility sheet. Specify a user subroutine to calculate saturation concentration or crystallizer yield on the Advanced UserSubroutine sheet.

In general, when using the Solubility method, you should blank out the Chemistry ID field on the BlockOptions Properties sheet. If you specify chemistry when using the Solubility method, the chemistry must not contain the crystallizing component.

Supersaturation

The degree of supersaturation is the driving force for crystallization processes. Supersaturation is defined as:

S

= C − Cs

Where: 3

S

=

Supersaturation (kg of solute/m of solution)

C

=

Solute concentration

Cs

=

Solute saturation concentration

Because the crystallizer model assumes that the product magma is in phase equilibrium, this equation is not used. It is provided only for reference.

Crystal Growth Rate

The crystal growth rate can be expressed as a function of the degree of supersaturation (S):

Go

= kg S n

Where:

8-6

•

S o l i ds

Go

=

Growth rate dependence on supersaturation (m/s)

kg

=

Growth rate expression coefficient

n

=

Exponent


This expression is provided as background information only. o In Aspen Plus, G is calculated implicitly from the third moment of the population density.

For a size-dependent growth rate, the growth rate is a function of crystal length (L):

G = G o (1 + γL ) α

For 0 ≤ α

≤1

Where: = =

γ α

Constant Exponent

If the growth rate is independent of crystal size, then the values for γ and α are set to zero.

Crystal Nucleation Rate

The overall nucleation rate can be expressed as the sum of specific contributing factors (Bennett, 1984):

Bo

= kb G i MTj R k

Where:

B0 i, j, k

Population Balance

= =

Overall nucleation rate Exponents

kb

=

Overall nucleation rate expression coefficient

MT

=

Magma density = P/q (kg/m )

G

=

Crystal growth rate

R

=

Impeller rotation rate (revs/s)

P

=

Crystal mass flow rate (kg/s)

q

=

Volumetric flow rate of slurry in the discharge 3 (m /s)

3

If the feed stream contains no crystals, the population balance for a well-mixed continuous crystallizer can be written as (Randolph and Larson, 1988):

d ( nG ) dL

+

qn V

=0

Where:

G

=

Crystal growth rate

n

=

Population density (no. /m /m)

L

=

Crystal length (m)

V

=

Crystallizer volume (m )


3

3

Sol ids

•

8-7

q

=

Volumetric flow rate of slurry in the discharge 3 (m /s)

o o o The boundary condition is n = n at L = 0, where n = B / G is the population density of nuclei. For a constant crystal growth rate, the population density is:

n( L) = n o exp where

PSD Statistics

−L   Gτ 

τ=V/q

is the crystal residence time.

Aspen Plus calculates the crystal size distribution statistics once you select the Calculate PSD from Growth Kinetics option on the PSD PSD sheet. Properties of the distribution may be evaluated from the moment equations. The j-th moment of the particle size distribution is defined as:

mj

∞

= ∫0 Lnj L( d )L

The system reports several crystal size distribution statistics, measured on a volume or mass basis, including:

• • •

Mean size

•

The coefficient of variation (expressed as a percentage)

Standard deviation Skewness

The mean size is the mass-weighted average crystal size, as determined by the ratio of the fourth moment to the third moment, as follows:

L=

m4 m3

The skewness of a symmetric size distribution about the mean is zero. Negative values of skewness indicate the distribution is skewed toward the presence of small crystals. Positive values of skewness indicate the crystal distribution contains an excess of large crystals.

∑ f ( x − mean) 3 3 Skewness is defined as ( standard deviation) .

The system uses the coefficient of variation to calculate variation related to the cumulative volume (or mass) distribution.

8-8

•

S o l i ds


Coeff

− Var(%) = 100

pd @ (.84) − pd @ (.16) 2 pd @ (.50)

where pd@ (x) is the particle diameter corresponding to fractionx of the cumulative volume (or mass) distribution. The fraction can be entered as the Fractional Coefficient on the PSD CrystalGrowth sheet; otherwise, it defaults to .16.

Calculating PSD

The magma density, defined as total mass of crystals per unit volume of slurry, can be obtained from the third moment: ∞

MT

= ρ c k v ∫0

3

L n( L) dL

Where:

3

ρc

=

Density of crystal (kg/m )

kv

=

Volume shape factor of the crystal

Since:

n( L) = n o exp

no

=

and

−L   Gτ  ,

Bo Go ,

Bo

= kb G i MTj R k

these equations can be substituted into the third moment of population density, yielding:

MT

= cvρ k

where G

∫

∞

b0

L3 k

Gi − L M j R k exp  dL Go T  Gτ 

= G o (1 + γL)α .

Because L is made discrete by the increments of the particle size o distribution, the equations can be solved forG .

References

Bennett, R.C. "Crystallization from Solution", inPerry’s Chemical Engineers’ Handbook, 6th Ed., pp. 19.24-19.40, McGraw-Hill, 1984. Randolph, A.D. and Larson, M.A., Theory of Particulate Processes, 2nd Ed., Academic Press, 1988.


Sol ids

•

8-9

Crusher Reference Use Crusher to simulate the breaking of solid particles. Crusher can model the wet or dry continuous operation of:

• • •

Gyratory/jaw crushers Single-roll crushers Multiple-roll crushers

•

Cage mill impact breakers Crusher assumes the feed is homogeneous. The breaking process creates fragments with the same composition as the feed. Crusher calculates the power required for crushing, and the particle size distribution of the outlet solids stream. Crusher does not account for the heat produced by the breaking process. Use the following forms to enter specifications and view results for Crusher: Use this form

Flowsheet Connectivity for Crusher

To do this

Input

Enter crusher operating parameters, the Bond work index or the Hardgrove grindability index, and user-specified selection and breakage functions

BlockOptions


Results

View summary of Crusher results and material and energy balances

Feed

Crushed Solids

Work (optional)

Material Streams

inlet

One material stream with at least one solids substream


8-10

•

Solids

A s p e nP l u s1 1 .1U n iO t p e r a t i onM o d e ls

Each solids substream must have a particle size distribution (PSD) attribute. Work Streams

inlet

No inlet work streams

outlet One work stream containing the calculated power requirement (optional)

Specifying Crusher

Use the Input Specifications and Grindability sheets to specify operating conditions. You must enter the type of crusher and maximum particle diameter on the Input Specifications sheet. You must also specify the Bond work index or the Hardgrove grindability index for each solids substream on the Grindability sheet. The outlet flow rate of crushed product in thek-th size interval is:

Pk ( β ) =

∑∑ j

i

Fij S i ( β ) Bik ( β ) +

∑

[1 − S k ( β )]Fkj

j

Where:

Bik

=

Breakage function. Fraction of particles originally in size interval i that end up in size intervalk

Fij

=

Flow rate of feed in the size interval i and particle size distribution j

Pk

=

Flow rate of solid in size interval k

Si

=

Selection function. Fraction of feed particles in size interval i to be crushed at the outlet diameterβ

β

=

Crusher outlet diameter (Maximum Particle Diameter field)

i

=

Size interval counter within a PSD

j

=

PSD counter for multiple size distribution

If the inlet stream contains no liquid, then Crusher assumes dry crushing, and power requirements increase by 34%. You can enter tabular values for the breakage (Bik ) function on the S Input BreakageFunction sheet and for the selection ( i ) function on the Input SelectionFunction sheet, or let Crusher use the built-in tables (U.S. Bureau of Mines, 1977) (see the following two tables).

A s pe nP l u s1 1 . 1U n i tO pe r a t io nM o de l s

Soli ds

•

8-11

B (β )

Breakage Function Correlations ik

Ratio of product size to feed size

Feed size/solids outlet diameter >1.7

Feed size/solids outlet diameter <1.7

Multiple roll crusher

Gyratory/jaw Single roll crusher crusher

Cage mill All crushers crusher

1.0

1.0

1.0

1.0

1.0

1.0

0.8308

0.95

0.95

0.96

0.84

0.8972

0.5882

0.85

0.85

0.79

0.50

0.7035

0.4176 0.2065

0.65 0.35

0.70 0.35

0.45 0.20

0.32 0.15

0.54 0.2952

0.1041

0.22

0.20

0.10

0.052

0.1564

0.0522

0.14

0.19

0.05

0.019

0.0805

0.0368

0.11

0.17

0.03

0.011

0.0572

0.026

0.09

0.12

0.02

0.0066

0.0406

0.0131

0.03

0.08

0.0

0.002

0.0206

0.0

0.0

0.0

0.0

0.0

0.0

S (β ) Selection Function Correlations,i Ratio of feed size to outlet diameter

Prima ry crusher

Secondary crusher

0.95

0.5695

0.7693

0.9

0.3817

0.6962

0.8

0.1716

0.5695

0.7 0.6

0.0771 0.0347

0.4667 0.3817

0.5

0.0156

0.3128

0.4

0.007

0.256

0.3

0.00315

0.2096

0.2

0.00145

0.1716

0.1

0.0006

0.1405

0.05

0.00043

0.1271

0.001

0.00026

0.1153

0.0001

0.00026

0.1148

If the ratio of feed size to outlet diameter is greater than 1.0, then S i (β) = 0.85 .

Primary and Secondary Crushers

8-12

•

Solids

Crushing operations are usually performed in stages. The reduction ratio is the ratio of the maximum diameter of feed particles to product particles. The reduction ratio in crushers ranges from 3 to 6 per stage. Feed particles are fed to the primary crushers. Outlet particles from the primary crushers are reduced further by the secondary crushers.


Crusher uses different correlations for primary and secondary crushers. Use the Operating Mode field on the Input Specifications sheet to enter the type of crusher. To improve the efficiency of multistage crushers, use screens between stages.

Power Requirement

The following equation determines the power requirement for Crusher:

POWER =

0.01 X F

−

XP

× BWI × FLOWT

XF

× XP

Where:

POWER

=

Required power (Watt)

XF

=

Diameter larger than 80% of feed particle mass (m)

XP

=

Diameter larger than 80% of product particle mass (m)

BWI

=

Bond work index

FLOWT

=

Total solids mass flow rate (kg/s)

For dry crushing, power requirement increases by 34%. If X P is less than 70 micrometers, then the power required is further adjusted by:

POWER= POWER

10.6×10 −6 + X P



Bond Work Index

1.145 X P

  

The Bond equation defines the work consumed in size reduction:

E

XF

= Ei

− XF

XP

100

XP

Where:

E

=

Work required to reduce a unit weight of feed with 80% passing a diameter X F microns to a product with 80% passing a diameter X P microns

Ei

=

Bond work index, that is, the work required to reduce a unit weight from a theoretical infinite size to 80% passing a diameter of 100 micrometers

The Bond work index is a semi-empirical parameter that depends on the properties of the material processed. The Bond work indices have been measured experimentally for a wide range of materials,


Soli ds

•

8-13

and are available in Perry’s Chemical Engineers’ Handbook. Use experimental values with caution. The Bond work index is also a function of the:

• • Hardgrove Grindability Index

Particle size for non-homogeneous materials Efficiency of the size-reduction equipment

The Hardgrove grindability index indicates the difficulty of grinding coal based on physical properties such as hardness, fracture, and tensile strength. The Hardgrove grindability index can be approximated by:

BWI

=

435 HGI 0.91

Where:

BWI

=

Bond work index

HGI

=

Hardgrove grindability index

The HGI for some United States coals are available in Perry ’s Chemical Engineers’ Handbook.

References

Computer Simulation of Coal Preparation Plants , U.S. Bureau of Mines, Grant No. GO-155030, Final Report August (1977). Perry’s Chemical Engineers’ Handbook, 6th Ed., McGraw Hill, 1984.

8-14

•

Solids


Screen Reference Screen simulates the separation by screens of a mixture containing various sizes of solid particles into particles that have more uniform sizes than the srcinal mixture. You can use Screen to model wet or dry operations and upper or lower level screens. Screen calculates the separation efficiency of the screen from the size of screen openings you specify. Use the following forms to enter specifications and view results for Screen: Use this form

To do this

Input

Specify screen parameters, operating conditions, and user-specified screen separation strength and selection functions

Block Options


Results

View summary of Screen results and material and energy balances

Flowsheet Connectivity for Screen

Overflow Feed Underflow Material Streams

inlet


outlet One material stream for particles that do not pass through the screen (overflow) One material stream for particles that pass through the screen (underflow)

Each solids substream must have a particle size distribution attribute.

Specifying Screen

Use the Input Specifications sheet to enter:

• • • •


Screen size opening Operating level (Upper or Lower) Operating mode (Wet or Dry) Entrainments

Soli ds

•

8-15

You can also use the Input SelectionFunction sheet to enter the following functions: • Selection function (Si ) (optional)

• Upper and Lower Level Screens

Separation strength (optional)

You can specify the operating level as Upper or Lower. The most efficient configuration is a multiple-deck screen with a series of Screen blocks. The inlet stream is fed over the upper level screen. The underflow from the upper level screens is fed over the lower level screens. Screen uses different correlations for upper and lower level screens. Screen calculates the flow rate of the screen overflow stream as:

Fo

= ∑ Si ∑ Fij i

j

Where:

Selection Function and Separation Strength

Si

=

Selection function. The fraction of feed particles in size range i that passes over the screen into the overflow product

Fij

=

Flow rate of feed in size range i and particle size distribution attributej

Screen calculates the selection function for a certain size interval as: 1

S

i

Si

= exp[ A(1 − d p =1

So

for d p

)]

for d S

p

≥

< So

o

Where:

dp

=

Particle diameter

So

=

Size of screen opening

A

=

Separation strength

The default value of the screen separation strength,A, is a function of the size of the screen opening. Screen has four built-in functions (U.S. Bureau of Mines, 1977) for all possible combinations of screen types (see the table, Screen Separation Strength/Screen Size Correlation):

•• • • 8-16

•

Solids

Upper level dry Lower level dry Upper level wet Lower level wet A s p e nP l u s1 1 .1U n iO t p e r a t i onM o d e ls

You can enter your own separation strength value, separation strength correlation or selection function correlation on the Input SelectionFunction sheet. Screen then uses these selection function values for its mass balance calculation. Screen Separation Strength/Screen Size Correlation

Size of screen Dry, upper opening (m) level

Dry, lower level

Wet, upper level

Wet, lower level

0.457

60

60

60

60

0.152

20

20

20

20

0.038 0.0095

8 8

8 6

9 8.5

9 6.6

0.00635

5

4

5.5

4.5

0.00236

3

2

3.5

2.3

0.00059

0.7

0.7

0.8

0.8

0.00042

0.6

0.6

0.7

0.7

0.000295

0.5

0.5

0.55

0.55

Separation Efficiency

The separation efficiency of the screen is calculated as the ratio of the mass flow rate of the underflow to the fraction of the feed flow rate containing particles smaller than the screen openings.

Reference

Computer Simulation of Coal Preparation Plants , U.S. Bureau of Mines, Grant No. GO-155030, Final Report August (1977).


Soli ds

•

8-17

FabFl Reference FabFl is a gas-solids separator model used to separate an inlet gas stream containing solids into a solids stream and a gas stream carrying the residual solids. Use FabFl to simulate or design baghouse units in which solid particles are separated from the inlet gas stream. A baghouse consists of a number of cells in which vertically-mounted cylindrical fabric filter bags operate in parallel. You can use FabFl to rate or size baghouses. Use the following forms to enter specifications and view results for FabFl: Use this form

Flowsheet Connectivity for FabFl

To do this

Input

Enter operating conditions, baghouse characteristics, and separation efficiency

BlockOptions


Results

View summary of FabFl results and material and energy balances Gas (overflow)

Feed Solids (underflow)

Material Streams

inlet


outlet One overflow stream for the cleaned gas One underflow stream for the solids particles

Each solids substream must have a particle size distribution (PSD) attribute. Solids may be entrained in the overflow, based on the separation efficiency.

Specifying FabFl

8-18

•

Solids

Use the Input Specifications sheet to specify operating conditions and baghouse characteristics. For these calculations

Set M ode=

Rating

Simulation

And number of cells is

Specified

Sizing

Design

Calculated


For sizing or rating calculations: Ifyouenter

FabFlcalculates

Maximum allowable pressure drop Filtrationtime

Operating Ranges

Filtration time Pressuredrop

FabFl uses empirical models because no theoretical models exist. Expect unreliable results when operating conditions exceed the ranges of the experimental data on which the models are based. Your data should fall within these ranges:

•

Diameter of solid particles between10 −7 to 10 −4 m (0.1 to 100 micrometers)

•

Maximum gas velocity through the cloth between 0.1 and 0.2 m/s (20 to 40 ft/min)

The gas velocity is the ratio of gas volumetric flow rate to total filtering area.

Filtering Time

When rating fabric filters, FabFl calculates the filtering timet as: t

∆Pf − ∆Pi

=

CKVo2

Where:

∆Pf

=

Final pressure drop across collected dust and filter cloth

P

=

Pressure drop of the clean bag

∆

i

C

=

Dust concentration

K

=

Dust resistance coefficient

Vo

=

Air to cloth ratio (gas velocity through the cloth)

The air to cloth ratio

Vo

=

Vo

is:

Q ( N cell

−

Nshake ) Abag N b ag

Where:

Q

=

Volumetric flow rate of the gas

N cell

=

Number of cells

N shake

=

Number of cells being cleaned

Abag

=

Total filter surface of all bags

N bag

=

Number of bags per cell


Soli ds

•

8-19

Resistance Coefficient

The resistance coefficient K depends on the particle size and nature of solid particles. In an industrial-scale baghouse, the resistance coefficient also varies with time and bag position. If specific resistance coefficients are not available, the following values can be used as rough estimates (Air Pollution Engineering Manual, 1967): Dust particle diameter ( 10

−6

Resistance coefficients 2

[Pa/(kg/m ) (m/s)]

m)

Lessthan20

300,000

20 to 90 Greaterthan90

60,000 15,000

These coefficients were determined from a small fabric filter. The 3

2

filter has an air flow of 2 ft / min through 0.2 ft of cloth area (a filtering gas velocity of 10 ft/min). The pressure drop across the bag and dust was 8 inches of H 2 O . An approximation for the resistance coefficient (Billings, C.E. and Wilder, J.) is: K

=

1000

d p2

Where: dp

=

The average particle size in microns 2

The units for K are (inches of water)/(lbs dust/ft of area)(ft/min velocity).

8-20

•

Solids



The overall separation efficiency of the baghouse is:

∑∑Sη ij

ηo =

j

ij

i

Total inlet flow rate of solids

=

flow rate of solids removed from the inlet total inlet flow rate of solids

Where: Sij

=

Flow rate of solid j in size increment i

In FabFl, the separation efficiency is a function of the particle diameter of the solids. For large particles (greater than 10 ( ηi ) is micrometers in diameter), fractional collection efficiency 1.0. For particles smaller than 10 micrometers, efficiency decreases rapidly.

ηi

When

( d p ) av

1.0 ( d p ) av

0.0011 0.989 ( d p ) av 0.495 0.495

> 10 µm < 10 µm

1µm < (d p ) av ( d p ) av

< 1µm

You also can enter efficiency as a function of particle sizes on the Input Efficiency sheet to override the built-in correlations.

References

Air Pollution Engineering Manual, Public Health Service Publication No. 999-AP-40, pp. 106-135, Washington D.C., DHEW (1967). Billings, C.E. and Wilder, J., Handbook of Fabric Filter Technology, Vol. I, NIIS PB 200648.


Soli ds

•

8-21

Cyclone Reference Cyclone separates an inlet gas stream containing solids into a solids stream and a gas stream carrying the residual solids. Use Cyclone to simulate cyclone separators in which solid particles are removed by the centrifugal force of a gas vortex. You can use Cyclone to size or rate cyclone separators. In simulation mode, Cyclone calculates the separation efficiency and pressure drop from a user-specified cyclone diameter. In design mode, the cyclone geometry is calculated to meet the user-specified separation efficiencies and maximum pressure drop. In both calculation modes, the particle size distributions of the outlet solids streams are determined. Use the following forms to enter specifications and view results for Cyclone: Usethisform

To

Input

Enter cyclone specifications, dimensions, dimension ratios, separation efficiencies, and solids loading

BlockOptions


Results

View summary of Cyclone results and material and energy balances

Flowsheet Connectivity for Cyclone

Gas Feed

Solids Material Streams

inlet


outlet One stream for the cleaned gas One stream for the solids

Each solids substream must have a particle size distribution (PSD) attribute.

8-22

•

Solids


Specifying Cyclone

Use the Input Specifications sheet to specify the type of cyclone and operating conditions. Use the Input Dimensions sheet to enter cyclone dimensions, or use the Input Ratios sheet to enter ratios of cyclone dimensions. To perform these calculations

Specify

Cyclone calculates

Rating

Simulationmode Cyclone Diameter Number of Cyclones

Separation efficiency Pressure drop

Sizing

Designmode Separation Efficiency Maximum Pressure Drop (optional) Maximum Number of Cyclones (optional)

Cyclone diameter Number of cyclones

For rating calculations, if you specify Type=User-Specified or User-Specified Ratios, you can specify cyclone dimensions on the Input Dimensions or Input Ratios sheets. For design calculations, you must also enter the Maximum Number of Cyclones in parallel. If either of the following occurs, Cyclone calculates the number of cyclones in parallel:


•

The efficiency of a single cyclone is less than the required separation efficiency.

•

The calculated pressure drop exceeds the maximum pressure drop specified.

The overall separation efficiency is:

ηm =

flow rate of solids removed from the inlet total inlet flow rate of solids

ηm =

Co

− Ci

Co

=

Qo Co

−E

QooC

= 1− oo

E QC

Where: Co

=

Concentration of solids in inlet gas

Ci

=

Concentration of solids in outlet cleaned gas

Qo

=

Inlet gas flow rate

E

=

Outlet emission rate of solids in the cleaned gas

Cyclone attains higher separation efficiencies with particles that are 5 to 10 microns or greater in diameter. For particles smaller than 5 microns, Cyclone efficiency decreases. Even with large particles, it is difficult to obtain a collection efficiency greater than 95%.


Soli ds

•

8-23

If you enter a design efficiency higher than 95%, use either:

• •

Multi-stage cyclones Cyclone as a precleaner, followed by other collectors

You can specify the Efficiency Correlation field on the Input Specifications sheet. If Efficiency Correlation=User-Specified, you can enter efficiency as a function of particle sizes on the Input Efficiency sheet.

Operating Ranges

Cyclone uses correlations that are semi-empirical models. Do not expect satisfactory accuracy when the specified conditions exceed the ranges of experimental data from which the models were developed. In general, the pressure drop should be less than 2

2500 N / m (10 inches ofH 2 O ). The operating pressure should not exceed atmospheric pressure. The inlet gas velocity should be in the range of 15 to 27 m/s (50 to 90 ft/s). The Leith and Licht efficiency correlation is accurate for inlet velocities approximately 25 m/s (80 ft/s). The correlation overestimates the separation efficiency at high velocities. The Shepherd and Lapple correlation is accurate for particle sizes of 5 to 200 microns. This correlation tends to overestimate the efficiency of large particles (greater than 200 microns). The Shepherd and Lapple correlation also underestimates the efficiency of fine particles (smaller than 5 microns).

Pressure Drop

Cyclone calculates the pressure drop (Shepherd and Lapple, 1939) as: ∆P

= 0.0030 ρ f U t2 N h

Where:

ρf

=

Density of the fluid

Ut

=

Inlet gas velocity

Nh

=

Inlet velocity speeds

Use the Input SolidsLoading sheet to enter values to correct for solids loading. The inlet velocity speed,N h , is:

Nk

=K

ab De2

Where:

8-24

•

Solids

K

=

Dimensionless ratio

a

=

Inlet height of the cyclone


b

=

Inlet width of the cyclone

De

=

Outlet diameter of the cyclone

The dimensionless ratioK is:

K=

8(Vs + Vnl / 2)

abDc

Where: Vs

=

Annular shaped volume above the exit duct to

Vnl

=

midlevel of the entrance duct Effective volume of the cyclone calculated by natural length l

Dc

=

Body diameter of the cyclone

The annular shaped volumeVs above the exit duct to midlevel of the entrance duct is: Vs

Cyclone Diameter

=

π( s −a

/ 2D) (D

2 c

−

2 e

)

4

Cyclone calculates the diameter of the body of the cycloneDc as: Dc

 Qρ2f  (1 − b / Dc ) = 0.0502 × 2.2  a D b D µ ( ρ − ρ ) ( / ) ( / )  p f  c c

Where: Q

=

Overflow gas flow rate

ρf

=

Density of the fluid

µ

=

Viscosity of gas fluid

ρp

=

Density of the particles

0 . 454

In this empirical equation, units are: Unittype

Dimension Ratios

Un i t

Length

Feet

Mass

Pounds

Time

Seconds

Use the Input Dimensions sheet to enter the dimensions of a cyclone when Mode=Simulation and Type=User-Specified. If you specify Type=User-Specified Ratios, you can use the Input Ratios sheet to enter dimension ratios (dimension / cyclone diameter) for a cyclone.


Soli ds

•

8-25

The dimension ratios and some default values of the two built-in configurations are: Dimension ratio (dimension/ cyclone diameter)

Type = High efficiency

Type = Medium efficiency

Cyclonediameter

1.0

1.0

Inlet height

0.5

0.75

Inlet width

0.2

0.375

Lengthofoverflow

0.5

0.875

Diameterofoverflow

0.5

0.75

Lengthofconesection Overall length

1.5 4.0

Diameterofunderflow

1.50 4.0

0.375

Numberofgasturnincyclone 7.0

0.375 4.0

Maximumdiameter(m)

1.5

5.0

Minimumdiameter(m)

0.1

0.1

Cyclone calculates the dimensions of the built-in cyclones using these ratios and the cyclone diameter you specify. The built-in configurations (Type=High or Medium) may not be the best designs. It is recommended that you enter dimensions or dimension ratios, if available.

Vane Constant

8-26

•

Solids

Use the Vane Constant field on the Input Specifications sheet to specify the vane constant. The vane constant varies with the configuration of the inlet duct. In the common configuration, the inlet duct terminates at the wall of the cyclone. The vane constant is 16. To reduce friction loss, extend the duct into the interior of the cyclone. When the duct is in the middle of the cyclone separator, the vane constant is 7.5.


Cyclone Dimensions

The next figure shows the Cyclone geometry. The table following the figure shows the Cyclone dimensions. Dc De

b

s a

h

H

B Cyclone Geometry

The Cyclone design configurations are: Term

Description

Dc

Bodydiameter

1.0

High efficiency

1.0

High throughput

a

Inlet height

0.5

0.75

b

Inlet width

0.2

0.375

s

Outletlength

0.5

0.875

De

Outletdiameter

0.5

0.75

h

Cylinderheight

1.5

1.50

H

Overallheight

4.0

4.0

B

Dustoutletdiameter 0.375

0.375

Solids Loading Correction The feed concentration of solids affects the separation efficiency. 3 Concentration higher than 1.0 gm m usually leads to higher efficiency. Smolik (1975) presented the following relationship between the efficiency and solids concentration: 1 − ET* 1 − ET


 c*  =  c

a

Soli ds

•

8-27

Where: c*

=

1.0 gm / m 3

c

=

Solids concentration

=

Total efficiency

ET

=

"Low loading" total efficiency

α

=

Exponent

E

* T

Smolik gives values of α = 0.182. This form can only serve as a guide, because the effect of dust concentration depends on the nature of the solids, the humidity of the gas, and many other factors that do not figure in the existing correlations. The actual pressure drops with dust-laden gases are normally lower than those obtained with clean gas. Smolik gives an empirical correlation for the effect of feed concentration on pressure in the form:

∆p * = 1 − βc γ ∆p Where:

c

=

g / m3

∆p *

=

Pressure drop

∆p

=

Pressure drop with clean gas

β ,γ

=

Constants depending on the material

Smolik gives values of β = 0.02 and γ 0.6.

References

Shepherd, G.B. and Lapple, C.E., "Flow Pattern and Pressure Drop in Cyclone Dust Collectors,"Industrial and Engineering Chemistry, 31, pp. 972-984 (1939). Smolik, J. et al., Air Pollution Abatement, Part I. Scriptum No. 401-2099 (in Czech). Technical University of Prague (1975). Quoted by Svarovsky, L., "Solid-Gas Separation ," Handbook of Powder Technology, Williams, J.C. and Allen, T. (Eds.), Elsevier, Amsterdam (1981).

8-28

•

Solids


VScrub Reference Use VScrub to simulate venturi scrubbers. Venturi scrubbers remove solid particles from a gas stream by direct contact with an atomized liquid stream. You can use VScrub to rate or size venturi scrubbers. Use the following forms to enter specifications and view results for VScrub:

Use this form

To do this

Input

Specify operating parameters and throat operating conditions

Block Options


Results

View summary of VScrub results and material and energy balances Liquid

Flowsheet Connectivity for VScrub

Gas Feed Gas with Solids Material Streams

inlet

Liquid and Solids

One stream for solids with at least one solids substream One stream for the atomized liquid

outlet One stream for the cleaned gas One stream for the liquid with solid particles


Soli ds

•

8-29

Specifying VScrub

Use the VScrub Input Specifications sheet to specify operating conditions and parameters for sizing or rating calculations. To perform these Set Mode = Enter scrubber VScrub calculates calculations

Rating

Simulation

Throat Diameter Separation efficiency Throat Length Pressure drop

Sizing †

Design

Separation efficiency

Liquid flow rate Throat diameter Throat length Pressure drop

† Because the required liquid flow rate is varied to meet the efficiency, the material balance is not satisfied if the calculated liquid flow rate is different from the rate you enter.

In both modes, VScrub also calculates the particle size distributions of the solids in the outlet streams. VScrub assumes that the liquid stream is introduced before or at the beginning of the scrubber throat. It also assumes the separation of the solid particles from the gas stream occurs only at the scrubber throat.

Pressure Drop

VScrub calculates the pressure drop (Yung, S. et al., 1977)∆ p across the throat of the scrubber as:

∆p =

2ρ l Vt 2

gc

 Ql    (1 − x 2 +  Qg 

x4

− x2 )

Where:

ρl

=

Density of the liquid

Vt

=

Relative velocity of gas to liquid at the throat

gc

=

Conversion factor in Newton's law of motion

Ql

=

Liquid to gas volume flow rate

=

Dimensionless throat length defined by:

Qg

x

x

=

3lt C D ρ g 16 Dd ρ l

+1

Where:

8-30

•

Solids

lt

=

Throat length

CD

=

Drag coefficient, as a function of the Reynolds number (Dickinson and Marshall, 1968)N Re . 24 0. 6 CD = .22 + (1 + 0.15 N Re ) N Re


ρg

=

Density of the gas

ρl

=

Density of the liquid

Dd

=

Drop diameter (Sauter mean), defined by (Nukiyama, S., Tanasawa, Y. 1939): 585  σ l 

Vt

0. 5

   ρl 

 µ  + 597  l   σ lρ l 

0. 45

1000Ql     Qg 

1.5

Where:

σl µl Separation Efficiency

=

Surface tension

=

Viscosity of liquid

The separation efficiency (Yung, S., et al., 1978)ηo is defined as:

ηo = =

Mass flow rate of particles in outlet liquid stream Mass flow rate of particles in inlet gas stream

∑ Sη i

i

Total inlet flow rate of solids

Where:

References

ηi

=

Efficiency for size increment i

Si

=

Mass flow rate of size increment i

Yung, S. et al., Journal of the Air Pollution Control Association, 27, 348 (1977). Dickinson, D.R. and Marshall, W.R., AIChE Journal, 14, 541, (1968). Nukiyama, S. and Tanasawa, Y., Transcripts of the Society of Mechanical Engineers (Japan), 5, 63 (1939). Yung, S. et al., Environmental Science and Technology, 12, 456 (1978).


Soli ds

•

8-31

ESP Reference Use ESP to simulate dry electrostatic precipitators. Dry electrostatic precipitators separate solids from a gaseous stream. Electrostatic precipitators have vertically mounted collecting plates with discharge wires. The wires are parallel and positioned midway between the plates. The corona discharge of the high-voltage wire electrodes first charges the solid particles in the inlet gas stream. Then the electrostatic field of the collecting plate electrodes removes the solids from the gas stream. You can use ESP to size or rate electrostatic precipitators. Use the following forms to enter specifications and view results for ESP: Use this form

To do this

Input

Specify operating parameters and dielectric constants and precipitator dimensions

BlockOptions


Results

View summary of ESP results and material and energy balances Gas

Flowsheet Connectivity for ESP Feed


inlet


outlet One material stream for the cleaned gas One material stream for the solids

Each solids substream must have a particle size distribution (PSD) attribute.

8-32

•

Solids


Specifying ESP

Use the Input Specifications sheet to specify parameters for sizing or rating calculations. To perform these calculations

SetMode=

Enter

ESPcalculates

Rating

Simulation

Number of plates Plate height Plate length

Separation efficiency Power required Corona voltage Pressure drop Precipitator width

Sizing

Design

Separation efficiency

Number of plates Precipitator dimensions Power required Pressure drop

You can specify maximum dimensions for sizing calculations on the Input Specifications sheet.

Operating Ranges

The velocity of gas should be between 1 and 2.5 m/sec (for plate spacing 200 and 300 mm). If the gas velocity is larger than 3 m/s or less than 0.5 m/s, then the models for efficiency and pressure drop are not valid. This is because the transport of fine particles by turbulent diffusion may become more significant than transport by electrostatic force. ESP models wire-and-plate precipitators with relatively high dust 11 3 3 concentration ( ≥ 10 particles / m or 0.1 kg / m ). If the particle concentration is too low, ESP may overestimate the results. ESP is not suitable for a cylindrical electrostatic precipitator.


The separation efficiency is defined as (Crawford, M. 1976):

ηov =

Mass outlet flow rate of solids Total mass flow rate of the inlet solids substream

ηov = 1 −

Cnvs Cnvo

 ( X s − L)qps c E C    3πµdWV 

exp 

Where: Cnvs

=

Particle concentration atXs

Cnvo

=

Particle concentration at inlet

Xs

=

Point at which all particles have acquired a saturation charge

L q ps

= =

Plate length Particle saturation charge

Ec

=

Collecting field strength( = 0.25(E o ))


Soli ds

•

8-33

C

=

Conningham correction factor

µ

=

Viscosity of the gas

d

=

Particle diameter

W

=

Distance between wires and plates

V

=

Actual gas velocity through the precipitator

The point at which all particles have acquired a saturation charge X s , is defined as: 2

Xs

w sV C( nvo C = 0.332µεdW − nvs ) E C (0.8 E Ws − E oc

c

w

r)

0 0

Where: sw

=

Distance between two wires

εo

=

Electric permissivity constant= 8.85 x 10

Eo

=

Corona field strength (White, H. J., 1963)

ro

=

Corona radius

−12

c/vm

The collecting field strength Ec , is defined as: Ec

 T P = 0.25  − VB f  o + 0.03  TPo 

To P TPo ro

   

Where: VB

=

Breakdown voltage

f

=

Roughness factor of wire

To

=

Atmospheric temperature

Po

=

Atmospheric pressure

T

=

Temperature

P

=

Pressure

The particle concentration at the point where the particles first have saturation charge,Cnvs is:

Cnvs

=

0.212( k

Where: k =

8-34

•

Solids

kd 2

+ 2)

0.8 E c 0.427 Ws wEc

+ooE2r

Ws w

−o E

r

( 0w.533 Ws r o

−

)

Dielectric constant( = ε / ε o )


The particle saturation charge, q ps

Pressure Drop

=

3kπε o d

k

+2

2

2 2.5 Eo ro  Ec + Wsw  3

q ps

is:

 2 1.25 ro   −  Wsw  3

  

ESP calculates the pressure drop across the precipitator as:

∆p = 45.5 ρ g Vg2 Where:

Required Power

ρg

=

Gas density

Vg

=

Gas velocity

The power required (White, H. J., 1963)Pw to meet a specified separation efficiency is: Pw

= 52.75 ln(1 − ηov ) Q

Where:

Q

=

Volumetric gas flow rate

Gas Velocity

The models used in ESP are valid for inlet gas velocities ranging from 0.5 to 3 m/s. Outside this range, transport by turbulent diffusion becomes more significant than by electrostatic force and large errors should be expected.

Particle Diameter

You can use ESP to model the separation of fine particles with diameters ranging from 0.01 to 10 microns. ESP is accurate when the inlet particle concentration is high ( ≥ 1011 particles / m 3 or 0.1 kg / m 3 ). If the concentration is too low, the model tends to overestimate the separation efficiency.

References

Crawford, M., Air Pollution Control Theory, Chapter 8: Electrostatic Precipitation, p. 298-358. McGraw-Hill, New York, 1976. White, H.J., Industrial Electrostatic Precipitation, 204, pp. 91-92 (1963).


Soli ds

•

8-35

HyCyc Reference Use HyCyc to simulate hydrocyclones. Hydrocyclones separate solids from the inlet liquid stream by the centrifugal force of a liquid vortex. You can use HyCyc to rate or size hydrocyclones. In simulation mode (rating), HyCyc calculates the particle diameter with 50% separation efficiency from the user-specified hydrocyclone diameter. In design mode (sizing), HyCyc determines the hydrocyclone diameter required to achieve the user-specified separation efficiency of the solids with the desired particle size. In both calculation modes, pressure drop and the particle size distribution of the outlet solids streams are determined. Use the following forms to enter specifications and view results for HyCyc: Use this form

To do this

Input

Specify simulation parameters, dimensions, tangential velocity correlation parameters, and separation efficiency

BlockOptions


Results

View summary of HyCyc results and material and energy balances

Flowsheet Connectivity for HyCyc

Liquid

Feed


inlet

One liquid stream with at least one solids substream

outlet One stream for the cleaned liquid with residual solids One stream for solids

Each inlet solids substream must have a particle size distribution (PSD) attribute.

8-36

•

Solids


Specifying HyCyc

Use the Input Specifications sheet to specify hydrocyclone operating conditions. To perform these calculations

Ent e r

HyCyc calculates

Rating

Simulation Mode Hydrocyclone diameter

Separation efficiency Particle diameter with 50% separation efficiency Pressure drop, particle size distribution of outlet solids stream

Sizing

DesignMode Separation efficiency

Hydrocyclone diameter Pressure drop, particle size distribution of outlet solids stream

To obtain practical dimensions when sizing hydrocyclones, enter the:

• •

Maximum diameter of the hydrocyclone Maximum pressure drop allowed across the hydrocyclone

HyCyc designs multiple hydrocyclones in parallel if one of the following conditions exists:

Operating Ranges

•

The calculated diameter is greater than the maximum specified diameter.

•

The calculated pressure drop is greater than the maximum specified pressure drop.

HyCyc uses empirical and semi-empirical correlations. Expect unreliable results when operating conditions (Bradley, D., 1965) are outside the ranges of experimental data on which the models are based. In general, your data should fall within these ranges:

• • • •

Particle diameter between and (5 to 200 micrometers) Hydrocyclone diameter between 0.01 and 0.6 m Pressure drop between 35 and 345 kPa Separation efficiency between 2% and 98%

The solids concentration should be less than 11% of the volume fraction, or less than 25% of the weight fraction.


Separation efficiency E is defined as:

E

=

mass underflow rate of solids mass feedflow rate of solids

Reduced efficiency E’ is defined as the fraction of feed solids that go to the underflow minus the fraction of the feed liquid that also goes to the underflow.


Soli ds

•

8-37

E′ =

E − Rf 1 − Rf

R

Where f is the volumetric ratio of underflow to feed flow (see Material Split). The reduced efficiency is obtained from the following equation:

 

  d    d50

E=′ 100 −−1 exp −

 

0.115

3

    

Where:

d

=

Diameter of the solid particles to be separated

d 50

=

Particle diameter for which 50% of feed passes through underflow

d In turn, 50 is obtained from the following equation which includes operational and geometric parameters (Bradley, D., 1965):

d 50 Dc 2 i

D

=

3( 03 . 8) n

α

 µ Dc (1 − R f ) θ  0.5 tan   2  Q(σ − ρ )

Where:

Material Split

Q

=

Volumetric flow rate at inlet

Dc

=

Chamber diameter

Di

=

Inlet diameter

n

=

Power of R in the tangential velocity distribution function

α

=

Inlet velocity loss coefficient

σ

=

Density of solid

Rf

=

Underflow rate/feed rate

θ

=

Cone angle

ρ

=

Density of liquid

µ

=

Viscosity of liquid

HyCyc splits the feed according to the following empirical correlation (Moder, J.M. and Dahlstrom, D.A., 1952):

S = β ( Du ) 4.4 Q −.44 Do Where:

8-38

•

Solids


S

=

Volume split = underflow rate/overflow rate

β

=

A constant, 6.13

Du

=

Diameter for underflow

Do

=

Diameter for overflow

Q

=

Inlet volumetric flow rate (gal/min)

The flow ratio

Rf

(underflow rate/feed rate)is then obtained by:

1 1 − Rf

Tangential Velocity

= 1+ S

The following empirical correlation gives the tangential velocityV (Dahlstrom, D.A., 1954) in a hydrocyclone at a radiusR:

 Dc    2

n

VR n =constant=αVi  Where:

α

=

Inlet velocity loss coefficient

Vi

=

Inlet velocity

Dc

=

Diameter of the h ydrocyclone

n

=

Exponent of radial dependence

R

=

Radius

For most cases, α and n are determined experimentally to be 0.45 d and 0.8. These two variables are then used to determine 50 .

Dimension Ratios

Pressure Drop

Common hydrocyclones have the following ranges of dimension ratios (dimension/chamber diameter): Inletdiameter:

1/7

to

1/3

Length:

4

to

12

Overflow diameter:

1/8

to

1/2.3

Underflow diameter:

1/10

to

1/5

Coneangle:

9deg. to

20deg.

For the pressure drop correlation to be valid (overflow diameter/underflow diameter) should be 0.6 to 2.0. HyCyc uses the empirical pressure drop correlation (Dahlstrom, D.A., 1954): Q H 0.5

= 6.38 ( Do × Di ) 0.9

Where:


Soli ds

•

8-39

Hydrocyclone Dimensions

Q

=

Volumetric flow rate (US gallons/minute) at the inlet

H

=

Height of fluid (feet) or length of vortex finder

Do

=

Overflow diameter

Di

=

Inlet diameter

The next figure shows the HyCyc geometry. Dc

Inlet Di

Do

L

θ

Du Hydrocyclone Dimensions

The following table describes the HyCyc dimensions.

References

Term

Description

Dc

Chamber diameter

Di

Inlet diameter

Do

Overflow diameter

Du

Underflow diameter

L

Lengthofhydrocyclone

θ

Cone angle st

Bradley, D., The Hydrocyclone, 1 edition, Pergamon Press, London (1965). Yoshioka, H. and Hatta, Y., Kagaku Kagolar, Chemical Engineering, Japan, 19, 633 (1955).

8-40

•

Solids


Dahlstrom, D.A., "Mineral Engineering Techniques,"Chemical Engineering Progress Symposium Series 50, No. 15, 41 (1954). Moder, J.M. and Dahlstrom, D.A.,Chemical Engineering Progress, 48,75 (1952).


Soli ds

•

8-41

CFuge Reference Use CFuge to simulate centrifuge filters. The centrifuge filters separate liquids and solids by the centrifugal force of a rotating basket. Use CFuge to rate or size centrifuge filters. CFuge assumes that the separation efficiency of the solids equals 1, so that the outlet filtrate stream contains no residual solids. Use the following forms to enter specifications and view results for CFuge: Use this form

Flowsheet Connectivity for CFuge

To do this

Input

Specify centrifuge and filter cake parameters and centrifuge dimensions

BlockOptions


Results

View summary of CFuge results and material and energy balances Liquid

Feed Solids

Material Streams

inlet


outlet One material stream for the liquid One material stream for the solids

If you specify the particle size distribution (PSD), CFuge calculates the average particle size.

8-42

•

Solids


Specifying CFuge

Use the Input Specifications sheet to specify operating conditions and the Input FilterCake sheet to specify filter cake properties. To perform these calculations

Enter

CFugecalculates

Rating

Diameter Rate of revolution Filter cake properties

Filtrate flow rate Filter cake moisture content Height of centrifuge basket

Sizing

List of centrifuge diameters Filtrate flow rate and rates of revolution Filter cake moisture content Filter cake moisture content Height of centrifuge basket (CFuge estimates if not entered)

For sizing calculations, CFuge also calculates the liquid-handling capacities of all of the centrifuges you specify. CFuge selects the centrifuge with a liquid-handling capacity greater than or equal to the required filtrate flow rate. If more than one centrifuge satisfies this criterion, CFuge selects the one with the smallest capacity. If none of the centrifuges satisfies this criterion, CFuge selects the one with the highest filtrate flow rate. In both rating and sizing calculations, CFuge calculates the content and height of the centrifuge basket.

Filter Cake Characteristics

Use the Input FilterCake sheet to specify:

• • • • • •

Cake resistance Moisture Content Sphericity Medium resistance Porosity The average diameter of the solid particles in the cake

The filter cake moisture content is the ratio of the mass flow rate of liquid to that of the solid in the outlet solids stream. The filter cake moisture content is an important design parameter. You should provide it if possible. If you do not enter it, CFuge calculates an estimate from the average particle diameter and cake parameters (Dombrowski, H.S., and Brownell, L.E., 1954). If you enter the particle size distribution (PSD) of the inlet solid stream, CFuge calculates the average particle diameter, so you do not need to enter average diameter on the Input FilterCake sheet.


Soli ds

•

8-43

Filtrate Flow Rate

CFuge calculates the filtrate volumetric flow rate from:

Q=

1

ρl

(F

− WM )

Where:

Pressure Drop

F

=

Feed liquid volumetric flow rate

M

=

Moisture content, mass of liquid/mass of dried solid (specified as Moisture Content on the FilterCake sheet or calculated by the model)

W

=

Dry solids feed rate

ρl

=

Liquid density

CFuge calculates the pressure drop (Grace, H.P., 1953) across the filter cake as:

∆p =

ρ l ω 2 (r22

− r12 )

2

Where:


ω

=

Rotational speed

r1

=

Radius of liquid surface

r2

=

Radius of inner wall of bowl

ρl

=

Liquid density

Separation efficiency, E, is defined as: E=

underflow rate of solids feedflow rate of solids

CFuge assumes that the separation efficiency of the solids equals 1, so that the outlet filtrate stream contains no residual solids.

References

Dombrowski, H.S., and Brownell, L.E.,Industrial and Engineering Chemistry, 46, 6, 1207 (1954). Grace, H.P., Chemical Engineering Progress, 49, 8, 427 (1953).

8-44

•

Solids


Filter Reference Use Filter to simulate continuous rotary vacuum filters. You can use Filter to rate or size rotary vacuum filters. Filter assumes the separation efficiency of the solids equals 1, so that the outlet filtrate stream contains no residual solids. Use the following forms to enter specifications and view results for Filter: Use this form

To do this

Input

Specify filter and filter cake parameters

BlockOptions


Results

View summary of Filter results and material and energy balances

Flowsheet Connectivity for Filter

Filtrate Feed Solids

Material Streams

inlet


outlet One material stream for the liquid filtrate One material stream for the solids

Specifying Filter

Use the Input Specifications sheet to specify operating conditions and parameters. To perform these Enter calculations

Filter calculates

Rating

Simulation Pressure drop Diameter across filter Width Rate of revolution Filter cake characteristics (optional)

Sizing

Design

Diameter

Maximum allowable pressure drop Width across the filter cake and medium Rate of revolution Filter cake characteristics (optional) Width to diameter ratio (optional)


Soli ds

•

8-45

In both calculation modes, Aspen Plus determines the following:

• • • Filter Cake Characteristics

Filtrate volumetric flow rate Cake thickness Mass fraction of solids in the solids filter cake

Filter assumes:

• • •

The cake thickness is greater than 0.00635 m. The capillary number is greater than 1. The filter cake is incompressible or compacted uniformly throughout its thickness (Dombrowski, H. S., and Brownell, L.E., 1954).

When the specific cake resistanceα at the required pressure drop ∆P is not available, Filter can estimate it using the following empirical correlation: α

= α O ( ∆P) k

Where:

αO

=

Specific cake resistance at unit pressure drop

k

=

Cake compressibility

You can use this equation for interpolation and short-range extrapolation when some experimental data ofα O and ∆P are available.

α O is the intercept of the log-log plot ofα versus ∆P. α

and α O both have the units determined by the specified units set, and ∆P is always in Pascals. Use the Average Diameter field on the FilterCake sheet to specify the average diameter of solid particles in the filter cake. If you enter the particle size distribution (PSD) of the inlet solid stream, Filter calculates the average particle size.

Pressure Drop

Filter calculates the pressure drop (Brownell, L.E., and Katz, D.I., 1947) across the filter cake with:

Q = ωRHV

 2 ∆ pωθ V  =RH    µα W 

1/ 2

Where:

8-46

•

Solids

Q

=

Filtrate volume flow rate

ω R

= =

Angular velocity Radius

H

=

Width



V

=

Filtrate volume per unit area

∆p

=

Pressure drop

θ

=

Wetting angle

µ

=

Viscosity

α

=

Filtration resistance

W

=

Solid mass per unit area

Separation efficiency,E, is defined as: E=

underflow rate of solids feedflow rate of solids

Filter assumes the separation efficiency of the solids equals 1, so that the outlet filtrate stream contains no residual solids.

References

Brownell, L.E. and Katz, D. I.,Chemical Engineering Progress, 43, 11, 601 (1947). Dombrowski, H.S. and Brownell, L.E.,Industrial and Engineering Chemistry, 46, 6, 1207 (1954).


Soli ds

•

8-47

SWash Reference Use SWash to simulate solids washers in which dissolved components in the entrained liquid of a solids stream are recovered by a washing liquid. SWash simulates a single-stage solids washer; it does not consider the presence of a vapor phase. SWash calculates the flow rates and compositions of the outlet solids and liquid streams from a user-specified liquid-to-solid mass ratio of the outlet solids stream and the mixing efficiency of the washer. For non-adiabatic operations, SWash determines the outlet temperature when outlet pressure and heat duty are given. Alternatively, SWash calculates the required heat duty when outlet temperature and pressure are specified. Use the following forms to enter specifications and view results for SWash: Use this form

Flowsheet Connectivity for SWash

To do this

Input

Specify operating parameters, flash specifications, and convergence parameters

BlockOptions


Results

View summary of SWash results and material and energy balances

Liquid

Liquid

Solids

Solids

Heat (optional)

Heat (optional)

Material Streams

inlet

One stream for the solids particles with an entrained liquid One stream for the washing liquid

outlet One stream for the washed solids particles One stream for the washing liquid and entrained liquid from the inlet solids stream Heat Streams

inlet

One stream for heat duty (optional)

outlet One stream for net heat duty (optional)

8-48

•

Solids


If you specify only pressure on the Input OutletFlash sheet, SWash uses the inlet heat stream as a duty specification. Otherwise, SWash only uses the inlet heat stream to calculate the net heat duty. The net heat duty is the inlet heat stream minus the actual (calculated) heat duty. You can use an outlet heat stream for the net heat duty.

Specifying SWash

You must specify the mixing efficiency of the washer and the liquid-to-solid mass ratio of the outlet solids stream. For nonadiabatic operations, you must specify the pressure of the washer and one of the following: • The temperature of the washer

•

Heat duty (or an inlet heat stream without an outlet heat stream)

Alternatively, SWash calculates the required heat duty when outlet temperature and pressure are specified. SWash assumes adiabatic operations if neither temperature nor heat duty is specified.

Mixing Efficiency

The mixing efficiency of the washer, E, is defined as:

E

=

S x IN S x IN

S − xOUT L − xOUT

Where:

Bypass Fraction

S x IN

=

Mass fraction of dissolved components in the entrained liquid of the inlet solids stream

S xOUT

=

Mass fraction of dissolved components in the entrained liquid of the outlet solids stream

L x OUT

=

Mass fraction of dissolved components in the outlet liquid stream

The bypass fraction is the fraction of liquid in the feed that bypasses the mixing, when mixing efficiency is less than 1. It is calculated as: Bypass fraction


= (1 − mixing efficiency ) ×

liquid − to − solid ratio specified for SWash liquid − to − solid ratio in inlet solids stream

Soli ds

•

8-49

CCD Reference CCD simulates a counter-current decanter or a multistage washer. CCD calculates the outlet flow rates and compositions from:

• •

Mixing efficiency Liquid-to-solid mass ratio of each stage

CCD can calculate:

••

The heat duty profile from a specified temperature profile The temperature profile from a specified heat duty profile

CCD does not consider a vapor phase. Use the following forms to enter specifications and view results for CCD: Use this form

To do this

Input

Specify operating parameters, temperature profile parameters, pseudostream information, and convergence parameters

BlockOptions


Results

View summary of CCD results, material and energy balances, and stage profiles Solids (Top feed)

Flowsheet Connectivity for CCD

Overflow

1

Feed To Underflow (optional) Product From Underflow (optional)

Nstage

Underflow

Product From Overflow (optional)

Feed To Overflow (optional) Washing Liquid (Bottom feed)

Material Streams

inlet

8-50

•

Solids

One solids inlet material stream (top feed) One liquid inlet material stream (bottom feed) Any number of optional inlet material side streams per stage


outlet One top product stream (overflow) One bottom product stream (underflow) One optional stream per stage for the solids (underflow) One optional stream per stage for the liquid (overflow) Any number of pseudoproduct streams (optional)

Any number of pseudoproduct streams can represent internal underflows or overflows. A pseudoproduct stream does not affect the results of the simulation.

Specifying CCD

Use the CCD Input Specifications sheet to enter the number of stages, pressure, mixing efficiency, and liquid-to-solid mass ratio. Use the CCD Input Streams to enter feed, product, and optional heat stream locations. On the CCD Input Temp-DutyProfiles sheet, note the following: Ifyouenter

Stagetemperature Stageheatduty Stage overall heat transfer coefficient

CCDcalculates

Stageheatduty. Stagetemperature. Stage temperature.

You cannot enter both temperature profiles and heat duties or overall heat transfer coefficients. If you enter stage heat duty and/or an overall heat transfer coefficient, and you do not enter values for all stages, the system assumes unspecified values to be zero. Enter the medium temperature of each stage when you enter overall heat transfer coefficients. Use the Estimated Temperature field to enter estimated stage temperatures. Note: CCD interpolates unspecified values and, by default, assumes them to be the same as the ambient temperature. Use the CCD Input PseudoStream sheet to transfer the internal overflow or underflow of a stage to a pseudostream.

Component Attributes

CCD does not consider the mixing of component attributes and PSDs. CCD assumes all outlet solids streams have the same attributes and PSD as the solids feed stream to stage one. CCD also assumes all outlet liquid streams have the same attributes and PSD as the liquid feed stream throughout the final stages.

Multistage Washer Profiles

For any CCD profile, such as mixing efficiency, liquid-to-solidratio, temperature, duty, enter a value for every stage, as information becomes available. If you enter only some of the values for some stages, CCD generates the complete profile by linear interpolation of the given values. If you enter only one value, CCD assumes a constant profile of that value throughout the washer.


Soli ds

•

8-51

Mixing Efficiency

The mixing efficiency of stagen is defined as:

E

=

S x IN S x IN

S − xOUT L − xOUT

Where: S x IN

=

Mass fraction of dissolved components in the entrained liquid of the total inlet solids stream to stage n.

S x OUT

=

Mass fraction of dissolved components in the entrained liquid of the total outlet solids stream from stage n.

L x OUT

Medium Temperature

=

Mass fraction of dissolved components in the outlet liquid stream from stagen.

The duty for each stage is calculated according to the following equations:

Qi

= UA −Tmed i i(Tcalc i

)

Where:

8-52

•

Solids

Qi

=

Heat duty for stage i

UAi

=

Product of heat transfer coefficient and area for stage i

Tcalci

=

Calculated outlet temperature of stage i

Tmed i

=

Temperature of the heat transfer medium at stage i


C HA P TE R 9

User Models

This chapter describes the models that allow you to add custom extensions to Aspen Plus. User and User2 allow you to write your own unit operation models as Fortran subroutines. These subroutines must follow the guidelines described in theAspen Plus User Models reference manual. User2 can also be used with a unit operation model written as an Excel spreadsheet. User3 allows you to use custom or external models with equation-oriented formulations. The models are: M odel

Description

Purpose

User

User-defined unit operation model

Model a unit operation using a Unit operations with four (or fewer) user-supplied Fortran subroutine inlet and outlet streams

User2

User-definedu nit operation model

Model a unit operation using a Unit operations with no limit on user-supplied Fortran subroutine. number of streams

User3

User-defined or Run built-in models from RTUnit operations with equationexternal unit-operation Opt, Aspen EO models from the oriented formulations model PML model library, or models written by a user that may contain proprietary models

ACMUser3 Aspen Custom Modeler models

Models a unit operation using Aspen Custom Modeler

UseFor

Unit operation models created with Aspen Custom Modeler

Hierarchy blocks allow you to organize complex flowsheets in a hierarchical manner. When a user model template containing multiple blocks is placed on a flowsheet, it automatically appears inside a Hierarchy block. See theAspen Plus User Guide, chapter 16, for more information on creating these templates. You may also use Hierarchy blocks directly, without using a template. M odel

Description

Purpose

Hierarchy Hierarchical structure Create a hierarchical structure to organize complex flowsheets.


UseFor

Container for other blocks

U s e rM o de l s

•

9-1

User Reference User can model any unit operation model. You must write a Fortran subroutine to calculate the values of the outlet streams based on the inlet streams and parameters you specify. User and User2 differ only in the number of inlet and outlet streams allowed and the argument lists to the model subroutine. User is limited to a maximum of four material and one heat or work inlet stream and a maximum of four material and one heat or work outlet stream. User2 has no limits on the number of inlet and outlet streams. Use the following forms to enter specifications and view results for User: Use this form

To do this

Input

Specify name and parameters for user subroutine, calculation options, and outlet stream conditions and flash convergence parameters

BlockOptions


Results

View summary of User results and material and energy balances

Material

Flowsheet Connectivity for User

Heat (optional) Work (optional)


Material Streams

inlet

One to four inlet material streams

outlet One to four outlet material streams Heat Streams

inlet

One heat stream (optional)

outlet One heat stream (optional) Work Streams

inlet

One work stream (optional)

outlet One work stream (optional)

9-2

•

U s e rM od e l s

A s p e nP l u s1 1 . 1U ni tO p e r a t i onM o d e ls

Specifying User

You must specify the name of the subroutine model on the Input Specifications sheet. You have the option of specifying:

• •

A report subroutine name

•

Values of the integer and real arrays passed to the user model subroutine

• • •

Length of integer and real workspace vectors

Size of the integer and real arrays (INT and REAL) passed to the user model subroutine

Thermodynamic conditions of each outlet stream Type of flash calculations (vapor, liquid, two-phase, threephase)

For information on writing Fortran subroutines for user models, see Aspen Plus User Models reference manual.


U s e rM o de l s

•

9-3

User2 Reference User2 can model any unit operation model. You must write a Fortran subroutine to calculate the values of the outlet streams based on the inlet streams and parameters you specify. User and User2 differ only in the number of inlet and outlet streams allowed and the argument lists to the model subroutine. User2 has no limits on the number of inlet and outlet streams. User is limited to a maximum of four material and one heat or work inlet stream, and a maximum of four material and one heat or work outlet stream. Use the following forms to enter specifications and view results for User2: Usethisform

Flowsheet Connectivity for User2

Todothis

Setup

Specifyname and parameters fortheuser subroutine, excel file name, values of configured variables, calculation options, outlet stream conditions, and flash convergence parameters

BlockOptions


Results

View summary of User2 results, material and energy balances, and the values of the configured variables.

Material Heat (optional) Work (optional)


Material Streams

inlet


outlet At least one outlet material stream Heat Streams

inlet


outlet Any number of heat streams (optional) Work Streams

inlet Any number of work streams (optional) outlet Any number of work streams (optional)

9-4

•

U s e rM od e l s


Specifying User2

You must specify the name of the subroutine model on the User2 Input Specifications sheet. You have the option of specifying:

• •


•


• • •




For information on writing Fortran subroutines for user models, see Aspen Plus User Models reference manual.


U s e rM o de l s

•

9-5

User3 Reference User3 models are used to simulate features that are not in the standard Aspen Plus models. They can be one of three types: old built-in models from RT-Opt (like R3HTUA), Aspen EO models from the PML model library (like EOTRAYDP) or models written by a user that may contain proprietary models (like a reactor). Use the following forms to enter specifications and view results for the User3 model: Use this form

To do this

Setup

Specify name and parameters for the user subroutine or Aspen EO model, values of configured variables, calculation options, outlet stream conditions, and flash convergence parameters.

Parameters

Specify Jacobian calculation options and run options for the Aspen EO model.

Attributes

Specify attributes of variables and equations of the model.

Block Options

Override global values for physical properties, simulation options, diagnostic message levels, and report options for this block.

Results

View summary of User3 results, material and energy balances, and the values of the configured

EO Variables

Flowsheet Connectivity for User3

variables. Specify equation-oriented variable attribute changes for this block, for the current run only.

EO Input

Specify the equation-oriented variables for this block.

Spec Groups

Specify the specification groups for this block.

Ports

Specify the EO variables collected to form ports for this block.

Material (optional) Heat (optional) Work (optional)

inlet

Material (optional) Heat (optional) Work (optional)

Any number of inlet material, heat, and/or work streams

outlet Any number of outlet material, heat, and/or work streams

The number and types of streams connected to a User3 model depends on the type and configuration of that specific model.

9-6

•

U s e rM od e l s


Specifying User3

You must specify the name of the model subroutine or Aspen EO model on the User3 Input Specifications sheet. You have the option of specifying:

• •


•


•


• •


•

Name and location of the configuration file, if using an Aspen EO model

•

Values of variables on the Attributes form, as needed to make the problem square


To import a User3 model written for RT-Opt version 3 or 10 with Aspen Plus 11: 1

Export an .inp file from the prior version of RT_OPT.

2

Replace the word STRVAR with ANALYZER.

3

Delete any EBS setup scripts.

4

Use the version 11 engine to generate a .bkp file from the .inp file with the command ASPEN filename /mmbackup /itonly You can retain your graphics by copying the graphic section from the previous version’s .bkp file to this newly created .bkp file.

EO Usage Notes for User3

5

Load the new .bkp file. The User3 forms should be populated.

6

On the top-level EO Configuration EO Options form, select the Model Types sheet.

7

From the list of models selectUSER3. Click Additional Options.

8

In the EO Formulation field, choose mole flows.


• •


Flash specifications Features which are globally unsupported

U s e rM o de l s

•

9-7

ACMUser3 Reference ACMUser3 allows models created with Aspen Custom Modeler (ACM) to be used as unit operation models in Aspen Plus. Use the following forms to enter specifications and view results for ACMUser3: Use this form

To do this

Setup

Specify ports for inlet and outlet streams, values of ACM variables, calculation options, and outlet stream flash options

BlockOptions


Results

View material and energy balances and values of the ACM variables.

Flowsheet Connectivity for ACMUser3 Feed

Product

Material Streams

inlet A number of material streams defined by the ACM model outlet A number of material streams defined by the ACM model

ACMUser3 does not allow heat or work streams.

Specifying ACMUser3 ACMUser3 requires one stream to be attached to each inlet and outlet port defined in the Aspen Custom Modeler model.

Adding ACM Models to the Aspen Plus Model Library

9-8

•

U s e rM od e l s

To use an ACM model with Aspen Plus, first build an Aspen Plus model library file (.apm file) within ACM (see the ACM documentation for more information). To use this model in Aspen Plus: 1

From the Library menu, select References...

2

Click the Browse button and select the file containing the library.

3

Select the check box next to the name of the new model.

4

Click A new tab in containing the ACM model will be added to the OK. Model Library Aspen Plus.


To save this setting, so that this model will always appear in the Model Library in Aspen Plus, from the Library menu, select Save Default. Now, you may use this model in Aspen Plus in the same way as any other model.


U s e rM o de l s

•

9-9

Hierarchy Reference Use Hierarchy blocks to provide hierarchical structure to complex simulations. Also, Hierarchy blocks may be added automatically when importing templates into a simulation. Hierarchy blocks may contain streams and other blocks (even other Hierarchy blocks) as well other features like design specifications and sensitivity problems. Hierarchy blocks contain Setup and Properties forms with some of the same information as the top-level Setup and Properties forms. The settings on these forms override the settings on the corresponding forms at higher-level Hierarchy blocks or the top level of the simulation for blocks within the Hierarchy block. Hierarchy blocks also contain forms for Streams, Blocks, Convergence, Flowsheeting Options, Model Analysis Tools, and Results Summary. These forms are used for working with such objects within the Hierarchy block, and they will not affect higherlevel Hierarchy blocks or the top level of the simulation except through the outlet streams of the Hierarchy block. Use the following forms to enter specifications and view results for Hierarchy: Use this form

9-10

•

Us e rM o de l s

To do this

Input

Specify components for use within the Hierarchy block, and view connections to streams outside the Hierarchy block.

Setup

Override settings from the top-level Setup forms.

Properties

Override settings from the top-level Properties forms.

Streams

View or enter information about streams within the Hierarchy block.

Blocks

View or enter information about blocks within the Hierarchy block.

Convergence

Define convergence and sequence information within the Hierarchy block.

Flowsheeting Options

Define design-specs, calculator, transfer, balance, and pressure relief blocks within the Hierarchy block.

Model Analysis Tools

Define sensitivity, optimization, constraint, and data-fit blocks within the Hierarchy block.

Results Summary

View a summary of stream results within the Hierarchy block.

A s p e nP l u s1 1 . 1U ni tO p e r a t ionM o d e ls

Flowsheet Connectivity for Hierarchy

A Hierarchy block may have any number of inlet and outlet streams of any types (material, heat, and work). Each external stream connected to the Hierarchy block is attached to a stream within the Hierarchy block. Each stream within the Hierarchy block with an unconnected source or destination creates a port to which an external stream may be connected.

Specifying Hierarchy

Hierarchy normally does not need any specifications. You may specify the group of components to be shown within the Hierarchy block on the Input Specifications Sheet. To access the flowsheet within a Hierarchy block, double-click on the block. A new flowsheet window will open, containing the flowsheet inside the Hierarchy block.


U s e rM o de l s

•

9-11

9-12

•

Us e rM o de l s

A s p e nP l u s1 1 . 1U ni tO p e r a t ionM o d e ls

C H A P T E R 10

Pressure Relief

This section contains detailed reference information on the Aspen Plus Pres-Relief model for pressure relief calculations. For information on using Pres-Relief, see the Aspen Plus User Guide, Chapter 33. This section describes the following topics:

• • • • • • • • • • • • • • •


Relief scenarios Code compliance checks Stream and vessel compositions and conditions Rules to size the relief valve piping Reactions Relief system Data tables for pipes and relief devices Valve cycling Vessel types Disengagement models Stop criteria Solution procedure for dynamic scenarios Flow equations Calculation and convergence methods Vessel insulation credit factor

P r e s s u r eR e l i e f

•

10-1

Pres-Relief Reference Use Pres-Relief to do either of the following:

•

Determine the steady-state flow rating of pressure relief systems

•

Dynamically model vessels undergoing pressure relief due to a fire or heat input specified by the user. You may specify that reactions occur in the vessel.

Use the following forms to enter specifications and view results for Pres-Relief. Use this form

To do this

Setup

Specify pressure relief scenario, general specifications, stream or initial vessel conditions, design rules, and any reactions that occur

Relief Device

Specify the type of relief device and configuration, and the characteristics of the device

Inlet Pipes

Specify piping, fittings, and valves immediately upstream of the relief device

Tail Pipes

Specify piping, fittings, and valves immediately downstream of the relief device

Dynamic Input

Specify parameters describing the dynamic event

Operations

Specify criteria that will terminate the dynamic simulation

Convergence

Override default methods and convergence parameters for the algorithms involved in the pressure relief simulation

Block Options

Override default methods and options for property calculation, simulation, diagnostics, and reporting

Steady State Results

Review calculated results and profiles for the steadystate scenarios

Dynamic Results Review calculated results and profiles for the dynamic scenarios

Specifying PresRelief

Use Pres-Relief to do either of the following:

•

Determine the steady-state flow rating of pressure relief systems

•

Dynamically model vessels undergoing pressure relief due to a fire or heat input specified by the user. You may specify that reactions occur in the vessel

Use the Setup form to specify the pressure relief scenario, general specifications such as the discharge pressure and the estimated

10-2

•



flow rate, inlet stream conditions, initial vessel conditions, design rules, and any reactions (dynamic scenarios only) that occur. Use the Relief Device form to specify the relief system. You must select a relief device and specify its characteristics. You must also specify the vessel neck and the number of inlet and tail pipe sections to be used. Use the Dynamic Input form to specify the required parameters for dynamic scenarios. These include vessel specifications, disengagement models and details specific to the chosen scenario. For the to fire you the must specifyisthe fire standard and the credits bescenario, used. When scenario Dynamic run with specified heat flux, you must specify the heat input parameters. When the number of inlet and tail pipe sections exceeds 0, you must specify the details for each section in the Inlet Pipes and Tail Pipes forms. For dynamic scenarios, use the Operations form to specify one or more variables to be used as stop criteria. The simulation will stop when the value of any of these variables exceeds the user-specified limit.

Scenarios

Scenarios are situations that cause venting through the pressure relief system to occur. Pres-Relief supports the following scenarios:

• • • •

Dynamic run with vessel engulfed by fire Dynamic run with specified heat flux into vessel Steady state flow rating of relief system Steady state flow rating of relief valve

Dynamic Run with Vessel Use this scenario to model a vessel engulfed by fire. You must Engulfed by Fire specify the vessel geometry and initial composition. Aspen Plus can compute the energy input for this scenario according to the following standards:

• • •

NFPA-30 API-520 API-2000

Aspen Plus assumes the calculated energy input is constant during the entire venting transient. Aspen Plus uses credit factors for drainage, water-spray, fire-fighting equipment, and insulation to reduce energy input, if appropriate for the chosen standard. You may specify a total credit factor instead of individual credit factors. You must specify the fire duration time. This is a dynamic scenario. The vessel contents and relief rate change as a function of time.



•

10-3

Aspen Plus calculates wetted area, energy input, and credit factors differently for each of the three standards.

Calculation of Wetted Area Vessel type

NFPA-30

API-2000

API-520

Horizontal 75% of total exposed area

75 % of total area or area to a height of 30 ft. above grade, whichever is greater

Wetted area up to 25 ft. above grade (based on specified liquid level)

Vertical

Area up to 30 ft. above grade. Bottom plate is included if exposed

Area up to 30 ft. above grade. If Wetted area up to 25 ft above grade on ground, bottom plate is not (based on specified liquid level). included. Bottom plate is included if exposed.

Sphere

55 % of total exposed area

55% of surface area, or surface Up to a maximum horizontal area to a height 30 ft. above diameter or up to height of 25 ft. grade, whichever is greater above grade, whichever is greater

Calculation of Q (Btu/hr), Based on Area (sq ft)

NFPA-30 and API-2000

Arearange

20 < Area < 200

Heatinput

Q

=credit ( factor

) 20,000 Area

200 < Area < 1000

Q = (credit factor )199,300Area

0.566

1000 < Area < 2800

Q = (credit factor ) 963,400Area

0.338

2800 < Area


0.82

For NFPA-30 , QMAX=14,090,000 at 2800 square feet if operating pressure < 1 PSIG API-520

Heat input


10-4

•


0.82

,thede fault credit factor being 1


Calculation of Credit Factors Type

NFP A-30

Insulationonly

API-2000

.3

API-520

F=K(1660-TF)/21,000t

Same as API-2000

You must specify F Drainageonly

.5

1.

Not defined

(Area > 200 sq. ft.) Wateranddrainage

.3

Water, insulation, and drainage

1. .15

Notdefined NSUL

Notdefined

Notdefined

Notdefined

(Area > 200 sq. ft.)

Insulation and drainage .15 (Area > 200 sq. ft.) Drainage and prompt fire fighting effort

Nocredit

Portable

Nocreditfactors allowed

Dynamic Run with Specified Heat Flux into Vessel

Notdefined Notdefined

0.6*INSUL Notdefined

This scenario is similar to the fire exposure scenario, except it can model any energy input. Aspen Plus can compute the energy input for this scenario in three ways depending on whether you specify:

• • •

A constant duty A duty profile An area for heat transfer, a heat transfer coefficient, and a source fluid temperature

This scenario is a dynamic scenario and is typically used for electrical heaters and other energy sources.

Steady State Flow Rating Use this scenario to find the flow rate through a specified relief of Relief System system at the specified composition. For this scenario, you must enter your own :

• • • •

Relief rate Piping description Feed stream composition Feed stream condition

Steady State Flow Rating Use this scenario to find the flow rate through a valve, given the of Relief Valve composition and condition at the entrance to the valve. This is the simplest scenario. It is similar to the steady state flow rating of relief system scenario, except no piping is allowed.



•

10-5

Compliance with Codes

Pres-Relief allows two types of runs:

• •

Code capacity Actual capacity

The primary purpose of the code capacity run is to ensure that the capacity of the relief system, rated as required by code, exceeds the maximum capacity dictated by the scenario. The maximum pressure reached during the relief event must be less than the code allowable accumulation. The Code Capacity run includes the:

• • •

ASME valve rating factor of .90 Valve flow coefficient A combination coefficient

The combination coefficient is only included if a rupture disk/relief valve combination is being designed. Typical combination coefficients for NBBI certified combinations are close to 1.00. If the combination is not certified, the ASME code requires a combination coefficient of .90. The primary purpose of the actual capacity run is to provide the best estimate of the actual flow through the system. Design of downstream equipment (other than the tail pipe) is one example why you might need this information. The actual capacity run contains the valve flow coefficient, but not the ASME valve rating factor of .90 or the combination coefficient.

Stream and Vessel Compositions and Conditions

For the steady-state scenarios, you must specify the composition and conditions (two of temperature, pressure, and vapor fraction) of the feed stream. You can do this on the Setup Streams sheet in two ways:

• •

Reference an Aspen Plus stream Give the composition and conditions of the stream as input to Pres-Relief

For the dynamic scenarios, you must specify the composition and the conditions in the vessel at the beginning of the pressure relief calculations. Do this by referencing an Aspen Plus stream, or by specifying the composition and two of temperature, pressure, and vapor fraction on the Setup Vessel Contents sheet. As with the steady-state scenarios, you may reference an Aspen Plus stream or give the composition and conditions as input to Pres-Relief. When vapor fraction is not specified, you may also specify:

• •

Initial liquid fill fraction (fillage) of the vessel Pad-gas pressure and Component ID

Only two of temperature, pressure, and vapor fraction can be specified or referenced from a stream.

10-6

•



Rules to Size the Relief Valve Piping

Aspen Plus uses several rules (3% rule, X% rule, and 97% rule) to size the inlet and outlet piping with PSVs. The rules use the following terminology:

DSP

=

Differential set pressure

CBP

=

Constant back pressure

Psta

=

Static pressure

Ptot

=

Static pressure + velocity pressure

IDP

=

Inlet pressure drop

=

Ptot (vessel) - Ptot (valve in)

=

Built-up back pressure

=

Psta (valve out) - CBP

BBP

These rules are applied for both actual and code capacity runs and are applied at the converged solution for the steady-state scenarios. For dynamic scenarios, the 3% Rule and X% Rule are applied once, at 10% overpressure. If all pressures are above 10% overpressure, the test is not performed and a warning is issued. If all pressures are below 10% overpressure, the highest pressure value is scaled up to 10% overpressure, and the scaled values are used in applying the rule. The 97% rule is applied when the pressure at the valve inlet is at or above 10% overpressure. None of the required standards mentions any of these rules except for the X% rule with X=10. The X% rule is mentioned in the nonmandatory appendix of the ASME code.

3% Rule

According to the 3% rule, the total pressure loss in the inlet must be less than 3% of the differential set pressure when the flow rate is equal to the code capacity of the valve at 10% overpressure.

IDP ≤ 0.03DSP For cases where the overpressure does not reach 10%, adjust the pressure drop rule by multiplying by the ratio of the maximum flowing pressure to 10% overpressure (psig).

IDP ≤ 0.03 X% Rule

RP 11 . SP

According to the X% rule, the built-up back pressure must be less than X% of the differential set pressure when the flow rate is equal to the code capacity of the valve at 10% overpressure.

BBP ≤


X DSP 100


•

10-7

For cases where the overpressure does not reach 10% adjust the pressure drop rule by multiplying by the square of the ratio of the maximum flowing pressure to 10% overpressure (psig).

BBP ≤ 97% Rule

 RP  2   100  11 . PS  X

According to the 97% rule, 97% of the differential set pressure must be available across the valve anytime the over pressure is equal to or above 10% with a flow through the valve based on code capacity.

RP − CBP −

−IDP ≥

BBP

0.97 DSP

For cases where the overpressure does not reach 10%, apply the rule at peak overpressure.

Recommendations for Specific Valve Types

For standard spring loaded valves o r pop action pilot valves with unbalanced pilots vented to the discharge : The differential set pressure is the set pressure minus the constant back pressure.

DSP = SP − CBP Size the inlet piping using the 3% rule. Size the outlet piping using the 97% rule. -OrSize the outlet piping with the X% rule using X = 10.

For balanced bellows spring loaded valves : The differential set pressure is the set pressure.

DSP = SP Size the inlet piping using the 3% rule. Size the outlet piping with the X% rule using X = 30.

For modulating pilot operated valves with balanced pilots or pilots vented to atmosphere: The differential set pressure is the set pressure.

DSP = SP You can use the scenario required flow rather than the valve capacity for pressure drop calculations as an option. This can easily be simulated by changing the input orifice area until the overpressure reaches 10%. There is no inlet pressure drop rule. Size the outlet piping with the X% rule using X = 50.

10-8

•



Reactions

If the protected vessel is a vertical, horizontal, API, spherical , or user-specified tank, you may model it with or without reactions. Specify the reactions by giving the Reactions ID on the Setup Reactions sheet.

Relief System

The venting system consists of:

• • • •

A vessel neck One or two sections of inlet pipe The relief device itself One or two sections of tail pipe

In a simulation, the system being modeled may consist of an inlet pipe without a relief device, or a relief device connected to the vessel without an inlet pipe. The tail pipe is optional.

Relief Devices

Pres-Relief can model the following types of relief devices:

• • • • •

Safety relief valves (PSVs; both liquid and gas/2-phase) Rupture disks (PSDs) Emergency relief valves (ERVs) SRV/rupture disk combinations Open vent pipes

Internal tables (accessed from the ReliefDevice SafetyValve sheet) contain several standard commercially available valves, along with all the mechanical specifications and certified coefficients needed in the relief calculations. You may choose one valve from the tables, or enter your own valve specifications and coefficients. For liquid service valves, you must also specify the full-lift overpressure. This allows Aspen Plus to simulate some of the older style valves which do not achieve full lift until 25% overpressure is reached. For gas/2-phase service valves, you must also specify the average opening and closing factors. The valve does not open until the pressure drop across the valve reaches (opening factor * Dif-Setp). The valve closes when the pressure drop across it reaches (closing factor * Dif-Setp). In an actual capacity run, the rupture disk is modeled as a bit of resistance using the pipe model. The default value of L/D is 8 for a rupture disk with a diameter of 2 inches or less and 15 if the diameter is greater than 2 inches. You can override the default by specifying a value on the Relief Device Rupture Disk sheet. In the code capacity run, the rupture disk is modeled as an ideal nozzle with a certified discharge coefficient. If no certified discharge coefficient is available, a value of 0.62 is suggested.



•

10-9

In a code capacity run in combination with a safety relief valve, the resistance of the rupture disk is modeled by the combination coefficient in the valve model. The emergency relief vent is modeled as a nozzle. A de-rating factor of 0.9 is used in a code capacity run.

Piping System

The inlet piping system can be made of one of the following:

• •

One pipe section Two sections of pipe plus a vessel neck, all with different diameters

The tail pipe can be made of one section of pipe or of two sections of pipe with different diameters. For each pipe section, specify:

• • • •

Pipe diameter Length Elevation Whether the pipes are screwed together or held together with flanges or welds

If pipes of different diameters are used, reducer and expander resistance coefficients ("K" factors) can be specified. Aspen Plus uses the equation K =4*fr*(L/D) to convert from resistance coefficients to equivalent L/D, where the term "fr" is the friction factor. Optional information for each section consists of the number of 90 degree elbows, straight tees, branched tees, gate valves, butterfly valves, transflo valves, and control valves. You can add other fittings not listed by specifying the L/D value. Aspen Plus calculates a total equivalent L/D before modeling the pipe section. You may also specify:

• •

Ambient temperature at the inlet and outlet of the pipe A heat transfer coefficient to exchange heat with the pipe contents

While modeling the pipe section, Aspen Plus detects the choked condition in the pipe by keeping track of the Mach Number as integration down the pipe proceeds. If the Mach Number goes above 1.0, integration is stopped and a flag is returned to indicate that the pipe choked. Pipeline pressure drop modeling can work in two ways. You may specify one of the following:

• • 10-10

•

P r es s u r eR el i e f

Rigorous flashes are to be done at each step in the integration A flash table is used during pipe integration

A s p e nP l u s1 1 .1U ni tO p e r a t ionM o de ls

If you request a table, specify the number of temperature and pressure points in the table. At each temperature-pressure pair, Aspen Plus performs a flash and calculates all necessary properties (density, viscosity, surface tension, and so on). As integration proceeds, Aspen Plus interpolates in this table to get the necessary properties. If properties outside the table are needed, a rigorous flash is performed at that point. In general, the pipe integration proceeds faster if the flash table is used. Several correlations are available, depending on the pipe inclination. The default method for all inclinations (holdup and frictional pressure loss) is Beggs and Brill. Other available options are: • Darcy

• • •


Lockhart-Martinelli Dukler for frictional loss Lockhart-Martinelli, Slack, and Flanigan for holdup

P r e s s u r eR e li e f

•

10-11

Pres-Relief includes several customizable tables that list the

Data Tables for Pipes available options for pipes, general purpose valves, safety relief and Relief Devices

valves, emergency relief vents, and rupture disks. You can modify the tables by changing data files. Then process the files through ModelManager Table Building System (MMTBS).

Pipes

Pres-Relief includes a table of actual diameters for several steel pipe schedules. Use this table when choosing the piping for the inlet and tail pipes. You can modify this table by including more pipe materials and/or schedules. The table is organized as follows: first material of construction number of types first type number of diameters nominal diameter actual diameter nominal diameter actual diameter . . second type number of diameters nominal diameter actual diameter nominal diameter actual diameter . . second material of construction number of types first type number of diameters nominal diameter actual diameter nominal diameter actual diameter . . second type number of diameters nominal diameter actual diameter nominal diameter actual diameter . .

10-12

•



General-Purpose Valves

For general-purpose valves in the inlet or tail pipes, Pres-Relief includes a table of various manufacturers’ valves from 1 inch to 10 inches. The valves include:

• • • • •

Durco Plug Tufline Plug Jamesbury Ball AGCO Selector KTM Ball (L-Port and T-Port)

For each manufacturer, the table contains:

• • • •

Valve type (for example., L-Port or T-Port) Nominal diameter Port area Flow coefficient

The table is organized as follows: first manufacturer number of types first type number of diameters nominal diameter port area nominal diameter port area . . second type number of diameters nominal diameter port area nominal diameter port area . .


flow coeff flow coeff

flow coeff flow coeff


•

10-13

Safety Relief Valves

’ safety relief valves. Pres-Relief includes a table of manufacturers It contains valves for liquid and gas/2-phase service. For each valve, the table contains:

• • • • • • • • •

Service Type Manufacturer Series, size (for example, 3L4) Throat diameter Inlet diameter Outlet diameter Discharge coefficient Overpressure factor (for liquid service valves)

The table is organized as follows: Service (Liquid, Gas, or 2-phase) number of types first type number of manufacturers first manufacturer number of series first series number of sizes first size number of throat diameters throat diam throat diam . . throat diam throat diam

10-14

•


inlet diam outlet diam dischg coeff over pr factor inlet diam outlet diam dischg coeff over pr factor

inlet diam outlet diam dischg coeff over pr factor inlet diam outlet diam dischg coeff over pr factor


Emergency Relief Vents

This table contains:

• • •

Nominal diameter Effective diameter Allowed setpoint for several Protectoseal and Groth emergency relief vents

You must specify an over-pressure factor. The table is organized as follows: first manufacturer # of types first type # of nominal diameters nominal diameter effective diameter allowed setpoint nominal diameter effective diameter allowed setpoint . .

Rupture Disks

This table contains manufacturers’ information on rupture disks. Each entry contains:

• • • • •

A manufacturer Type Nominal diameter Actual diameter Discharge coefficient

The table is organized as follows: first manufacturer number of types first type number of nominal diameters first nominal diam actual diam discharge coeff second nominal diam actual diam discharge coeff . .

Valve Cycling

If a relief valve is too large for a given application, valve cycling may occur. In this situation, the pressure in the vessel builds up to a point where the valve opens, but then closes almost immediately because enough material is released to lower the vessel pressure below the closing pressure. In some simulations, the valve may open and close several times per second. The simulation may run for a long time, just opening and closing the valve over and over. To stop such a simulation, you can specify whether or not to stop cycling, and how many openings and closings of the valve are allowed in a specified amount of time.



•

10-15

Vessel Types

You must enter vessel geometry for the dynamic scenarios. You can choose one of the following vessel types:

• • • • • •

Vertical Vessel Horizontal Vessel API Tank Sphere Heat exchanger shell Vessel jacket

User-specified •If you choose user-specified, you must specify surface area and volume. Surface area is also required for vessel jacket. Maximum Allowable Working Pressure (MAWP) with corresponding temperature is required for all vessel types. Some vessel types require diameter, length, and volume of internals.

Vertical Vessel, Horizontal Vessel, and API Tank

If you choose vertical vessel, horizontal vessel, or API tank, choose one of these head types:

• • •

Flanged and dished Ellipsoidal User-specified

If you choose user-specified head type, you must specify the area and volume of a head.

Sphere

If the protected vessel is a sphere, you must specify:

• • •

Diameter MAWP with corresponding temperature Volume of internals

Heat Exchanger Shell

If the protected vessel is a heat exchanger shell, in addition to the items specified for a vertical vessel you must also specify whether the vessel is mounted vertically or horizontally.

Vessel Jacket

If the protected vessel is a vessel jacket, you must specify:

• • • User-Specified

10-16

•


MAWP with corresponding temperature Volume of internals Jacket volume

If the protected vessel is user-specified, you must specify:

•

Volume

•• •

Area MAWP with corresponding temperature Volume of internals


Disengagement Models

The following disengagement options are available: Option

Description

Homogeneous

Vapor fraction leaving vessel is the same as vapor fraction in vessel

All-vapor

All vapor leaving vessel

All-liquid

All liquid leaving vessel

Bubbly

DIERS bubbly model

Churn-turbulent DIERS churn-turbulent model User-specified

Homogeneous venting until vessel vapor fraction reaches the user-specified value, then all vapor venting

For the bubbly and churn-turbulent methods, Aspen Plus uses the DIERS "switch-point" calculations to compute the point at which total vapor-liquid disengagement occurs. Use the bubbly and churn-turbulent models only for vertical or API tanks.

Stop Criteria

For dynamic scenarios, stop criteria need to be specified which will terminate the simulation. You must:

• •

Select a specification type

•

Select a component and substream for component-related specification types

•

Specify which approach direction (above or below) to use in stopping the simulation

Enter a value for the specification at which the simulation will stop

You may select from the following specification types: • Simulation time

• • • • • • • • • •


Vapor fraction in the vessel Mole fraction of a specified component Mass fraction of a specified component Conversion of a specified component Total moles or moles of a specified component Total mass or mass of a specified component Vessel temperature Vessel pressure Vent mole flow rate or mole flow rate of a component Vent mass flow rate or mass flow rate of a component


•

10-17

You must also select the location of the stop criteria specification. You may select from the following locations:

• • •

Vessel Relief vent system Accumulator

Certain restrictions apply depending on the location selected. When location = vessel, mole and mass flow rate are not allowed. When location = vent accumulator, only the following specifications are allowed:

• • • •

Mass fraction of a specified component Mole fraction of a specified component Total moles of a specified component Total mass of a specified component

When location = vent, only the flowing specifications are allowed

• • • • Solution Procedure for Dynamic Scenarios

Mass fraction of a specified component Mole fraction of a specified component Vent molar flow rate Vent mass flow rate

The problem to be solved is: Given the initial conditions in the vessel, a description of the pressure reliefthrough system,the and the heatrelief flowsystem into theand vessel, calculate the flow rate pressure determine if the pressure relief system meets code requirements. The problem is solved as outlined below. This algorithm is for the Heat-Input and Fire Scenarios. 1

Given the heat input to the vessel, solve the energy balance and flash equations along with the reaction equations for the vessel at the present time step. If any of the termination criteria are met, go to Step 6. The options for specifying termination criteria include:

• • • •

10-18

•


Time for scenario exceeded Specified vapor fraction reached Vessel contents have reached specified value Pressure in the vessel is greater than the maximum allowed

2

If the pressure in the vessel is less than the device opening pressure, increment time and go to Step 1.

3

Calculate the maximum flow rate possible through the pressure relief system. This value is calculated by finding the smallest


diameter of any pipe or valve in the system, and calculating the sonic velocity through that diameter. 4

Calculate the pressure at the end of the vessel neck, after each section of the inlet pipe, after the pressure relief device, and after each section of the tail pipe based on the current flow estimate. If the pressure at the end of any section is less than the user-specified discharge pressure, it is not necessary to do the calculations for the next section.

5

If the pressure at the end of the pressure relief system is within tolerance of the user-specified discharge pressure, increment time and go to Step 1. Otherwise, calculate a new guess for the flow through the relief system and go to Step 4.

6

Given the flow at any time, check where the choke point is. If the choke point is not at the pressure relief valve, the system is unacceptable. Check if any applicable codes are violated. If so, the system is unacceptable.

Flow Equations

The next sections describe pipe flow and nozzle flow equations.

Pipe Flow

This is the general differential equation for flow through a constant diameter pipe:



 

υ dp +G d2 υ υ +f  4



υ2   Φ  dL +g sin dL 2D 

=0

(1)

Where:

υ

=

Specific volume of stream

p

=

Static (flowing) pressure of stream

G

=

Mass flow rate per unit area

f

=

Friction factor

D

=

Inside diameter of pipe

L

=

Equivalent pipe length

g

=

Acceleration due to gravity

sin Φ

=

Vertical rise/equivalent pipe length

Φ represents the physical angle of the pipe with respect to the horizontal only if the equivalent pipe length is the same as the physical flow path length (that is, only pipe, no fittings or other resistances). The potential energy term in the equation assumes that the vertical elevation is distributed evenly along the entire equivalent length.



•

10-19

For example, you have only a single 20 meter length of pipe that rises a total of six meters, then sin Φ =

6 20

= 0.3

If the same system also includes a fitting resistance of 5 equivalent meters, then: sin Φ =

6 20 + 5

= 0.24

Equation (1) applies to any flow system (all vapor, non-flashing liquid, flashing two-phase, non-flashing two-phase, etc.). All that is needed to solve the equation is the proper relationship between the pressure (p) and the stream specific volume (υ ). This relationship is determined by the type of constraint chosen. For adiabatic flow, the defining equation is:

H + KE

+ PE = CONSTANT

Where:

H

=

Stream enthalpy

KE

=

Kinetic energy of stream

PE

=

Potential energy of stream

Between points 1 and 2:

H11+ KE+

PE = 1+ H+2

KE 2

PE 2

Thus:

H2

= H1 − ∆KE − ∆PE

Aspen Plus flash routines can be used to calculate enthalpy at point 2.

Nozzle Flow

Aspen Plus calculates nozzle flow by treating the flow as adiabatic through a perfect nozzle which has no friction losses and is short enough so that any potential energy effects can be neglected. The actual flow is then calculated by applying a correction factor (the flow coefficient, Cd) to the flow calculated as if the nozzle behaved as perfect. Frictionless flow is described by:

udu +υdp

=0

(2)

Where:

u υ

10-20

•


= =

Stream linear velocity Specify volume of stream


For adiabatic flow:

  u2 +PV + + PE  = 0  2 

d U

Where:

U

=

Internal energy

PV

=

Pressure-volume product

Neglecting PE, and combining the definition of enthalpy (H = U + PV) into this equation gives: dH + udu = 0

(3)

Combining (2) and (3) gives:

dH =υdp

(4)

By definition:

dH =Tds

+ υdp

(5)

(4) and (5) yield:

Tds = 0 or

ds = 0 Thus, adiabatic frictionless flow is isentropic. The flow equation (2) can be integrated to describe the flow through a perfect nozzle as follows: Let p0 = The upstream stagnation pressure where the velocity is zero (u0 = 0). Let p1 = The pressure in the nozzle throat at which the flow is accelerated to velocityu. Thus, the integrated form of (2) becomes:

1 2 u 2

p1

= − ∫ υ dp p01

which can be re-written (noting thatu = Gυ ): (6)

p1

Gv2

2 1

= −2dp ∫υ p0

Equation (6) provides the means to calculate the flow rate through a perfect nozzle given the upstream stagnation pressure and the proper p-v relationship (which is isentropic). As one integrates (6)



•

10-21

from p0 to p1, a maximum G indicates that the flow has become choked at the current value ofp. (6) also serves as a method for converting between stagnation and static pressures at any point in the flow system (pipe or nozzle).

Calculation and Convergence Methods

Aspen Plus uses the same equations used to model the safety relief valve as to model the conversion from stagnation to flowing pressure and back again. To be completely accurate, the valve should be modeled as in equation (6) in the Nozzle Flow section. This model requires that constant entropy flashes be performed at each point in the integration of equation (6). This is a very time consuming calculation, so several options are provided to speed up the calculations. First, you can choose to do constant enthalpy flashes rather than constant entropy flashes through the nozzle. This speeds up the calculations by an order of magnitude, since the constant entropy flash is modeled by a series of constant enthalpy flashes converging on entropy. Aspen Plus also provides a shortcut method to calculate molar volume as a function of pressure during the nozzle integration. This method was developed by L. L. Simpson and gives very good results. Instead of doing a flash calculation to calculate the molar volume at each point in the integration, two flashes are done at the start and parameters are calculated which allow you to calculate the molar volume at other pressures without doing flashes. Reference

Simpson, L.L., "Estimate Two-Phase Flow in Safety Devices",

Vessel Insulation Credit Factor

Chemical Engineering, August, 1991, pp. 98-102. When Fire Standard API-520 or API-2000 is used, you may claim an insulation credit factor calculated from the formula: F

=

k (1660 − Tf ) 21000t

Where:

k

T

=

Thermal conductivity of insulation, in British thermal units per hour per square foot per degree Fahrenheit per inch at mean temperature.

=

Temperature of vessel contents at relieving conditions, in degrees Fahrenheit.

=

Thickness of insulation, in inches.

Assuming a k value of 4.0, and T f of 0.0, the following table, which was taken from API-2000, gives values ofF for various values of insulation thickness:

10-22

•



Insulationthickness(t)

F Factor

6 inches(152 millimeters)

0.05

8 inches (203 millimeters)

0.037

10 inches (254 millimeters)

0.03

12 inches (305 millimeters) or more

Additional Reading

0.025

"Sizing, Selection, and Installation Of Pressure-Relieving Devices in Refineries" Part I - Sizing and Selection, API Recommended Practice 520, American Petroleum Institute, 1220 L Street Northwest, Washington, D.C. 20005. "Venting Atmospheric and Low Pressure Storage Tanks", (Nonrefrigerated and Refrigerated), API Standard 2000, American Petroleum Institute, 1220 L Street Northwest, Washington, D.C. 20005.



•

10-23

10-24

•



A P P EN D IX A

Advanced Distillation Features

This appendix contains information applicable to several of the distillation column models in Aspen Plus. The topics are:

• •

Sizing and Rating for Trays and Packing Column Targeting

A s pe n P l u s 1 1 . 1 Un i t O pe r a t i o n M od e l s

A d v a nc e d D i s t i l la t i o n F e a t u r es• A-1

Sizing and Rating for Trays and Packings: Overview Aspen Plus has extensive capabilities to size, rate, and perform pressure drop calculations for trayed and packed columns. Use the following Tray/Packing forms to enter specifications:

• • • •


These capabilities are available in the following column unit operation models:

• • •

RadFrac MultiFrac PetroFrac

You can choose from the following five commonly-used tray types:

• • •

Bubble caps

••

Koch Flexitray Nutter Float Valve

Sieve ®

Glitsch Ballast

®

Aspen Plus can model a variety of random packings. You can also use any of the following types of structured packings:

• • • • • •

®

Goodloe

®

Glitsch Grid

Norton Intalox Structured Packing Sulzer BX, CY, Mellapak, and Kerapak Koch Flexipac, Flexeramic, Flexigrid Raschig Super-Pak and Ralu-Pak

For sizing and rating calculations, Aspen Plus divides a column into sections. Each section can have a different tray type, packing type, and diameter. The tray details can vary from section to section. A column can have an unlimited number of sections. In addition, you can size and rate the same section with different types of trays and packings.

A-2

•

A d v a n c e d D i s t i l l a t i on F e a t u r e s

A s p e n P l u s 1 1 .1 U n i t O p e r a t i on M od e l s

The calculations are based on vendor-recommended procedures whenever these are available. When vendor procedures are not available, well-established literature methods are used. Aspen Plus calculates sizing and performance parameters such as:

• • • •

Column diameter Flooding approach or approach to maximum capacity Downcomer backup Pressure drop

These parameters are based on: • Column loadings

• • •

Transport properties Tray geometry Packing characteristics

You can use the computed pressure drop to update the column pressure profile.

Single-Pass and Multi-Pass Trays

You can use the column models in Aspen Plus to:

• •

Size one- and two-pass trays Rate trays with up to four passes

Schematics of one-, two-, three-, and four-pass trays are shown in the next four figures. Aspen Plus performs and reports rating calculations for all panels. When specifying Weir heights, cap positioning, and number of valves: For

Specify

One-pass tray

A single value

Two-pass tray

Up to two values, one for each panels A and B

Three-pass tray

Up to three values, one for each panel (A, B and C)

Four-pass tray

Up to four values, one for each panel (A, B, C and D)

The values for the number of caps and number of valves applies for each panel. For example, two-pass trays have two A panels for tray AA, and two B panels for tray BB. Therefore, the number of caps per panel is the number of caps per tray divided by two. Similar consideration is necessary for three- and four-pass trays. If you specify only one value for multi-pass trays, that value applies to all panels.



When specifying downcomer clearance and width: For

Specify

One-pass tray

A single value for the side downcomer

Two-pass tray

Up to two values, one for the side downcomer, one for the center downcomer

Three-pass tray

Up to two values, one for the side downcomer, one for the off-center downcomer

Four-pass tray

Up to three values: one for the side downcomer, one for the center downcomer, and one for the off-center downcomer Column Diameter

th g n e L ir e W t e lt u O

DC-WTOP WEIR-HT DCWBOT

DC-HT

DC-CLEAR

A One-Pass Tray

A-4

•



Column Diameter


CTR. DC

CTR. DC

DC-WTOP

Below ~

~

DCWBOT

Panel A

WEIR-HT

Side Downcomer

DC-HT

DC-CLEAR

Tray AA

DCWTOP

Panel B Tray BB DC-HT

DCWBOT

Center Downcomer

DC-CLEAR

~

~

~

~

A Two-Pass Tray



Column Diameter OFF-CTR.DC


OFF-CTR.DC DC-WTOP

DC-WTOP

WEIR-HT DC-HT

Panel A. B. C. DCOF DC-WBOT

DCCLEAR

DC-WTOP B

A

B

A

C

Panel C. B. A.

Panel A. B. C.

A Three-Pass Tray

A-6

•



Column Diameter OFF-CTR.DC OFF-CTR.DC

th g n e L ri e W t e lt u O

SIDE DC

CTR.DC DC-WTOP

DC-WTOP

WEIR-HT DC-HT

Panel A. B. DC-WBOT

DC-WBOT DCCLEAR

D

D

C

Panel C. D.

DCOF

A

B

B

A

Panel A. B.

A Four-Pass Tray

Modes of Operation for Trays

Aspen Plus provides two modes of operation for trays:

• •

Sizing Rating

In either mode, you can divide a column into any number of sections. Each section can have a different column diameter, tray type, and tray geometry. You can re-rate or re-design the same section with different tray types and/or packings. Aspen mode, Plus performs the calculations one section at a time. sizing the column model determines tray diameter toIn satisfy the flooding approach you specified for each stage. The largest diameter is selected.



In rating mode, you specify the column section diameter and other tray details. For each stage, the column model calculates tray performance and hydraulic information such as flooding approach, downcomer backup, and pressure drop.

Flooding Calculations For bubble caps and sieve trays, Aspen Plus provides two for Trays procedures for calculating the approach to flooding. The first procedure is based on the Fair method. The second uses the Glitsch procedure for ballast trays. This procedure de-rates the calculated flooding approach by 15% for bubble caps and by 5% for sieve trays. All other hydraulic calculations are based on the Fair and Bolles methods. You can also supply your own calculation procedure: =

Specify

Ofnorm

Flooding calculation method = USER

TraySizing or TrayRating

Subroutinename

UserSubroutines

For valve trays (Glitsch Ballast, Koch Flexitray, and Nutter Float Valve trays), Aspen Plus uses procedures from vendor design bulletins. Two versions of vendor design bulletins are available for Koch Flexitray:

• •

Bulletin 960 Bulletin 960-1

You can use the Convergence form to specify which bulletin to use for all TraySizing and TrayRating sections for This a block. You can specify which bulletin to use for each section. specification overrides the block-wise specification. For valve type S, AO, and TO in the TrayRating sections, Aspen Plus always uses Bulletin 960-1 internally, regardless of the block-wise specification. For all other cases, the default is Bulletin 960. For Nutter Float Valve trays, two versions of curve fitting are provided for curves in the vendor design bulletin:

• •

Aspen90 Aspen96

Aspen96 is recommended. Use the Convergence form to specify which version to use.

A-8

•



Bubble Cap Tray Layout

RadFrac uses cap diameter only for tray type CAPS. Valid entries are: CapDiameter

DefaultWeirHeight

Inches

M illimeters

Inches

M illimeters

3

76.2

2.75

69.85

4

101.6

3.00

76.20

6

152.4

3.25

82.55

Use the cap diameter to retrieve cap characteristics based on standard cap designs. For columns with diameter

The default is

Up to 48 in (1219.2 mm).

3 in (76.2 mm)

Greater than 48 in (1219.2 mm)

4 in (101.6 mm)

The following table lists standard cap designs: M aterial Nomina Slize in,

StainlessSteel 3

4

6

Cap U.S.Standardgauge

16

16

16

OD, in

2.999

3.999

5.999

ID, in

2.875

3.875

5.875

Heightoverall,in

2.500

Number of slots

3.000

20

Type of slots

3.750

26 Trapezoidal

39 Trapezoidal

Trapezoidal

Slot width, in Bottom

0.333

0.333

Top

0.167

0.167

0.333 0.167

Slotheight,in

1.000

1.250

1.500

Heightshroudring,in

0.250

0.250

0.250

Riser U.S.Standardgauge

16

16

16

OD, in

1.999

2.624

3.999

ID, in

1.875

2.500

3.875

M aterial Nomina slize in,

StainlessSteel 3

4

6

Standard heights, in 0.5-inskirtheight

2.250

2.500

2.750

1.0-inskirtheight 1.5-inskirtheight

2.750 3.250

3.000 3.500

3.250 3.750

0.500

0.500

0.500

Riser-slotseal,in Cap areas, in



Riser

2.65

4.80

11.68

Reversal

4.18

7.55

17.80

Annular

3.35

6.38

14.55

Slot

5.00

8.12

14.64

Cap

7.07

12.60

28.30

Reversal/riser

1.58

1.57

1.52

Annular/riser

1.26

1.33

1.25

Slot/riser

1.89

1.69

1.25

Slot/cap

0.71

0.65

0.52

Area ratios

Pressure Drop Calculations for Trays

Normally, RadFrac, MultiFrac, and PetroFrac treat the stages you enter as equilibrium stages. You must enter overall efficiency to:

•

Convert the calculated pressure drop per tray to pressure drop per equilibrium stage

•

Compute the column pressure drop

If you do not enter overall efficiency, these models assume 100% efficiency. If you specify Murphree or vaporization efficiency, you should not enter overall efficiency. RadFrac, MultiFrac, and PetroFrac will treat the stages as actual trays.

Foaming Calculations Suggested values for Ballast trays are: for Trays Service SystemFoamingFactor Non-foamingsystems

1.00

Fluorinesystems Moderate foamers, such as oil absorbers, amine, and glycol regenerators

0.90 0.85

Heavy foamers, such as amine and glycol absorbers

0.73

Severe foamers, such as MEK units

0.60

Foam stable systems, such as caustic regenerators

0.30

Suggested values for Flexitrays are: Service

SystemFoamingFactor

Depropanizers

0.85-0.95

Absorbers

A-10

•

0.85

Vacuumtowers

0.85

Amineregenerators

0.85

Aminecontactors

0.70-0.80

High pressure deethanizers

0.75-0.80

Glycolcontactors

0.70-0.75


A s p e n P l u s 1 1 .1 U n i t O p e r a t ion M od e l s

Suggested values for Float valve trays are: Service

Packed Columns

SystemFoamingFactor

Non foaming

1.00

Low foaming

0.90

Moderatefoaming

0.75

High foaming

0.60

The calculations for packings are based on the height equivalent of a theoretical plate (HETP). HETP=packed height/number of stages. The HETP is required. You can provide it using one of the following methods: • Enter it directly on the PackSizing or PackRating forms

• Packing Types and Packing Factors

Enter the packing height on the same form

Aspen Plus can handle a wide variety of packing types, including different sizes and materials from various vendors. For random packings, the calculations require packing factors. Aspen Plus stores packing factors for the various sizes, materials, and vendors allowed in a databank. If you provide the following information, Aspen Plus retrieves these packing factors automatically for calculations:

• • •

Packing type Size Material

You may specify the vendor on the PackSizing or PackRating form. Is the vendor specified?

Aspen Plus uses

Yes

The packing factor published by the vendor

No

A value compiled from various literature sources

You can enter the packing factor directly to override the built-in values. Aspen Plus uses the packing type to select the proper calculation procedure. Literature Sources

Fair, J.R., et al., "Liquid-Gas Systems,"Perry’s Chemical Engineers’ Handbook, R.H. Perry and D. Green, ed., 6th ed. (New York: McGraw Hill, 1984).

Tower Packings, Bulletin No. 15 (Tokyo: Tokyo Special Wire Netting Company).


Ad v a n c e d D i s t i l l a t i o n F e a t u r es• A-11

Modes of Operation for Packing

The column models have two modes of operation for packing:

• •

Sizing Rating

In either mode, you can divide a column into any number of sections. Each section can have different packings. You can re-rate or re-design the same section with different packings and/or tray types. Aspen Plus performs the calculations one section at a time. In sizing mode, Aspen Plus determines the column section diameter from:

• •

The approach to the maximum capacity A design capacity factor you specify

You can impose a maximum pressure drop per unit height (of packing or per section) as an additional constraint. Once Aspen Plus has determined the column section diameter, it re-rates the stages in the section with the calculated diameter. In rating mode, you specify the column diameter. Aspen Plus calculates the approach to maximum capacity and pressure drop.

Maximum Capacity Calculations for Packing

Aspen Plus provides several methods for maximum capacity calculations. For random packings you can use: Method

Forthistypeofpackings

Mass Transfer, Ltd. (MTL) 1

MTL

Norton 2

Norton IMTP

3

Koch 4 Raschig

Koch Raschig

Eckert

Allotherrandompackings

For structured packings, Aspen Plus provides vendor procedures for each type. If you specify the maximum capacity factor, Aspen Plus bypasses the maximum capacity calculations. The definition of approach to maximum capacity depends on the type of packings. For Norton IMTP and Intalox structured packings, approach to maximum capacity refers to the fractional approach to the maximum efficient capacity. Efficient capacity is the operating point at which efficiency of the packing deteriorates due to liquid entrainment. The efficient capacity is approximately 10 to 20% below the flood point. For Sulzertostructured Kerapak, andapproach Mellapak), approach maximumpackings capacity(BX, refersCY, to the fractional to maximum capacity. Maximum capacity is the operating point at which a pressure drop of 12 mbar/m (1.47 in-water/ft) of packing

A-12

•



is obtained. At this condition, stable operation is possible, but the gas load is higher than that at which maximum separation efficiency is achieved. The gas load corresponding to the maximum capacity is 5 to 10% below the flood point. Sulzer recommends a usual design range between 0.5 and 0.8 for approach to flooding. For Raschig random and structured packings, approach to maximum capacity refers to the fractional approach to maximum capacity. Maximum capacity is at the loading point. For all other packings, approach to maximum capacity refers to the fractional approach to the flood point. Because there are different definitions for approach to maximum capacity, sizing results are not on the same basis for packings from different vendors, even when you use the same value for approach to maximum capacity. Direct performance comparison of packings from different vendors is not recommended. The capacity factor is:

CS = VS

ρV ρL

− ρV

Where: CS

=

Capacity factor

VS

=

Superficial velocity of vapor to packing

ρV

=

Density of vapor to packing

ρL

=

Density of liquid from packing

References

1

Cascade Mini-Ring Design Manual(Tokyo: Dodwell & Company, Ltd., 1984).

2

Intalox High-Performance Separation Systems, Bulletin IHP-1 (Akron: Norton Company, 1987).

3

McNulty, K.J., "Hydraulic Model for Packed Tower Design." Paper presented at the American Institute of Chemical Engineers Spring Meeting in Houston, 1993.

4

Billet, R., and Schultes, M., "Modeling of Packed Tower Performance for Rectification, Absorption and Desorption in rd the Total Capacity Range." Paper presented at the 3 KoreaJapan Symposium On Sep. Tech., October 25-27, 1993 in Seoul, Korea.



Pressure Drop Calculations for Packing

For random packings, Aspen Plus provides several built-in methods to compute the pressure drop. Vendor

Pressure drop method

MTL

Vendor 1

Norton

Vendor procedure

2,3,4

Koch

Vendorprocedure

5

Raschig

Vendor procedure

6

Not specified

Eckert GPDC 7, Norton GPDC 2,3,4, Prahl GPDC 8, Tsai 9 GPDC

If you specify the vendor, Aspen Plus uses the vendor procedure. If you do not specify the vendor, you can choose one of four different pressure drop methods. If you do not specify a method, Aspen Plus uses the Eckert generalized pressure drop correlation (GPDC). For structured packings, vendor pressure drop correlations are available for all packings: Packingtype

Pressuredropmethod

Goodloe

Vendorprocedure

10 11

GlitschGrid

Vendorprocedure

Norton Intalox Structured Packings

Vendor procedure

12

Sulzer BX, CY, Mellapak, and Kerapak

Vendor procedure

13

Super-PakandRalu-Pak

Vendorprocedure

Koch Flexipac, Flexeramic, and Flexigrid

Vendor procedure

6 14

References

1

Cascade Mini-Ring Design Manual(Tokyo: Dodwell & Company, Ltd., 1984).

2

Dolan, M.J. and Strigle, R.F., "Advances in Distillation Column Design," CEP, Vol.76, No.11 (November 1980), pp. 78-83.

3

Intalox High-Performance Separation Systems, Bulletin IHP-1 (Akron: Norton Company, 1987).

4

Intalox Metal Tower Packing, Bulletin IM82 (Akron: Norton Company, 1979).

5

McNulty, K.J., "Hydraulic Model for Packed Tower Design." Paper presented at the American Institute of Chemical Engineers Spring Meeting in Houston, 1993.

6

Billet, R., and Schultes, M., "Modeling of Packed Tower Performance for Rectification, Absorption and Desorption in rd

the Total Capacity On Range" as the 3 KoreaJapan Symposium Sep. Paper Tech.,presented October 25-27, 1993 in Seoul, Korea.

A-14

•



7

Fair, J.R. et al., "Liquid-Gas Systems," Perry’s Chemical Engineers’ Handbook, R.H. Perry and D. Green, ed., 6th ed. (New York: McGraw Hill, 1984), pp. 18-22.

8

McNulty, K.J. and Hsieh, C.L., "Hydraulic Performance and Efficiency of Koch Flexipac Structured Packings." Paper presented at American Institute of Chemical Engineers Annual Meeting in Los Angeles, 1982.

9

Tsai, T.C., "Packed Tower Program Has Special Features,"Oil and Gas Journal, Vol. 83 No. 35 (September, 1985), p. 77.

10

Goodloe, Bulletin 520A (Dallas: Glitsch, Inc., 1981). 11 Glitsch Grid-Grid/Ring Combination Bed, Bulletin No. 7070 (Dallas: Glitsch, Inc., 1978). 12 Norton Company, private communication, 1992. 13 Spiegel, L. and Meier, W., "Correlations of the Performance Characteristics of the Various Mellapak Types." Paper presented at the 4th International Symposium of Distillation and Absorption, Brighton, England, 1987. 14 McNulty, K.J., "Hydraulic Model for Packed Tower Design." Paper presented at the American Institute of Chemical Engineers Spring Meeting in Houston, 1993.

Liquid Holdup Calculations for Packing

Aspen Plus performs liquid holdup calculations for both random and structured packings. For Raschig packings, Aspen Plus uses the vendor procedure is used. The required parameters are void fraction and surface area. If you do not provide these parameters, Aspen Plus will retrieve them from the built-in databank. For other packings, Aspen Plus uses the Stichlmair correlation. The Stichlmair correlation requires these parameters:

• •

Packing void fraction and surface area Three Stichlmair correlation constants

When Stichlmair correlation is used, Aspen Plus provides these parameters for a variety of packings in the built-in packing databank. If these parameters are missing for a particular packing, Aspen Plus will not perform liquid holdup calculations for that packing. You can also enter these parameters to provide missing values, or to override the databank values.

Pressure Profile Update

You can update the pressure profile using:

• •

Computed pressure drops for the rating mode of both trays and packings The sizing mode of packings



If you choose to update the pressure profile, the column models solve the tray or packing calculation procedures simultaneously with the column-describing equations. For updating the pressure profile during calculations check Update Section Pressure Profile on the following forms:

• • •

TrayRating PackSizing PackRating

Also, you can fix the pressure at the top or bottom of the column and you can specify this option on the above forms. The stage pressures become additional variables. Aspen Plus uses the pressure specifications given on the Pres-Profile form to:

• • Physical Property Data Requirements

Initialize the column pressure profile Fix the pressure drop of stages for which the pressure profile is not updated

Several physical properties that are not normally used for heat and material balance calculations are required for column sizing and rating. These properties are:

• • •

Liquid and vapor densities Liquid surface tension Liquid and vapor viscosities

The physical property method that you specify for a unit operation model must be able to provide the required properties. In addition, the physical property parameters needed to calculate the required properties must be available for all components in the column. See the descriptions of properties in the Aspen Plus User Guide, Chapter 8, for details on specifying physical property methods and determining property parameter requirements.

References

Fair, J.R., et al., "Liquid-Gas Systems,"Perry’s Chemical th Engineers’ Handbook, R.H. Perry and D. Green, ed. 6 ed., New York: McGraw Hill, 1984. rd

Ballast Tray Design Manual, Glitsch, Inc. Bulletin No. 4900, 3 ed. Dallas, 1980. Smith, B.D., "Tray Hydraulics: Bubble Cap Trays" and "Tray Hydraulics: Perforated Trays,"Design of Equilibrium Stage Processes, New York: McGraw Hill, 1963, pp. 474-569.

Koch Flexitray Design Manual, Koch Engineering Co., Inc. Bulletin No. 90, Wichita. rd Ballast Tray Design Manual, Glitsch, Inc. Bulletin No. 4900, 3 ed. Dallas, 1980.

A-16

•



Koch Flexitray Design Manual, Koch Engineering Co., Inc. Bulletin No. 90, Wichita. Nutter Float Valve Design Manual, Tulsa: Nutter Engineering Co., 1976. Stichlmair, J., et al., "General Model for Prediction of Pressure Drop and Capacity of Countercurrent Gas/Liquid Packed Columns," Gas Separation and Purification, Vol. 3 (1989), p. 22.



Column Targeting The Aspen Plus Column Targeting tool offers capabilities for thermal and hydraulic analysis of distillation columns. During design or retrofit analysis of a process, these capabilities can be exploited to identify the targets for appropriate column modifications in order to:

•

Reduce utilities cost

• • •

Improve energy efficiency Reduce capital investment (by improved driving forces) Facilitate column debottlenecking

These capabilities are available for the following distillation column models:

• • • Column Targeting Thermal Analysis

RadFrac MultiFrac PetroFrac

The thermal analysis capability is useful in identifying design targets for improvements in energy consumption and efficiency. This capability is based on the concept of minimum thermodynamic condition for a distillation column. The minimum thermodynamic condition pertains to thermodynamically reversible column operation. In this condition, a distillation column would operate at minimum reflux, with an infinite number of stages, and with heaters and coolers placed at each stage with appropriate heat loads for the operating and equilibrium lines to coincide. In other words, the reboiling and condensing loads are distributed over the temperature range of operation of the column. The stage-enthalpy (Stage-H) or temperature-enthalpy (T-H) profiles for such a column therefore represent the theoretical minimum heating and cooling requirements in the temperature range of separation. These profiles are called the Column Grand Composite Curves (CGCCs). The Aspen Plus Column Targeting tool generates the CGCCs based on the Practical Near-Minimum Thermodynamic Condition (PNMTC) approximation (Dhole and Linnhoff). The enthalpies used in plotting the CGCCs are calculated at a given stage of the column by assuming that the equilibrium and operating lines coincide at this stage. This approximation takes into account the losses or inefficiencies introduced through practicalities of column design (such as pressure drops, multiple side-products, side strippers, etc.), while preserving the meaning of the CGCC. The equations for equilibrium and operating lines are solved simultaneously at each stage for designated light key and heavy

A-18

•



key components. The Aspen Plus Column Targeting tool has a built-in capability to select light key and heavy key components for each stage of the column. The CGCCs are helpful in identifying the targets for potential column modifications. These modifications include:

• • • •

Feed location Reflux ratio modifications Feed conditioning (heating or cooling) Side condensing or reboiling

An additional capability is provided through exergy analysis. The exergy profiles are plotted by calculating the exergy loss at each stage of the column, taking into account all entering and leaving material and heat streams. In general, the exergy loss profiles can be used as a tool to examine the degradation of potential work availability (irreversibility) in a distillation column due to:

• • • Column Targeting Hydraulic Analysis

Momentum loss (pressure driving force) Thermal loss (temperature driving force) Chemical potential loss (mass transfer driving force)

The hydraulic analysis capability is useful in understanding how the vapor and liquid flow rates in a distillation column compare with the minimum (corresponding to the PNMTC) and maximum (corresponding to flooding) limits. For packed and tray columns, jet flooding controls the calculation of vapor flooding limits. For tray columns, parameters such as downcomer backup control the liquid flooding limits. Hydraulic analysis can be used to identify and eliminate column bottlenecks.

Specifications for Column Targeting and Hydraulic Analysis

For RadFrac, MultiFrac, and PetroFrac, the column targeting thermal and hydraulic analysis capabilities can be activated by using the corresponding option buttons on the Report Property Options forms. Method for selecting light and heavy key components for the PNMTC calculations has to be specified. The component K-values based method is used as default. To calculate the maximum vapor and liquid flow rates due to flooding, you must specify tray or packing rating information for the entire column. In addition, you can specify allowable flooding factors (as fraction of total flooding) for flooding limit calculations. The allowable limit for vapor flooding can be specified on the TrayRating | Design/Pdrop or PackRating | Design/Pdrop sheets. The allowable limit for liquid flooding (due to downcomer backup) can be specified on theTrayRating | Downcomers sheet. The default values are 85% for the vapor



flooding limit and 50% for the liquid flooding limit. The liquid flooding limit specification is available only if the downcomer geometry is specified.

Selection of Key Components

Results of the column targeting analysis depend strongly on the selection of light key and heavy key components. The Aspen Plus Column Targeting tool provides the following four methods for judicious selection of these key components: M ethod

UseWhen

User defined

Allows you to specify the light key and heavy key

Based on component splitfractions

components. Selects the light key and heavy key components on the basis of component split-fractions in column product streams. This method is best suited for sharp or near-sharp splits.

Based on component Kvalues

Selects the light key and heavy key components on the basis of component K-values. This method is best suited for sloppy splits.

Based on column composition profiles

Selects the light and heavy key components on the basis of composition profiles. In principle, this method is similar to the K-value based method. It is best suited for sloppy splits and it is, in general, inferior to the K-value based method.

These methods can be chosen for the distillation models on the following sheets: M odel

For m

RadFrac

Report Targeting Options

MultiFrac

Columns Report Targeting Options

PetroFrac

Report Targeting Options Strippers Report Targeting Options

The associated parameters for each method can be chosen on the following sheets: M odel

For m

RadFrac

Report Targeting Specifications

MultiFrac

Columns Report Targeting Specifications

PetroFrac

Report Targeting Specifications Strippers Report Targeting Specifications

Selection of Key Components: User Defined

A-20

•

This method allows the user to define column sections and light key and heavy key components for each section. If the sections defined do not cover the entire column, extrapolations are used. If the selection of key components is inconsistent with the separation in the column, the column targeting calculations are skipped. In



both cases, appropriate warning messages are written to the control panel and to the history file. We highly recommend that you run the simulation and inspect the column split-fractions, composition profiles, and component Kvalues before using this method to designate key components.

Selection of Key Components Based on Component SplitFractions

In this method the column is divided into sections bounded by its product streams. For each section, the key components are selected based on the component split-fractions in its bounding product streams as: Component MoleFraction

Component Split Fraction

Designation

In the section bottomproduct > Composition tolerance

In the section top-product > Minimum split-fraction

Light key

In the section topproduct > Composition tolerance

In the section bottomproduct > Minimum splitfraction

Heavy key

If there is more than one light key component for a column section, the heaviest of these components is selected as the light key. Similarly, in case of multiple heavy keys for a column section, the lightest is selected as the heavy key. These selections are made based on the component K-values. If light key and/or heavy key components cannot be selected for a column section, appropriate extrapolations are used. If these extrapolations do not produce a meaningful selection, column targeting calculations are skipped. In both cases, appropriate warnings are written to the control panel and to the history file. The default values for the parameters used in this method are: Parameter

DefaultValue

Minimumsplit-fraction

0.9

Compositiontolerance

1e-6

K-valuetolerance

1e-5

These parameters can be manipulated to adjust the key selection. This method also allows for components to be excluded from key selection throughout the entire column. This method should be used for columns with sharp or near-sharp splits. Therefore, we highly recommend that you run the simulation and inspect the column split-fractions and composition profiles before choosing this method and adjusting its parameters.



Selection of Key Components Based on Component K-Values

In this method key components are selected based on their Kvalues on each stage as: Component MoleFraction

Component K- value

Designation

> Composition tolerance

> 1+K-value tolerance

Light key

> Composition tolerance

< 1-K-value tolerance

Heavy key

If light key and/or heavy key components cannot be selected for a stage, the components selected for the stage above are used. If these extrapolations do not represent a meaningful selection, column targeting calculations are skipped. In both cases, appropriate warnings are written to the control panel and to the history file. The default values for the parameters used in this method are: Parameter

DefaultValue

Compositiontolerance

1e-6

K-valuetolerance

1e-5

These parameters can be manipulated to adjust the key selection. This method also allows for components to be excluded from key selection throughout the entire column. Note that to represent the separation on each column stage, this method selects a group of components as light key and another group of components as heavy key. It is therefore, most suited for columns with sloppy splits. It is also the default key selection method.

Selection of Key Components Based on Column Composition Profiles

This method is similar to the K-value based method except that the component composition profiles in the column are used instead of their K-values. You can specify the composition tolerance and the stage span (the number of stages above and below the current stage that are used to evaluate the composition profile). The default values of these parameters are: Parameter

DefaultValue

Compositiontolerance Stage span

1e-6 2

These parameters can be manipulated to adjust the key-selection. This method also allows for components to be excluded from key selection throughout the entire column. If light key and/or heavy key components cannot be selected for a stage, the components selected for the stage above are used. If these extrapolations do not represent a meaningful selection,

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•



column targeting calculations are skipped. In both cases, appropriate warnings are written to the control panel and to the history file. This method is also suited for sloppy splits and may be used instead of the K-value based method.

Using Column Targeting Results

The column targeting results can be viewed on the following sheets for the three distillation column models: M odel

RadFrac

For m

Profiles Key Components Profiles Thermal Analysis Profiles Hydraulic Analysis

MultiFrac

Columns Profiles Key Components Columns Profiles Thermal Analysis Columns Profiles Hydraulic Analysis

PetroFrac

Profiles Key Components Profiles Thermal Analysis Profiles Hydraulic Analysis Strippers Profiles Key Components Strippers Profiles Thermal Analysis Strippers Profiles Hydraulic Analysis

The CGCCs, the exergy loss profile, and the hydraulic analysis profiles can be plotted using the PlotWizard. The thermal analysis results provide a practical approach to identifying and implementing potential modifications to the column design. The following order of review for column modifications, based on inspection of the CGCCs, is recommended: 1

Feed location (appropriate placement)

2

Reflux ratio modification (reflux ratio vs. number of stages)

3

Feed conditioning (heating or cooling)

4

Side condensing or reboiling

Let us briefly discuss each modification with the help of a distillation column that separates a mixture of n-heptane and noctane from heavier hydrocarbons (n-nonane, n-decane, and npentadecane).



Parameter

No.ofstages

Design1

15

Refluxratio

7.668

Feedlocation

3

Feed temperature

100 C

Condenser duty

-28.30 MW

Condenser temperature

141.03 C

Reboilerduty

41.00MW

Reboiler temperature

205.61 C

Side condenser duty

–

Side condenser temperature

–

Side reboiler duty

–

Side reboiler temperature

–

The design parameters of importance for the base case design (Design 1) of this column are summarized below:

• • • • Feed Location

Feed Location Reflux Ratio Modification Feed Conditioning Side Condensing or Reboiling

Inspection of the CGCC can identify any anomalies or distortions due to inappropriate feed placement. Normally, such distortions will be apparent as significant projections at the feed location (pinch point) on the Stage-H CGCC. This is due to a need for extra local reflux to compensate for the inappropriate feed placement. A feed introduced too high up in the column will show a sharp enthalpy change on the condenser side on the Stage-H CGCC and should be moved down. Similarly, a feed introduced too low in the column will show a sharp enthalpy change on the reboiler side on the Stage-H CGCC and should be moved up the column. A correctly placed feed not only removes the distortions in the Stage-H CGCC but also results in reduced condenser and reboiler duties. The Stage-H CGCC for Design 1 of our distillation column is shown in the following figure. It clearly shows a distortion on the condenser side at the pinch point (stages 2 and 3). Therefore, the feed must be moved down the column. The figure also shows the CGCC for Design 2, where the feed is moved down to stage 7.

A-24

•



Comparison of the design parameters also reveals a slight reduction in the condenser and reboiler duties. Parameter

No. of stages

Design1

15

Refluxratio Feed location

Design2

15 7.668

3

7.668 7

Feedtemperature

100C

Condenserduty

-28.30MW

-28.02MW


141.03C

140.58C

Reboilerduty

41.00MW

40.74MW


205.61 C

205.91 C

Side condenser duty

–

–


–

–

Side reboiler duty

–

–


–

–


100C


Reflux Ratio Modification

The horizontal gap between the T-H CGCC pinch point and the ordinate represents the scope for reduction in heat duties through reduction in reflux ratio. As the reflux ratio is reduced (while increasing the number of stages to preserve the separation), the CGCC will move towards the ordinate, thus reducing both the condenser and reboiler loads. The T-H CGCC for Design 2 of our distillation column is shown in the following figure. This figure also identifies the scope for reduction in condenser and reboiler duties by reducing the reflux ratio.

It must be noted that, as the reflux ratio is reduced, the number of stages required to achieve the desired separation increases. In order to make a judicious choice for the reflux ratio, the increase in the capital cost due to the increase in the number of stages should be traded-off against the savings in the operating costs due to reduced condenser and reboiler loads. For our distillation column, if we reduce the reflux ratio to 1.227 (Design 3), we have to use 30 stages to preserve the separation. The T-H CGCC for Design 3 is shown in the following figure:

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•



Comparison of the design parameters for Design 2 and Design 3 reveals the energy savings achieved by reducing the reflux: Parameter

No. of stages

Design2

15

Refluxratio Feed location

Design3

30 7.668

7

1.227 14

Feedtemperature

100C

Condenserduty

-28.02MW

100C -4.48MW


140.58C

140.58C

Reboilerduty

40.74MW

17.20MW


205.91 C

205.91 C

Side condenser duty

–

–


–

–

Side reboiler duty

–

–


–

–



Feed Conditioning

Scope for adjustment of feed quality can be identified from sharp enthalpy changes on the Stage-H or T-H CGCC. A feed that is excessively sub-cooled will show a sharp enthalpy change on the reboiler side of the CGCC. The extent of this change determines the approximate feed heating duty required. Similar arguments also apply for feed cooling. Changes in the heat duty of feed pre-heaters or pre-coolers will lead to similar duty changes in the column reboiler or condeser loads, respectively. The Stage-H CGCC for Design 3 of our distillation column is shown in the following figure. The enthalpy change the reboiler side is noticeably sharper. Therefore, our design canon benefit from addition of a feed pre-heater.

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•



Design 4 adds a feed pre-heater with a duty of 2.34 MW. The comparison of the design parameters for Design 3 and Design 4 is shown in the following table: Parameter

No. of stages

Design3

30

Design4

30

Refluxratio

1.227

1.227

Feed location

14

14

Feedtemperature

100C

123.19C

Condenserduty

-4.48MW

-4.50MW


140.58C

140.80C

Reboilerduty

17.20MW

14.87MW


205.91 C

205.73 C

Side condenser duty

–

–


–

–

Side reboiler duty

–

–


–

–

Note that feed preheating not only reduces the reboiler duty but also reduces the temperature levels at which the hot utility (for the reboiler and for the pre-heating the feed) needs to be supplied.

Side Condensing or

Feed conditioning is normally preferred to side condensing or side

Reboiling

reboiling, as such modifications are external to the column and potentially at a more convenient temperature level. The scope for side condensing or side reboiling can be identified from the area beneath or above the CGCC pinch point (area between the ideal and actual enthalpy profiles). If a significant area exists, say below the pinch, a side-condenser can be placed at an appropriate temperature level. This allows heat removal from the column using a cheaper cold utility. A similar converse argument applies to scope for placing a side reboiler.



The T-H CGCC for Design 4 is as shown below:

As shown by the red lines, we can reduce the area on the reboiler side of the CGCC by using a side reboiler at stage 22 with a duty of about 6.5 MW (Design 5). The T-H CGCC for Design 5 is shown in the following figure:

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•



The following table shows the comparison of design parameters for Design 4 and Design 5: Parameter

No. of stages

Design4

30

Design5

30

Refluxratio

1.227

1.227

Feed location

14

14

Feedtemperature

123.19C

123.19C

Condenserduty

-4.50MW

-4.50MW


140.80C

140.91C

Reboilerduty

14.87MW

8.37MW


205.73 C

Side condenser duty

–

–


–

–

Side reboiler duty Side reboiler temperature

– –

6.5 MW 184.49 C


205.64 C


Note that, the addition of the side reboiler, not only reduces the main reboiler duty but also reduces the temperature levels at which the hot utility (for the main reboiler and for the side reboiler) needs to be supplied. Exergy analysis provides a supplementary tool in identifying the above design modification targets. For example, the exergy loss profiles for Design 3 and Design 4 of our distillation column are shown below:

Note that the high exergy loss at the feed stage for Design 3 (due to the sub-cooled feed) has been reduced substantially in Design 4 by pre-heating the feed. The hydraulic analysis results show how the vapor and liquid flows in the column compare with the minimum and maximum limits. This comparison can be used separately or in conjunction with the thermal analysis results for removing possible bottlenecks in distillation columns. For example, let us consider that Design 2 of our distillation column contains single pass sieve trays of 4.25 m diameter. The

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hydraulic analysis results for vapor flow through the column are as shown:

For stages 22 to 29, the vapor flow through the column exceeds the flooding limit. This is a bottleneck, which can possibly be removed by increasing the column diameter for this bottom section of the column. Note that the sharp increase in the vapor flow at the feed stage (stage 14) is due to the liquid part of the feed at this stage. Therefore, another option to remove the bottleneck is to decrease the amount of liquid fraction of the feed to the column by preheating it. This is exactly what we did in Design 3.



The hydraulic analysis results for vapor flow through the column for Design 3 are as shown below:

Notice that feed pre-heating introduced in Design 2 not only improved the thermal efficiency of Design 2 but also eliminated the vapor flow bottleneck in Design 2. Reference

Dhole, V. R., and B. Linnhoff,“Distillation Column Targets, Computers Chem. Engng., 17, 549-560 (1993).

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Index sum-rates: 4-20, 4-24, 4-39, 4-40 Algorithms: 4-20, 4-24, 4-25, 4-26, 4-39, 4-

A

Absorbers 4-57 MultiFrac: 4-28 RadFrac: 4-9 RateFrac 4-57, 4-58 Absorbers: 4-9, 4-28 ACM Using with Aspen Plus: 9-8 ACM: 9-8 ACMUser3 flowsheet connectivity: 9-8 Overview: 9-8 specifying: 9-8 ACMUser3: 9-8 Aerotran flash specifications: 3-26 flowsheet connectivity: 3-25 overview: 3-25 physical properties: 3-26 solids: 3-26 specifying: 3-26 Aerotran: 3-25, 3-26 Air separation MultiFrac: 4-28 RadFrac: 4-21 Air separation: 4-21, 4-28 Air-cooled heat exchangers Aerotran: 3-25 Air-cooled heat exchangers: 3-25 Algorithms convergence: 4-20, 4-24, 4-25, 4-26, 4-39, 4-40, 4-53 dynamic scenario: 10-18 inside-out: 4-24, 4-40 Newton: 4-20, 4-24, 4-39, 4-40 nonideal: 4-20, 4-24 standard: 4-24, 4-39, 4-40

A s p e nP l u s1 1 . 1U n iO t p e r a t io nM o d e l s

40, 4-53, 10-18 analysis hydraulic A-18 thermal A-18 ASME method Compr: 6-9 MCompr: 6-15 ASME method: 6-9, 6-15 Aspen Custom Modeler Using with Aspen Plus: 9-8 Aspen Custom Modeler: 9-8 Azeotropic distillation RadFrac: 4-20 Azeotropic distillation: 4-20 B

Baffle geometry HeatX: 3-12 Baffle geometry: 3-12 Baghouses FabFl: 8-18 resistance coefficients: 8-20 separation efficiency: 8-21 Baghouses: 8-18, 8-20, 8-21 Ballast trays values: A-10 Ballast trays: A-10 Batch distillation BatchFrac: 4-78 Batch distillation: 4-78 Batch fractionation BatchFrac: 4-78 Batch fractionation: 4-78 Batch reactors RBatch: 5-24 Batch reactors: 5-24

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BatchFrac columns: 4-80, 4-81 flowsheet connectivity: 4-80 free-water calculations: 4-81 physical properties: 4-82 reactive distillation: 4-82 specifying: 4-80 three-phase calculations: 4-81 working with: 4-78 BatchFrac: 4-78, 4-80, 4-81, 4-82

filter cake: 8-43 filtrate flow rate: 8-44 flowsheet connectivity: 8-42 overview: 8-42 pressure drop: 8-44 rating: 8-43 separation efficiency: 8-44 sizing: 8-43 specifying: 8-43 CFuge: 8-42, 8-43, 8-44

B-JAC Aerotran interface: 3-25 Hetran interface: 3-23 B-JAC: 3-23, 3-25 Bolles method tray flooding calculations: A-8 Bolles method: A-8 Bond work index (BWI) Crusher: 8-11, 8-13 Bond work index (BWI): 8-11, 8-13 Brake horsepower Compr: 6-11 MCompr: 6-17 Brake horsepower: 6-11, 6-17 Bubble cap trays cap diameter: A-9

Chilton-Colburn RateFrac: 4-69,analogy 4-76 Chilton-Colburn analogy: 4-69, 4-76 ClChng flowsheet connectivity: 7-6 overview: 7-6 specifying: 7-6 stream class change: 7-6 ClChng: 7-6 Coal grinding: 8-14 Coal: 8-14 Column configuration RateFrac: 4-63 Column configuration: 4-63 Column Targeting A-18

Bubble cap trays: A-9

Columns 4-57,4-80, 4-584-81 BatchFrac: Distl: 4-5 DSTWU: 4-3 Extract: 4-84 MultiFrac: 4-28 operation: 4-81 packings: A-11 PetroFrac: 4-44 physical property requirements: A-16 pressure drop calculations: A-2 RadFrac: 4-9, 4-13 RateFrac 4-57 rating: A-2 SCFrac: 4-7 setup: 4-80 sizing: A-2 Columns: 4-3, 4-5, 4-7, 4-9, 4-13, 4-28, 444, 4-80, 4-81, 4-84, A-2, A-11, A-16 Component ratio

C

Cavitation index Valve model: 6-26 Cavitation index: 6-26 CCD component attributes: 8-51 flowsheet connectivity: 8-50 medium temperature: 8-52 mixing efficiency: 8-52 overview: 8-50 profiles: 8-51 pseudostreams: 8-51 specifying: 8-51 CCD: 8-50, 8-51, 8-52 Centrifuge filters CFuge: 8-42 Centrifuge filters: 8-42 CFuge

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A s p e nP l u s1 1 . 1U n iO t p e ra t io nM o d e ls

RateFrac: 4-68 Component ratio: 4-68 Component separators Sep: 2-10 Sep2: 2-12 Component separators: 2-10, 2-12 Compr ASME method: 6-9 flowsheet connectivity: 6-9 GPSA method: 6-9

Crude units: 4-7 Crusher Bond work index (BWI): 8-11, 8-13 breakage functions: 8-11 flowsheet connectivity: 8-10 Hardgrove grindability index (HGI): 8-11, 8-14 overview: 8-10 power requirement: 8-13 primary crusher: 8-12

isentropic mechanicalefficiency: efficiency:6-10 6-11 Mollier method: 6-9 net work load: 6-9 overview: 6-8 performance curves: 6-9 polytropic efficiency: 6-10 specifying: 6-9 steam pressure: 6-8 Compr: 6-8, 6-9, 6-10, 6-11 Compressors Compr: 6-8 Heater model: 3-2 MCompr: 6-13 Compressors: 3-2, 6-8, 6-13 Condensers

reduction 8-12 secondaryratios: crusher: 8-12 selection functions: 8-11 specifying: 8-11 Crusher: 8-10, 8-11, 8-12, 8-13, 8-14 Cryogenic applications RadFrac: 4-21 Cryogenic applications: 4-21 Crystallizer crystal growth rate: 8-6 crystal nucleation rate: 8-7 flowsheet connectivity: 8-3 magma recirculation: 8-5 overview: 8-3 particle size distribution (PSD): 8-8, 8-9 population balance: 8-7

PetroFrac: 4-48 RateFrac: 4-64 Condensers: 4-48, 4-64 Continuous stirred tank reactor RCSTR: 5-16 Continuous stirred tank reactor: 5-16 Convergence algorithms: 4-24, 4-39, 4-40 RateFrac: 4-69 Convergence algorithms PetroFrac: 4-53 Convergence algorithms: 4-53 Convergence: 4-24, 4-39, 4-40, 4-69 Coolers Heater model: 3-2 RadFrac: 4-15 RateFrac: 4-67 Coolers: 3-2, 4-15, 4-67 Crude units SCFrac: 4-7

recirculation: 8-5 saturation calculation: 8-6 solubility: 8-5 specifying: 8-4 supersaturation: 8-6 Crystallizer: 8-3, 8-4, 8-5, 8-6, 8-7, 8-8, 8-9 Cyclone design calculations: 8-23 diameter calculation: 8-25 dimension ratios: 8-25 dimensions: 8-23, 8-27 efficiency correlations: 8-24 flowsheet connectivity: 8-22 geometry: 8-27 Leith and Licht correlation: 8-24 operating ranges: 8-24 overview: 8-22 pressure drop: 8-24 rating calculations: 8-23 separation efficiency: 8-23


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Shepherd and Lapple correlation: 8-24 solids loading correction: 8-27 specifying: 8-23 vane constant: 8-26 Cyclone: 8-22, 8-23, 8-24, 8-25, 8-26, 8-27 D

Darcy correlation Pres-Relief: 10-10 Darcy correlation: 10-10

SCFrac: 4-7 Distillation: 4-3, 4-5, 4-7, 4-9, 4-23, 4-28, 444, 4-78 Distl Edmister approach: 4-5 flowsheet connectivity: 4-5 overview: 4-5 specifying: 4-6 Distl: 4-5, 4-6 DSTWU

Decanter model flowsheet connectivity: 2-6 Gibbs free energy: 2-8 KLL coefficients: 2-8 liquid phases: 2-7 liquid-liquid distribution coefficients: 2-8 overview: 2-6 phase-splitting methods: 2-8 separation efficiencies: 2-8 solids entrainment: 2-9 specifying: 2-6, 2-7 Decanter model: 2-6, 2-7, 2-8, 2-9 Decanters CCD: 8-50 Decanter model: 2-6 Flash3: 2-4

flowsheet Gilliland'sconnectivity: method: 4-3 4-4 overview: 4-3 reflux ratio: 4-3 specifying: 4-4 Underwood's method: 4-3 Winn's method: 4-3 DSTWU: 4-3, 4-4 Dukler correlation Pres-Relief: 10-10 Dukler correlation: 10-10 Dupl 7-4 flowsheet connectivity: 7-4 overview 7-4 specifying: 7-5 Dupl: 7-4, 7-5

RadFrac: 4-15, 4-26 Decanters: 2-4, 2-6, 4-15, 4-26, 8-50 Design mode RadFrac: 4-25 RateFrac: 4-68 Design mode: 4-25, 4-68 Design specification convergence MultiFrac: 4-41 Design specification convergence: 4-41 DIERS calculations Pres-Relief: 10-17 DIERS calculations: 10-17 Distillation 4-57 batch: 4-78 Distl: 4-5 DSTWU: 4-3

Dynamic scenario algorithm Pres-Relief: 10-18 Dynamic scenario algorithm: 10-18

MultiFrac: 4-28 PetroFrac: 4-44 RadFrac: 4-9, 4-23 RateFrac 4-57

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E

Edmister approach Distl: 4-5 Edmister approach: 4-5 Efficiencies Compr: 6-10, 6-11 MCompr: 6-16, 6-17 RadFrac: 4-19 Efficiencies: 4-19, 6-10, 6-11, 6-16, 6-17 Electrostatic precipitators ESP: 8-32 Electrostatic precipitators: 8-32 Emergency relief vents (ERV) Pres-Relief: 10-15 Emergency relief vents (ERV): 10-15 EO Usage Notes for User3: 9-7


Equilibrium constants REquil: 5-10 RGibbs: 5-14 Equilibrium constants: 5-10, 5-14 Equilibrium reactors REquil: 5-9 RGibbs: 5-11 Equilibrium reactors: 5-9, 5-11 ESP flowsheet connectivity: 8-32

overview: 8-18 resistance coefficients: 8-20 separation efficiency: 8-21 specifying: 8-18 FabFl: 8-18, 8-19, 8-20, 8-21 Fabric filters FabFl: 8-18 Fabric filters: 8-18 Fair method tray flooding calculations: A-8

gas velocity: 8-33, 8-35 operating range: 8-33 overview: 8-32 particle separation: 8-33, 8-35 power requirement: 8-35 pressure drop: 8-35 separation efficiency: 8-33 specifying: 8-33 ESP: 8-32, 8-33, 8-35 Ethylene plant primary fractionators MultiFrac: 4-28 PetroFrac: 4-44 Ethylene plant primary fractionators: 4-28, 4-44 Evaporators Flash2: 2-2

Fair Feedmethod: furnacesA-8 PetroFrac: 4-48, 4-49 Feed furnaces: 4-48, 4-49 Feed stream conventions RateFrac: 4-62 Feed stream conventions: 4-62 Feed streams PetroFrac: 4-48 Feed streams: 4-48 Film coefficients HeatX: 3-9, 3-14 Film coefficients: 3-9, 3-14 Filter model filter cake characteristics: 8-46 flowsheet connectivity: 8-45

Flash3: 2-42-2, 2-4 Evaporators: Exchanger configuration HeatX: 3-10 Exchanger configuration: 3-10 Exchanger geometry HeatX: 3-4 Exchanger geometry: 3-4 Extract flowsheet connectivity: 4-85 overview: 4-84 specifying: 4-85 Extract: 4-84, 4-85

overview:drop: 8-458-46 pressure separation efficiency: 8-47 specifying: 8-45 Filter model: 8-45, 8-46, 8-47 Filters CFuge: 8-42 FabFl: 8-18 Filter model: 8-45 Filters: 8-18, 8-42, 8-45 Flanigan correlation Pres-Relief: 10-10 Flanigan correlation: 10-10 Flash tables zone analysis: 3-21 Flash tables: 3-21 Flash2 electrolytes: 2-3 flowsheet connectivity: 2-2 overview: 2-2

F

FabFl calculation options: 8-18 filtering time: 8-19 flowsheet connectivity: 8-18 operating ranges: 8-19


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solids: 2-3 specifying: 2-3 Flash2: 2-2, 2-3 Flash3 electrolytes: 2-5 flowsheet connectivity: 2-4 overview: 2-4 solids: 2-5 specifying: 2-5 streams: 2-4

General purpose valves Pres-Relief: 10-13 General purpose valves: 10-13 Gibbs free energy Decanter model: 2-8 REquil: 5-10 RGibbs: 5-11 Gibbs free energy: 2-8, 5-10, 5-11 Gilliland's correlation DSTWU: 4-3

Flash3: Flashes 2-4, 2-5 Flash2: 2-2 Flash3: 2-4 Flashes: 2-2, 2-4 Flexitrays values: A-10 Flexitrays: A-10 Float valve trays values: A-10 Float valve trays: A-10 Flowsheet Connectivity for User3: 9-6 Fractionators PetroFrac: 4-44 Fractionators: 4-44 Free-water calculations

Gilliland's correlation: Glitsch Ballast method 4-3 tray flooding calculations: A-8 Glitsch Ballast method: A-8 GPSA method Compr: 6-9 MCompr: 6-15 GPSA method: 6-9, 6-15

BatchFrac: 4-43 4-81 MultiFrac: PetroFrac: 4-55 RadFrac: 4-18 RateFrac: 4-67 Free-water calculations: 4-18, 4-43, 4-55, 467, 4-81 FSplit flowsheet connectivity: 1-5 overview: 1-5 specifying: 1-6 FSplit: 1-5, 1-6

computational structure: 3-21 Heater model: 3-2 HeatX: 3-4 Hetran: 3-23 log-mean temperature difference: 3-7, 320 MHeatX: 3-19 multistream: 3-19 zone analysis: 3-21 Heat exchangers: 3-2, 3-4, 3-7, 3-19, 3-20, 3-21, 3-23, 3-25 Heat transfer coefficient HeatX: 3-8 Heat transfer coefficient: 3-8 Heater model electrolytes: 3-3

G

Gas-solid separators Cyclone: 8-22 ESP: 8-32 FabFl: 8-18 VScrub: 8-29 Gas-solid separators: 8-18, 8-22, 8-29, 8-32

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H

Hardgrove grindability index (HGI) Crusher: 8-11, 8-14 Hardgrove grindability index (HGI): 8-11, 8-14 Heat exchangers Aerotran: 3-25

flowsheet connectivity: 3-2 overview: 3-2 solids: 3-3 specifying: 3-2, 3-3


Heater model: 3-2, 3-3 Heaters Heater model: 3-2 MultiFrac: 4-36 RadFrac: 4-15 RateFrac: 4-67 Heaters: 3-2, 4-15, 4-36, 4-67 Heat-interstaged columns MultiFrac: 4-28 Heat-interstaged columns: 4-28

physical properties: 3-24 solids: 3-24 specifying: 3-24 Hetran: 3-23, 3-24 HyCyc dimension ratios: 8-39 dimensions: 8-40 feed splitting: 8-38 flowsheet connectivity: 8-36 geometry: 8-40

HeatX baffle geometry: 3-12 electrolytes: 3-16 exchanger configuration: 3-10 exchanger geometry: 3-4 film coefficients: 3-9, 3-14 flash specifications: 3-16 flowsheet connectivity: 3-5 heat transfer coefficient: 3-8 log-mean temperature difference: 3-7 model correlations: 3-14 nozzle geometry: 3-14 option sets: 3-16 overview: 3-4 physical properties: 3-16 pressure drop calculations: 3-9, 3-14

operating overview:ranges: 8-36 8-37 particle velocity: 8-39 pressure drop correlation: 8-39 rating: 8-37 separation efficiency: 8-37 sizing: 8-37 solids separation: 8-36 specifying: 8-37 velocity correlation: 8-39 HyCyc: 8-36, 8-37, 8-38, 8-39, 8-40 hydraulic analysis A-18 Hydraulic turbines Pump model: 6-2 Hydraulic turbines: 6-2 Hydrocyclones

pressure drop: 3-12,3-4, 3-13, 3-14 rating calculations: 3-6, 3-7, 3-8 shell-side film coefficient: 3-12 solids: 3-16 specifying: 3-6 streams: 3-5 TEMA shells: 3-10 tube geometry: 3-13 tube-side film coefficient: 3-13 zone analysis: 3-4 HeatX: 3-4, 3-5, 3-6, 3-7, 3-8, 3-9, 3-10, 312, 3-13, 3-14, 3-16 HETP packings calculations: A-11 RateFrac: 4-60, 4-68 HETP: 4-60, 4-68, A-11 Hetran flash specifications: 3-24 flowsheet connectivity: 3-23 overview: 3-23

HyCyc: 8-36 8-36 Hydrocyclones:


I

Inside-out algorithms MultiFrac: 4-40 RadFrac: 4-24 Inside-out algorithms: 4-24, 4-40 Isentropic compressors Compr: 6-8, 6-10 MCompr: 6-13 Isentropic compressors: 6-8, 6-10, 6-13 Isentropic turbines Compr: 6-8 MCompr: 6-13 Isentropic turbines: 6-8, 6-13 K

Knock-out drums Decanter model: 2-6

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Flash2: 2-2 Flash3: 2-4 Knock-out drums: 2-2, 2-4, 2-6 L

Leith and Licht correlation Cyclone: 8-24 Leith and Licht correlation: 8-24 Liquid-liquid extraction Extract: 4-84 Liquid-liquid extraction: 4-84 Liquid-solid separators CFuge: 8-42 Filter model: 8-45 HyCyc: 8-36 Liquid-solid separators: 8-36, 8-42, 8-45 LNG exchanger MHeatX: 3-19 LNG exchanger: 3-19 Lockhart-Martinelli correlation Pres-Relief: 10-10 Lockhart-Martinelli correlation: 10-10 Log-mean temperature difference HeatX: 3-7 MHeatX: 3-20 Log-mean temperature difference: 3-7, 3-20 M

Manipulators 7-4 ClChng: 7-6 Dupl 7-4 Mult: 7-2 Manipulators: 7-2, 7-6 MCompr ASME method: 6-15 brake horsepower: 6-17 flow coefficient: 6-18 flowsheet connectivity: 6-14 GPSA method: 6-15 head coefficient: 6-18 isentropic efficiency: 6-16 mechanical efficiency: 6-17 Mollier method: 6-15 overview: 6-13 parasitic pressure loss: 6-17 polytropic efficiency: 6-16

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specific diameter: 6-18 specific speed: 6-17 specifying: 6-14, 6-15 MCompr: 6-13, 6-14, 6-15, 6-16, 6-17, 6-18 MHeatX computational structure: 3-21 electrolytes: 3-22 flash tables: 3-21 flowsheet connectivity: 3-19 LNG exchanger: 3-19 log-mean difference: 3-20 overview:temperature 3-19 pinch points estimation: 3-21 solids: 3-22 specifying: 3-20 zone analysis: 3-19, 3-20, 3-21 MHeatX: 3-19, 3-20, 3-21, 3-22 Mixer model flowsheet connectivity: 1-2 overview: 1-2 specifying: 1-3 Mixer model: 1-2, 1-3 Mixers Heater model: 3-2 Mixer model: 1-2 Mixers: 1-2, 3-2 Model correlations HeatX: 3-14 Model correlations: 3-14 Mollier method Compr: 6-9 MCompr: 6-15 Mollier method: 6-9, 6-15 Mult flowsheet connectivity: 7-2 overview: 7-2 specifying: 7-2 Mult: 7-2 MultiFrac algorithms: 4-40 connecting streams: 4-34 convergence algorithms: 4-39, 4-40 design mode: 4-39 design specification convergence: 4-41 efficiencies: 4-38 ethylene plant primary fractionator: 4-28


feed stream conventions: 4-33 flow rate: 4-34, 4-36, 4-39 flow ratio: 4-37 flowsheet connectivity: 4-30 free-water calculations: 4-43 heaters: 4-36 initialization methods: 4-42 Murphree efficiency: 4-38 Newton algorithm: 4-40 overview: 4-28

Newton algorithm: 4-20, 4-24, 4-40, 4-69 Nonequilibrium fractionation 4-57 RateFrac 4-57 Nozzle geometry HeatX: 3-14 Nozzle geometry: 3-14 P

Packings calculations: A-11

packings: 4-27, 4-434-42 physical properties: property methods: 4-42 rating mode: 4-39 solids: 4-43 specifying: 4-31, 4-32 stream definitions: 4-32 streams: 4-30, 4-31, 4-33, 4-34, 4-39 sum-rates algorithm: 4-40 trays: 4-27, 4-43 vaporization efficiency: 4-38 MultiFrac: 4-27, 4-28, 4-30, 4-31, 4-32, 433, 4-34, 4-36, 4-37, 4-38, 4-39, 4-40, 4-41, 4-42, 4-43 Multistage fractionation units MultiFrac: 4-28

capacity calculations: A-12 liquid holdup calculations: A-15 MultiFrac: 4-27, 4-43 PetroFrac: 4-56 pressure drop calculations: A-14 pressure profile: A-15 RateFrac: 4-64 rating: A-12 sizing: A-12 specifying: A-2 Stichlmair correlation: A-15 types: A-2, A-11, A-12 Packings: 4-27, 4-43, 4-56, 4-64, A-2, A-11, A-12, A-14, A-15 Particle separation ESP: 8-33, 8-35

Multistageefficiency fractionation units: 4-28 Murphree MultiFrac: 4-38 PetroFrac: 4-52 RadFrac: 4-19 RateFrac: 4-60, 4-68 Murphree efficiency: 4-19, 4-38, 4-52, 4-60, 4-68

Particle separation: 8-33, 8-35 PetroFrac condensers: 4-48 convergence algorithms: 4-53 design mode: 4-54 efficiencies: 4-52 ethylene plant primary fractionator: 4-44 feed furnace: 4-48, 4-49 feed streams: 4-48 flowsheet connectivity: 4-46 free-water calculations: 4-55 liquid runback: 4-51 main column: 4-47, 4-48 Murphree efficiency: 4-52 overview: 4-44 packings: 4-56

N

Napthali-Sandholm algorithm RadFrac: 4-24 Napthali-Sandholm algorithm: 4-24 Nesting RadFrac: 4-25 Nesting: 4-25 Newton algorithm MultiFrac: 4-40 RadFrac: 4-20, 4-24 RateFrac: 4-69


physical properties: 4-55 property methods: 4-55 pumparounds: 4-51 rating mode: 4-54

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reboilers: 4-48 side strippers: 4-47, 4-51 solids: 4-55 specifying: 4-48 streams: 4-46 trays: 4-56 vaporization efficiency: 4-52 PetroFrac: 4-44, 4-46, 4-47, 4-48, 4-49, 451, 4-52, 4-53, 4-54, 4-55, 4-56 Petroleum refining fractionation

two-phase correlations: 6-32 valve modeling: 6-32 Pipe model: 6-28, 6-29, 6-30, 6-31, 6-32 Pipes Pipe model: 6-28 Pipes: 6-28 Piping system Pres-Relief: 10-10 Piping system: 10-10 Plug flow reactors

MultiFrac: 4-28 PetroFrac: 4-44 Petroleum refining fractionation: 4-28, 4-44 Petroleum/petrochemical applications RadFrac: 4-20 Petroleum/petrochemical applications: 4-20 Physical properties BatchFrac: 4-82 columns: A-16 HeatX: 3-16 Physical properties: 3-16, 4-82, A-16 Physical property methods RateFrac: 4-67 Physical property methods: 4-67 Pinch points estimating: 3-21

RPlug: Plug flow5-20 reactors: 5-20 Polytropic compressors Compr: 6-8, 6-10 MCompr: 6-13 Polytropic compressors: 6-8, 6-10, 6-13 Pres-Relief 3% rule: 10-7 97% rule: 10-8 Beggs and Brill correlation: 10-10 calculation methods: 10-22 capacity runs: 10-6 code compliance: 10-6 convergence methods: 10-22 credit factors: 10-3 Darcy correlation: 10-10

Pinchmodel points: 3-21 Pipe Design-Spec convergence loop: 6-31 downstream and upstream integration: 630 erosional velocity: 6-31 fittings modeling: 6-32 flash options: 6-30 flowsheet connectivity: 6-29 fraction factor correlations: 6-32 holdup correlations: 6-32 integration direction: 6-30 liquid holdup correlations: 6-32 methane gas systems: 6-32 overview: 6-28 physical property calculations: 6-30 pressure drop calculations: 6-30 pressure specification: 6-29 specifying: 6-29 stream specification: 6-30

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data tables: 10-12, 10-13, DIERS calculations: 10-1710-14, 10-15 disengagement options: 10-17 Dukler correlation: 10-10 dynamic scenarios: 10-2, 10-6, 10-16, 1017, 10-18 fire scenario: 10-3 flow equations: 10-19 heat exchanger shell: 10-16 heat flux scenario: 10-5 insulation credit factor: 10-22 Lockhart-Martinelli correlation: 10-10 manufacturers' tables: 10-12, 10-13, 1014, 10-15 nozzle flow equation: 10-20 overview: 10-2 pipe diameters: 10-12 pipe flow equation: 10-19 pipe specifications: 10-10 reactions: 10-9

A s p e nP l u s1 1 . 1U n iO t p e ra t io nM o d e l s

relief system flow rating scenario: 10-5 relief system: 10-9 relief valve flow rating scenario: 10-5 rupture disks: 10-15 safety relief valves: 10-14 sample solution: 10-18 scenarios: 10-3 sizing rules: 10-7, 10-8 Slack correlation: 10-10 specifying: 10-2, 10-9, 10-10 spheres: 10-16 steady-state scenarios: 10-6 stop criteria: 10-17 streams: 10-6 user-specified vessel: 10-16 valve cycling: 10-15 valve types: 10-9, 10-13 vents: 10-15 vessel geometry: 10-16 vessel head types: 10-16 vessel jacket: 10-16 X% rule: 10-7 Pres-Relief: 10-2, 10-3, 10-5, 10-6, 10-7, 10-8, 10-9, 10-10, 10-12, 10-13, 10-14, 10-15, 10-16, 10-17, 10-18, 10-19, 1020, 10-22 Pressure Compr:changers 6-8 MCompr: 6-13 Pipe model: 6-28 Pump model: 6-2 Valve model: 6-19 Pressure changers: 6-2, 6-8, 6-13, 6-19, 6-28 Pressure drop calculations HeatX: 3-9, 3-14 Pressure drop calculations: 3-9, 3-14 Pressure drop models HeatX: 3-12, 3-13, 3-14 Pipe model: 6-28 Pressure drop models: 3-12, 3-13, 3-14, 6-28 Pressure relief systems Pres-Relief: 10-2 Pressure relief systems: 10-2 Pump model flow coefficient: 6-6 flowsheet connectivity: 6-3


head coefficient: 6-6 net positive suction head (NPSH): 6-4 overview: 6-2 specific speed: 6-4 specifying: 6-3 suction specific speed: 6-5 Pump model: 6-2, 6-3, 6-4, 6-5, 6-6 Pumparounds RadFrac: 4-16 Pumparounds: 4-16 Pumps Heater model: 3-2 Pump model: 6-2 Pumps: 3-2, 6-2 R

RadFrac absorbers: 4-21 air separation: 4-21 algorithms: 4-20 azeotropic distillation: 4-20 column configuration: 4-12, 4-13 convergence algorithms: 4-20, 4-24 convergence methods: 4-24, 4-25, 4-26 coolers: 4-15 decanters: 4-15, 4-26 design mode convergence: 4-25 design mode: 4-22 design specifications: 4-25 efficiencies: 4-19 feed streams: 4-12 flowsheet connectivity: 4-11 free-water calculations: 4-18 heaters: 4-15 inside-out algorithms: 4-24 kettle reboilers: 4-13 Murphree efficiency: 4-19 Napthali-Sandholm algorithm: 4-24 nested algorithm: 4-25 Newton algorithm: 4-20, 4-24 nonideal systems: 4-20 overview: 4-9 petroleum/petrochemical applications: 420 physical properties: 4-26 property methods: 4-26

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pumparounds: 4-16 rating mode: 4-21 reactive distillation: 4-23 reboilers: 4-13 salt precipitation: 4-23 simultaneous convergence: 4-26 solids handling: 4-26 specifying: 4-11, 4-12 stage numbering: 4-12 streams: 4-11 strippers: 4-21 reboilers: 4-13 thermosyphon three-phase calculations: 4-18, 4-21 two-phase calculations: 4-21 UA calculations: 4-15 vaporizaton efficiency: 4-19 RadFrac: 4-9, 4-11, 4-12, 4-13, 4-15, 4-16, 4-18, 4-19, 4-20, 4-21, 4-22, 4-23, 4-24, 4-25, 4-26 Rate-based modeling RateFrac 4-57 RateFrac: 4-60 Rate-based modeling: 4-60 RateFrac 4-57 bubble-cap tray column: 4-74 Chilton-Colburn analogy: 4-69, 4-76 column numbering: configuration: 4-63 column 4-62 component ratio: 4-68 connecting streams: 4-64 convergence: 4-69 coolers: 4-67 correlations: 4-69, 4-71 design mode: 4-68 efficiencies: 4-60, 4-68 equilibrium stages: 4-66 feed stream conventions: 4-62 flowsheet connectivity: 4-59 Fortran subroutines: 4-69 free-water calculations: 4-67 heat transfer coefficients: 4-76 heaters: 4-67 HETP: 4-60, 4-68 interfacial areas: 4-69, 4-71, 4-72, 4-74, 475

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mass transfer coefficients: 4-69, 4-71, 472, 4-74, 4-75 Murphree efficiency: 4-60, 4-68 Newton algorithm: 4-69 overview 4-57 packing specifications: 4-64 physical property method: 4-67 rate-based modeling: 4-60 rating mode: 4-67 reactions: 4-66 reactive distillation: segments: 4-62, 4-64,4-66 4-68 side duties: 4-67 sieve tray column correlations: 4-75 solution times: 4-69 specifying: 4-59, 4-62, 4-64 stream definitions: 4-62 streams: 4-59 tray column correlations: 4-74, 4-75 tray column: 4-72 tray specifications: 4-64 utility exchangers: 4-67 valve tray column: 4-72 RateFrac: 4-59, 4-60, 4-62, 4-63, 4-64, 4-66, 4-67, 4-68, 4-69, 4-71, 4-72, 4-74, 4-75, 4-76 Rating mode4-67 RateFrac: Rating mode: 4-67 RBatch batch operation: 5-28 cycle time: 5-27 flowsheet connectivity: 5-24 mass balances: 5-27 overview: 5-24 reactions: 5-26 specifying: 5-25 stop criteria: 5-27 temperature controller: 5-26 RBatch: 5-24, 5-25, 5-26, 5-27, 5-28 RCSTR flowsheet connectivity: 5-16 overview: 5-16 phase volume: 5-17 reaction kinetics: 5-17 residence time: 5-18


scaling methods: 5-18 solids reactions: 5-18 specifying: 5-17 variable scaling: 5-18 RCSTR: 5-16, 5-17, 5-18 Reactions RateFrac: 4-66 Reactions: 4-66 Reactive distillation BatchFrac: 4-82

solids: 5-15 specifying: 5-12 RGibbs: 5-11, 5-12, 5-13, 5-14, 5-15 Rigorous distillation 4-57 MultiFrac: 4-28 PetroFrac: 4-44 RadFrac: 4-9 RateFrac 4-57 Rigorous distillation: 4-9, 4-28, 4-44 Rigorous extraction

RadFrac: 4-23 Reactive distillation: 4-23, 4-82 Reactors RBatch: 5-24 RCSTR: 5-16 REquil: 5-9 RGibbs: 5-11 RPlug: 5-20 RStoic: 5-3 RYield: 5-7 Reactors: 5-3, 5-7, 5-9, 5-11, 5-16, 5-20, 524 Reboilers PetroFrac: 4-48 RadFrac: 4-13 Reboilers: 4-13, 4-48

Extract:extraction: 4-84 Rigorous 4-84 RPlug coolant: 5-22 flowsheet connectivity: 5-20 overview: 5-20 reactions: 5-23 solids: 5-23 specifying: 5-22 RPlug: 5-20, 5-22, 5-23 RStoic flowsheet connectivity: 5-3 heat of reaction: 5-4 overview: 5-3 product selectivity: 5-4, 5-5 specifying: 5-4

Relief devices 10-9 Pres-Relief: Relief devices: 10-9 REquil equilibrium constants: 5-10 flowsheet connectivity: 5-9 Gibbs free energy: 5-10 net heat duty: 5-9 overview: 5-9 solids: 5-10 specifying: 5-10 streams: 5-9 REquil: 5-9, 5-10 RGibbs chemical equilibrium: 5-13 flowsheet connectivity: 5-11 overview: 5-11 phase equilibrium: 5-12, 5-14 reactions: 5-14 restricted chemical equilibrium: 5-14

stream5-3, specifications: 5-3 RStoic: 5-4, 5-5 RYield calculation types: 5-8 flowsheet connectivity: 5-7 heat duty specification: 5-7 overview: 5-7 specifying: 5-8 yield distribution: 5-8 RYield: 5-7, 5-8


S

Salt precipitation RadFrac: 4-23 Salt precipitation: 4-23 SCFrac crude units: 4-7 flowsheet connectivity: 4-7 overview: 4-7 specifying: 4-8

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vacuum towers: 4-7 SCFrac: 4-7, 4-8 Screen flowsheet connectivity: 8-15 operating levels: 8-16 overview: 8-15 screen size correlation: 8-16 selection function: 8-16 separation efficiency: 8-17 separation strength: 8-16

SCFrac: 4-7 Shortcut distillation: 4-3, 4-5, 4-7 Simultaneous convergence RadFrac: 4-26 Simultaneous convergence: 4-26 Sizing recommendations Pres-Relief: 10-8 Sizing recommendations: 10-8 Slack correlation Pres-Relief: 10-10

specifying: 8-15 8-17 Screen: 8-15, 8-16, Sep flowsheet connectivity: 2-10 inlet pressure: 2-11 outlet stream conditions: 2-11 overview: 2-10 specifying: 2-10 Sep: 2-10, 2-11 Sep2 flowsheet connectivity: 2-12 inlet pressure: 2-13 outlet stream conditions: 2-13 overview: 2-12 specifying: 2-12 substreams: 2-12

Slack Solidscorrelation: 10-10 Crystallizer: 8-3 Flash2: 2-3 Flash3: 2-5 Heater model: 3-3 MHeatX: 3-22 RGibbs: 5-15 Solids crushers Crusher: 8-10 Solids crushers: 8-10 Solids separators CFuge: 8-42 Crusher: 8-10 Cyclone: 8-22 ESP: 8-32

Sep2: 2-12, 2-13 Separators Decanter model: 2-6 Flash2: 2-2 Flash3: 2-4 Sep: 2-10 Sep2: 2-12 Separators: 2-2, 2-4, 2-6, 2-10, 2-12 Shell and tube heat exchangers Hetran: 3-23 Shell and tube heat exchangers: 3-23 Shell-side film coefficient HeatX: 3-12 Shell-side film coefficient: 3-12 Shepherd and Lapple correlation Cyclone: 8-24 Shepherd and Lapple correlation: 8-24 Shortcut distillation Distl: 4-5 DSTWU: 4-3

FabFl:model: 8-18 8-45 Filter HyCyc: 8-36 Screen: 8-15 VScrub: 8-29 Solids separators: 8-10, 8-15, 8-18, 8-22, 829, 8-32, 8-36, 8-42, 8-45 Solids washers CCD: 8-50 SWash: 8-48 Solids washers: 8-48, 8-50 Solids: 2-3, 2-5, 3-3, 3-22, 5-15, 8-3 Specifying User3: 9-7 Splitters FSplit: 1-5 Sep: 2-10 Sep2: 2-12 SSplit: 1-8 Splitters: 1-5, 1-8, 2-10, 2-12 SSplit

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flowsheet connectivity: 1-8 overview: 1-8 specifying: 1-8 SSplit: 1-8 Stichlmair correlation packings calculations: A-15 Stichlmair correlation: A-15 Stoichiometric reactors RStoic: 5-3 Stoichiometric reactors: 5-3

SSplit: 1-8 Substream splitters: 1-8 Sum-rates algorithm MultiFrac: 4-40 Sum-rates algorithm: 4-40 SWash bypass fraction: 8-49 flowsheet connectivity: 8-48 mixing efficiency: 8-49 overview: 8-48

Stream classes changing: 7-6 Stream classes: 7-6 Stream definitions RateFrac: 4-62 Stream definitions: 4-62 Stream manipulators 7-4 ClChng: 7-6 Dupl 7-4 Mult: 7-2 Stream manipulators: 7-2, 7-6 Stream mixers Mixer model: 1-2 Stream mixers: 1-2 Stream multiplication Mult: 7-2

specifying: SWash: 8-48, 8-49 8-49

Stream pressure multiplication: 7-2 Stream changers Pump model: 6-2 Stream pressure changers: 6-2 Stream splitters FSplit: 1-5 SSplit: 1-8 Stream splitters: 1-5, 1-8 Streams combining: 1-8 Flash3: 2-4 splitting: 2-10, 2-12 Streams: 1-8, 2-4, 2-10, 2-12 Strippers 4-57 MultiFrac: 4-28 PetroFrac: 4-47, 4-51 RadFrac: 4-21 RateFrac 4-57 Strippers: 4-21, 4-28, 4-47, 4-51 Substream splitters


T

TEMA shells HeatX: 3-10 TEMA shells: 3-10 thermal analysis A-18 Thermosyphon reboilers RadFrac: 4-13 Thermosyphon reboilers: 4-13 Three-phase calculations BatchFrac: 4-81 RadFrac: 4-18 Three-phase calculations: 4-18, 4-81 Trays Bolles method: A-8 bubble cap: A-9 downcomer specifications: A-3 Flexitrays: A-10 float valve: A-10 flooding calculations: A-8 foaming calculations: A-10 MultiFrac: 4-27, 4-43 PetroFrac: 4-56 pressure drop calculations: A-10 pressure profile: A-15 RateFrac: 4-64 rating: A-3, A-7 sizing: A-3, A-7 specifying: A-2 types: A-2 Trays: 4-27, 4-43, 4-56, 4-64, A-2, A-3, A7, A-8, A-9, A-10, A-15 Tube geometry HeatX: 3-13

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Tube geometry: 3-13 Tube-side film coefficient HeatX: 3-13 Tube-side film coefficient: 3-13 Turbines Compr: 6-8 MCompr: 6-13 Pump model: 6-2 Turbines: 6-2, 6-8, 6-13 U

UA calculations RadFrac: 4-15 UA calculations: 4-15 Underwood's method DSTWU: 4-3 Underwood's method: 4-3 Unit operation models user-supplied: 9-2, 9-4, 9-8 Unit operation models: 9-2, 9-4, 9-8 User model flowsheet connectivity: 9-2 Fortran subroutines: 9-3 overview: 9-2 specifying: 9-3 User model: 9-2, 9-3 User2 flowsheet connectivity: 9-4 Fortran subroutines: 9-5 overview: 9-4 specifying: 9-5 User2: 9-4, 9-5 User3 flowsheet connectivity: 9-6 specifying: 9-7 User3: 9-6, 9-7 V

Vacuum filters Filter model: 8-45 Vacuum filters: 8-45 Vacuum towers SCFrac: 4-7 Vacuum towers: 4-7 Valve model calculation types: 6-19

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cavitation index: 6-26 characteristic equation: 6-24 choked flow: 6-26 flow coefficient: 6-23 flowsheet connectivity: 6-19 overview: 6-19 piping geometry factor: 6-24 pressure drop calculation: 6-19, 6-26 pressure drop ratio factor: 6-20 pressure recovery factor: 6-22 specifying: Valve model: 6-19 6-19, 6-20, 6-22, 6-23, 6-24, 6-26 Valves cycling: 10-15 Heater model: 3-2 Pipe model: 6-32 safety relief: 10-14 types used in Pres-Relief: 10-9, 10-13, 1014, 10-15 Valve model: 6-19 Valves: 3-2, 6-19, 6-32, 10-9, 10-13, 10-14, 10-15 Vaporization efficiency MultiFrac: 4-38 PetroFrac: 4-52 RadFrac: 4-19 Vaporization efficiency: 4-19, 4-38, 4-52 Vents Pres-Relief: 10-15 Vents: 10-15 Venturi scrubbers VScrub: 8-29 Venturi scrubbers: 8-29 VScrub flowsheet connectivity: 8-29 overview: 8-29 pressure drop: 8-30 rating: 8-30 separation efficiency: 8-31 sizing: 8-30 specifying: 8-30 VScrub: 8-29, 8-30, 8-31 W

Winn's method


DSTWU: 4-3 Winn's method: 4-3 Working with Feedbl: 7-9 Working with Measurement: 7-14 Working with User3: 9-6 Y

Yield reactors


RYield: 5-7 Yield reactors: 5-7 Z

Zone analysis HeatX: 3-4 MHeatX: 3-19, 3-20, 3-21 Zone analysis: 3-4, 3-19, 3-20, 3-21

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ASPEN PLUS Unit Operation Models 11-1

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