Aspen+ Essential

Aspen+ Essential Workshop

2010-03-08

Aspen+ Getting Started - Essential

WonSeok Lee AspenTech Korea, Business Consultant

© 2010 Aspen Technology, Inc. All rights reserved

Flowsheet Simulation  What is flowsheet simulation? – Use of a computer program to quantitatively model the characteristic equations of a chemical process

 Uses underlying physical relationships – Mass and energy balance – Equilibrium relationships – Rate correlations (reaction and mass/heat transfer)

 Predicts – Stream flowrates, compositions, and properties – Operating conditions


AspenTech All Right Reserved

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Advantages of Simulation  Reduces plant design time – Allows designer to quickly test various plant configurations

 Helps improve current process – Answers “what if” questions – Determines optimal process conditions within given constraints – Assists in locating the constraining parts of a process (debottlenecking)


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General Simulation Problem

 What is the composition of stream PRODUCT? RECYCLE REACTOR COOL

FEED REAC-OUT

COOL-OUT

 To solve this problem, we need:

SEP

PRODUCT

– Material balances – Energy balances



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Good Flowsheeting Practice  Build large flowsheets a few blocks at a time – This facilitates troubleshooting if errors occur

 Not necessarily a one-to-one correspondence between pieces of equipment in the plant and Aspen Plus blocks  Ensure flowsheet inputs are reasonable  Check that results are consistent and realistic


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The User Interface Run ID

Next Button

Resize Window Buttons

Title Bar

Menu Bar

Tool Bars

Process Flow Diagram

Model Library Tabs Select Mode Button

Model Library

Help Line

Status Area © 2010 Aspen Technology, Inc. All rights reserved


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Basic Input


Useful Options

 GUI – Window->Workbook mode

 Automatic Naming of Streams and Blocks – Tools->Options>Flowsheet

 Result in Flowsheet – Tools->Options->Results View © 2010 Aspen Technology, Inc. All rights reserved


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Useful Options

 Save options – Tools->Options->General – Recommend *.BKP

File Type

Extension

Format

Description

Document

*.apw

Binary

File containing simulation input, results and intermediate convergence information

Backup

*.bkp

ASCII

Archive file containing simulation input and results

Compound

*.apwz

Binary

Compressed file which contains the model (the BKP or APW file) and external files referenced by the model. You can add additional files such as supporting documentation to the APWZ file.


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Benzene Flowsheet Definition Workshop  Objective: Create a graphical flowsheet – Start with the General with English Units template – Choose the appropriate icons for the blocks

VAP1 COOLER FEED

FL1

VAP2

COOL

FL2

LIQ1

LIQ2

When finished, save as BENZENE FLOWSHEET.BKP



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Data Browser Go Back Parent Button

Units

Previous Comments Sheet Next View Sheet Status List

Go Forward

Resource Link Tool

Next

Menu Tree

Status Area

Description Area


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Basic Input  The minimum required inputs to run a simulation are: – – – – –

Setup Components Properties Streams Blocks

 Enter data on the input forms in the above order by clicking the Next button  Or, these input folders can be located quickly using the Data menu or the Data Browser toolbar buttons



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Setup  Most of the commonly used Setup information is entered on the Setup Specifications Global sheet – – – – –

Flowsheet title to be used on reports Run type Input and output units Valid phases: vapor-liquid (default) or vapor-liquid-liquid Ambient pressure

 Stream report options are located on the Setup | Report Options | Stream sheet


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Components  Pure component databanks contain parameters such as molecular weight, critical properties, etc.; the databank search order is specified on the Databanks sheet  The Find button can be used to search for components  The Electrolyte Wizard can be used to set up an electrolyte simulation



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NIST Databank  The NISTV71 database contains a single databank called NISTTRC – Available from Aspen Plus 2006 only – Includes approximately 15,000 compounds (mostly organic)  13,000 new components  2,000 components already in Aspen Properties databanks

– The database is available in the Enterprise Database architecture only; it is not available in the legacy DFMS format NIST = US National Institute of Standards and Technology © 2010 Aspen Technology, Inc. All rights reserved

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Properties  Property methods are a collection of models and methods used to describe pure component and mixture behavior  Choosing the correct physical properties is critical for obtaining reliable simulation results



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Streams  Use Stream | Input forms to specify feed stream conditions, including two of the following: – Temperature – Pressure – Vapor Fraction

 Plus, for stream composition either: – Total stream flow and component fractions – Individual component flows

 Specifications for streams that are not feeds to the flowsheet are used as estimates © 2010 Aspen Technology, Inc. All rights reserved

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Streams  Stdvol – Standard liquid volume (1 atm and 60 F)

 Vol – Ref. Temperature

 Mole – Standard vapor volume (Ideal gas) – 14.696 psia & 60 F – 1 atm & 0 C



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Blocks  Each Block | Input or Block | Setup form specifies operating conditions and equipment specifications for the unit operation model  Some unit operation models require additional specification forms

Block Tin

Tout

Pin

Pout

Fin

Fout

Xin

Xout

 All unit operation models have optional information forms (e.g., Block Options form) e.g. Heater block needs both Tout and Pout operating specs © 2010 Aspen Technology, Inc. All rights reserved

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Starting the Run  Select Control Panel from the View menu or press the Next button to be prompted – Execute the simulation when all required forms are complete.

Run Step Stop Reinitialize Results

Start or continue calculations Step through the flowsheet one block at a time Pause simulation calculations Purge simulation results Check simulation results © 2010 Aspen Technology, Inc. All rights reserved


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Cumene Production Demo

RECYCLE REACTOR COOL

FEED REAC-OUT

T = 220°F P = 36 psia Benzene: 40 lbmol/hr Propylene: 40 lbmol/hr

Q = 0 Btu/hr Pdrop = 0 psi

COOL-OUT

SEP

P = 1 atm Q = 0 Btu/hr

T = 130°F Pdrop = 0.1 psi PRODUCT

C6H6 + C3H6  C9H12 Benzene Propylene Cumene (Isopropylbenzene) 90% Conversion of Propylene Use the RK-SOAVE Property Method


Filename: CUMENE.BKP

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Reviewing Results

 Control Panel Messages – Contains any generated errors or warnings – Block Results – Convergence

 Steam Results  Custom Stream Results  Block Summary Grid  Block Results



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Stream Results

 Contains stream conditions and compositions  Fraction basis in stream result – Data browser->Setup->Report options->Stream


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Custom Stream Results  This feature makes it much easier to customize the stream report format  With Custom Stream Summary Views you can: – – – – –

Select a list of streams to display Select the properties to be displayed Select the units of measure and numerical formats Specify calculation options for each property Eliminate or change the labels used in the table

 Custom stream summary views can be exported and imported as .APCSV files  You can use any number of custom views within the same simulation



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Benzene Flowsheet Conditions Workshop (1)  Objective: Add the process and feed stream conditions to a flowsheet. Start with the Benzene Flowsheet (BENZENE FLOWSHEET.BKP). VAP1 COOLER FL1 FEED

Feed

COOL

T = 100°F P = 500 psia

T = 200°F Pdrop = 0

T = 1000°F P = 550 psia

VAP2

FL2 LIQ1

Hydrogen: 405 lbmol/hr Methane: 95 lbmol/hr Benzene: 95 lbmol/hr Toluene: 5 lbmol/hr

P = 1 atm Q=0

LIQ2

When finished, save as filename: BENZENE.BKP

Use the PENG-ROB Property Method © 2010 Aspen Technology, Inc. All rights reserved

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Benzene Flowsheet Conditions Workshop (2)

 Results – What is the heat duty of the COOLER block? – What is the temperature in the FL2 block?

_________ _________

Note: Answers for all of the workshops are located in the back of the course notes in Appendix C



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Optional  Create a Custom Stream Summary with the following properties: – – – – – –

Temperature Pressure Total Mole Flow Liquid and Vapor Component Mole Flows Liquid and Vapor Mixture Mass Density in gm/cc Liquid and Vapor Mixture Viscosity in cP


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RadFrac


Rigorous Multistage Separation Using RadFrac

 Vapor-Liquid or Vapor-Liquid-Liquid phase simulation of: – – – – –

Ordinary distillation Absorption, reboiled absorption Stripping, reboiled stripping Azeotropic distillation Reactive distillation

 Configuration options – – – – –

Any number of feeds Any number of side draws Total liquid draw off and pumparounds Any number of heaters Any number of decanters © 2010 Aspen Technology, Inc. All rights reserved


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RadFrac Flowsheet Connectivity

Vapor Distillate

1

Top-Stage or Condenser Heat Duty

Heat (optional) Liquid Distillate Water Distillate (optional)

Feeds

Reflux Side Products (optional)

Heat (optional)

Pseudo Streams (optional) Pumparound (optional) Feed (optional)

Heat (optional) Heat (optional)

Bottom Stage or Reboiler Heat Duty

Boil-up

Decanter Return

Product

Nstage

Heat (optional)

Bottoms


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Some RadFrac Options  To set up an absorber with no condenser or reboiler, set condenser and reboiler to none on the RadFrac Setup Configuration sheet  Either Vaporization or Murphree efficiencies on either a stage or component basis can be specified on the RadFrac Efficiencies form  Tray and packed column design and rating is possible  A second liquid phase may be modeled if the user selects Vapor-liquid-liquid as Valid phases  Stage Wizard for adding/removing stages from column  Option to select different reboiler configurations  Reboiler and condenser heat curves can be generated



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RadFrac Demonstration

OVHD RadFrac specifications Flow = 1000 lbmol/hr T = 190°F P = 315 psia

Partial Condenser Kettle Reboiler 15 Stages Reflux Ratio = 1.5 (mole) Distillate to feed ratio = 0.6 Column pressure = 315 psia Feed stage = 8

COLUMN

FEED Mole fractions C1: 0.26 C2: 0.09 C3: 0.25 nC4: 0.17 nC5: 0.11 nC6: 0.12

BTMS

Filename: RADFRAC.BKP

Use the RKS-BM Property Method


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RadFrac Setup Configuration Sheet  Specify: – Number of stages – Condenser and reboiler configuration – Valid phases – Convergence – Two column operating specifications  Defaults: Distillate rate and reflux ratio



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RadFrac Setup Streams Sheet  Specify: – Feed stage location – Feed stream convention  Above-Stage  On-Stage  On-Stage-Liquid  On-Stage-Vapor  Decanter (for three phase calculations only) – Bottom and overhead product streams – Side products


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Feed Convention Above-Stage (default)

On-Stage

n-1 Vapor

n-1

Feed to stage n

Liquid

Feed to stage n

n n

• Above-Stage: RadFrac introduces the material stream between adjacent stages - the liquid portion flows to the specified stage and the vapor portion flows to the stage above • On-Stage: RadFrac introduces both liquid and vapor portions of the feed flow to the stage specified • On-Stage-Liquid and On-Stage-Vapor are similar to On-Stage, but no flash is ever performed with these specifications. Feed treated as being entirely in the phase specified.



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RadFrac Setup Pressure Sheet  Specify one of: – Top/Bottom pressure – Pressure profile – Section pressure drop


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Plot Wizard  The Plot Wizard guides you in the basic operations for generating a plot  In Step 2, click the plot type you wish to generate, then click Next> to continue  Click the Finish button to generate a plot with default settings



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Plot Wizard Demonstration  Use the Plot Wizard to create plots of temperature, flows, and compositions throughout the column


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Design Specs and Vary  Design specifications can be specified inside the RadFrac block using DesignSpecs and Vary forms  One or more RadFrac inputs can be manipulated to achieve specifications on one or more RadFrac performance parameters  The number of specs should, in general, be equal to the number of varies  The DesignSpecs and Varys in a RadFrac are solved in a “Middle loop”; if you get an error message saying that the middle loop was not converged, check the DesignSpecs and Varys you have entered



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Design Specs and Vary Demonstration  Part A – Record the molar composition of C3 in OVHD stream. _______ – What reflux ratio is required so that this value is 0.41? _______

 Part B – Change the current Design Spec so that the sum of light key (C1 + C2 + C3) molar compositions in the OVHD stream is set to 0.99. What happens to the predicted reflux ratio given this new specification? ___________________________________


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RadFrac Stage Wizard  Use the Stage Wizard to change the number of stages in the column while also updating stage numbers throughout the specifications for the block – Enter the New total number of stages – Choose Above or Below and specify a Stage number - the stages will be added or deleted according to the choices – Click OK to update the specifications



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Thermosiphon Configuration in RadFrac  RadFrac model supports various reboiler configurations


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Thermosiphons and columns  Traditional method

 Rigorous reboiler modeling

– Reboiler appears as simple heat input in column model – Column and reboiler designed and simulated separately – Feed composition to reboiler estimated – Reboiler and column models interact through: input liquid level, estimated feed composition and calculated flowrate and heat load

– Integrate heat exchanger model into column model  A Reboiler Wizard (Reboiler sheet) can be used to explicitly simulate the reboiler using a heat exchanger block (HeatX block - see Heat Exchangers section) or using a rigorous Aspen Shell & Tube Exchanger model to design, rate, or simulate the reboiler

– Correctly models column/reboiler interaction – Allows modelling of tower bottom baffle arrangement



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Specifying Efficiencies in RadFrac  RadFrac Efficiencies Options sheet


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Sizing and Rating for Trays and Packing  Extensive capabilities to size, rate, and perform pressure drop calculations for trayed and packed columns  Calculations are based on vendor-recommended procedures when available. When vendor procedures are not available, well-established literature methods are used – – – –

Bubble Cap Trays One pass tray Tray Spacing = 2 ft Diameter = 10 ft



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RadFrac Convergence Problems (1)  If a RadFrac column fails to converge, doing one or more of the following could help: – Check that physical property issues (choice of Property Method, parameter availability, etc.) are properly addressed – Ensure that column operating conditions are feasible – If the column err/tol is decreasing fairly consistently, increase the maximum iterations on the RadFrac Convergence Basic sheet


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RadFrac Convergence Problems (2)  Provide temperature estimates for some stages in the column using the RadFrac Estimates Temperature sheet (useful for absorbers)  Provide composition estimates for some stages in the column using the RadFrac Estimates Liquid Composition and Vapor Composition sheet (useful for highly non-ideal systems)  Experiment with different convergence methods on the RadFrac Setup Configuration sheet  Note: When a column does not converge, it is usually beneficial to Reinitialize after making changes



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RadFrac Workshop (1)  Objective: Set up a Methanol tower

63.2 wt% Water 36.8 wt% Methanol Flow = 120000 lb/hr Pressure 18 psia Saturated liquid

DIST 38 trays (40 stages) Feed tray = 23 (stage 24) Total condenser Top stage pressure = 16.1 psia Pressure drop per stage = 0.1 psi Distillate flowrate = 1245 lbmol/hr Molar reflux ratio = 1.3

COLUMN

FEED

BTMS

Use the NRTL-RK Property Method

Filename: MEOH_COL.BKP


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RadFrac Workshop (2)  Part A – Fix the simulation to eliminate any warning messages – Record the column duties:

 Condenser Duty: _________ _________

Reboiler Duty:

– Record compositions:

 Mass fraction of methanol in the distillate: __________  Mass fraction of water in the bottoms: __________ – Make plots of temperature, flows, and composition



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RadFrac Workshop (3)  Part B – Set up Design Specs within the column so that there is:

 99.95 wt% methanol in the distillate  99.90 wt% water in the bottoms – Vary the distillate rate (800-1700 lbmol/hr) and the reflux ratio (0.8-2) – Record the final values for:

 Distillate Rate: _________ Ratio: _________  Condenser Duty: _________ _________


Reflux Reboiler Duty:

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RadFrac Workshop (4)  Part C – Perform the same calculations after specifying a 65% Murphree efficiency for each tray. Assume condenser and reboiler have stage efficiencies of 90%. Determine how these efficiencies affect the column duties:

 Condenser Duty: _________ _________

Reboiler Duty:

 Part D – Perform a tray sizing calculation for the entire column, given that Bubble Cap trays are used

 Record the predicted column diameter: _________



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Reactor Models


Reactor Overview

Reactors

Balance Based RYield RStoic

Equilibrium Based REquil RGibbs



Kinetics Based RCSTR RPlug RBatch

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Balanced Based Reactors (1)  RYield – Requires a mass balance only, not an atom balance – Is used to simulate reactors in which inlets to the reactor are not completely known but outlets are known (e.g., to simulate a furnace)

RYield

1000 lb/hr Coal

70 lb/hr H2O 20 lb/hr CO2 60 lb/hr CO 250 lb/hr tar 600 lb/hr char

IN

OUT


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Balanced Based Reactors (2)  RStoic – Requires both an atom and a mass balance – Used in situations where both the equilibrium data and the kinetics are either unknown or unimportant – Can specify or calculate heat of reaction at a reference temperature and pressure

RStoic

C, O2 IN

2 CO + O2  2 CO2 C + O2  CO2 2 C + O2  2 CO C, O2, CO, CO2 OUT



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Equilibrium Based Reactors (1)  These reactors: – Do not take reaction kinetics into account – Solve similar problems, but specifications are different – Allow individual reactions to be at a restricted equilibrium

 REquil – Computes combined chemical and phase equilibrium by solving reaction equilibrium equations – Cannot do a three-phase flash – Useful when there are many components, a few known reactions, and when relatively few components take part in the reactions


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Equilibrium Based Reactors (2)  RGibbs – Useful when reactions occurring are not known or are high in number due to many components participating in the reactions – A Gibbs free energy minimization is done to determine the product composition at which the Gibbs free energy of the products is at a minimum – This is the only Aspen Plus block that will deal with vaporliquid-solid phase equilibrium



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Kinetic Reactors (1)  Kinetic reactors are RCSTR, RPlug and RBatch  Reaction kinetics are taken into account, and hence must be specified  Kinetics can be specified using one of the following built-in models, or with a user subroutine: – Power Law – Langmuir-Hinshelwood-Hougen-Watson (LHHW)

 A catalyst for a reaction can have a reaction coefficient of zero  Reactions are specified using a Reaction ID


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Kinetic Reactors (2)  RCSTR – Use when reaction kinetics are known and when the reactor contents have same properties as outlet stream – Allows for any number of feeds, which are mixed internally – Up to three product streams are allowed – vapor, liquid1, liquid2 or vapor, liquid, free water – Will calculate duty given temperature or temperature given duty – Can model equilibrium reactions simultaneously with ratebased reactions



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Kinetic Reactors (3)  RPlug – Handles only rate-based reactions – A cooling stream is allowed – You must provide reactor length and diameter

 RBatch – Handles rate-based kinetics reactions only – Any number of continuous or delayed feeds are allowed – Process duration can be specified using stop criteria, cycle time, and result time – Holding tanks are used to interface with steady-state streams of Aspen Plus


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Using a Reaction ID (1)  Reaction IDs are setup as objects, separate from the reactor, and then referenced within the reactor(s)  A single Reaction ID can be referenced in any number of kinetic reactors (RCSTR, RPlug and RBatch)  Multiple reaction sets can be referenced in the reactor models  Each Reaction ID can have multiple and/or competing reactions



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Using a Reaction ID (2)  To set up a Reaction ID, go to the Reactions, Reactions Object Manager – Click on New to create a new Reaction ID – Enter ID name and select the reaction type from the drop-down box – Enter appropriate reaction data in the forms


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Example of a Power Law Reaction ID (1) • The general Power Law kinetic reaction rate is: Reaction Rate



Kinetic Factor



[Componenti] Exponent

i

− [Componenti] : concentration of component i − Exponenti : kinetic exponent of component i  i

• Within a Reaction ID you need to specify: − Stoichiometry sheet: stoichiometric coefficient and kinetic exponent for each component i − Kinetic sheet: kinetic factor data



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Example of a Power Law Reaction ID (2)  For a reversible kinetic reaction, both the forward and reverse reactions have to be specified separately

Example:

2 A  3B

k1 

k 2

C  2D

Forward reaction

k1 2 A  3 B   C  2D

Reverse reaction

k2 C  2 D  2 A  3B

Assuming 2nd order in A

Assuming 1nd order in C and D (overall 2nd order)

− k1 : Kinetic factor for forward reaction − k2 : Kinetic factor for reverse reaction © 2010 Aspen Technology, Inc. All rights reserved

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Example of a Power Law Reaction ID (3) – Stoichiometry sheet • Stoichiometry coefficients quantitatively relate the amount of reactants and products in a balanced chemical reaction − By convention - negative for reactants and positive for products Forward reaction coefficients:

A:

B:

C:

D:

Reverse reaction coefficients:

A:

B:

C:

D:

• Kinetic exponents show how the concentration of each component affects the rate of reaction − Typically obtained from experimental data Forward reaction exponents:

A:

B:

C:

D:

Reverse reaction exponents:

A:

B:

C:

D:



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Example of a Power Law Reaction ID (4) – Stoichiometry sheet Forward reaction Coefficients Forward reaction: A: -2 B: -3 C: 1 D: 2 Reverse reaction: A: 2 B: 3 C: -1 D: -2

Reverse reaction

Exponents Forward reaction: A: 2 B: 0 C: 0 D: 0 Reverse reaction: A: 0 B: 0 C: 1 D: 1


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Example of a Power Law Reaction ID (5) Kinetic sheet  If reference temperature, T0, is specified, Kinetic Factor is expressed as:

Kinetic Factor



 E  kT n exp    RT  n

Kinetic Factor − − − −



 E  1 1  T  k   exp       T0   R  T T0  

k : Pre-exponential factor n : Temperature exponent E : Activation energy T0 : Reference temperature © 2010 Aspen Technology, Inc. All rights reserved


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Example of a Power Law Reaction ID (6) Kinetic sheet


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Heats of Reaction  Heats of reaction need not be provided for reactions  Heats of reaction are typically calculated as the difference between inlet and outlet enthalpies for the reactor (see Appendix A)  If you have a heat of reaction value that does not match the value calculated by Aspen Plus, you can adjust the heats of formation (DHFORM) of one or more components to make the heats of reaction match  Heats of reaction can also be calculated or specified at a reference temperature and pressure in an RStoic reactor



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Reactor Workshop (1)  Objective: Compare the use of different reactor types to model a reaction 70% conversion of ethanol P-STOIC

F-STOIC RSTOIC FEED Feed: Temp = 70°C DUPL Pres = 1 atm Water: 8.892 kmol/hr Ethanol: 186.59 kmol/hr Acetic Acid: 192.6 kmol/hr

F-GIBBS

P-GIBBS

RGIBBS

Length = 2 m

RPLUG

Diameter = 0.3 m

F-PLUG

P-PLUG

F-CSTR

P-CSTR

Use the NRTL-HOC property method RCSTR © 2010 Aspen Technology, Inc. All rights reserved

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Reactor Workshop (2)  Reactor Conditions: Temperature = 70°C, Pressure = 1 atm  Stoichiometry: Ethanol + Acetic Acid  Ethyl Acetate + Water  Kinetic Parameters: – Reactions are first order with respect to each of the reactants in the reaction (second order overall) – Forward Reaction: k = 1.9 x 108, E = 5.95 x 107 J/kmol – Reverse Reaction: k = 5.0 x 107, E = 5.95 x 107 J/kmol – Reactions occur in the liquid phase – Composition basis is Molarity

 Hint: Check that each reactor is considering both Vapor and Liquid as Valid phases

Filename: REACTORS.BKP © 2010 Aspen Technology, Inc. All rights reserved


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Reactor Workshop (3)  Results RStoic

RGibbs

RPlug

RCSTR

Amount of Ethyl Acetate produced (kmol/hr) Mass fraction Ethyl Acetate in product stream Heat duty (kcal/hr)


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Physical Properties



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Case Study – Acetone Recovery

 Correct choice of physical property models and accurate physical property parameters are essential for obtaining accurate simulation results OVHD

FEED

Specification: 99.5 mole % acetone recovery

COLUMN

BTMS

Ideal Approach

Equation of State Approach

Activity Coefficient Model

Predicted number of stages required

11

7

42

Approximate cost ($)

650,000

490,000


1,110,000 |

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How to Establish Physical Properties

Choose a Property Method

Check Parameters/Obtain Additional Parameters

Confirm Results

Create the Flowsheet



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Definition of Terms  Property Method – Set of property models and methods used to calculate the properties required for a simulation

 Property – Calculated physical property value, such as mixture enthalpy

 Property Model – Equation or equations used to calculate a physical property

 Property Parameter – Constant used in a property model

 Property Set (Prop-Set) – A method of accessing properties so that they can be used or tabulated elsewhere


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Physical Property Models

 Approaches to representing physical properties of components Physical Property Models

Ideal

Equation of State (EOS) Models

Activity Coefficient Models

Special Models

 Choice of model types depends on degree of non-ideal behavior and operating conditions © 2010 Aspen Technology, Inc. All rights reserved


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Ideal vs. Non-Ideal Behavior  What do we mean by ideal behavior? – Ideal Gas law and Raoult’s law

 Which systems behave as ideal? – Non-polar components of similar size and shape

 What controls degree of non-ideality? – Molecular interactions, e.g., Polarity, size and shape of the molecules

 How can we study the degree of non-ideality of a system? – Property plots (e.g., TXY & XY) y x © 2010 Aspen Technology, Inc. All rights reserved

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Comparison of EOS and Activity Models

Equation of State Models

Activity Coefficient Models

Good for vapor phase modeling and liquids of low polarity Limited in ability to represent non-ideal liquids Fewer binary parameters required Parameters extrapolated reasonably with temperature Consistent in critical region Examples:

Good for liquid phase modeling only

− PENG-ROB − RK-SOAVE

Can represent highly non-ideal liquids Many binary parameters required Binary parameters are highly temperature dependent Inconsistent in critical region Examples: − − − −

NRTL UNIFAC UNIQUAC WILSON



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Henry's Law  Henry's Law is used to determine the amount of a supercritical component or light gas in the liquid phase – It is only used with Ideal and Activity Coefficient models

 Declare any supercritical components or light gases (CO2, N2, etc.) as Henry's components on the Components Henry Comps Selection sheet  Then, select the Henry's components ID from the Henry Components dropdown list on the Properties Specifications Global sheet


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Choosing a Property Method – Review

Do you have any polar components in your system? N

Y

Use EOS Model

Y

Are the operating conditions near the critical region of the mixture? N Do you have light gases or supercritical components in your system?

References: Aspen Plus User Guide, Chapter 7, Physical Property Methods, gives similar, more detailed guidelines for choosing a property Method.

Y Use activity coefficient model with Henry’s Law



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N Use activity coefficient model

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Property Method Selection Assistant


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Choosing a Property Method – Example

System

Model Type

Property Method

Propane, Ethane, Butane

Equation of State

RK-SOAVE, PENG-ROB

Benzene, Water

Activity Coefficient

NRTL-RK, UNIQUAC

Acetone, Water

Activity Coefficient

NRTL-RK, WILSON

 Choose an appropriate Property Method for the following systems of components at ambient conditions: System

Property Method

Ethanol, Water Benzene, Toluene Acetone, Water, Carbon Dioxide Water, Cyclohexane Ethane, Propanol



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Property Analysis Plots

 Predicting non-ideal behavior: XY Plot showing an Azeotrope:

Ideal XY Plot: y-x diagram for METHANOL / PROPANOL

y-x diagram for ETHANOL / TOLUENE

(PRES = 14.7 PSI)

0

XY Plot showing two Liquid phases: y-x diagram for TOLUENE / WATER

(PRES = 14.7 PSI)

(PRES = 14.7 PSI)

0.2 0.4 0.6 0.8 1 LIQUID MOLEFRAC METHANOL

0

0 0.2 0.4 0.6 0.8 1 LIQUID MOLEFRAC TOLUENE

0.2 0.4 0.6 0.8 1 LIQUID MOLEFRAC ETHANOL

– When using a binary analysis to check for liquid-liquid phase separation, choose Vapor-Liquid-Liquid as Valid phases


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How to Establish Physical Properties – Review

1. Choose Property Method, based on: Components present in simulation – Operating conditions in simulation – Available data or parameters for the components –

2. Check Parameters –

Determine availability of parameters in the Aspen Plus databanks, and obtain additional parameters if necessary

3. Confirm Results –

Verify choice of Property Method and physical property data using the Property Analysis plotting tool



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Property Sets  A property set (Prop-Set) is a way of accessing a collection, or set, of properties as an object with a user-given name; only the name of the property set is referenced when using the properties in an application  Use property sets to report thermodynamic, transport, and other property values  Current property set applications include: – – – – –

Design specifications, Calculator blocks, Sensitivity analysis Stream reports Physical property tables (Property Analysis) Tray properties (RadFrac, MultiFrac, etc.) Heating/cooling curves (Flash2, HeatX, etc.)


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Properties Included in Prop-Sets  Available properties include: – – – – –

Thermodynamic properties of components in a mixture Pure component thermodynamic properties Transport properties Electrolyte properties Petroleum-related properties

 Properties commonly included in property sets include: – – – –

VFRAC BETA CPMX MUMX

Molar vapor fraction of a stream Fraction of L1 to total liquid for a mixture Constant pressure heat capacity for a mixture Viscosity for a mixture



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Specifying Property Sets  Select properties for a property set using the Properties Prop-Sets form – The Search button can be used to search for a property – The Units fields are optional;

 DataBrowser->Setup->Report Options->Stream – Click the Property Sets button and move the Prop-Set name from the available to selected area


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Cyclohexane Workshop Won-Seok Lee AspenTech Korea, Business Consultant



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Process Description  Part A: Create a flowsheet to model a cyclohexane production process – Cyclohexane can be produced by the hydrogenation of benzene in the following reaction: C6H6 + 3H2  C6H12 – The benzene and hydrogen feeds are combined with recycle hydrogen and cyclohexane before entering a fixed bed catalytic reactor. Assume a benzene conversion of 99.8% – The reactor effluent is cooled and the light gases separated from the product stream. Part of the light gas stream is fed back to the reactor as recycle hydrogen – The liquid product stream from the separator is fed to a distillation column to further remove any dissolved light gases and to stabilize the end product. The remaining portion is recycled to the reactor to aid in temperature control


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Process Flowsheet PURGE Total flow = 330 kmol/hr

92% flow to stream H2RCY

T = 50°C P = 25 bar Molefrac H2 = 0.975 N2 = 0.005 CH4 = 0.02

H2IN

VFLOW

H2RCY

VAP FEED-MIX

REACT HP-SEP

RXIN

BZIN T = 40°C P = 1 bar Benzene flow = 100 kmol/hr

T = 50°C Pdrop = 0.5 bar

RXOUT

T = 150°C P = 23 bar

T = 200°C Pdrop = 1 bar Benzene conv = 0.998

LIQ

CHRCY

COLFD LFLOW

LTENDS Theoretical Stages = 12 Reflux ratio = 1.2 Bottoms rate = 99 kmol/hr Partial Condenser with vapor distillate only Column Pressure = 15 bar Feed stage = 8

30% flow to stream CHRCY

PRODUCT

Use the RK-SOAVE property method

COLUMN Specify cyclohexane mole recovery in PRODUCT stream equal to 0.9999 by varying Bottoms rate from 97 to 101 kmol/hr

Filename: CYCLOHEXANE.BKP



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Sensitivity Analysis


Sensitivity Analysis Example

RECYCLE REACTOR COOL FEED REAC-OUT

COOL-OUT

SEP

Filename: CUMENE-S.BKP PRODUCT

 Determine the effect of cooler outlet temperature on the purity of the product stream – What is the manipulated (varied) variable?

» COOL outlet temperature – What is the measured (sampled) variable?

» Purity (mole fraction) of cumene in PRODUCT stream



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Sensitivity Analysis  Allows user to study the effect of changes in input variables on process outputs  Located under Data Browser | Model Analysis Tools | Sensitivity  Results can be viewed by looking at the Results form in the folder for the Sensitivity block  Plot results to easily visualize relationships between different variables


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Uses of Sensitivity Analysis  Studying the effect of changes in input variables on process (model) outputs  Graphically representing the effects of input variables  Verifying that a solution to a design specification is feasible  Rudimentary optimization  Studying time varying variables using a quasi-steady-state approach  Doing case studies



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Steps for Using Sensitivity Analysis  Specify measured (sampled) variable(s) – These are quantities calculated during the simulation to be used in step 4 (Define sheet)

 Specify manipulated (varied) variable(s) – These are the flowsheet variables to be varied (Vary sheet)

 Specify range(s) for manipulated (varied) variable(s) – Variation for manipulated variable can be specified either as equidistant points within an interval or as a list of values for the variable (Vary sheet) – Tip: You can check the Disable variable box to temporarily not vary that variable

 Specify quantities to calculate and tabulate – Tabulated quantities can be any valid Fortran expression containing variables defined in step 1 (Tabulate sheet) – Tip: Click the Fill Variables button to automatically tabulate all of the define variables © 2010 Aspen Technology, Inc. All rights reserved

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Plotting  Select the column containing the X-axis variable and then select X-Axis Variable from the Plot menu  Select the column containing the Y-axis variable and then select Y-Axis Variable from the Plot menu  (Optional) Select the column containing the parametric variable and then select Parametric Variable from the Plot menu  Select Display Plot from the Plot menu 

Note: To select a column, click the heading of the column with the left mouse button



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Workshop : Sensitivity Analysis  Part B: Add a sensitivity analysis to study the effect of the recycle flowrate on the reactor duty – Plot the variation of REACT duty as the recycle split fraction in LFLOW is varied from 0.1 to 0.4 – In addition to the split fraction, vary the conversion of benzene in the reactor from 0.9 to 1.0. Tabulate the reactor duty and construct a parametric plot showing the dependence of the reactor duty on recycle split fraction and the conversion of benzene – Note: Both of these studies should be set up within the same sensitivity analysis block


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Design Specifications Aspen Plus®: Process Modeling



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Design Specification Example RECYCLE REACTOR COOL FEED REAC-OUT

COOL-OUT

SEP

Filename: CUMENE-D.BKP PRODUCT

 Determine the cooler outlet temperature to achieve a cumene product purity of 98 mole percent: –

What is the manipulated (varied) variable?

–

What is the measured (sampled) variable?

» COOL outlet temperature » Mole fraction of cumene in PRODUCT stream –

What is the specification (target) to be achieved?

» Mole fraction of cumene in PRODUCT stream = 0.98 © 2010 Aspen Technology, Inc. All rights reserved

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Steps for Using Design Specifications (1)  Identify measured (sampled) variables – These are flowsheet quantities, usually calculated, to be included in the objective function (Define sheet)

 Specify objective function (Spec) and goal (Target) – This is the equation that the specification attempts to satisfy (Spec sheet)

 Set tolerance for objective function – The specification is converged when the objective function equation is satisfied to within this tolerance (Spec sheet)

 Specify manipulated (varied) variable – This is the variable whose value changes in order to satisfy the objective function equation (Vary sheet)



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Steps for Using Design Specifications (2)  Specify range of manipulated (varied) variable – These are the lower and upper bounds of the interval within which Aspen Plus will vary the manipulated variable (Vary sheet)

 By default, the units of the variable(s) used in the objective function (step 2) and those for the manipulated variable (step 5) are the units for that variable type as specified by the Units Set declared for the design specification; you can change the units using the Object-level Units dropdown list in the Data Browser toolbar; however, if you do, it changes the units for all sheets in this form; for example, if you change the units to MetCBar in the Specs sheet, the units in the Vary form are also MetCBar


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Workshop : Design Specification  Part C: Hide the sensitivity analysis and use a design specification to fix the heat load on the reactor by varying the recycle flowrate  The cooling system around the reactor can handle a maximum operating load of 4.7 MMkcal/hr. Determine the amount of cyclohexane recycle necessary to keep the cooling load on the reactor to this amount: ________ kmol/hr 

Note: The heat convention used in Aspen Plus is that heat input to a block is positive, and heat removed from a block is negative



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Heat Exchangers


Heater Model  The Heater block mixes multiple inlet streams to produce a single outlet stream at a specified thermodynamic state  A Heater can be used to represent: – – – – –

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

 Heater also can be used to set the thermodynamic conditions of a stream  Vapor fraction of 1 means dew point condition, 0 means bubble point



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Heat Streams  One outlet heat stream can be specified for the net heat load from a Heater – The net heat load is the sum of the inlet heat streams minus the actual (calculated) heat duty

 Heat streams flow in the direction that information (not heat) flows  When a heat stream is an inlet to a block, you only need one thermodynamic specification (temperature or pressure), Heater uses the sum of the inlet heat streams as a duty specification


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HeatX Model  HeatX can perform shortcut, detailed rating and simulation calculations, and rigorous design calculations  Shortcut rating calculations (simple heat and material balance calculations) can be performed if exchanger geometry is unknown or unimportant  For detailed and rigorous heat transfer and pressure drop calculations, the heat exchanger geometry must be specified



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HeatX Model  You can access Aspen rigorous heat exchanger modeling software directly within the HeatX block – – – – –

Aspen Shell & Tube Exchanger Aspen Air Cooled Exchanger Aspen Plate Exchanger Hetran Aerotran

 Information related to the heat exchanger configuration and geometry is entered through the individual program on the EDR Browser form


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HeatX Run Type

Shortcut Input

Detail / Shell & Tube Output

Input Duty or Tout

Output Geo*

Design

Duty or Tout

UA

Rating

Duty or Tout and UA

Over Design% Duty and Geo

Over Design%

Simulation

UA

Tout and Duty

Tout and Duty

Max. fouling

N/A

N/A

Geo

Tout : Stream condition in one of outlet streams. e.g. vapor fraction or temp Geo : HX geometry * : Available in only Shell & Tube (TASC+)



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HeatX Key Options

 Options – Valid phases

 Block Options – Property method – Water Solubility

 Setup->LMTD – Interval © 2010 Aspen Technology, Inc. All rights reserved

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HeatX versus Heater  Use HeatX when both sides are important  Use Heater when one side (e.g., the utility) is not important  Use two Heaters (coupled by a heat stream, Calculator block, or Design Spec) to avoid flowsheet complexity created by HeatX



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HeatX Workshop (1)  Objective: Compare the simulation of a heat exchanger that uses water to cool a hydrocarbon mixture using three methods: two Heaters connected with a Heat stream, a Heater using a Utility, and a detailed HeatX HCLD-IN

HCLD-OUT DHOT-OUT

HEAT-C

UHOT-IN

Q-TRANS

UHOT-OUT

DCLD-OUT

DCLD-IN

HEAT-U

DHEATX

DHOT-IN HHOT-IN

Tip: In HeatX, make sure that you connect cold streams to cold ports and hot streams to hot ports.

HHOT-OUT

HEAT-H

Filename: HEATX.BKP © 2010 Aspen Technology, Inc. All rights reserved

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HeatX Workshop (2)  Streams – Hydrocarbon stream: 200°C, 4 bar, 10000 kg/hr  50 wt% benzene, 20% styrene, 20% ethylbenzene, 10 wt% water

– Cooling water: 20°C, 10 bar, 60000 kg/hr water – Choose the appropriate Property Method for both the hot and cold sides of this system

 Unit Operations – For the Heater blocks:  Hydrocarbon stream exit has a vapor fraction of 0  No pressure drop in either stream



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HeatX Workshop (3) 

For the HeatX block: –   –

First run as a Shortcut model with: Hydrocarbon stream exit has a vapor fraction of 0 No pressure drop in either stream For the Detailed HeatX block: 1. Enter Geometry:  Shell diameter 1 m, 1 tube pass  300 bare tubes, 3 m length, pitch 31 mm, 21 mm ID, 25 mm OD  All nozzles 100 mm  5 baffles, 15% cut 2. Run in Rating mode where the hydrocarbons in the shell leave with a vapor fraction of 0 Required area ______ m2 Actual area ______ m2 Over/under-surfaced ______ % Hot outlet stream T ______ °C 3. Change the Calculation Type to Simulation and re-run Hot outlet stream T ______ °C 4. Create heat curves containing all info required for thermal design


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HeatX Workshop (4)  Utility – Cooling water  Inlet Conditions: 20°C, 10 bar  Outlet Conditions: 35°C, 10 bar  Price: 0.0001 $ / kg

– How much Cooling Water is needed?

 Bonus – Add a design specifications to determine how much cooling water is needed in stream HCLD-IN for HCLD-OUT to have a temperature of 35°C



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Cyclohexane HeatX Flowsheet Optional Workshop PURGE

H2RCY

LTENDS VFLOW

H2IN

VAP

REACT

FEED-MIX RXIN

WARMWAT

HP-SEP RXOUT

COLUMN

BZIN

STG2 COND

LFLOW CHRCY

COLFD

COOLWAT PRODUCT

CNDSATEB

Filename: HEATX-CYCLOHEXANE.BKP © 2010 Aspen Technology, Inc. All rights reserved

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Cyclohexane HeatX Workshop (1) Part A: Using a Utility in the Condenser 1. Create a new utility for cooling water; use the following state variables to specify the heat release of the water: Inlet

Outlet

Temperature (C) 5.0

20.0

Pressure (bar)

3.0

2.9

Purchase price

0.0005 $/kg

2. Associate the cooling water utility with the RADFRAC Block’s (“COLUMN”) condenser; Hint: This is done on the COLUMN | SETUP form’s Condenser sheet



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Cyclohexane HeatX Workshop (2)  Part B: Rigorous Rating of the Condenser  Add a new HEATX block called “COND” to the flowsheet  For the hot feed stream to the COND block, connect the source of the feed stream to the PSEUDO stream connection port on the right side of the COLUMN block; you will have to later navigate to the COLUMN | REPORT form’s PSEUDO sheet and define the stream as the vapor on stage 2  Add a new cold feed stream to the COND block and use the calculated cooling water flowrate and conditions from part A  Change the COND block’s calculation TYPE to “RATING” and change the exchanger specification field to “EXCHANGER DUTY”; for the value field, use the calculated condenser duty from the COLUMN block


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Cyclohexane HeatX Workshop (2) 

Specify the hot fluid on the SHELL side



Use the TEMA data sheet on the next page to enter the following information:



Shell inside diameter (see the size item in row 6 and the shell OD in row 42 of the TEMA sheet), number of tubes, tube OD, tube thickness, tube pitch, tube pattern, baffle type, baffle cut, center-to-center (c/c) baffle spacing, and all 4 nozzle diameters NOTE: Use 29 total baffles Allow all other input fields to use default values



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Aspen+ Essential

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