Aspen Examples

Aspen Dynamics™ 12.1

Aspen Dynamics Examples

Version: 12.1 August 2003 Copyright © 2003 by Aspen Technology, Inc. All rights reserved. AspenTech product names that are mentioned in this manual, e.g., Aspen Dynamics™, Aspen Custom Modeler®, Aspen Plus™, Enterprise Optimization and the aspen leaf logo are trademarks or registered trademarks of Aspen Technology, Inc., Cambridge, MA. 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 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.

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Contents

Introduction

iii

About This Guide.............................. ........................................................ ................................................................................. ......................... iii Associated Guides....................................... ................................................... .................... iii What You Need To Use This Guide .................................................. ................................ iv For More Information ............................................ ................................................... ......... iv Online Help................................................... Help ................................................... .................................................... ......................................................... ..... iv Printing the Portable Document Format Files (PDFs).............................................v World Wide Web ............................................ ................................................... ......v Technical Support....................................................................................................v

1 Example Simulations

1-1

DyBatch ................................................... ........................................................ ........................................................................ ................ 1-2 Using Script Script Automation in the DyBatch Example........................... .................. 1-3 Using Tasks in the DyBatch Example ............................................. .................... 1-4 Files Included with the DyBatch Example ....................................... ................... 1-4 Running the DyBatch Example ................................................ ........................... 1-4 BatchDistOpt ....................................................... ............................................................................................................... ............................................................ .... 1-8 Running the BatchDistOpt Example................................ .................................... 1-8 Creating the BatchDistOpt Example.................................... ................................ 1-9 BatchColumn ...................................................... .............................................................................................................. ........................................................... ... 1-11 The Aspen Plus Simulation.................................................. .............................. 1-11 Setting Up the Dynamic Simulation ........................................... ....................... 1-12 Running the BatchColumn Example .................................................. ............... 1-12 Initializing the the BatchColumn Example in Aspen Dynamics............................. Dynamics ............................. 1-12 BatchReactor............................................................. BatchReactor.......... ................................................... .................................................... ...................................................... 1-14 The Aspen Plus Simulation.................................................. .............................. 1-14 Setting Up the Dynamic Simulation ........................................... ....................... 1-14 Running the BatchReactor Example......................................... Example ......................................... ......................... 1-15 Initializing the BatchReactor Example in Aspen Dynamics Dynamics ............................. 1-15 DyC2splt .................................................. ....................................................... ...................................................................... ............... 1-16 DyEster ..................................................... ............................................................................................................. ..................................................................... ............. 1-17 DyEtoh ..................................................... ............................................................................................................ ...................................................................... ............... 1-19

Aspen Dynamics Examples Guide

Contents

i

DyFlash..................................................... DyFlash ............................................................................................................. ..................................................................... ............. 1-19 DyMCH................................................................... ....................................................... 1-20 DyPfdtut................................................................... DyPfdtut........... .............................................................................................................. ...................................................... 1-21 DyMTBE................................................................. ....................................................... 1-22 Pressure Relief Column Example ................................................... ............................... 1-23 Pressure Relief Reactor Example .............................................. .................................... 1-25 Running the Completed Relief Simulation........................................... Simulation ........................................... ............. 1-25 Creating the Reactor Relief Simulation ....................................... ...................... 1-26 BatchEster ................................................ ................................................... ................... 1-30 BatchEster1 ............................................. ................................................... ........ 1-31 BatchEster2 ............................................. ................................................... ........ 1-32 BatchEster3 ............................................. ................................................... ........ 1-33 Kinetics Estimation Estimation from from RC1 Calorimeter Results.............................................. Results. ............................................. ........ 1-34 Assumptions of the Kinetics Kinetics Example................................................ Example ................................................ ............... 1-34 Defining the Reaction Mechanism ............................................. ....................... 1-34 About the Experimental Data ........................................... ................................. 1-36 Running the Kinetics Estimation Example ......................................... ............... 1-37 GasHDPE....................................................... GasHDPE .............................................................................................................. ................................................................ ......... 1-38 Running the GasHDPE Example ........................................................ ....................................................................... ............... 1-40 Nylon6 ..................................................... ............................................................................................................. ...................................................................... .............. 1-41 Running the Nylon6 Example.................................. .......................................... 1-42 Polystyrene (PS) ................................................. .................................................... ........................................................... ....... 1-43 Running the Polystyrene (PS) Example....................................... ...................... 1-44 Reverse Flow Simulation............. .................................................... .................................................................................. .............................. 1-44 DIERS Benchmark Examples............................................................ Examples........ ................................................................................ ............................ 1-46

ii

Contents


Introduction

This chapter describes: The contents of this guide Associated guides Where to find further information

• • •

About This Guide This guide takes you through a series of worked simulations that run in Aspen Dynamics.

Associated Guides Aspen Dynamics also comes with these other guides: Guide Title

Description

Getting Started Guide

Contains three tutorials for you to work through, to familiarize yourself with Aspen Dynamics

Using Aspen Dynamics

Contains introductory information on Aspen Dynamics, as well as instructions for creating, editing and running simulations.

Reference Guide

Describes the models, physical property procedures and global parameters that are available in Aspen Dynamics


Introduction

iii

What You Need To Use This Guide To use this guide, you need Aspen Dynamics installed on your PC or a PC file server running Windows 2000 or Windows XP. For information on how to do this, read the AES the AES Installation Guide supplied with the product, or contact your system administrator.

For More Information You can obtain information on AES products by: Accessing the comprehensive online Help system Reading the printed guides supplied with your product Printing the Portable Document Format (PDF) files supplied on the installation CD Accessing Aspen Technology's web page

• • •

•

If you need more detailed assistance than that provided in the online Help and the PDF files, you can contact Technical Support. This section explains how to use the online help, print PDF files, find Aspen Technology on the web, and contact Technical Support.

Online Help

To access online Help: From the Help menu, click Help Topics and then do one of the following:

•

To

Do this

Display a hierarchy of topics by category

Click the Contents tab

Display an index of all Help topics

Click the Index tab and then type the word you require

Search for words or phrases within the Help topics

Click the Find tab and then type the word or phrase you require

Tip To display Help on buttons, fields, menu commands, and other screen elements, click the What's This button: or , at the top of the window, and then click the element.

iv

Introduction


Printing Online Help

To display information on how to print online Help: 1. Open your Aspen Dynamics product and from the the Help menu, click Help Topics. 2. On the Contents tab, double-click Using Help and then double-click Print Help Topics.

Printing the Portable Document Format Files (PDFs)

To print these guides, you must have Adobe Acrobat Reader installed on your machine. Tip If you do not have the Adobe Acrobat Reader, you can download a free copy from the Adobe web site at http://www.adobe.com . Note Adobe and Acrobat are trademarks of Adobe Systems, Incorporated.

After you have installed the Adobe Acrobat Reader, you can open the files to view and print the guides. To do this: From the Start menu, point to Programs, then AspenTech , Aspen Engineering Suite, Product Suite, Product Name 12.1, Documentation, and then click the name of the guide you want to access.

•

World Wide Web

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

Technical Support

AspenTech customers with a valid license and software maintenance agreement can register to access the Online Technical Support Center at http://support.aspentech.com. This web support site allows you to: • •

Access current product documentation Search for tech tips, solutions and frequently asked questions (FAQs)

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Search for and download application examples

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Search for and download service packs and product updates

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Submit and track technical issues

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Search for and review known limitations

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Send suggestions

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:


Introduction

v

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Technical advisories

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Product release announcements

Customer support is also available by phone for customers with a current support contract for this product. The hours listed are in local time. For the most current contact information, please see the Online Technical Support Center at http://support.aspentech.com.

vi

Introduction


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Introduction

vii

Fax Numbers

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viii

Introduction


1 Example Simulations

A number of example simulations are included in your Aspen Dynamics installation. If you have installed in the default location, these will be in the folder C:\Program Files\AspenTech\Aspen Dynamics 12.1\Examples. Many of the examples are supplied as an Aspen Plus backup (.bkp) file. To run one of these examples: 1. Copy the backup file and any associated text files to a convenient working folder. 2. Load it into Aspen Plus and proceed to create and run the dynamic simulation in the normal way. Some examples have more associated files. The files for each one of these examples are supplied in a separate sub-folder. The example descriptions include details of how to run these examples. This table summarizes the examples that are supplied: Example

Description

DyBatch

A batch distillation column

BatchDistOpt

Dynamic optimization of a batch distillation column

BatchReactor

A batch reactor initialized using script automation

BatchColumn

A batch distillation column initialized using script automation

DyC2splt

A C2 splitter column

DyEster

An esterification reactor

DyEtoh

Azeotropic distillation of ethanol and water

DyFlash

A simple flash drum

DyMCH

Extractive distillation of methyl-cyclohexane

DyPfdtut

Production of cyclohexane from benzene

DyMTBE

Control of an MTBE reactive distillation column

DyMCH

Extractive distillation of methyl-cyclohexane but extended to include pressure relief

continued overleaf…


Example Simulations

1-1

PRReactor

A reactor pressure relief system using an RCSTR with a simple esterification reaction

BatchEster

Batch reactor examples

KineticsEst

Estimating kinetic parameters with a dynamic tank reactor

MchDMC

Extractive distillation of methyl-cyclohexane using a DMCplus controller Note You need DMCplus Online to follow this example.

GasHDPE

Gas phase high density polyethylene using Polymers Plus with Ziegler Natta kinetics

Nylon6

Polymerization of caprolactam to Nylon 6 using Polymers Plus with step growth kinetics

PS

Polystyrene bulk polymerization by thermal initiation using Polymers Plus with free radical kinetics

Reverse flow

How to set up and run the reverse flow simulation example

DIERS Benchmark Examples

Design Institute for Emergency Relief systems (DIERS) pipe and safety relief valve benchmark examples.

Each of these examples is described in more detail later in this chapter.

DyBatch This is an example of batch distillation and illustrates these features of Aspen Dynamics: Pressure driven flow Script automation of a Aspen Dynamics flowsheet Use of tasks to start up and operate the batch column Use of flowsheet equations to include hydraulics for the reflux flow

• • • •

Note If you are using a Simulation Engine installation from a client machine, you must make sure that you run Aspen Plus using the same server and the same working folder as you have configured for Aspen Dynamics.

The solvents to be separated are isopropyl-acetate (IPA), methanol (MEOH), and tetrahydrofuran (THF). As can be seen by the residue curve below, this is a low-boiling azeotrope of THF and MEOH form.

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Example Simulations


The batch distillation will form the azeotrope in the condenser accumulator, thus leaving a pure IPA product as the bottom product.

The simulation starts with this Aspen Plus flowsheet.

Using Script Automation in the DyBatch Example

It is very useful to begin a batch distillation by starting with an empty distillation column. No distillation column is truly empty at start-up, and the presence of nitrogen is taken into account when there is no liquid present in the column. A gas purge stream and a condenser vent are also included in the simulation, since many start-ups include cycles of nitrogen purge and vacuum. In order to initialize the distillation column in an empty state, a script is used to initialize all of the molar hold-ups. Since the volume for each tray is known from the Aspen Dynamics simulation, the script easily calculates the molar hold-ups with the


Example Simulations

1-3

assumption that most of the composition is nitrogen, with on ly traces of other components. The script also a lso shuts off all of the feed and product flows to the column.

Using Tasks in the DyBatch Example

Aspen Dynamics can simulate batch or semi-batch ope rations with tasks. Time and event-dependent tasks are introduced to vary the controllers in the simulation just as operators would c hange the controllers in a batch distillation plant. The dynamic simulation starts by filling the distillation column sump with a charge transferred from the feed tank . This is done using the Fill task. After the sump is charged, the Heatup task ramps the reboiler steam temperature up to the operating value of 130 °C. During the Heatup operation the controller PC4 manipulates the position of valve V3 to allow the nitrogen to vent from the column. When the column reaches operating temperature, the task Pcontrol closes the vent valve, and activates the pressure controller REBPID. When the column reaches total reflux, task Step1 activates the reflux controller RRPID which manipulates the product v alve V7 to maintain the required reflux ratio. Task Step1 stops the simulation when the distillate IPA mole fraction rises to 0.004.

Files Included with the DyBatch Example

Running the DyBatch Example

The example includes these files: File Name

Description

DyBatch.bkp

The Aspen Plus backup file

DrumHydraulics.txt

The flowsheet equation for the reflux drum hydraulics

EmptyScript.txt

The initialization script

FillTask.txt

The fill task

HeatupTask.txt

The heatup task

PControlTask.txt

The pcontrol task

Step1Task.txt

The step1 task

To run the DyBatch example: 1. In Aspen Plus, open DyBatch.bkp. If you installed Aspen Dynamics in the defau lt location, DyBatch.bkp is in C:\Program Files\AspenTech\Aspen Dynamics 12.1\Examples\DyBatch. 2. Perform a run.

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Example Simulations


3. Export it as a pressure-driven dynamic simulation simulation file. 4. Exit Aspen Plus. Now you are ready to initialize the simulation in Aspen Dynamics. Initializing the DyBatch Example in Aspen Dynamics

To run the DyBatch example: 1. In Aspen Dynamics, open DyBatch.dynf. 2. Remove the LC6 level controller and its control connections. 3. Remove the LC3 level controller and its control connections. Add a Ratio control element (RR) and a new PID controller (RRPID) under stream 9 on the flowsheet. 4. Using a ControlSignal stream, connect: Input1 of RR to the total mass reflux flow of the BATCHCOL column (Reflux.Fm) Input2 of RR to the stream 3 total mass flow (STREAMS("3").Fm) Output of RR to the PV input of RRPID Controller output (OP) of RRPID to the input of V7 •

•

• •

5. Open the RRPID Configure form, form, and click Initialize Initialize Values to initialize settings for this controller. Change the Gain to 3, the Integral time to 8 minutes, and on the Ranges tab, change the process variable range to be from 0 to 50. Close the Configure form. 6. Add a second PID controller called REBPID and connect the PV input to the stage 1 pressure (Stage(1).P), and the output to the reboiler UA (Stage(15).UA). 7. Open the REBPID Configure form form and initialize initialize the controller. Change the gain to 30, the integral time to 12 minutes, and the controller action to Reverse. Close the Configure form. After the addition of the controllers, the flowsheet should look like this:


Example Simulations

1-5

8. In the All Items Items pane of the Simulation Explorer, select Flowsheet. In the Contents pane, double-click the Flowsheet icon to open Constraints. 9. In the text editor window, select the commented text, then click with the right mouse button and from the menu that appears, point to Insert then click File. Insert DrumHydraulics.txt. 10. Then click again with the right mouse button, point to Build then click Compile. The flowsheet is now over specified by 1. Close the text editor window. Running the DyBatch Example in Aspen Dynamics

To finish specifying and run the DyBatch example follow these steps: 1. Using Variable Find

, find the variable Reflux.Fmr.

2. Click with the right mouse button on the variable and click Properties. Change the specification from Fixed to Free, then click Apply. The flowsheet will now be square, and properly specified. Close the Variable Find window. 3. In the All Items Items pane of the Simulation Explorer, ensure Flowsheet is selected. In the Contents pane, double-click Add Script. 4. Enter a name for the script, for example, Empty. 5. In the text editor window, click the right mouse button and

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Example Simulations


point to Insert, then click File. Insert Empty Script.txt. 6. Again click the right mouse button and click Invoke Script. Close the text editor window. Now create a task called Fill. To do this: 7. In the Contents pane of the Simulation Explorer, double-click Add Task. Enter the name Fill. 8. In the text editor window, click the right mouse button and point to Insert, then click File. With the cursor positioned just above the End statement, insert FillTask.txt. 9. Again click with the right mouse button and click Compile. Close the text editor window. 10. In the Contents pane of the Simulation Explorer, double-click the task to activate it. Repeat steps 7 – 10 to create the Heatup, Pcontrol and Step1 tasks. 11. Change the run mode to Dynamic and perform a dynamic run. These steps are automatically performed and the run will stop on completion:


Time (hrs)

Task

Action

0.05 – 0.1

Fill

Ramp Valve V2 position to 20% (start filling column)

0.51 – 1.51

Heatup

Level in column > 0.5m, ramp-up reboiler duty

0.58 –0.63

Fill

Level in feed tank < 0.3m, ramp Valve V2 position to 0%

1.26

Pcontrol

Temperature at top of column > 58 °C, commission pressure control

1.68 -1.78

Step1

Reboiler on and steady, commission RefluxRatio control

2.71 - 3.14

Step1

As the IPA molefraction rises at top of column, increase reflux ratio

3.29

Step1

Step1 IPA molefraction reaches 0.004, pause run

Example Simulations

1-7

BatchDistOpt This example shows how to use Aspen Dynamics for the optimization of the operation of a batch distillation column. The column separates a mixture of acetone and iso-propyl alcohol (IPA). The objective is to find the best b est profile of reflux ratio versus time to minimize the time to separate the mixture, subject to constraints on the purity and yield of the acetone rich distillate. This example is created by starting with an a n Aspen Plus simulation, exporting this to Aspen Dynamics, and then configuring the simulation within Aspen Dynamics. The configured Aspen Dynamic file is provided. For details of how to run this see Running the BatchDistOpt Example. For detailed instructions on how to create the example from the Aspen Plus bkp file see Creating the BatchDistOpt Example. The procedure may help you in creating your own applications.

Running the BatchDistOpt Example

To run the BatchDistOpt example: 1. Locate the example folder BatchDistOpt. If you you installed installed Aspen Dynamics in the default location, this is in: C:\Program Files\AspenTech\Aspen Dynamics 12.1\Examples 2. Copy all of the files in the BatchDistOpt folder to a convenient working folder. 3. Load the backup file BatchDistOpt.bkp into Aspen Aspen Plus and run it. 4. From the File menu, click Save As and save the simulation as an Aspen Plus Document (.apw file), with name BatchDistOptdyn, then exit Aspen Plus. This creates the file BatchDistOptdyn.appdf which contains all of the physical properties data required for the dynamic simulation. The .apw file is not required, and you can delete this. 5. Load the file BatchDistOpt.dynf into Aspen Aspen Dynamics. Dynamics. 6. Select Snapshots from the the Tools menu. Double click on the result Init to use it to initialize the simulation, and then close the dialog box. 7. Click the run button to run run the simulation. 8. To see the progress of the optimization open the Flowsheet plot Reflux. This shows the reflux ratio versus time. You can see how this is manipulated by the optimizer during successive iterations towards the solution. You can also open the Flowsheet table OptSummary to see a summary of the

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Example Simulations


optimization results. Note. If you you want to do repeated optimization runs, after a run rewind to time zero before starting the next run. You may also want to load the result Init to be sure to start the run from this initial condition.

Creating the BatchDistOpt Example

To create the BatchDistOpt example starting with the Aspen Plus simulation: 1. Locate the example folder BatchDistOpt. If you installed installed Aspen Dynamics in the default location, this is in: C:\Program Files\AspenTech\Aspen Dynamics 12.1\Examples 2. Copy all of the files in the BatchDistOpt folder to a convenient working folder. 3. Load the simulation in BatchDistOpt.bkp in to Aspen Plus, and run the simulation. 4. After the run run completes, completes, select Export on the File File menu, and export the simulation as a flow driven d riven dynamic simulation. 5. Load the simulation in to Aspen Dynamics. 6. Delete the controllers PC1, PC1, LC1 and the control streams streams connecting them to the column. To do this go to the Dynamics folder in Explorer and open Scripts, Double click the RemoveControl script to run it. 7. Make the following changes to model the condenser as a total condenser with perfect vent pressure control: In stream CONDENS fix the pressure P In stream OVHD free the required flow FR In block COND fix the vapor fraction vf to a value of 0, and free the required condenser duty QR • • •

8. Shut off feed and product flows from the flowsheet by changing the values of Streams("FEED").FR to 0 Streams("BOT").FmR to 0 Streams("PROD").FmR Streams("PROD").FmR to 0 • • •

9. Initialize the the receiver to be empty at known temperature. To do this: Change the value of BLOCKS("RECEIVER").Mc("ACETONE") and BLOCKS("RECEIVER").Mc("IPA") to 0 Change the Spec of BLOCKS("RECEIVER").E to Free Change the spec of BLOCKS("RECEIVER").T to Initial •

• •


Example Simulations

1-9

10. For dynamic optimization it is necessary to en sure that the simulation is solved to a high degree of precision and that any noise is minimized. To help with this you must change from using local properties to using rigorous properties. In Explorer go to Simulation and open the SimulationOptions table. Change the Global property mode to Rigorous. 11. Perform an initialization run and save the result as “Init” for future use. 12. The next few steps configure the dynamic optimization problem. To begin, from the Tools menu select Optimization. 13. On the Setup tab select "Perform Dynamic Optimization". 14. On the Control Variables tab add the variable BLOCKS("REFSPLIT").sf("REFLUX"). 15. On the Control Discretization tab select Free for Final Time, deselect "Use Default Bounds" and change the lower bound to 0.2. Change Number of Elements to 5. 16. On the Objective Function tab select "Add final time to objective function". Close the Optimization window. 17. On the Dynamic Constraints tab add the variable blocks(“RECEIVER”).Mc(“Acetone”). Leave the Constraint type at the default of Final time. Click the edit button to edit the constraint and enter a lower bound of 0.07. Leave the upper bound at 1000000. 18. On the Dynamic Constraints tab add the variable blocks(“RECEIVER”).Out_P.Z(“IPA”). Leave the Constraint type at the default of Final time. Click the edit button to edit the constraint and enter an upper bound of 0.06. Leave the lower bound at 0. 19. Create a new Flowsheet Table to display a summary of the optimization results. Do this by clicking the New Table button on the Tools toolbar. Call the table OptSummary. Add the following variables to the table: BLOCKS("REFSPLIT").sf("REFLUX") BLOCKS("RECEIVER").z("IPA") BLOCKS("RECEIVER").Mc("ACETONE") 20. Create a new Flowsheet plot to display how the optimizer changes reflux versus time. You can do this by clicking the New Plot button on the Tools toolbar. Call the plot Reflux. Add the variable BLOCKS("REFSPLIT").sf("REFLUX"). Right mouse click on the time axis and select Edit. Change the axis range to 0 to 1. 21. For dynamic optimization it is necessary to tighten the solver

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Example Simulations


tolerances to reduce the noise seen by the optimizer. On the Run menu go to Solver Options and enter the following values: On the Tolerances tab: Absolute Variable tolerance = 1e-7 Relative Variable tolerance = 1e-7 On the Integrator tab: Minimum Integration step = 1e-5 Absolute Integration error tolerance = 1e-7 On the Optimizer tab: Solution Convergence Tolerance = 0.005 •

•

•

22. Change the run mode to Optimization and run the simulation. Note. If you you want to do repeated optimization runs, after a run rewind to time zero before starting the next run. You may also want to load the result Init to be sure to start the run from this initial.

BatchColumn This is an example of a batch column simulation and illustrates these features of Aspen Dynamics: •

•

Use of scripts to automate initialization of an Aspen Dynamics flowsheet Use of tasks to start up and operate the batch reactor

A mixture of methanol, ethanol and water is to be separated using a batch distillation column. The composition of the charge is 30% ethanol, 30% methanol and 40% water by weight. The required product purity is 68% w/w.

The Aspen Plus Simulation

Aspen Plus has been used to set up the flowsheet for the batch column, which will be exported to Aspen Dynamics and initialized to be full of nitrogen at 20 C and 1 atmosphere. Nitrogen has been added to the component list in Aspen Plus even though it is not used in the Aspen Plus simulation. The column has been modeled using a RadFrac block. Feed streams for the charge and nitrogen have been specified together with vapor and liquid distillate streams and a bottoms stream. The column has been specified with 10 stages, a partial vaporliquid condenser and a kettle reboiler. The column dimensions have been specified on the RadFrac Dynamic form together with the sump and reflux drum size and geometry. The LMTD heat


Example Simulations

1-11

transfer option has been selected for the condenser and the cooling medium temperature specified as 20 C. This represents cooling water. The Constant temperature heat transfer option has been selected for the reboiler and the medium temperature has been specified as 120 C. This represents steam heating. h eating.

Setting Up the Dynamic Simulation

Script automation is used to set up the dynamic simulation. The following steps are carried out using 2 scripts. A flowsheet level script called Setup and a RadFrac model script called Empty. The Flowsheet level script does the following: 1. Adds a reflux ratio controller 2. Sets the feed flow flow rates to zero 3. Calls the RadFrac Empty script to initialize the column to be full of nitrogen at 20 C and 1 atmosphere. 4. Performs an initialization run. 5. Saves a snapshot

Running the BatchColumn Example

To run the BatchColumn example: 1. In Aspen Plus, open BatchColumn.bkp. If you installed installed Aspen Dynamics in the default location, BatchColumn.bkp is in: C:\Program Files\AspenTech\Aspen Dynamics 12.1\Examples\BatchColumn.

2. Perform a run. 3. Export it as a flow-driven dynamic dynamic simulation simulation file. file. 4. Exit Aspen Plus. Now you are ready to initialize the simulation in Aspen Dynamics.

Initializing the BatchColumn Example in Aspen Dynamics

To initialize the BatchColumn Example in Aspen Dynamics: 1. In Aspen Dynamics, open BatchColumn.dynf. 2. In the All Items Items pane of the Simulation Explorer, ensure Flowsheet is selected. In the Contents pane, double-click Add Script. 3. Enter a name for the script, for example, Setup. 4. In the text editor window, click the right mouse button and point to Insert, then click File. Insert BatchColumnScript.txt. 5. Again click the right mouse button and click Invoke Script. Close the text editor window. 6. Now create a task called BatchOperation. To do this: 7. In the Contents pane of the Simulation Explorer, double-click

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Add Task. Enter the name BatchOperation. 8. In the text text editor window, window, select all of the existing text with the mouse (or use Ctrl-A). Click the right mouse button and point to Insert, then click File. Insert BatchOperationTask.txt. 9. Again click with the right mouse button and click Compile or press F8. Close the text editor window. 10. In the Contents pane of the Simulation Explorer, double-click the task to activate it. 11. Change the run mode to Dynamic and perform a dynamic run. Operating Sequence

The operating sequence defined by the tasks is: At time = 0.5 hours: 1. Ramp the mass mass flow rate of the Feed stream stream to 1000 kg/hr over 0.1 hours. 2. Wait until the cumulative mass flow of stream Feed is >= 1000 kg. 3. Step the mass flow rate of the Feed stream to 0 kg/hr. 4. Wait for 3 minutes. 5. Increase the flow flow of the Nitrogen feed stream to 0.1 kmol/hr. kmol/hr. This is needed to maintain the pressure in the column. 6. Ramp the reboiler medium medium temperature to 80 C over 30 minutes. 7. Wait until the reflux drum level >= 0.3 m. 8. Start the reflux flow. 9. Wait for 3 minutes. 10. Start the product draw. 11. Ramp the reboiler medium temperature to 90 over 30 minutes. 12. Wait until the mass fraction of methanol in the distillate receiver reaches 0.68. 13. Pause the simulation. 14. Use plots and tables to view the results of the simulation during the dynamic run. 15. If you wish to repeat the simulation, rewind to saved snapshot Empty_Initial and then run again.


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BatchReactor This is an example of batch reactor simulation and illustrates these features of Aspen Dynamics: •

•

Use of scripts to automate initialization of an Aspen Dynamics flowsheet Use of tasks to start up and operate the batch reactor

The reaction modeled is the production of carbon tetrachloride from tri-chloromethane CHCl3 + Cl2 ! CCl4 + HCl Note: The kinetics used are for illustration purposes only.

The Aspen Plus Simulation

Aspen Plus has been used to set up the flowsheet for the batch reactor, which will be exported to Aspen Dynamics and initialized to be full of nitrogen at 25 C and 5 bar. Nitrogen has been added to the component list in Aspen Plus even though it is not used in the Aspen Plus simulation. The reactor has been modeled using an RCSTR block. Feed streams for CHCl3 and Cl2 have been be en specified together with vapor and liquid product streams. The reactor volume has been specified together with the diameter and geometry. The reactor needs to be cooled so the LMTD heat transfer option has been selected and the cooling medium temperature specified as 20 C. This represents cooling water in a jacketed reactor. The mass and heat capacity of the reactor have been specified so that the dynamic effects of the equipment heat capacity can be modeled. The reactor vapor product stream is sent to a condenser, which has been modeled using an instantaneous HeatX block with refrigerant on the cold side. An instantaneous Flash2 block has been used to separate the liquid from the vapor. The liquid is returned to the reactor via a Heater block to increase the pressure while the vapor is sent to a vent stream.

Setting Up the Dynamic Simulation

Script automation is used to set up the dynamic simulation. The following steps are carried out using 3 scripts. A flowsheet level script called Setup and an RCSTR model script called Empty and a PID model script called Initialize. The Flowsheet level script does the following: 1. Sets the feed flow flow rates to zero.

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2. Adds temperature temperature controller TC3 to the flowsheet. 3. Connects TC3.PV to the reactor temperature. 4. Connects TC3.OP to the reactor cooling medium flow flow rate 5. Calls the PID controller Initialize script script to initialize TC3. 6. Calls the RCSTR Empty script to initialize the reactor to be full of nitrogen at 25 C and 5 bar. 7. Sets the temperature controller to manual, sets it’s output to 100 kg/hr and it’s setpoint to 25 C. 8. Performs an initialization run. 9. Saves a snapshot.

Running the BatchReactor Example

To run the BatchReactor example: 1. In Aspen Plus, open BatchReactor.bkp. If you installed installed Aspen Dynamics in the default location, BatchReactor.bkp is in: C:\Program Files\AspenTech\Aspen Dynamics 12.1\Examples\BatchReactor.

2. Perform a run. 3. Export it as a flow-driven dynamic dynamic simulation simulation file. file. 4. Exit Aspen Plus. Now you are ready to initialize the simulation in Aspen Dynamics.

Initializing the BatchReactor Example in Aspen Dynamics

To initialize the BatchReactor Example in Aspen Dynamics

1. In Aspen Dynamics, open BatchReactor.dynf. 2. In the All Items Items pane of the Simulation Explorer, ensure Flowsheet is selected. In the Contents pane, double-click Add Script. 3. Enter a name for the script, for example, Setup. 4. In the text editor window, click the right mouse button and point to Insert, then click File. Insert SetupScript.txt. 5. Again click the right mouse button and click Invoke Script. Close the text editor window. 6. Delete level controller LC1 and its control streams streams 7. Now create a task called ChargeFeed. To do this: In the Contents pane of the Simulation Explorer, double-click Add Task. Enter the name ChargeFeed. 8. In the text text editor window, window, select all of the existing text with


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the mouse (or use Ctrl-A). Click the right mouse button and point to Insert, then click File. Insert ChargeFeedTask.txt. 9. Again click with the right mouse button and click Compile or press F8. Close the text editor window. 10. In the Contents pane of the Simulation Explorer, double-click the task to activate it. 11. Repeat steps 6 – 10 to create tasks StartCl2, TempControl and PauseSim. Change the run mode to Dynamic and perform a dynamic run

The operating sequence defined by the tasks is: At time = 0.05 hours: 1. Step the mass flow rate of the CHCl3 feed stream to 5000 kg/hr. 2. Wait for 30 minutes. 3. Step the mass flow rate of the CHCl3 feed stream to 0 kg/hr. At time = 0.5 hours: 1. Ramp the mass flow rate of the Cl2 feed stream to 200 kg/hr over 15 minutes 2. Ramp the mass mass flow of the refrigerant to the condenser to 1000 kg/hr over 15 minutes When the reactor temperature reaches 60 C: 1. Switch the temperature controller to Auto. 2. Change the set point to 60 C. 3. Wait for 6 minutes and then then ramp the set set point to 80 C over 5 minutes. Pause the simulation when the mass holdup of CHCl3 in the reactor falls to less than 5 kg. Use plots and tables to view the results of the simulation during the dynamic run. If you wish to repeat the simulation, rewind to saved snapshot Empty_Initial and then run again.

DyC2splt This example models a C2 splitter distillation column which separates a mixture of mostly ethane and ethylene into two main product streams. A third top product stream contains mostly methane.

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The simulation uses the Aspen Plus tray rating ca pability to perform rigorous tray calculations. These same methods are used in the dynamic simulation. A typical use of dynamic simulation would be to evaluate and tune alternative control strategies for this distillation column. Note If you are using a Simulation Engine installation from a client machine, you must make make sure that you you run Aspen Plus Plus using the same server and the same working folder as you have configured for Aspen Dynamics.

DyEster This example simulates a process for production of dimethyl-ether from the esterification reaction between methanol and n-hexanoic acid. The reaction takes place in a continuous stirred tank reactor. Attached to this is a separation system for removing water from the reactor to help promote the esterification reaction.


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Although this example is formulated as a continuous c ontinuous process, the dynamic simulation can be operated in a batch or semi-batch way. A typical use of dynamic simulation would be to analyze different operating strategies for this process. Note If you are using a Simulation Engine installation from a client machine, you must make make sure that you you run Aspen Plus Plus using the same server and the same working folder as you have configured for Aspen Dynamics.

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DyEtoh This example models the separation of ethanol and water using azeotropic distillation, using cyclohexane as an entrainer to break the water-ethanol azeotrope. Because of the recycles between the columns the dynamics of this process can be quite complex. A dynamic simulation can be used to examine the response of this process to feed disturbances, and to help determine the best control scheme for the process. Note If you are using a Simulation Engine installation from a client machine, you must make make sure that you you run Aspen Plus Plus using the same server and the same working folder as you have configured for Aspen Dynamics.

DyFlash This is a simple example of the separation of water, ethanol and benzene in a flash drum.

Note If you are using a Simulation Engine installation from a client machine, you must make make sure that you you run Aspen Plus Plus using the same server and the same working folder as you have configured for Aspen Dynamics.


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DyMCH This example models the extractive distillation d istillation of methylcyclohexane and toluene, using phenol as an entrainer. The dynamic simulation can be used to evaluate and tune alternative control strategies for controlling the purity of the methylcyclohexane product.

Note If you are using a Simulation Engine installation from a client machine, you must make make sure that you you run Aspen Plus Plus using the same server and the same working folder as you have configured for Aspen Dynamics.

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DyPfdtut This example models the production of cyclohexane by the hydrogenation of benzene. The flowsheet includes the main reactor loop, and a downstream column for product purification.

The dynamic simulation can be used to examine the operability of this process, and to evaluate alternative control strategies. Note If you are using a Simulation Engine installation from a client machine, you must make make sure that you you run Aspen Plus Plus using the same server and the same working folder as you have configured for Aspen Dynamics.


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DyMTBE MTBE (Methyl-tert-Butyl-Ether) is produced to enhance the octane of gasoline. This chemical is often manufactured from the reaction of iso-butylene and methanol. This example illustrates how MTBE can be manufactured in a distillation column with catalytic packing.

The distillation column exhibits multiple-steady states. At least three steady states have been shown to occur. In Aspen Plus, a sensitivity study has been used to move the methanol feed location from the top of the column to tray 10. Tray 10 is the optimum feed location, and gives the highest MTBE yield. It is interesting to study the control of this column, since even small disturbances in the methanol feed rate can move the column to a lower yield steady state. Note If you are using a Simulation Engine installation from a client machine, you must make make sure that you you run Aspen Plus Plus using the same server and the same working folder as you have configured for Aspen Dynamics.

A Fortran subroutine is used to calculate the kinetics of the reaction. This is contained in the file RaMTBE.f. Before running the simulation you must: 1. Copy RaMTBE.f to the same folder as the backup file DyMTBE.bkp. 2. Open an Aspen Plus Simulation Engine window (MS-DOS). 3. In this window, move to the folder containing RaMTBE.f. 4. Compile RaMTBE.f using the command: aspcomp ramtbe.f

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Pressure Relief Column Example This example takes an existing Aspen Dynamics example, DyMch, and extends it to include pressure relief. Note. If you are using a Simulation Engine installation from a client machine, you must make make sure that you you run Aspen Plus Plus using the same server and the same working folder as you have configured for Aspen Dynamics.

Follow these steps to set up this example exa mple in Aspen Dynamics: 1. In Aspen Plus, open DyMch.bkp and run the simulation. If you installed Aspen Dynamics in the defau lt location, DyMch.bkp is in C:\Program Files\AspenTech\Aspen Dynamics 12.1\Examples. 2. Export the simulation as a Flow Driven Driven Dyn Simulation. 3. In Aspen Dynamics, open the file. 4. On the Run Control toolbar, set the Run Mode to Initialization. 5. Run the simulation. 6. Add an instance of the PSV PSV model just above the column. The PSV model is in the PressureRelief folder of the Aspen Dynamics library. 7. Connect the relief port of the column to to the inlet of the PSV using a stream of type MaterialStream. Also add a MaterialStream product to the outlet of the PSV. 8. Open the Configure form for the product stream stream and fix fix the pressure in the product stream. Enter your required product stream pressure.


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The flowsheet should look like this:

9. Open the Configure form form of the PSV and click Initialize. When the run has completed, enter this data: On the

Do this

Type Tab

Throat Diameter: 0.2 m Inlet Diameter: 0.22 m Outlet Diameter: 0.22 m

Flow Calcs Tab

Flow calculation method: Ideal HEM (Simpson)

Hysteresis Tab:

Set pressure: 1.2 atm Full lift pressure, opening: 1.3 atm Reset pressure: 1.1 atm atm

10. Click the Initialize button and wait a few moments for the run to complete.

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11. In the Simulation Explorer, ensure Flowsheet is selected and then add, compile and activate the following task: Task CondFail runs when time == 0.03 BLOCKS("PC2").automan BLOCKS("PC2").a utoman : 1; (BLOCKS("PC2").Opman (BLOCKS("PC2"). Opman : 0, End

This task simulates a loss of cooling water to the overhead condenser by stepping the output of the pressure controller to zero. 12. On the Integrator tab of Solver Options dialog: set the initial step size to 0.0001 hours; set the minimum step size to 1e-8 hours. h ours. 13. On the Run Options dialog, set the communication interval to 0.0001 hours. 14. Switch to Dynamic run mode and run the simulation.

Pressure Relief Reactor Example This is an example of a reactor pressure relief system. The reactor is an RCSTR with a simple esterification reaction. The relief system consist of a safety relief valve mounted on top of the reactor and a pipe attached to the end of the valve. In the example the contents of the reactor are heated at constant temperature and the effect this has on the pressure relief system can be observed. Note If you are using a Simulation Engine installation from a client machine, you must make make sure that you you run Aspen Plus Plus using the same server and the same working folder as you have configured for Aspen Dynamics.

For this example, you can either follow the instructions to create the reactor relief simulation example, starting from the Aspen Plus steady-state simulation, or you can run the completed relief simulation which is supplied.

Running the Completed Relief Simulation

To run the completed reactor reac tor relief simulation supplied: 1. In Aspen Plus, open PRReactor.bkp and run the simulation. If you installed Aspen Dynamics in the defau lt location, PRReactor.bkp is in C:\Program Files\AspenTech\Aspen Dynamics 12.1\Examples\PRReactor. 2. Export the simulation as a P Driven Driven Dyn Simulation (*.dynf & *dyn.appdf). 3. In Aspen Dynamics, open the file PRReactorA.dynf that is


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provided. 4. From the Tools menu, click Snapshots. This opens the Snapshot Management dialog box, which lists the available snapshots. 5. Click the DynStart snapshot, to highlight it for copying. 6. Click the Copy Values button. 7. Close the Snapshot Management dialog box. 8. On the Run Control toolbar, set the Run mode to Dynamic. 9. Open the ResultsReliefSummary form for the reactor. 10. Open the ResultsReliefPlot for the reactor reac tor and set the time axis range as 0 to 0.01 hours. 11. Run the simulation. Note that on the ReactorReliefSummary Rea ctorReliefSummary form, blue indicates the liquid height, and pink indicates the swell height.

Creating the Reactor Relief Simulation

Follow these steps to create the reactor rea ctor relief simulation from an Aspen Plus backup file. The reactor reac tor is an RCSTR with a simple esterification reaction. Opening and exporting the file Configuring the reactor Adding a PSV Adding a pipe Simulating a runaway reaction • • • • •

Opening and Exporting the Example

Follow these steps to create the reactor relief simulation: 1. In Aspen Plus, open PRReactor.bkp and run the simulation. If you installed Aspen Dynamics in the defau lt location, PRReactor.bkp is in C:\Program Files\AspenTech\Aspen Dynamics 12.1\Examples\PRReactor. 2. Export it as a P Driven Driven Dyn Simulation (*.dynf & *dyn.appdf). 3. In Aspen Dynamics, open the PRreactor.dynf generated. 4. On the Run Control toolbar, set the Run Mode to Initialization. 5. From the the Tools menu, point to Units of Measurement and select Metric. 6. Run the simulation. Now you can configure the reactor.

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Configuring the Reactor

Follow these steps to configure the reactor and create a reactor relief simulation: 1. Remove Temperature controller and its its control streams. 2. Remove Level controller and its its control streams. 3. Close valves B1 and B2. (To do this, open the Manipulate table and change the position to 0%.) 4. Open the Configure form form for the Reactor and under Advanced Options, select Perform Pressure Relief Vapor/Liquid Disengagement Calculations. 5. On the Configure form, form, click click the Setup button. 6. Choose Holdups tab. 7. Select N2 as Inert. 8. Check Specify Pressure and enter 1.2 bar. 9. Click the Setup button. 10. Check specify Temperature and enter 150 Deg C. 11. Click the Setup button. 12. Check Specify Vapor Volume Fraction and enter 0.1 (90% full of liquid). 13. Click the Setup button. 14. Select the Disengagement tab. 15. Choose DIERS Churn Turbulent as the method for disengagement. 16. Click the Setup button. The reactor is configured. Close the Configure form. Now you can add a PSV.


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Adding a PSV

Follow these steps to configure a PSV and create a reactor relief simulation: 1. From the the PressureRelief PressureRelief folder of the Dynamics library, library, drag and drop the PSV model to the flowsheet. 2. Using MaterialStream MaterialStream from the Dynamics Dynamics Library Library Stream Stream Types folder, join the Vapor outlet ou tlet to the Feed of the PSV and add a product stream from the outlet of the PSV. 3. Open the Configure form for the PSV instance and on the Type tab, enter 0.15m for the diameter. 4. Click the Initialize button. 5. On the Flow Calculations form, choose Ideal HEM (DIERS) (DIERS) as the flow method. 6. Click the Initialize button. 7. Choose the Hysteresis tab. 8. Set Valve Type to Balanced. 9. Enter these pressures: Set Pressure 2.0 bar Full Lift Pressure, Opening 2.5 bar Reset Pressure 1.5 bar The Full Lift Pressure, Closing, will be calculated from these three parameters. • • •

10. Ensure that the values look reasonable on the Hysteresis diagram tab. 11. Click the Initialize button and then close the Initialize form. With the PSV configured, now add a pipe. Adding a Pipe

Follow these steps to add a pipe and create a reactor relief simulation: 1. Drag and drop the Pipe2 model from the Dynamics library in the PressureChangers folder. 2. Connect output from PSV to to input of pipe and an outlet product using MaterialStream. 3. Open the Configure form form for the pipe. pipe. 4. On the Options form, form, choose Beggs-Brill as the friction friction correlation, and Dynamic as the momentum balance. 5. On the Dimensions form, form, enter diameter 0.15m and length 20m. 6. Click the Setup button.

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The pipe is now configured. Close the Configure form. Now you can simulate a runaway reaction. Simulating a Runaway Reaction

Follow these steps to simulate a runaway reaction and create a reactor relief simulation: 1. Open the Configure form for the reactor. reactor. 2. Select the Heat Transfer tab. 3. For the Heating Option, select select Constant Temperature. 4. Enter 300 °C for the Medium Medium Temperature. 5. Enter 224 kW/K for for the Overall heat transfer * area. 6. Close the Configure form and then change the run mode to Dynamic. 7. From the Run menu, click click Solver Solver Options. 8. On the Integrator tab: Set this option:

To:

Initial Integration Step

1E-5

Minimum Integration Step

1E-6

Maximum Integration Step

1E-3

Absolute Integration Error Tolerance

0.001

Tear Integration Error Tolerance

0.05

9. From the Run menu, click click Run Options. 10. Set the run mode to Dynamic. 11. Set the Communication Interval at 1E-4 and Pause at 0.05. 12. Open the ResultsReliefSummary form for the reactor. 13. Open the ResultsReliefPlot for the reactor reac tor and set the time axis range as 0 to 0.01 hours. 14. Run the simulation. Note that on the ReactorReliefSummary form, blue indicates the liquid height and pink indicates the swell height.


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BatchEster This is a set of three examples that tha t illustrate how to use Aspen Dynamics for batch reactor simulations. All three examples model the esterification of methanol and acetic acid to product methyl acetate. The three examples are: Example

Description

BatchEster1

Considers only the liquid phase in the reactor.

BatchEster2

Consider vapor and liquid. Includes a condenser.

BatchEster3

Consider vapor and two liquid phases. Includes a condenser.

These examples are designed to be used as templates that you can use as a starting point for your own o wn batch reactor simulations. Note If you are using a Simulation Engine installation from a client machine, you must make make sure that you you run Aspen Plus Plus using the same server and the same working folder as you have configured for Aspen Dynamics.

To run one of the examples: 1. Copy the Aspen Plus Plus backup file BatchEsterProps.bkp, and the relevant Aspen Dynamics input file to a convenient working folder. 2. Load the bkp file into Aspen Plus and run it. it. Note that this is a properties only input file, so you will not see a flowsheet within Aspen Plus. 3. Save the simulation as an Aspen Plus Document (.apw file), and exit Aspen Plus. This creates the file batchesterprops.appdf which contains all of the physical properties data required requ ired for the dynamic simulation. The .apw file is not required, and you can delete this. 4. Open the Aspen Dynamics Dynamics simulation simulation and run as required.

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BatchEster1

The following picture is the flowsheet for the BatchEster1 example:

This example simulates a fed batch reactor producing methyl acetate from acetic acid and methanol. The reactor configuration is entered on the reactor Configure form. This includes details of the reactor geometry, heating and cooling, and the reaction kinetics. The initial charge of the reactor is 20 kmol of acetic acid at 25 °C. The reactor pressure is fixed to 1 bar. These conditions are entered on the reactor Initialize form. A temperature controller measures the reactor temperature, and sends its output to a split range controller. This controls the amount of heating and cooling. If the reactor is too hot, cooling is applied, and if it is too cold, heating is applied. The heating in this example is provided by steam, and the cooling by cooling water. The flow of each of these is manipulated by the controller. A vent line is attached to the reactor. Because of this, the reactor will perform emissions calculations. As material is charged to the reactor, the displaced vapor is flashed at the vent condenser temperature specified on the Configure form. Any va por that is not condensed leaves in the vent stream. The cumulative vent flow is determined and can be viewed on the Results form for the R1Vent stream. To switch on calculation of cumulative flows the stream sensor was switched on using the ConfigureSensor C onfigureSensor form, and the Cumulative flows option was selected.


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The flowsheet section includes four tasks which are used to specify how the reactor will be operated. These are:

BatchEster2

Task

Description

R1Charge1Flow

Specifies that between 0.2 and 2.2 hours from the start of the batch, 10 kmol/hr of methanol is fed to the reactor

R1TCSP

Specifies that from 0.1 to 0.4 hours from the start of the batch the temperature controller set point is ramped from 20 to 60C.

StopCriterion1

Stops the simulation when the mole fraction of ester reached 0.45

StopCriterion2

Stops the simulation when the mole fraction of acid drops to 0.05.


This example is similar to BatchEster1, but also models the reactor condenser system. Use this modeling approach if boiling takes place in the reactor. Note that: The pressure calculated in the reactor is the vapor pressure of the reactor contents. The partial pressure of inerts is not modeled. If required, a nitrogen blanketing system could be modeled, but this will not normally have a significant effect on the results of the simulation. •

• •

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The vapor line from the reactor is connected through a Valve model which represents the small resistance to flow in the vapor line. A Flash2 model is used to represent the condenser. The Configure form is used to specify that the model is instantaneous (no holdup), and is cooled with cooling water at 25 °C. The Condenser vent pressure is fixed to 1 bar ba r on the Configure form for the R1Vent stream. The liquid from the condenser passes p asses to a reflux splitter. The Configure form is used to specify that all of the liquid is returned to the reactor.

BatchEster3


This example is similar to BatchEster2, but is also c apable of modeling two liquid phases in the overhead system. The condenser uses the Flash3 model to model both a condenser and decanter. There are two liquid streams leaving the condenser. Liquid 1 is less dense. Each of the two liquid phases leaving the condenser have a separate reflux splitter so that you can control the amount of each that is returned to the reactor.


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Kinetics Estimation from RC1 Calorimeter Results The kinetics estimation reactor model (KineticsEst) in Aspen Dynamics can be used to estimate kinetic parameters using experimental results from from a calorimeter, such as the MettlerToledo RC1e. This example uses the RC1e Tutorial example as shown in Chapter 5 and 11 of the RC1 Manual, hydrolysis of acetic anhydride. Note If you are using a Simulation Engine installation from a client machine, you must make make sure that you you run Aspen Plus Plus using the same server and the same working folder as you have configured for Aspen Dynamics.

In this example, 52 grams of acetic anhydride are added to 650 grams of water in a 2 liter RC1 calorimeter. The calorimeter determines the total heat release during the experiment, and also evaluates the heat released due to the reaction. Aspen Dynamics can use the Estimation run mode to estimate preexponential factors, activation energies, and other parameters. Heat evolution data coupled with reaction extent or composition data can be used to determine the basic kinetic parameters for most reactions.

Assumptions of the Kinetics Example

In this example, these assumptions are made: The reaction extent is complete at the end of the experiment. Rigorous physical properties from Aspen Plus give an a ccurate heat of reaction and heat capacity.

• •

Defining the Reaction The Reactions tab on the Configure form is used to specify the proposed kinetics for the reaction. This form could also be used to Mechanism specify multiple reactions as well as Langmuir-Hinshelwood kinetics.

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To see the Configure form: 1. Click the KineticsEst block R1 to select select it. 2. Click with the right right mouse button on the block. 3. From the the menu that appears, point to Forms then click Configure. 4. Select the Reactions tab:

To edit the reactions: 1. On the Reactions tab, click the the Edit button that is next to Include Power Law Reactions. The Power Law dialog box appears (see the picture on the next page):


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About the Experimental Data

The experimental conditions entered in the Excel data file Qflow_1M.CVS, are directly obtained from the RC1 run. The three columns of interest are: i.

Time (in seconds)

ii

Temperature, Tr (in degrees C)

iii. Corrected duty, Q (in W)

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Running the Kinetics Estimation Example

To run this example: 1. Locate the example folder KineticsEst. If you installed Aspen Dynamics in the default location, this is in: C:\Program Files\AspenTech\Aspen Dynamics 12.1\Examples 2. Copy all of the files in the KineticsEst folder to a convenient working folder. 3. Load the backup file KineticEstProps.bkp into Aspen Aspen Plus and run it. Note that this is a properties only on ly input file, so you will not see a flowsheet in Aspen Plus. 4. From the File menu, click Save As and save the simulation as an Aspen Plus Document (.apw file), then exit Aspen Plus. This creates the file KineticEstProps.appdf which con tains all of the physical properties data required requ ired for the dynamic simulation. The .apw file is not required, and you can delete this. 5. In Microsoft Excel, open the datafile datafile Qflow_1M.cvs. 6. In Aspen Dynamics, open the file KineticsEstimation.dynf. 7. Open the Configure form for block R1 on the flowsheet. 8. On the Estimated Variable tab, change the pre exponential variable Pre_exp(1) from Available to Selected. 9. On the Experiments tab, click Create Experiment and then click Edit Experiments. The standard Aspen Custom Modeler Estimation dialog box is displayed. 10. Change the run mode to Estimation 11. On the Run menu, select Run Options. Change the time units in which the user interface should display time to seconds. This is because the experimental data uses times in seconds. Now click OK to close the Run Options window. 12. Edit the experiment that you just created. To do this, click the experiment name KineticEstimation, and then click the Edit button. 13. On the Measured Variables tab, edit the variable Q (duty). To do this, click the variable R1.Q and then click the Edit button.


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14. In the Dynamic Measurement Data window, remove the single line of existing data. To do this, click on the cell that contains 0.0 for Time, click the right mouse button and then click Remove. 15. In Excel, copy all the values for the first six columns (columns Time to Q) and paste into the first cell in the Dynamic Measurement Data window. If you are p rompted "Are weights included in the end column?", click No. 16. Click OK to close the Dynamic Measurement Data window. 17. On the Fixed Variable tab, edit the variable R1.T (temperature). 18. In Excel, copy all the values for the first two columns (columns Time and Tr) and paste into the first cell in the Fixed Ramping Data window. 19. Click OK to close the Fixed Ramping Data window. 20. On the Fixed Variable tab, edit the variable R1.Fm_in(1) (inlet mass flowrate), and enter the following information: Time

Value

0

0

5560

0

5560.1

0.208

6460

0.208

6460.1

0

21. Click OK to close the Fixed Ramping Data window. 22. Click Done to close the Edit Estimation dialog box. 23. Run the simulation. 24. On the Estimation dialog box, go to the Estimated Variables tab to see the estimated value of the pre-exponential factor, which is approximately 0.125. You can also edit R1.Q in the dynamic experiment, and click the plot button to see the observed versus predicted values.

GasHDPE This example simulates a gas-phase high density polyethylene process. The feed stream, GFEED, contains the monomers: ethylene and butene, hydrogen to control the polymer molecular weight and nitrogen to control the pressure. Catalyst and cocatalyst are fed directly to the reactor in stream CFEED. The heat of reaction is removed in the high flow recycle stream.

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Example Simulations


This model uses Polymers Plus to capture the polymer characterization, the polymer thermophysical properties and phase equilibria and polymer polymer kinetics. The polymerization reaction is modeled using Ziegler Natta kinetics and the catalyst is characterized by 1 site type (polydispersity (po lydispersity = 2). Multiple site types must be used to characterize broader molecular weight distributions. The following illustration shows the flowsheet.

When the Aspen Plus model is sent to flow-driven Aspen Dynamics, default controllers are added for level, temperature, and pressure control. The temperature and pressure controllers need to be reconfigured to represent a typical gas phase process. The dynamic model can be used to: • •


Evaluate alternative grade transition policies Study alternative control schemes for controlling the polymer properties

Example Simulations

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Running the GasHDPE Example

To reconfigure the controllers: 1. Click on the output signal and reconnect destination to the new manipulated variable indicated: Controlled Variable (Input Signal)

Default Manipulated Variable

New Manipulated Variable

Level

Powder mass flow rate(Fml_outr)

Do not change

Pressure

Recycle gas mole flow rate(Fv_outr)

Nitrogen feed rate STREAMS("GF EED").FmcR("N 2")

Temperature

Reactor heat duty(Qr)

Cooler heat duty BLOCKS("COO LER").QR

2. After reconnection, re-initialize re-initialize the the temperature temperature and pressure controllers. To do this, on the controller Configure form, click the Initialize button. 3. For the the pressure controller, the action must be changed from from Direct to Reverse. This is because in the default scheme, increasing the manipulated variable (recycle rate) would decrease the pressure, whereas in the new scheme, increasing the manipulated variable (nitrogen feed) would increase the pressure. So the controller has the opposite action. 4. Click the Run button. The dynamic model will will start start integrating forward. After a few steps, you may change the run mode to Steady-State. The open equation model will converge to the same results as Aspen Plus. Try increasing the hydrogen feed rate and observe the effect it has on the polymer chain length. To do this: 1. Start the dynamic simulation. 2. Open the reactor form PolymerPlot and the GFEED Configure form. 3. Increase the hydrogen feed rate (say by 10%) and note that the polymer produced has a smaller molecular weight. Hydrogen is a chain transfer agent causing shorter polymer chains to be produced. 4. You can immediately view polymer results in tables and plots for the CSTR reactor.

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Example Simulations


5. To calculate additional polymer polymer attributes attributes for the product, or any other stream containing polymer, open the PolymerResults form, and change the DerivedAttributes parameter to Yes. This generates additional equations and variables in the model, and is Off by default to maximize performance. 6. Run again to calculate the additional attributes. attributes.

Nylon6 This model is also included in the Aspen Plus/ Polymers Plus examples, and it is fully described in the online Help for the steady-state Polymers Plus examples. It is included here with dynamic specifications for the column and the reactors. Briefly, caprolactum is polymerized in the presence of water to form Nylon6. This multi-stage model uses u ses Polymers Plus to capture the polymer characterization, the polymer thermophysical properties and phase equilibria and polymer kinetics. The polymerization reaction is modeled using step growth kinetics, and the phase equilibria using PolyNRTL. The model is used to study the effect of feed flow rate on caprolactam conversion, degree of polymerization, and extraction value.


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The following illustration shows the flowsheet.

The dynamic model can be used for: Operability studies, to look at strategies for chan ging the production rate while maintaining product quality. Control studies Safety studies Training for process engineers who want to learn about the process.

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Running the Nylon6 Example

To run the example: 1. When the Aspen Plus model is sent to flow-driven Aspen Aspen Dynamics, click the Run button. The dynamic simulation starts. 2. After a few steps, change the run mode to Steady-State. The open equation model converges to the same results as Aspen Plus. 3. You can immediately view polymer results, plots and DPN profiles for the CSTR and RPLUG reactors.

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Example Simulations


4. To calculate additional polymer attributes for the polymer polymer stream, open the PolymerResults form, and change the DerivedAttributes parameter to Yes. This generates additional equations and variables in the model, and is Off by default to maximize performance. 5. Run again to calculate the additional attributes. attributes.

Polystyrene (PS) This model is also included in the Aspen Plus/ Polymers Plus examples, and it is fully described in the online Help for the steady-state Polymers Plus examples. It is included here with dynamic specifications for the reactors, and counter-current cooling for the plug flow reactor. Briefly, bulk polystyrene is produced by the free-radical polymerization of styrene monomer. The process consists of two CSTR reactors followed by a plug flow reactor, and the devolatilization section. The following illustration shows the flowsheet.

Free radicals are formed by thermal initiation of styrene. Polymer is formed by initiation and propagation reactions, and the polymer molecular weight is controlled by termination reactions. This model uses Polymers Plus to capture the polymer characterization, the polymer thermophysical properties and phase equilibria and polymer kinetics. The polymerization reaction is modeled using Free Radical kinetics, and the phase equilibria using PolyNRTL. The dynamic model can be used for:


Example Simulations

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• • •

Running the Polystyrene (PS) Example

Operability studies, to look at strategies for chan ging the production rate while maintaining product quality, and ensuring the heating and cooling utilities can handle any demand peaks. Control studies Safety studies Training for process engineers who want to learn about the process

To run this example: 1. When the Aspen Plus model is sent to flow-driven Aspen Aspen Dynamics, click the Run button. The dynamic simulation starts. 2. After a few steps, change the run mode to steady state. The open equation model converges to the same results as Aspen Plus. 3. You can immediately view polymer results, plots, and DPN profiles for the CSTR and RPLUG reactors. 4. To calculate additional polymer polymer attributes attributes for the product, or any other stream containing polymer, open the PolymerResults form and change the DerivedAttributes parameter to Yes. This generates additional equations and variables in the model, and is Off by default to maximize performance. 5. Run again to calculate the additional attributes. attributes. 6. Try opening the FEED stream Configure Configure form and increasing the feed rate from 7000 kg/hr to 7500 kg/hr. Look at the temperature controller plots to see the peak heating and cooling demand, and the PolymerPlot in the PRODUCT stream to see the impact on polymer properties.

Reverse Flow Simulation This is an example of a pressure driven simulation where changes that occur dynamically give rise to pressure gradients that lead to flow reversal. The example uses the Flash2, Valve and Mixer models. At steady state, Flash F2 is at a higher h igher pressure than Flash F1. Vapor products from both units are vented through the Mixer to product stream VA. During dynamic simulation, Valve V3 on this product line is closed and the pressure gradients between F2 and F1 cause reverse flow of the vapor product line from F1.

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Example Simulations


This is the reverse flow simulation flowsheet:

Creating and Running the Reverse Flow Simulation Example

Follow these steps to create and run the reverse flow simulation example, starting from an Aspen Plus backup file: 1. In Aspen Plus, open reverse.bkp and run the simulation. simulation. If you installed Aspen Dynamics in the defau lt location, reverse.bkp is in C:\Program Files\AspenTech\Aspen Dynamics 12.1\Examples\ReverseFlow.

2. Export the simulation as a P Driven Driven Dyn Simulation (*.dynf & *dyn.appdf). 3. In Aspen Dynamics, open the file reverse.dynf. 4. On the Run Control toolbar, set the Run Mode to Initialization. 5. Run the simulation. Save a snapshot. 6. Using the Simulation Explorer, add a flowsheet level task under Simulation\Flowsheet to change the position of Valve V3 to 2 %. An example of a task to do this is provided in the text file V3Pos.txt, whose default location is: C:\Program Files\AspenTech\Aspen Dynamics 12.1\Examples\ReverseFlow


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7. Open the SimulationOptions table and change the value of the parameter GlobalRFlow to True. The SimulationOptions table is found in Simulation Explorer under Simulation. 8. With the Run Mode set to Initialization, Initialization, rerun the simulation and save a snapshot. This serves as a starting point for all simulations with the reverse flow functionality activated. 9. Switch the pressure controllers controllers PC4 and PC2 to manual, and activate task V3Pos. 10. Set the Run Mode to Dynamics and run the simulation again. Observe that, as Valve V3 closes, the pressure gradient between the two Flash units (via valves V1 and V7 and the Mixer) causes the flow to divert from F2 to F1, which in turn reverses the flow in Stream V1A. Reverse flow is indicated by negative flow rates.

DIERS Benchmark Examples The DIERS benchmark examples are a set of case studies that serve to validate computer software for rating pressure relief systems. They particularly focus on two-phase pressure relief. For a full description of the benchmark examples and details on how to set up and run each case study, refer refer to the Aspen Aspen Dynamics DIERS Benchmarks pdf file in the Examples\DiersBenchMarks folder of your Aspen Dynamics installation.

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Aspen Examples

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