173385804 Process Simulation and Control Using Aspen

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PROCESS SIMULATIONAND CONTROL USING

METHANOl

BUTENES

RDCOLUMN CCS

AMIYA K. JANA

Rs. 295.00

PROCESS SIMULATION AND CONTROL USING ASPEN

Amiya K. Jana

@ 2009 by PHI Learning Pnvate Limited, New Delhi. All rights reserved. No part of this book maybe reproduced In any form, by mimeograph or any other means, without permission in writing fromthe publisher.

ISBN-978-81-203-3659-9

The export rights of this book are vested solely with the publisher.

Published by Asoke K. Ghosh, PHI Learning Private Limited, M-97, Connaught Circus,New Delhi-110001 and Printed by Jay Print Pack Private Limited, New Delhi-110015.

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Preface

"The future success of the chemical process industries mostly depends on the ability todesign and operate complex, highly interconnected plants that are profitable and thatmeet quality, safety, environmental and other standards". To achieve this goal, the softwaretools for process simulation and optimization are increasingly being used in industry.

By developing a computer program, it may be manageable to solve a model structureof a chemical process with a small number of equations. But as the complexity of a plantintegrated with several process units increases, the solution becomes a challenge. Underthis circumstance, in recent years, we motivate to use the process flowsheet simulator tosolve the problems faster and more reliably. In this book, the Aspen software packagehas been used for steady state simulation, process optimization, dynamics and closed-loop control.

To improve the design, operability, safety, and productivity of a chemical processwith minimizing capital and operating costs, the engineers concerned must have a solidknowledge of the process behaviour. The process dynamics can be predicted by solvingthe mathematical model equations. Within a short time period, this can be achievedquite accurately and efficiently by using Aspen flowsheet simulator. This software tool isnot only useful for plant simulation but can also automatically generate several controlstructures, suitable for the used process flow diagram. In addition, the control parameters,including the constraints imposed on the controlled as well as manipulated variables.are also provided by Aspen to start the simulation run. However, we have the option tomodify or even replace them.

This well organized book is divided into three parts. Part I (Steady State Simulationand Optimization using Aspen Plus ) includes three chapters. Chapter 1 presents theintroductory concepts with solving the flash chambers. The computation of bubble pointand dew point temperatures is also focused. Chapters 2 and 3 are devoted to simulationof several reactor models and separating column models, respectively.

Part II (Chemical Plant Simulation using Aspen Plus ) consists of only one chapter(Chapter 4). It addresses the steady state simulation of large chemical plants. Severalindividual processes are interconnected to form the chemical plants. The Aspen Plussimulator is used in both Part I and Part II.

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viii PREFACE

The Aspen Dynamics package is employed in Part III (Dynamics and Control usingAspen Dynamics ) that comprises Chapters 5 and 6. Chapter 5 is concerned with thedynamics and control of flow-driven chemical processes. In the closed-loop control study,

the servo as well as regulatory tests have been conducted. Dynamics and control ofpressure-driven processes have been discussed in Chapter 6.

The target readers for this book are undergraduate and postgraduate students ofchemical engineering. It will be also helpful to research scientists and practising engineers.

Amiya K. -Jana


Acknowledgements

It is a great pleasure to acknowledge the valuable contributions provided by many of mywell-wishers. 1 wish to express my heartfelt gratitude and indebtedness to Prof. A.N.Samanta, Prof. S. Ganguly and Prof. S. Ray, Department of Chemical Engineering, IITKharagpur. I am also grateful to Prof. D. Mukherjee, Head, Department of ChemicalEngineering, IIT Kharagpur. My special thanks go to all of my colleagues for havingcreated a stimulating atmosphere of academic excellence. The chemical engineeringstudents at IIT Kharagpur also provided valuable suggestions that helped to improvethe presentations of this material.

I am greatly indebted to the editorial staff of PHI Learning Private Limited, for theirconstant encouragement and unstinted efforts in bringing the book in its present form.

No list would be complete without expressing my thanks to two most important peoplein my life-my mother and my wife. I have received their consistent encouragement andsupport throughout the development of this manuscript.

Any further comments and suggestions for improvement of the book would begratefully acknowledged.

rial

Contents

Preface viiAcknowledgements ix

Part I Steady State Simulation and Optimization

using Aspen Plus

1. Introduction and Stepwise Aspen Plus Simulation:

Flash Drum Examples 3-53

1.1 Aspen: An Introduction 3

1.2 Getting Started with Aspen Plus Simulation 4

1.3 Stepwise Aspen Plus Simulation of Flash Drums 71

.

3.

1 Built-in Flash Drum Models 7

13 2 Simulation nf a Flash nmm, , , _

81.3.3 Computation of Bubble Point Temperature 28

1.3.4 Computation of Dew Point Temperature 351

.3

.5 T-xy and P-xy Diagrams of a Binary Mixture 42Summary and Conclusions 50Prnhlpms

, , , ,

50

Reference 53

2, Aspen Plus Simulation of Reactor Models 54-106

2.

1 Built-in Rpartor Models 54

2.2 Aspen Plus Simulation of a RStoic Model 55

2.3 Aspen Plus Simulation of a RCSTR Model 652

.4 Aspen Plus Simulation of a RPlug Model 782

.5 Aspen Plus Simulation of a RPlug Model using LHHW Kinetics 93

Summary and Conclusions 104Prohlpms 704

Reference 106

v


VI CONTENTS

3. Aspen Plus Sinmlation of Distillation Models 107-1853 1 Rnilt-in nistillntinn Mndols 107

3.2 Aspen Plus Simulation of the Binary Distillation Columns 108

3 2 1 Simulation of a DSTWTT Mnripl IQfl

3 9. 9 Simulation of a RaHFrnr MoHpI 1223

.3 Aspen Plus Simulation of the Multicomponcnt Distillation Columns 1363

.

3 1 Simnlnt.ion of a RaHFrar MoHpI 13fi

3.3

.2 Simulation of a PetroFrac Model 148

3.4 Simulation and Analysis of an Absorption Column 164

3.5 Optimization using Aspen Plus 178

Summary and Conclusions 181Problems ffl2

Part II Chemical Plant Simulation using Aspen Plus

4. Aspen Plus Simulation of Chemical Plants 189-2264 1 TntrnHnrtion

4.2 Aspen Plus Simulation of a Distillation Train 1894

.3 Aspen Plus Simulation of a Vinyl Chloride Monomer (VCM)Production Unit 203

Summary and Conclusions 220Prnhlpms

; , -220

References 226

Part III Dynamics and Control using Aspen Dynamics

5. Dynamics and Control of Flow-driven Processes 229-284

5J Tnt.roHiirt.ion 2295.2 Dynamics and Control of a Continuous Stirred

Tank Reactor (CSTR) 230

5.3 Dynamics and Control of a Binary Distillation Column 255

Summary and Conclusions 279Prnhlpms

, , ,..279

References 284

6. Dynamics and Control of Pressure-driven Processes 285-313fil Tnt.rndnrtinn 2856.2 Dynamics and Control of a Reactive Distillation (RD) Column 286

Summary and Conclusions 310Problems 31JReferences 313

Index 315-317

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Part I

Steady State Simulation andOptimization using Aspen Plus

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CHAPTER

Introduction and StepwiseAspen Plus Simulation:Flash Drum Examples

1.1 ASPEN: AN INTRODUCTION

By developing a computer program, it may be manageable to solve a model structure ofa chemical process with a small number of equations. However, as the complexity of aplant integrated with several process units increases, solving a large equation setbecomes a challenge. In this situation, we usually use the process flowsheet simulator,such as Aspen Plus (AspenTech). ChemCad (Chemstations), HYSYS (Hyprotech)and PRO/II (SimSci-Esscor). In 2002, Hyprotech was acquired by AspenTech.However, most widely used commercial process simulation software is the Aspensoftware.

During the 1970s, the researchers have developed a novel technology at theMassachusetts Institute of Technology (MIT) with United States Department of Energyfunding. The undertaking, known as the Advanced System for Process Engineering(ASPEN) Project, was originally intended to design nonlinear simulation softwarethat could aid in the development of synthetic fuels. In 1981, AspenTech, a publiclytraded company, was founded to commercialize the simulation software package.AspenTech went public in October 1994 and has acquired 19 industry-leading companiesas part of its mission to offer a complete, integrated solution to the process industries(http://www.aspentech.eom/corporate/careers/faqs.cfm#whenAT).

The sophisticated Aspen software tool can simulate large processes with a highdegree of accuracy. It has a model library that includes mixers, splitters, phaseseparators, heat exchangers, distillation columns, reactors, pressure changers,manipulators, etc. By interconnecting several unit operations, we are able to develop aprocess flow diagram (PFD) for a complete plant. To solve the model structure of either

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4 PROCESS SIMULATION AND CONTROL USING ASPEN

a single unit or a chemical plant, required Fortran codes are built-in in the Aspensimulator. Additionally, we can also use our own subroutine in the Aspen package.

The Aspen simulation package has a large experimental databank forthermodynamic and physical parameters. Therefore, we need to give limited input datafor solving even a process plant having a large number of units with avoiding humanerrors and spending a minimum time.

Aspen simulator has been developed for the simulation of a wide variety ofprocesses, such as chemical and petrochemical, petroleum refining, polymer, and coal-based processes. Previously, this flowsheet simulator was used with limitedapplications. Nowadays, different Aspen packages are available for simulations withpromising performance. Briefly, some of them are presented below.

Aspen Plus-This process simulation tool is mainly used for steady state simulation ofchemicals, petrochemicals and petroleum industries. It is also used for performancemonitoring, design, optimization and business planning.

Aspen Dynamics-This powerful tool is extensively used for dynamics study and closed-loop control of several process industries. Remember that Aspen Dynamics is integratedwith Aspen Plus.

Aspen BatchCAD-This simulator is typically used for batch processing, reactions anddistillations. It allows us to derive reaction and kinetic information from experimentaldata to create a process simulation.

Aspen Chromatography-This is a dynamic simulation software package used for bothbatch chromatography and chromatographic simulated moving bed processes.

Aspen Properties-It is useful for thermophysical properties calculation.

Aspen Polymers Plus-It is a modelling tool for steady state and dynamic simulation,and optimization of polymer processes. This package is available within Aspen Plus orAspen Properties rather than via an external menu.

Aspen HYSYS-This process modelling package is typically used for steady statesimulation, performance monitoring, design, optimization and business planning forpetroleum refining, and oil and gas industries.

It is clear that Aspen simulates the performance of the designed process. A solidunderstanding of the underlying chemical engineering principles is needed to supplyreasonable values of input parameters and to analyze the results obtained. For example, auser must have good idea of the distillation column behaviour before attempting to useAspen for simulating that column. In addition to the process flow diagram, required inputinformation to simulate a process are: setup, components, properties, streams and blocks.

1.2 GETTING STARTED WITH ASPEN PLUS SIMULATION

Aspen Plus is a user-friendly steady state process flowsheet simulator. It is extensivelyused both in the educational arena and industry to predict the behaviour of a processby using material balance equations, equilibrium relationships, reaction kinetics, etc.Using Aspen Plus, which is a part of Aspen software package, we will mainly performin this book the steady state simulation and optimization. For process dynamics and

INTRODUCTION AND STEPWISE ASPEN PLUS SIMULATION 5

closed-loop control, Aspen Dynamics (formerly DynaPLUS) will be used in severalsubsequent chapters. The standard Aspen notation is used throughout this book. Forexample, distillation column stages are counted from the top of the column: thecondenser is Stage 1 and the reboiler is the last stage.

As we start Aspen Plus from the Start menu or by double-clicking the Aspen Plusicon on our desktop, the Aspen Plus Startup dialog appears. There are three choicesand we can create our work from scratch using a Blank Simulation, start from aTemplate or Open an Existing Simulation. Let us select the Blank Simulation optionand click OK (see Figure 1.1).

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FIGURE 1.1

The simulation engine of Aspen Plus is independent from its Graphical UserInterface (GUI). We can create our simulations using the GUI at one computer and runthem connecting to the simulation engine at another computer. Here, we will use thesimulation engine at 'Local PC'. Default values are OK.

Hit OK in the Connect to Engine dialog (Figure 1.2). Notice that this step is specificto the installation.

The next screen shows a blank Process Flowsheet Window. The first step indeveloping a simulation is to create the process flowsheet. Process flowsheet is simplydefined as a blueprint of a plant or part of it. It includes all input streams, unitoperations, streams that interconnect the unit operations and the output streams.Several process units are listed by category at the bottom of the main window in atoolbar known as the Model Library. If we want to know about a model, we can use theHelp menu from the menu bar. In the following, different useful items are highlightedbriefly (Figure 1.3).

Copyrighted material


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INTRODUCTION AND STKPWISK ASPEN PI.US SIMULATION 7

To develop a flowsheet, first choose a unit operation available in the Model Library.Proprietary models can also be included in the flowsheet window using User Modelsoption. Excel workbook or Fortran subroutine is required to define the user model. Inthe subsequent step, using Material STREAMS icon, connect the inlet and outlet streamswith the process. A process is called as a block in Aspen terminology. Notice that clickingon Material STREAMS, when we move the cursor into the flowsheet area red and blue

arrows appear around the model block. These arrows indicate places to attach streamsto the block. Red arrows indicate required streams and blue arrows are optional.

When the flowsheet is completed, the status message changes from Flowsheet NotComplete to Required Input Incomplete. After providing all required input data usinginput forms, the status bar shows Required Input Complete and then only the simulationresults are obtained. In the Data Browsery we have to enter information at locationswhere there are red semicircles. When one has finished a section, a blue checkmark

appears. In subsection 1.3.2. a simple problem has been solved, presenting a detailedstepwise simulation procedure in Aspen Plus. In addition, three more problems havealso been discussed with their solution approaches subsequently.

1.3 STEPWISE ASPEN PLUS SIMULATION OF FLASH DRUMS

1.3

.1 Built-in Flash Drum Models

In the Model Library, there are five built-in separators. A brief description of thesemodels is given below.

Flash 2: It is used for equilibrium calculations of two-phase (vapour-liquid) and three-phase (vapour-liquid-liquid) systems. In addition to inlet stream(s), this separator caninclude three product streams: one liquid stream, one vapour stream and an optionalwater decant stream. It can be used to model evaporators, flash chambers and othersingle-stage separation columns.

Flash 3: It is used for equilibrium calculations of a three-phase (vapour-liquid-liquid)system. This separator can handle maximum three outlet streams: two liquid streamsand one vapour stream. It can be used to model single-stage separation columns.

Decanter: It is typically used for liquid-liquid distribution coefficient calculations of atwo-phase (liquid-liquid) system. This separator includes two outlet liquid streams alongwith inlet stream(s). It can be used as the separation columns. If there is any tendencyof vapour formation with two liquid phases, it is recommended to use Flash3 instead ofDecanter.

Sep 1: It is a multi-outlet component separator since two or more outlet streams canbe produced from this process unit. It can be used as the component separation columns.

Sep 2: It is a two-outlet component separator since two outlet streams can bewithdrawn from this process unit. It is also used as the component separation columns.

At this point it is important to mention that for additional information regarding abuilt-in model, select that model icon in the Model Library toolbar and then press Flon the keyboard.


1.3

.2 Simulation of a Flash Drum

Problem statement

A 100 kmol/hr feed consisting of 10, 20, 30, and 40 mole% of propane, rc-butane,n-pentane, and n-hexane, respectively, enters a flash chamber at 15 psia and 50oF.The flash drum (Flash2) is shown in Figure 1.4 and it operates at 100 psia and 200oF.Applying the SYSOP0 property method, compute the composition of the exit streams.

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FLASH

FIGURE 1.4 A flowsheet of a flash drum.

Simulation approach

From the desktop, select Start button followed by Programs, AspenTech, AspenEngineering Suite, Aspen Plus Version and Aspen Plus User Interface. Then chooseTemplate option in the Aspen Plus Startup dialog (Figure 1.5).

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FIGURE 1.5

As the next window appears after hitting OK in the above screen, select Generalwith English Units (Figure 1.6).


INTRODUCTION AND STEPVV1SE ASPEN PLUSIM SIMULATION 9

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Then click OK. Again, hit OK when the Aspen Plus engine window pops up andsubsequently, proceed to create the flowsheet.

Creating flowsheet

Select the Separators tab from the Model Library toolbar. As discussed earlier, thereare five built-in models. Among them, select Flash2 and place this model in the window.Now the Process Flowsheet Window includes the flash drum as shown in Figure 1.7. Bydefault, the separator is named as Bl.

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10 PROCESS SIMULATION AND CONTROL USING ASPEN1

To add the input and output streams with the block, click on Streams section (lowerleft-hand comer). There are three different stream categories (Material, Heat and Work),as shown in Figure 1.8.

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Block Bl includes three red arrows and one blue arrow as we approach the blockafter selecting the Material STREAMS icon. Now we need to connect the streams withthe flash chamber using red arrows and the blue arrow is optional. The connectionprocedure is presented in Figure 1.9.

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INTRODUCTION AND STFPWISK ASPEN PLUS SIMULATION 11

Clicking on Material STREAMS, move the mouse pointer over the red arrow at theinlet of the flash chamber. Click once when the arrow is highlighted and move thecursor so that the stream is in the position we want. Then click once more. We shouldsee a stream labelled 1 entering the drum as a feed stream. Next, click the red arrowcoming out at the bottom of the unit and drag the stream away and click. This streamis marked as 2. The same approach has been followed to add the product stream at thetop as Stream 3. Now the flowsheet looks like Figure 1.10. Note that in the presentcase, only the red arrows have been utilized.

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We can rename the stream(s) and block(s). To do that highlight the object we wantto rename and click the right mouse button. Select Rename Block and then give a newname, as shown in Figure 1.11 for Block Bl.

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Alternatively, highlight the object, press Ctrl + M on the keyboard, change thename, and finally hit Enter or OK. After renaming Stream 1 to F, Stream 2 to L,Stream 3 to V and Block Bl to FLASH, the flowsheet finally resembles Figure 1.12.

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In order to inspect completeness for the entire process flowsheet, look at the statusindicator. If the message includes Flowsheet Not Complete, click on Material STREAMS.If any red arrow(s) still exists in the flowsheet window, it indicates that the process isnot precisely connected with the stream(s). Then we need to try again for properconnection. To find out why the connectivity is not complete, hit the Next button on theData Browser toolbar. However, if we made a mistake and want to remove a stream

(or block) from the flowsheet, highlight it. right click on it. hit Delete Stream (or DeleteBlock), and finally click OK.

Anyway, suppose that the flowsheet connectivity is complete. Accordingly, the statusmessage changes from Flowsheet Not Complete to Required Input Incomplete.

We have defined the unit operation to be simulated and set up the streams intoand out of the process. Next we need to enter the rest of the information using severalinput forms required to complete the simulation. Within Aspen Plus, the easiest way tofind the next step is to use one of the followings:

1. click the Next button

2.

find Next in the Tools menu

3. use shortcut key F4

As a consequence. Figure 1.13 appears.

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INTRODUCTION AND STKPWISK ASPEN PLUS SIMULATION 13

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Configuring settings

As we click OiC on the message. Aspen Plus opens the Data Browser window containingthe Data Browser menu tree and Setup/Specifications/Global sheet.

Alternatively, clicking on Solver Settings and then choosing Setup /Specifications inthe left pane of the Data Browser window, we can also obtain this screen (Figure 1.14).

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14 PROCESS SIMUIvVTION AND CONTROL USING ASPEN

Although optional, it is a good practice to fill up the above form for our project givingthe Title (Flash Calculations) and keeping the other items unchanged (Figure 1.15).

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In the next step (Figure 1.16), we may provide the Aspen Plus accounting information(required at some installations). In this regard, a sample copy is given with the followings:

User name: AKJANA

Account number: 1

Project ID: ANYTHINGProject name: AS YOU WISH

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We may wish to have streams results summarized with mole fractions or some other basisthat is not set by default. For this, we can use the Report Options under Setup folder. In thesubsequent step, select Stream sheet and then choose Mole fraction basis,

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As filled out, the form shown in Figure 1.17, final results related to all inlet andproduct streams will be shown additionally in terms ofmole fraction. Remember that allvalues in the final results sheet should be given in the British unit as chosen it previously.

Specifying components

Clicking on Next button or double-clicking on Components in the column at the left sideand then selecting Specifications, we get the following opening screen (Figure 1.18).

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16 PROCESS SIMULATION AND CONTROL USING ASPEN1"

Next, we need to fill up the table as suggested in Figure 1.18. A Component ID isessentially an alias for a component. It is enough to enter the formulas or names of thecomponents as their IDs. Based on these component IDs, Aspen Plus fills out the Type,

Component name and Formula columns. But sometimes Aspen Plus does not find anexact match in its library. Like, in the present simulation, we have the following screen(Figure 1.19) after inserting chemical formulas of the components in the Component IDcolumn.

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Obviously, only for Component ID C3H8, Aspen Plus provided the Component name(PROPANE) and Formula (C3H8). This simulator does not recognize the other threecomponents by their IDs. Therefore, we have to search in the following way(Figure 1.20) to obtain their names and formulas. Click on a component ID (say, N-C4H10),then hit Find button.

Now, we have to give a hint with Component name or formula (butane) and thenhit Enter or Find now button (Figure 1.21). Apart from component name or formula,we can also search a component by giving component class or molecular weight (range)or boiling point (range) or CAS (Chemical Abstracts Service) number. Click on Advancedbutton in the following screen to get these options.

INTRODUCTION AND STKPWISE ASPEN PLUS SIMULATION 17

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Aspen Plus suggests a number of possibilities. Among them, select a suitablecomponent name (N-BUTANE) and then click on Add. Automatically, the Componentname and Formula for Component ID N-C4H10 enter into their respective columns.For last two components, we follow the same approach. When all the components arecompletely defined, the filled component input form looks like Figure 1.22.

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The Type is a specification of how Aspen calculates the thermodynamic properties.For fluid processing of organic chemicals, it is usually suitable to use 'Conventional*option. Notice that if we make a mistake adding a component, right click on the rowand then hit Delete Row or Clear.

Specifying property method

Press Next button or choose Properties I Specifications from the Data Browser. Then ifwe click on the down arrow under Base method option, a list of choices appears. Set theSYSOPO' method as shown in Figure 1.23.

A Property method defines the methods and models used to describe pure componentand mixture behaviour. The chemical plant simulation requires property data. A widevariety of methods are available in Aspen Plus package for computing the properties.

Each Process type has a list of recommended property methods. Therefore, the Processtype narrows down the choices for base property methods. If there is any confusion, wemay select 'All' option as Process type.

Specifying stream information

In the list on the left, double click on Streams folder or simply use Next button. Insidethat folder, there are three subfolders, one for each stream. Click on inlet stream F, and

enter the temperature, pressure, flow rate and mole fractions. No need to provide anydata for product streams L and V because those data are asked to compute in the presentproblem (see Figure 1.24).

This property method assumes ideal behaviour for vapour as well as liquid phase.

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INTRODUCTION AND STEI'WISK ASPEN PLUS SIMULATION 19

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f5~

f, .rilll

'

I JIU-*"- I'M-

Im«7V= 31

nns Dt

-

.

, ri.ttn it:

*

.1. -.. .11. : ...

h o e czd- @ - it.

FIGURE 1.24

Specifying block information

Hitting Next button or selecting Blocks/FLASH in the column at the left side, we getthe block input form. After inserting the operating temperature and pressure, oneobtains Figure 1.25.

20 PROCESS SIMULATION AND CONTROL USING ASPRN

i :r~

.- u>i"i-

Toob Ron Piol Lfciaiy Wmdow Help

~

D - I I 'I -isil I lai alS*l

U3SE

did -J a M

UNIFAC Gioup 3_

) UN1FAC G<oup.

__J

Cl 0ot ,_

J A sJyBJ- PMP>SMi

O K>OE5I<iN0 tMCPMAL(#> TXPOftTO VIE

*. ilj AdvancedJQ- Lifl >=

-

Input

/Sp«c>rioalion>{ Floih.Ophwn | ErJ

EO varial

IS FLASH| Be

i Conv Op«noj

EO Conv Option*

O SetupDMOBasK

49 DMOAdv

-gp-n=-3

-i

Input CompteK

[1 Mbcwt/SpBtsit Sopjuato.. j HmI Exciwigsi t Columni | FtMclnt | Pfonuio Chonoe

: H 0 - 9 -CD-STREAMS ' Fl«h2 FlaihS Deca/Kei Sep 5ep2

FIGURE 1.25

Now the Status message (Required Input Complete) implies that all necessaryinformation have been inserted adequately. Moreover, all the icons on the left are blue.It reveals that all the menus are completely filled out. If any menu is still red, carefullyenter the required information to make it blue.

Running the simulation

Click on Next button and get the following screen (see Figure 1.26). To run the

simulation, press OK on the message. We can also perform the simulation selectingRun from the Run pulldown menu or using shortcut key F5.

r

Tl SJ b li"" 1 1 ] all*- -l±j"

cjJ_

Cl ~-T

-

Zl I - * I .IPI . I > in rnim

8! 7.1 CarrvOpllam33 to Conv Option*

3 £=1

.TfUAMt ' FWttJ SgM L -«o>i S p "fJ

3

FIGURE 1.26

The Control Panel, as shown in Figure 1.27, shows the progress of the simulation.It presents all warnings, errors, and status messages.

jNIRODUCTlON AND STEPW1SE ASPEN PLUS SIMULATION 4 21

Q rtm eai vw« DM* roota Lih..i..

I 1"! _=J 3?) H -iroh L_jih-

3 I

,QhrjAj*i j-j an .| ihi .j M

"

3 r "

3 r

.loch:

Pt.iofva and Po«U<**» Soipti

p" l t*«i * *S'«- f" '.. i ' r..:.

Command Lr» |

AI bkK+» h«v» bean .

0 6 -ciDSTREAMS FU>»K3 Fl<nH3 D«canl- Sup S»p2

FIGURE 1.27

Viewing results

HittingATex button and then clicking OK, the Run Status screen appears first (see Figure 1.28).

yil l .i.l.lJIII«.II..IIHIII.I.IMItMIIIIH.HI II.Wl'ltlll.Ml.llltHWI-I Ffe Edt VKm Data Tools Rvxi Mot Lbtoty Window htetp

ItflHI -I v| daHal-

3 m I _iJ_iMi_LB Ru-i Slatut 3 sQg r

S i Streams

QU RaMiU Swranarv-

Run Statu*

Streams

Convergence

Atpen Plui Vetswn

Lite

prrr[fLash CALCULATIONS

Dale and lime [JUNE 5. 2007 1 23621 Pm"

Uminam» [AOMIN IS TRATOBS*»\D |TEAM_EATMachnelypo [WIN32 Hott iCONTROLLAB

Use << and >> robiowie testitt

MBW./Scfcie.. S* . ) H»al E-changst | CcWa | Be«clor. e Chang** i Man« j Sobd. | U>«Mo4* |

(0-9 o 8 .

FIGURE 1.28

From the Data Browser, choose Results Summary /Streams and get the followingscreen that includes the final results of the given problem (see Figure 1

.29).

Save the work by choosing File/Save As/...from the menu list on the top. We canname the file whatever we want. Note that an Aspen Plus Backup file (*.bkp) takes

much less space than a normal Aspen Plus Documents file ( .apw).


1j Fto '. ,-V . - Took Run P

: JSbd JMSj-d HIP jsJ . j . i

» J/l Block*I I

£1 fo. * r "

3 5l<»amT»blf[

r rjj 1 - 350 0 2000 200 0

i f. nr i ion oo ion on

Vapo* Froc 0016 0 000 1 000

Mote Flow fcmot/hi 220 462 1 Tf 971 42 492Mas* Ftow b/h. 15906 41* 13312.698 2593 716

v. l:...- Flow culler 1039 561 382.439 3008 065

lE.Hh»lpy MMBtu/hi 16 583 1243? 2 236

Mole Flow bmolVIv

C3H8 22 046 9 275 12 771

NC4H10 44092 30124 13 969

66139 56 242 9 896

N.C6H14 eeies 82 329 5856

(V Mixw pMto! SoiMralof* { Heal Enchangon | Column* | Re»cto.. \ P-eume Chongeij \ Mo puMw* | So§*. | Um. Models )

HO 0 cdSTREAMS ' FVwh2 Flaih3 D>came> 3ep Sep2

For H*te, press Fi" ""

* Start}} Aspen Pkn - Simulatl_

C.\- .g Pol<tou\Ajper. PK» 11,1 ! NUM i - .. .. Av,4,>:-

FIGURE 1.29

If we click on Stream Table button, the results table takes a place in the ProcessFlowsheet Window, as shown in Figure 1.30.

Fie Edt View Data Tocfc Run Ffevaheet Librvy Whdow Help

1 global j |£e.| . I lai

F L V

Temptntuit F 50 0 200 0 200.0

Pttiiun pri 15 00 100 00 100.00

V*poi Fnc 0.018 0 000 1000

HoUFtow fcrnoVhi 220462 177 971 42 492

fcftu 15906 414 13312 698 2593 716

VokuntFlw 1639 561 382439 3008 065

EnlhJpy MMBtu/hi -16583 -12.499 -2236

Hole Flw

C3H8 22 046 9-275 12 771

H-C4H10 44 092 30 124 13569

K-C5H12 66139 56 242 9996

H-C6H14 88 185 82.329 5 856

Mok Trie

C3K8 0.100 0053 0 301

HX4HI0 0.200 0.169 0329

H-C5H12 OJOO 0 316 0233

H-C6H14 0 400 0 463 0.

138

Mm/Spitlan Sflprntms { Heat Eicchangeit { Cdum | Reactori | PrMtue Chmgeii j Mmpdalai | Soldi j Use. Models j-D-» <0-8-o

1

C:V.oF<*lefs\A»penMu»n.l

?1 1

FIGURE 1.30

INTRODUCTION AND STKPWISK ASPKN PI.US,M SIMUI.ATION 23

Viewing input summary

To obtain the input information, press Ctrl + Alt + I on the keyboard or select InputSummary from the View pulldown menu. The supervisor may ask to include the results,shown in Figure 1.30, along with the input summary in the final report on the presentproject (see Figure 1.31).

Fl» Ml ft >W He»

linput swimtrf crvaccd bv upen Plus "el. U.l tt tiiMtiS rrf jun a, 2007 ~;Dlr»ctory CtSproarur 11 TBc\Aspanrai:n\WDrklng Polaei ' j' iveft Plus 11.1 tllnnm*

mMPuisDPLUS RCSULTS-ON

TITLE 'PlHh Calculations '

IN-UNir» lii.

DEC-STRESS CONVtlt ALl

CCOUNI-tKEO KC0UNT>1 PROJECT-ID»*MtTHING 4ff>0)6C'OU WISH 0SE('-H**S-"«J/f«'

DGKRIPriON 'General Sl*u1al1e*< w<th English unl s :F, dsI, Ib/hf, lEf«ol/»». oiu/hr, eirft/hr,

Propariy Haihooi wona

eln* M*l» for Incur: NOll"

i r j - report : '. . Mola *lo»

PUBCII / AQUCOUS / SOLIDS / UttROANIC / ttOASPENPCO

PROP-IOURCES CUBEll / MJUCOUS / SOCIOl / INC>Ra»"IC

CJm8 C3h8 /N-camo caxio-z /

N-cenW CftHH-l

"lOWSHEETbicc> flash ih-e aut-v l

PROPERTIES SY5OP0

SUOSTRCAH -EO TEWB.lo. PBE5-11, »MLE-PLOB-i00. -ktcVr>->.*xe-fb»c ana o.i / w kio o.j / n-cihi? o. t / »

N-c6nl4 0.4

- - plash Flash;kabah rtwp- ao. "sr.-ic-j

.

FIGURE 1.31

Creating report file

To create a detailed report of the work we have done, including input summary, streaminformation, etc., select Export (Ctrl + E) from the File dropdown menu. Then save thework as a report file (e.g., C/Program Files/AspenTech/Working Folders/Aspen PlusVersion/ Flash.rep). Subsequently, we may open the saved report file (Flash.rep) goingthrough My Computer with using a program, such as the Microsoft Office Word orWordPad or Notepad. A report file for the present problem is opened below.

ASPEN PLUS IS A TRADEMARK OF HOTLINE:

ASPEN TECHNOLOGY. INC. U.S.A. 888/996-7001

TEN CANAL PARK EUROPE (32) 2/724-0100CAMBRIDGE. MASSACHUSETTS 02141

617/949-1000


PLATFORM: WIN32

VERSION: 11.1 Build 192

INSTALLATION: TEAM_

EAT

ASPEN PLUS PLAT: WIN32 VER: 11.1

JUNE 10, 2007SUNDAY

11:23:23 A.M.

06/10/2007 PAGE IFLASH CALCULATIONS

ASPEN PLUS (R) IS A PROPRIETARY PRODUCT OF ASPEN TECHNOLOGY, INC.(ASPENTECH), AND MAY BE USED ONLY UNDER AGREEMENT WITH ASPENTECH.RESTRICTED RIGHTS LEGEND: USE, REPRODUCTION, OR DISCLOSURE BY THEU

.S

.GOVERNMENT IS SUBJECT TO RESTRICTIONS SET FORTH IN

(i) FAR 52.227-14, Alt. Ill, (ii) FAR 52.227-19, (iii) DEARS252.227-7013(c)(l)(ii), or (iv) THE ACCOMPANYING LICENSE AGREEMENT,AS APPLICABLE. FOR PURPOSES OF THE FAR, THIS SOFTWARE SHALL BE DEEMEDTO BE "UNPUBLISHED" AND LICENSED WITH DISCLOSURE PROHIBITIONS.CONTRACTOR/SUBCONTRACTOR: ASPEN TECHNOLOGY, INC. TEN CANAL PARK,CAMBRIDGE, MA 02141.

TABLE OF CONTENTS

RUN CONTROL SECTION 1RUN CONTROL INFORMATION 1DESCRIPTION 1

FLOWSHEET SECTION 2FLOWSHEET CONNECTIVITY BY STREAMS 2FLOWSHEET CONNECTIVITY BY BLOCKS 2

COMPUTATIONAL SEQUENCE 2OVERALL FLOWSHEET BALANCE 2

PHYSICAL PROPERTIES SECTION 3COMPONENTS 3

U-O-S BLOCK SECTION 4

BLOCK: FLASH MODEL: FLASH2 4

STREAM SECTION 5

F L V 5

PROBLEM STATUS SECTION 6

BLOCK STATUS 6

ASPEN PLUS PLAT: WIN32 VER: 11.1 06/10/2007 PAGE 1FLASH CALCULATIONSRUN CONTROL SECTION

RUN CONTROL INFORMATION

THIS COPY OF ASPEN PLUS LICENSED TO

TYPE OF RUN: NEW

OUTPUT PROBLEM DATA FILE NAME:_

1437xbh VERSION NO. 1

INPUT FILE NAME:_

1437xbh.inm


LOCATED IN:

PDF SIZE USED FOR INPUT TRANSLATION:

NUMBER OF FILE RECORDS (PSIZE) = 0NUMBER OF IN-CORE RECORDS - 256

PSIZE NEEDED FOR SIMULATION - 256

CALLING PROGRAM NAME: apmainLOCATED IN: C:\PROGRA~ I\ASPENT~-1 \ASPENP~1.1 \Engine\xeq

SIMULATION REQUESTED FOR ENTIRE FLOWSHEET

DESCRIPTION

GENERAL SIMULATION WITH ENGLISH UNITS : F, PSI, LB/HR, LBMOL/HR,BTU/HR, CUFT/HR. PROPERTY METHOD: NONE FLOW BASIS FOR INPUT: MOLE

STREAM REPORT COMPOSITION: MOLE FLOW

ASPEN PLUS PLAT: WIN32 VER: 11.1 06/10/2007 PAGE 2

FLASH CALCULATIONS

FLOWSHEET SECTION

FLOWSHEET CONNECTIVITY BY STREAMS

STREAM SOURCE DEST STREAM SOURCE DEST

F FLASH V FLASH

L FLASH

FLOWSHEET CONNECTIVITY BY BLOCKS

BLOCK INLETS OUTLETS

FLASH F V L

COMPUTATIONAL SEQUENCE

SEQUENCE USED WAS:

FLASH

OVERALL FLOWSHEET BALANCE

MASS AND ENERGY BALANCE

CONVENTIONAL

C3H8

N-C4H10

N-C5H12

N-C6H14

IN

COMPONENTS

22.0462

44.0925

66.1387

88.1849

OUT

(LBMOL/HR)

22.0462

44.0925

66.1387

88.1849

RELATIVE DIFF.

0.101867E-09

0.326964E-10

-0.113614E-10

-0.332941E-10


TOTAL BALANCE

MOLE( LBMOL/HR) 220.462 220.462 0.000000E+00

MASS(LB/HR) 15906.4 15906.4 -0.782159E-11ENTHALPY(BTU/HR) -0.165833E+08 -0.147349E+08-0.111463


FLASH CALCULATIONS

PHYSICAL PROPERTIES SECTION

06/10/2007 PAGE 3

COMPONENTS

ID TYPE

C3H8 C

N-C4H10 C

N-C5H12 C

N-C6H14 C

FORMULA

C3H8

C4H10-1

C5H12-1

C6H14-1

NAME OR ALIAS

C3H8

C4H10-1

C5H12-1

C6H14-1

REPORT NAME

C3H8

N-C4H10

N-C5H12

N-C6H14


FLASH CALCULATIONS

U-O-S BLOCK SECTION

06/10/2007 PAGE 4

BLOCK: FLASH MODEL: FLASH2

INLET STREAM: F

OUTLET VAPOR STREAM: V

OUTLET LIQUID STREAM: L

PROPERTY OPTION SET: SYSOP0 IDEAL LIQUID / IDEAL GAS

*** MASS AND ENERGY BALANCE ***

IN OUT RELATIVE DIFF.

TOTAL BALANCE

MOLE(LBMOL/HR) 220.462MASS(LB/HR) 15906.4

220.462

15906.4

0.000000E+00

-0.782136E-11

ENTHALPY(BTU/HR) -0.165833E+08 -0.147349E+08 -0.111463

INPUT DATA

TWO PHASE TP FLASH

SPECIFIED TEMPERATURE

SPECIFIED PRESSURE

MAXIMUM NO. ITERATIONSCONVERGENCE TOLERANCE

F

PSI

200.000

100.000

30

0.000100000

*** RESULTS ***

OUTLET TEMPERATURE F 200.00


OUTLET PRESSURE

HEAT DUTY

VAPOR FRACTION

PSI

BTU/HR

100.00

0.18484E+07

0.19274

V-L PHASE EQUILIBRIUM:

COMP

C3H8

N-C4H10

N-C5H12

N-C6H14

F{I)0.10000

0.20000

0.30000

0.40000

X(I)0

.52117E-01

0.16926

0.31602

0.46260

Yd)0

.30055

0.32874

0.23290

0.13781

K(I)5

.7668

1.9422

0.73697

0.29790


FLASH CALCULATIONS

06/10/2007 PAGE 5

STREAM SECTION

F L V

STREAM ID

FROM :

TO

L

FLASH

FLASH

SUBSTREAM: MIXED

PHASE: MIXED

COMPONENTS: LBMOL/HR

C3H8 22.0462

N-C4H10 44.0925

N-C5H12 66.1387

N-C6H14 88.1849

COMPONENTS: MOLE FRAC

C3H8 0.1000

N-C4H10 0.2000

N-C5H12 0.3000

N-C6H14 0.4000

TOTAL FLOW:

LBMOL/HR 220.4623

LB/HR 1.5906+04

CUFT/HR 1839.5613

STATE VARIABLES:

TEMP F 50.0000

PRES PSI 15.0000

VFRAC 1.8002-02

LFRAC 0.9820

S FRAC 0.0

V

FLASH

LIQUID

9.2754

30.1237

56.2424

82.3291

5.2117-02

0.1693

0.3160

0.4626

177.9706

1.3313+04

382.4385

200.0000

100.0000

0.0

1.0000

0.0

VAPOR

12.7709

13.9688

9.8963

5.8558

0.3005

0.3287

0.2329

0.1378

42.4917

2593.7158

3008.0650

200.0000

100.0000

1.0000

0.0

0.0


ENTHALPY:

BTU/LBMOL -7.5221+04 -7.0232+04 -5.2612+04BTU/LB -1042.5543 -938.9019 -861.9118BTU/HR -1.6583+07 -1.2499+07 -2.2356+06

ENTROPY:

BTU/LBMOL-R -130.1235 -123.3349 -87.8846BTU/LB-R -1.8035 -1.6488 -1

.4398

DENSITY:

LBMOL/CUFT 0.1198 0.4654 1.4126-02

LB/CUFT 8.6469 34.8100 0.8623AVG MW 72.1503 74.8028 61.0406

ASPEN PLUS PLAT: WIN32 VER: 11.1 06/10/2007 PAGE 6FLASH CALCULATIONSPROBLEM STATUS SECTION

BLOCK STATUS

**********************************************************************

* *

* Calculations were completed normally ** *

* All Unit Operation blocks were completed normally ** *

* All streams were flashed normally ** *

************************************************************************:!:;!=

1.3

.3 Computation of Bubble Point Temperature

Problem statement

Compute the bubble point temperature at 18 bar of the following hydrocarbon mixture(see Table 1.1) using the RK-Soave property method.

TABLE 1.1

Component Mole fraction

Ci 0.05

c2 0.1

C3 0.15

i-Ci 0.1

n-Ci 0.2

i-C5 0.25

n-C5 0.15

Assume the mixture inlet temperature of 250C, pressure of 5 bar and flow rate of120 kmol/hr.

S,MULA'noN 29

Simulation approach

After starting the Aspen Plus simulator, the Aspen Plus Stnrt,., v i

Among the three choices, select Template option and then S e F Tl 3

L L J.-i..'i- I iM BlMtt i ~| S!| -j j jj g j

t ,J;'&9'lr.lrtoi\Ait«r.leI:MV l,1gffj ,AsinwiPtft.,..- "" TTrTtrtilVfnrt.i0ritliiiV>iWnrfca 11C 'Pi09'*T>F'f'''-!CW"lecl-AW1>t»>jFc«eii'A:Mr!rt,: n

H !i j

FIGURE 1.32

When the next window pops up (see Figure 1.33),select General with Metric Units

and then hit OK.

3 -II ...d..ji:;L: i 1 1 raliH

FIGURE 1.33

In the next,press OK in the Connect to Engine dialog. Once Aspen Plus connects to

the simulation engine, we are ready to begin entering the process system.


Creating flowsheet

Using the Flash2 separator available in the equipment Model Library, develop thefollowing process flow diagram (see Figure 1.34) in the Flowsheet Window by connectingthe input and output streams with the flash drum. Recall that red arrows are requiredports and blue arrows are optional ports. To continue the simulation, we need to clickeither on Next button or Solver Settings as discussed earlier. Note that whenever wehave doubts on what to do next, the simplest way is to click the Next button.

rjafn ..|-|..|. {k jl .15)1 I gl *w

.

0o

o-e-oi-ir-mm 1

_2£

£S-| »... >

FIGURE 1.34


From the Data Browser, choose Setup ISpecifications. The Title of the present problemis given as 'Bubble Point Calculations'. Other items in the following sheet remainuntouched (see Figure 1.35). However, we can also change those items (e.g., Units ofmeasurement. Input mode, etc).

-

3 -.1 ,b. i -. m -\u-

gag i 3 abi 3 »l alai

ij, u mit »

« "'E E3

FIGURE 1.35

INTKODUCTION AND STHPWISE ASFKN PLUSIM SIMULVTION 31

In the next, the Aspen Plus accounting information are given (see Figure 1.36).

'

_rt* tm ttw imt 'i** Hot its*

P|a»IBI -I -I frWi.-r

-

i h.i> rsr

.

.igi«]

ralt-Htl l-al l 3J . I I"! J?J 21 j J SiI _ti>|g| - I ' m

.I i Us*-**,

t.-'l(.

11 -

-< O Q <=>. @ . 4 . iKM a IV- II I MM »»»»» !r.i-».

FIGURE 1.36


Click on TVex button or choose Components /Specifications in the list on the left. Thendefine all components and obtain the following window (see Figure 1.37).

~

rfc r« mm Ma took " pw ia»»v »w««fc- t««.

PisgLBJ .1.1 H»l SI_

1-J~

I-I"I>raKifcKl-ai i H II JhJ ! jcj m

i j . i i xapji i iw 'H

rtgj <«irM »i cuari n.i

9 BmiMM VMM

I'

..X . 4 i

/ -. ii.- MMM

r-

.

L *. 11 d i it .jf

-

. l.w..-->., s-m

l 1

H 0 8 cd. g - tf .[ li itin ci «ri<«i im-i n I >o< >....-_i- ... i

FIGURE 1.37

Copyrlqhted material



Hit Next button or select Properties / Specifications in the column at the left side. InProperty method, scroll down to get RK-Soave. This equation of state model is chosenfor thermodynamic property predictions for the hydrocarbon mixture (see Figure 1.38).

.=1 3 JLi Si Mi bl

-

-

8 i 3;

F-3

-

. Q-S-o-'g-'iiD

FIGURE 1.38

Hitting ATex/ button twice, we have the following picture (see Figure 1.39). The binaryparameters are tabulated below. When we close this window or cbck OK on the message.it implies that we approve the parameter values. However, we have the opportunity toedit or enter the parameter values in the table. In blank spaces of the table, zeros arethere. It does not reveal that the ideal mixture assumption is used because manythermodynamic models predict non-ideal behaviour with parameter values of zero.

T£msxS\zi zl 2 '-I H 21 613 .ifLdB&teMMI)

:3

MIX

« MMI *

I-

nm

TTD-3

=w

FIGURE 1.39

INTRODUCTION AND STEPWISR ASI-KNJ>LU sim 33Specifying stream information

Click OK. Alternatively, use the Data Browser menu tree to navigate to the Streams/1/Input/Specifications sheet. Then insert all specifications for Stream 1 as shown in Figure 1 40

J . 1 1,, I* ~

n 1 1 i 1 igi

la

JO

1 ftdvaoced

r~

i Rpioftt

& Setup

Q| OMOAdvL55s?P Bos-:

El »l aUl

J &1

tcxnpojitior.

pr3 71 n

(5

rr s;; -J

s,. p-It ,111,. . l-v ...:...>, --r.-nlV-- H-lp'

[i hWs/Sphleu Ssp falais j He Esdw ers j Columns | Reaclw: [ Pies sine Changers j Manipulators : Solids j UferModefi

Matenal

STREAMS Flash2 Fla h3 Dncanie.

Fo. Help, p

Sep 5ep2

J Start j j A»pen plu, - Skmdab- Aspen Phjj Smxjlatton 2. . jC:V gFfWe'slflspanPbjs 11.1 MJM P* wrwl In*/

FIGURE 1.40


Hit Afort or select Blocks/BUBBLE from the Data Browser. After getting the blank inputform, enter the required inputs (Pressure = 18 bar and Vapour fraction = 0) for blockBUBBLE (see Figure 1.41).

"

3 *i I *! «iEi

- al>l

si - r

i Pr<*8rUw

J/) Prcpertr Metro

-

1

CJ 2~J 1

- 1

.

_)

9 ***

-a-»

/Speatifotnni FlathOcdoni ' Er**rrr«nl

0 0 QflSTREAMS Ri ? fWJ Ete i S<c S Bi

FIGURE 1.41



Press Next button and then hit OK to run the simulation. The following Control Panel

demonstrates the status of our simulation work (see Figure 1.42).

laillUJLIIIlllBIl

i f** t-t Vwi- Data Toofi Bun Lfciafy WVidwv/ Meto

JDlugB] atfij J-j

4-1 I "I JiJ S i l <| jjB] | IMI

ral-rlatl-l-qi l «ii [=5_d

.IjjJ -J SI affl e-i

i 3 - i i -i tim mi

ss 3 r i r

Inieriijpi DMO Sotver

J.NoEOFwm j

i - r-. - and Po:iiotve SckXi

Command Lr* f"

| Sepaislota | Heat ExchM oeic [ Cohjnmi | Rrac'txt | Prectuie Changed

o o e - it -STREAMS

'

flathZ Flail-.3 Decade. Sep Sepg

SoMt j Uiei Model: |

rC:\...oFoW«"\A«>enPtuj 1

'

«* (W Oi/fc &<$ 7:52 P

FIGURE 1.42

Viewing results

Clearly, Figure 1.42 includes the Status message: Results Available. As the simulationcalculations completed, click on Solver Settings and then double-chck on Blocks to obtainthe following screen (see Figure 1.43).

-

-

| ne c >' v«v. 0*a Toob Ain PM Lferarv Wmdcw Hcto

J_

l"

l-l-PT-j j b I 3 ±tti iiJfXi 32>J jaal n i

33 Set-*

2

O Setup

I

-CM <o 9 e i1 n.A? FWi3 Dac«4«> Sap

i SOU. | U-Moa* |

FIGURE 1.43

-

| ,Md«fl« .»-.. .

INTKODUCTION AND STKPWISK ASI'KN PLUS SIMULATION 35

Choosing Blocks/BUBBLE/Results in the column at the left side, we get thefollowing results summary for the present problem (see Figure 1.44).

JaflHI Ml *1mi

ra

IB 3(v«««iP»*Jl

fO Cor- OBban*

V

O 1tmt

WMllwilfc ii»»i»y

NM1 »»»

.j 0 - 6 -o- f.r.| SOU. | UnMaM |

111,1 ' MM *r

FIGURE 1.44

From the results sheet, we obtain the bubble point temperature = 42.75411960C.

1.3.4 Computation of Dew Point Temperature

Problem statement

Compute the dew point temperature at 1.5 bar of the hydrocarbon mixture, shown inTable 1.2, using the RK-Soavc property method.

TABLE 1.2


Ci 0.05

C2 0.

1

Ca 0.15

<-c4 0.1

n-CA 0.2

M3a 0.25

"-(>,0

.15

Assume the mixture inlet temperature of 250C, pressure of 5 bar and flow rate of120 kmol/hr.


Simulation approach

As we start Aspen Plus from the Start menu or by double-clicking the Aspen Plus icon onour desktop, theAspe?i Plus Startup dialog appears (see Figure 1.45). Select Template option

.

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FIGURE 1.45

As Aspen Plus presents the window after clicking OK as shown Figure 1.45, chooseGeneral with Metric Units. Then press OK (see Figure 1.46).

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FIGURE 1.46


Subsequently, dick OK when the Aspen Plus engine window pops up.

Creating flowsheet

In the next, we obtain a blank Process Flowsheet Window. Then we start to developthe process flowsheet by adding the Flash2 separator from the Model Librarytoolbar and joining the inlet and product streams by the help ofMaterial STREAMS(Figure 1.47).

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± if

itftLWfS n>rJ f* i c-*. --3 s«.-

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FIGURE 1.47

Now the process flow diagram is complete. The Status bar in the bottom right ofthe above window (see Figure 1.47) reveals Required Input Incomplete indicating thatinput data are required to continue the simulation.


Hitting Next button and then clicking OK, we get the setup input form. The presentproblem is titled as 'Dew Point Calculations' (see Figure 1.48).

In Figure 1.49, the Aspen Plus accounting information are provided.


Here we have to enter all the components we are using in the simulation. In the list onthe left, choose Components /Specifications and fill up the table following the procedureexplained earlier (see Figure 1.50).

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FIGURE 1.49


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FIGURE 1.50


From the Data Browser, select Properties /Specifications to obtain a blank property inputform. From the Property method pulldown menu, select RK-Soave (see Figure 1.51).

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FIGURE 1.51




In the column at the left side, choose Streams/1. As a result, a stream input form opens

Entering all required information, one obtains the screen as shown in Figure 1.52

.

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r-

SIS Mi-If Pi

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ili

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FIGURE 1.52


The final area that requires input is the Blocks tab. In the list on the left, double-clickon Blocks and then select DEW. Filling up the input form, we have Figure 1.53.

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too** Otn Wo» Library wmdcwi

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FIGURE 1.53

INTRODUCTION AND STEPWISK ASPEN PLUS 3!MUU\TION 41


Running the simulation, the following progress report is obtained (see Figure 1.54).

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FIGURE 1.54

Viewing results

First click on Solver Settings. From the Data Browser, choose Blocks/DEW/Results(see Figure 1.55) to get the dew point temperature = 22.19453840C.

i' r-ui>.i.rf

a -.

MM*MM*

JVM -

i* I- *

.MM

-I

.(O-e-o-i-it-hum 1 im*f n u t- w ' i

FIGURE 1.55


1.3

.5 T-xy and P-xy Diagrams of a Binary MixtureProblem statement

A binary mixture, consisting of 60 mole% ethanol and 40 mole% water, is introducedinto a flash chamber (Flash2) with a flow rate of 120 kmol/hr at 3 bar and 250C

.

(a) Produce T-xy plot at a constant pressure (1.013 bar)(b) Produce xy plot based on the data obtained in part (a)(c) Produce P-xy plot at a constant temperature (90oC)

Use the Wilson activity coefficient model as a property method.

Simulation approach

As usual, start Aspen Plus and select Template. Click OK to get the next screen andchoose General with Metric Units. Then again hit OK. In the subsequent step, click OKin the Connect to Engine window to obtain a blank Process Flowsheet Window.

Creating flowsheet

From the equipment Model Library at the bottom of the Aspen Plus process flowsheetwindow, select the Separators tab and insert the Flash2 separator. Then connect theseparation unit with the incoming and outgoing streams. The complete process is shownin Figure 1.56.

-CD o

-0 o

STfSAMS

9-o

1

FIGURE 1.56


After clicking on Solver Settings, select Setup /Specifications in the list on the left. TheTitle of the present problem is given as 'TXY and PXY Diagrams'. Subsequently, theAspen Plus accounting information are also provided [see Figures 1.57(a) and (b)].

INTKOIHTTION AND STKI'WISK ASl'liN I'l.l'S ' SIMULATION 43

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FIGURE 1.57(a)

213

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I -IE' - ;« 1

?33 <o'»-

-CH oeo.@.«t Mi(.i,tra5»«-i

FIGURE 1.57(b)


Hitting Next button and defining the components (ethanol and water) in the inputform, one obtains Figure 1.58.


The user input under the Properties tab is probably the most critical input required torun a successful simulation. Clicking Next button, we obtain the property input form.For this problem, choose the Wilson model by scrolling down (see Figure 1.59).


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FIGURE 1.59

Once the base property method has been selected and we click the Next button, awindow pops up asking whether to continue to the next step or to modify the properties(see Figure 1.60).

INTRODUCTION AND STEPWiSK ASPEN PLUS SIMULATION 45

Required Properties Input Complete

Go to the Next requiied step, or supplyadditional properties information,

Go to Next required input step

' Modify required property specifications

E nter property parameters

Enter raw properly data

i

OK Cancel

FIGURE 1.60


The next window includes a stream input form. Specifying temperature, pressure, flowrate and components mole fraction, one obtains Figure 1.61 as shown.

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FIGURE 1.61

(a) Creating T-xy plot: Selecting ToolslAnalysis IProperty I Binary, we haveFigure 1.62.



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P jT H il 3 s*»h

FIGURE 1.62

We must note that this option can be used to generate T-xy, P-xy or Gibbs energy ofmixing diagrams. Select Txy' for the present problem. We aim to do an analysis on themixture of ethanol and water; so select these components accordingly. The user has theoption of specifying, which component will be used for the x-axis (which component'smole fraction will be diagrammed). The default is whichever component is indicated ascomponent 1. Make sure that we are creating the diagram for the mole fraction of ethanol.Entering required information, Figure 1.62 takes the following form (see Figure 1.63).

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.-

IJ l-M- r»"

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lUj- "> ru.,

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|l

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rsKlfel i Kl tj ! |n| jl! M3

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FIGURE 1.63

Click on Go and get the T-xy plot at a constant pressure (1.013 bar) as shown in

Figure 1.64. Although the Status bar shows Required Input Incomplete,but there is no

problem to get the plot based on the given information.

INTRODUCTION AND STEPWISE ASPEN PLUS1 M SIMUL.\TION 47

5J Ji) Mr3ii-|*i*i<H»!l 2I -"IBI I' g 21!!

OltflBI lai Mel »l

i r-i-i-i>nr

FIGURE 1.64

It should be noted that if we move the T-xy plot slightly or close it, we findFigure 1.65 having a databank. Some of these values have been used to make theplot (Figure 1.64).

n3K|fc!»|-qM!!H 3i-

i i i .i .m- i m\

Mil* I MMI

rwrrc

Wtfm: : -

<o e-o-e-a;«Mp»iM.i lM«4Ml-

FIGURE 1.65



ru tut M* I** BiW H>«>> Vrt Ji-

.

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.

Mf.

n: j i i 'i mo; i i"i SM

REAMS ' ri«h2 fLwM C'mjtj- 'if f-'

j tRLAMb

FIGURE 1.62

We must note that this option can be used to generate T-xy, P-xy or Gibbs energy ofmixing diagrams. Select 'Txy' for the present problem. We aim to do an analysis on themixture of ethanol and water; so select these components accordingly. The user has theoption of specifying, which component will be used for the x-axis (which component

'

s

mole fraction will be diagrammed). The default is whichever component is indicated ascomponent 1. Make sure that we are creating the diagram for the mole fraction of ethanol.Entering required information. Figure 1.62 takes the following form (see Figure 1.63).

M il SI M SI

2 |W*TER~

3

fETHANOL

3

(\oflm<y cmms

-o-

FIGURE 1.63

Click on Go and get the T-xy plot at a constant pressure (1.013 bar) as shown in

Figure 1.64. Although the Status bar shows Required Input Incomplete,but there is no

problem to get the plot based on the given information.


Clicking on Go button, we have the following P-xy plot |see Figure 1.68(a)|at a constant temperature (90oC) and respective databank produced (Figure 1.68(b)|.

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L *-i

:

1 1 1 DM

.....-

11

FIGURE 1.68(a)

3/11 '' IBi.-l ' I

uoitnuc

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mti

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IU MM

FIGURE 1.68(b)



Notice that the plot window can be edited by right clicking on that window andselecting Properties. In the properties window, the user can modify the title

, axis scale,

font, colour of the plot, etc. Alternatively, double-click on the different elements of the

plot and modify them as we like to improve the presentation and clarity.

SUMMARY AND CONCLUSIONS

In this chapter, a brief introduction of the Aspen simulator is presented first. It is wellrecognized that the Aspen software is an extremely powerful simulation tool,

in which,

a large number of parameter values are stored in the databank and the calculations arepre-programmed. At the preliminary stage of this software course, this chapter mayhelp to accustom with several items and stepwise simulation procedures. Here,

four

simple problems (flash calculation, bubble point calculation, dew point calculation andT-xy as well as P-xy plot generation) have been solved showing all simulation steps.

PROBLEMS |1.1 A liquid mixture, consisting of 60 mole% benzene and 40 mole% toluene, is fed

with a flow rate of 100 kmol/hr at 3 bar and 250C to a flash chamber (Flash2)

operated at 1.2 atm and 100oC. Applying the SYSOP0 method, compute the

amounts of liquid and vapour products and their compositions.1.2 A liquid mixture, consisting of 60 mole% benzene, 30 mole% toluene and

10 mole% o-xylene, is flashed at 1 atm and 110oC. The feed mixture with a flowrate of 100 kmol/hr enters the flash drum (Flash2) at 1 atm and 80oC

. Using theSYSOP0 property method,

(a) Compute the amounts of liquid and vapour outlets and their compositions(b) Repeat the calculation at 1.5 atm and 120oC (operating conditions)

1.3 A hydrocarbon mixture with the composition, shown in Table 1.3, is fed to aflash drum at 50oF and 20 psia.

TABLE 1.3

Component Flow rate (lb moiyhr)

i-C4 12

n-C4(LK) 448

i-C5(HK) 36

Ce 23

C7 39.1

272.2

c9 31

876.3

The flash chamber (Flash2) operates at 180oF and 80 psia. Applying the SYSOP0thermodynamic model, determine the amounts of liquid and vapour products

and their compositions.

INTRODUCTION AND STEPWISK ASPEN PLUS SIMULATION 51

1.4 Find the bubble point and dew point temperatures of a mixture of 0.4 mole fractiontoluene and 0.6 mole fraction rso-butanol at 101.3 kPa. Assume ideal mixture

and inlet temperature of 50oC, pressure of 1.5 atm, and flow rate of 100 kmol/hr.1.5 Find the bubble point and dew point temperatures and corresponding vapour

and liquid compositions for a mixture of 33 mole% n-hexane, 33 mole% n-heptaneand 34 mole% n-octane at 1 atm pressure. The feed mixture with a flow rate of100 kmol/hr enters at 50oC and 1 atm. Consider ideality in both liquid and vapourphases.

1.6 Compute the bubble point and dew point temperatures of a solution ofhydrocarbons with the following composition at 345 kN/m2(see Table 1.4).

TABLE 1.4


c3 0.05

n-C4 0.25

n-C5 0.4

Ce 0.3

The ideal solution with a flow rate of 100 kmol/hr enters at 50oC and 1 atm.

1.7 Calculate the bubble point pressure at 40oC of the following hydrocarbon stream(see Table 1.5).

TABLE 1.6


c, 0.05

c2 0.1

Ca 0.15

i-C4 0.

1

n-C4 0.2

i-Cs 0.15

n-C5 0.15

c6 0.1

Use the SRK thermodynamic model and consider the inlet temperature of 30oC,pressure of 4.5 bar and flow rate of 100 kmol/hr.

1.8 A binary mixture, consisting of 50 mole% ethanol and 50 mole% 1-propanol, isfed to a flash drum (Flash2) with a flow rate of 120 kmol/hr at 3.5 bar and 30oC.

(a) Produce T-xy plot at a constant pressure (1.013 bar)(b) Produce P-xy plot at a constant temperature (750C)(c) Produce xy plot based on the data obtained in part (b)

Consider the RK-Soave thermodynamic model as a base property method.1.9 A ternary mixture with the following component-wise flow rates is introduced

into a decanter model run at 341.1 K and 308.9 kPa. To identify the secondliquid phase, select n-pentane as a key component (see Table 1.6).


TABLE 1.6

Component Flow rate (kmol/hr)

n-pentaneethanol

water

10

3

7.5

Applying the NRTL property method, simulate the decanter block to computethe flow rates of two product streams.

1.10 A ternary mixture having the following flow rates is fed to a separator (Sep2) at50oC and 5 bar (see Table 1.7).

TABLE 1.7


n-pentaneethanol

water

33.623

0.476

3.705

To solve the present problem using Aspen Plus, the following specifications areprovided along with a T/F ratio of 0.905478 (see Table 1.8 and Figure 1.69).

TABLE 1.8

Component Split fraction in stream T

n-pentaneethanol

water

0.999

0.9

(calculated by Aspen)

B -O

FIGURE 1.69 A flowsheet of a separator.

Applying the SRK property method, simulate the flowsheet, shown in Figure 1.69,and determine the product compositions.

1.11 Repeat the above problem with replacing the separator Sep2 by Sep and usingsplit fraction of water 0.4 in Stream T.

1.12 A dryer, as specified in Figure 1.70, operates at 200oF and 1 atm. Apply the

SOLIDS base property method and simulate the dryer model (Flash2) to computethe recovery of water in the top product.

INTRODUCTION AND STKPWISE ASPEN PLUS SIMULATION 53

Wet

Temperature = 75DCPressure = 1 aim

Flow rates

S(02 = 800 Ib/hr

H20 = 5 Ib/hr

Air

Temperature = 200oCPressure = 1 atm

Flow rates = 50 Ibmol/hr

N2 = 80 mole%O, b 20 mole%

AiROur;

WET

AIR 0dry; O

DRYER

FIGURE 1.70 A flowsheet of a dryer

REFERENCE

AspenTech Official Site, When was the Company Founded?, http://www.aspentech.com/corporate/careers/faqs.cfm#whenAT.

C H A P T E R 2Aspen Plus Simulation

of Reactor Models

2.1 BUILT-IN REACTOR MODELS

In the Aspen Plus model library, seven built-in reactor models are available. Theyare RStoic, RYield, REquil, RGibbs, RCSTR, RPlug and RBatch. The stoichiometricreactor, RStoic, is used when the stoichiometry is known but the reaction kinetics iseither unknown or unimportant. The yield reactor, RYield, is employed in those caseswhere both the reactions-kinetics and stoichiometry-are unknown but the productyields Eire known to us. For single-phase chemical equilibrium or simultaneous phaseand chemical equilibrium calculations, we choose either REquil or RGibbs. REquil modelsolves stoichiometric chemical and phase equilibrium equations. On the other hand,RGibbs solves its model by minimizing Gibbs free energy, subject to atom balanceconstraints. RCSTR, RPlug and RBatch are rigorous models of continuous stirred tankreactor (CSTR), plug flow reactor (PER) and batch (or semi-batch) reactor

, respectively.Eor these three reactor models, kinetics is known. RPlug and RBatch handle rate-based kinetic reactions, whereas RCSTR simultaneously handles equilibrium and rate-based reactions. It should be noted that the rigorous models in Aspen Plus can usebuilt-in Power law or Langmuir-Hinshelwood-Hougen-Watson (LHHW) or user definedkinetics. The user can define the reaction kinetics in Fortran subroutine or in excelworksheet.

One of the most important things to remember when using a computer simulationprogram, in any application, is that incorrect input data or programming can lead tosolutions that are "correct" based on the program's specifications,

but unrealistic with

regard to real-life applications. For this reason, a good knowledge is must on the reactionengineering. In the following, we will simulate several reactor models using the AspenPlus software package. Apart from these solved examples, interested reader maysimulate the reactor models given in the exercise at the end of this chapter.

54

ASPEN PLUS SIMULATION OF REACTOR MODELS 55

2.2 ASPEN PLUS SIMULATION OF A RStolc MODEL

Problem statement

Styrene is produced by dehydrogenation of ethylbenzene. Here we consider anirreversible reaction given as:

CgHs-C2H5 -> CgHs-CH - CH2 + H2

ethylbenzene styrene hydrogen

Pure ethylbenzene enters the RStoic reactor with a flow rate of 100 kmol/hr at 260oCand 1.5 bar. The reactor operates at 250oC and 1.2 bar. We can use the fractional

conversion of ethylbenzene equals 0.8. Using the Peng-Robinson thermodynamic method,simulate the reactor model.

Simulation approach

As we start Aspen Plus from the Start menu or by double-clicking the Aspen Plus iconon our desktop, first the Aspen Plus Startup dialog appears (see Figure 2.1). ChooseTemplate option and then click OK.

iaj _1_J __J *j rv.Mft, I-Hid 3 I I l-J±]-J _J

_J

FIGURE 2.1

As the next window pops up (see Figure 2.2), select General with Metric Units andhit OK button.

Copyrighted materia

56 4 PROCESS SIMULATION AND CONTROL USING ASPEN

jzj

I M I I I lAl I I I - I

[5'.f»**-«i "v.* (Maj" *-** , /.r . - - ( 'to-.

JV--- *.j m . , _j

'jJ. mo; Mil E-v v 'Mi 3 'th B«MWr . jw*-N«ta»et« SkwtrM

. j .j--jc-r; ] f.-S- -.r 3 C j n-V; j «' if!: VV.

FIGURE 2.2

Here we use the simulation engine at 'Local PC. Click OK when the Connect toEngine dialog is displayed (see Figure 2.3). Note that this step is specific to the installation.

Connect to Engine

Server type:

User Info

Node name :

User name:

Password:

Working directory:

Local PC

O Save as Default Connection

OK Exit Help

FIGURE 2.3

Creating flowsheet

We are now ready to develop the process flow diagram. Select the Reactors tab fromthe Model Library toolbar, then choose RStoic icon and finally place this unit in theblank Process Flowsheet Window. In order to connect the feed and effluent streams

MODELS 57

with the reactor block, click on Material STREAMS tab in th 1As we move the cursor, now a crosshair, onto the process flnw fui , COriier

-

two red arrows and one blue arrow. Remember that red arrowf 'blue arrows are optional ports. arr0WS are re(luired ts and

Click once on the starting point, expand the feed line and click a~Hn tv,- f astream is labelled as 1. Addmg the outlet stream to the reactor tntJXwa WW

we make the image as shown in Figure 2.4. y' UIiaiiy

I .lal I Ml

= 03-

-Q a

In

i . i . S -O-M-io-

a Ri astt. tb pfvjj

FIGURE 2.4

After renaming Stream 1 to F, Stream 2 to P and Block Bl to REACTOR, theflowsheet looks like Figure 2.5.

c* .'r- C«J 'Kf! Pin ftr-Kl«- LI'-TV iWoc,-. i

DltflBI «BI Id iff! GN-|e>IM<iM h-I "I I IH -i

-Eh-

at rsms acs'R

FIGURE 2.5

»-l«IVl

Obviously, the Sia s md/cator in the bottom right of the mam window h changedthe message from Flowsheet Not Complete to Required Input /ncom ff . f ationto enter th* remaining data using several input forms required to complete the simulation.



Hitting Next icon and clicking OK on the message sheet displayed, we get the setup inputform. First the title of the present problem is given as 'Simulation of the RStoic Reactor'

In the next, the Aspen Plus accounting information (required at some installations)are provided.

User name: AKJANA

Account number: 5

Project ID: ANYTHINGProject name: YOUR CHOICE

Finally, select Report Options under Setup folder, choose 'Mole' as well as 'Mass'fraction item under Stream tab (see Figure 2.6(a), (b) and (c)).

_i_r- i - i- i jv -i « i iai

MM ±S

UMsi

[jjttiEjjftL- - .1

J.

l-U

I- S . S . § -Q-M-O-B.BM Bi

.u. '-.C--- KC TIi PFtjj Rfem.

FIGURE 2.6(a)

Jl-T - i I- fV I -M I lal fifj

FIGURE 2.6(b)

ASPEN PLUS SIMULATION OF REACTOR MODEI S 59

Mil

,: r-i-hi r» .! .|gi i ip' h-i

- it

Dm dm

r_ utM

-O-

'ftifc waw «

I i i I M>l Umomm I

FIGURE 2.6(c)


In the Data Browser window, choose Components /Specifications to obtain the componentinput form. Now fill out the table for three components, ethylbenzene, styrene andhydrogen (see Figure 2.7). If Aspen Plus does not recognize the components by theirIDs as defined by the user, use the Find button to search them. Select the componentsfrom the lists and then Add them. A detailed procedure is presented in Chapter 1.

I?!

i "" TH III

1 -1-

sr-l© 8 18 0IIU

FIGURE 2.7

fd materic



Choosing Properties /Specifications in the column at the left side, one obtains the

property input form. Use the Peng-Robinson thermodynamic package by selecting PENG-

ROB under the Base method tab (see Figure 2.8).

ol lBj_

J_J w] KW«>|<H m -1 H JpJjJ J

J * few Proc*li«t

U **-

3

r "

3""

31

"

3

"

33

STREAMS_

-

' 3M| #

RSldc fn'«M BE RSbte RCSTR fiPH) BB*

FIGURE 2.8


The Streams IFIInput ISpecifications sheet appears with the Data Browser menu tree inthe left pane. Entering the values for state variables (temperature, pressure and total

flow) and composition (mole fraction), we finally have the following screen (see Figure 2.9).

DZSMSSEGSSSD: fi* Hot Utorr Wrdo* H-fc

I r I -1 "I T» 'I -Ml I . 131

A|>Mdiedtio<n| FWiOwonTl|/M1XED

to'***

Ware 2mu«

(i a ******

1 'wr-S-

p3"

"

3~

3

i]

-

"

3

3

0D

ur1

'J -

m-1 - i - i q s uttBUH, ' reS Bl . BO f"" SSiS

. ,.JCT»J . :

FIGURE 2.9



From the Data Browser, select Blocks/REACTOR. Specifying operating conditions forthe reactor model, the form looks like Figure 2.10.

3Efb »|-.| ..IB q .>| ol,,! |

F tc. PCStB CTo Mvg-.

l-Qactg Mom. I » Vsm"

FIGURE 2.10

Specifying reaction information

In the next, either hit Next button or Reactions tab under Blocks /REACTOR. Chck iVeiy,

to choose the reactants and products using the dropdown list, input the stoichiometriccoefBcients and specify the fractional conversion. In the Aspen Plus simulator, coefficientsshould be negative for reactants and positive for products (see Figure 2.11).

** b* bo "e*

>'-'

J

RiACTQR

Wt<it BCSTR BtVn

FIGURE 2.11



In Figure 2.12, Status message includes Required Input Complete. It implies that allrequired input information have been inserted by the user. There are a few ways torun the simulation. We could select either the Next button in the toolbar which will tellus that all of the required inputs are complete and ask if we would like to run the

simulation. We can also run the simulation by selecting the Run button in the toolbar

(this is the button with a block arrow pointing to the right). Alternatively, we can go toRun on the menu bar and select 'Run' (F5).

MM.|8W«'!i ,l|Hllir

DMllI M ill

"" Elfb ImeicbahA«s8V.'Bend

RxnNo Specilicaiun type StochiotnebyIttrCanpi ETHYL-01 > STYREHE . KrtiflOGEN

UNIFAC Group* <l 1 -

I Comp-GroLps' Con-.p-Lis's

* 1 1 Cperty MethodsS tstrfi tficn': Jj Moiecua- Sbuctm> p ParameJers

D a

S Advanced

_

&reanS- Jfl :

(1 EOVsraH«CJ P

3 Bocks. RECTOR

/Sp«£tfeahont /Re-

Rcadicxs

, 1 Contujlion | HMHiResclion | Setacli«ly | PSO | EowmrtAm |

At tequfed npd u ocmpHe Y j can rui the MnuMlon nitw. wiiu can erttr more input To er4er more f-pj. Bated Cared th«nseled t e ooUont yoj mM tnyn Ihe Dais poldOAT-, menu

Rui ir-e sirxilatiwi now?

P Rwchom occu r ien«

Inpu C«nplete

[H " Mnwii/SpWer;-CH

STREAMS ' RStdc RYieW

RucloiHea<Ev.-. i9Pt; J.,, Chsnga, | M<n>M>t ( 5c«> j U»Mo*b |

F-

,r H«o,press F1

'-Stall *

.

Boot_

Aww.RaocDdr | « Awr.Mcd I

FIGURE 2.12

Viewing results

As we click OK on the above message, the Control Panel appears showing the progressof the simulation. After the simulation is run and converged,

we notice that the ResultsSummary tab on the Data Browser window has a blue checkmark

. Clicking on that tabwill open up the Run Status. If the simulation has converged,

it should state"Calculations were completed normally" (see Figure 2.13).

Pressing Next button and then OK, we get the Run Status screen.

In the subsequentstep, select Results Summary /Streams in the list on the left and obtain the final results(see Figure 2.14). Save the work done by choosing File/Save As/...in the menu list onthe top.

Ifwe click on Stream Table knob just above the results table, the results are recordedin the Process Flowsheet Window, as shown in Figure 2.15


' >k r« An [Mi Tot \r Um <.>«. MO

tnut iulmtiu imi." un nn i< nt ecu iiutiui tmrrrxz nm a tmh tmis us . unm

um wen* Mat- unic

-CH-

- - -

s ' w*. mw< n* w> ii>*j

FIGURE 2.13

-

T I M -I -lei

I I

-

3»"

3 "-'-IJ

a)-

55T:-

t« " <w"

is*" .,i i.

M», iMm

l>ii l«U

Man'*

m

cna

inpp BUB

Waw' VI | ****** | H»«U** .

m- @ . i . e u m uincMA ' irw« wto* MMt ac» S

"-I r

FIGURE 2.14


Ffc Edt Vfew 0«a Into ftjn nowheri Lfc fy VAk w Het

'-lup I , IT_

LiiE| | |a|

EES;: gIBl«l|Oi. £lal«l|'rj. .aaJj'lLMto SlAtM | Salami | HealEKclwgeij | Cokfwx naactan | pienueChange!i | Manpiaton | 5cM« [ UmModeb |

, S 0 U 31USTREAMS 1 BSinc BEoii HGMis RCSTB BPItg RBaM.

FIGURE 2.15

\ s FoWen JJswn Ru» H 1 HUMlfloAi Artfahie


For input information, press Ctrl + Alt + I on the keyboard or select Input Summaryfrom the View pulldown menu (see Figure 2.16).

CBSESFie £* Forw* >Atw

input Sugary created by Aspen Plus K«1. 11.1 at 12:U:CM Thu jul 5, 300?Oirecrory C: Proqr-5R Pi les'AspenTech .norfcing Pol ders'.Aspen Plus 11.1 Fllep

title 'SlmUllon of the fiStolc Reactor"

IN-UNITS KET VOLU> E-FLOS<-"

cuB hr ENTM*LPV-Fl.O-'*»lkcal/hr' AHCAT-TRAHS-C-

'

kcal/hr-sqn-K" PRESSURE"bar TEMPERATURE-C &VOLUHE-CUIT OELTA-T-C HEAD-neter httLE-DENSin'-'fcisol/cuni' &fASS-DENSITV-

'

kg.'CUH" W)LE-£NTHALP- kcal,'noV t,t-ASS-EWTM .P-

'

kcal/kg' HE*T-MMkcal t'OLE-CONC-'mol.

'T &POBOP-bar

OCF-STREAt'S COMVEN AIL

DESCRIPTIOH "General SlHllailoi) mith Metric units :C, bar, kg/hr, knclhr. MMKcal/hr, c\m/hr.

property Method: Mone

Flow basis for Input: Kole

Stream report cooposltlon: Kole flow

ROP-SOURCES PUBEll - AQUEOUS / SOLIDS f INORGANIC

COMPONENTSETHYL-01 C8H10-4 /STVRENE C8H8 ,'HVOfiOGEN H2

PBOPERTIFS PENG-ROB

5THCAH FSUBSTBEAf KIXEO TCHP-J60. PRE5-1.S MOLE-FLOW-100.W>LE-FMC ETHYL-01 1.

e Ci'

.Users-.akjana.AppMtaMocal Terep -ape906.tK}

' B i I vjnwi-* |- la»«Jtol | lto.»,-s || -WEME1 :« jpCittU

FIGURE 2.16

t 65- y wkjusu,jO f DO

If one may wish to generate a report file (* rep) for the nrp f u,instructions as presented in Chapter 1

.

P eSent Problem, follow the

2.3 ASPEN PLUS SIMULATION OF A RCSTR MODEL

Problem statement

The hydrogenation of aniline produces cyclohexylamine in a CSTR accord ffollowing reaction: ' accor(lirig to the

C6H5NH2 + 3H2 CeHnNHaaniline hydrogen cyclohexylamine

The reactor operates at 40 bar and 120oC, and its volume is 1200 ft3 (75% liquid) For

the liquid-phase reaction, the inlet streams have the specifications, shown in Table 2

.1

.

TABLE 2.1

Reactant Temperature (0C) Pressure (bar) Flow rate (kmol/hr)

Pure aniline 43 41 45

Pure hydrogen 230 41 160

Fake reaction kinetics data for the Arrhenius law are given as:

Pre-exponential factor = 5 x 105 m3/kmol s

Activation energy = 20,000 Btu/lbmol

[CJ basis = Molarity

Use the SYSOP0 base property method in the simulation. The reaction is first-order inaniline and hydrogen. The reaction rate constant is defined with respect to aniline.

Simulate the CSTR model and compute the component mole fractions in both the liquidas well as vapour product.

Simulation approachStart with the General with Metric Units Template, as shown in Figures 2.17(a) and (b).

Click OK in the above screen. When the Connect to Engine dialog appears, again

hit OK knob to obtain a blank Process Flowsheet Window.

Creating flowsheet

Select the Reactors tab from the Model Litwy tmodels available. Among them, choose RCSTR P ce it in tnAdding inlet and product streams and renaming them, the process flow magr

look like Figure 2.18.

PROCESS SIMULATION AND CONTROL USING ASPEN"

Q|a|B|_

JJ J_J nMfel I 1 :1 si 21 __1_L.J ni M M ®l

A1 ] c 8lor+. SmuWen

r OMUsnE.ulr.lSim.jl.j'i-

Aap«n Plus « Vf # i"

VSJ6

FIGURE 2.17(a)

g *apen IP= Strean Prx&hts

I Beetle, «|fa Enshh ijrit|aklnt«ill wth Medic IMi

Procws g fAs Unfa

nitpwi wi mmi

SpNtft/Chmic*

mnz Lines.

MMtajJ-V,arvtr

Propetty I lhod; None

Bow toss crinpiif 'tee

Strtom reaaicwrpcttEfi: Mote flow

' SUrti

FIGURE 2.17(b)

ASPEN PLUS1" SIMUIATION OF REACTOR MODELS 67

h W ..> 3a Hi* .<-»-» MMa

o|rf|y|giai_

lg|g rj|twi<H;j 3 I ("l jajgj

u

-I}-

tmuHt 1 Igj gMij gM Wii*. .Hi* ->

FIGURE 2.18


Hit Afe button and then OK and get the setup input form. The present project is titledas 'Simulation of the RCSTR Reactor' and the accounting information are given as'AKJANA/6/ANYTHING/YOUR CHOICE* (see Figures 2.19(a) and (b)).

Jim _iJ *! El &iMiid 3 I i"l 3 *I

- II -». w . ft -.-.

FIGURE 2.19(a)

68 PROCESS SIMULATION AND CONTROL USING ASPEN1 M

' Fie E« On TmH PU Lfrvy Wilder- *k>

0 Spiicfcii

. jfl IM-SHiO CuHsfflUnli

l.li«< MBW

Rovci ID

kfUCdRfMi

.11 -y-BoSTREAMS

' RSioc RYwId REgnl RGMw RCSTfl RWjg REafch

O * $3 17 1'.

FIGURE 2.19(b)

In the subsequent step, choose Setup/Report Options / Stream from the Data Browserwindow and select '

Mole' as well as 'Mass' fraction basis (see Figure 2.20).

B* E* Mxr CM* Todi ftr PW Uorv AWow h«b

i ajJJ iBJ J al-rlfeKKI I n>i ij J |h| a| 1 M

0 SkW* Qnl

. Jfl Ml S«t»

Cereal | Ftowiho* | Bbcf Ali j Roperty j AW |

turn U be ndmMr, tiiMm itpoii

P MtJa P Mcta

! r Uau P MmTFF [gENJ T]|S Standard fa0cdm>i

P S.>- .:abh tP Componerti t h (wo to-. 01 H-itDon

f " M- Sc*-.. | S».*n | HME

StfltW BV ffvuc RE.M- RGte. RCS1R RPI m j,

1 " -

(Bill

FIGURE 2.20

ASPEN PLUS SIMULATION OP REACTOR MODELS -f 69

Specifying componentsThe example reaction system includes three components. They are aniline, hydrogenand cyclohexylamine. Defining all these species in the component input form, one obtainsFigure 2.21.

V nt Eik 4n feu To* FU. Pla Uh

Ffesctons

~

3 Mdiilfs-3ij bj rl

AMIUNE C6H7I11

WyMOGEN K1T1R0G H

CYCLO H EWLAMICSH13W -01

Eire V/cw) UtwCMnd Rtttdei:

D' ""'""

in

MlI I Sotd. | U«>M«Mt t

RSac Brtrtj ftEqai RGfcb) flCStft RFtifl Rflaieh

FIGURE 2.21


We know that a property method is a bank of methods and models used to computephysical properties. For the sample reactor model, select SYSOP0 base property method(see Figure 2.22) after clicking on Next icon in the above screen.

Fk feu VW* D«» liA Fj, li -f V,Wfe/. hefc

urvac

_j F rm

i

I 3

I*

si* | .>j3l*J<>TtQ('«W -i.d"°°«*''",l''fi' Aipcn rim - Sani

FIGURE 2.22



As we hit Next followed by OK, a stream input form appears. For Stream A (pure

aniline) and Stream H (pure hydrogen), values of state variables and composition are

inserted in the following two forms, shown in Figures 2.23(a) and (b).

ffe * '-Am D«i T«ol« An Fix Uc**y Wnfe* ' k

mm >. Ittieiwj nH-clalsKM!sJ 31 ! HiJ21«) »)

m.mr.i

_j PiAiW

Strunu

fj EOVar-ittai

J-

3 i«*f

SIBEAMS BGMw BCSTH

FIGURE 2.23(a)

'

:: St Edi Mw* 0«« To* An a* ifc,. whd*. Htfc

103 Owerti

O UMFACQtsun

« Zj EMMbn

ra;

i Jy MIXED~

3-

3 :iu*f..3

-

3

ToW IT

BCSIB «fl, m»

FIGURE 2.23(b)


In the next, there is a block input form. Providing required information for the CSTRblock, we have the screen as shown in Figure 2.24.

ASPEN PI-US SIMULATION OF REACTOR MODEIiJ 71

lim -Vii.l.-l!,! II I M ---. E« Sm 'mm Lbw> MrtM 4a

B.'i -I

..f

9 - .

' i -

ff. j .

-.

s

d « « |.if.|.iu«-.| ne

'- I' I.. -Ip=-31 -r-3

i

- 1,--.J 1 J

I F~

3

Si-__-__

iir

r |®- 9 . S . 9 Q U OITXUK Mm fJte >-. -'« »-

FIGURE 2.24

Product streams have been defined with their phases (see Figure 2.25).

I r-M-|r |T 'I .ICI I Ml

71

I.

li:.-I

0 -p uj

» llji lli*! i j I t XMUtavn I UMa III Hi | tm*mammu | » mi I Ma I iMHwk j-o-

I1XJM

m 0 . 8 . o y JE DIMMI Ptmt hm. unit TVl ggg

Ifflll

0»>W ta< - <

FIGURE 2.25

Press Afexf button or click on Reactions and get the window (as shown in Figure 2.26).


ASPEN PI-US SIMULATION OF REACTOR MODEIiJ 71

lim -Vii.l.-l!,! II I M ---. E« Sm 'mm Lbw> MrtM 4a

B.'i -I

..f

9 - .

' i -

ff. j .

-.

s

d « « |.if.|.iu«-.| ne

'- I' I.. -Ip=-31 -r-3

i

- 1,--.J 1 J

I F~

3

Si-__-__

iir

r |®- 9 . S . 9 Q U OITXUK Mm fJte >-. -'« »-

FIGURE 2.24

Product streams have been defined with their phases (see Figure 2.25).

I r-M-|r |T 'I .ICI I Ml

71

I.

li:.-I

0 -p uj

» llji lli*! i j I t XMUtavn I UMa III Hi | tm*mammu | » mi I Ma I iMHwk j-o-

I1XJM

m 0 . 8 . o y JE DIMMI Ptmt hm. unit TVl ggg

Ifflll

0»>W ta< - <

FIGURE 2.25

Press Afexf button or click on Reactions and get the window (as shown in Figure 2.26).


72 PROCESS SIMULATION AND CONTROL USING ASPEN"

I UtaftCSTRflCCTn i

«b Ed* ««» DKB Tooit ftr Pta IJfewy Wirvis Hdp

_

fe|ej rgklaKKM "I ! I"l J JJ J ®lJJ

- i 1 i HT I leal; I M Hi, Setup

rWft af Studio

MvanMd

a h.

11 L

Bocta- C5TR

e s-up

(J EOVsnai>«O EOhpu -O Sp«c GfWJpt

Pott

Solsd .e ion Mlt lo be nciideii n ihs

Arabia i««clw wU i SriBctedttwc'cn'-

Peailileschon E3 ID

ii-

[1 " MiMMiyS{«ter9 | S«p«aU»i ] He*E hangefi j Coluwij Heoclou j Preiwe Changeii ] MfloipUaloft | Sf** | UiwH&Wi |-a->

Mated \

STREAMS REeril RGtb! fiCSTR RPbg

C \ fl FtAJerj'Aweo Piu) 11 i'

HUM

fi Ofttce Woni j f-toggft Pcwergjrt . l . j MjCe toX>< frofett f [~

FIGURE 2.26

Right click on Available reaction sets, hit New button, then either accept defaultname R-l or give a name as we want for the reaction set and finally click on OK.

Subsequently, select POWERLAW in the Enter Type list and hit OK to get the screenas shown in Figure 2.27.

Ffc &» *w tWa Toe* fU Fte Ubnr, Vttyfcw Hdp

MHl

r .-l-i- PT -.1 M- I Ml jW

£j Pwwt/HenccsLJ"

1 Mdecwer Su-me

J : -_j Data

i_V) ftco-S*:

+' Jfl Hi o l

- csrnO '

9 Sp«Gto*i

H SbeenRMub ,

./Spccft hm j/S««atm/Ba ljont] PSD j CwvwMAm [

Sdect (sacbcn tw to t« ndudsd r nwdel

<0 s s s o OLJ.

FIGURE 2.27


Specifying reaction informationHitting Next knob, we obtain the screen, shown in Figure 2.28.

** cm <%* fw » -.>=- **

S .

ul.i

* | SiMMt | HewE h-vjpr | a m- Rm om { Praiiu,Charge.! | H««a«» | I UmiH<mM |

i - s - § .©.mo-STfttAKS RStoc ff.W RtajJ RGttK flCSTR RPl RBWtf,

FIGURE 2.28

As we click on New; button, a form is displayed as shown in Figure 2.29. In this

form, we need to enter the stoichiometric coefficient as well as exponent for allcomponents. The exponents represent the order of the reaction with respect to eachcomponent. Note that there are two types of reactions [kinetic (rate-controlled reactions)and equilibrium] permitted under Power law reaction ID

.

Dli*lBj_

J_

J feiej *l nrMfcl-NM '»! 1 I H -I l?l 1 ®|I f~ l-.l. li IT ! -lEI I |gl

Caw** 1 CMtft** 1 f.t * Cow«rt Co o**[_

r.i.-' |*

M. | |

-j

J

hB- 0 . i . 0iifitw4i f.4M Bf»J Km wifl

1 1

ft j A J » " .» 1 »*r**:««w«i-Lij<* * -*,»1 1 i ' . || 5-i - «ft ' 11"

FIGURE 2.29

74 PROCESS SIMULATION AND CONTROL USING ASPENT

As stated, the reaction

C6H5NH2 + 3H2 C6HnNH2

is first-order in aniline and hydrogen. Also, the reaction rate constant is defined withrespect to aniline. Accordingly, we may use the following information to specify thereaction (see Table 2.2).

TABLE 2.2

Component Coefficient Exponent

aniline -1 1

hydrogen -3 1

cyclohexylamine 1 0

Recall that in Aspen Plus terminology, coefficients must be negative for reactantsand positive for products. As we fill up the form, it looks like Figure 2.30.

aj}.f*, Fe> iw tup Tcotr

i'lltiliiiiESS

BoacMrNo.: |7i 3RuctMi -

Reaction type:

Product!

"

3

Comnonent Coefficient Enponent 1 CompafieW Coelficient Ej<ponent

ANILINE 1 j ; CYCLO-01 1

-IYDR0GEN .3 j *

* 1 i

Ctote

Bock,

- y Reactiomr J Chemolry

B Peacuons

ft R-I1 Convefgcnce

fj Rowaheetng Onions

.r1

Edt Delete

Reojrad tipul hcowMe

IT Mam pKen | Sepaators | HeatEndiangen | Cokams Haachm | PtenueOiaven ]

KWariel

STREAMS RSIoic RYieU

1.0 .y-U-U-HMj RStb. RCStfl BPIm Rieldi

SoUt UnModeb

ForHefc.weMfl

« « b3

"

!C\i,fi*ta.vW«iHi.111 , HUH-

ReuMtnO

FIGURE 2.30

If we do not specify the exponent for a species, Aspen Plus takes a default value ofzero. In Figure 2.31, the resulting relation is displayed in the stoichiometry sheet.

In the subsequent step (see Figure 2.32), we move on to Kinetic tab.


PHPI-Liasigl

.

if?:.-

3aft l"-" JSldilJP BiiJfllalfil

. j am

- 1 <I» j 0-.

) - .IW I I I Ihmt

<o- y i Q on o

FIGURE 2.31

"KiMWiingwrr~ » !

r.

*IM .Q C3WA\*\<M H "I I"! -I vl -I 9|

Irl |x|

"

3alt: »l*l <<Jp »| Gh-t ml

' jfl

99 .

. jfl .

. -* P '

* jfl

-1.-.,.

-I 3

ft into mn*&*B**n*

t.

ta

3

.m* Vm m t> mam >ew*

r.

-. KIT

FIGURE 2.32

76 PROCESS SIMULATION AND CONTROL USING SPEN]

As directed in the problem statement, we use 'Molarity' basis. Accordingly, the

Power law is expressed as:n E n 1

r= k [T0;exp

R(2.1)

where r is the rate of reaction, K the reaction rate constant (kinetic factor in AspenPlus terminology), k the pre-exponential or frequency factor, T the temperature m degree

K Tn the datum temperature in degree K, n the temperature exponent S the activation

energy R the universal gas constant, C the molarity in kmol/m , a the concentration

exponent, i the component index, and 0 the product operator.

If To is ignored, the Power law expression has the following form:

where,

r= kTn

exp

K = kTn exp

E

RT

E

RT

n(G) (2.2)

(2.3)

In most of our simple cases, the reaction rate constant is represented by the Arrheniuslaw, that is

E NK - k exp

RT) (2.4)

Notice that when the Arrhenius formula is used, we put zero for n and nothing for T0

in the Aspen Plus window. Also, the units of the pre-exponential factor are identical tothose of the rate constant and vary depending on the order of the reaction.

As we

know, the dimensions of the rate constant for an nth order reaction are:

(time)-1 (concentration)1-'1

Next come back to the problem. The kinetic data are required to provide in the abovesheet. Here we use the Arrhenius law to represent the reaction rate constant. It isimportant to mention that the pre-exponential factor must be specified in SI unit. Forthe example CSTR problem, the pre-exponential factor and activation energy are givenas 5 x 105 m3/kmol s and 20,000 Btu/lbmol respectively (see Figure 2.33).


In the window shown in Figure 2.33, the Status bar clearly indicates that all requiredmputs are now complete. Hitting Next knob and clicking on OK

,we have the foUowing

Control Panel (see Figure 2.34).


.. ._ - -J »«. Pte Un* OMn m,

QMIHI -I .1 gJ al-i-|«>l*l<l*-| n.| | MI r l-'l-'l-JV

.

l .lalr : I: Ml

mam

"

3

s csm3

ll ; US

ANIUNE . 3 HYDROGEN -i CYaO-Cl

f LMMMto twite

-a-i

Kdlarai."*

stream

farHsfe.pnMn

| igiM afc. .| gdifcCT,«fi .. | g a»»ita 11 .arote. || S fSTI- « 45.},«.s

FIGURE 2.33

: Ffc Dm Taofai Run Lfesry Wirdiw KHp

DMB| al M -H x?! nklaKI I I »>| IS -I H g|-|3| @|;J

,J

"

1 1- i,JV -HaliLWjilSla)-

5@ CSTPJ

oxputatich carsB rsi

Bi«ck.- csra uc tai. rcstr

fV . j Sep«a(«> i HwlE-changer. [ Cokm* Hb«1o« | Pte eChsr rt | M npuWw: | StJd; 1 UiwModel: |

MitoJ

SIflEAMS RStM fffxM REquJ RCiibOi BC5TR B Jg ftSalchfo K o ..

..-

FIGURE 2.34

Viewing resultsIn the next

,select Solver Settings, choose figsuto Summary/Sf ms in the list on the

left and finally get the results shown in Figure 2.35 in a tabulated form.


B» Ebl V«- D*. TMi. Hun fW ijt MiiM m

I f I I i PT ! .leal I - Ml tM

J4J«J

nr »

"I i I i i I I i

"

3 '-" l

il il -

am nil 11000 0541

0«5

MUM nooo 0J30 0 001

-

mmmi tso 6011 ITTre

'

0«J

sm DOM MPPM

0 98)

| HuiE«*w> ! C<*jwi fl-ctet. | FYB.M.Change..

i -1 .QMi-O'i | UisrWodeU |

R&tac RVWd SEgJ HQtei RCSIR RPfaa RftWi

to* j 3 tecofQB.c .jjJ Hereto P yP j Jatwlpd | .Ei wprf [{ AwenPkw-S-

« 1*35

FIGURE 2.35

Save the simulation work in a folder giving a suitable file name.

2.4 ASPEN PLUS SIMULATION OF A RPlug MODEL

Problem statement

The combination of two benzene molecules forms one molecule of diphenyl and one ofhydrogen (Fogler, 2005). The elementary reversible vapour-phase reaction occurs in aplug flow reactor (PER).

2CqHq <-> C12H40 + H2benzene diphenyl hydrogen

The forward and reverse reaction rate constants are defined with respect to benzene.The vaporized benzene (pure) with a flow rate of 0.02 Ibmol/hr enters the reactor at1250oF and 15 Psi. The data for the Arrhenius law are given below.

Forward reaction: A; = 3.2 x lO-6 kmol/s . m3 . (N/m2)2

E = 30200 cal/mol

Reverse reaction: k = 1.0x lO-5 kmol/s . m3 . (N/m2)2

E = 30200 cal/mol

[C,] basis = Partial pressure

The reactor length is 36 in and diameter is 0.6 in. It operates at inlet temperature.Applying the SYSOP0 thermodynamic model,

(a) compute the component mole fraction in the product stream, and(b) produce a plot ofreactor molar composition

' (mole fraction) vs i-eactor length' (in).

ASPEN PLUS SIMULATION OF REACTOR MODEI S 79

Simulation approach

Select Aspen Plus User Interface. When the Aspen Plus window pops up, chooseTemplate and click on OK (see Figure 2.36).

i -

....

-

...

iwmmmlt mm

FIGURE 2.36

In the next step (see Figure 2.37), select General with English Units and hit OK button.

1 V-

I-

- -

FIGURE 2.37

Click O/C when the Aspen Plus engine window appears.


80 PROCESS SIMULATION AND CONTROL USING ASPENTM

Creating flowsheet

In the Model Library, select the Reactors tab. Expanding the RPlug icon, the following

screen is obtained (see Figure 2.38).

Uj _

jS's - s - § oSIftEAMS ' RStoc flY»fc) W»J RCte RCSTR RBtfd<

li,-1?-:-:?-- IM

FIGURE 2.38

Inserting the left bottom symbol in the Process Flowsheet Window, adding the feed and

product streams, and renaming the block as well as streams, finally we see Figure 2.39.

Be £* *> &M ro* ftj> Uonn WnSo* H*

r|ttF..U|-. -nr Nsi|--..| -MBi IN

>|[T><rr| h~o

,

I* -****** | f«M». t hmI- mw | c*-« iu««« I rM..1,o,_

i 1 '

-iS- SSI Gj q.S'W ' BS*» FTiMd ftc nstfa. HCSTB flfy, Tftj T

FIGURE 2.39


Configuring settingsAt this moment, we are sure that the process flow diagram is drawn correctly. The Status

message directs us to provide the input information. Hitting Next knob and clicking onOK, we obtain a form for setup specifications. First we input the Title of the presentnroject (Simulation of the RPlug Model), followed by the accounting information(AKJANA/7/ANYTHING/AS YOU WANT) and Report Options [see Figures 2.40(a) to (c)]

.

3Sif*r-~3 *m si I >>i fliai g

ISrolWoneilheHPVjgMocW

Vdd|*MMC |

-o-> i s u -= uSIKAMS ' HSteic tVM myt RG|tte. RC?tR Rptq RBtuh

FIGURE 2.40(A)

> nt Mm OKk TMIp An W L±>»v WWo* H*p

UaTSil

arsiaiobdj-/Deicnmn >/Acciwnlina| 0>agr>o«(«ci {

[T MMi- pdim I Smmnc I HulE«chv4«i | Cot-mi. flo«'«" | Pimm«C»W

hB- 1 -1 - 8 Q OSIRLWi

__

fl5ia R.'* RfrMl RGfaU; W Iff Hf''-.gMdiM-AiMf But " I

".' U

FIGURE 2.40(b)


dmbl Melm mbhjsM«!] 21 g

r m«i

» r SM

K C twwrH »4i , »« flow W 'IK

»O-S-0 y

FIGURE 2.40(c)


From the Data Browser, select Specifications under the Components folder. As we providethe chemical formula of the components in the Component ID column, the other columnsof the table are automatically filled up (see Figure 2.41).

< Fit E* Htw D«i Tat* ftji RsT Ihwf ffntotr Hife

_j «r<rCwwi

SET

r* rg '."

Bin

k«W iooxi Id* -J

drvJ

'

.cnttm

IMM FvmU,

cia<io

Mwl «*h TOIR

FIGURE 2.41


In the list on the left, choose Properties /Specifications to obtain the property inputform. Then choose SYSOPO by scrolling down (see Figure 2.42).


tmum

~

3

is1 I

I 3 "~I d r.I 3

.» r

u

ETREAfce ftStac FTV dd SEtMl RCSTS RPljg flgateh

FIGURE 2.42


In the left pane of the Data Browser window,select Streams IF and enter the values

for all state variables and composition as shown in Figure 2.43.

_

i_

r.

IF

UH**C i3rtu»

State vsmUm

{y MIXED

Miinii

"

3

~

3"

3r"

3|12SJ |f 3

1-5 |p. d

Toid flwr (m.,- 3|0 02 jbmot/N 3

H2

Tdat IT"

Hoi 'jmvUf.t

'i-1 . § . § u-i ji* Rfrfi be j note ncsm npijg m»a

FIGURE 2.43



In the next, select PFR by opening the Blocks folder. The reactor is specified in thewindow, shown in Figure 2.44.

i Wl ftfl P*l Lbtry Wn

r-.i:i i nrJill 'IMMM

*-J Ntw'QuwclWMldn

J/j Prcf n«

-J

> -a f

aock-

_J Readx

_J C -wssxe

-

3

I Sold* { UnrMixM. j

BE** ftGMn

FIGURE 2.44

Open the Configuration sheet and enter the reactor dimensions in the next form(see Figure 2.45).

F«* Edt ttm 043 Tuafc flun fVK tbwy Wndm H*

DlcglBl 1 M iteial *l uW\&\**\<\vi n>| Hi ! |Mi H i?i :HMa

_j . /- itarj

S_j PAttwn

?»cp(rtif Veered

a :

36

DwtmUt 06 . -J

a §is q-u' RStot Rrail flE<M Wite' BCS'R Bp

| Sohk | Um> Modab |

HUM

FIGURE 2.45


T the subsequent step, we define a reaction set for the simulation. The default name

R-l has been accepted. Then select Power law kinetics and obtain the picture, shown inFigure 2.46.

M *" D*« ** "rw*' r

i)' I 22

H®-1 j . I y aSIR£>M$ ' HStac ffiW RCqU RGtti RCSTR fiB BB*J>

FIGURE 2.46


Hitting Aforf button and clicking on New, we have the following forms (see Figures 2.47(a)and (b)) for reaction number 1 (2C6H6 -> C12H10 + H2). Since the reaction rate constantsare defined with respect to benzene, we convert the stoichiometric coefficient of benzeneto unity for both the reactions

. Obviously,the reactions are second-order.

Jala_jj iiei wj nHM'.teM ».| m .| |h| .| pi ®|1 r..l..|,.l it .1 .ibi- 1 / ial

Rmmm

I1-I'

A

v R 1

ii

-o-

-0 S 0 1J- a .a # 1

FIGURE 2.47(a)


D|tf|y| I I <«l aHM-KM~l ! |h| -i ~ij j

HI »l

05

*

J _2=J

.j i :

3-1-0 o-=uRE R6ife RnSTR f ue HB**

j y- Bi-KOT- W j K Mmrst* Moiod j r jj'

Aver. Plu< - 5M " ij.} 30» '

FIGURE 2.47(b)

As mentioned previously, when we do not specify the exponent for a component,

Aspen Plus uses a default value of zero. As the message on the screen, shown inFigure 2.47(b) reveals, it is true that the forward reaction rate does not depend on theproduct components. After completing the first reaction, select 'New' from the ReactionNo. list. Enter '2; for the reverse reaction QHe C H + H2) and click OK (see Figure 2.48).

3| |B|_JJ Mgl jgl nklaNUI I n-i 3

_LliiJ El J

.

-l.

-

.

-ff falaltfrfi .1 ilBl: I si«|-

1

r

Oeate a nm Redcton No.

a

PR

R-t

tMM Cir.-,.; I"..-.., n -.ni'R£aUS nS>« BCtM ftGbb. RCSTft RFVp ISFa-Htfc mm FI

""

" " ~

-'---- II *p»f\«-a»i «

FIGURE 2.48

Subsequently provide the stoichiometric coefficients along with exponents, and getthe screen, shown in Figure 2.49.

ASPEN PLUS SIMUIATION OF REACTOR MODELS 87

iViirtiT.r

1 n-i 1.1 nr -

.i ,ieii i mi *mi; i

433

71

am*. | CJk-<| [(onCI.X'6 >

'

wi [1. 1

. 1

J _i5Lj

jjWM REaJ gg»] HCs flft nawcft

FIGURE 2.49

Hit A exf knob and obtain two stoichiometric relations as shown in Figure 2.50.

. - y. To* An fV Lirwy (fntjrw MaiDMBI 1

-i-nr .1 w - i-

3>>J qLJniJ

_

j MHnnd

HmNo Stuctimttry

: Kn«c

E .11u ,. * c 1 r §, I Sehdt I Ui*M«Jrt )

61 bio's ' fif.ioc ff/ id he j* new- ftCMn flrv Rn»thc v e (BiiTffiirr ft* n-i " "

FIGURE 2.50

In the simulation of the present problem,we use partial pressure basis (applicable

for vapour only) and,therefore, the Power law expression has the following form:

( f >n E ri 1

r = k expR To,

(2.5)

where, P represents the partial pressure (N/m2). If fo is not specified, the above equation

18 replaced by:


r= kTn expRT,

mPif1 2.6)

For the prescribed reactions, values of the pre-exponential factor and activation energyare provided in the two forms, shown in Figures 2

.51(a) and (b). To apply the Arrhenius

law, we put zero for temperature exponent n and left the box, allotted for datumtemperature T0, empty.

I r mi r» ! .isi; I - IB!

i»f.i

as

ill

* ai F* a ?

Si Bacfai PR

0 R-1

±1

[i) cfwe-. sciwio."

3

1 dE §

StflEfiMS RSI ffrteM REqui Rtjfcto RCSTFI RPVJ5 RBVch

FIGURE 2.51(a)

. ». Ea »«, 0«, r i, a .

-i.'r u>i-«i» rr 'i-.joii

a i

"

HMfcl"" »|-»l «l|Ii 3 >>l Dj J n.|

i a *******

(31 50*10. 5m;. C6M6

KiMtel«daNUT/T>>|"*'(E<n|m'l/TB|

SfBtMK ' BStet R>wto Rt fjfl ,

8 i 0 aI Mill

"11 Lin i

FIGURE 2.51(b)

ASPKN PLUS SIMULATION OF REACTOR MODELS 89


Hitting Afert button and running the simulation, we obtain the Control Panel (Figure 2.52)showing the progress of the present simulation.

_i_r-i I !'f» -i-igi 1 w aisd

(0 9 S 8 O = UM t<< Of*

FIGURE 2.52

(a) Viewing results: Click on Solver Settings knob, choose Results Summary/Streams in the column at the left side and finally obtain the results for allstreams, shown in Figure 2.53.

I r-i-i -rf7 'i -Hi i in i*l

4 1-

J"

a S dIUWi 1-m-

"

TW

-tm-1"

no--*m- sub-

aaraocc--

ve- im

(stcsss: -rwm 1

LROT Ml

Mr-

oiTWIM

inuA mm mm mik --

I - I M»l

-I * I-

FIGURE 2.53

C ll


(b) Producing a plot of mole fraction vs length: Use the Data Browser menutree to navigate to the Blocks IPFRI Profiles sheet (see Figure 2.54).

MJi HillLlim-WPMlMli -. ..l»1.T71.

in Fte &*l V*t C#» Toe* H i PW L*f«7 >» : «. Wi V*» C#» roe* Hji pw Ltmv "«

Dloi|y| I -.1 EtelBl «d H H I"! li U

. ifl -

it Pt >wt«ft aa 9»um- e v.

- a pf

Utt Sutra.

f] nwdb

a 9fM- p«A m RNdm- QniMgra

P.OC..I Sbe«. I

it.

pn F z_

far-

bt !S iHo

IS TZZf&VS

sSiTFW"

; 15 r?55

.4

s !5 00001 u*?

Z' 5 m-

lb i55S

i* 15

IS last 1 [ri!DK4IIft

g LSiQFM,j

I Maroiato-s | So** ) UtaHvkk |

C :., a fciJen'j'jsei Pin v

FIGURE 2.54

In the next, select Plot Wizard from the Plot pulldown menu. Alternatively, pressCtrl+Alt+W on the keyboard and obtain Figure 2.

55.

a S5

1 a

9 EMif/ t** Ocw

ft Fa*

: PlOCCUtilMnKtXEflM

9 a EOCor-Ortcm

fj LSSOPBu

ft

;

IJ

jlE

E

;

ii

-

24 IE

ir

;

Wercome ta Aspen Plus Plat WU.rdl

I

-L J J

51 REAMS 1 HSbe1 i . i y=o

HVMJ REcU ROttx

FIGURE 2.55

Click on Next icon and get a variety of plots (see Figure 2.56).

ASI'KN PLUS SIMULATION OF REACTOR MODELS 91

pi-eniajaaisi =i r. -i ht a3f j

MM

a---

a tfmm

3fitf* I 3 4321 iiB1 3iil 3t J Id

9 -

? - mi

-

N1

n 117 f

n- R

rin 1

(< H

1

I

J I i

iTmao Nftj mfc < w- - " -

find* .. -_;=_

FIGURE 2.56

Among the available options, select one plot type that is titled as 'Composition' andpress Next button (see Figure 2.57).

r-l-

-|..l'fT 'i-lci 1 fi ita.l

3 i±d «JP-3a -''ail -ii-

r.a -- io -- j- m -a Bin

3S

- 3 '-'

-4

v- I i-*

{© 9 . i 0 Q -O-' w > mm "tj~ mm m> mm J

FIGURE 2.57

Again click on Next and get the form, shown in Figure 2.58.


I mim 1?! r3l-<-lfcl<.UM "-I H _jLH jd JEl

V) - ,

i.iJ PHI

PlOCBU SUUM j I I

f''V.I fi

,. -1I

5r .

i

.

i {

t

ri t

!_

Cvitl 'Sack

CIS-

ir i

-CH

STREWS

si y uRYaM TlSitd mt*» SCS?fl BWug BflWch

1« j-

FIGURE 2.58

9 -B- «M

Check whether the information displayed in the window, shown in Figure 2.58,are

ok or not. Hitting Finish knob. Figure 2.59 is obtained by plotting 'reactor molarcomposition

'

(mole fraction) as ordinate against 'reactor length' (in) as abscissa.

t- <\<- Dtfa Tooa Put trv. Wnsmr H(*>

Dl lHl am toivj ipi al-nal-KI I"»! Its I M .l lal yj

Block PFfi Cemmin

si u=u| Xnxan. | Sou | u>Mod> |

STROIMS RS'jc HTot) Qg RGtfc, ftCSIR ftFy

'

111 *.

" ' 8M,

FIGURE 2.59

Note that the plot window can be edited by right clicking on that window andselecting Properties. In the properties window,

the user can modify the title, axis scale,font and colour of the plot. Alternatively, double-click on the different elements of theplot and modify them as we like to improve the presentation and clarity.

ASPEN PLUS SIMULATION OK KKACTOR MOOEI 93

2.5 ASPEN PLUS SIMULATION OF A RPlug MODEL USING LHHWKINETICS

Problem statement

In acetic anhydride manufacturing, the cracking of acetone produces ketene and methaneaccording to the following irreversible vapour-phase reaction:

CH3COCH3 -> CH2CO + CH4acetone ketene methane

This reaction is first-order with respect to acetone. Pure acetone feed with a flowrate of 130 kmol/hr enters a PFR at 7250C and 1.5 atm. The kinetic data for the AspenPlus simulation are given below.

k = 1.1 s"1

E = 28.5 x 107 J/kmol

n=0

T0 = 980 K

The unit of pre-exponential factor clearly indicates the |C,1 basis. To use the Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetic model, set zero for all coefficients under Term 1and that for all coefficients except A under Term 2. Take a very large negative value forcoefficient A. The sample adiabatic PFR is 3 m in length and 0.6 m in diameter. Applyingthe SYSOP0 base method, compute the component mole fraction in the product stream.

Simulation approach

As we select Aspen Plus User Interface, first the Aspen Plus Startup window appears,as shown in Figure 2.60. Choose Template option and press OK.

2I=fflHJ-J-Lag Pl-W i-H=J Tl I I I 'IW *l

1

1 -I

I

**mmm*mH MM

FIGURE 2.60


In the next, select General with Metric Units and again hit OK button (see Figure 2.61).

pea

M

An IPE a-wm ftcpwl*

'<*-SxarPenmen Mair>

1

" 11 ' 'C*'

FIGURE 2.61

As the Connect to Engine dialog pops up,click OK.

Creating flowsheet

From the Model Library toolbar, we have selected RPlug reactor and developed theprocess flow diagram as displayed in Figure 2.62.

He & 3an Tocfc fir FW mI Jy»r, WnSe* Htfc

Qi lHI aiai |a| yj nl-i-iaKKi i w.| 3_

i_ii<j

_

j 3 _j_

|rlttF-I l- l PT I Mi I igl

H8- S . 8 - S QU Us,flt <SL zzz rsr izf

M awif- ~ -

FIGURE 2.62

ASPEN PLUS"1 SIMULATION OK REACTOR MODELS 95


In the list on the left, choose Setup /Specifications. For the present problem, we wish togive the Title as 'Simulation of the PFR'. and accounting information as 'AKJANA/8/ANYTHING/AS WE LIKE'. In addition, choose 'Mole' and 'Mass' fraction basis for the

streams under Report Options [see Figures 2.63(a), (b) and (c)l.

r

' i LU.

-Ml o . § 6 onum»t «>>.

FIGURE 2.63(a)

I'HIM ' - XM -i..

FIGURE 2.63(b)

Gopyngt-


ttn fci VV* CMi teds FLn Pw lirat, VAmtow

o|a!|ai I I tfeiel t?! phlftltl l'-l n) _L_L!iJ iJ 21 j2Ji r- i-i pt | -|m i - imi

3ip

Cor i j now***- I etod. /StaM»| p'««"y i I

ti-n» to hi NAKtad W

FkMbM hi--- 'i

P Hde PM*T Mm. P

TFf, IGEN.

M 3

P Cwowit nih IWO ib- «I'KUjn

SI REAMS PStoc frririi REqal ft6tU RCSIR RFV) BSatcfefHeb pcufl

~

CV flFoldenXAaDerPlB 1- 1 NUH : -r irt- rt.- r tr.-arpt-i

FIGURE 2.63(c)


Select Specifications under Components folder in the Data Browser window.As we

out the Component ID column, Aspen Plus provides the rest of the information incomponent input form, shown in Figure 2.64.

fle EJI Wen On tim» ft* Put Utray Vfrifcw to«

1 f~

-i i-i- r» jiAm \ m

3 S-L*

O SfamOM*

$ a«pm)<i

3 M"

£ i J nJ -3 »l Qj -.1 «*!

|1

i Bk«k>

Tim

tCEIO-JE SottTSe )3<roiitENE KEIENE bHJO

seths -pn»

stficwi wiac ff . Pfcu ns'

tu ncsTp

- 8 . 1 -y-lE-U

FIGURE 2.64

Specifying property methodHit Afort button and in property method (see Figure 2.65), scroll down to get SYSOPO

ASPEN PLUS SIMULATION OF REACTOR MODEI.S 97

l_

r_Ll_L_F -iCI I ! !

JtUI

9 "w-cwr.

j» -

I 3

.la

mr'iiir

.(0- 0 I : I jn U-t»* ia ).

FIGURE 2.65


In the left pane of the Data Browser window, select Streams IF. Inputting the valuesfor temperature, pressure, total flow and mole fraction, we have the picture as displayedin Figure 2.66.

I.UH- ;

figs?

g M

f|7 -. »

1 i iT

I, ,

I'.

-

I--...

I'- - 3

I'* 3

3 i--- 3

r--

I- 0 . i . 8 OMU»»«« gjfc «ani ggi

FIGURE 2.66


ASPEN PLUS SIMULATION OF REACTOR MODEI.S 97

l_

r_Ll_L_F -iCI I ! !

JtUI

9 "w-cwr.

j» -

I 3

.la

mr'iiir

.(0- 0 I : I jn U-t»* ia ).

FIGURE 2.65


In the left pane of the Data Browser window, select Streams IF. Inputting the valuesfor temperature, pressure, total flow and mole fraction, we have the picture as displayedin Figure 2.66.

I.UH- ;

figs?

g M

f|7 -. »

1 i iT

I, ,

I'.

-

I--...

I'- - 3

I'* 3

3 i--- 3

r--

I- 0 . i . 8 OMU»»«« gjfc «ani ggi

FIGURE 2.66




In the subsequent step (see Figure 2.67), select PFR under Blocks folder. Specify the

reactor as an adiabatic one.

i ffc Ed» We* Oto Ta* Rn Rot lisrary VAnJo* He*

OUIHI I I itelal i?l rsK NKiH »'| 3_

UjiJ _J -il SI313

- i KSS 3

_J AM H

.

_J y c

- 9MM- Jfl F

O BUM*:3;-* Ctro'

|~

| = 41111)Mta

O EOrw -J

J

aft I 3 »hJiii(s £i»iulwCcr/gi/Wcr. |wRtK(nni| Pitt*** j

STREAMS RVaM BEqut RGhta. .

BCSTfl SPlup HBateft

. 8 i US IJC ' g Foktect- apen FVi il l : HUM fW Ki rtsi muc s

r;;a«cfefZ-M!S j - jj.tii'ftoM } }LladuTtffi5- j .'debt AgttK Pr. |{ Plus - S

.

« 110760*

FIGURE 2.67

In the Configuration sheet, reactor length as well as diameter are given (see Figure 2.68).

Rfe E« 'rim 'tieo An PW

QNB|_u ie|jg] n|-<-|fcN M Hi a »l |n| .la l i|

36 ta SM

StMrtl. J6 f

rj f& ftdta

8

PnAn

f EOVw-b*.

a EOmpJ -

0D

-D-* iisi (

I 3

"

3i

"

3

SWMlttf I HtHEttl

StflE*MS RSlac frtM M*Ai -1 -o-n-o-

RBto PCSTR

FIGURE 2.68

In the next, we define a reaction set for the present simulation.

The default nameR-l is ok. Then select LHHW kinetics and obtain the screen

,exhibited in Figure 2.69.

ASPEN PUJSTM SIMULATION OF REACTOR MODELS 99

1 W-l-K-l..

- a .

(@- 0 g g u a u1 . - W W -G- Hi-' WS.

FIGURE 2.69


Press Nex/ knob and then click on New. Under Reactants, select 'ACETONE' from the

Component dropdown menu and set the coefficient to -1. Similarly under Products,select 'KETENE' and 'METHANE', and set both coefficients to 1 (see Figure 2.70).

i r.:i..i-u rr . mi-*ifc|

d*.

«- 1Ml' -

d

t 2 roK-. i.

I*-Q-

-<@ S 8 § Q»0in«Mt *a>. 'mh gi»

FIGURE 2.70

100 PROCESS SIMULATION ANnjWQlOLUSING ASPEN'

Hitting on Next and clicking Kinetic button, we get Aeldn ics input form. A littledescription is given below to understand the use of LHHW kmetxc model m Aspensimulator.

The LHHW rate expression is represented by:

r =

(kinetic factor) (driving force)(adsorption expression)

The kinetic factor (reaction rate constant) has the following form:

nE'

\ 1 >K = k exp

R kT To)

(2.1)

(2.8)

If Tq is ignored, Eq. (2.3) replaces the above expression. Note that all the notations

used in Eq. (2.8) have been defined earlier.

The driving force is expressed by:

f N An c?

and the adsorption is modelled as:

M

Li=i

N

nc"J

where,

In (Ki) =Ai + Bi/T + Ci IniT) + D.T (2.9)

Here, m is the adsorption expression exponent, M the number of terms in the adsorptionexpression, N the number of components, a the concentration exponent, K2, K, theequilibrium constants [Eq. (2.9)], A,, fit, Q, the coefficients and I Notice that theconcentration term C used in the above discussion is dependent on the [CJ basis. Sayfor example, when [CJ basis is selected as molarity, the concentration term representsthe component molar concentration (kmol/m3); similarly when [CJ basis is partialpressure, the concentration term represents the component partial pressure (N/m2).

Providing required data, we have the filled kinetic sheet

, shown in Figure 2.71.Click on Driving Force to obtain a blank form as shown in Figure 2.72.Select 'Term 1' and then 'Molarity' as [CJ basis. Under Concentration exponents for

reactants, set acetone exponent to 1. Similarly for products,

set ketene and methaneexponents to 0. Also enter zero for all four driving force constants as mentioned in theproblem statement (see Figure 2.73).

In the subsequent step (see Figure 2.74), select Term 2' from the pulldown Enterterm menu. Since the given reaction is first-order with respect to acetone and there isno second term, enter zero for all exponents and coefficients

. Owing to the methodAspen Plus uses to specify a reaction, we should insert a very large negative value forcoetticient A (say,

-106) to make Term 2 essentially zero [see Eq (2 9)1 Finally,click

on Next icon.

n- .


ft* 0m Om Ta«i .av* VMw

-L-T I I 'i r-i -I -lei I !«!

3

-~ .

j. ii wj9

O 'm<iaii '

-i

* Zj

:lUlllll fcuM.

j

J. Zj

a *-. j f.

-i.

D -.

- Ml

, 3

i am i(t/T«f

fF II | IWBMM | MlMnpn | Man W I | .W.w.Oa n | Mwwl-i | MB | IMMM |

ItWMn Tom. ggjl gjj MM. WWI

FIGURE 2.71

1IWJ'

<5 l-B

I Mk | - --

WB. B'Mt 'CM Wto. "lac*-

FIGURE 2.72


ft* 0m Om Ta«i .av* VMw

-L-T I I 'i r-i -I -lei I !«!

3

-~ .

j. ii wj9

O 'm<iaii '

-i

* Zj

:lUlllll fcuM.

j

J. Zj

a *-. j f.

-i.

D -.

- Ml

, 3

i am i(t/T«f

fF II | IWBMM | MlMnpn | Man W I | .W.w.Oa n | Mwwl-i | MB | IMMM |

ItWMn Tom. ggjl gjj MM. WWI

FIGURE 2.71

1IWJ'

<5 l-B

I Mk | - --

WB. B'Mt 'CM Wto. "lac*-

FIGURE 2.72


j 1

_j '.D- o-xr'

-I

-[-EETEEXSC

. 1

Idlbsw I

. p feis ep

BEoJ AG**!

FIGURE 2.73

Hi. a

_j

0)

lJu

_) Data

a.

SbMMF

. p

PFS

lj Omttry

_

G_j

u l» j

Rwcaigthsai jVapm

ErteHtrm [l«rm23

t(*clartr

Expowii

.

Q

.r' co(W,c*»1t A tewrddning low* J«m Ln(ccr.;fanl 21 - i f/fT"

- Ml . u T SeeHflte .

.Ci ytw tyw »fival«n enerw 'a t« J n poww law wpittWin

Mom

STRCAHS BE(M RSfcfa RCSTR

llQi<to; wcwrtw l j ig ito w J

FIGURE 2.74

FUin HUM


The Stoins bar displays a message of Required Input Complete in the bottom rightcomer of the window shown in Figure 2.74. Subsequently,

run the simulation and obtainthe status report as displayed in Figure 2 75

ASPEN PLUS SIMUUVTION OF REACTOR MODELS 103

_j_r-i-'i-i' nr -i \ m -sw

-

i --»- tii

-

'»**"' I II I -*« -- I . *"l »->

£r <@ 6 S 0 O H UIIIMH HlK «* Mm ".iril A* Mar

FIGURE 2.75

Viewing results

Pressing Solver Settings knob and selecting i?esw/ s Summary /Streams, we obtain thefinal results as reported in Figure 2.76.

i i-liisialiil:

"1 1 I -i

r[.- , ....

1 3el

i

fami_____ -ST

iffran1

ur

rzw

iBTTiW

'I'M

Tivi' i

M- Q . S . § U S UWii TM- l»-

FIGURE 2.76

Copynghied material

104 PROCESS SIMULATION AND CONTROL USING ASPF.N

SUMMARY AND CONCLUSIONS |

This chapter presents the simulation of several reactor models. Here, we have considereda variety of chemical reactions in the Aspen Plus simulator. Probably the most usefulkinetic models. Power law and Langmuir-Hinshelwood-Hougen-Watson (LHHW). havebeen used in the solved examples. A number of problems are given in the exercise forextensive practice.

PROBLEMS |2.1 Ethyl acetate is produced in an esterification reaction between acetic acid and

ethyl alcohol.

acetic acid + ethyl alcohol <-> ethyl acetate + water

The feed mixture, consisting of 52.5 mole% acetic acid, 45 mole% ethyl alcoholand 2.5 mole% water, enters the RCSTR model with a flow rate of 400 kmol/hr at

750C and 1.1 atm. The reactor operates at 70oC and 1 atm. Both the reactionsare first-order with respect to each of the reactants (i.e., overall second-order). Forthese liquid-phase reactions, the kinetic data for the Arrhenius law are given below:

Forward reaction: k = 2.0 x 108 m3/kmol - s

E= 6.0 x 107 J/kmol

Reverse reaction: k = 5.0 x 107 m3/kmol . s

E= 6.0 x 107 J/kmol

[C,l basis = Molarity

Perform the Aspen Plus simulation using the NRTL thermodynamic model andreactor volume of 0.15 m3

.

2.2 Repeat the above problem replacing RCSTR model by RStoic model with 80%conversion of ethyl alcohol.

2.3 Simulate the reactor (Problem 2.1) for the case of an RGibbs model.2.4 An input stream, consisting of 90 raole% di-tert-huty\ peroxide, 5 mole% ethane

and 5 mole% acetone, is introduced in a CSTR at 10 atm and 1250C and a flow

rate of 0.2 kmol/hr. The following elementary irreversible vapour-phase reactionis performed isothermally with no pressure drop.

(CH3)3COOC(CH3)3 C2H6 + 2CH3COCH3

Fake kinetic data for the Arrhenius formula are given as:

k = 1.67 x 104 kmol/m3 s (N/m2)

£ = 85 x 103 kJ/kmol

LCJ basis = Partial pressure

The reactor operates at 50oC and its volume is 6 m3. Using the SYSOP0thermodynamic method, simulate the CSTR model and compute the componentmole fractions in the product stream.

ASPEN PLUS SIMULATION OK REACTOR MODELS 105

2.5 A feed stream, consisting of di-tert-buty\ peroxide, ethane and acetone, enters aRYield model at 10 atm and 1250C. The reactor operates at 10 atm and 50oC.Use the SYSOP0 property method and assume the following component-wiseflow rates in the feed and product streams (see Table 2.3).

TABLE 2.3

Component Feed flow rate (kg/hr) Product flow rate (kg/hr)

di-tert-hntyl peroxide 26.321 1.949

ethane 0.301 5

.314

acetone 0.581 19.94

Simulate the RYield reactor and compare the results (mole fractions in theproduct) with those obtained for Problem 2.4.

2.6 As stated in Problem 2.1, the reaction between acetic acid and ethanol givesethyl acetate and water.

CH3COOH + C2H5OH (-> CH3COOC2H5 + H20

The inlet stream, consisting of 50 mole% acetic acid, 45 mole% ethanol and5 mole% water, is fed to a REquil model with a flow rate of 400 kmol/hr at 750Cand 1.1 atm. The reactor operates at 80oC and 1 atm. Using the NRTL propertymethod, simulate the reactor model and report the compositions of the productstreams.

2.7 Ethylene is produced by cracking of ethane in a plug flow reactor. The irreversibleelementary vapour-phase reaction is given as:

C2H6 - C2H4 + Hgethane ethylene hydrogen

Pure ethane feed is introduced with a flow rate of 750 kmol/hr at 800CC and

5.5 atm. The reactor is operated isothermally at inlet temperature. The kinetic

data for the LHHW model are given below (Fogler, 2005).

k = 0.072 s"1

£ = 82 x 103 cal/mol

Tq = 1000 K

|C,] basis = Molarity

The reactor length is 3 m and diameter is 0.8 m. Using the SYSOP0thermodynamic model, simulate the reactor.

2.8 Repeat the above problem replacing the PFR by a stoichiometric reactor with80% conversion of ethane. If require, make the necessary assumptions.

2.9 In acetic anhydride manufacturing, the cracking of acetone occurs and producesketene and methane according to the following irreversible vapour-phase reaction:

CH3COCH3 i CHoCO + CH3


In the CSTR model, ketene is decomposed producing carbon monoxide andethylene gas.

K'

CH2CO-> CO + 0.5 C2H4where,

-rk = K'

K= exp

,1.5

22.8-

K' = exp 19.62-

26586

T

25589

mol/lit s . atm15

mol/lit . s

[C,] basis = Partial pressure

Here, -rA is the rate of disappearance of acetone (A), -rk the rate of disappearanceof ketene ik), PA the partial pressure of A, and K and K' the reaction rateconstants. Pure acetone feed with a flow rate of 130 kmol/hr enters the reactorat 7250C and 1.5 atm. The reactor with a volume of 1

.4 m3 operates at 700oCand 1.5 atm. Applying the SYSOPO base method, compute the component molefractions in the product stream.

REFERENCE |Fogler, H. Scott (2005), Elements of Chemical Reaction Engineering, Prentice-Hall of India

3rd ed.. New Delhi.

CHAPTER

Aspen Plus Simulation ofDistillation Models

3.1 BUILT-IN DISTILLATION MODELS

An Aspen simulation package has nine built-in unit operation models for the separatingcolumn. In the Aspen terminology, these packages are named as DSTWU, Distl, RadFrac.Extract. MultiFrac, SCFrac, PetroFrac, RateFrac and BatchFrac. Under these categories,several model configurations are available. Note that Extract model is used for liquid-liquid extraction. Among the built-in column models, DSTWU, Distl and SCFracrepresent the shortcut distillation and the rest of the distillation models perform rigorouscalculations.

DSTWU model uses Winn-Underwood-Gilliland method for a single-feed two-productfractionating column having either a partial or total condenser. It estimates minimumnumber of stages using Winn method and minimum reflux ratio using Underwoodmethod. Moreover, it determines the actual reflux ratio for the specified number ofstages or the actual number of stages for the specified reflux ratio, depending on whichis entered using Gilliland correlation. It also calculates the optimal feed tray and reboileras well as condenser duty. Remember that this model assumes constant molar overflowand relative volatilities.

Distl model includes a single feed and two products, and assumes constant molaroverflow and relative volatilities. It uses Edmister approach to calculate productcomposition. We need to specify a number of stages, e.g. feed location, reflux ratio,pressure profile and distillate to feed iD/F) ratio. Actually, when all the data areprovided, we can use this column model to verify the product results.

RadFrac is a rigorous fractionating column model that can handle any number offeeds as well as side draws. It has a wide variety of appUcations, such as absorption,stripping, ordinary distillation, extractive and azeotropic distillation, reactive distillation, etc.

MultiFrac is usually employed for any number of fractionating columns and anynumber of connections between the columns or within the columns. It has the ability tosimulate the distillation columns integrated with flash towers, feed furnaces, side

107


108 PROCESS SIMUKATION AND CONTROL USING ASPEN

strippers, pumparrounds, etc. This rigorous column model can be used as an alternative

of PetroFrac, especially when the configuration is beyond the capabilities of PetroFrac.

As mentioned earlier, SCFrac is a shortcut column model. It simulates a distillationunit connected with a single feed, multiple products and one optional stripping steam

.

It is used to model refinery columns, such as atmospheric distillation unit (ADU) andvacuum distillation unit (VDU).

PetroFrac is commonly employed to fractionate a petroleum feed. This rigorous modelsimulates the refinery columns, such as ADU, VDU, fluidized-bed catalytic cracking (FCC)fractionator, etc., equipped with a feed furnace, side strippers, pumparounds and so on.

RateFrac is a rate-based nonequilibrium column model employed to simulate alltypes of vapour-liquid separation operations, such as absorption, desorption anddistillation. It simulates single and interlinked columns with tray type as well as packedtype arrangement.

BatchFrac is a rigorous model used for simulating the batch distillation columns. Italso includes the reactions occurred in any stage of the separator. BatchFrac modeldoes not consider column hydraulics, and there is negligible vapour holdup and constantliquid holdup.

It is worthy to mention that for detailed information regarding any built-in AspenPlus model, select that model icon in the Model Library toolbar and press Fl.

In this chapter, we will simulate different distillation models, including a petroleumrefining column, using the Aspen Plus software. Moreover, an absorption column willbe analyzed. In addition to the steady state simulation, the process optimization willalso be covered in the present study.

3.2 ASPEN PLUS SIMULATION OF THE BINARY DISTILLATION

COLUMNS

3.2.1 Simulation of a DSTWU Model

Problem statement

A feed stream, consisting of 60 mole% ethane and 40 mole% ethylene,enters a DSTWU

column having a flow rate of 200 Ibmol/hr at 750F and 15 psia. This feed is required tofractionate in a distillation column capable of recovering at least 99

.6% of the light keycomponent in the distillate and 99.9% of the heavy key component in the bottoms. Thesample process operates at 300 psia with zero tray-to-tray pressure drop. The pressurein the reboiler as well as condenser is also 300 psia.

In the simulation, use total30 theoretical stages (including condenser and reboiler) and a total condenser

. Applyingthe RK-Soave property method, simulate the column and calculate the minimum refluxratio, actual reflux ratio

, minimum number of stages,actual number of stages, and

feed location.

Simulation approach

From the desktop, select Start button, and then click on Programs, AspenTech, Aspen

Engineering Suite, Aspen Plus Version and Aspen Plus User Interface. Then chooseTemplate option in the Aspen Plus Startup dialog and hit OK (see Figure 3.

1).

ASPEN PLUS SIMULATION OF DISTILLATION MODKUS 109

Q\a\m -I -I |r| <ri q-r-mi .l-Kl!d 2) I I l gj J -

I ' l-l-l I- 1 1 -I I ! 1-1

.

i

FIGURE 3.1

Select General with English Units as the next window appears (see Figure 3.2).

.4./MM

- Hi . -

...

mm ...

;

__l

FIGURE 3.2

C aterial


Again press OK to see the Connect to Engine dialog (see Figure 3.3). Here we chooseT,ocal PC by scrolling down. Hit OK knob and move on to develop the process flow diagram

.

Connect to Engine

Server type:

User Info

Node name:

User name:

Password:

Working directory:

a

Save as Default Connection

( OK 1 Exit Help

FIGURE 3.3

Creating flowsheet

As we select Columns tab in the bottom Model Library toolbar (Figure 3.4), Aspen Plusshows all built-in column models.

«a 6t Mr- 0*s locii Rfi Rewhart Ltrary Wxto- H«fc>

Model Library toolbarStftEAMS 1 DiTVU Ci-J R»fEjJikI M tfug Sffru PWtrf.te Rurf- Bwctfi -

FIGURE 3.4

ASPEN PLUS SIMULATION OK DISTILLATION MODELS 111

In the next, select DSTWU icon to represent the short-cut distillation process.Once we have selected the icon, place the icon on the flowsheet by clicking with the

cross-hair somewhere on the flowsheet background. When finished, click on K | symbolor right-click on the flowsheet background. By default, the column is named as Bl(see Figure 3.5).

i\n 'amiami I

Hi tM Dn <oaa 'hr nrann lw -«

Dfagyai aial id g] aififci K!--! "i i |m| ! v\ *\r|rrFf,.|..|..h HT 'MPl I Bl -fW

UJ_

-iT

-CH

"SAW. ' DIIMI Out "*l<m 1M MtfMi IW l*. ..

i c-.i C- a'aMAcwi a IM AM ru- MMC*

FIGURE 3.5

In the screen, shown in Figure 3.5. only the block is displayed; there are no incomingand outgoing streams connected with the block. Therefore, the Status message in thebottom right of the window includes Flowsheet Not Complete. Interestingly, afterconnecting all required streams with the unit, this message sometime may also beretained. This happens because of improper flowsheet connectivity.

To add a single feed stream and two product outlets (distillate and bottom), click onMaterial STREAMS tab in the lower left-hand corner. As we move the cursor

(a crosshair) onto the process flowsheet, suddenly three red arrows and one blue arrowappear around the block. These arrows indicate places to attach streams to the block.As we know, red arrows are required ports and blue arrows are optional ports. Clickonce on the connection point between the feed stream and the DSTWU block, enlargethe feed line and finally click again. By default, this stream is labelled as 1. In thesimilar fashion, we can add the two product streams, namely 2 and 3, to the distillationunit (see Figure 3.6).

Copyrighted malarial


He EA V«* data Tooti Rr. FtowtfiM Ut-av Wtxfaw H«to

rlRFi-|...httt lT 1 irol I - lal 1

0-

&

~

3

Ul .filf Mewt/SpUeu 1 Stpaatai | HwlEMhangwt Criumn* j ReKloit | PrwawOiangsi | MsripuWwi | SoW« | UMtMwWt j

STREAMS ' DSTWU Dntl Rrfisc EntisO Mutftw; SCFiac PeOoFi Ratrf.ac BWchFiac

J

Book rflOflCfcrJ-

FIGURE 3.6

After renaming Stream 1 to F, Stream 2 to D, Stream 3 to B and Block Bl toDSTWU, the flowsheet finally looks like Figure 3.7.

fte EiJI «ew OKa Tocti f**i fte«h«i Uxsy Wndm. H-t

MiBl alal lei 1 ni-rlftl Nkl H li! -

-0 O

E-

STREAMS ' DSVM Rrf(»e E**d MtAffc SCfttc PMcfiae RjuF.ic Eatctfr.. , - ~r IR Wfc. .nR*!!! MUM TW*o

'

.V n fco- I Qw i W l- O il W l UN T * || A -a .

FIGURE 3.7

ASPEN PLUS SIMULATION OF DISTILLATION MODELS 113

Now the Status bar in the window, shown in Figure 3.7, says Required InputIncomplete indicating that the flowsheet is complete and the input specifications arerequired to provide using available input forms for running the Aspen simulator.


Recall that within the Aspen simulation software, the simplest way to find the nextstep is to use one of the following equivalent commands:

(a) press the Next button

(b) find 'Next' in the Tools menu

(c) use shortcut key F4

and obtain Figure 3.8.

mF-M-i-i nr 'i -ici \-\m

c-Q-

-0-

D«pr, rce rout to**'

3 I

HmnnUBmt | VwMdi | HMUOwpn fil | Rmckb | Pm*j*0««Bi | Mar«i«Mn | iota | UwMolM

STRUMS ' DSrwU Pit Wi we 1*1 tOit WtwT Warfwe jtjjjg

| *,0-H-» Wot I tJO t ttoM I <]OmH»1 Mnw |aj<i»Otto»»« || AvxfV S ~ Ql'f. t*9t

FIGURE 3.8

Hitting OK on the above message, we obtain the setup input form. Alternatively,select Solver Settings knob and choose Setup /Specifications in the list on the left(see Figure 3.9).

Although optional, it is a good practice to fill out the above form with a title and toprovide the accounting information subsequently. The present project is titled as'Simulation of a Shortcut Distillation Column' (see Figure 3.10).


Sid

oltflBl A t Nel tfl rahclfc l lwl n J 21 JiJilJ zJ 2l J ©1

_

L_

r i-i rv 'I -ipi i w

I "'M'.

SintMC ' WIMAJ Cxi Brf.K MiJtfue 5Ct'«c Pk. i ftttrfii Brf.»f«:

FIGURE 3.9

i (Mi

3Mbl JMlJiilF Bid LJ

_J W«w

= 3 EOCsn.C«n

"

I-

3

'*,7 '*"' I ""I 1 -TO- I Mrow<w I Sold: t UtvUaMt (

FIGURE 3.10

In the next (see Figure 3.11) the Aspen Plus accounting information (requiredsome installations) are given in the following way.

User name: AKJANA

Account number: 9

Project ID: ANY ID

Project name: YOU CHOOSE

ASPEN PLUS'" SIMUI-ATION OF DISTILLATION MODELS 115

.l\ I r",

9 -

'

3f

a) - .a mi

5!

1 nlVI M (M* <M»_ fMa WlB Ir- .

) MB I - - - I

FIGURE 3.11

We may wish to have stream results summarized with mole fractions and/or someother basis that is not set by default. For this, we can use Report Options under Setupfolder. In the subsequent step, open Stream sheet and then choose 'Mole' fraction basis.In this regard, a sample copy is shown in Figure 3.12. although this is not essential forthe present problem.

i-d 3-J-itiiJa.ii

0 -»

1 .«*>*>

P <* ' i PBS .* luiTi 3

FIGURE 3.12

116 PROCESS SIMULATION AND CONTRQLUSING ASPEN

Specifying componentsUse the Data Browser menu tree to navigate to the Components/Specifications/Selection sheet (see Figure 3.13).

..

«t W DM T«ii ft*. PW tto¥ i HHP.

- . :

1 J

. 5 Drill-id!

Uyr-End Pmpoti

rHudocariiMW

ti aeehi

O ,

Caww*iD ComiKifun" WTO FamO)

iO II SiiKi ait to tr rMneved Itom dsiatw* J. erte< C<m(rt<*fK Haw « fom-ia SteHdp

[if Mtw SpUen | S«p»*« | HealEttJiWBen Cohmnt } flwcto« 1 P-essueO owt | MwpuWWi | Sate | UraM«W. j

STREAMS 1 OSTWJ Drti ErtaO Mutfrac'

-U * PatftFi ? Rahjiac BalchFrae

Sr«*,B«.ft-

r:siHa-Ai>i,ivini1

FIGURE 3.13

In the window, shown in Figure 3.13, the table has four columns; they are underthe headings oi Component ID, Type, Component name and Formula. Among them, theType is a specification of how an Aspen software calculates the thermodynamicproperties. For fluid processing of organic chemicals, it is generally suitable to useConventional optiom Remember that component ID column should be filled out by theuser. A Component ID is essentially an alias for a component.

It is sufficient to use thechemical formulas or names of the components as their IDs

.

On the basis of thesecomponent IDs, Aspen Plus may spontaneously fill up the Type,

Component name and

mateh inf T haPPen' * that AsPen Plu« to find an eXaCt

lt}lhrATyin °*er words' A«Pen Plus does not recognize the components byT86 fj!? 0 0 Search the components.

Select the components fromSubsectiri 3 detaiIs' See the solution aPProach in

(see lfir fo T6 0fi

COmPonent hane and ethylene, as thefr IDs

(see Figure 3.14). The other three columns have been automatically filled out.


tZSlTjiT j11'1!!?68 I?0118 meth0ds *** mod to compute the phyPron l 2 .

0ht th? Pr0Perty input f0rm' er hit Next icon or choose

Propernes/Specifications in the left pane of the Data Browser window.

Set RK-Soave

property method by scrolling down (see Figure 3.15).

ASPEN PLUS SIMULATION OK DISTILLATION MODELS 117

..i-j ;

3 .

FIGURE 3.14

Plata l I wi Qb3Mslllid5d 3I r-l I..|-f7 .: .id ! '« -It

» BS aJ9 -

zsjti D»ld -3l alig|g|

i ! r-

3S3

FIGURE 3.15


The Streams /F/Input / Specifications sheet appears with the Data Browser menu treein the left pane (see Figure 3.16). Here, we have to provide the values for all statevariables (temperature, pressure and total flow) and composition (component molefractions).


118 PROCESS SIMULATION ANnCO TROLJ-JSING ASPEN'

Ffe til '. Tut. Teal, r-m FW limy Wr*« H*

i r - I .i-l rv . j J-Igl M.mm m

111'

. J PltKTMM

- a) enjr,h«»caa

RK£6'J1

nrtxu i

ri UNKK Owe-

rj um(KO j>(m i

if1

5TR£JWS 1 DSTWU

21

r f: |pmtu«;l

-

THWIE-

1 - < - MJflK SCFlK PWoF E.- --" B-r*f,»-

FIGURE 3.16

Filling out the form, shown in Figure 3.16, with the data given in the problemstatement, one obtains the data, shown in Figure 3.17.

. He Ed! Vc« tata Took fe> FM Ltrary M*km -i*

. J/) sT»*r. M«hoC

- g , - . -

RXSBU-1

RKTKUI

Q E*anM*To-is

1J «.

.

_j «.w

3Mi] EOOpbora |

ll_

-o~*

h|Pini«o 2[is

Conmotnon

| Mole f-*: 3r

-

Corrconan

IS

04

lew [T

SIB6W6 : bStWU iJ- «.

! »2l

FIGURE 3.17


iw t Sfn ft under Blocks folder. As a result.a DianK block input form is displayed (see Figure 3.18).


FIGURE 3.18

Under Column specifications option, here we enter the number of stages that is 30.It is fairly true that we can alternatively specify the reflux ratio when the number ofstages is asked to compute. Note that ethylene is the light key and naturally ethane isthe heavy key. As mentioned in the problem statement, recovery of the light keycomponent in the distillate (= moles of light key in the distillate/moles of light key inthe feed) is 0.996 and recovery of the heavy key component in the distillate (= moles ofheavy key in the distillate/moles of heavy key in the feed) is 0.001. In addition, thepressure of the total condenser and reboiler is given as 300 psia. Entering all theseinformation, one obtains the result, shown in Figure 3.19.

i f-

-l-l ft',,

-1 I

-- |

-o-

FIGURE 3.19

CopynghlGd material


FIGURE 3.18

Under Column specifications option, here we enter the number of stages that is 30.It is fairly true that we can alternatively specify the reflux ratio when the number ofstages is asked to compute. Note that ethylene is the light key and naturally ethane isthe heavy key. As mentioned in the problem statement, recovery of the light keycomponent in the distillate (= moles of light key in the distillate/moles of light key inthe feed) is 0.996 and recovery of the heavy key component in the distillate (= moles ofheavy key in the distillate/moles of heavy key in the feed) is 0.001. In addition, thepressure of the total condenser and reboiler is given as 300 psia. Entering all theseinformation, one obtains the result, shown in Figure 3.19.

i f-

-l-l ft',,

-1 I

-- |

-o-

FIGURE 3.19

CopynghlGd material

120 PROCESS SIMULATION AND CONTROL USING ASPKN'


The Status message includes Required Input Complete indicating that we are in a position

to run the simulation. Simply press Next button and receive a message regarding the

present status (see Figure 3.20).

fiT TTJ

Jj UkifIC Gkc

. s*.

Smm

_

E0V»Mblw

- 33 Dsmnia -Q Be-* C-pua-i

Mb

H

[30 jgi i Cm*fioWI ]300

KiHictoipooert

Com [ETMYLEHE

flBMy: [0 0C1itjucioMtiTCienpu Totftw- x*npu «fccC*wM tt*n

STRWMS

FIGURE 3.20

Click OK on the above message and obtain the Control Panel window that shows

the progress of the simulation (see Figure 3.21).

F»» Efe «« £to T«* An iMy -AWto* -H*

]aj®iJ-i£ll w| KHIMKI h>\ 0 >Nh| *i lacal

-EH

*bs atrsitrro rkx sot iabli taw

HUM

fit -. I

FIGURE 3.21

ASPEN PLUS SIMU1.ATI0N OF DISTILLATION MgggUj 121

Hitting Next followed by OK, we have the Run Status screen (see Figure 3.22).

_i_r -i rr .i.ipi i ibi

-

.

f

HMtfmutt WIWW (M fMF(« iMMO *fik SOik fi*rfi«

FIGURE 3.22

HH-'Ifci '*. .

Viewing results

In the next, select Blocks/DSTWU/Results from the Data Browser. In the following(Figure 3.23), we get the answers as:

Minimum reflux ratio = 7.724

Actual reflux ratio = 8.751

Minimum number of stages = 33.943Actual number of stages = 67.887Feed location = 40.417

Save the work by choosing File ISave As /... in the menu list on the top. We can name thefile whatever we like. Remember that a backup file (*.bkp) takes much less space thana normal Aspen Plus documents file (*.apw).


Ifwe wish to have the input information, press Ctrl + Alt + I on the keyboard or selectInput Summary from the View pulldown menu (see Figure 3.24).

Copyrtghtod material


I r..|-M= IT -i .iai, I ibi

dim-

-i.'j-i

i a SH

r-

1S?497652

-

»3*J12.;3 Br.il.

ifM IM|NMM f

0399

HE IP

STREAMS DSmj OaK Hrf.K F M HJtfiflC SCR PeMFmc Wtfwc BteW,*

' sti| s_ I Oa j-WWtW Awcn PIl» - Static Q G9«

FIGURE 3.23

i Edi Font'

\kB 'lalxt

irpuc SuwMry creic«d by Aspen Plus Bel. 11.1 at

Directory c:\Pr09ran f nes'.Aspenrechvworklng foIi10:15:40 Tho Jol 12, 2007

.working FoldersVupen plus 11.1 Fllenw c :\users\4kjana\AppMt«\Local\Te«p-~ap6336. trt

[TITLE 'SinulatiorL of 3 Shortcut Cist Illation column'

I-UNITS EPXC

Ikf-STREjWS COMVEW ALL

bescfiiPTiON -Central simulation with Eoallih units :F. psl, Ib/hr

, Ibool/hr, Btu/hr. coft/hr.

property Method: nort

Flow basis for Input: Mole

Strea* report composition: HoU flow

PSOP-SDUSCES PUHEll

C0KPOMEKTS

ETHANE C2H5 /ElKfLEKE C2H>

PROPERTIES Pk-SOAVE

PROP-OATA RirSKD-lIH-W.ITS ENCPROP-LIST BKSKI3BPVAL ETHANE ETHYLENE . OlOOMOfriJOBPVAL ETMYLENE ETHANE .0100000000

iTREW F

S085TRE»t fIXEO TEKP"' 5. PRES-1S. t«0LE-FLOW-200

.

M016-FRAC ETHANE 0.6 - ETWlENt 0,4

-»± |.<1A .1I.». |Hn««»|.« | Mj ynn | |

FIGURE 3.24

Creating report file

To create a detailed report on the complete work we have done,including input

summary, stream information, etc., select Export from the File pulldown menu. Then

save the work as a report file (e.g., C/Program Files/AspenTech/Working Folders/Aspen

Plus Version/ DSTWU.rep). In the next, open the saved report file (DSTWU.rep) goingthrough My Computer and finally using a program, such as the Microsoft Office Wordor WordPad or Notepad. For the present problem, the final report is shown below.


ASPEN PLUS IS A TRADEMARK OF

ASPEN TECHNOLOGY, INC.TEN CANAL PARK

CAMBRIDGE, MASSACHUSETTS 02141617/949-1000

HOTLINE:

U.S.A. 888/996-7001

EUROPE (32) 2/724-0100

PLATFORM: WIN32

VERSION: 11.1 Buiid 192

INSTALLATION: TEAM.

EAT

JULY 12. 2007

THURSDAY

12:07:22 P.M.

ASPEN PLUS PLAT: WIN32 VER: 11.1 07/12/2007 PAGE I

SIMULATION OF A SHORTCUT DISTILLATION COLUMN

ASPEN PLUS (R) IS A PROPRIETARY PRODUCT OF ASPEN TECHNOLOGY. INC.(ASPENTECH). AND MAYBE USED ONLYUNDERAGREEMENTWITH ASPENTECH

RESTRICTED RIGHTS LEGEND: USE, REPRODUCTION. OR DISCLOSURE BY THEU

.S

.GOVERNMENT IS SUBJECT TO RESTRICTIONS SET FORTH IN

(i) FAR 52.227-14. Alt. Ill, (ii) FAR 52.227-19. (iii) DEARS252.227-7013(cMl)(ii). or (iv) THE ACCOMPANYING LICENSE AGREEMENT,ASAPPLICABLE. FORPURPOSES OFTHE FAR,THIS SOFTWARE SHALL BE DEEMED

TO BE "UNPUBLISHED" AND LICENSED WITH DISCLOSURE PROHIBITIONS.CONTRACTOR/SUBCONTRACTOR; ASPEN TECHNOLOGY. INC. TEN CANAL PARK.CAMBRIDGE. MA 02141.

TABLE OF CONTENTS

RUN CONTROL SECTION


DESCRIPTION

FLOWSHEET SECTION

FLOWSHEET CONNECTIVITY BY STREAMSFLOWSHEET CONNECTIVITY BY BLOCKS..

COMPUTATIONAL SEQUENCEOVERALL FLOWSHEET BALANCE

2

22

22


COMPONENTS33

U-O-S BLOCK SECTION

BLOCK: DSTWU MODEL: DSTWU

i

4

STREAM SECTIONEOF

55

PRORT.RM STATUS RfTnTION

ninr,K STATUS

ASPEN PLUS PLAT-WIN32 VER- 11 1 07/19/9007 PAGF/1SIMULATION OF A SHORTniTT DISTTT.T.ATION COLUMN

RUN CONTROL SECTION



THIS COPY OF ASPEN PLUS LICENSED TO

TYPE OF RUN: NEW

INPUT FILE NAME:_00341ji.inm

OUTPUT PROBLEM DATA FILE NAME:_00341ji VERSION NO.

1

LOCATED IN:

PDF SIZE USED FOR INPUT TRANSLATION:

NUMBER OF FILE RECORDS (PSIZE) = 0NUMBER OF IN-CORE RECORDS = 256

PSIZE NEEDED FOR SIMULATION = 256

CALLING PROGRAM NAME: apmainLOCATED IN: C:\PROGRA~l\ASPENT~l\ASPENP-l

.l\Engine\xeq

SIMULATION REQUESTED FOR ENTIRE FLOWSHEET

DESCRIPTION

GENERAL SIMULATION WITH ENGLISH UNITS : F, PSI, LB/HR, LBMOL/HR,

BTU/HR, CUFT/HR. PROPERTY METHOD: NONE FLOW BASIS FOR INPUT: MOLE

STREAM REPORT COMPOSITION: MOLE FLOW



FLOWSHEET SECTION

FLOWSHEET CONNECTIVITY BY STREAMS

STREAM SOURCE DEST STREAM SOURCE BESTF DSTWU D DSTWU

B DSTWU

FLOWSHEET CONNECTIVITY BY BLOCKS

BLOCK INLETS OUTLETSDSTWU F D B

COMPUTATIONAL SEQUENCE

SEQUENCE USED WAS:DSTWU

ASPEN PLUS SIMUIAT10N OF DISTILLATION MODELS 125

OVERALL FLOWSHEET BALANCE


IN OUT

CONVENTIONAL COMPONENTS (LBMOIVHR)ETHANE

ETHYLENE

TOTAL BALANCE

MOLE(LBMOIVHR)MASS(LB/HR)

120.000

80.0000

120.000

80.0000

200.000 200.000

5852.66 5852.66

ENTHALPY(BTU/HR) -0.252753E+07 -0.363687E+07

RELATIVE DIFF.

0.000000E+00

0.000000E+00

0.000000E+00

-0.155399E-15

0.305025

ASPEN PLUS PLAT: WIN32 VER: 11.1 07/12/2007 PAGESIMULATION OF A SHORTCUT DISTILLATION COLUMN


COMPONENTS

ID TYPE

ETHANE C

ETHYLENE C

FORMULA

C2H6

C2H4

NAME OR ALIAS

C2H6

C2H4

REPORT NAME

ETHANE

ETHYLENE



U-O-S BLOCK SECTION

BLOCK: DSTWU MODEL: DSTWU

INLET STREAM:

CONDENSER OUTLET:

REBOILER OUTLET:

PROPERTY OPTION SET:

F

D

B

RK-SOAVE STANDARD RKS EQUATION OF STATE


IN OUT

TOTAL BALANCE

MOLE(LBMOIVHR)

MASS( LB/HR)

200.000

5852.66

200.000

5852.66

RELATIVE DIFF.

0.000000E+00

-0.155399E-15

ENTHALPY(BTU/HR) -0.252753E+07 -0.363687E+07 0.305025

* * INPUT DATA *** .

HEAVY KEY COMPONENT ETHANE

RECOVERY FOR HEAVY KEY 0.00100000

LIGHT KEY COMPONENT ETHYLENE

RECOVERY FOR LIGHT KEY 0.99600

TOP STAGE PRESSURE (PSI) 300.000

BOTTOM STAGE PRESSURE (PSI) 300.000

126 PROCESS SIMULATION AND CONTROL USING ASPEN1"

NO. OF EQUILIBRIUM STAGESDISTILLATE VAPOUR FRACTION

*** RESULTS ***

30.0000

0.0

DISTILLATE TEMP. (F) -18.3114BOTTOM TEMP. (F) 20.4654MINIMUM REFLUX RATIO 7.72431ACTUAL REFLUX RATIO 8.75092MINIMUM STAGES 33.9434ACTUAL EQUILIBRIUM STAGES 67.8868NUMBER OF ACTUAL STAGES ABOVE FEED 39.4169DIST. VS FEED 0.39900

CONDENSER COOLING REQUIRED (BTU/HR) 3,034,310.NET CONDENSER DUTY (BTU/HR) -3,034,310.

REBOILER HEATING REQUIRED (BTU/HR) 1,924,980.NET REBOILER DUTY (BTU/HR) 1,924,980.

ASPEN PLUS PLAT: WIN32 VER: 11.1 07/12/2007 PAGE


STREAM SECTION

BDF

STREAM ID B D FFROM: DSTWU DSTWUTO : DSTWU

SUBSTREAM: MIXEDPHASE: LIQUID LIQUID VAPOUR

COMPONENTS: LBMOL/HRETHANE 119.8800 0

.1200 120.0000

ETHYLENE 0.3200 79.6800 80.0000

COMPONENTS: MOLE FRACETHANE 0

.9973 1

.5038-03 0

.6000

ETHYLENE 2.6622-03 0

.9985 0

.4000

TOTAL FLOW:

LBMOL/HR 120.2000 79.8000 200.0000LB/HR 3613.7256 2238.9320 5852.6576CUFT/HR 140.3489 82.0590 7

.5963+04STATE VARIABLES:

TEMP (F) 20.4654 -18.3114 75.0000PRES (PSI) 300.0000 300.0000 15.0000VFRAC 0

.0 0

.0 1

.0000

LFRAC 1.0000 1

.0000 0

.0

SFRAC 0.0 0

.0 0

.0

ENTHALPY:BTU/LBMOL -4

.1532+04 1.6983+04 -1

.2638+04


BTU/LB -1381.4403 605.3231 -431.8608

BTU/HR -4.9921+06 1

.3553+06 -2

.5275+06

ENTROPY:BTU/T.RMOL-R -58.6713 -30.5758 -28.8269

BTU/LB-R -1.9515 -1

.0898 -0.9851

DENSITY:

LBMOiyCUFT 0.8564 0

.9725 2

.6329-03

LB/CUFT 25.7482 27.2844 7.7046-02

AVGMW 30.0643 28.0568 29.2633

ASPEN PLUS PLAT: WIN32 VER: 11.1 07/12/2007 PAGE 6SIMULATION OF A SHORTCUT DISTILLATION COLUMN

PROBLEM STATUS SECTION

BLOCK STATUS

* *

* Calculations were completed normally ** All Unit Operation blocks were completed normally *« *

* All streams were flashed normally *« #

3.2

.2 Simulation of a RadFrac Model

Problem statement

We will continue the above problem with few modifications. A hydrocarbon stream,consisting of 60 mole% ethane and 40 mole% ethylene, enters a RadFrac column havinga flow rate of 200 Ibmol/hr at 750F and 15 psia. The distillation process that has total68 theoretical stages (including condenser and reboiler) and a total condenser operatesat 300 psia with zero pressure drop throughout. The distillate rate, reflux ratio andfeed tray location are given as 79.8 Ibmol/hr, 8.75 (mole basis) and 41 (above-stage),respectively. Consider the RK-Soave property method.

(a) Simulate the column and compute the compositions of top as well as bottomproducts.

(b) Is there any discrepancy in product compositions obtained from RadFrac andDSTWU columns? If yes, what is the main reason?

Note: In the comparative study (for part b), consider total 68 theoretical stages (includingcondenser and reboiler) keeping other entered data unchanged for the DSTWU column(see Subsection 3.2.1).

Simulation approach

(a) Start with the General with English Units Template, as shown in Figures 3.25(a)and 3.25(b).


I I

FIGURE 3.25(a)

Click OiiTin the screen, shown in Figure 3.25(b). When the Connect to Engine dialogpops up, again press OK button to obtain a blank Process Flowsheet Window.

FIGURE 3.25(b)

Creating flowsheet

Among the built-in columns in the Model Library of Aspen Simulator,select RadFrac

and place it in the flowsheet window. Connecting feed, distillate and bottom product

streams with the distillation column, and changing the default names of the block and

all streams, finally we get Figure 3.26.


r|gf7-| .|..|' pr .1 -tCi i iw IH

t 13 0

sne»fi muu am im mj** ujw

-J r- - <

FIGURE 3.26


In the subsequent step, simply hit Afert button followed by OK to open a setup inputform. These two windows, shown in Figures 3.27(a) and (b), include the Global andAccounting information for the present project.

. % fa M» Dm tM» * imh n m n*

9 i"--

9

- 3 >- w.

0 -

.I - 11 - I

i ii

ITOf Mr. ' MIUU Da toM IM*a «0<a Narfw ..McfiAB

FIGURE 3.27(a)



JaglHl :| Mftl yJ nWkfoKM 1 til .]J_nJ juJ 1 1 ill

v a*

ft-1 a4 Gfl

Skv

iwi-s«i

O METO METCfiAR

fl METCMGCM

f> 5V-C6AH

Sttwrnf

Flo»*e«bftg Opbon*MoM ,1-! Took

US YOU UKE

i 2Jil

STREAMS DSTWU Dim Rrft«c E- ad Muffnc SCFfac PaBcfiae Ratftac BatetfracfarHaip.pMn

| .si) Chapter 3 ttowJWcri | 4]Q>«pMf2-lto«rfi Wtrt H A xn Pkj. - SM«i . fi'"

FIGURE 3.27(b)

In the Setup/Report Options /Stream sheet,select ole' as well as 'Mass' fraction

basis as shown in Figure 3.28.

0 Becwrt Opdcro

.: fib b« on To* n« u»v rnvhw Hdp

r Uhv R 1 >IB3|- . { lal

iUMbl'1 -I -3>>JialajNil

G«mi4 I Ftatt««t j Btaek Vsi»m} Proper j ADA |

i jjj Bock.

; H«MtebancUWinsD««nMpwlFfaubwit FiMjonbMa ShWDfamM -

j f? Mote P Moio ; tff- [geTTe' r mm ' P S»S Iff Si«ndsd (BO octantT SUHovcAjw r SUi viAm ; r WUaPBcoUw)

_ 1 P SoK-rewatfwwKw*K ConpoAMvAweftMoftKlnn

Wo«tWu.iartwiw*

MOM

* tWSrtten | S Mtatt | HMEwhangm

SIRCMC ' DSTMJ<i-t-o:-§-iv-(i..#.c-r-DSTMl fag Arf E*ao. SCf >1>rf fl .ac e IK

FIGURE 3.28


Specifying componentsIn the list on the left, choose Components /Specifications to define the components.Using the component names, ethane and ethylene, as their IDs, we obtain the filledtable as shown in Figure 3.29.

=W 54 *» :«> T FV« itun Wr*s-

-r-i-i-i -i .w i -igi *m

3a !«

O si

o ,.-

Mn*

;lrM*N£ cats

.IHYUNC

>

Pttrfnc R«rfW:: B«ct#.*;

FIGURE 3.29

Specifying property methodFrom the Data Browser

, select Specifications under Properties folder and then set RK-Soave base method to compute the physical properties (see Figure 3.30).

' Fit CM

0|<*|H| - ;

>I>'.|--|T »MBJ|v

. mrai J «J|a.

IJ1

.

It

3B«i«»a(tw6 fflr.SOAVt. - - r

OwoCTylO j

1 J

5T««)J ' OSTWU

FIGURE 3.30



Use the Data Browser menu tree to navigate to the Streams /F/Input /Specificationssheet. Inserting the given values for the feed stream, Figure 3.31 is obtained.

r-itfi>t|

3EfSiF -q l-li Fi-Hid QUIH

1j

3 |m* dr

(200 jbrt*.

it,

1 Hm(t jr r: CMlma | FtMcicn | RMMfOungett | Htrie-Mm \ SiteJ UtftKoM |

Ejiki Mulfia: SCFlK FmfiK PmfiiK 9*0*1*:

FIGURE 3.31


In the left pane of the Data Browser window, select Blocks/RADFRAC/Setup. Fill up

the Configuration sheet as shown in Figure 3.32.

Sa To* Rn Pa tfea/ WMw Help

I r.-.|-.i-l fT Nv i 11] isN

g BO VMbki

a «*

3

H*o4erHcuv*i

O Dwt i

7]F 1 ?98 (trrotA,

-Ha

FIGURE 3.32


Under Setup subfolder, the filled Streams sheet looks like Figure 3.33.

.i 'to 1 « «!«.;

> | | MB I M»» |

-it r

FIGURE 3.33

In the next, simply input 300 psi under Stage 1/Condenser pressure. Aspen simulatorassumes that the column operates isobarically if no additional pressure information isprovided (see Figure 3.34).

IB I' W tl*)

i:.,ir.ir.ii.0.ii'.fi..#.s .j-.

FIGURE 3.34


To run the simulation, hit Next and then OK to observe the progress of the simulationin the Control Panel window, shown in Figure 3.35.


Under Setup subfolder, the filled Streams sheet looks like Figure 3.33.

.i 'to 1 « «!«.;

> | | MB I M»» |

-it r

FIGURE 3.33

In the next, simply input 300 psi under Stage 1/Condenser pressure. Aspen simulatorassumes that the column operates isobarically if no additional pressure information isprovided (see Figure 3.34).

IB I' W tl*)

i:.,ir.ir.ii.0.ii'.fi..#.s .j-.

FIGURE 3.34


To run the simulation, hit Next and then OK to observe the progress of the simulationin the Control Panel window, shown in Figure 3.35.


n* E# M«m Dal* Toch ft* Utrvy WMdaw M*.

_.

iJ~

-l i-.i T ai JfilpI l"l "li-dail 4;|

-*Hao«Miafl input «p«cl<tCiti.4B* ...

Ml JSTftllVtO fSON 3 Or tABLt IAELE tIAJa - KJWSTD

owpotatiom owata ro> tmi jiowshmt;

->C«lcaJ.«ttQn» t»«in . . .

Block: aAcrajkC «<mui raofsac

IS LOHM THM( JTXGJ *1 MKMVM D.7O*i«*07 (H/SSW1

Coif/«cg*nffi» iearttlOK*:01 KL IL Sce/Tol

ill Eo.oasa i j U.mJ 13 7.oc«a4 1 « i.73*fr

.

5.

i : i o.i6a»7i-ai

lli>ra»l

STREAMS PSTWU Dirf Radfw , lAaci MUtfxic; SCFuw fahoFrac Ratrffac Batetfrac ___

FIGURE 3.35

Viewing results

Click on Solver Settings followed by Results Summary and Streams, we have the table,shown in Figure 3.36, accompanying the results of all individual streams. Save thework in a folder as a file.

j He Ed) Urn Curt TooU Ron Plot Ifinry WndoM l-<*

JjlJ 121 1 1*1_da)

~J CcnvOotcm

ComOnta

3Mbl ±l±l«jPi-H JMaljjj

~

3 Sii.i»I«e|

1 i i

l»316 8 078 7*1154" 1

J982 13i5 752(1

|te.fr«:

OS* Um 0517"

TTfhUNE QOQi 0995 0383

tiHiilt 11371! 120«(«

CTHYIENC'

~

0498 73512 man)

EIHAHE 0 336 bou oeao

EIHYUNE 00M 03»

-

- cx.magttgicffTr-wi

FIGURE 3.36



Select Input Summary from the View dropdown menu to obtain all input informationof the present problem (see Figure 3.37).

ire«.i uiu-y itHin bv up*- »lia .>. It.I « ll.'S'l* Sal ).i 11,Olr.ciory I Pro m (tin -Oin! .s't-t .ic.r Hut II. 1

00'

Tin* 'SII»l1»T*("i .* UlM'M ts'w*

I-IIUVI CVfllD ILL

.ccolvi.ii>o xcow-io .Mie'-io-un 10 t

cavit 'i-. ill- - '- i-.'iM' .. :, ;a. B»«. fV*r> ll-al Kr. Hh.Vt , c H.O,

Ml> 'w live ">!.

'nrari (oiMitilax: Mil flo"

Miiauas main unimi yxio- ikkmiu 4

tiHu« ei-» -rmkM C!"

W'OITl Ultll'l

HWii ill wii:i

CfWuM EIMK .oio»Xo<»:

MCKMI VMB VMIK fi "IWl, ««ll "iw-.'OC.

1 ...

FIGURE 3.37

Results of the RadFrac column

TABLE 3.1

Composition (mole fraction)

Component B D

ethane

ethylene

0.996

0.

004

0.004

0.

99G

Results of the DSTWU column

TABLE 3.2

Composition (mole fraction)

Component B D

ethane

ethylene

0.997

0.003

0.002

0.998

From Tables 3.1 and 3.2, it is obvious that there is a little difference between the

product compositions. However, the main reason behind this fact is that the RadFracperforms rigorous calculations, whereas the DSTWU is a shortcut model. Anotherpossibility is the round-off error associated in the reflux ratio and feed tray position.

Copyrighled malarial

136 PROCESS SIMULATION AND CONTROL USING ASPEN'

3.3 ASPEN PLUS SIMULATION OF THE MULTICOMPONENT

DISTILLATION COLUMNS

3.3

.1 Simulation of a RadFrac Model

Problem statement

A multicomponent distillation column, specified in Figure 3.38, has total 20 stages(including condenser and reboiler) with 60% Murphree efficiency. A hydrocarbon feedmixture enters above tray 10 of the RadFrac column. Apply the Peng-Robinsoncorrelation and consider 120 psia pressure throughout the column.

(a) Simulate the model and calculate the product compositions, and(b) Produce a Temperature' (0F) vs. 'Stage' plot.

Feed Specifications

Flow rate = 100 Ibmol/hr

Temperature = 120F

Pressure = 120 psia

Component Mole%

C3 5

/-C4

15

n-C4 20

'-C5 25

A?-C5 35

< Vapour Distillate Specifications

Flow rate = 50 Ibmol/hrReflux rate = 125 Ibmol/hr

FIGURE 3.38 A flowsheet of a distillation column.

Simulation approach

(a) As we start Aspen Plus from the Start menu or by double-clicking the AspenPlus icon on our desktop, the Aspen Plus Startup dialog appears (see Figure 3.

39).Select Template option.

FIGURE 3.39

VSI'KN I'll 'S SIMl'LATION OF DISTOIATIOM MHHKl.S 137

As Aspen Plus presents the window after clicking OK in Figure 3.39, choose Generalwith English Units. Then hit OK (see Figure 3.40).

FIGURE 3.40

Click OK when the Aspen Plus engine window is displayed (see Figure 3.40).Remember that this step is specific to the installation.

Creating flowsheet

At present, we have a blank Process Flowsheet Window. So, we start to develop theprocess flow diagram by adding a RadFrac column from the Model Library toolbar anddrawing the inlet and product streams by the help of Material STREAMS.

Now the process flowsheet is complete. The Status bar in the bottom right of thescreen, shown in Figure 3.41, displays a message ofRequired Input Incomplete indicatingthat input data are required to enter to continue the simulation.


Hitting Next knob and then clicking OK, we get the setup input form. In Figures 3.42(a)and (b), the Title of the problem ('Simulation of a Multicomponent Column') followedby the Aspen Plus accounting information (AKJANA/ll/ANY ID/FINE) are provided.

Include the additional items in Report Options/Stream sheet under Setup folder(see Figure 3.43).

C aterial

PROCESS SIMULATION AND CONTROL USING ASPEN

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STREAMS ' DSm) Diiii Kvfiec E«liacl Muffiac SCFw PelroFiK Hattfims BUchFracFsrIMs.miFI i

'

cv Rto*>wn»'ii.i ihim| Chacte3 Wo«<!»W ,[ ]Oi«tcl-lto«tlW.. | Met* Acicla ftcfewl I IMS

FIGURE 3.41

. * Mi D». To* fo» PW litra unto* H*

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a aj s«i»mTbfJ Mil iilpi-3 »l oi l H

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rj Rearforj

_J RaKliSurray

til«

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::!|S«wiabor at a MJHcoffponent Colwrr»««« . GMMri

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CONVEN Sidd

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.SetHat,

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FIGURE 3.42(a)


illJIBI I ! fc(PJ S fJ- >l»l !-H 3 'I 1*1 i| TJ_

j JI f

~

-l -I-1 fV -1 -iC! i m\ MM

o--

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1-1

FIGURE 3.42(b)

.i -iff] i 1*1 -iti

5-I

' '" ''''

r.

aim

FIGURE 3.43


In the left pane of the Data Browser window, select Components /Specifications. Fillingout the Component ID column, we obtain the table as shown in Figure 3.44.

Copynghied material


mas.m Do* lock Br. PU Lbtwy Moo- HHp

±J-" - l-l hPT

:?j 'I

1 lai.

N

1© ?(«c -

fit SmJalicn 0*:<-i

CuBjn Uh*l

0 Papc"

L J-J 6-<J Pro»l»i

M CJ NtaOhMcMMMn

Prtcaties

PROPANE Convertonal fflOPWIE

SOBUfll S06UTAHE C4H10-2

wet* MEmtlBUIiJIt. 9UZ-3

JPCItTWIE

r

far Help p-eai M

FIGURE 3.44


In order to define the base property method, press Next icon or select Properties/Specifications in the column at the left side (Figure 3.45). From the Property methodpulldown menu, select PENG-ROB. This equation of state model is chosen forthermodynamic property predictions.

Ffe E* W Pa W

0|e?|B|

I Wsi «lStl

das

Jt Specficabom

lhUS«s

htufaoampemrti

Qj H-f»)rC<mpj; . unif«:qw*>!

O GLOBAL

1 (3 Enmaw

1 -ij PramMwi

F-CH

STREAMS

PiopBly method: t modHt

Ptoctislypw. F[PEHG-ROe

ftw-waioi method j-

-

: ChcntbylD j

r

Pfltefnc P fwt B#etf.K

FIGURE 3.45



In the next, use the Data Browser menu tree to navigate to the Streams /F/Input /Specifications sheet. Entering the values of all state variables and component molefractions, we get this picture (see Figure 3.46).

I rH-H-F " -IB I'll IW

I2S

Ml II- P=!J 3

I-~

3f» k 3

,

-&-3

I 3

' 'U*w 5? !?- Mftg «!- -*. -~ »

. ....

Ei-P-- M= 'O--------

FIGURE 3.46


Open the Configuration sheet choosing Blocks /RADFRAC in the list on the left. In theproblem statement, the information on number of stages, condenser type, vapourdistillate flow rate and reflux rate are given (see Figure 3.47).

3=

:3'

r£Z3_

. mam

tea.rauv s-.rv, Ma Cm mm «. .*>>

FIGURE 3.47



In the next, use the Data Browser menu tree to navigate to the Streams /F/Input /Specifications sheet. Entering the values of all state variables and component molefractions, we get this picture (see Figure 3.46).

I rH-H-F " -IB I'll IW

I2S

Ml II- P=!J 3

I-~

3f» k 3

,

-&-3

I 3

' 'U*w 5? !?- Mftg «!- -*. -~ »

. ....

Ei-P-- M= 'O--------

FIGURE 3.46


Open the Configuration sheet choosing Blocks /RADFRAC in the list on the left. In theproblem statement, the information on number of stages, condenser type, vapourdistillate flow rate and reflux rate are given (see Figure 3.47).

3=

:3'

r£Z3_

. mam

tea.rauv s-.rv, Ma Cm mm «. .*>>

FIGURE 3.47

142 4 PROCESS SIMULATION AND CONTROL USING ASPEN

In the subsequent step, specify the feed tray location in the Streams sheet as shownin Figure 3.48.

fl. Ml D«i T«* ft* PW Uom* VMcm N*

I

flow

20 Um4

CJ

. 31 P«p 3«.Q

i rj dv

S .t . .

9 , '0- RADFRAC

Hi j j flndxra

* Cj T3<*

SinDWS ! OSTW OiW ft K tm*t MJJ.tc Sgt*e fWuc.

Hwfi»e B*<(W-<«

FIGURE 3.48

Enter the coliunn pressure of 120 psi and get Figure 3.49 as shown in the screen.

5* pfboi

Cj b**<**tCi 'jruJACCwCj uwff«&o

t cj «~*

Cj

E ( J Vt. j xr-

* CJ .cj w

_ CJ fearfiMngCkUn

: f--3

f*M*'

Mfr !-

-1*1 xl

FIGURE 3.49

The Blocks/RADFRAC/Efficiencies/Options sheet appears with the Data Browsermenu tree in the left pane. To input the Murphree efficiency value for all trays (excludingthe condenser and reboiler)

, we have the screen, shown in Figure 3.50 first.


T He S« <*- Ma Tn* ft* Ft* Un, WMdw 4*

wal _U a|t1«>hNIH!£l 2l jiiiiii J ©ir.>i..i..|.-fT 'I .W I - W jgfel

Method

I

o

« Set*

Jj0:j

90

p llhMWHcuTrr. Smg

9

»00 Gsmaigra®0

1 " T' 4

STf&WS Km) Dha Hvfttc Eiftact Httfrac SCF»ac PdtoFiac Ra<eFt«c:

SalcbFiK

Aspen Phis - 9b.. /- AOeb« tooba j « l: i fM 1S<6

FIGURE 3.50

Press the knob to open the Vapour-Liquid sheet (see Figure 3.51).

tj He &t Uew Teob Rji Pie! liw/ VAvfcw heb

±Jr~--l h.b HT _ij_iM_J_Ua| M!d

O '

- a 'a

3HafaiEn. d±i±li5lPi BidoLaliid

- RSOfRAC

O a.

_j P*> Sir.)

© Eta««

5-

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Slartrg Endng

*

/Cx- iele

flT <**tmm I I He»L£»-J«wn 1 *-". | Re«a». | l> i«ei>w | Meroiae,. ) Sol* 1 UwHoA*-a-»

MeMTiel '. . -' 5 SEi . n. .... Dj.kT.

FIGURE 3.51

Assume the rectifying along with the stripping zone as Section 1 and fill up thetable

, shown in Figure 3.52.

144 -f PROCESS SIMULATION AND CONTROL USING ASPEN1

mmmammRU> &H \Aew Dats Tec*

i r-i y i nr am i m

.-J <

PAOFRAC

Mm CM

C vientm hi

Pock Sa j

EMMm

ReportUser Suooj-

LiJ_

STREAM?

'joc*w. St«V9

Ugp1 19

* 1

f -r.NUM o

Mobetuot* It

FIGURE 3.52


Hit Afcci button followed by OK and observe the progress of the simulation inControl Panel window as shown in Figure 3.53.

Fte E* Vtew 0«e To . Run Jbnrf VHvhw

±Jjij

D RADFRAC< Loading SlmXat cn Jngtn* lS:61r33 i

»;rDC«8»ing Input .p»ciftc»ti.=Ti« , . .

IHTOUUTTflH

eitJAfly PUJutfOTiRS paru can* set d roa hoo«l SEParrD

mie muivn from scf tasli . xuu kms - lsptste

slock: ftirraxc maids a*cnuc

« esM

1.2195

c ;j*4t

Jsasll

f " M«ii<$«aM> I SeMJtJ. I H«<£«»«w fill I Rajrtai | IWnCh n |

"V J

STREAMS OSTWU

M«.iJSra»> I S.O.*.. I IMiM vr- CM | (Won | Pa-nOwvn | MnuM i

' OSIVAJ Dfl« Rrfwc MJf« iCfiK FWrfnc R ft*: gaafwe

J'j jT«-tfc, i- *

FIGURE 3.53

ASPEN PLUS SINfULATION OF DISTILLATION MODELS 145

Viewing results

Click on Solver Settings knob and then choose Results Summary /Streams to obtain theproduct compositions (see Figure 3.54).

r-i .i.i>fv -jci

rl 3'-f 13 "--l

9_

JIM Mimmf ~ "

Hi 1"T» TBH

«.>* " TOB 1 l» . "| J

»*». -sin 1 "rtai-'-1

1 !Will ue in

TariT ' «« IM

lb i«»

i.«

aoni IJH- "TIB TM

ntn 1 . a l<» IIITf«5B 1

f» n hi 1 i I wr mi "in 1 « » hihi I "i |

|-<u« reWj M M« C-» Mta ti>« rmt» Km*~

.rw » -.«»«* I- .> '..

FIGURE 3.54

It is a good habit to save the work done at least at this moment. If we wish to seethe tabulated results with the process flow diagram in a single sheet, simply hit StreamTable button just above the results table (see Figure 3.55).

JMMI .til _!.) a nH-|»l%l<M ») r I i-l .IglJi £jlisf i -i -id urn

«-C3-

FIGURE 3.55



As stated previously, to obtain the input information, press Ctrl+Alt+I or select InputSummary from the View pulldown menu (see Figure 3.56).

imut Su«Hry cr«««d by Ajp«r Clul R«l. 11-1 it VMM Sun )ul IS, 2007

;Dlr«tory c '.froqriM fil« .AipefiT«ch\**ork1ng Folders Aspen Plus 11.1 Fileniw C userj ijjn* *ppOjt« local T*<Bp -*pt>a cn,

tiuC "SlBuUllor of a IMdCtCMpMM Colo o"

Is-unITS CNG

EXF-STREWS CONVIN ALL

ACCOUMT-INFO ACCOUHT-ll PROJECT-IO-AHY ID PRO JECT-NWI-"

FINE"

USE R - HAf E ""AK J AH* '

OtStRIPTION'

C»n»ral Slaulation wtth English units ;f, psl. Ib-tv. Itaol/hr. Btu hr. cuft/hr.

property method: none

fIoh basis for Input: Nola

Strcan report cowposlclon: t»ol« fl«

AOUEOUS / 50LIOS / INOBGANIC ,' A

PROP-SOURCES POREll.

aflUEOUS ,' SOLIDS / INORGANIC

CWPOWMTSPROPAXE ClHS ,'ISO»U-0l C4HI0-Z ,'N-«VT-01 CAMlO-l /2-t«ET-01 CiMl2-2 /N-PEN-&1 C5H12-1

rSHCETBLOCK RAOFR.AC IN-F OVT-OV B

PROPERTIES PEMG-ROB

>-DATA PRKIJ-1IN-UH1TS CPKtPROP-LiyT PRKI)BPVAL PROPAME ISOSU-01 -7.BOOOOOOE-3BPVAL PROPAhE N-BUT-01 3.300000001-3BPVAL PROPANE 2-MET-01 .0111000000

.'.tol # f> " to* t QwpW M I JO IW l lhAJT M- [ wnfta 5 } > AtWwAort* || -APF7EAJ > 1 17a>

FIGURE 3.56

(b) First, choose Blocks /RADFRAC /Profiles in the column at the left sideAccordingly, we have the stage-wise data as shown in Figure 3.

57.

3fl *«-

F oawnd

T- ft c I

fir

STntAMS

mm J >>j am wrmi I c 1

Vapofto.

r *jTiit

1 tasoU 1 "B--3 aj i

9TIJ3K?SI'

20 i 171 385017

195 3*a»6 20 j

20 i liJnuiiJlii i;oo 3ra 20 i

201354309 ia i

9 anwsssi }»

lit

n

llJ121)

||;:-

. . - i:iT:;nr-si

to

I HME | Mh | M.UoM |

jgwc tW-« H«rf.>i *mtr»C JFIGURE 3.57

ASPEN PLUS"" SIMULATION OF DISTILLATION MODELS 147

In the next, select Plot Wizard from the Plot dropdown menu or press Ctrl + Alt + Won the keyboard to get Figure 3.58.

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_

j

. «-Cj owl-

a 'mm

71 .1

1

| ram

ijte>

!tDM5

I Until-

1

Welcome to Aspen P!b» net Wlzwdl

15"-CH

MnrtJ D,> tuf<tc MJfac Sg-«c P trf.tc Ralrfrac Bl£tfi»c

FIGURE 3.58

Click on Next button in the Plot Wizard Step 1 dialog and get a variety of plot types,

shown in Figure 3.59.

i"l pi a)|

-3ffift ~

g «JI" d»| olaii n>iIPFQ | CwvoMora j KVAjW j

('

smvm*

_J T.w Sot,

_j

-J s- j

H4W

J 51 OK

naa

seisa

«2J!4

Wti*1

1 Join*

1

To bvn, MbM a (W lypo )>ouwh lo omniU

.

Q?1!* OowfMto fV**! Mva

,i

wFodo FkMntln CCCOTHI CQCQS H) Hv4m > BM

Pi"-CH

60 -.

JP""

' m& tS» so.. w«fafc.-A»»H.MI NU«

iQVjre 1740

FIGURE 3.59


Select the plot type under the heading of Temp and press Finish button to obtain aplot of Temperature' (0F) vs. 'Stage' (see Figure 3.60).

rinwii-ii

i io u £ 15 i« k w tr tt is-aI I J s <

: it

FIGURE 3.60

Recall that the above plot window can be edited by right clicking on that windowand selecting Properties. Then the user can easily modify the title, axis scale, font andcolour of the plot.

3.3

.2 Simulation of a PetroFrac Model

Problem statement

An artificial petroleum refining column (PRC), shown in Figure 3.61, consists of a feedfurnace and a distillation tower. The tower has two pumparound circuits, a partialcondenser and three side strippers. The furnace (single stage flash type) operates at25 psia and provides a fractional overflash of 40% (StdVol basis) in the tower. Theoutlet stream of the furnace goes to the tower on Stage 22. The tower has 26 stageswith a Murphree stage efficiency equal to 90%. A steam stream, STEAM, is introducedat the bottom of the fractionator (26th stage with on-stage convention). There are anotherthree steam streams, STM1, STM2 and STM3, used in the side strippers. The condenserruns at 15.7 psia with a pressure drop of 5 psi. The tower pressure drop is equal to4 psi. The distillate rate is 10000 bbl/day and the distillate vapour fraction in thecondenser is 0.2 (StdVol basis).


ASPEN PLUS SIMULATION OF EHSTILLATIQM MODELS 149

LIGHTS <

STMl

STM2

WATER

sir,-

BOT

FIGURE 3.61 A flowsheet of a petroleum refining column.

A hydrocarbon mixture with the following component-wise flow rates enters thefurnace at 1170F and 44.7 psia (see Table 3.3).

TABLE 3.3

Component Flow rate (bbl/day)

Ci 3

c2 65

C3 575

i-C4 1820

«-c4 7500

i-C5 30000

n-C5 42000

H2O 250

In Table 3.4, two pumparound circuits and three side strippers are specified.

TABLE 3.4

Loeatum Specifications

Pumparound Draw stage Return stage Flow rate Heat duty(drawoff type) (bbl/day) (MMBtu/hr)

1 (partial) 8 6 49000 -40 (for cooling)2 (partial) 1 12 1000 -17 (for cooling)

Location

Stripper No. of Stripper Draw Return Stripping Bottom productstages product stage stage steam flow rate (bbl/day)

1 5 SID1 6 5 STMl 11000

2 4 SID2 12 11 STM2 15000

3 3 SID31

19 18 STM3 8000


Four steam streams used in the column model are described in Table 3.5.

TABLE 3.5

Specifications 1

Steam stream Location Temperature (0F) Pressure (psia) Flow rate (lb/hr)

STEAM Main tower 350 50 11500

STM1 SID1 stripper 350 50 4000



Considering the 'BK10' base method under 'REFINERT process type, simulate thePetroFrac column and report the flow rates (bbl/day) of all product streams.

Simulation approach

Select Aspen Plus User Interface. When the Aspen Plus Startup dialog appears,

choose Template and click on OK (see Figure 3.62).

I I I I I I It

Cioata a Utm SmMan Using

A+ f Blank Smiiabon

A+ Temptale

"

OpendnEwiingSimulatior

e*r\ADU BOOK apwDAeoolAChaptesVAOU OWN xmD:V0ook\Chap(«sViDU.t*{>

I0«

| Adobe Ao-dia P,d«»« I Chace.s W \ 4]Q*i** 2 HmcHW || Av Pka

FIGURE 3.62

As the next window pops up (see Figure 3.63), select Petroleum with English Unitsand press OK knob

.


mm'Mm.

1

linn v-

...

L-EJ J-J

.. ..

FIGURE 3.63

Click OK when the Connect to Engine dialog appears. The next screen presents ablank process flowsheet.

Creating flowsheet

Select the Columns tab from the Model Library toolbar. As we expand the PetroFracblock icon, a variety of models is displayed as shown in Figure 3.64. Select a modelicon and press Fl to know more about that.

rinF. I- I-h HI I .Ml I lal iN

4. | turn* t

J? if" IT

[1 it Jb Jt&ir ifi

.

r # lb

ft ir Op

tr ffc* c J 1 -

i> Bp a.

#. I-

W 11 1

FIGURE 3.64

152 PROCKSS SIMULATION AND CONTROL USING ASPEN

As the distillation tower described in the problem statement, it is appropriate tochoose CDUIOF PetroFrac model. Then place it in the flowsheet window. Adding allincoming and outgoing streams and renaming the streams as well as block, the processflow diagram takes the shape as shown in Figure 3.65.

L'Mi- 111"A KM* 1W mm m 31* 1Mb -jM«.

FIGURE 3.65


Click Next to continue the simulation (see Figure 3.66). In the Title field, enter'Simulation of a Petroleum Refining Column'. Open the Accounting sheet keepinguntouched the other global defaults set by Aspen Plus.

t.

r

k-

.<i.i-?-ir-Q-ii'-i?--i i.-r<UbM

.

»»No M - -o- Ut- W» W.

FIGURE 3.66

Copyrlghtf


In the form, shown in Figure 3.67, the Aspen Plus accounting information are included.

.

I'MMI | i l"!1 1 F

9 -i*--- I 1 ,1'5-l-Mi-'-

3 »\ Q| -.i -1

s

»1 9i<>>

9 M Mjri '-c

. I"- 1

ITBUM :-1TMj ba 1m .kMnc tOM MXai Mai

FIGURE 3.67


In the subsequent step, use the Data Browser menu tree to navigate to the Components /Specifications sheet. Filling out the component input form, we have Figure 3.68.

U> ZlgjFi 3 >id <AP-Bid Lj'iaTJ*

3 gr

Lj i-r

1-

73-

T,

- -

1..

i -i;

it! T

r? f

-KJETTH tSruT

tntUM ' wraij a- B i. wo., ip i tw.. *****

FIGURE 3.68



We know that the thermodynamic models calculate the properties, such as vapourliquid equilibrium coefficient, enthalpy and density. In the list on the left

, shownFigure 3.69, choose Properties/Specifications to open the property input form

. In th"Process type field, select 'REFINERY

' and in the Base method field, select 'BKlO' (Brau

6

K-10 method).

Ea Tc<* ftr HO th*> .v v t

NBI I I a>|e| ¥?! nlt'lftKKI I >»l ~l i I "I -I *\ I JI f i i I fV .|:-liS|-. I .:M

"

3

-

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ficwtw |Bfni;tFf.

I 3

~

3

STRUMS'

KTVM OM fikfiK PtftaPut RatoFiv 8«=rfi«

FIGURE 3.69


Next the Streams /FEED /Input/Specifications sheet appears with the Data Browsermenu tree in the left pane. Entering the feed data, Figure 3.70 is obtained.

D|tfiB|_iJ e|jgJ njKjfti i-g -i ».i { |h| Miigj .}

_

j

Pn zi bJiiif -3 »J QN h

i 0.1

w,

1 ED-**

rv-D-

n

|n

biei

cs nm

!3J no

""!««' wwi » ., m,,, s ,« t«,« i i*

FIGURE 3.70


As we hit Next icon, an input form for Stream STEAM opens up. After filling out, itlooks like Figure 3.71

.

* t* V«« D*» T«w fVn PW Marwt VMem

M-i-rv

[ft HuTorCoew

. F/traBy

£ Mol(Qior Stioami: FtranKn

: g STE SS LGHTS

3 SE>13 O SlOS* a

-

3

31| EOOptan |

1*0 |r

dd

ictia 1H

11500

Total NlSOO"

itiputCMeM*'

fV MMd iAw. } SwoWort 1 HutEttharpei' Columw j Rwawt j h w O* | M*v niE | S<*t> | U«Modes |

ntnjl r. .1 Raifitc EntlKl MJtf.

t)_-.r... njj-._ b jj..STREAMS ' DSIWU SCfiac PtfwFrac Batefiae Bwctfiac

-S . * AwnWM t'

;NUVI cj/Ki i OTote

FIGURE 3.71

In Figures 3,72(a), (b) and (c), three filled input forms are shown for STM1, STM2and STM3 streams

,

' fitf csk Wew Dm Tooli H i PW Ibtw,

JMI mi9

"

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_J to

.

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.

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kM Cans,..

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d C1

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C4

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cs1

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1 J H20

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'

SWUM MTMI'MM* (renFI

FIGURE 3.72(a)


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. BIT

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, ns. JH FEED. LIGHTS

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._, sm

. srew

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31 [mmTfIcm 31"1"'

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FIGURE 3.72(b)

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FIGURE 3.72(c)


From the Data Browser, open Blocks /PRC/Setup /Configuration sheet and fill 11 up(see Figure 3.73).


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FIGURE 3.73

As we press Next icon, the Blocks /PRC/Setup /Streams sheet appears as shown inFigure 3.74.

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5

-

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feed me*"!

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FIGURE 3.74

n Figure 3.75, the pressure sheet shows the condenser pressure along with the topas well as bottom stage pressure of the distillation tower.

As given in the problem statement, enter 0.2 in the Distillate vapour fraction field

naer the heading of Condenser specification (see Figure 3.76).


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FIGURE 3.76

In the next step (see Figure 3.77), the feed furnace is specified by selecting the typeof furnace and giving the values of pressure and fractional overflash.



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- 3 iTm

F P 3

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FIGURE 3.75

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FIGURE 3.76

In the next step (see Figure 3.77), the feed furnace is specified by selecting the typeof furnace and giving the values of pressure and fractional overflash.



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FIGURE 3.77

In the left pane of the Data Browser window, select Blocks IPRC IEfficiencies andprovide 90% Murphree tray efficiency (see Figure 3.78).

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FIGURE 3.78

The three windows, shown in Figure 3.79(a), (b) and (c), specify the side strippers

tj d on the given input data.


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FIGURE 3.79(b)


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STREAMS DSTWU

fvHtki'

.fn

FIGURE 3.79(c)

Although the Status bar says Required Input Complete, we have to specify the twopumparound circuits connected with the main fractionator. Select Blocks/PRC/Pumparounds in the list on the left. Click on New as the object manager appears. Wemay accept the default Pumparound ID T-l'. Then specify the first pumparound circuit(see Figure 3.80).

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FIGURE 3.80

162 PROCESS SIMULATION AND CONTHOL USING ASI'KN"'

Select again Blocks/PRC/Pumparounds to reopen the pumparounds object manager.

By the same way, fill out the form for second pumparound circuit, shown in Figure 3.81.

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J Beck*

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_i

OS

1-.-. d

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FIGURE 3.81


Hit Next icon and click OiTto run the simulation. The Control Panel window is presented

in Figure 3.82.

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. Fr nxtcj input i(Mift«Hiau

oawjimiftp oawa rca the n-wsasir.

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FIGURE 3.82


Viewing results

From the Data Browser, choose Results Summary /Streams and obtain the table, shownin Figure 3.83, that includes the flow rates (bbl/day) of all product streams. Save thework done.

-o-

l.;,ft-i

FIGURE 3.83

To obtain the input information (see Figure 3.84), select Input Summary from theView pulldown menu.

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. fv irtm no- Ha. »»t.

titmm . uve. : * lid. flaa

.-

Cl CMut c*<ao ;Ml . ««0-|

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ncc* «c >uo s'*! ft.ii:o»T» fluw fc*Ti" iroa >tw «oj

FIGURE 3.84



3.4 SIMULATION AND ANALYSIS OF AN ABSORPTION COLUMN

Problem statement

A hydrocarbon vapour enters an absorption column below the bottom stage and theabsorbent enters above the top stage. The column operates at 75 psia with no pressuredrop and it has four equilibrium stages. The absorber is specified in Figure 3.85.

Absorbent

Pure n-C10Temperature = 90oFPressure = 75 psiaFlow rate = 1000 Ibmol/hr

ABSORBENT

oAo-rttu

GAS-PDT

Gas Feed

Temperature = 90oF

Pressure = 75 psia

Component Flow rate

(Ibmol/hr)280

c2 150

C3 240

n-C4 170

n-C5 150

LIQ-PDT

FIGURE 3.85 A Tlowsheet of an absorption column.

Apply the Peng-Robinson equation of state model in the simulation.

(a) Simulate the absorber model (ABSBR2 under RadFrac) and compute the productcompositions.

(b) Perform the sensitivity analysis by examining the effect of absorbent flow rateon the exiting C3 concentration in the top product.

(c) Compute the absorbent flow rate to keep 15 mole% of C, in the gas product(GAS-PDT). 3

Simulation approach

(a) Double-click Aspen Plus User Interface icon on the desktop. When Aspen Plus

window pops up, select General with English Units Template as shown mFigures 3.86(a) and (b).


;.

b,

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1 r OMn»E«F«Sai>H>

0 J.<* *h«MW«U»0

J

V.

.

FIGURE 3.86(a)

oi W_U

-

J_)ig| J2hm_L_kld 2J_LLJ_ia_i

1F

FIGURE 3.86(b)

Click OK when the Connect to Engine dialog is displayed and proceed to developthe process flow diagram.

Creating flowsheet

Select the Columns tab from the bottom toolbar. Among the available RadFrac models,

select ABSBR2 and then place it on the flowsheet by clicking with the cross hairsomewhere on the flowsheet background. Right-click to de-select the block. Connectingthe inlet and outlet streams and changing the all default labels, we have Figure d.»/.


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J1IM J_L-LJI .1 .tel. I IBI «g]*!j

O 1 «8-'H

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STREAMS S OSTWU CwU Ratfiac E»»[»c> MtlaP.ac SCfiv: PfUcfrac Raiefiae Batctfrac

; Slwl] S J " Botk j 4] Aapen_ Mo«by Mct | - Cha r3 Hritirft j jUwtdTwro Hwcao )[ Aapen PVj« . Soul « j

FIGURE 3.87


In the subsequent step, hit Next symbol and fill up the three setup input forms as shownin Figures 3.88(a), (b) and (c).

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n| |H|_

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STREAMS OST'VU QaU RxF.ac E«kI M F.oc P»tof.ac R<Mfi«c

FIGURE 3.88(a)


* -

FIGURE 3.88(b)

38

Tig-ISsir-:

FIGURE 3.88(c)


From the Data Browser, choose Components/Specifications. In the input form, shownin Figure 3.89, all components are defined.


In the list on the left, shown in Figure 3.90. select Properties /Specifications to obtainthe property input form. Set PENG-ROB property method.


168 PROCKSS SIMULATION AND CONTROL USING ASPEN11

& .! -m I W W

'I "

.

5!ESii11

-

LI

-D-

FIGURE 3.89

IF

. > --

-D-

W W >»«.» M«» -il> «-»»

FIGURE 3.90


In the next data entry step, press Next button and click on OK. Enter the feedinformation for both the gas stream and absorbent in two forms as shown inFigures 3.91(a) and (b).


Use the Data Browser menu tree to navigate to the Blocks/ABSORBER/Setup/Confi-guration sheet (see Figure 3.92).

168 PROCKSS SIMULATION AND CONTROL USING ASPEN11

& .! -m I W W

'I "

.

5!ESii11

-

LI

-D-

FIGURE 3.89

IF

. > --

-D-

W W >»«.» M«» -il> «-»»

FIGURE 3.90


In the next data entry step, press Next button and click on OK. Enter the feedinformation for both the gas stream and absorbent in two forms as shown inFigures 3.91(a) and (b).


Use the Data Browser menu tree to navigate to the Blocks/ABSORBER/Setup/Confi-guration sheet (see Figure 3.92).


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IVH3-

"

3 nr

IS 3.

,

FIGURE 3.91(a)

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FIGURE 3.91(b)

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SfEf«i -fe!

P-

3,

-

j\ r

Li ir

FIGURE 3.92


Select the Streams tab to specify stream location. Under Convention, there are twofeeding options: On-Stage and Above-Stage. In the present problem, the top stage isthe first stage and the bottom stage is the fourth one. Therefore the absorbent is fedabove Stage 1 and the gas feed is introduced above Stage 5 (see Figure 3.93).

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FIGURE 3.93

In the next step (see Figure 3.94), select Pressure tab to specify the pressure profileacross the absorption column. In this case, the column is operated isobarically at75 psia. Under Top stage / Condenser pressure, enter 75 psi. Aspen software assumesthat the column operates isobarically if no additional information is provided.

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E AflSOftSER

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fop ' Ccmkraii pftlfJI*

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FIGURE 3.94

ASPEN PLUS"' SIMULATION OF DISTILLATION MODELS 171


Hit Next foUowed by OK to run the simulation. The Control Panel window is shown inFigure 3.95.

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FIGURE 3.95

Viewing results

Choosing Results Summary /Streams in the left pane of the Data Browser window,we

get the results as shown in Figure 3.96.

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rr .ila .1 *LiJ «)W

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'

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US'-

RG dm 0012 cioo

mM OlOD

tcio 1000 np oca .1

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-a-

sifiEtw''

e '' j Dr.« ri.j,3, Ml<, '* SSffigB f,v'r'a- SftSf -. kM- j.

I a-w a i te ss i iaajgLg

FIGURE 3.96


(b) In the sensitivity analysis, we will manipulate the absorbent flow rate andexamine its effect on the exiting propane concentration. In the column at the

left side, double-click on Model Analysis Tools folder and then select Sensitivity.

As the Object manager is displayed, choose New. On the next window, shown inFigure 3.97, Aspen prompts us for an ID. Enter 'C3' as ID, and click OK.

- ft* idl .tea

1 MM Wl nMfcl-si-JI-i el r I L'iiliJJSll -1_

i_

r_

L m rv d |B|1

._, w

- :.-.

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I C mrtnI C-.**

i j Sohh | Utti

FIGURE 3.97

In the next step (see Figure 3.98), select New under Define tab. Then we areprompted to enter a variable name. Enter 'C3' and press OK. Subsequently, the followinginformation are required to provide:

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1 |B|

StaM l&i-iTOI

- > -

1 |

J.

4...,'. ., | MW. I H«,[Jw U>mm | taca>. | Bbu.Ow I M-MO, | U* I <lm*M I

n'

OITWU Cm R«fCMtt HJf*c «Tac IW'k n 'tc fc 't -

FIGURE 3.98

ASPEN PLUS*" SIMULATION OF DISTILLATION MODELS 173

Type: Mole-FracStream: GAS-PDT

Substream: MIXED

Component: C3Hit Next and select the Vary tab (see Figure 3.99) The manipulated variable i

specified with the following data:

Type: Mole-FlowStream: ABSORBEN

Substream: MIXED

Component: NC10

Overall range

Lower: 500

Upper: 1500Increment: 50

is

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i i»l.li:M;ii A_

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.

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Ina fsTHercxljbrti

Lm1 I

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FIGURE 3.99

In the subsequent step (see Figure 3.100), select the Tabulate tab. This screen isused by Aspen to set up tables. Insert T under Column No. Then right click on theadjacent cell under Tabulated variable or expression. Select Variable List and drag anddrop the variable name (C3) into the cell. We may also directly type '03' in the cell.

Then run the simulation and get the screen, shown in Figure 3.101.

174 PROCESS SlMULVriON AND CONTROL USING ASPEN

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et " .ft . .- u~

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s

.

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< w -m Ik

FIGURE 3.100

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ir-Qc>

> nn

I :mii

In Tm.

t trv

I Mil

t Mai

lil/TU'» «»«K ua

MtMi uut

' MIMU Om IW<k Umo >w i« IOai DMTw taXw

FIGURE 3.101

\SPEN PLUS SIMULATION OF DISTIUJVTION MODELS 175

From the Data Browser, select Model Analysis Tools/Sensitivity/C3/Results todisplay the tabulated data (see Figure 3.102).

5 -

-I » - " . - I rijo- - 11; .--

FIGURE 3.102

In order to represent the results graphically, highlight a column in the table andselect X-Axis Variable (Ctrl + Alt + X) from the Plot pulldown menu. By the similarway. select Y Axis Variable (Ctrl + Alt + Y) for the next column. Then select DisplayPlot (Ctrl + Alt + P) from the Plot menu and obtain Figure 3.103.

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I --. I - l- I

JFIGURE 3 103


(c) In the left pane of the Data Browser window {see Figure 3.104), openFlowsheeting Options folder and then select Design Spec. We need to providethis design spec a name in the same manner that we did for the sensitivityanalysis. Press New, enter 'DSC3* and click on OK.

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-o

_ AH .> Mfc. lw Mto W. W«

FIGURE 3.104

Select ihTettJ under Define tab. Then enter 'CS' as a variable name and press OK. Inthe next step (see Figure 3.105), the following information are required to input:

Type: Mole-FracStream: GAS-PDT

Substream: MIXED

Component: C3

v

.

.K-MJ-B-M-iM-f-

FIGURE 3.105

Copyrlghiod material

ASPEN PLUS1M SIMULATION OF DISTILLATION MODELS 177

In the subsequent step (see Figure 3.106), select the Spec tab. Design specificationdata are noted below:

Spec: C3Target: 0.15Tolerance: 0.001

;Ti=E4Mi DSTVU Dag R»Jf>: Erftaci M frac SCF»c PihoF-JC flyrf.K fcj'ctfix

FIGURE 3.106

Finally (see Figure 3.107), select the Vary tab and enter the following information:

> 4. Lfc Ar- Cm« to-Ji Hpi Ptoi Ubr, AWtow »H>

MHj_U jff) nkiaiaKiH n.| P >|'l"l I ~l 1 ffil_

j_

r iii nr imi i ibi i i

.' X

'U-

_i /-,

6-J

00Q ! M6'>

r-s.

_i >

o

1

r-3 "

r r

I -' - Tan, I > fi-'-:?

| HmMH I r>MMf'CM«M | Mr iW I SOW: | UwMaW- |

»gj ' I a

FIGURE 3.107

178 PROCESS SIMULATION AND CONTROL USING ASPKN"

Type: Mole-FlowStream: ABSORBEN

Substream: MIXED

Component: NC10

Manipulated variable limitsLower: 500

Upper: 1500

As we run the simulation, we get the screen, shown in Figure 3.108.

&k 'Aw U«j Tw, fu. w**«.

el w| Mii*MaJi£)!id r -I I "I 311 <Mj lai

Slock: ISSOAfilS USFUC

K. K. XL Ici Ir.

1 t 1

I 1 1 C.1K31

Lhtt i.e. sicwr- iMunuii ii - fl-.j.J. Hbi Ik/TcI 0 IS9ft«3

ML IL ttt/To)

i i » c.aui*

3TH£*«S ! OSTWU Dan Brfrac Um* UtffiK SOHk ftftrfwe RaUfwc Badftic

-

' ail * J " . »t

FIGURE 3.108

As we choose Streams subfolder under Results Summary folder in the list on the left(see Figure 3.109), we get the absorbent flow rate of 1179.467 Ibmol/hr to keep 15 moleof C3 in the gas product. This answer we can also obtain from the sensitivity plot.

3.5 OPTIMIZATION USING ASPEN PLUS

It is well known that Aspen Plus is capable to optimize a function.Here, we will continue

the above absorption problem (Section 3.4) for optimization. In the present study, wewish to maximize C3 mole fraction in the gas product (GAS-PDT) with respect toabsorbent inlet temperature (lower limit = 50oF and upper limit = 300oF).

Simulation approach

First solve part (a) of the previous absorption problem.It means, fill up the input

forms for setup, components, properties, streams and blocks. In the next, simulate tneoptimization problem as described in the following.


t -r4

« -

.

')M

"

TM Hlit

KB

rr,

_ 1 1

-

-- Si.- - JUBJ-

i>'«

IT iMT 1

.sna-fSBRI- - tc

U wra-; wimM .» i .«<-'.

rr owi t-rr* M Im* o»« '

FIGURE 3.109

In the column at the left side (see Figure 3.110), choose Model Analysis Tools/Optimization. As the Object manager is displayed, hit New button and accept the defaultID 0-1' Press OK and then New. Entenng variable name 'CS'. again click OK Providethe following information to maximize C3 mole fraction in the gas product.

N t)I'M*

FIGURE 3.110

180 PROCESS SIMULATION ANT) CONTROL USING ASPEN1

Hit Next knob twice and get the screen, shown in Figure 3.111.

T-Birrym.v.-.T'-iB

_

LilJ Jl]35l £vj:

- D i0C.-.~. Osbcn

- ii

D

2J

dp

a

- iJ

At o i

3 <<J[ --7]2>J DijdHd

fir Hitut/SpEttm j

STREAMS h!BM f 5&M S£p»

0 ' ioc*< p!9.,

FIGURE 3.111

Right-click in the empty cell with selecting Maximize option. Then select VariableList and drag and drop the variable name (C3) into the cell (see Figure 3.112). We canalso simply type C3 in the field.

E* fwe ~ada Z,r. \Jutr, Wrtie* Hnb

- HQ OfWlc*s 2u eSci

[5) Rma

S ij 01

U.. ..i'r

CbiKtive tundnn -

FIGURE 3.112

In the subsequent step, select the Vary tab. Under Variable number, as we choose'

New', automatically the number T appears. FillinR out the form, we have the windowas shown in Figure 3.113.

ASPEN PLUS'" SIMULATION OF DISTILLATION MODELS 181

!5)| I \£\ j l

21 Cw

_j rw-m

ffi nw aw i

-D-

FIGURE 3.113

Pressing iVex symbol and running the simulation, we get the answer (see Figure 3.114).

The maximum C3 mole fraction of 0.259 is obtained at absorbent inlet temperature of 179.80F

.

In vi>* C*i Kn fa ttnja,,

J~

1 i i fir -i-.bi 1 ibi

j 'Jr-.rr.

USC0 £»-

3 T i

>,K1.«pu 75 00

noco 10*

foosaoo HHwv.- lUHjUMMB Lit 5»SS7

"

4*m .

'

ft

Wfa>

c? mm 1?.'

*'

Ti PIVB170(00 i»S3

FIGURE 3.114


At the beginning of this chapter,a brief of all built-in column models of Aspen software

has been presented.Several separating columns, including a petroleum refining column

and an absorber,have been simulated using Aspen Plus. The process optimization has

also been discussed with an example. The present study covers both the binary as wellas multicomponent systems.

Interested readers may try to simulate the models givenin the exercise

.

182 PROCESS SIMULATION AND CONTROL USING ASPKN

PROBLEMS|3.1 A feed mixture, consisting of 60 mole% ethanol and 40 niole% water, is to be

separated by using a DSTWU model having a flow rate of 100 kmol/hr at 40oC

and 1 atm so as to recover at least 85% of the light key component in the liquiddistillate and 80% of the heavy key component in the bottoms. The columnoperates at 1 atm with no pressure drop throughout. In the simulation, considerthe reflux ratio of 1.5 and a total condenser. Applying the Wilson property method,simulate the column and find out the minimum number of stages, actual numberof stages, and feed position.

3.2 A feed stream, consisting of 50 mole% ethane and 50 mole% ethylene. enters aDistl column having a flow rate of 200 Ibmol/hr at 750F and 15 psia. This separatorruns at 300 psia with no tray-to-tray pressure drop. The pressure in the reboileras well as condenser is also 300 psia. The feed enters the model at 6th stage andthe column has total 15 theoretical stages (including condenser and reboiler)and a total condenser. If the reflux ratio is 7 and the distillate to feed ratio is

0.8

. compute the mole fraction of ethane in both the product streams with applyingthe RK-Soave equation of state model.

3.3 A feed mixture specified in Figure 3.115 is to be distilled by a rigorous RadFracmodel (FRACT2). The column consists of total 24 equilibrium stages (includingcondenser and reboiler) with a stage pressure drop of 2 kPa. Consider thecondenser (total) pressure of 125 kPa and the top stage (Stage no. 2) pressure of130 kPa. The distillate flow rate is 120 kmol/hr and the reflux ratio (mole basis)

is 2. A side product (vapour) is withdrawn from 14th stage. Applying the Soave-Redlich-Kwong (SRK) property method, simulate the column model and reportthe product compositions.

Feed

Temperature = 110nFPressure = 175 kPa

Feed stage = 10 (above stage)

Component Flow rate(Ibmol/hr)

benzene 250toluene 80

diphenyl 10


3.4 A reboiled stripper is to be employed to remove mainly propane and lightercomponents from a feed stream, shown in Figure 3.116. It has total 6 stages(including condenser and reboiler) and no condenser. The bottoms rate is100 Ibmol/hr and the column pressure is 150 psia throughout. Using the Peng-Robinson thermodynamic method, simulate the RadFrac model (STRIP2) andfind out the product compositions.

Dj O

Sj cC.

B\ $



Feed

Temperature = 40oFPressure = 300 psiaFeed stage = 1 (above stage)

Component Flow rate

(Ibmol/hr)

c, 60

c2 75

c3 150

n-C4 175

n-C5 60

n-Cs

35

D -

FIGURE 3.116 A flowsheet of a stripping column.

3.5 A feed mixture of cyclopentane and cyclohexane is to be separated employing a

liquid-liquid extraction unit at 250C and 1 atm with the use of methanol as asolvent. The schematic diagram of the process with feed specifications is givenin Figure 3.17. The process unit, having toted five stages, is operated adiabatically.Applying the UNIQUAC property method, simulate the extraction model (ICON1)and note down the product compositions.

Feed

Temperature = 30oC

Pressure = 1 atm

Feed stage = 1

Component Flow rate

(Ibmol/hr)

cyclopentane 250cyclohexane 750

Solvent

Temperature - 30DC

Pressure = 1 atm

Feed stage = 5

Component Flow rate(Ibmol/hr)

methanol 1000

FEED

-SOLVENT-

EXTRACT

'

,

RAFFINAT

FIGURE 3.117 A flowsheet of an extraction column.

3.6 A gas consisting of 40 mole% ammonia, 60 mole% air at 20CC, 25 psia, flowing atthe rate 120 kmol/hr, is to be scrubbed counter-currently with water (pure) enteringat 60oC and 30 psia at a rate 100 kmol/hr. The column operates at 1 atm throughoutand it has four stages. Using the UNIFAC thermodynamic model, (a) simulate theRadFrac absorber (ABSBR2) and determine the exiting ammonia concentration inthe gas product, (b) Perform the sensitivity analysis by examining the effect ofabsorbent flow rate on the exiting ammonia concentration in the top product.

Copyrlghled malarial


3.7 An artificial petroleum refining column (PRC) shown in Figure 3.118 consists ofa feed furnace and a fractionation tower. The tower includes one pumparound

circuit, a partial condenser and one side stripper. The furnace (single stage flashtype) operates at 20 psia and provides a fractional overflash of 50% (StdVol basis)in the tower. The outlet stream of the furnace enters the tower on stage 18

.

The column has total 20 stages. A steam stream, STEAM, is fed at the bottomof the fractionator (20th stage with on-stage convention). There is another steamstream, STEM1, used in the side stripper. The condenser runs at 15 psia with apressure drop of 5 psi. The tower pressure drop is equal to 5 psi. The distillaterate is 12000 bbl/day and the distillate vapour fraction in the condenser is 0.25(StdVol basis). The liquid product, SID1, is withdrawn from 5th stage with aflow rate of 2000 bbl/day.

A hydrocarbon mixture with the given component-wise flow rates (Table 3.6)enters the furnace at 120oF and 45 psia.

LIGHTS

FEED

WATER

STEM

IS -o

SID1

STEM1 -O

SID2 C>

BOT O

FIGURE 3.118 A flowsheet of a petroleum refining column

TABLE 3.6

Component Flow rate (bbl/day)

10

c2 100

C3 600

1800

n-C4

7500

30000

1-0,

42000

nrCt 250

H20 250

ASHEN PLUS SIMULATION OF DISTILLATION MODELS 185

The pomparound circuit (for cooling) and the side stnpper are specified with thefollowing information (see Table 3.7).

TABLE 3.7

Location Specifications

Pumparoundidrauoff type)

Draw

stage

Return

stage

i

Flaw rate

(bbl/day)Temperature

feF,

I (partial) 8 6 40000 20

Location

Stnpper No. of Stnpper Draw Return Stripping Bottom productstages product stage stage steam flow rate (bbl/day;

1 5 SID1 12 10 STEM1 15000

Two steam streams, used in the column model, are described in Table 3.8.

TABLE 3

Specifications

Steam stream Location Temperature (8F) Pressure (psia) Flow rate Ob/hr)

STEAM Main tower

STEM! Stnpper

350 50 12000

350 50 5000

Selecting the PENG-ROB base method under RE FINE RV process type,simulate

the model using a PetroFrac column and report the flow rates (bbl/day > of allproduct streams.

Part II

Chemical Plant Simulation

using Aspen Plus

Aspen Plus Simulation ofChemical Plants

4.1 INTRODUCTION

In the last three chapters, we have studied in detail the simulation of individualprocesses, such as flash drum, dryer, chemical reactor, distillation column includingpetroleum refining process, absorber, stripper and liquid-liquid extraction unit, usingAspen Plus software. Here, by a 'chemical plant' we mean a chemical processintegrated with several single process units. The chemical process industries usuallyinclude flash chamber, mixer, splitter, heat exchanger, pump, compressor, reactor,fractionator, filter and so on. It is easy to simulate even a large chemical plant by theuse of Aspen software package.

In the present chapter, the simulation of two chemical process flowsheets isdiscussed. They are a distillation train and a vinyl chloride monomer (VCM)manufacturing unit. After thoroughly reading this chapter and simulating the solvedexamples in hand, we will be able to use Aspen Plus flowsheet simulator for solving awide variety of chemical plants. To improve the flowsheet simulation skills, it isrecommended to solve the problems given in the exercise.

4.2 ASPEN PLUS SIMULATION OF A DISTILLATION TRAIN

Problem statement

A hydrocarbon stream H is supplied at 50C and 2.5 atm. The pump Pi discharges thefeed F at 10 atm. In Table 4.1 the component-wise flow rates are tabulated for stream H.

The schematic representation of the complete process integrated with a pump andfive DSTWU column models (Cl, C2, C3, C4 and C5) is shown in Figure 4.1.

189

Copyrk


TABLE 4.1

Component

n-C.

F/ouj rate (kmol/hr)

10

35

50

130

200

180

200

5

pi C1 C2 C3 C4

FIGURE 4.1 A flowsheet of a distillation train.

cs

For Aspen Plus simulation of the distillation train, required information are givenin Table 4.2.

TABLE 4.2

Column Condenser Reboiler

(abbreviation) pressure (aim) pressure (atm)

Deethanizer (CD 9 9

Depropanizer (C2) 5 6

Deisobutanizer (03) 4 4

Debutanizer (04) 3 3

Deisopentanizer (05) 2 2

All distillation models have total 20 theoretical stages (including condenser andreboiler) and a total condenser. For the light key (LK) and heavy key (HK), we expect99.9% and 0.1% recovery, respectively, in the distillate of all columns. Using the Peng-Robinson property method, simulate the distillation train and report the compositionsof all distillation products.

Simulation approach

From the desktop, select Start button followed by Programs, AspenTech, AspenEngineering Suite, Aspen Plus Version and finally Aspen Plus User Interface. Thenchoose Template option in the Aspen Plus Startup dialog (see Figure 4.2).

Copyrighled malarial

\SI'KN PWB SIMULATION OP CHKMK \l PLANTS 191

hmbj_lj__bJ'ii mmLii-jd .3 J.i.'isim i. :

si

In ro..-

AM n i.tu.

1

I

1-1" .' I 1 «

FIGURE 4.2

As wo hit OK button, the following window appears (sec Figure 13). Based on theunits used in the problem statement,

we select General with Metric Uliits,

.in-i

1»

1- . l-.

<- r< mil I-'

.- J - .

_J I"-. I

1

I'

FIGURE 4 3


Press OK and obtain the Connect to Engine dialog. Select 'Local PC as Server typeand click OK. Actually, this step is specific to our installation (see Figure 4.4).

Connect to Engine

Server type:

User Info

Node name:

User name;

Password;

Working directory:

Save as Delaull Connection

OK ] ExB Help

FIGURE 4.4

Creating flowsheet

The next screen represents a Process Flowsheet Window. Add a pump by selecting thePressure Changers tab from the Model Library toolbar. Moreover, in the library, selectthe Columns tab and then choose DSTWU model to include five such columns

consecutively on the flowsheet. Notice that to incorporate a block,click on the

appropriate icon and then place the block on the process flowsheet by clicking with thecross hairs somewhere on the flowsheet background. Right click to de-select the block.

Now we need to interconnect the blocks and add the inlet as well as outlet streams.Select Material STREAMS on the left of the toolbar at the bottom

.In the next, as we

move the cursor to the process flowsheet window, several red and blue arrows appeararound the blocks. The red arrows indicate required streams and the blue arrows areoptional. In the previous chapters, we have learned how to connect the feed and productstreams with a single block.

Let us observe Figure 4.5 to know how to interconnect the two blocks by a stream.Here, first we wish to interconnect the pump PI with the column Cl using the feedstream F. Right-click with highlighting feed block,

select Reconnect Destination andthen move the cursor to click on an arrow that is fed to the column Cl.

SOD-*-QD-o

m o

r ]-o

PI Cl

FIGURE 4.5

ASPEN PLUS SIMU1.ATION OF CHEMICAL PLANTS 193

We can select Reconnect Source instead of Reconnect Destination if we modifyFigure 4.5 to Figure 4.6.

j3LD1

B1 c>

C1

FIGURE 4.6

By the same way, interconnect remaining blocks. Renaming all blocks as well asincoming and outgoing streams, finally we have the screen shown in Figure 4.7. Torename a particular stream (or block), first select it, then right-click, next select RenameStream (or Rename Block) and finally enter the appropriate name.

Re E« Vto» On Took tin Uban Whfen Help

H _J iU _l J

kl

5","*,s Oirwu o,ai SCfuc PMiofioc BMefiai Boictfuc

C |iFold».mo»IVilH HUM fw»llr»J

FIGURE 4.7

The status indicator in the bottom right of the window, shown in Figure 4.7, saysRequired Input Incomplete indicating that the process flowsheet is complete and inputdata are required to enter for running the simulation.



As we hit Next icon and then click on OK, the following window pops up (see Figure 4.8).Remember that in the Data Browser, we need to enter information using data inputforms at locations where there are red semicircles. As we finish a section, a blue

checkmark appears.

» r- -i'iv

life,

-

FIGURE 4.8

It is always a good practice to represent a simulation problem with entering a title.In the Tattle field, enter 'Simulation of a Distillation Train'. Note that we may changethe input/output data units under Units of measurement (see Figure 4.9).

I r i-l I 17 -i.gi i «(i

V-H

-id* ~ ' . -

figur: m 9

The next window (see Figure 4.10) includes the Aspen Plus accounting information,

as given below, required at some installations.

ASPEN PLUS SIMULATION OF CHEMICAL PLANTS 195

User name: AKJANA

Account number: IIT-KGP

Project ID CHEMICALProject name: DT

1

,

-o- i S *

MM -

FIGURE 4.10

If we want the streams results summary sheet to display mole fractions,select

Report Options under Setup folder to the left Under the Stream tab,select 'Mole' as

Fraction basis (see Figure 4.11)

n fT7

i i- - .

-

:

*- . -

-»

u>U>i

.2}' I-

n . - .« <

FIGURE 4.11


Specifying componentsIn the subsequent step, use the Data Browser menu tree to navigate to the Components/

Specifications sheet. It is shown in Chapter 1 how to define components in the component

input form. Here, we have this table as shown in Figure 4.12.

ffc E* *p. ftw To* R»

i r l-l .l- fT >i -"Pi I iai

g :.r.: Fopui

C2

CJ

C*

IU

cs

.

* !S

*

_j wy tm

1: - . .

_J O pOa**

. i i r

id

5 -._

| > M<MVnt«« -J

FIGURE 4.12


In the list on the left, choose Properties/Specifications to obtain the property input form.A property method includes the models and methods to calculate the physical properties,such as vapour-liquid equilibrium coefficient

, enthalpy and density. For the exampleplant, set PENG-ROB base property method by scrolling down (Figure 4.13).

5* C*, T** P« U , Wnajt. tt*

-

-

J DM

. 3

I 3

PT

FIGURE 4.13

ASPEN PLUS SIMULATION OF CHEMICAL PLANTS -f 197

Note that there is no compulsion to use only a single thermodynamic propertymethod for all processes in a chemical plant. Aspen software provides an option tochoose different property methods for different processes. To do so, select Block Options!Properties under a particular model of Blocks folder in the list on the left and thenchoose the suitable property method.

Specifying stream InformationThe Streams/H/Input/Specifications sheet appears with the Data Browser menu tree in theleft pane. Entering the given data for stream H, we obtain the sheet as shown in Figure 4.14.

j-T-i i-i'r> i-w I'M -

tti»» .rtl.m '-if

2j twi- m*.

3"

3 j. a. -j],. ,. j

' ". : ww. r w sit.

FIGURE 4.14


As we hit Next button, the block input form appears. The deethanizer column is specified

with the given data as shown in Figure 4.15.

* & V- tm, r , m

31i£iai _U *iB| 51 nl-mi*!<l

arn<tv*\

.

_1 "

: ; £

it:

6 :

imua h** m tffl

FIGURE 4.15


Subsequently, the filled input forms are shown in Figures 4.16(a), (b), (c) and (d)for other four DSTWU columns.

fir. Prt Ubfwy WMM

-LT-

tap u**

»>y ctnponent

-1 F

i

C3

O St*: G<t<-C-.

(a

Ct«p fo~

Rww jo TO

neb*.

Condentei ipertcalun!

1

] .JtdiJ Trimr>n»m

FIGURE 4.16(a)

_

iJ~_J_

iiiJ JZi J

|0 IrcU

_j V- n

. ) .an d

i pi-

_j tjf

. U B3* 6--

_1

. U KI

_J W

. 0 02' _1 M-

_j W

j _, D£

S M Cl

- jfi : .

ftco- It*cm

RMI

t

P»u

3Mt I HJilJ -3 U

a Wumbe.

r Reftw .aha

CdaimxtOebor* j Convagervt

Ptuiite

Reba» fT

Ccrrp fic<

Reow (0 CO)

3]

I I Sob* I UMModrt t

kKm-

Fv H* cm F"

FIGURE 4.16(b)


Si ioj _U 51 riKifci- l-M 3) _J_JjiJ ji) 5j

i_

J «* Zl. S H

J '- J -

- 1 «

n

as

(7 ll**c»*

- r i »>-

-CHMM

M- FSptr SSpM

I HMtKfaan | Colm | Rucmt | Pimm*!

C iFMiStavPUtn NUN fi«w*Jkci41

FIGURE 4.16(c)

Pta Jrav

-

u «_

J w_

J .-

-I

ffiimii

CondEnia f"

f " HMra/lrfnan | Mraeon | Hn.f rp., | Coupni | RmcV<. | Prwtti.Ch»»n | tWiMi t Set* | UtpUM* |-CMHpflflUMS ' U** V,*

i-" | .f[«*jit | Him

C a(*t«J r tI> HUN ,«*«rJKmvwa u

FIGURE 4.16(d)

Click on Afert and specify the pump (PI) outlet by providing the discharge pressureof 10 atm (see Figure 4.17).


FU Jtnry Wndov. IMs

L-

TJ i iHA

J2J

"

3

Saiw

ij»t SutrciJine

£0 MM

Sw&wjm -1

r Preci.ie "iciMie

r Pt«tiu>«(Mo

|

I I) <Jfti«mr* (kthnjs condhoni

"

3

j <Ch« 'il-IA=r'Ari j 1 JAcw | -J U- q Tern} Atpei> Pk» - Simi

FIGURE 4.17

The status bar in the window, shown in Figure 4.17, includes a message ofRequiredInput Complete; it reveals that to run the simulator, sufficient data have been provided.But there is no such restriction that we cannot specify the process with more inputinformation. Again, as we click on Next, Aspen Plus shows a message under the headingof Required Input Complete as shown in Figure 4.18.

J-T 1-1. I pr H jsn l -iai

wni

D>38

0 EWSKj Rtcnc

/Specifcaliooij CflfcOalKr. OsHjw ] flaihOphor.t

P Result_

J

Al

I W ci- ai c;j a o. ai «

. a pi

EOCorwOpten

2

(? Ptmp

"

3"

3

Ptnp.

ro-jcertrterma'eincxJ To no'rr roi ed»i ijncd »Mea ' c fx :- Hm - * Osu .>: -- (Mnu.

-Q-

iM

. 9 -m *

FIGURE 4.18

ASPEN PLUS"' SIMULATION OF CHEMICAL PLANTS 201

Notice that if there are no red semicircles in the left, it can be said that the data

entry for running the Aspen simulator is complete.


As we approve the simulation run, the Control Panel, displayed in Figure 4.19, shows

the progress of the flowsheet simulation in addition to a message o[ Results Available.

.

1

-

.

B aB OB wZ '93

fi" -

us states; ~. Jt mu tjxll huz - jjtkt:

n a = c» n

z. =i3»i arc:

lice* a Bsmi: csrta

."v. ex. -vOS

FIGURE 4.19

Viewing results

Choose Results Summary /Streams in the column at the left side and obtain thecompositions of all distillation products as shown in Figure 4.20.

We may save the work by choosing File/Save As/...using the menu list on the top.W< tan give a name of the file whatever we like. Note that if we click on Stream Table,the results summary table is incorporated in the Process Flowsheet Window, as shownin Figure 4.

21.


If we wish to have the systematic input information, press Ctrl + Alt + I on the keyboardor select Input Summary from the View pulldown menu (see Figure 4*22).

In order to create a report file (*.rep) for the present problem, we may follow theapproach presented in Chapter 1. It is worthy to mention that the report file containsall necessary information on the solved Aspen Plus problem, including given processdata and computed results


3 >bJ.'<IP~~3»l-i g|

C- «~J Cv CMn

o .9 -e

.

-1

4 2j

MM. '

tmufi *M ««

1 Ja!

.

Wit T

B -

am"

TW"

nrwlTia HH i.r.T

"

n-

TTEB 1-

m- -

mid

e"

tUi sm 1 TOTB 11 nuif ' 1 m muff-B

~

nn-~TW

"

Mi-

IB"

ttd-'-

rw- rfq|p !. 11 nnu Tifi- BM 1RD -UB '

-

."Wi 1 Hm UK TW

TS ~

ra TBS"

713____ ,

us 1 TB 1"

BB S TRC-

IMl

irK."

iv-.

| U.I

FIGURE 4.20

i-MIBlJBI WPT |-3i-«Hil%l-g|w| -?i ! M .jiyialr|st7,|-|..|j fV .| .|E| Bj «i|fc|

lOmm* I " I Ho I.r

1

FIGURE 4.21

Copyhghied malarial


rrrvJ |t«i1«t<«i of a DUinUtlon TrtU

voilM-CM otir*-! MCW-aetrr i<ol( -OtNSrrr-'

tuol' c-ji

for Inpm: Ho1«

Stream report ct xnltiwi: «o1t fli

SOLIDS 1MMCAMIC

W-SDUKCS Wll / -QOWWS SOLIDS INOtMMC

CI C2M I( 1 ClHt1C4 C4H10-2 i' ' C4N10-1 /IC1 CSH12-; 'ici cvai-i /MCt CftfU-1

LCMMKT1LOW C» I«l-e4 O'JT-O) Bl.LOCK C4 IWt} O'.n-.oi Mukk ci in-c; out-03 el

u

FIGURE 4.22

4.3 ASPEN PLUS SIMULATION OF A VINYL CHLORIDE MONOMER

(VCM) PRODUCTION UNIT

Problem statement

The process flow diagram for Aspen Plus simulation of the vinyl chloride monomermanufacturing plant is shown in Figure 4.23. The flowsheet has been developed basedon the VCM production technology reported in a book by Seider et al. (1998).

O-fcmi

O-feu

BB 66 B7

F10

9

[purge]-o

FIGURE 4.23 A flowsheet of a vinyl chloride monomer production unit.

204 PROCESS SIMULATION AND CONTROL IISINO ASRKN

Pure ethylene, stored as a gas at 70oF and 1000 psia, with a flow rate of 20 tons/hr,

and pure chlorine, stored as a liquid at 70oF and 150 psia, with a flow rate of 50 tons/hrenter the mixer block Bl operated at 2 atm. The mixer outlet Fl then goes to thereactor B2 run at 363 K and 1.5 atm. In this stoichiometric reactor (RStoic), the followingchlorination reaction occurs with 98% conversion of ethylene to 1, 2-dichloroethane:

C2H4 + Cl2 -> C2H4C12

ethylene chlorine dichloroethane

In the next, mixer B3 operated at 1.4 atm allows the mixing of the recycled streamF12 with the reactor product F2. The outlet stream F3 is then condensed fully to liquidphase in block B4 at 298 K before being pumped to an evaporator. The pump B5 hasdischarged the liquid at 26 atm. The evaporator B6 performs the phase change operationand then the vapour temperature is increased in the same unit to 515 K. In thesubsequent step, stream F6 is introduced in the reactor B7 (RStoic) in which thefollowing pyrolysis reaction occurs:

C2H4C12 -> C2H3C1 + HC1

dichloroethane VCM hydrogen chloride

The dichloroethane is converted to VCM and it takes place spontaneously at 773 Kand 25 atm with 65% conversion. To reduce carbon deposition in the heat exchanger,the hot vapour stream leaving the reactor is quenched in block B8 yielding a saturatedvapour stream at 443 K. Quencher effluent stream F8 is condensed to liquid phase inblock B9 at 279 K and then fed to a DSTWU column B10 as stream F9. In the next

,

Stream F10 is introduced in another DSTWU column Bll. The first column mainlyseparates HC1 from other components, while the second column purifies VCM from therests. Both the distillation columns have 10 theoretical stages (including condenserand reboiler) and a total condenser along with the specifications,

shown in Table 4.3.

TABLE 4.3

% Recovery of LK/HK in distillate Pressure (atm)

Block Light key (LK) Heavy key (HK) Condenser Reboiler

B10

Bll

99.9% of HC1 0.1% of VCM

99.9% of VCM 0.1% of dichloroethane

20 22

7.5 8

Finally block B12 (FSplit) splits stream Fll to ensure the recycling of 99.999% ofFll as F12 stream to mixer B3. A purge stream is introduced to prevent accumulationof unreacted components.

Using the POLYSRK property method, simulate the complete plant to compute thecomposition of all streams.

Simulation approach

To start Aspen Plus package, select Aspen Plus User Interface under Programs. Whenthe Aspen Plus window pops up, choose Template and click on OK. In the next, selectPolymers with Metric Units (see Figure 4.24) and press OK button.


- . .r .ii.-i.*. Ti 3 . i i .rj 3 a

i : ; : I -i

-.

- :

HZ]

FIGURE 4.24

Click OA" when the Aspen Plus engine window appears to obtain a blank ProcessFlowsheet Window.

Creating flowsheet

We can develop the process flow diagram (see Figure 4.25) by incorporating the following

-IpF -I- I I- IT MCI I m ti

ED

? 4f413

FIGURE 4.25


built-in process units available in the Aspen Plus Model Library:two mixers (Bl and B3)

two Stoic' type reactors (B2 and B7)four 'Heater1 type heat exchangers (B4, B6, B8 and B9)

one Tump1

type pressure changer (B5)two T TWIT type columns (BIO and BID

one TSplit' type splitter (B12)

All the blocks and streams are renamed according to the problem definition.The status message directs us to provide the input information required to run the

complete Aspen Plus simulation program. In the subsequent sections, we will fill upseveral input forms one by one.


After creating the flowsheet for the VCM manufacturing unit, hit Next button followed

by OK to open the Setup /Specifications / Global sheet. In the following,the first screen

,

shown in Figure 4.26(a), includes the Title of the present project as Simulation of aVCM Production Unit' and the next screen

, displayed in Figure 4.26(b), shows theAspen Plus accounting information as given below.

User name: AKJANA

Account number: SAY X

Project ID: ANYTHINGProject name: AS YOU LIKE

ft* Edl ««. Dal* TotU f*jr. linry Wndw Help

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irouldars fwiTGfcbal jetting,

Input mods

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r Um see

3

313

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FIGURE 4.26(a)

ASPEN PLUS SIMUI.ATION OF CHEMICAL PLANTS 207

Qi BI_

LJ *j«J .] r5h-|ftl»N|w| mj rj J_iilj _J JI r -i-1-i Fir -t lei, I i«l MhJ

9

o

Mi*

FIGURE 4.26(b)

We wish to have streams results summarized with mass fraction basis that is not

set by default. Accordingly, we choose 'Mass' fraction basis in the Report Options/Stream sheet under Setup folder (see Figure 4.27).

«. Ea '<W Tm> V<-tat, AWl- -*k

DIQ*IHIJ'

.

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iJ

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P Hbi

P Ir-imi .«! no >» j tKW,

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FIGURE 4 27



The components that are involved in the monomer manufacturing process are ethylene(C2H4), chlorine (CI2), 1,2-dichloroethane (C2H4C12), vinyl chloride (C2H:iCl} and hydrogenchloride (HC1). In order to get a blank component input form, choose Components/Speciftcatiojis in the left pane of the Data Browser window. Defining all species in theSelection sheet, we have Figure 4.28.

510*101

1 (ComponaO Spooftoiioni . Dala Bnnrasr)

Data Tods fkn Plot Library Window Hdp

JT _1_M._

Tii.J J

ma

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_j Fo ert

PfOpefti«

| Stocks'

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I Corv-ergence'

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j Modd -ViaSyas TootsEOCorrfgurabon

z1

Selection] Pelidftum | Noraiorivenliona! j-/Dalabanl s |Define comp«*nli

Componerit ID Type Comconent name Foirtiula

::h4 Conventtonal ETHYLENE C2H4

CL2 Conventional IHLORINE ri;

C2H4CL2 Conventional 1 2-DICHL0R0ET r.:h4 .

Conventional VINYL-CHLORIDE C2H3CL

HCI Conventional HYDROGEN CHLC HCI

>

ElecWEatd UsetDelmed

fif Miyeu/Splittets | Sepaialoi

»m FSpS

Matei.at

STREAMS '

ForHe*j.pn»j Fl

'.ami s -

Heat Exchargeti ] Columns ) Reactots ) Ptestute Changei: ] Manpulatots j SoWs ) Usei Modeit ]

SSpK

C\. gFtAlfla\Aip«nPliji 11 1 NUM fiML«<! tTua netwowK

jjChapter4 1*00 | Oiapler I - Mero | T) Uidii Teimi I* | Aspen f\j» - VCM [| Aspen Plus « 9 C . '656

FIGURE 4.28


In the subsequent step, choose Properties/Specifications to set the property method.As mentioned in the problem statement, accordingly select POLYSRK base methodunder POLYMER process type (see Figure 4.29).


From the Data Browser,

choose Streams folder and see the name of all input, outputand intermediate streams. However, we have to provide information for only two input

streams, C2H4 and CL2,which are fed to the mixer block Bl. Figures 4.30(a) and (b)

show the filled stream input forms.

ASPEN PLUS SlMULVnON OF CHEMICAL PLANTS 209

IM ftp ... .' i ~ . .

CirftUl .-I i c|g| ni-«-|fcl%l-3M ml I M "I ?l -I_Li

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FIGURE 4.29

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-9

FIGURE 4.30(a)

ASPEN PLUS SlMULVnON OF CHEMICAL PLANTS 209

IM ftp ... .' i ~ . .

CirftUl .-I i c|g| ni-«-|fcl%l-3M ml I M "I ?l -I_Li

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FIGURE 4.29

|i*lB|

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-9

FIGURE 4.30(a)

210 PROCESS SIMULATION AND CONTROL USING ASI'KN

n. ton Pirn Stn.l*>on 1 [SlrBM C.L3 WATEBIAL) kyU - IMa ttowwrl

_

i_

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Data Tools Ruti rlol

3 ©[15 1st Z LJiiii"' jziJuUijiJ_

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Mo cJat Sttxicl'jie

t_j Pafanrten

_j Data

_j Mt*

PnapSel)* Jj y danced

J/J Streams- C2H«

© IhdJRajuJs

d EO Vanables- (a CL2

0 InpulRtsuls

Cf EO Vanables.

_j D1

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tt ._

, F3

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3 /Specilicalioni| Flash Oplor.i |SiMnamnaiM p MlxtD

Slate vaftaWe-.

| EO Option. |

d1" F .J

jpntttn djiso P« d

Total How Ma;-. d1 kgAr d

3Compojitioo

ComponenI Va>je

cm

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1 J-DOl

C2HXL

HCL

Total IST

ill ' "twulCompiete

jl " Mixeit/Splitteis | Sepiialois | Heal Exchinaeti

Material

STREAMS 1

FocHeto orevin

3*1 S i

FSpia SS|*

Cokjmu | Reactoi: [ Ptessuie Changei; | MarjpOaioii | Sold; j U;eiMc«Jd.-

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Chaptera Aipen Plus - Smjali

Rt»ju«ed ir<x£ TTC0ncJ«»t

FIGURE 4.30(b)


Unlike stream information, we need to input required data for all blocks of the process

flow diagram. As stated earlier, the flowsheet of the VCM plant consists of two mixers,two reactors, four heat exchangers, one pump, two distillation columns and one splitter.Although discussed during the Aspen Plus simulation of different single process unitsin the preceding chapters, we must remember the following points when we fill up theblock input forms.

To simulate a mixer model, at least provide the pressure data and valid phases.In the simulation of the reactor model

, coefficients should be negative forreactants and positive for products.

In the Vapour fraction field of a heater model, put 0 to indicate bubble point

and 1 to indicate dew point. For subcooled liquid and superheated vapour, useFlash specifications.

The windows, shown in Figures 4.31(a) to 4.31(n) display the block-wise informationusing the input forms.

ASPEN PLUS SIMULATION OF CHEMICAL PLANTS T

f* e* d*»'

** * *****

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FIGURE 4.31(a)

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FIGURE 4.31(b)

212 PROCKSS SIMULATION AND CONTROL USING ASPKN1"

jag|y| I I ite|ll8| ffj aMfkltKH H 2J-Liil)-2J iil -I J

Readarts

Compwienl

C2H4 i C2H4d2

12 i *

*

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H Heck Ooi"-.!!!

Spec Group)

Si p

r flMCtors occu «teiiot

[i Hiwit/Spttlef* j iepatalow ] HealE«hsrwi | Column) | Beattot) ] Ptftsauro Chanijers j ManpjIalMi [ SoWs | UwMwtei?

STREAMS M t.

forHab press F1

FSpS SSpH

jChapiy* Mcr: | --J;OacW I - IActi | -gjUxfJ Te M jj /open Pita Ag - MCg | » Q g Sffl

FIGURE 4.31(c)

Aapen Pk> CH4_

SeC_

4.3 - [Bocfc B3 (dtxer) tanner]

He b* Das

DMHj_LjM®l l nhl NK i n>| 3 I IMB J

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Mainum toohons E~

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youwrheofenure AtwoUe i OjW p.enue K value > 0 Ptaw/e *«, rW 0 Ga yrj; Oj!*. p,. -* lo-' 3h

MCorwca

STREAMS Hea a. Heat.- MHaaC Hwar.

PorHato-MiFl - ~HXFV* HrRCvlST

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JFIGURE 4.31(d)


i. j** On Toe* Urvt MMMt M r

aH|_iJ *1H r3ifH>|».KI | H II I l"l 'I jiil

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O EO«>a:: you Who mota. *ac«v ti*clon D 0 loc bubbte pwrJ 1 Olw (tew oo.nl Fm utorooled kjari o> wpcheaied vax* m l&Tpeia»u)fl sryj

iJwkfimitm

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FIGURE 4.31(e)

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FIGURE 4.31(f)

214 * PROCESS SIMULATION AND CONTROL USING ASPEN

< : E* «»« Ml T-)C<5 Run Pic' Uw> H*

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Lr i i i nr -Lm 71

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s ja be© InpUl:

"

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J BDVafcK*© EOkBU!

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STREAMS ' Mm FSpB

. Reactws j Pie-jyjie Char eis ] Mawpife!«; ] SoWs j User Modei:

5Sp5!

J[ Aspen Plus - . -py, v'CH [

FIGURE 4.31(g)

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m mm

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FIGURE 4.31(h)


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STREAMS ' Mm, FSct SSpt

fan* on.Fl

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FIGURE 4.31(i)

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FIGURE 4.31(j)


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STREAMS FSpM

«i you type (UtWWKrroeiafuo S«H*

.-cvy:.. | HeatEicch)ng»: | Ct-Unrj j ReflCioi)

=«. help prwi Fl

Book | AapcnPlu.NUM

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FIGURE 4.31(k)

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bd mill

Spec Graj-iPom

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| ScMi ) LiMrHodM |

FIGURE 4.31(1)

ASPKN PLUSIM SIMUI.VriON OF CHEMIC-VI PL\NTS 217

uMiei | i ibj I nhlit Hhi J "

I >I = |h| I Ji r -i i i nr -i -m \ m

1

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a

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FIGURE 4.31(m)

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i..

gr>i

re

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1

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FIGURE 4 31(n)

218 PROCESS SIMULATION AND CONTROL USING ASPEN'

1 M


As we press Next button, Aspen Plus displays a message as shown in Figure 4.32. Sincethe data entry is fully complete, the simulator seeks user permission to run the program.

Dltfiui j | fricl gj n\'(\%\**\<W\ H "I >! |h| ] v| gji r i-i i: nr mei i iai

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a

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raijc«rBf<tir:)r»ir>J Tc-BrtfBior* .nom'

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Rj in if.- rcn'

01t 1 1

STREAMS

lonnt/SplilUK |

1 Mew -SSpi

I rjOap:a4 t rjstfi Ware j jjte«". rtata MgM A>pm Ptu. - Sn-AW

FIGURE 4.32

As we hit O-K button on the message, the Control Panel window appears as displayedin Figure 4.33. It usually shows errors, warnings, convergence status, etc.

gaBSBEsai*) £ Cm IceM umj WrDo* m» 4uS

'

» .» %w,cj - lilSSEi

J £

FIGURE 4.33


Viewing results

Choose Results Summary /Streams in the column at the left side and rearrange the table toget the results in the form as shown in Figure 4.34

. Save the work positively at this moment.

_ _

r -i i I'-f -i HOI

jaTS i »M«Hr- ..|.|_.|n.|

il .1 .

'

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-

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io)A«tf j lb. 4«'

4'

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i axns ob (SB? ? 00 00

00 | BU wn"

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49 Q0 M 00 30-

51 H»»r ."IT 1583

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1 <«U< I UVMMW ]

Hmmt AMkw Kffto MTHM5T

FIGURE 4.34


To obtain the input information of the present project, select Input Summary from theView dropdown menu (see Figure 4.

35).

UK* e: umeI o«t.».'

sntew CiiM

."n -ncw cl2 y>. ctorn'tr*

UOC. BiO MT,«j

FIGURE 4.35


SUMMARY AND CONCLUSIONS |In the previous chapters, we have studied the steady state simulation of a large variety ofindividual process units using Aspen Plus package. In the present chapter, several chemicalprocesses have been assembled to develop the chemical plants and those plants havebeen simulated subsequently. The solved examples include a distillation train and a vinylchloride monomer unit. In the second example, the loop is closed by a recycle stream,whether in the first unit, there is no such complicacy. However, the straightforwardapproach to simulate a flowsheet is that after developing the process flow diagram in theflowsheet window of Aspen Plus, we can simply use Next button for data entry. As wereceive the message of Required Input Completey we can move on to run the simulation.In the next two chapters, we will study the process dynamics and closed-loop control of

flow-driven as well as pressure-driven processes using Aspen Dynamics package.

PROBLEMS|4.1 A hydrocarbon stream with component-wise flow rates, shown in Table 4.4, enters

the isentropic compressor at 120oF and 1 atm. The compressor has discharged thevapour stream at 3 atm.

TABLE 4.4


10

95

150

n-C4

25

/i-C3

10

n-C6

100

The complete process flowsheet for flashing and stripping operation is shown inFigure 4.36. The flash drum (Flash2) runs at 1250F and 2.8 atm. The stripper(STRIP2) has total 6 stages (including condenser and reboiler) and bottoms tofeed ratio (mole basis) is 0.8. The feed stream to the stripper is introduced abovethe top stage and the pressure throughout the column is 2 atm.

I 0 1

COMPRESS FLASH

V24

STHiPPER

FIGURE 4.36 A flowsheet for flashing and stripping operation.

CopyHghlod material

ASPEN PLUS SIMUIJUION OF CHKMICAL PLANTS 221

Using the UNIQUAC property method, simulate the plant to compute the productcompositions and flow rates.

4.2 A ternary mixture, as shown in Table 4.5, is fed as stream H at 100oF and 290

psia to a pump Pi employed to increase 20 psi pressure.

TABU 4.5

Component Flow rale (Ibmol/hn

500

300

" r 11, 10

The stripper (STRIP2) has total 100 stages (including condenser and reboilenwith a reboiler duty of 107 Btu/hr Stream F enters above 70th stage and StreamR) mien above 1st stage. The top stage pressure of the stripper is 280 psiawith a stage pressure drop of 0.5 psi The intercolumn pump P2 has increased25 psi pressure The RECT column has total 120 stages (including condenserand reboileri with a reflux ratio (mole basis) of 10 and a bottoms to feed ratio'mole basis) of 0.6. Stream Dl enters below 120th stage. In the simulation,consider condenser pressure of 275 psia with a pressure drop of 5 psi and astage pressure drop of 0.1 psi (see Figure 4.37).

-

.

0-0

PI 8TRIP2 ' w"

FIGURE 4.37 A flowsheet of a propylene-propane mixture separation process

Applying the RK-Soavc thormodynamit mod* I

(a; simulate the above propylene propane mixer Beparation plant and report theproduct compositions, and

(by perform the seneitivity aaalysifl to observe the effect of the second columnefficiency varied from 20'/. to 10091 on the propylene mole fraction in thedistillate


4.3 The hydrogenation of aniline produces cyclohexylamine in a CSTR according tothe following reaction:

CgHgNH;, + 3H2 -) CgHnNHsaniline hydrogen cyclohexylamine

To simulate the aniline hydrogenation process using Aspen Plus, we develop theprocess flow diagram as exhibited in Figure 4.38.

C>-I ANILINE

PUMP

FA

C>-| HYDROGEN I-I

S-o

El -CD-

CSTR

COMPRESS

FIGURE 4.38 A flowsheet for aniline hydrogenation.

The reactor model (RCSTR) operates at 580 psia and 2480F, and its volume is1200 ft3 (75% liquid). For the liquid-phase reaction, the inlet streams have thespecifications, shown in Table 4.6.

TABLE 4.6

Stream Temperature Pressure Flow rate(0F) (psia) (Ibmol/hr)

ANILINE (pure aniline)

HYDROGEN (pure hydrogen)

95 100 150

12 100 600

Both pump and compressor (isentropic) have discharged the fluids at 585 psia.Data for the Arrhenius law are given as:

Pre-exponential factor = 5x 105 m3/kmol . s

Activation energy = 20,000 Btu/lbmol

[CJ basis = Molarity

Use the SYSOPO base property method in the simulation. The reaction is first-order in aniline and hydrogen. The reaction rate constant is defined with respectto aniline. Simulate the process and compute the component mole fractions inthe liquid product and the vent stream.

4.4 The process flow diagram for an azeotropic distillation process is shown inFigure 4.39. The technique involves separating close boiling components(acetic acid and water) by adding a third component (vinyl acetate), called an



entrainer, to form a minimum boiling azeotrope which carries the water overheadand leaves dry product (acetic acid) in the bottom. The overhead vapour iscondensed and then separated in the decanter into two liquid phases: the organicphase and aqueous phase.

DECANTER

VA

1 FEEDf

DIST1 VA-RICHh

HW-RICHh

AA

RADFRAC

FIGURE 4.39 A flowsheet of an azeotropic distillation process.

A feed stream, namely FEED, enters above 15th stage of the azeotropic distillationcolumn at 330oF and 90 psia in addition to the flow rates, shown in Table 4.7.

TABLE 4.7

Component Flow rate (Ibmol/hr)

acetic acid

water

2700

500

The entrainer, VA (vinyl acetate), with a flow rate of 455 Ibmol/hr enters above12th stage of the column at 200oF and 100 psia. The azeotropic column (RadFrac)has the following specifications:

Number of stages (including condenser and reboiler): 55Condenser type: totalValid phases: vapour-liquid-liquidReflux ratio (mole basis): 4

Bottoms rate: 2700 Ibmol/hr

Condenser pressure: 66 psiaColumn pressure drop: 12 psiKey component in the second liquid-phase: waterStages to be tested for two liquid-phases: 1 to 55

The specifications for the decanter model are noted below:

Pressure: 50 psiaTemperature: 110oC

Key component in the second liquid-phase: waterUsing the NRTL-RK thermodynamic model,

simulate the process to compute thecomponent-wise product flow rates.


4.5 A hydrocarbon stream H is at 50C and 2.5 atm. The pump has discharged theliquid feed F at 5 atm. The component-wise flow rates are shown in Table 4.8 forstream H.

TABLE 4.8


C3

35

50

i-C,

130

n-C4

200

'-c5 180

n-C5 200

n-C6

5

In Figure 4.40 the schematic representation of a hydrocarbon separation processintegrated with a Pump, three DSTWU columns (Cl, C2 and C3) and two RadFrac(RECT) columns (CR1 and CR2) is shown.

G1

PUMP h

CRT

C3

DRl DR2

CR2

BRI

BR2|-0

C2

B3 | C1 B2}<>

FIGURE 4.40 A flowsheet of a hydrocarbon separation process.

AH DSTWU fractionators have total 20 stages (including condenser andreboiler) and two RECT models have 10 stages (including condenser and reboiler)with no reboiler. The specifications, shown in Tables 4.9(a) and (b), are requiredfor simulating the process.

«PEN PLUS SIMULXTION OF CHKMICAL PLANTS 225

TABLE 4.9(a)

* Recovery of LK/HK in distillate Pressure (atm)

Block Lighi key Heavy kev Condenser (type) Reboiler

IK (HK)

Cl 99 of r»-C4 1% of i-CB 4 (partial condenser with 4

all vapour distillate)C2 99* of t-C4 21 of n-C4 1

.5 (total condenser) 1

.5

C3 99* of 1-C5 4* of n-C5 3 (total condenser) 3

TABLE 4.9(b)

Block Condenser Distillate to feed ratio Pressure

(type) (mole basis) (atm)

CR1 Partial vapour 0.2 2

CR2 Total 0.5 15

Applying the Peng-Robinson property method, simulate the separation processto compute the flow rates and compositions of all product streams.

4.6 An inlet Stream H supplied at SOT and 300 psia is compressed to 4000 psia bythe use of an isentropic compressor Bl. Stream H has component-wise flow rates,shown m Table 4.10.

TABLE 4.10

Component Flow rate (Ibmol/hr)

mtrogen 100

hydrogen 300

ammonia 0

carbon dioxide 1

A flow diagram for the ammonia process (Finlayson, 2006) is shown in Figure 4.41.

B '

m-<

H-

0 H"

ED-0

Bl B2 B3 84

FIGURE 4 41 A flowsheet of an ammonia process


Stream Fl is mixed with the recycle stream F8 in a mixer block B2 operated at4000 psia. Before introducing into the reactor, the mixer effluent F2 is heated inblock B3 to 900oF at 4000 psia. Note that the reactor (RGibbs) B4 runs at 900oFand 3970 psia. In the next, the reactor outlet F4 is cooled in a heat exchangerB5 operated at 80oF and 3970 psia. The flash drum (FIash2) B6 produces StreamsBl and F6 at 80oF and 3970 psia. In the subsequent step, Stream F6 enters thesplitter (FSplit) B7 and 0.01% of it is used as purge. Finally, an isentropiccompressor B8 has discharged Stream F8 to the mixer block B2 at 4000 psia.Using the NRTL thermodynamic model and the Newton's iteration method (fromthe Data Browser, choose Convergence/Conu Options), simulate the ammoniaprocess to compute the component-wise flow rates and compositions of all streams.

REFERENCES |

Finlayson, B.A. (2006), Introduction to Chemical Engineering Computing, 1st ed., WileyInterscience, New Jersey.

Seider, W.D., J.D. Seider and D.R. Lewin (1998), Process Design Principles: Synthesis,Analysis, and Evaluation, 1st ed., John Wiley & Sons, New York.


Part III

Dynamics and Controlusing Aspen Dynamics1

CHAPTER

Dynamics and Control ofFlow-driven Processes

5.1 INTRODUCTION

Dynamic -imulation of a chemical process greatly helps to understand the transientbehaviour Aspen Dynamics , which is tightly integrated with Aspen Plus , is widelyused for process design and control. This powerful simulator can automatically initializethe dynamic simulation using the steady state results of the Aspen Plus simulation.

Interestingly, when the file containing the flowsheet is opened in Aspen Dynamics,the

default control structures are already installed on some loops. Usually, level, pressureand temperature controllers are included where appropriate However,

these default

control schemes can be modified or even replaced with other suitable control loopsavailable in Aspen Dynamic- package Note that there is a scope to include someadditional controllers for the used process Moreover, this simulation tool provides agraphical environment to show the process response.

To convert a steady state simulation into a dynamic simulation,there are several

items that should be taken care of For example, the size of all equipments must bespecified and the control structures must be devised For steady state simulation usingAspen Plus, the size of the equipment is not needed, except for reactors. On the otherhand

, for dynamic simulation using Aspen Dynamics, the inventories of materialcontained in all the piece* of equipment affect the dynamic response.

Therefore, the

physical dimensions of all process units must be known.When the steady state Aspen Plus simulation is exported into Aspen Dynamics, we

need to choose either simpler flow-driven dynamic simulation or more rigorous pressure-driven dynamic simulation Pres

.

-ure-driven simulations include pumps and compressorswhere needed to provide the required pressure drop for material flow Control valvesmust be installed where needed

, and their pressure drops selected For flow-drivensimulations

, however, no such arrangements are required.

229


In the present chapter, we wish to study the dynamics and control of the flow-driven processes. For this intention, we choose a reactor (RCSTR) as well as a distillationcolumn (RadFrac) example from the model library of Aspen simulator.

5.2 DYNAMICS AND CONTROL OF A CONTINUOUS STIRRED TANK

REACTOR (CSTR)

Problem statement

Ethyl acetate is produced in an esterification reaction between acetic acid and ethyl alcohol.

A feed mixture, consisting of 52.5 mole% acetic acid, 45 mole% ethyl alcohol and2.5 mole% water, enters the RCSTR model with a flow rate of 400 kmol/hr at 750C and1.1 atm. The reactor, as shown in Figure 5.1, operates at 70oC and 1 atm.

Both the reactions are first-order with respect to each of the reactants {i.e., overallsecond-order). For these liquid-phase reactions, the kinetic data for the Arrhenius laware given below:

Forward reaction: A = 2.0 x 108 m3/kmol s

S = 6.0 x 107 J/kmol

Reverse reaction: k = 5.0 x 107 m3/kmol . s

£ = 6.0 x 107 J/kmol

Composition basis = Molarity

Here, k is the pre-exponential factor and E represents the activation energy. The reactorgeometry data are reported below.

Vessel type: verticalHead type: flatDiameter: 0,45711 m

Volume: 0.15 m3

(a) Simulate the reactor model using the SYSOP0 thermodynamic model to computethe product compositions.

acetic acid + ethyl alcohol ethyl acetate + water

FIGURE 5.1 A flowsheet of a CSTR

Copyrighied malerial

)YNAMICS AND CONTROL OF PI.OW-DHrVKN PROCKSSKS 231

(b) Report the default controllers tuning parameters and control actions used, andconstraints imposed on variables.

(c) Investigate the servo performance of the default liquid level and temperaturecontrol algorithms and discuss the effect of loop interaction.

(d) Show the regulatory behaviour of both the controllers in presence of disturbancein feed temperature.

Simulation approach

(a) To open the Aspen Plus Startup dialog box. click the desktop Start button, thenpoint to Programs, AspenTech, Aspen Engineering Suite, Aspen Plus Versionand then click the Aspen Plus User Interface. Let's select the option withTemplate and then click OK (see Figure 5.2).

aWHl 1 I M*l oKlfcl MwiH -| I I I -I JL .H ! -i I i

-

o-tt rt m mots; am-

bHftmm 1 ; :_ tm

FIGURE 5.2

As the next window appears (see Figure 5.3), it is appropriate to select Generalwith Metric Units and hit OK button.

Here we use the simulation engine at 'Local PC When the Connect to Engine dialogpops up (see Figure 5.4), press OK. Note that this step is specific to the installation.

Creating flowsheet

The process flow diagram, shown in Figure 5.5, includes a reactor, namely RCSTR,with an incoming FEED stream and an outgoing PRODUCT stream.

Copyrlghiod material


E

Fot Help,

prws Fl

Start I r-

Nil Zl, _

iJ_l J JI I 1 1

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.

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,

G*n*rai wth English IJhta

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L FhamaceuticalaH Polymefs Mh Engis

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f. P,TT>fr«*atu / /.-eh£jj P>n)fr«(arur3y /. (h

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j j]Ch lei-5-Migiiio(IW | aw 2 - MCTtcB W . | - Aijob«/tarotei Pro(ett . | Aepoi Pka

FIGURE 5.3

111

Connect to Engine

Server type:

User Info

Node name:

User name:

PassiAiord:

Working directory:

Local PC

n Save as Default Connection

OK Exit Help

FIGURE 5.4

PVNAMICS AND CONTROL OF FLO\V DRl\-EN PROCESSES 233

M.rn,-» 1 « I I ---

-

- -;

e i i i y s a'

.*» MB Mtet acsT» ie«o-

.

i-

-

-

FIGURE 5.5


Hitting Next button, we get Global sheet of the Specifications form under Setup folderin the left pane of the Data Browser window. Enter the Title of the present problem-"Dynamic Simulation of a CSTR'. change the Input mode from 'Steady-State' to "Dynamic"and leave the remaining items at their defaults. The window looks like Figure 5.6.

* a

jLr~i

?,).!

.,81 V

3 I 1 !-! -'in: q >!i.

4-

ia

Km "ttm "CT on

js- b

FIGURE 5.6


In the next window, as shown in Figure 5.7, the Aspen Plus accounting information

required at some installations are provided.

_j_

r I I I [»" -I M I MHi _l 3 J J

O r-.i* - -

© Mm >-O R»MOttor#

i-

/GbUI] /OWbMoP -/AtcountIngj Di mn'ci |1 . PVil i . tr. I . " .

Accouxlrurbar

PrcrKtraw fr-OUH WISH

lnoMtCflinpi<»

[V Hm>iA(«m j $etur*» j --v . I C(*ftm RMEton | PreiMeChange | Marv ai j Sokb | UwMoiw |

STREAMS'

RSttK nvdd REtwl RGbb. RCSTR RPKi Rewch

For **> cr-u Ft C \ a FoMan'Aoen »us 11 NOM RwpM b ot ntr --

FIGURE 5.7

In the subsequent step (see Figure 5.8), select Stream sheet with opening the ReportOptions form under Setup folder and include Mole fraction item.

. tfe E* V1e» 0*4 '<xk Rn ftM Ufmy WMoh -.

1 hi .JSlal _Ji r-1 i i nr i -m \ |a! «|».|

-

3 »| j ,| H.|

0 RVMlOIMm

.

_l -r. - - -.

. Jj

P Gtf«<a(e»ii»xlsrJ*Mn-feKirt

tam'o br rcUM r lDcmti itpvt

iWhua Fi«cMntt*m

P Malt P Mole

r Urn* r Mm.

TIT fGEfTM

-CH

fffaM ftt PQbt. RCSTR HPhg ftfiad.

- s -

FIGURE 5.8

DVN VMICS AND CONTROL OF FLOW-DRIVEN PROCESSES 235

Specifying componentsIn the Data Browser window, choose Components /Specifications to obtain the componentinput form. Filling out the table with the components (acetic acid, ethanol, ethyl acetate andwateri involved in the present reaction system, the screen looks like Figure 5.9.

I

MM - . -

E-sC

aun

i 1

I*

cmt : ffstnc ff/wa w&mh ai:s,

Tft,,.

Re3''>

8 § O O.

* - -« MUM

FIGURE 5.9


Choosing Properties /Specifications in the column at the left side, one obtains theproperty input form. As shown in Figure 5.10, we use the SYSOPO base property method.

-

'KW -U MSI *) nKI*M-aH 1 3)

i.|jrrxl

9 «-.*«

. 2

I 8 y Ki)HflUwj Wfate ffft* t COM, hc IP

FIGURE 5.10



Use the Data Browser menu tree to navigate to the Streams/FEED IInput ISpecificationssheet. Specifying the FEED stream by its temperature, pressure, flow rate andcomposition, we have this window, shown in Figure 5.11.

o-j-

u l-w

-

-

3 ***** 1-

-

3

.3

I "in

T 3

('- * zh-i= 3 -

pr (n -%\I J

3 (.-. j| 3

> > Mat l«

FIGURE 5.11


In the list on the left, choose Blocks IRCSTRISpecifications to obtain the block inputform. It is filled with the given data as shown in Figure 5.12.

-o--#

.l-s-g-Q-m-g- j

'T*4m ! . » Iff ..-*-. |.;a .l»-. |<j w> r

FIGURE 5.12



Use the Data Browser menu tree to navigate to the Streams/FEED IInput ISpecificationssheet. Specifying the FEED stream by its temperature, pressure, flow rate andcomposition, we have this window, shown in Figure 5.11.

o-j-

u l-w

-

-

3 ***** 1-

-

3

.3

I "in

T 3

('- * zh-i= 3 -

pr (n -%\I J

3 (.-. j| 3

> > Mat l«

FIGURE 5.11


In the list on the left, choose Blocks IRCSTRISpecifications to obtain the block inputform. It is filled with the given data as shown in Figure 5.12.

-o--#

.l-s-g-Q-m-g- j

'T*4m ! . » Iff ..-*-. |.;a .l»-. |<j w> r

FIGURE 5.12

DYNAMICS AND CONTROL OF FLOW-DRIVEN PROCESSES 237

In the next step (Figure 5.13), select RCSTR I Dynamic! Vessel sheet under Blocksfolder and enter the reactor geometry data.

LMf ***** -**

JUIBI_

U 51 nMi>H<H 3 I H .-J JJ -1 Ji r i i i fv i lei I Pi 3>M

.i

J

STftfAMS WSw ffr-ipd Wgu* HGfcbi RCSIfl RPfc i BBwt*

C gUdms iw Pk* 111 MJU %

FIGURE 5.13

The forward reaction as well as the backward reaction is represented with theirstoichiometric coefficients and exponents in two sheets, shown in Figures 5.14(a) and (b).

J l-i I IT .1 .IBI I IBI.

J

_l ***

gff Vftrtc:

"ti »i nl i « !

EAC

.

ll

-CH-.1-0 LIZ U

FIGURE 5.14(a)


Mai_

1J Mffli MJ ahlahNN 1 Jl .! I"i _J El M Mi r i i i nr i m I issi

UMFAC Grows;

-

J 0"

Prop Sett

3 -"EEC_j PRODUCT

3 Becks. J/j 3CSTR

_j Ow stry

- Resctcr:

w R-lJ t eti e

71 f. .1 I .1 I .<lr:--7i »i nl «i uf\

Reaction No fyTReadmit Pto<k«<t

Compgnert EKpononi Cofr wrKf* '.v-

'i-.

-rv

1 V-

1

i

ll -

STREAMS flSloe RYidd.

REqul RGbtu FiCSTR March

FIGURE 5.14(b)

The power law data for both the reactions provided in the problem statement areentered in the two Kinetic sheets shown in Figures 5.15(a) and (b)

, nt Edt '.' en Can Toot Pir. fU Lfeery Wrxto-. He*

ar -i MM <<||AI~

3 »l o\s/Sto-Jwnwy *Kinebc| : - |

;'

| He«yG)mt>sUfUF Grauo*

}l) AA- EAL-) EAC . VATER d

- J/i Zcrvij&

| PIBpctfN

fiwc Cte, | . -J

; r«*c(actor.)jr/To/'e-(E »'/I'l/ro)

; k. 200000000 ["

Wi "

.

.. a P«* en i E::

_l 0**

> ) FEED£ PRODUCT

1 SCSTRy Reacscoi

_J Ow-wy-

- nn miiii

To- I(qi«w.

.

SIRtAHS

J- 90

FIGURE 5.15(a)


. «

-.- 1 3

I I

r

f " If Till I | MME->w. I C3k-s RMcMn | Ck . | IHD->

st e -' py.>- pew «ac cstr

FIGURE 5.15(b)

The status indicator in the above window reveals by the message Required InputComplete that no more input specifications are required to run the simulation.

Running steady state simulation

As we click on Next button to continue the simulation, the Required Input Complete

dialog box appears. Hitting OK on the message, we are displayed the Control Panelwhere the simulation messages during the run are recorded (see Figure 5.16).

- ?!

-MM

iT*0»r. Kmm. Pif W ji

i i Q D| -ii?»i u -J- I .ic- .i-a.-i. || .n, am, .. .. -_ |. «ij

FIGURE 5.16


Viewing steady state results

In the next, select Solver Settings, choose Results Summary /Streams in the list on theleft and finally get the steady state results as shown in Figure 5.

17.

.

'.md.m.x. 1 - |Ftei.*« Sumn»r Sreano - DUit Browser)

f Fte &» »ew D*> Todj Run Lbraiy WMow Htjp

as

3fl

Setup

Omponeras

Streams

Bocks

Reacts

Ccr.v«gefK«'

1 Conv Options£0 Conv Options

O S«up0M0 Bsslc

OMOAdv

lSSQP Base

LSSQP Ad*

ooo0Tear

1 Convei enceConv Ortef

Q| SequenceRowsheetng CtouonsModel Analvsis Too

EO CcHgurationP«Rit5 Summaiy

Q Run StatusQ Streams

Convetgence

1 I I 1

Displw"

3 foumi r~

3 Stie«mTatile|

4 1 d 1 d

Volume Flow cumyhi 24.497 24 01S

Enthalpy MMkcal/hi .35035 35 951

Mole Flow km*hi

M 2ia0CB 87110

EAl 180.000 57110

EAC 122,890

WATER mooo 132.890

id* fan

AA 0.525 0 218

EAL 0.450 0

.143

EAC 0.307

WATER 0.025 0

.332

JdllResults Avaisse

Mstets/SpittM! | Seoatatois | Heat Enchangeis \ Cokmra Hoactoti | Pressuie Chatlseis ] Minipulatois ) Sofds | Usei Models |

STREAMS ' RSIok: RYieM REqui RGibbs RCSTR RPlug RBalchRofHeb.ptessFl

. 1 . S -U-E-U- iC;\ .gFolde<s\A9penPlu3l1 1 : NUM

| j£]Oaiaer5-McmsollW..| 4]Cha(»er2-Wt!roseilW...|| Aspen flu. - SIimSI.. Adohe tolal Pntesai |« iS?t}); 1545

FIGURE 5.17

(b) Exporting dynamic simulation: In the subsequent stage (see Figure 5.18),we wish to carry out the simulation dynamically. Accordingly, at this moment,we have to follow the sequential steps noted below:

Click on Export from the pulldown File menu or simply press Ctrl+E on thekeyboard.Open the Drive and then Folder where we want to save the work as a file.Type 'ChS

.

S RCSTR' in the File name field.Choose 'Flow Driven Dyn Simulation (*.dynf & *dyn.appdf)' from the optionsavailable in the Save as type box.Finally, hit Save button.

Also, save the work done as a backup file (e.g., Ch5_5.2_RCSTR.bkp). We may usethe same folder within which the exported dynamic simulation file is saved. Originally

many files are saved along with the backup or dynamic file. Anyway, we are now ready

to run Aspen Dynamics and we may quit Aspen Plus.


9 Ljii=v.Tt*-

CJ OmwrngntCan***

I Pc««-««r«; Ctt '-*| M«W .V*** Tn»»

Jjj

.I I3 ±ljili<JF; »l jlalH

**, MW

-

M

EAL

WATER

I

.1 ,1-

SrniatTi r irTi i -o/r«Caned |

8 . S -O'll-O-cvi

| 0>»l»5-rfco...| *]am2-«*n,. \.*]Mll<m,-lic..\\ <»«,PIU.-C , '; teJu ft |'« igsj

FIGURE 5.18

Starting Aspen Dynamics

As we click the Start button, point to Programs, then AspenTech, then Aspen Engineering

Suite, then Aspen Dynamics Version and then click on Aspen Dynamics, a blank dynamicsimulation window appears as shown in Figure 5.19.

f*e Eat Tood ftowtfiMl Rr. VMoh Hcb

D H S Q W |Sl»dySl.lc j-J3

It*- Lfcr- f,:*.»

r «-Jt c ioos j a, k it

.

Jaw

FIGURE 5.19


Opening existing simulation

To open the flow-driven dynamic file, select Open from the File dropdown menu orpress Ctrl+O on the keyboard. In the Open dialog box, locate the drive, then folder and

finally the file 'Ch5_

5.2

_

RCSTR' (see Figure 5.20).

ij is H *»Q IS

UIMl r »-- SSmJatn

> Ft OinMITKt

l-llff. |.|9. HT» H.

Chi_

5i_CSTR !;

i

Ch5_EJ

,BCSTB

£l Hi

5*«» ICM

.

U.

f.ITS | CWn |

Opin

B i -r

FIGURE 5.20

As we press Open button, the process flowsheet consisting of the automaticallyinserted level (LCI) and temperature (TC2) controllers appears (see Figure 5.21).

fte &* Urn Twh HswhMt «jn Wr4» rtft

-

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FIGURE 5.21

DYNAMICS AND CONTROL OF FLOW-DRIven PROCESSES 243

Details of the two control loops, to be used finally, are given below.

Loop 1

Controller: LCI

Type of controller: proportional (P) onlyControlled variable: reactor liquid level

Manipulated variable: product flow rateController action: direct

Loop 2

Controller: TC2

Type of Controller: proportional integral (PI)Controlled variable: reactor temperature

Manipulated variable: heat duty (cooling operation)Controller action: reverse

Note that the direct acting control system increases the output signal as the inputsignal to the controller increases. On the other hand, as the input signal to the controlstructure increases, the output signal from the controller must decrease for the case ofreverse acting control strategy. The direct acting control law has negative gain andincrease/increase (or decrease/decrease) term is commonly used to represent it.

For the

reverse action, increase/decrease (or decrease/increase) term is used and controller gainhas positive sign.

The reactor flowsheet includes two (LCI and TC2) single-input/single-output (SISO)control loops. Therefore, we can say that this is a multi-input/multi-output (MIMO) orsimply a multivariable closed-loop system.

In Aspen terminology, the process variable or controlled variable is denoted by PV,the set point is represented by SP and the controller output or control variable ormanipulated variable is abbreviated by OP.

For the example CSTR system, level and temperature controllers are automaticallyimplemented when the Aspen Dynamics simulation is created.

The default values forSP

, PV and OP are computed from the steady state simulation. To achieve better closed-loop process response, the Aspen-generated control structures can be modified or evenreplaced by the suitable control schemes available in the control library of Aspensoftware

. In addition, the default values for controller tuning parameters, such as gain,integral time

, derivative time, and so on, can also be changed.

Most of the control strategies are easily tuned by simply using heuristics. As

suggested by Luyben (2004), all liquid levels should use P-only controllers with a gain

of 2. All flow controllers should use a gain of 0.5 and an integral time of 0.3 minute

'also enable filtering with a filter time of 0.1 minute). The author also mentioned thatthe default values in Aspen Dynamics for most pressure controllers seem to workreasonably well

. But temperature controllers often need some adjustments.

Viewing default values of variables

In Aspen Dynamics, the steady state values of process variable and controller outputar displayed in a table

. At this stage,the set point value, displayed in table, shown in


Figure 5.22, is same with the value of process variable. To show the results table ofloop I, highlight the controller block LCI, press the right mouse button, go to Formsand then select Results.

-

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a

El &m £

- (M M Has M ! ! i lull aw M-M

11 ..1 in

FIGURE 5.22

We can have the same information in a faceplate, shown in Figure 5.23, simply bydouble-clicking on the block LCI. But as a difference, the units are not mentioned herewith the values of SP. PV and OP.

.

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umar

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urn

FIGURE 5.23

Gopyngt-


Similarly, we have the results table, shown in Figure 5.24

, for the temperature loop 2.E3B

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ilation has 36J variablea 2(,0 equations and 91

FIGURE 5.24

Modifying controller tuning properties

First we need to open the sheet that contains the controller tuning information. To doso for the level controller, highlight the controller block LCI, press the right mousebutton, point to Forms and then select Configure (see Figure 5.25).

|iirjf;j>,l'l. fi S I PPQ UCI l-Q

r,.-:n-

.

rwutlolis'm* bo' .tiHinatad be aus* they had residuals over J»-00?oi IH equ»ii2rii (5'.J weie elmir.sted

LMien has HI *ui»tUi ito equiitjdni ar.d 'ifie

O-j ct Ij JOgggj j j Jctf Voty P-Vet || l Aspen gh f* J - * ,stM

FIGURE 5.25

246 PROCESS SIMULATION AND CONTROL USING ASPEN"1

Alternatively, to obtain the Configure dialog box, first double-click on the controllerblock LCI and then click on Configure symbol (yellow colour) in the faceplate as shownin Figure 5.26.

ll(i*H«a IS {Dyn.mlc 3 mvo t: tin a 13

I

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O

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Istion has J63 vortabies HO equations and 969 non-zeros

3

Ml

FIGURE 5.26

By the similar way, we obtain the tuning data sheet, shown in Figure 5.27, for thetemperature controller TC2.

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FIGURE 5.27


Note that the default Operator set point value is the steady state value of the processvariable (PV). The reactor liquid level is the PV for loop 1 and reactor temperature forloop 2. Bias signal is the output from the controller when the error (= SP-PV) is zero.From the results tables shown earlier, it is obvious that the error is zero for both loops.Therefore, Aspen Dynamics has set the value of OP as the bias value.

The proportional integral (PI) control methodology is automatically installed withdefault values for the controller gain (= 10 %/%), integral time (= 60000 minutes) andderivative time (= 0 minute) to monitor the reactor level. However, as mentionedpreviously, the proportional-only controller with a gain of 2 is sufficient to effectivelycontrol the liquid level. Remember that to make the integral action inactive, we canuse a very large value, for example 105 minutes (even the default value of 6 x 104minutes may also be accepted), for the integral term. For loop 1, the controller actionshould be 'Direct' as set by default (see Figure 5.28).

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Step 3074 Tiw 6 2504«+001 step size- 5 OOOOe-002 step facto 1 5000e+000 accepted

j

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Wggg [ ' Adotoc Vrote P.o<mc

FIGURE 5.28

In loop 2, we prefer to employ the proportional integral controller to monitor the

reactor temperature. In data sheet, shown in Figure 5.29, the default values are given.

The TC2 is truly a reverse acting controller. However, we may adjust the values ofcontroller tuning parameters (gain and integral time) during the closed-loop study ifthe control performance is not satisfactory.

Modifying ranges for process variables and controller outputsIn the Configure dialog box, hit the Ranges tab and get Figure 5.30 for level control loop.

248 PROCESS SIMULATION AND CONTROL USING ASPENIM

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--w-lPRoSucrt-H.

,.

alftulation ready for solutionequations were not eliMinated because they had residuals ever le-OOS

k total ol 109 equations (29 S'-i) were eliminatedSimulation has 363 variables 260 equations and 968 non-zeros

3

Rea*-

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-

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FIGURE 5.29

ftfts -n Dyn-wwca Ch5_5 2_HCSlH.dyrfBe Wew Tao* Run Wndow Help

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Simulation ready lor xoluiionequations were not eliminated because the? had residuals o*t

i total of 109 equations (29 S'O were elminated"

mulaiion has 36} rarimbles 260 equations and 989 nae~:ero«

-

3

I UCh e'M ty«m>ce«a

FIGURE 5.30


As shown in Figure 5.30, the default ranges for both the process and output variablesare too large (± 100% of the steady state values)

. It may be practical to consider thefollowing constraints.

Process variable

Range minimum: 0.6855 m (25% subtracted from steady state value of PV)Range maximum: 1.1425 m (25% added with steady state value of PV)

Output

Range minimum: 15812.7 kg/hr (25% subtracted from steady state value of OP)Range maximum: 26354.5 kg/hr (25% added with steady state value of OP)

Entering these upper and lower bounds, we have the window, shown in Figure 5.31,for the level controller.

ftv Ut» Wnd?* He«

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l-wtions <"-ie nol elikinst«d Ivrrsuse they had residuals over le-OOSh total ol 109 equations '29 S;| vete .Uaiaat«dStTOlation has H'i v«ri*&lM 260 aqtrnttoM end 989 iior-:eros

Vital iV«nw:*00(

FIGURE 5.31

Again the typical ranges for the temperature control loop are noted here.Process variable

Range minimum: 52.50C (25% subtracted)

Range maximum: 87.50C (25% added)

Output

Range minimum: 1.1447 MMkcal/hr (25% subtracted)

Range maximum: -0.

6868 MMkcal/hr (25% added)

The corresponding Aspen Dynamics window is shown in Figure 5.32. It is worthy to

mention that the negative value of heat duty reveals the cooling operation (heat removal).


o * y . a m w |n,..mic

'9

,r ..- j 1 1«t5) |MMlS3R

, .

Editing Siaulacion

Validation coBplete

urrent snapihois havo been saved to 11 le (r-pAflOOO anp

i- I

FIGURE 5.32

i

Both the control algorithms are completely specified above. In the next, the controllerperformance will be examined in terms of set point tracking (servo) and disturbancerejection (regulatory).

(c) Starting the Run: Before running the program, we must be accustomed withsome frequently used items of the toolbar as described in Figure 5.33.

Step Re-start Simulation

*c 601 lacJt R» Wnto*

.IMJSI

Run Pause Rewind to a saved Snapshot

FIGURE 5.33


We wish to carry out the simulation for a certain time, say 5 hours. To fix up this

time period, select Pause At from the Run pulldown menu or simply press Ctrl+F5 onthe keyboard. Then select Pause at time, type 5 in the field or whatever we want andclick on OK (see Figure 5.34).

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FIGURE 5.34

Viewing servo performance of LC1

As we double-click on LCI block in the flowsheet, first the faceplate appears. In thenext, press on Configure and Plot symbols in the faceplate. Alternatively, to open thefaceplate. Configure dialog box and ResultsPlot dialog box, first select LCI block, thenchoose Forms and subsequently press one-by-one on faceplate, Configure and ResultsPlot,respectively. Judiciously arrange all three items within the Aspen Dynamics window(see Figure 5.35) so that we can properly observe them together.

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FIGURE 5.35

252 4- PROCESS SIMULATION AND CONTROL USING ASPEN

First make sure that all the items in the Configure dialog box and faceplate arecorrect. In order to execute the dynamic closed-loop simulation

, click on Run button inthe toolbar. During the simulation run, give a step change in the set point value ofreactor liquid level from 0.914029 to 1.1 metre at time = 1

.5 hours. Typing the new set

point value in the faceplate, press Enter button on the keyboard so that the Operatorset point value in the Configure dialog box also changes automatically to 1

.1 meterNote that the new set point must be within the specified ranges of PV, In Figure 5 36the servo performance of the level controller is depicted for 5 hours as selected earlier

Obviously, the plot also includes the manipulated input profile.

EC

DlSySa IE -V | Dynamic 3

! Rowsheet

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Run coaplete

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||

0 0.5 1 15 2 25 3 35 4 45 5

Time Hours1 5000e*ODO. MDCepted

Paused

FIGURE 5.36

Figure 5.36 represents an excellent set point tracking performance of the levelcontroller (P-only). Obviously, the LCI provides process responses with almost nodeviation from the desired set point value and with very fast approach to reach thetarget liquid level.

Notice that the above plot can be edited by right clicking on that plot and selectingProperties option or by clicking on that plot and pressing Alt+Enter on the keyboard.In the properties window, user can modify the title, axis scale, font and colour of theplot. Alternatively, double-click on the different elements of the plot and modify them

as we like to improve the clarity and overall presentation.Now, we will discuss the interaction of two control loops. When we introduce a set

point step change in the reactor liquid level, the LCI scheme attempts to compensate

for the changes through the manipulation of the effluent flow rate. This, in turn, willdisturb the reactor temperature and loop 2 will compensate by manipulating the heat


removal of the CSTR appropriately. Thus we can say that loop 1 affects loop 2. In Figure 5.37,Aspen Dynamics window demonstrates the loop interaction under the same set pointstep change (0.914029 to 1.1 metre at time = 1.5 hours) as considered previously.

PS rKjTj F=~

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FIGURE 5.37

Viewing servo performance of TC2

As described in Figure 5.38, open the faceplate along with Configure dialog box and ablank plot sheet. Before starting the simulation run, carefully check all entries in thefaceplate as well as Configure dialog box. In the next, choose Initialization run mode inthe toolbar and then run the program once. After completion, go back to Dynamicmode from Initialization mode (see Figure 5.38).

'fehj

FIGURE 5.38

Now we wish to conduct the servo performance study for the TC2 controller with twoconsecutive set point step (pulse input) changes in reactor temperature (70 -) 750C attime = 1

.2 hours and then 75 -> 70oC at time = 3 hours).


Clearly, the proportional integral controller with default tuning parameters values

shows a high-quality temperature tracking performance. As stated, if the performance

of any controller is not satisfactory, we have the option to tune the parameters simplyby trial-and-error method.

If we introduce a set point change in the reactor temperature, the TC2 controllertakes necessary action with adjusting the heat duty to compensate for the changes

.

But interestingly, the liquid level remains undisturbed. Figure 5.38 confirms this fact.

At this point we can conclude that loop 1 affects loop 2, but loop 2 does not affect loop 1.

Actually here the interaction is in a single direction.(d) Viewing regulatory performance of LCI and TC2: To perform the

regulatory study, we need to introduce at least a single change in the inputdisturbance. However, here we consider two subsequent step changes in thefeed temperature. Initially, the feed temperature changes from 75 to 80oC attime = 2 hours and then the temperature (80oC) returns to 750C after 1.2 hours

.

To change the feed temperature twice as prescribed above, first we need to openthe feed data sheet by double-clicking on the FEED block in the process flowsheet(see Figure 5.39).

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il I

1

S 0000e-002. step tactor* 1 S000»*000 accepted

| Jaae S Xerox* Wort || 'U Met* K bm PxAatr j

FIGURE 5.39

In the subsequent step, run the program with Initialization run mode. As it isfinished, go back to Dynamic mode. Then, open the plot sheets for both the controllers.The regulatory behaviour is illustrated in Figure 5.40 giving changes in feed temperature


in the feed data sheet. For brevity, the faceplate and configure dialog boxincluded in the Aspen Dynamics window, shown in Figure 5.40.

are not

2 a ts 7 I Dynamic

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scripts ] VUue | Unrrtr RM -WOO - Mf

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-

3

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FIGURE 5.40

It is obvious that the reactor liquid level remains unchanged with a change in feedtemperature since there is no interaction involved

.On the other hand, the reactor

temperature is disturbed.However

, the TC2 controller provides satisfactory disturbancerejection performance under this situation.

So far we have studied mainly the closed-loop behaviour of a reactor system coupledwith Aspen-generated control schemes. We did not include any additional controller withthe CSTR model

. In Section 5.3, we consider a distillation example to elaborate this point.

5 3 DYNAMICS AND CONTROL OF A BINARY DISTILLATION COLUMN

Problem statement

A partially vaporized binary mixture of benzene and toluene enters a RadFracdistillation model as displayed in Figure 5.

41.

he column has total 25 theoretical stages (including condenser and reboiler) andoperates at a pressure in the reflux drum of 18 psia and reboiler of 21 psia. The

ow rate is 285 Ibmol/hr and reflux ratio is 2.2 (mole basis)

.


Feed Specifications

Flow rate = 600 Ibmol/hr

Temperature = 225° FPressure = 21 psiaFeed stage = 13 (above stage)

Component

benzene

toluene

Mole %

45

55

FEED

TOP o

BOTTOM


In Table 5.1, the reflux drum and the base of the column (the 'sump' in Aspenterminology) are specified. It is fair to use an aspect ratio (length to diameter ratio) of2 (Luyben, 2004).

TABLE 5.1

Item Vessel type Head type Height /Length (ft) Diameter (ft)

Reflux drum horizontal elliptical 5 2.5

Sump - elliptical 5 2.5

The column diameter is 5 ft. Use default values for other tray hydraulic parameters(e.g., tray spacing, weir height and weir length to column diameter ratio). Consider log-mean temperature difference (LMTD) assumptions for the total condenser. Actually,

the

LMTD is calculated using the temperatures of process fluid and coolant.In the simulation.

assume constant reboiler heat duty and apply the UNIFAC base property method.

(a)(b)

(0

Simulate the column model to obtain the products mole fractions.Keeping the default level and pressure control algorithms unaltered, inspectthe servo as well as regulatory performance of a proportional integral (PI1controller that is required to insert to control the benzene composition in thedistillate by manipulating the reflux flow rate.Devising an another PI control scheme to maintain the benzene composition inthe bottom product with the adjustment of heat input to the reboiler, observethe interaction effect between the top and bottom composition loops.

Simulation approach

(a) Select Aspen Plus User Interface and when the Aspen Plus window pops up.choose Template and press OK. In the subsequent step, select General withEnglish Units and hit OK button. To open the process flowsheet window, clickOK when the Aspen Plus engine window appears.

Creating flowsheet

From the Model Library toolbar, select the Columns tab. Place the RadFrac model onthe flowsheet window and add the feed as well as two product streams. Renaming allthe streams along with distillation block, we have Figure 5.42.

DYNAMICH AND rnNTKOI, OP KI-OW DIUVKN I'lfOCKHHKH 257

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FIGURE 5,42


Ah we hit Nt'xf followed by OK button, the ROtUp input Corni appcarH (h«m* Kitfun! .43).The diHtillation problem Is tilled oh: 'Cl0S6d-l00p Performanct; of a DihI illation ('olumn'Iniportuntly, une tin- 'Dynanne' input noxle

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FIGURE 6 43

258 PROCESS SIMULATION AND CONTKOI, IISINC ASPEN

Figure 5.44 includes the Aspen I'lus (iccon/ilin infornuition. We can fill up the

Accounting sheet with any name, number and ID.

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FIGURE 5.44

We like to see the composition of all incoming and outgoing streams in mole fractionbasis in the final results table. Accordingly, we use Stream sheet under the ReportOptions of Setup folder (see Figure 5.45).

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FIGURE 5.45

DYNAMICS \NI) CONTUOI, OK I'l.OW DRIVKN ('UOCICSSKS 259

Specifying componentsFrom (In- Data Brow.scr, hoIoc! (

'

oniponcnta/Speeipcctions to open the componont inputlorm In ill'' lahlc. shown in l-

'

i mc S 1 (>. Ihc Ivvo species are dclincd

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FIGURE 5.46

Specifying property method,,>(. li'i on Hm- Nil

. choose Properties/Specifications and gel the property Inpul form.in Aspen simulation

, a property method originall} Includes several models for calculatingthe physical properties For the distillation example, set the UNIPAC base method b>scrolling down (see Figure 5.47).

Specifying stream Information

," next, (.pen Streama IFEED IInput ISpecifications sheel Entering the givenValues lor all State variables and teed eompo ion.

Ihe slream mpnl lorm looks likeFigure 6 'IH


," lefl pane ol the Data Browser window,

select Blocks IRADFRACISetup to openConfiguration sheet and then insorl the required datn (see Figure 5.49)

260 . PROCESS SIMULATION AND CONTROL USING ASPEN

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DYNAMICS AND CONTROL OK KLOW-DKiVEN PROCESSES 261

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DYNAMICS AND CONTROL OK KLOW-DKiVEN PROCESSES 261

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262 PROCESS SIMULATION AND CONTROL USINKi ASPEN

In Figure 5.51, the column pressure profile is defined.

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FIGURE 5.51

Entering heat transfer data for condenser and reboiler

Next select Dynamic under RADFRAC of Blocks folder. There are three heat transferoptions: constant duty, constant medium temperature and LMTD. As mentioned in theproblem statement, the condenser heat duty depends on the log-mean temperaturedifferential between the process fluid and the coolant. The coolant inlet temperature isset constant. Here the temperature approach represents the difference between theprocess temperature and the coolant outlet temperature at the initial steady stateNote that among the heat transfer specifications, the coolant inlet temperature andtemperature approach may vary during a dynamic simulation,

whereas the specificheat capacity of the coolant is fixed during a dynamic run (see Figure 5.52).

For the reboiler, it is fair to use constant heat duty computed in the Aspen Plus

simulation. However, the reboiler duty may be changed at dynamic state either by

manually or automatically with employing a controller (see Figure 5.53).

Entering geometry data for reflux drum and sump

The reflux drum and sump are specified in Figures 5.54(a) and (b) with their givengeometry data. The information on vessel orientation, head type, length (or height)and diameter are used to compute the vessel holdup.

DYNAMICS AND CONTROL OF FLOW-DmVKN PROCKSSP S 263

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264 4- PROCESS SIMULATION AND CONTROL USING ASPEN

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Entering tray geometry

The example column has total 25 stages-Stage 1 being the condenser and Stage 25the reboiler. We already have inserted the necessary information for stages 1 and25. Now, we need to inform the simulator the tray geometry specifications for stages2 through 24. Note that the tray holdups are computed using these geometry data(see Figure 5.55).

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Running steady state simulation and viewing resultsHit Afecf button and press OK to run the steady state simulation. Finally, the result."table

, shown in Figure 5.

56, is obtained. At this time, we should save the work.(b) Exporting dynamic simulation: For process dynamics study, we wish to

export the steady state Aspen Plus simulation into flow-driven Aspen Dynamics

simulation giving a file name of'Ch5_

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Starting Aspen Dynamics

Open a blank dynamic simulation window for the example column, following a similarprocedure as previously shown for the CSTR problem. In the next, simply open theflow-driven dynamic file 'Ch5

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window appears (see Figure 5.57) accompanying with the closed-loop process flowdiagram. The flowsheet actually includes the three default control schemes LCI, PC2and LC3 to monitor the reflux drum liquid level, top stage pressure and column baseliquid level, respectively.

In the present discussion, we do not want to change anything of the threeautomatically inserted control strategies. All data, including timing parameters, ranges,

bias values and controller actions, remain untouched. A little detail of these controlstructures is given below.

Loop 1

Controller: LCI

Type of controUer: P-only (since integral time is very large (60000 minutes))Controlled variable: liquid level in the reflux drumManipulated variable: distillate flow rateController action: direct


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Loop 2

Loop 3

Controller: PC2

Type of Controller: PI

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{

Controller: LC3

Type of controller: P-onlyControlled variable: liquid level in the column baseManipulated variable: bottoms flow rateController action: direct

Adding a new PI controller for top composition loop

Now we wish to include a proportional integral (PI) law to control the benzenecomposition in the top distillation product by manipulating the reflux rate. In the top

left of the window,the Dynamics library is included within Simulation folder of Ml

Items pane. Click on expand (+) button ofDynamics subfolder. Consequently, the expand

button changes to collapse (-) button as shown in Figure 5.58.


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Again hit expand button next to the ControlModels icon. Then select PID controller,

drag it to the flow diagram and drop the control block near to the top product stream.

Renaming the top composition controller as CCT, we have Figure 5.59.

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Connecting controller with process variable (Controlled variable)Ixpand Stream Types under Dynamics subfolder and hold down the mouse button on

he ControlSignal icon. As we drag it onto the flowsheet window, many blue an-ow

appear around the process diagram. Interestingly, when we f l I Z S.

wiih holding the ControlSignal icon over a port, the name of that PAnyway, move the pointer and release the mouse button on the 0fe g wo

* *ame

OutputSignal originated from TOP (stream) block. To select the dastillate compos.tio

CONTROL OF FLOW DRTV rPPn cc 269

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As we press 0/!l button, the cursor becomes a solid black arrow representing theinput signal to the controller. To transmit this signal to the CCT block, connect theblack arrow with a port marked InputSignal. Since this signal conveys the processvariable (PV) information to the CCT controller,

select 'CCT.PV by name with 'Processvariable' by description in the Select the Control Variable dialog box (see Figure 5.61).

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Hit OK button and obtain Figure 5.62. Obviously, the CCT controller is partiallyconfigured. To complete the top composition loop, the controller output should be

connected with the manipulated variable to pass on the signal.

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Connecting controller with control variable (Manipulated variable)

Again hold the ControlSignal icon, drag it onto the process flowsheet and drop it onthe blue outgoing arrow marked OutputSignal from the CCT block. As Select theControl Variable dialog box appears (see Figure 5.63), choose 'CCT.OP' by name andpress OK.

Immediately, a solid black arrow representing the controller output signal isautomatically generated. Move the mouse pointer to reflux stream and make aconnection to InputSignal2 port. To use the reflux flow rate as control variable, select

'BLOCKSC'RADFRAC). Reflux.FmR' in the dialog box and click OK (see Figure 5.64).Now the binary distillation column is coupled with four control schemes, LCI,

PC2, LC3 and CCT, and the closed-loop process looks like Figure 5.65. The subsequentdiscussion includes the modification of different tuning properties of the CCTcontroller.

DYNAMICS AND CONTROL OK FLOW-DRIVKn PROCESSES 271

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Modifying controller tuning properties

First we wish to see the default tuning properties. So,double-click on the CCT block and

then hit Configure symbol in the faceplate to open the Configure dialog box (see Figure 5.66).

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Obviously, some of the default values set by Aspen Dynamics are not acceptable.For example, the operator set point value of process variable (benzene composition indistillate) should not be greater than L Secondly, the CCT controller action must be'Reverse'. In addition, the value of control variable (reflux flow rate) at steady state isusually used as bias value.

We have two options in our hand to correct the default values. Either manuallywe can do it or Aspen Dynamics can automatically initialize the values of set point

,

process variable, control variable, bias and ranges. Note that the controller action ischanged only manually. It is wise to initialize the values by the help of Aspen Dynamics.

For this, press Initialize Values button in the Configure dialog box and use 'Reverse'controller action. It is obvious in the window, shown in Figure 5.67, that the values ofSP, PV and OP in the faceplate change automatically to their steady state values. Ifthis approach fails to initialize the simulation of controller model with the steady statedata, check and replace, if necessary, the values of PV and OP with their steady statevalues by double clicking on signal transmission lines (input to the controller and outputfrom the controller).

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Modifying ranges for process variable and controller outputwe hit the Ranges tab, the Configure dialog box (see Figure 5.68) shows the default

ranges imposed on process variable and controller output.


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However, here we use the typical variable ranges, shown in Figure 5.69.

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Process variable

Range minimum: 0.85

Range maximum: 10

Output

Range minimum: 10000 Ib/hr

Range maximum: 120000 Ib/hr

It is important to mention that it is a good idea to carry out Initialization as wellas Dynamic run after each new change in the control scheme so that any error incontroller installation can be detected individually.

We have now completed all required control specifications for the top compositionloop In the ongoing study, we prefer to conduct the simulation experiment to observethe designed controller performance continuously for 5 hours. As done for the previousCSTR problem, similarly either simply press Ctrl+F5 on the keyboard or select PauseAt from the Run menu and put 5 hours as Pause at time.

In the next, we will inspect the CCT controller performance first dealing with theservo problem followed by the regulatory problem.

Viewing servo performance of CCT

As we double-click on the CCT controller block in the flowsheet window, the faceplate

appears. Then open the Configure as well as ResultsPlot dialog box.The second one is

basically a blank graph sheet that presents the variations of process variable, set pointand controller output with respect to time.

Before running the program, make sure that all the items in the Configure dialog boxand faceplate are correct. In the next, hit Run button to start the dynamic simulation. Theplots, shown in Figure 5 70, illustrate the servo behaviour of the PI control algorithm witha step increase (0.9437 - 0 97 at time = 1.51 hours) followed by a step decrease(0 97 - 0

.9 at time = 3 hours) in the set point value of the distillate composition of benzene.To achieve an improved closed-loop performance, we have used the values of proportionalgain of 10 %/% and integral time of 10 minutes. These values have been chosen basedon a pulse input test in the distillate composition of benzene and using the trial-and-error approach It should be kept in mind that the objective at this point is not to comeup with the best control structure or the optimum controller tuning. We only need acontrol scheme and tunings that provide a reasonably good tracking performance todrive the simulation to a new steady state.

Remember that to edit the plots, shown in Figure 5 70, double-click on differentelements of the plots and modify them as we like.

Viewing regulatory performance of CCT

In order to investigate the regulatory performance of the CCT controller, we give a stepinput change in the feed pressure (21 -» 23 psia) at time = 1.48 hours and that in the feedtemperature (225 -» 230oF) at time = 3 hours. The PI controller tuning set provides gooddisturbance rejection performance (see Figure 5.71) although the tuning parameter values. gain and integral time) have been chosen based on a pulse set point input change.

276 PROCESS SIMULATION AND CONTROL USfNG AST'EN

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(c) Adding a new PI controller for bottom composition loop: We have todevise another PI control scheme to monitor the bottoms composition of benzeneby adjusting the heat input to the reboiler. As developed, the CCT controllerfor the top loop, similarly we can configure the CCB controller for the bottomloop as shown in Figure 5.72.


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lm< uuuk.'* w-> Ml X-M i.. I.im mmttfll M*

FIGURE 5.72

We have chosen the following tuning properties (see Figure 5.73):Gain = 10 %/%

Integral time = 10 minutesController action: Direct

dub .a % » |M*«.. r"

3 . . nvm awocigi_

r :: f - >. »- »

!

1 ; 7T~

:'w.55 i i '».»« i .

-

f-

v..

r

c-

MM

i

.TIM mmm lia»

tl A I.. li.c...EkMIMi| "1 .MtMlM lftj« WMtlOM m4 M3» mm-two*

FIGURE 5.73

278 . PROCESS SIMULATION AND CONTROL USING ASPEN

In addition, the used constraints are reported below:

Process variable

Range minimum: 0.0Range maximum: 0.1

Output

Range minimum: 6000000 Btu/hrRange maximum: 18000000 Btu/hr

Viewing interaction effect between two composition loops

To observe the effect of interaction between two composition loops, the set point valueof bottoms composition of benzene has been changed twice. The simulation result isdepicted in Figure 5.74 for a step increase (0.0033 -> 0.0045 at time = 1.5 hours) followedby a step decrease (0.0045 -> 0.0025 at time = 3 hours).

ECHe Mew Toots fen Window net

| Dynamic h « CBS'S aiaocsH

-MS*}

9-

r Tt (0 05 3 i£ i « W 1*

%j amSP| 100025PV; I00O250PHH |12117835,;

Tunuvj | Ranges | Ffenr ] Olha

Opetatot set poi* (0 0025 jbmol/bfrolTurwtg paameten

S«t. [l1613W7r jBtu/WGart [ToIniegrafww. flO f iOwwabvetimei [o

-

Cortiolw action -

Drad

r Reverte

TEE

I.

s.

> £- S?

If

LCI

>o-

LCJ

>o-

{33-0

-->a-jCCT

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0 0 5 1 1 5 2 2 5 3 3 = 4 4,5 5

Time Hours

63

11

r

=inj_

l"

3

i1

i 2 2.5 3 13Time Hours

teed

FIGURE 5.74

Clearly, the CCB controller shows satisfactory set point tracking performanceagainst a pulse input change. It is observed from Figure 5.74 that owing to stronginteraction between the two composition loops of the distillation column, the set pointchanges in bottom loop affect the top product composition. Similarly, when any setpoint change is introduced in the top composition loop, the bottom product compositionwill also be affected.

DYNAMICS IND CONTROL OF FLOW-DRIN KN I'HOrKSSKS 279

SUMMARY AND CONCLUSIONS |This chapter has investigated the closed-loop process dynamic characteristics usingAspen Dynamic- package. To observ e the controller performance in terms of set pointtracking and disturbance rejection, a CSTR in addition to a distillation column havebeen illustrated The default control strategies have been tested for the reactor example,whereas the two additional composition control loops have been included along withthe default control laws for the distillation example. Several simulation experimentshave been executed for both the processes under flow-driven dynamic simulation. Notethat Chapter 6 presents the dynamic simulation and control of more rigorous pressure-driven dynamic process.

PROBLEMS|

5.1 A feed mixture of benzene and toluene is fed to a flash drum (Flash2). The

separator operates at 1.2 atm and 100oC. For dynamic simulation, required feed

specifications are provided in Figure 5.75.

Feed

Temperature = 25°C

Pressure = 3 bar

Flow rate = 100 kmol/hr


benzene 0.

6

toluene 0.

4

FLASH

>oPI

FIGURE 5.75 A flowsheet of a flash drum.

'a) Use the SYSOP0 property method to compute the amounts of liquid andvapour products and their compositions.

.b) As shown in Figure 5.75, employ a PI control scheme to monitor thetemperature in the flash drum by manipulating the heat duty.

(c) Show the closed-loop servo performance with +10% and then -10% stepchanges in the flash temperature.

(d) Report the tuning parameters obtained by trial-and-error method, controlleraction and ranges imposed.

5.2 A vapour mixture of toluene, methane and hydrogen is heated using a shell and

tube heat exchanger (HeatX). The superheated steam is used as a heating medium.Complete specifications required for closed-loop dynamic simulation are shown inFigure 5

.76.

280 PROCRSS SIMULATION AND CONTROL USING ASPEN

Cold Stream In

Temperature = 2780F

Pressure = 500 psia

Component Flow rate

(kmol/hr)

toluene 200

methane 2300

hydrogen 1000

Hot Stream Out

Pressure = 14 psia

IHOT-OUT

ICOLD-INf

Cold Stream Out

j cold-out hoi Temperature = HOOTPressure = 498 psia

HOT-INKDead time pi

>o>AT

ii

Hot Stream In

Temperature = 1160oFPressure = 14.7 psiaFlow rate = 5110 kmol/hr

FIGURE 5.76 A flowsheet of a heat exchanger.

(a) Simulate the heat exchanger model using the shortcut method, counter-current flow direction and NRTL-RK property method.

(b) Include a PI control structure to observe the set point (cold stream outlettemperature) tracking performance and the manipulated input (steam inflowrate) profile. In the closed-loop simulation experiment, assume that thetemperature sensor takes 1 minute time (dead time) to measure the controlledvariable. Report the used tuning properties.

(c) Examine the regulatory performance by introducing + 10% and subsequently-10% step changes in the inlet temperature of the cold stream.

5.3 Device a cascade control scheme for the above heat exchanger and investigatethe controller performance.

5.4 A liquid mixer model with a typical ratio controller (Seborg et al. 2003) is shownin Figure 5.77. The flow rates for both the disturbance or wild stream (Fw) andthe manipulated stream (FE) are measured, and the measured ratio, Rm = FE/Fw,

is calculated. The output of the ratio element is sent to a ratio controller (PI) thatcompares the calculated ratio Rm to the desired ratio Rd (set point) and adjuststhe manipulated flow rate accordingly.

Ratio

Input 2

>oPI > | POT >

Input 1

FIGURE 5.77 A flowsheet of a mixer

DYNAMICS AND CONTROL OF KLOW-DRIVKN PROCESSES 281

The input data are shown in Table 5.2 for simulation.

TABLE 5.2

Stream Temperature CO Pressure (aim) Flow rate (kmol/hr) Composition

E 50 1 Pe = 100 pure ethanol

W 60 1 = 150 pure water

Process variable at steady state = 0.667 (FE/FW = 100/150)

Controller output at steady state = 100 kmol/hr

Proportional gain = 4 %/%

Integral time = 20 minutesController action = reverse

(a) Appljang the SYSOPO base property method, simulate the mixer modeloperated at 1 atm.

(b) Using the given controller properties and default ranges, report theratio controller performance with two consecutive set point step changes(0.667 -> 0.72 0.65) in the ratio.

Hint: Double-click on Input 1 transmission line and fill up Tables 5.3(a) and (b).

TABLE 5.3(a)

Value Spec

>STREAMS("E*,).Fcn("ETHANOL")

<Ratio.Input!

100.0

100.0

Free

Free

Similar table for Input 2 is obtained as:

TABLE 5.3(b)

Value Spec

>STREAMS("Ww

).Fcn("WATER") 150.0 Free

<Ratio.Input2 150.0 Free

In the next, double-click on Ratio element and get Table 5.4.

TABLE 5.4

Description Value Units

Inputl Input signal 1 100.0 kmol/hr

Input2 Input signal 2 150.0 kmol/hr

Output Output signal, Inputl/lnput2 0.667

Use Initialize Values button and incorporate the given tuning properties beforerunning the program.

282 PROCESS SIMULATION AND CONTROL USING ASI'RN""

5,5 A reboiled stripper is used to remove mainly propane and lighter species from afeed stream, shown in Figure 5.78. It has total 6 stages (including condenserand reboiler) and no condenser.

The bottoms rate is 100 Ibmol/hr and the column top stage pressure is 150 psiawith a column pressure drop of 8 psi. The diameter of the stripper (Stages 1 to5) is 6.5 ft. The reboiler heat duty is assumed constant, although it changes atdynamic state. The sump has elliptical head with a height of 5 ft and diameterof 2.5 ft.

For the closed-loop simulation, use the following data:Dead time = 2 minutes

Magnitude of noise (standard deviation) = 0.01 Ibmol/lbmolProportional gain of PI = 1 %/%Integral time of PI = 20 minutesController action = Reverse

Feed

Temperature = 40oF

Pressure = 160 psiaFeed stage = 1 (above stage)

Component Flow rate

(Ibmol/hr)

c, 60

c2 75

C3 150

n-C4 175

n-C5 60

n-C8 35

PCI

Dead time Noise Pi

>o

FIGURE 5.78 A flowsheet of a stripping column.

(a) Using the Peng-Robinson thermodynamic method,simulate the RadFrac

(STRIP2) model and compute the product compositions.(b) Keeping the default controllers (PCI and LC2) unaltered

, configure acomposition control scheme (PI) coupling with a 'Dead

_

time' and 'Noise'

elements to maintain the propane mole fraction in the distillate bymanipulating the reboiler heat duty as shown in Figure 5.

79. Use the givenclosed-loop data and execute the dynamic simulations to test the developedcomposition controller performance.

5.6 Ethylene is produced by cracking of ethane in a stoichiometric reactor. Theirreversible elementary vapour-phase reaction is given as.

C2H6 -i C2H4 + H2

ethane ethylene hydrogen

Pure ethane feed enters the reactor model, shown in Figure 5.79, with a flow

rate of 750 kmol/hr at 800oC and 5.5 atm. The reactor operates at inlet

temperature and pressure with 80% conversion of ethane.

DYNAMICS AND CONTROL OF FTOW-DRIVKN PROCESSES 283

> M

pi

>o

FIGURE 5.79 A flowsheet of a reactor

U) Using the SYSOPO thermodynamic method, simulate the reactor model.(b) Develop a control loop as configured in the flow diagram to maintain the

desired reactor temperature by the adjustment of heat duty. Considering themeasurement lag of 1 minute, inspect the servo as well as regulatory controlperformance. Report the tuning properties used to achieve a satisfactoryclosed-loop performance.

5.7 A binary feed mixture consisting of methylcyclohexane fMCH) and toluene isintroduced above tray number 14 of a RadFrac distillation model, shown inFigure 5.80.

O 1 phenol [

O 1 FEED h

FIGURE 5.80 A flowsheet of a distillation column

It is difficult to separate this close-boiling system (MCH-toluene) by simple binarydistillation

. Therefore, phenol is used as an extractant and introduced abovetray number 7 of the column

. The two input streams have the followingspecifications

,shown in Table 5.5.

TABLE 5.5

Stream Temperature (*C) Pressure 'bar) Flow rate Mole fraction

PHENOL 105 1.4 100 nrVhr 1

.0

FEED 105 1.4 181.44 kmol/hr 0

.5/0.5

(MCH/toluene)

The column has 22 theoretical stages (including condenser and reboiler) with atotal condenser

. The distillate rate and reflux ratio are given as 90.72 kmol/hrand 8 (mole basisrespectively. The pressure profile is defined with Stage 1pressure of 1 10316 bar and Stage 22 pressure of 1.

39274 bar. Use LMTD

assumptions for the condenser The reboiler heat duty is assumed constant. Thereflux drum and sump are specified in Table 5.6.


TABLE 5.6

Item Vessel type Head type Height /Length Diameter(m) (m)

Reflux drum horizontal elliptical 1.5 0

.75

Sump - elliptical 1.5 0

.75

The column diameter and tray spacing are given as 2 m and 0.6 m, respectively,

(a) Simulate the distillation column using the UNIFAC property method tocompute the composition of MCH in the distillate and that of phenol in thebottom product.

(b) In addition to the default level and pressure controllers, insert a PID structureto control the MCH composition in the top product by manipulating the flowrate of PHENOL stream.

(c) Produce the plots to show the closed-loop control responses, and report thetuning parameters, control actions and operating ranges for controlled aswell as manipulated variables used.

REFERENCES|

Luyben, W.L., (2004), "Use of Dynamic Simulation to Converge Complex ProcessFlowsheets", Chemical Engineering Education, pp. 142-149.

Seborg, D.E., T.F. Edgar and D.A. Mellichamp, (2003), Process Dynamics and Control,2nd ed., John Wiley & Sons, Inc.

CHAPTER 6Dynamics and Control ofPressure-driven Processes

6.1 INTRODUCTION

To know the transient characteristics of a complicated chemical plant, we need a dynamicprocess simulator. It is well-recognized that Aspen Dynamics is such an efficient

flowsheet simulator used for dynamic process simulation. As we have seen in Chapter 5,Aspen Dynamics simulator can be employed to design a process as well as its associatedcontrol strategies.

Aspen Dynamics extends an Aspen Plus steady-state model into a dynamic processmodel. If the steady state Aspen Plus simulation is exported to Aspen Dynamics, there

is a necessity to choose either flow-driven dynamic simulation or pressure-drivendynamic simulation

. In a rigorous pressure-driven simulation, pumps and compressorsare inserted

, where needed, to provide the required pressure drop for material flow.Control valves are installed

,where needed, and their pressure drops selected. For good

control, the pressure drop across a control valve should be greater than 0.1 bar. The

fluid that flows through a valve should normally be liquid-only or vapour-only becausethe two-phase flow through a control valve is unusual.

It should be pointed out that for a pressure-driven case, we must not insert a valvein the suction of a pump or at the discharge of a compressor (compressor speed or itsequivalent compressor work is manipulated). The control valves are positioned on thefluid streams such that the controllers can manipulate the valve positions.

The simple flow-driven dynamic simulations have been discussed in detail in theprevious chapter. Therefore

,here we are intended to study the pressure-driven

simulation. A reactive or catalytic distillation column is exampled for the rigorous

pressure-driven Aspen Dynamics simulation as well as control.

285


6.2 DYNAMICS AND CONTROL OF A REACTIVE DISTILLATION (RD)

COLUMN

Problem statement

The methyl tertiary butyl ether (MTBE) column configuration (Jacobs and Krishna,1993) chosen for the simulation is shown in Figure 6.1.

Pure methanol (MeOH) feed(liquid)

Temperature = 320 KPressure = 1 aim

Flow rate = 711.30 kmol/hr

Feed stage = 10 (above-stage) 0| METHANOL Ft

Butenes feed (vapour)

Temperature = 350 KPressure = 1 aimFlow rale = 1965.18 kmol/hr

Feed stage = 11 (above-stage)

Component Mol fracl

/so-butene (IB) 0.36

n-butene (NB) 0.64

PUMP

CH butenes]-1

Jy tCl-fpisT-QCV2

"

1-H'

l-IbotI-<>CV3

RDCOLUUN

COMPRESS

FIGURE 6.1 A flowsheet for the production of MTBE.

The RD column (RadFrac) consists of 17 theoretical stages, including a total condenserand a partial reboiler. Reactive stages are located in the middle of the column, Stage 4down to and including Stage 11. In Aspen terminology, the numbering of the stages istop downward; the condenser is Stage 1 and the reboiler is the last stage.

MTBE is produced by reaction of IB and MeOH:

(CH3)2C = CHa + CH3OH «-»(CHgk COCH3IB MeOH MTBE

The liquid-phase reaction is catalyzed by a strong acidic macroreticular ion exchangeresin, for example Amberlyst 15. and n-butene does not take part in the reaction (inert).The forward and backward rate laws (Seader and Henley, 1998; Rehfinger and Hoffmann,1990) are derived in terms of mole fractions, instead of activities (products of activitycoefficient and mole fraction):

Forward rate: rf= 3.67 x 1012 exp

Backward rate: r,, = 2.67 x 1017 exp

'-9244(M

RT

-134454>

RT

.IB

xMeOH ,

VMTB!'

DYNAMICS AND CONTROL OF PRESSURE-DRIVEN PROCESSES 287

Here, z represents the liquid-phase mole fraction. The pre-exponential factors,including the activation energy (kJ/kmol), are given in SI units. The catalyst is providedonly for reactive stages (8 stages total), with 204.1 kg of catalyst per stage (Seader andHenley. 1998). The used catalyst is a strong-acid ion-exchange resin with 4.9 equivalentsof acid groups per kg of catalyst. So, the equivalents per stage are 1000 or 8000 for the8 stages. In some references, the equivalents per stage are directly given.

The column, starting from Stages 2 to 16, is packed with 'MELLAPAK' (vendor:SULZER) having a size of 250Y. Use 'Simple packing' hydraulics and the heightequivalent to a theoretical plate (HETP) may be considered as 1 m. The distillationcolumn diameter is 6 m. Stage 1 (condenser) pressure is 11 atm with a column pressuredrop of 0.5 atm. The reflux ratio is set to 7 (mole basis) and the bottoms flow rate is640.8 kmol/hr. In the MTBE synthesis process, it is desirable to obtain a bottom productcontaining high-purity MTBE and a distillate containing high-purity NB. In Table 6.1the reflux drum and the sump (the next-to-last stage in the column) are specified.

TABLE 6.1

Item Vessel type Head type Height/Length (m) Diameter (m)

Reflux drum horizontal elliptical 2 1

Sump - elliptical 2.2 1

.1

The pump delivers the liquid stream POUT at 11.7 atm. The compressor (isentropic)has discharged the vapour feed FV at 11.5 atm. The three control valves (adiabaticflash) CV1, CV2 and CV3 have the outlet pressures of 11.5 atm, 10.8 atm and 11.3 atmrespectively. Using the UNIFAC base property method,

(a) simulate the process flowsheet to obtain the distillation product summary, and(b) develop the control configurations to achieve the desired product purity under

disturbance input.

Simulation approach

(a) Start the Aspen program by double-clicking the Aspen Plus User Interface iconon the desktop. Then select Template option and press Oif (see Figure 6.2).

: aM

;

FIGURE 6.2


288 PROCESS SIMULATION AND CONTROL USING ASPEN"1

We choose General with Metric Units option and hit OK button (see Figure 6.3).

016*11_

L I _!_) *d U-i-lfcl I M 3 I I I J jU J Jl l I I l I HI J

_

J_J,

J U ali

.

mi in- I.

>.. I

0*. I ,.J h1

r -

P.*

FIGURE 6.3

When the Connect to Engine window appears, use the default Server type (Local PC).

Creating flowsheet

The process flow diagram includes a feed pump, a feed compressor, a distillation columnand three control valves. The complete process flowsheet drawn in an Aspen windowshould somewhat resemble the one shown in Figure 6.

4. Recall that Aspen has a tool

in the toolbar that automatically takes the user through the required data input in astepwise fashion. The blue Next button does this.

-o-

" if - *x

FIGURE 6.4

DYNAMICS AND CONTROL OF PRKSSIIRE-DRI\T,N PROCESSES 289


At the beginning of data entry, fill up Global sheet followed by Accounting sheet underSpecifications of Setup folder. Moreover, select 'Mole' fraction along with 'Std.liq.volume'flow basis in Stream sheet under Report Options [see Figures 6.5(a), (b) and (c)].

& -

r 3 EC

Sim

Pi bw |HUB .

MMH .

fMM,

ir S

41

FIGURE 6.5(a)

:.>-B| *ifi »] atmnn-at .! 3 I 1"! jiJ 3

-T i-l h r* .1 -IE; : II

-a*-=- =-aa-2-

FIGURE 6.5(b)


_j_

r I I -I 1,

;| .imi I M MgJ

0

_j RosrMru

CtiHomUtii

Optioni

nafhi >bJiiiF-a Jj

FV>-.bM> fmctmUm

f7 Mod P Mod

r mwi r mm

P S-dlQrt***. r Stdklvcim.

P Conconni 2«o Hnw or hKbm

P lr<Ul«il>«tmd«.CTvtlci.i

SUWlflHllH

Iff [.''.>. 3

r ...m.

..

[V . | ., , v . | --vr. w | CdUHM | RtKicni Pimtw*ClMngnt | MwdMrt | Scfcfc | UiaMotWi |

STREAMS Pmp Conif MCow fV»

FaH«te.(wun gFoUeiiVwenButllV HUM FUntiwIlrpj r cWc

FIGURE 6.5(c)


The components involved in the example system are MeOH (CH40),IB (C4H8-5), NB

(C4H8-1) and MTBE (C5H120-D2). Within the parentheses, the chemical formulasused in Aspen terminology are mentioned (see Figxire 6.6).

fh I* v** Date 1Mb Rui Pw itnuy Wndew

Iglg) _U *le) £1 raRI&Kl l-l n.| |I r M I IT I W! I [a) -«l»«l

3MS

.

_J PwoCh.

MEOH KTHANOL Hti

h EQWmfMi

NB i-BUIEHE C4HB'1

MIBE

. J Con

. - . PA

J Si 35! I u'*

|» tdMAriMi | SwMka. ) KMEKtw«p> | 4 . | fiMcm Pimm Ounv" | |

i »tr»iiiiin

FIGURE 6.6



The user input under the Properties tab is probably the most critical input required torun a successful simulation. This has been discussed in much greater detail in theprevious chapters. This key input is the Base method found in Global sheet underSpecifications option. Set UNIFAC for the present project (see Figure 6.7).

1 d 1 J1 3

'1 J1 d

1 J1 3I J

1 r

1 J

tfclj l f | HatfE**** i CAM | fiuuc- *-Ol«inii j 1 id* | UhWoMt |

FIGURE 6.7


Under the Streams tab, we have used Specifications sheets to input the data for boththe feed streams, BUTENES and METHANOL [see Figures 6.8(a) and (b)].

«k U DM I*M <k/. m lMm> Vnfc. rtw

9 S3HSa

.ass

r i j-j-i ..if; 3 ») qU I

wo

.1

1I

I-

FIGURE 6.8(a)


E« V*. D«j 1b.

i r m i nr i ei i m mi-

DgrfcR FH »| |..|[Tr) mum* i i

J r:-.

3

'

i SJIENIS

1 E0v«.

_j

_j Fl

*

-li FV

ICIHMBI

Res*;

la !.

il

HPS 3"lur

1Pi9

mibe

Evripn | C<A«n | fUicioa IWttraCkw«m | > ,,...-. | c«bk | UisModn |

FIGURE 6.8(b)

iKall-V HUM RtMndkwJfraOk


In Figures 6.9(a) to (d), first the feed compressor details are giver.. Subsequently, thethree control valves, CVl, CV2 and CV3, are specified.

_i

_

r- I -1 I- IT I lal I la

fir-.-

afbRTr H JulF 321) QLJ!!!!

q hmJ tUIENES

S PI

_J POUI

COMffltSi

Q Salup

f COVmUkfi tO Ira'

3

r

1

-CH

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. ; MM

FIGURE 6.9(a)

DYNAMICS AND CONTROL OF PRESSURE-DRIVEN PROCESSES

Ffc {« Am l""** If* fV LtMV r Or.

ir_

LUJV 'I'N Mai gH0

- a, nA. F\

- ij M(t>«nOL. ai n. ii w

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s t'J in"

Spk BMW

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wIflpul

Btae« Ophorj

tP .»rtNei

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i

a snear O-.ji

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-

5TREAKS_

f o Mtfc sen R

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D4M*.AOMiM] MUM

FIGURE 6.9(b)

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»i Dial n.i

| - 'MM

o

[23 ECVwwim

: :.

ni»pMii|tH f -3 * I-r c w**, I 1 1 r I

snWW m , r nti uai

D ttoA.

OiWMit HUM

1107

FIGURE 6.9(c)

294 PROCESS SIMl'UVnON AND CONTROL USING ASPEN

d (BfacK-VlrVJ.rllnpui 0* E* C«* Tadb Rrf, Plo i±1Mr wnx*. h*

"

3

© .:>-:_

J

2] Kea*:H EO-M.,

- ,

r CAii» la tMtodoUM Peru-Mr ,

I-

STfitWK Mm Ffp* SSt*

PaM essr; " '

£jc*_

?Ow»ii .HIM

FIGURE 6.9(d)

When the data entry for the feed pump is complete,the window should look like

Figure 6.10.

l_

r_

L_LLJV 'I -isi

a -'i

.-r - y

RiMP

f :

O Sim v _J

m r

£TRDMt

I MMMta. I tekk I J«M-M« I

J

FIGURE 6.10


In the list on the left, choose Blocks I RDCOLUMNISetup to fill up Configurationsheet (see Figure 6.11).

'Wal _LJ «m *) fJMfcl'.KM -I -il - I M -I 71 -I _Ji-T I I I' -I - Wl I Ml

3 3|.. ji :. -5j1 I

-D-

i | IWMMi | ttaMlKf***, | CAM | ftxtin Pmm Omw

FIGURE 6.11

Streams sheet defines both the feed streams (see Figure 6.12), FL and FV, as wellas product streams, PI and P2.

FTS C« vW. Dm r«* fW> fta -! i-

PWO|_Uaelgl ral-rlai-l-al l »l I I"! .! 1 'I J

r I M PT \ -m i wi

.«B ftH" Ml

It

-ia EseK J . -»...- >. " I MUM

FIGURE 6.12

The pressure profile of the sample RD column is described in window shown inFigure 6.

13.


p l|yi|yTff!l ?lWTfffF!ffBIHTi]f!Bl;I K | l]E* Vwm OVs Took Run PM Lb«v Window Help

DltflHI_

1J lOj WJ (3M*\*\<M 3 ' I |N|_

«J JJ J_i_

r i i -i f" i 'M i ibi

-I9J 'I

_J Pw,

- «3

B«nl.

_j PM

S'iMnRtnJii

.a n»

O IJi«Siix»i«

H.nii

0 EO Irvul0 Spec Grtt

Pa»i

- 1 RDCOLUMNQ Srtup

"

J Varv

] kfH l«" " d 1 I.aU id

3

|

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(|-/C0M»»ni« i

r

PieiM* lor f*tl ol CoUm (oprwiBll

r SUflep-eiuwAop |P Column pt 'Me <*op ffllT

lei Scwci r

Sep«alo(s [ H»al E'-changen ] Coktfrrtt | Re-scloit Pie*ii«e Channeli j MaMpUaloc. | ScW: | UswMotW; |7 5l*jte OPurcwo***!)

CV 0Foltas\AipennAlt.1

| -UCKy 6 Mno-.oliVoftl |[ Atpen Pkrt - Simutali..

FIGURE 6.13

In the left pane of the Data Browser window,select Blocks/RDCOLUMN/Reactions.

Filling out Specifications and Holdups sheets,we have two windows as shown in

Figures 6.14(a) and (b).

fit EcW Rin PW Lfcraiy Wrrfow Help

1*1 nl-rl&hHJidr l M.

-if**!

mil J EJ _J fiJi i i i isi

i*7 Haft !HtTr8.sd <<||ii zi»li=JUH

RsjJ:

(§ EOVanafcist

9 SpccGicmm_j PW:

Q S 'team RejJtja pump

O Se«»0 Peiiair.M e Cu0 Um Suboine0 bkK Opborc

Hen*.

(9 COVmMei0 EOlnptiQ Sc«c G-cmk

Seeen.Ren*i

) RDCOLUMN9 Sew

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STREAMS '

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FIGURE 6.14(a)

DYNAMICS AND CONTROL OK PRESSURE-DRIVEN PROCESSES 297

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FIGURE 6.14(b)

Pka 11 1 HUM

Select Pack Rating under RDCOLUMN of Blocks folder. Creating a new ID, T,and specifying the packing section as well as packing characteristics, we obtainFigure 6.15.

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i r-i-M nr -Mmi i ibi1

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FIGURE 6.15


Choose Blocks/RDCOLUMN/Convergence and fix up the maximum iterations to200 (see Figure 6.16).

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| 'ChapW& HwosdtWotii |[ Aipen Pku SueuM> .

FIGURE 6.16

y.. ie i8

In the next, dick Dynamic tab wader Blocks/RDCOLUMN. The design specificationsof the reflux drum and sump are reported in Figures 6.17(a) and (b).

' Fir EA View Data Took Run PW Lbmy WMm H«t>

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FIGURE 6.17(b)

Hydraulics sheet incorporates the information displayed in Figure 6.18.

Fh £* V*- luco Rir> Ltto Wi<*>. K-t

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_j - :sec;

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I

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>- -

S'-i r-C - )f -m3e:Au» Pi= II

FIGURE 6.18

300 PROCESS SIMULATION AND CONTROL USINd ASRKN1

Hit Next icon to open the Reactions folder. For the forward reaction (Reaction No. 1)

and the backward reaction (Reaction No. 2), the stoichiometric coefficients andexponents are defined under 'Kinetic' Reaction type in the two sheets as shown inFigures 6.19(a) and (b).

MBj _U *J -'IfeM M 3 1 M _1 ±J J J

ProA-tli

CetKotn 1 t**rm*

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sun I y-

FIGURE 6.19(a)

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FIGURE 6.19(b)


The Power law kinetdc data for both the reactions are provided in Figures 6.20(a) and (b).

_l_r

_L

-L

-i_

fV ! .mi 1 mi

3 :

us 5"'

o«flto.M1[iB-.p»*ii 1 mi - - .

FIGURE 6.20(a)

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MTBE MEOH. iB

UAod

a

FIGURE 6.20(b)

Running steady state simulation and viewing resultsAs we hit Next knob followed by OK, Control Panel window pops up. UnderSummary/Streams

, the results are displayed in Figure 6.21.

Results

302 PROCESS SIMULATION AND CONTROL USINd ASI'KN

- fie Edi Vww Data To<*

I y I'M i hi- Mojiin i) (Reiulls SummAiy Slic«)mi Data Hrowsni|

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1" Zi 1' zi I Zl 1 Zi {Volume Flow ciWhi 5922 949 146 743 97 974 146 743 97 971 29 549

40136 4053 10 396 41 770 .10 396 41 770 40150

Mete Flow kmcWn

MEOH 711,300 100 007 0 605 100 607 0605 711 300

IB 707 465 93 059 4 517 93 059 4 517

NB 1257,715 1231 290 26 425 1231 290 26 425

MTBE 0635 609 253 0.635 609 253

itcteFcac

MEOH 1000 0071 344 FfM 0071 944 PPM 1000

IB 0 360 0 065 01X17 0 065 0 007

NB 0640 0 664 0 041 0864 0 041

MTBE 446 PPM 0 951 446 PPM 0 951

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1126

FIGURE 6.21

The mole fraction of MTBE in BOT stream is computed as 0.951.(b) Exporting dynamic simulation: In order to conduct the dynamic process

simulations, export the steady-state Aspen Plus simulation into Aspen Dynamicswith saving as a pressure-driven dynamic file.

Opening existing simulation

As we press the Start knob, point to Programs, then AspenTech, then Aspen EngineeringSuite, then Aspen Dynamics Version and then select Aspen Dynamics, a blank dynamicsimulation window appears. In the next, open the pressure-driven dynamic file savedearlier. The screen looks like Figure 6.22.

It is obvious that the process flowsheet includes the automatically inserted twolevel controllers (LCI and LC3) and one pressure controller (PC2). Each of thesecontrollers has an operator set point (SP), a process variable (PV), also known as

controlled variable, and a controller output (OP), also called as manipulated variable,

whose values are obtained from the Aspen Plus simulation. These control structures

also have their own tuning parameters, and so on, suggested by Aspen Dynamics.

However, there is a scope to modify (or remove) the controller and its related items.The Aspen generated control loops defined below should be used in the closed-loop

study of the prescribed catalytic distillation column.

J SAND QNTROL OF PRF.SSURE-Drivkn PRnrPgg,Q t 303

HSJ-Jl-(»>.

1 nr- <nm

teTH

-,.,1 ,

J

FIGURE 6.22

Loop 1Controller: LCI

Type of controller: proportional (P)-only (since reset time is very large)Controlled variable, liquid level in the reflux drumManipulated variable: distillate (DIS) flow rate (percentage opening ofvalve CV2)Controller action: direct

Use all default data, except proportional gain of 2 (suggested by Luyben, 2004)

Loop 2Controller: PC2

Type of controller: proportional integral (PI)Controlled variable: top stage pressure

Manipulated variable: condenser heat removalController action: reverse

Use all default data (suggested by Luyben, 2004)

the condenser heat removal and P denotes the pressure to be controlled. Assumingdirect control action

,the controlle r equation can be rewritten for Aspen Dynamics

** Qr = - 47.48 - Kc {PSP - P), where 47.48 is the bias signal (Vr.s' "s

-'gn indicates heat removal (cooling operation). If we move from steady state position,'< is dear that when pressure (P) increases, the error (PS/. P) value becomes negahv..

.d ultimately,the neRative vain., ofQc decreases. Originally, the negative value should


increase because if pressure increases, there is a need to increase the heat removalrate. Therefore, our assumption is wrong and it should be reverse action in AspenDynamics.)

Loop 3Controller: LC3

Type of controller: P-onlyControlled variable: liquid level in the column base

Manipulated variable: bottoms (BOT) flow rate (percentage opening ofvalve CV3)Controller action: direct

Use all default data, except proportional gain of 2 (suggested by Luyben,2004)

Configuring new control loops

The primary objective of the example process is to produce a bottom MTBE product ofhigh purity. To achieve the desired product purity in presence of disturbance anduncertainty, several control algorithms need to be employed with the reactive distillation,

It should be noted that in the control system of a RD process, the liquid level andcolumn pressure controls constitute inventory control, maintaining the basic operationof the column. Thus, here emphasis is placed on the response of composition controlmethodologies to maintain product quality as well as correct stoichiometric ratio betweenthe feed streams. In the following, different control schemes have been discussed forthree distillation sections, namely feed section, top section and bottom section.

Feed section

For a chemical reaction with two reactants, the type of flowsheet depends on whether

we want to operate the catalytic distillation column with no-excess of either reactant orexcess reactant (Kaymak and Luyben, 2005). For a double-feed RD column,

if there is

any imbalance in the inflow of the two reactants ('excess reactant' case), the product

purity drops. This is because one of the reactants becomes excess and exits with theproduct stream, and this stream would have to be further processed to purify the productand recover the reactant for recycle. Obviously, the 'excess reactant' flowsheet requiresat least two separating columns and is therefore more expensive. However,

it is easier

to control. On the other hand, the 'no-excess reactant' flowsheet has better steady stateeconomics but presents challenging control problems because of the need to preciselybalance the stoichiometry of the reaction.

Several control structures used to maintain the correct stoichiometric ratio of the

reactants have been proposed by researchers (e.g., Al-Arfaj and Luyben, 2000; 2002;Wang et al., 2003). To meet this control objective, the controller requires some type offeedback of information from within the process to indicate the accumulation or depletionof at least one of the reactants. This can simply be done by the use of an internalcomposition controller by manipulating the flow rate of one of the fresh feeds. Thereare also other efficient control techniques (e.g.,

cascade control, inferential control)reported for stoichiometric balancing (Wang et al.,

2003). However, it is not practicalto simply ratio the two feed streams, as has been proposed in some of the literaturepapers. Flow measurement inaccuracies and feed composition changes doom to failure


any ratio controller that does not somehow incorporate information about compositionsinside the reactive system and feed this information back to adjust fresh feed.

For the concerned distillation column, the methanol composition is controlled on

10* stage by the adjustment of the methanol fresh feed. The butene feed rate is flowcontrolled. It is worthy to mention that manipulating the methanol feed to control aninternal methanol composition is preferred when the butene feed coming from theupstream units is not free to be adjusted. If this is not the case, then alternatively thef.so-butene concentration, instead of methanol concentration

, may be controlled on areactive stage by adjusting the butene feed rate.

We are now moving on to configure the composition controller for methanol feed.To do this, click on expand symbol (+) of Dynamics subfolder. Then again hit expandbutton of ControlModels icon. Subsequently, select the PID object, drag it to the flowdiagram, place the control block near to CVl block and rename it as CC4. In the next,expand Stream Types and use ControlSignal icon to complete the CC4 configuration,shown in Figure 6.23. Chapter 5 presents a detail of how to configure a control structurein Aspen Dynamics.

1

i a

. -Urn . - B-

FIGURE 6.23

A little detail of the composition control loop for methanol feed is demonstratedbelow

.

Loop 4Controller

.CC4

Type of controller: PIControlled variable: liquid phase mole fraction of MeOH on Stage 10Manipulated variable: fresh methanol (FL) flow rate (percentage opening of v alveCVl)

Controller action: reverse

306 PROCESS SIMULATION AND CONTROL USING ASPLN

Before executing the simulation run, it is customary to have a look on the data

sheet. For this, double-click on CC4 control block and then press Configure knob in the

faceplate to open the Configure dialog box. As mentioned in Chapter 5, it is wise to

click on Initialize Values button. Still one doubt is there: is the value of process variable(PV) displayed same with the steady state liquid phase concentration of MeOH onStage 10 obtained in the Aspen Plus simulation? Be sure about it

, choose Blocks/RDCOLUMN/Profiles with opening the Aspen Plus simulation file. Then select 'Liquid'in the View field in Compositions sheet and obtain the table shown in Figure 6.24, withliquid mole fraction of MeOH on 10th stage of 0.04886022. This value is identical withthat of PV in the Configure dialog box.

od* Run PV)

MBI : 1: 1 m|»l *lii

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STREAMS

0 w*.

?y3>Wl«

I[lr53

FIGURE 6.24

The controller CC4 is tuned by trial-and-error approach and the parameter valueshave been chosen as:


Integral time = 5 min

Use default values for other items including bias signal, ranges, etc.Notice that by the similar way, we can design the flow controller for butene feed of theRD column.

Top section

In addition to the LCI and PC2 control structures, the distillate composition can becontrolled by manipulating the reflux flow rate. In an alternative approach, along with

the pressure control (PC2), we can control the reflux drum level by the manipulation ofthe reflux rate and the distillate flow rate can be adjusted by a ratio control law to givea constant reflux ratio. In the present case, the former control scheme has been

incorporated for performance study.

DYNAMICS AND CONTROL OF PRESSURE-DRIVKN PROCESSES 307

Bottom section

In the bottom section of a distillation column, it is a common practice that either thebottom product purity or the tray temperature near the bottom of the column, whichhas a strong correlation with the product purity, is controlled at its desired value bythe manipulation of the reboiler heat duty. For the sample process, we have implementeda composition control structure for product quality control.

As the CC4 control block has been connected, similarly we can incorporate theother control structures discussed above with the distillation flowsheet. The window,shown in Figure 6.25, includes a closed-loop scheme in which the MTBE purity iscontrolled in the bottoms by adjusting the reboiler heat input and the methanol impurityin the top is controlled by manipulating the reflux flow rate. As stated earlier, theconcentration of methanol on the reactive stage it is being fed to (Stage 10) is measuredand controlled by the manipulation of the fresh methanol feed rate. The butene flowrate is flow-controlled. The liquid levels in the reflux drum and the base of the columnare maintained by the distillate flow rate and the bottoms flow rate, respectively. Thecondenser heat removal is manipulated to control the column pressure. All of thestructures are single-input/single-output (SISO) structures with PI controllers (P-onlyon levels).

c 0 a * q

-

-M

m 5JC»r.Lt»*v TV)-HM*

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-

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ll.

I

1

FIGURE 6.25

The details of control Loops 5, 6 and 7 are presented below.Loop 5

Controller: FC5

Type of controller: PI


Controlled variable: molar flow rate of butene feed (FV)

Manipulated variable: brake power (shaft power or brake power ofmotor or enginerequired to drive a compressor)Controller action: reverse

Proportional gain = 0.5 %/%Integral time = 0.3 minUse default values for other terms

Loop 6Controller: CC6

Type of controller: PIControlled variable: MTBE mole fraction in the bottoms

Manipulated variable: reboiler heat inputController action: reverse


Integral time = 5 minUse default values for other terms

Loop 7Controller: CC7

Type of controller: PIControlled variable: MeOH mole fraction in the distillate

Manipulated variable: reflux rate (mass flow)Controller action: reverse

Proportional gain = 5 %/%Integral time = 5 minUse default values for other terms

Now the flowsheet is ready for closed-loop performance study. Start the programas usual. It is important to mention that to restart a dynamic simulation,

click 'Restart'

(F7) from the Run menu or press 'Re-start Simulation' button on the Run Control toolbar.

Performance of the closed-loop RD process

In the present study, two consecutive step changes in methanol feed temperature (46.85-» 40oC at time = 1.7 hours and then 40 -> 460C at time = 3.9 hours) have been

introduced to examine the performance of the closed-loop RD process. A change in feedtemperature affects the internal composition in the reactive zone. This, in turn, maydeteriorate the product quality. The system responses to temperature disturbance areillustrated in Figure 6.26. It is obvious that the proposed structure is able to maintainthe MTBE purity in the bottoms under the influence of disturbance variable. It canalso prevent excessive losses of both methanol and iso-butene in the products.

Each Aspen Dynamics model includes different plots and tables from which we caneasily access the simulation inputs as well as results. For this, first highlight ablock or stream, then right-click to point Forms and finally select the item that wewant to access.


EBB

»5fl

ill 1 i4--

1

-A

-

1 r-

jf5A

FIGURE 6.26

Performance of the closed-loop RD process with Measurement lags

Aspen Dynamics screen, shown in Figure 6.27, includes three dead time blocks (DTI,DT2 and DT3) connected with three composition controllers (CC4, CC6 and CC7).

o5 3

Lii

Ot- [ZtK- F

4-x-i-mf

13iJ

FIGURE 6.27


The measurement lag of 15 sec (0.25 min) is used in all composition loops. Toincorporate a dead time for a measured variable

, say methanol mole fraction onStage 10, highlight DTI block, right-click on the block, point to Forms and then selectConfigure to open the configure table. In the Value cell

, enter 0.25 min as a sensordead time. Follow the same approach for other two dead time blocks

.

Here, we have used the proportional gain of 1 %/% and integral time of 20 min for

all composition controllers. The effects of disturbance in butene feed temperature have

been depicted in Figure 6.28.

mmFte View Took Wtxjow Heb

Q b: B SQi IS .iV I Dynamic 3 h « IB » ffl b? t! Cl B

SfnUahon r tt Tf Gi«i|oo5_j i; a* v» ' K

-I phut !-:-»&-

o<- gl«

3e+001, step =i=e- 5 0000e-002 sCepto 23 83to 23 84to 23 85to 23 86

-arfcad x se r-i-r*U>V>* | jjDlWS-MiCCToll.. I A«»»Pte-t..W. | y <iM»teot.inole«,,||k7 fapm D «o. ... « #r)0 IS26

FIGURE 6.28

Initially a step decrease (76.85 -> 650C at time = 8 hours) and subsequently a stepincrease (65 -> 760C at time = 15 hours) have been considered in the simulation study.The developed closed-loop process flowsheet responds satisfactorily under load variablechange and measurement lag.


In Chapter 5, we have studied the dynamics and control of the flow-driven chemicalprocesses. Here, a case study has been conducted on a MTBE catalytic distillation

column using the pressure-driven dynamics. The complete process flow diagram includes

a distillation column, a feed compressor, a feed pump and three control valves. In the

MTBE synthesis process, a bottom product containing high-purity MTBE and a topproduct enriched with n-butene are obtained. To maintain the MTBE purity in thebottoms stream, several control structures have been configured with the flowsheet in

DYNAMICS AND CONTROL OF PKKSSURK-DRIVKN PROCKSSKS .*J 1 1

Aspen Dynamics. All of the structures are SISO schemes with PI controllers (P-onlyon levels). The controllers have been tuned by simply using heuristics. The proposedclosed-loop process provides satisfactory results under disturbance input andmeasurement lag.

PROBLEMS

6.1 A binary mixture of ethanol and l-propanol enters a flash drum (Flash2) Thefeed specifications are shown in Figure 6.29 with the process flow diagram.

Liquid mixture(UQ-MIX)

Temperature = 90XPressure = 1,4 bar

Flow rate = 120 kmol/hr

Component Mol fract

ethanol 06

1-propanol 0.4

CV2

cCH liq-mix f»B-[fgiECV1

-(pF]->t'i-|pdt-uq1-oCV3

FIGURE 6.29 A flowsheet of a flash drum

The flash chamber operates at 90oC and 1.2 bar. The vertically placed separatorwith a length of 2 m and diameter of 1 m has elliptical head type. All the controlvalves have a pressure drop of 0.2 bar. Applying the RK-Soave thermodynamicmodel as a base property method,

(a) simulate the flowsheet to obtain the product compositions,(b) design the two control schemes to maintain the pressure and liquid level in

the flash chamber, and

(c) examine the performance of the designed controllers.6.2 Styrene is produced by dehydrogenation of ethylbenzene.

Here we consider an

irreversible reaction:

- C2H5 -> CgHs - CH = CH2 + H2

ethylbenzene styrene hydrogen

The process flow diagram that consists of a reactor (RSTOIC), a feed compressor(COMPRESS) and a control valve (CV) is shown in Figure 6.

30

An isentropic compressor discharges the FEED stream that enters the RStoicreactor at 2 bar The reactor runs at 260oC and 2 bar.

The control valve involves

a pressure drop of 0.2 bar Use the fractional conversion of ethylbenzene equals0

.

8. Applying the Peng-Robinson thermodynamic method.

(a) simulate the flowsheet,

and'b) observe the closed-loop process response employing the flow controllers.

312 PROCESS SIMULATION AND CONTROL USING ASPECT

Pure ethylbenzene

Temperature = 260oCPressure = 1 barFlow rate = 100 kmol/hr

M"

! [pptI-ocv

-|feed|-1COMPRESS RSTOIC

FIGURE 6.30 A flowsheet for the production of styrene.

6.3 The hydrogenation of aniline produces cyclohexylamine in a CSTR according tothe following reaction:

C6H5NH2 + 3H2 -> CeHnNHa

aniline hydrogen cyclohexylamine

The complete process flowsheet is provided in Figure 6.31. It includes a pumphaving a discharge pressure of 41.2 bar, an isentropic compressor having adischarge pressure of 41 bar, an elliptical head-type vertically placed reactorhaving a length of 1 m and three control valves with a pressure drop of 0.2 barin each.

F1

FEED

CV1

PUMP

F2

FL P1

> <

-u

CV2

>ff J 1 PDT-LIQ \-0CV3

COMPRESS RCSTR

FIGURE 6.31 A flowsheet for aniline hydrogenation

The reactor operates at 41 bar and 120oC, and its volume is 1200 ft3 (75% liquid). For

the liquid-phase reaction, the inlet streams, Fl and F2, are specified in Table 6.2.

TABLE 6.2

Reactant Temperature (°C) Pressure (bar) Flow rate (kmol/hr)

Pure aniline (Fl) 40 7 45

Pure hydrogen (F2) -12 7 160

DYNAMICS AND CONTROL OF PKKSSURE DRIVEN PROCESSES 313

Data for the Arrhemus law:

Pre-exponentiaJ factor = 5 x lO8 m3/kmol s

Activation energ>' = 20.000 Btu/lbmol

ICJ basis = Molanty

Use the SYSOP0 base property method in the simulation. The reaction is first-order in aniline and hydrogen, and the reaction rate constant is defined withrespect to aniline.

(a) Simulate the flowsheet to compute the product compositions,

ibi configure the control schemes for maintaining the liquid level, pressure andtemperature in the CSTR. and

(c) investigate the closed-loop process response under any disturbance input

6.4 Repeat the above problem with adding a time lag of 0.2 min in temperature

measurement and carry out the closed-loop process simulation to report thedisturbance rejection performance of the developed scheme

6.5 In addition to the level, pressure and temperature controllers, include the flowcontrollers with the flowsheet, shown in Problem 6.3. and inspect the closed-loopprocess response.

REFERENCES |Al-Arfaj. M A. and W L Luyben (2000).

"Comparison of Alternative Control Structuresfor an Ideal Two-product Reactive Distillation Column,

"

Ind. Eng. Chem. Res., 39,pp 3298-3307.

Al-Arfaj. M A and W L. Luyben (2002),"Control Study of Ethyl fert Butyl Ether Reactive

Di-tillation." Ind. Eng Chem. Res., 41, pp. 3784 -3796.Jacobs. R. and R Krishna

. (1993) "Multiple Solutions in Reactive Distillation for Methyltot-Butyl Ether Synthesis.

"

Ind. Eng. Chem. Res., 32. pp 1706-1709.Kaymak

, D B and W L. Luyben (2005),"Comparison of Two Types of Two-temperature

Control Structures for Reactive Distillation Columns,

" Ind. Eng. Chem. Res , 44,pp 4625-4640.

Luyben, W L. i2004i "Use of Dynamic Simulation to Converge Complex ProcessFlowsheets

.

" Chemical Engineering Education, pp. 142-149Rehfinger. A and U Hoffmann (1990)

,"Kinetics of Methyl Tertiary Butyl Ether Liquid

Phase Synthesis Catalyzed by Ion Exchange Resin-I. Intrinsic Rate Expression inLiquid Phase Activities

.

" Chem Eng. Set.. 45. pp. 1605-1617.Seader

. J D and E J Henley 11998).

"Separation Process Principles,' John Wiley &

Sons. In< . New York

W Bng, S J , I) s H WonK and E K Lee (2003)."Control of a Reactive Distillation Column

m the Kinetic Regime for the Synthesis of n Butvl Acetate.

" Ind Eng. Chem Re* .42

. pp B182-5194.

Index

ABSBR2. 164

AbNorplittn cnliunn, UMAnounlinK mformnhon. I I. 'M. 58Acetone, 93

Activation energy, (>r>Adsorption, 100Aniline, M

ArrhrniUH Inw, Bf*. 70ASPEN. :J

Aopen batchCAD, 1Aapen chroniHloKmphv. IAapen Dynamica, 1Ahpimi Dynaniica ,

22!)

Aapen HYSYS. 1Aapen Plus, IAapen polymers pliiH.

1

Anpcn prnpcrl ich I

Hhmc method,

)HBati hKrac

,I0H

Binary diatillation column,

'Mth

Binary mixture,\2

BK10 tr>iBlock

,7

Block inftirmation,

33'''"'-Me point

,28

('hmmnil phtnt, 180Compoaonl ))>, I Ml('

omponpnt tijuiii<, I it.

('onfiguro dialog bospli'io

Control pnncl, 20Control vnlvi'M. 22!)

(iontrol modali icon, 2(18('outI'ol Mi mil icon, 2(18

(!yclohoxylamina, (ir»

I cnniei', 7, 51

1 )(«(>( lianisuir column, n>7

DcHi n ipac, I7(iDi'w point, 35Direcl acting control, 243Diaplay plot, I7i>Diatillation, l()7Diatillation train, 180, 100Diatl, 107

I )nvirin tor i r, 100I )i mn modela, 7

Dryer, r>2D8TWII. 107. 108

I dynamic mode, 253i kynumicN library, 2(i7Dvnn I'M IS. r>

' t'tnlvtir dialillation,

28fiTOIJIOK

.152

flbemCad, .1

Mi hyll'onMtne, 56rixpOlll'lltN, 2il7

316 INDKX

Flash 2, 3, 7

Flow-driven, 229

Flow-driven simulation, 229

Formula, 116

Fraction basis, 195

FSpht, 204

Geometrv data, 237

HETP, 287

Hvdraulics sheet, 299

HYSYSTM, 3

Peng-Robinson,

60PetroFrac

,108

PetroFrac model,

1 48Plot wizard

,48. 90, 147

POLYSRK,

204Power law

,54, 87

Pre-exponential factor,65

Pressure-driven simulations,

229, 285PRO/1ITM

,3

Process flowsheet window,

9

Process variable,

249

Property method,18, 32. 39

Pulse input,253

Pumparound circuits,

149

Initialization mode, 253

Initialize values button, 273

Input summary, 23, 64

Ketene, 93

Kinetic, 74

Kinetic factor, 100

Kinetic reaction type, 300Kinetic sheets, 238

LHHW, 54, 93LMTD, 256

MTBE column, 286

Material STREAMS, 7

Measurement lags, 309, 310MELLAPAK, 287

Methane, 93

Model library, 5Molarity, 76Multi-input/multi-output, 243MultiFrac, 107

RadFrac, 107

RadFrac model, 127

Ranges tab, 247RateFrac, 108

RBatch, 54

RCSTR, 54

RCSTR model, 230

Reconnect destination, 192

Reconnect source, 193

REFINERY, 154

Regulatory performance, 254, 275Rename block, 11, 193Rename stream, 193

Report file, 23, 122Report options, 15Requil, 54Results plot dialog box, 251Reverse acting control, 243RGibbs, 54

RK-Soave, 28. 32

RPlug. 54, 78RStoic, 54, 55Run status, 62

RYield, 54

NRTL, 52

Object manager, 179Operator set point, 247Optimization, 178

Pause at time, 251

PENG-ROB, 140

SCFrac, 108

Sensitivity analysis,172

Sep 1, 2, 7Separators, 42Servo performance,

275

Setup, 15Side strippers,

149

Single-inputysingle-output, 243Solver settings, 13SRK, 52

INDEX 317

Stepwise, 7Stoichiometric coefficients, 237Stream information. 18. 33Stream table, 22

Styrene, 55SULZER, 287SYSOPO*. 18

UNIFAC. 287

User Models, 7

Vapour fraction,210

Variable number.

180

Vinyl chloride monomer, 189, 203

Temperature approach, 262Template. 5

Wilson model, 43

Winn-Underwood-Gilliland method,

107

PROCESS SIMULATIONAND CONTROL USING

ASPEN AMIYA K. JANA

As Ihe complexilv of a plant integrated with several process units increases, solving Ihe model structure with a large equationset becomes a challenging task. To overcome this situation, various process flowsheet simulators are used. This book describesthe simulation, optimisation, dynamics and closed-loop control of a wide variety of chemical processes using the most popularcommercial flowsheet simulator Aspen'"

.

The book presents the Aspen simulation of a large variety of chemical units, including flash drum, continuous stirred tank reactor(CSTR), plug flow reactor (PFR), petroleum refining column, heat exchanger, absorption lower, reactive dislittation, disiillationtrain, and monomer production unit. It also discusses the dynamics and control of flow-driven as well as pressure-driven chemicalprocesses using Ihe Aspen Dynamics package.

KEY FEATURES

Acquaints Ihe students with the simulation of large chemical plants with several single process units.* Includes a large number of worked out examples ittustrated in step fay-step format for easy understanding of the concepts.

Provides chaptered problems lor extensive practice.

This book is suitable for the undergraduate and postgraduate students of chemical engineering. It will also be helpful to researchscientists and practising engineers.

THE AUTHOR

Amiya K. Jana received his B.E. degree in chemical engineering in 1998 from Jadavpur University, M.Tech. in chemical engineeringin 2000 from IIT Kharagpur, and Ph.D. in chemical engineering in 2004 from IIT Kharagpur.

Presently. Or. Jana is Assistant Professor at IIT Kharagpur. His areas of research include control system, process intensification,and modelling and simulation. He is also the author of ChemiesJ Process Mode/ting and Computer Simukuon published byPHI learning.

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A Textbook of Chemical Engineering Thermodynamics, K.V. Narayanan

Rs. 295.00

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