Process Simulation and Control Using Aspen 1st Edition

astern

PROCESS SIMULATIONAND CONTROL USING

METHANOl

BUTENES

RDCOLUMN CCS

AMIYA K. JANA

Rs. 295.00

PROCESS SIMULATION AND CONTROL USING ASPENAmiya 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.

rPreface

"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 Optimizationusing Aspen Plus

1. Introduction and Stepwise Aspen Plus Simulation:

Flash Drum Examples 3-531.1 Aspen: An Introduction 3

1.2 Getting Started with Aspen Plus Simulation 4

1.3 Stepwise Aspen Plus Simulation of Flash Drums 7

1.

3.

1 Built-in Flash Drum Models 713 2 Simulation nf a Flash nmm

, , , _8

1.

3.3 Computation of Bubble Point Temperature 28

1.

3.4 Computation of Dew Point Temperature 35

1.

3.5 T-xy and P-xy Diagrams of a Binary Mixture 42

Summary and Conclusions 50Prnhlpms

, , , ,

50

Reference 53

2,

Aspen Plus Simulation of Reactor Models 54-1062.

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 65

2.4 Aspen Plus Simulation of a RPlug Model 78

2.

5 Aspen Plus Simulation of a RPlug Model using LHHW Kinetics 93Summary and Conclusions 104Prohlpms 704

Reference 106v


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 IQfl3 9. 9 Simulation of a RaHFrnr MoHpI 122

3.3 Aspen Plus Simulation of the Multicomponcnt Distillation Columns 136

3.

3 1 Simnlnt.ion of a RaHFrar MoHpI 13fi

3.

3.

2 Simulation of a PetroFrac Model 1483

.4 Simulation and Analysis of an Absorption Column 1643.5 Optimization using Aspen Plus 178

Summary and Conclusions 181Problems ffl2

Part II Chemical Plant Simulation using Aspen Plus4

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

4.2 Aspen Plus Simulation of a Distillation Train 189

4.3 Aspen Plus Simulation of a Vinyl Chloride Monomer (VCM)

Production Unit 203Summary and Conclusions 220Prnhlpms

; , -220

References 226

Part III Dynamics and Control using Aspen Dynamics5

. Dynamics and Control of Flow-driven Processes 229-2845J Tnt.roHiirt.ion 2295.2 Dynamics and Control of a Continuous Stirred

Tank Reactor (CSTR) 2305

.3 Dynamics and Control of a Binary Distillation Column 255Summary and Conclusions 279Prnhlpms

, , ,..279

References 284

6. Dynamics and Control of Pressure-driven Processes 285-313

fil 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).

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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 bluearrows 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 checkmarkappears. 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.

3-

FLASH

FIGURE 1.4 A flowsheet of a flash drum.

Simulation approachFrom 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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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 flowsheetSelect 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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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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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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INTRODUCTION AND STKPWISK ASPEN PLUS SIMULATION 13

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Configuring settingsAs 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: AKJANAAccount number: 1Project 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 componentsClicking 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 an

exact 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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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 methodPress 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 informationIn 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, andenter 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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Specifying block informationHitting 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

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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 simulationClick on Next button and get the following screen (see Figure 1.26). To run thesimulation, press OK on the message. We can also perform the simulation selectingRun from the Run pulldown menu or using shortcut key F5.

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

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

Viewing input summaryTo 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).

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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

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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 2COMPUTATIONAL SEQUENCE 2OVERALL FLOWSHEET BALANCE 2

PHYSICAL PROPERTIES SECTION 3COMPONENTS 3

U-O-S BLOCK SECTION 4BLOCK: FLASH MODEL: FLASH2 4

STREAM SECTION 5F L V 5

PROBLEM STATUS SECTION 6BLOCK 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 - 256PSIZE 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: MOLESTREAM REPORT COMPOSITION: MOLE FLOW

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

CONVENTIONALC3H8N-C4H10N-C5H12N-C6H14

INCOMPONENTS

22.046244.092566.138788.1849

OUT(LBMOL/HR)

22.046244.092566.138788.1849

RELATIVE DIFF.

0.

101867E-090

.

326964E-10-0

.

113614E-10-0

.

332941E-10


TOTAL BALANCEMOLE( LBMOL/HR) 220.462 220.462 0.000000E+00MASS(LB/HR) 15906.4 15906.4 -0.782159E-11ENTHALPY(BTU/HR) -0.165833E+08 -0.147349E+08-0.111463

ASPEN PLUS PLAT: WIN32 VER: 11.1FLASH CALCULATIONSPHYSICAL PROPERTIES SECTION

06/10/2007 PAGE 3

COMPONENTS

ID TYPEC3H8 CN-C4H10 CN-C5H12 CN-C6H14 C

FORMULAC3H8C4H10-1C5H12-1C6H14-1

NAME OR ALIASC3H8C4H10-1C5H12-1C6H14-1

REPORT NAMEC3H8N-C4H10N-C5H12N-C6H14

ASPEN PLUS PLAT: WIN32 VER: 11.1FLASH CALCULATIONSU-O-S BLOCK SECTION

06/10/2007 PAGE 4

BLOCK: FLASH MODEL: FLASH2INLET STREAM: FOUTLET VAPOR STREAM: V

OUTLET LIQUID STREAM: LPROPERTY OPTION SET: SYSOP0 IDEAL LIQUID / IDEAL GAS

*** MASS AND ENERGY BALANCE ***

IN OUT RELATIVE DIFF.TOTAL BALANCEMOLE(LBMOL/HR) 220.462MASS(LB/HR) 15906.4

220.46215906.4

0.

000000E+00-0

.

782136E-11ENTHALPY(BTU/HR) -0.165833E+08 -0.147349E+08 -0.111463

INPUT DATA

TWO PHASE TP FLASHSPECIFIED TEMPERATURESPECIFIED PRESSUREMAXIMUM NO. ITERATIONSCONVERGENCE TOLERANCE

FPSI

200.000100.000300

.

000100000

*** RESULTS ***

OUTLET TEMPERATURE F 200.00


OUTLET PRESSUREHEAT DUTYVAPOR FRACTION

PSIBTU/HR

100.000.

18484E+070.

19274

V-L PHASE EQUILIBRIUM:

COMPC3H8N-C4H10N-C5H12N-C6H14

F{I)0.

100000

.

200000

.

300000

.

40000

X(I)0

.

52117E-010.

169260

.

316020

.

46260

Yd)0

.

300550

.

328740

.

232900.

13781

K(I)5

.

76681

.

94220

.

736970

.

29790

ASPEN PLUS PLAT: WIN32 VER: 11.1FLASH CALCULATIONS

06/10/2007 PAGE 5

STREAM SECTIONF L V

STREAM IDFROM :TO

L

FLASHFLASH

SUBSTREAM: MIXED

PHASE: MIXEDCOMPONENTS: LBMOL/HR

C3H8 22.0462N-C4H10 44

.

0925N-C5H12 66

.

1387

N-C6H14 88.

1849

COMPONENTS: MOLE FRACC3H8 0.1000N-C4H10 0

.

2000

N-C5H12 0.

3000N-C6H14 0

.

4000TOTAL FLOW:

LBMOL/HR 220.4623LB/HR 1.5906+04

CUFT/HR 1839.5613STATE VARIABLES:

TEMP F 50.0000PRES PSI 15.0000VFRAC 1.8002-02LFRAC 0.9820S FRAC 0.0

V

FLASH

LIQUID

9.

2754

30.123756.2424

82.3291

5.

2117-020.

16930.

31600.

4626

177.97061.

3313+04382.4385

200.0000100.0000

0.

0

1.

00000.

0

VAPOR

12.770913.96889.

8963

5.

8558

0.

30050.

32870.

23290.

1378

42.49172593.71583008.0650

200.0000100.0000

1.

00000.

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 1.4126-02LB/CUFT 8.6469 34.8100 0.8623

AVG 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 fractionCi 0

.

05c2 0

.

1

C3 0.

15i-Ci 0.1n-Ci 0.2i-C5 0

.

25n-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 approachAfter starting the Aspen Plus simulator, the Aspen Plus Stnrt

,.,v iAmong 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\Aitr.leI:MV l,1gffj ,AsinwiPtft.,..- "" TTrTtrtilVfnrt.i0ritliiiV>iWnrfca 11C 'Pi09'*T>F'f'''-!CW"lecl-AW1>t>jFceii'A:Mr!rt,: n

H !i j

FIGURE 1.32

When the next window pops up (see Figure 1.33),

select General with Metric Unitsand 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 flowsheetUsing 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

Configuring settingsFrom 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|aIBI -I -I frWi.-r- i h.i> rsr

.

.igi]ralt-Htl l-al l 3J . I I"! J?J 21 j J Si

I _ti>|g| - I ' m

.

I i Us*-**,

t.-'l(.

11 -

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

FIGURE 1.36

Specifying componentsClick 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 iav wfc- t.

PisgLBJ .1.1 Hl SI_

1-

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

i j . i i xapji i iw 'Hrtgj


Specifying property methodHit 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.

TmsxS\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 informationClick 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 igila

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 UferModefiMatenal

STREAMS Flash2 Fla h3 Dncanie.Fo. Help, p

Sep 5ep2

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

FIGURE 1.40

Specifying block informationHit 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

34 PROCESS SIMULATION AND CONTROL USING ASPENRunning the simulationPress Next button and then hit OK to run the simulation

. The following Control Paneldemonstrates 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 enPtuj 1

'

* (W Oi/fc &' vv. 0*a Toob Ain PM Lferarv Wmdcw Hcto

J_

l" l-l-PT

-j j b I 3 tti iiJfXi 32>J jaal n i33 Set-*

2

O Setup

I

-CM Sap

i SOU. | U-Moa* |

FIGURE 1.43

-| ,Mdfl .-.. .

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(viP*Jl

fO Cor- OBban*V

O 1tmt

WMllwilfc iiiy

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

Component Mole fractionCi 0.05C2 0.1Ca 0.15

36 PROCESS SIMULATION AND CONTROL USING ASPENSimulation approachAs 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

.

l_.

LJ...l-:i.::.l JAI "-

I/I I J J_J_J_:J..J -gj JId *J 1PJ M _j.

1 empWis

3!

i C VProffwnFdc-. sptnTeehWA/oikaigFolitei'/Jiipen Plus 11C ogfam F,lt; Vi.ipenTBeh\W0il-n Plo: 11

For Help, prws Fl

ft? Start] j

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).

i i iMB

Peisonalj Bsfmeiy StmolahonsK..ihEris(

Pe'io jumF haimacouiKiJ: Ml

I Ptiarniaceijlical;"Polymei: wiinEr

PoWe*! "el'gi Pyiionie


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

Creating flowsheetIn 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).

gjfffc i Dm > Ha-w- Ifca* . .iffi J

3

-H c-

0 St*-CD c

if

itftLWfS n>rJ f* i c-*. --3 s.-

mt| -i>w. |>-icj- i.tanwr|| - # i

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.

Configuring settingsHitting 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.

Specifying componentsHere 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).

Copyrighted malenal


-

LT _l_LJ__rv 3 I I _lL

,J9J i

J U

v ...Sup SprtlfttaMoo,

5(re*T,GISUrj-Sti

.

J

. J JBlocks

LI

-

CorVrwoente*

-

J Fl- vsh cting Options*

_

J MjdH ArWyjo Tooli' Vj EO Cont"Juri n* Results

(iee waleicalculatrani

Text lo appeal on eorh page Ihe FTporl He See Help

0 o 8 ISTREAMS S tilCTh2 Flath3 Decaniei Sap Scp2

_

Fo He*i, prats Fl C:\ .,gFoders\AspwiPlu5 11.1 MUM ?qu)

FIGURE 1.48

Fie E* View Data Tools Run Plot Lfcrary Window HelpMi

al-f-jfeKI-glH N>i -I . | \*\ m\m ..:/;| [Lit r -3 >'H r *\*m\i-

|0 Specfenoh j/j Setup

SpecificationsSiroJatron OptionsStieam Class

bfe Subsbeams

S 1 3 Units-SetsQ Custom Unrts0 Report Options

*: | Components+ PropertiesI Streams

_

iJ BlocksSi Reactions+ Convergence+ FtowsheeSng Options* Mate'Analysts Tools*

.

ifl Cor/igurationQ] RtsJts Sunmary

/GlobalI ./Descnption /Arc Diapnoslici

jAKJANA ': Aspen Plus accounitng rioifnation

j U set name:Accouil luffnber:

I PtqedIDj Project name:

ANYTHING

jAS YDU UKEi

Project n.

Input Canvtete

pT MMea/SpiKm SefMHtais | HutEictangen | Cokmu | Reactat | Pteuute Changeu j ManpuWcs | Stfcfc | Us ModehH 0 -0 -0C < Flash? FImKI DmcmIm

fcHelc, press Fl


i--rr-i-!>-i' it

. Jj I 111t r

-

SlJ "" -l ""H I ~ I

-Q*.>lQl l!gJ

IMXooc

-I

i-

1 . i

=1Cfcc* i c*iiBMr opto* SHI

r . -.

WnmW 1 * | Haaf.ctaran I fi pi. | Hull

Mart!: A-a.-r*4 'P- .

J 13 tiB AH

FIGURE 1.51



Specifying stream informationIn the column at the left side

, choose Streams/1. As a result, a stream input form opensEntering all required information

,one obtains the screen as shown in Figure 1.52

.

D1l

_

j Cfctt/ runt

_

,.~J>

a .

-3

tum [Met. ]:fin f hr*"" .]

-II

ili

INTRODUCTION AND STEPWISK ASPEN PLUS 3!MUU\TION 41

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

-

j-

r-H'-hrr II . t .! -1031 I - ! !

HI 33 ,

mi r . .1:

-D-' ! I MM WWII | CMm I l-MI I *-- II in I -I I M*i I IM MB

o-e-oi-it-IIKMM

-I*. MM'I (Will

FIGURE 1.54

Viewing resultsFirst 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 Mixture

Problem statement

A binary mixture, consisting of 60 mole% ethanol and 40 mole% water, is introduced

into 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 approachAs 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 flowsheetFrom 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

Configuring settingsAfter 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

S!fll>l*l


i * Vlaw cyta Icob Biji n-j

-

L-

r,

j_

.

Lj.inr iL1 Specfrahon:

_

J Sot rr s

SpetKkattww' | iitM) .WwiO

flltr-ComOS' ) HerryCofroi

.

_

J P nwt

Strrars

. J_

j CwTy Ocunj-

_

21 EC Ccti. 0JOftt

l L__

!

v'Selertionj PtMeum | NoneonvtrMnal | Oat nki {

ComponnHIDiTHANOl

i Warn* I Um Drtned ! R*>* !!

IU MM

FIGURE 1.68(b)

Copyrighled material

50 PROCESS SIMULATION AND CONTROL USING ASPENNotice that the plot window can be edited by right clicking on that window and

selecting 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 well

recognized 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

,

foursimple 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 theamounts 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 a

flash drum at 50oF and 20 psia.

TABLE 1.3

Component Flow rate (lb moiyhr)i-C4 12n-C4(LK) 448i-C5(HK) 36

Ce 23C7 39.1

272.2

c9 31876.3

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

toluene and 0.6 mole fraction rso-butanol at 101.3 kPa. Assume ideal mixtureand 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 of

hydrocarbons with the following composition at 345 kN/m2(see Table 1.4).TABLE 1.4

Component Mole fractionc3 0.05

n-C4 0.25n-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

Component Mole fractionc, 0

.

05

c2 0.1Ca 0.15

i-C4 0.1n-C4 0.2i-Cs 0.15n-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, is

fed 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).

52 PROCESS SIMULATION AND CONTROL USING ASPENTABLE 1.6

Component Flow rate (kmol/hr)n

-pentaneethanolwater

10

3

7.

5

Applying the NRTL property method, simulate the decanter block to compute

the flow rates of two product streams.1.10 A ternary mixture having the following flow rates is fed to a separator (Sep2) at

50oC and 5 bar (see Table 1.7).TABLE 1.7

Component Flow rate (kmol/hr)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 Tn

-pentaneethanolwater

0.

9990

.

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 using

split 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 theSOLIDS 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 ratesS(02 = 800 Ib/hrH20 = 5 Ib/hr

Air

Temperature = 200oCPressure = 1 atm

Flow rates = 50 Ibmol/hrN2 = 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 withregard 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 + H2ethylbenzene 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 fractionalconversion of ethylbenzene equals 0.8. Using the Peng-Robinson thermodynamic method,simulate the reactor model.

Simulation approachAs 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 BMWr . jw*-Ntaet 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 flowsheetWe 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 a

rrowf 'blue arrows are optional ports. arr0WS are re(luired ts andClick 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- CJ 'Kf! Pin ftr-Kl- LI'-TV iWoc,-. i

DltflBI BI Id iff! GN-|e>IM


Configuring settingsHitting 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: AKJANAAccount number: 5Project ID: ANYTHINGProject name: YOUR CHOICEFinally, 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 iaiMM 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 dmr_ utM

-O-

'ftifc waw

I i i I M>l Umomm I

FIGURE 2.6(c)

Specifying componentsIn 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


Specifying property methodChoosing Properties /Specifications in the column at the left side

, one obtains theproperty 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>|


Specifying block informationFrom 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 informationIn 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 stoichiometric

coefBcients and specify the fractional conversion. In the Aspen Plus simulator, coefficients

should be negative for reactants and positive for products (see Figure 2.11).** b* bo "e*

>'-'

J

RiACTQR

Wt


Running the simulationIn 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 thesimulation. 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|HllirDMll

I M ill"" Elfb Imeicbah

As8V.'Bend

RxnNo Specilicaiun type StochiotnebyIttrCanpi ETHYL-01 > STYREHE . KrtiflOGEN

UNIFAC Group* j UMo*b |

F-,r Ho

,

press F1'

-Stall *.

Boot_

Aww.RaocDdr | Awr.Mcd I

FIGURE 2.12

Viewing resultsAs 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 " ii lUMan'*

m

cna

inpp BUB

Waw' VI | ****** | HU** .

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

"-I r

FIGURE 2.14


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

'-lup I , IT

_

LiiE| | |a|

EES;: gIBll|Oi. lall|'rj. .aaJj'lLMto SlAtM | Salami | HealEKclwgeij | Cokfwx naactan | pienueChange!i | Manpiaton | 5cM [ UmModeb |

,S 0 U 31U

STREAMS 1 BSinc BEoii HGMis RCSTB BPItg RBaM.

FIGURE 2.15

\ s FoWen JJswn Ru H 1 HUMlfloAi Artfahie

Viewing input summaryFor input information, press Ctrl + Alt + I on the keyboard or select Input Summary

from the View pulldown menu (see Figure 2.16).CBSES

Fie * Forw* >Atw

input Sugary created by Aspen Plus K1. 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-FLOSLE-FMC ETHYL-01 1.

e Ci'.Users-.akjana.AppMtaMocal Terep -ape906.tK}

' B i I vjnwi-* |- laJtol | lto.,-s || -WEME1 : jpCittU

FIGURE 2.16

t 65- y wkjusu,jO f DOIf 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 theC6H5NH2 + 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 45Pure 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, againhit 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 magrlook 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-

Aapn Plus Vf # i"

VSJ6

FIGURE 2.17(a)

g *apen IP= Strean Prx&hts

I Beetle, |fa Enshh ijrit|aklntill wth Medic IMiProcws 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* .

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 hb

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

0 SkW* Qnl. Jfl Ml St

Cereal | Ftowiho* | Bbcf Ali j Roperty j AW |turn U be ndmMr, tiiMm itpoii

P MtJa P Mcta! r Uau P Mm

TFF [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 " -

(BillFIGURE 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>MMt t

RSac Brtrtj ftEqai RGfcb) flCStft RFtifl Rflaieh

FIGURE 2.21

Specifying property methodWe 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*JTtQ('W -i.d"*''",l''fi' Aipcn rim - Sani

FIGURE 2.22


Specifying stream informationAs we hit Next followed by OK, a stream input form appears. For Stream A (pureaniline) and Stream H (pure hydrogen), values of state variables and composition areinserted in the following two forms, shown in Figures 2.23(a) and (b).

ffe * '-Am Di Tol 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)Specifying block informationIn 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.. -I

p=-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-

I1XJMm 0 . 8 . o y JE D

IMMI Ptmt hm. unit TVl ggg

Ifflll

0>W ta< - i HwlE-changer. [ Cokm* Hb1o | 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 theleft 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

J4JJ

nr

"I i I i i I I i

"3 '-" l

il il -

am nil 11000 0541

05

MUM nooo 0J30 0 001-

mmmi tso 6011 ITTre ' 0J

sm DOM MPPM0 98)

| HuiE*w> ! C

ASPEN PLUS SIMULATION OF REACTOR MODEI S 79

Simulation approachSelect 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 ASPEN TM

Creating flowsheetIn the Model Library, select the Reactors tab. Expanding the RPlug icon, the followingscreen is obtained (see Figure 2.38).

Uj _

jS's - s - oSIftEAMS ' RStoc flYfc) WJ RCte RCSTR RBtfd &M ro* ftj> Uonn WnSo* H*

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

>|[T>


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

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*pUaTSil

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

[T MMi- pdim I Smmnc I HulEchv4i | Cot-mi. flo'" | PimmCWhB- 1 -1 - 8 Q O

SIRLWi__

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

FIGURE 2.40(b)


dmbl Melm mbhjsM!] 21 g

r mi r SM

K C twwrH 4i , flow W 'IK

O-S-0 y

FIGURE 2.40(c)

Specifying componentsFrom 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 Di Tat* ftji RsT Ihwf ffntotr Hife

_

j r


tmum

~3

is1 I

I 3 "~I d r.I 3

. r

u

ETREAfce ftStac FTV dd SEtMl RCSTS RPljg flgateh

FIGURE 2.42

Specifying stream informationIn the left pane of the Data Browser window

,

select Streams IF and enter the valuesfor 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. dToid 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 ma

FIGURE 2.43


Specifying block informationIn 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\&\**\| Hi ! |Mi H i?i :H Ma

_

j . /- itarj

S_

j PAttwn

?cp(rtif Veered

a :

36

DwtmUt 06.

-J

a is q-u' RStot Rrail flE Modab |

HUM

FIGURE 2.45


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

Specifying reaction informationHitting 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 benzene

to 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 BCtM ftGbb. RCSTft RFVp ISFa-Htfc mm FI "" " " ~

-

'-

--- II *pf\-ai

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 87iViirtiT.r

1 n-i 1.1 nr -.i ,ieii i mi *mi; i

433

71

am*. | CJk->J qLJniJ

_

j MHnnd

HmNo Stuctimttry

: Knc

E .11u ,. * c 1 r , I Sehdt I Ui*MJrt )

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

FIGURE 2.50

In the simulation of the present problem, we use partial pressure basis (applicablefor vapour only) and

,

therefore, the Power law expression has the following form:( f > n E ri 1

r = k exp R To,

(2.5)

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

18 replaced by:


r= kTn exp RT,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 Arrheniuslaw, we put zero for temperature exponent n and left the box, allotted for datumtemperature T0, empty.

I r mi r ! .isi; I - IB!

if.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

KiMteldaNUT/T>>|"*'(Ewto Rt fjfl,

8 i 0 a I Mill"11 Lin i

FIGURE 2.51(b)

ASPKN PLUS SIMULATION OF REACTOR MODELS 89

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

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(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).

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In the next, select Plot Wizard from the Plot pulldown menu. Alternatively, press

Ctrl+Alt+W on the keyboard and obtain Figure 2.55.

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

ASI'KN PLUS SIMULATION OF REACTOR MODELS 91

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

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


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FIGURE 2.59

Note that the plot window can be edited by right clicking on that window andselecting Properties

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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 LHHW

KINETICS

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"1E = 28.5 x 107 J/kmoln=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 approachAs 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.

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

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As the Connect to Engine dialog pops up,

click OK.

Creating flowsheetFrom the Model Library toolbar

, we have selected RPlug reactor and developed theprocess flow diagram as displayed in Figure 2.62

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ASPEN PLUS"1 SIMULATION OK REACTOR MODELS 95

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

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FIGURE 2.63(b)

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FIGURE 2.63(c)

Specifying componentsSelect Specifications under Components folder in the Data Browser window

.

As weout the Component ID column

, Aspen Plus provides the rest of the information incomponent input form

, shown in Figure 2.64.

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ASPEN PLUS SIMULATION OF REACTOR MODEI.S 97

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Documents

Process Simulation and Control Using Aspen 1st Edition