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Stanley I. Sandler

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Herausgeber: John Wiley & Sons
Kategorie: Wissenschaft und neue Technologien
Sprache: Englisch

Beschreibung

A step-by-step guide for students (and faculty) on the use of Aspen in teaching thermodynamics

• Easily-accessible modern computational techniques opening up new vistas in teaching thermodynamics
A range of applications of Aspen Plus in the prediction and calculation of thermodynamic properties and phase behavior using the state-of-the art methods
• Encourages students to develop engineering insight by doing repetitive calculations with changes in parameters and/or models
• Calculations and application examples in a step-by-step manner designed for out-of-classroom self-study
• Makes it possible to easily integrate Aspen Plus into thermodynamics courses without using in-class time
• Stresses the application of thermodynamics to real problems

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Leseprobe

Using Aspen Plus® in Thermodynamics Instruction

A Step-by-Step Guide

Stanley I. Sandler

Department of Chemical and Biomolecular Engineering University of Delaware Newark, DE

A Joint Publication of the American Institute of Chemical Engineers and John Wiley & Sons, Inc.

Published by John Wiley & Sons, Inc., Hoboken, New Jersey.

Published simultaneously in Canada.

No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning, or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 750-4470, or on the web at www.copyright.com. Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, (201) 748-6011, fax (201) 748-6008, or online at http://www.wiley.com/go/permission.

Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives or written sales materials. The advice and strategies contained herein may not be suitable for your situation. You should consult with a professional where appropriate. Neither the publisher nor author shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages.

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Library of Congress Cataloging-in-Publication Data:

Sandler, Stanley I., 1940- author. Using Aspen plus in thermodynamics instructions : a step by step guide / by Stanley I. Sandler, Department of Chemical and Biomolecular Engineering, University of Delaware. pages cm Includes index. ISBN 978-1-118-99691-1 (paperback) 1. Thermodynamics–Data processing.2. Aspen plus.I. Title. QD504.S26 2015 536′.7028553–dc23

2014029629

Preface

An Introduction for Students

Chapter 1 Getting Started With Aspen Plus

PROBLEMS

Chapter 2 Two Simple Simulations

PROBLEMS

Chapter 3 Pure Component Property Analysis

PROBLEMS

Chapter 4 The NIST ThermoData Engine (TDE)

PROBLEMS

Chapter 5 Vapor–Liquid Equilibrium Calculations Using Activity Coefficient Models

5.1 PROPERTY ANALYSIS METHOD

5.2 THE SIMULATION METHOD

5.3 REGRESSION OF BINARY VLE DATA WITH ACTIVITY COEFFICIENT MODELS

PROBLEMS

Chapter 6 Vapor–Liquid Equilibrium Calculations Using an Equation of State

6.1 THE PROPERTY ANALYSIS METHOD

6.2 THE SIMULATION METHOD

6.3 REGRESSION OF BINARY VLE DATA WITH AN EQUATION OF STATE

PROBLEMS

Chapter 7 Regression of Liquid–Liquid Equilibrium (LLE) Data and Vapor–Liquid–Liquid Equilibrium (VLLE) and Predictions

7.1 LIQUID–LIQUID DATA REGRESSION

7.2 THE PREDICTION OF LIQUID–LIQUID AND VAPOR–LIQUID–LIQUID EQUILIBRIUM

7.3 HIGH PRESSURE VAPOR–LIQUID–LIQUID EQUILIBRIUM

PROBLEMS

Chapter 8 The Property Methods Assistant and Property Estimation

8.1 THE PROPERTY METHODS ASSISTANT

8.2 PROPERTY ESTIMATION

8.3 REGRESSING INFINITE DILUTION ACTIVITY COEFFICIENT DATA

PROBLEMS

Chapter 9 Chemical Reaction Equilibrium in Aspen Plus

PROBLEMS

Chapter 10 Shortcut Distillation Calculations

PROBLEMS

Chapter 11 A Rigorous Distillation Calculation: RadFrac

PROBLEMS

Chapter 12 Liquid–Liquid Extraction

PROBLEMS

Chapter 13 Sensitivity Analysis: A Tool for Repetitive Calculations

PROBLEMS

Chapter 14 Electrolyte Solutions

PROBLEMS

Index

EULA

List of Tables

Chapter 8

Table 8.1-1

Table 8.1-2

List of Illustrations

Chapter 1

Figure 1-1a

Aspen Plus V8.0 Start-up

Figure 1-1b

Aspen Plus V8.0 Start-up

Figure 1-2a

Aspen Plus V8.2 Start-up

Figure 1-2b

Figure 1-2c

Figure 1-3

Figure 1-4

Figure 1-5

Figure 1-6

Figure 1-7

Figure 1-8

Figure 1-9

Figure 1-10

Chapter 2

Figure 2-1

Figure 2-2

Figure 2-3

Figure 2-4

Figure 2-5

Figure 2-6

Figure 2-7

Figure 2-8

Figure 2-9

Figure 2-10

Figure 2-11

Figure 2-12

Figure 2-13

Figure 2-14

Figure 2-15a

Figure 2-15b

Figure 2-16

Figure 2-17

Figure 2-18

Figure 2-19

Figure 2-20

Figure 2-21

Figure 2-22

Figure 2-23

Figure 2-24

Figure 2-25

Figure 2-26

Figure 2-27

Figure 2-28a

Figure 2-28b

Figure 2-29

Figure 2-30

Figure 2-31

Figure 2-32

Figure 2-33

Figure 2-34

Figure 2-35

Figure 2-36

Figure 2-37

Figure 2-38

Figure 2-39

Figure 2-40

Figure 2-41

Figure 2-42

Chapter 3

Figure 3-1

Figure 3-2

Figure 3-3

Figure 3-4

Figure 3-5

Figure 3-6

Figure 3-7

Figure 3-8

Figure 3-9

Figure 3-10

Figure 3-11

Figure 3-12

Figure 3-13

Figure 3-14

Figure 3-15

Figure 3-16

Figure 3-17

Figure 3-18

Figure 3-19

Figure 3-20

Figure 3-21

Figure 3-22

Figure 3-23

Figure 3-24

Figure 3-25

Figure 3-26

Figure 3-27

Figure 3-28

Figure 3-29

Figure 3-30

Figure 3-31

Figure 3-32

Chapter 4

Figure 4-1

Figure 4-2

Figure 4-3

Figure 4-4

Figure 4-5

Figure 4-6

Figure 4-7

Figure 4-8

Figure 4-9

Figure 4-10

Figure 4-11

Figure 4-12

Figure 4-13

Figure 4-14

Figure 4-15

Figure 4-16a

Figure 4-16b

Chapter 5

Figure 5.0-1a

Figure 5.0-1b

Figure 5.0-1c

Figure 5.0-1d

Figure 5.0-1e

Figure 5.0-2

Figure 5.1-1

Figure 5.1-2

Figure 5.1-3

Figure 5.1-4

Figure 5.1-5

Figure 5.1-6

Figure 5.1-7

Figure 5.1-8

Figure 5.1-9

Figure 5.1-10

Figure 5.1-11

Figure 5.1-12

Figure 5.1-13

Figure 5.1-14

Figure 5.1-15

NRTL

Figure 5.1-16

UNIQUAC

Figure 5.1-17

Wilson

Figure 5.1-18

UNIFAC

Figure 5.1-19

Figure 5.1-20

Figure 5.1-21

Figure 5.1-22

Figure 5.1-23

Figure 5.2-1

Figure 5.2-2

Figure 5.2-3

Figure 5.2-4

Figure 5.2-5

Figure 5.2-6

Figure 5.2-7

Figure 5.2-8

Figure 5.2-9

Figure 5.2-10

Figure 5.2-11

Figure 5.2-12

Figure 5.2-13

Figure 5.2-14

Figure 5.2-15

Figure 5.2-16

Figure 5.2-17

Figure 5.2-18

Figure 5.3-1

Figure 5.3-2

Figure 5.3-3

Figure 5.3-4

Figure 5.3-5

Figure 5.3-6

Figure 5.3-7

Figure 5.3-8

Figure 5.3-9

Figure 5.3-10

Figure 5.3-11

Figure 5.3-12

Figure 5.3-13

Figure 5.3-14

Figure 5.3-15

Figure 5.3-16

Figure 5.3-17

Figure 5.3-18

Figure 5.3-19

Figure 5.3-20

Figure 5.3-21

Figure 5.3-22

Figure 5.3-23

Figure 5.3-24

Figure 5.3-25

Figure 5.3-26

Figure 5.3-27

Figure 5.3-28

Figure 5.3-29

Figure 5.3-30

Figure 5.3-31

Figure 5.3-32

Figure 5.3-33

Figure 5.3-34

Figure 5.3-35

Figure 5.3-36

Figure 5.3-37

Figure 5.3-38

Figure 5.3-39

Figure 5.3-40

Figure 5.3-41

Figure 5.3-42

Figure 5.3-43

Figure 5.3-44

Figure 5.3-45

Figure 5.3-46

Figure 5.3-47

Figure 5.3-48

Figure 5.3-49

Figure 5.3-50

Figure 5.3-51

Figure 5.3-52

Figure 5.3-53

Figure 5.3-54

Figure 5.3-55

Figure 5.3-56

Figure 5.3-57

Chapter 6

Figure 6.1-1

Figure 6.1-2

Figure 6.1-3

Figure 6.1-4

Figure 6.1-5

Figure 6.1-6

Figure 6.2-1

Figure 6.2-2

Figure 6.2-3

Figure 6.2-4

Figure 6.2-5

Figure 6.2-6

Figure 6.2-7

Figure 6.2-8

Figure 6.2-9

Figure 6.2-10

Figure 6.2-11

Figure 6.2-12

Figure 6.2-13

Figure 6.2-14

Figure 6.2-15

Figure 6.3-1

Figure 6.3-2

Figure 6.3-3

Figure 6.3-4

Figure 6.3-5

Figure 6.3-6

Figure 6.3-7

Figure 6.3-8

Figure 6.3-9

Figure 6.3-10

Figure 6.3-11

Figure 6.3-12

Figure 6.3-13

Figure 6.3-14

Figure 6.3-15

Figure 6.3-16

Figure 6.3-17

Figure 6.3-18

Figure 6.3-19

Figure 6.3-20

Figure 6.3-21

Figure 6.3-22

Figure 6.3-23

Figure 6.3-24

Figure 6.3-25

Figure 6.3-26

Figure 6.3-27

Figure 6.3-28

Figure 6.3-29

Figure 6.3-30

Figure 6.3-31

Figure 6.3-32

Figure 6.3-33

Figure 6.3-34

Figure 6.3-35

Chapter 7

Figure 7.1-1

Figure 7.1-2

Figure 7.1-3

Figure 7.1-4

Figure 7.1-5

Figure 7.1-6

Figure 7.1-7

Figure 7.1-8

Figure 7.1-9

Figure 7.1-10

Figure 7.1-11

Figure 7.1-12

Figure 7.1-13

Figure 7.1-14

Figure 7.1-15

Figure 7.1-16

Figure 7.1-17

Figure 7.1-18

Figure 7.1-19

Figure 7.1-20

Figure 7.1-21

Figure 7.1-22

Figure 7.1-23

Figure 7.1-24

Figure 7.1-25

Figure 7.1-26

Figure 7.1-27

Figure 7.1-28

Figure 7.1-29

Figure 7.1-30

Figure 7.2-1

Figure 7.2-2

Figure 7.2-3

Figure 7.2-4

Figure 7.2-5

Figure 7.2-6

Figure 7.2-7

Figure 7.2-8

Figure 7.2-9

Figure 7.2-10

Figure 7.2-11

Figure 7.2-12

Figure 7.2-13

Figure 7.2-14

Figure 7.2-15

Figure 7.2-16

Stream 1

Figure 7.2-17

1SPLIT

Figure 7.2-18

2DECANT

Figure 7.2-19

3FLASH3

Figure 7.2-20

4FLASH3 (same as 3Flash3 except at a higher temperature and lower pressure to ensure a three-phase split)

Figure 7.2-21

Figure 7.2-22

Figure 7.3-1

Figure 7.3-2

Figure 7.3-3

Figure 7.3-4

Figure 7.3-5

Figure 7.3-6

Figure 7.3-7

Figure 7.3-8

Figure 7.3-9

Figure 7.3-10

Figure 7.3-11

Figure 7.3-12

Figure 7.3-13

Chapter 8

Figure 8.1-1

Figure 8.1-2

Figure 8.1-3

Figure 8.1-4

Figure 8.1-5

Figure 8.1-6

Figure 8.1-7

Figure 8.1-8

Figure 8.1-9

Figure 8.1-10

Figure 8.2-1

Figure 8.2-2

Figure 8.2-3

Figure 8.2-4

Figure 8.2-5

Figure 8.2-6

Figure 8.2-7

Figure 8.2-8

Figure 8.2-9

Figure 8.3-1

Figure 8.3-2

Figure 8.3-3

Figure 8.3-4

Figure 8.3-5

Figure 8.3-6

Figure 8.3-7

Figure 8.3-8

Figure 8.3-9

Figure 8.3-10

Figure 8.3-11

Figure 8.3-12

Figure 8.3-13

Figure 8.3-14

Figure 8.3-15

Figure 8.3-16

Figure 8.3-17

Figure 8.3-18

Figure 8.3-19

Figure 8.3-20

Figure 8.3-21

Figure 8.3-22

Chapter 9

Figure 9-1

Figure 9-2

Figure 9-3

Figure 9-4

Figure 9-5

Figure 9-6

Figure 9-7

Figure 9-8

Figure 9-9

Figure 9-10

Figure 9-11

Figure 9-12

Figure 9-13

Figure 9-14

Figure 9-15

Figure 9-16

Figure 9-17

Figure 9-18

Figure 9-19

Figure 9-20

Figure 9-21

Figure 9-22

Figure 9-23

Figure 9-24

Figure 9-25

Figure 9-26

Figure 9-27

Figure 9-28

Figure 9-29

Figure 9-30

Figure 9-31

Figure 9-32

Figure 9-33

Figure 9-34

Figure 9-35

Figure 9-36

Figure 9-37

Figure 9-38

Figure 9-39

Figure 9-40

Figure 9-41

Figure 9-42

Figure 9-43

Figure 9-44

Figure 9-45

Figure 9-46

Figure 9-47

Figure 9-48

Chapter 10

Figure 10-1

(a) Schematic diagram of a distillation column, and (b) showing the tray-to-tray flows and compositions.

Figure 10-2

Figure 10-3

Figure 10-4

Figure 10-5

Figure 10-6

Figure 10-7

Figure 10-8

Figure 10-9

Figure 10-10

Figure 10-11

Figure 10-12

Figure 10-13

Figure 10-14

Figure 10-15

Figure 10-16

Figure 10-17

Figure 10-18

Figure 10-19

Figure 10-20

Figure 10-21

Chapter 11

Figure 11-1

Figure 11-2

Figure 11-3

Figure 11-4

Figure 11-5

Figure 11-6

Figure 11-7

Figure 11-8

Figure 11-9

Figure 11-10

Figure 11-11

Figure 11-12

Figure 11-13

Figure 11-14

Figure 11-15

Figure 11-16

Figure 11-17

Figure 11-18

Figure 11-19

Figure 11-20

Figure 11-21

Figure 11-22

Figure 11-23

Figure 11-24

Figure 11-25

Figure 11-26

Figure 11-27

Figure 11-28

Figure 11-29

Figure 11-30

Figure 11-31

Figure 11-32

Figure 11-33

Figure 11-34

Figure 11-35

Figure 11-36

Chapter 12

Figure 12-1

Figure 12-2

Figure 12-3

Figure 12-4

Figure 12-5

Figure 12-6

Figure 12-7

Figure 12-8

Figure 12-9

Figure 12-10

Figure 12-11

Figure 12-12

Figure 12-13

Figure 12-14

Figure 12-15

Figure 12-16

Figure 12-17

Figure 12-18

Figure 12-19

Figure 12-20

Figure 12-21

Figure 12-22

Figure 12-23

Figure 12-24

Figure 12-25

Figure 12-26

Chapter 13

Figure 13-1

Figure 13-2

Figure 13-3

Figure 13-4

Figure 13-5

Figure 13-6

Figure 13-7

Figure 13-8

Figure 13-9

Figure 13-10

Figure 13-11

Figure 13-12

Figure 13-13

Figure 13-14

Figure 13-15

Figure 13-16

Figure 13-17

Figure 13-18

Figure 13-19

Figure 13-20

Figure 13-21

Figure 13-22

Figure 13-23

Figure 13-24

Figure 13-25

Figure 13-26

Figure 13-27

Figure 13-28

Figure 13-29

Figure 13-30

Figure 13-31

Figure 13-32

Figure 13-33

Figure 13-34

Figure 13-35

Figure 13-36

Chapter 14

Figure 14-1

Figure 14-2

Figure 14-3

Figure 14-4

Figure 14-5

Figure 14-6

Figure 14-7

Figure 14-8

Figure 14-9

Figure 14-10

Figure 14-11

Figure 14-12

Figure 14-13

Figure 14-14

Figure 14-15

Figure 14-16

Figure 14-17

Figure 14-18

Figure 14-19

Figure 14-20

Figure 14-21

Figure 14-22

Figure 14-23

Figure 14-24

Figure 14-25

Figure 14-26

Figure 14-27

Figure 14-28

Figure 14-29

Figure 14-30

Figure 14-31

Figure 14-32

Figure 14-33

Figure 14-34

Figure 14-35

Figure 14-36

Figure 14-37

Figure 14-38

Figure 14-39

Figure 14-40

Figure 14-41

Figure 14-42

Figure 14-43

Figure 14-44

Figure 14-45

Figure 14-46

Figure 14-47

Figure 14-48

Figure 14-49

Figure 14-50

Figure 14-51

Figure 14-52

Figure 14-53

Figure 14-54

Figure 14-55

Figure 14-56

Figure 14-57

Figure 14-58

Figure 14-59

Figure 14-60

Figure 14-61

Figure 14-62

Figure 14-63

Figure 14-64

Figure 14-65

Figure 14-66

Guide

Cover

Table of Contents

Preface

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Preface

Aspen Plus® is a very powerful process simulator—that is, a tool for modeling chemical processes, including complete chemical and pharmaceutical plants and petroleum refineries. As such, it requires accurate models of thermodynamic properties and phase behavior.

The purpose of this book is to introduce the reader to the use of Aspen Plus in courses in thermodynamics; consequently, very few of the process simulation capabilities are considered here. In undergraduate chemical engineering degree programs, process simulation is heavily used in the capstone design course, and this is where its details and intricacies are generally taught. This book serves as a prelude to instruction in the more complex process simulation and provides a coherent approach to introducing the Aspen Plus simulator in undergraduate thermodynamics courses. I hope it will make such courses more interesting and relevant by allowing calculations of real processes that would otherwise be very tedious. One advantage of doing such calculations by computer is that repetitive calculations with varying parameters are quickly achieved, so that the student gains experience into the ways in which different input parameters affect the output. Such calculations develop engineering insight. Any instructor knows that asking students to do repetitive calculations by hand is met by moans and groans. Doing a calculation for one case is an important learning activity, while doing many cases by hand has much less pedagogical return for the student's time investment.

This book provides the reader with a self-study, step-by-step guide to doing thermodynamic calculations in Aspen Plus. It provides actual screenshots of the Aspen Plus interface to solve example problems of specific types, including vapor–liquid, liquid–liquid, vapor–liquid–liquid and chemical reaction equilibria, and simple applications to liquefaction, distillation, and liquid–liquid extraction. One important feature is that learning occurs by means of illustration. It is not a book of rules but of specific examples, encouraging readers to generalize from those examples and apply what they have observed to a specific problem. Designed for self-study, this book is not meant as an in-class textbook but for out-of-class use. However, there are places in this book where it is useful to refer to fundamental thermodynamic principles. In such cases, for convenience, I provide explicit references to my thermodynamics textbook, Chemical, Biochemical, and Engineering Thermodynamics, 4th ed., published by John Wiley & Sons, Inc., in 2006. However, the same material can be found in any standard thermodynamics textbook, so this book can be used with any thermodynamics textbook.

Let me reiterate that although the Aspen Plus program is designed to do process simulation, the purpose of this book is not to emphasize simulation. Examples of using the program for simulation are included, however, because some thermodynamics calculations can only be done in Aspen Plus by using simulation. These include vapor–liquid and vapor–liquid–liquid equilibrium flash calculations, especially an adiabatic flash (i.e., Joule–Thomson expansion) and chemical reaction equilibrium calculations. Please keep in mind that the Aspen Plus program has far greater capabilities than are demonstrated here.

This book is meant to be a step-by-step guide for individual study. As such, the book contains many screen images produced using Aspen Plus®. These screen images of Aspen Plus® are reprinted with permission of Aspen Technology, Inc. AspenTech®, aspenONE®, Aspen Plus®, and the AspenTech leaf logo are trademarks of Aspen Technology, Inc. All rights reserved.

All suggestions for improvement would be greatly appreciated. Please communicate those to me at [email protected].

Finally, I want to acknowledge the assistance provided by Aspen Technology, Inc., that provided an individual license to use Aspen Plus® so that I could work on this manuscript at home while attending to my wife during her final illness. I especially want to thank Chau-Chyun Chen, a former Aspen Technology employee, who made this possible and also provided many helpful comments on an early version of the manuscript. Suphat Watanasiri of Aspen Technology was also helpful in the process.

STANLEY I. SANDLER

January 2015

An Introduction for Students

As you are beginning to see in your courses, thermodynamic calculations for other than ideal gases can be quite time consuming. Also, in class you may have considered a single device, such as a Joule–Thomson valve, or in the case of liquefaction, just a few devices (e.g., a compressor, a heat exchanger, a Joule-Thomson valve and a separator.) Such calculations can require many iterations, both for each unit operation (e.g., equation of state calculations for the compressor) and, if there are recycle streams as in the Linde process, for the overall process as well. You can imagine how difficult and time-consuming such calculations would be for a whole chemical plant or petroleum refinery, with very many different pieces of process equipment and a complex web of many recycle streams. So how are such calculations done in industry, or how will you do them efficiently in your design course, especially if you want to consider many different design options? The answer is by using a complicated computer program known as a process simulator. Such a computer program allows the user to put together a flow sheet of the equipment in the process being considered and to connect all the equipment by the flows of mass (and in the case of heat exchangers and some other equipment by the flows of heat). Then, after the user specifies the components, the feed composition, the conditions, the constraints, and the thermodynamic models to be used, he or she is able to compute the amounts and compositions of all the streams in the process. After seeing the results, the user can easily make changes to the inlet stream and the conditions (e.g., temperature and/or pressure at various points of the process), and rerun the simulation. In this way the engineer acquires an understanding of how the process responds to changes in conditions, allowing the engineer to optimize the process for various metrics: profitability, minimum carbon dioxide or other waste emissions, minimum energy use, etc.

Why introduce process simulation in a course on thermodynamics? Several compelling reasons exist. First, as you progress through your thermodynamics classes you will see that the calculations involved become increasingly more complicated. This alone justifies the use of some type of computer software. Second, a calculation for a single set of process specifications can be tiresome, though doing only one allows the student to understand the basis of the calculation. But this understanding, while important, does not provide the student or engineer with any insight into the way the process will respond to changes in the variables or whether the current set of specifications is optimum. Such knowledge comes only from calculations involving a collection of other operational specifications, and these calculations can be done rapidly with a process simulator, allowing the user to better understand the behavior of the process. In this way he or she can develop engineering intuition that would not come from doing only a single calculation. Third, choosing the correct thermodynamic model(s) is critical to obtaining meaningful results in process simulation, so that thermodynamics and process simulation are linked together in a very important way.

I want to emphasize this last point since it is so important. As an example, suppose the process we want to model contains liquids, but we tell the process simulator to use the ideal gas law to describe the system. What will happen? The process simulator will provide answers, but the results will be nonsensical. A process simulator will do computations exactly as instructed, but it is unable to determine whether the result obtained is meaningful or not. That is the job of the engineer. In computer lingo there is an acronym, GIGO, which means “garbage in, garbage out.” Here it translates to bad thermodynamics, bad results. Unfortunately, in my consulting experience, I have observed another application of GIGO, meaning “garbage in, gospel out.” That is, the user of a process simulator accepts the results obtained without critical evaluation. This is often due to the fact that the engineer has had difficulty getting a completely unrelated process simulation calculation to converge (or converge to a reasonable answer) and has tried different thermodynamic models until one yielded a reasonable answer. From then on, the engineer has tended to use that model for all other processes, including the ones for which it is completely inappropriate. This is a serious error of engineering judgment that could prove expensive to rectify or dangerous if a chemical plant were built according to those faulty specifications.

The central point, therefore, is that while using a process simulator can eliminate the tedium of process calculations, the results will only be meaningful if the user has a sufficient understanding of thermodynamics and thermodynamic models to make informed choices. Anyone using a process simulator (or, for that matter, any computer tool for calculations) should carefully check the results against his or her engineering intuition, experience, and knowledge of thermodynamics. For example, in the chapter on chemical reactions, the principle of Le Chatelier and Braun can provide guidance as to how the equilibrium state of a chemically reacting system might shift in response to a pressure change. If the result of a process simulation indicates otherwise, one should make sure that the input and process choices are correct. Similarly, if a change of temperature in a process produces a result that is counterintuitive, further analysis is required. The point is that one should not blindly accept any result derived from a computer. Rather, one must analyze all the factors to see whether they make sense.

While most chemical and petroleum companies initially developed their own in-house process simulators, the expense of maintaining them, of introducing new thermodynamic and equipment models as they became available, and of servicing users became untenable. Consequently, the field of process simulation is now dominated by software from a few commercial vendors and some freeware through the CAPE-OPEN project. A web search will yield a number of available process simulators. Here we will consider only one, Aspen Plus—arguably, the one possessing the largest user base and, in addition, made available to universities at a very affordable price.

The main use of Aspen Plus is for process simulation, and various books and courses are devoted to instructing students in how to employ it. That is not our purpose here; we are interested solely in the way Aspen Plus can be used in undergraduate courses in thermodynamics. Therefore, while Aspen Plus has a wide range of capabilities, we will consider only the following:

Basic process simulation

Phase equilibria (vapor–liquid, liquid–liquid, and vapor–liquid–liquid)

The thermodynamic data regression capabilities

Property analysis

(pure fluids and mixtures)

The

NIST TDE

(thermodynamics data engine)

The

Property Method Selection Assistant

Simple distillation and extraction

Note: Throughout this text a word or words in bold font refer to a specific aspect or function of the Aspen Plus simulator identified as such. Readers of this book when using it to follow an example while using the Aspen Plus simulator, should select, by clicking on it, the relevant text indicated in bold.

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