PLIINTWIDE DYMMIC
SIMULATORS IN ClIEMICEIL
PROCESSING and CONTROL
CHEMICAL INDUSTRIES
A Series of Reference Books and Textbooks
Consulting Editor
HEINZ HEINEMANN
1. Fluid Catalytic Cracking with Zeolite Catalysts, Paul B. Venuto and E.
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Winter, and Karl Stork
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The Chemistry and Technology of Petroleum, James G. Speight
The Desulfurization of Heavy Oils and Residua, James G. Speight
Catalysis of Organic Reactions, edited by William R. Moser
Acetylene-Based Chemicals from Coal and Other Natural Resources,
Robert J. Tedeschi
7. Chemically Resistant Masonry, Walter Lee Sheppard, Jr.
8. Compressors and Expanders: Selection and Application for the Process
Industry, Heinz P. Bloch, Joseph A. Cameron, Frank M. Danowski,
Ralph James, Jr., Judson S. Swearingen, and Marilyn E. VVeightman
9. Metering Pumps: Selection and Application, James P. Poynton
10. Hydrocarbons from Methanol, Clarence D. Chang
11. Form Flotation: Theory and Applications, Ann N. Clarke and David J.
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12. The Chemistry and Technology of Coal, James G. Speight
13. Pneumatic and Hydraulic Conveying of Solids, 0. A. Williams
14. Catalyst Manufacture: Laboratory and Commercial Preparations, Alvin B.
Stiles
15. Characterization of Heterogeneous Catalysts,
Delannay
edited by Francis
BASIC Programs for Chemical Engineering Design, James H. Weber
Catalyst Poisoning. L. Louis Hegedus and Robert W. McCabe
Catalysis of Organic Reactions, edited by John R. Kosak
Adsorption Technology: A Step-by-Step Approach to Process Evaluation
and Application, edited by Frank L. Slejko
20. Deactivation and Poisoning of Catalysts, edited by Jacques Oudar and
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Henry Wise
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22. Catalysis of Organic Reactions, edited by Robert L. Augustine
23. Modem Control Techniques for the Processing Industries, T. H. Tsai, J.
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24. Temperature-Programmed Reduction for Solid Materials Character
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25. Catalytic Cracking: Catalysts, Chemistry, and Kinetics, Bohdan W.
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28. Corrosion Mechanisms, edited by Florian Mansfeld
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Ogino
30. Catalyst Deactivation, edited by Eugene E. Petersen and Alexis T. Bell
31. Hydrogen Effects in Catalysis: Fundamentals and Practical Applications,
edited by Zoltan Peal and P. G. Menon
32. Flow Management for Engineers and Scientists, Nicholas P. Chere-
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33. Catalysis of Organic Reactions, edited by Paul N. Rylander, Harold
Greenfield, and Robert L. Augustine
34. Powder and Bulk Solids Handling Processes: Instrumentation and
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35. Reverse Osmosis Technology: Applications for High-Purity-Water
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36. Shape Selective Catalysis in Industrial Applications, N. Y. Chen, William
E. Garwood, and Frank G. Dwyer
37. Alpha Olefins Applications Handbook, edited by George R. Lappin and
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Clathrate Hydrates of Natural Gases, E. Dendy Sloan, Jr.
Catalysis of Organic Reactions, edited by Dale W. Blackburn
Fuel Science and Technology Handbook, edited by James G. Speight
Octane-Enhancing Zeolitic FCC Catalysts, Julius Scherzer
Oxygen in Catalysis, Adam Biefanski and Jerzy Haber
The Chemistry and Technology of Petroleum: Second Edition, Revised
and Expanded, James G. Speight
Industrial Drying Equipment: Selection and Application, C. M. van't Land
Novel Production Methods for Ethylene, Light Hydrocarbons, and Aromatics, edited by Lyle F. Albright, Billy L. Crynes, and Siegfried Nowak
Catalysis of Organic Reactions, edited by William E. Pascoe
Synthetic Lubricants and High-Performance Functional Fluids, edited by
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Zoeller
50. Properties and Applications of Perovskite-Type Oxides, edited by L. G.
Tejuca and J. L. G. Fierro
51. Computer-Aided Design of Catalysts, edited by E. Robert Becker and
Carmo J. Pereira
52. Models for Thermodynamic and Phase Equilibria Calculations, edited by
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53. Catalysis of Organic Reactions, edited by John R. Kosak and Thomas A.
Johnson
54. Composition and Analysis of Heavy Petroleum Fractions, Klaus H. Altgelt
and Mieczyslaw M. Boduszynski
55. NMR Techniques in Catalysis, edited by Alexis T. Bell and Alexander
Pines
56. Upgrading Petroleum Residues and Heavy Oils, Murray R. Gray
57. Methanol Production and Use, edited by Wu-Hsun Cheng and Harold H.
Kung
58. Catalytic Hydroprocessing of Petroleum and Distillates, edited by Michael
C. Oballah and Stuart S. Shih
59. The Chemistry and Technology of Coal: Second Edition, Revised and
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60. Lubricant Base Oil and Wax Processing, Avilino Sequeira, Jr.
61. Catalytic Naphtha Reforming: Science and Technology, edited by
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62. Catalysis of Organic Reactions, edited by Mike G. Scams and Michael L.
Prunier
63. Catalyst Manufacture, Alvin B. Stiles and Theodore A. Koch
64. Handbook of Grignard Reagents, edited by Gary S. Silverman and Philip
E. Rakita
65. Shape Selective Catalysis in Industrial Applications: Second Edition,
Revised and Expanded, N. Y. Chen, William E. Garwood, and Francis
G. Dwyer
66. Hydrocracking Science and Technology, Julius Scherzer and A. J.
Gruia
67. Hydrotreating Technology for Pollution Control: Catalysts, Catalysis,
and Processes, edited by Mario L. Occelli and Russell Chianelli
68. Catalysis of Organic Reactions, edited by Russell E. Malz, Jr.
69. Synthesis of Porous Materials: Zeolites, Clays, and Nanostructures,
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70. Methane and Its Derivatives, Sunggyu Lee
71. Structured Catalysts and Reactors, edited by Andrzej Cybulski and
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72. Industrial Gases in Petrochemical Processing, Harold Gunardson
73. Clathrate Hydrates of Natural Gases: Second Edition, Revised and
Expanded, E. Dendy Sloan, Jr.
74. Fluid Cracking Catalysts, edited by Mario L. Occelli and Paul O'Connor
75. Catalysis of Organic Reactions, edited by Frank E. Herkes
76. The Chemistry and Technology of Petroleum, Third Edition, Revised
and Expanded, James G. Speight
77. Synthetic Lubricants and High-Performance Functional Fluids, Second
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78. The Desulfunzation of Heavy Oils and Residua, Second Edition,
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79. Reaction Kinetics and Reactor Design: Second Edition, Revised and
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80. Regulatory Chemicals Handbook, Jennifer M. Spero, Bella Devito, and
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81. Applied Parameter Estimation for Chemical Engineers, Peter Englezos
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82. Catalysis of Organic Reactions, edited by Michael E. Ford
83. The Chemical Process Industries Infrastructure: Function and Economics, James R. Couper, 0. Thomas Beasley, and W. Roy Penney
84. Transport Phenomena Fundamentals, Joel L. Plawsky
85. Petroleum Refining Processes, James G. Speight and Baki Ozurn
86. Health, Safety, and Accident Management in the Chemical Process
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87. Plantwide Dynamic Simulators in Chemical Processing and Control,
William L. Luyben
ADDITIONAL VOLUMES IN PREPARATION
Lubricant Additives: Chemistry and Applications, edited by Leslie R.
Rudnick
PIANTWIDE MIMIC
SIMOLOTORS IN CHEMICAL
PROCESSING and CONTROL
William L. Layben
Lehigh University
Bethlehem, Pennsylvania
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Preface
Dynamic simulation has been used by chemical engineers for over a half
century. The earliest studies used mechanical and electronic analog computers to
study dynamic processes such as batch distillation, chemical reactors and feedeffluent heat exchangers. It took many hours to program and set up analog computers, and their maintenance was a never-ending job. The relatively small number
of amplifiers limited the number of differential equations that could be used in the
model, so only small-scale systems could be studied. A typical distillation column
simulation (I00 to 200 ordinary differential equations) required a Iarge-scale and
very expensive analog facility. However, despite the costs, most of the chemical
and petroleum companies invested in equipment and manpower to operate large
and well-staffed computing groups in their engineering research centers. The payoff in improved design and control justified the large expenditures.
With the advent of the digital computer in the 1960s, limitations on problem
size were relaxed by many orders of magnitude. Systems with thousands of differential equations could be studied. Programming difficulty decreased, but a new set
of numerical methods had to be learned and developed as essential tools for successful simulations. The limitation became computing speed. The increases in
computer speed over that last 30 years has been phenomenal, to say the least. So
we can now tackle quite complex plantwide dynamic simulations.
The dynamic models used in the early days were almost always "home
grown." The engineer would sit down and write out the equations describing the
system (algebraic and differential), using the fundamental laws and principles of
physics and chemistry. One of the major benefits of deriving the model was the
insight it provided into the behavior and structure of the process.
The 1970s and 1980s saw the growth of commercial process simulation
software that could analyze the steady-state behavior of chemical processes. Finally in the 1990s, the increase in computer speed permitted the development of
commercial dynamic simulators. At the beginning of the new millennium, the current state of simulation reflects the widespread use of commercial simulators in
both industry and universities. The most widely used simulators are HYSYSTM
from Hyprotech inc. and AspenPlus"mIAspenDynamicsTM from Aspen Technology. Both of these simulators include dynamic analysis capability.
The importance of investigating both the dynamic and the steady-state performance of chemical plants has been recognized for many years. This concept of
"simultaneous design" was one of the central features of the pioneering work in
process control by Page Buckley of Du Pont. In the past, the traditional capstone
vi
Preface
design course in most universities only explored the steady-state aspects of process design. This limited treatment is rapidly giving way to a more comprehensive
study of both dynamic controllability and steady-state economics.
The steady-state simulation aspects of using commercial software are fairly
well covered in textbooks and vendor tutorials. However, the dynamic aspects
have received only sketchy coverage. There is no structured way for students and
young engineers to learn how to use these commercial dynamic simulation packages to develop and test dynamic plantwide control structures.
Learning how to use the dynamic simulators is a somewhat painful and slow
process. The number of examples provided in vendor tutorials is small, and the
processes are limited in scope. The documentation and help screens can often be
unclear and offer little guidance. On-line technical assistance is usually not available to students, so unless a very knowledgeable faculty member or graduate student is available, students can struggle with dynamic simulations. Of course, time
is one commodity that senior students have in very short supply. They have limited time to invest in learning the ins and outs of simulators since the typical design project must be completed in only a few months.
The purpose of this book is to help students and inexperienced engineers
learn how to rapidly and effectively use dynamic simulators. Using dynamic simulators requires more than just knowing the software. It requires the application of
some good solid engineering principles. Remember the old saying "garbage in,
garbage out!"
The engineering steps that are necessary in moving from a steady-state
simulation to a dynamic simulation are presented in this book. These include sizing equipment, getting the "plumbing" correct, sizing control valves, developing a
basic regulatory control structure and tuning controllers. The development of a
plantwide basic regulatory control scheme requires looking at the big picture and
recognizing that all the units must "dance together." We must make sure that the
structure balances the stoichiometry of the reactions by adjusting the flowrates of
the fresh feed streams. Of course inert components must have a way to leave the
system so that they do not accumulate and degrade the performance of the process.
Once the overall scheme is in place, it is often more efficient to look at the
individual units to do the controller tuning since simulations of a single unit run
much more quickly than the simulation of the whole plant. The secret to successful simulations is "divide and conquer."
Dynamic simulators can handle many of the important unit operations, but
not all. However, the Iist of process units whose dynamics can be accurately simulated grows each year. The field is a rapidly changing one, so new capabilities are
offered with each new version of the software.
A number of case-study examples are provided in this book. They range
from a simple single unit with two or three controllers to complex, interconnecting
units in a plantwide system with dozens of controllers and a complex control
structure. These case studies cover a broad range of systems. The accompanying
CD contains the HYSYS and AspenDynamics files of all the cases. It also con-
Preface
vii
tains MS® Word files that give alI the figures in the book. These can be useful in
your reading because they are in color and because you can enlarge the figures in
order to see more detail.
It is hoped that this book will serve as an effective learning tool for students
and inexperienced engineers and serve as an introduction to dynamic simulators.
The intent is not to develop experts who know all the nitty-gritty details of the
simulators and use all the bells and whistles. For example, there are typically three
different ways to do a task. We only cover what I have found to be the simplest
and most intuitive.
There are also many advanced capabilities offered by the simulators, including writing your own models. We do not attempt to cover any of these advanced
functionalities. The goal of this book is to provide a solid starting point for inexperienced engineers and to give students a good working knowledge of the basics.
I would like to thank Cris Muhrer, Bryon Manor, and Oliver Smith of Air
Products for their tutoring in AspenDynamics and AspenPlus. James Goom of
AspenTech provided technical help with several aspects of using AspenDynamics.
I thank Joe Sieben of Hyprotech for his help in applying UYSYS. Brad Price and
Paul Bader of Lehigh University provided invaluable assistance with software and
hardware issues. Thanks are also due to the many senior students at Lehigh University who have suffered through the pain of learning dynamic simulators. Their
struggles are what have prompted the writing of this book.
William L. Luyben
Contents
Preface
Part I — Fundamentals
I
Chapter 1 — Introduction
Chapter 2 — Moving from Steady-State to Dynamic Simulations
Chapter 3 — Tuning Controllers
3
9
25
Part II — Single-Unit Dynamic Simulations
39
Chapter 4 — Tank Process
Chapter 5 — Blending Process
Chapter 6 — CSTR Reactor Process
Chapter 7 — Plug-Flow Tubular Reactors
Chapter 8 — Distillation Columns
Chapter 9 — Heterogeneous Azeotropic Distillation
Chapter I0 — Reactive Distillation
41
87
105
125
155
181
199
Part III — Multi-Unit Dynamic Simulations
225
Chapter 1 I — Pressure-Swing Azeotropic Distillation Columns
Chapter 12 — Heat-Integrated Distillation Columns
Chapter 13 — Tubular Reactor with Gas Recycle Process
Chapter 14 — Reactor/Column with Liquid Recycle
227
249
27 I
283
Part IV — Complex Plantwide Processes
301
Chapter 15 — Hydrodealkylation Process
Chapter 16 — Alkylation Process
Chapter 17 — Ethyl Benzene Process
Chapter 18 — Methyl Antilles Process
Chapter 19 — Concluding Topics
303
329
357
375
403
index
427
ix
PUINTWIDE DYNAMIC
SIMULATORS IN CHEMICOL
PROCESSING and CONTROL
Part 1
Fundamentals
Chapter 1
Introduction
1 . 1 Status
Dynamic simulation has become increasingly important as processes become more complex and are designed and operated closer to constraints. The use
of intermediate buffer tanks has been greatly reduced because of environmental
and safety concerns. Increasing yields and suppressing the formation of undesirable and environmentally unfriendly by-products are often achieved by using
complex flowsheets with many recycle streams. Increasing energy costs keep
pushing design engineers toward more heat integration. All of these trends make
dynamic control more difficult and dynamic simulation more important. It is vital
that all the unit operations of a complex flowsheet be able to "dance" together in
the face of the inevitable disturbances. These include production rate changes, feed
composition variability, transitions to different product specifications and rapid
ambient temperature changes during storms.
Ideally the dynamics of the process should be considered at the very early
stages of the development of a process. Certainly at the pilot-plant stage, trade-offs
between design and control should be explored, and basic regulatory control structures should be developed and tested. The engineering time expended at the early
stages can reap enormous economic benefits later in the project in terms of rapid,
trouble-free startups, reduced product-quality variability, less-frequent emergency
shutdowns, reduced environmental contamination and safer operation.
Fortunately our ability to perform plantwide dynamic simulations has also
increased. There are several commercial software packages that have dynamic
capability. The two most widely used are "HYSYS" from Hyprotech Inc. and
"AspenPlus/AspenDynarnics" from Aspen Technology. These two simulators will
be used in this book. Although these simulators are far from perfect (we will highlight some of the weaknesses and "bugs" as we go through this book), they do
provide a reasonably effective tool for studying process dynamics. Unfortunately,
there are a variety of bugs in each new version of the software, but these are
gradually being eliminated.
We will only illustrate the development of conventional single-input-singleoutput control structures that use linear proportional-integral (PI) controllers.
However, dynamic simulators are needed to test any control structure, whether it is
3
4
Chapter 1
a conventional P1 structure or more advanced control structures such as "Model
Predictive Control" (MPC), nonlinear control or adaptive control. The dynamic
simulators provide a rigorous nonlinear model of the process, which we hope captures the true behavior of the process.
1.2 Need
Learning how to use steady-state simulators is reasonably well covered in
several textbooks and vendor tutorials. The recent CD-ROM by Lewin et al.
(ISBN: 0-411-44254-2) provides a good introduction to use of steady-state simulators. However, learning how to use dynamic simulators is not covered thoroughly
in the existing textbooks. The purpose of this book is to fill this gap in the educational phase of the technology.
There are some significant steps that must be taken and vital information
that must be available to go from a steady-state simulation to a dynamic simulation. The details of these steps are covered in this book, and they are illustrated by
a number of case-study examples.
A second need that this book fills is making available a number of case studies. These range from very simple systems to complex flowsheets. The simple
systems are useful for learning how to get started in using dynamic simulators.
The complex systems are useful in illustrating how to apply the concepts of plantwide control to a realistic process. Control researchers should find these complex
case studies useful in providing a challenging process on which to apply their
newly developed advanced control methods.
1.3 Scope
One effective pedagogical approach to learning how to use dynamic simulators is to start with a very simple dynamic system (for example, a single tank).
This simple process has two or three control valves and the same number of controllers. It requires that we learn the basic operations of moving from a steadystate simulation to a dynamic simulation.
1.3.1 Equipment Sizing
Sizing equipment is necessary so that the dynamic capacitance of the
equipment (tank sizes, column liquid holdups, heat-exchanger volumes, etc.) is
available to the simulator. It is not necessary to have all the details of the mechanical design of the equipment. Some good estimates of the gas volumes and liquid
holdups in a system are all that are necessary to predict realistic dynamic responses.
Introduction
5
Some equipment sizing (for example, distillation columns) is provided by
the simulators. But many components are not automatically sized. In this book, we
use simple heuristics to set the sizes of surge tanks, separators, column bases, etc.
Conceptual equipment sizing is covered in Chapter 2.
1.3.2 Plumbing
The dynamic simulators provide two modes of simulation: "flow-driven"
and "pressure-driven." The latter type is strongly recommended, especially for
students. It is a much more accurate representation of the real process in which
hydraulics and fluid mechanics are of vital importance. Pumps, compressors and
control valves are important parts of the design.
For realistic dynamic simulations, the "plumbing" in the flowsheet must be
correctly designed so streams can flow from one unit to the next. This is a major
area of weakness of many students (and professors). They learn the theory of fluid
mechanics in their undergraduate course, but their plumbing skills are typically
poor. For example, students often put a control valve in the suction of a pump or
put two control valves in a liquid-filled line. Controlling flow through a compressor cannot be achieved by putting a valve in the discharge line. Compressors are
volumetric devices that pump "actual volume per minute" flows at suction conditions. The most realistic approach to controlling flow through a compressor in the
simulator is to manipulate work to the compressor. This corresponds to changing
compressor speed.
A crucial part of the plumbing is control valve sizing. This means setting the
percent valve opening and the pressure drop over the valve at steady-state design
conditions. Most valves are designed to be 50% open at design conditions. However, valves that must be able to provide significant increases in flow (for example, a valve on the cooling water to the jacket of an exothermic chemical reactor)
must be designed to have smaller design openings.
The design pressure drop of a valve is one of the classical examples of the
ever-present tradeoff between dynamic controllability and steady-state economics.
The higher the valve pressure drop, the more the flow through the valve can be
changed (improved rangeability). This translates into better control because more
"power" is available to handle disturbances and valve saturation is reduced. However, larger valve pressure drops require pumps or compressors with higher discharge pressures, which means higher energy consumption. Since gas compression is much more expensive than liquid pumping, control valves are often eliminated in gas systems by the use of variable-speed compressor drives (typically
steam turbines).
This plumbing material is of vital practical importance in the design and operation of the real plant, and it should be part of the simulation. This material is
covered in Chapter 2.
6
Chapter 1
1.3.3 Installing Controllers and Tuning
Once the process equipment is established, controllers and strip-chart recorders must be added to the process flow diagram (PFD) in the simulation. The
detailed mechanics of doing this are different in the two simulators. The "dragand-drop" approach is the usual method. Each controller requires several specifications to begin the simulation:
1.
Initial values of the signal from the process sensor (the PV signal) and
the signal to the control valve (the OP signal) must be made available.
This requires establishing the ranges of the sensor/transmitter that is
generating the PV signal arid establishing the range of the controller
output signal. If the controller output signal is going to a valve, this
range is 0 to 100%. Some of the manipulated variables are set directly
from the controller (for example, reboiler heat input or coolant ternperature). In that case, the maximum and minimum values of the energy flow or the maximum and minimum coolant temperatures must
be specified.
2.
The correct "action" of the controller must be specified: direct or reverse.
3.
The controller tuning constants must be set. Tuning of level and flow
controllers is a "plug-in-the-numbers" operation, which requires no
dynamic testing. On the other hand, most temperature and composition loops require dynamic testing (for example, the simple relayfeedback test) to develop controller tuning constants. It is important to
use realistic lags and/or deadtimes in the temperature/composition
loops so that the predicted performance is not overly optimistic. Using
reasonable and conservative measurement lags in the temperature and
composition loops helps to guarantee that effective control is possible
in a real plant environment, not just on the simulator.
Strip-chart recorders are useful in following the dynamic changes oc4.
curring in the many variables. The variables to be observed need to be
selected, and all the chart properties (axis scales, labels, etc.) must be
specified.
These issues are covered in Chapter 3.
1.3.4 Case Studies
The rest of the book presents a series case studies. The approach is to start
with very simple process units that require only two or three controllers. Then
units with several controllers are considered. The complexity of the processes is
Introduction
7
progressively increased until the flowsheets represent typically complex industrial
processes. Each example is developed and discussed in detail. Simulations in both
1-1YSYS and AspenDynamics are given for each example.
Chapter 4 studies a simple tank process in which we control liquid level and
tank pressure by manipulating the flow of liquid and vapor leaving the tank for
disturbances in the flow entering the tank. All the steps of converting from steady
state to dynamics are covered in exhaustive detail. Controllers are installed and the
simulation is run. Strip-chart recorders are installed so that we can see the dynamic
transients in the variables of interest. We also discuss the case in which there is
only a liquid stream leaving the tank.
Chapter 5 considers another simple tank process in which there are two feed
streams of differing compositions that are blended in the tank. In addition to controlling level, we control the composition of the stream leaving the tank by manipulating one of the feed streams. The steps in installing dynamic elements (deadtimes and lags) in the composition loop are illustrated. Controllers are tuned using
the relay-feedback test. Performance is evaluated in the face of disturbances.
In Chapters 6 and 7 common reactor systems are studied: a continuous
stirred-tank reactor (CSTR) and a plug-flow reactor (PFR). The key issues in reactor systems are temperature control and heat transfer. Several alternative heattransfer models are available: direct heat-transfer rate Q, specified coolant temperature or specified coolant flowrate. These alternative models differ in the two
simulators. The choice of what model to use is important in achieving realistic
dynamic simulations of reaction systems.
Unit operations with a larger number of loops are presented in Chapters 8
through 10. Distillation column control is one of the most important areas of process control. Even a simple single-feed, two-product distillation column has six
control loops: feed flowrate, pressure, base level, reflux-drum level and two other
variables (typically one flow and one temperature on some tray in the column). A
conventional distillation example is given in Chapter 8, a heterogeneous
azeotropic distillation column is discussed in Chapter 9 and two reactive distillation columns are studied in Chapter 10.
Chapters 11 through 14 give examples of somewhat more complex processes with two units connected by recycle streams. Two-column distillation systems are discussed in Chapter 11 (pressure-swing azeotropic distillation) and
Chapter 12 (heat-integrated columns). Chapter 13 explores a tubular reactor system with gas recycle, and Chapter 14 studies a similar reactor with a liquid recycle
stream coming from a distillation column.
In Chapters 15-18 complete multi-unit plantwide process structures are considered. There are several interconnected unit operations with dozens of controllers to be installed and tuned. In addition to having educational content, these
cases should be useful to process control researchers by providing some realistically complex processes on which new control approaches can be tested.
Chapter 19 wraps up a few loose ends and discusses some advanced methods and hardware issues.
8
Chapter 1
1.4 Software Stability and Bugs
Both dynamic simulators are powerful tools and permit us to fairly easily
explore the dynamics of chemical processes. They provide reasonably accurate
models of a variety of industrially important unit operations.
However, they are far from perfect. Sometimes the software crashes for no
apparent reason, and error messages such as "The program has performed an illegal operation and will be shut down" are given. This software stability problem
seems to improve with each version of the software, but its occurrence is still more
frequent than it should be. The user should save the file quite frequently in order to
avoid losing information.
Software bugs are also more numerous than one would like. Things that
should work sometimes do not for no apparent reason. These problems should be
reporting to the software companies through their technical support or hot lines.
As the software is improved over the next several years, these problems should
occur less frequently, and this will make dynamic simulations easier and more
reliable.
The software used in this book is HYSYS.plant (version 2.4.1, Build 3870)
and AspenPIus/AspenDynamics (version 10.2.2).
1.5 Conclusion
In this chapter we have set the stage for the remaining chapters. The status
of dynamic simulation, the additional information needed and the scope of the
book have been discussed. We are ready to dig into the details of dynamic simulations.
It should be emphasized that the goal of this book is provide an introduction
to the use of commercial dynamic simulators. We do not attempt to provide all the
voluminous material to transform the reader into a simulation expert. This requires
many months of time and effort. Only the simple basic operations that are needed
to get started in dynamic simulation are discussed. The commercial simulators
offer many advanced features that can be useful after the engineer learns the basics. We hope this book is helpful in getting you off the ground in the important
and fascinating activity of dynamic simulation.