Process Dynamics, Modeling, and Control 0195091191, 9780195091199

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process dynamics, mo de lin g, an d control

TOPICS IN CHEMICAL ENGINEERING A Series of Textbooks and Monograph s SERIES EDITOR

ASSOCIATE EDITORS

KEITH E. GUBBINS Cornell University

MARK A. BARTEAU University of Delaware

KLAVS F. JENSEN Massachusetts Institute of Technology DOUGLAS A. LAUFFENBURGER University of lllinois MANFRED MORARI California Institute of Technology

W. HARMON RAY University of Wisconsin WILUAM B. RUSSEL Princeton University SERIES TITLES Receptors: Models for Binding, Trafficking, and Signalling D. Lauffenburger and f. Lindennan Process Dynamics, Modeling, and Control

B. Ogunnaike and W. H. Ray

process dynamics, modeling, and control BABATUNDE A. OGUNNAIKE E. I. DuPont de Nemours, Experimental Station, and Adjunct Professor, Department of Chemical Engineering University of Delaware

W. HARMON RAY Department of Chemical Engineering University of Wisconsin

New York Oxford OXFORD UNIVERSITY PRESS

1994

Oxford University Press Oxford New York Athens Auckla nd Bangkok Bombay Calcutt a Cape Town Dares Salaam Delhi Florence Hong Kong Istanbu l Karachi Kuala Lumpu r Madraa Madrid Melbourne Mexloo City Nairob i Paris Singap ore Taipei Tokyo Toront o and aasoda ted compan ies in Berlin Ibadan

Copy right@ 1994 by Oxford University Press, Inc. Publish ed by Oxford Univer sity Press, Inc., 200 Madiso n Avenue , New York, New York 10016 Oxford is a registe red tradem ark of Oxford Unlvem ty Press

All righta reserve d. No part of this publica tion may be reprodu ced, stored In a retrieva layatem , or transm itted, In any form or by any means, electronic, mec:hanlcal, photoco pying, reoordlng, or othenv lae, withou t the prior permis sion of Oxford Univer sity Press. Ubrary of Congress Cataloglng-ln-Publlcalion Data Ogunn alke, Babatu nde A. (Babatu nde Ayodeji) Proceas dynami cs, modeli ng, and contro l/ Babatu nde A Ogunnllike, W. Harmo n Ray. p. em. -(Topi cs in chemical enginee ring) Includes Indexes. 1SBN 0-19-509119-1 1. Chemic al process control. I. Ray, W. Harmo n (Wiilis Harmo n), 1940U. Title. m. Series: Topics In chemical enginee ring (Oxford Univer sity Press) TP155.75.036 1994 660'.2815---dc20 94-28307

1 3 5 7 9 8 6 4 2 Printed in the United States of America on add-fre e paper

To Anna and "the boys" (Damini and Deji), ... Agbaja owo ni n'gberu d'ori; and To decades of superb graduate student teachers, ... the heart of process control at Wisconsin.

CCONTJENTS

part I INTRODUCTION

Chapter 1. Introductory Concepts of Process Control 1.1 1.2 1.3 1.4 1.5 1.6

The Chemical Process An Industrial Perspective of a Typical Process Control Problem Variables of a Process The Concept of a Process Control System Overview of Control System Design Summary

Chapter 2. Introduction to Control System Implementation

2.1 Introduction 2.2 Historical Overview 2.3 Basic Digital Computer Architecture 2.4 Data Acquisition and Control 2.5 Some Examples 2.6 Summary

vii

5 5 8 13 15 19 30

35 35 36 38 46 56 61

viii

CONTEN TS

par tll PROCE SS DYNAMICS

Chapter 3. Basic Elements of Dynamic Analysis 3.1 3.2 3.3 3.4 3.5

Introduction Tools of Dynamic Analysis The Laplace Transform Characteristics of Ideal Forcing Functions Summary

Chapter 4. The Prcxess Model 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9

The Mathematical Description of Chemical Processes Formulating Process Models State-Space Models Transform-Domain Models Frequency-Response Models Impulse-Response Models Interrelationships between Process Model Forms The Concept of a Transfer Function Summary

Chapter 5. Dynamic Behavior of Linear Low Order-Systems 5.1 5.2 5.3 5.4 5.5 5.6

First Order Systems Response of First-Order Systems to Various Inputs Pure Gain Systems Pure Capacity Systems The Lead/La g System Summar y

Chapter 6. Dynamic Behavior of Linear Higher Order Systems 6.1 6.2 6.3 6.4 6.5 6.6 6.7

Two First-Order Systems in Series Second-Order Systems Response of Second-Order Systems to Various Inputs N First-Order Systems in Series The General Nth-Order System Higher Order Systems with Zeros Summary

67 67 68 71 80 86 89 89 92 104 108 110 111 115 128 134 139 139 142 153 157 161 166 175 175 183 188 200 204 205 211

ix

CONTENTS

Chapter 7. Inverse-Response Systems

225

225 7.1 Introduction 229 7.2 Inverse Response in Physical Processes 7.3 Dynamic Behavior of Systems with Single, Right-Half Plane 231 Zeros 7.4 Dynamic Behavior of Systems with Multiple, Right-Half 237 Plane Zeros 240 7.5 Summary Chapter 8. Time-Delay Systems 8.1 8.2 8.3 8.4 8.5 8.6 8.7

An Introductory Example The Pure Time-Delay Process Dynamic Behavior of Systems with Time Delays The Steam-Heated Heat Exchanger Rational Transfer Function Approximations Model Equations for Systems Containing Time Delays Summary

Chapter 9. Frequency-Response Analysis 9.1 9.2 9.3 9.4 9.5 9.6

Introduction A General Treatment Low-Order Systems Higher Order Systems Frequency Response of Feedback Controllers Summary

VChapter 10. 10.1 10.2 10.3 10.4 10.5 ,' Chapter 11. 11.1 11.2 11.3 11.4 11.5 11.6

245 245 249 252 257 261 265 267 275 275 277 288 295 305 306

Nonlinear Systems

311

Introduction: Linear and Nonlinear Behavior in Process Dynamics Some Nonlinear Models Methods of Dynamic Analysis of Nonlinear Systems Linearization Summary

312 313 314 320 326

Stability

333

Introductory Concepts of Stability Stability of Linear Systems Stability of Nonlinear Systems Dynamic Behavior of Open-Loop Unstable Systems . Stability of Dynamic Systems under Feedback Control Summary

333 337 343 349 353 355

X

CONTENTS

partlll PROCESS MODELING AND IDENTIFICATION

Chapter 12. 12.1 12.2 12.3 12.4 12.5 12.6 Chapter 13. 13.1 13.2 13.3 13.4 13.5 13.6 13.7

Theoretical Process Modeling

363

Introduction Development of Theoretical Process Models Examples cf Theoretical Model Formulation Parameter Estimation in Theoretical Models Validation of Theoretical Models Summary

363 366 368 380 399 401

Process Identification: Empirical Process Modeling

409

Introduction and Motivation Principles of Empirical Modeling Step-Response Identification Impulse-Response Identification Frequency-Response Identification Issues for Multivariable Systems Summary

409 412 417 422 436 447 450

xi

CONTENTS

part IV PROCESS CONTROL

PART IVA: Chapter 14. 14.1 14.2 14.3 14.4 14.5 14.6 14.7 14.8 Chapter 15. 15.1 15.2 15.3 15.4 15.5 15.6 15.7 Chapter 16. 16.1 16.2 16.3 16.4 16.5 Chapter 17. 17.1 17.2 17.3 17.4 17.5

SINGLE-WOP CONTROL Feedback Control Systems

461

The Concept of Feedback Control Block Diagram Development Classical Feedback Controllers Closed-Loop Transfer Functions Closed-Loop Transient Response Closed-Loop Stability The Root Locus Diagram Summary

461 464 467 468 472 486 496 504

Conventional Feedback Controller Design

513

Preliminary Considerations Controller Design Principles Controller Tuning with Fundamental Process Models Controller Tuning using Approximate Process Models Controller Tuning using Frequency-Response Models Controller Tuning without a Model Summary

513 519 525 532 541 555 557

Design of More Complex Control Structures

565

Processes with Significant Disturbances Processes with Multiple Outputs Controlled by a Single Input Processes with a Single Output Controlled by Multiple Inputs Antireset Windup Summary

565

ＨｾＸＩ＠

581

585 586

Controller Design for Processes with Difficult Dynamics

599

Difficult Process Dynamics Time-Delay Systems Inverse-Response Systems Open-Loop Unstable Systems Summary

599 603 608 617 619

xii

CONTE NTS

Chapt er 18. 18.1 18.2 18.3 18.4 18.5 Chapt er 19.

..J ｾ＠

19.1 19.2 19.4 19.5 19.6

Contro ller Design for Nonlin ear Systems

625

Nonlin ear Contro ller Design Philos ophies Linear ization and the Classical Appro ach Adapt ive Contro l Princi ples Variab le Transf ormati ons Summ ary

625 626 628 632 638

Model-Based Contro l

645

Introduction Contro ller Design by Direct Synthesis Intern al Model Contro l Generic Model Contro l Optim ization Appro aches Summ ary

645 648 665 671 674 675

PAR T IVB: MUL TIVA BIAB LE PRO CESS CON TROL Chapt er 20. 20.1 20.2 20.3 20.4 20.5 20.6 Chapt er 21. 21.1 21.2 21.3 21.4 21.5 21.6 21.7 21.8 21.9 21.10

Introd uction to Multiv ariable System s The Nature of Multiv ariable System s Multiv ariable Process Model s Open- Loop Dynam ic Analy sis in State Space Multivariable Transf er Functions and Open- Loop Dynam ic Analy sis Closed-Loop Dynam ic Analy sis SUIIIII\aJ.'}' Interac tion Analy sis and Multip le Single Loop Design s Introduction Prelim inary Consid eration s of Interac tion Analy sis and Loop Pairing The Relative Gain Array (RGA) Loop Pairing Using the RGA Loop Pairing for Nonlin ear Systems Loop Pairing for Systems with Pure Integr ator Modes Loop Pairing for Nonsq uare Systems Final Comm ents on Loop Pairing and the RGA Controller Design Proced ure Summ ary

683 683 688 694 702 712 716 723

723 724 728 735 742 748 750 754 759 764

CONTENTS

Chapter 22. 22.1 22.2 22.3 22.4 22.5 22.6

xiii

Design of Multivariable Controllers

773

Introduction Decoupling Feasibility of Steady-State Decoupler Design Steady-State Decoupling by Singular Value Decomposition Other Model-Based Controllers for Multivariable Processes Summary

773 776 792 805 806 807

PART IVC: COMPUTER PROCESS CONTROL Chapter 23. 23.1 23.2 23.3 23.4 23.5 23.6 23.7

J

Chapter 24. 24.1 24.2 24.3 24.4 24.5 Chapter 25. 25.1 25.2 25.3 25.4 25.5 Chapter 26. 26.1 26.2 26.3 26.4 26.5 26.6 26.7

Introduction to Sampled-Data Systems

821

Introduction and Motivation Sampling and Conditioning of Continuous Signals Continuous Signal Reconstruction Mathematical Description of Discrete-Time Systems Theoretical Modeling of Discrete-Time Systems Empirical Modeling of Discrete-Time Systems Summary

821 825 830 832 835 838 843

Tools of Discrete-Time Systems Analysis

847

Introduction The Basic Concepts of z-Transforms Inverting z-Transforms Pulse Transfer Functions Summary

847 848 860 867 877

Dynamic Analysis of Discrete-Time Systems

883

Open Loop Responses Characteristics of Open-Loop Pulse Transfer Functions Block Diagram Analysis for Sampled-Data Systems Stability Summary

883 893 917 933 943

Design of Digital Controllers

951

Preliminary Considerations The Digital Controller and Its Design Discrete PID Controllers from the Continuous Domain Other Digital Controllers Based on Continuous Domain Strategies Digital Controllers Based on Discrete Domain Strategies Digital Multivariable Controllers Summary

951 953 960 964 970 979 979

xiv

CONTENTS

partV SPECIAL CONTROL TOPICS

Chapter 27. 27.1 27.2 27.3 27.4 27.5 27.6 27.7 27.8 27.9

Chapter 28. 28.1 28.2 28.3 28.4 28.5 28.6 28.7

Chapter 29. 29.1 29.2 29.3 29.4 29.5

29.6 29.7

Model Predictive Control

991

Introduction General Principles of Model Predictive Control Dynamic Matrix Control Model Algorithmic Control (MAC) Commercial Model Predictive Control Schemes: A Qualitative Review Academic and Other Contributions Nonlinear Model Predictive Control Closing Remarks Summary

1017 1020 1023 1027

Statistical Process Control

1033

Introduction Traditional Quality Control Methods Serial Correlation Effects and Standard Process Control When is Traditional SPC Appropriate? Stochastic Process Control More Advanced Multivariate Techniques Summary

1034 1036 1046 1048 1050 1058 1059

Selected Topics in Advanced Process Control

1063

Control in the Absence of Good On-line Measuremen tsState Estimation Control in the Face of Process Variability and Plant/Model Mismatch- Robust Controller Design Control of Spatial Profiles - Distributed Parameter Controllers Control in a Changing Economic Environmen t- On-line Optimization Control in the Face of Component Failure Abnormality Detection, Alarm Interpretation , and Crisis Management Some Emerging Technologies for Advanced Process Control Concluding Remarks

992 996 1000 1008

1011

1063 1069 1083 1086

1088 1089 1094

XV

CONTENTS

Chapter 30.

Process Control System Synthesis- Some Case Studies

1097

30.1 30.2 30.3 30.4 30.5 30.6

Control of Distillation Columns Control of Catalytic Packed Bed Reactors Control of a Solution Polymerization Process Control of an Industrial Terpolymerization Reactor Guidelines for Characterizing Process Control Problems Summary

1097 1105 1113 1122 1133

1145

part VI APPENDICES

Control System Symbols used in Process and Instrumentation Diagrams

1149

Complex Variables, Differential Equations, and Difference Equations

1155

Appendix C.

Laplace and Z..Transforms

1177

Appendix D.

Review of Matrix Algebra

1209

Appendix E.

Computer-Aided Control System Design

1249

Appendix A.

Appendix B.

Author Index

1251

Subject Index

1255

preface Over the last two decades there has been a dramatic change in the chemical process industries. Industrial processes are now highly integrated with respect to energy and material flows, constrained ever more tightly by high quality product specifications, and subject to increasingly strict safety and environmental emission regulations. These more stringent operating conditions often place new constraints on the operating flexibility of the process. All of these factors produce large economic incentives for reliable, high performance control systems in modem industrial plants. Fortunately, these more challenging process control problems arise just at the time when inexpensive real time digital computers are available for implementing more sophisticated control strategies. Most new plants in the chemical, petroleum, paper, steel, and related industries are designed and built with a network of mini- and microcomputers in place to carry out data acquisition and process control. These usually take the form of commercially available distributed control systems. Thus digital computer data acquisition, process monitoring, and process control ·are the rule in process control practice in industry today. Because of these significant changes in the nature of process control technology, the undergraduate chemical engineer requires an up-to-date textbook which provides a modem view of process control engineering in the context of this current technology. This book is directed toward this need and is designed to be used in the first undergraduate courses in process dynamics and control. Although the most important material can be covered in one semester, the scope of material is appropriate for a two-semester course sequence as welL Most of the examples are taken from the chemical process industry; however, the text would also be suitable for such courses taught in mechanical, nuclear, industrial, and metallurgical engineering departments. Bearing in mind the limited mathematical background of many undergraduate engineers, all of the necessary mathematical tools are reviewed in the text itself. Furthermore, the material is organized so that modem concepts are presented to the student but the details of the most advanced material are left to later chapters. In this

xviii

PREFACE

way, those prefering a lighter treatment of the subject may easily select coherent, self-consistent material, while those wishing to present a deeper, more comprehensive coverage, may go further into each topic. By providing this structure, we hope to provide a text which is easy to use by the occasional teacher of process control courses as well as a book which is considered respectable by the professor whose research specialty is process control. The text material has been developed, refined, and classroom tested by the authors over many years at the University of Wisconsin and more recently at the University of Delaware. As part of the course at Wisconsin, a laboratory has been developed to allow the students hands-on experience with measurement instruments, real-time computers, and experimental process dynamics and control problems. The text is designed to provide the theoretical background for courses having such a laboratory. Most of the experiments in the Wisconsin laboratory appear as examples somewhere in the book. Review questions and extensive problems (drawn from many areas of application) are provided throughout the book so that students may test their comprehension of the material. The book is organized into six parts. In Part I (Chapters 1-2), introductory material giving perspective and motivation is provided. It begins with a discussion of the importance of process control in the process industries, with simple examples to illustrate the basic concepts. The principal elements of a modem process control scheme are discussed and illustrated with practical process examples. Next, a rudimentary description of control system hardware is provided so that the reader -can visualize how control schemes are implemented. This begins with a discussion of basic measurement and computer data acquisition methodology. Then the fundamentals of digital computers and interfacing technology are presented in order to introduce the basic concepts to the reader. Finally, control actuators such as pumps, valves, heaters, etc. are discussed. The purpose of the chapter is to provide some practical perspective, before beginning the more theoretical material which follows. Part II (Chapters 3-11) analyzes and characterizes the various types of dynamic behavior expected from a process and begins by providing an introduction to the basic mathematical and analysis tools necessary for the engineering material to be studied. This is followed by a discussion of various representations and approaches in the formulation of dynamic models. The emphasis is on learning how to select the model formulation most appropriate for the problem at hand. The essential features of state-space, transformdomain, frequency-response, and impulse-response models are presented and compared. Then comes a discussion of the fundamental dynamic response of various model types. Processes with time delays, inverse response, and nonlinearities are among the classes considered in some detail. The fundamentals of process stability analysis are then introduced and applied to the models under discussion. Methods for constructing process models and determining parameters for the model from experimental data are discussed in Part Ill (Chapters 12-13). Both theoretical and empirical models are discussed and contrasted. Complementing the usual material on step, pulse, or frequency response identification methods, is a treatment of parameter estimation for models represented by difference and differential equations. Sufficient examples are provided to allow the student to see how each method works in practice.

PREFACE

xix

In Part IV we begin the treatment of control system design. Part IVA (Chapters 14-19) deals with single loop control systems and introduces the basic principles of controller structure (e.g. feedback, feedforward, cascade, ratio, etc.) and controller tuning methodology. The choice of controller type is discussed for processes having the various types of process dynamics described in Part II. Physical examples are used to illustrate the control system design in practical engineering terms. Control system design for multivariable processes having interactions is introduced in Part IVB (Chapters 20-22). Methods of characterizing loop interactions, choosing loop pairing, and designing various types of multivariable controllers are presented and illustrated through physical process examples. While not bringing the reader to the frontiers of research, this section of the book acquaints one with the most important issues in multivariable control and provides approaches to control system design which will work adequately for the overwhelming majority of practical multivariable control problems encountered in practice. Part IVC (Chapters 23-26) introduces the principles of sampled-data process control. This begins with the modeling and analysis of discrete-time systems, develops stability analysis tools, and finally provides control system design methods for these dynamic systems. In Part V (Chapters 27-30), we provide the reader an overview of important special topics which are too advanced to be covered in great depth in this introductory book Among the subjects included are model predictive control, statistical process control, state estimation, robust control system design, control of spatial profiles (distributed parameter systems), on-line intelligence, and computer-aided-design of control systems. The practicing control engineer will find these approaches already in place in some industrial control rooms and thus needs to be aware of the basic concepts and jargon provided here. The last chapter in Part V consists of a series of case studies where the reader is led through the steps in control system synthesis for some representative chemical processes and then shown the performance of the process after employing the controller. Through these more involved example applications, which draw upon a variety of material from earlier chapters, the reader will have a glimpse of how modem process control is carried out by the practicing engineer. An important aspect of the book is the substantial material provided as Appendices in Part VI. Appendix A is devoted to a summary of modem instrumentation capabilities and P & I diagram notation. Appendix B provides a basic review of complex variables and solution methods for ordinary differential and difference equations. Appendix C provides a summary of important relations and transform tables for Laplace transforms and z-transforms. Matrix methods are reviewed in Appendix D. Finally in Appendix E, existing computer packages for computer-aided control system design are surveyed. There are many who contributed their efforts to this book. Undergraduate students at Wisconsin, Delaware, Colorado, and I.I.T. Kanpur provided extensive feedback on the material and helped find errors in the manuscript. Many graduate students, (especially the teaching assistants) tested the homework problems, caught many of the manuscript errors and contributed in other ways to the project. Special thanks go to Jon Debling, Mike Kaspar, Nolan Read, and Raymond Isaac for their help. We are indebted to Derin

XX

PREFACE

Adebeknn, Doug Cameron, Yuris Fuentes, Mike Graham, Santosh Gupta, and Jon Olson who taught from the manuscrip t and provided many helpful suggestions. Also we are grateful to Dave Smith who read the manuscri pt and provided detailed comment s, to Rafi Sela who provided help with examples , and to l-Lung Chien who contrihnh• cl tn {h,.rt."'" ?7 ｗｾ＠ ｡ｾ＠ indc"btcd tc Jcc Mill.-::r, Jill• Trainham, and Dave Smith of Dupont Central Science and Engineering for their support of this project. Our thanks to Sally Ross and others at the U.W. Center for Mathema tical Sciences for their hospitalit y during several years of the writing. The preparati on of the camera-re ady copy for such a large book required an enormous amount of work. We are grateful to Andrea Baske, Heather Flemming, Jerry Holbus, Judy Lewison, Bill Paplham, Stephanie Schneider, Jane Smith, and Aimee Vandehey for their contributions along the way. Special thanks to Hana Holbus, who gave her artistic talents to the figures and provided the diligence and skill required to put the manuscri pt in final form. Thanks also to David Anderson who did the copy editing. The book could not have been completed without the patience, support, and forbearance of our wives, Anna and Nell; to them we promise more time. Finally, the authors credit the atmosphere created by their colleagues at the University of Wisconsin and at the Dupont Company for making this book possible. May 15,1994

Babatunde A. Ogunnaike W. Harmon Ray

process dynamics, modeling, and control

part I KN1fJ RODU C1fliO N

I ｾ＠

CHAPTER l.

Introductory Concepts of Process Control

CHAPTER2.

Introduction to Control System Implement ation

Kif we couUfirst k_now wfiere we ar, antl wliitfier we are tencfing, we couU 6etter jucfge wfiat to d arui fww to tfo it. Abraham Lincoln (1809-1865)

part I KNTRODUCTKON In embarking upon a study of any subject for the first time, the newcomer is quite likely to fmd the unique language, idioms, and peculiar "tools of the trade" associated with the subject matter to be very much like the terrain of an unfamiliar territory. This is certainly true of Process Dynamics, Modeling, and Control - perhaps more so than of any other subject matter within the broader discipline of Chemical Engineering. It is therefore frequently advantageous to begin a systematic study of such a subject with a panoramic survey and a general introduction. The panoramic survey provides perspective, indicating broadly the scope, extent, and constituent elements of the terrain; an initial introduction to these constituent elements in turn provides motivation for the subsequent more detailed study. Part I, consisting of Chapters 1 and 2, provides just such an orientation tour of the Process Dynamics, Modeling, and Control terrain before the detailed exploration begins in the remaining parts of the book.

CHAP1rJEJR

1 INTRODUCTORY CONCEPTS OF PROCESS CONTROL A formal introduction to the role of process control in the chemical process industry is important for providing motivation and laying the foundation for the more ､･ｴｾ＠ study of Process Dynamics, Modeling, and Control ｣ｾｮｴ｡ｩ･､＠ in the ｩｊｫ｢ｭｮｾ｡ｰｴ･ｲｳＮ＠ Thus this chapter is an introductory oveAAew of process control and how it is practiced in the chemical process industry.

1.1

THE CHEMICAL PROCESS ｣ｬｵｯｾｊＧｚｉＰＮﾣＺＴＱｖｦ＠

In the chemical process industry, the primary objective is to combine chemical processing units, such as chemical reactors, distillation columns{; extractors, rl'e> ｉｗＮａｊｦＧｾ＠ evaporators, heat exchangers, etc., integrated in a rational fas ion into a chemical process in order to transform ｊ［｡ｷｦＧｭｾｉＺｩｬｳ＠ and input"eh"ergy into finished products. This concept is illustrated in Figure 1.1 and leads to the definition: ＴＧＤＮｾＡｲｦｅｯｳｩｮｧ＠

unit, _or combinations of ｰｲｯ｣･ｳｩｾｧ＠ ｾｮｩｴｳＬ＠ used for the converstofiroj raw matenals (through any combznahon of chemical, physical, mechanical, or thermal changes) into finished products, is a chemical process. ｭＭＮＢｴｄＺｲｾＬｑﾷｋｒｵ＠

ｱｾｴＮ＠

Ｌｾ［＠

..Ｚﾷ［ｾＭＮＬ＠

A concrete example of these somewhat abstract ideas is the crude fractionation section of a typical oil refinery illustrated in Figure 1.2. Here, the raw material (in this case,cf'Jde"':,iif"is numped from the "tank farms," ｾｬﾥ｟ｲａ＼＠ ""'Jo»f. ...,.,. ll>lt.o through the gas-fired preneater turnace, into the fractionator, where f-a•n•$ "lflrlv,.H. separation into such useful vroducts as· napthas, right gas oil, heavy gas oil, ｴ｣ｲｑｔ｢ｾＢ＠ nic,.c ･ＧｬｾｦｴＴＮＬ｟＠ ｲＬｾｦｃＩ［ｪｬ＠ and high boiling resid1:1e takes place. re 'Z.! ｴｬｲｾ＠

5

,.

·

r-

Ｍｾ＠

·tif ......,

INTRODUCTIO N

6

Energy

Figure 1.1. The chemical process.

Let us now compare this actual process with the abstract representatio n in Figure 1.1: • The processing units are the･ｯｔＢｂｲ｡ｬＮＬｰＺｫＴｾ＠ storage_ ｴ｡ｮｾｫｳ＠ &:.""' ｾ＠ the .furnace, and the equipment. a,p fractionator, along with their ｲ･ｦＬＺｬｾ｣ｴｩｶ＠ • The raw material is basically the crude oil; fte air and fuel gas fed into the furnace provide the energy input realized via firing in the furnace. In addition there are often other sources of energy input to the fractionator. • The condensation of lighter material at the top of the fractionator, effected by the cooling unit, constitutes enerK¥.J!,I!lJ?Ut. streams from the top • The (finished) products are the naptha and ｲｾｩ＿＠ and bottom, respectively, and the gas oil streams from the mid-sections.

.:ar..Y

The basic principles guiding the operation of the processing units of a chemical process are based on the following broad objectives: Ｚ＾ｕｯｾｻｱＮＬ＠

1.

.. (o operate !he processing units safely. It ｾｳ＠ ､｡ｦｩ｛ｾＡ＠ no Uhlt should be operated at, or near, cond1tions ThiS ｾ･｡ｮｃｊｴ＠ ..!P;t; -'llu