JWBK093-FM July 5, 2006 19:52 Char Count= 0 A Real-Time Approach to Process Control Second Edition William Y. Svrcek University of Calgary Calgary, Canada Donald P. Mahoney BDMetrics Inc. Baltimore, USA Brent R. Young The University of Auckland Auckland, New Zealand iii JWBK093-FM July 5, 2006 19:52 Char Count= 0 ii JWBK093-FM July 5, 2006 19:52 Char Count= 0 A Real-Time Approach to Process Control i JWBK093-FM July 5, 2006 19:52 Char Count= 0 ii JWBK093-FM July 5, 2006 19:52 Char Count= 0 A Real-Time Approach to Process Control Second Edition William Y. Svrcek University of Calgary Calgary, Canada Donald P. Mahoney BDMetrics Inc. Baltimore, USA Brent R. Young The University of Auckland Auckland, New Zealand iii JWBK093-FM July 5, 2006 19:52 Char Count= 0 Copyright C  2006 John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex PO19 8SQ, England Telephone (+44) 1243 779777 Email (for orders and customer service enquiries): cs-books@wiley.co.uk Visit our Home Page on www.wileyeurope.com or www.wiley.com All Rights Reserved. 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 under the terms of the Copyright, Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London W1T 4LP, UK, without the permission in writing of the Publisher. 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Other Wiley Editorial Offices John Wiley & Sons Inc., 111 River Street, Hoboken, NJ 07030, USA Jossey-Bass, 989 Market Street, San Francisco, CA 94103-1741, USA Wiley-VCH Verlag GmbH, Boschstr. 12, D-69469 Weinheim, Germany John Wiley & Sons Australia Ltd, 33 Park Road, Milton, Queensland 4064, Australia John Wiley & Sons (Asia) Pte Ltd, 2 Clementi Loop #02-01, Jin Xing Distripark, Singapore 129809 John Wiley & Sons Canada Ltd, 6045 Freemont Blvd., Mississauga, Ontario, Canada L5R 4JR Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books. Library of Congress Cataloging-in-Publication Data Svrcek, William Y. A real time approach to process control / William Y. Svrcek. – 2nd ed. p. cm. Includes bibliographical references and index. ISBN-13: 978-0-470-02533-8 (cloth) ISBN-10: 0-470-02533-6 (cloth) ISBN-13: 978-0-470-02534-5 (pbk. : alk. paper) ISBN-10: 0-470-02534-4 (pbk. : alk. paper) 1. Process control–Data processing. 2. Real-time control. I. Title. TS156.8.S86 2006 670.42  75433–dc22 2006010919 British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library ISBN-13 978-0-470-02533-8 (HB) ISBN-13 978-0-470-02534-5 (PB) ISBN-10 0-470-02533-6 (HB) ISBN-10 0-470-02534-4 (PB) Typeset in 10.5/12.5pt Times by TechBooks, New Delhi, India Printed and bound in Great Britain by Antony Rowe Ltd, Chippenham, Wiltshire This book is printed on acid-free paper responsibly manufactured from sustainable forestry in which at least two trees are planted for each one used for paper production. iv JWBK093-FM July 5, 2006 19:52 Char Count= 0 Tell me and I forget, Show me and I may remember, Involve me and I understand. Benjamin Franklin Scientist, Statesman v JWBK093-FM July 5, 2006 19:52 Char Count= 0 vi JWBK093-FM July 5, 2006 19:52 Char Count= 0 Contents Preface xi Acknowledgements xiii Endorsement xv About the authors xvii 1 A brief history of control and simulation 1 1.1 Control 1 1.2 Simulation 3 1.3 References 10 2 Process control hardware fundamentals 13 2.1 Control system components 13 2.2 Primary elements 14 2.3 Final control elements 30 2.4 References 50 3 Fundamentals of single input−single output systems 51 3.1 Open-loop control 51 3.2 Disturbances 52 3.3 Feedback control overview 53 3.4 Feedback control: a closer look 56 3.5 Process attributes: capacitance and dead time 61 3.6 Process dynamic response 71 3.7 Process modelling and simulation 73 3.8 References 92 4 Basic control modes 93 4.1 On−off control 93 4.2 Proportional (P-only) control 95 4.3 Integral (I-only) control 101 4.4 Proportional plus integral (PI) control 104 JWBK093-FM July 5, 2006 19:52 Char Count= 0 viii CONTENTS 4.5 Derivative action 105 4.6 Proportional plus derivative (PD) controller 107 4.7 Proportional integral derivative (PID) control 110 4.8 Choosing the correct controller 111 4.9 Controller hardware 113 4.10 References 115 5 Tuning feedback controllers 117 5.1 Quality of control and optimisation 117 5.2 Tuning methods 122 5.3 References 130 6 Advanced topics in classical automatic control 131 6.1 Cascade control 131 6.2 Feedforward control 135 6.3 Ratio control 138 6.4 Override control (auto selectors) 140 6.5 References 146 7 Common control loops 147 7.1 Flow loops 147 7.2 Liquid pressure loops 149 7.3 Liquid level control 151 7.4 Gas pressure loops 162 7.5 Temperature control loops 163 7.6 Pump control 170 7.7 Compressor control 170 7.8 Boiler control 177 7.9 References 180 8 Distillation column control 183 8.1 Basic terms 183 8.2 Steady-state and dynamic degrees of freedom 184 8.3 Control system objectives and design considerations 186 8.4 Methodology for selection of a controller structure 188 8.5 Level, pressure, temperature and composition control 190 8.6 Optimizing control 198 8.7 Distillation control scheme design using steady-state models 202 8.8 Distillation control scheme design using dynamic models 213 8.9 References 214 9 Using steady-state methods in a multi-loop control scheme 215 9.1 Variable pairing 215 9.2 The relative gain array 216 9.3 Niederlinski index 221 9.4 Decoupling control loops 221 9.5 Tuning the controllers for multi-loop systems 223 [...]... electromechanical areas from which these classical control techniques emerged) this approach is well suited As an approach to the control of chemical processes, which are often characterized by nonlinearity and large doses of dead time, classical control techniques have some limitations In today’s simulation-rich environment, the right combination of hardware and software is available to implement a ‘hands-on’... differential equations are encountered as in the frequency domain However, the major advantage of solving these equations in real time is the ability to observe the interactions of the process, control scheme and load variables much as the operator of a plant observes the behaviour of an actual plant Dynamic simulation allows for the comparison of several candidate control strategies and assesses the propagation... to the indispensable and commonplace tool that it is today 1.1 Control Feedback control can be traced back as far as the early third century BC [1] During this period, Ktesibios of Alexandria employed a float valve similar to the one found in today’s automobile carburettors to regulate the level in the water clocks of that time [2] Three centuries later, Heron of Alexandria described another float-valve... scenarios, practise start up and shutdown sequences, and respond to failure and alarm situations More recently, training simulators have provided links to a variety of DCS platforms By using the actual control hardware to run a dynamic model of the plant, operators have the added benefit of training on the same equipment that will be used to operate the real process It is important at this point to introduce... both parts of the hybrid simulation, i.e analog and digital The analog part was documented by using wiring diagrams These wiring diagrams quickly became outdated, as changes were made to the analog board that were not always added to the wiring diagram (human nature) 4 Simulations using hybrid computers were extremely time consuming An engineer had to reserve time in the hybrid simulation laboratory and... errors, and intimidating to many potential users Given today’s window environments and the 1.2 SIMULATION 9 new programming capabilities that languages such as object-oriented C++ provide, there is no need for batch-type simulation sessions It is imperative that a dynamic simulation is ‘packaged’ in a way that makes it easy to use and learn, yet still be applicable to a broad range of applications and... 269 3 Process capacity and dead time 275 4 Feedback control 283 5 Controller tuning for capacity and dead time processes 291 6 Topics in advanced control 297 7 Distillation control 307 8 Plant operability and controllability 315 Index 323 Preface For decades, the subject of control theory has been taught using transfer functions, frequency-domain analysis, and Laplace transform mathematics For linear... highly mathematical approach misses the point of what knowledge of control and dynamics the practicing process engineer requires If BS graduates in chemical engineering simply understood the basics of time based process dynamics and control (capacitance, dead time, PID control action and controller tuning, inventory, throughput, and distillation control) , the impact on process design and plant operations... fundamentals of chemical engineering For undergraduate programs looking to transition away from the traditional mathematical-based approach to a more applied, hands-on approach, this text will be an invaluable aid.’ Charles F Moore, Professor of Chemical Engineering, University of Tennessee ‘What BS degree chemical engineers need is a base level understanding of differential equations, process dynamics,... the day -to- day operation of the plant, simulation tools that are difficult to understand and use will never see any of the truly practical and value-adding applications By allowing plant engineers quickly and easily to test theories, illustrate concepts, or compare alternative control strategies or operating schemes, dynamic simulation can have a tremendous cumulative benefit Over the past several years, . looking to transition away from the traditional mathematical-based approach to a more applied, hands-on approach, this text will be an invaluable aid.’ Charles F. Moore, Professor of Chemical Engineering,. DuPont, and Paul Fruehauf from Applied Control Engineering. These gentlemen share a passion for the field and a commitment to the practical approach to both teaching and practising process control. As. 2006 19:52 Char Count= 0 A Real- Time Approach to Process Control Second Edition William Y. Svrcek University of Calgary Calgary, Canada Donald P. Mahoney BDMetrics Inc. Baltimore, USA Brent R.