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Integrated process control and automation
Automatica, Vol. 30, No. 2, pp. 365-371, 1994
Pergamon
Copyright (~ 1994 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0005-1098194 $6.00 + 0.00
Book
Reviews
Integrated Process Control and Automation* John E. Rijnsdorp
values' is shown to yield correct operating conditions in some cases while not in others. In particular, the optimum operating policy can involve periodic switching between low and high values of a key variable for some processes. While an excellent introduction to concepts and process applications, the coverage does not address important topics like model accuracy, model updating, or optimization technology in any depth. Setting dynamic operation, i.e. an operating plan over several days or weeks, is presented in four subsequent chapters, again through well chosen examples. A continuous operating plant with process performance which changes with operating conditions is optimized It is shown how momentary optimization is wholly inadequate for this situation, since the process exceeds its feasible region of operating conditions after just a few days; however, some sub-optimal approaches, like maintaining (more conservative) constant conditions for a long period of time, can closely approach the limiting maximum profit. Additional examples demonstrate the importance of time-varying operation in strategies for switching modes between product grades in continuous plants and recipe improvement in batch plants. The previous chapters provide a solid foundation for the design and implementation of process control to achieve the objectives specified at higher levels in the automation hierarchy. Rijnsdorp's coverage of process control is sparse, giving heuristic explanations which could guide the non-specialist but not prepare the engineer for implementing these concepts. True to his broader view of automation, he addresses sequencing control as well as continuous algorithms. Rijnsdorp sets his viewpoint apart from most academics by defining automation as 'a human assisted by computer in a shared task of operating a plant'. By including the plant personnel as the central part of the automation process, Rijnsdorp opens the automation topic to many important issues normally only given cursory attention. It is especially noteworthy that he reports on the studies of Kortland and Krakt (1980) who report that only 10% of the alarms in industrial plants result in an operator action! In addition, VDU display design is addressed, where Rijnsdorp makes the important point that parsimonious displays should be designed to direct the operators attention to the most important information, not to draw complex, colorful schematics. Finally, emergency shutdown systems are covered with an introduction to the reliability of various designs, e.g. majority voting systems. Since these automation features--scheduling, optimization, process control, and operator supervision---are crucial to success, one might assume that they would have required an entire book; however, the abbreviated coverage consumed only about two thirds of this 424 page monograph. This reviewer believes that the ailoction of space was a mistake and that the author has much more to contribute to these topics, which constitute a set of well defined, integrated topics. Rijnsdorp selected to address two additional major topics which involve the management of automation projects and equipment. The first is 'internal integration' and addresses issues like hardware and software specifications, information system design, and control room layout. Anyone beginning an automation project realizes the challenge in specifying the requirements in a manner that definitely fulfils the automation needs and yet can be achieved by products from
Reviewer: THOMAS E. MARLIN
Department of Chemical Engineering, McMaster University, Hamilton, Ontario, Canada L8S 4L7. Is 1982, A SERmS of technical meetings titled Process Systems Engineering were initiated with the purpose of promoting a holistic approach to the analysis of process systems. This effort, and subsequent initiatives like the series of meetings on FOCAPO (Foundations of Computer-Aided Process Operations) and ESCAPE, provide worthwhile counterpoints to the typical research papers which are, and for the most part must be, concise and focused on a narrow mathematical issue. In spite of these initiatives, the literature addressing the broad scope of technologies relevant to process automation remains very limited. A technical article is too brief to properly set the background, while only a single aspect of this topic, e.g. flowsheeting or model fidelity, can be addressed in a review article. It is this gap which Rijnsdorp addresses with his new book. It is well recognized that process automation is implemented in a hierarchical structure, with the upper levels giving specifications and performance requirements to the lower levels. The importance of this hierarchy for process control is obvious; there is no reason to control a variable like temperature tightly unless the proper reference value is defined and the importance of reducing variability determined. A great strength of this book is the comprehensive discussion of requirements that are served by the hierarchical structure along with important elements of each level. Rijnsdorp begins his overview of a three-level hierarchy at the business logistics level, where decisions are made regarding feed purchases, product sales, and inventory management. Then, the desired process operation is defined to satisfy the business decisions. Naturally, the desired operation is fundamentally different for continuous, blocked operation (periodic changes between modes) and batch plants; each translates business needs to desired operations plans in a unique manner regarding the time dependence of operating variables. Finally, the lower level of process control is presented as a means for achieving the desired plant operation. The reader is prepared by this introduction for more detailed discussions of 'momentary optimization' and 'dynamic operation', i.e. scheduling. Rijnsdorp's order, covering the middle before the top level, could be reversed to emphasize the priority in decision making, but the inclusion of substantial coverage of both items is a unique and valuable feature of the book. After all, the policy to maximize momentary profit, without regard for the future, could be to stop production and sell the in-plant inventory; it is only through the scheduling or 'look ahead' planning that the proper plant plan is established. Rijnsdorp covers the momentary optimization in four chapters through several examples which elucidate main issues such as degrees-of-freedom, operating window, defining the profit measure, and constrained and unconstrained operating conditions. One example of note clearly demonstrates the importance of proper mathematical analysis. In this example the heuristic of 'equal marginal * Integrated Process Control and Automation; Process Measurement and Control by John E. Rijnsdorp. Elsevier,
Amsterdam (1991). ISBN 0-444-8909%1 (paperback). 365 AUTO 30:2-M
366
Book Reviews
several vendors.. A common mistake is to define hardware and software structures. A better approach is to define functional requirements in terms of response times, controller calculations, display features, security, reliability, openness, and so forth. One would have hoped for more guidance in defining these critical, measurable system features and determining performance criteria relevant to the process industries. The second project topic addresses managing the project from scoping study through normal operation and maintenance. Perhaps this could be better handled in a separate monograph providing fill-in-the-blank projects specifications, along with estimating procedures for engineering time and equipment, installation, startup and maintenance costs. Overall, the author is to be commended for defining the most important automation issues and addressing them in an integrated manner. This will be appreciated by many readers who have experience in only one or a few of these issues. The major topic that does not receive sufficient emphasis is product quality control, at least within the context of process capability and continuing improvement that are all the rage today. A discussion of the relationship between automatic process control and statistical process control (e.g. MacGregor, 1988) would have been an especially valuable addition. No reviewer agrees with an entire book, and this situation is no exception. Perhaps the main issue I would take is with the discussion on automation benefits, which indicates that quantitative benefits estimate are not possible for specific strategies and that overall estimates, e.g. a few per cent throughout, are appropriate. However, standard methods are available and are in use for estimating future dynamics performance and economic benefits to be derived (Marlin et al., 1987; Harris, 1989). In addition to providing accurate quantitative estimates these approaches provide the needed detail for selecting sensors, process changes, and final elements and for designing control strategies to achieve the benefits. The material in the book emphasizes concepts over mathematical rigor and should be accessible to most graduate engineers. I believe that it might be a useful secondary reference for advanced undergraduate or graduate control courses which emphasize design and integration of control methods. However, it would not be adequate as a textbook for a course and should be supported with some lecture discussions for students who, without industrial experience, will not be able to appreciate many of the insights. There seem to be two categories of industrial practitioners most likely to benefit from this book. One is the younger engineer who is committed to building expertise in automation and who may have mastered several mathematical methods, but has not yet acquired an understanding of the integrated decision making in a plant. The second is the large group of engineers at the periphery of a control project, the process technologists, economic analysts, and project managers who must contribute to the project but
only fully comprehend their isolated feature of the integrated automation system for plant operations. The presentation is generally good, with clear writing and examples bringing home the material Rijnsdorp considers critical. In addition, a comprehensive set of symbols aids in understanding the process examples. Unfortunately, detailed information on the examples, models and data, is not provided in the book, nor are citations always given. Finally, the nature of the book motivates the reader to pursue many concepts in further detail, but the references provided are very limited, and many will be difficult or impossible to retrieve. Finally, I reiterate that this book is unique in the topics selected and method of coverage. It is tantalizing with its introduction to many important topics, yet is not entirely satisfying in the depth of coverage. Since the book is part of a series on Process Measurement and Control, it would seem worthwhile to dedicate several future titles in the series to the major headings in this book, specifically, dynamic operation (scheduling), momentary optimization, process control, and supervision by personnel, to more fully develop these topics within the context of the integrated view proposed by Rijnsdorp, and perhaps under his editorial guidance. References Harris, T. (1989). Assessment of control loop performance. Can. J. Chem. Eng., 67, 856-861. Kortland, D. and H. Kragt (1980). Process alarm systems as a monitoring tool for the operator. Third Int. Symp. on Loss Prevention and Safety Promotion in the Process Industries, Basle. MacGregor, J. (1988). Online statistical process control. CEP, 84, 10, 32-36. Marlin, T., J. Perkins, G. Barton and M. Brisk (1987). Advanced process control, warren centre study of opportunities and benefits. ISA, Research Triangle Park, U.S.A. About the reoiewer Dr Thomas E. Marlin received a Ph.D. degree from the University of Massachusetts in Chemical Engineering. After 15 years in industry at Exxon, and Stone and Webster, he joined McMaster University in 1987 as a Professor of Chemical Engineering holding the NSERC Industrial Research Chair in Process Control. At McMaster, he is Director of the McMaster Advanced Control Consortium, a group of 13 industrial companies and five professors collaborating on research in process automation and performance diagnostics. In addition to undergraduate and graduate courses, he teaches industrial short courses in process control, real-time optimization, and automation benefits/performance-audit studies. He is completing a textbook for undergraduates and industrial practitioners on Process Control for McGraw-Hill.
Pergamon
Copyright (~ 1994 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0005-1098194 $6.00 + 0.00
Book
Reviews
Integrated Process Control and Automation* John E. Rijnsdorp
values' is shown to yield correct operating conditions in some cases while not in others. In particular, the optimum operating policy can involve periodic switching between low and high values of a key variable for some processes. While an excellent introduction to concepts and process applications, the coverage does not address important topics like model accuracy, model updating, or optimization technology in any depth. Setting dynamic operation, i.e. an operating plan over several days or weeks, is presented in four subsequent chapters, again through well chosen examples. A continuous operating plant with process performance which changes with operating conditions is optimized It is shown how momentary optimization is wholly inadequate for this situation, since the process exceeds its feasible region of operating conditions after just a few days; however, some sub-optimal approaches, like maintaining (more conservative) constant conditions for a long period of time, can closely approach the limiting maximum profit. Additional examples demonstrate the importance of time-varying operation in strategies for switching modes between product grades in continuous plants and recipe improvement in batch plants. The previous chapters provide a solid foundation for the design and implementation of process control to achieve the objectives specified at higher levels in the automation hierarchy. Rijnsdorp's coverage of process control is sparse, giving heuristic explanations which could guide the non-specialist but not prepare the engineer for implementing these concepts. True to his broader view of automation, he addresses sequencing control as well as continuous algorithms. Rijnsdorp sets his viewpoint apart from most academics by defining automation as 'a human assisted by computer in a shared task of operating a plant'. By including the plant personnel as the central part of the automation process, Rijnsdorp opens the automation topic to many important issues normally only given cursory attention. It is especially noteworthy that he reports on the studies of Kortland and Krakt (1980) who report that only 10% of the alarms in industrial plants result in an operator action! In addition, VDU display design is addressed, where Rijnsdorp makes the important point that parsimonious displays should be designed to direct the operators attention to the most important information, not to draw complex, colorful schematics. Finally, emergency shutdown systems are covered with an introduction to the reliability of various designs, e.g. majority voting systems. Since these automation features--scheduling, optimization, process control, and operator supervision---are crucial to success, one might assume that they would have required an entire book; however, the abbreviated coverage consumed only about two thirds of this 424 page monograph. This reviewer believes that the ailoction of space was a mistake and that the author has much more to contribute to these topics, which constitute a set of well defined, integrated topics. Rijnsdorp selected to address two additional major topics which involve the management of automation projects and equipment. The first is 'internal integration' and addresses issues like hardware and software specifications, information system design, and control room layout. Anyone beginning an automation project realizes the challenge in specifying the requirements in a manner that definitely fulfils the automation needs and yet can be achieved by products from
Reviewer: THOMAS E. MARLIN
Department of Chemical Engineering, McMaster University, Hamilton, Ontario, Canada L8S 4L7. Is 1982, A SERmS of technical meetings titled Process Systems Engineering were initiated with the purpose of promoting a holistic approach to the analysis of process systems. This effort, and subsequent initiatives like the series of meetings on FOCAPO (Foundations of Computer-Aided Process Operations) and ESCAPE, provide worthwhile counterpoints to the typical research papers which are, and for the most part must be, concise and focused on a narrow mathematical issue. In spite of these initiatives, the literature addressing the broad scope of technologies relevant to process automation remains very limited. A technical article is too brief to properly set the background, while only a single aspect of this topic, e.g. flowsheeting or model fidelity, can be addressed in a review article. It is this gap which Rijnsdorp addresses with his new book. It is well recognized that process automation is implemented in a hierarchical structure, with the upper levels giving specifications and performance requirements to the lower levels. The importance of this hierarchy for process control is obvious; there is no reason to control a variable like temperature tightly unless the proper reference value is defined and the importance of reducing variability determined. A great strength of this book is the comprehensive discussion of requirements that are served by the hierarchical structure along with important elements of each level. Rijnsdorp begins his overview of a three-level hierarchy at the business logistics level, where decisions are made regarding feed purchases, product sales, and inventory management. Then, the desired process operation is defined to satisfy the business decisions. Naturally, the desired operation is fundamentally different for continuous, blocked operation (periodic changes between modes) and batch plants; each translates business needs to desired operations plans in a unique manner regarding the time dependence of operating variables. Finally, the lower level of process control is presented as a means for achieving the desired plant operation. The reader is prepared by this introduction for more detailed discussions of 'momentary optimization' and 'dynamic operation', i.e. scheduling. Rijnsdorp's order, covering the middle before the top level, could be reversed to emphasize the priority in decision making, but the inclusion of substantial coverage of both items is a unique and valuable feature of the book. After all, the policy to maximize momentary profit, without regard for the future, could be to stop production and sell the in-plant inventory; it is only through the scheduling or 'look ahead' planning that the proper plant plan is established. Rijnsdorp covers the momentary optimization in four chapters through several examples which elucidate main issues such as degrees-of-freedom, operating window, defining the profit measure, and constrained and unconstrained operating conditions. One example of note clearly demonstrates the importance of proper mathematical analysis. In this example the heuristic of 'equal marginal * Integrated Process Control and Automation; Process Measurement and Control by John E. Rijnsdorp. Elsevier,
Amsterdam (1991). ISBN 0-444-8909%1 (paperback). 365 AUTO 30:2-M
366
Book Reviews
several vendors.. A common mistake is to define hardware and software structures. A better approach is to define functional requirements in terms of response times, controller calculations, display features, security, reliability, openness, and so forth. One would have hoped for more guidance in defining these critical, measurable system features and determining performance criteria relevant to the process industries. The second project topic addresses managing the project from scoping study through normal operation and maintenance. Perhaps this could be better handled in a separate monograph providing fill-in-the-blank projects specifications, along with estimating procedures for engineering time and equipment, installation, startup and maintenance costs. Overall, the author is to be commended for defining the most important automation issues and addressing them in an integrated manner. This will be appreciated by many readers who have experience in only one or a few of these issues. The major topic that does not receive sufficient emphasis is product quality control, at least within the context of process capability and continuing improvement that are all the rage today. A discussion of the relationship between automatic process control and statistical process control (e.g. MacGregor, 1988) would have been an especially valuable addition. No reviewer agrees with an entire book, and this situation is no exception. Perhaps the main issue I would take is with the discussion on automation benefits, which indicates that quantitative benefits estimate are not possible for specific strategies and that overall estimates, e.g. a few per cent throughout, are appropriate. However, standard methods are available and are in use for estimating future dynamics performance and economic benefits to be derived (Marlin et al., 1987; Harris, 1989). In addition to providing accurate quantitative estimates these approaches provide the needed detail for selecting sensors, process changes, and final elements and for designing control strategies to achieve the benefits. The material in the book emphasizes concepts over mathematical rigor and should be accessible to most graduate engineers. I believe that it might be a useful secondary reference for advanced undergraduate or graduate control courses which emphasize design and integration of control methods. However, it would not be adequate as a textbook for a course and should be supported with some lecture discussions for students who, without industrial experience, will not be able to appreciate many of the insights. There seem to be two categories of industrial practitioners most likely to benefit from this book. One is the younger engineer who is committed to building expertise in automation and who may have mastered several mathematical methods, but has not yet acquired an understanding of the integrated decision making in a plant. The second is the large group of engineers at the periphery of a control project, the process technologists, economic analysts, and project managers who must contribute to the project but
only fully comprehend their isolated feature of the integrated automation system for plant operations. The presentation is generally good, with clear writing and examples bringing home the material Rijnsdorp considers critical. In addition, a comprehensive set of symbols aids in understanding the process examples. Unfortunately, detailed information on the examples, models and data, is not provided in the book, nor are citations always given. Finally, the nature of the book motivates the reader to pursue many concepts in further detail, but the references provided are very limited, and many will be difficult or impossible to retrieve. Finally, I reiterate that this book is unique in the topics selected and method of coverage. It is tantalizing with its introduction to many important topics, yet is not entirely satisfying in the depth of coverage. Since the book is part of a series on Process Measurement and Control, it would seem worthwhile to dedicate several future titles in the series to the major headings in this book, specifically, dynamic operation (scheduling), momentary optimization, process control, and supervision by personnel, to more fully develop these topics within the context of the integrated view proposed by Rijnsdorp, and perhaps under his editorial guidance. References Harris, T. (1989). Assessment of control loop performance. Can. J. Chem. Eng., 67, 856-861. Kortland, D. and H. Kragt (1980). Process alarm systems as a monitoring tool for the operator. Third Int. Symp. on Loss Prevention and Safety Promotion in the Process Industries, Basle. MacGregor, J. (1988). Online statistical process control. CEP, 84, 10, 32-36. Marlin, T., J. Perkins, G. Barton and M. Brisk (1987). Advanced process control, warren centre study of opportunities and benefits. ISA, Research Triangle Park, U.S.A. About the reoiewer Dr Thomas E. Marlin received a Ph.D. degree from the University of Massachusetts in Chemical Engineering. After 15 years in industry at Exxon, and Stone and Webster, he joined McMaster University in 1987 as a Professor of Chemical Engineering holding the NSERC Industrial Research Chair in Process Control. At McMaster, he is Director of the McMaster Advanced Control Consortium, a group of 13 industrial companies and five professors collaborating on research in process automation and performance diagnostics. In addition to undergraduate and graduate courses, he teaches industrial short courses in process control, real-time optimization, and automation benefits/performance-audit studies. He is completing a textbook for undergraduates and industrial practitioners on Process Control for McGraw-Hill.