A Real-Time Approach to Process Control

William Y. Svrcek, Department of Chemical and Petroleum Engineering, University of Calgary, Canada Donald P. Mahoney, Chemical Industry Business Solutions, SAP AG, USA Brent R. Young, Department of Chemical and Materials Engineering, University of Auckland, New Zealand

Author Biographies xi
Foreword and Endorsements xiii


Preface xv


Acknowledgements xvii


1 A Brief History of Process Control and Process Simulation
1


1.1 Process Control 1


1.2 Process Simulation 5


References 11


2 Process Control Hardware Fundamentals 15


2.1 Control System Components 15


2.2 Primary Elements 16


2.3 Final Control Elements 33


References 53


3 Fundamentals of Single-Input/Single-Output Systems
55


3.1 Open Loop Control 55


3.2 Disturbances 56


3.3 Feedback Control ? Overview 57


3.4 Feedback Control ? A Closer Look 60


3.5 Process Attributes ? Capacitance and Dead Time 66


3.6 Process Dynamic Response 74


3.7 Process Modelling and Simulation 76


References 93


4 Basic Control Modes 95


4.1 On?Off Control 95


4.2 Proportional (P-Only) Control 97


4.3 Integral (I-Only) Control 102


4.4 Proportional Plus Integral (PI) Control 105


4.5 Derivative Action 107


4.6 Proportional Plus Derivative (PD) Controller 108


4.7 Proportional Integral Derivative (PID) Control 111


4.8 Digital Electronic Controller Forms 112


4.9 Choosing the Correct Controller 112


4.10 Controller Hardware 114


References 117


5 Tuning Feedback Controllers 119


5.1 Quality of Control and Optimization 119


5.2 Tuning Methods 123


References 132


6 Advanced Topics in Classical Automatic Control 133


6.1 Cascade Control 133


6.2 Feedforward Control 137


6.3 Ratio Control 140


6.4 Override Control (Auto Selectors) 142


6.5 Split Range Control 147


References 149


7 Common Control Loops 151


7.1 Flow Loops 151


7.2 Liquid Pressure Loops 153


7.3 Liquid Level Control 155


7.4 Gas Pressure Loops 165


7.5 Temperature Control Loops 166


7.6 Pump Control 172


7.7 Compressor Control 172


7.8 Boiler Control 179


References 182


8 Distillation Column Control 185


8.1 Basic Terms 185


8.2 Steady-State and Dynamic Degrees of Freedom 186


8.3 Control System Objectives and Design Considerations 188


8.4 Methodology for Selection of a Controller Structure 190


8.5 Level, Pressure, Temperature and Composition Control 192


8.6 Optimizing Control 199


Section Sidestream 199


8.7 Distillation Control Scheme Design Using Steady-State Models
204


8.8 Distillation Control Scheme Design Using Dynamic Models
212


References 213


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 220


9.4 Decoupling Control Loops 220


9.5 Tuning the Controllers for Multi-loop Systems 222


9.6 Practical Examples 222


9.7 Summary 232


References 232


10 Plant-Wide Control 233


10.1 Short-Term versus Long-Term Control Focus 233


10.2 Cascaded Units 235


10.3 Recycle Streams 236


10.4 General Considerations for Plant-Wide Control 241


References 242


11 Advanced Process Control 245


11.1 Advanced Process Control 245


11.2 Model Predictive Control 246


11.3 Dynamic Matrix Control 249


11.4 General Considerations for Model Predictive Control
Implementation 253


References 254


Appendix A P&ID Symbols 257


Appendix B Glossary of Terms 261


Appendix C New Capabilities with Control Technology Hardware and
Software 267


Workshop 1 Learning through Doing 279


Workshop 2 Feedback Control Loop Concepts 283


Workshop 3 Process Capacity and Dead Time 289


Workshop 4 Feedback Control 295


Workshop 5 Controller Tuning for Capacity and Dead Time
Processes 303


Workshop 6 Topics in Advanced Control 311


Workshop 7 Distillation Control 321


Workshop 8 Plant Operability and Controllability 333


Index