An Introduction to Process Modelling Identification and Control for Engineers

This book is intended for under graduate as well as post graduate students of chemical, electrical, electronics and instrumentation branches of engineering disciplines pursuing process control as a subject and will be useful to research students of similar disciplines. This book focuses on the basics of process control, identification, PID controllers and autotuning with an objective to understand the basic concepts of process modeling, feedback loops and synthesis of PID controllers with practical ways of using closed-loop systems. This text book contains 10 chapters starting from introduction to advanced topics in the field of process modeling, identification and control to cater to needs of UG/PG students of E&I, ICE, Chemical, Leather and allied branches of engineering. For quick reference the required mathematical tools are presented at the appropriate places. Special emphasis is given to practice the theory with the help of examples to provide adequate software programs. Detailed closed-loop studies based on several typical case studies are also discussed. Some numerical problems are presented to understand theoretical concepts clearly. The book is written in simple sentences in an easily understandable manner. Exercise problems are also presented at the end of each chapter. The revision formula, review questions and short questions with answers are another value addition. Chapter one introduces process control explaining process, associated variables and the needs of closedloop control of stable systems covering batch, semibatch and continuous processes. General description of control schemes, regulatory & servo mechanisms, P&I diagram and steps in synthesizing control system design will be helpful to readers who have not undergone any prior course on control systems. Chapter two focuses mathematical tools for process modeling and control which will be appropriate for students without higher engineering mathematics background. Chapter three aims for process modeling which is essential for controlling a process. This will help in understanding dynamics of the system, obtaining different model structures from 1st principle & continuity equations of systems. Structures of SISO, MIMO and non-linear processes are also discussed in this chapter. Chapter 4 provides dynamic or transient information characteristics regarding a process. Trends of outputs due to changes in different types of input perturbations are also discussed in this chapter. Chapter 5 introduces methods of parametric estimations from process model of different types. It includes several important identification algorithms to obtain continuous / frequency domain transfer function models from measured input-output data sets. The estimated parameters will be useful for controller tuning and stability analysis. The structures of different modes of feedback control systems with different PID forms are presented in chapter 6. Tuning of PID controller parameters for different types of process model structures is discussed. Time, frequency domain and error based tuning criteria including autotuning features are discussed in this chapter. Frequency responses and stability analysis are presented in chapter 7. Chapter 8 provides information about valves, actuators, converters, valve sizing and smart control valves. PID enhancement incorporating direct-indirect acting control actions, anti-reset windup and advanced process control strategies are discussed in chapter 9. Case studies of closed-loop control on different practical process systems are described in chapter 10. Preface.................................. .................................................................................................................... v Chapter 1 ........................................................................................................................................... Introduction Needs for Process Control systems, process variables, open & closed-loop concepts, types of processes (batch / semibatch / continuous). Piping & Instrumentation diagrams, process control system terminology, steps in synthesis of control system design Chapter 2 ........................................................................................................................................... Mathematical tools for process control Laplace transform – definition, purpose of LT, initial value & final value theorem, LT of functions, solution of differential equations, inverse LT, numerical examples, Linearization techniques – Taylor series and solution of algebraic equations, Newtons method, solution of ODE, Euler, Runge-Kutta methods, solution of PDEs, finite difference & finite element techniques using implicit & explicit techniques, optimization Chapter 3 ........................................................................................................................................... Process modeling Development of mathematical models, steady state & dynamic models, time delay models, transfer function models, linearization of single / multi-variable non-linear systems, model structures (IPDT, FOPDT, SOPDT, HOPDT etc. with stable & unstable systems) & special model structures (inverse response & non-minimum phase systems) Chapter 4 ........................................................................................................................................... Dynamic behavior of processes Step, pulse, impulse, ramp and transient responses of FOPDT, SOPDT, HOPDT & other typical process models Chapter 5 ........................................................................................................................................... Parameter estimation Identification of transfer functions, methods of estimation – time domain & frequency domain estimation techniques least square, reaction curve, inflection point, relay feedback etc. for typical model structures, discrete transfer functions Chapter 6 ........................................................................................................................................... Feedback Control systems Closed-loop transfer functions, basic control actions, on-off, single speed floating, P, PI, PID, PD controllers, practical forms of PID controllers, realization of various control actions, tuning of controllers, tuning criteria based on ZN, ISE/ITAE, quarter decay, process reaction curve, continuous cycling, damped oscillation, Lcmax, Gain & Phase margins. Autotuning, model based tuning, loop shaping, intelligent schemes, performance evaluation Chapter 7 ........................................................................................................................................... Components of process control systems I / P converters, pneumatic and electronic actuators, valve positioners, types of control valves, characteristics of control valves, valve body, valve sizing, cavitation, flashing, selection of control valves, smart control valve features Chapter 8 ........................................................................................................................................... Frequency responses and stability analysis Bode, polar & Nyquist plots of transfer functions, stability criteria with Routh, Kharitonov, Bode, Nyquist; sensitivity and robustness Chapter 9 ........................................................................................................................................... PID enhancement Enhancement of PID control actions, direct & indirect acting controllers, reset feedback, anti reset windup, advanced control techniques like feed-forward, cascade, ratio, split range, inferential, adaptive, model based and predictive control schemes Chapter 10 ......................................................................................................................................... Case Studies Implementation issues and performance studies of closed-loop Reactors, CSTR, Heat exchanger, Distillation column, Gas absorber, Evaporator, Dryer, Boiler, Crystallizer and Leather Index................ .......................................................................................................................I.1 Offering a professional and modern view on process modelling, system identification and automatic control of physical and industrial processes, this is the first comprehensive text augmented with practical examples and their solution with MATLAB code to cater to the needs of engineering students of all levels. The book presents the topics of modelling of physical systems based on first principle with material and energy balances, Formulation of transfer functions and model structure with parametric identification supplemented by software, question and answers along with exercise problems. In order to address modern process control issues in process industries various topics are covered along with the associated mathematical tools to solve models involving ODE/PDE, optimization tools, transient behaviour of processes and transfer functions. This text explains auto tuning of PID controllers and related analysis for process identification for the first time using relay feedback by experts.