An Introduction to Process Control

In most process control courses for chemical engineers, the first part of the course normally deals with the development of dynamic process models from first principles (mass and energy balances), since these are used in the analysis of process dynamics and often also for controller tuning. In this chapter, however, the focus will be on process control and modelling will not be considered. Neither will the chapter consider 

The primary objective of process control is to maintain a process at the desired operating conditions, safely and efficiently, while satisfying environmental and product quality requirements. The subject of process control is concerned with how to achieve these goals. Luyben3 gives the following process control laws  

First law The simplest control system that will do the job is the best. Bigger is definitely not better in process control. 

Second law You must understand the process before you can control it. Ignorance about the process fundamentals cannot be overcome by sophisticated controllers. 

The process control system should ensure that the process is maintained at its specified operating conditions at all times. To be able to do this, we must first understand the process dynamics as advised by Luyben in his Second Law.3 The dynamics of a process tells us how the process behaves as a result of the changes. Without an understanding of the dynamics, it is not possible to design an appropriate control system for it. 

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An Introduction to Process Control System Design, Longmans, Green, London(1955)... 

The book is divided into five parts. Part I provides an introduction to process control and an in-depth discussion of process modeling. Control system design and analysis increasingly rely on the availabihty of a process model. Consequently, the third edition includes additional material on process modeling based on first principles, such as conservation equations and thermodynamics. Exercises have been added to several chapters based on MATLAB simulations of two physical models, a distillation column and a furnace. These simulations are based on the book. Process Control Modules, by Frank Doyle, Ed Gatzke, and Bob Parker. Both the book and the MATLAB simulations are available on the book Web site (www.wiley.com/college/seborg). National Instruments has provided multimedia modules for a number of examples in the book based on their Lab VIEW software. 

Wankat, P. C. (1990) Rate Controlled Separations, Elsevier Applied Science. Weber, T. W. (1978) An Introduction to Process Dynamics and Control, Wiley-Interscience. 

This chapter is an introduction to process dynamics and control for those students who have had little or no contact or experience with real chemical engineering processes. The objective is to illustrate where process control fits into the picture and to indicate its relative importance in the operation, design, and development of a chemical engineering plant. 

Weber, Thomas W. "An Introduction to Process Dynamics and Control", John Wiley Sons, New York, New York, 1973. 

When designing and evaluating an analytical method, we usually make three separate considerations of experimental error. First, before beginning an analysis, errors associated with each measurement are evaluated to ensure that their cumulative effect will not limit the utility of the analysis. Errors known or believed to affect the result can then be minimized. Second, during the analysis the measurement process is monitored, ensuring that it remains under control. Finally, at the end of the analysis the quality of the measurements and the result are evaluated and compared with the original design criteria. This chapter is an introduction to the sources and evaluation of errors in analytical measurements, the effect of measurement error on the result of an analysis, and the statistical analysis of data. 

Stephanopoulos, G. 1984. Chemical Process Control An Introduction to Theory and Practice. Prentice-Hall, New Jersey. 

Prasad, P. R., and Davis, J. F., A framework for knowledge-based diagnosis in process operations, in An Introduction to Intelligent and Autonomous Control (P. J. Antsaklis and K. M. Passino, eds.). Kluwer Academic Publishers, Boston, 1992, pp. 401-422. 

Volumes 1, 2 and 3 form an integrated series with the fundamentals of fluid flow, heat transfer and mass transfer in the first volume, the physical operations of chemical engineering in this, the second volume, and in the third volume, the basis of chemical and biochemical reactor design, some of the physical operations which are now gaining in importance and the underlying theory of both process control and computation. The solutions to the problems listed in Volumes 1 and 2 are now available as Volumes 4 and 5 respectively. Furthermore, an additional volume in the series is in course of preparation and will provide an introduction to chemical engineering design and indicate how the principles enunciated in the earlier volumes can be translated into chemical plant. 

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