Process Dynamics and Control

The field of process control is concerned with the analysis of dynamic behavior of processes, process simulation, design of automatic controllers, and associated instrumentation. Process control as practiced in the process industries has undergone significant changes since it was first introduced in the 1940's. Perhaps the most significant influence on the changes in process control technology has been the introduction of digital computers and instruments with greater capabilities than their analog predecessors. During the past 25 years automatic control has assumed increased importance in the process industries, which has led to the application of more sophisticated techniques.

To instrument and control a modern plant, it is necessary that the engineer have an understanding of the time-dependent behavior of typical processes. This in turn requires an appreciation of how mathematical tools can be employed in analysis and design of automatic control systems. In this chapter we present the basic ideas involved in developing dynamic models for typical processes and then discuss the use of control valves and proportional-integral-derivative (PID) feedback controllers for process control. Next, various types of advanced control methods that have seen commercial use are reviewed. Finally, some comments on computer control are included. For a thorough discussion of process instrumentation and measurement devices, the reader is referred to other entries in the section, "Control and Instrumentation Technology", in this handbook.