Chapter 15. Plantwide Control

A process engineer is concerned about more than the control of a single loop or multiple loops associated with a single-unit operation. Of real concern is the operation of the entire plant. After studying this chapter, the reader should be able to do the following:

• Develop an appreciation for some of the complexities of plantwide control

• Understand the control strategies associated with equipment/unit operations that are part of a typical chemical process plant

• Understand the "snowball effect" and how to fix a stream flow in the recycle loop to avoid it

• Understand that recycle can significantly change the process dynamics

• Understand the control and optimization hierarchy—that important operation and control decisions at different corporate levels are made on different timescales

The major sections of this chapter are as follows:

15.1 Background

15.2 Steady-State and Dynamic Effects of Recycle

15.3 Unit Operations Not Previously Covered

15.4 The Control and Optimization Hierarchy

15.5 Further Plantwide Control Examples

15.6 Summary