Masters Theses

Date of Award

5-1990

Degree Type

Thesis

Degree Name

Master of Science

Major

Chemical Engineering

Major Professor

Charles F. Moore

Committee Members

James J. Downs, Duane D. Bruns

Abstract

In recent years, rising material and energy costs have forced process design toward greater utilization of heat integration and material recycle. This trend has reduced the equipment overdesign and surge capacity availability frequently used to lessen the impact of disturbances, thus placing higher performance demands upon the control system. As this change has occurred, control system design has remained a highly designer-dependent process, based largely upon heuristics and experience. Process control system design has also traditionally been based on individual unit operations: however, today's increasing process complexity is driving designers to consider the entire plant. Considering the entire process allows designers to address the effect of interactions. Direction may be given to the design of a control system through utilization of steady-state analysis tools such as Singular Value Decomposition (SVD), Relative Gain Array (RGA), and Niederlinski Index. Currently, these tools can guide control system design for individual unit operations. The successful extension of steady-state analysis tools to entire plants would provide a method to aid in the design of control systems for integrated operating plants. Successful design of a control system for single-input single-out (SISO) control depends on correctly pairing the controlled and manipulated variables. During operation, the control law employs each manipulated variable to maintain a specific controlled variable at a desired value. This control law is a function of error between the controlled variable and a desired value and also a function of the integral and derivative of this error. A steady-state analysis of the plant may guide variable pairings. These pairings have a significant impact on plant performance. The purpose of this study is to apply steady-state analysis tools to process gain matrices to obtain information concerning control system design. Consideration of the relative importance of various performance objectives during the design phase appears critical to successful system implementation. A weighted analysis represents the relative importance of the controlled variables and the manipulated variables. This analysis provides information that can guide control system design for entire operating plants.

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