THROUGHPUT MANIPULATION IN PLANTWIDE CONTROL-STRUCTURES

A fundamental characteristic of a well-designed process plant regulatory control system is effective management of the rate of product manufacture and regulation of the inventories within the plant. Designers have tended to concentrate on the design of product quality controls, neglecting the impact of the production rate and inventory controls on final control system performance. Price and Georgakis have proposed guidelines for the development of production rate and inventory controls. These rules help a designer to ensure that these parts of the control structure are effectively designed before proceeding to the design of product quality controls. The structures which result satisfy the control objectives and maintain the plantwide characteristics of the problem. The applicability of these guidelines is illustrated using the complex test problem provided by the Tennessee Eastman Company. When the guidelines are applied to the Eastman problem, several candidate control structures can be developed. The major difference between the alternatives is the method used to adjust the production rate or throughput of the process. Simulation testing of the candidates makes clear that this decision is an important contributor to the success of the resulting control structure.