THROUGHPUT MANIPULATION IN PLANTWIDE CONTROL-STRUCTURES

A fundamental characteristic of a well-designed process plant regulato ry control system is effective management of the rate of product manuf acture and regulation of the inventories within the plant. Designers h ave tended to concentrate on the design of product quality controls, n eglecting the impact of the production rate and inventory controls on final control system performance. Price and Georgakis have proposed gu idelines for the development of production rate and inventory controls . These rules help a designer to ensure that these parts of the contro l structure are effectively designed before proceeding to the design o f product quality controls. The structures which result satisfy the co ntrol objectives and maintain the plantwide characteristics of the pro blem. The applicability of these guidelines is illustrated using the c omplex test problem provided by the Tennessee Eastman Company. When th e guidelines are applied to the Eastman problem, several candidate con trol structures can be developed. The major difference between the alt ernatives is the method used to adjust the production rate or throughp ut of the process. Simulation testing of the candidates makes clear th at this decision is an important contributor to the success of the res ulting control structure.