Design of plant-wide regulatory control systems

Current techniques for the design of control systems fail to account adequately for the complex interconnection and interaction of modern process plants. These complexities are best addressed by a plant-wide perspective on control system design.; Two frameworks for structuring the control design decision sequence are postulated. One of these, the "tiered" framework, divides the control design problem into subproblems according to the control tasks performed. This tiered framework is applicable at its current level of development. The other is a "modular" framework based on the arrangement of unit processes within the plant.; One module, a CSTR/column system with recycle, is extensively studied. Seventy different control structures and 318 implementations of these structures are examined. In addition to structural considerations, the consequences of level control tuning and control of intermediate compositions are examined. Each implementation is rigorously simulated for both feed composition and production rate changes. The performance of the implementations is compared based on the integral absolute error of the final product composition.; Insight from the simulation study enables the development of a set of guidelines for the design of production rate and inventory control structures. The guidelines are justified by the results of the CSTR/column study. It is proposed that these guidelines are valid for a variety of processes.; The key concept introduced by the guidelines is the definition of a "self-consistent" inventory control structure. An inventory control structure is said to be self-consistent if it is able to propagate a production rate change throughout the entire process without additional operator or control action. Inventory control structures which are not self-consistent typically perform poorly when compared to their self-consistent counterparts.; The use of the guidelines is illustrated by several application examples: an extractive distillation system, a plant for the hydrodealkylation of toluene to benzene, and the Tennessee Eastman process control challenge problem (Downs and Vogel, 1993). The control structures developed by applying the guidelines to the extractive distillation and HDA plants are qualitatively compared to published results. Simulation was used to show the effectiveness of the structures developed for the Eastman problem. These examples support the utility, generality, and effectiveness of the guidelines.; The dissertation also includes background material on the frequency response and steady state behavior of the CSTR/column system.; Reference. Downs, J. and Vogel, E., A Plant-Wide Industrial Process Control Problem. Comput. Chem. Eng., 17(3):245-255, 1993.