Plantwide Control for Throughput Maximization: A Case Study

The impact of the basic plantwide regulatory control structure oil maximizing the throughput using an explicit optimizing controller is quantitatively evaluated for a simple process module. The module consists of the reaction A + B -> C occurring in a continuously stirred tank reactor followed by a distillation column separating the product from the recycled unreacted reactants. The Column vapor boilup hitting a maximum acts as the bottleneck constraint limiting the throughput due to column flooding. Through an evaluation of reasonable plantwide control structures, the location of the throughput manipulator, the composition analyzer for overall component inventory balancing and the "local" column reflux management policy are shown to significantly affect the maximum throughput. Quantitative results show that locating the throughput manipulator close to and where possible at the bottleneck constraint reduces the throughput derating necessary due to disturbances. Designing the plantwide regulatory control system to minimize the process variability propagated into the bottleneck constraint emerges as the key heuristic from the case study.