On accounting for equipment-control interactions in economic model predictive control via process state constraints

摘要

Traditionally, chemical processes have been operated at steady-state; however, recent work on economic model predictive control (EMPC) has indicated that some processes may be operated in a more economically-optimal fashion under a time-varying operating policy. It is unclear how time-varying operating policies may impact process equipment, which must be investigated for safety and profit reasons. It has traditionally been considered that constraints on process states can be added to EMPC design to prevent the controller from computing control actions which create problematic operating conditions for process equipment. However, no rigorous investigation has yet been performed to analyze whether, when a process is operated in a time-varying fashion, constraints on the process states (rather than states of the equipment behavior itself) are the most appropriate way of preventing unsafe conditions. In this work, we investigate the use of process state constraints for preventing equipment damage due to the operating conditions set up by an EMPC over time when the equipment behavior is modeled within a context based on forces, deformation, and fracture. Through a chemical process example, we elucidate that there are situations in which process state constraints are likely to be adequate for use in preventing an EMPC from setting up operating conditions that may not be desirable, but that there also may be situations when process state constraints are not adequate and constraints on equipment states may be an alternative. We elucidate a number of challenges that remain to be addressed for this proposed method to be practical. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.