Swelling Constrained Control of an Industrial Batch Reactor Using a Dedicated NMPC Environment: OptCon

Abstract

This work presents the application of nonlinear model predictive control (NMPC) to a simulated industrial batch reactor subject to safety constraint due to reactor level swelling. The reactions are equilibrium limited, one of the products is in vapor phase, and the catalyst decomposes in the reactor. The catalyst is fed in discrete time steps during the batch, and the end-point objective is the maximum conversion in a fixed time. The reaction kinetics is determined by the temperature profile and catalyst shots, while the chemical equilibrium is shifted by operating at low pressure and removing one of the products. However, the formed vapor causes liquid swelling, due to the gas or vapor stream resulted from the reaction. As a result reaction mass may enter in the pipes and condenser, creating productivity losses and safety hazard. The end-point objective function (maximum conversion) of this problem can be converted into a level set point tracking problem. The control method is based on the moving horizon NMPC methodology and a detailed first-principles model of reaction kinetics and fluid hydrodynamics is used in the controller. The NMPC approach is based on the sequential quadratic programming (SQP) algorithm implemented in a user-friendly software environment, OptCon. The application of the fast real-time iteration scheme in the NMPC allows the use of small sampling period minimizing this way the violation of the maximum level constraints, due to disturbances within sampling period.