Model Predictive Control with Safety Constraint Embedded in Hazard and Operability Study

Abstract

Industrial accidents represent a critical issue in the chemical processes, which keep happening although all efforts to avoid them. There are many tools and methodologies employed in the industry to improve the safety of a chemical system, but they might still fail because accidents do not have a single or linear cause. Recently a new approach to process safety, based on a control-inspired view has gained attention, such as embedding model predictive control (MPC) with safety constraints developed from qualitative safety principles, for instance, HAZOP (Hazard and Operability study). MPC is a control technique formulated as an optimization problem, and consequently, it is possible to include mathematical constraints. In this context, this work proposes to investigate the use of an MPC with safety constraints for potential hazards, integrated with a dynamic simulation-based HAZOP methodology. We evaluated the effect of safety constraints as a recommendation to increase the safeguard of a styrene polymerization reactor, as a case study. To simulate potential hazards from a chemical process failure we used HAZOP deviations, and then evaluated the same disturbance to an MPC with a safety constraint, as a consequence of the HAZOP recommendation to avoid an accident. The simulation results present the effect of the safety constraint in the MPC as a recommendation to safeguard and the importance of the safety approach based on the control-inspired view, enhancing a safety system in a chemical process.