Integrating Safeness Index-Based Model Predictive Control and Safety Relief Valve Activation for Operational Safety of Chemical Processes

This work demonstrates an application of Safeness Index-based model predictive control to improve process operational safety in a safety critical chemical process application. Specifically, a high-pressure flash drum separator together with pressure relief valve as safety system is used to analyze the benefits of integrating Safeness Index-based considerations in model predictive control (MPC). Safeness Index function and Safeness Index threshold are developed using information collected from the process and safety system to indicate the safeness of the plant. Under an identified linear model, MPC is implemented with Safeness Index-based constraints and slack variables in a co-simulation of Matlab/Aspen. It is demonstrated that in the presence of a small disturbance, the drum pressure remains below the opening pressure of relief valve by Safeness Index-based MPC, so that the safety system is not activated. When there is a large disturbance, the controller working together with the relief valve ensures process operational safety before, during and after the pressure relief valve is turned on/off.