(382a) On Integration of Feedback Control and Safety Systems: Studying a High-Pressure Flash Drum Separator

The continued occurrence of incidents in the chemical process industries, despite efforts to prevent them is a testament to the need for continued work focused on enhancing process operational safety to protect human lives and the environment [1]. Traditional approaches to process safety like process design modifications neglect important aspects impacting process operational safety, such as multivariable interactions of process components and variables, limited control system authority due to limitations on the capacity of control actuators, and the manner in which the safety or relief system response may impact the effectiveness of the process control system. When a safety system identifies unsafe behaviors, the safety system automatically take actions, such as on/of-type valves and pressure relief valves, which drives the process state back to a safe operating region. Since these drastic actions change the dynamic of the process, research is conducted to investigate how the safety system influences control system functions.

In the present work, we focus on a high-pressure flash drum separator under proportional-integral (PI) control systems, where a pressure relief valve is installed to protect the drum from extraordinarily high pressure. Using a large-scale dynamic process simulator, we demonstrate that modifying the tuning parameters of one of these PI controllers based on the safety system being on or off leads to improved closed-loop performance compared to the case in which the tuning parameters of the PI controller remain the same regardless of the state of the safety system. In addition to PI control, we also investigate how model predictive control systems can be modified to handle safety system actions. We will present a comprehensive simulation study to evaluate the approach and demonstrate that the integration of safety and control system can significantly aid chemical process operational safety and performance.

[1] T. Marlin. Operability in process design: Achieving safe, profitable, and robust process operations. Ontario, Canada: McMaster University, 2012.