(658a) On Integration of Feedback Control and Safety Systems for Networked Chemical Processes

Safety is critical in the chemical process industries due to the severe consequences for both lives and property when safety is not maintained [1]. Despite many efforts to develop, characterize, and standardize effective safe process/plant design and operation procedures, accidents continue to occur causing significant human and capital losses [2]. Innovative operating strategies are required to eliminate unsafe process operation which may lead to catastrophic events. Recent advances in chemical process safety utilizing a system engineering perspective have sought to incorporate safety considerations within model predictive control (MPC) in the context of a single processing unit [3].

Motivated by the above considerations, we propose a distributed MPC design for chemical process networks that accounts for the activation of the safety system and changes the process model when the safety system is predicted to be activated at some time instant along the prediction horizon. An example of a continuous stirred-tank reactor (CSTR) coupled with a flash drum separator is considered to illustrate that model predictive control with varying models can control a process when the safety system is activated due to significant feed disturbances that lead to thermal runaway in the CSTR. This multi-unit chemical process is simulated in Aspen Plus Dynamics and a multi-variable distributed MPC is implemented to control the entire chemical process network as well as design and size the safety system. Disturbance and device failures are introduced to evaluate the distributed MPC performance for the cases in which it does and does not account for the activation of the safety system.

[1] The 100 largest losses 1974-2015: Large property damage losses in the hydrocarbon industry. Technical report, Marsh & McLennan Companies Inc., 2016.

[2] Center for Chemical Process Safety. Guidelines for Hazard Evaluation Procedures. John Wiley & Sons, Inc., New Jersey, 2008.

[3] Zhang, Z., Z. Wu, H. Durand, F. Albalawi and P. D. Christofides, "On Integration of Feedback Control and Safety Systems: Analyzing Two Chemical Process Applications,'' Chem. Eng. Res. & Des., 132, 616-626, 2018.