Operational safety of an ammonia process network via model predictive control

Abstract

Process safety is a crucial issue in the area of process systems engineering as accident prevention is a top priority in process operations. Operational safety needs to be directly incorporated into control system design to handle disturbances in the process. Motivated by the above considerations, this paper presents a practical application simulating multiple model predictive controllers within a multi-unit ammonia process, all of which integrate safety constraints of the process within their design. Specifically, catalytic deactivation in the shift reactor is a common and problematic disturbance that may trigger reaction thermal runaway in the methanator. Two controllers designed with the objective of improving operational safety are implemented on the ammonia plant under catalyst deactivation. Aspen Plus is a commercial process simulation software which is integrated with Matlab to run a closed-loop simulation for the ammonia process. The results demonstrate that under suitable design of the controllers, desirable closed-loop performance is achieved with high temperature extremities avoided during operation.