(167c) Simultaneous Design and Control of a Distillation Column Under Disturbance for Cost, Inherent Safety, and Controllability

Traditional inherent safety strategies in the early stages of design focus on reducing the overall hazard of a process without considering its operability. The process is first designed to be inherently safer with respect to a nominal, steady state case. Then, after the process is designed, layers of protection are added and operability issues are addressed.

However, the way a process is designed not only affects its safety but also heavily impacts its operability. An intensified process may contain less of a hazardous substance and thus be inherently less hazardous, but if the design restricts the controllability of the process, then the design may have a higher risk and be less safe overall. Therefore, in the early stages of design, it is necessary to consider of both the inherent hazard contained within the process and the ease by which these hazards can be controlled. With the dynamic behaviour of process systems becoming increasingly complex, the consideration of operability issues in the design stage becomes even more necessary to prevent incidents.

Simultaneous design and control is an effective method to predict and reduce operability issues that result from an uncontrollable process design. Incorporating traditional inherent safety metrics into simultaneous design and control subsequently allows for industry to investigate inherent safety in the early design stage along with an analysis of error tolerance and ease of control.

The objective of this research is to implement a strategy to simultaneously design and control an inherently safer distillation column. The PARametric Optimization and Control (PAROC) framework is used as a basis for the simultaneous design and control of a distillation column. gPROMS is used to perform dynamic optimization of a distillation column design. Multiparametric Model Predictive (mp-MPC) control is used to constrain the control limits of the control response, and the Safety Weighted Hazard Index (SWeHI) is incorporated into the PAROC framework to measure and constrain the safety of the system. Therefore, the distillation column is optimized for minimal cost under control and safety constraints.