Multiobjective Early Design of Complex Distillation Sequences Considering Economic and Inherent Safety Criteria

Inherent safety aspects are not usually considered as a driving force during the conceptual design stage of chemical plants. Instead, after the selection of the optimal economic flowsheet, safety is added to the design. However, this sequential design approach could be applied to inferior designs due to protection devices' cost overrun. The objective of this work is to implement a strategy to simultaneously design a profitable and inherently safer distillation train. Two safety indexes, a disaggregated version of the Safety Weighted Hazard Index and Dow's Fire and Explosion Index, have been adapted to quantify the inherent safety performance. A large-scale multiobjective MILP problem is formulated. Thus, two strategies of objective reduction are utilized: principal component analysis coupled with Deb's algorithm and a method based on the dominance structure. The results prove the suitability of these safety index as inherently safer metrics, and showcase the ability of the objective reduction methods to discriminate among the inherent safety criteria.