Adaptive superstructure for multiple-interconnection process synthesis: Eliminate unnecessary flowsheet predetermination to reduce complexity

The integrated distillation configurations have an enormous number of alternative flowsheets leading to great challenges for process synthesis. The superstructure-based approach can be the countermeasure but it is difficult to solve the complex networks using rigorous models due to the nonconvexity and nonlinearity. Although stochastic algorithms can robustly find high-quality solutions for a single predefined flowsheet, the performance will still degrade when dealing with complex superstructure models. This paper introduces an adaptive strategy to determine the substructure branches of the superstructure, which can reduce the complexity of the superstructure models optimized by stochastic algorithms. The improved method selects the downstream flowsheet based on the calculation results of the upstream modules, instead of predefining the branches before the simulation. Thereby, stochastic algorithms could optimize the simplified superstructure model with fewer sequence variables more robustly and efficiently. A multiple-effect distillation system and a double side-stream distillation system separating aromatics are optimized as case studies. The results show that the improved method, compared with the conventional approach, could find the optimized side-stream design with 17.8% lower cost more robustly, and find the optimized multi-effect distillation design with 2.4% lower cost within the same iterations.