Superstructure optimization for the synthesis of chemical process flowsheets: Application to optimal hybrid membrane systems

Abstract

The superstructure has proved an effective tool for the synthesis of chemical-engineering process flowsheets. The superstructure is assumed to contain all possible alternatives of a potential treatment network, including the optimal solution that is hidden. A common approach for formulating superstructures for process-synthesis problems involving heat and mass exchange has been to use the state-space framework. In this way, unit operations, utility units, and utility streams can be embedded in such a way that all the process synthesis alternatives can be realized. Such a framework has been applied to water and wastewater synthesis problems. This article reviews the optimization studies that have been carried out on membrane and hybrid membrane process-synthesis problems for wastewater treatment. Comparison is made between different representations and their mathematical programs to highlight the relationship between the superstructure representation and their mathematical programming formulations. From this analysis, possible improvement of these superstructures is suggested. Also, a generic representation is provided for a systematic and clear description for assembling hybrid membrane system superstructures via the state space approach. Several case studies are given in order to illustrate the proposed approach.

Keywords:

• superstructure optimization
• hybrid membrane system
• wastewater treatment
• waste reduction