Performance analysis and multi-objective optimization of a poly-generation system based on PEMFC, DCMD and heat pump

This paper proposes a novel poly-generation system consisting of proton exchange membrane fuel cell (PEMFC), direct contact membrane distillation (DCMD) and heat pump to recover low-grade waste heat of PEMFC for improving energy efficiency, which can simultaneously generate power and fresh water. The mathematical model is developed to evaluate the system performance, the results show that the proposed system overall thermal efficiency is increased by 49.44 % in comparison with standalone PEMFC with the largest exergy destruction occurring in PEMFC, followed by DCMD, Valve 1, and Separator 2 under given conditions. The parameter analysis results indicate that PEMFC current density, feed and permeate flow rates of DCMD have significant influence on the system performance. The multi-objective optimization is employed to search for the optimal solutions for all four optimization objectives by NSGA-II and entropy weight TOPSIS (technique for order preference by similarity to an ideal solution) method, demonstrating that the net power output, the freshwater productivity, the overall thermal and the exergy efficiencies are 14,070.72 W, 65.73 kg/h, 110.24 %, and 44.23 %, respectively. The research work provides useful reference for developing poly-generation systems based on PEMFC, DCMD and heat pump to utilize low-grade waste heat to improve the entire system energy efficiency.