Thermodynamic analysis and optimization of a waste heat recovery system for proton exchange membrane fuel cell using transcritical carbon dioxide cycle and cold energy of liquefied natural gas

Hybrid systems are receiving more and more attention due to their higher efficiencies compared with standalone systems. Higher efficiencies mean lower consumption of fuels and as a result lower environmental problems. In this paper, a hybrid system consists of a transcritical carbon dioxide cycle and a liquefied natural gas cycle is proposed to recover the waste heat produced in a proton exchange membrane fuel cell. A complete sensitivity analysis is performed on the system considering five key parameters, namely operating temperature of fuel cell, CO2 turbine inlet temperature, CO2 turbine inlet pressure and pinch temperature of condenser and preheater. Also to achieve the highest possible energy efficiency, an optimization technique is applied on the system. The results showed that using the proposed system, generated power of the system increases by 39% compared with a standalone fuel cell. Also its efficiency reached to 72% after optimization, while it was equal to 39% before using the waste heat recovery system.