Energetic, exergetic, economic, and exergoeconomic analysis of a phosphoric acid fuel cell-organic rankine cycle hybrid system

Abstract

A phosphoric acid fuel cell-organic Rankine cycle (PAFC-ORC) hybrid system is proposed to maximize the electrical efficiency of the PAFC system. The exhaust heat from the PAFC is used to heat working fluids flowing through the ORC to generate additional power. To optimize the system, a numerical model of the PAFC system was developed using Aspen Plus® and was validated by comparison with the experimental data of the current–voltage polarization curve. Energetic and exergetic analyses of the PAFC-ORC hybrid system were conducted by varying the operating temperature with six working fluids: R123, toluene, ammonia, methanol, R134a, and R141b. When the operating temperature of the PAFC is 190 ℃, and methanol is used as a working fluid for the ORC, the electrical efficiency of the hybrid system is the most efficient at 60.49%. The exergy destruction through the ORC is the lowest when methanol is used as a working fluid. Among the components of the hybrid system, the component where the most exergy destruction occurs is the PAFC stack, followed by the ORC and cathode heat exchanger. Economic and exergoeconomic analyses were performed with methanol at a PAFC coolant temperature of 150 ℃. The PAFC stack has the highest exergoeconomic factor of 87%, while the preheater and condenser have the lowest exergoeconomic factor of 5%.