Exergy and environmental assessments of the performance of a molten carbonate fuel cell cogeneration plant: External steam reforming against internal steam reforming

Abstract

Two different configurations of a system including a cogeneration plant based on molten carbonate fuel cell (MCFC) with internal steam reforming (IR-MCFC) and external steam reforming (ER-MCFC) for producing power and hot water are modeled and investigated thermodynamically. Energetic, exergetic and environmental analyses are performed for the proposed systems and compared with each other from different viewpoints. Effects of various parameters, namely after-burner emissions recycling, fuel utilization ratio, operating temperature of stack and current density are investigated on the output potential voltages and any kind of voltage losses, net generated power, CO₂ emission and energy and exergy efficiencies of two proposed cogeneration plants. The main sources of irreversibility are introduced for each system as well. The comparative analysis revealed that energy efficiencies of the IR-MCFC and IR-MCFC based cogeneration systems are about 14.85% and 4.82% larger than those of the ER-MCFC and ER-MCFC-based cogeneration systems, respectively. Also, exergy efficiencies of the IR-MCFC and IR-MCFC based cogeneration systems are about 14.46% and 11.08% more than exergy efficiencies of their external reforming types, respectively. The results indicated that CO₂ emission of ER-MCFC system (0.18 kg/MW) is almost two times of IR-MCFC system (0.36 kg/MW).