Exergy analysis of combined fuel processor-fuel cell system

Abstract

Exergy analysis and energy efficiency of a combined fuel processor-fuel cell system was performed. Experimental data were used for the performances of the ATR, WGS and PROX catalytic reactors assuming that the concentrations of the outlet streams obtained at the laboratory experiments can be achieved at the exit of the reactors. The catalyst performance data for IPOX reactor for pure propane, 50% propane – 50% butane and 75% propane – 25% butane feeds at different temperatures have been obtained from experimental works conducted in Catalyst Technology and Reaction Engineering Laboratory. The conversion level of the water-gas shift reactor was assumed as 70% of the equilibrium conversion at the corresponding reactor temperature level. 100% CO selectivity and 100% CO conversion were accepted for preferential oxidation reactor by using the above experimental results. Output composition from each reactor was based on the experimental data obtained from the experiments. Once mass flow rates were calculated for each stream, energy balances were carried out to calculate unknown outlet temperatures as well as the temperatures of the other units present in the combined system. The fuel cell conversions in the calculations were taken in the range of 75% - 85%. After all the streams in the system were determined, exergy balances were calculated for each unit and also for the whole system. The overall system exergy efficiencies were calculated as a function of IPOX reactor temperature. According to the results of this study, when IPOX reactor output temperature increased, except at 743 K, exergy efficiency of the system increased. Exergy analysis indicated that water-gas shift and preferential oxidation reactors have a minimum impact on the overall exergy of the system. The energy efficiency of the whole system was found sensitive to the methane content and the temperature level of the exhaust stream from the system.