Exergy analysis and optimization of methanol generating hydrogen system for PEMFC

An exergy analysis of methanol autothermal generating hydrogen system for PEMFC is presented. The process combines a catalytic combustion heat exchanger (CCHE), using partial off-gases containing hydrogen as feedstock, with an auto-thermal reformer (ATR), two water gas shift (WGS) reactors and four preferential oxidation (PROX) reactors. Energy and exergy of system were calculated and analyzed. The results demonstrated that inner exergy losses resulted from the irreversible heat transfer and reaction were the dominant factors. The most important destruction of exergy within the system was found to occur in the reformer and the catalytic combustion heat exchanger. Their ratios of exergy loss accounted for 25.03% and 24.95%, respectively, of the whole system. Based on results of thermodynamic and exergetic analysis, the reformer was optimized. The optimal W/MW/M (molar water to methanol) is around 1.5–2.0 and A/MA/M (molar air to methanol) is around 1.5. Certain recommendations were posed. The conclusions could help to optimize methanol autothermal generating hydrogen system for PEMFC.