Modeling And Analysis Of High Temperature PEM Fuel Cell Systems

High temperature proton exchange membrane fuel cell (HT-PEMFC) hasreceived considerable attention because of its environmentally friendly operation,high efficiency and high tolerance of CO. This study develops two HT-PEMFCsystem models, one is fueled by hydrogen directly (direct hydrogen system), andanother is fueled by methane (natural gas) with a steam methane reforming system(reformed hydrogen system). In this study, all of the equipment in the whole systemare simulated correspondingly, including the HT-PEMFC stack, air compressor,turbine, water pump, methane steam reformer (SMR) and water gas shift (WGS). Thethermodynamic performance of the two systems are studied with the method ofenergy and exergy analysis, which include both amount and quality of energy flowingand distributing in the systems, and the diagrams of energy balance and the plots ofequipment energy loss are obtained from the simulation. Different effects of operatingparameters, such as the stack temperature, pressure, air relative humidity (RH), airstoichiometry and the steam methane reforming temperature on the systemperformance are investigated based on the energy and exergy analyses.The results indicate that for both systems, an increment in the fuel cell stacktemperature tends to increase the efficiency and power output of the system. However,increasing the operating pressure, inlet RH and cathode stoichiometry have theinsignificant influence on improving the quality of both systems. For the directhydrogen system, the performance changes slightly with the increase of anodestoichiometry. But the efficiency of the reformed hydrogen system decreases greatlywhen the anode stoichiometry is increased. The results of the steam methanereforming system modeling indicate that the efficiency of the reformed hydrogensystem reaches the highest value when the temperature of SMR and WGS are700oCand220oC, respectively.The thermodynamic analyses of both systems show that fuel cell stack is theplace where exergy loss is the largest. Except for the fuel cell stack, the second largestexergy loss occurs in the air cooler in the direct hydrogen system, while in thereformed hydrogen system, the SMR has the second largest exergy loss. Aircompressor is the component with the highest power consumption when the operating pressure is2atm or higher. The results in this study could be used to provide guidancefor practical HT-PEMFC systems and give an insight into the system design andoptimization.