Study on the Thermal-Electrical Balance of the kW-zclass SOFC Stack

Solid oxide fuel cells (SOFC) can directly convert chemical energy into electrical energy with high power generation efficiency. However, the power generation process is always accompanied by the release of heat, and the balance of heat and electricity is important to the safe and stable operation of the SOFC stack. In this paper, a semi-empirical model of a kilowatt-level SOFC stack was established based on the experiment data that was operated in Xuzhou HuaTsing Jingkun Energy Co. Ltd. Based on this model, the effects of different operating temperatures, fuel and air flow rates, air-to-hydrogen ratio and other factors on the thermoelectric balance were analyzed with hydrogen fuel. In addition, methanol was also selected to study the thermo-electric balance performance. The results shows that the SOFC stack would meet the thermal balance on a special voltage, called self-heating balance voltage, but which varies under different conditions. With the increase of the fuel and air flow rates, the self-heating balance voltage and the limited voltage that shows the heat is surpass the power are decreases clearly. However, the self-heating balance voltage and the limited voltage changes differently under different air-to-hydrogen ratios. The air-to-hydrogen ratio enlarges from 2.4 to 3.6, the self-heating balance voltage and the limited voltage decreases by -4.14% and -2.42% by increasing air rates, however changes 1.26% and -3.07% by decreasing hydrogen rates, respectively.