Influence of Air Utilization on Power Generation Properties of a Non-Combined Cycle Pressurized SOFC System

In this study, we proposed the non-combined cycle pressurized IT-SOFC system for efficient use of compression hydrogen energy in a gas cylinder, and the possibility of the system was discussed by comparison of the SOFC power gain by pressurization and power consumption gain of an air compressor. Oxygen partial pressure p_O2 management on cathode side is also important because p_O2 directly influences to the polarization resistances. For estimation of the power densities as functions of air utilization U_air and pressurized air remaining factor χ(=(p_O2,cathode−0.021U_air)/(0.21(p_air−0.1))), the ac impedance data of a micro tubular single cell, which was developed in ceramic reactor project, was measured under the several p_O2 conditions on cathode side at atmospheric pressure (0.1MPa) and 0.3MPa. Area specific activation polarization resistance R_pol.act and concentration polarization resistance R_pol.conc. were obtained from the the ac impedance data, and the power generation curves of SOFC bundle under the several U_air and χ conditions were simulated using the R_pol.act and R_pol.conc. These simulations suggested that if χ is high enough, i.e. over 0.5, pressurization could dramatically reduce R_pol.act and R_pol.conc. even at U_air = 0.95. Based on these simulated power generation curves of the SOFC bundle, the preconditions of SOFC system were expanded up to 10kW class for practical comparison between SOFC power and power loss by the air compressor. This comparison is suggested that the maximum actual power Wact. of pressurized SOFC at 0.3MPa can be higher than that of atmospheric pressure SOFC if χ is over c.a. 0.5. The χ and U_air must be kept high enough for the high performance operation. It is found out that effective exhaust of low p_O2 gas from system is important for holding the high χ.