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An anode gas recycle (AGR) system using an ejector fo r 1 kW solid oxide fuel cells (SOFCs) was developed to increase the electrical efficiency o f combined power genera tion. We call this an AGR-SOFC. The effects o f recirculation ratio, externally steam feed rate, and fuel utilization were determined experimentally on the AGR-SOFC perform ance (i.e., output power, stack temperature, and gas composition) using a variable flow ejector and a recirculation ratio o f 0. 55-0.62, overall fuel utilization o f 0.720-84, and steam feed rate o f 0-1.5 glmin. A quadrupole mass spectrometer was used to identify the recirculation ratio, the gas composition o f reformed gas at the AGR-SOFC inlet, and that o f the recycle gas at the outlet. Compared to one-path SOFC systems, i.e., without an AGR, the AGR-SOFC was stable and generated about 15 W more electricity when the overall fuel utilization was 0.84 and the recirculation ratio was 0.622 with no steam sup ply. This improved performance was due to the reduced H20 concentration in the anodic gas. In addition, although the recirculation ratio did not affect the AGR-SOFC perform ance, a high recirculation ratio can provide steam produced via the electrochemical reaction to the injected fuel fo r the steam reforming process.In tro d u ctio n SOFCs applied to stationary power generation systems have two major advantages: (i) Highest efficiency among all fuel cells, (ii) lower cost by using nonplatinum catalysts. Furthermore, micro combined heat and power (mCHP) systems based on SOFCs are being actively researched to obtain an even higher efficiency by utilizing the high temperature exhaust gas (>700 °C) from the SOFC itself. Unlike gas turbine engines, Stirling engines are external combustion engines that can be combined with SOFCs at normal pressures with practical efficiencies of roughly 20% for small scale power generation about 1 kW class. In addition, oper ating temperature of a Stirling engine is near the exhaust tempera ture of an SOFC. Takahashi et al.[1] investigated the performance of a combined SOFC-Stirling engine system fueled with methane by means of thermodynamic system modeling. The results showed a 10% higher efficiency for the combined system at low excess air ratio (<2.0), compared with SOFC systems alone. They also stated the need to develop a steam reforming sys tem with an anode gas recirculation to improve the electrical effi ciency of combined power generation.Steam is required to convert hydrocarbon fuel to hydrogen and carbon monoxide. This method is called steam reforming process.Hydrogen and carbon monoxide are produced from methane under high temperature conditions via steam reforming reaction and water-gas shift reaction to prevent carbon deposition on the anode. Assuming that the inflow rate of the steam is 2.5 times higher than that of the fed methane fuel, 175kJ/mol of methane must be provided to convert water at 25 °C to steam at 800 °C. In other words, about 20% of the enthalpy of the methane combus tion (890kJ/mol) is consumed in the produc...

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