Soumei Baba 1 Thermal and Fluid System Group, Energy Technology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 1-2-1 Namiki, Tsukuba-shi, Ibaraki 305-8564, Japan e-mail: soumei.baba@aist.go.jp Nariyoshi Kobayashi Thermal and Fluid System Group, Energy Technology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 1-2-1 Namiki, Tsukuba-shi, Ibaraki 305-8564, Japan e-mail: nariyoshi-kobayashi@aist.go.jp Sanyo Takahashi Thermal and Fluid System Group, Energy Technology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 1-2-1 Namiki, Tsukuba-shi, Ibaraki 305-8564, Japan e-mail: takahashi.sanyo@aist.go.jp Satoshi Hirano Thermal and Fluid System Group, Energy Technology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 16-1 Onogawa, Tsukuba-shi, Ibaraki 305-8569, Japan e-mail: hirano.s@aist.go.jp Development of Anode Gas Recycle System Using Ejector for 1 KW Solid Oxide Fuel Cell An anode gas recycle (AGR) system using an ejector for 1 kW solid oxide fuel cells (SOFCs) was developed to increase the electrical efficiency of combined power genera- tion. We call this an AGR–SOFC. The effects of 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 of 0.55–0.62, overall fuel utilization of 0.720–84, and steam feed rate of 0–1.5 g/min. A quadrupole mass spectrometer was used to identify the recirculation ratio, the gas composition of reformed gas at the AGR–SOFC inlet, and that of 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 H 2 O 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 for the steam reforming process. [DOI: 10.1115/1.4028361] Introduction 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, 175 kJ/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 (890 kJ/mol) is consumed in the production of hot steam. For anodic gas recycle, steam produced via the electrochemical reac- tion can be used in steam reforming of methane, and thus there is no need for an external steam supply. Therefore, overall genera- tion efficiency of CHP, including bottoming engines, can be improved. For AGR system without an external steam supply, a large recirculation ratio is required to recycle enough steam to avoid carbon formation via methane cracking and Boudouard reactions. Steam leads to the carbon gasification reaction from carbon atoms to carbon monoxide, which proceeds rapidly. As background, we review here the existing research on anode gas recirculation. The first development of tubular SOFC with an- ode recycle driven by an ejector was reported by Westinghouse [2] in the early 1990s. Marsano et al. [3] reported the design and off- design performance of an AGR system with an ejector for methane-fueled SOFC hybrid systems by using a 1D modeling technique. They investigated the effects of AGR on SOFC perform- ance, i.e., steam-to-carbon ratio and CH 4 conversion at an external reformer. Ferrari and Massardo [4] developed an emulator rig instead of an actual fuel stack, and then emulated SOFC hybrid sys- tems with an anodic ejector at an electrical load 20–74.1 kW. They 1 Corresponding author. Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 11, 2014; final manuscript received July 16, 2014; published online September 10, 2014. Editor: David Wisler. 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