Development of high efficient power generation system with CO_2 recovery

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In order to develop a high-efficient power generation system based on chemical-looping combustion, we have carried out various experiments, and the following results were obtained.1. Development of circulating solid mediumIn the proposed system, fuel is oxidized by metallic oxide in a reactor and reduced metal is oxidized by air in another reactor. This scheme yields CO_2 recovery without any extra energy, high-efficient power generation, and avoidance of NO_x formation. These characteristics are brought by the solid medium that is circulated between two reactors. In addition to NiO/YSZ that has been used as a reaction medium, we developed two more promising candidates, i.c., NiO/NiAl_2O_4 and CoO-NiO/YSZ.2. Repeatability of solid mediumCyclic test (reduction by H_2 at 600ﾟC and oxidation by air at 1000ﾟC) was conducted using NiO/NiAl_2O_4 and CoO-NiO/YSZ particles. In comparison with NiO/YSZ paricle, these two particles have benefits for maintaining their microstructure, mechanical strength, and reactivity even after 10cycles of reaction.3. Avoidance of carbon depositionWhen the fuel contains carbon (e.g., Co or CH_4), NiO/YSZ had good resistance against carbon deposition as compared to NiO/NiAl_2O_4 and CoO-NiO/YSZ.For NiO/YSZ particle, carbon deposition can be completely avoided at the atmosphere of 50% CO-25%H_2O-25%N_2 at 600ﾟC,where this steam concentration was found to be much lower than that in steam reforming.4. Experiments in fixed-bed reactorPellet-shaped solid medium was reduced by H_2 or CH_4 and oxidized by air in the fixed-bed reactor. The exhaust gas from reactor was detected by GC-Mass. From these experiments, we got valuable information for the next step to design practical reactor.