Development of Combustor with CO_2 Capturing by Alternately Changing Fuel and Air Streams

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The chemical-looping combustion can be realized even in a fixed-bed reactor when we change the input gases between fuel and air at specified intervals. By this scheme, reduction and oxidation take place alternatively, and the produced high-temperature gas can be used to generate electricity by a single gas turbine. Since the solid particles are stationary in a fixed-bed reactor, the attrition, i.e., break of particles does not take place. Furthermore, the retrieval of CO_2 gas in high concentration can be achieved easily with no additional external energy by use of the proposed chemical-looping combustion scheme.First, by thermal gradient analysis (TGA), we measured the rates of oxidation by air and of reduction with several kinds of fuel (H2, CH4, simulated gas for coal gasification), and found that Ni and Co are desirable for the component of metallic oxide, and the addition of inert component such as Al_2O_3 and YSZ at 60wt% is effective to get satisfactory reaction rates. The natural gas and coal gasification gas are examined as fuel. These fuels cause carbon deposition on the surface of solid particles. However, we prevented it by adding water vapor into fuel. We found that coal gasification gas is suitable fuel for the proposed system, since for the natural gas, heat source for the steam reforming cannot be supplied in this system.Test results showed that for coal gasification gas, we can choose the period for the reduction 3.3 times longer than that for natural gas. This result is also favorable for operation. Furthermore, we examined various operations for the coal gasification gas. The selection of the periods of alternative reactions are the key factors to maintain the temperature of the exit gas at a desired point. The feasible condition is obtained when the length of the combustor is 5m, velocity of gas is 1 m/s, the reduction time is 80s and the oxidation time is 270s.