Comparative Studies on the Combustion Kinetics of Chars Prepared from Brown and Bituminous Coals under Air (O_2/N_2) and Oxy-fuel (O_2/CO_2) Conditions

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This paper deals with the application of a solid-gas reaction model which can describe the combustion and gasification mechanism for air (O_2/N_2) and oxy-fuel (O_2/CO_2) conditions. Loy Yang brown coal was used as a sample after pyrolysis, together with Newlands coal as bituminous coal for comparison of coal ranks. By carrying out the thermogravimetric analysis (TGA) run under non-isothermal conditions, chemical reaction rates of partial oxidation reaction and gasification reaction were estimated. Heat and mass transfer between the single pulverized char particle and gas were numerically simulated, thus, overall reaction rate including mass transfer rate, chemical reaction rate could be evaluated. In the low temperature region, the reaction rate is mainly controlled by the chemical reaction, on the other hand, it becomes dominated by mass transfer, (diffusion as well as convection effects), in high temperature region. Using this solid-gas reaction model, burn-off time of each char was also estimated under the various conditions, i.e., air (5% O_2/N_2) and oxy-fuel (5% O_2/CO_2) conditions with consideration of absence and presence of CO_2 gasification reaction effect.