Experimental Research Of Char Combustion Characteristics Under High Temperature And Bed Combustion Numerical Simulation

China's energy structure depends mainly on coal and about 500 million tons of coal is consumed by industrial boilers per year, which is second only to the largest consumption of coal-fired power plants. The widely used traveling grate boilers are researched and discussed in this paper. The complexity of bed combustion, lack of systematic study combined with long-standing lack of sufficient attention lead to relatively poor level of traveling grate boiler's design and operation also with prominent problem of low efficiency.The variation of char reactivity is studied for the difficulty of complete char burnout although under long residence time and high temperature in bed combustion. Main factors including coal type, temperature, residence time and minerals in the ash are experimentally studied and compared. The mechanism of char reactivity variation is explained from the perspective of micro-crystal structure changes. Experimental results show that the char reactivity decreased as the temperature increased, also with the residence time increased. Minerals play catalytic action for char combustion in the lower reaction temperature, however, catalytic action will gradually decrease as the temperature increases. The fundamental reason for the changes of char reactivity under high temperature is the ordering process of the coal crystal structure. According to the experimental data, a model was established for the changes of char reactivity, providing the calculation basis for the bed combustion model.Ash layer diffusion is one of the main resistances to reaction rate during the late stage of char combustion. A large coal particle combustion experimental bench was purposely setup to study the char combustion rate and ash thickness variation during combustion. The experimental results show that ash layer diffusion coefficient decreases as the combustion proceeds, which is in exponential relation with the ash thickness. The resistance through the ash layer increases as the reaction proceeds and its coefficient can be calculated by experimental data, providing the calculation basis for the bed combustion model.In order to verify the correctness of bed combustion model, a fixed bed experimental bench was purposely built and bed combustion characteristic was studied. According to the former research of char reactivity and ash layer diffusion coefficient, a bed combustion model was built including the two sub models. Model predicted results match reasonably well with the experimental data. The model could predict char reactivity and ash diffusion characteristic well and three main influent factors including air distribution, particle size and bed height were calculated and compared, providing theoretical guidance for optimized operation of actual boilers.Finally, a typical 20 t/h coal-fired traveling grate boiler was tested and modeled. The correctness of improved bed model for actual boilers was verified by comparison with the on-site test data. Different air distribution schemes were calculated and analyzed, proposing optimized operation. The calculated schemes were operated and adjusted on the actual boilers. The adjustment results matches with the model calculation, providing scientific basis for the optimization of traveling grate boilers'design and operation.