Char Surface Reaction Model for Pulverized Coal Combustion

Experimental and analytical study was performed for surface reaction model that was used for numerical simulation of pulverized coal firing boiler. Combustion efficiency in downstream of premixed flames was examined for a subbituminous coal, two bituminous coals and an anthracite. The influence of SR (stoichiometric ratio), combustion temperature, FR (fuel ratio) and initial particle diameter was examined. Reaction rates of oxidation and gasification, and surface area model of coal char were examined by comparison between experimental and analytical results. The outer surface area was assumed not to be changed during devolatilization, but to be reduced by surface reaction. Effective surface area for reaction was assumed to be decreased when ash content in char was increased. By using this surface area model, comparison of the predicted combustion efficiency with the experimental data showed good agreement for SR 0.5∼1.5. Reaction rates were decreased when FR of coal increased. The effect of coal type was significant for gasification reaction. The activation energy of gasification was smaller than the previous study that was obtained without oxygen. The reaction yield by gasification at SR 0.8 was about 10%, gasification was found to be important for numerical simulation of pulverized coal firing boiler.