A char combustion model was derived by assuming constant intrinsic activation energy for the different chars. The char combustion rates are affected by various diffusion processes within the different char pores. The fractal pore diffusion effects were characterized by three pore structure parameters (porosity, specific surface area, and fractal dimension) and the mean particle diameter. Three-dimensional numerical results for various char particles burned in drop tube furnaces obtained using the model compare well with experimental results to verify the model. The comparisons show that the model has good accuracy for a wide range of char, from lignite to anthracite.