Model for coal oxidation kinetics. 2. An effectiveness factor interpretation

Rate expressions are developed to describe the oxidation of coal in a fixed-bed reactor under conditions of significant diffusional effects. The model defines individual effectiveness factors for carbonic gas formation, oxygen deposition, and water production, to modify a chemical model derived previously. Experiments carried out on seven coals ranging in rank from lignite to bituminous to anthracite. All the coals exhibited particle size effects and the results fit the model in most cases to within ±10% both in the rate of overall oxidation and with respect to the individual reaction rates for several products. Activation energies and effectiveness factors were obtained for each coal and for each reaction. The effluent gas $\text{CO}{}_2\text{CO}$ ratio was found to be virtually constant for all five bituminous coals, being independent of reaction temperature, coal particle size, and oxygen partial pressure.