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In order to investigate coke degradation behavior due to CO 2 gasification reaction in the blast furnace, mass transfer analyses with the reaction and stress analyses for coke considering its structure after the reaction were performed. Using the finite element method, CO 2 gas diffusion in a coke lump and consumption of coke matrices owing to the gasification reaction were considered for the coke model in which the actual coke structure was reproduced. The rate-controlling step was also evaluated calculating the Thiele modulus and the effectiveness factor of catalyst obtained from CO 2 concentration distribution in a coke lump. Further, stress analyses assuming a uniaxial tensile test were carried out for the coke model after CO 2 gasification reaction, and the effect of the gasification reaction on a stress state in a coke lump was investigated. As a result, the reaction progressed mainly in the vicinity of the external surface with reaction temperature of 1 673 K while it did uniformly in the whole coke lump with 1 273 and 1 473 K. Thus, the rate-controlling step shifted from the reaction-controlling step to the diffusion-controlling step with an increase in a reaction temperature, and the Thiele modulus and the effectiveness factor of catalyst also showed the same trend. From the stress analysis, coke strength decreased uniformly in the whole coke lump in case of the reaction-controlling step whereas it did mainly in the vicinity of the external surface in case of diffusion-controlling step.

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A distributed activation energy model (DAEM) was applied to the kinetic analysis of CO 2 and H 2 O gasification reactions for pulverized metallurgical coke. The results of the scanning electron microscopy observations and CO 2 gas adsorption suggested that the gasification reaction occurs at the particle surface. Therefore, a grain model was employed as a gasification reaction model. The reaction rates of CO 2 and H 2 O gasification were evaluated based on the DAEM. The activation energy changed as the reaction progressed and hardly depended on the particle size. The activation energies were 200–260 kJ/mol in CO 2 gasification and 220–290 kJ/mol in H 2 O gasification. The frequency factor of H 2 O gasification was approximately 10 times larger than that of CO 2 gasification, regardless of the progress of the reaction. At the same activation energy level, the frequency factor showed a higher value with a decrease in the particle size. This result was consistent with the theory of the grain model and indicated that the gasification reaction of the pulverized coke with a micrometer scale occurs on the surface of the coke particle. Furthermore, the value predicted by the DAEM was in good agreement with the experimental one.