Numerical Investigation for the Temperature Dependency of Coke Degradation by CO₂ Gasification Reaction in a Blast Furnace

Abstract

To quantitatively evaluate the temperature dependency of coke degradation by CO 2 gasification reaction in a blast furnace, kinetic analyses of gasification reaction with mass transfer for the coke model with approx. 200 million voxels developed from X-ray CT images at the reaction temperatures of 1 373, 1 573, 1 773 and 1 973 K were performed. At high reaction temperature, the gas concentration of CO 2 was high in the external area of the coke model, and the coke matrix voxels vanished mainly around the external surface. Distinguishing surface area of interface between a carbon matrix voxel and a pore voxel with the gas concentration of CO2 at a neighbor pore voxel, although the surface area with the high gas concentration of CO 2 accounted for the majority of the total surface area at 1 373 K, the ratio was lower at over 1 573 K than at 1 373 K. In addition to this, from the effectiveness factor of catalyst, the initial rate-controlling step was chemical reaction at 1 373 K but pore diffusion at over 1 573 K. Also, although the frequency distribution of local porosity showed unimodal regardless of the progress of reaction, the standard deviation calculated from the distribution was changed by reaction. The change rate of the standard deviation by reaction seemed to be larger at high reaction temperature than at low reaction temperature. The logarithm of the change rate hardly depended on reaction temperature under 1 573 K but was proportional to the inverse of the temperature over 1 573 K. This study quantitatively showed that the rate-controlling step affects the coke structure after reaction largely.