Reactivity of coke with CO₂ and evaluation of strength after reaction

For the investigation on coke degradation in the blast furnace, reactivity of coke with CO₂, the morphological change after reaction and the change in its strength were examined. Five kinds of cokes were used. They were machined in the spherical form of 20 mm ø and reacted with pure CO₂ at 1073 to 1673K. After the reaction, the specimen were visually observed and the porosity distribution was estimated. Further, they were pressed by universal test machine to estimate the strength after reaction. The reaction mode changed at 1373K. At lower temperature, the reaction proceeded homogeneously throughout the specimen, while restricted near the surface at higher temperature. The porosity was almost uniform at lower temperature, but increased near the surface at higher temperature. The tensile strength was estimated indirectly from the results of compression test. The tensile strength was 0.85 to 1.77 MPa before the reaction. It decreased to 0.51 MPa after 50% reaction at 1273K. At 1573K, however, the strength did not decrease so much for the blast furnace coke and highly reactive coke. The strength of formed coke increased after 25% reaction. These changes in strength at 1573K can be attributed to the reaction mode where the reaction did not proceed to the core of specimen, and the crystallization proceeded in the core at higher temperature. The fracture energy, which might show the strength of matrix, decreased by the reaction in all case.