2023 年 63 巻 10 号 p. 1595-1606
Because the CO gas is usually used as the reduction gas in the blast furnace process, a huge CO2 gas has been emitted during the ironmaking process. Therefore, H2 reduction gas has been proposed as a potential alternative to the CO gas for achieving carbon neutrality. However, the diffusion behaviors of CO and H2 gases inside the iron-oxide particle are markedly different due to the higher gas diffusivity of H2 gas. The reaction surface is observed in the CO reduction whereas the H2 reduction has a broadly-reaction area. The conventional reduction analysis models were suitable for use in the CO reduction, as they assumed an exponential gas diffusion behavior through the certain reaction surface inside the particle. However, exponential diffusion is not sufficient to analyze the broad diffusion aspect of H2 gas. In this study, the H2-based reduction reactions is applied to the 3D diffusion model, which can accurately analyze the broad H2 diffusion behavior. The gas components considered were the CO–CO2–H2–H2O–N2, considering the conditions of the blast furnace. The necessity of the 3D diffusion model was analyzed by comparing the H2 reduction distributions with those obtained using the shrinking core model. The intra-particle distribution for reducing iron oxide particles, which have pellet and sintered ore shapes, were analyzed in CO–H2 and CO–CO2–H2–H2O–N2 gas to clarify the impact of H2 on reduction behavior. As the results, the presence of H2 gas affected the effective gas diffusivity of the gas mixture, the reduction rate increased with the H2 content.
