Evaluation of coke mixed charging based on packed bed structure and gas permeability changes in blast furnace by DEM-CFD model

Low reducing agent operation of the blast furnace has an important role in mitigating carbon dioxide emissions in the steel works. Low reducing agent operation results in a low coke rate in the blast furnace. In low coke rate operation, the permeability in the blast furnace is considered to change remarkably due to the increase in the ore-to-coke (O/C) ratio. Charging methods based on conventional layered charging should be improved to a new method such as coke mixed charging. In this study, a DEM-CFD model considering the softening behavior of ore particles in the cohesive zone was applied to evaluate the gas flow in low coke rate operation. First, the softening melting test was simulated by the overlapping of particles in DEM. The layer structure and void fraction distribution in the blast furnace were calculated for normal coke rate and low coke rate operation by DEM. Second, gas flow behavior was analyzed by the DEM-CFD model, focusing on the cohesive zone. From the results, it was estimated that the gas flow was influenced by the coke slit structure in the cohesive zone and the permeability of ore layers mixed with coke particles. Under the normal coke rate of 350 kg/t, coke mixed charging has little effect on permeability through the thin coke slit. However, in low coke rate operation, coke mixing can improve the permeability of the cohesive zone.