Agenda for low reducing agent operation of blast furnace - Reduction and melting phenomena of iron ore

Due to mitigation of CO₂ emission, low reducing agent operation of blast furnace is actively investigated. For blast furnace operation, low reducing agent indicates decreasing consumption of coke or PC with maintaining appropriate heat balance in the furnace. Accordingly, O/C of input burden increases with decreasing reducing agent rate. Coke particle acts as structural material for holding burden and making void in the packed bed for maintaining gas flow. Therefore, decreasing gas flow resistance is an issue in low reducing agent rate operation. In 1970's, dissection study of blast furnaces had been carried out, and that uncovered existence of cohesive zone. Solid and liquid phases coexist in the cohesive zone. Gas flow resistance increases with a decreasing void fraction in the cohesive zone. Where, coke slit composed with coke layer between half molten iron ore layers act as gas vent slit. However, low reducing rate operation that causes thin or no coke slit. How to increase gas permeability in the cohesive zone with thin coke slit would be a serious issue with a decreasing coke rate for blast furnace operation. In the present paper, investigations on cohesive zone and its permeability are reviewed and softening and melting behaviors of iron ore layer in the blast furnace are thermodynamically discussed.