Effect of nut coke on the reduction behavior in iron-making blast furnace

Ore-coke mixed charging is a potential technique for optimizing the charging pattern. Recently,the charging of small-sized coke( nut coke) with the ferrous burden layer has been applied to reduce rawmaterial usage and decrease costs. Various studies indicate that mixing nut coke with ferrous burden can enhance the reduction kinetics,improve the softening and melting properties,and have a positive effect on the permeability. Although mixed charging,especially the addition of nut coke to the burden layer,has been used in the industry for various reasons,the mechanisms and side effects for using nut coke are not well understood,and the mixing ratio remains limited in actual blast furnace operation.High-temperature experimental studies were conducted to increase the understanding of the complex process of reduction,softening and melting properties,and permeability in a blast furnace when mixing nut coke with an ore layer. The effect of the nut coke mixing ratio and nut coke size was investigated under various reducing conditions.To describe the reduction processes of burden materials,numerous experiments were interrupted at different stages of the reduction,and the collected materials were examined by using image analysis. The reduction degree of mixed charging( iron ore mixing with nut coke) was improved when using nut coke at the temperatures of 800 ℃ and above. The reaction rate of ore-nut coke mixed charging was higher than that of standard charging without the use of nut coke.