Mixed burden softening and melting phenomena in blast furnace operation Part 2 - Mechanism of softening and melting and impact on cohesive zone

The present work was designed to improve the current understanding of the softening and melting (SM) mechanism of ferrous materials and to identify their potential impact on the cohesive zone in the blast furnace (BF). The lump ore, direct reduced iron (DRI) and hot briquetted iron (HBI) were individually subjected to industrial trials and their results were compared with those obtained in the laboratory (SM) tests described in first part of the present paper.(1) The difference between melting and 10% bed shrinkage temperature obtained from the results of laboratory and industrial tests was compared and it was found within 10% limits. The SM temperatures were also correlated to the basicity, gangue and flux contents of the mixed burden. The liquid slag mass fraction was computed using FactSage software and compared with the deformation of the burden bed. These results indicated presence of a small amount of liquid at temperatures close to the softening temperature of the burden suggesting that the deformation of solid phases is the primary cause for softening of the burden. The melting of the mixed burden is dependent on the melting point of DRI and melt exudation occurs close to the meltdown of the burden. The impact of ferrous burdens on the cohesive zone was predicted on the basis of experimental results which indicated DRI/HBI is an excellent blast furnace feed material to improve the productivity and decrease the coke rate in the BF.