Mixed burden softening and melting phenomena in blast furnace operation

The cohesive zone in the blast furnace (BF) is largely affected by the high temperature properties of the ferrous burden. Lowering and minimising the width of this zone will increase the productivity and performance of the BF. Recently part of the BF ferrous burden has been replaced by direct reduced iron (DRI) and hot briquetted iron (HBI). The objective of the present work is to expand the current understanding of softening and melting (SM) mechanism of ferrous raw materials including DRI, HBI, pellets, lump ore and mixed burdens. A small scale deformation under load experiment was designed to examine the interaction of ferrous burdens. The SM tests were conducted with ferrous burdens in different combinations and parameters such as bed contraction, pressure loss, reduction degree, etc. were measured. In addition, the process was visualised using X-ray fluoroscopy. There were microstructural differences between the ferrous materials which governed the initial compaction of bed. The softening of the single burdens of DRI and HBI occurs owing to softening of iron phase. In mixed burdens composed of DRI and pellets/ lump ore, initial deformation is not affected by the presence of DRI; however the melting of the bed is dependent on the melting of DRI indicating its dominance over other burden components at later stages of deformation. The change in reduction degree between SM temperatures was found to be small.