Blast furnace burden softening and melting phenomena: Pellet bulk interaction observation

The cohesive zone in the blast furnace, where ferrous burden materials soften and melt, greatly affects the furnace’s performance. Minimizing the size and lowering the position of the cohesive zone will improve productivity and decrease the coke rate. This work was designed to better understand the softening and melting phenomena of ferrous feed materials. Different experimental techniques were used to allow the observation of different stages of softening and melting. This article examines the interaction between pellets at high temperatures under load. The pellets were reduced to 60 or 80 pct reduction degree (oxide basis), placed in a graphite crucible, and heated under N₂ gas flow, while X-ray pictures were taken at regular intervals. In addition, the contractions of the pellets and temperature were recorded. These experiments were performed with individual pellet types as well as with a mixed burden of fluxed with acid pellets at a ratio of 2:1. The dripping of liquid from the pellets occurred at different conditions depending on different reduction degrees. In those experiments where the pellets were reduced to 60 pct, the dripping also varied significantly between the basic fluxed and the other types of pellets. The meltdown of the pellets reduced to 80 pct seems to be controlled by the metallic iron shell. In the pellets reduced to 60 pct, it appears that both the metallic iron and the liquid slag determine the meltdown.