8th International Congress on Science and Technology of Ironmaking - ICSTI 2018

The present paper describes how the ferrous burden melts in a blast furnace and what consequences it has for blast furnace operation. For high PCI and high productivity operations, gas flow to and hence heat transfer from bosh gas to the solid/cohesive state of the ferrous burden is the rate limiting step in processing the ferrous burden, since the heat requirement of the direct reduction reaction of FeO determines the rate of heating of the primary slag. The processing and drainage of the liquid primary slag is determined by the FeO content of the slag, the slag composition and the voidage available in and below the cohesive zone. The iron fraction of the ferrous burden can only drain to the hearth once the direct reduction reaction is completed, since carbon dissolves in iron only when there is no FeO present. Analysis of operating blast furnaces shows that slag volume per ton is affecting productivity as well as maximum achievable coal injection rates. An estimate is that a decrease of slag volume of 10 kg per ton hot metal increases productivity by about 1,5% and reduces the metallurgical coke rate by 2-4 kg/tHM, while total fuel rate is reduced only by about 0,5 kg/t..