HOW IRON ORE MELTS IN A BLAST FURNACE. PART 1: FERROUS BURDEN, SLAG FLOODING, PRODUCTIVITY

摘要

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, heat transfer from bosh gas to the 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 temperature increase of the primary slag. The drainage of the liquid primary slag is determined by its temperature and FeO content as well as 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 iron becomes liquid when carbon is dissolved. This requires a low FeO% in the primary slag. Analysis of operating blast furnaces shows that slag volume per ton is affecting productivity as well as maximum achievable coal injection rates. A decrease of slag volume of 10 kg per ton hot metal increases productivity by about 1,5%, enables reduction of the metallurgical coke rate by 2-4 kg/tFDVI, while total fuel rate is reduced only by about 0,5 kg/t.