The Blast Furnace Process - Operating principles

The smelting plant is the first stage in the process of producing steel from coal and iron ore, which is the preferred route for obtaining high-quality steels for the most demanding applications in terms of usage properties, such as automotive, packaging and heavy plate. Blast furnaces reduce the iron oxides in ores and melt the metal. The transition to the liquid state, while energy-intensive, enables the metal to be purified by transferring major impurities into a liquid slag. The blast furnace delivers to the oxygen steelworks a liquid pig iron whose chemical quality and temperature are perfectly controlled. Worldwide, around 70% of steel production comes from the ore-blast furnace chain, while the scrap recycling chain accounts for 30%.

The knowledge acquired of blast furnace operation is the result of the joint efforts of research teams and operators over the past decades. The implementation of scientific concepts, advanced instrumentation and the use of numerical models have enabled us to gain a good understanding and effective control of the complex operation of the furnace, leading to remarkable progress in terms of operating reliability, productivity and overall process economy. The blast furnace has reached a degree of technological maturity such that, for the most advanced units, performance is close to the theoretical optimum in terms of energy consumption. Plant size has reached an economic optimum, with blast furnaces having a volume of 4,500 to 5,000 m ³ and a production capacity of 3 to 3.5 Mt/year, consistent with the downstream integrated plant, oxygen steel mill and strip mill.

The cost of cast iron represents a predominant part of the cost of the final steel. The cost of raw materials fed into the blast furnace accounts for around 80% of the cost price of cast iron, with energy in all its forms accounting for almost 50%. This justifies all efforts to reduce energy consumption and diversify raw materials.

Although the blast furnace itself performs remarkably well, it has a number of disadvantages that present a number of challenges. The very principle of the blast furnace – reduction of oxides, melting of materials – necessarily leads to high energy requirements, provided for the most part by fossil fuels, resulting in significant CO ₂ emissions, of the order of 1.8 t/t of cast iron. What's more, its operation requires prior treatment of raw materials using processes – agglomeration of ores [M 7 320]...