Blast furnace – Operational principles

Worldwide, around 70% of steel is produced by processing ores and coals in the oxygen blast furnace-converter process, while 30% is produced from scrap recycled in the electric furnace. Significant disparities exist between regions around the globe, with the ratio in Europe tending to be 60/40.

Considerable progress has been made in the understanding and control of blast furnaces, leading to a remarkable reduction in their energy requirements, of the order of 50% over the last forty years in Europe. Today's most efficient blast furnaces operate in conditions close to the theoretical optimum in terms of energy consumption. Generally speaking, the technologies used are highly mature and make extensive use of sophisticated instrumentation, information systems and numerical modelling tools. Over the past twenty years, the general trend has been to concentrate pig iron production on a limited number of large blast furnaces operating at high productivity, with remarkable reliability and a service life in excess of 20 to 25 years.

The blast furnace faces new challenges, essentially of three kinds: on the environmental front, with its high production of CO ₂ , inherent in the very principle giving a large part to the reduction of iron oxides by carbon; on the energy front, with the need to make energy sources flexible according to availability; on the raw materials front, with the need to adapt to the general deterioration in the quality of ores and coals and to wide fluctuations in market prices and demand.

Two types of response have been studied to meet these new challenges. On the one hand, numerous "reduction-smelting" processes capable of directly treating coal and ore without extensive preparation [M 7 550] have been devised, but few have been industrialized and their share of world production remains marginal. On the other hand, adaptations of the blast furnace process are being studied, with the aim of reducing CO ₂ production, for example the decarbonation of blast furnace gas and its recycling into the blast furnace (ULCOS project in Europe), the massive use of hydrogen as a reducing agent, the oxygen blast furnace or the low-temperature reserve zone blast furnace in Japan. All these developments are still at the laboratory or pilot scale.

This article presents the general principles of blast furnace operation, based...