Metallurgical coke. Manufacturing for the blast furnace

Coke is produced by baking coals at up to 1,000°C in airtight coke ovens. The properties of coke depend very much on the nature of the coals used to make it and the firing conditions.

The coals used are bituminous coals known as "coking coals", which have thermofusible properties when heated, enabling the grains to clump together and produce porous, mechanically resistant coke. Coking coals are generally blended with low-coking coals, for economic and technical reasons explained in the article. Rules for associating coals into families have been established to help in the formulation of blends. Coke quality prediction models also exist to quickly determine the use value of coals. Blend optimization generally involves trials in semi-industrial pilot furnaces of 400 to 500 kg capacity.

A coking plant comprises a number of coke ovens, grouped together in batteries according to the coke production required. In the vast majority of cases, the coking plant is integrated into a steelworks to produce the quantity of coke required by the blast furnaces. A typical steelworks coking plant produces 1.5 to 2 Mt of coke per year. Worldwide coke production is around 700 Mt per year.

The aim of this article is to outline the main rules for the preparation of coal mixtures and to show the importance of good control of firing parameters in order to produce coke of good metallurgical quality. Some elements of coke oven technology complete these aspects and highlight the complexity of a coking plant, which represents a very heavy investment and whose lifespan is today more than 50 years, thanks to good control of operating conditions and maintenance and repair.

A specific article [M 7 341] describes the properties of metallurgical cokes and their influence on blast furnace operation.

A glossary of the elements used and a table of acronyms and symbols are presented at the end of the article.