Metallurgical coke - Properties and consequences for the blast furnace

The use value of a metallurgical coke for the blast furnace results from its mechanical, chemical and physico-chemical properties.

Coke consumption in the blast furnace can vary significantly depending on its quality, and blast furnace operation can be greatly affected by poor-quality coke. The production of metallurgical coke is expensive: coking coals are more expensive than injection coals, and a coking plant represents a very high investment amortized over a very long period, with high maintenance costs. Today, the life expectancy of a modern coke oven battery is 50 years, with regular maintenance and partial renovation of the oven cells.

A coke that is mechanically resistant when cold and after partial gasification by CO ₂ at high temperature (via the Boudouard reaction) will allow a high injection rate of pulverized coal to the blast furnace tuyeres (over 200 kg/t of cast iron) and low coke consumption (less than 300 kg/t of cast iron). Overall, the injection coal + coke reducer ratio will be lower when the coke has high cold and hot mechanical strength after partial gasification.

After a brief description of the role of coke in the blast furnace, the article stresses the paramount importance of the particle size stability of coke subjected to mechanical stress between the coking plant and the blast furnace. The loaded coke must be mechanically stabilized if the blast furnace is to permeate properly.

Thermochemical properties, in particular the Boudouard reaction, are measured by laboratory tests. A test was ISO standardized some ten years ago, based on a test developed in Japan (CSR test) in the 1980s. This test is presented in the article, and the CSR index of coke is correlated with blast furnace operating parameters. Today, it is generally accepted that a high rate of pulverized coal injection to the tuyeres can only be achieved if the CSR of the coke is high. The correlations presented in this article will demonstrate this.

The manufacture of coke is the subject of a specific article [M 7 340] .

A glossary of terms and a table of acronyms are provided at the end of the article.