Coking coals are coals of middle stages of coalification, from which they get lump coke of certain size and durability under industrial coking in mixtures with other coals or without mixing.
Coking coal, unlike other coals, is transferred into a plastic state and sinters when it is heated without access of air. Its characteristics are: high heat of combustion, a small amount of volatile and mineral admixtures, suitability for the production of metallurgical coke. Coking coals are divided into 5 categories according to the ability to coking:
- coke oven coke;
- aliphatic coke;
- emaciated caking coke;
- gas coke;
- weakly caking coke.
Coking technology is significantly advanced in the mid-twentieth century when they have developed new coal deposits, as well as have created new coking technologies. For coking gas coal is mainly used. Now they works on technologies of using of coals which were not applied to coking before: lean, long-flame, brown, anthracites and semi-anthracites.
Today the tenth part of all mineral coal extracted in the world is turning into coke; it indicates that there is a great demand for coking coal from industry and power engineering.
Coal coke is used mainly in blast furnace method for the production of pig iron, where coke serves both as fuel and reductant of iron ore. In much smaller quantities coke is used in foundries, for ore agglomerating, chemical industry, non-ferrous metallurgy.