Coal is used to make coke for the iron and steel industry, foundries, and other industries. The presence of large domestic deposits of coking coal, or metallurgical coal, played an important role in the development of the U.S. iron and steel industry. Coke is used chiefly to smelt iron ore and other iron bearing materials in blast furnaces, acting both as a source of heat and as a chemical reducing agent, to produce pig iron, or hot metal. Coke, iron ore, and limestone are fed into the blast furnace, which runs continuously. Hot air blown into the furnace burns the coke, which serves as a source of heat and as an oxygen reducing agent to produce metallic iron.
Limestone acts as a flux and also combines with impurities to form slag.
It is in this last role that its properties are crucial. To produce high quality blast furnace coke, high quality coals must be used. The resulting product, coke, consists principally of carbon. A short ton of coal yields about 1,400 pounds of coke and a variety of by-products such as crude coal tar, light oils, and ammonia, which are refined to obtain various chemical products. About 1,000 pounds of coke are consumed for every short ton of pig iron produced.