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.

Foundries use coke as a source of heat for producing metal castings. Other industrial uses of coke include the smelting of phosphate rock to produce elemental phosphorous and the production of calcium carbide. Small sizes of coke, termed breeze, are used as fuel in sintering finely sized particles of iron ore and other iron bearing material to produce an agglomerate that can be used in a blast furnace.

Coke is made by baking a blend of selected bituminous coals (called metallurgical coal or coking coal) in special high temperature ovens without contact with air until almost all of the volatile matter is driven off. The resulting product, coke, consists principally of carbon. A short ton of coal yields about 1,400 pounds of coke and a variety of byproducts such as crude coal tar, light oils, and ammonia, which are refined to obtain various chemical products. About 1,100 pounds of coke are consumed for every short ton of pig iron produced.

The coke industry was once a major market for coal, accounting for about one fourth of U.S. coal consumption as recently as the late 1950s. Since then, coke production has fallen dramatically and its share of total coal consumption currently is about 4 percent because of a decline in the U.S. iron and steel industry, the principal consumer of coke. In general, the iron and steel industry now requires less coke because it produces smaller amounts of raw steel, relying on imports of finished and semifinished steel to help meet its needs, and because improved blast furnace technology has reduced the amount of coke needed to produce a ton of pig iron.

Furthermore, less coke is needed due to the greater use of certain steelmaking technologies, such as the basic oxygen furnace, which enables scrap iron to replace pig iron in some processes, and the electric arc furnace, which produces steel from a charge consisting of 99 percent scrap iron and recycled steel and 1 percent iron pellets. (The steel industry has not used the open hearth furnace since 1991.) The substitution of other products for steel (such as plastics, aluminum, magnesium, and titanium) has also indirectly reduced the need for coke.

Among the recent technological changes that are responsible for reducing the use of traditional coke in blast furnaces is the use of pulverized coal injection, a process developed in the 1960's by Armco Steel. By using pulverized coal injection, steel companies can reduce the need for coke by as much as 40 percent, cut down on environmental problems associated with coke production, and reduce the need for other, more costly supplemental blast furnace fuels, such as natural gas. Pulverized coal, which has the consistency of face powder, is made from the relatively abundant lower grades of coal and blown into the blast furnace. Granular coal, similar in size to sugar, is also being tested in blast furnaces.

At the beginning of 1994, 31 coke plants were in operation, less than half the number a decade earlier. Although some plants were closed because of the decline in the steel industry, many closings targeted older plants that were shut down because of the high cost of refurbishing them to meet air pollution standards. More than half of the active plants are furnace plants, operated by iron and steel companies to produce coke for their blast furnaces; these plants account for about 80 percent of the U.S. coke capacity. The other coke plants, called merchant plants, sell coke on the open market. Both segments of the coke industry are faced with the advanced age of many of their coke ovens and the rising costs of replacing them with environmentally clean ovens. Indiana and Pennsylvania are the leading coke producing States.

Adapted from Coal Data: A Reference, by the U.S. Department of Energy.