Difference Between Coal and Coke
Coal, a rock derived from wood and other plant tissues that flourished several hundred million years ago. Apparently the plants partially decayed and then were covered, preserved, and ultimately compacted by the other sediments that were deposited upon them. Although coals are sometimes described as forms of carbon, this is not strictly true; they are actually intricate mixtures of complex compounds of carbon. Coals differ from one another in composition and properties, and even the various constituents of any one coal may be quite unlike.
Coal as a fuel has played a vital part in the development of industry during the past few centuries. Coke obtained from coal has been used to reduce iron ore to iron for the large-scale manufacture of machinery, and coal has produced power to operate these machines. Today coal is used mainly for generating electric power and making coke for the steel industry, while petroleum-derived fuels and natural gas have displaced coal for some other purposes. In the United States, for example, the railroads have been completely converted to diesel or electric power since the 1930s, and gas has rapidly taken over the burden of domestic heating. Methods for converting coal to liquid and gaseous fuels are known, however, and it seems certain that such manufactured fuels will become important as supplements to petroleum and to natural gas.
Coke is formed as a residue when coal is heated in the absence of air.
Beginning in the 17th century, coke was produced in the type of beehive ovens developed earlier for charcoal production. Beehive ovens are still used for special kinds of coke, but modern rectangular coke ovens can hold far larger charges—up to 33 metric tons (36 U.S. tons) of coal—and also permit the recovery of a number of coal by-products. One ton of coal produces 0.7 tons of coke. The largest plants can discharge 5 to 10 million metric tons of coke annually.
Coke is about 90 percent carbon and has considerable mechanical strength. It is thus an excellent fuel for the blast furnace: it burns easily, acts as a reducing agent for the iron ore, and is strong enough to support the column of ore, coke, and stone. Blast furnaces consume about 870 kg (1,900 lb) of coke to produce one ton of pig iron.