Since the industrial revolution, coal consumption has increased in considerable proportions. In 1950, the share of coal still accounted for 57% of global consumption of commercial primary energy, and then declined to 27% in 2002. Since that date, it stays between 25% and 31%.

The importance of reserves and their distribution complementary to that of oil make it a serious potential competitor for the latter, the main obstacle to its use being its much greater impact on the environment.

Coal was formed from huge masses of plants mixed with minerals during the Carboniferous period (about 300 million years ago). These masses are composed of carbon, volatile matter (hydrogen), oil and ash.

There are three main types of coal (or solid fuels): peat, lignite and coal, including anthracite, which is a variety of superior quality :

• peat was formed in the Quaternary. Fibrous, lightweight, highly impregnated with water, it is a poor quality fuel, which is hardly traded internationally;

• lignite dates back to the Tertiary. Its fibrous structure reveals vestiges of branches and tree limbs. Though better than that of peat fuel, its efficiency is low. It is quite widely used, however there are also few international transactions;

• coal was formed in the Paleozoic era. Its heating value is much higher than that of lignite or peat. Coal includes various types of coals, which differ in their carbon content. Anthracite and lean coal are used as fuel, while distillation of coal provides fat lean gas, tar and coke.

Contrary to oil and gas, one refers to the coal industry rather than the coal chain.

Two main categories of products come out of the mine: high quality coal is either directly introduced on the market as coal and pellets after screening and treatment, or sold to the coking plant, while low quality products are used as fuel for the production of electricity.

In coking plants, a number of synthetic products (ammonia, methanol, etc.) are made in addition to coke, as well as coke oven gas and recovered products (tar, benzole, ammonium sulfate, etc.).

Coal mining takes place in mines, opencast or underground:

• the open pit mines are operated in a manner similar to quarries. Recovery rates can be very high (90% against 40% underground) and production costs are generally lower than underground. In contrast, open-pit mines can have disastrous effects on the environment. This form of production accounts for 80% of the production in Canada, 60% in the USA, 50% in Australia, 33% in Russia;

• underground mines need at least two wells to allow for ventilation, necessary to remove the gases and cooling the mine. Surface facilities are grouped around the wells. Various methods of exploitation exist, which the reader can look up in specialized books. Underground mines pose significant security problems, because of the risk of collapse, firedamp explosion (because of a flammable gas consisting mainly of methane) and flooding. Besides such accidents, working in underground mines can also cause lung diseases: silicosis and miner pneumoconiosis.

To meet user demand, extracted coal undergoes a transformation over several steps.

It is first cleaned, sorted, and graded to be separated according to size and quality.

Abundant and inexpensive varieties are used for the production of energy, known as steam-coal. The size of the production units is indeed such that they can adapt to various types of coal.

Additional transformations can be made to respond to specific requests or more stringent emission standards. Therefore, coal is nowadays crushed as finely as possible so as to increase the area of contact with the combustion air and get higher combustion temperatures. In doing so, the reaction efficiency increases while the emission of pollutants (nitrogen oxides, unburned) decreases.

One of the most promising techniques is the fluidized bed combustion, where coal, finely ground, is burnt in suspension in a current of air flowing upwards.

Coking or carbonization produces coke, fairly pure carbon that is essential to the metallurgy of cast iron.

Since 1973, a number of recovery processes have been studied:

• production of clean and desulfurized coal, under development in the United States;

• development of a mixture of coal / water to be burned in fuel boilers;

• coal liquefaction by hydrogenation to produce fuels (methanol) and raw materials for the chemical industry. The most used techniques were developed in Germany during the Second World War, as the Third Reich had an imperative need for fuel for its army, and could tap the coal deposits of the Ruhr region;

• in situ gasification of coal in order to convert resources not economically viable by conventional methods directly in the ground. To this end, incomplete combustion is achieved in deposits by injecting pressurized air. This produces a lean gas which can then be upgraded in various ways, either by direct combustion or for the production of synthetic hydrocarbons.

In producing countries, coal is mainly transported by rail. The development of pipeline coal or coal slurry is under consideration: the coal would be crushed and suspended in water conveyed in a pipe, then decanted and filtered on arrival.

Three quarters of the international coal trade is carried by sea, either by cargo ships or by tankers.