Uses of coal

After extraction, coal is washed and sorted. Depending on its type, the coal will be burned (domestic heating, industrial boilers, coal-fired power plants) or transformed into coke.
Coke is concentrated coal from which the majority of volatile materials have been eliminated. In a coking plant, a mixture of good quality coal types, known as coke paste, is brought up to a temperature of 1000°C. The coking process liberates a number of products, mainly pyrolysed gases, which are cooled and treated with solvents. In this way, some of the gases are recovered. The liberated products are:

- The tars;
- The essences from which benzol is extracted. Benzol is a mixture of aromatic hydrocarbons (benzene, toluene and xylene);
- Methane, which is dispatched into the gas distribution network once its impurities (hydrogen, sulphur and ammonia) have been removed.

From 1 million tons of coal, we recover 50 000 tons of tars, 15 000 tons of benzol and 500 million cubic metres of gas. The coke, a coal with a high pure carbon content, is used in blast furnaces or mixed with mineral iron to produce cast-iron (an alloy of iron and carbon, which was a forerunner of steel) by iron oxide reduction.
Large quantities of coke are rapidly produced in coking units, groups of several dozen eight metre high ovens.

Smaller pyrolysis units also exist, adapted to different types of coal. They produce special cokes, such as lignite coke, which can replace charcoal. And at a lower temperature to that of the coking process, at about 700°C, the pyrolysis process allows preservation of the heavy aromatic molecules, the phenol tars full of phenol and xylenol. After treatment, these aromatic alcohols are used in the manufacture of insecticides, fungicides, anti-oxidants and phenol-formaldehyde resins that are used as drying accelerators for varnish and ink.