Coal - A Resourceful Fuel

After being extracted from underground or open pit mines, coal is washed and sorted. This is when its end use is determined - for domestic heating, to feed industrial boilers, or to manufacture cast iron or synthetic gasoline. Depending on its quality, it can be burnt, turned into coke or gasified.

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Coal-burning stations

Coal is still used as a fuel today. Its use as a domestic fuel is falling and now its main use is the feeding of industrial boilers. Electricity production is thus themain use of coal nowadays¹, in fossil fuel power plants.

The principle is simple: the coal is burnt in a boiler. The released heat converts the water into steam. This drives a turbine connected to an alternator which generates electricity. As it passes through the condenser, the steam cools down and turns back into water, and is then sent back to the boiler.

The iron and steel industry

Coal with high levels of carbon concentrate, i.e. coke, is used in the iron and steel industry. 

It is used in blast furnaces and industrial furnaces, where it is mixed with iron ore to manufacture cast iron (an iron and carbon alloy that was a precursor of steel), through iron oxide reduction.

Manufacturing coke, or coking, involves bringing a mixture of good quality coal types, coke paste, to a temperature of 1000°C, a process which requires arrays of dozens of 8m-high furnaces.

Coke is concentrated coal from which most of the volatile matter has been expelled.

This pyrolysis releases gases that are cooled and treated with solvents. For 1 million tons of coal, the following is recovered:

   • 50,000 tons of tar 

   • 15,000 tons of benzol (a mixture of aromatic hydrocarbons)

   • 500 million m³ of methane, which is dispatched into the gas network once its impurities have been removed.

There are also smaller pyrolysis plants adapted to various coal types. These manufacture special coke, such as lignite coke, which can be used instead of charcoal.

At about 700°C, pyrolysis preserves heavy aromatic molecules, phenol tars. After processing, these are used to manufacture insecticides, fungicides, antioxidants and 

phenol-formaldehyde resin used as drying accelerators for varnish and ink.

Carbon chemistry: manufacturing hydrocarbons

Coal can be gasified in the presence of oxygen and steam to produce synthetic gas, a mixture of carbon monoxide and hydrogen.

This gas is an intermediate product that can be converted into different products (methanol, urea, pure hydrogen and dimethyl ether) and above all used to make synthetic fuel.

In the latter case, the product obtained is a wax containing many different types of hydrocarbons with varying numbers of carbon atoms. This wax undergoes a series of conversion processes to produce mostly high quality diesel and, to a lesser extent, LPG and gasoline.

The charcoal we use in our barbecues is natural coal.

False. It is obtained through wood pyrolysis, a process that requires a temperature of 400°C. It used to be made in woods in large kilns (piles of wood protected from the air to stop them burning) inside which a fire was lit. Today smaller, less polluting, automated industrial production facilitiesare used where pyrolysis is carried out through contact with hot gases. NB: charcoal is not just used to light barbecues. It is also used in filters, for example to treat wastewater.

quoted from: www.planete-energies.com