Coal
Coal is flammable mineral of brown to black colour, extracted from surface or underground mines. Coal consists chiefly of carbon; its non-carbon content includes volatile substances, water and ash. Coal can be divided into several basic types depending on composition, age and origin. Based on carbon composition, which is the basic quality criterion, we divide coal into the following categories.
| Coal types | Carbon content [%] | Calorific value [MJ/kg] |
| Lignite | 30-50 | 10-13 |
| Brown coal | 50-80 | 15-20 |
| Hard coal | 80-90 | 17-30 |
| Anthracite | >90 | 25-30 |
Coal is one of the most important of fossil fuels and is a key resource for electricity generation. Coal is heavily used in the energy, metallurgy and chemical industries.
The specific properties of extracted coal determine how coal is to be used: whether it will be used as an input material to produce coke or whether it will be used directly in the production of energy. In order to be used in the production of coke, coal must be able to go through a plastic state that results in a change in the coal’s structure and the creation of a new form of fuel: coke. The calorific value of coal is a key criterion for using coal directly in the production of energy.
Types of coal based on grain size:
| Fuel type | Grain size [mm] |
| Cube | 40-100 |
| Nutshell 1 | 20-40 |
| Nutshell 2 | 10-25 |
| Industrial mix | 0-40 |
| Coarse dust | 0-10 |
