Coal in its various modifications can have a color from brown to black. It is a good fuel, so it is used in the conversion of thermal energy into electrical energy. It is formed as a result of the accumulation of plant mass and the passage of physical and chemical processes in it.
Various modifications of coal
The accumulation of wood pulp in swampy soil leads to the formation of peat, which is the precursor to coal. The peat formula is quite complicated, in addition, there is no specific stoichiometric ratio for this type of coal. Dry peat is made up of carbon, hydrogen, oxygen, nitrogen and sulfur atoms.
Further, peat under prolonged exposure to high temperature and high pressures resulting from the course of geological processes, undergoes a number of the following coal modifications:
- Brown coal or lignite.
- Bitumen.
- Coal.
- Anthracite.
The end product of this chain of transformations is hard graphite or graphite-like coal, whose formula is pure carbon C.
Carboniferous wood
About 300 million years ago during the Carboniferous period, most of the land of our planet was covered with giant fern forests. Gradually, these forests died out, and the wood accumulated in the swampy soils on which they grew. A large amount of water and dirt created obstacles for the penetration of oxygen, so the dead wood did not decompose.
For a long time, newly dead wood covered the older layers, the pressure and temperature of which gradually increased. Associated geological processes eventually led to the formation of coal deposits.
Carbonization process
The term "carbonization" refers to the metamorphic transformation of carbon associated with an increase in the thickness of tree layers, tectonic movements and processes, as well as an increase in temperature depending on the depth of the strata.
Increase in pressure primarily changes the physical properties of coal, the chemical formula of which remains unchanged. In particular, its density, hardness, optical anisotropy and porosity change. An increase in temperature changes the very formula of coal towards an increase in carbon content and a decrease in oxygen and hydrogen. These chemical processes lead to an increase in the fuel characteristics of coal.
Coal
This modification of coal is very rich in carbon, which leads to a high heat transfer coefficient and leads to its use in the energy industry as the main fuel.
The coal formula consists ofbituminous substances, the distillation of which makes it possible to extract from it aromatic hydrocarbons and a substance known as coke, which is widely used in metallurgy processes. In addition to bituminous compounds, there is a lot of sulfur in coal. This element is the main source of air pollution from coal combustion.
Coal is black and burns slowly, creating a yellow flame. Unlike brown coal, its calorific value is higher and amounts to 30-36 MJ/kg.
The formula of coal has a complex composition and contains many compounds of carbon, oxygen and hydrogen, as well as nitrogen and sulfur. Such a variety of chemical compounds was the beginning of the development of a whole direction in the chemical industry - carbochemistry.
Currently, hard coal has almost been replaced by natural gas and oil, but two important uses continue to exist:
- main fuel in thermal power plants;
- source of coke produced by oxygen-free burning of hard coal in closed blast furnaces.
