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 coal modifications
The accumulation of wood pulp in marshy soil leads to the formation of peat, which is a precursor to coal. The peat formula is quite complex, in addition, for this kind of coal there is no specific stoichiometric ratio. Dry peat consists of carbon, hydrogen, oxygen, nitrogen and sulfur atoms.
Further, peat under prolonged exposure to high temperature and high pressures arising from the occurrence of geological processes undergoes a number of the following coal modifications:
- Brown coal or lignite.
- Bitumen.
- Coal.
- Anthracite.
The final product of this chain of transformations is solid graphite or graphite-like coal, the formula of which is pure carbon C.
Carbon 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 became extinct, and wood accumulated in the swampy soils on which they grew. A large amount of water and dirt blocked the penetration of oxygen, so dead wood did not decompose.
For a long time, the newly dead wood covered the older layers, the pressure and temperature of which gradually increased. Concomitant geological processes ultimately led to the formation of coal deposits.
Carbonation process
The term "carbonization" implies metamorphic transformations of carbon associated with an increase in the thickness of wood layers, tectonic movements and processes, as well as with an increase in temperature depending on the depth of the strata.
An 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 in the direction of increasing the carbon content and decreasing 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 determines its use in the energy industry as the main fuel.
The formula of coal consists of bituminous substances, the distillation of which allows to separate aromatic hydrocarbonates and a substance known as coke, which is widely used in metallurgy processes. In addition to bituminous compounds, coal contains a lot of sulfur. This element is the main source of air pollution during coal combustion.
Coal is black in color and burns slowly, creating a yellow flame. Unlike brown coal, its calorific value is greater and amounts to 30-36 MJ / kg.
The coal formula 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 area in the chemical industry - carbochemistry.
Currently, coal is almost replaced by natural gas and oil, however, two of its important areas of use continue to exist:
- main fuel in thermal power plants;
- source of coke obtained by oxygen-free burning of coal in closed blast furnaces.