The coal is the most abundant fossil fuel on earth. It is estimated that there are reserves for another 200 years of human consumption. It is usually black and shiny, although this characteristic may vary.
Origin and formation of coal
Mineral coal comes from the decomposition of forests that occurred in the Carboniferous period, from the primary era, being one of the ways in which the carbon element is found in the Terrestrial Globe, in the formation of mineral coal there is a process in which there is transformation of cellulose, with the output of hydrogen and oxygen ions and an increase in carbon enrichment.
This process can be caused by the decomposition of forests on the spot, or by the sedimentation of vegetable debris brought by the waters. Thus, it can be said that the coal deposits represent the remains of vegetables that have been transformed on the spot, or transported over long distances, where the decomposition of cellulose by the action of bacteria, such as Micrococus carbo , an anaerobic bacterium.
Types of coal
There are different types of coal, each formed in a different geological period. They can be classified according to the percentage of carbon they have, which increases over time, so that the richest carbon coals are also the oldest.
- The anthracite coal is coal with higher carbon content in 90 atom%. It is the oldest and the one with the greatest energy power.
- The coal has a carbon content ranging between 75% and 90% and has a high calorific value. It is the most used coal in thermal power plants.
- The lignite is about 70% carbon, and its calorific value is not very high. It is the youngest of the coals and has a dark brown color.
- The peat is coal class that has the lowest carbon content in 50 atom%. It is therefore the least profitable. In addition to fuel, peat is considered to be one of the best natural fertilizers.
The good quality of coal depends on the small amount of minerals in its composition, as these minerals do not burn and still steal heat.
The extraction and treatment of coal
Mineral coal can be mined in open pit or underground mines. Currently, there are few deposits in the open air, because they are already running out, so the most usual thing now is to extract coal from the underground, from very deep mines.
When opening a mine, it is important to first prospect the land to see if it will be profitable. Sometimes, the coal is so deep that the cost of extraction exceeds the final sale price or it is a coal with such a low carbon content that its extraction will not result in a profitable product.
Coal, as it leaves the mines, must be washed to eliminate sulfur residues. Then, it is ground and crushed until powdered. Finally, it is classified and separated into different types of coal.
The chemical energy contained in the coal extracted from the mines is transformed into electrical energy in the thermal power plants. In this process, sulfur dioxide is released into the air, a dangerous substance that must be filtered in the same plants.
Uses of coal
The use of coal has been known for more than 2,000 years, but it was only in the Middle Ages that it began to be used to produce heat. Its most intense use, however, came with the Industrial Revolution at the end of the 18th century.
The first steam engines, the main engine of industrialization, were based on coal energy. It is currently being replaced by oil. Its use occurs mainly in thermal power stations, where its chemical energy is used to obtain electrical energy.
In the plants, coal is burned to heat the water, which is transformed into steam and is capable of moving a turbine. The movement of the turbine drives a generator, and the mechanical energy is then transformed into electricity.
Coal is, in addition, an important component in the production of iron and steel, as well as in the chemical industry.