Eszterházy Károly College Faculty of Natural Sciences
Coal was the first fossil fuel, which was used as a source of vast amounts of energy. The reasons of its popularity is due to the higher heating value than wood, safe and economical transport abstraction. Today, the primary role is in electric power generation. In most of the advanced countries the role of coal is replaced by oil, gas and renewable energy sources such as wind, solar or water power. It has been relegated because of the polluting effects. The quality of the coal in the coal seams and its geological characteristics determine the economical use. The rating is depending on heating value, ash and water content which is the function the of maturity of carbon deposition..
Coal is buried plant material transformed as the result of temperature and pressure increase. The basis of the use of energy is released by combustion that the plant store up during its development. The coal occurs in marshy areas, after the withering plants are under water. Thus the oxidation of the organic material will not occur, on the other hand slunge clogging prevents the bacteria and fungi to decompose the plant material. The buried plant material in the slunges is forming into peat, which may contain 90% water. The peat will continue to evolve into coal, because if the area is slowly sinking additional sediment is built up on it. Then the peat becomes highly concentrated because of the increase in pressure, and loses most of its water.
Biochemical carbonization is called the initial stage of coal formation, which is carried out in degradation by micro-organisms. Then the vegetable lignin, cellulose and proteins are formed.into humic acids. This results peat, in which the plant material is still recognizable. This is followed by the geochemical coal session when the geological conditions are changing so the plant structure disappears as a result of the increasing engulfment and temperature. In this section, brown coal is created. Brown coal is formed up to 100 ° C (about 3 km depth). In the last stage of carbonization humic acids disintegrate, methane is released, resulting black coal and anthracite.
This temperature range is between100-400 ° C. If the temperature and the pressure continues to rise, from anthracite, graphite is formed under a small degree of metamorphosis conditions (PÁPAY 2003).
The chemical constituents of plants are coal (50%), oxygen (43%), hydrogen (6%), and nitrogen (1%).During carbonization the quantity proportions are shifted in favor of the coal, the content of elemental carbon increased from 50% to 100%. The departing components procreating gas. Of these, methane is dangering mining purposes, because when breaking loose from the pores it forms explosive mixture with the air of mine voids (firedamp).
The coal occurrences on the basis of formation conditions are divided into two groups: limnic (lake) and paralicus (coastal) occurrences. The limnic or paralicus can decide the nature of reactive layers based on fossil content (freshwater and marine forms), but the two types also differ in appearance. The limnic is characterized by fewer number but also thicker reactive layers than the colonies. In contrast, paralicus is caharacterised by more but thinner reactive layers.