Coal has dominated the world energy scenario since the Eighteenth century, up to 1970 and in 2019 it accounts for approximately 26.8% of the primary consumption of energy (Source: International Energy Agency (IEA) – Key World Energy Statistics 2021). The greatest limit of coal is that it is the most polluting source of energy and it negatively affects the state of the climate. When compared to natural gas, production of one kilowatt-hour of electricity from coal generates more than twice the amount of nitrogen oxide, eight times the amount of heavy metals, ten times the amount of fine dust, and it also produces a large amount of sulphur oxides.
The set of operations leading to the identification of coalfields and to their assessment is called mining prospecting.
As with oil, an analysis of airplane pictures is conducted to identify geologically interesting areas, then soil samples are studied to obtain more detailed information.
After having identified the coalfield and its position and shape, the mine building site is started. If the coal is found a at depth not exceeding 30 m, it is extracted in open pit mines, where the field is made accessible after the elimination of the top layers of rocks and soil by means of explosive charges. If the coal is deeper than 30m, the field is accessed by digging underground mines including at least two galleries to let miners and machines reach the coal.
In open pit mines the coal is extracted after having removed the rocks above. In the case of underground mines, the extraction is carried out in two ways: the method of “abandoned pillars” and that of “long faces”. The first method consists in extracting coal while leaving “pillars” to support the roof of the mine.
Treatment and transport
The market requires coal to have a high quality and purity. The coal extracted from mines contains a mixture of fractions of different sizes, sometimes containing rocks or compost.
Electric plants with coal
The first step for energy creation in a coal plant starts in the steam generator area, where the burners are located for the combustion of coal fuel oil. The steam generator is generally made up of a furnace where air and fuel are inserted.
In certain production sectors coal is still an important energy source. At present 39% of the world-wide electric energy output is obtained by burning coal. Moreover coal plays a vital role in the production of steel. On the other hand, the size of its reserves still does not envisage any problems in terms of depletion in the future. Moreover, the use of coal was decisive in the past for the industrial development and the prosperity of European countries, whereas today it is questioned because of the high pollution level deriving from its use as a fuel.
Limits and advantages of coal
The combustion of coal generates great quantities of carbon dioxide (CO2), greater than those produced by oil or natural gas. It should be remembered that carbon dioxide is the main culprit for the greenhouse effect, i.e. the increase of the earth’s temperature.
Coal mining has impacts on superficial and underground waters, soil, local land use and native flora and fauna. Each mine must have a reclamation or rehabilitation plan that covers all the phases of the mine lifecycle.
Clean technologies for coal
To achieve a less polluting use of this energy resource, over the last years technologies were developed leading to a reduction of the environmental impact in all the stages of the coal production cycle: from extraction to processing and combustion.