Hard coal belongs to sedimentary rocks generated in earth layers.
It is one of the most ancient fuels used by humans tens of thousands years ago.
How it is generated
Coal is generated in places where trees and other plants accumulate in one place, whereupon this large vegetation mass needs more time for degrading to nothing.
Oxygen-deficient marshy localities are ideal for this purpose. Most of modern reserves of this mineral were generated three hundred million years ago in the Paleozoic era
Types of hard coal and its composition
Composition and type of this fossil depends on its age and depth of occurrence. Anthracite, whose deposits are found at 5 km depth, may be attributed to the most ancient rock. It contains a lot of carbon, minimum of moisture, and has the highest (up to 7400 kcal/kg) heat of combustion.
Hard coal is in the middle of classification. Its deposits are found at up to 3 km depth. It contains near 12% of water, 32% of volatile substances and from 75 to 95% of carbons. It is inflammable, burns well and provides enough heat due to the minimum moisture amount.
Brown coal is one of the youngest species of this rock. Its deposits may be found at up to 1000 m depth. It contains over 40% of water, and a lot of volatile substances. It is well-flammable, burns pretty well however providing a little heat.
Hard coal deposits
Currently, there are near 3,700 coal basins worldwide covering circa 15 per cent of the total land area. Almost ¼ of global deposits of this natural fossil is located within the USA, Russia comes next with its deposits occupying 13% of global. China places No. 3 with its 11 per cent.
How it is mined
Mining method depends on coal depth. It may be whether open when solid rock sheet above the coal is exploded, or closed.
Where it is used
Coal is a commonly-used type of mineral resources deeply-seated below ground. Hard coal was generated many millions of years ago owing to gradual consolidation of animals and vegetative remains under conditions with minimum oxygen content (underground). It is recovered manually and in a semiautomatic way in deep underground coal mines.
Except of using hard coal as a fuel, it is used in the national economy and household:
- for obtaining sulphur, graphite, vanadium, naphthalene, lead and zinc;
- in metallurgy industry — in manufacturing iron, steel and cast iron;
- after liquefaction — for manufacturing liquid fuel or ash;
- after special treatment — for obtaining benzene and xylene afterwards used for manufacturing paints and varnishes, solvents and linoleum.
All together, more than four hundred industrial products are obtained during hard coal chemical processing.
What are the criteria coal quality is determined upon
Coal quality is determined by percentage of its foreign impurities content. The more amount of foreign impurities, the worse coal quality. Foreign impurities are non-combustible substances remaining in the form of slag after coal combustion. Depending on the territory of coal deposits occurrence, the percentage of mineral content in it may differ greatly. Coal quality is determined by the percentage of its moisture, minerals, ash compounds and sulphur content.
Sulphur is one of the most adverse foreign impurities. During combustion of coal with high percentage of sulphur compounds, large amount of sulphur acids is emitted to the atmosphere.
Ultimately, it results in defoliating acid rains falling out. Coal with over 4-8 % sulphur content is unusable in heat and power sphere.
DG UNITED supplies its products to countries of Asia–Pacific region, Turkey, India and others.
7,760,000 tons of cargo, including 7,700,000 tons of coal, were delivered to consumers in 2023.