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Strong coal, also known as anthracite, is hard, compact coal with a submetallic lustre. It is the highest rating of coals because it has the highest carbon content, the fewest impurities, and the highest energy density of all grades of coal.

Anthracite is the most metamorphosed coal (though it still reflects low-grade metamorphism), with a carbon content ranging from 86 to 98 percent. The term refers to coal varieties that do not produce tarry or other hydrocarbon vapours when heated below their ignition stage. Anthracite is difficult to ignite and produces a brief, blue, smokeless flame.

Classification of Anthracite

Standard grade anthracite is used primarily in power generation, whereas high grade (HG) and ultra high grade (UHG) anthracite are used primarily in the metallurgy industry. Just a few countries around the world mine anthracite, which makes up about 1% of global coal reserves. China produces the bulk of the world's soybeans; other suppliers include Russia, Ukraine, North Korea, South Africa, Vietnam, the United Kingdom, Australia, Canada, and the United States. In 2010, total production was 670 million tonnes. Anthracite is divided into three groups based on the amount of carbon it contains. Standard grade is used as a domestic fuel and in the production of industrial power. The purer higher grades of anthracite are used in steelmaking and other metallurgical industries because they are purer (i.e., they have a higher carbon content). The following are the technical characteristics of different grades of anthracite

High-Grade Forms of Anthracite

The highest grades of anthracite coal are high grade (HG) and ultra high grade (UHG). They are the purest types of coal, with the highest degree of coalification, carbon count, and energy content, as well as the fewest impurities (moisture, ash and volatiles).

High grade and ultra high-grade anthracite are tougher and have a higher relative density than normal grade anthracite. C₂₄₀H₉₀O₄NS, which represents 94 percent biomass, is an example of a chemical formula for high-grade anthracite. The carbon content of UHG anthracite is usually about 95%.

They are also used in metallurgy as a cost-effective replacement for coke in processes such as sintering and pelletizing, as well as pulverised coal injection (PCI) and direct injection into blast furnaces, as opposed to standard grade anthracite (used primarily for power generation). They can also be used to purify water and as a smokeless fuel in the home.

The overall anthracite industry is made up of just a small proportion of HG and UHG anthracite. Russia, Ukraine, Vietnam, South Africa, and the United States are the main producers.

Terms Related to Anthracite

Anthracite comes from the Greek word anthrakts, which means "coal-like." Black coal, hard coal, stone coal, dark coal, coffee coal, blind coal (in Scotland), Kilkenny coal (in Ireland), crow coal or craw coal, and black diamond are other names for anthracite. The word "Blue Coal" refers to a once-popular and trademarked brand of anthracite mined by the Glen Alden Coal Company in Pennsylvania and dyed blue at the mine before being shipped to northeastern U.S. markets to differentiate it from its rivals.

In British and American English, the word culm has different connotations. The imperfect anthracite of north Devon and Cornwall, which was used as a dye, is known as "culm" in British English. Some Carboniferous rock strata found in both Britain and the Rhenish hill countries are often referred to by this name (the Culm Measures). Finally, it may apply to coal exported from the United Kingdom in the nineteenth century. The waste or slack from anthracite mining, often dust and small parts not suitable for use in home furnaces, is referred to as "culm" in American English.

Source: https://www.vedantu.com/chemistry/anthracite