Anthracite Coal Structure Properties and Applications

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.

Structure of Anthracite Coal

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Composition of Anthracite Coal

• Carbon − 77% 

• Ash − 6-16%

• Trace elements like: 

• Sulfur − 0.23-1.2%

• Silica oxide − 2.2-5.4%

• Alumina − 2%

• Ferric oxide − 0.4%

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:

• Standard grade anthracite

• High-grade anthracite

• Ultra High-grade 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.

How is Anthracite Different From Bituminous?

Anthracite differs from ordinary bituminous coal in that it has a higher hardness (2.75–3), a higher relative density of 1.3–1.4, and a semi-metallic lustre with a mildly brown reflection. It has a high proportion of fixed carbon and a low proportion of volatile carbon. It's also free of any soft or fibrous notches, and it doesn't soil your fingers when you rub it. The transformation of bituminous coal into anthracite is known as anthracitization.

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Features of Anthracite

• Freshly mined anthracite usually has a moisture content of less than 15%. On a moist, mineral-matter-free basis.

• The heat content of anthracite varies from 26 to 33 MJ/kg (22 to 28 million Btu/short tonne). On an as-received basis, the heat content of anthracite coal consumed in the United States averages 29 MJ/kg (25 million Btu/ton) (i.e., containing both inherent moisture and mineral matter). 

• Density of anthracite is 1.3-1.8 g/cm³.

• The hardness of anthracite on the Mohs scale is 2.2-3.8.

• The moisture content of anthracite coal is 0.5-4%.

• The pH of a water suspension of anthracite is 7-7.8.

• Volatile content is 0.5-20% in anthracite.

• The resistivity of anthracite is 1×10⁻³ to 2×10⁵ Ω-m.

• Anthracite refuse or mine waste has been used for coal power generation as a method of recycling since the 1980s.

Anthracite is a chemical intermediate between ordinary bituminous coal and graphite, formed by the more or less complete removal of the volatile constituents of the former, and it is most abundant in areas subjected to significant stresses and pressures, such as the flanks of large mountain ranges. Anthracite is associated with highly deformed sedimentary rocks exposed to higher pressures and temperatures (but not metamorphic conditions), whereas bituminous coal is associated with less deformed or flat-lying sedimentary rocks.

Deep mined compressed layers of anthracite in the folded Ridge and Valley Province of the Appalachian Mountains of East-central Pennsylvania, for example, are extensions of the same layers of bituminous coal. These are mined on the Allegheny Plateau of Kentucky and West Virginia, Eastern Ohio, and Western Pennsylvania, where the sedimentary rocks are mostly smooth and undeformed. Similarly, South Wales' anthracite area is limited to the twisted section west of Swansea and Lanelle, with the central and eastern parts supplying steam coal, coking coal, and domestic house coals.

Anthracite's structure has been altered by the formation of secondary divisional planes and fissures, making the initial stratification lines difficult to see. The thermal conductivity is also higher; when kept in the warm hand, a lump of anthracite feels noticeably colder than a comparable lump of bituminous coal at the same temperature. In the article coal, the chemical composition of some common anthracites is given. Anthracite resembles a mineraloid jet in appearance and is often used as a jet substitute.

Use of Anthracite Coal

• Today, anthracite is primarily used as a domestic fuel in hand-fired stoves or automatic stoker furnaces. Therefore, it is known as anthracite domestic fuel. It provides a lot of energy for its weight and burns cleanly with little soot, so it's perfect for this. Its high cost renders it unsuitable for use in power plants. 

• The fine particles are often used as filter media and as a component in charcoal briquettes. 

• According to the United Kingdom's Clean Air Act of 1993, anthracite was an approved fuel that could be used within a specified Smoke Control Area, such as the central London boroughs.

Reserves of Anthracite

Russia, China, and Ukraine have the largest estimated recoverable anthracite reserves among current producers. Vietnam and North Korea are two other countries with significant reserves.

The Lackawant to Coal Mine in northeastern Pennsylvania, United States, in and around Scranton, Pennsylvania, is home to the world's largest and most concentrated anthracite deposit. The deposit, known locally as the Coal Region, spans 480 square miles (1,200 square kilometres) of coal-bearing rock that once contained 22.8 billion short tonnes (20.68 billion tonnes) of anthracite. The geographical area is approximately 100 miles (161 kilometres) long and 30 miles (48 kilometres) wide. It is estimated that 7 billion short tonnes (6.3 billion tonnes) of mineable reserves remain due to historical mining and growth of the lands overlying the coal. Smaller anthracite deposits, such as those traditionally mined in Crested Butte, Colorado, can also be found in the United States.

The Groundhog Anthracite Deposit is the world's largest previously undeveloped anthracite deposit, found in British Columbia, Canada. It is owned by Atrum Coal, an Australian publicly traded corporation with 1.57 billion tonnes of high-grade anthracite.

Anthracites from the Tertiary or Cretaceous period have been discovered in the Crowsnest Pass region of the Rocky Mountains in Canada, as well as in the Andes of Peru.

Different Forms of Anthracite Fuel

Burnglo Anthracite Smokeless Fuel

Burnglo Anthracite Smokeless Fuel is a great value for money standard grade coal that's ideal for smoke control areas. It produces a decent amount of heat over a long period of time and has a low, blue flame. Customers that use Burnglo Anthracite Smokeless Fuel in closed appliances such as room heaters, glass-fronted stoves, boilers, and cookers love it.

Anthracite Beans

Anthracite Beans are uniformly sized bits of high-grade coal that burn cleanly. They produce a lot of heat and burn with a low flame for a long time. Anthracite Beans produce little compact ash, making them ideal for use in gravity and hopper-fed boilers.

Anthracite Grains

Anthracite Grains are smaller, evenly sized pieces of coal with a long fire life and high heat production than Anthracite Beans. Anthracite Grains are used in gravity and hopper fed boilers to produce low, compact ash. 

Mining Sites of Anthracite

China currently mines the vast majority of the world's anthracite, accounting for more than three-quarters of total production. The majority of anthracite produced in China is of standard grade, which is used in power generation. Increased demand in China has turned the country into a net importer of the fuel, primarily from Vietnam, another major producer of anthracite for power generation, though Vietnam's exports may be curtailed due to rising domestic consumption.

Anthracite production in the United States is currently about 5 million tonnes per year. The state of Pennsylvania mined about 1.8 million tonnes of that total. Anthracite coal mining is still going strong in eastern Pennsylvania, contributing up to 1% of the state's gross domestic product. In 1995, over 2,000 workers worked in the anthracite coal mining industry. The majority of the mining at the time involved reclaiming coal from nearby closed mines' slag heaps (waste dumps from previous coal mining). There is also some underground anthracite coal being mined.

Russia and South Africa are two countries that produce HG and UHG anthracite. In various metallurgical coal applications, HG and UHG anthracite are used as a coke or coal replacement (sintering, PCI, direct BF charge, pelletizing). It's used to make ferroalloys, silicomanganese, calcium carbide, and silicon carbide, as well as ferroalloys, silicomanganese, calcium carbide, and silicon carbide. Lower-quality, higher-ash anthracite is exported from South Africa to Brazil for use in steel production.

Did You Know?

• Anthracite coal is sometimes referred to as "hard coal." Anthracite coal is a highly carbonated fossil fuel that produces the most heat of any fossil fuel on the market, and its low sulphur content makes it a very clean-burning fuel.

• Bituminous coal is also known as "soft coal," while anthracite is known as "hard coal."

• Nakomati anthracite is a private company located in South Africa. It is one of the famous anthracite mining industries.

• ZAC (zululand anthracite colliery) is known as the “sole producer of prime anthracite” in South Africa.