LeoGlossary: Coal

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Coal is a dark-colored type of sedimentary rock that is used to generate electricity, produce steel, and manufacture various industrial and commercial products. It is derived from the remains of ancient plants that have been buried for millions of years under layers of rock and sediment.

It is primarily composed of carbon, hydrogen, and oxygen, but it also contains small amounts of other elements such as sulfur, nitrogen, and trace metals. It is a fossil fuel, meaning that it was formed from the remains of ancient plants and animals that have been buried for millions of years.

There are four main types of coal, which are classified based on their carbon content: anthracite, bituminous, sub-bituminous, and lignite. Anthracite coal has the highest carbon content and is considered the highest quality, while lignite coal has the lowest carbon content and is considered the lowest quality.

Coal is mined from underground mines using various methods, including room and pillar mining, longwall mining, and mountaintop removal mining. It is then transported to power plants, steel mills, and other industrial facilities where it is used as a fuel source.

This is a controversial energy source due to its environmental impact. burning coal releases greenhouse gases, such as carbon dioxide and methane. Coal mining can have negative impacts on local ecosystems and communities, including air and water pollution, land degradation, and displacement of people.

Despite these concerns, coal remains a significant source of energy worldwide, particularly in countries with large reserves of coal, such as the United States, China, and India. However, there is a growing trend towards transitioning away from coal and towards cleaner, more sustainable energy sources, such as wind, solar, and natural gas.

Types

There are four main types of coal, which are classified based on their carbon content:

Anthracite: Anthracite coal has the highest carbon content, typically between 92% and 98%. It is considered the highest quality coal and is used primarily for generating electricity and producing steel. Anthracite is hard, brittle, and shiny, with a high BTU (British Thermal Unit) value, making it an efficient fuel source.
Bituminous: Bituminous coal has a carbon content between 45% and 86%, making it the most common type of coal used for electricity generation. It is soft, black, and has a high BTU value, making it suitable for generating electricity and producing steel.
Sub-bituminous: Sub-bituminous coal has a carbon content between 35% and 45%. It is soft, brown, and has a lower BTU value than bituminous coal. Sub-bituminous coal is used primarily for generating electricity and producing industrial products.
Lignite: Lignite coal has the lowest carbon content, typically between 25% and 35%. It is soft, brown, and has a low BTU value, making it less suitable for electricity generation. Lignite is primarily used for generating electricity and producing industrial products.

There are also other types of coal, such as peat, which is a precursor to coal and has a carbon content of less than 25%. Peat is not yet coal, but it can eventually become coal over millions of years of geological processes.

It's worth noting that the exact classification of coal can vary depending on the country and region, and different classification systems may be used. However, the four main types of coal - anthracite, bituminous, sub-bituminous, and lignite - are generally recognized and used worldwide.

Coal As An Energy Source

Coal is a fossil fuel that has been used as an energy source for centuries. It is formed from the remains of ancient plants that have been buried for millions of years under layers of rock and sediment. Coal is primarily composed of carbon, hydrogen, and oxygen, with smaller amounts of other elements such as sulfur and nitrogen.

The history of coal as an energy source dates back to ancient times, when it was used for cooking and heating. However, it wasn't until the Industrial Revolution in the 18th and 19th centuries that coal became a major source of energy for industry and transportation. The invention of the steam engine, which was powered by coal, revolutionized industry and transportation by allowing for the efficient use of coal to generate power.

Today, coal is still a major source of energy, although its use is declining in many parts of the world due to concerns about air pollution. In 2020, coal generated about 27% of the world's electricity, down from 33% in 2010.

There are several ways in which coal can be used to generate energy:

Burning coal to produce steam: Coal can be burned in a boiler to produce steam, which is then used to power a steam turbine to generate electricity. This method is commonly used in power plants.
Burning coal to produce electricity directly: Coal can also be burned directly in a power plant to generate electricity, without the need for a steam turbine.
Producing coal gas: Coal can be heated in the absence of air to produce a mixture of gases, including carbon monoxide, hydrogen, and methane. These gases can be used as a fuel to generate electricity or as a feedstock for the production of other chemicals.
Producing coal liquids: Coal can be converted into liquid fuels such as diesel and methanol through a process known as coal liquefaction.

How It Is Mined

Coal is mined through various methods depending on whether it is extracted from underground or surface mines. In underground mining, two primary methods are used: room-and-pillar mining and longwall mining.

Room-and-pillar mining: This method involves cutting a Network of 'rooms' into the coal seam and leaving behind 'pillars' of coal to support the mine roof. These pillars can make up to 40% of the total coal in the seam, with the possibility of extracting this coal at a later stage.
Longwall mining: In longwall mining, a long wall of coal is extracted in a single slice using mechanical shearers. The process involves the full Extraction of coal from a section of the seam, with self-advancing, hydraulically-powered supports temporarily holding up the roof while coal is extracted. Once the coal is removed, the roof collapses.

On the other hand, surface mining is used when the coal seam is near the surface. This method recovers a higher proportion of the coal deposit compared to underground mining, with 90% or more of the coal being recoverable. Surface mining involves breaking up the overburden of soil and rock using explosives, removing it with heavy equipment like draglines or shovels, exposing the coal seam, drilling it, and then systematically mining it in strips. The extracted coal is loaded onto trucks or conveyors for transport.

These methods vary in their efficiency, environmental impact, and suitability based on factors like depth of the coal seam, overburden characteristics, and regional geological conditions.

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