Coal

Not to be confused with Charcoal

Maramarua Open Cast Coal Mine in New Zealand, 1966

Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when dead plant matter decays into peat and is converted into coal by the heat and pressure of deep burial over millions of years. Coal is primarily used as a fuel. Coal is very soft ranking from 2 to 4 on the Mohs hardness scale, while sandstone ranks from 5 to 7.

A lump of subbituminous coal.

Coal can be found in a few different forms, these being Anthracite, Bituminous, Subbituminous and Lignite. The images on this article give some examples of their differing appearances.

Anthracite is the highest quality of coal, and is black, hard and quite glossy/shiny. It has a high carbon content, meaning it has a good heating value so it is the most desirable.

Bituminous and subbituminous coals are softer and don't tend to have the gloss of anthracite. They are the most common variants of coal, but have a lower carbon content with more impurities.

A picture of anthracite. Note the glossiness and almost crystal-like appearance of the lump.

Lignite is the lowest quality of coal, and often contains has some brown colouring. It is also soft and has the most impurities making it unwise to use for household heating due to the large amounts of pollutants being produced.

Uses

Because of its hot, consistent burning temperature and relative abundance, coal has had widespread use across history in heating, metalworking and powering coal engines. coal burns at a higher temperature than wood, and so allowed for easier production of iron and other metals. This high temperature also allowed for particularly high pressures to be achieved in steam engines with a lower volume of fuel. This ease of energy extraction was the basis of the industrial revolution.

Raw coal is often not desirable for making steel due to impurities such as Sulfur and other volatiles. This can be fixed by "coking" the coal to turn it into Coke which is the process of heating coal in the absence of oxygen at 600 degrees celsius for around 24 hours. This removes the impurities, which yields a fuel that can burn hotter than raw coal and can be added to Steel without contamination with compounds that lower its strength.

Extraction

Tools needed

• Earth-moving tools; shovel, pick, etc.

Coal is extracted from mines. Several methods can be used to extract it, each with differing levels of complexity and danger.

Room and pillar mining is common, in which pillars of the coal seam are left to support earth above. This can help prevent collapse, but reduces yield due to the coal left in the pillar.

Dangers

Mining

During coal mining, fine dust can be inhaled and cause chronic inflammation. Respiratory protection should be worn.

Pollution

Coal has Sulfur impurities, which create smelly and toxic fumes that can mess with your local environment. Coal tar is full of various organic compounds such as benzene and aldehydes which are toxic and carcinogenic. These can accumulate in a chamber where coal is being burnt.

It also often has some heavy metals such as Arsenic, Lead, and Nickel. These are released into the air or concentrated in the Ash of coal during combustion. Therefore, it is extremely important to dispose of Coal Ash properly and not use it in your garden or let it contaminate water sources.

Self-combustion

While on small scales this isn't a risk, coal is able to self-ignite. When coal is stored or transported in bulk it is watered to reduce this danger.

Dependencies

• Carbon
• Peat
  • Coal

  • 

    A pile of lignite coal. It has a noticeable brown tinge.

    Fuel

See also

• Raw material
• Coke(Fuel)
• Activated charcoal
• Carbon dioxide
• Charcoal
• Fire

References

This article uses material from the Wikipedia article Coal, which is released under the Creative Commons Attribution-ShareAlike 3.0 Unported License (view authors).