Coal has been used as a fuel source throughout man’s history, having been discovered in the fire pits of cave dwellings. The Chinese considered coal a ‘stone that could burn’ and were mining it over 3000 years ago. The Greek scientist, Theophrastus, recorded the use of coal for smelting metal around 300 BC and the Romans used coal to heat their public baths. The increased use of coal for power generation in Britain in the 18th century fuelled the global Industrial Revolution.
Coal is now one of the world’s largest sources of energy. Global coal consumption grew by 7.6% in 2010, with Asia Pacific countries accounting for 79.7% of the increase.
What is brown coal made from?
Coal is a combustible sedimentary rock found in layers under the earth known as coal seams or coal beds. Considered a fossil fuel, coal is formed when the build-up of organic material and fossil remains is pressurised over millions of years by layers of sediment. This pressure causes a breakdown of this material into hydrocarbons.
During its formation over millions of years, coal matures from a soft peat, through to its hardest form, anthracite. Coal is named either black or brown depending on both its colour and composition. Brown coal (or lignite) is the lowest grade of coal and is softer due to its water content. Its heating value is around one quarter of black coal
. Brown coal is not always brown and actually varies in colour from yellow to dark brown.
Coal is primarily composed of carbon (from 50 to 98 per cent) and hydrogen (3 to 13 percent) with the remainder comprised of varying amounts of oxygen, sulphur and nitrogen. Brown coal has a relatively low carbon content (60 to 75 percent on a dry basis), has a high oxygen content (up to 30 percent), and a high moisture content (30 to 70 percent).
Due to the high moisture content of brown coal, and its susceptibility to spontaneous combustion, it has traditionally been uneconomical to transport. However, improved processing technologies have led to drying techniques that enable brown coal to be converted into high-energy pellets and briquettes, allowing for easier transport (to compete with black coal).
How is brown coal used?
Brown coal is primarily used in electricity generation. It is burned to heat water, producing steam to run the power turbines.
The gasification of brown coal produces synthesis gas, also known as syngas, which is the precursor to some manufacturing processes. Syngas can be used to facilitate the separation and sequestration of carbon dioxide and is also a pathway to producing liquid fuel products.
Brown coal can be liquefied by various means to produce products such as synthetic crude oil and its range of applications.
There is further potential to refine brown coal into purer forms of carbon for the manufacture of products such as carbon fibre, carbon anodes, activated carbon, filter aids, pigments, graphite, lubricants and conductors.
Where is brown coal found?
Brown coal is found in coal beds under the earth at various depths and is often exposed at the surface, which aided its discovery by early humans. Mined from both the surface (open pit) and underground, surface mining is more economical and hence most common.
Most countries have coal deposits, however not all of them are commercially viable for extraction. The BP Statistical Review of World Energy
estimated the world’s brown coal reserves at approximately 456 billion tonnes in 2010. The countries containing the largest amount of brown coal reserves include:
- Russian Federation
China is the world’s largest consumer and producer of brown coal.
In 2009, Australia's economically recoverable brown coal resources were reported to be 37 billion tonnes, all of which is in Victoria, with over 90% in the La Trobe Valley. This equates to approximately 8.5% of the world’s brown coal reserves. In fact, the majority of Victoria’s power generation relies on brown coal.
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