Coal is a flammable black hard rock used as a solid fossil fuel. It is mainly made up of 65-95% carbon and also contains hydrogen, sulphur, oxygen and nitrogen. It is a sedimentary rock formed from peat, by the pressure of rocks laid down later on top. The harder forms of coal, such as anthracite, are metamorphic rocks because they were changed by higher temperature and pressure.
Peat, and therefore coal, is formed from the remains of plants which lived millions of years ago in tropical wetlands, such as those of the late Carboniferous period (the Pennsylvanian). A similar substance made from wood by heating it in an airless space is called charcoal.
Coal can be burned for energy or heat. About two-thirds of the coal mined today is burned in power stations to make electricity. Coal is becoming less popular in new power plants as less expensive and less polluting technologies such as natural gas and hydroelectricity take over.
Coke is a product of destructive distillation of coal, that is, coal is heated to about 400 degree celsius in the absence of oxygen to obtain coke. Coke is an almost pure form of carbon. The calorific value (energy produced when 1 Kg of a fuel is burnt) of coke is about 56,000 kilojoules/kilogram.
Types[change | change source]
Under suitable conditions, plant material is transformed step by step into
- Peat, which has industrial importance as a fuel in some regions, for example, Ireland and Finland. In its dehydrated form, peat is a highly effective absorbent for fuel and oil spills on land and water.
- Lignite (brown coal) is the lowest rank of coal and is used as fuel for electric power generation. Jet is a compact form of lignite that is sometimes polished and has long been used as an ornamental stone.
- Sub-bituminous coal is used as fuel for steam-electric power generation. Also, it is a source of light aromatic hydrocarbons for the chemical synthesis industry.
- Bituminous coal is a dense rock, black but sometimes dark brown. It is a relatively soft coal that breaks and burns readily and quickly. It used as fuel in electric power stations, and for heat and power applications in manufacturing; and to make coke.
- Steam coal was once widely used as a fuel for steam locomotives. In this specialized use it is sometimes known as sea-coal in the U.S. Small steam coal (dry small steam nuts or DSSN) was used as a fuel for domestic water heating.
- Anthracite is the highest quality: a harder, glossy, black coal. It is longer burning, and used mainly for residential and commercial space heating.
- Graphite is difficult to ignite and is not so commonly used as fuel: it was mostly used in pencils and, when powdered, as a lubricant.
Diamond is commonly believed to be the highest grade, but this is not true. Diamond is carbon but is not formed from coal.
Back in fashion[change | change source]
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After 50 or 60 years of decline, coal production increased in the early 21st century. Despite stringent carbon emissions targets in Europe designed to slow global warming and investment in renewable energy, more coal is mined per year than oil. In 2006 it was about 17 million tonnes of coal per day, vs 12 million tonnes of oil.
Coal-fired power stations are the cheapest way to provide energy. Population growth, especially in Asia, and the growth of the middle classes in China, are forces driving the need for more energy. To meet that need, people burn more coal. Here are the reasons:
- Oil and gas will run out, and became more expensive until fracking became more common early in the 21st century.
- Few atomic power stations are being built.
- Power from water turbines is only available in some places.
- Power from wind farms has problems such as expense, unreliability of supply and pollution of the living environment.
Some of the world's largest economies are turning to coal. "Germany's decision to scrap all nuclear power and build more coal-fired power stations can only boost production further". On the other hand, coal burning is the most polluting form of energy. Though carbon sequestration is possible, it is seldom done.
Coal was an important part of rail freight in the UK in the 20th century, forming the greater part of several companys' freight volume. Early in the 21st century most coal fired power stations were closed to reduce greenhouse gas emissions. Far less coal is moved by rail.
In other countries, coal is still an important cargo of rail freight.
Facts & figures[change | change source]
- Coal makes up about 40% of the world's carbon dioxide emissions from fuels
- Coal-fired power stations produce almost half the electricity produced in the US, and two thirds in China
- Coal, when burnt, gives off almost a third more carbon dioxide per unit of energy than oil, and 80% more than natural gas
- Coal provides about a quarter of the world's energy needs
- Almost 70% of world steel production depends on burning coal.
Since 1983 the world top coal producer has been China. In 2011 China produced 3,520 millions of tonnes of coal – 49.5% of 7,695 millions tonnes world coal production. In 2011 other large producers were United States (993 millions tonnes), India (589), European Union (576) and Australia (416). In 2010 the largest exporters were Australia with 328 million tonnes (27.1% of world coal export) and Indonesia with 316 millions tonnes (26.1%), while the largest importers were Japan with 207 million tonnes (17.5% of world coal import), China with 195 million tonnes (16.6%) and South Korea with 126 million tonnes (10.7%).
Related pages[change | change source]
|Wikimedia Commons has media related to Coal.|
References[change | change source]
- Funk and Wagnalls, quoted in "sea-coal". Oxford English Dictionary. 2nd ed, Oxford University Press. 1989.
- Anderson, Richard 2012. Coal resurgence calls undermines clean energy commitments. BBC News. 
- BP Statistical review of world energy 2012. British Petroleum. "BP Statistical review of world energy 2012" (XLS). British Petroleum. Retrieved 18 August 2011.
- EIA International Energy Annual – Total coal exports (thousand short tons). 
Other websites[change | change source]
- Coal Citizendium