Coal

What is coal?

Coal is an organic sedimentary rock which is the prehistoric vegetation that are deposited at swamps, subjected to heat and pressure over million of years. This is composed mainly of carbon, hydrogen and oxygen. Coal along with oil and gas is fossil fuel, can also be called combustible rock.
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.

Coal can be roasted (heated in high temperature in a place where there is no oxygen) to produce coke. Coke is even better fuel than coal, and can be used in smelting to reduce metals from their ores.

Formation of coal

Coal is formed by the deposition of plant debris in a swampy area where conditions are favourable for the generation of coal. Condition to form coal are area where water does not dry up, plant debris are continuously being submerged in the water that no decay process can be carried out. The plant debris accumulates slowly at a place which further generate into coal seam. For a few feet fifty or hundred feet area of coal seam, it takes a very long time about thousands of years at which the water level should remain constant so that no decay process can be stimulated or else seam generation won't be carried out. 

Coal formation started in the Carboniferous period, which is spanned as 360 to 290 million years ago is known as first coal age. Due to tectonic movements, silt and other sediments build together with the swamp and peat log areas buried at great depths. With burial of the plant remains to depths which are great enough with temperature and pressure, turned the plant debris into peat and then into coal.

Energy of coal

The energy we get from the coal is the solar energy stored by the plants during their life time by a process we will be well aware of, the photosynthesis. This stored energy remains in the body of a plant which in turn is submerged in the water of a swamp. If this plant is not preserved in the water to form coal, the energy stored will be released by the decay process.

Types of coal

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 steam-electric power generation, and for heat and power applications in manufacturing; also 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.[1] 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. Coal contains impurities. The particular impurities determine the use. Coking coal has little ash or sulphur or phosphorus. Those would spoil the iron made by the blast furnace.

Coal quality depends upon the following factors

• Vegetation variation from which it is formed
• Depths of burial
• Temperature and pressure at those depths
• Length of time taken by the coal deposits

The coal generation starts from the plant cooking and at first peat is converted into lignite with low organic maturity. To compare with other coal lignite is soft and colour varies dark black to various shades of brown.

Over many more million years of temperature and pressure continuous effect, lignite faces further changes with progressively organic maturity transforming it into sub-bituminous coals.

Further cooking under favourable continuous temperature and pressure, organic matter matures more and more forming bituminous and at last the high grade anthracite. These are hard coal with more blackish colour. 

Uses of coals

Coal has a wide range of uses, it can be used for different purposes. The most significant use of coal is generation of electricity in power plants. Electricity is generated by burning of coal in power plant which is also called as thermal coal. Another use of coal is in metallurgical industry, making of steel which is know as metallurgical coal. Coal also have domestic use which can be for heating purpose by coal fire or can be used for cooking, mostly barbecue. 

Facts & figures

• 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
• 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%).

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