Coal Basic Knowledge

Coal – How It Is Formed Coal is made from Peat that has been compressed and then subjected to high temperature ( + 100° Celcius) for a few million years to drive off moisture, methane and carbon dioxide bearing molecules. This process causes the peat to progress through brown coal, lignite, sub-bituminous coal and then to bituminous coal (the category most of Australia's coal currently mined belongs to) and finally anthracite. Through this process, the carbon content of the coal increases as does the energy content of the coal. Commensurate with this process is a reduction in the moisture content and oxygen content of the coal.

The process by which peat accumulates is complex but in general it:
• requires a source of vegetal material (plant material in the form of trees, branches, leaves, spores and resins),
• requires a preserving medium (normally water) where microbial activity is restricted.
• requires a sinking floor or rising water table for the duration of the peat formation
• requires a long period of time where quiescent condition predominate

Where Does Coal Form? Coal, as with most organic sediments, tends to accumulate in structures known as basins. These structures are normally controlled by a series of faults that provide the constant sinking of the floor of peat swamps. These basins may be several thousand kilometres long and several hundred kilometres wide and are normally associated with "Plate Tectonics" at the time of formation. These basins are often associated with the accumulation of many thousands of metres of sediment and are found behind zones of subduction where ocean floor sinks beneath crustal rocks depiceted below.

Coal Rank Progression
Coal is a sedimentary deposit (laid down in water) that comprises preserved plant material from ages past. Over time a great thickness of plant material accumulates that is broken down into peat. This represents a storehouse of organic matter produced via photosynthesis by plants using the sun's energy. In this form even the peat is a source of preserved solar energy. Peat contains a lot of water and subsequent burial of the peat results in the water being squeezed out. This process normally extinguishes bacterial activity and as temperatures rise with increasing depth of burial, the coalification processes begin to transform the peat to brown coal, then lignite, sub-bituminous coal, bituminous coal and finally to anthracite.
This coalification process is accompanied by a decrease in moisture, a decrease in volatile matter and increase in carbon and an increase in calorific value and a commensurate decrease in oxygen until the end of the bituminous rank shown in the table below.

Changes in coal properties as rank increases



 Volatile Matter

 Carbon Content

 Calorific Value

 Oxygen Content

 Coalification Stage

 As Recieved

 Dry Ash Free 

 Dry Ash Free


 Dry Ash Free



 69 - 63%


 3,500 kcal/kg



 35 - 55%

 63 - 53%

 65 - 70%

 4,000 - 4,200 kcal/kg


 Sub-bituminous C

 30 - 38%

 53 - 50%

 70 - 72% 

 4,200 - 4,600 kcal/kg


 Sub-bituminous B

 25 - 30%

 50 - 46%

 72 - 74%

 4,600 - 5,000 kcal/kg


 Sub-bituminous A

 18 - 25%

 46 - 42%

 74 - 76%

 5,000 - 5,500 kcal/kg


 High Volatile Bituminous C

 12 - 18%

 46 - 42%

 76 - 78%

 5,500 5,900 kcal/kg


 High Volatile Bituminous B

 10 -12%

 42 - 38%

 78 - 80%

 5,900 - 6,300 kcal/kg


 High Volatile Bituminous A

 8 - 10%

 38 - 31%

 80 - 82%

 6,300 - 7,000 kcal/kg


 Medium Volatile Bituminous

 8 - 10%

 31 - 22%

 82 - 86%

 7,000 - 8,000 kcal/kg


 Low Volatile

 8 - 10%

 22 - 14%

 86 - 90%

 8,000 - 8,600 kcal/kg



 8 - 10%

 14 - 8%


 7,800 8,000 kcal/kg



 7 - 9%

 8 -3%


 7,600 - 7,800 kcal/kg



 7 - 9%

 8 - 3%


 7,600 kcal/kg


Coal Basic Knowledge – There are four major types of coal.Coal is classified by hardness and harder the , the less moisture it contains and making a good home heating fuel.

1. Bituminous –It is a coal medium hard coal contains very little moisture and has high heat value .It is used to generate electricity and to make coke which is used in the steel industry.
2. Sub-Bituminous –It is a medium soft coal has much less moisture than lignite and is used mostly to produce steam for electricity generation.
3. Lignite –It is the softest coal contains a lot moisture .Its brownish black and crumbles easily.
4. Anthracite-It is the hardest coal and has a very high heat value burning slowly and making a good home heating fuel.

USES OF COAL - 1. Electric power generating plants burns coal to make steam .The steam turns turbines which generate electricity.
2. Coal is also used for making steel .It is baked in hot furnaces to make coke which is used to smelt iron ore in the steel making process.The carbon in coal gives steel the strength and versatility for products such as bridges and automobiles.
3. COAL IS ALSO USED FOR INDUSTRY , such as concrete and paper and ingredients of coal , such as methanol and ethylene are used in making plastics , synthetic fibers , fertilizers and medicine .


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