Classification of Coal

Classification of coal based on volatile matter and cooking power of clean material

Coal is a readily combustible rock containing more than 50 percent by weight of carbonaceous material formed from compaction and indurations of variously altered plant remains similar to those in peat.

coal

After a considerable amount of time, heat, and burial pressure, it is metamorphosed from peat to lignite. Lignite is considered to be "immature" coal at this stage of development because it is still somewhat light in color and it remains soft.

  • Lignite increases in maturity by becoming darker and harder and is then classified as sub-bituminous coal. After a continuous process of burial and alteration, chemical and physical changes occur until the coal is classified as bituminous - dark and hard coal.
  • Bituminous coal ignites easily and burns long with a relatively long flame. If improperly fired bituminous coal is characterized with excess smoke and soot.
  • Anthracite coal is the last classification, the ultimate maturation. Anthracite coal is very hard and shiny.
ClassVolatile matter1)
(weight %)
General description
101 < 6.1 Anthracites
102 3.1 - 9.0
201 9.1 - 13.5 Dry steam coals Low volatile steam coals
202 13.6 - 15.0
203 15.1 - 17.0 Cooking steams coals
204 17.1 - 19.5
206 19.1 - 19.5 Heat altered low volatile steam coals
301 19.6 - 32.0 Prime cooking coals Medium volatile coals
305 19.6 - 32.0 Mainly heat altered coals
306 19.6 - 32.0
401 32.1 - 36.0 Very strongly coking coals High volatile coals
402 > 36.0
501 32.1 - 36.0 Strongly coking coals
502 > 36.0
601 32.1 - 36.0 Medium coking coals
602 > 36.0
701 32.1 Weakly coking coals
702 > 36.0
801 32.1 - 36.0 Very weakly coking coals
802 > 36.0
901 32.1 - 36.0 Non-coking coals
902 > 36.0

1) Volatile matter - dry mineral matter free basis. In coal, those products, exclusive of moisture, given off as gas and vapor determined analytically.

Anthracite coal creates a steady and clean flame and is preferred for domestic heating. Furthermore it burn longer with more heat than the other types.

Typical Sulfur Content in Coal

  • Anthracite Coal : 0.6 - 0.77 weight %
  • Bituminous Coal : 0.7 - 4.0 weight %
  • Lignite Coal : 0.4 weight %

Typical Moisture Content in Coal

  • Anthracite Coal : 2.8 - 16.3 weight %
  • Bituminous Coal : 2.2 - 15.9 weight %
  • Lignite Coal : 39 weight %

Typical Fixed Carbon Content in Coal

  • Anthracite Coal : 80.5 - 85.7 weight %
  • Bituminous Coal : 44.9-78.2 weight %
  • Lignite Coal : 31.4 weight %

Typical Bulk Density of Coal

  • Anthracite Coal : 50 - 58 (lb/ft3), 800 - 929 (kg/m3)
  • Bituminous Coal : 42 - 57 (lb/ft3), 673 - 913 (kg/m3)
  • Lignite Coal : 40 - 54 (lb/ft3), 641 - 865 (kg/m3)

Typical Ash Content in Coal

  • Anthracite Coal : 9.7 - 20.2 weight %
  • Bituminous Coal : 3.3-11.7 weight %
  • Lignite Coal : 4.2 weight %

Related Topics

  • Heating - Heating systems - capacity and design of boilers, pipelines, heat exchangers, expansion systems and more
  • Combustion - Boiler house topics - fuels like oil, gas, coal, wood - chimneys, safety valves, tanks - combustion efficiency

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