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==Coal classification== | |||
There are many compositional differences between the coals mined from different coal deposit locations worldwide. The different types of coal are most usually classified by '''rank''' which depends upon the degree of transformation from the original source (i.e., decayed plants) and is therefore a measure of a coal's age. As the process of progressive transformation took place, the [[heating value]] and the fixed carbon content of the coal increased and the amount of volatile matter in the coal decreased. The method of ranking coals used in the United States and Canada was developed by the [[American Society for Testing and Materials (ASTM) and is based on those three parameters, namely: | |||
*''Heating value'': The energy released as heat when coal (or any other substance) undergoes complete [[combustion]] with [[oxygen]]. | |||
*''Volatile matter'': The portion of a coal which, when heated in the absence of air at prescribed conditions, is liberated as [[gas|gases]]. | |||
*''Fixed carbon'': The | |||
{| class = "wikitable" align="center" | {| class = "wikitable" align="center" | ||
|+ Classification of Coals by Rank<ref name=Perry/><ref name=Marks/><ref name=Kreith/><sup> (a)</sup> | |+ Classification of Coals by Rank<ref name=Perry/><ref name=Marks/><ref name=Kreith/><sup> (a)</sup> |
Revision as of 18:33, 1 May 2009
Coal classification
There are many compositional differences between the coals mined from different coal deposit locations worldwide. The different types of coal are most usually classified by rank which depends upon the degree of transformation from the original source (i.e., decayed plants) and is therefore a measure of a coal's age. As the process of progressive transformation took place, the heating value and the fixed carbon content of the coal increased and the amount of volatile matter in the coal decreased. The method of ranking coals used in the United States and Canada was developed by the [[American Society for Testing and Materials (ASTM) and is based on those three parameters, namely:
- Heating value: The energy released as heat when coal (or any other substance) undergoes complete combustion with oxygen.
- Volatile matter: The portion of a coal which, when heated in the absence of air at prescribed conditions, is liberated as gases.
- Fixed carbon: The
Class or Rank |
Group |
Fixed Carbon (b) (wt % dry mmf) |
Volatile Matter (b) (wt % dry mmf) |
Gross Heating Value (c) (MJ/kg moist mmf) | |||
---|---|---|---|---|---|---|---|
Equal or greater than |
Less than |
Greater than |
Equal or less than |
Equal or greater than |
Less than | ||
Anthracitic |
Metaanthracite (d) Anthracite (d) Semianthracite (d) |
98 92 86 |
98 92 |
2 8 |
2 8 14 |
||
Bituminous |
Low-volatile bituminous (d) Medium-volatile bituminous (d) High-volatile A bituminous High-volatile B bituminous High-volatile C bituminous (e) High-volatile C bituminous (f) |
78 69 |
86 78 69 |
14 22 31 |
22 31 |
32.55 30.23 26.74 24.41 |
|
Subbituminous |
Subbituminous A Subbituminous B Subbituminous C |
24.41 22.09 19.30 |
26.74 24.41 22.09 | ||||
Lignite |
Lignite A Lignite B |
14.65 |
19.30 14.65 | ||||
(a) This classification does not include a few coals (referred to as unbanded coals) having unusual physical and chemical properties falling within the fixed carbon and heating value ranges of the high-volatile bituminous and subbituminous ranks. (b) Percentage by weight on a dry and mineral matter free basis (mmf). |
Coal Rank |
Proximate Analysis (wt % ar) |
Ultimate Analysis (wt % maf) |
Net Heating Value (maf) (MJ/kg) | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Fixed carbon |
Volatile matter |
Moisture |
Ash |
C |
H |
O |
N |
S | |||
Anthracite | 81.8 | 7.7 | 4.5 | 6.0 | 91.8 | 3.6 | 2.5 | 1.4 | 0.7 | 36.2 | |
Bituminous | 54.9 | 35.6 | 5.3 | 4.2 | 82.8 | 5.1 | 10.1 | 1.4 | 0.6 | 36.1 | |
Subbituminous | 43.6 | 34.7 | 110.5 | 11.2 | 76.4 | 5.6 | 14.9 | 1.7 | 1.4 | 31.8 | |
Lignite | 27.8 | 24.9 | 36.9 | 10.4 | 71.0 | 4.3 | 23.2 | 1.1 | 0.4 | 26.7 | |
Notes: • wt % = percent by weight ar = as received maf = moisture and ash free |
- ↑ Cite error: Invalid
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- ↑ Cite error: Invalid
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- ↑ Cite error: Invalid
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- ↑ Chris Higman and Maarten van der Burgt (2008). Coal Gasification, 2nd Edition. Gulf Professional Publishers. ISBN 0-7506-8528-X.