Geology Reference
In-Depth Information
Proximate Composition
On a proximate basis, coal is composed of moisture, mineral matter, volatile matter, and fixed carbon (Table 1.1.3)
(ASTM, 2007; Hessley et al., 1986). Although one of the first effects of coalification is removal of H
2
O, some
physically and chemically bound H
2
O remains in coal. Volatile matter includes gases that are released by thermal
decomposition (pyrolysis) of coal, such as hydrogen, carbon monoxide (CO), methane, and other hydrocarbons, tar
vapors, ammonia, CO
2
, and H
2
O vapor other than residual moisture. The fixed carbon is the solid combustible
material in coal, the nonvolatile organic portion. It is estimated by difference, subtracting the percentages of
moisture, ash, and volatile matter from 100. The heating value and rank of the coal increase with increased fixed
carbon content (Figure 1.1.7). On a practical basis, coals are usually compared on a moisture and mineral matter-
free (mmmf) or dry ash-free (daf) basis.
Table 1.1.3
Examples of variation in proximate composition (wt.%) and calorific value (MJ/kg) of coal by rank.
Moisture
*
Ash
*
Calorific value
†
Coal rank
Volatile Matter
Fixed Carbon
Lignite
‡
29.86
*
26.5
*
35.43
8.06
23.0
Subbituminous
‡
36.42
*
37.8
*
14.74
10.97
33.5
Bituminous
‡
43.14
*
41.0
*
6.97
7.87
36.0
6.9
§
31
║
69
║
High-volatile bituminous
5.1
>
<
35.6
1.5
§
0.2
§
31
║
69
║
Medium volatile bituminous
36.0
0.8
§
1.2
§
22
║
78
║
Low-volatile bituminous
36.4
0.6
§
8.32
§
14
║
86
║
Semianthracite
36.0
1.4
§
1.6
§
8
║
92
║
Anthracite
35.2
2
║
98
║
Meta-anthracite
<
>
Note: The data should not be considered representative.
*
As received.
†
White (2002).
‡
White and Theisen (1913).
§
Kosanke (1952).
║
ASTM (2005).
100
an
ma
sa
lvb
80
mvb
hvCb
hvAb
60
sub C
sub B
Lignite
hvBb
sub A
Peat
40
5
6
7
8
9
10
11
12
13
14
15
16
Heating value, 10
3
Btu, mineral-matter-free
Key
sub A Subbituminous A
sub B Subbituminous B
sub C Subbituminous C
hvAb High-volatile A bituminous
hvBb High-volatile B bituminous
mvb Medium-volatile bituminous
l vb Low-volatile bituminous
sa Semianthracite
an Anthracite
ma Metaanthracite
hvCb High-volatile C bituminous
Figure 1.1.7. Progressive increase in fixed carbon and heating value for ranks of coal from peat to anthracite.
From Kim and Kissell 1988, p. 19.
