alone is extremely difficult. Nevertheless, the attempt by Seyler to classify coal should not be ignored or discredited as it offered an initial attempt at an introspective look at coal behavior.
The American Society for Testing and Materials has evolved a method of coal classification over the years; it is based on a number of parameters obtained by various prescribed tests for the fixed carbon value as well as other physical properties which can also be related to coal use (Table 2.4, Table 2.5). In the ASTM system (ASTM, D388), coal is classified based on certain gradational properties that are associated with the amount of change that the coal has undergone while still beneath the earth. The system uses selected chemical and physical properties that assist in understanding how the coal will react during mining, preparation and eventual use.
Figure 2.2 Classification by the Seyler System.
Thus, coal can be divided into four major types; (i) anthracite coal, (ii) bituminous coal, (iii) subbituminous coal, and (iv) lignite coal which show considerable variation in properties (Table 2.5). For the purposes of this text, peat is not classified as being a member of the coal series and, therefore, in this book peat is not included in this system of coal classification (Chapters 1, 2).
Anthracite is coal of the highest metamorphic rank; it is also known as hard coal and has a brilliant luster, being hard and shiny. It can be rubbed without leaving a familiar coal dust mark on the finger and can even be polished for use as jewelry. Anthracite coal burns slowly with a pale blue flame and may be used primarily as a domestic fuel.
Bituminous coal ignites relatively easily coal burns with a smoky flame and may also contain 15-20% w/w volatile matter. If improperly burned, such as a deficiency of oxygen, bituminous coal is characterized with excess smoke and soot. It is the most abundant variety of coal, weathers only slightly, and may be kept in open piles with very little danger of spontaneous combustion, although there is evidence that spontaneous combustion is generally considered to be a factor of extrinsic conditions such as the mining and storage practices and the prevalent atmospheric conditions (Chapter 4) (Berkowitz and Schein, 1951; Berkowitz and Speight, 1973; Chakravorty, 1984; Chakravorty and Kar, 1986; Speight, 2013). Bituminous coal is used primarily as fuel in steam-electric power generation, with substantial quantities used for heat and power applications in manufacturing and also to produce coke.
Table 2.4 Coal classification according to rank (ASTM D388).
| Class and group | Fixed carbona (%) | Volatile mattera (%) | Heating valueb(btu/lb) |
| Anthracitic | |||
| 1. Meta-anthracite | >98 | <2 | – |
| 2. Anthracite | 92–98 | 2–8 | – |
| 3. Semianthracite | 86–92 | 8–14 | – |
| Bituminous | |||
| 1. Low-volatile bituminous coal | 78–86 | 14–22 | – |
| 2. Medium-volatile bituminous coal | 69–78 | 22–31 | – |
| 3. High-volatile A bituminous coal | <69 | >31 | >14,000 |
| 4. High-volatile B bituminous coal | – | – | 13,000–14,000 |
| 5. High-volatile C bituminous coal | – | – | 10,500–13,000c |
| Subbituminous | |||
| 1. Subbituminous A coal | – | – | 10,500–11,500c |
| 2. Subbituminous B coal | – | – | 9,500–10,500 |
| 3. Subbituminous C coal | – | – | 8,300–9,500 |
| Lignitic | – | – | |
| 1. Lignitic A | – | – | 6,300–8,300 |
| 2. Lignitic B | – | – | <6,300 |
aCalculated on dry, mineral-matter-free coal.
bCalculated on mineral-matter-free coal containing natural inherent moisture.
cCoals with a heating value of 10,500–11,500 btu/lb are classified as high-volatile C bituminous coal if they have agglomerating properties and as subbituminous A coal if they are nonagglomerating.
Table 2.5 Typical properties of coal.
| Sulfur content in Coal |
| Anthracite: 0.6-0.77% w/w |
| Bituminous coal: 0.7-4.0% w/w |
| Lignite: 0.4% w/w |
| Moisture content |
| Anthracite: 2.8-16.3% w/w |
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Bituminous
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