Page 36 - New Trends In Coal Conversion

Coal 5

The degree of coal metamorphism (coalification degree) is denoted as the coal rank,
and it involves a progressive decrease in moisture and volatile functional groups with a
consequent increase in the carbon content of coal (Table 1.1). Coal rank is, therefore,
the property that makes it possible to distinguish the various classes of coals (usually
incorrectly called “types of coal” from the commercial point of view) existing in nature.

1.3 Coal resources

Coal resources refer to the amount of coal contained in a deposit or coalfield before
exploitation. However, not all coal resources are recoverable using the current avail-
able technology. After centuries of coal exploration, the location, size, and character-
istics of most coal resources worldwide are reasonably well known (World Coal
Association, 2018a). The assessed level of coal resources does not show any signifi-
cant variations with time, but the level classified as proved recoverable reserves tends
to be variable with time.

1.3.1 Geographical distribution of coal
The distribution of worldwide coal deposits is uneven, which is the result of peat for-
mation at different times in the geological record in predominantly tropical latitudes
and the subsequent drift of the continents to their present-day positions. The major re-
gions with coal deposits are located in the Northern Hemisphere, whereas the regions
in the Southern Hemisphere, with the exception of Australia, are relatively deficient in
this type of resource (Fig. 1.4).

1.3.2 Distribution of coal by geological age

The age of the coalfields is well known (Fig. 1.5) mainly because they have been thor-
oughly investigated, especially in the case of coalfields of economic interest. The
earliest coals in the geological record are of the Devonian age, but they are very scarce
and of little or no economic significance (Walker, 2000). The main coal deposits started
to develop during the Carboniferous period, particularly after the mid-Carboniferous.
There are three different geological periods (eras) in which coal was developed as fol-
lows: (1) the Paleozoic (Mid-Carboniferous and Permian), (2) the Mesozoic (end of the
Triassic and Cretaceous), and (3) the Cenozoic (Tertiary: Paleogene and Neogene).
Coalfields of economic importance of the Carboniferous age are mainly located in
the Eastern United States, Eastern Canada, Europe, CIS (Commonwealth of Indepen-
dent States or Russian Commonwealth), China, and some places in the Far East (e.g.,
North and South Korea, Laos, etc.). Carboniferous coals were the first to be exploited
at industrial scale because the most significant deposits of coals of this age occur pre-
dominantly in the Northern Hemisphere (Figs. 1.4 and 1.5). Permian coals are mainly
found in Australia, India, South Africa, South America, China, CIS, and to a lesser
extent in the Eastern United States, Eastern Canada, and the Far East.