Page 49 - New Trends In Coal Conversion

Coal 17

moderately high, and high ash coals. As can be seen, this ISO-11760 (2005) system provides
a simple classification method of descriptive categorization that can be applied to coal sam-
ples of all ranks, as long as the exact nature of the sample is known. Such samples may
include core seam sections, composite samples, raw coals, washed coals, blends of coals hav-
ing a similar coal rank and selected size fractions. This system of classification also provides
a method of comparison of coals as long as certain key characteristics are taken into account
and guidance to select the appropriate ISO standard procedures for coal analyses.
China has developed its own coal classification system (Shen Zhou Mining and Resources,
2007) on the basis of the volatile matter content by which coals are classified as brown coal,
bituminous coal, and anthracite. Brown coals are in turn classified into two types according to
the moisture content (in %) and the gross calorific value (MJ/kg moist, ash-free basis). Bitu-
minous coals are grouped according to some properties related to the potential/capacity of
coal to agglomerate during inert-atmosphere thermal treatment such as caking index, plastic
layer, and dilatometric characteristics. Finally, anthracites are subdivided into three cate-
gories according to their volatile matter content (% dry, ash-free basis).

1.5.2 Characterization of coal for industrial use

1.5.2.1 Coal utilization
Coal has many different and important uses worldwide. The most important are those
related to power generation, steel production, cement manufacturing, and as a liquid
fuel. In addition, other important users of coal (World Coal Association, 2018b)
include alumina refineries, paper manufacturers, and the chemical and pharmaceutical
industries. Coal and its derivative products are employed as precursors of other mate-
rials of high added value such as carbon materials (activated carbons, carbon fibers,
etc.). Coal combustion products (CCPs) are also used in the concrete industry, and
some of the leading players in the metal recovery sector are developing routes to
recover bulk minerals as well as metals from fly ash. On the other hand, commercial
metal extraction from coal is not new, and vanadium and silver extraction from
enriched coal sources dates back to more than two centuries ago, while germanium
extraction is still active (Tolhursth, 2018).
The conversion processes in which coal is used are mainly combustion, gasifica-
tion, liquefaction, and carbonization, the latter chiefly for the manufacture of metallur-
gical coke. Taking into consideration the different and varied uses of coal, a coal must
obviously be characterized before it is used, whether as a single coal or blended coal, to
determine its properties and quality and to predict its technological behavior with a
view to its end use. This characterization will determine whether the coal or coal blend
can or cannot be used commercially.

1.5.2.2 Coal characterization: analysis and test

Testing and assessing a coal takes into account first its rank, washability, hardness, and
inherent moisture content, followed by analyses of its chemical, physical, rheological,
and microscopic properties, and finally specific pilot tests depending on the end use
envisaged for the coal. As with coal sampling, national and international standard