end principal component analysis may offer a solution under certain conditions. However, the choice of the variables will be critical and the outcome is to determine if the methodology and the analysis can be repeated satisfactorily for other combinations of variables.
References
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ASTM D388. Classification of Coals by Rank. Annual Book of ASTM Standards. Section 05.05. American Society for Testing & and Materials, West Conshohocken, Pennsylvania.
Berkowitz, N., and Schein, H.G. 1951. Heats of Wetting and the Spontaneous Ignition of Coal. Fuel, 30: 94-96.
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Carpenter, A.M. 1988. Coal Classification. Report No. IEACR/12. International Energy Agency, London, United Kingdom.
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3
Recovery, Preparation, and Transportation
3.1 Introduction
Coal is composed of complex mixtures of organic and inorganic compounds (Chapter 1) and must be handled in the correct manner to prevent accidents and spontaneous ignition as well as spontaneous combustion (Chapters 1, 4, 5) (Speight, 2013; CFR, 2012; Speight, 2020).
The organic compounds, inherited from the plants that live and die in the swamps cannot be counted with even a minute degree of accuracy. On the other hand, the more than 100 inorganic compounds in coal either were introduced into the swamp from water-borne or wind-borne sediment or were derived from elements in the original vegetation; for instance, inorganic compounds containing such elements as iron and zinc are needed by plants for healthy growth. After the plants decompose the inorganic compounds remain in the resulting peat. Some of those elements combine to form discrete minerals, such as pyrite (FeS2). Other sources of inorganic compounds used by the plants may be the mud that coats the bottom of the mire, sediments introduced by drainage runoff, dissolved elements in the mire water, and wind-borne sand, dust, or ash.
Coal may contain elements in only trace amounts (on the order of parts per million). Occasionally, some trace elements may be concentrated in a specific coal bed, which may make that bed a valuable resource for those elements (such as silver, zinc, or germanium). Some elements, however, have the potential to be hazardous (for example, cadmium or selenium), particularly if they are concentrated in more than trace amounts. Although as many as 120 different minerals have been identified in coal, only approximately 33 of these minerals commonly are found in coal, and, of these, only approximately eight minerals are sufficiently abundant to be considered major constituents.
When coal is combusted, as in a coal-fired power plant to generate electricity, most of the mineral matter and trace elements generally form ash. However, some minerals break down into gaseous compounds, which go out through the furnace flue. Pyrite, for example, breaks down into the individual elements iron and sulfur and each element combines with oxygen to become, respectively, iron oxide and an oxide of sulfur – the sulfur oxides are emitted in the flue gases while the iron oxide become part of ash.
In some highly oxidative conditions, ferric oxide (Fe2O3) may be formed.
Some trace elements also dissociate from their organic or mineral hosts when coal is
