Coal-Fired Power Generation Handbook. James G. Speight
Table 2.10 Comparison of Various Coal Classification Systems.
Finally, it is difficult (if not impossible) to treat coal classification and coal terminology as separate entities. Indeed, the terms applied to the various coals as a result of a particular classification system invariably displace some of the older and less specific names of the coals. Thus, because of the various systems which have originated in the coal-producing (as well as the coal-consuming) nations, several names may have evolved for one) particular type of coal (Table 2.10).
Such a profusion of names can make cross-referencing very difficult and it is beneficial for the coal scientist to become as familiar as possible with the various terminologies that exist. The only means by which this problem could be alleviated would be the establishment of a truly international; system for the classification and nomenclature of coal.
In summary, all classification schemes have similar objectives. However, a classification system meant exclusively for combustion application (such as coal-fired power generation) does not exist and is unlikely to be developed with the present approaches. Many classification schemes are restricted to two or three coal (typically less than six properties) properties and so the picture of the suitability of coal for a power plant may not be complete. If too many properties are involved, the classification can become complicated (if not, confusing). In general, rank, calorific value, proximate and ultimate analyses, fuel and atomic ratios and petrography seem to be the most important variables for characterizing the behavior of coal during combustion. Such properties are highly interrelated. It may be possible to develop a classification system using all these properties and still achieve a reasonably simple grouping – to this 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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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