Coal classification

Coal classification is the grouping of different coals according to certain qualities or properties, such as coal type, rank, carbon-hydrogen ratio, and volatile matter. Thus, due to the worldwide occurrence of coal deposits, the numerous varieties of coal that are available, and its many uses, many national coal classification systems have been developed. These systems often are based on characteristics of domestic coals without reference to coals of other countries. However, it is unfortunate that the terms used to describe similar or identical coals are not used uniformly in the various systems. 

to classify coal, the calorific value and a proximate analysis (moisture, ash, volatile matter, and fixed carbon by difference) are needed. For lower-rank coals, the equilibrium moisture must also be determined. To calculate these values to a mineral-matter-free basis, the Parr formulas are used (ASTM D-388). 

Thus (Table 1.7), coal with a fixed carbon value in excess of 69% w/w or more, as calculated on a dry, mineral-matter-free basis, are classified according to the fixed-carbon value. Coal with a calorific value below 14,000 Btu/lb, as calculated on a moist, mineral-matter-free basis, is classified according to calorific value on a moist, mineral-matter-free basis, provided that the dry, mineral-matter-free fixed carbon is less than 69%. The agglomerating character is considered for coal 

Class Group Fixed Carbon Limits (%, Dry, Mineral-Matter-Free Basis) Equal to or Greater Less Than Than Volatile Matter Limits (%, Dry, Mineral-Matter-Free Basis) Equal to or Greater Less Than Than Calorific Value Limits (Btu/lb, Moist, Mineral-Matter-Free Basis) Equal to or Greater Less Than Than Agglomerating Character 

Group Number Alternative Group Parameters Sub- group Number Alternative Subgroup Parameters  

for example, possible to identify tarry substances and also their thermal decay products. Even artificially generated carbonaceous materials such as petroleum coke, soot, or wood char are revealed clearly. In the case of caking coals, the progress of caking can also be observed visually. 

In addition to organic substances, mineral matter appears under the microscope. Sometimes it is possible to determine the occurring species directiy (e.g., pyrite [Fe 2], carbonates). The thermal alteration of such substances occurring at well-defined temperatures can be further independent evidence for temperature estimation. 

Especially in the case of low-rank coals, it is sometimes possible to roughly estimate the fireshness of the sample because the degree of surface oxidation caused by air contact (weathering) can be observed. However, this can be also an early indicator that the coal may have a tendency for spontaneous ignition (see Section 3.10.3). 

Another problem remains, which is the wide scatter of different parameters within one rank or—seen from the other perspective—the variety of ranks for one volatile matter, heating value, or reflectance of vitrinite, which may be also contradicting each other in tendency. 

However, for engineering purposes, it is necessary to use a common nomenclature and, hence, the American Society for Testing and Materials (ASTM) and 

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On the macroscopic scale, two coal classifications have been used humic or banded coals and sapropeflc or nonbanded coals. Stratification in the banded coals, which result from plant parts, is quite obvious the nonbanded coals, which derive from algal materials and spores, are much more uniform. The physical and chemical properties of the different layers in a piece of coal or a seam can vary significantly. Therefore the relative amounts of the layers are important in determining the overall characteristics of the mined product. Coal petrography has been widely appHed in cokemaking and is important in coal hquefaction programs. 

Fig. 3. Simplified form of Seyler s coal classification chart (17). An updated version of Seyler s coal classification is described in Reference 6. Note that...

Ha.rd Coa.1, The amount of coal in international commerce since ca 1945 necessitated an international system of coal classification and in 1956 the Coal Committee of the European Economic Community agreed on a system designated the International Classification of Hard Coal by Type (3). Volatile matter and gross calorific value on a moist, ash-free basis are among the parameters considered. Table 4 shows the various classes of the international system and gives the corresponding national names used for these coals. 

Fig. 7. Coal classification system according to Hofmann where A = Eu plastic B = plastic C = Per plastic and D = Fluido plastic.

ASTM coal classification system, 6 710, 712 ASTM coating standards, 9 717 ASTM copper strip test, 23 624 ASTM D 381 chemical stability test,... 

Lignitic coal, classification by rank, 6 711t Lignocellulose, 5 367-368 10 295 Lignocellulose-based raw materials,... 

Seyler coal classification system, 6 709-710, 719 S-glass fibers, 26 758 SG sol-gel abrasives, 7 7 Shadow projection X-ray microscopy, 76 504... 

British system of coal classification used by the National Coal Board (15). ... 

Classilicalion of coals in Europe and other parts of the world differs somewhat from the American system. European classifications include ( ) the International Classification of Hard Coals by Type and (2) the International Classification of Brown Coals. These systems were developed by a Classification Working Party established in 1949 by the Coal Committee of die Economic Commission for Europe. The term "hard coal" is defined as a coal with a clorific value of more than 10.260 Blu per pound (5705 Calories/kg) on the moist, ash-free basis. The term "brown coal" refers to a coal containing less than 10.260 Blu per pound (5705 Calories/kg). In European terminology, ihe term "type" is equivalent to rank in American coal classification terminology and the term class approximates ihe ASTM rank. Space docs not permit a full comparison or the various systems. Reference to various ASTM publications is suggested. 

Determination of the volatile matter content of coal (ASTM D-3175 ISO 562) is an important determination because volatile matter data are an integral part of coal classification systems (Chapter 1) and form the basis of evaluating coals for their suitability for combustion and carbonization. The methods for determining volatile matter content are based on the same principle and consist of heating a weighed sample of coal (usually about 1 g) in a covered crucible to a... 

The fixed-carbon value is one of the values used in determining the efficiency of coal-burning equipment. It is a measure of the solid combustible material that remains after the volatile matter in coal has been removed. For this reason, it is also used as an indication of the yield of coke in a coking process. Fixed carbon plus ash essentially represents the yield of coke. Fixed-carbon values, corrected to a dry, mineral-matter-free basis, are used as parameters in the coal classification system (ASTM D-388). 

Apparent rank rank designation obtained on samples other man channel samples, but otherwise conforming to procedures of coal classification (ASTM D-388). 

Poland 114 and the World 2500 Classification, Properties and Uses of Coal. Coal is marketed in lumps, black or brownish in color, and in a wide range of sizes. Because of the technical and commercial importance of coal, many systems of classification have been proposed. Years of work by a technical committee of US and Canadian representatives resulted in the adoption in 1937 39 of "American Standards for coal classification which are now widely accepted and used... 

Maevskaja, V. N., Coal Classification with Reference to Spontaneous... 

As unifying, underlying concepts, type and rank certainly can be employed to envision why coals have the properties that they do. However, it is time for a reevaluation of coal classification concepts. How can we measure rank when we analyze coals of different types and when there is no simple rank progression even when vitrinite or vitrinite-rich coals are compared And how can we assess type when maceral identification criteria are highly subjective, except for reflectance measurements that routinely are not even applied to the liptinite and highly variable inerti-nite macerals And, finally, how can coals be classified scientifically when empirical and derived properties like calorific value and fixed carbon yield are employed as classifying parameters ... 

The ASA-ASTM system established four classes or ranks of coal anthracite, bituminous, sub-bituminous, and lignite, based on fixed-carbon content and heating value measured in British thermal units per pound (BTU lb ). Anthracite, a hard black coal that burns with little flame and smoke, has the highest fixed-carbon content, 86-98% and a heating value of (9.2-10.7) 10 J kg (Speight 2006, see Tables 2.51 and 2.55). This classification was already used 100 years ago (Robertson 1919) and Seyler (1900) used the C/H ratio for the coal classification, from lignite ( 10) to anthracite (>26). Based on raw coal, the chemical composition varies widely (in %) ... 

Coal classification is almost 200 years old and was initiated by the need to establish some order to the confusion of different coals. Thus, several types of classification systems arose (1) systems that were intended to aid scientific studies and (2) systems that were designed to assist coal producers and users. The scientific systems of classification are concerned with the origin, composition, and fundamental properties of coal, while the commercial systems are focused on market issues, utilization, technological properties, and the suitability of coal for certain end uses. 

European and American researchers in the nineteenth and early twentieth centuries proposed several coal classification systems. The earliest, published in Paris in 1837 by Henri-Victor Regnault (1810-1878), classified coal types according to their proximate analysis (determination of component substances, by percentage), that is, by their percentages of moisture, combustible matter, fixed carbon, and ash. This system is still favored, in modified form, by many American coal scientists (Speight, 2005). 

Eventually, the need arose to describe each individnal sample of coal in terms that would accurately (even adequately) depict the physical and/or chemical properties (Kreulen, 1948 Van Krevelen and Schuyer, 1957 Francis, 1961). Conseqnently, the terminology that came to be applied to coal essentially came into being as part of a classification system and it is difficult (if not impossible) to separate terminology from classification to treat each as a separate subject. This is, of course, in direct contrast to the systems nsed for the nomenclature and terminology of petroleum, natural gas, and related materials (Speight, 1990, 2007). Indeed, the coal classification stands apart in the field of fossil fuel science as an achievement that is second to none insofar as the system(s) allow classification of all the coals that are known on the basis of standardized parameters. 

Thus, there is a need to accurately describe the various coals in order to identify the end use of the coal and also to provide data which can be used as a means of comparison of the various worldwide coals. Hence, it is not surprising that a great many methods of coal classification have arisen over the last century or so (ASTM, 2011 ISO, 2011). 

Seyler s attempt at coal classification should not be ignored or discredited as it offered an initial attempt at an introspective look at coal behavior. 

The ASTM (2011) has evolved a method of coal classification over the years and is based on a number of parameters obtained by various presaibed tests for the fixed carbon value as well as other physical properties (Table 2.9) which can also be related to coal use (Figure 2.4). In the ASTM system, 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. 

Coal Classification according to Rank (ASTM System) ... 

National Coal Board (UK) System of Coal Classification... 

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