Coal rank defined

Coals (the plural is deliberately used because coal has no defined, uniform nature or structure) are fossil sources with low hydrogen content. The structure of coals means only the structural models depicting major bonding types and components relating changes with coal rank. Coal is classified, or ranked, as lignite, subbituminous, bituminous, and anthracite. This is also the order of increased aromaticity and decreased volatile matter. The H C ratio of bituminous coal is about 0.8, whereas anthracite has H C ratios as low as 0.2. 

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. 

The overall objective of current fluorescence studies at Southern Illinois University at Carbondale is to determine the kinds and relative amounts of fluorescent macerals in various coals and to classify and discriminte them on the basis of their fluorescence spectra. Additional objectives are to define the manner in which the fluorescent macerals vary with coal rank, and to determine which of the macerals are of primary and secondary origin. 

The most serious problem in the study of humic substances is the lack of reproducibility of analytical results. One would expect soil humates to vary with soil type, aquatic humates to vary with water sources, and coal humates to vary with coal rank. But even within one well-defined source, the elemental composition will vary between samples, depending on extraction and fractionation procedures. There are cases in which the same authors have used the same source and the same extraction procedure and have obtained significantly different elemental analyses. Before any meaningful structural conclusions can be deduced from elemental analysis, a rational definition of humic substances will have to be established (MacCarthy, 1976 Malcolm and MacCarthy, 1979). 

Although coal rank plays an important role in defining coal use, coal type and coal grade are also extremely important consideration (Table 4.12). These parameters are the primary factors that influence a coal s specific physical and chemical properties and these properties in turn determine the overall quality of the coal and its suitability for specific purposes. 

High-volatile bituminous coal Three related rank groups of bituminous coal as defined by the ASTM, which collectively contain less than 69% fixed carbon on a dry, mineral-matter-free basis more than 31% volatile matter on a dry, mineral-matter-free basis and a heat value of more than 10,500 Btu/lb on a moist, mineral-matter-free basis. 

The maceral content defines the coal type sapropelic, with >50% liptinite, or humic, more abundant, usually presenting a banded structure. On the other hand, based on the different optical properties of macerals, the reflectance of vitrinite is an essential characteristic used in coal identification and related to rank. A good analysis of maceral content provides knowledge about the chemical composition of a coal, their behavior in different conversion processes, and can also be used as a parameter of coal rank (see section on Petrographic analysis). 

Low pressure low density polyethylene (LDPE), 70 595 Low pressure tanks, 24 288 Low Q-state, 74 674 Low rank coal, defined, 6 828 Low resistivity joints, 23 847 Low silica zeolites, 76 833... 

Subbing formulations, gelatin in, 12 444 Subbituminous coal, 6 703 classification by rank, 6 1 lit defined, 6 829... 

The above observations point to the importance of rank and depositional environment in defining the molecular characteristics of the mobile phase as well as the network phase of coals. 

The M2.J, pyrograms for the pure Inertlnltes representative of the two lower rank coal subsets (Figures 3 and 4) Indicate little molecular mobility In the temperature region of coal thermoplasticity (l.e. 700 K). However, the well defined minimum... 

Generally we will be interested in comparing the relation between reaction rate and rank under different reaction conditions. If we define the reactivity of a coal under certain reaction conditions as the ratio of its reaction rate to the reaction rate of a standard coal, from Equations 1 and 2 we can write that... 

Semibituminous Coat. Coal that ranks between bituminous coal and semianthracile. It is harder and more brittle than bituminous coal, has a high fuel ratio and bums without smoke. Semibituminous coal is also known as metabituminous coal which is defined as containing 89-91.2% carbon, analyzed on a dry. ash-free basis. The term smokeless coal also is used. 

There have been many attempts to define solvent behavior in terms of one or more physical properties of the solvent, and not without some degree of success. However, it is essential to note that the properties of the coal also play an important role in defining behavior of a solvent, and it has been reported that the relative solvent powers of two solvents may be reversed from one coal type to another. Thus, two properties that have found some relevance in defining solvent behavior with coal (as well as with other complex carbonaceous materials, such as petroleum asphaltenes) are the surface tension and the internal pressure (Speight, 1994, p. 201). However, the solvent power of primary aliphatic amines (and similar compounds) for the lower-rank coals has been attributed to the presence of an unshared pair of electrons (on the nitrogen atom). 

Slag Viscosity/Composition Correlations. Several attempts have been made in the past to define the linear portion of the viscosity/ temperature curve based on the composition of the coal ash. In the mid-1960 s, workers at the British Coal Utilization Research Association (BCURA) developed. two such correlations based on work with British (bituminous) coals, now generally referred to as the Watt-Fereday (4) and S (3) correlations (6). Unfortunately, attempts to apply this correlation to low-rank coal slags, using either ash or slag composition data, have been generally unsuccessful. 

Blom et al. (20) presented a correlation between the amount of oxygen estimated to be present in coal as carboxyl groups and rank as defined by carbon content (daf). Figure 4 compares their correlation with the amount of oxygen evolved as C02 during pyrolysis of some 19 different coals of varying rank and represents results from this and from four other laboratories (7,21-25). Final temperatures ranged from... 

Because of the complexity of the coalification processes, different measures are used to define different levels of rank (Table I) high moisture, low heating value, and nonagglomerating character of the coal define the rank (group) within the lignite and subbituminous classes and volatile matter (or fixed carbon) define the various groups of rank in the bituminous and anthracite classes. In addition to these properties, the reflectance of vitrinite, carbon content of the coal (dry, mineral matter free), and some other properties change proportionately as rank increases (Table I). 

Oxidation-corrosion data obtained from the pilot plants generally compare well with laboratory data in ranking of high-temperature alloys. Pilot plant results, however, indicate more severe corrosion than laboratory oxidation-corrosion data. This should be expected because of cyclic operation of pilot plants and additional variables comprising the pilot plant environments. The contribution of erosion and erosion-corrosion by coal ash, char, and sulfur sorbents to the corrosion process in the pilot plants has not been defined. 

The coalification process (coal-forming process) is, simply defined, the progressive change in the plant debris as it becomes transformed from peat to lignite and then through the higher ranks of coal to anthracite (Francis, 1961 Sunavala, 1990). 

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