Organic coal properties

Pieces of coal are mixtures of materials somewhat randomly distributed in differing amounts. The mineral matter can be readily distinguished from the organic, which is itself a mixture. Coal properties reflect the individual constituents and the relative proportions. By analogy to geologic formations, the macerals are the constituents that correspond to minerals that make up individual rocks. For coals, macerals, which tend to be consistent in their properties, represent particular classes of plant parts that have been transformed into coal (40). Most detailed chemical and physical studies of coal have been made on macerals or samples rich in a particular maceral, because maceral separation is time consuming. 

The design of a new generation of conversion processes will require a deeper understanding of coal s intrinsic properties and the ways in which it is chemically transformed under process conditions. Coal properties such as the chemical form of the organic material, the types and distribution of organics, the nature of the pore structure, and the mechanical properties must be determined for coals of different ranks (or degrees of coalification) in order to use each coal type most effectively. 

Another factor that must be taken into acconnt in determining coal quality is the degree of coal oxidation. Oxidation may affect both the organic and inorganic components and may lead to deterioration of the coal properties. Another possible conseqnence of coal oxidation is the spontaneous combustion (Misra and Singh, 1994 Beamish et al., 2001 Lyman and Volkmer, 2001 Beamish, 2005). The propensity to oxidation is mainly determined by the coal s rank in conjunction, perhaps, with the maceral and mineral (e.g., pyrite) content. Low-rank coals are particularly prone to spontaneous combustion. Other factors, such as the access of air to coal stockpiles, may need to be controlled in order to reduce the risk of spontaneous combustion. Petrographic examination may help to identify coals that have become oxidized. 

The organic constituents of coal (liptinite, inertinite, and huminite/vitrinite) are individually and in combination (microlithotypes) fundamental to many coal properties. Vitrinite is the most common maceral group in many coals, especially in the Carboniferous coals of the Northern Hemisphere, and it is the properties of vitrinite, together with the variations in those properties with rank, that to a large extent determine the properties of the coal concerned. 

Physical Properties. Physical properties of waste as fuels are defined in accordance with the specific materials under consideration. The greatest degree of definition exists for wood and related biofuels. The least degree of definition exists for MSW, related RDF products, and the broad array of ha2ardous wastes. Table 3 compares the physical property data of some representative combustible wastes with the traditional fossil fuel bituminous coal. The soHd organic wastes typically have specific gravities or bulk densities much lower than those associated with coal and lignite. 

Although the molecular conformation of organic solids profoundly affects their properties, In the case of coals this characteristic has been little studied compared to their chemical composition and functionality Studies of coal at any level of structure are difficult because of the complex heterogeneity of any particular coal and the great variability of coal types that occur ... 

Coals are considered macromolecular solids.(l) Although they are not polymers in the sense that they possess a repeating unit, they do possess several fundamental properties typical of synthetic crosslinked polymers.(2) One of these properties is the ability of coals to swell in organic solvents without dissolving. 

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