Coal, carbonization composition

Numerous tests indicated the factors that influence the results of shotfiring and showed, in particular, that variations in results are caused by changes in the composition of the methane-air mixture (e.g. when gas produced by coal carbonization, which is liable to variations in composition, or natural gas which varies in composition depending on its origin, was used for testing instead of pure methane). This emphasized the need to use a test gas of constant composition. 

Possible inter relationships of natural substances are important. Similarities of the low molecular weight alkane isomers from crude oil and Fischer-Tropsch synthesis product have been reported. A similar composition for high temperature coal carbonization has been found. The C4 to C7 alkane isomers from these sources can be calculated quantitatively with equations developed for Fischer-Tropsch products. A reversal of the concentrations of the monomethyl isomers from CG (2 Me > 3 Me) to C7 (3 Me > 2 Me) occurs in all three products comparisons at higher carbon numbers indicate some dissimilarities. Naphthene isomers for crude oil and high temperature coal carbonization also have similar compositions. Aliphatic hydrocarbons from low temperature coal processes are considerably different. The C1 isotopic composition of pure compounds from the various sources are being compared in order to provide information on their origin. 

The sorbent and leaching characteristics of fly ash can be related to operating temperatures in the boiler and to coal ash compositions that provide low ash fusion temperatures. Boiler temperatures that favor the fusion of the ash and maintain the ash in the fused state reduce the amount of trace elements leached from the fly ash and improve the sorbent characteristics of the fly ash for removal of these elements from ash pond effluents. In addition, the leachable amounts of each of the elements analyzed in this study can be correlated with the fly ash particle area and with their bulk compositions in the original coal. No correlation could be identified between the sorbent characteristics of fly ashes and their particle size and bulk, major, minor and trace elemental compositions, with the exception of the carbon content. Only organic removals, as measured by COD from ash pond effluent could be correlated with the carbon content of the fly ash particles. 

The anode carbon for the cell is usually a baked composite of calcined petroleum-coke filler bound with coal-tar pitch coke. The carbon composite may either be compacted into blocks which are baked before use in the cell (prebake anode), or be baked in place (as a single block) above the cell as the green paste moves downward toward the anode electrolytic face (Soderberg anode) (1,2.,.2D. For prebake cells, electrical connection is made by inserting a steel conductor rod, or pin, into the top of the anodes, Soderberg anodes may have either vertical (VS) or near-horizontal (HS) conductor rods. 

Figure 25. Translation of fiber strength and interlaminar shear stress (ILSS) of the carbon/carbon composites of Figure 24 after four impregnation and carbonization (1000°C) cycles with coal-tar pitch and 12.5% sulfur (34).

Figure 30. High-temperature strength of unidirectional carbon/carbon composites fabricated with rayon-based Thorne1 75 fibers and coal-tar pitch as matrix precursor to a density of 1.51 g/cmJ (31,54), in comparison with a 3D composite (55), pyrolytic graphite, and a commercial graphite.

Figure 31. Weight-loss of unidirectional carbon/carbon composites by isothermal oxidation in air, as affected by Zn2 207 inhibitor or by SiC coating (32,49) The composites were fabricated with 50 vol.-% high-modulus Modmor I fibers, coal-tar pitch as matrix precursor, four densification cycles, and final heat treatment to 1400°C.

Figure 34. Comparison of the flexural strengths of unidirectional carbon/carbon composites (left-hand side) with those of hybrid composites in which the final impregnation is made with an epoxy resin (34) The composites were fabricated with high-modulus fibers rigidized with phenolic resin, and subjected to four densification cycles with coal-tar pitch plus sulfur.

Coals, particularly the bituminous and sub-bituminous varieties, undergo primary decomposition in the temperature range of 700—800 K. If coal carbonization could attain thermodynamic equilibrium over this temperature range, the hydrocarbon products with the exception of methane, if any, would be decomposed mainly to carbon and hydrogen. In practice, thermodynamic equilibrium is not attained, and the composition of the hydrocarbon by-products is mainly determined by the temperature and the kinetics of the process. 

Thermoplastic carbon composite materials are a favonrable material combination for bipolar plates becanse they can be mannfactnred by the mass production process of injection monlding [102]. Electrical condnctivity of a carbon composite requires a high content of carbon, nsnally a mixtnre of graphite and active coal. The percolation limit of the graphite in the polymer binder has to be exceeded, leading to direct contact between graphite particles. Additionally, a basic condnctivity of the polymer matrix by the smaller active carbon particles is achieved. The injection... 

Table 4.4 Typical composition of benzole from coal carbonization...

The composition of coal tar varies with the carbonization method but consists, largely, of mononuclear and polynuclear aromatic compounds and their derivatives. Coke oven tars are relatively low in aliphatic and phenolic content while low-temperature tars have much higher contents of both. 

Prior to methanation, the gas product from the gasifier must be thoroughly purified, especially from sulfur compounds the precursors of which are widespread throughout coal (23) (see Sulfurremoval and recovery). Moreover, the composition of the gas must be adjusted, if required, to contain three parts hydrogen to one part carbon monoxide to fit the stoichiometry of methane production. This is accompHshed by appHcation of a catalytic water gas shift reaction. 

Cmde gas leaves from the top of the gasifier at 288—593°C depending on the type of coal used. The composition of gas also depends on the type of coal and is notable for the relatively high methane content when contrasted to gases produced at lower pressures or higher temperatures. These gas products can be used as produced for electric power production or can be treated to remove carbon dioxide and hydrocarbons to provide synthesis gas for ammonia, methanol, and synthetic oil production. The gas is made suitable for methanation, to produce synthetic natural gas, by a partial shift and carbon dioxide and sulfur removal. 

The conditions of pyrolysis either as low or high temperature carbonization, and the type of coal, determine the composition of Hquids produced, known as tars. Humic coals give greater yields of phenol (qv) [108-95-2] (up to 50%), whereas hydrogen-rich coals give more hydrocarbons (qv). The whole tar and distillation fractions are used as fuels and as sources of phenols, or as an additive ia carbonized briquettes. Pitch can be used as a biader for briquettes, for electrode carbon after coking, or for blending with road asphalt (qv). 

Anthracite. Anthracite is preferred to other forms of coal (qv) in the manufacture of carbon products because of its high carbon-to-hydrogen ratio, its low volatile content, and its more ordered stmcture. It is commonly added to carbon mixes used for fabricating metallurgical carbon products to improve specific properties and reduce cost. Anthracite is used in mix compositions for producing carbon electrodes, stmctural brick, blocks for cathodes in aluminum manufacture, and in carbon blocks and brick used for blast furnace linings. 

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