Coal distribution

The prevention of coal-gas dynamic disasters in coal mines is the worldwide problem (He 2010), and threat seriously the safety of the underground hves of mine workers and high production efficiency. Coal-gas dynamic disasters include coal and gas outburst, gas (and coal dust) explosion, rock burst and larger roof fall, etc, and affected by coal distribution, minefield layout, mining technology and other factors. 

Because of the randomness of cave gangue and residual coal distribution, the goaf area is com-sidered as isotropic porous media. Permeability does not change with time ... 

The major areas of coal distribution are principally in the Northern Hanisphere with the exception of Australia, the southern continents are relatively deficient in coal deposits. This relatively uneven distribution is the result of the deposition and maturation of the plant at different times in the geological past in predominantly tropical latitudes, and the subseqnent drift of the continents to their present-day positions. The oldest coals of any economic significance date from the Middle Carboniferous Period— the earliest geological strata in which coal has been identified are of Devonian age bnt they are generally of little economic significance. With the exception of parts of the Triassic Period, major coal deposits have been forming somewhere in the world throughout the last 320 million years. Sedimentary sequences of the last 2-3 million years do not contain coal— there has been insufficient time for them to develop from plant debris. 

Cylindrical or conical metal sheets (skirt) The simple and robust standard design for noncaking coals is the so-called Bosman s skirt, which is a fixed metal cylinder as shown in Figure 6.36. The coal distribution can be supported by a hanging cone or cone ring. The space outside the coal-filled skirt is filled with product gas that streams toward the gas outlet [188,189]. 

Sasol produces synthetic fuels and chemicals from coal-derived synthesis gas. Two significant variations of this technology have been commercialized, and new process variations are continually under development. Sasol One used both the fixed-bed (Arge) process, operated at about 240°C, as weU as a circulating fluidized-bed (Synthol) system operating at 340°C. Each ET reactor type has a characteristic product distribution that includes coproducts isolated for use in the chemical industry. Paraffin wax is one of the principal coproducts of the low temperature Arge process. Alcohols, ketones, and lower paraffins are among the valuable coproducts obtained from the Synthol process. 

Other includes net imports of coal coke and electricity produced from wood, waste, wind, photovoltaic, and solar thermal sources connected to electric utihty distribution systems. It does not include consumption of wood energy other than that consumed by electric utiUty industry. 

Coal, tar, and heavy oil fuel reserves are widely distributed throughout the world. In the Western hemisphere, Canada has large tar sand, bitumen (very heavy cmde oil), and coal deposits. The United States has very large reserves of coal and shale. Coal comprises ca 85% of the U.S. recoverable fossil energy reserves (6). Venezuela has an enormous bitumen deposit and Brazil has significant oil shale (qv) reserves. Coal is also found in Brazil, Colombia, Mexico, and Pern. Worldwide, the total resource base of these reserves is immense and may constitute >90% of the hydrocarbon resources in place (see... 

Step 4 of the thermal treatment process (see Fig. 2) involves desorption, pyrolysis, and char formation. Much Hterature exists on the pyrolysis of coal (qv) and on different pyrolysis models for coal. These models are useful starting points for describing pyrolysis in kilns. For example, the devolatilization of coal is frequently modeled as competing chemical reactions (24). Another approach for modeling devolatilization uses a set of independent, first-order parallel reactions represented by a Gaussian distribution of activation energies (25). 

Analysis. Analyses of a number of lignitic coals are given in Table 3. Figure 1, a distribution plot of 300 U.S. coals according to ASTM classification by rank, indicates the broad range of fixed carbon values (18). According to the ASTM classification, fixed carbon for both lignite and subbituminous coals has an upper limit of 69%, but in practice this value rarely exceeds 61%. 

SASOL. SASOL, South Africa, has constmcted a plant to recover 50,000 tons each of 1-pentene and 1-hexene by extractive distillation from Fischer-Tropsch hydrocarbons produced from coal-based synthesis gas. The company is marketing both products primarily as comonomers for LLDPE and HDPE (see Olefin polymers). Although there is still no developed market for 1-pentene in the mid-1990s, the 1-hexene market is well estabhshed. The Fischer-Tropsch technology produces a geometric carbon-number distribution of various odd and even, linear, branched, and alpha and internal olefins however, with additional investment, other odd and even carbon numbers can also be recovered. The Fischer-Tropsch plants were originally constmcted to produce gasoline and other hydrocarbon fuels to fill the lack of petroleum resources in South Africa. 

Another preparation method is a sintering process where phosphate ore, sand, and coal are blended together and ignited on the grates of a sintering machine. Air is pulled through the blend, and the entire mass is allowed to bum. The resulting fused bed of material is then cmshed and screened to the appropriate size distribution, and the undersized material is reprocessed. 

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