Stability of coal

US coal prices have increased somewhat due to rising transportation costs (Figure 2.6). However, the overall trend in coal prices as measured at the mine (mine mouth) is downward as coal producers continue to find ways to increase the productivity of the average mine. The average delivered price for utilities increased just 5.7% during 2004 (EIA 2004), but 13.2% for industrial users. The widespread use of futures contracts in the coal industry has helped to keep prices stable. The overall stability of coal prices likely also will lead to a renewed interest in coal by utility officials and others, who until recently, believed natural gas was the fuel of the future. Anecdotal evidence purports an increase in coal use at the residential level. Homeowners with access to delivered coal found it is possible to heat less expensively with coal than natural gas or oil in the 2005-2006 heating season (Kamery 2006). 

Benefits of the Plant. The shortage of dumping space has led to a drastic increase in dumping costs, so that production of pure naphthalene by chemical refining is no longer economically possible. Development of this residue-free environmentally friendly process has made a decisive contribution to the stabilization of coal tar utilization in Germany. 

Jermy, C.A. and Bell, F.G. 1991. Coal bearing strata and the stability of coal mines in South Africa. Proceeding Seventh International Congress on Rock Mechanics, International Society Rock Mechanics, Wittke, W. (Ed.), Aachen, 2, A.A. Balkema, Rotterdam, 1125-1131. 

Eser, S., Song, C, Copenhaver, R.M., Perison, I, Schobert, H.H. (1990). Production of jet fuels from coal-derived liquids. Volume XV (Department of Materials Science and Engineering, Penn State University, University Park, PA) Thermal stability of coal derived jet fnels. Interim... 

GB/T 1573 2001 (2001) Determination of Thermal Stability of Coal. National Standards of the People s Republic of China, State Administration of Quality Supervision, Inspection and Quarantine,... 

The demand for energy is continually increasing and the highest energy consumption in the world occurs in the United States. In 1989 consumption totaled 8.6 x 10 MJ (81.3 x 10 Btu) or 11.7 metric tons of coal-equivalent per capita (85). World recoverable reserves were about 120 times the annual coal production in 1988 and about 10 times that for the additional reserves beheved to be in place (1). Estimated coal consumption reduces the known recoverable reserves at about 1%/yr. Whereas the use of bituminous coal is expected to continue to increase in terms of tonnage, the percentage of coal used in the United States has stabilized as shown in Table 11. 

Electric Power Generation. Coal is the primary fuel for thermal electric power generation. Since 1940 the quantity of bituminous coal consumed by electric utilities has grown substantially in each successive decade, and this growth is expected to continue for many years. Coal consumed by electric utilities increased from about 536 x 10 t in 1981 to 689 x 10 t in 1989 (2). The reasons for increased coal demand include availability, relative stability of decreasing coal prices, and lack of problems with spent fuel disposal as experienced in nuclear power plants (see Nuclearreactors). 

The sharpness of separation of the mineral from the gangue is dependent on (1) the stability of the suspension, which is influenced by the size of the medium (2) the specific gravity of the medium (3) the cleanliness of the medium (4) the cone angle (5) the size and ratios of the internal openings in the cyclone (inlet, apex, and vortex) and (6) the pressure at which the pulp is introduced into the cyclone. A 20° cone angle is the most common. Cyclone diameter will be determined by the separation to be made as well as by the capacity required. The 0.5- and 0.6-m (20- and 24-in) cyclones are most common in coal plants, whereas multiple cones of 0.25- or 0.3-m (10- or 12-in) diameter are used in higher-gravity separations. 

Size stability refers to the abihty of coal to withstand breakage during handhng and shipping. It is determined by twice dropping a 23-kg (50-lb) sample of coal from a height of 1.8 m (6 ft) onto a steel plate. From the size distribution before and after the test, the size stabdity is reported as a percentage factor (see ASTM D 440). The friability test... 

Several methods ean be employed to eonvert eoal into liquids, with or without the addition of a solvent or vehiele. Those methods which rely on simple pyrolysis or carbonization produce some liquids, but the mam produet is eoke or char Extraction yields can be dramatically increased by heating the coal over 350°C in heavy solvents sueh as anthraeene or eoal-tar oils, sometimes with applied hydrogen pressure, or the addition of a eatalyst Solvent eomponents whieh are espeeially benefieial to the dissolution and stability of the produets eontain saturated aromatic structures, for example, as found in 1,2,3,4 tctrahydronaphthalene Ilydroaromatie eompounds are known to transfer hydrogen atoms to the coal molecules and, thus, prevent polymerization... 

On our present course it is questionable whether economic oil and gas supplies will be available by the latter part of the century3. Although coal may be available for a century or two thereafter, it is more difficult and costly to transport throughout the world. Energy shortages may prevent the stabilization of world population at a decent standard of living. 

Conversion of coal to benzene or hexane soluble form has been shown to consist of a series of very fast reactions followed by slower reactions (2 3). The fast initial reactions have been proposed to involve only the thermal disruption of the coal structure to produce free radical fragments. Solvents which are present interact with these fragments to stabilize them through hydrogen donation. In fact, Wiser showed that there exists a strong similarity between coal pyrolysis and liquefaction (5). Recent studies by Petrakis have shown that suspensions of coals in various solvents when heated to 450°C produce large quantities of free radicals (. 1 molar solutions ) even when subsequently measured at room temperature. The radical concentration was significantly lower in H-donor solvents (Tetralin) then in non-donor solvents (naphthalene) (6). 

It has been proposed (17) that the portion of coal which is mobile under liquefaction conditions, contributes to the stabilization of thermally-generated radicals. Thus, coals which are highly fluid or contain large contents of extractable material might be expected to provide hydrogen and thus promote conversion. Collins has reported that vitrinite is a better donor of hydrogen than is Tetralin (20). Our own measurements of the aromatic content and elemental analyses of the coals (16,21) (or coal products) before and after conversion at short time are insufficient to confirm or deny the supposition that coal acts as its own H-donor even at short times. 

The fusible coals can give a high liquefaction yield if the high fluidity during the liquefaction is maintained by the liquefaction solvent to prevent the carbonization. The properties of the solvent required for the high yield with this kind of coal are miscibility, low viscosity, radical quenching reactivity and thermal stability not to be carbonized at the liquefaction temperature as reported in literatures (12). 

The important elementary reactions of coal liquefaction are the decomposition of coal structure with low bond dissociation energy, the stabilization of fragments by the solvent and the dissolution of coal units into the solution. 

A number of basic studies in the area of donor solvent liquefaction have been reported (2 -9). Franz (10J reported on the interaction of a subbituminous coal with deuterium-labelled tetra-lin, Cronauer, et al. (11) examined the interaction of deuterium-labelled Tetralin with coal model compounds and Benjamin, et al. (12) examined the pyrolysis of Tetralin-l-13C and the formation of tetralin from naphthalene with and without vitrinite and hydrogen. Other related studies have been conducted on the thermal stability of Tetralin, 1,2-dihydronaphthalene, cis-oecalin and 2-methylin-dene (13,14). 

Calculation of surplus wind generation Hourly time series of wind generation and electricity demand are used for the calculation of the surplus wind generation. Furthermore, some assumptions are made following the arguments in DENA (2005). At least 700 MW of nuclear power plants and 160 MW of coal power plants are necessary to secure grid stability. The transmission capacity of the grid is... 

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