Coal as-received

TABLE 27-3 Fischer-Assay Yields from Various Ranks of Coal (As-Received Basis)... 

Ubhayakar et al. [14] studied rapid devolatilization of pulverized coal in hot combustion gases, varying the input gas temperature between 1525 and 1975°C. They used three particle size distributions for the same type of coal as received, the fraction which remained on a 200 mesh screen and that which passed through the screen. The residence time in the gasifier was 7-70 x 10 s. The tests were conducted at a pressure of 1 atm, heating rates up to 10 °C/s, and volatile product yield up to 68% of the original dry-ash-free coal. 

Another possible correlation between coal structure and pyrolysis behavior is indicated by the temperature dependence of the evolution of pyrolytic water being strikingly different for the two coals. Figure 5 shows pyrolytic water evolution data for experiments in which the sample was heated at 1000°C/sec to the peak temperature indicated on the abscissa and then immediately allowed to cool at around 200°C/sec. The smooth curves are based on a single reaction, first-order decomposition model (7,8) and on the stated temperature-time history. Parameters used for the lignite have been published (8) while for the bituminous coal the Arrhenius frequency factor and activation energy were taken as 1013 sec"1 and 35 kcal/mol, respectively, with the yield of pyrolytic water ultimately attainable estimated from experimental measurements as 4.6 wt % of the coal (as-received). 

YIELD OF PYROLYTIC WATER, WT. / OF COAL (AS RECEIVED BASIS)... 

Basis 100 kg of coal as received The water formed on combustion is... 

The complex nature of coal as a molecular entity (2,3,24,25,35,37,53) has resulted ia the chemical explanations of coal combustion being confined to the carbon ia the system. The hydrogen and other elements have received much less attention but the system is extremely complex and the heteroatoms, eg, nitrogen, oxygen, and sulfur, exert an influence on the combustion. It is this latter that influences environmental aspects. 

Chemical Regeneration. In most MHD system designs the gas exiting the toppiag cycle exhausts either iato a radiant boiler and is used to raise steam, or it exhausts iato a direct-fired air heater and is used to preheat the primary combustion air. An alternative use of the exhaust gas is for chemical regeneration, ia which the exhaust gases are used to process the fuel from its as-received form iato a more beaeftcial oae. Chemical regeaeratioa has beea proposed for use with aatural gas and oil as well as with coal (14) (see Gas, natural Petroleum). 

Coal analyses are reported on severalbases, and it is customaiy to select the basis best suited to the application. The as-received basis represents the weight percentage of each constituent in the sample as received in the laboratoiy. The sample itself may be coal as fired, as mined, or as prepared for a particular use. The moisture-free (diy) basis is generally the most useful basis because performance calculations can be easily corrected for the ac tual moisture content at the point of use. The dry, ash-free basis is frequently used to approximate... 

The relationships between specific heat and water content and between specific heat and ash content are hnear. Given the specific heat on a dry, ash-free basis, it can be corrected to an as-received basis. The specific heat and enthalpy of coal to 1366 K (2000°F) are given in Coal Conversion Systems Technical Data Book (part lA, U.S. Dept, of Energy, 1984). 

Boron-containing carbons synthesized by co-pyrolysis of coal-tar pitch with pyridine-borane complex (series 25Bn) have already been considered as hosts for lithium insertion [4], Unlike the commercial graphites described above, the boron-doped carbon 25B2 (WUT) as received was not suitable for direct use in the cylindrical cell due to very large and hard particles. This feature makes the coating process very difficult. 

Each of these is reported in the proximate analysis. Coal analyses can be reported on several bases as-received, moisture-free (or dry), and mineral-matter-free (or ash-free). 

Pitch Coke and Petroleum Coke Pitch coke is made from coal-tar pitch, and petroleum coke is made from petroleum residues from petroleum refining. Pitch coke has about 1.0 percent volatile matter, 1.0 percent ash, and less than 0.5 percent sulfur on the as-received basis. There are two kinds of petroleum coke delayed coke and fluid coke. Delayed coke is produced by heating a gas oil or heavier feedstock to... 

The correlation of coal characteristics with liquefaction behaviour has received considerable attention (see, for example refs l-7> particularly since the renewed interest during the 1970s in the production of liquid fuels and chemical feedstocks directly from coal. As early as 1940, Storch and coworkers(8,9) demonstrated that coals containing up to 87% dmmf C give high yiel of soluble products (albeit under severe conditions) and materials which today would be classified as vitrinite and inertinite liquefy readily. More recently, the work... 

Figure 1. Relation of fixed carbon and heating value (dry, mineral-free basis) for Antarctic coal samples with less than 20% as-received ash...

All coals submitted to BCR for petrographic analysis are routinely checked for oxidation by comparing as-received analytical results with the established fresh coal R -volatile matter curve shown in Figure 1. Coals falling within reasonable limits of this correlation line (within Sy = 2.3%) are accepted as unoxidized all others are considered oxidized. 

Table I. Comparison of Coko Oven Stabilities Predicted from Highly Oxidized Coals on an As-Received and Corrected Basis...

Coal Blend No. A 500-lb. Oven Stability B As-Received Basis A-B C Corrected for Oxidation A-C... 

Tests on the activity of LP-produced Fe-based nanopowders for liquefaction of a sub-bituminous coal under high (688 K, 1 h of reaction) and low (658 K, 0.25 h of reaction) severity conditions have been reported.38 The catalysts tested were Fe7C3 (92 m2 g 1 (BET), particle size = 17 nm (XRD))and Fe XS (42 m2 g 1 (BET), particle size = 14 nm (XRD).38 For comparison, a commercial superfine iron oxide catalyst (SFIO, supplied by Mach I, Inc.) whose major phase has been identified in one study as y-Fe20339 (surface area = 195 m2 g 1 (BET), particle diameter = 3 nm (XRD)) and in other study as the ferrihydrite40 was also evaluated under similar conditions. The coal liquefaction experiments were carried out in 50 cm3 horizontal microautoclave reactors loaded with 3 g of sub bituminous Black Thunder coal and 5 g of tetralin used as hydrogen donor. Catalyst loadings of 0.7% and 1.4% of as-received coal... 

The final results of the proximate analysis of coal (ASTM D-3172 ASTM D-3173 ASTM D-3174 ASTM D-3175 ASTM D-5142 ISO 562) are usually reported to the first decimal place any subsequent figures have little or no significance. The final report of the analysis should always contain the results on a basis of air-dried coal (i.e., coal in its most stable condition and in which it was analyzed), but for purposes of classification or comparison it is often necessary to convert to another basis, such as dry coal, dry, ash-free coal, or as-received coal. 

The various forms of moisture in coal are described according to the manner in which they are measured by some prescribed standard method. These forms are (1) inherent moisture, (2) surface or free moisture, (3) total moisture, (4) air-dry loss moisture, (5) residual moisture, (6) as-received moisture, (7) decomposition moisture, and (8) water of hydration of mineral matter. 

---