Coal pretreatment

Alkylation Studies. Several preliminary experiments were completed to compare the extent of alkylation obtained with our coal pretreatment method to that obtained with Sternberg and Liotta alkylation. Results for Wyodak coal are summarized in Table III. Clearly, our procedure provides a very mild alkylation treatment compared with the other two methods and does not appear to be sensitive to differences in alkyl chain length (methyl vs. propyl). The increase in THF solubiliw was also small this result again suggests only a small extent of alkylation and in addition, shows that only minimal ion exchange (for example Ca by H ) occurred in the coal mineral matter. The effect of each pretreatment method on low severity liquefaction reactivity is discussed in the next section. 

Both reactions act to reduce hydrogen bonding within the coal structure which may have a direct positive impact on liquefaction reactivity. More indirectly, these reactions lower the concentration of OH species in coal-derived products and hence, reduce the extent of retrogressive condensation via ether bridge formation. Reducing production of THF-insoluble condensation products increases the net THF-soluble coal conversion observed during the liquefaction experiment. None of the spectra from coals pretreated with alkyl alcohols and HCl showed any significant evidence of alkylation at carbon sites in the coal. 

The first approach relies heavily on coal pretreatment. Although such pretreatment may be possible, the complete removal of inorganic minerals does not appear practical. 

The Fate of Some Trace Elements During Coal Pretreatment and Combustion... 

Ireland Mine coal pretreated with phenanthrene 15 1 15.6-... 

Hydrocarbonization processes are characterized by three primary independent variables - temperature, hydrogen pressure, and coal type - and five other, important independent variables -solid residence time, gas residence time, reactor configuration, coal pretreatment, and catalyst impregnation. Control of these variables permits control, over a wide range, of (1) the relative yields of liquid, gaseous, and solid products, (2) the quality of one or more of these products, (3) hydrogen consumption, and, ultimately (4) product cost. 

Hydrocarbonization yields may also be influenced by catalyst impregnation and coal pretreatment. For example, the yields of liquid and gasious products may be substantially increased by impregnation of the feed coal with ZnCl2 or other catalysts. (3)... 

In general, utilization of high-sulfur char as a boiler fuel does not appear to be economically attractive. Char may be utilized as a gasifier feedstock this possibility is particularly attractive when the char contains gasification catalyst used as a coal pretreatment prior to hydrocarbonization. Finally, as noted above, it is possible to optimize hydrocarbonization processes for the production of no net char. 

This decaking technique offers promise as part of an integrated coal pretreatment and high pressure steam-oxygen coal gasification process... 

Figure 1. Continuous-feed coal pretreatment unit...

Besides the visual evaluation from the agglomeration test, the volatile-matter content was chosen as the quantitative index of pretreatment severity. Operating experience with the hydrogasifier showed that minimum coal pretreatment must reduce the volatile matter to 24-26%. Various aspects of pretreatment are discussed in more detail below. 

Pittsburgh Coal Pretreated Ohio Coal Partially Hydrogasified Ohio Coal... 

All experiments used chars supplied by the Institute of Gas Technology. Char A was hydrogen-pretreated Pittsburgh Seam, Ireland Mine bituminous coal. Char B was also prepared from a Pittsburgh Seam, Ireland Mine coal pretreated (about 1 ft3 of oxygen/lb of fresh coal at... 

Materials evaluation in pilot plants covers all phases of the coal gasification process. Test specimens are installed in the coal pretreatment, gasification, gas quench systems, and methanation equipment in the plants. Three exposures, nominally 1, 3, and 6 months, at plant operating conditions are scheduled for each test location. Post-exposure corrosion evaluation employed in Phase II are the same as those used in other phases of the IITRI program, i.e., metallography combined with gravimetric analysis. 

Perhaps the most interesting studies are on the effeet of coal pretreatment, which enhances the magnetic properties of the mineral matter, on the subsequent magnetic separation. It has, for example, been shown that microwave treatment heats seleetively pyrite paitieles in coal without loss of coal volatiles, and converts pyrite to pyrrhotite, and as a result, faciUtates the subsequent magnetic separation. 

The importance of adequate coal pretreatment technologies must be emphasized many of the operating problems in cleaning plants are attributed to inadequate (inefficient) pretreatment, which results in large quantities of oversize (or undersize) material in the feeds to the various cleaning units which cause loss of cleaning efficiency, blockages, and even plant shutdown. 

At this time, a note on the various terms that relate to coal pretreatment is pertinent. 

In the presence of a solvent that has hydrogen-donating capabilities, the free radicals may abstract hydrogen from the solvent and, thereby, achieve stabilization (Gun et al., 1979). Thus, processes that produce char or coke are limited because the reactive intermediates lose their reactive capabilities and yield lower-molecular-weight species. Coal pretreatment also appears to have a beneficial effect on the liquefaction process (Rindt et al., 1992 Shams et al., 1992). 

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