The present study involved the assessment of potential generation of acid drainage from a coal mining area in India. Laboratory-based static and kinetic tests on overburden samples were conducted. Results of the static tests using acid base accounting indicate that all samples may be acid generators, and their generation capacity varied between likely, possible and low. To verify the acid generation potentiality of those samples showing a high acid drainage production in the static test, the kinetic test, using humidity cell, was conducted for a period of 15 weeks. The samples were leached with simulated rain water to mimic the chemical weathering under controlled laboratory conditions and imitate actual mine site leaching. Data obtained from chemical analysis of collected leachate were used to estimate production and reaction rates of acid generation and neutralizing capacity. Based on the kinetic test, it can be concluded that presently the neutralizing capacity of the samples is better than the oxidation capacity (acid generation). But due to the high weathering rate of carbonates, as reflected by the simulated leaching test, the neutralizing materials (carbonates) will eventually be exhausted earlier (since they showed dissolution rate) than the acid generation species (sulfates). Thus, acid drainage production is predicted from that point of time, when the neutralizing capacity has been exhausted for these mine sites.

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The coal-zinc chloride reaction, especially the pyrolytic behavior of zinc chloride impregnated coal (with 525% loading), has been reinvestigated. This reinvestigation appears to provide a deeper insight into the mechanism of the reaction and hence the nature of the coal structure. One of the crucial findings which has emerged is that a specific dehydrogenation, e.g., about &12% of the total hydrogen (in the bituminous range) in coal, is caused by ZnCl, well below pyrolytic conditions (even as low as 240 "C). Furthermore, a parallelism has also been observed between the coal-zinc chloride reaction on the one hand and the coal-aluminum chloride reaction (Scholl's reaction) on the other, insofar as both the nature and the extent of "dehydrogenation" are concerned, as well as the aftereffects of the reaction on the pyrolytic behavior in both cases. Attention is also drawn to a similar change in pyrolytic behavior that was observed earlier, Le., partial (but specific) or controlled dehydrogenation with S, Se, or halogens. On the basis of the above parallelisms, an interpretation of the coal-zinc chloride reaction is advanced along with some observations on the nature of the structure of coal.The coal-zinc chloride reaction received considerable attention since Georgiadis and Gaillard first observed' some remarkable changes in the pyrolytic behavior of some coking coals when they were impregnated with 3-4% ZnC1, and pyrolyzed at and up to 525 "C at the rate of 3 "C min-'.These were (1) a decrease in plasticity, (2) an increase in char yield with a corresponding decrease in tar yields (by about 2-3%), and (3) the evolution of a significantly greater volume of molecular hydrogen in gas. Similar findings, though quantitatively different, have since been reported by Bodily et a1.2-6 while extending the same investigation to a noncoking low-rank bituminous coal (Utah coal, % C = 79.5). With 12% ZnClz impregnation and a heating rate of 5 "C min-l, volatile matter was found to decrease by about 15%, which was reflected in near suppression of tar formation and, conversely, in the increase of char yield to a similar extent. Such a remarkable (and, at the same time, drastic) alteration in pyrolytic behavior was ascribed by these authors3" to be due to in situ dehydrogenation of hydroaromatic structure caused by ZnC1, during the early stages of the pyrolysis. In fact, evidence in support of the evolution of a significant proportion of hydrogen well below 400 "C (being initiated at as low a temperature as 200 "C) was noted versus very little or no hydrogen for untreated coal in the same temperature range. In support of this interpretation, earlier work by Mazumdar et a1.+l1 on coal dehydrogenation and the observation of almost complete inhibition of tar formation dependent upon the prior dehydrogenation of coal with either sulfur, selenium, or halogens were cited. Furthermore, the conceptlOJ1 of the origin of primary tar being essentially due to the hydroaromatic moieties of coal was also considered relevant to the interpretation...

Two Illinois He,rdn No. 6 coals and one Illinois showspromisefor the direct combustionof coalfor SpringfieldNo. 5 coal were separately combusted power generationin a cost-effective, reliable, and in a laboratory-scale (15-cm dia) pressurized environmentally acceptablemanner. Severaldemofluidized-bedcombustor(PFBC) combined with an nstrationand commercial plants are already being alkali sorber. These coals were combusted in a operated {1"aI.In PFBC/GTCCS, the high-temperafluidized bed of Tymochtee dolomite at ture, high-pressure(HTHP) flue gas exitingfromthe temperatures ranging from 910 to 950°C and a PFBC combu._,lor is expandedthrougha gas turbine system pressure of 9.2 atm absolute. Alkali-vapor to recoverthermal energyfor improvedoverallcycle emission (Na and K) in the PFBC flue gas was efficiency. To protect the gas turbine from erosion determined by the analytical activated-bauxite and hot corrosion, the entrained ash particulates sorber bed technique developed at Argonne and alkalis (such as chlorides and sulfates of National Laboratory.The test results showed that sodium and potassium)in the PFBC flue gas must sodium isthe major alkali-vapor speciespresentin be reducedto acceptable levels. the PFBC flue gas, and that the level of sodiumvapor emissioninc,'easeslinearlywith both Na and Alkaliexistsin bothcoal and 'the sorbent.In PFBC, CI contents in the coals. This suggests that the alkali can be transported to the gas turbine as sodium-vapor emission results from direct particulates and vapors. Several HTHP particulate vaporization of N_LCIpresent in the coals. The cleanup devices (such as SiC candle, ceramic measuredalkali-vaporconcentration(Na + K), 67 to membranecross-flow,and granular-bedfilters)have 90 ppbW, is more than 2.5 times greater than the been demonstrated to achieve acceptable allowable alkali limitof 24 ppb for an industrial gas particulate reduction for gas turbine systems. turbine. Combusting these coals in a PFBC for However, alkalivapor is still a concern because of power generationmay requiredevelopinga method its potential penetrability through the particulate to controlalkali vapors, cleanup devices. Alkali-vapor emission from coal can be functionsof coal and sorbentmineralogyand