The aim of this work has been to point out the possibility of using GACL process for chemical cleaning of brown coal Nováky (Slovakia) and Pittsburgh No. 8 coal. Simultaneous grinding and aqueous chemical leaching, which is the principle of the process, reduces the inorganic and inorganic sulfur content in both coals. Dearsenification nearly up to 96% is detected in GACL-treated samples of Nováky coal. The possibility of enhancing the recovery of humic acid as a consequence of GACL treatment is demonstrated. The process under study works under atmospheric pressure, temperature of 90°C and NaOH consumption, which is six times lower compared with the MCL process. Further research is needed to minimize the wear of grinding media and to improve the washing step.

Slovakian brown coal is a significant strategic resource of the power production sector of Slovakia. The coal is mined in five mines (Handlova, Cigel, Dolina, Zahorie and Novaky). Coal from Novaky is unique regarding its composition. It contains rare organic substances, and elevated levels of ash, sulfur and arsenic. The reduction of emitted oxides of the above components to environmentally acceptable levels, requires the use of costly combustion and post-combustion processing. This processing includes fluidized bed combustion and wet flue gas scrubbers using lime slurry. One possibility for increasing the coal quality for increased use without negative environmental impact, is cleaning before combustion. Physical methods of cleaning can be used for removing 80--90% of sulfide (mineral or inorganic) sulfur. The removal of organic sulfur by physical methods is not possible since extraction of sulfur from the coal matrix requires chemical reactions. Alkaline coal cleaning methods have been evaluated in the US. One process, known as MCL (Molten Caustic Leaching) is based on the interaction of molten NaOH and/or KOH with coal at a temperature of 350--400 C, for times in the range of 1--2 hours. After washing, the product fuel is relatively free of all mineral constituents, trace elements andmore » to a considerable degree, free of organic sulphur.« less

Controlled-atmosphere programmed-temperature oxidation (CAPTO) has been used to characterize several untreated/treated US and Chinese coals. The method involves measurement of evolved gas concentration versus temperature and is of particular interest for the characterization of chemically treated coals where classical methods may not be reliable. Coals characterized by this method exhibit distinctive CO{sub 2}, SO{sub 2}, and H{sub 2}O gas evolution profiles. From CAPTO data, a continuous plot of the H/C ratio versus temperature is readily accessible. The H/C ratio at lower temperatures is consistent with selective oxidation of predominantly non-aromatic organic structures. The ratio decreases with increasing temperature to a level consistent with oxidation of predominantly aromatic structures. To demonstrate the oxidative selectivity of CAPTO further, several US and Chinese coals were characterized. Using CAPTO, these coals were oxidized to a temperature corresponding with the minimum H{sub 2}O evolution observed between oxidation of non-aromatic and aromatic organic coal structures. Normal CAPTO conditions, consisting of: a sample dispersed in metal oxide; a plug flow stream of oxygen passing through the sample; and a slow linear temperature ramp, were used. If a selective oxidation is occurring, utilization of the temperature and conditions noted above should result in the oxidation of most ofmore » the non-aromatic organic structures in coal, while retaining most of the aromatic organic coal structures. The untreated and partially oxidized coals were analyzed using two methods: C CP-MAS NMR and CAPTO. Both methods show a striking decrease of non-aromatic organic structures in the partially oxidized coal samples in comparison with the untreated coals. The CAPTO profiles and the NMR results are discussed.« less

This paper describes the current status of an analytical procedure for the characterization of coal by programmed-temperature oxidation. Coal is mixed with a diluent to control the reaction and subjected simultaneously to oxidation and a linear increase in temperature up to 1000 °C. The evolved gases (CO2, H2O, SO2 and NO2) are monitored as functions of time and temperature. Distinctive evolution patterns are oberved among coals of different rank and between raw and treated coals. The SO2 evolution peaks obtained from oxidation of coal pyrite and decomposition of sulfate are resolved and appear at temperatures distinct from those observed from combustion of the organic structures in coal. Two major SO2 evolution maxima resulting from organic structures are observed. Each of the organic peaks has CO2 and H2O associated with it, implying that the organic matrix is oxidized in stages. Using model systems for comparison, these two major evolution maxima have been related to the probable structural types producing the evolutions. Analyses obtained with the oxidation procedure compare satisfactorily with ASTM values. Recent improvements in the oxidation conditions and detection system are discussed. The results obtained using the oxidation procedure to analyse model systems and numerous coals, including several treated coals, are discussed.