There are two fundamentally different lines of investigation of effective and environmentally friendly methods of salting coals treatment, which are being carried out at present. The first one assumes development of new ways of salting coals direct use without sodium and chlorinated addition agents removal. The second line assumes preliminary desalting with the subsequent use of the conditioned product in furnaces. Let us consider each of the mentioned approaches.
In Germany and England combustion of preliminary impoverished salting coal has been approved, with some clay added.[1,2] The solution is one of the simplest ones, but a considerable decrease in coal calorific efficiency reduces technical and economic indices of the process appreciably down to its unprofitableness.
Some engineering solutions provide for special addition agents to salting coals[3] (silicates of alkaline elements, silicic acids, quartz, magnesium oxide), which neutralize the negative effect of the alkaline salts while combustion. The experiments have shown the effectiveness of the method[4] but the addition agents usage worsens combustion processing indices, the way is considered to be uneconomical.
Several solutions are aimed at the development of new efficient technical means and ways of salting coals combustion. A.Lissner offered to burn the coals in special layer furnaces with furnace gas reclaiming and steam infusion. However, this method is only acceptable for furnaces of minor productivity.[5]
German scientists have attempted to create chloride burning furnaces which imply fuel burning at a lowered temperature and as fast furnace gas temperature reduction as possible which must decrease scorifying of the work surfaces. However, the probation of such furnaces has not given satisfactory results.
Some research on semicoking of salting coals has been done in Germany. It was observed that while processing of salting coal from Merceburg – East deposit, about 50% sodium oxide and 60-80% chlorine transform to semicoke.[6]
In the USA, Ukraine and Germany some experiments on salting coals liquefaction have been carried out. While hydrogenation of salting coals, any significant operating problems at the laboratory stage of the research have not been observed. Salting coals processing by hydrogenation has been recognized by scientists as a perspective line of research.
US scientists have observed that during open-air storage of salting coal for 8 weeks its natural cleaning from salt occurs due to the natural factors influence. This fact has some imperfections: its seasonal nature, desalting process dependence on the amount of atmospheric precipitation and, most importantly, active ground loosing in the area of the salting coal storage.
Several ways of salting coals treatment without desalting have been introduced by Ukrainian scientists (technologies of gasification, direct combustion, salting coals complex treatment).
The second line of research provides for preliminary coal cleaning from salt (desalting). Most of the suggested solutions are based on different variants of coal wet washing, in particular, the technologies of State Institute of Mineral Resources of Ukraine, RPA “Hymec”, Donetsk National Technical University.[7]
Researchers of DonNTU have developed a technology of desalting, based on the combination of wet washing and oil agglomeration processes. The suggested technology solves the problems in the field of mechanical dehydration of the washed coal and eliminates the phenomenon of secondary salt accumulation.
Crowngold G. and others have developed the original method of desalting, based on ion exchange. It allows reducing the sodium oxide content in salting coal ash by a factor of 20. However, the method did not find industrial application because of the high cost of the process.
Thus, the given overview shows that the problem of salting coals treatment is being actively investigated by scientists of different countries and some success has been achieved both in the field of salting coal direct use, and in the field of the coal cleaning from salt.
Links
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2. Hodges N.J., Lander W.R., Martin T.G. Clorene in Сoal: a Review of its Origin and Mode of Occurense.// J.Inst.Enegry. - 1983.№128. - P.158-169.
3. The Infiuense of Vineral Interactions upon the Behaviour during Combustion/ A.J. Botting, N.J. Hoges, D.G.Richards, F.O. Wood// Proc. Int. Conf. on Coal Sci.: - Tokio (Japan). - 1989 - Tom 1. - p.63-66.
4.Гоу М.Коррозионные действия примесей, содержащихся в топливе// Энергетика за рубежом. - M: 1965. - с.33.
5.Афанасенко Л.Я. Исследование характеристик и свойств засоленных углей Донбасса и их изменений при термической обработке. Авторефю дисю на соискание ученой степени канд. техн. наукю: 05.17.07/Харю политехню институт. - Харьков, 1990. - 20с.
6.Симонова В.В. Исследование состава, структуры и свойств соленых углей Западного Донбасса. Автореф. дис. на соискание ученой степени канд. хим. наук: 05.17.07/ Донецк Ин-т Физ.-орг. хим. и углехим. НАН Украины. - Донецк, 1992. - 121 с.
7.Исследование характера распределения соединений щелочный металлов в Новомосковском месторождении и обогатимости углей по соли путем промывки: Отчет о НИР/ Институт минеральных ресурсов Украины, руковод. Пожидаев С.Д. - № у41-9/484 - Д. - Днепропетровск, 1980. - 73 с.