Effect Of Hydrothermal Treatment On The Physico-chemical Properties Of Low Rank Coal

Low rank coal has the characteristics of high moisture, high volatile matter and high chemical reactivity characteristics etc, prone to moisture readsorption and spontaneous combustion after drying. Therefore, to seek effective deep dehydration upgrading technology is the key problem to low rank coal utilization. Among the low rank coal upgrading technologies, because of its good effects of dehydration and deep upgrading of low rank coal, hydrothermal upgrading technology has become a popular research field in recent years.Based on the above background, this paper choose Huolinhe lignite as the main object. When studying the hydrothermal dehydration and improvment of the quality of low rank coal physicochemical characteristics, we treat the coal under a nitrogen atmosphere to thermally upgrade for comparison, focusing on upgrading low rank coal moisture relapse and the change of spontaneous combustion characteristics. In addition, in order to solve the problems existing in the conventional hyd rothermal upgrading technology, the experimental method of separation was used to treat the low rank coal under saturated steam conditions, and hydrothermal upgrading samples was verified by comparing the technical feasibility. Through the different effect of different forms of water, the mechanism of water in the process of lignite was also studied.Research results show that the the carbon element content of lignite by hydrothermal upgrading increases, with oxygen content decreased, which are closer to higher rank coal. The surface of lignite tends to be smooth and dense, and effecrt of thermally upgraded under nitrogen atmosphere on rhe surface was not obviously. The oxygen functional groups of hydrothermal upgrading coals were significantly reduced and with temperature increasing, the removal of functional groups was significantly enhanced and the amount of removal is larger than that of conventional thermal treatment. The moisture adsorption ability of hydrothermal upgrading low rank coals decreased significantly and decreased faster than those under nitrogen heat treatment. With temperature rising, quality and water content of coal sample declined further, which with the interior of the lignite containing oxygen functional groups on the removal of highly connected. The spontaneous combustion tendency of hydrothermal lignite decreased after upgrading, but the upgrading process does not have a significant impact on the combustion performance. So compared to conventional thermal processing, the hydrothermal method has a better performance for dehydration and upgrading for low rank coals.The coal quality change of saturated steam coal upgrading is close to the hydrothermal upgrading. After the upgrading process, the moisture content of lignites decreased significantly, which equal to the reduce of water holding capacity; the element contentof carbon increased, with the oxygen and AO / C content decreased; the surface of saturated steam upgraded coals were partly similar to the hydrothermal coals, becoming smooth and dense with but some granular structure existing; saturated steam upgrading have a good performence on the removing of oxygen-containing functional groups, which is better than pure heat upgrading but slightly worse than conventional hydrothermal upgrading process. Different forms of water may play an important role in the removal process of oxygen-containing functional groups in the lignite. In the upgrading process water can promote the removal of oxygen-containing functional groups, which is closely related to the water forms. The effect liquid water on the removal of oxygen-containing functional groups is larger than saturated steam water. The results of this study show that the upgrading of coal-water separation process has similar performance with hydrothermal upgrading process, with high technical feasibility.