Study On Thermal Degradative Solvent Extraction Of Low-Rank Coals

The disadvantages of low-rank coal, such as high moisture content and low heating value, limit the efficient use of it. So the developing of coal upgrade technologies is essential to achieve the high efficiency and cleaning usage of low rank coal. As an efficiency coal upgrading technology, the thermal degradative solvent extraction could get the upgraded coal and high value extraction at the same time by organic solvent or water extraction. In this paper, the influence of the kind of coal, the solvent coal ratio, the moisture on the yields and properties of thermal extraction products were studied firstly. Then, the influence of solvent recycle was studied to lay foundation for the method’s application. At last, the pyrolysis and combustion properties of upgraded coal by thermal degradative solvent extraction was studied.The result of five kinds of Chinese low rank coal solvent extraction studies shows that the yields of products related with the H/C, the coal with higher H/C had a higher product yield. The study of the influence of coal solvent ratio on solvent extraction suggests that the yields of extracts were no changing with the decrease of coal solvent ratio before reduced to about to 5-7.5:1. When the ratio less than 5-7.5:1, the yields of extracts were significantly decreased. The study of the influence of moisture on solvent extraction shows that the moisture of coal could promoted the solvent extract of coal.The influence of solvent recycle on solvent extraction was also studied in this paper. With the increasing of solute concentration, the yield of soluble(SL), the extract soluble at the room temperature, was decreased; the yield of deposit(DP), the extract soluble at high temperature and insoluble at room temperature, was increased. The total yield of extract include DP and SL was not changed. The FTIR spectrums of SL and DP show the aromatic degree of SL and DP decreased. The ultimate analysis of product shows that the H/C ratio increased, the O/C ratio decreased. The pyrolysis of products shows that a part of SL which has a higher molecular weight might turn into DP with the increase of recycle numbers. So that the DP and UC were the target product of thermal extraction.The pyrolysis and combust properties of upgraded coal by solvent extraction were studied. Compared with the raw coal, the pyrolysis activities of upgraded coal was weakened. It is because a part of volatile in coal was separated by the solvent extraction. The combust test shows that the combust activities in air of upgrade coal’s char was strengthen than the raw coal’s char.