洗选对煤结构及其热解特性的影响

Effect of Washing Process on the Structure and Pyrolysis Characteristics of Coal

为了探讨煤炭洗选对煤结构及其热解特性的影响,本文选择贺西煤矿原煤(RC)、精煤(CC)、尾煤(TC)和脱灰煤(DC),利用X射线衍射(XRD)及傅里叶红外光谱(FT-IR)分析了洗选前后煤炭的结构变化,通过热重(TG/DTG)实验研究了煤热解特性,并对热解焦微晶结构作出分析。结果表明:煤炭洗选前后主要是灰分变化,对煤炭微晶结构和大分子结构的影响并不明显;从微观角度分析发现洗选造成脂肪富氢程度(Hal/Har)和脂芳氢比降低,特别是化学处理造成脂链上富氢基团(CH3、CH2)的脱落,但对脂链结构没有影响。在煤的热解过程中,灰分的存在降低了煤炭的热解缩聚程度,增加了热解活化能,造成热解特征温度均向高温区推移;并阻碍了煤焦基本晶格单元纵向的热缩聚,抑制了煤焦的石墨化进程。

The samples of raw coal（RC）,clean coal（CC）,tailings（TC） and demineralized coal（DC） used in this study were provided by Hexi Coal.The effects of coal preparation on the coal structure and pyrolysis characteristics were investigated by XRD,FT-IR and TG/DTG,and the crystalline structure of pyrolysis char has been analyzed simultaneously in this paper.The results indicate that coal preparation has a notable impact on the ash content of coal and little effect on the microcrystalline structure and macromolecular structure of coal.On a micro level,it was found that coal preparation led to the decrease of aliphatic hydrogen-enriched degree and the ratio of aliphatic hydrocarbon and aromatic hydrocarbon（Hal/Har）,especially the loss of hydrogen-enriched group from the aliphatic chain caused by the chemical treatment,while have no effect on chain structures of aliphatic.In the process of coal pyrolysis,the existence of ash reduced the polycondensation degree of the chars,increased the reaction activation energy and pushed the process of the pyrolysis into high temperature scale.Moreover,the ash in chars also hindered the longitudinal coalescence of basic crystalline structure unit,and cramped the progress of char graphitizing.