不同镜惰比低阶煤的结构特征及其热解行为

Structural characteristics and pyrolysis behavior of low-rank coal with different vitrinite/inertinite ratio

热解是煤液化、气化等洁净煤技术的基础,尤其是对于低阶煤的利用上。为进一步研究低阶煤的热解特征,以一系列不同镜惰比赵家庄(ZJZ)、马蹄罕(MTH)、豆塔(DT)煤(V/I分别为0.1、0.76、1.76)为研究对象,采用傅里叶变换红外光谱(FTIR)与X射线衍射(XRD)技术分析样品的化学结构;通过热重−质谱(TG-MS)联用技术,检查了样品在30~900℃的热解过程及其气体逸出行为。结果表明:不同镜惰比低阶煤中的化学结构含量有较大差异,与富惰质组ZJZ煤相比,富镜质组煤有着相对丰富的脂肪族结构,长脂肪侧链,以及含氧官能团,尤其DT煤中含有丰富的C-O。相应的芳香结构含量随着镜惰比增加而减少。同时,随着煤中镜惰比增加,芳香层片间距d_(002)、横向延展度与纵向堆砌高度之比(L_(a)/L_(c))增大,芳香层堆砌高度L_(c)、芳香层尺寸L_(a)以及堆砌层数N减小。DT、MTH、ZJZ煤在热解中失重量依次为36.4%、32.2%、28.9%,随着镜惰比降低,最终热解气态产物产率以及最大热解速率相应降低。在热解过程中有H_(2)、H_(2)O、CH_(4)、CO、CO_(2)等小分子物质释放;此外,释放气体含量与显微组分息息相关,富惰质组煤产生的小分子物质量少于镜质组较多的煤。由于镜质组中含有较多的脂肪侧链结构,芳香层之间的缩聚能力较强,热分解过程中容易形成自由基再结合生成气体。

Pyrolysis is the basis of clean coal technologies such as coal liquefaction and gasification,especially for the low-rank coal.To further investigate the pyrolysis characteristics of low-rank coals,a series of different vitrinite/inertinite ratio ZJZ,MTH,and DT coals(V/I:0.1,0.76,and 1.76 respectively)are used as the research objects.The chemical structure of the sample was analyzed with Fourier transform infrared spectroscopy(FTIR)and X-ray diffraction technology(XRD).The pyrolysis process and gas release behavior of coal samples at 30−900℃ was checked by TG-MS.The results show that the chemical structure content of low-rank coals with different V/I is quite different.Compared with the inertinite-rich ZJZ coals,the vitrinite-rich coals have relatively rich aliphatic structures,long aliphatic chains,and oxygen functional groups.Especially for DT coal,it has more C—O content.The corresponding aromatic structure content decreases with the increase of the mirror-inert ratio.With the increase of V/I in the coal,the aromatic layer spacing d002,the ratio of the aromatic layer size to the aromatic layer stacking height(L_(a)/L_(c))increase,and L_(c),La and the number of stacking layers(N)decrease.The weight loss ratio of DT,MTH,and ZJZ coal during pyrolysis is 36.4%,32.2%,and 28.9%respectively.As the V/I decreases,the final pyrolysis gaseous product yield and the maximum pyrolysis rate decrease accordingly.During the pyrolysis process,the small molecular gas,such as H_(2),H_(2)O,CH_(4),CO,CO_(2),are released;In addition,the content of released gas is closely related to the maceral composition.The mass of small molecules produced by inertinite-rich coal is almost lower than that produced by vitrinite-rich coal.Because the vitrinite in coal contains more aliphatic structures,and the polycondensation capacity between the aromatic layers is stronger,the free radicals fragment are easily formed during the thermal process and then combined into gas.