褐煤热解过程表面微观结构演变及水分吸附对自燃的诱导效应

Lignite is easy spontaneous combustion. It is generally believed that its spontaneous combustion is related to oxygen uptake, There is still a lot of controversy about the promotion or suppression of spontaneous combustion of lignite, mainly due to the fact that the mechanism of spontaneous combustion of water is still not fully revealed. In this paper, the transformation rules of Surface micro-structures in five kinds of coal samples were investigated systematically from minerals, functional groups, porosity and microcrystalline structure. The evolvement behavior of micro-structure was mainly reconstructed by small angle X-ray diffraction and low-field NMR. Evolutionary model and crushing mechanism were used to study the porosity and specific surface area evolution, and the applicability and error correction of the pore characterization technique were also analyzed. Secondly, the effects of the microstructure on the moisture content of the lignite were studied by thermogravimetric and low field, nuclear the desorption mechanism of the lignite was studied by using the in situ infrared technique, and the adsorption isotherm and penetration curve of the lignite were obtained by adiabatic reactor. The effects of single or two components of O2 and H2O on lignite, the effects of surface water and oxygen adsorption on the spontaneous combustion of lignite were studied. Finally, the kinetic model of oxidation reaction of lignite under water adsorption was established. The mechanism of spontaneous combustion of lignite under the action of water adsorption was explored.

褐煤易自燃，一般认为其自燃与吸氧有关，关于水分吸附对褐煤自燃是促进还是抑制仍存在很大争议，主要是因为水分对自燃作用机制至今仍未完全揭示。本课题计划从矿物质、官能团、孔隙、微晶结构四个方面系统地考察褐煤热解过程中表面微观结构的转化规律，利用小角X射线衍射和低场核磁技术考察其孔隙率及比表面积演变规律，同时还对孔隙表征技术的适用性和误差校正进行分析，建立热解过程中褐煤孔隙转变机理与模型，其次通过热重和低场核磁技术研究微观结构改变后褐煤对水分的吸、脱附特性，结合原位红外技术考察其水分赋存差异，确定热解过程褐煤水分吸、脱附机理；之后利用绝热反应器获得褐煤吸附等温线和穿透曲线，分别探讨单/双组份的O2 和H2O 在褐煤上的吸附平衡和吸附动力学，研究褐煤表面水、氧吸附耦合作用对其自燃的影响。在上述研究基础上，揭示水分吸附诱导作用下褐煤自燃反应机理，建立褐煤在水分吸附诱导下的氧化反应动力学模型。

本项目从矿物质、官能团、孔隙、微晶结构等方面系统地考察褐煤热解过程中微观结构的转化及其对水分吸附和自燃倾向的影响，获得热解过程中褐煤结构演变规律及水分子吸附机理模型并对水分吸附诱导作用下褐煤自燃反应机理进行了探索。首先利用质子核磁共振(1H-NMR)分析了半焦孔隙分布并基于三次样条插值法构建了函数模型，重点考察了温度阈值范围；其次考察了褐煤盐酸洗煤/焦微结构演变特性，发现盐酸洗脱的矿物质会抑制芳环的有序化排列，同时促进褐煤中芳环簇的缩聚，造成煤焦晶体结构缺陷增加；第三，利用1H-NMR、热重分析等技术分析了褐煤半焦(25-950℃)与水分子的吸/脱附过程，发现“醚键”在水分子吸附中起着特殊作用，300℃和950℃半焦中“醚键”含量较大，改变了褐煤水分子的变化趋势，延长了水分子脱附时间，煤样吸附水总量随热解温度增加先减小后增大，但最大吸附力先增大后减小，这是孔隙和含氧官能团相互作用的结果，基于上述分析，建立了褐煤水分子吸附机理模型；第四，考察了固有矿物质脱除及添加对煤样水分复吸性能的影响，发现固有矿物质含量与煤样的平衡吸附含水率(EMC)呈正相关，固有矿物质的脱除削弱了褐煤对水分子的吸附作用力，外加自燃残灰会促进煤样的吸附，其与煤样中的含氧官能团结合形成中间过渡态，增强煤表面水分子的结合力；最后，采用氧化炉-GC联用装置，对不同含水率样品进行低温氧化实验，考察气体产生变化规律，通过TG /DTG实验，考察了煤样的自燃倾向，结果表明，水洗煤比其他煤样的吸氧量大，着火点低，产生气体温度低，自燃倾向性高。水洗过程产生的油状漂浮物对抑制自燃有重要作用。本研究建立了褐煤热解过程孔隙演变模型，基于“醚键”对于褐煤水分吸附的特殊作用建立了褐煤水分吸附机理模型，提出矿物质与水分形成中间态，并加强了水分吸附力的矿物质吸附机理模型，并进一步获得水洗过程对褐煤吸氧量及自燃倾向的影响，为开发和应用褐煤清洁利用技术奠定理论基础。此外，本项目研发了新型褐煤提质工艺，并授权专利。