煤矿采空区复采、厚煤层分层开采和封闭火区启封过程中普遍存在氧化煤复燃现象。为揭示不同氧化程度的煤复燃特性，选取预氧化过程中的氧浓度（简称“预氧化氧浓度”）作为关键影响因素，对原煤及其氧化煤自燃过程的增失重阶段、特征温度、动力学特性、热效应和官能团变化规律等方面开展了理论研究工作，并建立氧化煤自燃特性与微观结构之间的构效关系，研究结果对煤复燃防治工作具有积极指导意义。

选取陕北矿区长焰煤为研究对象，利用TG-DSC同步热分析仪，将研磨的新鲜煤粉分别在 0%、5%、10%、15%和 20%氧浓度下缓慢氧化，待温度升至 155℃时绝氧降温至常温，得到氧化煤组，取编号为 Y-0%、Y-5%、Y-10%、Y-15%和 Y-20%。根据TG-DSC同步热分析实验结果，得出原煤及其氧化煤自燃过程的重量变化呈现出阶段性特征，预氧化处理对氧化煤的增失重过程以及特征温度具有促进和抑制双重效应；基于 FWO和KAS等转化率法，得出氧化煤吸氧增重、燃烧失重阶段的表观活化能普遍低于原煤，其中Y-15%煤样最低，更易于发生氧化燃烧反应。以5℃/min升温速率为例，预氧化处理能够增加氧化煤燃烧反应的温度范围；相较于原煤，氧化煤吸热量降低、放热量增加，从热效应角度说明氧化煤更容易自燃。

根据傅里叶原位红外光谱实验得出，氧化煤的官能团种类与原煤相似，但含量有所差异。实验煤样的羟基谱峰强度表现为波动性变化趋势，且Y-15%煤样的羟基含量显著高于其余煤样；脂肪烃的谱峰强度呈先缓慢变化后加速减小趋势，直至450℃附近时降至最低，而且受预氧化作用影响，各煤样之间的脂肪烃含量反应初期差异性明显；芳烃Ar-CH 键、C=C双键稳定性较强，500℃后迅速裂解、消耗，其中Y-15%煤样C=C双键变化幅度最小，但其含量也相对较低；含氧官能团中，羰基含量加速升高，直至450℃后急剧降低，而醚键普遍表现为缓慢下降趋势。各实验煤样之间存在差异性的主要原因是官能团结构消耗与产生相互作用的宏观表现。

采用主成分分析理论，将实验煤样的11种微观结构通过2～3个主成分代替，以主成分得分系数绝对值为判定依据，筛选出不同主成分的关键性指标，并结合综合得分模型系数和归一化指标权重值，确定出吸氧增重阶段的关键活性基团主要有甲基、亚甲基，燃烧失重阶段为亚甲基、甲基、C=C双键和羰基，但不同实验煤样的关键活性基团种类有所区别。在此基础上，利用多元线性回归模型建立实验煤样吸氧增重、燃烧失重阶段的关键活性基团与表观活化能之间的构效关系，计算结果均满足数学模型的有效性和可靠性检验，为煤自燃深入研究及测定提供理论依据。

The phenomenon of oxidized coal reburning is common in the process of remining goafs, stratified mining of thick coal seam and unsealing of closed fire area. In order to reveal the reburning characteristics of coal with different oxidation degrees, the oxygen concentration in the pre-oxidation process, referred to as “pre-oxidation oxygen concentration”, was selected as the key influencing factor to carry out theoretical research on the weight loss stages, characteristic temperature, oxidation kinetics, thermal effect and functional group change law of the spontaneous combustion process of raw coal and oxidized coal, and the structure-activity relationship between spontaneous combustion characteristics and microstructure of oxidized coal are established. The research results have a positive guiding significance for the prevention and control of coal reburning.

The long-flame coal in the northern Shaanxi mining area was selected as the research object, and the ground fresh pulverized coal was slowly oxidized at 0%, 5%, 10%, 15% and 20% oxygen concentrations by (TG-DSC) synchronous thermal analyzer, respectively. When the temperature reached 155 °C, the nitrogen was introduced for anaerobic cooling to room temperature, and then “oxidized coal” samples were obtained, marked as Y-0%, Y-5%, Y-10%, Y-15%, and Y-20%, respectively. According to the experimental results of TG-DSC synchronous thermal analysis, it  is concluded that the weight change of the raw coal and its oxidized coal in the process of spontaneous combustion presents the characteristics of stages, and pre-oxidation treatment has dual effects of promoting and inhibiting the weight loss and characteristic temperature of oxidized coal. Based on the calculation results of FWO and KAS methods, it was found that the apparent activation energy of oxidized coal during the stages of oxygen absorption weight gaining and combustion weight loss were lower than that of raw coal, and the coal sample with pre-oxidized oxygen concentration of 15% was more prone to combustion reaction. Taking the heating rate of 5 ℃/min as an example, pre-oxidation treatment can increase the temperature range of the combustion reaction of oxidized coal. Compared with raw coal, the heat absorption of oxidized coal decreases and the heat release increases, which indicates that oxidized coal is more prone to spontaneous combustion from the perspective of thermal effect.

According to the Fourier transform in situ infrared spectroscopy experiment, the functional groups of oxidized coal are similar to those of raw coal, but the content is different. During the process of oxidation and heating, the hydroxyl group of the experimental coal samples showed a fluctuating trend, and the hydroxyl content of the Y-15% coal sample was significantly higher than that of the other coal samples; The peak intensity of aliphatic hydrocarbon spectrum first changes slowly and then decreases rapidly, and then decreases to the lowest near 450 ℃. Due to the influence of pre oxidation, the content of aliphatic hydrocarbon among coal samples has obvious difference in the initial stage of reaction; The Ar-CH bond and C=C double bond of aromatic hydrocarbons had strong stability, and it is rapidly cracked and consumed after 500 ℃, among which the C=C double bond of the Y-15% coal sample has the smallest change, and its content is relatively low; In the oxygen-containing functional group, the carbonyl content increases rapidly, and decreases sharply after 450 °C, the ether bond generally showed a slow downward trend. The main reason for the difference between the experimental coal samples is the macroscopic manifestation of the interaction between the consumption and production of functional group structure.

Using the principal component analysis theory, the 11 microstructures of the experimental coal samples were replaced by 2～3 principal components. Based on the absolute value of principal component load coefficient, the key indexes of different principal components are selected. Combined with the comprehensive score model coefficient and normalized index weight, it is determined that the key active groups in the oxygen absorption and weight gain stage are mainly methyl group, C=C double bond and carbonyl group, and the key active groups in the combustion weight loss stage are methylene group and methyl group. On this basis, the structure-activity relationship between key active groups and apparent activation energy of the experimental coal samples at the stages of oxygen absorption weight gaining and combustion weight loss were established by using the multiple linear regression model, and the calculated results all met the validity and reliability test of the mathematical model, which provides a theoretical basis for the in-depth study and determination of coal spontaneous combustion.

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