The key causes and characteristics of spontaneous combustion of coal seams affected by igneous intrusion
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摘要: 为探明火成岩侵蚀导致侵蚀煤层自燃特性变化的关键致因，以受火成岩侵入范围广、煤自然发火严重的铁法煤田大兴煤矿为研究对象，采集火成岩侵蚀形成的变质煤和未受影响的原生煤进行研究。本文利用同步热分析仪、煤自燃特性测定装置等测试了煤样的产热升温特性、气体产生规律、微观结构参数的差异。结果表明，变质煤在低温阶段的放热量较原生煤显著提高，交叉点温度降低了13.2 ℃，更早进入氧化增重阶段；当环境温度超过90 ℃，变质煤的氧化产热与反应速率急速增加，CO和CO2等氧化气体产物生成速率显著升高，表明变质煤的氧化活性高于原生煤；火成岩侵蚀煤层的高温高压作用改变了煤体的孔隙结构，导致煤中有机物质热解与挥发，使得变质煤中的微孔和介孔孔容减小、比表面积降低，宏观孔的孔容达到原生煤的3倍，平均孔径和孔隙率显著增大，有利于氧气分子在煤体内部的输送运移与吸附反应，同时变质煤的含氧官能团较原生煤减少，脂肪烃含量由27.98 % 提高至29.07 %，增强了变质煤的氧化活性。此外，火成岩侵蚀活动导致侵蚀煤层开采时漏风加剧、遗煤氧化时间长、氧化带范围广。火成岩对煤层自然发火内在因素和外在因素的影响，导致侵蚀煤层面临严重的煤自燃灾害。Abstract: In order to find out the key causes of changes in spontaneous combustion characteristics of igneous intrusive coal seams, this paper took the Daxing Coal Mine in Tiefa Coalfield as example for analysis, which was widely invaded by igneous and had serious coal spontaneous combustion disasters.Metamorphic coal and unaffected primary coal were collected from the study area.Specifically, this paper studied the patterns of heat production and temperature rise, gas production rules, and microscopic structure parameters of coal samples by synchronous thermal analyzer and coal spontaneous combustion characteristic measuring device.The experimental results show that the igneous intrusion caused the mutation in the spontaneous combustion characteristics of the coal.Compared with the primary coal, there was significantly higher oxidation heat release of the metamorphic coal at the low temperature stage.Also, the crossing point temperature of metamorphic coal was reduced by 13.2 ℃, and it entered the stage of oxidation and weight gain earlier than the primary coal.When the environment temperature exceeded 90 ℃, the oxidation heat generation and reaction rate of metamorphic coal increased rapidly, which showed higher oxygen consumption rate and faster generation rate of oxidative gas products such as CO and CO2.This demonstrated higher oxidation activity of metamorphic coal than that of primary coal.The analytic results of physicochemical microstructure showed that the high temperature and pressure of igneous intrusion changed the pore structure of coal, which reduced the pore volume and specific surface area of micropores/mesopores in metamorphic coal, and the pore volume of macropores was three times higher than that of primary coal.The average pore size and porosity increased significantly, which was conducive to the transport, migration and adsorption reaction of oxygen molecules in the coal structure.At the same time, igneous intrusion reduced the oxygen-containing functional groups of metamorphic coal, and the content of aliphatic hydrocarbons with higher activity increased from 27.98 % to 29.07 %, which enhanced the oxidative activity of metamorphic coal.Moreover, igneous intrusion caused problems such as increased air leakage, long oxidation time of left coal, and wide oxidation zone during the mining, eventually leading to severe coal spontaneous combustion disasters.
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图 3 煤样氧化升温过程中炉温与煤温的变化曲线
Figure 3. Variation of coal temperature and furnace temperature during oxidation process
图 6 煤样在不同环境温度阶段产热与温升特性
Figure 6. Characteristics of heat production and temperature rise of coal samples in different ambient temperature stages
图 8 煤样孔径分布与阶段进汞量关系曲线
Figure 8. Relation curve between pore size distribution and stage mercury intake of coal
图 11 变质煤破碎后原始赋存气体与氧气置换示意图
Figure 11. The replacement of naturally occurring gas and oxygen after crushing metamorphic coal
表 1 实验煤样工业分析结果
Table 1. Proximate analysis of coal samples
% 煤样 工业分析 镜质组反射率Ro Mad FCad Vad Aad 原生煤 4.70 54.64 32.58 8.08 0.62 变质煤 3.49 64.66 23.43 8.42 1.14 
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表 2 煤样孔结构特征参数
Table 2. Pore structure parameters of coal samples
煤样 BET比表面积/(m2·g-1) 平均孔径/nm HK微孔孔容/(mm3·g-1) BJK介孔孔容/(mm3·g-1) 原生煤 15.5 4.85 5.05 10.9 变质煤 3.94 7.99 1.19 4.21
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表 3 煤样中各主要活性基团谱吸收峰面积占比
Table 3. Infrared absorption peak area proportion of main functional groups in coal
% 煤样 脂肪烃 芳香烃 含氧官能团 矿物 CH3/CH2/CH C=C OH、C=O、COOH等 钙矾石、硫铁矿等 原生煤 27.98 7.09 61.85 3.08 变质煤 29.07 7.17 56.70 7.06
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