温度和压力耦合作用下煤体瓦斯解吸−氧化特性与孔隙结构演化

    Desorption-oxidation characteristics of gas in coal and evolution of pore structureunder coupled temperature-pressure effects

    • 摘要: 针对深部开采“三高一扰动”环境下采空区煤自燃与瓦斯耦合灾害问题,通过物理相似模拟实验,系统研究了赋存温度与赋存压力的协同作用对采空区遗煤瓦斯解吸特性、煤自燃特性及孔隙变化特征的影响机制。研究结果表明:预吸附温度升高导致煤样瓦斯解吸量下降,且降幅随温度升高愈发显著;预吸附压力增大则会显著提升瓦斯解吸量,但增幅随压力升高逐渐趋缓;在温度低于110 ℃时,CO主要源于物理吸附态瓦斯解吸,在温度高于110 ℃后,其体积分数随温度升高呈指数型增长,可作为煤自燃的早期预警标志气体;CO2由于来源多样性,不宜作为煤自燃预测标志气体;C2H6来源于煤中固有烃类脱附与煤−氧反应,可作为煤自燃辅助预警标志气体;C2H2在140 ℃时开始出现,其生成温度相对较低;305工作面煤样等温吸附曲线均属 II 型,吸附回线呈 H3 型;压力升高促使煤样微孔闭合,大孔占比增加,进而导致煤样总孔体积和比表面积均减小,压力作用使表面分形维数降低、孔隙分形维数升高,煤样表面趋于光滑而孔隙结构复杂化;温度升高使煤样总孔体积和比表面积下降,温度作用使表面分形维数升高、孔隙分形维数降低,导致煤样表面粗糙化及孔隙分布均匀化,两者影响规律相异。温度和压力耦合作用下,温度升高会促进煤样瓦斯解吸,加剧煤自燃倾向;压力增大则会增强煤样瓦斯吸附作用,进而抑制煤自燃进程。因此,采煤过程中,需探明煤层瓦斯赋存温度和压力,监测瓦斯释放与自燃风险,以保障安全生产。

       

      Abstract: Aiming at the coupled disasters of coal spontaneous combustion and gas in goafs under the “three highs and one disturbance” geological environment of deep mining, physical similarity simulation tests are performed to systematically investigate the synergistic effects of in-situ temperature and in-situ pressure on gas desorption performance, spontaneous combustion characteristics and pore evolution of residual coal in goafs. The results show that the rise of pre-adsorption temperature reduces the gas desorption capacity of coal samples, and the reduction becomes more obvious with increasing temperature. The increase of pre-adsorption pressure remarkably improves the desorption amount of gas, whereas the growth rate gradually slows down as pressure rises. CO is mainly produced from desorption of physically adsorbed gas below 110 °C, and its volume fraction increases exponentially above 110 °C, which can be adopted as an early warning indicator gas for coal spontaneous combustion. Due to multiple generation pathways, CO2 is not suitable for coal spontaneous combustion prediction. C2H6 originates from both desorption of inherent hydrocarbons in coal and coal–oxygen oxidation, and can serve as an auxiliary early-warning indicator gas for coal spontaneous combustion. C2H2 is first detected at 140 °C with a relatively low initial generation temperature. The isothermal adsorption curves of coal samples from working face 305 belong to type II, and the adsorption hysteresis loops are type H3. Increasing pressure leads to micropore closure in coal samples and the growth of macropore proportion, thereby reducing total pore volume and specific surface area of coal samples; rising temperature also decreases total pore volume and specific surface area. Pressure reduces surface fractal dimension but elevates pore fractal dimension, resulting in smoother coal surface and more complex pore structure. In contrast, temperature increases coal surface fractal dimension and decreases coal pore fractal dimension, contributing to rougher coal surface and more uniform pore distribution; temperature and pressure exert opposite influences on pore structure. Under coupled thermo-pressure effects, increased temperature facilitates gas desorption and aggravates coal spontaneous combustion propensity, while increased pressure strengthens gas adsorption and restrains coal spontaneous combustion development. Accordingly, the in-situ temperature and pressure of coal seams should be clarified during coal mining, and gas emission as well as spontaneous combustion hazards need continuous monitoring to guarantee safe production.

       

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