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反复加卸荷煤体氧化特性研究

Study on the oxidation characteristics of coal under repeated loading-unloading

  • 摘要: 为研究采动载荷煤体因力学特性和孔裂隙变化发生初期氧化的演化规律,采用煤岩三轴蠕变、程序升温实验和FTIR、AFM技术对易自燃原煤样、反复加卸荷煤样进行氧化宏微观参数对比分析。研究表明,加卸荷煤样升温氧化过程中耗氧量和CO产生率均较前一工况增加,低温阶段,指标性气体参数值“骤降”和“陡升”点对应的临界温度值逐渐减小,加卸荷3次和加卸荷2次煤样较前一工况煤样增幅减小。加卸荷次数增加,氧化煤样中芳香烃含量逐渐增加,脂肪烃含量逐渐减少,羟基先减少后增多,羧基—COOH和羰基—C=O波峰呈“马鞍”状,判断出煤样氧化进程加快。煤体BJH比表面积、孔容值和吸附—脱附差量逐渐增大,可表征加卸荷作用致煤样中微孔增加,中孔、大孔塌陷裂变。加卸荷前3次较前一工况煤样的微观孔隙结构参数值增幅先增加后减小最终趋为0,综合加卸荷4次实验分析结果,推断出,实验工况的增加,煤体的微观孔隙结构参数值有减小的趋势,可证实存在最优的加卸荷次数(≥ 3次)和BJH比表面积(≥ 27.002 m2/g)使煤体氧化自燃能力最强。采掘工作面前方、煤层保护层及相邻近煤层受重复采动的影响,煤体孔裂隙再发育贯通性增强,破碎程度升高,氧化自燃的潜在危险性增大。

     

    Abstract: To investigate the evolutionary patterns of initial oxidation in coal subjected to mining-induced loads due to changes in mechanical properties and pore-fracture structures, coal rock triaxial creep tests programmed-temperature experiments,FTIR and AFM techniques were employed to conduct a comparative analysis of macro and micro parameters between raw coal samples prone to spontaneous combustion and coal samples subjected to repeated loading-unloading cycles. The study revealed that during the heating-oxidation process,the oxygen consumption and CO generation rates of loading-unloading coal samples increased compared to the previous working condition. In the low-temperature stage,the critical temperature values corresponding to the “sudden drop” and “sharp rise” points of indicator gas parameters gradually decreased,while the increase in these parameters for samples subjected to three and two loading-unloading cycles diminished compared to the prior working condition. As the number of loading-unloading cycles increased,the content of aromatic hydrocarbon in oxidized coal samples gradually rose,while the content of aliphatic hydrocarbon decreased. The content of hydroxyl group first declined and then increased,and the carboxyl (-COOH) and carbonyl (-C = O) peaks exhibited a “ saddle-shaped” trend, indicating an accelerated oxidation process. The BJH specific surface area,pore volume,and adsorption-desorption differential of the coal samples progressively increased,reflecting the growth of micropores and the collapse or fission of mesopores and macropores in coal samples due to loading-unloading effects. Compared with the previous working condition,the value of micro-pore structure parameters of the first three loading -unloading cycles initially rose,then declined,and eventually approached zero. Based on comprehensive analysis of four loading-unloading cycles,it was inferred that as experimental working conditions advanced,the microporous structural parameters of coal exhibited a decreasing trend. This confirmed the existence of an optimal number of loading- unloading cycles (≥ 3) and a BJH specific surface area (≥ 27. 002 m2/ g ) that maximize the oxidation and spontaneous combustion potential of coal. In mining faces,protective coal seams,and adjacent coal layers affected by repeated mining disturbances, the redevelopment and connectivity of cleat in coal is enhanced, and the degree of fragmentation is increased. The potential risk of oxidation spontaneous combustion is increased.

     

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