液氮冻融对煤体孔隙演变和吸附行为的影响研究
Effect of liquid nitrogen freeze-thawing on coal body pore evolution and adsorption behavior
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摘要: 为探究液氮冻融对煤体孔隙结构和吸附行为的影响，采用低温氮气和二氧化碳吸附法对冻融前后煤样孔隙结构进行表征，并开展了不同冻融次数下甲烷等温吸附实验。结果表明：冻融后煤样的滞后指数HI降低，孔隙系统的连通性得以改善，有利于煤中气体的运移；2~100 nm孔隙在冻融后均有不同程度的增加，一些孔隙演变为比自身孔径更小甚至小于2nm的孔隙；冻融后微孔孔径分布发生了变化，微孔孔容和微孔吸附量增加；随着液氮处理次数增加，对甲烷最终吸附量的影响不断减弱，达到4次处理后，液氮处理对煤体最终吸附量的影响几乎达到饱和；煤样经不同次数的液氮处理后朗格缪尔参数VL和pL均增加，pL越大越有利于煤层气的开采。Abstract: To investigate the effect of freeze-thawing of liquid nitrogen on the pore structure and adsorption behavior of coal, the pore structure of coal samples before and after freeze-thawing was characterized by low-temperature nitrogen and CO2 adsorption method, and methane isothermal adsorption experiments were carried out under different freeze-thawing times. The results show that the hysteresis index HI of coal samples decreased after freezing and thawing, and the connectivity of the pore system was improved, which is conducive to gas migration in coal. The pores between 2 nm and 100 nm increased to varying degrees after freezing and thawing, and some pores evolved into pores smaller than their own pore size or even less than 2 nm. The microporous pore size distribution has changed, with an increase in microporous pore volume and adsorption volume. With the increase of the number of liquid nitrogen treatments, the effect of liquid nitrogen treatment on the final adsorption amount of methane kept weakening, and after reaching four treatments, the effect of liquid nitrogen treatment on the final adsorption amount of coal body almost reached saturation. The Langmuir parameters VL and pL increased after the coal samples were treated with liquid nitrogen at different times, the larger the pL, the more favorable it was for the extraction of CBM.
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