两淮低渗煤的甲烷吸附相密度差异特征及影响因素分析

The Characteristics and Influencing Factors of Methane Adsorption Phase Density Differences in Low-Permeability Coal from Huainan and Huaibei Region

摘要: 甲烷吸附相密度的差异是煤中甲烷吸附量的关键影响因素。本文以两淮煤为例，通过开展煤的甲烷高压等温吸附实验，采用截距法计算并探讨了不同条件下甲烷吸附相密度的差异，结合压汞实验和低温液氮吸附实验分析了煤的孔隙结构，讨论了甲烷吸附相密度的控制因素。研究结果表明，在0~5 MPa压力区间内，甲烷的绝对吸附量和吸附相密度增长较快；在5 MPa至拐点压力时，甲烷的吸附量和吸附相密度增长速度减缓；超过拐点压力(约11 MPa)，甲烷的过剩吸附量随压力增加而减小，吸附相密度在拐点压力达到峰值后随压力增高出现下降，并最终趋于稳定；随着温度升高，甲烷在煤孔隙中的吸附能力减弱，煤中甲烷的吸附相密度呈现下降趋势。在孔径为0~10 nm和10~100 nm范围内，甲烷吸附相密度与孔容呈、比表面积呈负相关；在孔径为100~1000 nm和大于1000 nm的范围内，甲烷吸附相密度与孔容、比表面积呈正相关，甲烷吸附相密度与总孔容呈正相关，与总比表面积呈负相关，揭示煤中甲烷吸附以微孔充填为主。

Abstract: The difference in methane adsorption phase density is a key influencing factor for methane adsorption capacity in coal. Taking the coal from the Huainan and Huaibei area as an example, this paper carried out high-pressure isothermal adsorption experiments of methane in coal, calculated and discussed the differences in methane adsorption phase density under different conditions by using the intercept method. Combined with mercury intrusion porosimetry and low-temperature nitrogen adsorption experiments, the pore structure of coal was analyzed, and the controlling factors of methane adsorption phase density were discussed. The research results show that the absolute adsorption capacity and adsorption phase density of methane increase rapidly within the pressure range of 0~5 MPa; when the pressure is from 5 MPa to the inflection point pressure of adout 11 MPa, the growth rate of methane adsorption capacity and adsorption phase density slows down; when the pressure exceeds the inflection point pressure, the excess adsorption capacity decreases with the increase of pressure, and the adsorption phase density reaches the peak at the inflection point pressure, then decreases with the increase of pressure and finally tends to be stable. With the increase of temperature, the adsorption capacity of methane in pores of coal weakens, and the adsorption phase density of methane in coal shows a downward trend. In the pore size ranges of 0~10 nm and 10~100 nm, the methane adsorption phase density is negatively correlated with the pore volume and specific surface area; in the pore size ranges of 100~1000 nm and greater than 1000 nm, the methane adsorption phase density is positively correlated with the pore volume and specific surface area. The methane adsorption phase density is positively correlated with the total pore volume and negatively correlated with the total specific surface area, revealing that the methane adsorption in coal is dominated by micropore filling.