摘要
基于气体吸附理论,采用低温液氮吸附法(LT-N 2 GA),CO 2吸附法和扫描电镜法(SEM),从孔容、比表面积、孔径分布和孔隙形状4个方面,研究分析了8种不同变质程度煤样的孔隙结构。并结合煤粒瓦斯扩散实验,计算出煤样的迂曲度和瓦斯扩散通道长度,分析讨论了不同煤阶煤体孔隙结构对瓦斯解吸扩散规律的影响及机理。结果表明:不同煤阶煤样的吸附能力存在显著的差异。随变质程度的加深,吸附能力呈先降低后升高的U形规律;SEM观察结果与低温液氮吸附等温线分析的孔隙形态整体上较为一致,不同煤阶煤样的孔隙形态有很大差异,表明煤体表面的异质性;吸附分析显示中孔孔径呈多峰分布,孔容主要由2~15 nm的中孔贡献;煤体微孔段的吸附能力取决于0.6~0.9 nm和1.5~2.0 nm孔径段。煤质对瓦斯解吸扩散的影响主要与孔隙结构的差异有关。不同煤阶煤体孔隙率和迂曲度不同,瓦斯扩散通道长度不同,随着扩散通道长度的增加,瓦斯初始解吸速率呈指数形式减小;瓦斯在煤体孔隙中的扩散以微孔内的表面扩散为主,孔比表面积越大,表面扩散越显著;瓦斯解吸量和初始扩散系数与煤阶之间呈现不对称U形关系,在高阶煤阶段(V daf<15%),随着挥发分的增加,瓦斯解吸量和初始扩散系数显著减小。在中、低阶煤阶段(V daf>15%),随着挥发分的增加,二者缓慢增加。
Based on the gas adsorption theory,the low-temperature liquid nitrogen gas adsorption(LT-N 2GA),CO 2 adsorption and scanning electron microscopy(SEM)were used to analyze the pore structures of eight coal samples with different metamorphisms from the aspects of pore volume,specific surface area(SSA),pore size distribution and pore shape.Coal particle gas desorption and diffusion experiments were carried out.Tortuosity of the coal samples and the length of the gas diffusion channels were calculated.The influence and mechanism of pore structures on the gas desorption and diffusion were analyzed.The results show that there are strong differences in gas adsorption capacity between the coals studied.The U-shape relationship between adsorption constant a and volatile component(V daf)is observed,demonstrating that the adsorption capacity reduces first and then increases as the coalification effect increases,which is consistent with the relationship between the pore specific surface area and coal ranks.To a large extent,the pore shapes observed by SEM are consistent with the analysis of the LT-N 2GA isotherm.The pore shape of coals with different metamorphisms varies a lot,indicating the heterogeneity of coal surface.Adsorption analysis reveals that the mesopore size distributions are multimodal,and the pore volume is mainly contributed by the mesopores of 2-15 nm.The adsorption capacity of the micropores of coal body depends on the 0.6-0.9 nm and 1.5-2.0 nm aperture sections.The influence of coal ranks on gas desorption and diffusion is mainly related to the difference of pore structure.The porosity and tortuosity of various rank coals are different.The length of gas diffusion channels is also different.As the length of gas diffusion channel increases,the initial gas desorption rate decreases exponentially.Gas diffusion in various rank coals is dominated by surface diffusion on the micropores.The larger the pore SSA,the more significant the surface diffusion.The gas desorption quantity and initial diffusion coefficient show an asymmetric U-shaped relationship with coal ranks.For higher rank coals(V daf<15%),the gas desorption quantity and initial diffusion coefficient decrease significantly with the increase of V daf.In the middle and low rank coal stages(V daf>15%),both of them increase slowly with the increase of V daf.
作者
李祥春
李忠备
张良
高佳星
聂百胜
孟洋洋
LI Xiangchun;LI Zhongbei;ZHANG Liang;GAO Jiaxing;NIE Baisheng;MENG Yangyang(School of Emergency Management and Safety Engineering,China University of Mining and Technology(Beijing),Beijing 100083,China;State Key Lab of Coal Resources and Safe Mining,China University of Mining&Technology(Beijing),Beijing 100083,China;State Key Lab Cultivation Base for Gas Geology and Gas Control,Jiaozuo 454000,China)
出处
《煤炭学报》
EI
CAS
CSCD
北大核心
2019年第S01期142-156,共15页
Journal of China Coal Society
基金
国家重点研发计划资助项目(2018YFC0808301)
北京市自然科学基金面上资助项目(8192036)
河南省瓦斯地质与瓦斯治理重点实验室——省部共建国家重点实验室培育基地开放基金资助项目(WS2018B04)。
关键词
煤阶
孔隙结构表征
微孔
扩散通道
瓦斯解吸扩散规律
coal rank
pore structure characterization
micropore
gas diffusion channel
gas desorption and diffusion rules
