低阶煤广泛分布于我国西北、华北和东北地区且储量较大，但近年来部分低阶煤矿区瓦斯突出灾害严重。为研究低阶煤孔隙结构、瓦斯吸附放散特性及其对瓦斯灾害的影响，采用N₂/CO₂吸附法和小角X射线散射(SAXS)表征手段，开展瓦斯吸附/解吸试验，运用分形理论，对6组煤样开展系统研究。根据煤样孔隙结构参数和瓦斯吸附/解吸特性参数的关系，获得低阶煤微观孔隙结构与宏观瓦斯吸附放散特性的相关性。结果表明：试验低阶煤煤样≤2 nm的微孔孔容为0.055～0.064 cm³/g，总体上高于试验中阶煤样微孔孔容(0.026～0.060 cm³/g)；低阶煤介孔主要分布在2～8 nm，而中阶煤最发育孔径为2～4 nm。低阶煤介孔孔容和比表面积总体大于中阶煤；SAXS结果表明：低阶煤最发育孔径为10 nm左右，而中阶煤孔径在35 nm附近最发育。这与N2吸附法测得煤样最发育孔径约为3 nm存在较大差异，可能煤中存在闭孔或气体吸附法无法测到的孔。分形维数结果表明：低阶煤孔隙较中阶煤孔隙更为复杂。结合傅里叶变换红外光谱表明，低阶煤分子结构松散，含有较多长侧链的官能团，导致其微孔和介孔较为发育。微孔孔容与朗格缪尔体积(VL)存在正相关关系，介孔孔容与瓦斯扩散系数(D)亦存在正相关关系，而VL和D反映着煤体的吸附和放散特性。因此低阶煤具有相对较强的瓦斯吸附和放散能力，易于发生瓦斯异常涌出和瓦斯突出。

Low rank coal is widely distributed in the northwest, north and northeast of China and has large reserves, but some serious gas outburst disasters have occurred in recent years in some low rank coal coalfields. In order to study the pore structure of low rank coal and the characteristics of gas adsorption and diffusion, and its influence on gas disaster, the N₂/CO₂ adsorption, small angle X ray scattering (SAXS), gas adsorption/desorption experiments and fractal theory were used to study six groups of coal samples. According to the relationship between coal sample pore structure parameters and gas adsorption/desorption characteristic parameters, the correlation between the micropore structure of low rank coal and the macro gas adsorption and diffusion characteristics was obtained. Results show that the micropore (≤2 nm) volume of low rank coal is 0.055-0.064 cm³/g, which is generally higher than that of medium rank coal (0.026-0.060 cm³/g). The mesopores of low rank coal are mainly distributed in 2-8 nm, while the most developed pore diameters of medium rank coal are 2-4 nm. The mesoporous pore volume and specific surface area of low rank coal are generally larger than those of medium rank coal. SAXS results show that most developed pore size of low rank coal is about 10 nm, while the most developed pore size of medium rank coal is near 35 nm. This differs significantly from the most developed pore size of about 3 nm on the coal sample measured by N₂ adsorption method, which may be the presence of closed pores in the coal or pores that cannot be measured by gas adsorption method. The results of fractal dimension calculation show that the pores of low rank coal are more complex than those of medium rank coal. Combined with Fourier transform infrared spectroscopy analysis, low rank coal has a loose molecular structure and contains more functional groups with long side chains, which leads to the development of micropores and mesopores. There is a positive correlation between the pore volume of micropores and Langmuir volume (VL), and the pore volume of mesopores also has a positive correlation with gas diffusion coefficient (D). VL and D reflect the adsorption and diffusion characteristics of coal, so low rank coal has relatively strong gas adsorption and release capabilities, and is prone to abnormal gas gushing and gas outburst.

1 取样和试验方法

   1.1 取样与参数测定

   1.2 试验方法及原理

2 结果分析与讨论

   2.1 N₂/CO₂吸附试验结果

   2.2 小角X射线散射测试结果

   2.3 低阶煤孔隙结构的分形特征

   2.4 低阶煤孔隙结构对瓦斯吸附及放散特性的影响

   2.5 低阶煤分子结构演化对瓦斯吸附放散特性的影响

3 结论