柱状煤心瓦斯径向多尺度动态表观扩散模型与实验

Experiment and radial multi-scale dynamic apparent diffusion model of gas in cylindrical coal core

为了提高长钻孔瓦斯含量测定的准确性,进行了φ50 mm×100 mm柱状煤心径向和1~3mm颗粒煤球向瓦斯解吸流动实验。实验结果表明:常系数扩散模型不能准确描述柱状煤心瓦斯的径向流动全过程;90 min前,实验值大于理论值;90 min后,实验值小于理论值,这种现象是由于煤体的多尺度孔隙结构引起的。进而提出了柱状煤心瓦斯径向多尺度动态表观扩散系数新模型。计算表明:新的径向动态表观扩散模型能精确描述瓦斯在柱状煤心中的表观扩散;相同时间内柱状煤的径向解吸比率远小于颗粒煤球向解吸比例,损失量较小;因而,进行长钻孔长时间测定瓦斯含量时,柱状煤心比颗粒煤更有优势。

In order to improve the accuracy of measuring gas content in long borehole,experiments of gas desorption flow in radial direction of φ50 mm×100 mm cylindrical coal and 1-3 mm granular coal were carried out.The experimental results show that the constant coefficient diffusion model can not describe the whole process of gas flow in radial direction accurately.The experimental value is larger than the theoretical value before 90 min and smaller than the theoretical value after 90 min.This phenomenon is caused by the multi-scale pore structure of coal.Furthermore,a new model of gas radial multi-scale dynamic apparent diffusion coefficient of cylindrical coal core is proposed.The calculation shows that the new radial dynamic apparent diffusion model can accurately describe the gas apparent diffusion in the cylindrical coal core.In the same time,the radial desorption ratio of cylindrical coal is much smaller than that of granular coal and the loss is smaller.Therefore,the cylindrical coal core has more advantages than the granular coal when the gas content is measured for a long time.