方向性原煤CH_4扩散实验及矢量计算模型

Vector calculation model and diffusion experiments of CH_4 for directional raw coal

为了探讨温度、压力、扩散路径等因素对原煤CH4扩散特性的影响,采用规则块样结合气相色谱法进行不同温度、压力条件下方向性原煤CH4扩散实验。实验结果表明:原煤中CH4扩散速率较小,扩散系数大小处于10-8数量级上;原煤CH4扩散系数随围压、气压的增大,呈指数关系减小;随温度的升高,呈指数关系增大;扩散路径对扩散系数影响显著。分析表明:原煤CH4扩散实验不能用颗粒煤解吸实验简单替代;温度对气体分子扩散的控制是通过改变气体分子的均方根速度和平均自由行程,而围压、气压则受有效应力和煤粒收缩/膨胀变形两种因素的共同制约;方向性扩散系数是矢量,据此,推导建立了一种扩散系数矢量计算模型。

In order to investigate the influence and control mechanism to diffusion characteristics of CH4 in raw coal by temperature,air pressure,diffusion paths,and other factors,a combination of standard shaped coal samples and gas chromatography were applied to the diffusion experiments of CH4 under different temperature and pressure conditions. The experimental results show that the diffusion coefficient of CH4 in raw coal is on the order of 10- 8and the diffusion rate is slow; that the diffusion coefficient of CH4 in raw coal decreases at an exponential relationship with the increase of confining pressure and air pressure; and that the coefficient increases at an exponential relationship with the rise of temperature. Thusly,diffusion paths have significant effects on the diffusion coefficient. The analysis result indicates that the CH4 diffusion experiment of raw coal cannot be replaced by coal particles. The effects of temperature on gas molecular diffusion is to change the root mean square velocity and average free path of gas molecules,while confining pressure and air pressure are eventually controlled by both effective stress and contraction / expansion deformation of coal particles. As the directional diffusion coefficient is a kind of vector,a diffusion coefficient vector calculation model is established.