密度梯度驱动的煤粒瓦斯解吸扩散模型及试验研究

Gas desorption and diffusion model driven by density gradient in coal particle and its experimental study

为解决菲克扩散模型在煤粒瓦斯解吸扩散过程中存在较大偏差的问题,更好地解释瓦斯在煤粒中的解吸扩散机制,首先开展了封闭空间煤粒瓦斯解吸试验,得到不同初始解吸压力下的煤样瓦斯解吸数据,并评估了4种解吸经验公式的精确性;随后回顾了浓度梯度驱动的菲克扩散模型,提出了游离瓦斯密度梯度驱动的新扩散模型;在此基础上,建立了相关的解吸扩散数学方程,并采用有限差分数值方法进行数值解算;最后将新模型与菲克模型的解算结果以及试验数据进行比较,讨论了新瓦斯扩散模型的优势。结果表明:不同的解吸经验公式拟合试验数据的精确度差异较大,优选出了一种能够在全试验时间尺度下拟合情况良好的经验公式;4种不同初始解吸压力条件下的新扩散模型的数值预测结果在整个试验时间尺度内与试验数据基本一致;相对来说,基于菲克扩散模型数值解算的结果准确性不高;在保证理论预测精度的前提下,新扩散模型中的微孔道扩散系数不随时间和压力而改变;而建立在常扩散系数的假设之上的经典菲克扩散模型的解析解和数值解会产生较大误差。新模型可以更合理和准确地描述瓦斯解吸扩散行为。研究结果旨在为瓦斯解吸扩散机理的认识、瓦斯突出解吸指标及煤层瓦斯含量的标定等工作提供一些新的思路和参考。

In order to solve the fick diffusion model in coal particle gas desorption process has the problem of larger deviation,better explain the desorption diffusion mechanism in the gas in coal grains,first of all,gas desorption experiment in closed space was conducted,the different initial desorption gas desorption data under the pressure of coal samples,the accuracy of the empirical formula and compares four kinds of desorption;then the Fick diffusion model driven by concentration gradient is reviewed and a new diffusion model driven by free gas density is proposed.At the same time,the related equations of desorption and diffusion are established and solved numerically based on the finite difference numerical method.Finally,the results of the new gas diffusion model are compared with the Fick model and the experimental data,and the advantages of the new gas diffusion model are discussed.The results show that the different desorption empirical formulas have great differences in the accuracy of fitting experimental data,and the empirical formulas which can fit well in the whole experimental time scale are screened out.The numerical prediction results of the new diffusion model under four different initial desorption pressures are basically consistent with the experimental data in the whole experimental time scale.Relatively speaking,the numerical calculation results based on Fick diffusion model are not accurate.Under the premise of ensuring the prediction accuracy of the theory,the diffusion coefficient of the micro channel in the new diffusion model does not change with time and pressure.Compared with the analytical and numerical solutions of the classical Fick diffusion model which is based on the assumption of constant diffusion coefficient,the new model can describe the gas desorption diffusion behavior more reasonably and accurately.The research content is expected to provide some new ideas and references for understanding of mechanism of gas desorption and diffusion,index of gas outburst desorption and the calibration of coal seam gas content.