CH_(4)/H_(2)O/CO_(2)在煤大分子中自扩散的分子模拟  

Molecular simulation of self-diffusion of CH_(4),H_(2)O and CO_(2)in coal macromolecule

作　　者：许将 陈倩 李居云 XU Jiang;CHEN Qian;LI Juyun(Xi'an Coal Aviation Remote Sensing Information Co.,Ltd.,Xi'an 710199,China;Shaanxi Provincial Geological Survey Institute,Xi'an 710054,China)

机构地区：[1]西安煤航遥感信息有限公司,陕西西安710199 [2]陕西省地质调查院,陕西西安710054

出　　处：《煤矿安全》2024年第9期85-93,共9页Safety in Coal Mines

基　　金：陕西省自然科学基金研究计划资助项目(2022JQ-258)。

摘　　要：通过巨正则蒙特卡罗和分子动力学方法,计算不同系综条件下CH_(4)、CO_(2)、H_(2)O在煤分子中的扩散系数,并考察了温度和压力的影响。结果表明:在NPT系综下,随着温度的升高,CH_(4)和CO_(2)的扩散系数逐渐增大,H_(2)O的扩散系数呈现波动式增加;在每个温度下,H_(2)O扩散系数均大于CH_(4)和CO_(2);扩散活化能表现为E(H_(2)O)<E(CO_(2))<E(CH_(4)),表明CH_(4)的扩散最难发生,CO_(2)的扩散更容易发生;随着压力的升高,各种气体分子的溶胀率逐渐越大;高压时,分子溶胀作用显著,预示着H_(2)O和CO_(2)吸附在提高煤层气采收率过程中可以引起显著的煤基质溶胀,从而导致气体传输通道变窄,不利于煤层气的产出;CH_(4)、H_(2)O和CO_(2)扩散活化能均随着压力的升高而逐渐升高,且增幅有增大的趋势,预示着在压力较高时激活CH_(4)、H_(2)O和CO_(2)扩散需要克服更高的分子结构能垒,CO_(2)应以较快的速度注入煤体中,从而提高煤层气采收率。In this paper,the self-diffusion coefficients(SDC)of CH_(4)/CO_(2)/H_(2)O in coal molecules under different ensemble conditions and the effects of temperature and pressure are calculated by grand canonical Monte Carlo and molecular dynamics(MD)methods.Results indicated that the self-diffusion coefficients of CH_(4) and CO_(2) gradually increase with the increasing temperature under the NPT ensemble.The SDC of H_(2)O increases undulatory and it is higher than that of CH_(4) and CO_(2) at each temperature,where the diffusion activation energy followed the order of E(H_(2)O)<E(CO_(2))<E(CH_(4)),indicating that the CH_(4) diffusion was the most difficult to occur,and the diffusion of CO_(2) is more easy to occur.With the increase of pressure,the swelling rate of various gas molecules gradually increases.At high pressure,the molecular swelling effect is significant,indicating that the adsorption of H_(2)O and CO_(2) in the enhanced coalbed methane recovery process can cause significant coal matrix swelling,resulting in narrow gas transmission channels,which is not conducive to the production of coalbed gas.The diffusion activation energies of CH_(4),H_(2)O and CO_(2) all increase gradually with the increase of pressure,and the increase trend is increasing,indicating that the self-diffusion of CH_(4),H_(2)O and CO_(2) needs to overcome the higher molecular structure energy barrier when the pressure is high.CO_(2) should be injected into coal body at a faster rate,so as to improve the recovery rate of coalbed methane.

关 键 词：煤层气采收率 CH_(4)/CO_(2)/H_(2)O 煤大分子 自扩散 分子结构能垒 活化能 

分 类 号：TD712[矿业工程—矿井通风与安全]