大佛寺井田4号煤CH_4与CO_2吸附解吸实验比较

以迅速降低大佛寺4号煤含气量,提高地面煤层气井采收率为目标,进行CO2驱替CH4技术的实验研究。对采自大佛寺矿井40114工作面的样品,进行多个温度点柱体原煤与60~80目平衡水样的CH4与CO2吸附解吸对比实验。结果表明:CO2在煤孔隙表面与CH4一致,吸附过程符合Langmuir方程,解吸过程可用解吸式描述;由热力学计算可知,柱体原煤升压过程CO2吸附热为56.827 kJ/mol,CH4吸附热为12.662 kJ/mol,降压过程CO2吸附热为115.030 kJ/mol,CH4吸附热为23.602 kJ/mol,无论升压过程还是降压过程CO2吸附热远大于CH4吸附热,两种气体在煤孔隙表面竞争吸附时CO2占据优势,导致置换解吸;吸附势、吸附空间计算验证了这个结论;利用CO2驱替CH4技术,提高煤层气采收率,理论依据充分可行。

Contrastive experiment of adsorption-desorption between CH4 and CO2 in Coal Seam 4 of Dafosi Coal Mine

The study investigated the technology of the replacement of CH4 by CO2 in order to rapidly reduce the coalbed methane content in coal seam 4 at Dafosi Coal Mine and improve the recovery factor of the ground coalbed methane wells.Contrastive experiments on adsorption and desorption of CH4 and CO2 of cylinder raw coal and 60-80 mesh equilibrium water samples at different temperatures are conducted using the samples collected from the working face 40114 at Dafosi Coal Mine.The results indicate：the adsorption and desorption of CO2 on coal pore surface is consistent with that of CH4，the pressure-rising process abiding by Langmuir equation and the pressure-dropping process being described by desorption expression.Based on thermodynamic calculation，in cylinder raw coal during pressure-rising process，the adsorption heat of CO2 is 56.827 kJ/mol while that of CH4 is 12.662 kJ/mol.During pressure-dropping process，the adsorption heat of CO2 is 115.030 kJ/mol while that of CH4 is 23.602 kJ/mol.In both processes，the adsorption heat of CO2 is far greater than that of CH4，which proves that CO2 is more competitive over CH4 in their adsorption on coal pore surfaces，leading to replacement desorption.The conclusion is verified by the calculations of adsorption potential and adsorption space.The technology of replacing CH4 by CO2 is feasible with strong theoretical ground，and useful for improving the recovery factor of coalbed methane.