煤层瓦斯含量测定过程气成分差异研究

Trace and determination of the gas compositional difference in the coal seam gas content testing

煤层瓦斯成分是煤矿瓦斯灾害防治和煤层气资源开发利用的基础参数。不同测试方法或不同测试阶段煤层瓦斯成分的较大差异给生产实践带来较大困扰和使用上的不便。通过对以往地面和井下瓦斯(煤层气)含量测试结果中气成分的数据分析,研究了气成分在瓦斯含量测定不同测试阶段的差异及其影响因素。结果表明,瓦斯含量脱气法测定过程中开罐分选和破碎煤样对气成分测定结果的差异有显著影响,当经过加温脱气后的瓦斯罐进行开罐分选、破碎煤样时,空气中N2、CO2和O2等迅速占用煤样空闲吸附位,而扣除空气过程只能扣除球磨罐内游离的空气以及被吸附的少部分,导致粉碎后气体成分中N2和CO2体积分数增加。为消除上述影响,提出了煤芯全程密闭式瓦斯含量测定方法,并研制了现场取样和实验室球磨粉碎煤芯两用的全程密闭式瓦斯解吸罐,该技术方法实现了煤芯在现场装罐后直至脱气结束的全程密闭测定,可有效避免因测定过程中开罐、倒罐引起前后的气成分差异。现场应用表明,该方法可大幅缩小煤芯粉碎前后气成分中甲烷体积分数的差异,提高瓦斯含量测定结果的准确度。

The paper is aimed at determining the difference of the gas composition status-in-situ of the coal seam gas in the different testing stages of the gas content rates. As is well known,the coal seam gas is the basic or principal parameter for preventiing and controlling the coal mining gas disaster or calamity,particularly when the coalbed methane resources are exploited and utilized due to the great difference in the composition of the coalbed gas with the different testing methods in different testing stages,when the gas composition has to be analyzed as to the coalbed methane content results. And,it would be possible for the preliminary parameter analysis to reveal that the separation of the crushed coal samples in the middle of the gas content determination may have significant impact on the difference of the gas composition determination. For instance, when the gas tank is opened for separation,the gas composition results can be significantly different. When the coal samples are crushed,N2,CO2 and O2 in the air may take over the free adsorption sites quickly,while the deduction process can only deduct the free air and a small amount of the adsorbed air in the ball mill tank,which may lead to increase of the concentration of N2 and CO2 in the gas components after crushing. In order to eliminate the above-mentioned influence,we would like to present a method of the gas content measurement in the closed coal core bed. A full-course closed gas tank for the coal core bed can be developed by using both the field sampling and the laboratory ball milling. In doing so,the entire processing course can be made closed with the gas tank for the coal core,and can be realized by filling the tank on site until the end of the degassing,so as to get rid of the interruption of the measuring process,effectively. The reason is that the difference in the coal gas composition between the front side and the backside of the cylinder can be caused by the tanks. The field application shows that the given method we have proposed can significantly reduce the difference of methane concentration in the coal gas before and after the coal core crushing.