煤中超临界甲烷等温吸附模型研究

Study on Supercritical Isothermal Adsorption Model of Methane in Coal

为了从数学模型上深入了解煤层气在煤中吸附的物理机理,利用参数具有物理意义的吸附模型,如Langmuir、Freundlich、Toth、Langmuir-Freundlich、扩展的Langmuir、BET、D-R、D-A模型,分别对3个不同煤级样品的空气干燥基和干燥无灰基甲烷等温吸附数据进行拟合,对BET模型、D-R模型、D-A模型中涉及的p0,采用虚拟饱和蒸气压的概念,用3种方法计算。通过对模型参数拟合值的分析,比较了空气干燥基和干燥无灰基煤的吸附特征,对微观吸附机理进行了解释。比较了各模型对单煤级和3个煤级作为整体的拟合效果,认为B-BET-1模型、B-BET-2模型对于3个煤级样品均没有物理意义,D-R-3模型和D-A-3模型不能用于描述长焰煤的吸附特性,T-BET-3模型异常高的最大吸附量所反映的吸附机理尚待研究。综合分析,认为T、L-F、E-L、B-BET-3、TBET-1和T-BET-2模型用于描述煤中甲烷超临界吸附较为理想。

In order to understand the physical mechanism of coalbed methane adsorption in coal in the light of mathematical models,the measurements of the isothermal methane adsorption from three coal samples with different ranks under the air dry and dry ash-flee basis were fitted by the models of Langmuir,Freundlich,Toth, Langmuir-Freundlich, Extended Langmuir, BET, D-R and D-A in which the parameters have physical meanings. The p0 was defined as the virtual saturated vapor pressure in the BET, D-R and D-A models and computed via three means. Methane adsorption behaviors of samples on two bases were compared and the microscopic mechanisms of the adsorption were discussed based on the fitted values of the parameters. The fitted effects of each model respectively for a single and all three samples were analyzed comparatively. It was suggested that the B-BET-1 and B-BET-2 models have no physical meaning for the coal samples,D-R-3 and D-A-3 models can not characterize the adsorption of the flame coal,and the mechanism of abnormally high maximum adsorption capacity form the T-BET-3 model is subjected to further discussion. Comprehensively, the T, L-F, E-L, B-BET-3, T-BET-1 and T-BET-2 models are suitable to describe the supercritical isothermal adsorption of methane in coal.