煤变质程度对CH_4吸附行为影响研究

Effects of the Degree of Coal Metamorphism on CH_4 Adsorption Behaviors

为分析变质程度对CH_4吸附行为的影响,构建了肥煤、焦煤、瘦煤、贫煤和无烟煤等5种不同变质程度煤的大分子结构模型,采用巨正则系综蒙特卡洛方法(GCMC)研究了CH_4在5种不同变质程度煤中的吸附行为。研究结果表明,CH_4吸附能力强弱顺序为无烟煤、贫煤、瘦煤、焦煤、肥煤,均为范德华能与静电能的相互作用,且吸附相稳定性差别不大;CH_4分子吸附量均随温度增加线性减少,减少幅度相近;CH_4分子吸附量均随含水率增加而线性减少,且煤变质程度越低,含水率对其CH_4分子吸附量影响越大;CH_4与H_2O同时吸附时,均呈现CH_4分子吸附量极小,且不再符合Langmuir等温吸附特征现象。煤层瓦斯含量与煤变质程度有关,受水分影响较大,且煤变质程度越低影响越显著,温度改变对不同变质程度煤层瓦斯含量影响几乎相同。

Coals with varying degrees of metamorphism(fat,coking,lean,and meagre coals and anthracite)were studied using macromolecular structural models and grand canonical Monte Carlo(GCMC)method,in order to analyze how the degree of coal metamorphism affects their CH4 adsorption.The results indicate that anthracite has the highest capacity for CH4 adsorption,followed by meagre coal,lean coal,coking coal,and finally fat coal.Regardless of the degree of metamorphism,the adsorption of CH4 in coals is mediated by van der Waals and electrostatic interactions,and the stability of their adsorption states varies very little.The different coal samples show a linear decrease of CH4 adsorption with increasing temperature,and the magnitudes of change are similar.CH4 adsorption also decreases linearly with increasing water content,and this effect is more pronounced for lower degrees of metamorphism.When CH4 and H2O are both present,the adsorption of CH4 on the coals becomes extremely small,and the adsorption process no longer fits the characteristics of isothermal adsorption described by the Langmuir adsorption model.Therefore,the gas content of coal is related to its degree of metamorphism.The water content also strongly affects the gas content,especially at lower degrees of metamorphism.It was also found that the effects of temperature on coal gas content are virtually independent of the degree of metamorphism.