Molecular simulation of CO(2)/CH(4)/H(2)O competitive adsorption and diffusion in brown coal.
Molecular simulation of CO(2)/CH(4)/H(2)O competitive adsorption and diffusion in brown coal.
复制标题
褐煤中CO2/CH4/H2O竞争吸附与扩散的分子模拟
作者：
二氧化碳提高煤层气采收率(CO2-ECBM)被认为是一种既能提高天然气采收率，又能减少向大气中排放二氧化碳的有前途的技术。CO2/CH4混合物的吸附和扩散对预测CO2-ECBM项目的效果，即煤层气的产量和二氧化碳的地质封存潜力起着关键作用。本文采用巨正则蒙特卡罗和分子动力学模拟方法研究了CO2/CH4/H2O混合气体在褐煤中的竞争吸附和扩散机理。考察了温度和压力对竞争吸附和扩散行为的影响。结果表明，CO2在褐煤上的吸附能力远强于CH4。CO2/CH4的吸附量随压力的升高而增加，随温度的升高而减小。当压力低于0.1 Mpa时，对CO2/CH4具有较高的吸附选择性。此外，还考察了褐煤中水分含量对吸附特性的影响。模拟结果表明，湿褐煤对CO2/CH4的吸附能力明显受到抑制。CO_2/CH_4/H_2O的竞争吸附遵循H_2O、≫、CO_2和GT；CH_4的趋势。此外，结果还表明，水分含量对CO2/CH4的自相关系数有很大的影响。与干煤相比，含水率为7.59wt%的褐煤中CO2和CH4的自扩散系数分别降低了78.7%和75.4%。本研究提供的微观观点将有助于理解CO2/CH4/H2O在褐煤中的竞争吸附和扩散机理，并为CO2-ECBM项目提供一些基础数据。
Carbon dioxide enhanced coalbed methane recovery (CO2-ECBM) has been proposed as a promising technology for the natural gas recovery enhancement as well as mitigation of CO2 emissions into the atmosphere. Adsorption and diffusion of CO2/CH4 mixture play key roles in predicting the performance of CO2-ECBM project, i.e., the production of coalbed methane as well as the geological sequestration potential of carbon dioxide. In the present work, the mechanism of competitive adsorption and diffusion of CO2/CH4/H2O mixture in brown coal were investigated by employing grand canonical Monte Carlo and molecular dynamics simulation. The effects of temperature and pressure on competitive adsorption and diffusion behaviours were explored. It is found that CO2 has much stronger adsorption ability on brown coal than CH4. The adsorption amounts of CO2/CH4 increase with pressure but have a decreasing trend with temperature. High adsorption selectivity of CO2/CH4 is observed with pressure lower than 0.1 MPa. In addition, the effects of moisture content in brown coal on the adsorption characteristics have been examined. Simulation results show that the adsorption capacities of CO2/CH4 are significantly suppressed in moist brown coal. The competitive adsorption of CO2/CH4/H2O follows the trend of H2O ≫ CO2 > CH4. Moreover, the results reveal that moisture content has great effects on the self-coefficients of CO2/CH4. Compared with dry coal, the self-diffusion coefficients of CO2 and CH4 reduce by 78.7% and 75.4% in brown coal with moisture content of 7.59 wt%, respectively. The microscopic insights provided in this study will be helpful to understand the competitive adsorption and diffusion mechanism of CO2/CH4/H2O in brown coal and offer some fundamental data for CO2-ECBM project.
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