煤层封存CO_2性能的晶格理论模型及应用

Lattice theory model and its application on CO_2 storing performance of coal seam

为了更好地在煤层中封存CO_2,开展CO_2在煤体上跨越临界点的大范围吸附规律(随压力非单调递增)研究尤为重要。基于晶格热力学方程,建立了微孔吸附超临界流体的晶格模型,并对不同温度下不同变质程度煤样的CO_2的吸附等温线进行了预测,研究结果表明:CO_2在煤上的吸附等温线随压力增加先增大后减小,不再满足I型等温线;CO_2分子之间作用势εa虽然远小于CO_2分子与孔壁之间的作用势εs,但忽略εa将导致理论吸附量与实测吸附量误差变大;作用势εs与温度正相关,而εa与温度负相关。晶格理论模型(εa≠0)拟合CO_2在煤上吸附出现极值的等温线效果良好,相关系数均在0.99以上,其对不同温度下不同变质程度煤的CO_2的吸附等温线进行预测结果与实测结果基本一致,其相对误差不超过5%。

In order to better store CO_2 in coal seam,it is very important to study the large range adsorption laws（ non-monotonically increasing with pressure） of CO_2 over the critical point in coal body. Basing on the lattice thermodynamics equation,a lattice model on microporous adsorption of supercritical fluids was established to predict the CO_2 adsorption isotherm of coal with different metamorphic grade under different temperature. The results showed that the CO_2 adsorption isotherm increased first and then decreased with the increasing pressure,which did not satisfy the type I isotherm. The interaction potential εaamong CO_2 molecules was much less than the interaction potential εsbetween CO_2 molecule and pore wall,but if we ignored the εa,the error of adsorption capacity between theory and experiment would become bigger. There existed a positive correlation between interaction potential εsand temperature,but a negative correlation between interaction potentialεaand temperature. The fitting results of lattice theory model（ εa≠0） on the isotherm when CO_2 adsorption appeared the extreme value,and the correlation coefficient was more than 0. 99. The predicted results of CO_2 adsorption isotherm for coal with different metamorphic grade under different temperature were in good agreement with the measured results,and its relative error were all less than 5%.