水对采空区遗煤吸附电厂烟气影响的理论计算

为研究电厂烟气注入采空区时,煤中含水率和烟气中水分对于封存温室气体CO_2和抑制煤自燃的影响,建立干煤和湿煤结构模型,采用巨正则系综蒙特卡洛方法,计算了不同水分含量的烟气组分CO_2/O_2/N2/H_2O在干煤以及不同含水率的湿煤中的吸附行为。结果表明,烟气中CO_2竞争性最强吸附量最大,O_2的物理吸附量极小,烟气中H_2O含量不影响CO_2、N2和O_2的吸附量,可不进行干燥处理直接将电厂烟气注入采空区。随着煤中含水率增加,水分占据孔隙空间,范德华作用减弱,H_2O-H_2O之间的氢键作用增强且提供了额外吸附位。H_2O的等量吸附热升高,吸附位移向吸附作用更强的低相互作用能区域,吸附大量水形成水团簇,与CO_2竞争吸附位,并且占据吸附空间抑制CO_2、O_2、N2的吸附,使其吸附量降低50%以上,因此,注入烟气时应充分考虑采空区煤体的含水率问题。

Theoretical calculation of water effect on power plant flue gas adsorption by goaf coal

To investigate the effect of water content in flue gas and moisture in coal on the greenhouse gas CO₂ storage and coal spontaneous combustion when injecting power plant flue gas into goaf, the dry and wet coal structural models were established. The adsorption behavior of flue gas mixtures of CO₂/O₂/N₂/H₂O with different water contents by dry coal and wet coal with various moisture contents was simulated using Grand Canonical Monte Carlo method. The result shows that the competitive adsorption ability and capacity of CO₂ in flue gas are the strongest, while the physical adsorption amount of O₂ is the least. The H₂O content in flue gas has little effect on the adsorption amount of CO₂, N₂ and O₂. So the power plant flue gas can be directly injected into the goaf without drying. As the water content in the coal increases, the pore space is occupied by water, the Van der Waals force decreases, and the hydrogen bonding between H₂O-H₂O increases to provide additional adsorption sites. However, because the isosteric heat of H₂O increases and the adsorption sites move toward a lower interaction region where the adsorption is stronger, a large amounts of water is adsorbed to form water clusters and compete the adsorption sites and space with CO₂, O₂, N₂, leading to a decrease in gas adsorption amount by more than 50%. Therefore, the water content in goaf coal should be fully taken into account when the flue gas is injected.