Numerical Investigation on Gas Emission from Three Landfill Soil Covers under Dry Weather Conditions
Numerical Investigation on Gas Emission from Three Landfill Soil Covers under Dry Weather Conditions
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DOI：
10.2136/vzj2014.12.0180
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发表时间：
2015-08-01
影响因子：
2.8
通讯作者：
Chen, Rui
中科院分区：
文献类型：
--
作者：
Ng, Charles W. W.;Liu, Jian;Chen, Rui
现有的土壤堆填区最终盖层的设计，例如单粘土层盖层或具有毛细阻隔效应（CCBE）的盖层，目的是限制水的渗透，而不是减少堆填气体的排放。我们提出了一种替代的三层毛细屏障填埋场覆盖层，在CCBE下面添加粘土层，以提高限制气体排放的有效性。通过对水、气耦合流动的有限元分析，研究并比较了三种类型的土覆盖层在连续34干d条件下的气体排放性能。由于蒸发作用，单粘土层覆盖层的吸力增加大于其进气量，导致空气渗透系数显著增加。对于CCBE来说，蒸发也导致了淤泥层的水分损失，淤泥层不能作为气体屏障。相反，在替代的三层毛细管屏障覆盖体系中，底部粘土被相对干燥的砂层保护，砂层起到屏障的作用，最大限度地减少了粘土层的水分流失。这是因为干砂层的透水性很低。结果表明，三种盖层中，可选三层毛细阻隔盖层的瓦斯涌出率最低。这一比率低于碳农业倡议（Carbon Farming Initiative）设定的标准，表明即使在干燥的天气条件下，替代的三层毛细管屏障覆盖物也可能是减少气体排放的屏障。
The design of existing soil landfill final covers, e.g., a single clay layer cover or a cover with capillary barrier effect (CCBE), aims at limiting water infiltration rather than minimizing landfill gas emissions. We propose an alternative three-layer capillary barrier landfill cover with an added clay layer underneath a CCBE to improve the effectiveness of limiting gas emission. Finite element analyses of coupled water and gas flow were performed to investigate and compare the performance of these three types of soil covers regarding gas emission under a continuous duration of 34 dry d. Due to evaporation, suction in the single clay layer cover increased larger than its air-entry value, causing a significant increase in the air coefficient of permeability. For the CCBE, evaporation also led to water loss in the silt layer, which cannot serve as a gas barrier. On the contrary, the bottom clay in the alternative three-layer capillary barrier cover system was protected by a relatively dry sand layer, which acts as a barrier, minimizing water loss from the clay layer. This is because the dry sand layer has a very low water permeability. As a result, the gas emission rate through the alternative three-layer capillary barrier cover was the lowest among the three types of covers. This rate was lower than the criterion set by the Carbon Farming Initiative, indicating that the alternative three-layer capillary barrier cover is a possible barrier to minimize gas emission even under dry weather conditions.