One-dimensional analytical model for contaminant transport through CCL under thermal diffusion and its application
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摘要: 建立了污染物在对流、分子扩散和热扩散作用下压实黏土衬垫（CCL）的一维运移解析模型，并获得解析解。无量纲设计曲线表明对流作用对污染物在CCL中运移的影响至关重要；然而随着热扩散作用的增强，对流作用的影响会有所减弱。参数敏感性分析结果表明，当渗滤液水头达到3 m时，10 a的底部浓度和通量分别是无对流情况下的3.5~4.9倍和5.9~15.1倍；当热扩散作用较强（M=-5）时，10 a底部浓度和通量是无热扩散作用下的2.6倍和3.5倍；温度升高会增大土的渗透系数，从而影响污染物在CCL中的运移，在衬垫系统设计过程中应予以考虑。提出了衬垫厚度设计简化计算方法，并以西安江村沟填埋场为例，对CCL进行了简化设计；结果表明：若要保证渗滤液中的Cl-和As击穿CCL的时间大于50 a，则CCL的厚度分别需要不小于11.16 m和1.75 m。Abstract: A one-dimensional analytical model as well as the analytical solution for the contaminant transport in compacted clay liner (CCL) is proposed. The dimensionless design curves show that the advection has significant effects on the contaminant transport in CCL. However, with the increases of thermal diffusion, the effects of the advection will decrease. The results of parameter sensitive analysis show when the leachate head reaches 3 m, the 10-year bottom concentration and flux increase by the factors of 3.5~4.9 and 5.9~15.1, respectively, compared with those without the advection. When the thermal diffusion is great enough (M=-5), the bottom concentration and flux increase by the factors of 2.6 and 3.5, respectively, compared with those without the thermal diffusion. The effects of the temperature on the permeability coefficient of CCL should be considered in the design of landfill clay liners. A simplified method for determination of the thickness of the landfill liner is proposed. The simplified method is used to design the liner system at the Jiangcungou Landfill site in Xi 'an. When considering the chloride (Cl-) and arsenic (As) as the index contaminants, the breakthrough time will be longer than 50 years in the case with the thickness of CCL larger than 11.16 m and 1.75 m, respectively.
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Keywords:
- analytical model /
- temperature /
- thermal diffusion /
- leachate /
- simplified design
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图 2 本文解和数值法的结果对比
Figure 2. Comparison between proposed analytical solutions and numerical results
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图 4 渗滤液水头对污染物在CCL中运移的影响(ST=1×10-2K-1，ΔT=-40 K)
Figure 4. Effects of leachate head on contaminant transport in CCL (ST=1×10-2 K-1, ΔT=-40 K)
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图 5 渗滤液水头对污染物在CCL中运移的影响(ST=5×10-2K-1，ΔT=-100 K)
Figure 5. Effects of leachate head on contaminant transport in CCL (ST=5×10-2 K-1, ΔT=-100 K)
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图 6 热扩散作用对污染物在CCL中运移的影响(hw=0.3 m)
Figure 6. Effects of thermal diffusion on contaminant transport in CCL (hw=0.3 m)
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图 7 热扩散作用对污染物在CCL中运移的影响(hw=3 m)
Figure 7. Effects of thermal diffusion on contaminant transport in CCL(hw=3 m)
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图 8 不同温度下渗透系数对污染物在膨润土中运移的影响
Figure 8. Effects of permeability coefficient on contaminant transport in bentonite liner under different temperatures
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图 9 污染物击穿CCL衬垫时厚度随渗滤液水头变化的线性拟合结果
Figure 9. Linear fitting results of relationship between thickness of CCL and leachate head based on breakthrough of contaminant
表 1 污染物在CCL中运移的参数取值表
Table 1 Parameters of contaminant transport in CCL
参数 符号 取值 渗滤液中污染物浓度 C0/(mg·L-1) 100 渗滤液水头 hw/m 0.3/3.0 有效扩散系数 D*/(m2·s-1) 4×10-10 黏土厚度 L /m 2.0 索雷特系数 ST /K-1 3×10-2 黏土层孔隙度 n 0.4 黏土层渗透系数 k /(m·s-1) 1×10-9 阻滞因子 Rd 1.0 黏土层两端温差 ΔT /K -50 
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表 2 不同温度污染物在膨润土中运移的参数取值
Table 2 Transport parameters for contaminant in bentonite liner under different temperatures
膨润土平均温度
T0/℃膨润土渗透系数
k/(m·s-1)渗滤液水头
hw/m有效扩散系数
D*/(m2·s-1)膨润土厚度
L/m30 2.12×10-13 0.3 3.5×10-12 0.1 60 4.29×10-13 90 6.48×10-13
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