Research on the effect of atmospheric pressure fluctuation on the migration and transformation of benzene in soil based on TMVOC simulation
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摘要:
为探究大气压力波动下苯系物（BTEX）的迁移转化规律，提升石化污染场地土壤地下水污染治理水平，以西北某炼化场地为研究对象，结合室内土柱试验与TMVOC软件模拟，开展BTEX泄漏模拟，研究不同大气压力波动幅度下苯在包气带与含水层中的迁移转化规律。结果表明：大气压力循环波动会引起包气带中的气相苯发生相间非平衡态迁移，导致气相质量分数增加0.1%~0.5%；非水相液体（NAPL）污染物转化为气相污染物，进而通过大气挥发是主要的质量损失方式，该转化会造成场地及周边的大气环境污染；同时大气压力波动的幅度与气相转变发生时间存在负线性相关关系。研究显示，大气压力波动显著影响了苯的相态转化与迁移过程，促进了苯的相态转化，使得更多的苯转化为气相，造成大气环境污染。
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关键词:
- 挥发性有机化合物(VOCs) /
- 包气带 /
- 大气压力波动 /
- TMVOC
Abstract:In order to explore the migration and transformation law of benzene series (BTEX) under the fluctuation of atmospheric pressure, and improve the control level of soil and groundwater pollution in petrochemical-polluted sites, a refinery site in northwest China was taken as the research object and, combined with indoor soil column experiment and TMVOC software simulation, BTEX leakage simulation was carried out to explore the migration and transformation law of benzene in the vadose zone and aquifer under different amplitude of atmospheric pressure fluctuation. The results show that the atmospheric pressure cycle fluctuation can cause the gaseous benzene in the vadose zone to migrate to the non-equilibrium state, resulting in the increase of the gaseous mass fraction by 0.1%-0.5%. The conversion of non-aqueous liquid (NAPL) phase pollutants into vapor phase pollutants and their volatilization through the atmosphere is the main way of leakage quality loss, and this transformation will cause atmospheric pollution in the site and its surroundings. At the same time, the amplitude of atmospheric pressure fluctuation is negatively correlated with the time of gaseous transition. The study shows that the atmospheric pressure fluctuation significantly affects the phase transformation and migration process of benzene, promotes the phase transformation of benzene, and makes more benzene transform into gas, resulting in atmospheric environmental pollution.
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Key words:
- volatile organic compounds(VOCs) /
- vadose zone /
- atmospheric pressure fluctuation /
- TMVOC
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图 3 TMVOC所考虑的相组成与相变
注：g为气相；w为液相（溶解相）；n为NAPL相；gw为液相-气相；wn为液相-NAPL相；gn为NAPL相-气相。
Figure 3. Phase compositions and phase changes considered by TMVOC
图 4 在不同迁移时间及采样深度下A、B土壤柱中苯浓度的分布情况
Figure 4. Distribution of concentration benzene in soil columns A and B at different migration times and depth
图 5 不同深度下A、B土壤柱在24和48 h后的苯浓度分布情况
Figure 5. Distribution of benzene concentration in soil columns A and B at different depths after 24 h and 48 h
图 6 模拟大气压力波动下BTEX的NAPL相质量分数变化
Figure 6. NAPL phase mass fraction of BTEX under simulated atmospheric pressure fluctuations
图 7 模拟大气压力波动下BTEX气相质量分数变化
Figure 7. Gaseous mass fraction of BTEX under simulated atmospheric pressure fluctuations
图 8 模拟大气压力波动下BTEX液相质量分数变化
Figure 8. Aqueous mass fraction of BTEX under simulated atmospheric pressure fluctuation
图 9 气压波动下不同深度土壤中苯的不同相态质量分数变化
Figure 9. Mass fraction of benzene in different phases in soil at different depths under different atmospheric pressures
图 10 不同大气压力下−40和−50 cm处的苯各相态质量分数变化
Figure 10. Mass fraction of benzene in different phases at −40 and −50 cm under different atmospheric pressures
图 11 不同表层气压下−10 cm处气相苯的质量分数变化
Figure 11. Mass fraction of benzene in gas phase at −10 cm under different surface pressures
表 1 苯的理化性质
Table 1. Physical and chemical properties of benzene
摩尔质量/（g/mol） 标准沸点/K 临界温度/K 临界压力/kPa 临界体积/（cm3/mol） 密度/（kg/m3） 偏心因子 偶极矩 分配系数（Koc）/（m3/kg） 78.114 353.2 562.2 4.82×106 259.0 885.0 0.212 0.0 0.089 1 
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表 2 试验设计与取样时间
Table 2. Experimental design and sampling schedule
土壤柱 0~3 d气压波动设置 A柱 1）加压1 000 Pa，并维持8 h；
2）恢复气压至标准大气压，静置18 hB柱 初始状态与A柱保持一致，不加压，
之后的采样时间同样与A柱保持一致
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表 3 概化模型参数
Table 3. Generalized model parameters
渗透系数/（cm/s） pH 土壤容重/（kg/m3） 含水率/% 孔隙度 5.6×10−4 6.2 1 650 21 0.15
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表 4 苯的扩散系数
Table 4. Diffusion coefficient of benzene
气相中扩散
系数/（m2/s）液相中扩散
系数/（m2/s）NAPL相扩散
系数/（m2/s）水中溶解度/
（mol/mol）7.7×10−6 6.0×10−10 6.0×10−10 4.11×10−2
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