Kaslusky Scott F, Udell Kent S
Department of Mechanical Engineering, University of California at Berkeley, Berkeley, CA 94720, USA.
J Contam Hydrol. 2005 May;77(4):325-47. doi: 10.1016/j.jconhyd.2005.02.003.
When steam is injected into soil containing a dense volatile non-aqueous phase liquid contaminant, the DNAPL vaporized within the heated soil region condenses and accumulates ahead of the steam condensation front. If enough DNAPL accumulates, gravitational forces can overcome trapping forces allowing the liquid contaminant to flow downward. By injecting air with steam, a portion of the DNAPL vapor remains suspended in equilibrium with the air, decreasing liquid contaminant accumulation ahead of the steam condensation front, and thus reducing the possibility of downward migration. In a previous work, a theoretical model was developed to predict the optimum injection ratio of air to steam that would eliminate accumulation of DNAPL ahead of the temperature front and thus minimize the potential for downward migration. In this work, the theoretical model is summarized, and an experiment is presented in order to evaluate the optimum injection ratio prediction. In the experiment, a two-dimensional water saturated sand pack is contaminated with a known mass of TCE (DNAPL). The system is then remediated by co-injecting air and steam at the predicted optimum injection ratio, calculated based on the average contaminant soil concentration in the sand pack. Results for the co-injection of air and steam are compared to results for the injection of pure steam or pure air. Injection at the predicted optimum injection ratio for a volumetric average NAPL saturation, reduced accumulation of the contaminant ahead of the condensation front by over 90%, as compared to steam injection alone. This indicates that the optimum injection ratio prediction is a valuable tool for limiting the spreading of DNAPL during steam-enhanced extraction. Injection at the optimum injection ratio resulted in earlier recovery of contaminant than for steam injection alone. Co-injection of steam and air is also shown to result in much higher recovery rates than air injection alone.
当蒸汽注入含有致密挥发性非水相液体污染物的土壤中时，在加热的土壤区域内汽化的重质非水相液体（DNAPL）会在蒸汽冷凝前沿之前冷凝并积聚。如果积聚了足够的DNAPL，重力就可以克服捕集力，使液体污染物向下流动。通过将空气与蒸汽一起注入，一部分DNAPL蒸汽会与空气保持平衡悬浮状态，减少蒸汽冷凝前沿之前的液体污染物积聚，从而降低向下迁移的可能性。在之前的一项工作中，开发了一个理论模型来预测空气与蒸汽的最佳注入比例，该比例可消除温度前沿之前DNAPL的积聚，从而将向下迁移的可能性降至最低。在这项工作中，总结了该理论模型，并进行了一项实验以评估最佳注入比例预测。在实验中，一个二维水饱和砂柱被已知质量的三氯乙烯（DNAPL）污染。然后根据砂柱中污染物的平均土壤浓度计算出预测的最佳注入比例，同时注入空气和蒸汽对该系统进行修复。将空气和蒸汽共同注入的结果与纯蒸汽或纯空气注入的结果进行比较。对于体积平均非水相液体（NAPL）饱和度，以预测的最佳注入比例进行注入时，与单独注入蒸汽相比，冷凝前沿之前的污染物积聚减少了90%以上。这表明最佳注入比例预测是限制蒸汽强化萃取过程中DNAPL扩散的一个有价值的工具。以最佳注入比例进行注入比单独注入蒸汽能更早地回收污染物。还表明，蒸汽和空气共同注入的回收率比单独注入空气要高得多。
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