Department of Civil and Environmental Engineering, University of Western Ontario, London, Ontario N6A 5B9, Canada.
Environ Sci Technol. 2011 Apr 1;45(7):2980-6. doi: 10.1021/es102969z. Epub 2011 Feb 25.
Smoldering combustion has been introduced recently as a potential remediation strategy for soil contaminated by nonaqueous phase liquids (NAPLs). Published proof-of-concept experiments demonstrated that the process can be self-sustaining (i.e., requires energy input only to start the process) and achieve essentially complete remediation of the contaminated soil. Those initial experiments indicated that the process may be applicable across a broad range of NAPLs and soils. This work presents the results of a series of bench-scale experiments that examine in detail the sensitivity of the process to a range of key parameters, including contaminant concentration, water saturation, soil type, and air flow rates for two contaminants, coal tar and crude oil. Smoldering combustion was observed to be self-sustaining in the range 28,400 to 142,000 mg/kg for coal tar and in the range 31,200 to 104,000 mg/kg for crude oil, for the base case air flux. The process remained self-sustaining and achieved effective remediation across a range of initial water concentrations (0 to 177,000 mg/kg water) despite extended ignition times and decreased temperatures and velocities of the reaction front. The process also exhibited self-sustaining and effective remediation behavior across a range of fine to coarse sand grain sizes up to a threshold maximum value between 6 mm and 10 mm. Propagation velocity is observed to be highly dependent on air flux, and smoldering was observed to be self-sustaining down to an air Darcy flux of at least 0.5 cm/s for both contaminants. The extent of remediation in these cases was determined to be at least 99.5% and 99.9% for crude oil and coal tar, respectively. Moreover, no physical evidence of contamination was detected in the treatment zone for any case where a self-sustaining reaction was achieved. Lateral heat losses to the external environment were observed to significantly affect the smoldering process at the bench scale, suggesting that the field-scale lower bounds on concentration and air flux and upper bound on grain size were not achieved; larger scale experiments and field trials where lateral heat losses are much less significant are necessary to define these process limits for the purposes of field application. This work provides valuable design data for pilot field trials of both in situ and ex situ smoldering remediation applications.
闷烧燃烧最近被引入作为一种修复受非水相液体（NAPL）污染土壤的潜在策略。已发表的概念验证实验表明，该过程可以自我维持（即，仅需要能量输入即可启动该过程），并可实现受污染土壤的基本完全修复。这些初始实验表明，该过程可能适用于广泛的 NAPL 和土壤。这项工作介绍了一系列台式实验的结果，这些实验详细研究了该过程对一系列关键参数的敏感性，包括污染物浓度、水饱和度、土壤类型以及两种污染物（煤焦油和原油）的空气流速。在基础案例空气通量下，观察到煤焦油的闷烧燃烧在 28400 至 142000mg/kg 的范围内和原油的 31200 至 104000mg/kg 的范围内是自我维持的。尽管点火时间延长，反应前沿的温度和速度降低，但该过程仍保持自我维持，并在初始水浓度（0 至 177000mg/kg 水）范围内实现了有效的修复。该过程还在细至粗砂粒尺寸范围内表现出自我维持和有效的修复行为，直至 6mm 至 10mm 之间的最大阈值。传播速度高度依赖于空气通量，对于两种污染物，观察到在空气达西通量至少为 0.5cm/s 时，闷烧是自我维持的。在这些情况下，修复的程度分别确定为原油和煤焦油的至少 99.5%和 99.9%。此外，在所实现的自我维持反应的任何情况下，在处理区均未检测到污染的物理证据。在台式规模上，向外部环境的横向热损失被观察到对闷烧过程有显著影响，这表明现场规模上的浓度和空气通量下限以及粒度上限未达到；需要更大规模的实验和现场试验，其中横向热损失要小得多，以便为现场应用定义这些过程限制。这项工作为原位和异位闷烧修复应用的试点现场试验提供了有价值的设计数据。
