土壤復育現地注氣法-飽和層氣流之特性研究; The Study of Air Flow in Saturated Porous Media under Air Sparging Condition

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題名:	土壤復育現地注氣法-飽和層氣流之特性研究;The Study of Air Flow in Saturated Porous Media under Air Sparging Condition
作者:	黃美娟;Mei-Chuan Huang
貢獻者:	中國醫藥學院環境醫學研究所
關鍵詞:	現地注氣法;揮發性有機物質;非水溶相液體;Air sparging system;VOCs;NAPLs
日期:	1999
上傳時間:	2009-11-30
摘要:	現地注氣法(Air Sparging System)為一處理受到揮發性有機物(Volatile Organic Compounds, VOCs)污染之土壤及地下水復育技術；此工法將空氣經由泵直接加壓注入地表受VOCs污染的飽和層中，待污染物質經脫附、擴散及揮發等作用傳輸至注入氣流後，再將含有汙染物之氣流於非飽和層中抽除，並導入地面相關設備作進一步處理、處置，而達到整治效益。本研究於實驗室內設計一Air Sparging土柱模型，當改變不同實驗控制因子時，以X-ray照射之顯影探討注入氣流在飽和石英砂中的生成及分佈現象。均質飽和含水模擬實驗中發現，在平均粒徑為0.4及0.7 mm之石英砂中，氣流均以氣柱型態流動；而平均粒徑為1.8及2.9 mm時，氣流則為氣泡的形式。本研究於不同粒徑的實驗中均發現，增加注氣量將擴大影響半徑；但持續增加注氣量，影響半徑(radius of influence, ROI)將不再有明顯之變化。因此，增加注氣量可能不會得到較大的ROI。顯影結果發現ROI與石英砂之平均粒徑成正比關係，而三種石英砂之透水係數隨平均粒徑增加。因此，於透水性佳的孔隙介質，則可能會有較大ROI。在平均粒徑0.4~1.8 mm三種石英砂中，氣域外緣與水平面之夾角?約為60~78度，且粗質地的石英砂因ROI較大故?較小。同時，夾角?與注氣量略成反比關係；但當注氣量超過一定值時，夾角?維持一定的範圍。隨著注氣量的增加，飽和層內所含之空氣體積亦會隨之增加。同時，在d50=0.4 mm及d50=0.7 mm兩種石英砂中，隨著空氣體積的增加，氣域內之主要氣柱數量及氣柱大小亦會隨之改變。實驗結果發現在平均粒徑0.4 mm石英砂中，氣柱大小約0.1~0.8 cm；在相同流量時，氣柱大小與d50=0.7 mm石英砂差異不顯著。然而，d50=0.7 mm石英砂之主要氣柱數量約為d50=0.4 mm的兩倍。因此較粗之孔隙介質中，氣柱數量較多則可增加液氣相間接觸面積及縮短污染物擴散之距離。在含水飽和分層實驗發現之氣域形狀與均質條件時不同，氣流在粒徑較小石英砂中主要沿垂直方向移動；相同注氣條件下，其ROI均小於均質實驗。因此，土壤的非均質特性可能會限制Air Sparging System之處理範圍。 95無鉛汽油飽和層之實驗結果發現，氣流生成現象與均質含水飽和層並無明顯差異。同時，以95無鉛汽油模擬輕質非水溶相液體(Light Non-Aqueous Phase Liquids, LNAPLs) ，實驗發現氣流將直接穿越LNAPLs，其ROI及氣域範圍均較均質飽和含水層大。因此，Air Sparging在LNAPL中可能較一般飽和層有較大之整治範圍。; Accident releases of volatile organic compounds (VOCs) from petroleum products and solvents have resulted in gross contamination of soils and groundwater. VOCs are found to be non-aqueous phase liquids (NAPLs) at many contaminated sites. Air sparging, also called “in situ air stripping”, is a remedial technology whereby contaminant-free air is induced into a contaminated aquifer to volatilize VOCs from the groundwater into the air phase. Several field-scale applications of the air sparging system have indicated that air sparging may be effective in remediating VOC-contaminated aquifers at a faster rate than the application of a pump-and-treat system. In this study, a bench-scale air sparging model with a thickness of 3 cm was set up and uniform sizes of glass beads were used as porous media to simulate an unconfined aquifer. As air sparged into the model, visualization experiments conducted by the X-ray image were to investigate the factors affecting of airflow in saturated porous media during air sparging. In homogeneous saturated porous media experiment, two distinct airflow regimes have been observed within the range of airflow rates tested. The type of airflow regime depended primarily upon grain size. For average grain size of 0.4 mm and 0.7 mm, the channel flow was observed. For average grain size of 1.8 mm and 2.9 mm, the airflow was observed in bubbles. Therefore, sparged air may flow like air channels in the sandy aquifer. The experiments indicated that radius of influence (ROI) increased with increasing airflow rates and approximately reached a constant value for a further increase in the airflow rate. From the X-ray photographs, the ROI was directly proportional to the average grain size and hydraulic conductivity of glass beads. This implies that the larger ROI could be expected to form in soil with high hydraulic conductivity. At various airflow rates, the angle between air plume and level were 60o~78o for three different glass beads with average grain size 0.4~1.8 mm. The experiments also showed that the angles were inversely proportional to airflow rates but did not obviously change for the higher airflow rates. At two-layer saturated porous media experiments, that the air plum was different from homogeneous porous media. At the same airflow rate, ROIs in the layer with finer grain size were less than the homogeneous porous media. Therefore, the heterogeneity of site may restraint the treatment extent of Air Sparging System. Further, air sparging experiments were conducted in the situation of 95 non-lead gasoline present in saturated porous media as light non-aqueous phase liquids (LNAPLs). Results showed that air flowed through LNAPLs with an enlarged ROI. This indicated that sparged air
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