大量油品滲漏場址截流溝浮油回收效率探討

Abstract

近年來，由於儲油槽洩漏和輸油管洩漏等因素，造成油品污染土壤及地下水事件層出不窮，且在油品污染之中，燃料油其含碳數高且不易揮發及移動之特性，因此，燃料油污染土壤及地下水之整治，困難度高於受汽油及柴油污染之地下環境。本研究以數值模擬軟體TMVOC模擬燃料油在含水層中之污染情境，並以截流溝(Free-Product Recovery Trench)加入抽水井，探討浮油回收效率。以四種變因進行討論，分別為截流溝位置、抽水井抽水深淺、土層滲透性及比較不同整治技術之影響。 模擬結果顯示截流溝距離洩漏點10 m處整治效率高達50 %，而截流溝距離洩漏點20 m處只有22 %。在相同截流溝位置，抽水井抽水位置越深整治效率越差。土層滲透性較低時，由於抽水產生較大洩降，因此浮油越容易被引導至截流溝中，整治效率反而較高。另外模擬顯示出土壤氣體抽除法(Soil Vapor Extraction, SVE)對於高密度和高黏度的燃料油整治效果差。 此外，經研究顯示截流溝中抽水對於溶解相苯濃度之整治效果皆顯著。但非飽和層之總石油碳氫化合物(Total Petroleum Hydrocarbon, TPH)濃度於整治前期效果明顯，整治後期濃度曲線趨於平緩，研判截流溝整治對於非飽和層油品殘留相整治效果不彰。若在整治後期使用截流溝搭配蒸氣注入(Steam Injection)輔助，可降低燃料油黏性，使吸附在土壤孔隙中的油品殘留相更容易移動，對非飽和層之TPH整治有明顯幫助。

In recent years, petroleum hydrocarbons released by storage tanks and pipelines contaminate soil and groundwater around refinery plants. Among those petroleum hydrocarbons, fuel oil is more difficult to remediate compared to gasoline and diesel fuel due to its characteristics of low volatility and low mobility. In this study, a numerical model software called TMVOC is used to simulate contamination of fuel oil within the aquifer and using recovery trench combined with pumping well to investigate the removal efficiency of free-product. Study the effect of four independent variables including recovery trench location, depth of pumping well, soil permeability and different remediation methods. The results show that when the distance between recovery trench and the spill point is 10 meter, the recovery rate can be up to 50%, but only 22% recovery rate will gain when the distance is 20 meter. In the same recovery trench location, the deeper the pumping well, the worse the remediation efficiency is. When the soil permeability is low, the efficiency is higher due to pumping lead to the high drawdown; therefore, free-product is guided to the recovery trench more easily. Another result showed that the efficiency of Soil Vapor Extraction is poor when treated to the fuel oil which has high density and high viscosity. The results of these research show that the remediation effect of recovery trench pumping to reduce the concentration of dissolved phase benzene is significant. Total petroleum hydrocarbons in the vadose zone decrease obviously at early stage; however, the concentration reduce rate is slow down at the late stage. So it is concluded that recovery trench has no significant effect on vadose zone residual phase oil removal. If using recovery trench assisted with steam injection in the late stage, it can reduce the viscosity of fuel oil, make the residual phase oil in the soil pores move more easily, and have a positive effect on remediating TPH in the vadose zone.