強(qiáng)熱化土壤氣相抽提過(guò)程中的污染物去除研究
發(fā)布時(shí)間：2019-06-10 04:48
【摘要】：近年來(lái),由于石油開(kāi)采、運(yùn)輸和石化產(chǎn)業(yè)的快速發(fā)展,以及加油站的大幅度增設(shè),部分石油烴和芳香烴類物質(zhì)滯留土壤表層和內(nèi)部,土壤有機(jī)污染在我國(guó)日趨嚴(yán)峻。作為原位修復(fù)技術(shù),土壤氣相抽提(Soil Vapor Extraction, SVE)廣泛運(yùn)用于土壤非飽和區(qū)揮發(fā)(VOCs)及部分半揮發(fā)性(SVOCs)有機(jī)污染物的清除。然而,當(dāng)VOCs和SVOCs遭遇慢解吸、慢擴(kuò)散、氣流再次吸附以及常溫下的污染物有限揮發(fā)時(shí),SVE傳質(zhì)下降而發(fā)生拖尾效應(yīng)。熱強(qiáng)化SVE技術(shù)能夠克服上述傳質(zhì)局限性,顯著改善有機(jī)物去除效率。在熱強(qiáng)化SVE操作中后期,土壤水相以及以NAPL(Non-aqueous Phase Liquid)相存在的VOCs和SVOCs逐漸減少甚至消失,此時(shí)僅存在氣流攜帶的揮發(fā)態(tài)VOCs和SVOCs與土壤固相之間的平衡分配,其傳質(zhì)過(guò)程與氣-固分離色譜相似。試驗(yàn)采用土壤柱氣相色譜技術(shù),以正己烷、正癸烷、正十四烷和甲苯四種典型碳?xì)浠衔餅楣┰囄廴疚?以色譜參數(shù)容量因子k'和拖尾因子Tf分別作為熱脫附速率與效率的量度,探討污染物熱強(qiáng)化SVE脫附過(guò)程的熱力學(xué)與動(dòng)力學(xué)機(jī)制。結(jié)果表明,當(dāng)溫度高于有機(jī)物沸點(diǎn)時(shí),此時(shí)為快脫附階段,解吸速率與沸點(diǎn)呈反比例函數(shù)關(guān)系；當(dāng)溫度低于沸點(diǎn)時(shí),此時(shí)為慢脫附階段,解吸速率與有機(jī)物的辛醇-水分配系數(shù)呈反比例關(guān)系。土壤有機(jī)質(zhì)含量對(duì)碳?xì)浠衔锏奈交罨苡酗@著影響。對(duì)于有機(jī)質(zhì)含量高的土壤,為克服活化能障礙,需要通過(guò)升高溫度來(lái)實(shí)現(xiàn)。載氣流速的增加則對(duì)慢脫附階段的吸附活化能具有反作用。試驗(yàn)搭建熱強(qiáng)化一維土柱模擬裝置,以正十三烷、正十四烷、正十五烷、正十六烷為供試污染物,分析溫度、土壤含水量、土壤有機(jī)質(zhì)以及污染物性質(zhì)對(duì)熱強(qiáng)化SVE污染物去除率的影響。結(jié)果表明,加熱溫度越高,有機(jī)物的土壤殘留率越低,當(dāng)溫度增加到180℃時(shí),絕大部分污染物已去除,繼續(xù)升高溫度污染物去除率變化不明顯。土壤含水量對(duì)有機(jī)污染物的去除效率影響是雙向的,并受溫度控制。有機(jī)物的去除率伴隨著土壤有機(jī)質(zhì)的增加而降低。溫度越高,土壤有機(jī)質(zhì)對(duì)有機(jī)污染物的去除效率影響越小。有機(jī)物的殘留率與沸點(diǎn)呈現(xiàn)正比例函數(shù)關(guān)系。
[Abstract]:In recent years, due to the rapid development of oil exploitation, transportation and petrochemical industry, as well as the large addition of gas stations, some petroleum hydrocarbons and aromatic hydrocarbons remain in the surface and interior of the soil, and soil organic pollution is becoming more and more serious in China. As an in-situ remediation technique, (Soil Vapor Extraction, SVE) extracted by soil vapor phase is widely used in the removal of volatile (VOCs) and some semi-volatile (SVOCs) organic pollutants in soil unsaturated region. However, when VOCs and SVOCs encounter slow desorption, slow diffusion, airflow readsorption and limited volatilization of pollutants at room temperature, the mass transfer of SVE decreases and the tail effect occurs. Thermal enhanced SVE technology can overcome the above limitations of mass transfer and significantly improve the removal efficiency of organic matter. In the middle and late stage of thermal enhanced SVE operation, the soil water phase and the VOCs and SVOCs in NAPL (Non-aqueous Phase Liquid) phase) gradually decreased or even disappeared, and there was only the equilibrium distribution between volatile VOCs and SVOCs carried by air flow and soil solid phase. The mass transfer process is similar to that of gas-solid separation chromatography. Four typical hydrocarbons, n-hexane, n-decane, n-tetradecane and toluene, were tested by soil column gas chromatography. The thermodynamic and kinetic mechanism of thermal enhanced SVE desorption process of pollutants was discussed by using chromatographic parameter capacity factor k 'and trailing factor Tf as measures of thermal desorption rate and efficiency, respectively. The results show that when the temperature is higher than the boiling point of organic matter, it is a fast desorption stage, and the desorption rate is inversely proportional to the boiling point. When the temperature is lower than the boiling point, it is a slow desorption stage, and the desorption rate is inversely proportional to the octanol-water partition coefficient of organic matter. The content of soil organic matter has a significant effect on the adsorption and activation energy of hydrocarbons. For soils with high organic matter content, in order to overcome the obstacle of activation energy, it is necessary to increase the temperature. The increase of carrier gas velocity is counterproductive to the adsorption activation energy in the slow desorption stage. A one-dimensional soil column simulation device for thermal strengthening was built. N-tridecane, n-tetradecane, n-pentadecane and n-hexadecane were used as pollutants to analyze temperature and soil water content. Effects of soil organic matter and pollutant properties on the removal rate of thermal enhanced SVE pollutants. The results showed that the higher the heating temperature was, the lower the soil residual rate of organic matter was. When the temperature increased to 180 鈩，
本文編號(hào)：2496183
[Abstract]:In recent years, due to the rapid development of oil exploitation, transportation and petrochemical industry, as well as the large addition of gas stations, some petroleum hydrocarbons and aromatic hydrocarbons remain in the surface and interior of the soil, and soil organic pollution is becoming more and more serious in China. As an in-situ remediation technique, (Soil Vapor Extraction, SVE) extracted by soil vapor phase is widely used in the removal of volatile (VOCs) and some semi-volatile (SVOCs) organic pollutants in soil unsaturated region. However, when VOCs and SVOCs encounter slow desorption, slow diffusion, airflow readsorption and limited volatilization of pollutants at room temperature, the mass transfer of SVE decreases and the tail effect occurs. Thermal enhanced SVE technology can overcome the above limitations of mass transfer and significantly improve the removal efficiency of organic matter. In the middle and late stage of thermal enhanced SVE operation, the soil water phase and the VOCs and SVOCs in NAPL (Non-aqueous Phase Liquid) phase) gradually decreased or even disappeared, and there was only the equilibrium distribution between volatile VOCs and SVOCs carried by air flow and soil solid phase. The mass transfer process is similar to that of gas-solid separation chromatography. Four typical hydrocarbons, n-hexane, n-decane, n-tetradecane and toluene, were tested by soil column gas chromatography. The thermodynamic and kinetic mechanism of thermal enhanced SVE desorption process of pollutants was discussed by using chromatographic parameter capacity factor k 'and trailing factor Tf as measures of thermal desorption rate and efficiency, respectively. The results show that when the temperature is higher than the boiling point of organic matter, it is a fast desorption stage, and the desorption rate is inversely proportional to the boiling point. When the temperature is lower than the boiling point, it is a slow desorption stage, and the desorption rate is inversely proportional to the octanol-water partition coefficient of organic matter. The content of soil organic matter has a significant effect on the adsorption and activation energy of hydrocarbons. For soils with high organic matter content, in order to overcome the obstacle of activation energy, it is necessary to increase the temperature. The increase of carrier gas velocity is counterproductive to the adsorption activation energy in the slow desorption stage. A one-dimensional soil column simulation device for thermal strengthening was built. N-tridecane, n-tetradecane, n-pentadecane and n-hexadecane were used as pollutants to analyze temperature and soil water content. Effects of soil organic matter and pollutant properties on the removal rate of thermal enhanced SVE pollutants. The results showed that the higher the heating temperature was, the lower the soil residual rate of organic matter was. When the temperature increased to 180 鈩，
本文編號(hào)：2496183
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