强热化土壤气相抽提过程中的污染物去除研究
发布时间：2019-06-10 04:48
【摘要】：近年来,由于石油开采、运输和石化产业的快速发展,以及加油站的大幅度增设,部分石油烃和芳香烃类物质滞留土壤表层和内部,土壤有机污染在我国日趋严峻。作为原位修复技术,土壤气相抽提(Soil Vapor Extraction, SVE)广泛运用于土壤非饱和区挥发(VOCs)及部分半挥发性(SVOCs)有机污染物的清除。然而,当VOCs和SVOCs遭遇慢解吸、慢扩散、气流再次吸附以及常温下的污染物有限挥发时,SVE传质下降而发生拖尾效应。热强化SVE技术能够克服上述传质局限性,显著改善有机物去除效率。在热强化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逐渐减少甚至消失,此时仅存在气流携带的挥发态VOCs和SVOCs与土壤固相之间的平衡分配,其传质过程与气-固分离色谱相似。试验采用土壤柱气相色谱技术,以正己烷、正癸烷、正十四烷和甲苯四种典型碳氢化合物为供试污染物,以色谱参数容量因子k'和拖尾因子Tf分别作为热脱附速率与效率的量度,探讨污染物热强化SVE脱附过程的热力学与动力学机制。结果表明,当温度高于有机物沸点时,此时为快脱附阶段,解吸速率与沸点呈反比例函数关系；当温度低于沸点时,此时为慢脱附阶段,解吸速率与有机物的辛醇-水分配系数呈反比例关系。土壤有机质含量对碳氢化合物的吸附活化能有显著影响。对于有机质含量高的土壤,为克服活化能障碍,需要通过升高温度来实现。载气流速的增加则对慢脱附阶段的吸附活化能具有反作用。试验搭建热强化一维土柱模拟装置,以正十三烷、正十四烷、正十五烷、正十六烷为供试污染物,分析温度、土壤含水量、土壤有机质以及污染物性质对热强化SVE污染物去除率的影响。结果表明,加热温度越高,有机物的土壤残留率越低,当温度增加到180℃时,绝大部分污染物已去除,继续升高温度污染物去除率变化不明显。土壤含水量对有机污染物的去除效率影响是双向的,并受温度控制。有机物的去除率伴随着土壤有机质的增加而降低。温度越高,土壤有机质对有机污染物的去除效率影响越小。有机物的残留率与沸点呈现正比例函数关系。
[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，
本文编号：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，
本文编号：2496183
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