热促土壤气相抽提过程中的气相传质及污染物去除研究

This research is focused on the technological basis of thermally-enhancecd SVE (soil vapor extraction) for remediating soils contaminated with petroleum and aromatic hydrocarbons. The simulated two-dimentionally experimental equipment will be constructed, and six organic chemicals including pentane, octane, decane, tetradecane, toluene and dichlorobenzene will be selected as test pollutants.In the experiments, the infuluences of heating process on the pollutant removal, the radial and longitudinal permeability, and pore-gas velocity will be explored in the SVE system through the computer simulation of pressure, temperature and moisture, so that the features of the ROI (radius of influence) as.well as gas flow field distribution for the thermally enhanced SVE will be revealed. Meanwhile, the reverse soil column gas chromatography will be adopted to determine the soil-air partitioning parameters and the other chromatography parameters of the test pollutants, which will be used to establish the gasous volatilizezing removal model for the pollutants without NAPL (non-aqueous phase liquids) existing in the soils. A small one-dimentional simulated soil column is also made to observe the.non-gasous volatilizezing removal of the pollutants from the soils. Based on the gas-solid chromatographic separation theory, the research will also explore the relationship between the exact SVE closure time and heating temperature, and therefore a new assessment method of the cease venting for the SVE system will be established based on the adsorption-desorption limitation of the pollutants. Combining the above all the tests,the research will demonstrate the thermal features and kinetic mechanisms of thermally-enhanced SVE remediating polluted sites, and thus provides the important technological references for the design, optimization and operation of thermally-enhanced SVE.

项目围绕热促土壤气相抽提（SVE）修复石油烃、芳烃污染场地的技术基础展开研究。拟以戊烷、辛烷、癸烷、十四烷、甲苯和二氯苯为供试有机污染物，构建二维SVE模拟中试试验装置，通过对压力及温湿度传感数据的计算机模拟，研究加热对SVE污染物去除的影响，以及SVE系统轴向、径向渗透性和孔隙流速的影响，揭示热促SVE系统作用半径改变特点及热促SVE气流场分布特征；构建土壤柱逆向气相色谱试验装置，测定污染物的土壤-空气分配参数及其它色谱参数，建立不存在NAPL相的污染物气态挥发去除模型；构建小型一维土壤柱模拟试验装置，研究污染物的非气态挥发过程。同时，项目在有机污染物气-固色谱分离理论基础上，研究SVE关停时间与加热温度的依变关系，建立基于吸附-解吸限制的SVE关停时间计算新方法。通过上述研究综合揭示热促SVE技术修复污染场地的热力学特征和动力学机制，为指导和优化热促SVE设计、运行提供重要技术依据。

热强化气相抽提技术（T-SVE）在修复半挥发性石油烃污染土壤方面极具应用潜力。本项目基于土壤柱气相色谱试验和热强化气相抽提一维、二维试验，研究了T-SVE修复机制和影响因素。在土壤柱气相色谱试验中，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。当温度高于有机物沸点时，此时为快解吸阶段，解吸速率与沸点呈反比例函数关系；当温度低于沸点时，此时为慢解吸阶段，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解吸阶段的吸附活化能具有反作用。在热强化气相抽提一维试验中，以正十三烷、正十四烷、正十五烷和正十六烷为供试污染物。结果表明，温度决定性地影响了石油烃污染土壤的修复效率，污染土壤残留率与加热温度基本呈反比。石油烃去除过程符合Elovich和Freundlich热脱附动力学方程。土壤含水量（5%~30%）的增加降低了石油烃去除效率。土壤有机质含量增加明显降低了石油烃去除率，尤其对于辛醇-水分配系数值高的石油烃。在热强化气相抽提二维试验中，布设多个温度和压力传感器。持续加热方式土体温度最高，间歇加热导致油浴近处温度波动较大。装置先加热后装土的方式温度最低，并且土体受热时间缩短。与表面开放相比，表面覆盖极大改变了压力和温度场分布。由于热辐射和热传导传热效率不同，整个土筒内温度呈“V”形由外向内降低。CMG-STARS软件数值模拟结果与实测传感数据有较高符合度。