有机污染土壤堆式热脱附过程中热湿迁移试验及数值模拟

堆式燃气热脱附技术因具有二次污染小、污染物去除率高和处理周期短等优势而得到快速发展. 土壤中的水分是影响堆体热修复过程中土壤升温的关键因素，然而其热湿迁移机理尚不明晰，工程设计主要依赖于实践经验. 该研究以山东省某污染场地的砂质壤土开展堆体热湿迁移试验，结合COMSOL仿真模拟，系统分析加热过程中土壤温度和湿度在竖直及水平方向上的变化规律. 结果表明:热源附近土壤水分呈逐渐升高并出现短暂峰值(高于初始值10.9%)后再下降的趋势，水分峰值随温度提高而升高；热源温度越高，土壤中水汽的对流和扩散作用愈加明显，当热源温度由50.0 ℃升至100 ℃时，监测点体积含水量下降率由4.50%升至27.2%，且水汽的浓度扩散机制在水分迁移过程中占主导作用；对于相同热源作用下，初始体积含水量较高的土壤具有相对较高的温度变化，温升过程中对流传热以及热传导的作用更显著，当初始体积含水量由0.0700 m3/m3升至0.160 m3/m3时，监测点的温度由37.1 ℃升至40.0 ℃，其中多孔基体间的热传导作用占主导. 研究显示，堆体热脱附过程中土壤水分迁移规律与土壤体积含水量、距热源的距离、热源温度有关，且多孔基体间的热传导是引起土壤升温的主要机制. 

Experiment and Numerical Simulation of Heat and Moisture Migration in Thermal Desorption Process

Pile thermal desorption technology has been developed rapidly due to its advantages of low secondary pollution, high pollutant removal rate and short treatment period. Soil moisture is the key factor affecting soil temperature rise in the process of pile thermal desorption. However, the mechanism of heat and moisture migration is still unclear, and engineering design mainly depends on practical experience. In this study, the sandy loam from a polluted site in Shandong Province was used to carry out the heat and moisture transfer experiment. Combined with COMSOL simulation, the variation law of soil temperature and humidity in the vertical and horizontal directions during the heating process was systematically analyzed. The results showed that the moisture of the soil close to the heat source gradually increased and then decreased after a short peak (10.9% higher than the initial value). The peak value of soil moisture increased with the increase of temperature. Furthermore, the convection and diffusion of water vapor in the soil were enhanced when the heat source temperature increased. When the heat source temperature increased from 50.0 ℃ to 100 ℃, the volumetric water content at the monitoring point decreased from 4.50% to 27.2%, and the concentration diffusion mechanism of water vapor played a dominant role in the water transfer process. For the same heat source, the soil with high initial volumetric moisture content had relatively high temperature change, and the convection heat transfer and heat conduction played a more significant role in the process of temperature increase. When the initial volumetric moisture content increased from 0.0700 m3/m3 to 0.160 m3/m3, the temperature at the monitoring point increased from 37.1 ℃ to 40.0 ℃, in which the heat conduction between porous substrates dominated. The study showed that the soil moisture transfer law in the pile thermal desorption process is related to the soil volumetric moisture content, the distance from the heat source and the temperature of the heat source. In addition, the heat conduction between porous substrates was the main mechanism causing the soil temperature increase.