Thermodynamic Modeling and Heat-Moisture Transfer Characteristic Analysis of in Situ Thermal Desorption System for Polluted Soil

In Situ Gas Thermal Desorption (ISGTD) is one of the effective approaches for organic contaminated soil. To investigate the heat-moisture transfer characteristics of soil during the heating process, a radially layered coupled heat-moisture model of the ISGTD system is established. The temperature and moisture distribution along the radial direction of the heat source, as well as the synergistic action of heat-moisture transfer at different heating stages are analyzed. The effects of heat intensity and initial water content on the heating performance are discussed. The results demonstrate that the liquid water migration driven by temperature gradient is greater than that driven by water content gradient and the liquid water migration in each soil unit increases from the heat-up stage to the superheating phase inside-out radially. The gas flow rate directly affects the stable temperature and heating time, while the initial water content only contributes to the heating time when the stable temperature remains unchanged. The correctness of the numerical model and results is verified by comparing them with on-site experimental data. Considering that high initial water content will lead to an extension of the heating time in the first two stages, further optimization design can be carried out for less gas flow rate and shorter heating time to achieve energy-saving remediation of high moisture soil. The above findings are of guiding significance in the engineering applications of contaminated soil remediation.