In recent years, ex-situ
thermal pile desorption has been used extensively to remove organic pollutants from polluted soil in engineering practices, due to its advantages of controllable secondary pollution, high pollutant removal rate and low operational costs; however, the mechanisms that governs the pollutant removal still needs to be systematically examined. In this study, an engineering scale ex-situ thermal pile desorption experiment of 2000 m³ was carried out to removal pollutants in contaminated soil from a decommissioned coking plant in north China. The effect of operational variables, such as temperature and soil humidity, on repair effect and energy consumption are systematically analyzed, and suggestions on improving the performance of ex-situ thermal pile desorption were given. The results show that when the pile temperature reached 175 ℃ (on day 35), the concentrations of pollutants in 12 groups of soil samples were below the Soil Environmental Quality Risk Control Standard for Soil Contamination of Development Land
(GB 36600-2018) which indicate that the remediation target is reached. The amount of water collected during thermal desorption was 310.4 m³, and the soil’s bulk water content decreased from 25.8% to about 10.3% (on day 39). Meanwhile, the waste heat from flue gas was reused, which reduced 11.5% of the energy consumption of ex-situ thermal pile and made the net energy consumption for each cubic meter of polluted soil remediation was lowered to 49.5 Nm³ of natural gas and 16 kW∙h of electricity. In addition, the temperature and humidity of the thermal pile were mathematically simulated and the average relative errors between the measured and the simulated results were less than 7.36% (temperature) and 7.49% (water content), respectively, which had a good agreement. The simulation results also showed that the average temperature of the bottom layer of the thermal pile was relatively low during the operation; therefore, it is suggested that increasing the temperature of the bottom heating pipe or installation of insulation measures (such as stone-wool board) can improve the remediation efficiency. The results of this study can provide technical support for the designing and operation of ex-situ thermal pile desorption for remediation of organic contaminated soil.