Experimental And Numerical Study Of Heat And Mass Transfer In Soil In-situ Thermal Conduction Remediation

With the acceleration of my country’s modernization construction,a large number of enterprises have been shut down and transferred,resulting in a large number of organically polluted sites,which has caused a series of safety problems.In-situ heat conduction remediation technology has the characteristics of high efficiency,reliability and wide applicability,and occupies an important position in the field of organic pollution site remediation.At present,the in-situ heat conduction remediation technology still has the defects of unclear heat and mass transfer mechanism inside the soil,inaccurate prediction of repair cycle,and high energy consumption for repair.In this paper,relying on the National Key R&D Program Funded Project "Complete Technology and Equipment for Soil Remediation Thermal Desorption of Organic Polluted Sites",experiments on heat and mass transfer mechanism were carried out,and a numerical prediction model was established and verified in pilot experiments,which is expected to be an in-situ heat conduction remediation technology Provide theoretical guidance.Firstly,in this paper,the effects of different heat source temperature,initial moisture content and negative pressure on soil heat and moisture migration were analyzed.The research shows that: 1)The soil temperature rise process can be divided into three stages: heating,boiling,and superheating,which is in line with the actual expectation;2)Increasing the initial water content makes the heating rate faster;3)Increasing the extraction negative pressure will reduce the boiling platform temperature,which is beneficial to shorten the time to reach the target temperature.The extraction effect of negative pressure at 200 ℃ is remarkable.Secondly,based on the law of heat and mass migration and the theory of heat and mass transport in porous media,a numerical model suitable for insitu heat conduction remediation was established,and the model was optimized and verified using basic experimental data.The effects of different temperatures,initial moisture content and negative pressure on in-situ heat conduction remediation were analyzed by numerical simulation.The results show that: 1)The evaporation rate is proportional to the distance from the temperature measurement point to the heat source,but when it reaches a certain threshold,the evaporation rate It no longer increases with the increase of temperature;2)The influence radius of the heat source is proportional to the heating temperature,but after a certain heating time,the influence radius no longer increases significantly.Finally,based on the pilot test of a decommissioning site in Liuzhou,the numerical model of in-situ heat conduction is modified to make it suitable for complex engineering situations.Using field experimental data and numerical simulations,it is found that when the temperature of the heating well is 800 ℃,the coupling action of multiple heating wells needs to run for more than 20 days,otherwise the energy loss will increase.In addition,it is necessary to set additional heating wells in the repaired area,and the moisture at the bottom of the repaired area has a side effect on the temperature increase of the repaired plot.This paper provides theoretical guidance for in-situ heat conduction remediation technology through experiments and numerical simulation studies,which is conducive to optimizing the spatial distribution of heating wells and extraction wells,and promoting the practical application of in-situ heat conduction remediation technology.