A numerical simulation method for thermal conduction enhanced vapor extraction of an organic contaminated site

Abstract

The application provides a simulation method for thermal conduction enhanced gas phase extraction of an organic contaminated site, comprising the following steps: S1, establishing a thermal conduction enhanced gas phase extraction finite element model; S2, meshing the thermal conduction enhanced gas phase extraction finite element model; S3, configuring corresponding parameters according to an actual site remediation process; S4, setting control calculation parameters for the thermal conduction enhanced gas phase extraction finite element model; S5, initializing the thermal conduction enhanced gas phase extraction finite element model under natural conditions; S6, assigning initial concentrations of pollutants to the thermal conduction enhanced gas phase extraction finite element model; and S7, executing a thermal conduction enhanced gas phase extraction numerical simulation program to realize remediation process simulation. The application solves the problem that the existing method cannot realize thermal conduction and gas phase extraction coupled remediation process simulation, can simulate the space-time distribution law of a temperature field and pollutants in a remediation process, and provides a reference and scientific basis for thermal conduction enhanced gas phase extraction remediation of an organic contaminated site.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of environmental protection, and particularly relates to a numerical simulation method for heat conduction enhanced vapor extraction of an organic contaminated site. BACKGROUND

[0002] Soil vapor extraction (SVE) as a common in-situ remediation technology for soil has the advantages of low cost, simple operation, high efficiency, and small impact on the surrounding environment, and can efficiently remove volatile organic compounds in soil. However, under normal temperature conditions, the SVE technology is easily limited by soil physical and chemical properties, pollutant characteristics and other factors. Coupling with in-situ thermal remediation technology can expand its application range and improve the remediation efficiency. Among them, the in-situ thermal conduction (TCH) technology based on heating elements can accelerate the removal of organic pollutants by soil particles and pore fluid heat conduction to heat the soil. Because of its short remediation period, controllable secondary pollution, strong applicability to soil texture and pollutant properties, and high remediation efficiency, heat conduction enhanced vapor extraction technology is generally considered as a promising organic contaminated site remediation technology.

[0003] At present, the design and operation of the heat conduction enhanced vapor extraction process of the contaminated site mostly refer to the empirical formula and limited site practice experience. However, the process remediation effect is jointly affected by many factors such as soil texture, hydrogeological characteristics, well layout, and aeration rate. Therefore, reducing energy waste and predicting the remediation process of the contaminated site to achieve precise remediation will be the trend of the future contaminated site remediation industry.

[0004] Numerical simulation technology as an important means of scientific research and engineering planning is widely used in various engineering practices. At present, the prediction models of the environmental behavior of organic pollutants in soil and groundwater mainly include TOUGH, STOMP and NAPL simulator. Among them, the numerical models of STOMP and NAPL simulator can only simulate the migration process of organic pollutants in soil and groundwater, and it is difficult to meet the technical needs of the prediction of the remediation effect of the vapor extraction technology for the organic contaminated site.

[0005] The TMVOC module in the TOUGH 2 software (a module in the PertraSim, a commercial visualization software of the TOUGH 2 software) can simulate the removal process of target pollutants in the vapor extraction remediation process of the organic contaminated site and predict the remediation effect of the vapor extraction technology on the organic contaminated site. However, TMVOC does not have the function of simulating the heat conduction heating process, resulting in that the research on the numerical simulation method for heat conduction enhanced vapor extraction of the organic contaminated site is almost blank. Summary of the Invention

[0006] This invention provides a numerical simulation method for enhanced gas-phase extraction (GPE) of organic contaminated sites by thermal conduction. It solves the problem that existing methods cannot simulate the coupled remediation process of thermal conduction and GPE. It can simulate the spatiotemporal distribution of temperature field and pollutants during the remediation process, and can provide a strong reference and scientific basis for the enhanced GPE remediation of organic contaminated sites by thermal conduction.

[0007] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0008] The invented numerical simulation method for heat conduction-enhanced gas-phase extraction of organic contaminated sites includes the following steps: S1. Establishing a finite element model for heat conduction-enhanced gas-phase extraction: Obtaining the geometric parameters of the actual site study area to build the model, and setting the layout of heating wells, extraction wells, and temperature measurement wells within the modeling area; S2. Meshing the finite element model for heat conduction-enhanced gas-phase extraction; S3. Configuring corresponding parameters according to the actual site remediation process; S4. Setting control calculation parameters for the finite element model for heat conduction-enhanced gas-phase extraction; S5. Initializing the finite element model for heat conduction-enhanced gas-phase extraction under natural conditions; S6. Assigning initial pollutant concentrations to the finite element model for heat conduction-enhanced gas-phase extraction; and S7. Executing the numerical simulation program for heat conduction-enhanced gas-phase extraction to simulate the remediation process. The heat conduction method is achieved by designing a heating grid, setting heating materials, and injecting heating power, while the gas-phase extraction method is achieved through a built-in module of the TMVOC model.

[0009] Preferably, the simulation method for heat conduction-enhanced gas-phase extraction in organic contaminated sites further includes fitting and validating the finite element model of heat conduction-enhanced gas-phase extraction, wherein the goodness-of-fit evaluation method adopts the linear regression equation R0. 2 It means that R 2 The closer the value is to 1, the higher the simulation accuracy; the fitting indices are the temperature rise data and the chlorobenzene concentration data after correction.

[0010] Preferably, in the above-mentioned simulation method for enhanced gas-phase extraction of heat conduction in organic contaminated sites, in step S1, the geometric parameters of the actual site study area include the coordinates of the inflection points of the study area, the thickness of each type of soil layer and the thickness of the insulation layer in the study area, and the model size is set according to the actual size of the site at a 1:1 scale. In the modeling area, the heating wells are distributed in equilateral triangles / regular hexagons, the extraction wells are distributed at the centroid of the equilateral triangles, and the temperature measuring wells are located on the line connecting the two heating wells.

[0011] Preferably, in the above-mentioned simulation method for enhanced gas-phase extraction of organic contaminated sites by heat conduction, in step S2, the vertical grid division adopts a custom method, which is set according to the specific pollution layer; the horizontal grid type adopts a polygonal grid, and the maximum grid area is set to 0.5 m². 2 The minimum improvement angle is set to 15°.

[0012] Preferably, in the above-mentioned simulation method for enhanced gas-phase extraction of organically contaminated sites by heat conduction, in step S3, the parameters include pollutant parameters, soil parameters, and process parameters. The pollutant parameters include the diffusion coefficients of water, air, and pollutants in the gas, liquid, and non-aqueous liquid phases, respectively. The soil parameters include soil density, porosity, horizontal permeability, vertical permeability, thermal conductivity, specific heat capacity, relative permeability, capillary pressure, and organic carbon content. The process parameters include heating power, extraction rate, and extraction pressure.

[0013] Preferably, in the above-mentioned simulation method for enhanced gas-phase extraction by heat conduction in organic contaminated sites, in step S4, the controlled calculation parameters include running time, step size, maximum number of steps, maximum number of iterations per step, conjugate gradient solver, maximum number of iterations, convergence criterion, relative error, absolute error, derivative increment factor, and maximum residual of iteration.

[0014] Preferably, in the above-mentioned simulation method for enhanced gas phase extraction by heat conduction in organic contaminated sites, in step S5, the natural conditions include phase state, pressure, temperature, and moisture content; the top grid is set as an atmospheric boundary, the bottom grid is set as a fixed boundary, and the surrounding area is set as a flux-free boundary.

[0015] Preferably, in the above-mentioned simulation method for enhanced gas-phase extraction of organically contaminated sites by heat conduction, in step S6, the initial concentration of the pollutants is assigned by setting a source-sink term of 1.0 × 10⁻⁶ near the designed leak point. -10 ~1.6×10 - 7 The initial concentration of pollutants at the site is determined by the following steps: 1) Using the initial results of natural condition initialization as the initial conditions; 2) Selecting chlorobenzene as the pollutant and setting its relevant parameters; 3) Designing the distribution of pollutant leakage points, setting source and sink terms, and determining the continuous leakage rate. During the assignment, the diffusion rate of chlorobenzene in the air is initially increased to 3 × 10⁻⁶ kg / s. -5 m 2 / s, after the pollutant leaks for "1" years, the leak point is removed, and the diffusion rate is then returned to the normal value of 7.6×10. -6 m 2 / s, free migration and diffusion for “1” years to bring it close to the initial contamination state; 4) After all contamination layers are assigned values, enable all contamination layers.

[0016] Preferably, in the above-mentioned simulation method for enhanced gas-phase extraction of organically contaminated sites by heat conduction, step S7 includes: 1) using the result of assigning initial pollutant concentrations as the initial conditions for execution; 2) laying out heating wells, extraction wells, and temperature measurement wells in the model based on actual site data and setting relevant parameters, wherein the bulk density of the heating material is 7930 g / cm³. 3 The thermal conductivity is 16.8 W / mK, and the heat power injected into the heating grid source and sink terms is 520 W / m. The extraction well is directly inserted by the TMVOC model; 3) The operation period is T=56 days, which is divided into 8 output time points, and the simulation program is run; 4) The output results after the model operation are visualized to obtain the simulated remediation effect cloud map of site heat conduction enhanced gas phase extraction; 5) The output results after the model operation are analyzed to obtain the simulated temperature rise law curve of the site and the change trend curve of the total mass of pollutants.

[0017] The beneficial effects of this invention are as follows:

[0018] Currently, the commonly used prediction model for the environmental behavior of organic pollutants in soil and groundwater, TMVOC, only has the function of simulating pollutant extraction and remediation. This invention, by designing a simulation approach for the heat conduction heating process, realizes the simulation of the coupled remediation process of heat conduction and gas phase extraction, filling the gap in simulation methods in this field. It has high reference value and guiding significance for the application of heat conduction-enhanced gas phase extraction remediation technology for organic contaminated sites. Attached Figure Description

[0019] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below.

[0020] Figure 1 This is a flowchart of the numerical simulation method for enhanced gas-phase extraction with thermal conduction in organic contaminated sites according to the present invention.

[0021] Figure 2 This is a layout diagram of the site heat conduction enhanced gas phase extraction system process;

[0022] Figure 3 It is a design drawing of the well location for a finite element model of heat conduction-enhanced gas-phase extraction;

[0023] Figure 4 This is a finite element model of heat conduction enhanced gas phase extraction, showing the layout of heating wells and extraction wells;

[0024] Figure 5 This is a finite element model diagram of temperature measurement wells for heat conduction-enhanced gas-phase extraction;

[0025] Figure 6This is a simulation diagram of temperature field changes;

[0026] Figure 7 This is a simulation diagram of the change in chlorobenzene concentration;

[0027] Figure 8 This is a simulation diagram showing the temperature rise pattern at different distances from a single well heat source;

[0028] Figure 9 This is a simulation diagram showing the change in the total mass of chlorobenzene. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0030] The numerical simulation method for enhanced gas-phase extraction of organically contaminated sites using thermal conduction is provided in this invention. Figure 1 As shown, it includes the following steps:

[0031] S1. Establish a finite element model for heat conduction-enhanced gas-phase extraction. Obtain the geometric parameters of the actual site study area to build the model. Within the modeling area, determine the layout of heating wells, extraction wells, and temperature measurement wells.

[0032] S2. Mesh generation was performed on the finite element model of heat conduction-enhanced gas-phase extraction. The vertical mesh generation used a custom method, set according to the specific contamination layer; the horizontal mesh type used was a polygonal mesh, with a maximum mesh area of ​​0.5 m². 2 The minimum improvement angle is set to 15°; and the grid near the heating well is refined.

[0033] S3. Configure appropriate parameters according to the actual site remediation process. These parameters include: pollutant parameters such as the diffusion coefficients of water, air, and pollutants in the gas, liquid, and non-aqueous liquid phases, respectively; soil parameters such as soil density, porosity, horizontal permeability, vertical permeability, thermal conductivity, specific heat capacity, relative permeability, capillary pressure, and organic carbon content; and process parameters such as heating power, extraction rate, and extraction pressure. Specifically, to ensure the heating effect of the heating well grid, the grid material is set to the appropriate heating material.

[0034] S4. Set the control calculation parameters for the heat conduction enhanced gas phase extraction finite element model; the control calculation parameters include running time, step size, maximum number of steps, maximum number of iterations per step, conjugate gradient solver, maximum number of iterations, convergence criterion, relative error, absolute error, derivative increment factor, and maximum residual of iteration.

[0035] S5. Initialize the finite element model for heat conduction-enhanced gas-phase extraction with natural conditions. Natural conditions include phase state, pressure, temperature, and water content; the top mesh is set as an atmospheric boundary, the bottom mesh is set as a fixed boundary, and the surrounding mesh is set as a flux-free boundary.

[0036] S6. Assign initial pollutant concentration values ​​to the finite element model of heat conduction-enhanced gas-phase extraction. The initial pollutant concentration is assigned by setting source and sink terms near the designed leak point with a concentration of 1.0 × 10⁻⁶. -10 ~1.6×10 -7 The pollutants are leaked at a rate of kg / s to assign an initial concentration value to the site.

[0037] S7. Execute the numerical simulation program for heat conduction-enhanced vapor extraction to simulate the repair process. The heat conduction-enhanced vapor extraction numerical simulation program is a pre-defined programming language; the heat conduction method is achieved by designing the mesh material and injecting heating power, while the vapor extraction method is implemented through a built-in module of the TMVOC model.

[0038] S8. The finite element model for heat conduction-enhanced gas-phase extraction was fitted and validated. The goodness-of-fit was evaluated using a linear regression equation R0. 2 It means that R 2 The closer the value is to 1, the higher the simulation accuracy; the fitting indices are the temperature rise data and the chlorobenzene concentration data after correction.

[0039] The method of the present invention will be described below with reference to specific embodiments.

[0040] The initialization method for the finite element model of heat conduction-enhanced gas-phase extraction includes:

[0041] 1) Establish a finite element model for heat conduction-enhanced gas-phase extraction. The model is built by acquiring the geometric parameters of the actual site study area. These parameters include the coordinates of the inflection points (approximate shape and area of ​​the calculation region), the thickness of various soil layers, and the thickness of the insulation layer. The model size is set at a 1:1 scale based on the actual site dimensions. Specifically, the vadose zone of the study area extends from 2 m to 15 m underground. The soil layers from -15 m to -6.5 m include clay-sandy silt and silty clay interbedded with thin silt masses. The soil layers from -6.5 m to -5.0 m are silty clay, -5.0 m to -3.5 m are sandy silt, -3.5 m to -2.0 m are silty clay, and the insulation layer (e.g., ...) is from -2.0 m to -1.8 m. Figure 2 (As shown) (from -2 m to 0 m was manually excavated); the main components of the site's heat conduction enhanced extraction system are as follows Figure 2As shown, the model includes a power control system 1, a tailwater treatment system 2, a tail gas control system 3, a heating well 4, an extraction well 5, and a heat insulation layer 6. The model includes three main process components: heating well 4, extraction well 5, and heat insulation layer 6. The size, layout, and quantity of these components are consistent with the actual site. Within the modeled area, the heating wells 4 are distributed in an equilateral triangle / hexagonal pattern, and the extraction wells 5 are located at the centroid of the equilateral triangles. Figure 3 As shown; the temperature measuring well is located on the line connecting the two heating wells, as... Figure 5 As shown.

[0042] 2) Mesh generation was performed on the heat conduction-enhanced gas-phase extraction finite element model. The vertical mesh layering used a custom method, set according to the contamination layer thickness (contamination depth from -2.0 m to -9.5 m). The z-axis was divided into 10 layers: from top to bottom, a 0.001 m atmospheric boundary layer, a 0.2 m insulation layer, five 1.5 m contamination layers, two 0.5 m and two 4.0 m uncontamination layers, and a 1.0 m fixed bottom boundary layer. The horizontal mesh type used was a polygonal mesh, with a maximum mesh area of ​​0.5 m². 2 The minimum improvement angle was set to 15°; since the TMVOC model lacks a heat treatment module, the mesh was refined in the model area corresponding to the actual site heating well locations, with the maximum mesh area for the heating well placement points set to 0.035 m². 2 Due to the irregular shape of the polygonal mesh, the area of ​​all heating well meshes after refinement is less than 0.04 m². 2 Left and right, consistent with the dimensions of the site and equipment, such as Figure 4 As shown.

[0043] 3) Configure appropriate parameters according to the actual site remediation process. Pollutant parameters include the diffusion coefficients of water, air, and chlorobenzene in the gas, liquid, and NAPL phases, respectively (see Table 1); soil parameters include soil density, porosity, horizontal permeability, vertical permeability, thermal conductivity, specific heat capacity, relative permeability, capillary pressure, and organic carbon content; to ensure the heating well grid achieves its heating effect, the grid material is set to the appropriate heating material (see Table 2). The relative permeability formula is “Stone's 3-Phase (IRP=6)”, and the capillary pressure formula is “Parker 3-Phase (ICP=8)”; the soil organic carbon content is 0.0087.

[0044] Table 1 Pollutant Parameter Table

[0045]

[0046] Table 2 Soil Parameter Table

[0047]

[0048] 4) Set the control calculation parameters for the heat conduction-enhanced gas-phase extraction finite element model. These include runtime, step size, maximum number of steps, maximum number of iterations per step, conjugate gradient solver, maximum number of iterations, convergence criterion, relative error, absolute error, derivative increment factor, and maximum iteration residual. The values ​​for each parameter are shown in Table 3.

[0049] Table 3 Simulation Program Control Calculation Parameter Setting Table

[0050]

[0051] 5) Execute the numerical simulation program for heat conduction-enhanced gas-phase extraction to simulate the initialization of natural conditions. The numerical simulation program is a pre-defined programming language program.

[0052] The above steps, through the simulation of natural conditions initialization of the model, determined the bottom pressure of the simulation study area, enabling the model to automatically calculate until gravity and capillary pressure are in equilibrium to simulate the natural initial state of the site.

[0053] Assigning initial pollutant concentrations to the model after initializing natural conditions, including:

[0054] 1) The result of the natural condition initialization in the initialization method of the thermal conduction enhanced gas phase extraction finite element model is used as the initial condition for execution.

[0055] 2) Chlorobenzene was selected as the pollutant, and the relevant parameters for chlorobenzene were set as shown in Table 1.

[0056] 3) Design the distribution of pollutant leakage points, set up source and sink terms, and determine the continuous leakage rate. Specifically, this includes setting up source and sink terms near the designed leakage points at a certain rate (1.0 × 10⁻⁶). -10 ~1.6×10 -7 A chlorobenzene sample leaked at a rate of kg / s. After a one-year period following the leak, the leak point was removed and the sample was allowed to diffuse freely for another one year to bring it close to its initial contamination state. Because the contamination concentrations at different depths at each sampling point were inconsistent and showed no clear distribution pattern, individual values ​​were assigned to each grid layer in the contaminated area. To prevent vertical migration and diffusion during the value assignment process, other layers were disabled when assigning concentration values ​​to a single grid layer, and the results of the previous run were used as the initial conditions for the next run (the SAVE file containing the results of the previous run was imported). To reduce the impact of excessively high initial migration and diffusion rates of pollutants caused by the value assignment method, the diffusion rate of chlorobenzene in the air was increased to 3 × 10⁻⁶ during the initial value assignment. -5 m 2 / s, at a certain rate (1.0×10 -10 ~1.6×10 -7After a 1-year period following a leak (kg / s), the leak point will be removed, and the diffusion rate will be adjusted back to the normal value of 7.6 × 10⁻⁶. -6 m 2 / s, free migration and diffusion for “1” years bring it close to its initial pollution state.

[0057] 4) Once all contaminated layers have been assigned values, enable all contaminated layers.

[0058] The TMVOC model itself does not have a module for assigning pollutant values. This method assigns the initial concentration of chlorobenzene at the site by setting a leak point, and reduces the error of this method by single-layer assignment, adjusting the chlorobenzene diffusion rate, and free diffusion.

[0059] The model, after initial pollutant concentration assignment, is used to perform a heat conduction-enhanced gas-phase extraction numerical simulation program to simulate the remediation process, including:

[0060] 1) The result of assigning the initial concentration of pollutants is used as the initial condition for execution.

[0061] 2) Based on actual site data, the model was configured with heating wells, extraction wells, and temperature measuring wells, and relevant parameters were set. Specifically, 45 heating wells, 19 extraction wells, and 14 temperature measuring wells were configured. See [link to specific layout details] for details. Figure 4 and Figure 5 The heat conduction method is achieved by designing a heating grid, setting heating materials, and injecting heating power, while the gas-phase extraction method is implemented through a built-in module of the TMVOC model. Specifically, the heating well grid locations in the model corresponding to the actual site heating well locations are shown in [reference needed]. Figure 4 The heating material settings are shown in Table 2. A heat power of 520 W / m is injected into the heating grid source and sink items. The extraction well locations in the model corresponding to the actual site extraction well locations are shown in Table 2. Figure 4 The extraction well was directly inserted using the TMVOC model, with the extraction pressure set to 70 kPa and the extraction rate set to 30 L / min.

[0062] 3) The running period T = 56 days is divided into 8 output time points, and the simulation program is run.

[0063] 4) Visualize the output results after the model run to obtain a cloud map of the simulated remediation effect of enhanced gas-phase extraction for site heat conduction. See details below. Figure 6 and Figure 7 .

[0064] 5) Perform data analysis on the output results after the model run to obtain the simulated temperature rise curve of the site and the trend curve of the total mass of pollutants (chlorobenzene). See details below. Figure 8 and Figure 9 .

[0065] Numerical simulations were conducted on the heat conduction-enhanced vapor-phase extraction remediation process for organically contaminated sites. Temperature field change cloud maps and chlorobenzene concentration change cloud maps were used to intuitively analyze the temperature field and chlorobenzene concentration changes during the remediation process. Data analysis also clarified the changes in temperature rise and total mass of pollutants (chlorobenzene) during the remediation process.

[0066] Methods for evaluating the goodness of fit of model simulation results include:

[0067] 1) The experimental and simulated values ​​of the average temperature at each time point in the temperature field during the heating process, and the experimental and simulated values ​​of the chlorobenzene concentration after repair were analyzed and the goodness of fit were evaluated. The statistical data are shown in Tables 4 and 5.

[0068] Table 4 Temperature Fitting Data

[0069]

[0070] Table 5. Fitting data of chlorobenzene concentration after repair

[0071]

[0072] 2) Select R 2 As an evaluation metric for goodness of fit, the closer this value is to 1, the better the model fits. Specifically, R0... 2 The calculation formula is as follows:

[0073]

[0074] In the formula: The test values ​​for the temperatures of the two zones, in g / m². 3 ; The average value of the test results, g / m 3 ; Simulated values ​​of temperature for two zones, g / m 3 ; The average value of the simulated values, g / m 3 .

[0075] 3) Analyze and calculate the data from step 1) based on the formula in step 2). According to the calculation, the goodness of fit of the temperature rise data in TCH-A and TCH-B regions are 0.995 and 0.989, respectively, and the goodness of fit of the chlorobenzene concentration data after repair is 0.914, indicating that the simulated values ​​calculated by the model have a good correlation with the experimental values.

[0076] The evaluation method shows that the goodness of fit between the simulation data and the experimental data of the simulation method of this invention is above 0.91, indicating a good correlation. This proves that the method has high reliability and can provide a strong reference and scientific basis for the thermal conduction-enhanced gas-phase extraction remediation of organic contaminated sites.

[0077] The above embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and are not intended to limit it. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or improve the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features, within the scope of the technology disclosed in the present invention; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A numerical simulation method for enhanced gas-phase extraction with thermal conduction in organically contaminated sites, characterized in that, Includes the following steps: S1. Establish a finite element model for heat conduction-enhanced gas phase extraction: Obtain the geometric parameters of the actual site study area to build the model, and set the layout of heating wells, extraction wells and temperature measurement wells within the study area; S2. Mesh the finite element model for enhanced heat conduction gas extraction; S3. Configure the corresponding parameters according to the actual site remediation process; S4. Set the control calculation parameters for the heat conduction enhanced gas phase extraction finite element model; S5. Initialize the finite element model for enhanced thermal conductivity gas extraction under natural conditions; S6. Assign initial pollutant concentration values ​​to the aforementioned heat conduction-enhanced gas-phase extraction finite element model; as well as S7. Execute a numerical simulation program for heat conduction-enhanced vapor-phase extraction to simulate the repair process. Heat conduction is achieved by designing a heating grid, setting heating materials, and injecting heating power. Vapor-phase extraction is implemented using a built-in module of the TMVOC model. In step S1, the geometric parameters of the actual site study area include the coordinates of the inflection points of the study area, the thickness of each type of soil layer, and the thickness of the insulation layer. The model size is set at a 1:1 scale according to the actual size of the site. Within the study area, the heating wells are distributed in an equilateral triangle, the extraction wells are located at the centroid of the equilateral triangle, and the temperature measuring wells are located on the line connecting two heating wells. In step S2, the vertical grid division uses a custom method, set according to the specific pollution layer; the horizontal grid type uses a polygonal grid, with a maximum grid area of ​​0.5 m². 2 The minimum improvement angle is set to 15°.

2. The numerical simulation method for enhanced gas-phase extraction based on thermal conduction in organically contaminated sites according to claim 1, characterized in that, The method also includes fitting and validating the heat conduction-enhanced gas-phase extraction finite element model, wherein the goodness-of-fit evaluation method adopts the linear regression equation R. 2 It means that R 2 The closer the value is to 1, the higher the simulation accuracy; the fitting indices are the temperature rise data and the chlorobenzene concentration data after correction.

3. The numerical simulation method for enhanced gas-phase extraction based on thermal conduction in organically contaminated sites according to claim 1, characterized in that, In step S3, the parameters include pollutant parameters, soil parameters, and process parameters. The pollutant parameters include the diffusion coefficients of water, air, and pollutants in the gas, liquid, and non-aqueous liquid phases, respectively. The soil parameters include soil density, porosity, horizontal permeability, vertical permeability, thermal conductivity, specific heat capacity, relative permeability, capillary pressure, and organic carbon content. The process parameters include heating power, extraction rate, and extraction pressure.

4. The numerical simulation method for enhanced gas-phase extraction based on thermal conduction in organically contaminated sites according to claim 1, characterized in that, In step S4, the control calculation parameters include running time, step size, maximum number of steps, maximum number of iterations per step, conjugate gradient solver, maximum number of iterations, convergence criterion, relative error, absolute error, derivative increment factor, and maximum residual of iteration.

5. The numerical simulation method for enhanced gas-phase extraction based on thermal conduction in organically contaminated sites according to claim 1, characterized in that, In step S5, the natural conditions include phase state, pressure, temperature, and water content; the top grid is set as an atmospheric boundary, the bottom grid is set as a fixed boundary, and the surrounding area is set as a flux-free boundary.

6. The numerical simulation method for enhanced gas-phase extraction based on thermal conduction in organically contaminated sites according to claim 1, characterized in that, In step S6, the initial concentration of the pollutant is assigned by setting a source-sink term of 1.0 × 10⁻⁶ near the designed leak point. -10 ~1.6×10 -7 The initial site concentration is assigned by leaking pollutants at a rate of kg / s, including: 1) Use the result of the initialization of natural conditions as the initial condition for execution; 2) Select chlorobenzene as the pollutant and set the relevant parameters for chlorobenzene; 3) Design the distribution of pollutant leakage points, set source and sink terms and continuous leakage rate, assign values ​​to each grid layer of the polluted area individually, disable other layers when assigning concentration values ​​to a single grid layer, use the results of the previous run as the initial conditions for the next run, and increase the diffusion rate of chlorobenzene in the air to 3×10 during the assignment. -5 m 2 / s, the pollutant leaked "1" years later, the leak point was removed, and the diffusion rate was then changed back to the normal value of 7.6×10. -6 m 2 / s, free migration and diffusion for "1" years to bring it close to the initial pollution state; 4) Once all contaminated layers have been assigned values, enable all contaminated layers.

7. The numerical simulation method for enhanced gas-phase extraction based on thermal conduction in organically contaminated sites according to claim 1, characterized in that, Step S7 includes: 1) The initial conditions for execution are based on the result of assigning the initial concentration of pollutants; 2) Based on actual site data, the model is used to lay out the heating wells, extraction wells, and temperature measuring wells, and relevant parameters are set. The bulk density of the heating material is 7930 g / cm³. 3 The thermal conductivity is 16.8 W / mK, and the heat power injected into the heating grid source and sink terms is 520 W / m. The extraction well is directly inserted by the TMVOC model. 3) The running period T = 56 days is divided into 8 output time points, and the simulation program is run. 4) Visualize the output results after the model runs to obtain a cloud map of the simulated remediation effect of enhanced gas phase extraction for site heat conduction. 5) Perform data analysis on the output results after the model runs to obtain the simulated temperature rise curve of the site and the trend curve of the total mass of pollutants.

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