In-situ electrically heated apparatus and method for contaminated soil remediation

Abstract

The application discloses a dynamic adjustable in-situ heat conduction type contaminated soil electric heating device and method, which comprises a power supply system arranged above the ground and a heating system penetrating into the ground. The heating system comprises a heating well and a heating assembly arranged in the heating well. The heating assembly comprises a fixed conductive connecting rod connected with positive and negative poles of the ground power supply cable respectively, a sliding conductive connecting rod and a spiral coil heating resistor surrounding the fixed conductive connecting rod. The spiral coil heating resistor is connected with the lower end of the fixed conductive connecting rod. The sliding conductive connecting rod can slide up and down and is connected with the spiral coil heating resistor through a conductive switch piece, so that the differential heating of the soil at different depths is realized. The application can realize the differential heating of the contaminated soil, that is, the required heating time gradually increases from top to bottom, is beneficial to the implementation of the precise depth heating, can effectively save the energy and reduce the carbon emission under the premise of ensuring the heating effect, and is convenient to operate.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of contaminated soil and groundwater remediation, and particularly relates to a dynamic adjustment type in-situ heat conduction type contaminated soil electric heating device and a heating method. BACKGROUND

[0002] For the soil contaminated by organic pollutants, especially the contaminated soil which is difficult to handle by traditional remediation processes such as polycyclic aromatic hydrocarbons, pesticides, petroleum hydrocarbons, etc., in-situ treatment technology, in-situ thermal desorption technology is widely used due to its good treatment effect, strong site adaptability and other advantages. At present, the mainstream in-situ thermal desorption technologies on the market include in-situ resistance heating, in-situ heat conduction-electric heating, in-situ heat conduction-gas heating and in-situ steam heating.

[0003] Among them, in-situ resistance heating and in-situ steam heating are limited by factors such as soil moisture content, electrical conductivity, soil homogeneity and soil permeability, and are less applicable to site types, and have a low application proportion. In-situ heat conduction heating is the mainstream technology of in-situ heating at present.

[0004] In-situ heat conduction heating is to build a heating well in the soil, heat the casing of the heating well by arranging electric heating rods or passing flue gas in the heating well, and continuously transfer heat to the surrounding soil through heat radiation of the heated casing, so as to heat the surrounding soil. According to the different energy supply situations, it can be divided into in-situ heat conduction-electric heating and in-situ heat conduction-gas heating. The in-situ heat conduction heating method is less affected by the physical and chemical properties of the soil, and has wider adaptability. However, due to the arrangement of the heating rods or the flue gas heating passage in the heating well, there are some problems in the in-situ heat conduction heating:

[0005] The electric heating pipe in the heating well used in the in-situ heat conduction-electric heating process adopts a U-shaped arrangement. This type of electric heating pipe arrangement can realize uniform heating of the whole heating well, but is limited by the fixed length of the electric heating pipe. If the heating power needs to be improved (in the case of a determined heating rod resistance heating temperature peak), only a larger power electric heating rod can be replaced, which limits the selection of heating well materials and increases the cost. In addition, the electric heating rod is vertically extended along the heating well, and the electric heating power is consistent, which cannot meet the differentiated heating needs of different depth soil layers.

[0006] Patent CN108311535B discloses a system and method for in-situ electric heating repair of organic contaminated soil. The core heating element of the electric heating pipe is made of non-metal carbon-silicon rod material. The silicon-carbon rod is connected to the power supply end and filled or poured with aluminum silicate fiber for heat insulation treatment. The in-situ electric heating treatment system has improved stability and effective temperature for treating contaminated soil. However, the invention does not disclose the specific structure, style and arrangement of the core heating element of the in-situ electric heating pipe.

[0007] Patent CN205673362U discloses a heating well of a contaminated site in-situ electric heating desorption repair device. The core component of the heating well is a single-wire stainless steel heating pipe. The heating pipe is installed with an electric heating wire and filled with crystalline magnesium oxide particles. The top wire of the electric heating pipe is connected to an electric wire sleeve made of insulating material. The drawing shows that the heating pipe is arranged in a U-shaped carbon steel sleeve, which can achieve uniform heating of the whole heating well and cannot achieve differential heating in the vertical direction. SUMMARY

[0008] The present application aims to provide a dynamic adjustable in-situ heat conduction type contaminated soil electric heating device, its application and heating method, which can achieve differential heating of the required total heat of contaminated soil from top to bottom, precise heating, energy saving and convenient operation. The purpose of the present application is achieved by the following technical solutions:

[0009] A dynamic adjustable in-situ heat conduction type contaminated soil electric heating device, comprising a power supply system arranged above the ground and a heating system deep into the ground, wherein the power supply system and the heating system are connected by a ground power cable; the heating system comprises a heating well and a heating assembly arranged in the heating well, wherein the heating assembly comprises a fixed conductive connecting rod connected to the positive and negative poles of the ground power cable, a sliding conductive connecting rod and a spiral coil heating resistor surrounding the fixed conductive connecting rod, the lower end of the spiral coil heating resistor is connected to the lower end of the fixed conductive connecting rod, and the upper end of the spiral coil heating resistor is a free end; the sliding conductive connecting rod can slide up and down and is connected to the spiral coil heating resistor by a conductive tab.

[0010] Further optimization, the power supply system comprises a power supply device and its control system and a temperature control system, the power supply device and its control system are connected to the ground power cable, the temperature control system is connected to the temperature sensor arranged in the contaminated soil at different depths, the temperature control system receives the signal of the temperature sensor and sends the signal to the power supply device and its control system to control the output of the electric current and the up and down sliding of the sliding conductive connecting rod.

[0011] Further optimization, the sliding conductive connecting rod is connected with a driving motor for controlling the up and down sliding, and the negative pole of the ground power cable is connected with the sliding conductive connecting rod through a brush connector.

[0012] The heating device is applied to auxiliary heating of organic contaminated soil pollutant extraction, and the required heating time of different vertical layers in the contaminated soil increases from top to bottom.

[0013] A contaminated soil in-situ heat conduction type heating method using the heating device comprises the following steps:

[0014] Step 1: determining the land characteristics of the region to be heated, wherein the land characteristics include land pollution characteristics, soil layer soil characteristics and hydrogeological characteristics;

[0015] Step 2: generalizing and layering the land to be heated in the vertical direction according to the land characteristics;

[0016] Step 3: setting the electric heating device in the region to be heated, and determining the heating time required for heating each layer of soil according to the power of the electric heating device and the characteristics of each layer of land;

[0017] Step 4: moving the conductive tab of the sliding conductive connecting rod for heating, wherein when the conductive tab is at the uppermost end, all the spiral coils heat the resistance as a whole, the heating interval gradually decreases as the conductive tab slides downward, and the heating interval gradually increases as the conductive tab slides upward.

[0018] A contaminated soil in-situ heat conduction type heating method using the heating device comprises the following steps:

[0019] Step 1: determining the land characteristics of the region to be heated, wherein the land characteristics include land pollution characteristics, soil layer soil characteristics and hydrogeological characteristics;

[0020] Step 2: generalizing and layering the land to be heated in the vertical direction according to the land characteristics;

[0021] Step 3: determining the heating target temperature of each layer of soil according to the characteristics of each layer of land;

[0022] Step 4: determining the heating cycle of the lowermost layer of land according to the overall construction period requirement and comprehensively considering the characteristics of the lowermost layer of land, wherein the heating cycle includes the heating-up time, the constant temperature time and the cooling-down time;

[0023] Step 5: calculating the heating influence range of a single set of heating device in the heating-up section according to the soil layer soil characteristics;

[0024] Step 6: calculating the power input of a single heating device in the unit depth of soil according to the land characteristics of the lowermost layer of soil, the heating-up time, the target temperature and the heating influence range.

[0025] Step seven: set the in-situ heating device in the contaminated soil area to be heated; and determine the longitudinal spacing and radial distance of the spiral coil heating resistor according to the calculation results of step six;

[0026] Step eight: derive the temperature rising time of all soil layers except the lowermost layer according to the power input of the single heating device in the unit depth of soil calculated in step six, the plot characteristics of each layer, and the target temperature, and determine the constant temperature time according to the plot characteristics;

[0027] Step nine: move the conductive toggle of the sliding conductive connecting rod to heat according to the temperature rising time and the constant temperature time of each layer. When the conductive toggle is at the uppermost end, all spiral coil heating resistors are heated as a whole. When the conductive toggle slides downward, the heating interval gradually decreases. When the conductive toggle slides upward, the heating interval gradually increases.

[0028] In step one, the plot contamination characteristics include the type of contaminant, the saturated vapor pressure of the contaminant, the boiling point of the contaminant, the spatial distribution range of the contaminant, and the concentration of the contaminant; the soil layer characteristics include the soil category, the soil water content, the soil particle density, the soil porosity, the heat capacity of the soil particles, the initial temperature of the soil, the soil permeability, the soil thermal conductivity, and the soil temperature conductivity coefficient; and the hydrogeological characteristics include the groundwater depth, the aquifer thickness, the hydraulic gradient, the soil permeability coefficient, and the groundwater flow rate.

[0029] Further optimization, in step six, when the final temperature T c of the soil heating is greater than 100℃, the power input in the unit depth of soil is calculated by the formula:

[0030]

[0031] In the formula, β represents the average power input of the single heating device in the unit depth, W·m -1 ; t b represents the time required for the water in the soil to completely vaporize, day; t c2 represents the time required for the soil to heat from 100℃ to the target temperature, day; A represents the influence range of the heat radiation of the single heating device, m 2 ; ρ s represents the soil particle density, g·m -3 ; C s represents the heat capacity of the soil particles, W·day·g -1 ·℃ -1 ; θ represents the soil porosity; ρ w represents the density of water, g·m -3 ; C w represents the heat capacity of water, W·day·g -1 ·℃-1 ; δ represents the saturation of water in the soil; T b represents the boiling point of water, ℃; T a represents the temperature of the soil before heating, ℃; T c represents the final temperature of the soil, ℃; h w represents the heat of vaporization of water, unit: W·day·g –1 .

[0032] Further optimization, in step six, when setting the final temperature T c of the soil heating is less than or equal to 100℃, the formula is used to calculate the power input within the soil depth:

[0033]

[0034] In the formula: σ is a 0-1 value, representing the proportion of water evaporation under the condition of heating temperature below 100℃; t c1 represents the time required for the soil to heat to the target temperature.

[0035] The advantages and beneficial effects of the present application are:

[0036] The present application can take targeted and different heating schemes based on the different types of pollutants, spatial distribution, soil quality, and hydrogeological conditions in contaminated soil remediation, which can realize the differentiated heating of the total heat required for the contaminated soil from top to bottom, which is beneficial to the implementation of precise depth and timing heating, can effectively save energy and reduce carbon emissions under the premise of ensuring heating effect, and is convenient to operate. BRIEF DESCRIPTION OF DRAWINGS

[0037] The present application will be further described below in conjunction with the drawings and examples.

[0038] Fig. 1 is a schematic view of the structure of the in-situ heating device;

[0039] Fig. 2 is a schematic view of the specific application scene of the heating method in the example;

[0040] Fig. 3 is a schematic view of the heating cycle in the example.

[0041] 11, heating well; 121, fixed conductive connecting rod; 122, sliding conductive connecting rod; 13, spiral coil heating resistance; 14, connecting point of conductive connecting rod and spiral coil heating resistance; 143, conductive push piece; 15, heating well outer sleeve; 16, heating well flange cover piece; 21, in-situ multi-phase extraction well; 22, open screen section; 23, solid pipe section; 24, multi-phase extraction well head; 25, liquid phase extraction pipeline; 26, submersible pump; 31, power supply device and control system; 32, temperature control system; 33, power supply cable; 34, power supply cable and conductive connecting rod connecting piece; 35, temperature sensor; 36, thermocouple; 37, temperature sensor lead; 4, tail water and tail gas treatment system; 51, horizontal barrier layer; 52, vertical barrier wall; 60, driving motor; 61, brush connector. DETAILED DESCRIPTION

[0042] Embodiment 1

[0043] A dynamically adjustable in-situ heat conduction type contaminated soil electric heating device, comprising a power supply system arranged above the ground and a heating system deeply into the ground, the power supply system and the heating system are connected through a ground power supply cable 33; the heating system comprises a heating well 11 and a heating assembly arranged in the heating well 11, the heating assembly comprises a fixed conductive connecting rod 121, a sliding conductive connecting rod 122 and a spiral coil heating resistance 13 wound outside the fixed conductive connecting rod 121, which are respectively connected to the positive and negative poles of the ground power supply cable 33, the lower end of the spiral coil heating resistance 13 is connected to the lower end of the fixed conductive connecting rod 121, and the upper end of the spiral coil heating resistance 13 is a free end; the sliding conductive connecting rod 122 can slide up and down and is connected to the spiral coil heating resistance 13 through a conductive push piece 143.

[0044] The power supply system comprises a power supply device and control system 31 and a temperature control system 32, the power supply device and control system 31 is connected to the ground power supply cable 33, and the temperature control system 32 is connected to a temperature sensor 35 arranged in contaminated soil at different depths, the temperature control system 32 receives signals from the temperature sensor 35 and sends signals to the power supply device and control system 31 to control the output of electric current and the up-and-down sliding of the sliding conductive connecting rod 122. The sliding conductive connecting rod 122 is connected to a driving motor 60 for controlling the up-and-down sliding thereof, and the negative pole of the ground power supply cable 33 is connected to the sliding conductive connecting rod 122 through a brush connector 61.

[0045] The fixed conductive connecting rod 121 is connected with the spiral coil heating resistor 13 through a high-temperature-resistant lead-out wire; the heating well 11 comprises a bottom and a heating well outer sleeve 15 around the periphery and a heating well flange cover plate 16 arranged on the top. The spiral coil heating resistor 13 is a nickel-chromium or iron-chromium alloy wire, and high-purity magnesium oxide powder is arranged around the spiral coil heating resistor in the heating well as an insulating material; the conductive connecting rod is made of stainless steel; and the high-temperature-resistant lead-out wire is a high-temperature glass fiber wire or a silica gel wire.

[0046] Embodiment 2

[0047] Based on the heating method of the dynamic adjustment type in-situ heat conduction type contaminated soil electric heating device in Embodiment 1, the spiral coil of the heating device in Embodiment 1 is set on site, and the method comprises the following steps:

[0048] Step one: determine the land characteristics of the area to be heated: the land characteristics include land pollution characteristics, soil layer soil characteristics and hydrogeological characteristics; the land pollution characteristics include the types of pollutants, the saturated vapor pressure of pollutants, the boiling point of pollutants, the spatial distribution range of pollutants and the concentration of pollutants; the soil layer soil characteristics include soil category, soil water content, soil particle density, soil porosity, soil particle heat capacity, soil initial temperature, soil permeability, soil thermal conductivity and soil temperature conductivity coefficient; the hydrogeological characteristics include groundwater depth, aquifer thickness, hydraulic gradient, soil permeability coefficient and groundwater flow rate. In this embodiment, the vertical distribution of pollutants is divided into three parts: the upper layer is mainly benzene series, chlorinated hydrocarbons and other VOCs, which are easy to volatilize; petroleum hydrocarbons and part of PAHs with boiling points below 250℃ are semi-volatile; the lower layer is mainly pesticides with boiling points above 250℃, which are relatively difficult to volatilize; the soil properties are uniformly distributed vertically. The properties of the pollutants are shown in Table 1:

[0049] Table 1

[0050] No. Contaminant category Volatile characteristic Heating zone 1 Benzene series, chlorinated hydrocarbons, etc. VOCs Easily volatile 60-120℃ 2 Petroleum hydrocarbons, PAHs with part of boiling point below 250°C Semi-volatile 120-220℃ 3 PAHs with boiling point above 250°C, PCBs, pesticides Less volatile 220-350℃

[0051] Step two: according to the land characteristics, the land to be heated is generalized and layered in the vertical direction; this embodiment is divided into three layers.

[0052] Step three: according to the land characteristics of each layer, the heating target temperature of each layer of soil is determined; the heating target temperatures of the upper layer, the middle layer and the lower layer are respectively determined as 90℃, 150℃ and 300℃,

[0053] Step four: according to the overall construction period requirement and comprehensively considering the land characteristics of each layer, the heating cycle of the lowermost layer is determined, and the heating cycle comprises a heating-up time, a constant-temperature time and a cooling-down time;

[0054] Step five: according to the soil layer soil characteristics and temperature conductivity coefficient of each layer of soil, the heating influence range A of a single set of heating device in the heating-up section is calculated;

[0055] Step six: Calculate the heating power input of single heating device in the unit depth of the lowest layer according to the results determined in step two to step five;

[0056] Because the target temperature of the lowest layer is higher than 100℃, the heating power input in the unit depth of the soil is calculated by formula (1);

[0057] Step seven: Set the in-situ heating device described in embodiment 1 in the area to be heated in the contaminated soil; and determine the longitudinal spacing and radial distance of the spiral coil heating resistance according to the calculation results of step six;

[0058] Step eight: Derive the heating time of all soil layers except the lowest layer according to the heating power input of single heating device in the unit depth of the soil calculated in step six and the characteristics of each layer, target temperature; the middle layer uses formula (1) to inverse, and the upper layer uses formula (2). Then determine the constant temperature time according to the characteristics of the pollutants such as the concentration of the pollutants.

[0059] Step nine, according to the heating time and constant temperature time of each layer, move the conductive slide of the sliding conductive connecting rod to heat, when the conductive slide is at the uppermost end, all spiral coil heating resistances are heated as a whole, the heating interval gradually decreases as the conductive slide slides downward, and the heating interval gradually increases as the conductive slide slides upward. The heating method can be selected as first heating as a whole, and then sliding the conductive slide from top to bottom; or vice versa, first heating the lower part, and then sliding the conductive slide from bottom to top to increase the new heating section.

[0060] This embodiment is applied to auxiliary heating for organic pollutant contaminated soil pollutant extraction, and the specific use state is as shown in Fig. 2 The horizontal barrier layer 51 and the vertical barrier wall 52 are arranged at the edge of the in-situ heating area, the in-situ heating device is arranged in the middle of the in-situ heating area, the in-situ heating device is arranged in a triangular or hexagonal shape, the in-situ multiphase extraction device (including the in-situ multiphase extraction well 21, the open screen section 22, the solid pipe section 23, the multiphase extraction well head 24, the liquid phase extraction pipeline 25, and the submersible pump 26) is arranged in the middle of the in-situ heating device, the in-situ heating device is connected to the power supply system, and the in-situ multiphase extraction device is connected to the tail water and tail gas treatment device 4.

[0061] Embodiment 3

[0062] Based on the heating method of the dynamic adjustable in-situ heat conduction type contaminated soil electric heating device of embodiment 1, the heating device in embodiment 1 is used, the spiral coil of the heating device is fixed, and the power is fixed, including the following steps:

[0063] Step 1: Determine the plot characteristics of the region to be heated: the plot characteristics include plot pollution characteristics, soil layer soil characteristics, and hydrogeological characteristics; the plot pollution characteristics include the types of pollutants, the saturated vapor pressure of the pollutants, the boiling point of the pollutants, the spatial distribution range of the pollutants, and the concentration of the pollutants; the soil layer soil characteristics include soil category, soil water content, soil particle density, soil porosity, soil particle heat capacity, soil initial temperature, soil air permeability, soil thermal conductivity, and soil temperature conductivity coefficient; the hydrogeological characteristics include groundwater depth, aquifer thickness, hydraulic gradient, soil permeability coefficient, and groundwater flow rate. In this embodiment, the vertical distribution of pollutants is divided into three parts: the upper layer is mainly benzene series, chlorinated hydrocarbons, and other VOCs, which are easy to volatilize; petroleum hydrocarbons and part of PAHs with boiling points below 250°C are semi-volatile; the lower layer is mainly pesticides with boiling points above 250°C, which are more difficult to volatilize; the soil properties are uniformly distributed vertically.

[0064] Step 2: According to the plot characteristics, the plot to be heated is generalized and layered vertically; this embodiment is divided into 3 layers.

[0065] Step 3: Set the electric heating device in the region to be heated, and determine the heating time required to heat each layer of soil according to the power of the electric heating device and the characteristics of each layer of soil.

[0066] According to the maximum fixed power, the heating time can be deduced by formula (1) or formula (2), and the constant temperature time can be determined according to the plot pollution characteristics combined with experience. The heating time of each layer is lower layer > middle layer > upper layer.

[0067] Step 4: Move the conductive toggle of the sliding conductive connecting rod to heat, when the conductive toggle is at the uppermost end, all the spiral coils heat the resistance as a whole, the heating interval gradually decreases as the conductive toggle slides downward, and the heating interval gradually increases as the conductive toggle slides upward. The heating method can be to heat the whole first, then slide the conductive toggle from top to bottom; or it can be operated in reverse, first heat the lower layer of soil, then slide the conductive toggle from bottom to top to add new heating sections.

[0068] This embodiment is simpler to operate than embodiment 2 and has universality. However, embodiment 2 is more targeted in combination with the actual construction period requirements.

[0069] Finally, it should be noted that the above is only used to illustrate the technical solutions of the present application and is not limiting. Although the present application has been described in detail with reference to the preferred arrangement, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A heating method based on a dynamically adjustable in-situ heat conduction type electric heating device for contaminated soil, characterized in that: The heating device includes a power supply system installed above ground and a heating system extending underground, connected by a ground power cable (33). The heating system includes a heating well (11) and a heating assembly installed within the heating well (11). The heating assembly includes a fixed conductive connecting rod (121) connected to the positive and negative terminals of the ground power cable (33), a sliding conductive connecting rod (122), and a spiral coil heating resistor (13) surrounding the fixed conductive connecting rod (121). The lower end of the spiral coil heating resistor (13) is connected to the lower end of the fixed conductive connecting rod (121), and the upper end of the spiral coil heating resistor (13) is a free end; the sliding conductive connecting rod (122) can slide up and down and is connected to the spiral coil heating resistor (13) through a conductive paddle (143); the sliding conductive connecting rod (122) is connected to a drive motor (60) that controls its up and down sliding, and the negative terminal of the ground power supply cable (33) is slidably connected to the sliding conductive connecting rod (122) through a brush connector (61); The method includes the following steps: Step 1: Determine the characteristics of the land parcel to be heated: The characteristics of the land parcel include the characteristics of land pollution, the characteristics of the soil strata, and the characteristics of hydrogeology; Step 2: Based on the characteristics of the land parcels, the land parcels to be heated are generalized into layers along the vertical direction; Step 3: Determine the target heating temperature for each soil layer based on the characteristics of each plot. Step 4: Based on the overall construction period requirements and taking into account the characteristics of the lowest plot, determine the heating cycle of the lowest plot, which includes the heating time, the constant temperature time, and the cooling time. Step 5: Calculate the heating influence range of a single heating device within the heating section based on the soil strata and soil characteristics; Step 6: Based on the characteristics of the plot, heating time, target temperature, and heating influence range of the lowest soil layer, calculate the power input of a single heating device per unit depth of soil. Set the final temperature for soil heating. When the temperature is greater than 100℃, the power input per unit depth in the soil is calculated using formula (1): （1） In the formula: This represents the average power input per unit depth of a single heating device, expressed in W⋅m. -1 ; The time required for water in the soil to completely vaporize, expressed in days; The time required for soil to be heated from 100℃ to the target temperature, expressed in days; Indicates the range of influence of thermal radiation from a single heating device, in meters (m). 2 ; This represents soil particle density, g⋅m -3 ; W represents the heat capacity of soil particles, day = g -1 ⋅℃ -1 ; Indicates soil porosity; The density of water is expressed in g⋅m. -3 ; The heat capacity of water is expressed as W⋅day⋅g. -1 ⋅℃ -1 ; Indicates the water saturation level in the soil; The boiling point of water is indicated in °C. This indicates the temperature of the soil before heating, in °C. The final temperature in the soil is expressed in °C. h w This represents the heat of vaporization of water, and the unit is W⋅day⋅g. –1 ; When setting the final temperature for soil heating When the temperature is less than or equal to 100℃, the power input within the soil depth is calculated using formula (2): （2） In the formula: It is a value between 0 and 1, representing the percentage of water that evaporates when the heating temperature is below 100℃; This indicates the time required to heat the soil to the target temperature, expressed in days. Step 7: Install the heating device in the area to be heated in the contaminated soil; and determine the longitudinal spacing and radial distance of the spiral coil heating resistors based on the calculation results of Step 6; Step 8: Based on the power input of a single heating device per unit depth in the soil calculated in Step 6, as well as the characteristics of each layer and the target temperature, derive the heating time for all soil layers except the bottom layer, and then determine the constant temperature time based on the characteristics of the soil layer. Step 9: Based on the heating time and constant temperature time of each layer, move the conductive tab of the sliding conductive connecting rod to heat the layers. When the conductive tab is at the top, all the spiral coil heating resistors are heated as a whole. Sliding the conductive tab downwards gradually reduces the heating range, while sliding the conductive tab upwards gradually increases the heating range. In step one, the pollution characteristics of the land parcel include pollutant type, pollutant saturated vapor pressure, pollutant boiling point, pollutant spatial distribution range, and pollutant concentration; the soil characteristics of the strata include soil type, soil moisture content, soil particle density, soil porosity, soil particle heat capacity, soil initial temperature, soil permeability, soil thermal conductivity, and soil thermal conductivity coefficient; the hydrogeological characteristics include groundwater depth, aquifer thickness, hydraulic gradient, soil permeability coefficient, and groundwater flow velocity.

2. The heating method according to claim 1, characterized in that: The power supply system includes a power supply device and its control system (31) and a temperature control system (32). The power supply device and its control system (31) are connected to a ground power supply cable (33). The temperature control system (32) is connected to temperature sensors (35) installed in contaminated soil at different depths. The temperature control system (32) receives signals from the temperature sensors (35) and sends signals to the power supply device and its control system (31) to control the output of current and the up-and-down sliding of the sliding conductive connecting rod (122).

3. The application of the heating method according to claim 1, characterized in that: An auxiliary heating method for extracting pollutants from soil contaminated with organic pollutants, wherein the heating time required for different horizontal layers in the contaminated soil increases from top to bottom.

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