Multi-stage active on-off in-situ thermal conduction soil electric heating device and heating method

Abstract

The application discloses a multi-section active switch type in-situ thermal conduction soil electric heating device and a heating 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 spiral coil heating resistor and a plurality of vertical conductive connecting rods. Different conductive connecting rods are connected to the spiral coil heating resistor at different depths. The power supply system and the spiral coil heating resistor are connected to any two conductive connecting rods through a control circuit to form a closed loop circuit, so that the spiral coil heating resistor at different depths is heated. The control circuit is provided with a switch for controlling the opening and closing of different closed loop circuits. The application can flexibly and specifically meet the differentiated heating requirements of different depth soil layers, realize accurate heating, and save energy.

Description

TECHNICAL FIELD

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

[0002] For soil contaminated by organic pollutants, especially soil contaminated by polycyclic aromatic hydrocarbons, pesticides, petroleum hydrocarbons and other pollutants that are difficult to treat by traditional remediation processes, in-situ thermal desorption technology is widely used in in-situ treatment technology 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 for 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 an electric heating rod or passing flue gas in the heating well, and continuously transfer heat to the surrounding soil through heat radiation of the heated casing, thereby achieving the purpose of heating 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. In-situ heat conduction heating is less affected by the physical and chemical properties of the soil, and has wider adaptability. However, due to the arrangement of the heating rod or the flue gas heating passage in the heating well, there are some problems in in-situ heat conduction heating:

[0005] The electric heating pipe in the heating well used in in-situ heat conduction-electric heating process adopts a U-shaped arrangement. This type of electric heating pipe arrangement can achieve 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 increased (under the condition that the heating peak of the electric resistance heating of the heating rod is determined), only a larger power electric heating rod can be replaced, which limits the selection of the material of the heating well 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 remediation of organically contaminated soil. The invention provides an in-situ electric heating remediation system for organically contaminated soil. The core heating element of the electric heating tube is made of a non-metallic carbon-silicon rod. The silicon-carbon rod is connected to the power supply and is filled or cast with aluminum silicate fiber for insulation. This significantly improves the stability and effective temperature of the in-situ electric heating treatment system for contaminated soil. However, the invention does not describe the specific structure, design, or layout of the core heating element within the tube.

[0007] Patent CN205673362U discloses a heating well for an in-situ electric heating desorption remediation device for contaminated sites. The core component of this heating well is a single-lead stainless steel heating tube, which houses a heating wire and is filled with crystalline magnesium oxide particles. The top lead of the heating tube is connected to an insulating wire sheath. The accompanying drawings show the heating tube arranged in a U-shape within the carbon steel sheath, achieving uniform heating across the entire well but preventing differentiated heating in the vertical direction. Summary of the Invention

[0008] In response to the above problems, the present invention aims to provide a multi-stage active switching in-situ heat conduction contaminated soil electric heating device and heating method. This device can flexibly and specifically meet the differentiated heating requirements of soil layers at different depths, achieving precise heating and saving energy. This objective is achieved through the following technical solutions:

[0009] A multi-stage active switching in-situ heat conduction soil electric heating device includes a power supply system arranged above the ground and a heating system deep underground, the power supply system and the heating system being connected via a ground power supply cable; the heating system includes a heating well and a heating assembly arranged within the heating well, the heating assembly including a spiral coil heating resistor and a plurality of vertical conductive connecting rods, different conductive connecting rods being connected to different depths of the spiral coil heating resistor, the power supply system and the spiral coil heating resistor being connected to any two conductive connecting rods via a control circuit to form a closed-loop circuit to achieve heating of the spiral coil heating resistor at different depths, and the control circuit being provided with switches for controlling the opening and closing of different closed-loop circuits.

[0010] The spiral coil heating resistor is a connected whole or divided into multiple sections; the spacing between the spiral coils of the spiral coil heating resistor is equal, or the spacing between the spiral coils of each section is unequal.

[0011] An optimization solution is: the spiral coil heating resistor is a connected whole, the conductive connecting rod includes a main conductive connecting rod and multiple secondary conductive connecting rods, the spiral coil heating resistor surrounds the main conductive connecting rod, the main conductive connecting rod is connected to the bottom end of the spiral coil heating resistor, and multiple secondary conductive connecting rods are connected to the spiral coil heating resistor at different depths, and the spacing between the spiral coils of the spiral coil heating resistor is equal.

[0012] Another optimization solution is: the spiral coil heating resistor is divided into at least two disconnected sections, and the sections are arranged in sequence up and down, and the upper and lower ends of any section of the spiral coil heating resistor are respectively connected to a conductive connecting rod.

[0013] Another optimization scheme is that the spiral coil heating resistor is divided into at least two sections, and each section is arranged in sequence up and down, the conductive connecting rod includes a main conductive connecting rod and multiple auxiliary conductive connecting rods, each section of the spiral coil heating resistor is surrounded by the main conductive connecting rod and the bottom end is connected to the main conductive connecting rod at different depths, and the upper end of each section of the spiral coil heating resistor is connected to a auxiliary conductive connecting rod.

[0014] Furthermore, the power supply system includes 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 supply cable, and the temperature control system is connected to temperature sensors installed in contaminated soil at different depths. The temperature control system receives signals from the temperature sensors and sends signals to the power supply device and its control system to control the output of current and the opening and closing of different closed-loop circuits.

[0015] The electric heating device is used for auxiliary heating of pollutant extraction in organic contaminated soil, and different vertical horizontal layers in the contaminated soil require different heating times.

[0016] A heating method based on the multi-stage active switching type in-situ heat conduction soil electric heating device comprises the following steps:

[0017] Step 1: Determine the land characteristics of the area to be heated: the land characteristics include land pollution characteristics, soil characteristics and hydrogeological characteristics;

[0018] Step 2: Based on the characteristics of the land, the land to be heated is generalized and layered along the vertical direction;

[0019] Step 3: Install the electric heating device in the area to be heated, and determine the heating time required to heat each layer of soil based on the power of the electric heating device and the characteristics of each layer of soil;

[0020] Step 4: Control the heating of the spiral coil heating resistor in the soil layers at different depths by controlling the switch of the circuit.

[0021] Another heating method based on the multi-stage active switching type in-situ heat conduction soil electric heating device comprises the following steps:

[0022] Step 1: Determine the land characteristics of the area to be heated: the land characteristics include land pollution characteristics, soil characteristics and hydrogeological characteristics;

[0023] Step 2: Based on the characteristics of the land, the land to be heated is generalized and layered along the vertical direction;

[0024] Step 3: Determine the heating target temperature of each layer of soil based on the characteristics of each layer of land;

[0025] Step 4: Determine the heating cycle based on the overall construction period requirements and taking into account the characteristics of the soil layer that requires the most heat. The heating cycle includes a heating time, a constant temperature time, and a cooling time.

[0026] Step 5: Calculate the heating influence range of a single heating device within the heating section based on the soil stratum characteristics;

[0027] Step 6: Calculate the power input of a single heating device per unit depth of soil based on the plot characteristics, heating time, target temperature, and heating impact range of the soil layer with the most heat required;

[0028] Step 7: Install the electric 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 resistor based on the calculation results of step 6;

[0029] Step 8: Determine the heating time and constant temperature time of each soil layer based on the power input of the single heating device within the unit depth of the soil calculated in step 6, the plot characteristics of each layer, and the target temperature;

[0030] Step nine: The control circuit controls the heating of the spiral coil heating resistors at different depths to achieve differential heating of soil layers at different depths.

[0031] In step one, the land pollution characteristics include the type 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 characteristics of the stratum include soil type, soil moisture content, soil particle density, soil porosity, heat capacity of soil particles, 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 and groundwater flow rate.

[0032] Further optimization, in step 6, when setting the final temperature of soil heating T c When the temperature is greater than 100℃, the power input per unit depth of soil is calculated using the formula:

[0033]

[0034] In the formula: β represents the average power input per unit depth of a single heating device, W·m -1 ; t b represents the time required for 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 range of influence of the thermal radiation of a single heating device, m 2 ; ρ s represents the density of soil particles, g·m -3 ; C s represents the heat capacity of 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, with the unit being W·day·g –1 .

[0035] Further optimization, in step six, when the final temperature T c of soil heating is less than or equal to 100℃, the power input in each layer of soil depth is calculated using the formula:

[0036]

[0037] In the formula: σ is a number between 0 and 1, representing the proportion of water evaporation under the condition that the heating temperature is less than 100℃, t c1 represents the time required for the soil to heat to the target temperature.

[0038] The advantages and beneficial effects of the present application are:

[0039] The present application can adopt targeted and different heating schemes based on the different types of pollutants, spatial distribution, soil quality, and hydrogeological conditions in contaminated soil remediation, achieve different heating temperatures at different depths, and facilitate precise depth and timing heating, effectively saving energy and reducing carbon emissions under the premise of ensuring heating effect.

[0040] This invention uses temperature sensors embedded at varying depths in the soil surrounding the heating well to detect the heating temperature of soil in different strata, enabling precise heating at a specific depth, time, and power. This significantly improves the accuracy of heating duration and temperature measurements at different depths and strata, and also enhances construction efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The present invention will be further described below with reference to the accompanying drawings and examples.

[0042] Figure 1 This is a structural diagram of the electric heating device of Example 1;

[0043] Figure 2 This is a schematic diagram of the use state of the electric heating device of Example 1;

[0044] Figure 3 The control circuit in Example 1;

[0045] Figure 4 This is a structural diagram of the electric heating device of Example 2;

[0046] Figure 5 This is a structural diagram of the electric heating device of Example 3;

[0047] Figure 6 Schematic diagram of the heating cycle in the embodiment.

[0048] 11. Heating well; 121. Main conductive connecting rod; 122, 123, 124 auxiliary conductive connecting rods; 125. First conductive connecting rod; 126. Second conductive connecting rod; 127. Third conductive connecting rod; 128. Fourth conductive connecting rod; 13. Spiral coil heating resistor; 14. Connection point between conductive connecting rod and spiral coil heating resistor; 15. Heating well outer casing; 16. Heating well flange cover; 21. In-situ multiphase extraction well; 22. Screen section; 23. Solid pipe section; 24. Multiphase 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. Connector between power supply cable and conductive connecting rod; 35. Temperature sensor; 36. Thermocouple; 37. Temperature sensor wire; 38. Distribution box; 4. Tail water and exhaust gas treatment system; 51. Horizontal barrier layer; 52. Vertical barrier wall. R11 to R13 represent resistors, and S1 to S6 represent switches. DETAILED DESCRIPTION

[0049] Example 1

[0050] A multi-stage active switching type in-situ heat conduction contaminated soil electric heating device, such as Figure 1As shown, it comprises a power supply system arranged above the ground and a heating system deep into the ground, the power supply system and the heating system are connected through the ground power 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 main conductive connecting rod 121, a spiral coil heating resistor 13 arranged outside the main conductive connecting rod 121, and three auxiliary conductive connecting rods 122, 123 and 124 connected with the spiral coil heating resistor 13 at different depths, the power supply system and the spiral coil heating resistor 13 are connected through a control circuit and any two conductive connecting rods to form a closed loop circuit to realize the heating of the spiral coil heating resistor 13 at different depths, the auxiliary conductive connecting rods 122, 123 and 124 are connected with the spiral coil heating resistor 13 at different depths, and the main conductive connecting rod 121 is connected with the bottom end of the spiral coil heating resistor 13. In this embodiment, the spiral coil heating resistor 13 is a whole, and the spacing of each spiral coil is the same. A control circuit of this embodiment is shown in Figure 3

[0051] As shown in Figure 2 The power supply system comprises 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 with the ground power cable 33, and the temperature control system 32 is connected with the temperature sensor 35 arranged in the contaminated soil at different depths, the temperature control system 32 receives the signal of the temperature sensor 35 and sends the signal to the power supply device and its control system 31 to control the output of the current and the opening and closing of the switch on the different closed loop circuits.

[0052] The conductive connecting rod 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 at 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.

[0053] Embodiment 2

[0054] A multi-section active switch type in-situ heat conduction type contaminated soil electric heating device, as shown in Figure 4 ​As shown in the figure, it comprises a power supply system arranged above the ground and a heating system deeply underground, the two are connected by a ground power 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 spiral coil heating resistor 13 and four vertical conductive connecting rods, the spiral coil heating resistor 13 is divided into two non-communicating sections arranged in sequence from top to bottom, the upper and lower ends of the upper section spiral coil heating resistor 13 are connected with the first conductive connecting rod 125 and the second conductive connecting rod 126 respectively; the upper and lower ends of the lower section spiral coil heating resistor 13 are connected with the third conductive connecting rod 127 and the fourth conductive connecting rod 128 respectively.

[0055] Other settings are the same as in Example 1.

[0056] Example 3

[0057] A multi-section active switch type in-situ heat conduction type contaminated soil electric heating device, as shown in the figure, comprises a power supply system arranged above the ground and a heating system deeply underground, the two are connected by a ground power cable 33; the heating system comprises a heating well 11 and a heating assembly arranged in the heating well 11, the spiral coil heating resistor 13 is divided into three sections, and each section is arranged in sequence from top to bottom, the conductive connecting rod comprises a main conductive connecting rod 121 and three auxiliary conductive connecting rods 122, 123 and 124, each section of the spiral coil heating resistor 13 is wrapped outside the main conductive connecting rod 121 and connected with the main conductive connecting rod 121 at different depths, and the upper end of each section of the spiral coil heating resistor 13 is connected with an auxiliary conductive connecting rod 122, 123 or 124. Figure 5 Other settings are the same as in Example 1.

[0058] Example 4

[0059] The heating method of the electric heating device in Example 1, if the spiral coil spacing of the electric heating device has not been determined, the power can be adjusted, comprising the following steps:

[0060]

[0061] ​Step 1: Determine the plot characteristics of the area to be heated: the plot characteristics include plot pollution characteristics, soil layer characteristics and hydrogeological characteristics; the plot pollution characteristics include pollutant types, pollutant saturated vapor pressure, pollutant boiling point, pollutant spatial distribution range and pollutant concentration; the stratum soil characteristics include soil type, soil moisture content, soil particle density, soil porosity, heat capacity of soil particles, soil initial temperature, soil permeability, soil thermal conductivity and soil thermal conductivity; the hydrogeological characteristics include groundwater depth, aquifer thickness, hydraulic gradient, soil permeability and groundwater flow rate. In this embodiment, the vertical distribution of pollutants is divided into three parts. The upper layer is mainly VOCs such as benzene series and chlorinated hydrocarbons, which are volatile; petroleum hydrocarbons and some PAHs with boiling points below 250°C are semi-volatile; the lower layer is mainly pesticides with boiling points above 250°C, which are difficult to volatilize; the soil properties are evenly distributed vertically. The properties of the pollutants are shown in Table 1:

[0062] Table 1

[0063] Serial number 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 below 250°C, PCBs, pesticides Less volatile 220-350℃

[0064] Step 2: Based on the characteristics of the land, the land to be heated is generally layered in the vertical direction; in this embodiment, it is divided into 3 layers.

[0065] Step 3: Determine the target heating temperature of each layer of soil according to the characteristics of each layer of land; set the heating target temperatures of the upper layer, middle layer and lower layer to 90℃, 150℃ and 300℃ respectively.

[0066] Step 4: According to the overall construction period requirements and taking into account the characteristics of each layer of land, determine the heating cycle of the lowest layer. The heating cycle includes heating time, constant temperature time and cooling time. The heating cycle is as follows: Figure 6 shown.

[0067] Step 5: Calculate the heating influence range A of a single heating device in the heating section based on the characteristic thermal conductivity of each soil layer;

[0068] Step 6: Based on the results determined in steps 2 to 5, calculate the heating power input of a single heating device within a unit depth of the lowest soil layer;

[0069] Because the target temperature of the lower layer is higher than 100°C, the heating power input per unit depth of soil is calculated using formula (1);

[0070] Step 7: Install the electric heating device described in Example 1 in the area to be heated in the contaminated soil; and determine the longitudinal spacing and radial distance of the spiral coil heating resistor based on the calculation results of Step 6;

[0071] Step 8: Based on the heating power input per unit depth of the soil by the single heating device calculated in Step 6, the plot characteristics of each layer, and the target temperature, deduce the heating time of all other soil layers; the middle layer is inverted using formula (1), and the upper layer is inverted using formula (2). The constant temperature time is then determined based on the characteristics of the pollutant plot, such as the concentration of the pollutant.

[0072] Step 9: Based on the heating time and constant temperature time determined in step 8, the control circuit controls the heating of the spiral coil heating resistors at different depths to achieve differential heating of different soil layers.

[0073] This embodiment is applied to auxiliary heating for extracting pollutants from organic contaminated soil. The specific usage is as follows: Figure 2 As shown, a horizontal barrier layer 51 and a vertical barrier wall 52 are set at the inner edge of the in-situ heating area, an electric heating device is set in the middle of the in-situ heating area, and two groups of in-situ multi-phase extraction devices are set on both sides of the electric heating device. The electric heating device is connected to the power supply system, and the in-situ multi-phase extraction device is connected to the tail water and exhaust gas treatment device 4.

[0074] Example 5

[0075] The heating method of the electric heating device in Example 1, if the pitch of the spiral coils of the electric heating device is fixed and the power is fixed, includes the following steps:

[0076] Step 1: Determine the plot characteristics of the area to be heated: The plot characteristics include plot pollution characteristics, soil layer characteristics, and hydrogeological characteristics; the plot pollution characteristics include pollutant type, pollutant saturated vapor pressure, pollutant boiling point, pollutant spatial distribution range, and pollutant concentration; the stratum soil characteristics 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; the hydrogeological characteristics include groundwater depth, aquifer thickness, hydraulic gradient, soil permeability, and groundwater flow rate. In this embodiment, the vertical distribution of pollutants is divided into three parts. The upper layer mainly consists of VOCs such as benzene series and chlorinated hydrocarbons, which are volatile; petroleum hydrocarbons and some PAHs with boiling points below 250°C, which are semi-volatile; and the lower layer mainly consists of pesticides with boiling points above 250°C, which are difficult to volatilize. The soil properties are evenly distributed vertically.

[0077] Step 2: Based on the characteristics of the land, the land to be heated is generally layered along the vertical direction; in this embodiment, it is divided into 3 layers.

[0078] Step 3: Install the electric heating device in the area to be heated, and determine the heating time required to heat each layer of soil based on the power of the electric heating device and the characteristics of each layer of soil; the heating time for each layer is lower layer > middle layer > upper layer;

[0079] According to the maximum fixed power, the heating time can be inferred by formula (1) or formula (2), and the constant temperature time can be determined based on the pollution characteristics of the plot and experience.

[0080] Step 4: Control the heating of the spiral coil heating resistor in the soil layers at different depths by controlling the switch of the circuit.

[0081] Compared with Example 4, this embodiment is simpler to operate and has universal applicability, but Example 4 is more targeted in combination with actual construction period requirements.

[0082] Finally, it should be noted that the above is only used to illustrate the technical solution of the present invention and is not limiting. Although the present invention is described in detail with reference to the preferred arrangement scheme, ordinary technicians in this field should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A heating method based on a multi-stage active switching type in-situ heat conduction soil electric heating device, the multi-stage active switching type in-situ heat conduction soil electric heating device comprising a power supply system arranged above the ground and a heating system deep underground, the power supply system and the heating system being connected via a ground power supply cable (33); the heating system comprising a heating well (11), and a heating component arranged in the heating well (11), the heating component comprising a spiral coil heating resistor (13) and a plurality of vertical conductive connecting rods, different conductive connecting rods being connected to different depths of the spiral coil heating resistor (13), the power supply system and the spiral coil heating resistor (13) being connected to any two conductive connecting rods via a control circuit to form a closed loop circuit to achieve heating of the spiral coil heating resistor (13) at different depths, the control circuit being provided with a switch for controlling the opening and closing of different closed loop circuits; and characterized in that: The following steps are involved: Step 1: Determine the plot characteristics of the area to be heated: the plot characteristics include plot pollution characteristics, soil layer characteristics, and hydrogeological characteristics; the plot pollution characteristics include pollutant type, pollutant saturated vapor pressure, pollutant boiling point, pollutant spatial distribution range, and pollutant concentration; the stratum soil characteristics 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, and groundwater flow velocity; Step 2: Based on the characteristics of the land, the land to be heated is generalized and layered along the vertical direction; Step 3: Determine the heating target temperature of each layer of soil based on the characteristics of each layer of land; Step 4: Determine the heating cycle based on the overall construction period requirements and taking into account the characteristics of the soil layer that requires the most heat. The heating cycle includes a heating time, a constant temperature time, and a cooling time. Step 5: Calculate the heating influence range of a single heating device within the heating section based on the soil stratum characteristics; Step 6: Calculate the power input of a single heating device per unit depth of soil based on the plot characteristics, heating time, target temperature and heating impact range of the soil layer with the most heat required; when the final temperature of soil heating is set to T c When the temperature is greater than 100°C, the following formula is used to calculate the power input per unit depth of soil: Where: β represents the average power input per unit depth of a single heating device, W·m -1 ;t b Indicates the time required for the water in the soil to completely evaporate, day; t c2 represents the time required to heat the soil from 100℃ to the target temperature, day; A represents the range of influence of heat radiation of a single heating device, m 2 ρ s represents the soil particle density, g·m -3 ; C s represents the heat capacity of soil particles, W·day·g -1 ℃ -1 ; θ represents 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 water saturation in the soil; T b Indicates the boiling point of water, ℃; T a Indicates the temperature of the soil before heating, ℃; T c Indicates the final temperature in the soil, °C; h w Represents the heat of vaporization of water, unit is W·day·g –1 . When the final temperature of soil heating is set to T c When the temperature is less than or equal to 100°C, the power input in each soil layer is calculated using the following formula: Where: σ is a value from 0 to 1, representing the proportion of water evaporation under the condition of heating temperature below 100℃, t c1 Indicates the time required for the soil to heat to the target temperature; Step 7: Install the electric 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 resistor based on the calculation results of step 6; Step 8: Determine the heating time and constant temperature time of each soil layer based on the power input of the single heating device within the unit depth of the soil calculated in step 6, the plot characteristics of each layer, and the target temperature; Step nine: The control circuit controls the heating of the spiral coil heating resistors at different depths to achieve differential heating of soil layers at different depths.

2. The heating method according to claim 1, wherein: The spiral coil heating resistor (13) is a connected whole or divided into multiple sections; the spacing between the spiral coils of the spiral coil heating resistor (13) is equal, or the spacing between the spiral coils of each section is unequal.

3. The heating method according to claim 2, wherein: The spiral coil heating resistor (13) is a connected whole, the conductive connecting rod comprises a main conductive connecting rod (121) and a plurality of auxiliary conductive connecting rods, the spiral coil heating resistor (13) surrounds the main conductive connecting rod (121), the main conductive connecting rod (121) is connected to the bottom end of the spiral coil heating resistor (13), the plurality of auxiliary conductive connecting rods are connected to the spiral coil heating resistor (13) at different depths, and the spacing between the spiral coils of the spiral coil heating resistor (13) is equal.

4. The heating method according to claim 2, wherein: The spiral coil heating resistor (13) is divided into at least two disconnected sections, and each section is arranged in sequence up and down, and the upper and lower ends of any section of the spiral coil heating resistor (13) are respectively connected to a conductive connecting rod.

5. The heating method according to claim 2, wherein: The spiral coil heating resistor (13) is divided into at least two sections, and each section is arranged in sequence up and down. The conductive connecting rod includes a main conductive connecting rod (121) and a plurality of auxiliary conductive connecting rods. Each section of the spiral coil heating resistor (13) surrounds the main conductive connecting rod (121) and its bottom end is connected to the main conductive connecting rod (121) at different depths. The upper end of each section of the spiral coil heating resistor (13) is connected to a auxiliary conductive connecting rod.

6. The heating method according to claim 2, wherein: 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 a temperature sensor (35) set in contaminated soil at different depths. The temperature control system (32) receives a signal from the temperature sensor (35) and sends a signal to the power supply device and its control system (31) to control the output of current and the opening and closing of different closed-loop circuits.

7. Application of the heating method according to claim 1, characterized in that: The invention is applied to auxiliary heating for extracting pollutants from organic contaminated soil, wherein different vertical horizontal layers in the contaminated soil require different heating times.

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