Static in-situ thermal conduction type pollution soil layering differential electric heating method and application

Abstract

The application discloses a static in-situ heat conduction type pollution soil layering differentiation electric heating method and application thereof, and comprises the following steps: 1) determining the plot characteristics of the to-be-heated area; 2) extending the to-be-heated plot vertically and generalizing layering; 3) determining the heating target temperature of each layer of soil; 4) determining the heating period; 5) determining the heating influence range of a single heating device in the temperature rising section; 6) calculating the power input of a single heating device in each layer of soil unit depth; 7) setting the longitudinal in-situ heating device in the to-be-heated area of the pollution soil, and determining the number of turns and the spacing of the heating coil of the spiral coil heating resistor in each layer of soil depth according to the power input of a single heating device in each layer of soil unit depth; and 8) heating. The application can flexibly and pertinently realize the differentiation heating requirement of different depth soil layers, realizes accurate heating, and saves energy.

Description

TECHNICAL FIELD

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

[0002] For the soil contaminated by organic pollutants, especially the contaminated soil which is difficult to be treated 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 an electric heating rod or passing flue gas in the heating well, and the heated casing continuously transfers heat to the surrounding soil through heat radiation, 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 has less influence on 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 U-shaped arrangement. This type of electric heating pipe arrangement can realize uniform heating of the whole heating well, but it is limited by the fixed length of the electric heating pipe. If the heating power needs to be improved (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 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 differential 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, so that the stability of the in-situ electric heating treatment system for treating contaminated soil is improved and the effective temperature is increased. However, the specific structure, style and arrangement of the core heating element of the in-situ electric heating pipe are not described.

[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 arrangement of the heating pipe in the carbon steel sleeve is U-shaped, which realizes uniform heating of the whole heating well and cannot realize differential heating in the vertical direction. SUMMARY

[0008] The present application aims to provide a static in-situ heat conduction type pollution soil layered differential electric heating method and its application based on the above problems, which can flexibly and specifically realize the differential heating requirements of different depth soil layers, realize accurate heating and save energy. The purpose of the present application is achieved by the following technical solutions:

[0009] A static in-situ heat conduction type pollution soil layered differential electric heating method, comprising the following steps:

[0010] Step one: determine the plot characteristics of the area to be heated: the plot characteristics include plot pollution characteristics, soil layer soil characteristics and hydrogeological characteristics;

[0011] Step two: according to the plot characteristics, the plot to be heated is generalized and layered in the vertical direction;

[0012] Step three: according to the characteristics of each layer of the plot, determine the heating target temperature of each layer of soil;

[0013] Step four: according to the overall construction period requirement, and considering the characteristics of each layer of the plot, determine the heating period, which includes the heating time, the constant temperature time and the cooling time;

[0014] Step five: according to the stratum soil characteristics of each layer of soil, determine the heating influence range of a single heating device in the heating section;

[0015] Step six: according to the results determined in steps two to five, calculate the power input of a single heating device in each layer of soil per unit depth;

[0016] Step seven: set up longitudinal in-situ heating devices in the contaminated soil area to be heated, the in-situ heating device comprises a heating well and a heating assembly arranged in the heating well, the heating assembly comprises two longitudinally arranged conductive connecting rods connected with the positive and negative poles of the power supply cable respectively and a spiral coil heating resistor connecting the two conductive connecting rods; the number of turns and the pitch of the heating coil of the spiral coil heating resistor in each layer of soil are determined according to the power input of the single heating device in the unit depth of each layer of soil determined in step six;

[0017] Step eight: use the heating device of step seven to heat according to the power determined in step six and the heating period determined in step four.

[0018] In step one, the soil block contamination 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 stratum characteristics include the soil category, the soil water content, the soil particle density, the soil porosity, the heat capacity of soil particles, the initial temperature of soil, the soil air permeability, the soil thermal conductivity and the soil temperature conductivity coefficient; the hydrogeological characteristics include the groundwater depth, the aquifer thickness, the hydraulic gradient, the soil permeability coefficient and the groundwater flow rate.

[0019] Further optimization, in step six, when the final temperature T c of soil heating is greater than 100℃, the power input of the unit depth of the single heating device is calculated by formula (1):

[0020]

[0021] In the formula, β represents the average power input of the unit depth of the single heating device, 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 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 aT represents the temperature before soil heating, ℃; T c T represents the final temperature in the soil, ℃; h w T represents the heat of vaporization of water, and the unit is W·day·g –1 .

[0022] Further optimization, in step six, when setting the final temperature T c of soil heating is less than or equal to 100 ℃, the heating power input in each layer of soil depth is calculated by formula (2):

[0023]

[0024] In the formula: σ is a 0-1 value, representing the proportion of water evaporation under the condition that the heating temperature is lower than 100 ℃; t c1 T represents the time required for soil heating to the target temperature, day.

[0025] Further, in step six, the in-situ heating device further 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, and 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 current.

[0026] The spiral coil heating resistance is a nickel-chromium or iron-chromium alloy wire; the conductive connecting rod is made of stainless steel.

[0027] The application of the heat conduction type electric heating method to the auxiliary heating of organic contaminated soil pollutant extraction. Especially, the required heat of the vertical different horizontal layers in the contaminated soil is different.

[0028] The advantages and beneficial effects of the present application are:

[0029] The present application can adopt targeted and different heating schemes based on the differences in pollutant types, spatial distribution, soil quality and hydrogeological conditions in contaminated soil remediation, realize different heating temperatures at different depths, and is beneficial to the implementation of precise depth heating. On the premise of ensuring the heating effect, energy can be effectively saved, and carbon emissions can be reduced.

[0030] The present application adjusts the spacing of the coil in the longitudinal direction to change the heating power of the electric heating device per unit depth; so as to better adapt to the needs of different depths and different heating.

[0031] The present application detects the heating temperature of different strata soil by burying temperature sensors of different depths in the soil around the heating well, realizes precise heating with fixed depth and power, greatly improves the precision of heating temperature of different strata at different depths, and improves the efficiency of construction. BRIEF DESCRIPTION OF DRAWINGS

[0032] The application will be further described in conjunction with the accompanying drawings and examples.

[0033] Figure 1 The operation flow chart in Example 1;

[0034] Figure 2 The structure schematic diagram of in-situ heating device in Example 1;

[0035] Figure 3 The specific application scene schematic diagram of heating method in Example 2;

[0036] Figure 4 The heating cycle schematic diagram;

[0037] Figure 5 The structure schematic diagram of in-situ heating device in Example 3;

[0038] Figure 6 The structure schematic diagram of in-situ heating device in Example 4.

[0039] 11, heating well; 12, conductive connecting rod; 13, spiral coil heating resistance; 14, connecting point of conductive connecting rod and spiral coil heating resistance; 15, heating well outer casing; 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. S-1, upper layer; S-2, middle layer; S-3, lower layer. RD represents heating section. DETAILED DESCRIPTION

[0040] Example 1

[0041] A static in-situ heat conduction type pollution soil layering differential electric heating method, as shown in the figure, comprises the following steps: Figure 1

[0042] ​Step one: determine the plot characteristics of the area 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 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 uniform, and the pollutants are petroleum hydrocarbons, PAHs with part of the boiling point below 250℃, semi-volatile, and the upper and lower layers of soil have little difference in properties, and the central soil has poor thermal conductivity.

[0043] Step two: according to the plot characteristics, the plot to be heated is divided into layers in the vertical direction; in this embodiment, it is divided into three layers.

[0044] Step three: determine the heating target temperature of each layer of soil according to the plot characteristics of each layer; according to the types and properties of pollutants, the heating range is 120-220℃, and according to the soil layer and hydrogeological characteristics, the heating target temperatures of the upper layer, the middle layer and the lower layer are determined as 125℃, 200℃ and 150℃ respectively.

[0045] Step four: according to the overall construction period requirement, and considering the plot characteristics of each layer, determine the heating period, which includes the heating time, the constant temperature time and the cooling time.

[0046] Step five: according to the soil layer soil characteristics (temperature conductivity coefficient) of each layer of soil, calculate the heating influence range A of a single heating device in the heating section.

[0047] Step six: according to the results determined in steps two to five, calculate the power input of a single heating device in each layer of soil per unit depth.

[0048] Because the target temperature is higher than 100℃, formula (1) is used to calculate the power input per unit depth of each layer of soil.

[0049] Step seven: set up longitudinal in-situ heating devices in the area to be heated in the contaminated soil, such as Figure 2As shown, the in-situ heating device comprises a heating well 11 and a heating assembly arranged in the heating well 11, the heating assembly comprises two longitudinally arranged conductive connecting rods 12 connected with the positive and negative poles of the power supply cable respectively and a spiral coil heating resistor 13 connecting the two conductive connecting rods 12; the number of turns and the pitch of the heating coil of the spiral coil heating resistor 13 in each layer of soil depth are determined according to the heating power input of the single heating device in each layer of soil depth determined in step six. The spiral coil heating resistor 13 is a nickel-chromium or iron-chromium alloy wire; the conductive connecting rod 12 is made of stainless steel.

[0050] Step eight: using the heating device of step seven, heating according to the heating power determined in step six and the heating period determined in step four.

[0051] Example 2

[0052] A static in-situ thermal conduction type layered differential electric heating method for contaminated soil, comprising the following steps:

[0053] Step one: determine the characteristics of the land block to be heated: the characteristics of the land block include the characteristics of the contaminated land block, the characteristics of the soil layer and the hydrogeological characteristics; the characteristics of the contaminated land block 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 characteristics of the soil layer 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; the hydrogeological characteristics include the depth of groundwater, the thickness of the aquifer, the hydraulic gradient, the soil permeability coefficient and the flow rate of groundwater. In this embodiment, the vertical distribution of the pollutants is divided into three parts: the upper layer is mainly benzene series, chlorinated hydrocarbons and other VOCs, which are easy to volatilize; the middle layer is mainly petroleum hydrocarbons and part of PAHs with boiling points below 250℃, which 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:

[0054] Table 1

[0055] 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 above 250°C, PCBs, pesticides Less volatile 220-350℃

[0056] Step two: according to the characteristics of the land block, the land block to be heated is generalized and layered vertically; this embodiment is divided into three layers.

[0057] Step three: according to the characteristics of each layer of the land block, determine the heating target temperature of each layer of soil; the heating target temperatures of the upper layer, the middle layer and the lower layer are determined as 90℃, 150℃ and 300℃ respectively,

[0058] Step four: determine the heating period according to the overall construction period requirement and taking into account the characteristics of each layer of the land block, the heating period includes the heating time, the constant temperature time and the cooling time;

[0059] Step five: according to the soil layer characteristics (temperature coefficient) of each layer of soil, the heating range A of a single heating device in the heating period is calculated;

[0060] Step six: according to the results determined in steps two to five, the power input of a single heating device in the unit depth of each layer of soil is calculated;

[0061] Because the target temperature of the lower layer is higher than 100℃, the power input in the unit depth of each layer of soil is calculated by formula (1); and because the target temperature of the upper layer is lower than 100℃, the power input in the unit depth of each layer of soil is calculated by formula (2); the heating cycle is shown in Figure 4 .

[0062] Step seven: longitudinal in-situ heating devices are arranged in the contaminated soil area to be heated, as shown in Figure 3 , the in-situ heating device includes a heating well 11 and a heating assembly arranged in the heating well 11, the heating assembly includes two longitudinally arranged conductive connecting rods 12 connected with the positive and negative poles of the power supply cable 33 respectively and a spiral coil heating resistor 13 connecting the two conductive connecting rods 12; the number of turns and the pitch of the heating coil of the spiral coil heating resistor 13 in the depth of each layer of soil are determined according to the heating power input of a single heating device in the unit depth of each layer of soil determined in step six; the in-situ heating device further 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 with the ground power supply cable 33, 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 and sends the signal to the power supply device and its control system 31 to control the output of the current. The conductive connecting rod 12 is connected with the spiral coil heating resistor 13 through a high-temperature-resistant lead wire; the heating well 11 includes 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 nichrome or iron-chromium alloy wire, 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 12 is made of stainless steel; the high-temperature-resistant lead wire is a high-temperature glass fiber wire or a silicone wire.

[0063] Step eight: the heating device of step seven is used to heat according to the heating power determined in step six and the heating cycle determined in step four.

[0064] This embodiment is applied to auxiliary heating for organic contaminated soil pollutant extraction, the required heat of different vertical layers in the contaminated soil is different, and the specific use state is shown in Figure 3As shown, horizontal barrier layer 51 and vertical barrier wall 52 are arranged at the edge of the in-situ heating area, 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, in-situ multi-phase extraction device (including in-situ multi-phase extraction well 21, open screen section 22, solid pipe section 23, multi-phase extraction well head 24, liquid phase extraction pipeline 25, submersible pump 26) is arranged in the middle of the in-situ heating device, the in-situ heating device is connected to electrical device and its control system 31, and the in-situ multi-phase extraction device is connected to tail water and tail gas treatment device 4.

[0065] Example 3

[0066] A static in-situ heat conduction type contaminated soil layering differential electric heating method has the same operation steps as example 1, only because the characteristics of the land are different, the target temperature determined in step three is different, the power input in each layer of soil per unit depth determined in step six is different, and the coil distribution of the heating device in step seven is different, such as Figure 5 As shown, the uppermost section is provided with 0 helical coils, which is a non-heating area.

[0067] Example 4

[0068] A static in-situ heat conduction type contaminated soil layering differential electric heating method has the same operation steps as example 1, only because the characteristics of the land are different, the target temperature determined in step three is different, the power input in each layer of soil per unit depth determined in step six is different, and the coil distribution of the heating device in step seven is different, such as Figure 6 As shown, the middle section is provided with 0 helical coils, which is a non-heating area.

[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 by equivalents without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A static in-situ heat conduction method for stratified differentiated electric heating of contaminated soil, characterized in that: 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, soil properties, and hydrogeological features; 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 each plot, determine the heating cycle, which includes the heating time, the constant temperature time, and the cooling time. Step 5: Based on the soil characteristics of each soil layer, determine the heating influence range of a single heating device within the heating section; Step Six: Based on the results determined in Steps Two to Five, calculate the power input of a single heating device per unit depth in each soil layer; when the final soil heating temperature T is set... c When the temperature is above 100℃, the power input per unit depth of each soil layer is calculated using formula (1): In the formula: β represents the average power input per unit depth of a single heating device, W·m -1 ;t b The time required for water in the soil to completely vaporize is expressed as day; t c2 A represents the time required to heat soil from 100℃ to the target temperature, expressed in days; A represents the range of thermal radiation from a single heating device, expressed in meters. 2 ;ρ s Soil particle density, g·m -3 C s The heat capacity of soil particles is expressed in W·day·g. -1 ·℃ -1 θ represents soil porosity; ρ w The density of water is expressed in g·m. -3 C w The heat capacity of water is expressed in W·day·g. -1 ·℃ -1 δ represents the water saturation level in the soil; T b The boiling point of water is expressed in °C (°C); T a The temperature of the soil before heating is expressed in °C (°C); T c The final temperature in the soil is expressed in °C; h w This represents the heat of vaporization of water, measured in W·day·g. –1 ; When the final temperature T for soil heating is set c When the temperature is less than or equal to 100℃, the power input within each soil depth is calculated using formula (2): In the formula: σ is a value from 0 to 1, representing the percentage of water evaporation under heating temperatures below 100℃, and t c1 The time required to heat the soil to the target temperature is indicated in days; Step 7: Install a longitudinal in-situ heating device in the area to be heated in the contaminated soil. The in-situ heating device includes a heating well and a heating component installed in the heating well. The heating component includes two longitudinally arranged conductive connecting rods connected to the positive and negative terminals of the power supply cable, respectively, and a spiral coil heating resistor connecting the two conductive connecting rods; Determine the number of turns and spacing of the heating coil of the spiral coil heating resistor in each soil layer depth based on the power input of a single heating device in each unit depth of each soil layer determined in Step 6; Step 8: Using the heating device from Step 7, heat the device according to the power determined in Step 6 and the heating cycle determined in Step 4.

2. The static in-situ heat conduction method for stratified differentiated electric heating of contaminated soil according to claim 1, characterized in that: 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.

3. The static in-situ heat conduction method for stratified differentiated electric heating of contaminated soil according to claim 1, characterized in that: In step six, the in-situ heating device also includes a power supply device and its control system, as well as 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.

4. The static in-situ heat conduction method for stratified differentiated electric heating of contaminated soil according to claim 1, characterized in that: The heating resistor of the spiral coil is made of nickel-chromium or iron-chromium alloy wire; the conductive connecting rod is made of stainless steel.

5. The application of the differentiated electric heating method according to claim 1, characterized in that: Auxiliary heating for extracting pollutants from organically contaminated soil.

6. The application of the differentiated electric heating method according to claim 5, characterized in that: The amount of heat required varies for different horizontal layers in the contaminated soil.

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