Method for installing heating well

Abstract

To provide a method of installing a heating well, the method enabling higher heating efficiency in in-situ remediation of contaminated soil.SOLUTION: A method of installing a heating well that is used for in-situ remediation of contaminated soil and includes an outer tube, and a non-insulated heating wire and an insulated heater arranged inside the outer tube. The method comprises: Step 1: placing the outer tube in the contaminated soil; Step 2: positioning the non-insulated heating wire and the insulated heater within the outer tube, and filling gaps between the inner wall surface of the outer tube and the non-insulated heating wire and the insulated heater with a granular or powdered substance having insulation, heat conductivity, and heat resistance; and Step 3: eliminating moisture in the heating well by heating with the insulated heater.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for installing a heated well for use in the in-situ remediation of contaminated soil. [Background technology]

[0002] One known method for purifying contaminated soil with volatile organic compounds (VOCs) is to excavate and remove the contaminated soil (excavation and removal method). This method is a reliable method for purifying contaminated soil. However, the excavation and removal method required the removal and transportation of large amounts of contaminated soil, resulting in enormous transportation and disposal costs.

[0003] From the perspective of reducing costs such as transportation and processing costs, it is possible to consider using in-situ remediation methods that remove contaminants in situ. Known in-situ purification methods include bioremediation, which activates microorganisms to decompose pollutants, and chemical decomposition methods (such as the Fenton process) that use hydrogen peroxide. However, even when using in-situ remediation methods, if the local soil is clayey or silty with low permeability, it is extremely difficult for the treatment chemicals to reach the contaminated areas, and remediation takes a long time.

[0004] Another method for removing pollutants in situ is known as in situ thermal desorption, which is generally classified into three types: electric heater type, electric resistance type, and steam type. Among these, the in-situ thermal desorption method using an electric heater can heat the local soil to over 100°C, expanding the soil skeletal pores as the soil pore water evaporates, allowing the contaminants to be desorbed and carried away by the water vapor.This makes it a method that can efficiently remove contaminants from the soil.

[0005] An example of an in-situ thermal desorption method using an electric heater is proposed in Patent Document 1. Patent Document 1 describes a method in which heat is applied to a treatment area containing contaminants to vaporize some of the contaminants, which are then sucked in and removed from the treatment area. The invention of Patent Document 1 aims to increase the efficiency of contaminant removal by in-situ heating and vapor extraction. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 4509558 Summary of the Invention [Problem to be solved by the invention]

[0007] The heating well (heating well) of Patent Document 1 has an electric heating wire disposed as a heater inside a sleeve pipe (outer pipe), and the outer pipe and the electric heating wire are insulated by air. In this configuration, heat from the heating wire heated to a high temperature (for example, 100°C or higher) is transferred to the area to be treated by radiation. Heat transfer by radiation is less efficient (heating efficiency) than heat transfer by conduction.

[0008] The present invention has been made in consideration of the above circumstances, and aims to provide a method for installing a heating well that can further improve the heating efficiency of a method for in-situ remediation of contaminated soil. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention has the following aspects. [1] A method for installing a heating well used for in-situ remediation of contaminated soil, the heating well having an outer pipe and a non-insulated electric heating wire and an insulated heater installed inside the outer pipe, comprising the steps of: step 1 of installing the outer pipe in the contaminated soil; step 2 of installing the non-insulated electric heating wire and the insulated heater inside the outer pipe and filling the gap between the inner surface of the outer pipe and the non-insulated electric heating wire and the insulated heater with a granular or powdered insulating, thermally conductive, and heat-resistant material; and step 3 of removing moisture from the heating well by heating with the insulated heater. [2] The method for installing a heating well according to [1], wherein the material is magnesium oxide, aluminum oxide, silica, or mica. [3] In step 2, the space forming the bottom of the outer tube is filled with the substance, and then the non-insulated heating wire and the insulated heater are installed in the space above the bottom space filled with the substance inside the outer tube, in a method for installing a heating well described in [1] or [2]. [4] A method for installing a heating well described in any one of [1] to [3], wherein in step 2, the substance is filled into the gap between the inner surface of the outer tube and the non-insulated heating wire and the insulated heater. [Effects of the Invention]

[0010] According to the heating well installation method of the present invention, the heating efficiency of the in-situ remediation method for contaminated soil can be further improved. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a cross-sectional view schematically showing an example of the installation process of the heating well of the first embodiment. [Figure 2] FIG. 2 is a cross-sectional view schematically showing an example of the installation process of the heating well of the first embodiment. [Figure 3] FIG. 2 is a cross-sectional view schematically showing an example of the installation process of the heating well of the first embodiment. [Figure 4] FIG. 2 is a cross-sectional view schematically showing an example of the installation process of the heating well of the first embodiment. [Figure 5]FIG. 2 is a cross-sectional view schematically showing an example of the installation process of the heating well of the first embodiment. [Figure 6] 1 is a cross-sectional view schematically showing a first embodiment of a heating well of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] The heating well installed by the installation method of the present invention is used for in-situ soil purification by heating the area to be treated where contaminated soil contaminated with pollutants is present, thereby volatilizing the pollutants or increasing the temperature to reduce the viscosity of the pollutants, thereby increasing their fluidity and facilitating suction treatment (hereinafter also referred to as "volatilization, etc."). Hereinafter, a heating well installed by the installation method of the present invention and one embodiment of the installation method of the heating well will be described with reference to the drawings.

[0013] [Heating well] As shown in FIG. 6, the heating well of this embodiment has an outer pipe 10, an insulating heater 20, and a bare nichrome wire 30, which is an example of a non-insulated heating wire. The outer pipe 10 is disposed so as to extend in the depth direction downward from the ground surface G. The insulating heater 20 and the bare nichrome wire 30 are disposed inside the outer pipe 10.

[0014] The heating well is installed in the treatment target area A where contaminated soil exists. The heating well is positioned so as to extend in the depth direction downward from the ground surface G. The upper surface of the heating well is covered with a concrete layer 40. The concrete layer 40 is preferably made of air mortar, which has high thermal insulation properties, from the viewpoint of energy efficiency. Although not shown, a suction well may be provided separately from the heating well to suck up contaminants underground.

[0015] The outer pipe 10 is the casing of the heating well. The outer pipe 10 is provided for the purpose of separating the soil to be purified from the insulating heater 20 and bare nichrome wire 30, which are heating devices arranged inside the outer pipe 10. The bottom of the outer pipe 10 may be closed or open. In the illustrated example, the bottom of the outer pipe 10 is closed, and is closed (blocked) by the bottom surface 10a. The bottom 10a of the outer pipe 10 is preferably closed. If the bottom 10a of the outer pipe 10 is closed, it is possible to prevent groundwater from seeping into the heating well.

[0016] Although not shown, after the heating well is installed, the top of the outer pipe 10 may be closed with a cover member or the like. The cover member may be further covered with a concrete layer 40. The material of the cover member may also be the same as that of the outer pipe 10.

[0017] The length of the outer pipe 10 can be set arbitrarily depending on the treatment target area A where contaminated soil exists. For example, it may be 3 to 10 m, or if the depth of the contaminated soil is about 20 to 30 m, it may be about 18 to 32 m, or about 19 to 31 m. If the length of the outer pipe 10 is too short, contaminants are likely to be insufficiently removed. If the length of the outer pipe 10 is too long, construction becomes difficult or construction costs increase, so it is preferable to set the length within a range that is unlikely to cause these inconveniences.

[0018] The shape of the outer pipe 10 is not particularly limited. For example, it may be cylindrical or polygonal. Examples of the outer pipe 10 include carbon steel pipes for piping (SGP pipes), stainless steel pipes, etc. The diameter of the outer pipe 10 is approximately 50 mm to 200 mm, for example.

[0019] The inside of the outer tube 10 is filled with a material that has high insulating properties, thermal conductivity, and heat resistance. For example, as shown in the figure, magnesium oxide 14 is used. Magnesium oxide is preferably used because it is inexpensive and has high insulating properties. Other than magnesium oxide, examples of the material that can be used include aluminum oxide, silica, mica, and other inorganic materials. By filling the inside of the outer tube 10 with magnesium oxide 14 or the like, which has high insulating properties, thermal conductivity, and heat resistance, it is possible to prevent electrical leakage. Furthermore, by filling the inside of the outer tube 10 with magnesium oxide 14 or the like, the air inside the outer tube 10 is replaced with magnesium oxide 14 or the like. With this configuration, the heat transfer mechanism changes from being mainly radiation to being heat conduction, and the heat transfer efficiency increases. The average particle size of the above-mentioned substance such as magnesium oxide is, for example, in the range of 0.5 to 20.0 μm as a guideline. If it is equal to or less than the upper limit value, the packing density will be further increased. The average particle size is calculated by measuring the maximum diameter of 100 randomly selected particles of the above-mentioned substance by a conventional method and averaging the results.

[0020] The insulating heater 20 is cylindrical and extends along the longitudinal direction of the outer tube 10, and includes a heater sheath (outer cover) and a heating wire. The insulating heater 20 is also insulating. The gap between the heating wire and the heater sheath is filled with an insulating material. An example of an insulating material is magnesium oxide. Magnesium oxide is a preferred insulating material because it is inexpensive and has high insulating properties.

[0021] The insulating heater 20 is disposed inside the outer pipe 10 along the longitudinal direction of the outer pipe 10. The length of the insulating heater 20 can be set arbitrarily depending on the treatment target area A where the contaminated soil exists. Furthermore, for example, when the depth of the contaminated soil is about 20 m to 30 m, multiple insulating heaters 20 can be installed in one heating well depending on the treatment target area A where the contaminated soil exists.

[0022] There are no particular limitations on the material of the heating wire that is the heat source of the insulating heater 20. Examples include metals such as nichrome, tungsten, graphite, and platinum, ceramics, and carbon fiber. Alternatively, the material may be a non-metallic compound such as silicon carbide.

[0023] The insulating heater 20 may be electrically connected to a surface-based power source 32 . The power source 32 is not particularly limited, and may be, for example, a heating power source device. In this case, by electrically connecting the power supply 32 to, for example, the insulating heater 20, a voltage can be applied to the heating wire of the insulating heater 20, thereby heating the heating wire. The power supply 32 may be capable of supplying power by itself, or may be supplied with power from an external power supply facility or the like via wiring or the like.

[0024] The bare nichrome wire 30 is used as a non-insulated heating wire. In other words, any non-insulated heating wire will do, and it is not limited to bare nichrome wire. From the viewpoint of cost, bare nichrome wire is preferable. Here, "non-insulated heating wire" means a heating wire with an exposed conductive surface. Other than the bare nichrome wire 30, metals such as tungsten, graphite, and platinum can be used.

[0025] The bare nichrome wire 30 can be electrically connected to a power source 34 located on the surface of the earth. The power source 34 is not particularly limited, and may be, for example, a heating power source device. In this case, the power source 34 is electrically connected to the bare nichrome wire 30, so that a voltage can be applied to the bare nichrome wire 30, and the bare nichrome wire 30 can be heated. The power supply 34 may be capable of supplying power by itself, or may be supplied with power from an external power supply facility or the like via wiring or the like.

[0026] [How to install a heating well] The method for installing a heating well of this embodiment includes the following steps (a) to (e). The steps are preferably performed in the order of (a) to (e), but are not limited to this order. For example, steps (b) and (c) may be performed simultaneously or in reverse order (c → b). That is, they may be performed in the order of a → b, c → d → e, or a → c → b → d → e. Alternatively, steps (a), (b), and (c) may be performed simultaneously, that is, in the order of a, b, c → d → e, etc. Step (a): A step of placing magnesium oxide 14 or the like into an outer tube 10 that is installed facing downward in a treatment area where contaminated soil contaminated with pollutants is present, and filling the space that forms the bottom of the outer tube 10 with magnesium oxide 14 or the like. Step (b): A step of placing a bare nichrome wire 30 in the space above the bottom space of the outer tube 10 filled with magnesium oxide 14 or the like. Step (c): A step of installing an insulating heater 20 in the space above the bottom space of the outer tube 10 filled with magnesium oxide 14 or the like. Step (d): After the bare nichrome wire 30 and the insulating heater 20 are installed, magnesium oxide 14 or the like is poured into the outer tube 10 up to the top, and the space inside the outer tube is filled with magnesium oxide or the like. Step (e): A step of removing moisture in the heating well by heating with an insulating heater 20.

[0027] The above step (a) is a step of introducing granular or powdered magnesium oxide or the like into the outer tube 10, which is provided for the purpose of separating the inside and outside of the outer tube 10. As shown in FIG. 1, this step is carried out by adding granular or powdered magnesium oxide or the like from the opening of the heating well (the top of the outer tube 10).

[0028] By this step (a), the space forming the bottom of the outer tube 10 can be filled with magnesium oxide or the like, which has high insulating properties, thermal conductivity, and heat resistance. This makes it possible to more reliably fill the entire interior of the outer tube 10, including the space forming the bottom, with magnesium oxide 14 or the like. Therefore, the heat transfer mechanism changes from being mainly radiation to being thermal conduction, further enhancing the effect of increasing heat transfer efficiency. The substance to be filled is not particularly limited as long as it has high insulating properties, thermal conductivity, and heat resistance. Magnesium oxide is particularly preferred from the viewpoint of being inexpensive and usable in addition to having insulating properties, thermal conductivity, and heat resistance.

[0029] The space formed by the bottom of the outer tube 10 (the space at the bottom filled with magnesium oxide or the like in the outer tube 10 in the above step (a)) is not particularly limited as long as it is within a range that allows the steps from step (b) onwards to be carried out without any problems. Typically, it is about several percent to 10% when the space surrounded by the inner surface of the outer tube 10 is taken as 100%.

[0030] The above-mentioned step (b) is a step of placing the bare nichrome wire 30 inside the outer tube 10. See Fig. 2. In step (a), the space forming the bottom of the outer tube 10 is filled with magnesium oxide 14 or the like. The bare nichrome wire 30 is placed in the space above the bottom space filled with magnesium oxide 14 or the like. The bare nichrome wire 30 is preferably disposed in parallel with the longitudinal direction of the outer tube 10 .

[0031] The above step (c) is a step of installing an insulating heater 20 inside the outer tube 10. See Fig. 3. In step (a), the bottom of the outer tube 10 is filled with magnesium oxide 14 or the like. The insulating heater 20 is installed in the space above the bottom space filled with magnesium oxide 14 or the like. It is preferable that the bare nichrome wire 30 and the insulating heater 20 are arranged in parallel. Furthermore, when looking down the outer tube 10 in the longitudinal direction, it is preferable that the insulating heater 20 is installed near the center of the outer tube 10, and the bare nichrome wire 30 is installed outside the insulating heater 20 (on the inner surface of the outer tube 10). With this arrangement, the bare nichrome wire 30 is placed outside the center of the circle, which has the effect of making heat conduction to the outer tube 10 more efficient.

[0032] The above step (d) is a step of adding granular or powdery magnesium oxide 14 or the like to the outer tube 10. As shown in FIG. 4, this step is carried out by introducing granular or powdered magnesium oxide 14 or the like into the opening of the heating well (the top of the outer pipe 10).

[0033] By this step (d), the entire inside of the outer tube 10 can be filled with magnesium oxide 14 or the like, which has high insulating properties, thermal conductivity, and heat resistance. As a result, the magnesium oxide 14 or the like can be filled in the gaps between the bare nichrome wire 30, the insulating heater 20, and the outer tube 10. By including this step (d), magnesium oxide or the like can be filled into the gap between the bare nichrome wire 30, the insulating heater 20, and the outer tube 10, unlike methods that separate the outer tube 10 and the insulating heater 20 with air, which has low heat transfer efficiency. Therefore, the air between the bare nichrome wire 30, which is the main heater of this heating well, and the outer tube 10 is replaced with magnesium oxide 14 or the like. With this configuration, the heat transfer mechanism changes from radiation to heat conduction, increasing heat transfer efficiency. In other words, the heating well installation method of this embodiment can provide a heating well installation method that can further improve heating efficiency. The substance to be filled is not particularly limited as long as it has high insulating properties, thermal conductivity, and heat resistance. Magnesium oxide is particularly preferred from the viewpoint of being inexpensive and usable in addition to having insulating properties, thermal conductivity, and heat resistance.

[0034] The above-mentioned step (e) is a step of removing moisture from the heating well by heating with the insulating heater 20 before the start of heating with the heating well (heating with the bare nichrome wire 30). That is, in this step (e), although the insulating heater 20 is used, the heating well has not yet reached the stage of actual use (heating with the bare nichrome wire 30, which is the main heater of the heating well, has not yet been carried out), and this is one step in the installation method.

[0035] By providing this step (e), if moisture is present in the heating well at the stage before heating (i.e., at the installation stage), the moisture can be removed from the heating well. The inside of the heating well is heated using an insulating heater 20 that is free from the risk of electrical leakage, and the water in the heating well is converted into steam. Steam has a lower specific gravity than the atmosphere inside the heating well. Therefore, by venting the steam from the opening above ground in the heating well (the top of the outer tube 10), moisture can be removed from inside the heating well, preventing contact between the magnesium oxide and water. In other words, by providing this step (e), it is possible to suppress the deterioration of the insulating properties of magnesium oxide due to contact with water, thereby further improving the heat transfer efficiency obtained by replacing the air between the bare nichrome wire 30, which is the main heater of this heating well, and the outer tube 10 with magnesium oxide. This also allows for the safe operation of a heating well that uses the bare nichrome wire 30 as the main heater. According to the method of this embodiment, the insulating heater 20 is mainly used during the installation stage of the heating well, so the use of the insulating heater 20 is minimized. On the other hand, the bare nichrome wire 30 used as the main heater of the heating well is inexpensive. Therefore, according to the method of this embodiment, a heating well can be installed that is inexpensive and has high heat transfer efficiency.

[0036] The order of performing each step is preferably (a) to (e). This order further enhances the effects of each step described above. Specifically, by performing step (a) first, the entire interior of the outer tube 10, including the space forming the bottom, can be more reliably filled with magnesium oxide 14 or the like. This shifts the heat transfer mechanism from radiation to conduction, further enhancing the effect of increasing heat transfer efficiency. Furthermore, by performing step (e) after steps (b), (c), and (d), it is possible to suppress the deterioration of the insulation properties of magnesium oxide due to contact with water. This further enhances the heat transfer efficiency achieved by replacing the air between the bare nichrome wire 30, the main heater of this heating well, and the outer tube 10 with magnesium oxide. In addition, by performing step (b) of installing the bare nichrome wire 30, which serves as the main heater of the heating well, after step (a), the bare nichrome wire 30 can be installed in the space above the bottom space of the outer tube 10, which is filled with magnesium oxide 14, etc., without any other material installed. This makes it easy to install the bare nichrome wire 30, which serves as the main heater, in the desired location according to the conditions and characteristics of the treatment area A. Furthermore, by performing step (c) after step (b), it becomes easy to install the insulating heater 20 in the desired location. From the above, the method of this embodiment makes it possible to install a heating well that is inexpensive and has high heat transfer efficiency.

[0037] Contaminant removal can be achieved, for example, by using a suction well (not shown) to suck up fluid containing contaminants that have been desorbed from the soil by heating.

[0038] Examples of pollutants include volatile organic compounds (VOCs), oil, mercury, polychlorinated biphenyls (PCBs), and dioxins. Examples of VOCs include benzene, toluene, and halogenated hydrocarbons (such as trichloroethylene). Examples of oils include hydrocarbons having 5 to 44 carbon atoms. Hydrocarbons having 5 to 18 carbon atoms can be recovered mainly as gas. Hydrocarbons having 19 or more carbon atoms can also be recovered as liquid by reducing their viscosity. These hydrocarbons may be saturated or unsaturated. These hydrocarbons may be linear, branched, or cyclic. Specific examples of these hydrocarbons include n-pentane, isopentane, n-hexane, and cyclohexane. Examples of mercury include metallic mercury, inorganic mercury, and organic mercury. Examples of inorganic mercury include mercury oxide, mercury sulfide, mercury chloride (HgCl, HgCl), and mercury nitrate. Examples of organic mercury include alkyl mercury (e.g., methyl mercury, ethyl mercury), and phenyl mercury (e.g., phenyl mercury acetate).

[0039] Examples of PCBs include 3,3',4,4'-tetrachlorobiphenyl, 3,4,4',5-tetrachlorobiphenyl, 3,3',4,4',5-pentachlorobiphenyl, 3,3',4,4',5,5'-hexachlorobiphenyl, 2,3,3',4,4'-pentachlorobiphenyl, 2,3,3',4,4',5-hexachlorobiphenyl, and 2,3,3',4,4',5,5'-heptachlorobiphenyl. Examples of dioxins include 2,3,7,8-tetrachloroparadioxin and 2,3,4,7,8-pentachlorodibenzofuran. [Explanation of symbols]

[0040] 10, 10a... outer tube, 14... magnesium oxide, 20... insulating heater, 30... bare nichrome wire, 32, 34... power source, 40... concrete layer

Claims

1. A method for installing a heating well used for in-situ remediation of contaminated soil, the heating well having an outer pipe, an uninsulated heating wire and an insulated heater provided inside the outer pipe, comprising: Step 1: Installing the outer pipe in the contaminated soil; Step 2: installing the non-insulated heating wire and the insulated heater inside the outer tube, and filling a granular or powdery material having insulating properties, thermal conductivity, and heat resistance into gaps between the inner surface of the outer tube and the non-insulated heating wire and the insulated heater; A method for installing a heating well, comprising step 3 of removing moisture from the heating well by heating with the insulating heater.

2. 10. The method of claim 1, wherein the material is magnesium oxide, aluminum oxide, silica, or mica.

3. In step 2, The space forming the bottom of the outer tube is filled with the substance, and then 2. The method for installing a heating well according to claim 1, wherein the non-insulated heating wire and the insulated heater are installed in a space above the bottom space filled with the substance within the outer tube.

4. In step 2, 4. The method for installing a heating well according to claim 3, wherein the substance is filled into the gap between the inner surface of the outer tube and the non-insulated heating wire and the insulated heater.

Images