Structure of preventing contamination diffusion

Abstract

To prevent contamination diffusion of contaminated soil in an in-situ purification method.SOLUTION: A structure of preventing contamination diffusion is used together with a heating well of an in-situ thermal desorption type, where the heating well is equipped with an outer pipe embedded downward from the vicinity of a ground surface of contaminated soil, the structure of preventing contamination diffusion is equipped with a space adjacent to the outer pipe in the vicinity of the ground surface, and the outer pipe has an overflow prevention fin for guiding contaminant overflown from a gap between an outer face of the outer pipe and the contaminated soil to the vicinity of the ground surface into the space.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a contamination prevention structure for use with a heating well used in an in-situ thermal desorption system. [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 in-situ remediation is used, 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.

[0006] While in-situ thermal desorption using an electric heater, as proposed, can heat the soil to over 100°C, this can cause contaminants to overflow to the surface and spread. Specifically, as the ground temperature rises due to heating, the ground temperature around the heating well can become too high. If the ground temperature becomes too high, and the pressure underground becomes too high, it can exceed the negative pressure created by the suction well. In this situation, contaminated water or vapor can overflow to the surface through the gap between the outer pipe and the soil (the space around the heating well), potentially spreading the contamination. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 4509558 Summary of the Invention [Problem to be solved by the invention]

[0008] One possible method for preventing the spread of contaminants when using in-situ thermal desorption with an electric heater is to place a crushed stone layer between the original ground and the air mortar, and direct the overflowing contaminated water or vapor into the crushed stone layer. However, in this case, the crushed stone layer becomes the target of purification in addition to the contaminated soil. Furthermore, since the contaminated water or vapor is merely directed into the crushed stone layer, it is not necessarily easy to control the spread of contamination. The above-mentioned Patent Document 1 does not describe any measures to prevent the spread of contamination caused by contaminated water or contaminated steam passing through the gap between the outer pipe and the soil and overflowing onto the ground surface.

[0009] The present invention has been made in view of the above circumstances, and has as its object a contamination diffusion prevention structure in an in-situ remediation method for contaminated soil. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention has the following aspects. [1] A contamination diffusion prevention structure used in conjunction with a heating well used in an in-situ thermal desorption method, the heating well having an outer pipe buried downward from near the surface of contaminated soil, the contamination diffusion prevention structure having a space adjacent to the outer pipe near the surface, and the outer pipe having overflow prevention fins for guiding contaminants that have overflowed near the surface from the gap between the outer surface of the outer pipe and the contaminated soil into the space. [2] The contamination diffusion prevention structure described in [1], wherein the overflow prevention fin is a plate-shaped member that protrudes outward from the outer surface of the outer pipe near the ground surface. [3] The contamination diffusion prevention structure described in [1] or [2], wherein the space is a tank having a double structure consisting of an upper space A and a lower space B, and the space A is a water tank that can store water inside. [4] The contamination diffusion prevention structure described in [3], wherein the bottom surface of the space A is common to the top surface of the space B. [5] A contamination diffusion prevention structure described in [3] or [4], wherein the space B is a collection tank that collects the contamination guided by the overflow prevention fins. [6] A pollution diffusion prevention structure described in any one of [3] to [5], wherein space B has a pipe for transporting the pollutants to a treatment facility, and space B is adjusted to a negative pressure by the pipe. [7] A pollution diffusion prevention structure according to [1] or [2], wherein the space has a pipe for transporting the pollutants to a treatment facility, and the space is adjusted to a negative pressure by the pipe. [Effects of the Invention]

[0011] The contamination diffusion prevention structure of the present invention can prevent contamination diffusion in the in-situ remediation method for contaminated soil. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a cross-sectional view schematically showing a first embodiment of a contamination diffusion prevention structure of the present invention. [Figure 2] FIG. 4 is a cross-sectional view schematically showing a second embodiment of the contamination diffusion prevention structure of the present invention. [Figure 3] FIG. 2 is a front view showing the overflow prevention fins of the first and second embodiments. [Figure 4] FIG. 4 is a plan view showing the overflow prevention fins of the first and second embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0013] The contamination diffusion prevention structure of the present invention is used together with a heating well used in the in-situ remediation method for contaminated soil. The heating well is used to purify the soil by heating the area to be treated where contaminated soil contaminated with contaminants is present, thereby volatilizing the contaminants or reducing their viscosity by increasing the temperature, thereby increasing their fluidity and facilitating suction treatment (hereinafter also referred to as "volatilization, etc."). Hereinafter, an embodiment of the contamination diffusion prevention structure of the present invention will be described with reference to the drawings.

[0014] [Heating well] The heating well is installed in the treatment target area A where contaminated soil exists. The heating well is positioned so as to extend from near the ground surface downward in a depth direction. Here, "near the ground surface" refers to a location approximately several meters above the ground surface G, the ground surface G itself, or a location excavated several meters below the ground surface G. In this embodiment, the ground surface G around the heating well is covered with a concrete layer 40. The concrete layer 40 is preferably formed of air mortar, which has high thermal insulation properties, from the perspective 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 heater 20, which is a heating device disposed inside the outer pipe 10. The bottom of the outer pipe 10 is closed, and is closed at the bottom surface 10a.

[0016] The outer pipe 10 has overflow prevention fins 34, the details of which will be described later, as the contamination diffusion prevention structure of this embodiment. The overflow prevention fins 34 are provided on the outer surface (outer wall) of the outer pipe 10.

[0017] Although not shown, the upper part of the outer tube 10 may be closed by a lid member or the like. The lid member may be made of the same material as the outer tube 10.

[0018] 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. The shape of the outer tube 10 may be, for example, cylindrical or polygonal, with the cylindrical shape being particularly preferred. 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, for example, approximately 50 mm to 200 mm.

[0019] The bare nichrome wire 20 is the heater of the heating well. The bare nichrome wire 20 is disposed inside the outer tube 10 .

[0020] The bare nichrome wire 20 is not particularly limited as long as it has the heating effect of a heater for a heating well. For example, an insulating heater can be used instead. (Hereinafter, the bare nichrome wire 20 and the insulating heater may be simply referred to as heaters.) The insulating heater comprises a heater sheath and a heating wire, and the gap between the heating wire and the heater sheath is filled with an insulating material. Magnesium oxide is preferred as an insulating material because it is inexpensive and has high insulating properties.

[0021] The material of the heating wire that is the heat source of the insulating heater is not particularly limited. Examples include metals such as nichrome, tungsten, graphite, and platinum, ceramics, and carbon fiber. Other examples include non-metallic compounds such as silicon carbide.

[0022] The length of the heater can be set arbitrarily depending on the area to be treated that the contaminated soil is in. In addition, for example, when the depth of the contaminated soil is about 20 to 30 m, multiple heaters can be installed in one heating well depending on the area to be treated that the contaminated soil is in.

[0023] Although not shown, the heater may be electrically connected to a surface-based power source. The power source is not particularly limited, and examples thereof include a heating power source device. In this case, by electrically connecting the power supply to the heater, a voltage can be applied to the heating wire of the heater, thereby heating the heating wire. The power supply may be one that can supply power by itself, or one that receives power from an external power supply facility or the like via wiring or the like.

[0024] [Contamination diffusion prevention structure] As shown in FIG. 1, the contamination diffusion prevention structure of this embodiment is used together with a heating well used in an in-situ thermal desorption method. The pollution diffusion prevention structure 1 of the first embodiment includes a space 31 adjacent to the outer pipe 10 near the ground surface. The space 31 includes a space A30, a space B32, and a support pillar 50. Hereinafter, the space A30 may be simply referred to as space A, and the space B32 may be simply referred to as space B. Note that the support pillar 50 may be omitted. The contamination diffusion prevention structure 1 also includes overflow prevention fins 34 for guiding contaminants 36 that have overflowed into the vicinity of the ground surface from the gap between the outer surface of the outer pipe 10 and the contaminated soil into the space 31.

[0025] Spaces A and B are arranged on the ground surface adjacent to the outer pipe 10. The arrangement surface is not particularly limited. They may or may not be arranged on a concrete layer 40 covering the ground surface G. Also, for example, as in the illustrated example, a configuration may be adopted in which a portion of space B is surrounded and supported by the concrete layer 40. Although not illustrated, a configuration may be adopted in which, in addition to space B, a portion of space A is surrounded and supported by the concrete layer 40.

[0026] In this embodiment, space 30 is a tank with a double upper and lower structure. Space A is located above (upper) space B and is a water tank that can store water inside. Space B, located below (lower), is a collection tank for contaminants 36. Spaces A and B are separated so that they can each store a different liquid. The bottom surface of space A is common with the top surface (ceiling surface) of space B. With this configuration, the water stored in space A functions as cooling water, and space B can be cooled more efficiently. Note that, as long as cooling by space A is possible, the bottom surface of space A and the top surface of space B are not limited to being common, but a common configuration is preferable from the viewpoint of obtaining a sufficient cooling effect. The sides of spaces A and B opposite the heating well may or may not be continuous between spaces A and B, but a continuous configuration is preferable. A continuous configuration will further enhance the cooling effect of space B by the water stored in space A.

[0027] The materials for spaces A and B are not particularly limited as long as they can withstand corrosion by the contaminants 36. Among them, metals (e.g., SUS, aluminum or aluminum alloy, copper or copper alloy, etc.) are preferred because of their high thermal conductivity, particularly from the viewpoint of more efficient cooling by the water stored in space A. Furthermore, for the bottom surface of space A (the upper surface of space B), a material with high thermal conductivity, which has a particularly large impact on cooling efficiency, or a material with excellent load-bearing capacity that allows the bottom surface of space A (the upper surface of space B) to be made thin is preferred.

[0028] There are no particular limitations on the thickness of the surface material surrounding spaces A and B. From the viewpoint of cooling efficiency, the bottom surface of space A (the upper surface of space B) is preferably thin, and a guideline would be, for example, several mm to 10-odd mm.

[0029] The size (volume) of spaces A and B is not particularly limited. For example, it can be appropriately selected depending on the size (depth) of the area to be treated and the amount and characteristics of the contaminants 36 contained therein. As a guideline, for example, space A: 0.1 to several m 3 , Space B:0.05~0.2m 3 Examples include:

[0030] The shapes of spaces A and B are not particularly limited. A shape that matches the shape of the outer pipe 10 is preferred, and a shape that follows the outer surface of the outer pipe 10 is more preferred. In particular, a configuration in which the outer pipe 10 is cylindrical and spaces A and B are annular (doughnut-shaped) is preferred. The outer pipe 10 can be installed at the center, with annular spaces A and B surrounding its outer surface. A cylindrical outer pipe 10 facilitates the installation of heating wells and further enhances the heating effect (improved heating efficiency) of the heating wells. If spaces A and B are annular to match the cylindrical outer pipe 10, spaces A and B can be positioned adjacent to each other around the entire circumference of the outer pipe 10, but slightly spaced apart. Here, "slight" refers to a gap sufficient to allow the contaminants 36 to overflow. With this configuration, the overflowing contaminants 36 can be collected in all directions surrounding the heating well without leakage. This effectively prevents the diffusion of contaminants.

[0031] Space A may be sealed, semi-sealed, or open to the atmosphere. If it is sealed, it may have a pressure regulating valve. Space A is also designed to allow water to be pumped in and stored. Normally, it is a sealed structure when in use.

[0032] Space A can use the water stored inside to guide contaminants 36 that have risen in vapor state along the outer surface of the outer pipe 10 into space 30 and cool them. Within space 30, the contaminants 36 that have risen in vapor state are cooled mainly by the bottom surface of space A. This cooling causes the contaminants 36 in vapor state to liquefy, and they can be stored in space B. In other words, by providing space A, it is possible to collect contaminants 36 that have risen in vapor state and prevent the spread of contamination.

[0033] It is preferable that the bottom surface of space A (the upper surface of space B) slopes downward from the heating well side toward the opposite side. In this configuration, the contaminant 36 that has risen in vapor form can be liquefied at the bottom surface of space A (the upper surface of space B) and then flow down the side of space B opposite the heating well side. This not only allows the contaminant 36 to be recovered more efficiently, but also prevents the liquefied contaminant 36 from flowing back into the gap between the heating well and space B.

[0034] The angle of the downward diagonal direction of the bottom surface of space A (the upper surface of space B) is not limited, but is preferably about 0.5 to 10 degrees from the horizontal. It is preferable to adjust the angle appropriately to a preferred angle depending on the condition of the contaminant 36, such as about 3 to 10 degrees when there is a lot of contaminant 36 rising in vapor form, or about 0.5 to 5 degrees when there is not much contaminant 36 rising in vapor form. Selecting a preferred angle can prevent liquefied contaminant 36 from flowing back into the gap between the heating well and space B, thereby achieving an even greater effect in preventing the diffusion of contaminants.

[0035] A portion of the side surface adjacent (facing) the outer pipe 10 that constitutes the heating well of space B has an open structure. The sides of space B other than the side surface adjacent to the outer pipe 10, the bottom surface, and the top surface are joined without any gaps to form a tank, and only the side surface adjacent to the outer pipe 10 has a partially open (open) structure. The side surface adjacent to the outer pipe 10 is connected to all surfaces except the top surface. In other words, only the area between the side surface adjacent to the outer pipe 10 and the top surface is open. The side surface adjacent to the outer pipe 10 is also connected to the bottom surface and has a certain height. With this configuration, contaminants 36 can enter space B through the open structural portion and be stored or retained in space B until they are treated.

[0036] The height of the open side of space B is not particularly limited as long as the contaminants 36 once entering space B do not flow back into the gap between the heating well and space B. From the viewpoint of removing all of the contaminants 36 in the gap between the heating well and the soil, it is preferable that the height is low enough to prevent backflow of the contaminants 36 once they have entered space B. With this configuration, even contaminants 36 that do not rise very fast can be collected, and they can be retained in space B until they are treated without being allowed to flow back.

[0037] The bottom surface forming space B may be horizontal, or may slope downward obliquely from the heating well side to the opposite side. In particular, if the height of the open side of space B is configured low enough to prevent backflow of contaminants 36 once they have entered space B, it is preferable that the bottom surface forming space B slopes downward obliquely from the heating well side to the opposite side. This configuration can recover contaminants 36 that do not rise very quickly, and can retain them in space B until they are treated without backflowing, thereby achieving an even greater effect of preventing the diffusion of contaminants.

[0038] Space B may have a pipe for transporting the contaminants 36 collected in space B to a treatment facility. Furthermore, a negative pressure can be created in space B by applying suction to an external treatment facility through the pipe. With this configuration, vapor-like contaminants 36 are drawn into space B under negative pressure and then sucked into the treatment facility through the pipe. The pipe is preferably configured to be located away from the heating well, such as on the side opposite the heating well. With this configuration, the negative pressure can be used to guide the vapor contaminants 36 away from the heating well. This allows for more reliable recovery of all vapor contaminants 36 for treatment. In other words, even if the negative pressure is insufficient and all vapor contaminants 36 are not sucked into the treatment facility through the pipe, the negative pressure can be used to guide the vapor contaminants away from the heating well, allowing them to be cooled in space A and recovered as a liquid. In this way, the combination of multiple effects can provide an even greater effect in preventing the spread of contamination.

[0039] The overflow prevention fins 34 are provided on the outer pipe 10 . The location where the fins are provided is preferably higher than the upper end of the side surface of the adjacent space B. By providing the overflow prevention fins 34 with this configuration, even if the overflow of the contaminated material 36 rises at a high rate, it is possible to prevent the contaminated material 36 from passing through the space B and overflowing onto the ground surface. In addition, the contaminated material 36 can be guided into space B and collected. The outer pipe is preferably provided at a position higher than the upper end of the side surface of the adjacent space B, and lower than the side surface of the adjacent space A. This positional relationship further enhances the effect of guiding the contaminants 36 into space B and collecting them.

[0040] The overflow prevention fins 34 are preferably, for example, plate-shaped members that protrude outward from the outer surface of the outer pipe 10 near the ground surface. The outer tip of the plate-shaped member preferably protrudes and projects into the opening on the side of space B. If the overflow prevention fins 34 are plate-shaped members, the angle (protrusion angle) relative to the outer surface of the outer pipe 10 can be easily adjusted. In addition, like a mousetrap provided on the pillar, the overflow prevention fins 34 can change the direction of travel of contaminants 36 that have risen up the outer surface of the outer pipe 10, making it easier to guide them into space B.

[0041] The angle of the overflow prevention fins 34 may be completely horizontal or may be inclined. Preferably, they have a diagonally downward structure. A specific example is an umbrella-shaped structure in which the overflow prevention fins 34 are continuously formed around the outer surface of the outer pipe 10, as shown in FIG. 3. By having such a downward inclination, the contaminants 36 can be guided unidirectionally into space B and collected without stagnation or backflow in the gap between the heating well and space B.

[0042] As shown in Figure 4, a preferred structure is one in which the outer pipe 10 forming the heating well is passed through a hole in the center of the overflow prevention fin 34. With this structure, the overflow prevention fin 34 and the outer pipe 10 can be easily joined by welding, and the overflow prevention fin 34 and the outer pipe 10 can be joined without any gaps. As a result, the overflow prevention fin 34 is joined without any gaps around the entire periphery of the outer pipe 10, and the contaminants 36 are collected in space B without leaking.

[0043] The horizontal length of the overflow prevention fins 34 (the length in the direction away from the outer pipe 10) is not particularly limited. When the outer pipe 10 is placed at a position lower than the side surface of the adjacent space A, it is preferable that the overflow prevention fins 34 have a length that overlaps with the space A when viewed from above. With this configuration, all contaminants 36, including contaminants 36 that have risen in vapor form, can be guided to the space B and collected. In order to allow the contaminants 36 rising in vapor form to quickly come into contact with the bottom surface of space A and be liquefied, it is preferable that the horizontal length of the overflow prevention fins 34, when viewed from above, the area where the overflow prevention fins 34 overlap with space A is approximately 3 to 10% of the total area of ​​space A. With this configuration, the contaminants 36 rising in vapor form can be more efficiently liquefied, retained in space B, and collected.

[0044] There are no particular limitations on the thickness of the plate material that constitutes the overflow prevention fins 34. It can be appropriately selected in consideration of ease of joining by welding, material costs, etc. One example is 1 to 10 mm.

[0045] The material of the overflow prevention fins 34 is not particularly limited as long as it can withstand corrosion by the contaminants 36, but it is preferably a metal. The type of metal is preferably the same as that of the outer pipe 10. This is because it makes joining by welding easier, allows for a stronger bond without gaps, and allows the contaminants 36 to be collected in the space B without leakage.

[0046] The support pillar 50 is provided in the space B, with its lower end in contact with the bottom surface of the space B and its upper end in contact with the bottom surface of the space A, thereby physically supporting the space A. The number of support columns 50 is not particularly limited as long as it does not impair the effect of the contamination diffusion prevention structure of this embodiment. The number of support columns 50 may be one or more.

[0047] The material of the support columns 50 is not particularly limited as long as it can withstand corrosion caused by the contaminants 36. Preferably, the support columns 50 are made of the same metal as the bottom surface of the space A (the upper surface of the space B) and the bottom surface of the space B. If the support columns 50 are made of the same metal, joining by welding becomes easier.

[0048] Next, a second embodiment will be described with reference to FIG. The contamination diffusion prevention structure of the second embodiment includes a space B32, an overflow prevention fin 34, and a support column 50. Hereinafter, the space B32 may be simply referred to as space B. Items common to the first embodiment are designated by the same reference numerals as in Figure 1, and their description will be omitted.

[0049] The contamination diffusion prevention structure of the second embodiment includes a space B having a pipe for transporting contaminants 36 to a treatment facility. A negative pressure is maintained within the space B via the pipe. This allows the vapor contaminants 36 to be sucked into the pipe and then into the treatment facility. In this way, the vapor contaminants 36 in the space B can be transported to the treatment facility and treated. Contaminants 36 other than vapor, for example, liquid or particulate contaminants 36, can be allowed to remain in space B.

[0050] The space B has a bottom surface and side surfaces. It may or may not have a top surface. If it has a top surface, it also has a support column 50.

[0051] The pipes in space B are preferably arranged in a position close to the heating well, which makes it possible to more reliably collect all of the vaporous contaminants 36 as treatment targets. [Explanation of symbols]

[0052] 10, 10a... outer pipe, 20... bare nichrome wire, 30... space A, 32... space B, 31... space A + space B, 34... overflow prevention fin, 36... contaminant, 40... concrete layer, 50... support column, 52... power supply A, 60... pipe

Claims

1. A contamination prevention structure for use with a heating well used in an in-situ thermal desorption system, comprising: The heating well includes an outer pipe buried downward from near the surface of the contaminated soil, the contamination diffusion prevention structure includes a space adjacent to the outer pipe near the ground surface, The outer pipe has an overflow prevention fin for guiding contaminants that have overflowed into the vicinity of the ground surface from the gap between the outer surface of the outer pipe and the contaminated soil into the space, thereby forming a contamination diffusion prevention structure.

2. 2. The contamination diffusion prevention structure according to claim 1, wherein the overflow prevention fin is a plate-like member that protrudes outward from the outer surface of the outer pipe near the ground surface.

3. 2. The contamination diffusion prevention structure according to claim 1, wherein the space is a tank having a double structure consisting of an upper space A and a lower space B, and the space A is a water tank capable of storing water therein.

4. 4. The contamination diffusion prevention structure according to claim 3, wherein the bottom surface of said space A is common with the top surface of said space B.

5. 4. The contamination diffusion prevention structure according to claim 3, wherein the space B is a collection tank that collects the contaminants guided by the overflow prevention fins.

6. 6. The contamination diffusion prevention structure according to claim 5, wherein the space B has a pipe for transporting the contaminants to a treatment facility, and the space B is adjusted to a negative pressure by the pipe.

7. 3. The contamination diffusion prevention structure according to claim 1, wherein the space has a pipe for transporting the contaminants to a treatment facility, and the space is adjusted to a negative pressure by the pipe.

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