Soil purification device

Abstract

To provide an electric heater type soil purification device capable of efficiently recovering a target substance while enhancing thermal efficiency by reducing number of heating wells installed in a processing target area.SOLUTION: A soil purification device includes: a heating well 10 that generates water vapor using an underwater heater 11 installed at the bottom, with a mesh pipe arranged in a processing target area E; a steam injection well 20 that introduces the water vapor into the mesh pipe and directly injects the water vapor into the surrounding soil to heat it; a recovery well 30 that collects steam G containing the target substances that have evaporated due to the heating of the water vapor by the mesh pipe; a gas-liquid recovery unit 35 that liquefies the water vapor generated by the heating well 10 and the steam collected by the recovery well 30 to recover the target substances; and a re-vaporization unit 37 that re-vaporizes the residual water after recovering the target substances in the gas-liquid recovery unit 35, introducing the re-vaporized water vapor into each steam injection well 20 via the steam connection piping 21.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an electric heater type soil purification apparatus that can efficiently recover target substances while increasing thermal efficiency by reducing the number of heating wells installed in the area to be treated. [Background technology]

[0002] Conventionally, soil contaminated with volatile organic compounds (VOCs), heavy metals, perfluoroalkyl and polyfluoroalkyl compounds (PFAS), polychlorinated biphenyls (PCBs), dioxins, oils, etc. (hereinafter referred to as target substances) has been purified by, for example, in-situ thermal desorption, which is a purification method in which the target substances are volatilized and recovered by heating them in situ, without excavating the contaminated soil.

[0003] The target substances exemplified above are adsorbed to soil particles, causing soil contamination, and dissolve into groundwater, causing groundwater contamination. Various methods for heating soil in conventional purification equipment using in-situ thermal desorption have been proposed (electric heater type, electric resistance type, steam type). For example, the electric heater type involves installing a heating well (or heating hole) that leads to the area of ​​the soil to be purified, and inserting a heater into the hollow part of the heating well to heat the soil to a specified temperature. The in-situ thermal desorption method using the electric heater is advantageous over other soil heating methods because it can heat the soil uniformly, can target a wide range of substances, has a heating temperature of 100°C or higher, and can be applied to unsaturated zones and clayey soils.

[0004] Patent Document 1 discloses a system (ISTD: In-Situ Thermal Desorption) that directly heats soil in situ using a heating well to desorb target substances from the soil or decompose them underground, and the shape of the heater used for heating. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 4509558 Summary of the Invention [Problem to be solved by the invention]

[0006] However, conventional soil purification equipment using electric heaters uses a heat source (electric heating wire such as nichrome wire) installed in a heating well to heat the soil, and it is necessary to install many heating wells in the area to be treated. This requires a large number of heaters to be installed, which increases the electricity cost for heating.

[0007] In addition, in conventional soil purification equipment using electric heaters, the heater characteristics make the area near the heating well hot (over 300°C), which has the advantage of being able to heat the ground to over 100°C. However, the pollutants are collected using a blower, which exhausts the air and leaks heat along with the pollutants, so the thermal efficiency is not necessarily good. Furthermore, because the temperature around the heating well becomes so high, groundwater evaporates and steam erupts from the area near the heating well, which can waste the energy used for heating.

[0008] Therefore, a soil purification device can be considered in which groundwater is heated by a heater in a mesh-shaped pipe heating well to generate steam, and this steam is injected into the soil, while the steam generated by the heating well is circulated and injected into the soil from a mesh-shaped pipe steam injection well that is arranged around the heating well and connected to the heating well via a steam connection pipe in the ground. This steam injection type soil purification device can increase thermal efficiency, but there is a possibility that groundwater that may contain pollutants is vaporized, and the pollutants are directly reinjected into the ground, resulting in localized concentration of the pollutants in the ground.

[0009] The present invention has been made in consideration of the above, and aims to provide an electric heater type soil purification device that can efficiently recover target substances while reducing the number of heating wells installed in the treatment area to increase thermal efficiency. [Means for solving the problem]

[0010] In order to solve the above-mentioned problems and achieve the object, the present invention provides a soil purification device that purifies a target area of ​​ground by heating the area to be treated and volatilizing target substances, the device comprising: one or more heating wells in which mesh pipes are arranged extending from an unsaturated zone to an aquifer along the depth direction of the target area of ​​the ground, and which generate steam using an underwater heater provided at the bottom and directly inject a portion of the steam into the surrounding soil to heat the soil; one or more steam injection wells in which mesh pipes are arranged around the heating wells extending along the depth direction of the ground to a lower part of the unsaturated zone, and which introduce steam and directly inject the steam into the surrounding soil to heat the soil; The system is characterized in that it comprises mesh-like pipes extending depthwise in the ground to the bottom of the unsaturated zone, which are arranged around the heating well and the steam injection well, one or more recovery wells for recovering steam containing the target substance that has been volatilized by heating the steam injected by the heating well and the steam injection well, a gas-liquid recovery unit for liquefying the steam generated by the heating well and the steam recovered by the recovery well to recover the target substance, and a re-steaming unit for re-steaming the remaining water after recovery of the target substance in the gas-liquid recovery unit and introducing the re-steamed steam into each steam injection well via a steam connection piping.

[0011] In addition, the present invention is characterized in that, in the above-mentioned invention, a mesh pipe extending beyond the aquifer along the depth direction in the ground is arranged around the heating well and the steam injection well, and water piping extending from the ground to the aquifer is arranged within this mesh pipe, and steam containing the target substance volatilized by heating the steam injected by the heating well and the steam injection well is introduced into the gas-liquid recovery unit and recovered, and groundwater containing the target substance is introduced into the gas-liquid recovery unit via the water piping for recovery.

[0012] In addition, the present invention is characterized in that, in the above invention, a heat exchanger is provided for converting thermal energy generated during liquefaction in the gas-liquid recovery unit into thermal energy used during vaporization in the re-vaporization unit.

[0013] In addition, in the above-mentioned invention, the heating well is a cylindrical pipe except for the area surrounding the underwater heater, and water vapor generated by the underwater heater is introduced into the gas-liquid recovery unit.

[0014] In addition, in the above-mentioned invention, the present invention is characterized in that the treatment area is surrounded by a water-impermeable wall extending beyond the aquifer in the depth direction to define the horizontal direction, and the ground surface is covered by a lid portion.

[0015] In addition, in the above-mentioned invention, the present invention is characterized in that the steam connection piping is arranged along the underside of the lid from directly below the steam generation unit, and the steam re-vaporized by the steam generation unit is introduced into each steam injection well.

[0016] In addition, the present invention is characterized in that, in the above invention, the invention further comprises a plurality of temperature sensors provided in a temperature observation hole extending depthwise in the ground beyond the aquifer and arranged depthwise within the temperature observation hole, a pressure sensor for detecting the pressure of the water vapor in the recovery well, and a control unit for controlling the heating of the underwater heater and the vaporization of the re-vaporization unit so that the detection value of the temperature sensor is within a predetermined temperature range and the detection value of the pressure sensor is within a predetermined pressure range, stopping the recovery of steam including from the recovery well until the detection value of the pressure sensor exceeds the predetermined pressure, and recovering steam including from the recovery well when the detection value of the pressure sensor exceeds the predetermined pressure. Effect of the Invention

[0017] According to the present invention, the number of heating wells installed in the area to be treated can be reduced, thereby increasing thermal efficiency and efficiently recovering the target substance. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic configuration of a soil purification apparatus according to the present embodiment. [Diagram 2] FIG. 2 is a plan view showing a schematic arrangement of wells provided in the soil purification apparatus shown in FIG. [Diagram 3] FIG. 3 is a diagram comparing the configurations of a conventional heating well and the heating well of this embodiment. [Figure 4] FIG. 4 is a cross-sectional view that shows a schematic configuration of a soil purification apparatus that is a first modified example of this embodiment. [Diagram 5] FIG. 5 is a cross-sectional view that illustrates a schematic configuration of a soil purification apparatus that is a second modification of this embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a cross-sectional view showing a typical configuration of a soil purification apparatus 1 according to the present embodiment. Fig. 2 is a plan view showing a typical arrangement of wells provided in the soil purification apparatus 1 shown in Fig. 1. This soil purification apparatus 1 is an apparatus for purifying a treatment target area of ​​the ground by heating the treatment target area with water vapor to volatilize the target substances.

[0020] As shown in Figures 1 and 2, the ground EG of the treatment target area E, where soil purification is required, is partitioned underground by a water impermeable wall W. The water impermeable wall W is, for example, driven into the ground in the depth direction. The upper end of the water impermeable wall W is exposed at the ground surface S, and the lower end reaches an impermeable layer F into which groundwater has difficulty penetrating. In the ground EG of the treatment target area E, a groundwater water level S10 in an aquifer EW is formed.

[0021] The soil purification apparatus 1 includes a heating well 10, a steam injection well 20, a recovery well 30, a gas-liquid recovery well 40, a gas-liquid recovery unit 35, and a resteaming unit 37. The heating well 10 is a mesh pipe extending from the unsaturated zone EN to the aquifer EW along the depth direction in the treatment target area E, and generates steam using an underwater heater 11 installed at the bottom. Part of the steam is directly injected into the surrounding soil to heat the soil, and the upper part of the well is a cylindrical pipe 10a above the ground surface S, which is connected to the gas-liquid recovery unit 35 on the ground via a valve V1, and the generated steam is introduced into the gas-liquid recovery unit 35. Note that a plurality of heating wells 10 may be provided in the treatment target area E. In addition, it is preferable that the heating well 10 is provided in the central part of the treatment target area E.

[0022] The steam injection wells 20 are one or more wells in which mesh-like pipes extending in the depth direction in the ground EG to the bottom of the unsaturated zone EN are arranged around the heating wells 10, and introduce the steam generated by the resteaming unit 37 and directly inject the steam into the surrounding soil to heat the soil. Each steam injection well 20 is connected to the aboveground resteaming unit 37 via a steam connection pipe 21, which is a cylindrical pipe.

[0023] The recovery well 30 is one or more wells in which mesh-like pipes extending in the depth direction in the ground EG to the bottom of the unsaturated zone EN are arranged around the heating well 10 and the steam injection well 20, and which recover steam G containing the target substance that has been volatilized by heating the steam injected by the heating well 10 and the steam injection well 20. The recovery well 30 has a cylindrical pipe 30a above the ground surface S, which is connected to a gas-liquid recovery unit 35 on the ground via a valve V2, and the recovered steam is introduced into the gas-liquid recovery unit 35.

[0024] The gas-liquid recovery well 40 is one or more wells in which mesh pipes extending beyond the aquifer EW along the depth direction in the ground EG are arranged around the heating well 10 and the steam injection well 20, and water piping 41 extending from the ground to the aquifer EW is arranged inside the mesh pipes, and the steam containing the target substance is recovered by heating the steam injected by the heating well 10 and the steam injection well 20, and groundwater containing the target substance is recovered through the water piping 41. The reason for recovering groundwater is that the steam containing the target substance in the ground EG is condensed and liquefied to be recharged in the groundwater. In addition, the recovery well 30 and the gas-liquid recovery well 40 are preferably in an area surrounded by the heating well 10 and the steam injection well 20. The gas-liquid recovery well 40 has a cylindrical pipe 40a above the ground surface S, and is connected to the gas-liquid recovery unit 35 on the ground via a valve V3, and the recovered steam and groundwater recovered through the water piping 41, 41a are introduced into the gas-liquid recovery unit 35. The cylindrical pipes 10a, 30a, and 40a are examples of tubular pipes.

[0025] A power supply unit 15 is disposed on the aboveground side of the heating well 10. The power supply unit 15 is connected to the underwater heater 11 and controls the amount of electricity supplied to the underwater heater 11. Note that the valve V1 is always open during operation of the device in order to guide the water vapor from the heating well 10 to the gas-liquid recovery unit 35.

[0026] The gas-liquid recovery unit 35 liquefies the water vapor introduced from the heating well 10 and the steam introduced from the recovery well 30 and the gas-liquid recovery well 40, recovers target substances from the recovery liquid including groundwater introduced from the gas-liquid recovery well 40, and leads the remaining water after recovery to the re-steaming unit 37. The gas-liquid recovery unit 35 uses an adsorbent such as activated carbon to capture volatile target substances that have evaporated into the gas phase. The captured target substances are rendered harmless by thermal decomposition and chemical treatment in the gas-liquid recovery unit 35. The groundwater is collected by the gas-liquid recovery well 40 by sucking it up with a pump.

[0027] The resteaming unit 37 resteams the water introduced from the gas-liquid recovery unit 35 , and introduces the resteamed steam into each steam injection well 20 via the steam connection pipe 21 .

[0028] Because the ground EG becomes highly pressurized due to steam on the ground surface S of the treatment area E, a lid CC made of insulating mortar or the like is formed to cover the treatment area E. That is, the treatment area E above the impermeable layer F is defined by the lid CC and the water shielding wall W. The lid CC has insulating properties and prevents heat leakage from the ground surface S. In addition, the steam connection pipe 21 is placed in the ground EG to prevent heat leakage, but is also placed along the ground surface S, which is the underside of the lid CC, and connected to each steam injection well 20.

[0029] A temperature observation hole 50 is provided in the ground EG, extending in the depth direction beyond the aquifer EW, and multiple temperature sensors S1 are arranged in the temperature observation hole 50 in the depth direction. A pressure sensor S2 is also arranged to detect the pressure of the steam in the recovery well 30. Furthermore, a pressure sensor S3 is also arranged to detect the pressure of the steam in the gas-liquid recovery well 40.

[0030] A control unit 60 is also arranged on the ground side, and the control unit 60 is connected to the temperature sensor S1, the pressure sensors S2 and S3, the power supply unit 15, the gas-liquid recovery unit 35, and the resteaming unit 37. Based on the detection results of the temperature sensor S1 and the pressure sensors S2 and S3, the control unit 60 controls the heating of the underwater heater 11 and the steaming of the resteaming unit 37 so that the detection value of the temperature sensor S1 is within a predetermined temperature range and the detection value of the pressure sensors S2 and S3 is within a predetermined pressure range, closes the valves V2 and V3 to stop the recovery of steam by the recovery well 30 and the gas-liquid recovery well 40 until the detection value of the pressure sensors S2 and S3 exceeds the predetermined pressure, and opens the valves V2 and V3 to recover steam and groundwater by the recovery well 30 and the gas-liquid recovery well 40 when the detection value of the pressure sensors S2 and S3 exceeds the predetermined pressure. The opening and closing of the valves V2 and V3 is controlled via the gas-liquid recovery unit 35. In addition, the control unit 60 grasps the recovery state of the target substance in the ground EG based on the detection value of a concentration sensor (not shown) that detects the concentration of the recovered target substance installed in the gas-liquid recovery unit 35, and determines whether to continue soil purification based on changes in this recovery state, such as a saturated state.

[0031] <Outline of soil purification treatment> First, the control unit 60 opens valve V1 to control the heating of the underwater heater 11 and the vaporization of the re-vaporization unit 37 so that the detection value of the temperature sensor S1 is within a predetermined temperature range and the detection values ​​of the pressure sensors S2, S3 are within a predetermined pressure range, then closes valves V2, V3 to stop the recovery of steam and groundwater by the recovery well 30 and the gas-liquid recovery well 40 until the detection values ​​of the pressure sensors S2, S3 exceed the predetermined pressure, and when the detection values ​​of the pressure sensors S2, S3 exceed the predetermined pressure, opens valves V2, V3 to recover steam and groundwater by the recovery well 30 and the gas-liquid recovery well 40.

[0032] When the treatment target area E reaches a predetermined temperature range, the target substance in the ground EG is vaporized by steam, and when the temperature and pressure reach the predetermined range, steam containing the target substance is introduced from the recovery well 30 and the gas-liquid recovery well 40 to the gas-liquid recovery unit 35 to recover the target substance, and groundwater is introduced from the gas-liquid recovery well 40 to the gas-liquid recovery unit 35 to recover the target substance. Note that the steam generated by heating the underwater heater 11 of the heating well 10 is constantly introduced to the gas-liquid recovery unit 35 to recover the target substance. Note that the recovery of steam by the recovery well 30 and the gas-liquid recovery well 40 is performed because the pressure in the ground EG is high within a predetermined pressure range due to the injection of steam, and no blower or the like is required to recover the steam containing the target substance, and the steam is guided to the gas-liquid recovery unit 35 by the steam pressure.

[0033] Therefore, other than the steam injected directly into the ground by heating well 10, that is, the steam introduced from heating well 10 and which may contain the target substance, the steam introduced from recovery well 30 and gas-liquid recovery well 40, and the groundwater introduced from gas-liquid recovery well 40, all have the target substances recovered by gas-liquid recovery unit 35, and the remaining water after the target substances have been removed is vaporized by re-steamer unit 37, so the target substance is not contained in the steam injected into the ground from steam injection well 20. As a result, the amount of the target substance circulating in the ground is reduced, and soil remediation by the steam injection method can be carried out efficiently.

[0034] Here, as the groundwater is vaporized by the underwater heater 11, the water level S10 of the aquifer EW around the heating well 10 drops, but since the groundwater flows toward the center of the treatment area E, the movement of the target substance outside the treatment area E is small, but the pressure in the unsaturated zone of the ground EG increases as the steam is injected, and the overall water level S10 drops to the water level S20. For this reason, a water shielding wall W made of partition sheet piles or the like is provided, and the water shielding wall W prevents the movement of steam and groundwater within the treatment area E outside the treatment area E and the leakage of heat.

[0035] <Construction of soil purification equipment> First, a water-stopping impermeable wall W such as a sheet pile is installed to surround the treatment target area E. Then, a hole for installing the heating well 10 is drilled to the aquifer EW, and the heating well 10 with the underwater heater 11 installed is installed. Similarly, the steam injection well 20 is installed. Furthermore, the recovery well 30 and the gas-liquid recovery well 40 are installed. Furthermore, a temperature observation hole 50 is drilled, and a temperature sensor S1 is placed. Then, the steam connection pipe 21 is placed between the steam injection well 20 and the resteaming unit 37, and the cover part CC is formed by pouring heat insulating mortar on the steam connection pipe 21 and the ground surface S. Then, the power supply unit 15, the gas-liquid recovery unit 35, the resteaming unit 37, and the control unit 60 are installed, and piping connections including valves and electrical system connections are made between each unit and between the heating well 10, the recovery well 30, and the gas-liquid recovery well 40.

[0036] <Heating well> FIG. 3 is a diagram comparing the configuration of a conventional heating well with that of the present embodiment. The conventional heating well 110 shown in FIG. 3(a) uses a dedicated stainless steel pipe to insert a nichrome wire heater 111 inside, and the bottom is capped to prevent groundwater from entering the inside. In addition, the diameter is large (about 80 mm), the drilling diameter is 165 mm, and grout injection was required between the stainless steel pipe and the ground EG. In addition, since the heating wells 110 are installed at intervals of about 2 m, a large number of heating wells 110 are required when the treatment target area E is large, and the cost of drilling and well construction for this purpose is high.

[0037] In contrast, the heating well 10 of this embodiment shown in Figure 3(b) uses a heating well with the same structure as a general groundwater observation well, and since it is a full strainer type (mesh pipe) well structure and it is sufficient to install the underwater heater 11 below the groundwater level in the hole, a small diameter is not a problem. However, the mesh pipe needs to be made of a material that can withstand temperatures of about 100°C.

[0038] In addition, in this embodiment, the groundwater in the hole at the current location is heated by an underwater heater 11 to generate steam, and the re-steaming unit 37 injects steam obtained by removing target substances from the steam generated in the heating well 10, steam obtained by removing target substances from the steam recovered from the recovery well 30 and the gas-liquid recovery well 40, and steam obtained by removing target substances from the groundwater recovered from the gas-liquid recovery well 40 into the ground from steam injection wells 20 that do not use heaters and are located near the heating well 10, thereby reducing the number of heating wells 10 that use heaters.

[0039] In this embodiment, the steam injection well 20 is also a fully strained well structure, and heating occurs due to the injection of steam from which the target substances have been removed into the ground EG, and the associated heating occurs due to thermal conduction. This significantly reduces the costs of drilling and well construction compared to conventional methods.

[0040] As described above, in this embodiment, steam from which target substances have been removed from a portion of the steam generated in the heating well 10, steam from which target substances have been removed from the steam recovered from the recovery well 30 and the gas-liquid recovery well 40, and steam from which target substances have been removed from the groundwater recovered from the gas-liquid recovery well 40 are injected into the ground from steam injection wells 20 located around the heating well 10, thereby reducing the amount of target substances circulating within the ground and allowing for efficient soil purification using the steam injection method, and since steam is injected into the ground from the steam injection well 20 that does not use a heater, the number of heating wells 10 that use heaters can be reduced.

[0041] Furthermore, the heaters used in the heating well 10 need only be placed in locations where groundwater can be vaporized, making it possible to reduce the number of heaters required compared to conventional heaters that are placed throughout the heating well. Furthermore, the soil is heated not by thermal conduction from the heater, but by allowing the steam generated by the heater to permeate the soil, making it possible to heat the soil evenly. Furthermore, the target substance is not recovered by forced recovery using a blower or the like, but by recovery using steam pressure, which simplifies the device configuration and increases thermal efficiency without unnecessary heat leakage.

[0042] In addition, since the temperature around the heating well 10 does not become extremely high, it is possible to suppress the occurrence of localized steam eruptions, etc. Furthermore, in this embodiment, the temperature environment in the treatment target area E only needs to be controlled by adjusting the heating output of the underwater heater 11 and adjusting the steam pressure, resulting in simple control with few control items.

[0043] <Variation 1> 4 is a schematic cross-sectional view showing the configuration of a soil purification apparatus 2 according to Modification 1 of this embodiment. In the soil purification apparatus 2 according to Modification 1, a heat exchanger 39 is provided between the gas-liquid recovery unit 35 and the re-steaming unit 37. The heat exchanger 39 converts thermal energy generated during liquefaction of steam in the gas-liquid recovery unit 35 into thermal energy used during steaming of the remaining water introduced into the re-steaming unit 37. This makes it possible to reduce the thermal energy used during steaming by the re-steaming unit 37, and further to increase the thermal efficiency of the purification apparatus.

[0044] <Variation 2> 5 is a schematic cross-sectional view showing the configuration of a soil purification apparatus 3 according to Modification 2 of this embodiment. The heating well 10 of the soil purification apparatus 3 according to Modification 2 is made of mesh pipes only around the submersible heater 11, and is made of cylindrical pipes elsewhere, so that all of the water vapor generated by the submersible heater 11 is introduced into the gas-liquid recovery unit 35. As a result, all of the water vapor injected into the ground is water vapor from which the target substance has been removed, and the target substance does not circulate within the ground, allowing for more efficient soil purification by the water vapor injection method.

[0045] Note that the configurations illustrated in the above embodiments and modifications are merely functional schematics and do not necessarily have to be physically configured as illustrated. In other words, the distribution and integration of each device and component is not limited to that illustrated, and all or part of them can be functionally or physically distributed and integrated in any unit depending on various usage conditions, etc. [Explanation of symbols]

[0046] 1,2,3 Soil purification equipment 10,110 Heating wells 10a, 30a, 40a Cylindrical pipe 11 Underwater heater 15 Power supply unit 20 Steam Injection Wells 21 Steam connection pipe 30 Recovery Well 35 Gas-Liquid Recovery Unit 37 Re-steaming unit 39 Heat exchanger 40 Gas-liquid recovery well 41,41a Water piping 50 Temperature observation hole 60 Control Unit 111 Heater CC lid E Processing area EG ground EN Unsaturated Zone EW aquifer F Impermeable layer G Steam S ground surface S1 Temperature Sensor S2, S3 pressure sensor S10,S20 water level V1~V3 valves W Water-resistant wall

Claims

1. A soil purification device that purifies a target area of ​​the ground by heating the target area to volatilize the target substances, one or more heating wells in which mesh-like pipes are arranged extending from the unsaturated zone to the aquifer along the depth direction in the treatment area, and water vapor is generated by an underwater heater installed at the bottom, and a portion of the water vapor is directly injected into the surrounding soil to heat the soil; one or more steam injection wells, each having a mesh-like pipe extending along a depth direction of the ground to a lower portion of the unsaturated zone and disposed around the heating well, for introducing steam and injecting the steam directly into the surrounding soil to heat the soil; one or more recovery wells, in which mesh-like pipes extending to a lower portion of the unsaturated zone along a depth direction in the ground are arranged around the heating well and the steam injection well, and which recover steam containing the target substance that has been volatilized by heating the steam injected by the heating well and the steam injection well; a gas-liquid recovery unit that liquefies the steam generated by the heating well and the steam recovered by the recovery well to recover the target substance; a resteaming unit that resteams the remaining water after the target substance is recovered in the gas-liquid recovery unit and introduces the resteamed water into each steam injection well via a steam connection pipe; A soil purification device comprising:

2. The soil purification apparatus of claim 1, further comprising: a mesh pipe extending beyond the aquifer along the depth direction in the ground and arranged around the heating well and the steam injection well; water piping extending from the ground to the aquifer is arranged within this mesh pipe; and one or more gas-liquid recovery wells are provided which introduce and recover steam containing the target substance volatilized by heating the steam injected by the heating well and the steam injection well into the gas-liquid recovery unit, and which introduce groundwater containing the target substance into the gas-liquid recovery unit via the water piping for recovery.

3. 3. The soil purification apparatus according to claim 1, further comprising a heat exchanger for converting thermal energy generated during liquefaction in the gas-liquid recovery unit into thermal energy used during vaporization in the revaporization unit.

4. 3. The soil purification apparatus according to claim 1, wherein the heating well is a cylindrical pipe except for a periphery of the underwater heater, and the water vapor generated by the underwater heater is introduced into the gas-liquid recovery unit.

5. 3. The soil purification apparatus according to claim 1, wherein the treatment target area is surrounded in the horizontal direction by a water impermeable wall extending beyond the aquifer in the depth direction, and the ground surface is covered by a lid.

6. The soil purification apparatus according to claim 5, characterized in that the steam connection pipe is arranged from directly below the steam generation unit along the underside of the lid, and introduces the steam re-vaporized by the steam generation unit into each steam injection well.

7. A temperature observation hole is provided in the ground, the temperature observation hole extends in a depth direction beyond the aquifer, and a plurality of temperature sensors are arranged in the temperature observation hole in a depth direction; a pressure sensor for detecting the pressure of the steam in the recovery well; The soil purification apparatus of claim 1, further comprising a control unit that controls the heating of the underwater heater and the steam re-vaporization unit so that the detection value of the temperature sensor is within a predetermined temperature range and the detection value of the pressure sensor is within a predetermined pressure range, stops the recovery of steam including from the recovery well until the detection value of the pressure sensor exceeds the predetermined pressure, and recovers steam including from the recovery well when the detection value of the pressure sensor exceeds the predetermined pressure.

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