Soil purification device

Abstract

To provide an electric heater type soil purification device capable of reducing number of heating wells installed in a processing target area, and capable of enhancing heating efficiency.SOLUTION: A soil purification device includes: a heating well 10 where a mesh pipe extending along the depth direction to the aquifer EW is arranged in the processing target area E, water vapor is generated by a submerged heater 11 provided at the bottom, and which directly injects the water vapor into the surrounding soil; a steam injection well 20 which is connected to the heating well 10 through water vapor connecting piping 21 while a mesh pipe which extends along the depth direction to the bottom of the unsaturated zone in a soil EG is arranged around the heating well 10, and which introduces water vapor generated by the heating well 10 to directly inject it into the surrounding soil; and one or more collection wells 30 where a mesh pipe extending along the depth direction to the bottom of the unsaturated zone is arranged around the heating well 10 and the steam injection well 20 to collect steam containing target substances evaporated due to the heating of the water vapor.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an electric heater type soil purification apparatus that can reduce the number of heating wells to be installed in an area to be treated and can increase thermal efficiency. [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] The present invention has been made in consideration of the above, and aims to provide an electric heater type soil purification device that can reduce the number of heating wells to be installed in the area to be treated and improve thermal efficiency. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems and achieve the object, the present invention provides a soil purification device that purifies a soil treatment area 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 area to be treated, and which generate steam using an underwater heater installed at the bottom and directly inject the steam into at least the surrounding soil to heat the soil; one or more steam injection wells that are connected to the heating wells via steam connection piping and are arranged around the heating wells, and which introduce the steam generated by the heating wells and directly inject the steam into the surrounding soil to heat the soil; and one or more recovery wells in which mesh pipes are arranged around the heating wells and extend along the depth direction of the ground to the bottom of the unsaturated zone, and which recover steam containing the target substances that have volatilized by heating the steam injected by the heating wells and the steam injection wells.

[0010] In addition, the present invention is characterized in that, in the above-mentioned invention, a mesh pipe extending depthwise in the ground beyond the aquifer 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 one or more gas-liquid recovery wells are provided 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, and which recover groundwater containing the target substance via the water piping.

[0011] 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.

[0012] In the present invention, in the above-mentioned invention, the water vapor connection pipe is disposed along a lower surface of the lid portion.

[0013] In addition, the present invention is characterized in that, in the above-mentioned invention, a temperature observation hole is provided in the ground extending depthwise beyond the aquifer, multiple temperature sensors are arranged depthwise in the temperature observation hole, a pressure sensor for detecting the pressure of the water vapor is arranged in the water vapor connection pipe, the heating of the underwater heater is controlled so that the pressure sensor is within a predetermined pressure range, and a control unit is provided that, based on the temperature detected by the temperature sensor, stops recovery of steam containing the target substance until the temperature of the treatment area reaches a predetermined temperature, and controls the water vapor to circulate within the treatment area. Effect of the Invention

[0014] According to the present invention, the number of heating wells to be installed in the area to be treated can be reduced and thermal efficiency can be increased. [Brief description of the drawings]

[0015] [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. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] 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 target area of ​​the ground by heating the target area to be treated and volatilizing the target substances.

[0017] 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.

[0018] The soil purification apparatus 1 has a heating well 10, a steam injection well 20, a recovery well 30, and a gas-liquid recovery well 40. The heating well 10 is a mesh pipe arranged extending from the unsaturated zone EN to the aquifer EW in the depth direction in the treatment target area E, and generates steam using an underwater heater 11 installed at the bottom, which is then injected directly into at least the surrounding soil to heat the soil. Note that multiple heating wells 10 may be installed in the treatment target area E. It is also preferable to install the heating well 10 in the central part of the treatment target area E.

[0019] The steam injection well 20 is one or more wells that are connected to the heating well 10 via a steam connection pipe 21, and have mesh-like pipes arranged around the heating well 10 that extend depthwise in the ground EG to the bottom of the unsaturated zone EN, and introduce steam generated by the heating well 10 and inject the steam directly into the surrounding soil to heat the soil.

[0020] The recovery well 30 is one or more wells in which a mesh-like pipe extending depthwise in the ground EG to the bottom of the unsaturated zone EN is arranged around the heating well 10 and the steam injection well 20, and which recovers steam containing the target substance that has been volatilized by heating the steam injected by the heating well 10 and the steam injection well 20.

[0021] 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 gas-liquid recovery well 40 recovers steam containing the target substance volatilized by heating the steam injected by the heating well 10 and the steam injection well 20, and recovers groundwater containing the target substance through the water piping 41. The reason for recovering groundwater is that the steam containing the target substance in the ground EG solidifies and becomes liquid, which is then recharged into the groundwater. 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.

[0022] A power supply unit 15 is disposed above ground via a valve V1 above the heating well 10. The power supply unit 15 controls the amount of electricity supplied to the underwater heater 11. The valve V1 is always closed to prevent the steam from the heating well 10 from leaking.

[0023] A gas recovery unit 35 is connected to the ground side of the recovery well 30 via a valve V2. The gas recovery unit 35 recovers target substances from the steam flowing in from the recovery well 30. The gas 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 or chemical treatment in the gas recovery unit 35.

[0024] A gas-liquid recovery unit 45 is connected to the aboveground side of the gas-liquid recovery well 40 via a valve V3. The gas-liquid recovery unit 45 recovers target substances from the steam and groundwater flowing in from the gas-liquid recovery well 40. The gas-liquid recovery unit 45 captures the target substances and performs detoxification treatment in the same manner as the gas recovery unit 35. The groundwater is collected by being sucked up by a pump.

[0025] Because the ground EG becomes highly pressurized due to water vapor 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. The water vapor connection pipe 21 is placed in the ground EG to prevent heat leakage, but construction is facilitated by placing it along the ground surface S, which is the underside of the lid CC.

[0026] A temperature observation hole 50 is provided in the ground EG so as to extend beyond the aquifer EW in the depth direction, and a plurality of temperature sensors S1 are arranged in the temperature observation hole 50 in the depth direction. A pressure sensor S2 for detecting the pressure of water vapor is also arranged in the water vapor connection pipe 21.

[0027] Also, a control unit 60 is disposed on the ground side, and is connected to a temperature sensor S1, a pressure sensor S2, a power supply unit 15, a gas recovery unit 35, and a gas-liquid recovery unit 45. Based on the detection results of the temperature sensor S1 and the pressure sensor S2, the control unit 60 controls the heating of the underwater heater 11 via the power supply unit 15, and controls the opening and closing of a valve V2 via the gas recovery unit 35 and a valve V3 via the gas-liquid recovery unit 45.

[0028] <Outline of soil purification treatment> First, the control unit 60 controls the heating of the underwater heater 11 so that the detection result of the pressure sensor S2 is within a predetermined pressure range. The underwater heater 11 heats the groundwater to steam at approximately 100°C. Then, based on the temperature detected by the temperature sensor S1, the control unit 60 closes the valves V2 and V3 to stop the recovery of steam and groundwater containing the target substance until the temperature of the treatment target area E reaches a predetermined temperature, and controls the circulation of the steam within the treatment target area E. In other words, the steam generated by the underwater heater 11 continues to be injected into the ground EG from the heating well 10 and the steam injection well 20 until the treatment target area E reaches the predetermined temperature.

[0029] When the treatment area E reaches a predetermined temperature, the target substance in the ground EG is vaporized by the water vapor at the predetermined temperature, valves V2 and V3 are opened, and the steam containing the target substance is recovered from the recovery well 30 and the gas-liquid recovery well 40, and groundwater containing the target substance is recovered from the gas-liquid recovery well 40. Note that the pressure in the ground EG is high within a predetermined pressure range due to the injection of water vapor, so that no blower or the like is required when recovering the steam containing the target substance, and the steam is guided into the gas recovery unit 35 and the gas-liquid recovery unit 45, respectively, due to the steam pressure.

[0030] 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.

[0031] <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. In addition, a temperature observation hole 50 is drilled and a temperature sensor S1 is placed. Then, the steam connection pipe 21 is placed between the heating well 10 and the steam injection well 20, and the heat insulating mortar is poured on the steam connection pipe 21 and the ground surface S to form a cover part CC. Then, the power supply unit 15, the gas recovery unit 35, the gas-liquid recovery unit 45, 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.

[0032] <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 covered 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.

[0033] 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.

[0034] 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 by connecting it to steam injection wells 20 located nearby with steam connection piping 21, the number of heating wells 10 using heaters can be reduced.

[0035] In this embodiment, the steam injection well 20 is also a fully strained well structure, and heating occurs due to the injection of steam itself into the ground EG and the associated heat conduction. This significantly reduces the costs of drilling and well construction compared to conventional methods.

[0036] As described above, in this embodiment, since part of the steam generated in the heating well 10 is introduced into the steam injection well 20 to heat the soil, the number of heating wells 10 having heaters can be reduced, and thermal efficiency can be improved. In addition, the heaters used in the heating wells 10 need only be placed in the places where groundwater can be vaporized, and the number of heaters can be reduced compared to conventional heaters that are placed throughout the heating well. Furthermore, the soil is heated not by thermal conduction by the heater, but by allowing the steam generated by the heater to permeate the soil, making it possible to heat the soil evenly. In addition, the target substance is not recovered by forced recovery using a blower or the like, but by recovery using the pressure of the steam, so that the device configuration is simplified and thermal efficiency can be improved without unnecessary heat leakage.

[0037] 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.

[0038] 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]

[0039] 1. Soil purification equipment 10. Heating Wells 11 Underwater heater 15 Power supply unit 20 Steam Injection Wells 21 Steam connection pipe 30 Recovery Well 35 Gas Recovery Unit 40 Gas-liquid recovery well 41 Water piping 45 Gas-Liquid Recovery Unit 50 Temperature observation hole 60 Control Unit 110 Heating Well 111 Heater CC lid E Processing area EG ground EN Unsaturated Zone EW aquifer F Impermeable layer S ground surface S1 Temperature Sensor S2 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 in which water vapor is generated by an underwater heater installed at the bottom and the water vapor is directly injected into at least the surrounding soil to heat the soil; one or more steam injection wells, which are connected to the heating well via steam connection piping and have mesh-like pipes arranged around the heating well, the mesh pipes extending in the depth direction of the ground to the bottom of the unsaturated zone, and which introduce the steam generated by the heating well and directly inject the steam 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 soil purification device comprising:

2. The soil purification apparatus according to claim 1, characterized in that 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 one or more gas-liquid recovery wells are provided 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, and which recover groundwater containing the target substance via the water piping.

3. 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.

4. 4. The soil purification apparatus according to claim 3, wherein the water vapor connection pipe is disposed along a lower surface of the lid.

5. providing a temperature observation hole in the ground extending in a depth direction beyond the aquifer, arranging a plurality of temperature sensors in the temperature observation hole in a depth direction, and arranging a pressure sensor in the water vapor connection pipe for detecting the pressure of the water vapor; The soil purification apparatus described in claim 3, characterized in that it is equipped with a control unit that controls the heating of the underwater heater so that the pressure sensor is within a predetermined pressure range, and based on the temperature detected by the temperature sensor, controls to stop recovery of steam containing the target substance and circulate the water vapor within the treatment area until the temperature of the treatment area reaches a predetermined temperature.

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