JP2001149915A - Treating apparatus for making soil containing halogenated organic substance harmless - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a treating apparatus for making the soil harmless which allows a halogenated organic substance in the soil to be subjected to the harmless treatment economically and efficiently. SOLUTION: This treating apparatus for making the soil harmless is constituted in such a manner that a gas containing the halogenated organic substance is extracted from a vacuum extraction well 1 which is embedded in the soil containing the halogenated organic substance by using a vacuum pump 12, the moisture included in the gas after extraction is separated by a gas-liquid separator 10, the gas including the halogenated organic substance after the moisture is separated is transferred into a normal pressure low temperature plasma device such as a normal pressure low temperature microwave plasma device 20, subjected to a plasma decomposition treatment in the device 20 and made to be harmless, hydrogen halide generated during the decomposition treatment in the device 20 is treated with a means such as an alkali scrubber 40 which brings the gas into contact with alkali liquid and, thereby, the soil including the halogenated organic substance is made harmless.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for detoxifying a soil containing an organic halogenated substance, and more particularly to an apparatus utilizing a normal-pressure low-temperature plasma apparatus.

[0002]

2. Description of the Related Art Trichloroethylene, 1,1,1-trichloroethane, tetrachloroethylene, carbon tetrachloride, 1,1,2-dichloroethylene used for degreasing and cleaning in various industries such as a machine industry, an electronics industry, and a cleaning industry.
Plant effluent containing organic halogenated substances such as trichloroethane and 1,2-dichloroethane penetrates underground, contaminates the soil, and the organic halogenated substances pass through the unsaturated zone above the groundwater level and go below. It is a problem that it permeates the saturated zone and contaminates groundwater.

[0003] In order to purify such contaminated soil, conventionally, there is a method of excavating the contaminated soil and drying or heating it in the sun to remove the organic halide contained therein. . In addition, water or steam is injected into the soil, and solid-liquid contact or gas-liquid contact is performed in the soil to desorb the organic halogenated substance. There is a method of discharging together.

[0004] In addition to the above-described method, there is known a method of extracting contaminated gas containing an organic halogenated substance from soil contaminated with the organic halogenated substance by a vacuum pump and treating the contaminated gas. For example, in Japanese Patent Application Laid-Open No. 5-76618,
In a soil that may be contaminated by organic halogenated substances, a porous tube formed by dispersing a large number of vents is buried,
A vacuum pump is connected to the perforated pipe to extract a contaminated gas containing an organic halogenated substance from soil, and the contaminated gas after water is separated by a gas-liquid separator is provided with an activated carbon-containing adsorbent. To a solvent recovery unit consisting of an activated carbon adsorption tower,
A method of recovering an organic halogenated substance by adsorbing the organic halogenated substance on an adsorbent made of an activated carbon material and thermally desorbing the same is disclosed.

Japanese Patent Application Laid-Open No. 8-963 discloses a method in which a vacuum extraction well is buried in soil contaminated with an organic halogenated substance, and the contaminated soil containing the organic halogenated substance in the soil is vacuum-pumped from the vacuum extraction well. Means for extracting gas and oxidatively decomposing pollutant gas using a catalyst in the presence of oxygen and water vapor are disclosed.

[0006]

However, the above-mentioned conventional methods have the following problems with respect to the purification of soil contaminated with an organic halide. The method of excavating soil containing an organic halogenated substance and drying or heating it in the sun has an environmental problem because the organic halogenated substance released from the soil diffuses into the air and causes air pollution. Further, in the method of discharging the organic halogenated substance in the soil together with water, water vapor, or the like, it is necessary to further treat the discharged water containing the organic halogenated substance, and further equipment and labor are required.

Further, in the method of extracting an organic halogenated substance from soil and treating the obtained gas containing the organic halogenated substance, there is no environmental problem, but the following problems are caused. Have. The adsorption treatment method of adsorbing organic halogenated substances in gas onto activated carbon, etc., does not decompose the organic halogenated substances, but simply separates them, and finally heat-treats the organic halogenated substances adsorbed on activated carbon. Thus, the organic halogenated substance is recovered by being desorbed from the activated carbon, and the collected organic halogenated substance requires additional equipment for separate detoxification treatment.

In the catalytic decomposition method in which an organic halogenated substance in a gas is decomposed by a catalyst, the decomposition efficiency of the organic halogenated substance under low concentration conditions is poor. Since the concentration of the halogenated substance is low, a concentration means may be required. In addition, since the catalytic reaction is inhibited by the coexisting substance, a means for pretreating the gas before the reaction may be required in some cases. Further, since the catalytic reaction tower itself is relatively large, the installation area of the entire apparatus becomes large.

The present invention has been made in view of such circumstances, and the apparatus for detoxifying a soil containing an organic halogenated substance according to the first aspect of the present invention removes the organic halogenated substance in the soil. It is an object of the present invention to provide a detoxifying apparatus for soil containing an organic halogenated substance according to the second aspect of the present invention, which can economically and efficiently detoxify the organic halogenated substance in the soil. The present invention also provides a detoxifying apparatus for soil containing an organic halogenated substance according to the third aspect of the present invention. In addition to the object, it is an object of the present invention to prevent secondary contamination caused by hydrogen halide generated during the treatment, and to make the soil harmless treatment apparatus containing an organic halogenated substance according to the invention according to claim 4 an object. It is claim 1, aims to allow better even more economical and efficient detoxification by the invention according to claims 2 and 3.

[0010]

According to the present invention, there is provided a vacuum extraction well buried in soil containing an organic halogenated substance, a vacuum pump for sucking a gas through the vacuum extraction well, and the vacuum pump. An atmospheric pressure low-temperature plasma apparatus for decomposing an organic halogenated substance contained in a gas sucked by a pump, and a detoxification apparatus for soil containing an organic halogenated substance. Also,
According to a second aspect of the present invention, there is provided the soil detoxification apparatus according to the first aspect, further comprising a gas-liquid separator for separating moisture from gas sucked by a vacuum pump. Provided is an apparatus for detoxifying soil containing a substance. According to a third aspect of the present invention, there is provided the soil detoxification apparatus according to the first or second aspect, further comprising a unit for bringing the exhaust gas after the treatment with the normal-pressure low-temperature plasma apparatus into contact with an alkali solution. A soil harmless treatment apparatus containing an organic halogenated substance is provided. According to a fourth aspect of the present invention, there is provided an apparatus for detoxifying soil containing an organic halogenated substance according to the first, second, or third aspect, wherein the normal-pressure low-temperature plasma apparatus includes a normal-pressure low-temperature micro apparatus. Provided is a detoxification apparatus for soil containing an organic halogenated substance, which is a microwave plasma apparatus or a normal-pressure low-temperature discharge plasma apparatus.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION As an organic halogenated substance to be treated in the present invention, for example, trichloroethylene,
1,1,1-trichloroethane, tetrachloroethylene, carbon tetrachloride, 1,1,2-trichloroethane, 1,
2-dichloroethane, Freon-12 (CFC-1
2), Freon-113 (CFC-113), methyl bromide and the like, but are not limited thereto.

Next, FIG. 1 shows a flow sheet of an apparatus for detoxifying soil containing an organic halogenated substance, which is an embodiment of the present invention, and this will be described below. In FIG. 1, reference numeral 1 denotes a vacuum extraction well, which is buried in soil Z which is an unsaturated zone above a saturated zone W in a groundwater body and is contaminated with an organic halogenated substance such as trichlorethylene. The vacuum extraction well 1 is usually about 5 to 100 m in length, and is buried in a required number according to the degree of contamination and the area of soil to be detoxified. In addition, for example, at a location corresponding to a depth portion where the organic halogenated substance does not exist in the soil Z according to the region where the pollutant gas is present, the periphery of the vacuum extraction well 1 is covered with a sheet so as not to be sucked. For example, an organic halogenated substance can be sucked from a predetermined region and used.

Each of the vacuum extraction wells 1 shown in FIG.
It is constituted by spirally winding a wire 3 around the steel rod 2, and in a portion buried in the soil Z, through a gap between the wires 3 and a gap between the steel rod 2 and the wire 3. It sucks a gas containing an organic halogenated substance and water vapor. The vacuum extraction well 1 is not limited to the embodiment shown in FIG. 1 as long as the organic halogenated substance can be extracted from the soil using the vacuum pump 12. A porous tube formed by dispersion may be used. The burial of the vacuum extraction well 1 is carried out, for example, in a borehole having a diameter of 200 mm and a diameter of 150 mm
As in the case of inserting a vacuum extraction well 1 mm in diameter, the vacuum extraction well 1 is inserted into a drilled hole larger than the diameter of the vacuum extraction well 1. At this time, depending on the properties of the soil Z, coarse sand is packed around the vacuum extraction well 1 to prevent intrusion of soil or the like,
Palms and screens can be provided.

The upper end of the steel rod 2 is connected to a steel pipe 4 by welding or the like, and the steel pipe 4 is connected via a pipe 5 to a gas-liquid separator 10.
It is connected to the. The gas-liquid separator 10 is provided with a demister 11 that clumps stainless fibers or the like and attaches and removes droplets.
Is decorated. The gas-liquid separator 10 is connected to a vacuum pump 12 via a pipe 13. According to the above configuration, a gas containing an organic halogenated substance and water vapor in the soil Z is extracted by vacuum suction, and mixed water can be separated by the gas-liquid separator 10 on the suction side of the vacuum pump 12. ing. The water separated by the gas-liquid separator 10 is discharged from the drain 14 as wastewater. From the viewpoint of preventing secondary contamination by the organic halogen substance in the wastewater, air is blown into the gas-liquid separator 10 and aerated. Drive out organic halogenated substances in the water,
Alternatively, it is desirable to expel by heating and release as water free of organic halogenated substances.

As the above-described vacuum pump 12, for example, a non-water-sealed vacuum pump such as a screw vacuum pump and a water-sealed vacuum pump such as a Nash pump, as long as it can extract organic halogenated substances from a vacuum extraction well. Any vacuum pump, such as a vacuum pump, can be used.

In the embodiment shown in FIG. 1, the gas containing the organic halide substance sucked from the soil is contained in the embodiment shown in FIG. 1 because the relative humidity at the temperature at the time of suction is close to saturation or contains water droplets in many cases. The formed water is removed by the gas-liquid separator 10. However, since the sucked gas has a low relative humidity and does not include water droplets, the gas-liquid separator 10 may not be included when gas-liquid separation is not required.

An atmospheric pressure low-temperature plasma apparatus is connected to the exhaust side of the vacuum pump 12 via a pipe 15, and the gas containing the organic halide separated by the gas-liquid separator 10 is separated by the vacuum pump 12. It is transferred to a normal-pressure low-temperature plasma device. In the normal-pressure low-temperature plasma apparatus, the organic halogenated substance in the transferred gas reacts with the plasma to be decomposed, and the gas after the decomposition reaction is discharged from the normal-pressure low-temperature plasma apparatus. The normal-pressure low-temperature plasma device is a plasma device that generates plasma in which only the electron temperature is extremely high under normal pressure, as long as it can decompose an organic halide substance, and is preferably used. An ordinary-pressure low-temperature microwave plasma apparatus or an ordinary-pressure low-temperature discharge plasma apparatus is mentioned. FIG. 1 shows an ordinary-pressure low-temperature microwave plasma apparatus 20.

The normal-pressure low-temperature microwave plasma apparatus 2 shown in FIG.
0 has a microwave source 21 which is connected by a waveguide 22 to a microwave cavity 23 in which a container 24 is placed. When the microwave source 21 is turned on, a microwave field is generated in the microwave cavity 23, and a microwave field is also generated in the container 24 installed therein. The container 24 is provided with a gas inlet 27, and a gas containing an organic halogenated substance transferred from the pipe 15 connected to the exhaust side of the vacuum pump 12 is introduced into the container 24 through the gas inlet 27, and the plasma 26 fuels. The microwave power normally required to generate the plasma 26 is between 0.3 and
5 kW. In view of the high temperature of the plasma 26 in the container 24, the container wall is made of a heat-resistant material such as quartz.

The container 24 is also provided with an ignition port 28, and an electrode 29 is inserted through the ignition port 28 when generating plasma. The presence of the electrode 29 in the container 24 increases the intensity of the microwave field at a portion adjacent to the tip of the electrode 29, and discharge starts when the intensity of the microwave field in this region becomes sufficiently large. As a result, the gas around the electrode 29 is ionized, and the plasma 26 is formed and floats on the upper part in the container 24. After the plasma 26 is generated in the container 24, the electrode 29 is pulled out of the container 24. The electrode 29 is an elongated member having a pointed tip, and may be made of a conductive material. From the viewpoint of not affecting the microwave field, the electrode material is preferably carbon fiber. The size of the plasma 26 in the container 24 is adjusted by changing the output level of the microwave source 21. An exhaust port 25 is provided at a lower portion of the container 24, and a gas after the organic halide reacts with the plasma is exhausted from the exhaust port 25.

FIG. 2 is a vertical sectional view of a normal-pressure low-temperature discharge plasma apparatus which is another embodiment of the normal-pressure low-temperature plasma apparatus which can be used in the soil detoxification apparatus of the present invention.
The cylindrical normal-pressure low-temperature discharge plasma apparatus shown in FIG. 2 is of a packed-bed discharge type and has an internal electrode 31 and an external electrode 32. Porous adsorbent 33 and granular ferroelectric substance 3
4 are physically mixed and filled. A high voltage is applied between the internal electrode 31 and the external electrode 32 by the power supply 35. At both ends of the plasma processing chamber 39, a Teflon cap 36 and a holding plate 37 are provided. The apparatus also has a gas inlet 38 through which a gas containing an organic halogenated substance is introduced. The introduced gas containing the organic halogenated substance is mixed with the porous adsorbent 33 into the ferroelectric substance 34 through the through hole of the Teflon-made pressing plate 37 at one end in the flow path indicated by the arrow a to fill the plasma. After being introduced into the processing chamber 39 and the organic halogenated substance is decomposed by the plasma, the processed gas is discharged from the exhaust port 40 as a flow indicated by an arrow b through the through hole of the holding plate 37 at the other end. .

As the porous adsorbent 33, a non-conductive substance is used from the viewpoint of generating plasma, and an inorganic porous substance is preferable. For example, Al ₂ O ₃ , Si
O ₂ , zeolite (A type, X type, Y type, etc.), TiO ₂
And the like. The ferroelectric substance 34 and the porous adsorbent 33 are preferably in a granular form so that a gas passage can be formed in the packed bed. As for the size of the granule, the diameter of the bottom surface of the cylindrical body, the ellipse or the spherical body is 1 to 3 mm, and more preferably 1 to 2 mm. The voltage applied between the internal electrode 31 and the external electrode 32 by the power supply 35 varies depending on the concentration of the organic halogenated substance in the gas to be treated and the like, but is usually 1 to 10 kV / cm, preferably 1 to 5 kV / cm.
cm.

FIG. 2 shows an ordinary-pressure low-temperature discharge plasma apparatus.
In addition to those shown in, for example, surface discharge, barrier discharge,
Examples include, but are not limited to, a plasma device using a discharge method such as pulse discharge or capillary tube discharge.

The exhaust gas after the treatment by the normal-pressure low-temperature plasma apparatus can be released as it is, but can also be released after the exhaust gas is further subjected to a neutralization treatment by means of contacting with an alkaline solution. In the embodiment shown in FIG. 1, a means for contacting the exhaust gas treated by the normal-pressure low-temperature plasma device with the alkali liquid is connected after the normal-pressure low-temperature plasma device. With this configuration, when an organic halogenated substance is decomposed in a normal-pressure low-temperature plasma apparatus, an acid gas of hydrogen halides such as hydrogen chloride produced as a by-product is absorbed in the alkaline liquid, and the gas is treated in the exhaust gas after the treatment. It is possible to prevent secondary contamination due to the contained harmful acidic gas. As a means for bringing the exhaust gas into contact with the alkaline liquid, any means can be used as long as the hydrogen halide gas by-produced in the normal-pressure low-temperature plasma apparatus can be brought into contact with the alkaline liquid to neutralize the exhaust gas. For example, an alkali scrubber having a means for spraying and supplying an aqueous alkali solution to a treated exhaust gas containing hydrogen halides to make gas-liquid contact, or a special porous plate having an extremely fine air passage hole may be used. A packed tower or the like having a means for passing the treated exhaust gas containing hydrogen hydride to form fine bubbles and contact the alkaline solution on the porous plate is exemplified. The means for bringing the exhaust gas into contact with the alkaline liquid is preferably an alkaline scrubber 40 as shown in FIG. 1 from the viewpoint of economy and efficiency.

The alkaline scrubber 40 has a lower water tank 44 of a packed tower 43 filled with a contact material 42 such as Raschig ring or teralet packing, and a spray nozzle 45 provided above the contact material 42 with a circulation pump 46 interposed therebetween. The lower water tank 44 is connected through a circulation pipe, and is connected to a storage tank 48 of a relatively high concentration alkaline solution by a supply pipe 49 via a supply pump 47. A pH meter for measuring the pH of the alkaline aqueous solution is attached to the circulation pipe, and the supply pump 47 is controlled to be on and off so that the pH of the alkaline aqueous solution measured by the pH meter is maintained at a constant value. Can be configured. Further, a gas inlet 41 for introducing a gas containing hydrogen halide exhausted from the normal-pressure low-temperature plasma apparatus into the tower is provided at a lower part of the packed tower 43, and a gas inlet 41 is provided at an upper part of the packed tower 43 after treatment. An exhaust port 50 for discharging the gas is provided. With this configuration, the acidic gas of hydrogen halides generated by the decomposition of the organic halogenated substance in the normal-pressure low-temperature plasma device is:
The gas is supplied from the gas inlet 41 into the packed tower 43,
From the spray nozzle 45 of the spray solution. As a result, the acidic gas component is absorbed and removed in the aqueous alkaline solution, and the treated gas is exhausted from the exhaust port 50.

As the alkaline liquid used in the means for bringing the exhaust gas into contact with the aqueous alkaline solution, any alkaline liquid can be used as long as it can neutralize hydrogen halides, but from the viewpoint of economy and easy handling. From
An aqueous sodium hydroxide solution or an aqueous sodium carbonate solution is preferred. As the alkaline solution, any pH solution can be used as long as it is alkaline. However, the pH is 8.0 in consideration of the durability of the apparatus, the neutralization efficiency, the ease of handling, and the like.
The range of ~ 12.0 is preferred.

[0026]

As described above, according to the apparatus for detoxifying a soil containing an organic halogenated substance according to the first aspect of the present invention, the organic halogenated substance contained in the soil is extracted from the soil. Since the decomposition treatment is performed by the normal-pressure low-temperature plasma apparatus, an environmental problem such as the diffusion of the organic halogenated substance into the air is not caused. Further, since the organic halogenated substance present in the soil can be directly decomposed as well as isolated, the detoxification treatment after desorption in the adsorption treatment method becomes unnecessary. Further, even if the concentration of the organic halogenated substance contained in the extracted gas is low, it can be efficiently decomposed at low cost because an operation such as concentration in the catalyst treatment method is unnecessary. Further, it is advantageous in terms of equipment and space as compared with the treatment of organic halogenated substances by conventional means.

According to the detoxification apparatus for soil containing an organic halogenated substance according to the second aspect of the present invention, after the organic halogenated substance contained in the soil is extracted from the soil, the gas-liquid separation apparatus is used. Since water can be separated, in addition to the effect of the invention according to claim 1, even in soil containing water and the relative humidity is close to saturation, the organic halogenated substance can be efficiently detoxified. .

According to the detoxification apparatus for soil containing an organic halogenated substance according to the third aspect of the present invention, a gas containing an organic halogenated substance is extracted from soil containing an organic halogenated substance, and the gas is extracted from the soil. 3. The apparatus according to claim 1, wherein the organic halogenated substance is decomposed by a low-temperature plasma apparatus under normal pressure and means for neutralizing and removing hydrogen halide generated by the decomposition processing is provided. In addition, secondary contamination by hydrogen halide, which is an acidic substance, can be prevented, and the organic halogenated substance can be economically and efficiently detoxified as a whole.

According to the detoxifying apparatus for soil containing an organic halogenated substance according to the fourth aspect of the present invention, the effects of the apparatuses according to the first, second and third aspects are more excellent. Can be something.

[Brief description of the drawings]

FIG. 1 is a flow sheet showing one embodiment of an apparatus for detoxifying soil according to the present invention.

FIG. 2 is an embodiment of a normal-pressure low-temperature discharge plasma processing apparatus that can be used in the soil detoxification processing apparatus according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vacuum extraction well 10 Gas-liquid separator 12 Vacuum pump 20 Normal-pressure low-temperature microwave plasma apparatus 40 Alkaline scrubber

Claims (4)

[Claims] 1. A vacuum extraction well buried in soil containing an organic halogenated substance, a vacuum pump for sucking a gas through the vacuum extraction well, and an organic halogenated substance contained in the gas sucked by the vacuum pump. And a normal-pressure low-temperature plasma device for decomposing the soil, the detoxification device for soil containing an organic halogenated substance. 2. The apparatus for detoxifying soil according to claim 1, further comprising a gas-liquid separator for separating water from gas sucked by a vacuum pump, wherein the organic halogenated substance is contained. Of detoxifying soil. 3. The detoxifying apparatus for soil according to claim 1, further comprising a means for bringing the exhaust gas after the treatment with the normal-pressure low-temperature plasma apparatus into contact with an alkali solution. Detoxification equipment for soil containing organic halogenated substances. 4. An apparatus for detoxifying a soil containing an organic halogenated substance according to claim 1, 2 or 3, wherein the normal-pressure low-temperature plasma apparatus is a normal-pressure low-temperature microwave plasma apparatus or a normal-pressure low-temperature microwave plasma apparatus. Detoxification equipment for soil containing organic halogenated substances, which is a high-pressure low-temperature discharge plasma apparatus.