JP2003266059A - Melting treatment method and treatment container therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a melting treatment method which enables an increase in energy efficiency and the prevention of contamination to peripheral soil by inhibiting emission of gas generated from a melting region, to the periphery and influence of water from the periphery of a treatment area when melting contaminated soil, and a treatment container therefor. <P>SOLUTION: A water-impervious outer container 1 is buried under ground, and an inner container 2 is set in the outer container 1 so that clean soil CS exists between the containers. The contaminated coil is accommodated in the inner container, and is melted by applying current to electrodes ME1 and ME2 to be changed to a glass solidified body. The inner container is composed of a porous air-permeable inner layer body and an outer layer body having a sealing property to generated gas up to a temperature where contaminants are decomposed and volatilized. The gas generated during the melting treatment process of the contaminated soil is emitted into an off-gas hood through the inner layer body other than a path in the direction (a). <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a melt processing method and a processing container therefor, and more particularly, to melt processing contaminants in soil by using in-situ vitrification (ISV) technology.
The present invention relates to a melt processing method and a processing container for the same, which eliminates the influence of gases generated by melting of contaminants.

[0002]

2. Description of the Related Art Recently, environmental problems such as pollution of soil due to outflow of harmful chemicals used and residues containing harmful substances have become serious in factories and research sites in various places. . Therefore, a technique for recovering the contaminated soil to its original state or removing contaminants is required, and various studies have been made for that purpose.

Under such circumstances, as one of the measures,
In-situ vitrification (ISV) technology has been developed to purify contaminated soil by melting and vitrifying the soil itself in situ where the contaminant is present in the soil. Therefore, FIG. 3 shows a procedure of a melting treatment system for vitrifying the contaminated soil itself by using the ISV technique.

As shown in FIG. 3A, first, the surrounding soil S where the contaminated soil S2, which is the original position to be melt-processed, exists.
1, the clean soil is covered so as to cover the entire upper part of the contaminated soil S2 to be purified, and the offgas hood H
Set up. Further, the melting electrodes ME1 and ME2 are inserted into the clean soil cover soil. Next, a conductive resistance path R is formed between the melting electrodes ME1 and ME2 so as to enable the initial energization.

Here, each of the melting electrodes withstands high temperatures,
For example, a rod-shaped electrode made of graphite. Further, the offgas hood H is connected to a pipe for discharging the gas generated during the purification process from the contaminated soil S2 to be purified to the offgas treatment system.

When the preparation for melting is completed, the melting electrode M
Electric power supplied from a generator or grid power is supplied to E1 and ME2. At this time, since the conductive resistance path R exists, Joule heat is generated in the resistance path R, and the Joule heat melts the resistance path and the surrounding soil to form a magma.

As shown in FIG. 3 (B), when the electricity is continued and the soil is melted, the electric resistance of the melted portion is greatly reduced. Therefore, the resistance supplied by the electric power supplied from the melting electrodes ME1 and ME2 is reduced. The road R and the soil adjacent thereto are melted one after another, and the melted region MG is formed. The melting region MG gradually expands downward from above.

In response to the expansion of the melting, the melting electrode ME
1 and ME2 are also inserted further down. At this time, the melting electrode is inserted so as to sink downward according to the melting of the soil due to the weight of the electrode itself.

In this way, if the entire range of the contaminated soil S2 requiring purification treatment can be melted,
The power supply to the melting electrodes ME1 and ME2 is stopped.
As shown in FIG. 3C, the volume of the melting region MG in which the contaminated soil S2 is melted is 25 to 50% when viewed from the initial state.
Since it also decreases, the depressed portion is backfilled with new soil S3.

With this, one batch process for the contaminated soil S2 to be purified is completed, and the off-gas hood H is moved toward the next batch process.

According to the ISV technique described above, the detoxification process can be executed in-situ by using the portable equipment. Contaminated soil that is difficult to dig up can be treated as it is. Contaminated soil that can be dug up is stored in a special partition, can be melted in that partition, and clean soil can be backfilled, so it is transported to another place such as a disposal site. No need.

Further, when the ISV technique is used for melting and solidifying contaminated soil, for example, heavy metals and radioactive substances in the soil are confined in the melted and solidified vitrified body, or hardly decomposable harmful organic substances such as dioxins. On the other hand, when the soil is melted, they can be thermally decomposed and rendered harmless by the high temperature of 1600 to 2000 ° C.

Further, in addition to the contaminated soil, solid materials such as incinerated ash, refractory bricks and drums, and combustible materials such as plastics can be collectively processed in the same shape. Moreover, by melting and solidifying the soil, it is possible not only to reduce the volume of the soil, but also to reduce the volume.
It has the feature that it can maintain a stable state for a long time by vitrification.

[0014]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
Using technology, when contaminated soil or soil with embedded solids etc. is melted and vitrified, the pollutants contained in the soil, solids, etc. are burned, vaporized and evaporated, Alternatively, gas is generated in the melting process due to thermal decomposition or the like.
Since a small amount of harmful components are contained in the generated gas, as shown in FIG. 3, the contaminated soil to be melt-processed should be prevented from being released into the atmosphere during the melting process. An offgas hood H that covers S2 is installed. The generated gas collected in the off-gas hood H is sent to the off-gas processing device, is subjected to secondary heat treatment, a filter, etc., and is then released to the atmosphere.

Here, as shown in FIG. 3, the generation of gas during the melting process of the contaminated soil will be described by taking the case where the contaminated soil S2 is melted by the ISV technique as an example. 4A to 4C each show a state during the melting process in FIG. 3B.

In FIG. 4A, the contaminated soil S2 is melted,
The state where the melting region MG is formed is shown, and during the melting process, the gas generated from the melting region MG is
The generated gas a is mainly emitted from the upper surface of the region MG into the offgas hood H. However, during the melting process, the gas generated in the melting region MG is not only the generated gas a but also the surrounding soil S surrounding the region.
1 also diffuses as the generated gas b through the side surface or the lower surface of the region. It is considered that the diffused generated gas b permeates the surrounding soil S1 and is released as the generated gas c.

As shown in FIG. 4B, the peripheral soil S1 is also heated during the melting process, and as a result, the peripheral soil S1 around the melting region MG is dried and a dry zone D may be formed. is there. The dry zone D has better air permeability than before drying due to the drying of the soil itself. Therefore, the generated gas b that comes out of the molten region MG diffuses around the region MG, but the generated gas b
Passes through the dry zone D and is released as the generated gas d.

As described above, during the melting treatment of the contaminated soil S2, the generated gases a to d are generated and released or diffused. However, as described above, the generated gas contains harmful components. Therefore, the generated gases a and d are captured by the off-gas hood H, which is not a problem, but as shown in FIG. 4A, the generated gas c is directly discharged to the atmosphere,
Environmental pollution problems occur. Furthermore, a part of the generated gas b may become the generated gas c, or the generated gas b may stay in the surrounding soil S1 even after the melting region MG is cooled. As described above, there is a problem that if the harmful component remains in the surrounding soil S1, the contaminated soil itself can be treated, but the surrounding soil is contaminated.

On the other hand, when the melting treatment of the contaminated soil is carried out in rainy weather, the upper part of the treatment target area is covered with the offgas hood H for capturing the generated gas, so that the rainwater does not directly enter the melting region MG. . However, depending on the state of the surrounding soil S1, rainwater may penetrate into the soil and reach the periphery of the melting region MG. In such a case, the melting energy is consumed by the evaporation of the intruding rainwater, and extra power must be supplied from the melting electrodes ME1 and ME2. There is a problem that the melting efficiency is deteriorated, which makes the melting process difficult in rainy weather.

Further, the infiltration of water into the melting region MG is not limited to rainwater, and as shown in FIG. 4C, the contaminated soil S2 may be close to groundwater. In this case, the moisture W increases from the groundwater to the melting region MG one after another via the surrounding soil S1, and the evaporation energy of the rising moisture W consumes the melting energy significantly. In addition, there is a problem that the time for the melting process becomes long.

In some cases, the contaminated soil itself is a wetland, and it may be necessary to melt and treat it. Alternatively, as described above, solid matters are dumped into the wetland, and these are collectively melted together with the soil. It may have to be processed. However, even in these cases, the melting energy is largely consumed for the evaporation of the water contained in the wetland, which makes the in-situ contaminant melting process difficult.

Therefore, the present invention prevents the gas generated from the melting region from diffusing to the surroundings when the contaminant is melted by using the ISV technique, and is not affected by the water from the surroundings. It is an object of the present invention to provide a melt processing method and a processing container for the same, which prevent contamination of surrounding soil.

[0023]

In order to solve the above problems, in the present invention, in a melting method for melting an object, the object is melted in a container having an air-permeable layer member on its inner wall surface. A method of melting an object while accommodating the object and melting the object in the container by energizing the object and capturing gas generated in the melting process of the object. And

The object is contaminated soil,
Alternatively, the soil containing solid matter, the wall of the container, an inner layer by the layer member, and an outer layer for sealing the gas generated in the melting process of the object, the inner layer is formed into a porous shape, The outer layer is formed of a material having a gas sealing property at least up to the decomposition temperature of the substance contained in the object.

Further, the container is placed in an outer container formed in soil, and a space between the container and the outer container is filled with a filling material, and the filling material is clean soil. .

Further, according to the present invention, in order to melt and solidify an object by energizing the object, in a melting processing container for containing the object, an inner layer formed by an air permeable layer member and the object is generated. It is decided to provide a wall body including an outer layer having a function of sealing the gas.

The space between the wall body and the outer container, including the outer container surrounding the outer periphery of the wall body, is filled with a filling material, and the object is contaminated soil or solid matter. Was used as soil.

Furthermore, the layer member is formed in a porous shape and is made of a material having a sealing property up to the decomposition temperature of the substance a contained in the object, and the filling material is clean soil. And

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION Next, with reference to FIGS. 1 and 2, an embodiment of a melting treatment method and a treatment container therefor according to the present invention in which contaminants are melt-treated together with soil to be vitrified will be described.

As shown in FIG. 3 or FIG. 4, in the conventional vitrification of the contaminated material which is melt-processed by using the ISV technique, the contaminated material is melt-processed in its original state to be vitrified. Utilizing the feature of performing the above, the melting electrode was directly inserted into the contaminant to be melt-processed in the surrounding soil, and the electric power was supplied to it. There, the contaminants are melted by the electric power to form a melting region in the soil, which is in direct contact with the surrounding soil. Therefore, the gas generated from the melting region diffuses into the surrounding soil, or is affected by the moisture contained in the surrounding soil during the melting process.

Therefore, in the melting treatment of contaminants using the ISV technique according to the present embodiment, at the original position where the contaminants exist, the contaminants to be melt-treated can be stored in a state isolated from the surrounding soil. Was decided to be used. In this processing container, the melting region was formed by the electric power supplied from the electrode for melting the contaminants.

Further, the processing container used in the present embodiment has an inner container and an outer container, and the inner container comprises an inner layer body and an outer layer body, and the inner layer body is a breathable layer member. And the outer layer body is formed of a material having a function of sealing gas generated from contaminants to be melt-processed.

FIG. 1 shows a method for melting and treating contaminants using the ISV technique according to this embodiment. In Figure 1,
Similar to FIG. 3, the case where the contaminated soil S2 exists in the clean surrounding soil S1 is taken as an example. This contaminated soil S2 is
It is about to be melted and reduced in volume by V technology.
Here, the melting treatment method of FIG. 1 differs from the conventional method of FIG. 3 in that the contaminated soil S2 is stored in a treatment container and then melted.

Next, a specific example of the procedure of the melting treatment method according to the present embodiment will be explained. Here, contaminated soil S
No. 2 is buried in the surrounding soil S1, and it is not possible to dig this contaminated soil S2 and carry it to another place for environmental protection. Therefore, the treatment of the contaminated soil S2 must be performed in the site where the contaminated soil S2 exists, and the above-described processing container is installed in the area adjacent to the contaminated soil S2.

Therefore, first, the installation work of the processing container will be described. In the surrounding soil S1 in which the contaminated soil S2 is buried, a hole having a size in which the outer container 1 of the processing container is buried is dug.
The excavated clean soil is stored and later used for backfilling this hole. The excavated clean soil is also used as a filling material between the outer container and the inner container.

The outer container 1 is placed in the dug hole. The outer container 1 is made of a shielding material that does not allow generated gas or moisture to pass through,
For example, it is formed of a plate made of steel or the like. This outer container 1
Is the gas generated in the melting process of the contaminated soil and the surrounding soil S1.
To the surrounding soil S1 during the melting process.
It has the role of preventing water from entering.

If the volume of the contaminated soil S2 is known, the outer container 1 may be manufactured in advance according to the volume, or it may be assembled on site with a steel plate or the like. . Then, if the outer container 1 can be installed in the hole, a part of the clean soil CS that has been dug out in advance is spread over the bottom of the outer container 1 with a certain thickness, and then the inner container 2 is placed thereon. Further, the space formed between the outer container 1 and the inner container 2 is filled with the clean soil CS also dug out before. In this manner, the clean soil CS that is dug out is filled between the outer container 1 and the inner container 2 together with the molten glass solidified body of the contaminated soil, including the outer container 1, and left as it is at the treatment site. This can be assumed. The clean soil CS may be a separately prepared filling material or may be recycled for the next melting process.

When the outer circumference of the inner container 2 is filled with the clean soil CS, the processing container is set in the surrounding soil S1 as shown in FIG. Therefore, the contaminated soil S2 is dug out, and the contaminated soil S2 is stored in the inner container 2. As a result, as shown in FIG. 3 (A), the contaminated soil S2 is in a state similar to that it is buried in the surrounding soil S1, and then the contaminated soil S2 is covered with clean soil. The case of the present embodiment is different from the case of FIG. 3A in that the contaminated soil S2 is isolated in the surrounding soil S1 by the surrounding soil S1, the outer container 1, and the inner container 2.

Since the preparation for the melting process on the contaminated soil S2 is now completed, the off gas hood H is formed over the entire upper opening of the outer container 1 as shown in FIG. 3 (A).
Then, the melting electrodes ME1 and ME2 are inserted, and the conductive resistance path R is laid between the melting electrodes ME1 and ME2.
Then, the melting electrodes ME1 and ME2 are energized to start melting the contaminated soil S2. The subsequent melting process is performed in the same manner as in the conventional case, where the melting electrodes ME1 and ME2 sink due to their own weight and reach the bottom of the inner container 2, and the melting process in the depth direction of the contaminated soil S2 ends. Suppose As shown in FIG. 1, the contaminated soil S2 is stored in the inner container 2
It is the melting region MG inside. In this case, the contaminated soil S2 stored in the inner container 2 is melted, but the clean soil CS spread on the bottom of the outer container 1 is not melted.

Now, the structure of the inner container 2 will be described with reference to FIG. In FIG. 2, the partial cross section is expanded and shown. The wall of the inner container 2 is a composite layer, for example, two layers of an inner layer body 3 and an outer layer body 4. The inner layer body 3 and the outer layer body 4 may be fixed and combined, or may be overlapped at the time of construction. The inner layer body 3 is formed of a member having air permeability to the gas b generated by decomposing or volatilizing the pollutants during the melting process of the contaminated soil S2. This breathability can be achieved, for example, by forming it with a porous material. This inner layer body 3 is
Since it is in contact with the contaminated soil S2, during the melting process of the contaminated soil S2, the entire layer thickness does not melt,
Be sure to retain breathability.

On the other hand, the outer layer body 4 is formed of a material having a sealing property against the generated gas at least up to the temperature at which the pollutants contained in the polluted soil S2 are decomposed or volatilized. For example, a metal plate made of aluminum, steel, or the like, a composite ceramic, or the like can be selected according to the type of contaminant.

As shown in FIG. 2, the inner container 2 is placed in contact with the contaminated soil S2 on one side and the clean soil CS on the opposite side, respectively. Therefore, when the melting process on the contaminated soil S2 is started, the generated gas is generated along with the melting. At this time, the generated gas a which is directly emitted upward of the contaminated soil S2 and the generated gas b which is generated to the side are generated. The generated gas b is discharged into the inner layer body 3, and
It passes through the inner layer body 3 and is discharged to the off-gas hood H.

As described above, in the inner container 2, the inner layer body 3 has a high-temperature melting region MG during the melting treatment of the contaminated soil S2.
Is not formed and the entire layer is not melted, and the function of releasing the generated gas b into the offgas hood H is maintained. Even if the outer layer body 4 is melted at the temperature at which the melting region MG is generated, at this point, the pollutants have already been decomposed or volatilized. Therefore, there is no problem even if the outer layer body 4 melts here and thus does not have a sealing property against the generated gas.

By installing the treatment container as described above as shown in FIG. 1 and melting the contained contaminated soil by the ISV technique, the contaminated soil can be detoxified and the volume can be reduced. It can be performed. And
After the melting process, it can be made into a harmless vitrified body, so that it can be easily taken out from the processing container and the subsequent handling becomes easy. Further, when a large amount of contaminated soil is buried, it is only necessary to sequentially dig out the storage volume of the processing container in a batch manner and repeat the melting process.

[0045]

As described above, in the melting treatment of the contaminated soil according to the present invention, since the treatment container having the inner container and the outer container for containing the contaminated soil is used, the melting treatment including the treatment container is performed. Not only can the generated gas be prevented from diffusing out of the facility, but the generated gas can be prevented from diffusing into the surrounding soil or the atmosphere to prevent the secondary pollution associated with the melting process.

Furthermore, since the outer container is made of a water-blocking material, it is possible to prevent the infiltration of water or water from the surrounding soil, so that even in a place with a high groundwater level or in a wetland, there is an influence of water. Since the melting process can be performed without doing so, the electric power energy input for melting can be efficiently used for the treatment of contaminants.

Further, by using the inner container composed of the inner layer body and the outer layer body, the decomposed gas generated in the melting process is surely trapped in the off-gas hood. Moreover, when the generated gas contains an organic compound, the flow path through which the gas passes can be limited to a high temperature region, so that the efficiency of the detoxification treatment of this organic compound can be improved.

Due to the presence of the inner container, it is possible to clearly separate the range of formation of the molten glass solidified body produced after the melting treatment of the contaminant and the range of the sintered body produced by sintering the clean soil. The amount of molten glass solidified material can be minimized.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view in soil explaining an embodiment of a melting treatment method according to the present invention.

FIG. 2 is an enlarged view showing a partial cross section of an inner container used in the present embodiment.

FIG. 3 is a vertical cross-sectional view illustrating an application example of a conventional melt processing method using in-situ vitrification (ISV) technology.

FIG. 4 is a diagram illustrating an influence of generated gas and the like in a conventional melting treatment method.

[Explanation of symbols]

1 ... Outer container 2 ... Inner container 3 ... Inner layer 4 ... Outer layer a to d ... Generated gas CS ... Clean soil H ... Off-gas hood ME1, ME2 ... Melting electrodes MG: Melting area S1 ... Surrounding soil S2 ... Contaminated soil

Claims (15)

[Claims] 1. An object to be melted is stored in a container having a breathable layer member on an inner wall surface, and the object is melted in the container by energizing the object. While capturing the gas generated in the melting process of the object,
A melting processing method for melting the object. 2. The melting processing method according to claim 1, wherein the object is contaminated soil. 3. The melt processing method according to claim 1, wherein the object is soil containing solid matter. 4. The wall of the container has an inner layer formed by the layer member and an outer layer that seals gas generated in a melting process of the object. The melt processing method according to. 5. The melt processing method according to claim 4, wherein the inner layer is formed in a porous shape. 6. The melt processing according to claim 4, wherein the outer layer is formed of a material having a sealing property with respect to the gas at least up to a decomposition temperature of a substance contained in the object. Method. 7. The container according to claim 1, wherein the container is arranged in an outer container formed in soil, and a filling material is filled between the container and the outer container. The melt processing method according to any one of claims. 8. The melt processing method according to claim 7, wherein the filling material is clean soil. 9. A melting treatment container for containing an object for melting and processing by energizing the object, wherein an inner layer of a gas permeable layer member and a gas generated from the object are sealed. A melt processing container comprising an outer layer having a function. 10. The melt processing container according to claim 9, further comprising an outer container surrounding an outer periphery of the wall body, wherein a filling material is filled between the wall body and the outer container. 11. The melt processing container according to claim 9, wherein the object is contaminated soil. 12. The melt processing container according to claim 9, wherein the object is soil containing solid matter. 13. The melt processing container according to claim 9, wherein the inner layer is formed in a porous shape. 14. The melt processing according to claim 9, wherein the outer layer is formed of a material having a sealing property up to a decomposition temperature of a substance contained in the object. container. 15. The melt processing container according to claim 10, wherein the filling material is clean soil.