JP3345000B1 - Melting range control method - Google Patents

Abstract

An object of the present invention is to improve the energy efficiency by controlling the spread of a melting region of contaminated soil when performing melting treatment of contaminated soil, and to prevent gas generated in the melting process from diffusing to the surroundings. A method for controlling a melting range is provided. SOLUTION: A contaminated soil S2 is accommodated by forming a control layer of silica sand SS inside a hole dug in a surrounding soil S1. Electricity is supplied to the contaminated soil by the electrodes ME1 and ME2 to form a fused region MG of the contaminated soil. The silica sand of the control layer controls that the melting area of the contaminated soil spreads laterally due to the heat insulation effect. In the process of melting the contaminated soil, the gas b is released as c via the permeable control layer, and the diffusion of the generated gas to the surrounding soil is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a melting range, and more particularly to a method for controlling a solid content embedded in soil or a contaminated material such as contaminated soil by applying a current to the material.
The present invention relates to a melting range control method capable of controlling unnecessary expansion of a melting region due to contaminants when melting contaminants and coping with generated gas accompanying melting of the contaminants.

[0002]

2. Description of the Related Art Recently, environmental problems such as contamination of soil by spills of used harmful chemicals or residues containing harmful substances have been increasing in factories and laboratories in various places. . Therefore, a technique for restoring 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 countermeasures,
In situ vitrification (ISV) technology has been developed that purifies contaminated soil by melting and vitrifying the soil itself in situ where the contaminants are present in the soil. FIG. 3 shows a procedure of a melting treatment system for vitrifying contaminated soil itself using the ISV technology.

[0004] As shown in FIG. 3 (A), first, the surrounding soil S on which the contaminated soil S2, which is the original position to be melted, exists.
In 1, the off-gas hood H is covered with clean soil so as to cover the entire upper part of the contaminated soil S2 to be purified.
Is installed. Further, the melting electrodes ME1 and ME2 are inserted into the clean earth covering soil. Next, a conductive resistance path R that enables initial energization is formed between the melting electrodes ME1 and ME2.

[0005] Each melting electrode is a rod-shaped electrode that withstands high temperatures and is made of, for example, graphite. The offgas hood H is connected to a pipe for discharging gas generated during the purification process from the contaminated soil S2 to be purified to the offgas treatment system.

Power supplied from a generator or system power is supplied to the melting electrodes ME1 and ME2. At this time,
Since the conductive resistance path R exists, Joule heat is generated in the resistance path, and the resistance path and the surrounding soil are melted by the Joule heat to form a magma.

As shown in FIG. 3 (B), when the soil is melted by this energization, the electrical resistance of the melted portion is greatly reduced. Therefore, the power supplied from the melting electrodes ME1 and ME2 causes the resistance path R to be reduced. And the soil adjacent thereto are melted one after another, and a melted area MG is formed. The melting area MG gradually expands from above the contaminated soil S2 to a lower portion. Inside, it becomes magmatic and heat convection occurs.

[0008] Then, when the electric power is continuously supplied from the melting electrodes ME1 and ME2, the melting region MG spreads further downward or to the side. In accordance with the spread, the electrodes ME1 and ME2 for fusion are further inserted downward. At this time, the insertion of the melting electrode may be caused to sink down according to the melting of the soil by the weight of the electrode itself,
Alternatively, the molten state of the soil may be separately grasped and pushed.

[0009] In this way, if the contaminated soil S2 that needs melting treatment can be melted up to the entire area including the contaminated soil S2,
The power supply to the melting electrodes ME1 and ME2 is stopped.
As shown in FIG. 3 (C), the volume of the molten area MG in which the contaminated soil S2 has been melted is 25% to 50% when viewed from the initial state.
Therefore, the depressed portion is back-filled with new soil S3.

[0010] Since one batch process for the contaminated soil S2 to be melted is completed, the off-gas hood H is moved to the next batch process.

According to the ISV technology described above, detoxification processing can be executed at the original position by using portable equipment. Contaminants difficult to excavate contaminated soil can be treated as they are. Contaminated soil containing pollutable substances that can be dug up can be stored in a special container, melted in that container, and clean soil can be backfilled. There is no need to transport to another place.

When the ISV technology is used for melting and solidifying contaminated soil, for example, heavy metals and radioactive substances in soil are confined in the molten and solidified vitrified material, or hardly decomposable harmful organic substances such as dioxin. When the soil is melted, it can be detoxified by thermal decomposition at a high temperature of 1600 to 2000 ° C.

Furthermore, in addition to the contaminated soil, solid substances such as incineration ash, refractory bricks, drums, and the like, and combustible substances such as plastics can be collectively treated in the same shape. In addition, by melting and solidifying these solids together with the soil, not only can the volume be reduced to greatly reduce the volume, but also a long-term stable state can be maintained by vitrification.

On the other hand, in the above description, an example in which contaminants and the like are melted at the original position has been described. However, a hole is dug in an appropriate land for the contaminants to be melted or the solids and the like. When embedding contaminants and solids in the holes,
Using the SV technology, the melt processing can be performed in a batch manner. In this case, the state is the same as that shown in FIG. 3A, except that the contaminated soil S2 is replaced with contaminants, solids, and the like carried from another place. The melting process for the contaminants, solids, and the like is performed according to the melting process procedure shown in FIG.

[0015]

SUMMARY OF THE INVENTION However, the ISV
When the contaminated soil or the soil in which the solid material or the like is embedded is melt-processed by using the technology, as described above, the contaminant to be processed is inserted into the inserted melting electrodes ME1 and ME.
2, and the melted region sequentially melts the surrounding contaminated soil. Then, when the contaminated soil is melted, the resistance value of the contaminated soil itself is reduced, and the current is more likely to flow to a newly melted region, thereby generating large Joule heat. This phenomenon,
Propagating one after another to the soil in contact with the melting region MG, the melting region MG expands downward or to the side, and the melting range expands.

However, Joule heat is successively generated by the electric power continuously supplied between the melting electrodes ME1 and ME2. The generated heat not only melts the contaminated soil itself but also surrounds the contaminated soil. The surrounding soil S1 in contact with the contaminated soil is also melted. Therefore, the melting region MG grows beyond the range formed by the current paths formed by the melting electrodes ME1 and ME2 and extends to the neighboring soil S1 adjacent to the side.

As shown in FIG. 3, the contaminated soil S2 is
Even if it is in contact with the surrounding soil S1 in a vertical plane, the formed molten region MG crosses the boundary where the contaminated soil S2 exists, and melts the adjacent portion of the surrounding soil S1. The shape of the molten region MG is such that, for example, a persimmon fruit swells at the center in the horizontal direction.

From the viewpoint of the original purpose of the melting treatment, it is unnecessary to melt the swollen region at the center. Therefore, when the contaminated soil S2 is subjected to the melting treatment, extra melting energy is consumed for melting the swollen region in the central portion, and there is a problem that unnecessary energy is supplied.

In view of the above, the present invention provides a method for controlling the spread of a contaminant so that the contaminant can be melted only by using the ISV technique.
An object of the present invention is to provide a method for controlling a melting range in which a gas generated from a melting region can be released and energy efficiency is improved.

[0020]

According to the present invention, a control layer filled with particulate matter is formed adjacent to a surface of an object to be melted, and the object is energized. Thus, a melting range control method for melting the object is provided.

The object is contaminated soil,
Alternatively, it is assumed that the soil contains a solid, the control layer has a high melting point with respect to the object, the particle size of the granular material is characterized by being larger than the particles of the soil,
The above-mentioned granular material has a residue of 80% through a 1.18 mm mesh sieve.
It has the above particle size. Further, the granular material is any of silica sand, crushed stone, and ceramics.

Further, an outer container is arranged on the opposite side of the control layer from the object, and the outer container has a gas and water shielding property.

[0023]

Next, an embodiment of a melting range control method according to the present invention, in which contaminants are melted together with soil and vitrified, will be described.

As shown in FIG. 3, in the conventional vitrification of contaminated soil using the ISV technique, the contaminated soil is melted in situ and vitrified. Utilizing the characteristics, the electrode for melting is inserted directly into the contaminated soil to be melted in the surrounding soil and power is supplied to it, or the contamination to be melted carried from another place soil,
Even when a solid material or the like is embedded in a hole dug in an appropriate land and subjected to melting treatment, an electrode for melting is directly inserted into contaminated soil to be subjected to melting treatment, and power is supplied thereto.

In the conventional melting treatment method, even if the contaminated soil is melted by the electric power to form a melting region, the melting region is in direct contact with the surrounding soil in the process of melting the contaminated soil. As a result, it expanded to the surrounding soil, exceeding the range of the contaminated soil targeted for treatment.

Therefore, in the melting treatment of the contaminated soil using the ISV technology according to the present embodiment, when the contaminated soil to be melted is melted, the contaminated soil is surrounded so as not to come into direct contact with the surrounding soil. As described above, the control layer that is difficult to melt at the temperature of the melting region formed by melting the contaminated soil is arranged. This control layer is formed by the filling of the granular material, and in a process in which the contaminated soil is melted by the electric power supplied from the melting electrode, the extent of the melting region is controlled to be within the range surrounded by the control layer. I made it.

Further, since the control layer is disposed, the control layer has good air permeability so that gas generated in the process of melting the contaminated soil is not trapped in the melting region. Therefore, the control layer used in the melting range control method of the present embodiment is filled with a granular material. For this granular material, for example, silica sand, crushed stone or ceramic particles were used.

A method for controlling the melting range of contaminated soil using the ISV technology according to the present embodiment will be described with reference to FIGS.

As an embodiment according to the melting range control method of the present invention, a case is described in which a contaminated soil or a solid material to be treated is accommodated in a hole dug in an appropriate land, and the treated object is melted. Will be explained. Here, a polluted soil is mentioned as a specific example of the treatment target.

First, as shown in FIG.
Then, a hole larger than the volume of the contaminated soil S2 to be melted is dug. In the melting range control method of the present embodiment, the melting process can be performed in the soil, and the control layer is formed in direct contact with the surrounding soil S1. However, FIG. 1 shows a case where the outer container 1 conforming to the shape of the hole is provided for convenience of excavating the hole. The outer container 1 may be formed of, for example, a steel sheet pile.

The outer container 1 is not necessarily installed when the melting range control method is carried out. For example, at the construction site, the excavated hole is close to the groundwater level, and rainwater is removed. If there is a possibility that water may enter during the melting process due to infiltration or a wetland, the outer container 1 having a bottom plate can be provided. As described above, if water is prevented from entering the entire hole, the melting energy is not consumed for evaporating water during the melting process, and the energy efficiency can be further improved.

When the outer container 1 is installed, a steel sheet pile or the like is driven so as to surround the area where the hole is to be dug, and then the soil surrounded by the steel sheet pile or the like is removed. Good. In this case, the driven steel sheet pile or the like can be used as the outer container 1 as it is. Thus, after a hole of a predetermined size is dug or the outer container 1 is installed in the hole, the silica sand SS is spread as a granular material to a uniform thickness on the entire bottom surface of the hole. Then, a control layer at the bottom of the hole is formed.

Here, silica sand SS is used as an example of the granular material, but may be crushed stone or a particle made of a ceramic material. However, it is important that the size of the particles of the granular material is larger than the particle of the soil to be melted, and the particle size of the silica sand SS is 80% by screening using a 1.18 mm mesh sieve. %.

The selection of the granular material to be filled in this way is such that when the granular material is filled as a control layer, the particle size of the soil to be treated and the particle size of the granular material filled as the control layer Therefore, the temperature at which the control layer melts can be higher than the melting temperature of the soil that is the object to be treated. For example, their melting point difference can be set to 100 ° C. or higher, preferably 200 ° C. or higher. Silica sand, crushed stone, etc. have high melting point and good heat insulation properties, and do not produce low melting point materials,
It is possible to prevent the melt from entering the control layer.

Further, if the granular material has a particle size of 20% or more when passed through a 1.18 mm mesh sieve, it is impossible to sufficiently secure the air permeability of the control layer after the granular material is filled. is there.

Next, in order to form a space for accommodating the contaminated soil S2, the partition plates 2 are set apart from the wall surfaces of the holes and at intervals so as to form the control layer. Here, the use of the partition plate 2 makes it difficult to form the space simply by stacking the silica sand SS, so that a clear wall is easily formed by the silica sand SS, and the workability is improved. Then, between the outer container 1 and the partition plate 2, the silica sand SS having the above-mentioned particle size composition is filled up to the upper part of the hole.

As a result, a space for accommodating the contaminated soil to be treated has been secured, so that the contaminated soil S2 is packed in the space, and the off-gas hood H covering the entire upper opening of the outer container 1 is filled.
Place. Subsequently, the electrodes ME1 and ME2 for melting are inserted, and a conductive resistance path R is provided between the electrodes ME1 and ME2 for melting.

Since the partition plate 2 is used for convenience to secure a space for accommodating the contaminated soil S2, the partition plate 2 is pulled out and removed before the contaminated soil S2 is melted. Therefore, the material of the partition plate 2 is sufficient if it has appropriate hardness, and any material such as wood, iron, or the like may be used. If the material has a lower melting point than the silica sand SS and a high air permeability, it can be buried as it is. When performing the melting treatment while leaving the partition plate having poor air permeability, a large number of holes are previously formed in the plate surface of the partition plate, or the partition plate itself is made porous.

As described above, the side and bottom surfaces of the contaminated soil S2 are surrounded by the control layer of the silica sand SS, and the preparation for the melting treatment of the contaminated soil S2 is completed. Then, energization of the melting electrodes ME1 and ME2 is started, and the procedure of melting the contaminated soil S2 is the same as the procedure of the melting shown in FIG.

FIG. 2 shows the formation of a molten region when the partition plate 2 is pulled out, and the partition plate 2 is removed and not shown. The contaminated soil S2 is sequentially melted from the upper portion by a conventional melting process to form a melted area MG as shown in FIG. When the contaminated soil S2 is in direct contact with the surrounding soil S1 as in the conventional melting process shown in FIG. 3, the heat of the melting area MG formed in the process of melting the contaminated soil S2 causes the surrounding soil to contact. Although the soil S1 was also melted, in the melting process according to the present embodiment, a control layer of silica sand SS is disposed around the contaminated soil S2. The heat of the body is blocked by the control layer, and a molten region MG is formed in a range surrounded by the control layer. Even if a part of the magma-like melt may enter between the granular materials on the contact surface of the control layer, if the thickness of the control layer is adjusted in advance, the formation range of the melted area MG is naturally limited. Is done.

Further, in the melting process according to the present embodiment, since the control layer is disposed around the contaminated soil S2, not only the formation range of the melting region MG is limited by the control layer, but also the process of the melting process. The flow of the gas generated in the process is different from that in the case of the melting process shown in FIG. FIG. 2 shows a state during the melting process according to the present embodiment.

In the melting process of the contaminated soil S2, generated gases a and b are generated from the melting area MG due to decomposition, evaporation, volatilization, and the like by substances existing in the contaminated soil. The generated gas a is directly discharged into the off-gas hood H from the upper surface of the melting region MG. On the other hand, when the molten region MG is in direct contact with the surrounding soil S1 as in the case of the conventional melting treatment, the generated gas b is likely to diffuse into the surrounding soil S1, but according to the present embodiment. In the melting process, since the control layer is formed of a granular material such as silica sand SS and has sufficient air permeability, as shown in FIG. 2, when the molten region MG comes into contact with the silica sand SS, The generated gas b passes through the silica sand SS, becomes a generated gas c, and is discharged into the off-gas hood H.

The generated gas b is collected in the off-gas hood H according to the chimney effect due to the air permeability of the silica sand SS, and the generated gas b does not stay in the control layer. Therefore, even if the silica sand SS is in direct contact with the surrounding soil S1, diffusion of the generated gas b into the surrounding soil S1 can be prevented.

Further, when the outer container 1 is provided outside the control layer, if the outer container 1 itself has a gas shielding property, diffusion of the generated gas into the surrounding soil S1 is further prevented. Can be.

Further, since the generated gas b does not stay in the control layer, the silica sand SS can be reused. The same effect as described above is obtained even when other granular materials other than silica sand SS are used for the control layer.

In the melting range control method of the present embodiment described above, the contaminated soil is taken as an example of the object to be treated. However, if the object to be treated is a solid, the solid is
An initial conductive resistance path is formed in the control layer so as to be embedded in the clean soil. The procedure for melting this solid is the same as the procedure for melting the contaminated soil.

In the above description, the melting range control method of the present embodiment is applied in a hole dug in the soil. For example, the melting range control method of the present embodiment is applied in an outer container installed on the ground. can do. Also in this case, the procedure of the melting treatment for the contaminated soil is the same as that in the case where the melting is performed in a hole dug in the soil.

[0048]

As described above, in the method for controlling the melting range of contaminated soil according to the present invention, the contaminated soil is surrounded by a control layer filled with particulate matter and then subjected to melting treatment. The presence of this control layer controls the extent of the melted region formed by melting the contaminated soil.

The control layer surrounding the contaminated soil includes:
Granules such as silica sand and crushed stone were filled, and the granules had a particle size composition of 80% or more as determined by screening with a 1.18 mm mesh sieve. Since such a granular material has a high melting point and a good heat insulating property and does not produce a low melting point material, the control layer can suppress unnecessary expansion of a melting region accompanying melting of the contaminated soil. it can.

Therefore, energy efficiency in melting contaminated soil can be improved. Further, the molten glass solidified by the contaminated soil can be minimized.

Further, the gas generated in the process of melting the contaminated soil is reliably collected in the off-gas hood without being diffused to the surrounding soil.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an embodiment of a melting range control method according to the present invention.

FIG. 2 is a diagram illustrating the flow of generated gas when the present embodiment is applied.

FIG. 3 is a diagram illustrating an application example of a conventional melting treatment method using an in-situ vitrification (ISV) technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Outer container 2 ... Partition board ac ... Generated gas H ... Off gas hood ME1, ME2 ... Melting electrode MG ... Melting area S1 ... Peripheral soil S2 ... Contaminated soil SS ... Silica sand

Continuation of front page (56) References US Pat. No. 6,120,430 (US, A) James E. Hansen, Patrick S .; Lowery, Craig L. Timmerman, New GeoMeltTMvitrification technologies for difficult dosing site remediation needs, Proceedings of SPECTRUM'98 International Conference of National Conventions. . , United States, American Nuclear Society, 1998, Vol. 1034-1039 Motoshi Muraoka et al., Dioxin removal by geomelt technology, 100 selected environmental technology for protecting the earth, revised edition, Japan, Pollution Control Technology Co., Ltd., 2000, pp. 118-119 Shigeharu Nakachi, Considering Dioxin Contamination Treatment by the Geomelt Method, Environmental Monitoring, Japan, Medical Laboratories, Minamirokai, Environmental Monitoring Research Institute, 2001, No. 78, pp. 100 1-7 (58) Fields surveyed (Int. Cl. ⁷ , DB name) B09C 1/06 E02D 3/11 JICST file (JOIS) WPI (DIALOG)

Claims (8)

(57) [Claims] 1. A method for controlling a melting range in which a control layer filled with particulate matter is formed adjacent to a surface of an object to be melted, and the object is melted by energizing the object. 2. The method according to claim 1, wherein the object is contaminated soil. 3. The melting range control method according to claim 1, wherein the object is soil containing a solid matter. 4. The control layer according to claim 1, wherein a melting point of the control layer is higher than that of the object, and a particle size of the granular material is larger than a particle of the soil. Method for controlling the melting range. 5. The melting range control method according to claim 4, wherein the granular material has a particle size such that the residue is 80% or more on a 1.18 mm mesh sieve. 6. The method according to claim 1, wherein the granular material is any one of silica sand, crushed stone, and ceramics. 7. The melting range control method according to claim 1, wherein an outer container is arranged on a side of the control layer opposite to the object. 8. The method according to claim 7, wherein the outer container has a shielding property against gas and water.