Exhaust purifying filters, exhaust purifying devices

Abstract

To provide an exhaust cleaning filter which is unlikely to deteriorate by radiation from radioactive dusts.SOLUTION: An exhaust cleaning filter 7 is cylindrical, wherein radioactive dusts in exhaust air EH are captured by the exhaust cleaning filter 7 and purified exhaust air PEH is exhausted outside the exhaust cleaning filter 7 through a cylinder of the exhaust cleaning filter 7 in a process that the exhaust air EH passes from the outside of the exhaust cleaning filter 7 to the inside. The exhaust cleaning filter 7 has a main filter. The main filter includes a sheet of metal fiber. The exhaust cleaning filter 7 can be washed. In a step of washing the exhaust cleaning filter 7, compressed air jetted into the cylinder of the exhaust cleaning filter 7 passes from the inside of the exhaust cleaning filter 7 to the outside. In that process, the radioactive dusts captured by the exhaust cleaning filter 7 are blown off outside the exhaust cleaning filter 7.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an exhaust gas purification filter used to obtain purified exhaust gas by removing radioactive dust in the exhaust gas, an exhaust gas purification apparatus including the exhaust gas purification filter, and a radioactive dust removal system including the exhaust gas purification apparatus.

Background Art

[0002] In the decommissioning work of nuclear power plants and nuclear facilities, a large amount of radioactive dust (referring to dust containing radioactivity, dust with radioactivity. The same shall apply hereinafter) is generated. A large amount of radioactive dust may lead to exposure of decommissioning workers and the spread of radioactive contamination outside the decommissioning work area. Therefore, it is necessary to reduce the concentration of radioactive dust in the work area. At the same time, it is also necessary to maintain a negative pressure in the work area to prevent radioactive substances from leaking from the work area to the outside of the work area.

[0003] In such a site, it is preferable to use a filtration device equipped with a high-performance filter (for example, a HEPA filter) that removes fine radioactive dust. However, since this high-performance filter is likely to be clogged because it processes dust of various sizes, it must be replaced frequently. As a result, the amount of radioactive waste will increase. Since it is problematic from the perspective of exposure for a person to approach a high-performance filter that has captured a large amount of radioactive dust, it is desired to minimize the frequency of filter replacement.

[0004] As technologies for removing radioactive dust in exhaust gas, there are those disclosed in Patent Documents 1 and 2 below.

[0005] The secondary product recovery processing system disclosed in Patent Document 1 is characterized by comprising a local exhaust enclosure installed in the demolition environment area, a filter for filtering and recovering the secondary products recovered in the local exhaust enclosure, an exhaust fan connected to the outlet side of the filter, and a circulation line for returning the exhaust from the exhaust fan to the demolition environment area for circulation. The effects of this system include the efficient recovery of secondary products generated from the demolition site, and improved safety by treating the exhaust in a closed-system recovery system without releasing exhaust to the outside.

[0006] The dust cartridge filter disclosed in Patent Document 2 combines a hollow cylindrical filter body with a plate-shaped pre-filter to increase the filtration area and extend the filter's lifespan. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2003-185794 [Patent Document 2] Japanese Patent Publication No. 2000-300926 [Overview of the project] [Problems that the invention aims to solve]

[0008] In the secondary product recovery system described in Patent Document 1, it is not clear what type of filter is used as the filter installed upstream of the circulation line. If a general filter made of polyester resin or the like is used as this filter, it will have low resistance to radiation and will degrade easily.

[0009] Furthermore, if the exhaust from the demolition environment area contains sharp fine particles, these particles may damage the filter, which also leads to the problem of requiring more frequent filter replacement.

[0010] Furthermore, depending on the type of dust contained in the exhaust from the demolition environment area (for example, if the exhaust contains sparks from cutting with a torch or grinder), there was a risk that the filter could catch fire and cause a fire.

[0011] In the dust cartridge filter described in Patent Document 2, the filter body of the hollow cylindrical filter is made of glass fiber filter paper sandwiched between support media (polyester resin). In addition, nonwoven fabric is used as the plate-shaped pre-filter section.

[0012] However, filters using polyester resin, such as those described in Patent Document 2, have the same problems as those described in Patent Document 1. Specifically, they have various problems such as the risk of degradation due to radiation, the risk of damage due to sharp fine particles, and the risk of fire.

[0013] Therefore, the object of the present invention is to provide an exhaust gas purification filter that removes radioactive dust from exhaust gas containing radioactive dust generated in a work area, and which is less susceptible to deterioration due to radiation from the radioactive dust. [Means for solving the problem]

[0014] The present invention, which solves the above problems, is as follows.

[0015] (First aspect) An exhaust purification filter that removes radioactive dust from exhaust containing radioactive dust generated in a work area, The exhaust purification filter is cylindrical in shape, and as the exhaust passes from the outside to the inside of the exhaust purification filter, radioactive dust in the exhaust is captured by the exhaust purification filter, and the purified exhaust is discharged outside the exhaust purification filter after passing through the cylinder of the exhaust purification filter. The exhaust purification filter has a main filter, The main filter includes a sheet of metal fiber, The exhaust purification filter is washable. During the cleaning of the exhaust purifying filter, compressed air is injected into the cylinder of the exhaust purifying filter and passes from the inside to the outside of the exhaust purifying filter, and in the process, the radioactive dust captured by the exhaust purifying filter is blown to the outside of the exhaust purifying filter. An exhaust gas purification filter characterized by the following features.

[0016] (Effects and Benefits) Because the main filter of the exhaust gas purification filter contains a sheet of metal fibers, the exhaust gas purification filter is less susceptible to degradation from radiation emitted from radioactive dust in the exhaust gas.

[0017] Furthermore, since there is a risk of radiation exposure during the replacement of exhaust gas purification filters contaminated with radioactive dust, it is preferable to avoid replacing the exhaust gas purification filters as much as possible. However, with the exhaust gas purification filter of the first embodiment, the frequency of replacement can be reduced. In other words, with the exhaust gas purification filter of the first embodiment, even if a large amount of radioactive dust adheres to the exhaust gas purification filter and the purification capacity of the exhaust gas purification filter decreases, the exhaust gas purification filter can be regenerated by backwashing using compressed gas. Therefore, it is not necessary to replace the exhaust gas purification filter every time a large amount of radioactive dust adheres to it, and the need to replace the exhaust gas purification filter for a long period of time is eliminated. As a result, it is possible to prevent radiation exposure to workers associated with the replacement of exhaust gas purification filters and to prevent the generation of large amounts of radioactive waste (used exhaust gas purification filters). In addition, it is possible to reduce the interruption of exhaust gas purification treatment when replacing filters and to reduce the costs associated with the replacement and disposal of exhaust gas purification filters.

[0018] Furthermore, it was found that when cleaning the exhaust gas purification filter, applying compressed gas to the inside of the filter is more effective in removing radioactive waste attached to the filter than applying compressed gas to the outside of the filter. Therefore, as in the first embodiment, so-called backwashing of the exhaust gas purification filter has the advantage of allowing the filter to be replaced for a longer period of time.

[0019] Furthermore, even if the exhaust gas from the work area contains sharp fine powder or the like, the main filter of the exhaust gas purification filter includes a metal fiber sheet, so it is difficult for the exhaust gas purification filter to be damaged by the fine powder. Also, even if the exhaust gas from the work area contains sparks or the like that could cause a fire, since the main filter of the exhaust gas purification filter includes a metal fiber sheet, it is difficult for a fire to occur.

[0020] (Second aspect) The exhaust gas purification filter has shape-retaining means for retaining the shape of the main filter, The shape-retaining means includes a metal mesh member, The exhaust gas purification filter of the first aspect is formed by laminating the flat shape-retaining means on the front and back sides of the flat main filter, or on the front side or the back side of the flat main filter, and then folding the laminate into a bellows shape to form a cylinder.

[0021] (Function and effect) In the second aspect, regarding the configuration of the exhaust gas purification filter, the shape-retaining means including a metal mesh member is laminated on the front and back sides of the flat main filter, or on the front side or the back side of the flat main filter. With such a configuration, it becomes easier to retain the shape of the main filter including the metal fiber sheet. That is, since it is difficult to retain the shape only with the metal fiber sheet, it is preferable to laminate the shape-retaining means including the metal mesh member as in the second aspect. Also, by providing the shape-retaining means including the metal mesh member, the strength of the exhaust gas purification filter can be increased, and as a result, it becomes easier to withstand the pressure applied to the exhaust gas purification filter during backwashing of the exhaust gas purification filter (pressure by compressed gas).

[0022] Also, when the shape-retaining means including the metal mesh member is not provided, it is difficult to form the sheet of metal fibers into a bellows shape. Even if the sheet of metal fibers could be formed into a bellows shape, its morphological stability would be poor and it would be difficult to maintain the bellows shape. By using the shape-retaining means including the metal mesh member for the exhaust purification filter, the sheet of metal fibers can be formed into a bellows shape and the bellows shape can be maintained.

[0023] Note that by making the exhaust purification filter bellows-shaped, the filtration area increases, so there is an advantage that the exhaust purification throughput per unit time can be increased without increasing the size of the container (the container of the exhaust purification device) for housing the exhaust purification filter.

[0024] (Third Aspect) The main filter is composed of a laminated structure having a surface layer located outside the exhaust purification filter, a back layer located inside the exhaust purification filter, and an intermediate layer located between the surface layer and the back layer, and the exhaust purification filter of the first aspect in which the fiber diameter of the metal fibers in the surface layer and the back layer is larger than the fiber diameter of the metal fibers in the intermediate layer.

[0025] (Function and Effect) The main filter has a laminated structure consisting of a surface layer, an intermediate layer, and a back layer, with the fiber diameter of the metal fibers in the surface layer and the back layer being larger than that of the metal fibers in the intermediate layer. In this case, the metal fibers in the intermediate layer, which have a smaller fiber diameter, can remove radioactive dust and the like most effectively, but they have the disadvantage of being weak due to their small fiber diameter. Therefore, by providing a surface layer and a back layer made of metal fibers with a larger fiber diameter than the metal fibers in the intermediate layer, the weakness of the fibers in the intermediate layer can be compensated for by the strength of the fibers in the surface layer and the back layer. As a result, compared to the case where the main filter is a single layer (assuming the fiber diameter of the metal fibers constituting this single layer is the same as that of the metal fibers in the intermediate layer), the strength of the main filter can be increased, the shape stability of the main filter can be improved, and the filter can withstand the pressure (pressure due to compressed gas) applied to it during backwashing of the exhaust gas purification filter. In particular, the back layer of the main filter is subjected to the greatest pressure from compressed gas during backwashing, and by increasing the pressure resistance of the back layer, damage to the main filter due to compressed gas can be prevented.

[0026] Furthermore, if the metal fiber diameter of the layer located outside the main filter is large, it becomes easier to blow away radioactive dust and other particles trapped in the voids of that layer during backwashing, compared to when the metal fiber diameter of the layer located outside the main filter is small. This also has the advantage of improving the cleaning effect during backwashing.

[0027] Furthermore, by using a stacked structure for the main filter, it is possible to reduce the variation in performance between individual main filters when manufacturing multiple main filters, thereby stabilizing the performance of the main filter.

[0028] Furthermore, as in the second embodiment, shape-retaining means may be provided on the outside or inside of the main filter to further increase the pressure resistance of the exhaust gas purification filter so that it can withstand the pressure of compressed gas during backwashing.

[0029] (Fourth aspect) The aforementioned main filter consists of multiple layers, The exhaust purifying filter of the first embodiment, wherein the fiber diameter of the metal fibers in the layer located on the outside of the exhaust purifying filter is greater than the fiber diameter of the layer located on the inside of the exhaust purifying filter.

[0030] (Effects and Benefits) When the metal fiber diameter of the layer located outside the main filter is large, compared to when the metal fiber diameter of the layer located outside the main filter is small, it becomes easier to blow away radioactive dust and other particles trapped in the voids of the layer located outside the main filter during backwashing. Therefore, there is the advantage of increased cleaning efficiency during backwashing.

[0031] (Fifth aspect) An exhaust purification system equipped with an exhaust purification filter that removes radioactive dust from exhaust containing radioactive dust generated in a work area, The exhaust purification filter is cylindrical in shape, and as the exhaust passes from the outside to the inside of the exhaust purification filter, radioactive dust in the exhaust is captured by the exhaust purification filter, and the purified exhaust is discharged outside the exhaust purification filter after passing through the cylinder of the exhaust purification filter. The exhaust purification filter has a main filter, The main filter includes a sheet of metal fiber, The exhaust purification filter is washable. During the cleaning of the exhaust gas purification filter, the compressed air injected into the cylinder of the exhaust gas purification filter passes from the inside to the outside of the filter, and in this process, the radioactive dust captured by the exhaust gas purification filter is blown to the outside of the filter. An exhaust gas purification device characterized by the following features.

[0032] (Effects and Benefits) According to the fifth embodiment described above, the same effects and advantages as those of the first embodiment described above are achieved.

[0033] (Sixth aspect) The exhaust gas purification device is The exhaust purification filter has an injection unit that injects compressed air into the cylinder, The injection unit has an injection nozzle, The exhaust gas purification device according to the fifth embodiment, wherein the axial direction of the injection nozzle is the same as the axial direction of the exhaust gas purification filter.

[0034] (Effects and Benefits) By aligning the axis of the spray nozzle with the axis of the exhaust purification filter (the height direction of the cylinder), the gas sprayed from the nozzle reaches the inside of the exhaust purification filter with almost no loss of force, resulting in a higher cleaning effect for the exhaust purification filter. This provides a higher cleaning effect (the effect of brushing off radioactive dust adhering to the outer surface of the exhaust purification filter) compared to when the axis of the spray nozzle is perpendicular to the axis of the exhaust purification filter.

[0035] (Seventh aspect) The exhaust gas purification device is The interior space is divided into multiple smaller spaces by partition walls, The exhaust purification filter has an injection unit that injects compressed air into the cylinder, The exhaust purifying filters are each placed in one of the multiple small spaces formed by the partition wall. The aforementioned partition wall is The exhaust gas purification device of the fifth embodiment, wherein the compressed gas injected from the injection unit to the exhaust gas purification filter located inside some of the small spaces is prevented from directly colliding with the exhaust gas purification filter located inside other adjacent small spaces.

[0036] (Effects and Benefits) In the seventh embodiment, a partition wall is provided within the exhaust gas purification device. This partition wall prevents compressed gas injected from the injection unit into exhaust gas purification filters located in some small spaces from directly colliding with exhaust gas purification filters located in adjacent small spaces. As a result, it is possible to prevent compressed gas used to backwash exhaust gas purification filters located in some small spaces from colliding with exhaust gas purification filters located in other small spaces, thereby preventing adverse effects on the exhaust gas purification treatment by those filters.

[0037] (Eighth aspect) The exhaust gas purification device is provided with a mounting plate. It has an enclosure that supports the exhaust purification filter, The housing has an upper plate portion to which the exhaust purification filter is fixed, a front plate portion, a rear plate portion spaced apart from the front plate portion, and a side plate portion connecting the sides of the front plate portion and the rear plate portion, and the upper edge of the front plate portion, the upper edge of the rear plate portion, and the upper edge of the side plate portion are each connected to the upper plate portion, forming a box shape with an open bottom. The exhaust gas purification device of the fifth embodiment, wherein the housing is fixed to the mounting plate.

[0038] (Effects and Benefits) During the backwashing stage, the pressure of the injected compressed gas blows the radioactive dust adhering to the outer surface of the exhaust purification filter outwards. However, because the enclosure is present, much of the blown-out radioactive dust scatters within the inner wall of the enclosure and falls to the ground. Therefore, the radioactive dust accumulated at the bottom of the exhaust scrubbing device can be easily recovered.

[0039] (Ninth aspect) The internal space of the aforementioned enclosure is When the shape is that of a truncated cone, and the circumference formed by the lower edge of the front plate, the lower edge of the rear plate, and the lower edge of the side plate is defined as the circumference of the lower surface of the truncated cone, and the circumference of the upper plate is defined as the circumference of the upper surface of the truncated cone, An exhaust gas purification device according to the eighth embodiment, wherein the perimeter formed by the lower edge of the front plate, the lower edge of the rear plate, and the lower edge of the side plate is longer than the perimeter of the upper plate.

[0040] (Effects and Benefits) If the internal space of the enclosure has the aforementioned shape, radioactive dust is less likely to adhere to the inner wall of the enclosure and will fall off easily, making recovery easier and contributing to long-term operation.

[0041] (Tenth aspect) The housing supporting the exhaust purification filter has a cartridge-type structure and is fixed to the mounting plate so as to be attachable and detachable. The aforementioned housing is designed to be removable from the casing of the exhaust gas purification device.

[0042] (Effects and Benefits) Because the exhaust gas purification filter has a cartridge-type structure, dust captured by the exhaust gas purification filter accumulates inside the filter, and when the pressure loss of the exhaust gas purification filter increases, it can be replaced.

[0043] (The eleventh aspect) An exhaust purification system equipped with an exhaust purification filter that removes radioactive dust from exhaust containing radioactive dust generated in the work area, The system includes a residual dust removal device that removes radioactive dust remaining in the purified exhaust gas discharged from the exhaust gas purification device, The exhaust purification filter is cylindrical in shape, and as the exhaust passes from the outside to the inside of the exhaust purification filter, radioactive dust in the exhaust is captured by the exhaust purification filter, and the purified exhaust is discharged outside the exhaust purification filter after passing through the cylinder of the exhaust purification filter. The exhaust purification filter has a main filter, The main filter includes a sheet of metal fiber, The exhaust purification filter is washable. During the cleaning of the exhaust purification filter, the compressed air injected into the cylinder of the exhaust purification filter passes from the inside to the outside of the exhaust purification filter, and in this process, the radioactive dust captured by the exhaust purification filter is blown to the outside of the exhaust purification filter. The aforementioned dust removal device is The purified exhaust gas has a residual dust removal filter that has a particle collection efficiency of 99.97% or more for dust particles with a particle size of 0.3 μm remaining in the purified exhaust gas. A radioactive dust removal system characterized by the following.

[0044] (Effects and Benefits) The radioactive dust removal system of the twelfth embodiment has the same effects as the first embodiment.

[0045] Furthermore, by using a residual dust removal filter that has a particle collection efficiency of 99.97% or more for dust particles with a diameter of 0.3 μm remaining in the purified exhaust, there is the advantage that radioactive dust is almost completely eliminated from the purified exhaust after it passes through the residual dust removal filter.

[0046] Furthermore, by installing an exhaust purification filter before the residual dust removal filter, and capturing most of the radioactive dust present in the exhaust gas with this filter, the frequency of replacing the residual dust removal filter can be reduced. As a result, the costs associated with replacing and disposing of the residual dust removal filter can be reduced.

[0047] Furthermore, it is preferable not to return the purified exhaust gas discharged from the exhaust purification filter to the work area. If the purified exhaust gas is returned to the work area, there is a risk that machinery in the work area may malfunction or workers working in the work area may be exposed to radiation from radioactive dust remaining in the returned purified exhaust gas. By not returning the purified exhaust gas to the work area, such problems can be prevented. However, since the purified exhaust gas that has passed through the residual dust removal filter is clean air and contains almost no radioactive dust, it is acceptable to return the purified exhaust gas to the work area. [Effects of the Invention]

[0048] According to the present invention, it is possible to provide an exhaust gas purification filter that removes radioactive dust from exhaust gas containing radioactive dust generated in a work area, and which is less susceptible to deterioration due to radiation from the radioactive dust. [Brief explanation of the drawing]

[0049] [Figure 1] This is a schematic diagram showing the radioactive dust removal system according to the present invention. [Figure 2]This is a magnified view of the exhaust purification filter of a radioactive dust removal system, showing the filter in the filtration process. [Figure 3] This is a magnified view of the exhaust purification filter of a radioactive dust removal system, showing it in the process of being cleaned. [Figure 4] This is a cross-sectional view AA in Figure 2. [Figure 5] Figure 4 is an enlarged view of the X portion of the exhaust purification filter. [Figure 6] This is a perspective view illustrating the upper seal portion. [Figure 7] This is a perspective view illustrating the lower seal portion. [Figure 8] This is an illustrative diagram showing an example of a main filter consisting of multiple metal fibers with air gaps between them. [Figure 9] This is a cross-sectional view showing an example of lamination of a metal fiber sheet and a metal mesh sheet. [Figure 10] This is a cross-sectional view showing another example of lamination of a sheet of metal fibers and a metal mesh sheet. [Figure 11] This is a side view of an exhaust gas purification system, showing a small space formed by a partition wall. [Figure 12] Figure 11 is a cross-sectional view of BB. [Figure 13] This is a cross-sectional view of BB similar to Figure 12, which shows another embodiment. [Figure 14] This is a schematic front view of an exhaust gas purification device equipped with a cartridge-type housing that supports an exhaust gas purification filter. [Figure 15] This diagram shows the enclosure fixed to the mounting plate. [Figure 16] This is a cross-sectional view of XX in Figure 15. [Figure 17] Figure 15 is a cross-sectional view of the YY direction. [Figure 18] This is a cross-sectional view of XX in Figure 15. [Figure 19] Figure 15 is a cross-sectional view of the YY direction. [Figure 20]This is a schematic side view of an exhaust gas purification device equipped with a cartridge-type housing that supports an exhaust gas purification filter. [Figure 21] This is a schematic diagram showing how the enclosure is attached to the mounting plate.

[0050] Preferred embodiments of the present invention will be described below with reference to the drawings. However, the following description and drawings merely illustrate one embodiment of the present invention, and the content of the present invention should not be interpreted as being limited to this embodiment.

[0051] (Radioactive dust removal system 1) Figure 1 shows an example of a radioactive dust removal system 1. This removal system 1 includes an exhaust gas purification device 3 that removes radioactive dust from exhaust gases (EH) containing radioactive dust generated in the work area 2, and a residual dust removal device 4 that removes any remaining radioactive dust from the purified exhaust gases (PEH) discharged from the exhaust gas purification device 3.

[0052] (Work Area 2) Work area 2 refers to a location where radioactive dust is present, such as a place where decommissioning work is carried out at a nuclear power plant, or a room for cutting and reducing the volume of radioactive metals. As shown in Figure 1, it is preferable to install an exhaust hood 6 in a location in work area 2 where there is a large amount of radioactive dust, and it is preferable to actively suck up the radioactive dust generated during demolition work carried out in work area 2 using this exhaust hood 6. By creating negative pressure within work area 2 through such suction, it is possible to prevent radioactive dust from being released to the outside from unintended locations. Suction from the exhaust hood 6 can be performed, for example, by a suction fan 5 installed downstream.

[0053] (Exhaust purifying device 3) Exhaust gas EH discharged from the work area 2 is supplied to the exhaust gas purification device 3 through the exhaust vent pipe L1. An exhaust gas purification filter 7 is housed inside the exhaust gas purification device 3. As shown in Figures 2 to 5, this exhaust gas purification filter 7 is formed in a cylindrical shape. Figures 2 to 5 illustrate an exhaust gas purification filter 7 with a perfectly circular cross-section, but it is not limited to this example, and any shape such as an elliptical, square, or hexagonal cross-section may be used. The configuration of the exhaust gas purification filter 7 is not particularly limited, but it is preferable to use a sheet of metal fibers (referred to as a metal fiber sheet, which constitutes the main filter 14 described later) made by gathering multiple metal fibers into a sheet, and sandwiching the top and bottom surfaces of the metal fiber sheet with metal mesh members (referred to as metal mesh members, which constitute the shape-retaining means 15 described later). As for the metal fibers of the metal fiber sheet, stainless steel fibers, tungsten steel fibers, aluminum fibers, nickel fibers, titanium fibers, etc. can be used. Of these metal fibers, stainless steel fibers (i.e., stainless steel fibers) are most preferable, and in the following explanation, a stainless steel fiber sheet using stainless steel fibers as the metal fiber will be used as an example. In other words, in the following explanation, "stainless steel fiber sheet" can be read as "metal fiber sheet."

[0054] An embodiment of the stainless steel fiber sheet is shown below. Note that the metal fiber sheet is not limited to a stainless steel fiber sheet, but may also include tungsten steel fibers, aluminum fibers, nickel fibers, or titanium fibers. The stainless steel fiber sheet may also be made by bending a single long stainless steel fiber many times to form a sheet. A conceptual diagram of the stainless steel fiber sheet is shown in Figure 8. The diameter (fiber diameter) of the stainless steel fiber is preferably about 2 to 4 μm, and the fiber diameter should be selected based on the particle size distribution of the generated dust and the radiation intensity of the dust. Furthermore, in order to increase the removal rate of radioactive dust in the exhaust gas (EH), the porosity of the stainless steel fiber sheet is preferably 65 to 80%. The performance of the exhaust gas purification filter 7 is preferably such that it has a particle collection efficiency of 90% or more for dust particles with a particle size of 0.3 μm or larger remaining in the exhaust gas (EH).

[0055] As described above, by using stainless steel fibers as the material for the exhaust gas purification filter 7, it is possible to make it resistant to degradation from radiation emitted from radioactive dust, thus reducing the frequency of filter replacement. In particular, it is excellent at capturing high-dose radioactive dust generated during decommissioning work at nuclear power plants. Furthermore, even if the exhaust gas (EH) from the decommissioning environment area contains sharp fine particles, there is little risk of the filter being damaged by these particles, which also reduces the frequency of filter replacement. In addition, it is possible to prevent the exhaust gas purification filter 7 from burning and causing a fire.

[0056] The exhaust gas purification filter 7 may simply be a flat stainless steel fiber sheet formed into a cylindrical shape, but to increase the filtration area, it is preferable to use a flat stainless steel fiber sheet that has been folded into a bellows shape and then formed into a cylindrical shape, as shown in Figure 5. Also, as shown in Figure 5, it is most preferable for the exhaust gas purification filter 7 to have shape-retaining means 15 to protect the main filter 14 on both sides (front and back) of the main filter 14, but it is also acceptable to have the shape-retaining means 15 on one side (front or back) of the main filter 14. By providing this shape-retaining means 15, the exhaust gas purification filter 7 can be maintained in the aforementioned bellows shape. That is, since the stainless steel fiber sheet constituting the main filter 14 has low morphological stability, it is difficult to maintain the bellows shape without the mesh sheet constituting the shape-retaining means 15, but by providing the shape-retaining means 15, the morphological stability of the exhaust gas purification filter 7 is increased and the bellows shape can be maintained. In addition, by providing the shape-retaining means 15, the strength of the exhaust gas purification filter 7 is increased, making it easier to withstand the pressure of compressed gas applied to the main filter 14 when cleaning it.

[0057] To allow the exhaust gas EH to reach the main filter 14, the shape-retaining means 15 is preferably made of a mesh sheet. If the gaps in the mesh of the shape-retaining means 15 are small, the exhaust gas filtration rate per unit time will decrease, and the risk of clogging of the shape-retaining means 15 will increase. Therefore, it is preferable that the size of the gaps in the mesh of the shape-retaining means 15 be larger than the size of the gaps in the main filter 14. Furthermore, it is preferable to use a material for the shape-retaining means 15 that does not easily deteriorate even when exposed to radiation emitted from radioactive dust, and specifically, stainless steel is preferred.

[0058] Figures 9 and 10 show examples of lamination of the main filter 14 and shape-retaining means 15 that constitute the exhaust gas purification filter 7. In Figures 9 and 10, the front side and top side refer to the outside (the side with the container 28 of the exhaust gas purification device 3) when the exhaust gas purification filter 7 is attached to the exhaust gas purification device 3, and the back side and bottom side refer to the inside (the side with the inner cylinder 8) when the exhaust gas purification filter 7 is attached to the exhaust gas purification device 3. Since the main filter 14 includes a metal fiber sheet and the shape-retaining means 15 includes a metal mesh member, the exhaust gas purification filter 7 can also be described as a laminate of a metal fiber sheet and a metal mesh member. The main filter 14 may also include materials other than metal fiber sheets, and the shape-retaining means 15 may also include materials other than metal mesh members. It is preferable to use a metal fiber sheet (especially a stainless steel fiber sheet) as the main material of the main filter 14, and it is preferable to use a metal mesh member as the main material of the shape-retaining means 15. The main filter 14 may be composed only of metal fiber sheets, and the shape-retaining means 15 may be composed only of metal mesh members. Furthermore, in Figures 9 and 10, the thickness of each layer constituting the exhaust purification filter 7 is exaggerated and shown as thicker for ease of understanding, but the actual thickness of each layer is not limited to these thicknesses.

[0059] In Figure 9, the main filter 14 has a three-layer structure in which the shape-retaining means 15 is laminated on the front side US (outside) and also on the back side DS (inside) of the main filter 14. From the viewpoint of protecting the main filter 14 and forming the main filter 14 into a bellows shape and maintaining that bellows shape, it is most preferable to provide the shape-retaining means 15 on both sides of the main filter 14 (front side US and back side DS) as shown in Figure 9, but it is also acceptable to provide the shape-retaining means 15 on only one side of the main filter 14 (front side US or back side DS). If it is not necessary to protect the main filter 14 and it is not necessary to form the main filter 14 into a bellows shape, the shape-retaining means 15 may not be provided at all. If the thickness of the shape-retaining means 15 is thin, the function of protecting the main filter 14 may be reduced, and if the thickness of the shape-retaining means 15 is thick, the airflow resistance may increase and the exhaust gas purification treatment amount per unit time may decrease. On the other hand, if the thickness of the main filter 14 is thin, it may not be able to adequately remove radioactive dust from the exhaust gas EH, and if the thickness of the main filter 14 is thick, the airflow resistance may increase, and the exhaust gas purification treatment rate per unit time may decrease. The thickness of the front shape-retaining means 15U and the back shape-retaining means 15B may be the same, or they may be different.

[0060] The basic structure of the exhaust purification filter 7 shown in Figure 10 is the same as in Figure 9, but the main filter 14 has a three-layer structure consisting of an upper main filter 14U, an intermediate main filter 14M, and a lower main filter 14D. When using such a three-layer structure, it is preferable that the diameter of the stainless steel fibers in the upper main filter 14U be 6 to 10 μm, the diameter of the stainless steel fibers in the intermediate main filter 14M be 2 to 4 μm, and the diameter of the stainless steel fibers in the lower main filter 14D be 6 to 10 μm.

[0061] When the main filter 14 has such a layered structure, the metal fibers of the intermediate layer main filter 14M, which have a small fiber diameter, are most effective at removing radioactive dust and the like. However, they have the disadvantage of being weak due to their small fiber diameter. Therefore, by providing an upper layer main filter 14U and a lower layer main filter 14D, which are made of metal fibers with a larger fiber diameter than the metal fibers of the intermediate layer main filter 14M, the weakness of the fibers of the intermediate layer main filter 14M can be compensated for by the strength of the fibers of the upper layer main filter 14U and the lower layer main filter 14D. As a result, compared to the case where the main filter 14 is a single layer (assuming the metal fibers constituting this single layer have the same fiber diameter of 2-4 μm as the metal fibers of the intermediate layer main filter 14M), the strength of the main filter 14 can be increased, the shape stability of the main filter 14 can be improved, and the exhaust purification filter 7 can withstand the pressure (pressure due to compressed gas) applied to it during backwashing. In particular, during backwashing, the most compressed gas pressure is applied to the back of the main filter 14. By increasing the pressure resistance of the lower main filter 14D, damage to the main filter 14 by the compressed gas PA can be prevented.

[0062] Furthermore, if the metal fiber diameter of the upper main filter 14U located outside the main filter 14 is large, it becomes easier to blow away radioactive dust and other particles trapped in the voids of the upper main filter 14U during backwashing, compared to when the metal fiber diameter of the upper main filter 14U located outside the main filter 14 is small. This also has the advantage of improving the cleaning effect during backwashing.

[0063] Furthermore, although Figure 10 shows an example where the main filter 14 has a three-layer structure, it may also have a structure with four or more layers. When using a structure with four or more layers, from the viewpoint of protecting the layers of metal fibers with small fiber diameters, it is preferable to make the fiber diameter of the stainless steel fibers smaller as you approach the center of the thickness direction TD of the main filter 14.

[0064] Furthermore, it is preferable that the porosity of the single-layer main filter 14, and the porosity of each layer when the main filter 14 has multiple layers, be 65-80%. This porosity can be determined from the following equations 1 and 2.

[0065] [Equation 1] P(%) = Basis weight of the main filter layer (g / m 2 ) / Specific gravity of the metal fibers constituting the main filter layer × T (thickness of the main filter layer (cm)) [Formula 2] Porosity (%)=100-P(%)

[0066] In Equation 1, the specific gravity of the metal fiber is 798, for example, if the metal fiber is stainless steel (SUS316L). Also, in Equation 1, "layer of the main filter" refers to the single layer if the main filter consists of a single layer. If the main filter consists of multiple layers and you want to find the porosity of each layer of the main filter, you can use the basis weight, metal fiber, and thickness of each layer of the main filter, respectively. If the main filter consists of multiple layers and you want to find the porosity of the entire main filter in a stacked state, you can use the basis weight, metal fiber, and thickness of the entire main filter, respectively.

[0067] Furthermore, when manufacturing the main filter 14, which consists of multiple layers, it is preferable to uniformly laminate the metal fibers that will be used as raw materials and then sinter (compress and fix) the laminated material.

[0068] Furthermore, it is preferable to provide a cylindrical inner cylinder 8 inside the exhaust purification filter 7. As this inner cylinder 8, a perforated sheet with multiple openings of a predetermined size formed into a cylinder can be used. The cross-sectional shape of this inner cylinder 8 is not particularly limited, and any shape such as a perfect circle as shown in Figure 4, an ellipse, square, or hexagon may be used.

[0069] As shown in Figure 5, when the exhaust purification filter 7 is made into a bellows shape, peaks 7X and valleys 7Y are created. As shown in Figures 4 and 5, when the shape of the exhaust purification filter 7 is made into a cylindrical shape by being bellows, the imaginary line IL connecting the multiple valleys 7Y of the exhaust purification filter 7 becomes circular in cross-sectional shape. It is preferable to make the shape of the inner cylinder 8 the same as this imaginary line IL (circular), so that the back surfaces of the multiple valleys 7Y of the exhaust purification filter 7 and the surface of the inner cylinder 8 are in contact, and it is even more preferable that the back surfaces of all the valleys 7Y of the exhaust purification filter 7 and the surface of the inner cylinder 8 are in contact. By pre-contacting the multiple valleys 7Y, 7Y and the inner cylinder 8, it is possible to avoid the exhaust purification filter 7 and the inner cylinder 8 colliding each time exhaust EH passes through the exhaust purification filter 7, thereby extending the life of the exhaust purification filter 7.

[0070] As shown in Figures 3 and 4, the upper and lower ends of the exhaust purification filter 7 and the upper and lower ends of the inner cylinder 8 are sealed, respectively, preventing exhaust gas containing radioactive dust from bypassing the exhaust purification filter 7 and entering the purified exhaust passage 13. The sealed portion of the exhaust purification filter 7 and the inner cylinder 8 is called the seal portion 9, and in the embodiments shown in Figures 3 and 4, there is an upper seal portion 9A that seals the upper end of the exhaust purification filter 7 and the upper end of the inner cylinder 8, and a lower seal portion 9B that seals the lower end of the exhaust purification filter 7 and the lower end of the inner cylinder 8.

[0071] As shown in Figure 6, the upper seal portion 9A is formed by fixing the upper end of the exhaust purifying filter 7 and the upper end of the inner cylinder 8 to an annular ring 20 fixed to the edge of the through hole 19 (a hole approximately the same size as the inner diameter of the inner cylinder 8) of the flange portion 7Z. Specifically, the cross-section of the annular ring 20 fixed to the flange portion 7Z has a U-shaped groove with an opening at the bottom. After inserting the upper end of the exhaust purifying filter 7 and the upper end of the inner cylinder 8 into this groove, adhesive is filled into the groove to fix the upper end of the exhaust purifying filter 7 and the upper end of the inner cylinder 8 to the annular ring. In this way, the upper end of the exhaust purifying filter 7 is integrated with the flange portion 7Z. Similarly, as shown in Figure 7, the lower seal portion 9B is formed by fixing a disc 21 to the lower end of the exhaust purifying filter 7 and the lower end of the inner cylinder 8. Specifically, the disc 21 has an upright wall 22 that rises upward from its peripheral edge, and the cross-section of the upright wall 22 has a U-shaped groove 23 with an opening at the top. The lower ends of the exhaust purifying filter 7 and the inner cylinder 8 are inserted into this groove 23, and then adhesive is filled into the groove 23 to fix the lower ends of the exhaust purifying filter 7 and the inner cylinder 8 to the disc 21. Also, in order to improve visibility, the exhaust purifying filter 7 and the inner cylinder 8 are shown as a single unit in Figures 6 and 7, but in reality they are made up of separate components.

[0072] The exhaust gas purification device 3 of the present invention has a casing 50 that houses an exhaust gas purification filter 7, and the inside of the casing 50 is divided into a pre-purification chamber and a post-purification chamber, and the pre-purification chamber and the post-purification chamber are separated by a mounting plate 10 provided on the casing 50 and the exhaust gas purification filter 7. The mounting plate 10 is provided with a through hole of the same shape as the through hole 19 of the flange portion 7Z, and the through hole 19 of the flange portion 7Z and the through hole of the mounting plate 10 face each other, and the flange portion 7Z is fixed in contact with the mounting plate 10 or via a gasket. 、An exhaust supply port 16 is provided on the wall of the pre-purification chamber side of the casing 50 for exhaust EH to flow into the casing 50, and a purified exhaust outlet 18 is provided on the wall of the post-purification chamber side of the casing 50 for purified exhaust PEH to flow out of the casing 50. The exhaust EH is configured to flow from the outside to the inside of the cylindrical exhaust purification filter 7. As the exhaust EH passes through the exhaust purification filter 7 from the outside to the inside, radioactive dust and other particles in the exhaust EH are captured by the exhaust purification filter 7. The purified exhaust PEH, which has been purified by passing through the exhaust purification filter 7, passes through the opening of the inner cylinder 8 from the outside to the inside and reaches the purified exhaust passage 13. Then, in the embodiment shown in Figure 2, the purified exhaust PEH moves from the bottom to the top of the purified exhaust passage 13, passing through the hole in the annular ring 20 of the upper seal portion 9A, the through hole 19 of the flange portion 7Z, and the through hole in the mounting plate 10, and reaches the top of the exhaust purification device 3. The exhaust gas is then discharged from the exhaust purification device 3 and sent through the purified exhaust vent pipe L2 to the dust removal device 4.

[0073] On the other hand, as the exhaust gas (EH) passes through the exhaust gas purification filter 7 from the outside to the inside, foreign matter such as radioactive dust captured by the exhaust gas purification filter 7 accumulates on the outer surface of the filter 7. If this layer of foreign matter such as radioactive dust accumulated on the outer surface becomes thick, the efficiency of the exhaust gas purification treatment will decrease, so it is preferable to backwash the exhaust gas purification filter 7 at a predetermined timing.

[0074] For example, as shown in Figure 3, compressed gas PA (e.g., compressed air) is injected into the exhaust purification filter 7 from an injection nozzle 11 located above the exhaust purification filter 7. The compressed gas PA injected from the injection nozzle 11 moves downward and enters the inside of the exhaust purification filter 7 (purified exhaust passage 13), then flows in the opposite direction to that shown in Figure 2. That is, after passing through the opening of the inner cylinder 8 from the inside to the outside, it passes through the exhaust purification filter 7 from the inside to the outside. As the compressed gas PA passes through the exhaust purification filter 7 in this way, the layer of foreign matter (foreign matter layer) such as radioactive dust that had accumulated on the outer surface of the exhaust purification filter 7 is peeled off and falls to the bottom of the exhaust purification device 3 and accumulates there. The accumulated material SD at the bottom of the exhaust purification device 3 is periodically discharged to the outside of the exhaust purification device 3.

[0075] As described above, by backwashing the exhaust gas purification filter 7 at a predetermined timing, the pressure loss and collection efficiency can be returned to near their initial values. This eliminates the need to discard the exhaust gas purification filter 7, thereby contributing to the effective use of global environmental resources and reducing the costs associated with replacing and disposing of the exhaust gas purification filter 7.

[0076] Furthermore, it is possible to perform backwashing while the exhaust gas (EH) is being purified by the exhaust gas purification filter 7, without stopping the purification process. This is because backwashing takes only a few seconds, so there is no need to stop the purification process. Also, since the clumps of radioactive dust and other foreign matter that detach from the exhaust gas purification filter 7 during backwashing have a certain amount of weight, even if the exhaust gas (EH) is flowing towards the exhaust gas purification filter 7, the flow of the exhaust gas (EH) will affect the likelihood of the clumps of radioactive dust and other foreign matter detached from the exhaust gas purification filter 7 reattaching to the filter 7. If it is necessary to reliably prevent the clumps of radioactive dust and other foreign matter detached from the exhaust gas purification filter 7 from reattaching to the filter 7, the purification process of the exhaust gas (EH) may be temporarily stopped, backwashing may be performed, and the purification process of the exhaust gas (EH) may be restarted after the backwashing is complete. However, if this process is performed, it will take some time to switch between the purification process and the washing (backwashing) process of the exhaust gas (EH), which has the disadvantage of slightly reducing the amount of purification process performed on the exhaust gas (EH).

[0077] Furthermore, as shown in the embodiments of Figures 11 and 12, it is preferable to provide multiple exhaust purification filters 7 inside the exhaust purification device 3, and to filter the exhaust gas EH with one exhaust purification filter 7 while the other exhaust purification filter 7 is being backwashed. For example, in the embodiments of Figures 11 and 12, partition walls 29 are provided to divide the internal space 26 of the exhaust purification device 3 into multiple small spaces, and an exhaust purification filter 7 is provided in each small space.

[0078] More specifically, as shown in Figure 11, the upper end of the partition wall 29 is fixed to the lower surface of the mounting plate 10 of the exhaust gas purification device 3, and the partition wall 29 extends downward from there, with the lower end of the partition wall 29 positioned near the lower end of the exhaust gas purification filter 7. In order to prevent the compressed gas PA during backwashing from directly colliding with the exhaust gas purification filter 7 located in other small spaces 27, it is preferable to position the lower end of the partition wall 29 near the lower end of the exhaust gas purification filter 7. Also, as shown in Figure 12, this partition wall 29 is installed to partition the space between adjacent exhaust gas purification filters 7. As shown in Figure 12, it is preferable that the partition wall 29 does not come into contact with the inner wall of the container 28 of the exhaust gas purification device 3, and that a predetermined gap is provided between the inner wall of the container 28 and the partition wall 29. Similarly, as shown in Figure 11, it is preferable that the partition wall 29 does not extend further down than the lower end of the exhaust gas purification filter 7, and that a predetermined gap is provided below the partition wall 29. In the exhaust gas purification process, this is to facilitate the passage of exhaust gas EH into the container 28 of the exhaust gas purification device 3 through the aforementioned gaps into the small spaces 27A and 27B.

[0079] The partition wall 29 installed in this manner divides the internal space 26 of the exhaust gas purification device 3 into two almost equal parts, forming a first small space 27A and a second small space 27B. The first small space 27A is provided with a first exhaust gas purification filter 7A, and the second small space 27B is provided with a second exhaust gas purification filter 7B.

[0080] By partitioning the internal space 26 of the exhaust gas purification device 3 with the partition wall 29 in this way, it is possible to prevent compressed gas PA injected from the injection unit (nozzle 11) into the exhaust gas purification filter 7 located in one of the small spaces 27, from directly colliding with the exhaust gas purification filter 7 located in the adjacent small space 27. As a result, the compressed gas PA used when backwashing the exhaust gas purification filter 7 located in one of the small spaces 27 is less likely to affect the exhaust gas purification filters 7 located in the other small spaces 27. In other words, when purifying exhaust gas EH using the exhaust gas purification filters 7 located in the other small spaces 27 while some of the exhaust gas purification filters 7 located in the small spaces 27 are being backwashed, the compressed gas PA is less likely to adversely affect the exhaust gas purification filters 7 that are being purified. Therefore, even while some of the exhaust gas purification filters 7 are being washed, the exhaust gas purification process can be carried out as usual using the other exhaust gas purification filters 7, which has the advantage of not reducing the efficiency of the exhaust gas purification process in the entire exhaust gas purification device 3.

[0081] The embodiments shown in Figures 11 and 12 illustrate a state in which exhaust gas purification is being performed by the first exhaust gas purification filter 7A located in the first small space 27A while the second exhaust gas purification filter 7B located in the second small space 27B is being backwashed. Of course, the opposite may also be true, where the exhaust gas purification is performed by the second exhaust gas purification filter 7B while the first exhaust gas purification filter 7A is being backwashed.

[0082] Furthermore, although Figures 11 and 12 show an example in which only one partition wall 29 is provided, multiple partition walls 29 may be provided. For example, as shown in Figure 13, by providing partition walls 29 in a cross shape in the internal space 26 of the exhaust gas purification device 3, four small spaces 27, from the first small space 27A to the fourth small space 27D, may be formed, and the first exhaust gas purification filter 7A to the fourth exhaust gas purification filter 7D may be placed in each of the small spaces 27A to 27D, respectively.

[0083] (Residual dust removal device 4) The residual dust removal device 4 has a residual dust removal filter that removes radioactive dust remaining in the purified exhaust gas PEH. Preferably, this residual dust removal filter has a particle collection efficiency of 99.97% or more for dust particles with a particle size of 0.3 μm remaining in the purified exhaust gas PEH.

[0084] Specifically, as the dust removal filter, for example, a HEPA filter (an air filter with a particle collection efficiency of 99.97% or more for particles with a diameter of 0.3 μm at the rated airflow rate, and an initial pressure loss of 245 Pa or less) or a ULPA filter (an air filter with a particle collection efficiency of 99.9995% or more for particles with a diameter of 0.15 μm at the rated airflow rate, and an initial pressure loss of 245 Pa or less) can be used.

[0085] If a dust removal filter is used that does not have a particle collection efficiency of 99.97% or more for dust particles with a particle size of 0.3 μm in the purified exhaust gas (PEH), there is a problem that a large amount of radioactive dust may be mixed into the purified exhaust gas (PEH) discharged from the dust removal device 4.

[0086] (Another form of filter 7) The following embodiment is also preferred as the exhaust gas purification device 3 according to the present invention. Specifically, the exhaust gas purification device 3 is provided with a mounting plate 110 and has a housing 34 that supports the exhaust gas purification filter 7. The housing 34 has an upper plate portion 34u to which the exhaust gas purification filter 7 is fixed, a front plate portion 34f, a rear plate portion 34b spaced apart from the front plate portion 34f, and side plate portions 34s, 34s ​​(for example, the side plate portions consist of two plates and are spaced apart from each other) that connect the sides of the front plate portion 34f and the rear plate portion 34b. The upper edge of the front plate portion 34f, the upper edge of the rear plate portion 34b, and the upper edges of the side plate portions 34s, 34s ​​are each connected to the upper plate portion 34u, forming a box shape with an open bottom. In this embodiment, the housing 34 is fixed to the mounting plate 110. In the exhaust gas purification device 3 to which the housing 34 is fixed, exhaust gas EH flows into the exhaust gas purification device 3 from the exhaust gas supply port 16 provided in the casing 50 of the exhaust gas purification device 3, enters the internal space 39 of the housing 34 from below, passes through the exhaust gas purification filter 7, becomes purified exhaust gas PEH, and is discharged outside the exhaust gas purification device 3 from the purified exhaust gas discharge port 18. The housing 34 is fixed to a mounting plate 110 provided in the casing 50, and the inside of the casing 50 is divided into a pre-purification chamber and a post-purification chamber by this mounting plate 110 and the exhaust gas purification filter 7. The exhaust gas EH goes from the pre-purification chamber through the exhaust gas purification filter 7 to the post-purification chamber, but there is no other flow path from the pre-purification chamber to the post-purification chamber. The internal space 39 of the housing 34 refers to the box-shaped interior enclosed by the upper plate portion 34u, front plate portion 34f, rear plate portion 34b and side plate portions 34s, 34s ​​that constitute the housing 34.

[0087] The shape of the front plate portion 34f, rear plate portion 34b, and side plate portions 34s, 34s ​​that form the housing 34, and the surface facing the internal space 39, may be curved or flat, but when the internal space 39 is a truncated cone as described below, it is preferable that it be flat.

[0088] Furthermore, the exhaust gas purification filter 7 can be fixed to the upper plate portion 34u of the housing 34 in the following manner: A flange portion is provided at the upper end of the exhaust gas purification filter 7, and this flange portion is fixed to the periphery of the through hole in the upper plate portion 34u. The flange portion of the exhaust gas purification filter 7 and the upper plate portion 34u of the housing 34 should be sealed by fixing them with adhesive or welding to prevent gas from passing through.

[0089] The number of exhaust purification filters 7 supported by the housing 34 can be adjusted as appropriate according to the volume of the work area where the exhaust purification device 3 is installed, the amount of airborne dust, etc., and is not particularly limited.

[0090] As shown in Figures 16 to 19, the shape of the internal space 39 formed by the components constituting the housing 34 may be a rectangular parallelepiped, but it may also be a truncated cone as shown below. For example, the internal space 39 of the housing 34 has the shape of a truncated cone, and the perimeter formed by the lower edge of the front plate portion 34f, the lower edge of the rear plate portion 34b, and the lower edges of the side plate portions 34s, 34s ​​(for example, the perimeter of a roughly square) is defined as the perimeter of the lower surface of the truncated cone, and the perimeter of the upper plate portion 34u is defined as the perimeter of the upper surface of the truncated cone. In this configuration (for example, a square pyramid), the perimeter formed by the lower edge of the front plate portion 34f, the lower edge of the rear plate portion 34b, and the lower edges of the side plate portions 34s, 34s ​​is longer than the perimeter of the upper plate portion (for example, the perimeter of a roughly square), which is preferable. In this configuration, the front plate portion 34f, the rear plate portion 34b, and the side plate portions 34s, 34s, each surface facing the internal space 39 (the surface facing the internal space 39) is arranged at an angle to the vertical line. Therefore, radioactive dust is less likely to adhere to the surface facing the internal space 39, and even if it does adhere, it is easily detached in the subsequent flow of radioactive dust. Thus, it is possible to prevent the housing 34 from being contaminated with high concentrations of radioactive dust.

[0091] In the case where the upper plate side of the internal space 39 of the housing 34 becomes the upper surface of the truncated cone, and the lower edge side of the internal space 39 becomes the lower surface of the truncated cone, the acute angle θ formed by the normal Lf5 extending from the surface of the front plate portion 34f constituting the internal space 39 facing the internal space 39 (i.e., the inner surface 34f1 of the front plate portion 34f) and the vertical line L6 intersecting the normal Lf5 is, for example, preferably less than 90° and 80° or more, more preferably 87° or less and 85° or more, and particularly preferably 87°. Similarly, the acute angle θ formed by the normal Lb5 extending from the inner surface 34b1 of the rear plate portion 34b and the vertical line L6 intersecting the normal Lf5 is, for example, preferably less than 90° and 80° or more, more preferably 87° or less and 85° or more, and particularly preferably 87°. Similarly, the acute angle θ formed by the normal Ls15 extending from the inner surface 34s1 of the first side plate portion 34s and the vertical line L6 intersecting the normal Ls15 is, for example, preferably less than 90° and 80° or more, more preferably 87° or less and 85° or more, and particularly preferably 87°. Similarly, the acute angle θ formed by the normal Ls25 extending from the inner surface 34s2 of the second side plate portion 34s and the vertical line L6 intersecting the normal Ls25 is, for example, preferably less than 90° and 80° or more, more preferably 87° or less and 85° or more, and particularly preferably 87°.

[0092] The truncated pyramid may be a frustum of a cone, a frustum of a polygon, or a frustum of a square, but a frustum of a square is particularly preferred considering the ease of attaching and detaching the housing 34.

[0093] The material of the housing 34 is not particularly limited, but metal is preferred, for example, stainless steel, tungsten, aluminum, nickel, and titanium, with stainless steel being particularly preferred. If the material is metal, it is preferable because it has strength resistance and radiation resistance.

[0094] The housing 34, which supports the exhaust gas purification filter 7, has a cartridge-type structure and can be fixed to the mounting plate 110 of the exhaust gas purification device 3 in a manner that allows for attachment and removal. If the exhaust gas purification device 3 is operated and decommissioning work is carried out continuously, even if the exhaust gas purification device 3 is backwashed periodically, radioactive materials may gradually adhere to the exhaust gas purification filter 7 or the exhaust gas purification filter 7 may become clogged. In this case, the exhaust gas purification filter 7 will need to be replaced, but if the housing 34 has a cartridge-type structure and is removable, workers can simply replace the entire housing during the replacement work, which improves work efficiency and reduces exposure to radioactive materials.

[0095] Referring to Figures 15 and 21, the housing 34 can be provided with a housing-side receiving portion 41 that extends upward from, for example, the upper plate portion 34u, so that the housing 34 can be fixed to the mounting plate 110. The form of the housing-side receiving portion 41 is not particularly limited, but a preferred form is a rectangular tube formed by connecting a member that extends further upward from the upper end of the front plate portion 34f of the housing 34, a member that extends further upward from the upper end of the rear plate portion 34b, and members that extend further upward from the upper ends of the side plate portions 34s, 34s.

[0096] On the other hand, the lower surface of the mounting plate 110 is provided with a plate-side receiving portion 110a that is substantially the same shape as the housing-side receiving portion 41 and faces the housing-side receiving portion 41 (if the housing-side receiving portion 41 is rectangular, the plate-side receiving portion 110a may also be cylindrical). The housing-side receiving portion 41 and the plate-side receiving portion 110a form a pair and are detachably fixed with the upper edge of the housing-side receiving portion 41 and the lower edge of the plate-side receiving portion 110a in contact. In addition, a gasket 33 may be interposed between the housing-side receiving portion 41 and the plate-side receiving portion 110a to improve airtightness. In this case, the gasket 33 should be provided at the lower edge of the plate-side receiving portion 110a.

[0097] A through-hole 110b is provided in the portion of the mounting plate 110 surrounded by the plate-side receiving portion 110a. This through-hole 110b is provided so that the purified exhaust gas PEH, which has flowed from the internal space of the housing 34 through the exhaust purification filter 7 into the purified exhaust passage 13, flows into the space above the mounting plate 110.

[0098] On the other hand, a lower support member 36 is provided below the housing 34 to support the housing 34 so that the housing-side support portion 41 and the plate-side support portion 110a remain in contact with each other. The lower support member 36 is also movable up and down, and its height is adjustable, allowing for adjustment of the height of the housing 34 placed on the lower support member 36. The height of the lower support member 36 can be adjusted by a height adjustment means 37 connected to the lower support member 36. The height adjustment means 37 is not particularly limited as long as it can adjust the height of the lower support member 36, but examples include an eccentric cam mechanism or a jack mechanism such as a floor jack or pantograph jack. The height adjustment means 37 only needs to be provided on the casing 50.

[0099] When attaching the housing 34 to the mounting plate 110, the housing 34 is placed on the lower support member 36, and the lower support member 36 is moved upward until the housing-side receiving portion 41 contacts the plate-side receiving portion 110a. On the other hand, when removing the housing 34 from the mounting plate 110, the lower support member 36 is moved downward.

[0100] The housing-side receiving portion 41 and the plate-side receiving portion 110a form a pair, and it is desirable that both have the same shape in order to maintain airtightness. However, as shown in Figures 18 and 19, because the shape of the internal space 39 of the housing 34 is a truncated cone, the circumference of the upper plate portion 34u of the housing 34 may be shorter than the circumference of the plate-side receiving portion 110a. In this case, it is preferable to extend the entire edge of the upper plate portion 34u radially so that the edge of the upper plate portion 34u protrudes outward from the upper edge of the front plate portion 34f, the upper edge of the rear plate portion 34b, and the upper edges of the side plate portions 34s, 34s, and then provide the housing-side receiving portion 41 on the outer surface of the extended upper plate portion 34u. Of course, the degree of expansion of the upper plate portion 34u does not need to be more than enough to allow the housing-side receiving portion 41 to be provided on the outer surface of the upper plate portion 34u.

[0101] The used housing 34, removed from the mounting plate 110, should be taken out of the casing 50 of the exhaust gas purification device 3. A new housing 34 should then be placed inside the casing 50 and attached to the mounting plate 110 before the exhaust gas purification device 3 can be restarted.

[0102] The wall of the casing 50 on the side of the pre-purification chamber is provided with an opening 35 for inserting and removing the housing 34, and a door 38 for closing the opening 35. The door 38 is closed while the exhaust gas purification device 3 is in operation.

[0103] A bag 31 for storing the used housing 34 removed from the casing 50 is provided at the opening 35. The opening of the bag 31 is continuous with the opening 35, so that the inside of the casing 50 and the inside of the bag 31 are sealed as a single space, and the atmosphere inside the casing 50 does not leak out of the bag 31. The process of removing the housing 34 with the used exhaust purification filter 7 fixed to it from the casing 50 and the process of inserting the housing 34 with the new exhaust purification filter 7 fixed to it into the casing 50 is preferably performed using a so-called bag-in / bag-out method, as this prevents workers from being exposed to radiation.

[0104] Preferred embodiments of the present invention are described below.

[0105] (Note 1) An exhaust purification system equipped with an exhaust purification filter that removes radioactive dust from exhaust containing radioactive dust generated in a work area, The exhaust purification filter is cylindrical in shape, and as the exhaust passes from the outside to the inside of the exhaust purification filter, radioactive dust in the exhaust is captured by the exhaust purification filter, and the purified exhaust is discharged outside the exhaust purification filter after passing through the cylinder of the exhaust purification filter. The exhaust gas purification device is provided with a mounting plate. It has an enclosure that supports the exhaust purification filter, The housing has an upper plate portion to which the exhaust purification filter is fixed, a front plate portion, a rear plate portion spaced apart from the front plate portion, and a side plate portion connecting the sides of the front plate portion and the rear plate portion, and the upper edge of the front plate portion, the upper edge of the rear plate portion, and the upper edge of the side plate portion are each connected to the upper plate portion, forming a box shape with an open bottom. The housing is fixed to the mounting plate. An exhaust gas purification device characterized by the following features.

[0106] (Note 2) The internal space of the aforementioned enclosure is When the shape is that of a truncated cone, and the circumference formed by the lower edge of the front plate, the lower edge of the rear plate, and the lower edge of the side plate is defined as the circumference of the lower surface of the truncated cone, and the circumference of the upper plate is defined as the circumference of the upper surface of the truncated cone, The perimeter formed by the lower edge of the front plate, the lower edge of the rear plate, and the lower edge of the side plate is longer than the perimeter of the top plate. Exhaust gas purification device as described in Appendix 1.

[0107] (Note 3) The housing supporting the exhaust purification filter has a cartridge-type structure and is fixed to the mounting plate so as to be attachable and detachable. The aforementioned housing is designed to be removable from the casing of the exhaust gas purification device. Exhaust gas purification device as described in Appendix 1. [Explanation of symbols]

[0108] 1: Radioactive dust removal system, 2: Work area, 3: Exhaust purification device, 4: Residual dust removal device, 5: Suction fan, 6: Exhaust hood, 7: Exhaust purification filter, 7A: First exhaust purification filter, 7B: Second exhaust purification filter, 7C: Third exhaust purification filter, 7D: Fourth exhaust purification filter, 7X: Peak section, 7Y: Valley section, 7Z: Flange section, 8: Inner cylinder, 9: Seal section, 9A: Upper seal section, 9B: Lower seal section, 10: Mounting plate, 11: Injection nozzle, 12: Compressed gas supply pipe, 13: Purified exhaust passage, 14: Me In-filter, 14U: Surface main filter (upper main filter), 14M: Intermediate main filter, 14D: Back main filter (lower main filter), 15: Shape retention means, 15U: Front shape retention means (upper shape retention means), 15D: Back shape retention means (lower shape retention means), 16: Exhaust supply port, 17: Metal fiber, 18: Purified exhaust outlet, 19: Through hole, 20: Annular ring, 21: Disc, 22: Upright wall, 23: Groove, 24: Sediment outlet, 25: Residual dust removal filter, 26: Internal space, 27: Small space, 27A: First small space, 27B: Second small space, 27C: Third small space, 27D: Fourth small space, 28: Exhaust purifying device container, 29: Partition wall, 31: Bag, 33: Gasket, 34: Housing, 34u: Top plate of housing, 34f: Front plate of housing, 34f1: Inner surface of front plate of housing, 34b: Rear plate of housing, 34b1: Inner surface of side plate of housing, 34s: Side plate of housing, 34s1, 34s2: Inner surface of side plate of housing, 35: Opening, 36: Lower support member, 37: Height adjustment means, 38: Door, 39: Housing Internal space, 40: through hole, 41: housing side support part, 50: casing, 110: mounting plate, 110a: plate side support part, 110b: through hole, IL: virtual line, EH: exhaust, Lf5: (virtual) normal extending from the inner surface of the front plate, inner surface of the rear plate, Lb5: (virtual) normal extending from the inner surface of the rear plate, Ls15, Ls25: (virtual) normals extending from the inner surfaces of the side plates 34s, 34s ​​respectively, L6: vertical line, PEH: purified exhaust, PA: compressed gas, SD: sediment, US: front side (upper side), DS: back side (lower side), TD: thickness direction

Claims

[Claim 1] An exhaust purification system comprising multiple exhaust purification filters and backwashing means for removing radioactive dust from exhaust containing radioactive dust generated in a work area, It has a casing with an exhaust supply port and a purified exhaust outlet, The mounting plate fixed inside the casing divides the area below the mounting plate into a purification pre-chamber having the exhaust supply port, and the area above the mounting plate into a purification post-chamber having the purification exhaust outlet. The exhaust purification filter has an opening at the top and is cylindrical with a bottom. The exhaust purifying filters are fixed to the mounting plate in a vertical and parallel arrangement, and the inside of the exhaust purifying filters communicates with through holes provided in the mounting plate. The exhaust gas flows into the pre-purification chamber from the exhaust supply port of the casing, and as it passes through the filter surface of the exhaust gas purification filter from the outside to the inside, radioactive dust in the exhaust gas is captured by the exhaust gas purification filter, and the purified exhaust gas passes through the inside of the exhaust gas purification filter and the through-hole, and is discharged to the outside of the casing from the purified exhaust gas outlet through the post-purification chamber. Each of the exhaust gas purification filters is provided with an injection unit in the post-purification chamber that constitutes the backwashing means for injecting compressed gas. The compressed gas injected from the injection unit enters the interior of the exhaust purification filter from the upper end and passes through the filter surface from the inside to the outside. A partition wall is provided between adjacent exhaust purifying filters, its upper end fixed to the mounting plate, and both ends and the lower end of the partition wall have gaps between them and the wall of the casing, so that the pre-purification chamber is partitioned by the partition wall into a small space containing the exhaust purifying filter. The aforementioned partition wall is such that the compressed gas injected during backwashing passes through the filter surface of the exhaust purification filter and does not collide with the adjacent exhaust purification filter. An exhaust gas purification device characterized by the following features.

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