JPH0477604B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a filter device and method with a filter plug for filtering hot gases emanating from a waste incinerator.

[Conventional technology and problems]

The nuclear industry generates large amounts of waste that is contaminated to the point that precautions must be taken to prevent its use in other industries.

In particular, very slightly contaminated high tonnage equipment and materials cannot be transported and dumped. Among the products mentioned above are rags, plastic parts, filters, paper and work pants.

It has long been considered to incinerate all of these organic products in order to limit storage without disseminating radioactivity.

Incineration produces hot gases, smoke, dust and ash.

Some of the radioactive contamination remains in the ash, but most of it escapes into the solid matter and is carried away by the hot gases.

For particles larger than 0.3 microns, a 99.99% efficiency filter is required before being released into the atmosphere. The first pass on hot gas (reaching a temperature of 750°C) should preferably have an efficiency of over 97%.

French Patent No. 1,498,522 describes a method for passing hot gases using porous filter plugs containing inorganic fibers (applied by spraying).

The above patent specification also does not indicate anything about the nature of the porous or fibrous material. However, it is mentioned that the filter substrate is placed inside a perforated tube. Dedusting this tube in an active environment is difficult due to its length and small diameter.

French Patent No. 2,397,703 describes a filter plug made of ceramic which acts as support and filler material. If that plug gets clogged, you'll have to replace it altogether. If the plug is damaged (especially by a thermal shock), it must be replaced altogether. Therefore, both the plug (in whole or in pieces) and the dust deposited on it must be stored as active waste.

[Summary of the invention]

In the present invention, the filter plug is constructed of a perforated metal tube to support the overfill material. The overfill material consists of a finely divided powder that is simply deposited on the surface of the metal tube.

The present invention uses a rolled and welded (or bonded) perforated sheet metal or a sintered metal tube as the perforated metal tube.

The invention also includes a method for removing debris contained in hot gases, particularly those generated from the combustion of radioactively contaminated materials.

In this method, a refractory oxide powder is deposited on the support of a filter plug and the gas to be purified is passed through said filter plug while still at a temperature of about 300-400°C.

〔Example〕

Hereinafter, the present invention will be specifically explained with reference to illustrated embodiments. FIG. 2 is a schematic diagram showing an incinerator in which a filter device is used. In the figure, reference numeral 1 denotes a charging shaft (furnace chest) of an incinerator, in which there is an inclined grid 2 on which incinerated waste is placed. grid 2
Pipe 4 below provides air for both combustion and grid cooling. Ash is collected in Ash Box 3.

The upper part of the grid 2 constitutes a combustion chamber surrounded by a refractory brick wall 5. Immediately adjacent to the combustion chamber is a post-combustion chamber 7 which communicates at the top and is filled with a refractory mixture 8. From the bottom of this post-combustion chamber 7, a pipe 9 (cooled if necessary) feeds gas into the overchamber 11. The chamber 11 is partitioned off to prevent leakage by a horizontal partition wall 12 provided with a hole into which a filter plug 13 is fixed.
The pipe 9 is inserted from above the partition wall 12 as shown at 101 or from above the partition wall 12 as shown at 102.
It opens into the overchamber from below.

The chamber 11 has a series of horizontal fingers 14 or vertical fingers 15.

Electric heating elements are arranged on these fingers. Figures 5 and 6 are partial cross-sectional views showing details of these heating fingers.

The filtered gas leaves the filter chamber 11 through the top pipe 17 or the bottom pipe 16.

These pipes correspond to each other as follows. When gas enters from the upper pipe 101, it passes through the filter plug 13 and exits from the bottom pipe 16, and when gas enters from the bottom pipe 102, it passes through the filter plug 13 and exits from the rear top pipe 17.
Go out more.

Pipes 101, 102, 16 and 17 have valve 1
8 is provided to blow air into the chamber 11 and to blow air into the chamber 11.
It is now possible to reduce the internal pressure.

The chamber 11 also has a flap 19 for emptying the ash box 103 and an upper observation flap 104.
There is.

To simplify the illustration, only two filter plugs 13, two horizontal fingers 14 and one vertical finger 15 are shown in FIG. The actual device includes
There are at least six filter plugs and four fingers.

FIG. 1 shows the filter plug in detail. 21 is a cylindrical metal core with a flange 2 at one end.
3 and a bottom 22 at the other end. The diameter of the hole in the horizontal partition wall 12 of FIG. 2 is sized such that the metal core 21 can easily slide into the hole and the flange 23 can hold the filter plug in place. Flange 23 is preferably made from a solid piece of metal having sufficient weight to hold filter plug 13 in place.

Fine powder 24 or 25 is applied to the outside or inside of the filter plug, respectively.

This powder is preferably deposited on the inside when the gas circulation direction is from pipes 101 to 16 and on the outside when it is from pipes 102 to 17.

3 and 4 are sectional views showing details of examples of the flange shape of the filter plug. In FIG. 3, the flange 31 rests on a horizontal partition wall 32 (corresponding to 12 in FIG. 2), and the hole in the partition wall 32 has a rim 33 for guiding the plug.
(rim) is provided.

For clarity, the gap between the rim and the metal core 34 has been exaggerated.

Another example of the flange is shown in FIG. This example:
In order to improve the airtightness between the partition wall 43 (corresponding to 12 in FIG. 2) and the flange 41, the hole is provided with an upwardly directed rim 44, which is inserted into the groove 42 cut in the flange 41. .

As before, the outer diameter of the core 45 is sized such that the filter plug can be inserted with a slight clearance into the hole having the rim 44 at its periphery.

FIG. 5 shows a vertical finger, such as finger 15 of FIG.

This figure at the same time shows the side walls of the overchamber more clearly. This wall is double layered, with thick fireproof metal plates 50 (vertical wall) and 58 (bottom plate) on the inside.
Consists of. A suitable material for this purpose is a heat-resistant steel such as NS30. The outside of the above wall is fiber
It consists of a fiber insulation 55 such as Frax (manufactured by Carbon Random Company) and a thin metal plate 57.

The bottom is not double walled.

The fingers consist of a sheath disposed between the wall 50 and the insulator 55. A flange 54 provides an airtight seal to the bottom 58 (joints not shown).

The electric heating element 53 placed inside the finger-shaped part is connected to a power source (not shown) whose voltage is regulated by an electric wire 52.
connected to.

The sheaths of these fingers are made of glassy silica,
Alumina or sintered carbon random (silicon carbide)
It is best to make it from fireproof material such as.

FIG. 6 is a horizontal sectional view showing the horizontal fingers and the structure around them. A metal tube 64 with one end closed is welded to the inner wall of the heat-resistant steel 61. This tube 64 is
It passes through the fiber insulation 62 and the outer metal plate 63 and is fixed to the outer metal plate 63 by a flange 65 .

This figure shows the fingers passing between the filter plugs 66.

The electric heating element 68 arranged inside the tube 64 is connected to the electric wire 69
is connected to an external power source (not shown). In this case, it is preferable to assemble the heating part so that it is located inside the chamber 61.

After the assembly procedure described above, the filter plug is placed in place. That is, the metal core is placed into a hole in the horizontal partition wall.

In the first case the overfill is outside the metal core and the overchamber is provided with pipes 102 and 17.

A large amount of alumina powder (if it is desired to make an alumina overfill material) is put in through the flap 19, the pressure is reduced through the pipe 17, and at the same time air is blown into the alumina through the pipe 102 to make the alumina float in the air.

Due to the effect of reduced pressure, the particles adhere to the outside of the metal core. The suction in the pores that are not yet covered is strong and particles are attracted to these pores, so that a self-regulating effect takes place. Once all the alumina has been deposited, the air blow is stopped and all filter plugs are over-primed. It is best to choose powders with small particle sizes to facilitate particle suspension.

Particles smaller than 125 microns are preferred.

In the second case the filter is inside the filter plug and the pipes 101 and 16 are provided in the filter chamber.

The powder and air are mixed and blown in through the flap 104, the flap is closed, and air is blown in through the pipe 101 and sucked through the pipe 16.

As in the previous case, a continuous layer is formed in the side body of the plug, particularly without holes or passages.

Powder used as an overfill material tends to absorb more moisture than air (or combustion gas) at room temperature, and
Alternatively, tests have shown that if the temperature is kept at 400°C, the internal atmosphere will be completely dry and the overcoat will maintain its permeability, so the overchamber will have a finger-shaped section into which an electric heating element will be inserted. Otherwise, the powder will get into the water and harden like glue, greatly reducing its transmittance.

Also, maintaining this temperature provides a very important effect. That is, no condensation of water (which contains many corrosive substances) occurs indoors. This means that the lifetime of this device is almost infinite.

When incinerated plastics contain chlorine or fluorine, especially polyvinyl chloride and polytetrafluoroethylene, the difference in corrosion is significant.

To maintain the equipment in good condition, the overchamber is kept hot permanently, even when the incinerator is closed.

Next, an example of the structure of the metal core will be described.

Example 1 The first material has dimensions of 900mm x 150mm and a thickness of
It is a 0.4 mm stretched metal sheet of Inconel (trade name) 601. The diamond-shaped hole measures approximately 0.5 x 2.5 mm.

This metal sheet is rolled to form a tube with a diameter of 42 mm, which is closed and joined by means of welding spots. The bottom is secured to one end of this tube and the flange is welded to the other end.

Example 2 The starting material is a metal tube obtained by sintering Inconel 601 powder with particles smaller than 50 microns. The final pipe dimensions are 5mm thick, 860mm long,
The diameter is 45mm. As before, weld the flange to this and attach the bottom.

Inconel 601 may be replaced by various heat-resistant, corrosion-resistant metals or alloys, especially Hastelloy or tantalum.

The metal core of the expanded sheet metal only supports the overfill and does not act to stop the particles. Using alumina powder with particles smaller than 25 microns will stop 98% of particles larger than 0.3 microns. It is clear that it is not the 0.5 x 2.5 mm holes in the wrought metal sheet that are overactive. In contrast, sintered metal cores have certain overfunctions.

The particle size of the alumina powder is preferably 0.025
mm~0.125mm.

After a certain operating time, the overfill becomes clogged and must be replaced.

In the first case, if there is powder outside the filter plug, the valve 18 in the passage 102 is closed and a strong pressure is temporarily applied through the passage 17, causing the powder to drop to the bottom 103 and be collected.

It will be seen that the upper part of the partition wall 12 is completely protected, although the area below where the dirty gas reaches will remain dirty powder.

Second case: If there is powder inside the filter plug, the powder is sucked out of the plug using an air suction machine through the inlet 104. Air is sucked in through the pipe 16 to assist in this action.

For example, when diluting superheated gas with cold air,
If the gas flow is very fast, it is advantageous to operate with the powder inside. If not,
It is easier to use if the powder is on the outside. In particular, it is easy to take out the powder.

Any refractory oxide may be used as long as it is not attacked by hot gases, which often contain chlorine or fluorine, such as alumina or zirconia. Also convenient are silicates or aluminosilicates such as mullite or talc. Furthermore, the above-mentioned components can also be mixed to form a surfill material.

〔Effect of the invention〕

As explained above, according to the present invention, it is not necessary to take out the entire filter plug to replace the filter material, and therefore, there is an advantage that only the dirt attached to the plug needs to be stored as active waste.
In addition, by keeping the inside of the chamber at 300 to 400℃,
It is possible to prevent a decrease in the permeability of the filter material and to suppress corrosion due to water condensation.

[Brief explanation of the drawing]

Figure 1 is a front view showing an example of a filter plug used in the present invention, Figure 2 is a schematic diagram showing how the filter plug shown in Figure 1 is used, and Figures 3 and 4 are examples of different flanges of the filter plug. FIGS. 5 and 6 are partial sectional views showing different examples of heating fingers. 21...metal core, 24, 25...excess material.

Claims (1)

[Scope of Claims] 1. A hot gas filter device for filtering hot gas emanating from an incinerator by passing it through at least one filter plug consisting of a core with pores and a non-agglomerated filter medium. , The core is a metal tube made by winding and welding a stretched sheet metal perforated to have a plurality of holes with an average particle size of 0.5 to 2.5 mm, and the filter medium has an average particle size of 0.025 mm and 0.125 mm.
A filter device for hot gas, characterized in that the powder is made of a powder of a refractory material, and the powder is adhered as is on the core. 2. The hot gas filter device according to claim 1, wherein the filter material is selected from alumina, zirconia, aluminosilicate, or a mixture of at least two of these. . 3. A hot gas filter method for filtering hot gas generated by incinerating equipment and materials contaminated with radioactivity, comprising a filter plug comprising a core with holes and a non-agglomerated filter material, The above core has average dimensions
A metal tube made of rolled and welded rolled sheet metal perforated with a plurality of holes of 0.5 to 2.5 mm, the filter medium being a fire-resistant material with an average particle size between 0.025 mm and 0.125 mm. providing a filter plug comprising a powder of, the powder being in situ deposited on the core; passing the hot gas through at least one of the filter plugs; A filter method for hot gas, characterized in that the hot gas is filtered at a temperature of 300 to 400 degrees. 4. The hot gas filter method according to claim 3, wherein the filter material is selected from alumina, zirconia, aluminosilicate, or a mixture of at least two of these. .