Exhaust treatment device

Abstract

To provide an exhaust treatment device capable of eliminating an adverse influence caused by gas to be treated.SOLUTION: An exhaust treatment device 1 comprises a gas treatment reactor 10 comprising a flow channel forming wall 12, and a double pipe structure 20. The double pipe structure 20 comprises an inner cylinder 21 into which at least a part of the flow channel forming wall 12 is inserted, and an outer cylinder 22 disposed outside the inner cylinder 21.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an exhaust gas treatment device.

Background Art

[0002] Vacuum pump devices are widely used as one of the manufacturing facilities for semiconductors, liquid crystals, solar panels, LEDs, etc. In these manufacturing processes, etc., a vacuum pump is connected to a vacuum chamber, and the processing gas introduced into the vacuum chamber is evacuated by the vacuum pump.

[0003] The gas evacuated by the vacuum pump may contain harmful flammable gases such as silane gas (SiH4), dichlorosilane gas (SiH2Cl2), ammonia (NH3), or halogen-based refractory gases such as NF3, ClF3, SF6, CHF3, C2F6, CF4, etc. Therefore, such gases cannot be directly released into the atmosphere.

[0004] In a vacuum pump device, a decontamination device (an example of an exhaust gas treatment device) for detoxifying the evacuated gas is provided downstream of the vacuum pump. As gas detoxification treatments, a wet method in which the processing gas is brought into contact with a liquid to remove foreign substances and water-soluble components, etc., and a combustion method in which the processing gas is burned are known.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] Patent Document 1 discloses a structure for forming a swirling spiral water film on the inner wall surface of a cylindrical body. The exhaust gas treatment apparatus of Patent Document 1 forms a water film to insulate the inner wall surface of the cylindrical body and washes away products and corrosive gases to prevent damage to the inner wall surface of the cylindrical body.

[0007] However, when a substance that reacts with water to form a solid (for example, dichlorosilane) is contained in the treatment gas, if the solid adheres to the gas-liquid interface (that is, the portion wetted by the incomplete water film around the water supply nozzle for forming the water film), the solid may grow and block the combustion chamber. The treatment gas may contain a halogen gas that forms acidic water when dissolved in water. In this case, the gas-liquid interface made of a metal such as stainless steel may be exposed to the treatment gas, and the gas-liquid interface may be corroded in a short period of time.

[0008] Patent Document 2 discloses a structure for forming a swirling spiral water film on the inner wall surface of a cylindrical body surrounding a combustion treatment chamber. The exhaust gas treatment apparatus of Patent Document 2 prevents the treatment gas from coming into contact with the gas-liquid interface by replacing the upper end portion of the water film and its surrounding atmosphere with a purge gas.

[0009] However, if the swirling flow of the treatment gas in the combustion treatment chamber is strong, the water of the water film may be splashed, and there is a risk that solids may be generated by the reaction between the splashed water and the treatment gas. If the flow rate of the purge gas is small, there is a risk that the treatment gas and water react at the gas-liquid interface and solids are generated. Conversely, if the flow rate of the purge gas is too large, the water of the water film may be splashed, and there is a risk that solids may be generated by the reaction between the splashed water and the treatment gas.

[0010] Therefore, an object of the present invention is to provide an exhaust gas treatment apparatus capable of eliminating the adverse effects of the treatment gas.

Means for Solving the Problems

[0011] In one aspect, an exhaust gas treatment apparatus is provided that includes a gas treatment reactor having a flow path forming wall that forms a flow path for a introduced treatment gas, and a double pipe structure that surrounds the gas treatment reactor. The double pipe structure includes an inner cylinder into which at least a part of the flow path forming wall is inserted, and an outer cylinder disposed outside the inner cylinder.

[0012] In one aspect, the exhaust gas treatment apparatus includes a liquid film forming device that forms a liquid film on the inner cylinder. The liquid film forming device is configured to supply a liquid to an outer gap between the outer cylinder and the inner cylinder, and form a liquid film on an inner wall surface of the inner cylinder by the liquid that overflows the inner cylinder. In one aspect, the liquid film forming device includes a liquid supply line connected to a liquid supply port formed in the outer cylinder, and a liquid supply source that supplies the liquid to the outer gap through the liquid supply line. In one aspect, the exhaust gas treatment apparatus includes a purge gas introduction device that introduces a purge gas into an inner gap between the inner cylinder and the flow path forming wall. The purge gas introduction device is configured to introduce the purge gas from above the inner cylinder.

[0013] In one aspect, the purge gas introduction device includes a gas introduction line connected to a gas introduction port disposed above the inner cylinder, and a gas introduction source that introduces the purge gas into the inner gap through the gas introduction line. In one aspect, a lower end of the flow path forming wall is disposed at a position lower than an end of the inner cylinder. In one aspect, the lower end of the flow path forming wall is disposed at a position 10 mm or more lower than an end of the inner cylinder.

[0014] In one aspect, the exhaust gas treatment apparatus includes a plate that extends from the outer cylinder toward the flow path forming wall and is disposed above the inner cylinder. In one aspect, the plate has a protrusion that extends from an inner end portion thereof toward an end portion of the inner cylinder. In one aspect, the plate is made of a material having corrosion resistance.

[0015] In one aspect, each of the outer cylinder and the inner cylinder is made of resin or stainless steel.

Advantages of the Invention

[0016] Since the exhaust gas treatment device has a structure in which at least a part of the flow path forming wall of the gas treatment reactor is inserted into the inner cylinder, the treatment gas passing through the flow path forming wall does not come into contact with the gas-liquid interface outside the flow path forming wall. Therefore, the exhaust gas treatment device can prevent adverse effects of the treatment gas, for example, damage to the gas-liquid interface caused by adhesion of the treatment gas to the gas-liquid interface.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

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Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings described below, the same or corresponding components are denoted by the same reference numerals and redundant descriptions are omitted. In the plurality of embodiments described below, the configuration of one embodiment that is not particularly described is the same as that of other embodiments, so the redundant description thereof is omitted.

[0019] FIG. 1 is a diagram showing an embodiment of an exhaust gas treatment apparatus. The exhaust gas treatment apparatus 1 is provided for detoxifying the gas (treatment gas) from a vacuum pump. A vacuum pump (not shown) is connected to the primary side (upstream side) of the exhaust gas treatment apparatus 1.

[0020] As shown in FIG. 1, the exhaust gas treatment apparatus 1 includes a gas treatment reactor 10 that subjects the treatment gas to a heat treatment reaction, and a double-tube structure 20 that surrounds the gas treatment reactor 10. The gas treatment reactor 10 includes an introduction pipe 11 for introducing the treatment gas, a flow path forming wall 12 that is connected to the introduction pipe 11 and forms a flow path for the introduced treatment gas, and a cover member 13 that closes the open end of the double-tube structure 20.

[0021] The treatment gas (i.e., combustion gas) burned by the fuel gas is introduced into the gas treatment reactor 10 through the inlet 11a of the introduction pipe 11 and flows through the double-tube structure 20 as a swirling flow. In the embodiment shown in FIG. 1, a flame burner is employed as the heat source applied to the exhaust gas treatment apparatus 1. However, in one embodiment, a plasma generator or an electric heater may be employed as the heat source.

[0022] The double-tube structure 20 includes an inner cylinder 21 into which at least a part of the flow path forming wall 12 is inserted, and an outer cylinder 22 disposed outside the inner cylinder 21. These inner cylinder 21 and outer cylinder 22 are arranged concentrically with the gas treatment reactor 10.

[0023] The treatment gas (i.e., combustion gas) flowing as a swirling flow along the flow path forming wall 12 passes through the gas flow path 15 formed inside the inner cylinder 21, is treated by a liquid tank casing (not shown) and a treatment casing (not shown), and then discharged to the outside. Here, the liquid tank casing is configured to store a liquid and reuse the stored liquid for the treatment of the exhaust gas treatment apparatus 1. The treatment casing is connected to the liquid tank casing and is configured to further exclude and discharge the treatment gas flowing in from the liquid tank casing.

[0024] As shown in Fig. 1, when the flow path forming wall 12 of the gas treatment reactor 10 is inserted into the inner cylinder 21 of the double pipe structure 20, the lower end 12a of the flow path forming wall 12 is disposed at a position lower than the end (upper end) 21a of the inner cylinder 21. Preferably, the lower end 12a of the flow path forming wall 12 is disposed at a position 10 mm or more and 100 mm or less lower than the end 21a of the inner cylinder 21.

[0025] In the embodiment shown in Fig. 1, both the flow path forming wall 12 and the inner cylinder 21 have a cylindrical shape. Therefore, when the flow path forming wall 12 is inserted into the inner cylinder 21, an annular gap (i.e., the inner gap) SP1 is formed between the outer wall surface of the flow path forming wall 12 and the inner wall surface of the inner cylinder 21. The inner gap SP1 is disposed outside the flow path forming wall 12 as a flow path for the treatment gas, and is a region not affected by the high-temperature treatment gas flowing through the flow path forming wall 12 as a swirling flow.

[0026] The exhaust gas treatment apparatus 1 includes a liquid film forming apparatus 30 that forms a liquid film on the inner cylinder 21. The liquid film forming apparatus 30 is configured to supply a liquid to the outer gap SP2 between the outer cylinder 22 and the inner cylinder 21, and form a liquid film F on the inner wall surface of the inner cylinder 21 with the liquid that has overflowed the inner cylinder 21.

[0027] More specifically, the liquid film forming apparatus 30 includes a liquid supply line 32 connected to a liquid supply port 31 formed in the outer cylinder 22 and communicating with the outer gap SP2, and a liquid supply source 33 that supplies the liquid to the outer gap SP2 through the liquid supply line 32. The liquid film forming apparatus 30 may include an on-off valve 34 connected to the liquid supply line 32. In the embodiment shown in Fig. 1, a single liquid supply port 31 is formed, but the number of liquid supply ports 31 is not limited to this embodiment. A plurality of liquid supply ports 31 may be formed.

[0028] As shown in Fig. 1, the exhaust gas treatment apparatus 1 includes a plate 23 that extends from the inner wall surface of the outer cylinder 22 toward the flow path forming wall 12 and is disposed above the inner cylinder 21 (more specifically, above the end 21a of the inner cylinder 21). The plate 23 has an annular shape and is made of a material having corrosion resistance (for example, resin).

[0029] The plate 23 does not contact the flow path forming wall 12, and the inner end portion 23a of the plate 23 is spaced apart from the outer wall surface of the flow path forming wall 12. In the embodiment shown in FIG. 1, the plate 23 is connected to the inner wall surface of the outer cylinder 22, but may be connected to the cover member 13. The plate 23 is a return member for changing the flow direction of the liquid supplied to the outer gap SP2, and the liquid rising in the outer gap SP2 collides with the plate 23. The liquid that has collided with the plate 23 changes its direction and flows down the inner wall surface of the inner cylinder 21 to form a liquid film F.

[0030] As shown in FIG. 1, a gas-liquid interface GL is formed between the upper end portion of the liquid film F and the lower surface of the plate 23. The gas-liquid interface GL is a boundary portion where the liquid overflowing the outer gap SP2 contacts the plate 23, and the gas-liquid interface GL is a portion wetted by the incomplete liquid film F.

[0031] FIG. 2 is a diagram showing the flow of the liquid supplied to the outer gap. As shown in FIGS. 1 and 2, the liquid supplied from the liquid supply source 33 to the outer gap SP2 through the liquid supply port 31 flows in a tangential direction of the inner cylinder 21 and swirls in the outer gap SP2. The liquid swirling in the outer gap SP2 rises as a swirling flow and eventually contacts the lower surface of the plate 23. In order to prevent the liquid contacting the lower surface of the plate 23 from lifting the plate 23, the flow rate of the liquid supplied to the outer gap SP2 is adjusted.

[0032] Due to the contact with the plate 23, the liquid whose flow direction has been changed forms a spiral liquid film F on the inner wall surface of the inner cylinder 21. The liquid film F can prevent foreign substances such as reaction by-products formed by the processing gas from depositing on the inner cylinder 21. Further, since the entire inner wall surface of the inner cylinder 21 is covered with the liquid film F, the surface temperature of the inner wall surface of the inner cylinder 21 is kept relatively low. By keeping the temperature of the inner cylinder 21 low, each of the inner cylinder 21 and the outer cylinder 22 may be made of not only an inexpensive metal such as stainless steel, but also a resin (for example, polyvinyl chloride (PVC), polypropylene (PP), etc.) that is excellent in corrosion resistance and less expensive than stainless steel.

[0033] Figure 3 is a diagram showing the purge gas introduction device. As shown in FIGS. 1 and 3, the exhaust gas treatment device 1 includes a purge gas introduction device 40 that introduces purge gas into the inner gap SP1 between the inner cylinder 21 and the flow path forming wall 12. The purge gas introduction device 40 is configured to introduce purge gas from above the inner cylinder 21.

[0034] More specifically, the purge gas introduction device 40 includes a gas introduction line 42 connected to a gas inlet 41 disposed above the inner cylinder 21, and a gas introduction source 43 that introduces purge gas into the inner gap SP1 through the gas introduction line 42. The purge gas introduction device 40 may include an on-off valve 44 connected to the gas introduction line 42.

[0035] In the embodiment shown in FIG. 3, the gas inlet 41 is formed in the cover member 13 of the gas treatment reactor 10. However, it is not necessarily formed in the cover member 13 as long as the purge gas can be introduced toward the upper end portion and its peripheral portion of the liquid film F. In one embodiment, the gas inlet 41 may be formed in the outer cylinder 22.

[0036] Examples of the purge gas include air or nitrogen gas. In one embodiment, the most desirable purge gas can be selected in consideration of factors such as the performance and efficiency of the exhaust gas treatment device 1 according to the composition of the treatment gas.

[0037] In the embodiment shown in FIG. 3, a single gas inlet 41 is formed, but the number of gas inlets 41 is not limited to this embodiment. In one embodiment, a plurality of gas inlets 41 may be formed. As shown in FIG. 3, the gas inlet 41 is disposed at a position higher than the upper end portion of the liquid film F (more specifically, above the plate 23). The purge gas introduction device 40 introduces the purge gas into the inner gap SP1 through the gas introduction line 42 and the gas inlet 41 by driving the gas introduction source 43. The purge gas introduced into the inner gap SP1 flows into the gas flow path 15 through the inner gap SP1.

[0038] The purge gas introduction device 40 can more reliably prevent the treatment gas from coming into contact with the gas-liquid interface GL by replacing the atmosphere around the upper end portion of the liquid film F with the purge gas. Therefore, the purge gas introduction device 40 can prevent the generation of solids caused by the reaction between the treatment gas and the liquid around the gas-liquid interface GL.

[0039] The purge gas introduction device 40 can prevent the high-temperature treatment gas from diffusing around the gas-liquid interface GL by supplying the purge gas from above the plate 23. With such a configuration, as the material of the plate 23, a resin (for example, polyvinyl chloride (PVC), polypropylene (PP), etc.) that is significantly less expensive than a corrosion-resistant material such as Inconel or Hastelloy or a material with a PFA coating can be employed. Since the resin has high corrosion resistance, even if the liquid forming the liquid film F is acidic, maintenance of the exhaust gas treatment device 1 over a long period of time is unnecessary.

[0040] FIG. 4 is a diagram showing another embodiment of the exhaust gas treatment device. In the embodiment shown in FIG. 4, the exhaust gas treatment device 1 does not include the plate 23. By not arranging the plate 23, the liquid rising in the outer gap SP2 collides with the cover member 13. The liquid that has collided with the cover member 13 changes its direction and flows down the inner wall surface of the inner cylinder 21 to form the liquid film F. As shown in FIG. 4, a gas-liquid interface GL is formed between the upper end portion of the liquid film F and the lower surface of the cover member 13.

[0041] Also in this embodiment, the purge gas introduction device 40 can more reliably prevent the treatment gas from coming into contact with the gas-liquid interface GL by replacing the atmosphere around the upper end portion of the liquid film F with the purge gas.

[0042] According to the above-described embodiment, since the exhaust gas treatment device 1 has a structure in which at least a part of the flow path forming wall 12 is inserted into the inner cylinder 21, the processing gas passing through the flow path forming wall 12 does not contact the gas-liquid interface GL outside the flow path forming wall 12 (see FIG. 1). Therefore, the exhaust gas treatment device 1 can prevent damage to the gas-liquid interface GL caused by the adhesion of the processing gas to the gas-liquid interface GL.

[0043] Since the exhaust gas treatment device 1 has a structure in which the gas-liquid interface GL is disposed outside the flow path forming wall 12, it is possible to prevent the gas-liquid interface GL from being directly exposed to the swirling flow of the processing gas. Therefore, even if the processing gas swirls vigorously, the risk of liquid splashing from the gas-liquid interface GL and the liquid film F around it due to the processing gas can be reduced as compared with the conventional techniques (for example, Patent Document 1 and Patent Document 2).

[0044] In the conventional technique, due to the fall of the product adhering to the inner wall of the burner, the product adheres to the inner wall of the combustion treatment chamber, and as a result, the liquid film on the inner wall of the combustion treatment chamber may be interrupted. The portion where the liquid film is interrupted (gas-liquid interface) is exposed to the high-temperature combustion gas containing acidic components, and there is a risk of holes being formed in the inner wall in a short period of time due to pitting corrosion.

[0045] According to the present embodiment, even if a hole is formed in the inner cylinder 21, the outside of the inner cylinder 21 (that is, the outer gap SP2) is always filled with the liquid for the liquid film F. Therefore, even if a hole is formed in the inner cylinder 21, since the liquid flowing through the outer gap SP2 flows out from the hole formed in the inner cylinder 21, the risk of significant damage to the inner cylinder 21 is low. Further, even if the inner cylinder 21 is corroded by pitting corrosion, since the inside of the outer cylinder 22 is always filled with liquid, the risk of corrosion of the inner wall surface of the outer cylinder 22 is low. Thus, the exhaust gas treatment device 1 having the configuration according to the present embodiment has high safety against gas leakage and liquid leakage as compared with the conventional exhaust gas treatment device.

[0046] If, by any chance, the inner cylinder 21 is severely damaged, the liquid flowing through the outer gap SP2 will flow out from the damaged part into the gas flow path 15, thus inhibiting the rise of the liquid. As a result, the inner wall surface of the outer cylinder 22 will be exposed to the high-temperature processing gas, and the temperature of the outer cylinder 22 may rise rapidly. Therefore, the exhaust gas treatment device 1 may be provided with a temperature sensor for measuring the surface temperature of the outer cylinder 22. With such a configuration, the operator can always monitor the surface temperature of the outer cylinder 22 and grasp the abnormal state before serious failures such as gas leakage and liquid leakage occur.

[0047] In the conventional technology, in order to improve heat resistance and corrosion resistance, the combustion treatment chamber has a structure in which metals such as stainless steel are welded. However, it is known that the corrosion resistance of the welded part of the combustion treatment chamber decreases due to sensitization. Therefore, in the combustion treatment chamber exposed to acidic gas or acidic water, corrosion may progress from the welded part.

[0048] According to the present embodiment, the outer cylinder 22 having a welded part is disposed outside the gas treatment reactor 10 with the inner cylinder 21 interposed therebetween and is spaced apart from the gas treatment reactor 10. Therefore, the risk of corrosion of the welded part of the outer cylinder 22 due to sensitization can be significantly reduced.

[0049] FIG. 5 is a diagram showing another embodiment of the exhaust gas treatment device. In the embodiment shown in FIG. 5, the exhaust gas treatment device 1 includes a plate 23 having a protrusion 23b. More specifically, the plate 23 has a protrusion 23b extending from its inner end 23a toward the end 21a of the inner cylinder 21.

[0050] In the embodiment shown in FIG. 5, the downwardly extending protrusion 23b has an annular shape. The protrusion 23b prevents the liquid colliding with the plate 23 from lifting the plate 23. The liquid colliding with the plate 23 is restricted from lifting from the plate 23 by the protrusion 23b. Therefore, the flow direction of the liquid colliding with the plate 23 is determined downward by the protrusion 23b.

[0051] If the liquid that raises the outer gap SP2 lifts the plate 23, a liquid with an appropriate flow rate may not flow down the inner cylinder 21, and as a result, the liquid film F may not be appropriately formed. Therefore, in this case, it is necessary to accurately control the flow rate of the liquid so that the liquid film F is appropriately formed. According to the present embodiment, since the protrusion 23b can prevent the liquid from rising, the liquid film F can be surely formed without accurately controlling the flow rate of the liquid.

[0052] FIG. 6 is a diagram showing another embodiment of the exhaust gas treatment apparatus. In the embodiment shown in FIG. 6, the inner cylinder 21 has a shape bent at a right angle. More specifically, the inner cylinder 21 has a bent portion 21b and is bent inward at the bent portion 21b. In other words, the bent portion 21b is bent toward the flow path forming wall 12. With such a shape, the end portion 21a of the inner cylinder 21 faces the flow path forming wall 12.

[0053] As described above, the liquid whose flow direction has been changed by contact with the plate 23 forms a spiral liquid film F on the inner wall surface of the inner cylinder 21. Therefore, the spiral liquid film F surely flows down the inner cylinder 21 without peeling off even if the inner cylinder 21 has a right-angled shape.

[0054] FIG. 7 is a diagram showing another embodiment of the exhaust gas treatment apparatus. In the embodiment shown in FIG. 7, the inner cylinder 21 has a plurality of bent portions 21b and 21c. The inner cylinder 21 is bent inward (i.e., toward the flow path forming wall 12) at the bent portion 21b, and further bent perpendicular to the bent portion 21b (i.e., parallel to the flow path forming wall 12 (and the outer cylinder 22)) at the bent portion 21c. With such a shape, the end portion 21a of the inner cylinder 21 faces the plate 23, and the bent portion 21c faces the flow path forming wall 12.

[0055] In the embodiment shown in FIG. 7, by opposing the end portion 21a of the inner cylinder 21 to the plate 23, the inner cylinder 21 has a portion that extends parallel to the flow path forming wall 12 (and the outer cylinder 22) (that is, the portion between the end portion 21a and the bent portion 21c). By forming such a portion, an inner gap SP1 having a certain height (distance) can be secured. As a result, the purge gas introduction device 40 can more stably replace the atmosphere around the upper end portion of the liquid film F with the purge gas, and can more reliably prevent the processing gas from coming into contact with the gas-liquid interface.

[0056] As described above, the embodiments of the present invention have been described. However, the present invention is not limited to the above embodiments, and various modifications are possible within the scope of the technical idea described in the claims.

Explanation of Reference Numerals

[0057] 1 Exhaust gas treatment device 10 Gas treatment reactor 11 Introduction pipe 11a Inlet 12 Flow path forming wall 12a Lower end 13 Cover member 15 Gas flow path 20 Double pipe structure 21 Inner cylinder 21a End portion (upper end) 21b Bent portion 21c Bent portion 22 Outer cylinder 23 Plate 23a Inner end portion 23b Projection 30 Liquid film forming device 31 Liquid supply port 32 Liquid supply line 33 Liquid supply source 34 On-off valve 40 Purge gas introduction device 41 Gas inlet 42 Gas introduction line 43 Gas introduction source 44 On-off valve F liquid film GL gas-liquid interface SP1 inner gap SP2 outer gap

Claims

1. It is an exhaust gas treatment device, A gas treatment reactor equipped with a channel-forming wall that forms a channel for the introduced treatment gas, The gas processing reactor comprises a double-tube structure surrounding the gas processing reactor, The aforementioned double-tube structure is An inner cylinder into which at least a portion of the flow path forming wall is inserted, An exhaust gas treatment apparatus comprising an outer cylinder disposed on the outside of the inner cylinder.

2. The exhaust gas treatment device includes a liquid film forming device that forms a liquid film on the inner cylinder, The exhaust gas treatment apparatus according to claim 1, wherein the liquid film forming apparatus is configured to supply liquid to the outer gap between the outer cylinder and the inner cylinder, and to form a liquid film on the inner wall surface of the inner cylinder by the liquid that overflows the inner cylinder.

3. The liquid film forming apparatus is A liquid supply line connected to a liquid supply port formed in the outer cylinder, The exhaust gas treatment apparatus according to claim 2, further comprising a liquid supply source that supplies liquid to the outer gap through the liquid supply line.

4. The exhaust gas treatment device includes a purge gas introduction device that introduces purge gas into the inner gap between the inner cylinder and the flow path forming wall. The exhaust gas treatment apparatus according to claim 1, wherein the purge gas introduction device is configured to introduce the purge gas from above the inner cylinder.

5. The aforementioned purge gas introduction device is A gas introduction line connected to a gas inlet located above the inner cylinder, The exhaust gas treatment apparatus according to claim 4, further comprising a gas introduction source for introducing purge gas into the inner gap through the gas introduction line.

6. The exhaust gas treatment apparatus according to claim 1, wherein the lower end of the flow path forming wall is positioned lower than the end of the inner cylinder.

7. The exhaust gas treatment apparatus according to claim 6, wherein the lower end of the flow path forming wall is positioned at a location 10 mm or more and 100 mm or less lower than the end of the inner cylinder.

8. The exhaust gas treatment apparatus according to claim 1, wherein the exhaust gas treatment apparatus comprises a plate that extends from the outer cylinder toward the flow path forming wall and is positioned above the inner cylinder.

9. The exhaust gas treatment apparatus according to claim 8, wherein the plate has a projection extending from its inner end toward the end of the inner cylinder.

10. The exhaust gas treatment apparatus according to claim 8, wherein the plate is made of a corrosion-resistant material.

11. The exhaust gas treatment apparatus according to claim 1, wherein each of the outer cylinder and the inner cylinder is made of resin or stainless steel.

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