Device for treating exhaust gas containing n2o (nitrous oxide)

Abstract

To provide a highly safe apparatus for treating exhaust gas containing N2O capable of preventing the generation of thermal NOx at the time of decomposition of N2O and capable of efficiently and certainly thermally decomposing harmful components in exhaust gas including N2O.SOLUTION: The apparatus for treating the exhaust gas containing N2O is equipped with an inlet scrubber 12 for liquid-washing the exhaust gas E containing N2O, a gas treatment oven 14 for thermally decomposing the exhaust gas E passed through the inlet scrubber 12 and an outlet scrubber 16 for liquid-washing the exhaust gas E thermally decomposed in the gas treatment oven 14. Further, a hydrogen feed unit 22 including a hydrogen generator 22a for generating hydrogen by electrolyzing pure water and a hydrogen feed pipe 22a for feeding the hydrogen generated in the hydrogen generator 22b to the exhaust gas E after passing through the inlet scrubber 12 and before being introduced into the gas treatment reactor 14 is provided. The inlet scrubber 12, the gas treatment furnace 14, the outlet scrubber 16 and the hydrogen supply unit 22 are housed in one cabinet 24.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a treatment device suitable for treating exhaust gas containing N2O to remove harmful substances. [Background technology]

[0002] In recent years, the use of high-purity N2O (nitrous oxide) as an oxidizing agent in the film-forming process in semiconductor manufacturing has expanded, resulting in a significant increase in consumption and an upward trend in emissions. Since N2O has a global warming potential (GWP) approximately 300 times that of CO2, it is known that discharging it untreated would cause significant damage to the global environment. For this reason, various technologies are being developed to remove used N2O from exhaust gases.

[0003] As a technology for detoxifying such exhaust gases containing NO, for example, Patent Document 1 (JP 2005-125285 A) listed below discloses a method for treating NO-containing exhaust gases, which comprises adding a reducing gas to exhaust gases containing NO to prepare a mixed gas, and heating the mixed gas in a reducing atmosphere to a temperature equal to or higher than the thermal decomposition temperature of the NO to detoxify harmful components in the exhaust gas. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-125285 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the above-mentioned conventional technology has the following problems: Since a reducing gas is added to exhaust gas containing NO to prepare a mixed gas, and then the mixed gas is thermally decomposed in a reducing atmosphere, it is possible to highly reliably ablate NO, which is the target component to be ablated, while minimizing the generation of thermal NOx. However, when hydrogen or ammonia is used as the reducing gas, these gases are difficult to handle because they are flammable gases that pose an explosion hazard, and it is necessary to take every possible measure to prevent leaks in the reducing gas supply system, such as the tanks that store these gases and the piping that serves as the supply route to the exhaust gas treatment device.

[0006] Therefore, the main object of the present invention is to provide a treatment device for NO-containing exhaust gas that can not only prevent the generation of thermal NOx during NO decomposition, but also is highly safe and can efficiently and reliably thermally decompose harmful components in exhaust gas, including NO. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention provides, for example, an apparatus 10 for treating N2O-containing exhaust gas, as shown in FIG. 1, configured as follows. That is, the system includes an inlet scrubber 12 that washes exhaust gas E containing NO with a liquid, a gas treatment furnace 14 that thermally decomposes the exhaust gas E that has passed through the inlet scrubber 12, and an outlet scrubber 16 that washes the exhaust gas E that has been thermally decomposed in the gas treatment furnace 14. The system also includes a hydrogen generator 22a that generates hydrogen by electrolyzing pure water, and a hydrogen supply unit 22 that includes a hydrogen supply pipe 22b that supplies the hydrogen generated in the hydrogen generator 22a to the exhaust gas E that has passed through the inlet scrubber 12 and before it is introduced into the gas treatment furnace 14. The inlet scrubber 12, the gas treatment furnace 14, the outlet scrubber 16, and the hydrogen supply unit 22 are housed in a single cabinet 24.

[0008] The present invention provides the following effects, for example. Because hydrogen (H), a reducing gas, is supplied from the hydrogen supply unit 22 to the liquid-washed flue gas E after passing through the inlet scrubber 12, oxygen produced by the thermal decomposition of NO is thought to immediately react with hydrogen and be fixed (to produce water) in the gas treatment space 18a of the gas treatment furnace 14. This prevents the nitrogen and oxygen produced by the thermal decomposition of NO in the flue gas E from recombining to produce nitrogen oxides, i.e., thermal NOx. In addition, because the hydrogen supply unit 22 is housed in a single cabinet 24 along with other components constituting the flue gas treatment device, the hydrogen required to detoxify NO-containing flue gas can be obtained simply by supplying safe pure water to the hydrogen generator 22a in the cabinet 24. In other words, there is no need to route hydrogen, a dangerous flammable gas, to the location within the factory where the cabinet 24 of the flue gas treatment device is installed, resulting in extremely safe operation.

[0009] In the present invention, it is preferable that the hydrogen supply unit 22 further includes an oxygen supply pipe 22c for supplying the oxygen generated in the hydrogen generator 22a into the gas processing furnace . In this case, for example, if the exhaust gas E contains persistent components such as CF4, CDA (Clean Dry Air) is supplied into the gas treatment furnace 14 to promote the decomposition of the persistent components. However, oxygen generated by the hydrogen generator 22a can be used instead of this CDA, which makes it possible to reduce or (in some cases) stop the use of CDA.

[0010] In the present invention, it is preferable that the cabinet 24 has a pressure-resistant and explosion-proof structure. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a treatment device for NO-containing exhaust gas that can not only prevent the generation of thermal NOx during NO decomposition, but also is highly safe and can efficiently and reliably thermally decompose harmful components in exhaust gas, including NO. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic flow diagram showing an example of an apparatus for treating N2O-containing exhaust gas according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the apparatus for treating N2O-containing exhaust gas of the present invention will be described with reference to the drawings. 1 is a schematic flow diagram showing an example of an NO-containing exhaust gas treatment device 10 according to one embodiment of the present invention. This NO-containing exhaust gas treatment device 10 is an apparatus that thermally decomposes and detoxifies NO-containing exhaust gas E, which is composed of NO and associated PFCs and is emitted from an emission source (not shown, for example, a semiconductor manufacturing process), and is roughly composed of an inlet scrubber 12, a gas treatment furnace 14, an outlet scrubber 16, a hydrogen supply unit 22, and a control device (not shown) that controls the operation of these components.

[0014] The inlet scrubber 12 is a wet scrubber that removes dust, water-soluble components, and the like contained in the exhaust gas E introduced into the gas processing furnace 14. In this embodiment, the inlet scrubber 12 includes a straight-tube scrubber body 12a and a spray nozzle 12b that is installed near the top of the interior of the scrubber body 12a and sprays a chemical solution such as water in a spray form. The inlet scrubber 12 is connected to an exhaust gas generation source (not shown), such as a semiconductor manufacturing device, via an exhaust gas duct 28.

[0015] The inlet scrubber 12 is installed upright on the chemical tank 30 (see FIG. 1) or (although not shown) is installed separately from the chemical tank 30 and the two are connected by piping so that the waste liquid is sent to the chemical tank 30. A circulation pump 32 is installed between the spray nozzle 12b and the chemical tank 30 so that the chemical liquid stored in the chemical tank 30 is lifted up to the spray nozzle 12b.

[0016] 1, not only the waste liquid from the inlet scrubber 12 but also the exhaust gas E after liquid washing is sent to the chemical tank 30, and the space between the liquid surface and the ceiling surface of this chemical tank 30 (upper space) is used as an exhaust gas flow path. Here, reference numeral 30a in Fig. 1 denotes a "partition wall" that partitions the area so that the exhaust gas E washed in the inlet scrubber 12 does not flow into the outlet scrubber 16 without passing through the gas treatment furnace 14.

[0017] The gas treatment furnace 14 is a device that thermally decomposes N 2 O, PFCs, and the like in the exhaust gas E using an electric heater 20 and the like, and in the illustrated embodiment, is roughly composed of a furnace body 18 and the electric heater 20.

[0018] The furnace body 18 is a sealed cylindrical vessel having at least its inner surface made of (coated with) a corrosion-resistant and heat-resistant (fire-resistant) refractory material such as castable or ceramics, and having a gas treatment space 18a formed therein. As shown in Fig. 1, the furnace body 18 is erected with its flat surface facing up and down during use, and has a gas inlet 18b drilled in the center of its bottom. Furthermore, a gas outlet 18c is drilled in the bottom of the furnace body 18 at a position close to the gas inlet 18b, for discharging the exhaust gas E thermally decomposed in the gas treatment space 18a.

[0019] In this embodiment, the furnace body 18 is formed in a sealed cylindrical shape, but the shape of the furnace body 18 may be any cylindrical shape with both ends sealed, for example, a sealed square cylinder.

[0020] The electric heater 20 serves as a heat source for heating the gas processing space 18a in the gas processing furnace 14. It is made of ceramics, preferably at least one selected from the group consisting of alumina, zirconia, silicon carbide, silicon nitride, molybdenum silicide, and lanthanum chromite. It has a cylindrical tubular member 20a with open longitudinal end faces. The cylindrical wall of the tubular member 20a contains a heating element (not shown) made of at least one ceramic selected from the group consisting of carbonaceous materials (graphite; C), zirconia (ZrO), silicon carbide (SiC), molybdenum silicide (MoSi), and lanthanum chromite (LaCrO), capable of generating heat at temperatures above 1350°C. In other words, all major components of the electric heater 20 of the present invention are made of ceramics.

[0021] The electric heater 20 is attached to the bottom of the furnace body 18 so that one end of the electric heater 20 surrounds the gas inlet 18b. The electric heater 20 extends across the gas treatment space 18a of the furnace body 18, and the other end of the electric heater 20 is located near the ceiling of the furnace body 18.

[0022] In this embodiment, the electric heater 20 (more specifically, the tubular member 20a) is formed in a cylindrical shape, but the shape of the electric heater 20 may be any tubular shape with both ends open, such as a square tube. The electric heater 20 is connected to a power supply unit (not shown) and receives power.

[0023] The gas processing furnace 14 configured as described above is equipped with a temperature measuring means, such as a thermocouple, for detecting the temperature of the gas processing space 18a, not shown, and the temperature data (temperature signal) detected by this temperature measuring means is sent via a signal line to a control means consisting of a CPU (Central Processing Unit), memory, input device, display device, etc. A power supply unit, not shown, is also connected to this control means, and these various devices are controlled by this control means.

[0024] The gas treatment furnace 14 configured as described above is disposed on the chemical tank 30, and an inlet pipe 34 having approximately the same inner diameter as the gas inlet 18b is connected at its upper end to the gas inlet 18b, and the lower end of the inlet pipe 34 is connected so as to communicate with a flow region of the exhaust gas E (before thermal decomposition) after passing through the inlet scrubber 12 in the chemical tank 30. Meanwhile, an outlet pipe 36 having approximately the same inner diameter as the gas outlet 18c is also connected at its upper end to the gas outlet 18c, and the lower end of the outlet pipe 36 is connected so as to communicate with a region in the chemical tank 30 different from the flow region of the exhaust gas E (before thermal decomposition) after passing through the inlet scrubber 12.

[0025] The outlet scrubber 16 is a wet scrubber that cools the pyrolysis-induced flue gas E that has passed through the gas treatment furnace 14 and ultimately removes dust and water-soluble components generated as by-products of pyrolysis from the flue gas E. In this embodiment, the outlet scrubber 16 includes a straight-tube scrubber body 16a, multiple perforated plates (not shown) installed vertically at intervals within the scrubber body 16a, and downward-facing spray nozzles 16b attached directly above the uppermost perforated plate and spraying a chemical solution such as water from above in a direction opposite to the flow direction of the flue gas E. The outlet scrubber 16 is installed in an area above the chemical tank 30 that is different from the flow area of ​​the flue gas E (before pyrolysis) that has passed through the inlet scrubber 12. The pyrolysis-induced flue gas E (discharged into the chemical tank 30 via the discharge pipe 36) is introduced into the outlet scrubber 16 from an opening at the bottom, and the chemical solution discharged from the spray nozzles 16b and then discharged into the chemical tank 30 is sent.

[0026] Furthermore, unlike the inlet scrubber 12 described above, the outlet scrubber 16 of this embodiment is configured to supply new chemical liquid such as new water to the spray nozzles 16b (see FIG. 1), but the spray nozzles 16b may be connected in communication with the discharge side of the circulation pump 32 so that the chemical liquid stored in the chemical liquid tank 30 is lifted up to the spray nozzles 16b. An exhaust fan 42 that releases treated exhaust gas E into the atmosphere is connected to the upper outlet of the outlet scrubber 16, and the upstream end of an exhaust duct 44 is connected to the delivery (discharge) side of the exhaust fan 42.

[0027] The hydrogen supply unit 22 is for supplying hydrogen, which is a reducing gas, to the flue gas E after it has passed through the inlet scrubber 12 and before it is introduced into the gas treatment furnace 14, and includes a hydrogen generator 22a and a hydrogen supply pipe 22b that supplies hydrogen generated by the hydrogen generator 22a to the flue gas E after it has passed through the inlet scrubber 12 and before it is introduced into the gas treatment furnace 14. If necessary, an oxygen supply pipe 22c is provided to supply oxygen, which is a by-product of hydrogen generation in the hydrogen generator 22a, to the gas treatment space 18a in the furnace body 18 of the gas treatment furnace 14. In the illustrated embodiment, the oxygen supply pipe 22c is disposed so that oxygen supplied from the oxygen supply pipe 22c is supplied to the flue gas E that has passed through the cylindrical electric heater 20 and reached the gas treatment space 18a.

[0028] Hydrogen generator 22a is a device that generates hydrogen by electrolyzing pure water using a solid polymer water electrolysis method that uses an ion exchange membrane, etc. To this end, the downstream end of raw water supply pipe 22d is connected to hydrogen generator 22a, and pure water, which is a hydrogen raw material, is supplied to hydrogen generator 22a via raw water supply pipe 22d.

[0029] The components of the NO-containing exhaust gas treatment device 10 configured as described above, namely the inlet scrubber 12, the gas treatment furnace 14, the outlet scrubber 16, and the hydrogen supply unit 22, are housed in a single cabinet 24. This cabinet 24 preferably has a pressure-resistant, explosion-proof structure that can withstand the explosion pressure that would occur if hydrogen generated in the hydrogen supply unit 22 leaked and exploded.

[0030] In this embodiment, the components of the NO-containing exhaust gas treatment apparatus 10, excluding the gas treatment furnace 14 and the hydrogen supply unit 22, are provided with corrosion-resistant linings or coatings made of vinyl chloride, polyethylene, unsaturated polyester resin, fluororesin, or the like to protect them from corrosion caused by corrosive components such as hydrofluoric acid contained in the exhaust gas E or generated by thermal decomposition of the exhaust gas E. Also, reference numeral 38 in Fig. 1 denotes an overflow vessel that adjusts the water level in the chemical tank 30 to a constant level.

[0031] Next, when performing detoxification treatment of exhaust gas E using the N2O-containing exhaust gas treatment device 10 configured as described above, first, the operation switch (not shown) of the treatment device 10 is turned on to operate the gas treatment furnace 14 and the electric heater 20, and heating of the gas treatment space 18a in the gas treatment furnace 14 begins.

[0032] Then, when the temperature within the gas processing space 18a reaches a predetermined temperature within the range of 800°C to 1400°C according to the type of material to be processed, including NO in the exhaust gas E, the exhaust fan 42 is activated, and introduction of the exhaust gas E into the processing device 10 begins. At the same time, operation of the hydrogen supply unit 22 is also initiated. The exhaust gas E then passes through the inlet scrubber 12, the gas processing furnace 14, and the outlet scrubber 16 in this order, and the components to be removed (i.e., NO, PFCs, etc.) in the exhaust gas E are removed.

[0033] In the NO-containing exhaust gas treatment device 10 of this embodiment, hydrogen is supplied as a reducing gas from the hydrogen supply unit 22 to the liquid-washed exhaust gas E after passing through the inlet scrubber 12. Therefore, oxygen generated by the thermal decomposition of NO is believed to immediately react with hydrogen and be fixed in the gas treatment space 18a of the gas treatment furnace 14. This prevents the nitrogen and oxygen generated by the thermal decomposition of NO in the exhaust gas E from recombining to produce nitrogen oxides, i.e., thermal NOx. Specifically, when the treatment flow rate of the exhaust gas E to be treated is 150 L (liters) / min, with 7 L / min of NO added at a rate of 3 L / min, and the treated exhaust gas E is thermally decomposed at 950°C, the NO removal efficiency can be 92% or more, and the NOx concentration in the treated exhaust gas E can be 20 ppm or less.

[0034] In the above embodiment, a cylindrical electric heater 20 is used as the heat source for the gas treatment furnace 14, but the heat source to be installed in the gas treatment furnace 14 is not limited to the cylindrical electric heater 20 and may be an electric heater of another shape, such as a flame burner or a non-transfer type or transfer type plasma torch, as long as it can supply high-temperature heat sufficient to thermally decompose the exhaust gas E. However, when the heat source is changed from the cylindrical electric heater 20 to another one, it goes without saying that the structure of the furnace body 18 must also be changed to match the heat source.

[0035] In the above embodiment, the gas inlet 18b of the gas treatment furnace 14 and the upper space of the chemical tank 30 (the exhaust gas flow path after liquid washing) are connected by the inlet pipe 34, and the gas outlet 18c and the upper space of the chemical tank (the exhaust gas flow path after thermal decomposition) are connected by the outlet pipe 36. In this case, however, it is preferable to provide a heat exchanger (not shown) between the inlet pipe 34 and the outlet pipe 36, that is, to preheat the exhaust gas E flowing through the inlet pipe 34 by applying the exhaust heat of the exhaust gas E flowing through the outlet pipe 36 to the exhaust gas E. This allows for even more efficient use of energy.

[0036] In addition, in the above embodiment, the oxygen by-produced in the hydrogen generator 22a is supplied to the gas processing space 18a of the gas processing furnace 14, but if oxygen is not required to detoxify the exhaust gas E to be processed, it may be exhausted without being supplied to the gas processing space 18a. Of course, various other modifications can be made within the scope of what can be imagined by those skilled in the art. [Explanation of symbols]

[0037] 10: N2O-containing exhaust gas treatment device, 12: inlet scrubber, 14: gas treatment furnace, 16: outlet scrubber, 18: furnace body, 18a: gas treatment space, 18b: gas inlet, 18c: gas outlet, 20: electric heater, 20a: cylindrical member, 22: hydrogen supply unit, 22a: hydrogen generator, 22b: hydrogen supply piping, 22c: oxygen supply piping, E: exhaust gas.

Claims

1. N ２ The N system comprises an inlet scrubber (12) for liquid washing of exhaust gas (E) containing O, a gas treatment furnace (14) for thermally decomposing the exhaust gas (E) that has passed through the inlet scrubber (12), and an outlet scrubber (16) for liquid washing of the exhaust gas (E) that has been thermally decomposed in the gas treatment furnace (14). ２ In an apparatus for treating an O-containing exhaust gas, The system further comprises a hydrogen supply unit (22) including a hydrogen generator (22a) that generates hydrogen by electrolyzing pure water, and a hydrogen supply pipe (22b) that supplies the hydrogen generated by the hydrogen generator (22a) toward the exhaust gas (E) after passing through the inlet scrubber (12) and before being introduced into the gas treatment furnace (14), The inlet scrubber (12), the gas treatment furnace (14), the outlet scrubber (16) and the hydrogen supply unit (22) are housed in one cabinet (24). ２ A device for treating exhaust gas containing oxygen.

2. N of claim 1 ２ In an apparatus for treating an O-containing exhaust gas, The hydrogen supply unit (22) further comprises an oxygen supply pipe (22c) for supplying oxygen generated in the hydrogen generator (22a) into the gas treatment furnace (14). ２ A device for treating exhaust gas containing oxygen.

3. N of claim 1 or 2 ２ In an apparatus for treating an O-containing exhaust gas, The cabinet (24) is characterized in that it has a pressure-resistant and explosion-proof structure. ２ A device for treating exhaust gas containing oxygen.

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