Device for treating exhaust gas containing n2o (nitrous oxide)

Abstract

To provide an apparatus for treating exhaust gas containing N2O capable of preventing the generation of thermal NOx at the time of decomposition of N2O, capable of efficiently and certainly thermally decomposing harmful components in exhaust gas including N2O and capable of efficiently performing stable continuous operation over a long period of time at a cost lower than that of a conventional apparatus.SOLUTION: A gas treatment furnace 14 includes a closed cylindrical furnace body 18 having a gas treatment space 18a formed inside and a gas introduction port 18b bored in the bottom part, a cylindrical electric heater 20 having one end attached to the bottom part in the furnace body so as to surround the gas introduction port and having the other end opened and extended so as to cross the gas treatment space to the position near the ceiling surface of the furnace body, and a reducing gas supplying means 22 made of a corrosion-resistant metal and supplying at least one of ammonia water and urea water to be a reducing gas G toward exhaust gas E introduced from the gas introduction port.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. Specifically, a reducing gas is added to exhaust gas containing NO to prepare a mixed gas, which is then thermally decomposed under a reducing atmosphere. This allows for highly accurate abatement of the NO, the target component, while minimizing the generation of thermal NOx. However, if the exhaust gas contains a persistent component, such as CF, which has a higher thermal decomposition temperature than NO, it is difficult to ablate the persistent component, necessitating secondary treatment of the exhaust gas. Furthermore, the above-mentioned conventional technology uses gases such as hydrogen, ammonia, and hydrocarbons as reducing gases. These gases require careful handling during transportation and storage, which also presents a problem.

[0006] Therefore, the main object of the present invention is to provide an apparatus for treating NO-containing exhaust gases that can not only prevent the generation of thermal NOx during NO decomposition, but also efficiently and reliably thermally decompose harmful components in exhaust gases, including NO, and that can operate stably and efficiently for a long period of time at a lower cost than conventional apparatuses. [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. The system is equipped with an inlet scrubber 12 that washes exhaust gas E containing NO with 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 with liquid. The gas processing furnace 14 is characterized in that it includes a sealed cylindrical furnace body 18 having a gas processing space 18a formed therein, the furnace body 18 having a gas inlet 18b and a gas outlet 18c drilled at its bottom, a cylindrical electric heater 20 having one end attached to the bottom of the furnace body 18 so as to surround the gas inlet 18b and the other end open and extending across the gas processing space 18a to a position close to the ceiling surface of the furnace body 18, and a reducing gas supply means 22 made of a corrosion-resistant metal and equipped with a transfer pipe 22a that penetrates the ceiling of the furnace body 18 and is arranged near the gas inlet 18b, the tip of which is surrounded by the electric heater 20, and that supplies at least one of ammonia water and urea water, which will become a reducing gas G, to the exhaust gas E introduced from the gas inlet 18b via the transfer pipe 22a.

[0008] The present invention provides the following effects, for example. After being scrubbed in the inlet scrubber 12, at least one of ammonia water and urea water is supplied from the reducing gas supply means 22 to the flue gas E introduced into the gas treatment furnace 14 through the gas inlet 18b. As the at least one of the ammonia water and urea water moves through the transfer pipe 22a, the heat from the electric heater 20 ensures that the water is evaporated (separated) and converted into ammonia (NH), which is a reducing gas G. The ammonia is then ejected from the tip of the transfer pipe 22a and mixed with the flue gas E near the gas inlet 18b. In the gas treatment space 18a of the gas treatment furnace 14, oxygen generated by the thermal decomposition of NO in the flue gas E immediately reacts with and is fixed in the reducing gas G (ammonia). This prevents the nitrogen and oxygen generated by the thermal decomposition of NO in the flue gas E from combining again to produce nitrogen oxides, i.e., thermal NOx. It is also worth noting that the reducing gas G mixed in during the thermal decomposition of the exhaust gas E is in the form of an aqueous solution such as at least one of ammonia water and urea water. This makes it easier to store and handle the reducing gas G than when it is handled as a gas.

[0009] In the present invention, the electric heater 20 is preferably constructed by housing a heating element made of at least one ceramic selected from the group consisting of carbonaceous (graphite), zirconia, silicon carbide, molybdenum disilicide, and lanthanum chromite in a ceramic cylindrical member 20a, and the inner surface of the furnace body 18 is preferably coated with a ceramic member 18d. In this case, it becomes possible to operate the N2O-containing exhaust gas treatment device 10 continuously for a long period of time at a high temperature of around 1350°C, which in turn makes it possible to increase the treatment volume of the N2O-containing exhaust gas E and also to thermally decompose difficult-to-decompose components such as CF4.

[0010] In addition, in the present invention, it is preferable to install a NOx meter 26 at the outlet of the outlet scrubber 16 and further provide a control device that controls the amount of at least one of the ammonia water and urea water supplied from the reducing gas supply means 22 toward the exhaust gas E based on the NOx concentration in the exhaust gas E measured by the NOx meter. In this case, the supply amount of at least one of the ammonia water and the urea water that become the reducing gas G can be optimized to eliminate waste in running costs.

[0011] Furthermore, in the present invention, it is preferable that the ceramic member 18d that coats the inner surface of the cylindrical member 20a and the furnace body 18 is made of at least one ceramic selected from the group consisting of alumina, zirconia, silicon carbide, silicon nitride, molybdenum disilicide, and lanthanum chromite. [Effects of the Invention]

[0012] 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 efficiently and reliably thermally decompose harmful components in exhaust gas, including NO, and that can operate stably and continuously for a long period of time at a lower cost and more efficiently than conventional devices. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is an explanatory diagram showing an outline of an apparatus for treating N2O-containing exhaust gas according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] 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 an explanatory diagram showing an outline of an apparatus 10 for treating NO-containing exhaust gas according to one embodiment of the present invention. This apparatus 10 for treating NO-containing exhaust gas is an apparatus for thermally decomposing and treating exhaust gas E containing NO (nitrous oxide) emitted from an emission source (not shown, for example, a semiconductor manufacturing process) to remove harmful substances, and is generally composed of an inlet scrubber 12, a gas treatment furnace 14, an outlet scrubber 16, and a control device (not shown) that controls the operation of these components.

[0015] 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.

[0016] 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. 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 is roughly composed of a furnace body 18 , the electric heater 20 , and a reducing gas supply means 22 .

[0018] The furnace body 18 is a sealed cylindrical vessel having at least its inner surface constructed (covered) with a ceramic member 18d having corrosion resistance and heat resistance (fire resistance) sufficient for long-term use at temperatures of 1350°C or higher, and having a gas treatment space 18a formed therein. In the illustrated embodiment, the furnace body 18 is formed by covering the ceramic member 18d on the outside with a heat insulating material 18e made of castable or the like. 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. A gas outlet 18c is drilled in the bottom of the furnace body 18 at a position adjacent to the gas inlet 18b for discharging the exhaust gas E thermally decomposed in the gas treatment space 18a.

[0019] The ceramic material forming the ceramic member 18d of the furnace body 18 is preferably at least one selected from the group consisting of alumina (Al2O3), zirconia (ZrO2), silicon carbide (SiC), silicon nitride (Si3N4), molybdenum disilicide (MoSi2), and lanthanum chromite (LaCrO3). 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. Similar to the furnace body 18, the electric heater 20 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. The electric heater 20 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. 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 is supplied with power by the power supply unit.

[0022] The reducing gas supply means 22 is a device for supplying at least one of ammonia water and urea water, which is converted into a reducing gas G (more specifically, ammonia) by heating at 100°C or higher, to the exhaust gas E introduced into the furnace body 18, and is roughly composed of a transfer pipe 22a, a flow rate control device 22b, a storage tank (not shown), and piping 22c. Note that as the ammonia water and urea water supplied by the reducing gas supply means 22, it is preferable to use general-purpose ammonia water (ammonium hydroxide) and urea water with a concentration of, for example, 10 to 35%.

[0023] The transfer pipe 22a is made of a corrosion-resistant metal such as Hastelloy (a registered trademark of Haynes Corporation), and is a straight pipe member that penetrates the ceiling of the furnace body 18 and is disposed near the gas inlet 18b, the tip of which is surrounded by the electric heater 20. A flow control device 22b, which is composed of a flow control valve or the like that adjusts the amount of at least one of ammonia water and urea water supplied to the gas inlet 18b, is attached to the base end of the transfer pipe 22a. A storage tank (not shown) that stores at least one of ammonia water and urea water is connected to the flow control device 22b via piping 22c. A check valve 22d is attached to the transfer pipe 22a as needed to prevent the fluid in the transfer pipe 22a from flowing back toward the flow control device 22b.

[0024] In the illustrated embodiment, the transfer pipe 22a is formed as a straight pipe, but the shape of the transfer pipe 22a is not limited to this, and for example, although not shown, the transfer pipe 22a may be formed as a spiral. By forming the transfer pipe 22a in a spiral shape in this way, turbulence is generated in the exhaust gas E and reducing gas G flowing inside the cylindrical electric heater 20, further promoting mixing of the two, and the residence time within the electric heater 20 is increased, further promoting thermal decomposition of the exhaust gas E.

[0025] The gas processing furnace 14 configured as described above is equipped with a temperature measuring means, such as a thermocouple (not shown), for detecting the temperature of the gas processing space 18a, 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, an input device, a display device, etc. The control means is also connected to the flow rate control device 22b of the reducing gas supply means 22 and a power supply unit (not shown), and these various devices are controlled by the control means.

[0026] 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.

[0027] 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.

[0028] 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 nozzle 16b (see FIG. 1), but this spray nozzle 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 nozzle 16b.

[0029] An exhaust fan 42 that discharges the treated exhaust gas E into the atmosphere is connected to the outlet of the outlet scrubber 16, and a NOx meter (NOx concentration measuring device) 26 that measures the NOx concentration in the exhaust gas that has passed through the outlet scrubber 16 is also attached, as necessary. Data on the NOx concentration in the exhaust gas E measured by the NOx meter 26 is sent to a control device (not shown), which controls the operation of the flow rate control device 22b of the reducing gas supply means 22 based on the NOx concentration data. Specifically, when the NOx concentration measured by the NOx meter exceeds a preset upper limit, the flow rate control device 22b is operated to increase the supply amount of at least one of ammonia water and urea water (i.e., the supply amount of reducing gas G). Conversely, when the NOx concentration measured by the NOx meter falls below a preset lower limit, the flow rate control device 22b is operated to decrease the supply amount of at least one of ammonia water and urea water. This maximizes the efficiency of use of at least one of ammonia water and urea water.

[0030] In addition, in the NO-containing exhaust gas treatment apparatus 10 of this embodiment, except for the gas treatment furnace 14, other parts are provided with a corrosion-resistant lining or coating made of vinyl chloride, polyethylene, unsaturated polyester resin, fluororesin, or the like to protect each part 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 activate the electric heater 20 of the gas treatment furnace 14, and heating of the gas treatment space 18a in the gas treatment furnace 14 begins.

[0032] When the temperature within the gas processing space 18a reaches a predetermined temperature within the range of 800°C to 1400°C, which is appropriate for the type of material to be processed, including NO, contained in the exhaust gas E, the exhaust fan 42 is activated, and the introduction of the exhaust gas E into the processing device 10 begins. The exhaust gas E then passes through the inlet scrubber 12, the gas processing furnace 14, and the outlet scrubber 16 in this order, whereby the components to be removed (i.e., NO, PFCs, etc.) in the exhaust gas E are removed. Furthermore, a control means (not shown) controls the amount of power supplied to the electric heater 20 of the gas processing furnace 14 so that the temperature within the gas processing space 18a is maintained at a predetermined temperature. Furthermore, the amount of at least one of ammonia water and urea water (i.e., reducing gas G) supplied from the reducing gas supply means 22 to the gas inlet 18b is controlled based on the NOx concentration in the exhaust gas E measured by the NOx meter 26.

[0033] In the NO-containing exhaust gas treatment device 10 of this embodiment, reducing gas G is supplied from the reducing gas supply means 22 to the liquid-washed exhaust gas E after passing through the inlet scrubber 12 at a predetermined stoichiometric ratio. Therefore, oxygen generated by the thermal decomposition of NO in the gas treatment space 18a of the gas treatment furnace 14 is thought to immediately react with the reducing gas G and be fixed (denitrified). 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. Additionally, the electric heater 20 is configured by housing a heating element made of a specified ceramic within a ceramic cylindrical member 20a, and the inner surface of the furnace body 18 of the gas treatment furnace 14 is coated with a ceramic member 18d, enabling long-term continuous operation at high temperatures of approximately 1350°C. This allows for an increased treatment volume of NO-containing exhaust gas E and also enables the thermal decomposition of persistent components such as CF4.

[0034] 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.

[0035] In addition, in the above-described embodiment, the electric heater 20 is configured by storing a heating element made of a specified ceramic in a ceramic tubular member 20a. However, if, for example, the thermal decomposition temperature of the exhaust gas E to be treated in the device of the present invention is below 1000°C, the electric heater 20 may be configured by storing a metal wire heating element such as nichrome wire or Kanthal (a registered trademark of Sandvik) wire in a ceramic tubular member 20a. [Explanation of symbols]

[0036] 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, 18d: ceramic member, 20: electric heater, 20a: cylindrical member, 22: reducing gas supply means, 22a: transfer pipe, 26: NOx meter, E: exhaust gas, G: reducing 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 gas processing furnace (14) is a closed cylindrical furnace body (18) having a gas treatment space (18a) formed therein and having a gas inlet (18b) and a gas outlet (18c) formed at the bottom thereof; a cylindrical electric heater (20) having one end attached to the bottom of the furnace body (18) so as to surround the gas inlet (18b) and the other end open and extending across the gas treatment space (18a) to a position close to the ceiling surface of the furnace body (18); and reducing gas supply means (22) made of a corrosion-resistant metal and equipped with a transfer pipe (22a) that penetrates the ceiling of the furnace body (18) and is disposed near the gas inlet (18b) whose tip is surrounded by the electric heater (20), for supplying at least one of ammonia water and urea water, which will become a reducing gas (G), to the exhaust gas (E) introduced from the gas inlet (18b) via the transfer pipe (22a). N characterized by 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 electric heater (20) is constructed by storing a heating element made of at least one ceramic selected from the group consisting of carbonaceous (graphite), zirconia, silicon carbide, molybdenum disilicide, and lanthanum chromite in a ceramic cylindrical member (20a), and The inner surface of the furnace body (18) is coated with a ceramic member (18d). 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, A NOx meter (26) is installed at the outlet of the outlet scrubber (16), The NOx meter (26) further includes a control device for controlling the amount of at least one of ammonia water and urea water to be supplied from the reducing gas supply means (22) to the exhaust gas (E) based on the NOx concentration in the exhaust gas (E) measured by the NOx meter (26). ２ A device for treating exhaust gas containing oxygen.

4. N of claim 2 ２ In an apparatus for treating an O-containing exhaust gas, The ceramic member (18d) covering the inner surface of the cylindrical member (20a) and the furnace body (18) is made of at least one ceramic material selected from the group consisting of alumina, zirconia, silicon carbide, silicon nitride, molybdenum disilicide, and lanthanum chromite. ２ A device for treating exhaust gas containing oxygen.

Images