Heat exchanger and exhaust gas treatment device using the same

Abstract

The present invention provides a heat exchanger capable of stably and continuously recovering heat over a long period of time, even when the target gas for heat recovery is an extremely corrosive gas, and an exhaust gas treatment device using such a heat exchanger. [Solution] The heat exchanger of the present invention is characterized by comprising a partition plate (14) made of refractory castable material that divides the inside of the casing (12) so that the low-temperature side fluid (LF) and the high-temperature side fluid (HF) flow in countercurrents, and a plurality of solid heat transfer rods (16) made of at least one ceramic selected from the group consisting of alumina, zirconia, silicon carbide, silicon nitride, molybdenum silicide, and lanthanum chromite, which are arranged to airtightly penetrate the front and back surfaces of the partition plate (14) and cross the flow paths of the low-temperature side fluid (LF) and the high-temperature side fluid (HF).

Description

Technical Field

[0001] The present invention mainly relates to a heat exchanger that can be suitably used in the detoxification treatment of exhaust gas containing hardly decomposable CF4, SF6, etc., and an exhaust gas treatment apparatus using the same.

Background Art

[0002] For example, in the manufacturing processes of semiconductor devices and liquid crystal displays, various types of fluorine compound gases are used as cleaning gases, etching gases, etc. Such fluorine compounds are called "PFCs", and typical examples include perfluorocarbons such as CF4, C2F6, C3F8, C4F8, C5F8, hydrofluorocarbons such as CHF3, and inorganic fluorine-containing compounds such as SF6 and NF3. Various types of PFCs used in the manufacturing processes of these semiconductor devices and liquid crystal displays are discharged as exhaust gas together with N2, Ar, etc. used as carrier gas, purge gas, etc.

[0003] Here, the proportion of PFCs in the entire exhaust gas is small compared to other gases such as N2 and Ar, but this PFC has a very large global warming potential (GWP) hundreds to tens of thousands of times that of CO2 and a very long atmospheric lifetime compared to CO2. Therefore, even if a small amount is discharged into the atmosphere, its impact is extremely large. Furthermore, perfluorocarbons represented by CF4 and C2F6 are known to be difficult to decompose because the C-F bond is stable (the bond energy is as large as 130 kcal / mol). For this reason, various technologies for detoxifying used PFCs from exhaust gas have been developed.

[0004] As a technology for detoxifying exhaust gas containing such persistent PFCs, for example, Patent Document 1 (Japanese Patent Publication No. 2002-188810) discloses an exhaust gas treatment device in which dust and other particles contained in the harmful exhaust gas are removed by an inlet scrubber, the exhaust gas is then heated and decomposed in an exhaust gas treatment furnace equipped with an electric heater, and the decomposed gas is detoxified by gas-liquid contact in a wet outlet scrubber. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2002-188810 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, the conventional technology described above had the following problems. Specifically, when the PFCs in the exhaust gas mainly consist of the recalcitrant CF4, the electric heater must be used at a very high temperature of 1400°C or higher. When using an electric heater in such a temperature range, the amount of electricity consumed increases, so it is necessary to recover the heat (waste heat) from the exhaust gas after pyrolysis using a heat exchanger to reduce the amount of electricity consumed. Here, the exhaust gas after pyrolysis is a high-temperature gas containing a large amount of hydrogen fluoride, which is extremely corrosive, but a heat exchanger that can continuously and stably recover the heat from such a highly corrosive gas over a long period of time has not yet been found.

[0007] Therefore, the main objective of the present invention is to provide a heat exchanger that can stably perform heat exchange for a long period of time, even when the gas to be heat-exchanged contains extremely corrosive gases, and an exhaust gas treatment device using such a heat exchanger. [Means for solving the problem]

[0008] To achieve the above objectives, the present invention provides, for example, a heat exchanger suitable for heat exchange of highly corrosive gases, as shown in Figures 1 and 2, as follows. In other words, it is characterized by comprising a partition plate 14 made of refractory castable material that divides the inside of the casing 12 so that the low-temperature fluid LF and the high-temperature fluid HF flow in countercurrents, and a plurality of solid heat transfer rods 16 made of at least one ceramic selected from the group consisting of alumina, zirconia, silicon carbide, silicon nitride, molybdenum silicide, and lanthanum chromite, which are arranged to airtightly penetrate the front and back surfaces of the partition plate 14 and cross the flow paths of the low-temperature fluid LF and the high-temperature fluid HF.

[0009] The present invention provides, for example, the following effects: Since the partition plates 14 that divide the fluid flow paths are made of refractory castable material and the heat transfer rods 16 are made of a predetermined ceramic material, corrosion of each component can be suppressed even if the fluid flowing through the heat exchanger is extremely corrosive. Furthermore, since the partition plates 14 and the heat transfer rods 16 are made of materials with relatively similar coefficients of thermal expansion, and the solid heat transfer rods 16 are structured to airtightly penetrate both the front and back surfaces of the partition plates 14, leakage of the low-temperature fluid LF and the high-temperature fluid HF to the opposite flow paths can be effectively prevented.

[0010] In the present invention, it is preferable that the thickness T of the partition plate 14 is 30 mm or more. Furthermore, it is preferable that the outer diameter of the heat transfer rod material 16 is 8 mm or more and 40 mm or less, and that the heat transfer rod material 16 is arranged in a staggered pattern in the direction of fluid flow.

[0011] The second invention in the present invention is an exhaust gas treatment device using the above-described heat exchanger, characterized in that a heat exchanger 10 is formed in the lower part of a casing 12, with a partition plate 14 installed so that the gas flows in the vertical direction, and an exhaust gas treatment furnace 22 is formed in which a heat source 18 is arranged above the heat exchanger 10 and a gas treatment space 20 is formed that communicates with the heat exchanger 10. This invention includes a heat exchanger 10 that can stably and continuously recover heat from highly corrosive gases over a long period of time. Therefore, it is possible to efficiently and continuously decontaminate PFCs, for example, which generate highly corrosive hydrogen fluoride after thermal decomposition, over a long period of time.

[0012] In the present invention, it is preferable to include at least one of an inlet scrubber 24 for pre-washing the exhaust gas E to be treated before introducing it into the exhaust gas treatment furnace 22, or an outlet scrubber 26 for cooling and washing the exhaust gas E that has been thermally decomposed in the exhaust gas treatment furnace 22. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a heat exchanger that can continuously and stably recover heat for a long period of time even if the target gas for heat recovery is an extremely corrosive gas, and an exhaust gas treatment device that uses such a heat exchanger and is suitable for decontaminating PFCs mainly composed of CF4 and C2F6. [Brief explanation of the drawing]

[0014] [Figure 1] This is an explanatory diagram showing an example of an exhaust gas treatment device using a heat exchanger according to one embodiment of the present invention. [Figure 2] Figure 2A shows a partial vertical cross-sectional view of the main part in a front view, and Figure 2B is a view taken along arrow A in Figure 2A. [Modes for carrying out the invention]

[0015] The following describes embodiments of the heat exchanger and exhaust gas treatment apparatus using the present invention, which can be suitably used for detoxifying exhaust gases containing persistent PFCs, such as those emitted from semiconductor manufacturing processes, with reference to the drawings. Figure 1 is an explanatory diagram showing an example of an exhaust gas treatment device X using a heat exchanger 10 according to one embodiment of the present invention. This exhaust gas treatment device X is a device that detoxifies exhaust gas E containing PFCs, N2O, etc., emitted from an emission source (mainly semiconductor manufacturing process) not shown, by thermal decomposition, and is generally composed of an exhaust gas treatment furnace 22, an inlet scrubber 24, an outlet scrubber 26, etc.

[0016] The exhaust gas treatment furnace 22 is a device that thermally decomposes PFCs and other substances in the exhaust gas E in a gas treatment space 20 inside a casing 12 where a heat source 18 is installed, and a heat exchanger 10 is integrated into it.

[0017] The heat exchanger 10 is located in the lower part of a cylindrical casing 12 that is erected with an open lower end, and comprises a partition plate 14 and heat transfer rods 16. The casing 12 forms the outer shell of the heat exchanger 10, and in this embodiment, at least the inner surface of the casing 12 of the heat exchanger 10 is made of ceramics or the like, which has excellent fire resistance and corrosion resistance, and extends upward, with its upper end sealed to form a ceiling. In other words, the casing 12 of the heat exchanger 10 is configured to also function as the casing 12 of the exhaust gas treatment furnace 22.

[0018] The partition plate 14 is made of fire-resistant castable material with excellent fire resistance and corrosion resistance, and is a plate material that partitions the inside of the casing 12 so that the exhaust gas E before thermal decomposition (=low temperature side fluid LF) and the exhaust gas E after thermal decomposition (=high temperature side fluid HF) flow in countercurrents. The thickness T of the partition plate 14 is preferably 30 mm or more, and more preferably 50 mm or more. If the thickness T of the partition plate 14 is less than 30 mm, it may be difficult to ensure airtightness during long-term use. There is no particular upper limit to the thickness T of the partition plate 14, but considering the heat exchange performance and the weight of the device, it is preferable to keep it at 100 mm or less.

[0019] The heat transfer rod 16 is a solid rod-shaped member made of at least one kind of ceramic selected from the group consisting of alumina, zirconia, silicon carbide, silicon nitride, molybdenum silicide, and lanthanum chromite, and is for propagating the heat received from the high-temperature side fluid HF to the low-temperature side fluid LF. The outer diameter of the heat transfer rod 16 is preferably 8 mm or more and 40 mm or less, more preferably 10 mm or more and 30 mm or less. If the outer diameter of the heat transfer rod 16 is less than 8 mm, there is a concern about insufficient strength required for continuous use over a long period. Conversely, if it exceeds 40 mm, although there is no strength problem, the specific surface area becomes small and efficient heat recovery or heat supply cannot be achieved.

[0020] Also, the heat transfer rod 16 is disposed so as to penetrate the front and back surfaces of the partition plate 14 airtightly and cross the flow paths of the low-temperature side fluid LF and the high-temperature side fluid HF. Although not shown, such a structure can be obtained, for example, by drilling a pair of insertion holes on the front and back for inserting the heat transfer rod 16 at a predetermined position of a mold made according to the size of the partition plate 14, fitting the heat transfer rod 16 into the insertion holes, then pouring a slurry-like refractory castable into the mold, and removing the mold after the refractory castable has hardened.

[0021] And as described above, the heat transfer rod 16 provided so as to penetrate the front and back surfaces of the partition plate 14 airtightly and cross the flow paths of the low-temperature side fluid LF and the high-temperature side fluid HF is preferably arranged in a staggered manner in the fluid flow direction as shown in FIG. 2B. By doing so, the exhaust gas E flowing through the heat exchanger 10 and the heat transfer rod 16 can come into sufficient contact, and the heat exchange efficiency can be further improved.

[0022] A heat source 18 is attached to the upper space inside the casing 12 in which the heat exchanger 10 is configured as described above, and this space functions as a gas treatment space 20. Here, any heat source 18 can be used as described above, such as an electric heater, a combustion burner, or a plasma torch, depending on the purpose. In the illustrated embodiment, multiple rod-shaped electric heaters made of ceramics such as silicon carbide (SiC), molybdenum disilide (MoSi2), or lanthanum chromite (LaCrO3) are installed so as to cross the flow of exhaust gas E passing through the gas processing space 20.

[0023] The exhaust gas treatment furnace 22, configured as described above, is equipped with temperature measuring means, such as thermocouples for detecting the temperature inside the gas treatment space 20 (not shown), and the temperature data (temperature signal) detected by this temperature measuring means is provided via a signal line to a control means consisting of a CPU (Central Processing Unit), memory, input device, and display device. A power supply unit (not shown) that supplies power to a heat source 18, which is composed of electric heaters, is also connected to this control means, and all these various devices are controlled by this control means.

[0024] Furthermore, the exhaust gas treatment furnace 22 configured as described above is installed on a storage tank 28 in which a chemical solution such as water is stored, and the storage tank 28 is provided with a partition wall 28a connected to the lower end of the partition plate 14, which divides the space above the liquid level inside the storage tank 28 into two sections.

[0025] The inlet scrubber 24 is a wet scrubber that removes dust and water-soluble components contained in the exhaust gas E introduced into the exhaust gas treatment furnace 22. It consists of a straight-tube scrubber body 24a, a spray nozzle 24b installed near the top of the inside of the scrubber body 24a for spraying a chemical solution such as water, and a packing material 24c for promoting gas-liquid contact between the chemical solution sprayed from the spray nozzle 24b and the exhaust gas E. The packing material 24c is installed as needed. This inlet scrubber 24 is connected to an exhaust gas source (not shown), such as semiconductor manufacturing equipment, via an exhaust gas duct 30.

[0026] Furthermore, the inlet scrubber 24 is erected on top of the storage tank 28 (see Figure 1), or (not shown) it is installed separately from the storage tank 28 and connected to it by piping so that the drained liquid is sent to the storage tank 28. A circulation pump 32 is installed between the spray nozzle 24b and the storage tank 28 to lift the stored chemical solution in the storage tank 28 to the spray nozzle 24b.

[0027] In this embodiment shown in Figure 1, not only the drained liquid from the inlet scrubber 24 but also the exhaust gas E after washing is sent to the storage tank 28. The space between the liquid level and the ceiling of the storage tank 28 (upper space) is used as an exhaust gas passage to supply the exhaust gas E after washing to the low-temperature fluid (LF) side passage of the heat exchanger 10.

[0028] The outlet scrubber 26 is a wet scrubber that cools the exhaust gas E after thermal decomposition that has passed through the exhaust gas treatment furnace 22, and ultimately removes dust, water-soluble components, etc., produced as by-products by thermal decomposition from the exhaust gas E. In this embodiment, it consists of a straight-tube scrubber body 26a, a downward-facing spray nozzle 26b installed near the top of the inside of the scrubber body 26a that sprays a chemical solution such as water from above, opposite to the direction of flow of the exhaust gas E, and a packing material 26c to promote gas-liquid contact between the chemical solution sprayed from the spray nozzle 26b and the exhaust gas E. The packing material 26c is installed as needed. This outlet scrubber 26 is erected in a region different from the flow area of ​​the exhaust gas E (before thermal decomposition) after it has passed through the inlet scrubber 24 on the storage tank 28. From the opening at the bottom, the exhaust gas E (after thermal decomposition, which has been discharged into the storage tank 28) is introduced, and the chemical solution that has been supplied by the spray nozzle 24b and then turned into wastewater is sent to the storage tank 28.

[0029] Furthermore, similar to the inlet scrubber 24 described above, in the illustrated embodiment, a circulation pump 32 is installed between the spray nozzle 26b and the storage tank 28 to lift the stored chemical solution in the storage tank 28 to the spray nozzle 26b. However, instead of the stored chemical solution in the storage tank 28, a new chemical solution such as fresh water may be supplied to the spray nozzle 26b.

[0030] Then, an exhaust fan 36 is connected to the atmospheric discharge piping system 34 near the top outlet of the outlet scrubber 26 to discharge the treated exhaust gas E into the atmosphere.

[0031] In addition, in the exhaust gas treatment apparatus X of this embodiment, parts other than the exhaust gas treatment furnace 22 are coated with corrosion-resistant linings or coatings made of polyvinyl chloride, polyethylene, unsaturated polyester resin, and fluororesin to protect each part from corrosion caused by corrosive components such as hydrofluoric acid contained in the exhaust gas E or produced by the decomposition of the exhaust gas E. Furthermore, the outside of the casing 12 of the exhaust gas treatment furnace 22 is covered with an insulating material 12a made of ceramic fiber or the like.

[0032] Next, when performing exhaust gas E decontamination treatment using the exhaust gas treatment device X configured as described above, first, the operation switch (not shown) of the exhaust gas treatment device X is turned on to activate the heat source 18 of the exhaust gas treatment furnace 22 and start heating inside the exhaust gas treatment furnace 22. Then, when the temperature in the gas processing space 20 reaches a predetermined temperature corresponding to the type of exhaust gas E to be processed, the exhaust fan 36 is activated and the introduction of exhaust gas E into the exhaust gas treatment device X begins. The exhaust gas E then passes through the inlet scrubber 24, the flow path on the low-temperature side (LF) of the heat exchanger 10 at the bottom of the exhaust gas treatment furnace 22, the gas processing space 20, the flow path on the high-temperature side (HF) of the heat exchanger 10, and the outlet scrubber 26 in this order, removing harmful components (such as PFCs and N2O) from the exhaust gas E. In addition, a control means (not shown) controls the amount of electricity supplied to the heat source 18 of the exhaust gas treatment furnace 22 so that the temperature in the gas processing space 20 is maintained at a predetermined temperature.

[0033] In the exhaust gas treatment device X of this embodiment, the partition plate 14 that divides the flow path of the exhaust gas E in the heat exchanger 10 is made of refractory castable material, and the heat transfer rod material 16 is made of a predetermined ceramic material. Therefore, even if the exhaust gas E flowing through the heat exchanger 10 is extremely corrosive, corrosion of each component can be suppressed. Furthermore, since the partition plate 14 and the heat transfer rod material 16 are made of materials with relatively similar coefficients of thermal expansion, and the solid heat transfer rod material 16 has a structure that airtightly penetrates the front and back surfaces of the partition plate 14, it is possible to effectively prevent the exhaust gas E before thermal decomposition (low-temperature side fluid LF) and the exhaust gas after thermal decomposition (high-temperature side fluid HF) from leaking to the opposite flow path. Furthermore, since the partition plate 14 and heat transfer rod material 16 are made of refractory castable and ceramic materials, which have a higher melting point and lower thermal conductivity compared to metal materials used in general heat exchangers, especially when the outside of the casing 12 is covered with insulating material 12a as in this embodiment, or when the casing 12 itself is made of insulating material, it is possible to achieve not only heat exchange but also a heat retention effect on the entire inside of the exhaust gas treatment furnace 22, thereby contributing to even greater energy savings.

[0034] In the above-described embodiment, the exhaust gas treatment device X is shown to be equipped with both an inlet scrubber 24 and an outlet scrubber 26. However, since the inlet scrubber 24 and the outlet scrubber 26 are provided as needed, it is also possible to provide only one of them.

[0035] Furthermore, in the above-described embodiment, when the exhaust gas E is supplied to the flow path on the low-temperature side fluid LF side of the heat exchanger 10, which is the inlet to the exhaust gas treatment furnace 22, only the exhaust gas E is supplied alone. However, a lower saturated hydrocarbon gas such as CH4 may also be supplied together as an additive gas to promote the reaction. By adding such an additive gas, the decomposition temperature of the exhaust gas E can be lowered, which can further contribute to energy saving. Of course, various modifications can be made within the scope that a person skilled in the art could foresee. [Explanation of Symbols]

[0036] 10: Heat exchanger, 12: Casing, 12a: Insulation material, 14: Partition plate, 16: Heat transfer rod, 18: Heat source, 20: Gas treatment space, 22: Exhaust gas treatment furnace, 24: Inlet scrubber, 26: Outlet scrubber, LF: Low-temperature side fluid, HF: High-temperature side fluid, E: Exhaust gas, T: Thickness (of the partition plate), X: Exhaust gas treatment device.

Claims

1. It consists of a fire-resistant castable partition plate (14) that divides the inside of the casing (12) so that the low-temperature fluid (LF) and the high-temperature fluid (HF) flow in countercurrents, A heat exchanger characterized by comprising a plurality of solid heat transfer rods (16) made of at least one ceramic selected from the group consisting of alumina, zirconia, silicon carbide, silicon nitride, molybdenum silicide, and lanthanum chromite, which are arranged to airtightly penetrate the front and back surfaces of the partition plate (14) and cross the flow path for the low-temperature side fluid (LF) and the flow path for the high-temperature side fluid (HF).

2. In the heat exchanger according to claim 1, A heat exchanger characterized in that the thickness (T) of the partition plate (14) is 30 mm or more.

3. In the heat exchanger according to claim 1 or 2, A heat exchanger characterized in that the outer diameter of the heat transfer rods (16) is 8 mm or more and 40 mm or less, and the heat transfer rods (16) are arranged in a staggered pattern in the direction of fluid flow.

4. An exhaust gas treatment apparatus using a heat exchanger according to claim 1 or 2, An exhaust gas treatment apparatus characterized by comprising an exhaust gas treatment furnace (22) having a heat exchanger (10) formed in the lower part of a casing (12) with a partition plate (14) installed so that gas flows in the vertical direction, and a gas treatment space (20) formed in communication with the heat exchanger (10) with a heat source (18) arranged above the heat exchanger (10).

5. An exhaust gas treatment apparatus using the heat exchanger of claim 3, An exhaust gas treatment apparatus characterized by comprising an exhaust gas treatment furnace (22) having a heat exchanger (10) formed in the lower part of a casing (12) with a partition plate (14) installed so that gas flows in the vertical direction, and a gas treatment space (20) formed in communication with the heat exchanger (10) with a heat source (18) arranged above the heat exchanger (10).

6. In the exhaust gas treatment apparatus of claim 4, An exhaust gas treatment apparatus characterized by comprising at least one of the following: an inlet scrubber (24) for pre-washing the exhaust gas (E) to be treated before being introduced into the exhaust gas treatment furnace (22), or an outlet scrubber (26) for cooling and washing the exhaust gas (E) that has been thermally decomposed in the exhaust gas treatment furnace (22).

7. In the exhaust gas treatment apparatus of claim 5, An exhaust gas treatment apparatus characterized by comprising at least one of the following: an inlet scrubber (24) for pre-washing the exhaust gas (E) to be treated before being introduced into the exhaust gas treatment furnace (22), or an outlet scrubber (26) for cooling and washing the exhaust gas (E) that has been thermally decomposed in the exhaust gas treatment furnace (22).

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