Deaeration system and deaeration method
The degassing system with a plate-type heat exchanger design and opposite flow directions stabilizes the liquid-sealed vacuum pump operation by preventing bacterial growth and maintaining flow rates, addressing contamination risks in ultra-pure water production.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- NOMURA MICRO SCI CO LTD
- Filing Date
- 2025-09-04
- Publication Date
- 2026-06-18
Smart Images
Figure JP2025031259_18062026_PF_FP_ABST
Abstract
Description
Degassing System and Degassing Method 【0001】 The present invention relates to a degassing system and a degassing method having a liquid-sealed vacuum pump for reducing the pressure of a degassing device. 【0002】 Ultra-pure water used in semiconductor manufacturing processes and the like is produced by an ultra-pure water production system including a primary pure water device and a secondary pure water device in this order. The primary pure water device has a reverse osmosis membrane device, an ion exchange device, a degassing device, etc., and these remove total organic carbon (TOC) components and ion components in raw water or pre-treated water to produce primary pure water. The secondary pure water device has a degassing device, an ultraviolet irradiation device, a non-regenerative ion exchange device, an ultrafiltration device, etc., and these remove trace amounts of impurities in the primary pure water to produce ultra-pure water. The produced ultra-pure water is sent to the point of use (POU) of the ultra-pure water and used here. As the degassing device, a device that removes dissolved gas in water by reducing the pressure on the gas phase side to vacuum, such as a vacuum degassing tower or a degassing membrane, is widely used. In the degassing device, since a gas containing water vapor is reduced to vacuum on the gas phase side, a dry vacuum pump or an oil rotary vacuum pump is not suitable, and a liquid-sealed vacuum pump is preferably used. Among these liquid-sealed vacuum pumps, there is one having a configuration in which a sealing liquid is circulated by a circulation flow path. 【0003】 Japanese Patent Application Laid-Open No. 2023-55128 【0004】In the liquid-sealed vacuum pump described above, a temperature control device such as a plate-type heat exchanger is installed in the liquid-sealed circulation path to cool the liquid-sealed fluid, for example, which has been heated by the heat from the liquid-sealed vacuum pump. If bacteria or other impurities proliferate in this temperature control device, there was a concern that these bacteria and other impurities could flow out of the temperature control device into the degassing device, contaminating the ultrapure water produced. One possible solution is to add a disinfectant such as hypochlorous acid to the liquid-sealed fluid. However, with this method, for example, if a degassing membrane is used as the degassing device, there is a risk that the degassing membrane may deteriorate due to the disinfectant if the liquid-sealed fluid flows back into the degassing membrane device when the degassing membrane is stopped (when the vacuum pump is stopped). On the other hand, if hypochlorous acid is not added to the liquid-sealed fluid, there is a concern that bacteria or other impurities may proliferate in the stagnant liquid due to the effect of the water temperature rise from the liquid-sealed vacuum pump. If bacteria or other impurities proliferate in the temperature control device such as a plate-type heat exchanger, there was a risk that water would not flow easily into the plate-type heat exchanger. When water flow becomes restricted within a plate-type heat exchanger, the heat exchanger often becomes clogged, leading to insufficient circulation of the sealing fluid and potentially causing the vacuum pump to malfunction. Therefore, it became necessary to periodically clean the inside of the heat exchanger. 【0005】 The inventors conducted thorough research and confirmed that the likelihood of bacterial growth in a plate-type heat exchanger varies depending on the structure of the heat exchanger. As a result, they have completed an invention relating to a degassing system that can maintain the flow rate within a plate-type heat exchanger and stably operate a liquid-sealed vacuum pump by suppressing the growth of bacterial growth within the plate-type heat exchanger. 【0006】The degassing system or degassing method of the embodiment has the following configuration: [1] A degassing system comprising: a degassing device arranged in a pure water production apparatus that processes water to be treated to produce pure water; a liquid-sealed vacuum pump that reduces the pressure on the gas phase side of the degassing device; a circulation channel that discharges a sealing liquid from the liquid-sealed vacuum pump and circulates the discharged sealing liquid back to the liquid-sealed vacuum pump; and a plate-type heat exchanger provided in the circulation channel, wherein the plate-type heat exchanger comprises: a plurality of stacked heat transfer plates; a first frame provided on one side in the stacking direction of the plurality of heat transfer plates and having an inlet for the sealing liquid; and a second frame provided on the other side in the stacking direction of the plurality of heat transfer plates and having an outlet for the sealing liquid. [2] The degassing system according to [1] or [2], wherein the plate-type heat exchanger has an inlet for a heat transfer medium in the second frame and an outlet for a heat transfer medium in the first frame. [3] The degassing system according to [1] or [2], wherein the flow direction of the sealing liquid and the flow direction of the heat transfer medium in the plate heat exchanger are opposite flows. [4] A degassing method for producing pure water by treating water to produce pure water, comprising the steps of: discharging the sealing liquid from a liquid-sealed vacuum pump that reduces the gas phase side of the degassing device, and in the process of circulating the discharged sealing liquid to the liquid-sealed vacuum pump, supplying the sealing liquid to a plate heat exchanger to adjust the temperature, wherein the plate heat exchanger comprises a plurality of stacked heat transfer plates, a first frame provided on one side in the stacking direction of the plurality of heat transfer plates, and a second frame provided on the other side in the stacking direction of the plurality of heat transfer plates, and in the step of adjusting the temperature, introducing the sealing liquid from the first frame to the plate heat exchanger and leading out the sealing liquid from the second frame. [5] The degassing method according to [4], wherein in the step of performing the temperature control, a heat transfer medium is introduced from the second frame of the plate-type heat exchanger and the heat transfer medium is discharged from the first frame. [6] The degassing method according to [4] or [5], wherein the flow direction of the sealing liquid and the flow direction of the heat transfer medium in the plate-type heat exchanger are opposite flows. The symbol "~" indicates a numerical range including the numbers before and after it. 【0007】 According to the degassing system and degassing method of the embodiment, the growth of viable bacteria and the like in the plate-type heat exchanger provided in the degassing system can be suppressed, thereby maintaining the flow rate of the sealing liquid in the liquid-sealed vacuum pump and enabling stable operation of the liquid-sealed vacuum pump. 【0008】 This is a schematic diagram of the degassing system of the embodiment. This is a schematic diagram of the plate-type heat exchanger of the embodiment. This is a schematic diagram of the heat transfer plate of the embodiment. This is a schematic diagram of another heat transfer plate of the embodiment. This is a schematic elevation view of the plate-type heat exchanger of the embodiment. This is a schematic elevation view of a conventional plate-type heat exchanger. This is a schematic diagram of a primary pure water system having the degassing system of the embodiment. This is a schematic diagram of a secondary pure water system having the degassing system of the embodiment. 【0009】 The degassing membrane system of an embodiment will be described below with reference to the drawings. Figure 1 is a schematic diagram showing the degassing system 10 of an embodiment. The degassing system 10 includes a degassing device 16, a liquid-sealed vacuum pump 18 that reduces the pressure on the gas phase side of the degassing device 16, and a circulation channel 40 that discharges the sealing liquid from the liquid-sealed vacuum pump 18 and circulates the discharged sealing liquid back to the liquid-sealed vacuum pump. A plate-type heat exchanger 1 is provided in the path of the circulation channel 40. The degassing device 16 and the liquid-sealed vacuum pump 18 are connected by vacuum piping 19. 【0010】 The degassing device 16 is a degassing membrane device or a vacuum degassing tower. Inside the degassing membrane, for example, a degassing membrane made of hollow fiber membrane is arranged, and this hollow fiber membrane divides the inside of the degassing device 16 into a gas phase section and a liquid phase section. In the case of a vacuum degassing tower, a degassing tower filled with a packing material (called Terralet) that controls the flow of liquid is used. In a vacuum degassing tower, the inside of the degassing tower is kept under vacuum, and the water to be treated is flowed down from the top of the tower. Dissolved gases in the water to be treated are removed by degassing them into the gas phase as the water reaches the bottom of the tower. 【0011】The water to be treated, which is to be degassed, is supplied to the liquid phase of the degassing device 16. Then, the gas phase of the degassing device 16 is depressurized by the liquid-sealed vacuum pump 18, causing the dissolved gases in the water to be treated to permeate through the hollow fiber membrane and move into the gas phase. As a result, dissolved gases such as oxygen and carbon dioxide are removed from the water to be treated. 【0012】 A circulation channel 40 is connected to the liquid-sealed vacuum pump 18 for circulating the sealing liquid of the liquid-sealed vacuum pump 18. A plate-type heat exchanger 1 is provided in the path of the circulation channel 40. The sealing liquid discharged from the liquid-sealed vacuum pump 18 contains gas that has been degassed by the degassing device 16. Therefore, the degassing system 10 of this embodiment has a gas-liquid separation tank 42 in the path of the circulation channel 40. In the gas-liquid separation tank 42, gas-liquid separation is performed on the sealing liquid. The gas-liquid separation tank 42 is provided with a sealing liquid discharge pipe 47, and the sealing liquid that overflows from the gas-liquid separation tank 42 is discharged through the sealing liquid discharge pipe 47. Note that the gas-liquid separation tank 42 and the sealing liquid discharge pipe 47 are not essential and are provided as needed. Also, if the amount of sealing liquid in the gas-liquid separation tank 42 falls below a specified amount, sealing liquid is replenished into the gas-liquid separation tank 42 from a supply pipe (not shown). It is preferable to use pure water from a pure water system, intermediate water from the manufacturing process, or pre-treated water as the sealing fluid to be replenished. 【0013】 The circulation channel 40 consists of circulation pipes 40A, 40B, and 40C, and is configured to circulate the sealing liquid from the liquid-sealed vacuum pump 18 back to the liquid-sealed vacuum pump 18 via the gas-liquid separation tank 42 and the plate-type heat exchanger 1. By circulating the sealing liquid in this way, it is possible to return the sealing liquid discharged from the liquid-sealed vacuum pump 18 to the liquid-sealed vacuum pump 18 for reuse. 【0014】First, the sealing liquid is supplied from the liquid-sealed vacuum pump 18 to the gas-liquid separator tank 42 via the circulation pipe 40A. The sealing liquid from which the gas has been removed by the gas-liquid separator tank 42 flows into the circulation pipe 40B and then to the plate-type heat exchanger 1. In the plate-type heat exchanger 1, heat exchange takes place between the sealing liquid and a heat transfer medium (not shown), and the temperature of the sealing liquid is adjusted to a predetermined range. The adjusted temperature of the sealing liquid is room temperature, for example, between 5°C and 25°C. The sealing liquid whose temperature has been adjusted by the plate-type heat exchanger 1 flows into the circulation pipe 40C and returns to the liquid-sealed vacuum pump 18 again. 【0015】 The plate-type heat exchanger 1 comprises a plurality of stacked heat transfer plates, a first frame provided on one side in the stacking direction of the plurality of heat transfer plates and having an inlet for the sealing liquid, and a second frame provided on the other side in the stacking direction of the plurality of heat transfer plates and having an outlet for the sealing liquid. As a result, the sealing liquid is introduced from the first frame side and discharged from the second frame side. 【0016】In the degassing system 10 of this embodiment, the plate-type heat exchanger 1 may be placed vertically or horizontally. Here, vertical placement is when the long side of the heat transfer plate is in the direction of gravity. Horizontal placement is when the short side of the heat transfer plate is in the direction of gravity. In both vertical and horizontal placement, the surface of the heat transfer plate is parallel to the direction of gravity. Since the suction pressure and discharge pressure of the sealing liquid of the liquid-sealed vacuum pump 18 are not large, vertical placement makes it difficult for the sealing liquid to circulate within the degassing system 10. In contrast, horizontal placement makes it easier for the sealing liquid to circulate within the plate-type heat exchanger 1 because the height (vertical position) of the inlet and outlet of the sealing liquid is relatively small. For this reason, it is preferable to place the plate-type heat exchanger 1 horizontally. Furthermore, in the degassing system 10 of this embodiment, it is preferable that the circulation channel 40 be installed on the same plane so that the flow path of the sealing liquid is as horizontal as possible. In other words, it is preferable that the liquid-sealed vacuum pump 18, the gas-liquid separation tank 42, and the plate-type heat exchanger 1 be installed such that the difference in height of the flow path of the sealing liquid in them is minimized. In particular, it is preferable that the gas-liquid separation tank 42, the circulation piping 40B, the plate-type heat exchanger 1, and the circulation piping 40C be arranged such that the difference in height of the flow path of the sealing liquid in them is minimized. It is also possible to install the plate-type heat exchanger 1 on the circulation piping 40A. 【0017】Figure 2 is a schematic diagram of the plate-type heat exchanger 1 of the above embodiment, and is a side view when the plate-type heat exchanger 1 is placed on the ground or the like, with the surface of the first frame facing forward. The plate-type heat exchanger 1 has a first frame 11 and a second frame 12. The first frame 11 and the second frame 12 are spaced apart, and a plurality of heat transfer plates 4 are arranged between the first frame 11 and the second frame 12. The first frame 11 is provided with an inlet 2a for the water to be treated, and the second frame 12 is provided with an outlet 2b for the water to be treated. The heat transfer plates 4 of the plate-type heat exchanger 1 of this embodiment are substantially rectangular, and their surfaces are made up of irregularities that serve as fluid passages. The heat transfer plates 4 have passage holes 5a, 5b, 13a, and 13b at the four corners of their irregular heat transfer surface, which serve as fluid inlets and outlets (see Figure 3). Gaskets 3 are provided between the outer peripheries of the multiple heat transfer plates 4, and the first frame 11 and the second frame 12 are fixed from both sides with tightening bolts (not shown). Between the multiple heat transfer plates 4, water passages 21a, 22a, 23a, 24a, 25a, 26a and heat transfer medium passages 21b, 22b, 23b, 24b, 25b, 26b, 27b are alternately formed. The water passages 21a to 26a are connected to an inlet 2a and an outlet 2b provided on the first frame 11. Heat from the heat transfer medium flowing through the heat transfer medium passages 21b to 27b is transferred to the water passages 21a to 26a via the heat transfer plates 4, and the water is heated or cooled. 【0018】Figure 3 is a schematic diagram of the heat transfer plate 4 of this embodiment. The heat transfer plate 4 has irregularities (not shown) formed on its surface that serve as fluid passages, and is usually made of a metal material such as stainless steel or titanium. The heat transfer plate 4 has fluid passage holes 5a, 13a, 5b, and 13b around its outer circumference. The passage holes 5a and 5b are a pair of fluid inlets 5a and outlets 5b. The passage holes 13a and 13b are a pair of fluid inlets 13a and outlets 13b. The heat transfer plate 4 has two pairs of inlets and outlets: inlet 5a and outlet 5b and inlet 13a and outlet 13b. Preferably, the pairs of inlets and outlets are spaced apart so that the passage for the water to be treated or the heat transfer medium flowing through the heat transfer plate is as long as possible. If the heat transfer plate 4 is substantially rectangular, the inlets and outlets are provided at two diagonal corners of the four corners of the rectangle. Specifically, the inlet 5a and outlet 5b are located at two diagonal corners, and the inlet 13a and outlet 13b are located at two diagonal corners. The heat transfer plate 4 has gaskets 3 near its outer circumference and near the outer circumferences of the passage holes 5a, 13a, 5b, and 13b. The heat transfer plate 4 shown in Figure 3 allows the water to be treated to flow through the flow path formed by the gaskets 3 and the heat transfer plate 4. The water to be treated flows in from the passage hole (inlet) 5a, flows in the direction of the dotted line in the figure, and flows out from the passage hole (outlet) 5b. Note that Figure 3 shows an configuration in which the inlet 5a and outlet 5b are located at two diagonal corners, but Figure 2 shows a configuration in which the inlet 5a and outlet 5b are located at adjacent corners for the sake of explanation. 【0019】 Figure 4 is a schematic diagram showing one of the multiple heat transfer plates 4 of the plate-type heat exchanger 1 of this embodiment. The heat transfer plate 4 shown in Figure 3 allows a heat transfer medium to flow through the flow path formed by the gasket 3 and the heat transfer plate 4. The heat transfer medium flows in from the passage hole (inlet) 13a, flows in the direction of the dotted line in the figure, and flows out from the passage hole (outlet) 13b. 【0020】In Figures 2 to 4, the gasket 3 is positioned at the outer edge of the heat transfer plate 4. The gasket 3 is made of an elastic material having a predetermined width and thickness, and has a sealing function to prevent fluid leakage by liquid-tightly sealing the outer edge of the heat transfer plate 4. Preferably, the gasket 3 is sandwiched between the heat transfer plate 4 and in surface contact with the heat transfer plate 4. Furthermore, it is preferable that the shape of the gasket 3 is such that its cross-section, at least the cross-section perpendicular to the longitudinal direction, is rectangular, and the outer edge of the gasket 3 facing the outside and inside of the plate-type heat exchanger 1 is a flat surface without curves. The rectangular cross-section minimizes the gap between the gasket 3 and the heat transfer plate 4, thereby suppressing water accumulation in the plate-type heat exchanger 1. Similarly, the flat outer edge minimizes the gap between the gasket 3 and the heat transfer plate 4, thereby suppressing water accumulation in the plate-type heat exchanger 1. Furthermore, since the plate-type heat exchanger 1 of this embodiment introduces the water to be treated from the first frame side and discharges the water to be treated from the second frame side, air is less likely to accumulate inside. Also, since an air outlet means can cause the accumulation of impurities, it is preferable that the plate-type heat exchanger 1 of this embodiment does not have an air outlet means. 【0021】 Furthermore, in Figures 2 to 4, it is preferable that the inner diameter of the inlet 2a and the inner diameter of the passage hole 5a be approximately the same as the inner diameter of the gasket 3 surrounding the inlet 2a and the passage hole 5a, thereby creating a shape that does not produce irregularities that could cause the accumulation of impurities in the inflow path of the water to be treated flowing into the plate-type heat exchanger 1. Similarly, it is preferable that the inner diameter of the outlet 2b and the inner diameter of the passage hole 5b be approximately the same as the inner diameter of the gasket 3 surrounding them. Moreover, it is preferable that the inner diameter of the passage hole 13b and the inner diameter of the gasket 3 surrounding them be approximately the same to suppress the accumulation of the water to be treated. The shape of the gasket 3 is preferably such that no accumulation areas such as irregularities are created between it and the passage hole provided on the heat transfer plate 4. The gasket 3 sandwiched between the two heat transfer plates 4 may be integrally molded, or multiple gaskets may be used. 【0022】In the degassing method of this embodiment, the water to be treated is introduced into the plate-type heat exchanger 1 from the inlet 2a of the first frame 11, flows through the flow path on the surface of the heat transfer plate 4, and is discharged from the outlet 2b of the second frame 12. 【0023】 The material of the plate-type heat exchanger 1 in the embodiment is stainless steel, titanium, iron, Hastelloy®, copper, etc. Since the quality of the sealing fluid is not a particular problem, it is preferable that the wetted surfaces of the heat transfer plates and the first and second frames be made of stainless steel or iron, from the standpoint of availability and cost. 【0024】Figure 5 is a simplified schematic diagram showing the passage of water to be treated within the heat exchanger (plate-type heat exchanger) 1 shown in Figure 2. It is an elevation view when the plate-type heat exchanger 1 is placed on the ground or the like, with the surface of the first frame 11 facing forward. The plate-type heat exchanger 1 shown in Figure 5 has a first frame 11 and a second frame 12. Multiple heat transfer plates 4 are arranged between the first frame 11 and the second frame 12. The first frame 11 is provided with an inlet 2a, and the second frame 12 is provided with an outlet 2b. In Figure 5, the dotted line represents the flow path of the water to be treated. The diagonal lines represent the passage of the heat transfer medium. In the plate-type heat exchanger 1 shown in Figure 5, water to be treated is introduced from the inlet 2a on the first frame 11 side, and the water to be treated is discharged from the outlet 2b on the second frame 12 side. As a result, all of the multiple water passages to be treated, located between the heat transfer plates, have the same length, so the flow velocity in each of the multiple water passages to be treated does not differ, and a common flow velocity can be ensured in all of the multiple water passages to be treated. As a result, the flow velocity of the water to be treated in the plate-type heat exchanger 1 tends to be uniform, and heat exchange can be performed efficiently. Therefore, even if the number of heat transfer plates is reduced or the flow rate introduced from the inlet 2a is increased, sufficient heat exchange can be performed, making it possible to miniaturize the plate-type heat exchanger. In addition, because the flow velocity in the heat exchanger is increased, water is less likely to stagnate inside. Therefore, for example, water stagnation at the boundary between the heat transfer plate 4 and the gasket 3 in the heat exchanger is less likely to occur, and it is less likely to become a source of bacterial growth. The plate-type heat exchanger 1 used in the degassing system 10 of this embodiment may be placed vertically or horizontally. If placed vertically, the height difference between the inlet and outlet of the sealing liquid becomes large, making it difficult for water to flow in the plate-type heat exchanger 1. Placing the plate-type heat exchanger horizontally is preferable because it reduces the height difference between the inlet and outlet, making it easier for water to flow within the heat exchanger. 【0025】Figure 6 is a simplified schematic diagram showing the passage of water to be treated in a conventional plate-type heat exchanger 100. The conventional plate-type heat exchanger 100 has both the inlet and outlet of water to be treated on the first frame 11 side, and other components are the same as the plate-type heat exchanger 1 shown in Figures 2 and 5. Therefore, components that perform the same function are given the same reference numerals and detailed explanations are omitted. Figure 6 is an elevation view of the plate-type heat exchanger 100 when it is placed on the ground or the like, with the surface of the first frame 11 facing forward. In Figure 6, the dotted lines represent the flow path of water to be treated. 【0026】 In the plate-type heat exchanger 100 shown in Figure 6, the water to be treated is introduced from an inlet 80a located on the first frame 11 side, and the water to be treated is discharged from an outlet 80b located on the first frame 11 side. As a result, the multiple water-to-treat passages located between the heat transfer plates become shorter the closer they are to the first frame 11 and longer the further they are from the first frame 11. This difference in length affects the flow velocity of the water to be treated. That is, the flow velocity in the multiple water-to-treat passages becomes higher the closer they are to the first frame 11 and lower the further they are from the first frame 11. As a result, heat exchange within the plate-type heat exchanger 100 tends to become inefficient. Consequently, in order to perform sufficient heat exchange, it is necessary to reduce the flow rate introduced from the inlet 2a, and reducing the flow rate slows down the flow velocity within the plate-type heat exchanger 100. This makes it easier for water to stagnate in areas where impurities are particularly likely to accumulate, such as the boundary between the heat transfer plates 4 and the gasket 3. Bacterial adhesion occurs in the stagnation, and biofouling is formed starting from this bacterial adhesion. When biofouling forms, the heat exchange performance of the plate heat exchanger deteriorates. Furthermore, when biofouling forms, the sealing fluid has difficulty flowing through the plate heat exchanger, and as a result, the flow rate within the plate heat exchanger decreases significantly due to the characteristics of liquid-sealed vacuum pumps, which do not have high suction or discharge pressures. Due to these factors, if the sealing fluid supplied to the liquid-sealed vacuum pump is not cooled sufficiently, the sealing fluid circulating in the degassing system 10 becomes hot, leading to a decrease in the performance of the vacuum pump and increasing the possibility of the vacuum pump breaking down. 【0027】Next, a primary pure water system using the degassing system 10 of this embodiment will be described. Figure 7 is a schematic diagram of the primary pure water system 60 of this embodiment. The primary pure water system 60 is equipped with a reverse osmosis membrane system (RO) 61, an ultraviolet irradiation device (TOC-UV) 62, a degassing device 16, and a mixed-bed ion exchange device (MB) 63 in this order, and processes raw water to produce primary pure water. 【0028】 The raw water can be city water, well water, groundwater, river water, industrial water, or spent ultrapure water (recovered water) from semiconductor manufacturing processes. The raw water may be pretreated by an activated carbon device, a cation exchange device (SC), a decarbonation tower (DG), etc., before being supplied to the primary pure water device 60. 【0029】 Activated carbon systems remove chrominance components such as humic substances and / or dissolved organic carbon (DOC) components derived from humic substances, and suspended solids from raw water using activated carbon. Humic substances are humic substances produced when plants and other materials are decomposed by microorganisms, and include humic acid, fulvic acid, etc. As for activated carbon, coconut shell-based or coal-based activated carbon can be used, molded into powder, granular, fibrous, plate-shaped, or honeycomb shape. 【0030】 The cation exchange device removes cation components from the raw water by exchanging them with a cation exchange resin. Either a strongly acidic cation exchange resin or a weakly acidic cation exchange resin, or both, can be used as the cation exchange resin. To prevent scaling in the subsequent reverse osmosis membrane device 61, it is preferable to use a strongly acidic cation exchange resin because it has excellent performance in removing alkaline earth metals. 【0031】 The decarboxylation device performs decarboxylation treatment on cation exchange treated water. In the decarboxylation treatment, dissolved carbon dioxide is removed from the water to be treated, producing decarboxylated water with a reduced carbon dioxide concentration. This prevents scale buildup in the reverse osmosis membrane device 61 of the primary pure water device 60. 【0032】Furthermore, the treated water from the decarbonation device may be supplied to the primary pure water device 60 after passing through a decomposition device. The decomposition device, for example, has one or more airtight treatment tanks, and the water to be treated is kept in the treatment tanks for a certain period of time to decompose and remove urea and other organic substances from the water to be treated. In the treatment tanks, chemicals are added to the water to be treated while the pH is adjusted to an appropriate value according to the substance to be decomposed. Oxidizing agents such as ozone, hydrogen peroxide, hypobromous acid, hypochlorous acid, and persulfuric acid are used as chemicals. Alternatively, the decomposition device may also perform biodecomposition treatment using a biological treatment tank or the like. When the decomposition device decomposes urea, for example, hypobromous acid can be added to the water to be treated while the pH of the water to be treated in the treatment tank is adjusted to 9 or higher to decompose the urea in the water to be treated. It is also possible to use an ion exchange device instead of a decomposition device. An ion exchange device has an ion exchange resin, which removes ionic components from the water. Ion exchange resins include cationic resins, anionic resins, boron-selective ion exchange resins, and catalytic resins. In this case as well, it is possible to maintain the optimal temperature of the treated water in the ion exchange device, thereby enabling the maintenance of good treated water quality. 【0033】 The reverse osmosis membrane apparatus 61 removes salts and impurities such as ionic and colloidal organic matter from the urea decomposition water to produce concentrated water and permeate. As the reverse osmosis membrane apparatus 61, a cellulose triacetate asymmetric membrane or a polyamide composite membrane can be used, and membrane modules such as sheet flat membranes, spiral membranes, tubular membranes, and hollow fiber membranes can be used. Among these, a polyamide composite membrane is preferred in order to increase the rate of impurity removal, and a spiral membrane shape is preferred. The rate of impurity removal may be improved by connecting two reverse osmosis membrane apparatuses 61 in series to form a two-stage reverse osmosis membrane apparatus. 【0034】The ultraviolet irradiation device 62 decomposes trace amounts of organic matter remaining in the treated water of the reverse osmosis membrane device 61 by irradiating it with ultraviolet light. The deaerating device 16 is the deaerating device 16 of the embodiment shown in Figure 1 and has a deaerating system 10. The deaerating device 16 removes gas, especially dissolved oxygen, from the treated water of the ultraviolet irradiation device 62 using a gas separation membrane (deaerating membrane) that does not allow water to pass through but allows gas to pass through. The pressure in the deaerating device 16 (pressure after depressurization) is preferably, for example, 10 to 100 Torr. In addition, a small amount of nitrogen may be supplied into the deaerating device 16, which improves the treated water quality of the deaerating device. The amount of nitrogen supplied is about 1 to 5 volume percent (at room temperature) relative to the amount of water to be treated. In addition, a vacuum deaerating tower can be used instead of a deaerating membrane as the deaerating device 16. The treated water from the deaerating device 16 is supplied to the mixed-bed ion exchange device 63. The mixed-bed ion exchange apparatus 63 adsorbs and removes organic acids and other substances produced by the decomposition of organic matter. Instead of the mixed-bed ion exchange apparatus 63, an electrodeionizer (EDI) may be installed, or an electrodeionizer (EDI) or a boron-selective ion exchange column may be installed immediately before the mixed-bed ion exchange apparatus 63. In the primary pure water apparatus 60 shown in Figure 6, the mixed-bed ion exchange apparatus 63 processes the treated water from the degasser 16, but the order of the degasser 16 and the mixed-bed ion exchange apparatus 63 may be reversed, with the mixed-bed ion exchange apparatus 63 installed before the degasser 16 so that the degasser 16 processes the treated water from the mixed-bed ion exchange apparatus 63. 【0035】 The primary pure water system 60 uses the deaeration system 10 of the above-described embodiment in the deaeration device 16. This suppresses the growth of viable bacteria and other microorganisms in the plate-type heat exchanger provided in the deaeration system 10. As a result, the flow rate in the plate-type heat exchanger can be maintained, and the liquid-sealed vacuum pump can be operated stably. 【0036】Figure 8 is a schematic diagram of the secondary pure water system 50 of this embodiment. Primary pure water produced by the primary pure water system 20 shown in Figure 7 is stored in the pure water tank 51 shown in Figure 7 and supplied to the secondary pure water system 50 by a pump 52. The secondary pure water system 50 has water treatment piping 50a, and the route of the water treatment piping 50a is equipped with a degassing membrane device 53, an ultraviolet irradiation device 54, a non-regenerative ion exchange device (polisher) 55, and an ultrafiltration membrane device 56. The order of the degassing membrane device 53 and the ultraviolet irradiation device 54 is not limited to this order, and the degassing membrane device may be provided after the ultraviolet irradiation device. A portion of the secondary pure water (ultrapure water) produced by the secondary pure water system 50 is supplied to the point of use (POU) 500 for use, and the unused secondary pure water is returned to the pure water tank 51 via the circulation piping 50b. In the secondary pure water system 50 shown in Figure 7, an oxidizing agent removal resin tower or a catalyst resin tower may be installed immediately before the non-regenerative ion exchange device (polisher) 55. Although the non-regenerative ion exchange device (polisher) 55 is located downstream of the degassing membrane device 53, the degassing membrane device 53 may be installed downstream of the non-regenerative ion exchange device (polisher) 55 so that the degassing membrane device 53 processes the treated water from the non-regenerative ion exchange device (polisher) 55. 【0037】 In the secondary pure water system 50 shown in Figure 8, the degassing membrane device 53 is the degassing device 16 of the embodiment shown in Figure 1, and has a degassing system 10. This suppresses the growth of live bacteria and other organisms in the plate-type heat exchanger provided in the degassing system 10. As a result, the flow rate in the plate-type heat exchanger can be maintained, and the liquid-sealed vacuum pump can be operated stably. 【0038】 Next, examples will be described. The present invention is not limited to the following examples. A degassing system similar to that shown in Figure 1 was used. A degassing membrane was used as the degassing device, and degassing was performed in a primary pure water system. The conditions were as follows: Degassing membrane: Lixel X40 36 units Vacuum pump: Nikuni water-sealed vacuum pump 2 units Circulation flow rate: 9 m ３ / h Heat Exchanger: The plate heat exchanger of the above embodiment (where the inlet and outlet of the sealed liquid are installed on the plates at both ends of the heat exchanger). Plate size: 40 cm × 90 cm. Number of plates: 10 (thickness with 10 plates: 5 cm). Heat medium (refrigerant): Chilled water (15°C) 【0039】 (Example 1) In Example 1, the plate heat exchanger was placed vertically, and the treated water was introduced from the first frame side of the plate heat exchanger and discharged from the second frame side opposite to the first frame side, and continuous operation was carried out for one year. In the case of the example, from the start of water flow, for one year, the water temperature of the outlet water of the heat exchanger was stable at 10°C, and also, the flow rate was stable at 8 m ３ / h, and since no decrease in the flow rate was observed, maintenance was not required. 【0040】 (Example 2) In Example 2, the plate heat exchanger was placed horizontally, and the treated water was introduced from the first frame side of the plate heat exchanger and discharged from the second frame side opposite to the first frame side, and continuous operation was carried out. In the case of the example, from the start of water flow, for one and a half years, the water temperature of the outlet water of the heat exchanger was stable at 10°C, and also, the flow rate was stable at 9 m ３ / h, and since no decrease in the flow rate was observed, maintenance was not required. 【0041】 (Comparative Example 1) In Example 1, except that the flow holes (inlet) and flow holes (outlet) of the treated water were changed to be installed on the plates on the same side of the heat exchanger, and the number of plates was changed to 20 (thickness with 20 plates: 10 cm), it was placed vertically and continuous operation was carried out for one year in the same manner as in Example 1. In Comparative Example 1, since the heat exchange performance of the heat exchanger was inferior to that of the example, the number of plates was increased compared to the example. In Comparative Example 1, the flow rate was 7 m ３ / h from the beginning, and at around the time when approximately four months had passed, the water temperature of the outlet water of the heat exchanger rose to 13°C, and also, the flow rate decreased to approximately 6 m ３ / h, so decomposition cleaning of the heat exchanger was required. 【0042】(Comparative Example 2) In Comparative Example 2, the heat exchanger was operated horizontally for one year, except that the heat exchanger was installed on the same side of the heat exchanger for the water passage (inlet) and the heat exchanger for the passage (outlet) was changed to one on the same side of the heat exchanger, and the number of plates was increased to 20 (a thickness of 10 cm with 20 plates). In Comparative Example 2, the heat exchange performance of the heat exchanger was inferior to that of the example, so the number of plates was increased compared to the example. In Comparative Example 2, the flow rate was 8 m³ from the beginning. ３ At a rate of 0 / h, after approximately 5 months, the water temperature at the outlet of the heat exchanger rises to 13°C, and the flow rate is approximately 6 m³. ３ The temperature dropped to / h, necessitating the disassembly and cleaning of the heat exchanger. 【0043】 1: Plate-type heat exchanger, 2a: Inlet, 2b: Outlet, 3: Gasket, 4: Heat transfer plate, 5a: Through hole (inlet), 5b: Through hole (outlet), 11: First frame, 12: Second frame, 13a: Through hole (inlet), 13b: Through hole (outlet), 20: Primary pure water system, 21: Reverse osmosis membrane system, 21a, 22a, 23a, 24a, 25a, 26a: Water to be treated passage, 21b, 22b, 23b, 24b, 25b, 26b, 27b: Heat transfer medium passage, 62: Ultraviolet irradiation device, 63 : Mixed-bed ion exchange system, 10: Degassing system, 16: Degassing device, 18: Liquid-sealed vacuum pump, 19: Vacuum piping, 40: Circulation channel, 42: Gas-liquid separation tank, 40A: Circulation piping, 40B: Circulation piping, 40C: Circulation piping, 50: Secondary pure water system, 50a: Water treatment piping, 50b: Circulation piping, 51: Pure water tank, 52: Pump, 53: Ultraviolet irradiation device, 54: Degassing membrane device, 56: Ultrafiltration membrane device, 47: Seal liquid discharge piping, 80a: Inlet, 80b: Outlet, 100: Plate-type heat exchanger
Claims
1. A degassing system comprising: a degasser arranged in a pure water production apparatus that processes water to be treated to produce pure water; a liquid-sealed vacuum pump that reduces the pressure on the gas phase side of the degasser; a circulation channel that discharges the sealing liquid from the liquid-sealed vacuum pump and circulates the discharged sealing liquid back to the liquid-sealed vacuum pump; and a plate-type heat exchanger provided in the circulation channel, wherein the plate-type heat exchanger comprises: a plurality of stacked heat transfer plates; a first frame provided on one side in the stacking direction of the plurality of heat transfer plates and having an inlet for the sealing liquid; and a second frame provided on the other side in the stacking direction of the plurality of heat transfer plates and having an outlet for the sealing liquid.
2. The degassing system according to claim 1 or 2, wherein the plate-type heat exchanger is provided with an inlet for a heat transfer medium in the second frame and an outlet for a heat transfer medium in the first frame.
3. The degassing system according to claim 1 or 2, wherein the flow direction of the sealing liquid and the flow direction of the heat transfer medium within the plate-type heat exchanger are opposite flows.
4. A method for producing pure water by treating water to be treated using a degasser, comprising the steps of supplying the sealing liquid to a plate-type heat exchanger for temperature control during the process of discharging a sealing liquid from a liquid-sealed vacuum pump that reduces the gas phase on the degasser side and circulating the discharged sealing liquid back to the liquid-sealed vacuum pump, wherein the plate-type heat exchanger comprises a plurality of stacked heat transfer plates, a first frame provided on one side in the stacking direction of the plurality of heat transfer plates, and a second frame provided on the other side in the stacking direction of the plurality of heat transfer plates, and in the step of temperature control, the sealing liquid is introduced into the plate-type heat exchanger from the first frame and the sealing liquid is discharged from the second frame.
5. The degassing method according to claim 4, wherein, in the step of performing the temperature control, a heat transfer medium is introduced from the second frame of the plate-type heat exchanger and the heat transfer medium is discharged from the first frame.
6. The degassing method according to claim 4 or 5, wherein the flow direction of the sealing liquid and the flow direction of the heat transfer medium in the plate-type heat exchanger are opposite flows.