Degassing system and degassing method

Abstract

The present invention provides a degassing system that suppresses the growth of bacteria and other microorganisms within a plate-type heat exchanger, thereby maintaining the flow rate within the plate-type heat exchanger and enabling stable operation of a liquid-sealed vacuum pump. [Solution] A degassing system comprising: a degasser 16 arranged in a pure water production apparatus that processes water to be treated to produce pure water; a liquid-sealed vacuum pump 18 that reduces the pressure on the gas phase side of the degasser; a circulation channel 40 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.

Description

Technical Field

[0001] The present invention relates to a degassing system and a degassing method having a liquid-sealed vacuum pump for decompressing a degassing device.

Background Art

[0002] Ultrapure water used in semiconductor manufacturing processes and the like is produced by an ultrapure 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 pretreated 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 extremely trace amounts of impurities in the primary pure water to produce ultrapure water. The produced ultrapure water is sent to the point of use (POU) of the ultrapure water and used here. As the degassing device, a device that removes dissolved gases in water by decompressing the gas phase side to a 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 decompressed to a 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. Some of these liquid-sealed vacuum pumps have a configuration in which a sealing liquid is circulated by a circulation flow path.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[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 is a concern that these bacteria and other impurities will 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 rise in water temperature 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 is a risk that water will 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. [Means for solving the problem]

[0006] Embodiments of the present invention have the following configurations. [1] A degasser is placed 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 for discharging the sealing liquid from the liquid-sealed vacuum pump and circulating the discharged sealing liquid back to the liquid-sealed vacuum pump, A degassing system having a plate-type heat exchanger provided in the aforementioned circulation channel, The plate-type heat exchanger comprises a plurality of stacked heat transfer plates, A first frame is provided on one side of the stacking direction of the plurality of heat transfer plates and has an inlet for the sealing liquid, A degassing system comprising: a second frame provided on the other side of the stacking direction of the plurality of heat transfer plates and having an outlet for the sealing liquid. [2] The plate-type heat exchanger is provided with an inlet for a heat transfer medium in the second frame, The degassing system according to [1] or [2], further comprising a heat transfer medium outlet 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 method for producing pure water by treating water to be treated, comprising a degassing method for the water to be treated, In the process of discharging the sealing liquid from a liquid-sealed vacuum pump that reduces the gas phase on the degassing device and circulating the discharged sealing liquid back to the liquid-sealed vacuum pump, The process involves supplying a sealing liquid to a plate-type heat exchanger to control the temperature. The plate-type heat exchanger comprises a plurality of stacked heat transfer plates, A first frame provided on one side of the stacking direction of the plurality of heat transfer plates, It comprises a second frame provided on the other side of the stacking direction of the plurality of heat transfer plates, A degassing method comprising the step of performing the temperature control, wherein 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] In the process of performing the temperature control, A heat transfer medium is introduced from the second frame of the plate-type heat exchanger. The degassing method according to [4], wherein a 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 heat exchanger are opposite flows. Note that the symbol "~" indicates a numerical range including the numerical values before and after it.

Advantages of the Invention

[0007] According to the degassing system and degassing method of the present invention, it is possible to suppress the growth of live bacteria and the like in the plate heat exchanger provided in the degassing system, and thereby maintain the flow rate of the sealing liquid of the liquid-sealed vacuum pump and stably operate the liquid-sealed vacuum pump.

Brief Description of the Drawings

[0008] [Figure 1] It is a diagram schematically showing the degassing system of the embodiment. [Figure 2] It is a diagram schematically showing the plate heat exchanger of the embodiment. [Figure 3] It is a diagram schematically showing the heat transfer plate of the present embodiment. [Figure 4] It is a diagram schematically showing another heat transfer plate of the present embodiment. [Figure 5] It is an elevation view schematically showing the plate heat exchanger of the embodiment. [Figure 6] It is an elevation view schematically showing a conventional plate heat exchanger. [Figure 7] It is a diagram schematically showing a primary pure water device having the degassing system of the embodiment. [Figure 8] It is a diagram schematically showing a secondary pure water device having the degassing system of the embodiment.

Modes for Carrying Out the Invention

[0009] Hereinafter, a deaeration membrane system according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram schematically showing a deaeration system 10 of the embodiment. The deaeration system 10 includes a deaerator 16, a liquid-sealed vacuum pump 18 for reducing the pressure on the gas phase side of the deaerator 16, and a circulation flow path 40 for discharging the sealing liquid from the liquid-sealed vacuum pump 18 and circulating 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 flow path 40. The deaerator 16 and the liquid-sealed vacuum pump 18 are connected by a vacuum pipe 19.

[0010] The deaerator 16 is a deaeration membrane device or a vacuum deaeration tower. Inside the deaeration membrane, a deaeration membrane made of hollow fiber membranes, for example, is disposed, and the inside of the deaerator 16 is partitioned into a gas phase part and a liquid phase part by the hollow fiber membranes. In addition, in the vacuum deaeration tower, a deaeration tower filled with a filler (called teralite) for controlling the flow-down of the liquid is used. The inside of the deaeration tower is kept in a vacuum state, and the water to be treated is allowed to flow down from the top of the tower, and the dissolved gas in the water to be treated is deaerated into the gas phase and removed before the water to be treated reaches the bottom of the tower.

[0011] The water to be treated, which is the object of deaeration, is supplied to the liquid phase part of the deaerator 16. Then, the gas phase part of the deaerator 16 is depressurized by the liquid-sealed vacuum pump 18, so that the dissolved gas in the water to be treated permeates through the hollow fiber membranes and moves to the gas phase part. Thereby, dissolved gases such as oxygen and carbonic acid are removed from the water to be treated.

[0012] A circulation channel 40 is connected to 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 this 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 from 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 liquid to be replenished.

[0013] The circulation channel 40 consists of multiple 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. 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, alternating water passages 21a, 22a, 23a, 24a, 25a, 26a and heat transfer medium passages 21b, 22b, 23b, 24b, 25b, 26b, 27b are 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, causing the water to be 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 approximately rectangular, the inlets and outlets are provided at two diagonal corners of the four corners of the rectangle. Specifically, inlets 5a and outlets 5b are located at two diagonally opposite corners, and inlets 13a and outlets 13b are located at two diagonally opposite 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 while Figure 3 shows an configuration in which inlets 5a and outlets 5b are located at two diagonally opposite corners, Figure 2 shows a configuration in which inlets 5a and outlets 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 2-4, 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 a rectangle in cross-section, at least the cross-section perpendicular to the longitudinal direction, and that 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 2-4, 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 in the inflow path of the water to be treated flowing into the plate-type heat exchanger 1 that could cause the accumulation of impurities. 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. In addition, 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 ultrapure water production 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 shaded line represents 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 stagnation inside is less likely to occur. Therefore, for example, water stagnation at the boundary between the heat transfer plate 4 and the gasket 3 inside 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 inside 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, allowing water to flow more easily 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 are 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 is 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 be 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 this 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, due to the characteristics of liquid-sealed vacuum pumps, which do not have high suction or discharge pressures, the flow rate within the plate heat exchanger decreases significantly. If the sealing fluid supplied to the liquid-sealed vacuum pump is not cooled sufficiently due to these factors, 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 likelihood 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 showing 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) 23 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 activated carbon equipment, cation exchange equipment (SC), decarbonation tower (DG), etc., before being supplied to the primary pure water system 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 offers superior removal performance for alkaline earth metals.

[0031] The decarboxylation unit 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 unit 61 of the primary pure water unit 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 retained 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 impurity removal rate, and a spiral membrane shape is preferred. The impurity removal rate 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. It is also possible to use a vacuum deaerating tower 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 unit 63 adsorbs and removes organic acids and other substances produced by the decomposition of organic matter. Instead of the mixed-bed ion exchange unit 63, an electrodeionizer (EDI) may be installed, or an electrodeionizer (EDI) and a boron-selective ion exchange column may be installed immediately before the mixed-bed ion exchange unit 63. In the primary pure water system 60 shown in Figure 6, the mixed-bed ion exchange unit 63 processes the treated water from the degasser 16, but the order of the degasser 16 and the mixed-bed ion exchange unit 63 may be reversed, with the mixed-bed ion exchange unit 63 installed before the degasser 16 so that the degasser 16 processes the treated water from the mixed-bed ion exchange unit 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 along the path of the water treatment piping 50a are an ultraviolet irradiation device 53, a degassing membrane device 54, a non-regenerative ion exchange device (polisher) 55, and an ultrafiltration membrane device 56. 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. The non-regenerative ion exchange device (polisher) 55 processes the treated water from the degassing membrane device 54. Alternatively, the order of the non-regenerative ion exchange device (polisher) 55 and the degassing membrane device 54 may be reversed so that the degassing membrane device 54 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 54 is the degassing device 16 of the embodiment shown in Figure 1, and has a degassing system 10. This suppresses the growth of viable 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. [Examples]

[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: Lixil X40 36 tubes Vacuum pumps: Two Nikuni water-sealed vacuum pumps Circulation flow rate: 9m 3 / h Heat exchanger: Plate-type heat exchanger of the above embodiment (with the inlet and outlet of the sealing fluid installed on plates at both ends of the heat exchanger) Plate size: 40cm x 90cm. Number of plates: 10 (thickness of 10 plates: 5cm). Heat medium (refrigerant): Cold water (15℃)

[0039] (Example 1) In Example 1, a plate-type heat exchanger was placed vertically, and the water to be treated was introduced from the first frame side of the plate-type heat exchanger and discharged from the second frame side opposite the first frame side, and the system was operated continuously for one year. In this example, the water temperature at the outlet of the heat exchanger remained stable at 10°C for one year from the start of water flow, and the flow rate was 8 m³. 3 The flow rate remained stable at / h, and no decrease in flow rate was observed, so maintenance was not required.

[0040] (Example 2) In Example 2, a plate-type heat exchanger was placed horizontally, and the water to be treated was introduced from the first frame side of the plate-type heat exchanger and discharged from the second frame side opposite the first frame side for continuous operation. In this example, the water temperature at the outlet of the heat exchanger remained stable at 10°C for 1.5 years from the start of water flow, and the flow rate was 9 m³. 3 The flow rate remained stable at / h, and no decrease in flow rate was observed, so maintenance was not required.

[0041] (Comparative Example 1) In Example 1, the heat exchanger was operated vertically for one year, except that the inlet and outlet of the water to be treated were installed on the same side of the plate, and the number of plates was increased to 20 (a thickness of 10 cm with 20 plates). In Comparative Example 1, 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 1, the flow rate was 7 m³ from the beginning. 3 At a rate of approximately 6 m³ / h, after about 4 months, the water temperature at the outlet of the heat exchanger rose to 13°C, and the flow rate was approximately 6 m³ / h. 3 The temperature dropped to / h, necessitating the disassembly and cleaning of the heat exchanger.

[0042] (Comparative Example 2) In 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 both the inlet and outlet of the water to be treated, 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 Example 1, so the number of plates was increased compared to Example 1. In Comparative Example 2, the flow rate was 8 m³ from the beginning. 3 At a rate of approximately 6 m³ / h, after about 5 months, the water temperature at the outlet of the heat exchanger rose to 13°C, and the flow rate was approximately 6 m³ / h. 3 The temperature dropped to / h, necessitating the disassembly and cleaning of the heat exchanger. [Explanation of Symbols]

[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 deaeration device is installed 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 for discharging the sealing liquid from the liquid-sealed vacuum pump and circulating the discharged sealing liquid back to the liquid-sealed vacuum pump, A degassing system having a plate-type heat exchanger provided in the aforementioned circulation channel, The plate-type heat exchanger comprises a plurality of stacked heat transfer plates, A first frame is provided on one side of the stacking direction of the plurality of heat transfer plates and has an inlet for the sealing liquid, A degassing system comprising: a second frame provided on the other side of the stacking direction of the plurality of heat transfer plates and having an outlet for the sealing liquid.

2. The plate-type heat exchanger is provided with an inlet for a heat transfer medium in the second frame. The degassing system according to claim 1 or 2, wherein the first frame is provided with an outlet for a heat transfer medium.

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 in the plate-type heat exchanger are opposite flows.

4. In a method for producing pure water by treating water to be treated, the method for degassing the water to be treated is as follows: In the process of discharging the sealing liquid from a liquid-sealed vacuum pump that reduces the gas phase on the degassing device and circulating the discharged sealing liquid back to the liquid-sealed vacuum pump, The process involves supplying a sealing liquid to a plate-type heat exchanger to control the temperature. The plate-type heat exchanger comprises a plurality of stacked heat transfer plates, A first frame provided on one side of the stacking direction of the plurality of heat transfer plates, It comprises a second frame provided on the other side of the stacking direction of the plurality of heat transfer plates, A degassing method comprising the step of performing the temperature control, wherein 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. In the process of performing the aforementioned temperature control, A heat transfer medium is introduced from the second frame of the plate-type heat exchanger. The degassing method according to claim 4, wherein a 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.

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