Ultrapure water production method and ultrapure water production apparatus

Abstract

To utilize desalinated seawater as raw water used for producing ultrapure water.SOLUTION: The ultrapure water production method includes a pretreatment step of removing suspended solids from raw water containing desalinated seawater 32 obtained by desalinating seawater 30 to obtain pretreated water, a primary treatment step of removing total organic carbon components and ion components from the pretreated water to produce primary pure water, and a secondary treatment step of removing impurities from the primary pure water to produce ultrapure water, wherein the boron concentration in the raw water is adjusted to be equal to or less than an allowable value calculated from the boron concentration required for the ultrapure water.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an ultrapure water production method and an ultrapure water production apparatus. [Background technology]

[0002] For example, Patent Document 1 discloses an ultrapure water production system that uses industrial water or other water as raw water and produces ultrapure water from the raw water. The ultrapure water production system is provided with a boron adsorption resin tower that removes boron from the raw water using a boron adsorption resin. Furthermore, for example, Patent Document 2 discloses a reverse osmosis treatment device that removes boron and other substances from treated water by passing feed water at a high pH through a reverse osmosis membrane unit. Furthermore, for example, Patent Document 3 discloses a method for treating boron-containing water in which boron-containing water is passed through a high-pressure reverse osmosis membrane device and then treated with an ion exchange device. The boron-containing water used may be natural raw water such as river water, well water, or lake water, or recovered water from semiconductor manufacturing processes or treated water thereof. In the techniques described in the above Patent Documents 1 to 3, industrial water, natural raw water, water recovered from semiconductor manufacturing processes, or the like is used as raw water.

[0003] Furthermore, for example, Patent Document 4 discloses a reverse osmosis membrane separation device that includes a reverse osmosis membrane module unit and desalinates seawater. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 8-89956 [Patent Document 2] Special Publication No. 2000-511109 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-20131 [Patent Document 4] Japanese Patent Application Laid-Open No. 2000-51663 Summary of the Invention [Problem to be solved by the invention]

[0005] For example, ultrapure water production systems that supply ultrapure water to semiconductor manufacturing facilities may use tap water such as city water or well water, recycled water such as industrial water, or wastewater (sometimes called recovered water) from ultrapure water used in semiconductor manufacturing.

[0006] However, because a large amount of ultrapure water is used in the manufacture of semiconductors and other products, the amount of tap water used to produce ultrapure water is also increasing. Because the supply of tap water is limited, measures are being sought to reduce the amount of tap water used in ultrapure water production so that tap water does not run short for other uses. In addition, there is a limit to the use of the above-mentioned recycled water, so although it is effective in reducing raw water use, it is not sufficient to accommodate the current increase in the size of semiconductor and other manufacturing factories. Furthermore, due to the current environmental and climate change issues, the supply of drinking water is becoming unstable, and it has become necessary to secure new sources of raw water.

[0007] Desalination-treated seawater (seawater desalination-treated water) is one possible new source of raw water. However, to desalinate seawater, for example, a seawater desalination plant must be used. Seawater desalination plants often use high-pressure reverse osmosis membrane devices as their main equipment, which entails significant operating costs. Therefore, it has not been common to use treated seawater desalination plants as raw water for ultrapure water production plants. Seawater desalination plants are a technology that has generally been used to produce drinking water.

[0008] None of the technologies described in Patent Documents 1 to 3 use desalination-treated seawater as raw water. Furthermore, the technologies described in Patent Documents 1 to 3 have difficulty dealing with the high concentration of boron contained in seawater. Furthermore, Patent Document 4 above describes a reverse osmosis membrane separation device that desalinates seawater, but does not describe how it can be applied to an ultrapure water production device that produces ultrapure water from raw water.

[0009] The inventors of the present disclosure have considered using treated water from a seawater desalination plant as raw water for an ultrapure water production plant, and have found that the following problems exist. That is, 1) The treated water from a seawater desalination plant contains a higher concentration of boron than that found in tap water or recycled water. In other words, when treated water from a seawater desalination plant is used as drinking water, it is designed to meet the drinking water boron concentration standard of 1 mg / L, and therefore the boron concentration may be relatively higher than that of other tap water. On the other hand, ultrapure water production plants have a low boron removal capacity and are designed to accommodate typical boron concentrations found in other tap water, e.g., at most 0.1 to 0.2 mg / L, so some countermeasure is required. For example, if treated water from a seawater desalination plant is used directly as raw water for an ultrapure water plant, the amount of ion exchange resin in the boron-selective ion exchange resin device installed in the ultrapure water plant will be increased, resulting in problems such as the elution of organic TOC from the boron-selective ion exchange resin device. 2) In seawater desalination treated water, fluctuations in boron concentration can occur depending on the operating conditions of the seawater desalination treatment facility. These concentration fluctuations tend to occur over a period of several tens of days, so it is necessary to respond to these fluctuations. Furthermore, investigations have revealed that these fluctuations are related to maintenance such as cleaning of the high-pressure reverse osmosis membrane equipment and membrane replacement. An example of fluctuations in the quality of treated water from a seawater desalination plant is shown in Figure 2.

[0010] Semiconductor manufacturing processes often operate continuously for years, making a stable supply of ultrapure water essential. Therefore, when using desalinated seawater as raw water for ultrapure water for semiconductor manufacturing, it is necessary to take the above measures to supply raw water with as stable a boron concentration as possible.

[0011] In consideration of the above, the present disclosure aims to make it possible to use desalinated seawater, which is seawater that has been desalinated, as raw water for producing ultrapure water. [Means for solving the problem]

[0012] The method for producing ultrapure water according to the first aspect includes a pretreatment step in which suspended solids are removed from raw water, including desalination-treated seawater, to obtain pretreated water; a primary treatment step in which total organic carbon components and ionic components are removed from the pretreated water to produce primary pure water; and a secondary treatment step in which impurities are removed from the primary pure water to produce ultrapure water, and the boron concentration of the raw water is adjusted to be equal to or less than an allowable value calculated from the boron concentration required for the ultrapure water.

[0013] In this method for producing ultrapure water, the boron concentration of raw water containing desalination-treated seawater is adjusted to be equal to or lower than the allowable value calculated from the boron concentration required for ultrapure water, so that desalination-treated seawater can be used as the raw water. For example, when desalination-treated seawater and tap water are used as raw water, the amount of tap water used can be reduced compared to when only tap water is used as raw water.

[0014] In a second aspect, in the ultrapure water manufacturing method according to the first aspect, when the boron concentration in the desalination treated seawater exceeds the allowable value, a boron removal treatment is performed to remove boron contained in the desalination treated seawater before the pretreatment.

[0015] In this method for producing ultrapure water, when the boron concentration in the desalination-treated seawater exceeds the allowable value, the boron in the desalination-treated seawater is removed by a boron removal treatment prior to the pretreatment, thereby reducing the boron concentration in the desalination-treated seawater to or below the allowable value. This also enables the desalination-treated seawater to be used as raw water for producing ultrapure water.

[0016] In a third aspect, in the method for producing ultrapure water according to the second aspect, the boron removal treatment includes one or more of treating the desalination treated water with a high-pressure reverse osmosis membrane, treating the desalination treated water with an alkali-added reverse osmosis membrane, treating the desalination treated water with a boron-selective ion exchange resin, treating the desalination treated water with an anion exchange resin, and treating the desalination treated water with an electrodeionization exchange device.

[0017] This ultrapure water production method involves one or more of the following: treating seawater desalination water with a high-pressure reverse osmosis membrane; treating seawater desalination water with an alkali-added reverse osmosis membrane; treating seawater desalination water with a boron-selective ion exchange resin; treating seawater desalination water with an anion exchange resin; and treating seawater desalination water with an electrodeionization device. This allows for efficient removal of boron from the seawater desalination water.

[0018] In a fourth aspect, in the method for producing ultrapure water according to the first or second aspect, the allowable value is changed depending on the amount of ultrapure water used.

[0019] For example, the boron removal capacity of each unit device of the primary and secondary pure water systems, or of the main unit device that removes boron, changes depending on the amount of ultrapure water used. In this ultrapure water production method, the allowable value can be changed depending on the amount of ultrapure water used, making it possible to efficiently remove boron from seawater desalination treated water.

[0020] An ultrapure water manufacturing apparatus according to a fifth aspect includes a pretreatment device that removes suspended solids from raw water, including desalination-treated seawater, to obtain pretreated water; a primary water purification device that removes total organic carbon components and ionic components from the pretreated water to produce primary pure water; a secondary water purification device that removes impurities from the primary pure water to produce ultrapure water; and a measuring unit that measures the boron concentration of the desalination-treated seawater, and adjusts the boron concentration of the raw water to be equal to or lower than an allowable value calculated from the boron concentration required for the ultrapure water.

[0021] In this ultrapure water production system, the boron concentration of raw water, including desalinated seawater, is adjusted to be equal to or lower than the allowable value calculated from the boron concentration required for ultrapure water, so that desalinated seawater can be used as the raw water. For example, when desalinated seawater and tap water are used as raw water, the amount of tap water used can be reduced compared to when only tap water is used as raw water.

[0022] In a sixth aspect, the ultrapure water production system according to the fifth aspect further comprises a boron treatment device that removes boron from the desalination treated seawater.

[0023] In this ultrapure water production system, when the boron concentration of the desalination-treated seawater exceeds the allowable value, the boron contained in the desalination-treated seawater is removed by a boron treatment device prior to pretreatment, thereby reducing the boron concentration of the desalination-treated seawater to below the allowable value. This also allows the desalination-treated seawater to be used as raw water for ultrapure water production.

[0024] In a seventh aspect, in the ultrapure water producing apparatus according to the sixth aspect, the boron treatment device includes one or more of a high-pressure reverse osmosis membrane device that treats the desalination treatment water using a high-pressure reverse osmosis membrane, a reverse osmosis membrane device that has an addition section that can add alkali to the desalination treatment water and treats the desalination treatment water using a reverse osmosis membrane, a boron-selective ion exchange resin device that treats the desalination treatment water using a boron-selective ion exchange resin, an anion exchange resin device, and an electrodeionization exchange device.

[0025] This ultrapure water production system can efficiently remove boron from desalination water using one or more of the following: a high-pressure reverse osmosis membrane device; a reverse osmosis membrane device that adds alkali to desalination water and processes it using a reverse osmosis membrane; a boron-selective ion exchange resin device; an anion exchange resin device; and an electric deionization exchange device.

[0026] An eighth aspect is the ultrapure water producing system according to the fifth aspect, further comprising a seawater desalination treatment device that treats seawater with at least a reverse osmosis membrane to obtain the desalinated seawater.

[0027] In this ultrapure water production system, the seawater desalination treatment device treats seawater using a reverse osmosis membrane to obtain desalinated seawater, so that the required amount of desalinated seawater can be secured. [Effects of the Invention]

[0028] According to the present disclosure, it is possible to use desalinated seawater obtained by desalination of seawater as raw water for producing ultrapure water. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a block diagram showing an overview of an ultrapure water production system according to a first embodiment. [Figure 2] 1 is a graph showing an example of changes in boron concentration and electrical conductivity of desalination treated seawater over operation time. [Figure 3] FIG. 10 is a block diagram showing an overview of an ultrapure water production system according to a second embodiment. [Figure 4] FIG. 10 is a block diagram showing an overview of an ultrapure water production system according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0030] Hereinafter, embodiments for implementing the technology of the present disclosure will be described with reference to the drawings. Components indicated by the same reference numerals in each drawing are the same or similar components. Note that duplicated explanations and reference numerals may be omitted in the embodiments described below. Furthermore, all drawings used in the following description are schematic, and the dimensional relationships, ratios, etc. of each element shown in the drawings do not necessarily match those of reality. Furthermore, the dimensional relationships, ratios, etc. of each element between multiple drawings do not necessarily match.

[0031] [First embodiment] FIG. 1 shows an ultrapure water production system 100 according to the first embodiment.

[0032] In FIG. 1, an ultrapure water production system 100 according to the first embodiment receives desalination-treated seawater (desalinized seawater) and produces ultrapure water. The ultrapure water production system 100 includes a pretreatment device 10, a primary water purification system 11, and a secondary water purification system 12. The ultrapure water production system 100 also includes a seawater desalination system 40, a boron meter 48, and a boron removal system 60. Here, seawater refers to water from the ocean, containing approximately 3.5% by weight of many inorganic salts, primarily sodium salts and calcium salts. While the concentrations of the components contained in seawater vary depending on the ocean area, the composition is generally constant.

[0033] The pretreatment device 10 is a device that removes suspended solids from raw water, including desalination-treated seawater 32, to obtain pretreated water. For example, impurities such as residual chlorine and large debris in the raw water are filtered using a sand filter filled with media such as filter sand, a packed tank filter tower such as an MMF (multimedia filter tower), a membrane filter using filters such as an MF (microfilter) or an UF (ultrafiltration membrane), and / or a granular activated carbon tower. In the first embodiment, the raw water includes industrial water 14. The industrial water 14 is water used for industrial purposes. City water, well water, recycled water, etc. may be used instead of the industrial water 14. City water is so-called tap water obtained by subjecting natural water such as river water, lake water, and well water to a coagulation and sedimentation process and a filtration process at a water treatment plant. The boron concentration of city water is, for example, 40 μg / L (conductivity 200 μS / cm) or less. Well water and recycled water generally have the same water quality as city water. The industrial water 14 is stored as raw water in a raw water tank, for example, a PIT 20, and used to produce ultrapure water.

[0034] The primary deionization system 11 produces primary deionized water by removing total organic carbon (TOC) and ionic components from pretreated water. For example, the primary deionized water is purified by combining a reverse osmosis membrane device that uses a semipermeable membrane to reverse osmose the pretreated water, an ion exchange resin device filled with ion exchange resin, an electrodeionization device (EDI), an ultraviolet light irradiation device that decomposes organic matter, and a degassing membrane device that degasses dissolved gases. The primary deionization system 11 may also be equipped with a urea decomposition device, such as a high-pressure reverse osmosis membrane device or an oxidation reaction tank that decomposes urea by adding hypobromous acid, as needed. The ion exchange resin device is filled with cation exchange resin and anion exchange resin in a single-bed, multiple-bed, or mixed-bed configuration, but preferably contains a boron-selective ion exchange resin. A boron-selective ion exchange resin device may be installed alone as the ion exchange resin device. The produced primary deionized water is supplied to the pure water tank 22.

[0035] The secondary pure water system 12 is a system that further removes impurities from the primary pure water to produce ultrapure water. For example, trace amounts of inorganic ions contained in the primary pure water are removed using a non-regenerative ion exchange tower (polisher). It also incorporates an ultraviolet irradiation device, a hydrogen peroxide decomposition device, a degassing device, and the like. An ultrafiltration membrane is installed at the end of the secondary pure water system 12 to remove fine particles. The produced ultrapure water is supplied to a POU (Point of Use) 19 and used in semiconductor manufacturing, etc., and a portion is circulated to a pure water tank 22 via a circulation line 28.

[0036] The seawater desalination apparatus 40 is provided upstream of the PIT 20 in which raw water is stored. The seawater desalination apparatus 40 includes multiple seawater desalination treatment units 42 that desalinate seawater 30. The multiple seawater desalination treatment units 42 desalinate the seawater 30, thereby producing desalination-treated seawater 32. Although FIG. 1 shows three seawater desalination treatment units 42, the number of seawater desalination treatment units 42 can be changed. As an example, seawater 30 is stored in a tank 31, and a pipe 43 connected to the tank 31 branches into three pipes 44, which are connected to the three seawater desalination treatment units 42, respectively. By providing multiple (e.g., three) seawater desalination treatment units 42, if one unit is unable to operate due to a malfunction or the like, treatment can be performed by the other seawater desalination treatment units 42. In addition, in the ultrapure water manufacturing apparatus 100, a pump is provided to supply fluids such as seawater 30 or desalination treated seawater 32 to the pipe 43 or the pipe 44, etc., but in this disclosure, the pump is not shown in the figure to make the configuration easier to understand.

[0037] As an example, the seawater desalination unit 42 includes a pretreatment facility, multiple (e.g., two) reverse osmosis membrane (RO) units, and a posttreatment facility. The pretreatment facility performs sand filtration and filtration using an ultrafiltration (UF) membrane. The first-stage reverse osmosis membrane (RO) unit adjusts the pH to, for example, 6.0 to 6.5, and then processes the water using a reverse osmosis membrane. The second-stage reverse osmosis membrane (RO) unit adjusts the pH to, for example, 9 to 10, in order to remove boron, and then processes the water using a reverse osmosis membrane. In either case, a CA (cellulose acetate) high-pressure reverse osmosis membrane is often used as the first reverse osmosis membrane. In the posttreatment facility, acid is added to the permeate treated by the reverse osmosis membrane to adjust the pH, and then calcite is used to adjust the hardness components and sodium hypochlorite is used to sterilize the water. The configuration of the seawater desalination unit 42 is variable.

[0038] The desalination water 32 treated by the seawater desalination apparatus 40 is stored in a seawater desalination tank 46. As an example, the three pipes 44 are joined into one pipe 43 downstream of the three seawater desalination treatment units 42 and connected to the seawater desalination tank 46.

[0039] The boron meter 48 is provided in the pipe 43 connected downstream of the seawater desalination treatment tank 46. The boron meter 48 is an example of a measuring unit, and measures the boron concentration of the seawater desalination treatment water 32.

[0040] To adjust the boron concentration of the desalination treated seawater 32 to be equal to or less than the allowable value calculated from the boron concentration required for ultrapure water, the ultrapure water producing system 100 of the first embodiment is provided with a boron removal device 60 that removes boron from the desalination treated seawater 32. The boron removal device 60 is an example of a boron treatment device. The boron concentration required for the ultrapure water in the POU 19 is, for example, 50 ng / L, preferably 1 ng / L. From this, the allowable value calculated from the boron removal performance of each unit device of the secondary desalination system and the primary desalination system, or the main unit device that removes boron, is, for example, 0.2 mg / L for the PIT 20, i.e., the water supplied to the pretreatment system 10. Furthermore, since the boron removal capacity of each unit device of the primary and secondary pure water systems, or of the main unit device that removes boron, changes depending on the amount of ultrapure water used, it is possible to change the above allowable value taking this into consideration. For example, in the above case, if the amount of water used at the end point is reduced to half, the allowable value can be set at 0.3 mg / L.

[0041] As an example, pipe 52 is connected via a switching valve 50 to pipe 43 connected downstream of seawater desalination treatment tank 46, and a boron removal device 60 is provided on pipe 52. Furthermore, pipe 52 is connected downstream of boron removal device 60 to pipe 43 downstream of seawater desalination treatment tank 46. As a result, after the boron concentration of desalination treatment water 32 is measured by boron meter 48, if it is desirable to remove boron from desalination treatment water 32, the flow in pipe 43 is switched to pipe 52 by switching valve 50. As a result, desalination treatment water 32 is introduced into pipe 52, and the desalination treatment water 32 is treated by boron removal device 60. Instead of the switching valve 50, a flow control valve may be used to supply a portion of the desalination treated seawater 32 to the boron removal device 60, with the other portion bypassing the boron removal device 60. This configuration makes it possible to more flexibly respond to changes in the boron concentration of the desalination treated seawater 32. For example, an increase in the boron concentration of the desalination treated seawater 32 can be accommodated by increasing the supply rate to the boron removal device 60.

[0042] Furthermore, a pipe 75 through which the industrial water 14 is supplied is connected to a tank 74 that stores the industrial water 14. The pipe 43 through which the desalinated seawater 32 flows is joined with the pipe 75 through which the industrial water 14 flows to form a single pipe 76, which is connected to the PIT 20. A valve 73 that opens and closes the pipe 43 is provided upstream of the junction with the pipe 75 on the pipe 43.

[0043] The boron removal device 60 is equipped with a high-pressure reverse osmosis membrane device (high-pressure RO) 62. The high-pressure reverse osmosis membrane device 62 has a high boron removal rate. An existing high-pressure RO can be used as the high-pressure reverse osmosis membrane device 62, and specific examples include the SWC series (manufactured by Hydeanautics), the TM800 series (manufactured by Toray Industries, Inc.), and the SW series (manufactured by The Dow Chemical Company).

[0044] The boron removal device 60 is provided with an addition unit 64 that is located upstream of a high-pressure reverse osmosis membrane device (high-pressure RO) 62 and that can add alkali 65 to the desalination treatment seawater 32 flowing through a pipe 52. As an example, the addition unit 64 includes a storage unit 64A that stores the alkali 65, a supply pipe 64B that connects the storage unit 64A to the pipe 52, and an adjustment valve 64C that is provided on the supply pipe 64B. The addition unit 64 may also include a pump (not shown) that supplies the alkali 65. By adding the alkali 65 to the desalination treatment seawater 32 using the addition unit 64, the seawater desalination treatment seawater 32 is adjusted to a high pH (for example, a pH of 9 or more and 10 or less). Operating the high-pressure reverse osmosis membrane device 62 at a high pH increases the removal rate of boron contained in the desalination treatment seawater 32 and also makes it easy to adjust the removal rate. In the boron removal device 60, when alkali 65 is added in the addition section 64, the pH of the treated water from the boron removal device 60 may become too high, which may affect the treatment in the subsequent stages. In such cases, an upper limit such as pH 10 may be set, and if this limit is exceeded, a mineral acid such as hydrochloric acid or sulfuric acid may be added as appropriate at any position downstream of the high-pressure reverse osmosis membrane device (high-pressure RO) 62 to adjust the pH to a level suitable for the treatment in the subsequent stages.

[0045] Furthermore, a boron meter 70 is provided in the pipe 52 downstream of the high-pressure reverse osmosis membrane device 62 to measure the boron concentration of the desalination treated seawater 32 after it has been treated by the high-pressure reverse osmosis membrane device 62. For example, if the boron concentration measured by the boron meter 48 exceeds an allowable value (e.g., 0.2 mg / L), the flow in the pipe 43 is switched to the pipe 52 by the switching valve 50, and at least a portion of the desalination treated seawater 32 is passed through the boron removal device 60 for treatment. In this embodiment, the boron removal device 60 is also capable of removing turbidity, and therefore has the same function as the pretreatment device 10. Therefore, the treated water from the boron removal device 60 may be joined between the pretreatment device 10 and the primary deionized water system 11 without passing through the pretreatment device 10. In this case, if a tank or a pit (neither of which is shown) is generally installed between the pretreatment device 10 and the primary deionized water system 11, it is generally advisable to join the treated water at the tank or the pit. The concentrated water from the high-pressure reverse osmosis membrane device 62 has low hardness, so it may be supplied to a cooling tower and used as cooling tower water. Furthermore, if the boron concentration measured by the boron meter 70 greatly exceeds the allowable value (for example, 0.3 mg / L), the addition unit 64 can be operated to add alkali 65 to the seawater desalination treatment water 32, thereby increasing the boron removal rate.

[0046] FIG. 2 shows an example of changes in the boron concentration and electrical conductivity of desalination-treated seawater over time as the ultrapure water production system 100 operates. The electrical conductivity is measured using a conductivity meter, which is located in the same position as the boron meter 48 in the piping 43. As shown in FIG. 2, the electrical conductivity of the desalination-treated seawater 32 remains constant at around 30 μS / cm over time as the ultrapure water production system 100 operates, but the boron concentration of the desalination-treated seawater 32 changes significantly. This is because, with continued use of the seawater desalination system 40, the boron removal rate of the reverse osmosis membrane device (RO) in the seawater desalination treatment unit 42 decreases due to, for example, membrane deterioration caused by continued water flow or sterilization with chlorine or the like, membrane scaling, and biofouling. Therefore, the boron removal rate can be restored by cleaning the reverse osmosis membrane device (RO) in one or more of the multiple seawater desalination treatment units 42 with water or chemicals such as acid, alkali, or surfactant, or by replacing the membrane. In this way, the repeated cycle of a decrease in the boron removal rate and a recovery of the boron removal rate through cleaning changes the boron concentration in the desalination treated seawater 32. In addition to being periodically cleaned as described above, the seawater desalination treatment unit 42 also turns the reverse osmosis membrane device (RO) on and off depending on the amount of water used in the downstream stage. Although these operations are essential, they subject the reverse osmosis membrane to physical and chemical shocks, which may cause a decrease in the boron removal performance of the reverse osmosis membrane device (RO) over the long term. Furthermore, due to the effects of rising seawater temperatures and increasing summer-winter temperature variations caused by global warming in recent years, the boron concentration in desalinated seawater 32 may fluctuate over the long term. While rising water temperature itself is a factor that reduces the boron removal rate of reverse osmosis membranes, long-term operation at high temperatures is also a factor that causes reverse osmosis membrane degradation.

[0047] Figure 2 shows an example in which the ultrapure water production apparatus 100 switches operation when the boron concentration of the desalination treated water 32 measured by the boron meter 48 is between value A (0.2 mg / L) and value B (0.5 mg / L). Concentration A is a value determined from the maximum acceptable boron concentration for the ultrapure water production system, e.g., an allowable value calculated from the boron concentration required for ultrapure water. This concentration is determined based on the design conditions of the ultrapure water production system. Furthermore, it may be determined taking into account the mixing ratio of industrial water in PIT 20. Furthermore, concentration B is a concentration determined based on the boron removal performance of the boron removal device 60. For example, concentration B can be set to a concentration at which the maximum acceptable concentration of boron for the ultrapure water production system 100 cannot be achieved even when the high-pressure reverse osmosis membrane device 62 is operated with the addition of alkali 65.

[0048] As an example, when the boron concentration of the desalination treated seawater 32 measured by the boron meter 48 is equal to or less than value A (0.2 mg / L), the desalination treated seawater 32 by the seawater desalination plant 40 is blended with the industrial water 14. In this case, the boron removal device 60 is not used, and therefore the switching valve 50 closes the flow path from the pipe 43 to the pipe 52.

[0049] As another example, when the boron concentration of the desalination treated water 32 measured by the boron meter 48 exceeds value A (0.2 mg / L) and is equal to or lower than value B (0.5 mg / L), the boron removal device 60 is used. For example, the desalination treated water 32 from which boron has been removed by the boron removal device 60 is blended with the industrial water 14. In this case, the switching valve 50 opens the flow path from the pipe 43 to the pipe 52 in order to use the boron removal device 60. When the boron removal device 60 is configured as a reverse osmosis membrane device, alkali 65 may be added by the addition unit 64 in accordance with the boron concentration measured by the boron meter 48 (e.g., when the boron concentration is higher than a predetermined value). In this way, by using the boron removal device 60, the boron concentration of the desalination treated water 32 can be reduced to 0.2 mg / L or lower.

[0050] Furthermore, as an example, if the boron concentration of the desalination treated seawater 32 measured by the boron meter 48 exceeds the value B (0.5 mg / L), the use of the desalination treated seawater 32 by the seawater desalination plant 40 is stopped. In this case, the valve 73 of the pipe 43 is closed, and the ultrapure water production system 100 is operated with raw water containing only industrial water 14.

[0051] Furthermore, although not shown, the ultrapure water production system 100 may be provided with a switching means for switching the flow path to the cleaning tower between the boron meter 48 and the switching valve 50 in the pipe 43. This allows the boron removal device 60 to set the water quality for switching to the cooling tower depending on its boron removal performance, since there is a limit to the boron removal performance. For example, when the boron concentration of the desalination treated seawater 32 exceeds the value B in FIG. 2 (e.g., 0.5 mg / L), the desalination treated seawater 32 may be supplied to the cooling tower and used as water for the cooling tower.

[0052] Possible methods for adjusting the boron concentration in the raw water include changing the blend ratio of industrial water 14 and desalination treated seawater 32, or increasing the size of PIT 20. If the boron concentration in desalination treated seawater 32 is high, the boron concentration can be kept within the allowable value by increasing the proportion of industrial water 14.

[0053] Furthermore, if the PIT 20 is large, when the boron concentration of the desalination treated seawater 32 exceeds, for example, value B (0.5 mg / L), the use of the desalination treated seawater 32 can be stopped and ultrapure water can be produced while consuming raw water with a low boron concentration stored in the PIT 20. When the boron concentration falls below, for example, value B (0.5 mg / L), the use of the desalination treated seawater 32 can be resumed, thereby restoring the water storage capacity of the PIT 20. In this case, industrial water 14 may also be used as raw water. The capacity of the PIT 20 can be determined taking into consideration the water quality trends of the desalination treated seawater 32, the supply amount of ultrapure water, and the consumption amount of industrial water 14, etc.

[0054] (action) In the first embodiment, the boron concentration of desalinated seawater 32 obtained by desalination of seawater 30 is adjusted to be equal to or less than the allowable value calculated from the boron concentration required for ultrapure water, so that the desalinated seawater 32 can be used as raw water. When desalinated seawater and tap water are used as raw water, the amount of tap water used can be reduced compared to when only tap water is used as raw water.

[0055] Furthermore, when the boron concentration of the desalination treated seawater 32 obtained by desalination treatment of seawater exceeds the allowable value, the boron contained in the desalination treated seawater 32 can be removed by the boron removal device 60, which is an earlier stage of pretreatment, to reduce the boron concentration of the desalination treated seawater 32 to or below the allowable value. This also allows the desalination treated seawater 32 to be used as raw water for producing ultrapure water.

[0056] The boron removal device 60 also includes an addition unit 64 capable of adding alkali 65 to the desalination treatment water 32, and a high-pressure reverse osmosis membrane device 62 that treats the desalination treatment water 32 using a high-pressure reverse osmosis membrane. Depending on the boron concentration in the desalination treatment water 32, the desalination treatment water 32 can be treated using the high-pressure reverse osmosis membrane without adding alkali 65, or the desalination treatment water 32 can be treated using the high-pressure reverse osmosis membrane after adding alkali 65. Adding alkali 65 to the desalination treatment water 32 and treating it using the high-pressure reverse osmosis membrane increases the boron removal rate. This allows for efficient removal of boron from the desalination treatment water 32.

[0057] Furthermore, in the case of the high-pressure reverse osmosis membrane device 62, it is effective to gradually increase the amount of the desalination treatment seawater 32 supplied to the boron removal device 60 as the boron concentration of the desalination treatment seawater 32 increases. Furthermore, if the boron concentration of the desalination treatment seawater 32 increases, the addition of alkali 65 also becomes effective. In this case, when the boron concentration of the desalination treatment seawater 32 is low, the device is operated without adding alkali 65, which prevents an increase in the amount of chemicals used.

[0058] According to the first embodiment, it is possible to use the desalination treated seawater 32 as raw water for producing ultrapure water.

[0059] Although not shown in the figures, a configuration may be adopted in which multiple lines of high-pressure reverse osmosis membrane devices 62 are connected in parallel. The high-pressure reverse osmosis membrane devices 62 consume a lot of power. When the amount of desalination treated seawater 32 supplied to the boron removal device 60 is small, in a configuration in which multiple lines of high-pressure reverse osmosis membrane devices 62 are connected in parallel, boron can be removed using one of the parallel devices, and the number of lines used can be increased as the supply amount increases. Other devices may be installed as appropriate in the boron removal device 60. For example, depending on the water quality of the desalination treated seawater 32, a softener such as a sodium cation exchange device, a degassing tower, a carbon dioxide removal device such as a degassing membrane, etc. may be installed. Also, a line may be installed to directly supply raw water such as industrial water to the boron removal device 60. In this case, if the boron concentration in raw water such as industrial water suddenly increases for some reason, the boron removal device 60 can be temporarily used as a boron removal device for raw water such as industrial water.

[0060] [Second embodiment] Next, an ultrapure water production system according to a second embodiment will be described. Note that the same components as those in the first embodiment described above will be assigned the same reference numerals and their description will be omitted.

[0061] An ultrapure water production system 200 according to the second embodiment is shown in Fig. 3. As shown in Fig. 3, in the ultrapure water production system 200, a boron removal system 210 is provided in the piping 52 instead of the boron removal system 60 provided in the ultrapure water production system 100 of the first embodiment. The boron removal system 210 includes a boron-selective ion exchange resin system 212. The boron-selective ion exchange resin system 212 is an example of a boron treatment system, and removes boron contained in the desalination treatment water 32 using a boron-selective ion exchange resin.

[0062] As an example, the boron-selective ion exchange resin is an ion exchange resin having n-methylglucamine groups, and examples thereof include CRB02, CRB03, CRB05 (manufactured by Mitsubishi Chemical Corporation), Amberlite IRA743 (registered trademark; Rohm and Haas Company), etc. The boron-selective ion exchange resin selectively adsorbs boron regardless of the salt concentration, and therefore can remove boron regardless of the salt concentration, and thus functions suitably as a boron removal device.

[0063] If the change in boron concentration in the desalination treated water 32 is known in advance, as shown in Figure 2, the amount of boron-selective ion exchange resin (BTC: once-through capacity) can be determined based on the maximum boron concentration, for example, so that the regeneration is performed once every 1 to 5 days. Because the boron concentration in the desalination treated water 32 fluctuates over a long period, when the boron removal device 210 is used, it is expected to operate for a long period (e.g., several days to several tens of days). Therefore, since it is difficult to operate the device without breakthrough of the selective ion exchange resin during this period, the boron-selective ion exchange resin is operated by alternating between water flow and regeneration. If the boron-selective ion exchange device 212 has multiple boron-selective ion exchange resin columns in parallel, regeneration can be performed sequentially. If there is only one boron-selective ion exchange resin column, raw water can be secured during regeneration by using industrial water or raw water from the pit. In this embodiment, the boron-selective ion exchange resin can handle high boron concentrations, so operation can continue even if the boron concentration increases, although the frequency of regeneration of the boron-selective ion exchange resin increases.

[0064] Instead of boron-selective ion exchange resins, inorganic boron adsorbents can be used. Specific examples include cerium-based adsorbents such as READ-B (manufactured by Nihonkaisui Co., Ltd.). Boron-selective ion exchange fibers can also be used. Examples include Killespearl CH351 and the Killes Fiber GRY series (manufactured by Killes Co., Ltd.). Hereinafter, the term "boron-selective ion exchange resin" is intended to include inorganic boron adsorbents, boron-selective ion exchange fibers, etc. The other configurations of the ultrapure water producing system 200 are the same as those of the ultrapure water producing system 100 of the first embodiment. In this embodiment, an anion exchange resin tower or an electrodeionization exchange device can be used instead of the boron-selective ion exchange fiber, etc. Since these devices can remove all anion exchange resins, it is difficult to selectively remove only boron. However, as shown in Figure 2, the conductivity of the desalination treated seawater 32 is lower than that of ordinary raw water such as city water, so these devices can also be used. Examples of anion exchange resins include commercially available strong basic anion exchange resins such as the Diaion PA series, Diaion HPA series, and Diaion SA series (all manufactured by Mitsubishi Chemical Corporation) and the 550A series (manufactured by Dow Chemical), and examples of electrodeionization exchange devices include commercially available devices such as the VNX55EX (manufactured by Evoqua Water Technologies). Note that the VNX55EX (manufactured by Evoqua Water Technologies) has high carbon dioxide removal performance and does not experience a decrease in boron removal performance due to carbon dioxide, making it suitable for use as the boron removal device 312. When the boron concentration in the treated water increases, the anion exchange resin is regenerated using an alkali such as sodium hydroxide or potassium hydroxide using existing methods to continue operation. In addition, the regenerant for the boron-selective ion exchange resin, the regenerant for the anion resin, and the concentrated water from the electrodeionization exchange device all have low hardness, so they may be supplied to a cooling tower and used as cooling tower water.

[0065] The ultrapure water production system 200 has the same configuration as the ultrapure water production system 100 of the first embodiment, and can provide the same functions and effects.

[0066] The boron removal device 210 also includes a boron-selective ion exchange resin device 212 that treats the desalination treated seawater 32 with a boron-selective ion exchange resin. Therefore, in the ultrapure water production system 200, the boron removal device 210 can remove boron from the desalination treated seawater 32 regardless of the salt concentration of the seawater. Instead of the switching valve 50, a flow control valve may be used to supply a portion of the desalination treated seawater 32 to the boron removal device 210, with the other portion bypassing the boron removal device 210. In this configuration, it is possible to more flexibly respond to changes in the boron concentration of the desalination treated seawater 32. For example, an increase in the boron concentration of the desalination treated seawater 32 can be accommodated by increasing the supply rate to the boron removal device 210. In this way, it is possible to minimize the frequency of regeneration of the boron-selective ion exchange resin 212. Other devices may be installed as appropriate in the boron removal device 210. For example, depending on the water quality of the desalination treated seawater 32, a softener such as a sodium cation exchange device, a degassing tower, a carbon dioxide removal device such as a degassing membrane, etc. may be installed.

[0067] [Third embodiment] Next, an ultrapure water production system according to a third embodiment will be described. Note that the same components as those in the first and second embodiments will be given the same reference numerals and their description will be omitted.

[0068] FIG. 4 shows an ultrapure water production system 300 according to the third embodiment. As shown in FIG. 4, in the ultrapure water production system 300, a boron removal device 310 is provided in the piping 52 instead of the boron removal device 60 provided in the ultrapure water production system 100 according to the first embodiment. The boron removal device 310 includes an addition section 64 and a reverse osmosis membrane device (RO) 312. The reverse osmosis membrane device 312 may be a medium-pressure, low-pressure, or ultra-low-pressure reverse osmosis membrane device. Since it is difficult to remove boron in the reverse osmosis membrane device 312 without adding alkali 65, alkali 65 is added from the addition section 64 when the reverse osmosis membrane device 312 is in use. Commercially available reverse osmosis membrane devices can be used as the medium-pressure, low-pressure, or ultra-low-pressure reverse osmosis membrane device 312. Examples include the TM700 series and the TML series (manufactured by Toray Industries, Inc.). The RO used in this embodiment consumes less power during operation than high-pressure RO, so even if the amount of desalination-treated seawater 32 supplied to the boron removal device 310 increases, the power consumption is less likely to increase.

[0069] For example, if the boron concentration increases, it is effective to increase the amount of alkali 65 added as the boron concentration increases. For example, if the pH of the water supplied to the low-pressure RO is increased from 7 to 8 to 9 to 10 as the boron concentration increases, the boron removal rate can be increased. In this case, the amount of desalination treated seawater 32 supplied to the boron removal device 310 may be increased as the boron concentration increases. In the boron removal device 60, when alkali 65 is added in the addition section 64, the pH of the treated water from the boron removal device 60 may become too high, which may affect the treatment in the subsequent stages. In such cases, an upper limit such as pH 10 may be set, and if this limit is exceeded, a mineral acid such as hydrochloric acid or sulfuric acid may be added as appropriate at any position downstream of the high-pressure reverse osmosis membrane device (high-pressure RO) 62 to adjust the pH to a level suitable for the treatment in the subsequent stages.

[0070] Other configurations of the ultrapure water production system 300 are similar to those of the ultrapure water production system 100 or 200 of the first embodiment.

[0071] The ultrapure water production system 300 has the same configuration as the ultrapure water production systems 100 and 200 of the first and second embodiments, and can provide the same functions and effects.

[0072] The ultrapure water production system 300 is equipped with a boron removal device 310 that adds alkali 65 to the desalination treated seawater 32 and treats it with a reverse osmosis membrane device 312. The boron removal device 310 can efficiently remove boron contained in the desalination treated seawater 32. Instead of the switching valve 50, a flow control valve may be used to supply a portion of the desalination treated seawater 32 to the boron removal device 310, with the other portion bypassing the boron removal device 310. This configuration makes it possible to more flexibly respond to changes in the boron concentration of the desalination treated seawater 32. For example, an increase in the boron concentration of the desalination treated seawater 32 can be accommodated by increasing the supply rate to the boron removal device 310. Other devices may be installed as appropriate in the boron removal device 300. For example, depending on the water quality of the desalination treated seawater 32, a softener such as a sodium cation exchange device, a degassing tower, a carbon dioxide removal device such as a degassing membrane, etc. may be installed. In this embodiment, the boron removal device 60 is also capable of removing turbidity, and therefore has the same function as the pretreatment device 10. Therefore, the treated water from the boron removal device 60 may be joined between the pretreatment device 10 and the primary deionized water system 11 without passing through the pretreatment device 10. In this case, if a tank or a pit (neither of which is shown) is generally installed between the pretreatment device 10 and the primary deionized water system 11, it is generally advisable to join the treated water at the tank or the pit. The concentrated water from the high-pressure reverse osmosis membrane device 62 has low hardness, so it may be supplied to a cooling tower and used as cooling tower water.

[0073] [Ultra pure water production method] The ultrapure water production methods according to the first to third embodiments include a pretreatment step in which suspended solids are removed from raw water, including desalination-treated seawater 32 obtained by desalination-treated seawater 30, to obtain pretreated water; a primary treatment step in which all organic carbon components and ionic components are removed from the pretreated water to produce primary pure water; and a secondary treatment step in which impurities are removed from the primary pure water to produce ultrapure water, and the boron concentration of the raw water is adjusted to be equal to or less than the allowable value calculated from the boron concentration required for ultrapure water. This allows the downstream ultrapure water production equipment to operate while dealing with the high boron concentration of the desalination treated seawater 32. Furthermore, fluctuations in the boron concentration of the desalination treated seawater 32 can also be dealt with by changing the operating conditions of the boron removal equipment.

[0074] Here, if the boron concentration of the seawater desalination treated water 32 obtained by desalination treatment of seawater 30 exceeds an allowable value, a boron removal process may be performed to remove the boron contained in the seawater desalination treated water 32 before pretreatment.

[0075] In addition, the boron removal process may include one or more of treating the seawater desalination water 32 with a high-pressure reverse osmosis membrane, adding alkali to the seawater desalination water 32 and treating it with a reverse osmosis membrane, and treating the seawater desalination water 32 with a boron-selective ion exchange resin.

[0076] The ultrapure water production method of the present disclosure can handle the high boron concentration of desalination treated seawater 32, so it can be used without modifying the ultrapure water production equipment. Therefore, by simply adding a boron removal device to an existing ultrapure water production equipment, it becomes possible to use the desalination treated seawater 32 as raw water. Furthermore, this method can be easily implemented in the case of a new ultrapure water production equipment, as no new design is required.

[0077] [Other embodiments] The above describes one example of an embodiment of the present disclosure, but the embodiment of the present disclosure is not limited to the above, and it goes without saying that various modifications can be made without departing from the spirit of the present disclosure.

[0078] For example, a line may be provided to treat industrial water 14 with boron removal device 60, boron removal device 210, or boron removal device 310. By installing such a line, it is possible to respond to the unlikely event that the water quality of river water temporarily deteriorates due to heavy rain or the like, causing a temporary increase in the boron concentration in city water or the like.

[0079] For example, in an ultrapure water production system, a first boron removal device equipped with a high-pressure reverse osmosis membrane device 62 or a reverse osmosis membrane device 312 and an addition section 64 may be used in combination with a second boron removal device equipped with a boron-selective ion exchange resin device 212. [Explanation of symbols]

[0080] 10 Pretreatment device 11 Primary water purification device 12 Secondary water purification device 30 Seawater 32 Desalinated seawater 40 Seawater desalination equipment 48 Boron meter (example of measuring unit) 60 Boron removal device (an example of a boron treatment device) 62 High-pressure reverse osmosis membrane equipment 64 Additive part 65 Alkaline 100 Ultrapure water production equipment 200 Ultrapure water production equipment 210 Boron removal equipment (an example of a boron treatment equipment) 212 Boron-selective ion exchange resin device 300 Ultrapure water production equipment 310 Boron removal equipment (an example of a boron treatment equipment) 312 Reverse osmosis membrane equipment

Claims

1. a pretreatment step of removing suspended solids from raw water containing desalination water obtained by desalination of seawater to obtain pretreated water; a primary treatment for removing all organic carbon components and ionic components from the pretreated water to produce primary pure water; a secondary treatment for removing impurities from the primary pure water to produce ultrapure water, The method for producing ultrapure water includes adjusting the boron concentration of the raw water to be equal to or less than an allowable value calculated from the boron concentration required for the ultrapure water.

2. 2. The method for producing ultrapure water according to claim 1, wherein, when the boron concentration of the desalination treated seawater exceeds the allowable value, a boron removal treatment is performed to remove boron contained in the desalination treated seawater before the pretreatment.

3. 3. The method for producing ultrapure water according to claim 2, wherein the boron removal treatment includes one or more of treating the desalination treated seawater with a high-pressure reverse osmosis membrane, treating the desalination treated seawater with an alkali and then treating it with a reverse osmosis membrane, treating the desalination treated seawater with a boron-selective ion exchange resin, treating it with an anion exchange resin, and treating it with an electrodeionization exchange device.

4. 3. The method for producing ultrapure water according to claim 1, wherein the allowable value is changed according to the amount of ultrapure water used.

5. a pretreatment device for removing suspended solids from raw water containing desalination-treated seawater to obtain pretreated water; a primary water purification device for producing primary pure water by removing total organic carbon components and ionic components from the pretreated water; a secondary pure water device for producing ultrapure water by removing impurities from the primary pure water; a measuring unit that measures the boron concentration of the desalination treated water, The ultrapure water production apparatus adjusts the boron concentration of the raw water to be equal to or less than an allowable value calculated from the boron concentration required for the ultrapure water.

6. 6. The ultrapure water producing system according to claim 5, further comprising a boron treatment device for removing boron from the desalination treated seawater.

7. 7. The ultrapure water producing system according to claim 6, wherein the boron treatment device comprises one or more of: a high-pressure reverse osmosis membrane device that performs treatment using a high-pressure reverse osmosis membrane; a reverse osmosis membrane device that has an addition unit capable of adding alkali to the desalination treatment water and that treats the desalination treatment water using a reverse osmosis membrane; a boron-selective ion exchange resin device that treats the desalination treatment water with a boron-selective ion exchange resin; an anion exchange resin device; and an electrodeionization exchange device.

8. 6. The ultrapure water producing system according to claim 5, comprising a seawater desalination treatment system for treating seawater with at least a reverse osmosis membrane to obtain the desalinated seawater.

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