Method of producing ultrapure water, and ultrapure water production apparatus

Abstract

The ultrapure water manufacturing method disclosed herein includes a pretreatment process to remove suspended matter from raw water containing desalinated water obtained by seawater desalination treatment, thereby obtaining pretreated water; a primary treatment process to remove at least one of total organic carbon and ionic components from the pretreated water to produce primary pure water; and a secondary treatment process to remove impurities from the primary pure water to produce ultrapure water; wherein the boron concentration of the raw water is adjusted to a permissible value calculated based on the boron concentration required for ultrapure water.

Description

Technical Field

[0001] This disclosure relates to a method and apparatus for producing ultrapure water. Prior Technology

[0002] For example, Patent Document 1 (Japanese Patent Application Publication No. 8-89956) discloses an ultrapure water manufacturing apparatus that uses industrial water or other water as raw water to produce ultrapure water. The ultrapure water manufacturing apparatus includes a boron adsorption resin tower that uses boron adsorption resin to remove boron from the raw water. For example, Patent Document 2 (Japanese Patent Publication No. 2000-511109) discloses a reverse osmosis treatment device that removes boron and other substances from treated water by passing the supply water through a reverse osmosis membrane unit at a high pH. For example, Patent Document 3 (Japanese Patent Application Publication No. 2015-20131) discloses a method for treating boron-containing water by passing it through a high-pressure reverse osmosis membrane device and then treating it with an ion exchange device. The boron-containing water is natural raw water such as river water, well water, or lake water, or recycled water or treated water from semiconductor manufacturing processes. In the technologies described in the aforementioned patent documents 1 to 3 (Japanese Patent Application Publication No. 8-89956, Japanese Patent Application Publication No. 2000-511109, and Japanese Patent Application Publication No. 2015-20131), the raw water source is the common water source, natural raw water, or recycled water from semiconductor manufacturing processes.

[0003] For example, Patent Document 4 (Japanese Patent Application Publication No. 2000-51663) discloses a reverse osmosis membrane separation device for desalinating seawater, which includes a reverse osmosis membrane module unit. Summary of the Invention

[0004] [The problem the invention aims to solve] For example, in ultrapure water manufacturing equipment that supplies ultrapure water to semiconductor manufacturing equipment, the raw water may be tap water, well water, industrial water, or waste water (also called recycled water) used in semiconductor manufacturing.

[0005] However, due to the increased use of ultrapure water in semiconductor manufacturing and other industries, the amount of feedwater used in ultrapure water production has also increased. Since the supply of feedwater is limited, measures are needed to reduce the amount of feedwater used in ultrapure water production to ensure sufficient feedwater for other applications. Furthermore, while reducing the use of raw water is effective, it cannot adequately address the increasing scale of modern semiconductor and other manufacturing plants, as the utilization of recycled water also has its limitations. Furthermore, given the ongoing environmental and climate change issues, the supply of water is becoming increasingly unstable, creating a need to secure new sources of raw water.

[0006] As a new source of raw water, desalinated seawater (i.e., treated seawater) can be considered. However, to desalinate seawater, it is necessary to use a seawater desalination plant. Seawater desalination plants often use high-pressure reverse osmosis membrane devices as their main equipment. Due to the high operating costs, seawater desalination is generally not used as raw water for ultrapure water production plants. Currently, seawater desalination is a technology commonly used in the production of drinking water.

[0007] None of the technologies described in the aforementioned patent documents 1-3 (Japanese Patent Application Publication No. 8-89956, Japanese Patent Application Publication No. 2000-511109, and Japanese Patent Application Publication No. 2015-20131) use desalinated seawater as raw water. Furthermore, the technologies described in the aforementioned patent documents 1-3 are difficult to apply to seawater containing high concentrations of boron. Furthermore, although the aforementioned Patent Document 4 (Japanese Patent Application Publication No. 2000-51663) describes a reverse osmosis membrane separation device for desalination of seawater, it does not describe a corresponding device for producing ultrapure water from raw water.

[0008] The inventors of this disclosure explored the use of water treated by seawater desalination equipment as an ultrapure water production device, and discovered the following problems. 1) The boron concentration in the treated water from seawater desalination plants is higher than that in feedwater or recycled water. In other words, when seawater treated by desalination plants is used as drinking water, it is designed to meet the boron concentration standard of 1 mg / L for drinking water, resulting in a higher boron concentration than other feedwater. On the other hand, ultrapure water production plants have a lower boron removal capacity to begin with, and since the boron concentration of other feedwater is generally designed, for example, at most 0.1~0.2 mg / L, certain corresponding measures are required. For example, when the treated water from the seawater desalination plant is used directly as the feedwater for the ultrapure water plant, the amount of ion exchange resin in the boron selective ion exchange resin unit installed in the ultrapure water plant will increase, resulting in the leaching of total organic carbon (TOC) from the boron selective ion exchange resin unit. 2) In seawater desalination, the boron concentration in the treated water may fluctuate depending on the operating conditions of the desalination equipment. Since these fluctuations can occur over several days, there is a need to address them. Investigations have shown that these fluctuations are related to maintenance procedures such as cleaning or membrane exchange of the high-pressure reverse osmosis membrane unit. Figure 2 illustrates an example of the variation in water quality of the treated water from a seawater desalination plant.

[0009] Many semiconductor manufacturing processes operate continuously for years, making a stable supply of ultrapure water essential on an annual basis. Therefore, when using desalinated seawater as the source of ultrapure water for semiconductor manufacturing, it is necessary to supply raw water with a stable boron concentration as much as possible.

[0010] This disclosure takes into account the above facts and aims to use desalinated water, which can be used as raw water for the production of ultrapure water, as a raw water source for the production of desalinated seawater. [Methods for solving the problem]

[0011] The first-state ultrapure water manufacturing method includes: pretreatment to remove suspended matter from raw water containing desalinated water obtained by seawater desalination treatment, thereby obtaining pretreated water; primary treatment to remove at least one of total organic carbon and ionic components from the pretreated water to produce primary pure water; and secondary treatment to remove impurities from the primary pure water to produce ultrapure water, wherein the boron concentration of the raw water is adjusted to a tolerance value calculated based on the boron concentration required for the ultrapure water.

[0012] In this ultrapure water production method, the boron concentration of the raw water, which includes desalinated seawater, is adjusted to a value below the allowable value calculated based on the boron concentration required for ultrapure water. Therefore, desalinated seawater can be used as the raw water. For example, when using both desalinated seawater and feedwater as raw water, the amount of feedwater used can be reduced compared to using only feedwater as raw water.

[0013] The second state sample is an ultrapure water production method of the first state sample, in which the adjustment is performed by boron removal treatment to remove the boron contained in the seawater desalination water before the pretreatment when the boron concentration in the seawater desalination water exceeds the allowable value.

[0014] In this ultrapure water production method, when the boron concentration in the desalinated seawater exceeds the permissible value, a boron removal treatment preceding the pretreatment is performed to remove the boron from the desalinated seawater, thereby reducing the boron concentration in the desalinated seawater to below the permissible value. Furthermore, desalinated seawater can be used as the raw water for ultrapure water production.

[0015] The third state is the ultrapure water production method of the second state, wherein the boron removal treatment includes any one or more of the following: treating the seawater desalination water with a high-pressure reverse osmosis membrane, adding an alkaline substance to the seawater desalination water and treating it with a reverse osmosis membrane, treating the seawater desalination water with a boron selective ion exchange resin, treating it with an anion exchange resin, or treating it with an electro-deionization device.

[0016] This ultrapure water production method involves treating seawater desalination water via high-pressure reverse osmosis membrane, adding alkaline substances to seawater desalination water and then treating it via reverse osmosis membrane, treating seawater desalination water via boron selective ion exchange resin, treating it via anion exchange resin, or treating it via an electro-deionization unit. This method can efficiently remove boron from the seawater desalination water.

[0017] The fourth state sample refers to the ultrapure water manufacturing method of the first or second state sample, in which the allowable value corresponds to the change in the amount of ultrapure water used.

[0018] For example, the boron removal capacity of each unit in the primary and secondary pure water units, or the main unit for boron removal, will change in response to variations in the amount of ultrapure water used. In this ultrapure water manufacturing method, by adjusting the allowable values ​​to correspond to changes in the amount of ultrapure water used, boron contained in seawater desalination water can be removed efficiently.

[0019] The fifth type of ultrapure water manufacturing apparatus includes: a pretreatment unit for removing suspended matter from raw water containing desalinated water after seawater desalination treatment to obtain pretreated water; a primary pure water unit for removing at least one of total organic carbon and ionic components from the pretreated water to produce primary pure water; a secondary pure water unit for removing impurities from the primary pure water to produce ultrapure water; and a measuring unit for measuring the boron concentration of the desalinated water, wherein the boron concentration of the raw water is adjusted to a value below the allowable value calculated based on the boron concentration required for ultrapure water.

[0020] In this ultrapure water production apparatus, the boron concentration of the raw water, which includes desalinated seawater, is adjusted to be below the allowable value calculated based on the boron concentration required for ultrapure water. Therefore, desalinated seawater can be used as the raw water. For example, when using both desalinated seawater and feedwater as raw water, the amount of feedwater used can be reduced compared to when only feedwater is used as raw water.

[0021] The sixth state sample, in the ultrapure water production apparatus of the fifth state sample, further includes: a boron treatment device, which is located upstream of the pretreatment device in the flow direction to remove boron from the seawater desalination water.

[0022] In this ultrapure water production apparatus, when the boron concentration in the desalinated seawater exceeds the permissible value, a boron treatment device preceding the pretreatment stage removes the boron from the desalinated seawater, thereby reducing the boron concentration to below the permissible value. Furthermore, this allows the desalinated seawater to be used as the raw water for ultrapure water production.

[0023] The seventh state sample is an ultrapure water production device of the sixth state sample. The boron treatment device includes one or more of the following: a high-pressure reverse osmosis membrane device that treats the seawater via a high-pressure reverse osmosis membrane; a reverse osmosis membrane device that has an addition section for adding alkaline substances to the seawater desalination water and treats the seawater desalination water via a reverse osmosis membrane; a boron selective ion exchange resin device that treats the seawater desalination water via a boron selective ion exchange resin; an anion exchange resin device; and an electro-deionization device.

[0024] In this ultrapure water production device, boron contained in seawater desalination water can be effectively removed by any one or more of the following methods: high-pressure reverse osmosis membrane device, reverse osmosis membrane device with alkaline substances added to seawater desalination water, boron selective ion exchange resin device, anion exchange resin device, and electro-deionization device.

[0025] The eighth state sample is an ultrapure water production device of the fifth state sample, which further includes a seawater desalination treatment device, which treats seawater at least through a reverse osmosis membrane to obtain the seawater desalinated water.

[0026] In this ultrapure water production unit, which is also used as a seawater desalination unit, the seawater is treated via a reverse osmosis membrane to obtain desalinated water, ensuring the necessary amount of desalinated water. [Effects of the Invention]

[0027] This disclosure shows that desalinated seawater can be used as the raw water for the production of ultrapure water. Simple Explanation of the Diagram

[0028] [Figure 1] is a block diagram showing the outline of the ultrapure water production apparatus of the first embodiment. [Figure 2] is a graph showing an example of the change in boron concentration and conductivity of desalinated water over time. [Figure 3] is a block diagram showing the outline of the ultrapure water production apparatus in the second embodiment. [Figure 4] is a block diagram showing the outline of the ultrapure water production apparatus of the third embodiment. Implementation

[0029] The following description, with reference to the drawings, illustrates the specific configurations used to implement the disclosed technology. The same symbols used in each drawing represent the same or similar constituent elements. Furthermore, repeated descriptions or symbols in the following embodiments may be omitted. Please also note that the drawings used below are schematic diagrams, and the dimensional relationships and scales of the elements shown may not necessarily correspond to the actual situation; even between different drawings, the dimensional relationships and scales of the elements may not necessarily match.

[0030] [First Implementation Example] Figure 1 shows the ultrapure water production apparatus 100 of the first embodiment.

[0031] In Figure 1, the first embodiment of the ultrapure water production apparatus 100 can receive desalinated seawater (i.e., seawater desalination water) after seawater desalination treatment to produce ultrapure water. This ultrapure water production apparatus 100 includes a pretreatment unit 10, a primary pure water unit 11, and a secondary pure water unit 12. Furthermore, the ultrapure water production apparatus 100 includes a seawater desalination unit 40, a boron monitor 48, and a boron removal unit 60. Here, seawater refers to water from the ocean, containing at least 3.5% by weight of inorganic salts, primarily sodium or calcium salts. The concentration of these components in seawater varies approximately depending on the sea area.

[0032] The pretreatment device 10 is an apparatus that removes suspended solids from the raw water, including the desalinated seawater 32, to obtain pretreated water. As an example, impurities such as residual chlorine or large debris in the raw water are filtered using sand filters (filled with filter media such as sand), packed tank filters (such as MMF, i.e., multilayer media filter towers), membrane filters (such as MF, i.e., microporous membranes or UF, i.e., ultrafiltration membranes), and / or granular activated carbon towers. In the first embodiment, the raw water includes industrial water 14. Industrial water 14 refers to water used for industrial purposes. Municipal water, well water, or recycled water can also be used as alternatives. Municipal water refers to tap water obtained by treating natural water such as river water, lake water, and well water through processes such as coagulation, sedimentation, and filtration at a water treatment plant. The boron concentration of the municipal water is, for example, 40 μg / L or less (e.g., conductivity 200 μS / cm). Well water and recycled water are roughly the same quality as municipal water. Industrial water 14 is used as raw water and stored in a raw water tank, such as a PIT (storage pit) 20, for use in the production of ultrapure water.

[0033] The primary pure water unit 11 is an apparatus for producing primary pure water by removing at least one of the total organic carbon (TOC) and ionic components from the pretreated water. As an example, it combines a reverse osmosis membrane unit that uses a semi-permeable membrane to reverse osmosis the pretreated water, an ion exchange resin unit filled with ion exchange resin, an electro-deionization (EDI) unit, an ultraviolet irradiation unit for decomposing organic matter, and a degassing membrane unit for removing dissolved gases to purify the primary pure water. Depending on the needs, the primary pure water unit 11 may also include at least one of a high-pressure reverse osmosis membrane unit and an oxidation reaction tank for decomposing urea by adding hypobromic acid, etc. Furthermore, the ion exchange resin unit may be filled with cation exchange resin or anion exchange resin using a single-bed, multi-bed, or mixed-bed method, with boron-selective ion exchange resin being preferred. Alternatively, boron-selective ion exchange resin may be installed separately as the ion exchange resin unit. The produced primary pure water is supplied to the pure water tank 22.

[0034] The secondary pure water unit 12 is a device that 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 by passing them through a non-regenerative ion exchange tower (e.g., a polisher). Furthermore, it is combined with an ultraviolet irradiation device, a hydrogen peroxide decomposition device, a degassing device, etc. An ultrafiltration membrane is installed at the end of the secondary pure water unit 12 to remove microparticles. The produced ultrapure water is supplied to a POU (Point of Use) 19 for use in semiconductor manufacturing, etc. A portion of the ultrapure water is circulated back to the pure water tank 22 via a circulation line 28.

[0035] A seawater desalination unit 40 is located upstream of the PIT 20, which stores raw water. The desalination unit 40 includes multiple desalination processing units 42 for desalinating seawater 30. Seawater 30 is desalinated via these multiple desalination processing units 42 to obtain desalinated water 32. In Figure 1, there are three desalination processing units 42, but the number of units can be varied. For example, seawater 30 is stored in a tank 31, and the pipe 43 connected to the tank 31 branches into three pipes 44, each connected to one of the three desalination processing units 42. Because it has multiple (e.g., three) desalination processing units 42, if one unit malfunctions or cannot operate, the remaining units can handle the water. Furthermore, the three pipes 44 merge into a single pipe 43 downstream. In the ultrapure water manufacturing apparatus 100, a pump is provided in pipe 44 or pipe 43 for supplying fluids such as seawater 30 or desalinated water 32. However, for ease of understanding of the structure, the diagram of the pump is omitted in this disclosure.

[0036] As an example, the seawater desalination treatment unit 42 includes pretreatment equipment, multiple stages (e.g., two stages) of reverse osmosis membrane units (i.e., RO), and post-treatment equipment. In the pretreatment equipment, filtration is performed using sand filtration and ultrafiltration membranes (i.e., UF membranes). In the first stage of the reverse osmosis membrane unit (RO), for example, the pH is adjusted to between 6.0 and 6.5 before treatment via the reverse osmosis membrane. In the second stage of the reverse osmosis membrane unit (RO), for example, to remove boron, the pH is adjusted to between 9 and 10 before treatment via the reverse osmosis membrane. In either case, the initial treatment reverse osmosis membrane often uses a CA (cellulose acetate) type high-pressure reverse osmosis membrane. In the post-treatment equipment, acid is added to the permeate after reverse osmosis treatment to adjust the pH, followed by calcite permeate to adjust hardness, and sodium hypochlorite sterilization. However, the configuration of the seawater desalination treatment unit 42 can be modified.

[0037] The desalinated water 32 processed by the seawater desalination unit 40 is stored in the seawater desalination tank 46. As an example, downstream of the three seawater desalination units 42, three pipes 44 merge into one pipe 43, which is connected to the seawater desalination tank 46.

[0038] A boron monitor 48 is installed on a pipe 43 connected downstream of the seawater desalination tank 46. The boron monitor 48 is an example of a measuring unit that measures the boron concentration in the seawater desalination water 32.

[0039] To adjust the boron concentration of the desalinated water 32 to the permissible value calculated based on the boron concentration required for ultrapure water, the ultrapure water production apparatus 100 of the first embodiment includes a boron removal device 60 for removing boron from the desalinated water 32. The boron removal device 60 is an example of a boron treatment device. The boron concentration required for ultrapure water at POU 19 is, for example, 50 ng / L, preferably 1 ng / L. Thereafter, the permissible value calculated from the boron removal performance of each unit of the secondary pure water unit 12, the primary pure water unit 11, or the main unit for boron removal, is, for example, 0.2 mg / L for the water supplied to PIT 20, i.e., the pretreatment unit 10. Furthermore, in response to changes in the amount of ultrapure water used, the boron removal performance of each unit in the primary and secondary pure water systems, or the main unit for boron removal, will change. Therefore, taking this into account, the above-mentioned allowable values ​​may also change. For example, in the above situation, when the water usage at the end is 1 / 2, the allowable value can be 0.3 mg / L, etc.

[0040] As an example, pipe 43, connected downstream of the seawater desalination tank 46, is connected to pipe 52 via a switching valve 50. Pipe 52 is equipped with a boron removal device 60. Furthermore, downstream of the boron removal device 60, pipe 52 is connected to both the seawater desalination tank 46 and pipe 43 downstream of the switching valve 50. Thus, after measuring the boron concentration in the desalinated water 32 using a boron monitor 48, and considering the optimal removal of boron from the desalinated water 32, the flow direction of pipe 43 is switched to pipe 52 via the switching valve 50. Consequently, the desalinated water 32 is introduced into pipe 52 and processed by the boron removal device 60. Alternatively, instead of switching valve 50, a flow regulating valve can be used to supply a portion of the desalinated water 32 to the boron removal device 60. Other methods of bypassing (i.e., detouring) the boron removal device 60 with the desalinated water 32 are also possible. This approach allows for more flexible handling of changes in the boron concentration of the desalinated water 32. For example, in response to an increase in the boron concentration of the desalinated water 32, the proportion supplied to the boron removal device 60 can be increased accordingly.

[0041] Furthermore, the tank 74 for storing industrial water 14 is connected to the pipe 75 supplying industrial water 14. The pipe 43 for the flow of seawater desalination water 32 merges with the pipe 75 for the flow of industrial water 14 to form a single pipe 76, which is connected to PIT 20. A valve 73 for opening and closing the pipe 43 is provided on the upstream side of the merging section of the pipe 43 and the pipe 75.

[0042] The boron removal device 60 includes a high-pressure reverse osmosis membrane unit (i.e., high-pressure RO) 62. The high-pressure reverse osmosis membrane unit 62 has a high boron removal rate. As the high-pressure reverse osmosis membrane unit 62, existing high-pressure RO systems can be used, specifically, for example, the SWC series (manufactured by HYDEANAUTICS), the TM800 series (manufactured by TORAY), or the SW series (manufactured by Dow Chemical), etc.

[0043] The boron removal device 60 is located upstream of the high-pressure reverse osmosis membrane unit (i.e., high-pressure RO) 62, and includes an addition section 64 for adding alkali (alkaline substance) 65 to the desalinated water 32 flowing through the pipe 52. As an example, the addition section 64 includes a storage section 64A for storing alkali 65, a supply pipe 64B connecting the storage section 64A to the pipe 52, and an adjustment valve 64C located on the supply pipe 64B. Alternatively, the addition section 64 may include a pump (not shown) for supplying alkali 65. By adding alkali 65 to the desalinated water 32 via the addition section 64, the pH of the desalinated water 32 is adjusted to a higher level (e.g., pH 9 or higher and 10 or lower). Operating the high-pressure reverse osmosis membrane unit 62 at a higher pH increases the removal rate of boron in the desalinated water 32 and also makes it easier to adjust the removal rate. In the boron removal unit 60, where alkali 65 is added via the addition section 64, there are also cases where the pH of the treated water from the boron removal unit 60 is too high, affecting subsequent treatment. In such cases, for example, an upper limit of pH 10 can be set. If this is exceeded, mineral acids such as hydrochloric acid or sulfuric acid can be appropriately added at any point downstream of the high-pressure reverse osmosis membrane unit (i.e., high-pressure RO) 62 to adjust the pH to a more favorable level in subsequent treatment.

[0044] Furthermore, a boron monitor 70 is installed on the downstream pipe 52 of the high-pressure reverse osmosis membrane unit 62 to measure the boron concentration of the desalinated seawater 32 treated by the high-pressure reverse osmosis membrane unit 62. For example, if the measured boron concentration of the boron monitor 48 exceeds the allowable value (e.g., 0.2 mg / L), the flow direction of the pipe 43 is switched to the pipe 52 via the switching valve 50, so that at least a portion of the desalinated seawater 32 flows into the boron removal unit 60 for treatment. In the first embodiment, the boron removal device 60 can also remove turbidity, thus having the same function as the pretreatment device 10. Therefore, the treated water from the boron removal device 60 can bypass the pretreatment device 10 and be combined between the pretreatment device 10 and the primary pure water device 11. In this case, generally, if a tank or pit (either is not shown) is provided between the pretreatment device 10 and the primary pure water device 11, the water can be combined in the tank or pit. The concentrated water from the high-pressure reverse osmosis membrane unit 62 has low hardness, so it can be supplied to the cooling tower and used as cooling tower water. Furthermore, when the measured boron concentration of the boron monitor 70 far exceeds the permissible value (e.g., 0.3 mg / L), the addition unit 64 is activated, and alkali 65 is added to the seawater desalination water 32 via the addition unit 64, thereby improving the boron removal rate.

[0045] Figure 2 shows an example of the changes in boron concentration and conductivity of the seawater desalination water over the operating time of the ultrapure water production unit 100. Conductivity is measured using a conductivity meter, which is omitted from the diagram, but the conductivity meter is located in the same position in pipe 43 as the boron monitor 48. As shown in Figure 2, over the operating time of the ultrapure water production unit 100, the conductivity of the seawater desalination water 32 remains relatively stable around 30 μS / cm, while the boron concentration of the seawater desalination water 32 varies considerably. This is because when the desalination unit 40 continues to be used, for example, due to membrane degradation caused by continuous water flow or sterilization with chlorine, or due to scaling or biofouling on the membrane, the boron removal rate through the reverse osmosis membrane device (i.e., RO) of the seawater desalination unit 42 decreases. Therefore, in any one or more of the seawater desalination treatment units 42, the reverse osmosis membrane unit (i.e., RO) is cleaned with water, acid, alkali, or surfactants, or subjected to membrane exchange, to restore the boron removal rate. In this way, by repeatedly reducing the boron removal rate and restoring it through cleaning, the boron concentration in the desalinated water 32 will change. In addition to the periodic cleaning described above, the seawater desalination treatment unit 42 also switches the reverse osmosis membrane unit (i.e., RO) on or off according to the water usage in the downstream section. Although these operations are necessary and indispensable procedures, the physical or chemical impact on the reverse osmosis membrane may, in the long term, cause a decline in the boron removal performance of the reverse osmosis membrane unit (i.e., RO). Furthermore, the effects of global warming in recent years, such as rising seawater temperatures and increased temperature differences between summer and winter, may also cause long-term fluctuations in the boron concentration in the desalinated water 32. The rise in seawater temperature itself reduces the boron removal rate of the reverse osmosis membrane, and prolonged operation at high temperatures will also contribute to the degradation of the reverse osmosis membrane.

[0046] Figure 2 illustrates an embodiment in which the boron concentration of the desalinated water 32, measured by the boron monitor 48, in the ultrapure water production apparatus 100 switches between values ​​A (e.g., 0.2 mg / L) and B (e.g., 0.5 mg / L). Concentration A is the value required by the ultrapure water manufacturing apparatus 100 based on the maximum acceptable concentration of boron, for example, the allowable value calculated based on the required boron concentration of ultrapure water. This concentration is determined by the design conditions of the ultrapure water manufacturing apparatus 100. Alternatively, it can be determined by considering the mixing ratio of industrial water 14 in PIT 20. Furthermore, concentration B is the concentration determined based on the boron removal performance of the boron removal device 60. For example, in the high-pressure reverse osmosis membrane device 62, if the addition of alkali 65 still fails to achieve the maximum acceptable boron concentration of the ultrapure water production device 100, this concentration can be used as concentration B.

[0047] As an example, if the boron concentration of the desalinated water 32 measured by the boron monitor 48 is below value A (e.g., 0.2 mg / L), the desalinated water 32 from the desalination unit 40 is mixed with industrial water 14. In this case, since the boron removal device 60 is not used, the flow path from pipe 32 to pipe 52 is closed via the switching valve 50.

[0048] Furthermore, as an example, if the boron concentration of the desalinated water 32 measured by the boron monitor 48 exceeds value A (e.g., 0.2 mg / L) but is below value B (e.g., 0.5 mg / L), the boron removal device 60 is used. For example, the desalinated water 32 after boron removal treatment by the boron removal device 60 is mixed with industrial water 14. In this case, because the boron removal device 60 is used, the flow path from pipe 32 to pipe 52 is opened via the switching valve 50. Also, if the boron removal device 60 is constructed as a reverse osmosis membrane device, when using the boron removal device 60, alkali 65 can be added by the addition unit 64 according to the measured boron concentration value by the boron monitor 48 (e.g., if it is higher than a predetermined value). In this way, by using the boron removal device 60, the boron concentration of the desalinated water 32 can be reduced to below 0.2 mg / L.

[0049] As another example, if the boron concentration of the desalinated water 32 measured by the boron monitor 48 exceeds the B value (e.g., 0.5 mg / L), the use of the desalinated water 32 from the desalination unit 40 shall be stopped. In this case, valve 73 of pipe 43 shall be closed, and the ultrapure water production unit 100 shall be operated with raw water containing only industrial water 14.

[0050] Furthermore, although the diagram is omitted, in the ultrapure water production apparatus 100, a switching means for switching the flow path to the cooling tower may be provided between the boron monitor 48 in pipeline 43 and the switching valve 50. Therefore, in the boron removal apparatus 60, since the boron removal performance has limitations, the switching water quality to the cooling tower can be set according to the boron removal performance. For example, when the boron concentration of the seawater desalination water 32 exceeds the B value in Figure 2 (e.g., 0.5 mg / L), the seawater desalination water 32 can be supplied to the cooling tower and used as cooling tower water.

[0051] As a way to adjust the boron concentration in the raw water, changes in the mixing ratio of industrial water 14 and seawater desalination water 32, or larger-scale PIT 20, can also be considered. If the boron concentration in the seawater desalination water 32 increases, the boron concentration can be brought back to the allowable value by increasing the proportion of industrial water 14.

[0052] Furthermore, if PIT 20 is large, and the boron concentration of the desalinated water 32 exceeds, for example, the B value (e.g., 0.5 mg / L), the use of the desalinated water 32 should be stopped, and ultrapure water production can be carried out while consuming the raw water stored in PIT 20 with a lower boron concentration. Once the boron concentration falls below, for example, the B value (e.g., 0.5 mg / L), the use of the desalinated water 32 can be resumed, allowing the water storage capacity of PIT 20 to be restored. In this case, industrial water 14 can also be used as raw water. Furthermore, the capacity of PIT 20 can be determined by considering the water quality characteristics of the desalinated water 32, the supply of ultrapure water, and the usage of industrial water 14.

[0053] (effect) In the first embodiment, the boron concentration of the desalinated water 32 after desalination of seawater 30 is adjusted to be below the allowable value calculated based on the boron concentration required for ultrapure water, so that the desalinated water 32 can be used as raw water. When both desalinated water 32 and feedwater are used as raw water, the amount of feedwater used can be reduced compared to when only feedwater is used as raw water.

[0054] Furthermore, when the boron concentration in the desalinated water 32 after desalination of seawater 30 exceeds the permissible value, the boron contained in the desalinated water 32 can be removed by a boron removal device 60 located before pretreatment, thereby reducing the boron concentration in the desalinated water 32 to below the permissible value. In this way, the desalinated water 32 can be used as the raw water for ultrapure water production.

[0055] Furthermore, the boron removal apparatus 60 includes an addition section 64 for adding alkali 65 to the desalinated water 32, and a high-pressure reverse osmosis membrane apparatus 62 for treating the desalinated water 32 via a high-pressure reverse osmosis membrane. Therefore, depending on the boron concentration contained in the desalinated water 32, the desalinated water 32 can be treated via the high-pressure reverse osmosis membrane without adding alkali 65, or with alkali 65 added. Adding alkali 65 to the desalinated water 32 via the high-pressure reverse osmosis membrane improves the boron removal rate. Thus, boron contained in the desalinated water 32 can be removed efficiently.

[0056] Furthermore, in the case of the high-pressure reverse osmosis membrane unit 62, as the boron concentration of the desalinated water 32 increases, it is effective to increase the supply of desalinated water 32 to the boron removal unit 60 in stages. Moreover, if the boron concentration of the desalinated water 32 increases, the addition of alkali 65 will also be effective. In this case, when the boron concentration of the desalinated water 32 decreases, the increase in the amount of chemicals used can be suppressed because alkali 65 is not added during operation.

[0057] Through the first embodiment, seawater desalination water 32 can be used as the raw water for the production of ultrapure water.

[0058] Although the diagram is omitted, the high-pressure reverse osmosis membrane unit 62 can also be configured with multiple parallel lines. The high-pressure reverse osmosis membrane unit 62 consumes a large amount of electricity. When the supply of seawater desalinated water 32 to the boron removal unit 60 is small, in the configuration of multiple parallel lines of the high-pressure reverse osmosis membrane unit 62, one of the parallel lines can be used to remove boron, and the number of lines used can be increased along with the increase in supply. Other devices may be appropriately installed in the boron removal device 60. For example, depending on the water quality of the desalinated water 32, a carbonic acid removal device such as a softener, degassing tower, or degassing membrane, which consists of a sodium cation exchange device, may be installed. Alternatively, a line can be installed to directly supply raw water, such as water for public use, to the boron removal device 60. In this case, if the boron concentration in the raw water for public use rises rapidly for any reason, the boron removal device 60 can be used as a temporary boron removal device for the raw water for public use.

[0059] [Second Implementation Format] The ultrapure water production apparatus of the second embodiment will now be described. Components identical to those in the first embodiment will be labeled with the same numbers and their descriptions will be omitted.

[0060] Figure 3 shows the ultrapure water production apparatus 200 of the second embodiment. As shown in Figure 3, in the ultrapure water production apparatus 200, instead of the boron removal device 60 provided in the ultrapure water production apparatus 100 of the first embodiment, a boron removal device 210 is provided in the pipeline 52. The boron removal device 210 includes a boron selective ion exchange resin device 212. The boron selective ion exchange resin device 212 is an example of a boron treatment device, through which boron contained in the seawater desalination water 32 is removed.

[0061] As an example, boron-selective ion exchange resins are ion exchange resins with n-methylglucosamine groups, such as CRB02, CRB03, CRB05 (manufactured by Mitsubishi Chemical Corporation), or AMBERLITE IRA743 (registered trademark; Rohm and Haas). Boron-selective ion exchange resins can selectively adsorb boron regardless of salt concentration, thus enabling boron removal regardless of salt concentration and functioning effectively as boron removal devices.

[0062] The variation in boron concentration in the desalinated water 32 is shown in Figure 2. Knowing this beforehand, the boron selective ion exchange resin (BTC: continuous flow exchange capacity) is determined based on the maximum boron concentration, for example, by regenerating (restoring) it once every 1 to 5 days. Since the boron concentration in the desalinated water 32 varies over a long period, the boron removal unit 210 is expected to operate for an extended period (e.g., several to several tens of days). Therefore, during this period, it is difficult to operate the selective ion exchange resin without exceeding the flow limit, so the boron selective ion exchange resin will alternately undergo water circulation and regeneration. If the boron selective ion exchange resin unit 212 has multiple parallel boron selective ion exchange resin towers, they can be regenerated sequentially. If there is an odd number of boron selective ion exchange resin towers, the raw water during regeneration can be ensured by using industrial water 14 or raw water from PIT 20. In this embodiment, the boron-selective ion exchange resin system can cope with even high boron concentrations, and therefore can continue to operate even as the boron concentration increases. However, the regeneration frequency of the boron-selective ion exchange resin will increase.

[0063] Furthermore, inorganic boron adsorbents can also be used as alternatives to boron-selective ion exchange resins. Specifically, cerium-based adsorbents such as READ-B (manufactured by Nippon Seawater Co., Ltd.) can be used. Additionally, boron-selective ion exchange fibers can also be used, such as Chelest-Pearl CH351 or the Chelest-Fiber GRY series (manufactured by Chelest Co., Ltd.). The aforementioned boron-selective ion exchange resin should include inorganic boron adsorbents or boron-selective ion exchange fibers, etc. Furthermore, the other components of the ultrapure water production apparatus 200 are the same as those of the ultrapure water production apparatus 100 in the first embodiment. In the second embodiment, instead of boron-selective ion exchange fibers, anion exchange resin towers or electro-deionization devices can also be used. Since any of these devices can remove various anions, it is difficult to selectively remove boron. However, as shown in Figure 2, these devices can still be used because the conductivity of desalinated water 32 is lower than that of ordinary raw water such as municipal water. Commercially available strong-base anion exchange resins include, for example, the Diaion PA series, Diaion HPA series, Diaion SA series (all manufactured by Mitsubishi Chemical Corporation), or the 550A series (manufactured by Dow Chemical). Commercially available electro-deionization devices include, for example, the VNX55EX (manufactured by Evoqua Water Technologies). The VNX55EX (manufactured by Evoqua Water Technologies) also exhibits superior carbonic acid removal performance and does not suffer from reduced boron removal performance due to carbonic acid, thus making it a suitable candidate for boron removal device 210. When the boron concentration in the treated water increases, the anion exchange resin can continue to operate after regeneration using existing methods with alkalis such as sodium hydroxide and potassium hydroxide. Furthermore, the regenerators of boron selective ion exchange resins, anion exchange resins, and concentrated water from electro-deionization devices all have low hardness. Therefore, these can be supplied to cooling towers and used as cooling tower water.

[0064] The ultrapure water production apparatus 200 has the same configuration as the ultrapure water production apparatus 100 in the first embodiment, and can achieve the same function and effect.

[0065] Furthermore, the boron removal device 210 includes a boron selective ion exchange resin device 212 for treating the seawater desalination water 32 with a boron selective ion exchange resin. Therefore, in the ultrapure water production apparatus 200, boron removal can be performed by the boron removal device 210 regardless of the salt concentration of the seawater desalination water 32. Alternatively, instead of switching valve 50, a flow regulating valve can be used to supply a portion of the desalinated water 32 to the boron removal unit 210. Other methods of bypassing (i.e., detouring) the boron removal unit 210 with the desalinated water 32 are also possible. This approach allows for more flexible handling of changes in the boron concentration of the desalinated water 32. For example, in response to an increase in the boron concentration of the desalinated water 32, the supply ratio to the boron removal unit 210 can be increased accordingly. This minimizes the regeneration frequency of the boron-selective ion exchange resin unit 212. Other devices may be appropriately installed in the boron removal device 210. For example, depending on the water quality of the desalinated water 32, a carbonic acid removal device such as a softener, degassing tower, or degassing membrane, which consists of a sodium cation exchange device, may be installed.

[0066] [Third Implementation Mode] The ultrapure water production apparatus of the third embodiment will now be described. Components identical to those in the first and second embodiments will be labeled with the same numbers and their descriptions will be omitted.

[0067] Figure 4 shows the ultrapure water production apparatus 300 of the third embodiment. As shown in Figure 4, in the ultrapure water production apparatus 300, instead of the boron removal device 60 provided in the ultrapure water production apparatus 100 of the first embodiment, a boron removal device 310 is installed in the pipeline 52. The boron removal device 310 is an example of a boron treatment device. The boron removal device 310 includes an addition unit 64 and a reverse osmosis membrane device (i.e., RO) 312. The reverse osmosis membrane device 312 can be any medium-pressure, low-pressure, or ultra-low-pressure reverse osmosis membrane device. In the reverse osmosis membrane device 312, it is difficult to remove boron without the addition of alkali 65. Therefore, when using the reverse osmosis membrane device 312, alkali 65 is added from the addition unit 64. As a medium-pressure, low-pressure, or ultra-low-pressure reverse osmosis membrane device 312, a commercially available reverse osmosis membrane device can be used. For example, the TM700 series or the TML series (manufactured by TORAY Corporation) can be used. Compared to high-pressure RO, the RO used in the third embodiment consumes less power during operation, so even if the supply of seawater desalinated water 32 to the boron removal unit 310 is increased, the power consumption is less likely to increase.

[0068] For example, when the boron concentration increases, increasing the amount of alkali 65 added along with the increase in boron concentration will be effective. For example, when the boron concentration increases and the pH of the water supplied to the low-pressure RO increases from 7→8→9→10, it is possible to increase the boron removal rate. In this case, increasing the supply of seawater desalination water 32 to the boron removal unit 310 along with the increase in boron concentration is also possible. In the boron removal device 310, when alkali 65 is added at the addition section 64, there is a possibility that the pH of the treated water in the boron removal device 310 may be too high, affecting subsequent treatment. In this case, for example, an upper limit value of pH 10 can be set. If this upper limit value is exceeded, mineral acids such as hydrochloric acid or sulfuric acid can be appropriately added at any point downstream of the reverse osmosis membrane device (i.e., RO) 312 to adjust the pH to a better level in subsequent treatment.

[0069] The other components of the ultrapure water manufacturing apparatus 300 are the same as those of the ultrapure water manufacturing apparatus 100 in the first embodiment or the ultrapure water manufacturing apparatus 200 in the second embodiment.

[0070] The ultrapure water production apparatus 300 has the same configuration as the ultrapure water production apparatus 100 or 200 in the first embodiment or the second embodiment, and can achieve the same function and effect.

[0071] The ultrapure water production apparatus 300 includes a boron removal device 310 for treating seawater desalination water 32 by adding alkali 65 to the water via a reverse osmosis membrane device 312. The boron removal device 310 can efficiently remove boron contained in the seawater desalination water 32. Alternatively, instead of switching valve 50, a flow regulating valve can be used to supply a portion of the desalinated water 32 to the boron removal device 310. Other methods of bypassing (i.e., detouring) the boron removal device 310 with the desalinated water 32 are also possible. This approach allows for more flexible handling of changes in the boron concentration of the desalinated water 32. For example, in response to an increase in the boron concentration of the desalinated water 32, the proportion supplied to the boron removal device 310 can be increased accordingly. Other devices may be appropriately installed in the boron removal device 310. For example, depending on the water quality of the desalinated water 32, carbonic acid removal equipment such as a softener, degassing tower, or degassing membrane composed of a sodium cation exchange device may also be installed. In the third embodiment, the boron removal device 310 can also remove turbidity, thus having the same function as the pretreatment device 10. Therefore, the treated water from the boron removal device 310 can bypass the pretreatment device 10 and be combined between the pretreatment device 10 and the primary pure water device 11. In this case, generally, if a tank or pit (either is not shown) is provided between the pretreatment device 10 and the primary pure water device 11, the water can be combined in the tank or pit. The concentrated water from the reverse osmosis membrane unit 312 has low hardness, so it can be supplied to the cooling tower and used as cooling tower water.

[0072] [Methods for producing ultrapure water] The ultrapure water manufacturing methods of the first to third embodiments include: a pretreatment process to remove suspended matter from raw water containing desalinated water 32 obtained by desalinating seawater 30, thereby obtaining pretreated water; a primary treatment process to remove at least one of total organic carbon and ionic components from the pretreated water to produce primary pure water; and a secondary treatment process to remove impurities from the primary pure water to produce ultrapure water; wherein the boron concentration of the raw water is adjusted to a permissible value calculated based on the boron concentration required for ultrapure water. Therefore, the high boron concentration in the desalinated water 32 makes it possible to operate the downstream ultrapure water production unit. Furthermore, changes in the boron concentration in the desalinated water 32 can be addressed by adjusting the operating conditions of the boron removal unit.

[0073] Therefore, if the boron concentration in the desalinated water 32 after desalination of seawater 30 exceeds the allowable value, boron removal treatment can be performed before pretreatment to remove the boron contained in the desalinated water 32.

[0074] Furthermore, the boron removal treatment system may include any one or more of the following: treating the desalinated water 32 with a high-pressure reverse osmosis membrane, adding alkaline substances to the desalinated water 32 and treating it with a reverse osmosis membrane, or treating the desalinated water 32 with a boron selective ion exchange resin.

[0075] When using the ultrapure water manufacturing method disclosed herein, since it can handle the high boron concentration of seawater desalination water 32, an ultrapure water manufacturing unit can be used without modification. Therefore, by simply adding a boron removal device to the existing ultrapure water manufacturing unit, seawater desalination water 32 can be used as raw water. Furthermore, in the case of a newly installed ultrapure water manufacturing unit, no new design is required, and it can be easily implemented.

[0076] [Other implementation options] The foregoing has illustrated one example of the implementation of this disclosure, but the implementation of this disclosure is not limited to the above content. Of course, various modifications and implementations can be made without departing from its spirit.

[0077] For example, industrial water 14 can be treated using boron removal devices 60, 210, or 310. Such a system can accommodate situations where, for example, river water quality temporarily deteriorates during heavy rains, or the boron concentration in municipal water temporarily increases.

[0078] For example, in an ultrapure water production apparatus, 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 unit 64, and a second boron removal device equipped with a boron selective ion exchange resin device 212 may also be used.

[0079] The entire disclosure of Japanese Patent Application 2024-105194 is incorporated herein by reference. All documents, patent applications and technical standards described in this specification, whether or not individually cited in the specification, shall be deemed to be incorporated herein by reference to an equal degree.

[0080] 10: Pre-treatment device 11: Primary pure water system 12: Secondary pure water system 14: Industrial water 19: POU 20: PIT 22: Pure water tank 28: Loop circuit 30: Seawater 31: slot 32: Seawater desalination treatment 40: Seawater desalination unit 42: Seawater Desalination Treatment Department 43, 44, 52, 75, 76: Pipelines 46: Seawater desalination tank 48, 70: Boron monitor 50: Switching valve 60, 210, 310: Boron removal device 62: High-pressure reverse osmosis membrane unit 64: Additions 64A: Storage Section 64B: Supply pipe 64C: Adjusting valve 65: Alkali 73: Valve 74: Groove 100, 200, 300: Ultrapure water production equipment 212: Boron selective ion exchange resin packaging 312: Reverse osmosis membrane device

Claims

1. A method for producing ultrapure water, comprising: pretreatment to remove suspended solids from raw water comprising mixed industrial water and desalinated water obtained by seawater desalination, to obtain pretreated water; primary treatment to remove at least one of total organic carbon and ionic components from the pretreated water to produce primary pure water; and secondary treatment to remove impurities from the primary pure water to produce ultrapure water, wherein... The boron concentration of the raw water is adjusted to be below the allowable value calculated based on the boron concentration required for ultrapure water. The adjustment is made by performing boron removal treatment on the desalinated water before mixing when the boron concentration of the desalinated water exceeds the allowable value, so as to remove the boron contained in the desalinated water.

2. The ultrapure water manufacturing method as described in claim 1, wherein the boron removal treatment comprises any one or more of the following: treating the seawater desalination water with a high-pressure reverse osmosis membrane, adding an alkaline substance to the seawater desalination water and treating it with a reverse osmosis membrane, treating the seawater desalination water with a boron selective ion exchange resin, treating it with an anion exchange resin, or treating it with an electro-deionization device.

3. The method for producing ultrapure water as set forth in claim 1, wherein the allowable value corresponds to the variation in the amount of ultrapure water used.

4. An ultrapure water manufacturing apparatus, comprising: a pretreatment unit for removing suspended solids from raw water comprising mixed industrial water and desalinated water obtained by seawater desalination, to obtain pretreated water; a primary pure water unit for removing at least one of total organic carbon and ionic components from the pretreated water to produce primary pure water; a secondary pure water unit for removing impurities from the primary pure water to produce ultrapure water; a boron treatment unit disposed upstream of the pretreatment unit in the flow direction, for performing boron removal treatment on the desalinated water before mixing to remove boron contained in the desalinated water; and a measuring unit for measuring the boron concentration of the desalinated water, wherein... The boron concentration of the raw water is adjusted to a value below the allowable value calculated based on the boron concentration required for ultrapure water.

5. The ultrapure water production apparatus as described in claim 4, wherein the boron treatment apparatus comprises any one or more of the following: a high-pressure reverse osmosis membrane apparatus for treating the desalinated water via a high-pressure reverse osmosis membrane; a reverse osmosis membrane apparatus having an addition section for adding alkaline substances to the desalinated water and for treating the desalinated water via a reverse osmosis membrane; a boron selective ion exchange resin apparatus for treating the desalinated water via a boron selective ion exchange resin; an anion exchange resin apparatus; and an electro-deionization apparatus.

6. The ultrapure water production apparatus as described in claim 4 further includes: a seawater desalination treatment apparatus that treats seawater at least through a reverse osmosis membrane to obtain the desalinated water.

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