Pure water production method, pure water production apparatus, and ultrapure water supply system

Abstract

In this pure water production method, water to be treated is subjected to an activated carbon treatment in an activated carbon apparatus 5, and the activated carbon-treated water treated with activated carbon is subjected to a desalting treatment by a desalting apparatus to produce pure water. A plurality of activated carbon towers 51-5n which are filled with activated carbon are arranged in parallel in the activated carbon apparatus 5, and at least a plurality of desalting units are arranged in parallel in the desalting apparatus. The pure water production method comprises: a water intake step in which water to be treated is passed through all of the plurality of activated carbon towers 51-5n; and a regeneration step in which passing of water to be treated is stopped in at least one of the plurality of activated carbon towers 51-5n, or at least some of the plurality of desalting units are regenerated. The water flow space velocity of the activated carbon towers in the regeneration step is 10 / h or less.

Description

Pure water production method, pure water production apparatus, and ultrapure water supply system

[0001] The present invention relates to a pure water manufacturing method and apparatus for manufacturing pure water, and an ultrapure water supply system.

[0002] In the manufacturing processes of semiconductor devices and liquid crystal display devices, ultrapure water, from which organic matter, ionic components, fine particles, bacteria, etc. have been highly removed, is used as cleaning water, etc. In particular, when manufacturing electronic components including semiconductor devices, a large amount of ultrapure water is used as cleaning water in the cleaning process, and the demands for water quality are increasing year by year. For example, if organic matter is contained in ultrapure water used in the cleaning process, etc., the organic matter may carbonize in the subsequent heat treatment process, resulting in poor insulation, etc. Therefore, there is a demand for ultrapure water with an extremely low level of total organic carbon (TOC), and more preferably, ultrapure water from which persistent organic matter such as urea has been highly efficiently removed.

[0003] As shown in FIG. 1 , ultrapure water is generally produced in an ultrapure water production system 100, which is composed of a primary pure water system 101 that produces pure water and a subsystem 102 that further removes impurities from the pure water produced in the primary pure water system. The primary pure water system 101 is primarily composed of an activated carbon unit 105, a 2B3T (two-bed, three-tower ion exchange unit) 106, a reverse osmosis membrane unit 107, an ultraviolet irradiation unit 108, a double-bed pure water system (SBP) 109, and a degassing unit 110. The subsystem 102 is primarily composed of an ultraviolet irradiation unit 111, an ion exchange unit 112, a degassing unit 113, and an ultrafiltration membrane unit 114. It is preferable to remove as much persistent organic matter as possible, such as total organic compounds (TOC) and urea, in the primary pure water system 101. Furthermore, a pretreatment unit 104, such as a filtration unit, may be provided upstream of the primary pure water system 101. The primary pure water system 101 may have different component technologies depending on the nature of the impurities in the raw water and the required quality of the treated water. For example, instead of the 2B3T 106, an EDI (electrodeionized water production device) may be provided downstream of the reverse osmosis membrane device 107.

[0004] Patent Document 1 describes a water treatment method for producing primary pure water by using biological treatment to remove urea from water to be treated. This water treatment method uses activated carbon as a biological carrier, so-called biological activated carbon. Patent Documents 2 and 3 describe pure water production methods for performing biological treatment on water to be treated that contains organic matter (e.g., urea) to remove a portion of the organic matter. This pure water production method uses an activated carbon tower filled with biological activated carbon. From the perspective of maintenance, multiple activated carbon towers are arranged in parallel.

[0005] JP 2011-230093 A JP 2022-187347 A JP 2022-30031 A

[0006] In the operation of a pure water production system, multiple activated carbon towers are arranged in parallel, and some of the activated carbon towers may be replaced or cleaned while water is being sampled. Furthermore, to prevent bacterial growth on the activated carbon in the activated carbon towers, water to be treated is usually passed through the activated carbon towers when they are not being cleaned or replaced. Since all activated carbon towers are passed through when they are not being cleaned or replaced, the conditions for passing water through the activated carbon towers change when some of the activated carbon towers are being cleaned or replaced, which in turn changes the end water quality, i.e., the quality (TOC) of the pure water (or ultrapure water) being sampled. For this reason, stabilizing the end water quality is a challenge.

[0007] SUMMARY OF THE INVENTION An object of the present invention is to provide a method and apparatus for producing pure water that can solve the above problems and stabilize the quality of water at the end of the process.

[0008] In order to achieve the above-mentioned object, according to one aspect of the present invention, there is provided a method for producing pure water, in which water to be treated is treated with activated carbon in an activated carbon device, and the activated carbon-treated water is desalted in a desalting device to produce pure water, wherein the activated carbon device has a plurality of activated carbon towers filled with activated carbon arranged in parallel, and the desalting device has at least a plurality of desalting devices arranged in parallel, the method comprising: a water sampling step in which the water to be treated is passed through all of the plurality of activated carbon towers; and a regeneration step in which the passage of water through at least one of the plurality of activated carbon towers is stopped or at least a portion of the plurality of desalting devices is regenerated, and the pure water production method in the regeneration step has a water space velocity of 10 / h or less.

[0009] According to another aspect of the present invention, there is provided a pure water production system comprising: an activated carbon device that treats water to be treated with activated carbon; and a desalination device that desalinates the activated carbon-treated water from the activated carbon device to produce pure water, wherein the activated carbon device has a plurality of activated carbon towers arranged in parallel, each filled with activated carbon, and the desalination device has at least a plurality of desalination devices arranged in parallel, the system comprising control means that performs a water sampling process in which the water to be treated is passed through all of the plurality of activated carbon towers, and a regeneration process in which the passage of water through at least one of the plurality of activated carbon towers or the regeneration of at least a portion of the plurality of desalination devices, wherein the space velocity of water passing through the activated carbon tower in the regeneration process is 10 / h or less.

[0010] According to yet another aspect of the present invention, there is provided an ultrapure water supply system comprising: a primary pure water system having at least the above-described pure water production apparatus; a subsystem that produces ultrapure water by removing impurities from the pure water produced in the primary pure water system; and a recovery system that recovers ultrapure water used at a point of use where the ultrapure water produced in the subsystem is used and returns it to the primary pure water system.

[0011] According to the present invention, the quality of water at the end of the pure water production system can be stabilized.

[0012] FIG. 1 is a block diagram showing the configuration of an ultrapure water production apparatus. FIG. 2 is a block diagram showing the configuration of a pure water production apparatus to which the pure water production method according to the first embodiment of the present invention is applied. FIG. 3 is a schematic diagram for explaining an example of an operating process carried out in the pure water production method according to the first embodiment of the present invention. FIG. 4 is a diagram for explaining an operating process when there are three activated carbon towers. FIG. 5 is a diagram for explaining an operating process when there are five activated carbon towers. FIG. 6 is a diagram for explaining an operating process when there are seven activated carbon towers. FIG. 7 is a block diagram showing the configuration of a pure water production apparatus to which the pure water production method according to the second embodiment of the present invention is applied. FIG. 8 is a diagram for explaining an example of an operating process carried out in the pure water production method according to the second embodiment of the present invention. FIG. 9 is a block diagram showing the configuration of a pure water production apparatus to which the pure water production method according to the third embodiment of the present invention is applied. FIG. 10 is a schematic diagram for explaining an operating process including a regeneration / cleaning step of an ion exchange resin. FIG. 11 is a schematic diagram for explaining an operating process including a regeneration / cleaning step of an ion exchange resin. FIG. 12 is a schematic diagram for explaining an operating process including a regeneration / cleaning step of an ion exchange resin. FIG. 2 is a schematic diagram for explaining an operation process including a regeneration / cleaning process of an ion exchange resin.

[0013] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the components described in the embodiments are merely examples and are not intended to limit the scope of the present invention.

[0014] 2 is a block diagram showing the configuration of a pure water production system (primary pure water system) to which a pure water production method according to a first embodiment of the present invention is applied. Referring to FIG. 2, the pure water production system 1 has a raw water tank 2, a filtration device 3, a filtered water tank 4, an activated carbon device 5, a 2B3T device 6, and downstream equipment 13. The activated carbon device 5 has a plurality of activated carbon towers 51 to 55. n are arranged in parallel. The water to be treated in the filtered water tank 4 is treated in the activated carbon device 5 and supplied to the 2B3T device 6. The number of activated carbon towers arranged in parallel can be set appropriately.

[0015] The raw water tank 2 stores the water to be treated. The water to be treated may be, for example, industrial water, well water, city water, surface water, wastewater provided inside or outside a customer's factory, treated sewage water, or desalinated seawater, and one or more of these waters are stored in the raw water tank 2. The filtration device 3 is connected to the raw water tank 2 via piping. The water to be treated stored in the raw water tank 2 is supplied to the filtration device 3. The filtration device 3 filters the water to be treated using, for example, sand as a filter medium. The filtered water tank 4 is connected to the filtration device 3 via piping. The filtration device 3 is used to store the filtered water from the filtration device 3. Note that the filtration device 3 may be considered a pretreatment device installed upstream of the primary pure water system 1, but here the filtration device 3 is referred to as the primary pure water system 1.

[0016] Multiple activated carbon towers 51-5 n is connected to the filtered water tank 4 via piping. n Both of these are filled with activated carbon with a porous structure, and the filtered water supplied from the filtered water tank 4 is passed through the activated carbon. The activated carbon adsorbs and removes organic matter from the filtered water. In addition, the organic matter is decomposed by attaching microorganisms to the activated carbon and by growing the microorganisms in the activated carbon layer.

[0017] The activated carbon treated water is treated in a 2B3T device (desalting device) 6. The 2B3T device 6 is a two-bed, three-tower water purification device. The 2B3T device 6 is composed of a cation exchange resin tower (K ​​tower), a decarbonation tower (D tower), and an anion exchange resin tower (A tower). The 2B3T device 6 is composed of multiple K towers 101 to 10 m and multiple D Towers 111-11 m and multiple A Towers 121-12 m Here, the K tower is an ion exchange resin tower packed with a strongly acidic cation exchange resin (cation exchange resin). The D tower is a decarbonation tower. The A tower is an ion exchange resin tower packed with a strongly basic anion exchange resin (anion exchange resin). The K towers 101 to 10 m is connected to multiple activated carbon towers 51 to 5 via piping. n It is connected to multiple K towers 101 to 10 m are multiple activated carbon towers 51 to 55 nActivated carbon-treated water is supplied from the K tower, and the cations in the activated carbon-treated water are ion-exchanged using a strongly acidic cation exchange resin. The number of K towers arranged in parallel can be set appropriately.

[0018] Multiple D Towers 111-11 m is connected to a plurality of K towers 101 to 101 through piping. m It is connected to multiple D towers 111-11 m are multiple K towers 101 to 10 m Ion-exchange treated water is supplied from the tower D, and carbon dioxide and the like in the ion-exchange treated water are removed. For example, carbon dioxide gas in the treated water can be degassed (removed) using a decarbonation membrane that allows gas to pass through. The number of parallel D towers can be set as appropriate.

[0019] Multiple A Towers 121-12 m is connected to a plurality of D towers 11 to 11 via piping. m It is connected to multiple Towers A 121-12 m are multiple D towers 111 to 11 m The decarbonated water is supplied from the column A, and the anions in the decarbonated water are ion-exchanged using a strong basic anion exchange resin. The number of columns A arranged in parallel can be set appropriately.

[0020] In the pure water production method of this embodiment, a plurality of activated carbon towers 51 to 55 n The space velocity (SV) when water is passed through the activated carbon towers in parallel is set as a reference value, and when water is not being taken from part of the activated carbon tower due to cleaning or replacement of the activated carbon tower (a partial water taking stop process, hereinafter also referred to as a "regeneration process", including the case where the ion exchange resin tower described below is regenerated), that is, when the space velocity of the activated carbon tower through which water is passed increases, the activated carbon tower is operated so that the space velocity of the activated carbon tower through which water is passed is 1.5 times or less of the reference value. By performing such an operation, it is possible to stabilize the terminal water quality.

[0021] Here, the water collection process is carried out in all activated carbon towers 51 to 55. n The partial water sampling stop process involves operating multiple activated carbon towers 51 to 55. nThis is an operating process performed when some of the activated carbon towers are not used for water sampling. The space velocity indicates how many times the volume of water is passed through a unit volume of activated carbon (in other words, how many times the volume of activated carbon is treated per unit time). The operating process, including the water sampling process and the partial water sampling stop process, is performed by a control means (also called a control device) not shown. Note that this operating process may also be performed manually.

[0022] In general, the space velocity is expressed by the flow rate of filtrate supplied to activated carbon per unit time divided by the volume of activated carbon. When n activated carbon towers are arranged in parallel, the "flow rate of filtrate supplied to activated carbon" means the total flow rate of water to be treated passed through the n activated carbon towers, and the "volume of activated carbon" means the total volume of activated carbon in the n activated carbon towers. However, in the case of a parallel arrangement, the same activated carbon towers are usually arranged, so even if the space velocity is calculated using the "flow rate of filtrate supplied to activated carbon" and the "volume of activated carbon" per tower, it will be the same value as when calculated for all towers.

[0023] Normally, the specifications of the activated carbon equipment (such as the amount of activated carbon packed, the number of towers, and the flow rate of water) are designed based on the quality of the water to be treated and the required water quality at the end, taking into account the cleaning and replacement of the activated carbon towers. nIn a water collection system including the above, when a portion of the activated carbon tower is cleaned (backwashed) or replaced, or when an ion exchange resin tower (such as a K tower or an A tower) in a downstream 2B3T device 6 is regenerated, the water flow conditions for the activated carbon tower change. This can lead to improper organic matter treatment in the activated carbon tower, resulting in deterioration of the activated carbon-treated water and ultimately the quality of the terminal water (the quality of the pure water (or ultrapure water) being collected). In particular, when the activated carbon in the activated carbon tower is biologically activated carbon, biological treatment is performed in addition to the adsorption effect of the activated carbon in organic matter treatment, making the mechanism of organic matter treatment by the activated carbon complex. Therefore, when the water flow conditions for the activated carbon tower change, the activated carbon treatment may not be performed as designed, which is thought to result in deterioration of the terminal water quality. Based on this knowledge, the inventors have found that when a partial water sampling stop process (cleaning (backwashing), replacement, regeneration, etc.) is performed in which the space velocity of the activated carbon tower through which water passes increases, the terminal water quality can be stabilized by operating the activated carbon device so that the fluctuations in the space velocity fall within a certain range based on the space velocity of the activated carbon device during the water sampling process.

[0024] An application example of the pure water producing method of this embodiment will be described below as an example of the partial water withdrawal stop step.

[0025] (Application Example 1: When there are three activated carbon towers) Figure 3 is a diagram for explaining the operating steps performed in the pure water production method of this embodiment when there are three activated carbon towers. In Figure 3, (a) is a schematic diagram showing the water flow state during the water sampling step, and (b) is a schematic diagram showing the water flow state during the cleaning step. In this operating step, one of the three activated carbon towers 51 to 53 is operated separately.

[0026] In the water collection process shown in FIG. 3(a), the flow rate of the filtered water at the inlet side of the three activated carbon towers 51 to 53 is Q [m 3 / h]. Normally, the activated carbon towers 51 to 53 are each set to the same capacity V [m ３ ] is packed in the activated carbon, so the flow rate of each of the three activated carbon towers 51 to 53 is Q / 3 [m 33(b), the activated carbon tower 53 of the three activated carbon towers 51 to 53 is isolated from the water sampling system, and water is sampled using the two activated carbon towers 51 and 52 while backwashing is performed on the activated carbon tower 53. Washing water is supplied from outside the water sampling system and passed in the opposite direction to the flow of the filtered water.

[0027] During the cleaning process, the flow rate of the activated carbon towers 51 and 52, which continue to collect water, is Q / 3 [m 3 / h] to Q / 2 [m 3 / h]. That is, the space velocity is 1.5 times that during the water sampling process. When the SV during the partial water sampling stop process is 1.5 times or less than the SV during the water sampling process, the quality of the activated carbon-treated water, and therefore the terminal water quality, remains stable. Note that when water sampling is stopped from one of the three activated carbon towers due to cleaning or the like, the SV ratio is theoretically 1.5 times, but in reality, the SV ratio may exceed 1.5 times due to pressure loss, one-sided flow, etc. within the activated carbon tower. In such cases, the terminal water quality becomes unstable, so the SV ratio is set to 1.5 times or less by adjusting the flow rate according to the second embodiment described below.

[0028] (Application Example 2: When there are five activated carbon towers) Figure 4 is a diagram illustrating the operating steps performed in the method for producing pure water of this embodiment when there are five activated carbon towers. In Figure 4, (a) is a schematic diagram showing the water flow state during the water sampling step, (b) is a schematic diagram showing the water flow state during the cleaning step, and (c) is a schematic diagram showing the water flow state when the water flow is stopped to replace some of the activated carbon towers during the cleaning step.

[0029] In the water collection process shown in FIG. 4(a), the flow rate of the filtered water at the inlet side of the five activated carbon towers 51 to 55 is Q [m 3 / h]. Normally, the activated carbon towers 51 to 55 are each set to the same capacity V [m ３ ] is packed in the activated carbon towers 51 to 55, the flow rate of each is Q / 5 [m 3 / h], and the space velocity SV is Q / 5V [ / h]. In the cleaning process (partial water sampling stop process) shown in Figure 4(b), of the five activated carbon towers 51 to 55, activated carbon tower 55 is isolated from the water sampling system, and water is sampled using the four activated carbon towers 51 to 54, while backwashing is performed on activated carbon tower 55. Cleaning water is supplied from outside the water sampling system and passed in the opposite direction to the flow direction of the filtered water. In the cleaning and replacement process (partial water sampling stop process) shown in Figure 4(c), of the five activated carbon towers 51 to 55, activated carbon tower 55 is isolated from the water sampling system for cleaning, and activated carbon tower 54 is isolated from the water sampling system for replacement, and water is sampled using the three activated carbon towers 51 to 53.

[0030] During the cleaning process, the flow rate of the activated carbon towers 51 to 54, which continue to collect water, is Q / 5 [m 3 / h] to Q / 4 [m 3 / h]. In other words, the space velocity is 1.25 times that during the water sampling process. In this way, when the SV during the partial water sampling stop process is 1.5 times or less than the SV during the water sampling process, the quality of the activated carbon treated water, and ultimately the terminal water quality, remains stable. Furthermore, during the cleaning and replacement processes, the flow rates of the activated carbon towers 51 to 53, which continue to sample water, are all increased to Q / 5 [m] during the water sampling process. 3 / h] to Q / 3 [m 3 / h]. That is, the space velocity is 1.67 times that during the water sampling process. When the SV during the partial water sampling stop process exceeds 1.5 times the SV during the water sampling process, the quality of the activated carbon treated water, and ultimately the terminal water quality, becomes unstable. When the SV ratio exceeds 1.5 times, the SV ratio is set to 1.5 times or less by adjusting the flow rate according to the second embodiment described below. Furthermore, even if the SV ratio theoretically exceeds 1.5 times, if the SV ratio during actual operation is 1.5 times or less, flow rate adjustment is not necessary.

[0031] Furthermore, it is preferable that the SV of the activated carbon tower during normal operation (during the water sampling process) is 10 / h or less. If the SV of the activated carbon tower during normal operation (during the water sampling process) exceeds 10 / h, the terminal water quality may become unstable even if the SV during the partial water sampling stop process is about 1.5 times.

[0032] Furthermore, it is preferable that the SV of the activated carbon tower during the partial water collection stop step is 10 / h or less.

[0033] (Application Example 3: When there are seven activated carbon towers) Figure 5 is a diagram illustrating the operating steps performed in the method for producing pure water of this embodiment when there are seven activated carbon towers. In Figure 5, (a) is a schematic diagram showing the water flow state during the water sampling step, (b) is a schematic diagram showing the water flow state during the cleaning step, and (c) is a schematic diagram showing the water flow state when the water flow is stopped to replace some of the activated carbon towers during the cleaning step.

[0034] In the water collection process shown in FIG. 5(a), the flow rate of the filtered water at the inlet side of the seven activated carbon towers 51 to 57 is Q [m 3 / h]. Normally, the activated carbon towers 51 to 57 are each set to the same capacity V [m ３ ] is packed in the activated carbon, so the flow rate of each of the seven activated carbon towers 51 to 57 is Q / 7 [m 3 / h], and the space velocity SV is Q / 7V [ / h]. In the cleaning process (partial water sampling stop process) shown in Figure 5(b), of the seven activated carbon towers 51 to 57, activated carbon tower 57 is isolated from the water sampling system, and water is sampled using six activated carbon towers 51 to 56, while backwashing is performed on activated carbon tower 57. Cleaning water is supplied from outside the water sampling system and flows in the opposite direction to the flow direction of the filtered water. In the cleaning and replacement process (partial water sampling stop process) shown in Figure 5(c), of the seven activated carbon towers 51 to 57, activated carbon tower 57 is isolated from the water sampling system for cleaning, and activated carbon tower 56 is isolated from the water sampling system for replacement, and water is sampled using five activated carbon towers 51 to 55.

[0035] During the cleaning process, the flow rate of the activated carbon towers 51 to 56, which continue to collect water, is Q / 7 [m 3 / h] to Q / 6 [m 3 / h]. In other words, the space velocity is 1.17 times that during the water sampling process. In this way, when the SV during the partial water sampling stop process is 1.5 times or less than the SV during the water sampling process, the quality of the activated carbon treated water, and ultimately the terminal water quality, remains stable. Furthermore, during the cleaning and replacement processes, the flow rates of the activated carbon towers 51 to 55, which continue to sample water, are all increased to Q / 7 [m 3 / h] to Q / 5 [m3 / h]. That is, the space velocity is 1.4 times that during the water sampling process. In this way, when the SV during the partial water sampling stop process is 1.5 times or less the SV during the water sampling process, the terminal water quality remains stable. Note that if the SV ratio exceeds 1.5 due to pressure loss, one-sided flow, or the like within the activated carbon tower, the terminal water quality becomes unstable, so the SV ratio is set to 1.5 times or less by adjusting the flow rate according to the second embodiment described below. Also, when three or more activated carbon towers are separated from the water sampling system, the SV exceeds 1.5 times the SV during the water sampling process, making the terminal water quality unstable, so the SV ratio is set to 1.5 times or less by adjusting the flow rate.

[0036] Furthermore, it is preferable that the SV of the activated carbon tower during normal operation (during the water sampling process) is 10 / h or less. If the SV of the activated carbon tower during normal operation (during the water sampling process) exceeds 10 / h, the terminal water quality may become unstable even if the SV during the partial water sampling stop process is about 1.5 times.

[0037] Furthermore, it is preferable that the SV of the activated carbon tower during the partial water collection stop step is 10 / h or less.

[0038] As described above, according to the method for producing pure water of this embodiment, the terminal water quality can be stabilized by operating the activated carbon tower so that fluctuations in the space velocity fall within a certain range based on the space velocity in the activated carbon tower during the water sampling process.

[0039] The above-mentioned flow rate values ​​and the number of activated carbon towers are merely examples and can be changed as appropriate. For example, as long as the activated carbon towers used for water sampling can be operated so that the space velocity is 1.5 times or less the reference value, the number of activated carbon towers separated from the water sampling system may be two or more. Furthermore, the terminal water quality may be determined based on urea, which is one of the TOC components, or may be determined based on other persistent TOC components.

[0040] Second Embodiment Fig. 6 is a block diagram showing the configuration of a pure water production system to which a pure water production method according to a second embodiment of the present invention is applied. The pure water production system 1A shown in Fig. 6 differs from the pure water production system 1 described in the first embodiment in that it includes a flow control valve 7. The components other than the flow control valve 7 are basically the same as those of the pure water production system 1, so a description of these components will be omitted here.

[0041] The flow control valve 7 is connected to the plurality of activated carbon towers 51 to 55. n The filtered water stored in the filtered water tank 4 is supplied to the activated carbon towers 51 to 55 via a flow control valve 7. n The flow control valve 7 is connected to the activated carbon towers 51 to 55. n The flow rate on the inlet side can be adjusted.

[0042] In the method for producing pure water according to this embodiment, similar to the first embodiment, the activated carbon towers 51 to 55 are used during the water collection process. n The reference value is the space velocity when water is passed through the activated carbon towers in parallel, but unlike the first embodiment, when a partial water sampling stop step is performed, the flow rate on the inlet side is adjusted by the flow control valve 7 so that the space velocity of the activated carbon tower used for water sampling is 1.5 times or less the reference value. This adjustment makes it possible to stabilize the terminal water quality.

[0043] As an example, an operating process will be described below for a water sampling system equipped with two activated carbon towers 51 and 52, in which the flow rate is adjusted so that the space velocity of the activated carbon tower used for water sampling becomes 1.3 times the reference value.

[0044] 7A and 7B are diagrams illustrating an example of an operating process performed in the pure water production method of this embodiment. In Fig. 7A, (a) is a schematic diagram showing the water flow during the water sampling process, and (b) is a schematic diagram showing the water flow during the cleaning process. In this operating process, one of the two activated carbon towers 51 and 52 is operated separately.

[0045] In the water collection process shown in FIG. 7(a), the flow rate of the filtered water at the inlet side of the two activated carbon towers 51 and 52 is controlled by the flow control valve 7. 3 In this case, the flow rates of the activated carbon towers 51 and 52 are set to Q / 2 [m3 / h]. The activated carbon packing capacity of each activated carbon tower is V [m ３ ], SV is Q / 2V [ / h]. In the cleaning process shown in Figure 7(b), of the two activated carbon towers 51 and 52, activated carbon tower 52 is separated from the water collection system, and water is collected using activated carbon tower 51 while backwashing is performed on activated carbon tower 52. The flow rate of filtered water at the inlet side of the two activated carbon towers 51 and 52 is Q [m 3 / h], the SV of the activated carbon tower 51 from which water is collected is Q / V [ / h], and the SV ratio is doubled, exceeding 1.5 times. Therefore, here, the flow rate of the filtered water on the inlet side of the activated carbon tower 51 is controlled to q [m ３ / h] (<Q [m 3 / h]) so that the SV ratio is 1.5 or less. This makes it possible to stabilize the water quality at the terminal.

[0046] The above-mentioned flow rate values ​​and the number of activated carbon towers are merely examples and can be changed as appropriate. For example, as long as the flow rate can be adjusted so that the space velocity of the activated carbon tower used for water sampling is 1.5 times or less the reference value, the number of activated carbon towers connected in parallel may be three or more, and the number of activated carbon towers separated from the water sampling system may be two or more.

[0047] (Third Embodiment) Figure 8 is a block diagram showing the configuration of a pure water production system to which a pure water production method according to a third embodiment of the present invention is applied. The pure water production system 1B shown in Figure 8 differs from the pure water production system 1A described in the second embodiment in that it includes a replenishment device 8. Since the components other than the replenishment device 8 are basically the same as those of the pure water production system 1A, a description of these components will be omitted here.

[0048] When the flow control valve 7 adjusts the flow rate on the inlet side, it may not be possible to ensure the amount of water supplied to the 2B3T device 6. In this embodiment, when the amount of water supplied to the 2B3T device 6 cannot be ensured, the replenishing device 8 replenishing the shortage to the 2B3T device 6. For example, the replenishing device 8 can replenishing surplus water, such as recovered water obtained from the 2B3T device 6, to the activated carbon-treated water or treated water obtained by treating the activated carbon-treated water.

[0049] Although not shown in FIG. 8 , if a reverse osmosis (RO) membrane device or an electrodeionization (EDI) device is provided downstream of the A tower in the 2B3T system 6, the surplus water can be the concentrated water from the RO membrane device, the concentrated water from the EDI, or even circulating surplus water from equipment that treats the permeate from the RO membrane device. The surplus water supply point is not limited to the outlet of the activated carbon tower. For example, the surplus water can be supplied to the inlet of the K tower or an RO tank provided upstream of the RO membrane device. Supplying surplus water to the inlet of the K tower allows the desalination process to be performed on the make-up water as well, allowing for more efficient use of the surplus water.

[0050] Furthermore, an analyzer (not shown) may analyze the quality of the surplus water (make-up water) from the replenishing device 8, and surplus water with predetermined components below a threshold value may be replenishing the primary pure water system. The predetermined components include, for example, conductivity, residual salt concentration, TOC value, and urea concentration. The threshold value differs depending on the replenishing point, but it is desirable that the threshold value be equivalent to the water quality at the replenishing point during steady-state operation.

[0051] By managing the quality of surplus water (make-up water) in this way and using only water that meets the standards for make-up, it is possible to further stabilize the water quality at the terminal.

[0052] Alternatively, for example, a water tank may be provided downstream of the 2B3T device 6, and the supply of makeup water from the replenishment device 8 may be controlled according to the water level in the water tank. For example, upper and lower limits for the water level in the water tank may be set in advance. When the water level reaches the lower limit, replenishment begins, and when the water level reaches the upper limit, replenishment stops. This allows surplus water to be replenished with the minimum necessary amount of replenishment.

[0053] Alternatively, the required amount of surplus water may be calculated based on the rate of water level decrease and the remaining time of the activated carbon backwashing process at predetermined intervals, and the amount of surplus water may be adjusted based on the calculated value. This method also allows surplus water to be replenished with the minimum necessary amount. For example, when the cleaning process shown in FIG. 7B is performed, surplus water can be replenished with the minimum necessary amount based on the measured water level. This not only stabilizes the water quality at the end, but also allows surplus water to be replenished efficiently.

[0054] (Fourth Embodiment) A pure water production method according to a fourth embodiment of the present invention will be described. As described above, the 2B3T device 6 provided downstream of the activated carbon device 5 typically has multiple K towers. All of the multiple activated carbon towers in the activated carbon device 5 are used for water sampling during normal operation, but at least one K tower is generally kept in a standby state and is not used for water sampling.

[0055] 9A to 9F are schematic diagrams illustrating the operation process including the regeneration / cleaning process of the ion exchange resin. In Fig. 9A to 9F, there are five activated carbon towers (activated carbon towers 51 to 55), and three K towers, D towers, and A towers (K towers 101 to 103, D towers 111 to 113, and A towers 121 to 123).

[0056] In the water sampling process, one of the three K towers 101 to 103 is placed on standby, and the remaining two K towers are used to sample water. When regeneration / cleaning of the ion exchange resin of one of the two operating K towers is required, the standby K tower is operated to perform regeneration / cleaning of the K tower to be regenerated / cleaned.

[0057] Specifically, as shown in Figure 9A, K tower 101 is in a standby state, and water is sampled using K towers 102 and 103. K tower 101 is isolated from the water sampling system, and the ion exchange resin has been regenerated. Components other than K tower 101 are in operation (operating) for water sampling. A flow rate Q [m ３ / h] of water is supplied. Therefore, the flow rate of each of the activated carbon towers 51 to 55 is Q / 5 [m 3 The activated carbon treated water is supplied to the K towers 10 and 10, and the flow rate is Q / 2 [m 3 / h]. Tower K 103 is the next target for regeneration.

[0058] Next, as shown in Figure 9B, the K tower 101 is idled (prepared for water collection). Specifically, the same amount of activated carbon treated water as that of the K towers 102 and 103 is passed through the K tower 101, and the treated water from the K tower 101 is returned to the filtered water tank 4. Therefore, the flow rate of the produced pure water is Q [m 3 / h], the flow rate of water supplied to the entire K column is 3Q / 2 [m 3 / h], and the flow rate of each of the five activated carbon towers 51 to 55 is 3Q / 10 [m 3 Therefore, the flow rate of each of the activated carbon towers 51 to 55 is Q / 5 [m 3 / h] to 3Q / 10 [m 3 / h], the SV ratio is 1.5 times. If the SV ratio is 1.5 times or less, the terminal water quality is stable.

[0059] Next, as shown in FIG. 9C, a chemical passing step is performed on the K tower 103. Specifically, the K tower 103 is separated from the water sampling system, and the ion exchange resin is regenerated using, for example, hydrochloric acid. During this regeneration (chemical passing) step, the components other than the K tower 103 are in operation (operating) for water sampling. The flow rate of each of the activated carbon towers 51 to 55 is set to Q / 5 [m 3 The activated carbon treated water is supplied to the K towers 10 and 10, and the flow rate of each is Q / 2 [m 3 / h].

[0060] Next, as shown in FIG. 9D, the pushing process of the K tower 103 is carried out. Specifically, clear water is used to push out the hydrochloric acid remaining in the K tower 103. In this pushing process, the components other than the K tower 103 are in operation (operating) for collecting water. The flow rate of each of the activated carbon towers 51 to 55 is Q / 5 [m 3 The activated carbon treated water is supplied to the K towers 10 and 10, and the flow rate is Q / 2 [m 3 / h].

[0061] Next, as shown in FIG. 9E, a cleaning step of the K tower 103 is carried out. Specifically, the K tower 103 is cleaned using activated carbon treated water. Specifically, the activated carbon treated water is passed through the K tower 103 in the same amount as the water in the K towers 101 and 102, and the water used to clean the K tower 103 is discharged outside the system. The flow rate of each of the K towers 101 to 103 is Q / 2 [m 3 / h]. Therefore, the flow rate of the pure water produced is Q [m 3 / h], the flow rate of water supplied to the entire K column is 3Q / 2 [m 3 / h], and the flow rate of each of the five activated carbon towers 51 to 55 is 3Q / 10 [m 3 Therefore, the flow rate of each of the activated carbon towers 51 to 55 is Q / 5 [m3 / h] to 3Q / 10 [m 3 / h], the SV ratio is 1.5 times. If the SV ratio is 1.5 times or less, the terminal water quality is stable.

[0062] Next, as shown in FIG. 9F, the K tower 103 is placed on standby, and the remaining two K towers 101 and 102 are used to collect water. The components other than the K tower 103 are in operation (operating) for collecting water. The flow rate of each of the activated carbon towers 51 to 55 is Q / 5 [m 3 The activated carbon treated water is supplied to the K towers 10 and 10, and the flow rate is Q / 2 [m 3 / h]. Tower K 102 is the next target for regeneration.

[0063] In the operation process including the regeneration / cleaning process of the ion exchange resin described above, the space velocity of the activated carbon towers 51 to 55 increases during the idling operation (preparation for water collection) shown in Figure 9B and the cleaning process shown in Figure 9E, which may result in a deterioration in the end water quality. m One of the towers is separated from the water passage for activated carbon-treated water, and water other than activated carbon-treated water is passed through the separated tower K. This prevents an increase in the space velocity of the activated carbon tower and prevents the deterioration of the terminal water quality.

[0064] In any of the above-described first to fourth embodiments of the pure water production method, it is possible to operate the activated carbon tower used for water sampling so that the space velocity of the activated carbon tower used for water sampling is 1.5 times or less the reference value during the partial water sampling stop step, thereby stabilizing the terminal water quality. Hereinafter, the results of measuring the urea concentration by changing the space velocity of the activated carbon tower using one activated carbon tower will be described.

[0065] (Example 1) In an ultrapure water production system equipped with three activated carbon towers arranged in parallel, filtered water with a raw water urea concentration of 10 ppb was passed through the activated carbon towers. The space velocity of the activated carbon towers was 6 h －１ The urea concentration at the outlet of the activated carbon tower was 1 ppb, and the TOC concentration at the P.O.U (Point-of-Use) (TOC concentration in ultrapure water) was 0.2 ppb.

[0066] Next, one of the three activated carbon towers was backwashed for 30 minutes, and the space velocity in the remaining activated carbon tower was increased to 1.5 times (space velocity 9 h －１ In this case, the urea concentration at the outlet of the activated carbon tower was 1.3 ppb, and the TOC concentration of the P.O.U. was 0.26 ppb (see the table below).

[0067] (Comparative Example 1) Next, one activated carbon tower was backwashed for 30 minutes, and the space velocity in the remaining activated carbon tower was doubled (space velocity 12 h －１ The activated carbon tower was operated under the conditions of 0.5 ppb, 1.0 urea concentration at the outlet of the activated carbon tower was 3.5 ppb, and the TOC concentration of the P.O.U. was 0.5 ppb (see the table below).

[0068]

[0069] From the results of Example 1 and Comparative Example 1 described above, it can be seen that when water flow through one tower is stopped, the terminal water quality can be stabilized by operating the activated carbon tower through which water is flowing so that the space velocity is 1.5 times or less the reference value (SV value when water is flowing through all towers).

[0070] (Comparative Example 2) In an ultrapure water production system equipped with three activated carbon towers arranged in parallel, filtered water with a raw water urea concentration of 10 ppb was passed through the activated carbon towers. The space velocity of the activated carbon towers at this time was 11.0 h －１ (>10h －１ The TOC concentration of the P.O.U. (TOC concentration of ultrapure water) was 0.2 ppb. After that, one tower was backwashed and water was passed through the remaining two towers. The space velocity of the activated carbon tower at this time was 16.5 h －１ (SV ratio = 1.5), and the TOC concentration of P.O.U (TOC concentration of ultrapure water) was 0.5 ppb (see the table below).

[0071]

[0072] From the results of the above-mentioned Comparative Example 2, it was found that when water flow through one tower is stopped, even if the space velocity of the activated carbon tower through which water flows is 1.5 times the reference value (SV value when water flows through all towers), if the SV value during the water sampling process is high (exceeding 10 / h), the terminal water quality during the partial water sampling stop process becomes unstable.

[0073] Example 2 In an ultrapure water production system equipped with five activated carbon towers arranged in parallel, filtered water with a raw water urea concentration of 10 ppb was passed through the activated carbon towers. The space velocity of the activated carbon towers was 4.0 h －１ The TOC concentration of the P.O.U. (TOC concentration of ultrapure water) was 0.2 ppb. After that, one tower was backwashed and water was passed through the remaining four towers. The space velocity of the activated carbon tower at this time was 5.0 h －１ (SV ratio = 1.25), and the TOC concentration of P.O.U (TOC concentration of ultrapure water) was 0.25 ppb (see the table below).

[0074] (Comparative Example 3) One tower was replaced and water was passed through the remaining three towers. The space velocity of the activated carbon tower at this time was 7.0 h －１ (SV ratio = 1.75), and the TOC concentration of P.O.U (TOC concentration of ultrapure water) was 0.28 ppb (see the table below).

[0075]

[0076] In each of the pure water producing methods of the first to fourth embodiments described above, components described in other embodiments may be combined, provided that the operation is not impaired. Furthermore, in each embodiment, the collected pure water may be further processed to produce even more highly pure ultrapure water. For example, additional processes such as RO treatment, EDI treatment, ultraviolet oxidation treatment, degassing treatment, regenerative ion exchange treatment, non-regenerative ion exchange treatment, temperature adjustment treatment, and final filtration treatment may be performed to remove ionic components, metals, organic matter, dissolved gases, fine particles, live bacteria, and the like, thereby improving the final water quality.

[0077] Furthermore, in the first to fourth embodiments, examples have been given in which multiple K-towers and A-towers installed in parallel are used as demineralization equipment. However, the demineralization equipment may be replaced with multiple RO membrane devices installed in parallel. For example, the demineralization equipment may be a so-called RO-EDI system consisting of an RO membrane device and an EDI (electrodeionized water production system) that treats the RO membrane permeate. The regeneration process regenerates at least one of the multiple RO membrane devices. Here, regeneration refers to cleaning or replacement of the RO membrane device. For example, when multiple RO membrane devices installed in parallel are used, water may be passed through all of the RO membrane devices in the water sampling process, as with the activated carbon tower. Alternatively, as with the resin tower (K-tower), one (or some) of the multiple RO membrane devices may be placed in a standby state, and the remaining RO membrane devices may be used to sample water. In the former case, at least one of the multiple RO membrane devices is isolated and regenerated in the regeneration process. In this case, the system is operated so that the fluctuations in the space velocity are within a certain range, based on the space velocity of the activated carbon device during the water sampling process. In the latter case, the regeneration process involves operating a standby RO membrane device to clean or replace the target RO membrane device. At this time, the target RO membrane device is disconnected from the water passage for activated carbon-treated water, and water other than the activated carbon-treated water is passed through the disconnected RO membrane device. This prevents an increase in the space velocity of the activated carbon tower.

[0078] The pure water production method of the present invention can be applied to existing ultrapure water production systems (e.g., the ultrapure water production system 100 shown in FIG. 1 ). Furthermore, an ultrapure water supply system can be configured using a pure water production system to which the pure water production method of the present invention is applied. The ultrapure water supply system includes, for example, a primary pure water system having at least one of the pure water production systems described in the first to fourth embodiments, a subsystem that produces ultrapure water by removing impurities from the pure water produced in the primary pure water system, and a recovery system that recovers ultrapure water used at a point-of-use where the ultrapure water produced in the subsystem is used and returns it to the primary pure water system. In this ultrapure water supply system, activated carbon control in the primary pure water system eliminates the need for activated carbon in the recovery system.

[0079] Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

[0080] This application claims priority based on Japanese Patent Application No. 2024-114993, filed on July 18, 2024, the disclosure of which is incorporated herein in its entirety by reference.

[0081] 1. Pure water production equipment 2. Raw water tank 3. Filtration equipment 4. Filtration tank 51-5 n Activated carbon tower 6 2B3T device 13 Post-stage equipment 101-10 m K Tower 111-11 m D Tower 121-12 m A tower

Claims

1. A method for producing pure water, in which water to be treated is treated with activated carbon in an activated carbon device, and the activated carbon-treated water is desalted in a desalination device to produce pure water, wherein the activated carbon device comprises a plurality of activated carbon towers filled with activated carbon arranged in parallel, and the desalination device comprises at least a plurality of desalination devices arranged in parallel, the method comprising: a water sampling step in which the water to be treated is passed through all of the plurality of activated carbon towers; and a regeneration step in which the passage of water through at least one of the plurality of activated carbon towers is stopped or at least a portion of the plurality of desalination devices is regenerated, wherein the space velocity of water passing through the activated carbon tower in the regeneration step is 10 / h or less.

2. The method for producing pure water according to claim 1, wherein the space velocity of water passing through the activated carbon tower in the water sampling step is 10 / h or less.

3. The method for producing pure water according to claim 1 or 2, wherein the activated carbon device has five or more activated carbon towers arranged in parallel, and the regeneration step stops the flow of water through one or two of the activated carbon towers.

4. The method for producing pure water according to claim 3, wherein the regeneration step is performed while water is stopped from passing through two of the activated carbon towers, one of which is stopped for replacement, and another of which is stopped for backwashing.

5. A method for producing pure water according to claim 1 or 2, wherein water is passed through the activated carbon tower so that the ratio of the space velocity of water passing through the activated carbon tower in the regeneration step to the space velocity of water passing through the activated carbon tower in the water sampling step is 1.5 times or less.

6. A method for producing pure water as described in claim 1 or 2, wherein, when the ratio of the space velocity of water flowing through the activated carbon tower in the regeneration step to the space velocity of water flowing through the activated carbon tower in the water sampling step exceeds 1.5, the water flow rate through each activated carbon tower in the regeneration step is adjusted to make said ratio 1.5 or less.

7. The pure water production method according to claim 1 or 2, wherein the demineralization equipment is a plurality of ion exchange devices filled with ion exchange resin, at least some of the plurality of ion exchange devices being in a standby state in which water sampling is not performed, and the regeneration process comprises: a water sampling preparation process in which treated water from the activated carbon tower is passed through all of the plurality of ion exchange devices before the next water sampling process; and a chemical passing process in which the ion exchange devices in the standby state are used to sample water in the next water sampling process, and at least one of the ion exchange devices used to sample water during the water sampling process is separated from water sampling and regenerated by passing a chemical therethrough; and wherein the water sampling preparation process comprises sending water passed through the ion exchange devices in the standby state to a stage upstream of the activated carbon device.

8. The method for producing pure water according to claim 1 or 2, wherein the demineralization equipment is a reverse osmosis membrane device, and the regeneration step regenerates at least one of the plurality of demineralization equipment.

9. A pure water production system comprising an activated carbon device that treats water to be treated with activated carbon, and a demineralization device that demineralizes the activated carbon-treated water from the activated carbon device to produce pure water, wherein the activated carbon device has a plurality of activated carbon towers arranged in parallel, each filled with activated carbon, and the demineralization device has at least a plurality of demineralization devices arranged in parallel, and the system has control means for performing a water sampling process in which the water to be treated is passed through all of the plurality of activated carbon towers, and a regeneration process in which the passage of water through at least one of the plurality of activated carbon towers or the regeneration of at least a portion of the plurality of demineralization devices, wherein the space velocity of water passing through the activated carbon tower in the regeneration process is 10 / h or less.

10. The pure water production system according to claim 9, wherein the space velocity of water passing through the activated carbon tower in the water sampling step is 10 / h or less.

11. An ultrapure water supply system comprising: a primary pure water system having at least the pure water production apparatus according to claim 9 or 10; a subsystem that produces ultrapure water by removing impurities from the pure water produced in the primary pure water system; and a recovery system that recovers the ultrapure water used at a point of use where the ultrapure water produced in the subsystem is used and returns it to the primary pure water system.

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