Liquid circulation system

Abstract

This liquid circulation system is provided with: a circulation path provided with a supply pipe for supplying a liquid in a tank to a point of use via a plurality of processing units, and a return pipe for returning the liquid from the point of use to the tank; a first pump provided in the middle of the plurality of processing units on the supply pipe; a pressure detection unit that is provided to the return pipe; a regulating valve that is provided downstream of the pressure detection unit on the return pipe and that regulates the pressure inside the return pipe on the basis of the pressure detected by the pressure detection unit; a flow rate detection unit that is provided between the most downstream processing unit on the supply pipe and the use point, and that detects the flow rate of the liquid inside the supply pipe; and a first pump control unit that, on the basis of the flow rate detected by the flow rate detection unit, controls the first pump such that the flow rate of the liquid flowing through the supply pipe becomes a prescribed flow rate.

Description

Technical Field

[0001] The present disclosure relates to a liquid circulation system. Background Art

[0002] Conventionally, there are known devices for producing pure water.

[0003] Japanese Patent Publication No. 2023-8823 discloses a pure water production device comprising a pump that circulates pure water from a tank into a circulation line, and a water supply line that branches from the circulation line downstream of the pump and connects to a point of use. The pure water production device includes a control unit that switches the pump speed based on detection of pure water flowing into the water supply line or changes in the flow rate of pure water flowing through the water supply line.

[0004] Japanese Patent No. 7011958 discloses a liquid supply device comprising a pump that supplies liquid from a tank to a point of use, piping that returns liquid from the point of use to the tank, a pressure gauge for measuring the return pressure within the piping, and a flowmeter for measuring the return flow rate within the piping. This liquid supply device includes a control unit that controls a pressure regulating unit for adjusting the return pressure based on the return pressure and return flow rate. The control unit determines a target return pressure value based on the return flow rate and controls the pressure regulating unit to maintain the return pressure at the target value. Summary of the Invention

[0005] Problems to be solved by the invention

[0006] The amount of ultrapure water used at a point of use varies depending on factors such as the operating conditions of the semiconductor manufacturing equipment installed at the point of use. Furthermore, semiconductor manufacturing equipment requires ultrapure water to be supplied at a substantially constant pressure at all times. Fluctuations in pressure can affect the yield of the semiconductors being manufactured. Therefore, ultrapure water production equipment must maintain a substantially constant pressure even when the flow rate fluctuates.

[0007] In particular, when processing a flow rate of 50m 3 When using ultrapure water production equipment with a capacity of more than 1000 liters / hour, the equipment itself becomes larger, and multiple ultrapure water production equipment are often installed side by side. Furthermore, as the scale of the use point, i.e., the factory, increases, the distance of the supply piping from the end of the ultrapure water production equipment (e.g., UF) to the use point becomes longer. Simultaneously, the return piping also becomes longer, increasing the pressure loss in the supply and return piping.

[0008] The pure water production device described in Japanese Patent Publication No. 2023-8823 includes a water supply line that branches from the circulation line downstream of the pump and connects to the point of use. Therefore, the structure of the pure water production device described in Japanese Patent Publication No. 2023-8823 cannot be applied to devices with a circulation path that returns pure water from the point of use to a tank, leaving room for improvement. Furthermore, since there are typically multiple water supply lines delivering water to the point of use, it is necessary to accurately measure the flow rate of each water supply line, requiring multiple flow meters. As the number of measuring instruments increases, the sources of water quality deterioration also increase.

[0009] Furthermore, in the liquid supply device described in Japanese Patent No. 7011958, a target return pressure is determined based on the return flow rate, and a pressure regulating unit is controlled to maintain the return pressure at the target value. For example, in a configuration where the pump speed is controlled based on the pressure within the supply piping supplying the liquid to the point of use, changing the target return pressure when controlling the pressure regulating unit would alter the flow rate of the liquid supplied to the point of use, potentially degrading the water quality. Furthermore, this system becomes complex, making it difficult to implement practically.

[0010] The present disclosure has been made in view of the above-mentioned problems, and an object thereof is to provide a liquid circulation system capable of suppressing fluctuations in the flow rate of liquid supplied to a usage point, regardless of whether the liquid is used at the usage point.

[0011] Solution

[0012] As a result of intensive research, the inventors discovered that flow rate fluctuations in the supply piping and return piping from the end of the ultrapure water device to the use point are caused by pressure fluctuations at the use point, thereby completing the technology disclosed herein.

[0013] The liquid circulation system of the first embodiment comprises: a tank for storing liquid; a plurality of processing units for performing different processing on the liquid supplied from the tank; a circulation path having a supply pipe and a return pipe, the supply pipe supplying the liquid in the tank to a point of use as a supply destination via the plurality of processing units, and the return pipe returning the liquid from the point of use to the tank; a first pump provided midway between the plurality of processing units on the supply pipe to supply the liquid to one side of the point of use; and a first pressure detection unit provided on the return pipe. , detecting the pressure inside the return pipe; a regulating valve, which is arranged on the downstream side of the first pressure detecting part on the return pipe, and adjusts the pressure inside the return pipe according to the pressure detected by the first pressure detecting part; a flow detecting part, which is arranged between the most downstream processing part among the multiple processing parts of the supply pipe and the use point, and detects the flow rate of the liquid inside the supply pipe; and a first pump control part, which controls the first pump according to the flow rate detected by the flow detecting part so that the liquid flowing in the supply pipe becomes a specified flow rate.

[0014] According to the first embodiment, a liquid circulation system is provided with a liquid circulation path comprising supply piping and return piping. Liquid within a tank is supplied via the supply piping through multiple processing units to a point of use, serving as a supply destination. The multiple processing units perform different treatments on the liquid supplied from the tank. Furthermore, the liquid is returned from the point of use to the tank via the return piping. Thus, the liquid circulates within the circulation path.

[0015] The return pipe is provided with a first pressure detector that detects the pressure inside the return pipe. A regulating valve is provided downstream of the first pressure detector on the return pipe to regulate the pressure inside the return pipe based on the pressure detected by the first pressure detector.

[0016] Furthermore, a flow rate detection unit is provided between the most downstream processing unit of the multiple processing units in the return piping and the point of use. This flow rate detection unit detects the flow rate of the liquid within the supply piping. Furthermore, based on the flow rate detected by the flow rate detection unit, the first pump control unit controls the first pump so that the liquid flowing through the supply piping reaches a predetermined flow rate. This suppresses fluctuations in the flow rate supplied from the flow rate detection unit to the point of use. Therefore, regardless of whether the liquid is being used at the point of use, fluctuations in the flow rate of the liquid supplied to the point of use can be suppressed. Furthermore, since fluctuations in the flow rate are minimal, deterioration in the ultrapure water quality caused by fluctuations in the flow rate is minimized.

[0017] The liquid circulation system described in the second embodiment is based on the liquid circulation system described in the first embodiment and includes: a second pump, which is arranged on the downstream side of the tank on the supply piping to supply the liquid in the tank to one side of the plurality of processing units; a second pressure detecting unit, which is arranged on the upstream side of the first pump on the supply piping to detect the pressure inside the supply piping; and a second pump control unit, which controls the second pump based on the pressure detected by the second pressure detecting unit so that the pressure inside the supply piping becomes a specified pressure.

[0018] According to the second embodiment of the liquid circulation system, a second pump is provided downstream of the tank on the supply piping, and the second pump supplies the liquid in the tank to one side of the multiple processing units. A second pressure detector is provided upstream of the first pump on the supply piping, and the second pressure detector detects the pressure inside the supply piping. Furthermore, the second pump control unit controls the second pump based on the pressure detected by the second pressure detector, so that the pressure inside the supply piping reaches a predetermined pressure. Therefore, when the second pump supplies the liquid in the tank to one side of the multiple processing units through the supply piping, fluctuations in the pressure inside the supply piping at the location of the second pressure detector can be suppressed.

[0019] Regarding the liquid circulation system described in the third embodiment, based on the liquid circulation system described in the first embodiment, the first pressure detection unit is arranged at a position where the distance from the last stage of the return pipe branching from the usage point is less than 20% of the length of the return pipe between the last stage and the tank.

[0020] In the liquid circulation system according to the third aspect, the first pressure detection unit is positioned at a position on the return pipe that is less than 20% of the return pipe length between the last stage of the return pipe and the tank. For example, if the return pipe length between the tank and the use point is long, and the first pressure detection unit is positioned at a position that is at least 20% of the return pipe length between the last stage of the return pipe and the tank, when the liquid begins to be used at the use point, if the return pipe diameter remains the same, the liquid flow rate in the return pipe decreases, reducing pressure loss. Therefore, in a configuration where the first pressure detection unit is positioned at a position that is at least 20% of the return pipe length between the last stage of the return pipe and the use point, the regulating valve may not be able to properly adjust the internal pressure of the return pipe.

[0021] In contrast, if the first pressure detector is located in the return pipe at a position less than 20% of the return pipe's length, even if the return pipe's liquid flow rate decreases, the reduction in pressure loss is negligible. Consequently, the return pipe's internal pressure can be appropriately adjusted using the regulating valve based on the pressure detected by the first pressure detector.

[0022] Regarding the liquid circulation system described in the fourth embodiment, in addition to the liquid circulation system described in the first embodiment, the first pressure detecting unit is arranged on the side of the last stage of the branch to the usage point closer to the tank than the return piping, and is arranged at a position where the pressure difference is within 9.8 kPa when the pressure difference when the flow rate of the liquid in the return piping is maximum and when the flow rate of the liquid in the return piping is minimum is compared.

[0023] In the liquid circulation system according to the fourth aspect, the first pressure detection unit is located on the return pipe, closer to the last stage of the branch from the use point than the tank, and is located at a position where the pressure difference between the maximum and minimum flow rates of the liquid in the return pipe is within 9.8 kPa. For example, if the return pipe between the tank and the use point is long, and the first pressure detection unit is located on the return pipe, closer to the tank than the last stage of the branch from the use point, and is located at a position where the pressure difference exceeds 9.8 kPa between the maximum and minimum flow rates of the liquid in the return pipe, when the liquid begins to be used at the use point, if the return pipe has the same diameter, the flow rate of the liquid in the return pipe decreases, reducing pressure loss. Therefore, in a first pressure detection unit located close to the tank, the pressure inside the return pipe may not be properly adjusted by the regulating valve.

[0024] In contrast, if the first pressure detector is located on the return pipe, closer to the final branch from the point of use than the tank, and at a location where the pressure difference between the maximum and minimum flow rates of the return pipe's liquid is within 9.8 kPa, even if the return pipe's liquid flow rate decreases, the pressure loss is less likely to be affected. Therefore, the pressure inside the return pipe can be appropriately adjusted by the regulating valve based on the pressure detected by the first pressure detector.

[0025] A fifth aspect of the liquid circulation system is the liquid circulation system according to the first aspect, wherein the first pump is a booster pump that pressurizes a portion of the supply pipe where the pressure is insufficient to supply the liquid.

[0026] In the liquid circulation system described in the fifth aspect, the first pump disposed midway between the multiple treatment units in the supply piping is a booster pump that pressurizes the under-pressure portion of the supply piping to supply liquid. This facilitates controlling the liquid flow rate at the outlet of the booster pump based on the liquid flow rate within the supply piping, as detected by a flow rate detector between the most downstream of the multiple treatment units in the supply piping and the point of use. Consequently, fluctuations in the liquid flow rate supplied to the point of use can be more reliably suppressed.

[0027] Regarding the liquid circulation system described in the sixth embodiment, based on the liquid circulation system described in the first embodiment, the multiple treatment sections include a filtration device that constitutes the most downstream treatment section and is equipped with an ultrafiltration membrane, and an ion exchange device that is arranged on the upstream side immediately before the filtration device and is equipped with an ion exchange resin, and the ion exchange device has two or more ion exchange resin treatment sections, and the two or more ion exchange resin treatment sections are connected in parallel on the supply piping, and liquid is introduced into and discharged from the respective sections.

[0028] According to the sixth aspect of the liquid circulation system, the ion exchange device includes two or more ion exchange resin treatment sections connected in parallel on the supply piping. Liquid is introduced into each of the two or more ion exchange resin treatment sections, and the liquid treated by each ion exchange resin is discharged. This allows one of the two or more ion exchange resin treatment sections to be stopped for maintenance, while the liquid is passed through the remaining ion exchange resin treatment sections. Therefore, maintenance can be performed on one of the two or more ion exchange resin treatment sections while the liquid circulation system continues to operate.

[0029] The seventh embodiment of the liquid circulation system is based on the sixth embodiment of the liquid circulation system, wherein when the ion exchange device is maintained, one of the ion exchange resin treatment sections is stopped and the liquid that has passed through the other ion exchange resin treatment sections is supplied to the filtration device.

[0030] According to the liquid circulation system of the seventh aspect, when the ion exchange device is maintained, one ion exchange resin treatment section is stopped, and the liquid that has passed through the other ion exchange resin treatment section is supplied to the filtration device.

[0031] For example, in a configuration where the first pump is controlled based on the pressure within the supply piping, as detected by a pressure gauge installed between the most downstream treatment unit and the point of use, simultaneously changing the amount of liquid used at the point of use and stopping one ion exchange resin treatment unit requires both controlling the first pump via the pressure gauge and controlling the regulating valve via the first pressure detector. Since two pressure controls are required in this configuration, predicting the liquid flow rate and pressure is impossible, and the operating flow rate of the liquid may fluctuate depending on timing, potentially making it impossible to return to its original state (for example, the operating flow rate of the liquid in the liquid circulation system may become unstable).

[0032] In contrast, in the aforementioned liquid circulation system, when the amount of liquid used at a point of use is changed and one of the ion exchange resin treatment units is stopped simultaneously, the first pump is controlled based on the liquid flow rate detected by the flow rate detector between the most downstream treatment unit and the point of use in the supply piping. Therefore, since the flow rate detector controls the first pump and the first pressure detector controls the regulating valve, the operating flow rate of the liquid in the liquid circulation system can be stabilized.

[0033] Regarding the liquid circulation system described in the eighth embodiment, based on the liquid circulation system described in the sixth embodiment, the liquid circulation system is configured so that, when maintaining the ion exchange device, liquid is introduced into one of the ion exchange resin treatment sections to clean the ion exchange resin, the cleaned liquid is discharged into a discharge channel other than the supply piping, the liquid is introduced into another of the ion exchange resin treatment sections, and the liquid passing through the other of the ion exchange resin treatment sections is supplied to the filtration device.

[0034] According to the liquid circulation system described in the eighth aspect, when maintaining the ion exchange device, liquid is introduced into one ion exchange resin treatment section to clean the ion exchange resin, the cleaned liquid is discharged to the discharge channel, and the liquid that has passed through the other ion exchange resin treatment section is supplied to the filtration device.

[0035] For example, in a configuration where the first pump is controlled based on the pressure within the supply piping, as detected by a pressure gauge installed between the most downstream treatment unit and the point of use, simultaneously changing the amount of liquid used at the point of use and cleaning the ion exchange resin in one ion exchange resin treatment unit requires both controlling the first pump via the pressure gauge and controlling the regulating valve via the first pressure detector. In this case, since two pressure controls are required, predicting the liquid flow rate and pressure becomes unpredictable, and the liquid flow rate may fluctuate depending on timing, potentially making it impossible to return to its original state (for example, the liquid flow rate in the liquid circulation system may become unstable).

[0036] In contrast, in the aforementioned liquid circulation system, when simultaneously changing the amount of liquid used at a point of use and cleaning the ion exchange resin in one ion exchange resin treatment unit, the first pump is controlled based on the liquid flow rate detected by the flow rate detector between the most downstream treatment unit and the point of use in the supply piping. Therefore, since the flow rate detector controls the first pump and the first pressure detector controls the regulating valve, the operating flow rate of the liquid in the liquid circulation system can be stabilized.

[0037] Effects of the Invention

[0038] According to the liquid circulation system of the present disclosure, regardless of whether the liquid is used at the use point, fluctuations in the flow rate of the liquid supplied to the use point can be suppressed.

[0039] The technology disclosed in the present invention can be widely applied to liquid supply devices and liquid supply systems with a circulation system, and is preferably applied to ultrapure water production devices and ultrapure water production systems. In particular, it can be more preferably applied to liquid supply devices with a supply volume of 50m 3 / h or more ultrapure water production apparatus and ultrapure water production system, and / or multiple ultrapure water production apparatus and ultrapure water production systems arranged in parallel. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a structural diagram showing the liquid circulation system of the first embodiment.

[0041] Figure 2 This is a structural diagram showing the second ion exchange device, ultrafiltration membrane, and use point of the liquid circulation system according to the first embodiment.

[0042] Figure 3 This is a block diagram showing the hardware configuration of the liquid circulation system according to the first embodiment.

[0043] Figure 4 It is a structural diagram showing the second ion exchange device, the ultrafiltration membrane, and the use point of the liquid circulation system according to the first embodiment, and is a diagram showing a state in which liquid is used at the use point.

[0044] Figure 5 It is a structural diagram showing the second ion exchange device, the ultrafiltration membrane, and the use point of the liquid circulation system according to the first embodiment, and is a diagram showing a state in which the first ion exchange resin treatment unit is stopped.

[0045] Figure 6 This is a structural diagram showing the second ion exchange device, ultrafiltration membrane, and use point of the liquid circulation system according to the first embodiment, and is a diagram showing a state in which resin cleaning of the first ion exchange resin treatment unit is in progress.

[0046] Figure 71 is a diagram showing the configuration of a liquid circulation system according to a first comparative example.

[0047] Figure 8 1 is a structural diagram showing a second ion exchange device, an ultrafiltration membrane, and a use point of a liquid circulation system according to a first comparative example.

[0048] Figure 9 It is a structural diagram showing a second ion exchange device, an ultrafiltration membrane, and a use point of the liquid circulation system of the first comparative example, and is a diagram showing a state after the liquid is used at the use point.

[0049] Figure 10 It is a structural diagram showing a second ion exchange device, an ultrafiltration membrane, and a use point of a liquid circulation system according to a second comparative example, and is a diagram showing a state after liquid is used at the use point.

[0050] Figure 11 It is a structural diagram showing the second ion exchange device, ultrafiltration membrane, and use point of the liquid circulation system of the first comparative example, and is a diagram showing a state where the first ion exchange resin treatment unit is stopped without using liquid at the use point.

[0051] Figure 12 It is a structural diagram showing a second ion exchange device, an ultrafiltration membrane, and a use point of the liquid circulation system of the first comparative example, and shows a state in which the liquid is used at the use point and the first ion exchange resin treatment unit is stopped.

[0052] Figure 13 It is a structural diagram showing the second ion exchange device, ultrafiltration membrane, and use point of the liquid circulation system of the first comparative example, and shows a state where resin cleaning of the first ion exchange resin treatment unit is performed at the use point without using liquid.

[0053] Figure 14 It is a structural diagram showing the second ion exchange device, ultrafiltration membrane, and use point of the liquid circulation system of the first comparative example, and is a diagram showing a state where the liquid is used at the use point and resin cleaning of the first ion exchange resin treatment unit is performed. DETAILED DESCRIPTION

[0054] Hereinafter, embodiments of the present disclosure will be described based on the accompanying drawings. In the drawings, drawings that are less relevant to the present disclosure are omitted.

[0055] [Overall structure of the liquid circulation system]

[0056] exist Figure 1 The entire structure of the liquid circulation system of the first embodiment is shown in FIG. In the liquid circulation system of the first embodiment, supply and recovery of ultrapure water are described as an example of liquid.

[0057] like Figure 1 As shown, the liquid circulation system 10 has a pre-treatment device 12, a primary pure water device 14, a pure water tank 16, a secondary pure water device 20, and a use point 50. In addition, the secondary pure water device 20 includes a circulation pump (i.e., P1) 22, a heat exchanger (i.e., HEX) 24, an ultraviolet irradiation device (i.e., UV) 26, a first ion exchange device (i.e., Polisher-1) 28, a membrane degassing device (i.e., MDG) 30, a booster pump (i.e., P2) 32, a second ion exchange device (i.e., Polisher-2) 34, and an ultrafiltration device (i.e., UF) 36.

[0058] The liquid circulation system 10 also includes a supply pipe 62 and a return pipe 64. The supply pipe 62 supplies the liquid (primary pure water, described later in the first embodiment) in the pure water tank 16 to the point of use 50, which is the supply destination, via the secondary pure water device 20. The return pipe 64 returns the liquid from the point of use 50 to the pure water tank 16. In the liquid circulation system 10, the supply pipe 62 and the return pipe 64 constitute a circulation path 60 for circulating the liquid in the pure water tank 16. The heat exchanger 24, ultraviolet irradiation device 26, first ion exchange device 28, membrane degassing device 30, second ion exchange device 34, and ultrafiltration device 36 within the secondary pure water device 20 are one example of a plurality of treatment units that perform different treatments on the liquid.

[0059] In addition, the liquid circulation system 10 includes a control device 80 for controlling each part of the liquid circulation system 10. Figure 1 Although one control device 80 is shown in FIG, the control device 80 may be composed of a plurality of control units arranged at separate positions.

[0060] The liquid circulation system 10 also includes a pressure detector (i.e., PT1) 40 and a flow rate detector (i.e., FT1) 42. The pressure detector (i.e., PT1) 40 is provided in the supply piping 62 between the membrane degassing device 30 and the second ion exchange device 34, and the flow rate detector (i.e., FT1) 42 is provided in the supply piping 62 between the ultrafiltration device 36 at the farthest downstream end and the point of use 50. Furthermore, the liquid circulation system 10 includes a pressure detector (i.e., PT2) 66 and a regulating valve 68. The pressure detector (i.e., PT2) 66 is provided in the return piping 64, and the regulating valve 68 is provided on the return piping 64 downstream of the pressure detector 66.

[0061] (Pretreatment device)

[0062] Raw water is supplied to the pretreatment device 12. Pretreatment device 12 removes turbidity from the supplied raw water using a coagulation and sedimentation unit, sand filtration unit, membrane filtration unit, or the like, producing pretreated water from which some suspended matter and organic matter have been removed. Examples of raw water include industrial water, tap water, groundwater, and river water.

[0063] (First-level pure water device)

[0064] The primary pure water system 14 further purifies the pretreated water obtained by the pretreatment system 12 to remove impurities, producing primary pure water. Specifically, various devices are available, including a desalination system to remove impurity ions, a reverse osmosis membrane system to remove inorganic ions, organic matter, and particulates, a vacuum degassing system or membrane degassing system to remove dissolved gases such as dissolved oxygen, and a regenerative mixed-bed desalination system or an electroregenerative desalination system to remove residual ions.

[0065] (Pure water tank)

[0066] The primary pure water obtained by the primary pure water device 14 is sent to the pure water tank 16. The pure water tank 16 is an example of a tank. The pure water tank 16 is a container for temporarily storing the primary pure water obtained by the primary pure water device 14. As the pure water tank 16, there is no particular limitation on its material and shape as long as it can stably store the primary pure water without dissolving components from the container or rusting. For example, it is preferred to use materials such as fiber reinforced plastics (i.e., Fiber Reinforced Plastics, FRP), polyethylene, SUS304, SUS316, and materials lined with fluororesins such as polytetrafluoroethylene. In addition, in order to prevent the absorption of impurity gases such as carbon dioxide and oxygen, the upper part of the pure water tank 16 is preferably purged with pure nitrogen.

[0067] As will be described later, when the ultrapure water produced is recycled and unused at the point of use 50, it is mixed with the above-mentioned primary pure water and stored in the pure water tank 16. Hereinafter, the mixed water of the primary pure water stored in the pure water tank 16 and the ultrapure water returned from the point of use is also referred to as "primary pure water."

[0068] (Secondary pure water device)

[0069] like Figure 1 As shown, in the secondary pure water device 20, primary pure water is supplied from the pure water tank 16 to one side of the heat exchanger 24 via a circulation pump 22 provided downstream of the pure water tank 16 on the supply pipe 62. The circulation pump 22 is an example of a second pump. The circulation pump 22 is connected to a power source 44.

[0070] Furthermore, in the secondary pure water device 20, the ultrapure water produced by the secondary pure water device 20 is supplied to one side of the use point 50 via a booster pump 32 provided between the membrane degassing device 30 and the second ion exchange device 34 on the supply piping 62. The booster pump 32 is a pump that pressurizes the insufficient pressure portion of the supply piping 62 to supply the primary pure water. The booster pump 32 is an example of a first pump. The booster pump 32 is connected to a power source 46.

[0071] The temperature of the primary pure water is regulated by heat exchange (e.g., heating or cooling) with the primary pure water in the heat exchanger 24 of the secondary pure water device 20. The heat exchanger 24 may be a flat plate heat exchanger, for example, but the specific structure is not particularly limited.

[0072] The primary pure water, after being temperature-controlled by the heat exchanger 24, is sent to the ultraviolet irradiation device 26. In the ultraviolet irradiation device 26, the primary pure water is irradiated with ultraviolet rays to decompose organic matter in the primary pure water and sterilize live bacteria. As the ultraviolet irradiation device 26, as long as it is equipped with an ultraviolet lamp capable of irradiating a wavelength of, for example, about 185nm or about 254nm, it can reliably decompose or sterilize organic matter in the primary pure water. There is no particular limitation on the ultraviolet lamp used, but a low-pressure mercury lamp is preferred for ease of operation.

[0073] The first ion exchange device 28 uses ion exchange resin to remove impurity ions such as hydrogen peroxide and organic acids generated in the ultraviolet irradiation device 26. Examples of the ion exchange resin include anionic resins and mixed bed resins comprising a mixture of anionic and cationic resins. The first ion exchange device 28 is, for example, a cylindrical sealed container filled with ion exchange resin.

[0074] The membrane degassing device 30 uses a gas separation membrane that is impermeable to water but permeable to gases, thereby removing gases, particularly dissolved oxygen, from the primary pure water. The primary pure water treated by the membrane degassing device 30 has a low dissolved oxygen concentration. The primary pure water, with its dissolved oxygen concentration reduced by the membrane degassing device 30, is then delivered to the second ion exchange device 34 by a booster pump 32.

[0075] The second ion exchange device 34 is the same as the first ion exchange device 28 and is a device that uses ion exchange resin to remove impurity ions such as organic acids. As the ion exchange resin, for example, an anion resin or a mixed bed resin formed by mixing an anion resin and a cationic resin can be used. It should be noted that in the secondary pure water device 20, the first ion exchange device 28 is provided, but it is also possible to have a structure in which only the second ion exchange device 34 is provided without the first ion exchange device 28. The primary pure water after the impurity ions are removed by the second ion exchange device 34 is sent to the ultrafiltration device 36. The structure of the second ion exchange device 34 will be described later.

[0076] The ultrafiltration device 36 is a device that has an ultrafiltration membrane and produces ultrapure water by removing particles through the ultrafiltration membrane. The ultrafiltration device 36 is an example of a filtration device. The ultrafiltration device 36 is arranged at the end of the supply direction of the supply pipe 62 in the secondary pure water device 20, and constitutes the most downstream processing part inside the secondary pure water device 20. The ultrapure water obtained by the secondary pure water device 20 is supplied to the use point 50 as the use place through the supply pipe 62. The structure of the ultrafiltration device 36 will be described later. It should be noted that in the present disclosure, the outlet side of the ultrafiltration device is the end of the ultrapure water device.

[0077] It should be noted that the secondary pure water device 20 may also include an oxidant removal device, such as one equipped with a catalyst resin carrying Pt or Pd metal, or a reducing resin carrying sulfite, bisulfite, or nitrite groups, or a boron-selective ion exchange device. Furthermore, the resins of these devices may be filled into the first or second ion exchange device.

[0078] The pressure detector 40 detects the pressure inside the supply pipe 62 between the membrane degasser 30 and the booster pump 32. The pressure detector 40 is an example of a second pressure detector. For example, a pressure transmitter is used as the pressure detector 40. A pressure transmitter is a communication device that converts pressure data into a signal and transmits it as radio waves. The control device 80 controls the circulation pump 22 based on the pressure detected by the pressure detector 40 so that the pressure inside the supply pipe 62 reaches a predetermined pressure. Control of the circulation pump 22 will be described later.

[0079] The flow detector 42 detects the flow rate of ultrapure water inside the supply pipe 62 between the ultrafiltration device 36 at the most downstream end in the secondary pure water device 20 and the point of use 50. The flow detector 42 is an example of a flow path detection unit. As the flow detector 42, for example, a flow transmitter is used. The flow transmitter is a communication device that converts flow data into a signal and emits it as an electric wave. The control device 80 controls the booster pump 32 according to the flow rate detected by the flow detector 42 so that the ultrapure water flowing through the supply pipe 62 becomes a specified flow rate. The control of the booster pump 32 will be described later.

[0080] Figure 2 The second ion exchange device 34, the ultrafiltration device 36 and the structure near the use point 50 are shown. Figure 2 As shown, the second ion exchange device 34 includes a first ion exchange resin treatment unit (i.e., polishing unit 2-1) 102 and a second ion exchange resin treatment unit (i.e., polishing unit 2-2) 104, connected in parallel to the supply pipe 62. Specifically, the supply pipe 62 branches into two inlet pipes 106A and 106B. Inlet pipe 106A is connected to the first ion exchange resin treatment unit 102, and inlet pipe 106B is connected to the second ion exchange resin treatment unit 104. Thus, primary pure water is introduced from the supply pipe 62 via inlet pipes 106A and 106B to the first ion exchange resin treatment unit 102 and the second ion exchange resin treatment unit 104, respectively. Valves 107A and 107B are provided on inlet pipes 106A and 106B, respectively, to open and close the flow paths.

[0081] A discharge pipe 108A is connected to the first ion exchange resin treatment section 102, and a discharge pipe 108B is connected to the second ion exchange resin treatment section 104. Discharge pipes 108A and 108B merge with the downstream supply pipe 62. Discharge pipes 108A and 108B are respectively provided with valves 109A and 109B for opening and closing the flow paths.

[0082] Discharge channels 110A and 110B are connected to the discharge pipes 108A and 108B, respectively. Valves 111A and 111B for opening and closing the flow paths are provided on the discharge channels 110A and 110B, respectively. When the secondary pure water device 20 is normally used, the valves 111A and 111B are closed (see Figure 2 Thus, the primary pure water treated by the first ion exchange resin treatment unit 102 is supplied to the supply pipe 62 via the discharge pipe 108A, and the primary pure water treated by the second ion exchange resin treatment unit 104 is supplied to the supply pipe 62 via the discharge pipe 108B.

[0083] It should be noted that, although the second ion exchange device 34 is provided with two first ion exchange resin treatment sections 102 and two second ion exchange resin treatment sections 104 , it may alternatively include three or more ion exchange resin treatment sections.

[0084] like Figure 2 As shown, the ultrafiltration device 36 is configured as a unit comprising two ultrafiltration membrane treatment units 120A and 120B. The primary pure water treated by the second ion exchange device 34 is introduced via supply piping 62 to the two ultrafiltration membrane treatment units 120A and 120B, respectively, where it is filtered by the ultrafiltration membranes. The ultrapure water filtered by the two ultrafiltration membrane treatment units 120A and 120B is then supplied to the point of use 50 via supply piping 62.

[0085] (Point of Use)

[0086] like Figure 1 and Figure 2 As shown, the ultrapure water supplied is used at the use point 50. Of the ultrapure water supplied to the use point 50, the unused ultrapure water is recycled to the pure water tank 16 via the return pipe 64 and stored in the pure water tank 16 together with the primary pure water. In addition, when the ultrapure water is not used at the use point 50, the ultrapure water supplied from the secondary pure water device 20 to the use point 50 is directly returned to the pure water tank 16 via the return pipe 64 (see Figure 2 ).

[0087] As an example, the use point 50 is set in a clean room 52, and the clean room 52 is arranged at a position far away from the secondary pure water device 20 (refer to Figure 1 The supply pipe 62 from the most downstream end of the secondary pure water device 20 to the connection portion of the use point 50 and the return pipe 64 from the branch with the use point 50 to the pure water tank 16 constitute a relatively long flow path. The length L1 of the supply pipe 62 from the downstream end of the secondary pure water device 302 to the connection portion of the use point 50 (refer to Figure 1 ) is, for example, 0.1 km or more and 1.5 km or less. In addition, the length of the return piping 64 from the branch with the use point 50 to the pure water tank 16 is, for example, 0.1 km or more and 1.5 km or less.

[0088] The material of the supply piping 62 or the return piping 64 is not particularly limited, and PVDF (i.e., polyvinylidene fluoride), PVC (i.e., polyvinyl chloride), or stainless steel such as SUS304 or SUS316 can be used. However, when the liquid is ultrapure water, PVDF is preferably used.

[0089] A pressure detector 66 is provided in the return pipe 64 connected to the point of use 50 and detects the internal pressure of the return pipe 64. The pressure detector 66 is an example of a first pressure detection unit. For example, a pressure transmitter is used as the pressure detector 66. A regulating valve 68, provided downstream of the pressure detector 66 in the return pipe 64, regulates the internal pressure of the return pipe 64.

[0090] The pressure detector 66 is preferably installed at a position on the return pipe 64 at a distance from the branch at the use point 50 that is less than 20% of the length of the return pipe 64 between the branch and the pure water tank 16, more preferably less than 10% of the length of the return pipe 64, and even more preferably less than 5% of the length of the return pipe 64. The length of the return pipe 64 refers to the length of the return pipe 64 from the branch at the use point 50 to the connection with the pure water tank 16.

[0091] It should be noted that, although not shown in the figure, the liquid circulation system 10 may also include multiple branch points leading to the use point 50 in the circulation path 60. In this case, the pressure detector 66 is preferably provided at a position on the return piping 64 where the distance from the last stage of the branch leading to the use point 50 is less than 20% of the length of the return piping 64 between the last stage and the pure water tank 16.

[0092] (Hardware structure of liquid circulation system)

[0093] Figure 3 FIG. 1 is a block diagram showing the hardware structure of the liquid circulation system 10. Figure 3 As shown, the control device 80 includes a CPU (i.e., Central Processing Unit) 81, a ROM (i.e., Read Only Memory) 82, a RAM (i.e., Random Access Memory) 83, a memory 84, and an input / output interface 85. These components are interconnected via a bus 86.

[0094] The CPU 81 is a central processing unit that executes various programs and controls various components. Specifically, the CPU 81 reads programs from the ROM 82 or memory 84 and executes them using the RAM 83 as a work area. The CPU 81 controls the various components described above and performs various calculations based on the programs stored in the ROM 82 or memory 84. In the first embodiment, the ROM 82 or memory 84 stores a liquid circulation processing program.

[0095] ROM 82 stores various programs and data. RAM 83 temporarily stores programs and data as a work area. Memory 84, comprised of a hard disk drive (HDD) or solid state drive (SSD), stores various programs and data, including the operating system.

[0096] Pressure detector 40 , flow rate detector 42 , pressure detector 66 , and regulating valve 68 are connected to input / output interface 85 . Circulation pump 22 and booster pump 32 are connected to input / output interface 85 via power supply 44 and 46 , respectively.

[0097] The pressure value detected by the pressure detector 40 in the supply pipe 62 is input to the control device 80. Based on the pressure detected by the pressure detector 40, the control device 80 controls the frequency of the electricity supplied from the power supply 44 to the circulation pump 22. This regulates the pressure and flow rate at the outlet of the circulation pump 22. The control device 80 is an example of a second pump control unit. The control device 80 controls the frequency of the electricity supplied from the power supply 44 to the circulation pump 22 so that the pressure at the pressure detector 40 reaches a predetermined pressure.

[0098] The value of the flow rate of ultrapure water detected by the flow detector 42 of the supply piping 62 is input to the control device 80. The control device 80 controls the frequency of the electricity supplied from the power supply 46 to the booster pump 32 based on the flow rate of ultrapure water detected by the flow detector 42. The booster pump 32 is a pump that pressurizes the insufficient pressure portion of the supply piping 62 to supply primary pure water. In this way, the pressure and flow rate at the outlet of the booster pump 32 are adjusted. The control device 80 is an example of a first pump control unit. For example, the control device 80 controls the frequency of the electricity supplied from the power supply 46 to the booster pump 32 so that the flow rate of ultrapure water at the flow detector 42 is 80m 3 / h(Refer to Figure 2 ).

[0099] The control device 80 inputs the pressure value detected by the pressure detector 66 of the return pipe 64. The control device 80 adjusts the internal pressure of the return pipe 64 by controlling the opening state of the regulating valve 68 according to the pressure detected by the pressure detector 66. For example, the control device 80 controls the regulating valve 68 so that the pressure of the pressure detector 66 is 343 kPa (i.e., 3.5 kgf / cm 2 ) (refer to Figure 2 ).

[0100] [Functions and Effects of the First Embodiment]

[0101] Next, the operation and effects of the first embodiment will be described.

[0102] like Figure 1 As shown, the liquid circulation system 10 includes a circulation path 60 having a supply pipe 62 and a return pipe 64. The primary pure water in the pure water tank 16 is supplied via the supply pipe 62 to the use point 50 via the secondary pure water device 20. In the secondary pure water device 20, the primary pure water is treated by the heat exchanger 24, the ultraviolet irradiation device 26, the first ion exchange device 28, the membrane degassing device 30, the second ion exchange device 34, and the ultrafiltration device 36, respectively, to produce ultrapure water. The ultrapure water obtained by the secondary pure water device 20 is supplied to the use point 50. Furthermore, the ultrapure water not consumed at the use point 50 is returned to the pure water tank 16 via the return pipe 64.

[0103] like Figure 1 and Figure 2 As shown, a pressure detector 66 is provided on the return pipe 64, and the pressure inside the return pipe 64 is detected by the pressure detector 66. A regulating valve 68 is provided on the downstream side of the pressure detector 66 on the return pipe 64, and the pressure inside the return pipe 64 is adjusted by the regulating valve 68 according to the pressure detected by the pressure detector 66.

[0104] In addition, if Figure 1 and Figure 2 As shown, a flow rate detector 42 is provided between the ultrafiltration device 36 at the most downstream end of the secondary pure water device 20 in the supply piping 62 and the point of use 50. The flow rate of the liquid in the supply piping 62 is detected by the flow rate detector 42. Furthermore, based on the flow rate detected by the flow rate detector 42, the booster pump 32 is controlled by the control device 80 so that the primary pure water flowing through the supply piping 62 reaches a predetermined flow rate. This suppresses fluctuations in the flow rate of the ultrapure water supplied from the flow rate detector 42 to the point of use 50 in the supply piping 62. Therefore, regardless of whether the ultrapure water is used at the point of use 50, fluctuations in the flow rate of the ultrapure water supplied to the point of use 50 can be suppressed.

[0105] In addition, if Figure 1As shown, in the liquid circulation system 10, a circulation pump 22 is provided downstream of the pure water tank 16 on the supply pipe 62. The circulation pump 22 supplies the primary pure water in the pure water tank 16 to one side of the heat exchanger 24 of the secondary pure water device 20. A pressure detector 40 is provided upstream of the booster pump 32 on the supply pipe 62. The pressure detector 40 detects the pressure inside the supply pipe 62. The control device 80 controls the circulation pump 22 based on the pressure detected by the pressure detector 40 so that the pressure inside the supply pipe 62 reaches a predetermined pressure. Therefore, when the circulation pump 22 supplies the primary pure water in the pure water tank 16 through the supply pipe 62 to one side of the heat exchanger 24 of the secondary pure water device 20, fluctuations in the pressure inside the supply pipe 62 at the location of the pressure detector 40 can be suppressed.

[0106] Furthermore, in the liquid circulation system 10, a booster pump 32 is provided between the membrane degassing device 30 and the second ion exchange device 34 in the supply piping 62. This facilitates control of the flow rate of the primary pure water at the outlet of the booster pump 32 based on the flow rate of the ultrapure water detected by the flow rate detector 42 between the ultrafiltration device 36 located most downstream in the supply piping 62 and the point of use 50. Consequently, fluctuations in the flow rate of the ultrapure water supplied to the point of use 50 can be more reliably suppressed.

[0107] (Example of not using ultrapure water at the point of use)

[0108] Here, an example in which ultrapure water is not used at the use point 50 in the liquid circulation system 10 will be described. Figure 2 The case where no ultrapure water is used at the use point 50 (ie, the amount of ultrapure water used is 0 m 3 / h).

[0109] like Figure 2 As shown, the control device 80 controls the frequency of the power supply 46 that supplies power to the booster pump 32 so that the flow rate of the ultrapure water of the flow detector 42 is 80m 3 / h. At this time, at the use point 50, for example, the required pressure is 343kPa (ie, 3.5kgf / cm 2 ), the actual pressure is 343kPa (i.e., 3.5kgf / cm 2 The pressure at the use point 50 is measured by a pressure gauge (not shown). Thus, the flow rate of ultrapure water supplied to the use point 50 through the supply pipe 62 is 80m 3 / h, the pressure difference (ie, ΔP) between the pressure of the pressure detector 40 and the pressure of the use point 50 is 49 kPa (ie, 0.5 kgf / cm 2 ).

[0110] In this example, since ultrapure water is not used at the use point 50, the flow rate of ultrapure water returned to the pure water tank 16 through the return pipe 64 is 80m 3 / h. The control device 80 controls the pressure inside the return pipe 64 through the regulating valve 68 so that the pressure of the pressure detector 66 installed on the side of the return pipe 64 branching from the use point 50 is 343 kPa (i.e., 3.5 kgf / cm 2 ).

[0111] (Example of using ultrapure water at the point of use)

[0112] Next, use Figure 4 , an example in which ultrapure water is used at the use point 50 in the liquid circulation system 10 will be described.

[0113] like Figure 4 As shown, the control device 80 controls the frequency of the power supply 46 that supplies power to the booster pump 32 so that the flow rate of the ultrapure water of the flow detector 42 is 80m 3 / h. At this time, at the use point 50, the required pressure is 343kPa (ie 3.5kgf / cm 2 ), the actual pressure is 343kPa (ie 3.5kgf / cm 2 Therefore, the flow rate of ultrapure water supplied to the use point 50 through the supply pipe 62 is 80m 3 / h, the pressure difference (i.e., ΔP) between the pressure inside the supply pipe 62 (i.e., the pressure near the flow detector 42) and the pressure at the use point 50 is 49 kPa (i.e., 0.5 kgf / cm 2 ).

[0114] At the point of use 50, for example, since the amount of ultrapure water used is 50m 3 / h, so the flow rate of ultrapure water returned to the pure water tank 16 through the return pipe 64 is 30m 3 / h. The control device 80 controls the pressure inside the return pipe 64 through the regulating valve 68 so that the pressure of the pressure detector 66 installed on the side of the return pipe 64 close to the branch with the use point 50 is 343kPa (i.e. 3.5kgf / cm 2 ).

[0115] As described above, in the liquid circulation system 10, regardless of whether ultrapure water is used at the use point 50, fluctuations in the flow rate of ultrapure water supplied to the use point 50 can be suppressed. Furthermore, in the liquid circulation system 10, since fluctuations in the flow rate of ultrapure water are small, deterioration in the quality of the ultrapure water due to fluctuations in the flow rate is minimized.

[0116] (Location of pressure detector)

[0117] In the liquid circulation system 10 , the pressure detector 66 is provided at a position of the return pipe 64 at a distance from a branch to the use point 50 that is less than 20% of the length of the return pipe 64 between the branch and the pure water tank 16 .

[0118] For example, in the case where the return piping between the pure water tank and the point of use is long, a configuration is described in which the pressure detection unit is located at a position at least 20% of the length of the return piping 64, from the branch at the point of use to the pure water tank 16. In this configuration, when ultrapure water begins to be used at the point of use, if the return piping has the same diameter, the flow rate of ultrapure water in the return piping decreases, reducing pressure loss. Therefore, in a pressure detection unit located at a position at least 20% of the length of the return piping 64, from the branch at the point of use, the pressure inside the return piping may not be properly regulated by the regulating valve 68.

[0119] In contrast, in the liquid circulation system 10, the pressure detector 66 is installed in the return pipe 64 at a location less than 20% of the length of the return pipe 64, at the point where it branches off from the use point 50. This allows for negligible reduction in pressure loss even when the flow rate of ultrapure water in the return pipe 64 decreases. Therefore, the pressure inside the return pipe 64 can be appropriately adjusted by the regulating valve 68 based on the pressure detected by the pressure detector 66. It should be noted that the regulating valve 68 can be installed in any location, as long as it is downstream of the pressure detector 66 in the return pipe 64.

[0120] [Liquid Circulation System of First Comparative Example]

[0121] Here, a liquid circulation system of a first comparative example will be described. Components identical to those of the first embodiment are denoted by the same reference numerals and their description will be omitted.

[0122] like Figure 7 As shown, as a structure different from the liquid circulation system 10 of the first embodiment, the liquid circulation system 300 of the first comparative example includes a two-stage pure water device 302 and a control device 320. In the two-stage pure water device 302, a second pressure detector (for example, PT2) 310 for detecting the pressure inside the supply pipe 62 is provided between the ultrafiltration device 36 at the most downstream and the use point 50. The control device 320 controls the frequency of the power supply 46 that supplies power to the boost pump 32 based on the pressure detected by the second pressure detector 310. That is, in the liquid circulation system 300, the flow rate detector 42 (see FIG. 4 ) as in the liquid circulation system 10 of the first embodiment is not provided. Figure 1In the liquid circulation system 300 , the length L2 of the supply pipe 62 from the downstream end of the secondary pure water device 302 to the connection portion of the use point 50 is, for example, not less than 0.5 km and not more than 1.5 km.

[0123] Furthermore, in the liquid circulation system 300, as a configuration different from the liquid circulation system 10 of the first embodiment, a third pressure detector (e.g., PT3) 312 is provided on the upstream side of the regulating valve 68 on the return pipe 64 and on the side close to the pure water tank 16 to detect the pressure inside the return pipe 64. The control device 320 adjusts the pressure inside the return pipe 64 by controlling the opening state of the regulating valve 68 based on the pressure detected by the third pressure detector 66. The control device 320 adjusts the pressure inside the return pipe 64 by controlling the opening state of the regulating valve 68, for example, so that the pressure of the third pressure detector 312 is 294 kPa (i.e., 3 kgf / cm 2 In the liquid circulation system 300, the length of the return pipe 64 from the branch at the use point 50 to the third pressure detector 312 is, for example, 0.5 km or more and 1.5 km or less. The third pressure detector 312 is, for example, located at a position at which the return pipe 64 branches from the use point 50 and is at least 80% of the length of the return pipe 64.

[0124] (Example of not using ultrapure water at the point of use)

[0125] like Figure 8 As shown, in the liquid circulation system 300 of the first comparative example, when no ultrapure water is used at the use point 50 (ie, the amount of ultrapure water used is 0 m 3 / h), the control device 320 controls the frequency of the power supply 46 that supplies power to the boost pump 32, so that the pressure of the second pressure detector 310 is 392kPa (ie, 4kgf / cm 2 At this time, at the use point 50, the required pressure is 343kPa (i.e. 3.5kgf / cm 2 ), the actual pressure is 343kPa (ie 3.5kgf / cm 2 The flow rate of ultrapure water supplied to the use point 50 through the supply pipe 62 is 80m 3 / h, the pressure difference (ie, ΔP) between the pressure of the second pressure detector 310 and the pressure of the use point 50 is 49 kPa (ie, 0.5 kgf / cm 2 ).

[0126] Since no ultrapure water is used at the use point 50 (ie, since the amount of ultrapure water used is 0 m 3 / h), so the flow rate of ultrapure water flowing to the pure water tank 16 side through the return pipe 64 is 80m3 / h. The control device 320 controls the pressure inside the return pipe 64 through the regulating valve 68 so that the pressure of the third pressure detector 312 of the return pipe 64 is 294kPa (ie 3kgf / cm 2 At this time, the pressure difference (ie, ΔP) between the pressure at the use point 50 and the pressure at the third pressure detector 312 is 49 kPa (ie, 0.5 kgf / cm 2 ).

[0127] (Example of using ultrapure water at the point of use)

[0128] exist Figure 9 FIG shows a liquid circulation system 300 in which 50 m is used at a point of use 50. 3 / h of ultrapure water. Figure 9 As shown, in the return pipe 64, the set pressure of the regulating valve 68 is controlled at 294 kPa (ie, 3 kgf / cm 2 When the ultrapure water starts to be used at the use point 50, if the diameter of the return pipe 64 is the same, the flow rate of the ultrapure water returned to the return pipe 64 is reduced, and the pressure loss is reduced. For example, the pressure difference (i.e., ΔP) between the pressure at the use point 50 and the pressure of the third pressure detector 312 is reduced from 49 kPa (i.e., 0.5 kgf / cm 2 ) becomes 29.4kPa (i.e. 0.3kgf / cm 2 ).

[0129] At the use point 50, the required pressure is 343 kPa (3.5 kgf / cm 2 ), the actual pressure is 323.4kPa (ie 3.3kgf / cm 2 ), the pressure drops. At this time, the pressure of the second pressure detector 310 is controlled to 392kPa (i.e. 4kgf / cm2), and the pressure difference (i.e. ΔP) between the pressure of the second pressure detector 310 and the pressure of the use point 50 is 68.6kPa (i.e. 0.7kgf / cm2). 2 ), the pressure loss increases, and the supply flow rate increases. For example, the supply flow rate of ultrapure water supplied to the supply pipe 62 is actually to be 80m 3 / h flow, but the supply flow rate is increased to 100m 3 / h. That is, the actual flow rate of ultrapure water supplied to pipe 62 increases relative to the designed flow rate. Therefore, pressure fluctuations may affect the quality of the ultrapure water. Furthermore, changes in operating conditions of semiconductor manufacturing equipment installed at the point of use may also affect product yield.

[0130] It should be noted that, for ease of maintenance, the third pressure detector 312 and the regulating valve 68 are generally installed near the pure water tank 16. Specifically, if the third pressure detector 312 and the regulating valve 68 were installed near the point of use, for example, in a different building or on a different floor than the building housing the pure water system, or further installed inside or near a clean room, this would significantly impair maintainability, and therefore, such installation is generally not practiced.

[0131] [Liquid Circulation System of Second Comparative Example]

[0132] Next, a liquid circulation system of a second comparative example will be described. Components identical to those of the first and second embodiments are denoted by the same reference numerals, and their description will be omitted.

[0133] (Example of using ultrapure water at the point of use)

[0134] exist Figure 10 FIG. 3 shows a liquid circulation system 330 of the second comparative example, for example, using 50 m3 of liquid at a use point 50. 3 Example of ultrapure water per hour. Figure 10 is immediately followed by Figure 9 An example of changing the setting of the third pressure detector 312 after the state of Figure 10 As shown, in the liquid circulation system 330 of the second comparative example, the set pressure of the third pressure detector 312 is manually changed to be controlled at 323.4 kPa (ie 3.3 kgf / cm 2 ), narrowing the opening of the regulating valve 68. Thus, compared with the liquid circulation system 330 of the first comparative example, the flow rate of the ultrapure water returned through the return pipe 64 is reduced from 50m 3 / h reduced to 30m 3 / h, the pressure loss of the return pipe 64 is reduced. The pressure at the use point 50 becomes 343 kPa (i.e., 3.3 + 0.2 = 3.5 kgf / cm 2 ). Furthermore, the pressure difference (ie, ΔP) between the second pressure detector 310 of the supply pipe 62 and the use point 50 is restored to 49 kPa (ie, 0.5 kgf / cm 2 ), the supply volume of ultrapure water supplied to the pipe 62 is also restored to 80m 3 / h.

[0135] However, in the liquid circulation system 330, if the set pressure of the third pressure detector 312 is suddenly manually changed to 323.4 kPa (ie 3.3 kgf / cm 2), the quality of the ultrapure water may deteriorate. Furthermore, since the control device 320 requires two pressure controls: control of the booster pump 32 by the second pressure detector 310 and control of the regulating valve 68 by the third pressure detector 312, the control of the operating system becomes complicated.

[0136] In contrast, in the liquid circulation system 10 of the first embodiment, the control device 80 controls the frequency of the power supply 46 that supplies power to the booster pump 32 based on the flow rate of ultrapure water in the supply piping 62 between the ultrafiltration device 36 and the point of use 50. This suppresses fluctuations in the flow rate of ultrapure water supplied from the supply piping 62 to the point of use 50. Consequently, regardless of whether the ultrapure water is being used at the point of use 50, fluctuations in the flow rate of ultrapure water supplied from the supply piping 62 to the point of use 50 can be suppressed.

[0137] Furthermore, in the liquid circulation system 10, the pressure detector 66 is located at a position within the return pipe 64, less than 20% of the length of the return pipe 64, at the branch point from the use point 50. Therefore, even if the flow rate of ultrapure water in the return pipe 64 decreases, the reduction in pressure loss is negligible. Therefore, the pressure inside the return pipe 64 can be appropriately adjusted using the regulating valve 68 based on the pressure detected by the pressure detector 66.

[0138] [First Example of Maintenance in the Liquid Circulation System of the First Embodiment]

[0139] Next, a first example of maintenance in the liquid circulation system 10 according to the first embodiment will be described.

[0140] Figure 5 FIG. 1 shows a state in which the first ion exchange resin treatment unit 102 of the second ion exchange device 34 is stopped during maintenance of the liquid circulation system 10. Figure 5 As shown, in the liquid circulation system 10, the change of the usage amount of ultrapure water at the usage point 50 and the first ion exchange resin treatment unit 102 are performed simultaneously. At the usage point 50, the usage amount of ultrapure water is 50m 3 / h.

[0141] In the liquid circulation system 10, valve 107A of the inlet pipe 106A and valve 109A of the outlet pipe 108A are closed, preventing the primary pure water from flowing into the first ion exchange resin treatment section 102. This stops the first ion exchange resin treatment section 102, allowing maintenance of the first ion exchange resin treatment section 102. Valves 111A and 111B are also closed. Furthermore, valve 107B of the inlet pipe 106B and valve 109B of the outlet pipe 108B are opened, allowing the primary pure water to flow only into the second ion exchange resin treatment section 104. The primary pure water treated in the second ion exchange resin treatment section 104 is supplied from the outlet pipe 108B via the supply pipe 62 to the ultrafiltration device 36.

[0142] The control device 80 controls the frequency of the power supply 46 that supplies power to the booster pump 32 so that the flow rate of the ultrapure water in the flow detector 42 is 80m 3 Thus, the supply amount of ultrapure water supplied to the use point 50 through the supply pipe 62 is 80m 3 / h.

[0143] Here, the operation and effects based on the structure of the second ion exchange device 34 of the liquid circulation system 10 according to the first embodiment will be described.

[0144] In the liquid circulation system 10, the second ion exchange device 34 includes a first ion exchange resin treatment section 102 and a second ion exchange resin treatment section 104 connected in parallel to the supply pipe 62. When the valve 107A and the valve 109A of the first ion exchange resin treatment section 102 are opened and the valve 107B and the valve 109B of the second ion exchange resin treatment section 104 are opened, primary pure water is introduced into the first ion exchange resin treatment section 102 and the second ion exchange resin treatment section 104, respectively, and the primary pure water treated in the first ion exchange resin treatment section 102 and the second ion exchange resin treatment section 104 is discharged (see Figure 4 In this configuration, by stopping one of the first ion exchange resin treatment unit 102 and the second ion exchange resin treatment unit 104 for maintenance, the primary pure water can be passed through the other of the first and second ion exchange resin treatment units 102 and 104. Therefore, maintenance can be performed on either the first or second ion exchange resin treatment unit 102, 104 while the liquid circulation system 10 continues to operate.

[0145] Furthermore, in the liquid circulation system 10, when the second ion exchange device 34 is maintained, one of the first ion exchange resin treatment section 102 and the second ion exchange resin treatment section 104 is stopped, and the primary pure water passing through the other of the first ion exchange resin treatment section 102 and the second ion exchange resin treatment section 104 is supplied to the ultrafiltration device 36. For example, the first ion exchange resin treatment section 102 is stopped, and the primary pure water passing through the second ion exchange resin treatment section 104 is supplied to the ultrafiltration device 36 (see Figure 5 ).

[0146] like Figure 5 As shown, in the liquid circulation system 10, the booster pump 32 is controlled based on the flow rate of ultrapure water detected by the flow rate detector 42 between the ultrafiltration device 36 at the most downstream end of the supply pipe 62 and the use point 50. For example, the control device 80 controls the frequency of the power supply 46 supplying power to the booster pump 32 so that the flow rate of ultrapure water measured by the flow rate detector 42 is 80m / s. 3 / h. Thus, due to the dual control of the booster pump 32 by the flow rate detector 42 and the control of the regulating valve 68 by the pressure detector 66, the operating flow rate of the ultrapure water in the liquid circulation system 10 can be stabilized. Therefore, in the liquid circulation system 10, even if the amount of ultrapure water used at the use point 50 is changed and the first ion exchange resin treatment unit 102 is stopped simultaneously, the flow rate of ultrapure water supplied to the use point 50 and the pressure at the use point 50 can be maintained substantially constant.

[0147] [First Example of Maintenance in the Liquid Circulation System of the First Comparative Example]

[0148] Next, a first example of maintenance in the liquid circulation system 300 of the first comparative example will be described.

[0149] Figure 11 An example of maintenance of the second ion exchange device 34 is shown in the liquid circulation system 300 of the first comparative example when the amount of ultrapure water used at the use point 50 does not change (ie, when ultrapure water is not used). Figure 11 As shown, if the first ion exchange resin treatment section 102 of the second ion exchange device 34 is stopped, the pressure loss in the second ion exchange resin treatment section 104 increases. This increase in pressure loss is compensated by increasing the frequency of the power supply 46 supplying the booster pump 32.

[0150] Figure 12 The following shows the case where the amount of ultrapure water used is changed at the use point 50 in the liquid circulation system 300 of the first comparative example (for example, 50 m 3 An example of maintenance of the second ion exchange device 34 (in the case of ultrapure water of / h). Figure 12As shown, in liquid circulation system 300, when simultaneously changing the amount of ultrapure water used at point of use 50 and stopping first ion exchange resin treatment unit 102, it is necessary to control booster pump 32 via second pressure detector 310 and control regulating valve 68 via third pressure detector 312. In this case, because two automatic pressure controls exist within the same system, fluctuations in the flow rate and pressure of the ultrapure water are unpredictable. Consequently, the operating flow rate of liquid circulation system 300 fluctuates depending on the timing, potentially preventing the operating flow rate from returning to its original state and causing instability in the operation of liquid circulation system 300.

[0151] In contrast, in the liquid circulation system 10 of the first embodiment, the booster pump 32 is controlled based on the flow rate of ultrapure water detected by the flow rate detector 42 between the ultrafiltration device 36 at the most downstream position in the supply piping 62 and the use point 50. This results in control of the booster pump 32 by the flow rate detector 42 and control of the regulating valve 68 by the pressure detector 66. Therefore, in the liquid circulation system 10, even if the amount of ultrapure water used at the use point 50 is changed and the first ion exchange resin treatment unit 102 is stopped simultaneously, the flow rate of ultrapure water supplied to the use point 50 and the pressure at the use point 50 can be maintained substantially constant.

[0152] [Second Example of Maintenance in the Liquid Circulation System of the First Embodiment]

[0153] Next, a second example of maintenance in the liquid circulation system 10 of the first embodiment will be described.

[0154] Figure 6 FIG. 1 shows a state in which the ion exchange resin of the first ion exchange resin treatment section 102 of the second ion exchange device 34 is cleaned during maintenance of the liquid circulation system 10. Figure 6 As shown, in the liquid circulation system 10, the change of the amount of ultrapure water used at the use point 50 and the cleaning of the ion exchange resin in the first ion exchange resin treatment unit 102 are performed simultaneously. At the use point 50, the amount of ultrapure water used is 50m 3 / h.

[0155] In the liquid circulation system 10, the valve 107A of the inlet pipe 106A is opened, the valve 109A of the discharge pipe 108A is closed, and the valve 111A of the discharge channel 110A is opened, thereby discharging the primary pure water that has passed through the first ion exchange resin treatment section 102 to the discharge channel 110A. This allows the ion exchange resin of the first ion exchange resin treatment section 102 to be cleaned. In addition, the valve 107B of the inlet pipe 106B is opened, the valve 109B of the discharge pipe 108B is opened, and the valve 111B is closed, thereby supplying the primary pure water that has passed through the second ion exchange resin treatment section 104 from the discharge pipe 108B to the ultrafiltration device 36 via the supply pipe 62. The flow rate when cleaning the ion exchange resin of the first ion exchange resin treatment section 102 is 10m 3 / h.

[0156] The control device 80 controls the frequency of the power supply 46 that supplies power to the booster pump 32 so that the flow rate of the ultrapure water in the flow detector 42 is 80m 3 Thus, the supply amount of ultrapure water supplied to the use point 50 through the supply pipe 62 is 80m 3 / h.

[0157] In the liquid circulation system 10, when the second ion exchange device 34 is maintained, primary pure water is introduced into the first ion exchange resin treatment section 102 to clean the ion exchange resin, and the cleaned liquid is discharged to the discharge channel 110A. At the same time, the primary pure water that has passed through the second ion exchange resin treatment section 104 is supplied to the ultrafiltration device 36. At this time, the booster pump 32 is controlled based on the flow rate of ultrapure water detected by the flow detector 42 between the ultrafiltration device 36 at the most downstream end of the supply piping 62 and the use point 50. For example, the control device 80 controls the frequency of the power supply 46 that supplies power to the booster pump 32 so that the flow rate of ultrapure water measured by the flow detector 42 is 80 m / s. 3 / h. Thus, the booster pump 32 is controlled by the flow rate detector 42, and the regulating valve 68 is controlled by the pressure detector 66, thereby stabilizing the operating flow rate of the ultrapure water in the liquid circulation system 10. Therefore, in the liquid circulation system 10, even if the amount of ultrapure water used at the use point 50 and the ion exchange resin used to clean the first ion exchange resin treatment unit 102 are changed simultaneously, the flow rate of ultrapure water supplied to the use point 50 and the pressure at the use point 50 can be maintained substantially constant.

[0158] [Second Example of Maintenance in the Liquid Circulation System of the First Comparative Example]

[0159] Next, a second example of maintenance in the liquid circulation system 300 of the first comparative example will be described.

[0160] Figure 13An example of maintenance of the second ion exchange device 34 is shown in the liquid circulation system 300 of the first comparative example when the amount of ultrapure water used at the use point 50 does not change (ie, when ultrapure water is not used). Figure 13 As shown, when the ion exchange resin in the first ion exchange resin treatment unit 102 is cleaned, the cleaning flow rate discharged to the discharge channel 110A increases. This increase in cleaning flow rate is compensated by increasing the frequency of the power supply 46 that supplies power to the booster pump 32.

[0161] Figure 14 The figure shows the case where the amount of ultrapure water used is changed at the use point 50 in the liquid circulation system 300 of the first comparative example (for example, 50 m 3 An example of maintenance of the second ion exchange device 34 (in the case of ultrapure water of / h). Figure 14 As shown, in liquid circulation system 300, when simultaneously changing the amount of ultrapure water used at point of use 50 and cleaning the ion exchange resin in first ion exchange resin treatment unit 102, it is necessary to control booster pump 32 via second pressure detector 310 and control regulating valve 68 via third pressure detector 312. In this case, because two automatic pressure controls exist within the same system, fluctuations in the flow rate and pressure of ultrapure water cannot be predicted, further destabilizing the operating state of liquid circulation system 300.

[0162] In contrast, in the liquid circulation system 10 of the first embodiment, the booster pump 32 is controlled based on the flow rate of ultrapure water detected by the flow rate detector 42 between the ultrafiltration device 36 at the farthest downstream end of the supply piping 62 and the point of use 50. This results in two types of control: control of the booster pump 32 by the flow rate detector 42 and control of the regulating valve 68 by the pressure detector 66. Therefore, in the liquid circulation system 10, even if the amount of ultrapure water used at the point of use 50 and the ion exchange resin used for cleaning the first ion exchange resin treatment unit 102 are changed simultaneously, the flow rate of ultrapure water supplied to the point of use 50 and the pressure at the point of use 50 can be maintained substantially constant.

[0163] [other]

[0164] It should be noted that the position of the pressure detector 66 may be changed under the following conditions instead of the structure of the liquid circulation system 10 of the first embodiment. The pressure detector 66 is preferably installed on the return pipe 64 on the side closer to the use point 50 than the pure water tank 16, and is installed so that the differential pressure when the flow rate of the ultrapure water in the return pipe 64 is the maximum and the flow rate of the ultrapure water in the return pipe 64 is the minimum is compared. 2) is within the range of 4.9 kPa (i.e., 0.05 kgf / cm 2 ) within a position, and is further preferably set at a pressure difference of 2.94 kPa (i.e., 0.03 kgf / cm 2 ) within the position.

[0165] For example, if the pressure detector 66 is installed on the side of the return pipe 64 closer to the use point 50 than the pure water tank 16 and the pressure difference between the flow rate of ultrapure water in the return pipe 64 is at its maximum and the flow rate of ultrapure water in the return pipe 64 is at its minimum is 9.8 kPa (i.e., 1 kgf / cm 2 ), even if the flow rate of the ultrapure water sent back to the piping 64 is reduced, it is not easily affected by the reduction in pressure loss. Therefore, the pressure inside the return piping 64 can be appropriately adjusted by the regulating valve 68 based on the pressure detected by the pressure detector 66.

[0166] In a configuration in which a plurality of branch points leading to the use point 50 are provided in the circulation path 60, the pressure detector 66 may be provided on the return pipe 64 at the last stage of the branch leading to the use point, closer to the pure water tank 16, and provided so that the pressure difference when comparing the pressure difference between the maximum flow rate of the liquid in the return pipe and the minimum flow rate of the liquid in the return pipe is 9.8 kPa (i.e., 0.1 kgf / cm2). 2 ) within the position.

[0167] It should be noted that although the present disclosure has been described in detail with reference to specific embodiments, the present invention is not limited to the described embodiments, and various other embodiments may be present within the scope of the present disclosure, which is obvious to those skilled in the art.

[0168] [Preferred Mode of the Present Disclosure]

[0169] Hereinafter, preferred embodiments of the present disclosure will be supplementally described.

[0170] [Supplementary Note 1]

[0171] A liquid circulation system, wherein the liquid circulation system comprises:

[0172] a tank storing a liquid;

[0173] a plurality of processing units that respectively perform different processing on the liquid supplied from the tank;

[0174] a circulation path including a supply pipe and a return pipe, wherein the supply pipe supplies the liquid in the tank to a use point as a supply destination via the plurality of processing units, and the return pipe returns the liquid from the use point to the tank;

[0175] a first pump provided midway between the plurality of treatment sections on the supply pipe and configured to supply the liquid toward one side of the use point;

[0176] a first pressure detection unit provided in the return pipe and configured to detect the pressure inside the return pipe;

[0177] a regulating valve provided on the return pipe at a downstream side of the first pressure detecting portion and regulating the pressure inside the return pipe according to the pressure detected by the first pressure detecting portion;

[0178] a flow rate detection unit provided between the most downstream processing unit among the plurality of processing units in the supply pipe and the use point, and detecting a flow rate of liquid in the supply pipe; and

[0179] A first pump control unit controls the first pump based on the flow rate detected by the flow rate detection unit so that the liquid flowing through the supply pipe reaches a predetermined flow rate.

[0180] [Supplementary Note 2]

[0181] The liquid circulation system according to Supplementary Note 1, wherein the liquid circulation system comprises:

[0182] a second pump provided on the downstream side of the tank on the supply pipe and supplying the liquid in the tank to one side of the plurality of treatment units;

[0183] a second pressure detecting unit provided on the upstream side of the first pump on the supply pipe and detecting the pressure inside the supply pipe; and

[0184] A second pump control unit controls the second pump based on the pressure detected by the second pressure detection unit so that the pressure inside the supply pipe reaches a predetermined pressure.

[0185] [Supplementary Note 3]

[0186] The liquid circulation system according to Supplementary Item 1 or Supplementary Item 2, wherein the first pressure detection unit is provided at a position of the return pipe at a distance from the last stage of the branch to the usage point that is less than 20% of the length of the return pipe between the last stage and the tank.

[0187] [Supplementary Note 4]

[0188] A liquid circulation system according to Note 1 or Note 2, wherein the first pressure detecting unit is arranged on the side of the last stage of the branch of the return piping that is closer to the usage point than the tank, and is arranged at a position where the pressure difference is within 9.8 kPa when comparing the pressure difference when the flow rate of the liquid in the return piping is maximum and when the flow rate of the liquid in the return piping is minimum.

[0189] [Supplementary Note 5]

[0190] The liquid circulation system according to any one of Supplementary Items 1 to 4, wherein the first pump is a booster pump that pressurizes a pressure-deficient portion of the supply pipe to supply the liquid.

[0191] [Supplementary Note 6]

[0192] The liquid circulation system according to any one of Supplementary Items 1 to 5, wherein:

[0193] The plurality of processing units include:

[0194] a filtration device constituting the most downstream processing section and comprising an ultrafiltration membrane; and

[0195] an ion exchange device, the ion exchange device being provided on the upstream side immediately before the filtration device and comprising an ion exchange resin,

[0196] The ion exchange device includes two or more ion exchange resin treatment units, which are connected in parallel to the supply pipe and into which liquid is introduced and discharged.

[0197] [Supplementary Note 7]

[0198] The liquid circulation system according to Supplementary item 6, wherein the liquid circulation system is configured to stop one of the ion exchange resin treatment sections and supply the liquid that has passed through the other ion exchange resin treatment section to the filtration device during maintenance of the ion exchange device.

[0199] [Supplementary Note 8]

[0200] The liquid circulation system according to Supplementary Note 6, wherein:

[0201] The liquid circulation system is configured so that when the ion exchange device is maintained,

[0202] introducing a liquid into one of the ion exchange resin treatment sections to clean the ion exchange resin, and discharging the cleaned liquid into a discharge channel other than the supply pipe;

[0203] The liquid is introduced into the other ion exchange resin treatment section, and the liquid having passed through the other ion exchange resin treatment section is supplied to the filtration device.

[0204] The disclosure of Japanese Application No. 2023-098744 is incorporated herein by reference in its entirety.

[0205] All documents, patent applications, and technical standards described in this application are hereby incorporated by reference into this application to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A liquid circulation system, wherein: The liquid circulation system comprises: a tank storing a liquid; a plurality of processing units that respectively perform different processing on the liquid supplied from the tank; a circulation path including a supply pipe and a return pipe, wherein the supply pipe supplies the liquid in the tank to a use point as a supply destination via the plurality of processing units, and the return pipe returns the liquid from the use point to the tank; a first pump provided midway between the plurality of treatment sections on the supply pipe and configured to supply the liquid toward one side of the use point; a first pressure detection unit provided in the return pipe and configured to detect the pressure inside the return pipe; a regulating valve provided on the return pipe at a downstream side of the first pressure detecting portion and regulating the pressure inside the return pipe according to the pressure detected by the first pressure detecting portion; a flow rate detection unit provided between the most downstream processing unit among the plurality of processing units on the supply pipe and the use point, and detecting a flow rate of the liquid inside the supply pipe; as well as A first pump control unit controls the first pump based on the flow rate detected by the flow rate detection unit so that the liquid flowing through the supply pipe reaches a predetermined flow rate.

2. The liquid circulation system according to claim 1, wherein: The liquid circulation system comprises: a second pump provided on the downstream side of the tank on the supply pipe and supplying the liquid in the tank to one side of the plurality of treatment units; a second pressure detecting unit provided on the upstream side of the first pump on the supply pipe and configured to detect the pressure inside the supply pipe; as well as A second pump control unit controls the second pump based on the pressure detected by the second pressure detection unit so that the pressure inside the supply pipe reaches a predetermined pressure.

3. The liquid circulation system according to claim 1, wherein: The first pressure detection unit is provided at a position of the return pipe at a distance from a final stage of the branch to the use point that is less than 20% of a length of the return pipe between the final stage and the tank.

4. The liquid circulation system according to claim 1, wherein: The first pressure detecting unit is arranged on the side of the last stage of the branch to the usage point closer to the tank than the return pipe, and is arranged at a position where the pressure difference is within 9.8 kPa when the pressure difference when the flow rate of the liquid in the return pipe is maximum and when the flow rate of the liquid in the return pipe is minimum is compared.

5. The liquid circulation system according to claim 1, wherein: The first pump is a booster pump that pressurizes a portion of the supply pipe where the pressure is insufficient to supply the liquid.

6. The liquid circulation system according to claim 1, wherein: The plurality of processing units include: a filtration device constituting the most downstream processing section and comprising an ultrafiltration membrane; and an ion exchange device, the ion exchange device being provided on the upstream side immediately before the filtration device and comprising an ion exchange resin, The ion exchange device includes two or more ion exchange resin treatment units, which are connected in parallel to the supply pipe and into which liquid is introduced and discharged.

7. The liquid circulation system according to claim 6, wherein: The liquid circulation system is configured to stop one of the ion exchange resin treatment sections during maintenance of the ion exchange device and supply the liquid that has passed through the other ion exchange resin treatment section to the filtration device.

8. The liquid circulation system according to claim 6, wherein: The liquid circulation system is configured so that when the ion exchange device is maintained, introducing a liquid into one of the ion exchange resin treatment sections to clean the ion exchange resin, and discharging the cleaned liquid into a discharge channel other than the supply pipe; The liquid is introduced into the other ion exchange resin treatment section, and the liquid having passed through the other ion exchange resin treatment section is supplied to the filtration device.

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