Liquid circulation system

Abstract

A liquid circulation system according to the present disclosure comprises: a circulation path that is provided with supply piping for supplying a liquid in a tank to a use point via a plurality of processing units and return piping for returning the liquid from the use point to the tank; a first pump that is disposed at an intermediate point between the plurality of processing units in the supply piping; a pressure detection unit that is disposed in the return piping; an adjustment valve that is disposed on the downstream side of the pressure detection unit in the return piping and adjusts the pressure inside the return piping according to the pressure detected by the pressure detection unit; a flow rate detection unit that is disposed between a processing unit located on the most downstream side in the supply piping and the use point and detects the flow rate of the liquid inside the supply piping; and a first pump control unit that controls the first pump so that the liquid flowing through the supply piping has a predetermined flow rate according to the flow rate detected by the flow rate detection unit.

Description

Liquid Circulation System

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

[0002] 2. Description of the Related Art Conventionally, there has been known an apparatus for producing pure water.

[0003] Japanese Patent Application Laid-Open No. 2023-8823 discloses a pure water production system including a pump that circulates pure water in a tank through a circulation line, and a water supply line that branches off from the circulation line downstream of the pump and is connected to a use point. This pure water production system is provided with a control means that switches the rotation speed of the pump based on the results of detecting whether pure water is flowing through the water supply line or a change in the flow rate of pure water flowing through the water supply line.

[0004] Japanese Patent No. 7011958 discloses a liquid supply device including a pump that supplies liquid from a tank to a use point, a pipe that returns the liquid returned from the use point to the tank, a pressure gauge that measures the return pressure in the pipe, and a flow meter that measures the return flow rate in the pipe. This liquid supply device is provided with a control unit that controls a pressure adjustment means for adjusting the return pressure based on the return pressure and return flow rate. The control unit determines a target value for the return pressure based on the return flow rate and controls the pressure adjustment means so that the return pressure becomes the target value.

[0005] The amount of ultrapure water used at a use point varies depending on the operating status of the semiconductor manufacturing equipment installed at the use point. Furthermore, semiconductor manufacturing equipment requires ultrapure water to be supplied at a nearly constant pressure, and fluctuations in pressure can affect the yield of semiconductors being manufactured. Therefore, ultrapure water production equipment is required to supply fluid at a nearly constant pressure even if the flow rate fluctuates. In particular, ３ In the case of ultrapure water production systems with a treatment flow rate of 1000 kJ / h or more, the scale of the ultrapure water production system itself becomes larger, and in many cases, multiple ultrapure water production systems are installed in parallel. Furthermore, as the point of use, i.e., the scale of the factory, becomes larger, the distance of the supply piping from the end of the ultrapure water production system (e.g., UF) to the point of use becomes longer. At the same time, the return piping also becomes longer, resulting in greater pressure loss in the supply piping and return piping.

[0006] The pure water production system described in JP 2023-8823 A includes a water supply line that branches off from the circulation line downstream of the pump and is connected to a use point. Therefore, the configuration of the pure water production system described in JP 2023-8823 A cannot be applied to systems that include a circulation path that returns pure water via a use point to a tank, leaving room for improvement. Furthermore, since multiple water supply lines to the use point are typically provided, the flow rate of each line must be accurately measured, necessitating the provision of multiple flow meters. The increased number of measuring devices also increases the sources of water quality degradation.

[0007] Furthermore, in the liquid supply device described in Japanese Patent No. 7011958, a target value for return pressure is determined based on the return flow rate, and the pressure adjustment means is controlled so that the return pressure reaches the target value. For example, in a configuration in which the pump rotation speed is controlled based on the pressure in the supply pipe that supplies liquid to the point of use, changing the target value for return pressure when controlling the pressure adjustment means could change the flow rate of the liquid supplied to the point of use, potentially resulting in a deterioration in water quality. Furthermore, the control system becomes complicated, making it difficult to use.

[0008] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide a liquid circulation system that can suppress fluctuations in the flow rate of liquid supplied to a use point, regardless of whether or not the liquid is used at the use point.

[0009] After careful consideration, the inventors discovered that fluctuations in flow rate in the supply and return pipes from the end of the ultrapure water system to the use point are the cause of pressure fluctuations at the use point, and completed the technology of the present disclosure. a first pump control unit that controls the first pump so that the liquid flowing through the supply pipe reaches a predetermined flow rate according to the flow rate detected by the flow rate detection unit. The liquid circulation system according to a first aspect of the present invention has a circulation path including a tank for storing liquid, a plurality of processing units that perform different processes on the liquid supplied from the tank, a supply pipe that supplies the liquid in the tank to a use point that is a destination of the liquid via the plurality of processing units, and a return pipe that returns the liquid from the use point to the tank; a first pump that is provided in the supply pipe between the plurality of processing units and that supplies the liquid to the use point; a first pressure detection unit that is provided in the return pipe and that detects the pressure inside the return pipe;

[0010] According to the liquid circulation system of the first aspect, a liquid circulation path is provided, which includes a supply pipe and a return pipe. The liquid in a tank is supplied to a use point, which is a supply destination, via the supply pipe via multiple treatment units. The multiple treatment units each perform different treatments on the liquid supplied from the tank. Furthermore, the liquid is returned from the use point to the tank via the return pipe. This circulates the liquid through the circulation path. A first pressure detection unit is provided in the return pipe, and the first pressure detection unit detects the pressure inside the return pipe. A regulation valve is provided in the return pipe downstream of the first pressure detection unit, and the regulation valve adjusts the pressure inside the return pipe in accordance with the pressure detected by the first pressure detection unit. Furthermore, a flow rate detection unit is provided in the supply pipe between the most downstream treatment unit of the multiple treatment units and the use point, and the flow rate detection unit detects the flow rate of the liquid inside the supply pipe. Then, a first pump control unit controls the first pump so that the liquid flowing through the supply pipe is at a predetermined flow rate in accordance with the flow rate detected by the flow rate detection unit. This suppresses fluctuations in the flow rate of the liquid supplied from the flow rate detector to the use point. Therefore, fluctuations in the flow rate of the liquid supplied to the use point can be suppressed regardless of whether the liquid is being used at the use point. Furthermore, because the flow rate fluctuations are small, deterioration of the quality of the ultrapure water due to flow rate fluctuations is minimized.

[0011] The liquid circulation system described in the second aspect is the liquid circulation system described in the first aspect, and further includes a second pump provided on the supply pipe downstream of the tank and supplying the liquid in the tank to the side of the plurality of processing units, a second pressure detection unit provided on the supply pipe upstream of the first pump and detecting the pressure inside the supply pipe, and a second pump control unit that controls the second pump so that the pressure inside the supply pipe becomes a predetermined pressure in accordance with the pressure detected by the second pressure detection unit.

[0012] According to the liquid circulation system of the second aspect, a second pump is provided on the supply pipe downstream of the tank, and the second pump supplies the liquid in the tank to the plurality of processing units. A second pressure detection unit is provided on the supply pipe upstream of the first pump, and the second pressure detection unit detects the pressure inside the supply pipe. The second pump control unit controls the second pump in accordance with the pressure detected by the second pressure detection unit so that the pressure inside the supply pipe becomes a predetermined pressure. Therefore, when the second pump supplies the liquid in the tank to the plurality of processing units through the supply pipe, fluctuations in the pressure inside the supply pipe at the position of the second pressure detection unit can be suppressed.

[0013] The liquid circulation system described in the third aspect is the liquid circulation system described in the first aspect, wherein the first pressure detection unit is located at a point from the last stage of the return pipe branching off from the use point to less than 20% of the length of the return pipe between the last stage and the tank.

[0014] According to the third aspect of the liquid circulation system, the first pressure detection unit is located less than 20% of the length of the return pipe between the tank and the last stage of the return pipe branching from the use point. For example, if the return pipe between the tank and the use point is long and the first pressure detection unit is located more than 20% of the length of the return pipe between the last stage of the return pipe branching from the use point and the tank, when the liquid begins to be used at the use point, the flow rate of the liquid in the return pipe decreases and pressure loss decreases, assuming the return pipe has the same diameter. Therefore, if the first pressure detection unit is located more than 20% of the length of the return pipe from the last stage of the return pipe branching from the use point, the pressure inside the return pipe may not be properly adjusted by the adjustment valve. In contrast, if the first pressure detection unit is located less than 20% of the length of the return pipe from the last stage of the return pipe branching from the use point, the reduction in pressure loss becomes negligible even if the flow rate of the liquid in the return pipe decreases. Therefore, the pressure inside the return pipe can be appropriately adjusted by the adjusting valve in accordance with the pressure detected by the first pressure detecting unit.

[0015] The liquid circulation system described in a fourth aspect is the liquid circulation system described in the first aspect, wherein the first pressure detection unit is located on the return pipe closer to the final stage of the branch with the use point than the tank, and is located at a position where the differential pressure when the liquid flow rate in the return pipe is maximum and minimum is within 9.8 kPa.

[0016] In the liquid circulation system of the fourth aspect, the first pressure detection unit is located on the return pipe closer to the end of the branch to the use point than the tank, where the pressure difference between the maximum and minimum liquid flow rates 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 end of the branch to the use point, where the pressure difference between the maximum and minimum liquid flow rates in the return pipe is greater than 9.8 kPa, when liquid begins to be used at the use point, the flow rate of the liquid in the return pipe decreases and pressure loss is reduced if the diameter of the return pipe is the same. Therefore, if the first pressure detection unit is located closer to the tank, the adjustment valve may not properly adjust the pressure inside the return pipe. In contrast, if the first pressure detection unit is located closer to the end of the return pipe branching off from the use point than the tank, and the differential pressure between the maximum and minimum flow rates of the liquid in the return pipe is within 9.8 kPa, the return pipe will be less susceptible to reduced pressure loss even if the flow rate of the liquid in the return pipe decreases. Therefore, the pressure inside the return pipe can be appropriately adjusted by the adjustment valve in accordance with the pressure detected by the first pressure detection unit.

[0017] A liquid circulation system according to a fifth aspect is the liquid circulation system according to the first aspect, wherein the first pump is a booster pump that pressurizes the supply pipe to compensate for a pressure deficiency and supplies the liquid.

[0018] In the liquid circulation system of the fifth aspect, the first pump provided in the supply pipe between the plurality of treatment sections is a booster pump that supplies liquid by pressurizing the supply pipe to compensate for any pressure shortfall. This makes it easier to control the flow rate of liquid on the outlet side of the booster pump in accordance with the flow rate of liquid inside the supply pipe detected by a flow rate detector between the most downstream treatment section of the plurality of treatment sections in the supply pipe and the point of use. This makes it possible to more reliably suppress fluctuations in the flow rate of liquid supplied to the point of use.

[0019] The liquid circulation system described in a sixth aspect is the liquid circulation system described in the first aspect, wherein the multiple processing units constitute the most downstream processing unit and include a filtration device equipped with an ultrafiltration membrane, and an ion exchange device provided upstream just before the filtration device and equipped with ion exchange resin, and the ion exchange device has two or more ion exchange resin processing units connected in parallel to the supply piping and into which liquid is respectively introduced and discharged.

[0020] According to the sixth aspect of the liquid circulation system, the ion exchange device has two or more ion exchange resin treatment sections connected in parallel to a supply pipe, and 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 makes it possible to stop one of the two or more ion exchange resin treatment sections, perform maintenance on that ion exchange resin treatment section, and pass the liquid through the other ion exchange resin treatment sections. This makes it possible to perform maintenance on one of the two or more ion exchange resin treatment sections while continuing to operate the liquid circulation system.

[0021] The liquid circulation system described in the seventh aspect is the liquid circulation system described in the sixth aspect, and is configured such that, during maintenance of the ion exchange device, one of the ion exchange resin treatment units is stopped and the liquid that has passed through the other ion exchange resin treatment unit is supplied to the filtration device.

[0022] According to a seventh aspect of the liquid circulation system, during maintenance of the ion exchange device, one ion exchange resin treatment unit is stopped, and the liquid that has passed through the other ion exchange resin treatment unit is supplied to the filtration device. For example, in a configuration in which the first pump is controlled based on the pressure inside the supply pipe detected by a pressure gauge installed between the most downstream treatment unit in the supply pipe and the point of use, if the amount of liquid used at the point of use is changed and one of the ion exchange resin treatment units is stopped simultaneously, it is necessary to control the first pump using the pressure gauge and the regulating valve using the first pressure detection unit. In this case, because two pressure controls are performed, the liquid flow rate and pressure cannot be predicted, and the operating flow rate of the liquid may change depending on the timing, making it impossible to restore the original state (e.g., the operating flow rate of the liquid in the liquid circulation system may become unstable). In contrast, in the above liquid circulation system, if the amount of liquid used at the 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 detection unit installed between the most downstream treatment unit in the supply pipe and the point of use. Therefore, the first pump is controlled by the flow rate detection unit and the regulating valve is controlled by the first pressure detection unit, so that the operating flow rate of the liquid in the liquid circulation system can be stabilized.

[0023] The liquid circulation system described in the eighth aspect is the liquid circulation system described in the sixth aspect, and is configured such that, during maintenance of 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 to a discharge path other than the supply piping, liquid is introduced into another of the ion exchange resin treatment sections, and the liquid that has passed through the other ion exchange resin treatment section is supplied to the filtration device.

[0024] According to the eighth aspect of the liquid circulation system, during maintenance of 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 into the drain, and the liquid that has passed through the other ion exchange resin treatment sections is supplied to the filtration device. For example, in a configuration in which the first pump is controlled based on the pressure inside the supply pipe detected by a pressure gauge installed between the most downstream treatment section in the supply pipe and the point of use, if the amount of liquid used at the point of use and the ion exchange resin in one ion exchange resin treatment section are simultaneously changed, it is necessary to control the first pump using the pressure gauge and the adjustment valve using the first pressure detection section. In this case, because two pressure controls are performed, the liquid flow rate and pressure cannot be predicted, and the operating flow rate of the liquid may change depending on the timing, making it impossible to restore the original state (e.g., the operating flow rate of the liquid in the liquid circulation system may become unstable). In contrast, in the above-described liquid circulation system, when the amount of liquid used at the point of use and the ion exchange resin in one ion exchange resin treatment unit are changed simultaneously, the first pump is controlled in accordance with the flow rate of the liquid detected by the flow rate detection unit between the most downstream treatment unit in the supply piping and the point of use. As a result, the first pump is controlled by the flow rate detection unit and the adjustment valve is controlled by the first pressure detection unit, thereby stabilizing the operating flow rate of the liquid in the liquid circulation system.

[0025] According to the liquid circulation system of the present disclosure, fluctuations in the flow rate of liquid supplied to a point of use can be suppressed regardless of whether or not the liquid is being used at the point of use.

[0026] The technology of the present disclosure is widely applicable to liquid supply devices and liquid supply systems having a circulation system, but is particularly applicable to ultrapure water production devices and ultrapure water production systems. ３ The present invention is more preferably applicable to ultrapure water production apparatuses and ultrapure water production systems with a supply rate of 1000 kJ / hour or more, and / or to ultrapure water production apparatuses and ultrapure water production systems in which a plurality of ultrapure water production apparatuses and ultrapure water production systems are provided in parallel.

[0027] FIG. 1 is a configuration diagram showing a liquid circulation system of a first embodiment. FIG. 1 is a configuration diagram showing a second ion exchange device, an ultrafiltration membrane, and a use point of the liquid circulation system of the first embodiment. FIG. 2 is a block diagram showing the hardware configuration of the liquid circulation system of the first embodiment. FIG. 2 is a configuration diagram showing a second ion exchange device, an ultrafiltration membrane, and a use point of the liquid circulation system of the first embodiment, showing a state in which liquid has been used at the use point. FIG. 3 is a configuration diagram showing a second ion exchange device, an ultrafiltration membrane, and a use point of the liquid circulation system of the first embodiment, showing a state in which the first ion exchange resin treatment unit is stopped. FIG. 4 is a configuration diagram showing a second ion exchange device, an ultrafiltration membrane, and a use point of the liquid circulation system of the first embodiment, showing a state in which resin cleaning of the first ion exchange resin treatment unit is being performed. FIG. 5 is a configuration diagram showing a liquid circulation system of a first comparative example. FIG. 6 is a configuration diagram showing a second ion exchange device, an ultrafiltration membrane, and a use point of the liquid circulation system of the first comparative example. FIG. 7 is a configuration diagram showing a second ion exchange device, an ultrafiltration membrane, and a use point of the liquid circulation system of the first comparative example, showing a state in which liquid has been used at the use point. 1 is a configuration diagram showing a second ion exchange device and an ultrafiltration membrane and a point of use in a liquid circulation system of a second comparative example, showing a state in which liquid has been used at the point of use. FIG. 2 is a configuration diagram showing a second ion exchange device and an ultrafiltration membrane and a point of use in a liquid circulation system of a first comparative example, showing a state in which no liquid is used at the point of use and the first ion exchange resin treatment unit is stopped. FIG. 3 is a configuration diagram showing a second ion exchange device and an ultrafiltration membrane and a point of use in a liquid circulation system of a first comparative example, showing a state in which liquid is used at the point of use and the first ion exchange resin treatment unit is stopped. FIG. 4 is a configuration diagram showing a second ion exchange device and an ultrafiltration membrane and a point of use in a liquid circulation system of a first comparative example, showing a state in which no liquid is used at the point of use and resin cleaning of the first ion exchange resin treatment unit is being performed. FIG. 5 is a configuration diagram showing a second ion exchange device and an ultrafiltration membrane and a point of use in a liquid circulation system of a first comparative example, showing a state in which liquid is used at the point of use and resin cleaning of the first ion exchange resin treatment unit is being performed.

[0028] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each drawing, elements that are less relevant to the present disclosure are omitted.

[0029] 1 shows the overall configuration of a liquid circulation system according to the first embodiment. The liquid circulation system according to the first embodiment will be described as an example in which ultrapure water is supplied and recovered as an example of a liquid.

[0030] 1, the liquid circulation system 10 includes a pretreatment device 12, a primary deionization device 14, a deionized water tank 16, a secondary deionization device 20, and a point-of-use device 50. The secondary deionization device 20 further 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 degasser (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.

[0031] The liquid circulation system 10 also includes a supply pipe 62 that supplies the liquid in the pure water tank 16 (primary pure water, described later in the first embodiment) to a use point 50, which is the supply destination, via the secondary pure water apparatus 20, and a return pipe 64 that returns the liquid from the use point 50 to the pure water tank 16. In the liquid circulation system 10, the supply pipe 62 and the return pipe 64 form a circulation path 60 that circulates 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 inside the secondary pure water apparatus 20 are examples of multiple processing units that perform different processes on the liquid.

[0032] The liquid circulation system 10 also includes a control device 80 that controls each part of the liquid circulation system 10. Although one control device 80 is shown in Fig. 1, the control device 80 may be configured with multiple control units located at different locations.

[0033] The liquid circulation system 10 also includes a pressure detector (i.e., PT1) 40 provided in the supply pipe 62 between the membrane degassing device 30 and the second ion exchange device 34, and a flow rate detector (i.e., FT1) 42 provided in the supply pipe 62 between the most downstream ultrafiltration device 36 and the point of use 50. The liquid circulation system 10 also includes a pressure detector (i.e., PT2) 66 provided in the return pipe 64, and an adjustment valve 68 provided in the return pipe 64 downstream of the pressure detector 66.

[0034] (Pretreatment Device) Raw water is supplied to the pretreatment device 12. The pretreatment device 12 clarifies the supplied raw water using a coagulation settling means, a sand filtration means, a membrane filtration means, or the like to obtain pretreated water from which suspended solids and a portion of organic matter have been removed. Examples of raw water include industrial water, tap water, groundwater, and river water.

[0035] (Primary Pure Water System) The primary pure water system 14 further purifies the pretreated water obtained by treatment in the pretreatment system 12 to remove impurities from the pretreated water, thereby obtaining primary pure water. Specifically, the system includes various devices such as a demineralizer that removes impurity ions, a reverse osmosis membrane device that removes inorganic ions, organic matter, and particulates, a vacuum degasser or membrane degasser that removes dissolved gases such as dissolved oxygen, and a regenerative mixed-bed demineralizer or electrical regenerative demineralizer that removes remaining ions, etc.

[0036] (Pure Water Tank) The primary pure water obtained in the primary pure water system 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 that temporarily stores the primary pure water obtained in the primary pure water system 14. The material and shape of the pure water tank 16 are not particularly limited as long as it can stably store the primary pure water without causing component elution or rusting from the container. For example, materials such as fiber reinforced plastics (i.e., FRP), polyethylene, SUS304, SUS316, and materials made from these materials lined with a fluororesin such as polytetrafluoroethylene are preferably used. In addition, the upper part of the pure water tank 16 is preferably purged with pure nitrogen to prevent absorption of impurity gases such as carbon dioxide and oxygen.

[0037] As will be described later, the pure water tank 16 stores unused ultrapure water mixed with the primary pure water when it is circulated and recovered from the use point 50. The mixture of the primary pure water stored in the pure water tank 16 and the ultrapure water returned from the use point will also be referred to as "primary pure water" hereinafter.

[0038] 1, in the secondary pure water system 20, a circulation pump 22 provided downstream of the pure water tank 16 in the supply pipe 62 supplies primary pure water from the pure water tank 16 to the heat exchanger 24. The circulation pump 22 is an example of a second pump. A power supply 44 is connected to the circulation pump 22.

[0039] In the secondary pure water system 20, the ultrapure water produced by the secondary pure water system 20 is supplied to the point of use 50 by a booster pump 32 provided in the supply pipe 62 between the membrane degassing device 30 and the second ion exchange device 34. The booster pump 32 is a pump that pressurizes the supply pipe 62 to compensate for any pressure deficiency and supplies primary pure water. The booster pump 32 is an example of a first pump. A power source 46 is connected to the booster pump 32.

[0040] The heat exchanger 24 of the secondary pure water system 20 adjusts the temperature of the primary pure water by heat exchange (e.g., heating or cooling) with the primary pure water. The heat exchanger 24 may be, for example, a plate-type heat exchanger, but the specific structure is not particularly limited.

[0041] The primary pure water whose temperature has been adjusted 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 light to decompose organic matter in the primary pure water and sterilize live bacteria. If the ultraviolet irradiation device 26 is equipped with an ultraviolet lamp capable of irradiating light with a wavelength of around 185 nm or around 254 nm, for example, it can reliably decompose organic matter in the primary pure water and sterilize it. The ultraviolet lamp to be used is not particularly limited, but a low-pressure mercury lamp is preferred in terms of ease of handling.

[0042] The first ion exchange device 28 is a device that uses an ion exchange resin to remove impurity ions such as hydrogen peroxide and organic acids generated in the ultraviolet irradiation device 26. As the ion exchange resin, for example, an anion resin or a mixed bed resin that is a mixture of an anion resin and a cation resin is used. The first ion exchange device 28 has a structure in which, for example, an ion exchange resin is filled in a cylindrical sealed container.

[0043] The membrane degassing device 30 is a device that removes gases, particularly dissolved oxygen, from primary pure water using a gas separation membrane that blocks water but allows gas to pass through. The primary pure water treated by the membrane degassing device 30 has a low concentration of dissolved oxygen. The primary pure water whose dissolved oxygen concentration has been reduced by the membrane degassing device 30 is sent to a second ion exchange device 34 by a booster pump 32.

[0044] The second ion exchange device 34, like the first ion exchange device 28, is a device that removes impurity ions such as organic acids using an ion exchange resin. Examples of ion exchange resins that can be used include an anion resin and a mixed-bed resin that is a mixture of anion resin and cation resin. While the secondary pure water system 20 includes the first ion exchange device 28, it may also be configured with only the second ion exchange device 34, without including the first ion exchange device 28. The primary pure water from which the impurity ions have been removed by the second ion exchange device 34 is sent to the ultrafiltration device 36. The configuration of the second ion exchange device 34 will be described later.

[0045] The ultrafiltration device 36 is equipped with an ultrafiltration membrane and is a device that produces ultrapure water by removing fine particles using the ultrafiltration membrane. The ultrafiltration device 36 is an example of a filtration device. The ultrafiltration device 36 is disposed at the end of the supply pipe 62 in the secondary pure water system 20 in the supply direction, and constitutes the most downstream processing section inside the secondary pure water system 20. The ultrapure water obtained by the secondary pure water system 20 is supplied to a point-of-use 50, which is the place of use, via the supply pipe 62. The configuration of the ultrafiltration device 36 will be described later. In the present disclosure, the outlet side of the ultrafiltration device is the end of the ultrapure water system.

[0046] The secondary deionization system 20 may also be equipped with an oxidant removal device or a boron-selective ion exchange device provided with, for example, a catalytic resin carrying Pt or Pd metal, or a reducing resin carrying sulfite, bisulfite, or nitrite groups. The resins of these devices may also be packed into the first or second ion exchange device.

[0047] The pressure detector 40 detects the pressure inside the supply pipe 62 between the membrane degassing device 30 and the booster pump 32. The pressure detector 40 is an example of a second pressure detection unit. For example, a pressure transmitter is used as the pressure detector 40. The pressure transmitter is a communication device that converts pressure data into a signal and transmits it as a radio wave. The control device 80 controls the circulation pump 22 in accordance with the pressure detected by the pressure detector 40 so that the pressure inside the supply pipe 62 becomes a predetermined pressure. Control of the circulation pump 22 will be described later.

[0048] The flow rate detector 42 detects the flow rate of ultrapure water inside the supply pipe 62 between the ultrafiltration device 36, which is the most downstream device in the secondary pure water system 20, and the point of use 50. The flow rate detector 42 is an example of a flow path detection unit. For example, a flow rate transmitter is used as the flow rate detector 42. The flow rate transmitter is a communication device that converts flow rate data into a signal and transmits it as a radio wave. The control device 80 controls the booster pump 32 in accordance with the flow rate detected by the flow rate detector 42 so that the ultrapure water flowing through the supply pipe 62 maintains a predetermined flow rate. Control of the booster pump 32 will be described later.

[0049] 2 shows the configuration of the second ion exchange device 34, the ultrafiltration device 36, and the vicinity of the point of use 50. As shown in FIG. 2, the second ion exchange device 34 includes a first ion exchange resin treatment section (i.e., polisher 2-1) 102 and a second ion exchange resin treatment section (i.e., polisher 2-2) 104, which are connected in parallel to a supply pipe 62. Specifically, the supply pipe 62 branches into two inlet pipes 106A and 106B, with the inlet pipe 106A connected to the first ion exchange resin treatment section 102 and the inlet pipe 106B connected to the second ion exchange resin treatment section 104. As a result, primary pure water is introduced from the supply pipe 62 into the first ion exchange resin treatment section 102 and the second ion exchange resin treatment section 104 via the inlet pipes 106A and 106B, respectively. The inlet pipes 106A and 106B are provided with valves 107A and 107B that open and close the flow paths, respectively.

[0050] 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. The discharge pipes 108A and 108B are joined to the downstream supply pipe 62. The discharge pipes 108A and 108B are provided with valves 109A and 109B, respectively, for opening and closing the flow paths.

[0051] Discharge lines 110A and 110B are connected to the discharge lines 108A and 108B, respectively. Valves 111A and 111B are provided in the discharge lines 110A and 110B to open and close the flow paths, respectively. During normal use of the secondary pure water system 20, the valves 111A and 111B are closed (see FIG. 2). This allows primary pure water treated in the first ion exchange resin treatment section 102 to be supplied to the supply line 62 via the discharge line 108A, and primary pure water treated in the second ion exchange resin treatment section 104 to be supplied to the supply line 62 via the discharge line 108B.

[0052] In addition, 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, but instead, it may be configured to have three or more ion exchange resin treatment sections.

[0053] 2, the ultrafiltration device 36 is configured as a unit including two ultrafiltration membrane treatment sections 120A and 120B. The primary pure water treated by the second ion exchange device 34 is introduced into the two ultrafiltration membrane treatment sections 120A and 120B via a supply pipe 62 and filtered by the ultrafiltration membranes. The ultrapure water filtered by the two ultrafiltration membrane treatment sections 120A and 120B is supplied to the point of use 50 via the supply pipe 62.

[0054] 1 and 2, the supplied ultrapure water is used at the point of use 50. Unused ultrapure water supplied to the point of use 50 is circulated and recovered to the pure water tank 16 via the return pipe 64, and is stored in the pure water tank 16 together with the primary pure water. Furthermore, when the ultrapure water is not used at the point of use 50, the ultrapure water supplied from the secondary pure water system 20 to the point of use 50 is returned directly to the pure water tank 16 via the return pipe 64 (see FIG. 2).

[0055] As an example, the point of use 50 is provided in a clean room 52 (see FIG. 1 ) located away from the secondary pure water system 20. The supply pipe 62 from the most downstream end of the secondary pure water system 20 to the connection to the point of use 50 and the return pipe 64 from the branch to the point of use 50 to the pure water tank 16 form relatively long flow paths. The length L1 (see FIG. 1 ) of the supply pipe 62 from the downstream end of the secondary pure water system 302 to the connection to the point of use 50 is, for example, 0.1 km or more and 1.5 km or less. In addition, the length of the return pipe 64 from the branch to the point of use 50 to the pure water tank 16 is, for example, 0.1 km or more and 1.5 km or less.

[0056] There are no particular limitations on the materials for the supply pipe 62 and the return pipe 64, but PVDF (i.e., polyvinylidene fluoride), PVC (i.e., polyvinyl chloride), or stainless steel such as SUS304 or SUS316 can be used, but when the liquid is ultrapure water, it is preferable to use PVDF.

[0057] The pressure detector 66 is provided in the return pipe 64 connected to the point of use 50 and detects the pressure inside 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. An adjustment valve 68 is provided in the return pipe 64 downstream of the pressure detector 66 and adjusts the pressure inside the return pipe 64.

[0058] The pressure detector 66 is preferably provided at a position from the branch point of the return pipe 64 to the use point 50 to less than 20% of the length of the return pipe 64 between the branch point and the pure water tank 16, more preferably at a position less than 10% of the length of the return pipe 64, and even more preferably at a position less than 5% of the length of the return pipe 64. Here, the length of the return pipe 64 is the length from the branch point of the return pipe 64 to the use point 50 to the connection point with the pure water tank 16.

[0059] Although not shown, in the liquid circulation system 10, the circulation path 60 may have a plurality of branch points to the use point 50. In this case, the pressure detector 66 is preferably provided at a position from the final stage of the return pipe 64 where the return pipe 64 branches off to the use point 50 to less than 20% of the length of the return pipe 64 between the final stage and the pure water tank 16.

[0060] (Hardware Configuration of Liquid Circulation System) Fig. 3 shows a block diagram of the hardware configuration of liquid circulation system 10. As shown in Fig. 3, control device 80 has components including a CPU (i.e., Central Processing Unit) 81, a ROM (i.e., Read Only Memory) 82, a RAM (i.e., Random Access Memory) 83, storage 84, and an input / output interface 85. These components are connected to each other via a bus 86.

[0061] The CPU 81 is a central processing unit that executes various programs and controls each part. That is, the CPU 81 reads the programs from the ROM 82 or the storage 84 and executes the programs using the RAM 83 as a work area. The CPU 81 controls the above-mentioned components and performs various arithmetic processing in accordance with the programs recorded in the ROM 82 or the storage 84. In the first embodiment, the ROM 82 or the storage 84 stores a liquid circulation processing program.

[0062] The ROM 82 stores various programs and various data. The RAM 83 temporarily stores programs or data as a working area. The storage 84 is configured with an HDD (i.e., hard disk drive) or an SSD (i.e., solid state drive) and stores various programs including the operating system and various data.

[0063] The input / output interface 85 is connected to the pressure detector 40, the flow rate detector 42, the pressure detector 66, and the regulating valve 68. Furthermore, the input / output interface 85 is connected to the circulation pump 22 via the power supply 44, and to the booster pump 32 via the power supply 46.

[0064] The control device 80 receives an input of the pressure value detected by the pressure detector 40 of the supply pipe 62. The control device 80 controls the frequency of the electricity supplied from the power source 44 to the circulation pump 22 in accordance with the pressure detected by the pressure detector 40. This adjusts 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 source 44 to the circulation pump 22 so that the pressure detected by the pressure detector 40 becomes a preset pressure.

[0065] The control device 80 receives an input of the value of the flow rate of the ultrapure water detected by the flow rate detector 42 of the supply pipe 62. The control device 80 controls the frequency of electricity supplied from the power source 46 to the booster pump 32 in accordance with the flow rate of the ultrapure water detected by the flow rate detector 42. The booster pump 32 is a pump that pressurizes the supply pipe 62 to compensate for any pressure deficiency, thereby supplying primary pure water. This adjusts the pressure and flow rate at the outlet of the booster pump 32. The control device 80 is an example of a first pump control section. For example, when the flow rate of the ultrapure water detected by the flow rate detector 42 is 80 m / s, the control device 80 controls the frequency of electricity supplied from the power source 46 to the booster pump 32 in accordance with the flow rate of the ultrapure water detected by the flow rate detector 42. ３ The frequency of the electricity supplied from the power source 46 to the booster pump 32 is controlled so as to be equal to or greater than 1 / h (see FIG. 2).

[0066] The control device 80 receives an input of the pressure value detected by the pressure detector 66 of the return pipe 64. The control device 80 adjusts the pressure inside the return pipe 64 by controlling the opening state of the adjustment valve 68 in accordance with the pressure detected by the pressure detector 66. For example, when the pressure detected by the pressure detector 66 is 343 kPa (i.e., 3.5 kgf / cm ２ ) (see FIG. 2).

[0067] [Operations and Effects of First Embodiment] Next, operations and effects of the first embodiment will be described.

[0068] 1 , the liquid circulation system 10 is provided with a circulation path 60 including a supply pipe 62 and a return pipe 64, and primary pure water in a pure water tank 16 is supplied via the supply pipe 62 to a point of use 50 via a secondary pure water system 20. In the secondary pure water system 20, the primary pure water is treated by a heat exchanger 24, an ultraviolet irradiation device 26, a first ion exchange device 28, a membrane degassing device 30, a second ion exchange device 34, and an ultrafiltration device 36, thereby producing ultrapure water. The ultrapure water produced by the secondary pure water system 20 is supplied to the point of use 50. Furthermore, ultrapure water not used at the point of use 50 is returned to the pure water tank 16 via the return pipe 64.

[0069] 1 and 2, a pressure detector 66 is provided in 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 downstream of the pressure detector 66 in the return pipe 64, and the regulating valve 68 regulates the pressure inside the return pipe 64 in accordance with the pressure detected by the pressure detector 66.

[0070] 1 and 2 , a flow rate detector 42 is provided in the supply pipe 62 between the ultrafiltration device 36, which is the most downstream device of the secondary pure water system 20, and the point of use 50, and the flow rate detector 42 detects the flow rate of the liquid inside the supply pipe 62. Then, in accordance with the flow rate detected by the flow rate detector 42, the control device 80 controls the booster pump 32 so that the primary pure water flowing through the supply pipe 62 is maintained at a predetermined flow rate. This suppresses fluctuations in the flow rate of the ultrapure water supplied from the flow rate detector 42 in the supply pipe 62 to the point of use 50. Therefore, fluctuations in the flow rate of the ultrapure water supplied to the point of use 50 can be suppressed regardless of whether or not ultrapure water is being used at the point of use 50.

[0071] 1 , in the liquid circulation system 10, a circulation pump 22 is provided on the supply pipe 62 downstream of the pure water tank 16, and the circulation pump 22 supplies primary pure water from the pure water tank 16 to the heat exchanger 24 side of the secondary pure water system 20. A pressure detector 40 is provided on the supply pipe 62 upstream of the booster pump 32, and the pressure detector 40 detects the pressure inside the supply pipe 62. The controller 80 controls the circulation pump 22 in accordance with the pressure detected by the pressure detector 40 so that the pressure inside the supply pipe 62 is maintained at a predetermined pressure. Therefore, when the circulation pump 22 supplies primary pure water from the pure water tank 16 through the supply pipe 62 to the heat exchanger 24 side of the secondary pure water system 20, fluctuations in the pressure inside the supply pipe 62 at the position of the pressure detector 40 can be suppressed.

[0072] Furthermore, in the liquid circulation system 10, a booster pump 32 is provided in the supply pipe 62 between the membrane degassing device 30 and the second ion exchange device 34. This makes it easier to control the flow rate of primary pure water on the outlet side of the booster pump 32 in accordance with the flow rate of ultrapure water detected by the flow rate detector 42 between the most downstream ultrafiltration device 36 in the supply pipe 62 and the point of use 50. This makes it possible to more reliably suppress fluctuations in the flow rate of ultrapure water supplied to the point of use 50.

[0073] (Example of no use of ultrapure water at the use point) Here, an example of no use of ultrapure water at the use point 50 in the liquid circulation system 10 will be described. FIG. 2 shows a case where no ultrapure water is used at the use point 50 (i.e., the amount of ultrapure water used is 0 m ３ / h) are shown.

[0074] As shown in FIG. 2, the control device 80 detects that the flow rate of the ultrapure water detected by the flow rate detector 42 is 80 m ３ / h. At this time, at the point of use 50, for example, the required pressure is 343 kPa (i.e., 3.5 kgf / cm ２ ), whereas the actual pressure is 343 kPa (i.e., 3.5 kgf / cm ２The pressure at the use point 50 is measured by a pressure gauge (not shown). As a result, the flow rate of the ultrapure water supplied to the use point 50 through the supply pipe 62 is 80 m ３ / h, and the pressure difference (i.e., ΔP) between the pressure at the pressure detector 40 and the pressure at the use point 50 is 49 kPa (i.e., 0.5 kgf / cm ２ )

[0075] In this example, since no ultrapure water is 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 80 m ３ The control device 80 detects that the pressure of the pressure detector 66 provided on the side of the return pipe 64 where it branches off from the use point 50 is 343 kPa (i.e., 3.5 kgf / cm ２ The pressure inside the return pipe 64 is controlled by the adjusting valve 68 so that the pressure becomes equal to the pressure in the return pipe 64 .

[0076] (Example of Using Ultrapure Water at a Point of Use) Next, an example of using ultrapure water at a point of use 50 in the liquid circulation system 10 will be described with reference to FIG.

[0077] As shown in FIG. 4, the control device 80 detects that the flow rate of the ultrapure water detected by the flow rate detector 42 is 80 m ３ At this time, the required pressure at the point of use 50 is 343 kPa (i.e., 3.5 kgf / cm ２ ), whereas the actual pressure is 343 kPa (i.e., 3.5 kgf / cm ２ Therefore, the flow rate of the ultrapure water supplied to the point of use 50 through the supply pipe 62 is 80 m ３ / h, and the pressure difference (i.e., ΔP) between the pressure inside the supply pipe 62 (e.g., the pressure near the flow rate detector 42) and the pressure at the use point 50 is 49 kPa (i.e., 0.5 kgf / cm ２ )

[0078] At the point of use 50, for example, the amount of ultrapure water used is 50 m ３ / h, the flow rate of the ultrapure water returned to the pure water tank 16 through the return pipe 64 is 30 m ３The control device 80 detects that the pressure of the pressure detector 66 provided on the return pipe 64 near the branch to the use point 50 is 343 kPa (i.e., 3.5 kgf / cm ２ The pressure inside the return pipe 64 is controlled by the adjusting valve 68 so that the pressure becomes equal to or larger than the pressure inside the return pipe 64 .

[0079] As described above, the liquid circulation system 10 can suppress fluctuations in the flow rate of ultrapure water supplied to the point of use 50, regardless of whether ultrapure water is being used at the point of use 50. Furthermore, since the liquid circulation system 10 has small fluctuations in the flow rate of ultrapure water, deterioration of the quality of the ultrapure water due to fluctuations in flow rate is minimized.

[0080] (Position of pressure detector) In the liquid circulation system 10, the pressure detector 66 is located at a position less than 20% of the length of the return pipe 64 between the branch with the use point 50 on the return pipe 64 and the pure water tank 16.

[0081] For example, a configuration will be described in which, when the length of the return pipe between the pure water tank and the use point is long, the pressure detection unit is provided at a position that is 20% or more of the length of the return pipe 64 from the branch of the return pipe to the use point to the pure water tank 16. In this configuration, when ultrapure water begins to be used at the use point, if the diameter of the return pipe remains the same, the flow rate of ultrapure water in the return pipe decreases, thereby reducing pressure loss. Therefore, with a pressure detection unit provided at a position that is 20% or more of the length of the return pipe 64 from the branch of the return pipe to the use point, there is a possibility that the pressure inside the return pipe will not be properly adjusted by the adjustment valve 68.

[0082] In contrast, in the liquid circulation system 10, the pressure detector 66 is provided at a position on the return pipe 64 that is less than 20% of the length of the return pipe 64 from its branch with the use point 50, so that even if the flow rate of ultrapure water in the return pipe 64 decreases, the reduction in pressure loss can be ignored. Therefore, the pressure inside the return pipe 64 can be appropriately adjusted by the adjustment valve 68 in accordance with the pressure detected by the pressure detector 66. There are no particular restrictions on where the adjustment valve 68 can be installed, as long as it is located downstream of the pressure detector 66 on the return pipe 64.

[0083] [Liquid Circulation System of First Comparative Example] Here, a liquid circulation system of a first comparative example will be described. Note that the same components as those in the first embodiment described above are designated by the same reference numerals and description thereof will be omitted.

[0084] As shown in FIG. 7 , the liquid circulation system 300 of the first comparative example differs from the liquid circulation system 10 of the first embodiment in that it includes a secondary deionization system 302 and a control device 320. The secondary deionization system 302 includes a second pressure detector (e.g., PT2) 310 that detects the pressure inside the supply piping 62 between the most downstream ultrafiltration device 36 and the point of use 50. The control device 320 controls the frequency of the power supply 46 that supplies power to the booster pump 32 based on the pressure detected by the second pressure detector 310. That is, the liquid circulation system 300 does not include the flow rate detector 42 (see FIG. 1 ) that is included in the liquid circulation system 10 of the first embodiment. In the liquid circulation system 300, the length L2 of the supply piping 62 from the downstream end of the secondary deionization system 302 to the connection to the point of use 50 is, for example, 0.5 km or more and 1.5 km or less.

[0085] Furthermore, the liquid circulation system 300 differs from the liquid circulation system 10 of the first embodiment in that a third pressure detector (e.g., PT3) 312 that detects the pressure inside the return pipe 64 is provided on the upstream side of the adjustment valve 68 in the return pipe 64 and closer to the pure water tank 16. The control device 320 adjusts the pressure inside the return pipe 64 by controlling the opening state of the adjustment valve 68 in accordance with the pressure detected by the third pressure detector 66. The control device 320 adjusts the pressure inside the return pipe 64 when the pressure detected by the third pressure detector 312 is 294 kPa (i.e., 3 kgf / cm ２ The pressure inside the return pipe 64 is adjusted by controlling the opening state of the adjustment valve 68 so that the pressure inside the return pipe 64 is equal to or greater than the pressure inside the return pipe 64. In the liquid circulation system 300, the length of the return pipe 64 from where it branches off to 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 provided, for example, at a position 80% or more of the length of the return pipe 64 from where it branches off to the use point 50.

[0086] (Example of case where ultrapure water is not used at the point of use) As shown in FIG. 8, in the liquid circulation system 300 of the first comparative example, when no ultrapure water is used at the point of use 50 (i.e., when the amount of ultrapure water used is 0 m ３ / h), the control device 320 detects, for example, that the pressure of the second pressure detector 310 is 392 kPa (i.e., 4 kgf / cm ２ At this time, the frequency of the power source 46 that supplies power to the booster pump 32 is controlled so that the required pressure at the point of use 50 is 343 kPa (i.e., 3.5 kgf / cm ２ ), whereas the actual pressure is 343 kPa (i.e., 3.5 kgf / cm ２ The flow rate of the ultrapure water supplied to the point of use 50 through the supply pipe 62 is 80 m ３ / h, and the pressure difference (i.e., ΔP) between the pressure of the second pressure detector 310 and the pressure at the use point 50 is 49 kPa (i.e., 0.5 kgf / cm ２ )

[0087] Since no ultrapure water is used at use point 50 (i.e., the amount of ultrapure water used is 0 m ３ / h), the flow rate of the ultrapure water flowing to the pure water tank 16 side through the return pipe 64 is 80 m ３ The control device 320 detects that the pressure of the third pressure detector 312 in the return pipe 64 is 294 kPa (i.e., 3 kgf / cm ２ The pressure inside the return pipe 64 is controlled by the adjusting valve 68 so that the pressure difference (i.e., ΔP) between the pressure at the use point 50 and the pressure at the third pressure detector 312 is 49 kPa (i.e., 0.5 kgf / cm ２ )

[0088] (Example of using ultrapure water at a use point) FIG. 9 shows a liquid circulation system 300 in which ultrapure water is supplied to a use point 50 by 50 m ３ 9, in the return pipe 64, the third pressure detector 312 detects that the set pressure of the regulating valve 68 is 294 kPa (i.e., 3 kgf / cm ２) When the use of ultrapure water begins at the use point 50, if the diameter of the return pipe 64 remains the same, the flow rate of ultrapure water in the return pipe 64 decreases, and the pressure loss decreases. For example, the pressure difference (i.e., ΔP) between the pressure at the use point 50 and the pressure at the third pressure detector 312 is 49 kPa (i.e., 0.5 kgf / cm ２ ) to 29.4 kPa (i.e., 0.3 kgf / cm ２ )

[0089] At the use point 50, the required pressure is 343 kPa (i.e., 3.5 kgf / cm ２ ), whereas the actual pressure is 323.4 kPa (i.e., 3.3 kgf / cm ２ ) and the pressure drops. At this time, the pressure detected by the second pressure detector 310 is 392 kPa (i.e., 4 kgf / cm ２ ), and the pressure difference (i.e., ΔP) between the pressure of the second pressure detector 310 and the pressure at the use point 50 is 68.6 kPa (i.e., 0.7 kgf / cm ２ ), the pressure loss increases and the supply flow rate increases. For example, the supply flow rate of ultrapure water in the supply pipe 62 is actually 80 m ３ / h, but the supply flow rate is 100m ３ / h. In other words, the actual supply flow rate of ultrapure water increases relative to the design flow rate of ultrapure water in the supply pipe 62. This means that changes in pressure may affect the quality of the ultrapure water. In addition, changes in the operating conditions of semiconductor manufacturing equipment and the like installed at the point of use may affect product yields.

[0090] For ease of maintenance, the third pressure detector 312 and the regulating valve 68 are generally installed near the pure water tank 16. That is, if the third pressure detector 312 and the regulating valve 68 were installed near the point of use, they would be installed, for example, in a building different from the building where the pure water system is installed, on a different floor, or even inside or near a clean room, which would significantly impair maintainability, and is therefore not generally done.

[0091] [Liquid Circulation System of Second Comparative Example] Next, a liquid circulation system of a second comparative example will be described. Note that the same components as those in the first embodiment and the first comparative example described above are designated by the same reference numerals, and their description will be omitted.

[0092] (Example of Using Ultrapure Water at a Use Point) FIG. 10 shows a liquid circulation system 330 of a second comparative example in which, for example, 50 ml of ultrapure water is supplied to a use point 50. ３ 10 shows an example in which the setting of the third pressure detector 312 is changed immediately after the state shown in FIG. 9 is reached. That is, as shown in FIG. 10, in the liquid circulation system 330 of the second comparative example, the set pressure of the third pressure detector 312 is manually changed to 323.4 kPa (i.e., 3.3 kgf / cm ２ ) and narrow the opening of the adjusting valve 68. As a result, the flow rate of the ultrapure water returned by the return pipe 64 is reduced by 50 m compared to the liquid circulation system 330 of the first comparative example. ３ / h to 30m ３ / h, and the pressure loss in the return pipe 64 is reduced. The pressure at the use point 50 is 343 kPa (i.e., 3.3 + 0.2 = 3.5 kgf / cm ２ Furthermore, the pressure difference (i.e., ΔP) between the second pressure detector 310 of the supply pipe 62 and the use point 50 is 49 kPa (i.e., 0.5 kgf / cm ２ ), and the supply amount of ultrapure water from the supply pipe 62 is also reduced to 80 m ３ Return to / h.

[0093] However, in the liquid circulation system 330, the set pressure of the third pressure detector 312 is manually and suddenly set to 323.4 kPa (i.e., 3.3 kgf / cm ２ ), the quality of the ultrapure water may be deteriorated. In addition, the control device 320 needs to control two pressures: the booster pump 32 using the second pressure detector 310 and the regulating valve 68 using the third pressure detector 312, which complicates the control of the operating system.

[0094] 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 in accordance with the flow rate of ultrapure water measured by the flow rate detector 42 between the ultrafiltration device 36 and the point of use 50 in the supply piping 62. This suppresses fluctuations in the flow rate of ultrapure water supplied to the point of use 50 through the supply piping 62. Therefore, regardless of whether ultrapure water is being used at the point of use 50, fluctuations in the flow rate of ultrapure water supplied to the point of use 50 through the supply piping 62 can be suppressed.

[0095] Furthermore, in the liquid circulation system 10, the pressure detector 66 is located at a position on the return pipe 64 that is less than 20% of the length of the return pipe 64 from the branch point with the use point 50. Therefore, even if the flow rate of ultrapure water in the return pipe 64 decreases, the decrease in pressure loss can be ignored. Therefore, the pressure inside the return pipe 64 can be appropriately adjusted by the adjustment valve 68 in accordance with the pressure detected by the pressure detector 66.

[0096] [First Example of Maintenance in the Liquid Circulation System of the First Embodiment] Next, a first example of maintenance in the liquid circulation system 10 of the first embodiment will be described.

[0097] 5 shows a state in which the first ion exchange resin treatment section 102 of the second ion exchange device 34 is stopped during maintenance of the liquid circulation system 10. As shown in FIG. 5, in the liquid circulation system 10, the amount of ultrapure water used at the point of use 50 is changed and the first ion exchange resin treatment section 102 is operated simultaneously. At the point of use 50, the amount of ultrapure water used is changed to 50 m ３ / h.

[0098] In the liquid circulation system 10, the valve 107A of the inlet pipe 106A and the valve 109A of the outlet pipe 108A are closed, thereby preventing primary pure water from flowing through 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 to be performed. Valves 111A and 111B are also closed. Furthermore, the valve 107B of the inlet pipe 106B is opened, and the valve 109B of the outlet pipe 108B is opened, allowing primary pure water to flow only through the second ion exchange resin treatment section 104. The primary pure water treated in the second ion exchange resin treatment section 104 is supplied to the ultrafiltration device 36 from the outlet pipe 108B via the supply pipe 62.

[0099] The control device 80 detects that the flow rate of the ultrapure water detected by the flow rate detector 42 is 80 m ３ / h. As a result, the supply amount of ultrapure water supplied to the point of use 50 through the supply pipe 62 is 80 m ３ / h.

[0100] Here, the operation and effect of the configuration of the second ion exchange device 34 of the liquid circulation system 10 of the first embodiment will be described.

[0101] In the liquid circulation system 10, the second ion exchange device 34 has 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 valves 107A and 109A of the first ion exchange resin treatment section 102 are open and the valves 107B and 109B of the second ion exchange resin treatment section 104 are open, 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 FIG. 4 ). In this configuration, one of the first ion exchange resin treatment section 102 and the second ion exchange resin treatment section 104 can be stopped for maintenance, and primary pure water can be passed through the other of the first ion exchange resin treatment section 102 and the second ion exchange resin treatment section 104. Therefore, maintenance of one of the first ion exchange resin treatment section 102 and the second ion exchange resin treatment section 104 can be performed while the liquid circulation system 10 continues to operate.

[0102] Furthermore, in the liquid circulation system 10, during maintenance of the second ion exchange device 34, 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 that has passed 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 that has passed through the second ion exchange resin treatment section 104 is supplied to the ultrafiltration device 36 (see FIG. 5 ).

[0103] 5, in the liquid circulation system 10, the booster pump 32 is controlled in accordance with the flow rate of the ultrapure water detected by the flow rate detector 42 between the most downstream ultrafiltration device 36 in the supply pipe 62 and the point of use 50. For example, the control device 80 controls the booster pump 32 in accordance with the flow rate of the ultrapure water detected by the flow rate detector 42 when the flow rate of the ultrapure water detected by the flow rate detector 42 is 80 m / s or less. ３ / h. This controls the frequency of the power supply 46 that supplies power to the booster pump 32 so that the flow rate of the booster pump 32 is equal to or greater than 1 / h. This results in two controls: the flow rate detector 42 controls the booster pump 32, and the pressure detector 66 controls the regulating valve 68, making it possible to stabilize the operating flow rate of 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 point of use 50 is changed and the first ion exchange resin treatment unit 102 is stopped 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 kept approximately constant.

[0104] [First Example of Maintenance of Liquid Circulation System of First Comparative Example] Next, a first example of maintenance of the liquid circulation system 300 of the first comparative example will be described.

[0105] 11 shows an example of maintenance of the second ion exchange device 34 in the liquid circulation system 300 of the first comparative example when there is no change in the amount of ultrapure water used at the point of use 50 (i.e., when no ultrapure water is used). As shown in Fig. 11, when 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 for by increasing the frequency of the power supply 46 that supplies power to the booster pump 32.

[0106] FIG. 12 shows the results when the amount of ultrapure water used at the point of use 50 is changed (for example, when the amount of ultrapure water is increased by 50 m ３ 12 shows an example of maintenance of the second ion exchange unit 34 (when used 100 / h). As shown in FIG. 12 , in the liquid circulation system 300, if the amount of ultrapure water used at the point of use 50 is changed and the first ion exchange resin treatment unit 102 is stopped simultaneously, the booster pump 32 must be controlled by the second pressure detector 310 and the regulating valve 68 must be controlled by the third pressure detector 312. In this case, because there are two automatic pressure controls in the same system, fluctuations in the flow rate and pressure of ultrapure water cannot be predicted. Therefore, depending on the timing, the operating flow rate of the liquid circulation system 300 may change, making it impossible to restore the operating flow rate to its original state, resulting in an unstable operating state of the liquid circulation system 300.

[0107] In contrast, in the liquid circulation system 10 of the first embodiment, the booster pump 32 is controlled in accordance with the flow rate of ultrapure water detected by a flow rate detector 42 between the ultrafiltration device 36 at the most downstream position in the supply piping 62 and the point of use 50. As a result, the booster pump 32 is controlled by the flow rate detector 42, and the regulating valve 68 is controlled 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 is changed and the first ion exchange resin treatment section 102 is stopped at the same time, the flow rate of ultrapure water supplied to the point of use 50 and the pressure at the point of use 50 can be kept approximately constant.

[0108] [Second Example of Maintenance in Liquid Circulation System of First Embodiment] Next, a second example of maintenance in the liquid circulation system 10 of the first embodiment will be described.

[0109] 6 shows a state in which the ion exchange resin in the first ion exchange resin treatment section 102 of the second ion exchange device 34 is being cleaned during maintenance of the liquid circulation system 10. As shown in FIG. 6, in the liquid circulation system 10, the amount of ultrapure water used at the point of use 50 is changed and the ion exchange resin in the first ion exchange resin treatment section 102 is cleaned at the same time. At the point of use 50, the amount of ultrapure water used is changed to 50 m ３ / h.

[0110] In the liquid circulation system 10, the valve 107A of the inlet pipe 106A is opened, the valve 109A of the outlet pipe 108A is closed, and the valve 111A of the outlet passage 110A is opened, whereby the primary pure water that has passed through the first ion exchange resin treatment section 102 is discharged into the outlet passage 110A. This allows the ion exchange resin in the first ion exchange resin treatment section 102 to be washed. Furthermore, by opening the valve 107B of the inlet pipe 106B, opening the valve 109B of the outlet pipe 108B, and closing the valve 111B, the primary pure water that has passed through the second ion exchange resin treatment section 104 is supplied from the outlet pipe 108B to the supply pipe 62 and to the ultrafiltration device 36. The flow rate during washing of the ion exchange resin in the first ion exchange resin treatment section 102 is 10 m ３ / h.

[0111] The control device 80 detects that the flow rate of the ultrapure water detected by the flow rate detector 42 is 80 m ３ / h. As a result, the supply amount of ultrapure water supplied to the point of use 50 through the supply pipe 62 is 80 m ３ / h.

[0112] In the liquid circulation system 10 described above, during maintenance of the second ion exchange device 34, primary pure water is introduced into the first ion exchange resin treatment section 102 to wash the ion exchange resin, and the washed liquid is discharged into the discharge path 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 in accordance with the flow rate of ultrapure water detected by the flow rate detector 42 between the most downstream ultrafiltration device 36 and the point of use 50 in the supply piping 62. For example, when the flow rate of ultrapure water detected by the flow rate detector 42 is 80 m / s, the control device 80 controls the booster pump 32 in accordance with the flow rate of ultrapure water detected by the flow rate detector 42. ３ / h. This controls the frequency of the power supply 46 that supplies power to the booster pump 32. Because the booster pump 32 is controlled by the flow rate detector 42 and the regulating valve 68 is controlled by the pressure detector 66, it is possible to stabilize the operating flow rate of 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 point of use 50 is changed and the ion exchange resin in the first ion exchange resin treatment section 102 is cleaned 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 kept approximately constant.

[0113] [Second Example of Maintenance in Liquid Circulation System of First Comparative Example] Next, a second example of maintenance in the liquid circulation system 300 of the first comparative example will be described.

[0114] 13 shows an example of maintenance of the second ion exchange device 34 in the liquid circulation system 300 of the first comparative example when there is no change in the amount of ultrapure water used at the point of use 50 (i.e., when ultrapure water is not used). As shown in Fig. 13, when the ion exchange resin in the first ion exchange resin treatment section 102 is cleaned, the cleaning flow rate discharged into the discharge path 110A increases. This increase in the cleaning flow rate is compensated for by increasing the frequency of the power supply 46 that supplies power to the booster pump 32.

[0115] FIG. 14 shows the liquid circulation system 300 of the first comparative example when the amount of ultrapure water used at the point of use 50 is changed (for example, when the amount of ultrapure water is increased by 50 m ３ 14 shows an example of maintenance of the second ion exchange device 34 in a case where the amount of ultrapure water used at the point of use 50 is changed and the ion exchange resin in the first ion exchange resin treatment section 102 is cleaned at the same time. As shown in Fig. 14, in the liquid circulation system 300, when the amount of ultrapure water used at the point of use 50 is changed and the ion exchange resin in the first ion exchange resin treatment section 102 is cleaned, it is necessary to control the booster pump 32 with the second pressure detector 310 and the regulating valve 68 with the third pressure detector 312. In this case, since there are two automatic pressure controls in the same system, fluctuations in the flow rate and pressure of ultrapure water cannot be predicted, making the operating state of the liquid circulation system 300 even more unstable.

[0116] In contrast, in the liquid circulation system 10 of the first embodiment, the booster pump 32 is controlled in accordance with the flow rate of ultrapure water detected by a flow rate detector 42 between the ultrafiltration device 36 at the most downstream position in the supply piping 62 and the point of use 50. This results in two controls: 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 is changed and the ion exchange resin in the first ion exchange resin treatment section 102 is cleaned 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 approximately constant.

[0117] [Others] Instead of the configuration of the liquid circulation system 10 of the first embodiment, the position of the pressure detector 66 may be changed under the following conditions: The pressure detector 66 is located on the side of the return pipe 64 closer to the point of use 50 than the pure water tank 16, and when the differential pressure when the flow rate of the ultrapure water in the return pipe 64 is maximum and minimum is compared, the differential pressure is 9.8 kPa (i.e., 0.1 kgf / cm ２ ) and the differential pressure is preferably within 4.9 kPa (i.e., 0.05 kgf / cm ２ It is more preferable that the pressure difference is within 2.94 kPa (i.e., 0.03 kgf / cm ２ ) or less.

[0118] For example, the pressure detector 66 is located on the side of the return pipe 64 closer to the use point 50 than the pure water tank 16, and detects that the differential pressure between the maximum and minimum flow rates of the ultrapure water in the return pipe 64 is 9.8 kPa (i.e., 0.1 kgf / cm ２ ), even if the flow rate of ultrapure water in the return pipe 64 decreases, the influence of reduced pressure loss is reduced. Therefore, the pressure inside the return pipe 64 can be appropriately adjusted by the adjustment valve 68 in accordance with the pressure detected by the pressure detector 66.

[0119] In addition, in a configuration in which a plurality of branch points to the use point 50 are provided in the circulation path 60, the pressure detector 66 is located closer to the final stage of the branch to the use point than the pure water tank 16 in the return pipe, and when the differential pressure when the liquid flow rate in the return pipe is maximum and minimum is compared, the differential pressure is 9.8 kPa (i.e., 0.1 kgf / cm ２ ) or less.

[0120] Although the present disclosure has been described in detail with respect to specific embodiments, it will be apparent to those skilled in the art that the present disclosure is not limited to such embodiments, and that various other embodiments are possible within the scope of the present disclosure.

[0121] [Preferred Aspects of the Present Disclosure] Preferred aspects of the present disclosure will be additionally described below.

[0122] a supply pipe that supplies the liquid in the tank to a use point that is a supply destination via the plurality of processing parts, and a return pipe that returns the liquid from the use point to the tank; a first pump that is provided in the supply pipe midway between the plurality of processing parts and supplies the liquid to the use point; a first pressure detection unit that is provided in the return pipe and detects the pressure inside the return pipe; a regulation valve that is provided in the return pipe downstream of the first pressure detection unit and adjusts the pressure inside the return pipe in accordance with the pressure detected by the first pressure detection unit; a flow rate detection unit that is provided in the supply pipe between the use point and a most downstream processing part of the plurality of processing parts, and detects the flow rate of the liquid inside the supply pipe; and a first pump control unit that controls the first pump so that the liquid flowing through the supply pipe maintains a predetermined flow rate in accordance with the flow rate detected by the flow rate detection unit.

[0123] [Supplementary Item 2] The liquid circulation system according to Supplementary Item 1, comprising: a second pump provided on the supply pipe downstream of the tank, supplying the liquid in the tank to the side of the plurality of processing units; a second pressure detection unit provided on the supply pipe upstream of the first pump, detecting the pressure inside the supply pipe; and a second pump control unit that controls the second pump in accordance with the pressure detected by the second pressure detection unit so that the pressure inside the supply pipe becomes a predetermined pressure.

[0124] [Supplementary Item 3] The liquid circulation system according to Supplementary Item 1 or Supplementary Item 2, wherein the first pressure detection unit is provided at a location from the final stage of the return pipe where it branches off from the use point to less than 20% of the length of the return pipe between the final stage and the tank.

[0125] [Supplementary Item 4] The liquid circulation system according to Supplementary Item 1 or Supplementary Item 2, wherein the first pressure detection unit is provided on the return pipe closer to the final stage of the branch with the use point than the tank, and at a location where the pressure difference when the liquid flow rate in the return pipe is maximum and minimum is 9.8 kPa or less.

[0126] [Supplementary Item 5] The liquid circulation system according to any one of Supplementary Items 1 to 4, wherein the first pump is a booster pump that pressurizes the supply pipe to compensate for a pressure deficiency and supplies the liquid.

[0127] [Supplementary Item 6] The liquid circulation system according to any one of Supplementary Items 1 to 5, wherein the plurality of processing sections include: a filtration device constituting the most downstream processing section and equipped with an ultrafiltration membrane; and an ion exchange device provided immediately upstream of the filtration device and equipped with an ion exchange resin, the ion exchange device being connected in parallel to the supply piping and having two or more ion exchange resin processing sections into which and from which liquid is respectively introduced and discharged.

[0128] [Supplementary Item 7] The liquid circulation system according to Supplementary Item 6, wherein, during maintenance of the ion exchange device, one of the ion exchange resin treatment units is stopped, and the liquid that has passed through the other ion exchange resin treatment unit is supplied to the filtration device.

[0129] [Appendix 8] The liquid circulation system according to appendix 6, configured so that during maintenance of the ion exchange device, a liquid is introduced into one of the ion exchange resin treatment sections to wash the ion exchange resin, the washed liquid is discharged to a discharge path other than the supply pipe, the liquid is introduced into another of the ion exchange resin treatment sections, and the liquid that has passed through the other of the ion exchange resin treatment sections is supplied to the filtration device.

[0130] The disclosure of Japanese Patent Application No. 2023-098744 is incorporated herein by reference in its entirety. All publications, patent applications, and technical standards mentioned herein are incorporated herein by reference to the same extent as if each individual publication, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

a first pump provided in the return pipe between the processing sections and a pressure detector provided in the return pipe for detecting a pressure inside the return pipe; a control valve provided in the return pipe downstream of the first pressure detector for adjusting the pressure inside the return pipe in accordance with the pressure detected by the first pressure detector; a flow rate detection unit provided in the supply pipe between the processing section that is the most downstream of the processing sections and the use point, and a first pump control unit for controlling the first pump so that the liquid flowing through the supply pipe is at a predetermined flow rate in accordance with the flow rate detected by the flow rate detection unit.

2. A liquid circulation system as described in claim 1, comprising: a second pump provided on the supply piping downstream of the tank for supplying liquid in the tank to the side of the plurality of processing units; a second pressure detection unit provided on the supply piping upstream of the first pump for detecting the pressure inside the supply piping; and a second pump control unit for controlling the second pump in accordance with the pressure detected by the second pressure detection unit so that the pressure inside the supply piping becomes a predetermined pressure.

3. A liquid circulation system as described in claim 1, wherein the first pressure detection unit is located at a location less than 20% of the length of the return piping between the final stage of the branch to the use point in the return piping and the tank.

4. A liquid circulation system as described in claim 1, wherein the first pressure detection unit is located on the return piping closer to the final stage of the branch with the use point than the tank, and where, when comparing the differential pressure when the liquid flow rate in the return piping is maximum and minimum, the differential pressure is within 9.8 kPa.

5. A liquid circulation system according to claim 1, wherein the first pump is a booster pump that pressurizes the supply pipe to compensate for a pressure deficiency and supplies liquid.

6. The liquid circulation system described in claim 1, wherein the multiple processing sections include a filtration device constituting the most downstream processing section and equipped with an ultrafiltration membrane, and an ion exchange device provided upstream just before the filtration device and equipped with an ion exchange resin, the ion exchange device being connected in parallel to the supply piping and having two or more ion exchange resin processing sections into which liquid is respectively introduced and discharged.

7. A liquid circulation system as described in claim 6, configured such that, during maintenance of the ion exchange device, one of the ion exchange resin treatment sections is stopped and liquid that has passed through the other ion exchange resin treatment section is supplied to the filtration device.

8. The liquid circulation system according to claim 6, wherein during maintenance of the ion exchange device, a liquid is introduced into one of the ion exchange resin treatment sections to wash the ion exchange resin, the washed liquid is discharged into a drainage path other than the supply piping, liquid is introduced into the other ion exchange resin treatment section, and the liquid that has passed through the other ion exchange resin treatment section is supplied to the filtration device.

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