Ultrapure water production device and ultrapure water production method

Abstract

To save energy in an apparatus for producing ultrapure water, by effectively utilizing a pressure energy of ultrapure water flowing in a return line.SOLUTION: An apparatus 1A for producing ultrapure water includes: at least one water processing apparatus for producing the ultrapure water; a mother pipe L1, provided with at least one water processing apparatus and connected to a use point P.O.U., for supplying the ultrapure water to the use point P.O.U.; a return line L2 for returning the ultrapure water not used at the use point P.O.U. to the mother pipe L1; at least one hydropower generator 21 provided in the return line L2; a bypass line L5 bypassing the at least one hydropower generator 21; and a back pressure-controlling valve V2 provided in the bypass line L5.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In the manufacturing processes of semiconductor devices and liquid crystal devices, ultrapure water, from which impurities have been highly removed, is used for various purposes, such as cleaning processes. Ultrapure water is generally produced by sequentially treating raw water (river water, groundwater, industrial water, etc.) in a pretreatment system, a primary pure water system, and a secondary pure water system (subsystems). Water treatment devices for producing ultrapure water are installed along the main pipes of the subsystems. The ultrapure water produced in the water treatment devices is supplied from the main pipes to points of use (POUs). Ultrapure water not used at the points of use is returned to the main pipes through return lines (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-030087 Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, the pressure of ultrapure water at the use point is required to be within a specified range. Because the pressure at the use point is usually higher than the pressure at the junction of the main pipe and return line, the ultrapure water flowing in the return line is reduced in pressure upstream of the junction with the main pipe. However, the pressure energy of the ultrapure water flowing in the return line is not effectively utilized.

[0005] An object of the present invention is to provide an ultrapure water production system that effectively utilizes the pressure energy of ultrapure water flowing through a return line, thereby realizing energy savings. [Means for solving the problem]

[0006] The ultrapure water production system of the present invention comprises at least one water treatment device for producing ultrapure water, a main pipe equipped with the at least one water treatment device and connected to a use point for supplying ultrapure water to the use point, a return line for returning ultrapure water not used at the use point to the main pipe, at least one hydroelectric power generation device provided in the return line, a bypass line for bypassing the at least one hydroelectric power generation device, and a back pressure control valve provided in the bypass line. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an ultrapure water production system that effectively utilizes the pressure energy of the ultrapure water flowing through the return line and achieves energy savings. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic configuration diagram of an ultrapure water production system according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram of a back pressure valve. [Figure 3] FIG. 1 is a schematic configuration diagram of an ultrapure water production system according to a second embodiment of the present invention. [Figure 4] 1 is a schematic diagram of an ultrapure water production system according to an embodiment of the present invention; [Figure 5] 3 shows operational data of the hydroelectric power generation device in the embodiment. [Figure 6] 1 shows operation data of an ion exchange device in an example. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the embodiment described below, a hydroelectric power generation device installed in a return line generates electricity and uses the obtained electricity to operate various devices. Table 1 shows possible patterns for using the electricity obtained by the hydroelectric power generation device and the storage battery.

[0010] [Table 1]

[0011] (First embodiment) FIG. 1 shows an overview of the subsystems of an ultrapure water production system 1A according to a first embodiment of the present invention. The subsystem is a system for producing ultrapure water to be supplied to a point-of-use POU from pure water produced in a primary pure water system (not shown), and is also called a secondary pure water system. Although the present invention relates to an ultrapure water production system, it is characterized by the configuration of the subsystems. Therefore, the following description of the ultrapure water production system 1A will focus on the subsystems unless otherwise specified, and the subsystems will sometimes be referred to as the ultrapure water production system 1A.

[0012] The subsystem of the ultrapure water production system 1A includes a main pipe L1 connected to a point-of-use POU, at least one water treatment device installed on the main pipe L1 for producing ultrapure water, and a return line L2 for returning unused (more precisely, unused) ultrapure water to the main pipe L1. On the main pipe L1, a pure water tank 11, a pure water supply pump 12, a heat exchanger 13, an ultraviolet oxidation device 14, an ion exchange device 15, a membrane degassing device 16, a booster pump 17, and an ultrafiltration membrane device 18 are arranged in series along the direction D of pure water flow in the listed order. The ultraviolet oxidation device 14, the ion exchange device 15, the membrane degassing device 16, and the ultrafiltration membrane device 18 are examples of the water treatment devices described above. Multiple supply lines L3 branch off from the main pipe L1 to supply ultrapure water to each point-of-use POU. Multiple recovery lines L4 for recovering unused ultrapure water from each point-of-use POU merge with the return line L2. The return line L2 is connected to the pure water tank 11. The ultrapure water that flows into the return line L2 from the recovery line L4 passes through the return line L2 and the pure water tank 11 and is returned to the main pipe L1.

[0013] The pure water tank 11 stores pure water produced in the primary pure water system. The pure water supply pump 12 supplies the pure water stored in the pure water tank 11 to the heat exchanger 13. The ultraviolet oxidation device 14 irradiates the pure water, whose temperature has been adjusted by the heat exchanger 13, with ultraviolet light to decompose organic matter contained in the pure water. The ion exchanger 15 removes ionic components from the pure water. The ion exchanger 15 is a non-regenerative cartridge polisher filled with a mixed bed of cation exchange resin and anion exchange resin. The membrane degassing device 16 degasses the pure water, i.e., removes dissolved oxygen and carbon dioxide from the pure water. The booster pump 17 is provided to pressurize the pure water, for example, when the point-of-use POU is installed at a high location. The booster pump 17 may be omitted depending on the location of the point-of-use POU. An ion exchanger (not shown) may be provided downstream of the booster pump 17 to mainly remove fine particles and particulate components generated by the booster pump 17. The ultrafiltration membrane device 18 finally removes fine particles contained in the pure water. The ultrafiltration membrane device 18 may use a membrane with a molecular weight cutoff of approximately 4000 to 6000, which can efficiently remove minute particles. A hydrogen peroxide removal device (not shown) that decomposes hydrogen peroxide generated by ultraviolet irradiation may be provided between the ultraviolet oxidation device 14 and the ion exchange device 15. Removing hydrogen peroxide prevents the downstream ion exchange device 15 from being damaged by oxidizing substances.

[0014] A first flow meter F1 is disposed in the mother pipe L1 between the ultrafiltration membrane device 18 and the point of use POU. A second flow meter F2 is disposed in the return line L2 between the junction S1 with the mother pipe L1 and the pure water tank 11. The first flow meter F1 measures the flow rate of ultrapure water supplied to the point of use POU. The second flow meter F2 measures the flow rate of ultrapure water flowing through the return line L2. A first pressure meter P1 is disposed in the mother pipe L1 between the ultrafiltration membrane device 18 and the point of use POU. A second pressure meter P2 is disposed in the mother pipe L1 between the branch S2 of the most downstream supply line L3 and the junction S1 with the return line L2. The first pressure meter P1 measures the pressure of ultrapure water supplied to the point of use POU. The second pressure meter P2 measures the pressure of ultrapure water downstream of the point of use POU. A first resistivity meter C1 and a second resistivity meter C2 that measure the resistivity of pure water are provided at the inlet and outlet, respectively, of the ion exchange device 15. The ion removal performance of the ion exchange device 15 can be monitored from the measurement results of the first resistivity meter C1 and the second resistivity meter C2. A conductivity meter, which will be described in the examples, can also be used instead of the resistivity meter.

[0015] Generally, the pressure of the ultrapure water at the point of use POU is required to be within a first predetermined range. Whether the pressure of the ultrapure water at the point of use POU is within the first predetermined range is determined by whether the measurement value of the second pressure gauge P2 is within a second predetermined range (0.1 to 0.7 MPa (preferably 0.2 to 0.6 MPa)) corresponding to the first predetermined range. Then, the flow rate of the booster pump 17 (or the pure water supply pump 12 if there is no booster pump 17) is controlled based on the measurement value of the first pressure gauge P1 so that the measurement value of the second pressure gauge P2 is within the second predetermined range. The control is performed by a control device (not shown) connected to the first pressure gauge P1 and the booster pump 17 or the pure water supply pump 12.

[0016] As described above, the ultrapure water supplied to the point of use POU is pressurized by the booster pump 17 or the pure water supply pump 12. Therefore, the pressure of the ultrapure water supplied to the point of use POU is generally higher than the pressure at the junction (the pure water tank 11 in this embodiment) of the return line L2 and the main pipe L1. Therefore, the pressure of the ultrapure water at the point of use POU must be maintained at a constant pressure (first predetermined pressure) higher than the pressure at the junction. For this purpose, a backpressure control valve V2 is provided in the bypass line L5 branching off from the return line L2. That is, the ultrapure water sent to the point of use POU is usually boosted by the booster pump 17 or the pure water supply pump 12, and the pressure of the boosted ultrapure water (the primary pressure of the backpressure control valve V2) is maintained at a constant value by the backpressure control valve V2. The ratio of the flow rate of ultrapure water supplied to the hydroelectric power generation device 21 to the flow rate of ultrapure water supplied to the backpressure control valve V2 is preferably selected based on the amount of ultrapure water used at the point of use POU and the specifications of the hydroelectric power generation device 21, which will be described later. A first valve V1 is disposed on the main pipe L1 between the branch point S2 of the most downstream supply line L3 and the connection point S1 with the return line L2. By adjusting the opening of the first valve V1, it is possible to adjust the flow rate of ultrapure water flowing through the main pipe L1, thereby controlling the pressure at the point of use POU.

[0017] In this embodiment, the back pressure control valve V2 is a back pressure valve 30. Figure 2 shows a schematic configuration of the back pressure valve 30. The back pressure valve 30 includes a valve box 31, an inner box 32 housed inside the valve box 31, a valve element 33 that is capable of opening and closing an opening 38 of the inner box 32, a flexible partition wall 34 that is provided inside the valve box 31 and holds the valve element 33, a first spring 35 fixed to the partition wall 34 on the outside of the partition wall 34, and a second spring 36 fixed to the tip of the valve element 33 and the bottom of the inner box 32. The valve box 31 communicates with the upstream side (primary side), and the inner box 32 communicates with the downstream side (secondary side). Ultrapure water on the upstream side (primary side) flows into the valve box 31 through an inlet opening 37 of the valve box 31. As shown in FIG. 2(a), the combined biasing force of the first spring 35 and the second spring 36 causes the valve element 33 to close the opening 38 of the internal box 32, preventing ultrapure water from flowing into the internal box 32. When the pressure on the upstream side (primary side) increases, as shown in FIG. 2(b), the pressure inside the valve box 31 overcomes the combined biasing force of the first spring 35 and the second spring 36, causing the valve element 33 to open the opening 38 of the internal box 32, allowing ultrapure water to flow into the internal box 32. This transfers the pressure of the ultrapure water on the upstream side (primary side) to the downstream side (secondary side). In this way, when the pressure on the upstream side exceeds a predetermined set value, the backpressure valve 30 releases that pressure downstream. However, when the pressure on the upstream side is equal to or lower than the predetermined set value, the backpressure valve 30 remains closed, preventing the pressure of the ultrapure water on the upstream side (primary side) from falling below the set value.

[0018] A control valve can also be used as the back pressure control valve V2. Specifically, a third pressure gauge P3 (shown by a dashed line in FIG. 1) is provided in the return line L2, and the third pressure gauge P3 and the control valve V2 are connected by a regulator (not shown). The third pressure gauge P3 measures the pressure between the control valve V2 and the point of use POU. The regulator receives a pressure signal from the third pressure gauge P3 and controls the opening of the control valve V2 so that the pressure measured by the third pressure gauge P3 is maintained within a predetermined range.

[0019] As a result of providing the back pressure control valve V2, the ultrapure water flowing through the return line L2 is reduced in pressure upstream of the junction with the main pipe L1 (the pure water tank 11). The pressure at the junction is set to a value below the pressure resistance capacity of the pure water tank 11. However, it cannot be said that the pressure energy of the ultrapure water flowing through the return line L2 is being used effectively. In one example, the ultrapure water is reduced in pressure by approximately 0.5 MPa by the back pressure control valve V2. In other words, pressure energy equivalent to approximately 0.5 MPa is lost. This value can vary depending on the difference in installation level between the point of use POU and the pure water tank 11 and pressure loss in the piping, but generally speaking, pressure energy equivalent to a head of several tens of meters is lost without performing any work as the ultrapure water returns from the point of use POU to the pure water tank 11.

[0020] Therefore, the ultrapure water production system 1A of this embodiment has at least one hydroelectric power generation system 21 (hereinafter, sometimes simply referred to as the hydroelectric power generation system 21) for recovering the pressure energy of the ultrapure water flowing through the return line L2 as electric power. The hydroelectric power generation system 21 is provided in the return line L2 and generates electric power using the ultrapure water flowing through the return line L2. The generated electric power is used for various purposes, as will be described below. Such a hydroelectric power generation system 21 allows the pressure energy of the ultrapure water flowing through the return line L2 to be used for other equipment in the ultrapure water production system 1A, thereby improving the energy efficiency of the ultrapure water production system 1A as a whole.

[0021] The hydroelectric power generation system 21 includes a water turbine 22 and a generator 23 connected to the water turbine 22. There are no particular limitations on the configuration of the water turbine 22, as long as it can convert the pressure energy (potential energy and kinetic energy) of the ultrapure water into electrical energy. Any suitable water turbine 22 known in the art can be used depending on the flow rate of the ultrapure water and the required amount of power generation. Considering the typical flow rate of the return line L2 and the effective head of the water turbine 22 in the ultrapure water production system 1A, an impeller-type water turbine, in which an impeller rotates in response to the flow of ultrapure water through the return line L2, is preferred. An example of an impeller-type water turbine is a Francis turbine. In particular, a water turbine configured to detect the flow rate of ultrapure water from the rotation speed of the impeller is preferred. Using such a water turbine 22 eliminates the need to install a flow meter near the water turbine 22. There are also no particular limitations on the type of generator 23; either a DC generator or an AC generator can be used. However, as described in the examples, a power conditioner (not shown) for converting the output of the generator 23 may be provided as needed.

[0022] The hydroelectric power generation device 21 and the back pressure control valve V2 are provided in parallel. Specifically, a bypass line L5 is provided that branches off from the return line L2 upstream of the hydroelectric power generation device 21, merges with the return line L2 downstream of the hydroelectric power generation device 21, and bypasses the hydroelectric power generation device 21, and the back pressure control valve V2 is provided on the bypass line L5. As described above, the back pressure control valve V2 maintains the pressure upstream of the back pressure control valve V2. This allows fluctuations in the pressure of the ultrapure water supplied to the point of use POU to be kept to a negligible level, even when the hydroelectric power generation device 21 is installed.

[0023] A flow control valve V3 is provided in the return line L2 between the branch point S3 of the bypass line L5 and the turbine 22 of the hydroelectric power generation device 21. The flow control valve V3 controls the flow rate of ultrapure water supplied to the turbine 22 of the hydroelectric power generation device 21. The flow rate of ultrapure water flowing through the return line L2 varies depending on the amount of ultrapure water used at the point of use POU. If the flow rate of ultrapure water flowing through the return line L2 increases, the aperture of the flow control valve V3 is narrowed, and if the flow rate of ultrapure water decreases, the aperture of the flow control valve V3 is widened. This makes it possible to control the flow rate of ultrapure water supplied to the turbine 22 of the hydroelectric power generation device 21 within an appropriate range.

[0024] Multiple hydroelectric power generation devices 21 can be installed. The multiple hydroelectric power generation devices 21 may be connected in series or in parallel. In the case of a series connection, the flow rate of ultrapure water supplied to the multiple hydroelectric power generation devices 22 is the same, but the effective head varies depending on the hydroelectric power generation device 22, potentially requiring the preparation of multiple hydroelectric power generation devices 22 with different specifications. In the case of a parallel connection, the flow rate and effective head are the same, so hydroelectric power generation devices 22 with the same specifications can be used. On the other hand, the flow rate of ultrapure water required to generate the same amount of power is lower in a series connection than in a parallel connection. In general, a parallel connection is suitable for large flow rates and low heads, while a serial connection is suitable for small flow rates and high heads. Therefore, it is preferable to select an appropriate configuration from a series connection or a parallel connection depending on the total flow rate and pressure of ultrapure water supplied to the hydroelectric power generation device 21, and a combination of series and parallel connections is also possible.

[0025] The electricity generated by the hydroelectric power generation system 21 is used to operate electrically operated machines (hereinafter referred to as electrically operated machines M). The ultrapure water production system 1A is provided with various electrically operated machines M that can operate using the electricity generated by the hydroelectric power generation system 21. The electrically operated machines M are electrically connected to the generator 23 of the hydroelectric power generation system 21 (possibly via a power conditioner). The electrically operated machines M are also connected to an external power source 25. One example of an electrically operated machine M is the vacuum pump of the membrane degassing system 16. In general, in the membrane degassing system 16, a gas-liquid contact material is filled in the degassing tower to increase the surface area of the water, and the gas in the degassing tower is depressurized by the vacuum pump, creating a vacuum state in the pure water and removing dissolved oxygen, etc. Another example of an electrically operated machine M is the ultraviolet lamp of the ultraviolet oxidation system 14, which irradiates ultraviolet light onto the pure water. The ultraviolet oxidation system 14 uses an ultraviolet lamp that emits ultraviolet light with at least one of the following wavelengths: 365 nm, 254 nm, 185 nm, and 172 nm. At least one of the vacuum pump of the membrane degassing device 16 and the ultraviolet lamp of the ultraviolet oxidation device 14 can be operated by the electricity generated by the hydroelectric power generation device 21. The electrically operated machine M is not limited to a subsystem device, but may also be a device of a pretreatment system or a primary pure water system.

[0026] Another example of an electrically operated machine M is a measuring instrument for ultrapure water. The measuring instrument is not limited as long as it is electrically operated, but examples include the first flow meter F1, the second flow meter F2, the first pressure gauge P1, the second pressure gauge P2, the first resistivity meter C1, and the second resistivity meter C2 described above. Although not shown, total organic carbon (TOC) meters and particle meters are also examples of electrically operated machines M. Because the power required by measuring instruments is smaller than that required by vacuum pumps and ultraviolet lamps, it is preferable to select measuring instruments when the amount of power generation is small. If the hydroelectric power generation plant 21 has sufficient power generation capacity, it is possible to operate the vacuum pump and ultraviolet lamp, and in some cases, the hydroelectric power generation plant 21 can also operate the measuring instruments.

[0027] The power supplied from the hydroelectric power generation device 21 can be used under normal circumstances (pattern A1 in Table 1) or as a backup in an emergency (pattern A2 in Table 1). In pattern A1, the electrically operated machine M operates on the power supplied from the hydroelectric power generation device 21 under normal circumstances, and operates on the external power source 25 when the power supply from the hydroelectric power generation device 21 is abnormal. In pattern A2, the electrically operated machine M operates on the external power source 25 under normal circumstances, and operates on the power supplied from the hydroelectric power generation device 21 when the power supply from the external power source 25 is abnormal. Pattern A1 is more advantageous than pattern A2 in terms of energy conservation, since it uses the power supplied from the hydroelectric power generation device 21 under normal circumstances. Pattern A2 uses the external power source 25 instead of the power supplied from the hydroelectric power generation device 21 under normal circumstances, and therefore may be a preferable choice when the amount of power generated by the hydroelectric power generation device 21 fluctuates greatly. In the unlikely event that the power supply from the external power source 25 becomes abnormal, the operation of the ultrapure water manufacturing apparatus 1A can be continued by temporarily switching the power source to the hydroelectric power generation apparatus 21 until the external power source 25 is restored.

[0028] The ultrapure water production system 1A described above operates as follows. Ultrapure water is produced by at least one water treatment device provided in the main pipe L1. The ultrapure water produced by the at least one water treatment device is supplied from the main pipe L1 to the point of use POU. Ultrapure water not used at the point of use POU is returned to the main pipe L1 through a return line L2 connected to the main pipe L1. At least one hydroelectric power generation device 21 is provided in the return line L2. While a portion of the ultrapure water is supplied to the bypass line L5, the remainder of the ultrapure water is supplied to the at least one hydroelectric power generation device 21, and electricity is generated in the at least one hydroelectric power generation device 21. The electrically operated machine M is operated using electricity generated by the hydroelectric power generation device 21.

[0029] (Second embodiment) FIG. 3 shows an overview of the subsystems of an ultrapure water production system 1B according to a second embodiment of the present invention. The following explanation will focus on the differences from the first embodiment. Configurations and effects that are not described are similar to those of the first embodiment. The ultrapure water production system 1B of this embodiment has a storage battery 24. The storage battery 24 is electrically connected to the generator 23 of the hydroelectric power generation system 21 and can store the power generated by the hydroelectric power generation system 21. The storage battery 24 is also electrically connected to an external power source 25 and can store the power supplied from the external power source 25. The electrically operated machine M is electrically connected to the generator 23 of the hydroelectric power generation system 21, the storage battery 24, and the external power source 25 and can operate using the power supplied from these sources. It is preferable to provide multiple storage batteries 24. In this embodiment, patterns B1 to B6 shown in Table 1 are possible depending on the normal driving power source of the electrically operated machine M, the backup power source in case of a malfunction of the normal power source, and the charging method of the storage battery 24.

[0030] In patterns B1 to B3, the electrically operated machine M normally operates on power generated by the hydroelectric power generation device 21. When an abnormality occurs in the power supply from the hydroelectric power generation device 21, the electrically operated machine M operates on the storage battery 24. When an abnormality occurs in the power supply from the hydroelectric power generation device 21, the storage battery 24 and the external power source 25 may be used together. When an abnormality occurs in the power supply from the storage battery 24, the power source can also be switched to the external power source 25. In patterns B4 to B6, the electrically operated machine M normally operates on the storage battery 24. When an abnormality occurs in the power supply from the storage battery 24, the electrically operated machine M operates on power generated by the hydroelectric power generation device 21. When an abnormality occurs in the power supply from the storage battery 24, the hydroelectric power generation device 21 and the external power source 25 may be used together. When an abnormality occurs in the power supply from the hydroelectric power generation device 21, the power source can also be switched to the external power source 25.

[0031] In patterns B1 to B3, the electrically operated machine M is directly operated by the power generated by the hydroelectric power generation device 21, but in patterns B4 to B6, the power generated by the hydroelectric power generation device 21 is temporarily stored in the storage battery 24, and the electrically operated machine M is operated by the power stored in the storage battery 24. In patterns B4 to B6, the electrically operated machine M is driven by stable power stored in the storage battery 24, so it is less susceptible to fluctuations in the amount of power generated by the hydroelectric power generation device 21. Patterns B1 to B3 are advantageous over patterns B4 to B6 in terms of power usage efficiency because no energy loss (energy loss based on the difference between the amount of charged energy and the amount of discharged energy) occurs in the storage battery 24 under normal conditions. Furthermore, because charging and discharging are not repeated frequently, patterns B1 to B3 are also advantageous in terms of the lifespan of the storage battery 24.

[0032] Several configurations are possible for charging the storage battery 24. In patterns B1 and B4, the storage battery 24 is charged by the external power source 25. In patterns B2 and B5, the storage battery 24 is charged with power generated by the hydroelectric power generation device 21. In patterns B3 and B6, the storage battery 24 is charged with power generated by the external power source 25 and the hydroelectric power generation device 21.

[0033] Although several embodiments of the present invention have been described above, the present invention is not limited to these embodiments. For example, the concentrated water from the ultrafiltration membrane device 18 can be used as an additional driving source for the hydroelectric power generation device 21. Because the pressure of the concentrated water is generally high, it can be suitably used as a driving source for the hydroelectric power generation device 21. Most of the water is filtered in the ultrafiltration membrane device 18 and passes through the ultrafiltration membrane device 18, but some water is discharged from the ultrafiltration membrane device 18 as concentrated water. Although not shown in the figure, the pressure energy of the concentrated water discharged from the ultrafiltration membrane device 18 can be utilized by merging the discharge line for the concentrated water with the return line L2.

[0034] Furthermore, in this embodiment, the electricity generated by the hydroelectric power generation system 21 is used to operate various electrically operated machines in the ultrapure water production systems 1A and 1B, but the use of the electricity generated by the hydroelectric power generation system 21 is not limited to this. The electricity generated by the hydroelectric power generation system 21 can also be used as a power source for devices and equipment other than the ultrapure water production systems 1A and 1B.

[0035] (Example) The example confirmed that the hydroelectric power generation system can generate stable power and that the measuring instruments function normally with the power generated by the hydroelectric power generation system. Figure 4 shows an overview of the subsystem of the example. Water was circulated through a circulation line L6, which included a tank 41, a pump 42, and a hydroelectric power generation system 43, while the hydroelectric power generation system 43 generated power. Pressure gauges P11 and P12 and a flow meter F11 were installed on the circulation line L6, and these gauges measured the inlet and outlet pressures and the supply water flow rate of the hydroelectric power generation system 43, respectively. The power (three-phase AC) generated by the hydroelectric power generation system 43 was converted to single-phase AC by a power conditioner 44, and a first conductivity meter C11' installed at the inlet of the ion exchange system 45 and a second conductivity meter C12' installed at the outlet were operated. Water to be treated containing ionic components was supplied to the ion exchange system 45, and the ion removal performance of the ion exchange system 45 was measured using the first conductivity meter C11' and the second conductivity meter C12'.

[0036] Figure 5 shows the operating data for the hydroelectric power generation device 43. Except for the period immediately after the start of operation, the inlet pressure, outlet pressure, supply water flow rate, turbine effective head, and power generation output of the hydroelectric power generation device 43 were all stable, confirming that stable power generation was possible. Figure 6 shows the operating data for the ion exchange device 45. Except for the period immediately after the start of operation, the supply water flow rate of the ion exchange device 45 was stable. The salt rejection rate (%) was calculated by (1 - outlet water conductivity of ion exchange device 45 / inlet water conductivity of ion exchange device 45) x 100. The conductivity and salt rejection rates of the inlet water and outlet water of the ion exchange device 45 were within the expected range, and it was confirmed that the first conductivity meter C11' and second conductivity meter C12' were operating normally. [Explanation of symbols]

[0037] 1A,1B Ultrapure water production equipment 14. Ultraviolet oxidation equipment 16 Membrane degassing device 18 Ultrafiltration Membrane Device 21 Hydroelectric power generation equipment 22 Waterwheel 23 Generator 24 Storage battery 25 External power supply L1 main tube L2 Return Line L5 bypass line M Electrically operated machine POU Use Point V2 Back pressure control valve V3 flow control valve

Claims

1. at least one water treatment device for producing ultrapure water; a header pipe provided with the at least one water treatment device and connected to a use point to supply the ultrapure water to the use point; a return line for returning the ultrapure water not used at the point of use to the mother pipe; at least one hydroelectric power generating device provided in the return line; a bypass line bypassing the at least one hydroelectric power plant; a back pressure control valve provided in the bypass line; An ultrapure water production apparatus having:

2. 2. The ultrapure water producing system according to claim 1, further comprising a pump provided in said mother pipe, said pump being controlled so that the pressure of said ultrapure water at said point of use falls within a predetermined range.

3. 3. The ultrapure water production system according to claim 1, further comprising an electrically operated machine that operates on the electricity generated by said at least one hydroelectric power generation device.

4. 4. The ultrapure water production system according to claim 3, wherein the electrically operated machine operates on power supplied from the at least one hydroelectric power generation device and operates on an external power source when the power supply from the at least one hydroelectric power generation device fails.

5. 4. The ultrapure water production system according to claim 3, wherein the electrically operated machine is powered by an external power source and is powered by electricity supplied from the at least one hydroelectric power generation device when a power supply failure occurs from the external power source.

6. It has a storage battery, 4. The ultrapure water production system according to claim 3, wherein the electrically operated machine is operated by the electric power generated by the at least one hydroelectric power generation device and is operated by the storage battery when the power supply from the at least one hydroelectric power generation device is abnormal.

7. It has a storage battery, 4. The ultrapure water production system according to claim 3, wherein the electrically operated machine is powered by the storage battery and is powered by the electric power generated by the at least one hydroelectric power generation device when the power supply from the storage battery is abnormal.

8. 8. The ultrapure water manufacturing apparatus according to claim 1, further comprising a flow control valve provided in the return line between the branching portion of the bypass line and the at least one hydroelectric power generation unit, for controlling the flow rate of the ultrapure water supplied to the at least one hydroelectric power generation unit.

9. 9. The ultrapure water production system according to claim 1, further comprising an ultrafiltration membrane device provided in the main pipe, and wherein the at least one hydroelectric power generation device is driven by concentrated water from the ultrafiltration membrane device.

10. Producing ultrapure water by at least one water treatment device provided in the header pipe; supplying the ultrapure water produced by the at least one water treatment device from the header pipe to a point of use; returning the ultrapure water not used at the point of use to the main pipe through a return line provided with at least one hydroelectric power generating device and connected to the main pipe; generating electricity with the at least one hydroelectric power generation device while supplying a portion of the ultrapure water to a bypass line that bypasses the at least one hydroelectric power generation device and is provided with a back pressure control valve.

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