Control method for a pure water production system

Abstract

This invention provides a control method for a pure water production system that can control the total water supply volume of the entire system, particularly one with multiple tanks, according to the amount of water used. [Solution] The pure water production system 3 includes a filtration tank 301, a water supply pump 305A equipped with a pump inverter 305B, and water treatment equipment, and primary pure water W2 can be stored in a sub-tank 41. Downstream of the water treatment equipment, a pressure gauge 311 for the primary pure water W2 and a level-sensing control valve 312 are provided. A water level gauge 313 is provided in the sub-tank 41. Furthermore, a circulation line 314 is provided upstream of the level-sensing control valve 312, and a pressure-sensing control valve 315 is provided in this circulation line 314. The pump inverter 305B, the level-sensing control valve 312, and the pressure-sensing control valve 315 are controlled according to the amount of primary pure water W2 supplied to the sub-tank 41.

Description

[Technical Field]

[0001] The present invention relates to a control method for a pure water production system for producing ultrapure water used in the electronics industry, such as semiconductors and liquid crystals, and more particularly to a control method for a pure water production system that can control the water supply amount according to the amount of water used. [Background technology]

[0002] Traditionally, ultrapure water used in the electronics industry, such as semiconductors, is produced by treating raw water in an ultrapure water production system that consists of a pretreatment system, a primary pure water system, and a subsystem for processing the primary pure water.

[0003] For example, as shown in Figure 1, the ultrapure water production system 1 consists of three stages: a pretreatment device 2, a primary pure water device (pure water production system) 3, and a secondary pure water production device (subsystem) 4 as a pure water usage device. In the pretreatment device 2 of such an ultrapure water production system 1, the raw water W is pretreated by filtration, coagulation and sedimentation, and microfiltration membranes, mainly to remove suspended solids.

[0004] The primary pure water system 3 includes, for example, a water tank 31 for storing pre-treated water (water to be treated) W1, a high-pressure pump 32 for supplying the pre-treated water W1, a reverse osmosis membrane device 33, a membrane degasser 34 for removing dissolved gases, an ultraviolet oxidation device 35, and an electrodeionizer 36. This primary pure water system 3 removes most of the electrolytes, fine particles, live bacteria, etc. from the pre-treated water W1 and decomposes organic matter.

[0005] Subsystem 4 consists of a sub-tank 41, which serves as a pure water tank located downstream of the electrodeionizer that stores the primary pure water W2 produced by the primary pure water system 3; an ultraviolet oxidation system 42, a non-regenerative mixed-bed ion exchange system 43, and an ultrafiltration (UF) membrane 44 as a membrane filtration system, which process the primary pure water W2 supplied from the sub-tank 41 via a pump (not shown); and an RO membrane separation system, etc., may also be provided as needed. In this subsystem 4, the ultraviolet oxidation system 42 oxidizes and decomposes trace amounts of organic matter (TOC components) contained in the primary pure water W2, and then the non-regenerative mixed-bed ion exchange system 43 processes it to remove residual carbonate ions, organic acids, anionic substances, and even metal ions and cationic substances by ion exchange. Then, the ultrafiltration (UF) membrane 44 removes fine particles to produce ultrapure water W3, which is supplied to the use point 5, and the unused ultrapure water is returned to the sub-tank 41.

[0006] In this ultrapure water production system 1, in order to stably supply primary pure water of a predetermined quality, an excess amount of primary pure water W2 was produced in advance, and only the necessary amount was supplied to the sub-tank 41, with the surplus being recycled and reused.

[0007] However, with the conventional control method of the ultrapure water production system 1 described above, more water than necessary is supplied to the electrodeionizer 36 and other devices for processing, so there is room for improvement in terms of energy efficiency.Therefore, it is conceivable to vary the processing amount of the primary pure water device 3 in accordance with the amount used at use point 5, but this is not only difficult to keep up with the fluctuations in the amount used at use point 5, but it also leads to a decrease in the quality of the desalinated water produced by electrodeionization.

[0008] Therefore, as a control method for an ultrapure water production system capable of producing primary pure water according to the amount used at the point of use, the applicant has filed a patent application for a control method for an ultrapure water production system comprising a primary pure water system having a reverse osmosis membrane, an electrodeionizer, and a water supply pump provided upstream of the electrodeionizer, a water storage tank (sub-tank) equipped with a water level measuring means located downstream of the electrodeionizer, and a subsystem for further processing the primary pure water produced by the primary pure water system, wherein the method involves inverter-controlled control of the pump supplied by the electrodeionizer so as to maintain the water level in the water storage tank, as measured by the water level measuring means, at a substantially constant level (Patent Document 1).

[0009] Furthermore, the applicant has proposed a control method for a pure water production system as shown in Figure 4 (Japanese Patent Application No. 2023-033118). In Figure 4, the pure water production system includes a water tank 51 for storing pre-treated water W1, a water supply pump 52A for the pre-treated water W1, an inverter-controllable high-pressure pump 52B for controlling the water supply output of the water supply pump 52A, water treatment equipment (not shown), and a pressure gauge 58, which then branches into two lines, each of which is equipped with control valves 59A and 59B, sub-tanks 60A and 60B, and water level gauges 61A and 61B. Reference values ​​for the water levels of sub-tanks 60A and 60B are predetermined, and when the amount of water used at each use point decreases and the measured water levels of water level gauges 60A and 60B rise above these reference values, a control means (not shown) throttles the control valves 59A and 59B, respectively, to reduce the amount of water supplied to sub-tanks 60A and 60B. As a result, the total amount of water supplied by both decreases, causing the water supply pressure at the pressure gauge 58 to rise. Therefore, the control means reduces the output of the high-pressure pump 52B by inverter control so that the measured value of the pressure gauge 58 remains approximately constant with respect to a predetermined value, based on the measurement value of the pressure gauge 58. On the other hand, if the amount of water used at each use point increases and the measured water levels of sub-tanks 60A and 60B fall below this reference value, the control means (not shown) opens the control valves 59A and 59B, respectively, to increase the amount of water supplied to sub-tanks 60A and 60B. As a result, the total amount of water supplied by both increases, causing the water supply pressure at the pressure gauge 58 to decrease. Therefore, the control means increases the output of the high-pressure pump 52B by inverter control so that the measured value of the pressure gauge 58 remains approximately constant with respect to a predetermined value, based on the measurement value of the pressure gauge 58. This reduces the amount of excess water supplied. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Patent No. 6863510 [Overview of the Initiative] [Problems that the invention aims to solve]

[0011] However, the control method for the ultrapure water production system described in Patent Document 1 has the problem that control becomes complicated when there are multiple storage tanks, such as when there are multiple use points or when there are multiple subsystems, such as in large ultrapure water production systems. Furthermore, a control method for a pure water production system that can supply water to subsystems more reliably with simpler control would be desirable in terms of controlling an ultrapure water production system.

[0012] Furthermore, in the control method for the ultrapure water production system described in Japanese Patent Application No. 2023-033118, when the pump is controlled by an inverter, the range in which the inverter can efficiently control the system is a predetermined range (for example, around 20-50 Hz), and upper and lower limits are set within this range. While control is possible as long as the flow rate fluctuates within this range, if the amount of water used falls below the amount of water supplied at the lower limit of the inverter control frequency, the adjustment by the pump inverter is insufficient, and the pressure in the system rises. As a countermeasure, it becomes necessary to stop the control by the pump inverter and release some of the water to the upstream tank via the circulation line (return line to the upstream tank). However, in this case, since it is difficult to set a trigger to resume operation that fluctuates the flow rate using only the pump inverter and pressure control, manual verification becomes necessary for recovery, which presents a problem.

[0013] This invention has been made in view of the above problems, and aims to provide a control method for a pure water production system that can control the amount of water supplied according to the amount of water used. [Means for solving the problem]

[0014] In view of the above objectives, the present invention provides a control method for a pure water production system comprising a water supply source, a water supply pump connected to the water supply source, a pressure gauge provided downstream of the water supply pump, and water treatment equipment provided between the water supply pump and the pressure gauge, for supplying pure water produced in the pure water production system from a pure water supply path to pure water using equipment downstream of the pressure gauge, wherein the control method includes a first flow rate adjustment mechanism between the pressure gauge and the pure water using equipment for adjusting the flow rate of pure water supplied to the pure water using equipment, and the amount of pure water supplied by the first flow rate adjustment mechanism is adjusted according to the amount of water used by the pure water using equipment, and The invention provides a control method for a pure water production system (Invention 1), in which the water supply pump is controlled by a pump inverter so that the water supply output of the water supply pump is substantially constant, while when the amount of water used by the pure water-using equipment falls below the lower limit of an arbitrary set range of the water supply output of the water supply pump by the pump inverter, the water supply output of the water supply pump by the pump inverter is fixed to a fixed value, and the flow rate of a circulation line having a second flow rate control means installed upstream of the pure water-using equipment in the pure water supply path is controlled by the second flow rate control means so that the measured value of the pressure gauge is substantially constant.

[0015] According to this invention (Invention 1), the first flow rate adjustment mechanism controls the amount of pure water supplied to the equipment using pure water in accordance with the increase or decrease in the amount of pure water used. As the supply pressure increases or decreases with this increase or decrease in supply, the water supply output of the water supply mechanism can be controlled so that the water supply pressure remains approximately constant relative to a predetermined value, thereby enabling independent control of the pure water supply and the output of the water supply mechanism. This makes it possible to achieve simple and highly versatile control. Furthermore, even if the amount of pure water supplied to the equipment using pure water falls below the lower limit of an arbitrary setting range of the water supply output of the water supply pump controlled by the pump inverter (for example, the water supply output at the lowest frequency of the pump inverter), the flow rate of the circulation line can be adjusted accordingly by the second flow rate adjustment mechanism, making it possible to operate the system even when there are very large fluctuations in the amount of pure water used.

[0016] In the above invention (Invention 1), a pure water tank for storing pure water supplied to the pure water-using equipment is provided between the latter stage of the pressure gauge and the former stage of the pure water-using equipment, and a first flow control mechanism is provided in the pure water supply line between the latter stage of the pressure gauge and the former stage of the pure water tank, and it is preferable to control the flow rate by the first flow control mechanism according to the water level of the pure water tank (Invention 2).

[0017] According to such an invention (Invention 2), by controlling the first flow adjustment mechanism so as to increase or decrease the supply amount of pure water according to the water level of the pure water tank, it is possible to realize simple and highly versatile control. Further, even when the supply amount of pure water to the pure water-using equipment falls below the lower limit value of an arbitrary setting range of the water supply output of the water supply pump by the pump inverter (for example, the water supply output by the lowest frequency of the pump inverter), by adjusting the flow rate of the circulation line by the second flow adjustment mechanism, it is possible to carry out an operation corresponding to a case where the variation in the amount of pure water used is very large.

[0018] In the above invention (Invention 2), it is preferable that the water treatment equipment is one or more selected from a reverse osmosis membrane, an ultraviolet oxidation device, a degassing membrane, an electro-deionization device, a regenerative ion exchange device, and a non-regenerative ion exchange device (Invention 3).

[0019] According to such an invention (Invention 3), it becomes possible to apply it to various general-purpose primary pure water devices.

[0020] In the above invention (Invention 3), it is preferable that there are two or more types of the water treatment equipment, there is one water supply pump for controlling the water supply output by the pump inverter, the water treatment equipment is in one series, and the pressure gauge is provided at the latter stage of any one of the two or more types of water treatment equipment (Invention 4).

[0021] According to such an invention (Invention 4), when there is one series of water treatment equipment, by providing a pressure gauge after any of the water treatment equipment, the flow rate adjustment mechanism is controlled so as to increase or decrease the supply amount of pure water according to the water level of the pure water tank, it becomes possible to realize simple and highly versatile control.

[0022] In the above invention (Invention 1), it is possible to switch to a constant flow rate operation in which the water supply output of the water supply pump is kept constant and the control by the second flow rate adjustment mechanism is performed so that the pressure of the pressure gauge becomes substantially constant according to the amount of pure water used by the pure water using equipment (Invention 5).

[0023] According to such an invention (Invention 5), it is possible to supply pure water corresponding to a wider range of pure water usage situations.

[0024] In the above invention (Invention 2), the water treatment equipment that controls the water supply output by the pump inverter is in a plurality of series, and an operation can be performed in which the supply amount of pure water based on the amount of pure water used by the pure water using equipment is varied for the remaining series in a state where one of the plurality of series of water treatment equipment is stopped (Invention 6).

[0025] According to such an invention (Invention 6), even in the control by the first flow rate adjustment mechanism that supplies pure water to a plurality of series, the water supply pressure decreases or increases according to the increase or decrease of the supply amount of pure water. However, even in a state where one series is stopped due to maintenance or the like, by controlling the water supply output of the water supply mechanism so that the water supply pressure for the remaining series becomes substantially constant with respect to a predetermined value, it is possible to make the control of the supply of pure water and the control of the output of the water supply mechanism independent. Also, even when the supply amount of pure water to the pure water using equipment falls below the lower limit value of an arbitrary setting range of the water supply output of the water supply pump by the pump inverter (for example, the water supply output by the minimum frequency of the pump inverter), by adjusting the flow rate of the circulation line by the second flow rate adjustment mechanism, it becomes possible to perform an operation corresponding to a very large variation in the amount of pure water used.

Advantages of the Invention

[0026] According to the present invention, even if the amount of water used by the pure water-using equipment falls below the lower limit of the arbitrary settable range of the water supply output of the water supply pump by the pump inverter, the operating output of the pump is fixed, and the flow rate of the circulation line having a second flow rate control means installed upstream of the pure water-using equipment in the pure water supply path is controlled so that the measured value of the pressure gauge becomes approximately constant, thereby enabling operation that can handle even when the amount of pure water used fluctuates greatly. [Brief explanation of the drawing]

[0027] [Figure 1] This is a flowchart showing an ultrapure water production system to which the control method for the pure water production system of the present invention can be applied. [Figure 2] This is a flow diagram showing a pure water production system (primary pure water device) to which the control method for a pure water production system according to the first embodiment of the present invention can be applied. [Figure 3] This is a flow diagram showing a pure water production system (primary pure water device) to which the control method for a pure water production system according to the second embodiment of the present invention can be applied. [Figure 4] This is a schematic diagram illustrating the control method of a conventional pure water production system. [Modes for carrying out the invention]

[0028] The control method for the pure water production system of the present invention will be described below with reference to the attached drawings.

[0029] [First Embodiment] (Pure water production system) This embodiment is characterized by its control of the pure water production system (primary pure water system) that constitutes the ultrapure water production system.

[0030] There are no particular restrictions on the pure water production system (primary pure water system). Various pure water production systems can be applied as long as they include a water supply pump for supplying water to be treated, a pressure gauge installed downstream of the water supply pump, and a pure water tank installed downstream of the pressure gauge for storing the produced pure water, with one or more types of water treatment equipment installed between the water supply pump and the pressure gauge. For example, it can be suitably applied to the pure water production system shown in Figure 2.

[0031] In Figure 2, the primary pure water system (pure water production system) 3 comprises a filtration tank 301 as a water supply source for storing pre-treated water W1, a water supply pump 302 for supplying the pre-treated water W1, a cooler 303 located downstream of the water supply pump 302, a safety filter 304, a water supply pump 305A equipped with a pump inverter 305B for controlling the water supply output, a first reverse osmosis membrane device 306, a second reverse osmosis membrane device 307, a membrane degasser 308, and an electrodeionizer (CDI) 309. The treated water (primary pure water) W2 from the electrodeionizer 309 can be stored in a sub-tank 41 connected to a subsystem that uses pure water. In this embodiment, the water treatment equipment is composed of four elements: the first reverse osmosis membrane device 306, the second reverse osmosis membrane device 307, the membrane degasser 308, and the electrodeionizer 309.

[0032] In this primary pure water system 3, a pressure gauge 311 for treated water and a level-sensing control valve 312 as a first flow rate adjustment mechanism are provided downstream of the electrodeionizer 309, and a water level gauge 313 is provided in the sub-tank 41. These pressure gauge 311 and water level gauge 313 can transmit information to a control mechanism (not shown), and the control mechanism can control the water supply pump 305A by the frequency of the pump inverter 305B so that the value measured by the pressure gauge 311 is approximately constant (for example, ±5%) to a predetermined value, and can also control the opening degree of the level-sensing control valve 312 based on the value measured by the water level gauge 313. Furthermore, a circulation line 314 is provided downstream of the pressure gauge 311 and upstream of the level-sensing control valve 312, which is connected to the filtration tank 301. This circulation line 314 is equipped with a pressure-sensing control valve 315 as a second flow rate adjustment mechanism, and the opening degree of the pressure-sensing control valve 315 can be controlled based on the measurement value of the pressure gauge 311.

[0033] 321 is the concentrated water recovery line for the first reverse osmosis membrane device 306. This recovery line 321 is equipped with a flow meter 322, a flow control valve 323, and a recovered water tank 324. The flow rate of the concentrated water is restricted so that the measurement value of the flow meter 322 reaches a predetermined value, and the water is stored in the recovered water tank 324. The concentrated water from the first reverse osmosis membrane device 306 is reused after undergoing necessary processing, such as by returning it to the filtration tank 301. 331 is the concentrated water recovery line for the second reverse osmosis membrane device 307, and 334 is the concentrated water recovery line for the electrodeionizer 309. These lines merge into the recovery circulation line 340 and are returned to the filtration tank 301. The recovery line 331 is equipped with a flow meter 332 and a flow control valve 333, and the flow rate of the concentrated water from the second reverse osmosis membrane device 307 is restricted so that the measurement value of the flow meter 332 reaches a predetermined value.

[0034] (Control method for a pure water production system) Next, we will explain the control method for the pure water production system shown in Figure 2. The water supply pump 302 is started to supply pre-treated water (water to be treated) W1 from the filtration tank 301. This pre-treated water W1 passes through the cooler 303 and the safety filter 304, and is then supplied to the downstream water treatment equipment by the water supply pump 305A equipped with a pump inverter 305B. The pure water (primary pure water) W2 produced by sequentially treating it in the first reverse osmosis membrane device 306, the second reverse osmosis membrane device 307, the membrane deaeration device 308, and the electrodeionization device (CDI) 309 is stored in the sub-tank 41. The required amount of primary pure water W2 stored in the sub-tank 41 is then supplied to the use point (not shown).

[0035] In the water production process using the primary pure water system 3 described above, the sub-tank 41 is equipped with a water level gauge 313, which can be controlled as follows. First, a reference value for the water level of the sub-tank 41 (which may be a value within a predetermined range) is set in advance. Also, the pressure-sensing control valve 315 installed in the circulation line 314 is set to be completely closed, or closed to a lower design opening that allows only a very small amount of primary pure water W2 to flow. Then, when the amount of primary pure water W2 used at the point of use decreases and the measured water level of the water level gauge 313 rises above this reference value, the control means (not shown) throttles the level-sensing control valve 312 to reduce the amount of water supplied to the sub-tank 41. As a result, the amount of water supplied to the sub-tank 41 decreases, and the water supply pressure of the pressure gauge 311 rises. Based on this measured value of the pressure gauge 311, the control means reduces the output of the water supply pump 305A by controlling the frequency of the pump inverter 305B so that the measured value of the pressure gauge 311 becomes approximately constant relative to a predetermined value. On the other hand, if the amount of primary pure water W2 used at the point of use increases and the measured water level in the sub-tank 41 falls below this reference value, the control means (not shown) opens the level-sensing control valve 312 to increase the amount of water supplied to the sub-tank 41. As a result, the amount of water supplied increases, and the water supply pressure on the pressure gauge 311 decreases. Therefore, the output of the water supply pump 305A is increased by controlling the frequency of the pump inverter 305B so that the measured value on the pressure gauge 311 becomes approximately constant relative to a predetermined value. At this time, the flow control valves 323 and 333 should be PID controlled based on the measured values ​​of the flow meters 322 and 332 so that the amount of concentrated water in the first reverse osmosis membrane device 306 and the second reverse osmosis membrane device 307 remains constant.

[0036] However, with frequency control of the pump inverter 305B, the maximum discharge rate of the water supply pump 305A can only be controlled to about 50-60%. Therefore, if the amount of pure water used at the point of use falls below the lower limit of the arbitrary settable range of the water supply output of the water supply pump 305A controlled by the pump inverter 305B (for example, the water supply output at the lowest frequency of the pump inverter), the control described above will not be able to keep up. Therefore, when the frequency of the pump inverter 305B falls below a predetermined value (for example, the lowest frequency of the pump inverter 305B), the frequency control of the pump inverter 305B by the pressure gauge 311 is stopped, and the frequency of the pump inverter 305B is fixed at a constant value (for example, the lowest frequency) to operate at a constant flow rate. Meanwhile, the water level in the sub-tank 41 is maintained at a predetermined reference water level by the level-sensing control valve 312 in a restricted state. As a result, the measured value of the pressure gauge 311 tends to rise relative to a predetermined value. However, in this embodiment, the opening degree of the pressure-sensing control valve 315 installed in the circulation line 314 is controlled by PID control so that the measured value of the pressure gauge 311 remains approximately constant relative to a predetermined value.

[0037] Then, if the usage of the use point increases again and water supply is required that exceeds the lower limit of the arbitrary set range of the water supply output of the water supply pump 305A controlled by the pump inverter 305B, the control of the opening degree of the pressure-sensing control valve 315 by the pressure gauge 311 is stopped, and the pressure-sensing control valve 315 is returned to a state where it is completely closed or closed to the lower limit design opening degree, allowing only a very small amount of primary pure water W2 to flow. Then, the frequency control of the pump inverter 305B by the pressure gauge 311 can be resumed.

[0038] By switching in accordance with fluctuations in water usage at the point of use, even if the amount of pure water used at the point of use falls below the lower limit of the frequency control of the pump inverter 305B, the production of primary pure water W2 can be continued without stopping the water treatment equipment.

[0039] [Second Embodiment] (Pure water production system) As shown in Figure 3, the pure water production system 3 of this embodiment has the same configuration as the first embodiment described above, except that it has three series of water treatment equipment (composed of a first reverse osmosis membrane device 306, a second reverse osmosis membrane device 307, a membrane degasser 308, and an electrodeionizer 309) 300A, 300B, and 300C. The pressure gauge 311 is installed downstream of the point where the treated water from the three series of water treatment equipment 300A, 300B, and 300C converge.

[0040] (Control method for a pure water production system) Next, the control method for the pure water production system of the second embodiment will be described. The control method for the pure water production system in the second embodiment is basically the same as that of the first embodiment described above.

[0041] Specifically, in Figure 3, the water supply pump 302 is started to supply pre-treated water (water to be treated) W1 from the filtration tank 301. This pre-treated water W1 passes through the cooler 303 and the safety filter 304, and is then supplied to the downstream water treatment equipment 300A, 300B, and 300C respectively by the water supply pump 305A equipped with a pump inverter 305B. The primary pure water (pure water) W2 produced by these water treatment equipment then merges with the pre-treated water W1 and is stored in the sub-tank 41. The required amount of primary pure water W2 stored in the sub-tank 41 is then supplied to the use point (not shown).

[0042] In the water production process using the primary pure water system 3 described above, the sub-tank 41 is equipped with a water level gauge 313, which can be controlled as follows. First, a reference value for the water level of the sub-tank 41 (which may be a value within a predetermined range) is set in advance. Also, the pressure-sensing control valve 315 installed in the circulation line 314 is set to be completely closed, or closed to a lower design opening that allows only a very small amount of primary pure water W2 to flow. Then, when the amount of primary pure water W2 used at the point of use decreases and the measured water level of the water level gauge 313 rises above this reference value, the control means (not shown) throttles the level-sensing control valve 312 to reduce the amount of water supplied to the sub-tank 41. As a result, the amount of water supplied to the sub-tank 41 decreases, and the water supply pressure of the pressure gauge 311 rises. Based on this measured value of the pressure gauge 311, the control means reduces the output of the water supply pump 305A by controlling the frequency of the pump inverter 305B so that the measured value of the pressure gauge 311 becomes approximately constant relative to a predetermined value. On the other hand, if the amount of primary pure water W2 used at the point of use increases and the measured water level in the sub-tank 41 falls below this reference value, the control means (not shown) opens the level-sensing control valve 312 to increase the amount of water supplied to the sub-tank 41. As a result, the amount of water supplied increases, and the water supply pressure on the pressure gauge 311 decreases. Therefore, the output of the water supply pump 305A is increased by controlling the frequency of the pump inverter 305B so that the measured value on the pressure gauge 311 becomes approximately constant relative to a predetermined value. At this time, the flow control valves 323 and 333 should be PID controlled based on the measured values ​​of the flow meters 322 and 332 so that the amount of concentrated water in the first reverse osmosis membrane device 306 and the second reverse osmosis membrane device 307 remains constant.

[0043] However, the frequency-based control of the pump inverter 305B can only control the maximum discharge rate of the water supply pump 305A to about 50-60%. Therefore, if the amount of pure water used at the point of use falls below the lower limit of the arbitrary settable range of the water supply output of the water supply pump 305A controlled by the pump inverter 305B (for example, the water supply output at the lowest frequency of the pump inverter), the control described above will not be able to keep up. Therefore, when the frequency of the pump inverter 305B falls below a predetermined value (for example, the lowest frequency), the frequency-based control of the pump inverter 305B by the pressure gauge 311 is stopped, and the frequency of the pump inverter 305B is fixed at a constant value (for example, the lowest value) to operate at a constant flow rate. Meanwhile, the water level in the sub-tank 41 is maintained at a predetermined reference water level by the level-sensing control valve 312 in a restricted state. As a result, the measured value of the pressure gauge 311 tends to rise relative to a predetermined value. However, in this embodiment, the opening degree of the pressure-sensing control valve 315 installed in the circulation line 314 is controlled by PID control so that the measured value of the pressure gauge 311 remains approximately constant relative to a predetermined value.

[0044] Then, if the usage of the use point increases again and water supply is required that exceeds the lower limit of the arbitrary set range of the water supply output of the water supply pump 305A controlled by the pump inverter 305B, the control of the opening degree of the pressure-sensing control valve 315 by the pressure gauge 311 is stopped, and the pressure-sensing control valve 315 is returned to a state where it is completely closed or closed to the lower limit design opening degree, allowing only a very small amount of primary pure water W2 to flow. Then, the frequency control of the pump inverter 305B by the pressure gauge 311 can be resumed.

[0045] Even when multiple water treatment devices are arranged in parallel, they can be controlled in the same manner. However, in this case, the pressure gauge 311 needs to be positioned further down the chain than the confluence point of the treated water (primary pure water) W2 from the multiple water treatment devices 300A, 300B, and 300C. In this embodiment, when multiple water treatment devices are arranged in parallel, it is not necessary for all chains to be in operation. When one or more of the multiple water treatment devices are stopped for maintenance, the remaining chains may be operated by varying the supply amount of pure water based on the amount of pure water used by the pure water-using devices. Alternatively, the water supply output of the water supply pump 305A may be kept constant, and a constant flow rate operation may be used in conjunction with the control of the pressure-sensing control valve 315 so that the pressure on the pressure gauge 311 remains approximately constant according to the amount of pure water used by the pure water-using devices.

[0046] Although the present invention has been described above based on the embodiments described above, the present invention is not limited to the embodiments described above, and various modifications are possible. For example, the elements constituting the water treatment equipment can be selected in various ways as desired, and one or more types such as reverse osmosis membranes, ultraviolet oxidation devices, degassing membranes, electrodeionizers, regenerative ion exchange devices, and non-regenerative ion exchange devices can be used. [Examples]

[0047] The present invention will be described more specifically below based on examples, but the present invention is not limited to the following examples.

[0048] [Example 1] Using the pure water production system 3 shown in Figure 3, the amount of pure water used at the point of use (POU) is 45-9 m³. 3 The flow rate is varied to / h, and the output of the water supply pump 305A is controlled by the pump inverter 305B from 100% to 60%, with a pure water usage of 45m³. 3 / h to 27m 3 / h as the first condition (Example 1-1), 27m 3 / h less than 9m 3Taking / h as the second condition (Example 1-1), the operation of the pure water production system was carried out through the following steps, and the pure water usage amount (required water amount) of the POU, the water production amount of pure water W2, and the water amount in the circulation line 314 were measured. The results are shown in Table 1.

[0049] (First operating condition) The pure water usage amount of the POU was 45 m 3 / h. With the output of the pump inverter 305B set to 100%, 45 m 3 / h of the raw water W1 was supplied from the water supply pump 305A to operate the pure water production system 3. At this time, since the followability of the pressure sensing control valve 315 deteriorated when it was fully closed, the pressure sensing control valve 315 was slightly opened to always ensure a negligible flow rate.

[0050] The pure water usage amount of the POU was gradually reduced to 27 m 3 / h. When the water level gauge 313 detected that the level of the sub-tank 41 became higher than a predetermined value, the level sensing control valve 312 was controlled to throttle. As a result, the value of the pressure gauge 311 increased, so the frequency of the pump inverter 305B was decreased to maintain the value of the pressure gauge 311 almost constant. Then, the control of the output of the water supply pump 305A by the pump inverter 305B was adjusted to the lower limit value within the arbitrary setting range of the water supply output of the water supply pump 305A by the pump inverter 305B (here, the lower limit value by the minimum frequency of the inverter: 27 m 3 / h) until the control by this level sensing control valve 312 was maintained.

[0051] (Second operating condition) When the pure water usage amount of the POU became less than 27 m 3 / h, the frequency of the pump inverter 305B was held at the minimum value and the control was switched to that by the pressure sensing control valve 315. Then, the pure water usage amount of the POU was adjusted to 9 m 3The flow rate was gradually reduced to / h, and when the water level gauge 313 detected that the level of the sub-tank 41 had risen above a predetermined value, the level-sensing control valve 312 was controlled to throttle. As a result, the value on the pressure gauge 311 rose, but the pressure-sensing control valve 315 was controlled to open, increasing the flow rate to the circulation line 314 and keeping the value on the pressure gauge 311 nearly constant.

[0052] [Comparative Example 1] Using the pure water production system 3 shown in Figure 3, the pure water usage of POU is 45-9 m³. 3 The output of the 305A water supply pump is set to 45m / h, and the output is set to 45m / h. 3 The system was operated using a fixed rate of / h, following the steps outlined below, and the amount of pure water used by the POU (required water volume), the amount of pure water produced by W2, and the water volume in the circulation line 314 were measured. The results are shown in Table 1.

[0053] (Driving conditions) POU's pure water usage: 45m³ 3 At / h, assuming the output of the water supply pump 305A is 100% via the pump inverter 305B, the water supply pump 305A is connected to 45m 3 The pure water production system 3 was operated by supplying the water to be treated W1 at a rate of / h.

[0054] POU's pure water usage is 9m³ 3 The flow rate was gradually reduced to / h, and when the water level gauge 313 detected that the level in the sub-tank 41 had risen above a predetermined value, the level-sensing control valve 312 was controlled to throttle. As a result, the reading on the pressure gauge 311 rose, so the flow rate to the circulation line 314 was increased to maintain the reading on the pressure gauge 311 at a nearly constant level.

[0055] [Table 1]

[0056] As is clear from Table 1, the control in Example 1 can significantly reduce the amount of water flowing into the circulation line 314. [Explanation of Symbols]

[0057] 1. Ultrapure water production system 2 Pre-treatment device 3. Primary pure water system (pure water production system) 4. Secondary pure water production system (subsystem) 5 Youth Points 300A, 300B, 300C Water Treatment Equipment 301 Filtration tank (source of treated water) 305A Water supply pump 305B Pump Inverter 306 First reverse osmosis membrane apparatus (water treatment equipment) 307 Second reverse osmosis membrane system (water treatment equipment) 308 Membrane-type degassing equipment (water treatment equipment) 309 Electrodeionizer (CDI) (Water Treatment Equipment) 311 Pressure Gauge 312 Level-sensing control valve (first flow rate adjustment mechanism) 313 Water level gauge 314 Circulation Line 315 Pressure-sensing control valve (second flow rate adjustment mechanism) W Raw Water W1 Pre-treated water (water to be treated) W2 Primary pure water (pure water) W3 Secondary pure water (ultra pure water)

Claims

1. A control method for a pure water production system comprising a water supply source, a water supply pump connected to the water supply source, a pressure gauge installed downstream of the water supply pump, and water treatment equipment installed between the water supply pump and the pressure gauge, wherein pure water produced by the pure water production system is supplied from a pure water supply path to pure water using equipment downstream of the pressure gauge, Between the pressure gauge and the pure water-using equipment, there is a first flow rate adjustment mechanism for adjusting the flow rate of pure water supplied to the pure water-using equipment, and the amount of pure water supplied is adjusted by the first flow rate adjustment mechanism according to the amount of water used by the pure water-using equipment, and the water supply pump is controlled by a pump inverter so that the water supply output of the water supply pump is approximately constant as the measured value of the pressure gauge, A control method for a pure water production system, wherein when the amount of water used by the pure water-using equipment falls below the lower limit of an arbitrary settable range of the water supply output of the water supply pump by the pump inverter, the water supply output of the water supply pump by the pump inverter is fixed to a fixed value, and the flow rate of the circulation line having a second flow rate control means installed upstream of the pure water-using equipment in the pure water supply path is controlled by the second flow rate control means so that the measured value of the pressure gauge becomes approximately constant.

2. A control method for a pure water production system according to claim 1, wherein the system has a pure water tank for storing pure water to be supplied to the pure water-using equipment, located downstream of the pressure gauge and upstream of the pure water-using equipment, and a first flow rate control mechanism is provided in the pure water supply path, located downstream of the pressure gauge and upstream of the pure water tank, and the flow rate is controlled by the first flow rate control mechanism according to the water level in the pure water tank.

3. A control method for a pure water production system according to claim 2, wherein the water treatment equipment is one or more selected from a reverse osmosis membrane, an ultraviolet oxidation device, a degassing membrane, an electrodeionizer, a regenerative ion exchange device, and a non-regenerative ion exchange device.

4. The control method for a pure water production system according to claim 3, wherein there are two or more types of water treatment equipment, the number of water supply pumps controlling the water supply output by the pump inverter and the number of water treatment equipment are in one series, and the pressure gauge is provided downstream of any of the two or more types of water treatment equipment.

5. The control method for a pure water production system according to claim 1, wherein the water supply output of the water supply pump is kept constant, and the system switches to constant flow rate operation, in which a second flow rate adjustment mechanism controls the pressure of the pressure gauge to be substantially constant according to the amount of pure water used by the pure water equipment.

6. The control method for a pure water production system according to claim 2, wherein there are multiple series of water treatment equipment whose water supply output is controlled by the pump inverter, and with one of the multiple series of water treatment equipment stopped, the remaining series are operated in such a way that the amount of pure water supplied is varied based on the amount of pure water used by the pure water equipment.

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