Control method for pure water production system

Abstract

A pure water production system 3 has a filtered water tank 301, a water supply pump 305A provided with a pump inverter 305B, and a water treatment apparatus, wherein primary pure water W2 can be stored in a sub tank 41. A pressure gauge 311 for the primary pure water W2 and a level sensing-type control valve 312 are provided at the rear stage of the water treatment apparatus. The sub-tank 41 is provided with a water level gauge 313. A circulation line 314 is provided in the front stage of the level sensing-type control valve 312, and a pressure sensing-type control valve 315 is provided in the circulation line 314. The pump inverter 305B, the level sensing-type control valve 312, and the pressure sensing-type control valve 315 are controlled in accordance with the supply amount of the primary pure water W2 to the sub-tank 41. Such a control method for a pure water production system makes it possible to control the amount of water supply of the entire system, particularly one having a plurality of tanks, in accordance with the amount of water usage.

Description

Control method for pure water production system

[0001] The present invention relates to a method for controlling a pure water production system for producing ultrapure water used in the electronics industry, such as semiconductors and liquid crystal displays, and more particularly to a method for controlling a pure water production system capable of controlling the amount of water supply according to the amount of water used.

[0002] Conventionally, ultrapure water used in the semiconductor and other electronics industries is produced by treating raw water in an ultrapure water production system that is composed of a pretreatment system, a primary pure water equipment, and a subsystem that treats the primary pure water.

[0003] 1, an ultrapure water production system 1 is composed of three stages of equipment: a pretreatment device 2, a primary pure water production system (pure water production system) 3, and a secondary pure water production system (subsystem) 4, which uses pure water. In the pretreatment device 2 of this ultrapure water production system 1, raw water W is subjected to pretreatment using filtration, coagulation sedimentation, microfiltration membranes, etc., and mainly suspended solids are removed.

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

[0005] Subsystem 4 comprises a subtank 41 (a pure water tank) downstream of the electrodeionization system for storing 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 (a membrane filtration system) for treating the primary pure water W2 delivered from the subtank 41 via a pump (not shown). Subsystem 4 may also include an RO membrane separator, if necessary. 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. The non-regenerative mixed-bed ion exchange system 43 then processes the water to remove residual carbonate ions, organic acids, anionic substances, and even metal ions and cationic substances by ion exchange. The ultrafiltration (UF) membrane 44 then removes particulates to produce ultrapure water W3, which is then supplied to the point of use 5, with unused ultrapure water returning to the subtank 41.

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

[0007] However, in the conventional control method of the ultrapure water production system 1 described above, more water than necessary is supplied to the electrodeionization device 36 and other devices for treatment, leaving room for improvement in terms of energy efficiency. Therefore, it is conceivable to vary the treatment volume of the electrodeionization device 36 in accordance with the amount of water used at the point of use 5. However, this not only makes it difficult to follow the fluctuations in the amount of water used at the point of use 5, but also leads to a deterioration in the quality of the deionized water produced by the electrodeionization process.

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

[0009] The present applicant has also proposed a control method for a pure water production system as shown in Fig. 4 (Japanese Patent Application No. 2023-033118). In Fig. 4, the pure water production system includes a water tank 51 for storing pretreated water W1, a water supply pump 52A for the pretreated 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. The system then branches into two lines, each of which is provided with control valves 59A and 59B, sub-tanks 60A and 60B, and water level gauges 61A and 61B. A reference value for the water level of the sub-tanks 60A and 60B is set in advance. When the amount of water used at each use point decreases and the water level measured by the water level gauges 60A and 60B rises above this reference value, a control means (not shown) throttles the control valves 59A and 59B, respectively, to reduce the amount of water supplied to the sub-tanks 60A and 60B. As a result, the total amount of water supplied decreases, and the water supply pressure indicated by pressure gauge 58 increases. Based on the measurement value of pressure gauge 58, the control means reduces the output of high-pressure pump 52B by inverter control so that the measurement value of pressure gauge 58 remains approximately constant relative to a predetermined value. On the other hand, if the amount of water used at each use point increases and the measurement values ​​of the water levels of sub-tanks 60A and 60B fall below this reference value, the control means (not shown) opens 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 increases, and the water supply pressure indicated by pressure gauge 58 decreases. Based on the measurement value of pressure gauge 58, the control means increases the output of high-pressure pump 52B by inverter control so that the measurement value of pressure gauge 58 remains approximately constant relative to a predetermined value. This reduces the amount of excess water supplied.

[0010] Patent No. 6863510

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

[0012] Furthermore, in the control method for an ultrapure water production system described in Japanese Patent Application No. 2023-033118, when the pump is inverter-controlled, the inverter can efficiently control a predetermined range (e.g., approximately 20 to 50 Hz), and upper and lower limits are set within this range. Control is possible as long as the flow rate fluctuates within this range. However, if the water usage falls below the water volume delivered at the lower limit of the inverter control frequency, the pump inverter cannot adjust the flow rate, and the pressure in the system rises. To address this issue, it becomes necessary to stop the pump inverter control and release some of the water to the upstream tank via a circulation line (a return line to the upstream tank). However, in this case, it is difficult to set a trigger to resume operation with variable flow rates using only the pump inverter and pressure control, which necessitates manual confirmation for recovery.

[0013] The present invention has been made in view of the above-mentioned problems, and has as its object to provide a method for controlling a pure water producing system that can control the amount of water supplied in accordance with the amount of water used.

[0014] In view of the above object, the present invention provides a method for controlling a pure water producing system including a source of water to be treated, a water supply pump connected to the source of water to be treated, a pressure gauge provided downstream of the water supply pump, and a water treatment device provided between the water supply pump and the pressure gauge, in which pure water produced in the system is supplied from a pure water supply line to a pure water-using device downstream of the pressure gauge, the method comprising: a first flow rate adjustment mechanism between the pressure gauge and the pure water-using device for adjusting the flow rate of the pure water supplied to the pure water-using device; and a control mechanism for adjusting the supply rate of pure water by the first flow rate adjustment mechanism in accordance with the amount of water used by the pure water-using device; The present invention provides a method for controlling a pure water manufacturing system, in which the water supply pump is controlled by a pump inverter so that the water supply output of the water supply pump maintains an approximately constant value as measured by the pressure gauge, and 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 controlled by the pump inverter, the water supply output of the water supply pump controlled by the pump inverter is set to a fixed value, and the flow rate of a circulation line having a second flow control means provided upstream of the pure water-using equipment in the pure water supply path is controlled by the second flow control means so that the measurement value of the pressure gauge maintains an approximately constant value (Invention 1).

[0015] According to this invention (Invention 1), the first flow rate adjustment mechanism controls the amount of pure water supplied to the pure water-using equipment in response to changes in the amount of pure water used. Since the water supply pressure fluctuates with this increase or decrease in supply rate, the water supply output of the water supply mechanism is controlled so that the water supply pressure remains substantially constant relative to a predetermined value, thereby enabling independent control of the pure water supply and the output of the water supply mechanism. This allows for simple and versatile control. Furthermore, even if the amount of pure water supplied to the pure water-using equipment falls below the lower limit of the desired setting range of the water supply output of the water supply pump controlled by the pump inverter (e.g., the water supply output at the lowest frequency of the pump inverter), the second flow rate adjustment mechanism adjusts the flow rate of the circulation line accordingly, enabling operation that can accommodate significant fluctuations in the amount of pure water used.

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

[0017] According to this invention (Invention 2), simple and versatile control can be realized by controlling the first flow rate adjustment mechanism to increase or decrease the amount of pure water supplied depending on the water level in the pure water tank. Furthermore, even if the amount of pure water supplied to the pure water-using equipment falls below the lower limit of the arbitrary setting range of the water supply output of the feedwater pump set by the pump inverter (for example, the water supply output at the lowest frequency of the pump inverter), by adjusting the flow rate of the circulation line with the second flow rate adjustment mechanism, it is possible to perform operation that can accommodate even very large fluctuations in the amount of pure water used.

[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 electrodeionization device, a regenerative ion exchange device, and a non-regenerative ion exchange device (Invention 3).

[0019] According to this invention (Invention 3), it is possible to apply the invention to various general-purpose primary pure water apparatuses.

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

[0021] According to this invention (Invention 4), when there is one line of water treatment equipment, by providing a pressure gauge downstream of one of the water treatment equipment, it is possible to control the flow rate adjustment mechanism to increase or decrease the amount of pure water supplied depending on the water level in the pure water tank, thereby realizing simple and versatile control.

[0022] In the above invention (Invention 1), the water supply output of the water supply pump is kept constant, and the operation can be switched to constant flow rate operation in which the second flow rate adjustment mechanism controls the pressure on the pressure gauge so that it remains approximately constant depending on the amount of pure water used by the pure water-using equipment (Invention 5).

[0023] According to this invention (Invention 5), pure water can be supplied in accordance with a wider range of usage conditions for pure water.

[0024] In the above invention (Invention 2), the water treatment equipment whose supply water output is controlled by the pump inverter is of multiple series, and while one series of the water treatment equipment of the multiple series is stopped, the remaining series can be operated by varying the amount of pure water supplied based on the amount of pure water used by the pure water-using equipment (Invention 6).

[0025] According to this invention (Invention 6), even when a first flow rate adjustment mechanism supplies pure water to multiple lines, the water supply pressure increases or decreases in response to an increase or decrease in the amount of pure water supplied. However, even if one line is stopped for maintenance or the like, the water supply output of the water supply mechanism can be controlled so that the water supply pressure for the remaining lines remains approximately constant at a predetermined value, thereby making it possible to separate the control of the pure water supply from the control of the output of the water supply mechanism. Furthermore, even when the amount of pure water supplied to the pure water-using equipment falls below the lower limit of the arbitrary setting range of the water supply output of the feed pump set by the pump inverter (for example, the water supply output based on the minimum frequency of the pump inverter), by adjusting the flow rate of the circulation line with the second flow rate adjustment mechanism, it becomes possible to perform operation that can accommodate very large fluctuations in the amount of pure water used.

[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 setting range of the water supply output of the water supply pump by the pump inverter, the operating output of the pump is set to a fixed value, and the flow rate of the circulation line having the second flow control means installed upstream of the pure water-using equipment in the pure water supply line is controlled so that the measurement value of the pressure gauge remains approximately constant, thereby making it possible to perform operation that can accommodate even very large fluctuations in the amount of pure water used.

[0027] Fig. 1 is a flow diagram showing an ultrapure water producing system to which the method for controlling a pure water producing system of the present invention can be applied. Fig. 2 is a flow diagram showing a pure water producing system (primary pure water apparatus) to which the method for controlling a pure water producing system according to a first embodiment of the present invention can be applied. Fig. 3 is a flow diagram showing a pure water producing system (primary pure water apparatus) to which the method for controlling a pure water producing system according to a second embodiment of the present invention can be applied. Fig. 4 is a schematic diagram showing a conventional method for controlling a pure water producing system.

[0028] A method for controlling a pure water production system according to the present invention will now be described with reference to the accompanying drawings.

[0029] First Embodiment (Pure Water Manufacturing System) This embodiment is characterized by the control of a pure water manufacturing system (primary pure water apparatus) that constitutes an ultrapure water manufacturing system.

[0030] There are no particular limitations on the pure water production system (primary pure water apparatus), and 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 provided downstream of the water supply pump, and a pure water tank for storing the produced pure water, also provided downstream of the pressure gauge, and one or more types of water treatment equipment are provided between the water supply pump and the pressure gauge. For example, the present invention can be suitably applied to a pure water production system as shown in FIG.

[0031] 2 , the primary pure water system (pure water production system) 3 includes a filtration tank 301 as a water supply source for storing pretreated water W1, a water pump 302 for the pretreated water W1, a cooler 303 provided downstream of the water 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 degassing device 308, and an electrodeionization device (CDI) 309. Treated water (primary pure water) W2 from the electrodeionization device 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 degassing device 308, and the electrodeionization device 309.

[0032] In this primary pure water system 3, a treated water pressure gauge 311 and a level-sensing control valve 312 serving as a first flow rate adjustment mechanism are provided downstream of the electrodeionization device 309, and a water level gauge 313 is provided in the sub-tank 41. These pressure gauge 311 and water level gauge 313 are capable of transmitting 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 remains approximately constant (for example, ±5%) with respect to a predetermined value, and can also control the opening of the level-sensing control valve 312 based on the value measured by the water level gauge 313. In addition, a circulation line 314 that continues to the filtered water tank 301 is provided downstream of the pressure gauge 311 and upstream of the level-sensing control valve 312, and this circulation line 314 is provided 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] Reference numeral 321 denotes a recovery line for concentrated water from the first reverse osmosis membrane device 306. This recovery line 321 is provided 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 becomes a predetermined value, and the concentrated water is stored in the recovered water tank 324. The concentrated water from the first reverse osmosis membrane device 306 is reused by returning it to the filtered water tank 301 after undergoing necessary treatment. Reference numeral 331 denotes a recovery line for concentrated water from the second reverse osmosis membrane device 307, and reference numeral 334 denotes a recovery line for concentrated water from the electrodeionization device 309. These lines merge with a recovery circulation line 340 and are returned to the filtered water tank 301. The recovery line 331 is provided with a flow meter 332 and a flow control valve 333. 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 becomes a predetermined value.

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

[0035] In the freshwater production process using the primary pure water system 3 described above, the sub-tank 41 is provided with a water level gauge 313, which can be controlled as follows. First, a reference value (which may be a value within a predetermined range) for the water level in the sub-tank 41 is determined in advance. The pressure-sensing control valve 315 provided in the circulation line 314 is closed completely or closed to its lowest design opening, allowing only a small amount of primary pure water W2 to flow. When the amount of primary pure water W2 used at the point of use decreases and the water level measured by the water level gauge 313 rises above this reference value, a 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 measured by the pressure gauge 311 increases. Based on the 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 remains approximately constant relative to the 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, a 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 measured by the pressure gauge 311 decreases. Therefore, the output from the water supply pump 305A is increased by controlling the frequency of the pump inverter 305B so that the measured value of the pressure gauge 311 remains approximately constant relative to a predetermined value. At this time, the flow control valves 323 and 333 may be PID-controlled based on the measured values ​​of the flow meters 322 and 332 so that the amounts of concentrated water in the first reverse osmosis membrane device 306 and the second reverse osmosis membrane device 307 remain constant.

[0036] However, control based on the frequency of pump inverter 305B can only control the maximum discharge rate of feedwater pump 305A to approximately 50 to 60%. Therefore, when the amount of pure water used at the point of use falls below the lower limit of the desired setting range for the water supply output of feedwater pump 305A controlled by pump inverter 305B (e.g., the water supply output at the minimum frequency of the pump inverter), the control described above becomes ineffective. Therefore, when the frequency of pump inverter 305B falls below a predetermined value (e.g., the minimum frequency of pump inverter 305B), control based on the frequency of pump inverter 305B using pressure gauge 311 is stopped, and the frequency of pump inverter 305B is fixed at a constant value (e.g., the minimum frequency) to operate at a constant flow rate. Meanwhile, level-sensing control valve 312 is maintained in a throttled state so that the water level in subtank 41 is at a predetermined reference water level. As a result, the measurement value of the pressure gauge 311 tends to rise relative to a predetermined value, but in this embodiment, the opening of the pressure-sensing control valve 315 provided in the circulation line 314 is PID controlled so that the measurement value of the pressure gauge 311 remains approximately constant relative to the predetermined value.

[0037] Then, if the usage at the use point increases again and it becomes necessary to supply water above the lower limit of the arbitrary setting range of the water supply output of the feedwater pump 305A by the pump inverter 305B, the control of the opening 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 where only a small amount of primary pure water W2 flows. Then, the control of the frequency of the pump inverter 305B by the pressure gauge 311 can be resumed.

[0038] By switching in this way according to fluctuations in the amount of water used at the use point, even if the amount of pure water used at the use point falls below the lower limit of control by the frequency of the pump inverter 305B, it is possible to continue producing primary pure water W2 without stopping the water treatment equipment.

[0039] 3, the pure water producing system 3 of this embodiment has the same configuration as the first embodiment, except that it has three series of water treatment equipment 300A, 300B, and 300C (each consisting of a first reverse osmosis membrane device 306, a second reverse osmosis membrane device 307, a membrane degassing device 308, and an electrodeionization device 309). A pressure gauge 311 is provided downstream of the point where the treated water from the three series of water treatment equipment 300A, 300B, and 300C joins together.

[0040] (Method of Controlling the Pure Water Production System) Next, a method of controlling the pure water production system according to the second embodiment will be described. The method of controlling the pure water production system according to the second embodiment is basically the same as that according to the first embodiment.

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

[0042] In the freshwater production process using the primary pure water system 3 described above, the sub-tank 41 is provided with a water level gauge 313, which can be controlled as follows. First, a reference value (which may be a value within a predetermined range) for the water level in the sub-tank 41 is determined in advance. The pressure-sensing control valve 315 provided in the circulation line 314 is closed completely or closed to its lowest design opening, allowing only a small amount of primary pure water W2 to flow. When the amount of primary pure water W2 used at the point of use decreases and the water level measured by the water level gauge 313 rises above this reference value, a 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 measured by the pressure gauge 311 increases. Based on the 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 remains approximately constant relative to the 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, a 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 measured by the pressure gauge 311 decreases. Therefore, the output from the water supply pump 305A is increased by controlling the frequency of the pump inverter 305B so that the measured value of the pressure gauge 311 remains approximately constant relative to a predetermined value. At this time, the flow control valves 323 and 333 may be PID-controlled based on the measured values ​​of the flow meters 322 and 332 so that the amounts of concentrated water in the first reverse osmosis membrane device 306 and the second reverse osmosis membrane device 307 remain constant.

[0043] However, control based on the frequency of pump inverter 305B can only control the maximum discharge rate of feedwater pump 305A to approximately 50 to 60%. Therefore, when the amount of pure water used at the point of use falls below the lower limit of the arbitrary setting range of the feedwater output of feedwater pump 305A controlled by pump inverter 305B (e.g., the feedwater output at the minimum frequency of the pump inverter), the above-described control cannot keep up. Therefore, when the frequency of pump inverter 305B falls below a predetermined value (e.g., the minimum frequency), control based on the frequency of pump inverter 305B using pressure gauge 311 is stopped, and the frequency of pump inverter 305B is fixed at a constant value (e.g., the minimum value) to operate at a constant flow rate. Meanwhile, level-sensing control valve 312 is maintained in a throttled state so that the water level in subtank 41 is at a predetermined reference water level. As a result, the measurement value of the pressure gauge 311 tends to rise relative to a predetermined value, but in this embodiment, the opening of the pressure-sensing control valve 315 provided in the circulation line 314 is PID controlled so that the measurement value of the pressure gauge 311 remains approximately constant relative to the predetermined value.

[0044] Then, if the usage at the use point increases again and it becomes necessary to supply water above the lower limit of the arbitrary setting range of the water supply output of the feedwater pump 305A by the pump inverter 305B, the control of the opening 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 where only a small amount of primary pure water W2 flows. Then, the control of the frequency of the pump inverter 305B by the pressure gauge 311 can be resumed.

[0045] As described above, similar control can be performed even when multiple lines of water treatment equipment are connected in parallel. However, in this case, the pressure gauge 311 must be positioned at the confluence point of the treated water (primary pure water) W2 of the multiple lines of water treatment equipment 300A, 300B, and 300C, either at the later or earlier stage. When multiple lines of water treatment equipment are connected in parallel, as in this embodiment, not all lines need to be operating. When one or more of the multiple lines of water treatment equipment are stopped for maintenance or other purposes, the remaining lines may be operated by varying the pure water supply rate based on the amount of pure water used by the pure water-using equipment. Alternatively, a constant flow rate operation may be performed in which the water supply output of the water supply pump 305A is kept constant and the pressure on the pressure gauge 311 is controlled by the pressure-sensing control valve 315 in accordance with the amount of pure water used by the pure water-using equipment, so that the pressure is kept approximately constant.

[0046] Although the present invention has been described above based on the above-described embodiment, the present invention is not limited to the above-described embodiment and various modifications are possible. For example, the elements constituting the water treatment equipment can be selected from various types as desired, and one or more of a reverse osmosis membrane, an ultraviolet oxidation device, a degassing membrane, an electrodeionization device, a regenerative ion exchange device, a non-regenerative ion exchange device, etc. can be used.

[0047] The present invention will be described in more detail 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 FIG. 3, the amount of pure water used at the point of use (POU) was 45 to 9 m ３ / h, and the output of the water supply pump 305A is controlled by the pump inverter 305B to 100% to 60%, and the amount of pure water used is 45 m ３ / h to 27m ３ / h under the first condition (Example 1-1), 27 m ３ / h to 9m ３ / h as the second condition (Example 1-1), the pure water production system was operated according to the following steps, and the amount of pure water used (required amount of water) of the POU, the amount of pure water W2 produced, and the amount of water in the circulation line 314 were measured. The results are shown in Table 1.

[0049] (First operating condition) POU pure water consumption: 45 m ３ / h, with the output of the pump inverter 305B set to 100%, the water supply pump 305A is 45m ３ / h of water to be treated W1 was supplied to operate the pure water producing system 3. Since the response of the pressure-sensing control valve 315 would be poor if the valve were fully closed, the pressure-sensing control valve 315 was slightly opened to ensure a negligible flow rate at all times.

[0050] POU pure water consumption: 27m ３ / h, and when the water level gauge 313 detects that the level of the sub-tank 41 has exceeded a predetermined value, the level sensing control valve 312 is controlled to throttle down. As a result, the reading on the pressure gauge 311 rises, so the frequency of the pump inverter 305B is lowered to keep the reading on the pressure gauge 311 almost constant. Then, the control of the output of the water supply pump 305A by the pump inverter 305B is set to the lower limit of the arbitrary setting range of the water supply output of the water supply pump 305A by the pump inverter 305B (here, the lower limit due to the minimum frequency of the inverter: 27 m ３ The control by the level-sensing control valve 312 was maintained until the temperature reached 100°C / h.

[0051] (Second operating condition) POU pure water consumption is 27 m ３ / h, the frequency of the pump inverter 305B was held at the minimum value, and control was switched to the pressure-sensing control valve 315. Then, the amount of pure water used by the POU was reduced to 9 m ３ / h, and when the water level gauge 313 detected that the level in the sub-tank 41 had exceeded a predetermined value, the level sensing control valve 312 was controlled to throttle down. As a result, the reading on the pressure gauge 311 rose, but the pressure sensing control valve 315 was controlled to open, and the flow rate to the circulation line 314 was increased, thereby maintaining the reading on the pressure gauge 311 at an approximately constant value.

[0052] Comparative Example 1 Using the pure water production system 3 shown in FIG. 3, the pure water consumption of the POU was 45 to 9 m ３ / h, and the output of the water supply pump 305A is changed to 45m ３The system was operated according to the following steps, and the amount of pure water used (required amount of water) of the POU, the amount of pure water W2 produced, and the amount of water in the circulation line 314 were measured. The results are also shown in Table 1.

[0053] (Operating conditions) POU pure water consumption: 45m ３ / h, the output of the water supply pump 305A by the pump inverter 305B is set to 100%, and the water supply from the water supply pump 305A is 45m ３ The pure water production system 3 was operated by supplying the water to be treated W1 at a rate of 1 / h.

[0054] POU pure water consumption of 9m ３ / h, and when the water level gauge 313 detected that the level in the sub-tank 41 had exceeded a predetermined value, the level-sensing control valve 312 was controlled to throttle down. As a result, the reading on the pressure gauge 311 rose, so the flow rate into the circulation line 314 was increased to keep the reading on the pressure gauge 311 almost constant.

[0055]

[0056] As is clear from Table 1, the amount of water entering the circulation line 314 can be significantly reduced by the control in Example 1.

[0057] 1 Ultrapure water production system 2 Pretreatment device 3 Primary pure water production device (pure water production system) 4 Secondary pure water production device (subsystem) 5 Point of use 300A, 300B, 300C Water treatment equipment 301 Filtration water tank (source of water to be treated) 305A Water supply pump 305B Pump inverter 306 First reverse osmosis membrane device (water treatment equipment) 307 Second reverse osmosis membrane device (water treatment equipment) 308 Membrane degassing device (water treatment equipment) 309 Electrodeionization device (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 Pretreated water (water to be treated) W2 Primary pure water (pure water) W3 Secondary pure water (ultra pure water)

Claims

1. A method for controlling a pure water production system comprising a source of water to be treated, a water supply pump connected to the source of water to be treated, a pressure gauge provided downstream of the water supply pump, and water treatment equipment provided between the water supply pump and the pressure gauge, in which pure water produced in the system is supplied from a pure water supply line to a pure water-using device downstream of the pressure gauge, the method comprising: providing a first flow rate adjustment mechanism between the pressure gauge and the pure water-using device for adjusting the flow rate of pure water supplied to the pure water-using device; adjusting the amount of pure water supplied by the first flow rate adjustment mechanism in accordance with the amount of water used by the pure water-using device; and controlling the water supply output of the water supply pump by a pump inverter so that the value measured by the pressure gauge is approximately constant; A method for controlling 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 setting range of the water supply output of the water supply pump controlled by the pump inverter, the water supply output of the water supply pump controlled by the pump inverter is set to a fixed value, and the flow rate of a circulation line having a second flow control means provided upstream of the pure water-using equipment in the pure water supply line is controlled by the second flow control means so that the measurement value of the pressure gauge remains approximately constant.

2. A method for controlling a pure water manufacturing system as described in claim 1, further comprising the step of providing a pure water tank downstream of the pressure gauge and upstream of the pure water-using equipment for storing pure water to be supplied to the pure water-using equipment, and a first flow control mechanism is provided in the pure water supply line downstream of the pressure gauge and upstream of the pure water tank, and the flow rate is controlled by the first flow control mechanism in accordance with the water level in the pure water tank.

3. The method for controlling a pure water production system according to claim 2, wherein the water treatment equipment is one or more selected from the group consisting of a reverse osmosis membrane, an ultraviolet oxidation device, a degassing membrane, an electric deionization device, a regenerative ion exchange device, and a non-regenerative ion exchange device.

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

5. In the above invention (Invention 1), the water supply output of the water supply pump is kept constant, and the method switches to constant flow operation in which control is performed by a second flow rate adjustment mechanism so that the pressure on the pressure gauge remains approximately constant depending on the amount of pure water used by the pure water-using equipment.

6. A method for controlling a pure water production system as described in claim 2, wherein the water treatment equipment whose supply water output is controlled by the pump inverter is multiple series, and while one series of the water treatment equipment of the multiple series is stopped, the remaining series are operated by varying the amount of pure water supplied based on the amount of pure water used by the pure water-using equipment.

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