Control method for pure water production system

Abstract

When the use amount at each use point is reduced and the measured value of the water level of the water level gauges (61A, 61B) is increased, the opening degrees of the control valves (59A, 59B) are respectively reduced, and the amount of water supplied to the pure water tanks (60A, 60B) is reduced. As a result, since the water supply pressure of the pressure gauge (58) increases, the output of the high-pressure pump (52B) is reduced by inverter control on the basis of the measurement value of the pressure gauge (58). On the other hand, when the usage amount at each usage point is increased and the measured value of the water level of the pure water tanks (60A, 60B) is reduced than the reference value, the opening degree of the control valves (59A, 59B) is opened to increase the amount of water supplied to the pure water tanks (60A, 60B). Thus, since the water supply pressure of the pressure gauge (58) is reduced, the output of the high-pressure pump (52B) is increased by the inverter control so that the measurement value of the pressure gauge (58) is substantially constant. According to this method for controlling a pure water production system, the amount of water supplied, in particular, to the entire system having a plurality of tanks, can be controlled in accordance with the amount of water used.

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 electronic industry such as semiconductors and liquid crystals, and in particular to a control method for a pure water production system capable of controlling the water supply amount according to the water usage amount. Background Art

[0002] Conventionally, ultrapure water used in the semiconductor and other electronics industries has been produced by treating raw water in an ultrapure water production system consisting of a pretreatment system, a primary pure water device, and a subsystem for treating the primary pure water.

[0003] For example, Figure 1 As shown, the ultrapure water production system 1 is composed of three stages: a pretreatment unit 2, a primary pure water unit (pure water production system) 3, and a secondary pure water production unit (subsystem) 4. In the pretreatment unit 2 of the ultrapure water production system 1, raw water W is pretreated by filtration, coagulation and sedimentation, and microfiltration membranes, primarily to remove suspended matter.

[0004] The primary pure water device 3 includes a treated water tank 31 for storing pretreated water (treated water) W1, a high-pressure pump 32 for delivering the pretreated water W1, a reverse osmosis membrane device 33, a first degassing membrane device 34A for removing dissolved gases using air, a second degassing membrane device 34B for further degassing dissolved gases using nitrogen, an ultraviolet oxidation device 35, an electrodeionization device 36, and a water supply pump 37 for supplying water to the electrodeionization device 36. The primary pure water device 3 removes most electrolytes, particulates, and live bacteria from the pretreated water W1 and decomposes organic matter.

[0005] Subsystem 4 consists of a sub-tank 41, serving as a pure water tank, located downstream of the electrodeionization device that stores the primary pure water W2 produced by the primary pure water unit 3; an ultraviolet oxidation device 42, which treats the primary pure water W2 supplied from sub-tank 41 by a pump (not shown); a non-regenerative mixed-bed ion exchange device 43; and an ultrafiltration (UF) membrane 44, serving as a membrane filtration device. Furthermore, an RO (reverse osmosis) membrane separation device may be provided as needed. In subsystem 4, trace organic matter (TOC: total organic carbon) contained in the primary pure water W2 is oxidatively decomposed by the ultraviolet oxidation device 42. Subsequently, the water is treated in the non-regenerative mixed-bed ion exchange device 43 to remove residual carbonate ions, organic acids, anionic substances, and metal ions or cationic substances through ion exchange. Particles are then removed by the ultrafiltration (UF) membrane 44, resulting in ultrapure water W3, which is then supplied to the point of use 5. Unused ultrapure water is returned to sub-tank 41.

[0006] In the ultrapure water production system 1 , in order to stably supply primary pure water of a predetermined quality, an excess of primary pure water W2 is produced in advance, only the required amount is supplied to the sub-tank 41 , and the remaining amount is circulated and used.

[0007] However, in the conventional control method for ultrapure water production system 1 described above, since more water than required is supplied to electrodeionization device 36 and the like for treatment, there is room for improvement in energy efficiency. Therefore, it is possible to adjust the processing capacity of electrodeionization device 36 based on the usage at point of use 5, with respect to the processing capacity of primary pure water device 3. However, this not only makes it difficult to track changes in usage at point of use 5, but also leads to a decrease in the quality of the desalted water during the electrodeionization process.

[0008] Therefore, as a control method for an ultrapure water production system that can produce primary pure water according to the usage amount at the usage point, the applicant has obtained a patent for a control method for an ultrapure water production system, wherein the ultrapure water production system comprises: a primary pure water system having a reverse osmosis membrane, an electrodeionization device, and a water supply pump arranged at the front end of the electrodeionization device; a water storage tank (sub-tank) equipped with a water level measuring unit arranged at the rear end of the electrodeionization device; a subsystem that further processes the primary pure water produced in the primary pure water system, wherein the supply pump of the electrodeionization device is inverter-controlled in such a manner that the water level of the water storage tank measured by the water level measuring unit is kept approximately constant (patent document 1).

[0009] Prior art literature

[0010] Patent Literature

[0011] Patent Document 1: Japanese Patent No. 6863510. Summary of the Invention

[0012] Problems to be solved by the invention

[0013] 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 use points or when there are multiple water storage tanks in a large-scale ultrapure water production system with multiple subsystems. In addition, any control method for a pure water production system that can more reliably supply water to the subsystems through simple control would be ideal for controlling ultrapure water production systems.

[0014] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a control method for a pure water production system capable of controlling the water supply rate of the entire system including a plurality of tanks according to the amount of water used.

[0015] Means for solving problems

[0016] In view of the above-mentioned purpose, the present invention provides a control method for a pure water manufacturing system, which supplies pure water manufactured by a pure water manufacturing system having a treated water supply source, a water supply mechanism connected to the treated water supply source, a water supply pressure gauge arranged at the rear section of the water supply mechanism, and one or more water treatment equipment arranged between the water supply mechanism and the pressure gauge to a pure water tank arranged at the rear section of the pressure gauge, wherein a flow regulating mechanism for supplying pure water to the pure water tank is provided between the pressure gauge and the pure water tank, and a water level measuring unit for the pure water tank is provided, and based on the measured value of the water level of the pure water tank measured by the water level measuring unit, the supply amount of pure water is regulated by the flow regulating mechanism in such a manner that the water level of the pure water tank becomes within a constant range, and the water supply output of the water supply mechanism is controlled in such a manner that the measured value of the pressure gauge becomes approximately constant (Invention 1).

[0017] According to this invention (Invention 1), since the water level in the pure water tank drops / rises according to the increase or decrease in the amount of pure water used, the flow rate regulating mechanism is controlled in such a way that the amount of pure water supplied to the pure water tank is increased when the water level in the pure water tank drops, and the amount of pure water supplied to the pure water tank is reduced when the water level in the pure water tank rises. As the supply amount increases or decreases, the water supply pressure decreases or increases without any control. Therefore, by controlling the water supply output of the water supply mechanism in such a way that the water supply pressure becomes approximately constant relative to a predetermined value, the control of the water level in the pure water tank and the control of the output of the water supply mechanism can be made independent. Thus, even if the number of pure water tanks increases, simple and highly versatile control can be achieved for each pure water tank.

[0018] In the above invention (Invention 1), preferably, 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 2).

[0019] According to this invention (Invention 2), it is applicable to various general-purpose primary pure water devices.

[0020] Effects of the Invention

[0021] According to the present invention, based on the measured value of the water level of the pure water tank measured by the water level measuring unit, the flow rate of pure water is adjusted by the flow regulating mechanism in such a manner that the water level of the pure water tank becomes within a constant range, and the output of the water supply mechanism is controlled in such a manner that the measured value of the pressure gauge becomes approximately constant relative to a predetermined value. Since the control of the water level of the pure water tank and the control of the output of the water supply mechanism can be made independent, even if the number of pure water tanks is increased, simple and highly versatile control can be achieved according to each pure water tank. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a flowchart showing an ultrapure water production system to which a control method of a pure water production system according to one embodiment of the present invention can be applied.

[0023] Figure 2 This is a flowchart showing a pure water production system (primary pure water device) to which a control method of a pure water production system according to one embodiment of the present invention can be applied.

[0024] Figure 3 This is a schematic diagram illustrating a control method for the pure water production system according to the embodiment.

[0025] Figure 4 This is a graph showing the amount of water used at the use point in the pure water production system (primary pure water device) of Example 1, the amount of water treated by the electrodeionization device, and the water level in the water storage tank. DETAILED DESCRIPTION

[0026] Hereinafter, a control method of a pure water production system according to the present invention will be described with reference to the accompanying drawings.

[0027] (Pure water production system)

[0028] The present embodiment is characterized in controlling a pure water production system (primary pure water device) constituting an ultrapure water production system.

[0029] There are no special restrictions on the pure water manufacturing system (primary pure water device). As long as it has a water supply pump for supplying treated water, a water supply pressure gauge installed at the rear of the water supply pump, a pure water tank installed at the rear of the pressure gauge and storing the produced pure water, and one or more water treatment equipment between the water supply pump and the pressure gauge, it can be applied to various pure water manufacturing systems. For example, it can be preferably applied to Figure 2 The pure water production system shown.

[0030] exist Figure 2 In the present invention, a pure water device (pure water manufacturing system) 3 has a treated water tank 51 as a treated water supply source, a water supply pump 52A of this pretreated water W1, a high-pressure pump 52B that can be controlled by an inverter, a reverse osmosis membrane device 53, a first degassing membrane device 54A based on air, a second degassing membrane device 54B based on nitrogen, an ultraviolet oxidizing device 55, an electrodeionization device (CDI) 56, a water supply pump 57 that supplies water to this electrodeionization device 56, and the treated water (pure water W2) that is constituted by the electrodeionization device 56 is stored in the structure of pure water tank 60. Then, water supply mechanism is constituted by water supply pump 52A and high-pressure pump 52B. The pure water W2 stored in this pure water tank 60 is transported to boron chelate resin tower 63 and processed by liquid feeding pump 62, and can be stored in the sub-tank 41 that constitutes the subsystem.

[0031] In the primary pure water device 3, a water supply pressure gauge 58 and a control valve 59 serving as a flow regulating mechanism are provided at the rear section of the electrodeionization device 56, and a water level gauge 61 is provided in the pure water tank 60. These pressure gauges 58 and water level gauges 61 can transmit information to a control mechanism not shown in the figure. The control mechanism can perform inverter control on the high-pressure pump 52B in such a way that the measurement value of the pressure gauge 58 becomes approximately constant (for example, ±5%) relative to a predetermined value, and can control the opening of the control valve 59 based on the measurement value of the water level gauge 61.

[0032] It should be noted that reference numeral 71 denotes the recovery line for concentrated water from the reverse osmosis membrane device 53. This recovery line 71 is equipped with a flow control valve 72, a flow meter 73, a concentrated water tank 74, a water supply pump 75, and a recovery reverse osmosis membrane 76, thereby returning the treated water from the recovery reverse osmosis membrane 76 to the treated water tank 51. Furthermore, reference numeral 81 denotes the recovery line for concentrated water from the electrodeionization device 56. This recovery line 81 is equipped with a flow control valve 82 and a flow meter 83. The concentrated water from the electrodeionization device 56 is transported to a dilute system recovery reverse osmosis membrane (not shown) for treatment.

[0033] (Control method of pure water production system)

[0034] Next, explain Figure 2 A control method for a pure water production system is shown.

[0035] exist Figure 2 In the embodiment of the present invention, start water supply pump 52A and high-pressure pump 52B with inverter and supply pre-treated water (treated water) W1 from treated water tank 1, process in reverse osmosis membrane device 53, the first degassing membrane device 54A, the second degassing membrane device 54B, ultraviolet oxidation device 55 and electrodeionization device (CDI) 56, pure water (primary pure water) W2 is stored in pure water tank 60. Then, the primary pure water W2 stored in this pure water tank 60 is transported to boron chelate resin tower 63 and processed by liquid feeding pump 62 according to the usage at the point of use (not shown in the figure), then stored in the sub-tank 41 that constitutes subsystem, according to the usage at the point of use, prepare ultrapure water in subsystem, and required amount is supplied to the point of use.

[0036] In the water production process of the primary pure water device 3 as described above, the pressure gauge 58 for water supply, the control valve 59, the pure water tank 60, the water level gauge 61 and the high-pressure pump 52B which can be controlled by the inverter become Figure 3 The control system shown in Figure 1. Figure 3 In the figure, the electrodeionization device 56 is divided into two series at the rear stage and there are two control valves 59A, 59B, two pure water tanks 60A, 60B and two water level gauges 61A, 61B. Figure 3Other components are omitted.

[0037] First, a reference value (or a value within a specified range) is predetermined for the water levels in pure water tanks 60A and 60B. Then, when usage at each point decreases and the water level measured by water level gauges 61A and 61B increases above this reference value, a control unit (not shown) closes control valves 59A and 59B, respectively, reducing the amount of water supplied to pure water tanks 60A and 60B. As a result, the combined water supply decreases, causing the water supply pressure measured by pressure gauge 58 to rise. Therefore, based on the measured value of pressure gauge 58, the control unit reduces the output of high-pressure pump 52B through inverter control so that the measured value of pressure gauge 58 remains approximately constant relative to the predetermined value. On the other hand, when usage at each point increases and the water level measured by pure water tanks 60A and 60B decreases above this reference value, the control unit (not shown) opens control valves 59A and 59B, respectively, increasing the amount of water supplied to pure water tanks 60A and 60B. As a result, the water supply pressure of the pressure gauge 58 decreases due to the increase in the total water supply volume. Therefore, based on the measurement value of the pressure gauge 58, the control unit increases the output of the high-pressure pump 52B through inverter control so that the measurement value of the pressure gauge 58 remains approximately constant relative to a predetermined value. While the above description describes a case where the measured values ​​of the water levels in the pure water tanks 60A and 60B increase or decrease relative to a predetermined reference value, even if the measured values ​​of the water levels in the water level gauges 61A and 61B are opposite (one increases, the other decreases), the same control can be performed based on the increase or decrease in the total water supply volume to the pure water tanks 60A and 60B controlled by the control valves 59A and 59B.

[0038] For example, as Figure 3 An example of control shown is shown in Table 1 below, where two series are composed of the same equipment, the pressure value of the pressure gauge is determined to be 0.1 MPa, and the reference value of the water level of tanks A and B is controlled to be 1 m. When the opening of control valve A is changed to 20% → 20% → 60% → 60%, and the opening of control valve B is changed to 20% → 50% → 50% → 10%, the frequency control of the inverter of the high-pressure pump of four processes is changed.

[0039] [Table 1]

[0040]

[0041] As mentioned above, although the present invention has been described based on the above-mentioned embodiment, the present invention is not limited to the above-mentioned embodiment, and various modifications can be made. For example, as a pure water manufacturing system 3 to which the present invention can be applied, as long as it is a pure water manufacturing system 3 having a treated water tank 51, a water supply pump 52A and a high-pressure pump 52B as a water supply mechanism connected to the treated water tank 51, a pressure gauge 58 arranged at the rear section of the water supply pump 52A and the high-pressure pump 52B that can be controlled by an inverter, and one or more water treatment equipment arranged between the water supply pump 52A and the high-pressure pump 52B and the pressure gauge 58, there is no particular limitation on adjusting the flow rate of the primary pure water W2 based on the control valves 59A and 59B so that the water levels of the pure water tanks 60A and 60B become within a constant range based on the pressure gauge 58 and the measured values ​​of the water levels of the pure water tanks 60A and 60B measured by the water level gauges 61A and 61B as the flow rate of pure water supplied to the pure water tanks 60A and 60B, and controlling the output of the high-pressure pump 52B so that the measured value of the pressure gauge 58 becomes approximately constant. For example, the one or more water treatment devices positioned between the water supply pump 52A, the high-pressure pump 52B, and the pressure gauge 58 are not particularly limited and can be composed of one or more selected from a reverse osmosis membrane, an ultraviolet oxidation device, a degassing membrane, an electrodeionizer, a regenerative ion exchanger, and a non-regenerative ion exchanger. Alternatively, the inverter-controlled high-pressure pump 52B alone can be used as the water supply mechanism. Furthermore, a water level gauge can be installed in the sub-tank to serve as the pure water tank 60.

[0042] Example

[0043] Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to the following examples.

[0044] [Example 1 and Comparative Example 1]

[0045] As a test device, we prepared Figure 2 The pure water production system 3 of the structure shown in the figure is shown in the figure. In this test device, the maximum water treatment capacity of the electrodeionization device 56 is set to 23m 3 / h, the amount of water treated by the electrodeionization device 56 during the output control of the high-pressure pump 52B was manually measured so that the water level in the pure water tank 60 remained substantially constant, along with the change in the amount of water supplied from the sub-tank 41 to the point of use (the amount of water used at the point of use) (Comparative Example 1). The results are shown together with the amount of water used at the point of use. Figure 4 .

[0046] Then, based on the change in the water level in the pure water tank 60 caused by the change in the amount of water supplied from the sub-tank 41 to the point of use (the amount of water used at the point of use), the opening of the control valve 59 was adjusted, and the output of the high-pressure pump 52B was inverter-controlled so that the measured value of the pressure gauge 58 would be approximately constant. At this time, the amount of water treated by the electrodeionization device 56 was measured (Example 1). The results are shown together with the amount of water used at the point of use. Figure 4 It should be noted that Figure 4 In FIG. 1 , the water level of the pure water tank 60 is set to a reference value of 2.5 m, and for convenience, the relative change is shown in the upper part.

[0047] from Figure 4 As can be seen, according to Example 1 using inverter control, the amount of water used at the point of use can be tracked to adjust the amount of water treated by the electrodeionization device 56 (equivalent to the amount of primary pure water W2 produced), thereby reducing the operating power of the high-pressure pump 52B. In contrast, in Comparative Example 1 using manual control, only simple step-by-step control can be performed based on the amount of water used at the point of use. This results in an excess of water treated by the electrodeionization device 56, and excessive power consumption by the high-pressure pump 52B.

[0048] Explanation of symbols

[0049] 1: Ultrapure water production system.

[0050] 2: Pretreatment device.

[0051] 3: Primary pure water device (pure water manufacturing system).

[0052] 31: Processed water tank.

[0053] 32: High pressure pump.

[0054] 33: Reverse osmosis membrane device.

[0055] 34A: First degassing membrane device.

[0056] 34B: Second degassing membrane device.

[0057] 35: Ultraviolet oxidation device.

[0058] 36: Electrodeionization device.

[0059] 37: Water supply pump.

[0060] 4: Secondary pure water production device (subsystem).

[0061] 41: Sub-jar.

[0062] 42: Ultraviolet oxidation device.

[0063] 43: Non-regenerative mixed bed ion exchange unit.

[0064] 44: Ultrafiltration (UF) membrane.

[0065] 5: Use point.

[0066] 51: Treated water tank (treated water supply source).

[0067] 52A: Water supply pump (water supply mechanism).

[0068] 52B: High pressure pump (water supply mechanism).

[0069] 53: Reverse osmosis membrane device.

[0070] 54A: First degassing membrane device.

[0071] 54B: Second degassing membrane device.

[0072] 55: Ultraviolet oxidation device.

[0073] 56: Electrodeionization device (CDI).

[0074] 57: Water supply pump.

[0075] 58: Pressure gauge.

[0076] 59, 59A, 59B: control valve (flow regulating mechanism).

[0077] 60, 60A, 60B: Pure water tank.

[0078] 61, 61A, 61B: Water level gauge.

[0079] 62: Liquid delivery pump.

[0080] 63: Boron chelating resin tower.

[0081] 71: Recycling line.

[0082] 72: Flow control valve.

[0083] 73: Flow meter.

[0084] 74: Concentrated water tank.

[0085] 75: Water supply pump.

[0086] 76: Recover reverse osmosis membrane device.

[0087] 81: Recycling line.

[0088] 82: Flow control valve.

[0089] 83: Flow meter.

[0090] W: raw water.

[0091] W1: pretreated water (treated water).

[0092] W2: primary pure water (pure water).

[0093] W3: Secondary pure water (ultrapure water).

Claims

1. A control method for a pure water production system, wherein pure water produced by the pure water production system having a treated water supply source, a water supply mechanism connected to the treated water supply source, a water supply pressure gauge provided at a downstream end of the water supply mechanism, and one or more water treatment devices provided between the water supply mechanism and the pressure gauge is supplied to a pure water tank provided at a downstream end of the pressure gauge, wherein: A flow regulating mechanism for supplying pure water to the pure water tank and a water level measuring unit for the pure water tank are provided between the pressure gauge and the pure water tank. Based on the measured value of the water level of the pure water tank measured in the water level measuring unit, the supply amount of pure water is regulated by the flow regulating mechanism in such a manner that the water level of the pure water tank becomes within a constant range, and the water supply output of the water supply mechanism is controlled in such a manner that the measured value of the pressure gauge becomes approximately constant.

2. The control method of the pure water production system according to claim 1, wherein: 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.

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