Pure water production device control method

Abstract

In the present invention, when the water quantity of circulating water is fixed to 20 m3 / h, a design maximum discharge amount of water feed pumps 32A, 32B, and 32C is 60 m3 / h, and the usage amount of primary pure water W2 in a sub-system is 80 m3 / h, the number of operating pumps becomes 1.67≤2 (pumps). Thus, number of operating water feed pumps is set to 2, and the water supply pumps 32A, 32B are operated. At such time, the output of the water feed pumps 32A, 32B is set to 83% by inverter control so as to produce 100 m3 / h of the primary pure water W2. 80 m3 / h is fed to a sub tank 37 by a control valve 55, and the surplus 20 m3 / h is fed to a circulation passage 54 which communicates with a to-be-treated water tank 31. According to such a pure water production device control method, a water feeding amount can be controlled by adjusting the operation power of the water feed pumps according to the amount of water to be used in a post-stage system or a point of use.

Description

Method for controlling a pure water production device

[0001] The present invention relates to a method for controlling a pure water production apparatus suitable 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 apparatus capable of controlling the amount of water supplied in accordance with the amount of water used in downstream systems or at use points.

[0002] Conventionally, ultrapure water used in the semiconductor and other electronics industries is produced, for example, by an ultrapure water production system as shown in Fig. 6. In Fig. 6, the 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.

[0003] The pretreatment device 2 comprises a coagulation treatment device 21 and a turbidity removal UF membrane device 22. In this pretreatment device 2, the raw water W is subjected to pretreatment such as coagulation sedimentation and membrane filtration, and mainly suspended solids are removed.

[0004] The primary pure water system 3 includes a water tank 31 for storing pretreated water (water to be treated) W1, a water pump 32 for transporting the pretreated water W1, a reverse osmosis membrane device 33, a membrane degassing device 34, an ultraviolet oxidation device 35, and an electrodeionization device 36. In the primary pure water system 3, the reverse osmosis membrane device 33 removes fine particles and ions from the pretreated water W1, the membrane degassing device 34 reduces dissolved oxygen, and the ultraviolet oxidation device 35 decomposes organic matter (TOC components). The electrodeionization device 36 then removes metal ions, carbonate ions, organic acids, and the like to produce primary pure water (pure water) W2. The produced primary pure water W2 is stored in a sub-tank 37 for supply to the subsystem 4.

[0005] The subsystem (secondary pure water system) 4, which handles the final step in ultrapure water production, is composed of a pump 41 that delivers primary pure water W2 from a subtank 37, an ultraviolet oxidation device 42 that processes the primary pure water W2, a membrane degassing device 43, a non-regenerative mixed-bed ion exchanger 44, and an ultrafiltration (UF) membrane 45 as a membrane filtration device. An RO membrane separator or other device may also be installed as needed. In this subsystem 4, the ultraviolet oxidation device 42 oxidizes and degasses trace amounts of organic matter (TOC components) contained in the primary pure water W2, and then the non-regenerative mixed-bed ion exchanger 44 removes residual carbonate ions, organic acids, anionic substances, and even metal ions and cationic substances by ion exchange. The ultrafiltration (UF) membrane 45 then removes particulates to produce ultrapure water W3, which is then supplied to a point-of-use 5.

[0006] The primary pure water production system 3 in the above-described ultrapure water production system 1 generally has multiple water pumps 32A, 32B, and 32C (three pumps in FIG. 7 ) as shown in FIG. 7 . A water treatment system 30 consisting of a reverse osmosis membrane device, a membrane degasser, an ultraviolet oxidation device, and an electrodeionization device is located downstream of the water pumps. In the primary pure water production system 3 shown in FIG. 6 , reference numeral 51 denotes a chemical feeder for pH adjusters and the like for the water to be treated by the reverse osmosis membrane. A water supply line 52 connected to the water treatment system 30 branches into a supply line 53 communicating with the sub-tank 37 and a circulation line 54 communicating with the tank 31 for treated water. A control valve 55 is provided at this branch point as a flow rate regulator.

[0007] In order to stably supply primary pure water W2 to subsystem 4, water supply pumps 32A, 32B, and 32C are driven at their maximum designed discharge rates to produce an excess amount of primary pure water W2, and the amount required by subsystem 4 is supplied to sub-tank 37 from supply path 53, with the excess being returned to the treated water tank 31 via circulation path 54 by control valve 55 for circulation.

[0008] As shown in FIG. 7, the amount of primary pure water W2 used (required amount) in subsystem 4 is 140 m ３ / h, and the maximum designed discharge capacity of the water pumps 32A, 32B, and 32C is 60 m３ / h, the water pumps 32A, 32B, and 32C are operated at their maximum designed discharge rates, and ３ / h of primary pure water W2 is produced. Then, 140 m ３ / h is sent to the sub-tank 37, and the surplus 40 m ３ / h is sent to the circulation path 54 communicating with the tank 31 for treated water, and the amount of the returned primary pure water W2 is increased or decreased depending on the amount of primary pure water W2 used in the subsystem 4.

[0009] However, in the control method of the conventional ultrapure water production system as described above, the water pumps 32A, 32B, and 32C are operated at their maximum designed discharge rates. For example, as shown in FIG. 8, when the amount of primary pure water W2 used in the subsystem 4 is 100 m ３ / h, the rate is 80m ３ / h of water is returned from the circulation path 54. In other words, more primary pure water W2 than necessary is produced. This causes the water pumps 32A, 32B, and 32C, the ultraviolet oxidation device, the electrodeionization device, and other devices to operate excessively, leaving a problem of significant room for energy reduction. In particular, since the power consumption of the pumps accounts for approximately 60% of the power consumption in the ultrapure water production system 1, reducing the power consumption of the water pumps 32A, 32B, and 32C would make a significant contribution to energy conservation.

[0010] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a control method for a pure water production apparatus that can control the amount of water supplied by adjusting the operating power of a water supply pump according to the amount of water used in downstream systems or use points.

[0011] In view of the above object, the present invention provides a method for controlling a pure water production system that includes a storage tank for water to be treated, three or more water supply pumps for supplying the water to be treated stored in the storage tank, and one or more water treatment devices installed downstream of the water supply pumps, and that has a water supply channel for supplying pure water produced by the water treatment devices to a downstream system or use point, and a circulation channel for returning excess pure water branched off from the water supply channel to the storage tank, and that controls the number of operating water supply pumps and / or the output of the water supply pumps according to the amount of pure water required by the downstream system or use point (Invention 1).

[0012] According to this invention (Invention 1), the number of operating water pumps is controlled in response to the increase or decrease in the amount of pure water required by the downstream system or use point, and the output of the water pumps is controlled as needed based on this number of operating pumps. This prevents excessive pure water from being returned from the circulation path to the storage tank, and reduces excessive pump energy consumption.

[0013] In the above invention (Invention 1), it is preferable to control the number of operating water pumps and / or the output of the water pumps so that the amount of water circulated through the circulation path is 20% or less of the total designed maximum discharge volume of the water pumps (Invention 2).

[0014] According to this invention (Invention 2), it is possible to suppress the production of excessive pure water, and to efficiently reduce the energy consumption of the pure water production device and pump.

[0015] In the above invention (invention 2), it is preferable that the output of the water pump is controlled to 60 to 100% of the designed maximum discharge rate of the water pump (invention 3).

[0016] According to this invention (Invention 3), the amount of water to be fed can be adjusted in response to a wide range of fluctuations in the flow rate of pure water fed to a downstream system or a use point.

[0017] In the above invention (Invention 3), it is preferable to control the number of operating pumps so that the value obtained by dividing the amount of pure water delivered by the maximum designed discharge rate of each pump is rounded up to a natural number (Invention 4).

[0018] According to this invention (Invention 4), the amount of water to be fed can be adjusted appropriately in response to fluctuations in the flow rate of pure water fed to a downstream system or a use point.

[0019] In the above inventions (Inventions 1 to 4), it is preferable to provide a chemical injection device in the water supply channel for the pure water produced by the primary pure water system, and to adjust the amount of chemicals added from the chemical injection device depending on the amount of pure water produced by the primary pure water system (Invention 5).

[0020] According to this invention (Invention 5), the amount of pure water produced by the water treatment device is reduced, which leads to cost reduction by reducing the amount of chemicals added.

[0021] In the above inventions (Inventions 1 to 4), it is preferable to supply the pure water produced in the primary water purification system to a downstream system, and to perform adjustment operation of the downstream system depending on the amount of water supplied to the downstream system (Invention 6).

[0022] According to this invention (Invention 6), the amount of pure water produced by the water treatment device is reduced, thereby enabling energy savings in the operation of the water treatment device.

[0023] According to the present invention, a pure water device has three or more series of water supply pumps, and supplies the produced pure water to a downstream system or use point, while returning excess pure water to a storage tank.The number of operating water supply pumps and / or the output of the water supply pumps are controlled according to the amount of pure water required by the downstream system or use point.This prevents excess pure water from being returned from the circulation path to the storage tank, and reduces excessive pump energy consumption.

[0024] FIG. 1 is a flow chart showing a pure water production system to which the control method for a pure water production system according to a first embodiment of the present invention can be applied. FIG. 2 is a flow chart showing a control method for a pure water production system according to a second embodiment of the present invention. FIG. 3 is a flow chart showing a control method for a pure water production system according to the second embodiment. FIG. 4 is a flow chart showing a control method for a pure water production system according to the third embodiment. FIG. 5 is a flow chart showing a control method for a pure water production system according to the third embodiment. FIG. 6 is a flow chart showing an ultrapure water production system to which the control method for a pure water production system of the present invention can be applied. FIG. 7 is a flow chart showing a control method for a conventional pure water production system. FIG. 8 is a flow chart showing a control method for a conventional pure water production system.

[0025] A method for controlling a pure water producing apparatus according to the present invention will now be described with reference to the accompanying drawings.

[0026] First Embodiment (Pure Water Production System) FIG. 1 is a schematic diagram of a pure water production system to which the method for controlling a pure water production system of the present invention can be applied. The basic configuration is the same as that of FIG. 7 , and the same components are designated by the same reference numerals. In FIG. 1 , the primary pure water production system 3 includes a water tank 31 for storing pretreated water (water to be treated) W1 and multiple series (n series: n is a positive integer) of water pumps 32A to 32n connected by header pipes. Each of the water pumps 32A to 32n is equipped with an inverter as an output control means. Downstream of the water pump 32A are multiple water treatment devices, namely, a water treatment system 30, which in this embodiment includes a reverse osmosis membrane device, a membrane degasser, an ultraviolet oxidation device, and an electrodeionization device. The water treatment system 30 is equipped with a chemical feeder 51, such as a pH adjuster, for adjusting the pH of the water to be treated by the reverse osmosis membrane. A water supply line 52 is also connected to the water treatment system 30. The water supply line 52 branches into a supply line 53 that communicates with the sub-tank 37 and a circulation line 54 that communicates with the tank 31 for treated water, and the branching point is provided with a control valve 55 as a flow rate regulator. Furthermore, the circulation line 54 is provided with a flow meter 56, and the water supply line 52 is also provided with a flow meter 57.

[0027] These flow meters 56 and 57 are capable of communicating information to a control means (not shown), which is capable of inverter-controlling the operation and stop of the water pumps 32A to 32n and the output of the water pumps 32A to 32n within a range of 60 to 100% of the maximum designed discharge volume of the water pumps based on the measured values ​​of the flow meters 56 and 57, and is also capable of controlling the control valve 55 so that the circulating water volume and the amount of water used are predetermined.

[0028] (Method of Controlling Pure Water Production Apparatus) In the pure water production apparatus described above, the water supply rate of the water supply pumps 32A to 32n, the amount of primary pure water used, and the amount of circulating water are expressed by the following formula (1). ３ / h) = Water consumption x (m ３ / h) + circulating water amount y (m ３ / h) = x + y(m ３ / h) ...(1)

[0029] Here, the circulating water volume y (m ３ / h) is preferably set to be 20% or less of the total of the designed maximum discharge rates of the water pumps 32A to 32n, and this circulating water rate may be a fixed value or a variable value. Here, the total of the designed maximum discharge rates is the designed maximum discharge rate (m ３ / h) × number of water pumps (n).

[0030] The number of operating water pumps is controlled to be the minimum natural number that satisfies the following formula (2): Number of operating pumps ≥ Water supply volume (m ３ / h) / Maximum designed discharge of water pump (m ３ / h) ... (2)

[0031] By changing the number of operating water pumps 32A to 32n based on the calculation results of equation (2), the amount of circulating water can be kept below the maximum designed discharge rate per water pump. Furthermore, by using an inverter to control the output of the operating water pumps within a range of 60 to 100% of the maximum designed discharge rate of the water pump, the amount of circulating water can be further reduced, ensuring that the amount of circulating water is always constant. Then, the control valve 55 can be controlled to maintain the desired amount of circulating water and water usage.

[0032] By performing such control, not only can the energy associated with the operation of the water pumps 32A to 32n be reduced, but the amount of chemicals injected from the chemical injection device 51 can also be reduced, and the operating energy of the water treatment device 30 can also be suppressed.

[0033] [Second embodiment] (Pure water production apparatus) Figures 2 and 3 show a second embodiment of the present invention, which is a specific example in which the embodiment shown in Figure 1 described above is configured with three water pumps, 32A, 32B, and 32C, and the outputs of the water pumps 32A to 32C are not inverter controlled.

[0034] Figure 2 shows the amount of circulating water at 20 m ３ / h, and the designed maximum discharge volume of the water pumps 32A, 32B, and 32C is set to 60 m ３ / h, the usage (required amount) of primary pure water W2 in the subsystem is 160 m ３ / h. Here, the number of pumps in operation is (160 + 20 (m ３ / h)) / 60(m ３ / h) = 3 (units), so the water pumps 32A, 32B, and 32C are operated at their maximum designed discharge rates, and the water is treated in the water treatment device 30 to produce 180 m ３ / h of primary pure water W2 is produced. Then, 160 m ３ / h is sent to the sub-tank 37, and the surplus 20m ３ / h is sent to a circulation path 54 communicating with the tank 31 for treated water.

[0035] As shown in FIG. 3, the amount of primary pure water W2 used in the subsystem is 100 m ３ / h, the circulating water from the circulation path 54 is 20 m ３ Since the fixed value is 100 / h, the number of pumps in operation is (100 + 20 (m ３ / h)) / 60(m ３ Therefore, the number of operating water pumps is reduced to two, that is, the water pump 32C is stopped, and the water pumps 32A and 32B are operated at their maximum designed discharge rates. The water is treated by the water treatment device 30, and 120 m ３ / h of primary pure water W2 is produced. Then, 100 m ３ / h is sent to the sub-tank 37, and the surplus 20m ３ / h is sent to the circulation path 54 communicating with the treated water tank 31. In this embodiment, if the value obtained by dividing the circulating water volume + the water usage volume by the designed maximum discharge volume of the water supply pump is not a positive integer, the circulating water volume can be increased by that amount.

[0036] According to this embodiment, the number of operating water pumps is determined and the start and stop of the water pumps is controlled based on this, so the operating energy of the pure water production system can be reduced and the amount of circulating water can be reduced compared to the conventional examples shown in Figures 7 and 8. Furthermore, since the amount of water treated by the water treatment device 30 is reduced, the amount of chemical solution M injected from the chemical injection device 51 can be reduced.

[0037] [Third embodiment] (Pure water production apparatus) Figures 4 and 5 show a third embodiment of the present invention, which is a specific example of inverter control of the outputs of the water pumps 32A to 32C in the embodiment shown in Figure 2 described above.

[0038] Figure 4 shows the circulating water volume at 20 m ３ / h, and the designed maximum discharge volume of the water pumps 32A, 32B, and 32C is set to 60 m ３ / h, and the amount of primary pure water W2 used (required amount) in the subsystem is 80 m ３ / h. Here, the number of pumps in operation is (80 + 20 (m ３ / h)) / 60(m ３ / h) = 1.67≦2 (units). Therefore, the number of operating water pumps is set to two, that is, water pump 32C is stopped and water pumps 32A and 32B are operated. In this case, if water pumps 32A and 32B are operated at the maximum designed discharge rate (100%), the discharge rate will be 120 m ３ / h of primary pure water W2 will be produced, and the amount of circulating water will be 40 m ３ / h, but in this embodiment, the output of the water pumps 32A and 32B is operated at 83% by inverter control, and the water is treated in the water treatment device 30 to produce 100 m ３ / h of primary pure water W2 is produced. Then, 80 m３ / h is sent to the sub-tank 37, and the surplus 20m ３ / h is sent to the circulation path 54 communicating with the tank 31 for treated water. This allows the primary pure water W2 to be sent without increasing the amount of circulating water.

[0039] As shown in FIG. 5, the amount of primary pure water W2 used in the subsystem is 30 m ３ / h, the amount of circulating water from the circulation path 54 is 20 m ３ / h, the number of pumps in operation is (30 + 20 (m ３ / h)) / 60(m ３ / h) = 0.67 ≦ 1 (unit). Therefore, the number of operating water pumps is set to one, that is, water pumps 32B and 32C are stopped and only water pump 32A is operated. In this case, if water pump 32A is operated at the maximum designed discharge rate (100%), the discharge rate will be 60 m ３ / h of primary pure water W2 will be produced, and the amount of circulating water will be 30 m ３ / h, but in this embodiment, the output of the water supply 32A is operated at 83% by inverter control, and the water is treated by the water treatment device 30 to produce 50 m ３ / h of primary pure water W2 is produced. Then, 30 m ３ / h is sent to the sub-tank 37, and the surplus 20m ３ / h is fed to the circulation path 54 communicating with the tank 31 for water to be treated. This allows the primary pure water W2 to be continuously fed without increasing the amount of circulating water.

[0040] According to this embodiment, the number of operating water pumps is determined, and the start and stop of the water pumps is controlled based on this, and the output of the water pumps is then inverter-controlled, so the pure water production system requires less energy to operate than the conventional systems shown in Figures 7 and 8, and can operate with a small amount of circulating water. Furthermore, since the amount of water treated by the water treatment device 30 is reduced, the amount of chemical solution M injected from the chemical injection device 51 can be reduced.

[0041] While the present invention has been described above based on the above-described embodiments, various modifications are possible. For example, the pure water production system 3 to which the present invention can be applied is not particularly limited as long as it has three or more water pumps, one or more water treatment devices downstream of the water pumps, a water supply line for supplying the pure water produced by the water treatment devices to a downstream system or point of use, and a circulation line branching off from the water supply line for returning excess pure water to a storage tank. Furthermore, the water treatment device downstream of the water supply pump is not particularly limited and can be composed of one or two types selected from 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. Furthermore, the present invention is not limited to cases in which primary pure water W2 is supplied to a subsystem of an ultrapure water production system, but can also be applied to cases in which primary pure water W2 is supplied to a point of use.

[0042] The present invention will be described in more detail below based on examples, but the present invention is not limited to the following examples.

[0043] Example 1 When the water supply amount is controlled only by turning on and off the water supply pumps 32A to 32C without inverter control as in the second embodiment shown in Figure 2, the amount of water supply, circulating water amount, water consumption amount, number of operating pumps, and reduced power consumption of the primary pure water W2 are shown in Table 1. The power consumption per water supply pump is 10 kWh.

[0044]

[0045] [Comparative Example 1] Table 2 shows the amount of primary pure water W2 supplied, the amount of circulated water, the amount of water used, the number of operating pumps, and the amount of reduced power consumption when the third water pumps 32A to 32C are constantly operated at their maximum designed discharge rate, as in the conventional example shown in Figure 7.

[0046]

[0047] As is clear from Table 1 and Table 2, the control method for the pure water production system of Example 1 can reduce power consumption by controlling the number of operating pumps, and can also reduce the amount of circulating water, compared to the control method for the pure water production system of Comparative Example 1.

[0048] 1 Ultrapure water production system 2 Pretreatment device 21 Coagulation treatment device 22 Turbidity removal UF membrane device 3 Primary pure water system (pure water production system) 30 Water treatment device 31 Tank for treated water 32 Water pump 32A, 32B, 32C Water pump 33 Reverse osmosis membrane device 34 Membrane degassing device 35 Ultraviolet oxidation device 36 Electrodeionization device 37 Sub-tank 4 Secondary pure water production system (subsystem) 41 Pump 42 Ultraviolet oxidation device 43 Membrane degassing device 44 Non-regenerative mixed bed ion exchange device 45 Ultrafiltration (UF) membrane 5 Point of use (UP) 51 Chemical injection device 52 Water supply channel 53 Supply channel 54 Circulation channel 55 Control valve 56 Flow meter 57 Flow meter W Raw water W1 Pretreated water (water to be treated) W2 Primary pure water W3 Ultra pure water (secondary pure water)

Claims

1. A method for controlling a pure water production system comprising a storage tank for water to be treated, three or more water supply pumps for supplying the water to be treated stored in the storage tank, and one or more water treatment devices installed downstream of the water supply pumps, a water supply channel for supplying the pure water produced by the water treatment devices to a downstream system or use point, and a circulation channel for returning excess pure water branched off from the water supply channel to the storage tank, wherein the method controls the number of operating water supply pumps and / or the output of the water supply pumps according to the amount of pure water required by the downstream system or use point.

2. A method for controlling a pure water production apparatus as described in claim 1, wherein the number of operating water pumps and / or the output of the water pumps are controlled so that the amount of water circulated through the circulation path is 20% or less of the total designed maximum discharge volume of the water pumps.

3. The method for controlling a pure water production system according to claim 2, wherein the output of the water pump is controlled to 60 to 100% of the maximum designed discharge rate of the water pump.

4. A method for controlling a pure water production apparatus as described in claim 3, in which the number of operating pumps is controlled so that the value obtained by dividing the amount of pure water delivered by the maximum designed discharge amount of each pump is rounded up to a natural number.

5. A method for controlling a pure water production system according to any one of claims 1 to 4, wherein a chemical injection device is provided in a water supply path for pure water produced by the primary pure water system, and the amount of chemicals added from the chemical injection device is adjusted according to the amount of pure water produced by the primary pure water system.

6. A method for controlling a pure water production system according to any one of claims 1 to 4, wherein the pure water produced in the primary pure water system is supplied to a downstream system, and the downstream system is operated in an adjusted manner according to the amount of water supplied to the downstream system.

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