Control method for an electrodeionization device

Abstract

The control method of the electrodeionization device (1) of the present application keeps the flow rate of concentrated water (W5) discharged from the electrodeionization device (1) constant and periodically reduces the flow rate of feed water (W1) supplied to the electrodeionization device (1). According to the control method of the electrodeionization device, the increase in electric conductivity can be prevented even when the flow rate of the feed water supplied to the electrodeionization device is reduced, thereby suppressing the generation of scale.

Description

TECHNICAL FIELD

[0001] The present application relates to a control method of an electrodeionization device. BACKGROUND

[0002] Conventionally, ultrapure water used in the field of electronics industry such as semiconductors is manufactured by treating raw water by an ultrapure water manufacturing device composed of a pretreatment system, a primary pure water manufacturing device, and a secondary pure water manufacturing device (subsystem) that treats the primary pure water.

[0003] The primary pure water manufacturing device included in such an ultrapure water manufacturing device is a highly versatile system used not only in the field of ultrapure water manufacturing devices but also in various fields such as pharmaceutical and food industries. As a configuration of the primary pure water manufacturing device, it is generally composed of a reverse osmosis membrane (RO membrane) device and an electrodeionization device, and the reverse osmosis membrane (RO membrane) device removes silica, salts, and ion-type and colloid-type TOC.

[0004] Here, the electrodeionization device generally has a structure in which cation exchange membranes and anion exchange membranes are alternately arranged between a cathode and an anode to alternately form desalination chambers and concentration chambers, and ion exchange resins are filled in the desalination chambers, and removal of various inorganic or organic anions and cations is performed.

[0005] When water is supplied to the desalination chambers of the electrodeionization device, ions in the water move in the direction of any one of the ion exchange resins in the anode / cathode in the desalination chambers under the action of their electric charges. The moving ions pass through the ion exchange resins and enter the concentration chambers, and thus, highly desalinated pure water is manufactured in the desalination chambers. On the other hand, the ions that move to the concentration chambers are discharged as concentrated water.

[0006] From the viewpoint of stably manufacturing primary pure water of a prescribed water quality, the electrodeionization device is operated so that the supply conditions of water to the electrodeionization device are fixed. Therefore, the following operation is performed: the required amount of primary pure water manufactured by the primary pure water manufacturing device including the electrodeionization device is supplied to a sub-tank of a secondary pure water manufacturing device, and on the other hand, the excess production of primary pure water is recycled in the primary pure water manufacturing device. SUMMARY

[0007] PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] However, as described above, in the conventional operation method of the primary pure water manufacturing apparatus, water supply exceeding the required amount is supplied to the electrodeionization device or the like and treated, and thus there is room for improvement in terms of energy efficiency. Therefore, it is considered that the treatment amount of the electrodeionization device is changed according to the required amount of the primary pure water, and in the operation of the electrodeionization device, when the flow rate of the water supply to the electrodeionization device is temporarily reduced, the conductivity of the concentrated water temporarily increases. When the conductivity of the concentrated water increases, the ion concentration in the concentration chamber increases, and there is a problem that scale is easily generated.

[0009] The present application was completed in view of the above problems, and an object thereof is to provide a control method of an electrodeionization device that prevents an increase in conductivity even when the flow rate of water supply to the electrodeionization device is reduced, thereby suppressing scale generation.

[0010] Means for solving the problem

[0011] In view of the above object, the present application provides a control method of an electrodeionization device, which is a control method of an electrodeionization device in which the flow rate of concentrated water discharged from the electrodeionization device is kept constant, and the flow rate of water supply to the electrodeionization device is reduced in stages (Invention 1).

[0012] According to the above-described application (Invention 1), by keeping the flow rate of concentrated water discharged from the electrodeionization device constant and reducing the flow rate of water supply to the electrodeionization device in stages, an increase in the conductivity of the concentrated water is prevented, and thus scale generation can be suppressed.

[0013] In the above-described application (Invention 1), the flow rate of the water supply reduced in each stage can be a flow rate of 10% or less of the maximum flow rate in the electrodeionization device (Invention 2).

[0014] In the above-described application (Invention 1 or 2), the time of each stage when the flow rate of the water supply is reduced in stages can be 1 to 10 minutes (Invention 3).

[0015] In the above-described application (Inventions 1 to 3), the flow rate of the water supply to the electrodeionization device can be reduced in stages by PID control (Invention 4).

[0016] Effects of the Invention

[0017] According to the article receiving system of the present application, a control method of an electrodeionization device that prevents an increase in conductivity even when the flow rate of water supply to the electrodeionization device is reduced, thereby suppressing scale generation, can be provided. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1This is a flowchart illustrating an ultrapure water manufacturing apparatus to which the control method of the electro-deionization device of the present invention can be applied.

[0019] Figure 2 This is a schematic diagram illustrating the control structure of the electro-deionization device in the control method of the electro-deionization device of the present invention.

[0020] Figure 3 This is a schematic diagram illustrating the electro-deionization apparatus used in the control method of the electro-deionization apparatus of the present invention.

[0021] Figure 4 This is a schematic diagram showing the water flow state of the electro-deionization device used in the control method of the electro-deionization device of the present invention.

[0022] Figure 5 This is a schematic diagram showing the control structure of the electro-deionization device of Example 1.

[0023] Figure 6 This is a graph showing the change in conductivity (mS / m) of the concentrated water discharged from the electro-deionization device per unit time in Example 1.

[0024] Figure 7 This is a graph showing the change in conductivity (mS / m) of the concentrated water discharged from the electro-deionization unit in Comparative Example 1 over a unit of time.

[0025] Figure 8 This is a graph showing the change in conductivity (mS / m) of the concentrated water discharged from the electro-deionization device per unit time in Comparative Example 2.

[0026] Figure 9 This is a graph showing the change in conductivity (mS / m) of the concentrated water discharged from the electro-deionization device per unit time in Comparative Example 3. Detailed Implementation

[0027] The control method of the electrode deionization device of the present invention will be described below with reference to the accompanying drawings. It should be noted that, for illustrative purposes, a portion of the electrode deionization device is included in the ultrapure water manufacturing apparatus in the drawings; however, the control method of the electrode deionization device of the present invention is not limited to this ultrapure water manufacturing apparatus and can be used in various fields such as pharmaceuticals and food.

[0028] (Electrodeionization device)

[0029] Figure 1 This diagram illustrates an ultrapure water manufacturing apparatus A capable of implementing the control method of the electrodeionization device 1 according to an embodiment of the present invention. Figure 1 As shown, the ultrapure water production device A consists of a pretreatment device 2 and an electro-deionization device 1. Figure 1The system consists of three stages: a primary pure water production unit 3 (referred to as CDI) and a secondary pure water production unit (subsystem) 4. In the pretreatment unit 2 of this ultrapure water production unit A, pretreatment based on raw water W is carried out, including filtration, flocculation sedimentation, and microfiltration membranes, mainly to remove suspended solids.

[0030] The primary pure water production apparatus 3 includes a reverse osmosis membrane unit 5, a degassing membrane unit 6, an ultraviolet oxidation unit 7, an electro-deionization unit 1, and a water supply pump 8 for supplying the pretreated water W1 to the electro-deionization unit 1. In this primary pure water production apparatus 3, most of the electrolytes, particles, live bacteria, etc., in the pretreated water W1 are removed, and organic matter is decomposed.

[0031] Subsystem 4 consists of a secondary tank 11, which stores desalinated water (in this embodiment, the electro-deionization device 1 is located at the end of the primary pure water production device 3, and is therefore equivalent to primary pure water, the same applies below) W2 produced in the primary pure water production device 3, and is arranged as a water storage tank at the downstream end of the electro-deionization device 1; an ultraviolet oxidation device 12, which processes the primary pure water W2 transported from the secondary tank 11 via a pump (not shown); a non-regenerative mixed-bed ion exchange device 13; and an ultrafiltration (UF) membrane 14, which serves as a membrane filtration device. Sometimes, an RO membrane separation device may also be provided as needed. In this subsystem 4, the trace amounts of organic matter (TOC components) contained in the primary pure water W2 are oxidized and decomposed by the ultraviolet oxidation device 12, and then processed by the non-regenerative mixed-bed ion exchange device 13, thereby removing residual carbonate ions, organic acids, anionic substances, metal ions, cationic substances, etc. through ion exchange. Furthermore, ultrafiltration (UF) membrane 14 is used to remove particulates to form ultrapure water W3, which is supplied to the point of use 15, and unused ultrapure water W3 is returned to the auxiliary tank 11.

[0032] In this embodiment, such as Figure 2 As shown, the primary pure water production apparatus 3 has a water supply pump 8 for controlling the flow rate of water supply W1 supplied to the electro-deionization device 1. The electro-deionization device 1, which is connected to the water supply pump 8, has a DC power supply 9 that can supply demineralized water W2 from the electro-deionization device 1 to a secondary tank 11, which is located at the rear of the electro-deionization device 1 and serves as a water storage tank.

[0033] In addition, a control valve 26 and a flow meter 27 for arbitrarily controlling the flow rate of the concentrated water W5 are provided in the flow path 25 of the electro-deionization unit 1. Furthermore, a control valve 23 and a flow meter 24 are also provided in the flow path 22 of the demineralized water W2 of the electro-deionization unit 1.

[0034] The control device 28, equipped with a personal computer or similar device, can increase or decrease the flow rate of the water supply W1 to the electro-deionization unit 1 by controlling the water supply pump 8, and can arbitrarily increase or decrease the flow rate of flow path 22 and / or flow path 25 by controlling control valves 23 and 26. Furthermore, the control device 28 can transmit measurement data from flow meters 24 and 27 respectively. Additionally, a level switch 21 for measuring the water storage capacity can be installed in the auxiliary tank 11, allowing control of the production rate of demineralized water W2 based on the measurement data of the water storage capacity in the auxiliary tank 11.

[0035] Here, as the electro-deionization device 1, it is preferable to use a device having Figure 3 and Figure 4 The device with the structure shown.

[0036] exist Figure 3 In the electrode deionization device 1, multiple anion exchange membranes 33 and cation exchange membranes 34 are alternately arranged between electrodes (anode 31, cathode 32) to alternately form a concentration chamber 35 and a desalination chamber 36. In the desalination chamber 36, ion exchangers (anion exchangers and cation exchangers) composed of ion exchange resins, ion exchange fibers, or graft exchangers are mixed or filled in a multilayered manner. In addition, ion exchangers are also filled in the concentration chamber 35, the anode chamber 37, and the cathode chamber 38.

[0037] In this electro-deionization device 1, a water supply mechanism (not shown) is provided for supplying water W1 to the desalination chamber 36 and removing demineralized water W2, and a concentrated water supply mechanism (not shown) is provided for supplying concentrated water W4 to the concentration chamber 35. In this embodiment, the concentrated water W4 is introduced into the concentration chamber 35 from the side of the desalination chamber 36 near the outlet of the demineralized water W2, and flows out from the side of the desalination chamber 36 near the inlet of the supply water W1. That is, the structure is such that the concentrated water W4 is introduced into the concentration chamber 35 from the direction opposite to the flow direction of the supply water W1 in the desalination chamber 36, and the concentrated water W5 is sprayed out. It should be noted that, for ease of explanation in this specification, the water supplied to the electro-deionization device 1 obtained by treating the pretreated water W1 through the reverse osmosis membrane device 5, the degassing membrane device 6, and the ultraviolet oxidation device 7 is also referred to as supply water W1.

[0038] As the concentrated water W4 introduced into the concentration chamber 35, the supply water W1 supplied to the desalination chamber 36 can be used, such as... Figure 4 As shown, the concentrated water W4 is preferably the desalinated water W2 obtained from the desalination chamber 36.

[0039] (Control method for the electro-deionization device)

[0040] The control method of the electro-deionization device 1 of this embodiment will be described below.

[0041] The control method of the electrodeionization device 1 in this embodiment maintains a constant flow rate of concentrated water W5 discharged from the electrodeionization device 1 and gradually reduces the flow rate of water supply W1 supplied to the electrodeionization device 1. This control method prevents an increase in the conductivity of the concentrated water W5, thereby suppressing scale formation.

[0042] As described above, the control method of the electro-deionization device 1 in this embodiment reduces the flow rate of the water supply W1 supplied to the electro-deionization device 1 in stages. Figure 2 As shown, water supply W1 is supplied to the electro-deionization device 1 via a water supply pump 8 that can control the flow rate. The flow rate of water supply W1 supplied to the electro-deionization device 1 can be reduced in stages using a pump inverter (not shown) attached to the water supply pump 8.

[0043] In one embodiment of the control method, the flow rate of water supply W1 reduced in each stage is preferably less than 10% of the maximum flow rate in the electro-deionization device 1. Furthermore, the flow rate of water supply W1 reduced in each stage is preferably more than 1% of the maximum flow rate in the electro-deionization device 1. If the flow rate of water supply W1 reduced in each stage is greater than 10%, the ion concentration of the concentrated water W5 increases, potentially leading to scale formation. As a more specific example of the water supply W1 reduction process, when the maximum flow rate in the electro-deionization device 1 is 5.0 L / min, it can be reduced in stages to 4.5 L / min, 4.0 L / min, 3.5 L / min, and 3.0 L / min. It should be noted that the reduction in the flow rate of water supply W1 in each stage does not necessarily need to be constant; the reduction in the flow rate of water supply W1 in each stage can vary within the above range. Furthermore, the overall reduction in the flow rate of water supply W1, summing the reductions in the flow rates of water supply W1 in all stages, is preferably less than 70% of the flow rate before the reduction of water supply W1 begins.

[0044] In one embodiment of the control method, the duration of each stage of progressively reducing the flow rate of the water supply W1 supplied to the electro-deionization device 1 is preferably 1 to 10 minutes. Within this range, it has the effect of suppressing the increase in the ion concentration of the concentrated water W5. As a more specific example, as described above, when the flow rate of the water supply W1 is progressively reduced to 5.0 L / min, 4.5 L / min, 4.0 L / min, 3.5 L / min, and 3.0 L / min, for example, it is possible to maintain 5.0 L / min for 10 minutes, then maintain it at 4.5 L / min for 10 minutes, then maintain it at 4.0 L / min for 10 minutes, then maintain it at 3.5 L / min for 10 minutes, and then maintain it at 3.0 L / min for 10 minutes.

[0045] In the control method of this embodiment, the flow rate of concentrated water W5 discharged from the electro-deionization device 1 is controlled to remain constant. For example, as Figure 2 As shown, based on the change in the water supply W1, the control device 28 controls the control valves 23 and 26 to control the flow rates of the demineralized water W2 and concentrated water W5 in the electro-deionization unit 1, thereby achieving the following: That is, the flow rate of concentrated water W5 is kept constant, and the amount of demineralized water (primary pure water) W2 is adjusted to change the recovery rate. Here, keeping it constant means that the flow rate of concentrated water W5 discharged from the electro-deionization unit 1 is within the range of 90% to 110%.

[0046] In addition, in one embodiment of the control method, there is no particular limitation on the amount of water recovered by the electro-deionization device 1, which is preferably 50% to 99%.

[0047] In one embodiment of the control method, the conductivity of the water supply W1 supplied to the electro-deionization device 1 is not particularly limited, but is preferably 0.1 to 5 mS / m. Furthermore, the current efficiency of the water supply W1 supplied to the electro-deionization device 1 is preferably 1 to 30%.

[0048] In one embodiment of the control method, the flow rate of the water supply W1 to the electro-deionization device 1 can be reduced in stages using PID (Proportional-Integral-Differential) control. For example, measuring... Figure 2 The water storage capacity of the secondary tank 11 shown is... Figure 5 The flow rate of demineralized water W2 flowing in the demineralized water flow path 54 shown is determined based on these target values, through... Figure 2 Water supply pump 8 Figure 5 The output of the water supply pump 55 is controlled by PID, which can reduce the flow rate of water supply W1 supplied to the electro-deionization device 1 in stages.

[0049] Example

[0050] The present invention will be described in more detail below based on embodiments, but the present invention is not limited to the following embodiments.

[0051] [Example 1]

[0052] use Figure 5Experiments were conducted using a test apparatus 51 for controlling the electro-deionization device 1 shown. This test apparatus 51, in addition to the electro-deionization device 1, includes a water supply path 52, a concentrated water flow path 53, and a demineralized water (primary pure water) flow path 54. Furthermore, in the water supply path 52, a water supply pump 55 for controlling the flow rate of the water supply W1 to the electro-deionization device 1 is connected to a calcium chloride solution tank 56, which serves as a calcium ion source, via a chemical solution pump 56A, and a conductivity meter 57A is installed. In the concentrated water flow path 53, a control valve 59B for controlling the flow rate to an arbitrary amount and a flow meter 58B are installed, and a conductivity meter 57B is also connected. Additionally, in the demineralized water flow path 54, a control valve 59A and a flow meter 58A are installed, and a resistivity meter 60 is connected. It should be noted that, as the electro-deionization device 1, a... Figure 3 and Figure 4 The structure shown.

[0053] During the operation of the aforementioned test apparatus 51, the flow rate of concentrated water W5 discharged from the electro-deionization unit 1 was maintained at a constant value (1.0 L / min) using control valves 59A and 59B. The flow rate of water W1 supplied to the electro-deionization unit 1 was periodically reduced using the water supply pump 55 to reach 5.0 L / min, 4.5 L / min, 4.0 L / min, and 3.5 L / min every 10 minutes. The conductivity (mS / m) of the concentrated water W5 flowing in the concentrated water flow path 53 caused by this operation was measured over time using a conductivity meter 57B. The results are presented as follows: Figure 6 It should be noted that the above operation begins from time 0 in the diagram. Figures 7-9 Similarly). In addition, the current value of the electro-deionization device 1 in the experiment was 4.0A, the calcium concentration in the water supply W1 after adding calcium chloride was 400μg / L (calculated as CaCO3), and the conductivity of the water supply W1 was in the range of 0.10 to 0.12mS / m.

[0054] [Comparative Example 1]

[0055] The same test apparatus 51 as in Example 1 was used to conduct the test of Comparative Example 1. During operation of this test apparatus 51, when the flow rate of concentrated water W5 discharged from the electro-deionization unit 1 was instantaneously reduced from 1.0 L / min to 0.7 L / min, the flow rate of supply water W1 to the electro-deionization unit 1 was also instantaneously reduced from 5.0 L / min to 3.5 L / min. The change in conductivity (mS / m) of the concentrated water W5 flowing in the concentrated water flow path 53 caused by this operation was measured over time using a conductivity meter 57B. The results are shown below. Figure 7 It should be noted that other conditions are the same as in Example 1.

[0056] [Comparative Example 2]

[0057] The same test apparatus 51 as in Example 1 was used to conduct the test of Comparative Example 2. During operation of this test apparatus 51, the flow rate of concentrated water W5 discharged from the electro-deionization unit 1 was maintained at a constant value (1.0 L / min), and the flow rate of supply water W1 supplied to the electro-deionization unit 1 was instantaneously reduced from 5.0 L / min to 3.5 L / min. The change in conductivity (mS / m) of the concentrated water W5 flowing in the concentrated water flow path 53 caused by this operation was measured over time using a conductivity meter 57B. The results are shown below. Figure 8 It should be noted that other conditions are the same as in Example 1.

[0058] [Comparative Example 3]

[0059] The same test apparatus 51 as in Example 1 was used to conduct the test of Comparative Example 3. During operation of this test apparatus 51, the flow rate of concentrated water W5 discharged from the electro-deionization unit 1 was progressively reduced to 1 L / min, 0.9 L / min, 0.8 L / min, and 0.7 L / min every 10 minutes. Similarly, the flow rate of supply water W1 to the electro-deionization unit 1 was also progressively reduced to 5.0 L / min, 4.5 L / min, 4.0 L / min, and 3.5 L / min every 10 minutes. The change in conductivity (mS / m) of the concentrated water W5 flowing in the concentrated water flow path 53 caused by this operation was measured over time using a conductivity meter 57B. The results are shown below. Figure 9 It should be noted that other conditions are the same as in Example 1.

[0060] [Results and Investigation]

[0061] Depend on Figures 6-9 It can be seen that no increase in the conductivity of the concentrated water W5 caused by operation was observed in Example 1, while the conductivity of the concentrated water W5 increased in Comparative Examples 1 to 3. That is, the control method of the electro-deionization device 1 in Example 1 can prevent the increase in conductivity, thereby suppressing the formation of scale. On the other hand, in the control methods of Comparative Examples 1 to 3, the conductivity of the concentrated water W5 increased, therefore, scale may form.

[0062] The embodiments described below are for the purpose of facilitating understanding of the present invention and are not intended to limit the present invention. Therefore, the essence of the elements disclosed in the above embodiments also includes all design changes and equivalent substitutions that fall within the technical scope of the present invention.

[0063] Explanation of reference numerals in the attached figures

[0064] A Ultrapure Water Production Unit

[0065] 1. Electrodeionization device

[0066] 2. Pre-treatment device

[0067] 3. Primary Pure Water Production Unit

[0068] 4. Secondary Pure Water Production Unit (Subsystem)

[0069] 5. Reverse osmosis membrane unit

[0070] 6. Degassing membrane device

[0071] 7. Ultraviolet Oxidation Device

[0072] 8 Water supply pumps

[0073] 9 DC power supply

[0074] 11. Secondary tank

[0075] 12 Ultraviolet Oxidation Device

[0076] 13 Non-regenerative mixed-bed ion exchange devices

[0077] 14 Ultrafiltration (UF) Membrane

[0078] 15 water points

[0079] 21. Horizontal switch (water level measuring mechanism)

[0080] 22. Flow path of desalinated water

[0081] 23, 26 Control valves

[0082] Flow meters 24 and 27

[0083] 25. Concentrated water flow path

[0084] 28. Control device

[0085] 31 Anode (Electrode)

[0086] 32 Cathode (Electrode)

[0087] 33 Anion exchange membrane

[0088] 34 Cation exchange membrane

[0089] 35 Concentration Chamber

[0090] 36 Desalination Chamber

[0091] 51 Experimental Apparatus

[0092] 52 Water supply path

[0093] 53 Concentrated Water Flow Path

[0094] 54 Desalinated water flow path

[0095] 55 Water supply pump

[0096] 56 Calcium chloride solution tank, 56A chemical solution pump

[0097] 57A and 57B conductivity meters

[0098] 58A and 58B flow meters

[0099] 59A and 59B control valves

[0100] 60 Resistivity Meter

[0101] W raw water

[0102] W1 Pre-treated water (water supply)

[0103] W2 is a primary purified water (demineralized water) solution.

[0104] W3 Ultrapure Water (Secondary Pure Water)

[0105] W4 was concentrated water

[0106] W5 Concentrated Water.

Claims

1. A control method for an electro-deionization device, wherein, The flow rate of concentrated water discharged from the electro-deionization unit is kept constant, and the flow rate of water supplied to the electro-deionization unit is reduced in stages. The water flow rate is reduced to less than 10% of the maximum flow rate in the electro-deionization device at each stage.

2. The control method for the electro-deionization device as described in claim 1, wherein, The duration of each stage of the phased reduction of the water supply flow is 1 to 10 minutes.

3. The control method for the electro-deionization device as described in claim 1 or 2, wherein, The flow rate of water supplied to the electro-deionization device is reduced in stages by using PID control.

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