Electrodeionization system and control method of electrodeionization system

Abstract

This invention provides an electro-deionization system and its control method. The electro-deionization system includes multiple electro-deionization devices, which suppress scale formation caused by reduced water flow to each electro-deionization device and reduce production costs. An electro-deionization system 1 and its control method are provided. The electro-deionization system 1 includes multiple electro-deionization devices 1A arranged in parallel, and includes: a water supply flow rate variation component to vary the water supply flow rate to the multiple electro-deionization devices 1A; a concentrate flow rate adjustment component to adjust the flow rate of concentrate W4 discharged from each of the multiple electro-deionization devices 1A for each of the multiple electro-deionization devices 1A; and a concentrate flow rate maintenance component to maintain the flow rate of concentrate W4 discharged from each of the multiple electro-deionization devices 1A at a certain level or above. The concentrate flow rate maintenance component is only provided in the main flow path 23 and the main path 25. The main flow path 23 is formed by combining multiple secondary flow paths 22 for the flow of demineralized water W2 produced by each of the multiple electro-deionization devices 1A, and the main path 25 is formed by combining multiple secondary flow paths 24 for the flow of concentrate W4 discharged from each of the multiple electro-deionization devices 1A.

Description

Technical Field

[0001] This invention relates to an electro-deionization system having multiple electro-deionization devices and a control method thereof. Prior Technology

[0002] Ultrapure water used in the semiconductor and other electronics industries is produced by treating raw water using an ultrapure water manufacturing device, which includes a pretreatment system, a primary pure water system, and a subsystem for treating the primary pure water.

[0003] This type of ultrapure water production equipment includes a primary pure water production unit, which is a highly versatile system used not only in ultrapure water production but also in various fields such as pharmaceuticals and food. The primary pure water system typically comprises a two-stage reverse osmosis (RO) membrane unit and an electro-deionization unit. The RO membrane unit removes silica or salts and also removes ionic and colloidal total organic carbon (TOC).

[0004] Here, the electro-deionization device typically has a structure in which cation exchange membranes and anion exchange membranes are alternately arranged between the cathode and the anode to form desalination chambers and concentration chambers, and the desalination chambers are filled with ion exchange resin to remove various inorganic or organic anions and cations.

[0005] If water is supplied to the desalination chamber of the electro-deionization device, the ions in the water move towards the ion exchange resins at either the anode or cathode within the desalination chamber due to their charge. The moving ions pass through the ion exchange resins and enter the concentration chamber, thus producing highly desalinated pure water within the desalination chamber. Conversely, the ions that have moved to the concentration chamber remain there and are eventually discharged as concentrated water.

[0006] In situations requiring the treatment of large volumes of water, this type of electrodeionization device is often used in electrodeionization systems with multiple devices arranged in parallel. Such systems typically adjust the water supply conditions to the electrodeionization system based on the conditions of the systems preceding and following them. For example, in the electrodeionization system used in the primary pure water system of an ultrapure water production plant, the water supply flow rate to the electrodeionization system is increased or decreased according to the pure water usage in the combined subsystems, thereby controlling the primary pure water production volume. Summary of the Invention

[0007] [The problem that the invention aims to solve]

[0008] However, when the water supply flow rate is reduced during the operation of the electro-deionization system, there is a problem of scale formation due to excessive concentration of concentrated water in each of the multiple electro-deionization units.

[0009] The present invention was made in view of the aforementioned problems, and its object is to provide an electro-deionization system that suppresses scale formation caused by a reduction in the water supply flow to each electro-deionization device and reduces production costs. [Methods for solving problems]

[0010] In view of the aforementioned objective, firstly, the present invention provides an electro-deionization system comprising a plurality of electro-deionization devices arranged in parallel, and comprising: a water supply flow rate variation component for varying the water supply flow rate to the plurality of electro-deionization devices; a concentrate flow rate adjustment component for adjusting the flow rate of concentrate discharged from each of the plurality of electro-deionization devices for each of the electro-deionization devices; and a concentrate flow rate maintenance component for maintaining the flow rate of concentrate discharged from each of the plurality of electro-deionization devices at a certain level or above, wherein the concentrate flow rate maintenance component is only provided in the main flow path and the main path, the main flow path being a combination of a plurality of secondary flow paths for the flow of demineralized water produced by each of the plurality of electro-deionization devices, and the main path being a combination of a plurality of secondary flow paths for the flow of concentrate discharged from each of the plurality of electro-deionization devices (Invention 1).

[0011] According to the invention (Invention 1), even when the flow rate (also called water supply flow rate) of the water supplied to multiple electro-deionization devices varies, the flow rate (also called concentrated water flow rate) of the concentrated water discharged from each electro-deionization device can be kept constant, thereby suppressing scale formation. Furthermore, even without installing concentrated water flow rate maintaining components in each secondary flow path or secondary path, as long as concentrated water flow rate maintaining components are installed only in the main flow path of the demineralized water and the main path of the concentrated water, the flow rate of the concentrated water can be kept constant, thus reducing the production cost of the electro-deionization system.

[0012] In the invention (Invention 1), the water supply flow rate changing component can also increase or decrease the water supply flow rate within the range of 30% to 100% (Invention 2).

[0013] In the invention (invention 1 or invention 2), the concentrated water flow maintaining component may also be a first control valve provided in the main flow path and a second control valve provided in the main flow path (invention 3).

[0014] In the inventions (Inventions 1 to 3), the concentrated water flow rate adjustment component may also be a manual valve equipped in the secondary path (Invention 4).

[0015] Furthermore, secondly, the present invention provides a control method for an electro-deionization system, which includes a control method for an electro-deionization system comprising multiple electro-deionization devices arranged in parallel, comprising: a water supply flow rate variation step, which varies the water supply flow rate to the multiple electro-deionization devices; a concentrate flow rate adjustment step, which adjusts the flow rate of concentrate discharged from each of the multiple electro-deionization devices for each of the electro-deionization devices; and a concentrate flow rate maintenance step, which uses a first control valve provided only in the main flow path and a second control valve provided only in the main path to maintain the flow rate of concentrate discharged from each of the multiple electro-deionization devices at a certain level or above, wherein the main flow path is formed by combining multiple secondary flow paths for the flow of demineralized water produced by each of the multiple electro-deionization devices, and the main path is formed by combining multiple secondary flow paths for the flow of concentrate discharged from each of the multiple electro-deionization devices (Invention 5).

[0016] According to the invention (Invention 5), in an electro-deionization system comprising multiple electro-deionization devices, even when the water supply flow rate to each electro-deionization device varies, the flow rate of concentrated water discharged from each electro-deionization device can be kept constant, thereby suppressing scale formation. Furthermore, even if control valves are not provided in the sub-paths or sub-paths, control valves installed only in the main flow path supplying demineralized water and the main flow path supplying concentrated water can be used to maintain a constant flow rate of concentrated water, thus reducing the operating cost of the electro-deionization system.

[0017] In the invention (invention 5), the water supply flow rate variation step can also be: the water supply flow rate increases or decreases within the range of 30% to 100% (invention 6). [The effects of the invention]

[0018] According to the present invention, an electro-deionization system can be provided that suppresses scale formation caused by a reduction in the water supply flow to each electro-deionization device and reduces production costs. Simple Explanation of the Diagram

[0019] Figure 1 is a flowchart illustrating an ultrapure water manufacturing apparatus to which the electrodeionization system of the present invention can be applied. Figure 2 is a schematic diagram showing the electro-deionization system of the present invention. Figure 3 is a schematic diagram showing the control structure of the experimental setup used in the verification experiment. Figure 4 is a graph showing the changes in the flow rate (water volume) of desalinated water and concentrated water relative to the change in water supply flow rate during the verification experiment. Figure 5 is a graph showing the changes in pressure loss of desalinated water and concentrated water relative to changes in water supply flow rate during the verification experiment. Implementation

[0020] The electrodeionization system of the present invention will now be described with reference to the accompanying drawings. Furthermore, for the purpose of explanation, a portion of the figures showing the electrodeionization system installed in an ultrapure water production apparatus will be used for illustration. However, the electrodeionization system and its control method are not limited to this ultrapure water production apparatus and can be used in various fields such as pharmaceuticals and food.

[0021] (Electrodeionization system) Figure 1 is a diagram showing an ultrapure water production apparatus A capable of being installed with an electro-deionization system 1 based on an embodiment of the present invention. As shown in Figure 1, the ultrapure water production apparatus A comprises three sections: a pretreatment unit 2, a primary pure water production unit 3 containing the electro-deionization system 1 (represented in Figure 1 as a CDI (Capacitive Deionization) system), and a secondary pure water production unit (subsystem) 4. In the pretreatment unit 2 of this ultrapure water production apparatus A, pretreatment of the raw water W is performed through filtration, coagulation and sedimentation, and microfiltration membranes, primarily removing suspended solids.

[0022] The primary pure water production apparatus 3 includes a reverse osmosis membrane device 5, a degassing membrane device 6, an ultraviolet oxidation device 7, and an electro-deionization system 1 for treating pretreated water (also known as supply water) W1. This primary pure water production apparatus 3 removes most of the electrolytes, microparticles, and live bacteria from the pretreated water W1, and decomposes organic matter.

[0023] Subsystem 4 includes: a sub-tank 11 serving as a storage tank, storing primary purified water (demineralized water) W2 produced by the primary purified water production unit 3, located downstream of the electro-deionization system 1; and an ultraviolet oxidation unit 12, a non-regenerative mixed-bed ion exchange unit 13, and an ultrafiltration (UF) membrane 14 serving as a membrane filtration unit, for treating the primary purified water W2 supplied from the sub-tank 11 via a pump (not shown). Subsystem 4 may also be further equipped with an RO membrane separation unit as needed. In this subsystem 4, the trace amounts of organic matter (TOC components) contained in the primary purified water W2 are oxidized and decomposed by the ultraviolet oxidation unit 12, and then treated by the non-regenerative mixed-bed ion exchange unit 13, thereby removing residual carbonate ions, organic acids, anionic substances, and subsequently metal ions or cationic substances through ion exchange. Then, ultrapure water W3 is produced by removing microparticles using ultrafiltration (UF) membrane 14 and supplied to point of use 15. Unused ultrapure water is returned to sub-tank 11.

[0024] FIG2 will be used to describe an embodiment of the electro-deionization system 1 of the present invention. As shown in FIG2, the electro-deionization system 1 of an embodiment of the present invention includes a plurality of electro-deionization devices 1A arranged in parallel.

[0025] In the electro-deionization system 1, firstly, water W1 of any flow rate is supplied to each electro-deionization unit 1A through flow path 21 by a water supply pump 1B that can vary the water supply flow rate to the electro-deionization unit 1A. The water W1 supplied to each electro-deionization unit 1A is processed by each electro-deionization unit 1A to become demineralized water (primary pure water) W2 and concentrated water W4.

[0026] The demineralized water W2 produced by each electro-deionization unit 1A flows through a secondary flow path 22 and merges with the main flow path 23. A manual valve 1C and a flow meter 1D are installed in the secondary flow path 22, and a first control valve 1E and a flow meter 1F are installed in the main flow path 23. Concentrated water W4 discharged from each electro-deionization unit 1A flows through a secondary path 24 and then merges with the main path 25. A manual valve 1G and a flow meter 1H are installed in each secondary path 24, and a second control valve 1I and a flow meter 1J are installed in the main path 25.

[0027] Additionally, the electro-deionization system 1 may also be equipped with a control device (not shown), which can control the first control valve 1E equipped in the main flow path 23 and the second control valve 1I equipped in the main path 25 according to the flow rate change of the water supply W1 from the pump 1B.

[0028] The water supply flow rate regulating component, corresponding to pump 1B in Figure 2, is a component that regulates the flow rate of water W1 supplied to the multiple electro-deionization units 1A. This component can vary the flow rate of water W1 within a range of 30% to 100%, assuming the original flow rate is set to 100%. Here, the original flow rate of water W1 is the flow rate at which the sum of the maximum flow rates specified in the catalogues of each electro-deionization unit 1A is set to its maximum value. By keeping the variation in the flow rate of water W1 within this range, as shown in the verification experiment described later, the flow rates of demineralized water W2 produced by each electro-deionization unit 1A and the concentrated water W4 discharged from each electro-deionization unit 1A change approximately proportionally to the change in the flow rate of water W1, thus making it easier to maintain a constant flow rate of concentrated water W4.

[0029] In addition, the water supply flow rate variation component is shown as pump 1B in Figure 2, but it is not limited to pump 1B as long as the flow rate of water W1 supplied to the electro-deionization device 1A can be varied. For example, the water pump or high-pressure pump (not shown) that supplies water to the RO (reverse osmosis membrane device) 5 in Figure 1 can also be used.

[0030] The concentrate flow rate adjustment component, equivalent to the manual valve 1G in Figure 2, is used to adjust the flow rate of the discharged concentrate W4 for each electro-deionization unit 1A. The concentrate flow rate adjustment component is installed in each secondary path 24 of the flow path of the concentrate W4 discharged from each electro-deionization unit 1A. During startup or the initial stage of operation of the electro-deionization system 1, the concentrate flow rate adjustment component is used to adjust the flow rate of the discharged concentrate W4 for each electro-deionization unit 1A to a predetermined value. Then, the concentrate flow rate maintenance component (described later) is used to adjust the flow rates of the demineralized water W2 and the concentrate W4, thereby maintaining a constant flow rate of the concentrate W4 even if the flow rate of the water supply W1 changes.

[0031] In addition, the concentrate flow rate adjustment component is shown as a manual valve 1G in Figure 2, but there are no particular restrictions as long as the flow rate of the concentrate W4 discharged from each electro-deionization unit 1A can be adjusted. For example, a constant flow valve can also be used.

[0032] The concentrate flow rate maintaining component, corresponding to the first control valve 1E in the main flow path 23 and the second control valve 1I in the main path 25 in Figure 2, is a component that maintains the flow rate of concentrate W4 discharged from each electro-deionization unit 1A at a certain level or higher. Furthermore, as shown in Figure 2, this concentrate flow rate maintaining component is only provided in the main flow path 23 and the main path 25. The main flow path 23 is formed by integrating multiple secondary flow paths 22 generated by each of the multiple electro-deionization units 1A for the flow of demineralized water W2, and the main path 25 is formed by integrating multiple secondary flow paths 24 for the flow of concentrate W4 discharged from each of the multiple electro-deionization units 1A.

[0033] In this concentrated water flow maintaining component, for example, based on the change in the flow rate of the water supply W1 from pump 1B, the first control valve 1E equipped in the main flow path 23 and the second control valve 1I equipped in the main path 25 are controlled, thereby controlling the flow rates of the demineralized water W2 and the concentrated water W4 of the electro-deionization unit 1A. That is, when the flow rate of the water supply W1 decreases, by reducing the flow rate of the demineralized water W2, the flow rate of the concentrated water W4 can be kept constant or higher.

[0034] By using the concentrate flow rate maintaining component and the concentrate flow rate adjusting component, the flow rate of concentrate W4 discharged from each of the multiple electro-deionization devices 1A can be maintained at a certain value for each electro-deionization device 1A, thereby suppressing scale formation. Furthermore, by installing the concentrate flow rate maintaining component only in the main flow path 23 and the main path 25, compared to installing it in multiple secondary flow paths 22 or multiple secondary paths 24, the number of concentrate flow rate maintaining components can be reduced, thus reducing the manufacturing cost of the electro-deionization system 1.

[0035] In addition, the concentrate flow rate maintenance component is shown in Figure 2 with the first control valve 1E and the second control valve 1I as examples, but there are no particular restrictions as long as the flow rate of concentrate W4 can be maintained at a certain level or above. For example, the constant flow valve equipped in the main path 25 can also be used.

[0036] (Control method for electro-deionization system) Next, the control method of the electro-deionization system 1 of this embodiment will be described.

[0037] The control method of the electro-deionization system 1 according to one embodiment of the present invention is a control method for an electro-deionization system 1 including multiple electro-deionization devices 1A arranged in parallel, and includes a water supply flow rate variation step, a concentrate flow rate adjustment step, and a concentrate flow rate maintenance step. Hereinafter, each step will be described using FIG2.

[0038] In one embodiment of the control method for the electro-deionization system 1, the water supply flow rate variation step involves using a water supply pump 1B to vary the water supply flow rate to each electro-deionization unit 1A to an arbitrary amount. Furthermore, the concentrate flow rate adjustment step involves using a manual valve 1G equipped in each sub-path 24 to adjust the flow rate of concentrate W4 discharged from each electro-deionization unit 1A to a predetermined value for each unit 1A.

[0039] Furthermore, the concentrate flow rate maintenance step is as follows: The flow rate of concentrate W4 discharged from each of the multiple electro-deionization units 1A is maintained at a certain level or higher using a first control valve 1E located only in the main flow path 23 and a second control valve 1I located only in the main path 25. The main flow path 23 is formed by combining multiple secondary flow paths 22 for the flow of demineralized water W2 produced by each of the multiple electro-deionization units 1A, and the main path 25 is formed by combining multiple secondary flow paths 24 for the flow of concentrate W4 discharged from each of the multiple electro-deionization units 1A. As an example of the concentrate flow rate maintenance step, when the flow rate of the supply water W1 decreases, the flow rate of the demineralized water W2 can be reduced by using the first control valve 1E, thereby maintaining the flow rate of the concentrate W4 at a certain level or higher.

[0040] The control method of the electro-deionization system 1 includes a concentrate flow rate adjustment step and a concentrate flow rate maintenance step. Even if the supply flow rate changes during the supply flow rate variation step, the flow rate of the concentrate W4 can be kept constant, thus suppressing scale formation. In addition, by using control valves installed only in the main flow path 23 and the main path 25, rather than in each of the secondary flow paths 22 or 24, the concentrate flow rate maintenance step can be performed, thereby reducing the operating cost of the electro-deionization system 1.

[0041] The water supply flow rate variation step can also be performed by setting the initial water supply flow rate to 100% and then varying the flow rate within a range of 30% to 100%. By keeping the water supply flow rate within this range, as in the verification experiment described later, the concentrated water W4 discharged from each electro-deionization unit 1A changes approximately proportionally to the change in water supply flow rate, thus making it easy to maintain a constant concentration of concentrated water W4. Furthermore, in the water supply flow rate variation step, pump 1B is used to vary the water supply flow rate, but this is not a limitation; various pumps, such as high-pressure pumps, can also be used.

[0042] Furthermore, in the water supply flow rate variation step, the time from the start of the variation to its end (e.g., from the water supply flow rate from 100% to 30%) is preferably 1 minute to 30 minutes. By keeping the variation time within this range, the amount of concentrated water W4 discharged from each electro-deionization unit 1A becomes more proportional to the change in water supply flow rate, thereby making it easier to maintain a constant flow rate of concentrated water W4.

[0043] In the concentrated water flow rate adjustment step, a method is shown to use the manual valve 1G equipped in the sub-path 24 to make the flow rate of concentrated water W4 discharged from each electro-deionization unit 1A a specified value for each electro-deionization unit 1A, but it is not limited to this and a method using a constant flow valve may also be used.

[0044] In addition, in the concentrated water flow maintenance step, the following method is used: the flow rate of concentrated water W4 is kept constant or higher by using a first control valve 1E provided in the main flow path 23 and a second control valve 1I provided in the main path 25. The main flow path 23 is formed by combining the secondary flow path 22 for the flow of demineralized water W2, and the main path 25 is formed by combining the secondary flow path 24 for the flow of concentrated water W4 discharged from each of the multiple electro-deionization devices 1A. However, it is not limited to this, and the method of using a constant flow valve equipped in the main path 25 can also be used.

[0045] (Verification Experiment) Next, a verification experiment to confirm the effectiveness of the present invention was conducted using the test apparatus 31 for controlling the electro-deionization device 1A shown in Figure 3. This test apparatus 31, in addition to the electro-deionization device 1A, also includes a water supply tank 32, a water supply path 33, a pump 1B, a demineralized water (primary pure water) path 34, and a concentrated water path 35. The demineralized water W2 produced by the electro-deionization device 1A and the concentrated water W4 discharged from the electro-deionization device 1A flow through the demineralized water path 34 and the concentrated water path 35, respectively, and then flow back into the water supply tank 32. Furthermore, the electro-deionization device 1A uses a counter-current method, and a flow meter and a pressure gauge (neither shown) are respectively equipped in the demineralized water path 34 and the concentrated water path 35.

[0046] In the test apparatus 31, with the flow rate of the initial water supply W1 set to 100%, pump 1B was used to reduce the water supply flow rate to the electro-deionization device 1A from 100% to 30% within 20 minutes. The changes in flow rate and pressure loss of the primary purified water W2 and concentrated water W4 relative to this change in water supply flow rate were measured. Next, the water supply flow rate to the electro-deionization device 1A was returned from 30% to 100% within 20 minutes, and the changes in flow rate and pressure loss of the primary purified water W2 and concentrated water W4 relative to this change in water supply flow rate were measured. The results of repeating this operation twice are shown in Figures 4 and 5. Furthermore, flow meters and pressure gauges, respectively installed in the demineralized water flow path 34 and the concentrated water flow path 35, were used in the measurements.

[0047] As shown in Figures 4 and 5, it can be confirmed that even when the flow rate of the water supply W1 varies between 100% and 30%, the flow rate and pressure of the primary pure water W2 and the concentrated water W4 remain approximately proportional to the change in the flow rate of the water supply W1. Based on these results, it is believed that even in an electro-deionization system 1 including multiple electro-deionization devices 1A as in this invention, as long as the amount of concentrated water W4 discharged from each electro-deionization device 1A can be adjusted to a predetermined value, the flow rate of concentrated water W4 discharged from each electro-deionization device 1A can be controlled at a certain value simply by using the first control valve 1E equipped in the main flow path 23 and the second control valve 1I equipped in the main path 25.

[0048] The embodiments described above are provided to facilitate understanding of the present invention and are not intended to limit the invention. Therefore, the elements disclosed in the embodiments also encompass all design changes or equivalents that fall within the scope of the present invention.

[0049] 1: Electrodeionization system 1A: Electrodeionization device 1B: Pump 1C, 1G: Manual valve 1D, 1F, 1H, 1J: Flow meters 1E: First control valve 1I: Second control valve 2: Pre-treatment device 3: Primary pure water production device 4: Secondary pure water production unit (subsystem) 5: Reverse osmosis membrane unit (RO) 6: Degassing membrane device 7, 12: Ultraviolet Oxidation Device 11: Sub-slot 13: Non-regenerative mixed-bed ion exchange device 14: Ultrafiltration (UF) membrane 15: Points of Use 21: Water supply path 22: Secondary flow path of demineralized water 23: The Mainstream Path of Desalinated Water 24: Secondary pathways of concentrated water 25: Main path of concentrated water 31: Test Apparatus 32: Water supply tank 33: Water supply path 34: Demineralized water (primary pure water) flow path 35: Concentrated water flow path A: Ultrapure water production equipment W: raw water W1: Pre-treated water (water supply) W2: Primary purified water (demineralized water) W3: Ultrapure water (secondary purified water) W4: Concentrated Water

Claims

1. An electro-deionization system comprising a plurality of electro-deionization devices arranged in parallel, and further comprising: A water supply flow rate variation component causes the water supply flow rate to the plurality of electro-deionization devices to vary. A concentrate flow rate adjustment component adjusts the flow rate of concentrate discharged from each of the plurality of electro-deionization devices for each of the aforementioned electro-deionization devices; The system includes a concentrate flow rate maintaining component to maintain the flow rate of concentrate discharged from each of the plurality of electro-deionization devices at a certain level. The concentrate flow rate maintaining component is only provided in the main flow path and the main path. The main flow path is formed by combining multiple secondary flow paths for the flow of demineralized water produced by each of the plurality of electro-deionization devices. The main path is formed by combining multiple secondary flow paths for the flow of concentrate discharged from each of the plurality of electro-deionization devices.

2. The electro-deionization system as described in claim 1, wherein, The water supply flow rate variable component allows the water supply flow rate to increase or decrease within the range of 30% to 100%.

3. The electro-deionization system as described in claim 1 or claim 2, wherein, The concentrated water flow maintaining components are a first control valve in the main flow path and a second control valve in the main flow path.

4. The electro-deionization system as described in claim 1 or claim 2, wherein, The concentrated water flow rate adjustment component is a manual valve equipped in the secondary path.

5. The electro-deionization system as described in claim 3, wherein, The concentrated water flow rate adjustment component is a manual valve equipped in the secondary path.

6. A control method for an electro-deionization system, comprising multiple electro-deionization devices arranged in parallel, including: The water supply flow rate variation step causes the water supply flow rate to the plurality of electro-deionization devices to vary. The concentrated water flow rate adjustment step involves adjusting the flow rate of concentrated water discharged from each of the plurality of electro-deionization devices for each of the aforementioned electro-deionization devices. The process includes a concentrate flow rate maintenance step, in which a first control valve located only in the main flow path and a second control valve located only in the main path are used to maintain the flow rate of concentrate discharged from each of the plurality of electro-deionization devices at a certain level or above. The main flow path is formed by combining multiple secondary flow paths for the flow of demineralized water produced by each of the plurality of electro-deionization devices, and the main path is formed by combining multiple secondary flow paths for the flow of concentrate discharged from each of the plurality of electro-deionization devices.

7. A control method for the electro-deionization system as described in claim 6, wherein, The water supply flow rate variation step allows the water supply flow rate to increase or decrease within the range of 30% to 100%.

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