Control method for an electrodeionizer

Abstract

This invention provides an operating method for an electrodeionizer that prevents a deterioration in treated water quality when operating with varying water flow rates. [Solution] The control method for the electrodeionizer of the present invention involves operating the electrodeionizer 1 by changing the amount of water supplied. While keeping the flow rate of concentrated water W5 discharged from the electrodeionizer 1 constant, the flow rate of water W0 supplied to the desalination chamber 36 of the electrodeionizer 1 is changed to a flow rate of 50% / min or less relative to the maximum flow rate of water supplied to the desalination chamber 36 of the electrodeionizer 1.

Description

Technical Field

[0001] The present invention relates to an operation method of an electric deionization device, and particularly to an operation method of an electric deionization device for preventing deterioration of treated water quality when performing an operation of changing the water flow rate.

Background Art

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

[0003] The primary pure water production device constituting such an ultrapure water production system is a highly versatile system that is also used in various fields such as pharmaceuticals and food outside the field of ultrapure water production systems. As the configuration of the primary pure water production device, a two-stage reverse osmosis membrane (RO membrane) device and an electric deionization device are generally used. The reverse osmosis membrane (RO membrane) device removes silica and salts, and also removes ionic and colloidal TOC.

[0004] Here, the electric deionization device generally has a configuration 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 the desalination chambers are filled with ion exchange resins, and various inorganic or organic anions and cations are removed.

[0005] When water is supplied to the desalination chamber of this electric deionization device, the ions in the water move in the direction of the ion exchange resin of either the anode or the cathode in the desalination chamber due to their charge. The moved ions pass through the ion exchange resin and enter the concentration chamber, so highly desalinated pure water is produced in the desalination chamber. On the other hand, the ions that have moved to the concentration chamber are discharged as concentrated water.

[0006] From the perspective of stably producing primary pure water of a predetermined quality, the electrodeionizer was operated under constant water supply conditions. Therefore, the primary pure water produced by the primary pure water production system, including the electrodeionizer, was supplied in the required amount to the sub-tank of the secondary pure water production system, while any surplus primary pure water produced was circulated and reused within the primary pure water production system.

[0007] However, as mentioned above, conventional operating methods for primary pure water production systems involve supplying more water than necessary to electrodeionizers and other equipment for processing, leaving room for improvement in terms of energy efficiency. Therefore, Patent Document 1 discloses a method for controlling the amount of water supplied to an electrodeionizer so as to maintain a constant water level in the tank downstream of the electrodeionizer. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Patent No. 6368510 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] However, according to our investigation, as described in Patent Document 1, changing the flow rate of the electrodeionizer can cause a decrease in the quality of the treated water, and this tendency is particularly pronounced when the feedwater to the desalination chamber of the electrodeionizer contains a relatively large amount of carbonate ions.

[0010] The present invention has been made in view of the above problems, and aims to provide an operating method for an electrodeionizer that prevents a decrease in treated water quality when operating with varying water flow rates. [Means for solving the problem]

[0011] In view of the above objectives, the present invention provides a control method for an electrodeionizer that operates by changing the amount of water supplied to the electrodeionizer, wherein the flow rate of the water supplied to the desalination chamber of the electrodeionizer is changed by 50% / min or less relative to the maximum flow rate of the water supplied to the desalination chamber of the electrodeionizer (Invention 1).

[0012] According to the present invention (Invention 1), if the water flow rate change in the desalination chamber of the electrodeionizer is 50% / min or less relative to the maximum water flow rate, the deterioration of treated water quality can be suppressed even if the water supply to the desalination chamber of the electrodeionizer is changed. This is because changing the flow rate in the desalination chamber of the electrodeionizer also changes the state of the adsorption zone of the ion exchange resin inside the electrodeionizer. When the flow rate in the desalination chamber of the electrodeionizer is reduced, ions adsorbed on the ion exchange resin at the bottom of the desalination chamber move to the concentration chamber, and the proportion of regenerative ion exchange resin in the bottom of the desalination chamber increases, which is assumed to improve the treated water quality. On the other hand, the concentration difference between the bottom of the desalination chamber and the bottom of the concentration chamber increases, and the movement of ions from the concentration chamber to the desalination chamber due to concentration diffusion increases, which deteriorates the treated water quality. If the rate of flow rate change is large, the effect of concentration diffusion becomes large, and it is thought that the treated water quality deteriorates. It is estimated that the threshold for this rate of flow rate change is 50% / min or less, and especially 25% / min or less.

[0013] In the above invention (Invention 1), the inorganic carbon concentration of the feedwater supplied to the desalination chamber may be 10 to 3000 μg / L as CO2 (Invention 2).

[0014] According to this invention (Invention 2), while a higher inorganic carbon concentration in the feedwater supplied to the desalination chamber tends to cause a deterioration in water quality, even with a high inorganic carbon concentration of 10 to 3000 μg / L as CO2, the deterioration of the treated water quality can be suppressed.

[0015] In the above invention (Invention 2), it is preferable to pass the water supply from the desalination chamber of the electrodeionizer or the treated water of the electrodeionizer through the concentration chamber of the electrodeionizer in the opposite direction to the water flow direction through the desalination chamber (Invention 3).

[0016] According to such an invention (Invention 3), even when the concentration of inorganic carbonic acid in the feed water supplied to the desalination chamber is high, the deterioration of the quality of the treated water can be further suppressed.

[0017] In the above inventions (Inventions 1 to 3), it is preferable that the minimum value of the water flow rate in the desalination chamber of the electro-deionization device is 30% or more with respect to the maximum flow rate of the feed water in the desalination chamber of the electro-deionization device (Invention 4).

[0018] According to such an invention (Invention 4), if the water flow rate in the desalination chamber of the electro-deionization device is changed significantly, it will cause a deterioration in the quality of the treated water of the electro-deionization device. However, by setting it to 30% or more, the deterioration in water quality caused by the decrease in the feed water of the desalination chamber will not occur.

Effect of the Invention

[0019] According to the control method of the electro-deionization device of the present invention, since the limit value of the flow rate change speed with respect to the maximum flow rate of the feed water in the desalination chamber of the electro-deionization device capable of suppressing the deterioration of the quality of the treated water is set to 50% / min or less, even if the flow rate of the feed water in the desalination chamber of the electro-deionization device is changed, the deterioration of the quality of the treated water can be suppressed.

Brief Description of the Drawings

[0020] [Figure 1] It is a flowchart showing an ultrapure water production system to which the control method of the electro-deionization device according to the present invention can be applied. [Figure 2] It is a schematic diagram showing the control structure of the electro-deionization device in the control method of the electro-deionization device according to the present invention. [Figure 3] It is a schematic diagram showing the electro-deionization device used in the control method of the electro-deionization device according to the present invention. [Figure 4] It is a schematic diagram showing the water flow state of the electro-deionization device used in the control method of the electro-deionization device according to the present invention. [Figure 5]It is a graph showing the change in the flow rate of the feed water supplied to the desalination chamber of the electro-deionization device in Example 1 and the resistivity (MΩ·cm). [Figure 6] It is a graph showing the change in the flow rate of the feed water supplied to the desalination chamber of the electro-deionization device in Comparative Example 1 and the resistivity (MΩ·cm).

Embodiments for Carrying out the Invention

[0021] Hereinafter, the control method of the electro-deionization device of the present invention will be described with reference to the accompanying drawings. For the sake of explanation, a diagram in which the electro-deionization device is provided in an ultrapure water production system will be partially used for the description. However, the control method of the electro-deionization device in the present invention is not limited to this ultrapure water production system and can be used in various fields such as pharmaceuticals and foods.

[0022] (Ultrapure Water Production System) FIG. 1 is a flowchart showing an ultrapure water production system capable of implementing the control method of the electro-deionization device 1 according to an embodiment of the present invention. As shown in FIG. 1, the ultrapure water production system 100 is composed of three-stage devices such as a pretreatment device 2, a primary pure water production device 3 including an electro-deionization device 1 (denoted as CDI in FIG. 1), and a secondary pure water production device (subsystem) 4. In the pretreatment device 2 of such an ultrapure water production system 100, pretreatment such as filtration, coagulation sedimentation, and microfiltration membranes of raw water W is performed, and mainly suspended substances are removed.

[0023] The primary pure water production device 3 has a reverse osmosis membrane device 5 for treating the pretreated water W1, a deaeration membrane device 6, an ultraviolet oxidation device 7, an electro-deionization device 1, and a feed water pump 8 for supplying the pretreated water W1 to the electro-deionization device 1. In this primary pure water production device 3, most of the electrolytes, fine particles, live bacteria, etc. in the pretreated water W1 are removed and organic substances are decomposed.

[0024] Subsystem 4 consists of a sub-tank 11, which is located downstream of the electrodeionizer 1 and stores primary pure water W2 produced by the primary pure water production device 3 (in this embodiment, since the electrodeionizer 1 is located at the end of the primary pure water production device 3, this corresponds to the treated water from the electrodeionizer 1; the same applies hereinafter), an ultraviolet oxidation device 12, a non-regenerative mixed-bed ion exchange device 13, and an ultrafiltration (UF) membrane 14 as a membrane filtration device, which treat the primary pure water W2 supplied from the sub-tank 11 via a pump (not shown). RO membrane separation devices may also be provided as needed. In this subsystem 4, the ultraviolet oxidation device 12 oxidizes and decomposes trace amounts of organic matter (TOC components) contained in the primary pure water W2, and then the non-regenerative mixed-bed ion exchange device 13 removes residual carbonate ions, organic acids, anionic substances, and even metal ions and cationic substances by ion exchange. Then, the ultrafiltration (UF) membrane 14 removes the fine particles to produce ultrapure water W3, which is supplied to the use point 15, and the unused ultrapure water W3 is returned to the sub-tank 11.

[0025] In this embodiment, as shown in Figure 2, the primary pure water production apparatus 3 is equipped with a water supply pump 8 for controlling the flow rate of water W0 supplied to the electrodeionizer 1. The electrodeionizer 1, which is in communication with the water supply pump 8, is equipped with a DC power supply 9, and the treated water W2 from the electrodeionizer 1 can be supplied to a sub-tank 11, which is a water storage tank located downstream of the electrodeionizer 1.

[0026] Furthermore, the flow path 25 of the concentrated water W5 in the electrodeionizer 1 is equipped with a control valve 26 and a flow meter 27 for arbitrarily controlling the flow rate of the concentrated water W5. In addition, the flow path 22 of the treated water (desalinated water) W2 in the electrodeionizer 1 is also equipped with a control valve 23 and a flow meter 24.

[0027] The control device 28, equipped with a personal computer and the like, can increase or decrease the flow rate of water W0 supplied to the electrodeionizer 1 by controlling the water supply pump 8, and can arbitrarily increase or decrease the flow rate of the flow path 22 and / or flow path 25 by controlling the control valves 23 and 26. The control device 28 can also transmit measurement data from the flow meters 24 and 27. In addition, the sub-tank 11 may be equipped with a level switch 21 for measuring the amount of water stored, and the amount of treated water W2 produced may be controlled according to the measurement data of the amount of water stored in the sub-tank 11.

[0028] (Electrodeionizer) Here, the electrodeionizer 1 can preferably be one having the configuration shown in Figures 3 and 4.

[0029] In Figure 3, the electrodeionizer 1 alternately forms a concentration chamber 35 and a desalination chamber 36 by arranging multiple anion exchange membranes 33 and cation exchange membranes 34 alternately between electrodes (anode 31, cathode 32). The desalination chamber 36 is filled with a mixture or multi-layered ion exchange material (anion exchange material and cation exchange material) consisting of ion exchange resin, ion exchange fiber, or graft exchange material. The concentration chamber 35, as well as the anode chamber 37 and cathode chamber 38, are also filled with ion exchange material.

[0030] This electrodeionizer 1 is provided with a water supply means (not shown) for passing water W0 through the desalination chamber 36 to extract treated water (desalination water) W2, and a concentrated water supply means (not shown) for passing water to be concentrated W4 through the concentration chamber 35. In this embodiment, the water to be concentrated W4 is introduced into the concentration chamber 35 from the side of the desalination chamber 36 closest to the outlet for treated water W2, and flows out from the side of the desalination chamber 36 closest to the inlet for water supply W0. In other words, the water to be concentrated W4 is introduced into the concentration chamber 35 from the opposite direction to the flow direction of water supply W0 in the desalination chamber 36, and concentrated water W5 is discharged.

[0031] The water to be concentrated W4 introduced into the concentration chamber 35 can be the same as the feedwater W0 supplied to the desalination chamber 36, but as shown in Figure 4, the treated water W2 obtained from the desalination chamber 36 can also be used as the water to be concentrated W4.

[0032] (Control method for electrodeionization equipment) The control method for the electrodeionizer 1 according to this embodiment will be described below.

[0033] The control method for the electrodeionizer 1 according to this embodiment involves changing the flow rate of the feedwater W0 supplied to the desalination chamber 36 of the electrodeionizer 1 while maintaining a constant flow rate of the concentrated water W5 discharged from the electrodeionizer 1. Normally, when the flow rate of the feedwater W0 of the electrodeionizer 1 is reduced, the concentration difference between the lower part of the desalination chamber 36 and the lower part of the concentration chamber 35 increases, and the movement of ions from the concentration chamber 35 to the desalination chamber 36 due to concentration diffusion tends to increase. Therefore, in this embodiment, the flow rate of the feedwater W0 in the desalination chamber 36 of the electrodeionizer 1 is changed to 50% / min or less, particularly 25% / min or less, relative to its maximum flow rate. This makes it possible to maintain the water quality (e.g., resistivity) of the treated water (desalination water) W2.

[0034] In one embodiment of the control method, it is preferable that the minimum flow rate of the feedwater W0 of the electrodeionizer 1 during flow rate fluctuations is 30% or more of the maximum flow rate of the feedwater in the desalination chamber of the electrodeionizer. If the flow rate of the feedwater W0 of the electrodeionizer 1 falls below the minimum value, the feedwater in the desalination chamber 36 may decrease too much, potentially degrading the quality of the treated water W2, which is undesirable.

[0035] In the control method according to this embodiment, the flow rate of concentrated water W5 discharged from the electrodeionizer 1 is controlled to be kept constant. For example, as shown in Figure 2, this can be achieved by controlling the control valves 23 and 26 with the control device 28 in accordance with changes in the amount of feedwater W0 to control the flow rates of treated water W2 and concentrated water W5 from the electrodeionizer 1. In other words, the amount of concentrated water W5 is kept constant, and the amount of treated water W2 is adjusted so that the recovery rate fluctuates. Here, "kept constant" means that the change in the flow rate of concentrated water W5 discharged from the electrodeionizer 1 is within the range of 90% to 110%.

[0036] Furthermore, in the control method according to one embodiment, the amount of water recovered by the electrodeionizer 1 is not particularly limited, but is preferably 50 to 99%.

[0037] In one embodiment of the control method, the conductivity of the feedwater W0 supplied to the desalination chamber 36 of the electrodeionizer 1 is not particularly limited, but is preferably 0.1 to 5 mS / m. Furthermore, in this embodiment, the inorganic carbon concentration of the feedwater W0 supplied to the desalination chamber may be at a relatively high level of 10 to 3000 μg / L as CO2. The higher the inorganic carbon concentration, the greater the rate of decrease in flow rate, which tends to degrade water quality, but in this embodiment, the effect of suppressing the deterioration of water quality is greater. The current efficiency of the feedwater W0 supplied to the electrodeionizer 1 is preferably 1 to 30%.

[0038] Although the present invention has been described above based on the embodiments described above, the present invention is not limited to the embodiments described above. The present invention is composed of a pretreatment device, a primary pure water production device, and a secondary pure water production device (subsystem), and as long as the primary pure water production device is an ultrapure water production system including an electrodeionizer, the configuration of each device is not limited and the present invention can be applied to various configurations. [Examples]

[0039] The present invention will be described more specifically below based on examples, but the present invention is not limited to the following examples.

[0040] [Example 1] Using the VNX-55EX-2 electrodeionizer (manufactured by Evoqua Water Technologies), water with a conductivity of 1 mS / m and an inorganic carbon concentration of 400 μg / L as CO2 was used as the feedwater W0 for the desalination chamber and the water to be concentrated W4. The water was passed through the chamber in the opposite direction (counterflow) to the treated water, as shown in Figure 3, with a recovery rate of 94-95%.

[0041] This electrodeionizer has a desalination chamber flow rate of 12.4 m³. 3 / h, concentration chamber flow rate 0.66m 3 While operating at / h, the desalination chamber flow rate is set to 2.7 m³ per minute. 3 The flow rate was reduced at / h (flow rate change rate: 22% / min), and the flow rate in the desalination chamber was set to 9.75 m³. 3 The value was set to / h. During this period, the change in the resistivity of the treated water and the change in the flow rate of the desalination chamber were measured. The results are shown in Figure 5.

[0042] [Comparative Example 1] Using the same electrodeionizer as in Example 1, water with a conductivity of 1 mS / m and an inorganic carbon concentration of 600 μg / L as CO2 was used as the feedwater W0 for the desalination chamber and the water to be concentrated W4. The water was passed through the chamber in the same direction as the treated water (parallel flow) with a recovery rate of 90-95%.

[0043] This electrodeionizer has a desalination chamber flow rate of 12.4 m³. 3 While operating at a concentration chamber flow rate of 0.66 m³ / h, the desalination chamber flow rate was increased to 6.4 m³ / min. 3 The flow rate was reduced at / h (flow rate change rate: 52% / min), and the flow rate in the desalination chamber was set to 6.00 m³. 3 The value was set to / h. The change in the resistivity of the treated water and the change in the flow rate of the desalination chamber were measured during this period. The results are shown in Figure 6.

[0044] As is clear from Figures 5 and 6, in Example 1, where the flow rate change rate was 22% / min, the resistivity of the treated water was maintained at 18.0 MΩ·cm or higher, whereas in Comparative Example 1, where the flow rate change rate was 52% / min, the resistivity decreased to approximately 17.5 MΩ·cm. This is because changing the flow rate in the desalination chamber of the electrodeionizer also changes the state of the adsorption zone of the ion exchange resin inside the electrodeionizer. When the flow rate in the desalination chamber of the electrodeionizer is reduced, ions adsorbed on the ion exchange resin at the bottom of the desalination chamber move to the concentration chamber, and it is assumed that the proportion of regenerative ion exchange resin in the bottom of the desalination chamber increases, improving the quality of the treated water. On the other hand, the concentration difference between the bottom of the desalination chamber and the bottom of the concentration chamber increases, and the movement of ions from the concentration chamber to the desalination chamber due to concentration diffusion increases, degrading the quality of the treated water. When the flow rate change rate is large, the effect of concentration diffusion becomes larger, and it is thought that the quality of the treated water deteriorates. It is estimated that the threshold for this flow rate change rate is 50% / min. [Explanation of Symbols]

[0045] 100 Ultrapure Water Production Systems 1. Electrodeionizer 2 Pre-treatment device 3 Primary water purification equipment 4. Secondary pure water production system (subsystem) 5 Reverse osmosis membrane equipment 6. Degassing membrane device 7. Ultraviolet oxidation apparatus 8. Water supply pump 9 DC power supply 11 Sub-tank 12. Ultraviolet oxidation apparatus 13 Non-regenerative mixed-bed ion exchange system 14 Ultrafiltration (UF) membrane 15 Youth Points 21. Level switch (water level measuring device) 22 Flow path for desalination water (treated water) 23, 26 Control valves 24, 27 Flowmeter 25. Concentrated water flow path 28 Control device 31 Anode (electrode) 32 Cathode (electrode) 33 Anion exchange membrane 34 Cation exchange membrane 35 Concentration chamber 36 Desalination room 37 Anode chamber 38 Cathode Chamber W Raw Water Water supply for W0 electrodeionizer W1 Pre-treated water (supply water) W2: Treated water (primary pure water) from an electrodeionizer. W3 Ultrapure water (secondary pure water) W4 Concentrate water W5 Concentrated water

Claims

1. In a control method for an electrodeionizer that operates by changing the amount of water supplied to the electrodeionizer, A control method for an electrodeionizer, comprising changing the flow rate of feedwater supplied to the desalination chamber of the electrodeionizer by 50% / minute or less relative to the maximum flow rate of feedwater in the desalination chamber of the electrodeionizer.

2. The inorganic carbon concentration of the water supplied to the desalination chamber is 10 to 3000 μg / L as CO2. ２ The control method for an electrodeionizer according to claim 1.

3. A control method for an electrodeionizer according to claim 2, wherein water from the desalination chamber of the electrodeionizer or treated water from the electrodeionizer is passed through the concentration chamber of the electrodeionizer in the opposite direction to the water flow direction of the desalination chamber.

4. A control method for an electrodeionizer according to any one of claims 1 to 3, wherein the minimum water flow rate in the desalination chamber of the electrodeionizer is 30% or more of the maximum water flow rate in the desalination chamber of the electrodeionizer.

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