Electrodialysis equipment

Abstract

To regulate an amount of water transferred through a nanofiltration membrane in an electrodialysis apparatus with the built-in nanofiltration membrane.SOLUTION: An electrodialysis apparatus according to the present invention includes: an electrodialyzer having a cathode, an anode, and a membrane member unit including at least three membrane members provided at intervals between the cathode and the anode, with a dilution chamber and a concentration chamber formed between adjacent membrane members; a liquid-to-be-treated supply device that causes a liquid to be treated to flow through the dilution chamber to obtain a diluted liquid; a concentrate liquid circulation device for causing a concentrate liquid to be concentrated to circulate through the concentration chamber; a circulation line through which the concentrate liquid flows to return to the concentration chamber after flowing out from the concentration chamber; a drainage line through which the diluted liquid flowing out from the dilution chamber flows; an extraction line for extracting a part of the concentrate liquid circulating through the circulation line from the circulation line; and at least one of a throttle member provided in the circulation line between a branch point where the extraction line branches off from the circulation line and an outlet of the concentration chamber to throttle the flow of the concentrate liquid, and a throttle member provided in the drainage line to narrow the flow of the diluted liquid.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to electrodialysis devices. [Background technology]

[0002] Patent Document 1 and Non-Patent Document 1 disclose an electrodialysis device having a stack configuration in which either a cation exchange membrane or an anion exchange membrane is replaced with a nanofiltration membrane, i.e., an electrodialysis device with integrated nanofiltration membrane (EDNF). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Chinese Patent Application Publication No. 107398181 [Non-patent literature]

[0004] [Non-Patent Document 1] L.Geetal et al. “Electrodialysis with nanofiltration membrane(EDNF) for high-efficiency cations fractionation” Journal of Membrane Science,498,192-200(2016) Summary of the Invention [Problem to be solved by the invention]

[0005] Because nanofiltration membranes are cheaper than ion exchange membranes, EDNF has the advantage of being able to reduce membrane costs and membrane replacement costs during maintenance compared to regular electrodialysis equipment. However, the amount of water movement associated with the movement of ions through the nanofiltration membrane increases, which creates the problem of high operating costs when attempting to dialysis a liquid with a high solute concentration. On the other hand, if there is a risk of scale deposition from a liquid with a high solute concentration due to the movement of ions through the nanofiltration membrane, there is also a need to promote the movement of water associated with the movement of ions through the nanofiltration membrane in order to suppress scale deposition.

[0006] In view of the above, at least one embodiment of the present disclosure aims to regulate the amount of water transport through a nanofiltration membrane in a nanofiltration membrane-integrated electrodialysis device. [Means for solving the problem]

[0007] In order to achieve the above object, the electrodialysis apparatus according to the present disclosure is an electrodialysis apparatus comprising an electrodialysis vessel having a cathode, an anode, and a membrane element unit including at least three membrane elements spaced apart from one another between the cathode and the anode, with at least one dilution compartment and at least one concentration compartment formed between adjacent membrane elements, wherein the membrane element unit includes at least two ion exchange membranes, which are either anion exchange membranes or cation exchange membranes, and two ion exchange membranes adjacent to the cathode and the anode, respectively, and at least one nanofiltration membrane, wherein the at least two ion exchange membranes and the at least one nanofiltration membrane are respectively arranged alternately, or includes at least two nanofiltration membranes, which are two nanofiltration membranes adjacent to the cathode and the anode, respectively, and at least one ion exchange membrane, which is either an anion exchange membrane or a cation exchange membrane, and wherein the at least the two nanofiltration membranes and the at least one ion exchange membrane are arranged alternately, and the electrodialysis apparatus comprises a liquid to be treated supplying device for circulating a diluted liquid by circulating a liquid to be treated through the at least one dilution compartment; a concentrated liquid circulating device for circulating the concentrated liquid to be concentrated through the at least one concentration compartment; the concentrated liquid circulating device comprises a circulation line through which the concentrated liquid flows so that the concentrated liquid flows back to the at least one concentration compartment after flowing out of the at least one concentration compartment; an extraction line for extracting from the circulation line a portion of the concentrated liquid circulating through the circulation line; a drain line through which the diluted liquid flowing out of the at least one dilution compartment flows; and at least one of a throttle member provided in the circulation line between a branch point where the extraction line branches off from the circulation line and an outlet of the at least one concentration compartment and for throttling the flow of the concentrated liquid, and a throttle member provided in the drain line and for throttling the flow of the diluted liquid. a thermometer for detecting the temperature of the liquid to be treated supplied to the at least one dilution chamber; Further equipped The throttle member that throttles the flow of the diluent is a flow rate control valve that adjusts the flow rate of the diluent flowing through the drain line, and the opening of the flow rate control valve is controlled based on the detected value of the thermometer. do. [Effects of the Invention]

[0008] According to the electrodialysis device of the present disclosure, the throttle member throttles the flow of the concentrate, thereby increasing the pressure in the concentration chamber, generating a driving force that moves water from the concentration chamber to the dilution chamber, and the potential difference partially offsets the driving force that moves water from the dilution chamber to the concentration chamber, thereby reducing the amount of water that moves as ions move from the dilution chamber to the concentration chamber. Furthermore, the throttle member throttles the flow of the dilution, thereby increasing the pressure in the dilution chamber, thereby increasing the driving force that moves water from the dilution chamber to the concentration chamber, thereby increasing the amount of water that moves as ions move from the dilution chamber to the concentration chamber. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram illustrating the configuration of an electrodialysis device according to a first embodiment of the present disclosure. [Figure 2] FIG. 1 is a schematic diagram illustrating the configuration of an electrodialyzer provided in an electrodialysis device according to a first embodiment of the present disclosure. [Figure 3] FIG. 2 is a diagram showing an example of a specific configuration of an electrodialyzer provided in the electrodialysis device according to the first embodiment of the present disclosure. [Figure 4] FIG. 10 is a schematic diagram illustrating the configuration of an electrodialysis device according to a second embodiment of the present disclosure. [Figure 5] FIG. 10 is a schematic diagram illustrating the configuration of an electrodialysis device according to a third embodiment of the present disclosure. [Figure 6] 1 is a schematic graph showing the temperature dependence of the degree of saturation of gypsum. [Figure 7] 4 is a schematic graph showing the relationship between the temperature of the liquid to be treated and the opening degree of the flow rate adjustment valve. [Figure 8] 4 is a schematic graph showing the relationship between the electrical conductivity of the liquid to be treated and the opening degree of the flow rate adjustment valve. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an electrodialysis apparatus according to an embodiment of the present disclosure will be described with reference to the drawings. The embodiment described below represents one aspect of the present disclosure, and is not intended to limit the present disclosure. Any modification can be made within the scope of the technical concept of the present disclosure.

[0011] (Embodiment 1) <Configuration of the electrodialysis device according to the first embodiment of the present disclosure> As shown in FIG. 1 , an electrodialysis apparatus 1 according to a first embodiment of the present disclosure includes an electrodialyzer 2 for separating a liquid to be treated, in which an ionic solute is dissolved, into a dilute liquid and a concentrate. The electrodialyzer 2 is connected to a liquid to be treated supply line 3 for supplying the liquid to the electrodialyzer 2 and a drain line 4 for discharging the dilute liquid obtained by electrodialysis using the electrodialyzer 2 from the electrodialyzer 2. The electrodialyzer 2 is also connected to a circulation line 5 through which the concentrate obtained by electrodialysis using the electrodialyzer 2 flows out of the electrodialyzer 2 and then returns to the electrodialyzer 2. The circulation line 5 may be provided with a concentrated liquid tank 6 for storing a portion of the concentrated liquid. The circulation line 5 is connected to an extraction line 7 for extracting a portion of the concentrated liquid circulating through the circulation line 5 from the circulation line 5. In the first embodiment, as an example, the circulation line 5 is provided with a concentrated liquid tank 6, and the extraction line 7 branches off from the circulation line 5 at the concentrated liquid tank 6.

[0012] The supply line 3 for the liquid to be treated is provided with a supply pump 11, which is a liquid to be treated supply device for supplying the liquid to be treated to the electrodialyzer 2, the circulation line 5 is provided with a circulation pump 12, which is a concentrated liquid circulating device for circulating the concentrated liquid, and the withdrawal line 7 is provided with an extraction pump 13 for extracting a portion of the concentrated liquid circulating through the circulation line 5 from the circulation line 5. The circulation line 5 is provided with a throttle member 10 for throttling the flow of the concentrated liquid between the outlet of the electrodialyzer 2 and a branch point (corresponding to the concentrated liquid tank 6 in the first embodiment) where the withdrawal line 7 branches off from the circulation line 5. The throttle member 10 may be, for example, a flow control valve or an orifice.

[0013] When the throttle member 10 is a flow rate control valve 10a, it is possible to adjust the flow rate of the concentrated liquid extracted from the circulation line 5. For this purpose, a flow meter 15 may be provided in the extraction line 7, and the opening of the flow rate control valve 10a may be controlled so that the flow rate of the concentrated liquid extracted from the circulation line 5 becomes a preset value.

[0014] <Configuration of the electrodialyzer provided in the electrodialysis device according to the first embodiment of the present disclosure> 2 shows an example of the configuration of an electrodialyzer 2. This electrodialyzer 2 has a cathode 21, an anode 22, and a membrane member unit 20 including three membrane members 20a, 20b, and 20c spaced apart from one another between the cathode 21 and the anode 22. The three membrane members 20a, 20b, and 20c are either ion exchange membranes, which are either anion exchange membranes or cation exchange membranes, or nanofiltration membranes, and are configured so that the ion exchange membranes and nanofiltration membranes are alternately arranged.

[0015] For example, when the membrane elements 20a and 20c adjacent to the cathode 21 and the anode 22, respectively, are cation exchange membranes and the membrane element 20b is a nanofiltration membrane, the chamber 23 formed between the membrane elements 20a and 20b is a dilution chamber through which the liquid to be treated flows, and the chamber 24 formed between the membrane elements 20b and 20c is a concentration chamber through which the concentrated liquid flows. That is, the inlet and outlet of the chamber 23 (dilution chamber) are connected to the supply line 3 for the liquid to be treated and the drain line 4, respectively, and the inlet and outlet of the chamber 24 (concentration chamber) are connected to one end and the other end of the circulation line 5 (see FIG. 1 ), respectively.

[0016] For example, when the membrane elements 20a and 20c adjacent to the cathode 21 and the anode 22, respectively, are anion exchange membranes and the membrane element 20b is a nanofiltration membrane, the chamber 23 formed between the membrane elements 20a and 20b is a concentration chamber through which the concentrated liquid flows, and the chamber 24 formed between the membrane elements 20b and 20c is a dilution chamber through which the liquid to be treated flows. That is, one end and the other end of the circulation line 5 (see FIG. 1) are connected to the inlet and the outlet, respectively, of the chamber 23 (concentration chamber), and the liquid to be treated supply line 3 and the liquid discharge line 4 are connected to the inlet and the outlet, respectively, of the chamber 24 (dilution chamber).

[0017] For example, when the membrane elements 20a and 20c adjacent to the cathode 21 and the anode 22, respectively, are nanofiltration membranes and the membrane element 20b is a cation exchange membrane, the chamber 23 formed between the membrane elements 20a and 20b is a concentration chamber through which the concentrated liquid flows, and the chamber 24 formed between the membrane elements 20b and 20c is a dilution chamber through which the liquid to be treated flows. That is, one end and the other end of the circulation line 5 (see FIG. 1) are connected to the inlet and the outlet, respectively, of the chamber 23 (concentration chamber), and the liquid to be treated supply line 3 and the liquid discharge line 4 are connected to the inlet and the outlet, respectively, of the chamber 24 (dilution chamber).

[0018] For example, when the membrane elements 20a and 20c adjacent to the cathode 21 and the anode 22, respectively, are nanofiltration membranes and the membrane element 20b is an anion exchange membrane, the chamber 23 formed between the membrane elements 20a and 20b is a dilution chamber through which the liquid to be treated flows, and the chamber 24 formed between the membrane elements 20b and 20c is a concentration chamber through which the concentrated liquid flows. That is, the inlet and outlet of the chamber 23 (dilution chamber) are connected to the supply line 3 for the liquid to be treated and the drain line 4, respectively, and the inlet and outlet of the chamber 24 (concentration chamber) are connected to one end and the other end of the circulation line 5 (see FIG. 1 ), respectively.

[0019] The membrane element unit 20 is not limited to a configuration including three membrane elements 20a, 20b, and 20c, and may include an odd number of membrane elements (three or more) as long as the membrane elements 20a and 20c adjacent to the cathode 21 and the anode 22 are ion exchange membranes or nanofiltration membranes, respectively. However, when the membrane element 20b includes an odd number of membrane elements (three or more), the ion exchange membranes and the nanofiltration membranes must be alternately arranged between the cathode 21 and the anode 22. In this case, two or more dilution compartments or two or more concentration compartments are formed.

[0020] An electrode chamber 25 formed between the cathode 21 and the membrane member 20a and an electrode chamber 26 formed between the anode 22 and the membrane member 20c are configured so that an electrode solution (for example, seawater) flows through each of them.

[0021] <Operation of the electrodialysis device according to the first embodiment of the present disclosure> Next, the operation of the electrodialysis device 1 according to the first embodiment of the present disclosure will be described. As shown in Fig. 1, when the supply pump 11 is started, the liquid to be treated flows through the supply line 3 for the liquid to be treated and flows into the electrodialysis device 2. When the circulation pump 12 is started, the concentrated liquid circulates through the circulation line 5. In the electrodialysis device 2, ionic solutes dissolved in the liquid to be treated move to the concentrated liquid in an operation described below, thereby diluting the liquid to be treated, which flows out of the electrodialysis device 2 as a diluted liquid and flows through the drainage line 4.

[0022] When the liquid to be treated is separated into a dilute liquid and a concentrated liquid in the electrodialyzer 2, some of the water in the liquid to be treated also moves to the concentrated liquid, increasing the flow rate of the concentrated liquid circulating through the circulation line 5. By throttling the flow of the concentrated liquid circulating through the circulation line 5 with the throttling member 10, some of the concentrated liquid can be extracted from the circulation line 5 to the extraction line 7 and some of the concentrated liquid can be discharged. If the throttling member 10 is a flow control valve 10a, the opening of the flow control valve 10a can be adjusted based on the detection value of the flow meter 15 to adjust the extraction flow rate of the concentrated liquid to a desired value.

[0023] Next, as shown in Figure 3, the operation of electrodialysis in the electrodialysis device 2 will be described using an example in which the membrane elements 20a and 20c are cation exchange membranes 20a1 and 20c1, respectively, the membrane element 20b is a nanofiltration membrane 20b1, and the liquid to be treated is seawater. In this case, the chamber 23 is the dilution chamber 23a, and the chamber 24 is the concentration chamber 24a.

[0024] Seawater flowing into the electrodialyzer 2 via the treated liquid supply line 3 flows into the dilution chamber 23a. The concentrated solution circulating through the circulation line 5 flows into the electrodialyzer 2 and then into the concentration chamber 24a. When current is applied between the cathode 21 and the anode 22, sodium ions in the seawater in the dilution chamber 23a are attracted toward the cathode 21, pass through the cation exchange membrane 20a1, and flow into the electrode chamber 25. Sodium ions in the electrode solution (seawater) in the electrode chamber 26 are also attracted toward the cathode 21, pass through the cation exchange membrane 20c1, and flow into the concentration chamber 24a. Chloride ions in the seawater in the dilution chamber 23a are attracted toward the anode 22, pass through the nanofiltration membrane 20b1, and flow into the concentration chamber 24a. This reduces the concentration of sodium chloride in the seawater in the dilution chamber 23a. In other words, the seawater is desalinated. On the other hand, the concentration of sodium chloride in the concentrate in the concentration compartment 24a increases due to the sodium ions flowing in from the electrode compartment 26 and the chloride ions flowing in from the dilution compartment 23a.

[0025] During the above-described electrodialysis operation, as chloride ions pass through nano-filtration membrane 20b1, water passes from dilution chamber 23a through nano-filtration membrane 20b1 and flows into concentration chamber 24a. In this embodiment 1, the flow of the concentrate flowing out of concentration chamber 24a is throttled by throttle member 10. This increases the pressure within concentration chamber 24a, generating a driving force that moves water from concentration chamber 24a to dilution chamber 23a. The potential difference partially offsets the driving force that moves water from the dilution chamber to the concentration chamber. As a result, the amount of water moving due to the movement of ions from dilution chamber 23a to concentration chamber 24a can be reduced. If throttle member 10 is a flow control valve 10a, the pressure difference between dilution chamber 23a and concentration chamber 24a via nano-filtration membrane 20b1 can be appropriately controlled, thereby appropriately reducing the amount of water moving due to the movement of ions from dilution chamber 23a to concentration chamber 24a.

[0026] Those skilled in the art will be able to understand the principle of electrodialysis operation and the ability to reduce the amount of water movement associated with the movement of ions from the dilution chamber 23a to the concentration chamber 24a by referring to the above operation, in any of the cases where the membrane elements 20a and 20c are anion exchange membranes, where the membrane elements 20a and 20c are nanofiltration membranes and the membrane element 20b is an ion exchange membrane, and where the membrane element 20b includes an odd number of membrane elements (three or more). Therefore, detailed explanations of these cases will be omitted.

[0027] <Modifications of the electrodialysis device according to the first embodiment of the present disclosure> In the first embodiment, only the concentrated liquid is circulated, but the diluted liquid may be circulated so that the diluted liquid flowing out of the dilution chamber 23a is supplied to the diluted liquid together with the liquid to be treated. In this case, the circulation line for the diluted liquid may be provided with components similar to the concentrated liquid tank 6 and the withdrawal line 7.

[0028] (Embodiment 2) Next, an electrodialysis device according to a second embodiment of the present disclosure will be described. The electrodialysis device according to the second embodiment is different from the first embodiment in that it is possible to promote the amount of water moving from the dilution chamber 23a to the concentration chamber 24a. In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0029] <Configuration of electrodialysis device according to embodiment 2 of the present disclosure> As shown in FIG. 4 , in an electrodialysis apparatus 1 according to a second embodiment of the present disclosure, a throttle member 30 for throttling the flow of the diluent is provided in the drain line 4. The throttle member 30 may be, for example, a flow control valve or an orifice. When the throttle member 30 is a flow control valve 30a, the flow rate of the concentrate extracted from the circulation line 5 can be adjusted by adjusting the amount of water moving from the dilution chamber 23a to the concentration chamber 24a using an operation described below. For this purpose, a flow meter 15 may be provided in the extraction line 7, and the aperture of the flow control valve 30a may be controlled so that the flow rate of the concentrate extracted from the circulation line 5 reaches a preset value. The other configurations are the same as those of the first embodiment, except that a throttle member 10 (see FIG. 1 ) is not provided in the circulation line 5. However, a throttle member 10 may be provided in the circulation line 5 so that the operation described in the first embodiment can be performed separately from the operation described in the second embodiment.

[0030] <Operation of the electrodialysis device according to the second embodiment of the present disclosure> In the electrodialysis apparatus 1, if the solute concentration of the concentrated liquid becomes high, there is a risk of scale deposition (for example, gypsum scale deposition when the liquid to be treated is seawater). In such a case, in the second embodiment, adjusting the aperture of the flow rate control valve 30a to increase the pressure in the dilution chamber 23a (see FIG. 3) promotes the movement of water from the dilution chamber 23a to the concentration chamber 24a (see FIG. 3), thereby increasing the flow rate of the concentrated liquid and suppressing scale deposition. Note that even if the throttle member 30 is an orifice or the like that cannot adjust the degree to which the diluted liquid is throttled, if it is known that a certain degree of throttle is required for the diluted liquid, the same effect as when the flow rate control valve 30a is provided can be obtained.

[0031] (Embodiment 3) Next, an electrodialysis device according to a third embodiment of the present disclosure will be described. The electrodialysis device according to the third embodiment is different from the second embodiment in that the amount of water moving through the nanofiltration membrane is promoted depending on the properties of the liquid to be treated. In the third embodiment, the same components as those in the second embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.

[0032] <Configuration of electrodialysis device according to embodiment 3 of the present disclosure> As shown in FIG. 5 , in an electrodialysis apparatus 1 according to a third embodiment of the present disclosure, a liquid-to-be-treated supply line 3 is provided with at least one of a thermometer 31 for detecting the temperature of the liquid flowing through the liquid-to-be-treated supply line 3 and a conductivity meter 32 for detecting the electrical conductivity of the liquid flowing through the liquid-to-be-treated supply line 3. The flow rate control valve 30a, the thermometer 31, and the conductivity meter 32 are each electrically connected to a control device 33. The control device 33 is configured to control the aperture of the flow rate control valve 30a based on the values ​​detected by at least one of the thermometer 31 and the conductivity meter 32, as described below. The control device 33 is configured, for example, with a central processing unit (CPU), random access memory (RAM), read-only memory (ROM), and a computer-readable storage medium. The CPU reads a program stored in the storage medium into the RAM and executes information processing and arithmetic operations, thereby controlling the aperture of the flow rate control valve 30a. The remaining configuration is the same as that of the second embodiment.

[0033] <Operation of the electrodialysis device according to the third embodiment of the present disclosure> First, the operation when a thermometer 31 is provided will be described. Assuming that gypsum scale will precipitate when the liquid to be treated is seawater, the degree of saturation (solubility product) of gypsum generally has temperature dependency as shown in Fig. 6, and in the general temperature range of 0 to 40°C when electrodialysis is performed, the higher the temperature, the greater the degree of saturation. In other words, the lower the temperature of the liquid to be treated, the greater the risk of scale precipitation.

[0034] For this reason, in the third embodiment, the detection value of the thermometer 31 is transmitted to the control device 33 during electrodialysis, and the control device 33 controls the aperture of the flow rate control valve 30 so as to promote the movement of water from the dilution chamber 23a (see FIG. 3) to the concentration chamber 24a (see FIG. 3) as the detection value decreases. Specifically, the control device 33 controls the aperture of the flow rate control valve 30a to decrease as the detection value of the thermometer 31 decreases. When the aperture of the flow rate control valve 30a is decreased, the flow in the drain line 4 is restricted, thereby increasing the pressure in the dilution chamber 23a, and promoting the movement of water from the dilution chamber 23a to the concentration chamber 24a. As a result, the solute concentration of the concentrated water decreases, thereby reducing the risk of scale deposition.

[0035] In order for the control device 33 to control the opening degree of the flow rate control valve 30a in this manner, for example, the relationship between the temperature of the liquid to be treated and the opening degree of the flow rate control valve 30a as shown schematically in Figure 7 is stored in a storage medium or the like of the control device 33, and the control device 33 can determine the opening degree of the flow rate control valve 30a from the detection value of the thermometer 31 based on this relationship.

[0036] Next, we will explain the operation when an electrical conductivity meter 32 is provided. As with the case where a thermometer 31 is provided, we will assume that gypsum scale will precipitate when the liquid to be treated is seawater. Although the salinity of seawater may fluctuate throughout the year, it is known that the abundance ratio of various ions does not change even if the salinity fluctuates. Therefore, the higher the salinity, the greater the risk of scale deposition. Fluctuations in the salinity of seawater can be monitored by the electrical conductivity of the seawater.

[0037] For this reason, in the third embodiment, the detection value of the electrical conductivity meter 32 is transmitted to the control device 33 during electrodialysis, and the control device 33 controls the aperture of the flow rate control valve 30a to promote the movement of water from the dilution chamber 23a (see FIG. 3) to the concentration chamber 24a (see FIG. 3) as the detection value increases. Specifically, the control device 33 controls the aperture of the flow rate control valve 30a to decrease as the detection value of the electrical conductivity meter 32 increases. When the aperture of the flow rate control valve 30a is decreased, the flow in the drain line 4 is restricted, thereby increasing the pressure in the dilution chamber 23a, and promoting the movement of water from the dilution chamber 23a to the concentration chamber 24a. As a result, the solute concentration of the concentrated water decreases, thereby reducing the risk of scale deposition.

[0038] In order for the control device 33 to control the opening degree of the flow rate control valve 30a in this manner, for example, the relationship between the electrical conductivity of the liquid to be treated and the opening degree of the flow rate control valve 30a, as shown schematically in Figure 8, is stored in a storage medium or the like of the control device 33, and the control device 33 can determine the opening degree of the flow rate control valve 30a from the detection value of the electrical conductivity meter 32 based on this relationship.

[0039] <Modification of the electrodialysis device according to the third embodiment of the present disclosure> Although the aperture of the flow rate regulating valve 30a has been described as being controlled based on either the temperature or the electrical conductivity of the liquid to be treated, the aperture of the flow rate regulating valve 30a may be controlled based on both. In the third embodiment, the controller 33 controls the aperture of the flow rate regulating valve 30a based on at least one of the temperature and the electrical conductivity of the liquid to be treated, but this is not limiting. Even if the controller 33 is not provided, the operator of the electrodialysis device 1 may manually control the aperture of the flow rate regulating valve 30a based on at least one of the temperature and the electrical conductivity of the liquid to be treated.

[0040] The contents described in each of the above embodiments can be understood, for example, as follows.

[0041] [1] An electrodialysis apparatus according to one embodiment comprises: An electrodialysis apparatus (1) comprising an electrodialysis device (2) having a cathode (21), an anode (22), and a membrane element unit (20) including at least three membrane elements (20a, 20b, 20c) spaced apart from one another between the cathode (21) and the anode (22), wherein at least one dilution chamber (23a) and at least one concentration chamber (24a) are formed between adjacent membrane elements, The membrane member unit (20) is at least two ion exchange membranes (20a, 20c) including two ion exchange membranes (20a, 20c) that are either anion exchange membranes or cation exchange membranes and that are adjacent to the cathode (21) and the anode (22), respectively, and at least one nanofiltration membrane (20b), wherein the at least two ion exchange membranes (20a, 20c) and the at least one nanofiltration membrane (20b) are arranged alternately, or the system comprises at least two nanofiltration membranes (20a, 20c) including two nanofiltration membranes adjacent to the cathode (21) and the anode (22), respectively, and at least one ion exchange membrane (20b) which is either an anion exchange membrane or a cation exchange membrane, and the at least two nanofiltration membranes (20a, 20c) and the at least one ion exchange membrane (20b) are respectively arranged alternately; The electrodialysis device (1) comprises: a supply device for a liquid to be treated (supply pump 11) for supplying a diluted liquid by causing the liquid to be treated to flow through the at least one dilution chamber (23a); a concentrated liquid circulation device (circulation pump 12) for circulating the concentrated liquid to be concentrated through the at least one concentration chamber (24a); a circulation line (5) through which the concentrated liquid flows so that the concentrated liquid returns to the at least one concentration compartment (24a) after flowing out of the at least one concentration compartment (24a); a withdrawal line (7) for withdrawing a portion of the concentrated liquid circulating through the circulation line (5) from the circulation line (5); a drain line (4) through which the diluent flowing out of the at least one dilution chamber (23a) flows; At least one of a throttle member (10) that is provided in the circulation line (5) between a branch point (concentrate tank 6) where the extraction line (7) branches off from the circulation line (5) and an outlet of the at least one concentration compartment (24a) and throttles the flow of the concentrate, and a throttle member (30) that is provided in the drain line (4) and throttles the flow of the dilution liquid. Further provided are:

[0042] According to the electrodialysis device of the present disclosure, the throttle member throttles the flow of the concentrate, thereby increasing the pressure in the concentration chamber, generating a driving force that moves water from the concentration chamber to the dilution chamber, and the potential difference partially offsets the driving force that moves water from the dilution chamber to the concentration chamber, thereby reducing the amount of water that moves as ions move from the dilution chamber to the concentration chamber. Furthermore, the throttle member throttles the flow of the dilution, thereby increasing the pressure in the dilution chamber, thereby increasing the driving force that moves water from the dilution chamber to the concentration chamber, thereby increasing the amount of water that moves as ions move from the dilution chamber to the concentration chamber.

[0043] [2] An electrodialysis device according to another embodiment is the electrodialysis device according to [1], The throttle member (10) that throttles the flow of the concentrated liquid is a flow rate control valve (10a) that adjusts the flow rate of the concentrated liquid flowing through the circulation line (5).

[0044] With this configuration, the pressure difference between the dilution compartment and the concentration compartment via the nanofiltration membrane can be appropriately controlled, thereby appropriately reducing the amount of water movement associated with the movement of ions from the dilution compartment to the concentration compartment.

[0045] [3] An electrodialysis apparatus according to yet another embodiment is the electrodialysis apparatus according to [1], The throttle member (30) that throttles the flow of the diluent is a flow rate control valve (30a) that adjusts the flow rate of the diluent flowing through the drain line (4).

[0046] With this configuration, the pressure difference between the dilution compartment and the concentration compartment via the nanofiltration membrane can be appropriately controlled, thereby appropriately promoting the amount of water movement associated with the movement of ions from the dilution compartment to the concentration compartment.

[0047] [4] An electrodialysis device according to yet another embodiment is the electrodialysis device according to [3], a thermometer (31) for detecting the temperature of the liquid to be treated supplied to the at least one dilution chamber (23a); The opening of the flow rate control valve (30a) is controlled based on the value detected by the thermometer (31).

[0048] In general, the degree of saturation of a solute is temperature-dependent, and at typical temperatures used for electrodialysis, the higher the temperature, the greater the degree of saturation, while the lower the temperature, the greater the risk of scale deposition. In response to this, by controlling the aperture of the flow control valve so as to promote the movement of water from the dilution compartment to the concentration compartment as the temperature of the liquid to be treated decreases, it is possible to appropriately suppress scale deposition.

[0049] [5] An electrodialysis apparatus according to yet another embodiment is the electrodialysis apparatus according to [3] or [4], a conductivity meter (32) for detecting the electrical conductivity of the liquid to be treated supplied to the at least one dilution chamber (23a); The opening of the flow rate control valve (30a) is controlled based on the value detected by the electrical conductivity meter (32).

[0050] When the liquid to be treated is seawater, the salinity may fluctuate throughout the year, but it is known that the ratio of various ions does not change even if the salinity fluctuates. Therefore, the higher the salinity, the greater the risk of scale deposition. Therefore, by understanding the fluctuations in salinity based on the electrical conductivity of the liquid to be treated and controlling the opening of the flow control valve to promote the movement of water from the dilution compartment to the concentration compartment as the electrical conductivity increases, scale deposition can be appropriately suppressed. [Explanation of symbols]

[0051] 1. Electrodialysis equipment 2. Electrodialyzer 4 Drainage line 5 Circulation Line 7 Extraction line 10. Aperture member 10a Flow control valve 11 Supply pump (treated liquid supply device) 12 Circulation pump (concentrated liquid circulation device) 20 Membrane material unit 20a Membrane member 20b Membrane member 20c Membrane parts 20a1 Cation exchange membrane 20b1 Nanofiltration Membrane 20c1 Cation exchange membrane 23a Dilution chamber 24a Concentration room 30 Flow control valve 30a Flow control valve 31 Thermometer 32 Electrical conductivity meter

Claims

1. An electrodialysis apparatus comprising an electrodialysis device having a cathode, an anode, and a membrane element unit including at least three membrane elements spaced apart from one another between the cathode and the anode, wherein at least one dilution chamber and at least one concentration chamber are formed between adjacent membrane elements, The membrane member unit includes: At least two ion exchange membranes, each of which is either an anion exchange membrane or a cation exchange membrane, and includes two ion exchange membranes adjacent to the cathode and the anode, respectively, and at least one nanofiltration membrane, wherein the at least two ion exchange membranes and the at least one nanofiltration membrane are alternately arranged, or at least two nanofiltration membranes including two nanofiltration membranes adjacent to the cathode and the anode, respectively, and at least one ion exchange membrane which is either an anion exchange membrane or a cation exchange membrane, wherein the at least two nanofiltration membranes and the at least one ion exchange membrane are alternately arranged; The electrodialysis apparatus comprises: a treatment liquid supply device for supplying a treatment liquid to the at least one dilution chamber to obtain a diluted liquid; a concentrate circulating device for circulating the concentrate to be concentrated through the at least one concentration compartment; a circulation line through which the concentrated liquid flows so that the concentrated liquid returns to the at least one concentration compartment after flowing out of the at least one concentration compartment; an extraction line for extracting a portion of the concentrated liquid circulating through the circulation line from the circulation line; a drain line through which the diluent flowing out of the at least one dilution chamber flows; At least one of a throttle member provided in the circulation line between a branch point where the extraction line branches off from the circulation line and an outlet of the at least one concentration compartment, the throttle member throttling the flow of the concentrated liquid, and a throttle member provided in the drain line, the throttle member throttling the flow of the diluted liquid; a thermometer for detecting the temperature of the liquid to be treated supplied to the at least one dilution chamber; Furthermore, the throttle member that throttles the flow of the diluent is a flow rate control valve that adjusts the flow rate of the diluent flowing through the drain line, The electrodialysis apparatus is configured so that the opening degree of the flow rate control valve is controlled based on the value detected by the thermometer.

2. a conductivity meter for detecting the electrical conductivity of the liquid to be treated supplied to the at least one dilution chamber; 2. The electrodialysis apparatus according to claim 1, wherein the opening degree of the flow rate adjusting valve is controlled based on the detected value of the electrical conductivity meter.

3. An electrodialysis device comprising an electrodialyzer having a cathode, an anode, and a membrane element unit including at least three membrane elements spaced apart from one another between the cathode and the anode, with at least one dilution chamber and at least one concentration chamber formed between adjacent membrane elements, The membrane member unit includes: At least two ion exchange membranes, each of which is either an anion exchange membrane or a cation exchange membrane, and includes two ion exchange membranes adjacent to the cathode and the anode, respectively, and at least one nanofiltration membrane, wherein the at least two ion exchange membranes and the at least one nanofiltration membrane are alternately arranged, or at least two nanofiltration membranes including two nanofiltration membranes adjacent to the cathode and the anode, respectively, and at least one ion exchange membrane which is either an anion exchange membrane or a cation exchange membrane, wherein the at least two nanofiltration membranes and the at least one ion exchange membrane are alternately arranged; The electrodialysis apparatus comprises: a treatment liquid supply device for supplying a treatment liquid to the at least one dilution chamber to obtain a diluted liquid; a concentrate circulating device for circulating the concentrate to be concentrated through the at least one concentration compartment; a circulation line through which the concentrated liquid flows so that the concentrated liquid returns to the at least one concentration compartment after flowing out of the at least one concentration compartment; an extraction line for extracting a portion of the concentrated liquid circulating through the circulation line from the circulation line; a drain line through which the diluent flowing out of the at least one dilution chamber flows; At least one of a throttle member provided in the circulation line between a branch point where the extraction line branches off from the circulation line and an outlet of the at least one concentration compartment, the throttle member throttling the flow of the concentrated liquid, and a throttle member provided in the drain line, the throttle member throttling the flow of the diluted liquid; an electrical conductivity meter that detects the electrical conductivity of the liquid to be treated that is supplied to the at least one dilution chamber; Furthermore, the throttle member that throttles the flow of the diluent is a flow rate control valve that adjusts the flow rate of the diluent flowing through the drain line, The electrodialysis apparatus is configured so that the opening degree of the flow rate control valve is controlled based on the detected value of the electrical conductivity meter.

4. 4. The electrodialysis apparatus according to claim 1, wherein the throttle member that throttles the flow of the concentrated liquid is a flow rate control valve that adjusts the flow rate of the concentrated liquid circulating through the circulation line.

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