Electro-deionized water production system and operation method thereof

Abstract

To replace an EDI device while treating a fixed amount of treated water while maintaining a flow rate of the treated water in each EDI device at an appropriate value, in an EDI system comprising one or more EDI devices (electro-deionized water production devices).SOLUTION: When an EDI device 10 installed at a first installation location P1 is in an operating state and the EDI device 10 installed at a second installation location P2 is in a stopped state, a supply valve 41 and a discharge valve 42 corresponding to the first installation location P1 are closed and a supply valve 42 and a discharge valve 62 corresponding to the second installation location P2 are simultaneously opened, so that the EDI device 10 installed at the first installation location P1 is brought into the stopped state, and the EDI device 10 installed at the second installation location P2 is brought into the operating state.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an electrodeionization water production system in which one or more electrodeionization water production devices (EDI (Electrodeionization) devices) can be installed, and a method of operating the same. [Background technology]

[0002] An EDI device is one type of device that demineralizes feed water (also referred to as water to be treated) to produce deionized water as treated water. An EDI device operates by combining electrophoresis and electrodialysis and includes at least a deionization compartment separated by a diaphragm, such as an ion exchange membrane, between an anode and a cathode. The deionization compartment is filled with an ion exchanger, such as an ion exchange resin. By supplying feed water to the deionization compartment while applying a direct current between the anode and the cathode, deionization proceeds in the deionization compartment, and deionized water flows out of the deionization compartment. In EDI devices, the anode and cathode are generally disposed in the anode chamber and the cathode chamber, respectively. Concentration compartments may be disposed between the anode chamber and the deionization compartment, and between the deionization compartment and the cathode chamber. In this case, the concentration compartment and the deionization compartment are separated by a diaphragm, such as an ion exchange membrane, and the anode chamber and the concentration compartment, and the concentration compartment and the cathode chamber are also separated by diaphragms, such as ion exchange membranes. It is also preferable to fill the concentration compartment, anode compartment, and cathode compartment with an ion exchanger such as ion exchange resin. In EDI devices, water must be supplied to the anode compartment, cathode compartment, and concentration compartment, and wastewater from the anode compartment, cathode compartment, and concentration compartment is often directly discharged to the outside. Unlike general ion exchange devices that are simply filled with ion exchange resin, EDI devices have the advantage that it is not necessary to stop operation of the device to regenerate or replace the ion exchange resin.

[0003] In practice, EDI devices are often configured with deionization compartments and concentration compartments alternately arranged between an anode chamber and a cathode chamber in the anode-to-cathode direction. In this configuration, multiple deionization compartments are electrically arranged in series between the anode and cathode, while the water being treated is supplied to the multiple deionization compartments in parallel, thereby increasing the flow rate of the water being treated and the amount of deionized water produced per unit time. As described in Patent Documents 1 and 2, for example, such EDI devices are configured with rectangular frames with openings through which spaces for the deionization compartments and concentration compartments are formed, and multiple such frames are stacked with ion exchange membranes sandwiched between them. The interior of the frames is filled with ion exchange resin. Therefore, the EDI device has an external shape resembling a square prism placed on its side, with a roughly rectangular base and a height sufficiently greater than the length of the long side of the base.

[0004] Each EDI device has its own set of appropriate values ​​or ranges for the treated water flow rate (treatment volume), applied voltage, and applied current. Treating water at a flow rate exceeding the appropriate range can result in a decrease in the ionic impurity removal rate, making it impossible to adequately remove impurities. Therefore, when a large amount of deionized water is required beyond the appropriate treatment volume range of each device, multiple EDI devices are prepared and operated in parallel, resulting in the use of an EDI system configured to accommodate multiple EDI devices. While an EDI system typically has enough space to accommodate multiple EDI devices, depending on the demand for deionized water, it is possible to install only one EDI device in an EDI system during actual operation, leaving the remaining space empty. Because EDI devices do not require shutdown to regenerate or replace the ion exchange resin, EDI systems equipped with multiple EDI devices are widely used in semiconductor device manufacturing plants, where large amounts of pure water are continuously consumed.

[0005] When multiple EDI devices are operated in parallel, if the demand for deionized water decreases, the flow rate in each EDI device will become lower than appropriate, which could cause problems with the EDI devices, such as the formation of scale in the concentration compartments. Patent Document 3 discloses that in an EDI system equipped with multiple EDI devices configured to distribute supplied water between deionization compartments and concentration compartments, the amount of water supplied to the concentration compartments of each EDI device is kept constant by reducing the amount of deionized water discharged when the amount of water supplied to the EDI system decreases, in order to prevent the formation of scale in the EDI devices.

[0006] Patent Document 4 discloses a pure water production system that includes multiple EDI units (e.g., five or more units) arranged in parallel, each EDI unit consisting of two EDI devices connected in series with a booster pump in between. In this pure water production system, the operating state of each EDI unit can be switched depending on the degree of decline in the processing capacity of the EDI devices that make up each EDI unit, allowing the EDI unit to be selected for use. This allows the operation of the entire pure water production system to continue without being stopped, even if the control of one EDI device becomes unstable due to a decline in processing capacity, improving processing efficiency.

[0007] Patent Document 5, which relates to a primary pure water system that does not use an EDI device, discloses that multiple lines, each consisting of an ion exchange device and a reverse osmosis membrane device installed downstream, are arranged in parallel, and that operation of some lines is stopped when the ion exchange resin in the ion exchange device is regenerated or replaced or when the demand for primary pure water decreases. In the lines that are stopped from operating, maintenance such as regeneration or replacement of the ion exchange resin can be performed. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-575 [Patent Document 2] Japanese Patent Application Publication No. 2024-17877 [Patent Document 3] Japanese Patent Publication No. 2022-160867 [Patent Document 4] Japanese Patent Application Publication No. 2018-34103 [Patent Document 5] Japanese Patent Application Laid-Open No. 2013-215679 Summary of the Invention [Problem to be solved by the invention]

[0009] In the case of ion exchange devices that require frequent regeneration or replacement of ion exchange resins, in order to continue supplying deionized water at a constant flow rate over a long period of time, as described in Patent Document 5 and elsewhere, more ion exchange devices than are required to process the required flow rate are prepared. Then, maintenance, i.e., regeneration or replacement of the ion exchange resin, is performed on some ion exchange devices, while the remaining ion exchange devices perform ion exchange treatment of the water to be treated, rotating the ion exchange devices undergoing maintenance. In contrast, EDI devices do not require daily regeneration or replacement of ion exchange resins, but they do require replacement every few years. Therefore, in an EDI system, all EDI devices in the system are replaced every few years, for example. Potential failures in EDI systems include isolated failures of a single EDI device, but also damage to the ion exchange resins or ion exchange membranes in the EDI devices due to the inflow of water to be treated containing oxidizing substances. When water to be treated containing oxidizing substances is inflowed, all EDI devices operating in parallel in the EDI system are damaged, requiring replacement of all such EDI devices. For this reason, in the case of EDI systems, adopting a maintenance method in which more EDI devices than are necessary to process the required flow rate are installed in advance and maintenance is performed in sequence is not a rational method, considering the cost of the EDI devices installed as spares.

[0010] The object of the present invention is to provide an EDI system equipped with EDI devices, which can supply treated water to a place of use without interruption for a period of time, such as several years, while maintaining the flow rate of treated water in each EDI device at an appropriate value, and which allows the EDI device to be replaced while the treated water is being supplied, and an operating method for replacing EDI devices in such an EDI system. [Means for solving the problem]

[0011] The EDI system (electrodeionized water production system) of the present invention is an EDI system that can be equipped with one or more EDI devices (electrodeionized water production devices) and produces treated water that is deionized water, and includes two or more installation locations where each EDI device is installed, a first supply valve and a first discharge valve that are respectively installed in a path of water supplied to the EDI device and a path of water discharged from the EDI device corresponding to the first installation location, and the EDI device installed at the first installation location is in an operating state with the first supply valve and the first discharge valve that are respectively installed in a path of water supplied to the EDI device and a path of water discharged from the EDI device corresponding to the second installation location being opened, and a control device that performs switching control to close the first supply valve and the first discharge valve and simultaneously open the second supply valve and the second discharge valve, thereby placing the EDI device installed at the first installation location in a stopped state and the EDI device installed at the second installation location in an operating state, so that the flow rate of treated water discharged from the EDI system does not fluctuate and the flow rate of treated water in each EDI device in an operating state does not fluctuate when the second supply valve and the second discharge valve installed at the second installation location are closed and the EDI device installed at the second installation location is stopped. When treating water, one or more EDI devices are always in an operating state. Here, "EDI device in an operating state" refers to a state in which water is being passed through the EDI device, a DC voltage is being applied, and the EDI device is performing a desalination process. Meanwhile, a stopped state refers to a state in which at least one of the water flow and the application of DC voltage to the EDI device is stopped.

[0012] The operating method of the present invention is an operating method of an EDI system in which one or more EDI devices can be installed and which produces treated water that is deionized water, the EDI system having two or more installation locations where the EDI devices are respectively installed, the one or more EDI devices being in operation, and a first supply valve and a first discharge valve respectively provided in a path of water supplied to the EDI device corresponding to the first installation location and a path of water discharged from the EDI device being opened, the EDI device provided in the first installation location being in operation, and the path of water supplied to the EDI device corresponding to the second installation location being opened, When the second supply valve and second discharge valve, respectively provided in the path for water discharged from the EDI device and the EDI device, are closed and the EDI device provided at the second installation location is in a stopped state, a switching operation is performed in which the first supply valve and first discharge valve are closed and the second supply valve and second discharge valve are opened at the same time to stop the EDI device provided at the first installation location and to operate the EDI device provided at the second installation location, so that the flow rate of treated water discharged from the EDI system does not fluctuate and the flow rate of treated water in each EDI device that is in operation does not fluctuate. [Effects of the Invention]

[0013] According to the present invention, treated water can be continuously supplied to the point of use while maintaining the flow rate of treated water in each EDI device at an appropriate value, and EDI devices can be replaced without changing the flow rate during the supply of treated water. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram showing an EDI device. [Figure 2] 1 is a diagram showing an EDI system according to an embodiment of the present invention. [Figure 3] FIG. 10 is a diagram illustrating a first operation pattern. [Figure 4] FIG. 10 is a diagram illustrating a reference operation pattern. [Figure 5] FIG. 10 is a diagram illustrating a second operation pattern. [Figure 6]FIG. 10 is a diagram illustrating an EDI system according to another embodiment. [Figure 7] FIG. 10 is a diagram illustrating a third operation pattern. [Figure 8] 1 is a graph illustrating the results of Reference Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0015] Next, embodiments of the present invention will be described with reference to the drawings. Fig. 1 is a schematic diagram illustrating an EDI device (electrodeionized water production device) used in an EDI system (electrodeionized water production system), and Fig. 2 is a diagram showing the configuration of an EDI system according to one embodiment of the present invention.

[0016] The EDI system shown in FIG. 2 includes multiple EDI devices 10 operated in parallel to supply treated water (i.e., deionized water) to a point of use at a flow rate exceeding the capacity of each EDI device 10. As described in Patent Documents 1 and 2, the EDI device 10 has a configuration in which deionization compartments and concentration compartments are alternately arranged between an anode compartment containing an anode and a cathode compartment containing a cathode. The anode compartment and cathode compartment are collectively referred to as electrode compartments. In this embodiment, any known EDI device 10, including commercially available devices, can be used. In FIG. 1, the deionization compartment is represented by D, the concentration compartment by C, and the electrode compartment by E. When operating the EDI device 10, water must be passed through the deionization compartment D, the concentration compartment C, and the electrode compartment E, and a DC voltage must be applied between the anode (not shown) and the cathode (not shown). Therefore, the EDI device 10 is provided with a pipe 11D for supplying feed water to the deionization chamber D, a pipe 11C for supplying feed water to the concentration chamber C, a pipe 11E for supplying feed water to the electrode chamber E, a pipe 12D for discharging the outlet water (i.e., treated water) from the deionization chamber D, a pipe 12C for discharging the outlet water (i.e., concentrated water) from the concentration chamber C, a pipe 12E for discharging the outlet water (i.e., electrode water) from the electrode chamber E, a wiring 13 connected to an anode (not shown), and a wiring 14 connected to a cathode (not shown).

[0017] The illustrated EDI system has three installation locations P1 to P3, and one EDI device 10 can be removably installed in each of the installation locations P1 to P3. During normal operation of the EDI system, EDI devices 10 are installed in two of the three installation locations P1 to P3, and these EDI devices 10 are in operation. The remaining installation location is left as an empty space. The EDI system may be provided with four or more installation locations, and in that case, as long as there is at least one empty space, three or more EDI devices 10 can be installed in the EDI system during normal operation. The EDI system is provided with a DC power supply 15 corresponding to each of the installation locations P1 to P3.

[0018] At each of installation locations P1 to P3, connecting members 21D, 21C, 21E, 22D, 22C, and 22D are provided, as shown at installation location P3 in the figure, to supply feed water to deionization chamber D, concentration chamber C, and electrode chamber E of EDI device 10, and to discharge treated water, concentrated water, and electrode water from EDI device 10. Connecting members 21D, 21C, and 21E are members that can be detachably connected to pipes 11D, 11C, and 11E on the supply side of EDI device 10, respectively, and connecting members 22D, 22C, and 22E are members that can be detachably connected to pipes 12D, 12C, and 12E on the discharge side of EDI device 10, respectively. Connection members 21D, 21C, 21E, 22D, 22C, and 22E are configured, for example, with pipe joints, unions, connection valves, or nozzles. When EDI device 10 is installed at the installation location, they are connected to pipes 11D, 11C, 11E, 12D, 12C, and 12E to allow water to flow without causing leakage. Each of installation locations P1 to P3 is also provided with electrical connection members 23 and 24 that are detachably electrically connected to wiring 13 and 14 of EDI device 10, respectively, to apply a DC voltage between the anode (not shown) and cathode (not shown) of EDI device 10. Electrical connection members 23 and 24 are electrically connected to DC power source 15. By connecting wiring 13 and 14 of EDI device 10 to electrical connection members 23 and 24, the DC voltage generated in DC power source 15 is applied between the anode (not shown) and cathode (not shown) of EDI device 10.

[0019] In EDI device 10, water may be supplied from separate water sources to deionization compartment D, concentration compartment C, and electrode chamber E, respectively. However, in this embodiment, water from a common water source is supplied to deionization compartment D, concentration compartment C, and electrode chamber E as EDI feed water. The EDI system is provided with piping 30 for EDI feed water supplied from an external water source, and piping 30 is equipped with a pump P for feeding the EDI feed water. Downstream of pump P, piping 30 branches into piping 30D, 30C, and 30E for supplying feed water to deionization compartment D, concentration compartment C, and electrode chamber E, respectively. Inlet valves 40 are provided to adjust the flow rate and pressure in each of these piping 30D, 30C, and 30E. Downstream of the inlet valve 40, the pipe 30D branches into a pipe 31D that extends to the installation location P1 and connects to the connecting member 21D at the installation location P1, a pipe 32D that extends to the installation location P2 and connects to the connecting member 21D at the installation location P2, and a pipe 33D that extends to the installation location P3 and connects to the connecting member 21D at the installation location P3. Similarly, the pipe 30C branches into pipes 31C, 32C, and 33C, and the pipe 30E branches into pipes 31E, 32E, and 33E. A valve 41 that opens and closes the pipes 31D, 31C, and 31E is provided corresponding to the installation location P1. The valve 41 is an assembly of an on-off valve 41D provided in the pipe 31D, an on-off valve 41C provided in the pipe 31C, and an on-off valve 41E provided in the pipe 31E. Similarly, a valve 42 is provided for opening and closing pipes 32D, 32C, and 32E corresponding to installation location P2, and a valve 43 is provided for opening and closing pipes 33D, 33C, and 33E corresponding to installation location P3. Valves 41 to 43 are supply valves provided in the paths for supplying water to EDI devices 10 provided in installation locations P1 to P3, respectively.

[0020] The EDI system includes a pipe 50D for discharging treated water (deionized water) to the outside, a pipe 50C for discharging concentrated water to the outside, and a pipe 50E for discharging electrode water to the outside. An outlet valve 60 is provided to adjust the flow rate and pressure of these pipes 50D, 50C, and 50E. Upstream of the outlet valve 60, the pipe 50D branches into a pipe 51D extending to installation location P1 and connecting to the connecting member 22D at installation location P1, a pipe 52D extending to installation location P2 and connecting to the connecting member 22D at installation location P2, and a pipe 53D extending to installation location P3 and connecting to the connecting member 22D at installation location P3. Similarly, the pipe 50C branches into pipes 51C, 52C, and 53C, and the pipe 50E branches into pipes 51E, 52E, and 53E. A valve 61 is provided corresponding to installation location P1 to open and close the pipes 51D, 51C, and 51E. Valve 61 is an assembly of on-off valve 61D provided on pipe 51D, on-off valve 61C provided on pipe 51C, and on-off valve 61E provided on pipe 51E. Similarly, valve 62 is provided for opening and closing pipes 52D, 52C, and 52E corresponding to installation location P2, and valve 63 is provided for opening and closing pipes 53D, 53C, and 53E corresponding to installation location P3. Valves 61 to 63 are discharge valves provided in the paths for water discharged from EDI devices 10 provided at installation locations P1 to P3, respectively. The EDI system also includes a control device 70 that controls valves 41 to 43 and 61 to 63 and three DC power supplies 15.

[0021] In the above explanation, inlet valve 40 that adjusts the flow rate and pressure is provided in common to multiple installation locations P1 to P3 for each of the water supplied to deionization chamber D, the water supplied to concentration chamber C, and the water supplied to electrode chamber E, but a valve that adjusts the flow rate and pressure of the EDI supply water may be provided at each installation location P1 to P3, separately from valves 41 to 43 that are supply valves that only open and close. Similarly, outlet valve 60 that is provided on the outlet side of the EDI system to adjust the flow rate and pressure may be provided at each installation location P1 to P3, separately from valves 61 to 63 that are discharge valves that only open and close.

[0022] Next, the replacement of the EDI device 10 in the EDI system described above will be explained. Here, the water flow rate in the deionization compartment D of each EDI device 10 during operation is uniform, and similarly, the water flow rate in the concentration compartment C and the water flow rate in the electrode compartment E are also uniform between EDI devices 10, and when replacing an EDI device 10, these water flow rates are prevented from fluctuating. Naturally, the water flow rate in each EDI device 10 is set to a value determined as the appropriate value or rated value for that EDI device 10. As an example, in each EDI device 10, if the standard flow rate of treated water is 15 m 3 / h, and the minimum allowable range of treated water flow rate is 7.5 m 3 / h, with a maximum value of 22.5m 3 When such an EDI device 10 is used, in the following description, each EDI device 10 is set to a treated water flow rate of 22.5 m 3 / h, in which case the total amount of treated water in the EDI system is 45m 3 / h. Naturally, the treated water flow rate of each EDI device 10 can be set appropriately as long as it is within the rated range. In this embodiment, during normal operation, EDI devices 10 are installed at two of the three installation locations P1 to P3, but here, it is assumed that, in the initial state, an EDI device 10 is installed at each of installation locations P1 and P2, and installation location P3 is an empty space. The inlet valve 40 and outlet valve 60 are in a water-passing state. There are several possible procedures for replacing an EDI device 10, i.e., several operation patterns for the EDI system.

[0023] [First operation pattern] Figure 3 shows the installation status and operation status of EDI devices at each installation location P1 to P3 in the EDI system over time in the first operation pattern. In the figure, the rectangles adjacent to each symbol P1 to P3 indicating the installation location indicate what kind of device is installed at that installation location and whether that device is in operation. When the rectangle is dashed, that installation location is vacant. Furthermore, the elongated rectangles surrounding the entire installation locations P1 to P3 represent the EDI system. The arrows indicate the passage of time.

[0024] In FIG. 3, (a) shows the initial state, where existing EDI devices 10 are in operation at installation locations P1 and P2, and installation location P3 is an empty space. In the figure, the existing EDI device 10 is referred to as the "existing device." At this time, valves 41, 42, 61, and 62 are open, and valves 43 and 63 are closed. In this state, as shown in (b), a new EDI device 10 is installed at installation location P3, which is an empty space, and a connection is established between this new EDI device 10 and the EDI system using connection members 21D, 21C, 21D, 22D, 22C, and 22E and electrical connection members 23 and 24. In the figure, the newly installed EDI device 10 is referred to as the "new device." In this state, the new EDI device 10 is stopped, and valves 43 and 63 are closed. Next, under the control of the control device 70, valves 43 and 63 are opened and valves 41 and 61 are closed, and at the same time, application of DC voltage to the new EDI device 10 at installation location P3 is started and application of DC voltage to the existing EDI device 10 at installation location P1 is stopped. By performing this operation, as shown in (c), the existing EDI device 10 at installation location P1 is put into a stopped state and the new EDI device 10 at installation location P3 is put into an operating state.

[0025] Here, to prevent fluctuations in the flow rate of treated water discharged from the EDI system and fluctuations in the flow rate of treated water in each EDI device 10 in operation, switching control is performed to close valves 41 and 61 corresponding to installation location P1 and simultaneously open valves 43 and 63 corresponding to installation location P3, thereby putting the EDI device 10 installed at installation location P1 in a stopped state and putting the EDI device 10 installed at installation location P3 in an operating state. This operation of switching between operating EDI devices 10 is called a switching operation. Then, as shown in (d), the existing EDI device 10 at installation location P1 is removed, and installation location P1 becomes an empty space. During this time, the existing EDI device 10 at installation location P2 remains in an operating state.

[0026] Through the above operations, one EDI device 10 has been replaced. Next, another existing EDI device 10, i.e., the EDI device 10 at installation location P2, is replaced. In this case, similar to the above, a new EDI device 10 is installed in the vacant space of installation location P1. In this state, as shown in (e), the new EDI device 10 at installation location P1 is stopped, and the existing EDI device 10 at installation location P2 is operating. In this state, valves 41 and 61 are opened and valves 42 and 62 are closed, and application of DC voltage to the new EDI device 10 at installation location P1 begins, and application of DC voltage to the existing EDI device 10 at installation location P2 is stopped. Through these operations, as shown in (f), the new EDI device 10 at installation location P1 is operating, and the existing EDI device 10 at installation location P2 is stopped. After that, if the existing EDI device 10 at installation location P2 is removed, installation location P2 becomes an empty space as shown in (g). During the period shown in (d) to (f) in Figure 3, the new EDI device 10 at installation location P3 remains in operation.

[0027] According to the first operational pattern described above, two existing EDI devices 10 can be replaced with two new EDI devices 10 without changing the water flow rate of the operating EDI devices 10. If the water flow rate of the EDI devices 10 does not change, there is no need to adjust the voltage and current of the DC power supply 15, and there is no need to adjust the flow rate or pressure of the inlet valve 40 or the outlet valve 60. The overall amount of treated water in the EDI system does not change, and the number of EDI devices 10 into which the EDI feed water is diverted remains essentially two. This prevents fluctuations in the amount of water discharged by the pump P and the pressure, thereby suppressing the generation of fine particles in the pump P. In practice, because it takes some time to open and close the valves, strictly speaking, instantaneous switching between an operating EDI device 10 and a stopped EDI device 10 is not possible. During the transitional period of switching, there is a risk that both EDI devices 10 will be operating simultaneously. However, even if such a period occurs during the transitional period, it is only for a very short time, and in particular, by opening the valve that should be opened first and then closing the valve that should be closed, water will flow through both EDI devices 10 during the transitional period, and the flow rate per EDI device 10 will decrease, so this operation can be said to be an operation that improves the impurity removal rate.

[0028] The example shown in FIG. 3 explains the first operation pattern in the EDI system shown in FIG. 2, which has three installation locations and two EDI devices 10 installed therein. However, the first operation pattern can also be implemented in EDI systems other than the EDI system shown in FIG. 2. For example, even if the EDI system has four or more installation locations, three or more EDI devices 10 installed therein, and one or more free spaces are normally available, by repeating the above-described procedure, an EDI device 10 can be replaced without changing the flow rate of treated water in each EDI device 10 currently in operation. Furthermore, the procedure of the first operation pattern described above can also be applied to an EDI system with two installation locations and one EDI device 10 installed therein. In this case, by assuming that installation location P2 does not exist and focusing on installation locations P1 and P3, and performing steps (a) to (d) of the procedure shown in FIG. 3, the existing device installed at installation location P1 can be replaced with a new device installed at installation location P3.

[0029] In the above description, a DC power supply 15 is pre-installed at each of the installation locations P1 to P3 in the EDI system. However, a DC power supply 15 may not be installed in an installation location that is an empty space. In this case, when a new EDI device 10 is installed in an installation location that is an empty space, a DC power supply 15 corresponding to that installation location is installed, and when an EDI device is removed from an installation location, the DC power supply 15 corresponding to that installation location is also removed. Furthermore, two DC power supplies 15 may be installed in the EDI system, and a switch may be provided for each DC power supply 15 to select the installation location to which the DC power supply 15 is connected. When the EDI device 10 to which water is passed is switched by operating a valve, the switch to select the connection destination of the DC power supply 15 may also be operated, thereby switching the EDI device 10 to be in operation. This switch can be controlled by the control device 70. Furthermore, it is possible to replace the EDI device 10 together with the DC power supply 15, assuming that the DC power supply 15 is pre-connected to the EDI device 10.

[0030] [Reference operation pattern] FIG. 4 shows the procedure for replacing an EDI device 10 when an EDI device 10 is installed at each of the installation locations P1 to P3 in the EDI system described with reference to FIG. 2 and three EDI devices 10 are normally operated in parallel. The flow rate of treated water in the entire EDI system is 45 m, the same as that shown in FIG. 3 / h, and the appropriate flow rate value for each EDI device 10 is also assumed to be the same as that shown in Figure 2. In Figure 4, (a) shows the initial state, in which all of the existing EDI devices 10 are in operation at each of the installation locations P1 to P3. Since three EDI devices 10 are operating, the treated water flow rate per EDI device 10 is 15 m 3 / h.

[0031] Now consider the case where the EDI device 10 installed at installation location P2 is replaced. In this case, as shown in (b), operation of the existing EDI device 10 at installation location P2 is stopped, and then this existing EDI device 10 is removed. Installation location P2 from which the EDI device 10 has been removed becomes an empty space, as shown in (c). If the flow rate of treated water in the entire EDI system is not changed, the flow rate of treated water in the existing EDI devices 10 operating at installation locations P1 and P3 is 22.5 m / s each. 3 / h. After that, as shown in (d), a new EDI device 10 is installed in the vacant installation location P2. At this point, the EDI device 10 installed in the installation location P2 is in a stopped state, and the amount of water treated by the EDI devices 10 installed in the installation locations P1 and P3 is both 22.5 m 3 / h. Finally, as shown in (e), the operation of the newly installed EDI device 10 is started at the installation location P2. As a result, three EDI devices 10 are operated in parallel in the EDI system, and the flow rate of treated water in each EDI device 10 is 15 m 3 / h. Furthermore, by following the steps shown in (a) to (e) of FIG. 4, the existing EDI device 10 at installation location P2 is replaced with a new EDI device 10. If it is desired to also replace the existing EDI device 10 at installation location P1, the same steps can be repeated. Naturally, the flow rate of treated water at each EDI device 10 must be within the rated value range specified for that EDI device 10, and it is necessary to ensure that deviation from the rated value does not occur when the number of EDI devices 10 in operation changes.

[0032] The reference operation pattern shown in Figure 4 anticipates that the number of operating EDI devices 10 will be reduced when a replacement is performed, and a spare EDI device 10 is installed in the EDI system. During normal operation, all EDI devices 10, including the spare EDI device 10, operate in parallel. In this operation pattern, if the flow rate of treated water throughout the EDI system is maintained constant, the flow rate of treated water at each operating EDI device 10 will fluctuate. If the flow rate at each EDI device 10 changes, the applied current value at each EDI device 10 will also need to be adjusted. Furthermore, fluctuations in the flow rate of treated water at each EDI device 10 will also fluctuate, potentially resulting in fluctuations in the quality of the treated water obtained from the EDI system. Regarding pump P, while the flow rate of treated water delivered by pump P remains constant, the flow rate at each EDI device 10 changes, resulting in fluctuations in the differential pressure between the treated water and the pump. This requires adjustment of the operating pressure at pump P and the pressures at inlet valve 40 and outlet valve 60. When the reference operation pattern shown in Fig. 4 is used, the flow rate of treated water at each EDI device 10 changes compared to when the first operation pattern shown in Fig. 3 is used, which causes fluctuations in the quality of the treated water and requires various adjustments to be made in response to these flow rate changes. Furthermore, in the reference operation pattern, if water to be treated containing oxidizing substances flows into three EDI devices 10 operating in parallel, all three devices may be damaged. In contrast, in the first operation pattern, only two EDI devices 10 are operating and water is passed through them at the same time, which has the advantage that no single EDI device 10 is damaged compared to the reference operation pattern.

[0033] [Second operation pattern] When an EDI system includes a large number of EDI devices 10 or when multiple EDI systems are installed, an EDI device 10 that is used only during replacement work can be used separately from the new EDI device 10 to facilitate management of the EDI device 10 prepared for replacement. The EDI device 10 used only during replacement work is called a "backup device." The second operation pattern shown in Figure 5 illustrates an example in which two EDI devices 10 in the EDI system shown in Figure 2 are replaced using a backup device. Figure 5 (a) shows the initial state, where the existing EDI devices 10 are in operation at installation locations P1 and P2, and installation location P3 is an empty space. At this time, valves 41, 42, 61, and 62 are open, and valves 43 and 63 are closed. In this state, as shown in (b), a spare EDI device 10 is installed in installation location P3, which is an empty space, and a connection is established between this new EDI device 10 and the EDI system using connection members 21D, 21C, 21D, 22D, 22C, and 22E and electrical connection members 23 and 24. In this state, the spare EDI device 10 is in a stopped state, and valves 43 and 63 are closed. Next, under the control of the control device 70, valves 43 and 63 are opened and valves 41 and 61 are closed. At the same time, application of DC voltage to the spare EDI device 10 at installation location P3 is started, and application of DC voltage to the existing EDI device 10 at installation location P1 is stopped, as shown in (c), and the spare EDI device 10 at installation location P3 is put into operation.

[0034] Thereafter, as shown in (d), the existing EDI device 10 at installation location P1 is removed, leaving installation location P1 empty. Next, as shown in (e), a new EDI device 10 is placed at installation location P1, valves 41 and 61 are opened, valves 42 and 62 are closed, and application of DC voltage to the new EDI device 10 at installation location P1 is started, while application of DC voltage to the existing EDI device 10 at installation location P2 is stopped. This state is shown in (f) of FIG. 5. Next, as shown in (g), the existing EDI device 10 at installation location P2 is removed, leaving installation location P2 empty, and as shown in (h), a new EDI device 10 is installed in the now empty installation location P2. In this state, the newly installed EDI device 10 at installation location P2 is in an inactive state. In this state, valves 42 and 63 are opened and valves 43 and 63 are closed, and the application of DC voltage to the new EDI device 10 at installation location P2 is started, and the application of DC voltage to the spare EDI device 10 at installation location P3 is stopped. As a result, as shown in (i), the new EDI device 10 at installation location P2 is put into operation, and the spare EDI device 10 at installation location P3 is put into a stopped state. Through the above process, both of the existing EDI devices 10 at installation locations P1 and P2 have been replaced with the new EDI devices 10. At this time, the spare EDI device 10 placed at installation location P3 continues to be in operation during the period from (c) to (h) in FIG. 5. Finally, as shown in (j), the spare EDI device 10 is removed from installation location P3, making installation location P3 an empty space.

[0035] In the second operation pattern, a spare EDI device 10 is used. The spare EDI device 10 has basically the same specifications as the existing EDI device 10 or the EDI device 10 to be newly installed. However, for example, the spare EDI device 10 may be loaned from the manufacturer of the EDI device 10 when replacing the existing EDI device 10 with a new EDI device 10. Alternatively, the spare EDI device 10 may be owned by the operator of the EDI system and stored at the operator's premises to deal with accidental failures in the EDI device 10 in the EDI system. The spare EDI device 10 is isolated from the EDI system during normal operation, and therefore will not be damaged even if a water supply problem occurs in the EDI system, such as the inflow of treated water containing oxidizing substances.

[0036] The second operation pattern can be applied to any EDI system that normally has one or more free spaces. For example, even if the EDI system has four or more installation locations, three or more EDI devices 10, and normally has one or more free spaces, spare EDI devices 10 can be installed in the free spaces to sequentially replace the existing EDI devices 10 without changing the flow rate of treated water at each EDI device 10 in operation. The procedure described above as the second operation pattern can also be applied to an EDI system with two installation locations where one EDI device 10 is installed. In this case, assuming that installation location P2 does not exist, focus on installation locations P1 and P3, and perform steps (a) to (e) of the procedure shown in Figure 5. Then, start operation of the new device installed at installation location P1, stop operation of the spare device installed at installation location P3, and remove the spare device, thereby replacing the existing device installed at installation location P1 with the new device.

[0037] When an EDI system is installed in a business that uses a large amount of deionized water or pure water, multiple EDI systems may be installed. For example, four EDI systems are installed in five installation locations, each with four EDI devices 10 installed under normal conditions, and the flow rate of treated water in each EDI device 10 is set to 20 m 3 / h is a total of 320m 3 / h of deionized water may be generated. In such a case, one EDI device 10 may be provided as a spare device for the entire four-line EDI system, or one EDI device 10 may be provided as a spare device for each line. Furthermore, in addition to the four-line EDI system, another EDI system with the same configuration as the four-line EDI system may be provided as a spare line. When a spare EDI system is provided, the EDI system can be replaced by performing the same procedures as those described for the second operation pattern, with the existing device, new device, and spare device in the description of the second operation pattern being replaced with the existing EDI system, new EDI system, and spare EDI system, respectively.

[0038] In general, in the EDI device 10, as the treated water flow rate increases, the removal rate of weak anions, particularly boron and silica components, decreases. Furthermore, a decrease in the current value in the EDI device 10 also decreases the removal rate of boron and other components. According to the first and second operating patterns, the flow rate of the EDI device does not fluctuate during operation, allowing the boron and silica concentrations in the treated water to be kept constant. It is possible to increase the applied current to the EDI device 10 to compensate for the decrease in impurity removal rate that occurs with an increase in the treated water flow rate. However, the EDI device 10 generally has maximum values ​​for the applied current and voltage, and it may not be possible to increase the applied current in response to an increase in the treated water flow rate.

[0039] Generally, an EDI system is constructed as a structural unit including, for example, a rack or a housing capable of accommodating multiple EDI devices 10. Therefore, the installation locations P1 to P3 for the EDI devices 10 are provided, for example, within the structural unit of the EDI system. However, in the second operation pattern, the spare EDI device 10 is temporarily incorporated into the EDI system and is removed once the series of replacement operations are completed. From this perspective, the installation location for the spare EDI device 10 does not necessarily need to be provided within the structural unit of the EDI system, but may be a location temporarily secured outside the structural unit. In other words, if the installation location P3 in the EDI system shown in FIG. 2 is a dedicated installation location for the spare EDI device 10, the installation location P3 does not need to be provided within the structural unit of the EDI system, and it is not necessary to permanently secure the installation location P3 within the EDI system. It is sufficient for the spare EDI device 10 to be supplied with water via pipes 30D, 30C, and 30E when needed, and for water to be discharged via pipes 50D, 50C, and 50E. Therefore, the EDI system can be configured to be connectable to a portable standby EDI unit equipped with a standby EDI device 10. Figure 6 shows an example of the configuration of an EDI system according to another embodiment, in which a standby EDI unit 80 is removably connected.

[0040] 6 is obtained by removing installation location P3 and the piping 33D, 33C, 33E, 53D, 53C, 53E and valves 43 and 46 corresponding to installation location P3 from the EDI system shown in FIG. 2, and instead installing a removably installed spare EDI unit 80. The spare EDI unit 80 is provided with a spare EDI device 10, a DC power supply 15 for applying a DC voltage to the spare EDI device, piping 35D, 35C, 35E for supplying water to the deionization compartment D, concentration compartment C, and electrode compartment E of the spare EDI device 10, respectively, piping 55D, 55C, 55E for discharging water from the deionization compartment D, concentration compartment C, and electrode compartment E of the spare EDI device 10, valve 45 for opening and closing the piping 35D, 35C, 35E, and valve 65 for opening and closing the piping 35D, 35C, 35E. The pipes 35D, 35C, and 35E are detachably connected to the pipes 30D, 30C, and 30E of the EDI system via connecting members 81D, 81C, and 81E, and the pipes 55D, 55C, and 55E are detachably connected to the pipes 50D, 50C, and 50E via connecting members 82D, 82C, and 82E. The spare EDI device 10 does not need to be attached inside the spare EDI unit 80 so that it can be easily removed from the spare EDI unit 80. When the spare EDI unit 80 is used, a DC power supply 15 provided in a structural unit of the existing EDI system may be used, and the valves 45 and 65 may also be provided in the structural unit of the existing EDI system.

[0041] [Third operation pattern] The third operation pattern shown in FIG. 7 is also an operation pattern in the EDI system shown in FIG. 2, in which the EDI device 10 in the stopped state and the EDI device 10 in the operating state are switched without changing the flow rate of treated water through the operating EDI device 10. In the third operation pattern, EDI devices 10 are installed at all three installation locations P1 to P3 of the EDI system, but only two of them are operated, and the operating EDI devices 10 are switched in rotation. In FIG. 7, (a) shows the initial state, in which the existing EDI devices 10 are in operation at installation locations P1 and P2, and the existing EDI device 10 at installation location P3 is in the stopped state. At this time, valves 41, 42, 61, and 62 are open, and valves 43 and 63 are closed. DC voltage is applied to the EDI devices 10 at installation locations P1 and P2, but not to the EDI device 10 at installation location P3. In this state, for example, after a predetermined time has elapsed, valves 43 and 63 are opened and valves 42 and 62 are closed, and at the same time, application of DC voltage to EDI device 10 at installation location P3 is started and application of DC voltage to EDI device 10 at installation location P2 is stopped. By performing this operation, as shown in (b), EDI device 10 at installation location P2 is put into a stopped state and EDI device 10 at installation location P3 is put into an operating state.

[0042] Then, after a predetermined time has elapsed, valves 43 and 63 are opened and valves 42 and 62 are closed. At the same time, application of DC voltage to the EDI device 10 at installation location P3 is started and application of DC voltage to the EDI device 10 at installation location P2 is stopped. By performing this operation, as shown in (b), the EDI device 10 at installation location P2 is stopped and the EDI device 10 at installation location P3 is in operation. After another predetermined time has elapsed, valves 42 and 62 are opened and valves 41 and 61 are closed. At the same time, application of DC voltage to the EDI device 10 at installation location P2 is started and application of DC voltage to the EDI device 10 at installation location P1 is stopped. By performing this operation, as shown in (c), the EDI device 10 at installation location P1 is stopped and the EDI device 10 at installation location P2 is in operation. After this, valves 41 and 61 are opened and valves 43 and 63 are closed, and at the same time, application of DC voltage to the EDI device 10 at installation location P1 is started and application of DC voltage to the EDI device 10 at installation location P3 is stopped. By performing this operation, as shown in (d), the EDI device 10 at installation location P3 is put into a stopped state and the EDI device 10 at installation location P1 is put into an operating state. Since the state shown in (d) is the same as the state shown in (a), by repeating the same operation hereafter, the three EDI devices 10 in the EDI system will be operated in rotation.

[0043] In the third operation pattern, valves 41-43 and 61-63 must be opened and closed, and the DC voltage applied by DC power supply 15 must be turned on and off. These operations are automatically performed by control device 70. According to the third operation pattern, a redundant configuration capable of dealing with accidental failure of an EDI device 10 in the EDI system is adopted, and switching between EDI devices 10 can be performed without changing the flow rate of treated water at the operating EDI device 10. Furthermore, by increasing the number of stopped EDI devices 10 without changing the flow rate at the operating EDI device 10, a reduction in the flow rate of treated water required for the EDI system can be accommodated. Furthermore, in the third operation pattern, since one or more EDI devices 10 are always in the stopped state, the number of DC power supplies 15 installed in the EDI system can be reduced compared to the reference operation pattern. The procedure described above for the third operation pattern can also be applied when two EDI devices 10 are alternately operated in an EDI system with two installation locations.

[0044] [Reference example] Next, the present invention will be explained in more detail by explaining the results of experiments carried out by the inventors regarding the boron removal rate in an EDI device.

[0045] [Reference example 1] Ultrapure water with boron added to it to achieve a boron concentration of 25 μg / L was fed into the EDI device as the treated water. The boron concentration in the treated water discharged from the EDI device was measured to determine the boron removal rate. This was performed while varying the flow rate of the treated water through the EDI device. Two types of EDI devices, EDI device A and EDI device B, were used. The applied current value for each EDI device was kept constant regardless of the increase or decrease in the treated water flow rate. The results are shown in Figure 8. In Figure 8, the flow rate for each EDI device was normalized to a standard value of 1, i.e., the flow rate is shown as a ratio to the standard value. As shown in Figure 8, the boron removal rate for each EDI device decreased as the treated water flow rate increased. For example, for EDI device A, the removal rate was 99% when the flow rate ratio was 0.8, but dropped to 98.2% when the flow rate ratio was 1. This means that the boron concentration in the treated water rose from 250 ng / L to 450 ng / L, which could be a major problem if it is necessary to reduce the boron concentration in the treated water.

[0046] In order to suppress the decrease in boron removal rate due to an increase in the flow rate of treated water, it is necessary to increase the applied current value to the EDI device. However, since the EDI device has a rated maximum current value and the applied current value cannot be increased beyond that current value, it may not be possible to adopt the strategy of suppressing the decrease in boron removal rate by increasing the applied current value. According to the EDI system of each of the above-described embodiments, the flow rate of treated water for each EDI device 10 is kept constant, so the decrease in boron removal rate can be suppressed without increasing the applied current value. [Explanation of symbols]

[0047] 10 EDI equipment 15 DC power supply 21C, 21D, 21E, 22C, 22D, 22E, 81C, 81D, 81E, 82C, 82D, 82E Connection members 23,24 Electrical connection members 40 Inlet valve 41~43,45,61~63,65 Valves 60 Outlet valve 70 Control device 80 spare EDI units

Claims

1. 1. An electrodeionization water production system that can be equipped with one or more EDI devices that are electrodeionization water production devices and that produces treated water that is deionized water, comprising: two or more installation locations where the EDI devices are installed; a control device that performs switching control to close the first supply valve and the first discharge valve and simultaneously open the second supply valve and the second discharge valve, respectively, provided in a water path supplied to the EDI device and a water path discharged from the EDI device corresponding to a first installation location, so that the EDI device installed at the first installation location is in an operating state, and a control device that performs switching control to close the first supply valve and the first discharge valve and simultaneously open the second supply valve and the second discharge valve, so that the flow rate of treated water discharged from the electrodeionized water production system and the flow rate of treated water in each of the EDI devices in an operating state do not fluctuate, when a first supply valve and a first discharge valve, respectively, provided in a water path supplied to the EDI device and a water path discharged from the EDI device corresponding to a second installation location are open and the EDI device installed at the first installation location is in an operating state, and a control device that performs switching control to close the first supply valve and the first discharge valve and simultaneously open the second supply valve and the second discharge valve, so that the flow rate of treated water discharged from the electrodeionized water production system and the flow rate of treated water in each of the EDI devices in an operating state do not fluctuate, so that the EDI device installed at the first installation location is in a stopped state and the EDI device installed at the second installation location is in an operating state; and An electrodeionization water production system, wherein one or more of the EDI devices are in operation at all times when producing treated water.

2. a DC power supply that applies a DC voltage to the EDI device; 2. The electrodeionized water production system according to claim 1, wherein, when performing the switching control, the control device controls the DC power source to stop applying a DC voltage to the EDI device installed at the first installation location and start applying a DC voltage to the EDI device installed at the second installation location.

3. 3. The electrodeionized water production system of claim 1 or 2, wherein the installation locations are provided with connecting members that are removably connected to the EDI device, and the EDI device is removably installed at each of the installation locations, and the supply valves and discharge valves provided in the paths of water supplied to and discharged from the EDI device, respectively, are closed in correspondence with the installation locations that are empty spaces without the EDI device installed.

4. 4. The electrodeionized water production system according to claim 3, wherein there is one or more of said installation locations that are vacant spaces during said normal operation.

5. 1. A method of operating an electrodeionization water production system that can be equipped with one or more EDI devices that are electrodeionization water production devices and that produces treated water that is deionized water, comprising: the electrodeionized water production system includes two or more installation locations, each having an EDI device disposed therein; and a second supply valve and a second discharge valve, which are respectively provided in the paths for water supplied to the EDI device and the paths for water discharged from the EDI device corresponding to a second installation location, are closed, and the EDI device provided at the second installation location is stopped. The method of operation includes: performing a switching operation to stop the EDI device provided at the first installation location and to operate the EDI device provided at the second installation location by closing the first supply valve and the first discharge valve and simultaneously opening the second supply valve and the second discharge valve, so that the flow rate of treated water discharged from the electrodeionization water production system does not fluctuate and the flow rate of treated water in each of the EDI devices in operation does not fluctuate.

6. 6. The operating method according to claim 5, wherein, when the switching operation is performed, application of DC voltage to the EDI device installed at the first installation location is stopped and application of DC voltage to the EDI device installed at the second installation location is started.

7. 7. An operating method according to claim 5 or 6, wherein the EDI device is removably installed in each of the installation locations, and the supply valve and discharge valve respectively provided in the path of water supplied to the EDI device and the path of water discharged from the EDI device corresponding to the installation location where the EDI device is not installed and is an empty space are closed.

8. The operation method according to claim 7 , wherein there is one or more installation locations that are vacant spaces during the normal operation.

9. When replacing one or more of the existing EDI devices with the same number of new EDI devices, a replacement operation is performed to replace any one of the existing EDI devices in operation with one of the new EDI devices; The operation method described in claim 8, wherein the replacement operation comprises installing the new EDI device in a stopped state at the installation location which is the vacant space, performing the switching operation between the existing EDI device which is in operation and the new EDI device which is in a stopped state, and after the switching operation, removing the existing EDI device which is in a stopped state from the installation location to create the vacant space.

10. When replacing one or more existing EDI devices with the same number of new EDI devices, a spare EDI device is installed in a stopped state at the installation location, which is the empty space; the switching operation is performed between any one of the existing EDI devices in operation and the spare EDI device in a stopped state; and after the switching operation, the existing EDI device in a stopped state is removed from the installation location to create the empty space; performing a replacement operation to replace one of the existing EDI devices in operation with one of the new EDI devices while maintaining the standby EDI device in operation; When all of the existing EDI devices have been removed, the new EDI device is installed in a stopped state in the installation location, which is the vacant space, and the switching operation is performed between the spare EDI device in an operating state and the new EDI device in a stopped state, and after the switching operation, the spare EDI device in a stopped state is removed from the installation location to create the vacant space, The operation method described in claim 8, wherein the replacement operation comprises installing the new EDI device in a stopped state at the installation location which is the vacant space, performing the switching operation between the existing EDI device which is in operation and the new EDI device which is in a stopped state, and after the switching operation, removing the existing EDI device which is in a stopped state from the installation location to create the vacant space.

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