JP6158681B2 - Deionized water production system and operation method thereof - Google Patents

Description

  The present invention relates to a deionized water production system using an electric deionized water production apparatus (EDI (Electro Deionization) apparatus), and in particular, deionized water with reduced start-up time when restarting after stopping operation. The present invention relates to a method for operating a production system and a deionized water production system suitable for such a method.

  There is known a deionized water production apparatus in which water to be treated is passed through an ion exchanger such as an ion exchange resin and deionized by an ion exchange reaction. Such an apparatus is an ion exchange group of the ion exchanger. When the saturates, it is necessary to regenerate the ion exchanger with a chemical such as acid or alkali, so that there is a problem that the continuous operation cannot be performed and it takes time to replenish the chemical. Therefore, in recent years, as a solution to these problems, an electric deionized water production apparatus that does not require regeneration with a drug has been developed and put into practical use.

In an electric deionized water production apparatus, an ion exchanger (anion exchanger and / or cation exchange) is provided between a cation exchange membrane that allows only cations (cations) to pass therethrough and an anion exchange membrane that allows only anions (anions) to pass through. Body) to form a desalting chamber, a concentration chamber is arranged outside the cation exchange membrane and anion exchange membrane, and a basic configuration consisting of a desalination chamber and concentration chambers on both sides thereof is used as an anode. It arrange | positions between cathodes. At this time, as viewed from the desalting chamber, an anion exchange membrane is disposed between the desalting chamber and the anode, and a cation exchange membrane is disposed between the desalting chamber and the cathode. When water to be treated is passed through the desalting chamber in a state where a DC voltage is applied between the anode and the cathode, ion components in the water to be treated are captured by the ion exchanger in the desalting chamber. At the same time, the dissociation reaction of water proceeds due to the potential difference generated at the interface between the ion exchange membrane and the ion exchanger or the interface between the ion exchanger and the ion exchanger, and hydrogen ions (H ⁺ ) and hydroxide ions (OH ⁻ ). The ion component previously captured is ion-exchanged and released from the ion exchanger by the generated hydrogen ions and hydroxide ions. Of the liberated ionic components, the cations are driven by a direct current to move in the ion exchanger, and further pass through the cation exchange membrane and move to the concentration chamber on the cathode side. Similarly, of the released ionic component, the anion is driven by a direct current and moves in the ion exchanger, and further passes through the anion exchange membrane and moves to the concentration chamber on the anode side. As a result, the ion components in the for-treatment water supplied to the desalting chamber are transferred to the concentration chamber, and deionized water is obtained from the desalting chamber as treated water. At the same time, the ion exchanger in the desalting chamber Will be played. Although the ionic component is concentrated in the concentration chamber, the ionic component can be discharged out of the apparatus by flowing water through the concentration chamber.

  In the above, the basic structure (that is, the cell) consisting of [concentration chamber (C) | anion exchange membrane (AEM) | desalting chamber (D) | cation exchange membrane (CEM) | concentration chamber (C)] is the anode and cathode. A plurality of such cells are juxtaposed between the electrodes, and the plurality of cells are electrically connected in series with one end as an anode and the other as a cathode. It is also possible to increase the processing capacity. In this case, since adjacent concentrating chambers can be shared between adjacent cells, the configuration of the electrical deionized water production apparatus is [Anode | C | AEM | D | CEM | C | AEM | D | CEM | C | AEM | D | CEM | ... | C | cathode]. A device in which one or a plurality of cells are arranged in this way is called an EDI stack. An anode is disposed at one end of the EDI stack and a cathode is disposed at the other end.

  In the electric deionized water production apparatus, ions are removed by a plurality of processes including adsorption of impurity ions to the ion exchanger, electrical regeneration of the ion exchanger, and movement of impurity ions to the concentration chamber. For this reason, compared with the adsorption apparatus using a general ion exchange resin, there is a tendency that it takes time for the water quality to rise when the apparatus is activated. In particular, when the apparatus is stopped after being operated for a certain period of time, it may take a long time for the water quality to rise when the operation is resumed. This is because an electric deionized water production apparatus has, as its configuration, a demineralization chamber in which ions are removed and an ion concentration is reduced, and a concentration chamber in which the ion concentration is increased by ions moving from the demineralization chamber. If the apparatus is stopped and no voltage is applied between the anode and the cathode, it is based on the ion concentration gradient between the concentration chamber and the desalting chamber. This is because the ion component diffuses into the desalting chamber and is adsorbed on the ion exchanger in the desalting chamber. For this reason, in the electric deionized water production apparatus, a step of moving the impurity ions adsorbed on the ion exchanger in the demineralization chamber to the concentration chamber again is required at the start-up, and the apparatus returns to the state before the operation of the apparatus is stopped. In some cases, it takes several hours to several tens of hours.

  In addition, in the electric deionized water production device, in order to shorten the water quality rise time at the time of restarting, supply of water to the concentrating chamber is performed even after the application of DC voltage to the electrode is stopped when the device is stopped. By continuing, water that remains in the concentration chamber and contains a large amount of impurity ions may be discharged (blowed) out of the apparatus. This blow is performed until the conductivity of the water discharged from the concentrating chamber decreases to the same level as that of the water supplied to the concentrating chamber so as to suppress the effect of slowing down the water quality rise at the time of restart. Is called.

  In order to reduce the concentration of ions contained in deionized water as much as possible and to prevent the generation of scale in the electric deionized water production apparatus, the ion concentration in the treated water supplied to the demineralization chamber is reduced. It is desirable to lower it in advance. Therefore, a reverse osmosis membrane separation device is provided as a pre-stage device for the electric deionized water production device, and the permeated water from the reverse osmosis membrane separation device is supplied to the electric deionized water production device as treated water. In general, a reverse osmosis membrane separation device and an electrical deionized water production device are combined to constitute a deionized water production system. The electric deionized water production apparatus itself cannot remove nonionic impurities, but it is also possible to remove particulate nonionic impurities by providing a reverse osmosis membrane separation apparatus.

  In the reverse osmosis membrane separator, during the operation, the primary side (the side where raw water is supplied) and the secondary side (the side where the permeated water that has permeated through the reverse osmosis membrane) are sandwiched across the reverse osmosis membrane. For example, the difference in impurity concentration is several tens of times. When the operation of the apparatus is stopped on the assumption that such an impurity concentration difference is caused by the operation, a phenomenon occurs in which the concentration of ions on the primary side diffuses to the secondary side through the reverse osmosis membrane. When the operation of the membrane separation apparatus is resumed, the impurity concentration in the permeated water immediately after the restart temporarily rises. When the permeated water having an increased impurity concentration is supplied to the demineralization chamber of the electric deionized water production apparatus as treated water, sufficient deionization is not performed in the electric deionized water production apparatus. Impurity concentration in deionized water will increase.

  As described above, the electrical deionized water production device takes time to start up the water quality at the time of restart, and the reverse osmosis membrane separation device also temporarily increases the impurity concentration in the permeate at the time of restart. In the deionized water production system that combines the reverse osmosis membrane separation device and the electric deionized water production device, it takes time to start up the water quality when the system is restarted. Even if the electric deionized water production device continues to supply water to the concentrating chamber even when the device is shut down to reduce the concentration of impurity ions in the concentrating chamber, the electric deionized water from the reverse osmosis membrane separation device is restarted. Since the impurity concentration in the permeated water supplied to the ionic water production apparatus is high, it takes time to start up the quality of the deionized water obtained from the deionized water production system.

  In Patent Document 1, in order to solve the problem that it takes time to start up water quality at the time of restarting in a deionized water production system, a reverse osmosis membrane separation device and an electric The deionized water production system is continuously operated by circulating it in the demineralization chamber of the water-type deionized water production device, or when the operation is stopped, water is supplied to the demineralization chamber and the concentration chamber. It is disclosed that a voltage is applied between electrodes of an electric deionized water production apparatus even after stopping. However, in the method described in Patent Document 1, the power consumption due to the circulation operation and the constant operation of the DC power supply cannot be ignored, and the associated increase in the temperature of the circulating water and the water in the desalination chamber cannot be ignored. There are problems such as disappearance.

  In order to prevent the generation of scale in the concentration chamber and reduce the operating voltage in the electric deionized water production apparatus, Patent Document 2 discloses filling the concentration chamber with an ion exchange resin. According to the study by the present inventors, in such a type of electric deionized water production apparatus in which the ion exchange resin is also filled in the concentrating chamber, when the operation of the apparatus is stopped, it continues after the DC power supply is stopped. Even if a blow operation is performed on the concentration chamber, it is impossible to discharge the ions adsorbed on the ion exchange resin in the concentration chamber to the outside of the apparatus, and the ions adsorbed on the ion exchange resin gradually It was clarified that it was not possible to avoid the delay in the water quality rise when the operation was resumed.

JP-A-9-57271 JP 2001-259646 A

  It is required to operate a deionized water production system consisting of a reverse osmosis membrane separation device and an electric deionized water production device intermittently in order to reduce the demand for deionized water over time and reduce energy costs. . However, when the operation and stop of the deionized water production system are repeated, there is a problem that it takes time to start up the water quality when the operation is restarted from the stopped state as described above.

  An object of the present invention is to provide an operation method of a deionized water production system for speeding up the rising of water quality when operation is resumed from a stopped state, and a deionized water production system suitable for such an operation method. There is.

  The operation method of the deionized water production system of the present invention includes at least one of a desalting chamber filled with an ion exchanger and a pair of concentrating chambers disposed on both sides of the desalting chamber via an ion exchange membrane. An electric deionized water production apparatus in which two cells are arranged between the cathode and the anode, and a voltage is applied to the cathode and the anode from a DC power source, and electric deionization as treated water of the electric deionized water production apparatus A reverse osmosis membrane separation device for supplying reverse osmosis membrane permeated water to a water production device, wherein the deionized water production system is operated while the operation of the deionized water production system is stopped. And an impurity removing step for reducing the amount of impurities present on the primary side of the reverse osmosis membrane.

  The deionized water production system of the present invention includes at least one cell including a demineralization chamber filled with an ion exchanger and a pair of concentration chambers disposed on both sides of the demineralization chamber via ion exchange membranes, respectively. An electrical deionized water production apparatus that is disposed between a cathode and an anode and that applies a voltage from a DC power source to the cathode and the anode, and an electrical deionized water production apparatus as treated water of the electrical deionized water production apparatus And a reverse osmosis membrane separation device for supplying reverse osmosis membrane permeated water to the deionized water production system, wherein the reverse osmosis membrane separation device includes an impurity removal means for removing impurities present on the primary side of the reverse osmosis membrane. In addition, while the operation of the deionized water production system is stopped, the amount of impurities present on the primary side of the reverse osmosis membrane in the reverse osmosis membrane separation device is reduced by the impurity removing means.

  According to the present invention, the impurities present on the primary side of the reverse osmosis membrane in the reverse osmosis membrane separation device provided in the front stage of the electric deionized water production device while the operation of the deionized water production system is stopped. By reducing the amount of impurities, it is possible to prevent concentration diffusion of impurities from the primary side to the secondary side of the reverse osmosis membrane during the operation stop period. It is possible to prevent an increase in the impurity concentration in the reverse osmosis membrane permeated water supplied as the treated water to the ion water production apparatus. As a result, it was possible to eliminate the slow start of water quality at the time of resuming operation, which was a major problem with electric deionized water production equipment, and it was possible to significantly shorten the startup time of the deionized water production system. Become. By improving the water quality at the time of resuming operation, it is possible to reduce wasteful circulation operation to maintain the water quality and the time, power, water, etc. required for start-up operation at the time of starting up the equipment. Can be operated.

It is a block diagram which shows the structure of the deionized water manufacturing system of one Embodiment of this invention. It is a figure which shows an example of a structure of an electrical deionized water manufacturing apparatus. It is a block diagram which shows the structure of the deionized water manufacturing system of another embodiment of this invention. It is a figure which shows the structure of the electric deionized water manufacturing apparatus used in the deionized water manufacturing system shown in FIG. It is a figure which shows an example of a structure of the EDI stack provided in an electrical deionized water manufacturing apparatus.

  Next, a preferred embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the deionized water production system according to one embodiment of the present invention includes an electric deionized water production apparatus 30 and a reverse osmosis membrane separation provided in the preceding stage of the electric deionized water production apparatus 30. The apparatus 20 and the pump 10 which supplies raw | natural water to the reverse osmosis membrane separation apparatus 20 are provided. A reverse osmosis membrane 21 is provided inside the reverse osmosis membrane separation device 20. In the reverse osmosis membrane separation device 20, the side on which the raw water is supplied across the reverse osmosis membrane 21 is called the primary side, and the side from which the permeated water that has permeated the reverse osmosis membrane 21 is obtained is called the secondary side. FIG. 1 schematically shows a deionized water production system according to the present invention. The raw water line connected to the pump 10, the permeated water line from the reverse osmosis membrane separation device 20, and electric deionized water. You may install a tank, a pump, a valve, etc. in the line of the treated water from the manufacturing apparatus 30 suitably.

  A back pressure valve 22 and a flushing valve 23 for flushing the reverse osmosis membrane 21 are connected to the primary side of the reverse osmosis membrane separation device 20. During normal operation, the flushing valve 23 is completely closed, and when the raw water is pressurized by the pump 10 and supplied to the reverse osmosis membrane separation device 20, the primary side of the reverse osmosis membrane separation device 20 is fixed by the action of the back pressure valve 22. Therefore, a part of the raw water permeates through the reverse osmosis membrane 21, the impurities are removed at that time, and the reverse osmosis membrane permeated water from which the impurities are removed from the secondary side of the reverse osmosis membrane separation device 20. Is obtained. This reverse osmosis membrane permeated water is sent to the demineralization chamber of the electrical deionized water production apparatus 30 as treated water. A portion of the raw water that has not permeated the reverse osmosis membrane 21 is discharged to the outside through the back pressure valve 22 as concentrated water in which impurities are concentrated.

  FIG. 2 shows an example of the configuration of the electrical deionized water production apparatus 30. The electric deionized water production apparatus 30 includes an anode 31, a cathode 32, and an EDI stack 33. The EDI stack 33 includes a demineralization chamber filled with an ion exchanger such as an ion exchange resin, and the demineralization chamber. A cell having a pair of concentrating chambers disposed on both sides of the chamber via ion exchange membranes, and a voltage is applied from the DC power source 35 to the anode 31 and the cathode 32. It is. In the EDI stack 33, the ion exchange membrane disposed on the anode side in contact with the desalting chamber is an anion exchange membrane, and the ion exchange membrane disposed on the cathode side in contact with the desalting chamber is a cation exchange membrane. At least one of the pair of concentration chambers may be filled with an ion exchanger such as an ion exchange resin. As described in the background art section, the EDI stack 33 may be configured such that a plurality of cells are juxtaposed between the anode and the cathode. It is configured as a common cell.

  When a DC voltage is applied from the DC power source 35 to the anode 31 and the cathode 32 so that the anode 31 is positive and the cathode 32 is negative, reverse osmosis membrane permeated water is supplied to the desalting chamber in this state. The ionic components in the water to be treated are removed based on the treatment principle described in the background art column, and deionized water is obtained as treated water from the desalting chamber.

  In the electrical deionized water production apparatus 30 shown in FIG. 2, the positive output terminal of the DC power supply 35 is directly connected to the anode 31, but the wiring connecting the negative output terminal of the DC power supply 35 and the cathode 32 is used. The diode D for preventing the reverse current flowing from the EDI stack 33 through the anode 31 and the cathode 32 during the stop time of the electric deionized water production apparatus 30 is connected so that the anode is connected to the cathode 32. Has been inserted. According to the knowledge obtained by the present inventors, when the electric deionized water production apparatus is stopped and the application of the DC voltage to the electrode is stopped, the ionic component moved to the concentration chamber diffuses into the desalination chamber. At this time, it was found that a weak reverse current flows between the electrodes. This reverse current is considered to flow from the anode toward the cathode via the DC power supply in the stopped state. The reverse current is accompanied by the diffusion of ionic components. In other words, by blocking the reverse current, the diffusion of ionic components from the concentrating chamber to the desalting chamber can be suppressed. It is thought that the rise of can be made faster.

  Next, the operation method of the deionized water production system of this embodiment will be described.

  When deionized water is generated as treated water from the electric deionized water production apparatus 30 by this deionized water production system, the pump 10 is operated with the flushing valve 23 closed to operate the reverse osmosis membrane separation apparatus 20. In addition, while supplying the reverse osmosis membrane permeated water from the reverse osmosis membrane separation device 20 to the desalting chamber as the treated water, a DC voltage is applied to the anode 31 and the cathode 32 by the DC power source 35 to perform electrical deionization. The operation of the water production apparatus 30 is started.

  While stopping the operation of the deionized water production system in operation, that is, when trying to stop the operation of this deionized water production system, the DC power source 35 is stopped and the electric deionized water production apparatus 30 is operated. In order to stop the operation and speed up the water quality at the time of resuming the operation thereafter, an impurity removal step is performed to reduce the amount of impurities present on the primary side of the reverse osmosis membrane 21 in the reverse osmosis membrane separation device 20 After that, the entire system is brought into a stopped state. In the example shown here, by flushing the reverse osmosis membrane 21, impurities existing on the primary side of the reverse osmosis membrane 21 as flushing wastewater are discharged to the outside and are returned to the primary side in the reverse osmosis membrane separation device 20. Reduce the amount of impurities present.

  Flushing of a reverse osmosis membrane in a reverse osmosis membrane separator is generally performed by flowing most of the water supplied to the reverse osmosis membrane separator without passing through the reverse osmosis membrane to the primary side of the reverse osmosis membrane. This is a process of discharging impurities typified by those adhering to the osmosis membrane to the outside of the reverse osmosis membrane separation device. At this time, the impurities are discharged to the outside as flushing wastewater through the pipe connected to the primary side together with the water supplied to the reverse osmosis membrane separation device.

  In the case of the deionized water production system of this embodiment, flushing can be performed by opening the flushing valve 23 while the pump 10 is operated. At this time, the flushing drainage flows out through the flushing valve 23. The flushing is performed for several tens of seconds, for example, and then the reverse osmosis membrane separation device 20 is completely stopped by stopping the pump 10 and closing the flushing valve 23.

  In the deionized water production system of the present embodiment, when the operation is to be stopped, the reverse osmosis membrane separation device 20 performs a flushing process and discharges impurities present on the primary side of the reverse osmosis membrane 21 to the outside. Thus, it is possible to prevent the concentration diffusion of impurities from the primary side to the secondary side of the reverse osmosis membrane 21 during the operation stop period, whereby the reverse osmosis membrane separation device 20 and the electric deionized water production device can be used when the operation is resumed. It is possible to prevent an increase in impurity concentration in the reverse osmosis membrane permeated water supplied to 30 as treated water. As a result, as will be apparent from the examples described later, the water quality rises when the operation is restarted in the treated water from the electrical deionized water production apparatus 30 and the deionized water production system is early when the operation is resumed. Deionized water having a low impurity concentration can be obtained.

  In addition to the method shown in the present embodiment, flushing may be performed by reducing the discharge pressure of a water supply pump (pump 10 or the like) or opening the concentrated water outlet valve (back pressure valve). For example, there is a method in which the pressure on the primary side of the reverse osmosis membrane 21 is lowered to discharge the entire amount of water supply from the primary side without passing through the reverse osmosis membrane 21.

  FIG. 3 shows a configuration of a deionized water production system according to another embodiment of the present invention. In the deionized water production system shown in FIG. 1, the reverse osmosis membrane permeated water and the treated water can be circulated to the primary side of the reverse osmosis membrane separation device 20 and passed through the reverse osmosis membrane separation device 20. It is a thing. Therefore, in the deionized water production system shown in FIG. 3, the flow meter 60 provided at the treated water outlet of the electric deionized water production apparatus 30 and the inlet of the pump 10 are different from the deionized water production system shown in FIG. 1. A valve 61 provided on the side, and a pipe 62 branched from the outlet of the flow meter 60 and connected to the connection point between the valve 61 and the pump 10 to circulate water to the primary side of the reverse osmosis membrane separation device 20 A valve 63 provided in the pipe 62, a pipe 64 branched from the outlet on the secondary side of the reverse osmosis membrane separator 20 and connected to the outlet side of the valve 63, and a valve 65 provided in the pipe 64 are added. Has been. FIG. 3 schematically shows a deionized water production system based on the present invention. The raw water line connecting the valve 61 and the pump 10, the reverse osmosis membrane permeated water line, the treated water line, Tanks, pumps, valves, etc. may be installed.

  The flow meter 60 determines whether or not the electric deionized water production apparatus 30 is in a normal operation state by measuring the flow rate of the treated water flowing therethrough, and a control signal indicating the determination result is provided. Output. Since it is only necessary to know whether or not the electric deionized water production apparatus 30 is in a normal operation state, a pressure sensor may be provided in place of the flow meter 60, and the installation location thereof is also the electric deionized water production apparatus 30. It may be on the treated water side, which is the inlet side, or on the line connected to the concentration chamber or on the line connected to the electrode chamber. Furthermore, a control signal may be output from a control device or the like that controls the DC power supply 35 of the electric deionized water production apparatus 30 without providing a flow meter or a pressure sensor.

  FIG. 4 shows an electric deionized water production apparatus used in the deionized water production system shown in FIG. The electrical deionized water production apparatus shown in FIG. 4 is different from that shown in FIG. 2 in that a switch SW for short-circuiting the anode and cathode of the diode D is provided for the reverse current blocking diode D. The switch SW is turned on / off by a control signal. When the DC power supply 35 operates and the electric deionized water production apparatus is in an operating state assuming that the switch SW is not provided, a forward current flows through the diode D. A forward voltage drop occurs and the diode D generates heat. Therefore, in the electric deionized water production apparatus shown in FIG. 4, in order to prevent heat generation of the diode D, the switch SW is turned on by a control signal in a running state, and the diode D is short-circuited by the switch SW. It flows through the switch SW. Since the current flowing through the diode D is extremely small, the diode D does not generate heat. When the switch SW is not in the operating state, the switch SW is cut off, so that no current flows through the switch SW and the reverse current is blocked by the diode D. Even if the switch SW is provided in parallel to the diode D and both ends of the diode D are short-circuited by the switch SW when the electric deionized water production apparatus 30 is operated, the operation state of the electric deionized water production apparatus 30 is maintained. Will not have a big impact.

  Next, an operation method of the deionized water production system shown in FIG. 3 will be described.

  When deionized water is generated as treated water from the electric deionized water production apparatus 30 by this deionized water production system, the valve 10 is opened and the pump 10 is operated with the flushing valve 23 and the valves 63 and 65 closed. The reverse osmosis membrane separation device 20 is started to be operated, and the reverse osmosis membrane permeated water from the reverse osmosis membrane separation device 20 is supplied to the desalting chamber as treated water while being supplied to the anode 31 and the cathode 32 by the DC power source 35. The operation of the electric deionized water production apparatus 30 is started by applying a DC voltage.

  When trying to stop the operation of the deionized water production system during operation, the DC power supply 35 is stopped to stop the operation of the electric deionized water production apparatus 30, and the water quality rise at the time when the operation is resumed thereafter. In order to increase the speed, an impurity removal step for reducing the amount of impurities present on the primary side of the reverse osmosis membrane 21 in the reverse osmosis membrane separation apparatus 20 is performed, and then the entire system is stopped. In the example shown here, there are several modes as the impurity removal step.

  As the impurity removing step, flushing is performed in the reverse osmosis membrane separation apparatus 20 in the same manner as shown in FIG. In the deionized water production system shown in FIG. 3, the pipes 62 and 64 for circulating the reverse osmosis membrane permeated water and the treated water are provided. Water or treated water can be passed through the reverse osmosis membrane separation device 20 and used for flushing. When raw water is used for flushing, flushing may be performed in the same procedure as in the case of the deionized water production system shown in FIG. 1 with the valve 61 opened and the valves 63 and 65 closed.

  When flushing using reverse osmosis membrane permeated water, a part of the reverse osmosis membrane permeated water is stored in a tank (not shown) provided near the pump 10 on the pipe 62 during operation of the deionized water production system. The reverse osmosis membrane permeated water flushing valve 23 and the valve 65 may be opened while the pump 10 is operated during flushing, and the valve 61 may be closed. The flushing is performed for several tens of seconds, for example, and then the reverse osmosis membrane separation device 20 is completely stopped by stopping the pump 10 and closing the flushing valve 23 and the valve 65. When reverse osmosis membrane permeated water is used for flushing, the amount of impurities on the primary side of the reverse osmosis membrane 21 can be further reduced in the reverse osmosis membrane separation device 20 compared to when raw water is used. Impurity ions diffused from the primary side to the secondary side can also be reduced, and as will become clear from the examples described later, the water quality in the treated water obtained from the electric deionized water production apparatus 30 when the operation is resumed. Rise is faster.

  When the flushing is performed using the treated water from the electric deionized water production apparatus 30, a part of the treated water is supplied to a tank (not connected) near the pump 10 on the pipe 62 during the operation of the deionized water production system. It is sufficient that the flushing valve 23 and the valve 63 are opened while the pump 10 is operated during the flushing, and the valve 61 is closed. The flushing is performed for several tens of seconds, for example, and then the reverse osmosis membrane separation device 20 is completely stopped by stopping the pump 10 and closing the flushing valve 23 and the valve 63. Since treated water has a smaller impurity content than reverse osmosis membrane permeated water, when using treated water for flushing, of course, reverse osmosis membrane permeated water is used compared to when raw water is used. Compared to the case, the quality of treated water rises faster when operation is resumed.

  As another aspect of the impurity removal step in the deionized water production system shown in FIG. 3, instead of performing flushing, reverse osmosis membrane permeated water or treated water is passed as supply water to the reverse osmosis membrane separation device 20, There is one that operates the reverse osmosis membrane separation device 20 in the same manner as usual. When the reverse osmosis membrane separation apparatus 20 is operated using reverse osmosis membrane permeated water as supply water to perform the impurity removal step, part of the treated water is pumped on the pipe 62 during operation of the deionized water production system. It is stored in a tank (not shown) provided in the vicinity, and the electric deionized water production apparatus 30 is stopped at the time of flushing, and the valve 65 is opened while the pump 10 is operated, and the valve 61 is closed, and the reverse osmosis membrane permeation is performed. Water is supplied to the reverse osmosis membrane separation device 20 through the pipes 64 and 62. The flushing valve 23 remains closed. By maintaining this state for several tens of seconds, for example, impurities present on the primary side of the reverse osmosis membrane 21 in the reverse osmosis membrane separation device 20 are discharged to the outside as concentrated water. Thereafter, the pump 10 is stopped, the valve 65 is closed, and the entire system is stopped.

  On the other hand, when performing the impurity removal process by operating the reverse osmosis membrane separation device 20 using treated water as supply water, a part of the treated water is near the pump 10 on the pipe 62 during operation of the deionized water production system. In the tank (not shown) provided in the tank, the valve 63 is opened and the valve 61 is closed while the pump 10 is operated at the time of flushing, and the treated water is supplied to the reverse osmosis membrane separation device 20 via the pipe 62. So that The flushing valve 23 remains closed. At this time, the reverse osmosis membrane permeated water flows out from the secondary side of the reverse osmosis membrane separation device 20 and flows into the demineralization chamber of the electrical deionized water production device 30, so that the DC power source 35 is kept operating and is electrically operated. The deionized water production apparatus 30 is set in an operating state. By maintaining this state for several tens of seconds, for example, impurities present on the primary side of the reverse osmosis membrane 21 in the reverse osmosis membrane separation device 20 are discharged to the outside as concentrated water. Thereafter, the DC power supply 35 and the pump 10 are stopped, the valve 63 is also closed, and the entire system is stopped.

  In addition, the tank for storing a part of the reverse osmosis membrane permeated water and the treated water during the operation of the deionized water production system may also be used as a raw water tank provided on the upstream side of the valve 61.

  In the deionized water production system based on the present invention, the rise in the quality of treated water is accelerated when the operation is resumed by preventing an increase in the impurity concentration on the secondary side of the reverse osmosis membrane separator during the operation stop period. is there. Therefore, in the deionized water production system shown in FIGS. 1 and 3, for example, the reverse osmosis membrane separation is performed by providing a shut-off valve in a pipe connecting the reverse osmosis membrane separation device 20 and the electric deionized water production device 30. The apparatus 20 can be operated independently, and the reverse osmosis membrane separation apparatus 20 is periodically passed through the reverse osmosis membrane separation apparatus 20 during the operation stop period of the deionized water production system. It may be operated to reduce the impurity concentration on the secondary side of the reverse osmosis membrane separation device 20. At this time, the reverse osmosis membrane permeated water from the reverse osmosis membrane separation device 20 is prevented from flowing into the electrical deionized water production device 30 by a shutoff valve or the like. The reverse osmosis membrane separation device 20 may pass raw water or reverse osmosis membrane permeated water.

  Next, the present invention will be described in more detail by way of examples.

[Example 1]
The deionized water production system shown in FIG. 1 was assembled. As the reverse osmosis membrane separation device 20, a device having a reverse osmosis membrane (RO membrane) which is an ultra-low pressure membrane was used. Control was performed such that the temperature of the reverse osmosis membrane permeated water from the reverse osmosis membrane separation device 20 was 20 ± 2 ° C.

  As the electric deionized water production apparatus 30, the one shown in FIG. 2 was used. As the EDI stack 33, one having a single cell was used. FIG. 5 shows the configuration of the anode 31, the cathode 32, and the EDI stack 33 in the assembled electrical deionized water production apparatus. In FIG. 5, the portion excluding the anode 31 and the cathode 32 corresponds to the EDI stack 33. The anode 31 is provided in the anode chamber 41, and the cathode 32 is provided in the cathode chamber 51. Between the anode chamber 41 and the cathode chamber 51, a concentration chamber 43, a desalting chamber 40, and a concentration chamber 49 are arranged from the anode chamber 41 side, and between the anode chamber 41 and the concentration chamber 43, Cation exchange membranes 42 and 48 are provided between the concentration chambers 49, respectively. Anion exchange membranes 44 and 50 are provided between the concentration chamber 43 and the desalting chamber 40 and between the concentration chamber 49 and the cathode chamber 51, respectively.

  The desalting chamber 40 is divided into a first small desalting chamber 45 on the anode 31 side and a second small desalting chamber 47 on the cathode 32 side, and the first small desalting chamber 45 and the second small desalting chamber 47. An anion exchange membrane 46 is provided between them. Water to be treated which is reverse osmosis membrane permeated water is first supplied to the first small desalination chamber 45 from the upper side in the drawing, enters the lower end of the second small desalination chamber 47 from the lower end of the first small desalination chamber 45, and is treated. Water, deionized water, is discharged from the upper end of the second small desalting chamber.

  The dimensions of the anode chamber 41 were 100 × 300 × 4 mm, and the anode chamber 41 was filled with a cation exchange resin. The dimensions of the cathode chamber 51 were 100 × 300 × 4 mm, and the cathode chamber 51 was filled with an anion exchange resin. The concentrating chambers 43 and 49 are both 100 × 300 × 4 mm in size and filled with an anion exchange resin. About the 1st small desalting chamber 45, it filled with the anion exchange resin as a dimension of 100x300x8 mm. About the 2nd small desalting chamber 47, it was set as the size of 100x300x8 mm, the lower part was filled with the cation exchange resin, and the upper part was filled with the anion exchange resin.

  During operation of the deionized water production system, the reverse osmosis membrane permeated water is supplied from the reverse osmosis membrane separation device 20 to the desalting chamber 40 and also to the concentration chambers 43 and 49, the anode chamber 41, and the cathode chamber 51. It was made to be.

  First, as the initial operation, the reverse osmosis membrane separation device 20 is operated by driving the pump 10 with the flushing valve 23 closed. Further, in the electric deionized water production device 30, the anode 31 and the cathode 32 are supplied from the DC power source 35. The electric deionized water production apparatus 30 was operated by applying a DC voltage to the battery. At this time, the flow rate of water to be treated in the desalting chamber 40 is set to 20 L / h, the flow rate of water in the concentration chambers 43 and 49 is set to 5 L / h, respectively, and the flow rate in the anode chamber 41 and the cathode chamber 51 is set. The water flow rate of water was 10 L / h, respectively. This initial operation was carried out for 2 hours. The conductivity of raw water was measured at the start of initial operation, the conductivity of raw water and reverse osmosis membrane permeated water was measured at the end of initial operation, and the resistivity of treated water was measured as an indicator of the quality of treated water.

  Further, at the end of the initial operation, the pump 10 is continuously driven even after the application of voltage from the DC power source 35 is stopped, and at the same time, the flushing valve 23 is fully opened to perform the flushing of the reverse osmosis membrane 21 for 30 seconds. The amount of impurities present on the primary side of the reverse osmosis membrane 21 in the osmosis membrane separator 20 was reduced. Immediately after the flushing was completed, the pump 10 was stopped, the flushing valve 23 was also closed, and the entire deionized water production system was stopped.

  The stop state was maintained for 48 hours, and then the operation of the deionized water production system was resumed. The operating conditions after resuming operation are the same as in the initial operation. The conductivity of raw water and reverse osmosis membrane permeated water is measured at the time of restarting operation (ie, 50 hours after the start of initial operation), and the conductivity and treatment of raw water and reverse osmosis membrane permeated water after restarting operation. The time change of water resistivity was investigated.

  Table 1 shows the measurement results of conductivity and resistivity.

[Comparative example]
The deionized water production system was operated under the same conditions as in Example 1 except that flushing at the end of the initial operation was not performed, and the conductivity and resistivity were measured. The measurement results are shown in Table 2.

  Comparing Example 1 and the comparative example, when the reverse osmosis membrane was flushed at the end of the initial operation, the conductivity of the reverse osmosis membrane permeated water at the time of restarting the operation was smaller than that when the reverse operation was not performed. It can be seen that the amount of impurities in the reverse osmosis membrane permeated water is small. In addition, from the resistivity of treated water in 0.1 hour (50.1 hours in elapsed time) after restarting operation, flushing has higher resistivity and better quality of treated water, and the operation was stopped. It was found that the quality of the treated water at the time of resuming operation is improved by sometimes flushing the reverse osmosis membrane and discharging impurities present on the primary side of the reverse osmosis membrane to reduce the amount of impurities.

[Example 2]
The deionized water production system shown in FIG. 3 was assembled. As the reverse osmosis membrane separation device 20, a device having a reverse osmosis membrane (RO membrane) which is an ultra-low pressure membrane was used. Control was performed such that the temperature of the reverse osmosis membrane permeated water from the reverse osmosis membrane separation device 20 was 20 ± 2 ° C. As the electric deionized water production apparatus 30, the one shown in FIG. 4 was used. As the EDI stack 33, the same one as used in Example 1 was used. During operation of the deionized water production system, the reverse osmosis membrane permeated water is supplied from the reverse osmosis membrane separation device 20 to the desalting chamber 40 and also to the concentration chambers 43 and 49, the anode chamber 41, and the cathode chamber 51. It was made to be.

  First, as an initial operation, the raw water supply valve 61 is opened with the flushing valve 23 and the valves 63 and 65 closed, the pump 10 is driven to operate the reverse osmosis membrane separation device 20, and electric deionization is performed. In the water production apparatus 30, the electric deionized water production apparatus 30 was operated by applying a DC voltage from the DC power source 35 to the anode 31 and the cathode 32. At this time, the water flow rates for the desalting chamber 40, the concentration chambers 43 and 49, the anode chamber 41, and the cathode chamber 51 were the same as those in the first embodiment. This initial operation was carried out for 2 hours. The conductivity of raw water was measured at the start of initial operation, the conductivity of raw water and reverse osmosis membrane permeated water was measured at the end of initial operation, and the resistivity of treated water was measured as an indicator of the quality of treated water.

  Further, at the end of the initial operation, the pump 10 continues to be driven even after the application of voltage from the DC power source 35 is stopped. At the same time, the flushing valve 23 and the valve 65 are opened, and the valve 61 is closed. The reverse osmosis membrane 21 was flushed with water to reduce the amount of impurities present on the primary side of the reverse osmosis membrane 21. Immediately after the flushing, the pump 10 was stopped, the flushing valve 23 and the valve 65 were also closed, and the entire deionized water production system was stopped.

  The stop state was maintained for 48 hours, and then the operation of the deionized water production system was resumed. The operating conditions after resuming operation are the same as in the initial operation. The conductivity of raw water and reverse osmosis membrane permeated water is measured at the time of restarting operation (ie, 50 hours after the start of initial operation), and the conductivity and treatment of raw water and reverse osmosis membrane permeated water after restarting operation. The time change of water resistivity was investigated.

  Table 3 shows the measurement results of conductivity and resistivity.

  Regarding flushing at the end of the initial operation, raw water is used in Example 1, while reverse osmosis membrane permeated water is used in Example 2. Comparing the results of Example 1 and Example 2, the use of reverse osmosis membrane permeated water for flushing has a lower impurity concentration of reverse osmosis membrane permeated water at the time of restarting operation, and the elapsed time is 50.1 hours. It was found that the treated water resistivity is high, and the quality of treated water rises faster when operation is resumed.

[Reference example]
The difference due to the presence or absence of a diode for blocking reverse current was examined. The deionized water production system operates in the same manner as the comparative example except that the cathode 32 and the negative output terminal of the DC power supply 35 are directly connected without providing the reverse current blocking diode D in the electric deionized water production apparatus. The conductivity and resistivity were measured. The results are shown in Table 4.

  In the reference example in which no reverse current blocking diode is provided, the resistivity of the treated water is 14.4 even after 1 hour (51.0 hours in elapsed time) has elapsed after the restart of operation, compared to the comparative example in which the diode is provided. It was as bad as 1 MΩ · cm, and it was found that sufficient water quality rise could not be obtained.

DESCRIPTION OF SYMBOLS 10 Pump 20 Reverse osmosis membrane separator 21 Reverse osmosis membrane 22 Back pressure valve 23 Flushing valve 30 Electric deionized water production apparatus 31 Cathode 32 Anode 33 EDI stack 35 DC power supply 40 Desalination chamber 41 Anode chamber 42, 48 Cation exchange membrane 43 , 49 Concentration chamber 44, 46, 50 Anion exchange membrane 45 First small desalination chamber 47 Second small desalination chamber 51 Cathode chamber 60 Flow meter 61, 63, 65 Valve 62, 64 Piping D Diode SW switch

Claims (6)

At least one cell comprising a desalting chamber filled with an ion exchanger and a pair of concentrating chambers disposed on both sides of the desalting chamber via an ion exchange membrane is disposed between the cathode and the anode. , An electric deionized water production apparatus in which at least one of the pair of concentrating chambers is filled with an ion exchanger, and a voltage is applied to the cathode and the anode from a DC power source , and the electric deionized water production apparatus In a method for operating a deionized water production system, comprising a reverse osmosis membrane separation device that supplies reverse osmosis membrane permeated water to the electric deionized water production device as treated water,
While stopping the operation of the deionized water production system, performing an impurity removal step of reducing the amount of impurities present on the primary side of the reverse osmosis membrane in the reverse osmosis membrane separator ,
At least one diode provided in a path that electrically connects the anode and the cathode to the DC power source flows through the cathode and the anode during a stop time of the electric deionized water production apparatus. An operation method characterized by preventing reverse current .   The operation method according to claim 1, wherein the impurity removing step is a step of flushing the reverse osmosis membrane.   The impurity removal step is a step of passing at least one of a part of the reverse osmosis membrane permeated water and a part of the treated water from the electric deionized water production apparatus to the reverse osmosis membrane separation device. Item 2. The driving method according to Item 1. At least one cell comprising a desalting chamber filled with an ion exchanger and a pair of concentrating chambers disposed on both sides of the desalting chamber via an ion exchange membrane is disposed between the cathode and the anode. , An electric deionized water production apparatus in which at least one of the pair of concentrating chambers is filled with an ion exchanger, and a voltage is applied to the cathode and the anode from a DC power source , and the electric deionized water production apparatus In a deionized water production system comprising a reverse osmosis membrane separation device that supplies reverse osmosis membrane permeated water to the electric deionized water production device as treated water
Impurity removing means for removing impurities present on the primary side of the reverse osmosis membrane in the reverse osmosis membrane separator,
While stopping the operation of the deionized water production system, the impurity removal means reduces the amount of impurities present on the primary side of the reverse osmosis membrane in the reverse osmosis membrane separator ,
The electric deionized water production apparatus is provided in a path for electrically connecting the anode and the cathode to the DC power source, and the electric deionized water production apparatus passes through the cathode and the anode during a stop period of the electric deionized water production apparatus. characterized Rukoto and at least one diode to block reverse current through Te, water producing system. The impurity removing means is a flushing valve connected to a primary side of the reverse osmosis membrane in the reverse osmosis membrane separator, and the impurities are removed by opening the flushing valve and flushing the reverse osmosis membrane. The deionized water production system according to claim 4 , wherein the system is discharged from a reverse osmosis membrane separation device. The impurity removing means is a pipe that circulates at least one of the part of the reverse osmosis membrane permeated water and the part of the treated water from the electric deionized water production apparatus to the reverse osmosis membrane separator, and the pipe The deionized water production system according to claim 4 , wherein the impurities are discharged from the reverse osmosis membrane separation device by passing water passed through the reverse osmosis membrane separation device.

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