Pure water production apparatus

Abstract

Provided is a pure water production apparatus capable of realizing a sufficiently high flow velocity in deionized water production apparatuses and suppressing damage to the deionized water production apparatuses due to the application of an excessively high pressure. This pure water production apparatus comprises: a booster pump 3 disposed between deionized water production apparatuses 1, 2; and a pressure gauge 4b disposed between the booster pump 3 and the deionized water production apparatus 1 positioned on the upstream side of the booster pump 3. At least one deionized water production apparatus 1 positioned on the upstream side of the booster pump 3 and the pressure gauge 4b is an electric regeneration-type deionized water production apparatus. In the booster pump 3, at least one of the start of an operation and the stop of the operation is performed on the basis of a measurement value on the pressure gauge 4b.

Description

Pure water production equipment

[0001] The present invention relates to a water purifying apparatus.

[0002] Conventionally, when manufacturing semiconductor devices and liquid crystal devices, pure water (including ultrapure water) from which impurities such as organic matter, ionic components, fine particles, and bacteria have been highly removed has been used as cleaning water. In particular, demands for water quality have been increasing year by year for pure water used in the cleaning process of electronic components, including semiconductor devices. In particular, there has been a strong demand in recent years for reducing boron content. It is known that boron, a weakly acidic component, can be removed using a reverse osmosis membrane device (hereinafter referred to as an "RO device") or an electrochemical deionized water production device (hereinafter referred to as an "EDI device"). Recently, methods for reducing the boron concentration in treated water have been put into practical use, such as a multi-stage process using multiple EDI devices connected in series, as disclosed in Patent Document 1 (JP 2018-34103 A), and a multi-stage process combining an EDI device with other deionized water production devices (e.g., an ion exchange resin device or a boron-selective resin device).

[0003] EDI devices are expensive devices with a complex structure and many components compared to ion exchange resin devices. Therefore, in order to keep the processing cost of pure water production as low as possible, attempts are being made to increase the amount of treated water per unit time by treating the water at a high flow rate. When the number of EDI devices increases in multi-stage processing, the demand for a higher flow rate becomes even stronger.

[0004] Japanese Patent Application Publication No. 2018-34103

[0005] Increasing the flow rate of the liquid passing through the EDI device increases the difference in pressure between the liquid upstream and downstream of the EDI device (water flow differential pressure). When producing pure water through a multi-stage process, increasing the flow rate of the liquid passing through each of multiple EDI devices increases the water flow differential pressure of each EDI device. To achieve a high flow rate through all of the multiple EDI devices, it is necessary to apply a higher pressure to the liquid supplied to the upstream EDI device than to the liquid supplied to the downstream EDI device, taking into account the increased water flow differential pressure. In other words, the upstream EDI device must be supplied with a higher-pressure liquid by adding the desired water flow differential pressure of the downstream EDI device to its own desired water flow differential pressure. As a result, excessively high-pressure liquid may be supplied to the upstream EDI device, potentially damaging the EDI device. In particular, EDI devices generally have a stacked plastic frame structure and have structural characteristics that result in relatively low pressure resistance, making them prone to damage when high-pressure liquid is supplied to them. Therefore, if the liquid is supplied at a pressure that is not too high in order to prevent damage to the upstream EDI device, the downstream EDI device will not be able to obtain a supply water pressure that will achieve a sufficiently high flow rate, and the effect of reducing treatment costs will be reduced. Note that the same problem as described above will occur even in a configuration in which another deionized water production device (e.g., an ion exchange resin device or a boron-selective resin device) is installed instead of the downstream EDI device.

[0006] Therefore, an object of the present invention is to provide a pure water production system that can achieve a sufficiently high flow rate in each deionized water production system while preventing damage to the deionized water production system due to excessively high pressure being applied.

[0007] The pure water production system of the present invention includes a boost pump disposed between two deionized water production apparatuses and a pressure gauge disposed between the boost pump and the deionized water production apparatus located upstream of the boost pump. The boost pump and at least one of the deionized water production apparatuses located upstream of the pressure gauge are electrically regenerated deionized water production apparatuses, and the boost pump starts and stops at least one of its operations based on the pressure gauge reading. This configuration also includes cases where other devices (e.g., an ultraviolet oxidation device, a tank, a pump) are disposed between the deionized water production apparatuses in addition to the boost pump. The boost pump may start operating when the pressure gauge reading increases from below a first set pressure value to equal to or greater than the first set pressure value while the boost pump is stopped. The boost pump may stop operating when the pressure gauge reading decreases from above a second set pressure value to equal to or less than the second set pressure while the boost pump is operating. The boost pump may start operating when the pressure gauge reading increases from below a first set pressure value to equal to or greater than the first set pressure value while the boost pump is stopped, and the first set pressure value may be greater than the second set pressure value. The second set pressure value may be a value within a range of 0.00 MPa to 0.05 MPa. The first set pressure value may be a value within a range of 0.02 MPa to 0.1 MPa. The boost pump may start operating when a set time has elapsed since the start of liquid delivery to the inlet of the boost pump while the boost pump is stopped. A supply pump located upstream of the deionized water production apparatus in the forefront stage may stop operating simultaneously with the stop of the boost pump. Pure water may be produced in a state in which the differential pressure of water flow through at least one of the plurality of deionized water production devices is greater than 0.20 MPa, and the sum of the pressure at the inlet of the desalination compartment of the electrically regenerated deionized water production device located upstream of the boost pump and the pressure at the outlet of the boost pump is greater than 1.5 times the pressure value at the inlet of the desalination compartment of the electrically regenerated deionized water production device.A switching valve is provided upstream of the deionized water production apparatus on the upstream side of the boost pump to switch between a water supply line that supplies treated water to the deionized water production apparatus and a circulation line that returns treated water to the upstream side of the supply pump located upstream of the deionized water production apparatus located in the front stage, and a switching valve is provided downstream of the deionized water production apparatus on the downstream side of the boost pump to switch between a water supply line that sends treated water outside the deionized water production apparatus and another circulation line that returns treated water to the upstream side of the supply pump, and at least one of the switching valves may be a three-way valve.

[0008] According to the present invention, it is possible to realize a sufficiently high flow rate in each deionized water production device, and to prevent the deionized water production device from being damaged by excessively high pressure.

[0009] 10 is a block diagram showing a pure water production system according to a first embodiment of the present invention; FIG. 11 is a cross-sectional view showing an example of the internal configuration of an EDI device with one deionization compartment; FIG. 12 is a cross-sectional view showing an example of the internal configuration of an EDI device with two deionization compartments; FIG. 13 is a block diagram showing a pure water production system according to a first comparative example; FIG. 14 is a block diagram showing a pure water production system according to a second embodiment of the present invention; FIG. 15 is a graph showing the relationship between the measured values ​​of each pressure gauge and elapsed time when pure water is produced using the pure water production system shown in FIG. 5; FIG. 16 is a graph showing the relationship between the ratio of the actual flow rate of the EDI device to the standard flow rate and the differential pressure of the water passing through the deionization compartments; FIG. 17 is a cross-sectional view showing a schematic of a deionization compartment of an EDI device with two deionization compartments of the pure water production system shown in FIG. 5; FIG. 18 is a cross-sectional view showing a schematic of a deionization compartment of an EDI device with one deionization compartment; FIG. 19 is a block diagram showing a pure water production system according to a second comparative example; FIG. 19 is a graph showing the relationship between the measured values ​​of each pressure gauge and elapsed time when pure water is produced using the pure water production system shown in FIG. 1 is a block diagram showing a pure water production system according to a second embodiment of the present invention, 2 is a block diagram showing a pure water production system according to a third embodiment of the present invention, and 3 is a block diagram showing a pure water production system according to a fourth embodiment of the present invention.

[0010] Embodiments of the present invention will now be described with reference to the drawings. [First Embodiment] FIG. 1 is a block diagram schematically illustrating the basic configuration of a pure water production system according to a first embodiment of the present invention. In this embodiment, two deionized water production systems 1 and 2 are connected in series, with a booster pump 3 and a pressure gauge 4 provided between the deionized water production systems 1 and 2. The upstream deionized water production system 1 is an EDI system (an electrically regenerated deionized water production system). The downstream deionized water production system 2 may be an EDI system or another type of deionized water production system (e.g., an ion exchange resin system or a boron-selective resin system). However, the following description will be given, as an example, of an example in which both the upstream deionized water production system 1 and the downstream deionized water production system 2 are EDI systems.

[0011] EDI devices generally have a configuration in which a deionization compartment separated by a pair of ion exchange membranes is provided between an anode and a cathode, and the deionization compartment is filled with an ion exchange resin. The EDI devices 1 and 2 shown in Fig. 2 have a single deionization compartment configuration with a single deionization compartment 13. Between an anode compartment 20 equipped with an anode 18 and a cathode compartment 21 equipped with a cathode 19, a concentration compartment 24, a deionization compartment 13, and a concentration compartment 25 are provided, in this order from the anode compartment 20 side. The anode compartment 20 and the concentration compartment 24 are adjacent to each other across a cation exchange membrane (CEM) 26, the concentration compartment 24 and the deionization compartment 13 are adjacent to each other across an anion exchange membrane (AEM) 22, the deionization compartment 13 and the concentration compartment 25 are adjacent to each other across a cation exchange membrane 23, and the concentration compartment 25 and the cathode compartment 21 are adjacent to each other across an anion exchange membrane 27. The deionization compartment 13 is filled with ion exchange resin (generally including anion exchange resin (AER) and cation exchange resin (CER)). The anode compartment 20 is filled with cation exchange resin, and the cathode compartment 21 is filled with anion exchange resin. These EDI devices 1 and 2 perform desalination (deionization) of the water to be treated when the water is supplied to the deionization compartment 13 with a DC voltage applied between the anode 18 and the cathode 19. As a result, water from which ions have been removed is discharged from the deionization compartment 13 as treated water. Of the ion components removed from the water to be treated in the deionization compartment 13, anion components move to the concentration compartment 24 via anion exchange membrane 22 provided on the anode 18 side of the deionization compartment 13. Cation components move to the concentration compartment 25 via cation exchange membrane 23 provided on the cathode 19 side of the deionization compartment 13. The concentration compartments 24 and 25 are supplied with concentration compartment feed water and discharge concentrated water. Water supplied to the electrode chamber is supplied to the cathode chamber 21. The water supplied to the cathode chamber 21 passes through the cathode chamber 21, is then supplied to the anode chamber 20, and is discharged as electrode water from the anode chamber 20. The cation exchange membrane 26 and the anion exchange membrane 27 may be omitted, and the concentration chambers 24, 25 may also serve as the electrode chambers (anode chamber and cathode chamber).

[0012] The EDI devices 1 and 2 illustrated in FIG. 3 are configured as a two-compartment deionization chamber type having two adjacent deionization chambers 13 separated by an ion exchange membrane (anion exchange membrane) 12. Between an anode chamber 20 equipped with an anode 18 and a cathode chamber 21 equipped with a cathode 19, a concentration chamber 24, two deionization chambers 13, and a concentration chamber 25 are provided, in this order from the anode chamber 20 side. Of the two deionization chambers 13 located between the anode 18 and the cathode 19, the deionization chamber 13 on the anode 18 side is partitioned by anion exchange membranes 12 and 22 and filled with an ion exchange resin (at least a portion of which is an anion exchange resin). The deionization chamber 13 on the cathode 19 side is partitioned by anion exchange membrane 12 and a cation exchange membrane 23 and filled with an ion exchange resin (at least a portion of which is a cation exchange resin). The rest of the configuration is similar to that of the single-compartment deionization chamber type shown in FIG. 2 , and therefore description thereof will be omitted. In these EDI devices 1 and 2, with a DC voltage applied between the anode 18 and the cathode 19, water to be treated is supplied to the desalination compartment 13 on the anode 18 side and subjected to desalination (deionization) treatment, and then transferred to the desalination compartment 13 on the cathode 19 side for another desalination treatment, with the water from which ionic components have been removed being discharged as treated water from the desalination compartment 13 on the cathode 19 side. The treatments in the concentrating compartments 24 and 25, the cathode compartment 21, and the anode compartment 20 are similar to those in the single-compartment desalination compartment configuration shown in Figure 2, and therefore will not be described here. Note that the water flow direction can also be reversed from that shown in Figure 3, with the water to be treated supplied to the desalination compartment 13 on the cathode 19 side for desalination (deionization) treatment, then transferred to the desalination compartment 13 on the anode 18 side for another desalination treatment, with the water from which ionic components have been removed being discharged as treated water from the desalination compartment 13 on the anode 18 side.

[0013] In the pure water production system of this embodiment shown in FIG. 1 , a pressure gauge 4 is connected to the inlet side (upstream side) of the booster pump 3. A tank 5 for treated water is connected upstream of the upstream EDI device 1 (the EDI device located at the forefront in the example shown in FIG. 1 ), and a supply pump 6 is disposed between the upstream EDI device 1 and the tank 5. Therefore, from upstream, the tank 5, supply pump 6, upstream EDI device 1, pressure gauge 4, booster pump 3, and downstream EDI device 2 are connected in this order. Pure water is then delivered from the outlet of the downstream EDI device 2. The booster pump 3 starts and / or stops its operation based on the measurement value of the pressure gauge 4. For convenience, in this specification, water supplied to the upstream EDI device 1 is referred to as water to be treated, and water that passes through the upstream EDI device 1 and is supplied to the downstream EDI device 2 is referred to as intermediate treated water. Water that has passed through all of the EDI devices 1 and 2 is referred to as treated water or pure water.

[0014] The operation of the pure water production system of this embodiment will be described. First, the supply pump 6 is started to operate, and water is passed through the upstream EDI device 1. As a result, the measurement value of the pressure gauge 4 located downstream of the upstream EDI device 1 begins to rise. Then, while the operation of the boost pump 3 is stopped, when the measurement value of the pressure gauge 4 increases from a value below a predetermined value (first set pressure value) to equal to or greater than the first set pressure value, the boost pump 3 is started to operate. This allows a sufficient amount of intermediate treated water to be supplied to the downstream EDI device 2. In this way, the upstream EDI device 1 and the downstream EDI device 2 operate to produce pure water.

[0015] The effects of the pure water production system of the present embodiment described above will now be described. First, a pure water production system of a first comparative example will be described for comparison with the present embodiment. In the pure water production system of the first comparative example shown in FIG. 4 , similar to the first embodiment, a tank 5, a supply pump 6, an upstream EDI device 1, and a downstream EDI device 2 are connected in series from the upstream side. However, the pressure gauge 4 and the boost pump 3 are not present. When the supply pump 6 of the pure water production system of this comparative example begins operation, water is passed from the tank 5 to the upstream EDI device 1 and the downstream EDI device 2, thereby producing pure water. In this configuration, to reduce treatment costs, etc., it is assumed that the water flow differential pressures (desired water flow differential pressures) at which desired flow rates are achieved in the EDI devices 1 and 2 are X1 and X2, respectively. The pressure of the water to be treated supplied to the upstream EDI device 1 is IP1, and the pressure of the pure water delivered from the outlet of the downstream EDI device 2 is OP. Pressure OP is the desired pressure of the pure water produced and delivered during steady-state operation of this pure water production system. The pressure IP1 of the water to be treated supplied to the upstream EDI device 1 is calculated as IP1 = OP + X1 + X2. That is, this pressure IP1 is the pressure OP plus the water flow differential pressure X1 when the desired flow rate of the upstream EDI device 1 is achieved and the water flow differential pressure X2 when the desired flow rate of the downstream EDI device 2 is achieved, and is a relatively high pressure. In practice, pressure loss in the pathway (water flow line) must also be taken into consideration, so pressure IP1 needs to be even higher. Because pressure IP1 is so high, there is a possibility that the upstream EDI device 1 will be damaged. Note that the water flow differential pressure X1 when the desired flow rate of the upstream EDI device 1 is achieved may coincide with the water flow differential pressure X2 when the desired flow rate of the downstream EDI device 2 is achieved.

[0016] In contrast, in the first embodiment of the present invention shown in Figure 1, a boost pump 3 is interposed between the upstream EDI device 1 and the downstream EDI device 2. When the boost pump 3 increases the pressure of the intermediate treated water by Y, the pressure IP2 of the water to be treated supplied to the upstream EDI device 1 can be calculated as IP2 = OP + X1 + X2 - Y. This pressure IP2 is smaller than the pressure IP1 of the first comparative example by the pressure increase Y caused by the boost pump 3. Therefore, with this configuration, the desired flow rates of the EDI devices 1 and 2 can be achieved, reducing treatment costs, and the pressure IP2 of the water to be treated supplied to the upstream EDI device 1 can be kept low to prevent damage to the upstream EDI device 1.

[0017] As described above, by providing the boost pump 3 between the upstream EDI device 1 and the downstream EDI device 2, the pressure IP2 of the treated water supplied to the upstream EDI device 1 can be kept low. However, both the supply pump 6 and the boost pump 3 require some time to reach a steady state after starting operation. Therefore, the timing of starting operation of the boost pump 3 after starting operation of the supply pump 6 and starting water flow to the upstream EDI device 1 is important. If the supply pump 6 starts operation to start water flow to the upstream EDI device 1 but the boost pump 3 has not started operation, the pressure of the intermediate treated water supplied upstream of the boost pump 3 will increase. If the timing of starting operation of the boost pump 3 is delayed, the pressure upstream of the boost pump 3 will become excessively high, which will increase the pressure on the upstream EDI device 1 and potentially damage the EDI device 1. On the other hand, when the operation of the boost pump 3 is started, the intermediate treated water that has passed through the EDI device 1 in the preceding stage is immediately sent to the EDI device 2 in the following stage by the action of the boost pump 3. As a result, the pressure of the intermediate treated water upstream of the boost pump 3 drops. If the operation of the boost pump 3 is started too early, the pressure of the intermediate treated water upstream of the boost pump 3 will become too low and negative pressure will occur, which may cause malfunction of the boost pump 3 or damage to the EDI device 1. As a result, sufficient water will not be passed through the EDI device 2 in the following stage, and good pure water will not be produced.

[0018] Thus, if the timing of starting the boost pump 3 after starting the supply pump 6 and starting the flow of water to the upstream EDI device 1 is too early or too late, it may be difficult to produce good pure water or damage the EDI devices 1 and 2. Therefore, it is possible to start the boost pump 3 a certain amount of time after starting the supply pump 6. However, experimental results have shown that the relationship between the time elapsed since the start of the supply pump 6 and the pressure change of the liquid in the boost pump 3 is not necessarily constant and may vary. Because the state of the pure water production system when it stops operating and the condition of the destination device are not constant, even if a timer is used to adjust the timing of starting the boost pump 3 based on the time elapsed since the start of the supply pump 6, it may not be possible to start the boost pump 3 at an appropriate timing. Therefore, in the first embodiment of the present invention, a pressure gauge 4 for measuring the pressure of the intermediate treated water is disposed between the upstream EDI device 1 and the boost pump 3. The boost pump 3 is started when the measurement value of the pressure gauge 4 reaches a predetermined value (first set pressure value). As a result, regardless of the time that has elapsed since the start of operation of the supply pump 6, the boost pump 3 starts operating when the upstream side of the downstream EDI device 2 and the upstream side of the boost pump 3 reach an appropriate pressure.

[0019] Furthermore, if the pressure of the intermediate treated water upstream of the boost pump 3 drops for some reason after the boost pump 3 starts operating, this may cause the boost pump 3 to malfunction or the intermediate treated water to become negatively pressurized, as described above. Therefore, in this embodiment, when the measurement value of the pressure gauge 4 drops from a value exceeding a predetermined value (second set pressure value) to below the second set pressure value while the boost pump 3 is operating, the boost pump 3 is stopped. Furthermore, the supply pump 6 is also stopped simultaneously with the stop of the boost pump 3. By simultaneously stopping the boost pump 3 and the supply pump 6 in this manner, the flow of water to the EDI devices 1 and 2 is stopped, and the production of pure water is stopped. This makes it possible to suppress pressure fluctuations during shutdown, thereby preventing the production of insufficient quality pure water and damage to the EDI devices 1 and 2. In one example, the first set pressure value is a value within a range of 0.02 MPa to 0.1 MPa, and the second set pressure value is a value within a range of 0.00 MPa to 0.05 MPa, and the first set pressure value is preferably greater than the second set pressure value. Furthermore, even during normal shutdowns, by simultaneously stopping the boost pump 3 and the supply pump 6, damage to the device can be prevented and operation can be stopped stably. In this way, it is preferable that the start and stop of operation of the boost pump 3 disposed between the EDI devices 1 and 2 be based on the measurement value of the pressure gauge 4. However, a configuration in which only the start of operation of the boost pump 3 is based on the measurement value of the pressure gauge 4, or a configuration in which only the stop of operation of the boost pump 3 is based on the measurement value of the pressure gauge 4, are also preferable because they can provide some degree of effect. These configurations are also included in the scope of the present invention.

[0020] 1 , when only one deionized water production apparatus is installed upstream of boost pump 3, that deionized water production apparatus is EDI apparatus 1, and a pressure gauge 4 is disposed between the EDI apparatus 1 and boost pump 3. Although not shown, if multiple deionized water production apparatuses are installed upstream of boost pump 3, at least one of those deionized water production apparatuses, preferably the deionized water production apparatus closest to boost pump 3, is EDI apparatus 1, and a pressure gauge 4 is disposed between that EDI apparatus 1 and boost pump 3. Although not shown, one suitable configuration may also be employed in which, from the upstream side, a tank 5, a supply pump 6, an RO apparatus (not shown), an EDI apparatus 1 at the preceding stage, a pressure gauge 4, the boost pump 3, and an EDI apparatus 2 at the following stage are connected in this order.

[0021] Second Embodiment A pure water production system according to a second embodiment of the present invention, shown in Figure 5, includes a tank 5, a supply pump 6, an upstream EDI device 1, a pressure gauge 4b, a booster pump 3, and a downstream EDI device 2, similar to the pure water production system of the first embodiment. In addition, in this embodiment, an inverter 7 is connected to each of the supply pump 6 and the booster pump 3, and the acceleration time required to reach a set frequency is controlled to 2 to 10 seconds, more preferably 2 to 6 seconds. Furthermore, in the pure water production system of this embodiment, not only is a pressure gauge 4b ​​connected downstream of the upstream EDI device 1 and upstream of the booster pump 3, similar to the first embodiment, but a pressure gauge 4a is also connected upstream of the upstream EDI device 1, a pressure gauge 4c is connected upstream of the downstream EDI device 2 and downstream of the booster pump 3, and a pressure gauge 4d is connected downstream of the downstream EDI device 2. Furthermore, a water quality meter 8a is disposed upstream of the first-stage EDI device 1, between the supply pump 6 and the pressure gauge 4a. A water quality meter 8b is disposed downstream of the first-stage EDI device 1 and upstream of the second-stage EDI device 2, between the booster pump 3 and the pressure gauge 4c. A water quality meter 8c is disposed downstream of the second-stage EDI device 2, downstream of the pressure gauge 4d. Note that the water quality conditions measured by the water quality meter 8a and those measured by the water quality meters 8b and 8c differ greatly in cleanliness (few impurities). Therefore, the water quality meters 8a and 8b and 8c are different types of water quality meters. Specifically, the water quality meter 8a measures electrical conductivity, expressed in μS / cm; the smaller the value, the cleaner the water. Meanwhile, the water quality meters 8b and 8c measure resistivity, expressed in MΩ-cm; the larger the value, the cleaner the water. The pure water production system of this embodiment is provided with two circulation lines in addition to the water supply line connecting the upstream EDI device 1 and the downstream EDI device 2 in series. Specifically, a three-way valve 9a, which is a type of switching valve, is provided upstream of the upstream EDI device 1 and between the water quality meter 8a and the pressure meter 4a, and a return path 10 is provided to return the water to be treated from this three-way valve 9a to the tank 5.Furthermore, a three-way valve 9b, which is a type of switching valve, is provided downstream of the subsequent-stage EDI device 2 and downstream of the water quality meter 8c, and a return path 11 is provided for returning the treated water from this three-way valve 9b to the tank 5. It is also possible to replace the subsequent-stage EDI device 2 with another deionized water production device (for example, an ion exchange resin device or a boron-selective resin device). Of the switching valve provided upstream of the previous-stage EDI device 1 and between the water quality meter 8a and the pressure gauge 4a, and the switching valve provided downstream of the subsequent-stage EDI device 2 and downstream of the water quality meter 8c, at least one is preferably a three-way valve, and more preferably both are three-way valves.

[0022] The method for producing pure water using the pure water production system of this embodiment will now be described. Figure 6 shows the relationship between the elapsed time from the start of operation and the pressure values ​​measured by the pressure gauges 4a to 4d. First, the supply pump 6 is started. At this time, the three-way valve 9a blocks the downstream path (the water flow line) and opens the return path 10. This circulates the water to be treated (step S1). This is called pre-water circulation. The measurement value of the water quality meter 8a immediately downstream of the supply pump 6 is continuously or intermittently checked (step S2). At time T1, when the water quality meets a predetermined water quality condition (e.g., 10 μS / cm or less), the three-way valve 9a is switched to allow the water to flow downstream. This causes the water to pass through the upstream EDI device 1 and be desalinated (step S3). While the water is being passed through the upstream EDI device 1, the pressure gauge 4b ​​on the inlet side (upstream side) of the boost pump 3 is continuously or intermittently measured (step S4). When the measured pressure reaches a first set pressure (e.g., 0.02 MPa) at time T2, the boost pump 3 is activated. This causes the water to be passed through the downstream EDI device 2, where the intermediate treated water is further desalinated (step S5). At this stage, the three-way valve 9b blocks the path to the downstream side (the outlet of the pure water production system) and opens the return path 11. The measurement value of the water quality meter 8c on the outlet side (downstream side) of the boost pump 3 is continuously or intermittently monitored (step S6). When the condition (e.g., 18 MΩ cm or higher) is met at time T3, the three-way valve 9b is switched to allow the treated water to flow downstream (step S7). In this manner, pure water is produced by the pure water production system of this embodiment. Thereafter, although not shown in Figure 6, when the pressure measured by the pressure gauge 4b ​​on the inlet side (upstream side) of the boost pump 3 becomes equal to or less than a second set pressure value (e.g., 0.01 MPa), the operation of the supply pump 6 and the boost pump 3 is stopped.

[0023] Thus, in the pure water production system of this embodiment, the boost pump 3, located between the upstream EDI device 1 and the downstream EDI device 2, begins operation when the pressure gauge 4b ​​located on the inlet side of the boost pump 3 reaches or exceeds a first set pressure value. The operation then stops when the pressure gauge 4b ​​reaches or falls below a second set pressure value. However, as a variation of this embodiment, the boost pump 3 may be started when a predetermined time has elapsed since the supply pump 6 started to supply water to the upstream EDI device 1 and begin supplying intermediate treated water to the inlet side of the boost pump 3, i.e., since water flow from the upstream EDI device 1 to the downstream EDI device 2 has begun. This predetermined time is appropriately set within a range of 1 to 10 seconds, more preferably within a range of 1 to 6 seconds. This predetermined time (the time elapsed until the boost pump 3 is started) and the acceleration time controlled by the inverter 7 are appropriately set depending on the water flow rate, pipe diameter, etc. Specifically, when the treatment flow rate (flow rate of water) and the diameter of the pipe are large, it is preferable to adjust the time elapsed until the booster pump 3 is started and the acceleration time to be longer. For example, when the diameter of the pipe is 65A and the length is 20m, 3 For a treatment flow rate of about 1000 kJ / h, it is preferable to set the elapsed time until starting the boost pump 3 to about 2 seconds and the inverter acceleration time to about 5 seconds. This control method makes it possible to control the operation of the boost pump 3 at an appropriate timing according to fluctuations in conditions at start-up, which vary depending on the treatment conditions upstream of the EDI devices 1 and 2 and the conditions of the destinations of the pure water downstream of the EDI devices 1 and 2. This makes it possible to suppress extreme fluctuations in pressure, particularly in the upstream EDI device 1. Furthermore, in this embodiment, the operation of the supply pump 6 and the boost pump 3 is stopped when the pressure on the inlet side (upstream side) of the boost pump 3 drops. This also makes it possible to suppress pressure fluctuations when the device is stopped.

[0024] In this embodiment, in addition to the water supply lines (supply lines) that pass water through the EDI devices 1 and 2, a circulation line (return path 10) is provided that returns the water to be treated to the tank 5. When starting up the pure water production system, the water is initially circulated to the tank 5 without being supplied to the upstream EDI device 1. The water quality of the water to be treated is then checked using a water quality meter 8a located upstream of the upstream EDI device 1. Once the water quality requirements are met, the circulation line is switched to the water supply line to begin producing pure water. This configuration eliminates the need for water quality testing of the intermediate treated water that has passed through the upstream EDI device 1, and does not require a circulation line that returns the water to the tank 5 between the upstream EDI device 1 and the downstream EDI device 2. This allows for stable startup. In particular, using a three-way valve 9a to switch between the circulation line and the water supply line allows the two lines to be switched in perfect synchronization. Since the timing of valve opening and closing and variations in the degree of opening and closing are suppressed, temporary fluctuations in flow rate and pressure when switching between the circulation line and the water supply line can be suppressed. This three-way valve 9a is preferably one that does not fully close at any time during switching operation and has a structure in which all paths are connected at intermediate openings. For example, an L3-type three-way valve manufactured by Nippon Valve Controls Co., Ltd. can be used. This minimizes the number of valves that remain closed for long periods of time, preventing valve sticking and slow operation when re-operated.

[0025] There is also provided a circulation line (return path 11) that returns treated water from the downstream side of the EDI device 2 to the tank 5. Depending on the water quality of the pure water produced by this pure water production system according to its intended use and the capacity of the tank (not shown) that receives the produced pure water, it is determined whether the treated water is to be sent from the pure water production system or returned to the tank 5 for circulation. By using the three-way valve 9b for this switching as well, the same effects as those described above for the three-way valve 9a can be obtained.

[0026] Although not shown, a relief valve may be provided in the water supply line, for example, upstream of the upstream EDI device 1, to release pressure when a temporary pressure increase occurs during startup, thereby preventing excessive pressure from being applied to the upstream EDI device 1. The relief valve may discharge the water to be treated from the water supply line or return the water to a container such as the tank 5.

[0027] [Effects of the present invention] The EDI device is energized with a direct current and can be continuously electrically regenerated, so the flow rate per resin volume (space velocity: SV) is higher than that of a general ion exchange resin device, and the regeneration time is 150 to 250 h -1 Typically, EDI devices are operated at a flow rate of approximately 0.09 to 0.15 MPa, resulting in a water flow differential pressure of approximately 0.09 to 0.15 MPa. When producing pure water through multi-stage processing using multiple EDI devices, increasing the flow rate of each EDI device can be considered to improve processing efficiency and reduce processing costs. For example, as illustrated in the graph of Figure 7, when a conventional EDI device is operated at a flow rate of approximately 1.3 to 1.5 times the standard flow rate (also known as the nominal flow rate) specified in a catalog or other specification, the water flow differential pressure of each EDI device also increases by approximately 1.3 to 1.5 times. As an example, when the processing flow rate of an EDI device exceeds 1.2 times the standard flow rate, the differential pressure between the inlet and outlet of the desalination compartment becomes 0.2 MPa or higher. Although the specific values ​​vary to some extent depending on the EDI device, the relationship remains unchanged: as the processing flow rate increases, the differential pressure between the inlet and outlet of the desalination compartment also increases. Furthermore, when multiple EDI devices are connected in series and the treated water is supplied from a single supply pump, the treated water must be supplied to the upstream EDI device at a high pressure, which is the sum of the differential pressure of the downstream EDI device.

[0028] According to "JIS B 8265 Structure of Pressure Vessels," the test pressure in a pressure resistance test is specified as 1.5 times the working pressure in the case of water pressure. Therefore, if the flow rate of treated water supplied to the EDI unit is increased and a pressure exceeding 1.5 times the supply water pressure (the working pressure) during steady operation is applied, the pressure resistance capability of the EDI unit may be exceeded, and the EDI unit may be damaged. The conditions for operating the EDI unit at a high flow rate include a space velocity (SV) per volume of the ion exchange resin in the desalination compartment of 300 to 450 [h -1 ], and the current density was 0.8 to 1.2 [A / dm 2 It is preferable to apply a current such that the differential pressure of the water passing through the deionization compartment is 0.2 to 0.3 [MPa].

[0029] In the present invention, a boost pump 3 is provided in the water flow line between the upstream EDI device 1 and the downstream EDI device 2. This increases the pressure of the intermediate treated water as it flows through the water flow line, eliminating the need to maintain high pressure, including the differential pressure between the two EDI devices 1 and 2, in the treated water before supplying it to the upstream EDI device 1. However, in a configuration in which the boost pump 3 is provided between the upstream EDI device 1 and the downstream EDI device 2, if the time between starting the supply pump 6 and starting the boost pump 3 is too long when passing water through the EDI device at a high flow rate, the pressure of the treated water supplied to the upstream EDI device 1 may temporarily become too high. Conversely, if the time between starting the supply pump 6 and starting the boost pump 3 is too short, the pressure of the intermediate treated water at the inlet side of the boost pump 3 may be too low, resulting in negative pressure. Therefore, the timing of starting the boost pump 3 after starting the supply pump 6 is important. The timing to start the booster pump 3 can also be determined based on the time elapsed since the supply pump 6 was started. That is, the booster pump 3 may be started when a set time has elapsed since the start of feeding liquid to the inlet of the booster pump 3 while the booster pump 3 is stopped. However, it is more preferable to determine the timing to start the booster pump 3 based on the pressure on the inlet side of the booster pump 3. This allows water to flow at a relatively high flow rate while suppressing damage to the EDI devices 1 and 2, thereby efficiently producing pure water and reducing processing costs.

[0030] [First Example] A first example of the present invention will be described. In this example, pure water was produced using the pure water production apparatus of the second embodiment shown in Figure 5. As shown schematically in Figures 3 and 8, the EDI devices 1 and 2 in this example are two-compartment deionization chamber type devices having two deionization chambers 13 adjacent to each other via an ion exchange membrane 12. Using two such two-compartment deionization chamber type EDI devices 1 and 2, a pure water production apparatus as shown in Figure 5 was fabricated. In both the front-stage EDI device 1 and the rear-stage EDI device 2, the space velocity SV of the deionization chamber 13 was set to a high flow rate condition of 320 [h -1 ] and the current value was set to 1.0 [A / dm 2] and steps S1 to S7 described above were carried out. The space velocity SV is the flow rate (flow rate per unit time) of the liquid passing through the dilution compartment 13 divided by the volume of the ion exchange resin contained in the dilution compartment 13 (which essentially corresponds to the volume of the dilution compartment 13). The acceleration time of the inverter 7 connected to the boost pump 3 was set to 5 seconds. The relationship between the pressure and the time elapsed from start-up (when the supply pump 6 begins to operate) in this example is as shown in Figure 6.

[0031] To produce pure water, the supply pump 6 is started to circulate the water to be treated from the upstream side of the EDI device 1 back to the tank 5 (step S1). The measurement value of the water quality meter 8a immediately downstream of the supply pump 6 is continuously or intermittently checked (step S2). At time T1, when the measurement value falls below a set value (e.g., 10 μS / cm), the three-way valve 9a is switched to allow water to pass through the EDI device 1 (step S3). The measurement value of the pressure gauge 4b ​​on the inlet side (upstream side) of the boost pump 3 is continuously or intermittently checked (step S4). At time T2, when the measurement value rises to a first set pressure value (e.g., 0.02 MPa), the boost pump 3 is started to operate, allowing water to pass through the EDI device 2 (step S5). The measurement value of the water quality meter 8c on the outlet side (downstream side) of the boost pump 3 is continuously or intermittently checked (step S6), and at time T3 when the measurement value exceeds a set value (e.g., 18 MΩ cm), the three-way valve 9b is switched to allow the treated water to flow downstream (step S7). As shown in Figure 6, the pressure of the water to be treated (measured by the pressure meter 4a) supplied to the upstream EDI device 1 reaches a maximum value (0.28 MPa) near the start of operation of the boost pump 3, and then the measurement value decreases to a steady state (0.25 MPa). Note that if there is a time lag between when a start signal is input to the boost pump 3 and when water supply and discharge begin (until the motor rotation speed sufficiently increases), the pressure of the water to be treated reaches its maximum value after the start signal is input to the boost pump 3. Furthermore, in the example shown in Figure 6, the pressure gauge 4a measures intermittently (at 0.5-second intervals), resulting in a time lag between the actual pressure reaching its maximum and the measurement by the pressure gauge 4a. As a result, the pressure gauge 4a appears to reach its maximum value after the boost pump 3 starts operating. However, if these time lags are negligible, theoretically, the pressure of the water being treated reaches its maximum before the boost pump 3 starts operating, and the pressure of the water being treated gradually decreases when the boost pump 3 starts operating. In this way, pure water is continuously produced in a steady state where the pressure of the water being treated is constant. That is, the maximum pressure (0.28 MPa) upstream of the EDI device in the previous stage was suppressed to approximately 1.12 times the steady-state pressure (0.25 MPa). With a pressure increase of this magnitude, the EDI device 1 is unlikely to be damaged by pressure.In this example, the differential water pressure in the upstream EDI device 1 was 0.2 MPa, and the differential water pressure in the downstream EDI device 2 was 0.19 MPa. When a resin with a relatively small particle size (e.g., a resin with an average particle size of 100 to 400 μm) is used as the ion exchange resin filled in the desalting compartment 13, the differential water pressure increases compared to when a resin with a large particle size (e.g., a resin with an average particle size of more than 400 μm) is used. Therefore, when a resin with a relatively small particle size (e.g., a resin with an average particle size of 100 to 400 μm) is used as the ion exchange resin, it is particularly suitable to employ the present invention to prevent excessively high pressure from being applied to the upstream EDI device 1.

[0032] In the case of a two-compartment EDI device as shown in Figure 8, the difference in water flow pressure between the pressure of the water to be treated at the inlet of the deionization compartment 13 on the upstream side (anode side) in the direction of water flow and the pressure of the treated water at the outlet of the deionization compartment 13 on the downstream side (cathode side) is the water flow differential pressure. In a two-compartment EDI device, the flow rate Q [L / h] of the liquid passing through one deionization compartment 13 divided by the volume V1 [L] of the ion exchange resin contained in that deionization compartment 13 is Q / V1 [h -1 ] is the space velocity SV of that dilution compartment 13, and the flow rate Q [L / h] of the liquid passing through that dilution compartment 13 divided by the volume V2 [L] of the ion exchange resin contained in the other dilution compartment 13 is Q / V2 [h -1 ] is the space velocity SV of the desalting compartment 13.

[0033] As the EDI devices 1 and 2 of this embodiment, it is also possible to use a single-dilution-compartment EDI device as shown in Figures 2 and 9, instead of a two-dilution-compartment type as shown in Figures 3 and 8. In the case of a single-dilution-compartment EDI device, the difference in pressure between the water to be treated at the inlet of a single dilution compartment 13 and the pressure of the treated water at the outlet is the water flow differential pressure. The value Q / V [h] obtained by dividing the flow rate Q [L / h] of the liquid passing through a single dilution compartment 13 by the volume V [L] of the ion exchange resin contained in that single dilution compartment 13 is -1] is the space velocity SV. In this embodiment, even when a pure water production system using an EDI device with a single deionization compartment is employed, the same effect as that obtained when a pure water production system using an EDI device with two deionization compartments is employed (i.e., achieving a high flow rate while suppressing damage to the EDI devices 1 and 2) can be obtained. Furthermore, even in a pure water production system using an EDI device with a single deionization compartment, if a resin with a relatively small particle size is used as the ion exchange resin filled in the deionization compartment 13, a large water flow differential pressure will result, so it is particularly preferable to employ the present invention to prevent excessively high pressure from being applied to the EDI device 1 in the upstream stage. For example, when the space velocity SV is 150 to 450 [h -1 Even in a single-compartment EDI device operated under the conditions of [ ], when a resin having an average particle size of 100 to 400 μm is used for at least a portion of the resin filled in the deionization compartment 13, it is particularly preferable to employ the present invention to prevent excessively high pressure from being applied to the upstream EDI device 1.

[0034] [Second Comparative Example] As a second comparative example to be compared with the first embodiment described above, pure water was produced using the pure water production system shown in FIG. 10 . This pure water production system used a combination of two switching valves 14a and 14b instead of the three-way valve 9a, and a combination of two switching valves 14c and 14d instead of the three-way valve 9b. Other than that, the configuration was essentially the same as the pure water production system shown in FIG. 5 . In this comparative example, the timing at which the boost pump 3 was started was changed from that of the above-described embodiment. FIG. 11 shows the relationship between the elapsed time from the start of operation and the pressure values ​​measured by each of the pressure gauges 4a to 4d. As in the above-described embodiment, the supply pump 6 was started (step S1), the measurement value of the water quality meter 8a was continuously or intermittently checked (step S2), and at time T1 when the measurement value fell below a set value (e.g., 10 μS / cm), water was passed through the upstream EDI device 1 (step S3). The time elapsed since the start of water flow through the upstream EDI device 1 is measured (step S4'). At time T2', when the elapsed time reaches 4 seconds, the boost pump 3 is started to operate and water is passed through the downstream EDI device 2 (step S5). The measurement value of the water quality meter 8c on the outlet side of the boost pump 3 is continuously or intermittently checked (step S6). At time T3, when the measurement value reaches or exceeds a set value (e.g., 18 MΩ cm), the treated water is allowed to flow downstream (step S7). The relationship between the differential pressure of the water flow through each EDI device 1, 2 and the pressure of the water being treated supplied to each EDI device 1, 2 during steady operation in this comparative example is the same as in the first embodiment. However, as shown in FIG. 11, the maximum pressure of the water being treated supplied to the upstream EDI device 1 (measured by the pressure meter 4a) was 0.48 MPa. This is 1.92 times the pressure (e.g., 0.25 MPa) of the water being treated that is supplied in a steady state when only the upstream EDI device 1 is operating, and there is a possibility that this could cause damage to the EDI device 1. This increase in the pressure of the water being treated is thought to be partly due to the fact that the switching valves 14a to 14d are operating separately and are not synchronized properly, and partly due to the fact that it takes time (e.g., about 5 seconds) for the boost pump 3 to reach stable, steady-state operation after startup. In response to this, it is thought that the pressure increase can be kept low by shortening the time between startup of the supply pump 6 and the start of operation of the boost pump 3.However, if the time is too short, the pressure on the inlet side of the booster pump 3 will become negative, making it difficult to pass water smoothly.

[0035] [Comparison between the First Example and the Second Comparative Example] As described above, in the second comparative example, it is not easy to minimize the possibility of damage to the EDI devices 1 and 2 while maintaining good water flow. This is because it is difficult to appropriately set the timing for starting operation of the booster pump 3. However, as in the above-described embodiment of the present invention, if the start of operation of the booster pump 3 is determined based on the measurement value of the pressure gauge 4b ​​rather than on the elapsed time, it is possible to start operation of the booster pump 3 at an appropriate timing, making it easier to produce good pure water while minimizing damage to the EDI devices 1 and 2.

[0036] Second Embodiment A pure water production system according to a second embodiment of the present invention will be described with reference to FIG. 12 . One or more components may be installed between the upstream EDI device 1 and downstream EDI device 2 of the pure water production system of the first embodiment shown in FIG. 5 , more specifically, between the boost pump 3 and downstream EDI device 2. In the pure water production system of this embodiment, as an example, a pressure gauge 4e, a boron-selective resin device (a type of deionized water production system different from an EDI device) 17, an ultraviolet oxidation device 15, and an ion-exchange resin device (a cartridge polisher, a type of deionized water production system different from an EDI device) 16 are arranged in this order between the water quality meter 8b immediately downstream of the boost pump 3 and the pressure gauge 4c. The remaining configuration is the same as that of the pure water production system of the first embodiment, and therefore a description thereof will be omitted. Using the pure water production system of this embodiment, pure water was produced by performing the same steps S1 to S7 as in the first embodiment. In the steady state during the production of pure water, the pressure gauge 4a measured 0.31 MPa, the pressure gauge 4b ​​measured 0.11 MPa, the pressure gauge 4c measured 0.26 MPa, the pressure gauge 4d measured 0.07 MPa, and the pressure gauge 4e at the outlet of the booster pump 3 measured 0.46 MPa. At this time, the water flow differential pressure of the upstream EDI device 1 was 0.2 MPa, and the water flow differential pressure of the downstream EDI device 2 was 0.19 MPa.

[0037] The sum of the pressure of the water being treated supplied in a steady state when only the upstream EDI device 1 is operating (e.g., 0.31 MPa) and the pressure of the water being treated supplied in a steady state when only the downstream device of the boost pump 3 is operating (e.g., 0.46 MPa) is 0.31 MPa + 0.46 MPa = 0.77 MPa. This is 2.48 times the pressure of the water being treated supplied in a steady state when only the upstream EDI device 1 is operating (e.g., 0.31 MPa). If water being treated at this pressure were supplied to the EDI device 1, there is a high possibility that it would cause damage to the EDI device 1. However, in this embodiment, the boost pump 3 increases the pressure of the liquid in the water supply line, so the pressure of the liquid being supplied to the EDI device 1 can be reduced, thereby suppressing damage to the EDI device 1. The pure water production system of this embodiment is configured to include four deionized water production devices, namely, the upstream EDI device 1, the intermediate boron-selective resin device 17 and ion-exchange resin device 16, and the downstream EDI device 2. Even in this configuration, the operation of the boost pump 3 is controlled based on the measurement value of the pressure gauge 4b ​​on the inlet side (upstream side) of the boost pump 3, thereby preventing damage to the upstream EDI device 1 due to excessive pressure.

[0038] A pure water production system according to a third embodiment of the present invention will be described with reference to FIG. 13 . In this pure water production system, similar to the pure water production system of the first embodiment shown in FIG. 5 , a pressure gauge 4e, a boron-selective resin device (a type of deionized water production system different from an EDI device) 17, an ultraviolet oxidation device 15, and an ion-exchange resin device (a type of deionized water production system different from an EDI device) 16 are arranged in this order between the water quality meter 8b and the pressure gauge 4d immediately downstream of the booster pump 3. The pressure gauge 4c and the downstream EDI device 2 are not provided. The remaining configuration is similar to that of the pure water production system of the first embodiment, and therefore description thereof will be omitted. While the first embodiment uses the EDI device 2 as the downstream deionized water production system, this embodiment uses the boron-selective resin device 17 and the ion-exchange resin device 16 as downstream deionized water production systems. Using this pure water production system, pure water was produced by carrying out the same steps S1 to S7 as in Example 1. In the steady state during pure water production, the pressure gauge 4a measured 0.31 MPa, the pressure gauge 4b ​​measured 0.11 MPa, the pressure gauge 4d measured 0.10 MPa, and the pressure gauge 4e at the outlet of the booster pump 3 measured 0.30 MPa. At this time, the water flow differential pressure of the upstream EDI device 1 was 0.2 MPa, and the water flow differential pressure of the downstream boron-selective resin device 17, ultraviolet oxidation device 15, and ion exchange resin device (cartridge polisher) 16 was 0.20 MPa.

[0039] The sum of the pressure of the water being treated supplied in a steady state when only the upstream EDI device 1 is operating (e.g., 0.31 MPa) and the pressure of the water being treated supplied in a steady state when only the downstream device of the boost pump 3 is operating (e.g., 0.30 MPa) is 0.31 MPa + 0.30 MPa = 0.61 MPa. This is 1.96 times the pressure of the water being treated supplied in a steady state when only the upstream EDI device 1 is operating (e.g., 0.31 MPa). If water being treated at this pressure were to be supplied to the EDI device 1, there is a high possibility that it would cause damage to the EDI device 1. However, in this embodiment, the boost pump 3 increases the pressure of the liquid in the water supply line, so the pressure of the liquid being supplied to the EDI device 1 can be reduced, thereby suppressing damage to the EDI device 1.

[0040] A pure water production system according to a fourth embodiment of the present invention will be described with reference to FIG. 14 . In this pure water production system, a boron-selective resin device 17 is provided instead of the downstream EDI device 2 of the pure water production system of the first embodiment shown in FIG. 5 . The remaining configuration is similar to that of the pure water production system of the first embodiment, and therefore a description thereof will be omitted. While the EDI device 2 was provided as the downstream deionized water production system in the first embodiment, a boron-selective resin device 17 is provided as the downstream deionized water production system in this embodiment. Pure water was produced using this pure water production system, following the same steps S1 to S7 as in the first embodiment. During the steady state during pure water production, the pressure gauges 4a, 4b, and 4d measured 0.31 MPa, 0.11 MPa, and 0.10 MPa, respectively, while the pressure gauge 4c at the outlet of the boost pump 3 and the inlet of the boron-selective resin device 17 measured 0.18 MPa. At this time, the differential pressure of the water flowing through the EDI device 1 in the front stage was 0.2 MPa, and the differential pressure of the water flowing through the boron selective resin device 17 in the rear stage was 0.08 MPa.

[0041] The sum of the pressure of the water being treated supplied in a steady state when only the upstream EDI device 1 is operating (e.g., 0.31 MPa) and the pressure of the water being treated supplied in a steady state when only the downstream device of the boost pump 3 is operating (e.g., 0.18 MPa) is 0.31 MPa + 0.18 MPa = 0.49 MPa. This is 1.58 times the pressure of the water being treated supplied in a steady state when only the upstream EDI device 1 is operating (e.g., 0.31 MPa). If water being treated at this pressure were to be supplied to the EDI device 1, there is a high possibility that it would cause damage to the EDI device 1. However, in this embodiment, the boost pump 3 increases the pressure of the liquid in the water supply line, so the pressure of the liquid supplied to the EDI device 1 can be reduced, thereby suppressing damage to the EDI device 1.

[0042] Although the present invention has been described above with reference to exemplary embodiments, the present invention is not limited to the above embodiments. Various modifications that would be understood by a person skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention. This application claims priority based on Japanese Patent Application No. 2023-100016, filed on June 19, 2023, the entire disclosure of which is incorporated herein by reference.

[0043] 1, 2 EDI device (electrically regenerated deionized water production device) 3 Booster pump 4, 4a, 4b, 4c, 4d, 4e Pressure gauge 5 Tank 6 Supply pump 7 Inverter 8a, 8b, 8c Water quality meter 9a, 9b Three-way valve 10, 11 Return path 12 Ion exchange membrane 13 Deionization chamber 14a, 14b, 14c, 14d Switching valve 15 Ultraviolet oxidation device 16 Ion exchange resin device (cartridge polisher, deionized water production device) 17 Boron selective resin device (deionized water production device) 18 Anode 19 Cathode 20 Anode chamber 21 Cathode chamber 22, 27 Anion exchange membrane 23, 26 Cation exchange membrane 24, 25 Concentration chamber

Claims

1. A pure water production system comprising: a boost pump disposed between two deionized water production devices; and a pressure gauge disposed between the boost pump and the deionized water production device located upstream of the boost pump, wherein the boost pump and at least one of the deionized water production devices located upstream of the pressure gauge are electrically regenerated deionized water production devices, and the boost pump starts and stops at least one of its operations based on the measurement value of the pressure gauge.

2. The pure water producing apparatus of claim 1, wherein the boost pump starts operating when the measurement value of the pressure gauge increases from a value below a first set pressure value to a value equal to or greater than the first set pressure value while the boost pump is stopped.

3. The pure water producing apparatus of claim 1, wherein the boost pump stops operating when the measurement value of the pressure gauge drops from a value exceeding a second set pressure value to a value below the second set pressure value while the boost pump is operating.

4. The pure water producing apparatus of claim 3, wherein the boost pump begins operating when the measurement value of the pressure gauge increases from a value below a first set pressure value to a value equal to or greater than the first set pressure value while the boost pump is stopped, and the first set pressure value is a value greater than the second set pressure value.

5. The pure water production system according to claim 3 or 4, wherein the second set pressure value is a value within a range of 0.00 MPa to 0.05 MPa.

6. The pure water production system according to claim 2 or 4, wherein the first set pressure value is a value within a range of 0.02 MPa to 0.1 MPa.

7. The pure water producing apparatus of claim 3, wherein the boost pump starts operating when a set time has elapsed since the boost pump started to pump liquid to its inlet while the boost pump is stopped.

8. A pure water production system as claimed in any one of claims 3, 4 and 7, wherein the supply pump arranged upstream of the deionized water production system located at the forefront stage stops operating at the same time as the boost pump stops operating.

9. A pure water producing apparatus as claimed in any one of claims 1, 2, 3, 4 or 7, which produces pure water in a state in which the water flow differential pressure of at least one of the plurality of deionized water producing apparatuses is greater than 0.20 MPa, and the sum of the pressure at the inlet of the desalting compartment of the deionized water producing apparatus located upstream of the boost pump and the pressure at the outlet of the boost pump is greater than 1.5 times the pressure value at the inlet of the desalting compartment of the deionized water producing apparatus.

10. A pure water production apparatus as claimed in any one of claims 1, 2, 3, 4 or 7, wherein a switching valve is provided upstream of the deionized water production apparatus on the upstream side of the boost pump to switch between a water supply line that supplies treated water to the deionized water production apparatus and a circulation line that returns the treated water to the upstream side of a supply pump located upstream of the deionized water production apparatus located in the forefront stage, and a switching valve is provided downstream of the deionized water production apparatus on the downstream side of the boost pump to switch between a water supply line that sends treated water outside the deionized water production apparatus and another circulation line that returns the treated water to the upstream side of the supply pump, and at least one of the switching valves is a three-way valve.

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