Pure water production device

Abstract

To provide a pure water production device capable of realizing a sufficiently high flow rate in each deionized water production device and suppressing damage to the deionized water production device due to application of excessively high pressure.SOLUTION: A pure water production device has a boost pump 3 arranged between deionized water production devices 1 and 2, and a pressure gauge 4b arranged between the boost pump 3 and the deionized water production device 1 located upstream of the boost pump 3. At least one deionized water production device 1 located upstream of the boost pump 3 and the pressure gauge 4b is an electrically regenerated deionized water production device. At least one of starting and stopping of an operation of the boost pump 3 is performed based on a measurement value of the pressure gauge 4b.SELECTED DRAWING: Figure 5

Description

[Technical field]

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

[0002] Conventionally, when manufacturing semiconductor devices and liquid crystal devices, pure water (including ultrapure water) from which impurities such as organic matter, ion components, fine particles, and bacteria have been highly removed is used as cleaning water. In particular, the demand for water quality of pure water used in the cleaning process of electronic components including semiconductor devices is increasing year by year. In particular, in recent years, there has been a strong demand for reducing boron. It is known that boron, which is a weak acidic component, can be removed using a reverse osmosis membrane device (hereinafter referred to as "RO device") or an electrically regenerated deionized water production device (hereinafter referred to as "EDI device"). In recent years, a method for reducing the boron concentration in treated water has been put into practical use by a multi-stage treatment using multiple EDI devices connected in series as disclosed in Patent Document 1, and a multi-stage treatment combining an EDI device with another deionized water production device (for example, 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 water processed per unit time by passing the water through at a high flow rate. When the number of EDI devices is increased in multi-stage processing, the demand for a high flow rate becomes even higher. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-34103 A Summary of the Invention [Problem to be solved by the invention]

[0005] When the flow rate of the liquid passing through the EDI device is increased, the difference in pressure between the liquid on the upstream side and downstream side of the EDI device (water flow differential pressure) increases. When pure water is produced by multi-stage processing, when the flow rate of the liquid passing through each of the EDI devices is increased, the water flow differential pressure of each EDI device increases. When realizing a high flow rate in all of the EDI devices, it is necessary to apply a higher pressure to the liquid supplied to the EDI device in the previous stage than to the liquid supplied to the EDI device in the subsequent stage, taking into consideration the increase in the water flow differential pressure. That is, it is necessary to supply a higher pressure liquid to the EDI device in the previous stage by adding the desired water flow differential pressure of the EDI device in the subsequent stage to the desired water flow differential pressure of the EDI device in the previous stage. As a result, the EDI device in the previous stage is supplied with an excessively high pressure liquid, which may damage the EDI device. In particular, EDI devices generally have a structure in which plastic frames are stacked, and have a structural characteristic in which the pressure resistance is relatively low, so that they tend to be easily damaged when high-pressure liquid is supplied to them. Therefore, if liquid is supplied at a pressure that is not too high in order to prevent damage to the EDI device at the front stage, the EDI device at the rear stage cannot obtain a supply water pressure that can achieve a sufficiently high flow rate, and the effect of reducing treatment costs is reduced.The same problem as described above occurs even in a configuration in which another deionized water production device (for example, an ion exchange resin device or a boron selective resin device) is installed instead of the EDI device at the rear stage.

[0006] Therefore, an object of the present invention is to provide a pure water production apparatus that can achieve a sufficiently fast flow rate in each deionized water production device while preventing the deionized water production device from being damaged due to excessively high pressure being applied. [Means for solving the problem]

[0007] The pure water production system of the present invention includes a boost pump disposed between 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, 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. This configuration also includes cases where other devices (e.g., ultraviolet oxidation devices, tanks, pumps) are disposed between the deionized water production devices in addition to the boost pump. The boost pump may start operating when the measured value of the pressure gauge increases from a value 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 falls from a value exceeding a second set pressure value to a value equal to or lower than the second set pressure value during operation of the boost pump, and the boost pump may start operating when the pressure gauge reading increases from a value below a first set pressure value to a value equal to or higher than the first set pressure value during stoppage of operation of the boost pump, and the first set pressure value may be a value greater than the second set pressure value. The second set pressure value may be within a range of 0.00 MPa to 0.05 MPa. The first set pressure value may be 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. The supply pump disposed upstream of the deionized water production apparatus located at the forefront stage may stop operating at the same time as the boost pump stops operating. Pure water may be produced in a state in which the water flow differential pressure of at least one of the multiple deionized water production devices is greater than 0.20 MPa, and the sum of the pressure at the inlet of the desalting 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 desalting 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 the treated water to the upstream side of a supply pump located upstream of the deionized water production apparatus located at 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 may be a three-way valve. Effect of the Invention

[0008] According to the present invention, it is possible to realize a sufficiently high flow rate in each deionized water production device, while preventing the deionized water production device from being damaged due to excessively high pressure being applied. [Brief description of the drawings]

[0009] [Figure 1] 1 is a block diagram illustrating a pure water producing system according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view showing a schematic example of the internal configuration of a single-distillation-compartment type EDI device. [Diagram 3] FIG. 1 is a cross-sectional view showing a schematic example of the internal configuration of a two-dilution-chamber type EDI device. [Figure 4] FIG. 1 is a block diagram illustrating a pure water producing system according to a first comparative example. [Diagram 5] FIG. 4 is a block diagram showing a schematic diagram of a pure water producing system according to a second embodiment of the present invention. [Figure 6]6 is a graph showing the relationship between the measured value of each pressure gauge and the elapsed time when pure water is produced using the pure water producing apparatus shown in FIG. 5. [Figure 7] 1 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 water flow differential pressure in the desalting compartment. [Figure 8] FIG. 6 is a cross-sectional view showing a schematic diagram of a deionization compartment of a two-deionization compartment type EDI device of the pure water production apparatus shown in FIG. 5. [Figure 9] FIG. 2 is a cross-sectional view showing a schematic diagram of a desalting compartment of a single-desalting compartment type EDI device. [Figure 10] FIG. 11 is a block diagram illustrating a pure water producing system according to a second comparative example. [Figure 11] 11 is a graph showing the relationship between the measured value of each pressure gauge and the elapsed time when pure water is produced using the pure water producing apparatus shown in FIG. [Figure 12] FIG. 4 is a block diagram illustrating a pure water production system according to a second embodiment of the present invention. [Figure 13] FIG. 11 is a block diagram illustrating a pure water production system according to a third embodiment of the present invention. [Figure 14] FIG. 11 is a block diagram illustrating a pure water production system according to a fourth embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. [First embodiment] FIG. 1 is a block diagram showing a schematic basic configuration of a pure water production system according to a first embodiment of the present invention. In the pure water production system of this embodiment, two deionized water production systems 1 and 2 are connected in series, and a boost pump 3 and a pressure gauge 4 are provided between these deionized water production systems 1 and 2. The front-stage deionized water production system 1 is an EDI system (an electric regeneration type deionized water production system). The rear-stage deionized water production system 2 may be an EDI system or another deionized water production system (e.g., an ion exchange resin system or a boron selective resin system). However, in the following description, as an example, an example will be described in which both the front-stage deionized water production system 1 and the rear-stage deionized water production system 2 are EDI systems.

[0011] In general, an EDI device has a configuration in which a deionization compartment partitioned 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 illustrated in Fig. 2 have a single deionization compartment type configuration having a single deionization compartment 13, and a concentration compartment 24, a deionization compartment 13, and a concentration compartment 25 are provided in this order from the anode compartment 20 side between an anode compartment 20 equipped with an anode 18 and a cathode compartment 21 equipped with a cathode 19. 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 chamber 13 is filled with ion exchange resin (generally including anion exchange resin (AER) and cation exchange resin (CER)). The anode chamber 20 is filled with cation exchange resin, and the cathode chamber 21 is filled with anion exchange resin. The EDI devices 1 and 2 perform a desalination (deionization) process on the water to be treated when the water to be treated is supplied to the deionization chamber 13 with a DC voltage applied between the anode 18 and the cathode 19, and as a result, water from which ion components have been removed is discharged from the deionization chamber 13 as treated water. Anion components among the ion components removed from the water to be treated in the deionization chamber 13 move to the concentration chamber 24 via the anion exchange membrane 22 provided on the anode 18 side in the deionization chamber 13. Cation components move to the concentration chamber 25 via the cation exchange membrane 23 provided on the cathode 19 side in the deionization chamber 13. The concentration chambers 24 and 25 are supplied with concentration chamber feed water and discharge concentrated water. Electrode chamber feed water is supplied to the cathode chamber 21, and the electrode chamber feed water supplied to the cathode chamber 21 passes through the cathode chamber 21 before being supplied to the anode chamber 20 and discharged as electrode water from the anode chamber 20. Note that it is also possible to eliminate the cation exchange membrane 26 and the anion exchange membrane 27 and have the concentration chambers 24, 25 function 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 deionization chambers 13 adjacent to each other via 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. The deionization chamber 13 on the anode 18 side of the two deionization chambers 13 located between the anode 18 and the cathode 19 is partitioned by anion exchange membranes 12 and 22 and is filled with an ion exchange resin (at least a part of which is composed of an anion exchange resin). The deionization chamber 13 on the cathode 19 side is partitioned by anion exchange membrane 12 and cation exchange membrane 23 and is filled with an ion exchange resin (at least a part of which is composed of a cation exchange resin). The other configurations are the same as those of the one-compartment deionization chamber type illustrated in FIG. 2, so their explanations 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 desalting compartment 13 on the anode 18 side and subjected to desalting (deionization) treatment, and then moved to the desalting compartment 13 on the cathode 19 side where it is desalted again, and the water from which ion components have been removed is discharged as treated water from the desalting compartment 13 on the cathode 19 side. The treatments in the concentration compartments 24 and 25, the cathode compartment 21, and the anode compartment 20 are similar to the configuration of the single desalting compartment type shown in Fig. 2, and therefore will not be described here. Note that the water flow direction may be reversed from that shown in Fig. 3, so that water to be treated is supplied to the desalting compartment 13 on the cathode 19 side and subjected to desalting (deionization) treatment, and then moved to the desalting compartment 13 on the anode 18 side where it is desalted again, and the water from which ion components have been removed is discharged as treated water from the desalting compartment 13 on the anode 18 side.

[0013] In the pure water production system of this embodiment shown in FIG. 1, the pressure gauge 4 is connected to the inlet side (upstream side) of the boost pump 3. A tank 5 for treated water is connected to the upstream side of the front-stage EDI device 1 (the EDI device located at the front end in the example shown in FIG. 1), and a supply pump 6 is disposed between the front-stage EDI device 1 and the tank 5. Therefore, from the upstream side, the tank 5, the supply pump 6, the front-stage EDI device 1, the pressure gauge 4, the boost pump 3, and the rear-stage EDI device 2 are connected in this order. Then, pure water is sent out from the outlet of the rear-stage EDI device 2. The boost pump 3 starts and stops at least one of its operations based on the measured value of the pressure gauge 4. In this specification, for convenience, the water supplied to the front-stage EDI device 1 is called the water to be treated, and the water that passes through the front-stage EDI device 1 and is supplied to the rear-stage EDI device 2 is called the intermediate treated water. The water that has passed through all the EDI devices 1 and 2 is called treated water or pure water.

[0014] The operation of the pure water production apparatus of this embodiment will be described. First, the supply pump 6 starts to operate and passes water through the EDI device 1 at the front stage. As a result, the measurement value of the pressure gauge 4 located downstream of the EDI device 1 at the front stage starts 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 the first set pressure value or higher, the boost pump 3 starts to operate. As a result, a sufficient amount of intermediate treated water is supplied to the EDI device 2 at the rear stage. In this manner, the EDI device 1 at the front stage and the EDI device 2 at the rear stage operate to produce pure water.

[0015] The effects of the pure water production apparatus of the present embodiment described above will be described. First, a pure water production apparatus of a first comparative example for comparison with the present embodiment will be described. In the pure water production apparatus of the first comparative example shown in FIG. 4, a tank 5, a supply pump 6, an EDI device 1 in the front stage, and an EDI device 2 in the rear stage are connected in series in this order from the upstream side, as in the first embodiment. However, the pressure gauge 4 and the boost pump 3 are not present. When the supply pump 6 of the pure water production apparatus of this comparative example starts to operate, water is passed from the tank 5 to the EDI device 1 in the front stage and the EDI device 2 in the rear stage, and pure water is produced. In this configuration, in order to reduce processing costs, etc., it is assumed that the water passing differential pressures (desired water passing differential pressures) when the desired flow rates are realized in each of the EDI devices 1 and 2 are X1 and X2, respectively. Then, the pressure of the water to be treated supplied to the EDI device 1 in the front stage is IP1, and the pressure of the pure water sent out from the outlet of the EDI device 2 in the rear stage is OP. The pressure OP is the desired pressure of the pure water produced and discharged during normal operation of this pure water production system. The pressure IP1 of the water to be treated supplied to the EDI device 1 in the front stage is calculated by IP1=OP+X1+X2. That is, the pressure IP1 is a pressure obtained by adding the water flow differential pressure X1 when the desired flow rate of the EDI device 1 in the front stage is realized and the water flow differential pressure X2 when the desired flow rate of the EDI device 2 in the rear stage is realized to the pressure OP, and is a relatively high pressure. In reality, the pressure IP1 needs to be even higher because it is necessary to consider the pressure loss in the path (water flow line). Since the pressure IP1 is thus a very high pressure, the EDI device 1 in the front stage may be damaged. In addition, the water flow differential pressure X1 when the desired flow rate of the EDI device 1 in the front stage is realized and the water flow differential pressure X2 when the desired flow rate of the EDI device 2 in the rear stage are realized may coincide with each other.

[0016] In contrast, in the first embodiment of the present invention shown in Fig. 1, a boost pump 3 is interposed between the upstream EDI device 1 and the downstream EDI device 2. When the pressure of the intermediate treated water is increased by Y by this boost pump 3, the pressure IP2 of the water to be treated supplied to the upstream EDI device 1 is 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 value Y by the boost pump 3. Therefore, in this configuration, the desired flow rate of each EDI device 1, 2 can be realized, thereby reducing the treatment cost, 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 EDI device 1 in the front stage and the EDI device 2 in the rear stage, the pressure IP2 of the water to be treated supplied to the EDI device 1 in the front stage can be kept low. However, both the supply pump 6 and the boost pump 3 require a certain amount of time from the start of operation until they reach a steady operating state. Therefore, the timing of starting the operation of the boost pump 3 after the supply pump 6 is started to start the water supply to the EDI device 1 in the front stage is important. In a state in which the supply pump 6 is started to start the water supply to the EDI device 1 in the front stage and the boost pump 3 is not started to start, the pressure of the intermediate treated water supplied to the upstream side of the boost pump 3 increases. If the timing of starting the operation of the boost pump 3 is delayed, the pressure on the upstream side of the boost pump 3 becomes excessively high, and the pressure applied to the EDI device 1 in the front stage also becomes high, which may 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 front stage is immediately sent to the EDI device 2 in the rear stage by the action of the boost pump 3. As a result, the pressure of the intermediate treated water drops upstream of the boost pump 3. If 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, which may cause the boost pump 3 to malfunction or damage the EDI device 1. As a result, sufficient water cannot be passed through the downstream EDI device 2, making it impossible to produce good pure water.

[0018] Thus, if the timing of starting the boost pump 3 after starting the supply pump 6 and starting the water supply to the EDI device 1 in the previous stage 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 considered to start the boost pump 3 at a point in time after the supply pump 6 starts to operate. However, it has been experimentally found that the relationship between the time elapsed from the start of the supply pump 6 operation and the pressure change of the liquid in the boost pump 3 is not necessarily constant and may vary. Since the state of the pure water production device when it stops operating and the state of the device to which water is sent are not constant, even if a timer is used to adjust the timing of starting the boost pump 3 based on the time elapsed from the start of the supply pump 6 operation, the boost pump 3 may not be started at a suitable timing. Therefore, in the first embodiment of the present invention, a pressure gauge 4 for measuring the pressure of the intermediate treated water is arranged between the EDI device 1 in the previous stage and the boost pump 3. Then, the boost pump 3 is started to operate when the measured 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 supply pump 6 started to operate, the boost pump 3 starts to operate at the point 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 on the upstream side of the boost pump 3 becomes low 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 negative pressure, as described above. Therefore, in this embodiment, when the measured value of the pressure gauge 4 falls from a value exceeding a predetermined value (second set pressure value) to the second set pressure value or less during the operation of the boost pump 3, the boost pump 3 is stopped operating. Furthermore, the supply pump 6 is stopped at the same time as the boost pump 3 is stopped operating. In this way, by stopping the boost pump 3 and the supply pump 6 simultaneously, the water supply 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 the stop, and the production of pure water with insufficient quality and the damage to the EDI devices 1 and 2 can be suppressed. In one example, the first set pressure value is a value within a range of 0.02 MPa to 0.1 MPa, the second set pressure value is a value within a range of 0.00 MPa to 0.05 MPa, and it is preferable that the first set pressure value is greater than the second set pressure value. Furthermore, even during normal operation shutdowns, the boost pump 3 and the supply pump 6 can be stopped simultaneously to prevent damage to the device and to stably shut down operation. In this manner, it is preferable that the boost pump 3 disposed between the EDI devices 1 and 2 is started and stopped based on the measurement value of the pressure gauge 4. However, a configuration in which only the start 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 the boost pump 3 is based on the measurement value of the pressure gauge 4, are also preferable because they provide some degree of effect. These configurations are also within the scope of the present invention.

[0020] 1, when only one deionized water production apparatus is installed upstream of the boost pump 3, the deionized water production apparatus is the EDI device 1, and a pressure gauge 4 is disposed between the EDI device 1 and the boost pump 3. Although not shown, if a plurality of deionized water production apparatuses are installed upstream of the boost pump 3, at least one of the deionized water production apparatuses, preferably the deionized water production apparatus closest to the boost pump 3, is the EDI device 1, and a pressure gauge 4 is disposed between the EDI device 1 and the boost pump 3. Although not shown, as a preferred embodiment, a configuration in which a tank 5, a supply pump 6, an RO device (not shown), the EDI device 1 at the front stage, a pressure gauge 4, the boost pump 3, and the EDI device 2 at the rear stage are connected in this order from the upstream side can also be adopted.

[0021] [Second embodiment] The pure water production system according to the second embodiment of the present invention shown in FIG. 5 includes a tank 5, a supply pump 6, an upstream EDI device 1, a pressure gauge 4b, a boost pump 3, and a downstream EDI device 2, similar to the pure water production system according to the first embodiment. In addition, in this embodiment, an inverter 7 is connected to each of the supply pump 6 and the boost pump 3, and the acceleration time required to reach the set frequency is controlled to be 2 to 10 seconds, more preferably 2 to 6 seconds. In addition, in the pure water production system according to this embodiment, not only is a pressure gauge 4b ​​connected downstream of the upstream EDI device 1 and upstream of the boost pump 3, similar to the first embodiment, but a pressure gauge 4a is 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 boost 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 front-stage EDI device 1 and between the supply pump 6 and the pressure gauge 4a, a water quality meter 8b is disposed downstream of the front-stage EDI device 1 and upstream of the rear-stage EDI device 2 and between the boost pump 3 and the pressure gauge 4c, and a water quality meter 8c is disposed downstream of the rear-stage EDI device 2 and downstream of the pressure gauge 4d. Note that the water quality conditions measured by the water quality meter 8a and the water quality conditions measured by the water quality meters 8b and 8c are different types of water quality meters because there is a large difference in the level of cleanliness (fewness of impurities). Specifically, the water quality meter 8a measures electrical conductivity expressed in units of μS / cm, and the smaller the value, the cleaner the water. On the other hand, the water quality meters 8b and 8c measure resistivity expressed in units of MΩ·cm, and the larger the value, the cleaner the water. In the pure water production system of this embodiment, in addition to the water flow line in which the front-stage EDI device 1 and the rear-stage EDI device 2 are connected in series, two circulation lines are provided. Specifically, a three-way valve 9a, which is a type of switching valve, is provided at a position upstream of the front-stage EDI device 1 and between the water quality meter 8a and the pressure meter 4a, and a return path 10 is provided for returning 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 at a position downstream of the rear-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 change the latter-stage EDI device 2 to another deionized water production device (for example, an ion exchange resin device or a boron selective resin device). At least one of the switching valve provided upstream of the former-stage EDI device 1 and between the water quality meter 8a and the pressure meter 4a, and the switching valve provided downstream of the latter-stage EDI device 2 and downstream of the water quality meter 8c, is preferably a three-way valve, and more preferably both are three-way valves.

[0022] A method for producing pure water by the pure water production apparatus of this embodiment will be described. The relationship between the time elapsed from the start of the operation and the pressure values ​​measured by the pressure gauges 4a to 4d is shown in FIG. 6. First, the supply pump 6 is started. At this time, the three-way valve 9a blocks the path (water flow line) to the downstream side 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), and at time T1 when a predetermined water quality condition (for example, 10 μS / cm or less) is cleared, the three-way valve 9a is switched to flow the water to the downstream side. This causes the water to pass through the EDI device 1 at the front stage and desalt the water to be treated (step S3). In parallel with the flow of water to the EDI device 1 in the front stage, the pressure is measured continuously or intermittently by the pressure gauge 4b ​​on the inlet side (upstream side) of the boost pump 3 (step S4), and at the time T2 when the measured value rises to a first set pressure value (for example, 0.02 MPa), the boost pump 3 starts to operate. As a result, the water is passed through the EDI device 2 in the rear stage to further desalt the intermediate treated water (step S5). At this stage, the three-way valve 9b blocks the path to the downstream side (outlet of the pure water production device) and opens the return path 11. Then, the measured 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 the time T3 when the condition (for example, 18 MΩ·cm or more) is met, the three-way valve 9b is switched to flow the treated water to the downstream side (step S7). In this way, the pure water production device of this embodiment produces pure water. Thereafter, although not shown in FIG. 6, when the pressure measured by the pressure gauge 4b ​​on the inlet side (upstream side) of the boost pump 3 falls below 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] In this manner, in the pure water production system of this embodiment, the boost pump 3 located between the EDI device 1 in the front stage and the EDI device 2 in the rear stage starts to operate when the measured value of the pressure gauge 4b ​​located on the inlet side of the boost pump 3 becomes equal to or greater than the first set pressure value. Thereafter, when the measured value of the pressure gauge 4b ​​becomes equal to or less than the second set pressure value, the operation is stopped. However, as a modification of this embodiment, the boost pump 3 may start to operate when a predetermined time has elapsed since the supply pump 6 started to start to pass water to the EDI device 1 in the front stage and to start to supply intermediate treated water to the inlet side of the boost pump 3, that is, since the water started to pass from the EDI device 1 in the front stage to the EDI device 2 in the rear stage. 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 elapsed time until the boost pump 3 is started) and the acceleration time controlled by the inverter 7 are appropriately set according to the flow rate of water to be passed, the diameter of the pipe, and the like. 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 boost pump 3 is started and the acceleration time to be longer. For example, when the pipe diameter is 65A and the pipe length is 20m, 3 In the case of a processing flow rate of about 1000000 / h, it is preferable to set the elapsed time until the boost pump 3 is started to about 2 seconds and the acceleration time of the inverter 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 the fluctuation in the situation at the time of starting, which changes depending on the processing situation in the stage before the EDI devices 1 and 2 and the situation of the pure water destination in the stage after the EDI devices 1 and 2, and in particular to suppress extreme fluctuations in the pressure applied to the EDI device 1 in the upstream stage. Furthermore, in this embodiment, when the pressure on the inlet side (upstream side) of the boost pump 3 drops, the operation of the supply pump 6 and the boost pump 3 is stopped. This makes it possible to suppress pressure fluctuations when the device is stopped.

[0024] In this embodiment, in addition to the water supply line (supply line) that passes the EDI devices 1 and 2, a circulation line (return path 10) that returns the water to be treated to the tank 5 is provided. When starting up the pure water production system, the water to be treated is first circulated to the tank 5 without being supplied to the EDI device 1 at the front stage. Then, the water quality meter 8a located upstream of the EDI device 1 at the front stage checks the water quality of the water to be treated, and after the water quality conditions are met, the circulation line is switched to the water supply line to start production of pure water. With this configuration, there is no need to test the water quality of the intermediate treated water that has passed through the EDI device 1 at the front stage, and there is no need to provide a circulation line that returns the water to the tank 5 between the EDI device 1 at the front stage and the EDI device 2 at the rear stage. This allows for stable startup. In particular, when the circulation line and the water supply line are switched over using the three-way valve 9a, the two lines can be switched over completely in synchronization. Since the occurrence of timing discrepancies and variations in the degree of opening and closing of the valves is 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 have a timing at which it is fully closed 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 mentioned. This makes it possible to prevent valves from being closed for long periods of time as much as possible, and to prevent valves from sticking and becoming sluggish when re-operated.

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

[0026] Although not shown, a relief valve may be provided in the water flow line, such as 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 flow line or return the water to a container such as the tank 5.

[0027] [Effects of the present invention] The EDI device is powered by a direct current and can be continuously regenerated electrically, 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 hours. -1 Generally, the EDI devices are operated at a flow rate of about 1.5 to 2.0 MPa, and the differential pressure of the water flow at that time is about 0.09 to 0.15 MPa. When producing pure water by multi-stage processing using multiple EDI devices, it is possible to increase the flow rate of each EDI device to improve the processing efficiency and reduce the processing cost. For example, as illustrated in the graph of FIG. 7, when a conventional EDI device is operated at a flow rate of about 1.3 to 1.5 times the standard flow rate (also called the standard flow rate or nominal flow rate) in the specifications described in a catalog, the differential pressure of each EDI device also increases to about 1.3 to 1.5 times. As an example, when the processing flow rate of the 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 more. Although the specific numerical value varies to some extent depending on each EDI device, the relationship that the differential pressure between the inlet and outlet of the desalination compartment increases with an increase in the processing flow rate remains unchanged. Furthermore, when multiple EDI devices are connected in series and the water to be treated is supplied from a single supply pump, the water to be treated must be supplied to the EDI device in the preceding stage at a high pressure, which includes the differential pressure of the EDI device in the following stage.

[0028] According to "JIS B 8265 Structure of Pressure Vessels," the test pressure in a pressure test is stipulated to be 1.5 times the working pressure in the case of water pressure. Therefore, if the flow rate of treated water supplied to the EDI device is increased and a pressure exceeding 1.5 times the supply water pressure during normal operation (the working pressure) is applied, the EDI device may exceed its pressure resistance performance and be damaged. The conditions for operating the EDI device at a high flow rate are that the space velocity per volume of the ion exchange resin in the desalting compartment, SV, is 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 water flow differential pressure in the deionization compartment is 0.2 to 0.3 MPa.

[0029] In the present invention, the boost pump 3 is provided between the EDI device 1 at the front stage and the EDI device 2 at the rear stage in the water flow line. This increases the pressure of the intermediate treated water while it is flowing through the water flow line, so there is no need to keep the water to be treated at a high pressure including the differential water pressure of each of the two EDI devices 1 and 2 at the time of supplying it to the EDI device 1 at the front stage. However, in a configuration in which the boost pump 3 is provided between the EDI device 1 at the front stage and the EDI device 2 at the rear stage, if the time from the start of the supply pump 6 to the start of the boost pump 3 is long when water is passed through the EDI device at a high flow rate, the pressure of the water to be treated supplied to the EDI device 1 at the front stage may temporarily become too high. Conversely, if the time from the start of the supply pump 6 to the start of 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 of starting the boost pump 3 may also be determined based on the elapsed time from the start of the supply pump 6. That is, while the boost pump 3 is stopped, the boost pump 3 may be started when the elapsed time from when the liquid supply to the inlet of the boost pump 3 started reaches a set time. However, it is more preferable to determine the timing to start the boost pump 3 based on the pressure at the inlet side of the boost pump 3. This makes it possible to efficiently produce pure water by passing water at a relatively high flow rate while suppressing damage to the EDI devices 1 and 2, and to reduce the processing cost. EXAMPLES

[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 FIG. 5. The EDI devices 1 and 2 of this example are two-compartment type devices having two adjacent desalting compartments 13 with an ion exchange membrane 12 between them, as shown typically in FIGS. 3 and 8. Using two such two-compartment type EDI devices 1 and 2, a pure water production apparatus as shown in FIG. 5 was produced. In both the front-stage EDI device 1 and the rear-stage EDI device 2, the space velocity SV of the desalting compartment 13 was set to a high flow rate condition of 320 [h -1] and set the current value to 1.0 [A / dm 2 The space velocity SV was set to 0.05 V, and steps S1 to S7 described above were carried out. The space velocity SV is the flow rate (flow rate per unit time) of liquid passing through the dilution compartment 13 divided by the volume of the ion exchange resin contained in the dilution compartment 13 (which essentially coincides with 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 elapsed time from start-up (when the supply pump 6 begins to operate) in this embodiment is as shown in FIG. 6.

[0031] In producing pure water, the supply pump 6 is started to circulate the water to be treated from the upstream side of the EDI device 1 in the previous stage 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), and 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 pass water through the EDI device 1 in the previous stage (step S3). The measurement value of the pressure meter 4b on the inlet side (upstream side) of the boost pump 3 is continuously or intermittently checked (step S4), and 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 and pass water through the EDI device 2 in the subsequent stage (step S5). The measured 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 measured 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 Fig. 6, the pressure of the water to be treated (measured value of the pressure meter 4a) supplied to the upstream EDI device 1 reaches a maximum value (0.28 MPa) near the time when the boost pump 3 starts to operate, and then the measured 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 starts and discharge begins (until the motor rotation speed increases sufficiently), the pressure of the water to be treated reaches a maximum value after the start signal is input to the boost pump 3. Furthermore, in the example shown in FIG. 6, the pressure gauge 4a is measured intermittently (at 0.5 second intervals), and as a result of a time lag between the timing at which the actual pressure reaches its maximum value and the timing at which the pressure gauge 4a is measured, the measured value of the pressure gauge 4a appears to reach its maximum value after the boost pump 3 starts to operate. However, if these time lags can be ignored, theoretically, it is considered that the pressure of the water to be treated reaches its maximum value before the boost pump 3 starts to operate, and when the boost pump 3 starts, the pressure of the water to be treated gradually decreases. In this way, pure water is continuously produced in a steady state where the pressure of the water to be treated is constant. That is, the maximum pressure (0.28 MPa) on the upstream side of the EDI device in the previous stage was suppressed to about 1.12 times the pressure (0.25 MPa) in the steady state. With this level of pressure increase, the possibility that the EDI device 1 will be damaged by pressure is very low.In this embodiment, the differential water pressure in the front-stage EDI device 1 was 0.2 MPa, and the differential water pressure in the rear-stage 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 chamber 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 front-stage EDI device 1.

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

[0033] As the EDI devices 1 and 2 of this embodiment, a single-distillation compartment EDI device as shown in Figs. 2 and 9 can be used instead of a two-distillation compartment EDI device as shown in Figs. 3 and 8. In the case of a single-distillation compartment EDI device, the difference between the pressure of the water to be treated at the inlet of a single distillation 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 distillation compartment 13 by the volume V[L] of the ion exchange resin contained in that single distillation compartment 13 is -1] is the spatial velocity SV. In this embodiment, when a pure water production system using an EDI device with a single desalting compartment is used, the same effect as that obtained when a pure water production system using an EDI device with two desalting compartments is used (reducing damage to the EDI devices 1 and 2 while realizing a high flow rate) can be obtained. Furthermore, even in a pure water production system using an EDI device with a single desalting compartment, if a resin with a relatively small particle size is used as the ion exchange resin filled in the desalting 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 spatial velocity SV is 150 to 450 [h -1 Even in a single-compartment EDI device operated under the conditions above, it is particularly suitable to employ the present invention to prevent excessively high pressure from being applied to the upstream EDI device 1 when at least a portion of the resin filled in the distillation compartment 13 is a resin having an average particle size of 100 to 400 μm.

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

[0035] [Comparison between the first embodiment and the second comparative example] As described above, in the second comparative example, it is not easy to reduce 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 to start the operation of the boost pump 3. However, as in the above-described embodiment of the present invention, if the start of operation of the boost 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 the operation of the boost 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 Example] 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 EDI device 1 at the front stage and the EDI device 2 at the rear stage of the pure water production system according to the first embodiment shown in FIG. 5, more specifically, between the boost pump 3 and the EDI device 2 at the rear stage. In the pure water production system according to this embodiment, as an example, a pressure gauge 4e, a boron selective resin device (a deionized water production system of a different type from the EDI device) 17, an ultraviolet oxidation device 15, and an ion exchange resin device (a cartridge polisher, a deionized water production system of a different type from the 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 rest of the configuration is the same as that of the pure water production system according to the first embodiment, so a description thereof will be omitted. Using the pure water production system according to this embodiment, pure water was produced by carrying out the same steps S1 to S7 as those of 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 measured 0.46 MPa at the outlet of the boost pump 3. At this time, the water flow differential pressure of the front-stage EDI device 1 was 0.2 MPa, and the water flow differential pressure of the rear-stage EDI device 2 was 0.19 MPa.

[0037] The sum of the pressure of the water to be 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 to be 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 to be treated supplied in a steady state when only the upstream EDI device 1 is operating (e.g., 0.31 MPa), and if water to be 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 line, so the pressure of the liquid supplied to the EDI device 1 can be reduced, and damage to the EDI device 1 can be suppressed. The pure water production system of this embodiment is configured to include four deionized water production devices, namely, the front-stage EDI device 1, the boron selective resin device 17 and the ion exchange resin device 16 in the middle position, and the rear-stage EDI device 2. Even in this configuration, by controlling the operation of the boost pump 3 based on the measurement value of the pressure gauge 4b ​​on the inlet side (upstream side) of the boost pump 3, it is possible to obtain the effect of preventing the front-stage EDI device 1 from being damaged by excessive pressure.

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

[0039] The sum of the pressure of the water to be 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 to be 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 to be treated supplied in a steady state when only the upstream EDI device 1 is operating (e.g., 0.31 MPa), and if water to be 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 line, so the pressure of the liquid supplied to the EDI device 1 can be reduced, and damage to the EDI device 1 can be suppressed.

[0040] [Fourth Example] A pure water production system according to a fourth embodiment of the present invention will be described with reference to FIG. 14. In the pure water production system of this embodiment, a boron selective resin device 17 is arranged instead of the EDI device 2 at the rear stage of the pure water production system of the first embodiment shown in FIG. 5. The rest of the configuration is the same as that of the pure water production system of the first embodiment, so the description will be omitted. In the first embodiment, the EDI device 2 is provided as the rear stage deionized water production system, whereas in this embodiment, the boron selective resin device 17 is provided as the rear stage deionized water production system. Using this pure water production system, pure water was produced by carrying out the same steps S1 to S7 as in the first embodiment. In the steady state during the pure water production, the measured value of the pressure gauge 4a was 0.31 MPa, the measured value of the pressure gauge 4b ​​was 0.11 MPa, the measured value of the pressure gauge 4d was 0.10 MPa, and the measured value of the pressure gauge 4c at the outlet of the boost pump 3 and the inlet of the boron selective resin device 17 was 0.18 MPa. At this time, the water flow differential pressure of the EDI device 1 in the front stage was 0.2 MPa, and the water flow differential pressure of the boron selective resin device 17 in the rear stage was 0.08 MPa.

[0041] The sum of the pressure of the water to be 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 to be 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 to be treated supplied in a steady state when only the upstream EDI device 1 is operating (e.g., 0.31 MPa), and if water to be 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 line, so the pressure of the liquid supplied to the EDI device 1 can be reduced, and damage to the EDI device 1 can be suppressed. [Explanation of symbols]

[0042] 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 route 12 Ion exchange membrane 13 Desalination room 14a, 14b, 14c, 14d Switching valve 15. Ultraviolet oxidation equipment 16 Ion exchange resin equipment (cartridge polisher, deionized water production equipment) 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 booster pump disposed between the deionized water producing devices; a pressure gauge disposed between the boost pump and the deionized water production device located upstream of the boost pump; At least one of the deionized water production devices located upstream of the boost pump and the pressure gauge is an electrically regenerated deionized water production device, The pure water producing apparatus is characterized in that at least one of the start and stop of operation of the boost pump is performed based on the measurement value of the pressure gauge.

2. 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. 2. 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 equal to or lower than the second set pressure value while the boost pump is operating.

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

6. 5. The water purifying apparatus according to claim 2, wherein the first set pressure value is a value within a range of 0.02 MPa to 0.1 MPa.

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

8. 8. The pure water producing apparatus according to claim 3, wherein the supply pump arranged upstream of the deionized water producing apparatus located at the forefront stage stops operating simultaneously with the stop of operation of the boost pump.

9. 8. A pure water producing apparatus as claimed in any one of claims 1, 2, 3, 4 and 7, wherein pure water is produced 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 switching valve is provided upstream of the deionized water production device on the upstream side of the boost pump to switch between a water supply line that supplies the water to be treated to the deionized water production device and a circulation line that returns the water to be treated to the upstream side of a supply pump that is located upstream of the deionized water production device located at the forefront stage; 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 for sending treated water to the outside of the deionized water production apparatus and another circulation line for returning treated water to the upstream side of the supply pump; 8. The water purifying apparatus according to claim 1, wherein at least one of the switching valves is a three-way valve.

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