Control method of ultrapure water production device

Abstract

In the present invention, in a primary pure water device (3), a DC power supply (9A) is attached to an electrodeionization device (9) connected to a water supply pump (8), and the desalted water (W2) of the electrodeionization device (9) can be supplied to a sub-tank (11). A liquid level switch (21) is provided in the sub-tank (11). In addition, a control valve (23) and a flow meter (24) are provided on the flow path (22) of the desalted water (W2) of the electrodeionization device (9), and a control valve (26) and a flow meter (27) are also provided on the flow path (25) of the concentrated water (W5) of the electrodeionization device (9). Furthermore, the measurement data of the liquid level switch (21) and the flow meter (24, 27) can be sent to a control device (28), and the water supply pump (8) and the control valve (23, 26) can be controlled. In this way, a control method for an ultrapure water manufacturing device capable of manufacturing primary pure water according to the usage of the subsystem is provided.

Description

Technical Field

[0001] The present invention relates to a control method for an ultrapure water production device for producing ultrapure water used in the electronic industry such as semiconductors and liquid crystals, and more particularly to a control method for an ultrapure water production device capable of producing primary pure water according to the usage of a subsystem. Background Art

[0002] Conventionally, ultrapure water used in the semiconductor and other electronic industries is produced by treating raw water using an ultrapure water production apparatus, which is composed of a pretreatment system, a primary pure water apparatus, and a subsystem for treating the primary pure water.

[0003] For example, Figure 1 As shown, the ultrapure water production device 1 is composed of three stages of devices, namely, a pretreatment device 2, a primary pure water production device 3, and a secondary pure water production device (subsystem) 4. In the pretreatment device 2 of such an ultrapure water production device 1, pretreatment based on filtration, coagulation and sedimentation, precision filtration membrane, etc. of the raw water W is implemented to mainly remove suspended matter.

[0004] The primary pure water production device 3 includes a reverse osmosis membrane device 5 for treating the pre-treated water W1, a degassing membrane device 6, an ultraviolet oxidation device 7, an electrodeionization device 9, and a water supply pump 8 for supplying water to the electrodeionization device 9. In the primary pure water production device 3, most of the electrolytes, particles, live bacteria, etc. in the pre-treated water W1 are removed, and organic matter is decomposed.

[0005] The subsystem 4 is composed of a subtank 11 as a water storage tank, an ultraviolet oxidation device 12, a non-regenerative mixed bed ion exchange device 13, and an ultrafiltration (UF) membrane 14 as a membrane filtration device. The water storage tank stores the primary pure water W2 produced by the primary pure water production device 3 and is arranged at the rear stage of the electrodeionization device; the ultraviolet oxidation device 12 processes the primary pure water W2 supplied from the subtank 11 via a pump not shown in the figure, and an RO membrane separation device is sometimes provided in the subsystem 4 as needed. In the subsystem 4, the trace organic matter (TOC component) contained in the primary pure water W2 is oxidized and decomposed by the ultraviolet oxidation device 12, and then treated by the non-regenerative mixed bed ion exchange device 13, so that the residual carbonate ions, organic acids, anionic substances, metal ions, and cationic substances are removed by ion exchange. Then, the ultrafiltration (UF) membrane 14 removes particles to produce ultrapure water W3, which is supplied to the use point 15, and the unused ultrapure water flows back to the subtank 11.

[0006] In the ultrapure water production apparatus 1 described above, in order to stably supply primary pure water having a predetermined water quality, an excess amount of primary pure water W2 is produced in advance, only a required amount is supplied to the sub-tank 11, and the remaining amount is controlled for circulation. Summary of the invention

[0007] Problems to be solved by the invention

[0008] However, in the conventional control method of the ultrapure water production device 1 as described above, since more than the required amount of water is supplied to the electrodeionization device 9 and the like for processing, there is room for improvement in energy efficiency. Therefore, it is considered to change the processing amount of the electrodeionization device 9 so that the processing amount of the primary pure water production device 3 corresponds to the usage amount of the use point 15, but there is a problem that it is not only difficult to follow the change of the usage amount of the use point 15, but also the water quality of the desalted water in the electrodeionization will be reduced.

[0009] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a control method of an ultrapure water production apparatus capable of producing primary pure water according to the usage amount of a subsystem.

[0010] Means used to solve problems

[0011] In view of the above-mentioned purpose, the present invention provides a control method for an ultrapure water production device, which includes: a primary pure water system, which has a reverse osmosis membrane, an electrodeionization device, and a water supply pump arranged in the front stage of the electrodeionization device; a water storage tank, which is arranged in the rear stage of the electrodeionization device and is equipped with a water level measuring unit; and a subsystem for further processing the primary pure water produced by the primary pure water system, wherein the amount of water supplied to the electrodeionization device is controlled so that the water level of the water storage tank measured by the water level measuring unit is kept approximately constant (Invention 1).

[0012] According to the invention (Invention 1), by measuring the water level of a water storage tank arranged at the rear stage of the electrodeionization device, the amount of water supplied to the electrodeionization device is controlled to keep the water level approximately constant, thereby adjusting the production amount of primary pure water according to the operating conditions of the subsystem, thereby improving the operating efficiency of primary pure water in the ultrapure water production device.

[0013] In the above invention (Invention 1), it is preferred that the operating current of the electrodeionization device is controlled based on the amount of feed water supplied to the electrodeionization device and the quality of the feed water so as to achieve a predetermined quality of primary pure water (Invention 2).

[0014] According to this invention (Invention 2), if the amount of water supplied to the electrodeionization device is controlled, the water quality of the primary pure water obtained will change. Therefore, by controlling the operating current of the electrodeionization device according to the required water quality and water amount of the primary pure water, primary pure water of specified water quality can be supplied to the sub-tank.

[0015] In the above invention (Invention 1 or 2), it is preferred that the electrodeionization device comprises a cathode and an anode, a cation exchange membrane and an anion exchange membrane disposed between the cathode and the anode, and a desalting chamber and a concentrating chamber defined by the cation exchange membrane and the anion exchange membrane, the desalting chamber and the concentrating chamber being filled with ion exchangers, the electrodeionization device comprises a concentrated water introduction unit for introducing concentrated water into the concentrating chamber, and a unit for introducing supply water into the desalting chamber and taking out desalted water, the concentrated water introduction unit introducing concentrated water into the concentrating chamber from a side close to a desalted water outlet of the desalting chamber, and allowing concentrated water to flow out from a side close to a supply water inlet of the desalting chamber. In particular, in the above invention (Invention 3), it is preferred that the concentrated water introduction unit introduces desalted water formed by passing through the desalting chamber as concentrated water into the concentrating chamber from a side close to a desalted water outlet of the desalting chamber, and allows concentrated water to flow out from a side close to a supply water inlet of the desalting chamber (Invention 4).

[0016] According to the invention (Invention 3 or 4), the present inventors' research results show that when the amount of water supplied to the electrodeionization device is increased, the amount of water to be treated increases, and therefore the supply current needs to be increased. As a result, the water quality of the desalted water (equivalent to primary pure water) of the electrodeionization device may be reduced at one time. If the electrodeionization device is as specified in Invention 3, the reduction in water quality will be reduced. This is for the following reasons. That is, in the electrodeionization device, it is known that if concentrated water is introduced in the same direction as the water flow direction of the desalination chamber, then at the outlet side of the concentration chamber (the outlet side of the desalination chamber), carbonate ions (HCO3 － ) becomes the highest, so these ions tend to accumulate in the lower part of the concentration chamber. If the supply current supplied to the electrodeionization device is increased, the accumulated carbonate ions and the like diffuse back from the concentration chamber of the electrodeionization device to the desalination chamber side, resulting in a decrease in the water quality of the desalted water. In contrast, in the electrodeionization device specified in Invention 3, by passing the concentrated water in the direction opposite to the water flow direction of the desalination chamber, the ion concentration of carbonate ions and the like becomes the lowest on the inlet side of the concentration chamber (the outlet side of the desalination chamber). Since such back diffusion is suppressed, the electrodeionization device having such a structure is particularly suitable for the case where the flow rate of the primary pure water supplied to the subsystem is changed. In particular, in the electrodeionization device specified in Invention 4, since the desalted water formed by passing through the desalination chamber is used as the concentrated water, the back diffusion can be further suppressed.

[0017] Effects of the Invention

[0018] According to the present invention, by measuring the water level of a water storage tank disposed at the rear stage of the electrodeionization device, the amount of water supplied to the electrodeionization device is controlled so that the water level is kept substantially constant, thereby adjusting the production amount of primary pure water according to the status of the subsystem, thereby improving the operation efficiency of primary pure water in the ultrapure water production device. In particular, if the amount of water supplied to the electrodeionization device is controlled, the water quality of the obtained primary pure water will change, and the operation current of the electrodeionization device is controlled according to the required water quality and water amount of the primary pure water, so that primary pure water of a specified water quality can be supplied to the water storage tank. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a flow chart showing an ultrapure water production apparatus to which the control method of the ultrapure water production apparatus according to the first embodiment of the present invention can be applied.

[0020] Figure 2 This is a schematic diagram showing a control structure of an electrodeionization device in a control method of an ultrapure water production device according to the first embodiment of the present invention.

[0021] Figure 3 It is a schematic diagram showing the electrodeionization apparatus of this embodiment.

[0022] Figure 4 It is a schematic diagram showing the water flow state of the electrodeionization device according to this embodiment.

[0023] Figure 5 It is a schematic cross-sectional view showing another structure of the electrodeionization device used in the ultrapure water production apparatus of this embodiment.

[0024] Figure 6 This is a schematic cross-sectional view showing a preferred structure of an electrodeionization device used in the ultrapure water production apparatus of this embodiment.

[0025] Figure 7 This is a schematic diagram showing a control structure of an electrodeionization device in a control method of an ultrapure water production device according to a second embodiment of the present invention.

[0026] Figure 8 It is a schematic diagram showing the control structure of the electrodeionization device of Example 1.

[0027] Fig. 9 It is a schematic diagram showing the control structure of the electrodeionization device of Example 2 and Example 3.

[0028] Fig.10 It is a graph showing the change in water flow rate and water quality of the electrodeionization device in Example 2.

[0029] Fig.11 It is a graph showing the change in water supply load and water quality of the electrodeionization device in Example 3. DETAILED DESCRIPTION

[0030] Hereinafter, a control method of the ultrapure water production apparatus according to the present invention will be described with reference to the drawings.

[0031] (First Embodiment)

[0032] (Ultrapure water production equipment)

[0033] The present invention is an ultrapure water production device including a primary pure water device having an electrodeionization device, and is characterized in that the electrodeionization device is controlled. Therefore, as an ultrapure water production device to which the control method of the ultrapure water production device of this embodiment can be applied, as long as the primary pure water device includes an electrodeionization device, for example, it can be preferably applied Figure 1 The ultrapure water production device shown in FIG. Figure 1 In the ultrapure water production apparatus shown in the figure, the same components are denoted by the same reference numerals and described.

[0034] In this embodiment, if Figure 2 As shown, in the primary pure water device 3, a DC power supply 9A is attached to the electrodeionization device 9 connected to the water supply pump 8, and the desalted water W2 of the electrodeionization device 9 (in this embodiment, since the electrodeionization device 9 is located at the end of the primary pure water device 3, it is equivalent to primary pure water, and the same applies below) can be supplied to the sub-tank 11 as a water storage tank arranged at the rear stage of the electrodeionization device 9. A liquid level switch 21 as a water level measuring unit is provided in the sub-tank 11. In addition, a control valve 23 and a flow meter 24 are provided on the flow path 22 of the desalted water W2 of the electrodeionization device 9, and on the other hand, a control valve 26 and a flow meter 27 are also provided on the flow path 25 of the concentrated water W5 of the electrodeionization device 9. In addition, the measurement data of the liquid level switch 21, the flow meter 24 and the flow meter 27 can be sent to the control device 28 having a personal computer, etc., respectively, and the water supply pump 8, the control valve 23 and the control valve 26 can be controlled respectively.

[0035] Here, as the electrodeionization device 9, it is preferable to use a device having the following Figure 3 and Figure 4 Device of the structure shown.

[0036] exist Figure 3In the electrodeionization device 9, a plurality of anion exchange membranes 33 and cation exchange membranes 34 are alternately arranged between electrodes (anode 31, cathode 32), thereby alternately forming concentration chambers 35 and desalination chambers 36. In the desalination chambers 36, ion exchangers (anion exchangers and cation exchangers) composed of ion exchange resins, ion exchange fibers, or graft exchangers are mixed or multilayered and filled. In addition, the concentration chambers 35, the anode chambers 37, and the cathode chambers 38 are also filled with ion exchangers.

[0037] The electrodeionization device 9 is provided with: a water supply unit (not shown) for passing the supply water W1 into the desalination chamber 36 and taking out the desalted water W2; and a concentrated water supply unit (not shown) for passing the concentrated water W4 into the concentration chamber 35. In this embodiment, the concentrated water W4 is introduced into the concentration chamber 35 from the side close to the outlet of the desalted water W2 of the desalination chamber 36, and flows out from the side close to the inlet of the supply water W1 of the desalination chamber 36. That is, it has the following structure: the concentrated water W4 is introduced into the concentration chamber 35 from the direction opposite to the flow direction of the supply water W1 in the desalination chamber 36, and the concentrated water W5 is discharged. In addition, in this specification, for the convenience of explanation, the supply water of the electrodeionization device 9 after the pre-treated water W1 is treated by the reverse osmosis membrane device 5, the degassing membrane device 6 and the ultraviolet oxidation device 7 is also expressed as the supply water W1.

[0038] As the concentrated water W4 introduced into the concentration chamber 35, the feed water W1 supplied to the desalination chamber 36 can be used. Figure 4 As shown, it is preferred to use the desalted water W2 obtained from the desalination chamber 36 as the concentrated water W4.

[0039] By using such an electrodeionization device 9, the following effects can be obtained. Figure 5 As shown schematically, in the electrodeionization device 9, if the concentrated water W4 is passed in the same direction as the water flow direction of the desalination chamber, carbonate ions (HCO3 － ) etc. becomes the highest, so these ions tend to accumulate at the outlet side of the concentration chamber 35. When the supply current to the electrodeionization device 9 is increased, the accumulated carbonate ions and the like diffuse back from the concentration chamber 35 of the electrodeionization device 9 to the desalination chamber 36 side, which tends to cause a decrease in the quality of the desalted water. Therefore, by using the electrodeionization device 9 with the above-mentioned structure, Figure 6 As schematically shown, since the concentration of ions such as carbonate ions is the lowest at the inlet side of the concentration chamber 35 (the outlet side of the desalination chamber 36), the back diffusion can be suppressed. Therefore, even if the amount of desalted water in the electrodeionization device 9 is changed, the change in the water quality of the primary pure water W2 can be suppressed, so it can be said that it is suitable for the case where the flow rate of the primary pure water W2 supplied to the subsystem 4 is changed.

[0040] (Control method of ultrapure water production device)

[0041] A method for controlling the above-mentioned ultrapure water production apparatus will be described below.

[0042] like Figure 2 As shown, the water supply W1 is supplied to the electrodeionization device 9 via the water supply pump 8. At this time, the water level of the sub-tank 11 is measured by the liquid level switch 21, and the control device 28 performs frequency conversion control on the water supply pump 8 based on the water level data, so that if the water level is less than a substantially constant value (it can also be a specified range relative to a predetermined reference value), the delivery flow rate of the water supply W1 to the electrodeionization device 9 is increased, and on the other hand, if the water level is more than a substantially constant value, the delivery flow rate is reduced. And, according to the water volume of the water supply W1, the control valve 23 and the control valve 26 are controlled by the control device 28 to control the flow rates of the desalted water (primary pure water) W2 and the concentrated water W5 of the electrodeionization device 9. For example, the water volume of the concentrated water W5 can be kept constant, and the amount of the desalted water (primary pure water) W2 can be adjusted to change the recovery rate.

[0043] As described above, by controlling the amount of water W supplied by the water supply pump 8 to the electrodeionization device 9 according to the water level of the sub-tank 11 serving as a water storage tank arranged at the rear stage of the electrodeionization device 9, not only the driving power of the water supply pump 8 can be reduced, but also the operating efficiency of the electrodeionization device 9 can be optimized, thereby reducing the amount of electricity required for the operation of the ultrapure water manufacturing device 1.

[0044] (Second Embodiment)

[0045] (Ultrapure water production equipment)

[0046] The second embodiment basically has the same configuration as that of the first embodiment described above, and therefore the same configurations are denoted by the same reference numerals and detailed descriptions thereof are omitted.

[0047] In this embodiment, if Figure 7 As shown, a resistivity meter 29 is provided as a water quality measuring unit for measuring the water quality of the water supply W1, and the water quality information of the resistivity meter 29, the flow rate information of the desalted water (primary pure water) W2 of the electrodeionization device 9 by the flow meter 24, and the water level of the sub-tank 11 by the level switch 21 can be sent to the control device 28, and based on these, the amount of current supplied to the electrodeionization device 9 can be controlled by the DC power supply 9A. Here, as the electrodeionization device 9, similarly to the first embodiment, it is preferable to use a device having a Figure 3 and Figure 4 The structure shown.

[0048] (Control method of ultrapure water production device)

[0049] A method for controlling the above-mentioned ultrapure water production apparatus will be described below.

[0050] like Figure 7 As shown, the water supply W1 is supplied to the electrodeionization device 9 via the water supply pump 8. At this time, the water level of the sub-tank 11 is measured by the liquid level switch 21, and the control device 28 performs frequency conversion control on the water supply pump 8 based on the water level data. If the water level is less than a predetermined reference value (it can also be a specified range), the delivery flow rate of the water supply W1 to the electrodeionization device 9 is increased. On the other hand, if the water level is more than the predetermined reference value, the delivery flow rate is reduced. At this time, the load (water quality × flow rate) of the water supply W1 is calculated based on the water quality information of the resistivity meter 29 and the water supply amount of the water supply pump 8. According to the load of the water supply W1 and the flow rate of the desalted water (primary pure water) W2 of the electrodeionization device 9, the operating current value of the electrodeionization device 9 is set by the control device 28. By controlling the DC power supply 9A based on this, the desalted water (primary pure water) W2 of the specified water quality can be obtained. In addition, in the second embodiment, the control of the first embodiment can also be combined.

[0051] In this way, according to the water level of the sub-tank 11, the water delivery volume of the water supply W1 supplied by the water supply pump 8 to the electrodeionization device 9 is controlled, and according to the water quality of the water supply W1, the current supplied from the DC power supply 9A to the electrodeionization device 9 is controlled, thereby optimizing the operating efficiency of the water supply pump 8 and the electrodeionization device 9, reducing the current required for the operation of the ultrapure water manufacturing device 1, and maintaining the desalted water (primary pure water) W2.

[0052] In the first and second embodiments as described above, for example, when the usage at the use point 15 is small and the water level in the sub-tank 11 is too high, and when the water supply pump 8 cannot be fully controlled by frequency conversion control alone, the primary pure water device 3 may be stopped. In particular, when there are multiple series of primary pure water devices 3, more efficient operation control can be performed by combining the increase or decrease in the number of series operated by the primary pure water device 3 with the control of the first or second embodiment.

[0053] The present invention has been described above based on the above-mentioned embodiments, but the present invention is not limited to the above-mentioned embodiments, and various modifications can be made. For example, as an applicable ultrapure water manufacturing device 1, as long as an electrodeionization device is included in the primary pure water device 3, devices of various structures can be applied. In addition, as the electrodeionization device 9, it can also be a type of device having desalted water and concentrated water in the same direction. Moreover, in the above-mentioned embodiments, although the sub-tank 11 is used as a water storage tank arranged at the rear stage of the electrodeionization device 9, as long as it is a water storage tank located at the rear stage of the electrodeionization device 9, the water level can also be measured and controlled.

[0054] Example

[0055] Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to the following examples.

[0056] (Example 1)

[0057] (Test to confirm the behavior of desalted water quality with current value fluctuation)

[0058] Test equipment

[0059] Prepared Figure 8 The test device 51 includes an ultrapure water (UPW) flow path 52, an electrodeionization device 53, a desalted water (primary pure water) flow path 54, and a concentrated water flow path 55. In addition, a carbonate ion (HCO3) flow path 56A is connected to the ultrapure water (UPW) flow path 52 via a chemical liquid pump 56A. － ) source, that is, a sodium carbonate solution tank 56, and a conductivity meter 57A is provided. In addition, a flow meter 58A is provided on the desalted water flow path 54 and is connected to a resistivity meter 59. Moreover, a flow meter 58B is provided on the concentrated water flow path 55 and is connected to a conductivity meter 57B. In addition, as the electrodeionization device 53, an Figure 3 and Figure 4 The structure shown.

[0060] In the test device as described above, a sodium carbonate solution is added from the sodium carbonate solution tank 56 to the ultrapure water (UPW) to make the carbonate concentration become 1 mg / L as the supply water W1, and the solution is treated so that the recovery rate using the electrodeionization device 53 reaches 80% (5.0 L / min for desalted water W2 and 1.2 L / min for concentrated water W5). At this time, the current supplied to the electrodeionization device 53 is continuously changed in the order of 0.1A, 0.2A, 0.4A, 1A, 2A and 4A every 100 to 200 hours, and finally continuously operated at 4A. At this time, the resistivity value of the desalted water W2 and the time-dependent change of the conductivity of the concentrated water W5 are measured. The results are shown in Table 1 together with the conductivity of the supply water W1.

[0061] [Table 1]

[0062]

[0063] As can be seen from Table 1, the water quality (conductivity) of the supply water W1 is roughly constant (about 0.16mS / m). The higher the current value, the better the water quality of the desalted water W2. Moreover, if the operating current is 0.4A or more, even if the current value is changed, a stable water quality of about 18MΩcm can be maintained. On the other hand, the concentrated water shows the following tendency: the water quality deteriorates rapidly (conductivity increases) when the current value increases, and the increase is greater as the operating current increases. This is believed to be because when the current value increases, the amount of free radicals generated by the splitting of water increases, and the carbonate ions (HCO3 － ) is increased. Furthermore, if the operation is continued at a current value of 4A, it is confirmed that the conductivity of the concentrated water tends to converge to 0.8 mS / m, which is five times the concentration value of the feed water W1.

[0064] (Example 2)

[0065] (Performance confirmation test of desalinated water quality in response to fluctuations in water supply)

[0066] Test equipment

[0067] Prepared Fig. 9 The test device 61 has the following structure: Figure 8 In the device shown, instead of the sodium carbonate solution tank 56 and the chemical pump 56A, a sodium silicate (NaSiO3) solution tank 62 is connected to the ultrapure water flow path 52 via a chemical pump 62A as a silicon dioxide (SiO2) source, and a mixed solution tank 63 of boron hydroxide (B(OH)3) and sodium carbonate is connected to the ultrapure water flow path 52 via a chemical pump 63A as a boron source.

[0068] Water supply W1

[0069] Sodium silicate solution, a mixed solution of boron hydroxide and sodium carbonate are added to ultrapure water (UPW) from the sodium silicate solution tank 62 and the mixed solution tank 63 to obtain a solution with a silica concentration of 1000 μg / L, a boron concentration of 100 μg / L and a carbonic acid concentration of 10 mg / L, respectively, as feed water W1.

[0070] Using the test apparatus and the feed water W1 as described above, the electrodeionization device was continuously operated under the following three conditions.

[0071] Operating conditions 1

[0072] The water supply W1 is set at a flow rate of 0.3m3 / h is supplied to the electrodeionization device 53, and operated for about 20 hours at a current value of 4.0A and a recovery rate of 80%. The desalted water (desalted water W2) of the electrodeionization device 53 has a silica concentration of 1.2μg / L and a boron concentration of 0.13μg / L, both of which are high removal rates of more than 99.8%.

[0073] Operating conditions 2

[0074] Next, water supply W1 is set at a flow rate of 0.24m 3 / h is supplied to the electrodeionization device 53, and operated for about 20 hours at a current value of 4.0A and a recovery rate of 80%. The desalted water (desalted water W2) of the electrodeionization device 53 has a silica concentration of 0.79μg / L and a boron concentration of 0.11μg / L, both of which are high removal rates of about 99.9%.

[0075] Operating conditions 3

[0076] Furthermore, the electrodeionization device 53 was operated for about 20 hours under the same conditions as the operation condition 1. The desalted water (desalted water W2) of the electrodeionization device 53 had a silica concentration of 1.6 μg / L and a boron concentration of 0.15 μg / L, both of which were high removal rates of about 99.8% or more.

[0077] The resistivity of the desalted water W2 and the conductivity of the concentrated water W5 were measured over time under these operating conditions 1 to 3. The results are shown together with the conductivity of the feed water W1. Fig.10 .

[0078] from Fig.10 It can be seen that, although the conductivity of the concentrated water changes by changing the amount of the supply water W1 , the desalted water W2 can maintain a stable resistivity value of about 18 MΩcm.

[0079] (Example 3)

[0080] (Test to confirm the behavior of desalinated water quality in response to fluctuations in water supply load)

[0081] The following test was carried out using the same test apparatus as in Example 2.

[0082] Water supply W1

[0083] Sodium silicate solution, boron hydroxide and sodium carbonate mixed solution were added to ultrapure water from sodium silicate solution tank 62 and mixed solution tank 63 to obtain a solution with a silica concentration of 1000 μg / L, a boron concentration of 100 μg / L and a carbonic acid concentration of 10 mg / L, respectively, as 1-fold feed water W1.

[0084] Using the above-mentioned test apparatus and the water supply W1, the electrodeionization apparatus was continuously operated under the following three conditions.

[0085] Operating conditions 1

[0086] The water supply W1 was supplied to the electrodeionization device 53 at a flow rate of 0.3 m3 / h, and operated for about 20 hours at a current value of 4.0 A and a recovery rate of 80%. The desalted water (desalted water W2) of the electrodeionization device 53 had a silica concentration of 1.6 μg / L and a boron concentration of 0.15 μg / L, both of which were high removal rates of more than 99.8%.

[0087] Operating conditions 2

[0088] Next, the water supply W1 was diluted 20 times (0.05 times the concentration) and the water flow rate was 0.3m 3 / h is supplied to the electrodeionization device 53, and operated for about 20 hours at a current value of 4.0A and a recovery rate of 80%. The desalted water (desalted water W2) of the electrodeionization device 53 has a silica concentration of 0.38μg / L and a boron concentration of 0.12μg / L, both of which are high removal rates of about 99.9%.

[0089] Operating conditions 3

[0090] Furthermore, the electrodeionization device 53 was operated for about 20 hours under the same conditions as the operation condition 1. The desalted water (desalted water W2) of the electrodeionization device 53 had a silica concentration of 1.8 μg / L and a boron concentration of 0.17 μg / L, both of which were high removal rates of about 99.8% or more.

[0091] The resistivity of the desalted water W2 and the conductivity of the concentrated water W5 were measured over time under these operating conditions 1 to 3. The results are shown together with the conductivity of the feed water W1. Fig.11 .

[0092] from Fig.11 It can be seen that, although the conductivity of the concentrated water changes by changing the ion concentration of the feed water, the desalted water W2 can maintain a stable resistivity value of about 18 MΩcm.

[0093] It can be seen from these Examples 1 to 3 that the control method of the ultrapure water production device according to the present invention can supply desalted water (primary pure water) with stable water quality even if the water supply amount, water quality, operating current value, etc. supplied to the electrodeionization device are changed.

[0094] Description of reference numerals:

[0095] 1 Ultrapure water production device

[0096] 2 Pretreatment device

[0097] 3. Primary pure water production device

[0098] 4 Secondary pure water production device (subsystem)

[0099] 5 Reverse osmosis membrane device

[0100] 6 Degassing membrane device

[0101] 7. Ultraviolet oxidation device

[0102] 8 Water supply pump

[0103] 9 Electrodeionization device

[0104] 9A DC Power Supply

[0105] 11 Sub-jar

[0106] 12. Ultraviolet oxidation device

[0107] 13 Non-regenerative mixed bed ion exchange unit

[0108] 14 Ultrafiltration (UF) membrane

[0109] 15 Use Points

[0110] 21 Liquid level switch (water level measuring unit)

[0111] 29 Resistivity meter (water quality measurement unit)

[0112] 31 Anode (electrode)

[0113] 32 cathode (electrode)

[0114] 33 Anion exchange membrane

[0115] 34 Cation exchange membrane

[0116] 35 Concentration Room

[0117] 36 Desalination Chamber

[0118] W raw water

[0119] W1 Pre-treated water (water supply)

[0120] W2 primary pure water (desalted water)

[0121] W3 Ultrapure water (secondary pure water)

[0122] W4 Concentrated water

[0123] W5 Concentrated Water

Claims

1. A control method for an ultrapure water production device, the ultrapure water production device comprising: A primary pure water system comprising a reverse osmosis membrane, an electrodeionization device, and a water supply pump disposed in the front stage of the electrodeionization device; a water storage tank, arranged at the rear stage of the electrodeionization device and equipped with a water level measurement unit; and a subsystem for further processing the primary pure water produced by the primary pure water system, wherein: The control method of the ultrapure water production device comprises: controlling the amount of water supplied to the electrodeionization device so as to keep the water level of the water storage tank measured by the water level measuring unit substantially constant; controlling concentrated water of the electrodeionization device and primary pure water as desalted water according to the amount of water supplied to the electrodeionization device; and calculating the load of the water supply according to the amount of water supplied to the electrodeionization device and the resistivity value of the water supply, setting the operating current value of the electrodeionization device according to the load of the water supply and the flow rate of the primary pure water, and controlling the operating current of the electrodeionization device based on the operating current value, Controlling the concentrated water and the desalted water of the electrodeionization device includes: keeping the flow rate of the concentrated water constant, and adjusting the flow rate of the desalted water to change the recovery rate of the electrodeionization device.

2. The control method of the ultrapure water production device according to claim 1, wherein: The electrodeionization device comprises: a cathode and an anode; a cation exchange membrane and an anion exchange membrane, which are arranged between the cathode and the anode; and a desalination chamber and a concentration chamber, which are divided and formed by the cation exchange membrane and the anion exchange membrane. The desalting chamber and the concentrating chamber are filled with ion exchangers. The electrodeionization device comprises a concentrated water introduction unit for introducing concentrated water into the concentration chamber; and a unit for introducing supply water into the desalination chamber and taking out desalted water. The concentrated water introduction unit introduces concentrated water into the concentration chamber from a side close to the desalted water outlet of the desalting chamber, and makes the concentrated water flow out from a side close to the water supply inlet of the desalting chamber.

3. The control method of the ultrapure water production device according to claim 2, wherein: The concentrated water introduction unit introduces desalted water formed by passing through the desalting chamber as concentrated water into the concentrating chamber from a side close to a desalted water outlet of the desalting chamber, and flows out from a side close to a water supply inlet of the desalting chamber.

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