Pure water production system and pure water production method

Abstract

To provide a pure water production system and a pure water production method capable of achieving high purity of water quality of treated water and suppressing increase in production cost.SOLUTION: A pure water production system 1 includes a reverse osmosis membrane device 4, an electric deionized water production device 5 arranged in a later stage of the reverse osmosis membrane device 4, and a control device 8 for controlling treatment conditions of the reverse osmosis membrane device 4. The control device 8 controls any one or more of pH, recovery rate, pressure, and water temperature of water to be treated to the reverse osmosis membrane device 4 so that removal rate of a specific substance of the electric deionized water production device 5 is equal to or less than a threshold value, and concentration of the specific substance of the treated water of the electric deionized water production device 5 is equal to or less than a specified value, and specific resistance is equal to or more than a specified value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pure water production system and a pure water production method. [Background technology]

[0002] Conventionally, ultrapure water has been used for cleaning semiconductors, etc., but as semiconductors become more sophisticated, there is a demand for even higher purity pure water and ultrapure water. As described in Patent Document 1, a pure water production system is composed of a reverse osmosis membrane device (RO device), an electrodeionized water production device (EDI device), etc. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 11-244853 Summary of the Invention [Problem to be solved by the invention]

[0004] While there is a demand for higher purity of treated water, there is also a demand for cost reduction in ultrapure water production. To achieve high water purity in EDI equipment, it is necessary to increase the current applied to the EDI equipment. However, increasing the current applied to the EDI equipment increases manufacturing costs.

[0005] An object of the present invention is to provide a pure water production system and a pure water production method that can achieve high water purity of treated water while suppressing increases in production costs. [Means for solving the problem]

[0006] The pure water production system of the present invention includes a reverse osmosis membrane device, an electrodeionized water production device arranged downstream of the reverse osmosis membrane device, and a control device that controls the treatment conditions of the reverse osmosis membrane device, and is characterized in that the control device controls one or more of the pH, recovery rate, pressure, and water temperature of the water to be treated to the reverse osmosis membrane device so that the removal rate of a specific substance in the electrodeionized water production device is below a threshold, and so that the concentration of the specific substance in the treated water from the electrodeionized water production device is below a specified value and the resistivity is above a specified value. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a pure water production system and a pure water production method that can realize high purity of treated water and suppress an increase in production costs. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic configuration diagram of a pure water manufacturing system according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a schematic configuration diagram of a modified example of the pure water producing system shown in FIG. [Figure 3] 1. FIG. 4 is a schematic diagram showing another modified example of the pure water producing system shown in FIG. [Figure 4] FIG. 1 is a schematic configuration diagram of a pure water manufacturing system according to a second embodiment of the present invention. [Figure 5] FIG. 10 is a schematic configuration diagram of a pure water manufacturing system according to a third embodiment of the present invention. [Figure 6] FIG. 10 is a schematic configuration diagram of a pure water manufacturing system according to a fourth embodiment of the present invention. [Figure 7] FIG. 10 is a schematic configuration diagram of a pure water manufacturing system according to a fifth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. [First embodiment] FIG. 1 is a schematic diagram of a pure water production system according to a first embodiment of the present invention. In this embodiment, the pure water production system 1 includes a pump 3, a reverse osmosis membrane device (RO device) 4, and an electrodeionized water production device (EDI device) 5, connected in this order along the flow direction of the water to be treated. The water to be treated flowing through a water supply pipe 21 is pressurized by the pump 3 and supplied to the RO device 4. The water to be treated supplied to the RO device 4 is passed through a reverse osmosis membrane to produce concentrated water and permeated water. A concentrated water pipe 22 is connected to the concentration chamber of the RO device 4, and a permeated water pipe 23 is connected to the permeated chamber. The concentrated water flows through the concentrated water pipe 22, and the permeated water flows through the permeated water pipe 23. The concentrated water pipe 22 is equipped with a back-pressure valve 7. The permeated water from the RO device 4 is supplied to the EDI device 5 via the permeated water pipe 23 as the water to be treated, where ionic components, boron, and the like are removed from the water to be treated. A chemical injection system 2 is installed upstream of the pump 3. The chemical injection equipment 2 includes a chemical tank, a chemical injection pump 2A, and a chemical injection pipe 2B. The chemical injection pipe 2B is connected to a water supply pipe 21 upstream of the pump 3, and the chemical is injected from the chemical tank via the chemical injection pipe 2B into the water flowing through the water supply pipe 21. The pure water producing system 1 of this embodiment also includes a control device 8 that controls the treatment conditions of the RO device 4, and a measuring device 6 that is connected to sampling lines 24, 25 branching off from the pipes upstream and downstream of the EDI device 5 and measures the impurity concentration of the water supplied via the sampling lines 24, 25. In each drawing, solid lines indicate portions connected to allow liquids, gases, etc. to flow, and dashed lines indicate portions through which power or electrical signals can be transmitted without the flow of liquids, gases, etc.

[0010] A key feature of the pure water production system 1 of the present invention is the control operation of the control device 8. In the embodiment shown in FIG. 1, the measurement device 6 measures the boron concentration of the water to be treated before EDI treatment, which is supplied to the EDI device 5, and the boron concentration of the treated water after EDI treatment, which is discharged from the EDI device 5. The measurement device 6 then calculates the boron removal rate of the EDI device 5 based on the measured boron concentrations. The control device 8 inputs the boron removal rate of the EDI device 5 calculated by the measurement device 6 and, based on the input boron removal rate, controls the treatment conditions of the RO device 4, i.e., in the embodiment shown in FIG. 1, controls the operation of the chemical injection system 2 to adjust the pH of the water to be treated supplied to the RO device 4. Note that in this specification, the liquid supplied to a certain device and before treatment by that device is referred to as the water to be treated, and the treated liquid discharged from that device after treatment is referred to as the treated water. The boron removal rate can be calculated using the following formula: Boron removal rate [%] = (1 - boron concentration in treated water / boron concentration in untreated water) x 100

[0011] The technical significance of this embodiment will be explained. The primary purpose of the pure water production system 1 is to reduce the boron concentration in the treated water discharged from the EDI device 5 after EDI treatment. Generally, increasing the current applied to the EDI device 5 increases the boron removal rate of the EDI device 5 and reduces the boron concentration in the treated water after EDI treatment. However, the inventors discovered that once the boron removal rate reaches a certain level, a stage is reached where further increases in the applied current do not significantly improve the treatment capacity or increase the boron removal rate. That is, once the boron removal rate of the EDI device 5 reaches a certain threshold, further increases in the applied current do not significantly increase the boron removal rate, resulting in poor energy efficiency. Furthermore, increasing the supplied current increases power consumption and costs, but does not significantly improve the boron removal effect, resulting in poor cost-effectiveness. That is, the inventors discovered that in order to operate the EDI device 5 to remove boron in an energy-efficient and cost-effective manner, it is preferable to operate the EDI device 5 within a range where the boron removal rate is below a threshold. We experimentally found that this threshold is 99.7%.

[0012] Thus, it was found that the energy efficiency and cost-effectiveness of EDI treatment are excellent when the boron removal rate of the EDI device 5 is below a threshold value (99.7%). However, adjusting the treatment conditions of the EDI device 5 so that the boron removal rate is below 99.7% would reduce the boron removal capacity of the EDI device 5, potentially increasing the boron concentration in the treated water after EDI treatment, which is undesirable because it deviates from the original purpose of the pure water production system 1. Therefore, it is desirable to operate the EDI device 5 within a boron removal rate range of 99.7% or less to achieve high energy efficiency and high cost-effectiveness while lowering the boron concentration in the treated water after EDI treatment. The boron concentration of the treated water after EDI treatment is preferably 50 ng / L (ppt) or less, and the resistivity is preferably 17 MΩ·cm or more. Therefore, the specified value for boron concentration is 50 ng / L (ppt), and the specified value for resistivity is 17 MΩ·cm. From this perspective, in the present invention, rather than the treatment conditions of the EDI device 5 itself, the treatment conditions of the RO device 4 located upstream of the EDI device 5, such as one or more of the pH, recovery rate, pressure, and water temperature of the water being treated by the RO device 4, are controlled to keep the boron removal rate of the EDI device 5 below a threshold value (99.7%), and the EDI device 5 is operated so that the boron concentration of the treated water from the EDI device 5 is below a specified value (50 ng / L (ppt)) and the resistivity is above a specified value (17 MΩ·cm). Note that, in order to maintain the boron removal capacity of the EDI device 5, the boron removal rate of the EDI device 5 is preferably 90% or higher. If the boron concentration of the treated water from the EDI device 5 exceeds 50 ng / L (ppt), the current applied to the EDI device 5 is increased for operation. However, in this case, the power consumption of the EDI device 5 must be kept below a threshold value (350 W·h / m 3 ) in the range not exceeding the current applied to the EDI device 5.

[0013] In the embodiment shown in FIG. 1 , when the control device 8 detects that the boron removal rate of the EDI device 5 calculated by the measurement device 6 exceeds 99.7%, the control device 8 adjusts the pH of the water being treated by the RO device 4 so that the boron removal rate of the EDI device 5 is 99.7% or less, the boron concentration of the water treated by the EDI device 5 is 50 ng / L (ppt) or less, and the resistivity is 17 MΩ·cm or more. Specifically, the control device 8 controls the amount of chemical solution injected from the chemical solution injection equipment 2 upstream of the RO device 4 to inject a pH adjuster (an alkaline agent in this embodiment) into the water being treated and supplied to the RO device 4 to increase the pH. This improves the boron removal performance (boron removal rate) of the RO device 4, and therefore, when the current applied to the EDI device 5 is constant, the boron concentration of the water treated by the EDI device 5 decreases. Therefore, it becomes possible to operate the EDI device 5 with a lower boron removal rate by reducing the current applied to the EDI device 5 according to the degree of decrease in the boron concentration of the treated water when the applied current is constant. The current applied to the EDI device 5 may be adjusted by the control device 8. In this case, for example, the control device 8 calculates the current value by taking the difference between the decreased boron concentration of the treated water of the EDI device 5 and the specified value of the boron concentration.

[0014] By controlling the amount of chemical solution injected from the chemical solution injection equipment 2 so that the boron removal rate of the EDI device 5 is 99.7% or less, the EDI device 5 can be operated with good energy efficiency and cost-effectiveness. Furthermore, by controlling the amount of chemical solution injected from the chemical solution injection equipment 2 so that the boron removal rate of the EDI device 5 is, for example, 99.5% or more and 99.7% or less, the boron removal rate of the entire pure water production system 1, including the RO device 4 and the EDI device 5, can be maintained high. Because excessive injection of pH adjuster reduces the resistivity of the EDI-treated water and increases the cost of producing fresh water, it is preferable to adjust the pH to a range of 9.2 to 10.0. Note that even if a pH adjuster is injected into the water to be treated supplied to the RO device 4 to raise the pH, other treatment conditions of the RO device 4 (recovery rate, temperature, pressure) do not change.

[0015] Although not shown in detail, the RO device 4 included in the pure water production system of the present invention uses a single pressure vessel (vessel) filled with one or more RO membrane elements, or a combination of multiple pressure vessels. There are no limitations on the configuration of multiple pressure vessels combined, and a configuration in which multiple pressure vessels are combined in series or parallel in multiple stages may be used. The type of RO membrane element used can be selected without limitation depending on the intended use, the quality of the water to be treated, the desired quality of the treated water, the recovery rate, etc. Specifically, any of ultra-low pressure, ultra-low pressure, low pressure, medium pressure, and high pressure RO membrane elements may be used.

[0016] The EDI device 5 is capable of producing deionized water without the need for separate regeneration of the ion exchange resin. Specifically, the EDI device 5 has a deionization compartment formed by filling an ion exchanger (anion exchanger and / or cation exchanger) made of an ion exchange resin or the like between a cation exchange membrane that allows only cations (positive ions) to pass through and an anion exchange membrane that allows only anions (negative ions) to pass through. Concentration compartments are disposed outside the cation exchange membrane and the anion exchange membrane, and the basic configuration, consisting of a deionization compartment and two concentration compartments on either side of the deionization compartment, is disposed between an anode and a cathode. The EDI device 5 is operated by applying a current between the anode and the cathode while passing the water to be treated through the deionization compartment. However, the specific structure of the EDI device 5 is not particularly limited in the present invention, and any structure may be used.

[0017] In the modification of this embodiment shown in FIG. 2 , when the control device 8 detects that the boron removal rate of the EDI device 5 calculated by the measuring device 6 exceeds 99.7%, the control device 8 adjusts the recovery rate of the RO device 4 to 99.7% or less, and to ensure that the boron concentration of the treated water from the EDI device 5 is 50 ng / L (ppt) or less and the resistivity is 17 MΩ·cm or more. Specifically, the inverter value of the pump 3 connected upstream of the RO device 4 and the back-pressure valve 7 connected to the RO device 4 are adjusted to increase the recovery rate of the RO device 4. For example, the recovery rate of the RO device 4 can be increased by increasing the inverter value of the pump 3 to throttle the back-pressure valve 7, or by throttling the back-pressure valve 7 without changing the inverter value of the pump 3, or by increasing the inverter value of the pump 3 without changing the opening of the back-pressure valve 7. The recovery rate of the RO device 4 is the ratio of the amount of treated water (permeate) passing through the RO device 4 to the amount of water to be treated (raw water) supplied to the RO device 4. By gradually increasing this recovery rate by any amount, the ion concentration in the treated water (permeate) of the RO device 4 increases, thereby decreasing the boron removal rate of the EDI device 5. Furthermore, if the boron removal rate of the EDI device 5 decreases and the boron concentration of the treated water from the EDI device 5 becomes greater than 50 ng / L (ppt) or the resistivity becomes less than 17 MΩ·cm, conversely, by lowering the recovery rate of the RO device 4 and decreasing the ion concentration in the treated water from the RO device 4, it becomes possible to maintain a boron concentration of 50 ng / L (ppt) or less and a resistivity of 17 MΩ·cm or more in the treated water while maintaining the boron removal rate of the EDI device 5 at 99.7% or less.

[0018] By adjusting the inverter value of the pump 3 and the back pressure valve 7 so that the boron removal rate of the EDI device 5 is 99.7% or less, the EDI device 5 can be operated in an energy-efficient and cost-effective manner. Moreover, by controlling the inverter value of the pump 3 and the back pressure valve 7 so that the boron removal rate of the EDI device 5 is, for example, 99.5% or more and 99.7% or less, the boron removal rate of the entire pure water producing system 1, including the RO device 4 and the EDI device 5, can be maintained high. Note that the pure water producing system 1 shown in FIG. 2 does not need to be equipped with the chemical solution injection equipment 2 shown in FIG. 1.

[0019] In a configuration similar to the modified example of this embodiment shown in FIG. 2 , when the control device 8 detects that the boron removal rate of the EDI device 5 calculated by the measurement device 6 exceeds 99.7%, the control device 8 can adjust the pressure applied to the RO device 4 to make the boron removal rate of the EDI device 5 99.7% or less, and to make the boron concentration of the treated water from the EDI device 5 50 ng / L (ppt) or less and the resistivity 17 MΩ·cm or more. In this example, the inverter value of the pump 3 connected upstream of the RO device 4 and the backpressure valve 7 connected to the RO device 4 are adjusted to reduce the pressure applied to the RO device 4. The reduction in pressure applied to the RO device 4 increases the ion concentration in the treated water from the RO device 4, thereby reducing the boron removal rate of the EDI device 5. Furthermore, if the boron removal rate of EDI device 5 decreases and the boron concentration of the treated water becomes greater than 50 ng / L (ppt) or the resistivity becomes less than 17 MΩ·cm, the pressure applied to RO device 4 can be increased to lower the ion concentration in the treated water from RO device 4. This makes it possible to maintain a boron concentration of 50 ng / L (ppt) or less and a resistivity of 17 MΩ·cm or more in the treated water while maintaining the boron removal rate of EDI device 5 at 99.7% or less.

[0020] By adjusting the inverter value of the pump 3 and the back pressure valve 7 so that the boron removal rate of the EDI device 5 is 99.7% or less, the EDI device 5 can be operated in an energy-efficient and cost-effective manner. Moreover, by controlling the inverter value of the pump 3 and the back pressure valve 7 so that the boron removal rate of the EDI device 5 is, for example, 99.5% or more and 99.7% or less, the boron removal rate of the entire pure water production system 1, including the RO device 4 and the EDI device 5, can be maintained high.

[0021] In a modification of this embodiment shown in FIG. 3 , when the control device 8 detects that the boron removal rate of the EDI device 5 calculated by the measuring device 6 exceeds 99.7%, the control device 8 adjusts the temperature of the water to be treated supplied to the RO device 4 so that the boron removal rate of the EDI device 5 is 99.7% or less, and the boron concentration of the water treated by the EDI device 5 is 50 ng / L (ppt) or less and the resistivity is 17 MΩ·cm or more. Specifically, a heat exchanger 9 is connected upstream of the pump 3 of the pure water production system 1, and a valve 10 that adjusts the inflow rate of a heat source or a cooling source is connected to the heat exchanger 9. In this pure water production system 1, when the control device 8 detects that the boron removal rate of the EDI device 5 calculated by the measuring device 6 exceeds 99.7%, the control device 8 adjusts the valve 10 connected to the heat exchanger 9 upstream of the RO device 4 to control the inflow rate of the heat source or the cooling source flowing into the heat exchanger 9, thereby raising the temperature of the water to be treated. As the temperature of the water to be treated increases, the ion concentration in the treated water from the RO device 4 increases, thereby lowering the boron removal rate of the EDI device 5. If the boron removal rate of the EDI device 5 decreases and the boron concentration of the treated water becomes greater than 50 ng / L (ppt) or the resistivity becomes less than 17 MΩ·cm, conversely, by lowering the temperature of the water to be treated and lowering the ion concentration in the treated water from the RO device 4, it becomes possible to maintain a boron concentration of 50 ng / L (ppt) or less and a resistivity of 17 MΩ·cm or more in the treated water while maintaining a boron removal rate of 99.7% or less from the EDI device 5.

[0022] By adjusting the valve 10 connected to the heat exchanger 9 so that the boron removal rate of the EDI device 5 is 99.7% or less, the EDI device 5 can be operated in an energy-efficient and cost-effective manner. Moreover, the boron removal rate of the entire pure water production system 1, including the RO device 4 and the EDI device 5, can be maintained high. The pure water production system 1 shown in FIG. 3 does not need to be equipped with the chemical injection equipment 2 shown in FIG. 1.

[0023] Table 1 shows the experimental results of specific examples and comparative examples of the embodiment shown in FIG.

[0024] [Table 1]

[0025] According to the experimental results of Examples 1 to 4 shown in Table 1, by increasing the pH of the water to be treated supplied to the RO device 4 (pH = 9.2 to 10.0) and setting the boron removal rate of the EDI device 5 to 99.7% or less, the power consumption of the EDI device 5 can be kept low (power consumption = 155 W·h / m 3 ~193W·h / m 3 ), the boron removal rate of the entire pure water production system 1 can be maintained high (boron removal rate = 99.8% to 99.9%). As a result, the boron concentration of the treated water from the EDI device 5 can be reduced (boron concentration = 20 ppt to 45 ppt). Note that the units of the Na concentration and boron concentration of the water to be treated and the treated water from the RO device 4 listed in the table are μg / L (ppb). The unit of the boron concentration of the treated water from the EDI device 5 is ng / L (ppt). The power consumption of the EDI device 5 is the power consumption per treatment flow rate, and is a value calculated based on the following formula (unit: W·h / m 3 ) are shown. Power consumption per processed flow rate of EDI equipment = (voltage x current) ÷ processed flow rate

[0026] According to the experimental results of Comparative Examples 1 and 2 shown in Table 1, when the pH of the water to be treated supplied to the RO device 4 is set independently of the boron removal rate of the EDI device 5, and the current setting value of the EDI device 5 is increased, and the boron removal rate becomes greater than 99.7% (boron removal rate = 99.76%), the power consumption of the EDI device 5 increases (power consumption = 353 W·h / m 3 ~394W·h / m 3 Although the boron removal rate of the entire pure water production system 1 is high (boron removal rate = 99.8% to 99.9%), the high power consumption of the EDI device 5 results in low energy efficiency and high costs. Furthermore, Comparative Example 3 is not preferable because the resistivity is reduced due to sodium leakage.

[0027] The recovery rate of the RO devices 4 in Examples 1 to 4 and Comparative Examples 1 to 3 shown in Table 1 was 90%, and the boron removal rate of the RO devices 4 in Examples 1 to 4 was 45% to 77%. The boron removal rate of the RO devices 4 in Comparative Examples 1 to 3 was 28% to 81%.

[0028] Table 2 shows the experimental results of specific examples and comparative examples of the embodiment shown in FIG.

[0029] [Table 2]

[0030] According to the experimental results of Examples 5 to 8 shown in Table 2, by increasing the recovery rate of the water to be treated supplied to the RO device 4 (recovery rate = 60% to 90%) and setting the boron removal rate of the EDI device 5 to 99.7% or less, it was possible to keep the power consumption of the EDI device 5 low (power consumption = 162 W·h / m 3 ~183W·h / m 3 ), the boron removal rate of the entire pure water production system 1 can be maintained at a high level (boron removal rate = 99.8% to 99.9%).

[0031] In Comparative Example 4 shown in Table 2, the recovery rate of RO device 4 was set independently of the boron removal rate of EDI device 5, and the boron concentration in the treated water from EDI device 5 was high (boron concentration = 70 ppt), which did not meet the required treated water quality. In other words, the pure water production system of Comparative Example 4 was unable to produce highly pure water.

[0032] The pH of the water to be treated supplied to the RO device 4 in Examples 5 to 8 and Comparative Example 4 shown in Table 2 was 9.2, and the boron removal rate of the RO device 4 in Examples 5 to 8 was 45% to 60%. The boron removal rate of the RO device 4 in Comparative Example 4 was 38%.

[0033] [Second embodiment] FIG. 4 is a schematic diagram of a pure water production system 1 according to a second embodiment of the present invention. The pure water production system 1 of this embodiment includes multiple RO devices 4A and 4B. The multiple RO devices 4A and 4B are connected in series, and treated water from the first RO device 4A is treated again by the second RO device 4B. The number of RO devices is not limited to two and may be three or more. As in the first embodiment, the control device 8 of this embodiment controls the final RO device (RO device 4B in the configuration shown in FIG. 4) to achieve a boron removal rate of 99.7% or less, a boron concentration of the treated water from the EDI device 5 of 50 ng / L (ppt) or less, and a resistivity of 17 MΩ·cm or more. The remaining configuration is the same as in the first embodiment, and therefore a description thereof will be omitted. In this embodiment, the recovery rate, pressure, or water temperature of the final RO device 4B may be controlled to operate the EDI device 5 within a range where the boron removal rate is 99.7% or less.

[0034] [Third embodiment] FIG. 5 is a schematic diagram of a pure water production system 1 according to a third embodiment of the present invention. The pure water production system 1 of this embodiment is provided with a degassing device (decarbonation device) 11 upstream of the RO device. In this configuration, similar to the example shown in FIG. 1, the degassing device 11 removes dissolved gases, primarily carbon dioxide, from the water to be treated before adjusting the pH of the water to be treated by the RO device. This is to achieve a boron removal rate of 99.7% or less in the EDI device 5, a boron concentration of 50 ng / L (ppt) or less in the treated water, and a resistivity of 17 MΩ·cm or more in the treated water. This allows for more accurate adjustment of the pH of the water to be treated by the RO device (e.g., to a pH of 9.2 to 10.0), and allows for accurate control of the boron removal rate of the RO device. As shown in FIG. 5, when multiple RO devices are provided as in the second embodiment, a degassing device 11 is placed before the final RO device (RO device 4B in the configuration shown in FIG. 5) and the pH of the water to be treated in the final RO device (RO device 4B in the configuration shown in FIG. 5) is adjusted to make the boron removal rate of the EDI device 5 99.7% or less. The other configurations are the same as those in the first embodiment, and therefore their explanations are omitted. In this embodiment, the recovery rate, pressure, or water temperature of the final RO device 4B may be controlled to operate the EDI device 5 in a range where the boron removal rate is 99.7% or less.

[0035] [Fourth embodiment] FIG. 6 is a schematic diagram of a pure water production system 1 according to a fourth embodiment of the present invention. The pure water production system 1 of this embodiment has multiple EDI devices 5A, 5B (two in the illustrated example). The multiple EDI devices 5A, 5B are arranged in series, and the treated water from the previous EDI device 5A is treated again by the subsequent EDI device 5B. The number of EDI devices is not limited to two and may be three or more. The control device 8 of this embodiment controls the treatment conditions (e.g., pH of the water being treated) of the RO device 4 located upstream of the final EDI device 5B so that the boron removal rates of each of the multiple EDI devices 5A, 5B are all below a threshold value (99.7%), and the boron concentration of the treated water from the final EDI device 5B is 50 ng / L (ppt) or less and the resistivity is 17 MΩ·cm or more. The remaining configuration is similar to that of the first embodiment, and therefore will not be described further. In this embodiment, the EDI devices 5A, 5B may be operated so that the boron removal rate is 99.7% or less by controlling the recovery rate, pressure, or water temperature of the RO device 4. Furthermore, when multiple RO devices 4 are provided and an RO device 4 is disposed upstream of each of the EDI devices 5A, 5B, the treatment conditions of each RO device 4 may be individually controlled so that the boron removal rate of each of the EDI devices 5A, 5B is 99.7% or less, and the boron concentration of the treated water from each of the EDI devices 5A, 5B is 50 ng / L (ppt) or less and the resistivity is 17 MΩ cm or more. Furthermore, a resin device (not shown) for removing boron may be installed downstream of the EDI devices 5A, 5B to further reduce the boron concentration of the treated water.

[0036] In the first to fourth embodiments described above, the measuring device 6 determines the boron removal rate by measuring the boron concentration in the water to be treated supplied to the EDI device 5 and the boron concentration in the treated water discharged from the EDI device 5. However, the boron concentrations in the water to be treated and the treated water in the EDI device 5 may be measured separately and input to the control device 8, which then determines the boron removal rate.

[0037] In the first to fourth embodiments described above, the EDI device 5 is operated to achieve a boron removal rate of 99.7% or less, and the treatment conditions of the RO device 4 are controlled to obtain good treated water quality. Raw water with a boron concentration of 20 μg / L (ppb) to 200 μg / L (ppb) is supplied to the RO device 4, treated, and then passed through the EDI device 5. The treated water is controlled to have a boron concentration of 50 ng / L (ppt) or less and a resistivity of 17 MΩ·cm or more, thereby providing high-purity EDI-treated water at low cost. One or more of the pH, recovery rate, pressure, and water temperature of the treated water from the RO device 4 can be adjusted to satisfy both the boron removal rate and treated water quality of the EDI device 5. This enables efficient boron removal through EDI treatment, resulting in the production of high-quality pure water at low cost. In particular, if the boron removal rate of the RO device 4 located in the upstream stage of the EDI device 5 is 40% to 80%, the boron in the treated water of the EDI device 5 is sufficiently reduced.

[0038] The magnitude of the current supplied to the EDI device 5 is not particularly limited as long as it is within a range in which the boron removal rate is 99.7% or less. However, if the current value is reduced too much, the quality of the water treated by the EDI device 5 will deteriorate, so it is preferable to determine the lower limit of the current value so as not to cause a deterioration in the quality of the water treated by the EDI device 5.

[0039] The pure water production system of the present invention can also sufficiently reduce water quality factors other than boron concentration, such as resistivity, hardness, carbonate concentration, and silica concentration. For example, the silica concentration in the treated water of the RO device 4 can be reduced to 0.5 μg / L (ppb) to 20 μg / L (ppb), and the silica concentration in the treated water of the EDI device 5 can be reduced to 50 ng / L (ppt) or less. In this way, the treatment conditions of the RO device 4 can be controlled based on the removal rate of a specific substance contained in the water to be treated by the EDI device 5. This specific substance may be boron, silica, or another substance, as described above.

[0040] [Fifth embodiment] 7 is a schematic diagram of a pure water manufacturing system 1 according to a fifth embodiment of the present invention. In the pure water manufacturing system 1 of this embodiment, a power measuring device 12 is connected to the EDI device 5 instead of the measuring device 6 in the configuration shown in FIG. 1. The power measuring device 12 calculates that the power consumption of the EDI device 5 is 350 W·h / m 3 When it is detected that the power consumption of the EDI device 5 has exceeded the threshold value (for example, 350 W·h / m), the control device 8 controls the treatment conditions (for example, the pH of the water to be treated) of the RO device 4 located upstream of the EDI device 5, and reduces the power consumption of the EDI device 5 to the threshold value (for example, 350 W·h / m) in the same manner as in the embodiment shown in FIG. 3 ) or less, and the boron concentration of the treated water from the EDI device 5 is adjusted to 50 ng / L (ppt) or less and the resistivity to 17 MΩ·cm or more. The other configurations are the same as those of the first embodiment, so a description thereof will be omitted. In this embodiment, the control device 8 controls the recovery rate, pressure, or water temperature of the RO device 4, thereby reducing the power consumption of the EDI device 5 to 350 W·h / m 3 In this embodiment, the boron concentration of the treated water that has passed through the EDI device 5 can be adjusted to 50 ng / L (ppt) or less and the resistivity to 17 MΩ·cm or more, so that EDI-treated water of high purity can be supplied at low cost. Instead of using the power measuring device 12, the power consumption of the EDI device 5 can be measured by reading the displayed value of the DC power source connected to the EDI device 5. 3 It is also possible to control the treatment conditions (for example, pH of the water to be treated) of the RO device 4 located upstream of the EDI device 5 so that they are as follows.

[0041] 2 to 6, as in the fifth embodiment, the power consumption of the EDI device 5 can be calculated as 350 W·h / m by connecting a power measuring device 12 (not shown) to the EDI device 5 instead of the measuring device 6 or by reading the displayed value of the DC power source connected to the EDI device 5. 3 It is also possible to control the treatment conditions (for example, pH of the water to be treated) of the RO device 4 located upstream of the EDI device 5 so that they are as follows.

[0042] In the present invention, the EDI device 5 consumes 350 W·h / m3 The operation method described below also includes controlling the treatment conditions of the RO device 4 and then adjusting the current applied to the EDI device 5 to an appropriate level.

[0043] When a degassing device 11 is provided in the pure water producing system of the present invention, as in the third embodiment, the position and number of the degassing device 11 can be arbitrarily determined. The degassing device 11 may be installed upstream of the RO device 4, or an additional degassing device 11 may be installed downstream of the RO device 4. A single or multiple degassing device 11 may be installed between the RO device 4 and the EDI device 5. Furthermore, a single or multiple degassing device 11 may be installed upstream and downstream of the EDI device 5. The pure water producing system 1 of the present invention may also include an ultraviolet oxidation device, a cartridge polisher (CP), a Pd catalyst-supported resin (an ion exchange resin supported with a platinum group metal catalyst such as palladium or platinum), and other components (not shown). Furthermore, depending on the treatment conditions of the RO device 4 controlled by the control device 8 (at least one of the pH, recovery rate, pressure, and temperature of the water to be treated), it is possible to add or omit necessary components from the configurations shown in FIGS. 1 to 7 .

[0044] The pure water production system 1 described above may be used as an independent system or as part of an ultrapure water production system. For example, the pure water production system of the present invention may be used as a primary pure water production system located between a pretreatment system and a secondary pure water production system of an ultrapure water production system. [Explanation of symbols]

[0045] 1. Pure water production system 2 Chemical injection equipment 3. Pump 4,4A,4B Reverse osmosis membrane device (RO device) 5, 5A, 5B Electrodeionized Water Production Equipment (EDI Equipment) 6. Measuring equipment 7 Back pressure valve 8 Control Device 9 Heat exchanger 10 valves 11 Degassing device (decarbonation device) 12 Power measurement device

Claims

1. a reverse osmosis membrane device; an electrodeionized water production device disposed downstream of the reverse osmosis membrane device; and a control device that controls treatment conditions of the reverse osmosis membrane device, The control device controls one or more of the pH, recovery rate, pressure, and water temperature of the water to be treated in the reverse osmosis membrane device so that the removal rate of a specific substance in the electrodeionization water production device is below a threshold, and the concentration of the specific substance in the treated water from the electrodeionization water production device is below a specified value and the resistivity is above a specified value.

2. 2. The water purification system according to claim 1, wherein the removal rate of the specific substance is a boron removal rate.

3. The water purification system of claim 2 , wherein the threshold value is 99.7%.

4. 4. The pure water producing system according to claim 2, wherein at least one of the pH, recovery rate, pressure, and water temperature of the water to be treated in the reverse osmosis membrane device is controlled so that the boron concentration of the treated water from the electrodeionized water producing device is 50 ng / L or less and the resistivity is 17 MΩ cm or more.

5. a reverse osmosis membrane device; an electrodeionized water production device disposed downstream of the reverse osmosis membrane device; and a control device that controls treatment conditions of the reverse osmosis membrane device, The control device is configured to control the power consumption of the electrodeionized water production device to be 350 W·h / m 3 and controlling the treatment conditions of the reverse osmosis membrane device so that the boron concentration of the treated water from the electrodeionization water production device is 50 ng / L or less and the resistivity is 17 MΩ cm or more.

6. A pure water production system including a reverse osmosis membrane device and an electrodeionized water production device disposed downstream of the reverse osmosis membrane device is used, setting one or more of the pH, recovery rate, pressure, and water temperature of the water to be treated in the reverse osmosis membrane device so that the removal rate of a specific substance in the electrodeionization water production device is equal to or less than a threshold value, and so that the concentration of the specific substance in the treated water from the electrodeionization water production device is equal to or less than a specified value and the specific resistance is equal to or greater than a specified value, and operating the reverse osmosis membrane device; A method for producing pure water, comprising: supplying the liquid that has passed through the reverse osmosis membrane device to the electrodeionized water production apparatus; and operating the electrodeionized water production apparatus so that the removal rate of the specific substance is below a threshold value, and the concentration of the specific substance in the treated water from the electrodeionized water production apparatus is below a specified value and the resistivity is above a specified value.

7. 7. The method for producing pure water according to claim 6, wherein the removal rate of the specific substance is a removal rate of boron.

8. 8. The method for producing pure water according to claim 7, wherein the threshold value is 99.7%.

9. 9. The method for producing pure water according to claim 7, wherein one or more of the pH, recovery rate, pressure, and water temperature of the water to be treated in the reverse osmosis membrane device are set so that the boron concentration of the treated water from the electrodeionized water production device is 50 ng / L or less and the resistivity is 17 MΩ cm or more.

10. A pure water production system including a reverse osmosis membrane device and an electrodeionized water production device disposed downstream of the reverse osmosis membrane device is used, The power consumption of the electrodeionized water production device is 350 W·h / m 3 and operating the reverse osmosis membrane device under treatment conditions set so that the boron concentration of the treated water from the electrodeionization water production device is 50 ng / L or less and the specific resistance is 17 MΩ cm or more; The liquid that has permeated the reverse osmosis membrane device is supplied to the electrodeionized water production device, and the power consumption of the electrodeionized water production device is 350 W·h / m 3 and operating the electrodeionized water production apparatus so that the boron concentration of the treated water from the electrodeionized water production apparatus is 50 ng / L or less and the resistivity is 17 MΩ cm or more.

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