JP6040789B2 - Pure water production method and apparatus - Google Patents

Description

  The present invention relates to a pure water production method and a pure water production device using an electric deionization apparatus, and more particularly to a pure water production method and apparatus for preventing silica accumulation in an electric deionization apparatus.

  A method and apparatus for producing pure water by deionizing raw water with an electric deionization apparatus are used in various industries such as semiconductor manufacturing factory, liquid crystal manufacturing factory, pharmaceutical industry, food industry, electric power industry, etc. Etc. (for example, Patent Documents 1 to 5).

  In the case of deionizing with an electric deionizer, the removal performance of ions having a low degree of ion dissociation such as silica and boron is low. Therefore, Patent Document 1 describes that the silica concentration in the feed water to the electric deionization apparatus is 500 ppb or less by treating the raw water with a reverse osmosis membrane apparatus (RO apparatus) provided in multiple stages. . Patent Document 2 describes that the removal rate of silica is improved by returning the cathode water of the electric deionization device to the inflow side of the concentration chamber. In Example 1 of Patent Document 2, the silica concentration of raw water is 490 μg / L.

  Patent Document 3 discloses that raw water is treated with a reverse osmosis membrane, then anion exchange treatment with an anion exchange resin, and then passed through an electrical deionization device to prevent scale generation in the electrical deionization device. Is described. In paragraph 0031 of Patent Document 3, it is described that silica is removed when an OH type anion exchange resin is used as an anion exchange resin.

  Patent Document 4 describes that raw water is deturbed and degassed, then passed through an anion exchange resin tower, then RO-treated, and then passed through an electric deionizer.

  In Patent Document 5, water having a silica and boron concentration lower than that of raw water is passed through a concentration chamber of an electric deionization apparatus in a direction opposite to the direction of running water in the demineralization chamber, so that silica and boron are advanced. It is described to be removed.

JP 2000-61271 A JP-A-11-165176 JP2001-219161 JP-A-11-262771 JP2002-205069

  The electric deionizer is operated by controlling the applied voltage so that the current density is constant. When the silica concentration in the raw water is high, silica accumulates in the ion exchange resin in the electric deionizer, increasing the electrical resistance and increasing the operating voltage. If the amount of accumulated silica is further increased, the current density may be reduced, and the quality of the treated water may be deteriorated.

  In Patent Document 1, the raw water is treated with a two-stage or three-stage RO device to reduce the silica concentration in the water supply of the electric deionization device. However, providing the RO device in multiple stages in this way is costly. In addition, when the silica concentration of the raw water is high and the pH is low, the silica concentration may not be sufficiently lowered even if the RO apparatus is installed in multiple stages.

  In this case, when the pH of the RO water supply is increased (for example, 9 to 10 or more), the removal rate of silica with RO may be increased, which may be used. However, since calcium scale can be easily formed, it is necessary to pay attention to the calcium concentration and to consider sufficient pretreatment (softening treatment etc.).

  In Patent Document 3, since the RO-treated water is always treated with an anion exchange resin, the frequency of regeneration or exchange of the anion exchange resin is increased, and as a result, the treatment cost is increased.

  In Patent Document 4, since the anion exchange resin tower is arranged at the front stage of the RO apparatus, the ion load on the anion exchange resin tower is large, and the frequency of regeneration or exchange of the anion exchange resin is increased. As a result, the processing cost is reduced. Get higher.

  The present invention eliminates the above-mentioned conventional problems, and when silica concentration such as lake water becomes temporarily high, a method for producing pure water that can prevent silica from accumulating in an electric deionizer at low cost And an apparatus.

  The pure water production method of the present invention is a pure water production method in which water to be treated is treated with a reverse osmosis membrane and then treated with an electric deionization apparatus. In the pure water production method, silica in reverse osmosis membrane inflow water and / or reverse osmosis membrane treatment water is used. If the concentration is higher than the reference value, the reverse osmosis membrane water is subjected to anion exchange treatment by an anion exchange means, and then treated with the electric deionization device, and the reverse osmosis membrane inflow water and / or reverse osmosis membrane treatment water When the silica concentration is lower than the reference value, the reverse osmosis membrane treated water is treated by the electric deionizer without passing through the anion exchange means.

  The pure water production apparatus of the present invention measures the silica concentration in raw water and / or reverse osmosis membrane treated water in a pure water production apparatus that treats raw water with a reverse osmosis membrane device and then treats it with an electrical deionization device. An electric deionization device comprising a silica concentration measuring means, and when the silica concentration measured by the silica concentration measuring means is higher than a reference value, the reverse osmosis membrane treated water is subjected to anion exchange treatment by an anion exchange means; When the silica concentration measured by the silica concentration measuring means is lower than the reference value, the reverse osmosis membrane treated water is supplied to the electric deionizer without passing through the anion exchange means. It is comprised by these.

  This pure water production apparatus selects a flow path for supplying the reverse osmosis membrane treated water to the anion exchange means, and supplies the reverse osmosis membrane treated water to the electric deionizer by bypassing the anion exchange means. It is preferable to provide a flow path switching means for switching between flow path selection.

  In the pure water production method and apparatus of the present invention, when the silica concentration of the inflow water to the reverse osmosis membrane is higher than the reference value, the reverse osmosis membrane permeated water is passed through the anion exchange means for anion removal treatment. The silica concentration in the inflow water of the type deionizer is lowered, and silica accumulation in the electric deionizer is prevented.

  Further, when the silica concentration in the inflow water to the reverse osmosis membrane is lower than the reference value, the reverse osmosis membrane permeated water is treated with an electric deionizer without passing through the anion exchange resin means. The frequency of regeneration or exchange is reduced, and the maintenance cost of the anion exchange resin tower is reduced.

  Thus, according to the present invention, silica accumulation in the electric deionization apparatus can be prevented, voltage rise can be prevented, and performance degradation (deterioration of treated water quality) due to this can be prevented. In addition, it is possible to easily and economically cope with seasonal raw water quality deterioration due to lake water.

  In the present invention, the flow path selection for supplying the reverse osmosis membrane treated water to the anion exchange means, and the flow path selection for supplying the reverse osmosis membrane treated water to the electric deionization device bypassing the anion exchange means, By adopting the flow path switching means for switching between, it is possible to easily switch between water flow to the anion exchange means and bypass (bypass).

It is a block diagram of the pure water manufacturing apparatus which concerns on embodiment. It is a block diagram of the pure water manufacturing apparatus which concerns on embodiment. It is a graph which shows the relationship between a water supply silica density | concentration and water temperature. It is a graph which shows the relationship between a feed water silica density | concentration and a desalination cell flow volume.

  Hereinafter, embodiments will be described with reference to the drawings.

  FIG. 1 shows a pure water production apparatus according to a first embodiment of the present invention. Raw water is treated by a pretreatment apparatus 1 and then reverse osmosis membrane apparatus (RO apparatus) 3 through a pipe 2. Supplied to. Examples of the pretreatment device 1 include one or more treatments such as coagulation sedimentation, sand filtration, activated carbon filtration, pressurized flotation, and membrane pretreatment. Depending on the quality of the raw water, this pretreatment may be omitted. In addition, this invention is suitable for processing raw | natural water whose silica density | concentration fluctuates according to a season etc., such as lake water. The range of silica concentration in lake water is about 20 to 100 ppm (μg / L).

  It is preferable that at least a part of the concentrated water of the RO device 3 is returned to the pretreatment device 1. The permeated water of the RO device 3 is passed through the pipe 4 to the anion exchange resin tower 5 and anion removal treatment is performed by the anion exchange resin. The effluent water from the anion exchange resin tower 5 is passed through the pipe 6 to the electric deionizer 7 and treated water (product water) is taken out as pure water through the pipe 8. The produced water may be further processed to obtain high quality pure water.

  As described in Patent Document 5, the electric deionization apparatus includes an anode chamber having an anode, a cathode chamber having a cathode, and a plurality of anion exchange membranes and cations between the anode chamber and the cathode chamber. Concentration chambers and desalting chambers alternately formed by alternately arranging exchange membranes are provided, the desalting chambers are filled with ion exchangers, and the ion exchangers, activated carbon or electrical conductors are filled in the concentration chambers. A filled electrical deionizer can be used. In this case, as in Patent Document 5, water having a silica concentration lower than that of raw water (for example, produced water) is passed in the direction opposite to the flow direction of the water to be treated in the desalination chamber as the concentrated water passing through the concentration chamber. However, the present invention is not limited to this.

  In this embodiment, a three-way valve 9 is provided in the pipe 4, and one end side of the bypass pipe 10 is connected to the three-way valve 9. The bypass pipe 10 is installed so as to bypass the anion exchange resin tower 5, and the other end side of the bypass pipe 10 is connected to the pipe 6. The three-way valve 9 is for selectively switching between the flow path selection for flowing the permeated water of the RO device 3 to the anion exchange resin tower 5 and the flow path selection for flowing to the bypass pipe 10.

  The pipe 2 is provided with a silica concentration meter 11 for measuring the silica concentration. A detection signal of the silica concentration meter 11 is input to the controller 12, and the three-way valve 9 is switched by the controller 12. In this embodiment, when the silica concentration measured by the silica densitometer 11 is higher than the reference value (first reference value), the permeated water of the RO device 3 is passed through the anion exchange resin tower 5 and the silica densitometer. When the silica concentration measured by 11 is lower than the reference value, the three-way valve 9 is switched by the controller 12 so that the permeated water of the RO device 3 flows through the bypass pipe 10 and bypasses the anion exchange resin tower 5.

  In this case, the reference value (first reference value) is preferably a value selected from 20,000 to 100,000 ppb (20 to 100 ppm), particularly 30,000 to 50,000 ppb (30 to 50 ppm). Even when the pretreatment device 1 is not installed, the reference value is preferably a value selected from the above range.

  Thus, when the silica concentration of the inflow water of the RO device 3 is higher than the reference value, the permeated water of the RO device 3 is passed through the anion exchange resin tower 5 to perform anion removal treatment. The silica concentration in the inflowing water is reduced, and silica accumulation in the electric deionizer 7 is prevented.

  Further, when the silica concentration in the inflow water of the RO device 3 is lower than the reference value, the permeated water of the RO device 3 flows into the bypass pipe 10 and bypasses the anion exchange resin tower 5, so that the anion exchange resin is regenerated or exchanged. And the maintenance cost of the anion exchange resin tower 5 is reduced.

  In FIG. 1, the silica concentration meter 11 is installed in the pipe 2, but the silica concentration meter 11 is installed in the pipe 4 to measure the silica concentration in the permeated water from the RO device 3, and this silica concentration is the reference value (second reference value). If it is higher, the water may be passed through the anion exchange resin tower 5, and if it is lower than the second reference value, the anion exchange resin tower 5 may be bypassed by flowing into the bypass pipe 10. The second reference value is preferably a value selected from 500 to 800 ppb, particularly from 600 to 800 ppb. In addition, the upper limit of the silica concentration in the water supply to the electric deionizer varies depending on the water temperature and the flow rate. Although the upper limit of the reference value increases with an increase in the water temperature and a decrease in the feed water flow rate, 700 ppb can be used as one reference at 25 ° C. and 170 L / h. Further, it can be based on 600 ppb at 20 ° C. and 800 ppb at 140 L / h.

  FIG. 2 shows a pure water production apparatus according to the second embodiment of the present invention. In this embodiment, joints 15 and 16 are provided at the downstream end of the pipe 4 and the upstream end of the pipe 6, respectively, so that the anion exchange resin tower 5 can be removed. In FIG. 2A, an anion exchange resin tower 5 is installed, and the permeated water of the RO device 3 passes through the anion exchange resin tower 5 before being supplied to the electric deionization device 7. In FIG. 2 (b), the anion exchange resin tower 5 is removed, and the joints 4 and 6 are directly connected by a pipe 17. Therefore, the permeated water of the RO device 3 is supplied to the electric deionization device 7 as it is without being subjected to anion exchange treatment.

  When the silica concentration in the inflow water to the RO device 3 is higher than the first reference value or the silica concentration in the permeated water of the RO device 3 is higher than the second reference value, anion exchange is performed as shown in FIG. When the resin tower 5 is installed and the silica concentration is lower than the reference value, the anion exchange resin tower is removed and the pipes 4 and 6 are directly connected by the pipe 17 as shown in FIG. In the case of lake water, there is a period when the silica concentration becomes high for about one week to two months in one year. Therefore, the structure shown in FIG. 2 (a) is used at such time, and the structure shown in FIG. 2 (b) is used at other times. It is preferable to do this. The removed anion exchange resin tower 5 can be returned to the factory for recycling and reused, or it can be used as an ion exchange resin for use in pure water equipment of a lower purity grade.

  In the case of FIG. 2 as well, a silica densitometer may be provided in the pipe 2 or 4, and the configuration shown in FIGS. 2A and 2B may be switched. Analysis may be performed, and the configuration shown in FIGS. 2A and 2B may be switched according to the result.

  In the present invention, a sensor for detecting a water quality index value (for example, electrical conductivity) other than the silica concentration is provided in the pipe 2 or 4, and this sensor detected value is on the better water quality side than the reference value (for example, 300 μS). When the electrical conductivity is lower than the reference value (for example, when the electric conductivity is lower than the reference value), the sensor detection value is on the side of poorer water quality than the reference value (for example, the electric conductivity is higher than the reference value). ) In some cases, water is passed through the anion exchange resin tower 5 for the time being, and the silica concentration is analyzed. When the actual silica concentration is higher than the first or second reference value, the state (passage through the anion exchange resin tower 5) is determined. Water), and when the actual silica concentration is lower than the first or second reference value, it may be returned to a configuration in which water does not pass through the anion exchange resin tower 5.

[Example 1]
Lake water was used as raw water, and after this raw water was pretreated and RO treated, the operation of passing water through an electric deionizer was operated for 12 months from April to March. In addition, the anion exchange resin tower was installed in the front stage of the electric deionizer as shown in FIG. The other period is the flow of FIG.

As pretreatment, activated carbon tower water passing treatment was performed after aggregation (flocculating agent polyaluminum chloride) and filtration (filtration device MF membrane filtration device manufactured by Kurita Kogyo Co., Ltd.). As an electric deionization apparatus, KCDI-UPz (registered trademark) manufactured by Kurita Kogyo Co., Ltd. (rated treated water volume 15 m ³ / h) was used, and the current value was set to 10A. The amount of water flow to the electric deionizer was 15 m ³ / h.

  Table 1 shows the silica concentration of the raw water and the RO treated water, the voltage of the electric deionizer, and the changes in the quality of the treated water over time.

[Comparative Example 1]
The treatment was performed for 12 months from April to March under the same conditions as in Example 1 except that the anion exchange resin tower was not installed in September. The results are shown in Table 1.

  As is apparent from Table 1, in Example 1, the voltage value of the electric deionizer was stable at 300 to 310 V throughout the entire period, and the quality of the treated water was stable at 18.2 MΩ · cm or more.

  On the other hand, in Comparative Example 1, the voltage of the electric deionizer rose to 420 V in September. The voltage started to decrease from October, but it was 350V in December. This is thought to be due to the fact that a large amount of silica adhered to the electric deionization apparatus in September, and the amount of silica adhered gradually decreased, but the amount of silica adhered remained for the next 3 to 4 months. It is done.

  Hereinafter, the result at the time of changing the water flow conditions to an electrical deionization apparatus is demonstrated.

KCDI-UPz (1 m ³ / h) manufactured by Kurita Kogyo Co., Ltd. was used as an electric deionization apparatus. Industrial water was used as raw water in the same manner as in Example 1 except that it was agglomerated, filtered, activated carbon treated and RO treated. This raw water was passed through and subjected to electric deionization while controlling the applied voltage so that the current density was constant.

  FIG. 3 is a plot of the relationship between the water supply silica concentration and the water temperature at the standard treated water amount (170 L / h / cell). As the water temperature rises, the limit silica allowable concentration increases, and when the water temperature rises by 5 ° C., the silica allowable concentration increases by 10%. However, since it is difficult to control the water temperature, it is understood that it is better to set the limit silica allowable concentration to 700 μg / L based on 25 ° C. in view of the safety factor.

  FIG. 4 is a plot of the relationship between the silica concentration of the feed water and the desalting cell flow rate at the standard treatment water temperature (25 ° C.). By reducing the cell flow rate from 170 L / h to 140 L / h, no increase in voltage was observed even when the critical silica concentration exceeded 800 μg / L. Therefore, in consideration of the cost merit of high flow rate at the design stage, the allowable limit silica concentration can be set to 800 μg / L by designing the desalting cell flow rate to 140 L / h or less.

  3 and 4, the upper limit of the reference value increases with an increase in the water temperature and a decrease in the feed water flow rate, but 700 ppm can be used as one reference at 25 ° C. and 170 / L. In addition, the reference value of the allowable limit silica concentration can be set according to the water temperature and flow rate of the feed water, and when the reference value exceeds the reference value, water is passed through the anion exchange means to increase the voltage of the electric deionizer. Suppressing and long-term stable operation is possible.

3 RO device 5 Anion exchange resin tower 7 Electric deionization device 11 Silica concentration meter 15, 16 Joint 17 Piping

Claims (6)

  In a pure water production method in which treated water is treated with a reverse osmosis membrane and then treated with an electrical deionization device, when the silica concentration in the reverse osmosis membrane inflow water and / or reverse osmosis membrane treatment water is higher than the reference value The reverse osmosis membrane treated water is subjected to anion exchange treatment by an anion exchange means and then treated with the electric deionization device, and the silica concentration in the reverse osmosis membrane inflow water and / or reverse osmosis membrane treated water is lower than the reference value. In this case, a process for producing pure water is characterized in that reverse osmosis membrane treated water is treated by the electric deionizer without passing through the anion exchange means.   In Claim 1, the said reference value of the silica concentration in reverse osmosis membrane inflow water is a value chosen from 20000-100,000 ppb, and the said reference value of the silica concentration in reverse osmosis membrane treated water is a value chosen from 500-800 ppb A method for producing pure water, wherein   3. The pure water manufacturing method according to claim 1, wherein the raw water is lake water. In a pure water production apparatus that treats water to be treated with a reverse osmosis membrane device and then treats it with an electrical deionization device,
Having silica concentration measuring means for measuring silica concentration in raw water and / or reverse osmosis membrane treated water,
When the silica concentration measured by the silica concentration measuring means is higher than the reference value, the reverse osmosis membrane treated water is subjected to anion exchange treatment by an anion exchange means, and then supplied to the electric deionizer, and the silica concentration measurement is performed. When the silica concentration measured by the means is lower than the reference value, the reverse osmosis membrane treated water is supplied to the electric deionizer without passing through the anion exchange means. Pure water production equipment.   5. The flow path selection according to claim 4, wherein the reverse osmosis membrane treated water is supplied to the anion exchange means, and the reverse osmosis membrane treated water is bypassed the anion exchange means and supplied to the electric deionization device. An apparatus for producing pure water, comprising flow path switching means for switching between selection.   In Claim 4 or 5, the reference value of the silica concentration in the reverse osmosis membrane inflow water is a value selected from 20000 to 100,000 ppb, and the reference value of the silica concentration in the reverse osmosis membrane treated water is selected from 500 to 800 ppb. A pure water production apparatus characterized by

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