JP2000000571A - Electric deionized water apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the subject apparatus keeping deionizing capacity by preventing the scale precipitation of a hardness component in a concn. chamber or an electrode chamber even in water to be treated containing a large amt. of a hardness component. SOLUTION: In an electric deionized water making apparatus 1 having a desalting chamber, a concn. chamber and an electrode chamber and obtaining deionized water from the desalting chamber by applying voltage across a pair of electrodes, a mixed soln. of containing an acidic soln. and a scale inhibitor is added to a conc. water storage tank 2 storing conc. water discharged from the concn. chamber and this added soln. is returned to the inflow side of the concn. chamber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric deionized water producing apparatus for preventing the precipitation of scale of a hardness component in a concentration chamber or an electrode chamber and maintaining deionization performance.

[0002]

2. Description of the Related Art Conventionally, an ion exchange resin has been used for producing deionized water. This ion exchange resin
Usually requires regeneration with drugs. Therefore, the combination of deionization using the ion exchange resin and electrodialysis,
2. Description of the Related Art An electric deionized water producing apparatus that does not require regeneration with a chemical and obtains highly deionized water is known.

The electric deionized water producing apparatus is, for example,
Basically, a gap formed by the cation exchange membrane and the anion exchange membrane is filled with an ion exchanger to form a desalination chamber, and water to be treated is passed through the ion exchanger, and the water is passed through both ion exchange membranes. A DC current is applied to produce deionized water while electrically removing ions in the water to be treated from the concentrated water flowing outside the ion exchange membranes. Therefore, ions are concentrated in the concentrated water.

[0004] The concentrated water is discharged out of the apparatus, but is reused instead of being discarded in order to improve the water utilization rate (recovery rate) of the electric deionized water producing apparatus. That is, the water to be treated is used as concentrated water, and the concentrated water is circulated and used, and a part of the water is discharged to the outside of the apparatus to improve the water utilization rate and maintain an appropriate ion concentration of the concentrated water. As described above, in the method of circulating the concentrated water, the electric conductivity of the concentrated water increases because the ion concentration in the concentrated water increases. Therefore, electricity easily flows, and the amount of current flowing through the device increases. Therefore, the ion removal rate also improves. Further, since the voltage applied to the device can be reduced, there is an effect that power consumption is reduced.

[0005] However, on the other hand, hardness components such as Ca and Mg which are initially present in a trace amount in the concentrated water are also concentrated by circulating for a long period of time and are likely to precipitate as scale in the concentration chamber or the electrode chamber. When scale is generated in the concentration chamber or the electrode chamber, the electric resistance in that part increases, and it becomes difficult for current to flow. That is, in order to flow the same current value as when there is no scale generation, the voltage needs to be increased, and power consumption increases. Further, when the amount of scale adhesion further increases, the voltage further increases, and when the voltage exceeds the maximum voltage value of the apparatus, the current value decreases. In this case, a current value required for ion removal cannot be passed, and the quality of treated water is reduced.

As methods for preventing the hardness component from being concentrated in the concentrated water, there are (1) a method of softening water to be treated in a reverse osmosis membrane device, and (2) a method of permeating water (electrically A method for softening the water to be treated in the ionized water producing apparatus),
(3) A method of increasing the discharge amount of the concentrated water and reducing the concentration of the hardness component in the concentrated water.

[0007]

However, the above methods (1) and (2) require installation of a water softening apparatus and management of a regenerating agent, resulting in an increase in cost and an increase in complexity of equipment. Further, the method (3) has a problem that when the concentration of the hardness component of the water to be treated is relatively high, the water utilization rate (recovery rate) of the apparatus is reduced.

Accordingly, it is an object of the present invention to provide an electric deionized water producing apparatus which prevents scale precipitation of a hardness component in a concentration chamber or an electrode chamber and maintains desalination performance.

[0009]

Under such circumstances, the present inventors have made intensive studies and as a result, generally, the pH value of the water to be treated in the electric deionized water producing apparatus is in the range of 5 to 7, and the concentration of concentrated water. The pH value is in the range of 4 to 8, and the hardness component concentrated in the concentrated water has poor dissolving power in this pH range and scale is easily generated. Therefore, when the pH value of the concentrated water is set to the acidic side, the dissolving power of the hardness component is increased, and the generation of scale can be prevented. However, if it is made strongly acidic, corrosion of the metal part of the device is likely to occur. Therefore, it has been found that if a scale generation inhibitor is further added to the concentrated water, a sufficient scale generation preventing effect can be obtained even if the pH value of the concentrated water is maintained at a high level, and metal corrosion can be prevented. It was completed.

That is, the present invention relates to an electric deionized water producing apparatus which has a deionization chamber, a concentration chamber and an electrode chamber, and obtains deionized water from the deionization chamber by applying a voltage to a pair of electrodes. It is an object of the present invention to provide an electric deionized water producing apparatus for adding a scale generation inhibitor and an acid solution to concentrated water supplied to the concentrating chamber.

According to such an electric deionized water producing apparatus, the concentrated water is adjusted to the acidic side and is circulated. For this reason, the concentrated water has an increased ability to dissolve the hardness components such as Ca and Mg. Further, the scale in which silica and a hardness component are combined is dispersed by, for example, charge repulsion due to micelle formation, or is stabilized by chelation by the scale generation inhibitor. Therefore, even if the concentrated water is concentrated to a high concentration, the generation of scales such as calcium carbonate and calcium silicate in the concentration chamber or the electrode chamber is reliably prevented by the dissolving, dispersing and stabilizing actions of both agents. Can be. As described above, the synergistic effect of the scale generation inhibitor and the acidic solution allows the pH value of the concentrated water to be maintained higher than when only the acidic solution is added to the concentrated water. Can also be prevented at the same time.
Further, the scale generation inhibitor is stable in an acidic solution, and its effectiveness is maintained even after long-term storage. Therefore,
It is preferable to prepare a mixed solution of the scale generation inhibitor and the acidic diluting solution in advance, and to add the mixed solution, because the supply equipment is simplified.

[0012]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an electric deionized water producing apparatus according to an embodiment of the present invention. The water to be treated flows into an electric deionized water producing apparatus (hereinafter, also referred to as an EDI apparatus) 1. The EDI apparatus 1 includes a desalting chamber filled with an ion exchanger such as an ion exchange resin and an ion exchange fiber, a concentrating chamber separated from the desalting chamber and an ion exchange membrane, and a desalting chamber and a concentrating chamber. An electrode chamber having an electrode for applying a voltage to the chamber is provided. Then, by flowing the water to be treated through the desalting chamber and the concentrated water through the concentration chamber, the salts are moved into the concentrated water flowing through the concentration chamber via the ion exchange membrane. Thereby, the treated water (deionized water) from which the salts have been removed can be obtained, and the concentrated water in which the salts have been concentrated can be obtained in the concentration chamber. Therefore, the treated water is discharged from the desalting chamber, and the concentrated water is discharged from the concentration chamber. Concentrated water (electrode water) also flows through the electrode chamber that houses the pair of electrodes. Therefore, electrode water is discharged from the electrode chamber.

On the other hand, the entire amount of the concentrated water discharged from the concentration chamber of the EDI device 1 and a part of the replenishment water to be treated flow into the concentrated water storage tank 2. A predetermined amount of a mixture of the scale generation inhibitor and the acidic liquid (hereinafter, referred to as “mixture”) is added to the concentrated water storage tank 2 through the mixture injection pipe 3. The concentrated water stored in the concentrated water storage tank 2 and adjusted to a predetermined acid concentration and a scale generation inhibitor concentration is supplied to the EDI device 1.
Are supplied to the concentration chamber and the electrode chamber, respectively. A part of the concentrated water in the concentrated water storage tank 2 is blown to adjust the ion concentration.

According to the embodiment of the present invention, the pH of the concentrated water is maintained acidic by the mixture added to the concentrated water, and the dissolving power of the scale is increased. Further, the scale generation inhibitor having a predetermined concentration disperses, for example, a scale in which silica and a hardness component are combined by charge repulsion due to micelle formation, or stabilizes the scale by chelation. Therefore, even if the concentrated water is concentrated to a high concentration, it is possible to prevent the generation of scale in the concentration chamber. For this reason, in the device 1, it is possible to prevent a decrease in performance due to an increase in electric resistance due to generation of scale.
In addition, since the concentrated water can be used after being concentrated to a high concentration, the water utilization rate of the device 1 can be improved,
The applied voltage can be reduced, and power consumption can be reduced.

The water to be treated is not particularly limited, and may be city water, permeated water obtained by treating industrial water with a reverse osmosis membrane, or washing wastewater discharged when a semiconductor wafer is washed with ultrapure water. . In addition, C contained in the water to be treated
The amounts of the hardness components such as a and Mg and the amount of silica vary depending on the hardness component concentration of the raw water and the divalent ion removal performance of the reverse osmosis membrane device used, but are about 0.01 to 2 mg / L. The present invention is particularly effective when water containing a large amount of a hard component and silica is used as the water to be treated.

The scale generation inhibitor is not particularly limited as long as it suppresses or prevents generation and precipitation in the concentration chamber and the electrode chamber by dispersing and stabilizing scale such as calcium silicate. Organic polymer compounds such as acrylic acid (co) polymer, maleic acid (co) polymer, sulfonic acid (co) polymer and itaconic acid (co) polymer; orthophosphoric acid, 2-hydroxyethylidene- Organic or inorganic phosphorus compounds such as 1,1-diphosphonic acid, phosphonobutanetricarboxylic acid or a salt thereof; amine-based polymers such as ethylenediamine, diethylenetriamine or nitrilotriacetic acid, ethylenediaminetetraacetate;
Aminocarboxylic acid-based copolymers such as diethylenetriaminepentaacetic acid or gluconic acid, citric acid, oxalic acid, formic acid,
Chelating agents such as tartaric acid, phytic acid, succinic acid, lactic acid and the like. In addition, one or more of these scale generation inhibitors can be used.

The amount of the scale inhibitor to be added is not particularly limited, but may be 0.01 to 1,000 mg / L in concentrated water.
It is preferable to be within the range. If the addition amount is less than 0.01 mg / L, the scale removal efficiency is inferior, and if it exceeds 1,000 mg / L, the scale removal effect is saturated and the cost increases.

The acidic liquid to be mixed with the scale generation inhibitor is not particularly limited, but industrial chemicals such as hydrochloric acid and sulfuric acid are easily available and are suitable because of their low cost. The acidic solution may be added so that the pH value of the concentrated water is in the range of 2.0 to 4.0. 1. The pH value of the concentrated water is 2.
If it is less than 0, the tendency to corrode metal parts in the apparatus increases. When hydrochloric acid is used as the acid, addition of a large amount of acid to the concentrated water generates hypochlorous acid by electrolysis in the electrode chamber, and the strong oxidizing power causes the surface of the ion exchange membrane to be oxidized and deteriorated. In addition, in the case of sulfuric acid, a large amount of acid added to the concentrated water may react with Ca in the concentrated water to generate calcium sulfate scale. Therefore, in the present invention, the pH value of the concentrated water is set to a slightly higher range of 3.0 to 3.5, and the scale generation inhibitor is added to the concentrated water at a pH of 0.1 to 3.5.
It is preferable to use it by adding 01 to 0.04 mg / L.
Thereby, the effect of preventing scale generation is sufficiently exhibited, and the generation of hypochlorous acid to the extent that the surface of the ion exchange membrane is oxidized and degraded is eliminated, and the generation of scale of calcium sulfate can be suppressed.

In the present invention, there are no particular restrictions on the method of preparing the mixture or adjusting the concentration, and examples thereof include a method of mixing an acid solution of a stock solution with a scale inhibitor, a method of diluting an acid solution such as hydrochloric acid and sulfuric acid, and a method of scaling. Examples of the method include a method of mixing a generation inhibitor, and among them, a method of mixing a dilute acid solution and a scale generation inhibitor is preferable.

The location for injecting the mixture into the concentrated water is not particularly limited, and may be a method of injecting into the pipe 4 of the concentrated water circulation line in addition to the above-described embodiment. Further, the method of injecting the mixed solution into the concentrated water may be either a continuous injection method or an intermittent injection method. Further, a method may be used in which the acid solution and the scale generation inhibitor are added to the concentrated water via separate injection pipes or the like instead of the mixed solution.

[0021]

Next, the present invention will be described more specifically with reference to examples. Example 1 A processing experiment for 20 days was performed using an EDI device having the following specifications and the device shown in FIG. The water to be treated was prepared by adding silica and a calcium carbonate solution to the permeated water obtained by treating tap water with a reverse osmosis membrane device to reduce the Ca concentration to 0.2 mg / L and the silica concentration to 0.2 mg-SiO ₂ / L. The adjusted electric conductivity is 5.0 μS / cm
Of water was used. The mixed solution was a solution in which a scale generation inhibitor and an acidic solution were mixed at a volume ratio of 1:10, and the added amount was 15 ppm of the scale generation inhibitor in concentrated water. At this time, the pH of the concentrated water was 3 to 3.5. The evaluation was performed by measuring the resistivity of the treated water after 20 days, and visually observing the scale adhesion in the concentration chamber and the electrode chamber. Table 1 shows the results.

(EDI device etc.) ・ Size of desalination room; length 1
As shown in FIG. 1, there are two concentrating chambers between the three desalting chambers, and a pair of condensing chambers outside the three desalting chambers. An electrode chamber is provided, and the thickness of each of the anode chamber and the electrode chamber is about 3.5 mm.・ Amount of treated water: about 15 L / h per unit ・ Applied voltage and current: 80 V, 0.2 A ・ Water temperature: 25 ° C. ・ Ion exchanger used: Cation exchange resin Amberlite IR120B Anion exchange resin Amberlite IRA402 (both ROHM) And Haas) 1: 1 mixture ratio of cation exchange resin and anion exchange resin
(Volume ratio)-Ion exchange membrane used: Cation exchange membrane C-66, anion exchange membrane AMH (all manufactured by Tokuyama Corporation)-Scale generation inhibitor: Acrylic acid-based copolymer (trade name "Acuma 2000" Rohm and Haas)・ Acid solution: 10% hydrochloric acid solution

Comparative Example 1 The procedure of Example 1 was repeated, except that only the scale generation inhibitor was added to the concentrated water storage tank without adding the acidic liquid. The pH of the retentate was in the range of 6.8-7.4. Table 1 shows the results.

Comparative Example 2 The same procedure as in Comparative Example 1 was carried out except that the concentration of the scale generation inhibitor was added so as to be 40 ppm in the concentrated water.

Comparative Example 3 The same procedure as in Example 1 was carried out except that only the acid solution was added to the concentrated water storage tank without adding the scale generation inhibitor. The pH of the retentate was in the range of 3.0-3.5. Table 1 shows the results.

Comparative Example 4 The same procedure as in Comparative Example 3 was carried out, except that the acidic solution was added so that the pH of the concentrated water was in the range of 1.8 to 2.2.
The pH of the retentate was in the range of 1.8-2.2. Table 1 shows the results.

Comparative Example 5 The same procedure as in Example 1 was carried out except that no mixed solution was added. The pH of the retentate was in the range of 6.8-7.4.
Table 1 shows the results.

[0028]

[Table 1]

From Table 1, it can be seen that in Example 1, Comparative Example 2 and Comparative Example 4, no scale deposition was observed and the quality of the treated water was not reduced. Comparative Example 2 has a problem that the amount of the scale generation inhibitor added is 2.7 times that of Example 1 and the cost is increased. In Comparative Example 4, the concentrated water is strongly acidic, and may corrode metal parts. On the other hand, in Example 1, the addition amount of the scale generation inhibitor was smaller than that of Comparative Example 2, and no scale deposition was observed, despite the addition amount of the acidic liquid being smaller than that of Comparative Example 4. There was no decrease in treated water quality. Further, the pH value is slightly higher, and there is no danger of corrosion of metal parts of the apparatus. Thus, in Example 1, a synergistic effect of the scale generation inhibitor and the acidic liquid is recognized. Further, when scale is generated in the enrichment chamber as in Comparative Example 1, Comparative Example 3, and Comparative Example 5, the electric resistance at that portion becomes large, and it becomes difficult for current to flow. Therefore, it becomes difficult to regenerate the impurity ions adsorbed on the ion exchanger, and as a result, the deionization performance of the electric deionized water producing apparatus is reduced.

[0030]

According to the present invention, the concentrated water is adjusted to the acidic side and recycled. For this reason, the concentrated water has an increased ability to dissolve the hardness components such as Ca and Mg. Further, the scale in which silica and a hardness component are combined is dispersed by, for example, charge repulsion due to micelle formation, or is stabilized by chelation by the scale generation inhibitor.
Therefore, even if the concentrated water is concentrated to a high concentration, the generation of scales such as calcium carbonate and calcium silicate in the concentration chamber or the electrode chamber is reliably prevented by the dissolving, dispersing and stabilizing actions of both agents. Can be. As described above, due to the synergistic effect of the scale generation inhibitor and the acidic solution, compared to the case where only the acidic solution is added to the concentrated solution, p
Since the H value can be kept high, the occurrence of corrosion of the metal part of the device can be prevented at the same time. Further, the scale generation inhibitor is stable in an acidic solution, and its effectiveness is maintained even after long-term storage. Therefore, it is suitable to use a mixed solution of a scale generation inhibitor and an acidic dilution solution as a previously prepared drug. As described above, in the device, it is possible to prevent performance degradation due to an increase in electric resistance due to generation of scale. Further, since the concentrated water can be used after being concentrated to a high concentration, the water utilization rate of the device can be improved, the applied voltage can be reduced, and the power consumption can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an electric deionized water producing apparatus according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electric deionized water production apparatus 2 Concentrated water storage tank 3 Mixed liquid injection pipe 4 Concentrated water circulation line

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Claims (3)

[Claims] 1. An electric deionized water producing apparatus having a deionization chamber, a concentration chamber, and an electrode chamber, wherein voltage is applied to a pair of electrodes to obtain deionized water from the deionization chamber. An electric deionized water producing apparatus, wherein a scale generation inhibitor and an acid solution are added to the supplied concentrated water. 2. An electric deionized water producing apparatus having a deionization chamber, a concentration chamber, and an electrode chamber, wherein voltage is applied to a pair of electrodes to obtain deionized water from the desalination chamber. An electric deionized water producing apparatus, wherein a mixed liquid containing a scale generation inhibitor and an acidic liquid is added to the supplied concentrated water. 3. The electric deionized water producing apparatus according to claim 1, wherein the scale generation inhibitor is one or more selected from an organic polymer compound, an organic or inorganic phosphorus compound, and a chelating agent. .