JP2000296314A - Method and device for electrical desalting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent economically and industrially favorably the scale formation at an electric desalting device and to execute stable and efficient treatment over a long period of time. SOLUTION: In the method in which desalting treatment is executed by supplying raw water to an electric desalting device 1 provided with a desalting chamber 2, a concentrating chamber 3 and an electrode chamber 4, either one influent among desalting chamber influent, concentrating chamber influent and electrode chamber influent is subjected to an anion exchange treatment. In the electric desalting device 1, an anion polisher 5 is provided at either influent introducing piping among the desalting chamber 2, the concentrating chamber 3 and the electrode chamber 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a desalination method and an electric desalination apparatus using an electric desalination apparatus, and more particularly, to a method for preventing a decrease in performance due to scale generation in an electric desalination apparatus and ensuring a stable and effective operation for a long time. The present invention relates to an electric desalination method and an electric desalination apparatus capable of performing a general desalination treatment.

[0002]

2. Description of the Related Art In recent years, semiconductor manufacturing plants, liquid crystal manufacturing plants,
As a means for producing pure water or ultrapure water used in various industries or research facilities such as the pharmaceutical industry and the food industry, a plurality of anion exchange membranes are provided between an electrode chamber (anode chamber and a cathode chamber) having electrodes. An electric desalination apparatus in which cation exchange membranes are alternately arranged to form a concentration chamber and a desalination chamber alternately has been used.

[0003] The electric desalination apparatus is excellent in that it is capable of efficient desalination treatment, does not require regeneration like an ion exchange resin, is capable of complete continuous water sampling, and can obtain extremely high purity water. It has the effect. Note that, in the electric desalination apparatus, there are a desalination chamber in which an anion exchange resin and a cation exchange resin are mixed and filled, and a desalination chamber in which an ion exchange resin is not filled, From the viewpoint of improving the quality of treated water, it is more effective to use a deionization chamber filled with an ion exchange resin.

In an electric desalination apparatus, ions in raw water flowing into a desalination chamber move in the direction of an electrode to which an electric potential is applied based on affinity, concentration and mobility (in a direction perpendicular to the flow of the water to be treated). In addition, it moves across a cation exchange membrane or an anion exchange membrane that separates the desalting chamber and the concentrating chamber, so that charge neutralization is maintained in all chambers. Then, due to the semi-osmotic characteristics and the potential of the ion exchange membrane, the ions in the raw water decrease in the desalting chamber and are concentrated in the adjacent concentrating chamber. Therefore, desalinated water is recovered from the desalination chamber.

[0005] In general, as raw water for the electric desalination apparatus, water obtained by subjecting city water or the like to activated carbon treatment and then subjecting to reverse osmosis (RO) membrane separation treatment is used. To raise the concentration, only a part of the effluent from the concentration chamber is discharged out of the system, and the remainder is circulated to the inlet side of the concentration chamber.

[0006] In such an electric desalination apparatus, there is a problem that the scale is generated in the electric desalination apparatus due to the continuous flow of water, and the performance is reduced. "Clean Technology" (1998.10), pp. 62-65, explains that the hardness component in the concentrated water due to the increase in OH ^- concentration in the boundary layer on the side of the concentration chamber of the anion exchange membrane is a factor of the scale generation. It is described that it precipitates. That is, generally, the raw water of the electrodesalination apparatus is subjected to the RO membrane separation treatment at the preceding stage,
Even if this RO membrane separation treatment is performed, it is difficult to sufficiently remove the hardness components such as Ca ²⁺ , and the hardness component still remaining after the RO membrane separation treatment causes scale deposition in the electrodeionization apparatus. .

JP-A-7-8948 and 10-2
JP-A-16749 describes a configuration in an ultrapure water production system incorporating an electric desalination apparatus, in which anion exchange treatment is performed at a stage preceding the electric desalination apparatus, particularly for the purpose of removing TOC.

Japanese Patent Application Laid-Open No. H11-42498 describes a method for preventing the generation of scale in an electric desalination apparatus by passing water through an electric desalination apparatus after cation exchange.

[0009]

There is no description in JP-A-7-8948 or JP-A-10-216749 about the relationship between the anion exchange treatment and the scale. The method of performing the anion exchange treatment on the entire amount of inflow water of the apparatus is economically and industrially disadvantageous because the processing cost is increased, the apparatus is increased in size, and the frequency of maintenance is increased.

Further, as described in JP-A-11-42498, in the method in which water is passed through an electric desalination apparatus after cation exchange, carbonic acid components which are difficult to remove by the electric desalination apparatus are sufficiently removed in the preceding stage. If not, the quality of the treated water could be reduced.

[0011] The present invention solves the above-mentioned conventional problems, and economically and industrially advantageously prevents scale formation in an electric desalination apparatus, thereby enabling stable and efficient treatment for a long period of time. An object of the present invention is to provide a desalination method and an electric desalination apparatus.

[0012]

According to the present invention, there is provided a method for desalination by supplying raw water to an electric desalination apparatus having a desalination chamber, a concentration chamber and an electrode chamber. It is characterized in that any one of the salt room inflow water, the concentration room inflow water and the electrode room inflow water is subjected to anion exchange treatment.

An electric desalination apparatus according to the present invention is an electric desalination apparatus comprising a desalination chamber, a concentration chamber and an electrode chamber, wherein any one of the inflow water of the desalination chamber, the inflow water of the concentration chamber and the inflow water of the electrode. An anion polisher is provided in one inflow water introduction pipe.

By performing anion exchange treatment on the influent water of the electric desalination apparatus, the carbonic acid component, which is a main factor of the scale production, can be removed in advance to prevent scale production in the electric desalination apparatus.

According to the present invention, the anion exchange treatment is performed on only one of the inflow water of the desalination chamber, the inflow water of the concentration chamber, and the inflow water of the electrode chamber, instead of the entire amount of the inflow water of the electric desalination apparatus. In addition, it is possible to prevent an increase in the size of equipment for the anion exchange treatment, to greatly reduce maintenance, and to reduce the treatment cost.

It has not heretofore been recognized at all that treatment of only a part of the inflow water of the electric desalination apparatus can prevent generation of scale in the electric desalination apparatus. This is the technical matter that was first clarified. In the present invention, scale precipitation in an electric desalination apparatus can be effectively prevented with a minimum necessary amount of anion exchange treatment water, and its industrial utility is extremely large.

The anion exchange treatment is particularly preferably performed on the inflow water of the concentration chamber, whereby the precipitation of scale mainly generated in the concentration chamber can be more directly and effectively prevented. That is, the main cause of scale formation, the anion OH in concentrating compartment side of the exchange membrane ^- and HCO ₃ ^- anions concentration of such increases, also increase the cation concentration of Ca ^2+, such as in concentrating compartment side of the cation exchange membrane However, this is because scale such as calcium carbonate is generated on the surface of the ion exchange membrane in the concentration chamber. Therefore, the scale can be effectively prevented by performing anion exchange treatment on the inflow water of the concentration chamber.

For the anion exchange treatment, it is preferable to use a non-regeneration type anion exchange tower (anion polisher) filled with an anion exchange resin from the viewpoint of reducing maintenance. The use of an anion polisher is extremely advantageous because the frequency of replacement is extremely low because of its small amount.

Further, as described above, in order to improve the water recovery rate, it is preferable to circulate the effluent of the enrichment chamber to the inflow side of the enrichment chamber, and in this case, to circulate the circulated water to the inlet side of the anion polisher. By circulating, a good scale prevention effect can be obtained by treating the circulating water in which the scale-forming component is concentrated.

[0020]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a system diagram showing an embodiment of an electric desalination treatment method and an electric desalination apparatus of the present invention.

In FIG. 1, in an electric desalination apparatus 1, water obtained by subjecting water such as tap water to pretreatment of an activated carbon tower and then performing RO membrane separation treatment is used as raw water as a desalination chamber 2, a concentration chamber 3, The water is introduced into the electrode chambers 4 and the effluent from the desalting chamber 2 is taken out as desalinated water (treated water). Part of the effluent from the concentration chamber 3 is discharged out of the system, and the remainder is circulated to the inlet side of the concentration chamber 3 by the pump P. The effluent from the electrode chamber 4 is discharged out of the system.

In the electric desalination apparatus 1 shown in FIG. 1, of the raw water introduced into each of these chambers, the raw water flowing into the concentration chamber 3 is subjected to an anion exchange treatment by the anion polisher 5. By returning the circulating water to the inlet side of the anion polisher, the circulating water is also subjected to an anion exchange treatment.

Examples of the anion polisher is preferably one filled with strongly basic anion-exchange resin, water passing speed SV = 20 to 100 m ³ - water / m ³ - preferably treated at about resin · hr. By performing the treatment with the anion polisher in this manner, the carbonic acid component, which is the main factor of scale generation, contained in the water flowing into the concentration chamber 3 can be almost completely removed, and the scale in the electrodeionization apparatus 1 can be removed. Precipitation can be effectively prevented.

According to the present invention, one of the inflow waters in each of the chambers of the electric desalination apparatus is subjected to anion exchange treatment. An anion exchange treatment may be performed. However, as described above, the scale is likely to be generated near the anion exchange membrane surface of the concentration chamber. Therefore, it is most effective to subject the inflow water of the concentration chamber to anion exchange treatment.

The anion exchange treatment is not limited to the anion polisher, and a regeneration type anion exchange tower can be used. However, it is preferable to use an anion polisher from the viewpoint of reducing maintenance. Even in the case of using an anion polisher as described above, in the present invention,
The anion polisher does not need to be replaced frequently because only a part, but not the entire amount, of the influent water of the electrodesalting apparatus is subjected to the anion exchange treatment.

The circulation of the effluent from the concentrating chamber is performed to improve the water recovery rate. The amount of the circulating water is about 70 to 90% of the effluent of the concentrating chamber. The operation is preferably carried out under a condition of a recovery rate of about 0.8 to 0.95.

The electrodeionization apparatus used in the present invention comprises a concentration chamber and a desalination chamber in which a plurality of anion exchange membranes and cation exchange membranes are alternately arranged between an anode chamber having an anode and a cathode chamber having a cathode. Are alternately formed, and the desalting chamber may be filled with a mixed resin of an anion exchange resin and a cation exchange resin, or may not be filled. From the viewpoint of improving the quality of the treated water, it is preferable that the desalting chamber is filled with a mixed resin of an anion exchange resin and a cation exchange resin.

The ion exchanger to be filled in the desalting chamber may be a fibrous material other than the above resinous composition, and is not limited to these as long as it has an ion exchange function.

[0030]

The present invention will be described more specifically below with reference to examples and comparative examples.

The electric desalination apparatus used in the examples and comparative examples is a small test apparatus provided with three desalination chambers.
In this electric desalination apparatus, a strongly basic anion exchange resin and a strongly acidic cation exchange resin are contained in a desalination chamber at a ratio of 35:65 (by volume).
Is filled with. As the anion polisher, an anion polisher filled with a strongly basic anion exchange resin was used.

Example 1 Tap water is treated with activated carbon ("Kuraray Coal K" manufactured by Kuraray Co., Ltd.)
W10 / 32 ", SV = 20 hr ^-1 ), and water obtained by RO membrane separation treatment (RO membrane made of polyamide) through a security filter (opening of 25 μm) was used as raw water to obtain the electric desalination shown in FIG. Processed on equipment. The amount of raw water introduced into the electric desalination apparatus was 63 L / hr, of which 40 L / hr, 6 L / hr (supplementary supply) and 17 L / hr were introduced into the desalination room, the concentration room, and the electrode room, respectively. The amount of circulating water in the room is 28
L / hr.

The inflow water in the concentrating chamber is supplied to the anion polisher by S
Water was passed at V = 20 hr ^-1 . Further, the water recovery rate of the electric desalination apparatus in terms of the amount of desalinated water and the amount of concentrated water discharged was set to 0.87.

Under these conditions, water was passed continuously for three months, and the quality of the treated water after three months was examined. The results are shown in Table 1.

Further, the electric desalination apparatus was disassembled and the state of scale adhesion inside was examined. The results are shown in Table 1.

Comparative Example 1 In Example 1, water was passed continuously for three months in the same manner as in Example 1 except that the treatment with the anion polisher was not performed at all, and the quality of the treated water and the state of scale adhesion inside the electrodeionization apparatus were examined. The results are shown in Table 1.

COMPARATIVE EXAMPLE 2 In Example 1, an anion polisher was provided also in the inflow water introduction pipe of the desalination chamber and the electrode chamber as shown by a broken line in FIG. 1 so that the entire amount of raw water was treated by the anion polisher. Except for this, water was passed continuously for three months in the same manner, and the quality of the treated water and the state of adhesion of scale inside the electrodeionizer were checked. The results are shown in Table 1.

Table 1 shows that the cost of the anion exchange treatment by the anion polisher required for the treatment for 3 months in Example 1 (calculated from the exchange frequency of the anion polisher) was 100, and that in Comparative Example 2 was 100. The results of calculating the anion exchange treatment cost index are also shown.

[0039]

[Table 1]

As is clear from Table 1, according to the present invention, it is possible to prevent the generation of scale in the electro-desalination apparatus and to obtain treated water having good water quality over a long period of time.

Further, as is clear from the comparison between Comparative Example 2 and Example 1, the effect is equivalent to the case where the entire amount of the influent water of the electrodesalting apparatus is subjected to anion exchange treatment. , Because the amount of anion exchange treated water is small,
The cost required for the anion exchange treatment can be significantly reduced.

[0042]

As described above in detail, according to the method and apparatus for desalination of the present invention, the apparatus and maintenance of the apparatus and the apparatus for desalination are not caused to increase significantly. Can effectively prevent the formation of scale, and a stable and efficient desalination treatment can be performed over a long period of time.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an embodiment of an electric desalination treatment method and an electric desalination apparatus of the present invention.

[Description of Signs] 1 Electric desalination device 2 Desalination room 3 Concentration room 4 Electrode room 5 Anion polisher

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D006 GA17 HA42 HA47 JA57A KA02 KA17 KA31 KA41 KA63 KB11 KB12 KB14 KD19 KE02P KE03P KE04P KE30Q MA13 MA14 PA01 PB06 PC02 4D025 AA04 AB16 BA14 BB02 DA03 DA06 DA06 DA03 DA03 DA03 EB01 EB13 EB37 EB39 FA06 FA08 FA09 FA13 GA21 GC02

Claims (5)

[Claims] 1. A method for performing a desalination treatment by supplying raw water to an electric desalination apparatus having a desalination chamber, a concentration chamber, and an electrode chamber, comprising: Wherein any one of the influents is subjected to anion exchange treatment. 2. The method according to claim 1, wherein the inflow water of the concentration chamber is subjected to anion exchange treatment. 3. The method according to claim 2, wherein the inflow water of the concentration chamber is subjected to anion exchange treatment with an anion polisher, wherein the effluent of the concentration chamber is circulated to the inlet side of the anion polisher. Desalination method. 4. An electric desalination apparatus comprising a desalination chamber, a concentration chamber, and an electrode chamber, wherein an introduction pipe for any one of the inflow water of the desalination chamber, the inflow water of the concentration chamber, and the inflow electrode of the electrode. An electric desalination apparatus characterized in that an anion polisher is provided in the apparatus. 5. The electric desalination apparatus according to claim 4, wherein an anion polisher is provided in the introduction pipe of the inflow water of the concentration chamber.