JP6571312B2 - Pure water production method - Google Patents

Description

  The present invention relates to a pure water production method, and more particularly, to an economically advantageous pure water production method using a reverse osmosis membrane device (RO) and an electric deionization device (EDI) disposed in the subsequent stage.

  In general, a pure water production system for producing high-purity pure water incorporates RO as a pretreatment device and EDI as a deionization device for advanced treatment of the obtained RO permeated water ( For example, Patent Documents 1 to 3).

  By the way, EDI basically includes a plurality of sets of desorptions that are sequentially formed by alternately arranging an anion exchange membrane and a cation exchange membrane between an anode chamber having an anode and a cathode chamber having a cathode. It is composed of a salt chamber and a concentration chamber, and a mixture of a cation exchanger and an anion exchanger is accommodated in the desalting chamber.

  When direct current is passed from the anode and the cathode, impurity ions in the water to be treated (RO permeated water) are captured and removed by the anion exchange group and the cation exchange group in each desalting chamber, and pure water is produced. The trapped impurity ions are electrodialyzed by an anion exchange membrane and a cation exchange membrane which are also a membrane of the desalting chamber, move to an adjacent concentration chamber, and are concentrated and discharged.

  And although the water flow direction to said each desalination chamber and concentration chamber of EDI is not restrict | limited, it is desalted from a viewpoint of preventing the entrainment of the air concerned when passing water from the top to the bottom. It is common for both the chamber and the concentration chamber to flow upward.

JP 2000-317457 A JP 2001-104959 A JP 2002-320971 A

  By the way, the EDI water to be treated has a water quality limit value because there is a concern about the blockage of the deposited component (silica which is weak electrolyte) on the ion exchange membrane. Therefore, the water quality limit value is also set for the treated water of RO arranged in the previous stage of EDI. To protect the EDI water quality limit value, the RO is doubled, the RO recovery rate is lowered, etc. Measures are taken, but this leads to complication of the processing system and an increase in processing costs. As a measure for reducing processing costs, when the RO recovery rate is increased, it is conceivable that the replacement frequency increases due to the use of RO over time. Incidentally, the silica concentration of RO permeate supplied to EDI as treated water is usually 1.0 mg / L or less, preferably 1.0 mg / L or less.

  This invention is made | formed in view of the said situation, The objective is improving the removal effect of the silica in EDI, and the passage of RO treated water exceeding the water quality limit value of the treated water of EDI prescribed | regulated is the objective. An object of the present invention is to provide an economically advantageous method for producing pure water.

  As a result of intensive investigations, the present inventors have surprisingly found that the removal effect of silica differs depending on the direction of water flow to the desalination chamber and the concentration chamber of EDI. In other words, the inventors have found that the silica removal effect is remarkably enhanced.

The present invention has been completed on the basis of the above knowledge, and the gist of the present invention is that in a pure water production method using a reverse osmosis membrane device and an electric deionization device arranged in a subsequent stage, The system consists of multiple sets of desalting chambers and concentrating chambers that are sequentially formed by alternately arranging anion exchange membranes and cation exchange membranes between an anode chamber with an anode and a cathode chamber with a cathode. In addition, an electric deionization device in which a mixture of a cation exchanger and an anion exchanger is accommodated in the desalting chamber and the concentration chamber is used, and the water flow direction of each of the above desalting chambers is set as an upward flow. By flowing downward in the direction of water flow to each of the concentration chambers, the water flow direction of each of the desalting chambers and the direction of water flow to each of the above-described concentration chambers are made counter-current directions, and electric drainage is performed. Silica concentration of permeated water of reverse osmosis membrane device supplied to ion device as treated water It consists in pure water production method characterized by the range of 1.5~3.0mg / L.

  According to the present invention, it is possible to reduce the number of water softeners, reduce the number of ROs introduced or improve the RO water recovery rate, and reduce the frequency of replacement when RO deteriorates. A pure water production method capable of continuous operation for a long period of time is provided.

FIG. 1 is a schematic vertical front view of an example of EDI.

  Hereinafter, the present invention will be described in detail. In the pure water manufacturing method of this invention, RO and EDI arrange | positioned in the back | latter stage are utilized.

  The type of RO and the type of membrane are not particularly limited, and various types of RO used in the water treatment field can be used. The same applies to processing conditions such as operating pressure.

  The EDI is the same as described above, and is not particularly limited. For example, the one shown in FIG. 1 proposed by the present applicant in Japanese Patent Laid-Open No. 2001-137859 can be used.

  The EDI (1) shown in FIG. 1 includes an anion exchange membrane (61) and a cation exchange between an anode chamber (3) having an anode (2) and a cathode chamber (5) having a cathode (4). It comprises a plurality of sets of desalting chambers (81), (82)... And concentration chambers (91), (92).

  That is, a desalination chamber (81) is configured by being sandwiched between an anion exchange membrane (61) and a cation exchange membrane (71), and similarly, an anion exchange membrane (62) and a cation exchange membrane (72). A second desalting chamber (82) is formed between the two. In this way, the anion exchange membrane (61) and the cation exchange membrane (71) are alternately arranged, and in the case of the illustrated apparatus, five desalting chambers are formed. On the other hand, a first concentration chamber (91) is formed between the cation exchange membrane (71) and the anion exchange membrane (62). Similarly, the cation exchange membrane (72) and the anion exchange membrane (63) are formed. ) To form a second concentration chamber (92). In this way, in the case of the illustrated apparatus, four concentration chambers are formed. And the mixture (A) of a cation exchanger and an anion exchanger is accommodated in each of the five desalting chambers. Further, the mixture (a) of the cation exchanger and the anion exchanger is accommodated in each of the four concentration chambers.

  The EDI (1) shown in FIG. 1 has a feature of excellent electrical stability because the mixture (a) of the cation exchanger and the anion exchanger is accommodated in the concentration chamber as described above.

  As the ion exchange membrane for forming the desalting chamber and the concentrating chamber, those used in ordinary EDI are used. For example, trade names “Celemion (Asahi Glass Co., Ltd.)”, “Neocepta (Tokuyama) ) "," Aciplex (Asahi Kasei Corporation) "and the like.

  As the ion exchanger filled in the desalting chamber, ion exchange fibers processed into a non-woven fabric having a predetermined thickness are used in addition to the ion exchange resin used for the desalting treatment during normal pure water production. Can be used. The ion exchange resin is appropriately selected from ion exchange resins employed for normal pure water production. For example, “Diaion (registered trademark) SK1B” and “PK208” as strong acid cation exchange resins, and “Diaion SA10A” and “PA316” as strong base anion exchange resins. Etc. Specific examples of the ion exchange fibers include those obtained by introducing ion exchange groups into a composite fiber of polystyrene fiber and auxiliary agent, those obtained by introducing ion exchange groups into a fiber base material of polyvinyl alcohol, and radiation on polyolefin fibers. Commercially available products such as those in which an ion exchange group is introduced by using radiation graft polymerization by irradiation with the above can be used. The cation exchanger and the anion exchanger are generally used in such an amount that both exchange capacities are the same.

  In addition, the ion exchanger may be used in either a regeneration type or a salt type, but it is preferable to use the regeneration type in order to speed up the water quality. An example of the regenerated mixed resin of cation exchange resin and anion exchange resin is “SMT100L” manufactured by Mitsubishi Chemical Corporation.

  The greatest feature of the present invention is that the EDI is operated as the water to be treated by performing the EDI operation with the water flow direction of each of the desalting chambers and the water flow direction of each of the concentration chambers as a countercurrent direction. The silica concentration of the RO permeate supplied is increased to a range of 1.5 to 3.0 mg / L (preferably 1.5 to 2.5 mg / L). The countercurrent method significantly enhances the silica removal effect in EDI (in other words, the above-mentioned high concentration can be achieved without severely limiting the silica concentration of RO permeated water supplied to EDI as treated water. The reason for possible concentration ranges is estimated as follows.

  In the case of counterflow, naturally, the concentrated water inlet side and the treated water outlet side are in parallel, and the concentrated water outlet side and the treated water inlet side are in parallel. At this time, the salt component of to-be-processed water moves to the concentrated water side by electric desalination, and raises the salt concentration of concentrated water. This upward tendency is greater on the inlet side of the water to be treated. As a result, with the countercurrent system, even if the salt concentration of the concentrated water rises, the concentrated water can be drained immediately from the outlet, and the concentrated water is placed inside the concentration chamber (ion exchange membrane, particularly anion exchange membrane). The contact time is short, and it becomes possible to suppress precipitation of salt components in the concentration chamber (cause of voltage increase and desalting efficiency decrease).

  If precipitation of the salt component in the concentration chamber can be suppressed, the current flow is not inhibited, the desalting efficiency is easily maintained, and the effect of removing the weak electrolyte (silica component) is improved. In other words, the weak electrolyte (silica component) removal effect is maintained by suppressing the precipitation of the salt component in the concentration chamber, which is the cause of the increase in voltage and the decrease in desalting efficiency.

  In the EDI (1) used in the present invention, since the mixture of the cation exchanger and the anion exchanger is accommodated in the concentrating chamber, there is almost no influence such as drift due to the entrainment of air, and the concentrating chamber passes through. The water direction can be either upward or downward. Therefore, it is possible to adopt a countercurrent system in which the water flow direction of the desalting chamber is a downward flow and the water flow direction of the concentration chamber is an upward flow.

  However, as shown in FIG. 1, a counter-current system in which the water flow direction to the desalination chamber is an upward flow and the water flow direction to the concentration chamber is a downward flow is recommended. This is because in the desalination chamber where ion exchange and ion flow occur, a more stable flow is required, and the upward flow in the water flow direction prevents the chance of air entrainment more reliably. It is because it is preferable.

  The EDI (1) shown in FIG. 1 is operated as follows. To the five desalting chambers, water to be treated (RO permeated water) is supplied in parallel from the desalting chamber side inflow pipe (131). The deionized water (pure water) flows out from the desalting chamber side outflow pipe (132). Concentrated water is supplied to the four concentration chambers in parallel from the concentration chamber side inflow pipe (141). The concentrated water supplied to each concentration chamber is discharged from the concentration chamber side outflow pipe (142) as concentrated water in which impurity ions are concentrated. Simultaneously with the supply of concentrated water to the concentration chamber, water to be treated (electrode water) is supplied from the anode chamber side inflow pipe (121) to the anode chamber (3) and from the cathode chamber side inflow pipe (123) to the cathode chamber ( 5) and discharged from the anode chamber side outflow pipe (122) and the cathode chamber side outflow pipe (124), respectively.

  When a direct current is passed from the anode (2) and the cathode (4) while allowing water to flow through each of the flow paths described above, impurity ions in the water to be treated are mixed with the cation exchanger and the anion exchanger in each desalting chamber. The anion exchange groups and cation exchange groups possessed by the cation exchange groups produce pure water, and the impurity ions trapped in the mixture of cation exchangers and anion exchangers are anions that also serve as a membrane for the desalination chamber. It is electrodialyzed by the ion exchange membrane and the cation exchange membrane, moves to the adjacent concentration chamber, is concentrated, and is discharged from the concentration chamber side outflow pipe (142).

  In the present invention, RO and EDI disposed in the subsequent stage are used. However, since the silica removal rate in EDI is increased, RO is not only required for one-stage treatment, but also water quality limitation of EDI treated water. There is no need to reduce the RO recovery rate considering the value regulation more than necessary. Therefore, in order to realize an economically advantageous pure water production method, the silica concentration of RO permeated water (EDI treated water) in the present invention is significantly higher than the conventional 1.0 mg / L or less, that is, 1.5-3.0 (preferably 1.5-2.5) mg / L.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited to a following example, unless the summary is exceeded.

Example 1:
The module “SU-710” (manufactured by Toray Industries, Inc.) was used for RO. An EDI having the structure shown in FIG. 1 and having the following specifications was used.

(EDI specifications)
As the anion exchange membrane, Selemion AMD (manufactured by Asahi Glass Co., Ltd., Selemion is a registered trademark of the company) was used, and as the cation exchange membrane, Selemion CMD (manufactured by Asahi Glass Co., Ltd.) was used. As the ion exchange resin filled in the desalination chamber and the concentration chamber, a regenerated mixed resin of cation exchange resin and anion exchange resin (product “Diaion SMT100L” manufactured by Mitsubishi Chemical Corporation: water content 50% by weight) It was used. The number of desalting chambers is 45, the number of concentrating chambers is 44, and the desalting chamber is 390 mm long, 130 mm wide, and 2 mm thick. The concentration chamber is 390 mm long, 130 mm wide, and 2 mm thick.

  Yokohama city water is used as raw water, treated with an activated carbon tower and then treated with RO to obtain permeated water having a silica concentration of 1.5 mg / L and an electric conductivity of 20 μS / cm. The pure water was manufactured by supplying and processing.

  In the operation of EDI, a counter-current system was adopted in which the water flow direction to the desalination chamber was an upward flow and the water flow direction to the concentration chamber was a downward flow. The amount of water flow to the desalting chamber and the concentration chamber was both LV 100 m / h, and simultaneously with the water flow, a 4 A direct current was applied to the electrode plates of both electrode chambers. The water passing time was 700 hours, and the EDI water recovery rate was 90%.

  For comparison, in the operation of EDI, pure water was produced by performing the same operation as above except that the flow direction to the concentrating chamber was changed to an upward flow and a parallel flow system was adopted.

  As a result of analyzing the silica in the obtained pure water and comparing the silica removal rate between the above countercurrent method and the cocurrent method, the silica removal rate of the countercurrent method is 4.9 compared to the cocurrent method. It was twice as high. Silica was analyzed by molybdenum blue absorptiometry.

1: EDI
2: Anode 3: Anode chamber 4: Cathode 5: Cathode chamber 61: Anion exchange membrane 71: Cation exchange membrane 81: Desalination chamber 91: Concentration chamber 121: Anode chamber side inflow pipe 122: Anode chamber side outflow pipe 123 : Cathode chamber side inflow tube 124: Cathode chamber side outflow tube 131: Desalination chamber side inflow tube 132: Desalination chamber side outflow tube 141: Concentration chamber side inflow tube 142: Concentration chamber side outflow tube A: Cation exchanger and Mixture of anion exchanger a: Mixture of cation exchanger and anion exchanger

Claims (1)

In a pure water production method using a reverse osmosis membrane device and an electric deionization device disposed at a subsequent stage, an electric deionization device is provided between an anode chamber having an anode and a cathode chamber having a cathode. It consists of multiple sets of desalting chambers and concentrating chambers formed by alternately arranging anion exchange membranes and cation exchange membranes, and the desalting chambers and concentrating chambers contain cation exchangers and anion exchangers. Using an electric deionization apparatus containing the mixture, the water flow direction of each demineralization chamber is an upward flow, and the water flow direction to each concentration chamber is downward flow, The concentration of silica in the permeated water of the reverse osmosis membrane device supplied as treated water to the electric deionization device with the water flow direction of each demineralization chamber and the water flow direction to each concentration chamber as a countercurrent direction Of pure water, characterized in that the range of 1.5 to 3.0 mg / L .

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