CN106029580B

CN106029580B - Method and apparatus for recovering cooling water

Info

Publication number: CN106029580B
Application number: CN201580009395.4A
Authority: CN
Inventors: 早川邦洋; 内田隆彦
Original assignee: Kurita Water Industries Ltd
Current assignee: Kurita Water Industries Ltd
Priority date: 2014-03-14
Filing date: 2015-01-22
Publication date: 2020-06-16
Anticipated expiration: 2035-01-22
Also published as: TWI642635B; CN106029580A; MY175667A; TW201600468A; JP2015174030A; JP5773013B1; WO2015136992A1; SG11201607245XA

Abstract

When RO membrane treatment is performed on cooling discharge water such as discharge water of a circulating cooling water system and water recovery is performed, the cost of water treatment is reduced, and the improvement and stabilization of the water recovery rate are achieved. In water recovery in which effluent from a circulating cooling water system is treated by a water recovery system including a pretreatment film and an RO film and the treated water is returned to the circulating cooling water system, a dispersant that permeates the pretreatment film is added to the circulating cooling water system as a dispersant for dispersing scale components. By using a pretreatment film that allows a dispersant to permeate as a pretreatment film for an RO film and effectively utilizing the dispersant added to a circulating cooling water system in a water recovery system, it is possible to reduce the cost of water treatment and to improve and stabilize the water recovery rate.

Description

Method and apparatus for recovering cooling water

Technical Field

The present invention relates to a method and an apparatus for recovering cooling water discharged from a cooling device used in industrial processes such as building air conditioning, chemical industry, paper industry, iron industry, and power industry.

Background

In a heat transfer surface or a pipe in contact with water in a cooling water system, a boiler water system, or the like, scale inhibition occurs. In particular, from the standpoint of resource and energy saving, when the high concentration operation is performed by reducing the amount of coolant discharged (discharged) from the system, the salts dissolved in the water are concentrated, the heat transfer surface is easily corroded, and the insoluble salts are formed and scale. If scale adheres to the wall surface of the apparatus, the operation of the boiler or the heat exchanger is seriously hindered, for example, by a decrease in thermal efficiency or a blockage of piping.

In recent years, for the purpose of water saving and energy saving, a tendency to make the most efficient use of water as much as possible has become remarkable. In the case of performing the high concentration operation, there is a limit to the inhibition of the deposition of scale.

There has been constructed a structure in which the drain water of the cooling water is recovered by a recovery system and the treated water is returned to the cooling tower. As this recovery system, in general, salts (ions) are removed by a reverse osmosis membrane (RO membrane), and the treated water is returned to the cooling tower. For example, the following systems have been studied (patent documents 1 to 3).

The system 1: agglutination → sand filtration → safety filter → RO membrane

And (3) system 2: agglutination → sand filtration → pretreatment membrane → RO membrane

And (3) system: agglutination → pressurized floating → sand filtration → safety filter → RO membrane

And (4) system: decarbonizing tower → pretreatment membrane → RO membrane

And (5) the system: RO membrane

Although the system 5 is a simple system having only an RO membrane device, it is difficult to perform stable treatment because the RO membrane is clogged by turbid substances contained in the wastewater.

As shown in systems 1 to 4, the RO membrane treatment can be stabilized by removing turbid materials in the wastewater by an aggregation treatment or a pretreatment membrane at the front stage of the RO membrane. However, the drainage water contains a dispersant added to the circulating cooling water system, and this dispersant hinders the flocculation treatment. Therefore, in the flocculation treatment of the systems 1 to 3, the amount of the flocculant to be added required for the treatment becomes extremely large.

In the RO membrane apparatus, a dispersant is required to disperse scale components and stabilize the treatment at a high water recovery rate, but since the dispersant in the wastewater is removed by the coagulation treatment, it is necessary to add a dispersant to the RO membrane feed water in order to achieve the scale dispersion in the RO membrane and the stabilization of the treatment.

In the system 4 for removing turbid materials in the wastewater by the pretreatment membrane without performing the coagulation treatment, since the dispersant in the wastewater is removed by the pretreatment membrane in the same manner, it is necessary to add the dispersant to the feed water of the RO membrane to stabilize the treatment of the RO membrane system.

Patent document 1: japanese patent laid-open publication No. 2003-1256;

patent document 2: japanese patent laid-open publication No. 2002-18437;

patent document 3: japanese patent laid-open No. 2009 and 297600.

Disclosure of Invention

In the water recovery system according to the related art, in order to stably operate the RO membrane device, it is necessary to add a dispersant to the water supplied to the RO membrane, which causes costs and work, and increases the treatment cost.

The invention provides a method and a device for recovering cooling drainage water, which can reduce the cost of water treatment and improve and stabilize the water recovery rate when performing RO membrane treatment on the cooling drainage water such as drainage water of a circulating cooling water system and recovering water.

The present inventors have made extensive studies to solve the above problems, and as a result, have obtained the following findings. When RO film treatment is performed on cooling discharge water such as drain water of a circulating cooling water system and water is recovered, a pretreatment film that permeates a dispersant added to the circulating cooling water system is used as a pretreatment film for the RO film, and the dispersant added to the circulating cooling water system and contained in the cooling discharge water is effectively used as a dispersant for the RO film by permeating the pretreatment film, so that it is not necessary to add a dispersant to the water recovery system, or the amount of the dispersant to be added can be reduced. This can reduce the cost of water treatment and improve and stabilize the water recovery rate.

The present invention has been achieved based on the above knowledge, and the gist thereof is as follows.

[1] A method for recovering cooling effluent, which comprises treating the effluent from a circulating cooling water system to which a dispersant for dispersing scale components has been added in a water recovery system comprising a pretreatment membrane and a reverse osmosis membrane, and returning the treated water to the circulating cooling water system,

in the circulating cooling water system, the dispersant permeates the pretreatment film.

[2] The method for recovering cooling effluent as described in [1], wherein the transmittance of the dispersant calculated by the following numerical formula of the pretreated film is 80% or more,

the transmittance (dispersant concentration of permeated water in the pretreatment film/dispersant concentration of supplied water to the pretreatment film) × 100.

[3] The method for recovering cooling effluent as described in [1] or [2], wherein the pretreatment membrane is a microfiltration membrane or an ultrafiltration membrane.

[4] The method for recovering cooling drain water according to any one of [1] to [3], wherein the pH of the feed water to the pretreatment film is 5 or more.

[5] The method for recovering cooling effluent as described in any one of [1] to [4], wherein the molecular weight cut-off of the pretreatment membrane is 30000 or more.

[6] The method for recovering cooling drain water according to any one of [1] to [5], wherein the dispersant is a polymer having a sulfonic acid group and a carboxyl group.

[7] The method for recovering cooling effluent as described in [6], wherein the dispersant is a copolymer obtained by copolymerizing methacrylic acid and/or acrylic acid with 3-allyloxy-2-hydroxy-1-propanesulfonic acid and/or 2-acrylamido-2-methylpropanesulfonic acid.

[8] The method for recovering cooling water discharge according to any one of [1] to [7], wherein the pH of the feed water to the reverse osmosis membrane is adjusted to 4.0 to 7.5.

[9] The method for recovering cooling discharge water according to any one of [1] to [8], wherein a concentration of the dispersant in the feed water of the reverse osmosis membrane is measured, and the dispersant is added to the feed water of the reverse osmosis membrane so that the concentration of the dispersant becomes a predetermined concentration.

[10] The method for recovering cooling effluent according to any one of [1] to [9], wherein the conductivity of at least one of the effluent, the reverse osmosis membrane feed water and the reverse osmosis membrane concentrated water is measured, and the water recovery rate of the reverse osmosis membrane is adjusted based on the measured value of the conductivity.

[11] The method for recovering cooling discharge water according to any one of [1] to [10], wherein a concentration of the dispersant in the discharge water and/or the reverse osmosis membrane feed water is measured, and a water recovery rate of the reverse osmosis membrane is adjusted based on the measured value of the concentration of the dispersant.

[12] The method for recovering cooling drain water according to any one of [1] to [11], wherein a polymer compound having a phenolic hydroxyl group is added to the drain water.

[13] The method for recovering cooling drain water according to any one of [1] to [12], wherein the reverse osmosis membrane permeate is circulated when the water recovery system is stopped, or pure water or deionized water is passed through the system, and the water recovery system is stopped after an operation for discharging the reverse osmosis membrane concentrated water to the outside of the system is performed.

[14] A recovery device for cooling discharged water, comprising a pretreatment membrane device for passing discharged water from a circulating cooling water system, a reverse osmosis membrane device for passing permeate of the pretreatment membrane device, and a return device for returning permeate of the reverse osmosis membrane device to the circulating cooling water system,

the circulating cooling water system is provided with a dispersant adding device for adding a dispersant for dispersing the scale component into the water system, wherein the dispersant can penetrate through the pretreatment film.

[15] The apparatus for recovering cooling effluent as described in [14], wherein the transmittance of the dispersant calculated by the following equation of the pretreated film is 80% or more,

[16] The apparatus for recovering cooling effluent as described in [14] or [15], wherein the pretreatment membrane is a microfiltration membrane or an ultrafiltration membrane.

[17] The apparatus for recovering cooling drain water according to any one of [14] to [16], wherein the pH of the feed water to the pretreatment film is 5 or more.

[18] The apparatus for recovering cooling drain water according to any one of [14] to [17], wherein a cut-off molecular weight of the pretreatment membrane is 30000 or more.

[19] The apparatus for recovering cooling drain water according to any one of [14] to [18], wherein the dispersant is a polymer having a sulfonic acid group and a carboxyl group.

[20] The apparatus for recovering cooling drain water according to [19], wherein the dispersant is a copolymer obtained by copolymerizing methacrylic acid and/or acrylic acid with 3-allyloxy-2-hydroxy-1-propanesulfonic acid and/or 2-acrylamido-2-methylpropanesulfonic acid.

[21] The apparatus for recovering cooling drain water according to any one of [14] to [20], comprising: and a pH adjusting device for adjusting the pH of the feed water to the reverse osmosis membrane to 4.0 to 7.5.

[22] The apparatus for recovering cooling drain water according to any one of [14] to [21], comprising: a dispersant concentration measuring device for measuring the concentration of the dispersant in the feed water to the reverse osmosis membrane, and a dispersant adjusting device for adding the dispersant to the feed water to the reverse osmosis membrane so that the concentration of the dispersant measured by the dispersant concentration measuring device becomes a predetermined concentration.

[23] The apparatus for recovering cooling drain water according to any one of [14] to [22], comprising: a conductivity measuring device for measuring the conductivity of at least one of the discharged water, the reverse osmosis membrane feed water and the reverse osmosis membrane concentrated water, and a water recovery rate adjusting device for adjusting the water recovery rate of the reverse osmosis membrane based on the measured value of the conductivity measuring device.

[24] The apparatus for recovering cooling drain water according to any one of [14] to [23], comprising: a dispersant concentration measuring device for measuring the concentration of the dispersant in the discharged water and/or the reverse osmosis membrane feed water, and a water recovery rate adjusting device for adjusting the water recovery rate of the reverse osmosis membrane based on the measured value of the dispersant concentration measuring device.

[25] The apparatus for recovering cooling drain water according to any one of [14] to [24], comprising: and a coagulation auxiliary agent adding device for adding phenolic hydroxyl groups to the discharge water.

[26] The apparatus for recovering cooling drain water according to any one of [14] to [25], wherein the reverse osmosis membrane apparatus comprises: a permeate circulating means for circulating the reverse osmosis membrane permeate at a stage preceding the reverse osmosis membrane apparatus, a means for passing pure water or deionized water through the reverse osmosis membrane apparatus, and a concentrated water discharging means for discharging the concentrated reverse osmosis membrane water to the outside of the system,

the cooling drain water recovery device further includes: and a control device for circulating the reverse osmosis membrane permeate at a preceding stage or introducing pure water or deionized water thereto, and stopping the recovery device of the cooling effluent after performing an operation for discharging the reverse osmosis membrane concentrate to the outside of the system, when the recovery device of the cooling effluent is stopped.

[ Effect of the invention ]

According to the present invention, the cooling effluent is treated by the pretreatment membrane at the previous stage of the RO membrane, whereby the turbid matter in the cooling effluent is removed, and the RO membrane treatment at the subsequent stage can be stabilized.

In the present invention, the dispersant added to the circulating cooling water system and contained in the cooling discharge water is configured to permeate the pretreatment film, and thus the dispersant can be effectively used as a dispersant for the RO film. Therefore, it is not necessary to add the dispersant removed at the previous stage of the RO membrane as in the system of the prior art, and it is possible to achieve further efficiency in both the economic aspect and the treatment operation, and to significantly reduce the treatment cost. Further, the dispersion agent having permeated the pretreatment film can stabilize the RO membrane treatment and improve the water recovery rate.

For these reasons, according to the method and apparatus for recovering cooling effluent of the present invention, scale inhibition of the RO membrane apparatus can be prevented with a simpler system, and stable water recovery can be performed over a long period of time.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail.

Cooling water discharge

In the present invention, as the cooling water to be subjected to the water recovery process, typically, the water discharged from the cooling tower is mentioned, but the present invention is not limited to the water discharged, and the present invention can be applied to all water discharged from the circulating cooling water system. For example, the circulating cooling water system may be configured such that a part or all of the circulating cooling water is taken out from a circulation pipe of the circulating cooling water system, treated according to the present invention, and then returned to the circulating cooling water system. The water may be collected by using, as a treatment target, the water discharged from the side filter (サイドフィルター) or the light filter (ライトフィルター) branched from the piping.

In the present invention, the cooling effluent is treated in sequence by the pretreatment membrane apparatus and the RO membrane apparatus as the water to be treated, and the treated water is returned to the circulating cooling water system.

Water filter (purifier)

Although the above-described cooling effluent may be treated directly by the pretreatment membrane device, since coarse turbid materials and foreign substances may be contained in the cooling effluent, it is preferable to provide a water filter in a stage preceding the pretreatment membrane device, remove the turbid materials and foreign substances by passing them through the water filter, and then perform the turbidity removal treatment in the pretreatment membrane device. Although the operation can be performed even if the water filter is omitted, in this case, the pretreatment membrane may be damaged by coarse turbid materials or foreign substances in the cooling discharge water.

As the water filter, an automatic water filter which automatically performs a cleaning process is particularly preferably used.

The shape of the water filter is not particularly limited, and any shape such as a Y-shape or a barrel-shape can be used.

The pore diameter of the water filter is preferably 100 to 500 μm. If the pore size of the water filter is smaller than 100 μm, the clogging of the water filter becomes serious. If the pore diameter of the water filter exceeds 500 μm, the possibility of damage to the pretreatment membrane due to coarse turbid materials or foreign substances that have passed through the water filter increases.

Instead of the water filter, a cartridge filter (notch きフィルター), a pleated filter (プリーツフィルター), or the like may be used. From the viewpoint of exchange frequency and cleaning efficiency, a water filter is preferable.

Pretreatment membrane device

The cooling water or the cooling water subjected to the turbidity removal treatment by the water filter is then treated by the pretreatment membrane device.

The pretreatment membrane device is a device for removing turbid substances or colloidal components in the cooling effluent water, which causes membrane fouling of the RO membrane device, and a microfiltration membrane (MF membrane) or an ultrafiltration membrane (UF membrane) can be used. The type of the membrane of the pretreatment membrane device is not particularly limited, and a hollow fiber type, a spiral type, or the like membrane filtration device can be used. The filtration method of the pretreatment membrane device is not particularly limited, and any of internal pressure filtration, external pressure filtration, cross-flow filtration and total volume filtration can be applied.

The cut-off molecular weight of the UF membrane as the pretreatment membrane is preferably 30000 or more. If the UF membrane has a molecular weight cut off of 30000 or less, the dispersant in the cooling effluent cannot permeate therethrough, and there is a possibility that it is necessary to add a dispersant separately at a stage before the RO membrane apparatus. The upper limit of the cut-off molecular weight of the UF membrane is not particularly limited, but when it is 1000000 or less, it is possible to remove high molecular weight polysaccharides and the like that may cause clogging of the RO membrane in the cooling effluent. The pore diameter of the MF membrane as the pretreatment membrane is preferably about 0.1 to 0.01 μm for the same reason as the molecular weight cut-off of the UF membrane.

In the pretreatment film, the transmittance of the dispersant to be described later, which is calculated by the following numerical expression, is preferably 80% or more, and particularly preferably 85% or more. If the transmittance of the dispersant of the pretreated film is lower than the above lower limit, the effects of the present invention cannot be effectively obtained. The upper limit of the transmittance of the dispersant for the pretreatment film is usually 100%.

Transmittance (dispersant concentration of permeated water in the pretreatment film/dispersant concentration of supplied water in the pretreatment film) × 100

In order to obtain the above-mentioned dispersant transmittance, it is preferable to use an appropriate dispersant as described later, and to set the pH of the feed water to the pretreatment film to 5 or more in the pretreatment film apparatus. If the pH of the feed water to the pretreatment membrane is lower than 5, the permeability of the pretreatment membrane may be low even if a polymer having a sulfonic acid group and a carboxyl group, which will be described later, is used as the dispersant, and the effects of the present invention may not be obtained. The pH of the feed water for the pretreatment film is not particularly limited as long as it is 5 or more. In general, the cooling effluent such as cooling tower effluent has a pH of 8 to 10, usually about 8 to 9, and therefore it is preferable to treat the effluent directly by a pretreatment film apparatus.

< dispersant >

In the present invention, the dispersant to be added to the circulating cooling water system is a dispersant which is permeable to the pretreatment film.

As the dispersant, a polymer having a sulfonic acid group and a carboxyl group is preferably used.

The dispersant is more likely to dissociate and improve the function as a dispersant under higher pH conditions, but in the RO membrane apparatus at the subsequent stage of the pretreatment membrane apparatus, since calcium and the like concentrated in the RO membrane apparatus are likely to precipitate as scale under high pH conditions, the treatment is performed under low pH conditions as described later. In the RO membrane apparatus under such low pH conditions, if the dispersant is a dispersant having only a carboxyl group and no sulfonic acid group, the dispersant is insoluble and the function as a dispersant cannot be obtained. Therefore, as the dispersant, a polymer having a sulfonic acid group and a carboxyl group is preferably used.

Examples of the polymer having a sulfonic acid group and a carboxyl group suitable as the dispersant include a copolymer between a monomer having a sulfonic acid group and a monomer having a carboxyl group, and a terpolymer between monomers copolymerizable with these monomers.

Examples of the monomer having a sulfonic acid group include: conjugated diene sulfonic acids such as 2-methyl-1, 3-butadiene-1-sulfonic acid, unsaturated (meth) allyl ether monomers having a sulfonic acid group such as 3- (meth) allyloxy-2-hydroxypropanesulfonic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid, 2-hydroxy-3-acrylamidopropanesulfonic acid, styrenesulfonic acid, methallylsulfonic acid (methallylsulfonic acid), vinylsulfonic acid, allylsulfonic acid, isopentenylsulfonic acid (isoallylsulfonic acid), or salts thereof, and preferably 3-allyloxy-2-hydroxy-1-propanesulfonic acid (HAPS) or 2-acrylamido-2-methylpropanesulfonic Acid (AMPS). The sulfonic acid group-containing monomers may be used alone in 1 kind or in combination of 2 or more kinds.

As the monomer having a carboxyl group, there may be mentioned: acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, ethylene acetic acid, Atropic acid (Atropic acid), maleic acid, fumaric acid, itaconic acid, hydroxyethylacrylic acid, or salts thereof, and the like, and acrylic acid and methacrylic acid are preferable. The carboxyl group-containing monomers may be used alone in 1 kind or in a mixture of 2 or more kinds.

Examples of the monomer copolymerizable with these monomers include amides such as N-t-butylacrylamide (N-tBOA) and N-vinylformamide.

Examples of dispersants suitable for the present invention include: acrylic Acid (AA) was reacted with 2-acrylamido-2-methylpropanesulfonic Acid (AMPS) at an AA: and AMPS is 70-90: 10-30 (molar ratio), and the molar ratio of AA to amides such as AMPS and N-tert-butyl acrylamide (N-tBOA) is as follows: AMPS: amide-based (40-90): 5-30: 5-30 (molar ratio), and mixing AA and 3-allyloxy-2-Hydroxypropanesulfonic Acid (HAPS) in the ratio of AA: HAPS 70-90: and copolymers obtained by copolymerization at a ratio of 10 to 30 (molar ratio), but the copolymer is not limited to these.

The weight average molecular weight of the polymer having a sulfonic acid group and a carboxyl group is preferably 1000 to 30000. If the weight average molecular weight of the polymer is less than 1000, the dispersing effect is insufficient. If the weight average molecular weight of the polymer exceeds 30000, the polymer becomes difficult to permeate through the pretreatment membrane, and the polymer itself may be adsorbed on the pretreatment membrane or RO membrane to cause membrane clogging.

The amount of the dispersant added to the circulating cooling water system is preferably 3 to 30mg/L, more preferably 5 to 20mg/L, as the concentration of the active ingredient (i.e., the polymer) from the viewpoint of the dispersing effect in the cooling tower, the economy, and the dispersing effect in the RO membrane feed water. The method and place of addition of the dispersant are not particularly limited.

As the dispersant, other polymers, phosphoric acid compounds such as phosphonic acid, and the like may be used as long as they can obtain a sufficient dispersing effect, in addition to the above-described polymers having a sulfonic acid group and a carboxyl group. The dispersant may be one which accurately grasps the scale components that may be generated from the quality of raw water in the circulating cooling water system and which is added in a concentration that can provide an effect.

RO membrane apparatus

The treated water (pretreated membrane permeate water) obtained by treating the cooling effluent by passing the cooling effluent through the aforementioned pretreated membrane device is then desalted by passing the treated water through an RO membrane device.

The type of RO membrane used in the RO membrane apparatus is not particularly limited, and may be suitably determined depending on the quality of the treated cooling effluent (the quality of the raw water supplied to the circulating cooling water system, the concentration ratio in the circulating cooling water system). The RO membrane preferably has a salt rejection of 80% or more, particularly 85% or more. If the desalination rate of the RO membrane is lower than this, the desalination efficiency is poor, and treated water (permeate) having good water quality cannot be obtained. As the material of the RO membrane, any one of a polyamide composite membrane, a cellulose acetate membrane, and the like can be used. The shape of the RO membrane is not particularly limited, and any of a hollow fiber type, a spiral type, and the like can be used.

In the RO membrane feed water (water passed through the RO membrane apparatus as water to be treated), an appropriate pH is present as follows. In order to adjust the pH of the RO membrane feed water, it is preferable to provide a pH adjusting device for adjusting the pH by adding an acid between the pretreatment membrane device and the RO membrane device. Examples of the pH adjusting device include a device in which an acid is directly added to a feed water introduction line of the RO membrane or a line stirrer provided in the line by a chemical injection pump or the like, or an acid is added to a separately provided pH adjusting tank. The acid used here is not particularly limited, and inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid can be suitably used.

In general, in a circulating cooling water system, the pH of the circulating cooling water rises to about 8 to 9 due to the concentration cycle operation. Such a high pH is desirable for the permeation of the dispersant through the pre-treatment membrane device. In the RO membrane apparatus, the cooling effluent is further concentrated, and therefore, scale may be generated. From the viewpoint of scale inhibition, it is preferable to operate the RO membrane apparatus by lowering the pH. The pH range of the RO membrane feed water is preferably 4.0 to 7.5. If the pH of the RO membrane feed water exceeds 7.5, scale such as calcium carbonate, calcium phosphate, calcium sulfate, and barium sulfate may be precipitated depending on the water quality.

When the concentration of silica in the cooling effluent exceeds 30mg/L, the pH of the RO membrane feed water is preferably lowered to 4.0 to 5.5 in order to suppress precipitation. From the viewpoint of preventing the precipitation of scale, the lower the pH of the RO membrane feed water is, the more preferable. In order to lower the pH of the RO membrane feed water to less than 4.0, the amount of acid required increases, which is not economically desirable.

If the cooling discharge water contains a large amount of humic acid or fulvic acid, the RO membrane may be clogged. In this case, the pH of the cooling water is preferably 5.5 to 7.0, particularly preferably 5.5 to 6.5. In such a pH range, clogging of the RO membrane due to acid dissociation of humic acid or fulvic acid is suppressed, Ca in the cooling water is effectively dispersed by the dispersant, and a complex with fulvic acid is hardly formed.

In the present invention, as the dispersant to be added to the circulating cooling water system, a dispersant that permeates the pretreatment film is used, and the dispersant contained in the cooling effluent and brought into the water recovery system is allowed to permeate the treatment water (permeate water) of the pretreatment film, and the scale dispersion treatment in the RO membrane apparatus is performed by the dispersant that has permeated the pretreatment film. Therefore, in the RO membrane feed water, it is necessary to contain a dispersant at a concentration effective for scale dispersion treatment.

The concentration of the dispersant in the RO feed water required for the scale dispersion treatment in the RO membrane apparatus varies depending on the quality of the cooling discharge water, the treatment conditions (water recovery rate) of the pretreatment membrane and the RO membrane, and the like, and cannot be generally specified. In general, the concentration of the dispersant in the RO membrane feed water is 3mg/L or more, and particularly preferably about 5 to 30 mg/L.

When the concentration of the dispersant in the RO membrane feed water is not sufficient to obtain a sufficient scale dispersion effect in the RO membrane apparatus, it is preferable to add the dispersant additionally on the inlet side of the RO membrane apparatus (between the pretreatment membrane apparatus and the RO membrane apparatus). As the dispersant to be added here, a dispersant suitable as the dispersant used in the circulating cooling water system described above can be used, but the dispersant is not absolutely required to be the same as the dispersant added in the circulating cooling water system, and a different dispersant can be used.

The concentration of the dispersant in the RO membrane feed water may be measured, and the amount of the dispersant to be added may be controlled so that the concentration of the dispersant becomes a predetermined concentration. As a method for measuring the concentration of the dispersant, a method based on a turbidimetric method (for example, the method described in Japanese patent application laid-open No. 2006-64498) can be used. The dispersant may be additionally added to the RO membrane feed water by, for example, a dispersant addition device interlocked with a dispersant concentration measurement device of the RO membrane feed water.

According to the present invention, in order to utilize the dispersant added to the circulating cooling water system as the dispersant of the RO membrane device, the dispersant contained in the cooling discharge water after being added to the circulating cooling water system and discharged needs to have activity that can function only as the dispersant when reaching the RO membrane device. Since the residence time of the cooling water in the cooling tower of the circulating cooling water system affects the activity of the dispersant, it may be preferable to adjust the residence time of the cooling tower of the circulating cooling water system so that the dispersant can exhibit sufficient activity in the RO membrane apparatus.

The water recovery rate in the RO membrane apparatus is preferably determined in consideration of the tendency of scale deposition in the RO membrane apparatus. Since the conductivity of the cooling effluent treated in the present invention and the concentration of Ca, Mg, and the like in the cooling effluent, which is a cause of fouling, may vary, the water recovery rate of the RO membrane may be adjusted according to the conductivity, Ca concentration, Mg concentration, and the like of the RO concentrate. The water recovery rate may be set by determining whether or not scale is generated based on pH, dispersant concentration, water quality, and the like.

Specifically, there may be mentioned: a conductivity meter for measuring the conductivity of at least one of the cooling effluent, the RO membrane feed water and the RO membrane concentrate is provided, and the scale deposition tendency in the RO membrane apparatus is evaluated on the basis of the measured value, and the water recovery rate of the RO membrane apparatus is controlled. In this case, when the measured value of the conductivity meter is high, it is judged that the scale deposition tendency is high, and the valve opening degree on the permeate water extraction side of the RO membrane is reduced so that the water recovery rate is low. Conversely, when the measured value of the conductivity meter is low, it is determined that the scale deposition tendency is low, and the valve opening degree on the permeate water extraction side of the RO membrane apparatus is increased so as to increase the water recovery rate.

Alternatively, the concentration of the dispersant in the cooling discharge water and/or the feed water to the RO membrane is measured, and when the measured value of the concentration of the dispersant is high, the valve opening on the permeate water extraction side of the RO membrane apparatus is determined to be low and the water recovery rate is increased, and conversely, when the measured value of the concentration of the dispersant is low, the valve opening on the permeate water extraction side of the RO membrane apparatus is determined to be high and the water recovery rate is decreased.

In the case where there is a concern about the occurrence of silica scale in the RO membrane apparatus, it is preferable to perform self-evaporation (flashing) by using cooling discharge water that is not concentrated in the apparatus, RO membrane permeate water, pure water, or deionized water when the RO membrane apparatus is stopped. The reason for this is that: when the RO membrane apparatus is stopped with the concentrate remaining in the RO membrane apparatus, silica scale or other scales may be generated depending on the stop time, and the RO membrane apparatus may not be stably operated when the operation is restarted. In this case, there may be mentioned: for example, when the operation of the RO membrane device is stopped, the RO membrane permeate is circulated to the inlet side of the RO membrane device, the RO membrane concentrate is discharged to the outside of the system, and both the primary side (water supply side) and the secondary side (concentrate side) of the RO membrane in the RO membrane device are replaced with the RO membrane permeate.

Other treatment

In the circulating cooling water system of the present invention, as a Slime control agent, there may be added: hypochlorite such as sodium hypochlorite (NaClO), chlorine gas, chloramine, chlorine trimeric isocyanate, chlorine bonding agent such as monochloroamino sulfonic acid (モノクロルスルファミン acid), chlorine bonding agent after reaction of chlorine such as monochloroamino sulfonic acid with amidosulfuric acid, a compound having amidosulfuric acid group, hypobromite such as sodium hypobromite, bromine bonding agent such as dibromohydantoin (dibromohydantoin), bromine bonding agent after reaction of bromine with amine or ammonia, a compound having amidosulfuric acid group, organic agent such as DBNPA (dibromonitrilopropionamide), MIT (methylisothiazolinone), hydrazine, hydantoin (5, 5-dimethylhydantoin), and the like. These can be added alone in 1 kind, or in combination of plural kinds.

In the RO membrane apparatus, the slime control treatment may be performed by using the slime control agent added to the circulating cooling water system. The slime control treatment may be performed by further adding a slime control agent to the upstream stage of the RO membrane apparatus. In the case where oxidative deterioration of the RO membrane due to chlorine or the like is a problem, the chlorine in the cooling effluent may be reduced and removed, and then a slime control agent may be separately added.

These mucus control agents may be added in 1 kind, or 2 or more kinds may be added simultaneously or alternately. The addition may be continuous or intermittent.

When the cooling effluent contains heavy metal ions such as copper and iron from the heat exchanger, the RO membrane may be accelerated to deteriorate in the presence of a chemical having an oxidation-reduction action (for example, sodium hypochlorite or hydrazine) and the heavy metal ions. In this case, by adding a substance having a chelating action of a heavy metal (for example, EDTA), it is possible to prevent the film from coming into contact with the heavy metal and to prevent the promotion of deterioration.

The polyamide-based RO membrane is deteriorated by contact with hypochlorite regardless of the presence or absence of heavy metals. Since hypochlorite is highly likely to cause membrane deterioration, it is preferably avoided as much as possible, and when it is applied, it is preferable to remove residual chlorine and then pass water through the RO membrane apparatus.

In order to stabilize the pretreatment membrane apparatus and the RO membrane apparatus, a polymer compound having a phenolic hydroxyl group (hereinafter, sometimes referred to as "phenolic polymer") may be added as a coagulation aid to the cooled effluent water as the water to be treated.

Examples of the phenolic polymer include: polyvinyl phenol-based polymers of vinyl phenol alone, modified vinyl phenol alone, copolymers of vinyl phenol and modified vinyl phenol, and copolymers of vinyl phenol and/or modified vinyl phenol and a hydrophobic vinyl monomer; phenol resins such as polycondensates of phenol and formaldehyde, polycondensates of cresol and formaldehyde, and polycondensates of xylenol and formaldehyde. As the phenolic polymer, particularly, a reaction product obtained by performing a resol-type 2-time reaction on a novolak-type phenol resin as described in japanese patent application laid-open nos. 2010-131469, 2013-255922, 2013-255923, and the like is preferably used.

The melting point of the phenolic polymer obtained by reacting the novolak-type phenol resin 2 times with resol-type phenol resin is 130 to 220 ℃, and particularly preferably 150 to 200 ℃. The weight average molecular weight of the phenolic polymer is preferably 5000 to 50000, more preferably 10000 to 30000.

The amount of the phenolic polymer to be added varies depending on the quality of the cooling effluent, and is not particularly limited, but the concentration of the active ingredient is preferably about 0.01 to 10 mg/L.

When the amount of the obtained treatment water (permeate) is reduced due to clogging of a pretreatment membrane device such as an MF membrane device or an RO membrane device caused by long-time treatment of the cooling discharge water (that is, when the water recovery rate is reduced), the amount of the treatment water is recovered by removing the clogging by performing the washing treatment on these membrane devices. The chemical used in the washing treatment may be suitably selected depending on the clogging substance and the membrane material, and for example, hydrochloric acid, sulfuric acid, nitric acid, sodium hypochlorite, sodium hydroxide, citric acid, oxalic acid, and the like may be selected.

[ examples ]

The present invention will be described more specifically with reference to examples below, but the present invention is not limited to the following examples without departing from the gist of the present invention.

[ dispersing agent ]

The specifications of the dispersant used in the following examples and reference examples are as follows.

AA/AMPS: copolymers of acrylic acid with AMPM, acrylic acid: AMPM (molar ratio) 70: 30, weight average molecular weight 10000;

AA/HAPS: copolymers of acrylic acid with HAPS, acrylic acid: HAPS (molar ratio) 70: 30, weight average molecular weight 8000;

AA/AMPS/N-tBAA: terpolymer of acrylic acid with AMPS and N-tert-butylacrylamide, acrylic acid: AMPM: N-tBAA (molar ratio) 70: 20: 10, weight average molecular weight 12000;

AA/MA: copolymers of acrylic acid with maleic acid, acrylic acid: maleic acid (molar ratio) 70: 30, weight average molecular weight 25000.

[ Cooling Drain Water ]

The cooling water effluent to be subjected to the water recovery treatment in the following examples and reference examples is cooling tower effluent (hereinafter simply referred to as "effluent") of a circulating cooling water system in which industrial water of thousand leaves is used as raw water and the concentration ratio is 3.5 times.

In this circulating cooling water system, the dispersants described in the examples and comparative examples were added so that the dispersant concentration in the system became a predetermined holding concentration, and sodium hypochlorite (NaClO) was added so that the residual chlorine concentration in the system became 0.5mg/L, thereby performing slime control treatment.

The pH of the discharged water is 8.5 to 8.9 (about 8.8).

[ example 1]

As the pretreatment membrane, an MF membrane was used, and water was recovered by treating the drainage water in the order of a water filter, an MF membrane apparatus, and an RO membrane apparatus.

The mesh size of the water filter was 400. mu.m. The MF membrane was prepared by using "ピューリア GS (product name) (hydrophilized PVDF, pore size 0.02 μm, external pressure type)" manufactured by Coli corporation (クラレ Co.). The RO membrane was manufactured by Katsuka Kogyo K.K. "KROA-2032-SN (Polyamide ultra-low pressure RO membrane)" of Tatsuma industries. The frequency of cleaning of the MF membrane apparatus was set to 1 time/30 minutes.

The drainage was passed through a water filter and an MF membrane device in this order without pH adjustment, and then sulfuric acid was added to the inlet side of the RO membrane device to adjust the pH to 5.0. Similarly, sodium hydrosulfite was added on the inlet side of the RO membrane apparatus so that the residual chlorine concentration became 0.05mg/L or less, and 10mg/L of "クリバーター (registered trademark) IK-110" (conjugated chlorine-based slime control agent) manufactured by Takaki Kaisha was added to the RO membrane apparatus, thereby carrying out slime control treatment.

The water recovery rates of the MF membrane device and the RO membrane device were 90% and 80%, respectively, and the total water recovery rate was 72%. Since the organic matter concentration of the wastewater is high, the water recovery rates of the MF membrane device and the RO membrane device gradually decrease with time. When the water recovery rate of the MF membrane device or RO membrane device becomes less than 50%, the device is temporarily stopped and the cleaning process is performed, and water flow is restarted under the condition that the total water recovery rate becomes 72%. Under these conditions, water was continuously supplied for 1 month and the recovery treatment was continued.

In the above-described water recovery treatment, the feed water of the pretreatment membrane (MF membrane) had a dispersant concentration of 10.5mg/L, the feed water of the RO membrane had a dispersant concentration of 10.3mg/L, and the average water recovery rate in one month was 70%.

[ example 2]

Drainage was collected by the same method as in example 1 except that AA/HAPS was used instead of AA/AMPS as a dispersant. The dispersant concentrations and the average water recovery rates of the feed water for the pretreatment membrane and the RO membrane were as shown in table 1.

[ example 3]

Drainage water was collected by the same method as in example 1 except that AA/AMPS/N-tBOA was used as a dispersant in place of AA/AMPS. The dispersant concentrations and the average water recovery rates of the feed water for the pretreatment membrane and the RO membrane were as shown in table 1.

[ example 4]

The drainage was collected by the same method as in example 1, except that the pH of the feed water to the MF membrane was adjusted to 5.5. The dispersant concentrations and the average water recovery rates of the feed water for the pretreatment membrane and the RO membrane were as shown in table 1.

[ example 5]

Drainage water was collected by the same method as in example 1, except that the retention concentration of the dispersant in the circulating cooling water system was set to 3mg/L and 7mg/L of the dispersant was additionally added to the RO membrane feed water. The dispersant concentrations and the average water recovery rates of the feed water for the pretreatment membrane and the RO membrane were as shown in table 1.

[ example 6]

The waste water was collected by the same method as in example 1 except that 1mg/L of an alkaline solution of a phenolic polymer having a weight-average molecular weight of 12000 and a melting point of 170 ℃ (active ingredient concentration of 16 wt%, pH12) produced by the method of example I-1 of Japanese patent application laid-open No. 2013-255923 was added to the waste water as an active ingredient concentration. The dispersant concentrations and the average water recovery rates of the feed water for the pretreatment membrane and the RO membrane were as shown in table 1.

[ reference example 1]

The drainage was collected by the same method as in example 1, except that the pH of the MF membrane feed water was adjusted to 4.5. The dispersant concentrations and the average water recovery rates of the feed water for the pretreatment membrane and the RO membrane were as shown in table 1.

[ reference example 2]

Drainage was collected by the same method as in example 1, except that a UF membrane having a molecular weight cut-off of 10000 ("PW 2540C 30" manufactured by GE corporation) was used as the pretreatment membrane. The dispersant concentrations and the average water recovery rates of the feed water for the pretreatment membrane and the RO membrane were as shown in table 1.

[ reference example 3]

The drainage was collected by the same method as in example 1, except that the pH of the RO membrane feed water was adjusted to 7.0. The dispersant concentrations and the average water recovery rates of the feed water for the pretreatment membrane and the RO membrane were as shown in table 1.

[ reference example 4]

Drainage water was collected by the same method as in example 1, except that AA/MA was used instead of AA/AMPS as the dispersant. The dispersant concentrations and the average water recovery rates of the feed water for the pretreatment membrane and the RO membrane were as shown in table 1.

[ reference example 5]

Drainage water was collected by the same method as in example 1, except that the retention concentration of the dispersant in the circulating cooling water system was set to 1 mg/L. The dispersant concentrations and the average water recovery rates of the feed water for the pretreatment membrane and the RO membrane were as shown in table 1.

*1: a dispersant was additionally added on the inlet side of the RO membrane.

*2: a flocculation aid for a phenol-based polymer is added to the drainage water.

*3: a UF membrane with a molecular weight cut-off of 10000 was used.

From table 1, the following facts can be understood.

According to the present invention, by performing the treatment in such a manner that an effective amount of the dispersant remains in the feed water to the RO membrane, stable treatment can be continued with a high water recovery rate.

In reference example 1, since the feed water pH of the membrane was set to a low value, the dispersant permeation rate of the pretreatment membrane was low, and the dispersant concentration of the feed water to the RO membrane was low, so that the average water recovery rate was lowered.

In reference example 2, since the UF membrane having a small molecular weight cut-off was used as the pretreatment membrane, the permeability of the pretreatment membrane for the dispersant was low, and the concentration of the dispersant in the feed water to the RO membrane was low, and therefore, the average water recovery rate was lowered.

In reference example 3, since the pH of the feed water to the RO membrane was high, there were problems of precipitation of calcium scale and membrane clogging in the RO membrane, and therefore, the average water recovery rate was lowered.

In reference example 4, since the polymer having only carboxyl groups and no sulfonic acid groups was used as the dispersant, if the pH of the feed water to the RO membrane was set to a low value, insolubilization occurred and did not act as a dispersant, and therefore, the RO membrane treatment was not stable, and the average water recovery rate was lowered.

In reference example 5, since the dispersant retention concentration in the circulating cooling water system was low, the dispersant concentration of the RO membrane feed water was low even though the pretreatment membrane was permeated, and therefore, the RO membrane treatment was not stable, and the average water recovery rate was lowered.

While the present invention has been described in detail with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes can be made therein without departing from the spirit and scope thereof.

This application is based on the application filed in japanese patent application No. 2014-052048, filed 3/14 2014, the entire contents of which are hereby incorporated by reference.

Claims

1. A method for recovering drainage from a circulating cooling water system, which comprises treating drainage from a circulating cooling water system to which a dispersant for dispersing scale components has been added in a water recovery system comprising a pretreatment film and a reverse osmosis film, and returning the treated drainage to the circulating cooling water system,

the dispersant added to the circulating cooling water system is used as the dispersant for the reverse osmosis membrane after passing through the pretreatment membrane,

the pH of the discharged water of the circulating cooling water system is 8-10,

the pretreatment membrane is a microfiltration membrane or an ultrafiltration membrane, the ultrafiltration membrane has a molecular weight cut-off of 30000 or more and 1000000 or less, the microfiltration membrane has a pore diameter of 0.1 to 0.01 μm, and the pretreatment membrane has a permeability of the dispersant calculated by the following numerical formula of 80% or more,

the transmittance (concentration of the dispersant in the water permeated through the pretreatment film/concentration of the dispersant in the water supplied to the pretreatment film) × 100%,

the pH of the feed water for the pretreatment film is set to 5 or more,

the foregoing dispersant is a polymer having a sulfonic acid group and a carboxyl group, the weight average molecular weight of the polymer being 1000-30000,

adjusting the pH of the feed water to the reverse osmosis membrane to 4.0 to 7.5,

the discharged water of the circulating cooling water system is treated by the pretreatment membrane device as it is, or by a pretreatment membrane device after coarse and large turbid materials or foreign materials are removed in advance by a water filter provided at a stage preceding the pretreatment membrane device,

the effluent from the circulating cooling water system passes through the pretreatment membrane device without undergoing coagulation treatment.

2. The method for recovering drain water from a recirculating cooling water system as set forth in claim 1,

the dispersant is a copolymer obtained by copolymerizing methacrylic acid and/or acrylic acid with 3-allyloxy-2-hydroxy-1-propanesulfonic acid and/or 2-acrylamido-2-methylpropanesulfonic acid.

3. The method for recovering drain water from a recirculating cooling water system as set forth in claim 1,

the concentration of the dispersant in the feed water to the reverse osmosis membrane is measured, and the dispersant is added to the feed water to the reverse osmosis membrane so that the concentration of the dispersant becomes a predetermined concentration.

4. The method for recovering drain water from a recirculating cooling water system as set forth in claim 1,

measuring the conductivity of at least one of the discharged water, the reverse osmosis membrane feed water and the reverse osmosis membrane concentrated water, and adjusting the water recovery rate of the reverse osmosis membrane based on the measured value of the conductivity.

5. The method for recovering drain water from a recirculating cooling water system as set forth in claim 1,

the concentration of the dispersant in the discharged water and/or the feed water to the reverse osmosis membrane is measured, and the water recovery rate of the reverse osmosis membrane is adjusted based on the measured value of the concentration of the dispersant.

6. The method for recovering drain water from a recirculating cooling water system as set forth in claim 1,

when the water recovery system is stopped, the reverse osmosis membrane permeate is circulated, or pure water or deionized water is passed through the system, and after an operation of discharging the reverse osmosis membrane concentrated water to the outside of the system is performed, the water recovery system is stopped.

7. A recovery device for the discharged water of a circulating cooling water system, which is provided with a pretreatment membrane device for passing the discharged water from the circulating cooling water system, a reverse osmosis membrane device for passing the permeated water of the pretreatment membrane device, and a return device for returning the permeated water of the reverse osmosis membrane device to the circulating cooling water system,

the circulating cooling water system is provided with a dispersant adding device for adding a dispersant for dispersing scale components into the water system, the dispersant added by the dispersant adding device is used as the dispersant for the reverse osmosis membrane after penetrating the pretreatment membrane,

the pH of the discharged water of the circulating cooling water system is 8-10,

the pH of the feed water for the pretreatment film is set to 5 or more,

the apparatus for recovering the discharged water of the circulating cooling water system further comprises a pH adjusting device for adjusting the pH of the feed water of the reverse osmosis membrane to 4.0 to 7.5,

8. The apparatus for recovering drain water of a recirculating cooling water system as set forth in claim 7,

9. The apparatus for recovering drain water of a recirculating cooling water system as set forth in claim 7,

it is provided with: a dispersant concentration measuring device for measuring the concentration of the dispersant in the feed water to the reverse osmosis membrane, and a dispersant adjusting device for adding the dispersant to the feed water to the reverse osmosis membrane so that the concentration of the dispersant measured by the dispersant concentration measuring device becomes a predetermined concentration.

10. The apparatus for recovering drain water of a recirculating cooling water system as set forth in claim 7,

it is provided with: a conductivity measuring device for measuring the conductivity of at least one of the discharged water, the reverse osmosis membrane feed water and the reverse osmosis membrane concentrated water, and a water recovery rate adjusting device for adjusting the water recovery rate of the reverse osmosis membrane based on the measured value of the conductivity measuring device.

11. The apparatus for recovering drain water of a recirculating cooling water system as set forth in claim 7,

it is provided with: a dispersant concentration measuring device for measuring the concentration of the dispersant in the discharged water and/or the reverse osmosis membrane feed water, and a water recovery rate adjusting device for adjusting the water recovery rate of the reverse osmosis membrane based on the measured value of the dispersant concentration measuring device.

12. The apparatus for recovering drain water of a recirculating cooling water system as set forth in claim 7,

the reverse osmosis membrane device comprises: a permeate circulating means for circulating the permeate of the reverse osmosis membrane at the inlet side of the reverse osmosis membrane device, a means for passing pure water or deionized water through the reverse osmosis membrane device, and a concentrated water discharging means for discharging the concentrated water of the reverse osmosis membrane to the outside of the system,

the recovery device for the discharged water of the circulating cooling water system includes: and a control device that, when the recovery device of the discharge water from the circulating cooling water system is stopped, circulates the reverse osmosis membrane permeate on the inlet side of the reverse osmosis membrane device or passes pure water or deionized water through the reverse osmosis membrane device, and stops the recovery device of the discharge water from the circulating cooling water system after an operation of discharging the reverse osmosis membrane concentrate to the outside of the system is performed.