JP5773013B1 - Cooling discharge water recovery method and recovery device - Google Patents

Abstract

[PROBLEMS] To reduce the water treatment cost and improve and stabilize the water recovery rate in recovering water by subjecting cooling discharge water such as blow water of a circulating cooling water system to RO membrane treatment. Dispersion that disperses scale components in a circulating cooling water system when water discharged from the circulating cooling water system is treated with a water recovery system including a pretreatment membrane and an RO membrane, and the treated water is returned to the circulating cooling water system. As the agent, one that permeates the pretreatment film is added. The RO membrane pretreatment membrane uses a permeation agent that is permeable to the dispersant and effectively uses the dispersant added in the circulating cooling water system in the water recovery system, thereby reducing water treatment costs and improving the water recovery rate. And to stabilize. [Selection figure] None

Description

  The present invention relates to a cooling exhaust water recovery method and recovery device in a cooling facility used in an industrial process such as a building air conditioner, a chemical industry, a paper industry, an iron industry, or an electric power industry.

Scale failure occurs on heat transfer surfaces and piping that come into contact with water such as cooling water systems and boiler water systems. In particular, from the standpoint of resource saving and energy saving, when high concentration operation is performed by reducing the amount of cooling water discharged (blow) out of the system, salts dissolved in water are concentrated and the heat transfer surface is corroded. And scales as a sparingly soluble salt. If the scale adheres to the wall surface of the apparatus, a serious obstacle occurs in the operation of the boiler and heat exchanger, such as a decrease in thermal efficiency and blockage of piping.
In recent years, the movement to effectively use water as much as possible for the purpose of saving water and saving energy has become prominent. However, in the case of further highly concentrated operation, there is a limit in suppressing the precipitation of scale. Is a well-known fact.

  Therefore, in some cases, cooling water blow water is collected by a collection system, and the treated water is returned to the cooling tower. As a recovery system, a reverse osmosis membrane (RO membrane) removes salts (ions) and returns treated water to a cooling tower. For example, the following systems are being studied (patents) Literatures 1-3).

System 1: Agglomeration-> Sand filtration-> Safety filter-> RO membrane System 2: Agglomeration-> Sand filtration-> Pretreatment membrane-> RO membrane System 3: Agglomeration-> Pressurization flotation-> Sand filtration-> Safety filter-> RO membrane System 4: Decarbonation tower → Pretreatment membrane → RO membrane System 5: RO membrane

Among the conventional systems 1 to 5 described above, the system 5 is a simple system using only the RO membrane device. However, since turbidity contained in the blow water blocks the RO membrane, it is difficult to perform a stable treatment.
As in systems 1 to 4, RO membrane treatment can be stabilized by agglomeration treatment at the previous stage of the RO membrane and removal of turbidity in the blown water by the pretreatment membrane. Since a dispersant added in an aqueous system is included and this dispersant inhibits the aggregation treatment, the addition amount of the aggregation agent necessary for the treatment is very large in the aggregation treatment of the systems 1 to 3. On the other hand, in the RO membrane device, a dispersant is required to disperse the scale components and stabilize the treatment with a high water recovery rate, but the agglomeration treatment removes the dispersant in the blow water. For this reason, it is necessary to add a dispersant to the RO membrane water supply in order to disperse the scale in the RO membrane and stabilize the treatment.
Even in the system 4 in which the turbidity in the blown water is removed by the pretreatment membrane without performing the agglomeration treatment, the dispersant in the blown water is removed by the pretreatment membrane. It is necessary to add a dispersant to the RO membrane water supply.

JP 2003-1256 A JP 2002-18437 A JP 2009-297600 A

  As described above, in the conventional water recovery system, it is necessary to add a dispersant to the RO membrane water supply for stable operation of the RO membrane device, and the cost and work for that purpose have increased the processing cost.

  The present invention relates to a cooling drainage recovery method that reduces the water treatment cost and improves and stabilizes the water recovery rate when recovering the cooling drainage water such as blow water of the circulating cooling water system by performing RO membrane treatment. It is another object of the present invention to provide a recovery device.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors, as a pretreatment membrane of the RO membrane, circulated as a RO membrane pretreatment membrane for recovering water by cooling the cooling discharge water such as blow water of the circulating cooling water system. Use a dispersant that permeates the dispersant added in the cooling water system, and use the dispersant added in the circulating cooling water system and contained in the cooling discharge water as a dispersant for the RO membrane through the pretreatment membrane. Has found that it is not necessary to add a dispersant in the water recovery system, or that the amount of dispersant added can be reduced, the water treatment cost can be reduced, and the water recovery rate can be improved and stabilized. .

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

[1] Discharge water from the circulating cooling water system to which a dispersant for dispersing scale components is added is treated with a water recovery system including a pretreatment membrane and a reverse osmosis membrane, and the treated water is returned to the circulating cooling water system. in the method of recovering the cooling water discharge, the dispersing agent added in the circulating cooling water system, after passing through the pretreatment film, there the recovery process of the cooling water discharged utilized as dispersants for the reverse osmosis membrane The pretreatment membrane is a microfiltration membrane or an ultrafiltration membrane, the pretreatment membrane has a feedwater pH of 5 or more, and the dispersant is a polymer having a sulfonic acid group and a carboxyl group. Cooling discharge water recovery method characterized by.

[2] The method for recovering cooling effluent according to [1], wherein the pretreatment film has a permeability of the dispersant calculated by the following formula of 80% or more.
Permeability = (dispersant concentration of pretreated membrane permeated water / dispersant concentration of pretreated membrane feed water) × 100

[3] [1] or Oite in [2], the method of recovering the cooling water discharged to fractional molecular weight of the pretreatment film is characterized in that at least 30,000.

[ 4 ] In any one of [ 1 ] to [3], the dispersant is methacrylic acid and / or acrylic acid, 3-allyloxy-2-hydroxy-1-propanesulfonic acid and / or 2-acrylamide-. A method for recovering cooling discharged water, which is a copolymer obtained by copolymerizing 2-methylpropanesulfonic acid.

[ 5 ] In any one of [1] to [ 4 ], the pH of the reverse osmosis membrane feed water is adjusted to 4.0 to 7.5.

[ 6 ] In any one of [1] to [ 5 ], the concentration of the dispersant in the reverse osmosis membrane feed water is measured, and the dispersion is added to the reverse osmosis membrane feed water so that the dispersant concentration becomes a predetermined concentration. A method for recovering cooling effluent, comprising adding an agent.

[ 7 ] In any one of [1] to [ 6 ], the conductivity of the discharged water, the reverse osmosis membrane water supply and / or the reverse osmosis membrane concentrated water is measured, and the reverse is determined according to the measured value of the conductivity. A method for recovering cooling effluent, comprising adjusting a water recovery rate of an osmosis membrane.

[ 8 ] In any one of [1] to [ 7 ], the dispersant concentration of the discharged water and / or reverse osmosis membrane water supply is measured, and the water in the reverse osmosis membrane is measured according to the measured value of the dispersant concentration. A method for recovering cooling effluent, wherein the recovery rate is adjusted.

[ 9 ] The method for recovering cooling effluent according to any one of [1] to [ 8 ], wherein a polymer compound having a phenolic hydroxyl group is added to the effluent.

[ 10 ] In any one of [1] to [ 9 ], when the water recovery system is stopped, the reverse osmosis membrane permeated water is circulated, or pure water or deionized water is passed through the reverse osmosis membrane. A cooling drainage recovery method characterized by stopping the water recovery system after performing an operation of discharging concentrated water out of the system.

[ 11 ] A pretreatment membrane device through which drained water from the circulating cooling water system is passed, a reverse osmosis membrane device through which the permeated water of the pretreatment membrane device is passed, and the permeated water of the reverse osmosis membrane device in the recovery device of the cooling water discharged and a returning means for returning the circulating cooling water system, the circulating cooling water system has a dispersing agent addition means for adding a dispersing agent to disperse the scale components to the aqueous system, said dispersant additive means A cooling drainage recovery device used as the dispersant for the reverse osmosis membrane after the dispersing agent added in the step passes through the pretreatment membrane , wherein the pretreatment membrane is a microfiltration membrane or an ultrafiltration membrane. An apparatus for recovering cooled and discharged water, which is a filtration membrane, wherein the pH of feed water of the pretreatment membrane is 5 or more, and the dispersant is a polymer having a sulfonic acid group and a carboxyl group .

[ 12 ] The cooling wastewater recovery device according to [ 11 ], wherein the permeability of the dispersant calculated by the following formula of the pretreatment film is 80% or more.
Permeability = (dispersant concentration of pretreated membrane permeated water / dispersant concentration of pretreated membrane feed water) × 100

[13] [11] or Oite to [12], collecting device of the cooling water discharged, wherein the molecular weight cutoff of the pretreatment film is 30,000 or more.

[ 14 ] In any one of [ 11 ] to [13], the dispersant is methacrylic acid and / or acrylic acid, 3-allyloxy-2-hydroxy-1-propanesulfonic acid and / or 2-acrylamide-. An apparatus for recovering cooling effluent, which is a copolymer obtained by copolymerizing 2-methylpropanesulfonic acid.

[ 15 ] In any one of [ 11 ] to [ 14 ], the apparatus for recovering cooling drainage water has pH adjusting means for adjusting the pH of the reverse osmosis membrane feed water to 4.0 to 7.5. .

[ 16 ] In any one of [ 11 ] to [ 15 ], a dispersant concentration measuring means for measuring the dispersant concentration of the water supplied to the reverse osmosis membrane, and the dispersant concentration measured by the dispersant concentration measuring means. And a cooling agent recovery means for adding the dispersing agent to the reverse osmosis membrane water supply so that the concentration of water becomes a predetermined concentration.

[ 17 ] In any one of [ 11 ] to [ 16 ], conductivity measuring means for measuring conductivity of the discharged water, reverse osmosis membrane water supply and / or reverse osmosis membrane concentrated water, and measurement of the conductivity measuring means A cooling wastewater recovery apparatus comprising: a water recovery rate adjusting means for adjusting a water recovery rate of the reverse osmosis membrane according to a value.

[ 18 ] In any one of [ 11 ] to [ 17 ], the dispersant concentration measuring means for measuring the dispersant concentration of the discharged water and / or reverse osmosis membrane water supply, and the measured value of the dispersant concentration measuring means And a water recovery rate adjusting means for adjusting the water recovery rate of the reverse osmosis membrane.

[ 19 ] In any one of [ 11 ] to [ 18 ], there is provided an apparatus for recovering cooling effluent, characterized by having a coagulant assistant adding means for adding a phenolic hydroxyl group to the effluent.

[ 20 ] In any one of [ 11 ] to [ 19 ], the reverse osmosis membrane device is a permeated water circulating means for circulating the reverse osmosis membrane permeated water upstream of the reverse osmosis membrane device, or pure water or deionized water. Means for passing water through the reverse osmosis membrane device, and concentrated water discharge means for draining the reverse osmosis membrane concentrated water out of the system. Control to circulate water in the previous stage, or to pass pure water or deionized water, and to stop the cooling drainage recovery device after performing an operation to discharge the reverse osmosis membrane concentrated water out of the system Means for Collecting Cooled Drainage Water

According to the present invention, by treating the cooling discharge water with the pretreatment film upstream of the RO membrane, turbidity in the cooling discharge water can be removed and the subsequent RO membrane treatment can be stabilized.
Moreover, in the present invention, the dispersing agent added in the circulating cooling water system and contained in the cooling discharge water permeates through the pretreatment membrane, so that the dispersing agent is effectively used as a dispersing agent for the RO membrane. can do. For this reason, unlike the conventional system, it is not necessary to re-add the dispersant removed in the previous stage of the RO membrane, and the efficiency can be improved economically and in terms of processing operation, and the processing cost is greatly reduced. Can do. And the dispersion | distribution agent which permeate | transmitted the pre-processing film | membrane can be aimed at stabilization of RO membrane process and the improvement of a water recovery rate.
For this reason, according to the cooling drain water recovery method and recovery device of the present invention, it is possible to prevent the scale failure of the RO membrane device with a simpler system and perform stable water recovery over a long period of time. .

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

<Cooling discharge water>
In the present invention, cooling discharge water used for water recovery treatment typically includes blow water from a cooling tower, but is not limited to blow water, and the present invention includes all discharges discharged from a circulating cooling water system. Can be applied to water. For example, a part or all of the circulating cooling water may be extracted from the circulating piping of the circulating cooling water system, treated according to the present invention, and then returned to the circulating cooling water system. In addition, it is possible to collect water from the discharged water branched and discharged from the side filter and light filter pipes.
In the present invention, such cooling discharge water is treated as water to be treated, sequentially treated by the pretreatment membrane device and the RO device, and the treated water is returned to the circulating cooling water system.

<Strainer>
The cooling discharge water can be treated as it is in the pretreatment membrane device, but since the cooling discharge water may contain coarse turbidity and foreign matter, a strainer is provided in the front stage of the pretreatment membrane device. It is preferable to perform turbidity treatment in the pretreatment membrane device after removing these in advance with a strainer. Operation is possible even if the strainer is omitted, but in this case, the pretreatment film may be damaged by coarse turbidity or foreign matter in the cooling discharge water.

  As the strainer, an auto strainer that performs a cleaning process automatically is particularly preferably used.

The shape of the strainer is not particularly limited, and any shape such as a Y shape or a bucket shape can be used.
The strainer preferably has a pore diameter of 100 to 500 μm. When the pore size of the strainer is smaller than 100 μm, the strainer is severely blocked, and when it exceeds 500 μm, there is a high possibility that coarse turbidity or foreign matter that has passed through the strainer may damage the pretreatment film.

  A filter such as a thread winding filter or a pleated filter may be used instead of the strainer, but a strainer is preferable from the viewpoint of replacement frequency and cleaning efficiency.

<Pretreatment membrane device>
Preferably, the cooled discharged water after the turbidity treatment with the strainer is then treated with a pretreatment membrane device.

  The pretreatment membrane device is for removing turbidity and colloidal components in the cooling discharge water that cause membrane contamination of the RO membrane device. It is a microfiltration membrane (MF membrane) and ultrafiltration membrane (UF membrane). Can be used. The membrane type is not particularly limited, and a membrane filtration device such as a hollow fiber type or a spiral type can be employed. Moreover, there is no restriction | limiting also in the filtration system, Any system of internal pressure filtration, external pressure filtration, crossflow filtration, and total amount filtration is applicable.

  The molecular weight cutoff of the UF membrane as the pretreatment membrane is preferably 30,000 or more. If the molecular weight cut off of the UF membrane is smaller than 30,000, the dispersant in the cooling discharge water cannot be permeated, and it may be necessary to add the dispersant again before the RO membrane device. The upper limit of the molecular weight cut-off of the UF membrane is not particularly limited, but it is preferably 1,000,000 or less because it is possible to remove polymer polysaccharides and the like that can cause clogging of the RO membrane in the cooling discharge water. The pore size 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 such a pretreatment film, the transmittance of the below-described dispersant calculated by the following formula is preferably 80% or more, particularly 85% or more. When the transmittance of the dispersant is lower than the above lower limit, the effect of the present invention cannot be obtained effectively. The upper limit of the transmittance of the dispersant is usually 100%.
Permeability = (dispersant concentration of pretreated membrane permeated water / dispersant concentration of pretreated membrane feed water) × 100

  In order to obtain the above-mentioned dispersant permeability, it is preferable to use a suitable dispersant described later as the dispersant, and in the pretreatment membrane device, the pH of the feed water of the pretreatment membrane is 5 or more. When the pH of the feed water of the pretreatment membrane is lower than 5, even if a polymer having a sulfonic acid group and a carboxyl group, which will be described later, is used as a dispersant, the transmittance of the pretreatment membrane is lowered, and the effect of the present invention is obtained. It may not be possible. The pH of the feed water of the pretreatment membrane may be 5 or more, and the upper limit is not particularly limited, but cooling discharge water such as cooling tower blow water is usually about pH 8 to 10, usually about 8 to 9 Therefore, it is preferable to process this as it is with a pretreatment film device.

<Dispersant>
In the present invention, the dispersant added to the circulating cooling water system permeates the pretreatment membrane.

As this dispersant, a polymer having a sulfonic acid group and a carboxyl group is preferably used.
That is, the dispersing agent dissociates and the function as the dispersing agent becomes higher as the pH becomes higher. However, in the RO membrane device at the rear stage of the pretreatment membrane device, the concentration in the RO membrane device occurs under the high pH condition. Since the calcium and the like thus deposited easily become a scale, the treatment is performed under low pH conditions as will be described later. In the RO membrane apparatus under such a low pH condition, if the dispersant has only a carboxyl group and does not have a sulfonic acid group, it becomes insoluble and cannot function as a dispersant. For this reason, it is preferable to use a polymer having a sulfonic acid group and a carboxyl group as the dispersant.

  As a polymer having a sulfonic acid group and a carboxyl group suitable as a dispersant, a copolymer of a monomer having a sulfonic acid group and a monomer having a carboxyl group, or, further, these monomers And terpolymers with other monomers that can be copolymerized with the monomer. Among these, monomers having a sulfonic acid group include 2-methyl-1,3-butadiene-1-sulfonic acid, etc. Conjugated dienesulfonic acid, 3- (meth) allyloxy-2-hydroxypropanesulfonic acid and other unsaturated (meth) allyl ether monomers having a sulfonic acid group and 2- (meth) acrylamide-2-methylpropanesulfone Acid, 2-hydroxy-3-acrylamidepropanesulfonic acid, styrenesulfonic acid, methallylsulfonic acid, vinylsulfonic acid, allylsulfonic acid, isoamylensul Acid, or salts thereof, preferably 3-allyloxy-2-hydroxy-1-propanesulfonic acid (HAPS), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), and one of these May be used alone, or two or more may be mixed and used.

  On the other hand, the monomer having a carboxyl group is preferably acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, vinyl acetic acid, atropic acid, maleic acid, fumaric acid, itaconic acid, hydroxyethylacrylic acid or a salt thereof. Examples thereof include acrylic acid and methacrylic acid, and one of these may be used alone, or two or more may be used in combination.

  Examples of monomers copolymerizable with these monomers include amides such as N-tert-butylacrylamide (N-tBAA) and N-vinylformamide.

  As a suitable dispersant for the present invention, in particular, acrylic acid (AA) and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) at a ratio of AA: AMPS = 70 to 90:10 to 30 (molar ratio). Copolymerized copolymer, amides such as AA, AMPS and N-tert-butylacrylamide (N-tBAA), AA: AMPS: amides = 40 to 90: 5 to 30: 5 to 30 (molar ratio) ) Copolymerized at a ratio of AA and 3-allyloxy-2-hydroxypropanesulfonic acid (HAPS), and copolymerized at a ratio of AA: HAPS = 70 to 90:10 to 30 (molar ratio). However, the present invention is not limited to these.

  The weight average molecular weight of the polymer having a sulfonic acid group and a carboxyl group is preferably 1,000 to 30,000. When the weight average molecular weight of this polymer is less than 1,000, the dispersion effect is insufficient, and when it exceeds 30,000, it becomes difficult to permeate the pretreatment film. It may be adsorbed on the RO membrane and cause membrane clogging.

  The amount of the dispersing agent added to the circulating cooling water system is 3 in particular as the concentration of the active ingredient (that is, the above-mentioned polymer) from the viewpoint of the dispersion effect and economical efficiency in the cooling tower, and the dispersion effect in the RO membrane water supply. It is preferable to set it to -30 mg / L, especially 5-20 mg / L. There are no particular restrictions on the method of adding the dispersant and the location of addition.

  As the dispersant to be added, in addition to the above-described polymer having a sulfonic acid group and a carboxyl group, other polymers and phosphoric acid compounds such as phosphonic acid can be used as long as a sufficient dispersion effect can be obtained. It can also be used. As for the dispersant, a scale component that can be generated from the quality of the raw water of the circulating cooling water system is identified, and a type of dispersant that can prevent the generation of the dispersant may be added so as to obtain a concentration at which an effect can be obtained.

<RO membrane device>
The treated water (pretreated membrane permeated water) after the cooling discharged water has been treated with the aforementioned pretreatment membrane device is then desalted with the RO membrane device.

  The type of RO membrane of the RO membrane device is not particularly limited and is appropriately determined depending on the quality of the cooling discharge water to be treated (the quality of the raw water supplied to the circulating cooling water system and the concentration rate in the circulating cooling water system). The salt ratio is preferably 80% or more, particularly 85% or more. When the desalting rate of the RO membrane is lower than this, desalting efficiency is poor, and treated water (permeated water) with good water quality cannot be obtained. As the material of the RO membrane, any material such as a polyamide composite membrane or a cellulose acetate membrane can be used. There is no restriction | limiting in particular also about the shape of RO membrane, Any things, such as a hollow fiber type and a spiral type, can be used.

  In the present invention, the RO membrane water supply (water passed through the RO membrane device as treated water) has a suitable pH as follows, and the pretreatment membrane device and the RO are adjusted to adjust the pH of the RO membrane water supply. It is preferable to provide a pH adjusting means for adjusting pH by adding an acid between the membrane device. Examples of the pH adjusting means include means for adding an acid directly to a RO membrane water supply introduction line or a line mixer provided in the line or to a pH adjusting tank provided separately by a chemical injection pump or the like. The acid used here is not particularly limited, and inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid can be suitably used.

As described above, normally, in the circulating cooling water system, the pH of the circulating cooling water rises to about 8 to 9 due to the concentration circulation operation, and such a high pH is more suitable for the permeation of the dispersant in the pretreatment membrane device. Is preferred. On the other hand, in the RO membrane device, since the cooling discharge water is further concentrated, there is a concern about generation of scale. In terms of scale suppression, it is preferable that the RO membrane device is operated at a reduced pH. The pH range of the RO membrane water supply is preferably 4.0 to 7.5. When pH exceeds 7.5, depending on the water quality, scales such as calcium carbonate, calcium phosphate, calcium sulfate, and barium sulfate may be precipitated.
Further, when the silica concentration in the cooling discharge water exceeds 30 mg / L, it is preferable to lower the pH of the RO membrane water supply to 4.0 to 5.5 in order to suppress the precipitation. The lower the pH of the RO membrane feed water, the better in terms of preventing scale precipitation. However, in order to make the pH lower than 4.0, the amount of acid required becomes large, which is not economically preferable.
In addition, when a large amount of humic acid or fulvic acid is contained in the cooling discharge water, the RO membrane may be clogged. In that case, the pH of the cooling discharge water is set to 5.5 to 7.0, particularly It is preferable to set it as 5.5-6.5. Within this pH range, humic acid and fulvic acid are dissociated and the RO membrane is blocked, and Ca in the cooling water is effectively dispersed by the dispersant to form a complex with fulvic acid. It becomes difficult.

  In the present invention, as the dispersant added to the circulating cooling water system, a dispersant that permeates the pretreatment membrane is used to disperse the dispersant contained in the cooling discharge water and brought into the water recovery system according to the present invention. The scale dispersion treatment in the RO membrane apparatus is performed with the dispersant that is permeated into the treated water (permeated water) and permeated through the pretreatment membrane. Therefore, the RO membrane water supply needs to contain a dispersant at a concentration effective for the scale dispersion treatment.

  In this case, the dispersant concentration of the RO membrane water supply necessary for the scale dispersion treatment of the RO membrane device differs depending on the quality of the cooling discharge water, the treatment conditions (water recovery rate) of the pretreatment membrane and the RO membrane, and is generally defined. In general, however, the dispersant concentration of the RO membrane water supply is preferably 3 mg / L or more, particularly about 5 to 30 mg / L.

  When the concentration of the dispersant in the RO membrane water supply is insufficient to obtain a sufficient scale dispersion effect in the RO membrane device, the dispersant is added on the inlet side of the RO membrane device (between the pretreatment membrane device and the RO membrane device). Additional addition is preferred. As the dispersant added here, those suitable as the dispersant used in the circulating cooling water system described above can be used, but it is not necessarily the same as the dispersant added in the circulating cooling water system, and is different. A dispersant may be used.

  In this case, the dispersant concentration can be controlled so that the dispersant concentration of the RO membrane water supply is measured and the dispersant concentration becomes a predetermined concentration. As a method for measuring the dispersant concentration, a method using a turbidimetric method (for example, a method described in JP-A-2006-64498) can be employed. The dispersant can be additionally added to the RO membrane water supply by, for example, a dispersant addition unit that is linked to the dispersant concentration measurement unit of the RO membrane water supply.

  In order to use the dispersant added to the circulating cooling water system as a dispersing agent for the RO membrane device according to the present invention, the dispersant discharged into the cooling discharge water after being added to the circulating cooling water system is RO When it reaches the membrane device, it needs to remain active enough to function as a dispersant. Since the residence time of the cooling water in the cooling tower of the circulating cooling water system affects the activity of the dispersing agent, the residence time of the cooling tower of the circulating cooling water system so that the dispersant exhibits sufficient activity in the RO membrane device. It may be preferable to adjust the value.

  The water recovery rate in the RO membrane device is preferably determined in consideration of the precipitation tendency of the scale in the RO membrane device. For example, the conductivity, Ca concentration, and Mg concentration of the RO concentrated water may vary because the conductivity of the cooling discharge water treated in the present invention and the concentration of Ca, Mg, etc. in the cooling discharge water that causes the scale may vary. The water recovery rate of the RO membrane may be adjusted according to the above. Further, the water recovery rate may be set by determining the presence / absence of scale from pH, dispersant concentration, water quality, and the like.

  Specifically, a conductivity meter for measuring the conductivity of cooling discharge water, RO membrane water supply and / or RO membrane concentrated water is provided, and the scale deposition tendency in the RO membrane device is evaluated based on the measured value. Controlling the water recovery rate of the membrane device. In this case, if the measured value of the conductivity meter is high, it is judged that the tendency of scale precipitation is high, and the valve opening on the permeate water extraction side of the RO membrane is reduced so that the water recovery rate is low, and conversely the conductivity When the measured value of the meter is low, it is determined that the tendency of scale deposition is low, and the opening degree of the valve on the permeate water extraction side of the RO membrane device is increased so that the water recovery rate becomes high.

  Alternatively, the dispersion concentration of the cooling discharge water and / or the RO membrane feed water is measured, and when the measured value of the dispersion concentration is high, it is judged that the tendency of scale precipitation is low, and the RO membrane device is set so that the water recovery rate becomes high. If the measured value of the dispersant concentration is low, it is judged that the tendency of scale precipitation is high, and the RO membrane device has a low water recovery rate. For example, reducing the opening of the permeated water outlet valve.

  In addition, in the RO membrane device, particularly when there is a concern about the generation of silica scale, when stopping the RO membrane device, cooling exhaust water that is not concentrated inside the device, RO membrane permeated water, pure water, or Flushing with deionized water is preferred. This is because when the RO membrane device is stopped while the concentrated water remains in the RO membrane device, silica scale and other scales may be generated depending on the stop time, and the RO membrane device cannot be stably operated when the operation is resumed. Because there is. In this case, 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 concentrated water is discharged out of the system, and the inside of the RO membrane device is moved to the primary side of the RO membrane ( For example, the water supply side) and the secondary side (concentrated water side) may be replaced with RO membrane permeate.

<Other processing>
In the circulating cooling water system according to the present invention, as a slime control agent, a hypochlorite such as sodium hypochlorite (NaClO), a chlorine agent such as chlorine gas, chloramine, chlorinated isocyanurate, monochlorosulfamic acid, etc. Chlorine and amidosulfuric acid, a compound containing amidesulfuric acid, a combined chlorinating agent, a brominating agent such as dibromohydantoin, an organic agent such as DBNPA (dibromonitrilopropion acid) and MIT (methylisothiazolone), hydrazine, and hydantoin (5,5) 5-dimethylhydantoin) or the like may be added.
In addition, in the RO membrane device, slime control treatment may be performed using these slime control agents added in the circulating cooling water system, and further slime control agent is added in the previous stage of the RO membrane device. May be performed. In addition, when oxidation degradation of the RO membrane due to a chlorine agent or the like becomes a problem, a slime control agent may be added separately after reducing and removing the chlorine agent in the cooling discharge water.
One type of these slime control agents may be added, or two or more types may be added simultaneously or alternately. Further, it may be added continuously or intermittently.

Also, when heavy metal ions such as copper and iron derived from heat exchangers are contained in the cooling discharge water, an RO membrane in the presence of an agent having a redox action such as thorium hypochlorite and hydrazine and heavy metal ions. May undergo accelerated degradation. In that case, by adding a substance having a chelating action of heavy metal (for example, EDTA), contact between the membrane and heavy metal can be prevented, and accelerated deterioration can be prevented.
The polyamide RO membrane deteriorates upon contact with hypochlorite regardless of the presence or absence of heavy metals. Hypochlorite has a high possibility of causing membrane deterioration. Therefore, it is preferable to avoid application as much as possible, and to apply it, after removing residual chlorine, it is preferable to pass water through the RO membrane device.

Further, in the present invention, in order to stabilize the pretreatment membrane device and the RO membrane device, a polymer compound having a phenolic hydroxyl group (hereinafter referred to as “phenolic polymer”) as an agglomeration aid in cooling discharge water that is the water to be treated. May also be added.) May be added.
Examples of the phenolic polymer include vinylphenol homopolymer, modified vinylphenol homopolymer, copolymer of vinylphenol and modified vinylphenol, vinylphenol and / or modified vinylphenol and hydrophobic vinyl monomer. Polyvinyl phenolic polymers such as copolymers; phenolic resins such as polycondensates of phenol and formaldehyde, polycondensates of cresol and formaldehyde, and polycondensates of xylenol and formaldehyde; Use a reaction product obtained by performing a resol-type secondary reaction on a novolak-type phenolic resin described in JP2010-131469A, JP2013-255922A, JP2013-255923A, or the like. Is preferred.

The melting point of the phenolic polymer obtained by subjecting the novolac type phenol resin to the resol type secondary reaction is preferably 130 to 220 ° C, particularly 150 to 200 ° C. Further, the weight average molecular weight of the phenolic polymer is preferably 5,000 to 50,000, and more preferably 10,000 to 30,000.
The amount of these phenolic polymers added varies depending on the quality of the cooling effluent, and is not particularly limited, but is preferably about 0.01 to 10 mg / L as the active ingredient concentration.

  In the present invention, the treatment of cooling and draining water for a long time obstructs a pretreatment membrane device such as an MF membrane device or an RO membrane device, and the amount of treated water (permeated water) obtained is reduced (ie, water When the recovery rate is reduced), these membrane devices can be washed to remove clogs and recover the amount of treated water. The chemicals used for the cleaning treatment can be appropriately selected according to the occluding substance and membrane material. For example, hydrochloric acid, sulfuric acid, nitric acid, sodium hypochlorite, sodium hydroxide, citric acid, oxalic acid, etc. are selected. be able to.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples as long as the gist of the present invention is not exceeded.

[Dispersant]
The specifications of the dispersant used in the following Examples and Reference Examples are as follows.
AA / AMPS: copolymer of acrylic acid and AMPM, acrylic acid: AMPM (molar ratio) = 70: 30, weight average molecular weight 10,000
AA / HAPS: copolymer of acrylic acid and HAPS, acrylic acid: HAPS (molar ratio) = 70: 30, weight average molecular weight 8,000
AA / AMPS / N-tBAA: terpolymer of acrylic acid, AMPS, and N-tert-butylacrylamide, acrylic acid: AMPM: N-tBAA (molar ratio) = 70: 20: 10, weight average molecular weight 12, 000
AA / MA: copolymer of acrylic acid and maleic acid, acrylic acid: maleic acid (molar ratio) = 70: 30, weight average molecular weight 25,000

[Cooling discharge water]
The cooling discharge water used for water recovery treatment in the following examples and reference examples is a cooling tower blow water (hereinafter, simply referred to as a circulating cooling water system) operating at a concentration factor of 3.5 times using Chiba industrial water as raw water. "Blow water").
In this circulating cooling water system, the dispersants described in the respective examples and comparative examples are added so that the dispersant concentration in the system becomes a predetermined retention concentration, and sodium hypochlorite (NaClO) is added in the system. The slime control treatment is performed by adding the residual chlorine concentration of 0.5 mg / L.
The pH of the blow water is 8.5 to 8.9 (about 8.8).

[Example 1]
MF membrane was used as a pretreatment membrane, and water was collected by treating blow water in the order of strainer, MF membrane device, and RO membrane device.
The mesh pore size of the strainer was 400 μm, and “Pureia GS (hydrophilic PVDF, pore size 0.02 μm, external pressure type)” manufactured by Kuraray Co., Ltd. was used as the MF membrane. As the RO membrane, “KROA-2032-SN (polyamide ultra-low pressure RO membrane)” manufactured by Kurita Kogyo Co., Ltd. was used. The cleaning frequency of the MF membrane device was 1 time / 30 minutes.

  The blow water was sequentially passed through the strainer and the MF membrane device without adjusting the pH, and then sulfuric acid was added on the inlet side of the RO membrane device to adjust the pH to 5.0. Similarly, sodium bisulfite is added at the inlet side of the RO membrane device so that the residual chlorine concentration is 0.05 mg / L or less, and “Kuriverter (registered trademark) IK-110” manufactured by Kurita Kogyo Co., Ltd. ( Bonded chlorine-based slime control agent) was added at 10 mg / L to perform slime control treatment of the RO membrane device.

  The water recovery rates of the MF membrane device and RO membrane device started from 90% and 80%, respectively, and the total water recovery rate was 72%. Since the blow water has a high organic substance concentration, the water recovery rate of the MF membrane device and the RO membrane device gradually decreases with time. For this reason, when the water recovery rate falls below 50%, the device is once stopped and washed, and the water flow is resumed again under the condition that the total water recovery rate becomes 72%. The recovery process was continued.

  In the above water recovery process, the dispersant concentration of the pretreatment membrane (MF membrane) feed water is 10.5 mg / L, and the dispersant concentration of the RO membrane feed water is 10.3 mg / L. The recovery rate was 70%.

[Example 2]
Blow water was collected in the same manner as in Example 1 except that AA / HAPS was used instead of AA / AMPS as the dispersant. Table 1 shows the dispersant concentration of the pretreatment membrane and RO membrane and the average water recovery rate.

[Example 3]
Blow water was recovered in the same manner as in Example 1 except that AA / AMPS / N-tBAA was used instead of AA / AMPS as the dispersant. Table 1 shows the dispersant concentration of the pretreatment membrane and RO membrane and the average water recovery rate.

[Example 4]
Blow water was collected in the same manner as in Example 1 except that the pH of the MF membrane feed water was adjusted to 5.5. Table 1 shows the dispersant concentration of the pretreatment membrane and RO membrane and the average water recovery rate.

[Example 5]
Blow water was collected in the same manner as in Example 1 except that the retention concentration of the dispersant in the circulating cooling water system was 3 mg / L and that 7 mg / L of dispersant was added to the RO membrane water supply. Table 1 shows the dispersant concentration of the pretreatment membrane and RO membrane and the average water recovery rate.

[Example 6]
An alkaline solution of a phenolic polymer (active ingredient concentration 16% by weight, pH 12) having a weight average molecular weight of 12000 and a melting point of 170 ° C. produced according to the method of Example I-1 of JP2013-255923A is used as blow water. The blow water was recovered in the same manner as in Example 1 except that 1 mg / L was added as the active ingredient concentration. Table 1 shows the dispersant concentration of the pretreatment membrane and RO membrane and the average water recovery rate.

[Reference Example 1]
Blow water was collected in the same manner as in Example 1 except that the pH of the MF membrane feed water was adjusted to 4.5. Table 1 shows the dispersant concentration of the pretreatment membrane and RO membrane and the average water recovery rate.

[Reference Example 2]
Blow water was collected in the same manner as in Example 1 except that a UF membrane (“PW2540C30” manufactured by GE) having a molecular weight cut-off of 10,000 was used as the pretreatment membrane. Table 1 shows the dispersant concentration of the pretreatment membrane and RO membrane and the average water recovery rate.

[Reference Example 3]
Blow water was collected in the same manner as in Example 1 except that the pH of the RO membrane feed water was 7.0. Table 1 shows the dispersant concentration of the pretreatment membrane and RO membrane and the average water recovery rate.

[Reference Example 4]
Blow water was recovered in the same manner as in Example 1 except that AA / MA was used in place of AA / AMPS as the dispersant. Table 1 shows the dispersant concentration of the pretreatment membrane and RO membrane and the average water recovery rate.

[Reference Example 5]
Blow water was collected in the same manner as in Example 1 except that the concentration of the dispersant retained in the circulating cooling water system was 1 mg / L. Table 1 shows the dispersant concentration of the pretreatment membrane and RO membrane and the average water recovery rate.

Table 1 shows the following.
According to the present invention, by performing the treatment so that an effective amount of the dispersant remains in the RO membrane water supply, a stable treatment can be continued with a high water recovery rate.

In Reference Example 1, since the membrane feed water pH was lowered, the dispersant permeability of the pretreatment membrane was low, and the dispersant concentration of the RO membrane feed water was low, so the average water recovery rate was lowered.
In Reference Example 2, since a UF membrane having a small fractional molecular weight was used as the pretreatment membrane, the dispersant permeability of the pretreatment membrane was low, and the dispersant concentration of the RO membrane water supply was low, so the average water recovery rate was reduced. ing.
In Reference Example 3, since the pH of the RO membrane water supply is high and there are problems of calcium scale precipitation and membrane blockage in the RO membrane, the average water recovery rate is lowered.
In Reference Example 4, since a polymer containing only carboxyl groups and no sulfonic acid groups was used as the dispersant, it became insoluble when the pH of the RO membrane water supply was lowered, and it did not function as a dispersant, so the RO membrane treatment was stable. The average water recovery rate has declined.
In Reference Example 5, since the dispersant retention concentration in the circulating cooling water system is low and the dispersant concentration in the RO membrane water supply is low even if it passes through the pretreatment membrane, the RO membrane treatment is not stable and the average water recovery rate is reduced. doing.

Claims (20)

Cooled discharged water which treats the discharged water from the circulating cooling water system to which the dispersant for dispersing the scale component is added with a water recovery system including a pretreatment membrane and a reverse osmosis membrane and returns the treated water to the circulating cooling water system. in the process of recovering, said dispersing agent being added in the circulating cooling water system, after passing through the pretreatment film, a method of recovering the cooling water discharged utilized as dispersants for the reverse osmosis membrane,
The pretreatment membrane is a microfiltration membrane or an ultrafiltration membrane,
The pH of the pretreatment membrane feed water is 5 or more,
The method for recovering cooled discharged water, wherein the dispersant is a polymer having a sulfonic acid group and a carboxyl group . The method of claim 1, wherein the pretreatment membrane has a permeability of the dispersant calculated by the following formula of 80% or more.
Permeability = (dispersant concentration of pretreated membrane permeated water / dispersant concentration of pretreated membrane feed water) × 100 3. The method for recovering cooling effluent according to claim 1, wherein the pretreatment membrane has a molecular weight cut-off of 30,000 or more. 4. The dispersant according to claim 1 , wherein the dispersant is methacrylic acid and / or acrylic acid, 3-allyloxy-2-hydroxy-1-propanesulfonic acid, and / or 2-acrylamido-2-methyl. 5. A method for recovering cooling effluent, which is a copolymer obtained by copolymerizing propanesulfonic acid. The method for recovering cooling drainage according to any one of claims 1 to 4 , wherein the pH of the reverse osmosis membrane feed water is adjusted to 4.0 to 7.5. 6. The dispersant of any one of claims 1 to 5 , wherein the concentration of the dispersant in the reverse osmosis membrane feed water is measured, and the dispersant is added to the reverse osmosis membrane feed water so that the dispersant concentration becomes a predetermined concentration. A method for recovering cooling effluent. The electrical conductivity of the discharged water, reverse osmosis membrane water supply and / or reverse osmosis membrane concentrated water is measured according to any one of claims 1 to 6 , and according to the measured value of the conductivity, A method of recovering cooling effluent characterized by adjusting a water recovery rate. In any 1 item | term of the Claims 1 thru | or 7 , the said dispersing agent density | concentration of the said discharged water and / or reverse osmosis membrane water supply is measured, The water recovery rate of this reverse osmosis membrane is set according to the measured value of this dispersing agent density | concentration. A method of recovering cooling effluent characterized by adjusting. In any one of claims 1 to 8, the method of recovering the cooling water discharged, characterized by adding a polymer compound having a phenolic hydroxyl group in the discharge water. 10. The reverse osmosis membrane concentrated water according to any one of claims 1 to 9 , wherein when the water recovery system is stopped, the reverse osmosis membrane permeated water is circulated or pure water or deionized water is passed therethrough. A cooling drainage recovery method characterized by stopping the water recovery system after performing an operation of discharging to the outside of the system. A pretreatment membrane device through which discharged water from the circulating cooling water system is passed, a reverse osmosis membrane device through which the permeated water of the pretreatment membrane device is passed, and a circulating cooling water system that passes the permeated water of the reverse osmosis membrane device in the recovery device of the cooling water discharged and a returning means for returning to the circulation cooling water system has a dispersing agent addition means for adding a dispersing agent to disperse the scale components in the water-based, is added in the dispersing agent addition means In addition, after the dispersant has permeated the pretreatment membrane, the cooling drainage water recovery device used as the dispersant for the reverse osmosis membrane,
The pretreatment membrane is a microfiltration membrane or an ultrafiltration membrane,
The pH of the pretreatment membrane feed water is 5 or more,
The apparatus for recovering cooling and draining water, wherein the dispersant is a polymer having a sulfonic acid group and a carboxyl group . The cooling wastewater recovery device according to claim 11 , wherein the pretreatment membrane has a permeability of the dispersant calculated by the following formula of 80% or more.
Permeability = (dispersant concentration of pretreated membrane permeated water / dispersant concentration of pretreated membrane feed water) × 100 13. The apparatus for recovering cooling effluent according to claim 11 or 12 , wherein a fractional molecular weight of the pretreatment film is 30,000 or more. 14. The dispersant according to claim 11 , wherein the dispersant is methacrylic acid and / or acrylic acid, 3-allyloxy-2-hydroxy-1-propanesulfonic acid and / or 2-acrylamido-2-methyl. An apparatus for recovering cooling effluent, which is a copolymer obtained by copolymerizing propanesulfonic acid. In any one of claims 11 to 14, the recovery device of the cooling water discharged, characterized in that it has a pH adjusting means for adjusting the pH of the feed water of the reverse osmosis membrane to 4.0 to 7.5. 16. The dispersant concentration measuring means for measuring the dispersant concentration of the reverse osmosis membrane water supply, and the dispersant concentration measured by the dispersant concentration measuring means is a predetermined value according to any one of claims 11 to 15 . Dispersing agent adjusting means for adding the dispersing agent to the reverse osmosis membrane feed water so as to have a concentration. The conductivity measuring means for measuring the conductivity of the discharged water, reverse osmosis membrane water supply and / or reverse osmosis membrane concentrated water according to any one of claims 11 to 16 , and according to the measured value of the conductivity measuring means And a water recovery rate adjusting means for adjusting the water recovery rate of the reverse osmosis membrane. 18. The dispersant concentration measuring means for measuring the dispersant concentration of the discharged water and / or reverse osmosis membrane water supply according to any one of claims 11 to 17 , and the measured value of the dispersant concentration measuring means according to the measured value of the dispersant concentration measuring means. A cooling drainage recovery apparatus comprising water recovery rate adjusting means for adjusting the water recovery rate of the reverse osmosis membrane. The apparatus for recovering cooled discharged water according to any one of claims 11 to 18 , further comprising a coagulant assistant adding means for adding a phenolic hydroxyl group to the discharged water. 20. The reverse osmosis membrane device according to any one of claims 11 to 19 , wherein the reverse osmosis membrane device circulates the reverse osmosis membrane permeated water to the front stage of the reverse osmosis membrane device, or pure water or deionized water. Means for passing water through the osmosis membrane device and concentrated water discharge means for draining the reverse osmosis membrane concentrated water out of the system, and when the cooling drainage recovery device is stopped, And a control means for stopping the cooling drainage recovery device after performing an operation of circulating pure water or deionized water and discharging the reverse osmosis membrane concentrated water out of the system. A cooling drainage recovery device characterized by that.