JPH11253761A - Solution separator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solution separation device capable of efficiently separating a solution with low energy and low cost by operating at a low pressure. SOLUTION: Supply liquid 0.05% by weight saline solution, temperature 25
C. and a permeation flux of 0.5 m ³ / m ² / pH 6.5.
MPa / day or more and a feed solution of 0.05% by weight saline,
Reverse osmosis membrane modules 4, 8 and 1 having a salt rejection of 99% or more after operation at 5 MPa, a temperature of 25 ° C. and a pH of 6.5 for 30 minutes.
2 are arranged in multiple stages. A stock solution is supplied to the first reverse osmosis membrane module 4, a concentrated solution discharged from the first reverse osmosis membrane module 4 is supplied to the second reverse osmosis membrane module 8, and a third reverse osmosis module is supplied. The permeated liquid discharged from the first and second reverse osmosis membrane modules 4 and 8 is supplied to the osmosis membrane module 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solution separation device, and more particularly, to a solution separation device suitable for separating a highly concentrated solution such as seawater.

[0002]

2. Description of the Related Art One of the fields in which a method for separating a high-concentration solution using a reverse osmosis membrane is practiced is desalination of seawater.

[0003] In recent years, the amount of rainfall has decreased, living standards have been improved,
The damage of water shortages due to the increase in water demand due to diversification of industries has spread throughout the country, and it is urgently necessary to establish a stable supply method of water resources. Among them, desalination of seawater by a reverse osmosis membrane is regarded as the most promising because of its advantages such as energy saving, space saving and low cost.

The seawater desalination method using a reverse osmosis membrane is a method in which a pressure higher than the osmotic pressure of seawater is applied to the reverse osmosis membrane. At present, in a seawater desalination plant using a reverse osmosis membrane that is in practical use, by applying a pressure of 5 to 6 MPa or more, permeated water of about 40% by volume with respect to the supplied seawater amount can be obtained. .

[0005] Desalination of seawater using this reverse osmosis membrane is required to be further reduced in cost, although it is lower in cost than other seawater desalination methods. Specifically, in order to reduce the desalination cost in seawater desalination using a reverse osmosis membrane, it is necessary to reduce the power cost consumed by a high-pressure pump or the like.

However, in a seawater desalination plant currently in practical use, it is necessary to apply a pressure of about 6 MPa to a reverse osmosis membrane in order to obtain a permeate of about 40% by volume based on the supplied seawater amount. The high-pressure pumps required for such large-sized pumps are large, and the power consumed there is enormous.
On the other hand, as a method for obtaining freshwater from seawater at a high recovery rate, Japanese Patent Application Laid-Open Nos. 8-108048 and 8-206460 have been disclosed.
There are methods proposed in Japanese Patent Application Laid-Open Publication Nos. H11-27139, and these methods require an even higher pressure of 9 MPa in order to obtain fresh water, and even if the recovery rate is improved, cost reduction and energy saving can be solved. Not.

[0007]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a solution separating apparatus capable of efficiently separating a solution at low cost by saving energy by operating at a low pressure. .

[0008]

In order to achieve the above object, a solution separation apparatus according to the present invention comprises a reverse osmosis membrane module arranged in multiple stages, and the reverse osmosis membrane module has the following permeation flux and salt rejection. Having a rate. Flux: 0.0
The permeation flux is 0.5 m ³ / m ² / MPa / day or more under the conditions of 5% by weight saline, temperature of 25 ° C. and pH 6.5. Salt rejection: The salt rejection after running for 30 minutes under the conditions of a feed solution of 0.05 wt% saline, 0.5 MPa, a temperature of 25 ° C., and a pH of 6.5 is 99% or more.

According to the apparatus in which the reverse osmosis membrane modules having a large permeation flux and a high salt rejection ratio at a low operating pressure are arranged in multiple stages, a high permeation flow rate can be obtained even at a low pressure. And the power consumption can be reduced.

The salt rejection is obtained by the following equation. In the following equation, Cp is the solute concentration of the feed solution, and Cf is the solute concentration of the permeate.

Salt rejection (%) = (1−Cp / Cf) × 100

In the apparatus of the present invention, the raw solution is supplied to the first-stage reverse osmosis membrane module, and the previous reverse osmosis membrane modules are supplied to the second and subsequent reverse osmosis membrane modules. Is preferably supplied. In this way, by supplying the concentrated liquid once discharged to another reverse osmosis membrane module to perform solution separation, it is possible to improve the recovery rate of the permeated liquid with respect to the original solution even when operating at a low pressure. It becomes possible. Also, the concentrated liquid discharged from the reverse osmosis membrane module has pressure,
By utilizing this, the solution can be separated again by the reverse osmosis membrane module, and in this respect, energy saving and cost reduction can be achieved.

[0013] In the apparatus of the present invention, it is preferable that the permeate discharged from the reverse osmosis membrane module in the last stage is supplied to the last osmosis membrane module. As described above, if the solution separation step is performed twice or more, a permeate having a high degree of purification can be obtained.

The apparatus of the present invention has a first reverse osmosis membrane module, a second reverse osmosis membrane module, and a third reverse osmosis membrane module, wherein the first reverse osmosis membrane module contains a stock solution. The concentrated liquid discharged from the first reverse osmosis membrane module is supplied to the second reverse osmosis membrane module, and the first and second second osmosis membrane modules are supplied to the third reverse osmosis membrane module. Preferably, a permeate discharged from the reverse osmosis membrane module is supplied. According to this apparatus, even if the apparatus is operated at a low pressure, the recovery rate and the solution separation ability can be simultaneously improved.

In the apparatus of the present invention, it is preferable that the concentrated solution discharged from the reverse osmosis membrane module at the final stage is supplied to the reverse osmosis membrane module located at an earlier stage. The concentrated solution discharged from the reverse osmosis membrane module in the final stage has a lower solute concentration than the solution supplied to the reverse osmosis membrane module in a stage preceding the final stage. Therefore, the supply solution is diluted by supplying the concentrated liquid discharged from the reverse osmosis membrane module in the last stage to the reverse osmosis membrane module located in a stage preceding the last stage. Due to this dilution effect, the osmotic pressure of the feed solution decreases,
Furthermore, it is possible to operate at a lower pressure, and it is possible to obtain a larger amount of permeate, and the recovery rate of the permeate is improved. Here, optimally, the concentrated liquid of the final reverse osmosis membrane module is supplied to the first reverse osmosis membrane module together with the raw solution.

The apparatus according to the present invention may further comprise a pressure increasing means for increasing the pressure of the concentrated solution discharged from the reverse osmosis membrane module when the concentrated solution discharged from the reverse osmosis membrane module is sent to the subsequent reverse osmosis membrane module. preferable. As described above, the concentrated solution discharged from the reverse osmosis membrane module has a pressure, but it is better to transfer the concentrate to a certain degree of pressure in order to perform efficient separation in the next reverse osmosis membrane module. It is. The pressurizing means is not particularly limited as long as it can supply the concentrated solution to the reverse osmosis membrane module of the next stage and can provide an operation pressure necessary for separating the same, for example, a booster pump. A booster such as a turbocharger can be used.

In the apparatus of the present invention, means for recovering the pressure energy of the concentrated liquid discharged from the reverse osmosis membrane module and not supplied to the other reverse osmosis membrane module and supplying it to the supply liquid to the reverse osmosis membrane module It is preferable to provide As described above, by collecting and reusing the pressure energy of the concentrated liquid, energy saving and cost reduction can be achieved. The supply destination of the pressure energy is appropriately determined depending on the scale of the apparatus of the present invention, the arrangement of the modules, and the like, but is not particularly limited, for example,
It may be a supply liquid to a module for discharging the concentrated liquid, or a supply liquid to the other modules.

The means for recovering the pressure energy is not particularly limited, and for example, a method using a power recovery turbine, a water turbine or the like can be adopted. As the turbine, a Pelton type, a reverse pump type (Francis type), a turbocharger type, or the like can be generally used, and a reverse pump type is particularly preferable.

In the apparatus of the present invention, when the pressure energy recovered is provided through the pressurizing means or a pressurizing means for applying pressure to a liquid supplied to the reverse osmosis membrane module, the pressurizing means It is preferable to supply to the supply liquid via For example, by supplying the recovered pressure energy to the booster, the pressurizing pump, or the like, their shaft power is reduced, and energy saving and cost reduction can be achieved. Examples of the supply liquid supplied through the pressurizing unit include an original solution sent to the first-stage module and a permeate sent to the last-stage module. A stock solution requiring particularly large energy is preferred.

The apparatus of the present invention preferably comprises at least one of pH adjusting means and scale inhibitor adding means for the permeate sent to the final reverse osmosis membrane module. The pH range of the permeate is appropriately determined depending on the solution to be treated.
In the case of seawater desalination, the pH range is usually pH
It is 4.5 to 6, preferably pH 5 to 6. As described above, by adjusting the pH of the permeate, the soluble substance present therein can be dissociated, and the rejection of the soluble substance in the reverse osmosis membrane module can be improved. Note that boron exists in a solution in a non-dissociated state when the pH range is acidic to neutral, but is dissociated in an alkaline range. In this case, it is preferable to adjust the pH to alkaline. Also, precipitation of calcium carbonate and the like can be prevented by adjusting the pH.

Further, by adding the scale inhibitor, the solubility of the salt is enhanced, and the deposition of scale substances such as silica and metal salts on the surface of the reverse osmosis membrane can be suppressed. Therefore, a decrease in the permeation flux of the reverse osmosis membrane module is suppressed, and the recovery rate of the permeated liquid can be improved.
The scale inhibitor is not particularly limited, and includes, for example, those which form a complex with a scale substance such as a metal and a polyvalent metal ion in a solution and solubilize them, and have such properties. Organic or inorganic ionic polymers or ionic monomers can be used. The amount of the scale agent to be added is not particularly limited as long as it does not hinder the solution separation operation.

In the apparatus of the present invention, it is preferable that a filtering means for the raw solution is provided, and the raw solution filtered by the filtering means is supplied to the first-stage reverse osmosis membrane module. Examples of the filtration means include sand filtration, activated carbon filtration, ultrafiltration, membrane filtration, and microfiltration.
Particularly preferred is membrane filtration. By filtration, for example,
Since the suspended solids and the like contained in the original solution are removed and clogging or the like of the reverse osmosis membrane module can be prevented, a decrease in the permeation flux of the module is suppressed, and the solution can be more efficiently separated.

In the apparatus of the present invention, the ratio (recovery rate) of the permeate discharged from the reverse osmosis membrane module in the final stage to the raw solution is preferably 40% by volume or more. 4
This is because a recovery rate of 0% by volume or more is a recovery rate that can be operated at a sufficiently practical level, for example, in desalination of seawater.

In the apparatus of the present invention, the reverse osmosis membrane constituting the reverse osmosis membrane module is preferably a composite membrane in which a crosslinked aromatic polyamide skin layer is formed on a porous support layer. This is because such a reverse osmosis membrane is excellent in performance, strength and the like.

In the apparatus of the present invention, the average surface roughness of the crosslinked aromatic polyamide skin layer defined by the above formula (Equation 1) is preferably 55 nm or more, particularly preferably 60 nm or more. The surface of the crosslinked aromatic polyamide skin layer having a surface average roughness in such a range,
Large surface with rough surface. By using a module composed of such a reverse osmosis membrane, the permeation flux is further increased, and the apparatus of the present invention can be operated at a lower pressure.

The average surface roughness can be measured, for example, by using a general measuring device such as an atomic force microscope, a friction force microscope,
It can be measured using a tunnel microscope, a scanning electron microscope, a transmission electron microscope, or the like.

[0027]

Next, the present invention will be described in detail.

[0028] The solution separation apparatus of the present invention is a multi-stage reverse osmosis membrane module having the specific permeation flux and salt rejection.

The permeation flux is preferably 0.5 to 2
m ³ / m ² / MPa / day, particularly preferably 0.5
１．５1.5 m ³ / m ² / MPa / day. Further, the salt rejection is preferably 99.0% or more, and particularly preferably 99.5% or more.

The form of the reverse osmosis membrane module is as follows.
The type is not particularly limited, and examples thereof include a spiral type, a hollow fiber type, a tubular type, and a plate and frame type. Among these, the spiral type is preferable.

As the material of the reverse osmosis membrane constituting the reverse osmosis membrane module, for example, acetyl cellulose, polyvinyl alcohol, polyamide or the like can be used. Among these, it is preferable to use polyamide because of its high blocking performance against organic substances such as trihalomethane and tribromomethane. More preferably, a skin layer that is a reverse osmosis membrane is a composite membrane formed on the porous support layer,
Particularly preferred is a composite membrane in which a crosslinked aromatic polyamide skin layer is formed on a porous support layer as described above. The crosslinked aromatic polyamide skin layer is a thin film containing a crosslinked aromatic polyamide as a main component.

The thickness of the skin layer is usually from 0.08 to 0.08.
It is 1.5 μm, preferably 0.1 to 1.0 μm.

The porous support layer is not particularly limited as long as it can support the skin layer. For example, a polysulfone porous layer, a polyethersulfone porous layer,
A polyimide porous layer, a polyvinylidene fluoride porous layer, or the like can be used. Among these, a polysulfone porous layer is preferable for reasons such as chemical, mechanical and thermal stability.

The thickness of the porous support layer is usually 50 to 50.
It is 250 μm, preferably 50-100 μm.

Next, the multistage arrangement of the reverse osmosis membrane modules will be described.

As described above, in the apparatus of the present invention, the stock solution is supplied to the first-stage reverse osmosis membrane module,
It is preferable that the concentrated liquid discharged from the reverse osmosis membrane module at an earlier stage is supplied to the reverse osmosis membrane modules at the second and subsequent stages.

In such an arrangement, for example, an undiluted solution is supplied to the first-stage module, the concentrated liquid discharged from the first-stage module is supplied to the second-stage module, and the concentrated liquid discharged from the second-stage module is discharged from the second-stage module. There is a serial arrangement in which the concentrated liquid is supplied to the third-stage module, and the concentrated liquid is sequentially supplied to the subsequent modules.
However, in this case, the concentration of the concentrated solution increases in the later stage, and the degree of purification of the obtained permeate also decreases.
The number of stages is usually two to three. In addition, the original solution is supplied to the first-stage module, the concentrated liquid discharged from these is supplied to two or more modules, respectively, and the concentrated liquid discharged from these is further supplied to two or more modules. Parallel arrangements such as supply may be combined.
In the apparatus of the present invention, the number of reverse osmosis membrane modules is appropriately determined according to the scale of the apparatus, the purpose of use, the type of the solution to be treated, and the like.

In such a series or parallel arrangement, the permeate can be recovered from each module. As described below, the permeate is supplied to the last module, and the permeate is supplied to the last module. The separation can be performed again to recover the permeate.

Next, as described above, a Pelton type, a reverse pump type (Francis type), a turbocharger type, or the like can be generally used as a turbine used for recovering pressure energy.

The Pelton type turbine is usually operated at a high pressure,
The efficiency is high even in the case of small capacity and low flow rate, and the turbine efficiency is 80% or more. Since this turbine has no braking action, it can be started while being directly connected to a pump or the like from the beginning, and is easy to operate.

Next, the reverse pump type turbine generally has lower efficiency than the Pelton type at a small capacity, but the efficiency increases as the capacity increases, and the turbine efficiency becomes:
It is around 75%. Since the turbine has a braking action when the flow rate is small, it is necessary to separate the turbine from the motor or the pump when starting the pump or the like, and to connect the turbine or the like via a clutch or the like when the turbine reaches a constant rotation. There is. When the scale is not large, the capacity of the turbine is reduced to simplify the operation, and the turbine and the motor can be directly connected from the beginning. Further, since the drainage of the solution after the recovery of the pressure energy can maintain the discharge pressure of the turbine, the pressure can be directly sent to the discharge water tank.

Next, the turbocharger type turbine is generally used to increase the discharge pressure of the pump after converting the pressure energy of the concentrated liquid into pressure by a pump (turbocharger). Therefore, the rotation speeds of the pump and the turbine do not need to match, and the occurrence of a braking action is less likely.

The type of the turbine is not particularly limited, and is appropriately determined according to the type of the solution to be treated, the scale and arrangement of the solution separation device, and the like.

The device of the present invention may include other devices in addition to the reverse osmosis membrane module and the like. As such an apparatus, there is a pretreatment unit in addition to the above-described scale inhibitor addition apparatus and pH adjustment apparatus. This allows, for example,
Organic substances, inorganic substances, suspended substances, and the like can be removed from the stock solution to be separated, and sterilization and the like can be performed. As the processing means in the pretreatment unit, for example, a means for adding a reagent such as a flocculant, a pH adjuster, a reducing agent, and a bactericide, or the above-described removal means by filtration can be employed. Moreover, you may process combining these means. The amounts of the various reagents to be added are appropriately determined according to the type and use of the solution to be treated, and are not particularly limited as long as they do not hinder the solution separation device. For example, in the case of seawater desalination, the pretreatment of the raw solution in the pretreatment unit can be performed as described below. That is, first, seawater is supplied to a sedimentation basin, and refuse, particles, and the like are precipitated and separated. Then, after sterilizing by adding a bactericide or the like, a flocculant is added and sand filtration is performed. The obtained filtrate is stored in a storage tank, and the pH is adjusted.
After the treatment, the bactericide is eliminated by adding a reducing agent, and the like, the treated solution is filtered, and the filtrate is supplied to the module. The method of the pretreatment is appropriately determined according to the type and use of the solution to be treated.

In the solution separation device of the present invention, the target solution is not particularly limited, but as described above,
This device is ideal for separating highly concentrated solutions. Examples of the high concentration solution include seawater, brackish water, industrial wastewater, leachate of garbage, fruit juice, and the like. Among them, the apparatus of the present invention is most preferably used for desalination of seawater because of its energy saving and low cost.

Next, two examples of the solution separation device of the present invention will be described with reference to FIGS. 1, 2 and 3, respectively.

First, the apparatus shown in FIG. 1 comprises a first module 4, a second module 8 and a third module 12
And a pre-processing unit 2 for pre-processing the raw solution. The pretreatment unit 2 is connected to a pipe 1 for introducing a raw solution to be treated. A pipe 17 for discharging the pretreated raw solution is led out of the pretreatment unit 2, the tip of which is connected to the first module 4, and the pressure pump 3 is disposed in the middle of the pipe 17. ing. First module 4
A pipe 5 for discharging the concentrated liquid is led out,
The tip is connected to the second module 8, and a booster pump 7 is arranged in the middle of the pipe 5. From the first module 4, a pipe 6 for discharging the permeated liquid is provided.
The tip is connected to the third module 12, and in the middle of the pipe 6, the scale inhibitor adding device 1 is connected.
5. The pH adjusting device 16 and the pressure pump 11 are arranged in this order. From the second module 8, a pipe 10 for discharging the permeated liquid is led out.
The pipe 6 is connected to a portion upstream of the position where the scale inhibitor adding device 15 is disposed. Also, the second module 8
Leads out a pipe 9 for discharging the concentrated liquid. From the third module 12, a pipe 14 for discharging the permeate and a pipe 1 for returning the concentrated water
3 have been derived. The tip of the pipe 13 is the pipe 1
7 is connected to the upstream part of the arrangement position of the pressure pump 3. The distal end of the pipe 14 is connected to a permeate collection unit (not shown).

The solution separation using this apparatus is performed, for example, as follows. First, the raw solution to be treated is introduced into the pretreatment unit 2 through the pipe 1, and the pretreatment by the filtration or the like is performed. Then, the pretreated raw solution is pressurized by the pressurizing pump 3 and sent to the first module 4 through the pipe 17. The pressure at this time is usually in the range of 5 to 7 MPa, preferably in the range of 5 to 6 MPa. The solution is separated in the first module 4 to be separated into a concentrated liquid and a permeated liquid. The concentrated liquid is pressurized by the pressure increasing pump 7 and sent to the second module 8 through the pipe 5, where the solution is again separated into a concentrated liquid and a permeated liquid.
In the transfer of the concentrate from the first module 4 to the second module 8, since the concentrate has a pressure, the pressure may be compensated by a pressure increasing device, and a pressurizing pump is used here. No need. The transfer pressure of the concentrate to the second module 8 is the same as the above-mentioned pressure range. The concentrate of the second module 8 is discharged out of the apparatus through a pipe 9. On the other hand, the permeate of the first module 4 passes through the pipe 6, is subjected to the addition of the scale inhibitor and the adjustment of the pH by the scale inhibitor adding device 15 and the pH adjusting device 16, and is further pressurized by the pressurizing pump 11. hand,
It is sent to the third module 12. Also, the permeate of the second module 8 passes through the pipes 10 and 6,
It is sent to the third module 12. At this time, as described above, the mixture is subjected to the addition of the scale inhibitor and the adjustment of the pH, and further pressurized. The pressure conditions for transferring the permeate to the third module 12 are the same as described above. Then, the solution is separated in the third module 12 to be separated into a concentrated solution and a permeate, and the permeate is collected by the permeate collection unit through the pipe 14. The concentrated liquid of the third module 12 passes through the pipe 13 and is returned to the pipe 17 upstream of the pressurizing pump 3, and is again pressurized in a state of being mixed with the treated raw solution, and the first concentrated liquid is then compressed. Module 4
To separate the solution. By returning the concentrated liquid of the third module 12 to the first module 4, the above-described dilution effect can be obtained, thereby also achieving energy saving and cost reduction. Although the concentrated liquid of the third module 12 may be returned to the second module 8, it is preferable to return the concentrated liquid to the first module 4 from the viewpoint of the efficiency of the dilution effect.

In the apparatus shown in FIG. 1, when the raw solution is seawater, the salt concentration of the obtained permeate (fresh water) is usually 10%.
0 to 200 ppm, and the amount of permeated water is usually 80 to 90 m ³ / day at a recovery of 40% by volume. The operating pressure is as described above, and the power consumption in this case is usually 11 to 14 kW, which is sufficiently lower than the power consumption of a conventional seawater desalination plant of 18 to 22 kW.

Next, the apparatus shown in FIG. 2 is further provided with an energy recovery apparatus in the apparatus shown in FIG. 1, and the other configuration is the same as the apparatus shown in FIG. In FIG. 2, the same parts as those in FIG. 1 are denoted by the same reference numerals. As shown, in this device, an energy recovery device 18 is arranged in the middle of a pipe 9 for discharging the concentrate from the second module 8. A large amount of pressure energy remains in the concentrated liquid discharged from the second module 8, and this is recovered by the energy recovery device 18 and
As shown by 9, the pressure is supplied to a booster pump 7 arranged in the middle of the pipe 5. FIG. 3 shows an example in which an energy recovery turbine is used as the energy recovery device 18 and connected to the booster pump 7.

As shown in the figure, an energy recovery turbine 18a is disposed in the middle of the pipe 9, and this shaft is connected to a motor shaft of a booster pump motor 7b for driving a booster pump (boost pump) 7a and a clutch 20. Connected. The energy recovery turbine 18a
Is a reversing pump type. Note that the pipe 5 is a pipe for discharging the concentrated liquid from the first module 4.

Next, the solution separation using the apparatus shown in FIG. 2 is basically performed in the same manner as the apparatus shown in FIG.
The difference is that the pressure energy of the concentrate discharged from the second module 8 is recovered and reused. This will be described with reference to FIG. As shown, the concentrated liquid discharged from the second module 8 passes through the pipe 9 and rotates the energy recovery turbine 18a disposed on the way. At a stage where the rotation has exceeded a certain level, the clutch 20 is engaged, and the rotation is transmitted to the motor shaft of the booster pump 7b by the turbine shaft. As a result, the shaft power of the motor 7b is supplemented, whereby the booster pump 7a can be driven with low shaft power, and the energy required for this can be saved. The number of rotations when connecting to the clutch is appropriately determined according to the size of the pump and the like. It should be noted that when the above-mentioned various turbines are used, the shaft power of the booster pump can be supplemented, and the same effect can be obtained.

In the apparatus shown in FIGS. 2 and 3, when the raw solution is seawater, the salt concentration of the obtained permeate (fresh water) is as follows:
Usually, it is 100 to 200 ppm, and the amount of permeated water is usually 80 to 90 m ³ / day at a recovery of 40% by volume. The operation pressure is as described above. The power consumption in this case is usually 8.8 to 11.2 kW, which is even lower than the power consumption required for the device shown in FIG. As described above, in this apparatus, by having the energy recovery apparatus, it is possible to reduce the power consumption by about 20% as compared with the apparatus shown in FIG. Therefore, if this device is used, seawater can be desalinated more efficiently at lower cost.

[0054]

Next, examples of the present invention will be described together with comparative examples.

(Example 1) In the apparatus having the structure shown in Fig. 1, a third reverse osmosis using a product name: ES20-D8 (manufactured by Nitto Denko Corporation) as the first and second reverse osmosis membrane modules. The product name: ES20-D4 (manufactured by Nitto Denko Corporation) was used as the membrane module. These modules have a permeation flux of 0.5 m ³ / m ² / MPa / day or more under the conditions of a feed solution of 0.05 wt% saline, a temperature of 25 ° C., and a pH of 6.5, and a feed solution of 0.1 wt%. The salt rejection after operating for 30 minutes under the conditions of a 0.5% by weight saline solution, 0.5 MPa, a temperature of 25 ° C., and a pH of 6.5 is 99.8% or more. In addition, the reverse osmosis membrane of these modules uses a cross-linked aromatic polyamide skin layer,
Its average surface roughness is 80 nm.

First, as a pretreatment of seawater, a coagulant was added to seawater in the pretreatment unit 2 of this apparatus, and then coagulation sand filtration was performed. The obtained pretreated seawater is 4.5MP
a, and sent to the first module 4. The concentrated liquid discharged from the first module 4 was pressurized to 5.1 MPa and sent to the second module 8. Then, the permeate of the first module 4 and the permeate of the second module 8 were sent to the third module 12, and the permeate from this module 12 was collected. In addition, the concentrate of the second module 8 was discharged out of the apparatus. The concentrate of the third module 12 was returned to the first module 2.

The salt concentration of the recovered permeate (fresh water) is 1
It was 50 ppm, and could be sufficiently used as drinking water and industrial water. The amount of permeated water is 90 m ³
/ Day, and the recovery rate of permeate (fresh water) with respect to seawater is 4
At 0% by volume, no decrease in the amount of permeated water was observed even after lapse of 2,000 hours from the start of operation. The power consumption at this time is
It is 13 kW, and it can be said that a large amount of seawater was desalinated with energy saving and low cost.

Example 2 Desalination of seawater was performed using a solution separator having the structure shown in FIGS. The first, second and third reverse osmosis membrane modules are the same as those of the first embodiment.
The same module was used.

First, a coagulant was added to seawater as a pretreatment of seawater in the pretreatment unit 2 of the apparatus, and then coagulated sand filtration was performed. The obtained pretreated seawater is 4.5MP
a, and sent to the first module 4. The concentrated liquid discharged from the first module 4 was pressurized to 5.1 MPa and sent to the second module 8. Then, the permeate of the first module 4 and the permeate of the second module 8 were sent to the third module 12, and the permeate from this module 12 was collected. The concentrate of the third module 12 was returned to the first module 4. In this apparatus, pressure energy was recovered as follows. First, when the apparatus was started (when the pressurizing pumps 3 and 11 and the booster pump motor 7b were started), the clutch 20 was released. In this state,
The concentrated liquid discharged from the second module 8 is supplied to a pipe 9
To the energy recovery turbine 18a, and rotated. Then, when the required number of rotations was reached, the clutch 20 was engaged, and the rotation was transmitted to the motor shaft of the booster pump motor 7b by the turbine shaft. Thus, the shaft power of the motor 7b was supplemented, and the booster pump 7a was driven. The turbine 18a
After the was rotated, the concentrated liquid was discharged out of the apparatus.

The permeate obtained by this apparatus had a salt concentration of 150 ppm, and was sufficiently usable as drinking water and industrial water. The amount of permeated water is 90m
Is ³ / day, with 40% by volume recovery of permeate for seawater (freshwater), was not observed reduction in water permeate flow even after the start of operation 2000 hours elapsed. The power consumption at this time was 11 kW, and it can be said that a large amount of seawater was desalinated at a lower cost and at lower cost than the apparatus of the first embodiment.

(Comparative Example 1) Desalination of seawater was performed using only a single-stage reverse osmosis membrane module. The reverse osmosis membrane module used was a product name: NTR-70SWC-S8 (manufactured by Nitto Denko Corporation).
The permeation flux under the conditions of saline solution, temperature 25 ° C., pH 6.5 is 0.4 m ³ / m ² / MPa / day or more, and 0.05 wt% saline solution of feed solution, 0.5 MPa, temperature 25 ° C, p
The salt rejection after running at H6.5 for 30 minutes is 99% or more.

Then, pretreatment was performed in the same manner as in Example 1.
Seawater is pressurized to 6.0 MPa and the reverse osmosis membrane module is pressed.
And the solution is separated at a recovery rate of 40%.
Collected. As a result, the salt concentration of the permeate was 150 pp
m and the amount of permeate is 90 m ^Three/ Day.

As described above, when desalination of seawater is performed using a single-stage reverse osmosis membrane module, a high pressure of 6 MPa is required to operate at a recovery rate of 40%.
It was as large as kW. In this module, no decrease in the amount of permeated water was observed after a lapse of 2000 hours from the start of operation.

Comparative Example 2 Seawater desalination was performed using one reverse osmosis membrane module (ES20-D8) as in Example 1. That is, seawater that had been subjected to the same pretreatment as in Example 1 was pressurized to 4.5 MPa, sent to the module, subjected to solution separation at a recovery rate of 40%, and the permeate was recovered.

As a result, the salt concentration of the permeate was 400
ppm, the amount of permeate was 90 m ³ / day, and the power consumption was 13 kW.

Comparative Example 3 ES20-D8 and ES2
In place of 0-D4, a reverse osmosis membrane model outside the predetermined conditions of the present invention is used.
Jules as the first, second and third module
Except for using, desalination of seawater was performed in the same manner as in Example 1.
Was. The reverse osmosis membrane module has a supply liquid of 0.05 weight
% Permeate, temperature 25 ° C, pH 6.5
Is 0.4m ^Three/ M^Two/ MPa / day and the supply liquid is 0.05
Wt% saline, 0.5 MPa, temperature 25 ° C, pH 6.5
Is 99.7% after 30 minutes of operation under the above conditions.
belongs to.

As a result, the salt concentration of the permeate was 170
ppm and the amount of permeate is 90 m ^Three/ Day, consumption
The power was 18 kW.

[0068]

As described above, the solution separation apparatus of the present invention is capable of separating the solution with low energy and low energy by arranging the reverse osmosis membrane modules having a large amount of permeate in multiple stages even when operated at a low pressure. It can be performed efficiently at low cost. Further, if the pressure energy is reused by using the energy recovery device, it is possible to further reduce energy and cost. Therefore, for example, if the apparatus of the present invention is used for desalination of seawater, it becomes possible to supply a large amount of drinking water, industrial water and the like at low cost.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of one embodiment of a solution separation device of the present invention.

FIG. 2 is a configuration diagram of another embodiment of the solution separation device of the present invention.

FIG. 3 is a configuration diagram of the energy recovery device of the embodiment.

[Explanation of symbols]

 1, 5, 6, 9, 10, 13, 14, 17 Pipe 2 Pretreatment unit 3, 11 Pressure pump 4 First reverse osmosis membrane module 7 Boost pump 7a Booster pump 7b Booster pump motor 8 Second reverse osmosis Membrane module 12 Third reverse osmosis membrane module 15 Scale inhibitor addition device 16 pH adjuster 18 Pressure energy recovery device 18a Energy recovery turbine 19 Arrow indicating the flow of recovered pressure energy 20 Clutch

Claims (14)

[Claims] 1. A reverse osmosis membrane module is arranged in multiple stages,
A solution separator, wherein the reverse osmosis membrane module has the following permeation flux and salt rejection. Permeation flux: supply liquid 0.05
The permeation flux is 0.5 m ³ / m ² / MPa / day or more under the conditions of a weight% saline solution, a temperature of 25 ° C., and a pH of 6.5. Salt rejection: feed solution 0.05 wt% saline, 0.5 MPa, temperature 25
A salt rejection of 99% or more after operation at 30 ° C. and pH 6.5 for 30 minutes. 2. The raw solution is supplied to the first-stage reverse osmosis membrane module, and discharged from the second-stage and subsequent reverse-osmosis membrane modules from the preceding reverse-osmosis membrane module. The apparatus of claim 1 wherein a concentrate is provided. 3. The apparatus according to claim 1, wherein the permeated liquid discharged from the reverse osmosis membrane module in the last stage is supplied to the last stage osmosis membrane module. 4. A module having a first reverse osmosis membrane module, a second reverse osmosis membrane module and a third reverse osmosis membrane module, wherein the first reverse osmosis membrane module is supplied with a stock solution, A concentrated liquid discharged from the first reverse osmosis membrane module is supplied to the second reverse osmosis membrane module,
The apparatus according to any one of claims 1 to 3, wherein the third reverse osmosis membrane module is supplied with a permeate discharged from the first and second reverse osmosis membrane modules. 5. The apparatus according to claim 3, wherein the concentrated liquid discharged from the reverse osmosis membrane module at the last stage is supplied to a reverse osmosis membrane module located at an earlier stage. 6. A pressure increasing means for increasing the pressure of the concentrated solution discharged from the reverse osmosis membrane module when the concentrated solution discharged from the reverse osmosis membrane module is sent to a subsequent reverse osmosis membrane module. An apparatus according to any one of the preceding claims. 7. A means for recovering pressure energy of the concentrated liquid discharged from the reverse osmosis membrane module and not supplied to other reverse osmosis membrane modules and supplying the same to the supply liquid to the reverse osmosis membrane module. The device according to any one of claims 2 to 6. 8. The apparatus according to claim 7, wherein the recovered pressure energy is supplied to the supply liquid via a pressure increasing means. 9. The method according to claim 7, further comprising pressurizing means for applying pressure to the liquid supplied to the reverse osmosis membrane module, and supplying the recovered pressure energy to the liquid supply via the pressurizing means. apparatus. 10. The apparatus according to claim 3, further comprising at least one of pH adjusting means and scale inhibitor adding means for the permeated liquid sent to the reverse osmosis membrane module at the final stage.
An apparatus according to any one of the preceding claims. 11. The method according to claim 2, further comprising a filtration means for the raw solution, wherein the first-stage reverse osmosis membrane module is supplied with the raw solution filtered by the filtration means. Equipment. 12. The apparatus according to claim 3, wherein a ratio of the permeate discharged from the reverse osmosis membrane module in the final stage to the raw solution is 40% by volume or more. 13. The reverse osmosis membrane constituting the reverse osmosis membrane module is a composite membrane in which a crosslinked aromatic polyamide skin layer is formed on a porous support layer. Equipment. 14. The crosslinked aromatic polyamide skin layer has an average surface roughness defined by the following formula (Equation 1) of 55 nm.
14. The apparatus according to claim 13, which is the above. (Equation 1)