JPH11128702A - Membrane separation method and membrane separation apparatus for method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent substances from adhering to the surface of a permeation membrane, keep permeation flow flux and prevent deterioration of the efficiency of permeation without requiring frequency washing process by a chemical agent. SOLUTION: In this apparatus, an object liquid in a tank 1 is supplied by a pump 3 to one side of a pressure container 5, which is divided into one side and the other side by a permeation membrane. While clogging of the permeation membrane being prevented by vibrating the permeation membrane, the object liquid is passed through the membrane to the other side. The difference of the inner pressure in both sides of the permeation membrane is lowered by either decreasing the inner pressure in one side by opening an automatic valve 13 or increasing the inner pressure in the other side by closing an automatic valve 15. Consequently, the substances adhering to the surface in one side of the permeation membrane are parted. The automatic valve 13 is also used for controlling the concentration ratio by opening or closing a concentrated liquid taking out route 35.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a latex concentrate,
The present invention relates to a membrane separation method useful for colloidal silica concentration, valuable resource recovery, waste liquid treatment, metal classification, tap water filtration, activated sludge treatment, and the like, and a membrane separation device used for the same. The present invention relates to a membrane separation method in which permeation efficiency is increased by performing separation, and a vibration type membrane separation device used for the method.

[0002]

2. Description of the Related Art Conventionally, in the fields of chemical industry, paper industry, wastewater treatment, etc., a membrane separation method of filtering a liquid to be treated such as latex, wastewater or the like by a permeable membrane has been adopted. This membrane separation method separates a permeated component from a non-permeated component by a permeable membrane having micropores. However, clogging of micropores (fouling) due to the non-permeated component and permeation flow due to the clogging are caused. There is a problem that the transmission efficiency is reduced due to the reduction of the bundle.

[0003] A vibration type membrane separation apparatus for performing permeation while vibrating a permeable membrane in order to prevent clogging is disclosed in Japanese Patent Application Laid-Open No. HEI 2 (1994) -197686.
No. 241524. This conventional vibration type membrane separation device will be described with reference to FIG. This membrane separation device includes a tank 101, a pump 1 as a supply unit.
03 and a pressure vessel 105. Pressure vessel 105
Is separated into one side 117 and the other side 119 by a permeable membrane 107. The liquid to be treated stored in the tank 101 is supplied to one side 117 of the pressure vessel 105 through the pump 103 in a pressurized state. One side 11 of the permeable membrane
There is an internal pressure difference between 7 and the other side 119. The internal pressure difference is usually set at about 2 to 40 atm. Due to this internal pressure difference, the permeated component passes through the micropores of the permeable membrane 107 and moves to the other side 119 of the pressure vessel 105. A concentrate is taken out from one side 117 of the pressure vessel 105 through a concentrate take-out path 109, and a permeate is taken out from the other side 119 through a permeate take-out path 111.

In FIG. 3, only one permeable membrane 107 is schematically shown in the pressure vessel 105. However, in practice, many (for example, several hundred) permeable membranes 107 are provided in a multi-stage manner. ing. Then, for example, the concentrated liquid concentrated in the first-stage permeable membrane 107 is supplied to the second-stage permeable membrane 107,
A permeation process is performed as a liquid to be processed by the second-stage permeable membrane 107. In this way, the concentrated liquid sequentially concentrated by the large number of permeable membranes 107 finally passes through the concentrated liquid take-out path 109.
Taken out through.

A vibration means (not shown) is connected to the pressure vessel 105.
Vibration is applied to 05, and vibration is also applied to the permeable membrane 107. Vibration of the permeable membrane prevents micropores from being clogged by non-permeable components. In addition, as the vibration means,
For example, as disclosed in Japanese Patent Application Laid-Open No. 4-222667, an eccentric weight is rotated by a motor to generate vibration, and the vibration is transmitted to a permeable membrane.

As described above, in the vibration type membrane separation apparatus, clogging is prevented by the vibration of the permeable membrane, but when continuous operation is performed for a long time, one side 117 and the other side 119 of the permeable membrane are used. Due to the internal pressure difference, the organic substance and the like adhere to the surface of the one side 117 of the permeable membrane, and the adhered substance lowers the permeation flux, resulting in a reduction in permeation efficiency.
In order to recover the permeation flux, the valve 113 is closed to temporarily suspend the permeation process of the liquid to be treated, the valve 115 is opened to supply the chemical solution into the pressure vessel 105, and the surface of the permeable membrane is washed. There is a need. If this washing step is performed frequently, there is a problem that the operation efficiency of the membrane separation device is reduced by the amount that the permeation process is interrupted. In addition, there is a problem that the chemical solution used in the cleaning step has a high unit price, and thus increases the operating cost of the membrane separation device.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of these problems, and no deposits adhere to the surface of a permeable membrane even if a washing step with a chemical solution is not frequently performed. It is an object of the present invention to provide a membrane separation method in which the flux is maintained and the permeation efficiency is hardly reduced, and a membrane separation apparatus used for the method.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem. One aspect of the present invention provides a pressure vessel in which one side and the other side are formed by being partitioned by a permeable membrane. In the membrane separation method of supplying the liquid to be treated, transmitting the permeated component to the other side while vibrating the permeable membrane, taking out the concentrated liquid from one side, and taking out the permeated liquid from the other side, the one side is temporarily A membrane separation method characterized in that an internal pressure is reduced to reduce an internal pressure difference between one side and the other side, thereby removing adhered substances adhered to one side of the permeable membrane (claim 1). .

Another invention made to solve the above-mentioned problem is a pressure vessel in which one side and the other side are formed by being partitioned by a permeable membrane, and a treatment vessel is provided on one side of the pressure vessel. Supply means for supplying the target liquid, vibrating means for vibrating the permeable membrane, a concentrated liquid extraction path for extracting the concentrated liquid from one side of the pressure vessel, and a permeate liquid extraction for extracting the permeated liquid from the other side of the pressure vessel A membrane separation device comprising a path, wherein the concentrated liquid take-out path is provided with pressure adjusting means for adjusting the internal pressure on one side of the pressure vessel. (Claim 2).

According to these inventions, the internal pressure on one side is temporarily reduced by the pressure adjusting means for adjusting the internal pressure on one side of the pressure vessel to reduce the internal pressure difference between the one side and the other side. be able to. For this reason, the attached matter adhering to the surface on one side of the permeable membrane can be peeled off in combination with the vibration effect of the permeable membrane, and the permeation flux can be increased.

As the pressure adjusting means for adjusting the internal pressure on one side, an opening / closing means for opening / closing the concentrated liquid taking-out path is preferable. By opening and closing the opening and closing means, the time during which the liquid to be treated stays in the pressure vessel can be adjusted, whereby the concentration rate of the concentrated liquid can be controlled (claim 5).

[0012] Still another invention for solving the above-mentioned problem is to provide a pressure vessel having one side and the other side formed by being partitioned by a permeable membrane. In the membrane separation method of supplying the target liquid, permeating the permeated component to the other side while vibrating the permeable membrane, taking out the concentrated liquid from one side, and taking out the permeated liquid from the other side, the internal pressure of the other side is temporarily reduced. The membrane separation method is characterized in that, by increasing the internal pressure difference between the one side and the other side by increasing the pressure, the adhered matter adhering to one side of the permeable membrane is separated (claim 3).

Still another invention made to solve the above-mentioned problem is a pressure vessel in which one side and the other side are formed by being partitioned by a permeable membrane, and a pressure vessel in which one side is formed. Supply means for supplying the liquid to be treated, vibrating means for vibrating the permeable membrane, a concentrated liquid extracting path for extracting the concentrated liquid from one side of the pressure vessel, and a permeated liquid for extracting the permeated liquid from the other side of the pressure vessel A membrane separation device comprising an extraction path, wherein the permeate extraction path is provided with pressure adjusting means for adjusting the internal pressure on the other side of the pressure vessel, (Claim 4).

According to these inventions, the internal pressure on the other side is temporarily increased by the pressure adjusting means for adjusting the internal pressure on the other side of the pressure vessel, and the internal pressure difference between the one side and the other side is reduced. be able to. For this reason, the attached matter adhering to the surface on one side of the permeable membrane can be peeled off in combination with the vibration effect of the permeable membrane, and the permeation flux can be increased.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings.

FIG. 1 shows a path diagram of a membrane separation apparatus according to one embodiment of the present invention. This membrane separation device
Tank 1 and pump 3 similar to the membrane separation device shown in FIG.
And a pressure vessel 5. In addition, automatic valves 7, 9, 11, 13, 15, 17 and manual valves 19, 21, 23, 25, which will be described in detail later, are provided in the path. A three-way valve 27 is provided between the pump 3 and the pressure vessel 5. Further, a back pressure regulator 31 is provided in parallel with the automatic valve 15.

During a steady operation, the automatic valve 9 is closed, and the manual valve 19 and the automatic valve 7 are open. Then, the liquid to be treated in the tank 1 is supplied into the pressure vessel 5 through the manual valve 19, the automatic valve 7, the pump 3 and the three-way valve 27 as supply means. At this time, the three-way valve 27 is controlled by adjusting the opening of the manual valve 23.
The flow rate of the liquid to be processed, which is sent to the pressure vessel 5 through the flow path, is adjusted, and the excess liquid to be processed is returned to the tank 1 through the manual valve 23 and the return path 33. Note that a pressure adjusting valve may be provided instead of the three-way valve 27 and the manual valve 23, and the flow rate may be adjusted by the pressure adjusting valve.

Vibration means (not shown) is provided in the pressure vessel 5.
Are connected. The vibrating means rotates the eccentric weight by a motor to generate reciprocating rotational vibration having a small amplitude, and transmits the vibration to the pressure vessel 5 through the torsion bar. As a result, the permeable membrane 39 (see FIG. 2) generates a reciprocating rotational vibration with a minute amplitude in the horizontal plane. In addition,
The setting of the amplitude of the permeable membrane 39 is performed by adjusting the frequency of the motor using an inverter.

FIG. 2 is a sectional view of a part of the pressure vessel. In the pressure vessel 5 of this embodiment, 100 permeable membranes 39 are used, and each permeable membrane 39 is arranged so as to extend in the horizontal direction, and is provided in multiple stages in the vertical direction at a predetermined interval. ing. The upper side in the figure of each permeable membrane 39 is one side 45, and the lower side in the figure is the other side 47.
On the other side 47 of the permeable film 39, a drain cloth 41 and a metal plate 42 made of a nonwoven fabric are laminated.

When the liquid to be treated is supplied to the one side 45, the internal pressure of the one side 45 is set to be higher than the internal pressure of the other side 47 by about 2 to 40 atm. Components, that is, components smaller than the micropores of the permeable membrane 39, pass through the micropores and reach the other side 47.
The residue after the permeation component permeates is sent to one side 45 of the next stage of the permeable membrane 39, where the permeate component further passes through the micropores of the permeable membrane 39. During this permeation process, the permeable membrane 39 continues to reciprocate with a minute amplitude in a reciprocating rotational vibration, so that a shear force acts on the interface between the permeable membrane 39 and the liquid to be treated, and the micropores may be clogged. Few. The permeation process is sequentially performed in this manner, and the finally obtained concentrated liquid passes through the manual valve 25 and the automatic valve 13. During the steady operation, the automatic valve 11 is closed and the automatic valve 17 is open. It is taken out through 17. The permeated liquid that has reached the other side 47 passes through the eyes of the drain cloth 41 and is taken out through the permeated liquid taking-out path 37 and the manual valve 21 provided in the permeated liquid taking-out path 37. One side 4
5 is set to be higher than the internal pressure of the other side 47, the permeable membrane 39 is kept in contact with the drain cloth 41 and the metal plate 42.
The backing of the permeable membrane 39
Is not damaged. In addition, the manual valve 25 is provided for applying a back pressure to the outlet of the concentrated liquid in the pressure vessel 5, whereby the pressure of the concentrated liquid outlet is adjusted. In the membrane separation device of this embodiment, the pressure vessel 5 and the automatic valve 13
The manual valve 25 is provided between the
The automatic valve 13 may be provided between the pressure vessel 5 and the manual valve 25 with the positions of the manual valve 3 and the manual valve 25 reversed.

In this membrane separation device, the automatic valve 13
Functions as a pressure adjusting means for adjusting the internal pressure of the one side 45 as described later, and also functions as an opening / closing means of the concentrated liquid extracting passage 37. That is, when the automatic valve 13 is closed, the concentrated liquid is not taken out from the one side 45, and the liquid to be treated is retained in the pressure vessel 5 for a long time. During the stay, the liquid to be treated continues to be concentrated. When the automatic valve 13 is opened after a lapse of a predetermined time, a concentrated solution concentrated to a desired concentration ratio can be taken out. The opening and closing timing of the automatic valve 13 may be controlled by a timer, or may be controlled by a load value detected from a motor included in the vibration means.

Next, a description will be given of a start-up operation of the membrane separation apparatus performed prior to such a steady operation. First, the pressure at the concentrated liquid outlet of the pressure vessel 5 is adjusted by operating the manual valve 25 in advance. Then, the automatic valve 7, the automatic valve 17, the manual valve 19, the manual valve 21, and the manual valve 23 are opened, and the automatic valve 9, the automatic valve 11, the automatic valve 13, and the automatic valve 15 are closed. Pump 3
Is started, and the automatic valve 13 is opened. A few seconds later, the automatic valve 15 is opened. Automatic valve 13 rather than automatic valve 15
Is opened first to prevent the permeable film 39 from being lifted from the drain cross 41 due to a reverse pressure applied to the permeable film 39 and damaged. When the one side 45 of the pressure vessel 5 reaches a predetermined internal pressure, the vibrating means is started, and reciprocating rotational vibration having a small amplitude is applied to the permeable membrane 39. After the internal pressure of the pressurized container reaches the operating pressure, the operation is switched to the steady operation.

When the above-mentioned steady operation is continuously performed for a long time,
The deposit adheres to the surface on one side 45 of the permeable membrane 39.
For this reason, the permeation flux decreases and the permeation efficiency decreases. Physical cleaning is performed to restore the permeate flux. The physical cleaning is performed using the automatic valve 13 as a pressure adjusting means for adjusting the internal pressure on one side 45 or the automatic valve 15 as a pressure adjusting means for adjusting the internal pressure on the other side 47.

When physical cleaning is performed using the automatic valve 13, the automatic valve 1 is first opened while the automatic valve 15 is opened.
Keep releasing 3 for some time. Then, the pressure vessel 5
The internal pressure on one side 45 of the
And the internal pressure difference between them. For this reason, the deposits adhering to the surface of the one side 45 of the permeable membrane 39 are separated from the permeable membrane 39 by a synergistic effect with the vibration of the permeable membrane 39, and the permeation flux is recovered.

When physical cleaning is performed using the automatic valve 15, the automatic valve 15 is closed by adjusting the opening of the manual valve 25 to an appropriate value while keeping the automatic valve 13 open. Then, the internal pressure on the other side 47 of the pressure vessel 5 increases, and the internal pressure difference between the one side 45 and the other side 47 decreases.
For this reason, the deposits adhering to the surface of the one side 45 of the permeable membrane 39 are separated from the permeable membrane 39 by a synergistic effect with the vibration of the permeable membrane 39, and the permeation flux is recovered. Automatic valve 1
5 is provided with a back pressure regulator 31 so that the internal pressure of the other side 47 does not exceed the internal pressure set by the back pressure regulator 31. Thereby, it is possible to prevent the permeable membrane 39 from being damaged by applying a reverse pressure to the permeable membrane 39.

As described above, the physical cleaning is performed by either lowering the internal pressure of the one side 45 by the automatic valve 13 or increasing the internal pressure of the other side 47 by the automatic valve 15. Of course, the physical cleaning may be performed with a small amount.

As described above, during normal operation, one side 45
And the other side 47 is set to have an internal pressure difference of about 2 to 40 atm. In order to enhance the effect at the time of physical cleaning, this internal pressure difference may be reduced as much as possible. However, if the internal pressure difference is completely eliminated, the permeable membrane 39 may be lifted, and a back pressure may be generated for some reason to damage the permeable membrane 39. Therefore, in consideration of a certain safety factor at the time of physical cleaning, when the internal pressure difference in the steady operation is about 5 atm or less, the internal pressure difference is about 1 atm or more and less than 2 atm. When the pressure exceeds the atmospheric pressure, the valve may be opened and closed so that the internal pressure difference is about 1 to 4 atm.

The physical cleaning may be performed at a frequency of about once every 30 to 60 minutes in a steady operation. In a single physical cleaning, the state where the internal pressure difference is reduced as described above is from 30 seconds to 60 seconds. It may be performed so that the degree is maintained. The timing and period of the physical cleaning may be controlled by controlling the opening and closing of the automatic valve 13 and the automatic valve 15 by a timer.

As described above, the permeation flux can be maintained by performing the physical cleaning. However, even if the physical cleaning is performed, the permeable membrane 39 may be clogged or the permeable membrane 39 may be maintained.
Deposits may adhere to the surface of the. In this case, cleaning with a chemical solution may be performed. Specifically, once the pump 3
Is stopped, the automatic valve 7 is closed and the automatic valve 9 is opened,
The pump 3 is started again. Then, the chemical is supplied into the pressure vessel 5 through the automatic valve 9 and the surface of the permeable membrane 39 is washed with the chemical. After the cleaning, the chemical solution is supplied to the concentrated solution removal path 35.
And discharged through the permeate extraction path 37. By closing the automatic valve 17 and opening the automatic valve 11, the cleaning solution may be discharged through the circulation path 33. The type of the chemical used is appropriately selected according to the type of the liquid to be treated. Whether or not to vibrate the permeable membrane 39 by the vibrating means at the time of cleaning with a chemical is determined according to the type of the liquid to be treated and the type of the chemical used.

After the washing with the chemical, the chemical remains in the system of the membrane separation device. In order to discharge the residual chemical, fresh water may be supplied into the system through the automatic valve 9 and the chemical may be pushed out. If the permeation process of the liquid to be treated is continued after the chemical solution is discharged in this way, it is possible to prevent the chemical solution from being mixed into the concentrated liquid and the permeated liquid that have been taken out.

According to the findings of the present inventors, when physical cleaning is not performed, cleaning with a chemical solution has to be performed once every three to four days. As a result, the permeation flux was recovered from about 10% to about 20%, and it was found that if the physical cleaning was performed once every 60 minutes, it would be sufficient if the cleaning with the chemical solution was performed once every three weeks. As described above, by introducing the physical cleaning step, the stop time of the permeation process by the chemical solution cleaning can be reduced, and the operation efficiency of the membrane separation device can be increased. In addition, the use amount of the chemical solution can be reduced, and the operating cost of the membrane separation device can be reduced.

Next, the stop operation of the membrane separation device will be described. First, the vibration means and the pump 3 are stopped. Then, the automatic valves 13 and 15 are opened. next,
The automatic valve 7 is closed, the automatic valve 9 is opened, and the pump 3 is started. Through this automatic valve 9, fresh water is supplied into the system. When the one side 45 of the pressure vessel 5 reaches a predetermined internal pressure, the vibration means is activated. In this state, the operation is continued, and the liquid to be treated in the system is replaced with fresh water. The discharged liquid to be treated (including a mixture of fresh water) is discharged through the concentrated liquid extracting path 35 and the permeated liquid extracting path 37. The liquid to be treated may be discharged through the circulation path 33 by closing the automatic valve 17 and opening the automatic valve 11.

When the replacement with the fresh water is completed, the vibration means and the pump 3 are stopped, and the automatic valve 9 is closed. After the pressure in the system becomes substantially atmospheric pressure, the automatic valve 15 is closed, and then the automatic valve 13 is closed. The reason why the automatic valve 15 is closed before the automatic valve 13 is to prevent the permeable membrane 39 from being damaged due to a reverse pressure applied to the permeable membrane 39.
By replacing the liquid to be treated in the system with fresh water in this way, it is possible to prevent the liquid to be treated remaining in the pressure vessel 5 during operation stop and prevent the liquid to be treated from deteriorating the permeable membrane 39. it can. Further, by filling the inside of the pressure vessel 5 with fresh water, the deterioration of the permeable membrane 39 due to drying can be prevented. When stopping operation for a long time, use the manual valve 1
9 and the manual valve 21 are also closed to reliably prevent the fresh water from flowing out of the system.

[0034]

As described above, according to the present invention,
By reducing the internal pressure on one side of the pressure vessel or increasing the internal pressure on the other side, it is possible to reduce the pressure difference on both sides of the permeable membrane and to separate the deposit. Therefore, the permeation flux can be recovered and the permeation efficiency can be increased. As a result, it is possible to reduce the frequency of cleaning with the chemical solution, increase the operation efficiency of the membrane separation device, and reduce the usage amount of the chemical solution to reduce the operation cost of the membrane separation device.

Further, by opening and closing the concentrate taking-out path, the liquid to be treated can be subjected to membrane separation while controlling the concentration ratio of the concentrate.

[Brief description of the drawings]

FIG. 1 is a route diagram illustrating a membrane separation device according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a part of a pressure vessel of the membrane separation device shown in FIG. 1;

FIG. 3 is a path diagram showing a conventional membrane separation device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Tank 3 ... Pump 5 ... Pressure vessel 7, 9, 11, 13, 15, 17 ... Automatic valve 19, 21, 23, 25 ... Manual valve 27 ... Three-way valve DESCRIPTION OF SYMBOLS 31 ... Back pressure regulator 33 ... Recirculation path 35 ... Concentrated liquid taking-out path 37 ... Permeate taking-out path 39 ... Permeable membrane 41 ... Drain cross 42 ... Metal plate 45 ..One side 47 ... the other side

Claims (6)

[Claims] 1. A pressurized liquid to be processed is supplied to one side of a pressure vessel having one side and the other side formed by being partitioned by a permeable membrane, and the permeable component is vibrated while the permeable membrane is vibrated. In the membrane separation method in which the concentrated liquid is taken out from the other side, the concentrated liquid is taken out from the one side, and the permeated liquid is taken out from the other side. Temporarily lowering the internal pressure on one side to reduce the internal pressure difference between the one side and the other side A method for separating a membrane, comprising the steps of: removing a substance attached to one side of a permeable membrane. 2. A pressure vessel having one side and the other side formed by being partitioned by a permeable membrane, a supply means for supplying a liquid to be treated to one side of the pressure vessel, and a vibrating means for oscillating the permeable membrane. A condensed liquid extracting path for extracting a concentrated liquid from one side of the pressure vessel, and a permeated liquid extracting path for extracting a permeated liquid from the other side of the pressure vessel. A membrane separation device, wherein a pressure adjusting means for adjusting an internal pressure on one side of a pressure vessel is provided in an extraction path. 3. A liquid to be treated in a pressurized state is supplied to one side of a pressure vessel in which one side and the other side are formed by being partitioned by a permeable membrane, and the permeable component is vibrated while the permeable membrane is vibrated. In the membrane separation method, the internal pressure of the other side is reduced by temporarily increasing the internal pressure of the other side in a membrane separation method in which the concentrated liquid is taken out from the other side, the concentrated liquid is taken out from one side, and the permeated liquid is taken out from the other side. The method according to claim 1, wherein the adhering matter adhered to one side of the permeable membrane is removed. 4. A pressure vessel having one side and the other side formed by being partitioned by a permeable membrane, supply means for supplying a liquid to be treated to one side of the pressure vessel, and vibration of the permeable membrane A vibrating means for causing the liquid to pass through, a concentrated liquid taking-out path for taking out the concentrated liquid from one side of the pressure vessel, and a permeate taking-out path for taking out the permeated liquid from the other side of the pressure vessel. A membrane separation device, wherein a pressure adjusting means for adjusting the internal pressure on the other side of the pressure vessel is provided in the takeout path. 5. A pressurized liquid to be treated is supplied to one side of a pressure vessel having one side and the other side formed by being partitioned by a permeable membrane, and the permeable component is vibrated while the permeable membrane is vibrated. In the membrane separation method in which the concentrated solution is taken out from the other side, the concentrated solution is taken out from one side, and the permeated solution is taken out from the other side, the path for taking out the concentrated solution is controlled by controlling the concentration rate of the concentrated solution. Characterized membrane separation method. 6. A pressure vessel having one side and the other side formed by being partitioned by a permeable membrane, supply means for supplying a liquid to be treated to one side of the pressure vessel, and vibrating the permeable membrane. A condensed liquid extracting path for extracting a concentrated liquid from one side of the pressure vessel, and a permeated liquid extracting path for extracting a permeated liquid from the other side of the pressure vessel. A membrane separation device, wherein an opening / closing means for opening / closing the concentrated liquid taking-out path is provided in the taking-out path, and the concentration rate of the concentrated liquid can be controlled by opening / closing the opening / closing means.