JP2009011924A - Membrane separation apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane separation apparatus which prevents a separation membrane semi-permeable membrane and piping and the like constituting a permeating liquid passage from being damaged owing to the operation error of a valve. <P>SOLUTION: The membrane separation apparatus is provided with a separation membrane semi-permeable membrane unit having a reverse osmosis membrane and/or nano filtration membrane which separates a feed liquid stock solution to a permeating liquid and a condensed liquid, a feed liquid passage to supply the feed liquid to the separation membrane semi-permeable membrane unit, a feed liquid stock solution booster pump installed at the feed liquid passage, a condensed liquid passage to withdraw the condensed liquid separated by the separation membrane semi-permeable membrane unit, a permeating liquid passage to withdraw the permeating liquid separated by the separation membrane semi-permeable membrane unit, a reflux liquid passage which is branched from each of the condensed liquid passage and the permeating liquid passage which communicates with the feed liquid passage and a washing liquid tank installed at the reflux liquid passage. The apparatus is further provided with a three-way valve to close the reflux liquid passage or close the more downstream side than the junction of the permeating liquid passage with the opening and closing operation at the junction where the reflux liquid passage is branched from the permeating liquid passage. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a membrane separation device capable of preventing a reverse osmosis membrane and / or a nanofiltration membrane (hereinafter referred to as a semipermeable membrane) from being damaged by a reverse pressure applied from the permeate side to the concentrate (feed solution) side. The present invention relates to an apparatus that can be used for various membrane separation semipermeable membranes, such as desalination of brine and seawater, reuse of wastewater, and recovery of valuable materials.

  The semipermeable membrane is a semipermeable membrane that allows some components in the mixed liquid to be separated, for example, a solvent to permeate and does not allow other components to permeate. As the material, polymer materials such as cellulose acetate polymer, polyamide, polyester, polyimide, vinyl polymer are often used. In addition, the membrane structure has a dense layer on at least one side of the membrane, an asymmetric membrane having fine pores gradually increasing from the dense layer to the inside of the membrane or the other side, and another layer on the dense layer of the asymmetric membrane. There are composite membranes with a very thin active layer formed of a material. In this composite film, there is a problem that the active layer peels off from the dense layer due to the reverse pressure.

  By the way, in order to maintain the performance of a device using a semipermeable membrane such as a reverse osmosis membrane or a nanofiltration membrane, it is necessary to periodically stop the device and perform maintenance such as cleaning. During cleaning, the pipe valves around the semipermeable membrane are opened / closed and the cleaning liquid supply pump is started / stopped as appropriate according to the operation procedure. In general, a membrane separation apparatus using a semipermeable membrane has a supply liquid flow path, a concentrated liquid flow path, and a permeate flow path, and each flow path is further a normal flow path and a cleaning flow path connected to a cleaning liquid tank. They are divided and each has a switching valve. That is, the number of switching valves included in the membrane separation device is at least 2 in total in the supply liquid flow path (1 normal operation flow path and 1 washing flow path), 2 in each of the concentrate liquid flow path and the permeate flow path. There are a total of six each (one normal operation channel and one cleaning channel). When the membrane separation device has a multi-stage membrane module configuration, the number of these switching valves further increases.

  However, the valve opening / closing operation at the time of cleaning is complicated and there is a risk of erroneous operation. Incorrect operation may cause a back pressure from the permeate side of the semipermeable membrane to the concentrated liquid (supply liquid) side, which may cause the semipermeable membrane to peel off.

  As a specific example in FIG. 1, in the cleaning of the membrane separation apparatus constituted by the two-stage membrane modules 2 and 3, the two-way valve (V3) provided in the flow path during the normal operation of the permeate is “closed”. In addition, the case where the flow path valve (V4) during the cleaning operation is erroneously closed is shown. At this time, the cleaning liquid supplied from the cleaning liquid supply pump 5 to the first-stage membrane module 2 does not escape to the permeate side, but the entire amount flows on the concentrated liquid side and is supplied to the second-stage membrane module 3. Flows through the concentrate flow path, returns to the cleaning liquid tank 4 and circulates. When the cleaning liquid circulates, a pressure loss of 0.1 to 0.2 MPa usually occurs in the membrane modules 2 and 3, so the relationship between the pressure of the cleaning liquid flowing from the supply liquid flow path to the concentrate flow path is the first-stage module. 2 input pressure (P1), output pressure (P2) of the module 2, input pressure (P2) of the second stage module 3, and output pressure (P3) of the module 3, P1> P2> P3. However, the pressure loss between the first-stage module and the second-stage module is relatively small and can be ignored. Here, since the permeate flow path is in a fully closed state, the pressure is P2 which is the same as the output pressure of the first-stage module 2. On the other hand, the output pressure of the second-stage module 3 is P3, and the permeate-side pressure is higher than the concentrate-side pressure downstream of the second-stage module 3 (close to the output) from the above-described relational expression. The problem of active layer peeling on the surface of the permeable membrane occurs.

  In addition, as shown in FIG. 2, when the operation of the semipermeable membrane device is restarted with all the valves (V3 and V4) in the permeate flow path closed, the supply liquid pressure is increased for seawater desalination. When the discharge pressure of the pump is as high as about 7 MPa, there is a risk of damaging piping or the like constituting the permeate flow path.

As a countermeasure against such a problem that occurs in the fully closed state of the permeate channel, a method of improving the reverse pressure resistance of the semipermeable membrane itself and preventing film peeling due to the reverse pressure is disclosed (for example, Patent Document 1). However, the semipermeable membrane with improved reverse pressure resistance is compatible with a supply liquid having a salt concentration of about 2,000 ppm, and is difficult to apply in seawater applications. In addition, a check valve is provided in the permeate flow path to prevent reverse pressure from being applied to the semipermeable membrane. However, there is a problem of foreign matter biting in the check valve and the aging of the packing on the seal surface. There is a problem of non-return failure due to deterioration or the like, and it cannot be expected to permanently prevent the semipermeable membrane from being applied with a back pressure.
JP-A-6-346

  An object of the present invention is to provide a membrane separation apparatus capable of more reliably preventing damage to a semipermeable membrane or piping constituting a permeate flow path due to such a valve misoperation.

The present invention for solving the above-described problems is characterized by either of the following (1) and (2).
(1) A semipermeable membrane unit having a reverse osmosis membrane and / or a nanofiltration membrane that separates a supply solution into a permeate and a concentrated solution, and a supply solution channel for supplying the supply solution to the semipermeable membrane unit A supply liquid booster pump provided in the supply liquid flow path, a concentrate flow path for taking out the concentrate separated by the semipermeable membrane unit, and a permeate for taking out the permeate separated by the semipermeable membrane unit A permeate flow path that branches off from each of the concentrate liquid flow path and the permeate liquid flow path and communicates with the supply liquid flow path, and a cleaning liquid tank provided in the recycle liquid flow path. Provided with a three-way valve that closes the reflux liquid channel by opening / closing operation or closes the downstream side of the permeate channel from the branch point at the branch point where the reflux liquid channel branches from the liquid channel Membrane separator.
(2) The semipermeable membrane unit is connected so that a plurality of membrane modules each having a reverse osmosis membrane and / or a nanofiltration membrane are supplied to the other membrane module with the concentrate of one membrane module; The permeate obtained from each membrane module is collected and allowed to flow through the permeate channel, and the concentrated liquid of the one membrane module is pressurized and supplied to the other membrane module. The membrane separator according to (1), further including a concentrated pressure boosting pump.

  According to the present invention, at the branch point where the reflux liquid channel branches off from the permeate flow channel, the reflux liquid channel is closed by an opening / closing operation, or the downstream side of the permeate flow channel from the branch point is closed. There is a valve, that is, a three-way valve that always opens either the downstream side of the permeate flow path or the reflux liquid flow path, preventing the permeate flow path from being fully closed, and always open to the atmosphere. Can be made. Therefore, there is no possibility that a reverse pressure from the permeate side is applied to the semipermeable membrane, the semipermeable membrane can be prevented from being damaged, and the piping can also be prevented from being damaged.

  In the membrane separation apparatus of the present invention, for example, as shown in FIG. 3, a semipermeable membrane unit 9 provided with at least one of a reverse osmosis membrane and a nanofiltration membrane (hereinafter referred to as a semipermeable membrane), and the semipermeable membrane unit A supply liquid flow path 10 for supplying a supply liquid to 9, a supply liquid booster pump 1 provided in the supply liquid flow path 10, a concentrated liquid flow path 11 for taking out the concentrated liquid separated by the semipermeable membrane 9, A permeate flow path 12 for taking out the permeate separated by the semipermeable membrane unit 9 is provided. The concentrated liquid flow path 11 and the permeated liquid flow path 12 are connected to a circulating liquid flow path 13 that is branched from the concentrated liquid flow path 11 and communicates with the supply liquid flow path 10. In addition, a cleaning liquid supply pump 5 is provided. At the branch point where the reflux liquid channel 13 branches from the permeate channel 12, the reflux liquid channel 13 is closed by opening / closing operation or the downstream side of the branch point of the permeate channel 12 is closed. A three-way valve V7 is provided.

  Further, in the apparatus shown in FIG. 3, the semipermeable membrane unit 9 has a two-stage membrane module, and is connected so as to supply the concentrated liquid of one membrane module to the other membrane module. In addition, the permeate obtained from each membrane module is collected and allowed to flow through the permeate channel 12.

  When performing a normal operation such as seawater desalination using the membrane separation apparatus shown in FIG. 3, the two-way valves V1 and V5 are opened and the reflux liquid channel 13 is closed. The two-way valves V2 and V6 are “closed”, and the c-side of the three-way valve V7 is “closed” (between a and b is “open”). On the other hand, when the apparatus is cleaned, the two-way valves V1 and V5 are “closed”, the two-way valves V2 and V6 are “open”, and the three-way valve V7 is opened so as to open the reflux liquid flow path 13. B side is closed (a-c is "open").

  Here, conventionally, since the two-way valve is provided in each of the permeate channel and the reflux liquid channel branched from the permeate channel, both the two-way valves are “closed” if the order is incorrect. However, in the present invention, since the three-way valve V7 is provided at the branch point where the permeate liquid channel 12 branches from the permeate channel 12, the downstream of the branch point. There is no risk of causing time for both of the two flow paths on the side to be “closed”. That is, since the three-way valve V7 is always “open” between a and b or a and c, there is no time for the permeate flow path to be fully closed, and an open atmosphere can always be created. Therefore, there is no possibility that reverse pressure is applied to the semipermeable membrane from the permeate side.

  In the present invention, the above-described embodiment shown in FIG. 3 may be modified as shown in FIGS.

  The membrane separation device shown in FIG. 4 is a mode in which a branch point of the reflux liquid channel 13 is provided upstream from the point where the permeate channels of a plurality of membrane modules merge, and the three-way valve V7 has individual membranes. There are as many modules as there are modules. Others are the same as the embodiment of FIG.

  The membrane separation apparatus shown in FIG. 5 includes a concentrate booster pump 6 that boosts the concentrate of the first-stage membrane module 2 and supplies it to the second-stage membrane module 3. In this embodiment, the cleaning liquid exiting the cleaning liquid supply pump 5 enters the second-stage membrane module 3 from the first-stage membrane module 2 via the concentrated liquid booster pump 6. For example, the cleaning liquid supply having a discharge pressure of about 0.5 MPa is used. In the circulating flow by the pump, the concentrated liquid booster pump does not work as a booster pump and becomes a resistance in the flow path, resulting in a pressure loss of 0.1 to 0.2 MPa. Therefore, if there is no three-way valve V7 and a two-way valve as shown in FIGS. 1 and 2 is provided, the inlet pressure (P2) of the concentrate booster pump 6 and the outlet pressure (P3) of the pump 5 are provided. The difference of 0.1 to 0.2 MPa is further added to the reverse pressure of 0.1 to 0.2 MPa generated in the embodiment of FIGS. 1 and 2, and the first stage module output pressure (P2) and the second stage The difference in module output pressure (P4), that is, the back pressure generated when the conventional two-way valve system is operated erroneously, is 0.2 to 0.4 MPa. This is about twice the back pressure generated in the embodiment of FIGS. 1 and 2, and there is a high risk that the degree of film peeling will increase. However, in the membrane separation apparatus according to the present invention specifically shown in FIG. 5, the reflux liquid channel 13 is closed or permeated by an opening / closing operation at a branch point where the reflux liquid channel 13 branches from the permeate channel 12. Since the three-way valve V7 that closes the downstream side of the branch point of the liquid channel 12 is provided, that is, the three-way valve that always opens either the downstream side of the branch point of the permeate channel or the reflux liquid channel is provided. There is no possibility that reverse pressure is applied to the semipermeable membrane from the permeate side. The mode shown in FIG. 5 is the same as the mode shown in FIG. 3 except for the points described above.

  Furthermore, the number of stages of the membrane modules constituting the semipermeable membrane unit 9 is not limited to two, but may be three or more, or may be one as shown in FIG. Good.

  When the number of stages of the membrane module is 1, even if the permeate flow path is fully closed during circulation of the cleaning liquid, the difference in pressure loss between the first stage membrane module and the second stage membrane module or the concentrated liquid booster pump There is no concern of back pressure generated by pressure loss at However, for example, when the permeate flow path is fully closed at the end of cleaning and the cleaning liquid supply pump is stopped with the residual pressure remaining, the supply liquid and concentrate flow path side is released and instantaneously reverse pressure is generated, causing the membrane to There is a risk of peeling. Therefore, as shown in FIG. 6, the reflux liquid channel 13 is closed by the opening / closing operation at the branch point where the reflux liquid channel 13 branches from the permeate channel 12 or from the branch point of the permeate channel 12. It is also preferable to provide a three-way valve V7 that closes the downstream side, that is, a three-way valve that always opens either the downstream side or the reflux liquid channel from the branch point of the permeate channel. Thus, even if the number of the membrane modules constituting the semipermeable membrane unit 9 is 1, by providing a three-way valve at the branch point where the reflux liquid channel 13 branches from the permeate channel 12, There is no risk of pressure being applied to the semipermeable membrane from the permeate side.

It is a schematic diagram which shows the conventional membrane separator. It is a schematic diagram which shows the conventional membrane separator. It is a schematic diagram which shows one Embodiment of the membrane separator concerning this invention. It is a schematic diagram which shows one Embodiment of the membrane separator concerning this invention. It is a schematic diagram which shows one Embodiment of the membrane separator concerning this invention. It is a schematic diagram which shows one Embodiment of the membrane separator concerning this invention.

Explanation of symbols

1: Supply pressure booster pump 2: Membrane module (first stage)
3: Membrane module (second stage)
4: Cleaning liquid tank 5: Cleaning liquid supply pump 6: Concentrated liquid booster pump 9: Semipermeable membrane unit 10: Supply liquid flow path 11: Concentrated liquid flow path 12: Permeate flow path 13: Recirculating liquid flow path V1: Two-way valve V2: Two-way valve V3: Two-way valve V4: Two-way valve V5: Two-way valve V6: Two-way valve V7: Three-way valve

Claims (2)

  A semipermeable membrane unit having a reverse osmosis membrane and / or a nanofiltration membrane that separates the supply solution into a permeate and a concentrated solution, a supply liquid channel for supplying the supply solution to the semipermeable membrane unit, and the supply A supply liquid booster pump provided in the liquid flow path, a concentrated liquid flow path for taking out the concentrated liquid separated by the semipermeable membrane unit, and a permeate flow path for taking out the permeated liquid separated by the semipermeable membrane unit; A permeate flow path that branches off from each of the concentrate liquid flow path and the permeate liquid flow path and communicates with the supply liquid flow path, and a washing liquid tank provided in the recycle liquid flow path. Membrane separation provided with a three-way valve that closes the reflux liquid channel by opening / closing operation or closes the downstream side of the permeate channel from the branch point at the branch point where the reflux liquid channel branches from apparatus.   The semipermeable membrane unit is connected so that a plurality of membrane modules each having a reverse osmosis membrane and / or a nanofiltration membrane are supplied to the other membrane module with the concentrated liquid of one membrane module. Concentrated liquid that is configured to collect the permeate obtained from the module and flow it to the permeate flow path, and pressurizes the concentrate of the one membrane module and supplies it to the other membrane module The membrane separation apparatus according to claim 1, comprising a booster pump.

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