JP4765874B2 - Membrane module cleaning method - Google Patents

Description

  The present invention relates to a method for cleaning a membrane module for water treatment, and more particularly to a method for cleaning a primary side of a membrane module.

  I. As a method for cleaning the primary side of a water treatment membrane module such as a reverse osmosis membrane module, there is one described in JP-A-11-104636. The membrane module of the same publication is a reverse osmosis membrane module, which introduces raw water to the primary side of the membrane module via raw water supply piping, and takes out permeated water of the membrane element via production water piping, The concentrated water on the primary side is taken out through a piping for concentrated water. When cleaning the primary side, a gas-liquid two-phase flow is introduced to the primary side through this concentrated water pipe, and the cleaning wastewater is discharged through the raw water supply pipe.

  II. As a membrane module loaded in a membrane separation device such as a microfiltration device, an ultrafiltration device, or a reverse osmosis membrane separation device, there is a spiral membrane module in which a separation membrane is wound around the outer periphery of a water collecting pipe. In this spiral membrane module, as seen in the following non-patent document, a bag-shaped separation membrane (leaf) is wound around the outer circumference of the water collecting pipe through a mesh-like spacer to constitute a spiral membrane element. Has been.

  The water collecting pipe has an opening communicating with the inside and outside of the pipe. The separation membrane has a bag-like shape, and its central part is bonded to the water collecting pipe or wraps around the water collecting pipe. A channel material made of mesh spacers or the like is inserted into the bag-shaped separation membrane, and the inside of the bag-shaped separation membrane is a permeate channel.

  This spiral membrane element is accommodated in a cylindrical housing (pressure vessel) to constitute a spiral membrane module. A raw water inflow space is formed facing the front end face of the membrane element, and a concentrated water outflow space is formed facing the rear end face. The end of the water collecting pipe extends from the central portion of the rear end surface of the housing or is connected to the permeate water extraction portion of the central portion.

  Raw water flows into the raw water inflow space from the raw water inlet provided in the housing, then flows into the raw water flow path between the bag-like membranes from the front end surface of the membrane element, and flows in the longitudinal direction of the membrane element as it is, It flows out from the rear end face of the membrane element. While flowing through this raw water flow path, water permeates the bag-like separation membrane, enters the inside thereof, flows into the water collection pipe, and is taken out of the module from the rear end side of the water collection pipe.

The concentrated water that has passed through the rear end surface of the membrane element is taken out of the housing from the concentrated water outflow space through the concentrated water outlet provided in the housing. The raw water flow path, raw water inflow space and concentrated water outflow space between the bag-shaped separation membranes are the “primary side”, and the inner side of the bag-shaped separation membrane and the water collection pipe are the “secondary side”. is there.
JP-A-11-104636 Water Treatment Management Manual P233 (1998 Maruzen Co., Ltd.)

  When cleaning the primary side of the membrane element, it is desirable to distribute the cleaning fluid as uniformly as possible on the entire primary side of the membrane element. However, the cleaning fluid flows unevenly and is partially insufficiently cleaned. A spot may occur.

  In particular, when the membrane module is a spiral membrane module, such a drift tends to occur. This is because, as will be described in detail later, the water collecting pipe is arranged at the axial center position of the cylindrical housing, so that both the raw water inlet and the concentrated water outlet are arranged at the non-axial center position of the housing. Because it becomes.

  An object of the present invention is to solve the above problems and to provide a method for cleaning a membrane module that can sufficiently clean the primary side of the membrane module.

In the membrane module cleaning method of the present invention (Claim 1) , a reverse osmosis membrane element (3) in which a reverse osmosis membrane is wound around the outer periphery of a water collecting pipe (4) is accommodated in a cylindrical housing (2), A raw water inflow space (8) is provided on one end side of the reverse osmosis membrane element (3), a concentrated water outflow space (9) is provided on the other end side, and raw water is supplied to the raw water inflow space (8) , A method for washing a membrane module (1 ) from which permeated water is taken out from a water collecting pipe (4) , wherein raw water is introduced into a raw water inflow space (8) from a washing fluid inlet (2a) provided in the housing (2). And a gas are supplied simultaneously, and a cleaning fluid comprising a gas-liquid mixed phase flow is circulated from the primary side of the membrane element (3) to the concentrated water outflow space (9), and a cleaning fluid outlet provided in the housing (2) part discharge of the detergent Kiyoshi fluid from (2b) In the cleaning method that the membrane module, the cleaning fluid inlet portion during the cleaning of the primary side pressure of the cleaning fluid (2a) and P _1, the cleaning fluid outlet pressure of the cleaning fluid (2b) and P ₂ In this case, the cleaning fluid is circulated so that P ₂ / (P ₁ -P ₂ ) is 1.2 to 10.

Further, it is preferable that the _{P 1} 0.05 MPa or more.

As a result of various studies by the present inventors, when cleaning the primary side of the membrane module, the pressure P ₂ at the cleaning fluid outlet of the housing is made higher than the water flow differential pressure P ₁ -P ₂ of the membrane element. It has been found that the cleaning fluid flows evenly through the membrane element. The present invention is based on such knowledge, and according to the present invention, the primary side of the membrane element can be sufficiently cleaned.

In the present invention, in order to perform the cleaning so that P ₂ > (P ₁ -P ₂ ), it is preferable to control the outlet pressure by providing a variable throttle on the outlet or the downstream side of the cleaning fluid in the housing. .

In the present invention, at the time of cleaning the primary side of the membrane element, the pressure on the inlet side of the cleaning fluid is increased to some extent, specifically, by setting P ₁ ≧ 0.05 MPa, the cleaning fluid is supplied to the primary side. Can be distributed evenly.

Membrane elements for use in the present invention is Ru reverse osmosis membrane element der. The material of the film is not particularly limited.

  Hereinafter, embodiments will be described with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view in the axial direction of the membrane module used in the embodiment, FIG. 2 (a) is a front view of the membrane module in FIG. 1, and FIG. Fig. 3 is a system diagram of water flow to the membrane module. 4 and 5 are explanatory views of the flow of the cleaning fluid in the membrane module, FIG. 6 is a cross-sectional view showing another configuration example of the membrane module, and FIG. 7 shows the state of contamination of the membrane element in the comparative example. It is a typical perspective view.

  As shown in FIG. 1, the membrane module 1 used in this embodiment is a spiral membrane module, and a spiral membrane element 3 is disposed coaxially with a housing 2 in a cylindrical housing 2. Yes.

  In this membrane element 3, a bag-like separation membrane 5 is wound around the outer circumference of a water collecting pipe 4 via a mesh-like spacer (not shown).

  The water collecting pipe 4 is provided with an opening 4a communicating between the inside and outside of the pipe. The separation membrane 5 has a bag shape, and its central portion is bonded to the water collecting pipe 4 or wraps around the water collecting pipe 4. A channel material (not shown) made of mesh spacers or the like is inserted into the bag-shaped separation membrane 5, and the inside of the bag-shaped separation membrane 5 is a permeate channel.

  A ring-shaped top-side sealing material 6 is disposed between the outer peripheral surface of the membrane element 3 and the inner peripheral surface of the housing 2.

  An end cap 7 is attached to the front end (left end in the figure) of the water collecting pipe 4, and the rear end (right end in the figure) is fitted to a permeate outlet 2 c provided in the housing 2. In this embodiment, the permeated water is configured to be taken out from one end (the right end in the figure) of the water collecting pipe 4, but may be configured to flow out from both ends.

  A raw water inflow space 8 is formed facing the front end surface of the membrane element 3, and a concentrated water outflow space 9 is formed facing the rear end surface.

  An inlet 2a for raw water or the like is provided on one end surface of the housing 2, and an outlet 2b for concentrated water or the like is provided on the other end surface. As shown in FIG. 2, the inlet 2 a and the outlet 2 b are arranged on opposite sides of the axis of the housing 2.

As shown in FIG. 3, raw water is introduced into the inflow port 2a through a raw water pump 11, a valve 12, and a pipe 13. A pressure gauge 14 is provided in the vicinity of the inlet 2 a in the pipe 13. Detected pressure of the pressure gauge 14 is _{P 1.} Air is blown into the pipe 13 through the compressor 15, the pipe 16, and the valve 17 when the primary side is washed.

An outflow pipe 18 for concentrated water or the like is connected to the outlet 2b, and a pressure gauge 19 is installed in the pipe 18. Detected pressure of the pressure gauge 19 is _{P 2.} Although not shown, a flow path resistance member such as a variable throttle is provided downstream of the pressure gauge 19 in the pipe 18 so that the pressure at the outlet 2b can be adjusted.

  A permeated water outlet pipe 20 and a valve 21 are provided at the permeated water outlet 2c.

  Next, the operation of the membrane module configured as described above will be described.

[Membrane separation operation of raw water]
When the raw water is subjected to membrane separation, the compressor 15 is stopped and the valve 17 is closed.

  When the valves 12 and 21 are opened and the raw water pump 11 is operated, the raw water flows into the inflow space 8 from the inlet 2a and then flows into the raw water flow path between the separation membranes 5 from the front end face of the membrane element 3. Then, it flows in the longitudinal direction of the membrane element 3 and flows out from the rear end face of the membrane element 3. While flowing through this raw water flow path, water permeates the separation membrane 5 and enters the inside thereof, flows into the water collecting pipe 4 from the opening 4a, and is taken out of the membrane module 1 from the right end side of the water collecting pipe 4.

  The concentrated water that has passed through the rear end surface of the membrane element 3 is taken out of the housing 2 from the outflow space 9 through the outflow port 2 b and the pipe 18.

  The raw water flow path, the inflow space 8 and the outflow space 9 between the separation membranes 5 are “primary side”, and the inside of the bag-like separation membrane 5 and the inside of the water collecting pipe 4 are “secondary side”. is there.

[Cleaning of the primary side of the membrane module 1]
When the primary side of the membrane module 1 for cleaning with gas, we adopt the following A, B, and C of the C.

  A: Supply only air, mix with the water retained in the membrane module 1, and wash as a gas-liquid mixed phase state. In this case, the valve 12 is closed, the raw water pump 11 is stopped, the valve 17 is opened, and the compressor 15 is operated. The washing waste water from the pipe 18 is discharged out of the system.

  B: After draining water from the membrane module 1, air is supplied, gas-liquid cleaning is performed by mixing with retained water slightly remaining in the membrane module 1 (cleaning method with a large gas-liquid ratio), and finally the cleaning liquid ( For example, raw water) is supplied, and dirt components are pushed out from the pipe 18 and removed. The waste water from the pipe 18 is discharged out of the system.

  In order to drain water from the membrane module 1, the valve 12 is closed, the raw water pump 11 is stopped, the valve 17 is opened, and air is sent from the compressor 15 into the membrane module 1. Further, although not shown in the figure, the housing 2 may be provided with a water drain port and an air release port, and the water may be drained by opening them.

  C: Raw water and air are simultaneously supplied to the membrane module 1 and washed as a gas-liquid mixed phase state.

  In this case, the valves 12 and 17 are opened, and the raw water pump 11 and the compressor 15 are operated. The washing waste water from the pipe 18 is discharged out of the system.

  In this method, the gas-liquid ratio can be arbitrarily set. In addition, when the gas and liquid having different viscosities alternately pass through the film surface, vibration is given to the film surface deposit, and the peeling effect can be enhanced, which is preferable.

  The gas-liquid ratio in this C cleaning method is not particularly limited, but is preferably at least twice the flow rate of raw water when flowing the liquid phase (raw water treatment operation), and the gas phase flow rate is also The raw water flow rate should be twice or more, and the gas-liquid ratio should be 2: 1 to 1: 2.

  The duration of washing is not particularly limited, but in the case of the method C in particular, the longer the washing time, the more water used for washing and the lower the water recovery rate. Depending on the flow rate during cleaning, the cleaning time is preferably about 10 seconds to 5 minutes.

  There is no particular limitation on the frequency of cleaning. However, when the frequency of implementation increases, the water recovery rate decreases, so a frequency of 30 minutes to once every few days is preferable.

  In the cleaning method C, raw water is circulated as a cleaning fluid to the primary side, but it may be treated water subjected to membrane separation.

  In any of the cleaning methods A, B, and C, it is preferable to close the valve 21 so that the cleaning fluid or the like does not permeate the separation membrane 5 when supplying the cleaning fluid.

  When raw water or the like is used as a cleaning fluid, it is preferable to remove coarse turbidity (for example, particles having a particle diameter of about 1 mm or more). The same applies to the operation of membrane separation treatment of raw water.

  In the cleaning methods A, B, and C, air is supplied from the compressor. However, if there is another pressure source, it may be used, and the gas is not limited to air.

In the illustrated embodiment, that have allowed to flow the cleaning fluid to the raw water membrane separation process during the raw water passage direction (forward direction).

When the primary side of the membrane module 1 is cleaned , P _{2 is set} to 1.2 times or more of (P ₁ -P ₂ ) in any cleaning method.

To increase the magnification of the P ₂ with respect to (P 1 _{-P 2)} is either squeeze under certain conditions the P _1, the valve (not shown) provided on the downstream side of the pressure gauge 19 (outlet pipe valve), the valve open the supply pressure of the cleaning fluid be increased to increase the P _1. If the supply pressure of the cleaning fluid is kept constant and the outflow piping valve is throttled, the flow rate of the cleaning fluid decreases and the cleaning effect decreases. While cleaning effect by increasing P ₁ the flow rate of cleaning fluid faster increases, while there will not change the cleaning effect to be a certain value or more, breakage of the film, preferably economically it requires equipment for applying high pressure Absent. Therefore, the magnification of the upper limit is 10 times or less with respect to the _{P 2 (P 1 -P 2)} , particularly preferably from 5 times or less, also, it is preferable to be _{P 1} is 0.05MPa or more, further 1MPa or less In particular, the pressure is preferably 0.5 MPa or less.

Thus, by increasing the pressure P ₂ at the outlet side of the cleaning fluid during the cleaning of the primary side higher than a predetermined value, (including inhibition) preventing uneven flow of the cleaning fluid in the membrane module, and a sufficient cleaning effect Can be obtained.

  INDUSTRIAL APPLICABILITY The present invention can be suitably used not only for the production of ultrapure water, but also for the washing of reverse osmosis membranes that are recovered by desalinating drainage and blown cooling water. Furthermore, the present invention exhibits an excellent effect against turbid film contamination. Therefore, when the present invention is used for washing the reverse osmosis membrane as described above, a turbidity device (ultrafiltration membrane, microfiltration membrane and other filter) usually provided in the front stage of the reverse osmosis membrane device is used. It can be omitted. If these turbidizers are omitted, there is a risk that coarse contaminants may be supplied to the reverse osmosis membrane device and damage the membrane, or block the raw water inflow passage of the membrane element. It is preferable to provide a filter, a spring filter, or the like.

  In the spiral membrane module, the reason why the drift tends to occur during the cleaning of the primary side will be described with reference to FIGS. 4 and 5. FIG.

FIG. 4 is an explanatory diagram when the cleaning fluid is flowed so as not to satisfy P ₂ > (P ₁ -P ₂ ) in the membrane module of FIG. As shown in FIGS. 3 (a) and 3 (b), the inlet 2a and the outlet 2b are located on opposite sides of the axis of the housing 2. In FIG. 4, the cleaning fluid flows in a short circuit between the inlet 2 a and the outlet 2 b in a direction oblique to the axis of the housing 2. Therefore, in the inflow space 8 side of the membrane element 3, the inlet 2a from easily occurs washed insufficient area D ₁ on the far side. Further, in the outlet space 9 side of the membrane element 3, the outlet 2b from easily occurs washed insufficient area D ₂ on the far side.

  FIG. 5 shows the cleaning fluid when the inlet 2a faces the outlet 2b, that is, the straight line connecting the inlet 2a and the outlet 2b is parallel to the axis of the housing 2. The flow status is shown.

In this case, the cleaning fluid flows in a short circuit between the inlet 2a and the outlet 2b in a straight line. Therefore, easily occurs washed insufficient area D ₃ on the opposite side of the inlet 2a and the outlet 2b and the housing axial line of the membrane element 3.

When the cleaning fluid is circulated under the condition of P ₂ > (P ₁ -P ₂ ) as in the present invention, such a drift is prevented and the occurrence of an insufficiently cleaned region such as D _{1 to} D ₃ is prevented. .

  In the membrane module 1 shown in FIGS. 2 to 5, one membrane element 3 is installed in the housing 2. However, as in the membrane module 1A shown in FIG. 6, two or more in the housing 2A are used. The membrane element 3 may be arranged. In FIG. 6, the water collecting pipes 4 of the adjacent membrane elements 3 are connected by a joint 24. The water flowing out from the raw water flow path of the left membrane element 3 flows into the raw water flow path of the right membrane element 3 through the space 25 between the left and right membrane elements 3 and 3, and flows to the outlet 2b.

When raw water is used as a cleaning fluid , a raw water added with chemicals such as an oxidizing agent such as sodium hypochlorite, an alkali such as sodium hydroxide, and an acid such as sulfuric acid may be used.

  Hereinafter, examples and comparative examples will be described.

Example 1
As raw water, 100 mg / L of polyaluminum chloride (industrial reagent) was added to city water to prepare simulated drainage using aluminum hydroxide floc as simulated turbidity.

The membrane module and its water flow system are as shown in FIG. 2 except that the membrane module is placed vertically, that is, installed so that the longitudinal direction (axial direction) of the membrane element is the vertical direction. The membrane element is a reverse osmosis membrane element (ES20-D4, Nitto Denko Corporation). Constant permeation flux operation with a permeation flux of 0.4 m / d (permeate flow rate of 2.8 m ³ / d), and repeated primary-side gas-liquid cleaning once every 12 hours for about 7 days Continued operation.

Respectively inlet pressure _{P 1} of the raw water treatment time the outlet pressure _{P 2} is, 0.70 MPa, was 0.68Mpa.

  The flow direction of the feed water was from the lower part to the upper part of the membrane module, and the raw water inlet and the concentrated water outlet were axisymmetric with respect to the center of the module end face as shown in FIGS.

  Gas-liquid cleaning for cleaning the primary side was the above-described C method. Gas liquid was simultaneously supplied to the membrane element under the conditions of a cleaning liquid flow rate of 120 L / Hr and a cleaning air flow rate of 180 NL / Hr.

  Simulated waste water as feed water was supplied as the cleaning liquid, and air was supplied as the cleaning gas using a high-pressure pump and a compressor for water supply, respectively, and the gas-liquid cleaning time was 30 seconds / time.

When the gas-liquid washing, the inlet pressure _{P 1} and the outlet pressure _{P 2} is _P 1 ₌ 0.21 MPa, P 2 = 0.18 MPa, _{respectively,} since it is _{P 1 -P 2 = 0.03MPa P 2} / (P ₁₋ P ₂ ) = 6 .

  After the continuous water flow, the membrane element was taken out and the inlet end surface portion of the membrane element was confirmed. As a result, no clogging of turbidity was observed. In addition, when the membrane element was disassembled and the membrane surface was observed, a slight amount of turbidity adhered was confirmed, but there was no unevenness in the adhesion of the turbidity, and a uniform cleaning effect was obtained within the membrane element. It was recognized that

Example 2
A test similar to Example 1 was performed except that the liquid flow rate during gas-liquid cleaning was 75 L / Hr and the air flow rate was 120 NL / Hr.

Respectively inlet pressure _{P 1} during the gas-liquid cleaning outlet pressure _{P 2 is,} P _{1 =} 0.09 MPa, a P 2 = 0.05 _MPa, because it is P ₁ -P 2 = 0.04 MPa, _{P 2} / (P ₁ −P ₂ ) = 1.25 .

  After the continuous water flow, the membrane element was taken out and the inlet end surface portion of the membrane element was confirmed. As a result, no clogging of turbidity was observed. Also, when the membrane element was disassembled and the membrane surface was observed, a slight amount of turbidity was confirmed, but there was no unevenness in the turbidity adhesion, and a uniform cleaning effect was obtained within the membrane element. It was recognized that

Comparative Example 1
The test was conducted in the same manner as in Example 1 except that the outlet side pipe 18 was removed from the downstream side of the pressure gauge 19 and the outlet 2b was opened during the gas-liquid cleaning. Respectively inlet pressure _{P 1} during the gas-liquid cleaning outlet pressure _{P 2 is,} P _{1 =} 0.05 MPa, a P 2 = 0.01 _MPa, because it is P ₁ -P 2 = 0.04 MPa, _{P 2} / (P ₁ −P ₂ ) = 0.25 .

After the continuous water flow, the membrane element was taken out and the inlet end surface portion of the membrane element was confirmed. As a result, partial clogging of the end surface due to turbidity could be confirmed at the portion opposite to the feed water inlet position. Further, when the membrane element was disassembled and the membrane surface was observed, in the portion corresponding to the opposite side with respect to the water supply inlet position as in the end face, as shown in FIG. 7, about 1/3 length from the inlet end face toward the outlet end face. washed insufficient space D ₁ adhesion amount is large in the turbid was present. From this result, it was confirmed that a drift occurred during gas-liquid cleaning in the membrane element, and a uniform cleaning effect could not be obtained.

It is typical sectional drawing of the axial center line direction of the membrane module used for embodiment. (A) is a front view of the membrane module, and (b) is a rear view of the same. It is a water distribution system figure to a membrane module. It is explanatory drawing of the flow of the cleaning fluid in a membrane module. It is explanatory drawing of the flow of the cleaning fluid in a membrane module. It is sectional drawing which shows another structural example of a membrane module. It is a typical perspective view which shows the dirt condition of the membrane element in a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,1A Membrane module 2,2A Housing 3 Membrane element 4 Water collecting pipe 5 Separation membrane 11 Raw water pump 15 Compressor

Claims (3)

Reverse osmosis membrane element of the reverse osmosis membrane was wound (3) is housed in a cylindrical housing (2) in the outer periphery of the water collecting pipe (4), on one end side of the reverse osmosis membrane elements (3) water inlet space ( 8) is provided, the concentrate outflow space (9) is provided on the other end, the raw water flows into the raw water in the space (8) is supplied, the membrane module (1, will permeate is removed from the water collecting pipe (4) )
Raw water and gas are simultaneously supplied to the raw water inflow space (8) from a cleaning fluid inlet (2a) provided in the housing (2) , and a cleaning fluid comprising a gas-liquid mixed phase flow is supplied to the membrane element (3). is circulated to the concentrated water outlet space (9) from the primary side, in the cleaning method of the membrane module discharging the detergent purification fluid cleaning fluid outlet from (2b) provided on the housing (2),
The cleaning fluid inlet portion during the cleaning of the primary side pressure of the cleaning fluid (2a) and P _1, the cleaning fluid outlet pressure of the cleaning fluid (2b) is taken as P _2, P ₂ / ( A cleaning method for a membrane module, characterized in that a cleaning fluid is circulated so that P ₁ -P ₂ ) is 1.2 to 10. Oite to claim 1, a method of cleaning membrane modules, characterized in that the the _{P 1} 0.05 _~1 MP a. In Claim 1 or 2 , the flow rate of the liquid phase of the gas-liquid mixed phase flow is at least twice the flow rate of the raw water during the raw water treatment operation, the flow rate of the gas phase is at least twice the flow rate of the raw water during the raw water treatment operation, A method for cleaning a membrane module, wherein the gas-liquid ratio is 2: 1 to 1: 2 .

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