GB2557610A - Membrane cleaning method and apparatus - Google Patents

Membrane cleaning method and apparatus Download PDF

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Publication number
GB2557610A
GB2557610A GB1621056.9A GB201621056A GB2557610A GB 2557610 A GB2557610 A GB 2557610A GB 201621056 A GB201621056 A GB 201621056A GB 2557610 A GB2557610 A GB 2557610A
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Prior art keywords
permeate
membrane
valve
port
water
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GB201621056D0 (en
Inventor
Liberman Boris
Levitin Vitaly
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IDE Technologies Ltd
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IDE Technologies Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D65/00—Accessories or auxiliary operations, in general, for separation processes or apparatus using semi-permeable membranes
    • B01D65/02—Membrane cleaning or sterilisation ; Membrane regeneration
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
    • B01D61/025—Reverse osmosis; Hyperfiltration
    • B01D61/026—Reverse osmosis; Hyperfiltration comprising multiple reverse osmosis steps
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
    • C02F1/441—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by reverse osmosis
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2313/00—Details relating to membrane modules or apparatus
    • B01D2313/18—Specific valves
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2313/00—Details relating to membrane modules or apparatus
    • B01D2313/20—Specific housing
    • B01D2313/201—Closed housing, vessels or containers
    • B01D2313/2011—Pressure vessels
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2321/00—Details relating to membrane cleaning, regeneration, sterilization or to the prevention of fouling
    • B01D2321/04—Backflushing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2321/00—Details relating to membrane cleaning, regeneration, sterilization or to the prevention of fouling
    • B01D2321/40—Automatic control of cleaning processes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A20/00—Water conservation; Efficient water supply; Efficient water use
    • Y02A20/124—Water desalination
    • Y02A20/131—Reverse-osmosis

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Water Supply & Treatment (AREA)
  • Nanotechnology (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Hydrology & Water Resources (AREA)
  • Environmental & Geological Engineering (AREA)
  • Organic Chemistry (AREA)
  • Separation Using Semi-Permeable Membranes (AREA)

Abstract

A method and system for cleaning a semi-permeable membrane (3) in a pressure vessel (2) preferably of a desalination plant. The membrane having a feed side (FS) and an opposite permeate side (PS) and extending between a front end and a rear end of the vessel. The vessel has a front end feed port (12) and a rear-end brine port (14) in communication with the feed side of the membrane. At least one permeate port (16, 17) is in communication with the permeate side of the membrane. In a normal separation process through the membrane feed water passes from the feed side to the permeate side to provide residual brine water (BS) from the rear-end brine port and a permeate water from the permeate port. In a cleaning process a washing water is delivered from an external source to the permeate side under higher pressure than the permeate pressure during the normal separation process. The higher permeate pressure causing a change in a net driving differential pressure across the membrane to cause a change in the direction of flow across the membrane from the permeate side thereby separating foulant from the membrane and withdrawing water (solution) together with the foulant from the feed side of the membrane to the brine port. The change in direction of flow of the permeate water back through the membrane is at least partially effected internally of the pressure vessel preferably by at least one selectively operable internal valve (50, 60).

Description

(54) Title of the Invention: Membrane cleaning method and apparatus Abstract Title: Membrane cleaning method and apparatus (57) A method and system for cleaning a semi-permeable membrane (3) in a pressure vessel (2) preferably of a desalination plant. The membrane having a feed side (FS) and an opposite permeate side (PS) and extending between a front end and a rear end of the vessel. The vessel has a front end feed port (12) and a rear-end brine port (14) in communication with the feed side of the membrane. At least one permeate port (16, 17) is in communication with the permeate side of the membrane. In a normal separation process through the membrane feed water passes from the feed side to the permeate side to provide residual brine water (BS) from the rear-end brine port and a permeate water from the permeate port. In a cleaning process a washing water is delivered from an external source to the permeate side under higher pressure than the permeate pressure during the normal separation process. The higher permeate pressure causing a change in a net driving differential pressure across the membrane to cause a change in the direction of flow across the membrane from the permeate side thereby separating foulant from the membrane and withdrawing water (solution) together with the foulant from the feed side of the membrane to the brine port. The change in direction of flow of the permeate water back through the membrane is at least partially effected internally of the pressure vessel preferably by at least one selectively operable internal valve (50, 60).
Figure GB2557610A_D0001
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FIG.10
Figure GB2557610A_D0002
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Figure GB2557610A_D0003
FIG.2B
PRIOR ART
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Figure GB2557610A_D0004
Figure GB2557610A_D0005
FIG.4
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Figure GB2557610A_D0006
FIG.5
PRIOR ART
Figure GB2557610A_D0007
FIG.7
Figure GB2557610A_D0008
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FIG.6
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Figure GB2557610A_D0009
FIG. 8
Figure GB2557610A_D0010
FIG. 9
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Figure GB2557610A_D0011
7/9
80—~
Figure GB2557610A_D0012
FIG.13A
Figure GB2557610A_D0013
FIG.13B PL /S £Fsha/t:P|_- Fg £Fsha/t = Ρ|_- Fg
PL= CLEAN WATER PRESURE FORCE
Fs= SPRING FORCE
FIG.13C
8/9
Figure GB2557610A_D0014
FIG.15A FIG.15B FIG.15C
9/9
Figure GB2557610A_D0015
FIG.16A
Figure GB2557610A_D0016
62a
Figure GB2557610A_D0017
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FIG.16B £^shq/t;P^- P^ + P5
FIG.16C £Fsha/t = Fg
P|_l= WASHING PRESURE FORCE
Fs= SPRING FORCE
MEMBRANE CLEANING METHOD AND APPARATUS
This invention relates to an improved method and apparatus for cleaning fouled membranes, in particular reverse osmosis (RO) membranes in desalination and water treatment plants.
TECHNICAL FIELD.
The method of RO is an effective and energy-saving method of desalination which is widely employed for obtaining water for industrial use, for agriculture, potable water and ultrapure water. The method consists in applying mechanical (gauge) pressure over a saline solution (such as sea water), which is higher than the osmotic pressure of the same solution, in a volume delimited by a semi-permeable membrane (RO membrane). The solvent is squeezed through the membrane to its ‘permeate’ side while dissolved salts remain in solution at the ‘feed’ side of the membrane.
Herein, osmotic pressures of solutions are referenced to pure solvent, i.e. if a given saline water solution has an osmotic pressure PO, this means that pure water from the other side of an osmotic membrane will permeate towards this solution as if under gauge pressure PO.
The continued long-term use of a RO membrane for the separation of salts results in the accumulation of other components of the raw solution (termed ‘foulants’ herein), such as suspended particles, organic matter and colloids, on the feed surface of the membrane. Some dissolved salts may also precipitate on the surface, forming scale. A fouled membrane has reduced separability, increased pressure losses and therefore has to be cleaned.
There are various known methods for cleaning RO membranes. Many involve stopping the process and pumping cleaning chemical solutions to wash the fouled surface. This is costly, not very effective and environmentally unfriendly.
A more effective method of cleaning is by using direct osmosis wherein saline solution is fed to the fouled feed side of the RO while supplying solvent (water) to the permeate side of the membrane. The higher osmotic pressure at the feed side sucks water from the permeate side to the feed side of the RO membrane whereby the water penetrates into the interface between the membrane and the accumulated foulant and separates the foulant from the membrane surface. The saline solution may be provided to the feed side without pressure and the water is supplied to the permeate side without pressure resulting in cleaning water being sucked back to the feed side as a result of the net differential pressure between the two osmotic pressures. However, this may result in remote areas of the membrane not being cleaned.
l
A RO membrane is typically a tight multi-layered structure with very narrow passages where water flows very slowly. Some areas of the membrane are close to the channel supplying water while other areas are remote. The high net differential between sea water and water leads to a very fast back-suction of water from the permeate side to the feed side causing water to not reach remote areas of the membrane while the concentration at both side of the membrane in close areas soon becoming equalised, stopping the cleaning process.
US 2007/0246425 A1 describes an improved direct osmosis cleaning method and system that provides a pressurized source of dilute saline solution and a pressurized source of saline solution. A plurality of RO modules are provided and connected in parallel and the system includes a source of raw solution with a high pressure feed pump, a common highpressure raw solution feed line connecting front end ports of the modules to the source of raw solution, a common high pressure brine collection line connecting the rear end brine ports of the modules to a first brine discharge outlet and a common permeate collection line connecting the permeate ports of the modules to a product storage tank or next stage separator. A plurality of valves are provided adapted to open or close the ports and common lines so as to allow performance of the normal separation process and the cleaning method on each RO module in turn.
The cleaning method comprises feeding dilute saline solution to the permeate side of the RO membrane under gauge pressure (PD4) and osmotic pressure (PO4), feeding concentrated saline solution to the feed side of the RO membrane under gauge pressure (PC5) and osmotic pressure (PO5) and withdrawing the concentrated saline solution together with the separated foulant and the penetrated water from the feed side of the RO membrane.
This aforementioned method and system does enhance the cleaning of the membrane by allowing all parts of the membrane to be reached and enables cleaning to occur in particular modules of the desalination plant while other modules continue to operate. However, the implementation of the process requires high pressure pipes and valves which is costly and increases the footprint of the plant.
Other semi-permeable membrane processes also suffer from fouling and therefore require cleaning. Examples include nanofiltration (NF), pressure-retarded osmosis (PRO) and forward osmosis (FO) processes.
It is an object of the present invention is to provide an improved method for cleaning a fouled membrane, particularly but not exclusively a RO membrane, that aims to overcome, or at least alleviate, the abovementioned drawbacks.
It is a further object of the present invention to provide an improved system for cleaning fouled membranes, particularly not exclusively RO membranes, that aims to overcome, or at least alleviate, the abovementioned drawbacks.
SUMMARY OF THE INVENTION.
A first aspect of the present invention provides a cleaning system for cleaning semipermeable membranes, for example cleaning a RO membrane in a desalination plant, the system comprising a plurality of modules each module comprising a pressure vessel housing at least one semi-permeable membrane, said membrane having a feed side and an opposite permeate side and extending between a front end and a rear end of the vessel, the vessel having a front end feed port and a rear-end brine port in communication with the feed side of the membrane, at least one permeate port in communication with said permeate side of the membrane, wherein each module has a normal separation mode and a cleaning mode wherein in the normal separation mode feed water passes from the feed side to the permeate side to provide residual brine water from the rear-end brine port and permeate water from said permeate port and in the cleaning mode washing water is delivered from an external source to the permeate side under higher pressure than the permeate pressure during the normal separation process, the higher permeate pressure causing a change in the net driving differential pressure across each membrane in, and along the length of, the module to cause a change in the direction of flow of fluid across the or each membrane, thereby separating foulant from the membrane, and withdrawing the solution together with the foulant from the feed side of the membrane to the brine port, wherein each vessel is provided with at least one internal valve selectively operable to at least partially assist in changing the direction of flow of fluid across the membrane during switching between the separation and cleaning modes.
Preferably, all of the valves that are responsible for providing the change in direction of the flow of fluid across the or each membrane are provided within the vessel itself.
The cleaning system is particularly suitable for cleaning RO membranes.
In the context of this disclosure, the feed water comprises seawater, generally having a salinity of around 3.6%. The residual brine water is sea water that is concentrated in the normal separation process to a higher salinity. The permeate water is the product water in the normal separation process, having a lower salinity than the feed water. The washing water is provided from an external source and has a similar salinity to the permeate water.
In one embodiment, each permeate port is provided with the internal valve, each valve being independently operable and configured to allow permeate water to flow out of the port during the separation mode, at least one of the permeate ports allowing permeate washing water to flow in to the vessel through the port during the cleaning mode. The washing water may be provided to a front end, rear end or both ends of the vessel during the cleaning mode but permeate is prevented from leaving the permeate side of the membrane in this mode.
The invention provides internal valves within the pressure vessel itself for switching the direction of the flow of fluid across the membrane thereby removing the need for external valves and piping that must be able to withstand high pressures.
In an embodiment, the front end of the vessel houses an adapter with internal valves, the valves being configured to allow feed water to enter the feed side of the membrane in the separation mode and to allow washing water to enter the permeate side of the membrane in the cleaning mode. The rear end of the vessel may also be provided with an internal valve, the valve being configured to allow permeate water to exit the permeate port in the separation mode and to prevent permeate water from exiting the permeate port in the cleaning mode.
Preferably, the front end valve and rear end valve are connected by a command pipe extending through the pressure vessel whereby operation of one valve causes operation of the other valve. More preferably, the command pipe and valves are configured to effect closure of the rear end valve to prevent permeate water exiting the permeate port upon opening of the front end valve to the washing water.
The internal valves are preferably provided in an adapter at one or both ends of the pressure vessel. The front end valve may comprise an inlet adapter for the washing water inlet for controlling entry of permeate water into the permeate side of the membrane and a main body, a pipe connected to the main body, an elastic tube inwardly of the main body, a sealing stand and membrane adapter. The rear end valve may comprise an outlet adapter and a main body, spring, shaft and seal.
A second aspect of the present invention provides a method for cleaning a fouled semipermeable membrane in a module, such as cleaning a RO membrane used for RO separation, said module comprising a pressure vessel housing at least one semi-permeable membrane, said membrane having a feed side and an opposite permeate side and extending between a front end and a rear end of the vessel, the vessel having a front end feed port and a rear-end brine port in communication with the feed side of the membrane and at least one permeate port in communication with the said permeate side of the membrane, the method of cleaning comprising changing from a normal separation process through the membrane wherein feed water passes from the feed side to the permeate side to provide residual brine water from the rear-end brine port and a permeate water from said permeate port to a cleaning process wherein washing water is delivered from an external source to the permeate side under higher pressure than the permeate pressure during the normal separation process, the higher permeate pressure causing a change in the net driving differential pressure across each membrane in, and along the length of, the module to cause a change in direction of flow of fluid across the or each membrane from the permeate side to the feed side of the membrane thereby separating foulant from the membrane and withdrawing the solution together with the foulant from the feed side of the membrane to the brine port, characterized in that the change in direction of flow of the permeate water back through the membrane is at least partially effected internally of the pressure vessel.
The method may further comprise operating a front end valve provided in the front end of the pressure vessel wherein in the normal separation mode the valve is shut but in the cleaning mode the valve is opened to allow entry of washing water from an external source into the permeate side of the membrane.
In an embodiment, the method further comprises operating a rear end valve provided in the rear end of the pressure vessel wherein in the normal separation mode the valve allows permeate to exit the permeate port and in the cleaning mode the valve prevents exit of the permeate water through the permeate port. The rear end valve may also allow entry of washing water from an external source into the permeate side of the membrane during the cleaning mode.
Preferably, opening of the front end valve to washing water causes closing of the rear end valve to the exit of permeate water.
BRIEF DESCRIPTION OF THE DRAWINGS.
Embodiments of the invention shall now be described, by way of example only, with reference to the accompanying drawings in which:
Figure 1 is a schematic diagram of a prior art reverse osmosis train equipped with a direct osmosis cleaning system;
Figure 2A illustrates the normal desalination process through cross-section A-A of Figure 1 at the beginning of a pressure vessel;
Figure 2B illustrates the normal desalination process through cross-section B-B of Figure 1 towards the end of a pressure vessel;
Figure 3 is a schematic diagram of an internal valve for a permeate port of a pressure vessel according to an embodiment of the invention, shown in the RO separation mode;
Figure 4 shows the internal valve of Figure 3 in the cleaning mode;
Figure 5 is a cross-sectional view of a main adapter for an end of a pressure vessel according to the prior art;
Figure 6 illustrates separately a front end internal valve adapter and a rear end internal valve adapter, together with their positioning when installed in a pressure vessel, according to an embodiment of the present invention;
Figure 7 is a cross-sectional view of the front end internal valve adapter shown in Figure 6;
Figure 8 is a cross-sectional view of the rear end internal valve adapter shown in Figure 7;
Figure 9 is a schematic cross-sectional view of the components of Figure 6 illustrating the arrangement of a command tube in relation to the internal valves;
Figure 10 illustrates operation of the apparatus shown in Figure 6 during the RO separation mode;
Figure 11 illustrates operation of the front end valve of Figure 6 during the RO separation mode;
Figures 12A to 12C are expanded views of components of the front end valve during the RO 20 separation mode;
Figure 13A illustrates operation of the rear end valve of Figure 6 during the RO separation mode;
Figure 13B is a cross-sectional view of a main body of the rear end valve of Figure 13A;
Figure 13C illustrates clean pressure force Pl and the spring force Fs during operation of the 25 rear end valve in the RO separation mode;
Figure 14 illustrates operation of the apparatus shown in Figure 6 during its cleaning mode;
Figure 15A illustrates operation of the front end valve of Figure 6 during the cleaning mode;
Figures 15B to 15C are expanded views of components of the front end valve during the cleaning mode;
Figure 16A illustrates operation of the rear end valve of Figure 6 during the cleaning mode;
Figure 16B is a cross-sectional view of a main body of the rear end valve of Figure 16A; and
Figure 16C illustrates washing pressure force PH and the spring force Fs during operation of the rear end valve in the cleaning mode;
DETAILED DESCRIPTION.
The present invention relates to an improved method and system for cleaning fouled membranes, in particular reverse osmosis (RO) membranes in desalination and water treatment plants. However, the method and system is also applicable to other osmostic driven processes across a semipermeable membrane, such as nanofiltration, pressure retarded osmosis and forward osmosis processes used in various industries, such as desalination, water treatment, food production and chemical processing. The crux of the invention is the ability to allow permeate water (“product water”) to flow out from the permeate side of the membrane during the normal separation process and, during the cleaning mode of the pressure vessel, close or lock the permeate outflow flow before it leaves a pressure vessel while allowing permeate water (“washing water”) from an external source to be delivered to the permeate side of the membrane. The internal positioning of the valve within the pressure vessel reduces the cost and complexity of the DOC process by avoiding the need for expensive high pressure pipes and valves outside of the pressure vessel.
Figure 1 of the accompanying drawings illustrates a conventional reverse osmosis train equipped with a direct osmosis cleaning system according to the prior art. The illustrated system is shown carrying out the normal desalination process. The system includes a high pressure pump 1, connected by pipes to a series of pressure vessels 2, 4, 6, 8, 10 each containing a reverse osmosis membrane 3. Waste brine recovered from the feed side of the vessels is fed to a pelton turbine 15 for energy recovery. Permeate ports from the permeate side of each membrane are connected to a series of pipes with valves Vi, V2 provided in permeate manifolds. Valves Vi are open during normal operation of the system and valves V2 are closed to enable the removal of product (permeate) from the permeate side of the membranes for delivery to the client. Additionally, a further pressure vessel 20 acts as a permeate injector of permeate water (“washing water”) from an external source and is only operational during the direct osmosis cleaning phase. The pressure vessel has a piston 22 but no membrane and is connected at one end to the high pressure feed by valves V2 and at the other end to the permeate manifolds by valves V3. This pressure vessel is full of permeate but is isolated from the rest of the system during the normal desalination process by valves V2 being shut.
During normal operation, sea water that has been pre-treated is fed via the high pressure pump 1 to the series of pressure vessels 2, 4, 6, 8, 10 containing the reverse osmosis membranes 3. This produces a permeate or product water stream PS and a waste concentrated brine stream BS. Figures 2A and 2B illustrate the flow of fluid through the membranes, demonstrating the respective gauge and osmostic pressures of the fluids that provide a net driving force through the membrane. The feed stream is at -65 bar gauge pressure and the osmostic pressure of the sea water is -33 bar. The permeate stream is -1 bar gauge pressure and the osmotic pressure of the permeate is -0.3 bar. This provides a net driving force for desalination of -31.3 bar. Foulants 30 are deposited on the feed side of the membrane during flow of fluid from the feed to the permeate side of the membrane.
Direct osmosis cleaning of the foulant deposited on the membrane is carried out by shutting off valves Vi and opening valves V2 and V3 so that feed is directed onto the piston 22 so that permeate water (“washing water”) is fed under pressure back through the permeate manifolds into the permeate side of each pressure vessel. This causes the flow of fluid through the membrane to reverse and the passage of fluid from the permeate side to the feed side serves to lift foulant 30 from the membrane 3 which is then removed from the vessels prior to reversal of the process back to the normal desalination process by the closing of valves V2 and opening of valves Vi. Due to the high pressures required for the process, the permeate ports for all vessels have to be kept at 65 bar requiring the pipework and valves Vb V2, V3and V4 to be made of stainless steel 316 to enable to withstand and maintain the required pressure. This pipework and valving greatly increases the cost and footprint of the system.
Figures 3 and 4 of the accompanying drawings illustrate schematically one embodiment of the present invention in which the valves for enabling reversal of the permeate flow are provided within each pressure vessel. Figure 3 illustrates a permeate port in the form of a main adapter 40 provided with valve 42. As shown by the arrows, in Figure 3 permeate is able to flow out of the pressure vessel 2 during normal operation of the reverse osmosis desalination system. In contrast, in Figure 4 the valve 42 is shut off to prevent flow from the vessel but opens to allow permeate to flow into the permeate side of the vessel. The ability to provide valves within the high pressure vessel removes the need to have valves outside of the vessel with associated pipework that must be able to withstand high pressures. While
Figures 6 to 16C of the accompanying drawings illustrate in further detail a permeate pressurization device for carrying out the process of the present invention that allows the flow of fluid across the membrane of each pressure vessel to be independently reversed to allow for cleaning of the membrane without the need for external high pressure pipework and valves. However, it is to be appreciated that other designs of valve within the vessel pressure may be utilised.
The permeate pressurization device is composed of two valves 50, 60 located at each end of a standard RO membrane pressure vessel 2, as shown in Figure 6. Figure 5 illustrates an end section of a standard membrane pressure vessel which is modified by placing a valve 50 or 60 in place of the adapter 70. The permeate pressurization device has a front valve 50 provided at the feed inlet end of the vessel and a rear valve 60 provided at the permeate outlet end of a pressure vessel. Front valve 50 serves to selectively open/close a permeate outlet and a washing water (permeate or other water source) inlet, as explained in further detail below. Rear valve 60 selectively opens and closes permeate outlet only.
Figure 7 is a front valve section illustrating the components of the front valve 50. The valve is provided in main adapter 40 and includes an inlet adapter 51 for the washing water inlet connected to a pipe 52 connected to the main body 53 of the valve. Inwardly of the body is an elastic tube 54, sealing stand 55 and membrane adapter 56. A smaller diameter metal command pipe 80 extends from the membrane adapter through the pressure vessel 2.
Figure 8 is a rear valve section illustrating the components of the rear valve 60. The rear valve is again provided in a main adapter 40 and the valve includes an adapter 61, main body 62, spring 63, shaft 64 and seal 65. The smaller command pipe 80 that extends from the front valve 50 serves to connect the two valves 50, 60 as shown in Figure 9, enabling the front valve 50 to command the rear valve 60.
Figures 10 to 13C illustrate operation of the valves 50, 60 during a normal RO desalination process. Feed water FS enters the inlet 12 to the pressure vessel 2 at high pressure and passes across the membrane 3 to provide a brine stream BS and a permeate stream PS. The brine stream BS exits through a brine water outlet 14 and the permeate stream PS exits at low pressure through front and rear outlets 16, 17 via the valves 50, 60, in a flow rate of around 20% through the front valve and 80% through the rear valve (as indicated by direction of arrows in Figure 10).
Figures 11 to 12C illustrate the operation of the front valve 50 in further detail during this normal operational procedure. The front permeate flow through the valve is indicated by the arrows with the front permeate flowing through the membrane adapter 56 into the elastic tube 54, squeezing the tube radially (see Figure 12C). The front permeate passes the sealing stand 55 and goes inside it through holes 55a (see Figure 12B). The permeate stream then flows throw holes 53a in the main body 53 (see Figure 12A) and around the pipe 52 to exit the permeate outlet 16. Port 58 connected to command pipe 80 is sealed to the front permeate.
In normal operation, the rear valve 60 stays in the open position (see Figures 13A to 13C). The rear permeate stream pressure force Pl is bigger than the force Fs of spring 63 to enable permeate to pass through holes 62a in the main body 62 and exit the adapter permeate outlet 17.
Figures 14 to 16C of the accompanying drawings illustrate operation of the valves 50, 60 during the direct osmotic cleaning (DOC) mode of the system. High pressure washing water for delivery to the permeate side of the membrane 3 is introduced through a washing water inlet of adapter 51 and flows through the front valve 50. This water passes through the membrane 3 to the feed-brine side, thereby cleaning the membrane. During this stage, rear valve 60 must be shut, as detailed below. Figures 15A to 15C illustrate operation of the front valve 50 in the DOC mode. The high pressure washing water comes into the adapter through the inlet 51 and flows into the pipe 52 and main body 53 (see arrows on Figure 15A). The water exits outside from the main body through holes 53a and then goes back inside through a network of holes 53b provided on the outer surface of the main body (see Fig. 15B). This then squeezes the elastic tube 54 and flows through the membrane adapter 56 to the membrane 3. The sealing surface of the tube prevents flow of water to the back side (see Fig. 15C). During this process, the high pressure washing water comes into contact with the command pipe 80 that extends through the shaft 64 to the spring 63 space. At this time, the shaft has the same pressure Ph in back and front sides but in opposite directions. The spring 63 applies force Fs on the left surface of the shaft and pushes it towards the seal 65, thereby shutting off the valve 60 preventing permeate stream from exiting through outlet 17, see Figures 16A to 16C.
The arrangement of the front and rear end valves within the pressure vessel itself removes the need for valves Vi and V2 of the prior art that are external to the vessel. This removes the need for valves and piping outside of the vessel that must be constructed of materials that can withstand high pressures and reduces the foot print of the apparatus.
io

Claims (15)

  1. CLAIMS.
    1. A cleaning system for cleaning semipermeable membranes, the system comprising a plurality of modules, each module comprising a pressure vessel housing at least one semi-permeable membrane, said membrane having a feed side and an opposite permeate side and extending between a front end and a rear end of the vessel, the vessel having a front end feed port and a rear-end brine port in communication with the feed side of the membrane, at least one permeate port in communication with said permeate side of the membrane, wherein each module has a normal separation mode and a cleaning mode wherein in the normal separation mode feed water passes from the feed side to the permeate side to provide residual brine water from the rear-end brine port and permeate water from said permeate port and in the cleaning mode a washing water stream is delivered from an external source to the permeate side under higher pressure than the permeate pressure during the normal separation process, the higher permeate pressure causing a change in the net driving differential pressure across the or each membrane in, and along the length of, the module to cause a change in the direction of flow of fluid across each membrane, thereby separating foulant from the membrane, and withdrawing the solution together with the foulant from the feed side of the membrane to the brine port, wherein each vessel is provided with at least one internal valve selectively operable to at least partially assist in changing the direction of flow of fluid across the membrane during switching between the separation and cleaning modes.
  2. 2. A cleaning system as claimed in claim 1 wherein each permeate port is provided with the internal valve, each valve being independently operable and configured to allow permeate water to flow out of the port during the separation mode and to allow washing water to flow in to the vessel through the port during the cleaning mode.
  3. 3. A cleaning system as claimed in claim 1 or claim 2 wherein the front end of the vessel houses an internal valve, the valve being configured to allow permeate water to leave the permeate side of the membrane in the normal separation mode and to allow washing water from an external source to enter the permeate side of the membrane in the cleaning mode.
  4. 4. A cleaning system as claimed in claim 1,2 or 3 wherein the rear end of the vessel is provided with an internal valve, the valve being configured to allow permeate water to exit the permeate port in the separation mode and to prevent permeate water from exiting the permeate port in the cleaning mode.
  5. 5. A cleaning system as claimed in claim 4 wherein the internal valve of the rear end of the vessel allows entry of washing water from an external source to the permeate
    5 side of the membrane in the cleaning mode.
  6. 6. A cleaning system as claimed in claim 5, when dependent from claim 4, wherein the front end valve and rear end valve are connected by a command pipe extending through the pressure vessel whereby operation of one valve causes operation of the other valve.
    10 7. A cleaning system as claimed in claim 6 wherein the command pipe and valves are configured to effect closure of the rear end valve to prevent permeate water exiting the permeate port upon opening of the front end valve to the washing water during the cleaning mode.
    8. A cleaning system as claimed in any one of claims 3 to 7 wherein the front end
    15 valve comprises an inlet adapter for the washing water inlet and a main body, a pipe connected to the main body, an elastic tube inwardly of the main body, a sealing stand and membrane adapter.
    9. A cleaning system as claimed in any one of claims 4 to 8 wherein the rear end valve comprises an outlet adapter and a main body, spring, shaft and seal.
    20 10. A cleaning system as claimed in any one of the preceding claims wherein the internal valves are provided in an adapter provided at one or both ends of the pressure vessel.
    11. A method for cleaning a fouled semi-permeable membrane in a module, said module comprising a pressure vessel housing at least one semi-permeable membrane, said
    25 membrane having a feed side and an opposite permeate side and extending between a front end and a rear end of the vessel, the vessel having a front end feed port and a rear-end brine port in communication with the feed side of the membrane and at least one permeate port in communication with the said permeate side of the membrane, the method of cleaning comprising changing from a normal separation
    30 process through the membrane wherein feed water passes from the feed side to the permeate side to provide residual brine water from the rear-end brine port and a permeate water from said permeate port, to a cleaning process wherein washing water is delivered from an external source to the permeate side under higher pressure than the permeate pressure during the normal separation process, the higher permeate pressure causing a change in the net driving differential pressure across each membrane in, and along the length of, the module to cause a change in direction of flow of fluid across the or each membrane from the permeate side to the feed side of the membrane thereby separating foulant from the membrane and
    5 withdrawing the solution together with the foulant from the feed side of the membrane to the brine port, characterized in that the change in direction of flow of the permeate water back through the membrane is at least partially effected internally of the pressure vessel.
    12. A method according to claim 11 further comprising operating a front end valve
    10 provided in the front end of the pressure vessel wherein in the normal separation mode the valve allows exit of permeate water from the permeate side of the membrane and in the cleaning mode the valve allows entry of washing water from an external source into the permeate side of the membrane.
    13. A method according to claim 11 or 12 further comprising operating a rear end valve
    15 provided in the rear end of the pressure vessel wherein in the normal separation mode the valve allows permeate water to exit the permeate port and in the cleaning mode the valve prevents exit of the permeate water through the permeate port.
    14. A method according to claim 13 further comprising operating the rear end valve to allow washing water from an external source to enter the permeate port during the
    20 cleaning mode.
    15. A method according to claim 13 or 14, when dependent from claim 12, wherein opening of the front end valve to washing water causes closing of the rear end valve to the exit of permeate.
    Amendments to the claims have been made as follows:
    CLAIMS.
    25 08 17
    1. A cleaning system for cleaning semipermeable membranes, the system comprising a plurality of modules, each module comprising a pressure vessel housing at least one semi-permeable membrane, said membrane having a feed side and an opposite permeate side and extending between a front end and a rear end of the vessel, the vessel having a front end feed port and a rear-end brine port in communication with the feed side of the membrane, at least one permeate port in communication with said permeate side of the membrane, wherein each module has a normal separation mode and a cleaning mode wherein in the normal separation mode feed water passes from the feed side to the permeate side to provide residual brine water from the rear-end brine port and permeate water from said permeate port and in the cleaning mode a washing water stream is delivered from an external source to the permeate side under higher pressure than the permeate pressure during the normal separation process, the higher permeate pressure causing a change in the net driving differential pressure across the or each membrane in, and along the length of, the module to cause a change in the direction of flow of fluid across each membrane, thereby separating foulantfrom the membrane, and withdrawing a solution together with the foulant from the feed side of the membrane to the brine port, wherein each vessel is provided with at least one internal valve selectively operable to at least partially assist in changing the direction of flow of fluid across the membrane during switching between the separation and cleaning modes.
    2. A cleaning system as claimed in claim 1 wherein each permeate port is provided with the internal valve, each valve being independently operable and configured to allow permeate water to flow out of the port during the separation mode and to allow washing water to flow in to the vessel through the port during the cleaning mode.
    3. A cleaning system as claimed in claim 1 or claim 2 wherein the front end of the vessel houses an internal valve, the valve being configured to allow permeate water to leave the permeate side of the membrane in the normal separation mode and to allow washing water from an external source to enter the permeate side of the membrane in the cleaning mode.
    4. A cleaning system as claimed in claim 1,2 or 3 wherein the rear end of the vessel is provided with an internal valve, the valve being configured to allow permeate water to exit the permeate port in the separation mode and to prevent permeate water from exiting the permeate port in the cleaning mode.
    25 08 17
    5. A cleaning system as claimed in claim 4 wherein the internal valve of the rear end of the vessel allows entry of washing water from an external source to the permeate side of the membrane in the cleaning mode.
    6. A cleaning system as claimed in claim 5, when dependent from claim 4, wherein the front end valve and rear end valve are connected by a command pipe extending through the pressure vessel whereby operation of one valve causes operation of the other valve.
  7. 7. A cleaning system as claimed in claim 6 wherein the command pipe and valves are configured to effect closure of the rear end valve to prevent permeate water exiting the permeate port upon opening of the front end valve to the washing water during the cleaning mode.
  8. 8. A cleaning system as claimed in any one of claims 3 to 7 wherein the front end valve comprises an inlet adapter for the washing water inlet and a main body, a pipe connected to the main body, an elastic tube inwardly of the main body, a sealing stand and membrane adapter.
  9. 9. A cleaning system as claimed in any one of claims 4 to 8 wherein the rear end valve comprises an outlet adapter and a main body, spring, shaft and seal.
  10. 10. A cleaning system as claimed in any one of the preceding claims wherein the at least one internal valve is provided in an adapter provided at one or both ends of the pressure vessel.
  11. 11. A method for cleaning a fouled semi-permeable membrane in a module, said module comprising a pressure vessel housing at least one semi-permeable membrane, said membrane having a feed side and an opposite permeate side and extending between a front end and a rear end of the vessel, the vessel having a front end feed port and a rear-end brine port in communication with the feed side ofthe membrane and at least one permeate port in communication with the said permeate side of the membrane, the method of cleaning comprising changing from a normal separation process through the membrane wherein feed water passes from the feed side to the permeate side to provide residual brine water from the rear-end brine port and a permeate water from said permeate port, to a cleaning process wherein washing water is delivered from an external source to the permeate side under higher pressure than the permeate pressure during the normal separation process, the higher permeate pressure causing a change in the net driving differential pressure across each membrane in, and along the length of, the module to cause a change in
    25 08 17 direction of flow of fluid across the or each membrane from the permeate side to the feed side of the membrane thereby separating foulant from the membrane and withdrawing the solution together with the foulant from the feed side of the membrane to the brine port, characterized in that the change in direction of flow of the permeate water back through the membrane is at least partially effected internally of the pressure vessel.
  12. 12. A method according to claim 11 further comprising operating a front end valve provided in the front end of the pressure vessel wherein in the normal separation mode the valve allows exit of permeate water from the permeate side of the membrane and in the cleaning mode the valve allows entry of washing water from an external source into the permeate side of the membrane.
  13. 13. A method according to claim 11 or 12 further comprising operating a rear end valve provided in the rear end of the pressure vessel wherein in the normal separation mode the valve allows permeate water to exit the permeate port and in the cleaning mode the valve prevents exit of the permeate water through the permeate port.
  14. 14. A method according to claim 13 further comprising operating the rear end valve to allow washing water from an external source to enter the permeate port during the cleaning mode.
  15. 15. A method according to claim 13 or 14, when dependent from claim 12, wherein opening of the front end valve to washing water causes closing of the rear end valve to the exit of permeate.
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    Application No: GB1621056.9
GB1621056.9A 2016-12-12 2016-12-12 Membrane cleaning method and apparatus Withdrawn GB2557610A (en)

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Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2015171687A1 (en) * 2014-05-08 2015-11-12 Georgia Tech Research Corporation Cyclic filtration system

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2015171687A1 (en) * 2014-05-08 2015-11-12 Georgia Tech Research Corporation Cyclic filtration system

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