EP1971846A1

EP1971846A1 - Method and device for testing the integrity of filtration membranes

Info

Publication number: EP1971846A1
Application number: EP06841924A
Authority: EP
Inventors: Marc Petry
Original assignee: Degremont SA
Current assignee: Suez International SAS
Priority date: 2005-12-20
Filing date: 2006-12-13
Publication date: 2008-09-24
Also published as: WO2007080260A1; FR2894843B1; CN101341389A; FR2894843A1

Abstract

The integrity test method applied to hollow-fibre filtration membranes are of the type with an internal skin, the concentrate compartment (J) being formed by the lower part of the hollow fibres and the permeate compartment (K) being formed by the part on the outside of the hollow fibres; a pressurized gas is made to flow through the concentrate compartment (J) for draining the hollow fibres, which are open at their ends; the method starts by leaving the permeate compartment (K) to the atmosphere, so as to allow the liquid on the surface of the membrane to migrate through the membrane; the permeate compartment (K) is then isolated; the pressure rise in the permeate compartment (K), caused by the circulation of gas in the concentrate compartment (J) and the flow of gas towards the permeate compartment, is measured; and, after a defined time, the pressure rise is compared with that observed when an integral membrane is used.

Description

METHOD AND DEVICE FOR INTEGRITY TESTING OF FILTRATION MEMBRANES

The invention relates to a method for testing the integrity of filtration membranes, namely ultrafiltration, microfiltration, nanofiltration or hyperfiltration membranes, of tubular geometry, implemented in a module composed of a casing grouping a set of hollow fibers.

Real physical barriers for the elimination of coliform bacteria, Giardia and Cryptosporidium cysts, ultrafiltration and microfiltration membranes have emerged in the field of water treatment both for the production of drinking water and for the treatment of wastewater as a viable alternative to conventional disinfection processes.

A lack of integrity of the membrane can nevertheless lead to pollution of the filtered water circuit which then becomes re-contaminated. The need to control the integrity of the physical barrier constituted by the membrane has therefore naturally imposed itself.

Known integrity test methods exploit the principle of bubbling pressure. Below a given air pressure, the membrane is very little permeable to air, the flow of air passing being very weak, governed solely by the diffusion of air within the liquid contained in the membrane. . Beyond an air pressure necessary and sufficient to evacuate the water from the pores and allow the passage of air, the membrane becomes permeable to air. This pressure is defined as the bubbling pressure. The measurement of this bubble pressure, or bubbling point, of the membrane is a laboratory method commonly employed by those skilled in the art to determine any integrity defect of a porous membrane. These measures involve regularly subjecting the membrane to an air pressure greater than its bubbling pressure, which can be damaging over time and, potentially, beyond the maximum acceptable pressure for a so-called "low pressure" membrane.

Another method, known as the "pressure decay test", provides an answer by isolating a face of the previously pressurized membrane at a gas pressure lower than its bubbling pressure. The procedure then consists in measuring the evolution of the pressure on the side of the pressurized side for a determined duration, generally from 5 to 15 minutes. The diffusion of gas within the liquid generates a slight decrease in pressure, which is defined as a loss of pressure maximum acceptable for a specified period of time. A decrease in pressure above this reference value means a gas leak interpreted as a lack of integrity.

WO 2005/077499 applies "pressure decay test" to hollow fiber type filtration membranes subjected to backwashing under gas pressure. The test is conducted after a backwash which is usually the phase where damage can be caused to the membranes. During the test, the inner portion of the hollow fibers is pressurized with gas and isolated, and the pressure decrease in the inner portion of the hollow fibers is measured and analyzed. The sensitivity of the test remains very dependent on the duration of the test and, when this duration is of the order of one minute as announced in this document, the sensitivity needs to be improved. In addition, in an industrial environment, this static test requiring the isolation of the inner parts of the membranes is very sensitive to valve leakage, which disrupts the results.

The object of the invention is, above all, to provide a filtration membrane integrity test method which, using a gas pressure, takes place in a reduced time of the order of a few minutes or less, while giving reliable results, insensitive to valve leaks. The sequencing of the process is as follows:

- emptying the concentrate by using a flow of air,

permeate compartment put in the atmosphere so that the surface liquid migrates through the membrane,

- integrity test by permeate compartment isolation or permeate quality analysis.

According to a first aspect of the invention, an integrity test method applied to hollow fiber type filtration membranes, mounted inside a liquid filtration assembly, with compartment delineation. concentrate where the retained materials accumulate, both in suspension and on the membranes, and a permeate compartment collecting the filtered liquid, comprises a step of pressurizing with a gas, in particular air, the inner part of the hollow fibers of the membranes under a pressure lower than the bubbling pressure of the membrane and greater than the pressure of the part outside the fibers, and is characterized in that - the test is carried out on membranes of the internal skin type, the compartment being concentrated constituted by the inner part of the hollow fibers, the permeate compartment consisting of the part outside the hollow fibers, the pressurized gas is circulated in the concentrated compartment for the emptying of the hollow fibers which are open at their ends,

the permeate compartment is left in the atmosphere to allow the liquid on the membrane surface to migrate through the membrane;

then the permeate compartment is isolated,

the pressure increase in the permeate compartment caused by the circulation of gas in the concentrated compartment and the passage of gas towards the permeate compartment are measured; and after a definite time, the pressure increase is compared to that observed when using an intact membrane.

According to another aspect of the invention, an integrity test method applied to hollow fiber type filtration membranes, mounted inside a liquid filtration assembly, with compartment delineation. concentrate where the retained materials accumulate, both in suspension and on the membranes, and a permeate compartment collecting the filtered liquid, comprises a step of pressurizing with a gas, in particular air, the inner part of the hollow fibers of the membranes under a pressure lower than the bubbling pressure of the membrane and greater than the pressure of the part outside the fibers, and is characterized in that:

the test is carried out on membranes of the internal skin type, the concentrate compartment being constituted by the inner part of the hollow fibers, the permeate compartment being constituted by the outer part of the hollow fibers, the gas under pressure being circulated in the concentrated compartment for the emptying of hollow fibers which are open at their ends,

the permeate compartment is left in the atmosphere, in particular with a purge of gas at a high point of this compartment, to allow the liquid on the membrane surface to migrate through the membrane;

and, after a defined time, the liquid quality of the permeate compartment, in particular that present at the purge of gas at the high point of the permeate compartment, is compared with that observed during the use of an integral membrane. The presence of a diphasic gas / water mixture demonstrates a non-integral membrane.

The test of the invention is dynamic since the gas flows continuously through the compartment concentrate during the test. According to the first aspect of the invention, the measurement of the pressure increase in the permeate compartment is insensitive to possible leakage of an isolation valve due to a continuous supply of circulating pressurized gas. According to the second aspect of the invention, the quality of the liquid present in the permeate compartment, in particular the purge of gas, is almost independent of an undesirable liquid flow.

The present invention makes it possible to associate the measurement of integrity with a two-phase air-plus-water wash by reducing the test duration to less than a few minutes; it also makes it possible to apply tests during the filtration and then allows the localization of the faulty modules.

The concentrate compartment can be filled with backwashing or filtration.

The integrity test can take place during each backwash, or cyclically after a number of backwashes, or cyclically during filtration.

The detection of the water quality, according to the second aspect of the method of the invention, can be carried out by a conductimetric measurement, or by a passage detection measurement, or by a visual measurement (video image analyzer). ). The invention also relates to an integrity test device applied to hollow fiber type filtration membranes, mounted inside a liquid filtration assembly, with delimitation of a concentrated compartment where accumulate the retained materials, both in suspension and on the membranes, and a permeate compartment collecting the filtered liquid, comprising means for pressurizing by a gas, in particular air, the inner part of the hollow fibers of the membranes under a lower pressure at the bubbling pressure of the membrane and greater than the pressure of the part outside the fibers, this device being characterized in that it comprises a booster, in particular a blower, means for connecting the outlet of the fan to the compartment concentrate formed by the internal parts of hollow-skin type membranes with internal skin, means for isolating the permeate compartment, draining means compartment concentrat to allow a flow of gas delivered by the booster, and means for measuring a permeate compartment parameter sensitive to a gas inlet into the permeate due to at least one unintegrated membrane. The measuring means may comprise a pressure gauge, sensitive to the pressure of the permeate compartment, and / or a bubble detector at the top of the permeate, and / or a conductivity meter for measuring the conductivity of the permeate, and / or a pass detector, and / or a video image analyzer.

The booster is advantageously constituted by a fan with a high air flow at a pressure of the order of 0.5 bar. The flow rate of the blower is in particular provided to ensure at the top of the module (reduced to the free section of the hollow fibers) an air flow rate of the order of 0.4 to 1.5 m / s.

The invention consists, apart from the arrangements set out above, in a certain number of other arrangements which will be more explicitly discussed below with regard to embodiments described with reference to the accompanying drawings, but which are not in no way limiting. On these drawings:

Fig. 1 is a diagram of a filtration installation implementing a method according to the invention.

Fig. 2 is a schematic of a hollow fiber type membrane module with internal skin.

Fig. 3 is a large scale schematic axial vertical section of an integrated filtration membrane subjected to the test according to the first aspect of the method.

Fig. 4 is a schematic axial section on a large scale of a damaged, unhealthy filtration membrane subjected to the test according to the first aspect of the process.

Fig. 5 is a diagram illustrating the evolution of the pressure in the permeate, expressed in bars and range on the ordinate, as a function of time in seconds, carried on the abscissa, in the case of an intact membrane and a damaged membrane, according to the first aspect of the process.

Fig. 6 is a schematic diagram of implementing the second aspect of the method with measurement of the liquid quality of the permeate compartment of a module.

Fig. 7 is a schematic large-scale axial section of a damaged filtration membrane, with air bleed at the high point of the permeate compartment, for a test according to the second aspect of the process, and

FIG. 8 is a diagram illustrating the evolution of the conductivity in the permeate, plotted on the ordinate, as a function of time in seconds, carried on the abscissa, in the case of an intact membrane and a damaged membrane.

Referring to Fig. 1 can be seen a filtration installation of the type described in the application FR 2 867 394 (04 02492) in the name of the same applicant company, implementing the method of the invention. A module composed of a casing C, shown schematically, groups together a set M (FIG. 2) of hollow fiber filtration membranes F with internal skin. Each module M comprises several thousand hollow fibers F, arranged in parallel between two ramps G, H distribution or collection in the direction of flow.

The casing C has two orifices E1, E2, respectively low and high, which can serve as outputs and / or inputs. The orifices E1, E2 are connected to the concentrate compartment J formed by the interior space of the hollow fibers. Inside the housing, the space around the membranes, and between them, forms the permeate compartment K which has an output A.

The installation comprises a feed pump 1 of the liquid to be filtered, the discharge of which is connected, via a supply valve 2, to the orifice E1. A drain connection between the valve 2 and the orifice E1 is provided with a drain valve 3. The pipe located downstream of the valve 3 opens into a device B discharge discharges.

A head-up backwash rejection valve 4 is connected to the orifice E2 of the casing C. A duct downstream of the valve 4 opens into the evacuation device B.

A valve 5 is mounted on a pipe connecting a booster 6 of gas, in particular air, to the orifice E2. The booster 6 is advantageously constituted by a fan S giving a high air flow, under a pressure of the order of 0.5 bar. The flow rate of the blower is provided to ensure at the top of the module (reduced to the free section of the hollow fibers) an air flow rate of the order of 0.4 to 1.5 m / s. A leak created by one or more non-intact membranes causes virtually no pressure drop of the air flowing in the hollow fibers.

A backwashing valve 7 is disposed on a pipe connecting the outlet of a backwashing pump 8 to the orifice A. The suction of the pump 8 is connected to a reservoir 9 of filtered liquid. Another pump 10 has its suction connected to a tank 11 containing an adjuvant, for example a disinfectant, oxidizing solution (for example, hypochlorite, di-oxide, etc.), or an acidic or even basic chemical compound. The discharge of the pump 10 is connected to a portion of pipe located between the valve 7 and the inlet A, with the interposition of a valve 10a. A manometer 12 is disposed on a pipe connected to the orifice A. The manometer 12 thus measures the pressure in the permeate compartment K. A detector 13 of the permeate quality is disposed on a gas purge pipe 14 connected to the part high compartment permeate. In the example of FIG. 1, the outlet A is located in the upper part of the permeate, and the pipe 14 is connected to the outlet A. A valve 15 is disposed on the pipe 14 upstream of the detector 13. This detector can be for example, a bubble detector 16 (FIG. 6) or a conductivity meter measuring the conductivity of the permeate.

A pipe 17 provided with a valve 18 connects the outputs of the valves 2 and 4.

In filtration mode, pump 1 is in action and valves 2 and 7 are open while all other valves are closed. The liquid to be treated enters the orifice E1 and the filtered liquid (permeate) leaves through the orifice A to be directed towards the reservoir 9.

For a backwash cleaning operation of hollow fibers, valves 2 and 4 are closed, while valve 3 is open for emptying. The valve 5 of the booster 6 is open and the booster is turned on to send air under pressure in the inner part of the hollow fibers and accelerate the emptying. The air circulates continuously and escapes through the open ends of the fibers and the valve 3 open. The valve 7 is open and the pump 8 is turned on to send, through the inlet A, the backwashing liquid. Thanks to two-phase backwashes (air and water), as described in patent FR 0402492, it is possible to implement an integrity test according to the invention when using backwashing phases with gas alone.

The first aspect of the process is explained with reference to FIGS. 1, 2,4 and 5.

The permeate side K previously purged is filled with water, and the concentrated side J of the membrane is pressurized by a gas below the bubbling pressure. The permeate side K first left to the atmosphere to allow the membrane surface liquid to migrate through the membrane. The permeate side K is then closed, ie isolated, by closing the various valves 7, 15, 10a connected to the outlet A (Fig.1). In Fig.3 the compartment K is shown closed schematically.

The concentrate side J of the membrane is pressurized by a gas below the bubbling pressure. According to Fig.1, the valve 4 is closed while the valve 5 is open and the fan 6 is turned on. The gas, the air in the example considered, while circulating continuously in the concentrate compartment J will migrate in part by diffusion through the membrane F and cause a slow increase in the pressure of the permeate compartment K. In the context of a non-integrity, illustrated in FIG. 4 by a damaged fiber Fd having a tear L, the increase in pressure will be faster.

After a while, the pressure value is read and compared to the value expected when the equipment was intact.

FIG. 5 illustrates the evolution of the pressure of the permeate compartment plotted on the ordinate, and expressed in bars, as a function of the time plotted on the abscissa and expressed in seconds in the case of an integral module (curve 19) and in the case of a module with a broken fiber (curve 20). It appears that the difference can be detected very quickly, in a few seconds.

The implementation, according to this first aspect, is therefore the following:

- Air purge of the permeate portion K filtration or backwashing;

- stopping filtration or backwashing;

pressurization in dynamics of the concentrate J portion of the membranes obtained by circulating a gas under pressure lower than the bubbling pressure.

The pressure will be stabilized at a value lower than the bubbling pressure of the membrane and greater than the pressure of the permeate portion. This pressurization will drain the concentrate almost instantly. According to the second aspect of the process of the invention (Fig.6, 7 and 8), the permeate compartment K remains open to the atmosphere, for example by a gas purge 21 (Figs 6 and 7) in the upper part of the permeate, equipped with a bubble detector 16.

An air purge of the permeate portion K is carried out by filtration or backwashing, then stopping filtration or backwashing, while leaving the permeate compartment in the atmosphere.

Pressurization is provided in dynamics of the concentrate J portion of the membranes obtained by circulating a gas under pressure less than the bubbling pressure, in particular a pressure of about 0.1 bar. If a fiber Fd is not integral with a tear R as illustrated in FIG. 7, air passes into the permeate compartment K in the form of bubbles, detected for example by a bubble detector 16.

After a defined time, the quality of the liquid present at the air purge at the high point of the module is compared with that observed during the use of integral membrane.

The presence of a two-phase gas / water mixture is demonstrative of a non-integral membrane.

Alternatively, the quality of the liquid can be appreciated by a measurement of conductivity using a conductivity meter that would replace the bubble detector. Fig. 8 illustrates the conductivity variations plotted on the ordinate, as a function of time, in seconds, plotted on the abscissa in the case of an integral module (curve 22), a module with a broken fiber (curve 23) and a module with five broken fibers (curve 24).

It also appears that the difference between integrated and unhealthy module can be detected very quickly, in a few seconds.

The concentrate can be filled with backwash or filtration. The integrity control method according to the present invention has many advantages: the measurement of the integrity detection can be done online, associated with the backwashing or the filtration, at a frequency such that it can appear as continuous, with minimal production interruptions; the accuracy of the measurement is adjustable by modifying the thresholds and test times; the technology and the setting device. described by the present invention are particularly simple. The result is an economical device, both in investment costs and in operation, which can be multiplied to refine the identification of non-intact membranes.

The method of the invention can be applied simultaneously to the modules of the block and makes it easy to locate the module (s) defective among the 10 to 50 modules present on a filtration unit.

Surprisingly for those skilled in the art, a brief integrity test can thus be performed dynamically during the short backwashing sequence or during filtration. The duration of the integrity test procedure is significantly shortened compared to the usual tests.

Integrity tests can then be initiated very frequently, during backwashing or even during filtration with minimal water loss and non-production times. They can be managed at the request of an operator or an operator.

An integrity test according to the invention is rapid thanks to the use of a circulation of gas under pressure, preferably coming from an external booster, to accelerate the emptying phase, to accelerate the equilibrium phase of the compressed air allowing the test. The gain in duration also results from the integration of the test with backwashing. The phases of production stoppage, filling and return to production would have been performed anyway during a two-phase backwashing (air + water). An industrial example concerns a water production unit of 24 modules each containing 35,000 fibers of internal diameter of 0.93 mm. The total section at the top of the module is 0.59 m ² (24 x 35000 x internal section of a fiber). The blower then provides an air flow of 1050 Nm ³ / h (for an air speed of 0.5 m / s) or 3150 Nm ³ / h (for an air velocity of 1, 5 m / s).

Claims

1. Integrity test method applied to hollow fiber type filtration membranes, mounted inside a liquid filtration assembly, with delimitation of a concentrated compartment where the retained materials accumulate , both in suspension and on the membranes, and a permeate compartment collecting the filtered liquid, comprising a step of pressurizing with a gas, in particular air, the inner part of the hollow fibers of the membranes under a pressure lower than the pressure bubbling of the membrane and greater than the pressure of the part outside the fibers, characterized in that:

the test is carried out on membranes (F, Fd) of the internal skin type, the concentrate compartment (J) being constituted by the inner part of the hollow fibers, the permeate compartment (K) being constituted by the outer part of the hollow fibers; ,

the pressurized gas is circulated in the concentrate compartment (J) for the emptying of the hollow fibers which are open at their ends,

the permeate compartment (K) is left in the atmosphere to allow the liquid on the membrane surface to migrate through the membrane;

then the permeate compartment (K) is isolated,

the pressure increase in the permeate compartment (K) caused by the circulation of gas in the concentrate compartment (J) and the passage of gas towards the permeate compartment (K) are measured;

and after a definite time, the pressure increase is compared to that observed when using an intact membrane.

2. Integrity test method applied to hollow fiber type filtration membranes, mounted inside a liquid filtration assembly, with delimitation of a concentrated compartment where the retained materials accumulate , both in suspension and on the membranes, and a permeate compartment collecting the filtered liquid, comprising a step of pressurizing with a gas, in particular air, the inner part of the hollow fibers of the membranes under a pressure lower than the pressure bubbling of the membrane and greater than the pressure of the part outside the fibers, characterized in that: the test is carried out on membranes (F ₁ Fd) of the internal skin type, the concentrate compartment (J) consisting of the inner part of the hollow fibers, the permeate compartment (K) being constituted by the outer part of the hollow fibers; the pressurized gas is circulated in the concentrate compartment for the emptying of the hollow fibers (F ₁ Fd) which are open at their ends,

the permeate compartment (K) is left in the atmosphere, to allow the liquid on the membrane surface to migrate through the membrane;

and, after a defined time, the liquid quality of the permeate compartment is compared with that observed when using an intact membrane.

3. Integrity test method according to claim 2, characterized in that a gas purge (21) is provided at a high point of the permeate compartment and that the quality of the liquid at the purge level is evaluated. gas (21).

4. Integrity test method according to one of claims 1 to 3, characterized in that fills the concentrate compartment (J) in backwash or filtration.

5. Integrity test method according to one of the preceding claims, characterized in that the integrity test takes place during each backwashing.

6. Integrity test method according to one of claims 1 to 4, characterized in that the integrity test takes place cyclically after a number of backwashing.

Integrity test method according to one of claims 1 to 4, characterized in that the integrity test takes place cyclically during filtration.

8. Integrity test method according to claim 2, characterized in that the detection is performed by a conductimetric measurement.

Integrity test method according to claim 2, characterized in that the detection is carried out by a passage detection measurement.

10. An integrity test method according to claim 2, characterized in that the detection is performed by a visual measurement (video image analyzer).

11. Integrity test device applied to hollow fiber type filtration membranes, mounted inside a liquid filtration assembly, with delimitation of a concentrate compartment where the retained materials accumulate , both in suspension and on the membranes, and a permeate compartment collecting the filtered liquid, comprising means for pressurizing by a gas, in particular air, the inner part of the hollow fibers of the membranes under a pressure lower than the pressure of bubbling of the membrane and greater than the pressure of the part outside the fibers, characterized in that it comprises a booster (6), in particular a blower (S), means for connecting the outlet of the blower to the concentrate compartment (J) formed by the inner parts of membranes (F ₁ Fd) of the hollow fiber type with internal skin, means (7, 10a, 15) for isolating the permeate compartment, means for emptying (3, B) of the compartment t concentrates to allow a flow of gas delivered by the booster, and measuring means (12; 13) of a permeate compartment parameter (K) sensitive to a gas inlet into the permeate due to at least one unintegrated membrane .

12. Device according to claim 11, characterized in that the measuring means comprise a manometer (12), sensitive to the pressure of the permeate compartment (K), and / or a bubble detector (16) at the head of the permeate, and or a conductivity meter for measuring the conductivity of the permeate.