JP2007263942A - Method and apparatus for detecting membrane defect, and filtering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for detecting membrane defect, and a filtering device, capable of accurately and efficiently detecting a defect caused in a separation membrane. <P>SOLUTION: The method for detecting membrane defect comprises continuously measuring a potential difference between a reference electrode and a detecting electrode set on the permeating liquid side of the membrane, and detecting a defect of the membrane by fluctuation of the potential difference. The apparatus for detecting membrane defect comprises a reference electrode 16; detecting electrodes 17a, 17b, 17c and 17d set at least on the permeating liquid side of the membrane; and a measuring means 18 for continuously measuring a potential difference between the reference electrode and each detecting electrode. The filtering device comprises a membrane; a filtering means provided with the membrane; a reference electrode provided at a liquid supply port of the filtering means; a detecting electrode provided except the liquid supply port of the filtering means; and a measuring means for continuously measuring a potential difference between the reference electrode and each detecting electrode. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a film defect detection method, a film defect detection apparatus, and a filtration apparatus.

  In the production of purified water, ultrapure water, pyrogen-free water, etc., ultrafiltration membrane (UF membrane) modules and microfiltration membrane (MF membrane) modules are used for the purpose of final particle removal, sterilization, and pyrogen removal. ing. In such a module, when a defect occurs in the membrane during use, the presence or absence of the defect is detected by measuring the quality of the produced water, for example, the number of fine particles, turbidity, and the number of bacteria. .

  In such a water purifier, a plurality of membrane modules are used, but a device for measuring fine particles and turbidity is collected not from each module but from a finally assembled water pipe and measured. Therefore, when the defect of the film | membrane in a module is few (for example, when one fiber in many hollow fiber modules is cut | disconnected), the detection of the defect was very difficult. In addition, it is conceivable to install a detection device for each module, but this is not practical in view of cost.

  Various methods have been proposed for detecting leaks and defects in a hollow fiber membrane module. For example, supplying pressurized air to the inside of the hollow fiber membrane to maintain a higher pressure than the outside of the hollow fiber membrane, and measuring the descending speed of the liquid level outside the hollow fiber membrane after a certain time at this time (See, for example, Patent Document 1) for detecting leaks, passing a gas in which fine particles of a predetermined size are dispersed at a constant concentration through a hollow fiber membrane module, and detecting inert particles that have passed through the hollow fiber membrane module A method for detecting defects (for example, refer to Patent Document 2), a method for injecting gas from the outside of the hollow fiber membrane, and a method for detecting leakage by the gas coming out to the hollow fiber membrane terminal inside the hollow fiber membrane (for example, Patent Reference 3).

However, these methods have a problem that the detection accuracy is not high because they are applied when detecting a defect of an unused hollow fiber membrane, or when the operation is temporarily stopped. In addition, when trying to measure the turbidity of permeated water during operation, the defect cannot be detected because the pinhole of the hollow fiber membrane or the defective part of the cutting thread is blocked with suspended substances in the liquid to be treated. Has the disadvantages. As described above, in the prior art, the defect of the hollow fiber membrane generated during the operation cannot be detected during the operation, or even if it is possible, the apparatus becomes complicated and the measurement is troublesome. . However, it is important for detecting the defect of the hollow fiber membrane and the presence or absence of cutting during the operation of the hollow fiber membrane module to stably supply the permeate. In particular, when used in liquid processing and drinking water applications for the electronics industry, it is indispensable to quickly detect contamination of fine particles and leakage of bacteria.
Japanese Patent Publication No. 8-2527462 JP-A-7-24273 JP-A-55-70258

  The present invention aims to solve the above problems. That is, an object of the present invention is to provide a membrane defect detection method, a membrane defect detection device, and a filtration device that can quickly and efficiently detect defects generated in a separation membrane even during operation.

  As a result of intensive studies to solve the above problems, the present inventors have conceived the following present invention and found that the problems can be solved.

  That is, the present invention is a film defect detection method for detecting a film defect, and continuously measures a potential difference between a reference electrode and a detection electrode installed on the permeate side of the membrane, and the potential difference is detected. The film defect detection method is characterized in that the defect of the film is detected based on the fluctuation of the film.

  The membrane defect detection method of the present invention detects a membrane defect from the fluctuation of the potential difference of the membrane potential generated when the liquid permeates the membrane (separation membrane). The membrane potential is generated as a potential on both sides of the membrane due to the interaction with the electric double layer on the surface of the membrane when a liquid such as water passes through the pores of the membrane. If defects (for example, pinholes or cracks) occur in the film, this potential changes. If this variation is detected while continuously measured by the reference electrode and the detection electrode, it can be detected instantaneously, with high accuracy and efficiently when a defect occurs even during operation.

  In the film defect detection method of the present invention, it is preferable to detect the presence of the film defect when the absolute value of the variation value of the potential difference is 1 mV or more. The membrane is preferably either an ultrafiltration membrane or a microfiltration membrane. Further, it is preferable to perform a correction process for correcting the pressure variation before measuring the potential difference variation. By such correction processing, the potential difference can be quickly measured continuously.

  Further, the present invention includes a reference electrode, a detection electrode installed at least on the permeate side of the membrane, and a measurement unit that continuously measures a potential difference between the reference electrode and the detection electrode. This is a characteristic film defect detection apparatus.

  Since the membrane defect detection apparatus of the present invention is optimal for carrying out the above-described film defect detection method of the present invention, it is possible to quickly and efficiently detect defects generated in the separation membrane even during operation. . In addition, in the conventional detection method using the particle counter, the detector is expensive. Therefore, it is not practical to install a large number of detectors in one apparatus because the cost increases. On the other hand, the film defect detection device of the present invention basically requires electrodes and measurement means, and is practical at low cost. Further, when there are a plurality of filtering means, it is only necessary to provide an electrode for each, and when a defect is detected, the filtering means may be replaced. In other words, when a defect is detected, it is not necessary to stop filtering by all the filtering means and specify the defective filtering means, so that the efficiency of the filtering process can be improved.

  In the film defect detection device of the present invention, it is preferable to detect the presence of the defect when the absolute value of the variation value of the potential difference is 1 mV or more. In a normal state in which there is no defect in the film, the potential difference hardly changes. On the other hand, when the absolute value of the fluctuation value of the potential difference is 1 mV or more, it is considered that a defect is generated. Therefore, it is possible to detect a film defect with high accuracy by determining that a defect is generated when the absolute value of the fluctuation value is 1 mV or more.

  In the membrane defect detection device of the present invention, the membrane is preferably either an ultrafiltration membrane or a microfiltration membrane. Since these films are used for removing fine particles and microorganisms and can basically be used continuously, it is preferable to determine the presence or absence of defects based on fluctuations in potential difference as in the present invention.

  Furthermore, the present invention provides a membrane, a filtration means provided with the membrane, a reference electrode provided at a liquid supply port of the filtration means, a detection electrode provided at other than the liquid supply port of the filtration means, And a measuring unit that continuously measures a potential difference between the reference electrode and the detection electrode.

  The filtration device of the present invention can perform filtration while carrying out the above-described film defect detection method of the present invention. Therefore, it is possible to quickly and efficiently detect defects generated in the separation membrane even during operation, and if a defect occurs in the membrane, it can be promptly and appropriately processed. . In addition, since the defect is detected while continuously measuring the potential difference, there is no need for sampling, and there is no need to stop the apparatus for each detection, so that the efficiency of the film processing can be maintained at a high level.

  In the filtration device of the present invention, as in the case of the membrane defect detection device of the present invention, the membrane is preferably one of an ultrafiltration membrane and a microfiltration membrane.

  According to the present invention, it is possible to provide a membrane defect detection method, a membrane defect detection device, and a filtration device that can quickly and efficiently detect defects generated in the separation membrane even during operation.

[Film defect detection method]
In the membrane defect detection method of the present invention, first, a reference electrode is installed at a supply port for supplying a liquid to the membrane, and a detection electrode is installed on the permeate side of the membrane. Then, the potential difference between these electrodes is continuously measured. When there is no defect in the film, the potential difference does not fluctuate greatly. On the other hand, when a defect occurs in the film, the potential difference changes instantaneously. By detecting this variation as a film defect, it is possible to detect defects (defects such as cracks and pinholes) quickly and efficiently with high accuracy even during operation.

  The potential of the detection electrode before the defect is generated is, for example, a flow potential generated when water permeates through the pores of the UF membrane (ultrafiltration membrane), and is represented by the following formula (1).

V / P = (ε ₀ ε _r ζ) / (ηκ) (1)
In the above formula (1), V is a flow potential (flow potential generated by water permeating through the hollow fiber membrane), P is a transmembrane pressure difference, ε ₀ and ε _r are vacuum and water permittivity, ζ Is the zeta potential, η is the viscosity of water, and κ is the electrical conductivity of water.

  Since the streaming potential changes depending on the pressure, water temperature, and electrical conductivity applied to the membrane, it is necessary to measure the pressure, flow rate, temperature, and electrical conductivity at the same time as measuring the potential, and correct the influence. However, even if corrections are made in consideration of these influences, if a change in potential is recognized, it can be determined that a defect has occurred in the film.

  In the film defect detection method of the present invention, it is preferable to detect the presence of a film defect when the absolute value of the variation value of the potential difference is 1 mV or more. Even in a normal state, the potential difference may slightly fluctuate due to some external influence. However, even if it fluctuates greatly, the absolute value of the fluctuation value does not exceed 1 mV. On the other hand, when a defect occurs in the membrane, the supply liquid side and the permeate side are directly connected, and the flow velocity fluctuates greatly. Therefore, the absolute value of the fluctuation value is 1 mV or more. Therefore, it can be said that it is practical and very efficient to detect a film defect based on this value.

  In the film defect detection method, the potential difference may not be stable at the initial stage of the film processing operation. In that case, it is preferable to wait until the absolute value of the fluctuation value of the potential difference becomes less than 1 mV, and then continuously perform the potential difference measurement for detecting the film defect. The term “continuous” as used herein means that the potential difference measurement is continuously performed during the membrane processing operation.

  In the membrane defect detection method of the present invention, the reference electrode is installed at the supply port for supplying the liquid to the membrane, and the detection electrode is installed on the permeate side of the membrane. It may be expanded.

  As the reference electrode, the detection electrode, and the means for measuring the potential difference, conventionally known ones can be used. Examples of the reference electrode include stainless steel and titanium rods and plates, and examples of the detection electrode include stainless steel and titanium rods and plates. As a means for measuring the potential difference, a voltmeter that measures the potentials of the reference electrode and the detection electrode can be used.

[Film defect detector]
The membrane defect detection device of the present invention comprises a reference electrode, a detection electrode installed at least on the permeate side of the membrane, and a measurement means for continuously measuring a potential difference between the reference electrode and the detection electrode. Have. The film defect detection apparatus of the present invention is an optimal apparatus for carrying out the film defect detection method of the present invention described above. The membrane defect detection device of the present invention can be used for membrane defect detection of various membrane separation devices.

  An example in which the membrane defect detection device of the present invention is applied to membrane defect detection of a hollow fiber membrane module as a filtering means will be described with reference to FIG.

  The hollow fiber membrane module 10 includes a number of hollow fiber membranes 12 inside a housing case 11. The ends of the hollow fiber membrane 12 are sealed at both ends of the housing case 11 by sealing portions 13a and 13b with the ends opened.

  This hollow fiber membrane module 10 is an internal pressure filtration system that filters from the inside to the outside of the hollow fiber membrane 12, and allows the fluid to be filtered to flow into the inner diameter flow path of the hollow fiber membrane 12 from one open end 14 in the direction of arrow A. . The permeated fluid that has passed through the hollow fiber membrane 12 flows out of the hollow fiber membrane module 10 from the inside of the housing case 11 through the outlets 15a and 15b.

  Here, in the film defect detection device of the present invention, the reference electrode 16 is provided in the opening end 14 (liquid supply port). The detection electrode is provided at least in the outlet pipe on the permeate side of the membrane (reference numerals 17a and 17b), but is preferably provided in the outlet pipe closest to the open end 14 (reference numeral 17a). And the voltmeter 18 which is a measurement means for measuring the electric potential difference between a reference electrode and a detection electrode continuously is connected through these electrodes and wiring. As shown in FIG. 1, a plurality of detection electrodes may be provided. That is, as shown in FIG. 1, the detection electrode 17d may be provided in the middle part of the hollow fiber membrane module 10, and the detection electrode 17c may be provided on the downstream side. When a plurality of detection electrodes are provided in the hollow fiber membrane module 10, it is preferable to provide them at an appropriate interval between the liquid supply port and the downstream end.

  It is preferable that a potential measured by the voltmeter is taken into a computer, and a mechanism is provided so that a warning is issued when the absolute value of the fluctuation value of the potential difference becomes, for example, 1 mV or more. The warning makes it possible to identify the hollow fiber membrane module in which a defect has occurred, and to quickly replace the hollow fiber membrane module.

  Next, an example in which the membrane defect detection device of the present invention is applied to membrane defect detection of a water purifier as a filtering means will be described with reference to FIG.

  The water purifier 20 includes a large number of hollow fiber membranes 22 inside the housing case 21. The end of the hollow fiber membrane 22 is sealed at the upper end of the housing case 21 by a sealing portion 23 with the end opened. The hollow fiber membrane 22 is usually bundled and bonded in a U shape, as shown in FIG. 2, and has a dead end filtration (indentation filtration) system.

  The water purifier 20 also allows a fluid to be filtered (for example, tap water) to flow into the inner diameter flow path of the hollow fiber membrane 22 from the raw water inlet 24 (liquid supply port). The permeated fluid (for example, purified water) that has passed through the hollow fiber membrane 22 flows out from the water purifier 20 from the inside of the housing case 21 through the outlet 25.

  Here, in the membrane defect detection device of the present invention, the reference electrode 16 and the detection electrode are arranged in the same manner as in the case of the hollow fiber membrane module. First, the reference electrode 16 is provided in the raw water inlet 24. The detection electrode is provided at least in the piping of the outlet 25 on the permeate side of the membrane (reference numeral 17a). And the voltmeter 18 which is a measurement means for measuring the electric potential difference between a reference electrode and a detection electrode continuously is connected through these electrodes and wiring. As in the case of the hollow fiber membrane module, a plurality of detection electrodes may be provided. That is, as shown in FIG. 2, the detection electrode 17b may be provided at the lower end of the housing case. Moreover, since the outside of the water purifier is often made of plastic, when the reference electrode and the detection electrode are made of stainless steel, it is preferable to embed them in plastic and fix them.

  It is preferable that a potential measured by the voltmeter is taken into a computer, and a mechanism is provided so that a warning is issued when the absolute value of the fluctuation value of the potential difference becomes, for example, 1 mV or more. The warning makes it possible to recognize the occurrence of a defect and quickly know when to replace the water purifier.

[Filtering equipment]
The filtration device of the present invention includes a membrane, a filtration means provided with the membrane, a reference electrode provided at a liquid supply port of the filtration means, a detection electrode provided other than the liquid supply port of the filtration means, and a reference Measuring means for continuously measuring a potential difference between the electrode and the detection electrode. Specifically, the film defect detecting device of the present invention is combined with a known filtering means. Therefore, as shown in FIG. 1 and FIG. 2, at least the hollow fiber membrane module 10 or the water purifier 20 as the filtering means is equipped with the membrane defect detection device of the present invention.

  The filtration device of the present invention may have a plurality of filtration means. In this case, a film defect detection device may be provided for each filtering means. As described above, since the film defect detection apparatus of the present invention has a simple configuration including electrodes and measurement means, the configuration of the apparatus is not complicated, and the cost can be reduced.

  In the film defect detection method of the present invention, the potential between the electrodes to be measured may vary depending on the operation status of the apparatus (for example, filtration pressure, temperature, flow rate at the module inlet, electrical conductivity of water, etc.). In this case, it may be difficult to determine whether the potential fluctuation observed during the measurement is due to the above-described operating condition or due to the occurrence of a defect. Therefore, for the purpose of further improving the measurement accuracy, it is preferable to perform a correction process for correcting pressure, flow rate, etc. (especially pressure) before measuring the fluctuation of the potential difference. As an outline of the processing, as shown in the above-described equation (1), the flow potential V is proportional to the transmembrane pressure difference P, but the measured potential is added with the potential generated by the flow inside the hollow fiber. Therefore, the change in potential due to the transmembrane pressure difference is measured in advance, and the change in pressure may be corrected. Similarly, it is preferable to correct other fluctuation factors.

  A hollow fiber membrane module (FUS1582 manufactured by Daisen Membrane Systems Co., Ltd.), which is the UF module shown in FIG. Two detection electrodes (the configuration is the same as the reference electrode) are provided, and the inlet pressure and outlet pressure of the UF module are changed as shown in Table 1 below to filter pure water, and the correction process as described above is performed. In this case, the potential of each electrode before and after the correction process was continuously measured. The results are shown in Table 1 below.

  From Table 1 above, the voltage measured by the detection electrode 17a and the detection electrode 17b fluctuates by 1 mV or more due to the fluctuation of the average transmembrane pressure difference. However, the fluctuation of the corrected potential is obtained by correcting the pressure. Is found to be within 1 mV. In this way, by correcting the potential that can vary depending on the operating conditions of the device, the potential variation in the normal operating state is more quickly kept within 1 mV, and only the potential variation due to a film defect is detected as a variation of 1 mV or more. Is done.

  Similarly, it is preferable that the film defect detection device and the filtration device also include correction means for performing the correction processing. As such correction means, measurement data from means such as a pressure transmitter, a flow transmitter, an electric conduction clock, and a thermometer normally installed in the filtration device are taken into the computer together with the measurement value from the potential measurement electrode, and those numerical values are stored. What is necessary is just to correct | amend an electric potential by a correction type | formula.

(Example)
As shown in FIG. 1, a hollow fiber membrane module (FUS1582 manufactured by Daisen Membrane Systems Co., Ltd.), which is a UF module, has a reference electrode (stainless steel wire: diameter 1 mm, length 1 cm) and two detection electrodes (the configuration is the same as the reference electrode). And provided. Pure water was filtered, and the difference from the potential of each electrode was continuously measured based on the potential of the reference electrode.

  After the absolute value of the fluctuation of the potential of each electrode was less than 1 mV, a pinhole having a diameter of about 0.5 mm was provided in one hollow fiber located at the middle portion in the longitudinal direction of the hollow fiber membrane module. At this time, the measurement of the potential of each electrode was continued. The filtration conditions are shown in Table 2 below, and the measurement results are shown in Table 3 below. The detection electrode (1) corresponds to the reference numeral 17a in FIG. 1, and the detection electrode (2) corresponds to the reference numeral 17d in FIG.

As is clear from Table 3 above, when a pinhole was provided, a large fluctuation in potential was immediately observed at each electrode. That is, in the detection electrode (1), the potential difference between the reference electrode and the detection electrode before the occurrence of the defect was 22 mV, but after the defect occurred, the potential difference fluctuated to 19 mV. The absolute value was 3 mV. Similarly, also in the detection electrode, the absolute value of the fluctuation value was 3 mV.
In this way, it is understood that the defect can be detected quickly, efficiently and efficiently by providing the reference electrode and the detection electrode in the filtering means, continuously measuring the potential, and observing the fluctuation.

It is a partial cross section cutting explanatory drawing explaining the aspect which applied the film | membrane defect detection apparatus of this invention to the filtration means. It is a partial cross section explanatory drawing explaining the aspect which applied the film | membrane defect detection apparatus of this invention to the other filtration means.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Hollow fiber membrane module 11, 21 ... Housing case 12, 22 ... Hollow fiber membrane 13a, 13b, 23 ... Sealing part 14 ... Open end 15a, 15b, 25 ... Outlet 16: reference electrodes 17a, 17b, 17c, 17d ... detection electrode 18 ... voltmeter 20 ... water purifier 24 ... inlet of raw water

Claims (9)

A film defect detection method for detecting a film defect,
A membrane defect detection method comprising: continuously measuring a potential difference between a reference electrode and a detection electrode installed on the permeate side of the membrane, and detecting a defect in the membrane by a change in the potential difference.   2. The film defect detection method according to claim 1, wherein the presence of a defect in the film is detected when an absolute value of a fluctuation value of the potential difference becomes 1 mV or more.   The membrane defect detection method according to claim 1 or 2, wherein the membrane is one of an ultrafiltration membrane and a microfiltration membrane.   The film defect detection method according to claim 1, wherein a correction process for correcting a pressure fluctuation is performed before the fluctuation of the potential difference is measured. A reference electrode;
A sensing electrode installed at least on the permeate side of the membrane;
A film defect detection apparatus comprising: a measurement unit that continuously measures a potential difference between the reference electrode and the detection electrode.   The film defect detection device according to claim 5, wherein the presence of the defect is detected when an absolute value of a fluctuation value of the potential difference becomes 1 mV or more.   The membrane defect detection device according to claim 5 or 6, wherein the membrane is one of an ultrafiltration membrane and a microfiltration membrane. A membrane,
Filtration means comprising the membrane;
A reference electrode provided at a liquid supply port of the filtering means;
A detection electrode provided in addition to the liquid supply port of the filtering means;
And a measuring means for continuously measuring a potential difference between the reference electrode and the detection electrode.   The filtration device according to claim 7, wherein the membrane is one of an ultrafiltration membrane and a microfiltration membrane.

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