JPH01228509A - Medium purifying equipment provided with membrane performance evaluation apparatus, method and equipment for evaluating membrane performance - Google Patents

Abstract

PURPOSE:To detect the electrification state of a porous membrane and to perform selection of the membrane, optimization of the operational conditions of the membrane and replacement period thereof with right judgment by measuring the electric physical quantity obtained between the electrodes provided to the upstream side and the downstream side of the porous membrane. CONSTITUTION:In a hollow yarn membrane filter 9 provided to the condensate treating system, etc., of a nuclear power station, the electrodes 19 are inserted into a hollow yarn membrane 12 and between the hollow yarn membranes 12 from the upper end face of a hollow yarn membrane module 13 so that the electrodes are opposed in the front and rear parts of the hollow yarn membrane 12 in the module 13; the leader lines 17 insulated from liquid are taken out from the electrodes 19 and connected to a measuring apparatus 18. The fluctuated potential or the signal of AC impedance of the front and rear parts of the membrane 12 is measured on-line with the measuring apparatus 18. In such a way, monitoring of electrification of the membrane and forecasting of contamination of the membrane are possible.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a membrane performance evaluation device for filters such as polymer membranes used for purifying condensate and wastewater in thermal power plants, nuclear power plants, etc. The present invention relates to a medium purification facility, a membrane performance evaluation device, and a membrane performance evaluation method.

[Conventional technology]

In recent years, condensate purification equipment in nuclear power plants has become mainstream in which hollow fiber membrane filters made of polymer membranes and bed desalters are installed in the condensate treatment system. An example of such a condensate treatment facility is shown in FIG. Incidentally, related devices of this type include, for example, JP-A-60-61089, JP-A-60-179104, and JP-A-60-206405.

In FIG. 10, steam 2 generated in a nuclear reactor drives a steam turbine 3, generates electricity in a generator 4, enters a condenser 5, is cooled by seawater 6, and becomes condensate 7. This condensate 7 contains small amounts of solid and ionic impurities (mainly iron oxides) due to corrosion of pipes, etc.
In order to further improve the safety and reliability of power plants, it is necessary to remove these impurities. Therefore, a hollow fiber membrane filter 9 and a bed type demineralizer 10 are installed in the flow path from the condenser 5 to the nuclear reactor 1 via the condensate pump 8 to constitute a condensate treatment system.

As shown in FIG. 11, the hollow fiber membrane filter 9 consists of about 100 hollow fiber membrane modules 13 filled with several thousand water bundles of hollow fiber membranes 12 made of a polymeric material such as polyethylene and having an outer diameter of about 1 mm. The book is attached to the filtration tower 14. The outer surface of the hollow fiber membrane 12 has a diameter of about 0.1 mm connected to the inner surface.
There are countless microscopic holes of μm in size, and the condensate is transported to the water inlet 15.
The solid impurities in the condensate are removed on the outer surface of the membrane by flowing from the condensate toward the water outlet 16.

[Problem to be solved by the invention]

In this way, hollow fiber membrane filters directly capture solid matter through extremely fine pores, and therefore have very high removal performance. Furthermore, there is no problem of the pre-coat material being generated as waste, unlike the case with pre-coat filters that capture solid matter through the pre-coat material. However, since polymeric materials such as polyethylene, which are the materials for hollow fiber membranes, are generally electrically insulating,
Water with extremely low conductivity (<0
．． 1μs/]) When used in water, it is known that a so-called flow charge occurs due to the relative motion between the hollow fiber membrane and water (References: Electrostatic Handbook, Japan Society of Electrostatics, etc.)
. When the membrane is charged, solid and ionic impurities in the liquid electrostatically adhere to the membrane, and when they accumulate, membrane contamination such as clogging of membrane pores progresses, and the water permeability of the membrane decreases. Membrane cleaning or membrane replacement becomes necessary. In the case of nuclear power plants,
Since a large amount of condensate of about 6500 m/h is purified by the hollow fiber membrane, the amount of hollow fiber membrane used is extremely large. Therefore.

When a contaminated membrane is cleaned, a large amount of the chemicals used for cleaning is generated as waste, and replacing the membrane with a new membrane is expensive, leading to a huge increase in running costs. Therefore.

It has been desired to develop a media purification system using a filter such as a hollow fiber membrane that prevents membrane contamination due to flow charging as much as possible, extends the membrane life as much as possible, is low cost, and generates a small amount of waste.

The purpose of the present invention is to provide a method and device for detecting the charging status of a membrane, and by using the device, it is possible to make correct judgments in membrane selection, optimization of membrane operating conditions, and determination of membrane replacement timing. The purpose of this invention is to provide media purification equipment that can perform the following steps.

[Means to solve the problem]

In order to achieve the above object, the medium purification equipment according to the present invention is equipped with a membrane performance evaluation device.

Here, the membrane performance evaluation device includes electrodes installed on the membrane upstream side and membrane downstream side of a filter consisting of a porous membrane that removes impurities in the medium, and an electric resistance between the electrodes connected to the electrodes. It consists of a measuring instrument that measures electrical physical quantities such as. The measuring device is determined depending on the electrical physical quantity, and examples include an electrometer, an ammeter, an AC resistance meter, and a static electricity monitor.

Further, as a method for evaluating membrane performance, there is a method of evaluating membrane performance by measuring electrical physical quantities between the membrane upstream side and the membrane downstream side of the filter.

Types of filters used in the media purification equipment include hollow fiber membrane filters for condensate purification in nuclear power plants and hydrophobic porous membranes used in vaporization permeation methods.

It is preferable that the media purification equipment is capable of adjusting the filtration flow rate through a filter, or that carbon dioxide gas is blown into the condensate to make the conductivity of the condensate variable.

In addition, the media purification equipment branches the condensate flow path to the filter body, installs a small filter with the same specifications as the filter in the branched flow path, and installs the membrane performance evaluation device on this small filter. is desirable.

[Effect]

By being equipped with a membrane performance evaluation device, the medium purification equipment according to the present invention can detect, for example, the flow charging state of the membrane, and can perform control to prevent membrane contamination as much as possible. In particular, if a small filter of the same specification is installed in the single-branched condensate flow path, which facilitates the control described above by changing the filtration flow rate or blowing carbon dioxide gas, various evaluations can be performed while the plant is operating.

The membrane performance evaluation device can measure the electrical and physical properties of the membrane simply by installing electrodes at predetermined positions on the filter.

〔Example〕

First, membrane performance evaluation will be explained. It can be easily evaluated by measuring the potential difference of the liquid before and after permeating the membrane and the AC impedance frequency response before and after the membrane. Figure 6 shows the results of measuring the potential difference of the liquid before and after membrane permeation using the apparatus shown in Figure 7. Electrodes made of platinum were inserted into the liquid on the upstream and downstream sides of the hollow fiber membrane, and the potential difference between the electrodes was measured. This is the result of measuring the potential with a voltmeter.

Hollow fiber membrane made of polyethylene has an electrical conductivity of 0.1μ
When water of less than S/cm (theoretical pure water is 0.055 μS/]) was permeated, a potential was generated between the electrodes in front and behind the membrane depending on the flow rate of the permeation, and flow charging could be detected. . For confirmation, we applied a conductive treatment to the membrane, which makes it difficult for fluid charging to occur, and almost no potential was generated between the electrodes, indicating that this method is effective in detecting fluid charging.

Next, FIG. 8 shows the results of measuring the AC impedance station wave number response before and after the membrane using the apparatus shown in FIG. 9. This involves applying a constant voltage of alternating current between platinum electrodes inserted before and after the membrane, and changing the frequency of the alternating current to examine the frequency dependence of alternating current resistance (impedance). As a result, it was found that the impedance of a film that is easily charged, that is, a film that has not been subjected to surface treatment, becomes high especially at low frequencies. It was found that the impedance of the membrane subjected to conductivity treatment was /J% lower in all frequency ranges, and that the AC impedance frequency response of the membrane was effective as an index of membrane band type.

As described above, as a means for understanding the flow charging of a membrane, specifically, there is a method of measuring the potential difference between the liquid before and after the membrane and the AC impedance frequency response before and after the membrane. Measuring the potential difference between the liquid before and after the membrane can be used for online measurement of flow charging, and measuring the AC impedance frequency response before and after the membrane can determine the aging of the membrane, predict membrane contamination, and extend the life of the membrane. It becomes possible. Therefore, it is possible to take appropriate measures against the progress of membrane contamination and to know when to replace the membrane.

It becomes possible to operate a hollow fiber membrane filter at low cost and with stable performance.

Hereinafter, one embodiment of the present invention will be described in detail based on FIGS. 1 to 4.

As shown in FIG. 4, steam 2 generated in the nuclear reactor 1 drives a steam turbine 3 and generates electricity in a generator 4, then enters a condenser 5, is cooled by seawater 6, and becomes condensate 7. Become. The condensate 7 is supplied by a condensate pump 8 to a hollow fiber membrane filter 9 and a bed-type salt clarifier 10 that constitute a condensate purification system, and after purification is supplied to the reactor 1 as feed water 11.

A lead wire 17 for transmitting a signal of flowing potential or alternating current impedance, which is an electrical physical force, comes out from the hollow fiber membrane filter 9, and is connected to a measuring device 18 for measuring voltage or impedance. Details will be explained with reference to FIGS. 1 to 3.

The hollow fiber membrane module 13 is installed in the filtration tower 14 of the hollow fiber membrane filter 9 so that the electrodes 19 face each other before and after the hollow fiber membrane 12 (FIG. 3). 13 Insert the electrode 19 into the hollow fiber membrane 12 and between the hollow fiber membranes 12 from the upper end surface, take out the lead wire 17 insulated from the liquid from the electrode 19, pass through the terminal part 20 of the filtration tower 14, and then insert the lead wire At 17, it is connected to the measuring device 18. The electrode 19 may be, for example, an electrochemically inert platinum wire. Furthermore, although it is sufficient to insert the electrode 19 at one location, the reliability of the measurement is further improved by detecting at multiple locations or using multiple hollow fiber membrane modules 13.

If it is difficult to insert the electrode 19 due to the inner diameter of the hollow fiber membrane 12 or the structure of the hollow fiber membrane module 13, the hollow fiber membrane 1
It is also possible to measure the overall streaming potential and impedance by arranging electrodes 19 on the upstream and downstream sides of 2.

In this way, the flow potential and impedance signals before and after the hollow fiber membrane can be obtained online, making it possible to monitor membrane charging and predict membrane contamination. That is, when the flowing potential is high, it indicates that the hollow fiber membrane is electrically charged, and it is understood that impurities in the liquid may be electrostatically attached and membrane contamination may proceed.

Also, if the membrane impedance increases over time, in the future,
This suggests that the electrostatic charge on the membrane may increase, so it can serve as a warning that it is necessary to pay close attention to the operation of the hollow fiber membrane filter and take countermeasures. The monitor may be determined by the electrical physical quantity to be measured, but in addition to an electrometer or an AC resistance meter, an ammeter or a static electricity monitor may also be used as the measuring instrument.

Examples of means for detecting the flowing potential and impedance before and after the hollow fiber membrane and automatically controlling and optimizing the operation of the hollow fiber membrane filter using the signals are as follows. When the flow potential is high and the membrane band type is large, the amount of water processed by the hollow fiber membrane filter is temporarily reduced to prevent further membrane contamination.

That is, the filtration flow rate can be adjusted. Specifically, in a hollow fiber membrane (conductive, insulating membrane), the streaming potential is 0,
5V (filtration flow rate 0.3m/h, water temperature 20℃, conductivity 0
．． It is desirable to control the voltage to be 1 μS/as or less (electrometer internal resistance 1013 MΩ) or less. In addition, the operation of blowing carbon dioxide gas into the liquid to increase the conductivity of the liquid is linked with a signal to prevent the membrane from being charged.

Next, a small hollow fiber membrane module 21 having the same hollow fiber membrane specifications is installed separately from the hollow fiber membrane filter 9 main body, another embodiment of which will be explained with reference to FIG. Flow potential and impedance signals are obtained by electrodes attached to the thread membrane module 21.

In this example, the measurement values of flowing potential and impedance can be compared by using various types of hollow fiber membranes, so that the optimum membrane can be easily selected.

Furthermore, on the premise that sufficiently simulated condensate can be obtained, streaming potential and impedance measurement methods using small modules can be used as a means of evaluating the performance of hollow fiber membranes in hollow fiber membrane manufacturing and research facilities. .

Although the above embodiment has been described with reference to a hollow fiber membrane filter for purifying condensate in a nuclear power plant, the present invention can also be applied to other membranes as described below. In vaporization permeation methods that utilize hydrophobic porous membranes, hydrophilicity of the membrane due to membrane contamination greatly reduces the performance of vaporization and permeation. Generally, when a membrane is made hydrophilic, liquid enters the membrane and the impedance across the membrane decreases. Therefore, in a hydrophobic membrane, by monitoring the impedance before and after the membrane, the progress of membrane contamination (hydrophilicization) can be grasped online.

〔Effect of the invention〕

According to the present invention, by evaluating the membrane performance, membrane contamination can be prevented as much as possible, and the life of an expensive membrane can be extended, thereby enabling stable operation at low cost.

Furthermore, the membrane performance evaluation device or method of the present invention requires only that the electrodes be installed before and after the membrane of the medium purification equipment, so installation is simple and evaluation is easy.

[Brief explanation of the drawing]

Fig. 1 is a partial sectional view of an embodiment of the equipment according to the present invention, Fig. 2 is a view taken in the direction of the ■ arrow in Fig. 1, Fig. 3 is a sectional view taken along the line -■ in Fig. 2, and Fig. 4 5 is a schematic configuration diagram of a nuclear power plant equipped with equipment according to the present invention, FIG. 5 is a schematic configuration diagram of another embodiment of the present invention, and FIG. 6 explains the measurement results of the flowing potential before and after the hollow fiber membrane. figure. Figure 7 is a diagram showing the configuration of the device that performs the measurements shown in Figure 6, Figure 8 is a diagram explaining the measurement results of the AC impedance frequency response before and after the hollow fiber membrane, and Figure 9 is a diagram of the equipment that performs the measurements shown in Figure 8. FIG. 10 is a schematic configuration diagram showing an example of a conventional condensate purification equipment for a nuclear power plant, and FIG. 11 is a structural diagram of a hollow fiber membrane filter of the conventional example. 1...nuclear reactor, 2...steam, 3...steam turbine,
4... Generator, 5... Condenser, 7... Condensate, 9.
・Hollow fiber membrane filter, 10...Bed type salt filter, 1"
-... Water supply, 12... Hollow fiber membrane, 13... Hollow fiber membrane module, ], 4... Filtration tower, 15... Water inlet, 1
-6... Water outlet, 17... Lead wire, ]8... Measuring device, 19... Electrode, 20... Terminal section, 21
...Small hollow fiber membrane module.

Claims (1)

[Claims] 1. Electrodes installed on the membrane upstream side and the membrane downstream side of a filter consisting of a porous membrane that removes impurities in a medium, and an electrical physical quantity connected to this electrode and between the electrodes. Media purification equipment characterized by being equipped with a membrane performance evaluation device consisting of a measuring device for measuring . 2. The media purification equipment according to claim 1, wherein the filter is a hollow fiber membrane filter for purifying condensate in a nuclear power plant. 3. The medium purification equipment according to claim 1, wherein the filter is made of a hydrophobic porous membrane used in a vaporization permeation method. 4. The medium purification equipment according to claim 1, wherein the filtration flow rate can be adjusted so that the electrical physical quantity corresponding to the membrane performance is equal to or less than the permissible value of the membrane. 5. The medium purification equipment according to claim 2, wherein the conductivity of the condensate is made variable by blowing carbon dioxide gas into the condensate so that the electrical physical quantity corresponding to the membrane performance is equal to or less than the allowable value of the membrane. 6. A claim in which the condensate flow path to the filter body is branched, a small filter having the same specifications as the filter is provided in the branched flow path, and the membrane performance evaluation device according to claim 1 is provided for this small filter. The medium purification equipment according to item 2. 7. The membrane performance evaluation device according to claim 1. 8. The membrane performance evaluation device according to claim 7, wherein the electrical physical quantity is voltage or electrical resistance. 9. The membrane performance evaluation device according to claim 7, wherein the measuring device is an electrometer, an ammeter, an AC resistance meter, or a static electricity monitor. 10. A membrane performance evaluation method characterized by evaluating the performance of a membrane by measuring electrical physical quantities between the membrane upstream side and the membrane downstream side of a filter consisting of a membrane that removes impurities in a medium. .