JPS63221886A - Purifying method and apparatus using hollow yarn membrane filter - Google Patents

Abstract

PURPOSE:To reduce operation cost, by injecting an oxidizing agent in the water on the upstream of a hollow yarn membrane filter to remove the metal ion or colloid dissolved in said water. CONSTITUTION:The steam 2 generated in a nuclear reactor 1 is supplied to a power generator turbine 3 to generate electricity by a generator 4. The steam from the turbine 3 is sent to a condenser 5 and cooled by cooling water 6 to obtain condensed water 7 which is, in turn, sent to a purifying treatment apparatus by a pump 8. The purifying apparatus is provided with a hollow yarn membrane filter 9 and a desalting device 10, and an oxygen injection apparatus 24 is provided on the upstream of the hollow yarn membrane filter 9 so as to be able to inject oxygen. Oxygen is injected to be mixed with the condensed water and reacted with an iron ion or iron colloid to form oxide. Impurities are grown into a solid state which is, in turn, caught on the surface of the hollow yarn membrane. By this structure, the impurities are prevented from penetrating into the pores and hollow parts of the membrane.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for removing fine impurities in water using a hollow fiber membrane filter and a purification device thereof, and in particular to a method for purifying water using a hollow fiber membrane filter, and particularly for condensate water in nuclear power plants and thermal power plants. and a method for purifying wastewater using a hollow fiber membrane filter, and a purification device therefor.

[Conventional technology]

Conventionally, in nuclear power plants, thermal power plants, etc., generated steam is condensed in a condenser and circulated for use. This condensate contains fine impurities, ions, colloids, etc. In particular, condensate from nuclear power plants contains radioactive materials, which must be removed, and large amounts of condensate can be almost completely removed. It needs to be purified.

Such a condensate purification device is disclosed in, for example, Japanese Patent Application Laid-Open No. 60-61089.
The condensate treatment system is equipped with a hollow fiber membrane filter and a bed-type salt analyzer, and a typical device is shown in Figure 4. In FIG. 4, steam 2 generated with one atom operates a steam turbine 3 and a generator 4 generates electricity. Thereafter, the steam is cooled by seawater 6 or the like in a condenser 5 and becomes condensate 7. This condensate water contains impurities such as solid matter, ions, colloids, etc. caused by corrosion of pipes, etc., and mainly oxides of iron and the like. Next, a hollow fiber membrane filter 9 and a bed-type desaltizer 10 are installed in the middle of the flow path in which the condensate 7 is returned to the reactor 1 via the condensate pump 8 to perform purification processing. As shown in FIG. 5, this hollow fiber membrane filter 9 is made of a polymeric material such as polyethylene and has an outer diameter of about 1.
A hollow fiber membrane module 16 is formed by bundling and filling approximately several thousand pieces of hollow fibers 15 whose surface pores pass through the inner hollow portion. 100 filters are attached to the filter tower 11, and condensate flows in through the inlet 13, and permeated water is discharged through the outlet 14. At this time, the hollow fiber 15 is porous and has a surface of 0.1
A large number of micropores on the order of μm are formed, allowing condensate to permeate from the outer surface of the hollow fiber 15 to the inner hollow portion, thereby filtering and removing particularly solid impurities in the condensate.

Next, the permeated water from the hollow fiber membrane filter 9 flows into the bed type salt analyzer 1o. Debasing 10 is a column filled with a mixed bed of granular ion exchange resin, and contains ionic impurities, especially Na when seawater leaks in condenser 5.
, CΩ ions, etc. are removed. In this way, the safety of power plants,
In order to maintain reliability, it is very important to remove impurities from condensate.

[Problem that the invention seeks to solve]

The conventional condensate purification device described above contributes to lowering radioactivity and reducing exposure in nuclear power plants.

However, the hollow fiber membrane filter, which is a component of the condensate purification device, uses a large amount of extremely precise and expensive hollow fiber membranes. For example, in a power plant with an output of 1,100 kW, the condensate is approximately 6.5 kW.
Since the treatment is performed at 00rn'/h, a large amount of hollow fiber membrane filters must be used. Therefore, it is desired to develop a condensate purification method and apparatus that extend the service life of hollow fiber membranes and reduce operating costs.

As the hollow fiber membranes are used for years, their mechanical strength deteriorates and they become easily damaged. In addition, the hollow fiber membrane becomes contaminated with impurities and the amount of permeated water decreases, so it is necessary to replace it with a new one. In addition, regarding the service life, the influence of contamination of the hollow fiber membrane is more dominant.

Regarding membrane contamination, as hollow fiber membrane filters trap solid impurities, the filtration pressure increases, so after a predetermined period of time, the membrane is washed to remove the trapped impurities and increase the filtration pressure. Perform operations to reduce This cleaning operation generally uses water and air to physically clean the filter.

However, it is difficult to completely remove impurities stuck to the hollow fiber membranes, and the bores of the hollow fiber membranes gradually become clogged, resulting in a decrease in the amount of permeable water, making the membranes unusable. In addition, there are chemical cleaning methods for cleaning hollow fiber membranes, such as the acid dissolution method using hydrochloric acid, etc. Although this method is powerful, it is not used in nuclear power plants due to its ease of operation and wastewater treatment. There are some difficulties in doing so.

Therefore, in order to extend the service life of hollow fiber membrane filters,
The object of the present invention is to provide a cleaning method using a hollow fiber membrane filter and an apparatus therefor, in which fine impurities are reduced to almost completely and easily cleaned by general physical cleaning, and then removed by a hollow fiber membrane filter. It is something.

[Means for solving problems]

A purification method using a hollow fiber membrane filter of the present invention to achieve the above object is a cleaning method for removing fine impurities in water using a hollow fiber membrane filter, in which an oxidizing agent is injected into the water upstream of the hollow fiber membrane filter. This is a purification method in which metal ions and colloids dissolved in water are oxidized and removed by the outer surface of the hollow fiber membrane.

In particular, dissolved metal ions are mainly iron ions and iron colloids dissolved from equipment materials in the condensate of nuclear or thermal power plants, and these are converted into oxides and precipitated and removed on the surface of the hollow fiber membrane, and are removed inside the pores of the membrane. This method prevents precipitation on the surface of the hollow part. The oxidizing agent is selected from the group of oxygen, air, ozone, and hydrogen peroxide, and the oxygen concentration in the water varies depending on the quality of the condensate water, but is generally used at 500 ppb or less.

Further, in the purification device of the present invention, an oxygen injection device for injecting oxygen into water is disposed upstream of the hollow fiber membrane filter,
This device is equipped with an oxygen cylinder or a PSA type oxygen generator as an oxygen source for the oxygen injector. In particular, an oxygen detector may be provided downstream of the hollow fiber membrane filter, and an oxygen control device may be provided to detect the amount of dissolved oxygen and control the amount of oxygen injected from the oxygen injector in conjunction with this. preferable.

[Effect]

The effect of injecting an oxidizing agent into the water upstream of the hollow fiber membrane filter will be described. First, Figure 2 shows the membrane contamination situation of the hollow fiber membrane filter. A stream of water 22 passes through the bore 18 from the outer surface 19 of the hollow fiber 15 .

The permeate flow 23 rises within the hollow space inside the hollow fibers 15 . Here, the state of membrane contamination can be determined by observing the hollow fiber cross section 17 using an electron microscope or the like, on the outer surface 19, inside the bore 20. Contaminants are deposited on the surface 21 of the hollow part, and the amount is less than the outer surface 19.
is the most common. However, contaminants adhering to the inside of the bore 20 and the surface of the hollow part 21 are generally very difficult to remove by physical cleaning methods, and remain and accumulate over the course of use, and membrane contamination has a large effect on the amount of permeated water. Reduces the amount of permeated water.

Contamination occurs in the bore interior 20 and the hollow surface 21 of the hollow fiber 15 because impurities with a bore diameter of about 0.1 μm or less are present in condensate, etc.
This is thought to be due to the fact that it adheres, precipitates, and grows.

Therefore, in order to prevent these contaminations, it is important to remove extremely small ionic or colloidal impurities from water. These impurities are leached from equipment and equipment piping, and although countermeasures have been taken to reduce the amount of leached substances, such as by using corrosion-resistant materials, hollow fiber membrane filters are still contaminated. Ru. Taking these into consideration, the best way to prevent contamination is to turn impurities into insoluble solids upstream of the hollow fiber membrane filter and prevent them from entering the bore. Most of the fine impurities in condensate are iron ions and iron colloids. Therefore, these iron ions and iron colloids are oxidized to form oxides to increase the size of impurities.1For example, the oxidation reaction is as shown below: %Formula %(), solid iron hydroxide is generated. In this way, fine impurities in condensate can be oxidized by injecting an oxidizing agent, preferably oxygen, into the upstream side of the hollow fiber membrane filter. Therefore, solid impurities that grow into large particles due to oxidation can be easily trapped on the outer surface of the hollow fiber membrane filter.

〔Example〕

A preferred embodiment of the present invention will be described with reference to the flow system for purifying condensate in a nuclear power plant shown in FIG. A nuclear reactor 1 generates steam 2, the steam 2 is supplied to a power generation turbine 3, and a generator 4 generates power.

Steam from the power generation turbine 3 is sent to a condenser 5 and converted into condensate 7 cooled with cooling water 6 such as seawater. This condensate 7 is sent to a purification treatment device by a pump 8. The purification treatment equipment is equipped with a hollow fiber membrane filter 9 and a demineralizer 10.
An oxygen injection device 24 is provided so that oxygen can be injected on the upstream side. This oxygen injection device 24 is a cylinder filled with oxygen gas or a PSA (Pressure Swin
An oxygen generator such as a g Adsorption system is provided as an oxygen source.

The injected oxygen is well mixed in the condensate and reacts with fine impurities in the condensate, mainly iron ions and iron colloids, to form oxides. Impurities grow into a solid form and are sent to the hollow fiber membrane filter 9, but impurities larger than the poff diameter are captured on the surface of the hollow fiber membrane. As a result, the amount of fine ionic or colloidal impurities is extremely reduced, most of the impurities are captured on the surface of the hollow fiber membrane, and intrusion into the bores and hollow parts of the membrane can be prevented as much as possible. Next, the permeated water from the hollow fiber membrane filter 9 is sent to a demineralizer 10, where impurity ions are removed using an ion exchange resin, and the condensate is purified.
Circulate to reactor 1. Note that oxygen may be directly injected into the upstream side of the membrane in the filtration tower of the hollow fiber membrane filter 9.

Here, as the hollow fiber membrane filter 9 captures impurities, the filtration pressure increases and the amount of permeation decreases, so the hollow fiber membrane filter 9 is cleaned at a predetermined time. According to the present invention, contamination in the bore of the hollow fiber membrane filter and contamination on the surface of the hollow part due to fine impurities is reduced, so that a sufficient cleaning effect can be achieved by ordinary physical cleaning with water and air.

Further, it is desirable to change the amount of oxygen injected depending on the amount of fine impurities in the condensate. Generally, the dissolved oxygen concentration in condensate is about 20~3゜ρρb before oxygen injection, but oxygen is injected to sufficiently oxidize iron ions, etc. in condensate, and generally 30~50ppb + preferably 100ppb
Make sure that it is at a certain level. At this time, a dissolved oxygen detector 26 is provided downstream of the hollow fiber membrane filter 9 to detect the dissolved oxygen concentration after the reaction in the condensate, and in conjunction with the detected value, the oxygen injection amount control device 25 controls the oxygen injector 24. It is preferable to control the amount of oxygen from the This allows operation without injecting too little or grossly excessive oxygen into the condensate.

Further, as an oxygen source, in addition to an oxygen cylinder or a PSA oxygen generator, oxygen generated by electrolysis of water can also be used.

In addition to oxygen, air, hydrogen peroxide, ozone, etc. can also be used.4 Especially when hydrogen peroxide is injected into condensate, hydrogen peroxide grows ionic and colloidal iron into oxides and is relatively inexpensive. Particles can be prevented from entering the hollow fiber membrane at a low processing cost. In addition, the amount of hydrogen peroxide injected is 50 ~
A range of 500 ppb is generally preferred. In addition, when ozone is injected into condensate, the strong oxidizing power of ozone causes ionic and colloidal iron to grow into oxides in a short time.
By increasing the particle size, it is possible to minimize intrusion into the hollow fiber membrane. The injection amount is generally 500 ppb or less, preferably 30 to 300 ppb. Furthermore, since ozone can be produced on-site, there is no need for storage equipment, and the amount of ozone produced can be changed by adjusting the voltage, making it possible to create a highly controllable system.

Next, a comparison will be made between a purification method according to the present invention in which oxygen is injected into condensate and a conventional purification method in which oxygen is not injected.

The same hollow fiber membrane filter and desalter were used in both cases. Table 1 shows the test conditions, ie, condensate properties, filtration line flow rate, cleaning timing, and cleaning method.

Table 1 The test results are shown in Figure 3, which shows the relationship between filtration differential pressure and cladding load and years of use. As the years of use increase, the amount of crud load attached to the hollow fiber membrane filter increases, and the filtration differential pressure increases accordingly.

In the case of the present invention, the filtration differential pressure at the first starting point ao is 1.0 kg/
ad, but as it was used, the filtration differential pressure was removed at point a', and S
kg/aJ, so air scrubbing and air surging were performed to return to point a1 to lower the filtration differential pressure. Repeat this sequentially, from point a2' to ax, from as' to a3, and so on. The filtration differential pressure was lowered to...

Further, the filtration differential pressure of the hollow fiber membrane filter immediately after air scrubbing and air surging with respect to the cladding load amount is shown by a straight line A. The filtration differential pressure of the hollow fiber membrane filter when the conventional example is operated in the same manner is shown by a straight line B. Comparing straight lines A and B, the conventional example shows that the allowable upper limit filtration differential pressure (
Membrane replacement period) Impurity capture amount 35g at 2.0kg/a+f
/Achieved with Po.

The service life of hollow fiber membrane filters is about 1 to 2 years. On the other hand, in the method of the present invention, the amount of impurities captured that reaches the allowable upper limit filtration differential pressure is 90 g/rd, and the service life of the hollow fiber membrane filter is about 3 to 5 years.

It has been confirmed that the method of the invention can significantly extend the service life. In addition, even in the method of the present invention, the filtration differential pressure of the hollow fiber membrane filter gradually increases with the age of use, but the contamination status of the hollow fiber membrane after the test can be observed using an electron microscope. Upon inspection, it was found that almost no impurities were observed inside the bore or on the surface of the hollow part. However, in the case of the conventional example, many impurities were attached to the inside of the bore and the surface of the hollow part.

〔Effect of the invention〕

According to the present invention, an oxygen agent is injected into the water on the upstream side of the hollow fiber membrane filter, oxidizes iron ions and iron colloids to form oxides, and grows particles. Because it prevents water damage and facilitates physical cleaning, it can minimize the decrease in permeated water amount due to membrane contamination, greatly extending the service life of hollow fiber membrane filters, and providing water purification with low operating costs. It can be used as a device. Further, the method of the present invention is suitable for condensate treatment in nuclear power plants, and can also be effectively used for condensate treatment in thermal power plants, and in the production of pure water for semiconductor manufacturing, biotechnology, and pharmaceuticals.

[Brief explanation of the drawing]

Fig. 1 shows the flow system for condensate purification according to the present invention, Fig. 2 shows the contamination status of hollow fiber membranes, Fig. 3 shows the test results of the present invention, and Fig. 4 shows the conventional condensate purification flow system. Purification Flow System, Figure 5 shows the structure of a hollow fiber membrane filter. DESCRIPTION OF SYMBOLS 1... Nuclear reactor, 3... Steam turbine, 4... Generator, 5... Condenser, 9... Hollow fiber membrane filter, 10
... Demineralizer, 12 ... Filtration tower, 15 ... Hollow fiber,
16... Hollow fiber membrane module, 18... Bore, 19
... Outer surface, 21 ... Hollow part surface, 24 ... Oxygen injection device, 25 ... Injection amount control device, 26 ... Dissolved oxygen detector.

Claims (1)

[Claims] 1. In a purification method for removing minute impurities from water using a hollow fiber membrane filter, an oxidizing agent is injected into the water upstream of the hollow fiber membrane filter to oxidize dissolved metal ions and colloids. A purification method using a hollow fiber membrane filter, characterized in that the removal is carried out on the outer surface of the hollow fiber membrane. 2. The purification method using a hollow fiber membrane filter according to claim 1, wherein the water is condensate or wastewater from a nuclear power plant, and the metal is mainly iron ions or iron colloids. 3. A purification method using a hollow fiber membrane filter according to claim 1 or 2, wherein the oxidizing agent is selected from the group of oxygen, air, ozone, and hydrogen peroxide. 4. Purification using a hollow fiber membrane filter according to any one of claims 1 to 3, characterized in that oxygen is injected so that the concentration of oxygen in water is 500 ppb or less Method. 5. In a purification device that removes minute impurities from water using a hollow fiber membrane filter, an oxygen injection device for injecting oxygen into the water upstream of the hollow fiber membrane filter is provided, and oxygen is used as an oxygen source for the oxygen injection device. cylinder or PSA (P
1. A purification device using a hollow fiber membrane filter, characterized in that it is equipped with a SwingAdsorption type oxygen generator. 6. An oxygen detector is provided downstream of the hollow fiber membrane filter, and an oxygen control device is provided to detect the amount of dissolved oxygen and control the amount of oxygen injected from the oxygen injection device in conjunction with this. A purification device using a hollow fiber membrane filter according to claim 5.