JPH0624612B2 - Filtration method using hollow fiber membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a condensate of a nuclear power plant, a thermal power plant, heater drain water or raw water containing insoluble substances such as other water, wastewater, etc. The present invention relates to improvement of a method of filtering with a filter tower arranged.

<Prior Art> When raw water containing an insoluble substance is treated with a filter tower to obtain filtered water from which the insoluble substance is removed, a filter tower of the type conventionally filled with a filter material, a cartridge type filter tower or Various filter towers such as a filter tower for pre-coating with a filter aid are used, but in recent years, a filter tower using a hollow fiber membrane has come to be used particularly for the treatment of condensate of nuclear power plants. There is. That is, in a filtration tower using a hollow fiber membrane, first, the clad caused by iron oxide, which is an insoluble substance in condensate, is removed, and then the filtered water is treated with a mixed bed of cation exchange resin and anion exchange resin to remove impurity ions. Is to be removed.

For example, the filtration tower used for condensate filtration will be described in more detail. A plurality of hollow fiber membranes having a large number of fine pores are bundled to form a hollow fiber module, and the hollow fiber modules are arranged in the filtration tower. The condensate is passed from the outside to the inside of the hollow fiber membrane to filter the clad caused by iron oxide on the surface of each hollow fiber membrane, and collect the filtered water flowing into the inside of each hollow fiber membrane. And flow out from the filtration tower.

When the differential pressure of the filtration tower increases due to the continuation of such filtration, the surface of the hollow fiber membrane to which the iron oxide is attached is bubbled with a gas such as air to remove most of the iron oxide, and then Clarified water such as filtered water or pure water is allowed to flow backward from the inside to the outside of the hollow fiber membrane to remove iron oxide remaining on the membrane surface to obtain a cleaning drainage liquid containing a large amount of iron oxide. After the completion of the washing, the filtration is restarted, and thereafter the filtration and the washing are sequentially repeated to perform the treatment.

As explained above, the filtration tower using the hollow fiber membrane directly filters the condensate with each hollow fiber membrane, so it is compared with the precoat type filtration tower using the finely powdered ion exchange resin as a filter aid which has been conventionally used. Moreover, the amount of solids contained in the liquid waste is extremely small, and it is particularly suitable for removing iron oxide containing radioactive substances like condensate of a boiling water nuclear power plant.

That is, in the case of a precoat type filtration tower, the cleaning wastewater containing an overwhelmingly large amount of the use agent and filter aid is discharged together with the iron oxide removed by filtration during the cleaning, and the radioactive waste treatment Although the burden on the system is large, the cleaning wastewater in the filtration tower using the hollow fiber membrane does not contain any such filter aids for use, so solid substances that are the target of radioactive waste treatment Has the advantage that it can be significantly reduced.

<Problems to be Solved by the Invention> However, in filtration using a conventional hollow fiber membrane,
Depending on the type of insoluble substance to be filtered, the insoluble substance adhering to the surface of the hollow fiber membrane cannot be completely peeled off during the washing, and the differential pressure increases with each washing, resulting in an initial difference. It has the drawback that the filtration process itself is impaired by the increase in pressure.

For example, in condensate water of a nuclear power plant or a thermal power plant, various forms of iron oxide are contained as an insoluble substance, and sometimes fine particle organic matter, fats and oils are contained. Among the insoluble substances, for example, the particle size is 1 to
About 10μ of α-Fe ₂ O ₃ (hematite), α-FeO
Iron oxides such as OH (goethite) and Fe ₃ O ₄ (magnetite) are easily peeled off from the film surface by the above-mentioned washing,
For example, iron oxide having a particle size of 1 μm or less, iron oxide hydroxide having a relatively high adhesiveness, fine particles of organic matter, fats and oils cannot be easily peeled off from the film surface by the washing.

Therefore, if insoluble substances have a relatively large abundance ratio of iron oxide having a particle size of 1 μm or less or hydrous iron oxide having a relatively high adhesiveness, or if it contains finely divided organic substances and / or fats and oils, it is washed. Each time, a part of the insoluble substance remains on the film surface, and as a result, the initial differential pressure gradually rises. In particular, the increase in the initial differential pressure that occurs when filtering condensate of a nuclear power plant or a thermal power plant with a hollow fiber membrane is often seen at the time of starting the power plant. It is considered that the abundance ratio of poorly soluble insoluble substances increases.

The present invention solves the above-mentioned drawbacks in the conventional filtration method using a hollow fiber membrane, and even if the raw water contains a large amount of an insoluble substance that is difficult to be peeled from the hollow fiber membrane, the insolubility during washing is high. Do not let the substance remain on the membrane surface,
It is an object of the present invention to provide a filtration method capable of effectively preventing the phenomenon that the initial differential pressure gradually rises each time washing is performed and performing stable filtration treatment.

<Means for Solving Problems> The technical means of the present invention for achieving the above-mentioned object is to arrange a hollow fiber module in which a large number of hollow fiber membranes are bundled in a filtration tower, Raw water containing an insoluble substance is passed from the outside to the inside, and when the insoluble substance is filtered on the surface of each hollow fiber membrane, before passing the raw water, water containing iron oxide fine particles with good peelability is used. Through a hollow fiber membrane to form a thin coating film of the iron oxide fine particles on the surface of each hollow fiber membrane, and then the raw water is passed through each hollow fiber membrane through the coating film. To do.

<Operation> The present invention will be described in detail below with reference to the drawings illustrating an example of an embodiment.

1 is a sectional view showing a hollow fiber module used in the present invention, FIG. 2 is an explanatory view showing a flow of a filtration tower used in the present invention, and FIG. 3 shows a state of a hollow fiber membrane during filtration. It is an enlarged explanatory view shown.

As shown in FIG. 1, the hollow fiber module 1 used in the present invention has an outer diameter of 0.3 to 1 having fine pores of 0.01 to 1 μm.
The hollow fiber membrane 2 having a diameter of 4 mm and an inner diameter of 0.2 to 3 mm is 100 to 50,
Approximately 000 pieces are housed in the outer cylinder 3, and the upper ends of the hollow fiber membranes 2 are adhered to each other by the upper joint portion 4 without closing the hollow portions, and the lower ends of the hollow fiber membranes 2 are closed by lower portions. The outer joint 3 is adhered at the joint 5, and the upper joint and the lower joint of the outer cylinder 3 are provided with the flow ports 6A and 6B, respectively, and the lower joint 5 is provided with the opening 7 so that the outer cylinder 3 is slightly extended downward. The skirt portion 8 is provided.

The hollow fiber membrane module described above is a single-end water collecting type in which filtered water obtained from the inside of the membrane is taken in only from the upper joint portion 4, but the lower joint portion 5 adheres without blocking the lower end of the hollow fiber membrane 2. Then, a small chamber (not shown) is provided below the lower joint portion 5, filtered water is also obtained from the lower joint portion 5 of the hollow fiber membrane 2 and collected in the small chamber, and stands up along the small chamber and the hollow fiber membrane 2. A double-end water collecting type in which filtered water is sent to the upper part by an installed water collecting pipe (not shown) is also used.

When arranging the hollow fiber module 1 in the filtration tower, as shown in FIG. 2, a partition plate 10 is provided above the filtration tower 9, and a large number of hollow fiber modules 1 are suspended on the partition plate 10. .

Further, a bubble distribution mechanism 11 is arranged below the inside of the filtration tower 9.
The bubble structure 11 includes a bubble distribution plate 12 and a bubble distribution plate 1
It consists of a bubble distribution pipe 13 attached to 2,
The bubble distribution pipe 13 is located immediately below the skirt portion 8 corresponding to each hollow fiber module 1.

In addition, one end of the filtered water outflow pipe 14 and one end of the compressed air inflow pipe 15A communicate with the upper part of the filtration tower 9, and one end of the raw water inflow pipe 16 and one end of the compressed air inflow pipe 15B and the drain pipe are connected to the lower part of the filtration tower 9. One ends of the air vent pipes 17 are communicated with each other, and one end of the air vent pipe 17 is communicated with the side body portion directly below the partition plate 10. 19 to 24 are valves,
25 is a baffle plate.

The filtration method of the present invention using the filtration tower 9 will be described below by taking condensate containing insoluble substances such as iron oxide as raw water.

In the present invention, prior to the filtration of the condensate, iron oxide fine particles having good releasability are dispersed in a water tank (not shown) while the partition plate 10 of the filtration tower 9 is filled with water and the valve is closed. By opening 19 and the valve 23, the water containing the iron oxide fine particles having good peelability in the water tank flows in from the raw water inflow pipe 16. The water rises in the inside of the filtration tower 9, and each bubble distribution pipe 1
3 through which the hollow fiber module 1 is opened, and the flow port 6 is provided.
It flows into each hollow fiber module 1 via A and 6B and passes from the outer side to the inner side of each hollow fiber membrane 2. At that time, iron oxide fine particles having good releasability in water are captured on the membrane surface. The filtered water rises inside the hollow fiber membranes 2, collects above the partition plate 10, and flows out from the filtered water outflow pipe 14. The filtered water may be used as the original filtered water, or may be returned to the aforementioned water tank (not shown).

By this step, as shown in FIG. 3, a thin coating film 26 of iron oxide fine particles having good releasability can be formed on the outer surface of each hollow fiber membrane 2. When forming the coating film 26, condensate containing iron oxide fine particles having good peelability is preliminarily introduced from the raw water inflow pipe 16 without using a water tank or the like, or iron oxide fine particles having good peelability are filtered in advance. After being placed in the tower 9, water or condensate is fed into the raw water inflow pipe 1
It does not matter if it flows in from 6.

After forming the coating film 26, the following filtration is continuously performed.

That is, the condensate containing the insoluble substance flows in from the raw water inflow pipe 16 with the valve opening left unchanged. Similar to the step of forming the coating film, the condensate is mostly the opening 7 of each hollow fiber module 1 and a part of the flow ports 6A, 6A.
It flows into the inside of each hollow fiber module 1 via B and passes from the outside to the inside of each hollow membrane 2 via the coating film 26. As a result, the insoluble substance contained in the condensate is captured by the coating film 26, and the insoluble substance 27 adheres to the upper portion of the coating film 26 as shown in FIG.

The filtered water in each hollow fiber membrane 2 rises inside and the partition plate 1
They are collected above 0 and flow out from the filtered water outflow pipe 14.

By continuing such filtration, when the pressure difference in the filtration tower 9 reaches a specified value, the filtration is stopped and the following washing is performed.

That is, the valves 19 and 23 are closed, the condensate that has flowed into the lower part of the partition plate 10 and the filtered water that is above the partition plate 10 are filled with the filtered water, and the valves 21 and 22 are opened to allow the compressed air inflow pipe 15B to flow. Introduce compressed air. The compressed air rises in the filtration tower 9 as bubbles, is received at one end above the bubble distribution plate 12, forms an air layer below the bubble distribution plate 12, and the air is separated into bubbles through the air layer. From small holes (not shown) opened on the side of the pipe 13, air bubbles rise up in the skirt portion 8 of the hollow fiber module 1 and then flow into the hollow fiber modules 1 through the openings 7. As the bubbles rise, the hollow fiber membranes 2 vibrate and the water in the hollow fiber modules 1 is agitated, the coating film 26 attached to the surface of each hollow fiber membrane 2 peels off, and the insoluble substance 27
Is also peeled off. The air bubbles flow out of the hollow fiber module 1 through the flow port 6B to the outside of the module 1, and then are discharged from the air vent pipe 17 to the outside of the filtration tower 9.

After sufficiently agitating with such bubbles, the valve 21 is closed while the valve 22 is open, the valve 20 is opened, and the drainage water 18 containing the cleaning wastewater mainly containing iron oxide separated from the hollow fiber membrane 2 is drained. Drain from. Although the above step of flowing out the cleaning waste water uses the head difference, it is also possible to carry out the compressed air through the air vent pipe 17 or the compressed air inflow pipe 15B to perform the rapid outflow using the air pressure.

After the outflow of the cleaning waste water is completed, the valves 20, 22, and 24 are opened and the other valves are closed, and the compressed air inflow pipe 15
Compressed air flows in from A, the filtered water existing above the partition plate 10 is caused to flow backward in each hollow fiber membrane 2 by the air pressure, and iron oxide fine particles remaining on the outer surface of each hollow fiber membrane 2 are It is washed off with the filtered water, and the washing waste water flows out from the drain pipe 18.

After the above-mentioned stirring process with compressed air, blowing of the cleaning waste water, and the cleaning process with the backflow of filtered water are completed, the above-mentioned coating film of iron oxide fine particles having good releasability is formed and filtered.

The iron oxide fine particles having good releasability used in the present invention refer to all iron oxide fine particles that can be easily peeled off by the above-mentioned washing step even if they adhere to the surface of the hollow fiber membrane _2.
It is preferable to use fine particles of O ₃ (hematite), α-FeOOH (goethite) and Fe ₃ O ₄ (magnetite). The iron oxide fine particles are non-adhesive, and even if a thin coating film is formed on the surface of the hollow fiber membrane, the iron oxide fine particles can be peeled off very easily in the washing step and are commercially available, so that they can be easily obtained. Even with such iron oxide fine particles, 1
Fine particles having a size of μ or less are not preferable because the releasability decreases, and with iron oxide particles having a large particle size of 10 μ or more, even if a coating film is formed with the particles, the particles in the raw water having a relatively small particle size are used. There is a problem that iron oxide will pass through the coating film.

Next, the thickness of the coating film of the iron oxide fine particles will be described. The present invention is completely different in technical concept from the so-called precoat type filtration in which a filter aid is precoated on a conventional filter support. Therefore, the thickness of the coating film is made extremely thin as compared with the case of precoat filtration.

That is, in the conventional precoat type filtration, a precoat layer is formed on a filter support, and the insoluble substance is removed by volumetric filtration in the precoat layer. Therefore, the precoat layer can be volume filtered. For example, 10 mm
Although a relatively thick layer before and after is required, since the present invention merely prevents the insoluble substance that is difficult to peel off from directly adhering to the hollow fiber membrane surface, the thickness of the iron oxide fine particles is extremely high. It may be thin, and usually 100 μm or less can sufficiently achieve the purpose. The thickness of the coating membrane is 1 m ² of the surface area of the hollow fiber membrane.
This can be done by depositing 0.5 to 10 g of the iron oxide fine particles.

Next, when most of the insoluble substance contained in the raw water is iron oxide, when forming the coating film of iron oxide fine particles having good releasability in the present invention, iron oxide having good releasability from the outside is formed. Iron oxide contained in raw water can be used without adding fine particles.

That is, raw water containing iron oxide is filtered through the hollow fiber membrane as it is, and then the iron oxide is peeled from the hollow fiber membrane in the above-mentioned washing step. The iron oxide particles are aggregated and physically bonded to each other, and as a result, iron oxide fine particles having good peelability are formed. Therefore, the aggregated iron oxide thus obtained can be used as the iron oxide fine particles having good releasability used in the present invention.
Specifically, after stirring with the compressed air described above, a part of the cleaning waste water containing the aggregated iron oxide in the filtration tower is not blown, but a part thereof is left, and then the raw water inflow pipe 16
Water may be introduced from each of the hollow fiber membranes to allow water containing the aggregated iron oxide to pass through each hollow fiber membrane to form a coating film of the aggregated iron oxide. Alternatively, a part of the cleaning drainage may be separately provided in a water tank. Alternatively, the hollow fiber membranes may be coated by diluting appropriately with water and then again flowing this into the filtration tower 9 through the raw water inflow pipe 16.

A specific example in which a part of the agglomerated iron oxide described above remains in the filtration tower is as follows. Ie the first
As a method of, a method of injecting water from a water inlet pipe (not shown) connected to the raw water inflow pipe 16 and discharging a part of aggregated iron oxide from the air vent pipe 17 after stirring with compressed air Is. This makes it possible to remove relatively fine iron oxide in advance. As a second method, after stirring with compressed air, washing wastewater containing agglomerated iron oxide is allowed to settle for a certain period of time, and water is introduced from a water inlet pipe (not shown) provided in the lower part of the body of the filtration tower 9. A part of the aggregated iron oxide is discharged from the air vent pipe 17. In this case, the amount of residual iron oxide can be adjusted by changing the attachment level of the water inlet pipe provided in the lower part of the filtration tower body and the sedimentation time of the aggregated iron oxide. As a third method, after stirring with compressed air, washing wastewater containing agglomerated iron oxide is allowed to settle for a certain period of time, and an air inlet pipe (not shown) provided below the partition wall 10 of the filtration tower body More compressed air is introduced, and aggregated iron oxide is discharged from a drain pipe (not shown) attached to the lower part of the filter column body. Also in this case, the amount of residual iron oxide can be adjusted by changing the attachment level of the drain pipe.

<Effect> As described above, according to the present invention, water containing iron oxide fine particles having good releasability is previously passed from the outer side to the inner side of each hollow fiber membrane, and iron oxide fine particles having good releasability are provided on the surface of each hollow fiber membrane. Since it is intended to form a thin coating film of, and then to filter the raw water containing the insoluble substance through the coating film, even if the raw water contains an insoluble substance having poor peelability, Since the insoluble substance is not directly attached to the surface of the hollow fiber membrane and is captured by the coating film, almost all of the iron oxide fine particle coating film, which is easily peeled off in the washing step, is peeled off. It is possible to effectively prevent the conventional drawback that the insoluble substance is peeled off, and thus the initial differential pressure increases with each cleaning.

Further, when the present invention is used, for example, in the treatment of condensate in the cooling system of a boiling water nuclear power plant, foreign substances other than iron oxide will not be mixed in the cleaning wastewater, and therefore the radioactive waste of the cleaning wastewater. Without adversely affecting the processing system,
Also, the amount of iron oxide fine particles to be coated beforehand is extremely small, 0.5 to 10 g per 1 m ^{2 of the} surface area of the hollow fiber membrane,
The increase of solids in the washing wastewater is extremely small.

Examples will be shown below in order to clarify the effects of the present invention.

Example-1 Outer diameter 1.2 mm and inner diameter 0.
170 mm of 7 mm long 2.0 mm hollow fiber membranes are bundled in an outer cylinder of 25 mm diameter to form a hollow fiber module as shown in FIG. 1, and one hollow fiber module is placed in a filtration tower. Then, a small-scale experimental filtration tower was constructed according to the flow shown in FIG. 2, and the following experiments were conducted.

That is, ² g of Fe having a particle size of 1 to ³ μm / m ^{2 of the} hollow fiber membrane
Water in which ₃ O ₄ was dispersed was previously passed from the outside to the inside of each hollow fiber membrane to form a coating film of the iron oxide fine particles on the surface of each hollow fiber membrane. Then, the simulated condensate containing a relatively large amount of iron oxide hydroxide is obtained which is obtained by dipping the steel material in a water tank and passing a weak electric current, which is difficult to separate and easily raises the filtration differential pressure, and passes through the hollow fiber membrane formed with the coating film. Then, the iron oxide was filtered. The amount of iron oxide in the simulated condensate is 100
It was ppb.

When 8 g of iron oxide in the simulated condensate was filtered per 1 m ² of the filtration surface of the hollow fiber membrane, the increase in differential pressure was 0.5 kg / cm ² , but after that, it was washed by the usual method, and after washing, The range of increase in differential pressure recovered to the initial differential pressure. Further, after the washing, the same amount of Fe ₃ O ₄ as described above was coated, the same simulated condensate was filtered again, and the washing was performed again. As a result, the differential pressure rise after the washing was the same as the initial differential pressure, The initial differential pressure did not rise with each wash. FIG. 4 shows how the differential pressure rises during filtration in this example and how the differential pressure is recovered by washing. In the figure, A is a coating process of iron oxide fine particles, B is a filtration process, and C is a cleaning process.

Example-2 Using the same small-scale experimental filtration tower as in Example-1, the same simulated condensate as used in Example-1 was directly filtered without forming a coating film of iron oxide fine particles in the initial stage. Then, washing was performed by a conventional method, and peeling was performed by stirring with air to obtain washing wastewater containing agglomerated iron oxide.

Next, a part of the washing drainage is collected, the washing drainage is diluted with water, and the washed hollow fiber membranes are passed from the outside to the inside, and the surface of each hollow fiber membrane is coated with the aggregated iron oxide. Let The coating amount was ² g per 1 m ² of the hollow fiber membrane.

Next, the same simulated condensate containing 100 ppb of iron oxide as in Example-1 was passed through the hollow fiber membrane having the coating film formed thereon,
The iron oxide was filtered.

After that, as a result of repeating coating with such agglomerated iron oxide, filtration and washing, the range of increase in differential pressure during filtration and the manner in which the differential pressure was recovered by washing became as shown in FIG. In the figure, A is a coating process of agglomerated iron oxide, B is a filtration process, and C is a washing process.

Comparative Example Using the same small-scale experimental filtration tower as in Example-1, the same simulated condensate as used in Example-1 was filtered as it was without forming a coating film of iron oxide fine particles, and then washed by a conventional method. When a conventional filtration method is performed in which filtration and washing are simply repeated, such as performing the same simulated condensate again, the increase in the differential pressure during filtration and the manner in which the differential pressure recovers due to washing is It became as shown in FIG. In the figure, B indicates a filtering step and C indicates a washing step.

[Brief description of drawings]

1 is a sectional view showing a hollow fiber module used in the present invention, FIG. 2 is an explanatory view showing a flow of a filtration tower used in the present invention, and FIG. 3 shows a state of a hollow fiber membrane during filtration. It is an enlarged explanatory view shown. In addition, FIG. 4 and FIG.
[Fig. 6] Fig. 6 is a graph showing the range of increase in the differential pressure during filtration and the manner in which the differential pressure is recovered by washing in Example-1 and Example-2, respectively. Fig. 6 is an increase in the differential pressure during filtration in the comparative example. 7 is a graph showing how the differential pressure is recovered by the width and the washing, and in each of FIGS. 5 to 6, the vertical axis shows the differential pressure increase width and the horizontal axis shows the load iron amount. 1 ... Hollow fiber module, 2 ... Hollow fiber membrane 3 ... Outer cylinder, 4 ... Upper joint part, 5 ... Lower joint part, 6 ... Flow port, 7 ... Opening part, 8 ... Skirt part, 9 ... ... filtration tower, 10 ... partition plate 11 ... bubble distribution mechanism, 12 ... bubble distribution plate 13 ... bubble distribution pipe, 14 ... filtered water outflow pipe 15 ... compressed air inflow pipe, 16 ... raw water inflow pipe 17 ... Air vent pipe, 18 ... Drain pipe 19-24 ... Valve 25 ... Baffle plate, 26 ... Coating film 27 ... Insoluble substance

Claims (4)

[Claims] 1. A hollow fiber module, in which a large number of hollow fiber membranes are bundled, is arranged in a filtration tower, and raw water containing an insoluble substance is passed from the outside to the inside of each hollow fiber membrane to obtain an insoluble substance. In filtering the surface of each hollow fiber membrane, before passing the raw water, water containing iron oxide fine particles having good releasability is passed through the hollow fiber membrane, and the iron oxide fine particles are applied to the surface of each hollow fiber membrane. 2. A filtration method using a hollow fiber membrane, which comprises forming a thin coating film of, and then allowing raw water to pass through each hollow fiber membrane through the coating film. 2. The surface area of the hollow fiber membrane is 0.5 to 10 per 1 m ^2.
The method for filtering using a hollow fiber membrane according to claim 1, wherein a coating film of iron oxide fine particles having good releasability of g is formed. 3. The iron oxide fine particles having a good peeling property have a particle diameter of 1 to 1.
The filtration method using the hollow fiber membrane according to claim 1 or 2, which is one or more kinds of iron oxide fine particles selected from 0 µ of α-Fe ₂ O ₃ , α-FeOOH, and Fe ₃ O ₄ . 4. When most of the insoluble substances contained in the raw water are iron oxides, the iron oxides are filtered on the surface of each hollow fiber membrane, and the aggregated iron oxides obtained by peeling the iron oxides are removed. A filtration method using the hollow fiber membrane according to claim 1 or 2, which is used as iron oxide fine particles having good releasability.