JPH01254208A - Method for backwashing hollow yarn membrane filter equipment - Google Patents

Abstract

PURPOSE:To efficiently perform backwash by injecting foams into the title equipment and generating a circulation flow in a filter module in the case of backwashing the hollow yarn membrane filter. CONSTITUTION:At a time of backwashing of a hollow yarn membrane filter equipment 1, firstly the filtrate reservoir 2 of a vessel containing a hollow yarn membrane is pressurized and the filtrate existing in this part is allowed to permeate by a method reverse to the processing of filtration. Then foams 12 are injected into the protection pipes 5 toward every one piece of a hollow yarn membrane filler module 4 from a foams injection line 8 provided to the lower part of a raw liquid reservoir 1 of the above vessel. The foams are discharged through a vent hole 7 provided to the upper part of the protection pipes 5. At this time, liquid is accompanied with the foams 12 raised through the gaps between the protection pipe in the protection pipes 5 and the module 4 by air lifting effect. Therefore the solid substance removed by backwashing is prevented from being settled but discharge through the vent hole 7.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method for backwashing a hollow fiber membrane filter device used for purifying cooling water in a nuclear power plant.

(Prior Art) Currently, in nuclear power plants, especially boiling water reactor plants, hollow fiber membrane filter devices are widely used as cooling water purification devices.

Hollow fiber membrane filters have the advantage that a compact processing device can be constructed because the membrane area per unit sound can be increased. In addition, it has excellent features such as the quality of the treated water is stable and good, it can be regenerated by backwashing, and there is no need for filtration aids, so there is no secondary waste.

By the way, in such a hollow fiber membrane, as the filtration time passes, the fine particles to be treated are captured and concentrated on the membrane surface, and the filtration performance gradually decreases, and the resistance when permeating through the membrane increases, resulting in a difference in filtration. The pressure may increase or the processing flow rate may decrease.

In such a situation, gas or liquid is introduced inside the hollow fiber membrane to permeate from the inside to the outside of the hollow fiber membrane, and at the same time, the gas or liquid is introduced from the inside of the hollow fiber membrane storage container to the outside from the side or bottom. A large number of air bubbles are ejected toward the hollow fiber membrane to agitate and vibrate the liquid in the container containing the hollow fiber membrane, thereby performing backwashing of the hollow fiber membrane filter, which removes fine particles adhering to the membrane surface. It is being said.

FIG. 1 is a diagram illustrating the structure of a hollow fiber membrane filter device. An example of the backwash operation will be explained in more detail with reference to FIG. First, the liquid reservoir 2 of the hollow fiber membrane storage container is pressurized, and the liquid in this area is allowed to permeate from the inside to the outside of the hollow fiber membrane, that is, in the opposite direction to the filtration direction. This results in
Solids trapped in the hollow fiber membrane filter are removed from the filter.

The water that has passed through the hollow fiber membrane and flowed into the stock solution reservoir 1 of the hollow fiber membrane storage container is discharged from the container vent 6 provided in the stock solution reservoir 1 to the outside of the container.

Next, bubbles 12 are ejected into the protective tube 5 toward each hollow fiber membrane filter module 4 from a bubble ejection line 8 installed below the stock solution reservoir 1 of the hollow fiber membrane storage container.

The air bubbles 12 are discharged to the outside of the protective tube from the vent hole 7 in the upper part of the protective tube 5, and are roughly discharged to the outside of the container from the container vent 6 of the stock solution reservoir 1 of the hollow fiber membrane storage container.

At this time, the bubbles 12 rising through the gap between the protective tube in the protective tube 5 and the hollow fiber membrane filter module 4 entrain the liquid due to the air lift effect. After the entrained liquid flows out from the vent hole 7 at the top of the protection tube 5 together with the gas, it is separated into gas and liquid on the outside of the protection tube 5, and only the liquid descends outside the protection tube 5 and exits from the bottom of the protection tube 5. flows into the protection tube 5,
The circulating flow again ascends between the hollow fiber membrane filter module 4 and the protective tube 5. This circulation flow is schematically shown in the second
As shown in the figure.

Due to the air lift effect caused by the bubbles rising inside the protection tube 5, the solids removed from the hollow fiber membrane filter during backwashing are prevented from settling downward, and are roughly carried upwards from the vent hole 7 to the protection tube 5. discharged outside. Therefore, if this circulating flow is maintained, the liquid in the stock solution reservoir 1 will be mixed uniformly, and the solid content will not be concentrated only in the protection tube 5.

By the way, the backwashing effect depends on the flow rate of the liquid flowing back from the inside to the outside of the hollow fiber membrane. Therefore, the container vent 6 must be installed at an appropriate distance below the lower end surface of the tube plate 3 to which the hollow fiber membrane filter module 4 is attached. Therefore, immediately after the start of backwashing, the liquid level outside the protection tube 5 is at the lower end position of the container vent 6. However, when the gas ejected from the bubble ejection line 8, passed through the gap between the hollow fiber membrane filter module 4 and the protection tube 5, and discharged from the vent hole 7 at the upper part of the protection tube is further discharged from the container vent 6, The liquid in 1 is accompanied. This tendency is particularly noticeable in the case of gas discharged from the vent hole 7 near the container vent 6. Therefore, the amount of liquid in the stock solution reservoir 1 gradually decreases, and the liquid level outside the protective tube 5 in the stock solution reservoir 1 moves further below the lower end position of the container vent 6.

When the amount of liquid in the stock solution reservoir 1 decreases, the amount of liquid flowing out from the vent hole 7 of the protection tube 5 along with the gas decreases, so the circulating flow amount decreases, and eventually the liquid no longer circulates. When the circulation flow ceases, the solids removed from the hollow fiber membrane filter by backwashing as described above are concentrated in the gap between the protection tube 5 and the hollow fiber membrane filter module 4.

After backwashing is completed, when the backwash water in the stock solution reservoir 1 is discharged, the solid denominator that re-adheres to the hollow fiber membrane filter module 4 depends on the solid content concentration in the backwash water; As the solid content becomes concentrated and backwashing is repeated, a large amount of solid content will adhere to the hollow fiber membrane filter module. If the number of adhering needles increases, problems such as a reduction in the backwashing effect and failure to discharge backwash water may occur, which may shorten the service life.

(Problems to be Solved by the Invention) The present invention has been made in view of the above-mentioned circumstances, and its purpose is to uniformly mix the liquid in the device and to clean it inside the protective tube when backwashing the hollow fiber membrane filter device. This prevents liquid with high solids content from accumulating in the tank, thereby extending the life of the hollow fiber membrane filter without causing a large amount of solids to re-adhere to the hollow fiber membrane filter module when backwash water is discharged. .

[Structure 1 of the Invention (Means and Effects for Solving the Problems) The above object is to supplement the amount of liquid discharged together with the bubbles when they are discharged from the device in the above-mentioned backwashing method by some method. ,
This is achieved by keeping the liquid level within the device constant.

That is, the present invention provides a method for backwashing a hollow fiber membrane filter device in which a protective tube with a vent hole in the upper part is provided for each hollow fiber membrane filter module, in which a liquid or gas is caused to flow back into the hollow fiber membrane filter and at the same time It is characterized by ejecting air bubbles to generate a circulating flow that rises through the gap between the hollow fiber membrane filter module and the protective tube and descends on the outside of the protective tube, and continues the circulating flow while keeping the liquid level in the device constant. The present invention relates to a backwashing method for a hollow fiber membrane filter device.

In the present invention, as described above, the liquid level is always kept constant by compensating for the decrease in the amount of liquid in the device. will not flow out, and the phenomenon of no circulating flow occurring within the device will not occur. Therefore, in the present invention, the solid content is not concentrated between the protection tube and the hollow fiber membrane filter module, and even if the number of backwashing increases, the backwashing effect does not deteriorate as in the conventional case.

(Example) Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram for explaining the structure of the hollow fiber membrane filter device as described above, and this device has the structure and functions as described above. An embodiment of the present invention will be explained using this device.

When water is purified using this device, as the filtration time elapses, solids are trapped on the surface of the hollow fiber membrane filter, and the filtration performance gradually decreases. Backwash there.

Backwashing is first performed using the conventional operating procedure. That is, first, the liquid reservoir 2 of the hollow fiber membrane storage container is pressurized, and the liquid in this area is transferred from the inside of the hollow fiber membrane to the outside, that is, from the inside of the hollow fiber membrane to the outside.
Permeate in the opposite direction of filtration. The water that has passed through the hollow fiber membrane and flowed into the stock solution reservoir 1 of the hollow fiber membrane storage container is discharged from the container vent 6 provided in the stock solution reservoir 1 to the outside of the container.

Next, air bubbles are ejected into the protective tube 5 from the air bubble ejection line 8 installed below the stock solution reservoir 1 of the hollow fiber membrane storage container toward each of the seven hollow fiber membrane filters 1-4. . These air bubbles generate a circulating flow within the apparatus as described above (see FIG. 2), and are finally discharged from the container vent 6 to the outside of the container.

As the bubbles are discharged, the liquid in the stock solution reservoir 1 is discharged along with it, so that the liquid level in the stock solution reservoir 1 is lowered. Therefore, the same amount of water as the amount of liquid discharged from the container vent 6 is injected into the stock liquid reservoir 1 from the liquid to be treated inlet 10.

In this way, the backwashing effect when backwashing is compared to the conventional method,
That is, the comparison was made with a case where the same operation was performed without replenishing the amount of the discharged liquid. The results are shown in FIG.

In FIG. 3, the solids recovery rate is the ratio between the amount of solids in the backwash water and the amount of solids captured by the hollow fiber membrane filter immediately before backwashing. Further, in the figure, a line connecting triangles represents the embodiment of the present invention, and a line connecting circles represents the conventional example.

As is clear from the figure, in the conventional backwashing method, the recovery rate decreases with the number of times of backwashing, whereas in this example, the recovery rate hardly decreases even if the number of backwashes increases. Furthermore, when we finally disassembled the device and observed the hollow fiber membrane filter module, we found that a large amount of solid matter had adhered to the comparative example, but only a small amount of solid matter had adhered to this example. Ta. This is because in this example, the liquid in the container was mixed uniformly due to the circulating flow inside and outside the protective tube, and also because the highly concentrated liquid was discharged from the container vent 6 and the same amount of water as the discharged amount was newly generated. This is because the concentration of backwash water in contact with the hollow fiber membrane filter module 4 in the protection tube was lower than that in the comparative example. In this example, the amount of backwash water increased due to the water injected during backwashing was 10 to 20% of the total amount.

Although water was injected in the above embodiment, the liquid discharged from the container vent may be injected again instead of water.

In this case, the same effect can be obtained without increasing the total number of backwash water droplets. Furthermore, in order to prevent the liquid from flowing out from the container vent along with the gas, when blowing out bubbles, the container vent 6 is closed and the tube sheet vent 9 is opened, so that only the gas is discharged from the tube sheet vent 9. has exactly the same effect as 1
be qed.

[Effects of the Invention] As explained above, according to the backwashing method of the present invention, the circulating flow generated inside and outside the protection tube can be maintained until the end of backwashing, so that the liquid inside the device can be mixed uniformly. This prevents liquid with a high solid content concentration from accumulating only in the gap between the protective tube and the hollow fiber membrane filter module. Therefore, when discharging backwash water, a large amount of solid matter does not adhere to the hollow fiber membrane filter module and cause problems such as a reduction in the backwashing effect or failure to discharge backwash water, and the hollow fiber membrane filter You can extend your life.

[Brief explanation of the drawing]

Fig. 1 is a diagram explaining the structure of a hollow fiber membrane filter device that has been used conventionally and is also used in the present invention, and Fig. 2 is a schematic diagram of the circulation flow generated inside and outside the protective tube in Fig. 1. , FIG. 3 is a diagram comparing the solid content recovery rate between the backwashing method of the present invention and the conventional backwashing method. 1... Raw solution reservoir 2... Furnace solution reservoir 3... Hollow fiber membrane filter module is installed on tube plate 4.
... Hollow fiber membrane filter module 5 ... Protection tube 6 ... Container vent 7 ... Protection tube vent hole 8 ... Bubble ejection line 9 ... Tube sheet vent 10 ... Liquid to be treated inlet Also backwash water outlet 11...Treatment liquid outlet 12...Bubbles (8733) Agent Patent attorney Yoshiaki Inomata (Idiot)
1 person) Figure 1↑ σ~12 Figure 5i-2

Claims (1)

[Claims] (1) In a backwashing method for a hollow fiber membrane filter device in which a protection tube with a vent hole at the top is provided for each hollow fiber membrane filter module, liquid or gas is allowed to flow back into the hollow fiber membrane filter and air bubbles are removed from the device. It is characterized by ejecting the liquid to generate a circulating flow that ascends through the gap between the hollow fiber membrane filter module and the protective tube and descends on the outside of the protective tube, and continues the circulating flow while keeping the liquid level in the device constant. Backwashing method for hollow fiber membrane filter equipment.