JPH04193332A - Apparatus for back-washing hollow yarn membrane - Google Patents

Abstract

PURPOSE:To reduce the damage of a membrane surface by dividing the operation at back-washing time, a clad generated in former stage is separated and kept, washing the clad with a diluted water in the next stage, and providing a tank to separate and store the clad generated in the former stage. CONSTITUTION:A storage part 9 holding a clad 7 settled at a lows part of a filter is provided and a dam 10 to allow the storage part 9 to work is provided, and a raw liquid inflowing pipe 11 is provided at an upper place than the storage part 9. In the back-washing by air bubbling in the state that the inside of the filter is fully filled with inflowing water, air is introduced from an air pipe 4 in a module for a constant time and the stuck substances on a hollow yarn membrane are separated. The air is discharged outside the system with vent, etc. On the other hand, the clad separated with the back-washing is isolated in the storage part 9 with naturally settling. Later, air is again introduced in the module and bubbling is carried out. After the back-washing is finished, the clad is conveyed from an outflowing pipe 13 to a clad liquid storage tank 14 outside the system. Thus, the damage of the membrane surface is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a backwashing device for a hollow fiber membrane filter used for purifying condensate of an atomic couplant.

[Conventional technology]

- In nuclear power plants, in order to suppress the rise in radiation levels, it is necessary to remove iron oxide components called crud, which are impurities in the water supply, in advance.

The cladding separation device is a desalination device filled with ion exchange resin,
A porous hollow fiber membrane filter is used in a filtration demineralizer that uses powdered ion exchange resin. A hollow fiber membrane filter is composed of a module in which several thousand hollow membranes with a diameter of about 111II are bundled, and each membrane has pores of 0.01 to 0.1 μm on the surface. The cladding is blocked at the membrane surface and only water passes through the pores.

In operation of this hollow fiber membrane filter, as with other filters, when the amount of crud deposit increases, the filtration differential pressure increases. When this happens, it is necessary to clean the cladding even during operation. Cleaning methods include a method of bubbling the deposits on the outer surface of the membrane with air bubbles and an air surge method of back-flowing high-pressure water from the inside of the membrane, each of which may be carried out singly or in combination. This air bubbling backwashing is usually performed with water in a filter container.

In this backwashing, membrane surface cladding is removed depending on the backwashing time. On the one hand, it is inevitable that the membranes will come into contact with each other as air bubbles rise inside a module containing several thousand members.

At this time, if the backwash liquid contains iron chloride, there is a concern that the membrane surface may be damaged upon contact.

Therefore, removal of deposits on the membrane surface within the module requires a method other than the conventional backwashing method with a cladding liquid.

[The problem that the invention attempts to solve]

In the above-mentioned conventional technique, surface damage to the hollow fiber membrane is not taken into account in the filter backwashing method, and there is a problem in that the damage due to deformation increases with the backwashing time.

The present invention aims to reduce membrane surface damage,
The goal is to adjust the concentration of crat in the backwash solution, which is the main cause of membrane damage.

An overview of hollow fiber membrane filters and the backwashing method will be shown below.

In Fig. 1, a filter 1 has a module 3 in which several thousand hollow fiber membranes 2 are fixed at the top and bottom in a cylindrical holder of about 150φ.
It is loaded with many books.

An air introduction pipe 4 for air bubbling is installed at the bottom of the filter. On the other hand, for air surge backwashing, there is a pipe 6 that can force-feed high-pressure water from the surge water storage tank 5 into the hollow fiber membrane. Regarding the backwashing method, especially air bubbling, the second
As shown in the figure, the cladding 7 adhering to the surface of the hollow fiber membrane 2 in the module 3 is separated by the shaking of the membrane caused by air bubbles 8 from below.

[Means to solve the problem]

In order to achieve the above objectives, we investigated the separation of deposits from the membrane during backwashing and the degree of damage to the membrane itself, and found that during backwashing, especially during air bubbling, the membrane sways due to air bubbles from below. The deposits are separated by contact between the membranes. On the other hand, when the membranes come into contact with each other, a crat acts as a contact material.

It was found that the membrane surface was damaged and the pores on the membrane surface were blocked.

Therefore, in order to prevent this membrane pore clogging, we need to adjust the crud content during air bubbling backwashing. Specifically, we divide the air bubbling backwashing process and isolate the crud from the previous stage by settling it at the bottom of the filter. In some cases, it is transferred to a storage tank outside the filter for separation. Afterwards, perform backwashing with a low concentration solution.

In the present invention, the cladding concentration, which causes membrane deformation that occurs during backwashing of a hollow fiber membrane filter, is reduced. This makes it possible to reduce deformation caused by clad particles between the membranes when the membranes come into contact with each other due to air bubbles.

The degree of influence of cladding on membrane deformation can be considered as follows. That is, as shown in FIG. 3, when the hollow fiber membrane 2 swings as the air bubbles 8 rise, it comes into contact with the adjacent membrane. When contact occurs underwater, almost no surface deformation occurs. If particles such as cladding are contained in the water, the particles will enter between the membranes, causing pressure on the membranes and roughening the surface due to displacement, and will also clog pores. The degree of influence of crat depends on the grain size of crat, but the largest factor is the crud concentration. This degree has a large influence when present at several hundred ppm.

〔Example〕

The present invention adjusts the crud concentration during backwashing in air bubbling backwashing. An example of this will be shown below.

<Example 1> The structure of a hollow fiber membrane filter suitable for the present invention is shown in FIG. A storage tank part 9 for holding the sedimented crud 7 is provided at the bottom of the filter, and in order to make this work, a weir 1o is provided, and the stock solution inflow pipe 11 is positioned above the storage tank part 9.

In this structure, in air bubbling backwashing, air is flowed into the module from the air pipe 4 for a certain period of time while the filter is filled with inflow water to separate deposits on the hollow fiber membranes. Air is released from the vent pipe 12 above the filter to the outside of the thread. On the other hand, the crud separated by backwashing is isolated in the storage tank 9 by natural sedimentation. After that, air is introduced into the module again to perform bubbling. When the backwashing is completed, the liquid is sent from the outflow pipe 13 at the bottom of the filter to the cladding liquid storage tank 14 outside the thread.

<Example 2> FIG. 5 shows a hollow fiber membrane filter having a system for separating the concentrated cladding liquid in the first stage of backwashing into a storage tank outside the filter fibers. The concentrated liquid after backwashing is temporarily stored in a storage tank 14 outside the thread. For the next backwash water, use the precipitated supernatant liquid from the storage tank, or
Alternatively, water 15 from another system flows in. At this time, the structure of the storage tank 15 is the same as that of the lower part of the filter, so that the inclined plate
It is also envisaged that 6 will be provided.

〔Effect of the invention〕

According to the present invention, it is possible to suppress a decrease in the amount of permeated water due to surface damage caused by backwashing of the hollow fiber membrane, so that the water permeability of the filter can be maintained and the life of the filter can be maintained for a long time.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of a hollow fiber membrane filter according to an embodiment of the present invention, Fig. 2 is a system diagram of a hollow fiber membrane filter according to another embodiment of the present invention, and Fig. 3 is an explanatory diagram of a hollow fiber membrane filter. , FIG. 4 is a front view of the hollow fiber membrane module, and FIG. 5 is an explanatory diagram of the situation in which membrane surface damage occurs during air bubbling. 13...outflow pipe, 14 cladding liquid storage tank.

Claims (1)

[Claims] 1. In a hollow fiber membrane filter that separates granular solids, the operation is divided during backwashing, the distant crud is separated in the previous stage, and washed with diluted water in the latter stage, A backwash hollow fiber membrane filter characterized by having a tank for separating and storing crud generated in the previous stage in a separate tank so as not to mix it into the backwash liquid. 2. The backwash hollow fiber membrane filter according to claim 1, wherein in the tank for separating or storing the cladding, a separation tank is provided below the container in which the filter is loaded, or another storage tank is provided outside the filter container. 3. In claim 1, in backwashing that performs air scrubbing by introducing air from the bottom of the membrane, when 50% or more of the adhered crud has been removed, the crud is once separated and then subjected to the next backwashing step. Backwash hollow fiber membrane filter device.