JPH0226625A - Back washing method of hollow fiber membrane filter - Google Patents

Abstract

PURPOSE:To promote back washing efficiencies by detecting liquid level during back washing so that the liquid level in a shell does not fall below a predetermined level and supplying water into the shell based on signals of this liquid level or supplying water periodically thereinto by means of a timer. CONSTITUTION:A hollow fiber membrane filter is composed of a tube plate 3 supporting porous hollow modules 1, protection cylinders 4 suspended from the tube plate 3 to protect each of the module 1, a shell 6 covering around the hollow fiber membranes 2, provided with a liquid inlet 8, a vent 9, and a back washing water outlet 11, and a lid 5 which is provided with at least a nozzle 10 and open to the inside of the membranes 2. Air from an air blow-off port 17 is used as a means for back washing and during back washing liquid levels are detected by a liquid level switch 7 so that the liquid level in the shell 6 does not go down below a predetermined level, whereby liquid is supplied into the shell 6 based on the signal of the liquid level or liquid is supplied thereinto periodically by means of a timer having been set in advance. As a result, back washing efficiencies can be improved.

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 used for removing impurities in a liquid.

(Prior Art) Generally, a hollow fiber membrane is a hollow fiber membrane having an outer diameter of about 0.3 to 3 m and having fine pores, and can have a large membrane area per unit line area.

In addition, because of its small outer diameter and excellent pressure resistance, it can be used as a filtration device for precision filtration, ultrafiltration, and reverse osmosis to produce pure water in fields such as the electronics industry, medicine, and nuclear power.

It is widely used for wastewater treatment, etc.

By the way, finding an efficient backwashing method for such hollow fiber membrane filters is very important in expanding the range of applications of hollow fiber membrane filters, and various inventions and ideas have been developed. being done. For example, Japanese Patent Application Laid-Open No. 53-108882 discloses a method in which adhered fine particles are peeled off by backwashing with pressurized air and at the same time, the adhered fine particles are removed by vibrating a hollow fiber membrane. Also, JP-A-60-. Publication No. 19002 discloses a method in which adhered fine particles are peeled off by backwashing with pressurized air, and air for moving the hollow fiber membrane is generated from the side or below of the hollow fiber membrane to remove the adhered fine particles. .

(Problems to be Solved by the Invention) However, Japanese Patent Laid-Open Nos. 53-108882 and 60-19002 do not describe the behavior of the liquid level in the body. When backwashing is performed using these methods, a phenomenon occurs in which the liquid level in the body gradually decreases during backwashing. As a result, the upper part of the hollow fiber membrane module is exposed to the air, which not only halves the effect of vibrating the hollow fiber membrane with air, but also causes the detached adhering particles to remain in the protective cylinder, causing the hollow fiber near the upper part of the liquid to evaporate. This causes the phenomenon of re-adhering to the thread membrane. In addition, depending on the type of hollow fiber membrane, the hollow fiber membrane may be exposed to the air, which may cause deterioration of the hollow fiber membrane, leading to a reduction in backwashing efficiency.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a method for backwashing a hollow fiber membrane filter with improved backwashing efficiency.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides a tube plate that holds a porous hollow fiber membrane module, and a tube plate that protects each hollow fiber membrane module from the tube plate. With a protective tube and at least a liquid end,
It consists of a body part having a vent and a backwash water outlet nozzle and covering the outside of the hollow fiber membrane, and a lid part having at least a liquid outlet nozzle and communicating with the inside of the hollow fiber membrane, using air as a backwashing means. In a method for backwashing a hollow fiber membrane filter, the liquid level during backwashing is detected so that the liquid level in the body does not decrease below a certain level during backwashing, and the liquid is replenished according to instructions from this liquid level signal. mosquito,
Alternatively, the liquid is periodically replenished into the body by a preset timer.

(Function) When backwashing is performed using a hollow fiber membrane filter, the liquid level in the body gradually decreases. Therefore, a liquid level drop signal or a preset timer is activated to replenish the liquid to a constant liquid level in the protection cylinder to maintain the air pump state. By maintaining this constant liquid level, backwashing efficiency is improved.

(Example) An embodiment of the present invention will be described with reference to FIG.

In the figure, reference numeral 1 indicates a hollow fiber membrane module, in which a large number of hollow fiber membranes 2 are folded back into a 0-shape with both ends facing upward, and the upper backbone is fixed with resin. The hollow fiber membrane modules 1 are vertically installed in a liquid-tight manner from tube sheet 3 to tube sheet 3, and a protective cylinder 4 is attached to tube sheet 3 so as to cover each hollow fiber membrane module 1. A vent hole 16 is provided in the upper part of the protective tube 4. The hollow fiber membrane filter has a liquid inlet nozzle 8, a vent nozzle 9, a backwash water outlet nozzle 11, and a bubbling air nozzle 12.
The tube plate 3 and the hollow fiber membrane module 1 are covered by a body part 6 having a diameter and a lid part 5 having a liquid outlet nozzle 10. Further, since the body 6 is provided with a liquid level switch 7 that is activated by the liquid level within the body, reference numeral 11 is an air outlet provided in the bubbling air nozzle 12.

When backwashing the hollow fiber membrane 2, first the liquid outlet nozzle 10
Backwash water is passed through the hollow fiber membrane 2 from the upper part of the hollow fiber membrane module 1 and flows into the body 6 to fill the body 6 with water.
Maintain a constant water level within the tank.

Next, the air outlet 1 is passed through the bubbling air nozzle 12.
When air is blown into the body 6 from 7, the hollow fiber membrane 2 is vibrated by the action of the air, and impurities adhering to the surface of the hollow fiber membrane 2 are peeled off and backwashed. When the backwashing is finished, the backwash water mixed with impurities in the body 6 is discharged from the backwash water outlet nozzle. During backwashing, a bubbling operation may be performed while flowing backwash water.

When a backwash operation is carried out with such a hollow fiber membrane filter, initially the inside of the protection tube 4 becomes in a so-called air pump state due to the action of bubbling air bubbles 14, as shown in FIG. 15 is vigorously jetted out from the vent hole 16 of the protection tube 4, and the water inside the protection tube 4 is in a circulating state. As a result, the lower end of the upper part of the hollow fiber membrane module 1 where the hollow fiber membrane 2 is fixed with the resin, that is, the root part of the hollow fiber membrane 2, is cleaned and the hollow fiber membrane 2 is removed from the hollow fiber membrane 2 into the protection tube 4. The peeled adhering impurities will not stay and re-adhere to the hollow fiber membrane 2.

However, as time passes, the liquid level inside the body 6 gradually decreases, and the water that was spouting out vigorously from the vent hole 16 of the protective tube 4 gradually loses its force, and the liquid level decreases as shown in Figure 3. decreases.

In this state, the air pump action will no longer be exerted,
At the base of the hollow fiber membrane 2, the root portion is no longer cleaned, and adhering impurities separated from the hollow fiber membrane 2 remain in the protective tube 4 and re-adhere to the hollow fiber membrane 2.

This means that even if the air bubbling time (backwash time) is, for example, 30 minutes, the backwash effect disappears after the air pump state is lost due to a drop in the liquid level in the body 6. Not only is the backwashing time not effectively utilized, but the backwashing effect may even be counterproductive as described above.

This state of drop in the liquid level is detected by the liquid level switch 7, and undiluted solution or make-up water is supplied until the inside of the protective cylinder 4 returns to the air pump state.

This water supply operation makes effective use of the backwashing time during which the air pump condition is constantly maintained, improving backwashing efficiency. Improving backwashing efficiency not only contributes to extending the lifespan of hollow fiber membrane modules, but it is also particularly useful when used, for example, in the treatment of radioactive waste liquid and condensate at nuclear power plants, and reduces the burden on workers during periodic inspections. It also leads to a reduction in radiation exposure.

Next, a second embodiment of the present invention will be described using FIG. 4. Components that are the same as those shown in FIG. 1 of the present invention are designated by the same reference numerals.

In the figure, reference numeral 1 denotes a hollow fiber membrane module, in which a large number of hollow fiber membranes 2 are folded back into a 0-shape with both ends facing upward, and the upper backbone is fixed with resin. This hollow fiber membrane module 1 is constructed from a tube sheet 3 to a tube sheet 3.
A protective cylinder 4 is attached to the tube plate 3 so as to cover each hollow module 1. A vent hole 16 is provided in the upper part of the protective tube 4. The hollow fiber membrane filter has a liquid inlet nozzle 8, a vent nozzle 9, a backwash water outlet nozzle 11, and a bubbling air inlet nozzle 12.
The tube plate 3 and the hollow fiber membrane module 1 are covered by a body part 6 having a liquid outlet nozzle 10 and a cover part 5 having a make-up water inlet nozzle 13.

When a backwashing operation is carried out with such a hollow fiber membrane filter, initially, as shown in FIG. 15 is vigorously jetted out from the vent hole 16 of the protection tube 4, and the water inside the protection tube 4 is in a circulating state. As a result, the lower end of the part where the hollow fiber membrane 2 is fixed with the resin on the upper part of the hollow fiber membrane module, that is, the root of the hollow fiber membrane 2, is cleaned, and the attached impurities that have peeled off from the hollow fiber membrane 2 are removed into the protective cylinder. will not remain and re-adhere to the hollow fiber membrane 2.

However, as time passes, the liquid level in the body gradually decreases, and the water that was spouting out from the vent hole 16 of the protection tube 4 gradually loses its force, resulting in a state as shown in FIG. 3. When this happens, the air pump state is no longer maintained, and the root portion of the hollow fiber membrane 2 is no longer cleaned, and adhering impurities separated from the hollow fiber membrane 2 remain in the protective cylinder and re-adhere to the hollow fiber membrane 2.

This means that even if the air bubbling time (backwashing time) is, for example, 30 minutes, once the air pump status is lost due to a drop in the liquid level in the body, the backwashing effect disappears, and that time is not effectively utilized. Rather, as mentioned above, it is thought that the backwashing effect is actually the opposite effect.

By grasping the temporal characteristics of this state, make-up water is periodically and automatically supplied from the make-up water inlet pipe 13 through the make-up water inlet pipe 13 using a timer or an alternative control means until the state returns to the air pump state.

As a result, the air pump condition is always maintained and the entire backwashing time is used effectively, improving backwashing efficiency.

Improving backwashing efficiency not only contributes to extending the life of hollow fiber membrane modules, but it is also particularly useful when used, for example, in the treatment of radioactive waste liquid and condensate at nuclear power plants, and reduces the exposure of workers during periodic inspections. It also leads to reduction.

[Effects of the Invention] According to the present invention, the efficiency of backwashing can be improved, and the life of the hollow fiber membrane can be extended by improving the efficiency of backwashing.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a hollow fiber membrane filter showing the first embodiment of the present invention, and Figs. 2 and 3 are enlarged views of the main parts inside the body of the hollow fiber membrane filter showing the action of the present invention. 4th cross-sectional view shown as
The figure is a sectional view of a hollow fiber membrane filter showing a second embodiment of the present invention. DESCRIPTION OF SYMBOLS 1...Hollow fiber membrane module 2...Hollow fiber membrane, 3...Tube plate 4...Protection cylinder, 5...Lid part 6...Body part, 7
...Liquid level switch 8...Liquid inlet nozzle, 9...
Vent nozzle 10...liquid outlet nozzle, 11...backwash water outlet nozzle 12...bubbling air nozzle 13...makeup water inlet nozzle 14...air bubble, 15...water 16...vent Hole, 17... Air outlet box diagram Figure 1

Claims (1)

[Claims] A tube plate for holding a porous hollow fiber membrane module, a protection cylinder for protecting each hollow fiber membrane module from the tube plate, and nozzles for at least a liquid inlet, a vent, and a backwash water outlet. A backwashing of a hollow fiber membrane filter using air as a backwashing means, comprising a body part covering the outside of the hollow fiber membrane, and a lid part having at least a liquid outlet nozzle and communicating with the inside of the hollow fiber membrane. In the method, the liquid level during backwashing is detected so that the liquid level in the body does not fall below a certain level, and the liquid is replenished based on this liquid level signal, or the liquid is periodically replenished by a preset timer. A method for backwashing a hollow fiber membrane filter characterized by replenishing liquid into the body.