JPS63171605A - Carbon dioxide cleaning method for hollow yarn membrane filter - Google Patents

Abstract

PURPOSE:To safely remove the deposits on the surfaces of hollow yarn membranes, by feeding water into which carbon dioxide is force-fed to filter surfaces on which particles stick from the inside thereof and stripping the deposits by the gas bubbles generated when the carbon dioxide-contg. liquid permeates the membranes. CONSTITUTION:The carbon dioxide from a carbon dioxide cylinder 15 is previously force-fed into a carbon dioxide force feeding tank 14 and is dissolved therein and such soln. is circulated in the hollow yarn membrane filter as back washing water from the inside of the hollow yarn in the case of back washing said filter in order to remove the clads sticking to the outside surfaces thereof. A pressure drop is generated during the flow through the membranes and the gas bubbles are formed by the dissolved carbon dioxide in the soln. according to the pressure difference between the inside and outside of the membranes. The deposits are stripped by such gas and the clads are simultaneously dissolved by the acidic liquid.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for cleaning hollow fiber membrane filters used for purifying condensate in nuclear power plants.

[Conventional technology]

In order to prevent increases in radiation levels at nuclear power plants, it is necessary to remove impurities in condensate, such as iron oxide components called crud and various dissolved ions, in advance, and a filtration demineralizer is used as a removal device.

Desalters etc. are v1f! has been done. In the filtration demineralizer, a rod-shaped element is precoated with powdered ion exchange resin, and the cladding is captured in the precoated portion.

However, this method has problems such as frequent operations such as pre-coating operations, short backwashing frequency, and above all, a large amount of waste resin is produced. On the other hand, a hollow fiber membrane filter is available as a method that does not use a precoating aid. This filter is composed of a module with a hollow membrane with a diameter of approximately 100 ml and several thousand water bundles, and the surface of each layer is coated with 0.01 to 0.0 ml of water.
There are two types of membranes: precision filtration membranes with pores of 1 μm and ultrafiltration membranes with even smaller pores.

This hollow fiber membrane module is suitable for separating crud from water, but like other separation devices, if there is a lot of deposits, the filtration differential pressure will increase. Needs to be washed. Cleaning methods include bubbling the deposits on the outer surface of the membrane with air bubbles;

There is a method of back-flowing water from inside the membrane, which can be carried out either alone or in combination. However, if the particle size of the deposit is small and the components are adsorbent, they may remain on the membrane surface even after cleaning. It will be done.

As a cleaning method when the membrane itself is contaminated in this way, it is possible to use a cleaning solution that dissolves the deposits, such as an acidic solution or a complexing agent solution. However, it is said that the atomic couplants currently in use cannot be used due to the generation of chemical waste. As an alternative to this, the patent application filed earlier in 1986-
Specification No. 226784 is mentioned. Here, a carbon dioxide-containing liquid is bubbled from the outer surface of the membrane instead of an acidic liquid to improve the solubility of deposits. Although this invention also has great effects, the present invention is also effective as an alternative to the water permeation method from the inner surface of the membrane.

In other words, the cladding clogging the pores of the membrane is attempted to be removed by the action of gasifying the carbon dioxide gas-containing liquid from within the membrane as it permeates through the membrane.

[Problems to be Solved by the Invention] The above-mentioned conventional technology has a problem in that it is difficult to safely remove deposits on the surface of the hollow fiber membrane.

An object of the present invention is to provide a method for removing deposits on a membrane surface by the foaming effect of carbon dioxide flowing from the inside into carbon dioxide gas.

[Means for solving problems]

The above purpose is to separate the solid matter adhering to the surface of the hollow fiber membrane filter by changing the partial pressure of the carbon dioxide gas dissolved in the solution to form gas bubbles, thereby peeling off the adhering material. This is achieved based on the principle that it is possible.

[Effect]

Carbon dioxide gas is dissolved and dissociated in the liquid as follows.

α COz + HzO−+ HzCOa ”(1)〈− According to equation (1), carbon dioxide gas is dissolved in proportion to carbon dioxide partial pressure Pcoz with absorption coefficient α.Furthermore, as shown in equation (2), dissolved carbonate Hzcoδ is Dissociates into H+ and bicarbonate ion HCOa- with a first dissociation constant of 1.Furthermore, (3
), HCO3− dissociates under the second dissociation constant of 2.

Therefore, as the partial pressure of carbon dioxide increases, the amount of carbon dioxide dissolved in the solution increases in proportion to it, and at the same time, the pH
decreases.

The state when the cladding is peeled off and dissolved using this reaction will be explained with reference to FIG. The cladding 2 adheres to the outer surface of the hollow fiber membrane 1 during filtration. When this is backwashed, a pressure loss occurs while the backwash water in which carbon dioxide gas is dissolved passes through the pores 3 of the membrane, and the dissolved carbon dioxide gas becomes gas bubbles at the membrane outlet. This gas allows the deposits to be removed and the acidic liquid dissolves the cladding at the same time.

〔Example〕

The device configuration when the present invention is applied to a hollow fiber membrane filter is shown in FIG. 1. The device body 6 is a container with cylindrical upper and lower flanges, and the hollow fibers are fixed to the upper flange 7 inside the cylinder. A module 8 is installed, which is a bundle of . The module is provided with a jacket 9 to prevent the membrane from flowing. Raw water 10 enters the apparatus through a lower flow pipe 11, removes solids as it permeates from the outside of the hollow fiber membrane, passes through the inside of the membrane, and exits from the upper flow pipe. In such an apparatus structure and purification system, if solid content in the raw water accumulates on the outer surface of the membrane, the resulting pressure loss will increase, making it impossible to operate the purification apparatus. Therefore, it is necessary to remove this deposit as necessary. This is an operation called backwashing.The usual method is to remove deposits by a combination of methods such as bubbling air from the bottom of the device and further circulating backwash water from within the membrane.

On the other hand, in the present invention, a carbon dioxide gas pressure injection tank 14 is provided outside the device.
is installed. This press-in tank is equipped with a press-in system 16 using a carbon dioxide gas cylinder 15, a press-in water supply pipe 17, a system 18 for introducing pure water into the press-in tank, and a pump 19. A predetermined amount of carbon dioxide gas is pressurized and dissolved in a carbon dioxide gas injection tank, and this solution is distributed from inside the hollow fiber. Pressure loss occurs while flowing through the membrane,
Carbon dioxide in the solution changes to carbon dioxide gas depending on the pressure difference between the inside and outside of the membrane. This gas helps remove deposits;
It is also necessary to perform normal air bubbling during or before backwashing.

Next, we will show the results of an experiment on the amount of carbon dioxide gas at the membrane outlet using water injected with carbon dioxide gas. Figure 3 shows the outline of the equipment used. 20. It consists of a carbon dioxide gas injection device 21 and a carbon dioxide gas collector 22. Pure water with a certain amount of carbon dioxide dissolved in it is sent through the filter, and the carbon dioxide generated from the membrane is measured using a collector above the filter. The measurement conditions varied with the amount of permeated water in order to change the pressure loss during membrane permeation. The results are shown in FIG. 4, where the horizontal axis shows the pressure difference ΔP between the membrane inlet and outlet, and the vertical axis shows the amount of carbon dioxide gas generated Cot. It can be seen from the figure that the amount of Co1 is proportional to ΔP. Therefore, in order to diffuse carbon dioxide gas from water where the amount of dissolved carbon dioxide gas is constant, it is sufficient to increase the amount of water that permeates through the membrane.

Next, the effect of cleaning using the backwashing method of the present invention using a filter with cladding is shown in FIG. 5. The experimental device used was the carbon dioxide gas production measuring device shown in FIG. 4. In the experimental method, cladding was attached to the hollow fiber membrane, and changes in the amount recovered by various cleaning methods were determined. The air surge method (A) is a normal method for permeating water from inside the membrane to the outside of the membrane. (B)
and (C) are the carbon dioxide injection water permeation method of the present invention, and the amounts of permeated water are different. As shown in the same table, (B) and (
C) has a higher recovery rate than (A).

It had an excellent removal effect.

〔Effect of the invention〕

According to the present invention, the cladding that blocks the membrane pores of the hollow fiber can be effectively removed by the peeling effect and dissolution effect of gas bubbles.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of a hollow fiber membrane filter cleaning device according to an embodiment of the present invention, Fig. 2 is an explanatory diagram of a hollow fiber membrane filter cleaning method of the present invention, and Fig. 3 is an explanatory diagram of a hollow fiber membrane filter cleaning device of the present invention. Fig. 4 is a diagram of the relationship between the amount of carbon dioxide gas generated and membrane pressure loss, and Fig. 5 shows the conventional backwashing method and It is a comparison diagram of the cleaning effect with the method according to the invention. 2...Clad.

Claims (1)

[Claims] 1. In a backwashing method for a hollow fiber membrane separator that separates fine particles, adhering substances are removed by introducing water pressurized with carbon dioxide gas from the inside of the filter surface to which particles have adhered. A method for cleaning hollow fiber membrane filters with carbon dioxide gas, which is characterized by dissolving.