JP2514933B2 - Method for cleaning hollow fiber modules - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention uses a hollow fiber module installed to remove a clad due to iron oxide contained in condensate of a thermal power plant, a nuclear power plant or the like. The present invention relates to a method for cleaning a hollow fiber module in a filtration tower when the hollow fiber module is contaminated with the iron oxide by continuing the filtration process.

<Prior art> As a method of treating condensate in a thermal power plant or a nuclear power plant, in recent years, a clad caused by iron oxide in condensate was first removed with a filtration tower using a hollow fiber module, and then A condensate treatment method has been proposed in which filtered water is treated with a mixed bed of a cation exchange resin and an anion exchange resin to remove impurity ions.

Explaining in more detail a filtration tower using the hollow fiber module, a hollow fiber module is formed by bundling a large number of hollow fibers having a large number of fine pores, and a large number of the hollow fiber modules are mounted in the filtration tower. External pressure type filtration, in which condensate is passed from the outside of each hollow fiber to filter iron oxide on the outside of each hollow fiber and the filtered water obtained from the inside is collected and discharged from the filtration tower, occupies the main stream. ing.

When the differential pressure of the filtration tower rises due to the continuation of such filtration, a gas such as air is introduced from below each hollow fiber module while the inside of the filtration tower is filled with water, and air bubbles are generated inside each hollow fiber module. A so-called bubbling step in which each hollow fiber flows in and vibrates each hollow fiber by the bubbles, or after performing the bubbling step, the filtered water existing above in the filtration tower is allowed to flow backward from the inside of each hollow fiber to the outside, if necessary. Washing is performed to remove iron oxide from the hollow fiber, washing is performed to obtain a washing drainage liquid containing a large amount of iron oxide, and the washing and the filtration are sequentially repeated to perform the treatment.

As described above, since the filter tower using the hollow fiber module directly filters the condensate with each hollow fiber, it is compared with the pre-coated filter tower using the filter aid such as the conventional fine powder ion exchange resin. In addition, the amount of solids contained in the cleaning effluent 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 precoating type filtration tower, the cleaning wastewater containing an overwhelmingly large amount of the used precoating agent than the iron oxide is discharged together with the iron oxide removed by filtration during the cleaning. Since the cleaning drainage in the filtration tower to be used does not contain such a used precoating agent at all, it has an advantage that the solid matter to be treated for radioactive waste can be significantly reduced.

<Problems to be Solved by the Invention> When the condensate is treated for a relatively long time in the filtration tower using the hollow fiber module as described above, even if the bubbling step or the backwashing is performed, the pressure difference is increased It may not return to the state.

The reason for this is that a small amount of iron oxide strongly adhered to the membrane surface is not removed even after the bubbling step or backwash, but remains on the membrane surface of the hollow fiber, and gradually accumulates.

Therefore, the hollow fiber module cannot be used again unless the iron oxide is contaminated by such a state, that is, the hollow fiber module contaminated with iron oxide is washed with an appropriate cleaning chemical solution.

A hollow fiber module contaminated with iron oxide
If it is washed with a reducing agent solution such as hydrosulfite, an oxalic acid solution, or a chemical solution such as a reducing acid or a chelating acid such as a citric acid solution, iron oxide firmly adhered to the film surface It can be dissolved and removed.

However, in a filtration tower that uses a hollow fiber module intended for the removal of iron oxide containing radioactive substances like condensate of boiling water nuclear power plants, the cleaning wastewater with the aforementioned chemical solution is the target of radioactive waste treatment, The reducing agent contained in the cleaning drainage, the salt produced by neutralizing the acid, and the like are not preferable in that they increase the solid matter in the radioactive waste treatment.

Therefore, it is possible to establish a cleaning method that effectively removes iron oxide strongly adhered to the membrane surface of the hollow fiber and does not increase solids other than the removed iron oxide in the cleaning drainage liquid. Is requested.

The present invention has been made in view of such problems in a filtration tower using a hollow fiber module, and an object thereof is a hollow fiber membrane that cannot be easily peeled off even after the bubbling step or backwashing. It is an object of the present invention to provide a method for cleaning a hollow fiber module, which is capable of effectively removing iron oxide strongly adhered to the surface and does not increase solid matters other than iron oxide in the cleaning drainage liquid.

<Means for Solving Problems> The inventors of the present invention conducted various experiments for cleaning the hollow fiber module contaminated with iron oxide, and found that the contaminated hollow fiber module was treated with a hydrogen peroxide solution or an ozone solution. It was found that the iron oxide strongly adhered to the membrane surface of the hollow fiber can be easily removed by carrying out the bubbling step after contacting with the iron oxide.

It was also found that the residual hydrogen peroxide and ozone in the cleaning waste water discharged by the cleaning can be easily decomposed by heat treatment or ultraviolet irradiation and do not increase salts at all.

The present invention is based on such knowledge, to form a hollow fiber module by bundling a large number of hollow fibers having a large number of fine pores,
A filtration tower comprising a configuration in which a large number of the hollow fiber modules are vertically installed at the lower part of a partition plate horizontally installed in the filtration tower, and a condensate containing iron oxide is passed through the hollow fibers from the outside to the inside. By cleaning the hollow fiber modules contaminated with iron oxide, the hollow fiber modules are brought into contact with a hydrogen peroxide solution or an ozone solution, and then a gas such as air flows in from below the hollow fiber modules. It is characterized by vibrating each hollow fiber in each hollow fiber module by the air bubbles generated by doing so to remove iron oxide from the membrane surface of each hollow fiber by peeling and removing it. The cleaning effluent is heated or irradiated with ultraviolet rays to decompose and remove hydrogen peroxide or ozone in the effluent.

<Operation> The present invention will be described in detail below.

The present invention does not remove the iron oxide firmly adhering to the membrane surface of the hollow fiber by dissolving it by using a reducing agent, a reducing acid or a chelating acid that has been conventionally used. By contacting the hollow fiber module with a hydrogen peroxide solution or an ozone solution, the iron oxide is transformed into a form that can be easily peeled off by bubble vibration, which is completely different from the conventional cleaning method. .

It is not clear yet why iron oxide strongly adhered to the film surface is transformed into a form that can be easily peeled from the film surface when brought into contact with a hydrogen peroxide solution or an ozone solution. It is a fact that iron oxide strongly adhered to the film surface easily peels off when contacted with a hydrogen peroxide solution or an ozone solution, as shown in Examples, and the effect of the present invention can be reliably achieved.

The concentration of the hydrogen peroxide solution or ozone solution used in the present invention needs to be at least 1% or more, and if the concentration is less than this, the iron oxide peeling effect is small, which is not preferable. Moreover, even if the concentration is higher than 5%, the peeling effect does not increase so much,
The concentration of the hydrogen peroxide solution or the ozone solution is 1 to 5% (wt%) because it only unnecessarily increases the processing cost.
It is desirable to set the range to.

Further, the contact time of the hydrogen peroxide solution or the ozone solution with the hollow fiber module needs to be at least 10 hours or more, and a contact time shorter than this is not preferable because the iron oxide peeling effect is small. Further, since the peeling effect of iron oxide reaches equilibrium within a contact time of 30 hours, the contact time is preferably in the range of 10 to 30 hours.

The present invention, by contacting a hollow fiber module contaminated with iron oxide with a hydrogen peroxide solution or an ozone solution inside or outside the filtration tower, and then vibrating each hollow fiber of the hollow fiber module by bubbles, The iron oxide is peeled off from the membrane surface of each hollow fiber, and an embodiment of the present invention will be described below.

The drawing is an explanatory view showing the flow of a filtration tower and a washing tank using an external pressure type hollow fiber module. In the filtration tower 1, a large number of hollow fiber modules 3 are hung vertically on a partition plate 2 provided inside the filtration tower 1. It is a thing. As shown in Japanese Patent Application No. 59-273579 previously disclosed by the applicant of the present invention, the hollow fiber module 3 bundles a large number of hollow fibers by opening the upper ends of the hollow fibers and closing the lower ends thereof. In addition, each hollow fiber module 3 has a skirt portion 4 at the lower end thereof so that air bubbles generated from the distributor 5 can be prevented.
At the lower end of the module 3 for receiving the air bubbles and passing the bubbles to the outer surface of each hollow fiber. When the condensate is filtered in the filtration tower 1, the condensate is introduced from the inflow pipe 6 attached to the lower part of the filtration tower 1, and the condensate is discharged from the through holes or the side portions of each hollow fiber module 3 into each hollow. It is introduced into the thread module 3, the iron oxide is filtered outside each hollow fiber, the filtered water inside each hollow fiber is collected above the partition plate 2, and the filtered water flows out from the outflow pipe 7. When the pressure loss increases due to the continuation of such filtration, the following bubbling step is performed.

That is, the water flow is interrupted, and condensate flows into the lower part of the partition plate 2 of the filtration tower 1 and air flows into the upper part of the partition plate 2 from the air inflow pipe 8A while being filled with the filtered water. The air rises in the form of bubbles from the distributor 5, and the raised bubbles flow into the inside of each hollow fiber module 3 through the through holes provided at the lower ends through the skirt portion 4 of each hollow fiber module 3 described above. , Each hollow fiber is vibrated, and the iron oxide adhering to the outer membrane surface of each hollow fiber is peeled off. The bubbles are discharged from the upper part of each hollow fiber module 3 and then discharged from the air vent pipe 17 attached to the upper part of the filtration tower 1.

After sufficiently vibrating each hollow fiber by the bubbles, the cleaning waste liquid containing a large amount of iron oxide flows out from the blow pipe 9 and is once received in the cleaning waste liquid tank 10, and the boiling water nuclear power plant In the case of the condensate treatment, the cleaning effluent in the tank 10 is transferred to the radioactive waste treatment system.

After performing such a bubbling step, or after backwashing if necessary after the bubbling step, the above-described filtration is continued again, but by repeating the filtration and the bubbling step, the membrane of each hollow fiber can be obtained. When iron oxide is strongly adhered to the surface and the pressure loss is not recovered so much in the above-mentioned cleaning and the filtration process is impaired, the following cleaning according to the present invention is performed.

That is, the upper end plate 11 of the filtration tower 1 is removed, and the partition plates 2 are lifted to the outside of the filtration tower and mounted in the cleaning tank 12 while the hollow fiber modules 3 are vertically installed.

Next, the cleaning tank 12 is driven by driving the pump 14 with a 1 to 5% (wt%) hydrogen peroxide solution which has been adjusted in advance in the chemical solution tank 13.
The hydrogen peroxide solution that has flowed in from the lower part of the above and passed through each hollow fiber is collected above the partition plate 2, and the overflowing hydrogen peroxide solution is circulated in the chemical solution tank 13.

In the present invention, it is sufficient to bring the hydrogen peroxide solution into contact with the hollow fiber module 3.
The drive of the pump 14 may be interrupted after the hydrogen peroxide solution is filled in the inside 12. Further, 15 is a heat exchanger provided for heating the hydrogen peroxide solution, and a heat medium such as steam 16 does not flow into the heat exchanger 15 except when the hydrogen peroxide is decomposed as described later.

Circulate or soak for 10 to 30 hours as above,
After sufficiently bringing each hollow fiber into contact with the hydrogen peroxide solution, the steam 16 flows into the heat exchanger 15 as a heat medium, and the pump 14 is driven to circulate while heating the hydrogen peroxide solution to about 80 ° C. To do.

The hydrogen peroxide is gradually decomposed by the heating circulation, and when the decomposition of the hydrogen peroxide is completed, the heating circulation is stopped and the partition plate 2 is installed while the hollow fiber modules 3 are suspended from the cleaning tank 12. It is lifted and mounted in the filtration tower 1, and then the upper end plate 11 is attached. Thereafter, the partition plate 2 is filled with pure water, filtered water, or condensate, which is raw water, below the partition plate 2, and air is introduced from the air inflow pipe 8A. Due to the inflow of the air,
In the same manner as described above, bubbles rise from the distributor 5, the bubbles flow into the inside of each hollow fiber module 3, vibrate each hollow fiber, and are easily separated from the membrane surface by the contact with the hydrogen peroxide solution. Remove the iron oxide that has become.

Next, if necessary, filtered water or pure water is press-fitted into the upper part of the partition plate 2 of the filtration tower 1 from the air inflow pipe 8B or another pipe, and the water is caused to flow backward from the inside to the outside of each hollow fiber to contain iron oxide. The cleaning drainage liquid flows out from the blow pipe 9, and the cleaning drainage tank
Get to 10.

A chemical tank for condensate treatment at boiling water nuclear power plants
A cleaning waste solution in which hydrogen peroxide in 13 is decomposed and a cleaning waste solution containing iron oxide in the cleaning waste solution tank 10 are transferred to a radioactive waste treatment system.

In the embodiment shown in the drawings, each hollow fiber module 3 is taken out from the filtration tower 1 and a separately provided cleaning tank 12 is used to remove iron oxide strongly adhered to the membrane surface that cannot be removed by normal cleaning. However, the installation of the washing tank 12 is omitted, and the hydrogen peroxide solution is supplied into the filtration tower 1 while the hollow fiber modules 3 are mounted in the filtration tower 1 to supply the hydrogen peroxide to the hollow fiber modules 3. It does not matter if the solution is contacted.

The same effect can be obtained by using a 1-5% (wt%) ozone solution instead of the hydrogen peroxide solution, and when decomposing hydrogen peroxide or ozone in the cleaning effluent, in addition to heating, the wavelength The same can be achieved by irradiation with ultraviolet rays around 260 nm.

<Effect> As described in detail above, according to the present invention, the iron oxide firmly adhered to the membrane surface of the hollow fiber, which cannot be easily separated by the mere vibration of bubbles or the reverse flow of gas, water, etc., can be easily separated. Can be made.

Further, the cleaning method of the present invention does not use any chemicals such as reducing agents and acids that increase solids, and hydrogen peroxide or ozone in the cleaning effluent discharged by cleaning is heated or irradiated with ultraviolet rays. Since it can be decomposed, solid matter is not increased even in the decomposition treatment.

Therefore, the cleaning method of the present invention is extremely effective in the case where the cleaning waste liquid must be further treated as radioactive waste, as in a boiling water nuclear power plant.

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

Example: A hollow fiber module with an inner diameter of 0.8 mm, an outer diameter of 1.2 mm, and 2000 hollow fibers of 1000 mm in length and having a diameter of 80 mm (total filtration area 7.6
One m ² ) was attached to the experimental filtration tower, and three of iron hydroxide, α-ferric oxide (α-Fe ₂ O ₃ ) and γ-iron oxide hydroxide (γ-FeOOH) were added to the condensate of the power plant. Synthetic water having 1 mg / l as a suspended solid added with various kinds of iron oxides was filtered at 1.75 m ³ / H as an external pressure type which passed from the outside to the inside of each hollow fiber.

After the filtration, the cycle of repeating vibration by bubbles and backflow of filtered water, and then filtering again was repeated, and the differential pressure at the beginning of water passage after 50 cycles was 1.25 kg / c.
It became m ^{2 at} 1.75m ³ / H.

Therefore, in the 51st cycle, a 5% by weight hydrogen peroxide solution was immersed in the contaminated module for 20 hours, and after that, washing was performed by vibration due to bubbles and backflow of filtered water. / cm ^{2 at} 1.75m ³ / H, the differential pressure recovered.

The above results are shown in Table 1 together with the differential pressure of the new module at the initial stage of water passage.

When the cleaning waste liquid discharged during the cleaning with the above-mentioned hydrogen peroxide solution was circulated and irradiated with ultraviolet rays having a wavelength of 260 nm for 5 hours, the hydrogen peroxide in the cleaning waste liquid could be almost completely decomposed.

[Brief description of drawings]

Drawing is an explanatory view showing a flow of a filtration tower and a washing tank showing an embodiment of the present invention. 1 ... Filtration tower, 2 ... Partition plate 3 ... Hollow fiber module, 4 ... Skirt part 5 ... Distributor, 6 ... Inflow pipe 7 ... Outflow pipe, 8 ... Air inflow pipe 9 ... Blow pipe, 10 ... Wash drainage tank 11 ... Upper end plate, 12 ... Cleaning tank 13 ... Chemical solution tank, 14 ... Pump 15 ... Heat exchanger, 16 ... Steam 17 ... Air vent tube

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-60-175504 (JP, A) JP-A-51-105988 (JP, A) JP-A-51-13391 (JP, A)

Claims (2)

(57) [Claims] 1. A hollow fiber module is formed by bundling a large number of hollow fibers having a large number of fine holes, and a large number of the hollow fiber modules are hung vertically at the bottom of a partition plate installed horizontally in a filtration tower. In cleaning the hollow fiber modules contaminated with iron oxide, the condensate containing iron oxide is filtered from the outside to the inside of each hollow fiber in the filtration tower, so that each hollow fiber module is peroxidized. The hollow fibers in each hollow fiber module are vibrated by the bubbles by being brought into contact with a hydrogen solution or an ozone solution, and then the gas generated by inflowing a gas such as air from below each hollow fiber module Method for cleaning hollow fiber module, characterized by removing iron oxide from the membrane surface 2. The cleaning of the hollow fiber module according to claim 1, wherein the cleaning waste liquid containing hydrogen peroxide or ozone is heated or irradiated with ultraviolet rays to decompose the hydrogen peroxide or ozone in the waste liquid. Method