JPH03238083A - Filtering and desalting device - Google Patents

Abstract

PURPOSE:To contrive the reduction of the volume of radioactive waste and of the space required for installing a filtering and desalting device by providing a filtering layer consisting of hollow fabric membrane filter and a desalting layer consisting of ion-exchange fiber as a constituent in the same container. CONSTITUTION:There are provided a filter layer consisting of hollow fabric membrane filter 2 and a desalting layer 8 consisting of ion-exchange fiber as at least a constituent. The filter layer and the desalting layer 8 are received in the same container to effect filtration through the hollow fabric membrane 2 and remove ionic components through the ion-exchange fiber. As a result, since the ion-exchange rate is large to improve water quality and the lifetime of the desalting layer can also be extended, a contrivance can be made of a way to reduce the volume of radioactive waste and the space required for installing the filtering and desalting device. The simplification of the device can also be contrived from the aspects of its operation. Moreover, this device is applicable not only to the field of nuclear power but also to the field requiring the use of a highly pure water, e.g. the water treatment in electronic industry, drug manufactures and hospitals.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is directed to an apparatus 1 for obtaining highly purified water required in nuclear power generation, electronic industry, pharmaceutical industry, etc., particularly for turbine circulating water inside a nuclear power plant. The present invention relates to a device for filtering and desalinating condensate, particularly for a BWR (boiling water) type nuclear power plant.

[Conventional technology] Condensate, which is the turbine circulating water inside a BWR nuclear power plant, contains solid suspended matter called cladding, which is mainly composed of iron oxide and iron hydroxide, as well as silica, carbonate ions, metal salts, etc. It is included. Therefore, in order to circulate the condensate again into the reactor, it is necessary to remove these floating substances, salts, etc. from the condensate in advance.

Conventionally, as a method for purifying condensate, a method of adsorbing and removing solid suspended matter and salts in condensate using a disposable ion exchange resin has been common. However, because it is disposable,
There are problems in that it is expensive and leads to an increase in the amount of radioactive waste, so recently many places are considering using backwashable hollow fiber membrane filters to filter condensate. .

[Problem to be solved by the invention] A condensate desalination system using a hollow fiber membrane filter, which replaces the early disposable ion exchange resin method, has shown good results as a condensate purification method in BWR nuclear power plants. It's starting to get worse. However, in this method, solid suspended matter in condensate is removed using a hollow fiber membrane filter device, and then residual ionic components are removed using an ion exchange demineralization tower. However, when using a hollow fiber membrane, Because the required membrane area of hollow fiber membranes is large, a considerable number of hollow fiber membrane filtration towers are required, and another ion exchange desalination tower is also required, so installing a filtration device requires more effort than conventional methods. There was a problem in that it required installation space.

In addition, in order to reduce the installation space of the purification equipment, we have developed a “filtration and desalination equipment” that can filter and desalinate condensate in the same tower.
(Unexamined Japanese Patent Publication No. 62-83003) has been proposed. This is to fill the empty space around the hollow fiber membrane filter of a filtration device that uses a hollow fiber membrane filter with ion exchange resin, etc., but the ion exchange resin etc. is taken out each time the hollow fiber membrane filter is backwashed. After temporary storage, it is necessary to refill the device after cleaning, which has the drawback of extremely poor workability. In addition, we have developed a "filtration desalination device element" that directly connects a packed column of ion exchange resin to the downstream side of a hollow fiber membrane filter (Japanese Patent Laid-Open No. 64-67206).
has also been proposed, and an attempt has been made to solve the problems encountered when cleaning conventional hollow fiber membrane filters, but in this case, an improvement is made in that it does not require the removal and refilling of ion exchange resin, etc. during cleaning operations. However, in terms of the volume occupied by the filtration equipment, simply integrating the current hollow fiber filtration tower and ion-exchange resin desalting tower does not lead to a reduction in the size of the equipment, but is an improvement in the current step. is desirable.

[Means for Solving the Problems] An object of the present invention is to provide a filtration/desalination device that includes a filtration layer made of a hollow fiber membrane filter and a desalination layer having at least one component of ion exchange fibers. , the filtration layer and the desalting layer are housed in the same container, and filtration with a hollow fiber membrane and removal of ionic components by the ion exchange fibers are performed, but the device is an over-desalination device. This is achieved by

In the method of passing the raw solution to be treated in the present invention, a small amount of ion exchange fiber is passed from the filtration layer consisting of a hollow fiber membrane filter to the desalination layer (which is one component), or it is passed from the desalination layer to the filtration layer. Either method is fine, but the former is preferable for water treatment at nuclear power plants.

The shape of the filtration device in the present invention may be such that the desalting layer having at least one component of the ion-exchange fibers and the filtration layer consisting of a hollow fiber membrane filter are located in series, but the device occupies a small volume. Therefore, it is preferable that the two be housed in the same container without any special inlet/outlet, connecting piping, etc. being used between them.

The ratio of the filtration layer to the desalting layer in the present invention is arbitrary, but considering the balance between the processing flow rate and ion exchange capacity, the volume ratio is 40:60 to 95:5, preferably 60.
:40-90:10 is preferable.

Membrane materials for the hollow fiber membrane filter in the present invention include:
The type is not particularly limited as long as it has a pore form that can filter out solid suspended matter such as crud and metal salts in condensate, but preferably a polyester having excellent durability as a hollow fiber membrane. Preferred are acrylonitrile, polyolefin, polysulfone, polyvinyl alcohol, cellulose acetate, polyamide, and fluorine-based polymers such as polyvinylidene fluoride, tetrafluoroethylene, and ethylene-tetrafluoroethylene copolymer. More specifically, the polyacrylonitrile contains at least 90 mol% of acrylonitrile, preferably 95 to 1
00% and a vinyl compound having copolymerizability with respect to the acrylonitrile: 10 mol% or less, preferably 0 to 5 mol%
It is an acrylonitrile homopolymer or an acrylonitrile copolymer consisting of. The above-mentioned vinyl compound may be any known compound having copolymerizability with acrylonitrile, and is not particularly limited. Preferred copolymerizable components include acrylic acid, itaconic acid, methyl acrylate, methyl methacrylate, and acetic acid. Examples include vinyl, sodium allylsulfonate, and sodium p-styrenesulfonate. Examples of the polyolefin include homopolymers such as ethylene, propylene, 4-methylpentene-1, vinylidene fluoride, and vinyl acetate, or copolymers of two or more thereof. Examples of polysulfone include polysulfone and polyethersulfone.

The hollow fiber membrane in the present invention includes a precision filtration membrane, an ultrafiltration membrane,
Any type of reverse osmosis membrane may be used, but for water treatment in nuclear power plants, the pore size is 0.001 to 1μ, preferably 0.001μ.
01~0. It is 5μ. The dimensions of the hollow fiber membrane are arbitrary, but if it is too thin, it will be difficult for water to flow, and if it is too thick, the container will become too thick.
μ ~ 3 mm, preferably inner diameter 100 μ ~ 2 m
m, and the film thickness is 20 μm to 1 mm.

Although the shape of the hollow fiber membrane filter in the present invention is not particularly limited, for example, it may be of a type with one end pulled out or a type with both ends pulled out.

The desalting layer in the present invention needs to be filled with ion exchange fibers or a composite and/or mixture of ion exchange fibers and ion exchange resin to remove residual ionic components in the filtered water. Since the ion exchange fiber is fibrous, it has a larger specific surface area than conventional granular ion exchange resins, so the ion exchange rate is significantly higher, and the volume of the desalting layer can be reduced. In particular, when considering applications for filtration of nuclear power plant condensate, the use of ion exchange fibers significantly reduces the size of the desalination layer compared to when conventional granular ion exchange resins are used.
This is convenient for use inside a nuclear power plant where the installation area and allowable space are limited, and this has great benefits.

The composition of the desalting layer is not particularly limited as long as it includes ion exchange fibers as one component, but examples include cation exchange fibers, anion exchange fibers, a mixture of cation exchange fibers and anion exchange fibers, and cation exchange fibers and anion exchange fibers. Mixing of fiber and cation exchange resin, mixture of cation exchange fiber, anion exchange fiber and anion exchange resin, mixture of cation exchange fiber, anion exchange fiber, cation exchange resin and anion exchange resin, cation exchange fiber, cation exchange resin and anion exchange Mixing of resins, mixing of cation exchange fibers and anion exchange resins, mixing of anion exchange fibers, cation exchange resins and anion exchange resins, mixing of anion exchange fibers and cation exchange resins, and mixing of chelate exchange fibers or chelate exchange resins with these. Examples include a mixture of these, and a combination of two or more of these. Among these, a composite in which the mixing of cation exchange fibers and anion exchange fibers and the mixing of cation exchange resins and anion exchange resins are performed upstream and the mixing of cation exchange fibers and anion exchange fibers is downstream is particularly preferred in terms of water purity.

The ion-exchange fibers used in the present invention include polystyrene-based ion-exchange fibers such as multifilamentary sea-island composite fibers in which a polystyrene component having a cation exchange group, an anion exchange group, or a chelate exchange group is used as a sea component, and a reinforcing polyolefin is used as an island component. , polyacrylonitrile-based ion-exchange fibers, polyvinyl alcohol-based ion-exchange fibers, cellulose-based ion-exchange fibers, etc., but polystyrene-based ion-exchange fibers, which have high acidity and basicity and excellent durability, are particularly preferred. used.

Examples of the ion exchange resin in the present invention include those obtained by introducing a cation exchange group, an anion exchange group, or a chelate exchange group into a styrene divinylbenzene copolymer.

In the present invention, the cation exchange group includes a sulfonic acid group, a phosphonic acid group, and a carboxylic acid group, and a sulfonic acid group is preferable. Examples of anion exchange groups include primary to tertiary amino groups and quaternary ammonium groups, with quaternary ammonium groups being preferred. As the chelate group, iminodiacetic acid group,
Examples include an iminodipropionic acid group, a polycarboxylic acid group, a peptide group, a β-diketone group, a pyridine group, a dithiocarbamate group, and an iminodiacetic acid group is preferred.

The shape of the ion exchange fiber of the present invention is (but not limited to)
For example, short fibers having a diameter of 500 microns or less, preferably 1 to 100 microns, and a fiber length of 100 mm or less, preferably 10 microns to 10 mm, are used.

The shape of the ion exchange resin of the present invention may be granular or powder, but from the viewpoint of pressure loss etc.
00μ grains are preferred.

Examples will be shown below, but the invention is not limited thereto.

[Example] FIG. 1 shows an example of a filtration and desalination apparatus according to the present invention. Condensate is supplied from side port 1 of the filtration device,
It permeates into the internal pores of the hollow fiber membrane from the outer periphery of the porous hollow fiber membrane 2 having micropores on its surface. The bundle of hollow fiber membranes is adhesively fixed on the upper end plate 3 and the lower end plate 4, and the internal holes of the hollow fiber membranes are opened so that the permeate can be taken out. The permeate that has passed through the hollow fiber membrane 2 is led to a permeate reservoir 6 either directly from the upper end plate 3 or from the lower end plate 4 through the central water collection pipe 5 . The permeate from the hollow fiber membrane, that is, the filtrate, passes through a stainless steel wire mesh 7 and a desalting layer 8 to remove residual metal ions, carbonate ions, and silica, and then passes through a stainless steel wire mesh 9 to condensate from an outlet 10. returned to the line.

The filtration and desalting device has a cylindrical shape of 10 cmφ×100 cm, of which 80% is a hollow fiber membrane and 20% is a desalting layer.

The hollow fiber membrane had a length of 80 cm, an inner diameter of 300 μm, and an outer diameter of 400 μm, and 12,000 hollow fibers were bundled together.

The amount of permeated water is 1300β/hr. The desalting layer is a mixture of cation exchange fiber/anion exchange fiber (1/1) 30
part is downstream, and 70 parts of the cation exchange resin/anion exchange resin mixture (1/1) is configured to be upstream.

The filtration desalination experiment was carried out using ferric hydroxide (Fe(OH)3)1
Water containing 0 ppm (in terms of iron) and NNaC1101)p was used. The flow rate was kept constant at 13006/h, and the differential pressure was measured. Regarding the permeated water, we used a commercially available membrane filter (0.1 μm), a cation exchange filter paper (RX-1, CPl, manufactured by Toshi), and an anion exchange filter paper (manufactured by Toshi, RX-1, CPl).
A filter with one layer of RX-1, AP-1) was installed, and the ferric hydroxide and Na"CI- that leaked and were captured on the membrane filter and filter paper were analyzed using atomic absorption spectrometry and ion chromatography. Quantitated.

As a result, compared to the initial differential pressure of 0.5 kg/cut, the time required for the pressure to rise by 0°3 kg/crl was 8 hours, and the differential pressure returned to the original level after backwashing, and there was no change even if the operation was repeated. There were hardly any. On the other hand, the concentration of ferric hydroxide 1 and Na+CI- was less than O, ippm, and the treatment could be carried out for 30 hours at that concentration.

Applying these results to an actual atomic couplant, it would be calculated that backwashing would be performed approximately once every 300 days, and that the desalination layer would not need to be regenerated for three years, even taking into account seawater removal.

[Comparative Example] The same experiment was carried out in the same container as in the example, with the hollow fiber membrane intact and the desalting layer filled with granular ion exchange resin (cation exchange resin: anion exchange resin-1:i).

Although the differential pressure and the ferric hydroxide concentration were the same as in the example, the Na'C1 concentration was as high as 0.5 to 1 ppm, and the concentration increased in about 25 hours.

[Effects of the Invention] Since the filtration desalination device of the present invention uses ion exchange fibers as one of the constituent elements of the desalination layer, it not only increases the ion exchange rate and improves water quality, but also extends the lifespan of the desalination layer. Since it can be extended, the volume of radioactive waste can be reduced, and the installation space for the filtration and desalination equipment can be reduced.

Therefore, it is suitable for condensate purification in nuclear power plants.

Also, as mentioned earlier, backwashing of hollow fiber membranes is carried out ↑ to 2 times per year.
It was found that it is sufficient to regenerate the desalination layer once every three years, which simplifies the operation of the equipment.

Furthermore, it can be used not only in the nuclear field, but also in fields that require highly purified water, such as water treatment fields such as the electronic industry, pharmaceutical industry, and hospitals.

[Brief explanation of drawings]

FIG. 1 is a sectional view schematically showing an embodiment of the filtration and desalination apparatus of the present invention. In the figure, 1... Inlet, 2... Hollow fiber membrane, 3... Dobe end plate,
4... Lower end plate, 5... Center water collection pipe, 6... Permeated water pool, 7... Stainless wire mesh 8... Desalination layer,
9...Stainless steel wire mesh, 10...Exit is shown, respectively.

Claims (1)

[Claims] (1) A filtration/desalination device equipped with a filtration layer consisting of a hollow fiber membrane filter and a desalination layer containing at least one component of ion exchange fiber, wherein the filtration layer and the desalination layer are placed in the same container. 1. A filtration/desalination device housed in a filtration/desalination device, which performs filtration with a hollow fiber membrane and removal of ionic components with the ion exchange fiber.