JPS62250923A - Filtering method - Google Patents

Abstract

PURPOSE:To prevent a precoated layer from getting cracked and make clad removing percentage more than 90% by using a precoating material of mixing fiber of fixed percentage with weak acid cation exchange resin and anion exchange resin. CONSTITUTION:To powder ion exchange resin, a mixture of weak acid cation exchange resin and anion exchange resin, fiber is added at the ratio of more than 10wt% and less than 40wt% against powder ion exchange resin as precoating material, and is filtered. For instance, after carboxylic acid family cation exchange resin 11, amine family anion exchange resin 12 and acryl family fiber 13 are put at the ratio of 2:1:1 into precoating tank 10 with purified water and adding a high-molecular aggregating agent, floc mixed uniformly by a stirrer 14 and suitable for precoating is sent into a filter desalting device 7 through a valve 15 by a precoating pump 16, and filter element is precoated and filtered.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a liquid filtration method, and particularly to a filtration method suitable for filtering condensate water in a nuclear reactor.

[Conventional technology]

At nuclear power plants, salt filters are installed to purify condensate. Here, a fine powdered ion exchange resin is coated on an element made of nylon or stainless steel, and the crud in the water is removed.

The powdered ion exchange resin is a mixture of a cation exchange resin having a sulfonic acid group and an anion exchange resin having a quaternary ammonium group at a certain ratio. Shows extremely high filtration performance.

However, since such powdered ion exchange resins are disposable, they become low-level radioactive waste at nuclear power plants.

Incineration and thermal decomposition methods are being developed as treatment technologies for radioactive waste, but ion exchange resins, especially strongly acidic cation exchange resins with sulfonic acid groups (hereinafter referred to as sulfonic acid resins), are being developed. It is difficult to dispose of because it is difficult to decompose (abbreviated).

In order to completely solve this problem, we replaced the conventional sulfonic acid resin with a weakly acidic cation exchange resin with carboxyl groups (
The use of carboxylic acid resins (hereinafter abbreviated as carboxylic acid resins) is being considered. In other words, we focused on the fact that weakly acidic cation exchange resins such as methacrylic carboxylic acid resins and acrylic carboxylic acid resins are extremely easy to decompose.
It is being considered to mix these weakly acidic cation exchange resins and anion exchange resins at a certain ratio and use this mixture as a bricoat material for filter demineralizers.

[Problem that the invention seeks to solve]

The performance required for a filtration demineralizer is the following two points7.The first point is that the filtration life is long. That is, as the filtration time becomes longer, the amount of crud adsorbed and removed by the precoat layer increases, which causes clogging in the precoat layer and increases the filtration pressure difference. This differential pressure is a constant value (usually Id
1.75 kg/crn”), the powdered ion exchange resin used as the pre-coat material is backwashed and discarded, and replaced with new pre-coat material. Therefore, in order to reduce costs and waste generation, it is necessary to It is desirable that the pressure rise is slow, that is, the filtration life is long.The required performance for @2 is a high crud removal rate from the water to be treated, and a removal rate of 90 or higher is usually required. .

As a result of basic experiments, when a weakly acidic cation exchange resin is used, the filtration life is longer than the conventional weakly acidic sulfonic acid resin, which is a desirable result, but cracks occur in the precoat layer during the filtration process. , crud removal rate is 60-90
It was found that there was a problem in that it was unsuitable for use in a filtration demineralizer as it was.

An object of the present invention is to provide a filtration method that prevents cranking in the precoat layer and provides a crud removal rate of 90 mm or more.

[Means for solving problems]

The above objective can be achieved by adding fibers to the powdered ion exchange resin used by mixing weakly acidic cation exchange resin and anion exchange resin gold so that the proportion thereof is 10 wt% or more and 40 wt% or less. The amount of pre-coating of the above mixture is most preferably 1 kg or more and 3 kg or less per 1 m'' of filtered elm.

[Effect]

By adding 19wt1 or more of fiber to the powdered carboxylic acid resin, it is possible to prevent the occurrence of cracks and improve the crud removal rate. Further, if the fiber ratio increases and the ratio of carboxylic acid resin in the precoat layer becomes extremely small, the crud removal rate decreases again, so it is desirable that the fiber ratio is 40wt4 or less. In addition, since carboxylic acid resin is weakly acidic, it is necessary to thicken the precoat layer in order to obtain a high crud removal rate, and specifically, it is desirable to make the precoat layer k1kg/m" or more. However, the precoat layer Since the filtration life becomes shorter as the thickness increases, the precoat amount is preferably 3 kg/m2 or less.

〔Example〕

Weakly acidic cation exchange resins include carboxylic acid resins, chelating resins, and the like, and first, a case in which carboxylic acid resins are used will be described.

As carboxylic acid resins, methacrylic carboxylic acid resins and acrylic carboxylic acid resins, which have molecular structures as shown in Figure 2, are known, but the performance when these are used as precoat materials is Since they are equivalent, they will be collectively referred to as carboxylic acid resins below. Furthermore, so-called granular resins having a particle size of about 500 μm are known as carboxylic acid resins. However, such granular resins have large particle diameters, making them unsuitable for precoating, as well as insufficient filtration effects and low efficiency of ion exchange reactions, making them impractical.

Therefore, the carboxylic acid resin was completely pulverized and the average particle size was approximately 50 μm.
A powdered carboxylic acid resin of m is prepared, mixed with powdered anion exchange resin gold at a ratio of 2:1, and further added with a small amount of a polymer flocculant (polyacrylic acid amide, etc.), It was made into a pre-coated material. Using this, water including cladding was filtered. The results are shown in FIG. 3 in comparison with the case where a conventional sulfonic acid resin was used as the cation exchange resin. From this, the filtration differential pressure increases with the filtration time, but with carboxylic acid resins, the filtration differential pressure increases more slowly than with sulfonic acid resins, and the filtration life is about 1.
5 times (however, the filtration life is defined as the optimum filtration time or the amount of crud captured when the filtration differential pressure reaches 1.75 kg/cm''), and it was found that favorable results could be obtained.

However, the crud removal rate decreases with the filtration time, and with carboxylic acid resin, the filtration pressure difference is 1.75 kg/cm 2
By this time, the number of staff will be approximately 75, and it will not be possible to secure the 90 or more staff that is generally considered necessary.

It was found that the cause of this was that cracks were completely generated in the precoat layer as the filtration time passed. The details will be explained with reference to FIG.

Generally, after forming a precoat layer 2 with a thickness of 2 to 20 mm on the filtration element 1, the water to be treated 3 and filtration are performed. This precoat layer contracts as the filtering time passes, so cracks 4 occur as shown in FIG. 4(b).
Crud removal rate decreases. Such a phenomenon is also known for conventional sulfo/acid resins, and crack 4
Adding fiber is also known to be effective as a preventive measure! The results for the sulfo/acid resin in Figure 3 were also obtained with the addition of fiber). It is known that in conventional sulfonic acid resins, the fiber addition t is suitably 30 to QQwt, and preferably 50Wt4. Therefore, after mixing the carboxylic acid resin and anion exchange resin, we added acrylic fibers (about 10 μm in thickness and several 100 μm in length) so that the fiber ratio was 50 wt1, and added this to the precoat material. A filtration experiment was conducted using The results are shown in FIG. 5 in comparison with the case where no fiber was added.

From this, it was found that the addition of fibers could significantly improve the crud removal rate and also prevent the occurrence of cracks in the precoat layer.

However, even when the fiber ratio is 50wt4, which is considered the optimum for sulfonic acid resins, as is clear from Figure 5,
There is a problem in that a cladding removal rate of 904 or higher, which is generally considered necessary, cannot be achieved all the time. Therefore, the inventor clarified the cause of this problem and found a countermeasure.

In order to clarify the cause of cracks in the precoat layer when using Carbo7eil resin, we first investigated the cause of cracks in conventional sulfonic acid resins. As a result, it was found that the cause of crack generation was due to the shrinkage of the precoat layer 2, and that the cause of the shrinkage of the precoat layer 2 was a synergistic effect of the following two factors. In other words, the first factor is that the particle surface of ion exchange resins is negatively charged for cation exchange resins and positively charged for anion exchange resins, and electrical repulsion occurs in the precoat layer that uses a mixture of both. Due to the force, it forms a loose layer called a flock. However, when the cladding is adsorbed, the surface charge is canceled out, so the electrical repulsion force decreases, and the precoat layer contracts and becomes a dense layer. The second factor is that conventional sulfonic acid resins are shrinkable resins whose resin particles shrink when they adsorb cladding, and this also causes the precoat layer to shrink, causing cracks to occur. In this way, with conventional sulfonic acid resins, cracks occur due to a decrease in electrical repulsion when the cladding is adsorbed and the shrinkage of the resin itself, and as a way to prevent this, fibers are added. I found out that there is.

In contrast, it has been newly discovered that the crack generation mechanism is different in carboxylic acid resins. That is, the first factor described above (reduction in air repulsion) is exactly the same, but the second factor is different. In other words, the carboxylic acid resin is an expandable resin in which the resin particles do not contract but rather expand even when the cladding is adsorbed. Therefore, it was found that the second factor acts to alleviate the shrinkage of the precoat layer, and that the amount of shrinkage of the precoat layer is smaller in the carboxylic acid resin than in the sulfonic acid resin. For this reason, while the preferred ratio of fibers for sulfo/acid-based resins is 30 to 60 Wtl, we believe that carbo/acid-based resins may be able to prevent cracks from occurring in the precoat layer even with a lower fiber ratio. Ta.

Therefore, Figure 6 shows that the filtration experiment was conducted by changing the fiber ratio, and the filtration pressure difference in the precoat layer was 1.75 kg/cm.
” shows the crud removal rate as a function of the fiber ratio. With sulfonic acid resins, if the fiber ratio is less than 30wt4, cracks occur in the precoat layer and the crud removal rate drops sharply. On the other hand, with carboxylic acid resin, as expected, no cracks occur even when the fiber ratio is low, and the crud removal rate is 90 even with a fiber ratio of iQwt4.
It was confirmed that the value was 4.

On the other hand, even in the region where the fiber ratio is large, the crud removal rate decreases again as shown in FIG. This is because as the fiber ratio increases, the ratio of ion exchange resin having high filtration performance decreases. Further, in the case of sulfonic acid resin, the crud removal rate is less than 901 when the fiber ratio is 60 Wte12 or more, but in the case of carboxylic acid resin, the removal rate is less than 904 when the fiber ratio is 40 Wt4 or more. The reason for this is that sulfonic acid resins are strongly acidic resins and have a high ability to remove crud, so they can maintain the desired performance even if the fiber ratio increases slightly, whereas carboxylic acid resins are weakly acidic resins. Therefore, the ability to remove crud is somewhat low, and therefore the fiber ratio cannot be increased very much.

As mentioned above, it has been found that because the properties of carboxylic acid-based resins and sulfonic acid-based resins are different, the optimum amount of fiber added is also different. That is, it has been found that with carboxylic acid resin, if the fiber ratio is in the range of 10 to 40 wt4, a crud removal rate of 901 or more can be ensured, which is extremely preferable as a filtration demineralizer. Note that the fibers may be of any type, such as acrylic fibers, nylon fibers, vegetable fibers, carbon fibers, etc., and the thickness of the fibers is in the range of several μm to several tens of μm, and the length is in the range of several tens of μm to several mm. As long as it is within the range of , it is the same as before.

From the above, the optimal amount of fiber added has been clarified, but
As already mentioned, carboxylic acid resins are weakly acidic and therefore have the drawback of inherently low crud removal ability. In other words, as can be seen from Figure 6, in the case of carboxyl/acid resin, the fiber ratio is approximately 20 wt%, and the maximum removal rate is 934.
In contrast, for sulfonic acid resins, the maximum coefficient is 97. In order to investigate the reason for this in more detail, we investigated the distribution of cladding adsorbed within the precoat layer.

FIG. 7 shows the results, where the vertical axis shows the concentration of the adsorbed cladding, and the horizontal axis shows the depth measured from the surface of the precoat 120 in the direction of the filtration element 1. This shows that the sulfonic acid resin has a high ability to remove crud because it is a strong acidic resin, and most of the crud is adsorbed near the surface of the precoat layer 2. On the other hand,
In the case of the carboxylic acid resin, which is a weakly acidic resin, it was found that crud was adsorbed throughout the precoat layer, and a portion of the crud even reached the filter element 1. Based on this new knowledge, the inventor thought that the crud removal rate of carboxylic acid resin could be improved by increasing the thickness of the precoat layer.

Therefore, after mixing powdered carboxylic acid resin and powdered anion exchange resin at a ratio of 2:10, 20wt4 of acrylic fiber was added to prepare a precoat material, and the precoat material was applied onto the filtration element 1. 0.4 kg/cm” (-i that is, filtration element 1
Precoat material 0.4kg/m2) to 3kg/m”
The filtration performance at this time was investigated. Figure 8 shows the crud removal rate and filtration life as a function of the amount of precoat when the filtration differential pressure is 1.75 kg/cm''. The lifespan fr: 1 is standardized when precoated at 1 kg/m'', which is commonly used. From FIG. 8, it was found that the crud removal rate improved as the amount of glycote increased. Also, the normally required crud removal rate is 90
To obtain 4 or more, the precoat amount is 1 kg/cm2
You can see what is needed above. However, as the amount of precoat increases, the thickness of the precoat layer increases, which increases the pressure loss and shortens the filtration life. From the figure, it is desirable that the precoat amount is 3 kg/cm'' or less.

Although the above explanation has been given using carboxylic acid resin as an example, other cation exchange resins can give the same results as long as they are weakly acidic and expandable, and examples of such resins include chelate resins.

Example 1 This example purifies condensate of a boiling water reactor, and FIG. 1 shows the system used in this example.

The condensate that drives the turbine 5 and is recovered by the condenser 6 is
After being filtered in the filtration demineralizer 7, it is circulated to the nuclear reactor 9 via the demineralizer 8. The salt filtering device 7 is pre-coated with powdered ion exchange resin by the following method. That is, in a pre-coat tank 10 containing pure water, a carboxylic acid-based cation exchange resin 11, an amine-based anion exchange resin 12, and an acrylic fiber 13 having an average particle size of about 40 μm are contained in a weight ratio of 2:1:1. It will be introduced at Further 0.05~
After adding 1wt4 of the polymer flocculant, the mixture is uniformly mixed using a stirrer 14. As a result, a so-called floc suitable for precoating is formed, and this floc is sent via the pulp 15 to the precoat pump 16 and to the filtration demineralizer 7. The filtration demineralizer 7 has a nylon filtration element, in which the flocs are present at a rate of 2 per ml of the filtration element.
pre-coated at a rate of kg.

Afterwards, as a result of filtering the condensate using this system, the filtration life was approximately 1% longer than that of conventional sulfonic acid resins.
．． It was 5 times longer, and the crud removal rate was always 901 or higher.

As described above, according to this embodiment, since the filtration life is extended, the burden on the operator such as pre-coating operations can be reduced.

Example 2 The used precoat material generated in Example 1 was incinerated in an incinerator for miscellaneous solids provided in a boiling water nuclear power plant.

The temperature inside the incinerator is about 1000℃, and as a result of putting the used precoat material (a mixture of cation exchange resin 11, anion exchange resin 12, and acrylic fiber 13) into it, it is completely incinerated. And as exhaust gas, Co, , H, O
etc. occurred.

When conventional sulfonic acid resins are used, the resin contains sulfur, which releases H and S when incinerated.

Since corrosive gases such as SO3 are generated, there is a possibility that problems such as piping corrosion may occur. However, since the carboxylic acid resin etc. according to the present invention does not contain sulfur, it does not generate corrosive gas and can be easily incinerated. [Effects of the Invention] According to the present invention, the filtration theory Since the life of filtration in the salt chamber is extended, the burden on operators at power plants can be reduced, and waste disposal becomes easier.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a molecular structure diagram of a carboxylic acid resin, Fig. 3 is a diagram showing drawbacks of the conventional method, and Fig. 4 is a cross-sectional view of a precoat layer. , FIG. 5 is a diagram showing the effect of the present invention, FIG. 6 is a diagram showing the optimum fiber amount,
FIG. 7 is an explanatory diagram showing the cladding distribution in the precoat layer;
FIG. 8 is a diagram showing the optimum range of precoat amount. 1...filtration element, 2...precoat layer, 7.
・・Filtration demineralizer, 10・Precoat tank, 13・
...Acrylic fiber.

Claims (1)

[Claims] 1. As a pre-coat material used in a filtration demineralizer to purify nuclear reactor condensate, the fiber percentage is 10 wt% or more and 40 wt%
A filtration method characterized by using the following mixture of the fibers, a weakly acidic cation exchange resin, and an anion exchange resin.