JPH039795B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improvement on the conventional ion exchange filtration method in which a filter element is precoated with a particulate ion exchange resin and a liquid containing impurities is passed through the precoat layer for treatment. Conventionally, it has been used to simultaneously remove undissolved substances such as colloidal substances and suspended substances along with ions in liquids in condensate systems and pure water systems of thermal power plants and nuclear power plants, or in drainage systems with relatively low ion concentrations. In this case, the ion exchange filtration method is used. Conventional ion exchange filtration method has a particle size of 2 to 250μ
A tube made of a mixture of fine particles of positive and negative ion exchange resin in the range of 200 to 3000 yen is formed using a stainless steel wire mesh, and a tube made by wrapping a thread made of nylon or polypropylene around the top surface of a support. The treatment is performed by pre-coating the filter element and passing a liquid containing impurities through the pre-coat layer, but this can cause cracks in the pre-coat layer, deteriorating the quality of the treatment liquid, or causing the pre-coat layer to deteriorate. Because it is too dense, it has the disadvantage that pressure loss increases quickly and throughput is small. Therefore, in recent years, it has become possible to pre-coat a mixture of fine particulate positive and anionic ion exchange resins and ion exchange fibers by mixing fine particulate positive and anionic ion exchange resins with ion exchange fibers, or to pre-coat a mixture of fine particulate positive and negative ion exchange resins and ion exchange fibers. It has been proposed to further overcoat polyacrylonitrile fibers on the precoat layer of a mixed positive/anion ion exchange resin to increase the strength of the precoat layer and thereby prevent the occurrence of the cracks. However, although both methods can achieve the purpose of preventing cracks from occurring in the precoat layer, they have the following drawbacks. First of all, the former method is problematic in terms of cost, considering that the pre-coat layer is disposable, as ion-exchange fibers are relatively expensive.Also, when pre-coating the mixture, fine particles of both positive and negative substances are added to the water. The ion exchange resin and ion exchange fibers are dispersed and this dispersion is passed over a filter element, but the ion exchange fibers form an aggregate in which the ion exchange fibers are intertwined to some extent in the dispersion, and the aggregate is used as a core and the surrounding area is dispersed. Since flocs with many particulate ion-exchange resins attached to the filter element are formed, the dispersion liquid does not have a uniform concentration, making it difficult to form a precoat layer of uniform thickness on the filter element. The porosity of the material is not constant, and dense parts and rough parts tend to occur. Therefore, there is a disadvantage that undissolved substances such as colloidal substances and suspended substances are likely to leak. In addition, in the latter method, undissolved substances with a relatively small particle size pass through the upper precoat layer of polyacrylonitrile fibers as they are and are captured by the lower precoat layer of fine particulate ion exchange resin. When processing a liquid containing many small undissolved substances, the upper precoat layer does not work effectively, and as the liquid continues to flow, the lower precoat layer is compacted and the voids become smaller. This has the disadvantage that the pressure loss increases quickly. The present invention provides an improved method of the ion exchange filtration method that does not have these drawbacks, and aims to increase the throughput by minimizing the increase in pressure loss in the precoat layer, and furthermore, it is possible to increase the throughput by minimizing the increase in pressure loss in the precoat layer. The purpose is to further improve the liquid quality of the processing liquid by forming a uniform pre-coat layer without any oxidation. That is, in the present invention, when removing impurities from a liquid, particles with a diameter of 2 to 2 are placed on a filter element.
250μ fine particle ion exchange resin and thickness 2~
A method for removing impurities from a liquid, characterized by precoating a layer of a mixture of rod-shaped polyacrylonitrile fibers with a length of 200μ and a length of 250 to 1000μ, and passing the impurity-containing liquid through the precoat layer. be. The present invention will be explained in detail below. The present invention involves precoating a mixture of particulate ion exchange resin and rod-shaped polyacrylonitrile fibers, and the precoating method involves dispersing the particulate ion exchange resin and rod-shaped polyacrylonitrile fibers in water and mixing them well. , the slurry of the mixture is passed over the filter element to pre-coat it to a predetermined thickness. In the present invention, a mixture of particulate ion exchange resin and rod-shaped polyacrylonitrile fibers is formed as a single precoat layer, so two layers, the polyacrylonitrile fiber layer and the particulate ion exchange resin layer as described above, are formed. The drawbacks of conventional methods for this are that undissolved substances with relatively small particle sizes are concentrated and trapped in the lower layer, or the lower layer is consolidated and the porosity decreases, resulting in a sudden increase in pressure loss. This does not occur, and the increase in pressure loss due to continued liquid flow is gradual, and therefore the throughput can be increased. In addition, the polyacrylonitrile fiber used in the present invention has a rod-like shape, and has the following properties that cannot be achieved with curly fibers used as conventional precoating materials or irregularly shaped fibers obtained by crushing. It has an effect. That is, the rod-shaped polyacrylonitrile fiber used in the present invention has long cellulose with a thickness of 2 to 200 μm,
It is obtained by cutting into a predetermined length of 250 to 1000μ, but if such rod-shaped polyacrylonitrile fibers are mixed with particulate ion exchange resin and precoated in the shape of a filter screen to form a precoat layer. The rod-shaped polyacrylonitrile fibers form a vertical, horizontal, and diagonal skeletal structure in the precoat layer, which not only prevents cracks from occurring in the precoat layer but also makes it difficult for the entire precoat layer to be consolidated. Therefore, even if the voids formed during precoating continue to pass through the liquid, they remain the same size, making it possible to increase the amount of undissolved substances trapped, and also to moderate the increase in pressure loss. can significantly increase the throughput. Note that when curly or irregularly shaped polyacrylonitrile fibers are used, the above-described skeletal structure cannot be formed within the precoat layer, and therefore the above-described effects cannot be achieved. Also, during pre-coating, since the polyacrylonitrile fibers are rod-shaped, they do not get entangled in water, and fine particulate ion exchange resin does not adhere to the fibers, which is similar to what was seen when using ion exchange fibers. No flocs are formed, so the concentration of the dispersion can be made uniform, and therefore a precoat layer of uniform thickness can be formed on the filter element, and no part of the precoat layer can be formed. Also, the sizes of the voids formed can be made equal. As mentioned above, the rod-shaped polyacrylonitrile fiber used in the present invention has a thickness of 2 to 200 μm and a length of 250 μm.
-1000μ is used, but if the thickness is less than 2μ, the voids formed will be too small, which is undesirable, and if the thickness is 200μ or more, the voids formed will be too large, which is undesirable. Also the length
If the length is less than 250μ, the voids formed will be too small, and if the length is more than 1000μ, the fibers will tend to settle in the dispersion when forming the precoat layer, forming a uniform precoat layer. This is not preferable as it makes it difficult to do so. In the present invention, it is usually preferable to use a material with a thickness of around 20 μm and a length of around 500 μm, and the ratio of thickness to length is 1:15 to 1:15.
It is preferable to use a rod-shaped one with a diameter of about 1:30. In addition, when using the fibers, select any thickness and length that are within the range described above, and make sure that all the rod-shaped polyacrylonitrile fibers used in the mixture have the same thickness and length. This is preferable because the size of the voids formed in the precoat layer becomes constant. Next, to explain the particulate ion exchange resin used in the present invention, the particulate ion exchange resin used in the conventional ion exchange filtration method with a particle size of 2 to 250μ can be used as is; It is preferable to use one with a diameter of 10 to 80μ. The types of particulate ion exchange resins are cation exchange resins and anion exchange resins when simultaneously removing ions such as cations and anions as well as undissolved substances such as colloidal substances and suspended substances in liquids. An anion exchange resin is used when a mixture of the following is used and the main purpose is to remove undissolved substances in the liquid. Generally, undissolved substances in a liquid are anionically charged, so a precoat layer made of a mixture of particulate anion exchange resin and rod-shaped polyacrylonitrile fibers is sufficient to remove the undissolved substances. can achieve the purpose. Next, to explain the mixing ratio of particulate ion exchange resin and rod-shaped polyacrylonitrile fibers, the larger the ratio of particulate ion exchange resin, the more
It is suitable when the particle size of the undissolved substances present in the liquid to be treated is small, and the smaller the proportion of the particulate ion exchange resin, the smaller the voids formed. It is suitable when the voids are large and therefore the particle size of undissolved substances present in the liquid to be treated is large. Therefore, the mixing ratio can be arbitrarily adjusted depending on the particle size of the undissolved substances present in the liquid to be treated, and this point is also one of the advantages of the present invention. In the case of curly or irregular shapes, it is difficult to adjust the size of the voids by changing the mixing ratio, and it is similarly difficult to adjust the size of the voids when using ion exchange fibers. As described above, in the present invention, the mixing ratio of the particulate ion exchange resin and the rod-shaped polyacrylonitrile fibers is arbitrarily adjusted according to the particle size of the undissolved substance to be removed from the liquid to be treated. Even if the amount of fine particulate ion exchange resin is increased, or even if the rod-shaped polyacrylonitrile fiber is excessively increased, the intended purpose of the present invention cannot be achieved. It is preferable that the mixing ratio of the acrylonitrile fibers is 2:8 to 8:2 by weight, and the mixing ratio is determined within this range depending on the particle size of the undissolved substance in the liquid to be treated. As explained above, in the present invention, since no cracks occur in the precoat layer, the processing liquid and liquid quality are good, and the processing amount for the predetermined precoat amount is larger than that of the conventional method, so running costs can be reduced. Furthermore, when the present invention is used to treat condensate or wastewater containing radioactive materials from a nuclear power plant, the amount of waste precoat material can be reduced relative to the predetermined amount of treatment, and the cost of waste treatment can be reduced accordingly. can be reduced. Examples will be described below to make the effects of the present invention more clear. Example 1 The compressibility of the precoat layer was compared between a mixed precoat layer of the rod-shaped polyacrylonitrile fiber and particulate ion exchange resin of the present invention and a conventional precoat layer of particulate ion exchange resin using the following experimental method. In other words, an acrylic resin column with an inner diameter of 25 mm
A 40 x 250 mesh screen is provided, each 30 mm pre-coat layer is formed on the screen, and the pre-coat layer is obtained by passing pure water containing no undissolved substances through the pre-coat layer and changing the water flow rate. Measure the thickness and pressure loss, and use the following formula:
The average pore radius of the precoat layer at each water flow rate was calculated, and the results are shown in FIG. So ² = ε ³ / (1-ε) ²・1/K・△P・A・gc/μ・qf・L ……(1) γp=2ε/(1−ε)・1/So ……( 2) In equations (1) and (2), So: Specific surface area per unit volume (cm ² /cm ³ ) ε: Porosity K: Carman's constant ≒ 50 μ; Fluid viscosity coefficient (g/cm・S ) qf: Flow rate (cm ³ /S) L: Thickness of pre-coat layer (cm) △P: Pressure loss of pre-coat layer (g force/cm ² ) A: Cross-sectional area of pre-coat layer (cm ² ) gc: Gravity conversion Coefficient (g・cm/g・weight S ² )≒980 γp; Average pore radius (cm) In Figure 1, straight line 1 indicates that the average particle diameter is
The results are shown when a 35μ particulate cation exchange resin and a particulate anion exchange resin are mixed at a ratio of 2:1, and the straight line 2 is a mixture of the mixed particulate ion exchange resin and a rod shape with a thickness of 20μ and a length of 500μ. When polyacrylonitrile fibers are mixed at a ratio of 1:1, straight line 3 has a thickness of 20 μm with the mixed fine particulate ion exchange resin.
When rod-shaped polyacrylonitrile fibers with a length of 500μ are mixed at a ratio of 3:7, and straight line 4 is a mixture of a particulate anion exchange resin with an average particle size of 35μ and a rod-shaped polyacrylonitrile fiber with a thickness of 20μ and a length of 500μ. The results are shown when polyacrylonitrile fibers were mixed at a ratio of 3:7. As can be seen in Figure 1, the average pore radius of the precoat layer containing only particulate ion exchange resin rapidly decreases as the water flow rate increases, whereas the average pore radius of the precoat layer of the present invention decreases rapidly as the water flow rate increases. Even when the water flow rate increases, it does not decrease significantly, indicating that the precoat layer of the present invention is less compressible. Example 2 The permeability of the precoat layer of the present invention was determined as follows along with a comparative example. That is, condensate with an average iron concentration of 30 ppb (average particle size 3.5 μ) was passed through the precoat layer below at a rate of 8 m/H,
The iron content and amount of treated water were determined and the results are shown in Table 1. The amount of precoating was 1 Kg/m ² -overarea in all cases. Present invention-1; 2:1 of fine particulate cation exchange resin and fine particulate anion exchange resin with an average particle size of 35μ
Pre-coat layer in which rod-shaped polyacrylonitrile fibers with a thickness of 20 μm and a length of 500 μm are mixed in a ratio of 5 to the mixture 5 of the present invention-2; Pre-coat layer Comparative Example 1 in which rod-shaped polyacrylonitrile fibers with a thickness of 20 μm and a length of 500 μm were mixed in a ratio of 7 to 2:1 ion exchange resin mixture 3; fine particulate cation exchange with an average particle size of 35 μm. Comparative Example 2 of a precoat layer in which a resin and a particulate anion exchange resin are mixed at a ratio of 2:1; an upper part of a precoat layer in which a particulate cation exchange resin and a particulate anion exchange resin with an average particle size of 35μ are mixed at a ratio of 2:1. A two-layer precoat layer in which a precoat layer of rod-shaped polyacrylonitrile fibers with a thickness of 20 μm and a length of 500 μm was formed, however, upper layer: lower layer = 3:7 Comparative example 3; Precoated layer of acrylonitrile fiber alone

[Table] As shown in Table 1, the single precoat layer of rod-shaped polyacrylonitrile fibers cannot withstand use due to the large amount of iron in the treated water, but the precoat layers of Invention-1 and Invention-2 are similar to the conventional precoat layer. Comparing Comparative Example 1 and Comparative Example 2, which are pre-coated layers, the amount of iron in the treated water is the same, but the processing time to reach 1.75 Kg/cm ² is 16 to 19 days with the conventional pre-coated layer, whereas the present invention The pre-coat layer is 26-35 days and the throughput is 1.4
~2-fold increase. Example 3 The permeability of the precoat layer of the present invention was determined as follows. That is, condensate with an average iron concentration of 31 ppb (average particle size 2 μ) was passed through the precoat layer below at a rate of 8 m/H,
The iron content and amount of treated water were determined and shown in Table 2.
The amount of precoating was 1 Kg/m ² -overarea in all cases. Present invention-3: 2:1 of particulate cation exchange resin and particulate anion exchange resin with an average particle size of 35μ
A pre-coat layer is prepared by mixing rod-shaped polyacrylonitrile fibers with a thickness of 20 μm and a length of 500 μm in a ratio of 5 to the mixture 5 of the present invention-4; 2:1 of ion exchange resin
A pre-coat layer in which rod-shaped polyacrylonitrile fibers with a thickness of 20μ and a length of 500μ are mixed in a ratio of 7 to the mixture 3 of the present invention-5; , a pre-coat layer made of rod-shaped polyacrylonitrile fibers with a thickness of 20μ and a length of 500μ mixed in a ratio of 7 parts.

[Table] The present invention using a mixed ion exchange resin of both cationic and anionic ion exchange resins as particulate ion exchange resin.
It was confirmed that non-dissolved iron having an average particle diameter of 2 μm could be removed satisfactorily in Examples 3 and 4, and Invention-5 in which only an anion exchange resin was used as the particulate ion exchange resin. Example 4 Using the precoat layer of the present invention having the same composition as that used in Example 3, an average iron concentration of 30.5 ppb (average particle size
5μ) of condensate was treated under the same conditions as in Example 3, and the amount of iron and amount of iron in the treated water were determined and shown in Table 3.

[Table] In the results of Example 4, fine particulate positive and negative mixed ion exchange resin: Rod-shaped polyacrylonitrile fiber =
The present invention-4' pre-coat layer of 3:7 is iron in the treated water.
The best results were obtained with 0.3 ppb and 38 days of treatment. Also, compared to Invention-4, which is a similar pre-coat layer in Example 3, the processing time is extended by 6 days.

[Brief explanation of the drawing]

FIG. 1 is a log-log graph showing the compressibility of the precoat layer of the present invention and the conventional precoat layer in Example 1, where the vertical axis shows the average pore radius and the horizontal axis shows the water flow rate.

Claims (1)

[Claims] 1. In order to remove impurities from a liquid, a particulate ion exchange resin with a particle size of 2 to 250μ and a diameter of 2 to 200μ and a length are placed on a filter element.
A method for removing impurities from a liquid, which comprises precoating a layer of a mixture of rod-shaped polyacrylonitrile fibers of 250 to 1000 microns, and passing a liquid containing impurities through the precoat layer. 2. The method for removing impurities from a liquid according to claim 1, wherein the particulate ion exchange resin and polyacrylonitrile fiber are mixed in a weight ratio of 2:8 to 8:2. 3. The method for removing impurities from a liquid according to claims 1 and 2, wherein the particulate ion exchange resin is a mixture of a cation exchange resin and an anion exchange resin. 4. The method for removing impurities from a liquid according to claims 1 and 2, wherein the particulate ion exchange resin is an anion exchange resin.