JPS62168520A - Filtering method - Google Patents

Abstract

PURPOSE:To reduce the generation of cracks in the powdery ion exchange resin bed formed on an element, by setting the shrinking degree of a powdery ion exchange resin aggregate due to the adsorption of a suspended substance to 0.8 or more. CONSTITUTION:In performing precoat filtering using an aggregate formed by mixing a powdery cation exchange resin and a powdery anion exchange resin as a filter aid, a value obtained by dividing the shrinking degree of the aggregate due to the adsorption of a suspended substance, that is, the volume of the aggregate having adsorbed the suspended substance by the volume of the aggregate adsorbing nothing is set to 0.8 or more. As a result, the shrinkage of the aggregate relating to the generation of cracks is prevented and the reliability of the powdery ion exchange resin at the time of filtering can be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a filtration method, and particularly to a filtration method using a powdered ion exchange resin as a filter aid.

[Background of the invention]

For advanced water treatment, there is a filtration method using a filter aid. In this method, a fine filter aid with a particle size of about 10 to 300 μm is precoated on an element made of nylon or stainless steel, and suspended solids in water are removed on the precoated filter aid. Diatomaceous earth and pulp cellulose are generally used as filter aids, but in places where advanced water treatment is required, such as nuclear power plants, crushed ordinary ion exchange resins (approximately 1+ m particle size) are used as filter aids. It is being used. This is the special public service of 1977-44.
According to Publication No. 903, approximately 60 to 400 meshes (40
~250 μm) anion exchange resin and cation exchange resin are mixed at a certain ratio.

Due to its characteristics, this powdered ion exchange resin exhibits characteristics different from those of ordinary filter aids. In other words, anion exchange resins and cation exchange resins have opposing charges, positive and negative, respectively, due to their ion exchange groups, and as a result, when two ion exchange resins are mixed, the 10
Forms aggregates with twice the volume. Furthermore, since the charge formed by the ion exchange group is strong, it has a great ability to remove suspended solids in water. Furthermore, since the base material is an ion exchange resin, it has ion removal properties that are not found in other filter aids.

However, when suspended substances in water are adsorbed to the aggregates formed by the powdered ion exchange resin, the volume of the aggregates decreases, and numerous cracks occur in the powdered ion exchange resin layer formed on the element. This is because the element is usually made of a material such as nylon with a nominal opening of about 1 μm, so there is no leakage of suspended solids from the cracked parts, but due to the element becoming dirty, it is difficult to replace it frequently. increase

For this reason, various countermeasures have been devised and implemented. One method is to add a polymer flocculant such as polyacrylic acid, polymethacrylic acid, polyacrylic acid amide, or polymethacrylic acid amide to reduce the volume of aggregates to a certain extent, which generates particles on the element during filtration. This is a method to reduce the amount of cracks that occur.

The second method is to add fibers with a length of about 2 mm when mixing the powdered cation exchange resin and powdered anion exchange resin, and pre-coat this on the element, which reduces the shrinkage of the aggregates. It's a method. The third method is to perform precoating in two stages. In this method, when cracks occur due to shrinkage of the aggregates, a second precoating is performed to fill in the cracks caused by filtration.

Although these methods yield good results in experiments using small filtration test equipment similar to the actual equipment, good results are not necessarily obtained in actual equipment.

Based on these facts, it is desired to clarify the usage conditions of powdered ion exchange resins using a test method that is compatible with actual equipment.

[Purpose of the invention]

An object of the present invention is to eliminate the drawbacks of the prior art described above, that is, to provide conditions for preparing powdery ion exchange resin aggregates with less cracking.

[Summary of the invention]

The feature of the present invention is that the volume of aggregates generated by mixing powdered cation exchange resin and powdered anion exchange resin and the volume of aggregates on which suspended substances are adsorbed are unidirectionally adjusted in consideration of the filtration state. The objective is to prepare aggregates such that the measured volume of the latter aggregate divided by the volume of the former aggregate becomes 0.7 or more by measuring while applying more pressure.

[Embodiments of the invention]

The present invention was made based on the results of evaluating the shrinkage of aggregates of powdered cation exchange resins and powdered anion exchange resins and the causes of cracking.

The details of the results will be described below. FIG. 2 schematically shows the shrinkage of aggregates and the causes of cracking.

There are two causes for shrinkage of aggregates: adsorption of suspended substances and increase in differential force during filtration. In the former case, a large amount of suspended matter is removed from the surface of the aggregate on the element, so the collection on the surface of the aggregate is large, and the inner surface of the aggregate becomes smaller.
Cracks occur as a result. - The latter case on the right is due to an increase in differential pressure during filtration, but since the initial differential pressure is 0.1 kg/d or less, the final differential pressure changes from 1 to 5 kg/cJ, so the shrinkage of the aggregates is large. Become. Figure 3 shows the relationship between differential pressure and contraction of the aggregate. As can be seen from this figure, there is a rapid contraction in the area where the differential pressure is small, and then a gradual contraction. The shrinkage is -~1 of the initial aggregate volume.

However, since the contraction due to this differential pressure occurs uniformly in the aggregate layer on the element, unlike the former contraction due to adsorption of suspended matter, no cracking occurs. Therefore, in order to correlate the shrinkage of aggregates with the occurrence of cracks, it is first necessary to eliminate shrinkage due to differential pressure and evaluate only shrinkage due to adsorption of suspended solids.

Hereinafter, a method for measuring the amount of shrinkage of aggregates due to adsorption of suspended matter will be described using drawings. FIG. 3 shows an example of a measuring device. In Figure 1, 1 is an aggregate, 2 is a cylinder, and 3
is a piston, 4 is a weight, and 5 is a perforated plate. First, using the apparatus shown in FIG. 1, the volume of the aggregate is measured without adsorbing suspended matter. In this procedure, first, a powdered cation exchange resin and a powdered anion exchange resin are mixed in water to prepare an aggregate. At this time, the mixing ratio of the powdered cation exchange resin and powdered anion exchange resin is adjusted to the usage conditions of the actual machine. The amount of water is 20mQ per 1g of powdered ion exchange resin.
Make sure that the above is achieved. The prepared aggregate is then placed into the cylinder 2 together with water.

Excess water passes through the perforated plate 5 and is discharged. Next, the piston 3 is inserted and a weight 4 is placed on the piston 3 so that the desired pressure is applied. After waiting until the movement of the piston 3 stops, the volume of the aggregate is calculated from the moving distance of the piston 3 and the inner diameter of the cylinder 2.

Next, the volume of the aggregates adsorbing the suspended matter is measured. In this case, after aggregates are formed in water, suspended substances are added and adsorbed onto the aggregates. The amount of suspended solids is added in excess of the adsorbed amount of the aggregates. Excess suspended solids are separated by decantation since the sedimentation rate of aggregates in water is greater than that of suspended solids. The volume of the suspended solids-adsorbed aggregates thus prepared is measured in the same manner as for the aggregates that do not adsorb suspended solids. The pressure at this time is the same for both.

The degree of shrinkage of the aggregate due to adsorption of suspended matter is evaluated from the aggregate volume thus measured. The degree of shrinkage is determined by dividing the volume of aggregates that have adsorbed suspended matter by the volume of aggregates that have not adsorbed anything.

As described above, the relationship between the degree of shrinkage of aggregates and the permeability of suspended solids at the appropriate time of filtration was investigated. The results are shown in Figure 1.

Here, powdered cation exchange resin and powdered anion exchange tree were used at a ratio of 2:1, and the polymer flocculant was used at 1 mg/g/g.
g resin was added and mixed to form aggregates. Considering the condensate filtration and desalination equipment of nuclear power plants, the suspended solids have a particle size of approximately 1.
-μm FezO8 was used.

In addition, the measurement pressure for the degree of shrinkage is 0.5, which causes many cracks.
kg/, n. As a result, F
The ezOδ transmittance also decreased. This is because cracking does not occur as explained in FIG. 2.

There are various ways to specifically implement the present invention. Hereinafter, preferred embodiments for carrying out the present invention will be described.

Example 1 A normal powdered ion exchange resin has an average particle size of about 40 μm, but the degree of shrinkage can be changed by changing the particle size. Figure 5 shows the results. Average particle size is 50
When it is more than μm, the degree of shrinkage is more than 0.8, and Fez
It can be seen that the O8 transmittance decreases, indicating that good filtration can be performed. Moreover, as the average particle size increases, FexOδ
The transmittance increases again, but this is because as the particle size increases, the surface area per unit weight of the particulate ion exchange resin also decreases, and the trapping power of FaxOa decreases.

Therefore, in order to make the shrinkage degree of the powdery ion exchange resin aggregate 0.8 or more depending on the particle size, the average particle size of the powdery ion exchange resin should be 50 to 15 from the viewpoint of Fez○δ transmittance.
0 μm is suitable.

Example 2 For ordinary powdered ion exchange resins, the amount of polymer flocculant added is 1 mg/g resin, but by increasing this, the degree of shrinkage is increased, that is, the amount of aggregates due to adsorption of suspended substances is increased. It is also possible to reduce the shrinkage of FIG. 6 shows the amount of polymer flocculant added and the degree of shrinkage of the aggregate. When the amount of polymer flocculant added is 10 mg/g resin or more, the degree of shrinkage is 0.
8 or more.

Therefore, the degree of shrinkage of the powdered ion exchange resin aggregate is set to 0.
In order to make it 8 or more, the amount of polymer flocculant added should be Lon
g/g resin or more.

Example 3 Powdered cation exchange resin and powdered anion exchange resin of powdered ion exchange resin were mixed in a ratio of 1=1. Alternatively, they are usually mixed at a ratio of 2:1°, but by changing this mixing ratio, the degree of shrinkage of the aggregate can be changed. FIG. 7 shows the relationship between the mixing ratio of the powdered ion exchange resin and the degree of shrinkage of the aggregate. The horizontal axis of FIG. 7 shows the ratio of the powdered cation exchange resin weight to the total powdered ion exchange resin weight of the powdered cation exchange resin and the powdered anion exchange resin. By the way, when the conventional mixing ratio of powdered cation exchange resin and powdered anion exchange resin is 2=1, the horizontal axis in Figure 7 is 0.66, and when it is 1:1, the horizontal axis in Figure 7 is 0.66. becomes 0.5. As can be seen from this figure, in order to achieve the aggregate shrinkage degree of 0.8 or more, which is the objective of the present invention, the weight of the powdered cation exchange resin should be reduced to 0.2 or less by the total weight of the powdered ion exchange resin. It may be 8 or more.

Example 4 In Examples 1 and 2.3, only the particle size of the powdered ion exchange resin, the amount of polymer flocculant added, and the mixing ratio of the powdered cation exchange resin and powdered anion exchange resin were set. Although an example is shown in which the values are changed, the same effect can be obtained even if two or more of these are combined.

Moreover, by these combinations, the shrinkage degree of the aggregate can be reduced to 0.
If the value is 9 or more, the reliability of crack prevention can be further improved.

According to Examples 1 to 4 above, it is possible to know in advance whether or not cracking will occur and to prevent it. Therefore, this method can be used for quality control at the manufacturing stage and performance confirmation immediately before use.

〔Effect of the invention〕

According to the present invention, it is possible to prevent the shrinkage of aggregates related to the occurrence of cracking, and improve the reliability of filtering powdered ion exchange resin in a timely manner.

[Brief explanation of drawings]

Figure 1 shows the powdery ion exchange resin FezO in the present invention.
a Diagram showing the relationship between shrinkage due to adsorption and filtration performance, Figure 2 is an explanatory diagram showing the relationship between shrinkage causes and cracking, and Figure 3
The figure is a cross-sectional view of an apparatus for measuring the shrinkage degree of aggregates according to an embodiment of the present invention, Figure 4 is a diagram showing the shrinkage of aggregates due to differential pressure, and Figure 5 is a powdered ion exchange resin. Figure 6 is a diagram showing the relationship between the particle size of the polymer flocculant and the shrinkage degree of the aggregates, Figure 7 is a diagram showing the relationship between the amount of polymer flocculant added and the shrinkage degree of the aggregate number FIG. 2 is a diagram showing the relationship between the mixing ratio of powdered anion exchange resin and the degree of shrinkage. 2... Cylinder, 3... Piston, 4... Weight, 5... Perforated plate.

Claims (1)

[Claims] 1. In pre-coat filtration using aggregates of a mixture of powdered cation exchange resin and powdered anion exchange resin as a filter aid, the volume measured under the condition of applying pressure from one direction of the aggregates is the volume of the target object to be treated. Filtration characterized by preparing aggregates such that the volume obtained by dividing the volume of the aggregates adsorbing suspended substances in wastewater under conditions of pressurization from one direction is 0.8 or more. Method.