JPH105761A - Purifying method of condensate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently remove impurities such as colloidal iron or the like from a condensate of a nuclear power plant, a thermal power plant or the like. SOLUTION: The condensate is treated with a polysulfone based hollow yarn membrane having a pore diameter continuously decreased from the inner surface of the membrane toward the outer surface and composed of an asymmetric structure having a dense layer having the smallest pore diameter in the vicinity of the outer surface. The hollow yarn membrane having a precoat layer of an adequate filter aid, which is formed on the outer surface, is particularly used and further the removing efficiency of a clad is improved by treating by an external pressure type full filtration.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying condensate in a nuclear power plant, a thermal power plant and the like.

[0002]

2. Description of the Related Art In cooling water of nuclear power plants and thermal power plants, since piping and equipment of a cooling water system are mainly made of steel, suspended solids such as corrosion products mainly composed of iron ("clad "). These suspended solids adhere to steam generators, such as reactors, boilers, or steam turbines, which can interfere with operation and, in nuclear power plants, increase the amount of radioactive material before they are supplied to the reactor. Need to be removed.

[0003] In order to remove these claddings, a precoat filter made of an ion exchange resin has been conventionally used. However, pre-coated filters made of ion-exchange resin have a short life and are radioactive at nuclear power plants, so they must be stored in drums. Hollow fiber membranes have been used.

However, polyolefin hollow fiber membranes are
In order to treat a large amount of condensate, a large number of membrane modules must be used due to low membrane permeability, resulting in an increase in the size of the equipment and an increase in the cost of condensate treatment. Due to `` scrubbing '' performed to restore the water permeability of the membrane contaminated by points and cladding, when used for a long time, the collapse of the membrane surface which seems to be caused by rubbing between hollow fiber membranes occurs, There has been a problem that the pores on the membrane surface are gradually crushed and closed, and the water permeability of the membrane is gradually reduced, so that filtration cannot be performed soon.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems by purifying condensate with a membrane having high membrane permeability and hardly causing pore collapse on the membrane surface. It is to provide a method.

[0006]

The present invention has solved the above-mentioned problems. In other words, the present invention provides a condensed water having a pore diameter continuously decreasing from the inner surface to the outer surface of the membrane and a polysulfone-based hollow fiber membrane having an asymmetric structure having a dense layer having the smallest pore diameter near the outer surface. The present invention relates to a method for purifying condensate, characterized by passing through.

The hollow fiber membrane made of a polysulfone resin used in the present invention has an asymmetric pore diameter in which the pore diameter decreases continuously from the inner surface to the outer surface of the membrane and has a dense layer having the smallest pore diameter near the outer surface. It is characterized by consisting of a distribution. This membrane is composed of a dense layer having the smallest pore diameter near the outer surface in order to improve the blocking performance of the clad, and a portion other than the dense layer is composed of a support layer having a larger pore diameter in order to obtain high membrane permeability. In particular, the size of the inner surface pores of the film reaches 20 μm to 40 μm. If the size of the inner surface pores is less than 20 μm, the strength of the film cannot be said to be sufficient, and a film having a pore size exceeding 40 μm tends to be difficult to produce.

In the step of filtering condensed water from the outer surface to the inner surface (referred to as "external pressure filtration"), the hollow fiber membrane used in the present invention captures large particles on the surface portion having large pores. Since the dense layer with the smallest pore size is located between the outer and inner surfaces of the film, the dense layer inside the film captures small particles. , The trapping volume is large, and can be efficiently removed.

The average diameter of the holes in the dense layer is not particularly limited as long as it does not pass through the clad, but is preferably 0.01 to 1.0 μm. 0.01
If it is less than μm, the water permeability of the membrane tends to decrease, and if it exceeds 1.0 μm, the performance of removing the clad tends to decrease. or,
A hollow fiber membrane made of a polysulfone-based resin has a high hardness and a small dimensional change during creep, so that the hollow fiber membranes during scrubbing tend not to be crushed due to rubbing between the hollow fiber membranes.

The polysulfone resin used in the hollow fiber membrane of the present invention includes those having a repeating unit represented by the following formula (1) or (2).

[0011]

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The condensate treatment is performed by a total filtration method and a cross-flow method, but the total filtration method is adopted because the apparatus can be simplified. When the treatment is performed by the total filtration method, the external pressure type total filtration is more preferable since the increase in the differential pressure of the membrane can be reduced as the membrane area increases. Furthermore, in external pressure type filtration, when the cladding is trapped on the membrane surface and the filtration capacity of the membrane is reduced, air can be blown into the outer surface of the membrane to recover the filtration capacity by a method called "scrubbing". It is preferable because the filtration ability can be kept stable for a long time. The condition of the scrubbing is not particularly limited as long as it is an air amount capable of removing the clad, but preferably 0.1 Nl / h · m
² (per membrane area) to 500 Nl / hour · m ² . If it is less than 0.1 Nl / hour · m ² , cleaning of the clad is insufficient, and if it exceeds 500 Nl / hour · m ² , the hollow fiber membrane may be damaged.

In the present invention, the efficiency of removing the clad can be further improved by forming a precoat layer in which an appropriate filter aid is precoated on the outer surface of the hollow fiber membrane. The precoat layer is a layer formed by attaching the filter aid to the outer surface of the membrane. In the present invention, the filter aid is intended to improve the efficiency of removing the clad, diatomaceous earth, a particulate ion exchange resin,
Carbon powder, powdery synthetic resin, iron oxide powder and the like are used.
The attached amount of the filter aid is important for efficiently removing the clad, and the attached amount is suitably from 0.1 to 20 g / m ² . If it is less than 0.1 g / m ² , the effect of the precoat layer is not sufficiently exhibited, and if it exceeds 20 g / m ² , the membrane water permeability tends to be greatly reduced.

Since the clad in the condensate contains a lot of ionic ones, the use of a hollow fiber membrane having a pre-coated layer improves the removability of the clad and improves the inner surface of the membrane. No crystals of the clad are deposited. The membrane water permeability, film thickness and inner diameter are not particularly limited, but usually the membrane water permeability is 100 to 30,000 liter / h.
r · m ² · atm, film thickness 10 to 250 μm, inner diameter 5
Those having a size of about 0 to 1000 μm are used. The compressive strength of the membrane is important for external pressure total filtration and is at least 5 kg / cm ² , preferably at least 9 kg / cm ² . 5kg / c
If it is less than m ² , flat or even deformation of the hollow fiber membrane may occur during long-term treatment.

This polysulfone porous hollow fiber membrane is
It is used as a membrane module in which a plurality of them are bundled in a linear or U-shape.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples are shown below, but the present invention is not limited to these. Each measuring method is as follows. The hollow fiber membranes used as measurement samples were all fully impregnated with water.

The water permeability of the hollow fiber membrane is 50
mm to transmit water from the inner surface to the outer surface of the hollow fiber membrane,
The amount was expressed in liter / hr · m ² · atm. However, the effective film area was converted to the inner surface. The compressive strength of the membrane is such that when water of 40 ° C. is transmitted from the outer surface to the inner surface of a hollow fiber membrane having a sample length of 100 mm, the water pressure is 0.5 kg / c.
m ^{2 at a} time, the maximum water pressure at which the hollow fiber membrane was not deformed such as crushing or flattening. Pressurization time is 1
The pressure was changed to 5 seconds, and the pressure was changed within 13 to 15 seconds.

The pore size of the membrane was measured by the air flow method described in ASTM F316-86.

[0019]

Embodiment 1 Embodiment 1 of Japanese Patent Application No. 7-328872
A hollow fiber membrane was prepared according to the membrane forming conditions described in (1). That is, polysulfone (manufactured by AMOCO Co.,
P-3500) 18% by weight, the water content after drying is 0.3
20% by weight of polyvinylpyrrolidone (K30, manufactured by BASF) having a weight average molecular weight of 45,000,
It was dissolved in 62% by weight of N-methyl-2-pyrrolidone to obtain a uniform solution.

The mixture was kept at 40 ° C. and spun (with a double annular nozzle 0.5 mm-
(0.7 mm-1.3 mm), passed through a 30 mm air gap, and immersed in a coagulation bath consisting of 70 ° C. water. At this time, the region from the spinneret to the coagulation bath was surrounded by a cylindrical tube, and the humidity of the air gap in the tube was 100%, and the temperature was 4%.
The temperature was controlled at 5 ° C. The spinning speed was fixed at 10 m / min.

The inner diameter of 650 μm thus prepared is
m, thickness 150 μm, membrane permeability 14,000 liters /
hr · m ² · atm, compressive strength 7.0 kg / cm ^2, polysulfone having a pore size is 0.28μm porous hollow fiber membrane 4
The effective length is obtained by bundling the two pieces in a substantially straight line, mounting them in a cylindrical case made of polysulfone, injecting an epoxy adhesive into both ends of the hollow fiber membrane, and heating and curing at 90 ° C. for 2 hours. A 25 cm membrane module having the structure shown in FIG. 1 was manufactured.

A clad having a particle size distribution of 0.3 to 0.5 μm in the secondary cooling water of a pressurized water reactor was sampled and the concentration was 1%.
The solution added to pure water at 0 ppb was used as simulated water for condensate. The simulated water temperature 30 ° C., 2 to outer surface of the membrane by passing liquid filtration pressure difference at 0.1 kg / cm ²
g / m ² of cladding was precoated. Thereafter, the simulated water was passed from the outer surface to the inner surface of the hollow fiber membrane of the membrane module at a temperature of 40 ° C. and a filtration pressure difference of 0.5 kg / cm ² , and scrubbing was performed every 10 days. . The scrubbing conditions were 3N l / h · m ² × 10 minutes × 20 times.

The initial module water permeability was 150 l / hr. The overconcentration of the cladding in the drainage during the 90 days of operation was always less than 0.1 ppb. There was no extreme decrease in the water permeability of the module, and no problems such as flattening of the hollow fiber membrane occurred. After washing with 15% hydrochloric acid, the water permeability of the membrane had recovered to 95% of the initial value. When the outer surface of the membrane was observed with an electron microscope, there was almost no change from before use.

[0024]

Comparative Example 1 A polyethylene porous hollow fiber membrane having an inner diameter of 670 μm, a film thickness of 290 μm, a membrane permeability of 5000 l / hr · m ² · atm, a compressive strength of 5.5 kg / cm ² and a pore diameter of 0.25 μm was prepared. And the same operation as in Example 1 was performed. Initial module permeability is 50 l / h
r, and the filtration concentration during operation for 90 days is always 0.1 p
pb or less. There was no extreme decrease in the water permeability of the module, and no problems such as flattening of the hollow fiber membrane occurred. Fifteen
% Hydrochloric acid, the membrane water permeation amount is 38% of the initial value.
When the outer surface of the membrane was observed with an electron microscope, the holes were crushed and almost disappeared.

[0025]

According to the method of the present invention, impurities such as iron colloid, so-called cladding, can be efficiently removed from condensed water of a nuclear power plant, a thermal power plant or the like.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a polysulfone-based porous hollow fiber membrane module used in Example 1 of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cylindrical case made of polysulfone 2 Adhesive part 3 Polysulfone hollow fiber membrane 4 Raw water introduction nozzle 5 Air release nozzle

Claims (3)

[Claims] 1. The condensate passes through a polysulfone-based hollow fiber membrane having an asymmetric structure having a dense layer having the smallest pore diameter near the outer surface, with the pore diameter decreasing continuously from the inner surface to the outer surface of the membrane. A method for purifying condensate water, characterized in that: 2. The method for purifying condensate according to claim 1, wherein the condensate is treated by external pressure type total filtration. 3. The method for purifying condensed water according to claim 1, wherein the hollow fiber membrane is a hollow fiber membrane having a precoat layer of a filter aid formed on an outer surface thereof.