JPH0353999B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating condensate such as condensate of a reactor primary cooling system or secondary cooling system of a nuclear power plant or a boiler condensate of a thermal power plant.

Since the piping and equipment of the condensate system are mainly made of steel, these condensates always contain suspended solids such as corrosion products mainly composed of iron. The suspended solid content is mainly Fe ₃ O ₄ , α−Fe ₂ O ₃ , γ−
It includes various chemical forms such as Fe ₂ O ₃ and FeooH, and its shape is also various, and the particle size has a wide distribution from 0.1 μm to several tens of μm.

The suspended solids deposit in steam generators such as nuclear reactors, boilers, or steam turbines not only impair the functionality of these devices and equipment, but also
Particularly in nuclear power plants, since radioactive substances increase, it is necessary to remove the suspended solids from condensate as much as possible.

Traditionally, when removing suspended solids from condensate,
Generally, precoating was carried out. This pre-coated filter is applied to a filter element consisting of an unglazed cylinder, a carbon cylinder, a wire mesh, a cylinder wrapped with thread, etc., and a supercharging aid such as diatomaceous earth, cellulose, particulate ion exchange resin, carbon powder, or powdered synthetic fiber. Condensate containing suspended solids is passed through a filter tower which houses a large number of pre-coated emeralds, and is filtered through the pre-coated layer of the filter element. Furthermore, recently, in place of the filter tower that performs the precoat filtration, a filter tower using an electromagnetic filter has been used to excessively remove suspended solids in condensate.

However, as mentioned above, the suspended solids contained in the condensate are widely distributed from 0.1 μm to several tens of μm, and in some cases, most of the suspended solids are 1 μm or less. Therefore, the pre-coating method described above has the disadvantage that fine suspended solids leak. Additionally, the pre-coat layer becomes clogged relatively quickly, which increases the amount of super-aid waste, and the filter element itself is also clogged with fine suspended solids, so that the filter element is sometimes Excessive elements that require extra operations such as cleaning with chemicals and cannot be recovered by such cleaning must be replaced. On the other hand, electromagnetic filters have the disadvantage that it is difficult to remove suspended solids of paramagnetic substances such as α-Fe ₂ O ₃ and FeOOH, so they cannot be used when condensate contains a large amount of paramagnetic substances. There is.

Conventional condensate treatment is, for example, when steam generated in a nuclear reactor is purified in order to be circulated to the reactor after passing through a turbine and condensing in a condenser. First, the condensate was passed through a filter column equipped with a backwash type pre-coated filter element to mainly remove suspended solids (crads) in the condensate, and the condensate from the outflow side was filled with an ion exchange resin. After being desalinated through a desalination tower, it is circulated to the nuclear reactor, and the total amount of condensed water is required for an 11 million kW class nuclear power plant.
However, in order to treat such a large amount of condensate using the ^precoat filtration method, the filtration tower must be backwashed frequently, and precoating is required after backwashing. This poses the problem of increasing the amount of radioactive waste, especially in condensate purification systems in nuclear power plant equipment.

The purpose of the present invention is to solve the drawbacks of conventional treatment methods in removing suspended solids from condensate. Condensate containing suspended solids such as corrosion products mainly composed of iron is passed through a filter column comprising a partitioning support plate and a large number of filter elements installed upright on the support plate on the inflow side. In the method for treating condensate by watering and over-treating, the above-mentioned permeation element is composed of a large number of permeable membrane tubes made of hollow capillary tubes bundled together, and the hollow part of each permeable membrane tube is communicated with the above-mentioned outflow side. , passing the entire amount of condensate containing the suspended solids from the inflow side to the outflow side through the membrane surface of each permeable membrane tube, and removing the suspended solids by passing through the membrane surface; It is characterized by:

A specific example of the permeable element used in the present invention is a permeable membrane with a micropore size of 0.001 to 0.1μ, or a permeable membrane with a molecular weight cutoff of 10,000 to 100,000, with an outer diameter of 0.5 to 2 mm and an inner diameter of 0.2 to 1.5 mm. A large number of permeable membrane tubes formed in the shape of hollow capillaries, e.g.
It is a bundle of over 500 pieces. Using such a filtration element, the entire amount of condensate containing suspended solids is passed through the membrane surface of the filtration membrane tube from the inflow side to the outflow side of the filtration column, and by filtration on the membrane surface, that is, permeation is carried out. Suspended solids in condensate are removed by the fine pores of the membrane, and even suspended solids as small as 0.1μ can be reliably removed by selecting an appropriate fine pore size for the permeable membrane. be able to.

In the conventional precoat filter method, a cylindrical filter element with an outer diameter of 1 to 4 inches and a length of 1 to 2 m is usually used, and the various filter aids described above are precoated on the outer peripheral surface of the filter element. Suspended solids are removed in the precoat layer, and in the case of such a perforation element, for example, the perforation area of one perforation element having an outer diameter of 2 inches and a length of 1.5 m is about 0.24 m ² . On the other hand, the over-element used in the present invention is a bundle of a large number of the above-mentioned permeable membrane tubes, and since each of the bundled permeable membrane tubes has a over-capacity, its over-area is extremely large. For example, a membrane tube with an outer diameter of 1.4 mm and a length of 1.5 m can be placed in the same volume as the conventional membrane tube with an outer diameter of 2 inches and a length of 1.5 m.
It is possible to bundle 800 elements, and the area of each element of the present invention is approximately 5.3 m ² . As described above, when comparing the overarea of the overelement of the present invention and the conventional overelement, the former is about 22 times as large as the latter, so the overelement of the present invention can significantly lengthen this elapsed time.

For example, the previously mentioned conventional outer diameter of 2 inches and length of 1.5 inches.
Normally, approximately 2 T/H of condensate is passed through a pre-coated filter element of 1.5 m, but if the condensate contains approximately 30 ppb of suspended solids, the pressure drop will increase after about 15 days. Once the specified value is reached, the precoat layer must be peeled off and a new precoat layer formed.

On the other hand, in the over-element of the present invention, when compared under the same conditions, the elapsed time can be about 30 days or more. In addition, the filtering element of the present invention can easily solve the problem by passing cleaning water in the opposite direction to the direction of condensate water flow when suspended solids adhere to the surface of the permeable membrane tube and pressure loss increases. Suspended solids can be washed and peeled off from the membrane surface.
After this cleaning, water flow can be continued again.

When removing suspended solids in a liquid using the ultrafiltration membrane device disclosed in Japanese Patent Application Laid-Open No. 49-86800, which precedes the present invention, the liquid to be treated is passed through the permeable membrane in a sweeping manner. , so-called cross-flow liquid passage is performed. The cross-flow liquid passes approximately 50% of the treated liquid through the permeable membrane to obtain a non-permeated liquid with concentrated suspended solids, and the remaining treated water is passed through the permeable membrane. It is used to obtain a permeate from which suspended solids have been removed by permeation.
In the case of condensate from nuclear power plants, thermal power plants, etc., the entire amount of condensate must be recycled and used, so it is difficult to employ such cross-flow liquid passage.

In carrying out the present invention, it is preferable that the permeation membrane tubes used in the permeation elements installed in large numbers in the permeation column have an outer diameter of approximately 0.5 to 2.0 mm, and this is due to the following reasons. .

For example, if the outer diameter of the tube is 0.5 mm or less, the number of tubes bundled within a certain volume can be increased, which has the advantage of increasing the excess area, but on the other hand, the inner diameter will be thinner. If the outer diameter of the tube is too large, the pressure loss of the fluid passing through it will become large, which is undesirable, and if the outer diameter of the tube is set to 2 mm or more, it will not be possible to bundle a large number of tubes together, making it impossible to increase the overarea. It disappears and is not desirable.

Therefore, it is desirable to use a tube with an outer diameter of 0.5 to 2 mm, preferably 0.8 to 1.2 mm, and a permeable membrane with a micropore diameter of 0.001 μ or less and a molecular weight cut-off of 10,000 or less. If used, the initial pressure loss will be too large to be practical, and a permeable membrane with a micropore diameter of 0.1 μ or more or a molecular weight cut-off of 100,000 or more is undesirable because fine suspended solids tend to leak. Therefore, it has a micropore diameter of 0.001 to 0.1μ, or a molecular weight cut-off of 10,000 to 10,000.
Preferably, a permeable membrane with a performance of 100,000 is used.

As explained above, the condensate treatment method of the present invention can significantly extend the passing time of the filter element per unit volume compared to the conventional pre-coating method, and therefore the frequency of backwashing is reduced. As a result, there is no need for pre-coating after backwashing, and the amount of radioactive waste can be significantly reduced in nuclear power plant equipment that implements the method of the present invention.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a partially cutaway external view of an embodiment of the permeable element used in the present invention. are fixed by an assembly cap 2 and a connector 3, and the outer surface of the assembly of permeable membrane tubes 1 is covered with a reinforcing material 4 such as a perforated plate or a wire mesh. The connector 3 is threaded on the inside so that it can be screwed into a support plate nozzle 7, which will be described later. Further, as shown by the dotted line in FIG. 1, the permeation element 5 passes the entire amount of condensate from the outside of each permeable membrane tube 1 through the membrane surface,
The water is collected inside the connector 3 and flows toward the outflow side of the tower.

FIG. 2 is a longitudinal cross-sectional view of a filter column equipped with a filter element used in the present invention, in which the filter column 6 is horizontally fixed in a container and has a support plate 8 that divides the container into an inflow side and an outflow side. A large number of over-elements 5 are attached to the lower side of the support plate 8 via support plate nozzles 7 in a suspended manner. The hollow portions of each permeable membrane tube of the filter element 5 are all communicated with the outflow side of the filter column 6. Note that 9 is a distributor having a large number of holes, and the condensate is fed from the distributor 9, and the entire amount of condensate is passed through the membrane surface of each filter element 5 as shown by the dotted line. The perfused water is collected by each support plate nozzle 7 and taken out from the upper outflow side of the support plate 8 to the outside of the filter tower 6.

FIG. 3 is an explanatory diagram showing the flow of the present invention,
When draining condensate, open valves 10 and 11.
The entire amount of condensate is allowed to flow into the lower part of the filter column 6 from the inlet pipe 12 and passed through each filter element 5,
The excess water is removed from the outflow pipe 13. As such filtration continues, the suspended solids in the condensate are passed through the outer surface of each filtration element 5, specifically, the outer peripheral membrane surface of each permeable membrane tube 1, and as a result, the pressure loss increases. When the pressure loss reaches a specified value, valves 10 and 11 are closed to interrupt the flow of condensate, and valve 1 is closed.
4 and 15 are opened, and compressed air is introduced from the upper part of the filter tower 6 from the air storage tank 16 through the air inflow pipe 17. Due to the inflow of the compressed air, the excess water on the upper part of the support plate 8 flows back into each excess element 5,
As the permeate water flows backward from the inside to the outside of each permeable membrane tube 1, the suspended solids adhering to the outside of each permeable membrane tube 1 are peeled off, and the concentrated solution of suspended solids is transferred to the backwash water. It is obtained from the outflow pipe 18. In addition, as the water level in the filter tower 6 decreases, the compressed air itself flows forcefully from the inside to the outside of each permeable membrane tube 1, thereby more reliably removing suspended solids attached to the outside of each permeable membrane tube 1. can.
Note that after performing such backwashing, the compressed air continues to flow in, and the valve 19 is further opened to allow backwash water to flow in from the backwash water inlet pipe 20 to ensure that the water is removed by air and water. I can do it.

After completing such backwashing, water is passed through again, but in this case, valve 10 and valve 21 are opened,
After closing the other valves, allowing condensate to flow into the filter tower 6 from the inlet pipe 12, and releasing the air in the filter tower 6 from the air vent pipe 22, closing the valve 21 and opening the valve 11,
Do the above mentioned mistake. Further, precoating work, which is performed in conventional precoating filtration after backwashing, is not necessary, and the downtime can be shortened.

As explained above, the present invention uses a permeable element in which a large number of thin permeable membrane tubes are bundled.
Since the excess area can be increased and the micropores of the permeable membrane are extremely small, the elapsed time per unit volume can be greatly increased, and even fine suspended solids can be reliably removed. I can do it. Further, since the filter element used in the present invention can pass condensate water without precoating with a filter aid, the amount of waste solid content resulting from the waste precoating agent in the backwash waste liquid can be reduced.

Examples will be described below to make the effects of the present invention more clear.

Example: A permeable membrane with a molecular weight cutoff of 13,000 and a thickness of 0.3 mm has an outer diameter of
800 tubes with a diameter of 1.4 mm, an inner diameter of 0.8 mm, and a length of 1.5 m were bundled in a volume of 2 inches in diameter and 1.5 m in length to form a superelement as shown in Figure 1. One filter element was installed on the support plate inside the small filter tower, and 34% of the particles had a particle size of 8μ or more, and 8μ or more.
Condensate containing 30 to 40 ppb of suspended iron with a particle size distribution of 24% of 3μ, 19% of 3μ to 0.4μ, and 23% of 0.4 or less is passed from the lower part of a small filter tower at 2.3T/H. , passed from the outside to the inside of each permeable membrane tube, and the permeate was collected through the top of the support plate. As a result, superhydration with an average suspended iron content of 0.5 ppb was obtained, and the process could be completed for about 30 days until the pressure drop became 1.5 Kg/cm ² .

The increase in pressure loss in the above water flow results is as shown by curve-1 in FIG.

On the other hand, for comparison, the conventional method is
Microparticulate ion exchange resin (fine particulate cation exchange resin: particulate anion exchange resin = 3:1) was applied to a single known pre-coated filter element with a length of 1.5 m at a rate of 1.0 kg/m ^2. (The amount of polymer electrolyte added was adjusted to V/Vo = 55% during precoating.), and the same condensate as used in the present invention was passed through the precoated element at the same flow rate. . the result,
The average amount of suspended iron in superhydration is 5 ppb, and about 17
The pressure loss was 1.5Kg/cm ² after water flow for one day. Furthermore, when we investigated the particle size distribution of the leaked 5ppb suspended iron, we found that 0% was 8μ or more, 10% was 8 to 3μ, and 3 to 0.4μ.
was 15%, and 75% was 0.4μ or less. Curve 2 in FIG. 4 shows the increase in pressure loss in the comparative example.

When the condensate treatment method according to the present invention is applied to a condensate purification system in nuclear power plant equipment, for example,
The filtration element of the filtration column used is constructed by bundling a large number of permeation membrane tubes made of hollow capillary tubes, and the hollow part of each permeation membrane tube is communicated with the above-mentioned outlet side, and contains the above-mentioned suspended solids. The entire amount of condensate is passed from the inflow side to the outflow side through the membrane surface of each permeable membrane tube, and the suspended solids are removed by filtration on the membrane surface, which is different from conventional backwashing. As an alternative to filter columns equipped with pre-coated filtration elements, it is possible to treat similar large volumes of condensate, but requires less backwashing than traditional pre-coated filtration, and has the advantage of reducing radioactivity. This method has a remarkable effect compared to conventional condensate treatment methods, in that the volume of industrial waste is significantly reduced.

[Brief explanation of drawings]

Fig. 1 to Fig. 3 all show embodiments of the present invention, Fig. 1 is a partially cutaway external view of the over-element used in the present invention, and Fig. 2 is a partially cutaway external view of the over-element used in the present invention. FIG. 3 is a vertical cross-sectional view of the filter tower, and FIG. 3 is an explanatory diagram showing the flow of the present invention. FIG. 4 is a graph showing the increase in differential pressure in the example, with the vertical axis showing the pressure loss and the horizontal axis showing the number of operating days. 1... Permeable membrane tube, 2... Collection cap,
3... Connector, 4... Reinforcing agent, 5... Passing element, 6... Passing tower, 7... Support plate nozzle, 8
... Support plate, 9 ... Distributor, 10,
11...Valve, 12...Inflow pipe, 13...Outflow pipe,
14, 15... Valve, 16... Air storage tank, 17...
Air inflow pipe, 18... Backwash water outflow pipe, 19...
Valve, 20... Backwash water inflow pipe, 21... Valve, 22...
...Air vent tube.

Claims (1)

[Claims] 1. A support plate horizontally fixed in a container and dividing the container into an inflow side and an outflow side, and a large number of over-elements erected on the support plate on the inflow side. In a condensate treatment method in which condensate containing suspended solids such as iron-based corrosion products is passed through a filter column for filter treatment, the filter element has a permeable membrane tube consisting of a hollow capillary tube. The hollow part of each permeable membrane tube is connected to the above-mentioned outflow side, and the entire amount of condensate containing the suspended solids is passed through the membrane surface of each permeable membrane tube to the above-mentioned inflow side. A method for treating condensate, characterized in that the suspended solids are removed by passing water from the membrane to the outflow side and filtering through the membrane surface.