JPH0727067B2 - Waste liquid treatment method and apparatus in nuclear power plant - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a waste liquid treatment method and apparatus in a nuclear power plant, and particularly to a salt by a membrane evaporative concentration apparatus using a hydrophobic porous membrane on an evaporation surface. The present invention relates to a waste liquid treatment method and apparatus for evaporating and concentrating a waste liquid to obtain condensed water of high purity.

[Conventional technology]

Membrane evaporative concentrators using a hydrophobic porous membrane on the evaporation surface of an evaporation chamber containing a solution containing salts include, for example, JP-B-49-
There is a structure shown in 45461. A waste liquid treatment method incorporating a membrane evaporative concentrator is disclosed in, for example, JP-A-61-1641.
There is a method shown in No. 95.

Since these film evaporative concentrators use a film on the evaporation surface, the evaporation surface can be freely set, and the device can be easily downsized. Further, since it is possible to generate steam from the waste liquid at medium temperature and normal pressure, a polymer material that is relatively resistant to corrosion can be used as a structural material. In view of the above, the membrane evaporative concentrator has many advantages over conventional evaporator concentrators made of metallic materials.

[Problems to be Solved by the Invention]

By the way, the waste liquid in a nuclear power plant may contain solids and a surfactant in addition to salts. The waste liquid mixed with such impurities, especially the surfactant, hydrophilizes the hydrophobic porous membrane used on the evaporation surface of the membrane evaporative concentrator, leaks the waste liquid from the membrane, and reduces the purity of condensed water. As described above, there is a problem that the waste liquid cannot be treated in the membrane evaporative concentrator in which the membrane is made hydrophilic, and this problem has not been solved by the conventional method. Therefore, an object of the present invention is to maintain the purity of condensed water and to regenerate a contaminated membrane in order to cope with the case where the membrane of the membrane evaporation concentrator is contaminated and made hydrophilic.

Further, there is a problem that a waste liquid is secondarily generated by a treatment reagent in the regeneration treatment of the contaminated film, and another object of the present invention is to reduce the amount of the reagent used for the regeneration treatment.
Further, there is a problem that the operation rate of the membrane evaporation / concentration device is lowered due to the interruption of the waste liquid treatment due to the regenerating treatment of the contaminated film, and another object of the present invention is to reduce the frequency of the regenerating treatment of the contaminated film. is there.

[Means for Solving the Problems]

In order to achieve the above-mentioned object, the present invention provides a method for treating waste liquid by a membrane evaporative concentrator, in which a waste liquid from which a surfactant has been removed in advance is passed through the membrane evaporative concentrator and the conductivity of condensed water obtained from the device is changed with time. When the conductivity value reaches a predetermined value, the waste liquid treatment by the membrane evaporative concentrator is interrupted, the membrane is acid washed and alcohol washed, and finally dried to adhere to the membrane. The waste liquid treatment is restarted after removing the existing liquid material.

In addition, in order to achieve the above-mentioned other purpose, an alcohol solution is used in the alcohol cleaning in the recycling process of the contaminated film.
It is heated to a temperature not lower than 35 ° C and not higher than the boiling point to bring it into contact with the contaminated film. Further, in order to achieve the above-mentioned other object, the waste liquid is subjected to a surfactant removal treatment in advance and then treated in a membrane evaporation concentration device.

In order to carry out the method, the device of the present invention may be configured as follows. That is, a waste liquid containing salts generated in the nuclear power plant is introduced into the outer cylinder of the membrane evaporation concentrator, and the vapor of the waste liquid generated in the outer cylinder is provided as a hydrophobic porous tubular membrane in the outer cylinder. In a waste liquid treatment apparatus for permeating and introducing into the inside thereof to concentrate salts and obtaining condensed water, a means for measuring the electric conductivity of condensed water flowing in the tubular membrane in the apparatus, and an acid washing liquid and alcohol in the tubular membrane A waste liquid treatment apparatus incorporating a membrane evaporative concentrator equipped with a means for regenerating a contaminated membrane, which comprises means for supplying a cleaning liquid and means for supplying warm air into a tubular membrane.

Furthermore, in order to carry out the other method, the present invention preferably comprises a waste liquid treatment system comprising the following elements (a) to (f).

(A) A waste liquid storage tank containing salts and a surfactant.

(B) A foam separator for blowing fine bubbles into the waste liquid sent from the storage tank.

(C) A foam storage tank in which the surfactant is concentrated and generated in the foam separator.

(D) The waste liquid treatment device for treating the waste liquid generated in the foam separation device and having the surfactant removed.

(E) Storage tank for concentrated waste liquid generated in the waste liquid treatment device.

(F) A dryer that turns the foam and concentrated waste liquid stored in each of the storage tanks into a dry powder.

In order to solve the above-mentioned problems, the influence of the condensed water on the conductivity when a salt solution containing a surfactant was treated as a stock solution (corresponding to a waste solution) in a membrane evaporation concentrator was examined.
As a result, as shown in Fig. 5, the surfactant (DB
It has been found that the conductivity of condensed water increases after a lapse of a predetermined time when S, dodecylbenzene sodium sulfonate is contained. Then, it was found that the time until the electric conductivity of the condensed water increases is inversely proportional to the surfactant concentration, and the higher the concentration, the shorter the electric conductivity of the condensed water increases. As a result of studying a method of regenerating a film in which the electric conductivity of the condensed water is increased, that is, the membrane contaminated by the undiluted solution, the present invention has been accomplished.

[Action]

In the waste liquid treatment method of the present invention, the electrical conductivity of the condensed water obtained from the membrane evaporative concentrator is measured over time. Accordingly, if the membrane is contaminated and the waste liquid leaks to the condensed water side, the electric conductivity of the condensed water is increased, so that the degree of the membrane contamination of the membrane evaporative concentrator can be detected. Also, the electric conductivity of condensed water is 10
When 100 μS / cm is reached, the waste liquid treatment by the membrane evaporative concentration device is interrupted to prevent the waste liquid from leaking to the condensed water side due to membrane contamination, and the condensed water can be maintained at a high purity. In addition, the contaminated film is washed with acid and alcohol,
By finally drying and removing the liquid substance adhering to the membrane and restarting the waste liquid treatment, the contaminated membrane can be regenerated, and the waste liquid treatment by the membrane evaporation concentrator can be performed again.

Furthermore, in the alcohol cleaning in the recycling process of the contaminated film, by heating the alcohol solution to a temperature not lower than 35 ° C and not higher than the boiling point and contacting the contaminated film, the same cleaning effect can be obtained with an alcohol solution having a relatively lower concentration than at room temperature. Can be obtained.

In addition, by treating the waste liquid in advance with a surfactant and then treating the waste liquid with a membrane evaporative concentrator, the progress of membrane contamination by the waste liquid can be delayed, and the time until the waste liquid leaks from the membrane can be lengthened.

〔Example〕

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

FIG. 1 shows a waste liquid treatment apparatus 1 according to the present invention, which incorporates a membrane evaporative concentrator 2. The waste liquid treatment apparatus 1 is mainly composed of a membrane evaporative condenser 2 and is composed of a waste liquid circulation system 3, 3A, a cooling water circulation system 4, 4A, a cleaning liquid circulation system 5, 5A and a dry air supply system 6. . The waste liquid circulation systems 3 and 3A are provided with a storage tank 7 for storing the waste liquid, a heater 8 such as a heater for heating the waste liquid, and a waste liquid circulation pump 9. In the cooling water circulation system 4, 4A,
A cooling water storage tank 10, a cooling device 11, a circulation pump 12, and a detection end 13 of a detector 13A for detecting the electric conductivity of condensed water are provided. Further, the cleaning liquid circulation system 5 is provided with a cleaning liquid storage tank 14 and a cleaning liquid circulation pump 15. A warm air supplier 16 is provided in the dry air supply system 6. Each circulation system is provided with valves 21 to 30 for switching between a waste liquid processing operation and a contaminated film regeneration operation.

The membrane evaporative concentrator 2 is composed of a tubular membrane module 17 and an outer cylinder 18 that houses the tubular membrane module 17. The inside of the tubular membrane is a cooling water flow passage 19, and the outside of the tubular membrane is a waste liquid flow passage. Forming 20. The tubular membrane 17 is a porous tubular membrane made of a hydrophobic material such as polytetrafluoroethylene, polyethylene, polypropylene and polysulfone. Membrane pore size is 0.
Those with a porosity of 50 to 85% are used.

Next, the waste liquid treatment method of the present invention using the waste liquid treatment device 1 will be described. The waste liquid stored in the storage tank 7 is heated by the heater 8.
Is heated to a predetermined temperature by means of the pump 9 and is supplied to the waste liquid flow path 20 of the membrane evaporator / concentrator 2 through the circulation system 3 by the pump 9.
It is circulated through the circulation system 3A. On the other hand, the pure water stored in the storage tank 10 is cooled to a predetermined temperature, passes through the circulation system 4 by the pump 12, and the cooling water flow path 19 in the tubular membrane 17 of the membrane evaporative concentrator 2 is passed.
And is circulated through the circulation system 4A. Here, the high temperature waste liquid in the flow path 20 and the low temperature cooling water in the flow path 19 are in a state of existing via the membrane wall of the tubular membrane 17. Since the tubular membrane 17 uses a hydrophobic porous membrane, only water vapor generated from the waste liquid passes through the pores of the membrane and is directly condensed into cooling water inside the tubular membrane to become condensed water. The increased amount of the condensed water thus obtained is discharged from, for example, the storage tank 10 of the circulation system 4, 4A. By such a treatment operation, the salts of the waste liquid can be concentrated and, at the same time, condensed water of high purity can be obtained and the waste liquid can be treated.

By the way, if solid content and surfactant are mixed in the waste liquid,
These adhere to the outer surface of the tubular membrane 17, and if the concentration is high, the membrane becomes contaminated over the treatment time. When the membrane becomes hydrophilic due to the contamination of the membrane, the waste liquid leaks to the side of the cooling water where the vapor condenses, so that high-purity condensed water cannot be obtained, and the waste liquid treatment operation by the membrane evaporation concentrator 2 is stopped. I have no choice.

Therefore, in the present invention, the detection end 13 of the detector 13A that measures the conductivity of the condensed water over time is provided in the cooling water circulation system 4A that can obtain the condensed water. If the waste liquid leaks to the cooling water side due to the contamination of the film, the conductivity will increase, so if the value becomes a predetermined value (10 to 100 μS / cm) or more, the detection end 13 detects it. A signal is emitted by the detector 13A and the processing of the waste liquid is interrupted. As a result, the influence of the leakage of the waste liquid from the tubular membrane 17 can be reduced, and high-purity condensed water can be maintained.

Next, after the waste liquid treatment is interrupted, the contaminated film of the tubular film 17 is regenerated. In this case, first, the valve 21 is opened, the waste liquid in the membrane evaporator / concentrator 2 is extracted and returned to the storage tank 7 via the circulation system 3B.
Next, the valves 22, 24, 26 and 27 are closed, the valves 23 and 25 are opened, and the pump 15 is operated from the cleaning liquid storage tank 14 to supply the cleaning liquid to the channel 19 of the tubular membrane 17. The cleaning liquid is an acid cleaning liquid and an alcohol cleaning liquid. The acid cleaning solution is H ₂
SO ₄ and oxalic acid are used. Further, as the alcohol cleaning solution, it is preferable to use a lower alcohol aqueous solution such as methanol or ethanol adjusted to a concentration capable of making the membrane hydrophilic. Here, the cleaning liquid, particularly the alcohol cleaning liquid, is heated to a temperature not lower than 35 ° C. and not higher than the boiling point, preferably not higher than the heat-resistant temperature of the film and brought into contact with the contaminated film of the tubular film 17 for cleaning. This enhances the cleaning effect of the cleaning liquid, reduces the amount of acid and alcohol used, and suppresses secondary generation of waste liquid. Furthermore, it is preferable that the cleaning liquid containing the surface-active agent after cleaning the contaminated film is contacted with, for example, activated carbon to remove the surface-active agent and regenerated. As a result, the cleaning liquid can be repeatedly used and secondary generation of waste liquid can be suppressed. Next, after removing the contaminants adhering to the inside and outside of the tubular membrane, the cleaning liquid is extracted from the inside of the membrane evaporation concentrator 2. After that, the valves 27, 28, 30 are opened, and warm air of a predetermined temperature is supplied from the warm air supplier 16 to remove the liquid substance adhering to the film.

By this regenerating operation of the contaminated film, the solid matter and the surfactant attached to the tubular film 17 can be removed, and the hydrophobicity of the film can be recovered.

As described above, the regeneration of the contaminated film of the tubular membrane 17 in the membrane evaporative concentrator 2 requires an operation of cleaning the contaminated membrane to remove contaminants from the membrane and finally drying the membrane. On the other hand, in the case of the conventional filtration apparatus for water treatment, the regeneration of the membrane fouling only needs to remove the fouling substances from the membrane by washing, and it is not necessary to finally dry the membrane. This is because the evaporation process by the film evaporation concentrator 2 is operated in a state where the tubular film 17 is hydrophobized, that is, in a state where no liquid substance exists in the pores of the film. The results of a comparative experiment are shown in FIG. 3 in order to confirm the effect of drying the membrane after washing.
FIG. 3 shows the change with time of the conductivity of the condensed water when the membrane was washed and A was kept as it was, and B was further dried and then Na ₂ SO ₄ solution was supplied again to evaporate and condense. Show. As a result, the conductivity of A increased immediately after the start of supplying the Na ₂ SO ₄ solution. This indicates that the hydrophobic state of the membrane has not recovered. On the other hand, in B, the conductivity of the condensed water did not increase over a long period of time. From this, in the regeneration of the contaminated film in the membrane evaporation concentrator 2, it is understood that it is important to dry the contaminated film after the contaminated film is finally washed.

Next, FIG. 4 shows changes in the dry state of the film in the drying step. Immediately after washing the membrane, as shown in (1) of FIG. 4, the liquid 40 is filled in the pores 17A, and the membrane is in a hydrophilic state. It is shown in FIG. 3 that the film evaporation operation cannot be performed with such a film. Once the membrane is dried, the tubular membrane 17
The liquid 40 attached to the pores 17A of FIG. 4 shifts from the state (2) of FIG. 4 to the state (4), and when the film is completely dried, the state of the state (4) of FIG. 4 is reached. Among them, FIG. 4 (2) shows a state in which only the surface of the membrane is dried and the liquid 40 remains inside the pores 17A of the membrane. When such a membrane is used for the evaporation operation, The liquid material 40 accumulates inside the pores of, and the waste liquid easily leaks. In addition, it takes a long time to dry in order to obtain a completely dry state as shown in FIG. Therefore, it is preferable to dry the membrane in the state of (3) in which a very small amount of liquid substance in a state of almost equilibrium with natural air is attached to the pores 17A of the membrane.

Therefore, close valves 23, 25, 28, 30 and open valves 22, 26, 24, 2
After opening 7,29, the waste liquid and the cooling water are supplied from the circulation systems 3,4 to the membrane evaporation concentrator 2, and the waste liquid treatment is started again.

By the waste liquid treatment method described above, it is possible to suppress the mixing of the waste liquid into the condensed water as much as possible and maintain the condensed water in high purity. In addition, it is possible to reduce the amount of secondary waste liquid generated by the cleaning liquid when the contaminated film is regenerated.

Next, a waste liquid treatment system in which the waste liquid treatment apparatus 1 of the present invention is combined with a surfactant removal treatment step in advance will be described with reference to FIG. This system is intended for treating, for example, high-conductivity waste liquid generated in a nuclear power plant. The waste liquid supplied from the storage tank 7 containing the waste liquid is sent to the pretreatment device 31. The pretreatment device 31 is, for example, a foam separation device,
The waste liquid is retained for a predetermined time, and fine bubbles are blown into the waste liquid. Since the surfactant is concentrated in the generated foam, the foam is separated from the waste liquid and sent to the storage tank 32. The waste liquid which has stayed in the pretreatment device 31 for a predetermined time and from which the surfactant has been removed is supplied to the waste liquid treatment device 1 incorporating the membrane evaporation concentrator 2 for treatment. In addition, in case of a sudden increase in the surfactant concentration in the liquid supply to the waste liquid treatment apparatus 1 in an unexpected situation, the surfactant concentration in the liquid supply is measured, and if the value reaches a predetermined value. For example, it is desirable to install a preliminary pretreatment device that bypasses the separately provided activated carbon layer and then supplies it to the waste liquid treatment device 1 (not shown). The waste liquid processed and concentrated in the waste liquid processing device 1 is sent to the storage tank 33. The waste liquids stored in the storage tank 32 and the storage tank 33 are supplied to the dryer 34, dried and powdered, and further molded into a pellet solidified by the solidifying machine 35 and stored in the storage tank 36.

On the other hand, the condensed water obtained by the waste liquid treatment apparatus 1 is further processed by the desalting device 37, stored in the storage tank 38, and reused as condensate makeup water. Here, when the membrane of the membrane evaporative concentrator 2 is contaminated by the waste liquid treatment for a long time, the conductivity of the condensed water increases, so that if the value reaches a predetermined value (10 to 100 μS / cm). If the waste liquid treatment is interrupted. Further, the contaminants are removed from the contaminated film by the above-mentioned washing method, and the hydrophobic property of the film is restored by drying, and then the waste liquid is supplied again to the film evaporation concentrator 2 to restart the waste liquid treatment.

The above waste liquid treatment system delays the progress of membrane contamination and improves the operation rate of the waste liquid treatment device 1.

〔The invention's effect〕

According to the method of the present invention, it is possible to prevent the waste liquid from mixing into the condensed water and maintain the condensed water to be recovered at a high purity, so that there is an effect of reducing the load of the desalting device which is the next treatment step. Further, since the amount of the reagent required for cleaning the contaminated film can be reduced and the secondary generation of waste liquid can be suppressed, there is an effect that the waste liquid treatment for that can be simplified. Further, there is an effect that the progress of membrane contamination can be delayed and the operation rate of the waste liquid treatment device can be improved.

Further, according to the apparatus of the present invention for carrying out the method, it is possible to accurately detect the degree of hydrophilization of the tubular membrane due to membrane contamination by measuring the electric conductivity of the condensed water flowing in the tubular membrane of the membrane evaporation concentration. At the same time, when the contaminated membrane is regenerated, an acid cleaning solution, an alcohol cleaning solution, and warm air are sequentially supplied into the tubular membrane, and the pores of the membrane are cleaned by this series of operations, and the liquid substance remaining in the pores Can be quickly removed to make it hydrophobic, and the waste liquid treatment can be restarted in a short time.

Furthermore, according to the wastewater treatment system of the present invention, by incorporating each element including the foam separation device in the line, the operation rate of the wastewater treatment device can be improved and efficient treatment can be performed.

[Brief description of drawings]

FIG. 1 is an explanatory view of a waste liquid treatment apparatus of one embodiment of the present invention, FIG. 2 is a waste liquid treatment system diagram of one embodiment of the present invention, and FIG. 3 is an effect of a membrane drying operation after cleaning a contaminated membrane. Graph of the experimental data shown, (1), (2), (3) and (4) in FIG.
FIG. 5 is an enlarged cross-sectional view showing the change in the dry state of the membrane, and FIG. 5 is a graph of experimental data showing the change in the electric conductivity of the condensed water when the waste liquid containing the surfactant is subjected to the membrane evaporation concentration treatment. 1 ... Waste liquid treatment device, 2 ... Membrane evaporative concentrator, 3, 3A ... Waste liquid circulation system, 4, 4A ... Cooling water circulation, 5, 5A ... Cleaning liquid circulation system, 6 ...
Hot air supply system, 13 ... Conductivity detection end, 13A ... Conductivity detector, 31 ... Pretreatment device.

Claims (6)

[Claims] 1. A waste liquid containing salts and a surfactant generated in a nuclear power plant is treated with a membrane evaporative concentrator using a hydrophobic porous membrane on the evaporation surface to concentrate salt and condense water. In the obtained waste liquid treatment method, after removing the surfactant in the waste liquid, the conductivity of the condensed water is measured, and when the value reaches a predetermined value, the waste liquid treatment by the membrane evaporation concentrator is interrupted, A method for treating waste liquid in a nuclear power plant, comprising: washing the membrane with an acid and alcohol, and then drying it to remove the liquid substance adhering to the porous membrane, and then restarting the waste liquid treatment. 2. The alcohol cleaning is performed by using an alcohol solution.
The method for treating waste liquid in a nuclear power plant according to claim 1, wherein the method is performed by heating to a temperature of not less than 0 ° C and not more than the boiling point to bring the porous membrane into contact with the porous membrane. 3. A waste liquid containing salts and a surfactant generated in a nuclear power plant is treated with a membrane evaporative concentrator using a hydrophobic porous membrane on the evaporation surface to concentrate salt and to remove condensed water. In the obtained waste liquid treatment method, the waste liquid is subjected to a surfactant removal treatment in advance and then supplied to the membrane evaporative concentration apparatus, the conductivity of the condensed water is measured, and the value is a predetermined value of 10 to 100 μS / cm. When it reaches the above, the waste liquid treatment by the membrane evaporative concentration device is interrupted, the porous membrane is washed with acid and alcohol, and then dried to remove the liquid substance adhering to the porous membrane, and A method for treating waste liquid in a nuclear power plant, comprising restarting the waste liquid treatment. 4. The alcohol cleaning is performed with an alcohol solution.
The method for treating waste liquid in a nuclear power plant according to claim 3, wherein the method is performed by heating to a temperature of not less than 0 ° C and not more than the boiling point to bring the porous membrane into contact with the porous membrane. 5. A waste liquid containing salts and a surfactant generated in a nuclear power plant is introduced into the outer cylinder of a membrane evaporation concentrator, and the vapor of the waste liquid generated in the outer cylinder is provided in the outer cylinder. Permeate through the hydrophobic porous tubular membrane and introduce into it,
In a waste liquid treatment device for condensing salts and obtaining condensed water, a means for previously removing a surfactant in the waste liquid before introducing the waste liquid into the membrane evaporative concentrator, and a condensing liquid flowing through the tubular membrane. A membrane evaporative concentrator equipped with means for regenerating a contaminated membrane, which comprises means for measuring conductivity of water, means for supplying an acid cleaning solution and alcohol cleaning solution into the tubular membrane, and means for supplying warm air into the tubular membrane. A waste liquid treatment device in a nuclear power plant characterized by being incorporated. 6. A waste liquid treatment system in a nuclear power plant comprising the following elements (a) to (f). (A) A waste liquid storage tank containing salts and a surfactant. (B) A foam separator for blowing fine bubbles into the waste liquid sent from the storage tank. (C) A foam storage tank in which the surfactant is concentrated and generated in the foam separator. The waste liquid treatment device according to claim 5, wherein (d) the waste liquid generated in the foam separation device and having the surfactant removed is treated. (E) Storage tank for concentrated waste liquid generated in the waste liquid treatment device. (F) A dryer that turns the foam and concentrated waste liquid stored in each of the storage tanks into a dry powder.