JPH02143198A - Operating method for waste liquid concentration system - Google Patents

Abstract

PURPOSE:To improve the efficiency of concentration by electrodialysis processing by returning residual liquid which is on the side of concentrated liquid before the an electrodialyser starts operating to the supply liquid tank of a reverse osmosis device. CONSTITUTION:The demineralized water on the side 6a of the supply liquid of the electrodialyser is recycled to the reverse osmosis supply liquid tank 2a through a line (j). Consequently, the salt concentration of intermediate concentrated liquid supplied to the electrodialyser 6 through a line (g) decreases gradually and when the concentration of the intermediate concentrated liquid reaches the density where the efficiency of the electrodialysis processing decreases, e.g. 30g/l, the line of the intermediate concentrated liquid is switched from (g) to (f) to quit the electrodialysis processing, thereby cyclic concentration by the reverse osmosis device. In this case, the residual liquid on the concentration side 6b of the electrodialyser decreases on the whole, so this residual liquid is returned to the reverse osmosis supply liquid tank 2a through the line (j). Consequently, a decrease in the concentration of the concentrated liquid obtained finally is prevented to some extent.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method of operating a waste liquid concentration system [7] Specifically, a method for concentrating radioactive waste liquid using a precision filtration membrane, a reverse osmosis membrane, and an electrodialysis membrane. In particular, the present invention relates to a method of operating a waste liquid concentration system that can prevent a decrease in the concentration of the concentrated liquid that is eventually obtained.

[Prior Art] Conventionally, floor drain and recycled waste liquid generated in nuclear power plants have been evaporated and concentrated using an evaporative concentrator, distilled water has been recovered, and the concentrated liquid has been sent to a solidification treatment system. Problems with this evaporative concentrator include: - Material corrosion caused by chlorine ions, etc.
■Complicated maintenance and high radiation exposure; ■High energy consumption due to the use of heavy oil boiler steam as a heating source; ■Increased installation space due to the need for maintenance.

Possible technologies to solve this problem include reverse osmosis equipment and electrodialysis equipment that utilize membrane separation technology (for example,
8-4034, JP-A-59-228988). The former discloses a method and apparatus for treating radioactive waste liquid using a combination of a reverse osmosis device and an electrodialysis device, and the latter discloses a method for recovering pure water from high conductivity water using a two or more stage reverse osmosis treatment device. Since these devices do not involve a phase change during concentration, they consume extremely little energy and do not pose the problem of material corrosion due to heating.

The present invention proposes a system using a microfiltration membrane, a reverse osmosis membrane, and an electrodialysis membrane as a system using such membrane separation technology.

This system uses a precision filtration device (membrane) to remove crud and other turbid components from the radioactive waste liquid, and then
Desalination is performed in the reverse osmosis device (membrane) in the second stage, and the desalted water is further desalted in the reverse osmosis device (membrane) in the second stage.
On the other hand, the concentrated liquid from which salts have been concentrated in the first stage reverse osmosis device is further concentrated in an electrodialysis device (membrane), and is led to a concentrated waste liquid tank, etc., where it is solidified. . The reason for using a two-stage reverse osmosis device in this system is: ■ The final recovered water properties are 21Nj/
i (Na 2 S Os ) or less, and ■ a salt concentration that can be treated by electrodialysis of approximately 30 g/jC.
It is necessary to concentrate it to a level higher than that of Na2S04). However, it is difficult to satisfy both conditions with a single stage reverse osmosis device, and both conditions can be satisfied by having a two stage reverse osmosis device. Therefore, there is no need for the reverse osmosis device to have three or more stages.

Possible operating methods for this system include a continuous treatment method, a batch treatment method, and a semi-batch treatment method.

Continuous treatment method (a treatment method in which waste liquid with a predetermined concentrated salt concentration from a reverse osmosis treatment device is continuously supplied to an electrodialysis device, although the amount of waste liquid fluctuates, and the final concentrated waste liquid with a predetermined salt concentration is also continuously obtained). Since the flow balance of the entire system changes depending on the salt concentration of the solution, it is necessary to install aluminum equipment such as pumps in each device, and its control becomes complicated, and the throughput and Since the fluctuation becomes large, there is a problem in that it is difficult to control the operation of electrodialysis treatment.

In addition, a batch treatment method (a treatment method in which each device is operated independently, in which the waste liquid is first concentrated to a predetermined salt concentration using a reverse osmosis treatment device, and then this concentrated solution is further concentrated using an electrodialysis device) ), the system is easy to control, but the process of filling the supply liquid tank of each device is a waste of time, and the throughput is low. Increasing the processing capacity further increases the number of tanks and the scale of the electrodialysis equipment, and the concentration of the liquid supplied to the first-stage reverse osmosis equipment increases, especially since the contents of the tank are concentrated to a predetermined amount. This causes a problem in that the required membrane area of the reverse osmosis membrane increases due to the increase in osmotic pressure.

Therefore, if the reverse osmosis device performs circulation concentration until the salt concentration of the concentrated solution in the reverse osmosis device reaches a predetermined value, then the concentrated solution is supplied to the electrodialysis device when the concentration of the concentrated solution reaches the predetermined value. The waste liquid whose salt concentration has decreased due to the dialysis treatment returns to the reverse osmosis treatment equipment supply liquid tank, so the salt concentration of the liquid in the tank decreases, and when the concentration falls below a predetermined value, the supply to the electrodialysis equipment is stopped. Then, circulatory concentration is performed again using a reverse osmosis device. On the other hand, the electrodialysis treatment is activated only when a predetermined amount or more of concentrated liquid in the reverse osmosis device is stored in the electrodialysis treatment device supply tank. In the present invention, this semi-batch processing method is adopted. In other words, in the semi-batch treatment method, the waste liquid is constantly concentrated using the reverse osmosis treatment equipment, and depending on the salt concentration of the first stage concentrated liquid, it is sent to electrodialysis treatment, or the waste liquid is supplied to the original reverse osmosis treatment equipment. This is a processing method that allows you to select whether to return the liquid to the liquid tank.

This semi-batch processing method has the following advantages.

In other words, ■ By operating the reverse osmosis device and the electrodialysis device independently, the flow balance of the entire system is constant, which simplifies equipment such as pumps and its control. ■ It is effective against fluctuations in salt concentration. Controlling the entire system is simple because it is handled by operating time; ■ There is no need to fill the tank with liquid, which is a waste of time; and the flow rate in the system is lower than in the case of a continuous type.

[Problems to be Solved by the Invention] However, when waste liquid is treated using a semi-batch treatment method, the electrodialysis treatment is performed in batches, so when the electrodialysis process is stopped, residual liquid with different concentrations in the electrodialysis machine is disposed of. Due to the diffusion phenomenon within the reactor, the salt concentration of the residual solution remaining on the concentrate side decreases and, conversely, the salt concentration on the feed solution side increases), causing problems that affect the recovery of highly concentrated concentrated salts.

As described above, although the semi-batch treatment method has the above-mentioned advantages, the continuous treatment method poses a problem of diffusion equilibration of the concentration of the liquid in the electrodialysis apparatus when the operation is stopped, which does not result in an interstitial layer.

The present invention was made in view of the above-mentioned problems, and when concentrating radioactive waste liquid by a semi-batch treatment method, the entire concentrated liquid is An object of the present invention is to provide a method of operating a waste liquid concentration system that can prevent dilution.

[Means and effects for solving the problems] The above-mentioned objects of the present invention are: (1) to return the residual liquid that was on the concentrate side before the start of operation of the electrodialysis device to the feed tank of the reverse osmosis device; increasing the degree of salting shrinkage in the infiltration treatment equipment;
achieved by.

That is, the present invention is a system for concentrating radioactive waste liquid using a semi-batch treatment method using a precision filtration membrane, a reverse osmosis membrane, and an electrodialysis membrane, and the salt concentration is concentrated to an allowable value by reverse osmosis treatment. supplying the liquid to the electrodialysis treatment, and returning the residual liquid remaining on the concentrated liquid side of the electrodialysis apparatus to the feed liquid tank of the reverse osmosis apparatus before starting operation of the electrodialysis apparatus using the electrodialysis membrane; and a method of operating a waste liquid concentration system, characterized in that the concentrated liquid is continuously supplied to the electrodialysis treatment until the salt concentration of the concentrated liquid in the reverse osmosis treatment reaches a predetermined value.

Hereinafter, the present invention will be specifically explained based on the drawings.

FIG. 1 is a schematic diagram showing an embodiment of the operating method of the present invention. In the figure, 1 is a precision filtration device, 2a and 2b are reverse osmosis feed liquid tanks, 3 is a first stage reverse osmosis device, and 4 is a second stage reverse osmosis device.
In the stage reverse osmosis apparatus, 5 is an electrodialysis feed liquid tank, 6 is an electrodialysis apparatus, 6a is a feed liquid side in the electrodialysis apparatus, 6b is a concentrate side in the electrodialysis apparatus, and 7 is an electrodialysis concentrate tank.

In FIG. 1, radioactive waste liquid is introduced into a precision aperture device 1. The purpose of this precision filtration device 1 is to prevent fouling of reverse osmosis membranes and electrodialysis membranes by removing crud and other suspended components in waste liquid, and a hollow fiber membrane type is preferable. It may be a flat membrane type or an ultrafiltration membrane.

The waste liquid from which the crud and the like have been removed passes through line a and is stored in the reverse osmosis supply liquid tank 2a, and is then introduced into the first stage reverse osmosis device 13 through line b, where it is salt-concentrated and desalted.

The desalinated water obtained here passes through line C and is stored in the reverse osmosis feed tank 2b, and then passes through line d to 74
It is introduced into the two-stage reverse osmosis device 4, where it is again concentrated and desalted. The concentration of the recovered water desalinated in this way is 2Q/J
(Na 2 S 04 ) or less. This recovered water is then roughly desalinated using an ion exchange resin and reused within the power plant. Further, the concentrated liquid in the second stage reverse osmosis device 4 is recycled to the reverse osmosis supply liquid tank 2a via line e.

In this way, the reverse osmosis membranes f3 and 4 are salt intermediate am.

Collect desalinated water (recovered water). This reverse osmosis device 3,
4 may be a spiral type or a tubular type, but a hollow fiber type is most desirable because it can handle a large amount of material since the cladding etc. are sufficiently removed.

On the other hand, the intermediate and lI condensate concentrated in the first stage reverse osmosis device 3 is recycled to the reverse osmosis feed liquid tank 2a through line f. Then, the concentration of the intermediate concentrate concentrated in the first stage reverse osmosis device FL3 was 30 g/J (Na 2 SO
4) When the intermediate concentrate is concentrated to the above level, the intermediate concentrate is transferred to line g
The electrodialysis feed liquid tank 5 is supplied through the electrodialysis feed liquid tank 5. The concentration of this intermediate concentrate is 30g/J (Na 2 SO4),
This is the lower limit of the salt concentration that can be processed by electrodialysis, and from the viewpoint of reverse osmosis treatment, low salt concentration concentration is preferable because it does not impose a load. This intermediate concentrated liquid is led to the electrodialyzer 6 via line h and further concentrated. This electrodialyzer 6 uses two types of membranes: a cation exchange membrane and an anion exchange membrane. These constitute an electrodialysis cell with spacers alternately stacked between them. The final condensate is temporarily stored in the electrodialysis concentrate tank 7 through line k, and then sent to a solidification treatment system (not shown). The concentration of the final concentrate at this time is 200g/! (Na 2 SO 4 ) is required.

Meanwhile, the demineralized water on the feed side 6a of the electrodialysis machine is recycled to the reverse osmosis feed tank 2a through line j. For this reason, the salt concentration of the intermediate ala solution supplied to the electrodialysis apparatus 6 from the line g gradually decreases, and the concentration at which the efficiency of the electrodialysis treatment decreases, for example, 30 g/l of the intermediate concentrated solution.
(Na 2 SO 4 ) or less, the intermediate concentrate line is switched from g to f, the electrodialysis treatment is stopped, and circulation concentration using a reverse osmosis device is performed. When the concentration of the intermediate concentrate reaches the desired concentration or higher, the line is switched from f to g again and the electrodialysis process is restarted, but at this time,
The concentration of the residual liquid remaining on the concentrating side 6b of the electrodialysis apparatus decreases due to diffusion and equalization during the operation stop time, and if the treatment is continued as it is, the overall concentration of the final concentrated liquid will decrease significantly. Therefore, in the present invention, this residual liquid is
through and returned to the reverse osmosis feed tank 2a. This return method is usually to send the diluted concentrate to line j using a pump in line i. It is also conceivable to send the concentrated liquid 6b to line k using the pump in line h when the operation is stopped. This can prevent a decrease in the concentration of the finally obtained concentrate to some extent. However, this was not sufficient, and the salt concentration of the reverse osmosis-treated intermediate concentrate supplied to the electrodialysis treatment equipment was increased from 30 g/1 to 50 g/! By doing this, the concentration of the electrodialyzed concentrate is reduced to the required 200 g.
/J (Na2504).

50 g/J (Na 2 S04) here refers to the first stage reverse osmosis treatment to ensure that the permeate salt concentration obtained by the two-stage cascade of reverse osmosis treatment equipment of the present invention is 2 q, /1 or less. This is the upper limit of the a-line of the concentrated liquid. Regarding electrodialysis treatment, there is no problem as long as it is 30 g/j or more.

This operation prevents the concentration of the finally obtained concentrate from decreasing.

[Example] Next, the present invention will be explained by examples and the like.

Examples 1-2 For waste liquids with Na2SO4 concentrations of 0.5 g/J and 20 g/J and a liquid temperature of 25°C, microfiltration treatment, reverse osmosis treatment, and electrodialysis treatment were performed in accordance with Fig. 1 in the semi-batch treatment method described above. It was done by In this process, the throughput of the first stage reverse osmosis equipment is 2.8m! /hr, and the reverse osmosis membranes used were HR-8355X 1 and HR-5355X 2.
(each manufactured by Toyobo Co., Ltd.), and the throughput of the second stage reverse osmosis device is 0.877+! /hr, and the reverse osmosis membrane used was HR-5255X 2 (manufactured by Toyobo Co., Ltd.).

In addition, the flow rate of the supply liquid and 'aM liquid of the electrodialyzer is 1.
At 8 i/hr, the electrodialysis membranes were Acibrex -101, a cationic membrane, and Acibrex A, an anionic membrane.
-201 (each manufactured by Asahi Kasei Corporation), 360 sheets were used.

In the first stage reverse osmosis treatment equipment, the waste liquid is treated at 50 g/J (Na
2 S04 ) and then fed to electrodialysis treatment. In this process, the residual liquid remaining on the concentrate side of the electrodialyzer when the electrodialysis process was restarted was returned to the first stage reverse osmosis feed tank.

Feed solution salt concentration from the first stage reverse osmosis treatment is 30 g/J
(Na2SO4) was supplied to the electrodialysis treatment apparatus.

Table 1 shows the salt concentration, stopping time, processing time, etc. of the six solutions at this time.

Comparative Examples 1 to 2 Na2SO4 concentration is 5 g/J and 208/J, liquid temperature is 25
C. The waste liquid was subjected to microfiltration treatment, reverse osmosis treatment and electrodialysis treatment in the same manner as in Examples 1 and 2 using the semi-batch treatment method described above according to FIG.

The conditions for supplying from the first stage reverse osmosis treatment device to the electrodialysis treatment device are - point control of 30 g/j (Na 2 S04), and when the electrodialysis treatment is restarted, the residual liquid remaining on the concentrate side is left as is. The state of

Table 1 shows the salt concentration, stopping time, processing time, etc. of the six solutions at this time.

As shown in Table 1, by the operating method of the present invention,
A highly concentrated concentrate is obtained. The effect is particularly significant when the system supply salt concentration (line a) is low.

[Effects of the Invention] As explained above, by the operating method of the present invention, concentration by electrodialysis treatment is performed extremely efficiently, and a highly concentrated concentrate can be obtained. Furthermore, compared to evaporation tn-condensation, it saves energy and has the effect of reducing the risk of exposure to radiation to about 115%.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of the operating method of the present invention. 1:a3:4:5:Precision filtration device1. 2b: reverse osmosis feed liquid tank, first stage reverse osmosis device, second stage reverse osmosis device, electrodialysis feed liquid tank, 6: electrodialysis device (6a: feed liquid side, 6b: I liquid supply side), 7: Electrodialysis concentrate tank, a-j Niline.

Claims (1)

[Claims] 1. A system for concentrating radioactive waste liquid using a semi-batch treatment method using a precision filtration membrane, a reverse osmosis membrane, and an electrodialysis membrane, wherein the salt concentration is reduced to an allowable value by reverse osmosis treatment. In addition to supplying the concentrated liquid to the electrodialysis process, before starting the operation of the electrodialysis apparatus using an electrodialysis membrane, the residual liquid remaining on the concentrated liquid side of the electrodialysis apparatus is transferred to the supply liquid tank of the reverse osmosis apparatus. 1. A method for operating a waste liquid concentration system, comprising: returning the concentrated liquid to the electrodialysis process, and continuing supply to the electrodialysis process until the salt concentration of the concentrated liquid in the reverse osmosis process reaches a predetermined value, thereby performing the concentration process. 2. The radioactive waste liquid is a solution whose main component is sodium sulfate, and the allowable value for reverse osmosis treatment is 50 g/
l(Na_2SO_4), the predetermined value is 30g/l(Na_
2SO_4) A method for operating a waste liquid concentration system according to claim 1.