JPS5924664B2 - Ion exchange resin cleaning method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ion exchange resin cleaning method, and more specifically, it is capable of effectively removing crud from a contaminated ion exchange resin by desalting condensate, and reducing the amount of waste liquid. Regarding ion-exchange resin cleaning methods ○ To ensure smooth operation of nuclear power plants, there are issues such as (1) reducing the amount of radiation exposure for operators, (2) improving maintainability and reducing the amount of waste liquid. There is an urgent need to develop effective ways to reduce radioactivity levels within the primary system.

Currently, (1) condensate desalination equipment and (2) reactor cleanup equipment are used to purify water in the primary system. The main method is using equipment.

The main part of the condensate desalination equipment is a mixed-bed type desalination tower made of anion and cation exchange resins, and by passing condensate through this, ionic components and crud components (mainly insoluble iron compounds) in the condensate are removed. The condensate is purified by ion exchange and filtration with an ion exchange resin layer.

The ionic components and crud components trapped in the ion exchange resin layer are removed by chemical regeneration of the ion exchange resin with acid and alkali and physical regeneration of the ion exchange resin through backwashing in the regeneration tower of the condensate desalination equipment. It can be separated from the exchange resin and discharged out of the system.

Therefore, if the regeneration operation, especially the backwashing operation, is incomplete, the crud content will accumulate in the system and the radioactivity level will increase, causing a serious problem in operation. , contaminated ion exchange resin (hereinafter simply referred to as resin) suspended in water from multiple desalination units is introduced into the bottom of the regeneration tower until the water level in the regeneration tower reaches the level of the freeboard drain pipe, and the bottom After blowing in more air and scrubbing to remove the crud from the resin, backwash water is supplied from the bottom of the regeneration tower, and the crud is discharged together with the backwash water from the overflow pipe at the top of the regeneration tower. The operation of backwashing and removing the freeboard drain pipe, which consists of discharging water still containing crud in the upper part from the freeboard drain pipe in the middle of the regeneration tower, is repeated two to three times, and then the ion exchange resin is removed. Separation and backwashing were performed.

However, in this method, the backwash water containing the crud is completely discharged from the overflow pipe, so most of the crud does not reach the overflow pipe and stagnates above the resin layer, resulting in poor efficiency. The disadvantage is that the amount of water increases and the amount of waste liquid increases.

The present invention was made in view of the current situation, and
The purpose is to provide an ion exchange resin cleaning method that can effectively remove crud from an ion exchange resin contaminated by desalination of condensate and reduce the amount of waste liquid after treatment.

The present invention has the following configuration to achieve the above object.

That is, in the ion exchange resin cleaning method of the present invention, in regenerating the ion exchange resin contaminated by the desalination treatment of condensate, (a) the contaminated ion exchange resin is removed from the freeboard drain pipe in the regeneration tower. (b) Close the vent valve and inject air for scrubbing from the bottom of the regeneration tower. The second step is to stop the supply of scrubbing air, open the overflow valve, and inject backwash water from the bottom of the regeneration tower in an amount equivalent to the amount of water stored in the regeneration tower below the freeboard drain pipe. and (c) a third step in which the overflow valve is closed to stop the supply of backwash water and the pressurized air valve is opened to discharge the contaminated water containing crud until the water level in the regeneration tower reaches the level of the freeboard drain pipe. This method is characterized by including a plurality of washing steps in which the steps are combined.

In the present invention, the crud adhering to the resin surface is removed into water by the scrubbing operation in the first step.

In the backwashing operation of the second step, the crud separated into the water is pushed up to the top of the resin layer by the backwash water injected from the bottom of the regeneration tower. The water can be injected to the middle of the overflow pipe (an amount of backwash water equivalent to the amount of water stored in the regeneration tower below the freeboard drain pipe can be injected before injection), and the water level is well below the overflow pipe. becomes.

Therefore, unlike the conventional method in which waste liquid containing crud is discharged from an overflow pipe, the crud that remains at the top of the resin layer due to the low water level is removed by the freeboard draining operation in the third step. As a result, the crud can be efficiently extracted from the freeboard drain pipe, and the amount of crud remaining in the regeneration tower is greatly reduced.

In the third step, pressurized air is injected from the top of the regeneration tower to effectively discharge waste liquid containing crud from the freeboard drain pipe.

According to the present invention, the above three steps are performed multiple times (about 3 to 4 times).
After repeating the process, by performing normal backwashing and settling operations, the crud can be effectively removed in a shorter time than in conventional methods, and the amount of waste liquid can be reduced.

Note that the amount of backwash water to be injected in the second step can be determined as follows.

The resin slurry suspended in water contains approximately 50% water by volume, and the height of the resin layer is a when the resin is injected to about 300 to 500 mm below the freeboard drain pipe of the regeneration tower. Then, the effective height of the amount of water in it is about a / 2.

Also, if the distance between the top surface of the resin layer and the level of the freeboard drain pipe is b, then (a/2+b)x (cross-sectional area of the regeneration tower)
is calculated as the volume of water to be injected, that is, backwash water. The volume of water is not necessarily limited, and can be adjusted as appropriate depending on the amount of water in the resin slurry and the type of resin slurry.

Next, the present invention will be explained in order of each step with reference to the drawings.

FIG. 1 is a schematic cross-sectional view of the device according to the present invention;
is a vent valve of the regeneration tower (hereinafter simply referred to as a vent valve), 2 is a pressurized air valve, and 3 is a water valve (not used in the present invention)
, 4 is a scrubbing air valve, 5 is an overflow valve,
Reference numeral 6 indicates a freeboard drain pipe flush valve, 7 indicates a freeboard drain valve, 8 indicates a backwash water valve, 9 indicates a regeneration tower, 10 indicates an air and water supply pipe, 11 indicates a freeboard drain pipe, and 12 indicates an overflow pipe.

First step (scrubbing) The resin suspended in water is introduced into the regeneration tower 9, and the resin is contained to a level of 1 degree 300 to 500 mm below the freeboard drain pipe 11, and the water level in the regeneration tower 9 is lowered to the freeboard drain pipe 11. level.

Next, the vent valve 1 and the scrubbing air valve 4 are opened, and air is injected into the lower part of the regeneration tower 9 from the air and water supply pipe 10 at the lower part of the resin layer to mix vigorously into the resin, causing it to adhere to the resin surface. The remaining crud is released into the water.

This operation continues for about 10 to 15 minutes.

Second step (backwashing) The vent valve 1 and the scrubbing air valve 4 are closed, the overflow valve 5 and the backwash water valve 8 are opened, and the crud separated in the first step is pushed up to the upper part of the resin layer.

In this case, the amount of backwash water to be injected is equivalent to the volume of water below the freeboard drain pipe 11 in the regeneration tower 9, and the water level in the regeneration tower 9 is well below the overflow pipe 12. Do it like this.

Third step (freeboard drain removal) Next, the overflow valve 5 and the backwash water valve 8 are closed, the pressurized air valve 2 and the freeboard drain valve 7 are opened, and in the second step, the water is pushed up to the top of the resin layer. Water containing crud is discharged from a freeboard drain pipe 11.

This operation is performed until the water level inside the regeneration tower reaches the freeboard drain pipe 11.
Continue until the level is reached.

The above three steps are repeated multiple times (about 3 to 4 times), and the number of times can be increased or decreased as appropriate depending on the degree of contamination to achieve optimal cleaning and to reduce the amount of waste liquid.

Next, after performing the scrubbing operation in the first step, only the overflow valve 5 and backwash water valve 8 are opened and the other valves are closed to perform normal backwashing, and then settling is performed to clear the shade inside the regeneration tower 9. Separate the ion exchange resin and cation exchange resin (based on the difference in specific gravity).

After separation, each resin is sent to an anion exchange resin tower and a cation exchange resin tower (not shown), and the resins are washed by repeating the first to third steps about three times in each tower. It can be done perfectly.

In addition, if the freeboard drain pipe 11 in the regeneration tower 9 was completely buried below the surface of the resin layer due to the equipment, a normal backwash separation operation was performed and each resin was sent to the respective regeneration tower. After that, the operations of the above-mentioned 1st to 3rd steps can be performed.

The series of operations including the three steps in the present invention may be performed manually, but can be completely automated by using a program timer, microcomputer, etc.

Next, the present invention will be explained with reference to Examples, but the present invention is not limited thereto in any way.

Example: The contaminated resin suspended in water transferred from the desalination tower was introduced into a regeneration tower, and the first to third steps of the present invention were repeated four times, followed by a normal backwash separation operation. Ta.

Table 1 shows the flow rate and amount of water and air used in each step, as well as the time required for each operation and the amount of waste liquid.

The graph in FIG. 2 shows the change in the total iron concentration in the waste liquid with respect to the amount of waste liquid in each process.

In the figure, A, B, C, and D each indicate the first to fourth cleaning operation stages, E indicates the backwashing stage, and F indicates the settling stage.

In addition, the amount of resin was 6.1 m''.For comparison purposes, the three steps of scrubbing, backwashing, and freeboard drain removal using the conventional method were performed twice, and after further scrubbing, normal backwashing separation was performed. performed the operation.

Table 2 shows the flow rate and amount of water and air used, their required time, and amount of waste liquid in each process.

Further, the graph in FIG. 3 shows the change in the total iron concentration in the waste liquid with respect to the amount of waste liquid in each process.

In addition, A and A2 in the figure indicate the first backwashing and freeboard drain stages, respectively, and B1 and B2 indicate the second stage.
The backwashing stage and the free card drain stage are shown respectively, where C shows the backwashing stage and D shows the settling stage.

As is clear from Tables 1 and 2 and Figures 2 and 3, the cleaning of the resin according to the present invention can be carried out in a relatively short time compared to the cleaning by the conventional method. compounds) can be removed efficiently, and the amount of waste liquid is small.

The changes in the cumulative iron concentration in the waste liquid with respect to the amount of waste liquid in this example and the comparative control (conventional method) are shown in the graph of Fig. 4 (I is the present example, ■ is the comparative control), and this shows that the above-mentioned The evaluation is supported.

As described above, according to the present invention, the crud content can be effectively removed from the ion exchange resin contaminated by the desalting treatment, and the amount of waste liquid after the treatment can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of the device according to the present invention, and FIG.
3 and 3 are graphs showing changes in the amount of waste liquid and the total iron concentration in the waste liquid for each process in the present invention and the conventional method,
FIG. 4 is a graph showing changes in the cumulative iron concentration with respect to the amount of waste liquid in the present invention and the conventional method. 1... Vent valve for regeneration tower, 2... Pressurized air valve, 3... Water valve, 4... Air valve for scrubbing, 5... ...overflow valve, 6.
...Freeboard drain pipe backwash valve, 7...
・Freeboard drain valve, 8...Backwash water valve, 9
... Regeneration tower, 10 ... Air and water supply pipe, 11 ... Freeboard drain pipe, 12 ...
...overflow pipe.

Claims (1)

[Claims] 1. When regenerating ion exchange resin contaminated by desalination treatment of condensate, (a) contain the contaminated ion exchange resin to a level below the freeboard drain pipe in the regeneration tower and lower the water level in the regeneration tower; Freeboard drain pipe level and
The first step is to open the vent valve of the regeneration tower and inject scrubbing air from the bottom of the regeneration tower, (b) close the vent valve to stop the supply of scrubbing air, open the overflow valve, and inject air from the freeboard drain pipe. The second step is to inject backwash water in an amount equivalent to the amount of water stored in the lower regeneration tower from the bottom of the regeneration tower. Ion exchange resin cleaning characterized by including a plurality of cleaning steps combined with a third step of opening a valve and discharging contaminated water containing crud until the water level in the regeneration tower reaches the level of the freeboard drain pipe. Method.