JPS63141604A - Method for removing deposit in centrifugal thin film drier - Google Patents

Abstract

PURPOSE:To remove scales from a heating surface and to discharge the scales as dried powder without generating cleaning waste liq. by supplying hot water to the heating surface deposited with scales from a waste liq. supply port and vaporizing the water. CONSTITUTION:The concd. waste liq. is introduced from the waste liq. supply port 14 and distributed onto the heating surface 17 by a distributor 15. THe distributor 15 consists of a rotating shaft 18 and a movable blade 19 on the shaft 18. When pulverization is carried out, scales are deposited on the heating surface 17. Accordingly, hot water is supplied from the waste liq. supply port 14 to dissolve the deposit on the heating surface. In this case, the flow rate of hot water is controlled so that the hot water is vaporized before the water is discharged from the device and the deposit is discharged from the bottom of the device as dried powder, the supply flow rate of the hot water is made higher than that of the concd. waste liq. during concd. waste liq. treatment or the temp. of the heating surface is made lower than that during concentration, and the hot water is vaporized before being discharged.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for removing deposits in a centrifugal thin film dryer for drying and pulverizing radioactive waste fluid generated from nuclear facilities.

[Conventional technology]

Radioactive waste liquid generated from nuclear facilities such as nuclear power plants is usually dried and powdered using a centrifugal thin film dryer, and then granulated into pellets and solidified in a dohum can. Second
The figure shows, as an example, radioactive waste liquid (recycled waste liquid whose main component is sodium sulfate) generated from boiling water nuclear power plants.
The flowchart of the volume reduction solidification equipment is shown in which the powder is dried and powdered using a centrifugal thin film dryer, and then turned into pellets using a granulator. As shown in Fig. 2, the regenerated waste liquid is concentrated to a predetermined concentration (approximately 20 wt) in a concentrator and stored in a supply tank 1.The concentrated waste liquid is continuously drawn out from the bottom of the tank by a circulation pump 2. It is taken out and returned to the tank to prevent the contained solids (crud, silica, etc.) from settling. The concentrated waste liquid is branched from this circulation line 3, and a part of it is sent to the supply pump 4 and the flow meter 5i.
It is then supplied to a centrifugal thin film dryer 6, where it is dried and pulverized. The powder produced in the centrifugal thin film dryer is granulated,
After being solidified into pellets in a machine 8, they are filled into drums 9.

FIG. 3 is a partial sectional view of the centrifugal four-way dryer.

The concentrated waste liquid is introduced into the centrifugal thin film dryer through the waste liquid supply port 14 and is evenly distributed by the distributor 15 to the heat transfer surface 17 of the evaporator vessel. This distributor 15 consists of a rotating shaft 18 provided at the center of the evaporator, a movable blade 19 attached to the rotating shaft 18, and a drive motor 12 for the rotating shaft. The blade 19 rotates close to the inner wall of the dryer*! +18, and spread outward due to the centrifugal force caused by rotation to come into contact with the inner wall 17 of the dryer. The waste liquid falling vertically on the heat transfer surface (dryer inner wall surface) 17 by gravity forms a liquid film on the heat transfer surface 17, and the heating jacket 1 on the outside of the container wall through which the heat medium flows.
6 and evaporated to dryness. As the heat medium flowing through the heating jacket 16, for example, high pressure steam is used. The blade 19 removes scale attached to the heat transfer surface 17 of the container wall as it rotates. From,
The liquid is reduced to dry powder, and the generated powder is taken out from the powder outlet 20 at the lower end of the centrifugal thin film dryer 6.In addition, the steam generated by the evaporation of the waste liquid is transferred to the centrifugal thin film dryer 6. The steam is discharged from the steam outlet 13 at the top of the tank and introduced into a mist separator and a condenser (not shown). The steam is converted to water in the condenser and reused.

Now, if concentrated waste liquid is continuously pulverized for a long time,
Solid matter may adhere to the blade 19, the pressing force of the blade may change, and solid matter may adhere to the heat transfer surface 17 of the centrifugal four-membrane dryer. This deposit is caused by the crystallization of sodium in the sulfur, which is the main component of the concentrated waste liquid, and has a large degree of rupture. Therefore, as this deposit grows and increases in thickness, the wear of the blade becomes significant. In addition, the heat transfer efficiency of the heat transfer surface decreases, and as the amount of water evaporated is small, the water content of the produced powder increases. When the moisture content of the produced powder exceeds 3 wt%, lumps are formed and pelletization becomes difficult.

Therefore, when the powder moisture content exceeds the standard value (3wt%),
Conventionally, hot water was filled inside the centrifugal thin film dryer to dissolve and wash away the solids on the heat transfer surface. This washing waste liquid is returned to the upstream concentrator inlet and mixed with the recycled waste liquid for treatment. After washing, the centrifugal thin film dryer ventilates steam, and performs drying and warming.

[Problem that the invention seeks to solve]

In the above conventional technology, waste liquid is generated as a result of cleaning the centrifugal thin film dryer, and this waste liquid is processed in the upstream concentrator, so there is a problem that the throughput of the concentrator becomes large, and Since centrifugal thin film dryers require drying and warming, there is a problem in that the operating efficiency, that is, the operating rate of the equipment is low.

An object of the present invention is to provide a method for removing deposits from a centrifugal thin film dryer that does not generate waste liquid and can improve operating efficiency.

[Failure to solve the problem]

The method for removing deposits from a centrifugal thin film dryer according to the present invention is to supply warm water from the concentrated waste liquid supply port to a centrifugal f'4M dryer with deposits attached to the heat transfer surface, and use the hot water to remove deposits from the heat transfer surface. The method is characterized in that the deposits are dissolved and the hot water is evaporated before the hot water flows out of the centrifugal thin film dryer, and the deposits are discharged from the lower part of the centrifugal thin film dryer as a dry powder.

As a preferred implementation and standard of the present invention, in order to remove the above-mentioned deposits, the supply flow rate of hot water is changed to @f! during concentrated waste liquid treatment. The temperature of the heat transfer surface should be larger than that of the waste liquid supply flow, or the temperature of the heat transfer surface should be lower than the temperature of the heat transfer surface during waste liquid treatment, and the temperature should be set so that the hot water evaporates before flowing out.

[Effect]

The deposits on the heat transfer surface of the centrifugal 4-membrane dryer are dissolved by hot water, and while flowing down the heat transfer surface, the hot water evaporates and the deposits become powder and are removed from the centrifugal thin film dryer. be done. Therefore,
No cleaning waste is generated when removing deposits.
Further, there is no need for subsequent drying and warming treatment in the centrifugal thin film dryer.

[Actual example]

Heat transfer area 1.2 yFI', heating jacket steam @ 1 degree
70℃, isobaric cuff Kf/!・G, blade rotation speed 48
A simulated concentrated waste liquid (Na, So,: 20 wt%, Fe, O,, S
io, solid content 20wt, remainder: water) at a temperature of 50°C.
A treatment flow of f80t7h was supplied, and drying and pulverization treatment was performed. After approximately 20 hours of operation under the supply of this simulated concentrated waste liquid, the physical properties of the powder decreased below the standard value, so the supply of the concentrated waste liquid was stopped, and 50°C hot water was instead supplied from the concentrated waste liquid supply port to B.
Supplied at 7h. After hot water was injected, powder fell from the bottom of the centrifugal thin film dryer. After 30 minutes, increase the hot water flow rate to 8
The speed was increased from 0 t/h to 110 t/h, and the blade rotation speed was increased from 48 Orpm to 56 Orpm and operated for 30 minutes. During this time, powder similarly fell from the lower part of the centrifugal four-membrane dryer. Since the supplied hot water contained no solid components, the powder that fell during this period was obtained by removing the solid matter that had adhered to the heat transfer surface. This mechanism can be considered as follows.

That is, the hot water injected into the centrifugal thin film dryer is heated to the edge and evaporates, but some of it flows down on the heat transfer surface. When hot water reaches the solids on the heat transfer surface, it dissolves the solids and turns into a slurry. It is thought that this slurry was heated as it flowed downward and was evaporated and dried into powder.

The amount of hot water injected must be adjusted within an appropriate range.

That is, when the amount of hot water injected is small, the hot water evaporates before reaching the solids on the heat transfer surface, so that no effect of dissolving the solids is produced. In addition, if the amount of hot water injected is too large, the amount of dissolution of solids on the heat transfer surface will increase, but the evaporation drying of the generated slurry will not be sufficient, and powder with a high water content or slurry-like It will be discharged and it will be impossible to make pellets.

The lower limit of the amount of hot water injection is the minimum value that hot water can reach the solids on the heat transfer surface, and this value is equal to the amount of water in the concentrated waste liquid supplied to the centrifugal thin film dryer during dry powder production. . In the case of this example, the feed flow of the concentrated waste liquid is 180 t/h, the solid content concentration is 22 Wt 1, and the specific gravity is 1.18 f/-, so the water content in the waste liquid is 80 t/h x 1.18 x 0.78 = 74
z/h, which is the lower limit of the hot water injection amount.

On the other hand, the upper limit value of the hot water injection amount is the maximum value that can evaporate hot water in the centrifugal thin film dryer, and this value is equal to the evaporation limit value of the centrifugal thin film dryer. The evaporation limit for one shift of a centrifugal thin film dryer is determined by the heat transfer [1jdR1 operating conditions, etc., but in the case of this example, the upper limit of the hot water injection rate is approximately 120 t/h.
It is.

From the above, in the case of this embodiment, the appropriate range of hot water injection amount is a value from 74 t/h to 120 z/h.

The above example is a case where the steam heating temperature of the heating jacket of the centrifugal thin film dryer is kept constant and the hot water flow rate is made larger than the radiation pressure waste liquid treatment flow rate, but instead, the hot water flow rate is made the same as the radioactive waste liquid treatment flow rate, It is also possible to carry out an embodiment in which the adhering material is removed by lowering the steam heating temperature of the heat jacket. Such an embodiment will be described below.

After supplying the simulated concentrated waste liquid to a centrifugal thin film dryer under the same conditions as in the previous example and drying and powdering it for 20 hours, the supply of the concentrated waste liquid was stopped, and instead, 80 tons of 50°C hot water was added.
/h for 30 minutes, then the hot water flow rate was the same,
Increase the steam pressure in the steam jacket from 7 KII/iG to 3.
The heating temperature was lowered to 150° C. by lowering the heating temperature to s K9/ca a, and the operation was continued for 30 minutes. The steam pressure in the steam jacket was adjusted using a pressure regulating valve 11 (FIG. 2). During this time, PtA was transferred from the bottom of the centrifugal thin film dryer.
The layered solid matter on the surface turned into powder and fell down. The lower limit of the pressure setting value is a pressure corresponding to a heating steam temperature that can evaporate 80 t/h of hot water. In the case of this example, the heating steam temperature is 145° C. and the steam pressure is 3.3 verses/iG.

When the steam pressure set point falls below this value, high water content powder or slurry is discharged. The mechanism by which solids are removed is hot water flow t, J! This is similar to the case of the previous embodiment in which the adjustment is performed.

After hot water is injected, it can be confirmed whether the solid matter on the heat transfer surface has been removed by detecting the temperature of the heat transfer surface.

If solid matter is attached, this will create resistance to heat transfer and increase the temperature of the heat transfer surface, but if the solid matter is dissolved and removed from the heat transfer surface, heat transfer will improve and the heat transfer will increase. surface temperature decreases,
Eventually it shows a certain value. Figure 1 shows the change in heat transfer surface temperature over time before and after hot water injection. In Figure 1, the curve ■ is the temperature measured with a thermocouple installed at a height of 0.8 times the effective height of the heat transfer surface of the centrifugal thin film dryer (measured from above). This graph shows the change in temperature over time measured by a thermocouple installed at the same location (<0.7 times the height measured from above), and it shows that deposits on the heat transfer surface were detected approximately 45° after hot water was poured. It can be seen that the removal is complete.

After injecting hot water as described above to remove the deposits inside the centrifugal thin film dryer, the concentrated waste liquid is again supplied to the centrifugal thin film dryer to perform drying and pulverization processing, and this series of operations is repeated one after another. The concentrated waste liquid and hot water injection operations were each carried out five times under the conditions described above, during which time the powder moisture content was below the reference value and good powder was produced.

In conventional operation, the concentrated waste liquid is pulverized for 20 hours, and approximately 7 hours are required for full water washing, drying, and warming, so the utilization rate of the centrifugal thin film dryer is 67%. On the other hand, in the embodiment of the present invention,
When the concentrated waste liquid and hot water injection are repeated 5 times each, the utilization rate of the centrifugal thin film dryer becomes 95%, which can greatly improve the utilization rate. In addition, since the present invention does not generate cleaning waste liquid,
It does not affect the upstream concentrator.

Although the above practical example has been described with respect to the g liquid generated from a boiling water nuclear power plant, the present invention can also be applied to a concentrated waste liquid whose main component is boric acid (IJ) generated from a pressurized water nuclear power plant. It is also applicable to waste liquid containing sodium nitrate as a main component generated from nuclear fuel reprocessing plants.

〔Effect of the invention〕

According to the present invention, when removing deposits from a centrifugal 4-membrane dryer, no cleaning waste is generated, no warm-up operation of the centrifugal thin-film dryer is required, and the operating efficiency of the centrifugal thin-film dryer is significantly improved. It has the effect of improving.

[Brief explanation of the drawing]

Figure 1 is an experimental graph showing the change over time in the heat transfer surface temperature of a centrifugal thin film dryer before and after hot water injection in an example of the present invention. The flow diagram, FIG. 3, is an elevational sectional view of the centrifugal thin film dryer. 6... Centrifugal thin film dryer 8... Granulator 12...
Motor 13... Steam outlet 14... Waste liquid supply port 16... Heating jacket 17... Heat transfer surface 18... Rotating shaft 19... Blade
20...Powder outlet. 1st sentry (minutes)

Claims (1)

[Claims] 1. Hot water is supplied from the concentrated waste liquid supply port to a centrifugal thin film dryer with deposits on the heat transfer surface, and the hot water dissolves the deposits on the heat transfer surface, and A method for removing deposits from a centrifugal thin film dryer, characterized in that the hot water is evaporated before flowing out from the centrifugal thin film dryer, and the deposits are discharged as dry powder from the lower part of the centrifugal thin film dryer. 2. The method for removing deposits from a centrifugal thin film dryer according to claim 1, wherein the flow rate of hot water supplied is larger than the waste liquid treatment flow rate of the centrifugal thin film dryer. 3. A method for removing deposits from a centrifugal thin film dryer according to claim 1, wherein the temperature of the heat transfer surface is lower than the temperature of the heat transfer surface during waste liquid treatment of the centrifugal thin film dryer.