JPS6323802B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solution evaporation treatment method using a centrifugal thin film evaporator, and in particular, a solution suitable for evaporation treatment of soluble substances such as radioactive solutions generated in nuclear power plants. The present invention relates to an evaporation treatment method.

At nuclear power plants, a radioactive solution is generated that dissolves soluble substances such as sodium sulfate, seawater components, and corrosion products, and is also radioactive. In order to prevent environmental contamination such as radioactive contamination, this radioactive solution must be highly concentrated or dried into powder to reduce its volume before being disposed of.In recent years, radioactive solutions have been highly concentrated or dried into powder. Therefore, a method has been proposed in which a radioactive solution is evaporated using a centrifugal thin film evaporator.

However, when a solution is evaporated by a centrifugal thin film evaporator, the heat transfer surface (hereinafter referred to as heat transfer surface) of the heat transfer cylinder of the centrifugal thin film evaporator is a region where the solution evaporates and concentrates and soluble substances begin to precipitate. (hereinafter abbreviated as enriched region)
, a region in which soluble substances precipitated as a result of evaporative concentration of the solution adhere to and grow on the heat transfer surface (hereinafter referred to as slurry region), and a region in which soluble substances deposited on the heat transfer surface as the evaporation concentration of the solution progresses further; The material is divided into three regions: the region where the fluidity of the material is lost and it is scraped off by the scraping force of the rotating rotor and turned into powder (hereinafter referred to as the "powder region"). During the evaporation process of the solution, soluble substances precipitated in the slurry region of the heat transfer surface adhere and grow during the process of evaporation and concentration of the solution, reducing the evaporation processing capacity of the heat transfer surface and causing problems in the centrifugal thin film evaporator. The operation must be periodically stopped to wash and remove the soluble substances that have grown in the slurry region on the heat transfer surface, which has the drawback of reducing the operating rate of the centrifugal thin film evaporator. Additionally, if the solution being evaporated in the centrifugal thin film evaporator is a radioactive solution, there is a high risk that workers will be exposed to radioactivity when cleaning and removing soluble substances that have grown on the slurry area of the heat transfer surface. There were also safety shortcomings.

The present invention aims to provide a solution evaporation treatment method that can significantly improve the operating rate of a centrifugal thin film evaporator, in which the heat transfer surface is divided into at least a concentration region, a slurry region, and a pulverization region. In a method of evaporating a solution using a centrifugal thin film evaporator, during the evaporation process of the solution, the slurry region during steady operation is the pulverization region or the concentration region during steady operation, and the slurry region during steady operation is The concentration region or the pulverization region is movable to the slurry region during steady operation, and the temperature of the heat transfer surface is lowered or raised than the temperature during steady operation, and the concentration region, slurry region, and pulverization region are moved. The temperature of the heat transfer surface is returned to the temperature during steady operation so that the temperature of the heat transfer surface can be returned to the original region during steady operation, and the slurry region of the heat transfer surface is returned to the slurry region of the heat transfer surface without stopping the operation of the centrifugal thin film evaporator. The purpose is to remove the soluble substances that have adhered and grown.

An embodiment of the present invention will be described with reference to FIGS. 1 and 2.

FIG. 1 shows the configuration of a centrifugal thin film evaporator, in which a heating jacket cylinder 12 is disposed outside a heat transfer cylinder 10.
is provided to form a heat medium chamber 13, and inside the heat transfer shell 10, a rotating shaft 16 to which a liquid distributor 14 and a plurality of stages of rotary blades 15 are attached is connected to an upper bearing box 17 and a lower bearing box 18. It is rotatably supported by a drive wheel 19. A solution inlet 20 is provided at a position opposite to the liquid distributor 14 of the heat transfer cylinder 10, an evaporate outlet 21 is provided at the top of the heat transfer cylinder 10, and a powder outlet 22 is provided at the bottom of the heat transfer cylinder 10. There is. Further, a heat medium inlet 23 is provided in the upper part of the heating jacket body 12, and a heat medium outlet 24 is provided in the lower part.

The solution supplied into the heat transfer shell 10 from the solution inlet 20 is uniformly distributed in the circumferential direction of the heat transfer shell 10 by the liquid distributor 14, which is integrally connected to the rotating shaft 16 and rotated by a drive wheel 19, and is then dispersed by gravity. It flows down the heat transfer surface (hereinafter abbreviated as heat transfer surface) of the heat transfer cylinder 10, and is rotated by the drive wheel 19 integrally with the rotating shaft 16, and the centrifugal force of the rotor blades 15 is applied to it, and it spreads out on the heat transfer surface. A thin layer of solution is formed. While flowing down the heat transfer surface by gravity, the thin film of this solution enters the heat medium chamber 13 from the heat medium inlet 23.
The powder is heated by the heat medium supplied to the heat medium and discharged from the heat medium outlet 24, evaporated and concentrated, and finally pulverized and discharged to the outside from the powder outlet 22.

In an evaporation experiment using a centrifugal thin film evaporator for a solution in which sodium sulfate was used as the soluble substance and its dissolved concentration was 20 wt%, the heat transfer surface during steady operation was divided into regions as shown in Figure 2. In Figure 2, the upper region Ha of the height He of the heat transfer surface is a concentrated region,
A region Hb approximately at the center of the 1/3 of the height He of the heat transfer surface is a slurry region in which precipitated sodium sulfate has grown attached to the heat transfer surface, and a region Hc below the slurry region Hb is a powdered region. Note that the area Hd is the heat transfer cylinder 1
Since this is a completely dry powder area and a margin area of the heat transfer surface of 0, adhesion of sodium sulfate does not occur. During steady operation, sodium sulfate adheres and grows in the slurry region Hb shown in FIG. This will spread to the lower part of the heating surface and further reduce the evaporation processing capacity, but once this state has progressed to a certain extent, for example, the temperature of the heating medium may be lowered below the temperature of the heating medium during steady operation, and the concentration area By expanding Ha to the slurry region Hb during steady operation, the slurry region moves to the pulverization region Hc during steady operation. As a result, sodium sulfate adheres and grows in area Hc, which has newly become a slurry area, but the sodium sulfate that adheres and grows in area Hb during steady operation is redissolved in the solution in the concentrated area, and the rotor blade 1
It is scraped and removed by the scraping force of 5. In addition, the sodium sulfate that has grown non-deposited in area Hc, which has become a new slurry area by lowering the temperature of the heating medium, is reduced to the temperature of the heating medium during steady operation after the sodium sulfate in area Hb is removed. By returning the temperature to
It is scraped off and powdered by the scraping force of 5. By repeating such operations according to the degree of adhesion and growth of sodium sulfate in the slurry region during steady operation, it is possible to remove the sodium sulfate that has adhered and grown in the slurry region without stopping the operation of the centrifugal thin film evaporator. Can be done.

Additionally, if the solution is radioactive, there is no risk of radiation exposure to workers.

In addition, the temperature of the heating medium is raised above the temperature of the heating medium during steady operation, and the slurry area is moved to the concentration area and the powdering area is moved to the slurry area, and the sodium sulfate that has grown in the slurry area is transferred to the rotor blade. It may be removed by scraping with a scraping force of 15 to turn it into powder.

FIG. 3 explains another embodiment of the present invention, in which the heat medium chamber 13 is partitioned by partition plates 25a to 25c at positions corresponding to the respective regions shown in FIG.
The partitioned heat medium chambers 13a to 13b have heat medium inlets 23a to 23d and heat medium outlets 24a to 2, respectively.
4d.

When the heat medium chamber is partitioned at positions corresponding to the respective regions shown in FIG. Even if the temperature is lowered below the steady operating temperature, the temperature of the heat carrier supplied to the heat carrier chamber 13d from the heat carrier inlet 23d and discharged from the heat carrier outlet 24d can be raised above the steady operating temperature regardless of this. Therefore, changes in the required heat transfer area can be further reduced.
In addition, although the amount of solution supplied to the heat transfer cylinder 10 is slightly reduced, a refrigerant such as water is supplied to a certain partitioned heat medium chamber, and the heat transfer surface of the heat transfer cylinder 10 corresponding to that heat medium chamber is By condensing the evaporates from the solution,
It is also possible to partially clean the heat transfer surface of the heat transfer cylinder 10 during operation of the centrifugal thin film evaporator.

According to the present invention, the soluble substances that have adhered and grown in the slurry region of the heat transfer surface can be removed without stopping the operation of the centrifugal thin film evaporator, which has the effect of significantly improving the operating rate of the centrifugal thin film evaporator. .

[Brief explanation of drawings]

FIGS. 1 and 2 illustrate an embodiment of the present invention. FIG. 1 is a longitudinal cross-sectional view of a centrifugal thin film evaporator, and FIG. 2 is a diagram showing each region of the heat transfer surface during steady operation. FIG. 3, a schematic diagram showing the distribution, explains another embodiment of the present invention, and is a longitudinal sectional view of a heat medium chamber in which the present invention of a centrifugal thin film evaporator is implemented. 10...Heat transfer cylinder, 11...Heating jacket cylinder,
13, 13a to 13d... heat medium chamber, 14...
Liquid distributor, 15...rotor blade, 20...solution inlet,
21... Evaporated matter outlet, 22... Powder outlet, 23,
23a to 23d...heat medium inlet, 24, 24a
to 24d... heat medium outlet, 25a to 25c...
...Partition board.

Claims (1)

[Claims] 1. In a method of evaporating a solution using a centrifugal thin film evaporator whose heat transfer surface is divided into at least a concentrating region, a slurry region, and a powdering region, the slurry region during steady operation during the evaporation of the solution The temperature of the heat transfer surface is set to the temperature during steady operation so that the temperature of the heat transfer surface can be moved to the pulverization region or concentration region during steady operation, and the concentration region or pulverization region during steady operation is movable to the slurry region during steady operation. The temperature of the heat transfer surface is returned to the temperature during steady operation so that the concentrated region, slurry region, and pulverization region that have been moved can be returned to their original regions during steady operation. A method for evaporating solutions.