JPH0450560B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application of the Invention) The present invention relates to granulation equipment for compressing powdered radioactive waste generated from nuclear facilities, such as nuclear power plants, into pellets.

(Background of the Invention) This type of granulation equipment generally includes a pair of rolls with pellet shapes engraved on them that press against each other, and a screw feeder that pushes the target powder to be compression-molded between the rolls. A granulator consisting of

On the other hand, the powder handled in such granulation equipment is, for example, radioactive liquid waste, radioactive used resin, or used filter sludge dried and powdered using a centrifugal thin film dryer, and radioactive combustible miscellaneous solid waste that is incinerated. Additives (binder) are added as necessary to the incineration ash resulting from incineration in a furnace, or additives (binder) are added as necessary to the dry powder obtained by mixing these in any ratio. Things, etc.
Covers many types.

Therefore, the dry powders, incinerated ash, or mixtures thereof (collectively referred to as powders) of these various radioactive wastes have different properties because they come from different sources, and are not the same. It is known that the powder properties of even waste generated from sources vary within a certain range. Above all, the bulk density of these powders is closely related to the strength of the pellets produced by the granulator, and in order to obtain pellets with a predetermined strength, it is necessary to control the rotation speed of the rolls according to the bulk density. In addition, it is important to select an appropriate shape for the screw feeder that forces the powder between the rolls.

That is, the bulk density of these powders is usually 0.5g/
cc to 1.0 g/cc, but especially for powders with relatively small bulk densities of about 0.5 g/cc, screws are used to increase the efficiency of pushing the powder between the granulator rolls. Even if measures such as increasing the rotational speed of the Euphida are attempted, when the rotational speed increases, the powder rotates with the screw and is no longer pushed in, a so-called slipping phenomenon.

In order to deal with various powders whose bulk density varies from about 0.5 g/cc to about 1.0 g/cc without causing such slippage, conventionally, a granulator is used according to the bulk density. It was necessary to select the shape of the screw feeder, and it was necessary to replace the screw feeder with one of an appropriate shape in response to changes in the bulk density of the target powder. However, such a process is complicated and undesirable in terms of work efficiency.

(Object of the Invention) The object of the present invention is to have a bulk density of about 0.5 as described above.
It is possible to stably granulate various radioactive waste powders ranging from g/cc to approximately 1.0 g/cc using the same granulator without the need to change the screw feeder. There is a granulation equipment to provide.

(Summary of the Invention) The granulating apparatus of the present invention uses a granulating machine having a pair of rolls having pellet shapes cut into them and pressed against each other, and a conical screw feeder for pushing powder between the rolls. Density is about 0.5g/cc to about 1.0g/cc
A radioactive waste granulation device that compresses and molds radioactive waste powder varying in cc into pellets, wherein the conical screw of the conical screw feeder has a longitudinal section including the center line of the cone of the screw. It is a double helix type in which the cone angle expressed as the apex angle of the conical top of the surface is in the range of about 25° to 35°, and the lead length of the helix is in the range of about 130 mm to about 160 mm. This makes it possible to stably granulate powder having the above-mentioned bulk density range to a sufficient strength without the need to replace the screw.

(Embodiment of the Invention) FIG. 1 is a system diagram showing an example of a radioactive waste pellet solidification facility to which an embodiment of the present invention is applied.

Radioactive concentrated waste liquid, used resin, used filter sludge, or a radioactive waste mixture of these in any proportion is stirred and homogenized in a supply tank 1 by a circulation pump 2. Then supply pump 3
The waste sent at a constant flow rate to the centrifugal membrane dryer 4 is here dried and pulverized by known methods. In the figure, 5 is a mist separator, 6 is a condenser, and 9 is a pipe that leads condensate from the mist separator to the wash water tank 13.

The dry powdered waste is sent to a hopper 8 located above the granulator 7. On the other hand, the combustible miscellaneous solid waste is incinerated by a known method in the incinerator 14, and the resulting incineration ash is sent to the hopper 8 by the feeder 15. Powder made of powder or incinerated ash received in hopper 8, or a mixture of any proportion thereof (these are simply referred to collectively as powder)
is compressed into pellets by a granulator 7. Note that 10 is a three-way valve for guiding wash water to the wash water tank 13 when washing the centrifugal thin film dryer 4.

FIG. 2 is a partially sectional view showing the structure of the granulator 7. As shown in FIG. In this example, this is a proven twin-screw briquetting type granulator, which consists of a pair of rolls 12 that are pressed against each other and rotate, and the powder is pushed between these rolls. It is equipped with a screw feeder 11. Entrance 1
The powder received from 8 into the hopper 8 is forced between two rolls 12 by a screw feeder 11. These rolls 12 are pressed against each other by a pressure device, and the powder pushed by the screw feeder 11 is formed into pellets by passing therethrough, and is discharged from the outlet 19. The roll 12 of the granulator has a diameter of approximately
650 mm and a width of approximately 65 mm, the screw feeder 11 has a cone angle (the apex angle of the top of the cone in the longitudinal section including the center line of the screw cone) of 25° to 35°.
Approximately 230 mm in upper diameter and approximately 230 mm in lower diameter within the angle range of
A double helix type conical screw with a length of 50 mm and a total length of about 300 mm was used.

FIG. 3 shows a screw feeder 11 of a granulator according to an embodiment of the invention. This is made into a shape that enables stable granulation of various powders, as explained below.

As mentioned above, the bulk density of the powder entering the granulator is approximately
It fluctuates in the range of 0.5g/cc or about 1.0g/cc. In order to select an appropriate shape of the screw feeder to stably obtain pellets with a predetermined strength for this powder, it is necessary to select a suitable screw feeder shape to stably obtain pellets with a predetermined strength. Cone angle 25°~35° with various lead lengths for cc powder
A granulation test was conducted using a double-helix conical screw feeder. In this test, the roll speed was kept at 1.25 RPM (usually in the range of 1-1.5 RPM).
In addition, the rotation speed of the screw feeder is adjusted from 13 to 13 in response to load fluctuations so that the roll load remains constant.
Adjusted in the range of 103RPM. Pellet strength was evaluated mainly by drop failure rate and crushing strength. The test results are shown in Figures 4 and 5.

The following can be understood from this result. By changing the lead length, which is one of the main specifications of a screw, the strength of the pellets produced changes greatly. When the lead length is set to around 100mm, the screw feeder automatically increases its rotation speed to ensure powder pushing efficiency.
Even if there are limitations due to the shape itself, pellets with the desired strength cannot be obtained. If the lead length is further reduced, the screw rotation speed will further increase, causing a slipping phenomenon, which will impede the powder pushing itself. Conversely, the lead length is 190mm.
If the size is increased to a close range, the powder compression effect within the screw feeder cannot be obtained sufficiently, and pellets having a predetermined compressive strength cannot be obtained.

Furthermore, it was confirmed that when the bulk density of the powder changes to become higher than about 0.5 g/cc, the influence of lead length on pellet strength decreases, which is the desired direction for pellet strength. It was done.

Based on the above knowledge, the bulk density ranges from about 0.5g/cc to about
In a granulator that compresses and pelletizes powder varying in the range of 1.0 g/cc, the cone angle is approximately 25° to 35°, which is responsible for pushing the powder between rolls.
The lead length of the double helix conical screw feeder can be selected from approximately 130 mm to approximately 160 mm.
It was found that these conditions are necessary to ensure the strength of the produced pellets within a sufficiently safe range and to obtain stable granulation performance. The conical screw feeder with two threads shown in FIG. 3 is an example having a lead length of 130 mm that satisfies this condition.

(Effects of the Invention) According to the present invention, in the granulation equipment that compresses and molds various types of radioactive waste powder into pellets,
With the same specifications and granulator, it is possible to create pellets with sufficient strength stably for various powders with different bulk densities, without the need to change the shape of the screw. , it is possible to improve work efficiency without complications.

[Brief explanation of the drawing]

Fig. 1 is a system diagram showing an example of radioactive waste pellet solidification equipment in which the present invention is implemented, Fig. 2 is a diagram showing the structure of a granulator according to an embodiment of the present invention, and Fig. 3 is a system diagram showing an example of a radioactive waste pellet solidification facility in which the present invention is implemented. An enlarged view of the screw according to the example, FIG. 4 is a test result showing the relationship between the lead length of a conical screw and pellet drop failure rate, and FIG. 5 is a test result showing the relationship between the lead length of a conical screw and pellet crushing strength. It is. 1... Supply tank, 4... Centrifugal thin film dryer, 5
... Mist separator, 6 ... Condenser, 7 ... Granulator, 8 ... Hopper, 11 ... Screw, 12
...Roll, 13...Washing water tank, 14...Incinerator, 15...Feeder.

Claims (1)

[Claims] 1 Using a granulator that has a pair of rolls with a pellet shape engraved on them that press against each other and a conical screw feeder that forces the powder between the rolls, the bulk density is about 0.5 g/cc to about 1.0 g/cc. A radioactive waste granulation device for compressing and molding radioactive waste powder varying in the range of cc into pellets, wherein the conical screw of the conical screw feeder has a longitudinal section including the center line of the cone of the screw. It is a double helix type in which the cone angle expressed as the apex angle of the conical top of the surface is in the range of about 25° to 35°, and the lead length of the helix is in the range of about 130 mm to about 160 mm. Granulation equipment.