JPS6148799A - Method and device for granulating waste dried powder containing spent ion exchange resin - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a granulation method and a granulation device for high-molecular organic powder, and in particular to a radioactive ion exchange resin containing spent ion exchange resin generated from nuclear power plants, etc. The present invention relates to a granulation method and granulation device suitable for waste dry powder.

[Background of the invention]

Radioactive waste generated from nuclear facilities such as nuclear power plants is currently temporarily stored on the premises of power plants, etc., as final disposal methods have not yet been determined. For this reason, various measures have been taken to reduce the volume of waste and make maximum use of storage space. The most effective method is a system in which radioactive waste, such as slurry of used ion exchange resin or recycled waste liquid, is dried and turned into powder, which is then turned into pellets and temporarily stored. The features of this system are that it has a large volume reduction effect, that it is easy to handle and prevent scattering of powder when it is made into 4 pellets, and that it is easy to use the final disposal method once the final disposal method has been decided. The reason is that there is a possibility of changing it into a suitable form.

However, when making pellets only from powder, some pellets do not have sufficient strength.
It has been considered to make pellets with sufficient strength using thermosetting or thermoplastic binders such as plastic or water glass. However, when such a binder is used, although it is possible to obtain 4lets with high strength, it becomes impossible to convert the 4lets once granulated into the original powder or other form. Therefore, the great advantage of compatibility with final disposal methods is lost in the aforementioned systems that dry powder and pelletize waste liquids and slurries.

From this point of view, there is a need for a method for creating 4lets that can be easily changed in shape to meet the final disposal method and that also has a specified strength necessary for temporary storage, that is, a powder granulation method. There is.

[Purpose of the invention]

The purpose of the present invention is to provide a granulation method and a granulation device for forming waste dry powder containing used ion exchange resin into pellets that can be changed in shape depending on the situation and have strength enough to withstand temporary storage. There is something to do.

[Summary of the invention]

The granulation method of the present invention is characterized by the discovery that the strength of the pellets made from the dried waste powder containing the used ion exchange resin is determined by the dried powder of the used ion exchange resin. Using this fact, dry powder,
The object of the present invention is to produce a reddable material having a strength capable of withstanding temporary storage by granulating the ion exchange resin contained therein at a temperature higher than the glass transition point and lower than the decomposition temperature.

Furthermore, the granulation device of the present invention includes a stirring container for the waste dry powder containing the used ion exchange resin, a heating device for heating the waste dry powder in the stirring container, and a heating device for heating the waste dry powder in the stirring container; A granulator that receives the dry powder and compression molds it; and a granulator that controls the temperature of the waste dry powder during compression molding in the granulator to a temperature higher than the glass transition point of the used ion exchange resin and lower than the decomposition temperature. and a control device that controls all of the heating means to maintain a predetermined temperature.

The present invention is based on a newly discovered fact as a result of experiments and analyzes conducted by the inventors as described below. FIG. 1 shows an overview of the granulation mechanism obtained by the inventors' analysis. Here, the dry powder is shown schematically as a sphere. The pressure applied during mass granulation causes the dry powder to clump and rearrange the powder, resulting in a close-packed state.

When the powder is in a close-packed state, pressure applied from the outside cannot escape, and pressure is applied to the powder itself. This causes changes in the powder, but the changes that occur vary significantly depending on the physical properties of the powder. That is, if the powder does not deform (if it is a rigid body), the powder is crushed and becomes a fine powder, which absorbs external pressure. In this case, when the external pressure is removed, the powder falls apart and no pellets (granules) having a uniform shape are formed. This is due to the fact that the area in which the powder comes into contact with other powders is small, which weakens the Van der Waals force acting as a binding force between the powders. On the other hand, when powder is plastically deformed by external pressure, the deformation of the powder decreases, but the deformation progresses from the point where the powders come into contact with each other, and the mutual contact area of the powders increases.

This creates a strong van der Waals force, which acts as a binding force between the powders, and it maintains a constant shape even when external pressure is removed. Therefore, whether or not the powder undergoes plastic deformation due to external pressure determines the granulation properties of the powder and the strength of the pellet after granulation.

By the way, the inventors investigated the physical properties of ion exchange resins and found that ion exchange resins have a glass transition point at approximately 90°C, are rigid at temperatures below this, and undergo plastic deformation at temperatures above this. I found it.

Unfortunately, it has been found that the resin begins to decompose at temperatures around 180°C. Based on the results of this experiment, we discovered that it is possible to create pellets with a specified strength sufficient for temporary storage by heating the ion exchange resin to a temperature above the glass transition point and below the decomposition point and granulating it through plastic deformation. .

It should be noted here that the styrene/divinylbenzene copolymer, which is the base material of ion exchange resins, is generally a thermosetting plastic and is said to have no glass transition point. This is because thermosetting plastics harden when heated, and once hardened, ζ plastics do not melt even when heated again, but are said to decompose when heated further. On the other hand, thermoplastic plastics, which are contrasted with thermosetting plastics, melt when heated to a glass transition point, and become solid when cooled; no matter how many times this thermal cycle is repeated, the same change occurs. It is characterized by repeated pages. Thermoplastics are better than this! I? Because of these characteristics, thermoforming is generally performed, and changes in physical properties due to heating, glass transition point, etc., have been well investigated.

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Therefore, the inventors discovered that the thermosetting plastic that makes up the ion exchange resin has a glass transition point, and by granulating it at a temperature above this temperature but below the decomposition point, the required strength can be achieved. It was not known in the prior art that pellets '6 could be made with It goes without saying that the present invention is essentially different from conventional thermoplastic thermoforming in this respect.

[Embodiments of the invention]

Example 1 FIG. 2 shows the relationship between pellet strength and granulation temperature when a dry powder containing an ion exchange resin and 20 wt % of a fibrous binder (described later) was granulated. Here, a styrene/divinylbenzene copolymer with an ion exchange group added was used as the ion exchange resin, a tablet machine was used as the granulator, and the pressure at that time was 3 t/arl. As a result, it was found that a pellet strength of 50 kg/piece, which is necessary for temporary storage of pellets, can be obtained at a granulation temperature in the range of 90° C. to 180° C. The reason why the pellet strength shows a constant granulation temperature range is that, as mentioned earlier, the ion exchange resin has a stress transition point at 90°C, and above this temperature it undergoes plastic deformation. The contact area between powders increases and the pellet strength increases, but at even higher temperatures (1
80C), it is thought that the gas generated by the decomposition of the ion exchange resin is intended to prevent contact between the powders.

Pellets having the required strength can be produced only by adjusting the flow and granulation temperature as described above.

Example 2 Next, we will discuss an example of granulation in the case of a dry powder in which a used ion exchange resin is mixed with sulfuric acid (IJ), which is the main component in the recycled waste liquid. Figure 3 shows the results. In the 130°C heated granulation according to the present invention, the pellet strength slightly decreases as the proportion of sodium sulfate decreases, but the strength is 97 or more to 50, which is required for temporary storage, regardless of the proportion of ion exchange resin powder. It can be seen that pellets with the desired strength can be obtained. On the other hand, it can be seen that in conventional granulation at room temperature, the pellet strength decreases as the proportion of resin increases, making it impossible to obtain pellets with the required strength.

Example 3 Next, the case of granulation of a three-component dry powder containing a fibrous binder, an ion exchange resin, and sodium sulfate will be described as an example. The fibrous binder mentioned here is vegetable fiber whose physical properties do not change depending on temperature, gold FAfp, fiber,
Glass fiber, etc. This v1! The miscellaneous binder is a binder that entangles with each other to take in the powder to be granulated and pelletize it, and satisfies the following moxibustion requirements.

t≧10d+2D・・・・・・・・・・・・・・・・・・
(1) Here, t is the average length of the fibers, d is the average diameter of the image fibers, and D is the diameter of the powder to be granulated.

The fibrous binder is collected in filter sludge, which is radioactive waste, and is added to the ion exchange resin slurry mixed with sodium sulfate. If that doesn't work, add another fibrous binder.

Figure 4 shows the range in which a pellet strength of 50 kg/unit can be obtained from this three-component system that has been dried and powdered. shows. According to the implementation of the present invention, it is possible to granulate in areas where a small amount of binder is added, and therefore, it is possible to increase the amount of original radioactive waste powder in the pellets, making it possible to create desirable pellets. You can see that it is happening.

Other effects include Guingu, sodium sulfate,
Even if the ion-exchange resin is not mixed well or unevenly depending on the operating conditions of the equipment, there is a very wide range of ratios that can create pellets with the required strength, so dry powder can be used. This facilitates the operation of equipment in a series of pelletizing and pelletizing systems.

In the present invention, as described above, the pellet strength does not decrease in any way, not only when the ion exchange resin is used alone, but also when the dry powder is mixed with other waste liquids, sludge, etc. Therefore, even if the composition of the dry powder is not uniform, that is, even if the composition of the waste liquid, slurry, etc. before drying is not constant, stable pellet granulation is possible. There is no need for a device to measure the

Example 4 Next, an example using an apparatus effective for carrying out the entire invention will be described in detail. Let us take as an example the radioactive waste treatment facility of a boiling water nuclear power plant shown in Figure 5. An aqueous sodium sulfate solution generated as a waste liquid during the regeneration of the ion exchange resin is concentrated in a concentrator (not shown) and then stored in a concentrated waste liquid storage tank IK. Additionally, used ion exchange resin and filter sludge can be stored in the resin tank 2. After mixing these wastes in the adjustment tank 3,
It is made into a dry powder using a centrifugal thin film dryer 4. The produced dry powders are mixed with each other and, if necessary, with a fibrous binder in a mixer 5, and compressed into pellets in a granulator 6. The pellets are stored in a storage tank 7.

Further details will be given next. The powder produced in the centrifugal thin film dryer 4 has an average particle size of 3 μm, and is stored in a powder holler/#8. The mixer 5 performs patch processing every 30 minutes, and the processing amount per time is 10 kg. The mixer 5 is connected to both the upper and lower lines by Perot, and its entire weight is measured by all load cells 9. First, measure the windshield weight, then
While the vibrating feeder 10 is operated to move the dry powder to the mixer 5, changes in the weight of the mixer 5 are continuously measured. The amount of powder transported is 10kl? The vibrating feeder 10 is stopped when the The binder hopper 11 is filled with cellulose fibers having a diameter of about 10 μm. This fiber length is 160μ or more as determined from the above equation (1). Further, the amount added is 20 wt% from the viewpoint of strength. The vibrating feeder 12 is activated and cellulose fibers are supplied from the binder hopper 11. When the weight of the mixer 5 is measured and two pieces of cellulose fiber have been fed, the operation of the photographic feeder 12 is completely stopped. After this, the temperature of the powder is set to 90°C or higher, the f-las transition point of the ion exchange resin, and the decomposition temperature is 18°C.
The heating heater 15 of the mixer 5 is heated so that the temperature is below 0°C.
The powder temperature is adjusted by a powder temperature controller 14 connected thereto. At this time, a stirring blade of 18 feet is operated for 5 minutes or more to mix the dry powder and cellulose fibers. When the temperature of the mixture of dry powder and cellulose fibers is in the range of 90 to 180°C, the pulp 19 is opened and the mixed powder is poured into a bowl.
42' After passing through 0, the pellets are allowed to fall by gravity to the granulator 6. Mixer 5
The operation is sequence controlled, and each part starts and stops according to signals from the controller 21. Furthermore, in order to prevent leakage of radioactive materials to the outside, the pressure inside the system is maintained at negative pressure by the proir 22 connected to the hoppers 8 and 20.

According to this example, even if the proportion of ion exchange resin in the dry powder increases, stable pellets can be produced.

In this example, a tablet machine is effective as the granulator. This is because no heat is generated inside the granulator, and the temperature of the powder is determined by a preset temperature. Therefore, when granulating with a tablet machine, operation becomes easy. However, the granulation speed is slower than that of a briquette machine. Since briquette machines generate heat, it is necessary to adjust the temperature by 7% to take this into account.

Example 5 Next, an example including temperature control using a briquette machine will be shown.

FIG. 6 is a sectional view showing details of a briquette machine (this is used as the granulator 6 in FIG. 5).

In the figure, the apparatus includes a hopper 20 as a storage means, a screw feeder 23 as a transfer means, and a roll 2 as a granulation means.
4 and 25, and pressurizing means 26. The screw feeder 23 is inserted into the funnel-shaped hopper 20 along the longitudinal central axis, and feeds two rolls 24 and 25.
is the discharge port 2 at the bottom of the conch/4' below the hopper 20.
They are placed in parallel and facing each other at positions that are almost in contact with 7.

When the treated powder 40 is supplied to the hopper 20, the rotating screw feeder 23 presses it down to the discharge port 27 at the bottom of the hopper while stirring the entire powder. Below the hopper 20, the roll 25 is pressed against the roll 24 by a pressure means 26 such as a spring or hydraulic pressure, and the hopper 20
The treated powder 40 discharged from the roller has a pattern engraved on the outer peripheral surface of the roll in the gap between two rotating rolls. ket 2
8 and compression molded into pellets 41.

Here, the temperature rise of the treated powder during the above granulation process will be described. The rotational kinetic energy of the screw feeder and rolls is transferred to the processed powder through compression.
This is mainly converted into internal R friction heat between the powder particles, and the total powder temperature can be increased by 20 to 100°C. FIG. 7 is a curve diagram showing the relationship between the rotation speed of the screw feeder and the temperature rise of the treated powder, and the powder example is ion exchange resin. It can be seen that the number of rotations and the temperature increase form a linear proportional line, and as the rotation of the screw feeder increases, the temperature of the powder increases. FIG. 8 is a curve diagram showing the relationship between the number of rotations of the roll and the temperature rise of the treated powder, and the powder example is also made of ion exchange resin. It can be seen that the number of rotations and the temperature increase show a downward curve similar to an inverse proportion, and even if the rotation of the rolls is increased, the increase in temperature of the powder is rather small. Further, if the number of rotations of the rolls is kept constant at 1.5 r, p, m, for example, it can be estimated that the temperature rises only by the rotation of the rolls at 20°C.

Summarizing both figures above, ΔT during temperature rise in the apparatus is the sum of ΔT during temperature rise in FIG. 7 and ΔTR during temperature rise in FIG. 8.

ΔTP = ΔT, +ΔTR When granulating with a briquette machine, the temperature of the powder in the mixer 5 shown in Figs. 5 and 9 must be controlled in consideration of the temperature rise within the device. Must be. FIG. 9 shows the specific temperature control means.

In FIG. 9, the mixer 5, hoppers 20, screw feeder 23, rolls 24, 25, screw feeder drive motor 35, roll drive motor 36, thermocouple 38 as temperature detection means, and temperature control inside the mixer 5 are shown. 14, and a control device 37 serving as speed control means. The screw feeder driving motor 35 and the roll driving motor 36 are arranged to rotate the screw feeder 23 and the roll 25 (or 24), respectively. A thermocouple 38 that measures the temperature of the powder supplied to the granulator is connected to the mixer 5.
I can break my legs. The control device 37 is a control minicomputer,
It is electrically connected to a thermocouple 38 and two drive motors 35,36.

Now, referring to FIG. 9 (other than this, it is assumed that the configuration is the same as that of FIG. 5), the control device 37 has the temperature rise characteristics shown in FIGS. 7 and 8, and the processing powder is (set value T of the desired powder temperature when compressed into pellets, (
90 to 180°C) is the memorization temperature. Since the number of rotations of the rolls is proportional to the amount of pellets discharged, that is, the amount of waste processed, it is desirable for the waste processing apparatus to be constant, and this is also set to a constant value in the control device 37 in advance.

This is also to determine ΔTR during the rise in powder temperature due to roll rotation. In addition to the above settings, thermocouple 3
8 measures and reports the temperature TM of the treated powder in the powder mixer 5, the control device 37, which has the necessary data, calculates ΔTP=ΔTP−ΔTR=T−T−ΔTRM, and calculates the following as shown in FIG. Based on the characteristic curve, a suitable rotational speed of the screw feeder is determined and outputted to the screw feeder driving motor 35. Illustrated by example. Desired powder temperature T during compression molding.

was set at 130°C. The rotation speed of the roll is 1.5r, p
lm, the temperature rise ΔTR due to the rotation of the roll stops at 20°C, as explained in FIG.

Furthermore, if the powder temperature TM in the powder mixer with a constant thermocouple is 80:C, the temperature difference ΔT, which is increased by the rotation of the screen feeder, is ΔT, = 130-
80-20=30, 30°C is obtained, and as explained in FIG.

corresponds to The control device may output this.

According to this example, the powder temperature during granulation was adjusted to the glass transition humidity of the ion exchange resin (90°C) according to the characteristics of the granulator.
) and below the decomposition temperature (180°C), making it possible to produce pellets with a strength that satisfies certain targets.

In the above embodiment, the temperature is controlled by taking into consideration the state of each part of the granulator, but if the temperature rise of the granulator is constant, it is possible to control the temperature only by adjusting the temperature inside the mixer 5. .

[Effects of the present invention]

According to the present invention, it is possible to stably pelletize dry waste powder mixed with ion exchange resin powder that is difficult to pelletize by simply controlling the temperature even when a large amount of ion exchange resin is mixed.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram modeling the granulation process according to the conventional method and the present invention, Fig. 2 is a diagram showing the relationship between granulation temperature and pellet strength according to the present invention, and Fig. 3 is a diagram showing the relationship between granulation temperature and pellet strength according to the present invention. Figure 4 shows a comparison of the pellet strength in the case of a mixture of ion exchange resin powder and ion exchange resin powder between the conventional example and the present invention. ? /([LiI] Figure 5 is a flowchart of an embodiment suitable for carrying out the present invention, Figure 6 shows the structure of a granulator suitable for carrying out the present invention. Figure 7 shows the relationship between the rotation speed of the scree feeder of the granulator and the temperature rise of the powder, and Figure 8 shows the relationship between the rotation speed of the granulator roll and the temperature rise of the powder. A diagram showing the relationship, and FIG. 9 is a diagram showing a temperature control system for controlling the temperature of powder during granulation within a predetermined range. (Explanation of symbols) 5... Mixer 6. ... Granulator 14...
Temperature regulator 15... Heater 37... Control device 38... Temperature sensor Figure 1 Figure 1 ~ Granulation humidity (°C) Sodium ratio (%) Resin ratio (y,) %4 Figure 5 Figure 7 Roll notification (rp, a')

Claims (1)

[Claims] 1. Disposal characterized by granulating a waste dry powder containing a used ion exchange resin at a predetermined temperature that is above the glass transition point and below the decomposition temperature of the ion exchange resin. Granulation method of dry powder. 2. The method for granulating dry waste powder according to claim 1, wherein the granulation is carried out at a temperature of 90°C or higher and 180°C or lower. 3. A method for granulating a dry waste powder according to claim 1, which comprises adding a fibrous binder to a dry waste powder containing an ion exchange resin and granulating the powder. 4. A stirring container for dry waste powder containing used ion exchange resin, a heating device for heating the dry waste powder in the stirring container, and receiving and compressing the dry waste powder from the stirring container. Controlling the granulator for molding and the heating means so that the temperature of the waste dry powder during compression molding in the granulator is a predetermined temperature that is higher than the glass transition point of the used ion exchange resin and lower than the decomposition temperature. A granulation device for waste dry powder containing a used ion exchange resin, characterized in that the device comprises: 5. The control device controls the heating means to maintain the temperature of the dry waste powder in the stirring container at a temperature obtained by subtracting the temperature rise of the dry waste powder in the granulator from the predetermined temperature. The waste dry powder granulation device according to item 4. 6. The granulator is equipped with a pair of granulating rolls and a screw feeder that presses powder between them, and the control device detects the temperature rise from the rotational speed of each of the granulating rolls and the screw feeder. Claim 5
A granulation device for dry powder of waste as described in Section 1.