JPS5822280B2 - Slurry drying/melting solidification method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for drying and melt-solidifying a slurry, more specifically, evaporating and concentrating a raw slurry, drying it into powder using a drier, and melt-solidifying the powder by microwave irradiation. The present invention relates to a method for processing a slurry comprising the following steps.

Among the wastes discharged from various industrial facilities, slurry and other large-volume wastes are inconvenient for processing operations.

In particular, concentrated wastewater from the bottom of evaporators discharged from nuclear facilities such as nuclear power plants, wastewater containing corrosion products, wastewater containing used ion exchange resins (granular and powdered resin), chemical wastewater, and chemical reagents (K4F e (CN) a, CuSO4, etc.)
sludge, laundry waste, etc. (in this specification,
If the waste liquid (referred to as "slurry") needs to be isolated and stored from the human environment, it can be "reduced in volume" by evaporation and concentration and drying into a powder, reducing the number of storage containers. It is economically advantageous as it saves storage space and reduces the amount of handling work.

Since the dry powder form is not suitable for long-term stable storage as it easily scatters, a method has been developed in which it is encapsulated in a solidified material (matrix) such as cement or asphalt to form a solid material. Some of them are put into practical use.

However, although these methods are excellent in terms of stabilizing the powder, they have the disadvantage that they involve an increase in volume due to the solidified material (matrix) required for encapsulation.

The present invention has been made in order to deal with the above-mentioned circumstances, and includes a ``pulverization process'' in which a raw material slurry is evaporated and concentrated, and then dried in a dryer to dry powder with an appropriate particle size. A new process for slurry that combines the process of exposing the resulting powder to microwave irradiation, melting it with dielectric heating, and then cooling it to form a glass-like solidified product. It provides law.

The method of the present invention will be explained in detail below.

According to the present invention, the raw material slurry is first subjected to a pulverization step of concentration and drying.

Concentration treatment involves the addition of a pH adjuster, appropriate component adjustment to combine with the slurry-containing substances to form a solid, or various flocculants (polymer flocculants or inorganic flocculants such as lime, bread soil, iron salts, etc.). After pretreatment to promote precipitation and concentration of the solid substance, such as addition of an agent), is carried out as necessary, the solid substance is subjected to an appropriate heating means to evaporate water.

The concentrated slurry obtained by the water evaporation is then passed through a suitable dryer to contain almost no water.

It is preferably dried into a dry powder having a moisture content of about 5 to 10% (weight, the same applies hereinafter).

This concentration/drying process is suitably carried out using a combination of an evaporator and a paddle type or double-headed dryer.

For example, after adjusting the pH of the raw material slurry to approximately 7 to 9 through neutralization treatment, it is introduced into a vertical thin film evaporator, and the slurry concentration is increased by evaporation of water, preferably with a water content of approximately 30 to 5.
It is concentrated to 0%, then fed to a paddle dryer, and while being transferred by a screw conveyor in the raw material flow path in the same equipment, most of the water is evaporated and removed by steam heating, reducing the water content to approximately 5 to 10%. % or less.

By performing the evaporative drying of the raw material slurry in two stages as described above, and by setting the pressure and temperature of the heating steam to appropriate values, clogging and transmission, which have traditionally been problems with this type of equipment, are avoided. It is possible to prevent troubles such as adhesion of heat surface hems and achieve smooth and efficient processing.

The "dry powder" obtained in the "dry granulation" process above is
Then, it is subjected to heating and melting treatment by microwave irradiation.

The principle of heating and melting the irradiated object and body by microwave irradiation is that heat generation and temperature rise due to dielectric loss caused by applying a high-frequency electric field (in the case of dielectric materials) or Joule heat due to conduction current (in real materials, both The dielectric material is generally silicon dioxide (Si).
O31,l Calcium oxide (CaO), iron oxide (F e
It is composed mainly of oxides such as 203).

This melting treatment can be carried out by charging the powder or granular material to be irradiated into an irradiation furnace, applying an appropriate electric power, for example, about 3 to 5 KW, and irradiating the powder or granular material with microwaves. In that case,
It is also possible to place the granular material in a suitable container, such as a glass or ceramic container, and perform irradiation, thereby melting the container and the granular material integrally.

After sufficiently melting the object to be irradiated, the microwave irradiation is stopped, and then the object is cooled to room temperature using an appropriate cooling means to obtain a solidified material, which is stored in a suitable container such as a drum according to prescribed procedures. Ru.

FIG. 1 is a system schematic diagram showing one specific example of the method of the present invention.

The figure shows the process of evaporating and drying the raw material slurry to obtain powder (■ in the same figure) and the process of melting and solidifying the powder by subjecting it to microwave irradiation ([■] in the same figure). ])).

In the figure [I], 1 is a raw material slurry pretreatment tank, 2 is an evaporator (for example, a thin film evaporator), and 3 is a horizontal paddle dryer.

In the figure [■], 4 is a microwave oscillator, 5 is an irradiation furnace, and 6 is a melt cooling device.

Raw material slurry, for example, evaporator bottom waste liquid A from a nuclear power plant facility, is fed into the pretreatment tank 1 through an introduction pipe L1, where impurities and the like are separated, and then supplied from the pretreatment solution tank 13. After undergoing neutralization treatment with an appropriate reagent and adjusting the pH to approximately 7 to 9, the feed pump P
It is sent to the evaporator 2 at the same time.

The raw material slurry in the evaporator 2 is heated by steam S1 fed into the can, and the generated steam is led out to the outside of the can 11 together with the heating steam.

The evaporated and concentrated slurry (for example, the water content is about 40 to 50%) is then fed into the dryer 3, where the water is evaporated and dried by introducing heating steam S2.

The generated steam and the like are appropriately discharged from t2, and the drain is appropriately discharged from t3.

Dry powder (preferably having a moisture content of about 5 to 10% or less) is obtained by evaporative drying in this dryer.

The obtained granular material is discharged to the weighing hopper 7.

The dry granular material received in the weighing hopper 7 is continuously fed to the powder feeder 8 by an appropriate transfer means L2, from which an appropriate amount of granular material is introduced into the irradiation furnace 5. .

The irradiation furnace 5 includes a microwave oscillator 4, a power monitor 9 for detecting and controlling microwave power, a three-stub tuner 10, and a blower 11 and air piping for supplying discharge prevention air. L3 is installed in parallel.

The powder and granular material supplied in an appropriate amount into the irradiation furnace 5 is irradiated with microwaves from the top of the furnace via the waveguide L4 from the microwave oscillator, heats up and heats up, and melts.

The generated molten material is discharged from the lower part of the furnace, fed into the cooler 6, and stored in the receiving hopper 12 as a solidified material.

The feeding of the powder into the irradiation chamber, melting by microwave irradiation (gas generated during heating and melting is discharged through the exhaust pipe), and delivery of the molten material to the cooler 6 are performed continuously. It will be done.

Note that for cooling the molten material in the cooler 6, appropriate cooling means such as blast air or cooling water are used.

The solidified material accommodated in the receiving hopper 12 is filled into, for example, a sealed container according to a predetermined procedure, and stored in a storage area.

In the above treatment, if the raw material slurry is discharged from a nuclear facility, that is, if the powder or granules contain radioactive materials, the radioactive materials can be removed by melting to form a molten solid with a glass composition. Since it is completely sealed in the solidified material and does not elute, it is also preferable from the viewpoint of preventing secondary pollution.

Therefore, when the powder or granule itself does not have a component composition that forms a glass-like solidified material, the powder or granule may be mixed with 5i02, Cab, MgO, Na2O, A40, etc.
B, K2O, pbo.

It is also possible to give a glass composition to the resulting solidified product by integrally melting it together with a glass or ceramic container containing CaF2 or the like.

Further, drying and granulating the powder using the above-mentioned means is very convenient for the subsequent heating and melting treatment of the powder and granular material by microwave irradiation.

In other words, in heating and melting by microwave irradiation,
The lower the moisture content of the heated melt, the smaller the particle size, the more uniform the particle size, and the larger the surface area, the higher the irradiation efficiency and the faster the melting can be completed.

like that. As the powder, particles having a moisture content of about 10% or less, particularly about 5 to 10%, and a particle size of about 0.01 to 0.2 mm are advantageously used.

According to the above means, it is easy to control the moisture content.
Powder and granular material having the above properties can be easily and stably supplied.

Other methods of "dry granulation" include microwave irradiation and incineration, but compared to these methods, the above method prevents jamming (clogging of raw materials, adhesion, etc.) within the equipment. It is advantageous in that it has excellent reliability, durability, and maintainability, with fewer troubles, and both the evaporator and dryer have a long life of about 40 years, and the inside is easy to clean.

In addition, according to the above means, it is possible to ensure continuous supply of an appropriate amount of the object to be irradiated (dry granular material) to the microwave irradiation furnace.

If supply to the irradiation furnace is carried out in batches and a large amount of powder or granular material is irradiated and heated at once, efficient melting cannot be achieved unless the irradiated object is rotated or irradiated from several points. As a result, the Ikioi device becomes complicated and large-scale.

However, when the above-mentioned method is adopted, an appropriate amount of powder or granules can be continuously supplied, so that the irradiation melting process can be efficiently achieved with a relatively compact device.

According to microwave irradiation, the volume reduction ratio of the solidified product obtained by melting and solidification is extremely large compared to other methods (for example, external heating method), so it is difficult to handle the solidified product during transportation, storage, etc. Very advantageous.

Furthermore, microwave energy is well absorbed when the object to be irradiated is in the form of powder.

Therefore, using microwaves as a heat source is
It is extremely suitable as a means for heating and melting the powder obtained from the "dry granulation" process.

In particular, if the powder or granular material has low heat conductivity and is mainly composed of oxides such as SiO This enables efficient processing.

Furthermore, since the melting process can be accomplished within a short period of time, the amount of exhaust gas produced is kept to a small amount, which is advantageous in that pollution problems are alleviated.

[Brief explanation of drawings]

FIG. 1 CI, l and [■] show a system schematic diagram of the method of the present invention. In the drawing, the main symbols are as follows. 1: Pretreatment tank, 2: Evaporator, 3: Dryer, 4: Microwave oscillator, 5: Irradiation furnace, 6: Cooler, 8: Powder feeder, Ll: Raw material slurry introduction pipe, L3: Discharge Air piping for prevention, L4: Waveguide, Sl, S2 Nisteam, P: Feed pump.

Claims (1)

[Claims] 1 After evaporating and concentrating the raw material slurry, it is dried in a dryer to a moisture content of 5 to 10% (weight) and a particle size of 0. O1~0.2tra
drying of a slurry, which is characterized in that the powder and granules are then supplied to a microwave irradiation furnace, heated and melted by microwave irradiation, and then cooled and solidified.
Melting solidification method.