RU2236307C2 - Method and device for extraction of solid sediments and suspensions from liquid media - Google Patents

Abstract

FIELD: separation of agents by settling or sorption methods; cleaning liquids (molten salts, aqueous solutions, oils); nuclear power engineering for processing nuclear fuels in molten salts by pyro-chemical methods.

SUBSTANCE: device proposed for realization of said method includes rotor made in form of hollow cylinder with blanked-off upper end, ports in upper part and restriction in lower part; its lateral surface has holes. Device is immersed in liquid to be clarified and recirculation of liquid is performed by rotation of rotor, thus sucking sediments and suspensions. Then rotor is raised above surface of liquid and sediment is squeezed to remove entrapped liquid, after which rotor is shifted to flushing fluid and then to volatile fluid for discharge of product and sediment if washed-off.

EFFECT: increased productivity; simplified procedure.

Description

The invention relates to processes for the separation of substances by precipitation or sorption methods, as well as to methods for purifying various liquids (for example, molten salts, aqueous solutions, oils) from solid sediments and suspensions, and can be used, in particular, in nuclear energy in the processing of nuclear fuel by pyrochemical precipitation method in molten salts.

Known methods for the extraction of solid sediments from liquid media, including operations of sludge and subsequent decantation or suction of clarified liquid [Kasatkin AG Basic processes and apparatuses of chemical technology. - Moscow, 1971, - p. 189-190].

The disadvantages of the methods are the long duration of the deposition process and the low separation efficiency of solid and liquid phases.

There is also known a method of extracting solid sediments and suspensions from liquid media by filtering [ibid, p. 194-196].

The disadvantage of this method is also low productivity, especially when solid precipitates are fine powders that clog the filter.

Closest to the proposed technical essence is a method implemented using a centrifuge, which contains a drive, a bearing assembly, a support plate, a screw pump immersed in the volume of the suspension, a rotor mounted on the shaft, and located outside the reactor, and connected to the pump via a pipeline with multi-way tap. [Kiryakov S.I., Shevelin B.M., Abdulmanov V.A. and others. Creation of special centrifuges and separators. // Proceedings of the Sverdlovsk Research Institute of Chemical Engineering. - Moscow, 1993, p.52-54]. The method consists in pumping the suspension from the reactor by a screw pump through the internal cavity of the rotating rotor, where the particles of the solid phase are deposited, and the clarified liquid is returned to the reactor, then the clarified liquid is removed from the reactor by means of a suction tube, and the sediment is discharged from the rotor again into the reactor by rapid braking, then the precipitate from the reactor is transferred to another centrifuge, in which the precipitate is separated (pressed) from the liquid, and drying is carried out using a heater discharging sediment from the centrifuge through its cutoff knife.

The disadvantages of this method are the complexity of the design of the equipment used, the duration of the process and the low efficiency of cleaning the product from impurities.

These drawbacks are due to the need for lengthy operations, such as the removal of liquid from the reactor, transferring the product to another centrifuge to free it from the trapped liquid, which reduces productivity and creates significant difficulties in their implementation under remote control of the process.

The complexity of the equipment design is due to the presence of a large number of executive bodies, such as a screw pump, a rotor located outside the reactor, and pipelines with a multi-way valve that transfer the suspension. To implement the method, you must have at least two centrifuges, as well as a device for loading the product. Additional difficulties arise when extracting sediments and suspensions from molten salts under remote maintenance conditions, for example, when reprocessing irradiated nuclear fuel by the pyrochemical precipitation method in protective chambers. In this case, additional devices are required to ensure heating of the rotor located outside the reactor and pipelines transferring the melt to the melting temperature of salts (up to 1000 ° C) to prevent freezing of the salt melt.

In addition, the absence of a washing operation leads to contamination of the extracted sediment with impurities.

The aim of the invention is to simplify the method and device while reducing the duration of the process and increasing the efficiency of cleaning the extracted sludge from impurities.

To achieve this goal, a method is proposed, including the deposition of a solid phase in the inner cavity of the rotor during its rotation, while the rotor is immersed in the volume of the clarified liquid, and they are placed in the immediate vicinity of the precipitation, and when the rotor rotates, an intensive circulation of liquid through it in the direction from the bottom up . Precipitation and suspension are sucked up by the fluid flow into the inner cavity of the rotor and, under the action of centrifugal forces, the solid phase is deposited on the wall inside the rotor, then the rotor with the sediment in a rotating state is raised above the surface of the liquid and the sediment is extracted from the entrained liquid, after which the device with the sediment is removed from the reactor.

Further, if it is necessary to wash the precipitate from trapped impurities (for example, salts), the rotor with the precipitate contained in it is transferred to the solvent of impurities and the rotation of the rotor creates the circulation of the solvent through the rotor with sediment. After the impurities are dissolved, the rotor is raised above the surface of the solvent and the precipitate is extracted from the solvent.

To unload the sediment, the rotor is moved to a container that is equipped with a heater and filled with a small amount of easily volatile liquid, and by one or more cycles of starting and stopping the rotor, the sediment is discharged (washed) into the container, and the rotor is removed from the container in a stationary state, and then heated container, the liquid is distilled off and the precipitate is dried.

Thus, the method allows to extract the precipitate from the liquid without carrying out the operations of draining the liquid from the reactor, reloading the product into another centrifuge, provides the possibility of washing the precipitate from impurities and significantly reduces the downtime of the reactor. To implement the method, only one device, simple in design, is used, the rotor of which simultaneously performs the functions of a pump, a centrifuge and an interoperation vehicle.

If it is necessary to deeply purify the liquid from very thin suspensions, or when the solid and liquid phases have an insignificant difference in densities, a powder of a material insoluble in it, having a higher density than the liquid that is absorbed into the rotor and forms a porous precipitate inside it, is added to the liquid, serving as a filter in the circulation of the liquid, and thus catch thin and light suspensions.

A device for implementing the method, comprising a drive, a bearing assembly, a rotor mounted on a shaft, and a base plate, has a significant difference in that the rotor immersed in the volume of the clarified liquid has the form of a hollow cylinder with windows in the upper part and the lower part of the rotor has a narrowing in the form of a truncated cone with a Central hole. In addition, a fixed cylinder is mounted coaxially with the rotor outside, mounted on a base plate, the lower part of which also has a narrowing in the form of a truncated cone, with holes for fluid flow on the side surface of the fixed cylinder, and an annular partition can be installed inside it above the holes, preventing the rise of fluid during rotation.

In order to increase the efficiency of phase separation inside the rotor, radial partitions can be installed, the presence of which prevents the lag of the liquid, thereby increasing its angular velocity of rotation, which significantly increases the phase separation factor.

In order to prevent entrainment of the solid phase with the fluid flow from the rotor, a horizontal annular partition can be installed inside it below the windows.

For more efficient squeezing of the precipitate from the trapped fluid, the inner wall of the cylindrical part of the rotor can be made in the form of a cone expanding to the top with an angle of up to 10 °.

Windows in the rotor can be made not on the lateral surface of the cylinder, but on the upper end at a distance from the axis of rotation greater than the radius of the lower central hole.

No significant new features of the claimed invention were found in the scientific and technical literature, the proposed solutions do not follow explicitly from the prior art, and the combination of features provides new properties, which allows us to conclude that the claimed solution meets the criterion of inventive step.

Figure 1 schematically shows a device for extracting solid sediments and suspensions from liquid media, and also shows the reactor with a cover and the direction of fluid flow during operation.

Figure 2 shows the rotor with radial and horizontal annular partitions.

The device consists of a drive 1, a bearing assembly 2, a base plate 3, a shaft 4, a rotor 5, mounted cantilever on the shaft, and a fixed cylinder 6, mounted on a base plate.

The rotor 5 has the shape of a cylinder with a damped upper end and having side windows 7 in the upper cylindrical part, and the lower part is made in the form of a truncated cone 8 with a central hole 9.

The fixed cylinder 6 is installed coaxially with the rotor 5, forming a gap 10, the lower part of the cylinder is also made in the form of a truncated cone 11, and the cylinder has holes 12 and an inner annular partition 13 mounted above the holes.

To increase the efficiency of delamination of the solid and liquid phases inside the rotor 5, radial 14 and annular horizontal 15 partitions can be installed.

The method is implemented in the device as follows.

Through the hole in the reactor lid, the rotor 5 and the lower end of the stationary cylinder 6 are immersed in a liquid containing sediments and suspensions. The device is fixed on the reactor cover using a base plate 3. At the same time, the rotor is placed in the immediate vicinity of the precipitation at a distance of not more than 10-15 mm. When the rotor rotates, the liquid inside it, under the action of centrifugal forces, is continuously ejected through the windows 7 into the gap 10. Inside the rotor, a vacuum is formed, due to which the liquid from the lower part of the reactor is also continuously sucked into the rotor through the lower hole 9, capturing the bottom sediments and suspend. Thus, continuous intensive circulation of the liquid through the inner cavity of the rotor in the direction from bottom to top is carried out. Under the action of centrifugal forces inside the rotor, the solid and liquid phases are separated and the solid phase is deposited on the walls. Ejected from the windows 7, the clarified liquid is further divided into two streams, one of which rushes down the gap 10 and stirs up the bottom sediment, facilitating its absorption into the rotor. The second fluid flow through the windows 12 rushes into the fluid volume in the reactor, circulating the entire fluid volume through the rotor, which allows trapping suspended suspensions and eliminates the appearance of stagnant zones.

After collecting the solid phase, the device with a rotating rotor is raised above the surface of the liquid. In this position, the liquid from the reactor ceases to flow into the rotor, and the remaining liquid is ejected from the rotor through the window 7 under the action of centrifugal forces. Thus, the precipitate is squeezed from the trapped liquid, which flows back into the reactor.

After that, the device is removed from the reactor and transferred to a container with a solvent to remove soluble impurities, where all operations are repeated.

Then the device is moved to a container with a small amount of easily volatile liquid, and by one or several start and stop cycles, the sediment is completely unloaded (washed off) from the rotor into the container. The fixed rotor device is then removed from the container. Then, by heating the container, the liquid is distilled off and the precipitate is dried.

Implementation of the proposed method and device was carried out in the well-known pyroelectrochemical technology for processing irradiated nuclear mixed oxide uranium-plutonium fuel of fast reactors using molten salts (alkali metal chlorides) as a solvent.

The processing technology consists in the fact that after releasing the fuel rods from the cladding, the fuel is dissolved by chlorination in a salt melt. Then, by treating the melt with oxygen, plutonium dioxide is precipitated. The resulting precipitate is extracted from the melt by the claimed method and device and washed from trapped salts and impurities. Then, uranium dioxide is extracted from the molten salt by electrochemical deposition on the cathode. After the extraction of uranium and plutonium dioxide, the chlorides of radioactive fission products remain in the melt, which are precipitated in the form of phosphates and extracted from the melt.

During the experimental verification of the proposed method and device, it was found that after 20 minutes of operation of the device, the amount of plutonium dioxide extracted from the molten salts was 99.9% of the original. After washing in a solvent, which was used water, the salt content on the surface of the grains of plutonium dioxide was not detected. Phosphates of fission products were recovered by 99.7% in a compact form, convenient for disposal. Alcohol was used as an easily volatile liquid when unloading products into a container. In the experiment, molten salts with a density of 1.6 g / cm ^{3 were used} . The melt volume was 20 liters. The density of the sediment of plutonium dioxide was ~ 10 g / cm ³ . The operating temperature during the process was 700 ° C. The rotor was placed at a height of 15 mm from the sediment. The windows on the rotor were made at a distance of 250 mm from the lower end, the rotor speed was 900 rpm, the gap between the rotor and the stationary cylinder was 10 mm. Despite the significant difference in the density of the sediment and the melt, the precipitate was collected almost completely. There were no difficulties in extracting precipitation by this method under conditions of remote control of the process.

Claims (10)

1. The method of extracting solid sediments and suspensions from liquid media, including the deposition of a solid phase in the inner cavity of the rotor during its rotation, characterized in that the rotor is immersed in the volume of the clarified liquid, and they are placed in the immediate vicinity of the precipitation, during the rotation of the rotor create an intensive circulation liquid through it in the direction from the bottom up, while the flow of liquid precipitates and suspensions are sucked into the inner cavity of the rotor, where, using centrifugal forces, the solid phase is deposited on the wall inside the mouth ora, then the rotor with the sediment in a rotating state is raised above the surface of the liquid and squeeze the sediment from the trapped liquid. 2. The method according to claim 1, characterized in that for cleaning the precipitate from solid impurities, the rotor with the collected precipitate is immersed in the solvent of impurities and the rotation of the rotor creates a circulation of the solvent through it, after dissolution of the impurities, the rotor is raised above the surface of the liquid and the precipitate is extracted from the solvent . 3. The method according to claim 1 or 2, characterized in that to remove the collected sediment from the rotor, the rotor is transferred to a container with easily volatile liquid and, by one or more cycles of starting and stopping the rotor, the precipitate is washed off into the container, and the rotor is removed from the rotor when stationary container, after which the liquid is distilled off and the precipitate is dried. 4. The method according to claim 1, characterized in that in order to ensure deep cleaning of the liquid from fine suspensions or with a slight difference in the densities of the solid and liquid phases, a powder of an insoluble material in it, whose density is greater than the density of the liquid, is added to the liquid. 5. A device for extracting solid sediments and suspensions from liquid media, comprising a drive, a bearing assembly, a rotor mounted on a shaft, and a base plate, characterized in that the rotor has the shape of a hollow cylinder with windows in the upper part, and the lower part of the rotor has a narrowing in the form of a truncated cone with a central hole, in addition, a fixed cylinder is mounted coaxially with the rotor on the outside, mounted on a base plate, the lower part of which also has a narrowing in the form of a truncated cone, and on the side surface of the fixed cylinder core provided with holes for fluid flow. 6. The device according to claim 5, characterized in that radial partitions are installed on the inner side surface of the rotor. 7. The device according to claim 5, characterized in that a horizontal annular partition is installed inside the rotor below the windows. 8. The device according to claim 5, characterized in that the inner wall of the cylindrical part of the rotor is made in the form of a cone, expanding upward with an angle of up to 10 °. 9. The device according to claim 5, characterized in that the windows on the rotor are made on the upper end at a distance from the axis of rotation greater than the radius of the lower central hole. 10. The device according to claim 5, characterized in that an annular partition is installed inside the stationary cylinder above the holes.

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