RU92424U1 - CONTINUOUS ELECTROLYZER FOR MELTED SALTS - Google Patents

Abstract

1. A continuous electrolyzer for molten salts, containing a heated bath with a lid, a device for loading the processed substance, a pipe for supplying reagent gas to the melt, a device for removing the cathode deposit and extracting it from the electrolyzer, an anode and a cylindrical cathode placed on the horizontal shaft with a drive for rotation, the mixing device is provided with a melt-permeable partition separating the cell into the cathode and anode parts, the loading device being processed a substance supply pipe in the reactant gas melt mixing device arranged in the anode and the cathode of the bath is provided with end insulators. ! 2. The electrolyzer according to claim 1, characterized in that it is equipped with a pipe for supplying gas to the cathode part of the melt. ! 3. The electrolyzer according to claim 1, characterized in that the bathtub made of an electrically conductive material is provided with an insulating material in the cathode part.

Description

The device relates to the metallurgical, chemical and radiochemical industry and is intended for conducting electrochemical and chemical processes in salt melts, mainly for processing and obtaining various electrically conductive substances (metals, oxides, etc.) by electrolysis of molten salts, for example, to obtain crystalline uranium dioxide or MOX fuel, electrochemical regeneration of spent nuclear fuel.

An electrolyzer is known for producing crystalline uranium dioxide from chloride salt melts (A.V. Bychkov, S.K. Vavilov, O. V. Skiba at al., Pyroelectrochemical Reprocessing of Irradiated FBR MOX Fuel. III. Experiment on High Burn-up Fuel of the BOR-60 Reactor, GLOBAL'97), which includes a metal case heated by an electric heater with a bathtub (crucible) containing an electrolyte and serving as an anode, a cooled lid with nozzles for the release of gases, a cylindrical cathode, and pipes for supplying the reagent gas to the melt. To prepare the electrolyte, a tube of a mixing pulsating device is installed in place of the cathode. All parts of the electrolyzer in contact with the melt (bath, cathode, pipes) are made of pyrocarbon.

The cell operates as follows. First, the required amount of salts, processed uranium oxides are loaded into the bath through the hole in the lid and, turning on the heater, the salts are transferred to the liquid state (melted). A mixing device is installed in the lid of the electrolyzer, chlorine reagent gas is introduced into the melt through a gas supply pipe and the mixing device is activated. After chlorination (dissolution) of uranium oxides in the melt, a mixing device is removed from the electrolyzer, a cathode is installed in its place and the electrolysis current is turned on. At the cathode, a precipitate of crystalline uranium dioxide is released, and the anode gas chlorine leaves the melt and is removed through a nozzle in the lid. At the end of the electrolysis process, a cathode with a precipitate of uranium dioxide is removed and the precipitate is removed. After loading the next portion of uranium oxides and adding salts, the process of chlorination and electrolysis is repeated. At the end of processing the batch of the product, the electrolyzer is cooled, the lid is removed and the solidified electrolyte is removed.

The main disadvantages of the described electrolyzer are:

- the frequency of work (the processes of dissolution of the starting materials and electrolysis are performed sequentially);

- the need for installation and removal of the mixing device, installation of the cathode, extraction of the cathode and removal of sediment and the associated time costs;

- depressurization of the electrolyzer during these operations, entailing the release of hot gases and electrolyte vapor into the atmosphere and ingress of oxygen into the electrolyzer, leading to the oxidation of its carbon and graphite parts;

- the resulting massive cathode deposit is then required to be crushed.

The well-known "Electrolyzer for producing metals from molten salts" (AS No. 387031, BI No. 27, 1973). It consists of a heated bath containing molten salt electrolyte, a cap with nozzles and placed in the anode bath, horizontally located above the anode of the hollow drum cathode with holes at the ends, mounted on a hollow shaft with a drive for rotation. A pusher is placed inside one shaft cavity for loading the processed substance into the cathode cavity, and in the other shaft cavity there is a tube for introducing gas into the melt inside the drum cathode. A device (knife) is pressed against the outer surface of the drum cathode to remove the deposited product into the receiver.

In contrast to the analogue, in this electrolyzer, processes of chemical dissolution in the melt of the initial processed substances and electrolysis with the formation of a cathode deposit are simultaneously and continuously conducted, as well as the operation of loading the starting materials, removal of the cathode deposit from the cathode without removing it from the cell and, accordingly, without depressurization of the cell .

For this, salts are first loaded and melted into the bath, the melt enters the cathode cavity through holes in the ends, and the starting materials loaded there through the hollow shaft of the cathode are dissolved by a gaseous reagent introduced through a curved tube on the other side of the hollow shaft of the rotating cathode. The resulting electrolyte flows from the cathode to the bath and vice versa. Turn on the electrolysis current. The crystalline product released during electrolysis on the cylindrical surface of a rotating cathode is removed by a knife pressed to the cathode and dumped into the receiver, while the starting materials are periodically or continuously loaded into the cathode cavity and gas is supplied to dissolve them. The anode gas released during electrolysis and the excess part of the gas used to dissolve the processed material initially and during the electrolysis are discharged through a pipe in the electrolyser cover.

The disadvantages of the cell are:

- design complexity;

- carried out only chemical dissolution of the processed substance;

- the possibility of getting insoluble particles of the original processed substance loaded into the cathode cavity into the cathode deposit (product) deposited on the outer surface of the cathode drum;

- the placement of the cathode above the anode leads to "washing" with its anode gas and a decrease in the cathode yield of the product;

- the deposition of the cathode product at the ends of the drum cathode, the removal of which is not provided, is not excluded.

The design of the cell in question is very complex. This is a hollow drum cathode mounted on a hollow shaft, as well as the placement in the shaft cavity of the pusher device of the loaded materials, and in another curved pipe for supplying the reagent gas. These parts must be made of hard-to-process carbon-graphite compositions, ceramics, and special alloys that are corrosion resistant at high temperatures to aggressive molten electrolytes (e.g., chloride salts) and gases (chlorine, oxygen, etc.). Seals are difficult to seal the stationary and rotating parts of the cell.

The disadvantage of the electrolyzer is that the constant chemical dissolution of the processed substances in the melt using a reagent gas during the whole process usually requires a large excess of it, and there are difficulties in coordinating the rates of dissolution of substances and cathodic release of the product.

The objective of this technical solution is to simplify the design of the electrolyzer, which allows continuous and simultaneous processes of electrochemical and chemical dissolution of the processed substance in molten salts, cathodic deposition of a crystalline product from a melt,

The problem is solved in that a continuous cell for molten salts, containing a heated bath with a lid, a device for loading the processed substance, a pipe for supplying reagent gas to the melt, a device for removing the cathode deposit and removing it from the cell, the anode and cylindrical placed in the bath the cathode on a horizontal shaft with a drive for rotation, the mixing device is equipped with a melt-permeable partition separating the cell into the cathode and anode parts, and ystvo to download the processed material supply pipe in the reactant gas melt mixing device arranged in the anode and the cathode of the bath is provided with end insulators.

The cell is additionally equipped with a pipe for supplying gas to its cathode part to adjust the composition of the melt.

When using electrically conductive material for the manufacture of a bath, the anode is the bath itself, while its cathode part is shielded by an insulating material.

The excess part of the reagent gas and the released anode gas are returned to the cell using a compressor.

The proposed electrolyzer is shown in section in figure 1., in figure 2. a top view of the cell is shown with a partial section along the cathode axis.

The cell contains a housing 1 with a bath 2 of non-conductive material, heated by a heater 3. Inside the bath there is a melt-permeable (porous) partition 4, anode 5, current supply to it 6, a cylindrical cathode 7 with end insulators 8, fixed by nuts 9 on the shaft 10, which is equipped with a sliding current lead 11, a rotation drive 12 and is supported by bearings 13 made of insulating material, equipped with seals (“glands”) 14. The housing 1 is sealed by a gasket 15 with a cover 16 having a cooling jacket 17. The cover is provided a pipe for the exit of gases 18, two pipes 19 for sensors for monitoring the composition of the electrolyte in the cathode and anode parts of the melt, a pipe for a pipe 20 for supplying corrective gas to the cathode part of the melt. On the anode part of the lid there are pipes for installation: - a device for loading salts and processed substances 21, - pipes 22 for supplying reagent and gas to the melt to adjust the composition of the melt, - mixing device 23, - current supply 6 to the anode 5. To the cylindrical cathode 7 the knife 24 is pressed, isolated from the cover 16 and docked with the box tray 25 attached to the cover 16, the collection container 26 is hermetically connected to the bottom of the tray. All nozzles with devices are sealed with seals.

In the manufacture of the bath from electrically conductive, for example, carbon-graphite materials, the Cathode part of the bath 2 is shielded with an insulating material 27.

The cell operates as follows. First, the required amount of salt is loaded into the bath 2 using the loading device 21 and, turning on the heater 3, it is transferred to a liquid state (melted). Then, with the same loading device 21, the processed substance is loaded into the melt 28 on the anode 5, the reagent gas is supplied through the pipe 22 and the mixing device 21, mainly of a pulsating type, is turned on. Chemical dissolution of the processed substance in a molten salt is carried out - electrolyte preparation. Upon reaching the required electrolyte composition behind the permeable baffle 4, in the cathode part of the bath, the electrolysis current is switched on through current leads 6 (to the anode 5) and 11 to the shaft 10 of the cathode 7. The permeable baffle 4 prevents the particles of the processed substance and the anode gas from entering the cathode 7 mechanically. The cathode 7 is rotated by the shaft 10 using the drive 12 continuously or periodically, depending on what kind of cathode deposit is to be obtained, which is also removed with the knife 24 during the rotation of the cathode and it enters the collection container 26 through the tray 25.

During electrolysis, depending on the current, anodic electrochemical dissolution of the processed substance, or simultaneous anodic dissolution and release of the anode gas, which also takes part in the dissolution process as a reactant gas, takes place at the anode 5. These anode processes significantly, by about 80-90%, allow reducing the external supply of the reagent gas, leaving only the amount necessary to compensate for the anode losses.

As necessary, the processed substance, as well as salts, are loaded into the electrolyzer using a loading device 21 to compensate for the loss of electrolyte captured by the cathode precipitate of the product.

The rotation modes of the cylindrical cathode 7 - continuous at different speeds or periodic with different frequencies - allow you to get product precipitation of a wide range of thickness and size of the crystals.

The end insulators 8 of the cathode 7 prevent the deposition of an unrecoverable product, and the insulating screen 27 prevents the release of the anode gas on the part of the bath made of electrically conductive (carbon-graphite) material and the surrounding cathode.

The cathodic and anodic composition of the electrolyte melt is controlled by sensors or by sampling through the nozzles 19, their compositions are adjusted by supplying the corresponding gases to the melt through the pipes 20 and 22, which makes it possible to better control the processing process or automate it.

The tightness of the design allows the gases leaving the cell through the pipe 18 to be returned both at the stage of the primary dissolution of the substance and during electrolysis, which further helps to reduce the consumption of reagent gas.

At the end of the campaign for processing a batch of substances, the melt from the electrolyzer is removed using a vacuum ladle, the suction pipe of which is lowered, for example, through the pipe of the mixing device 23.

Claims (3)

1. A continuous electrolyzer for molten salts, containing a heated bath with a lid, a device for loading the processed substance, a pipe for supplying reagent gas to the melt, a device for removing the cathode deposit and extracting it from the electrolyzer, an anode and a cylindrical cathode placed on the horizontal shaft with a drive for rotation, the mixing device is provided with a melt-permeable partition separating the cell into the cathode and anode parts, the loading device being processed a substance supply pipe in the reactant gas melt mixing device arranged in the anode and the cathode of the bath is provided with end insulators. 2. The electrolyzer according to claim 1, characterized in that it is equipped with a pipe for supplying gas to the cathode part of the melt. 3. The electrolyzer according to claim 1, characterized in that the bathtub made of an electrically conductive material is provided with an insulating material in the cathode part.