JP6970570B2 - How to dry the molten salt electrolytic cell - Google Patents

Description

The present invention relates to a method in which the inside of an electrolytic cell is a molten salt bath, and the molten salt electrolytic cell for electrolyzing the molten salt inside the electrolytic cell to generate molten metal is dried prior to the start of electrolysis. In particular, the present invention proposes a technique capable of more reliably suppressing the mixing of water into the molten salt, which causes wear of the electrode and reduction of current efficiency.

For example, magnesium chloride secondary to the production of metallic titanium by the Kroll process is decomposed into metallic magnesium and chlorine gas by electrolysis using a molten salt electrolytic tank, and the reduction of titanium tetrachloride and chlorine tetrachloride, respectively. It may be used for chlorination of titanium ore and reused.

In this type of electrolysis, in general, a molten salt such as magnesium chloride is stored inside the electrolytic cell to form a molten salt bath, and the molten salt is flowed from the storage chamber inside the electrolytic cell to the electrolytic cell, where the electrode is energized. Based on this, it decomposes into molten metal such as molten magnesium chloride and gas such as chlorine. The molten metal generated in the electrolytic cell is further circulated to the storage chamber inside the electrolytic cell, floats on the liquid surface of the molten salt bath due to the density difference with the molten salt, and then recovered, and the gas is electrolyzed by the molten salt. It is discharged to the outside of the electrolytic cell through the gas discharge passage provided in the tank.

By the way, when water is present inside the electrolytic cell and is mixed in the molten salt bath, problems such as shortening of the life of the molten salt electrolytic cell due to wear of electrodes and a decrease in current efficiency at the initial stage of electrolysis occur. .. That is, when the electrode is energized, the water in the molten salt bath is electrolyzed, and the oxygen generated thereby reacts with the graphite electrode to promote the oxidation of the electrode and consume the electrode at an early stage. Further, the water in the molten salt bath reacts with metallic magnesium or the like generated by electrolysis of the molten salt to form an oxide of the molten metal, for example, magnesium oxide, which further reacts with chlorine gas or the like and again. This is due to the consumption of current in the extra reaction of returning to magnesium chloride or the like.

In order to deal with such a problem, for example, Patent Documents 1 and 2 have proposed a method for drying a molten salt electrolytic cell in order to reduce the water content in the electrolytic cell as much as possible prior to the start of electrolysis.
In Patent Document 1, before supplying the molten salt to the molten salt electrolytic cell, a gas such as heated air is sent into the electrolytic cell and discharged to the outside of the electrolytic cell to keep the inside of the electrolytic cell at 100 ° C. or higher. A heat drying method and a bath holding drying method in which the molten salt is kept in a molten state without energization after supplying the molten salt to the molten salt electrolytic cell are described.

In Patent Document 2, regarding the above-mentioned bath-holding and drying method, the average temperature increase rate of the bath salt in the tank within 48 hours at the initial stage of drying within 48 hours from the start of bath-holding and drying is 0.75 to 2. It is disclosed that the temperature of the bath salt in the tank is raised to 5.5 ° C./hr.

Japanese Unexamined Patent Publication No. 2006-328450 Japanese Unexamined Patent Publication No. 2014-224288

Here, in drying the inside of the electrolytic cell before supplying the molten salt, in the gas heating and drying method described in Patent Document 1, the heated gas sent into the electrolytic cell is simply discharged naturally. In particular, water remained in the joints of the bricks constituting the outer wall of the molten salt electrolytic cell, and the water could not be sufficiently removed from the entire molten salt electrolytic cell. As a result, the wear of the electrodes and the decrease in current efficiency cannot be suppressed as expected.

An object of the present invention is to solve such a problem of the prior art, and the purpose of the present invention is to more effectively dry the inside of the electrolytic cell before supplying the molten salt. It is an object of the present invention to provide a method for drying a molten salt electrolytic cell, which can effectively suppress the consumption of electrodes and the decrease in current efficiency during electrolysis of molten salt.

The method for drying the molten salt electrolytic cell of the present invention is a method for drying the molten salt electrolytic cell used for producing molten metal by electrolysis of the molten salt inside the molten salt bath prior to the start of electrolysis. The inside of the electrolytic cell before supplying the molten salt is heated and sucked under reduced pressure.

Here, preferably, the air pressure inside the electrolytic cell is maintained at −500 Pa to −100 Pa by vacuum suction.
Further, preferably, the intake speed at the time of decompression suction is 7.5 × 10 ¹ L / min · m ^{3 to} 1.3 × 10 ² L / min · m ³ .

In the method for drying a molten salt electrolytic cell of the present invention, at least a part of the outer wall of the molten salt electrolytic cell is made of a breathable material, and the circumference of the molten salt electrolytic cell is surrounded by a tank having one or more intake ports. By sucking the inside of the electrolytic cell under reduced pressure using the intake port while covered with a case, the gas inside the electrolytic cell passes through the outer wall portion of the breathable material of the molten salt electrolytic cell and also passes through the intake port. It is preferable to be sucked.

In the method for drying the molten salt electrolytic cell of the present invention, it is preferable to heat the inside of the electrolytic cell by supplying a dry high-temperature gas to the inside of the electrolytic cell.
Alternatively, it is preferable that the inside of the electrolytic cell is heated by the heat generated by the electric heating heater or the immersion burner arranged inside the electrolytic cell.
Alternatively, the molten salt electrolytic cell has a temperature control tube for heating and / or cooling the molten salt bath, which is arranged so as to extend inside the electrolytic cell and whose portion located inside the electrolytic cell is sealed, and is inside the electrolytic cell. It is preferable that heating is performed by supplying a high-temperature gas to the temperature control tube.

The rate of temperature rise during heating inside the electrolytic cell is preferably 4 ° C./hr to 8 ° C./hr.
The holding temperature of the inside of the electrolytic cell during heating is preferably 420 ° C. or higher and 450 ° C. or lower.

The heat retention and depressurization time inside the electrolytic cell is preferably 48 hours or more.

According to the method for drying the molten salt electrolytic cell of the present invention, by heating the inside of the electrolytic cell before supplying the molten salt and sucking under reduced pressure, the water vapor vaporized by heating in the entire inside of the electrolytic cell is released into the electrolytic cell. Since it is effectively discharged to the outside of the electrolytic cell together with the gas sucked inside, the water content inside the electrolytic cell can be sufficiently reduced and the inside can be dried more effectively. As a result, it is possible to further suppress the early consumption of the electrode and the decrease in the current efficiency at the initial stage after the start of electrolysis of the molten salt.

It is sectional drawing along the depth direction of the molten salt bath which shows the molten salt electrolytic cell which can be used for the drying method of the molten salt electrolytic cell which concerns on one Embodiment of this invention. It is sectional drawing which shows the molten salt electrolytic cell of FIG. 1 together with the decompression pump, which is orthogonal to the depth direction. It is a side view of the molten salt electrolytic cell and the decompression pump of FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
As shown in FIG. 1, in FIG. 1, a _{molten salt having a container shape mainly made of a refractory brick such as Al 2} O ₃ or other suitable material, and a molten salt in which the molten salt supplied to the inside thereof is stored is stored. The molten salt electrolysis tank which electrolyzes a molten salt in a bath and produces a molten metal by the electrolysis is shown.

The molten salt electrolytic cell 1 has a partition wall 2 provided close to a lid member (not shown) that covers the upper opening inside the electrolytic cell, so that the inside of the electrolytic cell is located on the right side of FIG. 1 and the anode 3a and the cathode 3b are located. The electrolytic cell 1a in which the electrode 3 is arranged and the molten metal located on the left side of FIG. 1 flow into the molten metal obtained by electrolysis in the electrolytic cell 1a, and the molten metal is on the upper side due to the density difference with the molten salt. It is partitioned into a storage chamber 1b that collects in. It should be noted that one or more, preferably two or more, particularly preferably three or more multiple poles are charged between the anode 3a and the cathode 3b of the electrolytic chamber 1a, which may increase the number of electrolysis. Therefore, it is preferable in that the productivity can be increased.

Further, the illustrated molten salt electrolytic cell 1 has a temperature control tube 4 arranged so as to extend inside the electrolytic cell on the storage chamber 1b side. In the temperature control tube 4, in order to heat and / or cool the molten salt bath so that the molten metal and the molten salt reach the desired temperature, a gas or other fluid is flowed inside, and the molten metal and the molten salt bath are brought into contact with each other. It functions as a heat exchanger or the like that exchanges heat energy between them. Therefore, the temperature control tube 4 is sealed with a portion located inside the electrolytic cell immersed in the molten salt bath.
Here, as shown in FIG. 1, the temperature control pipe 4 has two or more main pipes 4a located apart from each other and extending in the depth direction of the molten salt bath, and the inside of the molten salt bath when performing electrolysis. It is assumed to have one or more branch pipes 4b which are located in the above and communicate with each other of the main pipes 4a.

The molten salt electrolytic cell 1 having such a configuration can be used, for example, for electrolysis of magnesium chloride (MgCl ₂ ) and the like, which are produced in association with the production of metallic titanium by the Kroll process.
Specifically, by energizing the electrode 3 from a rectifier or the like (not shown) connected to the anode 3a and the cathode 3b, chloride as a molten salt flowing into the electrolytic cell 1a from the storage chamber 1b through the vicinity of the bottom inside the electrolytic cell. Magnesium is electrolyzed into metallic magnesium (Mg) as a molten metal and chlorine gas (Cl _{2) as a gas.} The metallic magnesium produced in the electrolytic chamber 1a flows into the storage chamber 1b through the molten metal flow path provided in the partition wall 2, and then the metallic magnesium having a small specific gravity with respect to magnesium chloride is transferred to a shallow portion of the storage chamber 1b. It will surface and accumulate there, which can be recovered by a pump or the like (not shown). On the other hand, chlorine gas is discharged to the outside of the electrolytic cell from a gas discharge passage (not shown).

The metallic magnesium thus obtained can be used for the reduction of titanium tetrachloride in the Kroll process for producing metallic titanium, and the chlorine gas can be used for the chlorination of titanium ore in the same method.

By the way, when the molten salt bath contains water, when the molten salt is electrolyzed, the water is electrolyzed and oxygen is generated. Generally, the material of the anode 3a is graphite having chlorine resistance, but oxygen due to electrolysis of water reacts with the graphite electrode to accelerate the consumption due to oxidation of the graphite electrode and shorten the life. .. Further, when the water in the molten salt bath reacts with the metallic magnesium generated by electrolysis, magnesium oxide is produced, but a part of this magnesium oxide reacts with chlorine gas and returns to the original magnesium chloride again. In addition, some magnesium oxide becomes sludge and cannot be recovered. For these reasons, such reactions with water reduce current efficiency.

Therefore, in order to prevent early consumption of the anode 3a and suppress a decrease in current efficiency, it is important to remove as much water as possible inside the molten salt electrolytic cell 1 before starting electrolysis of the molten salt. Become.
Therefore, in the embodiment of the present invention, the molten salt electrolytic cell 1 is dried prior to starting electrolysis using the molten salt electrolytic cell 1, and specifically, the molten salt is placed in the molten salt electrolytic cell 1 in the molten salt electrolytic cell 1. The molten salt electrolytic cell 1 is sealed to some extent to heat the inside of the electrolytic cell and suck it under reduced pressure.

According to this, by heating the inside of the electrolytic cell to a relatively high temperature, not only the vaporization of the water existing in the electrolytic cell can be promoted, but also the pressure inside the electrolytic cell is lowered. By sucking with a decompression pump or the like, steam or the like is easily and surely discharged from the inside of the electrolytic cell to the outside, so that the molten salt electrolytic cell 1 can be effectively dried.

The heating and decompression suction will be described in detail. First, as illustrated in FIGS. Cover with the tank surrounding case 5. The tank surrounding case 5 has a rectangular enclosure shape in a plan view slightly larger than the outer wall 1c following the outer wall 1c of the side surface of the molten salt electrolytic cell 1, and each side surface of the tank surrounding case 5 has inner and outer surfaces. A plurality of intake ports 5a penetrating the are formed. In the illustrated example, each side surface of the tank surrounding case 5 is provided with two intake ports 5a at two different depth positions in the depth direction, for a total of four intake ports 5a.
Although not shown, the upper opening of the molten salt electrolytic cell 1 is provided with a semi-enclosed lid member, and if necessary, the gap between the lid members is filled with a heat insulating blanket or the like to suck the inside of the electrolytic cell. Make it airtight to the extent that it is depressurized.

Next, each intake port 5a of the tank surrounding case 5 is connected to, for example, one decompression pump 6 by a cable. Here, a moisture trap 7 for collecting the moisture in the sucked gas is provided between each intake port 5a and the decompression pump 6. A known moisture trap 7 can be used.

Then, while heating the inside of the electrolytic cell, the gas inside the electrolytic cell is sucked by the decompression pump 6 to reduce the pressure inside the electrolytic cell. Here, since the main part of the outer wall 1c of the molten salt electrolytic cell 1 is made of a breathable material such as brick, when the pressure is reduced and sucked by the decompression pump 6, the gas inside the electrolytic cell 1 c becomes the outer wall 1c of the molten salt electrolytic cell 1. It will be sucked from the portion made of the breathable material of the above through the intake port 5a. The outer wall 1c of the molten salt electrolytic cell 1 may be made of ceramics such as mortar, graphite, and silicon nitride in addition to bricks.

The heating at this time can be performed by various methods, but preferably, the supply of the dry high-temperature gas to the inside of the electrolytic cell, the heat generation of the electric heating heater or the immersion burner arranged inside the electrolytic cell, and the temperature control tube 4 By supplying high temperature gas to. As a result, the dried gas passes through the outer wall 1c of the molten salt electrolytic cell 1 made of brick or the like by decompression suction by the decompression pump 6 or the like, and the water present therein is effectively removed. As a result, it is possible to eliminate the risk of moisture contamination due to the combustion gas generated by combustion in the atmosphere being sent into the electrolytic cell.

The above-mentioned dry high-temperature gas can be obtained, for example, by heating a gas from which water has been removed in advance using a heat exchanger, and sends the gas into the electrolytic cell through a duct or the like. The dry hot gas can be, for example, dry air, dry CO _2, nitrogen, argon or the like.

An electric heating heater is a heater that directly or indirectly converts electric energy into heat energy to heat or cool an object. For conversion to heat energy, energization, electromagnetic induction, high frequency electric field, electromagnetic wave, light ( There are things that use radiation). By arranging such an electric heater inside the electrolytic cell to generate heat, it is possible to suppress the mixing of moisture from the outside air.
In addition, as an immersion burner, there is a burner that burns combustion air or fuel gas in a closed pipe and transfers the heat generated by the combustion to the outside of the pipe through the outer wall of the pipe. It is possible to prevent the water from getting into the inside of the electrolytic tank.

In order to use the temperature control tube 4 for heating the molten salt electrolytic cell 1 for drying, a high temperature gas is supplied to the inside of the temperature control tube 4. This hot gas may be either dry or moist. The portion of the temperature control tube 4 located inside the electrolytic cell is sealed, and even if the high temperature gas supplied there contains water, the water moves to the outside of the temperature control tube 4 inside the electrolytic cell 4. Because there is no. Therefore, the high temperature gas supplied to the temperature control tube 4 can be the atmosphere.

It is preferable that the air pressure inside the electrolytic cell is maintained at −500 Pa to −100 Pa by performing vacuum suction when the molten salt electrolytic cell 1 is dried. If the air pressure inside the electrolytic cell is too low, the air will be entrained through a small gap in the lid member of the electrolytic cell, and moisture in the atmosphere may easily be mixed in. On the other hand, the air pressure inside the electrolytic cell is too high. This is because there is a concern that hot air may be blown out of the electrolytic cell through the gap between the lid members.

The intake speed during decompression suction by the decompression pump 6 or the like is 7.5 × 10 ¹ L / min ・ m ³ [internal volume of the electrolytic cell] to 1.3 × 10 ² L / min ・ m ³ [electrolytic cell]. Internal volume of] is preferable. The "intake rate at the time of decompression suction" referred to here means a value obtained by dividing the intake capacity of the decompression pump 6 by the internal volume of the molten salt electrolytic cell 1. If this intake speed is too fast, the atmosphere may be entrained through a small gap in the lid member of the electrolytic cell, or mortar joint material that is not sufficiently dried may be sucked in. If it is too slow, the depressurized state may be maintained. There is a concern that it will disappear.

When heating the inside of the electrolytic cell, the rate of temperature rise, which is the temperature rise inside the electrolytic cell per hour, is preferably 4 ° C./hr to 8 ° C./hr. If the temperature rise rate is too fast, there is a risk of damage or deformation of the bricks, joint materials, cathode 3b, etc. of the outer wall 1c due to excessive heat input and local temperature rise. On the other hand, if the heating rate is too slow, it takes a lot of time to dry.
The temperature rise rate is calculated by recording the temperature inside the electrolytic cell, which is constantly monitored by a thermocouple installed inside the electrolytic cell, every 3 hours, dividing each recorded temperature by the time interval, and calculating the average. Ask by doing.

Further, when heating the inside of the electrolytic cell, it is preferable to hold the inside of the electrolytic cell at the maximum temperature for a predetermined time after reaching the predetermined maximum temperature, from the viewpoint of removing water, but the holding temperature (maximum temperature) at that time is , 100 ° C. or higher and lower than 500 ° C., and more preferably 420 ° C. or higher and 450 ° C. or lower. If the holding temperature is less than 100 ° C., there is a concern that the water inside the electrolytic cell will not be effectively vaporized. When the holding temperature is less than 420 ° C, a part of the vaporized water in the brick layer constituting the outer wall of the molten salt electrolytic cell can be recondensed at a temperature below the dew point and remain in the brick layer. On the other hand, if the temperature exceeds 450 ° C., there is a concern that the cathode 3b made of iron or the like may be curved due to the influence of the magnetic force in the factory or the like where the molten salt electrolytic cell 1 is installed.

The heat retention / depressurization time for maintaining the temperature at a predetermined temperature such as the above-mentioned holding temperature and sucking under reduced pressure is preferably 48 hours or longer, more preferably 60 hours or longer. This makes it possible to remove water more reliably.

When a graphite electrode is used as the anode 3a, the above-mentioned heating and vacuum suction during drying can be performed with the graphite electrode removed from the molten salt electrolytic cell 1. This is because if heating and vacuum suction are performed with the graphite electrode attached, oxidative consumption will occur to some extent from 400 ° C. or higher with ordinary graphite. However, when a graphite electrode subjected to oxidation resistance treatment is used, there is no problem even if the graphite electrode is attached and then dried. Further, the cathode 3b may be dried after being attached to the molten salt electrolytic cell 1.

After drying, the remaining electrolytic cell members such as the anode 3a are attached to the molten salt electrolytic cell, and the molten salt electrolytic cell is preheated before the molten salt is charged. The reason for performing the preheat treatment is to prevent the molten salt from solidifying by cooling at the time of bathing and to prevent the electrolytic cell member from cracking due to rapid heating.

Immediately after the preheat treatment, the molten salt is put into the electrolytic cell. When the molten salt containing magnesium chloride is added, in addition to magnesium chloride, calcium chloride and sodium chloride are contained in order to improve the electric conductivity of the molten salt, adjust the melting point of the molten salt, and adjust the density of the molten salt. In addition to magnesium chloride, calcium chloride and sodium chloride, molten salts containing magnesium chloride include magnesium fluorides, hydroxides, magnesium salts such as carbonates and nitrates, magnesium oxide, metallic magnesium, and calcium foot. It may contain a compound, a fluoride of sodium, a fluoride of potassium, a fluoride of lithium, lithium chloride, potassium chloride and the like.

Next, a molten salt electrolytic cell according to the drying method of the present invention was prototyped, and its effect was confirmed, which will be described below. However, the description here is for the purpose of mere illustration, and is not intended to be limited thereto.

In any of the comparative examples and examples described later, first, an iron cathode was installed on the electrolytic cell side of the molten salt electrolytic cell constructed from refractory bricks and mortar, and then the lid member was set. Then, the electrolytic cell was dried under each drying condition.
After drying, a graphite anode and a double pole were installed in the electrolytic cell, and the members in the electrolytic cell were preheated while adjusting the amount of heat. In the preheat treatment, the temperature in the tank was raised to 380 ° C. over 90 hours, and then kept at 380 ° C. for 48 hours.

Immediately after the preheat treatment was completed, the molten salt was put into the electrolytic cell. Regarding the bath composition of this molten salt, MgCl ₂ , CaCl ₂ , NaCl, and MgF ₂ are molten salts composed of 20%, 30%, 49%, and 1% by mass ratio, respectively, and the temperature of the molten salt is around 670 ° C. Adjusted to.

Forty-five hours after the molten salt was added, the molten salt was electrolyzed under the conditions shown below.
While the electrolysis of the molten salt is being continued, magnesium chloride, which is a by-product of the Kroll process, is supplied to the electrolytic tank as a supplementary molten salt in order to supplement magnesium chloride corresponding to the amount of metallic magnesium produced. The content of magnesium chloride in the molten salt was adjusted to be 15 to 20% by mass.

The average current efficiency for 7 days after the start of electrolysis of the molten salt was measured. In addition, three months after the start of electrolysis of the molten salt, the electrolysis was temporarily stopped, and the amount of wall thinning of the anode was measured. The results are shown in Table 1. The current efficiency is calculated by the following formula, and in the "average current efficiency" of Table 1, the current efficiency of Comparative Example 1 is 100, and the current efficiencies of Comparative Example 2 and Examples 1 to 3 are the currents of Comparative Example 1. It is shown as a relative value to efficiency.
Current efficiency = Mg mass recovered from the electrolytic cell / theoretically generated Mg mass

In Comparative Example 1, a tip opening burner tube arranged to extend inside the electrolytic cell is attached to a hole provided in the lid on the storage chamber side, and the combustion exhaust gas is directly sent into the electrolytic cell without decompression suction. Was dried.
At this time, 54 while adjusting the amount of combustion exhaust gas sent into the electrolytic cell so that the temperature rising rate of the electrolytic cell does not deviate from the range of 4 to 8 ° C./hr and the holding temperature is around 440 ° C. I kept it for a while. The exhaust gas introduced into the electrolytic cell was discharged from the duct provided on the lid of the electrolytic cell together with the steam vaporized by heating.

In Comparative Example 2, a dipping tube burner arranged to extend inside the electrolytic cell is attached to a hole provided in the lid on the storage chamber side to indirectly heat the inside of the electrolytic cell, and drying is performed without decompression suction. went.
At this time, the temperature of the electrolytic cell was maintained for 54 hours while being adjusted so that the temperature rising rate of the electrolytic cell did not deviate from the range of 4 to 8 ° C./hr and the holding temperature was around 440 ° C. The steam vaporized by heating was discharged from a duct provided on the lid of the electrolytic cell.

In the first embodiment, a dipping tube burner arranged to extend inside the electrolytic cell is attached to a hole provided in the lid on the storage chamber side to indirectly heat the inside of the electrolytic cell, and each intake port of the tank surrounding case is used. Was connected to a decompression pump, and drying was performed while depressurizing and sucking so that the air pressure inside the electrolytic cell was 280 Pa. At this time, the temperature was maintained for 54 hours while adjusting the immersion burner so that the heating rate of the electrolytic cell did not deviate from the range of 4 to 8 ° C./hr and the holding temperature was around 440 ° C.

In the second embodiment, the dry air heated from the pipe having the tip opening arranged to extend inside the electrolytic cell is directly sent into the electrolytic cell into the hole provided in the lid on the storage chamber side. Each intake port was connected to a decompression pump, and drying was performed while depressurizing and sucking so that the air pressure inside the electrolytic cell was 280 Pa. At this time, the temperature was maintained for 54 hours while adjusting the amount of dry air so that the heating rate of the electrolytic cell did not deviate from the range of 4 to 8 ° C./hr and the holding temperature was around 440 ° C.

In the third embodiment, a dipping tube burner arranged to extend inside the electrolytic cell is attached to a hole provided in the lid on the storage chamber side to indirectly heat the inside of the electrolytic cell, and each intake port of the tank surrounding case is used. Was connected to a decompression pump, and drying was performed while depressurizing and sucking so that the air pressure inside the electrolytic cell was −400 Pa. At this time, the temperature was maintained for 54 hours while adjusting the immersion burner so that the heating rate of the electrolytic cell did not deviate from the range of 4 to 8 ° C./hr and the holding temperature was around 440 ° C.

From the place shown in Table 1, in each of Examples 1 to 3 in which decompression suction was performed, the amount of wall thinning of the anode after 3 months was significantly reduced as compared with Comparative Examples 1 and 2, and the average current efficiency was reduced. It can be seen that was significantly improved. As a result, in Examples 1 to 3, it is presumed that the inside of the electrolytic cell could be effectively dried so that the water content inside the electrolytic cell was sufficiently reduced.

1 Molten salt electrolysis tank 1a Electrolysis chamber 1b Storage chamber 1c Outer wall 2 Partition 3 Electrode 3a Anode 3b Cathode 4 Temperature control pipe 4a Main pipe 4b Branch pipe 5 Tank enclosure case 5a Intake port 6 Decompression pump 7 Moisture trap

Claims (9)

This is a method of drying the molten salt electrolytic cell used for the production of molten metal by electrolysis of the molten salt inside the molten salt bath prior to the start of electrolysis. Heat and aspirate under reduced pressure,
At least part of the outer wall of the molten salt electrolyzer is made of breathable material,
By covering the circumference of the molten salt electrolytic cell with a tank surrounding case having one or more intake ports and sucking the inside of the electrolytic cell under reduced pressure using the intake port, the gas inside the electrolytic cell becomes the molten salt. A method for drying a molten salt electrolytic cell, which passes through an outer wall portion of a breathable material of the electrolytic cell and is sucked through the intake port. The method for drying a molten salt electrolytic cell according to claim 1, wherein the air pressure inside the electrolytic cell is maintained at −500 Pa to −100 Pa by suction under reduced pressure. The drying of the molten salt electrolytic cell according to claim 1 or 2, wherein the intake rate at the time of vacuum suction is 7.5 × 10 ¹ L / min · m ^{3 to} 1.3 × 10 ² L / min · m ^3. Method. The method for drying a molten salt electrolytic cell according to any one of claims 1 to 3 , wherein the inside of the electrolytic cell is heated by supplying a dry high-temperature gas to the inside of the electrolytic cell. The method for drying a molten salt electrolytic cell according to any one of claims 1 to 3 , wherein the inside of the electrolytic cell is heated by the heat generated by an electric heating heater or a immersion burner arranged inside the electrolytic cell. The molten salt electrolytic cell has a temperature control tube for heating and / or cooling the molten salt bath, which is arranged so as to extend inside the electrolytic cell and whose portion located inside the electrolytic cell is sealed.
The method for drying a molten salt electrolytic cell according to any one of claims 1 to 3 , wherein the inside of the electrolytic cell is heated by supplying a high-temperature gas to a temperature control tube. The method for drying a molten salt electrolytic cell according to any one of claims 1 to 6 , wherein the heating rate of the inside of the electrolytic cell during heating is 4 ° C./hr to 8 ° C./hr. The method for drying a molten salt electrolytic cell according to any one of claims 1 to 7 , wherein the holding temperature of the inside of the electrolytic cell during heating is 420 ° C. or higher and 450 ° C. or lower. The method for drying a molten salt electrolytic cell according to any one of claims 1 to 8 , wherein the heat retention and depressurization time inside the electrolytic cell is 48 hours or more.

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