Molten lunar soil electrolysis oxygen production device and method based on oxygen ion conductor

Abstract

The invention discloses a molten lunar soil electrolysis oxygen production device and method based on an oxygen ion conductor, and relates to the technical field of lunar in-situ resource utilization. The device comprises a shell, a crucible is installed in the shell, a first heating coil is arranged on the outer surface of the crucible, and the space between the crucible and the shell is filled with a heat preservation layer; the bottom of the crucible is arranged to be an inclined face, and a deslagging runner is formed in the middle of the bottom of the crucible. Oxygen is generated on the surface of the anode in the oxygen ion conductor immersed in the molten lunar soil instead of being generated on the surface of the anode immersed in the molten lunar soil, a gas-liquid separation process of oxygen-molten lunar soil does not exist, diffusion of the oxygen in the inner space of the oxygen ion conductor is easier than that of gas-liquid separation, and the oxygen-liquid separation efficiency is improved. Oxygen molecules can be quickly desorbed from electrochemical active sites of the anode, and during use, only the interior of an oxygen ion conductor needs to be airtight instead of a crucible and a space related to the upper part of the crucible, so that the complexity of the device is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of lunar in-situ resource utilization, and specifically to a device and method for producing oxygen by electrolyzing molten lunar soil based on an oxygen ion conductor. Background Art

[0002] The moon is an important target for human deep space exploration. In recent years, countries have shown great enthusiasm for lunar exploration, and have presented their mission plans or visions for lunar bases and lunar scientific research stations. The short-term goal is to carry out regular scientific exploration and resource utilization activities on the moon, and the long-term goal is to use the moon as a transit station to support human beings to go deeper into space. In-situ lunar resource utilization is a series of technical means to transform the available resources of the moon into various products required for lunar exploration missions. It can significantly reduce the mass of transportation between the earth and the moon, reduce dependence on the earth, and effectively save launch costs. It is an important basis for achieving long-term, low-cost lunar exploration.

[0003] The lunar surface is covered with lunar soil several meters thick. The main chemical components include silicon oxide (SiO2), aluminum oxide (Al2O3), ferrous oxide (FeO), titanium oxide (TiO2), etc. Oxygen, metals and other substances can be extracted through lunar soil oxygen production technology. Oxygen can be provided to astronauts for breathing, and liquid oxygen is a propellant for spacecraft. Metals can be prepared into functional and structural parts through casting, manufacturing and other processing for the construction of lunar facilities. The molten lunar soil electrolysis oxygen production technology is an electrochemical metallurgical technology.

[0004] The existing patent (Announcement No.: CN118007141A) discloses a device and method for in-situ comprehensive extraction of oxygen, alloy and glass on the lunar surface. When in use, the cathode and anode of the device are in direct contact with the molten lunar soil. The anode is easily consumed by the erosion of the molten lunar soil, high-temperature oxygen oxidation, and electrochemical oxidation, which is not conducive to long-term use. In addition, the anode is immersed in the molten lunar soil, which is not conducive to the separation of oxygen bubbles on the anode surface and the molten lunar soil under the low gravity state on the lunar surface. For this reason, we propose a device and method for electrolyzing oxygen from molten lunar soil based on oxygen ion conductors. Summary of the invention

[0005] The purpose of the present invention is to provide a device and method for producing oxygen by electrolysis of molten lunar soil based on oxygen ion conductors to solve the problems raised in the above-mentioned background technology.

[0006] To achieve the above-mentioned purpose, the present invention provides the following technical solutions: a molten lunar soil electrolysis oxygen production device based on oxygen ion conductor, comprising a shell, a crucible is installed inside the shell, a first heating coil is arranged on the outer surface of the crucible, and an insulation layer is filled between the crucible and the shell;

[0007] The bottom of the crucible is set as an inclined surface, and a slag discharge channel is opened in the middle of the bottom of the crucible, the outer surface of the slag discharge channel is wound with a second heating coil, and a cathode is installed on the inner wall of the crucible, and the cathode is electrically connected to a DC power supply through a wire;

[0008] An oxygen ion conductor is fixedly connected to the center of the top of the shell, an anode is installed at the bottom of the inner wall of the oxygen ion conductor, and the anode is electrically connected to a DC power supply through a wire;

[0009] A lunar soil feeding assembly is installed on the top of the shell, the lunar soil feeding assembly is located above the crucible, and an airtight assembly is installed on the top of the oxygen ion conductor.

[0010] Furthermore, a sealing plug is provided at the port of the slag discharge channel, and the sealing plug is configured to be high temperature resistant ceramic.

[0011] Furthermore, a slag discharge hole is provided at the bottom of the shell, and a channel for slag discharge is provided in the insulation layer.

[0012] Furthermore, the cathode is configured to be cylindrical, and is made of molybdenum, platinum or iridium.

[0013] Furthermore, the oxygen ion conductor is a hollow structure with an open upper end and a closed lower end. The top end of the oxygen ion conductor passes through the shell and is suspended above the crucible.

[0014] Furthermore, the oxygen ion conductor material is yttria-stabilized zirconia or magnesium oxide-stabilized zirconia.

[0015] Furthermore, the anode is an oxygen ion electron mixed conductive oxide film, the material of which is La 0.8 Sr 0.2 MnO 3-δ ,La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ ,La 0.6 Sr 0.4 Cr 0.5 Fe 0.5 O 3-δ ,La 0.8 Sr 0.2 MnO 3-δ or Sr2Fe 1.5 Mo 0.5 O 6-δ , and the thickness of the anode is set to 10um-500um;

[0016] Alternatively, the anode is a porous high temperature resistant metal, the material is set to platinum or iridium, and the pore size range of the porous high temperature resistant metal is 0.5mm-3mm.

[0017] Furthermore, the lunar soil feeding assembly includes a feed hopper fixedly connected to the shell, the bottom end of the feed hopper passes through the interior of the shell, and a feed valve is provided on the feed hopper.

[0018] Furthermore, the airtight component comprises a cover installed on the top of the oxygen ion conductor, an oxygen conduit is installed through the cover, and an oxygen valve is arranged on the oxygen conduit.

[0019] The present invention provides a method for producing oxygen by electrolysis of molten lunar soil based on an oxygen ion conductor, and the specific steps are as follows:

[0020] S1. Use a sealing plug to seal the slag discharge channel at the bottom of the crucible, and add lunar soil into the crucible through the lunar soil feeding assembly with the help of lunar surface operation equipment;

[0021] S2. Powering the first heating coil to heat the lunar soil in the crucible to above 1300° C., so that the lunar soil is melted and has a certain conductivity;

[0022] S6. Maintain the temperature in the crucible, turn on the DC power supply, pass DC power to the anode and cathode to start electrolysis, the anode in the oxygen ion conductor produces oxygen, and the cathode in the crucible produces an alloy;

[0023] S4. When the oxygen in the oxygen ion conductor reaches a certain pressure, the oxygen valve is opened and the gas is discharged through the oxygen conduit;

[0024] S5. When the mass ratio of oxygen produced by electrolysis to lunar soil is 10%-30%, the DC power supply is turned off to cut off power to the anode and cathode;

[0025] S6. Power on the second heating coil to heat the slag discharge channel, open the sealing plug to allow the molten material in the crucible to flow out from the slag discharge channel, and finally disconnect the power supplies of the first heating coil and the second heating coil in turn.

[0026] The present invention has at least the following beneficial effects:

[0027] (1) In the present invention, oxygen is generated inside the oxygen ion conductor, not on the surface of the anode immersed in the molten lunar soil. There is no gas-liquid separation process of oxygen-molten lunar soil. The diffusion of oxygen in the internal space of the oxygen ion conductor is easier than the gas-liquid separation. Oxygen molecules can quickly desorb from the electrochemical active sites of the anode, and the anode overpotential will decrease.

[0028] (2) When in use, the present invention only needs to seal the interior of the oxygen ion conductor, rather than the crucible and the space above it, thereby reducing the complexity of the device. In addition, oxygen is directly enriched in the oxygen ion conductor and discharged through the oxygen conduit, thereby reducing the difficulty of oxygen collection.

[0029] (3) The present invention avoids the contact between oxygen and the crucible and the wire connected to the cathode. The crucible, the wire connected to the cathode and other materials are not oxidized by high-temperature, high-purity oxygen, and their service life is increased.

[0030] (4) The present invention uses oxygen ion conductors to isolate the molten lunar soil from the anode. The oxygen ion conductors are ceramic materials and are more resistant to erosion by the molten lunar soil than precious metal anodes, thereby increasing the life of the molten lunar soil electrolysis oxygen production device. In addition, the oxygen ion electron mixed conductive oxide membrane is used as the anode, which greatly reduces the cost compared with precious metal anodes such as platinum and iridium, and is conducive to large-scale use.

[0031] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a cross-sectional schematic diagram of the overall structure of the present invention;

[0033] Figure 2 It is a cross-sectional schematic diagram of the slag removal process of electrolytic oxygen production according to the first embodiment of the present invention;

[0034] Figure 3 Schematic cross-sectional view of the anode structure of the second embodiment of the present invention.

[0035] Reference numerals:

[0036] 1. Feed hopper; 2. Feed valve; 3. Crucible; 4. First heating coil; 5. Insulation layer; 6. Shell; 7. Sealing plug; 8. Second heating coil; 9. Molten lunar soil; 10. Cathode; 11. Anode; 12. Oxygen ion conductor; 13. Wire; 14. DC power supply; 15. Cover plate; 16. Oxygen duct; 17. Oxygen valve; 18. Liquid alloy; 19. Molten slag. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present disclosure to clearly and completely describe the technical solutions in the embodiments of the present disclosure. Obviously, the described embodiments are only part of the embodiments of the present disclosure, rather than all of the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present disclosure.

[0038] Embodiment 1:

[0039] See also Figure 1-Figure 3 The present invention provides a technical solution: an oxygen electrolysis device for producing oxygen from molten lunar soil 9 based on an oxygen ion conductor 12, comprising a shell 6, a crucible 3 is installed inside the shell 6, a first heating coil 4 is arranged on the outer surface of the crucible 3, and a heat preservation layer 5 is filled between the crucible 3 and the shell 6;

[0040] The bottom of the crucible 3 is set as an inclined surface, and a slag discharge channel is opened in the middle of the bottom of the crucible 3. The outer surface of the slag discharge channel is wound with a second heating coil 8. A cathode 10 is installed on the inner wall of the crucible 3, and the cathode 10 is electrically connected to a DC power supply 14 through a wire 13;

[0041] An oxygen ion conductor 12 is fixedly connected to the top center of the shell 6, and an anode 11 is installed at the bottom of the inner wall of the oxygen ion conductor 12. The anode 11 is electrically connected to a DC power supply 14 through a wire 13;

[0042] A lunar soil feeding assembly is installed on the top of the shell 6 , the lunar soil feeding assembly is located above the crucible 3 , and an airtight assembly is installed on the top of the oxygen ion conductor 12 .

[0043] According to the technical solution of this embodiment, a sealing plug 7 is provided at the port of the slag discharge channel. The sealing plug 7 is configured as high-temperature resistant ceramics. The high-temperature resistant ceramics have strong corrosion resistance and high temperature resistance and can well seal the slag discharge channel.

[0044] Furthermore, a slag discharge hole is opened at the bottom of the shell 6, and a slag discharge channel is opened in the thermal insulation layer 5. When the lunar soil melt needs to be discharged, the sealing plug 7 is opened and the melt can be discharged to the outside of the shell 6 through the slag discharge hole.

[0045] According to the technical solution of this embodiment, the cathode 10 is set to be cylindrical, and the cathode 10 is made of molybdenum, platinum or iridium. This embodiment is not specifically limited here and can be selected according to actual needs. It should be noted that molybdenum, platinum and iridium all have high electrochemical activity, high temperature resistance and corrosion resistance, and are good cathode 10 materials.

[0046] According to the technical solution of this embodiment, the oxygen ion conductor 12 is a hollow structure with an open upper end and a closed lower end. The top end of the oxygen ion conductor 12 passes through the shell 6 and is arranged, and the bottom end is suspended above the crucible 3. The material of the oxygen ion conductor 12 is yttria-stabilized zirconia or magnesium-stabilized zirconia. This embodiment does not make any specific restrictions here and can be selected according to actual needs.

[0047] Furthermore, the anode 11 is an oxygen ion electron mixed conductive oxide film, the material of which is La 0.8 Sr 0.2 MnO 3-δ ,La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ ,La 0.6 Sr 0.4 Cr 0.5 Fe 0.5 O 3-δ ,La 0.8 Sr0.2 MnO 3-δ or Sr2Fe 1.5 Mo 0.5 O 6-δ , and the thickness of the anode is set to 10um-500um. The above-mentioned oxide film materials have good electrochemical properties and good thermal stability. They can not only effectively separate and oxidize oxygen ions to produce oxygen, but also maintain stable structure and chemical properties in a high temperature environment, which is conducive to the long-term stable operation of the equipment. The thickness is set in the range of 10um-500um, which can not only meet the control of the electrochemical reaction rate, but also effectively reduce the manufacturing cost and improve the economy of the equipment.

[0048] According to the technical solution of this embodiment, the lunar soil feeding assembly includes a feed hopper 1 fixedly connected to the shell body 6. The bottom end of the feed hopper 1 passes through the interior of the shell body 6, and a feed valve 2 is provided on the feed hopper 1. By opening the feed valve 2, lunar soil can be added to the crucible 3 by throwing it into the feed hopper 1 with the help of external lunar surface operating equipment. After the addition is completed, the feed valve 2 can be closed.

[0049] According to the technical solution of this embodiment, the airtight component includes a cover installed on the top of the oxygen ion conductor 12, and an oxygen conduit 16 is installed through the cover. An oxygen valve 17 is provided on the oxygen conduit 16. When the oxygen inside the oxygen ion conductor 12 reaches a certain pressure, the oxygen valve 17 is opened to discharge the oxygen from the oxygen conduit 16.

[0050] Embodiment 2:

[0051] like Figure 3 As shown, the fundamental difference between the second embodiment and the first embodiment is that the anode 11 is a porous high temperature resistant metal, the material is set to platinum or iridium, and the pore size of the porous high temperature resistant metal ranges from 0.5mm to 3mm. Platinum or iridium has better electrochemical activity, high melting point, oxidation resistance, and long-term stability. Platinum or iridium is processed into a porous structure, and oxygen ions lose electrons at the contact surface of the anode 11 and the oxygen ion conductor 12 to become oxygen. The porous structure provides a channel for oxygen to desorb and diffuse from the electrode. The porous structure has a large pore size and high porosity, which can reduce the use of platinum or iridium and save costs.

[0052] Embodiment three:

[0053] The present invention provides a method for producing oxygen by electrolysis of molten lunar soil 9 based on an oxygen ion conductor 12, and the specific steps are as follows:

[0054] S1. Use the sealing plug 7 to block the slag discharge channel at the bottom of the crucible 3, and add lunar soil to the crucible 3 through the lunar soil feeding assembly with the help of the lunar surface operation equipment;

[0055] S2. The first heating coil 4 is energized to heat the lunar soil in the crucible 3 to above 1300° C., so that the lunar soil is melted and has a certain conductivity;

[0056] S6. Maintain the temperature in the crucible 3, turn on the DC power supply 14, and start electrolysis by passing DC power to the anode 11 and the cathode 10. The anode 11 of the oxygen ion conductor 12 produces oxygen, and the cathode 10 in the crucible 3 produces an alloy;

[0057] S4. The oxygen in the oxygen ion conductor 12 reaches a certain pressure, the oxygen valve 17 is opened, and the gas is discharged through the oxygen conduit 16;

[0058] S5. When the mass ratio of oxygen produced by electrolysis to lunar soil is 10%-30%, the DC power supply 14 is turned off to cut off the power to the anode 11 and the cathode 10;

[0059] S6. The second heating coil 8 is powered on to heat the slag discharge channel, the sealing plug 7 is opened to allow the molten material in the crucible 3 to flow out from the slag discharge channel, and finally the power supplies of the first heating coil 4 and the second heating coil 8 are disconnected in sequence.

[0060] The use principle and process of the present invention are as follows: when it is necessary to electrolyze the lunar soil to produce oxygen, first, the slag discharge channel at the bottom of the crucible 3 is blocked by the sealing plug 7, and then the lunar soil is added to the crucible 3 by putting the lunar soil into the feed hopper 1 with the help of external lunar surface operation equipment. After the addition is completed, the feed valve 2 is closed, and then the first heating coil 4 is energized to heat the lunar soil in the crucible 3 to above 1300° C., so that the dusty lunar soil becomes molten and has a certain conductivity. The temperature in the crucible 3 is maintained, and the DC power supply 14 is turned on. DC power is supplied to the anode 11 and the cathode 10 to start electrolysis. During the electrolysis process, the metal / non-metal cations in the molten lunar soil 9 are reduced at the cathode 10 to produce alloys, and the oxygen ions (O 2- ) passes through the oxygen ion conductor 12 and migrates to the anode 11, where it is oxidized to oxygen. The oxygen is collected in the oxygen ion conductor 12. When the oxygen in the oxygen ion conductor 12 reaches a certain pressure, the oxygen valve 17 is opened to allow the gas to be discharged through the oxygen conduit 16. Then, electrolysis is performed until the mass ratio of the generated oxygen to the lunar soil is 10%-30%. The DC power supply 14 is turned off to cut off the power to the anode 11 and the cathode 10, and the second heating coil 8 is energized to heat the slag discharge channel. The sealing plug 7 is opened. At this time, the liquid alloy 18 and the molten slag 19 generated by electrolysis in the crucible 3 will flow out in turn. Finally, the power supplies of the first heating coil 4 and the second heating coil 8 are disconnected in turn, thereby completing one electrolysis process.

[0061] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0062] For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances. When an element is referred to as being "assembled on", "installed on", "fixed on" or "set on" another element, it can be directly on the other element or there can also be a centered element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be a centered element at the same time. The terms "vertical", "horizontal", "up", "down", "left", "right" and similar expressions used herein are only for illustrative purposes and are not intended to be the only implementation method.

[0063] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

[0064] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present disclosure. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

Claims

1. A molten lunar soil electrolysis oxygen production device based on an oxygen ion conductor, comprising a shell (6), characterized in that: A crucible (3) is installed inside the shell (6), a first heating coil (4) is arranged on the outer surface of the crucible (3), and a heat-insulating layer (5) is filled between the crucible (3) and the shell (6); The bottom of the crucible (3) is arranged as an inclined surface, and a slag discharge channel is provided in the middle of the bottom of the crucible (3), a second heating coil (8) is wound around the outer surface of the slag discharge channel, a cathode (10) is installed on the inner wall of the crucible (3), and the cathode (10) is electrically connected to a DC power supply (14) via a wire (13); An oxygen ion conductor (12) is fixedly connected to the center of the top of the shell (6), an anode (11) is installed at the bottom of the inner wall of the oxygen ion conductor (12), and the anode (11) is electrically connected to a DC power supply (14) via a wire (13); A lunar soil feeding assembly is installed on the top of the shell (6), the lunar soil feeding assembly is located above the crucible (3), and an airtight assembly is installed on the top of the oxygen ion conductor (12).

2. The oxygen electrolysis device for producing oxygen from molten lunar soil (9) based on an oxygen ion conductor (12) according to claim 1, characterized in that: A sealing plug (7) is provided at the port of the slag discharge channel, and the sealing plug (7) is configured to be high temperature resistant ceramic.

3. The oxygen electrolysis device for producing oxygen from molten lunar soil (9) based on an oxygen ion conductor (12) according to claim 2, characterized in that: The bottom of the shell (6) is provided with a slag discharge hole, and the insulation layer (5) is provided with a channel for slag discharge.

4. The oxygen electrolysis device for producing oxygen from molten lunar soil (9) based on an oxygen ion conductor (12) according to claim 2, characterized in that: The cathode (10) is arranged in a cylindrical shape, and the cathode (10) is made of molybdenum, platinum or iridium.

5. The device for producing oxygen by electrolysis of molten lunar soil (9) based on an oxygen ion conductor (12) according to claim 4, characterized in that: The oxygen ion conductor (12) is a hollow structure with an open upper end and a closed lower end. The top end of the oxygen ion conductor (12) is arranged through the shell (6), and the bottom end is suspended above the crucible (3).

6. The oxygen electrolysis device for producing oxygen from molten lunar soil (9) based on an oxygen ion conductor (12) according to claim 5, characterized in that: The material of the oxygen ion conductor (12) is yttria-stabilized zirconia or magnesium oxide-stabilized zirconia.

7. The oxygen electrolysis device for producing oxygen from molten lunar soil (9) based on an oxygen ion conductor (12) according to claim 6, characterized in that: The anode (11) is an oxygen ion electron mixed conductive oxide film, the material of which is La 0.8 Sr 0.2 MnO 3-δ ,La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ ,La 0.6 Sr 0.4 Cr 0.5 Fe 0.5 O 3-δ ,La 0.8 Sr 0.2 MnO 3-δ or Sr2Fe 1.5 Mo 0.5 O 6-δ , and the thickness of the anode (11) is set to 10um-500um; Alternatively, the anode (11) is a porous high temperature resistant metal, the material is set to be platinum or iridium, and the pore size range of the porous high temperature resistant metal is 0.5mm-3mm.

8. The oxygen electrolysis device for producing oxygen from molten lunar soil (9) based on an oxygen ion conductor (12) according to claim 6, characterized in that: The lunar soil feeding assembly comprises a feeding hopper (1) fixedly connected to a shell (6), the bottom end of the feeding hopper (1) passes through the interior of the shell (6), and a feeding valve (2) is provided on the feeding hopper (1).

9. The oxygen electrolysis device for producing oxygen from molten lunar soil (9) based on an oxygen ion conductor (12) according to claim 1, characterized in that: The airtight component comprises a cover installed on the top of the oxygen ion conductor (12), an oxygen conduit (16) is installed through the cover, and an oxygen valve (17) is arranged on the oxygen conduit (16).

10. A method for producing oxygen by electrolysis of molten lunar soil (9) based on an oxygen ion conductor (12), characterized in that: The specific steps are as follows: S1. Using a sealing plug (7) to seal the slag discharge channel at the bottom of the crucible (3), adding lunar soil to the crucible (3) through the lunar soil feeding assembly with the help of lunar surface operation equipment; S2. The first heating coil (4) is energized to heat the lunar soil in the crucible (3) to above 1300° C., so that the lunar soil is melted and has a certain conductivity; S6. Maintaining the temperature in the crucible (3), turning on the DC power supply (14), passing DC power to the anode (11) and the cathode (10) to start electrolysis, the anode (11) in the oxygen ion conductor (12) produces oxygen, and the cathode (10) in the crucible (3) produces an alloy; S4. When the oxygen in the oxygen ion conductor (12) reaches a certain pressure, the oxygen valve (17) is opened and the gas is discharged through the oxygen conduit (16); S5. When the mass ratio of oxygen produced by electrolysis to lunar soil is 10%-30%, the DC power supply (14) is turned off to cut off the power to the anode (11) and the cathode (10); S6. The second heating coil (8) is energized to heat the slag discharge channel, the sealing plug (7) is opened to allow the molten material in the crucible (3) to flow out from the slag discharge channel, and finally the power supplies of the first heating coil (4) and the second heating coil (8) are disconnected in turn.

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