Method and apparatus for producing metallic silicon

Abstract

Provided is a method and apparatus for producing metallic silicon. The method for producing metallic silicon involves supplying a raw material of a silicon source to a plasma torch (2) by a carrier gas (G1), and reducing the raw material by a plasma reaction to recover metallic silicon. According to this, it is possible to continuously produce metallic silicon in a short time without processing the silicon source into a block or a pellet, and without generating CO2.

Description

Technical Field

[0001] This invention relates to a method and apparatus for manufacturing metallic silicon. Background Technology

[0002] In recent years, initiatives aimed at significantly reducing waste generation through prevention, reduction, recycling, and reuse have become increasingly active. To achieve this goal, research and development on silicon recycling is underway.

[0003] Patent document 1 discloses a technology that generates silica ash by burning grain husks, straw, etc., which serve as silicon sources, and mixes it with a required amount of carbon. The raw materials are then heated from the inside by microwaves, thereby producing bio-derived metallic silicon.

[0004] Existing technical documents Patent documents

[0005] Patent Document 1: Japanese Patent Publication No. 2020-090429 Summary of the Invention

[0006] [The technical problem the invention aims to solve]

[0007] In addition, in the technology concerning the recycling of silicon, the technology in Patent Document 1 has the following technical problems: a carbon source is required to obtain metallic silicon, the carbon source will generate CO2, and environmental factors need to be considered in the treatment of CO2. In addition, the silica ash needs to be processed into blocks or granules by adding binders.

[0008] To address the aforementioned technical problems, the present invention aims to achieve continuous production of metallic silicon without processing the silicon source into block or granular form, reducing power consumption while preventing CO2 generation. This is intended to significantly reduce waste generation.

[0009] [Technical solutions used to solve technical problems]

[0010] One aspect of the present invention is a method for manufacturing metallic silicon, wherein a silicon source is supplied to a plasma torch via a carrier gas, and the raw material is reduced by plasma reaction to recover metallic silicon.

[0011] [Invention Effects]

[0012] According to one aspect of the present invention, there is no need to process the silicon source into block or granular form, which can reduce power consumption without generating CO2 and enable continuous production of metallic silicon. Attached Figure Description

[0013] Figure 1 This is a diagram showing the manufacturing apparatus of Embodiment 1.

[0014] Figure 2 This is a diagram showing the conditions for the verification experiment.

[0015] Figure 3 (A) and (B) in the figure represent experimental result 1.

[0016] Figure 4 This is a diagram showing the manufacturing apparatus of Embodiment 2.

[0017] Figure 5 This is a diagram showing the conditions for the verification experiment.

[0018] Figure 6 This is a graph representing experimental result 2.

[0019] Figure 7 This is a graph representing experimental result 3.

[0020] Explanation of reference numerals in the attached figures 1: Manufacturing apparatus for metallic silicon; 2: Plasma torch; 3: Outer cavity; 5: Inner cavity; 7: Filter cavity; 8: Filter; 9: Suction pump; 10: Raw material container; 11: Carrier gas pipeline; 12: Inlet pipe; 13: Sheath gas pipeline; 14: Internal gas pipeline; 15: Coil; 16: Coil housing; 21: Supply pipe. Detailed Implementation

[0021] (Implementation Method 1) (Structure of the manufacturing apparatus) Hereinafter, Embodiment 1 of the present invention will be described with reference to the accompanying drawings.

[0022] Figure 1 This is a diagram showing apparatus 1 for manufacturing metallic silicon. Metallic silicon refers to elemental silicon (Si).

[0023] The silicon manufacturing apparatus 1 has a plasma torch 2.

[0024] An outer cavity 3 is continuously formed on the plasma torch 2. An inner cavity 5 is housed within the outer cavity 3, and a filter cavity 7 is connected to the inner cavity 5. A filter 8 is housed within the filter cavity 7. Furthermore, a suction pump 9 is connected to the filter cavity 7.

[0025] A raw material container 10 is connected to the plasma torch 2. The raw material container 10 stores biologically derived powder raw materials as raw materials.

[0026] Biologically derived powder raw materials are obtained by finely grinding the ash or charcoal of rice husks, straws, bamboo leaves, corn leaves, stalks, etc., from plants such as rice and wheat, as well as bamboo leaves and corn stalks, into a silicon source. For example, the ash of grasses containing a large amount of silica is preferred as a biologically derived powder raw material. Alternatively, materials ground from low-grade silicon sources such as quartz glass and silica sand can also be used as raw materials.

[0027] The plasma torch 2 has an inlet tube 12 on the upstream side. A carrier gas pipe 11, a sheath gas pipe 13, and an internal gas pipe 14 are connected to the inlet tube 12. The inlet tube 12 is, for example, a triple tube.

[0028] As indicated by arrow G1, an inert gas such as Ar is supplied to the raw material container 10 through the carrier gas pipe 11. Through this carrier gas, the raw material in the raw material container 10 is transported to the plasma torch 2 through the inlet pipe 12.

[0029] The carrier gas can also be helium (He), nitrogen (N2), hydrogen (H2), etc.

[0030] Additionally, as indicated by arrow G2, a mixture of Ar and hydrogen sheath gas is supplied to the inlet pipe 12 of the plasma torch 2 through sheath gas pipe 13.

[0031] Sheath gas protects plasma torch 2 from thermal damage.

[0032] As shown by arrow G3, inert gas such as Ar is supplied to the inlet pipe 12 of the plasma torch 2 through the internal gas pipe 14.

[0033] The internal gas can also be helium (He), nitrogen (N2), hydrogen (H2), etc. The main components of the internal gas are converted into plasma.

[0034] Inside the inlet tube 12, for example, the sheath gas flows around the outer periphery of the carrier gas, and the internal gas flows around the outer periphery of the sheath gas.

[0035] The plasma torch 2 has a coil housing 16 and a coil 15 housed in the coil housing 16 on the downstream side of the inlet tube 12. A plasma power of a specified wattage is applied to the coil 15, and current flows at a specified frequency (e.g., 4 MHz), thereby causing a plasma reaction in the plasma torch 2, particularly within the coil housing 16. The coil 15 is connected to a device that applies an AC power source (not shown).

[0036] (Manufacturing method) Sheath gas and internal gas are supplied to plasma torch 2, and the raw material in raw material container 10 is transported to plasma torch 2 via carrier gas. In plasma torch 2, the raw material is reduced through plasma reaction to generate metallic silicon. That is, in plasma torch 2, silicon oxides such as silicon dioxide are reduced to generate elemental Si.

[0037] In plasma torch 2, because the process is carried out at ultra-high temperature, the reaction time to obtain metallic silicon is short, and metallic silicon can be generated in a short time, thus reducing power consumption.

[0038] Furthermore, since the plasma reaction takes place in hydrogen, there is no need to add an additional carbon source as in existing technologies, and no CO2 is produced, thus eliminating the need for environmentally conscious treatments. Moreover, it is not limited to plasma reactions in hydrogen. For example, it can also be applied to plasma reactions in carbon gases or fluorine gases.

[0039] The raw material is a powder derived from biological sources.

[0040] Accordingly, the raw materials can be used directly in powder form, without the need for binders to process them into blocks or granules as in existing technologies. Furthermore, as a powder supply, continuous processing is possible, making it suitable for assembly line production even with small-scale equipment.

[0041] The gas stream containing reactants, i.e., the main gas stream, is discharged from the plasma torch 2 into the inner cavity 5. Metallic silicon is recycled into the inner cavity 5, and a portion of it is recycled into the filter cavity 7. The silicon source material is instantaneously evaporated in the plasma torch 2, resulting in extremely fine particle sizes of the generated metallic silicon. Therefore, no subsequent process for pulverizing the metallic silicon is required.

[0042] To further improve the purity of metallic silicon, a solution treatment (HF treatment) can be performed to remove the natural oxide film on the surface of metallic silicon.

[0043] Alternatively, the Siemens process can be used, in which trichlorosilane (SiHCl3) obtained from metallic silicon is used as a raw material, reacted with hydrogen at high temperature and thermally decomposed to precipitate high-purity metallic silicon.

[0044] (Experimental Result 1) Reference Figure 2 The raw material was rice husk ash. The ratio of Ar to hydrogen in the sheath gas was set to 55.0:5.0, and the flow rate was set to 60 L / min. The flow rate of Ar in the internal gas was set to 5 L / min, and the flow rate of Ar in the carrier gas was set to 3 L / min. The plasma power was set to 30 kW, and a verification experiment for the fabrication of metallic silicon was conducted under atmospheric pressure.

[0045] Figure 3 This represents Experiment Result 1. Experiment Result 1 is the result of XRD (X-ray Diffraction). The vertical axis represents the X-ray intensity (in cps), and the horizontal axis represents the diffraction angle 2θ (in deg).

[0046] Figure 3 In the text, (A) represents rice husk ash before plasma treatment, and (B) represents rice husk ash after plasma treatment.

[0047] exist Figure 3After plasma treatment (B), peaks consistent with the database of metallic silicon were observed at three locations. Furthermore, the diffraction angles 2θ corresponding to the three peaks of metallic silicon were: 28.4 for the Miller index (111), 47.3 for the Miller index (220), and 56.1 for the Miller index (311). It can be seen that this peak was not observed before plasma treatment (A), and high-purity metallic silicon was generated after plasma treatment (B).

[0048] The inventors conducted various verification experiments and obtained the following findings.

[0049] The plasma power applied to the plasma torch 2 is, for example, in the range of 3 kW or more and 300 kW or less, preferably in the range of 15 kW or more and 50 kW or less.

[0050] If the plasma power is too low, the powder containing silica as a raw material cannot be sufficiently heated. Conversely, if the plasma power is too high, it may hinder the stable generation of plasma using existing plasma generation methods and introduce impurities. The pressure within the plasma generator is, for example, in the range of 10 kPa or higher to below atmospheric pressure.

[0051] The flow rate of the carrier gas used to deliver the silicon source to plasma torch 2 is ideally between 1 L / min and 5 L / min. If the carrier gas flow rate is too low, the raw material powder cannot be adequately introduced into the plasma. If the carrier gas flow rate is too high, the residence time of the raw material powder in the plasma becomes too short, resulting in insufficient processing.

[0052] The feed rate of the silicon source powder is preferably 50 mg / min or higher and 3000 mg / min or lower, more preferably 200 mg / min or higher and 800 mg / min or lower. If the feed rate is too fast, it will absorb heat from the plasma, which may cause the temperature in the plasma reaction zone to drop. If the feed rate is too slow, it may be easily oxidized due to the influence of trace amounts of oxygen mixed in within the manufacturing apparatus 1. In addition, if the feed rate is too fast, the reduction rate of reducing free radicals may decrease.

[0053] The flow rate of the sheath gas supplied to plasma torch 2 is preferably above 40 L / min and below 100 L / min. This sheath gas is introduced as a mixture of hydrogen molecules and inert gases such as argon, wherein the hydrogen molecules provide hydrogen atoms with strong reducing power.

[0054] The proportion of hydrogen molecules in the mixed gas introduced into the plasma torch 2 is preferably 10% or more and 100% or less, more preferably 20% or more and 50% or less.

[0055] If the proportion of hydrogen molecules in the flow rate is low, the supply of hydrogen atoms for reduction will be insufficient. If the proportion of hydrogen molecules in the flow rate is too high, the volume of the region where the plasma reaction occurs within the plasma torch 2, i.e., the plasma volume, will become smaller, which may lead to a narrowing of the plasma reaction region.

[0056] The flow rate of the internal gas supplied to the plasma torch 2 can be, for example, 1 L / min or more and 5 L / min or less.

[0057] The silicon source material is a biologically derived powder. The smaller the particle size of the powder material, the faster the reduction reaction proceeds; therefore, a smaller particle size is preferred. However, if the particle size is too small (e.g., less than 10 μm), it becomes difficult to supply the material. Conversely, if the particle size is too large (e.g., greater than 100 μm), it also becomes difficult to supply the material. Considering both the supply of the material and the rate of the reduction reaction, the particle size of the material is preferably between 10 μm and 100 μm.

[0058] (Implementation Method 2) (Structure of the manufacturing apparatus) Figure 4 This is a diagram illustrating implementation method 2. Figure 4 In the middle, to and Figure 1 Identical parts are labeled with the same reference numerals, and their descriptions are omitted.

[0059] In embodiment 2, a supply pipe 21 is disposed inside the inner cavity 5. The supply pipe 21 is used to supply quenching gas (as indicated by arrow G4) from the lower to the upper part of the inner cavity 5. The quenching gas is methane (CH4).

[0060] The supply tube 21 has an inlet at its lower end and an outlet at its upper end. The upper end can also be referred to as the tip of the supply tube 21. By causing CH4 to collide with ions or plasma generated in the plasma torch 2, the ions or plasma lose energy, thereby suppressing gas amplification.

[0061] (Experimental Result 2) Reference Figure 5 The raw material was rice husk ash. The ratio of Ar to hydrogen in the sheath gas was set to 55.0:5.0, and the flow rate was set to 60 L / min. The flow rate of Ar in the internal gas was set to 5 L / min, and the flow rate of Ar in the carrier gas was set to 3 L / min. The plasma power was set to 20 kW, and a verification experiment for the fabrication of metallic silicon was conducted at atmospheric pressure. The flow rate of CH4 quenching gas was set to 0.2 L / min.

[0062] Figure 6 This indicates experimental result 2.

[0063] Figure 6 This refers to rice husk ash after plasma treatment.

[0064] like Figure 6 As shown, after plasma treatment, peaks of metallic silicon were observed at three positions with diffraction angles 2θ of 28.4, 47.3, and 56.1.

[0065] Figure 7 This indicates experimental result 3.

[0066] In this case, the flow rate of the quenching gas was changed according to the conditions in Experiment 2, and set to 2.0 L / min. For example... Figure 7 As shown, in Experiment 3, compared with Experiment 2, no peak of metallic silicon was found.

[0067] Thus, if the flow rate of CH4 in the quenching gas is too high, it will be difficult to generate metallic silicon.

[0068] The inventors conducted various verification experiments and obtained the following findings.

[0069] The temperature within the plasma is approximately 7000–20000℃. Silicon dioxide is vaporized within the plasma into reduced Si and SiO, and further vaporized into hydrogenated SiH. The plasma containing these vaporized components is cooled by a gas stream, forming Si and SiO nuclei at approximately 2000–2500℃. The nucleated Si and SiO are then rapidly cooled to approximately room temperature. During this rapid cooling process, Si micropowder, SiO micropowder, and SiO2 micropowder are generated.

[0070] For the gas used in the cooling process at 1500℃~2000℃, introducing quenching gas containing carbon components such as methane can prevent Si micro powder and SiO micro powder from being oxidized again due to water vapor, etc.

[0071] Preferably, the flow rate of the quenching gas is above 0.1 L / min and below 0.5 L / min.

[0072] If the flow rate of the quenching gas is too low, it will be insufficient to prevent re-oxidation, and the yield of metallic silicon will not increase. If the flow rate of the quenching gas is too high, it will lead to the formation of impurities such as silicon carbide (SiC).

[0073] As the quenching gas introduction point, it is desirable to supply the gas to a position 100 mm or more but less than 200 mm away from the lower end of the plasma torch 2.

[0074] If the gas is too far from the lower end of plasma torch 2, the temperature of the introduced quenching gas will be too low, and the methane will not decompose sufficiently, thus failing to suppress re-oxidation. Conversely, if the gas is too close to the lower end of plasma torch 2, CH4 will be introduced into a high-temperature region exceeding 3000°C, leading to the formation of impurities such as silicon carbide (SiC).

[0075] Furthermore, the supply pipe 21 is configured to discharge a secondary gas flow containing quenching gas at a 180-degree angle relative to the main gas flow discharged from the plasma torch 2 into the inner cavity 5. With this structure, on the one hand, the ions or plasma generated in the plasma torch 2 can be cooled rapidly; on the other hand, the collision of the main gas flow and the secondary gas flow at a 180-degree angle may complicate the gas flow and reduce the yield of metallic silicon.

[0076] More specifically, if the airflow becomes complex, a circulating airflow is generated instantaneously, which cannot adequately cool the ions or plasma generated by the plasma torch 2, resulting in reheating and re-oxidation of the metallic silicon, which may reduce the yield of metallic silicon.

[0077] Therefore, the angle formed by the main airflow and the secondary airflow is not limited to 180 degrees, but can be greater than 45 degrees and less than 180 degrees. For example, when the angle formed by the main airflow and the secondary airflow is 90 degrees, the supply pipe 21 is arranged perpendicularly to the main airflow discharged from the plasma torch 2. Alternatively, for example, when the angle formed by the main airflow and the secondary airflow is 45 degrees, in the inner cavity 5, the supply pipe 21 is arranged from top to bottom at a 45-degree angle to the main airflow discharged from the plasma torch 2.

[0078] To halt the reaction in the main gas flow, the location of the auxiliary gas flow containing quenching gas is closely related to the temperature of the main gas flow during rapid cooling. The temperature of the main gas flow during rapid cooling is preferably around 1550°C or below, at which solid particles corresponding to metallic silicon can be formed. Therefore, the top end of the supply pipe 21, corresponding to the location where the quenching gas is supplied to the main gas flow, is preferably positioned where the temperature of the main gas flow is above 1200°C and below 1600°C.

[0079] (Other implementation methods) The above implementation method is only one approach and can be arbitrarily modified and applied.

[0080] (Structures supported by the above embodiments) The above implementation supports the following structures.

[0081] (Structure 1) A method for manufacturing metallic silicon involves supplying a silicon source material to a plasma torch via a carrier gas, and then reducing the material through a plasma reaction to recover metallic silicon.

[0082] According to Structure 1, raw materials can be continuously supplied via a carrier gas, and metallic silicon can be obtained through a plasma reaction with a short reaction time. Therefore, it is not necessary to process the silicon source into blocks or granules, which can reduce power consumption without generating CO2, and enables the continuous production of metallic silicon.

[0083] (Structure 2) According to the method for manufacturing metallic silicon as described in Structure 1, the raw material is a biologically derived powder raw material with a particle size of 10 μm or more and 100 μm or less.

[0084] According to Structure 2, since metallic silicon can be obtained from biologically derived raw materials that were originally waste, silicon recycling is possible. Furthermore, according to Structure 2, powdered raw materials can be easily supplied via a carrier gas.

[0085] (Structure 3) According to the method for manufacturing metallic silicon as described in Structure 1 or 2, a sheath gas is supplied to the plasma torch. The sheath gas is introduced as a mixture of hydrogen molecules and an inert gas, wherein the hydrogen molecules provide hydrogen atoms with strong reducing power, and the proportion of the flow rate of hydrogen molecules before being introduced into the plasma torch in the mixture is more than 10% and less than 100%.

[0086] According to structure 3, since hydrogen is used as a reducing agent, no CO2 is produced in the plasma reaction.

[0087] (Structure 4) According to the method for manufacturing metallic silicon as described in Structure 3, the flow rate of the sheath gas is above 40 L / min and below 100 L / min.

[0088] According to structure 4, the efficiency of plasma reaction reduction of raw materials is improved.

[0089] (Structure 5) According to the method for manufacturing metallic silicon as described in structure 3 or 4, the proportion of hydrogen molecules in the mixed gas is more than 20% and less than 50%.

[0090] According to structure 5, the supply of hydrogen atoms used for reduction is sufficient, and the volume in which the plasma reaction occurs is large enough, thereby ensuring the region of the plasma reaction.

[0091] (Structure 6) In the method for manufacturing metallic silicon according to any one of structures 1 to 5, the flow rate of the carrier gas is 1 L / min or more and 5 L / min or less.

[0092] According to structure 6, the efficiency of plasma reaction reduction of raw materials is improved.

[0093] (Structure 7) According to the method for manufacturing metallic silicon according to any one of structures 1 to 5, an internal gas is supplied to the plasma torch, wherein the flow rate of the internal gas is more than 1 L / min and less than 5 L / min.

[0094] According to structure 7, the efficiency of plasma reaction reduction of raw materials is improved.

[0095] (Structure 8) According to any one of the structures 1 to 7, in the method for manufacturing metallic silicon, a quenching gas is supplied downstream of the plasma torch, wherein the flow rate of the quenching gas is 0.1 L / min or more and 0.5 L / min or less.

[0096] According to structure 8, it is possible to suppress the re-oxidation of metallic silicon or Si compounds reduced by plasma reaction.

[0097] (Structure 9) According to the method for manufacturing metallic silicon according to any one of structures 1 to 8, the plasma power applied to the plasma torch is 3 kW or more and 300 kW or less.

[0098] According to structure 9, the raw materials can be fully heated and plasma can be generated stably.

[0099] (Structure 10) According to any one of structures 1 to 9, in the method for manufacturing metallic silicon, the inner cavity is continuous with the plasma torch, and a filter cavity is connected to the inner cavity, from which the metallic silicon is recovered respectively.

[0100] According to structure 10, the recovery of metallic silicon is easy.

[0101] (Structure 11) According to the method for manufacturing metallic silicon as described in structure 10, quenching gas is supplied downstream of the plasma torch, the flow rate of the quenching gas being above 0.1 L / min and below 0.5 L / min, and the inner cavity has a supply pipe through which the quenching gas is supplied.

[0102] According to structure 11, by colliding the quenching gas with ions or plasma generated in the plasma torch, the ions or plasma lose energy, thereby suppressing gas amplification.

[0103] (Structure 12) A silicon metal manufacturing apparatus includes a plasma torch, an outer cavity continuous with the plasma torch, an inner cavity housed in the outer cavity, and a filter cavity connected to the inner cavity. A silicon source is supplied to the plasma torch via a carrier gas, and the raw material is reduced by a plasma reaction to generate silicon metal. The silicon metal is recovered from the inner cavity and the filter cavity, respectively.

[0104] According to structure 12, raw materials can be continuously supplied via a carrier gas, and metallic silicon can be obtained through a plasma reaction with a short reaction time. Therefore, it is not necessary to process the silicon source into bulk or granular form, which can reduce power consumption without generating CO2, and enables the continuous production of metallic silicon.

Claims

1. A method for manufacturing metallic silicon, characterized in that, The raw material for the silicon source is supplied to the plasma torch via a carrier gas, and the raw material is reduced by plasma reaction to recover metallic silicon.

2. The method for manufacturing metallic silicon according to claim 1, characterized in that, The raw material is a biologically derived powder. The particle size of the raw material is above 10 μm and below 100 μm.

3. The method for manufacturing metallic silicon according to claim 2, characterized in that, Sheath gas is supplied to the plasma torch. The sheath gas is introduced as a mixture of hydrogen molecules and an inert gas, wherein the hydrogen molecules provide hydrogen atoms with strong reducing power. The proportion of the hydrogen molecules in the mixture before being introduced into the plasma torch is more than 10% and less than 100%.

4. The method for manufacturing metallic silicon according to claim 3, characterized in that, The flow rate of the sheath gas is above 40 L / min and below 100 L / min.

5. The method for manufacturing metallic silicon according to claim 3, characterized in that, In the mixed gas, the proportion of hydrogen molecules is above 20% and below 50%.

6. The method for manufacturing metallic silicon according to any one of claims 1 to 5, characterized in that, The flow rate of the carrier gas is above 1 L / min and below 5 L / min.

7. The method for manufacturing metallic silicon according to any one of claims 1 to 5, characterized in that, An internal gas is supplied to the plasma torch, the flow rate of which is above 1 L / min and below 5 L / min.

8. The method for manufacturing metallic silicon according to any one of claims 1 to 5, characterized in that, Quenching gas is supplied downstream of the plasma torch. The flow rate of the quenching gas is above 0.1 L / min and below 0.5 L / min.

9. The method for manufacturing metallic silicon according to any one of claims 1 to 5, characterized in that, The plasma power applied to the plasma torch is above 3kW and below 300kW.

10. The method for manufacturing metallic silicon according to claim 1, characterized in that, The inner cavity is continuous with the plasma torch, and a filter cavity is connected to the inner cavity. The metallic silicon is recovered from the inner cavity and the filter cavity, respectively.

11. The method for manufacturing metallic silicon according to claim 10, characterized in that, Quenching gas is supplied downstream of the plasma torch. The flow rate of the quenching gas is above 0.1 L / min and below 0.5 L / min. The inner cavity has a supply pipe through which the quenching gas is supplied.

12. An apparatus for manufacturing metallic silicon, characterized in that, It has a plasma torch, an outer cavity continuous with the plasma torch, an inner cavity housed within the outer cavity, and a filter cavity connected to the inner cavity. The raw material for the silicon source is supplied to the plasma torch via a carrier gas, and the raw material is reduced by plasma reaction to generate metallic silicon. The metallic silicon is then recovered from the inner cavity and the filter cavity, respectively.

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