阅读说明：本技术 工业硅精炼除硼的方法和系统 (Method and system for removing boron in industrial silicon refining ) 是由 吴志能 王鹏 周政 *** 谌庆春 廖添 胡三元 于 2019-09-24 设计创作，主要内容包括：本发明提出了工业硅精炼除硼的方法和系统,所述方法包括：(1)将造渣剂加入石墨坩埚中进行加热至熔化,以便获得造渣剂熔体；(2)将硅粉和氩气由所述石墨坩埚内的底部加入,所述硅粉熔化形成硅熔体并从底部上升至所述造渣剂熔体顶部；(3)反应完全后,将所述石墨坩埚内的造渣剂熔体由所述石墨坩埚底部的出料管道排出；以及(4)将所述硅熔体从所述石墨坩埚上部的浇嘴排出至水中,收集硅颗粒。由此,本发明的工业硅精炼除硼的方法不受限于硼在造渣剂和硅液中分配系数大小的影响,产品中硼含量低,操作简便、耗时短,成本低,适于规模化应用。(The invention provides a method and a system for removing boron in industrial silicon refining, wherein the method comprises the following steps: (1) adding a slagging agent into a graphite crucible to be heated to be molten so as to obtain a slagging agent melt; (2) adding silicon powder and argon gas from the bottom in the graphite crucible, wherein the silicon powder is melted to form a silicon melt and rises from the bottom to the top of the slagging agent melt; (3) after the reaction is completed, discharging the slag former melt in the graphite crucible from a discharge pipeline at the bottom of the graphite crucible; and (4) discharging the silicon melt from a nozzle at the upper part of the graphite crucible into water, and collecting silicon particles. Therefore, the method for removing boron in the industrial silicon refining is not limited by the influence of the distribution coefficient of boron in the slag former and the silicon liquid, has low boron content in the product, is simple and convenient to operate, consumes short time and is low in cost and suitable for large-scale application.)

1. A method for removing boron in industrial silicon refining is characterized by comprising the following steps:

(1) adding a slagging agent into a graphite crucible to be heated to be molten so as to obtain a slagging agent melt;

(2) adding silicon powder and argon gas from the bottom in the graphite crucible, wherein the silicon powder is melted to form a silicon melt, the silicon melt reacts with the slag former melt and rises from the bottom to the top of the slag former melt;

(3) after the reaction is completed, discharging the slag former melt in the graphite crucible from a discharge pipeline at the bottom of the graphite crucible; and

(4) and discharging the silicon melt from a nozzle at the upper part of the graphite crucible into water, and collecting silicon particles.

2. The method of claim 1, wherein the slag former comprises, based on the total mass of the slag former:

30 to 90 mass% of a calcium-containing compound selected from CaO and CaCO₃、Ca(HCO₃)₂Or Ca (OH)₂；

5 to 20 mass% of Na₂CO₃；

5 to 40 mass% of SiO₂。

3. The method according to claim 1, wherein the silicon powder has a boron content of not more than 40ppmw, a particle size of 10 to 200 meshes, and a mass ratio of the slag former to the silicon powder is (0.1 to 5): 1.

4. the method of claim 1, wherein the flow rate of the argon gas is 0.5 to 20L/min.

5. The method according to claim 1, wherein the steps (1) and (2) are independently performed at a temperature of 1600 to 2000 ℃.

6. The method as set forth in claim 1 wherein the silicon melt is discharged into water at a flow rate of 0.1 to 3 kg/min.

7. The method of claim 1, wherein the water is selected from pure water having an electrical resistivity of more than 10M Ω -cm and the water temperature is not lower than room temperature.

8. A system for implementing the boron removal method for industrial silicon refining according to any one of claims 1 to 7, comprising:

the graphite crucible is internally provided with an accommodating cavity for accommodating materials, and the upper part of the side wall of the graphite crucible is provided with a pouring nozzle which is suitable for discharging liquid in the graphite crucible when the graphite crucible is inclined;

the furnace lining is attached to the outer surface of the graphite crucible;

the induction coil is attached to the outer side wall of the furnace lining;

the furnace bottom is attached to the bottoms of the furnace lining and the induction coil; and

the discharge pipeline penetrates through the bottom of the graphite crucible, the bottom of the furnace lining and the bottom of the furnace bottom and is suitable for discharging the material liquid in the graphite crucible;

a water container into which the silicon melt discharged from the graphite crucible can enter;

the graphite crucible comprises a graphite crucible body, a containing cavity is arranged in the graphite crucible body, a hollow tubular component is arranged in the containing cavity, the lower end of the tubular component is located at the bottom of the containing cavity and is not in contact with the bottom wall, a feeding disc which is communicated and provided with a plurality of through holes is arranged at the lower end of the tubular component, and the feeding disc is suitable for feeding silicon powder and argon gas from the upper end of the tubular component and enters the bottom of the graphite crucible through the through holes.

9. The system of claim 8, wherein the through hole is provided on a surface of the susceptor facing an opening direction of the graphite crucible.

10. The system of claim 8, wherein the distance from the through hole to the bottom of the graphite crucible is 5 to 200 mm.

Technical Field

The invention relates to the field of metallurgy. In particular, the invention relates to a method and system for boron removal in industrial silicon refining.

Background

The metallurgical solar grade polysilicon performance indexes in the new material product catalog are as follows: low cost, low energy consumption, purity of more than 6N, boron (B) content of less than 0.15ppm and phosphorus (P) of less than 0.35 ppm. The purity of the industrial silicon used as the raw material for preparing the solar grade polysilicon by the metallurgical method is only 98-99%, the content of B is as high as 10-40 ppmw, and the content of P is 10-60 ppmw, so the production steps of the solar grade polysilicon by the existing metallurgical method are as follows: and (3) firstly, refining outside the furnace to remove B in the industrial silicon, then removing P, and finally removing metal impurities to obtain qualified solar grade polysilicon. The existing external refining boron removal technology comprises a hydrometallurgy method, an air blowing method, a slagging method, a plasma method or an air blowing slagging method combined with a vacuum technology and the like. The slagging method is the simplest in equipment and the easiest in industrial popularization, so the slagging method has the greatest prospect.

The accepted slagging mechanism is as follows: b in the industrial silicon is combined with oxygen in the slag agent to generate various boron oxides, and the boron oxides are combined with the slag agent to generate a more stable compound, so that the B is transferred from the industrial silicon into the slag agent, and the aim of removing the B is fulfilled.

The prior slagging method still has the following problems: (1) because of the solubility of boron oxide in slag agents, the prior art techniques for removing B tend to increase the partition coefficient value as much as possible to obtain low boron silicon, and therefore require a feedstock with as low a B content as possible. However, this reduces the range of raw materials and increases the cost, and the resulting low borosilicate has an unstable B content and a limit value. If the B content in the slag is 1.5ppmw, the silicon content finally obtained even in the case of a plurality of refinements can only reach 0.33ppmw, calculated according to the highest partition coefficient of 4.5 to date. (2) The refining heat preservation time is too long, and the cost is increased. (3) The slag and the silicon are not easy to separate after refining.

Therefore, the method for removing boron from industrial silicon still remains to be studied.

Disclosure of Invention

The present invention aims to solve at least to some extent at least one of the technical problems of the prior art. Therefore, the invention provides a method and a system for removing boron in industrial silicon refining, which are not limited by the influence of the distribution coefficient of boron in a slag former and a silicon liquid, have low boron content in a product, are simple and convenient to operate, consume less time and have low cost, and are suitable for large-scale application.

In one aspect of the invention, a method for boron removal in industrial silicon refining is provided. According to an embodiment of the invention, the method comprises: (1) adding a slagging agent into a graphite crucible to be heated to be molten so as to obtain a slagging agent melt; (2) adding silicon powder and argon gas from the bottom in the graphite crucible, wherein the silicon powder is melted to form a silicon melt, the silicon melt reacts with the slag former melt and rises from the bottom to the top of the slag former melt; (3) after the reaction is completed, discharging the slag former melt in the graphite crucible from a discharge pipeline at the bottom of the graphite crucible; and (4) discharging the silicon melt from a nozzle at the upper part of the graphite crucible into water, and collecting silicon particles.

The slagging agent is firstly melted, then the silicon powder is added from the bottom, the silicon powder is slowly raised to the top of the slagging agent melt from the bottom after being melted into fine silicon melt, so that the oxidation reaction area of the silicon melt and the slagging agent melt is increased, a part of boron is more easily transferred into the slagging agent melt from the silicon melt, and the rest boron is more easily oxidized into boron oxide. The slag former melt is discharged from the bottom, so that boron in the slag former is prevented from diffusing in an atomic form and returning to silicon in the cooling process, the boron content in the product is prevented from increasing, and the silicon and the slag former are prevented from being difficult to separate after being cooled simultaneously. The silicon melt is discharged into water, boron oxide in the silicon melt reacts with water vapor to generate various boron hydroxide gases with low boiling points, and the boron oxide gases are dissipated into the atmosphere, so that the aim of efficiently and thoroughly removing boron is fulfilled. Meanwhile, the low-borosilicate material can be conveniently collected by cooling in water, and the cost of bearing a crucible, the cost of manually separating silicon and the cost of crushing the silicon material are not needed. Therefore, the method for removing boron in the industrial silicon refining according to the embodiment of the invention is not limited by the influence of the distribution coefficient of boron in the slag agent and the silicon liquid, has low boron content in the product, is simple and convenient to operate, consumes short time and has low cost, and is suitable for large-scale application.

According to the embodiment of the invention, the method for removing boron in industrial silicon refining can also have the following additional technical characteristics:

according to an embodiment of the invention, the slag former comprises, based on the total mass of the slag former: 30 to 90 mass% of a calcium-containing compound selected from CaO and CaCO₃、Ca(HCO₃)₂Or Ca (OH)₂(ii) a 5 to 20 mass% of Na₂CO₃(ii) a 5 to 40 mass% of SiO₂。

According to the embodiment of the invention, the content of boron in the silicon powder is not more than 40ppmw, and the particle size is 10-200 meshes.

According to the embodiment of the invention, the mass ratio of the slag former to the silicon powder is (0.1-5): 1.

according to the embodiment of the invention, the flow of the argon is 0.5-20L/min.

According to an embodiment of the invention, the steps (1) and (2) are independently carried out at a temperature of 1600-2000 ℃.

According to the embodiment of the invention, the flow rate of discharging the silicon melt into water is 0.1-3 kg/min.

According to an embodiment of the present invention, the water is selected from pure water having an electrical resistivity of more than 10 M.OMEGA.cm, and the water temperature is not lower than room temperature.

In another aspect of the invention, the invention is a system for carrying out the foregoing method for boron removal in industrial silicon refining. According to an embodiment of the invention, the system comprises: the graphite crucible is internally provided with an accommodating cavity for accommodating materials, and the upper part of the side wall of the graphite crucible is provided with a pouring nozzle which is suitable for discharging liquid in the graphite crucible when the graphite crucible is inclined; the furnace lining is attached to the outer surface of the graphite crucible; the induction coil is attached to the outer side wall of the furnace lining; the furnace bottom is attached to the bottoms of the furnace lining and the induction coil; the discharge pipeline penetrates through the bottom of the graphite crucible, the bottom of the furnace lining and the bottom of the furnace bottom and is suitable for discharging the material liquid in the graphite crucible; a water container into which the silicon melt discharged from the graphite crucible can enter; the graphite crucible comprises a graphite crucible body, a containing cavity is arranged in the graphite crucible body, a hollow tubular component is arranged in the containing cavity, the lower end of the tubular component is located at the bottom of the containing cavity and is not in contact with the bottom wall, a feeding disc which is communicated and provided with a plurality of through holes is arranged at the lower end of the tubular component, and the feeding disc is suitable for feeding silicon powder and argon gas from the upper end of the tubular component and enters the bottom of the graphite crucible through the through. Therefore, the system provided by the embodiment of the invention is simple, convenient to operate, low in cost and suitable for large-scale production.

According to the embodiment of the invention, the through hole is formed in the surface of the material holding disc facing the opening direction of the graphite crucible.

According to the embodiment of the invention, the distance between the through hole and the bottom of the graphite crucible is 5-200 mm.

Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.

Drawings

The above and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

fig. 1 shows a schematic diagram of a system configuration for implementing a method for boron removal in industrial silicon refining, according to an embodiment of the present invention.

Reference numerals:

a graphite crucible 100; a furnace lining 200; an induction coil 300; a furnace bottom 400; a discharge duct 500; a water container 600; a tubular member 110; a batch pan 120; a through hole A; a nozzle 130.

Detailed Description

The following describes embodiments of the present invention in detail. The following examples are illustrative only and are not to be construed as limiting the invention.

The invention provides a method for removing boron in industrial silicon refining and a system for implementing the method, which are respectively described in detail below.

Method for removing boron in industrial silicon refining

In one aspect of the invention, a method for boron removal in industrial silicon refining is provided. According to an embodiment of the invention, the method comprises: (1) adding a slagging agent into a graphite crucible to be heated to be molten so as to obtain a slagging agent melt; (2) adding silicon powder and argon from the bottom in the graphite crucible, melting the silicon powder to form a silicon melt, reacting with the slag former melt, and ascending from the bottom to the top of the slag former melt; (3) after the reaction is completed, discharging the slag former melt in the graphite crucible from a discharge pipeline at the bottom of the graphite crucible; and (4) discharging the silicon melt from a nozzle at the upper part of the graphite crucible into water, and collecting silicon particles.

According to the embodiment of the invention, the method for removing boron in industrial silicon refining can also have the following advantages compared with the prior art:

1. compared with the prior art that the industrial silicon powder and the slagging agent are uniformly mixed and then melted and refined, the invention melts the slagging agent firstly, then slowly adds the silicon powder from the bottom, the silicon powder is heated and melted into tiny spherical silicon melt, and then slowly rises to the top of the slagging agent melt, in the process, the silicon melt can fully contact with the slagging agent melt, the reaction area is increased, so that part of boron is easier to transfer from the silicon melt into the slagging agent melt, and the rest boron is easier to oxidize into boron oxide.

2. Compared with the mixed gas of argon, water vapor and oxygen which is introduced into the mixed melt in the prior art, the method uses the slag former to oxidize boron in silicon into boron oxide, then pours the boron oxide into water, so that the boron oxide in high-temperature silicon melt reacts with the water to generate various boron hydroxide gases with low boiling points, and the boron oxide gases are dissipated into the atmosphere to achieve the aim of efficiently and completely removing boron. And the silicon melt forms a porous structure in the cooling process, so that the reaction area can be further increased. Meanwhile, the low-borosilicate material can be conveniently collected by cooling in water, and the cost of bearing a crucible, the cost of manually separating silicon and the cost of crushing the silicon material are not needed.

3. The silicon powder is completely added and melted, and then the next operation can be carried out, so that the heat preservation time is avoided, and the time cost is reduced.

4. Before the silicon melt is poured into water, the slagging agent melt is emptied in a bottom discharging mode, the increase of boron content in silicon caused by the fact that boron diffuses from the slagging agent in an atomic form and returns to the silicon in the cooling process is avoided, the silicon and the slagging agent are prevented from being difficult to separate after being cooled simultaneously, and the slagging agent melt can be reused for multiple times.

5. The silicon melt is poured into water for cooling, so that the low-borosilicate material can be conveniently collected, and the cost for bearing a crucible and crushing and separating is saved.

According to an embodiment of the invention, the slag former comprises, based on the total mass of the slag former: 30 to 90 mass% of a calcium-containing compound selected from the group consisting of CaO and CaCO₃、Ca(HCO₃)₂Or Ca (OH)₂(ii) a 5 to 20 mass% of Na₂CO₃(ii) a 5 to 40 mass% of SiO₂. In some embodiments, the slag former comprises: 40 to 80 mass% of a calcium-containing compound; 8 to 15 mass% of Na₂CO₃(ii) a 10 to 30 mass% of SiO₂. In other embodiments, the slag former comprises: 50 to 70 mass% of a calcium-containing compound; 10 to 12 mass% of Na₂CO₃(ii) a 18 to 24 mass% of SiO₂. Therefore, boron can be efficiently oxidized into boron oxide, so as to achieve the purpose of removal.

According to the embodiment of the invention, the content of boron in the silicon powder is not more than 40ppmw, and the particle size is 10-200 meshes. In some embodiments, the silicon powder has a boron content of 5 to 20ppmw and a particle size of 30 to 180 mesh. In other embodiments, the silicon powder has a boron content of 25-35 ppmw and a particle size of 150-180 mesh. In other embodiments, the silicon powder has a boron content of 18-22 ppmw and a particle size of 60-110 mesh. One refining with too high boron content can not meet the requirement, and multiple refining is needed; too large a particle size results in too long a melting time and too small a contact area, which may reduce the boron removal effect. The silicon powder with low boron content and small particle size is too expensive, which increases the production cost.

According to the embodiment of the invention, the mass ratio of the slag former to the silicon powder is (0.1-5): 1. in some embodiments, the mass ratio of the slag former to the silicon powder is (1-4): 1. in other embodiments, the mass ratio of the slag former to the silicon powder is (2-3): 1. in the prior art, the mass ratio of the industrial silicon melt to the slagging agent melt is thousands to one, but the mass ratio of the industrial silicon melt to the slagging agent melt is 1: 0.1-5, and the large mass ratio can enable a larger amount of boron atoms in silicon to be diffused into the slagging agent melt in an atomic form more quickly so as to achieve the purpose of efficiently removing boron.

According to the embodiment of the invention, the flow of the argon is 0.5-20L/min. In some embodiments, the flow rate of argon is 1-8L/min. In some embodiments, the flow rate of argon is 10 to 18L/min. Thus, the silicon powder can be fed into the graphite crucible and can be used as a shielding gas.

According to an embodiment of the invention, the steps (1) and (2) are independently carried out at a temperature of 1600-2000 ℃. The slag former and the silicon powder can be completely melted at 1600-2000 ℃, so that the subsequent separation is facilitated.

According to the embodiment of the invention, the flow rate of discharging the silicon melt into water is 0.1-3 kg/min. In some embodiments, the flow rate of the silicon melt discharged into the water is 0.2 to 1 kg/min. In some embodiments, the silicon melt is discharged into the water at a flow rate of 1.5 to 2.5 kg/min. By adopting the flow velocity, the silicon melt can slowly enter water, so that the reaction area is increased, boron oxide can more fully react with the water to generate various boron hydroxide gases with low boiling points to escape into the atmosphere, and the boron removal effect is further realized. Specifically, the manner of how to discharge the silicon melt from the graphite crucible is not strictly limited, and for example, the silicon melt may be discharged by tilting the graphite crucible and utilizing the gravity, or a pump may be provided in the graphite crucible to pump the silicon melt, and the manner may be flexibly selected according to the actual situation.

According to an embodiment of the present invention, the water is selected from pure water having a resistivity of more than 10 M.OMEGA.cm, and the water temperature is not lower than room temperature. In some embodiments, the temperature of the water is 30-90 ℃. In other embodiments, the temperature of the water is 50-80 ℃. The water with low resistivity contains a lot of impurities, particularly boron, and the impurities are introduced, so that the boron content in the product is high. The inventors have found that water at and above room temperature is more conducive to the formation of low boiling point borohydride gases than low temperature water, with the product having a low boron content.

System for implementing boron removal method for industrial silicon refining

In another aspect of the invention, the invention is a system for carrying out the foregoing method for boron removal in industrial silicon refining. According to an embodiment of the invention, referring to fig. 1, the system comprises: a graphite crucible 100, wherein a containing cavity is formed in the graphite crucible 100 and is used for containing materials; a furnace lining 200, wherein the furnace lining 200 is attached to the outer surface of the graphite crucible 100; an induction coil 300, wherein the induction coil 300 is attached to the outer side wall of the furnace lining 200; a furnace bottom 400, wherein the furnace bottom 400 is attached to the bottoms of the furnace lining 200 and the induction coil 300; and a discharge pipe 500, the discharge pipe 500 penetrates the bottom of the graphite crucible 100, the bottom of the furnace lining 200 and the bottom of the furnace bottom 400, and is suitable for discharging the feed liquid in the graphite crucible 100; a water container 600 into which the silicon melt discharged from the graphite crucible 100 can be introduced; the hollow tubular component 110 is arranged in the accommodating cavity, the lower end of the tubular component is positioned at the bottom of the accommodating cavity and is not contacted with the bottom wall, and the lower end of the tubular component is provided with a feeding disc 120 which is communicated and is provided with a plurality of through holes A and is suitable for feeding silicon powder and argon gas from the upper end of the tubular component and entering the bottom of the graphite crucible through the through holes; the upper portion of the sidewall of the graphite crucible 100 is provided with a nozzle 130 adapted such that the feed liquid therein can be discharged through the nozzle 130 when the graphite crucible 100 is tilted.

By applying a voltage to the induction coil, the generated heat can be conducted to the graphite crucible for heating the material therein. Specifically, the slag former is added into the graphite crucible to be heated, after the slag former is completely melted, silicon powder and argon gas are added from the upper part of the hollow tubular component, under the action of the argon gas, the silicon powder can be sprayed into the graphite crucible from the through hole on the feeding disc, and the silicon powder is heated and melted to form fine silicon melt and rises to the top of the slag former melt from the bottom. After the reaction is completed, the slag former melt can be discharged from a discharge pipeline at the bottom (a valve is arranged on the discharge pipeline and is opened or closed to control the outflow of the feed liquid), the silicon melt can be discharged from a pouring nozzle to a water container filled with water for cooling, and silicon particles are collected so as to obtain the low-borosilicate material. Therefore, the system provided by the embodiment of the invention is simple, simple and convenient to operate, low in cost and suitable for large-scale production.

According to the embodiment of the invention, the through hole A is arranged on the surface of the material holding disc facing to the opening direction of the graphite crucible. Thereby, the silicon powder is fed into the graphite crucible easily and is not hindered from moving upward after the silicon melt is formed.

According to the embodiment of the invention, the distance between the through hole A and the bottom of the graphite crucible 100 is 5-200 mm. In some embodiments, the distance from the through hole A to the bottom of the graphite crucible 100 is 10 to 50 mm. In some embodiments, the distance from the through hole A to the bottom of the graphite crucible 100 is 80 to 160 mm. Thereby, the oxidation reaction area of the silicon melt and the slag former melt is sufficiently increased.

The scheme of the invention will be explained with reference to the examples. It will be appreciated by those skilled in the art that the following examples are illustrative of the invention only and should not be taken as limiting the scope of the invention. The examples, where specific techniques or conditions are not indicated, are to be construed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are conventional products which are commercially available, and are not known to manufacturers.