Production method of industrial silicon with low impurity content

Abstract

The invention discloses a production method of industrial silicon with low impurity content, which comprises the following steps: proportioning, smelting in an electric furnace, refining and removing impurities, and casting and molding: proportioning the following components in parts by mass: 45-60 parts of silica, 7-15 parts of caking coal, 25-35 parts of non-caking coal and 10-15 parts of wood chips. The 421 # industrial silicon product capable of meeting the requirements of 421 # silicon on impurity elements is prepared by adopting a full-coal process, reasonably designing the ratio of silica, the caking coal and the uncaking coal, controlling chemical components of the caking coal, the uncaking coal and the silica and matching with adjustment of smelting process parameters of a submerged arc furnace. A full-coal process is adopted, petroleum coke and charcoal do not need to be added, the raw material cost is reduced, and the market competitiveness of the product is improved.

Description

Technical field:

[0001] The invention relates to a method for producing industrial silicon, in particular to a method for producing industrial silicon with low impurity content. Background technology:

[0002] At present, the mainstream grades of industrial silicon on the market are 99 silicon, 521# silicon, 421# silicon, etc. Among them, 421# silicon has relatively high requirements for impurity elements, that is, 421# industrial silicon refers to the mass percentage of iron ≤0.4%, the mass percentage of aluminum ≤0.2%, and the mass percentage of calcium ≤0.1%. The market price is also relatively high, and it is also the main industrial silicon production grade of many companies. 421# industrial silicon is widely used. After further purification processes such as Siemens method and modified Siemens method, it can produce solar grade polysilicon and electronic grade polysilicon. 421# industrial silicon is an important basic raw material for the production of organosilicon compounds. By reacting with methyl chloride, etc., intermediates such as methylchlorosilane can be produced, and then various organosilicon products such as silicone rubber, silicone oil, silicone resin, etc. can be synthesized. In the production of aluminum alloys, 421# industrial silicon is an important alloy element additive. It can significantly improve the strength, hardness and heat resistance of aluminum alloys. For example, in the manufacturing of automobile engine cylinder blocks, cylinder heads and other parts, adding an appropriate amount of industrial silicon can enhance the mechanical properties of aluminum alloys, enable them to better withstand the high temperature and high pressure during engine operation, and improve the reliability and service life of the engine. 421# industrial silicon is used as a deoxidizer and alloying agent in steel production, which can effectively remove oxygen from steel, improve the quality and performance of steel, and improve the strength, toughness and corrosion resistance of steel. 421# industrial silicon can be used to produce some high-performance refractory materials, such as siliceous refractory bricks. These refractory materials have the characteristics of high temperature resistance, wear resistance, and erosion resistance. Therefore, 421# industrial silicon is usually used in the polysilicon industry, silicone industry, aluminum alloy industry, steel industry, refractory materials, etc.

[0003] 421# silicon is usually produced using a semi-coal and semi-coke process. The semi-coal and semi-coke process for industrial silicon refers to a production process that uses coal and petroleum coke as reducing agents in the production process of industrial silicon. By reasonably adjusting the ratio of coal and petroleum coke, the impurity content in industrial silicon products can be controlled within a certain range to meet the requirements of 421# silicon for impurity elements. However, the cost of petroleum coke is higher than that of coal, resulting in high raw material costs for 421# industrial silicon products, which reduces the market competitiveness of the products. For this reason, it is necessary to develop a production method for 421# industrial silicon with low raw material costs and that can meet the requirements of 421# silicon for impurity elements. Summary of the invention:

[0004] The object of the present invention is to provide a method for producing industrial silicon with low cost and low impurity content.

[0005] The present invention is implemented by the following technical scheme: a method for producing industrial silicon with low impurity content, which includes batching, electric furnace smelting, refining and impurity removal, and casting and molding. The batching is carried out according to the following mass parts: 45-60 parts of silica, 7-15 parts of bonding coal, 25-35 parts of non-bonding coal, and 10-15 parts of wood chips.

[0006] The present invention adds bonding coal and reasonably designs the addition ratio of bonding coal, so that the charge particles can be bonded to each other to form a material layer with certain strength and porosity, which is beneficial to the circulation and heat transfer of gas and improves the permeability of the charge; the bonding coal can also increase the mechanical strength of the charge, making it difficult to break and pulverize during transportation, charging and smelting, and maintaining the stability of the charge structure; under high-temperature smelting conditions, the carbon element in the bonding coal can undergo a reduction reaction with silicon dioxide in silica, etc., to provide a reducing atmosphere and a carbon source for the generation of industrial silicon. The addition amount and properties of the bonding coal can affect the resistance characteristics of the charge, thereby regulating the current distribution, power input and heat generation in the smelting process, etc., and helping to control the temperature and reaction rate of the smelting process. The simmering time of the charge can also be increased, the temperature and heat loss of the ore-fired furnace can be reduced, and the recovery rate of Si can be improved.

[0007] The carbon in the caking coal reacts chemically with the silicon dioxide in the silica under high temperature conditions, participates in the reduction process of silicon, and provides the required carbon element for the formation of silicon; at the same time, it releases a certain amount of heat during the combustion process, which helps to maintain the high temperature environment in the furnace and meet the temperature conditions required for industrial silicon production; the impurity components in the caking coal react with other substances to form slag, which helps to remove impurities and improve the purity of industrial silicon.

[0008] The use of binding coal and non-binding coal can better control the smelting process. On the one hand, the reduction reaction can be carried out more fully and efficiently. On the other hand, the particle size of binding coal is usually fine. If it is used alone, the permeability of the charge will be poor, which is not conducive to the escape of gas and the reaction. The binding index of non-binding coal is very low, usually not exceeding 20%, which cannot make the charge particles bond to each other and cannot form a material layer with a certain strength and porosity, affecting the permeability of the charge. The present invention combines the binding coal with finer particle size with the non-binding coal with larger particle size and wood chips with loosening effect to ensure the permeability of the charge. At the same time, adding non-binding coal and wood chips can further reduce the cost of raw materials. In addition, the types and contents of impurities brought in by different reducing agents are different. By reasonably matching reducing agents, the entry and removal of impurities can be better controlled, thereby ensuring the quality of industrial silicon.

[0009] Furthermore, the silica includes the following chemical components in percentage by mass: SiO2≥99.0%, Fe2O3≤0.03%, Al2O3≤0.35%, CaO≤0.45%, P2O5≤0.0300%, TiO2≤0.0100%, and B2O3≤0.0080%.

[0010] Furthermore, the caking coal includes the following chemical components in percentage by mass: air-dried fixed carbon 50.0% to 65.0%, Fe2O3≤0.135%, Al2O3≤1.8%, CaO≤0.5%, P2O5≤0.0130%, TiO2≤0.0200%, B2O3≤0.0250%, and total S≤2.0%.

[0011] Furthermore, the caking coal includes the following chemical components in percentage by mass: air-dried fixed carbon 50.0% to 65.0%, Fe2O3≤0.135%, Al2O3≤0.8%, CaO≤0.5%, P2O5≤0.0200%, TiO2≤0.0150%, and B2O3≤0.0250%.

[0012] Furthermore, the electric furnace smelting adopts an ore-fired furnace, the active power of the ore-fired furnace is controlled at 25500-28500KW, the primary current is controlled at 420A-580A, and the electrode current is controlled at 75KA-110KA.

[0013] Furthermore, the mass proportion of the caking coal with a particle size distribution in the range of 5 mm to 30 mm is not less than 90%.

[0014] Furthermore, the caking index of the caking coal is not less than 85%.

[0015] Furthermore, the mass proportion of the caking-free coal with a particle size distribution in the range of 2 mm to 30 mm is not less than 90%.

[0016] Advantages of the present invention:

[0017] The present invention adopts the full coal process, through the reasonable design of the ratio of silica, caking coal and non-caking coal, and the control of the chemical composition of caking coal, non-caking coal and silica, and the adjustment of the smelting process parameters of the submerged arc furnace, to prepare the 421# industrial silicon product that can meet the requirements of 421# silicon for impurity elements. The present invention adopts the full coal process, does not need to add petroleum coke and charcoal, reduces the raw material cost, and improves the market competitiveness of the product. Specific implementation method:

[0018] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solution of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] Embodiment 1:

[0020] (1) The carbonaceous reducing agent used in this embodiment is binding coal and non-binding coal, and the loosening agent is wood chips. The proportion of ingredients is: 200 kg of silica B, 30 kg of binding coal, 115 kg of non-binding coal, 45 kg of wood chips, a total of 390 kg. The process formula ratio is actually 8 times the amount of ingredients. Among them, 2.5 kg of calcium chloride is added to every 350 kg of ingredients. The addition of calcium chloride can reduce the melting point of slag, improve the conductivity in the furnace, and promote the silica reduction reaction.

[0021] In this embodiment, the mass proportion of the caking coal with a particle size distribution in the range of 5 mm to 30 mm is not less than 90%; the caking index of the caking coal is 90%.

[0022] In this embodiment, the mass proportion of the caking-free coal with a particle size distribution in the range of 2 mm to 30 mm is not less than 90%.

[0023] (2) Requirements for physical and chemical indicators of raw materials

[0024]

[0025]

[0026] (3) Requirements for smelting in an ore-fired furnace: The smelting equipment used in this embodiment is an ore-fired furnace, the active power is controlled at 25500-28500 kW, the primary current is controlled at 420A-580A, and the electrode current is controlled at 75KA-110KA.

[0027] (4) Production process:

[0028] The steps are as follows: batching through the batching system according to the formula ratio, raw materials entering the furnace, smelting in the ore-fired furnace, unloading from the furnace, refining outside the furnace, casting, sampling, finishing and packaging.

[0029] The quality inspection data of 4 batches of finished silicon prepared by the method of this embodiment are shown in Table 1. It can be seen from the data in Table 1 that the finished silicon prepared by the method of this embodiment can meet the impurity element requirements of 421# silicon.

[0030] Table 1: Quality test data of 4 batches of finished silicon prepared by the method of this embodiment

[0031]

[0032] The silicon content in Table 1 is the value obtained by subtracting the sum of the iron, aluminum and calcium contents from 100%. See the national standard "GB / T2881_2023 Industrial Silicon".

[0033] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for producing industrial silicon with low impurity content, comprising batching, electric furnace smelting, refining and impurity removal, and casting, characterized in that: The ingredients are prepared according to the following mass proportions: 45-60 parts of silica, 7-15 parts of binding coal, 25-35 parts of non-binding coal, and 10-15 parts of wood chips.

2. The method for producing industrial silicon with low impurity content according to claim 1, characterized in that: The silica includes the following chemical components in percentage by mass: SiO2≥99.0%, Fe2O3≤0.03%, Al2O3≤0.35%, CaO≤0.45%, P2O5≤0.0300%, TiO2≤0.0100%, and B2O3≤0.0080%.

3. The method for producing industrial silicon with low impurity content according to claim 1, characterized in that: The caking coal includes the following chemical components in percentage by mass: air-dried fixed carbon 50.0% to 65.0%, Fe2O3≤0.135%, Al2O3≤1.8%, CaO≤0.5%, P2O5≤0.0130%, TiO2≤0.0200%, B2O3≤0.0250%, and total S≤2.0%.

4. The method for producing industrial silicon with low impurity content according to claim 1, characterized in that: The caking coal includes the following chemical components in percentage by mass: fixed carbon on an air-dried basis 50.0% to 65.0%, Fe2O3≤0.135%, Al2O3≤0.8%, CaO≤0.5%, P2O5≤0.0200%, TiO2≤0.0150%, and B2O3≤0.0250%.

5. The method for producing industrial silicon with low impurity content according to claim 1, characterized in that: The electric furnace smelting adopts an ore-fired furnace, the active power of the ore-fired furnace is controlled at 25500-28500KW, the primary current is controlled at 420A-580A, and the electrode current is controlled at 75KA-110KA.

6. The method for producing industrial silicon with low impurity content according to any one of claims 1 to 5, characterized in that: The mass proportion of the caking coal with a particle size distribution within the range of 5 mm to 30 mm is not less than 90%.

7. The method for producing industrial silicon with low impurity content according to any one of claims 1 to 5, characterized in that: The caking index of the caking coal is not less than 85%.

8. The method for producing industrial silicon with low impurity content according to any one of claims 1 to 5, characterized in that: The mass proportion of the non-caking coal with a particle size distribution in the range of 2 mm to 30 mm is not less than 90%.

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