A reducing agent for industrial silicon smelting and its preparation method

Abstract

A reducing agent for industrial silicon smelting and its preparation method are disclosed. The reducing agent raw materials include 80 wt.%–90 wt.% low-rank non-caking coal powder and 10 wt.%–20 wt.% biomass binder. In the preparation of the reducing agent, biomass and low-rank non-caking coal are separately ground into powder. The biomass powder is then subjected to alkali treatment and hydrothermal treatment to obtain the biomass binder. The biomass binder and the low-rank non-caking coal powder are mixed evenly. Simultaneously, during the mixing process, a solution of alkali metal or alkaline earth metal, water, and an inorganic binder solution are sequentially and uniformly sprayed onto the mixture. The materials are mixed evenly and agglomerated. Then, they are cold-pressed under a pressure of 10-15 MPa to obtain pellets. The pellets are then calcined at a temperature of 400-600℃ under anaerobic conditions for 10-30 hours, and cooled to room temperature in the furnace to obtain composite carbonaceous reducing agent pellets for industrial silicon smelting. The reactivity of the composite carbonaceous reducing agent pellets of this invention can reach more than 99% at 1000℃, with fixed carbon of not less than 75 wt.%, volatile matter of 12 wt.%-20 wt.%, moisture of less than 2 wt.%, and ash of less than 4 wt.%.

Description

Technical Field

[0001] This invention belongs to the field of industrial silicon smelting technology, specifically relating to a reducing agent for industrial silicon smelting and its preparation method. Background Technology

[0002] Currently, most carbonaceous reducing agents used in my country's silicon smelting industry are mixed reducing agents composed of charcoal, petroleum coke, wood blocks, semi-coke, and washed coal in certain proportions. With the expansion of my country's industrial silicon products in domestic and international markets, a shortage and price increase of the main carbonaceous reducing agent materials used in silicon production have occurred. The source of charcoal and wood blocks comes at the cost of forest depletion, resulting in limited supply and high prices, which is detrimental to enterprise development. Petroleum coke, a byproduct of crude oil cracking, has very low ash content (<0.3%), a porosity second only to charcoal (46%), and a high fixed carbon content, making it a potential substitute for charcoal in industrial silicon production. However, petroleum coke also suffers from drawbacks such as high conductivity, low reactivity, low resistivity, and premature crystallization, leading to the formation of highly hazardous silicon carbide, directly affecting silicon quality and hindering industrial silicon production. Coal has a high fixed carbon content and low resistivity, and is not easily graphitized, making it a viable alternative to charcoal in industrial silicon production. However, with the continuous depletion of high-quality resources such as anthracite and coking coal in China, the price of coking coal has been rising, and the status of low-rank coal in the energy structure has been increasing. This series of problems will also increase the production cost of industrial silicon, cause environmental pollution, and reduce energy efficiency. Therefore, it is necessary to continuously develop and research new reducing agents to reduce or solve the problems existing in the silicon production process.

[0003] Patent application number 202211156507.7 discloses a reducing agent for silicon smelting containing semi-coke and its preparation method. It uses raw materials such as semi-coke, charcoal, particle size coke, high-viscosity coal, medium-viscosity coal, non-viscosity coal, and low-viscosity coal. This method replaces part of the petroleum coke and bituminous coal with semi-coke and charcoal, which reduces the cost of industrial silicon-carbon reducing agents by 2-6%. However, it requires a large number of admixtures, which is inconvenient to produce in the industrial process and is not conducive to industrial application. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, the present invention aims to provide a reducing agent for industrial silicon smelting and its preparation method. Biomass and low-rank non-caking coal are ground into powders respectively. The biomass powder is then subjected to alkali treatment and hydrothermal treatment to obtain a biomass binder. The biomass binder and the low-rank non-caking coal powder are mixed evenly. Simultaneously, during the mixing process, a solution of alkali metal or alkaline earth metal, water, and an inorganic binder solution are sequentially and uniformly sprayed onto the mixed material. After the material is evenly mixed and agglomeration occurs, it is cold-pressed into pellets, calcined at low temperature under anaerobic conditions, and cooled to room temperature in the furnace to obtain composite carbonaceous reducing agent pellets for industrial silicon smelting. This method improves the economic utilization value of waste resources, enhances the chemical reactivity and resistivity of carbon materials, reduces the raw material cost of industrial silicon smelting, and improves the production efficiency of the smelting process.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A reducing agent for industrial silicon smelting, comprising low-rank non-caking coal powder and biomass binder, wherein the total mass is 100 wt.%, the low-rank non-caking coal powder accounts for 80 wt.% to 90 wt.%, and the biomass binder accounts for 10 wt.% to 20 wt.%.

[0007] The fixed carbon content of the low-rank non-caking coal is 56-65 wt.%, and the particle size of the low-rank non-caking coal powder is 0.075-0.147 mm.

[0008] The biomass binder is made of one or more biomass powders, including fruit shells, rice husks, straw, and sugarcane bagasse, with a particle size of no more than 0.595 mm.

[0009] The preparation method of the biomass binder is as follows:

[0010] 1) Mix biomass powder and NaOH solution evenly to obtain mixture A, where the mass ratio of biomass powder to NaOH solution is 1:12 to 1:16;

[0011] 2) Mixture A is subjected to hydrothermal treatment at 80-100℃ for 60-180 minutes to obtain a liquid biomass binder;

[0012] 3) Dry the liquid biomass binder and then grind it until the particle size is less than 0.177 mm to obtain the biomass binder.

[0013] The concentration of the NaOH solution in step 1) is 5–10 wt.%.

[0014] A method for preparing reducing agent pellets using a reducing agent for industrial silicon smelting, comprising the following specific steps:

[0015] Step 1: Grind the biomass and low-rank non-caking coal into biomass powder with a particle size of no more than 0.595 mm and low-rank non-caking coal powder with a particle size of 0.075-0.147 mm, respectively.

[0016] Step 2: The biomass powder obtained in Step 1 is subjected to alkali treatment and hydrothermal treatment in sequence to obtain biomass binder;

[0017] Step 3: Mix 10wt.% to 20wt.% of biomass binder and 80wt.% to 90wt.% of low-rank non-sticky coal powder. While mixing, spray the alkali metal or alkaline earth metal solution, water and inorganic binder solution onto the mixed material in sequence and evenly. Continue mixing until agglomeration occurs. Then, place it under a pressure of 10 to 15 MPa to cold press and form pellets with a diameter of 50 to 70 mm.

[0018] Step 4: Place the pellets obtained in Step 3 at a temperature of 400-600℃ under anaerobic conditions for low-temperature roasting for 10-30 hours, and then cool them to room temperature in the furnace to obtain composite carbonaceous reducing agent pellets for industrial silicon smelting.

[0019] The method for alkali treatment and hydrothermal treatment of the biomass binder in step 2 is as follows:

[0020] 1) Mix biomass powder and NaOH solution with a concentration of 5-10 wt.% evenly to obtain mixture A, where the mass ratio of biomass powder to NaOH solution is 1:12-1:16;

[0021] 2) Mixture A is subjected to hydrothermal treatment at 80-100℃ for 60-180 minutes to obtain a liquid biomass binder;

[0022] 3) Dry the liquid biomass binder and then grind it until the particle size is less than 0.177 mm to obtain the biomass binder.

[0023] In the reducing agent pellets described in step 3, the alkali metal or alkaline earth metal solution accounts for 0.5 wt.% to 2 wt.% of the total mass of the pellets, water accounts for 6 wt.% to 9 wt.% of the total mass of the pellets, and the inorganic binder solution accounts for 1 wt.% of the total mass of the pellets; the concentration of the alkali metal or alkaline earth metal solution is 1.5 to 3.5 mol / L, and the concentration of the inorganic binder solution is 36 to 40 wt.%.

[0024] In the reducing agent pellets described in step 4, the fixed carbon is not less than 75 wt.%, the volatile matter is 12-20 wt.%, the moisture is less than 2 wt.%, the ash content is less than 4 wt.%, the cold strength is 8-12 MPa, and the resistivity is 3000-6000 Ω·cm.

[0025] The alkali metal or alkaline earth metal solution is one or more of sodium carbonate solution, sodium hydroxide solution, calcium chloride solution, and sodium chloride solution, wherein the alkaline earth metal solution is calcium chloride solution; the alkali metal solution is sodium carbonate solution, sodium hydroxide solution, and / or sodium chloride solution; and the inorganic binder solution is water glass.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] (1) This invention effectively utilizes relatively abundant low-rank non-caking coal resources, expands coking coal resources, and can resolve the contradiction between resource scarcity and industrial production and economic development.

[0028] (2) In this invention, after the biomass is treated with alkali, the cellulose and lignin are fully exposed, and at the same time, substances such as pectin and tannin are produced. Hydrothermal treatment enhances the Brownian motion between molecules through higher temperature, making the reaction more complete and exposing more lignin and cellulose, thus increasing the viscosity.

[0029] (3) This invention uses waste biomass to prepare biomass binder, which makes comprehensive use of agricultural and sideline products, improves the economic value of waste resources, and solves the environmental and waste problems caused by the stockpiling of waste biomass; at the same time, it improves the chemical reactivity and resistivity of carbon materials and reduces the raw material cost of industrial silicon smelting.

[0030] (4) In this invention, alkali metal or alkaline earth metal solution is sprayed evenly onto the raw material to make it quickly wet and evenly dispersed; the added alkali metal or alkaline earth metal can improve the efficiency of the entire carbothermic reduction process during pyrolysis and is an important catalyst. The gaseous alkali metal released will also play a catalytic role in the steam reforming of volatiles, which can greatly improve the production efficiency of the smelting process.

[0031] (5) After roasting, the composite carbonaceous reducing agent pellets of the present invention release a large amount of volatile matter, with fixed carbon of not less than 75wt.%, volatile matter of 12wt.% to 20wt.%, moisture of less than 2wt.%, ash of less than 4wt.%, cold strength of 8 to 12MPa, and resistivity of 3000 to 6000Ω·cm, which is fully applicable to industrial silicon smelting.

[0032] In summary, compared with existing technologies, this invention improves the economic utilization value of waste resources, solves the environmental and waste problems caused by the stockpiling of waste biomass, and at the same time improves the chemical reactivity and resistivity of carbon materials, reduces the raw material cost of industrial silicon smelting, and improves the production efficiency of the smelting process. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to the embodiments.

[0034] Example 1:

[0035] A reducing agent for industrial silicon smelting, comprising 100 wt.% of low-rank non-caking coal powder and biomass binder, with the low-rank non-caking coal powder accounting for 85 wt.% and the biomass binder accounting for 15 wt.%.

[0036] The biomass binder is obtained by sequentially treating straw powder with a particle size of no more than 0.595 mm with alkali and hydrothermal treatment.

[0037] The methods for alkaline treatment and hydrothermal treatment of the biomass binder are as follows:

[0038] Step 1) Mix straw powder and a 10 wt.% NaOH solution evenly to obtain mixture A; the mass ratio of straw powder to NaOH solution is 1:14;

[0039] Step 2) Place mixture A in a hydrothermal environment at 90°C for 150 min to obtain a liquid biomass binder;

[0040] Step 3) Dry the liquid biomass binder at 70°C for 36 hours, and then grind it until the particle size is less than 0.177 mm to obtain the biomass binder;

[0041] A method for preparing reducing agent pellets using a reducing agent for industrial silicon smelting, comprising the following specific steps:

[0042] Step (1) grind rice straw and low-rank non-caking coal with a fixed carbon content of 59.6 wt.% into powder to obtain rice straw powder with a particle size of less than 0.595 mm and low-rank non-caking coal powder with a particle size of 0.125 mm.

[0043] Step (2) involves sequentially treating rice straw powder with alkali and hydrothermal treatment to obtain a biomass binder. Specifically, the straw powder and a 10 wt.% NaOH solution are mixed evenly to obtain mixture A; the mass ratio of straw powder to NaOH solution is 1:14; mixture A is subjected to hydrothermal treatment at 90℃ for 150 min to obtain a liquid biomass binder; the liquid biomass binder is dried at 70℃ for 36 h, and then ground until the particle size is less than 0.177 mm to obtain the biomass binder.

[0044] Step (3) Take 15 wt.% of the biomass binder obtained in step (2) through alkali treatment and hydrothermal treatment and 85 wt.% of low-rank non-sticky coal powder, and mix them in a spray mixer. At the same time, during the mixing process, the spray mixer sprays a 3 mol / L sodium hydroxide solution, water and a 37 wt.% water glass solution onto the mixed material in sequence. After the material is mixed evenly and agglomeration occurs, it is then cold-pressed under a pressure of 12 MPa to obtain pellets with a particle size of 60 mm. Among them, the sodium hydroxide solution accounts for 1 wt.% of the total mass of the pellets, the water accounts for 7.5 wt.% of the total mass of the pellets, and the inorganic binder solution accounts for 1 wt.% of the total mass of the pellets.

[0045] (4) The pellets were placed at a temperature of 500℃ and under oxygen-free conditions for low-temperature roasting for 15 hours, and then cooled to room temperature in the furnace to obtain reducing agent pellets with a particle size of 60mm for industrial silicon smelting.

[0046] In this embodiment, the reducing agent pellets for industrial silicon have a fixed carbon content of 77.8 wt.%, volatile matter of 16.9 wt.%, moisture content of 1.8 wt.%, ash content of 3.5 wt.%, a cold strength of 9 MPa, and a resistivity of 4000 Ω·cm.

[0047] 200 kg of silica (99.5% SiO2) was crushed into blocks with a particle size of 25-100 mm. After washing and screening, it was mixed evenly with 102 kg of composite carbonaceous reducing agent pellets and added to a submerged arc furnace for smelting. The industrial silicon product obtained after smelting had a Si content of >99.6 wt.%. The fixed carbon consumption for producing one ton of industrial silicon product was 0.941 tons, and the electricity consumption was 10536 kWh.

[0048] Example 2:

[0049] A reducing agent for industrial silicon smelting, comprising 100 wt.% of low-rank non-caking coal powder and biomass binder, with the low-rank non-caking coal powder accounting for 90 wt.% and the biomass binder accounting for 10 wt.%.

[0050] The biomass binder is obtained by sequentially treating coffee shell powder with a particle size of no more than 0.595 mm with alkali and hydrothermal treatment.

[0051] The methods for alkaline treatment and hydrothermal treatment of the biomass binder are as follows:

[0052] Step 1) Mix coffee shell powder and 8.5 wt.% NaOH solution evenly to obtain mixture A; the mass ratio of coffee shell powder to NaOH solution is 1:13;

[0053] Step 2) Mixture A is subjected to hydrothermal treatment at 80℃ for 180 min to obtain liquid biomass binder;

[0054] Step 3) Dry the liquid biomass binder at 80℃ for 36 hours, and then grind it until the particle size is less than 0.105 mm to obtain the biomass binder;

[0055] A method for preparing reducing agent pellets using a reducing agent for industrial silicon smelting, comprising the following specific steps:

[0056] Step (1) grind coffee shells and low-rank non-caking coal with a fixed carbon content of 63.5 wt.% into powder to obtain coffee shell powder with a particle size of less than 0.595 mm and low-rank non-caking coal powder with a particle size of 0.105 mm.

[0057] Step (2) involves sequentially treating coffee shell powder with alkali and then with hydrothermal treatment to obtain a biomass binder. Specifically, coffee shell powder and an 8.5 wt.% NaOH solution are mixed evenly to obtain mixture A; the mass ratio of coffee shell powder to NaOH solution is 1:13; mixture A is subjected to hydrothermal treatment at 80°C for 150 min to obtain a liquid biomass binder; the liquid biomass binder is dried at 70°C for 30 h, and then ground until the particle size is less than 0.177 mm to obtain the biomass binder.

[0058] Step (3) Take 10 wt.% of the biomass binder obtained in step (2) through alkali treatment and hydrothermal treatment and 90 wt.% of low-rank non-sticky coal powder, and mix them in a spray mixer. At the same time, during the mixing process, the spray mixer sprays sodium carbonate solution with a concentration of 2.5 mol / L, water and water glass solution with a concentration of 40 wt.% onto the mixed material in sequence. After the material is mixed evenly and agglomeration occurs, it is then cold-pressed under a pressure of 15 MPa to obtain pellets with a particle size of 50 mm. Among them, sodium carbonate solution accounts for 0.5 wt.% of the total mass of the pellets, water accounts for 8 wt.% of the total mass of the pellets, and inorganic binder solution accounts for 1 wt.% of the total mass of the pellets.

[0059] (4) The pellets were placed at a temperature of 600℃ and under oxygen-free conditions for 10 hours and then cooled to room temperature in the furnace to obtain reducing agent pellets with a particle size of 50mm for industrial silicon smelting.

[0060] In this embodiment, the composite carbonaceous reducing agent pellets for industrial silicon have a fixed carbon content of 84.5 wt.%, volatile matter of 12.6 wt.%, moisture of 1.5 wt.%, ash content of 1.4 wt.%, a cold strength of 11 MPa, and a resistivity of 5500 Ω·cm.

[0061] 200 kg of silica (99.5% SiO2) is crushed into blocks with a particle size of 25-100 mm. After washing and sieving, it is mixed evenly with 94 kg of composite carbonaceous reducing agent pellets and added to a submerged arc furnace for smelting. The industrial silicon product obtained after smelting has a Si content of >99.6 wt.%. The fixed carbon consumption for producing one ton of industrial silicon product is 0.909 tons, and the electricity consumption is 10199 kWh.

[0062] Example 3:

[0063] A reducing agent for industrial silicon smelting, comprising 100 wt.% of low-rank non-caking coal powder and biomass binder, with the low-rank non-caking coal powder accounting for 80 wt.% and the biomass binder accounting for 20 wt.%.

[0064] The biomass binder is obtained by sequentially treating rice husk powder with a particle size of no more than 0.595 mm with alkali and hydrothermal treatment.

[0065] The methods for alkaline treatment and hydrothermal treatment of the biomass binder are as follows:

[0066] Step 1) Mix rice husk powder and a 5 wt.% NaOH solution evenly to obtain mixture A; the mass ratio of rice husk powder to NaOH solution is 1:14;

[0067] Step 2) Mixture A is subjected to hydrothermal treatment at 100℃ for 60 minutes to obtain liquid biomass binder;

[0068] Step 3) Dry the liquid biomass binder at 80℃ for 20 hours, and then grind it until the particle size is less than 0.177 mm to obtain the biomass binder;

[0069] A method for preparing reducing agent pellets using a reducing agent for industrial silicon smelting, comprising the following specific steps:

[0070] Step (1) grind rice husks and low-rank non-caking coal with a fixed carbon content of 63.5 wt.% into powder to obtain rice husk powder with a particle size of less than 0.595 mm and low-rank non-caking coal powder with a particle size of 0.147 mm.

[0071] Step (2) involves sequentially treating rice husk powder with alkali and hydrothermal treatment to obtain a biomass binder. Specifically, rice husk powder and a 5 wt.% NaOH solution are mixed evenly to obtain mixture A; the mass ratio of rice husk powder to NaOH solution is 1:14; mixture A is subjected to hydrothermal treatment at 100℃ for 60 min to obtain a liquid biomass binder; the liquid biomass binder is dried at 80℃ for 20 h, and then ground until the particle size is less than 0.177 mm to obtain the biomass binder.

[0072] Step (3) Take 20 wt.% of the biomass binder obtained in step (2) through alkali treatment and hydrothermal treatment and 80 wt.% of low-rank non-sticky coal powder, and mix them in a spray mixer. At the same time, during the mixing process, the spray mixer sprays calcium chloride solution with a concentration of 1.5 mol / L, water and water glass solution with a concentration of 38 wt.% onto the mixed material in sequence. After the material is mixed evenly and agglomeration occurs, it is then cold-pressed under a pressure of 10 MPa to obtain pellets with a particle size of 55 mm. Among them, calcium chloride solution accounts for 1.5 wt.% of the total mass of the pellets, water accounts for 6 wt.% of the total mass of the pellets, and inorganic binder solution accounts for 1 wt.% of the total mass of the pellets.

[0073] (4) The pellets were placed at a temperature of 400℃ and under oxygen-free conditions for 30 hours and then cooled to room temperature in the furnace to obtain reducing agent pellets with a particle size of 55mm for industrial silicon smelting.

[0074] In this embodiment, the composite carbonaceous reducing agent pellets for industrial silicon have a fixed carbon content of 80.6 wt.%, volatile matter of 14.7 wt.%, moisture of 1.3 wt.%, ash content of 3.4 wt.%, a cold strength of 8 MPa, and a resistivity of 3500 Ω·cm.

[0075] 200 kg of silica (99.5% SiO2) is crushed into blocks with a particle size of 25-100 mm. After washing and sieving, it is mixed evenly with 99 kg of composite carbonaceous reducing agent pellets and added to a submerged arc furnace for smelting. The industrial silicon product obtained after smelting has a Si content of >99.6 wt.%. The fixed carbon consumption for producing one ton of industrial silicon product is 0.918 tons, and the electricity consumption is 10896 kWh.

[0076] Example 4:

[0077] A reducing agent for industrial silicon smelting, comprising 100 wt.% of low-rank non-caking coal powder and biomass binder, with the low-rank non-caking coal powder accounting for 88 wt.% and the biomass binder accounting for 12 wt.%.

[0078] The biomass binder is obtained by sequentially treating macadamia nut shell powder with a particle size of no more than 0.595 mm with alkali and hydrothermal treatment.

[0079] The methods for alkaline treatment and hydrothermal treatment of the biomass binder are as follows:

[0080] Step 1) Mix macadamia nut shell powder and a 9 wt.% NaOH solution evenly to obtain mixture A; the mass ratio of rice husk powder to NaOH solution is 1:15;

[0081] Step 2) Place mixture A in a hydrothermal environment at 90°C for 120 minutes to obtain a liquid biomass binder;

[0082] Step 3) Dry the liquid biomass binder at 60°C for 48 hours, and then grind it until the particle size is less than 0.177 mm to obtain the biomass binder;

[0083] A method for preparing reducing agent pellets using a reducing agent for industrial silicon smelting, comprising the following specific steps:

[0084] Step (1) grind macadamia nut shells and low-rank non-caking coal with a fixed carbon content of 58.6 wt.% into powder to obtain macadamia nut shell powder with a particle size of less than 0.595 mm and low-rank non-caking coal powder with a particle size of 0.075 mm.

[0085] Step (2) The macadamia nut shell powder is subjected to alkali treatment and hydrothermal treatment in sequence to obtain biomass binder. Specifically, macadamia nut shell powder and 9 wt.% NaOH solution are mixed evenly to obtain mixture A; the mass ratio of macadamia nut shell powder to NaOH solution is 1:15; mixture A is subjected to hydrothermal treatment at 90℃ for 120 min to obtain liquid biomass binder; the liquid biomass binder is dried at 60℃ for 48 h, and then ground until the particle size is less than 0.177 mm to obtain biomass binder.

[0086] Step (3) Take 12 wt.% of the biomass binder obtained in step (2) through alkali treatment and hydrothermal treatment and 88 wt.% of low-rank non-sticky coal powder, and mix them in a spray mixer. At the same time, during the mixing process, the spray mixer sprays 3.5 mol / L NaOH solution, water and 36 wt.% water glass solution onto the mixed material in sequence. After the material is mixed evenly and agglomeration occurs, it is then cold-pressed under a pressure of 13 MPa to obtain pellets with a particle size of 65 mm. Among them, NaOH solution accounts for 2 wt.% of the total mass of the pellets, water accounts for 9 wt.% of the total mass of the pellets, and inorganic binder solution accounts for 1 wt.% of the total mass of the pellets.

[0087] (4) The pellets were placed at a temperature of 500℃ and under oxygen-free conditions for low-temperature roasting for 24h, and then cooled to room temperature in the furnace to obtain reducing agent pellets with a particle size of 65mm for industrial silicon smelting.

[0088] In this embodiment, the composite carbonaceous reducing agent pellets for industrial silicon have a fixed carbon content of 78.6 wt.%, volatile matter of 17.3 wt.%, moisture of 1.1 wt.%, and ash content of 3 wt.%, a cold strength of 12 MPa, and a resistivity of 6000 Ω·cm.

[0089] 200 kg of silica (99.5% SiO2) was crushed into blocks with a particle size of 25-100 mm. After washing and screening, it was mixed evenly with 101 kg of composite carbonaceous reducing agent pellets and added to a submerged arc furnace for smelting. The industrial silicon product obtained after smelting had a Si content of >99.6 wt.%. The fixed carbon consumption for producing one ton of industrial silicon product was 0.912 tons, and the electricity consumption was 10143 kWh.

[0090] Example 5:

[0091] A reducing agent for industrial silicon smelting, comprising 100 wt.% of low-rank non-caking coal powder and biomass binder, with the low-rank non-caking coal powder accounting for 84 wt.% and the biomass binder accounting for 16 wt.%.

[0092] The biomass binder is obtained by sequentially treating sugarcane bagasse powder with a particle size of no more than 0.595 mm with alkali and hydrothermal treatment.

[0093] The methods for alkaline treatment and hydrothermal treatment of the biomass binder are as follows:

[0094] Step 1) Mix sugarcane bagasse powder and a 7 wt.% NaOH solution evenly to obtain mixture A; the mass ratio of sugarcane bagasse powder to NaOH solution is 1:16;

[0095] Step 2) Mixture A is subjected to hydrothermal treatment at 80℃ for 160 min to obtain liquid biomass binder;

[0096] Step 3) Dry the liquid biomass binder at 80℃ for 36 hours, and then grind it until the particle size is less than 0.177 mm to obtain the biomass binder;

[0097] A method for preparing reducing agent pellets using a reducing agent for industrial silicon smelting, comprising the following specific steps:

[0098] Step (1) Grind bagasse and low-rank non-caking coal with a fixed carbon content of 58 wt.% into powder to obtain bagasse powder with a particle size of less than 0.595 mm and low-rank non-caking coal powder with a particle size of 0.125 mm.

[0099] Step (2) involves sequentially treating sugarcane bagasse powder with alkali and hydrothermal treatment to obtain a biomass binder. Specifically, sugarcane bagasse powder and a 7 wt.% NaOH solution are mixed evenly to obtain mixture A; the mass ratio of sugarcane bagasse powder to NaOH solution is 1:16; mixture A is subjected to hydrothermal treatment at 80℃ for 160 min to obtain a liquid biomass binder; the liquid biomass binder is dried at 80℃ for 36 h, and then ground until the particle size is less than 0.177 mm to obtain the biomass binder.

[0100] Step (3) Take 16 wt.% of the biomass binder obtained in step (2) through alkali treatment and hydrothermal treatment and 84 wt.% of the low-rank non-sticky coal powder, and mix them in a spray mixer. At the same time, during the mixing process, the spray mixer sprays a 2 mol / L sodium chloride solution, water and a 37 wt.% water glass solution onto the mixed material in sequence. After the material is mixed evenly and agglomeration occurs, it is then cold-pressed under a pressure of 11 MPa to obtain pellets with a particle size of 70 mm. Among them, the sodium chloride solution accounts for 2 wt.% of the total mass of the pellets, the water accounts for 6 wt.% of the total mass of the pellets, and the inorganic binder solution accounts for 1 wt.% of the total mass of the pellets.

[0101] (4) The pellets were placed at a temperature of 600℃ and under oxygen-free conditions for 20 hours and then cooled to room temperature in the furnace to obtain reducing agent pellets with a particle size of 70mm for industrial silicon smelting.

[0102] In this embodiment, the composite carbonaceous reducing agent pellets for industrial silicon have a fixed carbon content of 76.9 wt.%, volatile matter of 19.2 wt.%, moisture of 0.8 wt.%, ash content of 3.1 wt.%, a cold strength of 9 MPa, and a resistivity of 3800 Ω·cm.

[0103] 200 kg of silica (99.5% SiO2) was crushed into blocks with a particle size of 25-100 mm. After washing and screening, it was mixed evenly with 104 kg of composite carbonaceous reducing agent pellets and added to a submerged arc furnace for smelting. The industrial silicon product obtained after smelting had a Si content of >99.6 wt.%. The fixed carbon consumption for producing one ton of industrial silicon product was 0.957 tons, and the electricity consumption was 10786 kWh.

[0104] Example 6:

[0105] A reducing agent for industrial silicon smelting, comprising 100 wt.% of low-rank non-caking coal powder and biomass binder, with the low-rank non-caking coal powder accounting for 80 wt.% and the biomass binder accounting for 20 wt.%.

[0106] The biomass binder is obtained by successively treating coffee straw powder with a particle size of no more than 0.595 mm with alkali and hydrothermal treatment.

[0107] The methods for alkaline treatment and hydrothermal treatment of the biomass binder are as follows:

[0108] Step 1) Mix coffee straw powder and a 6.5 wt.% NaOH solution evenly to obtain mixture A; the mass ratio of coffee straw powder to NaOH solution is 1:15;

[0109] Step 2) Place mixture A in a hydrothermal environment at 100°C for 100 min to obtain a liquid biomass binder;

[0110] Step 3) Dry the liquid biomass binder at 60°C for 45 hours, and then grind it until the particle size is less than 0.177 mm to obtain the biomass binder;

[0111] A method for preparing reducing agent pellets using a reducing agent for industrial silicon smelting, comprising the following specific steps:

[0112] Step (1) grind coffee straw and low-rank non-caking coal with a fixed carbon content of 62.8 wt.% into powder to obtain coffee straw powder with a particle size of less than 0.595 mm and low-rank non-caking coal powder with a particle size of 0.075 mm.

[0113] Step (2) involves sequentially treating coffee straw powder with alkali and hydrothermal treatment to obtain a biomass binder. Specifically, coffee straw powder and a 6.5 wt.% NaOH solution are mixed evenly to obtain mixture A; the mass ratio of coffee straw powder to NaOH solution is 1:15; mixture A is subjected to hydrothermal treatment at 100℃ for 100 min to obtain a liquid biomass binder; the liquid biomass binder is dried at 80℃ for 45 h, and then ground until the particle size is less than 0.177 mm to obtain the biomass binder.

[0114] Step (3) Take 11 wt.% of the biomass binder obtained in step (2) through alkali treatment and hydrothermal treatment and 89 wt.% of low-rank non-sticky coal powder, and mix them in a spray mixer. At the same time, during the mixing process, the spray mixer sprays calcium chloride solution with a concentration of 2.5 mol / L, water and water glass solution with a concentration of 38 wt.% onto the mixed material in sequence. After the material is mixed evenly and agglomeration occurs, it is then cold-pressed under a pressure of 14 MPa to obtain pellets with a particle size of 65 mm. Among them, calcium chloride solution accounts for 1.5 wt.% of the total mass of the pellets, water accounts for 7 wt.% of the total mass of the pellets, and inorganic binder solution accounts for 1 wt.% of the total mass of the pellets.

[0115] (4) The pellets were placed at a temperature of 500℃ and under oxygen-free conditions for low-temperature roasting for 25h, and then cooled to room temperature in the furnace to obtain reducing agent pellets with a particle size of 65mm for industrial silicon smelting.

[0116] In this embodiment, the composite carbonaceous reducing agent pellets for industrial silicon have a fixed carbon content of 80.6 wt.%, volatile matter of 14.7 wt.%, moisture of 1.3 wt.%, ash content of 3.4 wt.%, a cold strength of 8 MPa, and a resistivity of 3500 Ω·cm.

[0117] 200 kg of silica (99.5% SiO2) is crushed into blocks with a particle size of 25-100 mm. After washing and screening, it is mixed evenly with 100 kg of composite carbonaceous reducing agent pellets and added to a submerged arc furnace for smelting. The industrial silicon product obtained after smelting has a Si content of >99.6 wt.%. The fixed carbon consumption for producing one ton of industrial silicon product is 0.928 tons, and the electricity consumption is 10385 kWh.

[0118] The specific embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A reducing agent for industrial silicon smelting, characterized in that: The raw materials include low-rank non-caking coal powder and biomass binder. The total mass is 100 wt.%, with low-rank non-caking coal powder accounting for 80 wt.%~90 wt.% and biomass binder accounting for 10 wt.%~20 wt.%. The biomass and low-rank non-caking coal are ground into biomass powder with a particle size of no more than 0.595 mm and low-rank non-caking coal powder with a particle size of 0.075~0.147 mm, respectively. The obtained biomass powder was successively subjected to alkali treatment and hydrothermal treatment to obtain a biomass binder; Mix 10wt.%~20wt.% biomass binder and 80wt.%~90wt.% low-rank non-sticky coal powder evenly; while mixing, spray alkali metal or alkaline earth metal solution, water and inorganic binder solution evenly onto the mixed material in sequence, continue mixing and agglomeration occurs, and then place it under a pressure of 10~15MPa to cold press into pellets with a diameter of 50~70mm. The obtained pellets were placed at a temperature of 400~600℃ and under oxygen-free conditions for low-temperature roasting for 10~30h, and then cooled to room temperature in the furnace to obtain composite carbonaceous reducing agent pellets for industrial silicon smelting. The reducing agent pellets had a cold strength of 8~12MPa and a resistivity of 3000~6000Ω•cm. The biomass binder uses one or more biomass powders, including fruit shells, rice husks, straw, and sugarcane bagasse; the inorganic binder solution uses water glass.

2. The reducing agent for industrial silicon smelting according to claim 1, characterized in that: The fixed carbon content of the low-rank non-caking coal is 56~65 wt.%, and the particle size of the low-rank non-caking coal powder is 0.075~0.147 mm.

3. The reducing agent for industrial silicon smelting according to claim 1, characterized in that: The preparation method of the biomass binder is as follows: 1) Mix biomass powder and NaOH solution evenly to obtain mixture A, where the mass ratio of biomass powder to NaOH solution is 1:12 to 1:16; 2) Mixture A is subjected to hydrothermal treatment at 80~100℃ for 60~180 min to obtain liquid biomass binder; 3) Dry the liquid biomass binder and then grind it until the particle size is less than 0.177 mm to obtain the biomass binder.

4. The reducing agent for industrial silicon smelting according to claim 3, characterized in that: The concentration of the NaOH solution in step 1) is 5~10 wt.%.

5. A reducing agent for industrial silicon smelting according to claim 1, characterized in that: In the reducing agent pellets, the alkali metal or alkaline earth metal solution accounts for 0.5 wt.% to 2 wt.% of the total mass of the pellets, water accounts for 6 wt.% to 9 wt.% of the total mass of the pellets, and the inorganic binder solution accounts for 1 wt.% of the total mass of the pellets; the concentration of the alkali metal or alkaline earth metal solution is 1.5 to 3.5 mol / L, and the concentration of the inorganic binder solution is 36 to 40 wt.%.

6. The reducing agent for industrial silicon smelting according to claim 1, characterized in that: The reducing agent pellets contain at least 75 wt.% fixed carbon, 12-20 wt.% volatile matter, less than 2 wt.% moisture, and less than 4 wt.% ash.

7. The reducing agent for industrial silicon smelting according to claim 1, characterized in that: The alkali metal or alkaline earth metal solution is one or more of sodium carbonate solution, sodium hydroxide solution, calcium chloride solution, and sodium chloride solution.