CN116144922B - Preparation method of composite caking coal reduction pellets for industrial silicon - Google Patents

Abstract

The present invention belongs to the technical field of efficient and clean utilization of resources, and specifically relates to a method for preparing composite binding coal reduction pellets for industrial silicon. The reduction pellets use coal as a carbonaceous material, and are coated layer by layer with water and a binder to form a pellet; and the coating layer is greater than or equal to 1. The preparation method is: binder coals of different particle sizes and different bonding indexes are coated layer by layer according to the rule that small particles wrap large particles, and high bonding index wraps non-bonding index, and then baked at 500-600°C in isolation of air for 2-3 hours, and the composite binding coal reducing agent pellets are obtained after cooling. The present invention uses coal as a carbonaceous raw material, and uses a combination of different particle sizes and bonding properties to coat layer by layer to form a porous structure, and the strength and fixed carbon content of the pellets are increased by roasting the binding coal. The present invention can not only ensure that the product has a high fixed carbon content, good reaction activity, low ash content, suitable bonding index, and low cost, but also can produce high-quality industrial silicon, which can be fully used for the smelting and production of industrial silicon.

Description

A method for preparing composite bonding coal reduction pellets for industrial silicon

Technical Field

The invention belongs to the technical field of efficient and clean utilization of resources, and specifically relates to a method for preparing composite binding coal reduction pellets for industrial silicon.

Background technique

At present, most of the carbonaceous reducing agents used in my country's silicon smelting are traditional mixed carbonaceous reducing agents made of charcoal, petroleum coke, wood blocks, and semi-coke in a certain ratio. With the expansion of my country's industrial silicon products in the domestic and foreign markets, the supply of the main raw carbonaceous reducing agent materials for silicon production has been in short supply and the price has risen. Among them, the supply of charcoal and petroleum coke is very tight, the price has risen sharply, and the quality is unstable, and the bonding index is low, which undoubtedly makes industrial silicon production face great difficulties. Therefore, the market urgently needs a new type of reducing agent for the silicon industry.

Coal production and consumption in my country are dominant, among which coal has high specific resistivity, suitable bonding index, and is not easy to graphitize, and can replace charcoal as a reducing agent for the production of industrial silicon. If only whole coal is used as a reducing agent for industrial silicon smelting, the reaction speed of the charge will be accelerated under high current and low voltage conditions, and the reaction will be more complete. The silicon output has been increased while reducing energy consumption. However, the untreated coal has a low fixed carbon content and a high volatile content, which may cause serious ignition of the charge and cause problems such as waste of raw materials. At present, there are carbonaceous reducing agents mixed with charcoal, petroleum coke, and bituminous coal to reduce silica, such as patent CN115072724A, which designs to fully mix biomass carbon, blue charcoal, petroleum coke, coke reducing agent, bonding washed coal, and non-bonding washed coal according to the mass ratio, and use a feeding device to feed it into the submerged arc furnace for industrial silicon smelting production. Meanwhile, patent CN113636560A also obtains the reducing agent by mixing 40-45 parts of charcoal powder, 20-25 parts of washed coal powder, 8-12 parts of petroleum coke powder, 3-6 parts of microsilica powder, 4-5 parts of pre-impregnated glue solution, 6-8 parts of composite binder and 4-5 parts of NaOH solution. However, this mixing technology may still have problems such as low reducing agent activity, poor furnace charge permeability, and extra energy consumption.

Summary of the invention

The present invention aims at the problems of preparing bituminous coal reducing agents in the prior art and provides a method for preparing composite binding coal reduction pellets for industrial silicon. The composite binding coal is used as the carbonaceous raw material, and for the first time, a combination of different particle sizes and binding properties is used to coat the pellets layer by layer to form a porous structure. The strength and fixed carbon content of the pellets are improved by roasting the binding coal, so that the pellets reach a certain binding index, which not only ensures that the fixed carbon content is high, the reaction activity is good, the ash content is low, the binding index is suitable, and the cost is low, but also high-quality industrial silicon can be produced, which can be fully used for the smelting and production of industrial silicon.

A method for preparing composite binding coal reduction pellets for industrial silicon, using coal as a carbonaceous material, and coating it layer by layer with water and a binder into a pellet shape; and the coating layer is greater than or equal to 1; that is, the composite binding coal reduction pellets for industrial silicon include a first binding coal and a coating layer; wherein the particle size of the coal used in the first binding coal is greater than the particle size of the coal used in the coating layer; and the bonding index of the coal used in the first binding coal is less than the bonding index of the coal used in the coating layer. The preparation method is: firstly coating the first binding coal with a first coating layer, if the number of coating layers is greater than 2, it is necessary to coat the i-th coating layer on the i-1th coating layer; the i is greater than or equal to 2.

Preferably, the coating layer is greater than or equal to 2;

As a further preference, the first coating layer is directly coated on the first type of binding coal, and the second coating layer is coated on the first coating layer; and so on, the i-th coating layer is coated on the i-1-th coating layer, where i is greater than or equal to 2.

As a further preference, the particle size of the coal used in the (i-1)th coating layer is larger than the particle size of the coal used in the (i)th coating layer; the bonding index of the coal used in the (i-1)th coating layer is smaller than the bonding index of the coal used in the (i)th coating layer.

Preferably, the particle size of the first type of bonding coal is 5-16 mm, further optimized to 6-15.5 mm, and further preferably 6-15 mm; the bonding index is 0; the particle size of the coal used for the first coating layer (i.e., the second type of bonding coal) is 0.2-0.6 mm, and the bonding index is 50-85; the particle size of the coal used for the second coating layer (the third type of bonding coal) is <0.1 mm, and the bonding index is >85.

As one of the further preferred schemes, the particle size of the first bonding coal is 14-15.5 mm, and further optimized to 15 mm; the bonding index is 0; the particle size of the coal used for the first coating layer is 0.25-0.35 mm, and further optimized to 0.3 mm, and the bonding index is 85; the particle size of the coal used for the second coating layer is <0.1 mm, and the bonding index is 96; the mass ratio of the first bonding coal, the coal used for the first coating layer, and the coal used for the second coating layer is: 30:50:20.

As one of the further preferred schemes, the particle size of the first bonding coal is 14-15.5 mm, and further optimized to 15 mm; the bonding index is 0; the particle size of the coal used for the first coating layer is 0.25-0.35 mm, and further optimized to 0.35 mm, and the bonding index is 85; the particle size of the coal used for the second coating layer is <0.1 mm, and the bonding index is 94; the mass ratio of the first bonding coal, the coal used for the first coating layer, and the coal used for the second coating layer is: 20:40:40.

As one of the further preferred schemes, the particle size of the first bonding coal is 8-10 mm, and further optimized to 8 mm; the bonding index is 0; the particle size of the coal used for the first coating layer is 0.4-0.5 mm, preferably 0.45 mm, and the bonding index is 78; the particle size of the coal used for the second coating layer is <0.1 mm, and the bonding index is 96; the mass ratio of the first bonding coal, the coal used for the first coating layer, and the coal used for the second coating layer is: 25:30:45.

Furthermore, the composite binding coal reduction pellets for industrial silicon, when i=2, are prepared by the following steps:

Step 1, firstly, three kinds of coal with different caking indexes are crushed into particles of required particle size in the order of caking index from small to large; wherein the particle size of the first kind of caking coal is 6-10 mm, and the caking index is 0, the particle size of the second kind of caking coal is 0.3-0.5 mm, and the caking index is 65-85, and the particle size of the third kind of caking coal is less than 0.1 mm, and the caking index is greater than 85;

Step 2, adding the first caking coal to the second caking coal, and then adding 8wt.% to 12wt.% of water, 0.8-1.2wt.%, preferably 1wt.% of a binder, stirring until obvious agglomeration, and coating the first caking coal into agglomerate particles with a diameter of 20-30mm;

Step 3, adding the agglomerate particles in step 2 to the third caking coal, and then adding 8wt.% to 12wt.% of water, 0.8-1.2wt.%, preferably 1wt.% of a binder, stirring until obvious agglomeration, and coating the agglomerate particles in step 2 to form agglomerate particles with a diameter of 30-60mm;

Step 4, the agglomerate particles formed in step 3 are placed in an air-tight state at a temperature of 500-600° C. and roasted for 2-3 hours, and then cooled to room temperature to obtain composite binding coal reduction pellets.

In step 1, the mass ratio of the first caking coal, the second caking coal and the third caking coal is 20-30:30-50:20-50.

The low-temperature calcination temperature in step 4 is 500-600° C. and the time is 2-3 hours.

The fixed carbon content of the three coals with different caking indexes in step 1 is 55-65wt.%.

In the steps 2 and 3, the binder is an organic-inorganic composite binder, wherein the inorganic binder accounts for 20-40 wt.%, and the organic binder accounts for 60-80 wt.%. The inorganic binder is selected from water glass; and the organic binder is selected from deformed starch.

The composite bonding coal reduction pellets for industrial silicon prepared above have a bonding index of 60 to 80 and a cold strength of 8 to 12 MPa.

The beneficial effects of the present invention are:

1. The present invention uses composite bonding coal as the carbonaceous raw material, and utilizes the combination of different particle sizes and bonding properties of three bonding coals to coat layer by layer to form a porous structure. The smaller the particle size, the higher the bonding effect, resulting in a large number of gaps in the particles, which is helpful for full dispersion during use, ensuring full combustion of the carbonaceous material, and also improving combustion stability.

2. The present invention improves the strength of the pellets by roasting the bonding coal. The colloids produced by the coal at a certain temperature make the pellets more tightly bonded, thereby improving the strength of the reduced pellets of the composite bonding coal. At the same time, the increase in temperature enables the reduced pellets of the composite bonding coal to reach a certain bonding index, which not only ensures that the fixed carbon content is high, the reaction activity is good, the ash content is low, the bonding index is appropriate, and the cost is low, but also can produce high-quality industrial silicon, which can be fully used for the smelting and production of industrial silicon.

3. The composite binding coal reduction pellets for industrial silicon prepared by the present invention release a large amount of volatile matter after roasting, with a fixed carbon content of more than 75wt.%, a volatile content of 15wt.% to 20wt.%, an ash content of less than 4wt.%, a cold strength of 8 to 12MPa, and a bonding index of 60 to 80, which is fully suitable for industrial silicon.

4. The modified starch binder used in the composite binder coal reduction pellets for industrial silicon prepared by the present invention is released as volatile matter during the industrial silicon smelting process, so that the pellets form a porous structure and the chemical reaction activity is increased.

Detailed ways

The present invention is further described in detail below in conjunction with specific implementation modes, but the protection scope of the present invention is not limited to the described contents.

Example 1

The industrial silicon composite binding coal reduction pellets have a fixed carbon content of 77.4wt.%, a volatile content of 19wt.%, an ash content of 3.6wt.%, a bonding index G of 70, and a pellet cold strength of 10MPa.

The method for preparing composite binding coal reduction pellets for industrial silicon comprises the following steps:

Step 1, firstly, three kinds of coal with different caking indexes are crushed into particles of 10 mm, 0.5 mm, and 0.075 mm in the order of caking index from small to large, wherein the caking index of the first caking coal is 0, the caking index of the second caking coal is 75; the caking index of the third caking coal is 90, and the mass ratio of the first caking coal, the second caking coal, and the third caking coal is 20:50:30wt.%;

Step 2, adding the first bonding coal, 9wt.% of water, and 1wt.% of a binder to the second bonding coal, stirring until obvious agglomeration, and coating the first bonding coal to form agglomerate particles with a diameter of 25 mm, wherein the binder is an organic-inorganic composite binder, in which the inorganic binder accounts for 30wt% and the organic binder accounts for 70wt%, the inorganic binder is water glass, and the organic binder is modified starch;

Step 3, adding the agglomerate particles in step 2, 9wt.% of water, and 1wt.% of a binder to the third type of binding coal, stirring until obvious agglomeration occurs, and coating the agglomerate particles in step 2 to form agglomerate particles with a diameter of 45 mm, wherein the binder is an organic-inorganic composite binder, in which the inorganic binder accounts for 30wt% and the organic binder accounts for 70wt%, the inorganic binder is water glass, and the organic binder is modified starch;

Step 4, the agglomerate particles formed in step 3 are placed in an air-tight state at 500° C. and calcined for 2 hours, and then cooled to room temperature to obtain composite binding coal reduction pellets.

The raw materials used:

The first caking coal has a fixed carbon content of 60 wt.%, a volatile content of 32.6 wt.%, and an ash content of 1 wt.%;

The second caking coal has a fixed carbon content of 59 wt.%, a volatile content of 36.7 wt.%, and an ash content of 1.2 wt.%;

The third type of caking coal has a fixed carbon content of 55wt.%, a volatile content of 38.2wt.%, and an ash content of 0.4wt.%.

200 kg of silica (99.5% SiO ₂ , 0.05% Al ₂ O ₃ , 0.03% Fe ₂ O ₃ , 0.05% CaO) was crushed into blocks with a particle size of 20-100 mm, and after cleaning and screening, it was evenly mixed with 103 kg of the above-mentioned composite carbonaceous reducing agent, and added into a submerged arc furnace for smelting (the smelting temperature was 2200 degrees Celsius). The furnace condition was stable and smelting was carried out. After smelting, 85.4 kg of industrial silicon products were obtained, 12390 Kw.h. The components of the industrial silicon product were Si>99.5Wt.%, Fe≤0.19Wt.%, Al≤0.09Wt.%, and Ca≤0.05Wt.%.

Example 2

The industrial silicon composite binding coal reduction pellets have a fixed carbon content of 79.6wt.%, a volatile content of 17wt.%, an ash content of 3.4wt.%, a bonding index G of 80, and a pellet cold strength of 12MPa.

The method for preparing composite binding coal reduction pellets for industrial silicon comprises the following steps:

Step 1, firstly, three kinds of coal with different caking indexes are crushed into particles of 15 mm, 0.3 mm, and 0.068 mm in the order of caking index from small to large, wherein the caking index of the first caking coal is 0, the caking index of the second caking coal is 85; the caking index of the third caking coal is 96, and the mass ratio of the first caking coal, the second caking coal, and the third caking coal is 30:50:20wt.%;

Step 2, adding the first bonding coal, 12wt.% of water, and 1wt.% of a binder to the second bonding coal, stirring until obvious agglomeration, and coating the first bonding coal to form agglomerate particles with a diameter of 20 mm, wherein the binder is an organic-inorganic composite binder, in which the inorganic binder accounts for 20wt% and the organic binder accounts for 80wt%, the inorganic binder is water glass, and the organic binder is modified starch;

Step 3, adding the agglomerate particles in step 2, 12wt.% of water, and 1wt.% of a binder to the third type of caking coal, stirring until obvious agglomeration, and coating the agglomerate particles in step 2 to form agglomerate particles with a diameter of 50 mm, wherein the binder is an organic-inorganic composite binder, in which the inorganic binder accounts for 20wt% and the organic binder accounts for 80wt%, the inorganic binder is water glass, and the organic binder is modified starch;

Step 4, the agglomerate particles formed in step 3 are placed in an air-tight state at a temperature of 550° C. and roasted for 2 hours, and then cooled to room temperature to obtain composite binding coal reduction pellets.

The first caking coal has a fixed carbon content of 63wt.%, a volatile content of 33.6wt.%, and an ash content of 0.6wt.%;

The second caking coal has a fixed carbon content of 58 wt.%, a volatile content of 34.5 wt.%, and an ash content of 1.2 wt.%;

The third type of caking coal has a fixed carbon content of 56 wt.%, a volatile content of 36.2 wt.%, and an ash content of 1.6 wt.%.

200kg of silica (99.5% _SiO2 , 0.05% _Al2O3 , 0.03% _Fe2O3 , _0.05 % CaO) was crushed into blocks with a particle size of _20-100mm , and after cleaning and screening, it was evenly mixed with 100kg of the above-mentioned composite carbonaceous reducing agent, and added into a submerged arc furnace for smelting (the smelting temperature was 2200 degrees Celsius). The furnace condition was stable and smelting was carried out. After smelting, 91.3kg of industrial silicon products were obtained, 12290Kw.h, and the components of the industrial silicon product were Si>99.6Wt.%, Fe≤0.19Wt.%, Al≤0.09Wt.%, and Ca≤0.05Wt.%.

Example 3

The industrial silicon composite binding coal reduction pellets have a fixed carbon content of 81.5wt.%, a volatile content of 15wt.%, an ash content of 3.5wt.%, a bonding index G of 60, and a pellet cold strength of 9MPa.

The method for preparing composite binding coal reduction pellets for industrial silicon comprises the following steps:

Step 1, firstly, three kinds of coal with different caking indexes are crushed into particles of 5 mm, 0.4 mm, and 0.068 mm in the order of caking index from small to large, wherein the caking index of the first caking coal is 0, the caking index of the second caking coal is 65; the caking index of the third caking coal is 91, and the mass ratio of the first caking coal, the second caking coal, and the third caking coal is 30:50:20wt.%;

Step 2, adding the first bonding coal, 12wt.% of water, and 1wt.% of a binder to the second bonding coal, stirring until obvious agglomeration, and coating the first bonding coal to form agglomerate particles with a diameter of 24 mm, wherein the binder is an organic-inorganic composite binder, in which the inorganic binder accounts for 25wt% and the organic binder accounts for 75wt%, the inorganic binder is water glass, and the organic binder is modified starch;

Step 3, adding the agglomerate particles in step 2, 12wt.% of water, and 1wt.% of a binder to the third type of binding coal, stirring until obvious agglomeration occurs, and coating the agglomerate particles in step 2 to form agglomerate particles with a diameter of 35 mm, wherein the binder is an organic-inorganic composite binder, in which the inorganic binder accounts for 25wt% and the organic binder accounts for 75wt%, the inorganic binder is water glass, and the organic binder is modified starch;

Step 4, the agglomerate particles formed in step 3 are placed in an air-tight state at 600° C. and roasted for 3 hours, and then cooled to room temperature to obtain composite binding coal reduction pellets.

The first caking coal has a fixed carbon content of 59 wt.%, a volatile content of 31.6 wt.%, and an ash content of 0.7 wt.%;

The second caking coal has a fixed carbon content of 65wt.%, a volatile content of 33.5wt.%, and an ash content of 1.2wt.%;

The third type of caking coal has a fixed carbon content of 56 wt.%, a volatile content of 37.2 wt.%, and an ash content of 1.6 wt.%.

200kg of silica (99.5% _SiO2 , 0.05% _Al2O3 , 0.03% _Fe2O3 , _0.05 % CaO) was crushed into blocks with a particle size of _20-100mm , and after cleaning and screening, it was evenly mixed with 98kg of the above-mentioned composite carbonaceous reducing agent, and added into a submerged arc furnace for smelting (the smelting temperature was 2200 degrees Celsius). The furnace condition was basically stable. After smelting, 79.3kg of industrial silicon products were obtained, 12990Kw.h. The components of the industrial silicon product were Si>99.4Wt.%, Fe≤0.19Wt.%, Al≤0.09Wt.%, and Ca≤0.05Wt.%.

Example 4

The industrial silicon composite bonding coal reduction pellets have a fixed carbon content of 78wt.%, a volatile content of 19wt.%, an ash content of 3wt.%, a bonding index G of 75, and a pellet cold strength of 11MPa.

The method for preparing composite binding coal reduction pellets for industrial silicon comprises the following steps:

Step 1, firstly, three kinds of coal with different caking indexes are crushed into particles of 15 mm, 0.35 mm, and 0.065 mm in the order of caking index from small to large, wherein the caking index of the first caking coal is 0, the caking index of the second caking coal is 85; the caking index of the third caking coal is 94, and the mass ratio of the first caking coal, the second caking coal, and the third caking coal is 20:40:40wt.%;

Step 2, adding the first bonding coal, 10wt.% of water, and 1wt.% of a binder to the second bonding coal, stirring until obvious agglomeration, and coating the first bonding coal to form agglomerate particles with a diameter of 30 mm, wherein the binder is an organic-inorganic composite binder, in which the inorganic binder accounts for 40wt% and the organic binder accounts for 60wt%, the inorganic binder is water glass, and the organic binder is modified starch;

Step 3, adding the agglomerate particles in step 2, 10wt.% of water, and 1wt.% of a binder to the third type of binding coal, stirring until obvious agglomeration occurs, and coating the agglomerate particles in step 2 to form agglomerate particles with a diameter of 55 mm, wherein the binder is an organic-inorganic composite binder, in which the inorganic binder accounts for 40wt% and the organic binder accounts for 60wt%, the inorganic binder is water glass, and the organic binder is modified starch;

Step 4, the agglomerate particles formed in step 3 are placed in an air-tight state at a temperature of 550° C. and roasted for 3 hours, and then cooled to room temperature to obtain composite binding coal reduction pellets.

The first caking coal has a fixed carbon content of 55 wt.%, a volatile content of 34.6 wt.%, and an ash content of 0.5 wt.%;

The second caking coal has a fixed carbon content of 60wt.%, a volatile content of 36.5wt.%, and an ash content of 1.4wt.%;

The third type of caking coal has a fixed carbon content of 61 wt.%, a volatile content of 33.2 wt.%, and an ash content of 0.6 wt.%.

200kg of silica (99.5% _SiO2 , 0.05% _Al2O3 , 0.03% _Fe2O3 , _0.05 % CaO) was crushed into blocks with a particle size of _20-100mm , and after cleaning and screening, it was evenly mixed with 102kg of the above-mentioned composite carbonaceous reducing agent, and added into a submerged arc furnace for smelting (the smelting temperature was 2200 degrees Celsius). The furnace condition was stable and smelting was carried out. After smelting, 87.3kg of industrial silicon products were obtained, 11890Kw.h, and the components of the industrial silicon product were Si>99.6Wt.%, Fe≤0.19Wt.%, Al≤0.09Wt.%, and Ca≤0.05Wt.%.

Example 5

The industrial silicon composite binding coal reduction pellets have a fixed carbon content of 80.8wt.%, a volatile content of 18wt.%, an ash content of 1.2wt.%, a bonding index G of 65, and a pellet cold strength of 8MPa.

The method for preparing composite binding coal reduction pellets for industrial silicon comprises the following steps:

Step 1, firstly, three kinds of coal with different caking indexes are crushed into particles of 18 mm, 0.4 mm, and 0.065 mm in the order of caking index from small to large, wherein the caking index of the first caking coal is 0, the caking index of the second caking coal is 80; the caking index of the third caking coal is 89, and the mass ratio of the first caking coal, the second caking coal, and the third caking coal is 30:30:40wt.%;

Step 2, adding the first bonding coal, 11wt.% of water, and 1wt.% of a binder to the second bonding coal, stirring until obvious agglomeration, and coating the first bonding coal to form agglomerate particles with a diameter of 22 mm, wherein the binder is an organic-inorganic composite binder, in which the inorganic binder accounts for 20wt% and the organic binder accounts for 80wt%, the inorganic binder is water glass, and the organic binder is modified starch;

Step 3, adding the agglomerate particles in step 2, 11wt.% of water, and 1wt.% of a binder to the third type of binding coal, stirring until obvious agglomeration occurs, and coating the agglomerate particles in step 2 to form agglomerate particles with a diameter of 58 mm, wherein the binder is an organic-inorganic composite binder, in which the inorganic binder accounts for 20wt% and the organic binder accounts for 80wt%, the inorganic binder is water glass, and the organic binder is modified starch;

Step 4, the agglomerate particles formed in step 3 are placed in an air-tight state at 600° C. and roasted for 2 hours, and then cooled to room temperature to obtain composite binding coal reduction pellets.

The first caking coal has a fixed carbon content of 58 wt.%, a volatile content of 36.2 wt.%, and an ash content of 0.6 wt.%;

The second caking coal has a fixed carbon content of 60wt.%, a volatile content of 36.5wt.%, and an ash content of 0.3wt.%;

The third type of caking coal has a fixed carbon content of 65wt.%, a volatile content of 33.3wt.%, and an ash content of 0.2wt.%.

200 kg of silica (99.5% SiO ₂ , 0.05% Al ₂ O ₃ , 0.03% Fe ₂ O ₃ , 0.05% CaO) was crushed into blocks with a particle size of 20-100 mm, and after cleaning and screening, it was evenly mixed with 99 kg of the above-mentioned composite carbonaceous reducing agent, and added into a submerged arc furnace for smelting (the smelting temperature was 2200 degrees Celsius). The furnace condition was stable, and 80.3 kg of industrial silicon products were obtained after smelting, consuming 12590 Kw.h of electricity. The components of the industrial silicon product were Si>99.5Wt.%, Fe≤0.19Wt.%, Al≤0.09Wt.%, and Ca≤0.05Wt.%.

Example 6

The industrial silicon composite bonding coal reduction pellets have a fixed carbon content of 78.9wt.%, a volatile content of 17.4wt.%, an ash content of 3.7wt.%, a bonding index G of 77, and a pellet cold strength of 11MPa.

The method for preparing composite binding coal reduction pellets for industrial silicon comprises the following steps:

Step 1, firstly, three kinds of coal with different caking indexes are crushed into particles of 8 mm, 0.45 mm, and 0.075 mm in the order of caking index from small to large, wherein the caking index of the first caking coal is 0, the caking index of the second caking coal is 78; the caking index of the third caking coal is 96, and the mass ratio of the first caking coal, the second caking coal, and the third caking coal is 25:30:45wt.%;

Step 2, adding the first bonding coal, 10wt.% of water, and 1wt.% of a binder to the second bonding coal, stirring until obvious agglomeration, and coating the first bonding coal into agglomerate particles with a diameter of 22 mm, wherein the binder is an organic-inorganic composite binder, in which the inorganic binder accounts for 30wt% and the organic binder accounts for 70wt%, the inorganic binder is water glass, and the organic binder is modified starch;

Step 3, adding the agglomerate particles in step 2, 10wt.% of water, and 1wt.% of a binder to the third type of binding coal, stirring until obvious agglomeration occurs, and coating the agglomerate particles in step 2 to form agglomerate particles with a diameter of 60 mm, wherein the binder is an organic-inorganic composite binder, in which the inorganic binder accounts for 30wt% and the organic binder accounts for 70wt%, the inorganic binder is water glass, and the organic binder is modified starch;

Step 4, the agglomerate particles formed in step 3 are placed in an air-tight state at 500° C. and roasted for 3 hours, and then cooled to room temperature to obtain composite binding coal reduction pellets.

The first caking coal has a fixed carbon content of 64wt.%, a volatile content of 31.2wt.%, and an ash content of 0.9wt.%;

The second caking coal has a fixed carbon content of 57 wt.%, a volatile content of 34.5 wt.%, and an ash content of 1.2 wt.%;

The third type of caking coal has a fixed carbon content of 59 wt.%, a volatile content of 35.3 wt.%, and an ash content of 1.6 wt.%.

200 kg of silica (99.5% SiO ₂ , 0.05% Al ₂ O ₃ , 0.03% Fe ₂ O ₃ , 0.05% CaO) was crushed into blocks with a particle size of 20-100 mm, and after cleaning and screening, it was evenly mixed with 101 kg of the above-mentioned composite carbonaceous reducing agent, and added into a submerged arc furnace for smelting (the smelting temperature was 2200 degrees Celsius). The furnace condition was stable, and 91.1 kg of industrial silicon products were obtained after smelting. The electricity consumption was 11990 Kw.h. The components of the industrial silicon product were Si>99.6Wt.%, Fe≤0.19Wt.%, Al≤0.09Wt.%, and Ca≤0.05Wt.%.

The specific embodiments of the present invention are described in detail above, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims (10)

1. A preparation method of composite caking coal reduction pellets for industrial silicon is characterized by comprising the following steps: coal is taken as a carbonaceous material, water and a binder are matched to be coated layer by layer to form a pellet; and the coating layer is more than or equal to 1;

The composite caking coal reduction pellet for the industrial silicon comprises a first caking coal and a coating layer; wherein the first caking coal has a larger particle size than the coating coal; the caking index of the coal used for the first caking coal is smaller than the caking index of the coal used for the coating layer; a first coating layer in the coating layers is coated on the first bonding coal; the preparation method comprises the following steps: coating a first coating layer on the first bonding coal, and coating an ith coating layer on the ith-1 coating layer if the number of the coating layers is more than 2; and i is more than or equal to 2.

2. The method for preparing the composite caking coal reduction pellets for industrial silicon according to claim 1, which is characterized by comprising the following steps: the coating layer is more than or equal to 2.

3. The method for preparing the composite caking coal reduction pellets for industrial silicon according to claim 2, which is characterized by comprising the following steps: the first coating layer is directly coated on the first bonding coal, and the second coating layer is coated on the first coating layer; and by analogy, coating the ith coating layer on the ith-1 coating layer, wherein i is more than or equal to 2;

Wherein the particle size of the coal used for the i-1 th coating layer is larger than that of the coal used for the i-th coating layer; the caking index of the coal used for the i-1 th coating layer is smaller than that of the coal used for the i-th coating layer.

4. The method for preparing the composite caking coal reduction pellets for industrial silicon according to claim 3, wherein the method comprises the following steps: the particle size of the first kind of caking coal is 5-16mm; the bond index is 0; the particle size of the coal used for the first coating layer is 0.2-0.6mm, and the caking index is 50-85; the particle size of the coal used for the second coating layer is less than 0.1mm, and the caking index is more than 85.

5. The method for preparing the composite caking coal reduction pellets for industrial silicon according to claim 3, wherein the method comprises the following steps: when i=2, the composite caking coal reduction pellet for industrial silicon is prepared by the following steps:

step 1, firstly, crushing three kinds of coals with different caking indexes into particles with required granularity according to the order from small caking indexes to large caking indexes; wherein the first kind of caking coal has a grain size of 5-15.5mm, a caking index of 0, the second kind of caking coal has a grain size of 0.3-0.5mm, a caking index of 50-85, and the third kind of caking coal has a grain size of <0.1 mm, and a caking index of > 85;

Step 2, adding the first bonding coal into the second bonding coal, adding 8-12 wt wt.% of water, stirring 0.8-1.2wt.% of bonding agent until obvious caking, and cladding the first bonding coal into agglomerate particles with the diameter of 20-30 mm;

Step3, adding the agglomerate particles in the step 2 into the third caking coal, adding 8-12 wt wt.% of water, stirring 0.8-1.2wt.% of binder until obvious caking, and coating and forming the agglomerate particles in the step 2 into agglomerate particles with the diameter of 30-60 mm;

And 4, placing the agglomerate particles formed in the step 3 into an air-isolated low-temperature roasting furnace at 500-600 ℃ for 2-3 hours, and cooling the mixture to room temperature along with a furnace to obtain the composite caking coal reduction pellets.

6. The method for preparing the composite caking coal reduction pellet for industrial silicon according to claim 5, which is characterized in that:

the particle size of the first caking coal is 6-15mm, and the caking index is 0;

In the step 1, the mass ratio of the first bonding coal to the second bonding coal to the third bonding coal is 20-30:30-50:20-50.

7. The method for preparing the composite caking coal reduction pellet for industrial silicon according to claim 5, which is characterized in that:

The particle size of the first kind of caking coal is 14-15.5 mm; the bond index is 0; the particle size of the coal used for the first coating layer is 0.25-0.35 mm, and the bonding index is 85; the particle size of the coal used for the second coating layer is less than 0.1mm, and the bonding index is 96; the mass ratio of the first bonding coal to the first coating layer to the second coating layer is as follows: 30:50:20.

8. The method for preparing the composite caking coal reduction pellet for industrial silicon according to claim 5, which is characterized in that:

The particle size of the first kind of caking coal is 14-15.5 mm; the bond index is 0; the particle size of the coal used for the first coating layer is 0.25-0.35 mm, and the bonding index is 85; the particle size of the coal used for the second coating layer is less than 0.1mm, and the bonding index is 94; the mass ratio of the first bonding coal to the first coating layer to the second coating layer is as follows: 20:40:40.

9. The method for preparing the composite caking coal reduction pellet for industrial silicon according to claim 5, which is characterized in that:

the particle size of the first kind of caking coal is 8-10 mm; the bond index is 0; the particle size of the coal used for the first coating layer is 0.4-0.5mm, and the caking index is 78; the particle size of the coal used for the second coating layer is less than 0.1mm, and the bonding index is 96; the mass ratio of the first bonding coal to the first coating layer to the second coating layer is as follows: 25:30:45.

10. The method for preparing the composite caking coal reduction pellet for industrial silicon according to claim 5, which is characterized in that:

The fixed carbon content of the coal with three different caking indexes in the step 1 is 55 to 65wt.%;

The adhesive in the step 2 and the step 3 is an organic-inorganic composite adhesive, wherein the inorganic adhesive accounts for 20-40 wt% of the composite adhesive, and the organic adhesive accounts for 60-80 wt%; the inorganic binder is water glass; the organic binder is modified starch.