A method for preparing industrial silicon composite reducing agent by upgrading non-caking coal with biomass pyrolysis products

Abstract

The present application relates to a kind of industrial silicon composite reducing agent preparation method using biomass pyrolysis product upgrading non-sticky coal, belong to the technical field of composite reducing agent for industrial silicon smelting.The biomass powder is placed in pyrolysis gas atmosphere furnace and is quickly pyrolyzed to obtain biochar and pyrolysis gas, and the pyrolysis gas is quickly condensed to obtain bio-oil;Non-sticky coal powder, biochar and micro-silicon powder are mixed uniformly to obtain mixed powder, bio-oil is added to the mixed powder and is ground to material bonding into block to obtain mixed sample;Mixed sample is pressed into cylindrical pellet embryo;Cylindrical pellet embryo is placed in argon environment and is microwave calcined, and is cooled to room temperature with furnace to obtain industrial silicon composite reducing agent.The obtained composite reducing agent pellet for silicon smelting has a strength of 9-14 MPa, a bonding index of 52-78, a fixed carbon content of 75-90%, and a calorific value of 7000-8500 cal / g, which meets the needs of industrial silicon production.

Description

Technical Field

[0001] This invention relates to a method for preparing an industrial silicon composite reducing agent using biomass pyrolysis products to upgrade non-sticky coal, belonging to the technical field of composite reducing agents for industrial silicon smelting. Background Technology

[0002] As a raw material for the photovoltaic industry, industrial silicon demand has been increasing in recent years due to the continuous rise in photovoltaic installations. Currently, the smelting of industrial silicon both domestically and internationally mainly involves feeding silica and carbonaceous reducing agents into an electric arc furnace, where they undergo a carbothermic reduction reaction followed by refining. The carbonaceous reducing agents used in smelting are primarily composed of petroleum coke, charcoal, semi-coke, and coal in certain proportions. Coal constitutes the majority of the mixed feed, and the coal used is mainly caking coal with suitable resistivity and caking index that is not easily graphitized. With the continuous depletion of high-quality caking coal resources, the cost of using high-quality coal is gradually increasing, thereby increasing the production cost of industrial silicon and affecting the efficiency of silicon smelting. Therefore, in order to reduce the excessively high production cost of industrial silicon caused by the use of high-rank coal, research on the high-value utilization of low-rank coal (especially non-caking coal), which has extremely low industrial utilization rates, is very meaningful and aligns with the national requirements for optimizing the energy structure. Summary of the Invention

[0003] To address the energy imbalance caused by the low industrial utilization rate of low-rank non-caking coal and the environmental pollution caused by improper disposal of crop straw, this invention proposes a method for preparing industrial silicon composite reducing agents using biomass pyrolysis products to upgrade non-caking coal. The method involves rapidly pyrolyzing biomass powder to obtain biochar and bio-oil. The biochar, bio-oil, non-caking coal powder, and microsilica powder are then mixed. The rich porous structure and strong viscosity of the biochar and bio-oil ensure closer contact between the materials. Microwave heating accelerates the migration rate of alkali metals in the biochar, resulting in a more uniform distribution of alkali metals in the reducing agent, improving the reactivity of the pellets, and thus enhancing the performance of the composite reducing agent pellets. The resulting composite pellets have a strength of 9–14 MPa, a bonding index of 52–78, a fixed carbon content of 75–90%, and a calorific value of 7000–8500 kcal / g, meeting the requirements for preparing silicon smelting composite reducing agent pellets and suitable for industrial silicon production.

[0004] A method for preparing industrial silicon composite reducing agent using biomass pyrolysis products to upgrade non-caking coal, the specific steps of which are as follows:

[0005] (1) Vacuum-dried non-sticky coal and vacuum-dried biomass were pulverized and ground to obtain non-sticky coal powder and biomass powder, respectively.

[0006] (2) Biomass powder is placed in a pyrolysis atmosphere furnace for rapid pyrolysis to obtain biochar and pyrolysis gas. The pyrolysis gas is then rapidly condensed to obtain bio-oil.

[0007] (3) Non-sticky coal powder, biochar and microsilica powder are mixed evenly to obtain a mixed powder. Bio-oil is added to the mixed powder and it is ground until the material is bound into blocks to obtain a mixed sample.

[0008] (4) The mixture is pressed into a cylindrical pellet embryo.

[0009] (5) The cylindrical pellets were microwave-roasted in an argon atmosphere and then cooled to room temperature in the furnace to obtain an industrial silicon composite reducing agent.

[0010] The non-caking coal in step (1) has a fixed carbon content of 50-65 wt%, a calorific value of 6000-6500 kcal / g, and a caking index of 0-8.

[0011] The biomass in step (1) is crop straw; preferably, the crop straw is one or more of corn straw, wheat straw and rice straw.

[0012] The rapid pyrolysis in step (2) has a heating rate of 800-1300℃ / s, a pyrolysis temperature of 500-750℃, and a pyrolysis time of 1-2.5s.

[0013] The biochar in step (2) has a fixed carbon content of 40-55 wt%, a calorific value of 4000-5000 kcal / g, and a total alkali metal content of 5-10 wt%; the bio-oil has a calorific value of 3500-4500 kcal / g and a viscosity of 30-100 mPa·s.

[0014] The SiO2 content in the microsilica powder of step (3) is 84.7–87.4 wt.%.

[0015] By mass percentage, the mixed sample in step (3) contains 65-80% non-caking coal, 5-20% biochar, 3-8% microsilica powder, and 7-12% bio-oil.

[0016] The pressing pressure in step (4) is 10-20 MPa, the diameter of the cylindrical blank is 60-65 mm, and the height is 60-65 mm.

[0017] In step (5), the microwave roasting temperature is 400-600℃, the time is 1.5-3.5h, and the microwave power is 1-5kW.

[0018] The industrial silicon composite reducing agent pellets of this invention have a strength of 9-14 MPa, a bonding index of 52-78, a fixed carbon content of 75-90%, and a calorific value of 7000-8500 kcal / g.

[0019] The beneficial effects of this invention are:

[0020] (1) This invention utilizes biochar and bio-oil produced by the rapid pyrolysis of waste crop straw to prepare a composite reducing agent for silicon smelting. Biochar has a rich porous structure and alkali metals, which can provide a larger contact area and active sites for the preparation of composite pellets. At the same time, bio-oil has a strong viscosity and a high calorific value, which can be used as a binder for the preparation of pellets and to improve the calorific value of the composite reducing agent, thus realizing the clean and efficient resource utilization of waste crop straw.

[0021] (2) As a by-product of silicon smelting, microsilica powder has excellent properties such as high thermal conductivity, stable chemical properties and high hardness. In the preparation of composite reducing agent pellets, an appropriate amount of industrial silicon by-product microsilica powder is added, which provides some SiO2 components for the carbothermic reduction system and enhances the strength and wear resistance of the composite reducing agent pellets. At the same time, because microsilica powder has a high thermal conductivity, it is a high insulating material, which increases the specific resistance of the reducing agent pellets, thereby reducing carbon loss during smelting, improving the utilization rate of fixed carbon in the pellets and smelting efficiency, and achieving the purpose of recycling by-products.

[0022] (3) The composite reducing agent pellets prepared by the present invention have a strength of 9-14 MPa, a bonding index of 52-78, a fixed carbon content of 75-90%, and a calorific value of 7000-8500 kcal / g, which meet the preparation requirements of composite reducing agent pellets for industrial silicon smelting.

[0023] (4) The process of the present invention is clean and efficient, environmentally friendly, with low investment cost and energy consumption, and strong production safety. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0025] Example 1: A method for preparing industrial silicon composite reducing agent using biomass pyrolysis products to upgrade non-caking coal, the specific steps of which are as follows:

[0026] (1) Vacuum-dried non-sticky coal and vacuum-dried biomass (corn stalks) were pulverized and ground to a particle size of less than 0.15 mm to obtain non-sticky coal powder and biomass powder respectively;

[0027] (2) The biomass powder was placed in a pyrolysis atmosphere furnace and heated to 500°C at a heating rate of 1000°C / s and rapidly pyrolyzed and gasified for 2s to obtain biochar and pyrolysis gas. The pyrolysis gas was rapidly condensed to obtain bio-oil. In this embodiment, the fixed carbon content of the biochar was 40wt%, the calorific value was 4200 kcal / g, and the total alkali metal (K and Na) content was 8wt%. The calorific value of the bio-oil was 3550 kcal / g, and the viscosity was 50 mPa·s.

[0028] (3) Non-sticky coal powder, biochar and microsilica powder are mixed evenly to obtain a mixed powder. Bio-oil is added to the mixed powder and the mixture is ground until the material agglomerates into lumps to obtain a mixed sample. The non-sticky coal has a fixed carbon content of 55wt%, a calorific value of 6100 kcal / g, and a binding index of 2. The microsilica powder has a SiO2 content of 85.1wt.%. By mass percentage, the mixed sample contains 76% non-sticky coal, 8% biochar, 6% microsilica powder, and 10% bio-oil.

[0029] (4) The mixed sample was pressed under a pressure of 15MPa to obtain a cylindrical pellet embryo with a diameter of 60mm and a height of 63mm;

[0030] (5) The cylindrical pellet embryos were placed in a microwave tube furnace and argon gas was introduced at a flow rate of 1.5 L / min. The pellets were microwave-calcined in an argon atmosphere for 2.5 h and then cooled to room temperature with the furnace to obtain an industrial silicon composite reducing agent. The microwave calcination temperature was 400 °C and the microwave power was 1 kW.

[0031] In this embodiment, the industrial silicon composite reducing agent pellets have a strength of 9 MPa, a bonding index of 52, a fixed carbon content of 80%, and a calorific value of 7500 kcal / g.

[0032] Example 2: A method for preparing industrial silicon composite reducing agent using biomass pyrolysis products to upgrade non-caking coal, the specific steps of which are as follows:

[0033] (1) Vacuum-dried non-sticky coal and vacuum-dried biomass (wheat straw) are pulverized and ground to a particle size of less than 0.15 mm to obtain non-sticky coal powder and biomass powder respectively;

[0034] (2) The biomass powder was placed in a pyrolysis atmosphere furnace and heated to 700°C at a heating rate of 900°C / s and rapidly pyrolyzed and gasified for 1.5s to obtain biochar and pyrolysis gas. The pyrolysis gas was rapidly condensed to obtain bio-oil. In this embodiment, the fixed carbon content of the biochar was 50wt%, the calorific value was 5000 kcal / g, and the total content of alkali metals (K and Na) was 6wt%. The calorific value of the bio-oil was 4500 kcal / g, and the viscosity was 80 mPa·s.

[0035] (3) Non-sticky coal powder, biochar and microsilica powder are mixed evenly to obtain a mixed powder. Bio-oil is added to the mixed powder and the mixture is ground until the material agglomerates into lumps to obtain a mixed sample. The non-sticky coal has a fixed carbon content of 58wt%, a calorific value of 6500 kcal / g, and a binding index of 0. The microsilica powder has a SiO2 content of 86.8wt.%. By mass percentage, the mixed sample contains 70% non-sticky coal, 15% biochar, 3% microsilica powder, and 12% bio-oil.

[0036] (4) The mixed sample was pressed under 18MPa pressure to obtain a cylindrical pellet embryo with a diameter of 62mm and a height of 64mm;

[0037] (5) The cylindrical pellet embryos were placed in a microwave tube furnace and argon gas was introduced at a flow rate of 1L / min. The pellets were microwave-calcined in an argon atmosphere for 1.8h and then cooled to room temperature with the furnace to obtain an industrial silicon composite reducing agent. The microwave calcination temperature was 450℃ and the microwave power was 3kW.

[0038] In this embodiment, the industrial silicon composite reducing agent pellets have a strength of 11 MPa, a bonding index of 63, a fixed carbon content of 78%, and a calorific value of 7800 kcal / g.

[0039] Example 3: A method for preparing industrial silicon composite reducing agent using biomass pyrolysis products to upgrade non-caking coal, the specific steps of which are as follows:

[0040] (1) Vacuum-dried non-sticky coal and vacuum-dried biomass (rice straw) are pulverized and ground to a particle size of less than 0.15 mm to obtain non-sticky coal powder and biomass powder respectively;

[0041] (2) The biomass powder was placed in a pyrolysis atmosphere furnace and heated to 600°C at a heating rate of 1200°C / s and rapidly pyrolyzed and gasified for 2.3s to obtain biochar and pyrolysis gas. The pyrolysis gas was rapidly condensed to obtain bio-oil. In this embodiment, the fixed carbon content of the biochar was 45wt%, the calorific value was 4500 kcal / g, and the total content of alkali metals (K and Na) was 10wt%. The calorific value of the bio-oil was 4000 kcal / g, and the viscosity was 30 mPa·s.

[0042] (3) Non-sticky coal powder, biochar and microsilica powder are mixed evenly to obtain a mixed powder. Bio-oil is added to the mixed powder and the mixture is ground until the material agglomerates into blocks to obtain a mixed sample. The non-sticky coal has a fixed carbon content of 65wt%, a calorific value of 6350 kcal / g, and a binding index of 8. The microsilica powder has a SiO2 content of 84.7wt.%. By mass percentage, the mixed sample contains 80% non-sticky coal, 10% biochar, 3% microsilica powder, and 7% bio-oil.

[0043] (4) The mixed sample was pressed under 10MPa pressure to obtain a cylindrical pellet embryo with a diameter of 63mm and a height of 62mm;

[0044] (5) The cylindrical pellet embryos were placed in a microwave tube furnace and argon gas was introduced at a flow rate of 1.2 L / min. The pellets were microwave-calcined in an argon atmosphere for 2 hours and then cooled to room temperature with the furnace to obtain an industrial silicon composite reducing agent. The microwave calcination temperature was 600℃ and the microwave power was 5kW.

[0045] In this embodiment, the industrial silicon composite reducing agent pellets have a strength of 10 MPa, a bonding index of 57, a fixed carbon content of 75%, and a calorific value of 7000 kcal / g.

[0046] Example 4: A method for preparing industrial silicon composite reducing agent using biomass pyrolysis products to upgrade non-caking coal, the specific steps of which are as follows:

[0047] (1) Vacuum-dried non-sticky coal and vacuum-dried biomass (wheat straw and rice straw) are crushed and ground to a particle size of less than 0.15 mm to obtain non-sticky coal powder and biomass powder respectively;

[0048] (2) The biomass powder was placed in a pyrolysis atmosphere furnace and heated to 650°C at a heating rate of 1300°C / s and rapidly pyrolyzed and gasified for 1s to obtain biochar and pyrolysis gas. The pyrolysis gas was rapidly condensed to obtain bio-oil. In this embodiment, the fixed carbon content of the biochar was 55wt%, the calorific value was 4000 kcal / g, and the total alkali metal (K and Na) content was 5wt%. The calorific value of the bio-oil was 3500 kcal / g, and the viscosity was 70 mPa·s.

[0049] (3) Non-sticky coal powder, biochar and microsilica powder are mixed evenly to obtain a mixed powder. Bio-oil is added to the mixed powder and the mixture is ground until the material agglomerates into lumps to obtain a mixed sample. The non-sticky coal has a fixed carbon content of 60wt%, a calorific value of 6000 kcal / g, and a binding index of 5. The microsilica powder has a SiO2 content of 87.4wt.%. By mass percentage, the mixed sample contains 65% non-sticky coal, 20% biochar, 8% microsilica powder, and 7% bio-oil.

[0050] (4) The mixed sample was pressed under 12MPa pressure to obtain a cylindrical pellet embryo with a diameter of 61mm and a height of 60mm;

[0051] (5) The cylindrical pellet embryos were placed in a microwave tube furnace and argon gas was introduced at a flow rate of 1.8 L / min. The pellets were microwave-calcined in an argon atmosphere for 1.5 h and then cooled to room temperature with the furnace to obtain an industrial silicon composite reducing agent. The microwave calcination temperature was 550 °C and the microwave power was 2 kW.

[0052] In this embodiment, the industrial silicon composite reducing agent pellets have a strength of 14 MPa, a bonding index of 78, a fixed carbon content of 85%, and a calorific value of 8000 kcal / g.

[0053] Example 5: A method for preparing industrial silicon composite reducing agent using biomass pyrolysis products to upgrade non-caking coal, the specific steps of which are as follows:

[0054] (1) Vacuum-dried non-sticky coal and vacuum-dried biomass (corn stalks and rice stalks) are crushed and ground to a particle size of less than 0.15 mm to obtain non-sticky coal powder and biomass powder respectively;

[0055] (2) The biomass powder was placed in a pyrolysis atmosphere furnace and heated to 550°C at a heating rate of 1000°C / s and rapidly pyrolyzed and gasified for 1.8s to obtain biochar and pyrolysis gas. The pyrolysis gas was rapidly condensed to obtain bio-oil. In this embodiment, the fixed carbon content of the biochar was 43wt%, the calorific value was 4800 kcal / g, and the total content of alkali metals (K and Na) was 7wt%. The calorific value of the bio-oil was 4200 kcal / g, and the viscosity was 100 mPa·s.

[0056] (3) Non-sticky coal powder, biochar and microsilica powder are mixed evenly to obtain a mixed powder. Bio-oil is added to the mixed powder and the mixture is ground until the material agglomerates into lumps to obtain a mixed sample. The non-sticky coal has a fixed carbon content of 50wt%, a calorific value of 6200 kcal / g, and a binding index of 4. The microsilica powder has a SiO2 content of 85.8wt.%. By mass percentage, the mixed sample contains 80% non-sticky coal, 5% biochar, 4% microsilica powder, and 11% bio-oil.

[0057] (4) The mixed sample was pressed under a pressure of 16MPa to obtain a cylindrical pellet embryo with a diameter of 65mm and a height of 62mm;

[0058] (5) The cylindrical pellet embryos were placed in a microwave tube furnace and argon gas was introduced at a flow rate of 2L / min. The pellets were microwave-calcined in an argon atmosphere for 3 hours and then cooled to room temperature with the furnace to obtain an industrial silicon composite reducing agent. The microwave calcination temperature was 450℃ and the microwave power was 4kW.

[0059] In this embodiment, the industrial silicon composite reducing agent pellets have a strength of 12 MPa, a bonding index of 75, a fixed carbon content of 88%, and a calorific value of 8300 kcal / g.

[0060] Example 6: A method for preparing industrial silicon composite reducing agent using biomass pyrolysis products to upgrade non-caking coal, the specific steps of which are as follows:

[0061] (1) Vacuum-dried non-sticky coal and vacuum-dried biomass (corn stalks, wheat stalks and rice stalks) are crushed and ground to a particle size of less than 0.15 mm to obtain non-sticky coal powder and biomass powder respectively;

[0062] (2) The biomass powder was placed in a pyrolysis atmosphere furnace and heated to 750°C at a heating rate of 800°C / s and rapidly pyrolyzed and gasified for 2.5s to obtain biochar and pyrolysis gas. The pyrolysis gas was rapidly condensed to obtain bio-oil. In this embodiment, the fixed carbon content of the biochar was 52wt%, the calorific value was 4600 kcal / g, and the total content of alkali metals (K and Na) was 9wt%. The calorific value of the bio-oil was 3800 kcal / g, and the viscosity was 60 mPa·s.

[0063] (3) Non-sticky coal powder, biochar and microsilica powder are mixed evenly to obtain a mixed powder. Bio-oil is added to the mixed powder and the mixture is ground until the material agglomerates into blocks to obtain a mixed sample. The non-sticky coal has a fixed carbon content of 62wt%, a calorific value of 6180 kcal / g, and a binding index of 6. The microsilica powder has a SiO2 content of 86.2wt.%. By mass percentage, the mixed sample contains 75% non-sticky coal powder, 5% biochar, 8% microsilica powder, and 12% bio-oil.

[0064] (4) The mixed sample was pressed under a pressure of 20MPa to obtain a cylindrical pellet embryo with a diameter of 64mm and a height of 65mm;

[0065] (5) The cylindrical pellet embryos were placed in a microwave tube furnace and argon gas was introduced at a flow rate of 1.3 L / min. The pellets were microwave-calcined in an argon atmosphere for 3.5 h and then cooled to room temperature with the furnace to obtain an industrial silicon composite reducing agent. The microwave calcination temperature was 500 °C and the microwave power was 2 kW.

[0066] In this embodiment, the industrial silicon composite reducing agent pellets have a strength of 13 MPa, a bonding index of 60, a fixed carbon content of 90%, and a calorific value of 8500 kcal / g.

[0067] 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 method for preparing industrial silicon composite reducing agent using biomass pyrolysis products to upgrade non-caking coal, characterized in that, The specific steps are as follows: (1) Vacuum-dried non-sticky coal and vacuum-dried biomass are pulverized and ground to obtain non-sticky coal powder and biomass powder respectively; the non-sticky coal has a fixed carbon content of 50~65wt%, a calorific value of 6000~6500 kcal / g, and a caking index of 0~8. (2) The biomass powder is placed in a pyrolysis atmosphere furnace for rapid pyrolysis to obtain biochar and pyrolysis gas. The pyrolysis gas is rapidly condensed to obtain bio-oil. The heating rate of the rapid pyrolysis is 800~1300℃ / s, the pyrolysis temperature is 500~750℃, and the pyrolysis time is 1~2.5s. (3) Non-sticky coal powder, biochar and microsilica powder are mixed evenly to obtain a mixed powder. Bio-oil is added to the mixed powder and it is ground until the material agglomerates into lumps to obtain a mixed sample; the SiO2 content in the microsilica powder is 84.7~87.4 wt.%. (4) The mixed sample is pressed and molded to obtain a cylindrical blank; (5) The cylindrical blank is placed in an argon atmosphere for microwave calcination and then cooled to room temperature in the furnace to obtain an industrial silicon composite reducing agent; the microwave calcination temperature is 400~600℃, the time is 1.5~3.5h, and the microwave power is 1~5kW.

2. The method for preparing industrial silicon composite reducing agent using biomass pyrolysis products to upgrade non-caking coal according to claim 1, characterized in that: The biomass in step (1) is crop straw.

3. The method for preparing industrial silicon composite reducing agent using biomass pyrolysis products to upgrade non-caking coal according to claim 2, characterized in that: Crop straw can be one or more of corn straw, wheat straw, and rice straw.

4. The method for preparing industrial silicon composite reducing agent using biomass pyrolysis products to upgrade non-caking coal according to claim 1, characterized in that: Step (2) The fixed carbon content of biochar is 40~55wt%, the calorific value is 4000~5000 kcal / g, and the total alkali metal content is 5~10wt%; the calorific value of bio-oil is 3500~4500 kcal / g, and the viscosity is 30~100 mPa·s.

5. The method for preparing industrial silicon composite reducing agent using biomass pyrolysis products to upgrade non-caking coal according to claim 1, characterized in that: In terms of mass percentage, the mixed sample in step (3) contains 65-80% non-caking coal, 5-20% biochar, 3-8% microsilica powder, and 7-12% bio-oil.

6. The method for preparing industrial silicon composite reducing agent using biomass pyrolysis products to upgrade non-caking coal according to claim 1, characterized in that: Step (4) The pressing pressure is 10~20MPa, the diameter of the cylindrical blank is 60~65mm, and the height is 60~65mm.