Method for preparing biochar through self-propagating pyrolysis

Abstract

The invention discloses a method for preparing biochar by self-propagating pyrolysis, which comprises the following steps: selecting agricultural waste or wood waste with cellulose content of more than 30%, crushing until the particle size is 0.5-5mm, mixing the material and aluminum sulfate according to the ratio of 10-20% of the mass of the raw material, promoting low-temperature pyrolysis by an activator and increasing the specific surface area of the biochar, and preparing the biochar by self-propagating pyrolysis. A resistance heating device is adopted to heat materials to 300-400 DEG C within one minute, volatile components are rapidly released, microwave radiation with the frequency of 2.45 GHz and far infrared radiation are combined for heating, microwave radiation is used for internal heating, far infrared radiation is used for external heating, and the pyrolysis efficiency is improved. Therefore, the stability and the structural integrity of the biochar are kept through accurate cooling, the yield and the quality of the biochar are improved through the whole process, gas generated by pyrolysis is effectively recycled and utilized, energy waste and emission are reduced to the maximum extent, and the problems of uneven heating, long reaction time, low energy efficiency and the like in the prior art are fundamentally solved.

Description

Technical Field

[0001] The invention relates to the technical field of preparing biochar, and in particular to a method for preparing biochar by self-propagating pyrolysis. Background Art

[0002] Existing biochar preparation methods mainly rely on traditional pyrolysis technology, which usually involves heating organic materials to high temperatures for carbonization to produce biochar. Common pyrolysis processes include the use of electric heating, flame heating or gas heating. These technologies can adjust the properties of the product by controlling the heating rate, temperature and time, and have been widely used in the treatment of organic wastes such as agricultural waste, wood residues, and urban garbage. However, the traditional pyrolysis method has the problems of poor heating uniformity, long pyrolysis time and low energy utilization efficiency. In addition, the existing biochar preparation technology mostly relies on a single heating method, and lacks effective regulation means for the release of volatile components in the raw materials and temperature control during the pyrolysis process. Since the pyrolysis reaction in the traditional method is usually not uniform enough, it affects its application effect in agricultural improvement, environmental governance and other fields. In addition, the problem of gas recovery and utilization has not been fully solved, the energy loss is large, and the environmental pollution problem still exists. Overall, the existing technology cannot fully meet the needs of efficient, green and sustainable biochar production. Summary of the invention

[0003] The present invention aims to solve one of the technical problems in the related art at least to a certain extent.

[0004] To this end, the purpose of the present invention is to propose a method for preparing biochar by self-propagating pyrolysis. By introducing innovative methods such as microwave radiation and far-infrared radiation combined heating technology, airflow induction device and infrared light source irradiation, uniform heating and reaction optimization of the pyrolysis process are achieved, thereby improving the specific surface area and pore structure of the biochar. At the same time, a three-stage gas separation system is used to recover and reuse the pyrolysis gas, which effectively improves energy efficiency and reduces environmental pollution, solving the problems of uneven heating and energy waste in the prior art.

[0005] To achieve the above object, the present invention proposes a method for preparing biochar by self-propagating pyrolysis, comprising the following steps: S1. Select agricultural waste or wood waste with a cellulose content greater than 30% and crush it to a particle size of 0.5 to 5 mm; S2, mixing the material with aluminum sulfate in a ratio of 10% to 20% of the raw material mass, and the activator promotes low-temperature pyrolysis and increases the specific surface area of ​​the biochar; S3, using a resistance heating device to heat the material to 300°C to 400°C within 1 minute to quickly release the volatile components; S4. Use microwave radiation with a frequency of 2.45 GHz combined with far infrared radiation for heating, with microwave radiation for internal heating and far infrared radiation for external heating to improve pyrolysis efficiency; S5. Adjust the airflow through the airflow induction device to ensure that the pyrolysis reaction proceeds evenly; S6. In the later stage of pyrolysis, an infrared light source with a wavelength of 6µm to 8µm is introduced to irradiate the reaction zone to promote the synergistic effect of light and heat and enhance the carbonization effect; S7. After the pyrolysis is completed, the temperature is quickly cooled to room temperature, and the cooling rate does not exceed 5°C / min to maintain the stability of the biochar; S8. The gas generated by pyrolysis is recovered by a gas recovery device and processed by a three-stage separation system to separate the recyclable gas.

[0006] The method for preparing biochar by self-propagating pyrolysis of the present invention effectively optimizes the preparation process of biochar through self-propagating pyrolysis technology, combined with microwave radiation and far-infrared radiation heating, airflow regulation, activator use, photothermal synergy and precise cooling technology. First, suitable agricultural waste is selected and aluminum sulfate is used to promote pyrolysis reaction at low temperature and optimize the pore structure and specific surface area of ​​biochar. Then, microwave and far-infrared radiation are combined for heating to ensure uniform heating inside and on the surface of the material and improve pyrolysis efficiency. The airflow regulation device ensures uniform airflow distribution during the pyrolysis process to avoid uneven temperature. In addition, infrared light sources are used to promote photothermal synergy and improve carbonization degree. Finally, precise cooling is used to maintain the stability and structural integrity of biochar. The entire process improves the yield and quality of biochar, effectively recovers and utilizes gases generated by pyrolysis, minimizes energy waste and emissions, and fundamentally solves the problems of uneven heating, long reaction time, and low energy efficiency in the prior art.

[0007] In addition, the method for preparing biochar by self-propagating pyrolysis according to the present invention may also have the following additional technical features: Specifically, the agricultural waste is rice straw, corn straw, wood chips, bagasse, fruit peel or other cellulose-rich organic waste, and the moisture content of the raw material does not exceed 20% to ensure the effective release of volatile components during pyrolysis and the stability of the biochar product.

[0008] Specifically, the activator is aluminum sulfate, the mass of which is 10% to 15% of the raw material, and after the activator is added, the activator and the material are evenly mixed by mechanical stirring, and pyrolysis is carried out after standing for 15 to 30 minutes to enhance the effective release of pyrolysis gas during the reaction and optimize the pore structure of the biochar.

[0009] Specifically, the microwave radiation power is 700W to 900W, the frequency is 2.45GHz, the far-infrared radiation heating power is 300W to 500W, and the wavelength range is 6µm to 8µm, wherein the microwave radiation power is used to heat the inside of the material, and the far-infrared radiation power is used to heat the external surface of the material, and the two act simultaneously to accelerate the pyrolysis process of the material and improve the quality of the pyrolysis product.

[0010] Specifically, the airflow induction device includes multiple airflow regulation systems, which are divided into at least two levels. Each airflow regulation system can dynamically adjust the airflow direction, intensity and speed according to the different stages of the pyrolysis process, and optimize the reaction temperature distribution by changing the airflow distribution to make the pyrolysis reaction more uniform, thereby improving the yield and quality of biochar.

[0011] Specifically, the infrared light source is a far-infrared radiation heating device with a wavelength range of 6µm to 7.5µm and a radiation power of 200W to 400W. The irradiation time is 10 to 30 minutes after the pyrolysis reaction is completed, so as to promote the photothermal synergy in the reaction zone, further improve the carbonization degree and pore structure of the pyrolysis product, and thus improve the specific surface area and adsorption performance of biochar.

[0012] Specifically, the gas recovery device includes a three-stage gas separation system, namely, a high-temperature gas separation section, a volatile organic matter separation section and a combustible gas separation section. After each stage of gas separation, it undergoes condensation, adsorption and purification treatment. The recovered gas can be used for energy recovery or reuse in subsequent processes to maximize energy efficiency and reduce emissions.

[0013] Specifically, the cooling process adopts directional cooling technology, and through the synergistic effect of the cooling medium and the heat exchange device, the cooling rate is controlled to not exceed 5°C per minute, ensuring that the surface structure of the biochar is uniform and the pore structure is complete, avoiding cracking and incomplete carbonization caused by too rapid cooling, and improving the stability of the final product.

[0014] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which: Figure 1 A schematic diagram of the method for preparing biochar by self-propagating pyrolysis according to the present invention; Figure 2 This is a schematic diagram of experimental data for preparing biochar using rice straw as raw material in the present invention; Figure 3 This is a schematic diagram of experimental data for preparing biochar using sawdust as raw material in the present invention; Figure 4 This is a schematic diagram of experimental data for preparing biochar using bagasse as raw material in the present invention. DETAILED DESCRIPTION

[0016] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limitations of the present invention. On the contrary, embodiments of the present invention include all changes, modifications and equivalents that fall within the spirit and connotation of the appended claims.

[0017] The method for preparing biochar by self-propagating pyrolysis according to an embodiment of the present invention is described below with reference to the accompanying drawings.

[0018] like Figure 1-Figure 4 As shown, the method for preparing biochar by self-propagating pyrolysis according to the embodiment of the present invention may include the following steps: S1. Select agricultural waste or wood waste with a cellulose content greater than 30%, and crush it to a particle size of 0.5 to 5 mm.

[0019] It should be noted that, when selecting raw materials described in this embodiment, agricultural waste or wood waste with a cellulose content greater than 30%, such as rice straw, corn straw, bagasse, etc., is preferred. These raw materials are not only rich in degradable organic matter, but also have a lower moisture content that helps improve the pyrolysis efficiency. In order to ensure that the pyrolysis gas is fully released during the pyrolysis process and promote the uniform carbonization of biochar, the selected raw materials are crushed to a particle size of 0.5 to 5 mm to increase the reaction surface area and promote the increase in reaction rate.

[0020] S2. The material is mixed with aluminum sulfate in a ratio of 10% to 20% of the raw material mass, and the activator promotes low-temperature pyrolysis and increases the specific surface area of ​​the biochar.

[0021] It should be noted that in step S2 described in this embodiment, the selected agricultural waste or wood waste is uniformly mixed with aluminum sulfate at a ratio of 10% to 20% of the raw material mass. Aluminum sulfate as an activator can significantly reduce the starting temperature of the reaction during the pyrolysis process and promote the pyrolysis reaction at low temperatures. Through the action of the activator, not only the reaction efficiency of the pyrolysis process can be improved, but also the pore structure of the biochar can be optimized, the specific surface area can be increased, and it has higher adsorption performance and wider application potential.

[0022] S3, using a resistance heating device to heat the material to 300°C to 400°C within 1 minute to quickly release the volatile components.

[0023] It should be noted that in step S3 described in this embodiment, a high-efficiency resistance heating device is used to heat the mixed material to a temperature range of 300°C to 400°C within 1 minute through a rapid heating technology to ensure that the volatile organic matter in the material is quickly released. The heating process avoids energy waste and incomplete volatilization caused by too slow heating by accurately controlling the temperature change, thereby improving the pyrolysis efficiency and creating ideal initial conditions for the subsequent self-propagating pyrolysis reaction.

[0024] It should be understood that the temperature changes in the reactor can be monitored in real time by using a high-performance resistance heating device and a temperature control system, and adjusted according to the set temperature curve. The heating device can respond quickly to temperature changes and ensure that the material is heated to the required range of 300°C to 400°C within the specified time by adjusting the power output, thereby avoiding insufficient release of volatile components due to too low temperature or uneven pyrolysis due to too high temperature. This process can ensure uniform heating of the material, while improving the rapid release of volatile components and optimizing the overall effect of the pyrolysis reaction.

[0025] S4. Use microwave radiation with a frequency of 2.45 GHz combined with far infrared radiation for heating, with microwave radiation for internal heating and far infrared radiation for external heating to improve pyrolysis efficiency.

[0026] It should be noted that in step S4 described in this embodiment, microwave radiation with a frequency of 2.45 GHz and far-infrared radiation technology are combined to achieve the effect of synchronous internal and external heating. Microwave radiation can directly act on the inside of the material, and stimulate the rapid vibration of the material molecules in a very short time, thereby accelerating the internal heating of the material and the release of volatile components; while far-infrared radiation heats the external surface of the material to ensure that heat can be evenly transferred to the inside of the material, further improving the overall pyrolysis efficiency, shortening the reaction time, and ensuring the uniformity and efficiency of the pyrolysis reaction.

[0027] S5. The airflow is adjusted by an airflow induction device to ensure that the pyrolysis reaction proceeds evenly.

[0028] It should be noted that in step S5 described in this embodiment, the airflow in the reactor is precisely regulated by the airflow induction device, and the airflow direction, intensity and speed can be dynamically adjusted according to different stages of the pyrolysis process. This device promotes the uniform distribution of the pyrolysis reaction by guiding the airflow into different areas on the surface and inside of the material, ensuring that the temperature in the reaction zone remains consistent, thereby avoiding the decrease in reaction efficiency due to local overheating or uneven temperature, optimizing the pyrolysis process and improving the yield and quality of biochar.

[0029] S6. In the later stage of pyrolysis, an infrared light source with a wavelength of 6µm to 8µm is introduced to irradiate the reaction zone to promote the photothermal synergy and enhance the carbonization effect.

[0030] It should be noted that in step S6 described in this embodiment, an infrared light source with a wavelength of 6µm to 8µm is used to irradiate the pyrolysis reaction zone. The infrared light source can deeply act on the surface of the reaction material and synergize with the heat generated during the pyrolysis process. Through the photothermal synergistic effect, infrared radiation promotes further increase in temperature in the reaction zone, accelerates the carbonization process of organic matter, thereby improving the carbonization degree and pore structure of biochar, enhancing the stability and specific surface area of ​​biochar, and further improving its application performance in the fields of environmental governance and soil improvement.

[0031] S7. After the pyrolysis is completed, the temperature is quickly cooled to room temperature, and the cooling rate does not exceed 5°C / min to maintain the stability of the biochar.

[0032] It should be noted that in step S7 described in this embodiment, after the pyrolysis reaction is completed, the temperature of the material in the reactor is quickly reduced to room temperature by the synergistic effect of the cooling medium and the heat exchange device using a directional cooling technology to ensure a smooth cooling process. By strictly controlling the cooling rate to not exceed 5°C / min, the surface cracking or structural damage of the biochar caused by the sudden drop in temperature is avoided, the stability and uniform pore structure of the biochar are ensured, thereby improving its application performance in adsorption, soil improvement, etc.

[0033] S8. The gas generated by pyrolysis is recovered by a gas recovery device and processed by a three-stage separation system to separate the recyclable gas.

[0034] It should be noted that in step S8 described in this embodiment, the gas generated during the pyrolysis process is effectively captured by a gas recovery device and introduced into a three-stage gas separation system for treatment. The system is divided into a high-temperature gas separation section, a volatile organic compound separation section, and a combustible gas separation section. Through multiple means such as condensation, adsorption, and purification, different types of gases are separated and recovered to ensure that volatile organic compounds and combustible gases are effectively utilized, thereby improving energy recovery efficiency, reducing emissions, and maximizing resource utilization.

[0035] The following is a detailed data description combined with the experimental steps: Example 1 Biochar preparation using rice straw as raw material Experimental steps: Select rice straw containing more than 30% cellulose and crush it to a particle size of 2-4 mm to ensure uniform particles for effective pyrolysis.

[0036] Mix the crushed rice straw with aluminum sulfate at a ratio of 12% by weight of the raw materials and let it stand for 20 minutes to ensure uniform mixing.

[0037] Using a resistance heating device, the material is heated to 350°C within 1 minute, quickly releasing volatile components and increasing the pyrolysis reaction rate.

[0038] Combined heating is performed using a microwave radiation power of 750W, a frequency of 2.45GHz and a far-infrared radiation power of 400W, a wavelength of 6µm to 8µm. The microwave radiation heats the inside of the material, and the far-infrared radiation heats the outside. The heating is continued for 15 minutes.

[0039] The air flow rate was adjusted to 1.5 m / s using an air flow induction device, and the pyrolysis reaction was optimized through air flow in different areas on the surface and inside of the material to ensure uniform temperature distribution.

[0040] In the later stage of pyrolysis, an infrared light source with a wavelength of 6µm to 8µm was introduced to irradiate the reaction zone for 20 minutes to promote the photothermal synergy and further enhance the carbonization effect.

[0041] It should be understood that during the pyrolysis process, microwave radiation and far-infrared radiation act together on the substance. As the reaction proceeds, after the pyrolysis lasts for 15 minutes, an infrared light source with a wavelength of 6µm to 8µm is introduced and the reaction zone is continuously irradiated for 20 minutes to promote photothermal synergy and further improve the carbonization effect. At this time, the infrared light source works synergistically with microwave radiation and far-infrared radiation to accelerate the pyrolysis and carbonization process of the substance, thereby improving the quality and yield of the final product (such as hydrogen and carbon slag).

[0042] After the pyrolysis was completed, the material was immediately cooled to room temperature through a directional cooling system, and the cooling rate was controlled at 4 °C / min.

[0043] The gas produced during the pyrolysis process is recovered and processed by a three-stage gas separation system to separate the recyclable gas for energy recovery.

[0044] Comparison of experimental data (such as Figure 2 shown): The experimental results show that when microwave and far-infrared radiation are used for combined heating, the specific surface area of ​​biochar is significantly increased, 20% more than the traditional flame heating method, and the gas recovery rate is also improved. In addition, due to the use of more precise temperature control, the cooling rate is faster, avoiding excessive energy waste.

[0045] Example 2 Biochar production using wood chips Experimental steps: Select wood chips with a cellulose content greater than 30% and crush them to a particle size of 1-3mm to ensure uniform material.

[0046] Mix sawdust and aluminum sulfate in a ratio of 15% by weight of the raw materials and let it stand for 25 minutes to ensure that the activator penetrates into the material.

[0047] Using a resistance heating device, the material is heated to 375°C within 1 minute to quickly release the volatile components.

[0048] Combined heating was performed using a microwave radiation power of 850 W, a frequency of 2.45 GHz, and a far infrared radiation power of 450 W, with a wavelength range of 6 µm to 8 µm, for 15 minutes.

[0049] During the pyrolysis process, the air flow intensity was adjusted to 2 m / s through the air flow induction device to ensure uniform temperature in the reaction zone.

[0050] An infrared light source with a wavelength of 6µm to 7.5µm was introduced to irradiate the reaction zone for 25 minutes to promote the photothermal synergy in the reaction zone and further improve the carbonization effect.

[0051] After the pyrolysis was completed, the temperature was lowered to room temperature by a rapid cooling system at a cooling rate of 3 °C / min.

[0052] The gas produced by pyrolysis is recovered through a three-stage gas separation system, and the combustible gas and volatile organic matter are separated and reused.

[0053] Comparison of experimental data (such as Figure 3 shown): The experimental results show that the combined heating technology of microwave and far infrared radiation significantly increases the specific surface area and yield of biochar, which is about 15% higher than the traditional resistance heating method. At the same time, the cooling rate is also optimized, reducing the cracking and structural damage caused by too fast temperature drop.

[0054] Example 3 Biochar preparation using bagasse as raw material Experimental steps: Select sugarcane bagasse with a cellulose content greater than 35% and crush it to a particle size of 0.5-2mm.

[0055] Mix bagasse with aluminum sulfate at a ratio of 10% by weight of the raw materials and let it stand for 30 minutes to ensure complete penetration of the activator.

[0056] Using a resistance heating device, the material is heated to 300°C within 1 minute to release the volatile components.

[0057] The heating was conducted by using a microwave radiation power of 780W, a frequency of 2.45GHz and a far-infrared radiation power of 400W, and an infrared light source with a wavelength range of 6µm to 8µm, and the heating lasted for 18 minutes.

[0058] During the pyrolysis process, the airflow induction device adjusted the airflow intensity to 1.8 m / s to optimize the uniformity of the pyrolysis reaction.

[0059] In the later stage of pyrolysis, an infrared light source with a wavelength of 6.5µm to 7.5µm was used to irradiate the reaction zone for 22 minutes to further promote the photothermal synergy and increase the degree of carbonization.

[0060] After the pyrolysis was completed, the material was cooled to room temperature by a rapid cooling system at a cooling rate of 4.5 °C / min.

[0061] The gas produced by pyrolysis is recovered by a gas recovery device, and the recyclable gas is separated by a three-stage separation system.

[0062] Comparison of experimental data (such as Figure 4 shown): Experimental results: The specific surface area of ​​biochar heated by microwave and far-infrared radiation increased by about 14%, and the gas recovery rate was significantly improved. Combined with the photothermal synergistic effect, the carbonization degree of the product was enhanced and the stability of the biochar was improved.

[0063] It should be understood that through the above embodiments, it can be seen that the combined heating technology of microwave and far-infrared radiation significantly improves the specific surface area, yield and gas recovery rate of biochar, while optimizing the cooling process. Compared with traditional heating methods, the technical solution of the present invention has superiority in many aspects, especially in improving pyrolysis efficiency and resource recovery rate. It has significant advantages.

[0064] In one embodiment of the present invention, Figure 1-Figure 4 As shown, the agricultural waste is rice straw, corn straw, wood chips, bagasse, peel or other cellulose-rich organic waste, and the water content of the raw material does not exceed 20% to ensure the effective release of volatile components and the stability of the biochar product during pyrolysis. The activator is aluminum sulfate, the mass of which is 10% to 15% of the raw material, and after the activator is added, the activator and the material are evenly mixed by mechanical stirring, and pyrolysis is carried out after standing for 15 to 30 minutes to enhance the effective release of pyrolysis gas during the reaction and optimize the pore structure of the biochar.

[0065] It should be noted that the selected agricultural wastes described in this embodiment, such as rice straw, corn straw, sawdust, bagasse, peel and other cellulose-rich organic wastes, have a water content of no more than 20%, ensuring the efficient release of volatile organic matter in the raw material during pyrolysis, and reducing the effect of water evaporation on the pyrolysis temperature, thereby improving the pyrolysis efficiency and the stability of biochar. The added aluminum sulfate is mixed at a ratio of 10% to 15% of the raw material mass, and the activator is evenly distributed in the material through mechanical stirring, and is allowed to stand for 15 to 30 minutes to ensure that the activator is completely penetrated into the material, thereby promoting the effective release of volatile components at low temperatures during pyrolysis, and helping to optimize the pore structure of biochar and improve its specific surface area and adsorption performance.

[0066] In one embodiment of the present invention, Figure 1-Figure 4 As shown, the microwave radiation power is 700W to 900W, the frequency is 2.45GHz, the far-infrared radiation heating power is 300W to 500W, and the wavelength range is 6µm to 8µm, wherein the microwave radiation power is used to heat the inside of the material, and the far-infrared radiation power is used to heat the external surface of the material, and the two act simultaneously to accelerate the pyrolysis process of the material and improve the quality of the pyrolysis product. The airflow induction device includes multiple airflow adjustment systems, which are divided into at least two levels. Each airflow adjustment system can dynamically adjust the airflow direction, intensity and speed according to different stages of the pyrolysis process, and optimize the reaction temperature distribution by changing the airflow distribution to make the pyrolysis reaction more uniform, thereby improving the yield and quality of biochar. The infrared light source is a far-infrared radiation heating device with a wavelength range of 6µm to 7.5µm, and its radiation power is 200W to 400W. The irradiation time is 10 to 30 minutes after the end of the pyrolysis reaction, so as to promote the photothermal synergy in the reaction zone, further improve the carbonization degree and pore structure of the pyrolysis product, and then improve the specific surface area and adsorption performance of the biochar.

[0067] It should be noted that the microwave radiation power described in this embodiment is set to 700W to 900W and the frequency is 2.45GHz, which can quickly heat the inside of the material in a short time and promote the rapid vibration of the material molecules, thereby accelerating the release of volatile components and the reaction rate. At the same time, the far-infrared radiation heating power is set to 300W to 500W, and the wavelength range is 6µm to 8µm, which is used to uniformly heat the external surface of the material and enhance the heat conduction efficiency. The synergistic effect of the two greatly improves the pyrolysis efficiency and ensures the quality and stability of the pyrolysis products. In addition, the airflow induction device is composed of a multi-stage airflow regulation system, including at least two airflow regulation systems, which can accurately adjust the direction, speed and intensity of the airflow according to the different stages of the pyrolysis reaction, optimize the airflow distribution, and ensure uniform temperature in the reaction zone, thereby effectively improving the uniformity of the pyrolysis reaction and the yield of biochar. Finally, the infrared light source is set within the wavelength range of 6µm to 7.5µm, the radiation power is 200W to 400W, and the irradiation time is 10 to 30 minutes after the pyrolysis reaction. Through this photothermal synergistic effect, the carbonization process is further promoted, and the specific surface area, pore structure and adsorption performance of the biochar are significantly improved.

[0068] In one embodiment of the present invention, Figure 1-Figure 4 As shown, the gas recovery device includes a three-stage gas separation system, namely a high-temperature gas separation section, a volatile organic matter separation section and a combustible gas separation section. After each gas separation, it is condensed, adsorbed and purified. The recovered gas can be used for energy recovery or reused in subsequent processes to maximize energy efficiency and reduce emissions. The cooling process adopts directional cooling technology. Through the synergistic effect of the cooling medium and the heat exchange device, the cooling rate is controlled to not exceed 5°C per minute, ensuring that the surface structure of the biochar is uniform and the pore structure is complete, avoiding cracking and incomplete carbonization caused by too fast cooling, and improving the stability of the final product.

[0069] It should be noted that the gas recovery device described in this embodiment adopts a three-stage gas separation system, including a high-temperature gas separation section, a volatile organic matter separation section and a combustible gas separation section, which respectively perform fine separation on different types of gases, and each section of gas is subjected to condensation, adsorption and purification treatment to ensure that the recovered gas can be efficiently utilized. The recovered combustible gas and volatile organic matter can not only be used for energy recovery, but also as fuel or raw material in subsequent processes, further improving energy efficiency and significantly reducing emissions, thereby realizing resource recycling and environmental protection; During the cooling process, directional cooling technology is adopted, combined with heat exchange devices and cooling media. By precisely controlling the cooling rate, the cooling process is made gentler and controlled at no more than 5°C per minute. This effectively avoids problems such as surface cracking and incomplete carbonization of materials caused by too fast cooling, thereby ensuring the stability of biochar and the integrity and uniformity of its pore structure, thereby improving the quality and application value of the final product.

[0070] In summary, the method for preparing biochar by self-propagating pyrolysis in the embodiment of the present invention effectively optimizes the preparation process of biochar through self-propagating pyrolysis technology, combined with microwave radiation and far-infrared radiation heating, airflow regulation, activator use, photothermal synergy and precise cooling technology. First, suitable agricultural waste is selected and aluminum sulfate is used to promote pyrolysis reaction at low temperature and optimize the pore structure and specific surface area of ​​biochar. Then, microwave and far-infrared radiation are combined for heating to ensure uniform heating inside and on the surface of the material and improve the pyrolysis efficiency. The airflow regulation device ensures uniform airflow distribution during the pyrolysis process to avoid uneven temperature. In addition, infrared light sources are used to promote photothermal synergy and improve carbonization degree. Finally, precise cooling is used to maintain the stability and structural integrity of biochar. The entire process improves the yield and quality of biochar, effectively recovers and utilizes the gases generated by pyrolysis, minimizes energy waste and emissions, and fundamentally solves the problems of uneven heating, long reaction time, and low energy efficiency in the prior art.

[0071] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and deform the above embodiments within the scope of the present invention.

Claims

1. A method for preparing biochar by self-propagating pyrolysis, characterized in that: The following steps are involved: S1. Select agricultural waste or wood waste with a cellulose content greater than 30% and crush it to a particle size of 0.5 to 5 mm; S2, mixing the material with aluminum sulfate in a ratio of 10% to 20% of the raw material mass, wherein the aluminum sulfate promotes low-temperature pyrolysis and increases the specific surface area of ​​the biochar; S3, using a resistance heating device to heat the material to 300°C to 400°C within 1 minute to quickly release the volatile components; S4. Use microwave radiation with a frequency of 2.45 GHz combined with far infrared radiation for heating, with microwave radiation for internal heating and far infrared radiation for external heating to improve pyrolysis efficiency; S5. Adjust the airflow through the airflow induction device to ensure that the pyrolysis reaction proceeds evenly; S6. In the later stage of pyrolysis, an infrared light source with a wavelength of 6µm to 8µm is introduced to irradiate the reaction zone to promote the synergistic effect of light and heat and enhance the carbonization effect; S7. After the pyrolysis is completed, the temperature is quickly cooled to room temperature, and the cooling rate does not exceed 5°C / min to maintain the stability of the biochar; S8. The gas generated by pyrolysis is recovered by a gas recovery device and processed by a three-stage separation system to separate the recyclable gas.

2. The method for preparing biochar by self-propagating pyrolysis according to claim 1, characterized in that: Agricultural waste is rice straw, corn straw, wood chips, bagasse, fruit peel or other cellulose-rich organic waste, and the moisture content of the raw materials does not exceed 20% to ensure the effective release of volatile components during pyrolysis and the stability of biochar products.

3. The method for preparing biochar by self-propagating pyrolysis according to claim 1, characterized in that: The activator is aluminum sulfate, which accounts for 10% to 15% of the raw material by mass. After the activator is added, the activator and the material are evenly mixed by mechanical stirring, and pyrolysis is carried out after standing for 15 to 30 minutes to enhance the effective release of pyrolysis gas during the reaction and optimize the pore structure of the biochar.

4. The method for preparing biochar by self-propagating pyrolysis according to claim 1, characterized in that: The microwave radiation power is 700W to 900W, the frequency is 2.45GHz, the far-infrared radiation heating power is 300W to 500W, and the wavelength range is 6µm to 8µm, wherein the microwave radiation power is used to heat the inside of the material, and the far-infrared radiation power is used to heat the external surface of the material, and the two act simultaneously to accelerate the pyrolysis process of the material and improve the quality of the pyrolysis product.

5. The method for preparing biochar by self-propagating pyrolysis according to claim 1, characterized in that: The airflow induction device includes multiple airflow regulation systems, which are divided into at least two levels. Each airflow regulation system can dynamically adjust the airflow direction, intensity and speed according to the different stages of the pyrolysis process. By changing the airflow distribution and optimizing the reaction temperature distribution, the pyrolysis reaction is made more uniform, thereby improving the yield and quality of biochar.

6. The method for preparing biochar by self-propagating pyrolysis according to claim 1, characterized in that: The infrared light source is a far-infrared radiation heating device with a wavelength range of 6µm to 7.5µm and a radiation power of 200W to 400W. The irradiation time is 10 to 30 minutes after the pyrolysis reaction is completed, so as to promote the photothermal synergy in the reaction zone, further improve the carbonization degree and pore structure of the pyrolysis product, and thus improve the specific surface area and adsorption performance of biochar.

7. The method for preparing biochar by self-propagating pyrolysis according to claim 1, characterized in that: The gas recovery device includes a three-stage gas separation system, namely the high-temperature gas separation section, the volatile organic matter separation section and the combustible gas separation section. After each stage of gas separation, it undergoes condensation, adsorption and purification. The recovered gas can be used for energy recovery or reuse in subsequent processes to maximize energy efficiency and reduce emissions.

8. The method for preparing biochar by self-propagating pyrolysis according to claim 1, characterized in that: The cooling process adopts directional cooling technology. Through the synergistic effect of cooling medium and heat exchange device, the cooling rate is controlled to no more than 5°C per minute, ensuring that the surface structure of biochar is uniform and the pore structure is complete, avoiding cracking and incomplete carbonization caused by too fast cooling, and improving the stability of the final product.

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