A pyrolysis-water quenching prepared biomass charcoal and a method thereof for preparing iron ore pellets

Abstract

The application discloses a kind of pyrolysis-water quenching preparation of biomass charcoal and its method for preparing iron ore pellet, belong to iron ore pellet production technical field.Biomass raw materials are pyrolyzed, and the pyrolysis carbon generated by pyrolysis is rapidly water quenched at the pyrolysis temperature, and then filtered, dried and ground to obtain the biomass charcoal.The biomass charcoal has low ash content, low K and Cl content, high calorific value, low volatile content, good combustion performance and other characteristics, and can fully meet the requirements of pellet internal matching, can completely or partially replace fossil fuels, and can reduce the dependence on coal-based fossil fuels and the emission of CO2 and pollutants in the process of iron ore pellet production without affecting the normal production of iron ore pellets.

Description

Technical Field

[0001] This invention relates to a biochar, a method for preparing biochar by pyrolysis-water quenching, and the application of biochar as an internal fuel in iron ore pellet preparation, belonging to the field of iron ore pellet preparation technology. Background Technology

[0002] The steel industry is a major energy consumer and carbon emitter. With social development and increasing environmental awareness, the steel industry faces enormous pressure in terms of carbon and pollutant emissions. The root cause is the steel production's over-reliance on fossil fuels such as coal, resulting in high CO2 and pollutant emissions. Adopting clean raw materials and fuels is a key link and the most effective measure for reducing pollution and carbon emissions in the steel metallurgy industry.

[0003] Iron ore pellets are high-quality furnace feedstocks for both long and short processes in iron and steel metallurgy, characterized by high grade, uniform particle size, high cold strength, and good metallurgical properties. Magnetite is a high-quality pelletizing raw material due to its excellent pelletizing and roasting properties. In recent years, under the "dual carbon" background, pellets have received much attention due to their low energy consumption and low pollutant emissions during production. However, the increasing scarcity of high-quality magnetite resources has kept its price high. Furthermore, the development of "deep grinding and fine beneficiation" technology has resulted in excessively fine magnetite powder particles, leading to overly dense pellet structures and poor metallurgical properties. These problems severely restrict the development of the pelletizing industry. Although reducing the proportion of magnetite in the pelletizing raw material can reduce magnetite consumption to some extent, lowering the magnetite ratio reduces the heat released during the pelletizing process due to magnetite oxidation. This has an adverse effect on pellet consolidation and process energy consumption, and also reduces the compressive strength of the finished pellets. Adding solid fuel to the pelletizing raw material is an effective measure to address the insufficient self-heating in the production of low-magnetite pellets. Internal carbon addition not only stabilizes the internal thermal balance of pellets and improves pellet strength, but also reduces preheating-roasting fuel consumption and improves the metallurgical properties of the pellets. Furthermore, adding solid fuel to fine-grained magnetite can increase the porosity of the pellets and improve their metallurgical properties. Therefore, internal carbon addition to pellets is of great significance for low-carbon pellet production and the preparation of high-quality low-carbon furnace feedstock for iron and steel metallurgy.

[0004] Currently, the carbon source within pellet mills mainly comes from coal-based fossil fuels such as anthracite and coke. This indicates that the pelleting process still heavily relies on coal, meaning that the production process emits large amounts of CO2 and pollutants. Biomass energy is the fourth largest energy source after coal, oil, and natural gas. The CO2 released during the combustion of this type of renewable energy material originates from the CO2 absorbed during its growth. Therefore, biomass fuel has net-zero CO2 emissions. Among many renewable fuels, biomass is the only energy source that can produce solid carbon-rich fuels with coal-like characteristics. Using biomass as a carbon source within pellet mills can effectively alleviate the excessive dependence of the pelleting process on coal-based fossil fuels and reduce CO2 and pollutant emissions from pelleting production.

[0005] Regarding the preparation of carbon-containing pellets with biochar from biomass, Chinese patent (publication number: CN118703776A) discloses a method for preparing carbon-containing pellets from biomass, carbon-containing pellets, and metallized pellets. The method involves hydrothermal carbonization of biomass to obtain biochar; mixing the biochar, iron ore powder, binder, and solvent at a predetermined mass ratio to obtain a premix; and pelletizing and drying the premix to obtain carbon-containing pellets. By optimizing the ratio of biochar, iron ore powder, binder, and solvent, close contact between the iron ore powder and reducing agent within the carbon-containing pellets is ensured, thereby promoting the coupling effect of the gasification and reduction reactions in the carbon-containing pellets, resulting in excellent self-reducing performance. Simultaneously, it avoids carbon particles hindering the aggregation of the iron phase, improving the strength of the carbon-containing pellets. This solves the technical problem in existing technologies where carbon-containing pellets cannot simultaneously meet the requirements of high strength and high self-reducing properties. Chinese Patent (Publication No.: CN115354150A) discloses a method for preparing biomass carbon-containing pellets for blast furnace ironmaking. The method involves crushing biomass and then hydrothermally carbonizing it to prepare biomass hydrothermal char with low alkali metal content and high thermal extraction rate. A portion of the biomass hydrothermal char is then pyrolyzed to produce low-volatile biomass char, and another portion is thermally extracted to produce a biomass high-temperature binder. The biomass char, biomass high-temperature binder, iron ore powder, and solvent are crushed, mixed, and then hot-pressed to obtain biomass carbon-containing pellets. Through this method, the invention can prepare biomass with high volatile matter, high moisture content, and high harmful element content into biomass-based reducing agents and binders with high fixed carbon content, high binding properties, and low harmful element content. Furthermore, the hot-pressing method produces high-quality biomass carbon-containing pellets suitable for use as blast furnace feedstock, effectively reducing carbon emissions during ironmaking. Chinese Patent (Publication No.: CN116751971A) discloses a high-strength biomass carbon-containing pellet, its preparation method, and its application, relating to the field of blast furnace ironmaking technology. The pellet comprises the following raw materials by mass fraction: 70%–85% iron ore, 4%–15% binder, 5%–11% biochar, and 1%–3% basic flux. This invention's high-strength biomass carbon-containing pellet exhibits high strength and good wear resistance. Its high thermal detonation temperature and low thermal detonation index effectively reduce powder generation after entering the blast furnace. The high-strength biomass carbon-containing pellet exhibits superior reducibility, reductive expansion, and low-temperature reductive pulverization performance compared to traditional sintered ore, pellets, and lump ore. It can be directly used as blast furnace feedstock, reducing the amount of coke used in blast furnace smelting, thereby reducing ironmaking costs and CO2 emissions, resulting in significant economic, social, and ecological benefits.Chinese Patent (Publication No.: CN102586529A) discloses a rotary hearth furnace ironmaking method using biomass carbon-containing pellets as raw material. This method involves a rotary hearth furnace ironmaking process that uses biomass as both fuel and reducing agent. The process utilizes renewable, carbon-neutral biomass coke powder to replace pulverized coal. The biomass coke powder is blended with iron ore powder at a C / O ratio of 1.1–1.4, and a suitable binder is added to form pellets. These pellets are then heated and reduced in a rotary hearth furnace to obtain metallized pellets. Biomass coke is carbon-neutral, which fundamentally reduces CO2 and other pollutant emissions from coal consumption. The low impurity content of biomass coke solves the problem of excessively high sulfur content in products caused by coal use and improves overall product quality. The energy for biomass coke preparation can be provided by the biomass itself, essentially achieving green circular production. This invention broadens the energy sources for rotary hearth furnace ironmaking, reduces production costs, improves product quality and production efficiency, and reduces environmental pollution.

[0006] While the aforementioned methods have a positive effect on the carbon source for biomass pellet production and can theoretically reduce the dependence of pellet production on fossil fuels, they do not consider the actual situation of biomass resources. Charcoal, with its low ash content, high calorific value, and similar physicochemical properties to coal, is expensive due to its scarcity, making its use as a fuel in pellet production a luxury. Although straw resources are abundant and relatively concentrated, the vast majority of agricultural straw pyrolysis char is rich in harmful elements such as K / Cl and has a high ash content, resulting in a low calorific value. Blending it into pellets would affect pellet consolidation. Straw hydrothermal char also suffers from high volatile matter content, strong chemical activity, scattered heat release, and difficulty in preparation, making it unsuitable for pellet compounding. Nevertheless, agricultural straw resources are abundant, and using it as a carbon source for pellet compounding is the best choice for achieving biomass energy to replace coal-based fossil fuels in pellet compounding. Therefore, based on the performance requirements of the carbon source in the pellets, it is of great significance to develop biomass upgrading technologies, including agricultural straw, to achieve the economical and efficient preparation of high-quality biochar with low ash, low harmful elements, high calorific value, suitable volatile matter, concentrated heat release, and combustion and gasification characteristics similar to those of coal-free biochar. Summary of the Invention

[0007] To address the aforementioned problems, the first objective of this invention is to provide a biochar with characteristics such as low ash content, low K and Cl content, high calorific value, low volatile matter content, and good combustion performance, which meets the requirements for pellet formulation and can completely or partially replace fossil fuels in the preparation of iron ore pellets.

[0008] The second objective of this invention is to provide a method for preparing biochar, which uses biomass solid waste as raw material, is simple to operate, has low cost, and meets the requirements of industrial production.

[0009] The third objective of this invention is to provide a method for using biochar as an internal fuel in the preparation of iron ore pellets. Biochar prepared by the pyrolysis-water quenching method can partially or completely replace coal-based fuels such as anthracite and coke in the internal blending of pellets. On the one hand, it can alleviate the problems of high dependence on fossil energy and high pollutant emissions in the pellet production process. On the other hand, it can alleviate the dependence of pellet production on magnetite, stabilize the internal thermal balance of the pellets, improve the strength of the pellets, and at the same time reduce the preheating-roasting fuel consumption and improve the metallurgical properties of the pellets.

[0010] To achieve the above-mentioned technical objectives, the present invention provides a method for preparing biochar by pyrolysis-water quenching and its application in iron ore pelletizing. The method involves pyrolyzing biomass raw materials, rapidly quenching the generated pyrolyzed char at the pyrolysis temperature, and then filtering, drying, and grinding it to obtain the biochar.

[0011] The key to this invention lies in preparing biochar using a combination of pyrolysis and water quenching of biomass raw materials. Firstly, in the pyrolytic char produced by high-temperature pyrolysis, most of the harmful elements are converted into water-soluble ash. Water can dissolve most of this ash, and extensive research has shown that the higher the temperature, the better the dissolution effect of this ash in water. Therefore, this invention rapidly quenches the freshly pyrolyzed, hot biochar in water, resulting in a more thorough removal of ash. Secondly, during the water quenching process of the high-temperature pyrolytic char, the rapid cooling of the char particles causes thermal stress within the particles, and the high-temperature steam corrodes the biochar matrix. This leads to the formation of numerous cracks and pores on the surface of the biochar particles after water quenching. The formation of these cracks and pores, combined with the temperature and flow fields created around the biochar during water quenching, provides favorable thermodynamic and kinetic conditions for the removal of ash from the pyrolytic char. Thirdly, during the water quenching process, the chemically active hydrocarbon groups in the biochar are gasified by water vapor. In addition, the content of catalytically active alkali metals in the biochar decreases, leading to an increase in the combustion and gasification temperature. This makes the biochar's performance more similar to that of high-fixed-carbon coal-based fossil fuels such as anthracite and coke powder. Therefore, when incorporated into pellets, it offers advantages over pyrolytic char and hydrothermal char. In summary, this invention, by directly water quenching high-temperature pyrolytic char, can produce biochar with low ash content, low K and Cl content, high calorific value, low volatile matter content, and good combustion performance.

[0012] In the process of preparing biochar by pyrolysis-water quenching of the present invention, the water quenching treatment of high-temperature pyrolysis carbon not only accelerates the cooling process of pyrolysis carbon and improves the production efficiency of biochar, but also effectively uses the carbonization waste heat carried by biochar for the water leaching deashing process, thereby reducing the energy consumption in the ash leaching process.

[0013] As a preferred embodiment, the biomass raw material has a moisture content of less than 10 wt.%, an ash content of less than 20 wt.%, a volatile matter content of less than 85 wt.%, and a calorific value of 13–20 MJ / kg. As a preferred embodiment, the biomass raw material includes at least one of straw waste, orchard pruning materials, and wood processing waste. These biomass raw materials, after conventional pyrolysis, have high ash content and low calorific value; their inclusion in pellets can affect pellet consolidation. However, using a combined pyrolysis-water quenching method can obtain biochar with low ash content, low harmful elements, high calorific value, suitable volatile matter, concentrated heat release, and combustion and gasification performance similar to anthracite and coke powder. The biomass raw material includes, but is not limited to, straw waste from agricultural production such as corn, rice, wheat, soybeans, and cotton, and forestry waste such as orchard pruning materials and wood processing waste. The biomass raw material of this invention undergoes shearing and crushing pretreatment, with a length less than 30 mm and a maximum cross-sectional diameter less than 10 mm accounting for no less than 80 wt.%.

[0014] As a preferred embodiment, the pyrolysis conditions are: temperature between 300 and 900°C, and duration between 30 and 120 minutes. If the pyrolysis temperature is too low or the time is too short, incomplete pyrolysis will occur. Considering the influence of the pyrolysis temperature on the subsequent water quenching process, the preferred pyrolysis temperature is 600–800°C. The pyrolysis of the biomass raw material is preferably carried out in equipment similar to a coke oven. After carbonization, a device similar to a coke pusher can be used to quickly push the high-temperature biomass char out of the carbonization chamber and then water quench it.

[0015] As a preferred embodiment, the water quenching process involves either directly immersing the pyrolytic char in water or rapidly pouring water onto the pyrolytic char. The water quenching process rapidly cools the high-temperature pyrolytic char with water, including but not limited to immersing the high-temperature pyrolytic char in water and rapidly pouring water onto it. The amount of water used must be sufficient to submerge the biomass char. After water quenching, depending on the ash leaching characteristics and deashing degree of the biomass char, it can be immediately filtered to obtain the finished biomass char, or further wet milling and water immersion-enhanced deashing operations such as introducing hot flue gas can be carried out to prepare low-ash finished biomass char.

[0016] The heat source used in the pyrolysis process of this invention can be entirely or partially derived from the pyrolysis gas generated during the biomass pyrolysis process, thereby maximizing the self-exothermic pyrolysis of biomass.

[0017] In the drying process of the pyrolytic char of the present invention, the heat source is preferably the hot flue gas from a biomass pyrolysis furnace, and the drying method can be drum drying or exhaust drying.

[0018] The grinding process of the pyrolytic carbon of the present invention can be carried out using a high-speed coal mill or a ball mill.

[0019] The present invention also provides a biochar obtained by the aforementioned preparation method.

[0020] As a preferred embodiment, the biochar has an ash content of less than 5 wt.%, a potassium content of less than 1 wt.%, a chloride content of less than 0.1 wt.%, a calorific value of more than 25 MJ / kg, a volatile matter content of less than 25 wt.%, an initial combustion temperature of more than 350°C, and an initial gasification temperature of more than 700°C. The biochar prepared by pyrolysis-water quenching in this invention has physical and chemical properties more similar to those of high-fixed-carbon coal-based fossil fuels such as anthracite and coke powder.

[0021] The present invention also provides a method for using biochar to prepare iron ore pellets, wherein the method involves adding biochar to pellet raw materials, and sequentially performing pelletizing and roasting to obtain finished pellets.

[0022] As a preferred embodiment, the biochar is used as a single fuel in the pellet feedstock, or the biochar is used as a mixed fuel in the pellet feedstock in combination with at least one of pulverized coal, coke powder, charcoal, straw pyrolysis charcoal, and hydrothermal charcoal.

[0023] As a preferred embodiment, the proportion of biochar particles smaller than 74 micrometers is not less than 80 wt.%, and the size of the largest particle does not exceed 100 micrometers.

[0024] As a preferred embodiment, the biochar content is between 0.2% and 2 wt.%. Excessive biochar content can negatively impact the compressive strength of the pellets.

[0025] The present invention utilizes a belt roaster process to produce green pellets from biochar. Compared with the chain grate-rotary kiln process, the belt roaster can almost achieve static roasting of the pellets, resulting in a low pellet pulverization rate and a high yield.

[0026] The finished pellets prepared by this invention have well-developed porosity and good reducibility, and are preferentially used in direct reduction and electric arc furnace steelmaking.

[0027] The iron concentrate in the pellet raw materials of this invention includes at least one of hematite, limonite, magnetite, vanadium-titanium magnetite, and laterite nickel ore.

[0028] This invention relates to a method for preparing biochar via pyrolysis-water quenching, comprising the following steps:

[0029] S1: Agricultural and forestry biomass with moisture, ash, and volatile matter content below 10wt.%, 20wt.%, and 85wt.%, respectively, and a calorific value between 13 and 20 MJ / kg, is cut into small biomass pieces with a length less than 30 mm and a maximum cross-sectional diameter less than 10 mm. The biomass pieces are then placed in a pyrolysis furnace similar to a coke oven for pyrolysis and carbonization into pyrolysis char. The pyrolysis temperature is 300–900℃, and the pyrolysis time is 30–120 min. The carbonization heat can be obtained entirely or partially from the biomass pyrolysis gas.

[0030] S2: The hot pyrolysis char is quickly pushed out of the carbonization chamber by a char pushing device, and the hot biomass char is quenched with water. After water immersion, filtration, drying and grinding, biomass char for use in pelleting is obtained.

[0031] S3: Biochar is added to the pelletizing raw material to obtain raw pellets containing biochar. The raw pellets are then processed through a pellet roasting process to obtain finished pellets.

[0032] Compared with the prior art, the beneficial effects of the technical solution of this invention are as follows:

[0033] 1) In view of the technical problem that the use of agricultural biomass waste with abundant reserves is limited in the steel industry due to its high content of harmful substances, the present invention adopts a combination of pyrolysis and water quenching to convert biomass solid waste with high ash and high content of harmful elements into biochar with similar combustion and gasification performance to anthracite and coke powder. The technical solution of this invention utilizes direct water quenching of high-temperature pyrolytic char to efficiently dissolve the ash containing harmful elements from biomass char. Simultaneously, the rapid cooling process during water quenching generates thermal stress within the biomass char particles, and the high-temperature steam corrodes the biomass char matrix, resulting in numerous cracks and pores on the surface of the biomass char particles after water quenching. These cracks and pores, combined with the temperature and flow fields formed around the biomass char during water quenching, further facilitate ash removal. In particular, during water quenching, the chemically active hydrocarbon groups in the pyrolytic char are vaporized by water vapor. Furthermore, the content of catalytically active alkali metals in the biomass char decreases, leading to an increase in combustion and gasification temperatures. This makes the biomass char more similar in performance to high-fixed-carbon coal-based fossil fuels such as anthracite and coke powder. Therefore, when incorporated into pelletizing, it offers advantages over other types of biomass char, such as pyrolytic char and hydrothermal char.

[0034] 2) In the preparation process of biochar, the present invention performs water quenching on the freshly pyrolyzed hot biochar, which not only accelerates the cooling process and improves the production efficiency of biochar, but also effectively transfers the residual heat of carbonization carried by the biochar to the water leaching deashing system, thereby reducing the energy consumption in the ash leaching process.

[0035] 3) This invention replaces coal-based fossil fuels with biochar prepared from biomass solid waste in pellet compounding. It processes abundant agricultural biomass into coal- and coke-like biochar, effectively solving the problems of scarce and expensive high-quality charcoal resources, and the inability to use large quantities of pyrolysis and hydrothermal char directly in pellet compounding, without affecting the quality of the finished pellets. Using coal- and coke-like biochar obtained from the deheating and water quenching of agricultural and forestry biomass in pellet compounding ensures better quality of the produced pellets and provides stable fuel supply, effectively reducing the dependence on coal-based fuels and carbon emissions in pellet production. Attached Figure Description

[0036] Figure 1 This is a process flow diagram for preparing biochar using pyrolysis-water quenching and using it in the production of iron ore pellets.

[0037] Figure 2 The combustion weight loss curve of the water-quenched biochar prepared in Example 1.

[0038] Figure 3 The combustion weight loss curve of the water-quenched biochar prepared in Example 2. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0040] It should also be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and / or processing steps closely related to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0041] Additionally, it should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0042] Example 1:

[0043] Using 1 ton of corn stalks with a moisture content of 8 wt.%, ash content of 5 wt.%, volatile matter of 75 wt.%, and a dry basis calorific value of approximately 17 MJ / kg as biomass raw material, the biomass is crushed and sheared into small pieces less than 30 mm in length and with a maximum cross-sectional diameter of 10 mm. These pieces are then carbonized in a carbonization furnace with a structure similar to a coke oven. Natural gas is used as the start-up gas for pyrolysis. The biomass gas produced during pyrolysis is returned to the combustion chamber of the carbonization furnace for heating. As the temperature increases, the amount of biomass pyrolysis gas gradually increases while the amount of natural gas gradually decreases, with biomass gas being used as much as possible for heating the biomass char. The injection rates of natural gas and biomass gas throughout the pyrolysis process are controlled by a program. The pyrolysis temperature is raised to 600℃ within 60 minutes and held for 60 minutes. A pusher rod is used to push the hot biomass char from the outlet into a cylindrical steel water-quenching well, while simultaneously injecting 5 m³ of [unspecified material] into the well. 3 The biochar was quenched using clean water. A spiral agitator was installed at the bottom of a cylindrical steel water quenching well to ensure rapid contact and quenching between the biochar and water. The water-quenched biochar (referred to as water-quenched char) was then filtered out, dried by the hot flue gas generated by the pyrolysis furnace, and ground in a ball mill to a mesh size of -200 to obtain biochar for use in pelletizing. To clarify the advantages of the pyrolysis-water quenching method compared to traditional pyrolysis, corn straw pyrolysis char was prepared using the same equipment and pyrolysis parameters. The industrial analysis, elemental analysis, and calorific value of the two different biochars are shown in Table 1; ash composition is shown in Table 2; specific surface area and pore structure parameters are shown in Table 3; and combustion weight loss curves are shown in Table 4. Figure 2 The results all indicate that biochar produced by the pyrolysis-water quenching method has lower ash and harmful element content, while its higher calorific value and combustion temperature are more similar to those of anthracite and coke.

[0044] Table 1. Industrial analysis, elemental analysis, and calorific value of biochar.

[0045]

[0046]

[0047] Table 2 Ash composition of biochar

[0048]

[0049] Table 3 Specific surface area and pore structure parameters of biochar

[0050]

[0051] Two different types of biochar were used as carbon sources in the pelleting process (85 wt.% of the biochar was ground to a particle size of less than 74 micrometers, and the largest particle size was 100 micrometers). The amount of biochar in each case was 2 wt.%. The raw materials used for pelleting are shown in Table 4. The amount of bentonite added was 1.80 wt.%. After mixing, carbon-containing pellets were prepared using a disc pelletizer. Carbon-containing pellets made from anthracite from a certain pelleting plant's production line were used as a comparison. The drop strength test results of the pellets are shown in Table 5. It can be seen that water-quenched carbon has a greater advantage in terms of drop strength of the pellets. Two types of green pellets were placed in high-temperature alloy cages and then in the feed layer of a belt conveyor during production. Finished pellets were obtained under the same pellet roasting process conditions. The compressive strength, drum index, and abrasion resistance of the pellets are shown in Table 6. It can be seen that because the ash content and harmful elements in the raw water-quenched carbon are low and the calorific value is high, the compressive strength, drum index, and abrasion resistance of the obtained pellets are better than those of pyrolytic carbon and are very similar to those of pellets with anthracite added internally.

[0052] Table 4 Raw Materials for Pelletizing

[0053]

[0054] Table 5 Drop Strength of Carbon-Containing Green Balls

[0055]

[0056] Table 6 Indicators of Finished Balls

[0057]

[0058] Example 2

[0059] Using 1 ton of tobacco straw with a moisture content of 10%, ash content of 4%, volatile matter of 73%, and a dry basis calorific value of approximately 19 MJ / kg as biomass raw material, the biomass is crushed and sheared into small biomass blocks with a length of less than 30 mm and a maximum cross-sectional diameter of 10 mm. A carbonization furnace device with a structure similar to a coke oven is used for carbonization. Natural gas is initially used as the carbonization gas source. The biomass gas produced by pyrolysis is guided back to the combustion chamber of the carbonization furnace for heating. As the temperature rises, the amount of biomass pyrolysis gas gradually increases, while the amount of natural gas gradually decreases, with biomass gas being used as much as possible for heating the biomass char. The injection rates of natural gas and biomass gas throughout the pyrolysis process are controlled by a program. The pyrolysis temperature is raised to 800℃ within 80 minutes and held for 40 minutes. A coke pushing device pushes the biomass char from the coke outlet into a cylindrical steel water-quenching well, while simultaneously injecting 5 m³ of [unclear text - possibly a specific type of gas] into it. 3The biochar was quenched in water. A cylindrical steel water quenching well with a spiral agitator at the bottom ensured rapid contact between the biochar and water. The quenched biochar was then filtered out, dried by hot flue gas from the pyrolysis furnace, and ground in a ball mill to a mesh size below 200, producing biochar for use in pelletizing (referred to as water-quenched char). To clarify the advantages of the pyrolysis-water quenching method over traditional pyrolysis, tobacco straw pyrolysis char was prepared using the same apparatus and pyrolysis parameters. The industrial analysis, elemental analysis, and calorific value of the two different biochars are shown in Table 7; ash composition is shown in Table 8; specific surface area and pore structure parameters are shown in Table 9; and combustion weight loss curves are shown in Table 1. Figure 3 The results all indicate that biochar produced by the pyrolysis-water quenching method has lower ash and harmful element content, while its higher calorific value and combustion temperature are more similar to those of anthracite and coke.

[0060] Table 7. Industrial analysis, elemental analysis, and calorific value of biochar.

[0061]

[0062]

[0063] Table 8 Ash composition of biochar

[0064]

[0065] Table 9 Specific surface area and pore structure parameters of biochar

[0066]

[0067] Two different types of biochar were used as carbon sources in the pelleting process (85 wt.% of the biochar was ground to a particle size of less than 74 micrometers, and the largest particle size was 100 micrometers). The amount of biochar added was 2 wt.% for both types. The raw materials used for pelleting are shown in Table 10. The amount of bentonite added was 1.80 wt.%. After mixing, carbon-containing pellets were prepared using a disc pelletizer. Carbon-containing pellets made from anthracite coal from a pelleting plant's production line were used as a comparison. The drop strength test results of the pellets are shown in Table 11. It can be seen that there is no significant difference in the green pellet strength between the two types of biochar. Two types of raw pellets were placed in high-temperature alloy cages and then placed in the feed layer of a belt roaster during production. Finished pellets were obtained under the same pellet roasting process and conditions. The pellets' compressive strength, drum index, abrasion resistance index, and other pellet indicators are shown in Table 12. It can be seen that because the ash content and harmful elements in the raw water-quenched carbon are lower and the calorific value is higher, the compressive strength, drum index, abrasion resistance index, and other indicators of the obtained pellets are better than those of pyrolytic carbon, especially in the reduction expansion index, which is very obvious and is very similar to the indicators of pellets with internal anthracite.

[0068] Table 10 Raw Materials for Pelletizing

[0069]

[0070] Table 11 Drop Strength of Carbon-Containing Green Balls

[0071]

[0072] Table 12 Indicators of Finished Balls

[0073]

Claims

1. A method for using biochar to prepare iron ore pellets, characterized in that: Biochar is added to pellet raw materials, and pelletizing and roasting are carried out in sequence to obtain finished pellets. The biochar is prepared by the following method: the biomass raw material is pyrolyzed, and the resulting pyrolyzed char is rapidly quenched in water while maintaining the pyrolysis temperature. After filtration, drying and grinding, the biochar is obtained. The pyrolysis conditions are: temperature 300~900℃, duration 30~120min; The water quenching process is as follows: the pyrolytic carbon is directly pushed into the water, or water is quickly poured onto the pyrolytic carbon; The biochar has an ash content of less than 5 wt.%, a K content of less than 1 wt.%, a Cl content of less than 0.1 wt.%, a calorific value of more than 25 MJ / kg, a volatile matter content of less than 25 wt.%, an initial combustion temperature of more than 350℃, and an initial gasification temperature of more than 700℃.

2. The method for preparing iron ore pellets using biochar according to claim 1, characterized in that: The biomass char is added to the pellet feedstock as a single fuel, or the biomass char is added to the pellet feedstock as a mixed fuel in combination with at least one of pulverized coal, coke powder, charcoal, straw pyrolysis char, and hydrothermal char.

3. A method for preparing iron ore pellets using biochar according to claim 1 or 2, characterized in that: The biochar has a particle size of less than 74 micrometers, with a proportion of less than 80 wt.% and a maximum particle size of no more than 100 micrometers. The proportion of biochar in the pellet feedstock is between 0.2 and 2 wt.%.

4. A method for preparing iron ore pellets using biochar according to claim 1, characterized in that: The biomass raw material has a moisture content of less than 10 wt.%, an ash content of less than 20 wt.%, a volatile matter content of less than 85 wt.%, and a calorific value of 13~20 MJ / kg.

5. The method for preparing iron ore pellets using biochar according to claim 1, characterized in that: The biomass raw materials include at least one of straw waste, orchard trimmings, and wood processing waste.

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