Preparation method of composite clean fuel for sintering based on biomass heat treatment upgrading

Abstract

The invention discloses a preparation method of a composite clean fuel for sintering based on biomass heat treatment upgrading. The method comprises the following steps: 1) carrying out grinding and compression molding on a biomass raw material to obtain biomass particles; 2) placing the biomass particles in a protective atmosphere, firstly performing low-temperature baking treatment to remove low volatile components, and then performing medium-temperature carbonization treatment to obtain biomass charcoal fuel and pyrolysis oil gas; and 3) performing high-temperature cracking treatment on the pyrolysis oil gas in a composite atmosphere containing water vapor and carbon dioxide to obtain the biomass fuel gas. By means of the method, biomass solid fuel with the quality close to that of coke can be obtained, the biomass solid fuel can replace fossil fuel in a high proportion, and biomass fuel gas which is high in heat value and can be used for sintering material face injection to supplement heat can be obtained, so that a composite clean fuel structure for sintering is constructed, and energy conservation, carbon reduction and emission reduction are achieved from the source.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method of a composite clean fuel for sintering, in particular to a preparation method of a composite clean fuel for sintering based on biomass heat treatment upgrading, and belongs to the technical field of steel metallurgical fuel. BACKGROUND

[0002] In 2022, the carbon emissions of the steel industry exceeded 1.8 billion tons, accounting for about 15% of the total emissions in China. Each ton of crude steel produced generates 1.65-1.8 tons of CO2. As the main pre-iron process, the sintering process provides more than 75% of the iron-containing burden, and the carbon emissions account for about 11% of the total carbon emissions of the steel industry. Therefore, efficient CO2 control in the sintering process plays an important role in the steel industry's "carbon peak and carbon neutralization". Since the combustion of coal-based solid fuels is the main source of carbon emissions in the sintering process, source and process control technologies such as improving the utilization efficiency of coal-based solid fuels and replacing clean fuels are effective ways to achieve efficient carbon reduction in the steel industry. The sintering process energy efficiency improvement technologies represented by thick layer sintering, hot flue gas or hot exhaust gas circulation sintering, steam injection sintering, and oxygen-enriched sintering can reduce solid fuel consumption to a certain extent, but the energy structure dominated by coal-based solid fuels limits the carbon reduction space. Clean fuel replacement technologies represented by hydrogen-rich gas injection and biochar replacing coke powder have more potential to replace coal-based solid fuels on a large scale. Therefore, using carbon-neutral biomass energy to efficiently replace coal-based fuels is an important way to achieve efficient CO2 reduction in the sintering process.

[0003] Studies have shown that due to the excessively fast combustion speed of biomass fuel, it is difficult to meet the heat required for the generation of sufficient calcium ferrite binding phase in the sintering process, and excessive addition will lead to a significant decrease in sinter strength. Through methods such as high-pressure forming, pyrolysis carbonization, surface modification, coke or iron powder adhesion to optimize fuel performance, and process parameter optimization and raw material structure optimization to improve the thermal state, the replacement rate of biomass fuel can be improved to a certain extent, but the current technology does not solve the problem of high reactivity of biomass fuel. At the same time, as a typical biomass heat treatment upgrading method, there is less research on the performance optimization and value-added utilization of by-products (pyrolysis gas and tar), and the energy utilization efficiency is low. Compared with solid fuels distributed in the sintering layer in the form of scattered points, the distribution of fuel gas into the sintering layer is more uniform, the combustion efficiency is high, and the gas-solid heat exchange conditions are superior. Biomass pyrolysis gas can improve the replacement rate of biomass char and reduce fossil fuels in the sintering layer while not emitting additional CO2. By optimizing the process to improve the calorific value and proportion of combustible components of pyrolysis gas, biomass energy can be more efficiently used in the sintering process.

[0004] Overall, the products obtained by direct pyrolysis of biomass cannot fully meet the needs of clean fuel for sintering, and further upgrading and process optimization are needed. SUMMARY

[0005] In view of the fact that the existing biomass upgrading process by heat treatment is difficult to obtain clean fuel meeting the requirements of sintering, the present application aims to provide a preparation method of composite clean fuel for sintering based on biomass upgrading by heat treatment, which improves the existing biomass upgrading process by heat treatment, so that the performance of the biochar is close to that of coke breeze, the content of combustible components of the pyrolysis gas and its calorific value are higher, thereby constructing a composite clean fuel structure of biochar and pyrolysis gas, which is respectively used for solid fuel replacement and material surface gas injection in the sintering process, so as to achieve the purpose of low-carbon sintering.

[0006] In order to achieve the above technical purpose, the present application provides a preparation method of composite clean fuel for sintering based on biomass upgrading by heat treatment, which comprises the following steps:

[0007] 1) grinding and pressing the biomass raw material to obtain biomass particles;

[0008] 2) placing the biomass particles in a protective atmosphere, first performing low-temperature baking treatment to remove low-volatile components, and then performing medium-temperature carbonization treatment to obtain biomass char fuel and pyrolysis oil gas;

[0009] 3) performing high-temperature cracking treatment on the pyrolysis oil gas in a composite atmosphere containing water vapor and carbon dioxide to obtain biomass gas.

[0010] The key of the technical scheme is to optimize the biomass pyrolysis upgrading process in the prior art to obtain a biomass fuel that can better meet the needs of iron ore sintering. In the present application, the biomass fuel is first subjected to low-temperature baking treatment to preferentially remove most of the volatile matter in the biomass raw material, mainly carboxyl, hydroxyl and other oxygen-containing groups. These polar groups generate low-calorific-value gaseous products mainly composed of H2O and CO2, and these components can be fully utilized in the subsequent cracking process of pyrolysis oil and gas. The low-temperature baking treatment process gently removes the volatile matter, which is beneficial to ensuring the structural integrity and compactness of the biochar, thereby helping to generate biochar with low reactivity in the medium-temperature carbonization stage. In addition, the low-temperature baking process removes low-quality components in advance, avoiding their entry into the high-temperature cracking stage, which improves the quality of pyrolysis gas while significantly reducing the energy consumption of the high-temperature cracking process. After removing a large amount of oxygen-containing groups, the water content and acidic substance content in the pyrolysis oil and gas are reduced, and the aromatic hydrocarbon yield is effectively improved, which is beneficial to obtaining high-calorific-value fuel gas. At the same time, the main components of the gaseous by-products in the low-temperature baking process are H2O and CO2, which can be fully utilized in the high-temperature cracking stage to accelerate the cracking process, and the remaining gas can be recycled back to the heating furnace to fully utilize the energy and reduce the amount of useless substances. The solid product of low-temperature baking enters the medium-temperature carbonization process for deep carbonization, in which the volatile matter in the biomass is fully removed and the carbon structure is densified, thereby obtaining biochar products with low reactivity, which is close to the performance of coke. The pyrolysis oil and gas generated in the carbonization process directly enters the high-temperature cracking stage and is subjected to thermal cracking under the promotion of steam and carbon dioxide gas to generate high-calorific-value fuel gas, which can completely replace the injected fuel gas. In summary, the technical scheme of the present application combines low-temperature baking process and two-stage high-temperature treatment process to obtain a composite clean fuel for sintering, achieving high-value utilization of the energy of all components of biomass and promoting clean production of the sintering process.

[0011] As a preferred scheme, the biomass raw material includes at least one of agricultural waste straw, sawdust, and sugarcane residue. These biomass raw materials belong to solid waste resources, and the raw material cost is low. They are large in quantity and concentrated in distribution, which is conducive to collection, processing and large-scale application.

[0012] As a preferred scheme, the biomass raw material is ground to a particle size of 0.15-1.2 mm. If the particles are broken to a too fine size, high energy consumption is required, and the increased friction between the particles and the poor flowability may cause uneven compaction and damage to the structure of the raw material in the subsequent molding process. If the particles are broken to a too coarse size, it will be difficult for the raw material to tightly bond in the subsequent molding process, resulting in defects such as voids or cracks in the molded product, which reduces the strength and quality of the product. The particle size of 0.15-1.2 mm can reduce energy consumption and is conducive to ensuring the molding effect and product quality in the subsequent process.

[0013] As a preferred scheme, the pressing forming condition is that the mechanical pressure is 200-400 MPa and the time is 0.5-2.5 min. The energy density and strength of the raw material can be improved by pressing forming, the pore structure of the biomass charcoal can be controlled, the thermal stability and heat resistance are improved, and the combustion performance is improved. With the increase of pressure and time, the improvement of the pressing effect tends to be flat, and the energy consumption increases greatly, so the mechanical pressure is selected as 200-400 MPa and the time is selected as 0.5-2.5 min.

[0014] As a preferred scheme, the particle size of the biomass particles is 0.5-2 cm.

[0015] As a preferred scheme, the low-temperature torrefaction treatment condition is that the heating rate is 1-10 ℃ / min, the target temperature is 180-320 ℃, and the holding time is 10-40 min. The specific torrefaction parameters are determined according to the pyrolysis characteristic temperature of the biomass raw material and the characteristics of the torrefaction product. Under the preferred low-temperature torrefaction treatment condition, the oxygen-containing groups such as carboxyl and hydroxyl can be effectively removed in the form of H2O and CO2, and the structural integrity and compactness of the biochar can be ensured to the greatest extent. Further preferably, the low-temperature torrefaction temperature is 250-300 ℃.

[0016] As a preferred scheme, the medium-temperature carbonization treatment condition is that the heating rate is 1-10 ℃ / min, the target temperature is 600-1000 ℃, and the residence time is 10-40 min. With the increase of the carbonization temperature, the pore structure and surface area of the formed biochar gradually increase, but too high temperature can also cause deformation and collapse of some fine pore structures, and the porosity can also decrease at a higher temperature, mainly because high temperature can cause pore enlargement or coalescence of adjacent nanopores, thermal inactivation, and pore blockage caused by carbon melting. Further preferably, the carbonization temperature is 700-900 ℃.

[0017] As a preferred scheme, the high-temperature pyrolysis treatment condition is that the target temperature is 1000-1200 ℃, and the flow rate of the composite gas is controlled at 0.02-0.3 L / min. When the temperature is relatively low, such as below 1000 ℃, the pyrolysis of biomass oil gas mainly produces small molecule gas and liquid products, and with the further increase of the temperature to above 1000 ℃, the biomass oil gas can be efficiently converted into high-calorific-value fuel gas.

[0018] As a preferred scheme, the volume concentration of CO2 in the composite gas is 5-10%, and the volume concentration of H2O is 5-10%. The presence of a small amount of CO2 and H2O in the composite gas can accelerate the pyrolysis of the oil gas, is beneficial to the reforming reaction of methane to generate CO and H2, and the composite gas can be derived from the removal of low-volatile components in the low-temperature torrefaction process.

[0019] As a preferred scheme, the biomass charcoal fuel has a heat value of 30-38 MJ / kg, a volatile matter of 0.2-2%, a specific surface area of 10-25 m 2 / g, a porosity of 15-25%, and an apparent density of 1.8-2.5 g / cm 3 The biomass gas mainly comprises CO, H2 and CH4, has a heat value of 14-24 MJ / Nm 3 , a CO volume content of 30-50%, a H2 volume content of 12-25%, and a CH4 volume content of 8-20%, and is used as a blowing fuel.

[0020] Compared with the prior art, the technical scheme of the present application has the following beneficial effects:

[0021] (1) The technical scheme of the present application removes the gas of low-quality components in advance through a low-temperature baking process, avoids the gas from entering a subsequent high-temperature cracking process, and thus avoids a great waste of energy. The present application separates CO2 and H2O from the gas product removed through baking and uses the CO2 and H2O to promote the generation of high-quality gas in the high-temperature cracking stage, and the remaining gas is recovered and integrated back into the baking process to provide part of the heat for the low-temperature baking process of the biomass, thereby helping to reduce energy consumption and cost, improve the sustainability and economic feasibility of the baking process. In addition, the raw material after low-temperature baking treatment has lower water absorption, higher energy density, grindability and heat value, which is beneficial to the stability of the biomass raw material and the subsequent upgrading treatment and large-scale industrial application.

[0022] (2) The technical scheme of the present application obtains a variety of high-quality products through a simple preparation process. After low-temperature baking, the biomass raw material is subjected to a carbonization process at a temperature close to the coking temperature, and the deep carbonization is beneficial to the complete removal of the volatile matter of the biomass and the densification of the carbon structure, thereby obtaining a biochar with a significantly reduced reactivity. The high-temperature cracking treatment object is a high-concentration oil and gas substance. The present application removes low-quality components in advance through low-temperature baking and recombines the gas components through a medium-temperature carbonization process, so that the pyrolysis gas has a higher content of combustible components (H2, CH4, CO) and a higher heat value.

[0023] (3) The technical solution of the present invention promotes the more efficient use of biomass energy in the sintering process. The existing technology does not have a good method for treating the difficult-to-use, toxic and harmful biomass tar produced as a by-product of the biomass pyrolysis process. High-temperature cracking converts the tar into high-quality fuel gas, achieving the purpose of energy recovery, equipment protection and environmental protection. At the same time, the application of biomass gas in the sintering material layer injection can optimize the thermal state of the sintering material layer, thereby increasing the biochar replacement rate and reducing the amount of fossil fuel used in the sintering material layer. The composite clean fuel structure of biochar and biomass gas used in iron ore sintering can achieve isothermal replacement of 40-70% of fossil fuels and effectively control the SO2 content of sintering flue gas. x 、NO x 、CO x emission.

[0024] In summary, the present invention combines a low-temperature baking process with two high-temperature processes to produce two high-quality clean fuels: biochar and gas. This achieves multi-stage, multi-level conversion and utilization of biomass materials and energy, promoting efficient carbon emission reduction in the sintering process. Compared to existing conventional biomass pyrolysis processes, the present invention offers improved combustion performance, higher energy efficiency, reduced environmental pollution, and greater process economics. DETAILED DESCRIPTION

[0025] In order to facilitate understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

[0026] Example 1

[0027] Corn stalks were ground to a particle size of approximately 1 mm. The biomass was then compressed into biomass pellets at room temperature under a mechanical pressure of 300 MPa for a compression time of 1.5 minutes. The pellets were first heated to 300°C at a heating rate of 5°C / min and held for 20 minutes to complete the torrefaction pretreatment. The pellets were then heated to 900°C at a heating rate of 5°C / min and held for 15 minutes to complete the carbonization process. Finally, the biomass pyrolysis gas and biomass tar, byproducts of the carbonization process, were pyrolyzed at 1200°C at a flow rate of 0.1 L / min. The atmosphere conditions for the torrefaction pretreatment and carbonization were N2 at a gas flow rate of 0.1 L / min; the atmosphere conditions for the pyrolysis process were N2 88%, CO2 6%, H2O 6%, and a gas flow rate of 0.1 L / min. The characteristics of the prepared biochar and biogas are shown in Table 1. Replacing 50% of coke powder with equal heat of the two for iron ore sintering can obtain sintering indicators equivalent to those when coke powder is used entirely. The sintering indicators and pollutant emission reduction effects are shown in Table 2.

[0028] Example 2

[0029] The corn straw was ground to about 0.5 mm, and then the biomass was compressed into biomass particles under the conditions of mechanical pressure 250 MPa, compression time 1 min, and room temperature. The particles were first heated to 260°C at a heating rate of 10°C / min and stayed for 40 min to complete the torrefaction pretreatment, and then the particles were heated to 700°C at a heating rate of 10°C / min and stayed for 25 min to complete the carbonization treatment. Finally, the by-product biomass pyrolysis gas and biomass tar in the carbonization process were cracked at a temperature of 1100°C with a flow rate of 0.1 L / min. The atmosphere conditions for torrefaction pretreatment and carbonization treatment were N2, and the gas flow rate was 0.1 L / min; the atmosphere conditions for cracking treatment were N2 88%, CO2 6%, H2O 6%, and the gas flow rate was 0.1 L / min. The properties of the prepared biomass char and biomass fuel gas are shown in Table 1. When the two were used to replace 50% of the coke powder for iron ore sintering, the sintering indexes were comparable to those when coke powder was used completely, and the sintering indexes and pollutant emission reduction effects are shown in Table 2.

[0030] Example 3

[0031] The corn straw was ground to about 0.8 mm, and then the biomass was compressed into biomass particles under the conditions of mechanical pressure 250 MPa, compression time 1 min, and room temperature. The particles were first heated to 280°C at a heating rate of 5°C / min and stayed for 30 min to complete the torrefaction pretreatment, and then the particles were heated to 800°C at a heating rate of 5°C / min and stayed for 20 min to complete the carbonization treatment. Finally, the by-product biomass pyrolysis gas and biomass tar in the carbonization process were cracked at a temperature of 1000°C with a flow rate of 0.5 L / min. The atmosphere conditions for low-temperature torrefaction treatment and medium-temperature carbonization treatment were N2, and the gas flow rate was 0.1 L / min; the atmosphere conditions for high-temperature cracking treatment were N2 88%, CO2 6%, H2O 6%, and the gas flow rate was 0.1 L / min. The properties of the prepared biomass char and biomass fuel gas are shown in Table 1. When the two were used to replace 50% of the coke powder for iron ore sintering, the sintering indexes were comparable to those when coke powder was used completely, and the sintering indexes and pollutant emission reduction effects are shown in Table 2.

[0032] Comparative Example 1 (reference)

[0033] After the iron ore, flux, coke powder, and return fines were proportioned by mass percentage, they were mixed and granulated, and then were distributed to the sintering trolley. The sintering process was completed by air draft ignition, and the sintering indexes are shown in Table 2.

[0034] Comparative Example 2

[0035] The corn straw was ground to a particle size of about 1 mm, and then the biomass was compressed into biomass particles under a mechanical pressure of 300 MPa, a compression time of 1.5 min, and room temperature. The particles were heated to 900℃ at a heating rate of 5℃ / min and stayed for 15 min to complete the carbonization treatment. Finally, the byproduct biomass pyrolysis gas and biomass tar in the carbonization process were cracked at a temperature of 1200℃ with a flow rate of 0.1 L / min. The atmosphere condition for carbonization treatment was N2, and the gas flow rate was 0.1 L / min. The atmosphere condition for cracking treatment was N288%, CO26%, and H2O6%, and the gas flow rate was 0.1 L / min. The properties of the prepared biomass charcoal and biomass fuel gas are shown in Table 1. The two were used to replace 50% of the coke powder for iron ore sintering in equal heat quantity. The sintering indexes and pollutant emission reduction effects are shown in Table 2.

[0036] Comparative Example 3

[0037] The corn straw was ground to a particle size of about 0.5 mm, and then the biomass was compressed into biomass particles under a mechanical pressure of 250 MPa, a compression time of 1 min, and room temperature. The particles were first heated to 260℃ at a heating rate of 10℃ / min and stayed for 40 min to complete the baking pretreatment, and then the particles were heated to 700℃ at a heating rate of 10℃ / min and stayed for 25 min to complete the carbonization treatment. The atmosphere condition for baking pretreatment and carbonization treatment was N2, and the gas flow rate was 0.1 L / min. The properties of the prepared biomass charcoal and biomass fuel gas are shown in Table 1. The two were used to replace 50% of the coke powder for iron ore sintering in equal heat quantity. The sintering indexes and pollutant emission reduction effects are shown in Table 2. Due to the lack of high-temperature cracking treatment, a large amount of biomass pyrolysis oil cannot be converted into fuel gas, and the total amount of fuel gas and the proportion of combustible gas components (H2, CH4, CO) are significantly reduced. In addition, the pyrolysis oil has complex composition and unstable chemical properties, and has problems such as high acidity, high water content, high oxygen content, and low calorific value, which are difficult to utilize.

[0038] Comparative Example 4

[0039] The corn straw is ground to about 0.8 mm, and then the biomass is compressed into biomass particles under the conditions of mechanical pressure 250 MPa, compression time 1 min and room temperature. The particles are heated to 800 ℃ at a heating rate of 5 ℃ / min and stay for 20 min to complete the carbonization treatment. The atmosphere condition for carbonization treatment is N2, and the gas flow is 0.1 L / min. The properties of the prepared biomass charcoal are shown in Table 1, which is used to replace 50% of the coke powder for iron ore sintering. The sintering indexes and pollutant emission reduction effects are shown in Table 2. Due to the lack of low-temperature torrefaction treatment and high-temperature pyrolysis treatment, a large amount of biomass pyrolysis oil cannot be converted into fuel gas, and a large amount of low-quality components (CO2, H2O) cannot be removed. The total amount of fuel gas and the proportion of combustible gas components (H2, CH4, CO) are greatly reduced. The pyrolysis oil is complex in composition and unstable in chemical properties, and has problems such as high acidity, high water content, high oxygen content and low calorific value. The pyrolysis oil and gas are difficult to use.

[0040] Comparative Example 5

[0041] The corn straw is ground to about 0.5 mm, and then the biomass is compressed into biomass particles under the conditions of mechanical pressure 250 MPa, compression time 1 min and room temperature. The particles are first heated to 350 ℃ at a heating rate of 10 ℃ / min and stay for 15 min to complete the torrefaction pretreatment, and then the particles are heated to 700 ℃ at a heating rate of 10 ℃ / min and stay for 25 min to complete the carbonization treatment. Finally, the biomass pyrolysis gas and biomass tar by-produced in the carbonization process are cracked at a temperature of 1100 ℃ and a flow rate of 0.1 L / min. The atmosphere conditions for torrefaction pretreatment and carbonization treatment are N2, and the gas flow is 0.1 L / min. The atmosphere condition for cracking treatment is N288%, CO26%, H2O6%, and the gas flow is 0.1 L / min. The properties of the prepared biomass charcoal and biomass fuel gas are shown in Table 1, which are used to replace 50% of the coke powder for iron ore sintering. The sintering indexes and pollutant emission reduction effects are shown in Table 2.

[0042] Comparative Example 6

[0043] The corn straw was ground to about 0.8 mm, and then compressed into biomass pellets under the conditions of mechanical pressure 250 MPa, compression time 1 min, and room temperature. The pellets were first heated to 280℃ at a heating rate of 5℃ / min and stayed for 30 min to complete the torrefaction pretreatment, and then heated to 800℃ at a heating rate of 5℃ / min and stayed for 20 min to complete the carbonization treatment. Finally, the byproduct biomass pyrolysis gas and biomass tar from the carbonization process were cracked at a temperature of 1000℃ with a flow rate of 0.5 L / min. The atmosphere condition for the low-temperature torrefaction, medium-temperature carbonization, and high-temperature cracking treatment was N2, and the gas flow rate was 0.1 L / min. The properties of the prepared biomass char and biomass fuel gas are shown in Table 1. The two were used to replace 50% of the coke powder for iron ore sintering, and the sintering indexes and pollutant emission reduction effects are shown in Table 2.

[0044] Table 1 Properties of biomass char and biomass fuel gas

[0045]

[0046]

[0047] Table 2 Effects of biomass replacing fossil fuel on sintering indexes and pollutant emission reduction

[0048]

Claims

1. A method for preparing a composite clean fuel for sintering based on biomass thermal treatment and quality improvement, characterized by: The following steps are involved: 1) Grinding and pressing the biomass raw materials to obtain biomass particles; 2) placing the biomass particles under a protective atmosphere, first performing a low-temperature baking treatment to remove low-volatile matter, and then performing a medium-temperature carbonization treatment to obtain biomass charcoal fuel and pyrolysis oil and gas; 3) The pyrolysis oil and gas are subjected to high-temperature cracking treatment in a composite atmosphere containing water vapor and carbon dioxide to obtain biomass fuel gas.

2. The method for preparing a composite clean fuel for sintering based on biomass thermal treatment and quality improvement according to claim 1, characterized in that: The biomass raw material includes at least one of agricultural waste straw, sawdust, and sugarcane bagasse.

3. The method for preparing a composite clean fuel for sintering based on biomass thermal treatment and upgrading according to claim 1 or 2, characterized in that: The biomass raw material is ground to a particle size of 0.15 to 1.2 mm.

4. The method for preparing a composite clean fuel for sintering based on biomass thermal treatment and quality improvement according to claim 1, characterized in that: The conditions for the compression molding are: a mechanical pressure of 200 to 400 MPa and a time of 0.5 to 2.5 minutes.

5. The method for preparing a composite clean fuel for sintering based on biomass thermal treatment and quality improvement according to claim 1, characterized in that: The particle size of the biomass particles is 0.5 to 2 cm.

6. The method for preparing a composite clean fuel for sintering based on biomass thermal treatment and quality improvement according to claim 1, characterized in that: The conditions of the low-temperature baking treatment are: a heating rate of 1 to 10° C. / min, a target temperature of 180 to 320° C., and a holding time of 10 to 40 minutes.

7. The method for preparing a composite clean fuel for sintering based on biomass thermal treatment and upgrading according to claim 1, characterized in that: The conditions of the medium-temperature carbonization treatment are: a heating rate of 1 to 10°C / min, a target temperature of 600 to 1000°C, and a residence time of 10 to 40 minutes.

8. The method for preparing a composite clean fuel for sintering based on biomass thermal treatment and quality improvement according to claim 1, characterized in that: The conditions for the high-temperature cracking treatment are: a target temperature of 1000-1200° C., and a composite gas flow rate controlled at 0.02-0.3 L / min.

9. The method for preparing a composite clean fuel for sintering based on biomass thermal treatment and quality improvement according to claim 8, characterized in that: The volume concentration of CO2 in the composite gas is 5-10%, and the volume concentration of H2O is 5-10%.

10. The method for preparing a composite clean fuel for sintering based on biomass thermal treatment and upgrading according to claim 1, 2, 4, 5, 6, 7, 8 or 9, characterized in that: The biomass charcoal fuel has a calorific value of 30 to 38 MJ / kg, a volatile matter of 0.2 to 2%, and a specific surface area of ​​10 to 25 m 2 / g, porosity of 15-25%, apparent density of 1.8-2.5g / cm 3 , which replaces fossil fuels and is mixed with raw materials including iron ore, flux, and return ore for pelletizing; The main components of the biomass gas are CO, H2 and CH4, and the calorific value is 14-24MJ / Nm 3 The volume content of CO is 30-50%, the volume content of H2 is 12-25%, and the volume content of CH4 is 8-20%, which is used as injection fuel.

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