A method for preparing ultra-high-grade homogeneous microporous pellets for hydrogen-based shaft furnaces

Abstract

The present invention discloses a method for preparing ultra-high-grade homogeneous microporous pellets for hydrogen-based shaft furnaces, belonging to the technical field of pellet preparation. The method comprises the following steps: mixing ultra-high-grade iron concentrate with an organic binder, grinding, and pelletizing in sequence to obtain ultra-high-grade green pellets; the ultra-high-grade green pellets are then subjected to heat treatment in a blast drying section, an exhaust drying section, a preheating section, a temperature rising section, a microwave roasting section, a cooling section I, a cooling section II, and a cooling section III to obtain ultra-high-grade homogeneous microporous pellets; the method uses an organic binder to form pellets, optimizes the thermal system and the airflow system, controls the appropriate oxidation degree of the pellets at different stages, and combines microwave roasting to strengthen consolidation, thereby preparing pellets with high strength, containing a portion of Fe3O4, and having a uniform microporous structure. This method is beneficial for reducing energy consumption in pellet production, improving the reduction performance of the ultra-high-grade pellets in a hydrogen-based shaft furnace, and reducing the reduction expansion rate of the pellets.

Description

Technical Field

[0001] The present invention relates to a method for preparing pellets, in particular to a method for preparing ultra-high-grade homogeneous microporous pellets for a hydrogen-based shaft furnace, belonging to the technical field of pellet preparation. Background Art

[0002] Pellets offer advantages such as high iron grade, low process energy consumption, and low pollution emissions, making them a high-quality charge for hydrogen-based shaft furnace-electric furnace short-process smelting. Due to the low process temperature of the hydrogen-based shaft furnace, gangue and harmful elements in the pellets are retained in the direct reduced iron (DRI), increasing energy consumption and costs in subsequent smelting processes. Therefore, in the steelmaking short-process, the TFe grade of the pellets used should be as high as possible. Using ultra-high-grade pellets for hydrogen-based shaft furnace reduction not only reduces subsequent smelting energy consumption, but also produces high-purity direct reduced iron (DRI), a premium raw material for the short-process smelting of pure and specialty steels. Currently, pellets for hydrogen-based shaft furnaces are primarily made from high-grade iron ore concentrate with a TFe grade of 67-69 wt.%, combined with inorganic binders such as bentonite. This high-grade pellet with a TFe grade of approximately 67 wt.% is used in hydrogen-based shaft furnace direct reduced iron production.

[0003] In recent years, with the advancement of mineral processing technology, high-grade iron ore concentrates with TFe >71.5wt.% and SiO2 <0.5wt.% produced from medium- and low-grade iron ore resources through multi-stage beneficiation have been developed to meet the requirements for ultra-high-grade pellet production. However, the ultra-high-grade iron ore concentrates obtained through multi-stage beneficiation are characterized by fine particle size, high reactivity, and low gangue content. Ultra-high-grade pellets produced using either the chain grate-rotary kiln process or the belt roaster process suffer from low pellet consolidation strength, high roasting temperatures, uneven pellet structure, and a tendency to develop core-shell structures. This not only increases energy consumption during the ultra-high-grade pellet production process, but also affects the reduction rate during hydrogen-based shaft furnace reduction due to the uneven internal and external structure of the pellets, leading to more severe stress expansion, cracking, and pulverization. Summary of the Invention

[0004] The prior art process for producing ultra-high-grade pellets from high-grade iron ore concentrates presents technical challenges, such as high roasting temperatures, uneven pellet structures, and the susceptibility to stress expansion, cracking, and pulverization during hydrogen-based shaft furnace reduction. The present invention aims to provide a method for producing ultra-high-grade, homogeneous, microporous pellets for use in hydrogen-based shaft furnaces. This method produces ultra-high-grade pellets with high strength and a uniform microporous structure, imparting excellent hydrogen-based shaft furnace reduction performance and a low reduction expansion rate. This method also reduces energy consumption and emissions during the production of ultra-high-grade pellets, providing a foundation for the development of hydrogen-based shaft furnaces.

[0005] To achieve the above technical objectives, the present invention provides a method for preparing ultra-high-grade homogeneous microporous pellets for a hydrogen-based shaft furnace. The method comprises the following steps: mixing, grinding, and pelletizing an ultra-high-grade iron ore concentrate and an organic binder in sequence to obtain ultra-high-grade green pellets; and the ultra-high-grade green pellets are subjected to a heat treatment in a blast drying section, an exhaust drying section, a preheating section, a heating section, a microwave roasting section, a cooling section I, a cooling section II, and a cooling section III to obtain ultra-high-grade homogeneous microporous pellets.

[0006] The oxidation degree of the ultra-high-grade green balls is controlled within the range of 70-80% after the heating stage;

[0007] The process conditions of the microwave roasting section are: microwave power of 915-2450 MHz, roasting temperature of 1200-1250° C., and roasting time of 15-25 minutes.

[0008] The cooling section I adopts air cooling with oxygen removed to a volume fraction of less than 3%, and the hot exhaust gas generated in the cooling section I is reheated to 1150-1180°C and then circulated to the heating section;

[0009] The cooling section II is air cooled, and the hot exhaust gas generated in the cooling section II is circulated to the preheating section.

[0010] The key to the technical solution of the present invention is to use ultra-high-grade iron ore concentrate to prepare ultra-high-grade pellets with high strength and uniform microporous structure, which not only have good reducibility, but also can effectively inhibit expansion, cracking and pulverization during hydrogen-based reduction. More specifically, on the one hand, by using organic binders in combination with strong mixing, grinding and pelletizing processes, ultra-high-grade raw balls with uniform particle size distribution, high sphericity, uniform microporous structure and composition can be prepared, which can effectively inhibit the hot spot phenomenon caused by the accumulation of local electric fields during subsequent microwave roasting and avoid problems such as uneven heating of the pellets; on the other hand, by controlling the oxidation degree of the pellets to 70~80% before entering microwave roasting, and combining the thermal system of low-temperature oxidation, rapid heating and microwave roasting, while improving the solid-phase diffusion activity of the particles, the inner and outer layers of the pellets are promoted. Uniform consolidation can produce pellets with high strength and uniform microporous structure, which is beneficial to improving the reduction rate of pellets and inhibiting stress expansion, cracking and pulverization caused by uneven pellet structure. Thirdly, by optimizing the thermal system and air flow system of the pellet heat treatment and cooling process, not only can the oxidation rate of the pellets during the heating process be reduced, but also the degree of oxidation during the cooling process can be controlled to adjust the mineral composition of the ultra-high-grade pellets and retain a part of Fe3O4 in the pellets to reduce the expansion and pulverization caused by the Fe2O3 crystal transformation during the reduction process.

[0011] As a preferred solution, the ultra-high-grade iron concentrate has a TFe mass fraction of ≥71.5%, a FeO mass fraction of ≥27%, a particle size distribution of 0.5-70 μm, and a median particle size D 50 ≤20μm. Ultra-high-grade iron ore concentrate is a raw material that is easily obtained in existing technologies.

[0012] The ultra-high-grade homogeneous microporous pellets of the present invention refer to pellets made from ultra-high-grade iron ore concentrate.

[0013] As a preferred solution, the mass percentage of the ultra-high-grade iron ore concentrate and the organic binder is 99.94-99.80%:0.06-0.20%. The use of an organic binder can avoid the reduction in pellet grade caused by inorganic binders.

[0014] As a preferred solution, the organic binder includes at least one of sodium carboxymethyl cellulose, anionic polyacrylamide, soluble starch, and sodium humate. These organic binders are relatively common organic binders in the prior art.

[0015] As a preferred solution, the conditions for wet grinding are: the raw material moisture is controlled at 6-7.5 wt.%, and the wet grinding time is 3-5 minutes. The wet grinding process can improve the uniformity of component distribution and prevent uneven heating during microwave roasting.

[0016] As a preferred solution, the pelletizing is achieved using a disc pelletizer. During the pelletizing process, the moisture content of the ultra-high-grade green balls is controlled to 8.5-9.0 wt.%, the pelletizing time is 8-10 minutes, and the disc inclination angle is 43-45 degrees. By controlling the process parameters of the disc pelletizer, pellets with uniform particle size and high sphericity can be obtained, which is conducive to improving the uniformity of microwave roasting.

[0017] As a more preferred solution, the diameter of the ultra-high-grade green balls is 12-14 mm, and the sphericity is greater than 0.9.

[0018] As a preferred embodiment, the hot exhaust gas generated in Cooling Stage I is heated to 1150-1180°C by burners before being circulated to the heating stage. During this heating process, the burner's excess air coefficient is 1.05-1.1. The cooling gas used in Cooling Stage I of the present invention utilizes byproduct gas from air separation oxygen production equipment in the steel industry, with an oxygen volume fraction of less than 3%. By using a low-oxygen gas in Cooling Stage I, primarily due to the high pellet temperature in Cooling Stage I, pellet oxidation is reduced during the cooling process, thereby preserving some Fe₃O₄ and reducing the expansion and pulverization caused by Fe₂O₃ crystal transformation during hydrogen-based shaft furnace reduction. Furthermore, the hot exhaust gas from Cooling Stage I (if necessary, heated by burners to meet the pellet heating stage temperature requirements) is circulated to the heating stage for pellet heating, thereby reducing the pellet oxidation rate during the heating process and thus controlling the degree of pellet oxidation after heating.

[0019] The excess air coefficient involved in the present invention refers to the ratio of the actual air supply volume to the theoretical air requirement, which is called the excess air index.

[0020] As a preferred solution, the hot exhaust gas generated in the cooling stage II has a temperature of 750-820° C. and is circulated to the preheating stage.

[0021] As a preferred solution, the cooling stage III adopts air cooling, and the hot exhaust gas generated by the cooling stage III has a temperature of 300-400° C. and is circulated to the blast drying stage.

[0022] As a preferred solution, the temperature of the hot exhaust gas generated in the temperature rising section is 450-550°C and is circulated to the exhaust drying stage.

[0023] The present invention can effectively reduce process energy consumption and costs and achieve efficient utilization of waste heat by recycling hot waste gas.

[0024] As a preferred solution, the heat treatment time of the air drying section is 2 to 3 minutes.

[0025] As a preferred solution, the heat treatment time of the exhaust drying section is 4 to 5 minutes.

[0026] As a preferred solution, the heat treatment time of the preheating section is 8 to 10 minutes.

[0027] As a preferred solution, the heat treatment time in the temperature rising section is 3 to 4 minutes.

[0028] The ultra-high-grade homogeneous microporous pellets of the present invention have an Fe3O4 content of 4-10 wt.%, which can improve the hydrogen-based shaft furnace reducibility of the ultra-high-grade pellets while reducing the reduction expansion rate of the pellets.

[0029] The microwave roasting temperature of the present invention is more preferably 1220-1230°C.

[0030] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0031] (1) The present invention prepares ultra-high-grade green balls with uniform particle size distribution, high sphericity, uniform microporous structure and composition by combining an organic binder with strong mixing, grinding and a suitable pelletizing process. It can suppress the hot spot phenomenon caused by the accumulation of local electric fields during microwave roasting and avoid uneven heating of the pellets.

[0032] (2) The present invention controls the appropriate oxidation degree of the pellets before microwave roasting, and combines a thermal system of low-temperature oxidation, rapid heating, and direct heating during microwave roasting. This improves the solid-phase diffusion activity of the particles while promoting uniform consolidation of the inner and outer layers of the pellets, thereby preparing pellets with good strength and uniform microporous structure, which is beneficial to improving the reduction rate of the pellets and inhibiting stress expansion, cracking, and pulverization caused by uneven pellet structure.

[0033] (3) The present invention optimizes the thermal system and air flow system of the pellet heat treatment and cooling process, adjusts the mineral composition of the ultra-high-grade pellets, retains a portion of Fe3O4 in the pellets, and reduces the expansion and pulverization caused by the Fe2O3 crystal transformation during the reduction process.

[0034] (4) The present invention uses the by-product gas of the air separation oxygen production equipment in the steel industry to cool the pellets in the cooling section I. The low oxygen concentration gas obtained after deoxygenation is used to cool the pellets in the cooling section I, which can reduce the oxidation of the pellets during the cooling process, thereby retaining part of Fe3O4, so as to reduce the expansion and pulverization caused by the Fe2O3 crystal transformation during the hydrogen-based vertical furnace reduction process. The hot exhaust gas from the cooling section I has a low oxygen content and is circulated to the heating section to heat the pellets. This can not only reduce the oxidation rate of the pellets during the heating process, thereby controlling the oxidation degree of the pellets after heating, but also can be used in the pellet heating process, which can effectively reduce the process energy consumption and cost and achieve efficient utilization of waste heat. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a process flow for preparing ultra-high-grade homogeneous microporous pellets of the present invention, wherein 1 is a blast drying section; 2 is an exhaust drying section; 3 is a preheating section; 4 is a heating section; 5 is a microwave roasting section; 6 is a cooling section I; 7 is a cooling section II; 8 is a cooling section III; 9 is a burner; 10 is a flue gas treatment system; 11 is an air separation oxygen production equipment; and 12 is a fan.

[0036] Figure 2 This is the microstructure of the pellets prepared in Example 1.

[0037] Figure 3This is the microstructure of the pellets prepared in Comparative Example 1. DETAILED DESCRIPTION

[0038] In order to further illustrate the content of the present invention, the present invention will be described in more comprehensive and detailed manner in combination with preferred embodiments below, but the protection scope of the claims of the present invention is not limited to the following specific embodiments.

[0039] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0040] The test methods for the parameters in the following examples are all conventional test methods in the art:

[0041] Among them, the porosity and average pore size of the pellets are measured by mercury intrusion injection method; the hydrogen-based shaft furnace reduction performance test of pellets refers to GB / T 24235-2009 and GB / T 13240-2018; the sphericity is the ratio of the projected area of ​​the pellet to the area of ​​the minimum circumscribed circle.

[0042] The ultra-high-grade iron concentrate used in the following specific examples has a TFe mass fraction of 71.71%, a FeO mass fraction of 27.81%, a particle size distribution of 0.5-70 μm, and a median particle size D50 of 16.52 μm.

[0043] Example 1

[0044] Ultra-high-grade iron ore concentrate and sodium carboxymethyl cellulose were vigorously mixed and milled at a weight ratio of 99.94:0.06 for 3 minutes at a moisture content of 7.5 wt%. Under the pelletizing process parameters of 8.5 wt%, 10 minutes, and a disc inclination angle of 43°, ultra-high-grade green pellets with a diameter of 12-14 mm and a sphericity greater than 0.9 were produced. These green pellets were then dried with 300°C hot air (from the hot exhaust gas from Cooling Stage III) for 3 minutes, then dried with 450°C hot air (from the hot exhaust gas from the warming stage) for 5 minutes, preheated with 750°C hot air (from the hot exhaust gas from Cooling Stage II) for 10 minutes, and then heated to 1180°C hot air (from Cooling Stage I, supplemented by a burner with an excess air number of 1.05) for 3 minutes. The pellets achieved an oxidation degree of 75%. During the microwave roasting process, the microwave power was 2450 MHz. After microwave roasting at 1240°C for 15 min, the product entered the cooling section (cooling section I, cooling section II, and cooling section III in sequence). The volume fraction of oxygen in the cooling gas used in cooling section I was <3%.

[0045] The ultra-high-grade pellets prepared have a compressive strength of 2783N, a Fe3O4 mass fraction of 6%, a porosity of 24.67%, an average pore size of 1.85μm, and uniform consolidation of the pellets without obvious core-shell structure. The reduction expansion rate of the ultra-high-grade pellets prepared at 900℃ in HYL atmosphere is 13.3%, and the reduction powdering index (RDI) of the pellets at 500℃ in HYL atmosphere is 13.3%. +6.3 The microstructure of pellets is shown in the figure below. Figure 2 As shown, it can be clearly seen that the pellet structure is relatively uniform.

[0046] Example 2

[0047] Ultra-high-grade iron ore concentrate, anionic polyacrylamide, and soluble starch were vigorously mixed and milled in a weight ratio of 99.85:0.05:0.1 for 5 minutes at a moisture content of 6 wt.%. Then, under the pelletizing process parameters of a moisture content of 9.0 wt.%, a pelletizing time of 8 minutes, and a disc inclination angle of 45°, the prepared green pellets were blown and dried for 2 minutes with 400°C hot air (from the hot exhaust gas generated in the cooling stage III), exhausted and dried for 4 minutes with 550°C hot air (from the hot exhaust gas generated in the heating stage), preheated for 8 minutes with 800°C hot air (from the hot exhaust gas generated in the cooling stage II), and heated for 3 minutes with 1150°C hot air (from the hot exhaust gas generated in the cooling stage I, supplemented by a burner with an excess air number of 1.05). At this point, the pellet oxidation degree reached 70%. During the microwave roasting process, the microwave power was 915 MHz. After microwave roasting at 1210° C. for 25 min, the sample entered the cooling section. The volume fraction of oxygen in the cooling gas used in cooling section I was less than 3%.

[0048] The ultra-high-grade pellets prepared have a compressive strength of 2577N, a Fe3O4 mass fraction of 10%, a porosity of 24.14%, an average pore size of 2.17μm, and uniform consolidation of the pellets without obvious core-shell structure. The reduction expansion rate of the ultra-high-grade pellets prepared at 900℃ in HYL atmosphere is 10.5%, and the reduction powdering index (RDI) of the pellets at 500℃ in HYL atmosphere is 10.5%. +6.3 It is 96.44%.

[0049] Example 3

[0050] Ultra-high-grade iron ore concentrate, sodium carboxymethyl cellulose, and sodium humate were vigorously mixed and milled in a weight ratio of 99.8:0.05:0.15 for 3 minutes at a moisture content of 7.5 wt%. Under the pelletizing process parameters of 8.8 wt%, 10 minutes, and a disc inclination angle of 43°, ultra-high-grade green pellets with a diameter of 12-14 mm and a sphericity greater than 0.9 were produced. These green pellets were then dried with 350°C hot air (from the hot exhaust gas of cooling stage III) for 3 minutes, then dried with 500°C hot air (from the hot exhaust gas of the warming stage) by exhaust air for 5 minutes, preheated with 820°C hot air (from the hot exhaust gas of cooling stage II) for 10 minutes, and then heated to 1180°C hot air (from the hot exhaust gas of cooling stage I, supplemented by a burner with an excess air number of 1.10) for 4 minutes, achieving an oxidation degree of 80%. During the microwave roasting process, the microwave power was 915 MHz. After microwave roasting at 1230° C. for 20 min, the sample entered the cooling section. The volume fraction of oxygen in the cooling gas used in cooling section I was less than 3%.

[0051] The ultra-high-grade pellets prepared have a compressive strength of 2895N, a Fe3O4 mass fraction of 4%, a porosity of 23.88%, an average pore size of 1.68μm, and uniform consolidation of the pellets without obvious core-shell structure. The reduction expansion rate of the ultra-high-grade pellets prepared at 900℃ in HYL atmosphere is 15.8%, and the reduction powdering index (RDI) of the pellets at 500℃ in HYL atmosphere is 15.8%. +6.3 It is 97.68%.

[0052] Comparative Example 1

[0053] Compared with Example 1, the difference is that the preheating temperature is 860℃, the time is 14min, and the oxidation degree of the pellets is 90%. The compressive strength of the prepared ultra-high-grade pellets is 2313N, the Fe3O4 mass fraction is 1.6%, the porosity is 25.33%, the average pore size is 2.85μm, and the pellets have a clear shell-core structure. The reduction expansion rate of the prepared ultra-high-grade pellets at 900℃ and HYL atmosphere is 23.9%, and the reduction powder index RDI of the pellets at 500℃ and HYL atmosphere is 23.9%. +6.3 The pellets were 93.12% in weight. Compared with Example 1, the pellets were too oxidized before microwave roasting, and the solid-phase diffusion activity of the inner and outer layers of the pellets was quite different. After roasting, the pellets had an uneven structure and reduced strength. During the hydrogen-based shaft furnace reduction process, stress expansion, cracking, and pulverization were likely to occur. Figure 3 As shown, cracking can be clearly seen.

[0054] Comparative Example 2

[0055] Compared with Example 1, the difference is that the roasting stage adopts conventional heating method instead of microwave roasting for roasting, and ultra-high-grade pellets are obtained after roasting at 1270°C for 15 minutes. The compressive strength of the prepared pellets is 2591N (in order for the pellets to achieve a compressive strength similar to that of Example 1, a higher roasting temperature is required by conventional roasting), the Fe3O4 mass fraction is 5%, the porosity is 25.57%, the average pore size is 2.74μm, and the pellets have an obvious shell-core structure. The reduction expansion rate of the prepared ultra-high-grade pellets at 900°C and HYL atmosphere is 19.2%, and the reduction powdering index RDI of the pellets at 500°C and HYL atmosphere is 19.2%. +6.3 Compared with Example 1, microwave roasting is not used. After roasting, the outer layer of the pellets becomes denser, the pellet structure is uneven, and stress expansion, cracking and pulverization are easily caused during the hydrogen-based shaft furnace reduction process.

[0056] Comparative Example 3

[0057] Compared with Example 1, the difference is that the volume fraction of oxygen in the cooling gas used in cooling stage I is 8%. The compressive strength of the prepared pellets is 2916N, the Fe3O4 mass fraction is 1.2%, the porosity is 23.46%, the average pore size is 1.97μm, the pellets are uniformly consolidated and have no obvious shell-core structure. The reduction expansion rate of the prepared ultra-high-grade pellets at 900℃ in HYL atmosphere is 17.3%, and the reduction powder index RDI of the pellets at 500℃ in HYL atmosphere is 17.3%. +6.3 Compared with Example 1, the ultra-high-grade pellets were completely oxidized to Fe2O3, and the expansion and pulverization caused by the crystal transformation during the hydrogen reduction process increased.

[0058] Comparative Example 4

[0059] Compared with Example 1, the difference is that the ultra-high-grade iron concentrate is vigorously mixed with the organic binder and then directly pelletized, the pelletizing moisture is 9.3wt.%, the pelletizing time is 12min, and the disc inclination angle is 41°. Under the pelletizing process parameters, ultra-high-grade green balls with a diameter of 9~11mm and a sphericity of 0.7~0.85 are prepared. The prepared ultra-high-grade pellets have a compressive strength of 2213N, a Fe3O4 mass fraction of 5%, a porosity of 25.93%, an average pore size of 2.63μm, and obvious hot spots appear at the contact positions between pellets. The reduction expansion rate of the prepared ultra-high-grade pellets at 900℃ and HYL atmosphere is 18.7%, and the reduction powdering index RDI of the pellets at 500℃ and HYL atmosphere is 18.7%. +6.3 Compared with Example 1, the ultra-high-grade green pellets prepared had a smaller particle size and lower sphericity. The hot spot phenomenon between pellets during microwave roasting was more serious, resulting in reduced pellet strength and uneven pellet structure. Stress expansion, cracking and pulverization were more likely to occur during hydrogen-based shaft furnace reduction.

Claims

1. A method for preparing ultra-high-grade homogeneous microporous pellets for a hydrogen-based shaft furnace, characterized by: The ultra-high-grade iron ore concentrate and the organic binder are sequentially mixed, moist-grinded and pelletized to obtain ultra-high-grade green balls; the ultra-high-grade green balls are sequentially heat-treated through a blast drying section, an exhaust drying section, a preheating section, a heating section, a microwave roasting section, a cooling section I, a cooling section II and a cooling section III to obtain ultra-high-grade homogeneous microporous pellets; The oxidation degree of the ultra-high-grade green balls is controlled within the range of 70-80% after the heating stage; The process conditions of the microwave roasting section are as follows: microwave power of 915-2450 MHz, roasting temperature of 1200-1250°C, and roasting time of 15-25 min; The cooling section I adopts air cooling with oxygen removed to a volume fraction of less than 3%, and the hot exhaust gas generated in the cooling section I is reheated to 1150-1180°C and then circulated to the heating section; The cooling section II is air cooled, and the hot exhaust gas generated in the cooling section II is circulated to the preheating section; The grinding conditions are as follows: the moisture content of the raw materials is controlled at 6-7.5 wt.%, and the grinding time is 3-5 min.

2. The method for preparing ultra-high-grade homogeneous microporous pellets for a hydrogen-based shaft furnace according to claim 1, characterized in that: The ultra-high-grade iron concentrate has a TFe mass fraction of ≥71.5%, a FeO mass fraction of ≥27%, a particle size distribution of 0.5-70 μm, and a median particle size D 50 ≤20μm.

3. The method for preparing ultra-high-grade homogeneous microporous pellets for a hydrogen-based shaft furnace according to claim 1 or 2, characterized in that: The mass percentage composition of the ultra-high-grade iron concentrate and the organic binder is 99.94-99.80%:0.06%-0.20%.

4. The method for preparing ultra-high-grade homogeneous microporous pellets for a hydrogen-based shaft furnace according to claim 3, characterized in that: The organic binder includes at least one of sodium carboxymethyl cellulose, anionic polyacrylamide, soluble starch, and sodium humate.

5. The method for preparing ultra-high-grade homogeneous microporous pellets for a hydrogen-based shaft furnace according to claim 1, characterized in that: The pelletizing is achieved by a disc pelletizing machine, and the moisture content of the ultra-high-grade green balls is controlled to be 8.5-9.0 wt.% during the pelletizing process, the pelletizing time is 8-10 min, and the disc inclination angle is 43°-45°; The diameter of the ultra-high-grade green balls is 12-14 mm, and the sphericity is greater than 0.

9.

6. The method for preparing ultra-high-grade homogeneous microporous pellets for a hydrogen-based shaft furnace according to claim 1, characterized in that: The hot exhaust gas generated in the cooling stage I is heated to 1150-1180° C. by the burner and then circulated to the heating stage. The excess air coefficient of the burner during the heating process is 1.05-1.

1.

7. The method for preparing ultra-high-grade homogeneous microporous pellets for a hydrogen-based shaft furnace according to claim 1, characterized in that: The temperature of the hot exhaust gas generated by the cooling section II is 750~820℃; The cooling stage III adopts air cooling, and the hot exhaust gas generated by the cooling stage III has a temperature of 300-400° C. and is circulated to the blast drying stage.

8. The method for preparing ultra-high-grade homogeneous microporous pellets for a hydrogen-based shaft furnace according to claim 1, characterized in that: The hot exhaust gas generated in the temperature rising stage has a temperature of 450-550°C and is circulated to the exhaust drying stage.

9. A method for preparing ultra-high-grade homogeneous microporous pellets for a hydrogen-based shaft furnace according to claim 1, 2, 4, 5, 6, 7 or 8, characterized in that: The heat treatment time of the blast drying section is 2 to 3 minutes; The heat treatment time of the exhaust drying section is 4 to 5 minutes; The heat treatment time of the preheating section is 8 to 10 minutes; The heat treatment time in the temperature rising section is 3 to 4 minutes.

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