Preparation method of ultrahigh-grade homogeneous microporous pellets for hydrogen-based shaft furnace

Abstract

The invention discloses a preparation method of ultrahigh-grade homogeneous microporous pellets for a hydrogen-based shaft furnace, and belongs to the technical field of pellet preparation. According to the method, the ultrahigh-grade iron ore concentrate and an organic binder are sequentially subjected to uniform mixing, wet grinding and pelletizing, and ultrahigh-grade green pellets are obtained; the super-high-grade green pellets are sequentially subjected to heat treatment of a forced air drying section, an air draft 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, and the super-high-grade homogeneous microporous pellets are obtained; according to the method, an organic binder is adopted for pelletizing, the pellet which is high in strength, contains part of Fe3O4 and is of a uniform micropore structure is prepared by optimizing a thermal regulation and an air flow system and controlling the proper oxidation degree of the pellet in different stages in combination with a microwave roasting reinforced consolidation mode, the pellet production energy consumption is reduced, and the pellet production cost is reduced. And the reduction expansion rate of the pellets is reduced while the reduction performance of the ultrahigh-grade pellet hydrogen-based shaft furnace is improved.

Description

Technical Field

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

[0002] Pellet ore has the advantages of high iron grade, low process energy consumption, and low pollution emissions, and is a high-quality burden for the short-process smelting of a hydrogen-based shaft furnace - electric furnace. Due to the low process temperature of the hydrogen-based shaft furnace process, the gangue and harmful elements in the pellet remain in the DRI, which will increase the energy consumption and cost of the subsequent smelting process. Therefore, in the short-process steelmaking process, the TFe grade of the pellet ore used should be as high as possible. Using ultra-high-grade pellet ore for hydrogen-based shaft furnace reduction can not only reduce the subsequent smelting energy consumption, but also the prepared high-purity direct reduced iron is a high-quality raw material for producing clean steel and special steel in the short-process smelting. At present, the pellet ore for hydrogen-based shaft furnace is mainly prepared by using high-grade iron concentrate with a TFe grade of 67 - 69 wt.% and adding inorganic binders such as bentonite to prepare high-grade pellet ore with a TFe grade of about 67 wt.% for the production of direct reduced iron in the hydrogen-based shaft furnace.

[0003] In recent years, with the development of ore dressing technology, high-grade iron concentrate with TFe > 71.5 wt.% and SiO 2 <0.5 wt.% can be produced through multi-stage beneficiation of medium and low-grade iron ore resources, which can meet the requirements for the production of ultra-high-grade pellet ore. However, the ultra-high-grade iron concentrate obtained through multi-stage beneficiation has the characteristics of fine particle size, high reaction activity, and low gangue content. Whether using the grate-kiln process or the traveling grate process to prepare ultra-high-grade pellet ore, there are problems such as low pellet consolidation strength, high roasting temperature, uneven pellet structure, and easy generation of shell-core structure. This will not only increase the process energy consumption for preparing ultra-high-grade pellet ore, but also during the hydrogen-based shaft furnace reduction process, the uneven internal and external structure of the pellet ore will affect the reduction rate of the pellet ore, and lead to more serious stress expansion, cracking, and pulverization. Summary of the Invention

[0004] Aiming at the technical problems in the prior art that during the preparation of ultra-high-grade pellet ore from high-grade iron concentrate, there are problems such as high roasting temperature, uneven pellet structure, easy stress expansion, cracking, and pulverization during the hydrogen-based shaft furnace reduction process. The purpose of the present invention is to provide a method for preparing ultra-high-grade homogeneous microporous pellet ore for a hydrogen-based shaft furnace. This method can obtain ultra-high-grade pellet ore with high strength and a uniform microporous structure, endow it with good hydrogen-based shaft furnace reduction performance and a low reduction expansion rate, and at the same time reduce the energy consumption and emissions during the production process of ultra-high-grade pellet ore, providing a basic guarantee 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 pellet ore for a hydrogen-based shaft furnace. The method involves successively mixing, wet grinding, and pelletizing ultra-high-grade iron concentrate and an organic binder to obtain ultra-high-grade green pellets. The ultra-high-grade green pellets are successively subjected to heat treatment in a blast drying section, a suction drying section, a preheating section, a heating-up section, a microwave roasting section, a cooling I section, a cooling II section, and a cooling III section to obtain ultra-high-grade homogeneous microporous pellet ore.

[0006] After passing through the heating-up section, the oxidation degree of the ultra-high-grade green pellets is controlled within the range of 70 - 80%.

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

[0008] In the cooling I section, air with an oxygen content reduced to less than 3% by volume is used for cooling, and the hot waste gas generated in the cooling I section is reheated to 1150 - 1180 °C and then recycled to the heating-up section.

[0009] In the cooling II section, air cooling is used, and the hot waste gas generated in the cooling II section is recycled to the preheating section.

[0010] The key to the technical solution of the present invention lies in: using ultra-high-grade iron concentrate to prepare ultra-high-grade pellet ore with high strength and a uniform microporous structure, which not only has good reducibility but also can effectively inhibit expansion, cracking, and pulverization during the hydrogen-based reduction process. More specifically, on the one hand, by using an organic binder and combining processes such as strong mixing, wet grinding, and pelletizing, ultra-high-grade green pellets with uniform particle size distribution, high sphericity, and uniform microporous structure and composition can be prepared, which can effectively inhibit the hot spot phenomenon caused by local electric field accumulation during the subsequent microwave roasting process and avoid problems such as uneven heating of the pellet ore. On the other hand, by controlling the oxidation degree of the pellet ore before entering the microwave roasting to 70 - 80% and combining the thermal regime of low-temperature oxidation, rapid heating, and microwave roasting, while increasing the solid-phase diffusion activity of the particles, uniform consolidation of the inner and outer layers of the pellet is promoted, thereby preparing pellet ore with high strength and a uniform microporous structure, which is beneficial to improving the reduction rate of the pellet and inhibiting stress expansion, cracking, and pulverization caused by uneven pellet structure. On the third hand, by optimizing the thermal regime and air flow system of the pellet heat treatment and cooling process, not only can the oxidation rate of the pellet during the heating process be reduced, but also the oxidation degree during the pellet cooling process can be controlled to adjust the mineral composition of the ultra-high-grade pellet, and a part of Fe 3 O 4 is retained in the pellet ore to reduce the expansion and pulverization caused by the crystal form transformation of Fe 2 O 3 during the reduction process.

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

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

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

[0014] As a preferred solution, the organic binder includes at least one of sodium carboxymethylcellulose, anionic polyacrylamide, soluble starch, and sodium humate. These organic binders are relatively conventional types of 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 min. Through wet grinding treatment, the uniformity of the composition distribution can be improved, and uneven heating during the microwave roasting process can be prevented.

[0016] As a preferred solution, the pelletizing is realized by a disk pelletizer. During the pelletizing process, the moisture content of the ultra-high-grade green pellets is controlled at 8.5 - 9.0 wt.%, the pelletizing time is 8 - 10 min, and the disk inclination angle is 43° - 45°. By controlling the process parameter conditions of the disk pelletizer, pellet materials with uniform particle size and high sphericity can be obtained, which is beneficial to improving the uniformity of microwave roasting.

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

[0018] As a preferred solution, the hot waste gas generated in the first cooling stage is reheated to 1150 - 1180 °C by a burner and then circulated to the heating stage. Among them, the air excess coefficient of the burner during the reheating process is 1.05 - 1.1. The cooling gas used in the first cooling stage of the present invention is a by-product gas of an air separation oxygen production device in the iron and steel industry, and its oxygen volume fraction is less than 3%. By using a gas with a low oxygen concentration in the first cooling stage, mainly because the temperature of the pellets in the first cooling stage is high, and using a low-oxygen gas for cooling can reduce the oxidation of the pellets during the cooling process, thereby retaining part of the Fe 3 O 4 to reduce Fe during the reduction process in the hydrogen-based shaft furnace 2 O3 The expansion and pulverization caused by crystal form transformation, and the hot waste gas in the first cooling stage (supplementing heat with burners if necessary to meet the temperature requirements in the pellet heating-up stage) is circulated to the heating-up stage to heat up the pellets, thereby reducing the oxidation rate of the pellets during the heating-up process and controlling the oxidation degree of the pellets after heating-up.

[0019] The excess air coefficient involved in the present invention refers to the ratio of the actually supplied air volume to the theoretically required air volume, which is called the excess air index.

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

[0021] As a preferred solution, the third cooling stage uses air cooling, and the temperature of the hot waste gas generated in the third cooling stage is 300 - 400 °C and is circulated to the blast drying stage.

[0022] As a preferred solution, the temperature of the hot waste gas generated in the heating-up stage is 450 - 550 °C and is circulated to the suction drying stage.

[0023] By recycling the hot waste gas, the present invention can effectively reduce the process energy consumption and cost, and achieve efficient utilization of waste heat.

[0024] As a preferred solution, the heat treatment time in the blast drying stage is 2 - 3 min.

[0025] As a preferred solution, the heat treatment time in the suction drying stage is 4 - 5 min.

[0026] As a preferred solution, the heat treatment time in the preheating stage is 8 - 10 min.

[0027] As a preferred solution, the heat treatment time in the heating-up stage is 3 - 4 min.

[0028] In the ultra-high grade homogeneous microporous pellet ore of the present invention, the content of Fe 3 O 4 is 4 - 10 wt.%, which can improve the reducibility of the ultra-high grade pellet ore in a hydrogen-based shaft furnace while reducing the reduction expansion rate of the pellet ore.

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

[0030] Compared with the prior art, the beneficial effects of the technical solution of the present invention are as follows:

[0031] (1)The present invention prepares super-high-grade green pellets with uniform particle size distribution, high sphericity, and uniform microporous structure and composition through the combination of organic binders, strong mixing, wet grinding, and appropriate pelletizing processes, which can inhibit the hot spot phenomenon caused by the accumulation of local electric fields during microwave roasting and avoid uneven heating of the pellet ore.

[0032] (2)The present invention controls the appropriate oxidation degree of the pellet ore before microwave roasting, and combines the thermal regime of low-temperature oxidation, rapid heating, and direct heating by microwave roasting. While improving the solid-phase diffusion activity of the particles, it promotes uniform consolidation of the inner and outer layers of the pellets, thereby preparing pellet ore with good strength and a 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 regime and air flow system during the heat treatment and cooling process of the pellets, adjusts the mineral composition of the super-high-grade pellets, and retains a part of Fe 3 O 4 in the pellet ore, which can reduce the expansion and pulverization caused by the crystal form transformation of Fe 2 O 3 during the reduction process.

[0034] (4)The present invention uses the by-product gas of the air separation oxygen production equipment in the iron and steel industry to cool the pellets in the first cooling section. The low-oxygen concentration gas obtained after deoxygenation is used to cool the pellets in the first cooling section, which can reduce the oxidation of the pellets during the cooling process, thereby retaining a part of Fe 3 O 4 to reduce the expansion and pulverization caused by the crystal form transformation of Fe 2 O 3 during the reduction process in the hydrogen-based shaft furnace. And the low oxygen content of the hot waste gas in the first cooling section is recycled to the heating section for pellet heating. 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 be used for the pellet heating process, effectively reducing the process energy consumption and cost, and realizing efficient utilization of waste heat. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is the preparation process flow diagram of the super-high-grade homogeneous microporous pellet ore of the present invention. Among them, 1 is the blast drying section; 2 is the suction drying section; 3 is the preheating section; 4 is the heating section; 5 is the microwave roasting section; 6 is the first cooling section; 7 is the second cooling section; 8 is the third cooling section; 9 is the burner; 10 is the flue gas treatment system; 11 is the air separation oxygen production equipment; 12 is the fan.

[0036] Figure 2 is the microstructural diagram of the pellet ore prepared in Example 1.

[0037] Figure 3 is the microstructural diagram of the pellet ore prepared in Comparative Example 1. Specific Embodiments

[0038] To further illustrate the content of the present invention, the following will describe the present invention in a more comprehensive and detailed manner in combination with preferred embodiments. However, the protection scope of the claims of the present invention is not limited to the following specific embodiments.

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

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

[0041] Among them, the pellet porosity and average pore diameter are measured by mercury intrusion method; the test of the hydrogen-based shaft furnace reduction performance of pellet ore 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 smallest circumscribed circle.

[0042] In the following specific embodiments, the TFe mass fraction of the ultra-high-grade iron concentrate is 71.71%, the FeO mass fraction is 27.81%, the particle size distribution is 0.5 - 70 μm, and the median particle size D50 = 16.52 μm.

[0043] Example 1

[0044] The ultra-high-grade iron concentrate and sodium carboxymethylcellulose are strongly mixed and wet-ground according to a weight ratio of 99.94:0.06. The wet-grinding time is 3 min, and the wet-grinding moisture content is 7.5 wt.%. Then, under the pelletizing process parameters of a pelletizing moisture content of 8.5 wt.%, a pelletizing time of 10 min, and a disk inclination angle of 43°, ultra-high-grade green pellets with a diameter of 12 - 14 mm and a sphericity greater than 0.9 are prepared. The prepared green pellets are dried by hot air (from the hot waste gas generated in the third cooling section) at 300 °C for 3 min, dried by suction with hot air (from the hot waste gas generated in the heating section) at 450 °C for 5 min, preheated at 750 °C for 10 min, and heated up at 1180 °C for 3 min (the hot waste gas from the first cooling section passes through the burner for supplementary heating, and the air excess number of the burner is 1.05). At this time, the oxidation degree of the pellets is 75%. During the microwave roasting process, the microwave power is 2450 MHz. After microwave roasting at 1240 °C for 15 min, it enters the cooling section (the first cooling section, the second cooling section, and the third cooling section in sequence). Among them, the volume fraction of oxygen in the cooling gas used in the first cooling section is < 3%.

[0045] The compressive strength of the prepared ultra-high-grade pellet ore is 2783 N, Fe 3 O4 The mass fraction is 6%, the porosity is 24.67%, the average pore diameter is 1.85 μm, and the pellet consolidation is uniform without an obvious shell-core structure. The reduction swelling rate of the prepared ultra-high-grade pellet ore under the conditions of 900 °C and HYL atmosphere is 13.3%, and the pellet reduction degradation index RDI +6.3 is 98.72% under the conditions of 500 °C and HYL atmosphere. The microstructural diagram of the pellet ore is as Figure 2 shown, and it can be clearly seen that the pellet structure is relatively uniform.

[0046] Example 2

[0047] The ultra-high-grade iron concentrate, anionic polyacrylamide and soluble starch are strongly mixed and wet-ground according to a weight ratio of 99.85:0.05:0.1. The wet-grinding time is 5 min, and the wet-grinding moisture content is 6 wt.%. Then, under the pelletizing process parameters of a pelletizing moisture content of 9.0 wt.%, a pelletizing time of 8 min, and a disk inclination angle of 45°, the prepared green pellets are dried by hot air (from the hot waste gas generated in the third cooling section) at 400 °C for 2 min, dried by suction with hot air (from the hot waste gas generated in the heating section) at 550 °C for 4 min, preheated by hot air (from the hot waste gas generated in the second cooling section) at 800 °C for 8 min, and heated up at 1150 °C (the hot waste gas from the first cooling section is supplemented with temperature by a burner, and the air excess number of the burner is 1.05) for 3 min. At this time, the oxidation degree of the pellets is 70%. During the microwave roasting process, the microwave power is 915 MHz. After microwave roasting at 1210 °C for 25 min, it enters the cooling section, and the volume fraction of oxygen in the cooling gas used in the first cooling section is <3%.

[0048] The compressive strength of the prepared ultra-high-grade pellet ore is 2577 N, and the Fe 3 O 4 mass fraction is 10%, the porosity is 24.14%, the average pore diameter is 2.17 μm, and the pellet consolidation is uniform without an obvious shell-core structure. The reduction swelling rate of the prepared ultra-high-grade pellet ore under the conditions of 900 °C and HYL atmosphere is 10.5%, and the pellet reduction degradation index RDI +6.3 is 96.44%.

[0049] Example 3

[0050] Super high-grade iron concentrate, sodium carboxymethyl cellulose and sodium humate are strongly mixed and wet-ground according to a weight ratio of 99.8:0.05:0.15. The wet-grinding time is 3 min and the wet-grinding moisture content is 7.5 wt.%. Then, under the pelletizing process parameters of a pelletizing moisture content of 8.8 wt.%, a pelletizing time of 10 min, and a disk inclination angle of 43°, super high-grade green pellets with a diameter of 12 - 14 mm and a sphericity greater than 0.9 are prepared. The prepared green pellets are dried by hot air blowing at 350 °C (from the hot waste gas generated in the third cooling section) for 3 min, dried by hot air suction at 500 °C (from the hot waste gas generated in the heating section) for 5 min, preheated at 820 °C (from the hot waste gas generated in the second cooling section) for 10 min, and heated up at 1180 °C (the hot waste gas from the first cooling section is supplemented with temperature by a burner, and the air excess number of the burner is 1.10) for 4 min. At this time, the oxidation degree of the pellets is 80%. During the microwave roasting process, the microwave power is 915 MHz. After microwave roasting at 1230 °C for 20 min, it enters the cooling section. The volume fraction of oxygen in the cooling gas used in the first cooling section is <3%.

[0051] The prepared super high-grade pellet ore has a compressive strength of 2895 N, and the mass fraction of Fe 3 O 4 is 4%, the porosity is 23.88%, the average pore diameter is 1.68 μm, and the pellet consolidation is uniform without an obvious shell-core structure. The prepared super high-grade pellet ore has a reduction swelling rate of 15.8% at 900 °C and in a HYL atmosphere, and the pellet reduction degradation index RDI +6.3 is 97.68% at 500 °C and in a HYL atmosphere.

[0052] Comparative Example 1

[0053] Compared with Example 1, the difference is that the preheating section temperature is 860 °C and the time is 14 min. At this time, the oxidation degree of the pellets is 90%. The prepared super high-grade pellet ore has a compressive strength of 2313 N, and the mass fraction of Fe 3 O 4 is 1.6%, the porosity is 25.33%, the average pore diameter is 2.85 μm, and an obvious shell-core structure appears in the pellets. The prepared super high-grade pellet ore has a reduction swelling rate of 23.9% at 900 °C and in a HYL atmosphere, and the pellet reduction degradation index RDI +6.3 is 93.12% at 500 °C and in a HYL atmosphere. Compared with Example 1, the oxidation degree of the pellet ore is too high before microwave roasting, the difference in the solid-phase diffusion activity of the particles in the inner and outer layers of the pellets is large, the structure of the roasted pellet ore is uneven, the strength of the pellets is reduced, and stress expansion, cracking and degradation are likely to occur during the hydrogen-based shaft furnace reduction process. The micrograph of the pellet ore is as Figure 3 shown, and the cracking phenomenon can be clearly seen.

[0054] Comparative Example 2

[0055] Compared with Example 1, the difference is that: in the roasting section, conventional heating is used instead of microwave roasting for roasting. After roasting at 1270 °C for 15 min, super-high-grade pellets are obtained. The compressive strength of the prepared pellets is 2591 N (to achieve a compressive strength similar to that in Example 1, a higher roasting temperature is required for conventional roasting), and the Fe 3 O 4 mass fraction is 5%, the porosity is 25.57%, the average pore diameter is 2.74 μm, and an obvious shell-core structure appears in the pellets. The reduction expansion rate of the prepared super-high-grade pellets in a HYL atmosphere at 900 °C is 19.2%, and the reduction degradation index RDI of the pellets in a HYL atmosphere at 500 °C +6.3 is 94.82%. Compared with Example 1, without microwave roasting, the outer layer of the roasted pellets is denser, the pellet structure is uneven, and stress expansion, cracking, and pulverization are likely to occur 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 the first cooling section is 8%. The compressive strength of the prepared pellets is 2916 N, and the Fe 3 O 4 mass fraction is 1.2%, the porosity is 23.46%, the average pore diameter is 1.97 μm, the pellets are consolidated uniformly and have no obvious shell-core structure. The reduction expansion rate of the prepared super-high-grade pellets in a HYL atmosphere at 900 °C is 17.3%, and the reduction degradation index RDI of the pellets in a HYL atmosphere at 500 °C +6.3 is 94.38%. Compared with Example 1, when the super-high-grade pellets are completely oxidized to Fe 2 O 3 , the expansion and pulverization caused by the crystal form transformation during the hydrogen reduction process increase.

[0058] Comparative Example 4

[0059] Compared with Example 1, the difference is that: after the super-high-grade iron concentrate is strongly mixed with the organic binder, pelletizing is directly carried out. Under the pelletizing process parameters of a pelletizing moisture content of 9.3 wt.%, a pelletizing time of 12 min, and a disk inclination angle of 41°, super-high-grade green pellets with a diameter of 9 - 11 mm and a sphericity of 0.7 - 0.85 are prepared. The compressive strength of the prepared super-high-grade pellets is 2213 N, and the Fe 3 O 4 mass fraction is 5%, the porosity is 25.93%, the average pore diameter is 2.63 μm, and an obvious hot spot phenomenon appears at the contact positions between the pellets. The reduction expansion rate of the prepared super-high-grade pellets in a HYL atmosphere at 900 °C is 18.7%, and the reduction degradation index RDI of the pellets in a HYL atmosphere at 500 °C+6.3 It is 93.77%. Compared with Example 1, the prepared ultra-high-grade green pellets have smaller particle size and lower sphericity. The hot spot phenomenon among pellets during microwave roasting is more serious, resulting in a decrease in the strength of pellet ore and uneven pellet structure. During the reduction process in the hydrogen-based shaft furnace, stress expansion, cracking and pulverization are likely to occur.

Claims

1. A method for preparing ultra-high-grade homogeneous microporous pellets for a hydrogen-based shaft furnace, characterized in that: 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 stage are as follows: microwave power is 915-2450 MHz, roasting temperature is 1200-1250°C, and roasting time is 15-25 min; The cooling stage I adopts air cooling in which oxygen is removed to a volume fraction of less than 3%, and the hot exhaust gas generated in the cooling stage I is circulated to the heating stage after being supplemented with heat to 1150-1180°C; The cooling section II adopts air cooling, and the hot exhaust gas generated in the cooling section II is circulated to the preheating section.

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. A 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 grinding conditions are as follows: the moisture content of the raw material is controlled at 6-7.5wt.%, and the grinding time is 3-5min; The ball making is achieved by a disc ball making machine, and the moisture content of the ultra-high-grade raw balls is controlled to be 8.5-9.0wt.% during the ball making process, the ball making time is 8-10min, 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 a burner and then circulated to the heating stage, wherein 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°C; The cooling stage III adopts air cooling, and the hot exhaust gas temperature generated by the cooling stage III is 300-400° C., which 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 stage is 3 to 4 minutes.

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