A method for reducing the hydrogen-rich reduction expansion of pellet ore based on step-by-step reduction in a hydrogen-based shaft furnace

Abstract

The present invention discloses a method for reducing the hydrogen-rich reduction swelling of pellet ore based on stepwise reduction in a hydrogen-based shaft furnace, belonging to the technical field of direct reduced iron production. The pellet ore is successively reduced in the first-stage hydrogen-based shaft furnace (temperature: 780 - 880 °C, volume fraction of H2 + CO > 80%, and volume ratio of H2 / (H2 + CO) is 0.6 - 0.8) and the second-stage hydrogen-based shaft furnace (temperature: 980 - 1040 °C, volume fraction of H2 + CO > 90%, and volume ratio of H2 / (H2 + CO) ≥ 0.8), and then cooled to obtain direct reduced iron. This method can reduce the maximum reduction swelling rate of the entire pellet ore during the reduction process to less than 10% without using pellet additives such as calcium and magnesium. While ensuring the reduction efficiency of the hydrogen-based shaft furnace, it can produce direct reduced iron with quality indicators meeting the requirements and higher iron grade, which is conducive to realizing the clean, efficient, and short-process utilization of iron ore resources.

Description

Technical Field

[0001] The present invention relates to a method for reducing the reduction swelling of pelletized ore in a hydrogen-based shaft furnace, and particularly to a method for reducing the hydrogen-rich reduction swelling of pelletized ore based on stepwise reduction in a hydrogen-based shaft furnace, belonging to the technical field of direct reduced iron preparation. Background Art

[0002] The pelletized ore used in the hydrogen-based shaft furnace has a high iron grade and few gangues. Under the condition of hydrogen-rich reduction, the transformation of hematite crystal form and the difference in reduction rates between the inner and outer layers of the pellet will cause significant accumulation of internal stress in the pellet, and it is more likely to induce the formation of iron whiskers, promoting the reduction swelling of the pellet. The greater the reduction swelling of the pellet during the reduction process in the hydrogen-based shaft furnace, the lower the strength of the reduced pellet. Moreover, the pellet may crack and disintegrate during the reduction process, resulting in a decrease in the permeability index in the furnace, severely restricting the release of the production capacity of the hydrogen-based shaft furnace and the stable production of high-quality direct reduced iron. The existing technologies mainly reduce the reduction swelling of the pellet by optimizing the thermal regime in the pellet preparation process and adding calcium-based, magnesium-based fluxes or boron-containing components. For example, the literature ("Study on gas-based reduction mechanism of ultra-high-grade pellets with high basicity by experiment tests and first-principles calculation", Jie Lei, et al., Powder Technology; 2024; 436: 119462) discloses a method for reducing the reduction swelling rate of high-grade pelletized ore by adding calcium oxide. In addition, although improving the pellet strength by optimizing the preheating and roasting regime can resist the internal stress generated during pellet swelling to a certain extent, the effect is limited, and it will increase the energy consumption in the pellet preparation process. When the pellet strength is too high, it will also affect the reduction rate and is more likely to generate cracks during the reduction process. Using pellet additives faces the problem of applicability to different iron-containing raw materials, and inevitably reduces the iron grade of the pelletized ore, resulting in an increase in the slag volume, an increase in smelting energy consumption, and a decrease in productivity in the subsequent smelting process. Summary of the Invention

[0003] Due to the problems of easy reduction swelling of the pelletized ore used in the hydrogen-based shaft furnace, such as high iron grade and few gangues, the existing technologies mainly reduce the reduction swelling of the pellet by improving the pellet strength, adding calcium-based, magnesium-based fluxes or boron-containing components. However, the effect of suppressing reduction swelling by improving the pellet strength is limited, and it will increase the energy consumption in the pellet preparation process. When using pellet additives, on the one hand, there will be problems of applicability to different iron-containing raw materials, and on the other hand, it will inevitably reduce the iron grade of the pelletized ore and increase the smelting energy consumption.

[0004] In view of the above technical problems existing in the prior art, the object of the present invention is to provide a method for reducing the hydrogen-rich reduction expansion of pellet ore based on step-by-step reduction in a hydrogen-based shaft furnace. The key of this method is to adopt the way of step-by-step reduction in a hydrogen-based shaft furnace. After the pellet ore is reduced to a certain extent at medium and low temperatures, it is then rapidly reduced at high temperature in a hydrogen-rich atmosphere, so that the maximum reduction expansion rate of the pellet ore can be controlled below 10%. This method has a simple process, is easy to operate, and has strong raw material adaptability. Without using pellet additives such as calcium and magnesium, it can produce direct reduced iron with quality indicators meeting the requirements and higher iron grade, which is conducive to realizing the clean, efficient and short-process utilization of iron ore resources.

[0005] To achieve the above technical object, the present invention provides a method for reducing the hydrogen-rich reduction expansion of pellet ore based on step-by-step reduction in a hydrogen-based shaft furnace. The method is to sequentially reduce the pellet ore in the first-stage hydrogen-based shaft furnace and the second-stage hydrogen-based shaft furnace, and then cool it to obtain direct reduced iron;

[0006] In the first-stage hydrogen-based shaft furnace, the reduction temperature is 780-880 °C, the reducing gas satisfies that the volume fraction of H2+CO is greater than 80%, and the volume ratio H2 / (H2+CO) is 0.6-0.8, and the reduction degree of the pellet ore is controlled at 45-60%;

[0007] In the second-stage hydrogen-based shaft furnace, the reduction temperature is 980-1040 °C, the reducing gas satisfies that the volume fraction of H2+CO is greater than 90%, and the volume ratio H2 / (H2+CO) is ≥0.8, and the reduction degree of the pellet ore is controlled above 95%.

[0008] The key to the technical solution of the present invention lies in adopting a step-by-step reduction method during the hydrogen-based shaft furnace reduction process of pellet ore, which can control the maximum reduction expansion rate during the entire pellet ore reduction process below 10%, which is an unexpected effect. More specifically, the pellet ore is first preliminarily reduced in the first-stage hydrogen-based shaft furnace at a temperature of 780-880 °C, so that the reduction degree of the pellet is 45-60%. The low temperature in the first-stage hydrogen-based shaft furnace can not only effectively reduce the internal stress of the pellet caused by crystal form transformation and thermal expansion effect while ensuring the reduction efficiency of the pellet, but also effectively reduce the carbon deposition problem at the initial stage of the hydrogen-based shaft furnace reduction, improve the utilization rate of the reducing gas, and reduce the pellet expansion or fragmentation caused by the carbon deposition reaction and carbon deposition. At the same time, the temperature in the first-stage hydrogen-based shaft furnace is controlled within an appropriate range, which can reduce the thermal stress expansion generated by the sudden temperature change when the pellet enters the second-stage hydrogen-based shaft furnace. The pellet ore preliminarily reduced in the first-stage hydrogen-based shaft furnace is subjected to high-temperature hydrogen-rich rapid reduction in the second-stage hydrogen-based shaft furnace. Under the action of high temperature and hydrogen-rich reducing gas, the reduction rate in the later stage of the pellet ore reduction can be accelerated, promoting the aggregation, growth and consolidation of iron grains, so that the maximum reduction expansion rate of the pellet ore during the hydrogen-rich reduction process is less than 10%, and direct reduced iron with a dense structure, good strength and high iron grade is obtained. To sum up, by adopting a step-by-step reduction method and controlling conditions such as temperature and atmosphere during each stage of reduction, the present invention can control the maximum reduction expansion rate during the entire pellet ore reduction process below 10%, and at the same time produce direct reduced iron with quality indicators meeting the requirements and higher iron grade.

[0009] As a preferred solution, the average particle size of the pellet ore is 12-14 mm, and the compressive strength is 2500-3500 N. The strength of the pellet ore is preferably controlled within a suitable range. When the strength is too high, the structure of the pellet ore is too dense, and the pore structures of the inner and outer layers of the pellet ore are uneven. On the one hand, it will reduce the reduction rate of the pellet ore. On the other hand, it will cause structural stress due to the difference in pore structures between the inner and outer layers during the reduction process of the pellet ore, resulting in pellet expansion and cracking. If the strength of the pellet ore is too low, it will be difficult to meet the requirements of the hydrogen-based shaft furnace reduction.

[0010] As a preferred solution, the pressure of the reducing gas in the first-stage hydrogen-based shaft furnace is 0.5-0.7 MPa, and the flow rate of the reducing gas is 1400-1600 m per ton of direct reduced iron 3 . When the temperature in the first-stage hydrogen-based shaft furnace is determined, by regulating the pressure and flow rate of the reducing gas, the reduction rate of the pellet ore in the first-stage hydrogen-based shaft furnace can be ensured, and the utilization rate of the reducing gas can be improved. The present invention controls the temperature of the first-stage hydrogen-based shaft furnace to be medium and low temperature, and at the same time, at a relatively low pressure and flow rate of the reducing gas, to control the relatively low reduction rate of the pellet ore, which can effectively reduce the internal stress caused by crystal form transformation and thermal expansion effect at the initial stage of pellet reduction, and induce uniform nucleation and layer-by-layer growth of iron grains on the particle surface.

[0011] As a preferred solution, the pressure of the reducing gas in the second-stage hydrogen-based shaft furnace is 0.8 - 1.0 MPa, and the flow rate of the reducing gas is 1600 - 1800 m per ton of direct reduced iron. 3 In the present invention, the temperature of the second-stage hydrogen-based shaft furnace is controlled at a high temperature, and at the same time, under relatively high pressure and flow rate of the reducing gas, the rapid reduction of pellet ore is controlled, which can inhibit the formation of iron whiskers during the reduction process of pellet ore in the second-stage hydrogen-based shaft furnace and improve the utilization rate of the reducing gas.

[0012] As a preferred solution, the top gas generated in the second-stage hydrogen-based shaft furnace is purified and used to prepare the reducing gas in the first-stage hydrogen-based shaft furnace. This operation can effectively realize the recycling of the reducing gas and the efficient utilization of waste heat.

[0013] As a preferred solution, the apparent density of the direct reduced iron is 2.0 - 2.4 t / m 3 , and the compressive strength is greater than 500 N.

[0014] The pellet ore involved in the present invention is a conventional pellet ore in the art. It is obtained by mixing and pelletizing iron concentrate and binder and then subjecting to oxidation roasting. Among them, the iron concentrate includes at least one of magnetite concentrate, hematite concentrate, limonite concentrate and vanadium-titanium iron concentrate; the binder contains at least one of bentonite, sodium carboxymethyl cellulose and polyacrylamide. The preparation process of the pellet ore is also well-known in the prior art.

[0015] After being reduced in the first-stage hydrogen-based shaft furnace, the compressive strength of the pellet ore of the present invention is greater than 1000 N, which is beneficial to resisting the thermal stress expansion of the pellets in the second-stage hydrogen-based shaft furnace.

[0016] Compared with the prior art, the beneficial technical effects of the technical solution of the present invention are as follows:

[0017] The method provided by the present invention adopts the method of gradually reducing in a hydrogen-based shaft furnace. First, the pellet ore is reduced to a certain extent at medium and low temperatures, and then high-temperature rapid reduction is carried out. It can effectively reduce the internal stress caused by the crystal form transformation and thermal expansion effect in the initial stage of pellet reduction, induce uniform nucleation and layered growth of iron grains on the particle surface, promote the aggregation and growth of iron grains in the pellet during the subsequent reduction process, and make the maximum reduction expansion rate of the pellet ore less than 10% during the hydrogen-rich reduction process.

[0018] The method provided by the present invention can effectively reduce the carbon deposition problem in the initial stage of reduction of the hydrogen-based shaft furnace in the prior art while ensuring the reduction efficiency of the pellet. On the one hand, it is beneficial to improve the utilization rate of the reducing gas. On the other hand, it can reduce the pellet expansion or fragmentation caused by the carbon deposition reaction and carbon deposition.

[0019] The reducing atmosphere adopted by the method provided by the present invention is conducive to the uniform nucleation and aggregation growth of iron grains. At the same time, the top gas in the second-stage hydrogen-based shaft furnace is purified and used as the reducing gas in the first-stage hydrogen-based shaft furnace, realizing the recycling of the reducing gas and the efficient utilization of waste heat.

[0020] The method provided by the present invention has a simple process, is easy to operate, and has strong raw material applicability. It can produce direct reduced iron with a dense structure, good strength, and higher iron grade without using pellet additives such as calcium and magnesium, which is conducive to the clean, efficient, and short-process utilization of iron ore resources. Brief Description of the Drawings

[0021] Figure 1 It is a process flow chart of the present invention. Detailed Embodiments

[0022] To further illustrate the content of the present invention, the following will describe the present invention more comprehensively and in detail in combination with preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

[0023] 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.

[0024] Example 1

[0025] Magnetite concentrate and hematite are mixed into iron concentrate according to a weight ratio of 70:30, and then the iron concentrate, bentonite, and sodium carboxymethylcellulose are prepared into pellet ore after mixing, pelletizing, and oxidative roasting according to a weight ratio of 99.3:0.6:0.1. The average particle size of the pellet ore is 12 - 14 mm, and the compressive strength is 2850 N.

[0026] During the step-by-step reduction process in the hydrogen-based shaft furnace, the reduction temperature in the first-stage hydrogen-based shaft furnace is 880 °C, and the gas pressure is 0.5 MPa. The volume fraction of (H2 + CO) in the reducing gas in the first-stage hydrogen-based shaft furnace is 84%, the volume ratio of H2 / (H2 + CO) is 0.6, and the gas flow rate is 1600 m 3 / t. After reduction in the first-stage hydrogen-based shaft furnace, the reduction degree of the pellet ore is 60%, and the compressive strength is 1154 N. The reduction temperature in the second-stage hydrogen-based shaft furnace is 1040 °C, and the gas pressure is 0.8 MPa. The volume fraction of (H2 + CO) in the reducing gas in the second-stage hydrogen-based shaft furnace is 95%, the volume ratio of H2 / (H2 + CO) is 0.8, and the gas flow rate is 1800 m 3 / t. The maximum reduction expansion rate of the pellet during the step-by-step reduction process is 7.3%, and the apparent density of the obtained direct reduced iron is 2.4 t / m 3, the compressive strength is 583 N.

[0027] Example 2

[0028] Mix magnetite concentrate and vanadium-titanium magnetite concentrate in a weight ratio of 80:20 to form iron concentrate, and then prepare pellet ore by mixing iron concentrate, bentonite and polyacrylamide in a weight ratio of 99:0.8:0.2, followed by pelletizing and oxidative roasting. The average particle size of the pellet ore is 12 - 14 mm, and the compressive strength is 3057 N.

[0029] During the stepwise reduction in the hydrogen-based shaft furnace, the reduction temperature in the first-stage hydrogen-based shaft furnace is 780 °C, and the gas pressure is 0.7 MPa. The volume fraction of the reducing gas (H2 + CO) in the first-stage hydrogen-based shaft furnace is 90%, the volume ratio of H2 / (H2 + CO) is 0.8, and the gas flow rate is 1400 m 3 / t. After reduction in the first-stage hydrogen-based shaft furnace, the reduction degree of the pellet ore is 45%, and the compressive strength is 1082 N. The reduction temperature in the second-stage hydrogen-based shaft furnace is 980 °C, and the gas pressure is 1.0 MPa. The volume fraction of the reducing gas (H2 + CO) in the second-stage hydrogen-based shaft furnace is 95%, the volume ratio of H2 / (H2 + CO) is 1.0 (100% H2), and the gas flow rate is 1600 m 3 / t. The maximum reduction expansion rate of the pellets during the stepwise reduction process is 9.2%, and the apparent density of the obtained direct reduced iron is 2.0 t / m 3 , the compressive strength is 534 N.

[0030] Example 3

[0031] Mix magnetite concentrate and limonite concentrate in a weight ratio of 85:15 to form iron concentrate, and then prepare pellet ore by mixing iron concentrate, bentonite and sodium carboxymethylcellulose in a weight ratio of 99.5:0.4:0.1, followed by pelletizing and oxidative roasting. The average particle size of the pellet ore is 12 - 14 mm, and the compressive strength is 2963 N.

[0032] During the stepwise reduction in the hydrogen-based shaft furnace, the reduction temperature in the first-stage hydrogen-based shaft furnace is 820 °C, and the gas pressure is 0.6 MPa. The volume fraction of the reducing gas (H2 + CO) in the first-stage hydrogen-based shaft furnace is 86%, the volume ratio of H2 / (H2 + CO) is 0.72, and the gas flow rate is 1500 m 3 / t. After reduction in the first-stage hydrogen-based shaft furnace, the reduction degree of the pellet ore is 50%, and the compressive strength is 1034 N. The reduction temperature in the second-stage hydrogen-based shaft furnace is 1020 °C, and the gas pressure is 0.9 MPa. The volume fraction of the reducing gas (H2 + CO) in the second-stage hydrogen-based shaft furnace is 92%, the volume ratio of H2 / (H2 + CO) is 0.9, and the gas flow rate is 1700 m 3 / t. The maximum reduction expansion rate of the pellets during the stepwise reduction process is 5.1%, and the apparent density of the obtained direct reduced iron is 2.1 t / m 3 , and the compressive strength is 615 N.

[0033] Example 4

[0034] Pellet ore is prepared by mixing magnetite concentrate, bentonite and sodium carboxymethylcellulose in a weight ratio of 99.7:0.2:0.1, followed by pelletizing and oxidative roasting. The average particle size of the pellet ore is 12 - 14 mm, and the compressive strength is 3287 N.

[0035] During the stepwise reduction process in the hydrogen-based shaft furnace, the reduction temperature in the first-stage hydrogen-based shaft furnace is 840 °C, and the gas pressure is 0.6 MPa. The volume fraction of the reducing gas (H2 + CO) in the first-stage hydrogen-based shaft furnace is 86%, the volume ratio of H2 / (H2 + CO) is 0.72, and the gas flow rate is 1500 m 3 / t. After reduction in the first-stage hydrogen-based shaft furnace, the reduction degree of the pellet ore is 60%, and the compressive strength is 1123 N. The reduction temperature in the second-stage hydrogen-based shaft furnace is 1020 °C, and the gas pressure is 0.9 MPa. The volume fraction of the reducing gas (H2 + CO) in the second-stage hydrogen-based shaft furnace is 92%, the volume ratio of H2 / (H2 + CO) is 0.9, and the gas flow rate is 1700 m 3 / t. The maximum reduction expansion rate of the pellets during the stepwise reduction process is 3.7%, and the apparent density of the obtained direct reduced iron is 2.3 t / m 3 , and the compressive strength is 656 N.

[0036] Example 5

[0037] Magnetite concentrate and hematite are mixed into iron concentrate in a weight ratio of 30:70, and then the iron concentrate, bentonite and polyacrylamide are pelletized and oxidized and roasted in a weight ratio of 98.8:1:0.2 to prepare pellet ore. The average particle size of the pellet ore is 12 - 14 mm, and the compressive strength is 3166 N.

[0038] During the stepwise reduction process in the hydrogen-based shaft furnace, the reduction temperature in the first-stage hydrogen-based shaft furnace is 860 °C, and the gas pressure is 0.6 MPa. The volume fraction of the reducing gas (H2 + CO) in the first-stage hydrogen-based shaft furnace is 92%, the volume ratio of H2 / (H2 + CO) is 0.8, and the gas flow rate is 1500 m 3 / t. After reduction in the first-stage hydrogen-based shaft furnace, the reduction degree of the pellet ore is 55%, and the compressive strength is 1047 N. The reduction temperature in the second-stage hydrogen-based shaft furnace is 1020 °C, and the gas pressure is 0.9 MPa. The volume fraction of the reducing gas (H2 + CO) in the second-stage hydrogen-based shaft furnace is 92%, the volume ratio of H2 / (H2 + CO) is 0.92, and the gas flow rate is 1700 m 3 / t. The maximum reduction expansion rate of the pellets during the step-by-step reduction process is 8.5%, and the apparent density of the obtained direct reduced iron is 2.1 t / m 3 , and the compressive strength is 514 N.

[0039] Comparative Example 1

[0040] Compared with Example 1, the only difference is that: the temperature of the first-stage hydrogen-based shaft furnace reduction is 720 °C. After the first-stage hydrogen-based shaft furnace reduction, the compressive strength of the pellets is 942 N. The maximum reduction expansion rate of the pellet ore during the step-by-step reduction process is 18.3%, and the apparent density of the obtained direct reduced iron is 1.93 t / m 3 , and the compressive strength is 385 N.

[0041] Compared with Example 1, due to the lower temperature of the initial reduction of the pellets, it is not conducive to the uniform nucleation and layered growth of iron grains on the particle surface, and the pellet strength is lower. Moreover, due to the large temperature difference between the first-stage hydrogen-based shaft furnace reduction and the second-stage hydrogen-based shaft furnace reduction, the pellets are more likely to generate thermal stress expansion and crack when entering the second-stage hydrogen-based shaft furnace.

[0042] Comparative Example 2

[0043] Compared with Example 1, the only difference is that: the temperature of the first-stage hydrogen-based shaft furnace reduction is 930 °C. After the first-stage hydrogen-based shaft furnace reduction, the compressive strength of the pellets is 793 N. The maximum reduction expansion rate of the pellet ore during the step-by-step reduction process is 23.8%, and the apparent density of the obtained direct reduced iron is 1.87 t / m 3 , and the compressive strength is 341 N.

[0044] Compared with Example 1, due to the too high temperature of the initial reduction of the pellets, the internal stress generated by the crystal form transformation during the pellet reduction process is greater, and iron whiskers are more likely to be generated on the particle surface of the pellets at high temperature, resulting in an increase in the reduction expansion rate of the pellets and lower pellet strength.

[0045] Comparative Example 3

[0046] Compared with Example 1, the only difference is that: the reduction degree of the pellet ore after the first-stage hydrogen-based shaft furnace reduction is 30%. After the first-stage hydrogen-based shaft furnace reduction, the compressive strength of the pellets is 1067 N. The maximum reduction expansion rate of the pellet ore during the step-by-step reduction process is 25.6%, and the apparent density of the obtained direct reduced iron is 1.85 t / m 3 , and the compressive strength is 327 N.

[0047] Compared with Example 1, the pellets are reduced to 30% in the first-stage hydrogen-based shaft furnace and then enter the second-stage hydrogen-based shaft furnace for further reduction. On the one hand, there is still a small amount of hematite in the pellets that is not completely reduced, which causes expansion stress during the high-temperature reduction process. On the other hand, since the iron grains on the surface of the pellet particles have not completed sufficient nucleation, the growth of iron whiskers occurs during the high-temperature reduction process, resulting in an increase in the reduction expansion rate of the pellets.

[0048] Comparative Example 4

[0049] Compared with Example 1, the only difference is that after the pellets are reduced in the first-stage hydrogen-based shaft furnace, they enter the second-stage hydrogen-based shaft furnace at 950 °C for further reduction. The maximum reduction expansion rate of the pellet ore during the reduction process is 16.5%, and the apparent density of the obtained direct reduced iron is 1.96 t / m 3 , and the compressive strength is 422 N.

[0050] Compared with Example 1, due to the lower temperature of the second-stage hydrogen-based shaft furnace, it is not conducive to the aggregation and growth of iron grains in the pellets during the later stage of reduction, resulting in an increase in the pellet expansion rate and a decrease in the pellet strength.

[0051] Comparative Example 5

[0052] Compared with Example 1, the only difference is that the average particle size of the pellet ore used is 14 - 16 mm, and the compressive strength is 4055 N. The maximum reduction expansion rate of the pellet ore during the reduction process is 17.6%, and the apparent density of the obtained direct reduced iron is 2.04 t / m 3 , and the compressive strength is 557 N.

[0053] Compared with Example 1, the pellet ore used has a larger particle size and higher compressive strength, resulting in a greater difference in crystal consolidation and pore structure between the inner and outer layers of the pellets, leading to an increase in the internal stress of the pellets during the reduction process and an increase in the reduction expansion rate of the pellets.

[0054] Comparative Example 6

[0055] Compared with Example 1, the only difference is that during the reduction process in the first-stage hydrogen-based shaft furnace, the volume fraction of the reducing gas (H2 + CO) is 70%, and the volume ratio H2 / (H2 + CO) is 0.5. During the reduction process in the second-stage hydrogen-based shaft furnace, the volume fraction of the reducing gas (H2 + CO) is 80%, and the volume ratio H2 / (H2 + CO) is 0.7. The maximum reduction expansion rate of the pellets during the reduction process is 19.4%, and the apparent density of the obtained direct reduced iron is 1.88 t / m 3 , and the compressive strength is 388 N.

[0056] Compared with Example 1, the proportion of the reducing gas decreases, and the volume fraction of H2 in the reducing gas decreases. On the one hand, it affects the reduction rate of the pellets, and on the other hand, it promotes the formation of iron whiskers in the pellets. Therefore, the reduction expansion rate of the pellets increases.

Claims

1. A method for reducing the hydrogen-rich reduction expansion of pellet ore based on step-by-step reduction in a hydrogen-based shaft furnace, characterized in that: The pellet is successively reduced in the first-stage hydrogen-based shaft furnace and the second-stage hydrogen-based shaft furnace, and then cooled to obtain direct reduced iron; In the first-stage hydrogen-based shaft furnace, the reduction temperature is 780-880 °C, the reducing gas satisfies that the volume fraction of H2+CO is greater than 80%, and the volume ratio H2 / (H2+CO) is 0.6-0.8, and the reduction degree of the pellet is controlled at 45-60%; In the second-stage hydrogen-based shaft furnace, the reduction temperature is 980-1040 °C, the reducing gas satisfies that the volume fraction of H2+CO is greater than 90%, and the volume ratio H2 / (H2+CO) is ≥0.8, and the reduction degree of the pellet is controlled above 95%; the average particle size of the pellet is 12-14 mm, and the compressive strength is 2500-3500 N.

2. A method for reducing the hydrogen-rich reduction expansion of pellet ore based on stepwise reduction in a hydrogen-based shaft furnace according to claim 1, characterized in that: The pressure of the reducing gas in the first-stage hydrogen-based shaft furnace is 0.5 to 0.7 MPa, and the flow rate of the reducing gas is 1400 to 1600 m per ton of direct reduced iron 3 .

3. A method for reducing the hydrogen-rich reduction swelling of pellet ore based on stepwise reduction in a hydrogen-based shaft furnace, characterized in that: The pressure of the reducing gas in the second-stage hydrogen-based shaft furnace is 0.8 - 1.0 MPa, and the flow rate of the reducing gas is 1600 - 1800 m 3 per ton of direct reduced iron.

4. A method for reducing the hydrogen-rich reduction expansion of pellet ore based on stepwise reduction in a hydrogen-based shaft furnace according to claim 1, characterized in that: The top gas generated in the second-stage hydrogen-based shaft furnace is purified and used to prepare the reducing gas in the first-stage hydrogen-based shaft furnace.

5. A method for reducing the hydrogen-rich reduction expansion of pellet ore based on step-by-step reduction in a hydrogen-based shaft furnace according to any one of claims 1 to 4, characterized in that: The apparent density of the direct reduced iron is 2.0~2.4 t / m 3 , and the compressive strength is greater than 500 N.

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