Method for improving metallurgical performance of hematite and limonite pellets through layered pelletizing

Abstract

The invention discloses a method for improving the metallurgical performance of hematite and limonite pellets through layered pelletizing. The method comprises the following steps that hematite and limonite coarse powder is subjected to wet grinding or dry grinding to form hematite and limonite fine powder; the hematite and limonite fine powder, the boron-containing additive and the bentonite are subjected to strong mixing and high-pressure roller milling according to the proportion to form a first mixed material; intensively mixing the hematite and limonite fine powder, a carbon-containing material and bentonite in proportion, and performing high-pressure roller milling to form a second mixed material; feeding the first mixture into a fine material area of a pelletizing disc after the first mixture is discharged through a batching bin disc to form mother balls which grow up; after the particle size of the mother pellets is increased to 5-6 mm, adding a second mixed material into a pelletizing disc increasing area to form green pellets; and the green pellets enter a belt type roasting machine, and are dried, preheated, roasted and cooled to obtain the pellets meeting the requirements of the blast furnace. The method has the advantages that complementary advantages of the carbon-containing material and the boron-containing additive in pellet production are achieved, and the metallurgical performance of the hematite and limonite pellets is improved.

Description

Technical Field

[0001] The invention relates to the technical field of pellet production, and in particular to a method for improving the metallurgical properties of hematite pellets by layered pelletization. Background Art

[0002] The application of limonite in pellet production has become an important technical approach for the high-quality development of pellets in the future. However, limonite is easy to pulverize during the green ball roasting process due to its high crystallization water. In addition, the porosity of limonite pellets is higher than that of pellets produced by full magnetic concentrate, resulting in low compressive strength of high-proportion or even full-proportion limonite pellets, which is not conducive to increasing the proportion of pellets in the blast furnace charge structure.

[0003] In the existing pellet production technology, the compressive strength of high-proportion or even full-proportion hematite pellets can be improved by alkalinity control, but its alkalinity control is limited to low-silicon pellets, with silicon less than 4%. To avoid the alkalinity forbidden zone under high silicon, it is necessary to increase the use of calcium-containing materials. Because the calcium-containing materials are not completely digested and the liquid phase is too developed, the pellets are easy to compact. Some elements are also used to improve the compressive strength. For example, boron-containing additives are used to generate low-melting point substances and increase the bonding phase component of the pellets. However, low-melting point substances are easy to block pores, resulting in a sharp decrease in the reducibility of the pellets. According to actual production, the reducibility of the pellets using 5% B2O3 boron-containing additives is reduced to below 40, which is not conducive to controlling fuel consumption in the blast furnace. The use of hematite to prepare pellets to improve the compressive strength also requires measures such as increasing the roasting temperature, but Fe2O3 is unstable at 1300°C, which increases the difficulty of controlling the roasting of the pellets.

[0004] The existing technical solutions have the following problems: 1. The compressive strength of acidic pellets prepared with a high proportion or even a full proportion of hematite is reduced; 2. The use of boron-containing additives causes the pellets to easily form low-melting-point substances on the surface to block the pores, resulting in a sharp decrease in the reducibility of the pellets, reduced to less than 40%, affecting the increase in the proportion of pellets in the blast furnace charge structure; 3. The inner layer of hematite added with carbon-containing materials is affected by the diffusion coefficient, resulting in insufficient reducing atmosphere for the internal carbon-containing materials, resulting in the failure of Fe2O3 to form large continuous crystals under low-temperature roasting, causing fluctuations in the compressive strength of the pellets and other problems; 4. The roasting temperature of high-proportion or even full-proportion hematite is high. Summary of the invention

[0005] The purpose of the present invention is to provide a method for improving the metallurgical properties of hematite pellets by layered pelletization, so as to achieve complementary advantages of carbon-containing materials and boron-containing additives in pellet production and improve the metallurgical properties of hematite pellets.

[0006] The above technical objectives of the present invention are achieved through the following technical solutions:

[0007] A method for improving the metallurgical properties of hematite pellets by layered pelletizing, characterized in that it comprises the following steps:

[0008] The coarse hematite powder is wet-milled or dry-milled to form hematite concentrate;

[0009] The hematite concentrate, the boron-containing additive and the bentonite are mixed vigorously and subjected to high-pressure roller grinding according to a certain proportion to form a first mixed material;

[0010] The hematite concentrate, carbonaceous material and bentonite are mixed vigorously and subjected to high pressure roller grinding according to a certain proportion to form a second mixed material;

[0011] After the first mixture is discharged from the batching bin disc, it enters the fine material area of ​​the ball-making disc to form mother balls and grow;

[0012] After the mother ball size grows to 5-6mm, the second mixed material is added to the growth area of ​​the ball-making disk to form green balls;

[0013] The green balls enter the belt roaster, where they are dried, preheated, roasted and cooled to obtain pellets that meet the requirements of the blast furnace.

[0014] Preferably, the proportion of the hematite concentrate with a particle size of -200 mesh is greater than 78%, and the ratio of the hematite concentrate, the boron-containing additive, and the bentonite is: the hematite ratio is ≥90%, the boron-containing additive ratio is ≤8%, and the balance is bentonite. The boron-containing additive is ferroboron concentrate, in which the particle size requirement of -200 mesh is greater than 92%, and the B2O3 content is 4.5-5.5%.

[0015] Preferably, the ratio of the hematite concentrate, carbon-containing material and bentonite is: the hematite ratio is ≥99%, the carbon-containing material ratio is ≤0.5%, and the balance is bentonite. The carbon-containing material is coking dust ash, of which the proportion of particles below 0.5 mm is greater than 98%, and the carbon content is ≥85%.

[0016] Preferably, the diameter of the pelletizing disk is 7.5m, the inclination angle of the disk is 43°, the rotation speed is 6-8r / min, the side height of the disk is 650mm, the feeding point of the fine material zone of the pelletizing disk is set to a diameter of 6.8m, an angle of 330°, and a feeding width of 0.5m, and the feeding point of the growth zone of the pelletizing disk is set to a diameter of 5.8m, an angle of 45°, and a feeding width of 0.5m.

[0017] Preferably, the second mixture and the first mixture are added in a ratio of 3.6:1.

[0018] Preferably, the drying stage in the belt roaster includes a blast drying section and an exhaust drying section. The temperature of the blast drying section is 120-180°C, the blast drying time is 6 minutes, and the blast wind speed is 1.3-1.4 m / s. The wind temperature of the exhaust drying section is 200-350°C, the wind speed is 1.3-1.6 m / s, and the exhaust drying time is 6 minutes.

[0019] Preferably, the wind speed in the preheating section of the belt roaster is controlled to be 1.3-1.6 m / s, the wind temperature is 950-1000° C., and the preheating time is 7 minutes.

[0020] Preferably, the roasting stage controls the roasting temperature to 1240-1260° C. and the roasting time to 12-15 min.

[0021] Preferably, the cooling stage is a two-stage cooling, the wind speed of the first cooling stage is 2-2.6 m / s, the wind temperature is 600-900°C, and the cooling time is 12 min, and the wind speed of the second cooling stage is 2-2.6 m / s, the wind temperature is 100-600°C, and the cooling time is 5 min.

[0022] Preferably, the pellets meeting the requirements of the blast furnace have a compressive strength of >2450N / P, a reducibility of >65.5, and an expansion coefficient of <15%.

[0023] In summary, the beneficial effects of the present invention are as follows: the present invention realizes the method of layered balling of carbon-containing materials and boron-containing additives based on the zoning of the ball-forming disc to improve the compressive strength of hematite pellets, wherein the fine powder formed after the hematite grinding is strongly mixed with a certain proportion of boron-containing additives and bentonite, and then high-pressure roller milled to form a first mixed material, the fine powder formed after the hematite grinding is mixed with a certain proportion of coking dust ash and bentonite to form a second mixture, the first mixed material enters the fine particle area of ​​the ball-forming disc through the disc discharge to form a ball, and the mother ball A grows, the second mixed material enters the disc growth area through the disc discharge area, wraps the mother ball A, and forms a double-layer ball structure C in which B wraps A, the double-layer ball C is formed during the preheating and roasting process of entering the belt roasting machine, and the coking dust ash of the outer layer B is burned during the combustion process. The reducing atmosphere promotes the reduction of the hematite concentrate in the outer layer B to Fe3O4, which is then oxidized and roasted to form Fe2O3, forming regenerated continuous crystals, thereby ensuring the strength of the outer layer pellets. The boron-containing additives in the inner layer A are easy to form low-melting point substances at the roasting temperature, forming a bonding liquid phase with good strength, thereby improving the strength of the inner core pellets. By layering the carbon-containing materials and the boron-containing additives into pellets, the boron-containing additives are used to form low-melting point substances to improve the strength, while avoiding the problem of reduced reducibility caused by the use of boron-containing additives. At the same time, the problems of insufficient combustion of the carbon-containing materials in the inner layer of the pellets and insufficient reducing atmosphere resulting in the failure of Fe2O3 to form large continuous crystals under low-temperature roasting, causing fluctuations in the compressive strength of the pellets, etc., are solved, thereby achieving complementary advantages between the carbon-containing and boron-containing additives and improving the metallurgical properties of the hematite pellets. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The present invention is a flow chart of a method for improving the metallurgical properties of hematite pellets by layered pelletizing. DETAILED DESCRIPTION

[0025] The specific implementation manner of the present invention is further described below in conjunction with the accompanying drawings, and this embodiment does not constitute a limitation of the present invention.

[0026] like Figure 1 A method for improving the metallurgical properties of hematite pellets by layered pelletizing is shown, comprising the following steps:

[0027] The coarse hematite powder is wet-milled or dry-milled to form hematite concentrate, in which the hematite concentrate has a particle size of -200 mesh accounting for more than 78%.

[0028] The first mixed material is formed by intensive mixing and high-pressure roller grinding of hematite concentrate, boron-containing additives and bentonite in a ratio of hematite ≥ 99%, carbon-containing materials ≤ 0.5% and the balance of bentonite. The boron-containing additive is ferroboron concentrate, of which the particle size requirement is -200 mesh> 92%, and the B2O3 content is 4.5-5.5%.

[0029] The second mixed material is formed by intensive mixing and high-pressure roller grinding of hematite concentrate, carbon-containing material and bentonite in a ratio of hematite ≥ 99%, carbon-containing material ≤ 0.5% and the remainder bentonite. The carbon-containing material is coking dust ash, of which the proportion of particles below 0.5 mm is greater than 98%, and the carbon content is ≥ 85%.

[0030] After the first mixture is discharged from the batching bin disc, it enters the fine material area of ​​the ball-making disc to form mother balls.

[0031] After the particle size of the mother ball grows to 5-6 mm, the second mixed material is added to the growth area of ​​the ball-making disk to form green balls.

[0032] The green balls enter the belt roaster, and after drying, preheating, roasting and cooling, the pellets with compressive strength>2450N / P, reducibility>65.5, expansion coefficient<15% are obtained, which meet the requirements of blast furnace.

[0033] The diameter of the pelletizing disk is 7.5m, the inclination angle is 43°, the rotation speed is 6-8r / min, the side height is 650mm, the feeding point of the fine material area of ​​the pelletizing disk is set to a diameter of 6.8m, an angle of 330°, and a feeding width of 0.5m, and the feeding point of the growth area of ​​the pelletizing disk is set to a diameter of 5.8m, an angle of 45°, and a feeding width of 0.5m.

[0034] The second mixture and the first mixture are added in a ratio of 3.6:1.

[0035] The drying stage in the belt roaster includes a blast drying section and an exhaust drying section. The temperature of the blast drying section is 120-180°C, the blast drying time is 6 minutes, the blast wind speed is 1.3-1.4m / s, and the wind temperature of the exhaust drying section is 200-350°C, the wind speed is 1.3-1.6m / s, and the exhaust drying time is 6 minutes.

[0036] The wind speed in the preheating section of the belt roaster is controlled at 1.3-1.6m / s, the wind temperature is 950-1000℃, and the preheating time is 7min.

[0037] The roasting stage controls the roasting temperature to 1240-1260°C and the roasting time to 12-15 minutes.

[0038] The cooling stage is a two-stage cooling. The wind speed of the first cooling stage is 2-2.6m / s, the wind temperature is 600-900℃, and the cooling time is 12min. The wind speed of the second cooling stage is 2-2.6m / s, the wind temperature is 100-600℃, and the cooling time is 5min.

[0039] The present invention will be described in detail below with reference to the accompanying drawings in combination with embodiments and comparative examples.

[0040] Example 1

[0041] According to the ratio in Table 1, the hematite concentrate, ferroboron concentrate and bentonite are mixed vigorously and rolled with high pressure to form a first mixed material. The hematite concentrate, coking dust ash and bentonite are mixed vigorously and rolled with high pressure to form a second mixed material. After the first mixture is discharged from the batching bin disc, it enters the fine material area of ​​the ball making disc to form a mother ball and grow. After the mother ball particle size grows to 5-6mm, the second mixed material is added to the growth area. The second mixture and the first mixture are discharged in a ratio of 3.6:1 to obtain raw balls with a particle size of 10-16mm, which are then roasted in a belt roaster. The temperature of the blast drying section is 120-180℃, the blast drying time is 6min, the blast wind speed is 1.3-1.4m / s, the wind temperature of the exhaust drying section is 200-350℃, the wind speed is 1.3-1.6m / s, and the exhaust drying time is 6min.

[0042] Preheating, roasting and cooling are as follows: the wind speed in the preheating section is controlled at 1.3-1.6m / s, the wind temperature is 950-1000℃, and the preheating time is 7min; the roasting temperature in the roasting section is controlled at 1240-1260℃, and the roasting time is 12-15min; the roasted pellets are cooled in two stages, the wind speed in the first cooling section is 2-2.6m / s, the wind temperature is 600-900℃, and the cooling time is 12min; the wind speed in the second cooling section is 2-2.6m / s, the wind temperature is 100-600℃, and the cooling time is 5min. The metallurgical properties obtained are: compressive strength 2680N / P, reducibility 66.5%, and expansion index 13.6%.

[0043] Table 1 Ratio of materials in Example 1

[0044]

[0045] Example 2

[0046] According to the ratio in Table 2, the hematite concentrate, ferroboron concentrate and bentonite are mixed vigorously and rolled with high pressure to form a first mixed material. The hematite concentrate, coking dust ash and bentonite are mixed vigorously and rolled with high pressure to form a second mixed material. After the first mixture is discharged from the batching bin disc, it enters the fine material area of ​​the pelletizing disc to form a mother ball and grow. After the mother ball particle size grows to 5-6mm, the second mixed material is added to the growth area. The second mixture and the first mixture are discharged in a ratio of 3.6:1 to obtain raw balls with a particle size of 10-16mm, which are then roasted in a belt roaster. The temperature of the blast drying section is 120-180℃, the blast drying time is 6min, the blast wind speed is 1.3-1.4m / s, the wind temperature of the exhaust drying section is 200-350℃, the wind speed is 1.3-1.6m / s, and the exhaust drying time is 6min.

[0047] Preheating, roasting and cooling are as follows: the wind speed in the preheating section is controlled at 1.3-1.6m / s, the wind temperature is 950-1000℃, and the preheating time is 7min; the roasting temperature in the roasting section is controlled at 1240-1260℃, and the roasting time is 12-15min; the roasted pellets are cooled in two stages, the wind speed in the first cooling section is 2-2.6m / s, the wind temperature is 600-900℃, and the cooling time is 12min; the wind speed in the second cooling section is 2-2.6m / s, the wind temperature is 100-600℃, and the cooling time is 5min. The metallurgical properties obtained are: compressive strength 2610N / P, reducibility 67.6%, and expansion index 12.7%.

[0048] Table 2 Ratio of materials in Example 2

[0049]

[0050] Example 3

[0051] According to the ratio in Table 3, the hematite concentrate, ferroboron concentrate and bentonite are mixed vigorously and rolled with high pressure to form a first mixed material. The hematite concentrate, coking dust ash and bentonite are mixed vigorously and rolled with high pressure to form a second mixed material. After the first mixture is discharged from the batching bin disc, it enters the fine material area of ​​the ball making disc to form a mother ball and grow. After the mother ball particle size grows to 5-6mm, the second mixed material is added to the growth area. The second mixture and the first mixture are discharged in a ratio of 3.6:1 to obtain raw balls with a particle size of 10-16mm, which are then roasted in a belt roaster. The temperature of the blast drying section is 120-180℃, the blast drying time is 6min, the blast wind speed is 1.3-1.4m / s, the wind temperature of the exhaust drying section is 200-350℃, the wind speed is 1.3-1.6m / s, and the exhaust drying time is 6min.

[0052] Preheating, roasting and cooling are as follows: the wind speed in the preheating section is controlled at 1.3-1.6m / s, the wind temperature is 950-1000℃, and the preheating time is 7min; the roasting temperature in the roasting section is controlled at 1240-1260℃, and the roasting time is 12-15min; the roasted pellets are cooled in two stages, the wind speed in the first cooling section is 2-2.6m / s, the wind temperature is 600-900℃, and the cooling time is 12min; the wind speed in the second cooling section is 2-2.6m / s, the wind temperature is 100-600℃, and the cooling time is 5min. The metallurgical properties obtained are: compressive strength 2526N / P, reducibility 68.1%, and expansion index 13.4%.

[0053] Table 3 Material ratios in Example 3

[0054]

[0055] Example 4

[0056] According to the ratio in Table 4, the hematite concentrate, ferroboron concentrate and bentonite are mixed vigorously and rolled with high pressure to form a first mixed material. The hematite concentrate, coking dust ash and bentonite are mixed vigorously and rolled with high pressure to form a second mixed material. After the first mixture is discharged from the batching bin disc, it enters the fine material area of ​​the ball making disc to form a mother ball and grow. After the mother ball particle size grows to 5-6mm, the second mixed material is added to the growth area. The second mixture and the first mixture are discharged in a ratio of 3.6:1 to obtain raw balls with a particle size of 10-16mm, which are then roasted in a belt roaster. The temperature of the blast drying section is 120-180℃, the blast drying time is 6min, the blast wind speed is 1.3-1.4m / s, the wind temperature of the exhaust drying section is 200-350℃, the wind speed is 1.3-1.6m / s, and the exhaust drying time is 6min.

[0057] Preheating, roasting and cooling are as follows: the wind speed in the preheating section is controlled at 1.3-1.6m / s, the wind temperature is 950-1000℃, and the preheating time is 7min; the roasting temperature in the roasting section is controlled at 1240-1260℃, and the roasting time is 12-15min; the roasted pellets are cooled in two stages, the wind speed in the first cooling section is 2-2.6m / s, the wind temperature is 600-900℃, and the cooling time is 12min; the wind speed in the second cooling section is 2-2.6m / s, the wind temperature is 100-600℃, and the cooling time is 5min. The metallurgical properties obtained are: compressive strength 2713N / P, reducibility 61.1%, and expansion index 11.6%.

[0058] Table 4 Material ratios in Example 4

[0059]

[0060] Comparative Example 1

[0061] According to the ratio in Table 5, the hematite concentrate, ferroboron concentrate and bentonite are vigorously mixed and high-pressure roller milled to form a mixed material pellet to obtain raw balls with a particle size of 10-16 mm, which are then fed into a belt roaster for roasting. The temperature in the blast drying section is 120-180°C, the blast drying time is 6 minutes, the blast wind speed is 1.3-1.4 m / s, and the wind temperature in the exhaust drying section is 200-350°C, the wind speed is 1.3-1.6 m / s, and the exhaust drying time is 6 minutes.

[0062] Preheating, roasting and cooling are as follows: the wind speed in the preheating section is controlled at 1.3-1.6m / s, the wind temperature is 950-1000℃, and the preheating time is 7min; the roasting temperature in the roasting section is controlled at 1240-1260℃, and the roasting time is 12-15min; the roasted pellets are cooled in two stages, the wind speed in the first cooling section is 2-2.6m / s, the wind temperature is 600-900℃, and the cooling time is 12min; the wind speed in the second cooling section is 2-2.6m / s, the wind temperature is 100-600℃, and the cooling time is 5min. The metallurgical properties obtained are: compressive strength 2693N / P, reducibility 40.77%, and expansion index 14.5%.

[0063] Table 5 Ratio of materials in comparative example 1

[0064]

[0065] Comparative Example 2

[0066] According to the ratio in Table 6, the hematite concentrate, coking dust and bentonite are vigorously mixed and high-pressure roller milled to form a mixed material pellet to obtain raw balls with a particle size of 10-16 mm, which are then fed into a belt roaster for roasting. The temperature in the blast drying section is 120-180°C, the blast drying time is 6 minutes, the blast wind speed is 1.3-1.4 m / s, and the wind temperature in the exhaust drying section is 200-350°C, the wind speed is 1.3-1.6 m / s, and the exhaust drying time is 6 minutes.

[0067] Preheating, roasting and cooling are as follows: the wind speed in the preheating section is controlled at 1.3-1.6m / s, the wind temperature is 950-1000℃, and the preheating time is 7min; the roasting temperature in the roasting section is controlled at 1280-1295℃, and the roasting time is 12-15min; the roasted pellets are cooled in two stages, the wind speed in the first cooling section is 2-2.6m / s, the wind temperature is 600-900℃, and the cooling time is 12min; the wind speed in the second cooling section is 2-2.6m / s, the wind temperature is 100-600℃, and the cooling time is 5min. The metallurgical properties obtained are: compressive strength 2453N / P, reducibility 65.2%, and expansion index 13.4%.

[0068] Table 6 Ratio of materials in comparative example 2

[0069]

[0070] It can be seen from the above embodiments and comparative examples that the present invention provides a way to improve the metallurgical properties of acidic pellets produced from high-proportion or even full-proportion hematite, and the roasting temperature can be reduced by realizing layered pelletizing of carbon-containing materials and boron-containing additives based on the partitioning of the pelletizing disk. The outer layer of hematite concentrate is mixed with carbon-containing materials, and a reducing atmosphere is formed by the combustion of the carbon-containing materials. Through the oxidation and recrystallization of Fe3O4, regenerated hematite crystals are formed at a low roasting temperature to improve the strength of the pellets. The inner layer of hematite concentrate is mixed with boron-containing additives, and a low-melting-point substance is formed by the boron-containing additives to form a bonding liquid phase with good strength, which makes up for the reduction in pellet strength caused by insufficient combustion inside the hematite pellets, realizes the complementary advantages of carbon-containing materials and boron-containing additives in pellet production, and improves the metallurgical properties of hematite pellets.

[0071] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art may make various modifications or equivalent substitutions to the present invention within the essence and protection scope of the present invention, and such modifications or equivalent substitutions should also be deemed to fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for improving the metallurgical properties of hematite pellets by layered pelletizing, characterized in that: The steps include: The coarse hematite powder is wet-milled or dry-milled to form hematite concentrate; The hematite concentrate, the boron-containing additive and the bentonite are mixed vigorously and subjected to high-pressure roller grinding according to a certain proportion to form a first mixed material; The hematite concentrate, carbonaceous material and bentonite are mixed vigorously and subjected to high pressure roller grinding according to a certain proportion to form a second mixed material; After the first mixture is discharged from the batching bin disc, it enters the fine material area of ​​the ball-making disc to form mother balls and grow; After the mother ball size grows to 5-6mm, the second mixed material is added to the growth area of ​​the ball-making disk to form green balls; The green balls enter the belt roaster, where they are dried, preheated, roasted and cooled to obtain pellets that meet the requirements of the blast furnace.

2. The method for improving the metallurgical properties of hematite pellets by layered pelletizing according to claim 1, characterized in that: The proportion of the hematite concentrate with a particle size of -200 mesh is greater than 78%, and the ratio of the hematite concentrate, boron-containing additives and bentonite is: the proportion of hematite is ≥90%, the proportion of boron-containing additives is ≤8%, and the balance is bentonite. The boron-containing additive is ferroboron concentrate, in which the particle size requirement of -200 mesh is greater than 92%, and the B2O3 content is 4.5-5.5%.

3. The method for improving the metallurgical properties of hematite pellets by layered pelletizing according to claim 1, characterized in that: The ratio of the hematite concentrate, carbon-containing material and bentonite is: the ratio of hematite is ≥99%, the ratio of carbon-containing material is ≤0.5%, and the balance is bentonite. The carbon-containing material is coking dust ash, of which the proportion of particles below 0.5 mm is greater than 98%, and the carbon content is ≥85%.

4. The method for improving the metallurgical properties of hematite pellets by layered pelletizing according to claim 1, characterized in that: The pelletizing disk has a diameter of 7.5m, an inclination of 43°, a rotation speed of 6-8r / min, a side height of 650mm, a feeding point in the fine material zone of the pelletizing disk set at a diameter of 6.8m, an angle of 330°, and a feeding width of 0.5m, and a feeding point in the growth zone of the pelletizing disk set at a diameter of 5.8m, an angle of 45°, and a feeding width of 0.5m.

5. The method for improving the metallurgical properties of hematite pellets by layered pelletizing according to claim 1, characterized in that: The second mixture and the first mixture are added in a ratio of 3.6:

1.

6. The method for improving the metallurgical properties of hematite pellets by layered pelletizing according to claim 1, characterized in that: The drying stage in the belt roaster includes a blast drying section and an exhaust drying section. The blast drying section has a temperature of 120-180°C, a blast drying time of 6 minutes, and a blast wind speed of 1.3-1.4 m / s. The exhaust drying section has a wind temperature of 200-350°C, a wind speed of 1.3-1.6 m / s, and an exhaust drying time of 6 minutes.

7. The method for improving the metallurgical properties of hematite pellets by layered pelletizing according to claim 1, characterized in that: The wind speed in the preheating section of the belt roaster is controlled to be 1.3-1.6 m / s, the wind temperature is 950-1000° C., and the preheating time is 7 minutes.

8. The method for improving the metallurgical properties of hematite pellets by layered pelletizing according to claim 1, characterized in that: The roasting stage controls the roasting temperature to 1240-1260° C. and the roasting time to 12-15 minutes.

9. The method for improving the metallurgical properties of hematite pellets by layered pelletizing according to claim 1, characterized in that: The cooling stage is a two-stage cooling, the wind speed of the first cooling stage is 2-2.6m / s, the wind temperature is 600-900℃, and the cooling time is 12min, and the wind speed of the second cooling stage is 2-2.6m / s, the wind temperature is 100-600℃, and the cooling time is 5min.

10. The method for improving the metallurgical properties of hematite pellets by layered pelletizing according to claim 1, characterized in that: The pellets meeting the requirements of blast furnaces have a compressive strength of >2450N / P, a reducibility of >65.5, and an expansion coefficient of <15%.

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