Method for producing iron ore pellets, and iron ore pellets

Abstract

A method for producing an iron ore pellet according to one embodiment of the present invention is a method for producing a self-fluxing iron ore pellet used in blast furnace operation, the method comprising: a raw material blending step for blending an auxiliary raw material containing CaO and MgO into an ore raw material so that the CaO / SiO2 mass ratio is 0.8 or more and the MgO / SiO2 mass ratio is 0.4 or more; a granulation step in which green pellets having a porosity of 15-22% are granulated using the raw material mixture obtained in the raw material blending step; and a roasting step for roasting the green pellets at a temperature of 1200 DEG C or more and 1300 DEG C or less.

Description

Technical Field

[0001] The present invention relates to a method for producing iron ore pellets and iron ore pellets. Background Art

[0002] As for blast furnace operation, it is well known that iron ore and calcined ore containing iron oxide and coke as a carbon source are charged from the upper part of the blast furnace, air and oxygen are blown from the tuyere at the lower part, carbon monoxide is generated and a reduction reaction of removing oxygen from the iron oxide is carried out in the furnace, and pig iron is taken out from the lower part of the furnace.

[0003] In order to make this continuous operation go smoothly, it is important to supply air smoothly. For this reason, it is hoped that the air supply pressure is low and stable, that is, the air permeability is good. The air supply pressure depends on the properties of the charge. The iron ore, sintered ore, and iron ore pellets in the charge are exposed to high temperature and reducing atmosphere and undergo reduction reaction, becoming a mixture of metallic iron and oxides. At the same time, they soften and deform due to the load in the blast furnace. Since the softening and deformation fill the gaps between the charge particles, the air permeability in the furnace is hindered. The main cause of this phenomenon is called the pressure loss in the lower part of the furnace, and it is hoped to reduce this phenomenon.

[0004] As an iron ore pellet that can reduce the pressure loss in the lower part of the furnace, a self-fluxing pellet is known, CaO / SiO 2 The mass ratio is above 0.8, MgO / SiO 2 The mass ratio is 0.4 or more, and the particle size distribution is predetermined (see Japanese Patent Application Laid-Open No. 2008-280556).

[0005] In the above iron ore pellets, by making CaO / SiO 2 The mass ratio is above 0.8, MgO / SiO 2 The mass ratio is 0.4 or more, thereby improving the reducibility at high temperature, and air permeability is ensured by controlling the particle size distribution.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2008-280556 Summary of the invention

[0009] Problems to be solved by the invention

[0010] In the above-mentioned existing iron ore pellets, although air permeability can be ensured, the effect is relatively limited, and the ventilation resistance (upper pressure loss) in the relatively low temperature area of ​​the upper part of the vertical furnace is easy to deteriorate. In addition, recently, there has been an increase in the use of expensive coke by blowing pulverized coal from the tuyere of the blast furnace. As a result, there is a tendency that as the amount of pulverized coal blown in increases, the amount of coke that supports the air permeability in the blast furnace decreases, and the ventilation resistance tends to increase overall. Therefore, it is particularly necessary to reduce the ventilation resistance in the upper part of the blast furnace.

[0011] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing iron ore pellets and iron ore pellets which are excellent in reducibility at high temperatures and can reduce the upper ventilation resistance of a blast furnace.

[0012] Means of solving the problem

[0013] A method for producing iron ore pellets according to one embodiment of the present invention is a method for producing self-fluxing iron ore pellets for blast furnace operation, wherein the method comprises the following steps: a raw material mixing step, wherein the raw material is a mixture of CaO / SiO 2 The mass ratio is 0.8 or more, and MgO / SiO 2 Auxiliary raw materials containing CaO and MgO are blended into the ore raw materials in a manner such that the mass ratio becomes greater than 0.4; a granulation step, using the mixed raw materials obtained in the raw material blending step, to granulate green pellets with a porosity of greater than 15% and less than 22%; a roasting step, roasting the green pellets at a temperature of greater than 1200°C and less than 1300°C.

[0014] Another embodiment of the iron ore pellets of the present invention is a self-melting iron ore pellet for blast furnace operation, wherein CaO / SiO 2 The mass ratio is above 0.8, and MgO / SiO 2 The mass ratio is above 0.4 and the average compressive strength is above 270kg / p.

[0015] Effects of the Invention

[0016] The method for producing iron ore pellets of the present invention can produce iron ore pellets that are excellent in reducibility at high temperatures and can reduce the upper ventilation resistance of a blast furnace. In addition, the iron ore pellets of the present invention are excellent in reducibility at high temperatures and can reduce the upper ventilation resistance of a blast furnace. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a flowchart showing a method for producing iron ore pellets according to one embodiment of the present invention.

[0018] Figure 2 It is shown Figure 1 A schematic diagram of the structure of a production apparatus used in a method for producing iron ore pellets.

[0019] Figure 3 This is a graph showing the relationship between the powder ratio of 5 mm or less generated by the transportation of iron ore pellets and the average compressive strength. DETAILED DESCRIPTION

[0020] [Description of Embodiments of the Invention]

[0021] The inventors of the present invention have conducted intensive research on the ventilation resistance of the upper part of the blast furnace and have realized that even if the proportion of small-sized iron ore pellets related to the deterioration of pressure loss is suppressed during pellet production, it is inevitable that they will be broken and generate powder during the subsequent transportation and blast furnace charging process. It is known that if the powder generated from the iron ore pellets due to transportation and impact in the blast furnace is reduced, the ventilation resistance of the upper part of the blast furnace will be reduced. In addition, the inventors of the present invention have also confirmed that in order to reduce the powder, the average compressive strength can be increased to 270kg / p.

[0022] However, in order to improve the reducibility of iron ore pellets required in blast furnace operation, the CaO / SiO 2 The mass ratio is above 0.8, and MgO / SiO 2 Iron ore pellets with a mass ratio of 0.4 or more have not yet achieved an average compressive strength of 270 kg / p or more. This is believed to be due to the fact that CaO, MgO, SiO 2 and Fe 2 O 3 Coarse grains of the compound are generated during calcination, which reduces the strength. In other words, if the grains are large, the directions of the slip planes where dislocations are easy to move are easy to be consistent, and dislocations are easy to move under low stress and be destroyed.

[0023] The inventors of the present invention have further repeatedly studied and found that when the coarse grains are generated, the roasting temperature is high. The crystals of the mineral structure are generated and expanded due to diffusion. The higher the temperature, the greater the diffusion coefficient of Fe, Ca, Si, Mg, Al, etc. in the solid phase and the liquid phase. That is, the higher the roasting temperature, the more diffusion, the larger the grains, and the coarse grains are generated. Therefore, the inventors of the present invention believe that by lowering the roasting temperature, the generation of coarse grains can be suppressed.

[0024] On the other hand, if the roasting temperature is low, the problem of the pellets not being able to be solidified will occur. That is, the distance between the ore particles will increase, the contact points between the particles will decrease, and the force constituting the strength of the pellets will weaken, resulting in a tendency to reduce the compressive strength. As a result, even if the roasting temperature is lowered to suppress the formation of coarse grains, the compressive strength cannot be fully improved.

[0025] Here, the inventors of the present invention focused on the fact that if the roasting temperature is low and the pellets cannot be sintered, the porosity will not decrease. The reduction in porosity occurs because the ore particles approach and merge with each other through the diffusion phenomenon in order to reduce the surface energy of the iron ore particles so as to reduce the surface area. Therefore, it can be considered that in the high-porosity pellets, the distance between the ore particles is enlarged, the contact points between the particles are reduced, and the force constituting the strength of the pellets is weakened. Therefore, the inventors of the present invention considered that if the porosity can be controlled independently of the roasting temperature, the compressive strength can be fully improved. Therefore, by controlling the porosity in the green pellet stage, which has not been done before, it was confirmed that the compressive strength was fully improved, thereby completing the present invention.

[0026] That is, a method for producing iron ore pellets according to one embodiment of the present invention is a method for producing self-fluxing iron ore pellets for blast furnace operation, wherein the method comprises the following steps: a raw material blending step, wherein the raw material is a raw material comprising: a raw material blending step; 2 The mass ratio is 0.8 or more, and MgO / SiO 2 Auxiliary raw materials containing CaO and MgO are blended into the ore raw materials in a manner such that the mass ratio becomes greater than 0.4; a granulation step is performed using the mixed raw materials obtained in the raw material blending step to granulate green pellets having a porosity of greater than 15% and less than 22%; a roasting step is performed at a temperature of greater than 1200°C and less than 1300°C.

[0027] The iron ore pellets produced by the method for producing iron ore pellets are self-fluxing and have a CaO / SiO 2 The mass ratio is above the lower limit, and MgO / SiO 2 Since the mass ratio is above the lower limit, the reducibility is high. In addition, since the porosity at the green pellet stage is within the above range, the green pellet is roasted at a temperature within the above range in the roasting step, the compressive strength of the manufactured iron ore pellet can be sufficiently improved. Therefore, by using this method for manufacturing iron ore pellets, it is possible to manufacture iron ore pellets that are excellent in reducibility at high temperatures and can reduce the ventilation resistance of the upper part of the blast furnace.

[0028] In the granulation process, a tumbling granulator is used, and the porosity can be controlled by the raw material particle size in the raw material mixing process and the tumbling time in the granulation process. By controlling the porosity in this way, the porosity can be easily controlled to a desired value, and the compressive strength can be more reliably improved.

[0029] In the granulation step, the particle size range of the green pellets is adjusted so that the particle size after the calcination step is 4 mm or more and 20 mm or less. By adjusting the particle size after the calcination step to be within the above range, the reduction of the upper ventilation resistance of the blast furnace can be suppressed while maintaining the reducibility at high temperature.

[0030] In adjusting the particle size range of the green pellets, classification using a screen group having a large-size screen and a seed screen adjusted to a predetermined mesh size can be used. By adjusting the particle size range of the green pellets by classification, the particle size after the roasting step can be easily and reliably adjusted.

[0031] Another embodiment of the iron ore pellets of the present invention is a self-melting iron ore pellet for blast furnace operation, wherein CaO / SiO 2 The mass ratio is above 0.8, and MgO / SiO 2 The mass ratio is above 0.4 and the average compressive strength is above 270kg / p.

[0032] The iron ore pellets are self-fluxing and make CaO / SiO 2 The mass ratio is above the lower limit, and MgO / SiO 2 Since the mass ratio is above the lower limit, the reducibility is high. In addition, since the iron ore pellets have an average compressive strength above the lower limit, powder generated from the iron ore pellets due to transportation and impact in the blast furnace can be reduced, and the upper ventilation resistance of the blast furnace can be reduced.

[0033] The mass ratio of the iron ore pellets having a compressive strength of 100 kg / p or less may be 10% or less. By making the mass ratio of the iron ore pellets having a compressive strength of 100 kg / p or less below the upper limit, the powder generated from the iron ore pellets can be further reduced, and the upper ventilation resistance of the blast furnace can be further reduced.

[0034] Here, the “compressive strength” refers to the strength specified in JIS-M8718:2017, and the “average compressive strength” refers to the average value of the compressive strengths of at least 10 arbitrary iron ore pellets.

[0035] [Details of Embodiments of the Invention]

[0036] Hereinafter, a method for producing iron ore pellets and iron ore pellets according to an embodiment of the present invention will be described with reference to the drawings as appropriate.

[0037] [Method for producing iron ore pellets]

[0038] Figure 1 The method for producing iron ore pellets shown in FIG. 1 comprises a raw material blending step S1, a granulation step S2, a roasting step S3, and a cooling step S4. The method for producing iron ore pellets is as follows: Figure 2As shown, a grate-rotary kiln manufacturing device (hereinafter also referred to as "manufacturing device 2") can be used to manufacture self-melting iron ore pellets 1 for blast furnace operation. The manufacturing device 2 includes a pan pelletizer 3, a grate furnace 4, a kiln 5, and an annular cooler 6.

[0039] <Raw material mixing process>

[0040] In the raw material blending step S1, CaO / SiO 2 The mass ratio is 0.8 or more, and MgO / SiO 2 The auxiliary raw material containing CaO and MgO is blended with the ore raw material so that the mass ratio becomes 0.4 or more.

[0041] Specifically, in the raw material blending step S1 , limestone as a CaO source and dolomite as a MgO source are added as the auxiliary raw materials according to the iron grade of the iron ore (pellet material) as the ore raw material.

[0042] The ore raw material and the auxiliary raw material can be crushed by a ball mill or the like in advance or after blending as needed to adjust the particle size of the mixed raw material obtained by mixing the ore raw material and the auxiliary raw material. The present inventors have learned that the porosity of the green pellets P is proportional to the raw material particle size index. In other words, if the raw material particle size index is properly controlled, the porosity of the green pellets P can be controlled, and the strength of the iron ore pellets 1 can be controlled by the porosity of the green pellets P.

[0043] Here, the "raw material particle size index" can be specified by the following method. First, measure the particle size distribution of the mixed raw material. This measurement can use one of JIS-A-1204:2010, JIS-A-8815:1994, and JIS-Z-8825:2022. Next, using the mass ratio or volume ratio mi in each particle size range Pi (representative value), calculate the sum Σ3 / Pi·mi in the range of 3μm to 1000μm, and use it as the raw material particle size index.

[0044] The relationship between the raw material particle size index and the porosity of the raw pellets P is established in a mixed raw material formed by blending the same brand of iron ore and auxiliary raw materials at the same ratio. However, if the brand of the iron ore is different, for example, this proportionality coefficient may change due to the influence of surface shape and wettability. Therefore, the preferred value of the raw material particle size index can be determined by the following method. First, prepare at least two raw materials with raw material particle size indices in a mixed raw material with a specific mixing ratio, make raw pellets P and measure the porosity. Based on this result, the relationship between the raw material particle size index and the porosity can be calculated. As described later, since the porosity and the strength of the iron ore pellet 1 also have a proportional relationship, the required porosity can be calculated based on the required strength of the iron ore pellet 1. In this way, the raw material particle size index as the required porosity can be determined, and based on this, the particle size of the raw material can be adjusted according to the raw material particle size index. In addition, the adjustment of the particle size also includes purchasing raw materials with such a particle size.

[0045] Furthermore, a binder such as bentonite may be appropriately blended into the mixed raw material in order to obtain the strength of the green pellets P required for transportation within the production process.

[0046] <Granulation process>

[0047] In the granulation step S2, the mixed raw material obtained in the raw material blending step S1 is used to granulate green pellets P having a porosity of 15% or more and 22% or less. A tumbling granulator can be used for granulating the green pellets P. Figure 2 The disc granulator 3 or drum granulator shown.

[0048] Specifically, in the granulation step S2, water (granulation water) is added to the mixed raw material, and the granulation water-containing mixture (the mixed raw material containing granulation water) is fed into the pan granulator 3 and rotated to produce pellet-shaped green pellets P.

[0049] In the method for producing the iron ore pellets, the porosity of the green pellets P is controlled in the above manner. The lower limit of the porosity is preferably 15%, and more preferably 17%. On the other hand, the upper limit of the porosity is preferably 22%, and more preferably 20%. If the porosity is lower than the lower limit, a water vapor explosion (explosion phenomenon) may occur in the roasting step S3. On the contrary, if the porosity is higher than the upper limit, the crushing strength of the iron ore pellets 1 may be reduced.

[0050] The porosity can be controlled by the raw material particle size in the raw material mixing step S1 and the rolling time in the granulation step S2. By controlling the porosity in this way, the porosity can be easily controlled to a desired value, and the compressive strength can be more reliably improved.

[0051] In addition, the particle size range of the green pellets P can be adjusted in the granulation step S2 so that the particle size after the roasting step S3 is 4 mm or more and 20 mm or less, more preferably 6 mm or more and 15 mm or less. By making the particle size after the roasting step S3 within the above range, it is possible to maintain the reducibility at high temperature while suppressing the reduction of the upper ventilation resistance of the blast furnace.

[0052] In adjusting the particle size range of the green pellets P, classification using a screen group having a large-size screen (upper limit screen) adjusted to a predetermined mesh size and a seed screen (lower limit screen) can be used. By adjusting the particle size range of the green pellets P by classification in this way, the particle size after the roasting step S3 can be easily and reliably adjusted. In addition, it is preferable to crush the defective products that do not meet the specifications in the classification operation and reuse them as the mixed raw materials.

[0053] <Baking process>

[0054] In the calcining step S3, the green pellets P are calcined at a temperature of 1200°C or higher and 1300°C or lower. Figure 2 In the manufacturing apparatus 2 shown, the calcining step S3 uses the grate furnace 4 and the kiln 5 .

[0055] (Grate furnace)

[0056] Grate furnace 4, such as Figure 2 As shown, a moving grate 41 , a drying chamber 42 , a dehydration chamber 43 , and a preheating chamber 44 are provided.

[0057] The moving grate 41 is configured in an annular shape, and the green pellets P placed on the moving grate 41 can be moved in the order of the drying chamber 42 , the dehydration chamber 43 , and the preheating chamber 44 .

[0058] In the drying chamber 42 , the dehydrating chamber 43 and the preheating chamber 44 , the green pellets P are dried, dehydrated and preheated by the heating gas G1 , thereby obtaining preheated pellets H having a strength sufficient to withstand rotation in the kiln 5 .

[0059] Specifically, the following sequence is followed. First, in the drying chamber 42, the green pellets P are dried at an atmosphere temperature of about 250°C. Next, in the dehydration chamber 43, the dried green pellets P are heated to about 450°C, mainly to decompose and remove the crystal water in the iron ore. Furthermore, in the preheating chamber 44, the green pellets P are heated to about 1100°C, the carbonates contained in the limestone, dolomite, etc. are decomposed to remove carbon dioxide, and the magnetite in the iron ore is oxidized. Thus, preheated pellets H are obtained.

[0060] like Figure 2As shown, the heating gas G1 used in the dehydration chamber 43 is used as the heating gas G1 of the drying chamber 42. Similarly, the heating gas G1 of the preheating chamber 44 is used as the heating gas G1 of the dehydration chamber 43, and the combustion exhaust gas G2 used in the kiln 5 is used as the heating gas G1 of the preheating chamber 44. By using the high-temperature heating gas G1 or combustion exhaust gas G2 on the downstream side in this way, the heating cost of the heating gas G1 can be reduced. In addition, a burner 45 can be provided in each chamber to control the temperature of the heating gas G1. Figure 2 In the drying chamber 42, a burner 45 is provided in the dehydration chamber 43 and the preheating chamber 44. In addition, the heating gas G1 used in the drying chamber 42 is finally discharged from the chimney C.

[0061] (Kiln)

[0062] The kiln 5 is directly connected to the grate furnace 4 and is a cylindrical rotary kiln with a gradient. The kiln 5 roasts the preheated pellets H discharged from the preheating chamber 44 of the grate furnace 4. Specifically, the preheated pellets H are roasted by combustion using a kiln burner (not shown) arranged on the outlet side. Thus, high-temperature iron ore pellets 1 are obtained.

[0063] The lower limit of the roasting temperature for roasting the preheated pellets H is 1200°C, and more preferably 1220°C. On the other hand, the upper limit of the roasting temperature is 1300°C, and more preferably 1280°C. The present inventors have found that when the roasting temperature is within the above range, the porosity of the green pellets P is proportional to the strength of the iron ore pellets 1. In other words, if the roasting temperature is lower than the lower limit, the pellets cannot be sintered, and if the roasting temperature is higher than the upper limit, coarse grains are easily generated, so the crushing strength of the iron ore pellets 1 may be reduced. Conversely, if the desired strength is determined, the porosity of the green pellets P can be determined by this proportional relationship.

[0064] In the kiln 5, the atmospheric air used as the cooling gas G3 used in the ring cooler 6 is used as combustion air. In addition, the high-temperature combustion exhaust gas G2 used for preheating the pellets H for roasting is sent to the preheating chamber 44 as the heating gas G1.

[0065] <Cooling process>

[0066] In the cooling step S4, the high-temperature iron ore pellets 1 obtained in the roasting step S3 are cooled. In the cooling step S4, a ring cooler 6 is used. The iron ore pellets 1 cooled in the cooling step S4 are collected and used for blast furnace operation.

[0067] The ring cooler 6 can cool the iron ore pellets 1 by circulating the atmospheric air as the cooling gas G3 by the ventilation device 61 while moving the high-temperature iron ore pellets 1 discharged from the kiln 5 .

[0068] Furthermore, the cooling gas G3 whose temperature has risen after being used in the ring cooler 6 is fed into the kiln 5 and used as combustion air.

[0069] <Advantages>

[0070] The iron ore pellets 1 produced by the method for producing iron ore pellets are self-fluxing, and the CaO / SiO 2 The mass ratio is above 0.8, and MgO / SiO 2 The mass ratio is 0.4 or more, so the reducibility is high. In addition, the green pellets P are roasted at a temperature of 1200° C. to 1300° C. in the roasting step S3, on the basis of making the porosity of the green pellets P to be 15% to 22%, so that the compressive strength of the manufactured iron ore pellets 1 can be sufficiently improved. Therefore, by using this method for manufacturing iron ore pellets, it is possible to manufacture iron ore pellets 1 that are excellent in reducibility at high temperatures and can reduce the ventilation resistance of the upper part of the blast furnace.

[0071] 〔Iron ore pellets〕

[0072] Another embodiment of the iron ore pellet 1 of the present invention is a self-melting iron ore pellet for blast furnace operation. The iron ore pellet 1 is a high-strength agglomerate ore obtained by granulating and roasting fine powder ore, and can be produced by the above-mentioned method for producing iron ore pellets.

[0073] It is known that in the production of iron ore pellets 1, if a CaO-containing compound such as limestone is added to the ore raw material, the CaO / SiO ratio of the iron ore pellets 1 is increased. 2 The iron ore pellet 1 has a CaO / SiO mass ratio of 1. 2 The mass ratio is 0.8 or more.

[0074] When the raw materials are iron ore (iron oxide) and limestone (containing a CaO compound), during the roasting process, due to the solid phase reaction of CaO generated by thermal decomposition and iron oxide, a calcium ferrite compound is generated, and at the same time, the contact points are bonded by solid phase diffusion bonding. This bonding is local, and the fine pores existing before roasting are still maintained after roasting, and the iron ore pellet 1 becomes a porous body with relatively uniform fine pores.

[0075] During the operation of the blast furnace, the reducing gas diffuses and intrudes into the fine pores, so that the reduction reaction proceeds from the outer surface of the iron ore pellet 1 to the inner surface. Oxygen is removed from the iron oxide by the reduction reaction, thereby expanding the existing fine pores and generating new fine pores, and generating metallic iron. In the process of shrinking the outer shape of the iron ore pellet 1 due to the agglomeration of the metallic iron, the fine pores decrease in turn. As a result, the diffusion of the reducing gas into the interior of the iron ore pellet 1 is suppressed, and the reduction is likely to stagnate.

[0076] In order to suppress the reduction stagnation, it is effective to add a high melting point component that suppresses the disappearance of fine pores during the aggregation process of metallic iron. In particular, it is known that the addition of dolomite as a MgO source of a high melting point component improves the MgO / SiO ratio of the iron ore pellet 1. 2 Based on this finding, the MgO / SiO mass ratio of the iron ore pellet 1 is 2 The mass ratio is 0.4 or more.

[0077] The iron ore pellets 1 are self-fluxing. By making the iron ore pellets 1 self-fluxing, the melting of the reduced iron is easily promoted. The self-fluxing property of the iron ore pellets 1 depends on auxiliary raw materials and the like.

[0078] The lower limit of the average compressive strength of the iron ore pellets 1 is 270 kg / p, and more preferably 300 kg / p. As described above, if the powder generated from the iron ore pellets 1 due to transportation and impact in the blast furnace is reduced, the ventilation resistance of the upper part of the blast furnace will be reduced. Based on this understanding, the present inventors have conducted intensive research and concluded that the amount of the powder can be controlled by the average compressive strength. Figure 3 The relationship between the mass fraction of powder with a particle size of 5 mm or less (5 mm or less powder ratio) and the average compressive strength generated by the transportation of the iron ore pellets 1 is shown. The results are obtained based on the results of actual verification along the transportation route. Figure 3 CaO / SiO 2 Mass ratio lower than 0.8 and MgO / SiO 2 In the case where the mass ratio is lower than 0.4, it is known that regardless of these properties, in the iron ore pellets 1 having an average compressive strength of at least the lower limit, the powder rate of 5 mm or less is stably low. In addition, in the present invention, the upper limit of the average compressive strength of the iron ore pellets 1 is not particularly limited, but in reality, for example, the upper limit is 500 kg / p.

[0079] In the iron ore pellets 1, the mass ratio of the pellets having a compressive strength of 100 kg / p or less is preferably 10% or less, more preferably 5% or less, and further preferably 1% or less. It is considered that even when the average compressive strength of the iron ore pellets 1 is high, if the strength deviation of each individual pellet is large, the absolute amount of the iron ore pellets 1 that are pulverized increases. In this regard, by making the mass ratio of the pellets having a compressive strength of 100 kg / p or less below the upper limit, the powder generated from the iron ore pellets 1 can be further reduced, and the upper ventilation resistance of the blast furnace can be further reduced.

[0080] <Advantages>

[0081] The iron ore pellet 1 is self-fluxing, CaO / SiO 2 The mass ratio is above 0.8, and MgO / SiO 2 The mass ratio is 0.4 or more, so the reducibility is high. In addition, since the iron ore pellets 1 have an average compressive strength of 270 kg / p or more, powder generated from the iron ore pellets 1 due to transportation and impact in the blast furnace can be reduced, and the upper ventilation resistance of the blast furnace can be reduced.

[0082] [Other embodiments]

[0083] In addition, the present invention is not limited to the above-described embodiments.

[0084] In the above embodiment, the method of manufacturing iron ore pellets using a grate-rotary kiln manufacturing apparatus is described, but it is also possible to manufacture using a straight grate manufacturing apparatus. In the straight grate manufacturing apparatus, the grate furnace is equipped with a moving grate, a drying chamber, a dehydration chamber, a preheating chamber, and a roasting chamber, and the roasting process is completed only using the grate furnace. Specifically, in the drying chamber, the dehydration chamber, and the preheating chamber, the green pellets are dried, dehydrated, and preheated by heating gas until the final roasting is performed in the roasting chamber.

[0085] Example

[0086] Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

[0087] [No.1]

[0088] Iron ore is used as the raw material of ore, and limestone, dolomite and bentonite are used as auxiliary materials. 2 The mass ratio is 1.2, and MgO / SiO 2 The auxiliary raw material is blended into the ore raw material in a manner of a mass ratio of 0.4 to obtain a mixed raw material.

[0089] The mixed raw material was used to granulate green pellets using a disc granulator, and roasted at 1260° C. using a roasting device consisting of a fixed grate furnace and a kiln to obtain No. 1 iron ore pellets. The raw material particle size index corresponding to No. 1 iron ore pellets, the porosity of the green pellets, and the average compressive strength of the iron ore pellets are shown in Table 1.

[0090] [No.2]

[0091] No. 2 iron ore pellets were obtained in the same manner as No. 1 except that the mixed raw materials were pulverized in a ball mill for 30 minutes. The raw material particle size index, the porosity of the green pellets and the average compressive strength of the iron ore pellets corresponding to No. 2 iron ore pellets are shown in Table 1.

[0092] [No.3~No.5]

[0093] With respect to the raw material particle size index and the obtained iron ore pellets of No. 1 and No. 2, the raw material particle size index was set to 1.8 times, 2.0 times, and 2.2 times the raw material particle size index of No. 1 so that the average compressive strength was 270 kg / p or more, and the iron ore pellets of No. 3 to No. 5 were obtained in the same manner as No. 1. The raw material particle size index, the porosity of the raw pellets, and the average compressive strength of the iron ore pellets corresponding to the iron ore pellets of No. 3 to No. 5 are shown in Table 1.

[0094]

Table 1

[0095]

[0096] From the results in Table 1, we can see that in CaO / SiO 2 The mass ratio is 0.8 or more, and MgO / SiO 2 In iron ore pellets having a mass ratio of 0.4 or more, iron ore pellets having an average compressive strength of 270 kg / p or more can be obtained by setting the porosity of the green pellets to 15% or more and 22% or less and calcining at a temperature of 1200° C. or more and 1300° C. or less.

[0097] Industrial Applicability

[0098] The method for producing iron ore pellets of the present invention can produce iron ore pellets that are excellent in reducibility at high temperatures and can reduce the upper ventilation resistance of a blast furnace. In addition, the iron ore pellets of the present invention are excellent in reducibility at high temperatures and can reduce the upper ventilation resistance of a blast furnace.

[0099] Description of Reference Numerals

[0100] 1 Iron Ore Pellets

[0101] 2 Manufacturing equipment

[0102] 3 Pan Granulator

[0103] 4 grate furnace

[0104] 41 Mobile grate

[0105] 42 Drying room

[0106] 43 Dehydration Chamber

[0107] 44 Preheating Chamber

[0108] 45 Burner

[0109] 5 Kiln

[0110] 6 Ring cooler

[0111] 61 Ventilation

[0112] P Pellet

[0113] H Preheating the pellets

[0114] G1 Heating gas

[0115] G2 Combustion exhaust gas

[0116] G3 Cooling Gas

[0117] C. Chimney

Claims

1. A method for producing iron ore pellets, which is a method for producing self-fluxing iron ore pellets for blast furnace operation, wherein: The following processes are available: A raw material blending step of blending an auxiliary raw material containing CaO and MgO into the ore raw material in such a manner that the CaO / SiO2 mass ratio becomes 0.8 or more and the MgO / SiO2 mass ratio becomes 0.4 or more; a granulation step of granulating green pellets having a porosity of 15% or more and 22% or less using the mixed raw materials obtained in the raw material blending step; The calcining step is to calcine the green pellets at a temperature of 1200° C. or higher and 1300° C. or lower.

2. The method for producing iron ore pellets according to claim 1, wherein: In the granulation step, a tumbling granulator is used. The porosity is controlled by the particle size of the raw materials in the raw material mixing step and the rolling time in the granulation step.

3. The method for producing iron ore pellets according to claim 1 or claim 2, wherein: In the granulation step, the particle size range of the green pellets is adjusted so that the particle size after the calcination step is 4 mm or more and 20 mm or less.

4. The method for producing iron ore pellets according to claim 3, wherein: In adjusting the particle size range of the green pellets, classification using a screen group having a large-size screen adjusted to a predetermined mesh size and a seed screen is used.

5. An iron ore pellet, which is a self-fluxing iron ore pellet for blast furnace operation, wherein: The CaO / SiO2 mass ratio is greater than 0.8, and the MgO / SiO2 mass ratio is greater than 0.4, The average compressive strength is above 270kg / p.

6. The iron ore pellets according to claim 5, wherein: The mass ratio of materials having a compressive strength of 100 kg / p or less is 10% or less.

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