Method for determining high-temperature properties of iron ore pellets, 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 to be 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 such 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 the mixed raw material obtained in the raw material blending step is granulated into green pellets; and a briquetting step for imparting strength to the green pellets at a temperature T1 represented by formula 1 of 1100 DEG C or more or at a temperature T2 represented by formula 2 of 1350 DEG C or more. T1 = 1155-0.095 * Po2 + 15 * FeO0.5... 1T2 = 220 * C / S + 13.1 * M / S-23.13 * TFe + 2600... 2Po is the porosity [%] of the iron ore pellets, FeO is the proportion [mass%] of FeO, C / S is the CaO / SiO2 mass ratio, M / S is the MgO / SiO2 mass ratio, and TFe is the proportion [mass%] of the total iron component.

Description

Technical Field

[0001] The present invention relates to a method for determining high temperature properties of iron ore pellets, a method for producing iron ore pellets, and iron ore pellets. Background Art

[0002] As a blast furnace operation, the following method is known, in which 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 or oxygen is 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 are softened and deformed by 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 iron ore pellets capable of reducing the pressure loss at the bottom of the furnace, self-fluxing pellets are known, which have a CaO / SiO2 mass ratio of 0.8 or more, a MgO / SiO2 mass ratio of 0.4 or more, and a predetermined particle size distribution (see Japanese Patent Application Laid-Open No. 2008-280556).

[0005] In the iron ore pellets, the CaO / SiO2 mass ratio is set to be 0.8 or more, and the MgO / SiO2 mass ratio is set to be 0.4 or more, thereby improving the reducibility at high temperatures, and the 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] Blast furnace operation is carried out at high temperatures and requires a lot of energy, so low energy consumption is required. In order to reduce the energy consumption of blast furnace operation, it is important to reduce the heat that is transferred from the furnace wall to the outside and is not related to the reaction in the furnace (heat loss from the furnace wall). The heat loss of the blast furnace increases as the furnace wall temperature increases. The furnace gas near the furnace wall is high temperature and becomes high temperature when the flow rate is large, so it is important to reduce the gas flow rate near the furnace wall.

[0011] The ventilation in the blast furnace is greatly different with the soft melting zone formed by the high temperature softening of the ore as the boundary. It is known that solid ore and other charges exist on the low temperature side compared to the soft melting zone, that is, in the upper area of ​​the furnace, and the gas flow near the furnace wall is reduced by controlling the charge and arranging the charge with low air permeability near the furnace wall.

[0012] On the other hand, in the high temperature side compared to the soft melting zone, that is, in the lower area of ​​the furnace, there are only liquid iron and slag and solid coke, making it difficult to control the flow path of the gas. Therefore, in order to reduce the energy consumption of blast furnace operation, it is effective to place the soft melting zone at the bottom and expand the area where the gas flow near the furnace wall is reduced by charging.

[0013] In iron ore pellets containing CaO and MgO, the CaO-FeO compounds melt and soften, and a soft melting zone begins to form. The temperature at which the soft melting zone begins to form can be represented by the melting start temperature that indicates a 10% shrinkage rate in the load reduction test. If the temperature becomes higher, the MgO-FeO compounds that exist as solids also melt and shrink rapidly, and the formation of the soft melting zone ends. The temperature of this rapid shrinkage is called the rapid shrinkage temperature.

[0014] If the formation of the soft melting zone is completed, the method of reducing the gas flow rate near the furnace wall disappears, and the temperature of the furnace wall rises. Based on this, it can be considered that in order to achieve low energy consumption in blast furnace operation, the melting start temperature or the rapid shrinkage temperature can be high. However, the technology for raising the melting start temperature or the rapid shrinkage temperature of iron ore pellets has not yet been established.

[0015] The present invention is proposed based on such circumstances, and its purpose is to provide a method for determining high temperature properties of iron ore pellets that can determine that the melting start temperature or the rapid shrinkage temperature is high temperature, a method for producing iron ore pellets using the high temperature property determination method, and iron ore pellets.

[0016] Means for solving problems

[0017] A method for determining the high temperature properties of iron ore pellets according to one embodiment of the present invention is a method for determining the high temperature properties of self-fluxing iron ore pellets used in blast furnace operations, wherein the CaO / SiO2 mass ratio is greater than 0.8 and the MgO / SiO2 mass ratio is greater than 0.4, wherein the following formula 1 is used as the melting start temperature T1 or the following formula 2 is used as the rapid shrinkage temperature T2.

[0018] T1=1155-0.095×Po 2 +15×FeO 0.5 …1

[0019] T2=220×C / S+13.1×M / S-23.13×TFe+2600…2

[0020] In the above formula 1, Po is the porosity of the iron ore pellets [%], and FeO is the ratio of FeO to the iron ore pellets [% by mass].

[0021] In the above formula 2, C / S is the CaO / SiO2 mass ratio of the iron ore pellets, M / S is the MgO / SiO2 mass ratio of the iron ore pellets, and TFe is the ratio of the total iron component to the iron ore pellets [mass %].

[0022] Another method for producing iron ore pellets according to the present invention is a method for producing self-fluxing iron ore pellets used in blast furnace operations, which comprises the following steps: a raw material blending step, in which auxiliary raw materials containing CaO and MgO are blended into ore raw materials in such a manner that the CaO / SiO2 mass ratio is greater than 0.8 and the MgO / SiO2 mass ratio is greater than 0.4; a granulation step, in which raw pellets are granulated from the mixed raw materials obtained in the raw material blending step; and an agglomeration step, in which strength is imparted to the raw pellets so that the temperature T1 shown in the following formula 1 is greater than 1100°C, or the temperature T2 shown in the following formula 2 is greater than 1350°C.

[0023] T1=1155-0.095×Po 2 +15×FeO 0.5 …1

[0024] T2=220×C / S+13.1×M / S-23.13×TFe+2600…2

[0025] In the above formula 1, Po is the porosity of the iron ore pellets [%], and FeO is the ratio of FeO to the iron ore pellets [% by mass].

[0026] In the above formula 2, C / S is the CaO / SiO2 mass ratio of the iron ore pellets, M / S is the MgO / SiO2 mass ratio of the iron ore pellets, and TFe is the ratio of the total iron component to the iron ore pellets [mass %].

[0027] Another embodiment of the iron ore pellets of the present invention is a self-fluxing iron ore pellets used for blast furnace operations, wherein the CaO / SiO2 mass ratio is greater than 0.8, and the MgO / SiO2 mass ratio is greater than 0.4, and the temperature T1 represented by the following formula 1 is greater than 1100°C, or the temperature T2 represented by the following formula 2 is greater than 1350°C.

[0028] T1=1155-0.095×Po 2 +15×FeO 0.5 …1

[0029] T2=220×C / S+13.1×M / S-23.13×TFe+2600…2

[0030] In the above formula 1, Po is the porosity of the iron ore pellets [%], and FeO is the ratio of FeO to the iron ore pellets [% by mass].

[0031] In the above formula 2, C / S is the CaO / SiO2 mass ratio of the iron ore pellets, M / S is the MgO / SiO2 mass ratio of the iron ore pellets, and TFe is the ratio of the total iron component to the iron ore pellets [mass %].

[0032] Effects of the Invention

[0033] The method for determining the high temperature properties of iron ore pellets of the present invention can determine that the melting start temperature or the rapid shrinkage temperature is a high temperature. The method for producing iron ore pellets of the present invention using the method for determining the high temperature properties of iron ore pellets can produce iron ore pellets having a high melting start temperature or a high rapid shrinkage temperature. In addition, the melting start temperature or the rapid shrinkage temperature of the iron ore pellets of the present invention is a high temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a flow chart showing a method for producing iron ore pellets according to one embodiment of the present invention.

[0035] 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.

[0036] Figure 3 This is a diagram showing the correlation between the melting start temperature and the melting start temperature estimated value T1.

[0037] Figure 4 : is a graph showing the correlation between the rapid shrinkage temperature and the rapid shrinkage temperature estimated value T2.

[0038] Figure 5 is different from Figure 1 Flow chart of a method for producing iron ore pellets according to an embodiment of the present invention. DETAILED DESCRIPTION

[0039] [Description of Embodiments of the Invention]

[0040] A method for determining high temperature properties of iron ore pellets according to one embodiment of the present invention is a method for determining high temperature properties of self-fluxing iron ore pellets used in blast furnace operations, wherein the following formula 1 is used as the melting start temperature T1 or the following formula 2 is used as the rapid shrinkage temperature T2.

[0041] T1=1155-0.095×Po 2 +15×FeO 0.5 …1

[0042] T2=220×C / S+13.1×M / S-23.13×TFe+2600…2

[0043] In the above formula 1, Po is the porosity of the iron ore pellets [%], and FeO is the ratio of FeO to the iron ore pellets [% by mass].

[0044] In the above formula 2, C / S is the CaO / SiO2 mass ratio of the iron ore pellets, M / S is the MgO / SiO2 mass ratio of the iron ore pellets, and TFe is the ratio of the total iron component to the iron ore pellets [mass %].

[0045] The inventors of the present invention have conducted a thorough study on the melting start temperature T1 and found that the melting start temperature T1 can be approximated using the porosity and the ratio of FeO. That is, by using the above formula 1, the melting start temperature T1 can be estimated with high accuracy. In addition, the inventors of the present invention have conducted a thorough study on the rapid shrinkage temperature T2 and found that the rapid shrinkage temperature T2 can be approximated using C / S, M / S and TFe. That is, by using the above formula 2, the rapid shrinkage temperature T2 can be estimated with high accuracy. Therefore, by using the above formula 1 or the above formula 2, the formation temperature of the soft melting zone in the blast furnace operation can be easily determined.

[0046] The above formula 1 and the above formula 2 may be used simultaneously. By using the above formula 1 and the above formula 2 simultaneously, the formation temperature of the soft melting zone can be determined with higher accuracy.

[0047] Another embodiment of the method for producing iron ore pellets of the present invention is a method for producing self-fluxing iron ore pellets used for blast furnace operations, which comprises the following steps: a raw material blending step, in which auxiliary raw materials containing CaO and MgO are blended into ore raw materials in such a manner that the CaO / SiO2 mass ratio is greater than 0.8 and the MgO / SiO2 mass ratio is greater than 0.4; a granulation step, in which raw pellets are granulated from the mixed raw materials obtained in the raw material blending step; and an agglomeration step, in which strength is imparted to the raw pellets so that the temperature T1 shown in the following formula 1 is greater than 1100°C, or the temperature T2 shown in the following formula 2 is greater than 1350°C.

[0048] T1=1155-0.095×Po 2 +15×FeO 0.5 …1

[0049] T2=220×C / S+13.1×M / S-23.13×TFe+2600…2

[0050] In the above formula 1, Po is the porosity of the iron ore pellets [%], and FeO is the ratio of FeO to the iron ore pellets [% by mass].

[0051] In the above formula 2, C / S is the CaO / SiO2 mass ratio of the iron ore pellets, M / S is the MgO / SiO2 mass ratio of the iron ore pellets, and TFe is the ratio of the total iron component to the iron ore pellets [mass %].

[0052] In the method for producing iron ore pellets, the temperature T1 represented by the above formula 1 or the temperature T2 represented by the above formula 2 is set to be above the above lower limit. Since T1 obtained by the above formula 1 approximates the melting start temperature with high accuracy, by setting the above T1 to be above the above lower limit, the melting start temperature of the manufactured iron ore pellets can be easily increased. In addition, since T2 obtained by the above formula 2 approximates the rapid shrinkage temperature with high accuracy, by setting the above T2 to be above the above lower limit, the rapid shrinkage temperature of the manufactured iron ore pellets can be easily increased. Therefore, by using the method for producing iron ore pellets in which either T1 or T2 is above the specified temperature, iron ore pellets that can be operated in a blast furnace with low energy consumption can be produced.

[0053] The temperature T1 may be set to 1100° C. or higher, and the temperature T2 may be set to 1350° C. or higher. By setting the temperature T1 to 1100° C. or higher, and the temperature T2 to 1350° C. or higher, it is possible to produce iron ore pellets that enable blast furnace operation with lower energy consumption.

[0054] In the above raw material blending process, the amount of CaO, the amount of MgO, the amount of SiO2 and the amount of iron can be adjusted. By adjusting the amount of CaO, the amount of MgO, the amount of SiO2 and the amount of iron in the above raw material blending process, the value of T2 can be controlled.

[0055] The strength imparted in the agglomeration process is achieved by calcining the green pellets, and the amount of FeO can be adjusted by the calcination temperature. If the calcination temperature is increased, the amount of FeO increases, so the value of T1 can be controlled. In addition, the proportion of oxygen in the iron ore pellets decreases, and the iron component (TFe) increases, so the value of T2 can also be controlled.

[0056] The calcination temperature may be 1200° C. to 1300° C. By setting the calcination temperature within the above range, the porosity can be reduced by the sintering effect of the iron ore pellets whose surface tension is enhanced by high-temperature calcination. This can increase the value of T1.

[0057] The auxiliary raw materials include calcium ferrite minerals, magnesium ferrite minerals, and a binder, and the amount of FeO can be adjusted in the raw material blending process. When the auxiliary raw materials contain calcium ferrite minerals, magnesium ferrite minerals, and a binder, in the raw material blending process, the amount of FeO can be directly adjusted by the amount of calcium ferrite minerals and magnesium ferrite minerals, so the controllability of T1 is high.

[0058] Another embodiment of the iron ore pellets of the present invention is a self-fluxing iron ore pellets used for blast furnace operations, wherein the CaO / SiO2 mass ratio is greater than 0.8, and the MgO / SiO2 mass ratio is greater than 0.4, and the temperature T1 represented by the following formula 1 is greater than 1100°C, or the temperature T2 represented by the following formula 2 is greater than 1350°C.

[0059] T1=1155-0.095×Po 2 +15×FeO 0.5 …1

[0060] T2=220×C / S+13.1×M / S-23.13×TFe+2600…2

[0061] In the above formula 1, Po is the porosity of the iron ore pellets [%], and FeO is the ratio of FeO to the iron ore pellets [% by mass].

[0062] In the above formula 2, C / S is the CaO / SiO2 mass ratio of the iron ore pellets, M / S is the MgO / SiO2 mass ratio of the iron ore pellets, and TFe is the ratio of the total iron component to the iron ore pellets [mass %].

[0063] The iron ore pellets are self-fluxing and have a CaO / SiO2 mass ratio of 0.8 or more and a MgO / SiO2 mass ratio of 0.4 or more, so they are highly reducible. T1 obtained by the above formula 1 can approximate the melting start temperature with high accuracy, so when T1 is above the above lower limit, it means that the melting start temperature of the iron ore pellets is high. In addition, T2 obtained by the above formula 2 can approximate the rapid shrinkage temperature with high accuracy, so when T2 is above the above lower limit, it means that the rapid shrinkage temperature of the iron ore pellets is high. Therefore, by using the iron ore pellets with either T1 or T2 being above the specified temperature, low-energy blast furnace operations can be performed.

[0064] The temperature T1 may be 1100° C. or higher, and the temperature T2 may be 1350° C. or higher. By using the iron ore pellets having the temperature T1 of 1100° C. or higher and the temperature T2 of 1350° C. or higher, blast furnace operation can be performed with further lower energy consumption.

[0065] The shape of the iron ore pellets of the present invention is not limited to a spherical shape, but may take any three-dimensional shape.

[0066] [Details of Embodiments of the Invention]

[0067] Hereinafter, a method for determining high temperature properties of iron ore pellets, 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.

[0068] [Method for producing iron ore pellets]

[0069] [First embodiment]

[0070] Figure 1 The method for producing iron ore pellets shown in the figure comprises a raw material mixing step S1, a granulation step S2, an agglomeration step S3, and a cooling step S4. In the method for producing iron ore pellets, the strength is imparted in the agglomeration step S3 by roasting the green pellets, and the produced pellets are so-called roasted pellets.

[0071] The method for producing iron ore pellets can produce self-melting iron ore pellets 1 used for blast furnace operation using a grate kiln type production device (hereinafter also referred to as "production device 2"). The production device 2 includes a pan pelletizer 3, a grate furnace 4, a kiln 5, and an annular cooler 6.

[0072] <Raw material mixing process>

[0073] In the raw material blending step S1, an auxiliary raw material containing CaO and MgO is blended with the 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.

[0074] When the strength is imparted in the agglomeration step S3 by calcining the green pellets, limestone as a CaO source and dolomite as a MgO source are mixed as the auxiliary raw materials.

[0075] The above-mentioned ore raw materials and the above-mentioned auxiliary raw materials may be pulverized by a ball mill or the like in advance or after blending, as required, so as to adjust the particle size of the mixed raw material obtained by mixing the above-mentioned ore raw materials and the above-mentioned auxiliary raw materials.

[0076] At this time, if the raw material particle size index is properly controlled, the porosity of the green pellets P can be controlled. 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. For this measurement, one of JIS-A-1204:2010, JIS-A-8815:1994, and JIS-Z-8825:2022 can be used. Secondly, 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.

[0077] The relationship between this raw material particle size index and the porosity of the raw pellets P is established in a mixed raw material in which the same brand of iron ore and auxiliary raw materials are blended in the same ratio. However, if the brand of the iron ore is different, for example, this proportional 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. In this way, the raw material particle size index of the porosity required for the iron ore pellet 1 can be determined, and based on this, the particle size of the raw material can be adjusted in a manner to achieve the raw material particle size index. In addition, the adjustment of the particle size also includes purchasing raw materials with such a particle size.

[0078] Alternatively, the specific surface area based on the Blaine index can be used as an indicator of the raw material particle size. The lower limit of the specific surface area is preferably 1000 cm 2 / g, more preferably 2000cm 2 On the other hand, the upper limit of the specific surface area is preferably 5000 cm 2 / g, more preferably 4000cm 2 / g. If the above-mentioned specific surface area is lower than the above-mentioned lower limit, it may be difficult to make T2, which is an indicator of the rapid shrinkage temperature described later, reach 1350°C or above. On the contrary, if the above-mentioned specific surface area is higher than the above-mentioned upper limit, bursting may occur in the agglomeration step S3. Here, the so-called "specific surface area" means the value measured according to JIS-R5201 (2015).

[0079] In order to obtain the strength of the green pellets P required for transportation in the production process, a binder such as bentonite may be appropriately blended into the mixed raw material.

[0080] <Granulation process>

[0081] In the granulation step S2, the mixed raw material obtained in the raw material blending step S1 is used to granulate the green pellets P. A swing granulator can be used for granulating the green pellets P. Figure 2 The disc granulator 3, drum granulator and disc granulator shown.

[0082] Specifically, in the granulation step S2, after adding water (granulation water) to the mixed raw material, the granulation water-containing mixture (the mixed raw material containing granulation water) is put into the pan granulator 3 and tumbled to produce pellet-shaped green pellets P.

[0083] The lower limit of the porosity of the green pellets P is preferably 15%, and more preferably 17%. On the other hand, the upper limit of the porosity is preferably 25%, and more preferably 20%. If the porosity is lower than the lower limit, there is a possibility of causing a bursting phenomenon in the agglomeration step S3. On the other hand, if the porosity is higher than the upper limit, it may be difficult to make T1, which is an indicator of the melting start temperature described later, reach 1100°C or more.

[0084] The porosity can be controlled by the raw material particle size in the raw material blending step S1 and the rolling time in the granulation step S2. By controlling the porosity in this way, it is easy to control the porosity at a desired value, and T1 can be more reliably made to reach 1100°C or more. In addition, by making the volume ratio of pores below 20 μm in the pore size distribution preferably 80% or more, more preferably 85% or more, T1 can be more reliably made to reach 1100°C or more. Here, the "volume ratio of pores below 20 μm in the pore size distribution" can be measured by JIS-R-1655:2003.

[0085] In addition, the particle size range of the green pellets P may be adjusted in the granulation step S2 so that the particle size after the agglomeration 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 agglomeration step S3 within the above range, the reducibility at high temperature can be maintained while suppressing the reduction of the upper ventilation resistance of the blast furnace.

[0086] 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.

[0087] <Blocking process>

[0088] In the agglomeration step S3, strength is imparted to the green pellets P. In this method for producing iron ore pellets, the green pellets P are calcined in the agglomeration step S3. Figure 2 In the manufacturing apparatus 2 shown, the grate furnace 4 and the kiln 5 are used for the agglomeration step S3.

[0089] (Grate furnace)

[0090] 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.

[0091] 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 .

[0092] 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 .

[0093] Specifically, the following procedures are 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.

[0094] like Figure 2 As 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.

[0095] (Kiln)

[0096] 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.

[0097] The lower limit of the roasting temperature for roasting the preheated pellets H is preferably 1200°C, and more preferably 1220°C. On the other hand, the upper limit of the roasting temperature is preferably 1300°C, and more preferably 1280°C. 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 pores of the iron ore pellets 1 may become larger. On the contrary, by making the roasting temperature within the above range, the porosity can be reduced under the sintering effect of strengthening the surface tension of the iron ore pellets 1 by high-temperature roasting. This can increase the value of T1.

[0098] 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.

[0099] <Cooling process>

[0100] In the cooling step S4, the high-temperature iron ore pellets 1 obtained in the agglomeration 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 in blast furnace operation.

[0101] 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 .

[0102] 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.

[0103] <Rapid Shrinkage Temperature and Melting Start Temperature>

[0104] In the method for producing iron ore pellets, the temperature T1 represented by the following formula 1 is set to 1100° C. or higher, and the temperature T2 represented by the following formula 2 is set to 1350° C. or higher.

[0105] T1=1155-0.095×Po 2 +15×FeO 0.5 …1

[0106] T2=220×C / S+13.1×M / S-23.13×TFe+2600…2

[0107] In the above formula 1, Po is the porosity of the iron ore pellets [%], and FeO is the ratio of FeO to the iron ore pellets [% by mass].

[0108] In the above formula 2, C / S is the CaO / SiO2 mass ratio of the iron ore pellets, M / S is the MgO / SiO2 mass ratio of the iron ore pellets, and TFe is the ratio of the total iron component to the iron ore pellets [mass %].

[0109] The above formula 1 is an estimation formula for estimating the melting start temperature, and the above formula 2 is an estimation formula for estimating the rapid shrinkage temperature. By using these estimation formulas, it is possible to determine the high temperature properties of iron ore pellets, which is an embodiment of the present invention. Hereinafter, a method for determining the high temperature properties of iron ore pellets using these estimation formulas will be described.

[0110] A method for determining high temperature properties of iron ore pellets according to one embodiment of the present invention is a method for determining high temperature properties of self-fluxing iron ore pellets used in blast furnace operations, wherein the method uses the following formula 1 as the melting start temperature T1 and the following formula 2 as the rapid shrinkage temperature T2.

[0111] T1=1155-0.095×Po 2 +15×FeO 0.5 …1

[0112] T2=220×C / S+13.1×M / S-23.13×TFe+2600…2

[0113] In the above formula 1, Po is the porosity of the iron ore pellets [%], and FeO is the ratio of FeO to the iron ore pellets [% by mass].

[0114] In the above formula 2, C / S is the CaO / SiO2 mass ratio of the iron ore pellets, M / S is the MgO / SiO2 mass ratio of the iron ore pellets, and TFe is the ratio of the total iron component to the iron ore pellets [mass %].

[0115] (Melting start temperature)

[0116] The present inventors have made intensive studies on the melting start temperature T1 and found that the melting start temperature T1 can be approximated using the porosity and FeO. Figure 3 The correlation between the melting start temperature and the melting start temperature T1 estimated by the above formula 1 is shown in FIG. Figure 3That is, by using the above formula 1, the melting start temperature T1 can be estimated with high accuracy, and the formation temperature of the soft melting zone in the blast furnace operation can be easily determined.

[0117] The inventors of the present invention believe that the reason why the melting start temperature T1 can be approximated by the above formula 1 can be understood by the density of the structure of the iron ore pellet 1 near 1100°C. In other words, if a dense metal iron shell is maintained near 1100°C where the CaO-FeO system compound melts, the strength of the iron ore pellet 1 is maintained and the melting start temperature T1 rises. In order to maintain a dense metal iron shell, the rate of formation of metal iron in the reduction reaction can be slow. If the porosity is small, the diffusion of the reducing gas stagnates, which can slow down the rate of formation of metal iron. In addition, the matrix structure of the pellet containing FeO is glassy and does not contain pores. Therefore, T1 tends to decrease when the porosity Po is large and to increase when the FeO is large.

[0118] (Rapid Shrinkage Temperature)

[0119] The present inventors have conducted intensive studies on the rapid shrinkage temperature T2 and found that the rapid shrinkage temperature T2 can be approximated using C / S, M / S, and TFe. Figure 4 The rapid shrinkage temperature and the rapid shrinkage temperature T2 estimated by the above formula 1 are shown in FIG. Figure 4 That is, by using the above formula 2, the rapid shrinkage temperature T2 can be estimated with high accuracy, and the formation completion temperature of the soft melting zone in the blast furnace operation can be easily determined.

[0120] The inventors of the present invention believe that the reason why the rapid shrinkage temperature T2 can be approximated by the above formula 2 can be understood in a thermodynamic state. In other words, the amount of CaO and MgO shows an effect based on the ratio with SiO2, approximating the melting point of the oxide. The larger the CaO / SiO2 and MgO / SiO2, the higher the melting point. In addition, the more iron content TFe shows, the smaller the effect of CaO and MgO, which approximates the effect of FeO in the process of reduction on the melting point of the oxides of CaO and MgO. In detail, if CaO is insufficient, the reducibility to metallic iron decreases, and a large amount of FeO remains as an unreduced oxide. MgO and residual FeO form a high melting point MgO-FeO system compound, which increases the rapid shrinkage temperature T2, but if MgO is insufficient, there is no free FeO remaining to form a MgO-FeO system compound. In addition, the more FeO there is in the iron ore pellets, the more total iron content TFe there is. Here, since the effect of the amount of CaO and MgO itself is reflected as the coefficient of C / S and M / S, if the TFe term is added to the rapid shrinkage temperature T2, the effect of FeO is indicated. The larger the FeO, that is, the larger the TFe, the lower the melting point.

[0121] The above estimation formulas for T1 and T2 are considered to be valid up to the melting point of magnetite and wutite, 1597°C. The accuracy is high when TFe in iron ore pellets is above 55 mass%, and the accuracy is particularly high in iron ore pellets where the volume ratio of pores below 20 μm in the pore size distribution is above 80%.

[0122] In the method for producing the iron ore pellets, the temperature T1 represented by the above formula 1 is set to be above 1100°C. For example, the melting point of the compound of CaO-FeO and Al2O3-CaO-FeO is about 1100°C. In addition, in the method for producing the iron ore pellets, the temperature T2 represented by the above formula 2 is set to be above 1350°C. For example, the melting point of a part of the compound of the Al2O3-CaO-SiO2 system is about 1350°C. It can also be considered that the control of the above formulas 1 and 2 to be above the specified temperature is to suppress the formation of compounds having such a melting point. In this regard, it is preferred that the aluminum oxide (Al2O3) contained in the iron ore pellet 1 is below a certain amount, and its content is preferably 3.0 mass % or less.

[0123] (Control of T1 and T2)

[0124] The values ​​of T1 and T2 can be adjusted in various ways.

[0125] The porosity Po included in T1 can be reduced if fine powder or coarse powder raw materials are used in the raw material blending step S1. On the contrary, if carbonates and hydrates are added, they volatilize during roasting, resulting in a tendency for the porosity Po to increase. In addition, as described above, the porosity Po is reduced under the sintering effect in which the surface tension of the iron ore pellets 1 is enhanced by high-temperature roasting. If Po is reduced, T1 increases, and if Po is increased, T1 decreases.

[0126] The FeO contained in T1 varies with the increase or decrease of magnetite ore and iron oxide scale as raw materials containing FeO, and the FeO residue increases due to the atmospheric reduction and rapid cooling of the iron ore pellets 1 caused by high-temperature roasting. If FeO increases, T1 increases, and if FeO decreases, T1 decreases.

[0127] In the raw material mixing step S1, if the amount of CaO, the amount of MgO, the amount of SiO2, and the amount of iron are adjusted, the value of T2 can be controlled by increasing or decreasing them.

[0128] The content of CaO, MgO, and SiO2 can be adjusted by selecting raw materials containing them. For example, dolomite contains carbonates of CaO and MgO, and magnesite contains MgO and SiO2. Limestone contains carbonates of CaO, and silica contains SiO2. By adjusting their blending ratio, the values ​​of C / S and M / S can be adjusted. If C / S or M / S increases, T2 increases, and if C / S or M / S decreases, T2 decreases.

[0129] The content of TFe can be adjusted by selecting iron ore and blending ratio. For example, hematite is a high-iron component, and gangue components are mostly low-iron components. In addition, the amount of TFe will also change by increasing or decreasing the total amount of CaO, MgO and SiO2. If the above total amount is increased, the amount of TFe will decrease. Alternatively, if the roasting temperature is increased to increase the amount of FeO, the proportion of oxygen in the iron ore pellet 1 will decrease and TFe will increase. If TFe increases, T2 will decrease, and if TFe decreases, T2 will increase.

[0130] <Advantages>

[0131] In the method for producing iron ore pellets, the temperature T1 represented by the above formula 1 is set to be 1100°C or higher, and the temperature T2 represented by the above formula 2 is set to be 1350°C or higher. Since T1 obtained by the above formula 1 approximates the melting start temperature with high accuracy, by making T1 above the above lower limit, the melting start temperature of the manufactured iron ore pellets can be easily increased. In addition, since T2 obtained by the above formula 2 approximates the rapid shrinkage temperature with high accuracy, by making T2 above the above lower limit, the rapid shrinkage temperature of the manufactured iron ore pellets can be easily increased. Therefore, by using the method for producing iron ore pellets in which T1 and T2 are above the specified temperature, iron ore pellets that can be operated in a low-energy blast furnace can be produced.

[0132] Furthermore, by setting the temperature T1 to 1100° C. or higher and the temperature T2 to 1350° C. or higher, it is possible to produce iron ore pellets that enable blast furnace operation with lower energy consumption.

[0133] [Second embodiment]

[0134] Figure 5 The method for producing iron ore pellets shown in the figure comprises a raw material mixing step S11, a granulation step S12, and an agglomeration step S13. In the method for producing iron ore pellets, strength is imparted in the agglomeration step S13 by a binder, and the produced pellets are so-called uncalcined pellets.

[0135] The method for producing iron ore pellets can produce self-fluxing iron ore pellets used in blast furnace operations.

[0136] <Raw material mixing process>

[0137] In the raw material blending step S11, an auxiliary raw material containing CaO and MgO is blended with the 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.

[0138] In the raw material blending step S11, the auxiliary raw materials contain calcium ferrite minerals (CaO·Fe x O), magnesium ferrite minerals (MgO·Fe x O) and a binder (here 0.667≤x≤1.0). The auxiliary raw materials are blended according to the iron grade of the iron ore (pellet feed) as the above-mentioned ore raw material. In addition, when the auxiliary raw materials include ferrite minerals, in addition to the CaO monomer, CaO·Fe x The CaO contained in O is composed of MgO·Fe in addition to the monomer MgO in the MgO that determines the MgO / SiO2 mass ratio. x O contains MgO.

[0139] The above-mentioned calcium ferrite minerals and magnesium ferrite minerals can be synthesized. The synthesis of calcium ferrite minerals and magnesium ferrite minerals can be carried out by the following method: using an electric furnace or a sintering furnace, etc., to roast iron oxide, limestone, dolomite, magnesite at high temperature, or melt them, and then cool and crush them after the reaction. Since the temperature history at this time will cause the valence of iron oxide to be different, the value of x changes within the range of 0.667 to 1.0. The value of x represents the FeO concentration. If x = 0.667, it means that all the iron is Fe 3＋ ions, if x = 1, it means that all the iron is occupied by Fe 2＋ ions occupy. When X is in the middle, the ions of the two are mixed together. The closer to x = 0.667, the Fe 3＋ The higher the ratio of ions, the closer it is to x = 1, Fe 2＋ The higher the ratio of ions.

[0140] Examples of the binder include cement, sodium silicate, starch, synthetic polymers, etc. Examples of the synthetic polymer materials include acrylic resins, polyurethane resins, and ether cellulose (carboxymethyl cellulose (CMC)).

[0141] In addition, similarly to the raw material mixing step S11 of the first embodiment, the particle size of the mixed raw material may be adjusted by pulverization as required.

[0142] <Granulation process>

[0143] In the granulation step S12, green pellets are granulated from the mixed raw material obtained in the raw material blending step S11.

[0144] As a granulation method for raw pellets, similar to the granulation step S2 of the first embodiment, a rolling granulation method using a pan granulator, a drum granulator, a disk granulator, etc. can be adopted. In addition, there is a compression method in which the mixed raw material is placed in a mold such as a metal mold and compressed, and a molding method in which the mixed raw material is placed in an extruder and extruded from an extrusion die and cut and molded appropriately. In addition, if it is a non-calcined pellet, in the rolling granulation method, as in the case of the first embodiment, the porosity of the raw pellets can be controlled by appropriately controlling the raw material particle size index and the rolling time. In the compression method and the molding method, the porosity of the raw pellets can be controlled by the pressure conditions during compression or molding.

[0145] In either method, the porosity and particle size range of the green pellets are preferably in the same range as in the first embodiment.

[0146] <Blocking process>

[0147] In the agglomeration step S13, the green pellets P are given strength.

[0148] In the method for producing iron ore pellets, in the agglomeration step S13, an air curing method, a steam curing method, or the like is selected according to the type of binder. The air curing method is a method of leaving the green pellets in the air until they reach a predetermined strength, and can be used, for example, when the binder is cement. The steam curing method is a method of leaving the green pellets in high-temperature steam until they reach a predetermined strength, and can be used, for example, when the binder is sodium silicate and cement.

[0149] The agglomeration step S13 may be performed simultaneously with the granulation step S12. For example, depending on the type of binder, sufficient strength may be imparted together with the granulation. In this case, the agglomeration step S13 does not need to be performed separately from the granulation step S12, and the agglomeration step S13 can be completed during the granulation step S12.

[0150] <Rapid Shrinkage Temperature and Melting Start Temperature>

[0151] In the method for producing iron ore pellets, the temperature T1 represented by the following formula 1 is set to 1100° C. or higher, and the temperature T2 represented by the following formula 2 is set to 1350° C. or higher.

[0152] T1=1155-0.095×Po 2 +15×FeO 0.5 …1

[0153] T2=220×C / S+13.1×M / S-23.13×TFe+2600…2

[0154] In the above formula 1, Po is the porosity of the iron ore pellets [%], and FeO is the ratio of FeO to the iron ore pellets [% by mass].

[0155] In the above formula 2, C / S is the CaO / SiO2 mass ratio of the iron ore pellets, M / S is the MgO / SiO2 mass ratio of the iron ore pellets, and TFe is the ratio of the total iron component to the iron ore pellets [mass %].

[0156] In this method for producing iron ore pellets, by setting the temperature T1 represented by the above formula 1 to 1100° C. or higher and the temperature T2 represented by the above formula 2 to 1350° C. or higher, the same effects as those described in the first embodiment can be obtained. Therefore, detailed description is omitted.

[0157] (Control of T1 and T2)

[0158] The values ​​of T1 and T2 can be adjusted in various ways.

[0159] The porosity Po included in T1 can be reduced by using fine powder or coarse powder raw materials in the raw material mixing step. If Po is reduced, T1 increases, and if Po is increased, T1 decreases.

[0160] The FeO contained in T1 varies with the calcium ferrite mineral and the magnesium ferrite mineral as raw materials containing FeO. If FeO increases, T1 rises, and if FeO decreases, T1 decreases. In the control performed by the amount of calcium ferrite mineral and the magnesium ferrite mineral, the controllability of T1 is high because the amount of FeO can be directly adjusted.

[0161] In the raw material mixing step S11, if the amount of CaO, the amount of MgO, the amount of SiO2, and the amount of iron are adjusted, the value of T2 can be controlled by increasing or decreasing them.

[0162] The content of TFe can be adjusted by the selection of iron ore and the blending ratio. For example, hematite is a high-iron component, and gangue components are mostly low-iron components. In addition, the amount of TFe will also change by increasing or decreasing the total amount of CaO, MgO and SiO2. If the above total amount is increased, the amount of TFe will decrease. Alternatively, if the blending amount of calcium ferrite minerals and magnesium ferrite minerals is increased to increase the amount of FeO, the proportion of oxygen in the iron ore pellets will decrease and TFe will increase. If TFe increases, T2 decreases, and if TFe decreases, T2 increases.

[0163] <Advantages>

[0164] As in the first embodiment, by using the method for producing iron ore pellets in which the above-mentioned T1 and the above-mentioned T2 are equal to or higher than the predetermined temperature, it is possible to produce iron ore pellets capable of low-energy consumption blast furnace operation.

[0165] 〔Iron ore pellets〕

[0166] Another embodiment of the iron ore pellets of the present invention is a self-melting iron ore pellet used in blast furnace operation. The iron ore pellets 1 are agglomerated ore with high strength obtained by granulating and roasting fine ore or adding a binder, and can be produced by the above-mentioned iron ore pellet production method.

[0167] It is known that in the manufacture of the iron ore pellet 1, if a compound containing CaO such as limestone is added to the ore raw material to increase the CaO / SiO2 mass ratio of the iron ore pellet 1, the reducibility of the iron ore pellet 1 is improved. Based on this understanding, the CaO / SiO2 mass ratio of the iron ore pellet 1 is 0.8 or more.

[0168] When the raw materials are iron ore (iron oxide) and limestone (a compound containing CaO), during the roasting process, CaO generated by thermal decomposition reacts with the iron oxide in a solid phase to generate a calcium ferrite compound, and at the same time, the two are bonded by solid phase diffusion bonding at the contact point. This bonding is local, and the fine pores existing before roasting are also maintained after roasting, so that the iron ore pellet 1 becomes a porous body with relatively uniform fine pores.

[0169] During blast furnace operation, reducing gas diffuses and intrudes into the fine pores, and 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 at the same time, metallic iron is generated. 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 reducing gas into the inner surface of the iron ore pellet 1 is suppressed, and the reduction is likely to stagnate.

[0170] In order to suppress this 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 if dolomite is added as a MgO source of a high melting point component and the MgO / SiO2 mass ratio of the iron ore pellet 1 is increased, a high reduction stagnation suppression effect can be obtained. Based on this understanding, the MgO / SiO2 mass ratio of the iron ore pellet 1 is 0.4 or more.

[0171] The iron ore pellets 1 are self-fluxing. By making the iron ore pellets 1 self-fluxing, it is easy to promote the melting and falling of the reduced iron. The self-fluxing property of the iron ore pellets 1 depends on auxiliary raw materials and the like.

[0172] In the iron ore pellets 1, the temperature T2 represented by the following formula 1 is 1350°C or higher.

[0173] T2=220×C / S+13.1×M / S-23.13×TFe+2600…1

[0174] In the above formula 1, C / S is the CaO / SiO2 mass ratio of the iron ore pellets, M / S is the MgO / SiO2 mass ratio of the iron ore pellets, and TFe is the ratio of the total iron component to the iron ore pellets [mass %].

[0175] In addition, in the iron ore pellets 1, the temperature T1 represented by the following formula 2 is 1100°C or higher.

[0176] T1=1155-0.095×Po 2 +15×FeO 0.5 …2

[0177] In the above formula 2, Po is the porosity of the iron ore pellets [%], and FeO is the ratio of FeO to the iron ore pellets [% by mass].

[0178] <Advantages>

[0179] The iron ore pellet 1 is self-fluxing, has a CaO / SiO2 mass ratio of 0.8 or more, and a MgO / SiO2 mass ratio of 0.4 or more, so it has high reducibility. Since T1 obtained by the above formula 1 can approximate the melting start temperature with high accuracy, the above T1 is above the above lower limit, which means that the melting start temperature of the iron ore pellet 1 is high. In addition, since T2 obtained by the above formula 2 can approximate the rapid shrinkage temperature with high accuracy, the above T2 is above the above lower limit, which means that the rapid shrinkage temperature of the iron ore pellet is high. Therefore, by using the iron ore pellet 1 in which either T1 or T2 is above the specified temperature, low-energy blast furnace operation can be performed.

[0180] Furthermore, by using the iron ore pellets having the temperature T1 of 1100° C. or higher and the temperature T2 of 1350° C. or higher, blast furnace operation with lower energy consumption can be performed.

[0181] [Other embodiments]

[0182] In addition, the present invention is not limited to the above-mentioned embodiment.

[0183] In the first embodiment of the above-mentioned method for manufacturing iron ore pellets, a method for manufacturing iron ore pellets using a manufacturing device of a chain grate-rotary kiln method is described, but it is also possible to manufacture using a manufacturing device of a straight grate method. In the manufacturing device of the straight grate method, the grate furnace is equipped with a moving grate, a drying chamber, a dehydration chamber, a preheating chamber, and a roasting chamber, and the agglomeration process is completed only by 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.

[0184] In the above embodiment, the case where T1 is set to 1100°C or higher and T2 is set to 1350°C or higher in the method for producing iron ore pellets is described, but setting both T1 and T2 to a predetermined temperature or higher is not an essential component. Low energy consumption in blast furnace operation can be achieved by setting only T1 to 1100°C or higher or only T2 to 1350°C or higher.

[0185] Similarly, in the iron ore pellets described in the above embodiment, it is not essential to set T1 to 1100°C or higher and T2 to 1350°C or higher. Low energy consumption in blast furnace operation can be achieved when only T1 is 1100°C or higher or only T2 is 1350°C or higher.

[0186] Example

[0187] Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

[0188] [No.1]

[0189] Iron ore as an ore raw material and limestone, dolomite and bentonite as auxiliary raw materials were prepared. The auxiliary raw materials were blended into the ore raw material so that the CaO / SiO2 mass ratio (C / S) and the MgO / SiO2 mass ratio (M / S) were the values ​​shown in Table 1, respectively, to obtain a mixed raw material.

[0190] The mixed raw material was pulverized by a ball mill, and then the pulverized raw material was put into a disc pelletizer and tumbled while adding water to granulate into a particle size of 10 mm to 12 mm, thereby preparing green pellets.

[0191] The green pellets are placed in a grate furnace, and the green pellets are heated with high temperature air as heating gas, dried and pre-baked. The pre-baked pre-baked pellets are placed in a kiln and heated to obtain No. 1 iron ore pellets.

[0192] The measured values ​​of TFe, FeO, porosity, melting start temperature and rapid shrinkage temperature of the No. 1 iron ore pellet, and the values ​​of T1 and T2 based on the above-mentioned formula 1 and formula 2 are shown in Table 1. In addition, the measured values ​​are obtained by the load reduction test. The melting start temperature is calculated as the temperature at which the shrinkage rate reaches 10%. In addition, the rapid shrinkage temperature is the temperature at which the shrinkage rate first reaches 1% / minute or more within the temperature range from the temperature indicating the maximum pressure loss to the temperature at which the melting and falling ends (shrinkage rate 100%).

[0193] [No.2]

[0194] Iron ore pellet No. 2 was obtained in the same manner as in No. 1 except that the mixed raw material was adjusted so that C / S and M / S were the values ​​shown in Table 1. Table 1 shows the outlines of the obtained iron ore pellets.

[0195] [No.3]

[0196] In the iron ore pellets No. 1 and No. 2, the melting start temperature was lower than 1100°C and the rapid shrinkage temperature was lower than 1350°C, both in terms of measured values ​​and estimated values ​​(T1, T2). Therefore, TFe, FeO, C / S, and M / S were adjusted to the values ​​shown in Table 1 so that T1 was higher than 1100°C and T2 was higher than 1350°C, and No. 3 iron ore pellets were obtained. The outlines of the obtained iron ore pellets are shown in Table 1.

[0197] [No.4]

[0198] In the No. 4 iron ore pellet, it is planned to reduce the porosity by 5% compared with the No. 1 iron ore pellet, and at the same time, make the melting start temperature above 1100°C and the rapid shrinkage temperature above 1350°C. In order to reduce the porosity by about 5%, the ore and auxiliary raw materials are crushed to prepare raw materials with a particle size of 1.8 to 2.2 times the specific surface area based on the Blaine index. Using this crushed raw material, TFe, FeO, C / S, and M / S are adjusted to the values ​​shown in Table 1 so that T1 is above 1100°C and T2 is above 1350°C, and No. 4 iron ore pellets are obtained. The outlines of the obtained iron ore pellets are shown in Table 1.

[0199]

Table 1

[0200]

[0201] As described above, the iron ore pellets No. 1 and No. 2, which do not use the estimation formulas for T1 and T2, have a melting start temperature of less than 1100° C. and a rapid shrinkage temperature of less than 1350° C. In contrast, the iron ore pellets No. 3 and No. 4, which have each parameter adjusted so that the melting start temperature is 1100° C. or more and the rapid shrinkage temperature is 1350° C. or more using the estimation formulas for T1 and T2, have a melting start temperature of more than 1100° C. and a rapid shrinkage temperature of more than 1350° C. It is understood that by using the method for producing iron ore pellets of the present invention in this way, iron ore pellets having a high melting start temperature and a high rapid shrinkage temperature, which have never been achieved before, are obtained for the first time.

[0202] Industrial Applicability

[0203] The method for determining the high temperature properties of iron ore pellets of the present invention can determine that the melting start temperature or the rapid shrinkage temperature is a high temperature. The method for producing iron ore pellets of the present invention using this method for determining the high temperature properties of iron ore pellets can produce iron ore pellets having a high melting start temperature or a high rapid shrinkage temperature. In addition, the iron ore pellets of the present invention have a high melting start temperature or a high rapid shrinkage temperature.

[0204] Description of Reference Numerals

[0205] 1 Iron Ore Pellets

[0206] 2 Manufacturing equipment

[0207] 3 Pan Granulator

[0208] 4 grate furnace

[0209] 41 Mobile grate

[0210] 42 Drying room

[0211] 43 Dehydration Chamber

[0212] 44 Preheating room

[0213] 45 Burner

[0214] 5 Kiln

[0215] 6 Ring cooler

[0216] 61 Ventilation device

[0217] P Pellet

[0218] H Preheating the pellets

[0219] G1 Heating gas

[0220] G2 Combustion exhaust gas

[0221] G3 Cooling Gas

[0222] C. Chimney

Claims

1. A method for determining the high temperature properties of iron ore pellets, which is used in blast furnace operations, and is a method for determining the high temperature properties of self-fluxing iron ore pellets having a CaO / SiO2 mass ratio of 0.8 or more and a MgO / SiO2 mass ratio of 0.4 or more, wherein: Using the following formula 1 as the melting start temperature T1, or the following formula 2 as the rapid shrinkage temperature T2, T1=1155-0.095×Po 2 +15×FeO 0.5 …1 T2=220×C / S+13.1×M / S-23.13×TFe+2600…2 In the above formula 1, Po is the porosity of the iron ore pellets, in %, and FeO is the ratio of FeO to the iron ore pellets, in mass %. In Formula 2, C / S is the CaO / SiO2 mass ratio of the iron ore pellets, M / S is the MgO / SiO2 mass ratio of the iron ore pellets, and TFe is the ratio of the total iron component to the iron ore pellets, expressed in mass %.

2. The method for determining high temperature properties of iron ore pellets according to claim 1, wherein: The formula 1 and the formula 2 are used together.

3. A method for producing iron ore pellets, which is a method for producing self-fluxing iron ore pellets used in blast furnace operations, wherein: The following processes are available: A raw material blending step, blending an auxiliary raw material containing CaO and MgO into the ore raw material in such a manner that the mass ratio of CaO / SiO2 is greater than 0.8 and the mass ratio of MgO / SiO2 is greater than 0.4; A granulation step, granulating green pellets from the mixed raw materials obtained in the raw material blending step; The agglomeration step is to impart strength to the green pellets. The temperature T1 represented by the following formula 1 is set to 1100° C. or higher, or the temperature T2 represented by the following formula 2 is set to 1350° C. or higher, T1=1155-0.095×Po 2 +15×FeO 0.5 …1 T2=220×C / S+13.1×M / S-23.13×TFe+2600…2 In the above formula 1, Po is the porosity of the iron ore pellets, in %, and FeO is the ratio of FeO to the iron ore pellets, in mass %. In Formula 2, C / S is the CaO / SiO2 mass ratio of the iron ore pellets, M / S is the MgO / SiO2 mass ratio of the iron ore pellets, and TFe is the ratio of the total iron component to the iron ore pellets, expressed in mass %.

4. The method for producing iron ore pellets according to claim 3, wherein: The temperature T1 is set to be 1100° C. or higher, and the temperature T2 is set to be 1350° C. or higher.

5. The method for producing iron ore pellets according to claim 3 or claim 4, wherein: In the raw material blending step, the amounts of CaO, MgO, SiO2 and iron are adjusted.

6. The method for producing iron ore pellets according to claim 3 or claim 4, wherein: The strength imparted in the agglomeration step is achieved by calcining the green pellets. The amount of FeO is adjusted by the calcination temperature.

7. The method for producing iron ore pellets according to claim 6, wherein: The calcination temperature is set to 1200° C. or higher and 1300° C. or lower.

8. The method for producing iron ore pellets according to claim 3, wherein: The auxiliary raw materials include calcium ferrite minerals, magnesium ferrite minerals and a binder. In the raw material mixing step, the amount of FeO is adjusted.

9. An iron ore pellet, which is a self-melting iron ore pellet used in 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 temperature T1 represented by the following formula 1 is 1100° C. or higher, or the temperature T2 represented by the following formula 2 is 1350° C. or higher, T1=1155-0.095×Po 2 +15×FeO 0.5 …1 T2=220×C / S+13.1×M / S-23.13×TFe+2600…2 In the above formula 1, Po is the porosity of the iron ore pellets, in %, and FeO is the ratio of FeO to the iron ore pellets, in mass %. In Formula 2, C / S is the CaO / SiO2 mass ratio of the iron ore pellets, M / S is the MgO / SiO2 mass ratio of the iron ore pellets, and TFe is the ratio of the total iron component to the iron ore pellets, expressed in mass %.

10. The iron ore pellets according to claim 9, wherein: The temperature T1 is 1100° C. or higher, and the temperature T2 is 1350° C. or higher.

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