Method for determining the high-temperature properties of iron ore pellets and method for manufacturing iron ore pellets

Abstract

To provide a high temperature property determination method of iron ore pellet, a production method of iron ore pellet using the determination method.SOLUTION: There is provided a production method of self-fluxing iron ore pellet used for blast furnace operation, the method comprises: a step for blending to an ore raw material, an auxiliary material including CaO and MgO so that a CaO / SiO2 mass ratio becomes 0.8 or more and MgO / SiO2 mass ratio becomes 0.4 or more; a step for granulating green pellet from the mixed raw material; and an agglomerating step for adding intensity to the green pellet. A temperature T1 indicated by a formula 1 is set to 1100°C or more, or a temperature T2 indicated by a formula 2 is set to 1350°C or more, the formula 1 is: T1=1155-0.095×Po2+15×FeO0.5, and the formula 2 is: T2=220×C / S+13.1×M / S-23.13×TFe+2600, in the formulae, Po is porosity of the iron ore pellet [%], FeO is a ratio [mass%] of FeO, C / S is a CaO / SiO2 mass ratio, M / S is a MgO / SiO2 mass ratio, TFe is a ratio [mass%] of a total iron content.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a method for determining the high-temperature properties of iron ore pellets, a method for manufacturing iron ore pellets, and iron ore pellets themselves. [Background technology]

[0002] In blast furnace operation, it is known that iron ore containing iron oxides, calcined ore, and coke as a carbon source are charged into the upper part of the blast furnace, and air or oxygen is blown in from the tuyeres at the bottom to carry out the generation of carbon monoxide and the reduction reaction that removes oxygen from iron oxide inside the furnace, and pig iron is extracted from the lower part of the furnace.

[0003] To ensure smooth continuous operation, it is crucial to have a smooth airflow. For this to work, a low and stable airflow pressure, i.e., good air permeability, is desirable. This airflow pressure depends on the properties of the charged material. Among the charged materials, iron ore, sintered ore, and iron ore pellets undergo a reduction reaction when exposed to high temperatures and a reducing atmosphere, becoming a mixture of metallic iron and oxides. Simultaneously, they soften and deform under the load within the blast furnace. This softening and deformation fills the gaps between the charged material particles, hindering air permeability within the furnace. This phenomenon, primarily caused by this issue, is called lower furnace pressure drop, and efforts are made to reduce it.

[0004] As iron ore pellets that can reduce the pressure drop at the bottom of the furnace, self-solubilating pellets having 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 are known (see Japanese Patent Publication No. 2008-280556).

[0005] In the above iron ore pellets, the reducibility at high temperatures is enhanced by setting the CaO / SiO2 mass ratio to 0.8 or higher and the MgO / SiO2 mass ratio to 0.4 or higher, while ensuring permeability by controlling the particle size distribution. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2008-280556 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Blast furnace operation is performed at high temperatures and requires a large amount of energy, so energy reduction is needed. To reduce the energy consumption of blast furnace operation, it is important to reduce heat transferred from the furnace walls to the outside environment that is not related to the reaction inside the furnace (furnace wall heat loss). The heat loss in a blast furnace increases as the temperature of the furnace walls increases. The temperature of the furnace walls becomes high when the furnace gas near the walls is hot and has a high flow rate, so it is important to reduce the flow rate of the gas near the furnace walls.

[0008] The ventilation inside a blast furnace differs significantly on either side of the fusion zone formed by the high-temperature softening of the ore. On the lower temperature side of the fusion zone, i.e., in the upper region of the furnace, solid ore and other charges are present, and it is known that by controlling the charges and placing less permeable charges near the furnace walls, the gas flow rate near the furnace walls can be reduced.

[0009] On the other hand, in the region above the fusion zone, i.e., the lower part of the furnace, only liquid iron and slag and solid coke exist, making it difficult to control the gas flow. Therefore, to reduce the energy consumption of blast furnace operation, it is effective to position the fusion zone lower and expand the area where the gas flow rate near the furnace wall can be reduced by the charge.

[0010] In iron ore pellets containing CaO and MgO, the CaO-FeO compound melts, causing softening and deformation, and the formation of a fused zone begins. The temperature at which this fused zone formation begins can be represented by the fusion onset temperature, which shows a 10% shrinkage rate in load reduction tests. At even higher temperatures, the MgO-FeO compound, which was present as a solid, also melts and shrinks rapidly, ending the formation of the fused zone. This temperature at which rapid shrinkage occurs is called the rapid shrinkage temperature.

[0011] When the formation of the fusion zone ends, there is no means to reduce the gas flow rate near the furnace wall, and the temperature of the wall increases. Therefore, in order to reduce the energy consumption of blast furnace operation, it is considered that it is preferable that the fusion start temperature or the rapid shrinkage temperature is high. However, it cannot be said that the technology for increasing the fusion start temperature or the rapid shrinkage temperature of iron ore pellets has been established.

[0012] The present invention has been made based on the above circumstances, and an object thereof is to provide a method for determining the high-temperature properties of iron ore pellets capable of determining that the fusion start temperature or the rapid shrinkage temperature is high, a method for producing iron ore pellets using this method for determining high-temperature properties, and iron ore pellets.

Means for Solving the Problems

[0013] A method for determining the high-temperature properties of iron ore pellets according to one aspect of the present invention is a method for determining the high-temperature properties of self-fluxing iron ore pellets used in blast furnace operation, having a CaO / SiO2 mass ratio of 0.8 or more and a MgO / SiO2 mass ratio of 0.4 or more, and uses the following formula 1 as the fusion start temperature T1 or the following formula 2 as the rapid shrinkage temperature T2. T1 = 1155 - 0.095×Po

[0013] + 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 pellet, and FeO is the ratio [mass%] of FeO to the iron ore pellet. In the above formula 2, C / S is the CaO / SiO2 mass ratio of the iron ore pellet, M / S is the MgO / SiO2 mass ratio of the iron ore pellet, and TFe is the ratio [mass%] of the total iron content to the iron ore pellet.

[0014] A method for producing iron ore pellets according to another aspect of the present invention is a method for producing self-fusing iron ore pellets used in blast furnace operation, comprising a raw material blending step of blending a secondary raw material containing CaO and MgO with 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 of granulating green pellets from the mixed raw material obtained in the above raw material blending step, and a nodulization step of imparting strength to the green pellets, and the temperature T1 represented by the following formula 1 is 1100 °C or more, or the temperature T2 represented by the following formula 2 is 1350 °C or more. 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 pellet, and FeO is the ratio [mass%] of FeO to the iron ore pellet. In the above formula 2, C / S is the CaO / SiO2 mass ratio of the iron ore pellet, M / S is the MgO / SiO2 mass ratio of the iron ore pellet, and TFe is the ratio [mass%] of the total iron content to the iron ore pellet.

[0015] An iron ore pellet according to still another aspect of the present invention is a self-fusing iron ore pellet used in blast furnace operation, having a CaO / SiO2 mass ratio of 0.8 or more and a MgO / SiO2 mass ratio of 0.4 or more, and the temperature T1 represented by the following formula 1 is 1100 °C or more, or the temperature T2 represented by the following formula 2 is 1350 °C or more. T1 = 1155 - 0.095 × Po 2 + 15 × FeO 0.5 ···1T2 = 220 × C / S + 13.1 × M / S - 23.13 × TFe + 26OO ···2 In the above formula 1, Po is the porosity [%] of the iron ore pellet, and FeO is the ratio [mass%] of FeO to the iron ore pellet. In the above formula 2, C / S is the CaO / SiO2 mass ratio of the iron ore pellet, M / S is the MgO / SiO2 mass ratio of the iron ore pellet, and TFe is the ratio [mass%] of the total iron content to the iron ore pellet. [Effects of the Invention]

[0016] The method for determining the high-temperature properties of iron ore pellets according to the present invention can determine that the fusion onset temperature or rapid shrinkage temperature is high. The method for manufacturing iron ore pellets according to the present invention, which utilizes this method for determining the high-temperature properties of iron ore pellets, can produce iron ore pellets with a high fusion onset temperature or rapid shrinkage temperature. Furthermore, the iron ore pellets of the present invention have a high fusion onset temperature or rapid shrinkage temperature. [Brief explanation of the drawing]

[0017] [Figure 1] Figure 1 is a flowchart showing a method for manufacturing iron ore pellets according to one embodiment of the present invention. [Figure 2] Figure 2 is a schematic diagram showing the configuration of the manufacturing apparatus used in the iron ore pellet manufacturing method shown in Figure 1. [Figure 3] Figure 3 is a graph showing the correlation between the fusion onset temperature and the estimated fusion onset temperature T1. [Figure 4] Figure 4 is a graph showing the correlation between the rapid contraction temperature and the estimated rapid contraction temperature T2. [Figure 5] Figure 5 is a flowchart showing a method for manufacturing iron ore pellets according to a different embodiment than that shown in Figure 1. [Modes for carrying out the invention]

[0018] [Description of Embodiments of the Invention] A method for determining the high-temperature properties of iron ore pellets according to one aspect of the present invention is a method for determining the high-temperature properties of self-fluxing iron ore pellets used in blast furnace operation, having a CaO / SiO2 mass ratio of 0.8 or more and a MgO / SiO2 mass ratio of 0.4 or more, using the following formula 1 as the fusion 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 pellet, and FeO is the ratio of FeO to the iron ore pellet [% by mass]. In the above formula (2), C / S is the mass ratio of CaO / SiO2 of the iron ore pellet, M / S is the mass ratio of MgO / SiO2 of the iron ore pellet, and TFe is the ratio of the total iron content to the iron ore pellet [% by mass].

[0019] When the present inventors earnestly studied the sintering start temperature T1, they found that the sintering start temperature T1 can be approximated using the porosity and the ratio of FeO. That is, by using the above formula (1), it is possible to accurately estimate the sintering start temperature T1. Further, when earnestly studying the rapid shrinkage temperature T2, they 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), it is possible to accurately estimate the rapid shrinkage temperature T2. Therefore, by using the above formula (1) or the above formula (2), it is possible to easily determine the formation temperature of the cohesive zone in blast furnace operation.

[0020] It is preferable to use both the above formula (1) and the above formula (2). By using both the above formula (1) and the above formula (2) in this way, it is possible to more accurately determine the formation temperature of the cohesive zone.

[0021] A method for producing an iron ore pellet according to another aspect of the present invention is a method for producing a self - fluxing iron ore pellet used in blast furnace operation, including a raw material blending step of blending a secondary raw material containing CaO and MgO into an ore raw material so that the mass ratio of CaO / SiO2 is 0.8 or more and the mass ratio of MgO / SiO2 is 0.4 or more, a granulation step of granulating a green pellet from the mixed raw material obtained in the above raw material blending step, and a pelletizing step of imparting strength to the green pellet, and setting the temperature T1 represented by the following formula (1) to 1100 °C or more, or setting the temperature T2 represented by the following formula (2) to 1350 °C or more. 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 Equation 1 above, Po is the porosity [%] of the iron ore pellet, and FeO is the ratio [mass] of FeO to the iron ore pellet. In Equation 2 above, C / S is the CaO / SiO2 mass ratio of the iron ore pellet, M / S is the MgO / SiO2 mass ratio of the iron ore pellet, and TFe is the percentage of total iron content [mass%] relative to the iron ore pellet.

[0022] In the iron ore pellet manufacturing method described above, the temperature T1 shown in Equation 1 or the temperature T2 shown in Equation 2 is set to be above the lower limit. Since T1, determined by Equation 1, accurately approximates the fusion start temperature, setting T1 above the lower limit makes it easy to raise the fusion start temperature of the manufactured iron ore pellets. Furthermore, since T2, determined by Equation 2, accurately approximates the rapid shrinkage temperature, setting T2 above the lower limit makes it easy to raise the rapid shrinkage temperature of the manufactured iron ore pellets. For this reason, by using the iron ore pellet manufacturing method described above, in which either T1 or T2 is set to a predetermined temperature or higher, it is possible to manufacture iron ore pellets that enable low-energy blast furnace operation.

[0023] It is preferable to set the above temperature T1 to 1100°C or higher and the above temperature T2 to 1350°C or higher. By setting the above temperature T1 to 1100°C or higher and the above temperature T2 to 1350°C or higher in this way, it is possible to produce iron ore pellets that enable blast furnace operation with even lower energy.

[0024] In the raw material blending process described above, it is advisable to adjust the amounts of CaO, MgO, SiO2, and iron. By adjusting the amounts of CaO, MgO, SiO2, and iron in this raw material blending process, the value of T2 can be controlled.

[0025] The strength imparted in the above agglomeration process is due to the calcination of the raw pellets, and the amount of FeO can be adjusted by controlling the calcination temperature. Increasing the calcination temperature increases the amount of FeO, so the value of T1 can be controlled. In addition, the proportion of oxygen in the iron ore pellets decreases and the iron content (TFe) increases, so the value of T2 can also be controlled.

[0026] The firing temperature should be between 1200°C and 1300°C. By setting the firing temperature within this range, the porosity can be reduced through a sintering effect, where the surface tension of the iron ore pellets is strengthened by high-temperature firing. This allows for an increase in the T1 value.

[0027] The above 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 above auxiliary raw materials include calcium ferrite minerals, magnesium ferrite minerals, and a binder, the amount of FeO can be directly adjusted in the raw material blending process by changing the amounts of calcium ferrite minerals and magnesium ferrite minerals, thus providing high controllability of T1.

[0028] An iron ore pellet according to yet another aspect of the present invention is a self-fluxing iron ore pellet used in blast furnace operation, having a CaO / SiO2 mass ratio of 0.8 or more and a MgO / SiO2 mass ratio of 0.4 or more, and a temperature T1 represented by the following formula 1 of 1100°C or higher, or a temperature T2 represented by the following formula 2 of 1350°C or higher. T1 = 1155 - 0.095 × Po 2 +15×FeO 0.5 ···1T2=220×C / S+13.1×M / S-23.13×TFe+2600 ···2 In Equation 1 above, Po is the porosity [%] of the iron ore pellet, and FeO is the ratio [mass] of FeO to the iron ore pellet. In Equation 2 above, C / S is the CaO / SiO2 mass ratio of the iron ore pellet, M / S is the MgO / SiO2 mass ratio of the iron ore pellet, and TFe is the percentage of total iron content [mass%] relative to the iron ore pellet.

[0029] The iron ore pellets are self-soluble, have a CaO / SiO2 mass ratio of 0.8 or higher, and a MgO / SiO2 mass ratio of 0.4 or higher, thus possessing high reducibility. T1, calculated using Equation 1 above, accurately approximates the fusion onset temperature; therefore, if T1 is above the lower limit, it means that the fusion onset temperature of the iron ore pellets is high. Similarly, T2, calculated using Equation 2 above, accurately approximates the rapid shrinkage temperature; therefore, if T2 is above the lower limit, it means that the rapid shrinkage temperature of the iron ore pellets is high. For this reason, by using iron ore pellets in which either T1 or T2 is above a predetermined temperature, low-energy blast furnace operation becomes possible.

[0030] It is preferable that the above temperature T1 is 1100°C or higher and the above temperature T2 is 1350°C or higher. By using iron ore pellets in which the above temperature T1 is 1100°C or higher and the above temperature T2 is 1350°C or higher, it becomes possible to operate a blast furnace with even lower energy.

[0031] Furthermore, the shape of the iron ore pellets in this invention is not limited to a spherical shape, but any three-dimensional shape can be adopted.

[0032] [Details of the Embodiments of the Invention] The following describes a method for determining the high-temperature properties of iron ore pellets, a method for manufacturing iron ore pellets, and iron ore pellets according to one embodiment of the present invention, with reference to the drawings as appropriate.

[0033] [Method for manufacturing iron ore pellets] [First Embodiment] The method for manufacturing iron ore pellets shown in Figure 1 comprises a raw material blending step S1, a granulation step S2, an agglomeration step S3, and a cooling step S4. In this method for manufacturing iron ore pellets, the strength is imparted in the agglomeration step S3 by calcining the raw pellets, and the pellets produced are so-called calcined pellets.

[0034] The method for manufacturing iron ore pellets allows for the production of self-fluxing iron ore pellets 1 used in blast furnace operation using a great kiln type manufacturing apparatus (hereinafter also simply referred to as "manufacturing apparatus 2"). Manufacturing apparatus 2 comprises a pan pelletizer 3, a great furnace 4, a kiln 5, and an annular cooler 6.

[0035] <Raw material blending process> In the raw material blending process S1, auxiliary raw materials containing CaO and MgO are blended into the ore raw material so that the CaO / SiO2 mass ratio is 0.8 or higher and the MgO / SiO2 mass ratio is 0.4 or higher.

[0036] If the strength imparted in the agglomeration process S3 is achieved by calcining the raw pellets, limestone, which is a source of CaO, and dolomite, which is a source of MgO, are blended as auxiliary raw materials.

[0037] The above-mentioned ore raw materials and auxiliary raw materials may be crushed in a ball mill or the like beforehand or after blending, as needed, to adjust the particle size of the mixed raw material containing the above-mentioned ore raw materials and auxiliary raw materials.

[0038] At this time, the porosity of the raw pellet P can be controlled by appropriately controlling the raw material particle size index. Here, the "raw material particle size index" can be determined by the following method. First, measure the particle size distribution of the mixed raw materials. For this measurement, one of JIS-A-1204:2010, JIS-A-8815:1994, or JIS-Z-8825:2022 can be used. Next, using the mass ratio or volume ratio mi in each particle size range Pi (representative value), calculate the sum Σ3 / Pi·mi from the range of 3 μm to 1000 μm, and this is taken as the raw material particle size index.

[0039] The relationship between the raw material particle size index and the porosity of raw pellet P is valid for mixed raw materials made by blending the same brand of iron ore and auxiliary materials in the same ratio. However, if the brand of iron ore is different, for example, the proportionality coefficient may change due to the influence of surface shape, wettability, etc. Therefore, a suitable value for the raw material particle size index can be determined by the following method. First, prepare raw materials with at least two different particle size indices in a mixed raw material with a specific mixing ratio, produce raw pellet P, and measure the porosity. From this result, the relationship between the raw material particle size index and porosity can be calculated. Then, the raw material particle size index that results in the required porosity for iron ore pellet 1 can be determined, and the particle size of the raw material is adjusted to achieve this raw material particle size index. Note that adjusting the particle size also includes purchasing raw materials that have such a particle size.

[0040] Alternatively, the specific surface area calculated using the Blaine index can be used as an indicator of raw material particle size. The lower limit of the above specific surface area is 1000 cm². 2 / g is preferred, and 2000cm 2 / g is more preferable. On the other hand, the upper limit of the specific surface area is 5000 cm². 2 / g is preferred, and 4000cm 2 / g is more preferable. If the specific surface area is less than the lower limit, it may be difficult to make T2, an indicator of the rapid shrinkage temperature described later, 1350°C or higher. Conversely, if the specific surface area exceeds the upper limit, it may cause a bursting phenomenon in the agglomeration process S3. Here, "specific surface area" means the value measured in accordance with JIS-R5201 (2015).

[0041] The above mixed raw materials may contain binders such as bentonite as appropriate to obtain the necessary strength of the raw pellets P for transport during the manufacturing process.

[0042] <Granulation process> In the granulation process S2, raw pellets P are granulated from the mixed raw materials obtained in the raw material blending process S1. A rolling granulator can be used to granulate the raw pellets P. Examples of rolling granulators that can be used include the pan pelletizer 3 shown in Figure 2, a drum pelletizer, a disc pelletizer, etc.

[0043] Specifically, in the granulation process S2, water (granulation water) is added to the above mixed raw materials, and then this granulation water-containing mixture (the above mixed raw materials containing granulation water) is put into the pump pelletizer 3 and tumbled to produce mud-ball-shaped raw pellets P.

[0044] The lower limit of the porosity of the raw pellet 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 below the lower limit, it may cause a bursting phenomenon in the agglomeration process S3. Conversely, if the porosity exceeds the upper limit, it may become difficult to set T1, an indicator of the fusion start temperature described later, to 1100°C or higher.

[0045] The porosity described above can be controlled by the particle size of the raw materials in the raw material blending process S1 and the rolling time in the granulation process S2. By controlling the porosity in this way, it is easier to control the porosity to a desired value, and T1 can be more reliably set to 1100°C or higher. Furthermore, by setting the volume percentage of pores 20 μm or smaller in the pore size distribution to preferably 80% or more, and more preferably 85% or more, T1 can be more reliably set to 1100°C or higher. Here, the "volume percentage of pores 20 μm or smaller in the pore size distribution" can be measured according to JIS-R-1655:2003.

[0046] Furthermore, it is preferable to adjust the particle size range of the raw pellets P in the granulation process S2 so that the particle size after the agglomeration process S3 is 4 mm to 20 mm, more preferably 6 mm to 15 mm. By keeping the particle size after the agglomeration process S3 within the above range, it is possible to maintain reducibility at high temperatures while suppressing a decrease in the upper ventilation resistance of the blast furnace.

[0047] To adjust the particle size range of the raw pellets P, it is preferable to use a classification system with a sieve group having oversized screens (upper limit sieves) and seed screens (lower limit sieves) adjusted to predetermined sieve sizes. By adjusting the particle size range of the raw pellets P through classification in this way, the particle size after the agglomeration process S3 can be easily and reliably adjusted. It is preferable that any off-spec products that do not meet the specifications during the classification process are crushed and reused as mixed raw materials.

[0048] <Agglomeration process> In the agglomeration process S3, strength is imparted to the raw pellets P. In this method for manufacturing iron ore pellets, the raw pellets P are calcined in the agglomeration process S3. In the manufacturing apparatus 2 shown in Figure 2, a grate furnace 4 and a kiln 5 are used in the agglomeration process S3.

[0049] (Great Furnace) As shown in Figure 2, the grate furnace 4 comprises a traveling grate 41, a drying chamber 42, a water-freezing chamber 43, and a preheating chamber 44.

[0050] The traveling grate 41 is configured in an endless manner, and the raw pellets P placed on this traveling grate 41 can be moved in the order of drying chamber 42, water-free chamber 43, and preheating chamber 44.

[0051] In the drying chamber 42, the water-free chamber 43, and the preheating chamber 44, the raw pellets P are dried, water-free, and preheated with heating gas G1 to obtain preheated pellets H that have been given sufficient strength to withstand rolling in the kiln 5.

[0052] Specifically, the following procedure is followed. First, the raw pellets P are dried in the drying chamber 42 at an ambient temperature of approximately 250°C. Next, in the syneresis chamber 43, the dried raw pellets P are heated to approximately 450°C to decompose and remove the water of crystallization mainly in the iron ore. Furthermore, in the preheating chamber 44, the raw pellets P are heated to approximately 1100°C to decompose the carbonates contained in limestone, dolomite, etc., remove carbon dioxide, and oxidize the magnetite in the iron ore. This yields preheated pellets H.

[0053] As shown in Figure 2, the heating gas G1 used in the water-freezing chamber 43 is reused as the heating gas G1 for the drying chamber 42. Similarly, the heating gas G1 for the water-freezing chamber 43 is reused from the heating gas G1 for the preheating chamber 44, and the combustion exhaust gas G2 used in the kiln 5 is reused as the heating gas G1 for the preheating chamber 44. By reusing the high-temperature heating gas G1 or combustion exhaust gas G2 from the downstream side in this way, the heating cost of the heating gas G1 can be reduced. Burners 45 may also be provided in each chamber to control the temperature of the heating gas G1. In Figure 2, burners 45 are provided in the water-freezing chamber 43 and the preheating chamber 44. The heating gas G1 used in the drying chamber 42 is ultimately discharged from the chimney C.

[0054] (Kiln) Kiln 5 is directly connected to the grate furnace 4 and is a cylindrical rotary furnace with a gradient. Kiln 5 calcines the preheated pellets H discharged from the preheating chamber 44 of the grate furnace 4. Specifically, the preheated pellets H are calcined by combustion using a kiln burner (not shown) located on the outlet side. This yields high-temperature iron ore pellets 1.

[0055] The lower limit of the firing temperature for firing the preheated pellets H is preferably 1200°C, and more preferably 1220°C. On the other hand, the upper limit of the firing temperature is preferably 1300°C, and more preferably 1280°C. If the firing temperature is below the lower limit, the pellets will not be properly fired, and if the firing temperature exceeds the upper limit, coarse crystal grains are more likely to form, which may increase the porosity of the iron ore pellets 1. Conversely, by keeping the firing temperature within the above range, the porosity can be reduced by the firing effect, which strengthens the surface tension of the iron ore pellets 1 through high-temperature firing. This makes it possible to increase the value of T1.

[0056] In kiln 5, the air used as combustion air is the cooling gas G3 that was used in the annular cooler 6. In addition, the high-temperature combustion exhaust gas G2 used for firing the preheated pellets H is sent to the preheating chamber 44 as heating gas G1.

[0057] <Cooling process> In the cooling process S4, the high-temperature iron ore pellets 1 obtained in the agglomeration process S3 are cooled. An annular cooler 6 is used in the cooling process S4. The iron ore pellets 1 cooled in the cooling process S4 are piled up and used in blast furnace operation.

[0058] In the Annula Cooler 6, the high-temperature iron ore pellets 1 discharged from the kiln 5 are moved while air, which is the cooling gas G3, is passed through by the ventilation device 61 to cool the iron ore pellets 1.

[0059] Furthermore, the cooling gas G3, which has been used in Annular Cooler 6 and whose temperature has risen, is sent to Kiln 5 and used as combustion air.

[0060] <Rapid shrinkage temperature and fusion initiation temperature> In the method for producing iron ore pellets, the temperature T1 shown in the following formula 1 is set to 1100°C or higher, and the temperature T2 shown in 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 Equation 1 above, Po is the porosity [%] of the iron ore pellet, and FeO is the ratio [mass] of FeO to the iron ore pellet. In Equation 2 above, C / S is the CaO / SiO2 mass ratio of the iron ore pellet, M / S is the MgO / SiO2 mass ratio of the iron ore pellet, and TFe is the percentage of total iron content [mass%] relative to the iron ore pellet.

[0061] Equation 1 above is an estimation formula for estimating the fusion start temperature, and Equation 2 above is an estimation formula for estimating the rapid shrinkage temperature. By using these estimation formulas, the high-temperature properties of iron ore pellets can be determined, and this itself is one embodiment of the present invention. Below, a method for determining the high-temperature properties of iron ore pellets using these estimation formulas will be described.

[0062] A method for determining the high-temperature properties of iron ore pellets according to one aspect of the present invention is a method for determining the high-temperature properties of self-fluxing iron ore pellets used in blast furnace operation, having a CaO / SiO2 mass ratio of 0.8 or higher and a MgO / SiO2 mass ratio of 0.4 or higher, using the following formula 1 as the fusion start temperature T1 and 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 Equation 1 above, Po is the porosity [%] of the iron ore pellet, and FeO is the ratio [mass] of FeO to the iron ore pellet. In Equation 2 above, C / S is the CaO / SiO2 mass ratio of the iron ore pellet, M / S is the MgO / SiO2 mass ratio of the iron ore pellet, and TFe is the percentage of total iron content [mass%] relative to the iron ore pellet.

[0063] (Fusing start temperature) The inventors of this invention diligently investigated the fusion onset temperature T1 and found that it can be approximated using porosity and FeO. Figure 3 shows the correlation between the fusion onset temperature and the fusion onset temperature T1 estimated by Equation 1 above. As shown in Figure 3, the two agree well. In other words, by using Equation 1 above, it is possible to accurately estimate the fusion onset temperature T1 and easily determine the formation temperature of the fusion zone during blast furnace operation.

[0064] The inventors believe that the fusion onset temperature T1 can be approximated by the above formula 1 because of the density of the iron ore pellet 1's structure around 1100°C. In other words, if a dense metallic iron shell is maintained around 1100°C, when the CaO-FeO compound melts, the strength of the iron ore pellet 1 is maintained, and the fusion onset temperature T1 increases. To maintain a dense metallic iron shell, it is desirable that the rate of metallic iron formation in the reduction reaction is slow. When the porosity is low, the diffusion of the reducing gas stagnates, and the rate of metallic iron formation can be slowed. Also, the pellet matrix structure containing FeO is glassy and does not contain pores. Therefore, T1 tends to decrease when the porosity Po is high and increase when the FeO content is high.

[0065] (Rapid contraction temperature) The inventors of this invention diligently investigated the rapid shrinkage temperature T2 and found that it can be approximated using C / S, M / S, and TFe. Figure 4 shows the correlation between the rapid shrinkage temperature and the rapid shrinkage temperature T2 estimated by Equation 1 above. As shown in Figure 4, the two agree well. In other words, by using Equation 2 above, it is possible to estimate the rapid shrinkage temperature T2 with high accuracy, and the temperature at which the fusion zone formation is completed in blast furnace operation can be easily determined.

[0066] The inventors believe that the fact that the rapid shrinkage temperature T2 can be approximated by the above equation 2 can be understood in terms of thermodynamics. That is, the effects of the amounts of CaO and MgO are shown in their ratio to SiO2, and approximate the melting point of the oxide. The larger the CaO / SiO2 and MgO / SiO2 ratios, the higher the melting point. Furthermore, TFe shows that the effect of CaO and MgO decreases as the iron content increases, approximating the effect of FeO during reduction on the oxide melting points of CaO and MgO. To explain in more detail, if CaO is insufficient, the reducing ability to metallic iron decreases, and a large amount of unreduced oxide FeO remains. MgO forms a high-melting-point MgO-FeO compound with the remaining FeO, raising the rapid shrinkage temperature T2, but if MgO is insufficient, free FeO that does not form an MgO-FeO compound remains. In addition, in iron ore pellets, if there is a lot of FeO, the total iron content TFe will be high. Here, the effect of the amounts of CaO and MgO themselves is reflected as coefficients of C / S and M / S. Therefore, when the term TFe is added to the rapid shrinkage temperature T2, the effect of FeO is expressed, and the larger the amount of FeO, that is, the larger the TFe, the lower the melting point.

[0067] The above estimation formulas for T1 and T2 are considered valid up to 1597°C, which is the melting point of magnetite and wustite. The accuracy is high in the range where the TFe in the iron ore pellet is 55% by mass or more, and is particularly high for iron ore pellets where the volume proportion of pores smaller than 20 μm in the pore size distribution is 80% or more.

[0068] In the method for producing the iron ore pellets, the temperature T1 shown in Formula 1 is set to 1100°C or higher. For example, the melting points of CaO-FeO and Al2O3-CaO-FeO compounds are approximately 1100°C. In addition, in the method for producing the iron ore pellets, the temperature T2 shown in Formula 2 is set to 1350°C or higher. For example, the melting point of some Al2O3-CaO-SiO2 compounds is approximately 1350°C. It can be considered that controlling Formulas 1 and 2 to be above a predetermined temperature suppresses the formation of compounds with such melting points. In this regard, it is preferable that the amount of alumina (Al2O3) contained in the iron ore pellet 1 is below a certain amount, and its content is preferably 3.0% by mass or less.

[0069] (Control of T1 and T2) The values ​​of T1 and T2 can be adjusted in various ways.

[0070] The porosity Po contained in T1 can be reduced by using fine or coarse powder raw materials in the raw material blending process described above. Conversely, adding carbonates or hydrates tends to increase the porosity Po as they volatilize during firing. Also, as mentioned above, the sintering effect, where the surface tension of the iron ore pellet 1 is strengthened by high-temperature firing, reduces the porosity Po. Reducing Po increases T1, and increasing Po decreases T1.

[0071] The amount of FeO in T1 fluctuates in accordance with the increase or decrease of magnetite ore and iron oxide scale, which are FeO-containing raw materials. It also increases due to residual FeO resulting from the reduction of iron ore pellets 1 in the atmosphere and rapid cooling during high-temperature firing. When FeO increases, T1 rises, and when FeO decreases, T1 falls.

[0072] By adjusting the amounts of CaO, MgO, SiO2, and iron in the raw material blending process S1, the value of T2 can be controlled according to the increase or decrease in these amounts.

[0073] The amounts of CaO, MgO, and SiO2 can be adjusted by selecting raw materials containing them. For example, dolomite contains CaO and MgO carbonates, and magnesite contains MgO and SiO2. Limestone contains CaO carbonate, and silica contains SiO2. By adjusting the mixing ratio of these materials, the C / S and M / S values ​​can be adjusted. When C / S or M / S increases, T2 increases, and when C / S or M / S decreases, T2 decreases.

[0074] The amount of TFe can be adjusted by selecting the iron ore and adjusting the mixing ratio. For example, hematite is high in iron, while most gangue components are low in iron. The amount of TFe also changes by increasing or decreasing the total amount of CaO, MgO, and SiO2. Increasing the total amount of these components decreases the amount of TFe. Alternatively, increasing the calcination temperature and thus increasing the amount of FeO reduces the proportion of oxygen in the iron ore pellet, thus increasing TFe. When TFe increases, T2 decreases, and when TFe decreases, T2 increases.

[0075] <Advantages> In the iron ore pellet manufacturing method described above, the temperature T1 shown in Equation 1 is set to 1100°C or higher, and the temperature T2 shown in Equation 2 is set to 1350°C or higher. Since T1, determined by Equation 1, accurately approximates the fusion start temperature, setting T1 above the lower limit makes it easy to raise the fusion start temperature of the manufactured iron ore pellets. Furthermore, since T2, determined by Equation 2, accurately approximates the rapid shrinkage temperature, setting T2 above the lower limit makes it easy to raise the rapid shrinkage temperature of the manufactured iron ore pellets. Therefore, by using the iron ore pellet manufacturing method described above, in which T1 and T2 are set to above predetermined temperatures, it is possible to manufacture iron ore pellets that enable low-energy blast furnace operation.

[0076] Furthermore, by setting the above temperature T1 to 1100°C or higher and the above temperature T2 to 1350°C or higher, it is possible to produce iron ore pellets that enable blast furnace operation with even lower energy consumption.

[0077] [Second Embodiment] The method for manufacturing iron ore pellets shown in Figure 5 comprises a raw material blending step S11, a granulation step S12, and an agglomeration step S13. In this method for manufacturing iron ore pellets, the strength is imparted in the agglomeration step S3 by a binder, and the resulting pellets are so-called unfired pellets.

[0078] The method for producing iron ore pellets can be used to produce self-fluxing iron ore pellets for use in blast furnace operations.

[0079] <Raw material blending process> In the raw material blending process S11, auxiliary raw materials containing CaO and MgO are blended into the ore raw material so that the CaO / SiO2 mass ratio is 0.8 or higher and the MgO / SiO2 mass ratio is 0.4 or higher.

[0080] In the raw material blending process S11, the above auxiliary raw materials include calcium ferrite minerals (CaO·Fe) in addition to CaO and MgO. x O), magnesium ferrite minerals (MgO·Fe x The mixture includes 0), and a binder (where 0.667 ≤ x ≤ 1.0). The above auxiliary materials are blended according to the iron grade of the iron ore (pellet feed) which is the above ore raw material. If ferritic minerals are included in the auxiliary materials, the CaO used to determine the CaO / SiO2 mass ratio includes not only elemental CaO but also CaO·Fe x The CaO contained in the oxygen is also taken into account, and the MgO used to determine the MgO / SiO2 mass ratio includes not only elemental MgO but also MgO·Fe. x The MgO contained in the oxygen is taken into account.

[0081] The calcium ferrite and magnesium ferrite minerals used are those that have already been synthesized. The calcium ferrite and magnesium ferrite minerals can be synthesized by firing or melting iron oxide, limestone, dolomite, and magnesite at high temperatures in an electric furnace or sintering furnace, followed by cooling and crushing. The valence of iron oxide varies depending on the temperature history, and the value of x changes within the range of 0.667 to 1.0. This value of x represents the FeO concentration. If x = 0.667, all the iron is Fe 3+ This indicates that it is dominated by ions, and if x=1, all the iron is Fe 2+ This indicates that the sample is dominated by ions. If x is an intermediate value, both types of ions are present, and the closer x is to 0.667, the more Fe ions are present. 3+ The higher the proportion of ions, the closer x is to 1, the more Fe 2+ The proportion of ions is high.

[0082] Furthermore, examples of the binders mentioned above include cement, sodium silicate, starch, and synthetic polymer agents. Examples of the synthetic polymer agents include acrylic resins, urethane resins, and ether-based cellulose (carboxymethylcellulose (CMC)).

[0083] Furthermore, similar to the raw material blending step S11 of the first embodiment, the particle size of the mixed raw materials may be adjusted by grinding as needed.

[0084] <Granulation process> In the granulation process S12, raw pellets are granulated from the mixed raw materials obtained in the raw material blending process S11.

[0085] As for the granulation method of raw pellets, rolling granulation methods using pan pelletizers, drum pelletizers, disc pelletizers, etc., can be used, similar to the granulation process S2 of the first embodiment. In addition, there are pressure welding methods in which the mixed raw materials are placed in a mold and compacted, and molding methods in which the mixed raw materials are placed in an extruder, extruded from an extrusion mold, and cut as appropriate to form the pellets. In the case of non-calcined pellets, in rolling granulation methods, the porosity of the raw pellets can be controlled by appropriately controlling the particle size index of the raw materials and the rolling time, similar to the first embodiment. In pressure welding and molding methods, the porosity of the raw pellets can be controlled by the pressure conditions during compaction or molding.

[0086] In either method, it is preferable that the porosity and particle size range of the raw pellets be within the same range as in the first embodiment.

[0087] <Agglomeration process> In the agglomeration process S13, the raw pellets P are given strength.

[0088] In the method for manufacturing iron ore pellets, in the agglomeration process S13, methods such as air curing and steam curing are selected depending on the type of binder. Air curing is a method in which raw pellets are left to stand in the air until they reach a predetermined strength, and can be used, for example, when the binder is cement. Steam curing is a method in which raw pellets are left to stand in high-temperature steam until they reach a predetermined strength, and can be used, for example, when the binder is sodium silicate or cement.

[0089] The agglomeration process S13 may be performed simultaneously with the granulation process S12. For example, depending on the type of binder, sufficient strength may be imparted during granulation. In this case, there is no need to perform the agglomeration process S13 again after the granulation process S12; the agglomeration process S13 can be completed during the granulation process S12.

[0090] <Rapid shrinkage temperature and fusion initiation temperature> In the method for producing iron ore pellets, the temperature T1 shown in the following formula 1 is set to 1100°C or higher, and the temperature T2 shown in 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 Equation 1 above, Po is the porosity [%] of the iron ore pellet, and FeO is the ratio [mass] of FeO to the iron ore pellet. In Equation 2 above, C / S is the CaO / SiO2 mass ratio of the iron ore pellet, M / S is the MgO / SiO2 mass ratio of the iron ore pellet, and TFe is the percentage of total iron content [mass%] relative to the iron ore pellet.

[0091] In the method for producing the iron ore pellets, the same effects as described in the first embodiment can be obtained by setting the temperature T1 shown in Formula 1 to 1100°C or higher, and the temperature T2 shown in Formula 2 to 1350°C or higher. For this reason, a detailed explanation is omitted.

[0092] (Control of T1 and T2) The values ​​of T1 and T2 can be adjusted in various ways.

[0093] The porosity Po contained in T1 can be reduced by using fine or coarse powder raw materials in the raw material blending process described above. Reducing Po increases T1, and increasing Po decreases T1.

[0094] The amount of FeO in T1 fluctuates in accordance with the FeO-containing raw materials, calcium ferrite and magnesium ferrite minerals. When FeO increases, T1 rises, and when FeO decreases, T1 falls. Since the amount of FeO can be directly adjusted by controlling the amounts of calcium ferrite and magnesium ferrite minerals, T1 has high controllability.

[0095] Furthermore, by adjusting the amounts of CaO, MgO, SiO2, and iron in the raw material blending process S11, the value of T2 can be controlled according to the increase or decrease in these amounts.

[0096] The amount of TFe can be adjusted by selecting the iron ore and adjusting the mixing ratio. For example, hematite is high in iron, while most gangue components are low in iron. Also, increasing or decreasing the total amount of CaO, MgO, and SiO2 will change the amount of TFe. Increasing the total amount of these components will decrease the amount of TFe. Alternatively, increasing the amount of calcium ferrite and magnesium ferrite minerals will increase the amount of FeO, which will reduce the proportion of oxygen in the iron ore pellet and increase TFe. When TFe increases, T2 decreases, and when TFe decreases, T2 increases.

[0097] <Advantages> Similar to the first embodiment, by using the iron ore pellet manufacturing method in which T1 and T2 are set to a predetermined temperature or higher, it is possible to manufacture iron ore pellets that enable low-energy blast furnace operation.

[0098] [Iron ore pellets] An iron ore pellet according to yet another aspect of the present invention is a self-fluxing iron ore pellet used in blast furnace operation. The iron ore pellet 1 is obtained by granulating fine ore, calcining it, or by adding a binder to make a highly strong agglomerated ore, and can be manufactured, for example, by the iron ore pellet manufacturing method described above.

[0099] In the production of iron ore pellets 1, it is known that adding CaO-containing compounds such as limestone to the ore raw material increases the CaO / SiO2 mass ratio of the iron ore pellets 1, thereby improving the reducibility of the iron ore pellets 1. Based on this knowledge, the CaO / SiO2 mass ratio of the iron ore pellets 1 is 0.8 or higher.

[0100] When the raw materials are iron ore (iron oxide) and limestone (CaO-containing compound), during the calcination process, a solid-phase reaction occurs between the CaO produced by thermal decomposition and the iron oxide, generating a calcium ferrite compound. Simultaneously, solid-phase diffusion bonding occurs at the point of contact between these compounds. This bonding is localized, and the micropores that existed before calcination are maintained after calcination, resulting in the iron ore pellet 1 becoming a porous body with relatively uniform micropores.

[0101] During blast furnace operation, reducing gas diffuses into these micropores, causing a reduction reaction to progress from the outer surface to the interior of the iron ore pellet 1. The reduction reaction removes oxygen from iron oxide, leading to the expansion of existing micropores and the generation of new ones, while simultaneously producing metallic iron. As the outer shape of the iron ore pellet 1 shrinks due to the aggregation of this metallic iron, the number of micropores decreases. As a result, the diffusion of reducing gas into the interior of the iron ore pellet 1 is suppressed, and the reduction process tends to stagnate.

[0102] To suppress this reduction stagnation, the addition of high-melting-point components that inhibit the disappearance of micropores during the aggregation process of metallic iron is effective. In particular, it is known that adding dolomite as a source of MgO, which is a high-melting-point component, and increasing the MgO / SiO2 mass ratio of iron ore pellet 1 yields a high reduction stagnation suppression effect. Based on this finding, the MgO / SiO2 mass ratio of iron ore pellet 1 is 0.4 or higher.

[0103] The iron ore pellet 1 is self-fluxing. Making the iron ore pellet 1 self-fluxing facilitates the dissolution of reduced iron. The self-fluxing properties of the iron ore pellet 1 are determined by the auxiliary materials used.

[0104] The iron ore pellet 1 has a temperature T2 of 1350°C or higher, as shown in the following formula 1. T2=220×C / S+13.1×M / S-23.13×TFe+2600 ···1 In Equation 1 above, C / S is the CaO / SiO2 mass ratio of the iron ore pellet, M / S is the MgO / SiO2 mass ratio of the iron ore pellet, and TFe is the percentage of total iron content [mass%] relative to the iron ore pellet.

[0105] Furthermore, the iron ore pellet 1 has a temperature T1 of 1100°C or higher, as shown in the following formula 2. T1 = 1155 - 0.095 × Po 2 +15×FeO 0.5 ...2 In Equation 2 above, Po is the porosity [%] of the iron ore pellet, and FeO is the ratio [mass] of FeO to the iron ore pellet.

[0106] <Advantages> The iron ore pellet 1 is self-fluxing, has a CaO / SiO2 mass ratio of 0.8 or higher, and a MgO / SiO2 mass ratio of 0.4 or higher, thus having high reducibility. T1, calculated using Equation 1 above, accurately approximates the fusion onset temperature, so if T1 is above the lower limit, it means that the fusion onset temperature of the iron ore pellet is high. Similarly, T2, calculated using Equation 2 above, accurately approximates the rapid shrinkage temperature, so if T2 is above the lower limit, it means that the rapid shrinkage temperature of the iron ore pellet is high. Therefore, by using the iron ore pellet in which either T1 or T2 is above a predetermined temperature, low-energy blast furnace operation becomes possible.

[0107] Furthermore, by using iron ore pellets in which the above-mentioned temperature T1 is 1100°C or higher and the above-mentioned temperature T2 is 1350°C or higher, it becomes possible to operate the blast furnace with even lower energy consumption.

[0108] [Other embodiments] However, the present invention is not limited to the embodiments described above.

[0109] In the first embodiment of the method for manufacturing iron ore pellets described above, a method for manufacturing iron ore pellets using a great kiln type manufacturing apparatus was explained, but it is also possible to manufacture them using a straight grate type manufacturing apparatus. In a straight grate type manufacturing apparatus, the great furnace is equipped with a traveling grate, a drying chamber, a water-freezing chamber, a preheating chamber, and a firing chamber, and the agglomeration process is completed using only the great furnace. Specifically, in the drying chamber, water-freezing chamber, and preheating chamber, the raw pellets are dried, water-freezed, and preheated with heating gas, and then the final firing takes place in the firing chamber.

[0110] In the above embodiment, a case was described in which T1 is set to 1100°C or higher and T2 is set to 1350°C or higher in the method for manufacturing iron ore pellets. However, it is not an essential requirement that both T1 and T2 be above the predetermined temperature. Even if only T1 is set to 1100°C or higher, or only T2 is set to 1350°C or higher, it is possible to reduce the energy consumption of blast furnace operation.

[0111] Similarly, for the iron ore pellets described in the above embodiment, it is not a mandatory requirement that T1 be 1100°C or higher and T2 be 1350°C or higher. Even if only T1 is 1100°C or higher, or if only T2 is 1350°C or higher, it is possible to reduce the energy consumption of blast furnace operation. [Examples]

[0112] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0113] [No.1] Iron ore was prepared as the raw material for the ore, and limestone, dolomite, and bentonite were prepared as auxiliary materials. The auxiliary materials were blended with the ore raw material so that the CaO / SiO2 mass ratio (C / S) and MgO / SiO2 mass ratio (M / S) were the values ​​shown in Table 1, and a mixed raw material was obtained.

[0114] After grinding the above mixed raw materials in a ball mill, the ground raw materials were fed into a disc pelletizer granulator, and while adding water, they were tumbling to produce raw pellets with a particle size of 10 mm to 12 mm.

[0115] The raw pellets were placed in a grate furnace and heated with high-temperature air as the heating gas to dry and pre-calcine them. The pre-calcined pellets were then placed in a kiln furnace and heated to obtain iron ore pellet No. 1.

[0116] Table 1 shows the measured values ​​of TFe, FeO, porosity, fusion onset temperature, and rapid shrinkage temperature for this No. 1 iron ore pellet, as well as the T1 and T2 values ​​based on the above-mentioned Equations 2 and 1. The measured values ​​were obtained by load reduction tests. The fusion onset temperature was calculated as the temperature at which the shrinkage rate reached 10%. The rapid shrinkage temperature was defined as the temperature at which the shrinkage rate first exceeded 1% / min within the temperature range from the temperature showing maximum pressure loss to the end of meltdown (100% shrinkage rate).

[0117] [No.2] Iron ore pellets No. 2 were obtained in the same manner as No. 1, except that the mixed raw materials were adjusted so that the C / S and M / S values ​​were as shown in Table 1. The specifications of each of the obtained iron ore pellets are shown in Table 1.

[0118] [No.3] For iron ore pellets No. 1 and No. 2, both measured and estimated values ​​(T1, T2) showed that the fusion onset temperature was below 1100°C and the rapid shrinkage temperature was below 1350°C. Therefore, TFe, FeO, C / S, and M / S were adjusted to the values ​​shown in Table 1 so that T1 was 1100°C or higher and T2 was 1350°C or higher, to obtain iron ore pellet No. 3. The specifications for each of the obtained iron ore pellets are shown in Table 1.

[0119] [No.4] For iron ore pellet No. 4, the aim was to reduce the porosity by 5% compared to iron ore pellet No. 1, while achieving a fusion start temperature of 1100°C or higher and a rapid shrinkage temperature of 1350°C or higher. To reduce the porosity by approximately 5%, the ore and auxiliary materials were crushed to prepare raw materials with particle sizes that had a specific surface area 1.8 to 2.2 times greater than that of the Blaine index. Using these crushed raw materials, TFe, FeO, C / S, and M / S were adjusted to the values ​​shown in Table 1 so that T1 was 1100°C or higher and T2 was 1350°C or higher, thereby obtaining iron ore pellet No. 4. The specifications of each of the obtained iron ore pellets are shown in Table 1.

[0120] [Table 1]

[0121] As described above, in iron ore pellets No. 1 and No. 2, which do not use the estimation formulas for T1 and T2, the fusion onset temperature is less than 1100°C and the rapid shrinkage temperature is also less than 1350°C. In contrast, in iron ore pellets No. 3 and No. 4, in which the parameters were adjusted using the estimation formulas for T1 and T2 so that the fusion onset temperature is 1100°C or higher and the rapid shrinkage temperature is 1350°C or higher, the fusion onset temperature is 1100°C or higher and the rapid shrinkage temperature is also 1350°C or higher. Thus, it can be seen that by using the iron ore pellet manufacturing method of the present invention, it is possible to obtain iron ore pellets with high fusion onset temperatures and rapid shrinkage temperatures, which had not been achieved until now, for the first time. [Industrial applicability]

[0122] The method for determining the high-temperature properties of iron ore pellets according to the present invention can determine that the fusion onset temperature or rapid shrinkage temperature is high. The method for manufacturing iron ore pellets according to the present invention, which utilizes this method for determining the high-temperature properties of iron ore pellets, can produce iron ore pellets with a high fusion onset temperature or rapid shrinkage temperature. Furthermore, the iron ore pellets of the present invention have a high fusion onset temperature or rapid shrinkage temperature. [Explanation of Symbols]

[0123] 1. Iron ore pellets 2 Manufacturing equipment 3. Pumpelette 4 Great Furnaces 41 Traveling Great 42 Drying room 43 Sewer room 44 Preheating chamber 45 burners 5 kilns 6 Anura Cooler 61 Ventilation device P Raw Pellets H Preheating pellets G1 Heating Gas G2 Combustion exhaust gas G3 Cooling Gas C Chimney

Claims

1. Used in blast furnace operation, CaO / SiO ２ A mass ratio of 0.8 or higher, and MgO / SiO ２ A method for determining the high-temperature properties of self-fluxing iron ore pellets having a mass ratio of 0.4 or higher, A method for determining the high-temperature properties of iron ore pellets using the following formula 1 as the fusion start temperature T1 or the following formula 2 as the rapid shrinkage temperature T2. T1=1155-0.095×Po ２ +15×Fem 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 pellet [%], and FeO is the ratio of FeO to the iron ore pellet [mass%]. In the above formula 2, C / S is the CaO / SiO of the iron ore pellet. ２ The mass ratio, M / S, is MgO / SiO2 for iron ore pellets. ２ The mass ratio, TFe, represents the percentage of total iron content [mass%] relative to the iron ore pellets.

2. A method for determining the high-temperature properties of iron ore pellets according to claim 1, using both formula 1 and formula 2 described above.

3. A method for producing self-fluxing iron ore pellets used in blast furnace operation, CaO / SiO ２ A mass ratio of 0.8 or higher, and MgO / SiO ２ A raw material blending step in which auxiliary raw materials containing CaO and MgO are blended with ore raw materials so that the mass ratio is 0.4 or more, A granulation process is performed to granulate raw pellets from the mixed raw materials obtained in the above raw material blending process, A process of forming the raw pellets described above to impart strength to them, Equipped with, In the above raw material blending process, using the high-temperature property determination method for iron ore pellets described in claim 1, A method for producing iron ore pellets, wherein the temperature T1 shown in formula 1 is set to 1100°C or higher by controlling the porosity Po of the iron ore pellets and the ratio of FeO to the iron ore pellets (FeO), or the temperature T2 shown in formula 2 is set to 1350°C or higher by controlling the CaO / SiO₂ mass ratio C / S of the iron ore pellets, the MgO / SiO₂ mass ratio M / S of the iron ore pellets, and the ratio of total iron content TFe to the iron ore pellets.

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

5. In the above raw material blending step, the method for producing an iron ore pellet according to claim 3 or claim 4, wherein the amounts of CaO, MgO, SiO ２ amount and iron amount are adjusted.

6. The strength imparted in the above agglomeration process is due to the calcination of the raw pellets. A method for producing iron ore pellets according to claim 3 or claim 4, wherein the amount of FeO is adjusted by the firing temperature.

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

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

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