Blast furnace use block iron

Abstract

The present invention provides a blast furnace agglomerate ore having even higher reducibility, wherein the cross-sectional structure of the agglomerate has an area ratio of hematite of 40% or more and an area ratio of magnetite of 30% or less, and the average Feret diameter of hematite particles in the cross-sectional structure calculated from the distribution of crystal orientations of the hematite is 30 μm or more.

Description

[Technical Field]

[0001] The present invention relates to a blast furnace agglomerate ore. [Background technology]

[0002] Agglomerates are artificial ores produced primarily from iron ore and used in blast furnace operations. The quality of agglomerates is evaluated based on factors such as reducibility. If agglomerates have high reducibility, the amount of reducing materials such as coke breeze used in blast furnace operations can be reduced, which is expected to reduce CO2 emissions.

[0003] Agglomerates have a structure containing multiple mineral phases, and the structure of the agglomerates is one of the factors that affect reducibility. Therefore, the relationship between the phase fractions in the structure of the agglomerates and the reducibility of the agglomerates has been studied.

[0004] For example, Non-Patent Document 1 shows that sintered ore containing hematite and calcium ferrite as its main components has higher reducibility than sintered ore containing magnetite and slag as its main components.

[0005] Patent Document 1 proposes sintered ore having a relative ratio of hematite of 16% by mass or more and 24% by mass or less and a relative ratio of magnetite of 46% by mass or more and 54% by mass or less. According to Patent Document 1, when the sintered ore is reduced while being heated from room temperature, it is possible to achieve a reduction rate of 71% or more when the temperature reaches 1200°C. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-12141 [Non-patent literature]

[0007] [Non-Patent Document 1] N.Maeda, Y.Ono: Tetsu-to-Hagane, 72(1986), 775. Summary of the Invention [Problem to be solved by the invention]

[0008] However, even if the phase fractions of the various phases in the structure of the agglomerated ore were controlled according to the approach set forth in Non-Patent Document 1, there was still room for improvement in reducibility. Also, there was also room for improvement in reducibility with the technology proposed in Patent Document 1. Furthermore, in these prior art technologies, reducibility was evaluated assuming conditions under which a blast furnace is operated using a general reducing gas, but there was a demand for an agglomerated ore that would have high reducibility when used under operating conditions in which a gaseous reducing agent containing a hydrocarbon is injected into the blast furnace.

[0009] The present invention has been made in view of the above circumstances, and has as its object to provide a blast furnace agglomerate ore having even higher reducibility. [Means for solving the problem]

[0010] As a result of extensive investigation, the present inventors have found that the above object can be achieved by employing the following configuration.

[0011] 1. Agglomerates for blast furnaces, In the cross-sectional structure of the agglomerate, the area ratio of hematite is 40% or more and the area ratio of magnetite is 30% or less, The blast furnace agglomerate ore has an average Feret's diameter of hematite particles in the cross-sectional structure calculated from the distribution of the crystal orientation of the hematite of 30 μm or more.

[0012] 2. The blast furnace agglomerate according to 1 above, wherein the cross-sectional structure contains at least one selected from calcium ferrite, slag, and pores. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a blast furnace agglomerate ore having even higher reducibility. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described below. Note that the following description shows preferred embodiments of the present invention, and the present invention is not limited to the following description in any way.

[0015] First, we will explain the experiments conducted to complete the present invention. Agglomerates were reduced, and the cross-sectional structure of the reduced agglomerates was observed. The reduction conditions were a reducing gas composition of 31% CO, 19% H, and 50% N, a reduction temperature of 800°C, and a reduction time of 3 hours. The observations revealed that the hematite contained in the agglomerates could be classified into two types based on the state of reduced iron formation. That is, there were two types of hematite: a structure that was difficult to reduce, which formed a metallic iron shell around it during reduction, and a structure that was easy to reduce, which did not form a metallic iron shell and was reduced to metallic iron with a striped shape. The above observations also revealed that magnetite also formed a metallic iron shell during reduction. Based on the above experiments and further improvements, the present invention was completed.

[0016] The agglomerate ore according to the present invention will be specifically described below. In the cross-sectional structure of the agglomerate ore according to the present invention, the area ratio of hematite is 40% or more and the area ratio of magnetite is 30% or less. In addition, the average Feret diameter of the hematite particles in the cross-sectional structure of the agglomerate ore calculated from the distribution of the crystal orientation of the hematite is 30 μm or more.

[0017] Hematite area ratio: 40% or more Hematite has a structure that is easily reduced when it satisfies the conditions for hematite particles described below. If the hematite is less than 40% by area, the reducibility is low. Therefore, the area ratio of hematite in the cross-sectional structure of the agglomerate ore according to the present invention is set to 40% or more. The upper limit of the area ratio of hematite is not particularly limited, but it may be, for example, 100% or less, or 75% or less.

[0018] Magnetite area ratio: 30% or less Magnetite is a structure that is difficult to reduce and forms a metallic iron shell during reduction. If magnetite exceeds 30 area %, the reducibility is low. Therefore, in the cross-sectional structure of the agglomerate ore according to the present invention, the area ratio of magnetite is set to 30% or less. There is no particular restriction on the lower limit of the area ratio of magnetite, and it may be 0% or may not be contained, but magnetite may be contained, and the area ratio of magnetite may be, for example, more than 0% or 5% or more.

[0019] The cross-sectional structure of the agglomerate may further include at least one selected from calcium ferrite, slag, and pores. The cross-sectional structure of the agglomerate may consist of hematite, magnetite, calcium ferrite, slag, and pores.

[0020] (Calcium ferrite) There is no particular lower limit for the area ratio of calcium ferrite. However, calcium ferrite is a structure that is easily reduced without forming a metallic iron shell during reduction. Therefore, to further enhance reducibility, calcium ferrite is preferably 15 area % or more. For example, calcium ferrite may be 60 area % or less, or may be 50 area % or less.

[0021] (Slag) The area ratio of slag is not particularly limited. However, by reducing the area ratio of slag, the permeability of the agglomerated ore can be improved. Therefore, to further improve reducibility, the slag is preferably 10 area % or less. The lower limit of the area ratio of slag is not particularly limited, and it may be 0%, or it may not be present at all.

[0022] (stomata) The area ratio of the pores is not particularly limited. However, the pores serve as paths for the intrusion of the reducing gas. Therefore, to further enhance the reducibility, the pores are preferably 10% by area or more. For example, the pores may be 60% by area or less, or 45% by area or less.

[0023] The area ratio of each texture is determined by observing the cross-sectional texture of the agglomerate with an optical microscope. Specifically, it can be determined by the method described in the Examples.

[0024] Average Feret diameter of hematite particles calculated from the distribution of hematite crystal orientation: 30 μm or more The hematite contained in the agglomerates is composed of multiple hematite particles. As described above, hematite can be classified into two types of structures with different reducibility. The hematite particles contained in the easily reducible structure have a larger Feret diameter than the hematite particles contained in the less reducible structure. When the average Feret diameter of the hematite particles in the cross-sectional structure of the agglomerates is less than 30 μm, the agglomerates contain many less reducible structures, and the reducibility is low. Therefore, the average Feret diameter of the hematite particles in the cross-sectional structure of the agglomerates according to the present invention is set to 30 μm or more. The upper limit of the average Feret diameter of the hematite particles is not particularly limited, but may be, for example, 50 μm or less.

[0025] The average Feret diameter of hematite particles is calculated from the distribution of hematite crystal orientation. Because hematite is reduced in particle units with the same crystal orientation, the particle size based on the crystal orientation is important. Specifically, the cross-sectional structure of the agglomerate is observed using a polarizing microscope, and distribution information on the crystal orientation of hematite is obtained based on the brightness of the hematite region in the polarizing microscope image. The grain boundaries of the hematite particles are then defined from the distribution information. More specifically, the average Feret diameter can be determined using the method described in the Examples. Because crystal orientation information cannot be obtained from bright-field images using an optical microscope, there is a risk of overestimating the particle size in areas where small primary hematite particles aggregate. For this reason, it is necessary to observe the structure using a method that can determine the crystal orientation of hematite, such as the polarizing microscope described above.

[0026] The agglomerates may be sintered ore or fired pellets. Sintered ore is produced by sintering raw materials including iron ore (particularly fine ore). On the other hand, fired pellets are produced by granulating and firing raw materials including iron ore (particularly fine ore).

[0027] The agglomerate ore may have a reduction degree (RI) of 80% or more and 100% or less when reduced under the conditions of a reducing gas composition of 31% CO, 19% H, and 50% N, a reduction temperature of 800°C, and a reduction time of 3 hours. RI can be determined specifically by the method described in the Examples.

[0028] The agglomerated ore according to the present invention is used in a blast furnace. By charging the agglomerated ore into a blast furnace and operating it, reduced iron can be produced, and CO2 emissions during the production can be reduced. A method for operating a blast furnace using the agglomerated ore will be described below.

[0029] The agglomerates may be used under typical blast furnace operating conditions, such as blowing hot air (generally air heated to 1000 to 1300°C) through the tuyere. Furthermore, the agglomerates may also be suitably used under operating conditions in which a gaseous reducing agent containing at least one of hydrocarbons, hydrogen, and ammonia is blown into the blast furnace. Examples of hydrocarbons that may be contained in the gaseous reducing agent include methane. The gaseous reducing agent containing at least one of hydrocarbons, hydrogen, and ammonia may be a mixture of multiple gases, and may contain, for example, nitrogen as an impurity. When blowing a gaseous reducing agent containing at least one of hydrocarbons, hydrogen, and ammonia into the blast furnace, oxygen may also be blown into the blast furnace. The agglomerates exhibit high reducibility regardless of the operating conditions described above.

[0030] The amount of gaseous reducing agent containing at least one of hydrocarbon, hydrogen, and ammonia injected into the blast furnace is 100 Nm 3 / t or more is preferable. Here, the injection amount is expressed as the amount per ton of molten pig iron produced. In addition, when the gaseous reducing agent injected into the blast furnace is converted into another gaseous reducing agent in the blast furnace, the conversion value of the injection amount is obtained by converting it into the amount of the gaseous reducing agent after the conversion. For example, 3 When methane is injected into a blast furnace, it reacts with oxygen near the tuyere, resulting in a gas pressure of 1 Nm 3 of carbon monoxide and 2Nm 3These act as gaseous reducing agents. 3 When methane is injected into a blast furnace, the amount of gaseous reducing agent to be injected is equivalent to 3 Nm 3 For example, 1 Nm 3 When ammonia is injected into a blast furnace, the ammonia 3 of hydrogen and 0.5Nm 3 Nitrogen does not function as a gaseous reducing agent, so 3 When ammonia is injected into a blast furnace, the amount of gaseous reducing agent to be injected is equivalent to 1.5 Nm 3 The conversion value of the injection amount is calculated in the same way when the gas injected into the blast furnace contains other gases such as nitrogen. For example, when a gas containing nitrogen is injected into the blast furnace, the nitrogen does not function as a gaseous reducing agent, so the injection amount of nitrogen is not included in the conversion value. Also, when a gas containing hydrogen or carbon monoxide is injected into the blast furnace, these gases function as gaseous reducing agents as they are, so the injection amount of hydrogen or carbon monoxide is included as it is in the conversion value.

[0031] Furthermore, among the gaseous reducing agents containing at least one of hydrocarbon, hydrogen, and ammonia, the concentration of the gaseous reducing agent that actually contributes to reduction is preferably 90% by volume or more, and more preferably 95% by volume or more. Here, the gaseous reducing agent that actually contributes to reduction refers to hydrogen, carbon monoxide, and gases that are converted to either or both of carbon monoxide and hydrogen in the furnace (e.g., methane, ammonia, etc.). The remainder other than the gaseous reducing agent that actually contributes to reduction may be composed of impurities.

[0032] Next, an example of a method for producing the above-mentioned agglomerated ore will be described, but the present invention is not limited to the following description.

[0033] The raw materials for the agglomerated ore are not particularly limited and may be a mixture of components such as fine ore, auxiliary raw material powder, miscellaneous raw materials, and solid fuel. The fine ore may be a mixture of multiple brands of fine ore. Examples of the auxiliary raw material powder include limestone, silica, and serpentine. Examples of the miscellaneous raw materials include dust, scale, and return fines. The solid fuel is a raw material that is burned in a sintering apparatus to promote the sintering reaction, and examples of the solid fuel include fine coke. The ratio of the components can be changed as appropriate.

[0034] To produce sintered ore, raw materials are granulated and then sintered in a sintering machine, and the particle size of the resulting sintered body is adjusted. To produce fired pellets, raw materials are granulated to form pellets, and the resulting pellets are fired in a sintering machine. To sinter sintered ore, the granulated raw materials are loaded into a sintering machine, the top of the packed bed is ignited, and the gas introduced into the sintering machine is sucked from the top to the bottom of the packed bed, causing a sintering reaction. The sintering reaction stops when the combustion zone reaches the bottom of the packed bed. Examples of sintering machines include Dwight Lloyd sintering machines and sintering pots. Examples of sintering pots include Greenawalt sintering machines. To fire pellets, the granulated pellets are introduced into a sintering machine, and the sintering reaction is carried out using high-temperature firing gas. Examples of sintering machines include shaft furnaces, grate systems, and grate kilns.

[0035] In order to set the hematite area ratio, magnetite area ratio, and average Feret's diameter of hematite particles in the cross-sectional structure of the agglomerate within the above-mentioned ranges, the content of solid fuel in the raw materials and the oxygen concentration in the gas introduced into the sintering apparatus may be controlled. Increasing the solid fuel content can coarsen the hematite particles. On the other hand, if an excessive amount of solid fuel is included, excessive heat may result in a decrease in the hematite area ratio or an increase in the magnetite area ratio. Furthermore, increasing the oxygen concentration in the gas introduced into the sintering apparatus can increase the amount of melt produced during sintering, thereby coarsening the hematite particles. On the other hand, if the oxygen concentration is excessively high, there is a risk of a decrease in the hematite area ratio or an increase in the magnetite area ratio. [Example]

[0036] The present invention will be described below based on examples.

[0037] First, various agglomerates were produced by controlling the content of solid fuel in the raw materials and the oxygen concentration in the gas introduced into the sintering apparatus. A laboratory-scale sintering pot was used as the sintering apparatus. The cross-sectional structure of the obtained agglomerates was observed and their reducibility was evaluated using the following methods.

[0038] (Observation of cross-sectional structure) The obtained agglomerates were crushed to a particle size of 1 to 2 mm using a crusher, embedded in resin, and the surface to be evaluated (observation surface) was mirror-polished. The polishing was carried out using SiC paper with grits ranging from #120 to #400, followed by polishing with diamonds of 9 μm, 3 μm, 1 μm, and 0.25 μm.

[0039] Bright-field and polarized light microscope images were taken of the observation surface of the polished agglomerates using an optical microscope. These images were taken using an optical microscope with an imaging function at 100x magnification, with the field of view continuously changed across the entire observation surface of the evaluation sample. Here, the bright-field and polarized light microscope images were taken using the bright-field and polarized light modes, respectively, for the same field of view. When taking the polarized light microscope images, the polarizer and analyzer were shifted by several degrees from crossed Nicols to ensure clear contrast.

[0040] The obtained bright-field microscope images were segmented based on color tone using TWS (Trainable Weka Segmentation), an ImageJ plugin, and classified into hematite, magnetite, calcium ferrite, slag, and pores. The area ratio of each structure after classification was calculated using the Measure function in ImageJ. The area ratios of hematite, magnetite, calcium ferrite, slag, and pores obtained are shown in Table 1.

[0041] Next, using the segmentation results of the bright-field microscope image, the hematite region was identified in the polarizing microscope image, and regions other than hematite were masked to obtain a polarizing microscope image of only hematite. The brightness values ​​output in 256 gradations in the polarizing microscope image of only hematite were classified into 10 levels, and regions with the same brightness level were assigned to the same crystal orientation to obtain distribution information of crystal orientation.

[0042] Next, the outer edges of continuous regions with the same brightness gradation in the distribution of crystal orientations were defined as apparent grain boundaries of hematite particles. The hematite particles defined by the apparent grain boundaries were then classified into aggregate hematite particles, which exist as aggregates of three or more hematite particles in contact with each other, and the remaining discrete hematite particles. Next, using the distance between the centers of the discrete hematite particles and the crystal orientation, determination of whether two or more discrete hematite particles are a single hematite particle was performed for all discrete hematite particles, starting with the discrete hematite particles with the largest perimeter. The determination criterion used was that, when targeting a specific discrete hematite particle, discrete hematite particles located within a distance of the square root of the perimeter of the target hematite particle and having the same crystal orientation are the same hematite particle as the target hematite particle. This may result in cases where three or more discrete hematite particles are determined to be a single hematite particle in a chain reaction. For example, for discrete hematite particles A to C, A and B may be determined to be the same hematite particle, and B and C may be determined to be the same hematite particle. In this case, regardless of whether A and C were determined to be the same hematite particle, A to C were all determined to be the same hematite particle. Next, for two or more discrete hematite particles determined to be a single hematite particle, a rectangle circumscribing the two or more discrete hematite particles was defined as the grain boundary of that single hematite particle. For other hematite particles, the grain boundary was defined using the apparent grain boundary as is. The Feret diameter of each hematite particle was calculated from the defined grain boundary of the hematite particle, and the average Feret diameter of all the hematite particles was calculated. The obtained average Feret diameters are shown in Table 1.

[0043] (Evaluation of reducibility) Next, the reducibility of the agglomerates was evaluated. The agglomerates were crushed to a particle size of 19 to 21 mm using a crusher and classified, and 500 g of the resulting agglomerates were charged into a vertical reduction test furnace. The reduction test was carried out under the following conditions: reducing gas composition: CO 31% - H 2 19% - N 2 50%, reduction temperature: 800°C, reduction time: 3 hours. In order to calculate the JIS-RI, which is the reducibility index specified in JIS M8713, evaluation is carried out using a reducing gas with a composition of approximately 30% CO and approximately 70% N 2. In contrast, in this evaluation condition, a reducing gas containing H 2 was used to simulate the operating conditions in which a gaseous reducing agent containing hydrocarbons is injected into a blast furnace. In particular, the amount of gaseous reducing agent containing hydrocarbons injected into the blast furnace was 100 Nm 3 in terms of equivalent value. 3 The simulations were conducted under operating conditions in which the gaseous reducing agent concentration was 90% by volume or more and the gaseous reducing agent that actually contributed to reduction was 90% by volume or more. The reducibility index (RI) was calculated from the mass and chemical analysis values ​​of the agglomerates before and after the reduction test, similar to the calculation method for the JIS reduction degree achieved specified in JIS M8713. The results are shown in Table 1. The agglomerates that satisfied the conditions of the present invention had high reducibility.

[0044] [Table 1]

Claims

1. A blast furnace agglomerate comprising: In the cross-sectional structure of the agglomerate, the area ratio of hematite is 40% or more and the area ratio of magnetite is 30% or less, The average Feret diameter of the hematite particles in the cross-sectional structure calculated from the distribution of the crystal orientation of the hematite is 30 μm or more, The blast furnace agglomerate ore is sintered ore.

2. 2. The blast furnace agglomerate according to claim 1, wherein the cross-sectional structure contains at least one selected from calcium ferrite, slag, and pores.

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