JPH0430444B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a method for producing calcined agglomerate ore suitable as a raw material for blast furnaces or directly reduced iron. [Prior art and its problems] As a raw material for blast furnaces or raw material for direct reduction steelmaking,
Calcined agglomerate, which is made by pelletizing powdered iron ore and calcining it, is known, and its use is expanding. This calcined agglomerate ore is usually produced as follows. That is, a solvent consisting of at least one of quicklime, slaked lime, limestone, bentonite, granulated blast furnace slag, dolomite, etc. is added to powdered iron ore with a particle size of about 8 mm or less, and CaO/SiO ₂ in the calcined agglomerated ore is added to the powdered iron ore.
Add so that the value is about 1.0 to 2.5 and mix with a mixer. Then, the obtained mixture is supplied to a disk-type first granulator, water is added thereto, and the first
The mixture is granulated using a granulator, and formed into raw pellets having a particle size of, for example, about 3 to 13 mm. Next, the obtained raw pellets are supplied to a second disk-type granulator, and about 2.5 to 4.0 wt% of coke powder is added, and the raw pellets are further granulated by the second granulator. In this way, raw pellets whose surfaces are coated with coke powder are prepared. Then, the raw pellets obtained in this way are charged into an endless moving grate type kiln, and the layer of charged raw pellets is placed on the grate of the kiln, and the drying zone of the kiln is heated. Pass through the band and firing zone in sequence. In the drying zone, drying gas at a temperature of 150 to 350°C is blown into the layer of raw pellets from above to dry the raw pellets. At the ignition zone,
High-temperature combustion gas is blown into the layer of dried raw pellets from above to ignite the coke powder on the surface of the raw pellets. In the combustion zone, the hot combustion gas produced by the combustion of coke breeze is drawn downward through the bed of green pellets to heat the green pellets to the calcination temperature. The raw pellets are calcined by heating in a calcining zone into large blocks of calcined agglomerates consisting of calcined pellets bound together by at least one of calcium ferrite and slag formed on their surfaces. . The calcined agglomerate ore in the form of large blocks thus obtained is discharged from the downstream end of the calciner, crushed by a crusher, and then sieved by a screen, with a particle size of less than 3 mm. The sifted calcined agglomerate pieces are removed, and thus the calcined agglomerate ore in the form of a lump of multiple calcined pellets with a maximum particle size of about 50 mm and the particle size of a single calcined pellet in the form of 3 to 13 mm. A certain amount of calcined agglomerate ore is produced. The calcined agglomerate produced in the manner described above has excellent reducing properties, since it mainly contains a large amount of fine calcium ferrite and fine hematite, which have excellent reducing properties. In addition, not only when a plurality of fired pellets are combined into a lump, but also when a single fired pellet has an irregular shape, when charged into a blast furnace, Because it does not flow unevenly to the center of the blast furnace, and gaps are created between the fired agglomerated ores,
Smooth passage of reducing gas is not obstructed. Furthermore, even if it collapses due to shock during transportation,
Since the calcined agglomerate, which is in the form of a lump made up of a plurality of calcined pellets combined, is simply separated into single calcined pellets, it can be used without any problems. However, conventionally, powdered iron ore has a particle size of
Because a relatively coarse powdered iron ore was used with a composition consisting of 30 to 70wt% particles with a particle size of 0.5 mm or less and the remainder with a particle size of more than 0.5 mm, when the powdered iron ore was formed into pellets and fired, the resulting sintered Many macropores were not formed in the agglomerate ore, and as a result, the reduction rate of the calcined agglomerate ore was reduced. In addition, a solvent is added to powdered iron ore,
When granulated and formed into green pellets, dense green pellets with strong reinforcement cannot be obtained, and the resulting calcined agglomerates also have low drop strength. [Object of the Invention] In view of the above-mentioned current situation, the present invention involves adding a solvent to powdered iron ore, forming a mixture into raw pellets, coating the obtained raw pellets with coke powder,
It can be obtained by charging the raw pellets into an endless moving grate kiln to continuously produce calcined agglomerates, by selecting the particle size of the powdered iron ore used and its blending ratio. The purpose is to improve the reduction rate and falling strength of calcined agglomerates. [Summary of the Invention] This invention involves adding a solvent to powdered iron ore, granulating a mixture to form raw pellets, coating the obtained raw pellets with coke powder, and moving the raw pellets endlessly. In a method for producing calcined agglomerate ore, which is charged into a grate type calcining furnace and continuously calcined to thereby continuously produce calcined agglomerate ore, 10 to 80 wt of powdered iron ore having a particle size of 44 μm or less is used.
%, and the remainder has a particle size of 44 μm. [Structure of the Invention] Hereinafter, the method for producing calcined agglomerates of the present invention will be described in detail. The present inventors added a solvent to powdered iron ore, formed a mixture into raw pellets, coated the obtained raw pellets with coke powder, and charged the raw pellets into an endless moving grate type kiln. In order to improve the falling strength and reduction rate of calcined agglomerate ore when continuously producing calcined agglomerate ore, we have repeatedly investigated the fine iron ore to be used. If the blending ratio of fine-grained iron ore increases and the particle size of the iron ore used becomes relatively fine, the iron ore powder becomes a calcined agglomerate ore when formed into green pellets and fired. Since many macropores are formed inside, it is expected that the reduction rate of calcined agglomerates can be increased. In addition, a solvent is added to powdered iron ore,
When granulated and shaped into green pellets, strong and dense green pellets can be obtained, so it is expected that the falling strength of the fired agglomerates will also be increased. Therefore, we molded raw pellets by varying the particle size of the powdered iron ore used and its blending ratio.
An experiment was conducted to produce calcined agglomerate ore, and the reduction rate and falling strength of the calcined agglomerate ore were investigated. As a result, 10 to 80 wt% of particles with a particle size of 44 μm or less were
It was found that the reduction rate and falling strength of calcined agglomerate ore could be significantly improved by using powdered iron ore with a composition consisting of the remainder exceeding 44 μm. Figure 1 is a graph showing the relationship between the blending ratio of fine iron ore with a particle size of 44 μm or less in the used fine iron ore with a particle size of 8 mm or less and the reduction rate of the obtained calcined agglomerate; The figure is also a graph showing the relationship between the blending ratio of fine iron ore with a grain size of 44 μm or less and the falling strength of the obtained calcined agglomerate ore. As shown in Figure 1, as the blending ratio of fine iron ore with a particle size of 44 μm or less increases, the number of macropores in the obtained calcined agglomerate increases, and the reduction rate of the calcined agglomerate increases. The blending rate is 10wt.
%, the return rate is as high as 75% or more. As shown in Figure 2, when the blending ratio of fine iron ore with a grain size of 44 μm or less is 10 wt% or more, the raw pellets have sufficient density and strength, so the falling strength of the resulting calcined agglomerates is is high at over 85%. However, when the blending ratio exceeds 80wt%, the raw pellets tend to burst during ignition and the air permeability within the layer deteriorates, requiring a longer drying time, and when heated excessively. As it melts easily, it forms a vitreous slag, and its drop strength rapidly decreases. Therefore, in order to achieve a reduction rate of 75% or more and a drop strength of 85% or more for calcined agglomerate ore, it is necessary to use a powder with a powder composition consisting of 10 to 80wt% of particles with a particle size of 44μm or less and the balance of particles with a particle size of more than 44μm and 58 or less. Iron ore should be used. In this invention, as described above, the particle size
The reduction rate and falling strength of calcined agglomerates are significantly improved by using powdered iron ore with a composition consisting of 10 to 80 wt% of particles with a particle size of 44 μm or less and the balance of particles with a particle size of more than 44 μm. In this invention, the amount of coke powder coated on the raw pellets is preferably 2.5 to 4.0 wt%, as in the conventional method. This is because if the amount of coated coke powder is less than 2.5wt%, the firing efficiency of the green pellets in the calcining furnace cannot be increased, and the raw pellets cannot be calcined into high-strength calcined agglomerates in a short time. In addition, if the amount of coke powder to be coated exceeds 4.0wt%, the temperature of the green pellets during calcination becomes too high, and the structure of the calcined agglomerates becomes dense and has few pores, and at the same time, it becomes less reducible. This is because the structure becomes a melt-type structure with poor quality, that is, a structure containing many secondary hematite and rectangular calcium ferrite. In this invention, the particle size of the raw pellets is preferably about 3 to 13 mm, as in the conventional method. The reason is as follows. That is, if the particle size of the green pellets is less than 3 mm, the high-temperature combustion gas generated by the combustion of coke breeze will be inhibited from smoothly passing through the layer of green pellets when the green pellets are fired in the firing furnace. As a result, the production rate of calcined agglomerate ore decreases. In addition, since fired agglomerate ore in the form of single fired pellets has a particle size of less than 3 mm, when such small particle size calcined agglomerate is charged into a blast furnace, it is difficult for the reducing gas to flow smoothly. impede passage. As a result, shelving and slipping occur within the blast furnace, resulting in the problem of unstable blast furnace operation. On the other hand, if the particle size of the green pellets exceeds 13 mm, the resistance to impact becomes weak, resulting in the problem of the green pellets collapsing when they are transferred to a kiln. Furthermore, in a short firing time as in this process, heat is not transmitted to the core of the raw pellets, and high quality fired agglomerates cannot be obtained due to insufficient heat. Furthermore, since the particle size of each fired pellet of fired agglomerate ore exceeds 13 mm, when such large fired agglomerate ore is charged into a blast furnace, the reducing gas reaches the center of the fired agglomerate ore. It takes a long time to penetrate. As a result, the reducibility of the calcined agglomerate ore in the blast furnace deteriorates, and unreduced cores remain, resulting in the problem that the high temperature properties of the calcined agglomerate ore under load deteriorate. [Example] Fine iron ore with the particle size composition shown in Table 1 and the chemical composition shown in Table 2, and coarse iron ore with the particle size structure shown in Table 3 and the chemical composition shown in Table 4, Fifth
Shown in the table. By using the formulation within the scope of this invention, adding and mixing 2.7 wt% of quicklime with the particle size structure shown in Table 6 as a solvent and binder, and granulating the resulting mixture, The pellets were formed into raw pellets having a particle size distribution shown in Table 7 and a water content of 8 to 9 wt%. For comparison, the same fine iron ore was used in a formulation outside the scope of this invention, also shown in Table 5, and similarly formed into green pellets.

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[Table] Next, 3.5 wt % of coke powder having the particle size composition shown in Table 8 was added to the raw pellets for granulation, and the raw pellets were coated with the coke powder.

[Table] Then, raw pellets are charged to a thickness of 400 mm onto the grate of an endless moving grate type kiln, and the raw pellets are sequentially moved through the drying zone, ignition zone, and combustion zone of the kiln, and are baked into agglomerates. Fired into ore. and,
The large blocks of calcined agglomerate ore thus obtained are discharged from the downstream end of the kiln, and after being crushed by a crusher, the calcined agglomerate pieces under the sieve with a particle size of less than 3 mm are passed through a screen. In this way, calcined agglomerate in the form of a lump with a maximum particle size of about 50 mm, in which a plurality of calcined pellets are combined, and calcined agglomerate in the form of a single calcined pellet, with a particle size of about 3 to 13 mm, are produced. Ta. The reduction rate and falling strength of the calcined agglomerates produced as described above were as shown in Table 9.

〔Effect of the invention〕

According to this invention, by selecting the particle size of the powdered iron ore used and its blending ratio, it is possible to easily produce calcined agglomerate ore having a high reduction rate and falling strength.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the blending ratio of fine iron ore with a particle size of 44 μm or less in the used fine iron ore with a particle size of 8 mm or less and the reduction rate of the obtained calcined agglomerate; The figure is also a graph showing the relationship between the blending ratio of fine iron ore with a grain size of 44 μm or less and the falling strength of the obtained calcined agglomerate ore.

Claims (1)

[Scope of Claims] 1 A mixture of powdered iron ore and a solvent is added and mixed to granulate to form raw pellets, the obtained raw pellets are coated with coke powder, and the raw pellets are transferred to an endless moving grate. Charged into a kiln and fired continuously, thus continuously producing fired agglomerate ore.
In the method for producing calcined agglomerate ore, the powdered iron ore has a particle size of 44 μm or less, which is 10 to 10 μm.
A method for producing calcined agglomerate ore, characterized by using powdered iron ore having a composition of 80wt% and the remainder having a grain size of more than 44μm.