JPH0430446B2 - - 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, powdered iron ore with a particle size of about 8 mm or less is mixed with quicklime, slaked lime, limestone, bentonite, granulated blast furnace slag, dolomite, etc. as a solvent, and the value of CaO/SiO ₂ in the calcined agglomerate ore is about 1.0 to 2.5. Add and mix with a mixer. Then, the obtained mixture is supplied to a disk-type first granulator, water is added, and the mixture is granulated by the first granulator to form raw pellets with a particle size of, for example, about 3 to 13 mm. Shape. 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, igniting 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. Incidentally, among the solvents added to powdered iron ore, quicklime acts as a binder when powdered iron ore is granulated into green pellets. For this reason, quicklime is always added as mentioned above, but in the past, a large amount of 3.0 to 10.0 wt% was added to powdered iron ore, so the increased cost of quicklime could not be ignored, and the made the price high. [Purpose of the Invention] In view of the above-mentioned current situation, the present invention has been developed by granulating a mixture of powdered iron ore with quicklime and other solvents, forming raw pellets, and adding powder to the obtained raw pellets. By selecting the amount of quicklime added to powdered iron ore when coating coke and charging the green pellets into an endless moving grate type kiln to continuously produce burned agglomerate ore. ,
The purpose of this invention is to make it possible to reduce the manufacturing cost of calcined agglomerate ore without lowering the product yield of calcined agglomerate ore. [Summary of the Invention] This invention is based on the invention, in which quicklime and other solvents are added to powdered iron ore, and the CaO/SiO ₂ value in the calcined agglomerate ore is 1.0.
The mixture was added and mixed so as to have a concentration of ~2.5, and the mixture was granulated using a disc-type granulator to form raw pellets, the resulting raw pellets were coated with coke powder, and the raw pellets were made into endless pellets. A method for producing calcined agglomerate ore, in which the calcined agglomerate ore is continuously produced by charging into a moving grate calcining furnace and continuously calcining the calcined ore. Among the solvents, the additive of the quicklime to the powdered iron ore is 1.0 to 2.5 wt%. [Structure of the Invention] Hereinafter, the method for producing calcined agglomerates of the present invention will be described in detail. The present inventors added quicklime and other solvents to powdered iron ore, granulated the mixture to form raw pellets, coated the obtained raw pellets with coke powder, and made the raw pellets into endless powder. In order to reduce the manufacturing cost of calcined agglomerate ore when it is charged into a moving grate kiln and continuously produce calcined agglomerate ore, we have conducted repeated research on the amount of quicklime added to powdered iron ore. Conventionally, a large amount of quicklime (3.0 to 10.0wt%) was added to powdered iron ore.The reason is that when powdered iron ore is granulated into raw pellets, it is necessary to add a large amount of quicklime to enhance the granulation effect. This is because it was said that there was. However, as research progressed, it was discovered that a drum-type granulator was used to granulate powdered iron ore, and that not only quicklime and other solvents but also coke powder was added to the powdered iron ore. Regardless of the case of granulation, a disk-type granulator is used to granulate powdered iron ore, and coke powder is coated on the surface of raw pellets after granulation of powdered iron ore. When granulating into raw pellets by adding only quicklime and other solvents, the granulation properties of the raw pellets are good, so even if the amount of quicklime added to powdered iron ore is small, it can be easily powdered. It was discovered that iron ore could be formed into raw pellets. Therefore, it is possible to reduce the manufacturing cost of calcined agglomerated ore. However, in that case, there is a risk that the product yield and falling strength of the calcined agglomerate ore will be low due to the small amount of quicklime added. Therefore, we changed the amount of quicklime added to powdered iron ore, added quicklime and other solvents to powdered iron ore, formed raw pellets through granulation, and turned the raw pellets into calcined agglomerates. A firing production experiment was conducted to investigate the relationship between the amount of quicklime added and the product yield and falling strength of fired agglomerate ore. As a result, the amount of quicklime added to powdered iron ore was reduced to 1.0
It has been found that by setting the content to 2.5 wt%, the product yield and falling strength of calcined agglomerates can be maintained sufficiently high. Figure 1 is a graph showing the relationship between the amount of quicklime added to powdered iron ore and the yield of the obtained calcined agglomerates, and Figure 2 is a graph showing the relationship between the amount of quicklime added to powdered iron ore and the yield of the obtained calcined agglomerates. It is a graph which shows the relationship with the falling strength of calcined agglomerate ore. In addition, the particle size of powdered iron ore is approximately 8 mm or less,
The particle size of the raw pellets was approximately 3 to 13 mm, and the amount of coke powder added was 3.5 wt%. As shown in Figure 1, the product yield of calcined agglomerate ore increases as the amount of quicklime added to fine iron ore increases, and when the addition amount is 1.0wt% or more, the product yield exceeds 75%. It's getting old. When the amount of quicklime added exceeds 2.5wt%, the product yield is 85%.
However, the degree of increase is small and the disadvantage of increasing the amount of quicklime added increases. As shown in Figure 2, the falling strength of calcined agglomerates increases as the amount of quicklime added to powdered iron ore increases, and when the amount added is 1.0wt% or more, the falling strength is 85% or more. It's getting old. When the amount of quicklime added exceeds 2.5 wt%, the drop strength increases to more than 90%, but the degree of increase is similarly small. Therefore, the product yield of calcined agglomerate ore should be increased to 75% or more.
In order to maintain the fall strength at 85% or more and to reduce the amount of quicklime added to powdered iron ore, the amount of quicklime added to powdered iron ore should be 1.0 to 2.5 wt%. In this invention, as described above, the amount of quicklime added to powdered iron ore is set at 1.0 to 2.5 wt%, and the amount of quicklime added is increased from the conventional amount while maintaining the finished product yield and falling strength of the calcined agglomerates at a high level. It is to make it less. It goes without saying that other solvents such as limestone are added to the powdered iron ore together with quicklime to adjust the base so that the value of CaO/SiO ₂ in the calcined agglomerated ore is 1.0 to 2.5. In this invention, the particle size of the powdered iron ore used is preferably about 8 mm or less, as in the conventional method.
This is because fine iron ore with a particle size of more than 8 mm can be used as is without being converted into calcined agglomerate minerals, and it is iron ore fines with a particle size of 8 mm or less that needs to be converted into calcined agglomerate minerals. 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 means that the amount of coke powder to be coated is
If the amount is less than 2.5 wt%, the firing efficiency of raw pellets in the kiln cannot be increased, and the raw pellets cannot be fired into high-strength fired agglomerates in a short time. 4.0wt%
If the temperature exceeds , the temperature of the raw pellets during firing becomes too high, and the structure of the fired agglomerate becomes dense and has few pores, and at the same time it becomes a molten type structure with poor reducibility, i.e., secondary hematite or strip-shaped structure. This is because the tissue is rich in 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. It has also been observed that during the calcination process, the pellets are cooled before the center temperature reaches a sufficiently high temperature, resulting in a deterioration in quality, especially in the center. 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 a problem that the high temperature characteristics 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, Fine iron ore is used at a ratio of 40 wt% and coarse iron ore is used at a ratio of 60 wt%, and quicklime having a particle size composition shown in Table 5 is added as a solvent and a binder in an amount within the range of this invention, and other Limestone was added as a solvent to adjust the basicity so that the CaO/SiO ₂ value in the calcined agglomerate was 1.0 to 2.5. For comparison, quicklime was added to powdered iron ore in an amount outside the scope of the present invention, and limestone was similarly added to adjust the basicity. Then, after mixing the powdered iron ore to which quicklime and limestone have been added, it is granulated using a disk-type granulator to obtain a powder having a water content of 8 to 9 wt and having a particle size distribution shown in Table 6. % raw pellets.

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[Table] Next, 3.5 wt % of coke powder having the particle size composition shown in Table 7 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. is removed, and thus the maximum particle size of multiple calcined pellets combined is approximately
Calcined agglomerates in the form of blocks of 50 mm and calcined agglomerates in the form of single calcined pellets with grain sizes of approximately 3 to 13 mm were produced. Table 8 shows the product yield and falling strength of the calcined agglomerates produced as described above, as well as the amount of quicklime added to the fine iron ore.

〔Effect of the invention〕

According to this invention, by selecting the amount of quicklime to be added to fine iron ore, it is possible to inexpensively produce calcined agglomerate ore without reducing the product yield.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the amount of quicklime added to powdered iron ore and the yield of the obtained calcined agglomerates, and Figure 2 is a graph showing the relationship between the amount of quicklime added to powdered iron ore and the yield of the obtained calcined agglomerates. It is a graph which shows the relationship with the falling strength of calcined agglomerate ore.

Claims (1)

[Claims] 1. Adding quicklime and other solvents to powdered iron ore,
The mixture was added and mixed so that the CaO/SiO ₂ value in the calcined agglomerate was 1.0 to 2.5, and the mixture was granulated using a disk-type granulator to form raw pellets. A method for producing calcined agglomerate ore, which comprises coating raw pellets with coke powder, charging the raw pellets into an endless moving grate type kiln, and continuously calcining them, thereby continuously producing calcined agglomerate ore. Production of calcined agglomerate ore, characterized in that, among the quicklime and other solvents added to the iron ore powder, the amount of the quicklime added to the iron ore powder is 1.0 to 2.5 wt%. Method.