JPH0425327B2 - - 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, conventional calcined agglomerates have _SiO2 of 5.5
Since it contained about 6.0wt%, the reduction rate was 60~
The reduction rate was low at around 70%, and the reduction powdering rate was high at around 35-45%. In addition, calcined agglomerates have _SiO2 of 5.5~
Since it contains about 6.0 wt%, the slag ratio in the blast furnace is high, for example, 360 kg/ton, and the fuel ratio (or coke ratio) is also high, for example, 520 kg/ton. [Object of the invention] In view of the above-mentioned current situation, the present invention has been developed by adding a solvent to powdered iron ore, granulating a mixed mixture to form raw pellets, coating the obtained raw pellets with coke powder, The purpose is to improve the reduction rate and reduction powdering rate of calcined agglomerate ore when the raw pellets are charged into an endless moving grate type kiln to continuously produce calcined agglomerate ore. be. [Summary of the Invention] This invention involves adding a solvent to powdered iron ore, granulating the mixture in a disc-type granulator to form raw pellets, and coating the obtained raw pellets with coke powder. , in a method for producing fired agglomerate ore, in which the raw pellets are charged into an endless moving grate kiln and fired continuously, thus continuously producing fired agglomerate ore, as the powdered iron ore, in the calcined agglomerate ore.
It is characterized by the use of powdered iron ore containing 0.5 to 5.0 wt% of SiO ₂ . [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, granulated the mixed mixture to form raw pellets, coated the obtained raw pellets with coke powder, and fired the raw pellets using an endless moving grate. Charge it into the furnace,
In order to continuously produce calcined agglomerate ore, we have conducted intensive research to improve the reduction rate and reduction powdering rate of calcined agglomerate ore. Conventionally, fired agglomerate ores contained 5.0 to 6.0 wt% of SiO ₂ because, when raw pellets were fired, SiO ₂ in fine iron ore formed slag with CaO in the solvent. In order to combine powdered iron ores and form them into agglomerates, the SiO ₂ content in the calcined agglomerates must be approximately
This is because it was believed that it was necessary for powdered iron ore to contain SiO ₂ at a level of 5.0 wt% or more. However, as research progressed, it was discovered that a drum-type granulator was used to granulate powdered iron ore, and that powdered iron ore was granulated by adding not only a solvent but also coke powder. In the case of raw pellets,
A disk-type granulator is used to granulate the iron ore powder, and coke powder is coated on the surface of the iron ore powder after granulation, and only a solvent is added to the iron ore powder. In the case of raw pellets obtained by
It has good granulation properties and is formed into a good spherical lump, so even if the SiO ₂ content in the iron ore powder is low, the SiO ₂ in the iron ore powder is mixed with the solvent in the iron ore when the raw pellets are fired. It was found that by forming slag with CaO, fine iron ore could be bonded together and agglomerated well. Therefore, it becomes possible to improve the reduction rate and reduction powdering rate of the calcined agglomerate ore. Therefore, the particle size of formulations with different SiO ₂ contents is approximately 8
Experiments were conducted to produce calcined agglomerates by varying the SiO ₂ content using raw pellets prepared from each type of fine iron ore with a diameter of less than mm. Then, the SiO ₂ content, reduction rate, reduction powdering rate, product yield, and falling strength in the calcined agglomerate ore were investigated. As a result, the SiO ₂ content in calcined agglomerate ore was reduced to 0.5~
It was found that when the content is 5.0 wt%, the reduction rate and reduction powdering rate of calcined agglomerate ore can be significantly improved, and the product yield and falling strength are not reduced. Figure 1 is a graph showing the relationship between the SiO ₂ content and reduction rate in the obtained calcined agglomerate, and Figure 2 is a graph showing the relationship between the SiO ₂ content and reduction rate. , FIG. 3 is a graph showing the relationship between SiO ₂ content and fall strength, and FIG. 4 is a graph showing the relationship between SiO 2 content and fall strength.
It is a graph showing the relationship between SiO ₂ content and product yield. As shown in Figure 1, the reduction rate of calcined agglomerates decreases as the SiO ₂ content in the calcined agglomerates increases, but when the SiO ₂ content is 0.5 to 5.0 wt%
Within the range, it is high at over 80%. When the SiO ₂ content exceeds 5.0 wt%, the reduction rate drops rapidly below 80%. The reduction powdering rate of calcined agglomerate ore is
As shown in Figure 2, SiO ₂ in the calcined agglomerates
When the SiO 2 content is in the range of 0.5 to 5.0 wt%, it is less than 30%, but when the SiO ₂ content exceeds 5.0 wt%, the reduction powdering rate exceeds 30%. On the other hand, as shown in Figure 3, the fall strength of calcined agglomerates increases as the SiO ₂ content in the calcined agglomerates increases, but when the SiO ₂ content is 0.5
Even within the range of ~5.0wt%, the drop strength is approximately 85% or more and is sufficiently maintained. As shown in Figure 4, the product yield of calcined agglomerates increases as the SiO ₂ content in the calcined agglomerates increases, but when the SiO ₂ content is in the range of 0.5 to 5.0 wt%. The product yield is approximately 75% or more, which is maintained satisfactorily. In addition, in the above, the lower limit of SiO ₂ content in calcined agglomerate ore is set to 0.5wt% because the SiO ₂ content is
This is because it is almost difficult to obtain calcined agglomerates with a content of less than 0.5 wt% from the viewpoint of the quality of fine iron ore, and less than 0.5 wt% is practically meaningless. Therefore, in order to achieve a reduction rate of 80% or more and a reduction powdering rate of 30% or less of calcined agglomerate ore without reducing the product yield and falling strength of the calcined agglomerate ore, it is necessary to As iron ore, in calcined agglomerate ore
Powdered iron ore blended to have a SiO ₂ content of 0.5 to 5.0 wt% should be used. In this invention, as described above, as the fine iron ore used for calcination, the fine iron ore blended so that the SiO ₂ content in the calcined agglomerate is 0.5 to 5.0 wt% is used. This greatly improves the reduction rate and reduction powdering rate of agglomerate ore. 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
This is because if the amount is less than 2.5wt%, the firing efficiency of the raw pellets in the kiln cannot be increased, and the raw pellets cannot be fired into high-strength fired agglomerates in a short time, and the amount of coke powder to be coated is 4.0wt. %, the temperature of the raw pellets during calcination becomes too high, and the structure of the calcined agglomerates becomes dense and has few pores. This is because the structure contains many rectangular calcium ferrites. In this invention, the particle size of the powdered iron ore used is preferably about 8 mm or less, as in the prior art.
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 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 in 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. Not only that, the grain size of each fired pellet of fired agglomerate ore exceeds 13 mm, so when such large fired pellets of fired agglomerate ore are charged into a blast furnace, it is difficult to reach the center of the fired agglomerate ore. It takes a long time for the reducing gas to penetrate. As a result, the reducibility of the calcined agglomerate in the blast furnace deteriorates, and unreduced cores remain, resulting in
A problem arises in that the high temperature characteristics under load deteriorate. [Example] Five brands of fine iron ore A~ having the particle size composition shown in Table 1 and the chemical composition shown in Table 2
According to the present invention, E was blended in an appropriate ratio as shown in Table 3 so that the SiO ₂ content in the calcined agglomerate was within the range of 0.5 to 5.0 wt%. For comparison, the calcined agglomerates were blended in appropriate proportions as shown in Table 3 so that the SiO ₂ content was more than 5.0 wt%.

【table】

【table】

【table】

[Table] Next, 1.0 to 2.7 wt% of quicklime with the particle size composition shown in Table 4 was added and mixed as a solvent and binder to the powdered iron ore of these formulations, and the particle size shown in Table 5 was added for basicity adjustment. Using limestone of composition,
The basicity was adjusted to a range of 1.8-2.2. The mixture obtained here is granulated using a disk-type granulator, and the mixture has a particle size distribution shown in Table 6 and has a water content of 8 to 8.
It was formed into 9wt% raw pellets.

【table】

【table】

[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 firing 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, thus reducing the maximum particle size of multiple calcined pellets combined.
Calcined agglomerates in the form of blocks of 50 mm and calcined agglomerates in the form of single calcined pellets with grain sizes of 3 to 50 mm were produced. SiO ₂ in the calcined agglomerate produced as above
Table 8 shows the content and reduction rate of calcined agglomerates.

【table】

[Table] As shown in Table 8, the
Invention No. whose SiO ₂ content is within the scope of this invention.
In Nos. 1 to 6, the reduction rate and reduction pulverization rate of the calcined agglomerates are good, and the reduction rate and reduction pulverization rate are improved without lowering the drop strength and product yield. On the other hand, in Comparative Examples Nos. 7 and 8, in which the SiO ₂ content in the calcined agglomerates is outside the range of the present invention, although the falling strength and product yield of the calcined agglomerates are good, The reduction rate and reduction powdering rate have deteriorated. [Effects of the Invention] According to the present invention, the reduction rate and reduction powdering rate of calcined agglomerated ore can be easily improved.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the SiO ₂ content and reduction rate in the obtained calcined agglomerate, and Figure 2 is a graph showing the relationship between the SiO ₂ content and reduction rate. , FIG. 3 is a graph showing the relationship between SiO ₂ content and fall strength, and FIG. 4 is a graph showing the relationship between SiO 2 content and fall strength.
It is a graph showing the relationship between SiO ₂ content and product yield.

Claims (1)

[Scope of Claims] 1 A mixture of powdered iron ore and a solvent is added and mixed and granulated using a disk-type granulator to form raw pellets, and the resulting raw pellets are coated with coke powder,
A method for producing fired agglomerate ore, in which the raw pellets are charged into an endless moving grate kiln and fired continuously, thereby continuously producing fired agglomerate ore, wherein the iron ore powder is a calcined agglomerate. SiO ₂ in agglomerate ore
A method for producing calcined agglomerate ore, characterized by using powdered iron ore blended to have a content of 0.5 to 5.0 wt%.