JPS63149335A - Production of burnt agglomerated ore - Google Patents

Abstract

PURPOSE:To improve the reducing ratio and the dropping strength for burnt agglomerated ore by making raw material fine powdery iron ore of specific grain size at the time of producing green pellet for raw material of burnt agglomerated ore by coating powdery coke on the surface, after pelletizing by adding flux to the fine powdery iron ore. CONSTITUTION:At the time of producing the burnt agglomerated ore as the raw material for blast furnace or the raw material for directly reducing iron- making by an endlessly moving grate type burning furnace, the fine powdery iron ore having grain size distribution of 10-80% of <44mum grain size and the remaining part of >=44mum grain size is used as the raw material. Flux, such as lime, slaked lime, limestone, bentonite, dolomite, water granulated blast furnace slag, etc., is added to this, and kneaded together with water and pelletized into the green pellet having 3-13mm grain size and coated by 2.5-4.0wt% ratio of powdery coke on the surface. By burning this green pellet in the endless moving grate type burning furnace, the burnt agglomerated ore having excellent dropping strength and reducing ratio is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for producing calcined agglomerates suitable as raw materials for blast furnaces or directly reduced iron.

[Prior art and its problems]

Calcined agglomerate, which is made by pelletizing powdered iron ore and calcining it, is known as a raw material for blast furnaces or direct reduction iron manufacturing.
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 limestone, bentonite, granulated blast furnace slag, dolomite, etc. is added to powdered iron ore with a particle size of about 8 or less, and CaO/5i02 in the calcined agglomerated ore is added. The value of is 1.0 to 2.5
Add to the desired amount and mix with a mixer. Then, the obtained mixture is supplied to a disk-shaped first granulator, water is added thereto, and the υ mixture is granulated by a tenth granulator to form raw pellets with a particle size of, for example, about 3 to 13 m. Form into. Next, the obtained raw pellets are fed to a second disc-shaped granulator, and the steps 2.5 to 4. Approximately Owt% of coke powder is added and the raw pellets are further granulated by a second granulator, thereby preparing green pellets whose surfaces are coated with coke powder.

The green pellets thus obtained are charged into an endless moving grate type kiln, and the layer of the charged green pellets is placed on the grate of the kiln, and then placed in the drying zone of the kiln.
Pass through the ignition zone 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 green pellets from above to dry the green pellets. In the ignition zone, high-temperature combustion gas is blown into the layer of dried green pellets from above to ignite the coke powder on the surface of the green pellets. In the combustion zone, the hot combustion gas produced by the combustion of coke breeze is sucked downward through the green pellet bed to heat the green pellets to the calcination temperature. The green pellets are calcined by heating in a calcining zone into large block-like masses of calcined agglomerates consisting of calcined pellets bound by at least one of calcium ferrite and slag formed on their surfaces.

The calcined agglomerates in the form of large blocks thus obtained are discharged from the downstream end of the calciner, crushed by a crusher, and then sieved by a screen to remove particles with a particle size of less than 31. The calcined agglomerate pieces are removed, and the calcined agglomerate ore in the form of a plurality of calcined pellets combined has a maximum particle size of about 50 pieces, and the single calcined pellet has a particle size of about 3 to 13 pieces. Calcined agglomerate ore is produced.

The calcined agglomerate ore produced as described above has excellent reducibility, since it mainly contains a large amount of fine calcium ferrite and fine hematite, which have excellent reducibility. In addition, not only in the case of a lump-like shape in which multiple fired pellets are combined, but also in the case of a single fired pellet, it has an irregular shape, so when charged into a blast furnace, Since the reducing gas does not flow biasedly toward the center of the blast furnace, and gaps are formed between the fired agglomerated ores, smooth passage of the reducing gas is not obstructed. Furthermore, even if it collapses due to impact or the like during transportation, the calcined agglomerate, which is a lump of a plurality of calcined pellets combined, will simply separate into a single calcined pellet, so it can be used without any problem.

However, conventionally, powdered iron ore has a particle size of 0.5
Because a relatively coarse powdered iron ore was used with a composition of 30 to 70 wt% of particles below A and the remainder of particles with a particle size of more than 0.5 mm,
When fine iron ore is formed into pellets and fired, many macropores are not formed in the resulting fired agglomerate ore, resulting in a reduction rate of the fired agglomerate ore. In addition, when adding a solvent to fine iron ore and granulating it to form raw pellets, strong and dense raw pellets cannot be obtained.
The falling strength of the resulting calcined agglomerates is also low.

[Purpose of the invention]

In view of the above-mentioned current situation, this invention involves adding a solvent to fine iron ore, forming the mixture into raw pellets, coating the obtained raw pellets with coke powder, and firing the raw pellets using an endless moving grate. When charging into a furnace to continuously produce fired iron ore, the reduction rate and falling strength of the resulting fired iron ore can be adjusted by selecting the particle size of the fine iron ore used and its blending ratio. The purpose is to improve

[Summary of the invention]

This invention involves adding a solvent to powdered iron ore, granulating a mixed mixture to form raw pellets, coating the obtained raw pellets with coke powder, and placing the raw pellets in an endless moving grate type kiln. In a method for producing calcined agglomerate ore in which the iron ore powder is charged, continuously calcined, and smelt to continuously produce calcined agglomerate ore, the iron ore powder has a particle size of 44 μm11. The bottom is 1
It is characterized by using powdered iron ore having a composition of 0 to 80 wt% and the remainder having a particle size of more than 44 μm.

[Structure of the invention]

Hereinafter, the method for producing calcined agglomerate ore of the present invention will be described in detail.

The present inventors added a solvent to powdered iron ore, formed the mixture into green pellets, coated the obtained green pellets with coke powder, and charged the green 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 fired agglomerated ore obtained when the iron ore powder is 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, when a solvent is added to powdered iron ore and granulated to form green pellets, strong and dense green pellets are obtained, so it is expected that the falling strength of fired agglomerate ore will be increased. .

Therefore, we conducted an experiment in which the particle size and blending ratio of the fine iron ore used were varied, and green pellets were formed to produce fired agglomerate ore. I checked the strength.

As a result, it was found that 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 over 44 μm, the reduction rate and falling strength of calcined agglomerate ore could be greatly improved. .

Figure 1 shows the blending ratio of iron ore powder with a particle size of 44 μml J in the powdered iron ore with a particle size of 8 Is or less used.

Figure 2, a graph showing the relationship between the reduction rate of the obtained calcined agglomerate ore, also shows 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. This is a graph showing.

As shown in Figure 1, as the blending ratio of fine iron ore with a grain size of 44 μm or less increases, the number of macropores in the obtained calcined agglomerate increases, so the reduction rate of the calcined agglomerate increases. When the blending ratio is 10wt or more, the reduction rate is as high as 75% or more. As shown in Figure 2, particle size 4
When the blending ratio of fine iron ore/stone of 4 μm or less is 10 wt % or more, the green pellets have sufficient density and strength, so the drop strength of the obtained calcined agglomerates is as high as 85 cm. However, if the blending ratio exceeds 80wt%, the raw pellets tend to cause persing during ignition, and the air permeability within the layer deteriorates, requiring a longer drying time, and when heated excessively. Because it becomes easier to dissolve,
A vitreous slag is formed and the falling strength is rapidly reduced.

Therefore, in order to achieve a reduction rate of 75% or more and a drop strength of 85 cm or more for calcined agglomerate ore, the grain size of 44 μm or less must be
Powdered iron ore should be used with a composition of 80 wt %, the balance being 80 wt % with a particle size of more than 44 μm and no more than 8 μm.

In this invention, as shown in μ, the reduction rate and falling strength of the calcined agglomerated ore are 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. This is a significant improvement.

In this invention, the amount of coke powder coated on the green pellets is 2.5-4. It is preferable to set it as Qwt%.゛This is because if the amount of coated coke powder is less than 2.5 wt%, the firing efficiency of the green pellets in the firing furnace cannot be increased, and the raw pellets cannot be fired into high-strength fired agglomerates in a short time. In addition, if the amount of coke powder to be coated exceeds 4.0 wt%, the temperature of the green pellet during firing becomes too high, and the structure of the fired agglomerate becomes dense and has few pores. This is because the structure becomes a melt-type structure with poor reducibility, that is, a structure containing many secondary hematite and rectangular calcium ferrite.

In this invention, it is preferable that the particle size of the raw pellets is about 3 to 13 m, similar to the conventional method. The reason is as follows. That is, if the particle size of the green pellets is less than 3g1i, the high temperature combustion gas generated by the combustion of coke breeze during firing of the green pellets in the firing furnace will be inhibited from smoothly passing through the layer of green pellets. , a problem arises in which the production rate of calcined agglomerate ore decreases. In addition, fired agglomerate ore in the form of a single fired pellet has a particle size of less than three words, so when calcined agglomerate with such a small particle size is charged into a blast furnace, the reduction gas Obstructs smooth passage. As a result, shelf suspension and slippage 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 pellet exceeds 131, the resistance to impact becomes weak, resulting in the problem that the green pellet collapses when it is transferred to a firing furnace. Furthermore, in a short firing time as in this process, heat is not transmitted to the core of the green pellets, and high quality fired agglomerates cannot be obtained due to lack of heat. Furthermore, the particle size of each fired pellet of fired agglomerate is also 131EI.
Therefore, when calcined agglomerates made of such large calcined pellets are charged into a blast furnace, it takes a long time for the reducing gas to penetrate to the center of the calcined agglomerates. As a result, the reducibility of the calcined agglomerate ore in the blast furnace is poor, and unreduced cores remain, resulting in the problem that the high temperature properties of the calcined agglomerate ore under load are deteriorated.

〔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, are added to the fifth coating. When used in the formulation shown within the scope of this invention, 2.7 wt % of quicklime having the particle size structure shown in Table 6 is added as a solvent and a binder, and the resulting mixture is granulated. Therefore, the water content is 8 to 9 and has the particle size distribution shown in the seventh layer.
wt % green pellets. 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.

1"5 (-, CH) Table 4 Table 5 Table 6 (wt%) Table 7 Next, 3.5 wt% of coke powder having the particle size composition shown in Table 8 was added to the raw pellets. The raw pellets were granulated and coated with coke powder.

Then, place the raw pellets on the grate of the endless moving grate kiln 4001i1! The raw pellets were charged to a thickness of 100 mm, and then moved sequentially through the drying zone, ignition zone, and firing zone of the kiln, and were fired into fired agglomerates. The large block-shaped calcined agglomerate ore obtained in this way is 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 separated by a screen. It is removed and smelt to produce calcined agglomerate in the form of a lump with a maximum grain size of about 50 grains, in which multiple calcined pellets are combined, and calcined agglomerate in the form of a single calcined pellet with a grain size of 3 to 13 m. manufactured.

The reduction rate and falling strength of the calcined agglomerates produced as described above were as shown in Table 9.

Table 9 As shown in Table 9, in the present invention &1 to 5, which used powdered iron ore with a composition within the scope of the present invention, both the reduction rate and the falling strength of the calcined agglomerates were high. Ta.

On the other hand, in Comparative Examples & 6 and 8, which used powdered iron ore with a composition outside the scope of the present invention, the reduction rate or at least the falling strength of the calcined agglomerates was lower than that of the present invention. Ta.

〔Effect of the invention〕

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

[Brief explanation of the drawing]

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 words or less and the reduction rate of the obtained calcined agglomerate. Similarly, Figure 2 is a graph showing the relationship between the blending ratio of fine iron ore having a grain size of 44 μm or less and the falling strength of the obtained calcined agglomerates. Figure 1G)

Claims (1)

[Claims] A mixture of powdered iron ore and a solvent is added and mixed and granulated to form raw pellets, the obtained raw pellets are coated with coke powder, and the raw pellets are fired in an endless moving grate. In a method for producing calcined agglomerate ore, in which the iron ore powder is charged into a furnace and continuously calcined to continuously produce calcined agglomerate ore, the iron ore powder has a particle size of 44 μm or less of 10 to 80 w.
A method for producing calcined agglomerate ore, characterized in that powdered iron ore is used in a composition in which the remainder consists of t% and grain size of more than 44 μm.