JPH0437146B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a method of coating raw pellets with coke powder used in the production of calcined agglomerates as raw materials 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 applied to fine iron ore with a particle size of about 8 mm or less, and the 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 calcined agglomerate pieces under the sieve 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 ore produced in the above manner had excellent reducibility, since it mainly contained a large amount of fine calcium ferrite and fine hematite, both of which had excellent reducibility. 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, since the surface of the raw pellets is coated with coke powder using a granulator as described above, the following problems arise. In other words, when trying to coat the surface of raw pellets with coke powder using a granulator, the raw pellets tend to stagnate due to the difference in particle size; the larger the particle size, the shorter the residence time in the granulator. Because of the difference in time, the coating weight of coke powder per unit weight of raw pellets after coating differs depending on the particle size of the raw pellets, and the coating amount varies. , resulting in insufficient coke powder coverage. If the amount of coke powder covering the raw pellets with large particle sizes is large, when the raw pellets are charged into a kiln and fired, the lower layer of the raw pellet layer where large raw pellets are likely to be unevenly distributed will be affected. Since the firing of some parts is not carried out well due to lack of heat, in the case of coarse pellets, the effect of the size is added, and the temperature in the center of the pellet does not rise above the 1200℃ required for firing and agglomeration. This remains as a burnt part, leading to a decrease in the yield of the resulting burnt agglomerate ore and to a decrease in production rate. [Purpose of the Invention] In view of the above-mentioned current situation, the present invention aims to solve the problem of particle size when coating the surface of green pellets for calcined agglomerates with coke powder using a granulator. The object of the present invention is to provide a method for coating coke powder, which makes it possible to improve the product yield of calcined agglomerate ore by coating large green pellets well with coke powder. [Summary of the Invention] This invention provides raw pellets for calcined agglomerates obtained by adding and mixing a solvent to powdered iron ore and granulating it by a disk-type first granulator. ~4.0wt
% of coke powder is added and granulated by a disk-type or drum-type second granulator, thereby coating the surface of the raw pellets with the coke powder. The raw pellets are divided into a plurality of groups according to the size of the particles, and the amount of coke powder added is weighted so that the raw pellets in the group with a larger particle size are added with a larger amount of coke powder. This method is characterized by adding the coke powder to the pellets and coating them. [Structure of the Invention] The method of coating green pellets for calcined agglomerates with coke powder according to the present invention will be described in detail below. FIG. 1 is an explanatory diagram showing one embodiment of the coating method of the present invention. 1 is a drum mixer, 2 is a disk-type first granulator, 3a and 3b are disk-type second granulators, and 4 is a screen. In this invention, the raw pellets obtained by the first granulator 2 are divided into, for example, two groups depending on the particle size, and the amount of coke powder added to the raw pellets of the group with the larger particle size is determined. By adding coke powder in the second granulators 3a and 3b and granulating it by weighting the addition amount so that To improve the quality of the pellets, the raw pellets are coated with coke powder. Powdered iron ore having a particle size of about 8 mm or less, which is a raw material for raw pellets, and a solvent are supplied to a drum mixer 1 and mixed. The obtained mixture is supplied to the first granulator 2 and is granulated by adding water to form raw pellets having a particle size of, for example, about 3 to 13 mm. Next, the obtained raw pellets are fed to the screen 4, where they are sieved into large raw pellets with a particle size of more than 7 mm and less than 13 mm, and small raw pellets with a particle size of more than 3 mm and less than 7 mm. It is sorted into pellets. Next, the raw pellets in the large particle size group are sent to one side 3a of the second granulator, and the raw pellets in the small particle size group are sent to the other side 3b of the second granulator.
where coke powder is added separately.
By granulating, the surface is coated with coke powder. In the granulators 3a and 3b, the amount added to the raw pellets of the large particle group is equal to that of the small group of particles within the range where the amount added to the whole raw pellets is maintained at a predetermined range of 2.5 to 4.0 wt%. Coke powder is added with a weight that is greater than the amount added to raw pellets. The weight of the addition amount is
For example, when adding 3.5wt% of coke powder to the raw pellets as a whole, the amount added to the raw pellets with large particle size is 4.0 to 4.5wt%, and so on.
It is sufficient to add about ~1.0wt%. Then, since the raw pellets in the large particle size group have a large amount of coke powder added, the coke powder sufficiently adheres to the surface by granulation in the granulator 3a, and the pellets are well coated. In this case, if necessary, approximately 0.5 to 1.0 wt% of binder may be added in advance to the coke powder used to coat the raw pellets with large particle sizes, so that the coke powder can be coated on the surface of the raw pellets. strengthen the adhesion,
Better coverage may also be provided. As the binder, quicklime, slaked lime, limestone, bentonite, granulated blast furnace slag, dolomite, etc. can be used. On the other hand, since the raw pellets in the small particle size group originally have a small amount of coke breeze added, the coating in the granulator 3b results in an insufficient amount of coke breeze coating. However, for raw pellets with a small particle size group, heat can easily pass through to the center during firing, so even if the amount of coke powder coated is relatively small, the remaining powder charged into the firing furnace with the raw pellets With the help of coke, it can be easily calcined. Therefore, insufficient coverage of coke breeze is not so much of a problem. It should be noted that raw pellets in the small particle size group can be easily mixed with coke powder to further coat the pellets with coke powder without using strong stirring such as in granulation. Therefore, if necessary, for example, by giving a light agitation when discharging the raw pellets of a small particle size group and the raw pellets of a large particle size group onto a belt conveyor and conveying them together, The excess coke breeze discharged together with the green pellets of the larger particle size group may be further coated on the green pellets of the smaller particle size group to compensate for the lack of coverage. In the above embodiment, the raw pellets are divided into two groups according to the particle size, and coke powder is added to the raw pellets of each group by weighting the amount added to coat the raw pellets. Alternatively, the raw pellets may be divided into three or more groups depending on the particle size, and coke powder may be added and coated in the same manner. In addition, a disk-type granulator was used as the second granulator for coating the coke powder, but
A drum-type granulator may also be used. [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 40wt% and coarse iron ore is 60wt%, and 2.7wt% of quicklime having the particle size composition shown in Table 5 is added and mixed as a solvent and a binder, and the resulting mixture is made into a disc. By granulating with a type granulator, raw pellets having a particle size distribution shown in Table 6 and a water content of 8 to 9 wt% were formed.

【table】

【table】

【table】

【table】

【table】

[Table] Next, according to the present invention, the raw pellets are divided into two groups: grain size of 3 mm or more and 7 mm or less, and grain size of more than 7 mm and 13 mm or less, and as shown in Table 7, the raw pellets of the large grain size group are Coke powder is added separately with weights added so that the amount added to the pellets is larger than the amount added to the raw pellets of the small particle size group, and the coke is granulated using a disc-type granulator. It was granulated and the surface was coated with coke powder. For comparison, coke powder was added separately to raw pellets in the large particle size group and raw pellets in the small particle size group without weighting the amounts added, and the surface was coated with coke powder in the same manner. did. The particle size structure of the coke powder used was as shown in Table 8.

【table】

[Table] Table 9 shows the results of investigating the ratio of the weight of coke powder coated to the weight of raw pellets after coating.

[Table] Next, 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 to form a fired mass. It was fired into mature ore. The large block-shaped calcined agglomerates thus obtained are discharged from the downstream end of the kiln, and after being crushed by a crusher, the calcined agglomerates under the sieve with particle diameters of less than 3 mm are passed through a screen. The ore is removed, and in this way, fired agglomerate ore with a maximum grain size of about 5 mm in the form of a plurality of fired pellets combined and fired agglomerate ore with a maximum grain size of about 3 to 13 mm in the form of a single fired pellet are produced. did. The product yield and production rate of the calcined agglomerate ore produced as described above were as shown in Table 10.

〔Effect of the invention〕

According to the present invention, it is possible to satisfactorily coat raw pellets with large particle sizes, where coating with coke powder is a problem. Therefore, the product yield and production rate of calcined agglomerates obtained by calcining raw pellets can be improved.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing a first embodiment of the coating method of the present invention. In the drawings, 1... drum mixer, 2... first granulator,
3a, 3b... second granulator, 4... screen.

Claims (1)

[Scope of Claims] 1. Green pellets for calcined agglomerates obtained by adding and mixing a solvent to powdered iron ore and granulating it with a disk-type first granulator are mixed with 2.5 to 4.0 wt% of coke powder is added and granulated by a disk-type or drum-type second granulator, thereby coating the surface of the raw pellets with the coke powder, are divided into a plurality of groups according to the size of the particles, and the amount of coke powder added is weighted so that the amount of the coke powder added is larger for the raw pellets in the group with a larger particle size. A method for coating green pellets for fired agglomerates with coke powder, the method comprising adding the above-mentioned coke powder to the green pellets and coating the raw pellets with coke powder. 2. A patent characterized in that a binder is added and mixed in advance to the coke powder added to the raw pellets of a group with a large particle size among the coke powder added to the raw pellets for each of the plurality of groups. A method for coating green pellets for calcined agglomerates with coke powder according to claim 1.