JPS63153225A - Manufacture of agglomerate - Google Patents

Abstract

PURPOSE:To manufacture agglomerates having a high rate of reduction and a low rate of reduction powdering by reducing the SiO2 content in agglomerates to a specified range when the agglomerates for a blast furnace are manufactured by adding a flux to fine iron ore, pelletizing them, coating the surfaces of the resulting green pellets with coke breeze and firing the coated pellets. CONSTITUTION:Powder of quick lime, slaked lime, limestone, bentonite, dolomite, water granulated blast furnace slag or the like as a flux is added to fine iron ore and mixed so as to regulate the ratio of CaO to SiO2 in the mixture to 1.0-2.5. The powdery starting material mixture is kneaded with water and pelletized by means of a discoid pelletizer to form green pellets of 3-13mm diameter. The pellets and coke breeze are charged into a second discoid pelletizer and pelletized to coat the surfaces of the pellets with 2.5-4.0wt% coke breeze. The coated pellets are fired to manufacture agglomerates contg. 0.5-5.0wt% SiO2 and having a high rate of reduction and a low rate of reduction powdering in a blast furnace.

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 a raw material for direct reduction iron manufacturing.
Its use is expanding.

This calcined agglomerate ore is usually produced as follows.

That is, powdered iron ore with a particle size of about 81IB or less, quicklime,
A solvent consisting of at least one of slaked lime, limestone, bentonite, granulated blast furnace slag, dolomite, etc. is used when the value of CaO/SiO2 in the calcined agglomerate is 1.0 to 2.
Add so that it is about 5% and mix with a mixer. Then, the obtained mixture is supplied to a disk-shaped first granulator, water is added, and the mixture is granulated by the first granulator,
It is formed into green pellets having a particle size of, for example, about 3 to 13,111 mm. Next, the obtained raw pellets are fed to a second disc-shaped granulator, and the steps 2.5 to 4. About Q wt % of coke powder is added and the raw R-lets are further granulated by a second granulator, thereby preparing raw pellets whose surfaces are coated with coke powder.

The raw pellets obtained in this way are charged into an endless moving grade type kiln, and the layer of charged raw pellets is placed on the grade of the kiln, and then the drying zone of the kiln is placed.
Pass through the ignition zone and firing zone in sequence. In the drying zone, a 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 large glock-like lumps of calcined agglomerate 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 3Wk. Remove calcined agglomerated ore pieces,
In this way, calcined agglomerate ore in the form of a plurality of calcined pellets combined with a maximum particle size of about 50 particles and calcined agglomerate ore in the form of a single calcined pellet with a particle size of about 3 to 13 particles are 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, conventional calcined agglomerates have an sio2 of 5.5
~6. Since it contained about Owt%, the reduction rate was 60~
The reduction rate was low at about 70%, and the reduction powdering rate was high at about 35 to 45%. Furthermore, the calcined agglomerate has 5i02.
Since it contains 5 to 6.0 wt at 18 degrees Celsius, the slag ratio in the blast furnace is high, for example, 360 Kf/), and the fuel ratio (or coke ratio) is also high, for example, 520 Kf/).

[Purpose of the invention]

In view of the above-mentioned current situation, this invention involves adding a solvent to powdered iron ore, granulating a mixed mixture to form green pellets, coating the obtained green pellets with coke powder, and making the green pellets endless. The purpose is to improve the reduction rate and reduction powdering rate of calcined agglomerate ore when the calcined agglomerate ore is charged into a moving grade kiln and continuously produced.

[Summary of the invention]

This invention involves adding a solvent to fine iron ore and granulating the mixture with a disk-type granulator to form raw pellets.
Calcined agglomerate ore, in which the obtained green pellets are coated with coke powder, and the green pellets are charged into an endless moving grade calciner and continuously calcined, thus continuously producing calcined agglomerate ore. In the manufacturing method, as the fine iron ore, Sio2 in the calcined agglomerate ore is 5 to 5. It is characterized by using powdered iron ore blended so as to have Qvirt%.

[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, 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 grade system. We have conducted extensive research in order to improve the reduction rate and reduction powdering rate of calcined agglomerate ore when charging it into a furnace to continuously produce calcined agglomerate ore.

Conventionally, 5i02 was added to 5.0-6. The reason why Owt was also included was that when the raw pellets were fired, the 5i02 in the powdered iron ore was combined with CaO in the solvent to form slag, and in order to bond the powdered iron ore together and form agglomerates. This is because it was considered necessary that 5i02 be contained in the fine iron ore so that the 5io2 content in the calcined agglomerate ore is about 5.0w11 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. Regardless of the case of green hard red, a disk-type granulator is used to granulate the iron ore powder, coke powder is coated on the surface of the iron ore powder after granulation, and a solvent is used for the iron ore powder. In the case of raw pellets obtained by granulation with the addition of
It has good granulation properties and is formed into spherical lumps, so even if the 5i02 content in the iron ore powder is low, the 5i02 in the iron ore powder is mixed with CaO in the solvent when the raw pellets are fired. It has been found that slag can be formed together with powdered iron ore to bind together powdered iron ore, making it suitable for agglomeration. Therefore, it becomes possible to improve the reduction rate and reduction powdering rate of calcined agglomerate ore.

Therefore, the particle size of formulations with different s i02 contents is approximately 8
- Using green pellets prepared from each of the following fine iron ores, an experiment was conducted to produce calcined agglomerates by varying the 5io2 content. And 5i02 in calcined agglomerate ore
The content, reduction rate, reduction powdering rate, product yield, and falling strength were investigated.

As a result, the 5i02 content in the calcined agglomerate was reduced to 0.5
It was found that if the reduction rate and reduction powdering rate of the calcined agglomerate ore can be significantly improved by setting the reduction rate to 5.0% by weight, the product yield and falling strength will not be reduced.

Fig. 1 is a graph showing the relationship between the 5iOz content and the reduction rate in the obtained calcined agglomerate, and Fig.
Graph showing the relationship between tO2 content and reduction powdering rate, 3rd
This figure is a graph showing the relationship between 5io2 content and drop strength, and FIG. 4 is a graph showing the relationship between 5io2 content and product yield.

As shown in Fig. 1, the reduction rate of calcined agglomerates decreases as the 5i02 content in the calcined agglomerates increases, but when the 5iQz content increases from 0.5 to 5.0 wt.
Within the % range, it is as high as 80% or more. And the SiO2 content is 5. When the Owt limit is exceeded, the return rate drops rapidly below 80%. As shown in Figure 2, the reduction pulverization rate of calcined agglomerate ore is determined when the SiO2 content in the calcined agglomerate is 0.
．． Within the range of 5 to 5.0 wt%, it is less than 30%, but if the 5io2 content is 5. When the amount exceeds 100%, the reduction powdering rate is 30%.

On the other hand, as shown in FIG. 3, the fall strength of calcined agglomerates increases as the SiO□ content in the calcined agglomerates increases; 9w
Even within the range of t%, the drop strength is approximately 85 inches or more, which is sufficiently maintained. As shown in Figure 4, the product yield of calcined agglomerate ore increases as the 5102 content in the calcined agglomerate increases; Even within this range, the product yield is approximately 75% or more, which is maintained satisfactorily.

In addition, in the above, the lower limit of the 5i02 content in the calcined agglomerate ore is set to 0.5 wt% because the 5i02 content is Q, and obtaining the calcined agglomerate with less than 5 wt 4 is fine iron ore. It is almost difficult in terms of quality, and 0.5Wt
This is because a value less than 1 has no practical meaning.

Therefore, in order to achieve a reduction rate of 80% or more and a reduction pulverization rate of 30% or less without reducing the product yield and falling strength of the calcined agglomerate, it is necessary to As a stone, the SiO2 content in the calcined agglomerate is 0.5 to 5.
, 0wt% of powdered iron ore should be used.

In this invention, as described above, as the fine iron ore used for firing, the s i02 content in the fired agglomerate ore is 0.5 to 5. By using powdered iron ore blended so as to achieve Owt%, the reduction rate and reduction powdering rate of calcined agglomerated ore are significantly improved.

In this invention, it is preferable that the amount of coke powder coated on the green pellets is 2.5 to 4.0 wt% as in the conventional method. This means that the amount of coated coke powder is 2.5wt%.
If the amount is less than 4.0vrtdj, 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. If it exceeds the temperature, the temperature of the green pellet during firing becomes too high, and the structure of the fired agglomerate becomes dense and has few pores, and at the same time, a molten structure with poor reducibility, i.e., secondary hematite and This is because the structure has many rectangular calcium ferrites.

In this invention, the particle size of the fine iron ore used is preferably about 8'lIk or less, as in the prior art. This means that powdered iron ore with a grain size of 8g or more can be used as is without being turned into agglomerated mineralized by sintering, and it is necessary to turn it into agglomerated mineralized with a grain size of 8g1.
This is because it is powdered iron ore with a particle size of 1 or less.

In this invention, it is preferable that the particle size of the raw pellets is 3 to 13, which is the same as in the conventional method. The reason is as follows. That is, if the particle size of the raw pellets is less than 3W,
During the firing of green pellets in a firing furnace, the high-temperature molten gas generated by the combustion of coke powder is prevented from passing smoothly through the layer of green pellets, resulting in a reduction in the production rate of fired agglomerate ore. arise. In addition, since the fired agglomerate ore in the form of a single fired pellet has a particle size of less than 3W, when such a small particle size of the calcined agglomerate is charged into the blast furnace, the circle of reducing gas Prevents clear passage. As a result, shelving 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 13&, the resistance to impact becomes weak, resulting in the problem of the green pellet collapsing when it is transferred to a firing furnace. Not only that, the grain size of each fired pellet of fired agglomerate exceeds 131111, so when such a large fired pellet of fired agglomerate is charged into a blast furnace, it will not reach the center of the fired agglomerate. 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 that the high temperature characteristics of the calcined agglomerate under load deteriorate.

〔Example〕

Five brands of fine iron ore A to E having the particle size structure shown in Table 1 and the chemical composition shown in Table 2 were prepared according to the present invention so that the SiO2 content in the calcined agglomerate ore was 0. .5~5
, Owt%, as shown in Table 3, were blended in appropriate proportions. For comparison, the content of 5tO2 in the calcined agglomerate is 5. Similarly, as shown in Table 3, appropriate proportions were blended so that the amount exceeded Owt%.

Table 2 (wt section) Table 3 Next, as a solvent and binder, quicklime with a particle size structure shown in Table 4 was added to the powdered iron ore of these blends from 1.0 to 1.0.
2.7wt9j was added and mixed, and limestone with the particle size structure shown in Table 5 was used to adjust the basicity, and the basicity was adjusted to 1.8~
It was adjusted to a range of 2.2. The mixture obtained here was granulated using a disk-type granulator to form raw pellets having a particle size distribution shown in the sixth thorn and having a water content of 8 to 9 virt%.

Table 6 (wt%) Next, 3.5 wt% of coke powder having the particle size composition shown in Table 7 was added to the green pellets to granulate them, and the green pellets were coated with coke powder.

Table 7 Then, the green pellets were charged to a thickness of 400 m on the grade of the endless moving grade type kiln, and the green pellets were sequentially moved through the drying zone, ignition zone, and firing zone of the kiln, and were baked into agglomerates. Fired into ore. 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. The maximum particle size of a plurality of calcined pellets combined is 50.
Calcined agglomerates in the form of blocks of &3 and calcined agglomerates in the form of single calcined pellets with grain sizes of 3 to 50& were produced.

The SiO2 content in the calcined agglomerate produced as described above, the reduction rate of the calcined agglomerate, etc. are shown in the eighth thorn.

Table 8 As shown in Table 8, in the present invention Al to 6 in which the 5i02 content in the calcined agglomerate is within the range of this invention, the reduction rate of the calcined agglomerate ore and the reduction powder Good yield rate without reducing drop strength or product yield.
The reduction rate and reduction powdering rate are improved. On the other hand, in Comparative Examples A7 to A8, in which the 5i02 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 The powderization rate is getting worse.

〔Effect of the invention〕

According to this invention, the reduction rate and reduction powdering rate of calcined agglomerated ore can be easily improved.

[Brief explanation of the drawing]

Fig. 1 is a graph showing the relationship between the SiO2 content and the reduction rate in the obtained calcined agglomerate, and Fig.
2 Graph showing the relationship between content and reduction powdering rate, 3rd
This figure is a graph showing the relationship between the 5in2 content and the drop strength, and FIG. 4 is a graph showing the relationship between the 5i02 content and the product yield.

Claims (1)

[Claims] A mixture of powdered iron ore and a solvent is added and mixed, and the mixture is granulated using a disk-type granulator to form green pellets.The obtained green pellets are coated with coke powder, and the green pellets are processed into an endless moving grade type. In a method for producing calcined agglomerate ore, in which the iron ore powder is charged into a calcining furnace and continuously fired, S in the calcined agglomerate ore is used as the fine iron ore.
A method for producing calcined agglomerate ore, characterized by using powdered iron ore blended so that iO_2 is 0.5 to 5.0 wt%.