JPH01136936A - Manufacture of self-fluxing pellet for charging to blast furnace - Google Patents

Abstract

PURPOSE:To manufacture the present pellet having high reduction ratio by adding either dolomite or limestone having regulated grain size to powdery iron ores to form raw pellet, calcining it and specifying the value of CaO/SiO2. CONSTITUTION:At least either dolomite or limestone contg. >=90% one having 44mum-1mm grain size is added to the powdery iron ores. By this method, the material is formed into the raw pellet and is thereafter calcined at 1,200->=1,300 deg.C to regulate the value of CaO/SiO2 to >=0.8. In this way, the self-fluxing pellet having high reduction ratio in the range where no problem is produced in physical properties can be obtd. Its reducing characteristics are furthermore improved when the value of MgO/SiO2 after calcination is regulated to >=0.47. By this method, the reduction ratio of the self-fluxing pellet is regulated to >=80% and the quantity as the material for charging to a blast furnace is improved.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention relates to a method for producing self-fusing pellets with a high reduction rate at high temperatures (hereinafter simply referred to as reduction rate) as an iron raw material for charging into a blast furnace. .

(Prior art) For example, fine iron ore powder cannot be charged into a blast furnace as it is, so it is first granulated into raw pellets, then fired to make self-fusing pellets, which are then charged into a blast furnace. It is used as raw material for industrial use. In order to improve ironmaking efficiency, such self-soluble pellets are required to have high reducibility.

(Problems to be Solved by the Invention) By the way, the conventional self-soluble pellets mentioned above have a reduction rate of 75~
It is about 80%, and there is still room for improvement in the manufacturing method in order to obtain a product with even higher reducibility.

(Purpose of the invention) This invention was made in view of the above-mentioned circumstances, and its purpose is to make it possible to produce self-soluble pellets with high reducibility without causing problems in physical properties. shall be.

(Structure of the Invention) A feature of the present invention for achieving the above object is that at least one of dolomite and limestone containing 80% or more of particles with a particle size of 44JLm to 1+e++ is used as powdered iron ore as a pellet raw material. The point is that the raw pellets are made into raw pellets and then fired at a firing temperature of 1220°C to 1300°C so that the CaO/SiO2 value becomes 0.8 or more.

(Example) The present invention will be described in detail below.

As a pellet raw material for forming self-soluble pellets,
Powdered iron ore (
(including auxiliary raw materials such as slack) and turn it into raw pellets using a pan-type pelletizer etc.Next, the raw pellets are fired at a firing temperature of 1220°C to 1300°C to make CaO
The value of /SiO2 is set to be 0.8 or more.

In the above case, the pellet raw material is 44ILm~1!1
The reason why it was decided to contain 80% or more of particles having a particle size of No. 11 is as follows. That is, if the thickness is 44 layers or less, the pores 1 (cXl/g) of the molded self-soluble pellets may decrease and the desired reducibility may not be obtained. Further, if the thickness is 1 mm or more, it becomes difficult to form a slag layer, which causes a problem in physical properties that sufficient crushing strength cannot be obtained.

In addition, as mentioned above, the firing temperature was set to 1220°C to 1300°C.
The temperature was set at ℃ for the following reason. That is, if the above-mentioned temperature were to be lower than 1220° C., the firing would be insufficient, making it difficult to form a slag layer, and as mentioned above, there would be a problem in that sufficient crushing strength could not be obtained. Also, 130
This is because if the temperature is 0° C. or higher, the porosity decreases due to excessive firing, resulting in the inconvenience that the desired reducibility cannot be obtained.

Furthermore, CaO/S i 0 of the self-fusing pellet to be molded
The reason why the value of 2 (basicity) is set to 0.8 or more is because of this 0.8
This is because the above value significantly increases the reducibility.

Furthermore, if the MgO/SiO2 value of the self-soluble pellet is set to 0.47 or more, the reducibility will be further significantly improved.

It is known that if the amount (%) of 5i02 contained in self-fusing pellets is reduced, the amount of melt produced will be reduced when the self-fusing pellets are fed into a blast furnace, that is, the reducibility will be improved. In this case, desired reducibility can be obtained by setting the amount (%) of 5i02 to an amount that satisfies the following formula.

Further, the iron ore in the pellet raw material contains 25% or more of ore having a Blaine specific surface a (according to the JIS measurement method) of 1000 Ci/g or less, and the Blaine specific surface area of the pellet raw material is 1800 to 3800 alF.
/ g. In the above case, the Blaine specific surface area of the iron ore is 1000 co? The reason why iron ore is made to contain a large amount of less than /g is to make the iron ore coarser to some extent, that is, to
This is to increase the porosity of the self-soluble pellets and improve their reducibility. Further, the reason why the Blaine specific surface area of the pellet raw material is set to 1800 to 3800 cJ/g is to develop the strength necessary for pellet production and use in a blast furnace.

Next, the self-fusing pellets molded by the above manufacturing method will be explained with reference to the drawings.

In FIG. 1, reference numeral 1 indicates a self-soluble pellet of the present invention, and numerous pores (hereinafter referred to as blank spaces) 2 are formed inside the self-soluble pellet 1. Among these pores 2, those that communicate to the outside of the self-soluble pellet 1 are called open pores 2a.
The closed pores in the self-soluble pellet 1 are called closed pores 2b.

In this self-soluble pellet 1, the amount of open pores za with a diameter of 5 m or more is present at 0.045 (77 g or more).If the amount of open pores 2a is set as above, the reduction rate is 80%.
As described above, an improvement in reducibility is achieved compared to the reduction rate of conventional pellets, which is 75 to 80% or less.

Further, a gangue phase 3, which is a calcium ferrite structure, exists around the pores 2 having a diameter of 5ILffi or more.

This gangue phase 3 has a chemical formula of CaO Fe203,
Cafe 2Fa203 (hemi-calcium-ferrite), and this gangue Phase 3 has a thickness of 1
004 ra or more, CaO/SiO2 (basicity)
The value of is 1.4 or more. In the above case, the thickness of the gangue phase 3 may be 100 g ra or more over the entire area around the pore 2, or it may be partial. The reason for the presence of the gangue phase 3 having this is that this improves the reducibility.

Furthermore, this self-soluble pellet) 1 is composed of CaO/Si as a whole.
O2 value is 0.8 or more, and MgO/
The value of SiO2 is 0.47 or more.

Here, a method for calculating the amount of open pores 2a having a diameter of 5 cm or more will be explained.

First, the apparent density (Sa) (g/a
? ) is measured by the mercury displacement method (JIS 148718).

In addition, the true density (S) (g/al) is measured by the pyrometer method (JIS M8717).

Next, the porosity (P) (%) is calculated from the above measured values using the following formula.

On the other hand, the apparent density (Sc) (g/al) of the self-soluble pellet (1) containing closed pores 2b is measured. This measurement method is the same as the measurement of the true density described above (see the margin below), but in this case, the atmosphere around the self-soluble pellet 1 was set to 0.
By reducing the pressure to 01mIIH20 and replacing the open pores 2a with xylene, the apparent density (Sc) is determined.

Based on each of the above values, closed porosity (Pc) (%)
is calculated using the following formula.

Furthermore, based on each of the above numerical values, the amount of open pores (Vop) (cj
/g) using the following formula.Next, the diameter distribution of the pores 2 is measured. For this measurement,
A mercury intrusion porosimeter (manufactured by Italian company Luloerba) is used. Measurement range is 0.074p-ta ~ 125
#Lm, and anything less than 0.074 JL 1 is ignored. The amount of open pores za (Cj/g) from any diameter in the above range (hereinafter referred to as the margin) to 125 pm is determined. That is, for example, 5ILm~125IL! The open pore za amount (cmF/g) of l is determined.

Here, the measurement theory of the mercury intrusion porosimeter will be explained. That is, assuming that the cross section of the open pore 2a is circular,
If the radius is γ, the surface tension of mercury is σ, the wetting angle is θ, and the applied pressure is P, then the following equation holds true:

γ:2σcotθ/P Therefore, if you measure by gradually changing the pressure.

As mentioned above, open pores in a certain pore diameter range?
The amount of a can be determined.

With the above porosimeter, 5IL! 1 or less open pores 2a
If the amount (V-s) (al/g) is calculated, the amount of open pores 2a (V+s) (ar
/ g) is calculated by the following formula.

V's (j/g)mVop -V-s On the other hand, the method for evaluating the reducibility will be explained.

When the temperature in the blast furnace is below 950° C., most of the charged ores are reduced to Fe1-XO, and at temperatures higher than this, they are reduced to Fe1-XO→MeFe under rapid temperature rise. It is appropriate to evaluate the reducibility under simplified reduction conditions.

Therefore, the reduction conditions were two-stage reduction at 900°C (reducing gas Co/C02 = 1O/40) for 2 hours and 1250°C (reducing gas CO/N2 = 30/70) for 2 hours. The reduction rate is measured using a linear equation, where Wl is the weight before reduction, l1i2 is the weight after reduction at 1250° C., and T*Fe (%) and Fed (%) are those of the sample before reduction.

(Leaving space below) Nawa, if the self-fusing pellets 1 are molded as described above, the reduction rate will improve, which is preferable, but if these self-fusing pellets 1 are fed into the blast furnace as follows, the effect will be further improved. improves.

That is, when molding the self-fusing pellets 1, carbon content is attached to a plurality of raw pellets and then fired. Then, they adhere to each other, and one group of a plurality of self-soluble pellets becomes one block. Therefore, the particle diameter of each self-soluble pellet 1 can be made small, and therefore, the reducibility can be improved in this respect as well. In addition, when this is put into the furnace, it is difficult to roll, so it is cheap, and the angle can be made large, so it can be stacked in the furnace while maintaining a predetermined angle of inclination, which prevents uneven flow of gas. .

Next, specific examples of the method for manufacturing the self-soluble pellets 1 will be described.

(First specific example) As a raw material for pellets, dolomite containing 90% or more of particles with a particle size within a certain range as shown in the particle size range in Table 1 below is added, and this is made into raw pellets. , 1250
The pellets were fired at temperatures of 1275°C and 1275°C to form self-fusing pellets 1.

Each figure in Figure 2 is a cross-sectional photograph of the self-fusing pellet 1 when the firing temperature is 1250°C, and each figure in Figure 3 is a cross-sectional photograph of the self-fusing pellet 1 when the firing temperature is 1275°C. be. These photographs are 3x enlarged photographs, and are taken of particles in each particle size range as shown in Table 1.

(Table 1) According to each of the above figures, it can be seen that as the particle size of dolomite becomes coarser, the amount of pores 2 increases.

FIG. 4 shows the relationship between the amount of open pores 2a and the reduction rate (RI) for the self-fusing pellet 1 formed as described above. According to this figure, if open pores 2ai with a diameter of 5 gm or more are present at 0.045 cmF/g or more, the reduction rate will be significantly improved beyond the conventional highest level (80%). is understood.

The self-fusing pellet 1 formed as described above has a cross-sectional shape as shown in FIG. 5 and FIG. 6, which is a partially enlarged view of FIG. 5. In Fig. 6, gangue phase 3 with a thickness of 1004 m or more exists around pore 2. 4 is Fe203 and low basicity slag.

Table 2 below is for the case where the firing temperature is 1250 ° C., and shows the components of gangue phase 3 and the part indicated by code 5 in weight % in FIGS. 5 and 6 above, and C in each part
The values of aO/SiO2 (basicity) are shown.

(Margins below) (Table 2) (In the case of 1250°C) Table 3 below shows the results when the firing temperature was 1275°C.

(Table 3) (In the case of 1275°C) Fig. 7 shows a conventional example in which fine dolomite was added to the pellet raw material, and this figure corresponds to Fig. 86 above. In this case, there is no gangue phase 3 around the pores 2', and Table 4 below shows the components of the part indicated by 5' in Figure 7 above and the corresponding basicity. and are shown by firing temperature.

(Margins below) (Table 4) If we compare Tables 2 and 3 above with Table 4, we can see that the pores in the example are? It is understood that the CaO/SiO2 (basicity) in the vicinity is higher than that of the conventional one, thereby achieving an improvement in reducibility.

Figures 8 and 9 show the results when the self-fusing pellet 1 was molded at a firing temperature of 1250°C, and Figure 8 shows the CaO/Si02
This is a graph showing the relationship between the value of C and the return rate.
Although the open porosity of self-soluble pellet 1 is almost constant, the value of the reduction rate with respect to the value of aO/S i02 is
It changes depending on the value of O/S i02. Furthermore, gangue phase 3
Since it is not a uniform structure, there is a range in the value of CaO/SiO2. Therefore, it can be seen that it is appropriate to set this value to 1.4 or more in order to obtain a high return rate.

Figure 9 shows Can/SiO as a whole of self-soluble pellet 1.
2 and the reduction rate, and also includes a conventional example when fine dolomite of 441 Lm or less is used as the pellet raw material (shown by a chain line in the figure).0 According to the graph, the particle size is It is understood that the reduction rate increases if coarse dolomite having a diameter of 0.1 to 0.5 is used as a raw material. It can be seen that if the value of CaO/SiO2 is set to 0.8 or more, a high reduction rate can be obtained by adding dolomite with a particle size of 0.1 to 0.5 mm.

Figure 10 shows the firing temperature of 1250°C and 1275°C using coarse dolomite with a particle size of 0.1 to 0.5 cm as a raw material.
This is when self-fusing pellet 1 is molded at °C.
FIG. 2 is a graph diagram showing the relationship between the value of MgO/S i02 and the reduction rate. Currently, the highest reduction rate among industrially produced pellets is 80%.

Therefore, in order to obtain a higher reduction rate, MgO/
It can be seen that it is necessary to add MgO to make the SiO2 value 0.40 or more.

(Second specific example) As a pellet raw material, limestone containing 90% or more of particles with a particle size within a certain range as shown in the particle size range in Table 5 below is added, and this is made into raw pellets. Self-fusing pellets 1 were calcined at temperatures of 1250°C and 1275°C.
was molded.

Each figure in Fig. 11 is a cross-sectional photograph of the self-fusing pellet 1 when the firing temperature is 1250°C, and each figure in Fig. 12 is a cross-sectional photograph of the self-fusing pellet 1 when the firing temperature is 1275°C. . These photographs are 3x enlarged photographs, and are taken from particles in each particle size range as shown in Table 5.

(Margins below) (Table 5) According to each of the above figures, as the grain size of limestone becomes coarser,
It can be seen that the amount of pores 2 increases.

FIG. 13 shows the relationship between the amount of open pores 2a and the reduction rate for the self-fusing pellet 1 formed as described above. According to this figure, the amount of open pores 2a with a diameter of 53Ll1 or more is 0.
．． It is understood that if 045 cal''/1 or more is present, the reduction rate will be significantly improved beyond the conventional highest level of 80%.

In addition, the self-fusing pellet/ ) 1 formed as described above has a cross-sectional shape as shown in Fig. 14 and Fig. 15, which is a partially enlarged view of Fig. 14. . 1st
In Figure 5, the thickness around pore 2 is 150 to 400 IL.
Eleven gangue facies 3 are present.

4 is Fe203.

Table 6 below shows the results when the firing temperature is 1250°C, and shows each component in gangue phase 3 and the part indicated by code 5 in weight% in Figures 14 and 15 above. It shows the value of CaO/SiO2 (basicity) in the part.

(Table 6') (In the case of 1250℃) Also, see Table 7 below.
The table is based on a firing temperature of 1275°C.

(Leaving space below) (Table 7) (In the case of 1275°C) Figure 16 is a conventional example in which finely powdered limestone is added to the pellet raw material, and this figure corresponds to Figure 15 above. . In this case, the gangue phase 3 is located around the pore 2'.
Also, Table 8 below shows the components of the part indicated by the number 5' in Figure 12 above and the corresponding basicity by firing temperature.

(Table 8) Comparing Table 6.7 and Table 8 above, it is understood that the CaO/SiO2 of this example is higher than that of the conventional one. As in the first specific example, this results in an improved return rate.

(Effect of the invention) According to this invention, 44 pots ■～la can be used as pellet raw material.
At least one of dolomite and limestone containing 90% or more of particles with a particle size of Since the value of CaO/S i02 was set to be 0.8 or more, the reduction rate was 75 to 80% with conventional pellets, but it was 80% or more with the self-fusing pellets manufactured by the present invention, and it is suitable for blast furnace equipment. The quality of raw materials will improve.

[Brief explanation of the drawing]

The figures show embodiments of the present invention; FIG. 1 is a schematic cross-sectional view of a self-soluble pellet, FIGS. Cross section photo, 4th
The figure is a graph, Figure 5 is a cross-sectional view of self-soluble pellets, and Figure 6 is a cross-sectional view of self-soluble pellets.
The figure is a partially enlarged view of Figure 5, Figure 7 is a conventional example and corresponds to Figure 6, Figures 8 to 10 are graphs, and Figures 11 to 16 are the second concrete implementation. For example, Figures 11 and 12 are cross-sectional photographs of self-soluble pellets, Figure 13 is a graph, Figure 14 is a cross-sectional view of self-soluble pellets, Figure 15 is a partially enlarged view of Figure 14, and Figure 15 is a partially enlarged view of Figure 14. FIG. 16 is a diagram corresponding to FIG. 15 in a conventional example. l: self-soluble pellet, 2e: pores, 2a: open pores,
2b: closed pores, 3: gangue phase (calcium ferrite system). Patent applicant: Kobe Steel, Ltd. Figure 4, j, -1 open air a-t <c-η) 0'°-''9 2nd
Figure (b) Figure 2 (d,) 21st +%T(C) +☆) Figure (e) Translation stone female＾CaO/Si 02 (-) o, 5 f, 0 zu52,0CtO7S
&Oz ratio (-) Mf/5sO2 ratio (-) 0 2o go 60
80 Figure 16 Procedural Amendment (Method) % Formula % 1. Indication of the case 1988 Patent Application No. 294574 2. Title of the invention Method for manufacturing self-fusing pellets for blast furnace charging 3. Person making the amendment Related Patent applicant address (residence) 1-3-1 Wakihama-cho, Chuo-ku, Kobe, Hyogo Prefecture
No. 8 Name (119) Kobe Steel, Ltd. 4, Agent 531

Claims (1)

[Claims] 1. At least one of dolomite and limestone containing 90% or more of particles with a particle size of 44 μm to 1 mm is added to powdered iron ore as a pellet raw material, and this is made into raw pellets, and then 1220 A method for producing self-fusing pellets for charging into a blast furnace, characterized in that the pellets are fired at a firing temperature of 1300°C to 1300°C so that the value of CaO/SiO_2 is 0.8 or more. 2. The method for producing self-fusing pellets for blast furnace charging according to claim 1, characterized in that the value of MgO/SiO_2 after firing the green pellets is 0.40 or more. 3. The amount of SiO_2 after firing the raw pellets is SiO
_2(%)<1.14・([CaO]/[SiO_2]
)+1.65. The method for producing self-fusing pellets for charging into a blast furnace according to claim 1 or 2, wherein the method satisfies the following. 4. Blaine specific surface area of pellet raw material is 1000cm^
2/g or less of iron ore, and the Blaine specific surface area of this pellet raw material is 1800 to 3800c.
Claim 1 characterized in that m^2/g
A method for producing self-fusing pellets for charging into a blast furnace according to any one of items 3 to 3.