JPH0377854B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to self-soluble pellets that have 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 green pellets and then fired to make self-fusing pellets, which are then charged into a blast furnace. It is used as a raw material. In order to improve ironmaking efficiency, such self-soluble pellets are required to have high reducibility. (Problems to be Solved by the Invention) Incidentally, the conventional self-soluble pellets described above have a reduction rate of about 75 to 80%, and there is still room for improvement in aiming to further improve the reducibility. (Objective of the Invention) This invention was made in view of the above-mentioned circumstances, and aims to improve reducibility within a range that does not cause problems in physical properties. (Structure of the Invention) The feature of this invention for achieving the above object is that the amount of open pores with a diameter of 5 μm or more is 0.045
cm ³ /g or more, while the diameter including the above open pores
The thickness is 100 μm or more around the pores of 5 μm or more,
It has a calcium ferrite structure with a CaO/SiO ₂ value of 1.4 or more, and has an overall CaO/SiO2 structure.
The point is that the SiO ₂ value is 0.8 or more. (Example) Hereinafter, an example of the present invention will be described with reference to the drawings. In FIG. 1, reference numeral 1 indicates a self-soluble pellet of the present invention, and numerous pores 2 are formed inside this 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, and those that are closed within the self-soluble pellet 1 are called open pores 2b. This self-soluble pellet 1 has a diameter of 5 μm.
The amount of open pores 2a of 0.045 cm ³ /g or more is present. When the amount of open pores 2a is set as above,
The reduction rate is 80% or more, which improves reducibility compared to conventional pellets, which have a reduction rate of 75 to 80% or less. Furthermore, around the pores 2 with a diameter of 5 μm or more, a gangue phase 3, which is a calcium ferrite texture system, exists. The chemical formula of this gangue phase 3 is CaO・Fe ₂ O ₃
There are also those of CaO・2Fe ₂ O ₃ (hemicalcium ferrite). Moreover, this gangue phase 3 has a thickness of 100 μm or more, and a CaO/SiO ₂ (basicity) value of 1.4 or more. In the above case, the thickness of the gangue phase 3 may be 100 μm or more over the entire area around the pores 2, or may be partial. The reason why the gangue phase 3 having a certain thickness or more is made to exist around the pores 2 in this way is that this improves the reducibility. Furthermore, this self-soluble pellet 1 as a whole
The value of CaO/SiO ₂ is 0.8 or more. That is,
This is because when the above value is set to 0.8 or more, the effect of the pore amount on improving the reduction rate increases significantly. In addition, the above self-soluble pellet 1 as a whole
The value of MgO/SiO ₂ is set to be 0.40 or more. That is,
This is because when the above value is set to 0.40 or more, the return rate increases significantly. Here, the open pores 2a having a diameter of 5 μm or more are used.
The method of calculating the amount will be explained. First, the apparent density (Sa) of self-soluble pellet 1
(g/cm ³ ) is measured by the mercury substitution method (JIS M8716). Further, the true density (S) (g/cm ³ ) is measured by the pycnometer method (JIS M8717). Next, from the above measurement value, porosity (P) (%)
is calculated using the following formula. P=S−Sa/S×100 (%) On the other hand, the apparent density (Sc) (g/cm ³ ) of the self-soluble pellet 1 including closed pores 2b is measured.
This measurement method is the same as the measurement of the true density described above, but in this case, the atmosphere around the self-soluble pellet 1 is reduced to 0.01 mmH ₂ O, and the open pores 2a are replaced with xylene. The apparent density (Sc) is determined. Then, based on each of the above values, the closed porosity (Pc)
(%) is calculated using the following formula. Pc = (S-Sc/S) x Sa/Sc x 100 (%) Furthermore, based on the above values, open pore volume (Vop)
(cm ³ /g) is calculated using the following formula. Vop=P−Pc/Sa×1/100 Next, the diameter distribution of the pores 2 is measured. For this measurement, a mercury intrusion porosimeter (manufactured by Carlo Erba, Italy) is used. Measurement range is 0.074μm
~125 μm, ignoring values less than 0.074 μm.
The amount of open pores 2a (cm ³ /g) from any diameter in the above range to 125 μm is determined. That is, for example, the amount of open pores 2a (cm ³ /g) of 5 μm to 125 μm 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, and assuming that its radius is γ, the surface tension of mercury is σ, the wetting angle is θ, and the applied pressure is P, if we try to press mercury into the open pore 2a, then , the following equation holds. γ=2σcosθ/P Therefore, if the pressure is gradually changed and measured,
As described above, the amount of open pores 2a in a certain range of pore diameters can be determined. If the amount of open pores 2a of 5 μm or less (V _-5 ) (cm ³ /g) is determined using the above porosimeter, the initial target amount of open pores 2a of 5 μm or more (V ₊₅ ) (cm ³ /g) can be calculated using the following formula. Calculated by V ₊₅ (cm ³ /g) = Vop - V _-5 On the other hand, the method for evaluating the reducibility will be explained. When the temperature inside the blast furnace is below 950℃, most of the charged ores are reduced to Fe _1-X O, and at temperatures higher than this, Fe _1-X O→M・
Reduced to Fe. It is appropriate to evaluate the reducibility under simplified reduction conditions. Therefore, the reduction conditions were two-stage reduction: 900℃ (reducing gas CO/CO ₂ = 60/40) for 2 hours and 1250℃ (reducing gas CO/N ₂ = 30/70) for 2 hours. where w ₁ is the weight before reduction, w ₂ is the weight after reduction at 1250℃,
Using T·Fe (%) and FeO (%) as those of the sample before reduction, the reduction rate is measured using the following formula. RI(1250)=w ₁ −w ₂ /w ₁ ×1×10 ¹⁴ /{0.430・(T・Fe)−0.112・(FeO)
}(%) It is preferable to form the self-fusing pellets 1 as described above because the reduction rate improves, but if these self-fusing pellets 1 are further charged into the blast furnace as follows, the effect will be further improved. will improve. That is, when molding the self-fusing pellets 1, a plurality of raw pellets are attached with carbon and 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 also be improved in this respect. Furthermore, when this is put into the furnace, it is difficult to roll, so it is possible to have a large angle of repose, and therefore, it is possible to stack them in the furnace while maintaining a predetermined angle of inclination, so it is possible to prevent drifting of the gas. Next, a specific example of the self-soluble pellet 1 will be described. (First Specific Example) As a pellet raw material, dolomite containing 90% or more of particle size within a certain range as shown in the particle size range in Table 1 below is added to fine iron ore containing gangue components. After making this into raw pellets, it was heated to 1250℃.
Self-fusing pellets 1 were formed by firing at various temperatures of 1275°C. 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 as shown in Table 1, particles in each particle size range are photographed and shown.

[Table] 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-soluble pellet 1 formed as described above. According to this diagram, the diameter is 5μ
It is understood that if the amount of open pores 2a of 0.045 cm ³ /g or more is present, the reduction rate is significantly improved beyond the conventional highest level (80%) of the reduction rate. 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 Figure 6, there is a thickness l around the pore 2.
Gangue phase 3 with a diameter of 100 μm or more is present. 4 is
_It is _Fe2O3 . 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 Figures 5 and 6 above, and
The values of CaO/SiO ₂ (basicity) in each part are shown.

[Table] Table 3 below shows the results when the firing temperature was 1275°C.

[Table] Fig. 7 shows a conventional example in which fine dolomite is added to the pellet raw material, and this figure corresponds to Fig. 6 above. In this case, the gangue phase 3 does not exist around the pores 2'. Also,
Table 4 below shows the components of the portion indicated by the reference numeral 5' in FIG. 7 and the corresponding basicities according to the firing temperature.

[Table] Comparing Tables 2 and 3 above with Table 4,
It is understood that the CaO/SiO ₂ (basicity) near the pore 2 of the example is higher than that of the conventional one,
This achieves improvement in reducibility. Figures 8 and 9 relate to the above-mentioned self-fusing pellet 1 when the firing temperature was 1250°C.
The figure shows this self-soluble pellet 1 in gangue phase 3.
It is a graph diagram showing the relationship between the value _{of CaO/SiO 2 and} the reduction rate. Varies depending on the SiO ₂ value. Note that gangue phase 3 does not have a uniform structure, so CaO/
There is a wide range of SiO ₂ values. 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 CaO/
It is a graph diagram showing the relationship between SiO ₂ and reduction rate,
A conventional example in which fine powder dolomite of 44 μm or less is used as the pellet raw material is also co-aired (as shown by the chain line in the figure). According to the figure, it is understood that if coarse dolomite with a particle size of 0.1 to 0.5 mm is used as a raw material, the reduction rate increases. It can be seen that if the value of CaO/SiO ₂ is set to 0.8 or more, the reduction rate can be improved at the CaO/SiO ₂ level. Figure 10 shows that coarse dolomite with a grain size of 0.1 mm to 0.5 mm is used as a raw material, and the firing temperature is 1250°C and 1275°C.
FIG. 2 is a graph showing the relationship between the MgO/SiO ₂ value and the reduction rate in relation to the above-mentioned self-soluble pellet 1 when the temperature is expressed as °C. Currently, the highest reduction rate among industrially produced pellets is 80%. Therefore, in order to obtain a higher return rate,
It can be seen that it is necessary to add MgO to make the MgO/SiO ₂ 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 formed by firing at temperatures of 1250°C and 1275°C. 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 as shown in Table 5, particles in each particle size range are photographed and shown.

[Table] According to each of the above figures, it can be seen that as the particle size of limestone becomes coarser, 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-soluble pellet 1 formed as described above. According to this figure, if the amount of open pores 2a with a diameter of 5 μm or more is present at 0.045 cm ³ /g or more,
It is understood that this reduction rate is significantly improved, exceeding the conventional maximum level of 80%. 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. In FIG. 15, a gangue phase 3 with a thickness l of 150 to 400 μm exists around the pores 2. 4
is Fe ₂ O ₃ . Table 6 below shows the results when the firing temperature is 1250°C, and in Figures 14 and 15 above, gangue phase 3,
Each component in the portion designated by numeral 5 is shown in weight %, and the value of CaO/SiO ₂ (basicity) in each portion is shown.

[Table] Table 7 below shows the results when the firing temperature was 1275°C.

[Table] Fig. 16 shows a conventional example in which finely powdered limestone is added to the pellet raw material, and this figure corresponds to Fig. 15 above. In this case, the gangue phase 3 does not exist around the pores 2'. Also,
Table 8 below shows the components of the portion indicated by the reference numeral 5' in FIG. 12 and the corresponding basicity according to the firing temperature.

[Table] Comparing Tables 6 and 7 with Table 8 above, it can be seen that the CaO/SiO ₂ of this example is higher than that of the conventional example. As in the first specific example, this results in an improved return rate. (Effects of the Invention) According to the present invention, the amount of open pores with a diameter of 5 μm or more is present at 0.045 cm ³ /g or more, and on the other hand, the pores with a diameter of 5 μm or more including the open pores have a thickness of 100 μm or more.
m or more, it has a calcium ferrite structure with a CaO/SiO ₂ value of 1.4 or more, and the overall CaO/SiO ₂ value is 0.8 or more, so the reduction rate is 75 to 80 compared to conventional pellets. %, whereas in the self-fusing pellets of the present invention, it is 80% or more, improving the quality as a raw material for blast furnace charging.

[Brief explanation of drawings]

The figures show embodiments of the present invention; FIG. 1 is a schematic sectional view of a self-soluble pellet, FIGS. 2 to 10 are a first specific embodiment, and FIGS. A cross-sectional photograph showing the particle structure, Fig. 4 is a graph, Fig. 5 is a cross-sectional view of a self-soluble pellet, Fig. 6 is a partially enlarged view of Fig. 5, and Fig. 7 is a conventional example and corresponds to Fig. 6. Figures 8 to 10 are graphs, Figures 11 to 16 are the second specific example, and the first
Figures 1 and 12 are cross-sectional photographs showing the particle structure of self-soluble pellets, Figure 13 is a graph, Figure 14 is a cross-sectional view of self-soluble pellets, and Figure 15 is a partially enlarged view of Figure 14. FIG. 16 is a diagram corresponding to FIG. 15 in a conventional example. 1...Self-soluble pellet, 2...Stomata, 2a...
Open pores, 2b...closed pores, 3... gangue phase (calcium ferrite-based structure).

Claims (1)

[Claims] 1. The amount of open pores with a diameter of 5 μm or more is present at 0.045 cm ³ /g or more, and on the other hand, the pores including the open pores with a diameter of 5 μm or more have a thickness of 100 μm or more, and CaO/
It has a calcium ferrite structure with a SiO ₂ value of 1.4 or more, and has an overall CaO/SiO ₂
A self-fusing pellet for blast furnace charging, characterized in that the value of is 0.8 or more. 2. The self-fusing pellets for blast furnace charging according to claim 1, characterized in that the MgO/SiO ₂ value as a whole is 0.40 or more.