JPH01136937A - Self-fluxing pellet for charging to blast furnace - Google Patents

Abstract

PURPOSE:To improve the reducing characteristics of the present pellet by specifying the opening porous ratio of the pellet and permitting specific calcium-ferrite structure to present around the pores including opening pores. CONSTITUTION:The grain size of dolomite to be added to powdery iron ores is regulated to permit the >=0.045cm<3>/g amounts of opening pores having >=5mum diameter to present in the self-fluxing pellet after calcination. The value of CaO/SiO2 as the whole is furthermore regulated to >=0.8. The value of MgO/SiO2 is preferably regulated to about >=0.40 as well. By this method, the reduction ratio of the self-fluxing pellet is regulated to about >=80% and the quality as the material for charging to a blast furnace is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to self-fusing pellets that have a high reduction rate at high temperatures (hereinafter simply referred to as reduction rate) and are used 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 in aiming to further improve reducibility,
There is still room for improvement.

(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 ILm or more is 0.045 d /
CaO/Si
It has a calcium ferrite structure with an O2 value of 1.4 or more, and has an overall CaO/Si02 value of 0.8 or more.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, reference numeral 1 denotes a self-fusing pellet of the present invention, and inside this self-fusing pellet 1, numerous pores 2 are formed. 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 closed pores 2b.

In this self-soluble pellet (1), the amount of open pores 2a having a diameter of 5 pLm or more is present in an amount of 0.045 a//g or more. When the amount of open pores za is set as above, the reduction rate is 80
% or more, and an improvement in reducibility is achieved compared to the reduction rate of conventional pellets, which is 75 to 80% or less.

Further, around the pores 2 having a diameter of 5 pm or more, a gangue phase 3, which is a calcium ferrite structure system, exists. This gangue phase 3 has a chemical formula of GaO Fe203,
There is one made of Ca1m 2Fe203 (hemi-calcium ferrite). Moreover, this gangue phase 3 has a thickness of 1
00 gm or more, and the CaO/SiO2 (basicity) value is 1.4 or more. In the above case, the thickness of the gangue phase 3 may be 100 p,, ts or more over the entire area around the pore 2, or it may be partial. The reason for the presence of the thick gangue phase 3 is that this improves the reducibility.

Furthermore, this self-soluble pellet 1 is composed of CaO/Si as a whole.
The O2 value is 0.8 or more. In other words, the above value is set to 0
．． This is because when it is 8 or more, the effect of the pore amount on improving the reduction rate increases significantly.

In addition, the self-soluble beret) 1 is made of MgO/Si as a whole.
The O2 value is set to 0.40 or more. That is, if the above value is set to 0.40 or more, the return rate increases significantly.

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

First, the apparent density (Sa) (g/
al) is measured by the mercury displacement method (JIS M871fl).

Further, the true density (S) (g/'o/) is measured by the pyranometer method (JIS M8717).

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

On the other hand, the self-soluble pellet 1 has closed pores 2b.

The apparent density (Sc) (g/al) is measured. This measurement method is similar to the measurement of true density described above, but in this case, the atmosphere around the self-soluble pellet 1 is reduced to 0.
．． By reducing the pressure to 01 intestinal meal H20 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.

(Left below) Furthermore, based on the above values, open pore volume (VOp) (a?/
g) is calculated 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. The measurement range is 0.074 p-tm-125 l, and values less than 0.074 μm are ignored. The amount of open pores 2a (a//g) from any diameter in the above range to 125 ml is determined. That is, for example, 5I
The amount of open pores za (a//g) from L11 to 125 km 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,
Assuming that the radius is γ, the surface tension of mercury (below the margin) is σ, the wetting angle is θ, and the applied pressure is P, the open pore 2
If we try to inject mercury into a, the following equation holds true.

γ=2σ cos θ/P Therefore, by measuring while gradually changing the pressure, the amount of open pores za in a certain pore diameter range can be determined as described above.

The amount of open pores 2a of 5 pm or less (
V-s) (QIF/g), the amount of open pores 2a of 5JL11 or more (V+s) (
GIF/g) is calculated by the following formula.

V+'s (ci/g)=Vop -V-s On the other hand, the method for evaluating the reducibility will be explained below.

When the temperature inside the blast furnace is below 850°C, most of the charged ores remain reduced to Fel-1 (O), and at higher temperatures, Fel-3 (0→M・Fe
will be returned to. It is appropriate to evaluate the reducibility under simplified reduction conditions.

Therefore, the reduction conditions were as follows: 900°C (reducing gas GO/CO2 = go74G) and 1250°C (reducing gas Go/N2 = 30770) for 71112 hours during reduction.
A two-stage reduction with a reduction time of 2 hours was performed at
Using T*Fe (%) and Fed (%) as those of the sample before reduction, the reduction rate is measured using the following formula.

It should be noted that forming the self-fusing pellets 1 as described above is preferable because the reduction rate improves, but the effect is further improved if these self-fusing pellets 1 are further introduced into the blast furnace as follows.

That is, when molding the self-fusing pellets 1, carbon is attached to a plurality of green pellets and fired. (see margin below), these adhere to each other and form multiple self-soluble pellets 1
The group becomes one block. For this reason, pure white solubility
The particle size of Kit 1 can be made very large, so it is possible to improve the reducibility in this respect as well.Also, when it is put into the furnace, it does not roll easily, so Since the angle of repose can be set large and therefore the layers can be stacked in the furnace while maintaining a predetermined angle of inclination, it is possible to prevent gas drift.

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 particles with a particle size within a certain range as shown in the particle size range in Table 1 below is used as powdered iron ore containing gangue components. The raw pellets were made into raw pellets, which were then fired at temperatures of 1250°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 calcination temperature is 1250°C, and each figure in 3rd rM is a cross-sectional photograph of the self-fusing pellet 1 when the calcination temperature is 1275°C. be. These photographs are 3x magnified photographs, and are taken from 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 za and the reduction rate (R1) for the self-fusing pellets formed as described above. According to this figure, if the amount of open pores za with a diameter of 5 IL- or more is present at 0.045 al/g or more, the reduction rate will be significantly improved, exceeding the conventional highest level (80%). It is understood that

Further, the self-fusing pellets 1 formed as described above have a cross-sectional shape as shown in FIG. 5 and FIG. 6, which is a partially enlarged view of FIG. 5. In FIG. 6, a gangue phase 3 with a thickness of 1001 L or more is present around the pores 2. 4 is Fe203.

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.

(Table 2) (In the case of 1250°C) Table 3 below shows the results when the firing temperature is 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. 6 above. In this case, the gangue phase 3 is located around the pore 2'.
Also, Table 4 below shows the components of the part indicated by the number 5' in Figure 7 above and the corresponding basicity by firing temperature.

(Table 4) Above 2. Comparing Table 3 and Table 4, it can be seen that the CaO/5iOz (basicity) near pore 2 of the example is higher than that of the conventional example, and this improves reducibility. is achieved.

Figures 8 and 9 relate to the self-fusing pellet) 1 when the firing temperature was 1250°C, and Figure 8 shows the CaO/S i0 in the gangue phase 3 of the self-fusing pellet) 1.
2 is a graph showing the relationship between the value of CaO/SiO2 and the reduction rate, and even if the open porosity of the self-soluble pellets l is similar, the value of the reduction rate with respect to the value of CaO/SiO2 is
It changes depending on the value of. Furthermore, since the gangue phase 3 does not have a uniform structure, the value of CaO/SiO2 varies. 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 self-soluble pellets) 1 CaO/5j0 as a whole
2 is a graph showing the relationship between reduction rate and reduction rate, and also includes a conventional example when fine dolomite with a grain size of 44 or less is used as a pellet raw material (shown by a chain line in the figure). It is understood that if coarse dolomite having a diameter of 0.1 to 0.5 mm is used as a raw material, the reduction rate will increase. It can be seen that if the value of CaO/SiO2 is set to 0.8 or more, the reduction rate can be improved at the CaO/SiO2 level.

Figure 1θ shows coarse dolomite with a grain size of 0.1■■~0.5■■ as a raw material, and the firing temperature is 1250℃ and 12℃.
It is a graph diagram showing the relationship between the MgO/SiO2 value and the reduction rate, regarding the self-soluble pellet 1 at 75°C. Currently, the highest reduction rate among industrially produced pellets is 80%. Therefore, it can be seen that in order to obtain a higher reduction rate, it is necessary to add MgO in an amount that makes the value of MgO/SiO2 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. be. These photographs are 3x enlarged photographs, and are taken from particles in each particle size range as shown in Table 5.

(Table 5) According to 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 pellets 1 formed as described above. According to this figure, the amount of open pores 2a with a diameter of 5 cm or more is 0.0
45a! It is understood that if the ratio is 8 or more, the reduction rate will be significantly improved beyond the conventional highest level of 80%.

Further, 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 Figure 15, the thickness around pore 2 is 150 to 400 ILr.
Gangue facies 3 of a is 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 1000°C) Table 7 below shows the results when the firing temperature is 1275°C.

(Table 7) (In the case of 1275°C) 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 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, the amount of open pores with a diameter of 5 cm or more can be reduced to 0.0
45a//g or more, and on the other hand, a calcium ferrite structure having a thickness of 10041 or more and a CaO/SiO2 value of 1.4 or more is present around the pores having a diameter of 5μ or more including the open pores. And overall Ca
Since the O/S i02 value was set to 9.8 or more, the reduction rate was 75 to 80% for conventional pellets, but it was 80% or more for the self-fusing pellets of the present invention, making it suitable as a raw material for blast furnace charging. Quality improves.

[Brief explanation of the drawing]

The figures show embodiments of the present invention, in which Figure 1 is a schematic sectional view of a self-soluble pellet, Figures 2 to 10 are a first specific embodiment, and Figures 2 and 3 are a schematic cross-sectional view of a self-soluble pellet. 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, 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. φ pores, 2a.. Open pores,
2bΦ・closed pore, 3・・gangue phase (calcium ferrite type structure). Figure 4 Throat - Gourd) L't (C and) (iyo"°9#stone'tm
f Cab/Si Oz (-) Cc, 7 humiliation 02 ratio (-
) MyO7S Nanbi (-) Figure 16 Procedure Ne... Regular Book (Method) % Formula % 1. Indication of the incident 1985 Patent Application No. 294575 2. Name of the invention Self-propelling pellets for blast furnace charging 3. Amendment Relationship with the person who filed the patent application Patent applicant address (residence) 1-3-1 Wakihama-cho, Chuo-ku, Kobe, Hyogo Prefecture
No. 8 Name 11191 Kobe Steel, Ltd. 4, Agent 531

Claims (1)

[Claims] 1. The amount of open pores with a diameter of 5 μm or more is 0.045 cm^3/
CaO/Si
A self-fusing pellet for blast furnace charging, characterized in that it has a calcium-ferrite structure with an O_2 value of 1.4 or more, and has an overall CaO/SiO_2 value of 0.8 or more. 2. The self-fusing pellet for blast furnace charging according to claim 1, characterized in that the MgO/SiO_2 value as a whole is 0.40 or more.