JP7035869B2 - Sintered ore - Google Patents

Description

The present invention relates to a technique for producing a sinter having an excellent high temperature reduction rate.

In the pig iron operation of the blast furnace, it is important to reduce the ratio of reducing agents and ensure the air permeability in the furnace. In order to achieve these, various improvements have been made to the quality of the sinter, which is the main raw material of the blast furnace. Cold strength, reducing property, reducing pulverization property, and high temperature property are known as important quality items of sinter. However, it is difficult to satisfy these quality items at the same time.

The following patent documents are known as a method for solving the above-mentioned problems from the viewpoint of mineral composition. Patent Document 1 describes "SiO ₂ content is 5 wt.% Or less, and CaO (wt.%) / SiO ₂ (SiO 2%) / SiO 2 (SiO 2 content is 5 wt.% Or less, and CaO (wt.%) It has a chemical component whose basicity is in the range of 1.0 to 3.0 expressed by wt.%), And the formula: (hematite phase amount (area%)) / (magnetite phase amount (area%)). ) ≤ 0.5 (By the way, in terms of mass%, it is 0.41 or less). ”Sintered ore having an average constituent mineral structure and having an average pore ratio of 15 area% or more” is disclosed. ing.

Patent Document 2 describes a sinter having excellent softening and melting properties, which is one of the high temperature properties, for the purpose of improving air permeability in the blast furnace fusion zone, and has a connective tissue mainly composed of silicate slag and magnetite. Discloses a sinter of a sintered structure in which macropores are dispersed. Further, Patent Document 2 discloses a sinter containing hematite in a part of the connective tissue.

Patent Document 3 discloses a sinter having excellent reducible pulverization property while maintaining the reducibility to the conventional level. Specifically, the SiO ₂ content is 4.8% or less. , CaO content (%) / SiO ₂ content (%) is less than 2.0, and the sum of the composition ratio of magnetite and the composition ratio of olivine slag is 20% or more as the mineral composition, silicate-based. A sinter having a slag composition ratio of 5% or less and a residual composition ratio of hematite and magnetite is disclosed.

Further, from the blast furnace side, it is desired to increase the iron raw material by reducing the SiO ₂ content of the sinter.

Japanese Unexamined Patent Publication No. 10-265857 Japanese Unexamined Patent Application Publication No. 2003-049228 Japanese Unexamined Patent Publication No. 2003-129141

However, in view of the current iron ore situation, it is difficult to stably supply and supply iron ore having a low silica content, which is a raw material for the low silica sintered ore as described above. By using iron ore (fine ore) from which impurities have been removed by crushing and beneficiation of iron ore having a high silica content as a raw material for sintering, a sintered ore having a SiO ₂ content of 5% by mass or less is produced. The method is also known. However, since this concentrate is a fine powder, the air permeability of the sintering raw material is lowered, and the combustion progress rate is lowered, so that the sintering time becomes long. As a result, the pallet speed becomes slow and the productivity decreases.

In addition, since the basicity (CaO / SiO ₂ ) of the sinter is generally adjusted to a fixed value (about 1.8), lowering SiO ₂ also reduces CaO (that is, the amount of limestone compounded). There is a need. Here, since CaO becomes a bonding portion of the sinter during sintering, if CaO is reduced, the strength of the sinter may decrease.

In the sinter disclosed in Patent Document 2, since silicate slag and magnetite are the main constituents of the sinter structure, there is a concern that the reducibility, which greatly affects the ratio of reducing materials, is not sufficient.

Therefore, the present invention is based on the premise that ordinary iron ore having a relatively high SiO ₂ concentration (SiO ₂ concentration: more than 5.0% by mass and 5.5% by mass or less) is used as a sinter raw material. It is an object of the present invention to provide a sinter having excellent high temperature reducing property while maintaining the strength at the current level.

The above-mentioned high-temperature reducing property is not the reducing property at 900 ° C. discussed in Patent Documents 1 and 3, that is, the reducing property specified in JIS-RI: JIS-M8713, but a load softening test apparatus is used. It refers to the reached reduction rate when the sample temperature reaches 1200 ° C. when the sintered ore is reduced while heating from room temperature to 1600 ° C. The reason for selecting the ultimate reduction rate at 1200 ° C as an index of reducibility is the high temperature reducibility related to the reduction of pressure loss in the cohesive zone when the purpose is to improve the air permeability in the furnace. This is because it is preferable to do so. The fusion zone is the region from the start of softening and melting of the ore to the dropping of the ore, and is the region where the aeration resistance is highest in the blast furnace.

Therefore, the present inventor focused on the minerals hematite, magnetite, calcium ferrite, and slag in the sinter, and the ratios thereof and the reduction rate when the ambient temperature near the cohesive zone reached 1200 ° C. I investigated the relationship with. For calcium ferrite, a four-component system consisting of hematite, CaO, SiO ₂ and Al ₂ O ₃ was targeted. The slag targeted CaO and SiO ₂ which are the main components thereof.

Hematite was prepared by molding a reagent into a briquette having a diameter of about 10 mm and a height of about 10 mm, sintering it in an air atmosphere, and crushing it to 75 μm or less. Magnetite is made by briquetting a hematite reagent to a diameter of about 10 mm and a height of about 10 mm, and measuring the weight under a predetermined reducing atmosphere (reducing gas composition: 10% Co-90% CO ₂ , atmosphere temperature: 1000 ° C.). When the weight change disappeared, the reducing gas was switched to _N2 gas, cooled to room temperature in an _N2 gas atmosphere, and then pulverized to 75 μm or less.

For calcium ferrite, hematite, CaO, SiO ₂ , and Al ₂ O ₃ reagents were mixed according to the ratio in the upper part of Table 1, molded into a briquette having a diameter of about 10 mm and a height of about 10 mm, and calcined at 1000 ° C. for about 3 hours. After that, it was crushed and molded into a briquette again, heated to 1300 ° C. at 10 ° C./min, maintained at 1300 ° C. for 30 min, lowered to 1100 ° C. at 20 ° C./min, and then cooled with water for synthesis. The synthesized calcium ferrite was crushed to 75 μm or less.

The slag was prepared by mixing the reagents of CaO and SiO ₂ so as to have the ratio shown in the lower part of Table 1. The synthesis method was the same as that of calcium ferrite described above.

The ratios of the four types of minerals prepared by the above method are variously mixed, and the diameter is about 10 mm and the height is high under the conditions that the SiO ₂ content is 5.3% by mass and the basicity CaO / SiO ₂ is 1.8. It was molded into a briquette of about 10 mm in diameter. The weight of the briquette was determined so that the porosity of the briquette was 30% by volume. The reason why the conditions of the SiO ₂ content and the basicity CaO / SiO ₂ are set to 5.3% by mass and 1.8, respectively, is the typical chemical composition of the sinter corresponding to the ore currently distributed, and is currently present. This is because the composition is set so that the strength equivalent to that of the sinter used is obtained.

A packed bed of 500 g was formed using the molded briquette described above, and a load softening test was carried out using the test apparatus shown in FIG. This load softening test device includes a graphite crucible 13 on which a packed layer 11 is formed by the above-mentioned briquette, a load control device 15 arranged above the graphite crucible 13 and capable of applying a load to the packed layer 11. It is equipped with. The temperature at the measurement point 14 on the upper part of the graphite crucible 13 can be measured as the sample temperature. The reducing gas introduced from below the load softening test device passes through the packed bed 11 and is discharged from above the load softening test device.
The electric furnace 12 heats the packed bed 11 filled in the graphite crucible 13.

That is, a load is applied to the packed layer 11 in the graphite crucible 13 by the load control device 15, a reducing gas is introduced, and the packed layer 11 can be heated by the electric furnace 12. Then, by analyzing the composition of the exhaust gas, the reduction rate when reaching 1200 ° C. (hereinafter referred to as the reduction rate reaching 1200 ° C.) can be calculated.

The test results are shown in Table 2. When the reduction rate reaching 1200 ° C. was 71% or more, it was evaluated as ◯ as having an excellent reduction rate reaching 1200 ° C. When the reduction rate reaching 1200 ° C. was 70% or less, it was evaluated as x as the reduction rate reaching 1200 ° C. was poor.

Based on the above findings, the present inventor has created the following inventions. That is, the present invention is (1) a sintered ore having a SiO ₂ content of more than 5.0% by mass and 5.5% by mass or less, and the mass ratio of hematite, magnetite, and calcium ferrite in the sintered ore is Hm. When (mass%), Mm (mass%) and Fm (mass%), the relative ratio H of hematite represented by the formula (1) is 16% by mass or more and 24% by mass or less, and is represented by the formula (2). The sintered ore characterized in that the relative ratio M of the magnetite formed is 46% by mass or more and 54% by mass or less.
H = Hm / (Hm + Mm + Fm) ・ ・ ・ ・ ・ Equation (1)
M = Mm / (Hm + Mm + Fm) ・ ・ ・ ・ ・ Equation (2)

The relative ratio F of calcium ferrite can be calculated based on the following formula (3).
F = Fm / (Hm + Mm + Fm) = 100- (H + M) ・ ・ ・ ・ ・ ・ ・ ・ Equation (3)

Here, the area ratios of hematite, magnetite, calcium ferrite and slag to the solid portion in the sintered ore are defined as Ha, Ma, Fa and Sa, respectively, and the densities of hematite, magnetite, calcium ferrite and slag are defined as ρ _H , respectively. When defined as ρ _M , ρ _F and ρ _S , the calculation formulas for Hm (mass%), Mm (mass%) and Fm (mass%) are as follows.
Hm = ρ _H Ha / (ρ _H Ha + ρ _M Ma + ρ _F Fa + ρ _S Sa)
Mm = ρ _M Ma / (ρ _H Ha + ρ _M Ma + ρ _F Fa + ρ _S Sa)
Fm = ρ _F Fa / (ρ _H Ha + ρ _M Ma + ρ _F Fa + ρ _S Sa)

Substituting these equations into Hm, Mm and Fm of the equations (1) and (2), respectively, gives the following equations (4) and (5).
H = Hm / (Hm + Mm + Fm) = ρ _H Ha / (ρ _H Ha + ρ _M Ma + ρ _F Fa)
・ ・ ・ ・ ・ ・ ・ Formula (4)
M = Mm / (Hm + Mm + Fm) = ρ _M Ma / (ρ _H Ha + ρ _M Ma + ρ _F Fa)
・ ・ ・ ・ ・ ・ ・ Formula (5)
Ha, Ma and Fa can be calculated based on an image analysis method (see, for example, "Transactions ISIJ, 25 (1985), p. 257") in which the microstructure is determined from the cross-sectional image of the sinter based on the brightness. .. Here, ρ _H , ρ _M and ρ _F are 5.24 (g / cm ³ ), 5.17 (g / cm ³ ) and 3.98 (g / cm ³ ), respectively. The area ratio is Ha + Ma + Fa + Sa = 1 with reference to only the solid portion excluding the pores.

In the image analysis method, the area ratio of the slag cannot be accurately evaluated because the overlap of the luminance distributions of the pores and the slag is large. On the other hand, for hematite, magnetite and calcium ferrite, their area ratio can be evaluated relatively easily and with a certain accuracy. As described above, in the present invention, since the relative amounts of hematite and magnetite with respect to the sum of hematite, magnetite and calcium ferrite are the problems, it does not matter even if the slag quantification is poor.

According to the present invention, even if the SiO ₂ content is more than 5.0% by mass, the relative ratio H of hematite and the relative ratio M of magnetite are set within a predetermined range, so that the reduction rate reaching 1200 ° C. is excellent. Sintered ore can be provided. As a result, the amount of CO ₂ generated can be reduced while reducing the amount of reducing agent charged into the blast furnace.

It is a schematic diagram of the load softening test apparatus.

As described above, in the present invention, the first requirement is "the SiO ₂ content of the sintered ore is more than 5.0% by mass and 5.5% by mass or less", and the second requirement is "hematite, magnetite and calcium". The relative ratio H of hematite to the sum of ferrite is 16% by mass or more and 24% by mass or less, and the third requirement is that the relative ratio M of hematite to the sum of hematite, magnetite and calcium ferrite is 46% by mass or more and 54% by mass. Below. "

(About the first requirement)
The SiO ₂ content can be measured based on the general rule of iron ore analysis method (JIS_M8202) and the fluorescent X-ray analysis method of iron ore (JIS_M8205). Here, the basicity (CaO / SiO ₂ ) of the sinter is assumed to be about 1.8. This corresponds to the basicity of the sinter when adjusting the slag basicity of the blast furnace to 1.2 in general blast furnace operation (sinter compounding ratio of about 80%, etc.). be. Since it is necessary to maintain the basicity (CaO / SiO ₂ ) of the sinter at about 1.8, when SiO ₂ is reduced to less than 5.0% by mass, CaO is insufficient. As a result, the amount of limestone used as a solvent is reduced and the amount of melt produced during sintering is reduced, so that the connective tissue of the sinter is reduced and the strength of the sinter is reduced. Further, as described above, it is difficult to limit the SiO ₂ content to 5.0% by mass or less in view of the current supply and demand situation of iron ore. When the SiO ₂ content exceeds 5.5% by mass, the ratio of the slag phase of the sinter becomes excessive, and the reducibility is lowered.

(About the second and third requirements)
Since the method for measuring the relative ratio H of hematite and the relative ratio M of magnetite has been described above, the description will not be repeated. In the sinter having a SiO ₂ content of more than 5% by mass and 5.5% or less, as described above, the relative ratio H of hematite is limited to 16% by mass or more and 24% by mass or less, and the relative ratio M of magnetite is limited. By limiting the amount to 46% by mass or more and 54% by mass or less, the evaluation of high temperature reducibility can be enhanced to ◯.

The remaining mineral phase is amorphous (slag (S)), and is about 10% by mass in the sinter having a SiO ₂ content. In the present invention, the porosity of the sinter is not particularly specified. The porosity may be in the range of the sinter obtained in a normal sinter manufacturing process. Porosity is usually in the range of 25-45% by volume. The porosity can be calculated based on the pack method. Since the packing method is disclosed in a non-patent document (Kasama et al .: Iron and Steel, 83 (1997), p.109), the description thereof will be omitted.

Next, a method for producing a sinter having excellent high-temperature reducing properties (hereinafter referred to as the sinter of the present application) satisfying the above-mentioned first to third requirements will be described. The present inventor has found that the sinter of the present application can be efficiently obtained by adjusting the particle size of the carbonaceous material used in the sintering step to 1 mm or more. The reason for using a charcoal material of 1 mm or more is as follows.
(1) "Since the combustion rate of carbonaceous material having a particle size of 1 mm or more is slower than the combustion rate of carbonaceous material having a particle size of less than 1 mm, the amount of heat required to sufficiently generate a melt and to perform firm sintering. Can be supplied for a long time, and as a result, a strong substrate with low reduced pulverizability can be obtained. " The time can be extended and the presence of only poorly reducible minerals can be suppressed. "
(2) When the air permeability is improved, the cooling rate of the sinter is increased, so that the shape of the mineral becomes a fine structure having good reducibility.

(Example)
The present inventor carried out a sintering pot test using the ore raw materials shown in Table 3. 3 mm under powdered coke was used as the coagulant. However, in the example, the particle size was adjusted to remove the coke breeze under 1 mm. In the comparative example, the particle size of the coke breeze was not adjusted. Table 4 shows the particle size distribution of the coke breeze of Comparative Examples and Examples.

In the sintering pot test, a sintered pot having an inner diameter of 300 mm and a layer height of 600 mm was used. The sintered pot is formed in a cylindrical shape, and the inner bottom thereof is provided with a grate that allows ventilation. A wind box is installed at the bottom of the sintered pot. A suction blower is connected to the air box via an exhaust gas pipe that exhausts exhaust gas, and the exhaust gas can be sucked through the air box. Inside the air box, a temperature sensor that measures the temperature of the sintered exhaust gas is provided. In addition, an exhaust gas sampling pipe is installed between the air box and the suction blower.

The raw material was filled on the grade, the negative pressure under the pan of the sintering pot was adjusted to a predetermined value, and the upper part of the packed bed was ignited. The sintering reaction was allowed to proceed by sucking air from the upper part of the packed bed. In addition, the exhaust gas temperature was measured by a temperature sensor installed in the air box under the pot. The time when the exhaust gas temperature became maximum was defined as the sintering completion time.

Table 5 shows the chemical composition of the sinter measured after the completion of sinter. In addition, "C / S" in Table 5 is an abbreviation for "CaO / SiO ₂ which is the basicity of sinter". The area ratio Ha of hematite and the area ratio Ma of magnetite were calculated according to the above-mentioned image analysis method. The relative ratio H of hematite and the relative ratio M of magnetite were calculated according to the above formulas (4) and (5).

It was found that a sinter that satisfies the above-mentioned first to third requirements can be obtained by using the powdered coke from which the powdered coke of 1 mm under has been removed.

11 Packed bed 12 Electric furnace 13 Graphite crucible 14 Measurement points 15 Load control device

Claims (3)

Sintered ore with a SiO ₂ content of more than 5.0% by mass and 5.5% by mass or less.
When the mass ratios of hematite, magnetite and calcium ferrite in the sintered ore are Hm (mass%), Mm (mass%) and Fm (mass%), the relative ratio H of hematite represented by the formula (1). Is 16% by mass or more and 24% by mass or less, and the relative ratio M of magnetite represented by the formula (2) is 46% by mass or more and 54% by mass or less.
H = Hm / (Hm + Mm + Fm) ・ ・ ・ ・ ・ Equation (1)
M = Mm / (Hm + Mm + Fm) ・ ・ ・ ・ ・ Equation (2) The area ratios of hematite, magnetite and calcium ferrite to the solid part in the sinter are defined as Ha, Ma and Fa, respectively.
When the densities of hematite, magnetite and calcium ferrite are defined as ρ _H , ρ _M and ρ _F , respectively,
The sintering according to claim 1, wherein the formula (1) is rewritable to the following formula (4), and the formula (2) is rewritable to the following formula (5). Ore.
H = ρ _H Ha / (ρ _H Ha + ρ _M Ma + ρ _F Fa) ・ ・ ・ ・ ・ ・ ・ Equation (4)
M = ρ _M Ma / (ρ _H Ha + ρ _M Ma + ρ _F Fa) ・ ・ ・ ・ ・ ・ ・ Equation (5) The sinter according to claim 1 or 2, wherein the reduction rate when reaching 1200 ° C. is 71% or more.

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