JP7343768B2 - Method of blending raw materials for sintering - Google Patents

Description

The present invention relates to a method for blending raw materials for sintering.

The method for producing sintered ore is roughly as follows. First, raw materials for sintering, which are raw materials for sintered ore, are blended at a predetermined blending ratio to form a blended raw material, and then granulated with water. Here, the raw materials for sintering consist of iron-based raw materials that are the main raw materials, auxiliary raw materials necessary for the sintering reaction and component adjustment, carbonaceous materials (solid fuel) that are the heat source, miscellaneous raw materials, return ore, etc. be done. The iron-based raw material is, for example, iron ore such as fine ore and fine ore. The auxiliary raw materials include, for example, limestone, dolomite, converter slag, serpentine, silica, and olivine. Examples of the carbonaceous material include coke powder and anthracite. Miscellaneous raw materials are, for example, iron-containing recycled raw materials such as ironmaking dust, steelmaking dust, and scale. Among these raw materials for sintering, raw materials for sintering excluding carbonaceous materials and return ore are also referred to as new raw materials.

Next, the granulated material of the blended raw materials is loaded into a sintering pallet of a sintering machine in a layered manner. Here, the granulated material of the compounded raw material includes coarse core particles and an adhering powder layer attached to the surface of the core particles. Then, the solid fuel in the raw material packed bed is ignited from the surface of the raw material packed bed, and the solid fuel is sucked and ventilated from the top to the bottom of the raw material packed bed in the thickness direction. As a result, the combustion zone of the raw material packed bed is sequentially moved to the lower layer side, and the sintering reaction proceeds (sintering process). After firing, the sintered cake in the sintered pallet is crushed and sized to a predetermined particle size suitable for use as sintered ore for blast furnaces. Through the above steps, sintered ore is produced.

By charging the blended raw materials into granules into a sintering machine, it is possible to increase the porosity and pores of the raw material packed bed. Therefore, since the permeability of the raw material packed bed is improved, it is expected that the productivity of sintered ore will be improved.

By the way, in the sintering process, a liquid phase sintering reaction proceeds in which the remaining solid portion (ie, non-assimilated portion) is bonded by the fluid generated at a volume ratio of about 50 to 70%. On the other hand, the reactivity (reducibility) of sintered ore in a blast furnace is influenced by the pore structure of sintered ore and the reactivity of the dough (parts other than pores). Therefore, in order to produce sintered ore with excellent reducibility, it is important to control the characteristics of the fluid generated during the sintering process to create a pore structure and texture.

Japanese Patent Application Publication No. 58-039746

Sasaki et al., “Sintered ore structure and quality from the perspective of sintering reaction” (Tetsu to Hagane, 1982, Vol. 68, No. 6, p. 563-571) Sato et al., “Relationship between sintered ore structure and reduction properties” (Tetsu to Hagane, 1982, Vol. 68, No. 15, p. 2215-2222) Sakamoto et al., “Reaction kinetics of reducibility of sintered ore structure” (Tetsu to Hagane, 1984, Vol. 70, No. 6, p. 504-511) Hida et al., “Generation mechanism of acicular calcium ferrite in sintered ore” (Tetsu to Hagane, 1987, Vol. 73, No. 15, p. 1893-1900)

Regarding the structure of the fabric part, it is known that the reactivity of acicular calcium ferrite (CF) with a width of around 10 μm is better than that of columnar CF (Non-Patent Documents 1 to 3). Therefore, the more acicular CFs contained in the dough, the higher the reactivity of the dough and, in turn, the higher the reducibility of the sintered ore.

For this reason, research on the generation mechanism of acicular CF is being carried out intensively. For example, in the above-mentioned sintering process, acicular CF is easily generated by firing the blended raw materials at a low temperature of 1300°C or less, and a certain amount of veins such as SiO ₂ or Al ₂ O ₃ is required to generate acicular CF. It is known that stone components are required (Non-patent Documents 1 and 4).

However, the conventional knowledge is limited to qualitative evaluation, and quantitative conditions for increasing the content of acicular CF in the fabric portion have not been clarified. In particular, the mineral form of iron ore has changed compared to when the findings in Non-Patent Documents 1 to 4 were obtained, and the quality of iron ore resources is progressing in the medium to long term. Therefore, increasing the reducibility of sintered ore has become a very important issue. On the other hand, Patent Document 1 discloses a technique for controlling the components of a fluid generated during the sintering process. However, Patent Document 1 does not consider the influence of each component of the fluid on the generation of needle-like CF.

The present invention has been made in view of the above problems, and an object of the present invention is to increase the content of acicular CF in sintered ore, and thereby to improve the reducibility of sintered ore. The object of the present invention is to provide a new and improved method of blending raw materials for sintering.

In order to solve the above problems, according to one aspect of the present invention, the content of dense iron ore having an average particle size of 0.1 to 1.0 mm and a porosity of 10% by volume or less is a new raw material. New raw materials that are 5% by mass or more based on the total mass and excluding dense iron ore include new raw materials with a particle size of 1.0 mm or less , and new raw materials with a particle size of 1.0 mm or less meet the following conditions (1). ) and (2) are provided. A method for blending raw materials for sintering is provided, which is characterized by blending raw materials for sintering so as to satisfy (2).
(1) Basicity (mass ratio of CaO/SiO ₂ ) is 1.65 or more.
(2) Al ₂ O ₃ concentration is 1.5% by mass or more, or MgO concentration is 1.0% by mass or less.

According to the above aspect of the present invention, it is possible to increase the content of acicular CF in the sintered ore, thereby increasing the reducibility of the sintered ore.

It is a schematic diagram showing an example of the granulation line concerning this embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Note that, in this specification and the drawings, components having substantially the same functional configurations are designated by the same reference numerals and redundant explanation will be omitted.

<1. Study by the inventor>
In order to find a method for quantitatively evaluating the content of acicular CF in the dough, the inventors first observed the texture and element distribution of the dough of sintered ore by image analysis. Here, the fabric part structure is composed of silicate slag (SS), etc. in addition to the above-mentioned needle-like CF and columnar CF. As a result, it was found that many acicular CFs in the sintered ore were generated in areas where the Ca concentration gradient was large. Therefore, it is presumed that if many regions with large Ca concentration gradients can be formed in the sintered ore, many acicular CFs will be generated in the sintered ore.

Conditions that increase the concentration gradient of Ca include "low temperature calcination", "addition of dense iron ore (hereinafter also referred to as "compact ore")", "increasing the viscosity of the fluid generated during the sintering process", and " ``Increase in cooling rate'' was considered. Therefore, the present inventor conducted a basic experiment (tablet firing experiment) in order to find out the extent to which these contribute to the generation of acicular CF. In the tablet firing experiment, the following treatments were performed. First, iron-based raw materials and limestone were mixed based on the blending ratio of the blended raw materials. The mixture was then formed into tablets, and the resulting tablets were fired using a heat pattern that simulated an actual sintering reaction. Next, the texture and elemental distribution of the sintered ore were observed by image analysis of the cross section of the sintered body. As a result, the present inventor found that the addition of compact ore greatly contributes to the generation of acicular CF, and that the content of acicular CF can be further increased by increasing fluid viscosity in addition to adding compact ore. I found out. Furthermore, the present inventor conducted tablet firing experiments by varying the amount of compact ore added, particle size, and fluid viscosity, and measured the high temperature reducibility (R1200) of the obtained sintered bodies. A suitable range of parameters was identified. Based on the above findings, the inventors came up with a method for blending raw materials for sintering according to the present embodiment.

<2. Method of blending raw materials for sintering>
Next, a method for blending raw materials for sintering according to this embodiment will be explained. Here, the raw materials for sintering include, as mentioned above, iron-based raw materials that are the main raw materials, auxiliary raw materials necessary for the sintering reaction and component adjustment, carbonaceous materials (solid fuel) that are the heat source, miscellaneous raw materials, and Consists of return ore, etc. The iron-based raw material is, for example, iron ore such as fine ore and fine ore. Although details will be described later, the iron ore in this embodiment includes compact ore having an average particle size of 0.1 to 1.0 mm and a porosity of 10% by volume or less. The auxiliary raw materials include, for example, limestone, dolomite, converter slag, serpentine, silica, and olivine. Examples of the carbonaceous material include coke powder and anthracite. Miscellaneous raw materials are, for example, iron-containing recycled raw materials such as ironmaking dust, steelmaking dust, and scale. Among these raw materials for sintering, raw materials for sintering excluding carbonaceous materials and return ore are also referred to as new raw materials. In this embodiment, the raw materials for sintering are blended so that the following conditions A and B are satisfied.

(Condition A)
In this embodiment, the average particle size is 0.1 to 1.0 mm, and the content of compact ore with a porosity of 10% by volume or less is 5% by mass or more based on the total mass of the new raw material. Mix raw materials for sintering.

Here, the average particle size of the iron ore is measured by a dry method of stacked discontinuous mechanical sieving in accordance with JIS-M8706 (2008) "Iron ore and reduced iron - Measuring method of particle size distribution by sieving". The sieve used has five stages of 0.25 mm, 0.5 mm, 1.0 mm, 2.0 mm, and 4.0 mm, and the representative particle sizes of the six particle size categories are from fine to 0.125 mm, 0.375 mm, 0. They are 75mm, 1.5mm, 3mm, and 7mm. Calculation of average particle size follows Annex J. That is, the arithmetic mean is obtained by multiplying the representative particle size by the mass ratio of each particle size category.

The porosity of iron ore is measured by image analysis of its cross section. That is, the sample is buried and polished, and the cross-section of the obtained sample is image-analyzed to determine the area ratio (%) of the pores to the total area of the observation field. This area ratio is defined as the porosity of the sample. Similar processing is performed for several observation fields, and the arithmetic mean value of the obtained area ratios is taken as the representative porosity of the sample. The number of observation fields is a number such that the one digit of the representative value obtained as the arithmetic mean has sufficient accuracy. In the Examples described later, the average particle size and porosity were measured using these methods.

Thus, in this embodiment, relatively fine compact ore with an average particle size of 0.1 to 1.0 mm is used. Thereby, many regions with a large Ca concentration gradient can be formed in the sintered ore. More specifically, the number of regions where the Ca concentration gradient is large is large, and the total area of these regions is large. In the sintering process, a part of the raw material packed bed is assimilated to become a fluid, and this fluid bonds the remaining solid parts (i.e., non-assimilated parts) (liquid phase sintering reaction). The fluid is then cooled and solidified into the assimilation section. Therefore, the dough portion in the sintered ore includes an assimilated portion where the fluid solidified and a non-assimilated portion where the fluid was not assimilated. Compact ore with an average particle size of 0.1 to 1.0 mm is difficult to assimilate into the fluid during the liquid phase sintering reaction, and often remains in the fabric part as a non-assimilated part (in other words, a residual original ore part). Therefore, the Fe concentration gradient becomes large around such compact ores. In other words, the Fe concentration in each region in the dough portion becomes higher as the region is closer to compact ore. Then, a Ca concentration gradient is formed in a form that is a trade-off with such a Fe concentration gradient. In other words, the Ca concentration in each region in the dough portion becomes lower as the region is closer to compact ore. In the present embodiment, compact ore forming a large Ca concentration gradient is dispersed in the sintered ore, so many regions with a large Ca concentration gradient can be formed in the sintered ore.

The average particle size of compact ore is required to be 0.1 to 1.0 mm. When the average particle size of the compact ore is less than 0.1 mm, the compact ore is immediately assimilated with the fluid during the sintering process, and almost no Ca concentration gradient is formed. When the average particle size of the compact ore exceeds 1.0 mm, the compact ore is difficult to assimilate with the fluid, so a large Ca concentration gradient is formed around the compact ore. However, since the number of particles of compact ore decreases, the area where the Ca concentration gradient is formed decreases.

Table 1 below shows representative examples of iron ore. Among these examples, iron ores D and FG are classified as compact ores. Furthermore, iron ores F and G are compact ores used in this embodiment. In addition, in Table 1, the value of each component means mass % with respect to the total mass of iron ore. The mass % of each component is a value measured according to the general rules of JIS M8202 (2000). Note that the Al ₂ O ₃ concentration is measured according to M8220: Aluminum quantitative method, and the SiO ₂ concentration is measured according to M8214: Silicon quantitative method, or M8205: Fluorescent X-ray analysis method revised therewith. The methods for measuring porosity and average particle size are as described above.

In this embodiment, the mass % of compact ore having an average particle size of 0.1 to 1.0 mm is 5 mass % or more based on the total mass of the new raw material. Preferably it is 10% by mass or more. When the mass % of compact ore is less than 5 mass %, a sufficient Ca concentration gradient is not formed. When the mass % of the compact ore is 5 mass % or more, preferably 10 mass % or more, many regions with a large Ca concentration gradient can be formed.

(Condition B)
In this embodiment, the new raw materials excluding the compact ore include new raw materials with a particle size of 1.0 mm or less, and the new raw materials with a particle size of 1.0 mm or less satisfy the following conditions (1) and (2). , blend raw materials for sintering.
(1) Basicity (mass ratio of CaO/SiO ₂ , so-called C/S) is 1.65 or more.
(2) Al ₂ O ₃ concentration is 1.5% by mass or more, or MgO concentration is 1.0% by mass or less.

Condition B stipulates the conditions that must be met by a new raw material (excluding compact ores; the same applies hereinafter) having a particle size of 1.0 mm or less. The volume ratio of the fluid generated during the sintering process is considered to be approximately 50 to 70% of the total volume of the raw material packed bed. Taking into consideration the volume ratio of the fluid and the particle size distribution of common mixed raw materials, it is thought that the new raw materials with a particle size of 1.0 mm or less are almost completely assimilated during the sintering process and become a fluid. Therefore, it can be said that condition B defines the conditions that the new raw material that becomes the fluid must satisfy. Note that the new raw material with a particle size of 1.0 mm or less can be obtained by classifying all the new raw materials except the compact ore using a sieve with an opening of 1.0 mm.

Condition (1) defines the basicity of the new raw material. Basicity is the mass ratio of CaO and SiO ₂ contained in a new raw material with a particle size of 1.0 mm or less. The mass of the CaO component is measured according to JIS M8221: Calcium quantification method. The mass of the SiO ₂ component is measured by the method described above. According to the CaO-SiO ₂ -Fe ₂ O ₃ phase diagram disclosed in "Slag Atlas" by the German Iron and Steel Association, etc., CF is generated when the basicity is 1.65 or more.

Condition (2) stipulates the conditions that the Al ₂ O ₃ concentration or MgO concentration of the new raw material with a particle size of 1.0 mm or less should satisfy. Note that the Al ₂ O ₃ concentration is measured by the method described above. The MgO concentration is measured according to JIS M8222: Magnesium quantification method. When condition (2) is satisfied, the viscosity of the fluid generated during the sintering process becomes high, so that many regions with large Ca concentration gradients can be formed in the dough portion. More specifically, when condition (2) is satisfied, a highly viscous fluid surrounds the compact ore, which is difficult to assimilate. Such a high viscosity fluid solidifies while maintaining the Ca concentration gradient formed around the compact ore. Therefore, many regions with large Ca concentration gradients can be formed in the sintered ore, and in turn, many acicular CFs can be formed in the sintered ore.

Note that conventionally, for reasons such as increasing the strength of sintered ore, the viscosity of the fluid has been made as low as possible. In contrast, the present inventors have discovered that by increasing the viscosity of the fluid, many acicular CFs can be formed in the sintered ore, and as a result, the reducibility of the sintered ore can be improved. Ta. Therefore, the findings made by the present inventors have not been considered at all in the past.

The upper limit value of the Al ₂ O ₃ concentration and the lower limit value of the MgO concentration in condition (2) are not particularly limited. However, if the Al ₂ O ₃ concentration is too high or the MgO concentration is too low, the viscosity of the fluid may become very high and the strength of the sintered ore may decrease. From this viewpoint, the upper limit of the Al ₂ O ₃ concentration is preferably 2.2%, and the lower limit of the MgO concentration is preferably 0.5%.

(Method for adjusting Al ₂ O ₃ concentration)
If condition (2) is not satisfied, the Al ₂ O ₃ concentration may be adjusted, for example, by the following treatment. That is, the Al ₂ O ₃ components are mainly brought in from iron ore. Therefore, the amount of iron ore with a high Al ₂ O ₃ concentration may be increased, or the iron ore with a high Al ₂ O ₃ concentration may be pulverized so that the particle size is 1.0 mm or less.

(How to adjust MgO concentration)
If condition (2) is not satisfied, the MgO concentration may be adjusted, for example, by the following process. That is, the MgO component is contained in a large amount in some MgO-containing auxiliary raw materials (for example, periolite, etc.). Therefore, the amount of the MgO-containing auxiliary raw material may be reduced. Alternatively, the MgO-containing auxiliary raw material may be classified using a sieve with an opening of 1.0 mm to reduce the amount of the MgO-containing auxiliary raw material having a particle size of 1.0 mm or less. Alternatively, MgO-containing auxiliary raw materials with a particle size of 1.0 mm or less may be agglomerated to have a particle size of more than 1.0 mm.

As described above, according to the method of blending raw materials for sintering according to the present embodiment, by blending raw materials for sintering so as to satisfy conditions A and B, regions where the Ca concentration gradient is large in the sintered ore can be obtained. can be formed in large numbers. As a result, many acicular CFs can be formed in the sintered ore, and as a result, the reducibility of the sintered ore can be improved.

<3. Example of granulation line>
Next, an example of a granulation line for realizing the method of blending raw materials for sintering described above will be described. FIG. 1 is an example of a sintered ore manufacturing process according to this embodiment. A sintered ore production process (more specifically, equipment for realizing the sintered ore production process) 10 includes a granulation line 1 and a sintering machine 20. In the sintered ore manufacturing process 10, a raw material for sintering is granulated in a single granulation line.

The granulation line 1 includes a plurality of raw material hoppers 11, a granulator 12, and belt conveyors 1a and 1b. Each raw material hopper 11 supplies a different raw material for sintering to the belt conveyor 1a. Here, the raw materials for sintering include, as mentioned above, iron-based raw materials that are the main raw materials, auxiliary raw materials necessary for the sintering reaction and component adjustment, carbonaceous materials (solid fuel) that are the heat source, miscellaneous raw materials, and Consists of return ore, etc. The iron-based raw material is, for example, iron ore such as fine ore and fine ore. The auxiliary raw materials include, for example, limestone, dolomite, converter slag, serpentine, silica, and olivine. Examples of the carbonaceous material include coke powder and anthracite. Miscellaneous raw materials are, for example, iron-containing recycled raw materials such as ironmaking dust, steelmaking dust, and scale.

The particle size of the fine ore for sintering is, for example, 10 mm or less. The average particle size is about 2 to 3 mm. Fine ore is iron ore whose iron content has been increased through beneficiation. Its particle size is about 500 μm or less. Of course, the fine ore and fine ore applicable to this embodiment are not limited to these examples, and all iron ores called fine ore and fine ore in the field of sintered ore are applicable to this embodiment. Further, the iron-based raw material in this embodiment includes compact ore having an average particle size of 0.1 to 1.0 mm and a porosity of 10% by volume or less.

Each raw material hopper 11 supplies each raw material for sintering to the belt conveyor 1a at a predetermined mixing ratio. Here, each raw material hopper 11 supplies each raw material for sintering to the belt conveyor 1a so that the above-mentioned conditions A and B are satisfied. On the belt conveyor 1a, these raw materials for sintering are blended to form a blended raw material.

Next, the belt conveyor 1a supplies the blended raw materials to the granulator 12. The granulator 12 produces granules of the raw materials by granulating the raw materials. The granulator 12 may be any device that can granulate the blended raw materials. Examples of the granulator 12 include a drum mixer, a pan pelletizer, and the like. The granulator 12 discharges the granulated material of the blended raw materials onto the belt conveyor 1b. The belt conveyor 1b charges the granulated material of the blended raw materials into the sintering machine 20. The sintering machine 20 produces sintered ore by firing granules of mixed raw materials. Note that the granulation line in this embodiment is not limited to the granulation line 1, and may be any granulation line that can implement the above-described method of blending raw materials for sintering. For example, a granulation line having a plurality of granulation lines (a main granulation line and a sub-granulation line) may be used.

Next, an example of this embodiment will be described. In this example, it was confirmed that the reducibility of sintered ore increases when conditions A and B of this embodiment are satisfied. First, iron ores A to G shown in Table 1 were prepared as iron-based raw materials. These iron ores A to G, limestone, quicklime, periolitic rock, return ore, and carbonaceous material were blended to produce blended raw materials. The blending ratio of each sintering raw material was adjusted so that the conditions shown in Tables 2 and 3 were satisfied. The specific blending ratios are shown in Tables 4 to 6. Here, the Al ₂ O ₃ concentration in the new raw material with a particle size of 1.0 mm or less is calculated by changing the blending ratio of iron ore A with a high Al ₂ O ₃ concentration to 0, 10, 20, 30% by mass (total mass in the new raw material). % by mass). The MgO concentration in the new raw material with a particle size of 1.0 mm or less was adjusted by setting the blending ratio of periotite to either 1.0 or 1.5 mass% (mass% relative to the total mass in the new raw material). The mass % of the carbon material was 4.7 mass % based on the total mass of the new raw material. In Tables 4 to 6, the values for each sintering raw material are mass % based on the total mass of the new raw material. Therefore, the mass % of the new raw material is an inner number, and the mass % of return ore and coke (Coke) is an outer number.

Next, the blended raw materials and 7% by mass (mass% based on the total mass of the blended raw materials) of water were put into a drum mixer, and granulated by mixing for 1 minute and granulation for 4 minutes. Next, I did a pot test. The pot test was conducted under the following conditions: layer thickness of the raw material filling layer: 600 mm, negative pressure: 1500 mmAq, and ignition time: 60 sec. After completion of baking, the sinter cake was crushed by dropping it from a height of 2 m four times. The crushed sintered ore was classified using a sieve, and iron ore with a particle size of more than 15 mm and less than 20 mm was recovered. Next, the reducibility (R1200) of the recovered iron ore was determined by Hosoya et al., "Development of evaluation method for softening and melting properties of sintered ore" (Tetsu to Hagane, 1997, Vol. 83, No. 2, p. 97-102). Measured according to the measurement method described in . The results are shown in Tables 2 and 3.

As is clear from Tables 2 and 3, in Comparative Examples 1 to 8 using iron ore D (average particle size 0.057 mm) that does not satisfy condition A of the present embodiment, the reducibility (R1200) of the sintered ore was 60. It was as low as .8 to 64.5%. In Comparative Examples 9 and 10, iron ore F that satisfies condition A of the present embodiment is used, but condition B is not satisfied. Therefore, the reducibility (R1200) of the sintered ore was as low as 63.5 to 65.8. In Comparative Examples 11 and 12, iron ore G that satisfies condition A of the present embodiment is used, but condition B is not satisfied. Therefore, the reducibility (R1200) of the sintered ore was as low as 62.8 to 65.3. In Comparative Examples 13 to 20, C/S was less than 1.65, and Condition B was not satisfied. Therefore, the reducibility (R1200) of the sintered ore was as low as 62.1 to 64.3. In Comparative Examples 21 and 22, although the C/S was 1.65 or more, neither the Al ₂ O ₃ concentration nor the MgO concentration satisfied Condition B. On the other hand, in Examples 1 to 18 that satisfied both conditions A and B, the reducibility (R1200) of the sintered ore was as high as 66.7 to 67.5. Therefore, it was confirmed that by blending the sintering raw materials so as to satisfy conditions A and B, sintered ore with high reducibility could be produced.

Although preferred embodiments of the present invention have been described above in detail with reference to the accompanying drawings, the present invention is not limited to such examples. It is clear that a person with ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea stated in the claims. It is understood that these also naturally fall within the technical scope of the present invention.

10 Granulation system 1 Granulation line 11 Raw material hopper 12 Granulator 20 Sintering machine

Claims (1)

The content of dense iron ore with an average particle size of 0.1 to 1.0 mm and a porosity of 10% by volume or less is 5% by mass or more based on the total mass of the new raw material, and
The new raw materials excluding the dense iron ore include new raw materials with a particle size of 1.0 mm or less,
A method for blending raw materials for sintering, characterized in that the raw materials for sintering are blended so that the new raw materials having a particle size of 1.0 mm or less satisfy the following conditions (1) and (2).
(1) Basicity (mass ratio of CaO/SiO ₂ ) is 1.65 or more.
(2) Al ₂ O ₃ concentration is 1.5% by mass or more, or MgO concentration is 1.0% by mass or less.

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