JP7024649B2 - Granulation method of raw material for sintering - Google Patents

Description

The present invention relates to a method for granulating a raw material for sintering.

The method for producing sinter is as follows. First, a raw material for sinter, which is a raw material for sinter, is blended in a predetermined ratio, and then granulated together with water. Here, the raw material for sintering is composed of an iron-containing raw material as a main raw material, an auxiliary raw material necessary for the sintering reaction and component adjustment, a carbonaceous material (solid fuel) as a heat source, a return ore, and the like. The iron-containing raw material is, for example, iron ore such as powder ore, fine powder ore, iron-making dust (iron-making dust, steel-making dust, scale, etc.) and the like. Auxiliary raw materials are limestone, dolomite, converter slag, serpentinite, silica stone and peridotite. The charcoal material is, for example, coke powder and anthracite.

Then, the granulated material for sintering is charged into the sintering pallet of the sintering machine in layers. Then, the solid fuel in the packed bed is ignited from the surface of the packed bed, and is sucked and ventilated in the thickness direction from the top to the bottom of the packed bed. As a result, the combustion zone of the packed bed of the raw material is sequentially shifted to the lower layer side, and the sintering reaction proceeds. The sinter cake in the sinter pallet after firing is crushed and sized so as to have a predetermined particle size suitable for sinter for a blast furnace. By the above steps, sinter is produced.

By charging the sintering raw material into a granulating product and then charging the sintering machine, the porosity and pores of the raw material packed bed can be increased. Therefore, since the air permeability of the packed bed of the raw material is improved, it is expected that the productivity of the sinter is improved.

JP-A-2015-203132 Japanese Unexamined Patent Publication No. 2016-191122 Japanese Unexamined Patent Publication No. 2016-194113

By the way, in recent years, the iron content in iron ore has decreased and the gangue component has increased. As a countermeasure, the use of fine powder ore (also referred to as pellet feed (PF)) whose iron content has been increased by mineral processing. It is considered effective to increase the amount. However, since the fine powder ore is inferior in granulation property, when the amount of the fine powder ore used is increased, the particle size of the granulated product becomes smaller. As a result, there is a problem that the air permeability of the raw material packed bed described above is lowered, and eventually the productivity of the sinter is lowered. Patent Documents 1 to 3 disclose techniques for improving the productivity of sinter using fine ore.

The technique disclosed in Patent Document 1 discloses a technique for separating and granulating a raw material for sintering. Specifically, the granulated product AA is produced by granulating the sintering raw material A containing a large amount of fine ore. Then, another iron-containing raw material (sintered raw material B, kneaded dust) is attached to the surface of the granulated product AA. Here, when granulating the granulated product AA, a large amount of water is granulated together with the fine powder ore, while the amount of water contained in the other iron-containing raw materials is reduced. As a result, the granulated product AAB is produced.

The granulated product AAB disclosed in Patent Document 1 increases the amount of water used for granulating the fine powder ore in order to granulate the difficult-to-granulate fine powder ore. However, if nothing is done, the dispersibility of the granulated product AA deteriorates. If the raw material packed bed is formed with the granulated product AA having poor dispersibility, the water content may be unevenly distributed in the raw material packed bed, and firing defects may occur. Therefore, in Patent Document 1, the dispersibility of the granulated product AAB is enhanced by adhering another iron-containing raw material having a small water content to the surface of the granulated product AA.

However, in the technique disclosed in Patent Document 1, since the granulated product AA containing a large amount of fine ore is the core, there is a problem that the strength of the granulated product AAB is weak. Therefore, the granulated product AAB is liable to collapse due to an impact in a handling process such as transfer of a belt conveyor or charging into a sintering machine.

In the techniques disclosed in Patent Documents 2 and 3, a kneaded product is produced by adding a binder to an iron-containing raw material containing a powdered ore and a fine powdered ore and kneading the mixture. Then, the granulated product is produced by granulating the kneaded product. The granulated product disclosed in Patent Documents 2 and 3 has a structure in which the fine powder ore is attached to the surface of the core powder ore. Therefore, the granulated products disclosed in Patent Documents 2 and 3 have higher strength than the granulated products AAB disclosed in Patent Document 1. Further, according to the techniques disclosed in Patent Documents 2 and 3, it can be expected that the granulation property of the fine powder ore is improved, that is, the grain size of the granulated product is improved.

In the techniques disclosed in Patent Documents 2 and 3, in order to sufficiently increase the particle size of the granulated product, it is necessary to sufficiently knead the fine powder ore and the binder so that they are close to each other. However, in the techniques disclosed in Patent Documents 2 and 3, powder ore, fine powder ore and a binder are kneaded with one mixer. Therefore, when the fine powder ore and the binder are sufficiently kneaded, the powder ore collides with the stirring blade or other powder ore and is crushed, and there is a problem that the particle size of the powder ore becomes small. Since the powdered ore becomes the core of the granulated product, the smaller the particle size of the powdered ore, the smaller the particle size of the granulated product.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to produce granulated products having a large particle size even when fine powder ore is used as an iron-containing raw material. It is an object of the present invention to provide a new and improved method for granulating a raw material for sintering.

In order to solve the above problems, according to a certain viewpoint of the present invention, a sub-granulation step of granulating a sub-granulation raw material including powder ore, fine powder ore, and a binder among all the raw materials for sintering, and a burnout process. Among the knotting raw materials, the main granulation step of granulating the main granulation raw material other than the sub-sintering raw material is included, and the sub-granulation step involves kneading the fine powder ore and the binder with the first high-speed stirring mixer. The step of producing the first kneaded product, the step of producing the second kneaded product by kneading the first kneaded product and the powdered ore with the second high-speed stirring mixer, and the second step. The step of producing a granulated product of a raw material for substituting by granulating the kneaded product includes a step of producing a granulated product as a raw material for substituting, and the stirring time by the second high-speed stirring mixer is less than 90 seconds, and the first high-speed stirring mixer Provided is a method for granulating a raw material for sintering, which comprises a stirring time of 30 to 120 seconds .

Further, the binder may be an iron ore slurry containing iron ore for a binder having a particle size of less than 10 μm.

According to the above viewpoint of the present invention, the fine powder ore and the binder are kneaded in advance with the first high-speed stirring mixer to prepare the first kneaded product. As a result, the fine powder ore and the binder can be brought close to each other, so that the granulation property of the fine powder ore can be improved. Then, the first kneaded product and the powdered ore are kneaded with a second high-speed stirring mixer. Here, the secondary stirring time by the second high-speed stirring mixer is set to less than 90 seconds. That is, the secondary stirring time by the second high-speed stirring mixer is shortened. As a result, the fine powder ore can be attached to the surface of the powder ore while suppressing the crushing of the powder ore. As described above, the fine powder ore is sufficiently kneaded with the binder by the first high-speed stirring mixer in advance, so that the granulation property is improved. Therefore, even if the secondary stirring time is short, the fine powder ore can be attached to the surface of the powder ore. Further, since the core of the by-granulation product (granulation material as a raw material for sub-sintering) becomes powder ore, the strength of the by-granulation product can be increased. Furthermore, the crushing of powdered ore is suppressed. As a result, the particle size of the by-granulation increases.

Therefore, according to the present invention, even when fine powder ore is used as an iron-containing raw material, it is possible to produce granulated products having a large particle size.

It is explanatory drawing which shows the outline of the granulation line which concerns on embodiment of this invention. It is explanatory drawing which shows the outline of the granulation line which concerns on a comparative example. It is a graph which shows the correspondence relationship between the secondary stirring time (seconds) after the addition of powder ore, and the average particle size (mm) of a granulated matter.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present specification and the drawings, components having substantially the same functional configuration are designated by the same reference numerals, so that duplicate description will be omitted.

<1. Granulation system configuration>
First, the configuration of the granulation system 1 according to the present embodiment will be described with reference to FIG. The granulation system 1 includes a main granulation line 10, a sub-granulation line 20, and a sintering machine 30. Although the number of sub-granulation lines 20 is one in FIG. 1, a plurality of sub-granulation lines 20 may be prepared. As described above, the granulation system 1 according to the present embodiment performs separate granulation. Separate granulation is also referred to as selective granulation, split granulation, or the like.

The main granulation line 10 is a line for producing a granulated product of the main sintering raw material, that is, a main granulated product by granulating the main sintering raw material among all the sintering raw materials. Here, the raw material for sintering is composed of an iron-containing raw material as a main raw material, an auxiliary raw material necessary for the sintering reaction and component adjustment, a carbonaceous material (solid fuel) as a heat source, a return ore, and the like. The iron-containing raw material is, for example, iron ore such as powder ore, fine powder ore, iron-making dust (iron-making dust, steel-making dust, scale, etc.) and the like. Auxiliary raw materials are limestone, dolomite, converter slag, silica stone and peridotite. The charcoal material is, for example, coke powder and anthracite.

The powder ore is the balance of the lump ore that is directly put into the blast furnace from the excavated iron ore. Its particle size is, for example, less than 10 mm. The average particle size is about 2 to 3 mm. The particle size in this embodiment is measured by sieves having different openings. For example, when the powder ore is placed on a sieve having an opening of X mm, the particle size of the particles remaining on the sieve is X mm or more, and the particle size of the particles dropped from the sieve is less than X mm. The average particle size of the powder ore is measured by, for example, the following method. That is, the powdered ore is sieved by a plurality of types of sieves having different openings. Then, the average particle size is calculated based on the mass ratio of each particle size category and the representative particle size (for example, the intermediate value of the particle size category). Of course, the powder ore applicable to this embodiment is not limited to this example, and any iron ore referred to as powder ore in the field of sinter is applicable to this embodiment.

Fine ore is an iron ore whose iron content has been increased by mineral processing. Its particle size is less than about 500 μm. As mentioned above, the fine powder ore is inferior in granulation property. Therefore, in the present embodiment, the fine powder ore is firmly adhered to the powder ore by a binder (details will be described later, for example, a slurry containing iron ore for a binder having a particle size of less than 10 μm).

The main sintering raw material means a sintering raw material other than the sub-sintering raw material described later among all sintering raw materials. Although details will be described later, the raw material for subsintering includes, for example, powder ore, fine powder ore, and binder. The main sintering raw material is preferably adjusted to 70 to 90% by mass of the total sintering raw material. The mass% of the fine powder ore with respect to the total mass of the subsintering raw material is preferably 50 to 85% by mass, and the mass% of the fine powder ore with respect to the total mass of the total sintering raw material is preferably 10% by mass or more. Therefore, the raw materials for sintering other than these are the main raw materials for sintering.

The main granulation line 10 includes drum mixers 11 and 12. Here, the drum mixers 11 and 12 are arranged on the main granulation line 10 because the drum mixers 11 and 12 have a large processing amount per unit time. The granulation method of the main sintering raw material using the main granulation line 10 may be the same as the conventional granulation method. That is, the raw material for main sintering is charged into the drum mixer 11. Quicklime may be added to the main sintering raw material as a binder for improving the granulation property of the main sintering raw material. As a result, the particle size of the main granulated product is increased, and the air permeability of the raw material packed bed is improved. Further, fine powder ore may be added to the raw material for main sintering to the extent that the air permeability of the packed bed of the raw material is not deteriorated. The amount of fine ore added to the main sinter raw material may be approximately less than 10% by mass with respect to the total mass of the main sinter raw material.

The drum mixer 11 kneads the main sintering raw material and additives together with water. The drum mixer 12 produces a main granulated product by granulating the kneaded product of the main sintering raw material discharged from the drum mixer 11. Through the above steps, the raw material for main sintering is granulated. As described above, the drum mixer 11 (primary mixer) has a function of kneading the main sintering raw material, and the drum mixer 12 (secondary mixer) has a function of granulating the main sintering raw material.

Here, the drum mixers 11 and 12 may be anything as long as they are used for granulating the raw material for sintering. Further, in the present embodiment, the main sintering raw material is granulated by the drum mixers 11 and 12, but any device can be used as long as it can granulate the main sintering raw material. Is also good.

The sub-granulation line 20 is a line for producing a sub-granulation product by granulating the sub-sintering raw material among all the raw materials for sintering. Here, the raw material for subsintering includes, for example, powder ore, fine powder ore, and binder. The subsintering raw material preferably contains fine powder ore in an amount of 50 to 85% by mass with respect to the total mass of the subsintering raw material. That is, it is preferable that the fine powder ore occupies the majority of the raw material for subsintering. As described above, by separating the iron ore, which is relatively difficult to granulate, from the main granulation line 10 and granulating it, granulation can be efficiently performed. That is, by concentrating the fine powder ore that is difficult to granulate on the sub-granulation line 20, the binder may be concentratedly added to the sub-granulation line 20.

Since the raw material for subsintering contains fine ore, the granulation property is inferior. Therefore, in the present embodiment, the fine powder ore and the binder are brought close to each other by sufficiently kneading the fine powder ore and the binder in advance (that is, before kneading the fine powder ore with the powder ore). Then, the fine powder ore and the kneaded product of the binder (first kneaded product) and the powdered ore are kneaded. As a result, the fine powder ore and the binder are sufficiently kneaded, and the crushing of the powder ore is suppressed. Details will be described later.

The type of binder is not particularly limited, and any binder that can be used as a binder for fine ore is preferably used in this embodiment. Examples of the binder include quicklime and iron ore slurry.

The iron ore slurry is a slurry containing iron ore for a binder. The iron ore for binder is an iron ore having a particle size of less than 10 μm, and is, for example, a crushed ore. The iron ore slurry is produced, for example, by wet pulverizing iron ore. Specific manufacturing methods are disclosed in, for example, International Publication No. 2013/054471, Japanese Patent No. 5644955, JP-A-2016-79467, and the like. The iron ore used as a raw material for the iron ore slurry preferably contains a large amount of water of crystallization. Examples of such iron ore include Australia's Malamamba ore and pisolite ore.

Here, the iron ore for binder is preferably 3% by mass or more and less than 7% by mass with respect to the total mass of the raw material for subsintering. If the mass% of the iron ore for the binder is less than 3% by mass, the effect as a binder may be small, and if the mass% of the iron ore for the binder is 7% by mass or more, the by-granulation product. (Granulated material for subsintering) may be excessively coarsened. In this case, melt assimilation may not proceed sufficiently during firing.

The slurry concentration (mass% of iron ore for binder with respect to the total mass (including water) of iron ore slurry) is not particularly limited, but is preferably 40% by mass or more and less than 80% by mass. Fine ore has a high water retention capacity, and when it is brought from the iron ore yard to the granulation line, it contains more water than other powder ores. Especially for brands with high water content, the water content is the total amount of fine powder ore. It reaches about 10% by mass with respect to the mass. In the present embodiment, unless otherwise specified, each water content is a so-called external number.

Therefore, the slurry concentration is preferably a relatively high value, that is, 40% by mass or more. Thereby, the mass% of the iron ore for the binder can be set to 3% by mass or more and less than 7% by mass. When the slurry concentration is less than 40% by mass, the proportion of iron ore for binder in the slurry is small, and it may be difficult to make the mass% of iron ore for binder 3% by mass or more and less than 7% by mass. be. Further, when the slurry concentration is 80% by mass or more, it may be determined that the slurry loses its fluidity as a slurry and becomes a state close to a solid, that is, the fluidity reaches a so-called flow limit value.

The sub-granulation line 20 includes a first high-speed stirring mixer 21, a second high-speed stirring mixer 22, and a pan pelletizer 23. Since the raw material for subsintering contains a large amount of fine ore, it is difficult to granulate. Therefore, the drum mixer may not be able to sufficiently knead the raw material for subsintering. Therefore, in the present embodiment, the first high-speed stirring mixer 21 and the second high-speed stirring mixer 22 are used as devices for kneading the raw materials for subsintering.

The first high-speed stirring mixer 21 kneads the fine ore and the binder to prepare the first kneaded product. As described above, in the present embodiment, the fine powder ore and the binder are sufficiently kneaded in advance so that the fine powder ore and the binder are brought close to each other.

Here, the first high-speed stirring mixer 21 has a stirring blade (agitator) and a similar mechanism inside, and is a mixer that exerts a large mixing, stirring, and shearing force on the sample. Normally, the peripheral speed of the stirring blade (agitator) is adjusted to 3 to 30 m / sec (Ikuo Yusa: "Basics and Applications of Powder Technology", September issue of Chemical Equipment, Supplement, Industrial Communication Co., Ltd., 2005). As the first high-speed stirring mixer 21, for example, a vertical high-speed stirring mixer (manufactured by Nippon Eirich Co., Ltd.) that generates a large mixing stirring force by rotating the mixer container and the internal stirring blade (agitator) in opposite directions. ) Etc. can be mentioned. Further, as another example of the first high-speed stirring mixer 21, a Ladyge mixer / Proshare mixer (manufactured by Pacific Kiko Co., Ltd.), a Dow mixer and the like can be mentioned. Of course, the first high-speed stirring mixer 21 is not limited to these examples, and any one called a high-speed stirring mixer in the field of sinter can be applied to the present embodiment.

The drive method of the first high-speed stirring mixer 21 may be a batch type or a continuous type. When the first high-speed stirring mixer 21 is a batch type, the following processing is performed. That is, the raw materials (here, fine ore and binder) are put into the mixer inlet and the lid is put on. Then, the fine ore and the binder are kneaded in the first high-speed stirring mixer 21. Then, the first kneaded product is discharged from the same mixer inlet.

When the first high-speed stirring mixer 21 is a continuous type, the following processing is performed. That is, the fine powder ore and the binder before kneading are charged from one end of the first high-speed stirring mixer 21, for example, from the upper part, and the first kneaded material is discharged from the other end, for example, the bottom.

The stirring time by the first high-speed stirring mixer 21 (in other words, the residence time in the first high-speed stirring mixer 21) may be adjusted so that the particle size of the by-granulated product described later becomes a desired value or more. However, for example, it is preferably 30 to 120 seconds, and more preferably 50 to 70 seconds. Hereinafter, the stirring time by the first high-speed stirring mixer 21 is also referred to as “primary stirring time”. If the primary stirring time is less than 30 seconds, the particle size of the by-granulated product may not be sufficiently large. Even if the primary stirring time exceeds 120 seconds, the particle size of the by-granulated product hardly changes.

Here, the primary stirring time differs depending on the driving method of the first high-speed stirring mixer 21. When the first high-speed stirring mixer 21 is a batch type, the primary stirring time is the time when the first high-speed stirring mixer 21 is operated. That is, the primary stirring time does not include the time required for charging and discharging operations. Therefore, the primary stirring time can be adjusted by adjusting the operating time of the first high-speed stirring mixer 21.

On the other hand, when the first high-speed stirring mixer 21 is a continuous type, the fine powder ore and the binder are charged into the first high-speed stirring mixer 21 until they are discharged, that is, the fine powder ore and the binder are the first high-speed stirring mixer. The time existing in 21 becomes the primary stirring time. That is, the continuous first high-speed stirring mixer 21 is operated in a so-called steady state. In the steady state, the supply and emission of raw materials are almost constant. If the supply amount exceeds the discharge amount, the raw material overflows from the first high-speed stirring mixer 21, and if the supply amount exceeds the discharge amount, the inside of the first high-speed stirring mixer 21 becomes empty, so that the first high-speed stirring mixer 21 does not function. In order to operate the first high-speed stirring mixer 21 in a steady state, the raw material supply amount, the mixer device conditions, the operating conditions and the like may be appropriately adjusted.

When the first high-speed stirring mixer 21 is operated in a steady state, a substantially constant amount of raw materials are retained and mixed in the first high-speed stirring mixer 21.

Therefore, the primary stirring time is calculated from the amount of raw material supplied and the amount of raw material retained in the mixer. For example, when the supply amount and the discharge amount of the raw material are 1 t / min and the retention amount is 2 t, the raw materials are replaced in 2 min. Therefore, the primary stirring time is 2 min. In reality, some raw materials stay in the mixer for a longer period of time, and some of them pass through. Therefore, the primary stirring time is preferably an average value. For example, the primary stirring time is measured a plurality of times within a certain period, and these arithmetic mean values are used as the primary stirring time. The primary stirring time can be adjusted, for example, by adjusting the raw material input rate and the raw material discharge rate, adjusting the mixer capacity, and the like.

The second high-speed stirring mixer 22 produces a second kneaded product by kneading the first kneaded product and the powdered ore. The specific configuration of the second high-speed stirring mixer 22 is the same as that of the first high-speed stirring mixer 21.

The stirring time of the second high-speed stirring mixer 22, that is, the secondary stirring time is set to less than 90 seconds. As a result, the fine powder ore can be attached to the surface of the powder ore while suppressing the crushing of the powder ore. As described above, the fine powder ore is sufficiently kneaded with the binder by the first high-speed stirring mixer 21 in advance, so that the granulation property is improved. Therefore, even if the secondary stirring time is short, the fine powder ore can be attached to the surface of the powder ore. The secondary stirring time is preferably 60 seconds or less, and more preferably 30 seconds or less.

On the other hand, even if the secondary stirring time by the second high-speed stirring mixer 22 is too short, the kneading of the first kneaded product and the powdered ore may not proceed sufficiently. Therefore, the secondary stirring time is preferably 10 seconds or longer. The definition of the secondary stirring time is the same as that of the first high-speed stirring mixer 21.

The panperetizer 23 produces a by-granulation product by granulating the second kneaded product discharged from the second high-speed stirring mixer 21. The device for granulating the second kneaded product is not limited to the pan pelletizer 23. That is, any device may be used as long as it can granulate the second kneaded product.

The amount of water contained in the by-granulation is preferably about 9 to 12% by mass with respect to the total mass of the by-granulation. Therefore, the slurry concentration and the amount of slurry added may be determined so that the amount of water contained in the by-granulated product is within the above range. When the amount of water is insufficient, water may be added at the time of kneading with the first high-speed stirring mixer 21 or the second high-speed stirring mixer 22.

Additives may be added to the subsintering raw material as long as the effects of the present embodiment are not impaired. For example, when the Ca content as the melt source and the C content as the heat source are scarce, an auxiliary raw material, dust, or slag may be added to the auxiliary sintering raw material in order to supplement the melt source and the heat source.

After the sub-granulation is produced, the sub-granulation line 20 merges with the main granulation line 10. As a result, the sub-granulation is combined with the main granulation. After that, the main granulation product and the sub-granulation product are charged into the sintering machine 30. The sinter 30 produces a sinter by firing the main granulation and the sub-granulation.

<3. Granulation method of raw material for sintering ＞
Next, a method for granulating a raw material for sintering using the above-mentioned granulation system 1 will be described. The method for granulating the raw material for sintering includes a main granulation step of granulating the raw material for main sintering and a sub-granulation step of granulating the raw material for sub-sintering. The main granulation step is performed on the main granulation line 10, and the sub-granulation step is performed on the sub-granulation line 20. The main granulation step may be the same as before.

In the sub-granulation step, the fine powder ore and the binder are kneaded with the first high-speed stirring mixer 21 to prepare the first kneaded product, and the first kneaded product and the powder ore are mixed with the second high-speed stirring mixer. It includes a step of producing a second kneaded product by kneading at 22 and a step of producing a by-granulated product by granulating the second kneaded product with a panperetizer 23. Here, the primary stirring time by the first high-speed stirring mixer 21 is preferably 30 to 120 seconds. The secondary stirring time by the second high-speed stirring mixer 22 is set to less than 90 seconds.

As described above, in the present embodiment, the fine powder ore and the binder are kneaded in advance with the first high-speed stirring mixer 21 to prepare the first kneaded product. As a result, the fine powder ore and the binder can be brought close to each other, so that the granulation property of the fine powder ore can be improved. Then, the first kneaded product and the powdered ore are kneaded with the second high-speed stirring mixer 22. Here, the secondary stirring time by the second high-speed stirring mixer 22 is set to less than 90 seconds. That is, the secondary stirring time by the second high-speed stirring mixer 22 is shortened. As a result, the fine powder ore can be attached to the surface of the powder ore while suppressing the crushing of the powder ore. As described above, the fine powder ore is sufficiently kneaded with the binder by the first high-speed stirring mixer 21 in advance, so that the granulation property is improved. Therefore, even if the secondary stirring time is short, the fine powder ore can be attached to the surface of the powder ore. Further, since the core of the by-granulation becomes powder ore, the strength of the by-granulation can be increased. Furthermore, the crushing of powdered ore is suppressed. As a result, the particle size of the by-granulation increases. Further, in the present embodiment, since the fine ore and the binder are kneaded in advance, the function of the binder can be fully exerted. Therefore, it is possible to reduce the amount of binder required to bring the particle size of the granulated product to a predetermined value.

<1. Prerequisites>
In Examples 1 and 2 described below, a test simulating the sub-granulation line 20 was performed. That is, 80% by mass of the total sintering raw material was used as the main sintering raw material, and 20% by mass was used as the sub-sintering raw material. Originally, a raw material consisting of ordinary powder ore, an auxiliary raw material, and a carbonaceous material is mixed in the main sintering raw material, but in the experiment according to this example, neither the raw material preparation nor the granulation experiment was carried out. The breakdown of the raw materials for subsintering was 24% by mass of powdered ore, 71% by mass of fine powdered ore, and iron ore slurry (5% by mass of iron ore for binder). The iron ore slurry was prepared by crushing iron ore with water in a ball mill. The particle size of the iron ore for binder contained in the iron ore slurry was less than 10 μm. All the raw materials for subsintering except the iron ore slurry were dried in advance to make the water content 0% by mass before use.

<2. Example>
In the example, first, among the raw materials for subsintering, the fine powder ore excluding the powder ore and the iron ore slurry were kneaded with the first high-speed stirring mixer 21. As a result, the first kneaded product was prepared. The primary stirring time by the first high-speed stirring mixer 21 was set to 60 seconds. During stirring, water was added to the first high-speed stirring mixer 21 so that the water content contained in the fine powder ore and the iron ore for binder was 11.5% by mass. This is an adjustment for adjusting the water content of the by-granulation to 9.0% by mass.

The first kneaded product was discharged from the first high-speed stirring mixer 21, and powdered ore was added to the first kneaded product. Then, the powdered ore and the first kneaded product were kneaded with the second high-speed stirring mixer 22. The secondary stirring time by the second high-speed stirring mixer 22 was set to any of 30 seconds, 60 seconds, and 120 seconds. As a result, a second kneaded product was prepared. Then, the second kneaded product was granulated with a panperetizer 23 for 300 seconds. As a result, a by-granulation product was produced. The water content of the by-granulation was 9.0% by mass.

The average particle size of the granulated by-granulation was measured, and the average particle size was used as an evaluation index. Here, the average particle size was measured in the following steps. (1) About 500 g of the granulated product was collected and kept in a dryer kept at 105 ° C. for 5-10 minutes. This is an operation of reducing the water content on the surface of the granulated product in order to prevent the granulated product from adhering to the net and making the sieving difficult when sieving later. (2) The granulated product taken out from the dryer was sieved through several open sieves. (Uses a JIS standard compliant 200 mmφ round sieve of 9.5, 8.0, 4.75, 2.8, 2.0, 1.0 mm) (3) Mass ratio and representative value of each particle size category (intermediate of particle size category) The arithmetic mean particle size was calculated from the value). As described above, in the examples, the secondary stirring time was changed, and the average particle size corresponding to each secondary stirring time was obtained.

(Comparative Example 1)
In Comparative Example 1, a test assuming the granulation system 100 shown in FIG. 2 was performed. The granulation system 100 is obtained by removing the second high-speed stirring mixer 22 from the granulation system 1. In Comparative Example 1, the entire amount of the raw material for subsintering was kneaded with the first high-speed stirring mixer 21 while adding water so that the water content of the by-granulation was 9.0% by mass. Here, the stirring time by the first high-speed stirring mixer 21 was set to any of 30 seconds, 60 seconds, and 120 seconds. The stirring time here corresponds to the secondary stirring time of the example. That is, in Comparative Example 1, it can be considered that the primary stirring time is 0 seconds, the secondary stirring time is 30 seconds, 60 seconds, or 120 seconds.

The kneaded product prepared by the first high-speed stirring mixer 21 was granulated with a pan pelletizer 23 for 300 seconds. As a result, a by-granulation product was produced. The water content of the by-granulation was 9.0% by mass. The average particle size of the by-granulated product was measured and used as an evaluation index. That is, in Comparative Example 1, the stirring time by the first high-speed stirring mixer 21 was changed, and the average particle size corresponding to each stirring time was obtained. The method for measuring the average particle size was the same as in the examples.

(Comparative Example 2)
In Comparative Example 2, the test assuming the granulation system 100 shown in FIG. 2 was also performed. In Comparative Example 2, among the raw materials for subsintering, the fine powder ore excluding the powder ore and the iron ore slurry were kneaded with the first high-speed stirring mixer 21. The stirring time was 60 seconds. The stirring time here corresponds to the primary stirring time of the example. During stirring, water was added so that the water content of the by-granulated product was 9.0% by mass. That is, since the powder ore is not contained at this point, the water content of the fine powder ore and the iron ore for binder is temporarily 11.5% by mass. The ore powder was added to the kneaded product prepared by the first high-speed stirring mixer 21, and the mixture was granulated with a pan pelletizer for 300 seconds. As a result, a by-granulation product was produced. That is, in Comparative Example 2, it can be considered that the primary stirring time is 60 seconds and the secondary stirring time is 0 seconds. The water content of the by-granulation was 9.0% by mass. The average particle size of the by-granulated product was measured and used as an evaluation index. The method for measuring the average particle size was the same as in the examples.

(Discussion)
The results are summarized in FIG. The horizontal axis of FIG. 3 shows the secondary stirring time (seconds) after the addition of the powder ore, and the vertical axis shows the average particle size (mm) of the by-granulation. The point P1 shows the correspondence between the secondary stirring time and the average particle size of the by-granulation in the examples, and the graph L1 is an approximate straight line (by the least squares method) of the point P1. The point P2 shows the correspondence between the secondary stirring time and the average particle size of the by-granulation in Comparative Example 1, and the graph L2 is an approximate straight line (by the least squares method) of the point P2. Point P3 shows the correspondence between the secondary stirring time and the average particle size of the by-granulated product in Comparative Example 2.

In Comparative Example 1, the average particle size of the by-granulated product decreased as the secondary stirring time increased. In Comparative Example 1, since all the raw materials for subsintering are kneaded at once, the crushing of the powdered ore progresses as the secondary stirring time increases, and the number of nuclear particles, that is, the granulated matter increases. The average grain size seems to have decreased.

In Comparative Example 2, the powdered ore is kneaded with the fine powdered ore for the first time in the granulation step with the panperetizer. In Comparative Example 2, the average particle size of the by-granulation was larger than that of Comparative Example 1, but was lower than that of Example 1. Further, in Comparative Example 2, a by-granulation product having a kneaded product of fine ore and a binder as a core was also produced. Then, in the evaluation process (that is, the process of measuring the average particle size), the phenomenon that the nucleus composed of the kneaded material collapses was also observed. Therefore, in Comparative Example 2, the by-granulation product was insufficiently kneaded with the fine powder ore, and the kneaded product with insufficient strength became the core of the by-granulation product. It is considered that the average particle size of the above was lower than that of the examples.

On the other hand, in the examples, the average particle size of the by-granulation was larger than that in Comparative Examples 1 and 2. In the embodiment, the fine ore and the binder are sufficiently kneaded in advance by the first high-speed stirring mixer 21, so that it is considered that the fine ore and the binder are in close proximity to each other. It is considered that this improved the granulation property of the fine powder ore. However, the decrease in the average particle size of the by-granulated product with the increase in the secondary stirring time was the same as in Comparative Example 1. According to FIG. 3, it is estimated that the average particle size of the by-granulated product becomes the same as that of Comparative Example 2 with the secondary stirring time of 90 seconds, and the superiority disappears. Therefore, the preferred secondary stirring time is less than 90 seconds. By setting the secondary stirring time by the second high-speed stirring mixer 22 to less than 90 seconds, the crushing of the powdered ore is suppressed and the average particle size of the by-granulated product is increased.

Although the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that a person having ordinary knowledge in the field of technology to which the present invention belongs can come up with various modifications or modifications within the scope of the technical ideas described in the claims. , These are also naturally understood to belong to the technical scope of the present invention.

1 Granulation system 10 Main granulation line 11, 12 Drum mixer 20 Sub-granulation line 21 First high-speed stirring mixer 22 Second high-speed stirring mixer 23 Pampletizer

Claims (2)

A sub-granulation process for granulating sub-sintering raw materials including powder ore, fine powder ore, and binder among all sintering raw materials.
Among the total sintering raw materials, the main granulation step of granulating the main sintering raw material other than the sub-sintering raw material is included.
The sub-granulation step includes a step of producing a first kneaded product by kneading the fine powder ore and a binder with a first high-speed stirring mixer.
A step of producing a second kneaded product by kneading the first kneaded product and the powdered ore with a second high-speed stirring mixer.
Including the step of producing the granulated product of the subsintering raw material by granulating the second kneaded product.
The stirring time by the second high-speed stirring mixer is less than 90 seconds, and the stirring time is less than 90 seconds.
A method for granulating a raw material for sintering, which comprises a stirring time of 30 to 120 seconds by the first high-speed stirring mixer . The method for granulating a raw material for sintering according to claim 1 , wherein the binder is an iron ore slurry containing iron ore for a binder having a particle size of less than 10 μm.

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