JP6888387B2 - Granulation method for sintered raw materials - Google Patents

Description

The present invention relates to a method for granulating a sintered raw material containing a large amount of fine powder using a granulator.

If particles having a particle size of 0.25 mm or less (hereinafter referred to as "fine powder" in the present specification) among the sinter raw materials are present alone in the sinter, the air permeability during sintering is hindered and the sinter ore Productivity is reduced. Therefore, the sintering raw material is granulated into pseudo-particles to reduce the proportion of fine particles existing alone, and then charged into the sintering machine.

In recent years, due to the depletion of iron ore resources, there is no choice but to use iron ore with a large proportion of fine powder. As the amount of fine powder added increases, the amount of fine powder that exists alone without being granulated into pseudo-particles also increases in the conventional granulation method. Therefore, in order to secure the productivity of the sinter, a new granulation technique capable of efficiently reducing the proportion of fine powder existing alone is required as compared with the conventional one.

On the other hand, as a technique related to the fine powder treatment in the granulation process of the sintered raw material, Patent Document 1 states that the sintered raw material cut out from the raw material tank is tumbled and granulated by the first and second drum mixers and then classified. Technology that classifies coarse grains and fine grains with an apparatus, transports the coarse grains to a sintering machine, rolls and granulates the fine grains with a third drum mixer, and charges them again at the discharge end of the second drum mixer. Is disclosed.
Further, in Patent Document 2, in the granulation step of the sintering raw material, fine powder having a particle size of 3.0 mm or less is separated from the granulated products discharged from the drum mixer and sent to the charging side of the drum mixer. A technique for granulating while reducing is disclosed.

Japanese Unexamined Patent Publication No. 10-60550 Japanese Unexamined Patent Publication No. 60-21338

In the techniques described in Patent Documents 1 and 2, in the sintering process in which the sinter component is controlled by blending the raw materials, the sinter raw materials discharged from the drum mixer are screened according to the particle size, so that the sinter raw materials are charged into the sinter. There is a risk that the composition of the granulated product, and by extension, the composition of the adult sinter, will be different from the intended formulation.

The present invention has been made in view of such circumstances, and when granulating a raw material containing a large amount of fine powder, sintering can reduce the proportion of fine powder contained in the granulated product after granulation as compared with the conventional case. It is an object of the present invention to provide a method for granulating a raw material.

In order to achieve the above object, the present invention is a method for granulating a sintered raw material containing 13% by mass or more and 25% by mass or less of particles having a particle size of 0.25 mm or less using a granulator.
The drum mixer was placed in front of the granulator, the drum motion state of the sintered material was charged into the mixer jumps performed rpm in the process will belong to the region, before said Kishoyui material It is characterized by being charged into a granulator.

When granulating a sintered raw material containing 13% by mass or more and 25% by mass or less of particles (fine powder) having a particle size of 0.25 mm or less, the present inventors install a drum mixer in front of the granulator and use the drum mixer. It was found that the granulation property of the sintered raw material in the subsequent granulators is improved by increasing the number of rotations of the above. By increasing the number of revolutions of the drum mixer and operating in the jumping region instead of the normal rolling region, which was conventionally regarded as the appropriate operating point, the sintered raw material is consolidated, and the compacted sintered raw material is subsequently consolidated. It was found that the granulation of the granulated product is easy to proceed and the strength of the granulated product is increased, so that the granulated product is less likely to collapse.

In the method for granulating a sintered raw material according to the present invention, a drum mixer is installed in front of the granulator, the sintered raw material having a high fine powder ratio is charged into the drum mixer to be compacted, and then granulated by the granulator. Since it is granulated, the granulated product is unlikely to collapse. Therefore, the proportion of fine powder contained in the granulated product can be reduced as compared with the conventional case without re-granulating a part of the granulated product.

It is a graph which showed the relationship between the rotation speed of a primary drum mixer, and the fine powder reduction ratio. It is a schematic diagram which shows an example of the granulation equipment which carries out the granulation method of the sintering raw material which concerns on one Embodiment of this invention. It is a graph which showed the moving state of the sintered raw material in a drum mixer by the relation between the number of fluids and the space factor.

Subsequently, an embodiment embodying the present invention will be described with reference to the attached drawings, and the present invention will be understood.

[Technical Idea of the Present Invention]
The operating points of the drum mixer are divided into the following three regions according to the motion state of the raw materials in the drum mixer.
The normal rolling region is an operating region that has been conventionally oriented as having the highest granulation property. In this region, the raw material lifted by friction with the inner wall of the drum mixer falls while rolling on the raw material slope. Since granulation proceeds by rolling, granulation proceeds most in this region.
The region shifted to the higher rotation speed or lower space factor side than the normal rolling region is the jump region. In this region, the raw material lifted by friction with the inner wall of the drum mixer does not roll and falls in the drum mixer. In the initial stage of the jumping state, granulation is good because only a part of the raw material jumps, but once the whole is in the jumping state, the granulated material is re-crushed when it falls, so the granulation itself is not so much. Does not progress.
The region shifted to the lower rotation speed or higher space factor side than the normal rolling region is called the slip region. In the sliding region, the entire raw material lifted by friction with the inner wall of the drum mixer moves to a lower position so as to slide on the inner wall all at once, so that granulation does not proceed.
Therefore, in the operation of the drum mixer, the normal rolling region is directed, and the operation in the jumping region and the sliding region has been avoided.

On the other hand, in order to improve the granulation property of the sintered raw material having a high fine powder ratio, it is effective to consolidate the sintered raw material by using a strong kneader or the like that kneads the raw material with a rotary blade before granulation. is there.
The present inventors have aimed to promote consolidation of the sintered raw material with a drum mixer, and have focused on the jumping region of the drum mixer, and have said that there is a possibility that the raw material can be consolidated by the impact of a falling object. Thought.
When granulating with only one drum mixer, operation in this area should be avoided, but when there are two drum mixers, the front drum mixer is operated in this jumping area, and the rear drum mixer is rotated normally. If it is operated in a moving area and used as a granulator, it can be granulated after it is compacted into a sintered raw material that is easy to granulate, so that the granulation property of the sintered raw material is improved and the obtained granulation is performed. The strength of objects can be increased. Even if there is another granulator behind the drum mixer, the same effect can be obtained by operating the drum mixer in the jumping region and performing granulation with the granulator.

In a granulation facility in which two drum mixers are arranged in series, the number of rotations of the primary drum mixer in the previous stage is used as a parameter for sintered raw materials with different proportions of particles (fine powder) having a particle size of 0.25 mm or less. A grain test was performed. Specifically, a sintered raw material containing fine powder is charged into the primary drum mixer in the first stage, processing is performed at different rotation speeds, and the sintered raw material discharged from the primary drum mixer is used in the secondary drum mixer in the subsequent stage. The sintered raw material was granulated. The rotation speed of the secondary drum mixer was set to 6 rpm, which is the normal rolling range.
Then, the ratio of fine powder contained in the granules discharged from the secondary drum mixer is measured, and the reduction rate of the fine powder ratio after discharge of the secondary drum mixer with respect to the fine powder ratio before charging the primary drum mixer is the fine powder reduction ratio. Asked as. The result is shown in FIG.

In the case of the sintered raw material having a fine powder ratio of 10% by mass, the optimum value of the rotation speed of the primary drum mixer having the largest fine powder reduction ratio was 7 rpm. On the other hand, in the case of the sintered raw material having a fine powder ratio of 13% by mass and 17% by mass, the optimum value of the rotation speed of the primary drum mixer was 9 rpm.
In the primary drum mixer used in this test, the rotation speed at which the motion state of the sintered raw material shifts from the normal rolling region to the jumping region is 7.5 rpm. From this, it was found that in the case of a sintered raw material having a high fine powder ratio, when the primary drum mixer is operated in the jumping region, the granulation property of the sintered raw material is improved and the fine powder ratio is reduced.

The raw material in the drum mixer receives energy from the rotation of the drum mixer. This energy is mainly consumed in the form of raw material mixing, raw material granulation, raw material consolidation, and granulation collapse. Of these, consolidation of the raw material is to bring the distance between the particles constituting the raw material closer, and the consolidated raw material is likely to undergo subsequent granulation, and the strength of the granulated product is also increased, so that the granulated product collapses. It is less likely to occur. On the other hand, there is a limit to the consolidation of raw materials, and if the rotation speed of the drum mixer is increased beyond the limit, the demerit of granulation collapse becomes more remarkable than the advantage of consolidation. Therefore, it is estimated that the fine powder reduction ratio with respect to the rotation speed of the primary drum mixer has a maximum value as shown in FIG. Therefore, it is preferable to set the lower limit rotation speed + 3 rpm, which is the jumping region, as the upper limit value of the rotation speed of the primary drum mixer.

[Granulation method for sintered raw materials]
FIG. 2 shows an example of a granulation facility in which the method for granulating a sintered raw material according to an embodiment of the present invention is carried out. This granulation facility granulates the raw material tank 11 in which the sintered raw material is stored, the primary drum mixer 12 for compacting the sintered raw material, and the sintered raw material compacted by the primary drum mixer 12. It is equipped with a secondary drum mixer 13 (an example of a granulator).

Each raw material brand constituting the sintered raw material is cut out from the raw material tank 11, and the particle ratio of 0.25 mm or less for each raw material brand is weighted and averaged by the blending ratio to obtain 0.25 mm or less in the sintered raw material before granulation. Calculate the proportion of particles.
In the present embodiment, a sintered raw material containing 13% by mass or more and 25% by mass or less of particles (fine powder) having a particle size of 0.25 mm or less is targeted.

When granulating the sintered raw material, the rotation speed of the primary drum mixer 12 is set so that the motion state of the sintered raw material in the primary drum mixer 12 belongs to the jumping region. On the other hand, the secondary drum mixer 13 used as the granulator sets the rotation speed of the secondary drum mixer 13 so that the motion state of the sintering raw material in the secondary drum mixer 13 belongs to the normal rolling region.

The moving state of the sintered raw material in the drum mixer can be expressed by the relationship between the number of fludes Fr and the space factor φ (%) shown below.
Fr = D × N ² / (g × 3600) (1)
φ = 4 × Q × T / (D ² × π × L × ρ) (2)
Here , D: inner diameter of the drum mixer (m), N: rotation speed of the drum mixer (rpm), g: gravity acceleration (m / s ² ), Q: sintered raw material supply amount (ton / min), T. : Raw material residence time in the drum mixer (min), L: Drum mixer body length (m), ρ: Sintered raw material bulk density (ton / m ³ )

The motion state of the sintered raw material in the drum mixer, which is represented by the relationship between the number of fludes Fr and the space factor φ, differs depending on the structure in the drum mixer and the like. Therefore, it is necessary to carry out an experiment in advance and create a graph showing the motion state of the sintered raw material in the drum mixer in relation to the number of fludes Fr and the space factor φ.
If the space factor φ is determined from the supply amount of the sintered raw material, the bulk density of the sintered raw material, etc., the motion state of the sintered raw material in the drum mixer becomes a jumping state or a normal rolling range from the graph obtained in advance. The number of fludes Fr is determined, and the required number of revolutions of the drum mixer can be obtained from the equation (1).

Although one embodiment of the present invention has been described above, the present invention is not limited to the configuration described in the above-described embodiment, but is within the scope of the claims. It also includes other possible embodiments and variations. For example, in the above embodiment, the granulator is a drum mixer, but the present invention is not limited to this, and other granulators such as a pan pelletizer may be used.

The verification test carried out for verifying the effect of the present invention will be described.
Using the granulation equipment shown in FIG. 2, a granulation test of a sintered raw material containing 20% by mass of particles having a size of 0.25 mm or less was carried out.
The inner diameter D of the drum mixer is 4.8 m, the body length L is 17.1 m, the amount of sinter raw material supplied Q is 22 ton / min, the bulk density ρ of the sintered raw material is 1.8 ton / m ³ , and the raw material residence time in the drum mixer. T was 2 min. Substituting these values into Eq. (2), the space factor φ is 7.9%.

FIG. 3 shows the motion state of the sintered raw material in the drum mixer represented by the relationship between the fluid number Fr and the space factor φ obtained in advance for this drum mixer.
When the space factor φ is 7.9%, the number of fluds Fr in which the sintered raw material in the drum mixer is in a jumping state is more than 5.6 × 10 ^{-3 as} shown in FIG. Since the inner diameter D of the drum mixer is 4.8 m, the sintered raw material in the primary drum mixer is in a jumping state, and the required rotation speed of the primary drum mixer is more than 6.4 rpm from the equation (1).

Based on the above results, the rotation speed of the primary drum mixer was set to 9 rpm, and the sintering raw material was granulated. Further, for comparison, the sintering raw material was granulated by setting the rotation speed of the primary drum mixer to 6 rpm, which is a steady rolling region.
As a result, in the examples satisfying the conditions of the present invention, the reduction rate of fine powder after granulation was 11.8%, and in the comparative example not satisfying the conditions of the present invention, the reduction rate of fine powder after granulation was 8.0%. It became.

11: Raw material tank, 12: 1 primary drum mixer, 13: Secondary drum mixer (example of granulator)

Claims (1)

In a method of granulating a sintered raw material containing 13% by mass or more and 25% by mass or less of particles having a particle size of 0.25 mm or less using a granulator.
The drum mixer was placed in front of the granulator, the drum motion state of the sintered material was charged into the mixer jumps performed rpm in the process will belong to the region, before said Kishoyui material A method for granulating a sintered raw material, which is characterized by being charged into a granulator.

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