JP3376621B2 - Method for producing low CaO sintered ore - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention produces a sinter having a low CaO content (low CaO sinter) required for increasing the ratio of the sinter in the raw material charged into a blast furnace at a high yield. And low CaO capable of improving the cold strength of the sintered mineral product
The present invention relates to a method for manufacturing sinter.

[0002]

2. Description of the Related Art A general process for producing a sintered ore charged into a blast furnace is as follows. That is, first, sintering raw materials such as iron ore powder, coke powder, and limestone are granulated in a mixing granulator while adding an appropriate amount of water. The pseudo-granulated sintering raw material is loaded into a pallet of a sintering machine, ignited from the upper part of the sintering raw material packed bed, and air is sucked from the upper part of the packed bed to the lower part of the raw material. The coke is sequentially burned from the top to burn the sintering raw material. After firing, the pallet is tilted to take out a fired product (referred to as a sintered cake), which is crushed and cooled, and then a product having a certain particle size or more is provided as a blast furnace raw material.
It should be noted that the powder or granular material having a certain particle diameter or less (referred to as return ore) is used again as a sintering raw material.

In the above-mentioned firing process, the CaO component of limestone reacts with the iron oxide and is partially melted, and this melted portion has a function of binding the sintering raw material powder particles to each other and agglomerating them. Therefore, if the melting is insufficient, not only the return ore ratio increases and the yield decreases, but also the cold strength of the sintered ore product decreases and the blast furnace operation is adversely affected.

In recent years, since high-quality agglomerates have been depleted, it has become common practice to increase the ratio of sintered ore in the blast furnace charging raw material (called the sintering ratio). However, if the sintering ratio is increased by using a sinter having a normal CaO content, the basicity of the blast furnace slag increases, and the viscosity increases, which hinders the operation of the blast furnace. In order to avoid this, a so-called low CaO sinter having a low CaO content is required.

When the amount of limestone blended with the sintering raw material for producing a low CaO sinter is limited, the amount of melt produced during the sintering reaction decreases, so that the yield of the sintered product and the sintering rate are reduced. The cold strength of the ore decreases. It has been desired to develop a method for producing a low CaO sintered ore without such a decrease in product yield and cold strength.

Conventionally, as a method for improving the product yield and cold strength of the sintered ore, there are generally known two types of methods. The first is a method of enhancing the air permeability of the sintering raw material packed bed by strengthening the granulation and transferring the increased air permeability to the increase of the packed bed thickness of the sinter machine pallet. The second
Is a method of controlling the distribution state of the CaO component in the sintering raw material packed bed.

The first method will be described in detail below.

A drum mixer is mainly used as an apparatus used for granulation. However, when the sintering raw material becomes fine particles, granulation with a drum mixer becomes insufficient. Therefore, it is important to improve the granulation technology such as using a high performance granulator other than the drum mixer.

With respect to this granulation technique, many inventions have heretofore been disclosed. For example, Japanese Patent Laid-Open No. 3-166321 proposes to use a vibration type kneader and a vibration type granulator as a granulating machine for sintering raw materials. In this method, first, a sintering type raw material is pressure-kneaded by using a vibration type kneading machine to allow water to seep out to the surface of the raw material. Further, the raw materials are united with each other using a vibrating granulator that vibrates in a circular or horizontal oscillation. As a result, the pseudo particle size becomes large, and the air permeability of the sintering raw material packed layer is increased. As another example, JP-A-57-174420 proposes a method of treating a sintering raw material with a fret mill, a ball mill, an Erich mixer, a twin-screw kneader or the like. Both of these two inventions are based on the mechanism that the capillary force of the raw material is increased by uniformly coating the surface of the raw material with water, and as a result, the pseudo particle size is increased.

However, in these methods, an external force such as a shearing force is applied to the sintering raw material, so that the powder or granule itself may be crushed to reduce the particle size. In Japanese Patent Laid-Open No. 3-166321,
It is stated that the raw material after kneading becomes flakes,
Strictly speaking, it becomes an aggregate of fine powder. When the limestone in the sintering raw material is refined, the melting reaction between the iron ore and the limestone in the sintering reaction changes subtly, which affects the product yield of the sintering and the cold strength of the sintered ore. It is expected that. Therefore, it is necessary to select the mixing method in consideration of the raw material particle size after mixing, but this point has not been clarified.

The second method will be described in detail below.

In order to improve the product yield of the sintered product and the cold strength of the sintered ore, it is necessary to pay attention to the molten state of the raw material in the hot state in addition to the air permeability of the sintering raw material packed bed in the cold state. . In particular
In the production of low CaO sinter that requires effective utilization of CaO components, the molten state of the raw materials has a strong effect on the product yield of the sinter and the cold strength of the sinter.

Since limestone has a certain particle size, it is several mm
The CaO component is unevenly distributed in the following microscopic range.
Of course, macroscopically, the uneven distribution of CaO components is affected by the existence state of limestone particles. Such microscopic or macroscopic
The uneven distribution of CaO components affects the yield of sintered products and the cold strength of sinter. For example, “Materials and Processes” Volume 3 (1990
(Year) page 1065 reports the results of basic studies suggesting that if the CaO component is unevenly distributed to secure melt fluidity to some extent, the cold strength of the sinter increases. But,
The proper particle size of limestone and the proper existence state of limestone particles in the actual operation are not clarified. In "Iron and Steel", Vol. 78 (1992), p. 1037, the particle size of limestone is 7 mm.
It is reported that the larger the grain size is, the higher the cold strength is. However, it cannot be said that the proper particle size composition is quantitatively shown.

[0014]

As described above, in the production of sinter, if the CaO component in the blended raw material decreases, the melt produced during the sintering reaction becomes insufficient. As a result, the yield of sintering and the cold strength of sinter decrease. As a method of increasing the yield and the cold strength, there is a method of increasing the air permeability of the sintering raw material packed bed and transferring the increased amount of the air permeability to the increase of the packed bed thickness to operate. In order to increase the cold air permeability of the sintering raw material packed layer, it is necessary to mix the raw materials during granulation and evenly disperse the water on the surface of the raw materials. But,
When the raw materials are mixed so as to be crushed, refining the limestone that is the source of CaO has an unfavorable effect on the yield and cold strength.

On the other hand, by controlling the distribution state of limestone in the raw material, it is conceivable to enhance the function of the melt as a binder for powder and granules to increase the yield and cold strength. However, no clear guideline for proper distribution of limestone has yet been established.

The object of the present invention is to produce a low CaO sinter having high cold strength with a high product yield by optimizing the grain size composition of limestone, mixing of sintering raw materials, and granulation method. To provide.

[0017]

DISCLOSURE OF THE INVENTION The gist of the present invention is the following method for producing a low CaO sinter.

Converted to CaO concentration in the product sinter, 7.0-
Measured in a completely dry state so that it will be 9.0% by weight
A method for producing a low CaO sintered ore, which comprises mixing a sinter raw material containing limestone having a particle size distribution of 1 above with a mixer having a built-in high-speed rotating blade and firing the mixture.

Particles of 0.5 mm or less: 20% to 40% by weight
Particles exceeding 1 mm and 5 mm or less: 40% by weight to 60% by weight Particles exceeding 5 mm: 40% by weight or less.

In the present invention, mm representing the size of particles
Is a typical diameter of the sieve mesh.

The mixer with a built-in high-speed rotating blade used in the method of the present invention is a mixer in which a blade for the purpose of agitation is installed in a cylindrical pan, and both the pan and the blade are rotating. There is, for example, a typical mixer called an Erich mixer. This type of mixer has a high rotation speed of several hundred rpm of the blades and does not have a compaction effect, so that it is possible to perform uniform mixing, and even brittle components such as limestone can be unnecessarily crushed. Absent.

After mixing with a mixer having the above-mentioned high-speed rotating blades, it is desirable to further granulate using a rolling granulator.

In the method of the present invention, the limestone is blended so as to be 7.0 to 9.0% by weight in terms of the CaO concentration of the sintered mineral product, if the amount is less than 7.0% by weight, the CaO concentration is too low and agglomeration occurs. This is because the melt required for the conversion is insufficient, and on the other hand, a sinter having a CaO concentration of more than 9.0% by weight cannot be said to be a low CaO sinter, and if this is charged in a blast furnace at a high ratio, it will be slag This is because the unfavorable effect of excessive increase of

When the amount of CaO is large, the amount of melt to be described later is large and the yield and cold strength of the sintered ore product are high, so it is not necessary to dare to adopt the method of the present invention. In other words, the method of the present invention is a method for improving the yield and cold strength when producing a low CaO sinter.

[0025]

[Function] It is generally known that, for the purpose of uniform calcination, in a macroscopic range of several cm or more, it is generally known that the limestone is uniformly dispersed to increase the product yield and cold strength of the sintered ore. However, the present inventors examined in more detail the relationship between the mixing degree of limestone and the product yield and cold strength of sinter.
As a result, when a drum mixer is used as a mixer, the fine limestone is not sufficiently mixed, and the desired effect cannot be obtained even if the particle size composition of limestone is taken into consideration as described later. On the other hand, when using a mixer such as a vibration type kneader that gives a shearing force to the material to be mixed, the mixing itself will be sufficient, but the limestone powder will be crushed, resulting in an undesired particle size configuration, and also the desired effect. I can't get it. On the other hand, if a mixer with a high-speed stirring blade is used, it is possible to evenly distribute fine limestone, which is insufficiently mixed in the drum mixer, in the sintering raw material, and crushing of limestone is actually caused. Therefore, it was found that the yield and cold strength of the sintered ore were greatly improved.

FIG. 1 shows the pseudo-particle structures of the sintering raw material in comparison between the case of using a mixer having a high-speed stirring blade and the case of using a vibration type kneader. As shown in Fig. 1 (b), when a mixer with a built-in high-speed stirring blade is used, it is a pseudo particle in which coarse particles are used as nuclei and fine powder is attached around them. On the other hand, when the vibration type kneader is used, the raw materials are finely pulverized and then interconnected as shown in (a).

For each of the particles shown in FIG. 1, the pseudo particles after mixing were completely dried and decomposed to the level of constituent particles, and the particle size distribution was measured. When the mixer with the high-speed stirring blade of (b) was used, the particle size of each raw material powder was almost the same as the particle size when initially mixed. On the contrary,
In the case of (a) using the vibration type kneader, 80% by weight of the limestone had a particle size of more than 1.0 mm at the beginning of the blending, but after kneading, the limestone had a particle size of 0.125 mm or less and 30% by weight. %, 1.
The size was reduced to about 90% by weight at 0 mm or less.

From the above results, it is clear that the fine grain raw material can be uniformly mixed in the raw material layer without crushing the raw material by using the mixer having the high speed stirring blade built therein.

Next, as a result of investigating an appropriate grain size composition in a wide range of grain size distribution of limestone, it was found that the product yield and cold strength of the sintered ore are improved in the case of the following grain size distribution. .

Particles of 0.5 mm or less: 20% by weight to 40% by weight
Particles exceeding 1 mm and 5 mm or less: 40% by weight to 60% by weight Particles exceeding 5 mm: 40% by weight or less (Note that particles exceeding 0.5 mm and 1 mm or less are the balance.) Even if limestone is used, the initial effect cannot be obtained unless a mixer with a built-in high-speed rotary blade is used. This is because when other mixers are used, uniform mixing cannot be performed, or the limestone powder is further crushed and the particle size distribution is largely deviated.

The reason why the proper particle size distribution of limestone used in the method of the present invention is within the above range is considered as follows.

As described above, in order to improve the yield and the cold strength of products in the production of sinter, it is necessary to effectively utilize the melt generated in the sintering reaction.

As the particle size of limestone increases, microscopic uneven distribution of CaO components occurs. As a result, a large amount of high CaO locally
A melt of components is produced. This melt has good fluidity,
Largely agglomerates by taking in the surrounding ore widely. On the contrary, when fine limestone exists independently, even if it becomes a melt, its amount is very small. Therefore, in the next reaction, the melt contacts and assimilates with the surrounding iron ore and the CaO concentration in the melt is increased. Will drop instantly. When the CaO concentration decreases, the melting point rises, the melt solidifies, and agglomeration does not proceed. Therefore, coarse-grained limestone generally works more effectively for agglomeration. However, if the limestone particle size is too large, unreacted parts remain and the amount of melt in the entire raw material layer decreases. Therefore, the upper limit of the particle size of limestone powder is preferably limited to about 5 mm. In addition, when the ratio of coarse particles of limestone increases, limestone is unevenly distributed in the lower layer of the sintering raw material packed layer in the pallet due to segregation of charge, so that the product yield and cold strength of the sintered ore in the upper layer are Getting worse.

FIG. 2 shows the influence of the ratio of coarse-grained limestone having a grain size of more than 5 mm on the product yield of sintering (Fig. (A)) and the cold strength of sinter (Fig. (B)). Show. The definitions of the symbols in the figure are as follows.

∘: When the coarse limestone having a grain size of 5 to 1 mm is fixed at 40% by weight and the ratio of the coarse limestone exceeding 5 mm is changed, and the balance is a fine limestone having a grain size of 1 mm or less.

◯: In the case of a grain size composition in which the fine limestone having a grain size of 1 mm or less is kept constant at 30% by weight and the ratio of coarse limestone exceeding 5 mm is changed, and the balance is coarse limestone of 5 to 1 mm.

For mixing and granulating the sintering raw materials in this test, an Erich mixer was used in order to avoid crushing of limestone. The cold strength of the sinter is the tumbler rotation strength (T.
I.).

As shown in the figure, when the proportion of coarse-grained limestone exceeding 5 mm exceeds 40% by weight, the yield of sintered products and the cold strength (TI) of sinter rapidly deteriorate. This is because the adverse effect of the decrease in the melt volume due to the increase in unreacted limestone described above became apparent. From this data, it is clear that the proportion of coarse limestone of 5 mm or more needs to be 40% by weight as the upper limit.

Next, the yield and cold strength improving mechanism by the uniform distribution of fine-grained limestone in the raw material layer will be described. The melt in the sintering reaction is generated from coarse-grained limestone as described above, but in order to maintain the fluidity of this melt, the CaO component needs to be present around the melt generation site. This CaO
Even if the component does not melt itself, it may have a function of supplying the CaO component to this melt when it comes into contact with a nearby melt. When the CaO component is supplied to the melt, the melting point increase in the reaction between the melt and the iron ore can be suppressed, and the melt fluidizes over a wide range to promote agglomeration. This is the role of fine-grained limestone.

If the fine-grained limestone is not uniformly distributed in the raw material layer, the moving regions of the individually generated melts vary, and uniform agglomeration cannot be achieved. As a result, the yield and cold strength are reduced. In other words, the uniform distribution of coarse-grained limestone means the uniformization of melt generation points, while the uniform distribution of fine-grained limestone means uniform flow distance of the generated melt.

The present inventors further investigated the relationship between the limestone particle size and the meltability of the raw material for the purpose of quantifying the particle size that functions as coarse-grained limestone. As a result, they have found that the melt fluidity is remarkably improved when the particle size of limestone exceeds 1 mm. That is, it was confirmed that coarse limestone having a particle size of more than 1 mm functions as a melt generation source, and fine limestone having a particle size of 1 mm or less has a function of maintaining melt fluidity.

Here, the ratio of fine-grained limestone with a particle size of 0.5 mm or less is
The reason for limiting the content to 20% by weight to 40% by weight will be described below.

If the amount of fine limestone having a particle size of 0.5 mm or less is less than 20% by weight, the average particle size of limestone increases and the number of limestone particles decreases. It becomes difficult to maintain the fluidity of the liquid. If it exceeds 40% by weight, fine-grained limestone with a grain size of 0.5 mm or less is likely to be powdered with pseudo particles. Is not uniform, and moreover, the product yield of the upper layer sintered product and the cold strength of the sintered ore are deteriorated.

In the method of the present invention, the use of a mixer with a built-in high-speed stirring blade for mixing the raw materials means that this mixer does not crush limestone having an appropriate particle size constitution,
This is because uniform mixing in the raw material layer can be achieved while maintaining an appropriate particle size distribution.

A typical mixer having a built-in high-speed stirring blade is the above-mentioned mixer called Eirich mixer, but in addition to this, a granulator having rotary blades inside the drum mixer can also be used.

As described above, when the mixture is mixed by the mixer having the high-speed stirring blade and then granulated by using the tumbling granulator, for example, the drum mixer or the pan pelletizer, the pseudo particle size becomes large, and the baking is performed. The air permeability of the binder raw material filling layer is increased. As a result, the packed bed thickness can be increased, and the product yield of the sintered product and the cold strength of the sintered ore are further improved.

Since water can be exuded on the surface of the raw material by a mixer having a high-speed stirring blade, a rolling type granulator such as a drum mixer or a pan pelletizer is sufficient as a granulating machine used in the latter stage. .

The effects of the method of the present invention will be specifically described below with reference to examples.

[0049]

Example 1 In order to confirm the effect of the method of the present invention, a sinter pot test was conducted by changing the particle size composition, mixing and granulation method of limestone, and the yield of sintered product and the cooling of sinter ore. The inter-field strength was investigated.

The composition of the sintering raw material is as shown in Table 1, and the addition amount of limestone is calculated as CaO concentration of the product sintered ore.
It was set to 8.5%. Table 2 shows the particle size composition of the limestone used.

For mixing and granulating the sintering raw materials, an Erich mixer, which is a kind of mixer having a high-speed stirring blade, was used. The specifications of the Erich mixer are as follows.

Dimension: Diameter 630 mm, height 460 mm Rotation speed: Pan 50 rpm, agitator 500 rpm Residence time: 1 minute The amount of water added during granulation is mostly pseudo particles with a particle size of 5 to 10 mm. The water content was determined by a preliminary survey.

The sintering raw material after mixing and granulation is supplied to the ore by using a ore simulating device simulating the actual machine in order to make the effect of the segregation of charge similar to that of the actual machine, and then the upper, middle and lower layers are separately supplied. It sampled and used for the sintering pot test.

A sintering pot having a diameter of 300 mm was used, and the sintering was performed under constant conditions of a sintering layer thickness of 500 mm and a superficial air velocity of 20 Nm ³ / m ² . The reason why the firing was performed at a constant air velocity in the cylinder was to evaluate the product yield and cold strength under a constant heat pattern condition. The ignition condition is 2 LPG 87 liters / min.
The firing was completed at BTP (Burn Through Point, the highest reaching point of the waste gas temperature).

[0055]

Comparative Example 1 A sintering pot test was conducted under the same conditions as in Example 1 except that the particle size composition of limestone was outside the range defined in the present invention.

[0056]

Comparative Example 2 A sintering pot test was conducted under the same conditions as in Example 1 except that a two-stage drum mixer was used for mixing and granulating the sintering raw materials.

[0057]

[Comparative Example 3] The grain size composition of limestone was outside the range defined in the present invention, and a two-stage drum mixer was used for mixing and granulating the sintering raw materials. Other than that, the sintering pot test was performed under the same conditions as in Example 1.

The specifications of the drum mixers used in Comparative Examples 2 and 3 are as follows.

Dimensions: Diameter 600 mm, Length 1000 mm Rotation speed: 30 rpm Residence time: 4 minutes

[0060]

[Table 1]

[0061]

[Table 2]

In Table 2, the grain size composition of limestone is shown in the center,
The types of mixers are shown on the left and right. The indications of Example 1 and Comparative Examples 1, 2 and 3 in the table correspond to the above-mentioned examples.

3 (a) and 3 (b) show the effects of the limestone grain size composition on the product yield of the sintered product and the cold strength of the sintered ore in comparison with the examples and comparative examples. The symbols in the figure correspond to the test numbers in Table 2.

As shown in the drawing, the mixing and granulation methods are the conditions of the present invention, but in Comparative Example 1 in which the particle size composition of limestone is outside the range defined by the present invention, the product yield is 79.9 to 83.9%, Inter-strength (TI) is 53.9-59.0. 1 to 1 in Comparative Example 1
No. 5, 6 and 7 in which 5 mm particles are 40 to 60% by weight have high product yield and cold strength, and 1 to 5 mm particles are 70% by weight.
The product yields and cold strengths of Nos. 12, 13, and 14 were low.
In Nos. 8, 9, 10, and 11 in which particles of 1 to 5 mm were 20% by weight, the product yield was low, but the cold strength was high.

Although the particle size composition of limestone is within the range defined in the present invention, Comparative Example 2 (No. 1) using the conventional mixing and granulating method is used.
5, 16, 17, 18), the product yield slightly higher than that of Comparative Example 1.
83.3 to 85.5%, which is slightly lower than Comparative Example 1 in cold strength (T.
I.) 54.1-57.1 were obtained.

In Comparative Example 3 (No. 19 to 28) in which the limestone grain size composition was out of the range defined in the present invention and the conventional mixed granulation method was used, the product yield was 78.1 to 83.4% and the cold strength ( TI) is 50.3 ~
It was 56.6. Both the product yield and the cold strength are Comparative Example 2,
Many were even lower than 3.

On the other hand, Example 1 (No. 1, 2, 3,
In 4), the product yield (87.4 to 88.0) higher than that of any comparative example was obtained.
%) And cold strength (TI60.9 to 63.0) are obtained.

[0068]

[Example 2] A sintering pot test was conducted under the assumption of actual machine operation, while keeping the negative pressure constant and changing the layer thickness as shown in Table 3.
The other conditions were the same as in Example 1. The layer thickness was adjusted so that the firing times were substantially the same as those of Example 3, Comparative Example 4 and Reference Example described later. Table 3 also shows the particle size composition of limestone blended in the sintering raw material.

[0069]

Example 3 A sintering pot test was conducted under the same conditions as in Example 2 except that an Erich mixer was used for mixing the sintering raw materials and a drum mixer was used for granulation.

[0070]

[Comparative Example 4] A sintering pot test was conducted under the same conditions as in Example 2 except that a two-stage drum mixer was used for mixing and granulating the sintering raw materials.

[0071]

[Reference example] 9.9% by weight converted to CaO concentration in the product sintered ore
Limestone was added (in the above-mentioned raw material composition of Table 1, limestone was increased by 2% by weight and sintering feed was decreased by 2% by weight). Other than that, the sintering pot test was performed under the same conditions as in Comparative Example 4.

Table 3 shows the results of the sintering pot tests of the above-mentioned Example 2, Comparative Examples 3 and 4 and Reference Example.

As shown in Table 3, in Example 2 using the Eirich mixer, compared with Comparative Example 4 using the drum mixer, the yield of the sintered product and the cold strength (T.
I.) has been greatly improved.

Further, in Example 3 in which the Eirich mixer and the drum mixer were used in combination, the product yield and the cold strength were further improved by increasing the layer thickness by improving the air permeability.

This improvement effect exceeded the level of the reference example, which had a high CaO concentration of 9.9% normally used in a blast furnace.

[0076]

[Table 3]

[0077]

According to the method of the present invention, a low CaO sinter having a high cold strength can be produced with a high product yield. If the low CaO sintered ore obtained by the method of the present invention is used, stable operation of the blast furnace becomes possible even if the compounding ratio of the sintered ore is increased,
It can fully cope with the depletion of high quality lump ore materials.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing, in comparison, a pseudo particle structure of a sintering raw material in the case where a vibration type kneader and a mixer having a high-speed stirring blade built therein are used.

FIG. 2 is a diagram showing the influence of the ratio of coarse-grained limestone having a grain size of more than 5 mm on the product yield of sintering and the cold strength of sinter.

FIG. 3 is a diagram showing the influence of the grain size composition of limestone on the product yield of sintering and the cold strength of sinter.

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Claims (2)

(57) [Claims] 1. The value in terms of CaO concentration in the product sintered ore is 7.0-.
Measured in a completely dry state so that it will be 9.0% by weight
A method for producing a low CaO sintered ore, which comprises mixing a sinter raw material containing limestone having a particle size distribution of 1 above with a mixer having a built-in high-speed rotating blade and firing the mixture. Particles of 0.5 mm or less: 20% to 40% by weight, particles exceeding 1 mm and 5 mm or less: particles of 40% to 60% by weight, particles exceeding 5 mm: 40% by weight or less 2. The method for producing a low CaO sinter according to claim 1, wherein the sintering raw materials are mixed by a mixer having a high-speed rotating blade and then granulated by using a rolling granulator. .