JP2001049319A - Hot metal desulfurization method - Google Patents

Abstract

(57) [Problem] To provide a method for desulfurizing hot metal which is not only excellent in desulfurization than in the past but also has less troubles in equipment than in the past and can be operated stably. It is an object. A desulfurizing agent is added to a hot metal bath held in a molten metal refining vessel, and an impeller is immersed and rotated.
In the hot metal desulfurization method for stirring the hot metal bath, the impeller is rotated while moving up and down in the hot metal bath. The ratio of the outer diameter of the impeller to the inner diameter of the molten metal scouring vessel is set to 1/10 to 2/3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for desulfurizing hot metal, and more particularly to an improvement in the prior art in which hot metal is desulfurized by mechanical stirring before charging the hot metal into a converter.

[0002]

2. Description of the Related Art Conventionally, an impeller (a plurality of blades provided on a rotating shaft) is provided for desulfurization (hot-metal pretreatment) from hot metal charged into a converter. There is a technique for mechanically stirring the hot metal by using the above method.
For example, Japanese Patent Publication No. 42-12343 discloses a method of increasing a desulfurization reaction by rotating an impeller 2 immersed in a bath of hot metal 1 in a fixed direction and stirring the hot metal 1 as shown in FIG. Has been disclosed. However, in this method, when the impeller 2 is rotated, the flow of the hot metal 1 immediately reaches a steady state, the flow of the hot metal 1 is not so large, and a high reaction promoting effect cannot be obtained. Also, within a relatively short period of time after the start of use, the impeller 2 tends to wear unevenly with respect to the rotating shaft 4, resulting in a loss of rotational balance and a tendency for the stirring force of the impeller 2 to deteriorate. That is, since the blade surface of the impeller 2 collides with the hot metal 1 and the particles of the desulfurizing agent 3 at a high speed, the erosion is inevitable. Therefore, in the stirring of the hot metal 1 by only the above-described rotation in a certain direction, the impeller 2
However, there is a problem that the front side in the rotating direction is significantly melted and damaged as compared with the rear side, so that the stirring efficiency is lowered and the life of the impeller 2 itself is considerably shortened.

Therefore, Japanese Patent Publication No. Sho 63-6605 discloses that
A desulfurizing agent 3 is added to the hot metal 1 held in a molten metal refining vessel 5 such as a ladle, and an impeller 2 having a vertical rotating shaft 4 is immersed at a certain depth in the center of the hot metal 1 bath. A technique for stirring the hot metal 1 by rotating the impeller 2 forward and backward (the direction of reverse rotation is indicated by a dotted arrow) in the same axis for 1 to 3 minutes. As a result, a forward / reverse vortex is generated in the hot metal 1 bath, and turbulent stirring such as a reverse rotation wave generated at the time of forward rotation and reverse rotation also occurs. A fairly good mixing and stirring state could be created. Further, the particles of the desulfurizing agent 3 are fragmented or deformed by the forward and reverse stirring motions, and the area of the reaction interface with the hot metal 1 increases, so that the desulfurization can be further promoted as compared with the conventional method. Furthermore, the forward and reverse rotations made the surfaces of the blades of the impeller 2 uniform in abrasion opportunity, the erosion became uniform on both surfaces, and the life of the impeller 2 was improved.

However, in this technique for rotating the impeller 2 forward and backward, a rotation driving means (not shown) such as a motor is used.
Another problem is that a large load is frequently applied to the equipment, so that troubles in the equipment cannot be avoided and stable operation cannot be performed.

[0005]

SUMMARY OF THE INVENTION In view of such circumstances, the present invention not only excels in desulfurization than in the past,
It is an object of the present invention to provide a method for desulfurizing hot metal which has less troubles on equipment and can operate stably.

[0006]

Means for Solving the Problems In order to achieve the above-mentioned object, the inventor made an utmost effort to eliminate equipment troubles without lowering the desulfurization efficiency, and realized the results in the present invention.

That is, the present invention provides a method for desulfurizing hot metal in which a desulfurizing agent is added to a hot metal bath held in a molten metal refining vessel, the impeller is immersed and rotated, and the hot metal bath is agitated. A method for desulfurizing hot metal characterized by rotating while moving up and down in a hot metal bath.

In the present invention, the ratio of the outer diameter of the impeller to the inner diameter of the molten metal scouring vessel may be set at 1/10 to 2/3, or the speed of the vertical movement may be set at 0.5 to 3.0 m.
/ Min, which is a method for desulfurizing hot metal.

Further, the present invention is also a method for desulfurizing hot metal, wherein the rotation speed of the impeller is 30 to 150 rpm.

In this case, the impeller may be continuously rotated in the same direction, or may be reversely rotated during the processing to prevent uneven wear of the impeller. Further, when the impeller is reversed, it is preferable to once raise the impeller above the bath surface in order to prevent uneven wear.

According to the present invention, the efficiency of the desulfurization reaction can be significantly increased by rotating the impeller up and down at a low speed while rotating the impeller. Will not be applied. As a result, troubles in the equipment can be avoided, and the molten iron bath is evenly and uniformly stirred, so that stable operation can be performed without lowering the desulfurization efficiency as compared with the related art.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

In order to correct the drawbacks of the conventional technique of rotating the impeller only in one direction and the technique of rotating the impeller forward and backward, as shown in FIG. The idea was to rotate while moving up and down (indicated by arrow 7). When this raising and lowering movement is performed, the hot metal 1 is sequentially stirred at different depths depending on time, and the hot metal 1 is uniformly stirred without switching the impeller 2 in the forward and reverse directions within a short time and rotating the impeller 2. become able to. Therefore, the flow state of the hot metal 1 is
Violent compared to only one-way rotation, hot metal 1 and desulfurizing agent 3
The chance of contact with the particles increases, and the desulfurization reaction is accelerated. In addition, since no forward or reverse rotation is performed, a severe load is not applied to the driving means of the impeller 2 such as a motor. Further, since the stirring area is widened in the height direction of the molten metal container 5 (for example, a ladle or the like) holding the hot metal 1, erosion at a specific position of the refractory lining the container 5 is delayed, and the life of the container 5 is shortened. There was also the effect of extending.

Next, the inventor conducted a study for stably securing the stirring effect. As a result, they have found that it is better to limit the ratio of the outer diameter of the impeller to the inner diameter of the molten metal refining vessel to a certain range. That is, the ratio of the outer diameter of the impeller to the inner diameter of the molten metal scouring vessel is set to 1/10 to 2/3.
It is preferable to set it in the range.

Generally, the desulfurizing agent added to the hot metal has an average particle size of several mm and a specific gravity of about 2 which is smaller than that of the hot metal (specific gravity 7), so that the desulfurizing agent has a characteristic that it is not soaked deeply in the hot metal. That is, the desulfurizing agent added to the hot metal accumulates near the surface layer of the hot metal and does not disperse. Then, the inventor increased the outer diameter of the impeller to increase the dispersing power in the hot metal. The reason why the ratio of the outer diameter of the impeller to the inner diameter of the vessel is limited to the above range is that if it is less than 1/10, the desulfurizing agent stays only in the central part of the hot metal bath, so that the desulfurization efficiency does not improve much. If the value exceeds / 3, a predetermined heat size cannot be secured due to an increase in the amount of hot metal swelling.

Although it is clear that the load on the driving means of the impeller 2 is smaller than that in the case of the forward / reverse rotation within a short time, in the present invention, too, if this lifting / lowering movement is performed at a very high speed, The load on the driving means 2 becomes large. In addition, there is a danger that the level of the molten metal will increase and the hot metal will overflow from the ladle. Therefore, in the present invention, it is preferable to perform the elevating movement at a relatively low speed of 0.5 to 3.0 m / min. According to the inventors' experiments, 0.5
If it is less than m / min, it is too slow to complete the desulfurization treatment of the entire hot metal within a limited desulfurization operation period, and if it exceeds 3.0 m / min, troubles in the driving means and operation are expected. This is because the.

Further, in the present invention, as shown in FIG. 2 (b), the maximum upper limit depth of the impeller 2 immersed in the hot metal 1 bath is such that the upper end of the impeller does not come off from the surface of the hot metal 1 bath. Is preferred. If the height is higher than that, the desulfurizing agent stays on the wall surface of the ladle, the chance of contact between the hot metal and the desulfurizing agent decreases, and the effect of stirring decreases. In addition, the lower limit depth is, of course, a position where the impeller 2 does not contact the bottom of the container 5 and is not damaged (see FIG. 2A).

Further, in the present invention, the rotation speed of the impeller 2 is preferably in the range of 30 to 150 rpm. 30 rp
If it is less than m, the desulfurization efficiency is low and the operation time becomes too long. If it exceeds 150 rpm, the load on the driving means of the impeller 2 may increase.

The molten metal refining vessel for carrying out the present invention may be of a special shape such as a converter or a mixed iron wheel, but usually may be of a simple shape, such as a hot metal pot. Ladles are preferred.

[0020]

EXAMPLE In order to produce ultra-low sulfur steel, hot metal charged into a converter was desulfurized in advance. First, the hot metal 1 shown in Table 1 was treated with an inner diameter of 3500 mm and a depth of
It was charged into a 0-ton hot metal pot 5 and quick lime was charged as a desulfurizing agent 3. Its input amount is 2.5 kg / ton-hot metal. Next, the impeller 2 having an outer diameter of 1000 mm and four blades is immersed in the hot metal 1 bath so that the rotary shaft 4 coincides with the central axis of the hot metal 1 bath surface, and the rotation is immediately performed. Starting, the desulfurization method according to the present invention was implemented. that time,
The impeller 2 has a rotational speed of 100 r from the beginning to the end.
pm, and at a constant speed of 1.0 m / min, it was moved up and down between the uppermost and lowermost depths. In addition,
The operation time was 20 minutes, and the operation was performed smoothly. After the end of the operation, the composition of the hot metal 1 was analyzed, and the results of the composition analysis are shown in Table 1 above. The rotation direction of the impeller is switched for each charge to prevent uneven wear.

[0021]

[Table 1]

From Table 1, it is clear that according to the present invention, the sulfur content (indicated by the symbol S) of the hot metal 1 is considerably reduced.

Therefore, in order to compare with the conventional operation in which the impeller 2 is rotated only in one direction, hot iron desulfurization of a large number of charges was performed under the same conditions as described above. The result is impeller 2
FIG. 3 shows the relationship between the rotation speed and the desulfurization rate (expressed as (S before treatment-S after treatment) / S before treatment). According to the invention, 5
Even in a relatively low rotation speed range of 0 to 100 rpm, the desulfurization efficiency was large, and the result was much better than in the past. It is considered that this is because the flow state of the hot metal bath 1 was improved by the vertical movement of the impeller 2. At this time, the operation by the desulfurization method according to the present invention was carried out for a total of 50 charges, during which time there was no trouble and the operation was smooth. This suggests that the present invention is much more stable in terms of equipment maintenance than the conventional forward / reverse rotation type operation.

[0024]

As described above, according to the present invention, troubles in equipment can be avoided and the molten iron bath can be evenly and uniformly stirred. As a result, a stable desulfurization operation of hot metal can be performed without lowering the desulfurization efficiency as compared with the conventional case. In addition, the growth of umbrella-shaped ingots formed near the upper part of the impeller slowed down, which also contributed to the maintenance of the impeller.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a situation in which a hot metal desulfurization method according to the present invention is performed.

FIG. 2 is a diagram showing another embodiment different from FIG. 1;
In the figure, the impeller is at the lowest limit and (b) is at the highest limit.

FIG. 3 is a diagram comparing a desulfurization rate obtained by a method according to the present invention with a value obtained by a conventional method in which only one direction is rotated.

FIG. 4 is a longitudinal sectional view for explaining a conventional hot metal desulfurization method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Hot metal 2 Impeller 3 Desulfurizer 4 Rotation axis 5 Molten metal smelting vessel (hot metal pot) 6 Arrow indicating hot metal flow direction 7 Arrow indicating impeller raising / lowering direction

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shigeru Ogura 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Steel Co., Ltd. Chiba Works F-term (reference) 4K014 AA02 AC08 AD00

Claims (4)

[Claims] 1. A hot metal bath held in a molten metal refining vessel,
A desulfurization method for hot metal, in which a desulfurizing agent is added, the impeller is immersed and rotated, and the hot metal bath is agitated, wherein the impeller is rotated while moving up and down in the hot metal bath. Method. 2. The hot metal desulfurization method according to claim 1, wherein a ratio of an outer diameter of the impeller to an inner diameter of the molten metal refining vessel is 1/10 to 2/3. 3. The speed of the elevating movement is 0.5 to 3.0 m.
The method for desulfurizing hot metal according to claim 1 or 2, wherein the rate is / min. 4. The rotation speed of the impeller is 30 to 150.
The method for desulfurizing hot metal according to any one of claims 1 to 3, wherein the hot metal is set to rpm.