JPH08100210A - Generator of fine air bubble into molten steel - Google Patents

Abstract

PURPOSE: To generate fine air bubbles into molten steel having a high effect by a simple and safe method by projecting ceramic nozzles having an outside diameter of a specific size or below from the bottom in a molten steel container. CONSTITUTION: General refractories 9 and porous bricks 10 are installed on the bottom of, for example, a molten steel vessel 1 in such a manner that the surfaces of both are formed at the same horizontal level. The one-side ends of one piece or plural pieces of the ceramic nozzles 8 having the outside diameter of <=2mm are embedded into the porous bricks 10 and another-side ends are projected from the surface of the porous bricks 10. A refractory coating material 11 is applied on the surface in contact with the molten steel 7 of the porous bricks 10. An inert gas 6, supplied to the porous bricks 10, is admitted from the bottom of the ceramic nozzles 8 into the nozzles 8 and is made into air bubbles 5 at the front ends by the coating material 11. These air bubbles are supplied into the molten steel 7, by which the fine air bubbles of desired sizes are formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for generating fine bubbles in molten steel.

[0002]

2. Description of the Related Art In recent years, due to stricter quality requirement levels and intensifying competition with other materials, it is becoming more and more difficult to achieve high cleanliness required for steel, especially reduction of non-metallic inclusions in steel. As a conventional method for removing inclusions in steel, agglomeration between inclusions
Macro bubbling method focusing on promoting levitation,
The electromagnetic stirring method, the vacuum degassing method, etc. are implemented. However, with these methods, it is difficult to sufficiently remove minute inclusions of 50 μm or less in the molten steel and achieve the high degree of cleaning required in recent years.

Recently, attention has been focused on a method of removing inclusions by separating fine inclusions by trapping them in fine bubbles. It is presumed that fine bubbles having a diameter of 5 mm or less can effectively remove minute inclusions having a diameter of 50 μm or less existing in molten steel.

Porous bricks or perforated plates are usually used as a method for generating fine bubbles in molten steel, and various methods have been proposed. However, as will be described later, bubbles generated from small holes on the surface of porous bricks or holes in a perforated plate are likely to coalesce with each other at the outlet to form large bubbles, so that desired fine bubbles can be stabilized by this method. Is difficult to get.

As another method for producing fine bubbles, a method of shearing the produced large bubbles by rotating the nozzle or flowing molten steel in the vicinity of the nozzle outlet, and a method of blowing out the gas at a high speed to collide the coarse bubbles into fine bubbles A method of making it possible is also proposed. For example, Japanese Patent Publication No. 63-2616
As shown in FIG. 7, Japanese Unexamined Patent Publication No. 9 discloses that "magnetic force is applied to molten steel 7 in the lower portion of container 1 by electromagnetic coil 12 to obtain 0.8 cm / sec.
The above-mentioned method for cleaning molten steel in which the molten steel flow 13 is generated and the inert gas 6 is added to the molten steel flow 13 from the plug 15 via the gas pipe 14 is shown.

However, even with these methods, it is difficult to stably generate fine bubbles having a diameter of 5 mm or less for the same reason as described above. Further, the operation causes a strong turbulent flow in the molten steel, the inclusions may be re-entrained, and the agglomeration between the bubbles cannot be avoided, so that the effect of removing the inclusions cannot be expected. Furthermore, these methods also have the drawbacks that an expensive addition device that requires a complicated operation is required, and that the processing time becomes long and the cost is burdened.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to provide an apparatus for producing fine bubbles in molten steel which is easy to operate, low in cost, and highly effective. Especially.

[0008]

The gist of the present invention is as follows.
It is in the device for generating fine bubbles of (1) and (2).

(1) A device for generating fine bubbles in molten steel in which one or a plurality of ceramic nozzles having an outer diameter of 2 mm or less project into the molten steel from the bottom of the molten steel container.

(2) The bubble generating device comprises a porous brick and the above ceramic nozzle, one end of which is embedded in the porous brick and the other end is on the surface of the porous brick. A device for generating fine bubbles in molten steel in which a refractory paint is applied to the portion of the porous brick that is in contact with the molten steel.

[0011]

First, the mechanism for producing fine bubbles from the nozzle that is projected into the molten steel from the bottom of the molten steel container will be described in comparison with the case where the nozzles are not projected (target is water and molten steel).

FIG. 1 is a longitudinal sectional view conceptually showing a case where air bubbles in water are generated using a porous brick or a perforated plate. In FIG. 1, 1 is a container, 2 is water, 3 is a perforated plate (refractory material), 4 is a hole, 5 is a bubble, and 6 is an inert gas.

Usually, since the water 2 and the porous plate (refractory) 3 have very good wettability, as shown in FIG. 1, the bubbles 5 generated from the holes 4 do not coalesce with each other but separate from each other. Therefore, by using a perforated plate (refractory material) having small holes, it is possible to stably generate fine bubbles in water. This is also the case with porous bricks having a high porosity.

However, in the case of molten steel, unlike the case of water,
The wettability between molten steel and refractory materials such as porous bricks is very poor. For example, the contact angle between water and a perforated plate made of a normal material is almost 0 degree, but the contact angle between molten steel and the perforated plate made of alumina is 100 degrees or more. Due to this, the bubbles expand to the outer edge of the hole by the time they separate from the hole, and two nearby bubbles easily contact and coalesce into one large bubble.

FIG. 2 is a vertical sectional view conceptually showing the above situation. In FIG. 2, 1 is a container, 7 is molten steel, 3 is a perforated plate, 4 is a hole, 5 is a bubble, 5'is a large bubble, and 6 is an inert gas. As shown in the figure, the bubbles 5 generated from the holes 4 expand along the surface of the perforated plate 3 to the outer edge of the holes 4 and come into contact with each other, and then are separated from the holes 4 and immediately become large bubbles 5 '. Therefore, it is difficult to generate fine bubbles in molten steel by using a porous brick or a porous plate.

Next, the device of the present invention will be described with reference to FIGS. The apparatus of the present invention projects a nozzle into the molten steel from the bottom of the molten steel container, supplies gas for bubble generation to this nozzle, and generates fine bubbles in the molten steel.

FIG. 3 is a schematic vertical sectional view showing a structural example of the first apparatus of the present invention. The ceramic nozzle 8 is provided so as to penetrate the refractory 9 at the bottom of the container 1 containing the molten steel 7 and to project its upper end into the molten steel 7. The refractory 9 is a normal refractory used in a general furnace body or ladle, and is not a porous brick or a perforated plate. Although only one ceramic nozzle 8 can generate desired fine bubbles, a plurality of ceramic nozzles 8 can generate a large amount of fine bubbles per unit time to obtain an effect of effectively removing fine inclusions. You can In FIG. 3, the ceramic nozzle 8
Shows two examples.

The method of attaching the ceramic nozzle 8 to the refractory material 9 and the method of connecting the pipes for supplying the inert gas may be the same as those for the bottom blowing tuyere of a converter or a ladle. .

When the bubble-generating inert gas 6 is supplied from the ceramic nozzle 8, bubbles 5 are generated at the tip of the ceramic nozzle 8. However, by making the distance between two adjacent nozzles larger than the diameter of the bubble that separates from the tip of the nozzle, coalescence between bubbles as in the case of FIG. 2 does not occur, as shown in the figure.

The nozzle material was ceramic in order to maintain high fire resistance. Specific desirable materials are alumina, alumina graphite, and the like. The outer diameter of the ceramic nozzle suitable for obtaining fine bubbles having a diameter of 5 mm or less is 2 mm or less. The desirable lower limit of the outer diameter of this nozzle is 1 mm. The preferred inner diameter range is 0.2 to 0.8 mm
Is.

A desirable range of protrusion length of the ceramic nozzle into the molten steel is 2 to 10 mm.

Desirable nozzle number density is in the range of 0.1 to 0.8 nozzles / cm ² within the area of the lower portion of the container, and the ceramic nozzle is preferably provided at the center of the bottom of the molten steel container.

The gas used is an inert gas such as Ar or N ₂ , and the desirable gas pressure and flow rate ranges are 1 and 2, respectively.
-30 kg / cm ² , 0.01-1 Nm ³ / min-ton.

FIG. 4 is a diagram showing the relationship between the outer diameter of an alumina ceramic nozzle and the average bubble diameter when Ar gas is supplied to molten steel when the inner diameter is kept constant at 0.5 mm.
In this case, the number density of nozzles was 0.8 / cm ² , the protrusion length was 5 mm, and the average bubble diameter was measured by the frequency of bubble generation. As shown in FIG. 4, if a nozzle having an outer diameter of 2 mm or less is used, it is possible to stably generate fine bubbles having a diameter of 5 mm or less.

A second apparatus of the present invention is one in which one end of a ceramic nozzle is embedded in a porous brick used for a lower portion of a molten steel container and the other end is projected from the surface of the porous brick.

FIG. 5 is a schematic vertical sectional view showing a structural example of the second device of the present invention. The ceramic nozzle 8 has one end embedded in the porous brick 10 as shown and the other end protruding from the surface of the porous brick 10. Ceramic nozzle 8 to porous brick 10
As a method of embedding, a method such as providing a concave portion of a predetermined shape in the porous brick 10 and inserting the porous brick 10 may be used. Further, the gas passage may be removed, and the gap in the insertion portion may be filled and bonded with a refractory adhesive. The embedding depth is 1/3 of the thickness of the porous brick 10.
It is desirable to set it to about a degree. Ceramic nozzle 8 is 1
There are two or more, but two are shown in FIG.

A refractory paint 11 is applied to the surface of the porous brick 10 in contact with the molten steel 7.

Examples of the refractory paint include Al ₂ O ₃ 70%
It is preferable to use one composed of 30% SiO ₂ . A desirable coating thickness range is 1 to 3 mm.

As a method of supplying the inert gas 6 to the porous brick 10, although not shown, it is sufficient to apply the inert gas 6 having the same structure as that used at the bottom of the ordinary ladle.

At the bottom of the molten steel container 1, the surface of the general refractory 9 and the surface of the porous brick 10 are installed at the same horizontal level, and the projecting portion of the ceramic nozzle 8 is projected into the molten steel 7. The inert gas 6 is supplied to the porous brick 10 and not directly to the ceramic nozzle 8. However, since the refractory paint 11 is applied to the surface of the porous brick 10, the inert gas 6 enters the nozzle 8 from the bottom side of the ceramic nozzle 8 and becomes bubbles 5 at the tip and is supplied into the molten steel 7. As in the case shown in FIG. 3, the fine bubbles have a desired size. Refractory paint on porous bricks 11
Even if gas is emitted from the part where
It is possible to prevent the formation of large bubbles as shown in FIG.

In the apparatus shown in FIG. 3, the ceramic nozzle 8
Although there is a possibility that the molten steel 7 leaks from the molten steel 7, since the inert gas 6 is supplied through the porous brick 10 in the second device of the present invention shown in FIG. 5, there is no concern about the leakage of the molten steel 7. No complicated operation such as gas pressure or flow rate is required. Therefore, in addition to being safe, the gas can be supplied easily and stably.

Desirable conditions such as the material, shape, number density of mounting, gas and the like of the ceramic nozzle 8 are the same as those in the case of the first apparatus of the present invention described above.

[0033]

[Example] For Al deoxidized molten steel (temperature 1600 to 1700 ° C) housed in a 100-ton ladle, only porous bricks (comparative example) and the second apparatus of the present invention shown in Fig. 5 were used. ,
A comparative reduction test of inclusions in molten steel was carried out. The evaluation was performed by (concentration of inclusions in molten steel after treatment) / (concentration of inclusions in initial molten steel).

The conditions of the example of the present invention are as follows.

Ceramic nozzle material: Alumina Ceramic nozzle shape: Outer diameter 1.0 mm, inner diameter 0.6 mm Ceramic nozzle density: 0.7 pieces / cm ² (2000 pieces) Projection length of ceramic nozzle into molten steel: All 5 mm Refractory paint Coating thickness: Al ₂ O ₃ 70% SiO ₂ 30%, 2 mm Other basic conditions were as follows.

Inert gas: Ar (pressure 10 kg / cm ² , total flow rate 5 Nm ³ / min) Porosity of porous brick: 30% The results are shown in FIG. FIG. 6 is a diagram showing the relationship between the inclusion concentration ratio and the processing time. As shown in the figure, it is clear that the inclusions in the molten steel are removed more quickly by the method using the apparatus of the present invention than the method of the comparative example.

[0037]

According to the apparatus of the present invention, inclusions in molten steel can be effectively removed by a low cost, simple and safe method.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view conceptually showing a case where bubbles are generated in water by a perforated plate.

FIG. 2 is a vertical sectional view conceptually showing a case where bubbles are generated in molten steel by a perforated plate.

FIG. 3 is a schematic vertical cross-sectional view showing a configuration example of a first device of the present invention.

FIG. 4 is a diagram showing a relationship between an outer diameter of a ceramic nozzle and an average bubble diameter of Ar gas.

FIG. 5 is a schematic vertical sectional view showing a configuration example of a second device of the present invention.

FIG. 6 is a diagram showing a relationship between a concentration ratio of inclusions and a treatment time in an example.

FIG. 7 is a diagram illustrating a conventional method for generating fine bubbles.

[Explanation of symbols]

1: container, 2: water, 3: perforated plate, 4:
Hole, 5: bubble, 5 ': large bubble, 6: inert gas,
7: Molten steel, 8: Ceramic nozzle, 9: Refractory,
10: Porous brick, 11: Refractory paint,
12: electromagnetic coil, 13: molten steel flow, 14: gas pipe,
15: Plug

Claims (2)

[Claims] 1. An apparatus for generating fine bubbles in molten steel, wherein one or a plurality of ceramic nozzles having an outer diameter of 2 mm or less protrudes into the molten steel from the bottom of the molten steel container. 2. A bubble generator comprises a porous brick and the above ceramic nozzle, one end of which is embedded in the porous brick and the other end of which protrudes onto the surface of the porous brick. A refractory paint is applied to a portion of the porous brick that is in contact with the molten steel, and a device for generating fine bubbles in the molten steel.