JPH0434612B2 - - Google Patents

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention improves the efficiency of the molten metal bath in the electric arc furnace when melting and refining scrap and metal materials using a three-phase AC or DC arc. This invention relates to a method and apparatus for good stirring.

[Conventional technology]

Conventionally, in the operation of an electric arc furnace, oxygen is supplied from the furnace wall to an auxiliary burner and to promote melting in the process of melting charged raw materials such as scrap.
At this time, the bottom of the electric furnace is in a so-called shallow bath state, where the depth is extremely shallow relative to its diameter. For this reason, the power to stir the molten metal bath is extremely weak. In addition, the heat applied from the electrodes is also consumed to heat only the upper surface of the molten metal bath, making it difficult for convection to occur in the molten metal bath, resulting in non-uniform temperature and components.

Furthermore, since the stirring force is weak, the metallurgical reaction between the molten metal bath and the flux layer does not reach an equilibrium state, resulting in extremely low reaction efficiency. As a result, there were drawbacks such as a deterioration in the basic unit consumption of additives such as ferromanganese, ferrochrome, and silicon materials, and an increase in iron loss due to an increase in the total Fe in the slag. To avoid this drawback, if you strengthen the stirring power,
In addition to the above-mentioned solutions, it is possible to improve the decarburization rate and clean the steel by removing gases contained in the steel, which is expected to bring great benefits.

However, in the case of an electric arc furnace, shaking or violent rippling of the molten metal bath may lead to problems such as leakage of molten metal from openings, melting of water cooling panels, and instability of the arc. For this reason, it has been considered difficult in actual operation to avoid these risks and apply a strong stirring force to the molten metal bath. Therefore, methods have been proposed in which melting is promoted by blowing inert gas, oxidizing gas, or the like into the furnace from the hearth.

As a method for promoting dissolution in this electric furnace, there is a method described in, for example, Japanese Patent Application Laid-Open No. 1983-92807. This has a blowing nozzle placed at the bottom of the furnace to stir the molten metal bath, and employs a means of forcibly fluidizing the molten metal bath by blowing gas. The blowing nozzle is configured to blow gas in the tangential direction of an imaginary circle around the furnace core so that the molten metal bath swirls around the furnace body. By arranging the blowing nozzle so that the bath forms a swirling vortex around the furnace core, stirring of the molten metal bath is made possible.

[Problem that the invention seeks to solve]

However, in the arrangement of the blowing nozzle that gives the molten metal bath a swirling vortex around the furnace core, although the molten metal bath swirls, the movement at the center of the furnace is almost stagnant. In other words, the bath is fluidized by gas injection, but because the flow line is a circle around the furnace core, the flow velocity is high in areas with a large radius, and on the contrary, it absolutely stops in the furnace core. Bathing will occur. This has also been confirmed by experiments using tracers.

Therefore, although the bath is sufficiently stirred at locations with large radial positions, the flow is not substantially generated on the furnace core side, resulting in poor stirring, and the uniform mixing time, which is an indicator of the bath stirring intensity, is also insufficient. become longer.

In this way, only by providing a swirling flow of the molten metal bath around the furnace core using the blow nozzle, there is little relative movement of the bath within the furnace. As a result, overall, the stirring force is weak and the uniform mixing is insufficient, making it impossible to effectively improve the scrap dissolution rate and metallurgical reaction.

In view of these problems in electric arc furnaces, the present invention aims to accelerate the dissolution of solid charges and improve metallurgical reactions by arranging gas injection nozzles that uniformly and greatly agitate the bath in the furnace. It was developed for the purpose of improving temperature, uniformity of components, etc.

[Means for solving the problem] In order to achieve the object, the molten metal bath stirring method of the present invention has a radius of 0.3 to 0.8 R around the furnace core, where R is the inner radius of the furnace body. The total amount of gas for stirring or for powder transport and stirring that is blown into the furnace of the electric furnace from at least one rotating nozzle installed near the side wall of the hearth where gas can be blown so as to be tangential to the imaginary circle of The ratio Q ₁ /Q ₂ of the flow rate Q ₂ and the total flow rate Q ₁ of the stirring gas or the powder conveying and stirring gas blown from at least one central bottom blowing nozzle provided near the center of the hearth is set to 0.7 to In addition, the molten metal bath stirring device used for this purpose is a virtual circle with a radius of 0.3 to 0.8R centered on the furnace core, where R is the inner radius of the electric arc furnace. The present invention is characterized in that at least one rotating nozzle capable of blowing gas so as to be tangential to the hearth is provided near the side wall of the hearth, and at least one center bottom blowing nozzle for blowing gas is provided near the center of the hearth.

〔Example〕

Hereinafter, the present invention will be specifically described based on embodiments shown in the drawings.

1 and 2 are a longitudinal sectional view and a horizontal sectional view of an electric furnace in a first embodiment of the present invention.

Three electrodes 2 are provided at the center of the furnace body 1 of the electric furnace, and scraps and the like are melted by energizing these electrodes 2. A rotating nozzle 4 is provided on the side wall of the hearth 3 below the sill level of the furnace body 1 . Further, near the center of the furnace body of the hearth 3, a center bottom blowing nozzle 5 (hereinafter referred to as a center nozzle) is provided. In addition, on the left and right sides of the furnace body 1, a working hole 6 for charging the solid charge and a tapping hole 7 for discharging the molten steel after melting are provided, and a water cooling panel 8 for cooling is formed around the furnace body. There is. The swirl nozzle 4 and the center nozzle 5 are structured to blow gas into the molten metal bath within the furnace body 1, and communicate with an external oxidizing gas or inert gas supply source (not shown).
The center nozzle 5 is located approximately at the center of the furnace body 1 and is installed such that its gas blowing streamline is coaxial and vertical to the furnace axis.

On the other hand, the swirling nozzle 4 is a tangential nozzle whose direction is tangential to the streamline in order to swirl the molten metal bath in the furnace body 1 around the furnace core. That is, as is clear from FIG. 2, the axis of the rotating nozzle 4 passes through the furnace body 1, and is arranged so that this axis coincides with a tangent to a virtual circle inside the furnace. The vertical direction is inclined slightly downward toward the furnace core side, as shown in FIG. but,
Of course, the rotating nozzle 4 may be provided so as to be oriented in the horizontal direction without being restricted to this. Due to the arrangement and posture of the rotating nozzle 4, the blown gas can flow and stir the molten metal bath in a circular manner around the furnace core without being directed toward the furnace core.

Here, the behavior of the molten metal bath in which the central nozzle 5 does not exist and the molten metal bath is stirred in the furnace body 1 only by the rotating nozzle 4 is as shown in FIG. That is, when gas is blown from the rotating nozzle 4, the blowing pressure and gas flow are oriented in a tangential direction with a virtual circle around the furnace core, so the bath flows in a circle centered on the furnace core. As a result, the bath in the furnace flows in a counterclockwise swirling flow around the furnace core due to the propagation of the fluid force caused by the gas injection. If the amount of blown gas is increased, the swirling motion of the bath especially at the outer periphery of the furnace will increase, and the swirling flow will be faster toward the outer periphery.

However, the propagation of the fluid force to the furnace core is attenuated by the effects of the viscosity of the bath and the frictional resistance between it and the furnace bottom, and as a result, the bath does not flow in the furnace core and remains stagnant. The situation is as follows. Incidentally, such a phenomenon has been recognized through experiments using tracers, etc., and has already been described in the section of the prior art.

Therefore, stirring only by the swirl nozzle 4 that causes the bath to swirl around the furnace core does not promote mixing of the bath at the outer periphery and the center, and as a result, the mixing of the bath at the outer periphery and the center is not promoted. The stirring force is relatively small. Therefore, it is difficult to promote the melting of the scrap located at the bottom of the furnace core, and it is also insufficient to improve the metallurgical reaction and to uniformize the bath components and temperature.

On the other hand, if gas is blown simultaneously from the center nozzle 5 in addition to the swirling nozzle 4, stirring of the bath is favorably promoted. This will be explained with reference to FIG.

It was already mentioned in FIG. 3 that the gas flow from the swirling nozzle 4 promotes a flow in the bath around the furnace core. When gas is blown upward from the furnace core into this swirling flow, a swirling flow and an upward flow are generated. At this time, the bath receives these two flows, producing a downward flow shown by a dotted line in FIG. 4a and a plane or upward flow shown by a solid line. It goes without saying that these rising or descending flows are caused by the upward gas injection from the central nozzle 5, and as a result, the swirling flow around the furnace core does not stop and the vertical agitation is also good. . Furthermore, the combined flow of rising and falling allows mixing between the furnace core side and the furnace wall side.

From the above, by blowing gas upward from the central nozzle 5, the flow of the bath in the vertical direction around the furnace core is promoted, and mixing and stirring between the furnace core side and the furnace wall side is also sufficiently achieved. It will be done. Therefore, by using the swirling nozzle 4, which generates a swirling flow, and the central nozzle 5, which fluidizes the bath upward from the furnace core,
The result is that the bath can be uniformly stirred with a large stirring capacity. It is clear that if a plurality of rotating nozzles 4 are provided as shown in FIG. 4a, the stirring ability can be further improved.

In this way, the swirling nozzle 4 causes a swirling flow in the bath, and the center nozzle 5 causes an upward flow from the furnace core.
It has been found that uniform stirring of the bath can be carried out efficiently by using both. In order to achieve more effective agitation, the inventors were able to find the optimal amount of gas blown from both nozzles 4 and 5 and the orientation of the rotating nozzle 4.

The diagram shown in FIG. 5 shows the ratio Q 1 /Q 2 of the amount of blown gas Q ₁ from the central nozzle 5 to the amount Q ₂ of blown gas from the rotating nozzle 4 horizontally, and the ratio Q ₁ /Q ₂ of the blown gas The height H of the rise of the bath surface and the uniform mixing time τ required for uniform stirring.

From this diagram, the uniform mixing time τ, which is also an index of stirring intensity, tends to decrease as Q ₁ /Q ₂ increases. That is, when the amount of gas blown from the rotating nozzle 4 is constant, if the amount of gas blown from the center nozzle 5 is increased, the uniform mixing time τ becomes shorter, and the presence of the center nozzle 5 has the function of improving stirring. It is clear that the

Furthermore, the height H of the bath surface rises as Q ₁ /Q ₂ increases. Therefore, if the flow rate from the central nozzle 5 is too high or the flow rate from the rotating nozzle 4 is too low, ripples or the like will occur on the bath surface. However, fluctuations in the bath surface cause the arc to become unstable due to changes in the distance from the electrode 2, which limits the melting power. For this reason, it is necessary to set a certain upper limit for the height H of the rise of the bath surface.

According to the inventors' experience, if the uniform mixing time is 25 seconds or more, the stirring power for melting will be weakened, and the cost of gas injected into the molten steel will be opposite to the cost benefit obtained, so the uniform mixing time will be 25 seconds or less. It was necessary to do so.

On the other hand, when the height of the rise in the bath surface exceeded 100 mm, the arc became extremely unstable, causing problems in operation.

Based on the above two conditions of shortening the uniform mixing time τ and limiting the height H of the rise of the bath surface,
From the diagram in FIG. 5, it is found that Q ₁ /Q ₂ is optimally in the range of 0.7 to 3.5.

Furthermore, FIG. 6 is a plan view showing the optimum posture of the rotating nozzle 4, and FIG. 7 is a diagram for determining the optimum posture of the rotating nozzle 4.

In FIG. 6, the mounting position of the rotating nozzle 4 is determined based on the radius of a circle centered on the furnace core and tangent to the streamline of the injected gas, and FIG. It shows the relationship between the melting rate of the furnace wall (shown by the solid line) and the surface velocity of the bath in the area with a large radius on the furnace wall side (shown by the dotted line).

That is, according to the diagram in FIG. 7, the furnace radius R
If the orientation of the rotating nozzle 4 is such that it is tangent to a circle larger than 0.8R, the rate of erosion of the furnace wall will rapidly increase. Needless to say, this is the result of vigorous fluidized stirring by the gas blown from the swirling nozzle 4 on the furnace wall side.

On the other hand, if the orientation of the rotating nozzle 4 is such that the streamline of the blown gas is tangent to a circle smaller than 0.3R, the flow velocity on the bath surface on the furnace wall side becomes considerably small.
This results in a reduction in the stirring effect of the swirling nozzle 4 on the bath on the furnace wall side, which is inappropriate for achieving the original purpose.

Therefore, the attitude of the rotating nozzle 4 is such that the radius of the virtual circle centered on the furnace core, to which the streamline of the blown gas is tangent, is 0.3R to 0.8R, as shown in FIG.
It is preferable to make it fall within the range of .

As mentioned above, the center nozzle 5 and the rotating nozzle 4
By giving conditions to the flow rate ratio Q ₁ /Q ₂ of the blown gas and the attitude of the rotating nozzle 4, an optimal stirring effect can be obtained. As a result, improved dissolution ability,
Excellent metallurgical effects can be achieved, and uniformity of components and temperature can be achieved even more effectively.

In addition, the gas flow rate ratio Q ₁ /Q ₂ and the rotating nozzle 4
When adopting the condition of the attitude shown in FIG.
It has also been confirmed that the above-mentioned effects can be achieved even when five pieces are arranged.

8 and 9 show a second embodiment of the present invention. In these figures, components corresponding to those in FIGS. 1 and 2 are indicated by the same reference numerals, and their explanations are omitted. However, this example differs from the first example in that three rotating nozzles 4-1, 4-2, and 4-3 are provided.

On the furnace wall of the hearth 3 below the sill level of the furnace body 1,
Three rotating nozzles 4-1, 4-2, 4-3 are arranged at equal circumferential pitch. Further, a central nozzle 5 is provided near the hearth of the hearth 3. In addition,
FIG. 8 also shows a gas supply system.
That is, a rotating nozzle is connected to the gas supply pipe 10 of the supply device 9 for supplying oxidizing or inert gases such as CO ₂ , CO, Ar, N ₂ , O ₂ and air, or powders such as CaO using these gases as carrier gases. 4-1, 4-2, 4
-3 are connected to the pipes 11-1, 11-2, 11-3, and the center nozzle 5 is also connected to the pipe 12. And these piping 11-1,
11-2, 11-3 and 12 have control valves 13-1, 13- for adjusting the flow rate of gas, respectively.
2, 13-3, and 13-4 are provided.

The plurality of rotating nozzles 4-1, 4-2, 4-3 are
The optimal posture clarified from Figures 6 and 7 above, that is, the streamline of the blown gas is such that when the radius inside the furnace is R, the radius around the furnace core is
Install it so that it is included in the area of 0.3R to 0.8R.
In addition, these three rotating nozzles 4-1, 4-
The gas amount is set so that the ratio of the total gas amount Q ₂ blown in from 2 and 4-3 and the gas amount Q ₁ from the center nozzle 5 also satisfies the optimum conditions obtained from the diagram in Figure 5. .

In this way, if the operation is performed with the necessary conditions for stirring the bath, the molten metal bath in the furnace can be uniformly stirred with high stirring intensity, as in the case of the first embodiment.
In addition to improving the dissolving ability, it is possible to make the ingredients and temperature uniform.

10 and 11 show a third embodiment of the present invention. This is the same as the three rotating nozzles 4-1 and 4 shown in the second embodiment of FIGS. 8 and 9.
-2 and 4-3, the postures of these rotating nozzles 4-1, 4-2, and 4-3 are tilted upward. That is, as in the case of the above embodiment, each rotating nozzle 4 is located in an inclined area with a radius of 0.3 to 0.8R around the furnace core, where R is the radius inside the furnace.
The arrangement is such that the gas injection streamlines from -1, 4-2, and 4-3 reach each other, and the gas is supplied so that the gas streamlines are directed upward.

In this way, each rotating nozzle 4-1, 4-2, 4
When the gas from -3 is blown obliquely upward, the cooperative effect with the gas blown upward from the central nozzle 5 is improved, so that the molten metal bath can be uniformly stirred with a high stirring intensity.

FIG. 12 shows the detailed structure of the outer peripheral nozzle or the center nozzle.

The structure shown in Figure a has a structure in which a large number of small diameter pipes 31 are installed inside a fireproof nozzle 30, a wind box section 32 is provided at the bottom of the fireproof nozzle 30, and each of the small diameter pipes 31 is connected to a blow pipe 33. be.
This is known as a "small diameter porous nozzle," and the blowing gases are CO ₂ , CO , N ₂ ,
Ar, O ₂ and a mixed gas or powder thereof and their carrier gas are used. In this small-diameter porous nozzle structure, the small-diameter pipe 31 has a diameter of 1 to 4 mm.
This makes it possible to suppress the backflow of molten steel. Therefore, the flow rate can be changed from a region where the gas flow rate is significantly reduced to a large flow rate. Therefore, the present invention is particularly suitable when controlling the ripples over a wide range by handling a wide variable range of gas amount.

FIG. 12b shows a double tube nozzle structure, in which O ₂ or O ₂ is mainly discharged from the internal flow path 34 of the inner tube 35.
Powder such as CaO is supplied as a carrier gas,
To prevent oxidative combustion due to O ₂ , a coolant such as hydrocarbon gas or oil is blown into the annular flow path 37 between the outer tube 36 and the inner tube 35 . This coolant protects the entire nozzle and also functions as a combustion burner.

In this double pipe structure, the internal flow path 34
Since the diameter of the cylinder is usually 6 to 30 mm, it is suitable for cases where you want to increase the maximum amount of gas blown into the cylinder.
In addition, O ₂ is mainly supplied from the internal flow path 34,
Since hydrocarbons are blown into the annular flow path 37, when the scrap is not immersed in molten steel, it functions as a burner and can preheat the scrap as described above. Furthermore, O ₂ can burn the carbon in the steel and heat the molten steel, so it can be expected to further improve the dissolution rate, which is the objective of the present invention.

Furthermore, FIG. 12c shows a case where a porous plug 38 is used as the nozzle. This structure is suitable for simple operation by reducing the flow rate of the blown gas.

〔Effect of the invention〕

As explained above, in the present invention, stirring gas is blown from the center nozzle located approximately in the center of the hearth of the electric furnace, and at the same time, the stirring gas is Gas is blown in the tangential direction of a virtual circle of 0.8R through a swirling nozzle installed on the side wall of the furnace, and the gas flow rate ratio of each of the center nozzle and swirling nozzle is 0.7.
I try to have a relationship of ~3.5. like this,
The molten metal bath can be uniformly mixed and stirred with high stirring intensity, and the height of the rise of the bath surface can be limited by the gas blowing form and the combination of the upward flow from the center nozzle and the swirling flow from the swirling nozzle. I can do it. Therefore, a large stirring capacity can be provided to the molten metal bath, and as a result, the dissolution of the solid charge can be promoted and the refining reaction can be performed efficiently, and the temperature and components of the molten metal bath can be further made uniform. You can also do it. Furthermore, since the height of the rise of the bath surface can be limited, fluctuations in the bath surface are reduced and the arc between the electrodes is stabilized, making stable operation possible.

[Brief explanation of drawings]

Figures 1 and 2 are longitudinal and horizontal cross-sectional views showing the first embodiment of the present invention, Figure 3 shows the behavior of the bath in the furnace when gas is blown only by the rotating nozzle, and Figure 4 shows the behavior of the bath in the furnace when gas is blown only by the rotating nozzle. Figure 5 is an explanatory diagram showing the behavior of the bath in the furnace when gas is blown from both the center nozzle and the center nozzle. Fig. 6 is a plan view showing the optimum attitude of the rotating nozzle, and Fig. 7 shows the relationship between the attitude of the rotating nozzle, the melting rate of the furnace wall, and the surface flow velocity of the bath on the furnace wall side. Diagrams shown, Figures 8 and 9
The figures are a longitudinal sectional view and a horizontal sectional view showing a second embodiment of the present invention, Figs. 10 and 11 are a longitudinal sectional view and a horizontal sectional view showing a third embodiment of the invention, and Fig. 12 is a nozzle structure. This is an example.

Claims (1)

[Scope of Claims] 1. At least one at least one of at least 100 parts provided near the side wall of the hearth into which gas is blown so as to be tangent to an imaginary circle with a radius of 0.3 to 0.8R centered on the hearth, where R is the inner radius of the furnace body. The total flow rate Q ₂ of stirring or powder transport/stirring gas blown into the furnace inside the electric furnace from one rotating nozzle and from at least one central bottom-blowing nozzle installed near the center of the hearth. Ratio to the total flow rate Q ₁ of gas for stirring or powder transport and stirring
A method for stirring a molten metal bath in an electric arc furnace, characterized by adjusting Q ₁ /Q ₂ in the range of 0.7 to 3.5. 2. At least one rotating nozzle capable of injecting gas is provided near the side wall of the hearth so that it is tangential to a virtual circle with a radius of 0.3 to 0.8R centered on the furnace core, where R is the inner radius of the electric furnace. A molten metal stirring device for an electric arc furnace, characterized in that at least one central bottom blowing nozzle for blowing gas is provided near the center of the hearth.