JPS63121611A - Method and device for stirring molten metal bath for electric arc furnace - Google Patents

Abstract

PURPOSE:To suppress waving, turning and oscillating movements of the molten metal in a furnace and to thoroughly stir the molten metal by specifying the blowing rates of gases from central nozzles provided in the central part of the furnace bottom and precribed peripheral nozzles to prescribed flow rate ratios. CONSTITUTION:>=1 pieces of the peripheral nozzles 7 are provided to the furnace floor part 5 in a 0.2-0.8XR radius range (where R: inside radius of the shell 1a of a furnace body 1). >=1 pieces of the central nozzles 6 are provided to the central part of the furnace body 1. The ratio of the total flow rate Q1 of the gas for stirring or in common use for transporting the powder and for stirring to be blown from the central nozzles 6 and the total flow rate Q2 of the gas to be blown from the above-mentioned peripheral nozzles 7 is specified to 0.5-5 Q1/Q2.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention is a method of scrapping,
The present invention relates to a method and apparatus for efficiently stirring a molten metal bath in a 1-arc furnace when melting ore, metal materials, etc., and performing 1# refining.

[Conventional technology]

Conventionally, in the operation of an electric arc furnace, an auxiliary burner and oxygen for promoting melting are used from the furnace wall in the process of melting charged raw materials such as scrap.

In this case, the bottom of the electric arc furnace is in a so-called shallow path 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 within the molten metal bath, resulting in non-uniform temperature and composition.

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 poor reaction efficiency. As a result, there were drawbacks such as 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 total Fe in the slag.

If the stirring power is strengthened to avoid this drawback, in addition to solving the above problems, it will improve the decarburization rate and clean the steel by removing gases contained in the steel, and extremely great benefits are expected.

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 the opening, melting of the water cooling panel, and instability of the arc.

For this reason, it has been considered difficult in actual operation to avoid these dangers 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.

For example, stirring of molten steel by blowing gas through a nozzle installed in the hearth of an electric arc furnace was disclosed in Japanese Patent Laid-Open No. 50-9.
It is described in Publication No. 2807 and the like. Further, as a further development of this method, there are known methods such as attaching a nozzle to the bottom of the furnace in the cold zone of the steel bath, and blowing inert gas toward the hot zone.

[Problem that the invention seeks to solve]

Although it is possible to imagine that some effects could be achieved by injecting gas from the bottom of the furnace, the specific method and effects were unknown. In the current advanced type of electric arc furnace, most of the furnace wall is constructed with water-cooled panels, and in some cases, water-cooled panels are applied to about 300 m1 below the sill level.

In this type of electric arc furnace, when stirring gas is blown into the furnace bottom, the molten metal bath is stirred, but it has been found that the molten metal bath may hit the water-cooled panel due to the rocking phenomenon. Also, if you strengthen fsJl enough,
Molten metal bath and slag leak from the working opening, tap opening, etc. normally provided in the electric arc furnace. For this reason, the stirring strength is limited by the magnitude of the 18-movement of the molten metal bath, and there has been a problem that the expected sufficient effect cannot be achieved.

It was also found that when the amount of gas swells up in the molten metal bath directly above the nozzle by gas injection, the range of its fluctuation becomes larger. For this reason, when the nozzle is installed close to the electrode, the bath surface fluctuates greatly and a stable arc cannot be obtained. As a result, they are forced to operate under unstable arc conditions.

Furthermore, in the conventional example, the arrangement of the nozzle for blowing at↑ gas is very roughly defined, such as a cold zone or a hot zone, which are centered on receiving heat from the electrode, or two or less for a steel bath. was. However, the influence on stirring of the molten metal bath varies greatly depending on the position where the nozzle is installed. However, no nozzle arrangement for effecting such effective stirring has so far been proposed.

In view of these problems in electric arc furnaces, the present invention eliminates the risk of molten metal leaking out of the furnace, prevents melting of water-cooled panels, stabilizes the arc, and provides a large stirring capacity to the molten metal bath. It was developed for the purpose of promoting the dissolution of solid charges, refining reactions, and equalizing the temperature and components of the molten metal bath.

[Means for solving problems]

In order to achieve the purpose of the molten metal bath stirring method of the present invention, the inner radius of the iron shell of the furnace body is 0.2 to 0.8
A condensed flow lcg of stirring or powder transport/stirring gas is blown into the furnace of the electric arc furnace from at least one outer peripheral nozzle provided in the hearth in the range of ×R, and A small amount of gas (condensed flow N Q+ for stirring or powder conveying and stirring gas blown from one central nozzle)
Ratio Q.

/Q2 is adjusted in the range of 0.2 to 5.

In addition, the molten metal bath stirring device used for this purpose has at least one outer periphery for gas injection in the hearth part in the range of 0.2 to 0.8 x R, where R is the inner radius of the shell of the furnace body. [Embodiment] Hereinafter, with reference to the drawings, the features of the present invention will be explained by way of embodiments, with reference to the drawings. I will explain in detail.

FIG. 1 is a longitudinal sectional view of an electric arc furnace according to a first embodiment of the present invention, and FIG. 2 is a horizontal sectional view taken along the line I-1 in FIG. 1.

A water cooling panel 3 is attached to a furnace wall 2 of a furnace body 1 of an electric arc furnace equipped with an iron shell 1a. Further, three electrodes 4 are provided in the center of the furnace body 1, and these electrodes 4
By applying electricity to the electric arc furnace, raw materials such as scraps put into the electric arc furnace are melted. Further, a center nozzle 6 is provided near the center of the hearth 5 below the sill level of the hearth 1, and at least one outer peripheral nozzle 7 is provided at the outer periphery of the hearth 5. In this case, the vicinity of the center means the range within the pinch circle passing through the centers of the three electrodes 4.

3 and 4 are a longitudinal sectional view and a horizontal sectional view, respectively, of an electric arc furnace in a second embodiment of the present invention. In these figures, parts corresponding to those in FIGS. 1 and 2 are designated by the same reference numerals, and their explanations are omitted. however,
This example differs from the first example in that three outer peripheral nozzles 7, to 73 are provided.

Center nozzle 6 and outer peripheral nozzles 7I-7. A stirring gas is supplied to each of the pipes 8a to 8d through the respective pipes 8a to 8d. Control valves 9.1 to 9I are installed in the middle of these pipings 8+i to 8d.
I is provided with a center nozzle 6 and an outer periphery 71 nozzle 7.
゜～7. The flow rate of the stirring gas blown into the furnace is adjusted. In addition, these pipes 88 to 8d pass through the gas supply pipe 1O and supply COz+ CO+ Ar+ N2+ 0
2 + Gas supply source 1 of inert gas such as air or oxidizing gas
Connected to 1.

Now, for example, without operating the center nozzle 6, the outer nozzle 7
1-7. When the molten metal bath is stirred with
It behaves as shown in the figure. That is, assuming that the surface of the stationary bath is 8, at the initial stage of gas blowing, the outer peripheral nozzles 71 to 7
3 (however, the outer circumferential nozzle 7□ is not shown), the bath surface directly above it rises as shown in ial in the same figure. Furthermore,
Each of these raised portions B begins to rotate as shown at tb+ and tel in the figure.

After about 10 to 20 seconds have passed in this swirling state, the swirling motion of the raised portion B caused by the blown gas repeatedly interferes and moves, and the molten metal bath violently shakes outward as shown in +d+ in the same figure. move. In the next step, the molten metal that has flowed outward in this way repeats the movement of bouncing back toward the center of the furnace body, as shown in the figure (01).

At this time, as the number of gas injection stars from the outer circumferential nozzles 7 to 73 is increased, the molten metal bath undergoes extremely violent rocking motion, and as shown in fd+ in the same figure, the molten metal bath is The molten metal comes into contact with the water cooling panel 3. As a result, a large thermal shock and mechanical force are applied to the water-cooled panel 3, leading to a situation where an explosion may occur due to melting of the water-cooled panel 3 or water leakage from the water-cooling mechanism. Or the sixth
As shown in the figure, the working opening 14. Molten steel or slag leaks from openings such as the tapping port 13 and scatters to workers outside the furnace, resulting in an extremely dangerous situation.

For this reason, when using the conventional method, (8) the gas meter that is blown into the furnace for stirring the molten metal bath should be as narrow as possible to less than 0.1 Nrrr/hour/ton per ton of steel bath. If this happens, the original effects such as improving the dissolution rate and promoting metallurgical reactions will not be exhibited.

In addition, the diameter Dp (see FIG. 7) of the raised portion B of the molten metal bath changes depending on the depth II of the molten metal bath, as shown in FIG. For this reason, from the center of the electrode 4 to the outer circumferential nozzle 7, to 7. It is necessary to set the distance l to at least 0072 or more. As a result, the distance g between the tip of the electrode 4 and the surface of the molten metal bath is not affected by the raised portion B, so that a stable arc condition can be obtained.

Also, the diameter D0 of the raised portion shown by the dotted line in FIG.
The value of 9 was determined using the apparatus shown in Figs.
0 tons? 8 steel, three outer peripheral nozzles 71 to 7. The situation is shown when the flow rate IQz of the gas is 20 ONm/hour, and the gas flow rate IQz is 20 ONm/hour.

The solid line indicates that the total flow rate Q2 is the same as 20 ONm/hour, and the three outer peripheral nozzles 71 to 7. From 5ONn? With a flow rate of /hour x 3 and a flow rate of 5ONr//hour from the center nozzle 6,
90) shows the diameter of the raised portion when gas is blown into molten steel.

As is clear from this diagram, by blowing gas from the center nozzle 6, the diameter D0 of the raised portion B can be reduced to 1.0
m to 0.6 m. Incidentally, the two-dot chain line in the same figure indicates the diameter D0 of the single raised portion without taking into account the rocking shown in FIG. 7.

By the way, when gas is blown from the center nozzle 6, not only the diameter of the raised part of the molten metal bath decreases, but also
As a result, the fluctuation of the bath is also significantly suppressed. This thing,
This will be explained by referring to the relationship between the uniform mixing time and the height of ripples on the furnace wall with respect to the different blowing conditions shown in FIG.

In FIG. 9(al), the broken line in (a) indicates the outer peripheral nozzle 7,
~7. The solid line in (b) shows the ripples iW on each furnace wall when gas is blown in from the center nozzle 6 and the center nozzle 6 is not provided.
Show that. As is clear from this diagram, if the center nozzle 6 is provided and the amount of gas blown from the center nozzle 6 is increased compared to the case without the center nozzle 6, the ripple height llr will be significantly reduced. I understand that.

For example, for a steel bath of 90 tons, if the bottom-blown total gas star is 20 ON m / tl r CO If %/hour is injected,
The corrugation height llr, the value given by the broken line (A), is 0.4 m, which is shown at point A at the position of 2.2 on the horizontal axis. On the other hand, the total gas star blown from the outer nozzle 7 is 50
N rd / hour (b) Ripple height ll
r is 0.22 m shown at point B.

Also, if we take the time required to uniformly stir the entire bath by blowing gas, that is, the uniform mixing time τ, on the vertical axis,
If there is no center nozzle 6, the point will be point C on the dotted line (c), and if gas is blown by the center nozzle 6, it will be a point on the solid line (d).

From this diagram, when gas is blown at the flow rate under the above conditions, if only three outer peripheral nozzles 7 are used, the zero point value of 48 minutes is required for uniform stirring. On the other hand, due to the effect of gas injection from the central nozzle 6, uniform stirring was possible at the D point value of 25 minutes, and the time required for uniform stirring was significantly shortened.

As shown in FIG. 8, the swing diameter Dp also becomes smaller due to gas injection from the central nozzle 6, and the distance l from the electrode 4 also becomes l = 'A ((0,4~0.6) xll
By keeping the distance beyond the range of 1, it was possible to avoid the instability of the arc mentioned above.

By the way, as for the flow rate conditions in the diagram shown in FIG. 9 (al), the ratio of the gas amount Q1 of the center nozzle to the gas amount Q2 of the outer nozzle is Q, / Q, 50/150 =
It is 1/3. On the other hand, by changing this ratio,
Figure 9 (bl) explains how the behavior of the bath changes.
+ / Q The value of z is taken, and the height of the corrugated nail on the furnace wall vertically 11r and the uniform mixing time τ are taken, and Q +
/ Q Based on t=0.1 [where V is the solid line is the waving height I
lr and the dashed line represent the uniform mixing time τ.

From this diagram, it can be seen that as the amount of gas from the central nozzle 6 is reduced, the effect of the central nozzle 6 fades when Q + / Q z is around 0.2, and only the three outer nozzles 7 A similar phenomenon will occur. In other words, both the corrugation height Hr and the uniform stirring time τ increase, resulting in an unfavorable behavior of the bath.

On the other hand, when h is increased to Q+/, the gas injection star from the central nozzle 6 becomes excessive and the swell of the bath increases. Then, it begins to exhibit a movement similar to one of the rotational movements of the raised portion B shown in FIG.

From this, it is recognized that there is an optimal range for Q + /Q z. Therefore, the present inventors
Based on experimental results, this range has a Q + /Q zO value of 0.
It was discovered that good results were obtained when the ratio was 2 to 5, and the present invention was completed based on this finding. In addition, in this range of values, especially from 0.25 to fbl in Fig. 9,
It can also be seen that 3.0 is optimal.

Note that the effect obtained when the value of Ql/Q2 is set to 0.2 to 5 is obtained when the number of outer circumferential nozzles 7 is set to 1 to 1.
This is common even in cases where there are 0 or more pieces.

Moreover, the same effect is exhibited even when the central nozzle 6 is distributed into 1 to 5 pieces near the center of the furnace body 1.

Furthermore, as for the position of the outer peripheral nozzle 7, it is shown in FIG. 9 (
This will be explained using C1. The diagram shown in FIG. 9 [C] takes the ratio of the distance #r of the outer peripheral nozzle 7 from the center of the furnace body to the inner radius R of the furnace shell 1a, that is, r/R, on the horizontal axis, and Is the furnace wall refractory on the shaft? 8 loss velocity (solid line in the figure) and flow velocity of the bath at the outer periphery (dashed line in the figure).

As is clear from this diagram, when the outer peripheral nozzle 7 is arranged with the radius r from the center of the furnace body set to 0.8R or more, the distance from the furnace wall becomes significantly smaller. As a result, the flow of the bath If21't' increases near the wall due to gas injection from the outer peripheral nozzle 7, and as a result, the flow velocity of the bath increases as shown by the dotted line, and the melting of the furnace wall refractories occurs as shown by the solid line. The member becomes extremely large. In addition, in a normal case, the tower shape of an electric arc furnace is shallower at the outer periphery than at the center, so phenomena tend to occur in the atrium, resulting in insufficient stirring effects.

On the other hand, if the outer circumferential nozzle 7 is placed closer to the center and within the region of 0.2R or less, the melting on the outer circumference remains and the flow velocity of the bath in the area where scrap exists becomes slow as shown by the dotted line. It tends to saturate. This results in insufficient agitation of the bath at the outer periphery, resulting in the loss of scrap. 8. The effect of increasing the solution speed is diminished.

From the above, the optimal arrangement radius r of the outer peripheral nozzle 7 from the furnace core is 0.2 to 0.812 with respect to the inner radius R of the shell 1a.
It turns out that the range of is preferable. Furthermore, according to the diagram in FIG. 9 (C1), a value range of 0.2 to 0.7R is particularly effective.

Furthermore, FIGS. 10 and 11 show a third embodiment.

In this example, there are four outer peripheral nozzles 71 to 74, and the nozzles are arranged away from the tapping port and the working port. This arrangement is a practical example that is adopted when it is desired to suppress leakage of molten steel and slag from one working port of the steel tap as much as possible. In this example as well, it is theoretically possible to adopt the above conditions for setting the arrangement position of the outer peripheral nozzle 7 and the flow rate ratio with respect to the center nozzle 6.

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

The one shown in +a+ in the same figure has a structure in which a large number of small-diameter pipes 31 are installed inside a fireproof nozzle 30, a wind box part 32 is provided at the bottom of the fireproof nozzle 30, and it is further connected to a blowing pipe 33 through this. be. This is known as a "small diameter porous nozzle", and the blowing gas is CO□, Co
, N, , ^r, O□, a mixed gas of these or a body and its transport gas are used.

In this small-diameter porous nozzle structure, the small-diameter vibrator 31 is made with a diameter of 61 mm or less, so it is possible to suppress the occurrence of backflow of 78 steel. For this reason, it is possible to vary the flow rate from a region where the gas meteors are greatly constricted to large meteors.

Therefore, the present invention is particularly suitable for controlling the ripples over a wide range by widening the variable range of the gas j1. Furthermore, since the minimum flow rate to prevent clogging when throttled is small and only one blowing pipe 33 is required for each nozzle, the installation OAf can be simplified.

Fig. 12 fbl has a double tube nozzle structure, and the inner tube 3
02 (or powder and its general supply 0□) is mainly supplied from the internal flow path 34 of 5, and in order to prevent oxidation combustion due to 0 A coolant such as hydrocarbon gas or oil is injected. and,
This coolant protects the nozzle tip O::i section. In addition, since hydrocarbon-based gas or liquid is usually used as the coolant, this nozzle
The structure is such that it can also function as a combustion burner.

In this double-pipe structure, the diameter of the internal flow path 34 is usually made large, 6 to 30 mm, so it is suitable when the maximum amount of gas to be blown is desired to be large. 3
Since 02 is mainly supplied from No. 4 and hydrocarbons are blown from the annular flow path 37, No. 156 which is not infiltrated with the molten steel functions as a burner as described above and serves as a preheating function for the scrap. Also, by burning the carbon in the steel by 0□? Since it is possible to heat No. 8 steel, it is expected that the improvement in melting rate, which is the objective of the present invention, will be greatly improved.

Furthermore, in Fig. 12 (cl), the nozzle is connected to the porous plug 38.
This shows the case where This structure is suitable for reducing the size of the blown gas meteor and operating it sparingly.

〔Effect of the invention〕

As explained above, in the present invention, stirring gas is injected from the central nozzle located approximately at the center of the bottom of the electric furnace, and at the same time, the stirring gas is
．． Gas is also blown from the outer peripheral nozzles located in the area of 2 to 0.8×R, and the ratio of the gas meteors blown from the center nozzle and the outer peripheral nozzle is set to a relationship of 0.2 to 5. By setting the gas injection mode and the meteor injection from the center and outer circumference of the furnace,
The ripples and swirling I3 motion of the molten metal that occur inside the furnace are effectively controlled, allowing safe operation without molten metal leaking out of the furnace. Furthermore, since a large 6"l stirring capacity is provided to the 7-capacity molten metal bath, it is possible to promote the dissolution of solid charges, to homogenize the refining reaction, and to uniformize the temperature and composition of the molten metal bath.

[Brief explanation of the drawing]

1 and 2 are a longitudinal sectional view and a plan view showing a first embodiment of the present invention, FIGS. 3 and 4 are a longitudinal sectional view and a plan view showing a second embodiment, and FIG. 5 is a nozzle. Figure 6 is an explanatory diagram showing the behavior of the molten metal bath due to gas injection. Figure 6 is a diagram showing leakage from the furnace caused by stirring of the molten metal bath. Figure 3 is a diagram showing the relationship between the depth of the bath and the diameter of the rise, and Figure 9 (al is the relationship between uniform mixing time and ripple height with respect to the gas blowing flow rate). , Figure 9 (bl is the relationship between the ratio of the blowing flow velocity from the inner circumferential nozzle and the outer circumferential nozzle, the uniform mixing time, and the corrugation height, and Figure 9 (C1 is the relationship between the arrangement of the outer circumferential nozzle and the melting of the furnace wall refractories) Diagrams showing the relationship between the application rate and the flow rate at the outer circumference of the bath, respectively, FIGS. 10 and 11 are a longitudinal sectional view and a plan view of the third embodiment,
FIG. 12 shows an example of a nozzle structure. Patent applicant Nippon Steel Corporation (1 idiot) Agent Masu Kodo (2 others) Figure 8 H bath depth (m) Figure 1 Figure 2 Figure 7: Peripheral nozzle Figure 3 Figure 4 Figure 5 Figures (a) (d) Figure 6 Figure 9 Gas injection flow rate (Nrn'/square tons) (C) Q+102 r/R Figure 10 Figure 11 Figure 12

Claims (1)

[Claims] 1. When R is the inner radius of the furnace body, 0.2 to 0.8×
The total flow rate Q_2 of the gas for stirring or for powder transport and stirring that is blown into the furnace of the electric arc furnace from at least one outer peripheral nozzle provided in the hearth part in the radius range of R, and the An electric arc furnace characterized in that the ratio Q_1/Q_2 of the total flow rate Q_1 of stirring gas or powder conveyance/stirring gas blown from at least one central nozzle provided therein is adjusted in the range of 0.2 to 5. Method for stirring a molten metal bath. 2. When R is the inner radius of the furnace body of the electric arc furnace, 0.2~
At least one outer peripheral nozzle for blowing gas is provided in the hearth part in the range of 0.8×R, and at least one central nozzle for blowing gas is provided near the center of the furnace body. Molten metal bath stirring device in electric arc furnace.