JP6311324B2 - Method of bottom blowing stirring for arc furnace for steel making and arc furnace for bottom blowing stirring steel making - Google Patents

Description

  The present invention relates to a method for stirring molten metal with a gas in a steelmaking arc furnace, and to a steelmaking arc furnace for realizing the method.

  As disclosed in Non-Patent Document 1, an arc furnace for steelmaking uses a three-phase alternating current to generate an arc directly between a raw material charged in the furnace and an electrode, and uses the high temperature. The raw material is melted by heating, and its characteristics are described in detail in Non-Patent Document 1.

  In the iron and alloy iron manufacturing process, scrap, ore, iron alloy, etc. are used as raw materials, and these materials are melted and refined, and an arc furnace is used as a method for producing steel and molten iron alloys. At times, the bulk specific gravity of the raw material is generally small and fills the inside of the furnace, but as the melting progresses, the whole raw material sinks and part of the raw material gradually melts and deposits on the furnace bottom. In addition, since the raw materials are generally dissolved in the atmosphere, a part of the raw materials is oxidized, or when using ore together, a molten oxide mixture called slag is formed after melting, and the slag has a specific gravity. Since it is smaller than steel, it floats above the molten metal.

  After the dissolution is completed, a reducing agent such as silicon or aluminum is added, and valuable elements such as chromium lost in the slag as oxides are recovered. Here, the valuable element or the valuable metal is an element which is used as an alloy element such as Cr but becomes slag as an oxide. By reducing these and incorporating them into the steel, there is no need to add them again, and the alloy cost can be reduced.

  FIG. 7 is a diagram for explaining a conventional three-phase arc furnace, FIG. 8 is a diagram for explaining so-called hot spots and cold spots, and FIG. 9 is a diagram for explaining the flow of Joule heat in a conventional three-phase arc furnace. FIG. 10 is a diagram for explaining the temperature distribution of a conventional three-phase arc furnace.

   In FIG. 7, 1 is a furnace body, 2 is an electrode, 3 is a gas inlet, and 4 is a gas bubble. The arcs repel each other due to electromagnetic action, and are inclined toward the outer periphery of the furnace on the line connecting the electrode and the center of the furnace. Also, through the phenomenon of blowing the ambient air taken in by the arc to the bath surface, the molten metal flows toward the outer periphery of the furnace along the line connecting the electrode and the center of the furnace, and Joule heat from the arc moves to the periphery of the furnace wall.

  FIG. 8 (a) shows the Joule heat generated by the arc 20 generated from the electrode 2 heating the molten metal or slag immediately below the electrode 2 when focusing on one electrode 2 of the steelmaking arc furnace shown in FIG. This shows that the high-temperature molten metal or slag flow 19 generated by the flow causes the molten metal or slag to flow toward the furnace wall 12. The furnace wall 12 with which the high-temperature molten metal or slag collides becomes high temperature and is called a hot spot 12-A. On the other hand, the furnace wall 12 that collides with a low-temperature molten metal or slag is called a cold spot 12-B because the temperature is low.

  As shown in FIG. 8B, a high-temperature molten metal or slag flow 19 generated when Joule heat generated by the arc 20 generated by the three electrodes 2 heats the molten metal or slag immediately below the electrode 2 is a furnace. A hot spot 12-A is generated to heat the wall 12, and a cold spot 12-B is generated due to the low temperature of the furnace wall 12 where the flow of a low-temperature molten metal or slag collides. .

  The reason why the hot spot 12 -A and the cold spot 12 -B are generated at the position represented by FIG. 8B is that the direction of the arc generated by the electrode 2 is directed toward the furnace wall 12.

  In FIG. 9, the arrows 21 to 23 indicate the direction of the arc generated by the electrode 2 (when viewed from above), and 24 to 26 indicate the direction in which the molten metal generated by gas injection from the injection port flows (viewed from above). Is shown). As shown in FIG. 9, the direction of the high-temperature molten metal or slag flow 19 coincides with the arc direction 21 to 23, but the molten metal flow direction 24 to 24 generated by gas blowing from the blowing port. 26 is separate from the hot molten metal or slag stream 19.

  FIG. 10 is a diagram illustrating an image of a temperature distribution of a steelmaking arc furnace for performing a conventional method. In FIG. 10, the white portion indicates that the temperature is low, and the black portion indicates that the temperature is slightly higher than the surroundings.

  Now, in the arc furnace for steelmaking, if the power supply is increased to promote melting of the cold spot, the hot spot side becomes hot and damages the refractory, so at the expense of productivity, At the end of the period, an operation that suppresses power supply is performed, and in order to promote melting, a method is used in which gas is blown from the furnace bottom blowing port and gas stirring is performed.

  In Patent Document 1, a gas blowing nozzle is installed in a hearth below a slag line at a cold spot location of a steelmaking arc furnace, and oxidizing gas, reducing gas, and inert gas are passed through the nozzle to iron scrap. There is disclosed a rapid melting method in an arc furnace that is selected according to each operation stage from charging to discharging steel and sprayed on iron scrap and then blown into molten steel.

  However, in the method in which gas is simply blown into the electric furnace as disclosed in Patent Document 1, it is difficult to sufficiently flow the high-temperature molten metal into the cold spot, and it is difficult to improve the temperature of the cold spot. is there.

  Patent Document 2 discloses a method of operating an electric furnace that uses both melting and refining by electric arc heat. A gas is blown into a furnace from a nozzle provided on a hearth portion of the electric furnace, and the gas is used during melting. In order to promote melting of the charge in the furnace and to promote the chemical reaction of the steel bath during the refining period, three or less nozzles provided with an inert gas in the furnace floor as the gas to be blown into the furnace During the melting period, an inert gas is blown toward the hot spot in the furnace, and after the charge is completely dissolved, the inert gas is blown in a direction that converges almost at the center of the steel bath surface. An electric furnace operating method is disclosed.

  However, in the method disclosed in Patent Document 2, stirring of the bottom of the furnace, which is most likely to lower the temperature, is not performed, and this part controls rate of melting, and the slag existing in the central part stays, so that the valuable metal of that part It is difficult to solve the problem that the recovery rate decreases.

JP-A 57-161021 JP-A-60-103109

“4.4 Electric Furnace Steel Making Method” Iron and Steel Production Method (Volume 1) Issued April 10, 1972, Japan Iron and Steel Institute

  An object of the present invention is to provide a bottom-blown stirring method in a steelmaking arc furnace that promotes melting of furnace interior inclusions without reducing the recovery rate of valuable metals, and a steelmaking arc furnace that realizes this.

  In order to promote the melting of the furnace interior material without reducing the recovery rate of valuable metals, it is effective to stir the molten metal and actively reduce the cold spots.

  Accordingly, as a result of earnest research and development, the inventors have introduced a gas injection port for effectively injecting gas from the gas injection port provided at the center of the furnace bottom and other than the center of the furnace bottom and stirring the molten metal in the furnace effectively. The present invention was completed by finding the electrode arrangement conditions. The gist of the present invention is as follows.

(1) A method of blowing gas from the furnace bottom during arc heating,
The arc electrode starts from the center of the furnace bottom at an angle interval of 120 ° clockwise with reference to a straight line connecting the center of the furnace bottom and any one of the electrodes (hereinafter referred to as “electrode reference straight line”). Located at the intersection of any one of the straight lines and the circumference of radius r ₀ centered on the center of the furnace bottom,
r ₀ is defined as df ₀ as the depth of the molten steel bath at the center of the furnace bottom
d _f0 / 2 ≦ r ₀ (Formula 1)
Satisfying the steps,
The gas inlet is the center of the furnace bottom, and
r _f is the inner radius of the bottom of the furnace,
d _f0 is the depth of the molten steel bath at the center of the furnace bottom,
θ is an angle defined clockwise with respect to the electrode reference straight line,
θ _cp is one of 60 °, 180 °, and 300 °,
r is the distance from the center of the furnace,
d _f is the molten steel bath depth of position for blowing gas,
When
θ _cp −10 ° ≦ θ ≦ θ _cp + 10 ° (Formula 2)
r ₀ + d _f / 2 ≦ r ≦ r _f −d _f / 2 (Formula 3)
A step of arranging at least one in an area represented by (hereinafter referred to as a “gas inlet area”);
A bottom blowing stirring method for an arc furnace for steel making, comprising:

(2) The depth of the molten slag generated during arc heating is 0.6 m or more .
(1) The bottom blowing stirring method of the arc furnace for steel making characterized by these.

(3) The bottom blowing of the arc furnace for steel making according to (1) or (2), comprising a step of setting a diameter of a gas blowing port installed at the center of the furnace bottom to 5 to 25 (mm) Stirring method.

(4) The bottom blowing stirring method for an arc furnace for steel making according to any one of (1) to (3), wherein the method includes a step of selecting a collecting capillary or a porous refractory as the gas blowing method .

(5) An arc furnace for steel making in which gas is blown from the bottom of the furnace during arc heating,
The arc electrode has any one of straight lines starting from the furnace bottom center at an angle interval of 120 ° clockwise with respect to the electrode reference straight line, and a circumference having a radius r ₀ around the furnace bottom center. located in the intersection, r ₀ is when the molten steel bath depth of the hearth around the d _f0,
d _f0 / 2 ≦ r ₀ (Formula 1)
Satisfied,
The gas inlet is the center of the furnace bottom, and
r _f is the inner radius of the bottom of the furnace,
d _f0 is the depth of the molten steel bath at the center of the furnace bottom,
θ is an angle defined clockwise with respect to the electrode reference straight line,
θ _cp is one of 60 °, 180 °, and 300 °,
r is the distance from the center of the furnace,
d _f is the molten steel bath depth of position for blowing gas,
When
θ _cp −10 ° ≦ θ ≦ θ _cp + 10 ° (Formula 2)
r ₀ + d _f / 2 ≦ r ≦ r _f −d _f / 2 (Formula 3)
Arranging at least one in the gas inlet area represented by
An arc furnace for bottom-blown stirring steelmaking.

(6) The depth of the molten slag generated during arc heating is 0.6 m or more .
An arc furnace for bottom-blown stirring steelmaking as described in (5).

(7) The bottom blow-stirring steelmaking arc furnace according to (5) or (6), wherein the diameter of the gas blowing port installed at the center of the furnace bottom is 5 to 25 (mm).

(8) The bottom blow-stirred steelmaking arc furnace according to any one of (5) to (7), wherein a collecting capillary or a porous refractory is used as a gas blowing method.

  According to the present invention, the portion that was a cold spot in the prior art becomes a hot spot or a high-temperature portion equivalent thereto, the melting of the furnace interior is promoted, the refining efficiency is remarkably improved, and the valuable metal There is a remarkable effect of improving the recovery rate.

It is a figure explaining the position of the gas inlet in the arc furnace for steel manufacture which enforces the method of this invention. Fig.1 (a) is a figure showing the position of the gas inlet in the arc furnace for steelmaking of this invention. FIG.1 (b) is sectional drawing of the arc furnace for steel manufacture of this invention. It is a figure explaining the position of the gas inlet in the arc furnace for steel manufacture which enforces the method of this invention. Fig.2 (a) is a figure showing the position of the gas inlet in the arc furnace for steelmaking of this invention. FIG.2 (b) is sectional drawing of the arc furnace for steel manufacture of this invention. It is a figure of the arc furnace for steelmaking of this invention. Fig.3 (a) is the figure which looked at the arc furnace for steel making which has a blowing inlet in the furnace bottom center from the top. FIG.3 (b) is the figure which looked at the arc furnace which has a blowing inlet in the furnace bottom center of Fig.3 (a) in a certain cross section. It is an image figure of the flow of Joule heat (simulation) and the inclination of an arc in the arc furnace for steel making which implements the method of the present invention. It is a simulation result of the temperature distribution of the arc furnace for steelmaking when using the arc furnace for steelmaking of the present invention. It is a figure explaining the relationship between the diameter of a blowing inlet, a temperature rising amount, and durable time in the case of installing a blowing inlet in the furnace bottom center of the arc furnace for steel making. FIG. 6A is a graph showing the relationship, where the horizontal axis is the inlet diameter (mm) and the vertical axis is the temperature rise (° C.) of the cold spot. FIG. 6B is a graph showing the relationship, where the horizontal axis is the diameter of the inlet (mm) and the vertical axis is the endurance time (is Hour). It is a figure explaining the conventional arc furnace for steelmaking. Fig.7 (a) is the figure which looked at the arc furnace for steel making which does not have a blowing inlet in the furnace bottom center from the top. FIG.7 (b) is the figure which looked at the cross section of the arc furnace which does not have a blowing inlet in the furnace bottom center of Fig.7 (a). It is a figure explaining a hot spot and a cold spot. Fig.8 (a) is the figure which looked at the conventional arc furnace for steelmaking from the side surface. FIG.8 (b) is the figure which looked at the conventional arc furnace for steelmaking of Fig.8 (a) from the top. It is a figure explaining the flow (simulation) of the Joule heat of the arc furnace for steel making which implements the conventional method, and the inclination of an arc. It is a figure which illustrates typically the simulation result of the temperature distribution of the arc furnace for steel manufacture which enforces the conventional method. It is a figure explaining the position of the gas blowing inlet in the arc furnace for steel manufacture which implements the comparative example 4. FIG. Fig.11 (a) is the figure which looked at the arc furnace for steel manufacture which does not have a blowing inlet in the furnace bottom center but has four blowing openings other than the furnace bottom center from the top. FIG.11 (b) is the figure which looked at the arc furnace which does not have a blowing inlet in the furnace bottom center of Fig.11 (a), and has four blowing openings other than the furnace bottom center in a certain cross section.

(First embodiment)
1st Embodiment is an arc furnace for bottom blow stirring steelmaking which can blow in gas from a furnace bottom part during arc heating.

[Device configuration]
The arc electrode has any one of straight lines starting from the furnace bottom center at an angle interval of 120 ° clockwise with respect to the electrode reference straight line, and a circumference having a radius r ₀ around the furnace bottom center. located in the intersection, r ₀ is when the molten steel bath depth of the hearth around the d _f0,
d _f0 / 2 ≦ r ₀ (Formula 1)
And r _f is the inner radius of the furnace bottom, d _f0 is the depth of the molten steel bath at the center of the furnace bottom, and θ is defined clockwise with respect to the electrode reference straight line. The angle, θ _cp is one of 60 °, 180 °, and 300 °, and r is the distance from the center of the furnace,
θ _cp −10 ° ≦ θ ≦ θ _cp + 10 ° (Formula 2)
r ₀ ≦ r <r _f (Formula 3)
It is an arc furnace for bottom blowing stirring steel making which arrange | positions at least one gas blowing inlet in the gas blowing inlet area | region represented by these.

Further, the gas blowing outlet region further when d _f is the molten steel bath depth of position for blowing gas, to,
r ₀ + d _f / 2 ≦ r ≦ r _f −d _f / 2 (Formula 4)
This is an arc furnace for bottom-blown stirring steelmaking, which is a region narrowed down by.
[Solving problems of gas stirring]
The method of supplying heat to the flow stagnation part by adding gas agitation can devise the arrangement and flow rate of the equipment, but the gas blowing part is easily damaged and is not a thing that can be installed indefinitely In addition, for example, the arc position and the molten metal surface may fluctuate due to gas blowing. In such a case, the arc becomes unstable, which may cause an obstacle to stable operation (hereinafter referred to as “gas stirring problem”). Therefore, it was not considered a good idea to add a gas inlet. In addition, providing the inlet at the bottom of the furnace has the highest pressure of the molten steel, and stress against the high pressure tends to concentrate on the inlet, so it is more easily damaged than other locations, It is necessary to increase the amount of blown air. Therefore, it has been considered that if there is a blowing port in the center of the furnace bottom, it is likely to be damaged. For this reason, it was outside the scope of the idea to install a facility such as a collecting tube at the center of the furnace bottom for the purpose of blowing the bottom.

  However, as a result of earnest research and development, the inventors have found that the above-described problem of gas agitation can be solved by appropriately selecting the position of the electrode and the position where the gas blowing port is installed.

  Hereinafter, a method for solving the problem of gas stirring will be described.

[Number of gas inlets]
Since the gas injection port is easily damaged, it has been considered that fewer gas injection ports are better for improving the stability of the equipment.

  However, due to the recent development of refractory technology, in addition to the existing three points, if another fourth inlet is added to the center of the furnace bottom, the damage caused by the fourth inlet will be It was confirmed by simulation and experiment that it did not affect the steelmaking arc furnace.

  Therefore, it was decided to increase the inlet at the center of the furnace bottom.

[Diameter of inlet at the center of the furnace bottom]
When installing the inlet in the center of the furnace bottom, we examined how much the cold spot was heated by the diameter of the inlet and how much the endurance time was reduced.

  FIG. 6 is a diagram showing the relationship between the diameter of the inlet, the temperature rise, and the durability time when the inlet is installed at the center of the furnace bottom.

  FIG. 6A is a graph showing the relationship, where the horizontal axis is the inlet diameter (mm) and the vertical axis is the temperature rise (° C.) of the cold spot. Since the effect of this invention will be show | played when a blowing port diameter (mm) is enlarged, the minimum value of a blowing port diameter is determined from Fig.6 (a).

  When the diameter of the blow-in port is 5 mm or more, the temperature rise amount of the cold spot is 150 ° C. or more, and the effect of the present invention is exhibited. Therefore, the minimum value of the blow-out port diameter is set to 5 mm. Desirably, the minimum value of the diameter of the air inlet is 8 mm at which the temperature rise of the cold spot is 250 ° C. or more.

  FIG. 6B is a graph showing the relationship, where the horizontal axis is the diameter of the inlet (mm) and the vertical axis is the endurance time (is Hour). If the diameter of the air inlet is increased, the durability time is reduced, so that the maximum value of the air inlet diameter is determined from FIG.

  Since the endurance time (Hour) cannot be less than 1750 hours, the maximum diameter of the air inlet (mm) is 25 mm. Desirably, since it is desired to maintain the endurance time (Hour) at about 2000 hours, the diameter of the air inlet (mm) is desirably 20 mm or less.

[Position of electrode]
When a gas inlet is added to the center of the furnace bottom, how far it is appropriate to move the electrode away from the center of the furnace is `` to the extent that the phenomenon that the arc position and the surface of the metal fluctuate due to gas injection does not affect the operation. "Is it?"

As a result, the inventors have found that the molten steel bath depth at the gas inlet at the center of the furnace bottom is an important factor. As shown in FIG. 2 (b), it refers to the distance from the gas injection port 11 installed in the furnace bottom center with the bath depth d _f0 of position for blowing gas to the surface of the molten metal 5.

That is, when the molten steel bath depth of gas injection ports in the furnace bottom center is d _f0 is to position the center of the three electrodes, and the center of furnace bottom center, a circle the radius r ₀ (hereinafter , Pitch circle). ) And radius r ₀ is
d _f0 / 2 ≦ r ₀ (Formula 1)
I found that it was enough.

[Position of other gas inlets]
Next, the center of the bottom of the furnace is formed at an interval of 120 ° in the clockwise direction with respect to an electrode reference straight line that is one of the inlets at the center of the furnace bottom and the electrode is a straight line connecting any one electrode with the center of the furnace bottom. Assuming that it is on any straight line starting from the center of the furnace bottom and on the circumference of the radius r ₀ centered on the center of the furnace bottom, “the phenomenon that the arc position and the molten metal surface fluctuate due to gas blowing does not affect the operation. From the viewpoint of “how much will it be?”, We examined the position where the other inlets are appropriate.

  If the electrode and the gas inlet are close, the gas hits the arc and affects the arc, so the position of the inlet should be far from the electrode, but the inlet is installed at the center of the steelmaking arc furnace. In this case, it was found that if the electrode was installed on the edge side of the steelmaking arc furnace, the raw material at the center could not be sufficiently melted.

Therefore, paying attention to the bottom surface of the bottom of the arc furnace for steelmaking as a circle, set the polar coordinates starting from the center of the furnace bottom, based on the electrode reference straight line connecting the center of the furnace bottom and any one of the electrodes, Under the condition that the electrodes are installed at an angle of every 120 ° in the clockwise direction, it was examined in which position the blowing port can be installed to solve the problem of gas stirring.
[First area]
The inventors have defined that the gas inlet is defined as the center of the furnace bottom, r _f is the inner radius of the furnace bottom, d _f0 is the depth of the molten steel bath at the center of the furnace, and θ is clockwise with respect to the electrode reference line. Θ _cp is a value of 60 °, 180 °, or 300 °, and r is the distance from the center of the furnace,
θ _cp −10 ° ≦ θ ≦ θ _cp + 10 ° (Formula 2)
r ₀ ≦ r <r _f (Formula 3)
By arranging at least one in the gas inlet region represented by the above, the effect of the present invention is achieved, that is, the portion that was a cold spot in the prior art becomes a hot spot or a high-temperature portion equivalent thereto, and enters the furnace interior. It has been found that the melting of the product is promoted, the refining efficiency is remarkably improved, and the recovery rate of valuable metals is improved.

  Hereinafter, the knowledge obtained as a result of the study will be described with reference to FIGS.

  Fig.1 (a) is a figure showing the position of the gas blowing inlet in the arc furnace for steelmaking of this invention, FIG.1 (b) is sectional drawing of the arc furnace for steelmaking of this invention.

  In FIG. 1A, 8 is a furnace bottom center gas inlet, 2 is an electrode, and two circles drawn with solid lines centering on the furnace bottom center gas inlet 8 are the walls of the steel furnace arc furnace. The straight lines represented by dotted lines 15-A, 15-B, and 15-C are electrode reference straight lines.

In FIG. 2B, 3 is a gas blowing port, 5 is a molten metal, 6 is a slag, 7 is a gas, and 11 is a region where the blown gas is diffused. The bath depth d _f of position for blowing gas refers to the distance from the gas injection port 3 to the surface of the molten metal 5.

  Therefore, in order to simplify the description, the description will be made with reference to the 15-A electrode reference straight line.

Three straight lines (hereinafter referred to as “blowing inlet reference straight lines”) 16− described at positions that form angles of 60 °, 180 °, and 300 ° counterclockwise with respect to the electrode reference curve 15-A. A circle drawn with a dotted line with a radius of r _{f and} a dotted line with a radius of r ₀ sandwiched between two solid lines that make an angle of ± 10 ° with respect to A, 16-B, and 16-C. The region sandwiched between the circles drawn in (5) is the gas inlet region (A) 9 described in (Equation 2) and (Equation 3).

  The arc furnace for bottom-blown stirring steelmaking of the present invention has at least one gas blowing port in the gas blowing region (a) 9 described in (Formula 2) and (Formula 3) in addition to the center gas blowing port 8 in the furnace bottom. It was found that the problem of gas agitation can be solved by equipped with.

  The same explanation can be made using the electrode reference straight lines 15-B and 15-C.

[Second area]
The inventors examined a region where the effect of the present invention is preferable.
Gas injection port area further when d _f is the molten steel bath depth of position for blowing gas, to,
r ₀ ≦ r <r _f (Formula 3)
Narrowed down within the range stipulated in
r ₀ + d _f / 2 ≦ r ≦ r _f −d _f / 2 (Formula 4)
When satisfied, it has been found that a more favorable effect is achieved.

  FIG. 2A is a view showing the position of the gas inlet in the steelmaking arc furnace of the present invention, and FIG. 2B is a cross-sectional view of the steelmaking arc furnace of the present invention.

  Hereinafter, the knowledge obtained as a result of the study will be described with reference to FIGS.

  In FIG. 2A, 8 is a furnace bottom center gas inlet, 2 is an electrode, and two circles drawn with solid lines centering on the furnace center gas inlet 8 are the walls of the arc furnace for steelmaking. The straight lines represented by dotted lines 15-A, 15-B, and 15-C are electrode reference straight lines.

In FIG. 2B, 3 is a gas blowing port, 5 is a molten metal, 6 is a slag, 7 is a gas, and 11 is a region where the blown gas is diffused. The bath depth d _f of position for blowing gas refers to the distance from the gas injection port 3 to the surface of the molten metal 5.

  Therefore, in order to simplify the description, the description will be made with reference to the 15-A electrode reference straight line.

Air inlet reference straight lines 16-A, 16-B, which are straight lines with three dotted lines described at positions of 60 °, 180 °, and 300 ° counterclockwise with respect to the electrode reference curve 15-A, It is sandwiched between two solid lines that form an angle of ± 10 ° with respect to 16-C, and is outside the circle with a radius of r ₀ + d _f / 2 and inside the circle with a radius of r _f -d _f / 2. The region is the gas inlet region (b) 10 described in (Expression 2) and (Expression 4).

  The arc furnace for bottom blow stirring steel making of the present invention has at least one gas blow inlet in the gas blow area (b) 10 described in (Formula 2) and (Formula 4) in addition to the furnace bottom center gas blow opening 8. It has been found that the problem of gas agitation can be solved and that a more preferable effect can be obtained.

  The same explanation can be made using the electrode reference straight lines 15-B and 15-C.

(Second Embodiment)
The second embodiment is a bottom blow stirring method for a steel making arc furnace using the bottom blow stirring steel making arc furnace according to the first embodiment.

[Step 1] This is a step of arranging an arc electrode.
The arc electrode has any one of straight lines starting from the furnace bottom center at an angle interval of 120 ° clockwise with respect to the electrode reference straight line, and a circumference having a radius r ₀ around the furnace bottom center. located in the intersection, r ₀ is when the molten steel bath depth of the hearth around the d _f0,
d _f0 / 2 ≦ r ₀ (Formula 1)
To satisfy.

[Step 2] This is a step of arranging a gas inlet.
The number of gas inlets is the center of the furnace bottom and the other three, d _f0 is the depth of the molten steel bath at the center of the furnace bottom, θ is an angle defined clockwise with respect to the electrode reference straight line, and θ _cp is 60 Any value of °, 180 °, or 300 °, where r is the distance from the center of the furnace,
θ _cp −10 ° ≦ θ ≦ θ _cp + 10 ° (Formula 2)
At least one is arranged in the gas inlet region represented by

Further, the gas inlet is the center of the furnace bottom, r _f is the inner radius of the furnace bottom, d _f0 is the depth of the molten steel bath at the center of the furnace bottom, and θ is an angle defined clockwise with respect to the electrode reference straight line. , Θ _cp is one of 60 °, 180 °, and 300 °, and r is the distance from the center of the furnace,
θ _cp −10 ° ≦ θ ≦ θ _cp + 10 ° (Formula 2)
r ₀ ≦ r <r _f (Formula 3)
At least one is arranged in the gas inlet region represented by

Further, the gas blowing port area, r _f is the inner radius of the bottom portion of the furnace, when d _f is the molten steel bath depth of position for blowing gas, to,
r ₀ + d _f / 2 ≦ r ≦ r _f −d _f / 2 (Formula 4)
It may be a further narrowed region that satisfies the requirements.

[Step 3] This is a step of determining the diameter of the gas inlet installed at the center of the furnace bottom.
The diameter of the gas inlet installed in the center of the furnace bottom is 5 to 25 (mm).

[Step 4] This is a step of determining a gas blowing method.

  As a gas blowing method, a collecting tubule or a porous refractory is used.

(simulation)
In order to confirm the effect of the present invention, analysis was performed using general-purpose thermal fluid analysis software FLUENT.

[Analysis conditions]
The analysis area is the molten steel and molten slag in the electric furnace, and used the Volume of Fluid model for analyzing the free surface and the dispersed phase model that solves the equation of motion and couples it with the flow using the bottom blowing gas bubbles as particles.

Molten steel properties: density 7200 kg / m ³ , molecular viscosity 0.006 Pa · s, slag physical properties density 3000 kg / m ³ , molecular viscosity 0.1 Pa · s, interfacial tension between molten steel and molten slag 1 N / m, bubbles Considering only thermal expansion, the density was 0.3 kg / m ³ , the diameter was 1 cm, and the flow rate was a normal temperature and normal pressure flow rate of 300 NL / min from each blowing location. The standard k-ε model was used as the turbulent model. Since the flow is dominated by arc force and gas agitation, thermal convection, which is the effect of heat, was ignored.

  The flow of molten metal by an arc can express observations of achievements described in non-patent literature (Nanjo, Yaskawa: “On the productivity improvement of arc furnaces for steelmaking again”, Industrial Heating, Vol. 10-11). An area for applying a body force was set just below the electrode so that the flow corresponding to the model could be reproduced, and the body force for realizing a flow of 1 m / s forming an angle of 30 degrees from the horizontal plane was determined.

The shape and electrode position of the electric furnace are as shown in FIG. 3 (invention example) or FIG. 7 (comparative example). As a representative dimension, the furnace radius (r _f ) at the molten slag upper end position is 2. 4m, bath depth (d _f0 ) at the center is 0.7m, bath depth (d _f ) at the inlet other than the center is 0.5m, depth of molten slag is 0.6m, radius of pitch circle (R ₀ ) was 1.2 m. Further, the position of the gas inlet at the bottom of the furnace other than the center was a position having a radius of 1.5 m from the center of the furnace bottom.

[Analysis result]

<Method of the present invention>
As shown in FIG. 3, the result of the simulation of the case where gas was injected at a total of four locations, including the center of the furnace bottom and three other locations, will be described with reference to FIGS.
FIG. 4 is a diagram for explaining an image of Joule heat flow (simulation) and arc inclination in a steelmaking arc furnace for carrying out the method of the present invention.
In FIG. 4, 21-23 are the directions of the arc (when viewed from above), and 24-26 are the directions (when viewed from above) where the molten metal flows by the blown gas.
FIG. 5 is a diagram for explaining the simulation result of the temperature distribution of the steelmaking arc furnace for carrying out the method of the present invention.
In FIG. 5, a black part represents a part having a high temperature, and a white part represents a part having a low temperature.
As shown in FIG. 4, it can be seen that stirring at the center of the electric furnace is strengthened by bottom blowing at the center. In other words, it can be confirmed that gas injection does not adversely affect the electrode.
Moreover, as shown in FIG. 5, the high temperature part is implement | achieved in the furnace bottom center part and other 3 site | parts which installed the gas blowing inlet.

<Conventional method>
As shown in FIG. 7, the results of the simulation for the case of performing gas injection only at the other three locations excluding the center of the furnace bottom will be described with reference to FIGS. 9 and 10.
FIG. 9 is a diagram for explaining an image of Joule heat flow (simulation) and arc inclination in a conventional steelmaking arc furnace.
In FIG. 9, 21-23 are the directions of the arc (when viewed from above), and 24-26 are the directions (when viewed from above) where the molten metal flows by the blown gas.
FIG. 10 is a simulation result of temperature distribution in a conventional steelmaking arc furnace.
In FIG. 10, a black part represents a part having a high temperature, and a white part represents a part having a low temperature.
As shown in FIG. 10, the central portion has a low temperature, and the area of the high temperature portion in FIG. 10 is smaller than the area of the high temperature portion in FIG.

<Conclusion>
By implementing the method of the present invention, it was confirmed by simulation that the portion having a higher temperature can be increased as compared with the case where the conventional method is implemented.
Such an effect exists in and around the center of the furnace bottom and is hatched in FIG. 1 (a) or FIG. 2 (a). The gas inlet region (A) 9 or the gas inlet region (B) It is considered that the stirring effect from the three gas blowing ports provided in 10 is an effect caused by effectively interfering with each other.
In addition, such an effect leads to an effect that the valuable metal contained in the slag in the region is efficiently reduced because the region having a relatively high temperature spreads.
Furthermore, according to the arrangement of the gas blowing ports, the stress which is concerned that it is concentrated particularly on the blowing port at the center of the furnace bottom is dispersed and sufficiently relaxed, and damage to the blowing ports is avoided.

  The purpose of Example 1 is to confirm the effect of the presence or absence of center bottom blowing.

[Outline of equipment]
In a 100 ton three-phase arc heating type electric furnace with a diameter of 4 m, a height of 3 m, and a molten steel depth of 0.7 m at the time of complete melting, equipment for melting ferritic stainless steel scrap, ferrochrome alloy iron, etc. was used.
The three inlets other than the center of the furnace bottom were provided at positions corresponding to each other by rotating 120 degrees around the center of the furnace bottom on a circle having a radius of 1.75 m centered on the center of the furnace bottom.
The bottom of the arc furnace has a shape that can be approximated as a part of a sphere having a radius of 6 m, and the circumference (pitch circle) in which the electrodes are arranged has a radius of 1.2 m.
The bottom-blown tuyere is a collection tube in which five stainless steel pipes having an inner diameter of 2 mm are collected and embedded in a refractory.

<Invention Example>
Inventive Example 1, as shown in FIG. 3, 300 liters / minute of argon gas was allowed to flow at three locations in the circumferential direction, and the same collection tube tuyere was also installed at the center of the furnace bottom. It is what flows.

<Comparative example>
In Comparative Example 2, as shown in FIG. 7, argon gas of 300 liters / minute is flowed at three locations in the circumferential direction.
The comparative example 3 is a thing without bottom blowing.

[Evaluation method]
The point at which scrap or the like was no longer observed at the top of the molten steel was defined as “melting off”, and the time from when there was no unmelted scrap or ferroalloy to the furnace bottom was measured while occasionally stopping energization.
In the measurement, the presence of undissolved scrap and iron alloy was confirmed by inserting a rod.
Further, after complete dissolution, reducing silicon was added, and the concentration of oxides of valuable metals in the slag after 5 minutes was investigated by analyzing the slag sample in the furnace.

Table 1 shows the retention time index until complete dissolution and the valuable metal reduction rate index in the slag, with the case of Invention Example 1 as the reference “1”.
In the case of Invention Example 1 with bottom blowing, a significant improvement effect was obtained with respect to Comparative Example 1 and Comparative Example 2 without bottom blowing.
According to Invention Example 1, the life of the refractory used in the furnace is longer than that in Comparative Examples 1 and 2.
In particular, the life of the refractory in the hot spot portion in Invention Example 1 was increased by 50% or more compared to the refractory in the hot spot portion in Comparative Example 1 or Comparative Example 2.
This is because, as shown in the simulation, the temperature of the center of the furnace is increased by the effect of gas blowing, and as a result, the temperature of the hot spot is higher than that of Comparative Example 1 or Comparative Example 2. It is understood that the cause is that the deterioration of the refractory in the hot spot portion was alleviated because of the decrease.

From the above, it can be seen that if there is no center bottom blowing, the valuable metal reduction rate index in the slag deteriorates greatly.
Therefore, on the basis of the slag valuable metal reduction rate index of Example 1 of the present invention, the slag valuable metal reduction index of 0.60 or more is evaluated as pass (o), and the others are evaluated as reject (x). .

The purpose of Example 2 is to evaluate the influence of the displacement of the inlet other than the center of the furnace bottom on the valuable metal reduction rate index in the slag.
The equipment used is the same as that used in Example 1.
The reference inlet was determined as the inlet that was rotated 120 degrees clockwise around the center of the furnace when viewed from the top of the furnace, and the position was changed for evaluation.

That is, θ _{cp is set} to 120 degrees, θ in (Equation 2) is changed, and evaluation is performed with a deviation from the reference position θ _cp (Δθ = | θ−θ _cp |).
Based on Invention Example 1, the slag valuable metal reduction rate index was evaluated for one of the inlets that were not located at the center of the furnace bottom.
In the evaluation, a slag valuable metal reduction index of 0.60 or more is regarded as acceptable (◯).
Table 2 shows the results.

  From Table 2, it can be seen that when Δθ exceeds 10 degrees, the reduction rate index of the valuable metal is significantly lowered.

The purpose of Example 3 is (Formula 3)
r ₀ + d _f / 2 ≦ r ≦ r _f −d _f / 2 (Formula 3)
Is satisfied, it is confirmed that the valuable metal reduction index in the slag is 0.60 or more and passes (O).

The equipment used is the same as that used in Example 1.
In the invention example in Example 1, r ₀ = 1.2 m, d _f0 = 0.7 m, and r _f = 2m.
Further, since the shape of the bottom surface of the furnace is a part of a sphere having a radius r _s = 6 m centered at 13 in FIG. 2 (b), _assuming that the circumferential radius r is aligned with the gas blowing ports, the depth of the molten steel at the blowing ports is is a _{d f,} in FIG. 2 (b) from the geometric _{relationship,} focusing on the 14 which is the difference between _{d f0} and _{d f,
d f0 -d f = r s -} (r s 2 -r 2) 1/2
Because of the relationship
_{d f = d f0 -r s +} (r s 2 -r 2) 1/2 ... ( Equation 4)
It shows.

  r = 1.4 m, 1.6 m, and 1.8 m, and three inlets (Invention Example 3, Invention Example 4) at positions rotated about 120 degrees around the center of the furnace bottom on the circumference of the radius r Table 3 shows the results obtained when Invention Example 5) was provided. However, in any case, there was a blowing port at the center of the furnace bottom, and the diameter of the blowing port was 8 mm.

Invention Example 1 and Invention Example 4 are represented by (Formula 4)
r ₀ + d _f / 2 ≦ r ≦ r _f −d _f / 2 (Formula 4)
The valuable metal reduction index in slag is 0.90 or more, which is a very good pass (◎) in the valuable metal reduction index in slag.

Invention Example 4 and Invention Example 5 do not satisfy (Equation 4), but (Equation 3)
r ₀ ≦ r <r _f (Formula 3)
Is satisfied, and the valuable metal reduction index in slag is 0.63 and 0.62, respectively, and is a pass (◯).

The purpose of Example 4 is to confirm that the effect of the present invention is not obtained when the gas blowing at the center of the furnace bottom is not provided and the number of gas blowing ports other than the gas blowing at the center of the furnace is four. .
Only Comparative Example 4 is confirmed in Example 4.

As shown in FIG. 11, in Comparative Example 4, the electrodes were arranged as in the invention example, but the gas inlet was not provided at the center of the furnace bottom, and four gas inlets were provided in addition to the center of the furnace bottom. A square having a diameter of 8 mm is provided at the apex of a square having a center of 0.8 m on one side.
When the valuable metal reduction rate index in slag of Invention Example 1 was set to 1, the valuable metal reduction rate index in slag of Comparative Example 4 was evaluated to be 0.45.
This is probably because the temperature rise of the cold spot was not sufficient.
Thus, when the gas inlet is arranged at the apex of the square like the second eye, the temperature of the cold spot is not stably increased, and the slag valuable metal reduction rate index of Example 1 is set to 1. In this case, it was confirmed that the valuable metal reduction index in slag often did not exceed 0.50.

  INDUSTRIAL APPLICABILITY The present invention can be used for melting furnace interior materials in a steelmaking arc furnace.

DESCRIPTION OF SYMBOLS 1 Furnace 2 Electrode 3 Gas inlet 4 Gas bubble 5 Molten metal (molten steel)
6 Slag 7 Gas 8 Furnace bottom center gas inlet 9 Gas inlet area (A)
10 Gas inlet area (b)
Region 11 blown gas diffuses 12 furnace wall 12-A hot spot 12-B Cold difference 15-A electrode reference center 14 _{d f0} and _{d f} of the sphere when the spot 13 furnace bottom is part of a sphere Straight line 15-B Electrode reference line 15-C Electrode reference line 16-A Inlet reference line 16-B Inlet reference line 16-C Inlet reference line 19 High-temperature molten metal or slag flow 20 Arcs 21-23 Orientation (when viewed from above)
24-26 Flow direction of molten metal by blowing gas (when viewed from above)

Claims (8)

A method of blowing gas from the furnace bottom during arc heating,
The arc electrode starts from the center of the furnace bottom at an angle interval of 120 ° clockwise with reference to a straight line connecting the center of the furnace bottom and any one of the electrodes (hereinafter referred to as “electrode reference straight line”). and any one of a straight line, located at the intersection of the circumference of radius r ₀ about said furnace bottom center, r ₀ is when the molten steel bath depth of the hearth around the d _f0,
d _f0 / 2 ≦ r ₀ (Formula 1)
Satisfying the steps,
The gas inlet is the center of the furnace bottom, and
r _f is the inner radius of the bottom of the furnace,
d _f0 is the depth of the molten steel bath at the center of the furnace bottom,
θ is an angle defined clockwise with respect to the electrode reference straight line,
θ _cp is one of 60 °, 180 °, and 300 °,
r is the distance from the center of the furnace,
d _f is the molten steel bath depth of position for blowing gas,
When
θ _cp −10 ° ≦ θ ≦ θ _cp + 10 ° (Formula 2)
r ₀ + d _f / 2 ≦ r ≦ r _f −d _f / 2 (Formula 3)
A step of arranging at least one in an area represented by (hereinafter referred to as a “gas inlet area”);
A bottom blowing stirring method for an arc furnace for steel making, comprising: The depth of the molten slag generated during arc heating is 0.6 m or more ,
The bottom blowing stirring method of the arc furnace for steelmaking of Claim 1 characterized by these.   The bottom blowing stirring method for an arc furnace for steel making according to claim 1 or 2, further comprising a step of setting a diameter of a gas blowing port provided at a center of the furnace bottom to 5 to 25 (mm).   The bottom blowing stirring method for a steelmaking arc furnace according to any one of claims 1 to 3, further comprising a step of selecting a collecting capillary or a porous refractory as the gas blowing method. An arc furnace for steel making in which gas is blown from the bottom of the furnace during arc heating,
The arc electrode has any one of straight lines starting from the furnace bottom center at an angle interval of 120 ° clockwise with respect to the electrode reference straight line, and a circumference having a radius r ₀ around the furnace bottom center. located in the intersection, r ₀ is when the molten steel bath depth of the hearth around the d _f0,
d _f0 / 2 ≦ r ₀ (Formula 1)
Satisfied,
The gas inlet is the center of the furnace bottom, and
r _f is the inner radius of the bottom of the furnace,
d _f0 is the depth of the molten steel bath at the center of the furnace bottom,
θ is an angle defined clockwise with respect to the electrode reference straight line,
θ _cp is one of 60 °, 180 °, and 300 °,
r is the distance from the center of the furnace,
d _f is the molten steel bath depth of position for blowing gas,
When
θ _cp −10 ° ≦ θ ≦ θ _cp + 10 ° (Formula 2)
r ₀ + d _f / 2 ≦ r ≦ r _f −d _f / 2 (Formula 3)
Arranging at least one in the gas inlet area represented by
An arc furnace for bottom-blown stirring steelmaking. The depth of the molten slag generated during arc heating is 0.6 m or more ,
An arc furnace for bottom-blown stirring steel making according to claim 5.   The arc furnace for bottom-blown stirring steelmaking according to claim 5 or 6, wherein a diameter of a gas blowing port installed at the center of the furnace bottom is 5 to 25 (mm).   The bottom blow-stirring steelmaking arc furnace according to any one of claims 5 to 7, wherein a collecting capillary or a porous refractory is used as a gas blowing method.