JP2006249563A - Method for blowing oxygen or oxygen-containing gas in arc furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a simple method for blowing an oxygen or oxygen-containing gas with an equipment constitution where the wear of refractories at the furnace bottom can be suppressed as the effect of stirring molten metal by the blowing of the oxygen or oxygen-containing gas is retained, and further, running cost including maintenance in the operation can be suppressed, and simultaneously, to suppress the reduction of furnace temperature and to improve dust collection effect by sealing the inside of the furnace. <P>SOLUTION: An oxygen or oxygen-containing gas is blown into molten metal from a lance 20 fixedly mounted on the outer part of the furnace wall in an arc furnace. The blowing is performed in such a manner that the position of a discharge port 22 for an oxygen or oxygen-containing gas at the tip part 21 of the lance is made far by ≥700 mm in the vertical direction from a molten metal face, also, regarding the angle at which the oxygen or oxygen-containing gas discharged from the discharge port rushes in the molten metal face, in the face in the vertical direction, its angle from the molten metal face is controlled to the range of 30 to 60°, and the blowing speed of the oxygen or oxygen-containing gas from the discharge port at the tip part of the lance is decided so that its rushing speed onto the surface of the molten metal is controlled to the range of 150 to 300 m/s. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method of blowing oxygen or an oxygen-containing gas from a lance provided on a furnace wall of an arc furnace used for melting a metal material and refining molten metal.

  In an arc electric furnace for the purpose of decarburization and heating of a molten metal in a molten state and a molten state of a metal material (for example, metal scrap), a method of blowing oxygen or an oxygen-containing gas has often been used.

  In particular, in recent arc furnaces, when the metal material is melted and melted, refining is completed, and when the molten metal is discharged to the ladle outside the furnace, the steel outlet is unevenly distributed so as not to generate slag in the furnace as much as possible. A large number of cored core-centered steel arc furnaces have been installed.

  As a method of blowing oxygen or an oxygen-containing gas in such an arc furnace, a method of immersing a consumable pipe in molten metal has been conventionally used. However, pipe cost reduction and supply work when the pipe is consumed As a method for blowing oxygen or oxygen-containing gas from a water-cooled lance as shown in Patent Document 1, the height h from the surface of the molten metal to the blowing position of the water-cooled lance is 300 mm to 700 mm. And the angle θ between the surface of the molten metal and the blowing direction of the water-cooled lance is 30 degrees or more, and the depth L of the molten metal by blowing at the blowing point using the formula of [Equation 1] It has been proposed that the ratio of the molten metal bath depth H be blown so as to be in the range of 0.4 to 0.7.

  Further, as shown in Patent Document 2, the depth L of the concave portion generated in the molten metal by inserting a lance from the working port of the arc furnace and blowing an oxidizing gas from above the bath surface of the molten metal, and the molten metal It has been proposed that the oxidizing gas is blown from above the bath surface of the molten metal within a range where the depth H of the still bath satisfies 0.2 ≦ L / H ≦ 0.3.

Further, Patent Document 3 and Patent Document 4 show methods for injecting oxygen or an oxygen-containing gas while being fixedly mounted on the outside of the arc furnace wall in order to perform an operation in which the work port of the arc furnace is closed as much as possible. As shown, the fuel and secondary oxygen are injected into the furnace coaxially with the high-speed main gas (mainly oxygen) flow above the molten metal bath, and the fuel is burned with secondary oxygen to surround the high-speed main gas flow. A furnace feed method has been proposed in which a flame envelope is formed and a high velocity main gas stream is sent to the bath where the flame envelope substantially extends the full length of the high velocity main gas flow in the furnace to the bath. Yes.
JP-A-6-192718 JP 2003-151509 A Japanese Patent Laid-Open No. 10-259413 JP-A-10-263384

  However, in the methods disclosed in Patent Document 1 and Patent Document 2, for example, a water-cooled lance is inserted and the operation is performed with the work opening of the electric furnace open, so that a large amount of air enters from the work opening. As the temperature in the furnace becomes lower, the dust collection effect decreases. In addition, since a single water-cooled lance is inserted from the work port, the frequency of maintenance increases because a device that can be driven back and forth, up and down, and left and right is attached to enhance the stirring effect of the entire molten metal. In particular, since the heat transfer efficiency to the steel outlet side opposite to the work port is low, the temperature rise of the molten metal existing in the space protruding to the steel output side is particularly high in the furnace bottom eccentric type arc furnace. Has a slow drawback. In particular, in the method disclosed in Patent Document 2, since the oxidizing gas is blown by soft blow, the disadvantage that the temperature rise of the molten metal existing in the space projecting to the steel output side is remarkable appears.

  Further, in the methods shown in Patent Document 3 and Patent Document 4, the bath depth of the molten metal existing in the space projecting to the steel output side is particularly high even in an arc furnace having a 100 ton class molten metal held in the furnace. Since it is about 500 mm to 600 mm, if a gas that is kept in a supersonic state is blown into the molten metal, as shown in Patent Document 1 described above, the depth of the indentation of the molten metal is increased, and the fire resistance of the furnace bottom is increased. Increased wear and tear of objects. Furthermore, since the injection hole for injecting fuel and secondary oxygen faces the furnace inner surface at the tip of the lance, it is always from the initial stage of melting of the metal material so that the injection hole is not clogged by splash or slag from inside the furnace. Since it is necessary to blow in fuel and secondary oxygen or purge gas for preventing clogging of holes, the gas control system becomes complicated, and the maintenance cost as well as the fuel cost increases, so the running cost increases.

  The object of the present invention is to suppress the wear of the refractory at the bottom of the furnace while maintaining the stirring effect by blowing oxygen or oxygen-containing gas into the molten metal, and further, running including maintenance in operation In addition to providing a simple oxygen or oxygen-containing gas blowing method with an equipment configuration capable of reducing costs, the furnace is sealed to prevent a decrease in furnace temperature and to improve the dust collection effect. Furthermore, in the furnace bottom eccentric steelmaking type arc furnace, the stirring effect of the molten metal in the furnace space overhanging to the steel output side is improved.

  In the method of blowing oxygen or oxygen-containing gas in the present invention, the oxygen or oxygen is introduced from above onto the surface of the molten metal in the furnace wall by a lance fixedly mounted outside the furnace wall of the arc furnace for melting and refining the metal material. In the method of blowing the contained gas, the position of the discharge port of oxygen or oxygen-containing gas at the tip of the lance is kept 700 mm or more away from the molten metal surface in the vertical direction, and on the molten metal surface of oxygen or oxygen-containing gas discharged from the discharge port The angle of entry is in the range of 30 ° to 60 ° from the molten metal surface in the vertical plane, and the entry speed of oxygen or oxygen-containing gas on the molten metal surface is in the range of 150 m / sec to 300 m / sec. In this manner, the blowing speed from the discharge port at the tip of the lance is determined and blown.

  In addition, the plane mounting position is arranged in the range from the outermost end surface of the electrode arranged on the side of the steel outlet to the side of the steel outlet in the graphite electrode of the arc furnace, and inside the furnace core, and contains oxygen or oxygen The planar blowing direction of the gas is 90 ° ± 20 ° with respect to the axis line connecting the core of the arc furnace and the steel outlet core.

  The effects of the present invention are as follows.

1. A lance that blows oxygen or oxygen-containing gas is fixedly attached to the side wall of the furnace body, so that the work port can be closed during most operating hours by the work port door, and the furnace temperature is reduced by sealing the furnace. It is possible to suppress and further improve the dust collection effect.

2. The position of the oxygen or oxygen-containing gas discharge port at the tip of the lance is 700 mm or more away from the molten metal surface in the vertical direction, and the angle at which the oxygen or oxygen-containing gas discharged from the discharge port enters the molten metal surface in the vertical direction The angle of the surface of the lance is 30 ° to 60 ° at the surface, and the rush speed of oxygen or oxygen-containing gas on the molten metal surface is in the range of 150 m / sec to 300 m / sec. By determining the blowing speed from the discharge port and blowing it, it is possible to suppress damage to the lance, the water-cooled panel and the refractory on the opposite surface while fully teaching the stirring effect of the molten metal.

3. Attach the lance within the range from the outermost end surface of the graphite electrode located on the most steel outlet side of the graphite electrode to the inside of the furnace core, and connect the furnace core to the steel outlet core. By disposing the discharge port at the tip of the lance in the direction of 90 ° ± 20 ° with respect to the axis, the stirring efficiency to the molten metal is improved and the oxygen efficiency is improved.

4). Since the lance is fixedly mounted, no mechanism for driving the lance is required, so that the equipment maintenance cost is reduced.

5. Since only oxygen or oxygen-containing gas is allowed to flow through the lance, no fuel for secondary combustion or oxygen for fuel is required, so that the running cost can be suppressed.

  Below, the method of blowing in oxygen or an oxygen-containing gas for an arc furnace according to the present invention will be described based on one embodiment shown in FIGS. FIG. 1 is a cross-sectional view of an arc furnace, particularly a three-phase AC arc furnace, which is a bottom-centered steel arc furnace, and FIG. 2 is an installation of a lance for blowing oxygen or oxygen-containing gas for the arc furnace of the present invention. FIG. 3 is a plan sectional view of the arc furnace shown in FIG. 1, FIG. 4 is a horizontal axis showing the axial distance L from the outlet of the discharge port at the tip of the lance to the molten metal surface, and the vertical axis It is a graph which shows the discharge speed V0 of the discharge outlet exit of a lance front-end | tip part.

  In FIG. 1, an arc furnace is mainly composed of a furnace body 1 whose upper part is open for charging metal scrap, a furnace lid 2 for covering the open part of the upper part, and a graphite electrode 3 for emitting arc. In the case of a three-phase AC arc furnace, three graphite electrodes are used. Further, in the furnace bottom eccentric steelmaking type arc furnace, the overhanging portion 4 is discharged to the steeling side.

  A water-cooled panel 5 is attached to the inside of the furnace body iron skin 11 of the furnace body 1, and the lower part is composed of a refractory 7 for holding a molten metal 6 of scrap melted by an arc. 7 is provided with an opening (steel outlet) 8 for discharging molten metal in a vertical direction to a ladle (not shown), and the molten metal is exposed to the outside during melting of the scrap and refining of the molten metal. It is closed with a steel output pawl 9 so as not to flow out.

  In general, the work port 10 is opened for the internal inspection and inspection, the temperature measurement of the molten metal, and the sampling work on the projecting side and the facing side on the steel exit side. When the above work is not performed, the work port door 14 is opened. It is closed at. The depth of the molten metal in the furnace bottom eccentric steel arc furnace is deepest at the molten metal depth h0 at the center of the furnace body and becomes shallower as it approaches the outlet, and h0 is about 100 tons in the 100 ton class arc furnace. For a depth of 1000 mm, h1 is about 500 mm to 600 mm.

  FIG. 2 is a cross-sectional view showing the mounting arrangement of the lance 20 for blowing oxygen or oxygen-containing gas of the present invention into the arc furnace of FIG.

  The tip 21 of the lance 20 passes through the opening 12 of the furnace body skin 11 constituting the outer wall of the furnace body 1 and the opening 13 of the water-cooled panel 5 described above, and the mounting seat 32 and the lance 20 on the furnace body skin 11 side. It is fixedly attached to the side mounting seat 23.

  The lance 20 is a triple pipe including a central pipe through which oxygen or oxygen-containing gas can pass in the center, and an inner pipe and an outer pipe for supplying and draining cooling water for protection from high temperature heat load in the furnace. It is desirable that it be a water-cooled type.

  The lance 20 is fixedly mounted so that the vertical height H from the surface of the molten metal 6 to the oxygen or oxygen-containing gas discharge port 22 at the tip 21 of the lance 20 is 700 mm or more. The reason is that when the position of the discharge port 22 is brought close to the molten metal surface, the stirring effect by oxygen or an oxygen-containing gas increases, but the amount of scattered molten metal increases, and there is undissolved metal scrap in the molten metal. It is about 300-400mm that a large amount of molten metal jumps up when it suddenly reacts with oxygen and undergoes boiling, or when the molten metal solidified on the furnace wall falls into the molten metal. This is because it has been empirically confirmed that if the height of the lance tip is 700 mm or more, the lance tip is not damaged and the discharge port is not clogged with scattered molten metal. That.

  In the blowing method by the lance shown in the above-mentioned Patent Document 1, when the height is set within a range of 300 to 700 mm, emergency evacuation can be performed outside the furnace at the time of occurrence of boiling, but the outside of the furnace body. Since it cannot be retracted when it is fixedly mounted, it is preferable from a safety standpoint to keep it at least 700 mm away.

  Further, the discharge angle θ of oxygen or oxygen-containing gas from the discharge port 22 to the surface of the molten metal 6 is in the range of 30 to 60 degrees. This is because there is a high risk that the molten metal scatters and damages the expression panel 5 in a large amount, and when it exceeds 60 degrees, there is a high risk that the molten metal scatters and damages the tip of the lance.

In FIG. 2, when the discharge speed from the discharge port 22 at the tip of the lance is V0, the rush speed at the time of rushing into the surface of the molten metal 6 when the distance in the discharge axis direction of oxygen or oxygen-containing gas is L. Va can be obtained from the following equation (1) from turbulent flow theory and error curve theory.
Va / V0 = A × D0 / X · exp [−B / X ² ] (1)
In the above formula,
Va: Gas flow velocity (m / sec) at a position X distance away from the nozzle outlet
V0: gas flow velocity at the nozzle outlet (m / sec)
D0: Nozzle diameter (cm)
X: Distance from nozzle outlet (cm)
A: Constant
B: Constant

  The graph calculated | required from said (1) Formula is shown in FIG. The abscissa indicates the axial distance L from the outlet of the lance tip to the molten metal surface, and the ordinate indicates the discharge speed V0 of the outlet of the lance tip.

  When oxygen or oxygen-containing gas is blown into a conventional consumable pipe, the pipe outlet speed of oxygen or oxygen-containing gas is related to the pressure of oxygen or oxygen-containing gas so that the stirring effect in the molten metal can be taught. However, operation has been performed at a discharge speed of about 300 m / sec.

  However, when the bath depth of the molten metal in the furnace is around 1000 mm, even if it is blown at a speed of about 300 m / second, the refractory under the molten metal is not damaged. In the arc furnace, since the bath depth is 500 mm to 600 mm as described above, the refractory is damaged when blown at a discharge speed of 300 m / sec. Therefore, the present inventors changed the discharge rate of oxygen or oxygen-containing gas from the pipe in accordance with the bath depth of the molten metal in a 100-ton class bottom-centered steel arc furnace and damaged the refractory. As a result of investigating the discharge speed that does not give water, it was confirmed that it is desirable to decrease the discharge speed in proportion to the bath depth.

  Therefore, in an arc furnace having a molten metal bath depth of 500 mm to 1000 mm, the lance is adjusted so that the rush speed of oxygen or oxygen-containing gas on the surface of the molten metal is in the range of 150 m / sec to 300 m / sec in proportion to the bath depth. It is necessary to set the outlet outlet speed at the tip. This is because it has been found from the actual operation results that when the speed is less than 150 m / sec, the stirring effect of the molten metal on the steel output side decreases, and the temperature rise rate of the molten metal becomes slow.

  In FIG. 2, L is about 1000 mm when H = 700 mm and θ = 45 degrees. Therefore, from FIG. 4, V0 for securing Va of 150 m / sec or more at L = 1000 mm is about 510 m / sec or more. It is sufficient to ensure a discharge speed of approximately 1.5 or more when converted to the Mach number.

  Next, FIG. 3 is a plan cross-sectional view showing the mounting arrangement of the lance relating to the main blowing method in the furnace bottom eccentric steel extraction method. Generally, since the furnace body has a circular planar shape at the center of the furnace body, the molten metal also has a circular shape with the center of the furnace body as the core, and becomes an elongated elliptical shape as it moves toward the steel outlet. ing.

  In a three-phase AC arc furnace, the graphite electrodes are arranged in a regular triangle centered on the center of the furnace body in a plane, so that oxygen or oxygen-containing gas attacks the graphite electrode and does not accelerate the wear of the graphite electrode. In order not to damage the water-cooled panel and the refractory top surface of the lance-facing surface due to oxygen attack, the lance has a steel outlet more than the outermost end face 31 of the graphite electrode located closest to the steel outlet. It is desirable to install in the range of La which becomes the range to the inner side of the furnace body skin 11 on the side.

  In order to sufficiently teach the stirring effect on the molten metal by oxygen or an oxygen-containing gas, it is most effective to blow in the tangential direction with respect to the radius R axis of the molten metal circular surface. Therefore, the most effective blowing method is to dispose the discharge port at the tip of the lance in a direction substantially perpendicular to the axis connecting the furnace body center and the steel outlet center.

In FIG. 3, if the swing angle of θ ₂ is swung too much counterclockwise (on the steel outlet side), the distance from the lance discharge port to the water-cooled panel on the opposite surface or the refractory on the lower side is shortened, resulting in oxygen attack. If the damage increases and conversely swings in the clockwise direction (graphite electrode side) too much, wear due to oxygen attack on the graphite electrode increases, so the effect of stirring the molten metal is maintained while suppressing these effects of oxygen attack. For this reason, it is desirable that the deflection angle θ _{2 in the} direction of oxygen discharge from the lance is within a range of ± 20 degrees.

It is a fragmentary sectional view which shows typically the arc furnace of an arc furnace, especially a 3-phase alternating current arc furnace of a furnace bottom eccentric steeling system. It is use condition explanatory drawing which shows the attachment of the lance for blowing in oxygen for oxygen for an arc furnace of this invention, or oxygen-containing gas in a cross section. It is a use condition explanatory drawing which shows the attachment of the lance for blowing in oxygen or the oxygen containing gas for arc furnaces of this invention in the arc furnace of FIG. 1 planarly. The horizontal axis shows the axial distance L from the outlet of the discharge port at the tip of the lance to the molten metal surface, and the vertical axis shows the discharge speed V0 at the outlet of the discharge port at the tip of the lance.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Furnace body 2 Furnace lid 3 Graphite electrode 4 Overhang part 5 Water-cooled panel 6 Molten metal 7 Refractory 8 Opening (steel opening)
DESCRIPTION OF SYMBOLS 9 Steel outlet cover 10 Working port 11 Furnace iron shell 12 Opening 13 Opening 14 Working port door 20 Lance 21 Lance tip part 22 Discharge port 23 Lance side mounting seat 31 Outermost end surface of graphite electrode 32 Furnace side mounting seat

Claims (2)

  In a method in which oxygen or an oxygen-containing gas is blown from above onto the surface of the molten metal in the furnace wall by a lance fixedly attached to the outside of the furnace wall of the arc furnace for melting and refining the metal material, The position of the discharge port of the oxygen-containing gas is at least 700 mm away from the molten metal surface in the vertical direction, and the angle at which the oxygen or oxygen-containing gas discharged from the discharge port enters the molten metal surface is perpendicular to the molten metal surface. Blowing from the discharge port at the tip of the lance so that the angle of air is in the range of 30 ° to 60 °, and the rush speed of oxygen or oxygen-containing gas on the molten metal surface is in the range of 150 m / sec to 300 m / sec. A method of blowing oxygen or an oxygen-containing gas, characterized by blowing at a determined speed.   The plane mounting position is arranged from the outermost end surface of the electrode arranged on the side of the steel outlet in the graphite electrode of the arc furnace to the side of the steel outlet and inside the furnace shell. The method according to claim 1, further comprising: setting an appropriate blowing direction to 90 ° ± 20 ° with respect to an axis connecting the core of the arc furnace and the steel outlet core.

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