Direct-current electric furnace

Abstract

To provide a direct-current electric furnace capable of efficiently melting a melting raw material such as DRI and HBI with smaller density than that of molten iron in a short time.SOLUTION: In a direct-current electric furnace, when an intersection point of a vertical line and a molten metal surface of molten iron passing through a center of an upper electrode is designated as (±x0, y0), the radius of the upper electrode is as r and the current value per upper electrode is as I(kA), a raw material input pipe is provided on a side face or an upper face of a furnace body except for immediately above a high temperature area (x1, y1) expressed by the formula (i) and formula (ii), and a point (x, y), at which the melting raw material reaches a surface of the molten iron, is expressed by formulae (iii)-(v). (x1±x0)2+(y1-y0)2<r2...(i), -r<y1<r, -x0<x1<x0...(ii), (x±x0)2 / a2+(y-y0)2 / b2=1...(iii), a=0.0045I+1.475...(iv), b=0.019I-0.257...(v)SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a direct current electric furnace.

Background Art

[0002] Since the iron source produced by the blast furnace method is produced by reducing iron ore with coke, the amount of CO2 generated is large. As a means of reducing the amount of CO2 generated, there is a method of melting iron scrap, DRI (Direct Reduced Iron), etc. in an electric furnace to produce hot metal, and using the existing steelmaking process centered on a converter to produce molten steel. Melting is performed by an arc generated from an upper electrode provided in the electric furnace to the surface of the molten iron.

[0003] In a direct current electric furnace, it is known that an arc is deflected by a magnetic field caused by a current flowing through a cable from a bottom electrode. As a countermeasure, a magnetic field generating coil is provided around the bottom electrode so that a winding line circulates, and a direct current magnetic field having a rotationally symmetric component about the arc generating electrode axis is generated. As a result, since the arc rotates about the furnace center, a technique for realizing uniform melting by making the heat load in any direction uniform has been disclosed (Patent Document 1). Further, a technique for suppressing the deflection of the arc by setting the vertical component of the magnetic flux density to 90 Gauss or more and the horizontal component to 30 Gauss or less in the arc generation region by a coil wound around the periphery of the furnace bottom has been disclosed (Patent Document 2). Furthermore, a technique for improving the melting efficiency of scrap raw materials is disclosed by continuously charging scrap raw materials between two upper electrodes and directing the arcs of both electrodes toward the scrap raw materials at the center of the furnace body (Patent Document 3).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

[0005] Direct reduced iron is obtained by directly reducing iron ore or iron ore pellets with a reducing gas such as hydrogen, and is called DRI. Further, the DRI after the reduction treatment that is hot-compression molded is called HBI (Hot Briquetted Iron). The apparent density of DRI is about 3500 kg / m 3 and the apparent density of HBI is about 5000 to 5500 kg / m 3 Since the density of molten iron is about 7000 kg / m 3 , both DRI and HBI are lighter than molten iron and float on the surface of the molten metal.

[0006] In the technologies disclosed in Patent Documents 1 and 2, in order to efficiently heat the scrap deposited in the molten iron, it is possible to easily stir the molten iron near the scrap. However, when using reduced iron, since the density is smaller than that of molten iron, it is necessary to more efficiently melt DRI and HBI floating on the surface of the molten metal in a shorter time. Further, in the technology disclosed in Patent Document 3, since heat in the furnace easily escapes from the raw material inlet provided vertically between the two upper electrodes, it is difficult to ensure heat retention in the furnace, and there is a risk that the melting efficiency of reduced iron may decrease. There is also a problem that the raw material input pipe is easily damaged due to radiant heat damage.

[0007] Therefore, an object of the present invention is to provide a DC electric furnace capable of more efficiently melting melting raw materials such as DRI and HBI, which have a density smaller than that of molten iron and easily float on the surface of the molten metal, in a shorter time. MEANS FOR SOLVING THE PROBLEMS

[0008] [1] In a DC electric furnace comprising two upper electrodes and a raw material input pipe provided on a side surface or an upper surface of a furnace body for introducing a raw material containing a melting raw material having a density smaller than that of molten iron into the furnace, with a plane including the surface of the molten iron as the xy plane, the positions on the xy coordinates of the intersections of a vertical line passing through the center of the lower end surface of the upper electrode and perpendicular to the surface of the molten iron and the surface of the molten iron are respectively (x0, y0) and (-x0, y0), the radius of the upper electrode is r, and the current value per upper electrode is I (kA). The raw material input pipe is provided on the side surface or the upper surface of the furnace body other than directly above a high-temperature region where the position (x1, y1) on the xy coordinates is represented by the following formulas (i) and (ii). The positions (x, y) on the xy coordinates of the points where the introduced melting raw material reaches the surface of the molten iron are represented by the following formulas (ii) to (iv). (x1 ± x0) 2 +(y1 - y0) 2 < r 2 ···(i) -r < y1 < r, -x0 < x1 < x0 ···(ii) (x ± x0) 2 / a 2 +(y - y0) 2 / b 2 = 1 ···(iii) a = 0.0045I + 1.475 ···(iv) b = 0.019I - 0.257 ···(v) [2] The raw material input pipe according to [1], wherein the raw material input pipe is provided inclined with respect to the surface of the molten iron. [3] The raw material input pipe according to [1], wherein the raw material input pipe is provided perpendicular to the surface of the molten iron.

Advantages of the Invention

[0009] According to the above configuration, melting raw materials such as HBI, which have a lower density than molten iron and float on the surface of the molten metal, quickly reach the high-temperature region. In addition, since the installation position of the raw material input pipe is a part other than directly above the high-temperature region, the heat retention in the furnace can be ensured, and damage to the raw material input pipe due to radiant heat damage can be suppressed. Therefore, reduced iron materials such as DRI and HBI, which have a lower density than molten iron and are likely to float on the surface of the molten metal, can be melted more efficiently and in a shorter time.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Best Mode for Carrying Out the Invention

[0011] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and the drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant descriptions are omitted.

[0012] (Structure of a DC electric furnace according to an embodiment) FIG. 1 is a cross-sectional view showing the structure of a DC electric furnace 1 according to an embodiment of the present invention. In the figure and the following description, three mutually orthogonal directions are defined as the +x direction, +y direction, and +z direction. Although not shown, the direction opposite to the +x direction is the -x direction, the direction opposite to the +y direction is the -y direction, and the direction opposite to the +z direction is the -z direction. The plane including the molten iron surface of the molten iron 21 is defined as the xy plane, but the molten iron surface does not necessarily have to be a strict plane and may have irregularities.

[0013] As shown in the figure, the furnace body of the DC electric furnace 1 includes a ceiling 2, a furnace wall copper panel 3, a furnace wall refractory 4, and a furnace bottom refractory 5. Further, two upper electrodes 6 are provided on the ceiling 2, and a furnace bottom electrode 7 and a bottom blowing tuyere 8 are provided at the bottom of the furnace body. An upper electrode cable 6a is connected to the upper electrode 6. Also, a furnace bottom cable 7a is connected to the furnace bottom electrode 7. In a large DC electric furnace 1, the current per upper electrode 6 is about 100 kA to 140 kA at maximum. Therefore, the total current value is a large current of about 200 kA to 280 kA.

[0014] As the DC electric furnace 1, a tilting type in which the furnace body tilts can also be used, or a stationary type in which the furnace body does not tilt can also be used. Further, as iron sources, one or two of iron-containing scrap and reduced iron are charged into the DC electric furnace 1. As the reduced iron, HBI, DRI, etc. can be used. Iron-containing dust may be charged into the furnace as an iron source. As the iron-containing dust, granulated converter dust can be used. Pr in the figure indicates the point where the molten raw materials such as HBI charged from the raw material charging pipe 9 reach the surface of the molten iron 21. Hereinafter, this point is referred to as the charging position Pr. Further, hereinafter, the molten raw materials having a density smaller than that of the molten iron 21 are described as HBI, but are not limited to HBI, and may be raw materials such as DRI.

[0015] The furnace wall refractory 4 is provided with a tapping hole 10 for discharging the molten iron 21 and a slag tapping hole 11 for discharging the electric furnace slag 22. An arc 20 is emitted from the upper electrode 6 to melt raw materials such as reduced iron to produce the molten iron 21. By blowing gas from the bottom tuyere 8 to cause a circulating flow in the molten iron 21 and the electric furnace slag 22, heat transfer and melting of the surface of the molten iron 21 and the electric furnace slag 22 can be promoted.

[0016] In the DC electric furnace 1 according to the present embodiment, the raw material charging pipe 9 is provided on the side surface or the upper surface of the furnace body in a portion other than directly above the high-temperature region Rh. The reason for providing the raw material charging pipe 9 in a portion other than directly above the high-temperature region Rh is to avoid heat escaping from the furnace, making it difficult to ensure the heat retention in the furnace, and reducing the melting efficiency of the reduced iron. The raw material charging pipe 9 may be provided inclined as shown in the figure. By providing the raw material charging pipe 9 in this way, the heat retention in the furnace can be ensured, and damage to the raw material charging pipe 9 due to radiant heat damage can be suppressed.

[0017] Figure 2 is a cross-sectional view taken along line II-II of the DC electric furnace 1 shown in Figure 1. As shown in the figure, the DC electric furnace 1 has a circular horizontal cross-section. The two upper electrodes 6 each have a radius of r. Rh in the figure is a high-temperature region, which is a region having a higher temperature than other regions on the surface of the molten iron 21. The definition of the high-temperature region Rh will be described later.

[0018] (Outline and Conditions of Simulation for Evaluating Heat Flow in DC Electric Furnace) Since the arc 20 emitted from the upper electrode 6 is at high temperature and high speed, it is difficult to directly measure the temperature and flow velocity of the arc 20. Therefore, in this embodiment, a simulation is performed to evaluate the heat flow in the DC electric furnace 1 due to arc discharge. The simulation is based on the method described in Jonas ALEXIS, Marco RAMIREZ, Gerardo TRAPAGA and Par JONSSON, “Modeling of a DC Electric Arc Furnace-Heat Transfer from the Arc” ISIJ International, Vol.40 (2000), pp.1089-1097, and the outline thereof will be described below.

[0019] In the simulation, the arc 20 emitted from the upper electrode 6 is regarded as an electromagnetic fluid having conductivity, and a coupled calculation of electromagnetic field analysis, fluid analysis, and heat transfer analysis is performed. First, the method of electromagnetic field analysis will be described. When the current density flowing through the arc 20 is i (A / m 2 ), the relationship between the magnetic vector potential A and the current density i is expressed as in Equation (1). μ0 is the magnetic permeability of vacuum.

[0020] [Equation number]

[0021] The current density i is calculated using Equation (2) which is the conservation law of current density. Here, φ is the potential at the inlet side and the outlet side of the current set as the boundary condition, and σ is the conductivity (S / m) of the arc 20 which is a value depending on the temperature of the arc 20.

[0022] [Equation number]

[0023] From the current density distribution calculated from Equation (2), the magnetic vector potential A is calculated from Equation (3). Then, using the calculated magnetic vector potential A, the distribution of the magnetic flux density B (T) is calculated from Equation (3).

[0024]

Number

[0025] Next, the methods of fluid analysis and heat transfer analysis will be described. In a conductor through which an electric current is flowing in a magnetic field, a Lorentz force F (N / m 3 ) = i × B is generated. Also, the amount of Joule heat q (W / m 3 ) = i 2 / σ is generated. Using the calculated Lorentz force F and the amount of Joule heat q, fluid analysis and heat transfer analysis are performed. Note that hereinafter, the Lorentz force F is also referred to as the "electromagnetic force". In fluid analysis, the flow of the arc 20 is analyzed by the mass conservation law shown in Equation (4) and the Navier - Stokes equation shown in Equation (5). Here, u is the flow velocity, ρ is the density, t is the time, p is the pressure, μ is the viscosity, and g is the acceleration due to gravity.

[0026]

Number

[0027] Heat transfer analysis is performed using Equation (6), which is the governing equation of heat transfer analysis. Here, C p is the specific heat, T is the temperature, λ is the thermal conductivity, S r is the radiant energy, and Q t is the energy loss due to the Thomson effect.

[0028]

Number

[0029] By performing the electromagnetic field analysis, fluid analysis, and heat transfer analysis as described above, the temperature and flow velocity of the arc 20 can be obtained. As an example, the calculation conditions in the simulation were as follows: the diameter of the upper electrode 6 was 800 mm, the distance between the furnace center C and the center of the upper electrode 6 was 3400 mm, and the distance between the upper electrode 6 and the molten iron surface of the molten iron 21 was 500 mm. Also, the atmospheric gas in the furnace was Ar, and the potential of the molten iron surface of the molten iron 21 was set to 0. Furthermore, the current value flowing through each upper electrode 6 was 100 kA, and the starting point from which the arc 20 was emitted was the center of the lower end surface of the upper electrode 6.

[0030] Figure 3 is a diagram showing the temperature distribution and flow velocity distribution of the arc 20 emitted from the upper electrode 6, simulated in the DC electric furnace 1 shown in Figure 1. In Figure 3, (a) shows the temperature distribution and (b) shows the flow velocity distribution. In the DC electric furnace 1, since the upper electrode 6 is the negative electrode and the bottom electrode 7 is the positive electrode, the current flows from the bottom side towards the ceiling 2 side. The arcs 20 emitted from the two upper electrodes 6 incline so as to attract each other.

[0031] As shown in the figure, in the DC electric furnace 1, the molten iron surface near the furnace center C, which is the region surrounded by the two upper electrodes 6, is relatively high in temperature. Therefore, if the HBI accumulates in the high-temperature region Rh, which is the region surrounded by the two upper electrodes 6, due to the flow of the molten iron 21, the HBI will dissolve efficiently.

[0032] (Definition of the high-temperature region) As described above, the arcs 20 emitted from the two upper electrodes 6 incline so as to attract each other. Therefore, the molten iron surface directly below the upper electrode 6 and in the range surrounded by the upper electrodes 6 becomes the high-temperature region Rh. The high-temperature region Rh is defined as the range surrounded by the tangent lines of the upper electrode 6 as shown in Figure 2.

[0033] Assuming that the xy coordinates of the intersection points between the vertical line passing through the centers on the lower end surfaces of the two upper electrodes 6 and perpendicular to the molten iron surface of the molten iron 21 and the molten iron surface of the molten iron 21 are (x0, y0) and (-x0, y0) respectively, the positions (x1, y1) on the xy coordinates of the high-temperature region Rh are expressed by the following equations (7) and (8) using the radius r of the upper electrode 6. However, the range of equation (8) is -x0 < x1 < x0. Hereinafter, the coordinates of the centers on the lower end surfaces of the two upper electrodes 6 are also represented as (±x0, y0). (x1 ± x0) 2 +(y1 - y0) 2 < r 2 ···(7) -r < y1 < r ···(8)

[0034] (Structure of a DC electric furnace according to a modification of an embodiment) FIG. 4 is a cross-sectional view showing the structure of a DC electric furnace 1 according to a modification of an embodiment of the present invention. As shown in the figure, the furnace body of the DC electric furnace 1 includes a ceiling 2, a furnace wall copper panel 3, a furnace wall refractory 4, and a furnace bottom refractory 5. Further, two upper electrodes 6 are provided on the ceiling 2, and a furnace bottom electrode 7 and a bottom blowing tuyere 8 are provided at the bottom of the furnace body. An upper electrode cable 6a is connected to the upper electrode 6. Also, a furnace bottom cable 7a is connected to the furnace bottom electrode 7.

[0035] An arc 20 is emitted from the upper electrode 6 to melt raw materials such as reduced iron to produce molten iron 21. By blowing gas from the bottom blowing tuyere 8 to cause a circulating flow in the molten iron 21 and the electric furnace slag 22, it is possible to promote heat transfer and melting on the surface of the molten iron 21 and the electric furnace slag 22.

[0036] In the DC electric furnace 1 according to the modified example, the raw material charging pipe 9 is provided on the side surface or the upper surface of the furnace body at a portion other than directly above the high-temperature region Rh. However, unlike the DC electric furnace 1 according to the embodiment, it is provided perpendicular to the molten iron surface of the molten iron 21. The HBI is preferably dropped from the raw material charging pipe 9 into the region where the downward flow of the molten iron 21, which will be described later, is generated, so that the HBI can move to the high-temperature region Rh faster and stay in the high-temperature region Rh for a longer time at the charging position Pr. By providing the raw material charging pipe 9 in this way, the heat retention property inside the furnace can be ensured, and the raw material charging pipe 9 can be suppressed from being damaged by radiation heat damage.

[0037] (Flow analysis of molten iron) FIG. 5 is a diagram showing the distribution of the Lorentz force density by electromagnetic field analysis in the DC electric furnace 1 according to an embodiment of the present invention. In FIG. 5, (a) is a view of the distribution of the Lorentz force density on the molten iron surface of the molten iron 21 as seen from the ceiling 2 side, and (b) is a view of the distribution of the Lorentz force density on the furnace bottom as seen from the furnace bottom side. Further, (c) is a diagram showing the distribution of the Lorentz force density in the molten iron 21 in the cross-sectional view taken along line A-A directly below the upper electrode 6 in (a), and (d) is a diagram showing the direction of the electromagnetic force in the molten iron 21 in the cross-sectional view taken along line A-A.

[0038] As shown in the figure, directly below the upper electrode 6, a large Lorentz force density is generated in the molten iron 21, and an electromagnetic force in the direction of pushing the molten iron 21 is generated. Also, on the side of the bottom electrode 7, an electromagnetic force in the direction toward the molten iron surface of the molten iron 21 is generated, but since the current density is lower than that directly below the upper electrode 6, it can be seen that the Lorentz force density is small.

[0039] FIG. 6 is a diagram showing the result of analyzing the flow of the molten iron 21 based on the distribution of the Lorentz force density shown in FIG. 5. In FIG. 6, (a) is a view of the flow of the molten iron 21 on the molten metal surface as seen from the ceiling 2 side, and (b) is a view showing the flow of the molten iron 21 in the cross-sectional view taken along line B-B directly below the upper electrode 6. As shown, in the vicinity directly below the upper electrode 6, since the force pushing the molten iron 21 is strong, a downward flow of the molten iron 21 in the direction of the furnace bottom is formed. Then, after the molten iron 21 collides with the furnace bottom, an upward flow in the direction of the molten metal surface is formed. Near the molten metal surface, the molten iron 21 rises from the furnace bottom near the furnace center C to the molten metal surface, forming a flow in the direction toward the furnace wall. The HBI charged in such a situation where the flow of the molten iron 21 is formed flows near the furnace wall where it is not in the high-temperature region Rh, and the melting efficiency of the HBI decreases.

[0040] (Outline and Conditions of Simulation for Evaluation of Movement of HBI) Since the inside of the furnace is extremely hot, it is difficult to directly measure the trajectory of the HBI moving inside the furnace. Therefore, in this embodiment, a simulation for evaluating the trajectory of the HBI is performed. In order to evaluate the trajectory of the HBI when the HBI is charged from the raw material charging pipe 9 of the DC electric furnace 1, the following analysis was performed. The simulation is to be performed based on the method described in Turbulence Second Edition, HINZE, McGRAW-HILL, New York, 1975, p.460-462, and the outline thereof will be described below. The motion of a sphere in a fluid can be represented by the BBOT equation shown in the following equation (9). Here, v is the velocity of the particle, F D is the drag force, v f is the velocity of the fluid, and g is the acceleration due to gravity.

[0041] [Number]

[0042] Here, the densities of the particle and the fluid are ρ and ρ f respectively, the particle diameter is d, and the drag coefficient is C D respectively. Then, the coefficients C1, C2, and C3, and the drag force FD It is represented by the following formulas (10) and (11).

[0043]

Number

[0044] The second term on the right side of formula (9) is the total differential of the flow velocity. When expressed in another formula, it becomes the following formula (12).

[0045]

Number

[0046] Also, the viscosity of the hot metal 21 is 0.005 Pa·s, and the density is 7000 kg / m 3 , assuming the particle diameter is 5 cm and the fluid velocity range is from 0.05 to 1 m / s, the Reynolds number Re is about 420 to 84000. The drag coefficient C D in this region is about 0.4 to 0.5. Therefore, for HBI, the drag coefficient C D is 0.4, the diameter is 5 cm, the apparent density is 5500 kg / m 3 , the sphere, and the fluid is the hot metal 21 with a density of 7000 kg / m 3 . It was calculated that HBI floats near the surface of the hot metal 21 and does not move in the direction of the furnace bottom.

[0047] Also, the general size of HBI is about 30×50×130 mm. At this size, it is known that HBI dissolves in about 40 to 60 seconds for one HBI after being charged into the hot metal 21. The efficient dissolution of HBI in the DC electric furnace 1 means that the same dissolution rate as when one HBI is charged can be obtained. Therefore, it is preferable to make HBI reach the high-temperature region Rh within 40 seconds, which is the dissolution time, after the HBI is charged.

[0048] (Evaluation of the charging position and movement of HBI) FIG. 7 is a diagram for evaluating the HBI injection position Pr when the current value of the upper electrode 6 is 50 kA in the DC electric furnace 1 according to an embodiment of the present invention, in relation to the time taken for the HBI to reach the high-temperature region Rh and the residence time in the high-temperature region Rh. In FIG. 7, (a) is a diagram for evaluating the time taken for the HBI to reach the high-temperature region Rh within 40 seconds after injection, and (b) is a diagram for evaluating the residence time of the HBI in the high-temperature region Rh. In the figure, A indicates the region of the HBI injection position Pr that reaches the high-temperature region Rh within approximately 40 seconds after injection, and is assumed to be an ellipse.

[0049] As shown in (a), in the vicinity directly below the upper electrode 6, the time for the HBI to reach the high-temperature region Rh is short. This is presumably due to the HBI being drawn in in the region where the molten iron 21 forms a downward flow toward the furnace bottom. Also, as shown in (b), it can be seen that the region where the HBI stays in the high-temperature region Rh for a long time generally coincides with the region A of the HBI injection position Pr that reaches the high-temperature region Rh within approximately 40 seconds after injection. Region A is a range where the flow of the HBI is easily affected by the downward flow of the molten iron 21.

[0050] If the central coordinates on the lower end surfaces of the two upper electrodes 6 are (±x0, y0), the position (x, y) of region A on the xy coordinates is represented by the following equation (13). In this case, a = 1.7 and b = 1.2. The position (x, y) of the HBI injection position Pr on the xy coordinates is preferably the position represented by equation (13). (x ± x0) 2 / a 2 +(y - y0) 2 / b 2 = 1 ···(13)

[0051] FIG. 8 is a diagram for evaluating the HBI injection position Pr when the current value of the upper electrode 6 is 150 kA in the DC electric furnace 1 according to an embodiment of the present invention, in relation to the time taken for the HBI to reach the high-temperature region Rh and the residence time in the high-temperature region Rh. In FIG. 8, (a) is a diagram for evaluating the time taken for the HBI to reach the high-temperature region Rh within 40 seconds after injection, and (b) is a diagram for evaluating the residence time of the HBI in the high-temperature region Rh.

[0052] As shown in (a), in the vicinity directly below the upper electrode 6, the time for the HBI to reach the high-temperature region Rh is short. Also, as shown in (b), in region B of the injection position Pr of the HBI that reaches the high-temperature region Rh within approximately 40 seconds after injection, it can be seen that the HBI stays in the high-temperature region Rh for a long time. Region B is a range where the flow of the HBI is easily affected by the downward flow of the molten iron 21. Compared with region A in FIG. 7 where the current value of the upper electrode 6 is 50 kA, region B is a more extensive ellipse. When region B is expressed by formula (13), a = 2.2 and b = 2.6. From this, the values of a and b, that is, the range affected by the downward flow of the molten iron 21 in the furnace bottom direction, depend on the current value per upper electrode 6.

[0053] FIG. 9 is a graph showing the result of calculating the relationship between the current value per upper electrode 6 and a and b of formula (13). In FIG. 9, (a) shows the relationship between the current value per upper electrode 6 and a of formula (13), and (b) shows the relationship between the current value per upper electrode 6 and b of formula (13). As described above, the range affected by the downward flow of the molten iron 21 depends on the current value per upper electrode 6. In order to approximately represent the range affected by the downward flow of the molten iron 21, the current value of the upper electrode 6 was changed between 50 kA and 150 kA, and a and b of formula (13) were calculated. a and b were determined so that the HBI would move to the high-temperature region Rh within 40 seconds after injection.

[0054] From each of the graphs of (a) and (b), when the current value per upper electrode 6 is I (kA), the following approximate formulas (14) and (15) are obtained for a and b of formula (13). The units of a and b are m. a = 0.0045I + 1.475 ···(14) b = 0.019I - 0.257 ···(15)

[0055] As described above, in the DC electric furnace 1, by setting the charging position Pr of the HBI, which has a density smaller than that of the molten iron 21 and floats on the surface of the molten metal, to the regions A and B shown in formulas (13) to (15), the HBI can quickly reach the high-temperature region Rh. Also, since the installation position of the raw material charging pipe 9 is a part other than directly above the high-temperature region Rh, heat insulation in the furnace can be ensured, and damage to the raw material charging pipe 9 due to radiant heat damage can be suppressed. Therefore, the DC electric furnace 1 according to the present embodiment can more efficiently melt melting raw materials such as DRI and HBI, which have a density smaller than that of the molten iron 21 and are likely to float on the surface of the molten metal, in a short time.

[0056] As described above, the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings. However, the present invention is not limited to these examples. It is obvious that those skilled in the technical field to which the present invention pertains can conceive of various modification examples or correction examples within the scope of the technical idea described in the claims, and it is naturally understood that these also belong to the technical scope of the present invention.

Explanation of Reference Numerals

[0057] 1... DC electric furnace, 2... ceiling, 3... furnace wall copper panel, 4... furnace wall refractory, 5... furnace bottom refractory, 6... upper electrode, 7... furnace bottom electrode, 7a... furnace bottom cable, 9... raw material charging pipe, 20... arc, 21... molten iron, 22... electric furnace slag, A, B... regions, Pr... charging position, Rh... high-temperature region.

Claims

1. Two upper electrodes, a raw material input pipe provided on the side surface or the upper surface of the furnace body for introducing into the furnace a raw material containing a melting raw material having a density smaller than that of the molten iron, in a direct current electric furnace comprising: taking a plane including the surface of the molten iron as the xy plane, The positions on the xy coordinates of the intersection points of the vertical line passing through the center of the lower end surface of the upper electrode and perpendicular to the molten iron surface, and the molten iron surface are respectively (x ０ , y ０ ) and (-x ０ , y ０ ), and taking the radius of the upper electrode as r, when the current value per one of the upper electrodes is I (kA), The raw material input pipe is provided on the side surface or the upper surface of the furnace body other than directly above the high-temperature region where the position (x １ , y １ ) on the xy coordinates is represented by the following formulas (i) and (ii). a direct current electric furnace, wherein the position (x, y) on the xy coordinates of the point where the introduced melting raw material reaches the surface of the molten iron is represented by the following formulas (iii) to (v). (x １ ± x ０ ) ２ + (y １ - y ０ ) ２ < r ２ ・・・(i) -r < y １ < r, -x ０ < x １ < x ０ ... (ii) (x ± x ０ ) ２ / a ２ +(y - y ０ ) ２ / b ２ = 1 ··· (iii) a = 0.0045I + 1.475... (iv) b = 0.019I - 0.257... (v)

2. the raw material input pipe is provided inclined with respect to the surface of the molten iron, the direct current electric furnace according to Claim 1.

3. the raw material input pipe is provided perpendicular to the surface of the molten iron, the direct current electric furnace according to Claim 1.

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