Direct-current electrical melting furnace

Abstract

To provide a direct-current melting furnace capable of more sufficiently melting a melting raw material containing a raw material with density smaller than that of molten iron and easy to float to a molten metal surface, while restraining melting of metal on a furnace wall.SOLUTION: A direct-current electrical melting furnace according to the present invention comprises: a first upper electrode and a second upper electrode immersed with slag; and a raw material input pipe provided on a side face or an upper face of a furnace body and inputting a raw material containing a melting raw material with density smaller than that of molten iron into a furnace. A middle point of a straight line connecting the first upper electrode as a positive electrode and the second upper electrode as a negative electrode is matched with a furnace center. The distance R between the furnace center and the center of any of the first and second upper electrodes, the radius r of the upper electrode, and the inner radius d of the furnace on a surface of the iron metal satisfies a relationship of 0.05≤(R-r) / d≤0.18.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] In recent years, for CO2 emission reduction, the steelmaking process has been required to shift from the conventional blast furnace method to a method using an electric melting furnace with a lower carbon emission. However, in order to achieve the same molten steel production as the conventional blast furnace method, in addition to increasing the size of the furnace, it is necessary to use not only scrap but also direct reduced iron as raw materials. Therefore, it is important to efficiently melt direct reduced iron in a large electric melting furnace. Among electric melting furnaces, when the electrodes are immersed in the slag, it is considered that the melting efficiency of reduced iron is good because heat loss due to the radiant heat of the arc is prevented compared to the case where the electrodes are not immersed in the slag.

[0003] 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 (Direct Reduced Iron). Further, what is obtained by hot-compression molding DRI after the reduction treatment 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. Therefore, in order to more efficiently melt DRI and HBI floating on the surface of the molten metal, it is important to stir the molten iron. Non-Patent Document 1 discloses an electric melting furnace in which the electrodes of the anode and the cathode are immersed in the slag.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In order to efficiently melt the melting raw materials in a large electric melting furnace, it is necessary to disperse the melting raw materials over a wide range in the furnace. Therefore, how to stir the slag and molten iron by electromagnetic force becomes important. However, with the increase in the size of the electric melting furnace, the heating range by the electrodes becomes narrower with respect to the cross-sectional area of the furnace. Therefore, if the position of the electrodes is too close to the center of the furnace, problems such as a decrease in melting efficiency due to the localization of heat and stirring force will occur.

[0006] On the other hand, if the electrodes are installed close to the furnace wall to disperse the heating area by the electrodes, the metal coating that protects the furnace wall, which is important during continuous operation, will melt due to the stirring force generated near the furnace wall. Therefore, it is necessary to arrange the electrodes at an appropriate position. In a large electric melting furnace, a tapping volume of 300 tons per time is required, and for this purpose, a furnace diameter of about 18 m or more is required. The diameter of the electric melting furnace described in Non-Patent Document 1 is 8.4 m, and the capacity is small.

[0007] Therefore, an object of the present invention is to provide a direct current electric melting furnace that can more efficiently melt a melting raw material containing a raw material having a density smaller than that of molten iron and easily floating on the surface of the molten metal while suppressing the melting of the metal on the furnace wall.

Means for Solving the Problems

[0008] [1] In a direct current electric melting furnace comprising a first upper electrode and a second upper electrode immersed in slag, and a raw material charging pipe provided on a side surface or an upper surface of a furnace body for charging a raw material containing a melting raw material having a density smaller than that of molten iron into the furnace, a midpoint of a straight line connecting the first upper electrode, which is an anode, and the second upper electrode, which is a cathode, coincides with a furnace center, and a distance R between the furnace center and a center of either the first upper electrode or the second upper electrode, a radius r of the upper electrode, and an inner diameter d of the furnace at a molten iron surface satisfy 0.05 ≦ (R - r) / d ≦ 0.18 a direct current electric melting furnace satisfying the relation. [2] In a direct current electric melting furnace comprising a first upper electrode, a second upper electrode, a third upper electrode, and a fourth upper electrode immersed in slag, and a raw material charging pipe provided on a side surface or an upper surface of a furnace body for charging a raw material containing a melting raw material having a density smaller than that of molten iron into the furnace, the first upper electrode and the third upper electrode are anodes, the second upper electrode and the fourth upper electrode are cathodes, a shape formed by connecting centers of the respective electrodes in order of the first upper electrode, the second upper electrode, the third upper electrode, and the fourth upper electrode is a square, a straight line connecting the first upper electrode and the third upper electrode and a straight line connecting the second upper electrode and the fourth upper electrode intersect at the furnace center, and a distance R between the furnace center and a center of any one of the first upper electrode, the second upper electrode, the third upper electrode, or the fourth upper electrode, a radius r of the upper electrode, and an inner diameter d of the furnace at a molten iron surface satisfy 0.125 ≦ (R - r) / d ≦ 0.20 a direct current electric melting furnace satisfying the relation. [3] In a DC electric melting furnace comprising a first upper electrode, a second upper electrode, a third upper electrode, and a fourth upper electrode immersed in slag, and a raw material input pipe provided on the side surface or upper surface of the furnace body for charging into the furnace a raw material containing a melting raw material having a density smaller than that of molten iron, the first upper electrode and the second upper electrode are anodes, the third upper electrode and the fourth upper electrode are cathodes, and in the order of the first upper electrode, the second upper electrode, the third upper electrode, and the fourth upper electrode, the shape connecting the centers of the respective electrodes is a square, and the straight line connecting the first upper electrode and the third upper electrode and the straight line connecting the second upper electrode and the fourth upper electrode intersect at the furnace center. The distance R between the furnace center and the center of any one of the first upper electrode, the second upper electrode, the third upper electrode, or the fourth upper electrode, the radius r of the upper electrode, and the inner diameter d of the furnace at the molten iron surface satisfy 0.125 ≦ (R - r) / d ≦ 0.20 a DC electric melting furnace satisfying the relationship. [4] In a DC electric melting furnace comprising a first upper electrode, a second upper electrode, a third upper electrode, and a fourth upper electrode immersed in slag, and a raw material input pipe provided on the side surface or upper surface of the furnace body for charging into the furnace a raw material containing a melting raw material having a density smaller than that of molten iron, the first upper electrode is an anode provided at the furnace center, and the second upper electrode, the third upper electrode, and the fourth upper electrode are cathodes provided such that the shape connecting the centers of the respective electrodes is an equilateral triangle and the center of the equilateral triangle coincides with the furnace center. The distance R between the furnace center and the center of any one of the second upper electrode, the third upper electrode, or the fourth upper electrode, the radius r of the upper electrode, and the inner diameter d of the furnace at the molten iron surface satisfy 0.18 ≦ (R - r) / d ≦ 0.30 a DC electric melting furnace satisfying the relationship. [Advantages of the Invention]

[0009] According to the above configuration, by appropriately arranging the upper electrode, the Lorentz force acting on the slag and molten iron in a large DC electric melting furnace can be improved, and uniform melting can be performed by the stirring force acting on the slag and molten iron. Therefore, while suppressing the melting of the metal on the furnace wall, a melting raw material containing a raw material with a density smaller than that of the molten iron and likely to float on the molten metal surface can be melted more efficiently.

Brief Description of the Drawings

[0010]

Figure 1

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Figure 12

Embodiments 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 DC Electric Melting Furnace According to One Embodiment) FIG. 1 is a cross-sectional view showing the structure of a DC electric melting 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 surface of the molten iron 21 is defined as the xy plane, but the surface of the molten iron 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 melting 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 6a, 6b (hereinafter, also simply referred to as "upper electrode 6") are provided on the ceiling 2. The raw material input pipe 7 is provided on the side surface or the upper surface of the furnace body, and inputs raw materials including melting raw materials having a density smaller than that of the molten iron 21, such as at least DRI and HBI, into the furnace. In the following, the melting raw material having a density smaller than that of the molten iron 21 is assumed to be HBI, but it is not limited to HBI and may be a raw material such as DRI. The furnace bottom refractory 5 is provided with a tapping hole 8 for discharging the molten iron 21 and a slag tapping hole 9 for discharging the slag 20.

[0014] As the direct current electric melting 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 an iron source, one or two of iron-containing scrap and reduced iron are charged into the direct current electric melting 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.

[0015] The two upper electrodes 6a and 6b are immersed in the slag 20. It is assumed that the upper electrode 6a is the anode and the upper electrode 6b is the cathode. Between the upper electrodes 6a and 6b, current flows in the order of the slag 20, the molten iron 21, and the slag 20, and the melting raw material is melted by the resistance heat.

[0016] FIG. 2 is a cross-sectional view taken along line II-II of the direct current electric melting furnace 1 shown in FIG. 1. As shown in the figure, the direct current electric melting furnace 1 has a circular horizontal cross-section. Also, the midpoint of the straight line connecting the two upper electrodes 6a and 6b coincides with the furnace center C. Let the distance between the furnace center C and the center of either the upper electrode 6a or the upper electrode 6b be R, the radius of the upper electrodes 6a and 6b be r, the inner diameter of the furnace at the molten iron 21 surface be d, and the distance from the furnace center C to the surface of the upper electrodes 6a and 6b on the furnace center C side be a (=R - r).

[0017] FIG. 3 is a cross-sectional view showing the arrangement of the upper electrodes 6a, 6b, 6c, and 6d (hereinafter also simply referred to as "upper electrode 6") of the direct current electric melting furnace 1 according to the first modification of an embodiment of the present invention. As shown in the figure, the direct current electric melting furnace 1 has a circular horizontal cross-section. The upper electrode 6a and the upper electrode 6c are anodes, and the upper electrode 6b and the upper electrode 6d are cathodes. Also, they are arranged such that the shape formed by connecting the centers of the respective electrodes in the order of the upper electrode 6a, the upper electrode 6b, the upper electrode 6c, and the upper electrode 6d is a square. Further, the straight line connecting the upper electrode 6a and the upper electrode 6c and the straight line connecting the upper electrode 6b and the upper electrode 6d intersect at the furnace center C.

[0018] Here, although it is ideal to install the upper electrodes 6a, 6b, 6c, and 6d to form a square, a deviation of about the radius of the upper electrodes 6a, 6b, 6c, and 6d due to equipment constraints and a deviation of about ±5 degrees of the inner angles of the square are allowed and do not affect the effects of the present invention. Also, let the distance between the furnace center C and the center of any one of the upper electrodes 6a, 6b, 6c, and 6d be R, the radius of the upper electrodes 6a, 6b, 6c, and 6d be r, the inner diameter of the furnace at the molten iron surface 21 be d, and the distance from the furnace center C to the surface on the furnace center C side of the upper electrodes 6a and 6b be a (=R - r).

[0019] FIG. 4 is a cross-sectional view showing the arrangement of the upper electrodes 6a, 6b, 6c, and 6d (hereinafter also simply referred to as "upper electrode 6") of the DC electric melting furnace 1 according to the first modification of the embodiment of the present invention. As shown in the figure, the DC electric melting furnace 1 has a circular horizontal cross-section. The upper electrode 6a and the upper electrode 6b are anodes, and the upper electrode 6c and the upper electrode 6d are cathodes. Also, they are arranged such that the shape formed by connecting the centers of the respective electrodes in the order of the upper electrode 6a, the upper electrode 6b, the upper electrode 6c, and the upper electrode 6d becomes a square. Further, the straight line connecting the upper electrode 6a and the upper electrode 6c and the straight line connecting the upper electrode 6b and the upper electrode 6d intersect at the furnace center C.

[0020] Here, although it is ideal to install the upper electrodes 6a, 6b, 6c, and 6d to form a square, a deviation of about the radius of the upper electrodes 6a, 6b, 6c, and 6d due to equipment constraints and a deviation of about ±5 degrees of the inner angles of the square are allowed and do not affect the effects of the present invention. Also, let the distance between the furnace center C and the center of any one of the upper electrodes 6a, 6b, 6c, and 6d be R, the radius of the upper electrodes 6a, 6b, 6c, and 6d be r, the inner diameter of the furnace at the molten iron surface 21 be d, and the distance from the furnace center C to the surface on the furnace center C side of the upper electrodes 6a and 6b be a (=R - r).

[0021] FIG. 5 is a cross-sectional view showing the arrangement of the upper electrodes 6a, 6b, 6c, 6d (hereinafter also simply referred to as "upper electrode 6") of the first modified example of the direct-current electric melting furnace 1 according to an embodiment of the present invention. As shown in the figure, the direct-current electric melting furnace 1 has a circular horizontal cross-section. The upper electrode 6a is an anode provided at the furnace center C. The upper electrodes 6b, 6c, and 6d are cathodes provided such that the shape formed by connecting the centers of the respective electrodes is an equilateral triangle, and the center of the equilateral triangle coincides with the furnace center C.

[0022] Here, although it is ideal to install the upper electrodes 6b, 6c, 6d so as to form an equilateral triangle, a deviation of about the radius of the upper electrodes 6a, 6b, 6c, 6d due to equipment constraints, a deviation of about ±5 degrees in the interior angle of the equilateral triangle, and a deviation of about the electrode radius from the furnace center C at the center position of the upper electrode 6a which is the cathode are allowed and do not affect the effects of the present invention. Let the distance between the furnace center C and the center of any one of the upper electrodes 6b, 6c, 6d be R, the radius of the upper electrodes 6a, 6b, 6c, 6d be r, the inner diameter of the furnace at the molten iron 21 surface be d, and the distance from the furnace center C to the surface on the furnace center C side of the upper electrodes 6b, 6c, 6d be a (=R - r).

[0023] FIG. 6 is a cross-sectional view showing the arrangement of the upper electrode 91 of the electric melting furnace 90 according to the comparative example. The electric melting furnace 90 is an alternating-current electric melting furnace. As shown in the figure, the direct-current electric melting furnace 1 has a circular horizontal cross-section. Also, the three upper electrodes 91 are arranged such that the shape formed by connecting the centers of the respective upper electrodes 6 is an equilateral triangle, and a three-phase alternating current is supplied. Let the distance between the furnace center C and the center of any one of the upper electrodes 91 be R, the radius of the upper electrode 91 be r, the inner diameter of the furnace at the molten iron 21 surface be d, and the distance from the furnace center C to the surface on the furnace center C side of the upper electrode 91 be a (=R - r).

[0024] (Outline and conditions of simulation for evaluating heat flow in direct-current electric melting furnace) It is difficult to measure the temperature inside the furnace and the flow of the slag 20 and the molten iron 21. Therefore, in this embodiment, a simulation for evaluating the heat flow inside the DC electric melting furnace 1 is performed. The simulation is carried out 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.

[0025] In the simulation, 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. Assuming that the current density flowing through the slag 20, the molten iron 21, and the upper electrode 6 is i (A / m 2 ), the relationship between the magnetic vector potential A and the current density i is expressed as in Equation (1). Here, μ0 is the magnetic permeability of vacuum.

[0026]

Equation

[0027] 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 j is the conductivity (S / m) of the slag 20, the molten iron 21, or the upper electrode 6.

[0028]

Equation

[0029] Based on the current density distribution calculated from Equation (2), the magnetic vector potential A is calculated from Equation (1). Then, using the calculated magnetic vector potential A, the distribution of the magnetic flux density B (T) is calculated from Equation (3).

[0030] [Number]

[0031] Next, a method for 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 j is generated. Using the calculated Lorentz force F and Joule heat amount Q, fluid analysis and heat transfer analysis are performed. In fluid analysis, the flow of the fluid 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.

[0032] [Number]

[0033] Heat transfer analysis is performed using Equation (6), which is the governing equation for 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.

[0034] [Number]

[0035] By performing the electromagnetic field analysis, fluid analysis, and heat transfer analysis as described above, the temperature and flow velocity of the fluid can be obtained. In the simulation, electromagnetic field analysis was performed with the slag 20, molten iron 21, and upper electrode 6 present, and based on the results, fluid analysis and heat transfer analysis were performed for the slag 20 alone, which is the main heat source.

[0036] As an example, the calculation conditions in the simulation are as follows: the vertical thickness of the molten iron 21 is 700 mm, the thickness of the slag 20 is 500 mm, the conductivity of the molten iron 21 is 7.14×10 5 S / m, the conductivity of the slag 20 is 1.00×102 S / m, and the conductivity of the upper electrode 6 is 5.00×10 3 S / m. Also, the diameter of the upper electrode 6 is 1900 mm, the inner diameter of the furnace is 18000 mm and 22000 mm, and it is assumed that the upper electrode 6 is immersed 100 mm in the slag 20. A current is applied so that the total heat generation of the system is 60 MW, and based on the result of the electromagnetic field analysis, the initial temperature is set to 1873 K, and the thermal fluid calculation of the slag 20 up to t = 1000 s is performed. As the physical properties of the slag 20 during the thermal fluid calculation, the viscosity is 0.1 Pa·s, the density is 3000 kg / m 3 , the specific heat capacity is 600 J / kg / K, and the thermal conductivity is 20 W / m / K. As the boundary condition during the thermal fluid calculation, the surface in contact with the air is set as the slip condition with an ambient temperature of 300 K and a heat transfer coefficient of 300 W / m 2 , and the other surfaces are adiabatic and no-slip conditions.

[0037] Under the above simulation conditions, in each case of the arrangement of the upper electrode 6 in the DC electric melting furnace 1 of the embodiment shown in FIGS. 2 to 5 and the arrangement of the upper electrode 91 in the AC electric melting furnace 90 of the comparative example shown in FIG. 6, the distance from the center C to the surface of the upper electrodes 6a, 6b on the furnace center C side is changed to a, and the Lorentz force generated in the slag 20 and the molten iron 21 is calculated with the inner diameter d of the furnace.

[0038] Hereinafter, the arrangement of the upper electrode 91 in the AC electric melting furnace 90 of the comparative example shown in FIG. 6 is also referred to as "Case1", and the arrangements of the upper electrode 6 in the DC electric melting furnace 1 of the present embodiment shown in FIGS. 2 to 5 are also referred to as "Case2" to "Case5", respectively.

[0039] In the simulation, as an index of the stirring force acting on the slag 20 and the molten iron 21, the Lorentz force density (N / m 3) was evaluated for the total Lorentz force (N) integrated by volume. Also, for Case 2 to Case 5, under the conditions of the same furnace inner diameter d and the same total calorific value, the Lorentz force was shown as a ratio to the result of the AC electric melting furnace 90 (Case 1) which is a comparative example.

[0040] When a flow is generated in the slag 20 near the furnace wall, the melting of the metal (hereinafter also referred to as metal coating) is promoted by heat supply. The relationship between the melting rate v of the metal coating and the flow velocity u of the slag 20 is v = bu s using a constant b. It is known that the value of s is between 0.5 and 0.8.

[0041] From the results of numerical calculations, for any of the conditions of Case 1 to Case 5, the minimum value of the flow velocity of the slag 20 near the furnace wall is about 10 -4 m / s, and the lowest value of 0.5 is adopted as the value of s. At this time, if the flow velocity of the slag 20 is 0.05 m / s, the melting rate of the metal coating is about 20 times that of the part where the flow velocity of the slag 20 is the lowest.

[0042] Table 1 below shows the results of evaluating the Lorentz forces generated in the slag 20 and the molten iron 21 by changing the distance a and the furnace inner diameter d in each of the cases of Case 1 to Case 5. "Electrode arrangement" shows one of FIGS. 2 to 5 regarding the arrangement of the upper electrodes 6. "Furnace diameter" is the inner diameter d of the furnace, the furnace diameters of case 1 to Case 5 are 18000 mm, and the furnace diameters of case 1´ to Case 5´ are 22000 mm. "Distance a from the furnace center to the electrode surface" is the distance a from the furnace center C to the surface on the furnace center C side of the upper electrodes 6a, 6b, and "Ratio of distance a to furnace diameter" is the ratio of the distance a to the inner diameter d of the furnace. Also, "Total Lorentz force" is the Lorentz force acting on the slag 20 and the molten iron 21, and "Ratio of Lorentz force to AC furnace" is the ratio of the Lorentz force to the AC electric melting furnace 90 (case 1) according to the comparative example.

[0043] "Metal coating dissolution" in Table 1 evaluates the metal coating resistance of the furnace wall. When non-uniform dissolution of the metal coating occurs, the surface area of the part where the metal coating contacts the slag 20 increases due to dissolution, promoting further dissolution. Therefore, when the time-averaged flow velocity in the region within 50 cm from the furnace wall is 0.05 m / s or more on the lower surface of the slag 20, it is determined that the metal coating resistance dissolution is poor. Also, for the "evaluation", when the total Lorentz force increases compared to the case of the alternating current electric melting furnace 90 according to the comparative example (Case 1), and the metal coating resistance dissolution is good, the evaluation is marked as "〇".

[0044] As shown in Table 1, in the direct current electric melting furnace 1 according to the present embodiment (Case 2 to Case 5), by appropriately arranging the upper electrode 6, it can be seen that a stronger stirring force can be obtained compared to the case of the alternating current electric melting furnace 90 according to the comparative example (Case 1). On the other hand, it can be seen that when the upper electrode 6 is too close to the furnace wall, the metal coating resistance dissolution tends to be poor.

[0045]

Table 1

[0046] Figures 7 to 10 are graphs showing the results of numerically evaluating the relationship between the distance between the furnace center C and the upper electrode 6 and the Lorentz force generated in the slag 20 and the molten iron 21 in the direct current electric melting furnace 1 according to the present invention. Figure 7 is for Case 2, Figure 8 is for Case 3, Figure 9 is for Case 4, and Figure 10 is a graph plotting the results of Table 1 for each of the cases of Case 5. The horizontal axis represents the ratio of the distance a from the furnace center C to the surface on the furnace center C side of the upper electrodes 6a, 6b to the inner diameter d of the furnace. The vertical axis represents the ratio of the Lorentz force to that in the case of the alternating current electric melting furnace 90 according to the comparative example (Case 1). The broken line in the figure indicates the range where the evaluation is "〇" on the horizontal axis.

[0047] From the results shown in each figure, it can be seen that when the upper electrode 6 is too close to or too far from the furnace center C, the stirring force tends to weaken. On the other hand, as shown in Fig. 9, in the case of Case4, it can be seen that the stirring force increases as the upper electrode 6 approaches the furnace center C. Also, in Case4-a, as shown in Table 1 and Fig. 11(e), it can be seen that a flow of slag 20 occurred near the furnace wall.

[0048] According to the results of case2 shown in Fig. 7, when the ratio of the horizontal axis "distance a to the inner diameter d of the furnace" is 0.05 or more and 0.18 or less, the "evaluation" is ○. Therefore, when the upper electrode 6 is arranged as shown in Fig. 2, the distance R between the furnace center C and the center of either the upper electrode 6a or the upper electrode 6b, the radius r of the upper electrode 6, and the inner diameter d of the furnace at the molten iron 21 surface are 0.05 ≦ (R - r) / d ≦ 0.18 It is preferable to satisfy the relationship of. In this case, since the total Lorentz force increases and the refractory metal coating dissolution is good, while suppressing the dissolution of the base metal on the furnace wall, uniform dissolution can be performed by the stirring force acting on the slag 20 and the molten iron 21.

[0049] According to the results of case3 shown in Fig. 8, when the ratio of the horizontal axis "distance a to the inner diameter d of the furnace" is 0.125 or more and 0.20 or less, the "evaluation" is ○. Therefore, when the upper electrode 6 is arranged as shown in Fig. 3, the distance R between the furnace center C and the center of any of the upper electrodes 6a, 6b, 6c, 6d, the radius r of the upper electrode 6, and the inner diameter d of the furnace at the molten iron 21 surface are 0.125 ≦ (R - r) / d ≦ 0.20 It is preferable to satisfy the relationship of. In this case, since the total Lorentz force increases and the refractory metal coating dissolution is good, while suppressing the dissolution of the base metal on the furnace wall, uniform dissolution can be performed by the stirring force acting on the slag 20 and the molten iron 21.

[0050] According to the results of case 4 shown in Fig. 9, when the ratio of the "distance a to the inner diameter d of the furnace" on the horizontal axis is 0.125 or more and 0.20 or less, the "evaluation" is ○. Therefore, when the upper electrode 6 is arranged as shown in Fig. 4, the distance R between the furnace center C and the center of any one of the upper electrodes 6a, 6b, 6c, 6d, the radius r of the upper electrode 6, and the inner diameter d of the furnace at the molten iron surface 21 are 0.125 ≦ (R - r) / d ≦ 0.20 It is preferable to satisfy the relationship. In this case, since the total Lorentz force increases and the dissolution of the refractory metal coating is good, uniform dissolution can be performed by the stirring force acting on the slag 20 and the molten iron 21 while suppressing the dissolution of the base metal on the furnace wall.

[0051] According to the results of case 4 shown in Fig. 10, when the ratio of the "distance a to the inner diameter d of the furnace" on the horizontal axis is 0.18 or more and 0.30 or less, the "evaluation" is ○. Therefore, when the upper electrode 6 is arranged as shown in Fig. 5, the distance R between the furnace center C and the center of any one of the upper electrodes 6b, 6c, 6d, the radius r of the upper electrode 6, and the inner diameter d of the furnace at the molten iron surface 21 are 0.18 ≦ (R - r) / d ≦ 0.30 It is preferable to satisfy the relationship. In this case, since the total Lorentz force increases and the dissolution of the refractory metal coating is good, uniform dissolution can be performed by the stirring force acting on the slag 20 and the molten iron 21 while suppressing the dissolution of the base metal on the furnace wall.

[0052] Fig. 11 is a diagram showing the flow velocity distribution on the lower surface of the slag 20 simulated in the DC electric melting furnace 1 according to the present invention. In Fig. 11, (a) to (h) have a furnace diameter of 18000 mm, and show the flow velocity distribution on the lower surface of the slag 20 in the cases of case 2-a, case 2-d, case 3-a, case 3-c, case 4-a, case 4-c, case 5-a, and case 5-c shown in Table 1, respectively.

[0053] Each case has a furnace diameter of 18000 mm. Specifically, Case 2-a (electrode configuration: Figure 2, ratio of distance a to the inner diameter d of the furnace: 0.053, Lorentz force ratio to the AC furnace: 100.5%) Case 2-d (electrode configuration: Figure 2, ratio of distance a to the inner diameter d of the furnace: 0.331, Lorentz force ratio to the AC furnace: 91.1%) Case 3-a (electrode configuration: Figure 3, ratio of distance a to the inner diameter d of the furnace: 0.108, Lorentz force ratio to the AC furnace: 97.3%) Case 3-c (electrode configuration: Figure 3, ratio of distance a to the inner diameter d of the furnace: 0.281, Lorentz force ratio to the AC furnace: 95.6%) Case 4-a (electrode configuration: Figure 4, ratio of distance a to the inner diameter d of the furnace: 0.108, Lorentz force ratio to the AC furnace: 103.0%) Case 4-c (electrode configuration: Figure 4, ratio of distance a to the inner diameter d of the furnace: 0.281, Lorentz force ratio to the AC furnace: 92.2%) Case 5-a (electrode configuration: Figure 5, ratio of distance a to the inner diameter d of the furnace: 0.164, Lorentz force ratio to the AC furnace: 99.2%) and Case 5-c (electrode configuration: Figure 5, ratio of distance a to the inner diameter d of the furnace: 0.331, Lorentz force ratio to the AC furnace: 113.0%) are as follows.

[0054] As shown in the figure, it can be seen that the flow of the molten iron 21 is generated by the electromagnetic force acting on the upper electrode 6. Also, due to the arrangement of the upper electrode 6, the flow pattern of the slag 20 is different. More specifically, in (a), (c), and (g) where the upper electrode 6 is arranged at a position relatively close to the furnace center C, since the flow of the slag 20 is localized, it can be said that the melting efficiency of the slag 20 is not good. On the other hand, in (b), (d), (f), and (h) where the upper electrode 6 is arranged relatively close to the furnace wall side, since the flow of the slag 20 occurs in the region close to the furnace wall, it can be said that it is not a good condition from the viewpoint of refractory metal coating melting. Furthermore, in the case of (e) which is Case 4-a, although the upper electrode 6 is arranged at a position relatively close to the furnace center C, it can be seen that the flow of the slag 20 also occurs in the region close to the furnace wall.

[0055] FIG. 12 is a diagram showing the temperature distribution of the slag 20 simulated in the DC electric melting furnace 1 according to the present invention. In FIG. 12, (a) to (h) respectively show the temperature distribution of the lower surface of the slag 20 at t = 1000 seconds in the cases of case2-a, case2-c, case3-a, case3-c, case4-a, case4-c, case5-a, and case5-c shown in Table 1.

[0056] For each case, the furnace diameter is 18000 mm. Specifically, case2-a, case3-a, case3-c, case4-a, case4-c, case5-a, and case5-c are the same as those in FIG. 11. case2-c (electrode arrangement: FIG. 2, ratio of distance a to inner diameter d of the furnace: 0.200, ratio of Lorentz force to AC furnace: 99.0%) and so on.

[0057] As shown in the figure, it can be seen that the slag 20 is heated by the resistance heat acting on the upper electrode 6. Also, due to the arrangement of the upper electrode 6, the heat distribution of the slag 20 is different. In (b), (d), (f), and (h) where the upper electrode 6 is arranged relatively close to the furnace wall, the heat distribution is uniform. However, as shown in FIG. 11, since the flow of the slag 20 occurs in the region close to the furnace wall, it can be said that this is not a good condition from the viewpoint of metal coating melting.

[0058] Hereinafter, it is evaluated how much the immersion depth of the upper electrode 6 into the slag 20 and the diameter of the upper electrode 6 affect the Lorentz force. Table 2 shows the results of evaluating the Lorentz force by changing the immersion depth and diameter of the upper electrode 6 in the case of case2'-c in Table 1. The immersion depth is changed with reference to 100 mm as 0 mm, 200 mm, 300 mm, and 400 mm, and the diameter of the upper electrode 6 is changed with reference to 1900 mm as 1800 mm and 2000 mm.

[0059] As shown in Table 2, when only the diameter of the upper electrode 6 is changed, no influence on the Lorentz force is observed. On the other hand, when the upper electrode 6 is immersed deeper by the slag 20, it can be seen that the stirring force acting on the slag 20 and the molten iron 21 increases. In each case shown in Table 1, the immersion depth is as shallow as 100 mm. In actual operation, the upper electrode 6 is temporarily separated from the slag 20 only when the melting raw material and the upper electrode 6 are short-circuited. Therefore, there is no influence on the Lorentz force due to the difference in immersion depth in actual operation.

[0060]

Table 2

[0061] Also, hereinafter, when the arrangement of the upper electrode 6 is displaced in the horizontal direction, it is evaluated how much it affects the Lorentz force. Table 3 shows the results when the arrangement of the upper electrode 6 is displaced in the horizontal direction in case 5-b. As described above, in case 5-b, as shown in FIG. 5, the upper electrode 6a is an anode provided at the furnace center C, and the upper electrodes 6b, 6c, 6d are arranged such that the shape connecting the centers of the respective electrodes is an equilateral triangle, and the center of the equilateral triangle coincides with the furnace center C. It is a negative electrode arrangement.

[0062] In case 5'-b' shown in Table 3, one of the three upper electrodes 6b, 6c, 6d is displaced on the circumference of a circle formed so as to enclose the three upper electrodes 6, and the upper electrodes 6b, 6c, 6d are each connected to the center of the electrode. This is the evaluation result when the interior angles of each vertex of the triangle-shaped shape are 65°, 55°, and 60°, respectively. As shown in the table, it can be seen that even when the arrangement of the upper electrode 6 is displaced in the horizontal direction, the total Lorentz force is substantially the same as when the arrangement of the upper electrode 6 is not displaced. From this result, it can be seen that even if the upper electrode 6 is arranged somewhat unevenly, it has no influence on the Lorentz force.

[0063]

Table 3

[0064] As described above, in the DC electric melting furnace 1, when the distance R between the furnace center C and the center of either the upper electrode 6a or the upper electrode 6b, the radius r of the upper electrode 6, and the inner diameter d of the furnace at the molten iron surface 21 are considered, if the range of (R - r) / d is appropriate, the total Lorentz force increases and it can be said that the metal coating melting is good. From this, while suppressing the melting of the base metal of the furnace wall, uniform melting can be performed by the stirring force acting on the slag 20 and the molten iron 21. Therefore, the DC electric melting furnace 1 can more efficiently melt the melting raw material containing a raw material having a density smaller than that of the molten iron 21 and likely to float on the molten iron surface while suppressing the melting of the base metal of the furnace wall.

[0065] 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

[0066] 1... DC electric melting furnace, 2... ceiling, 3... furnace wall copper panel, 4... furnace wall refractory, 5... furnace bottom refractory, 6a, 6b, 6c, 6d... upper electrodes, 7... raw material input pipe, 8... tapping hole, 9... slag discharge hole, 20... slag, 21... molten iron, C... furnace center.

Claims

1. A first upper electrode and a second upper electrode immersed in slag, A raw material input pipe provided on the side or upper surface of the furnace body for charging a raw material containing a melting raw material having a density smaller than that of molten iron into the furnace, In a direct current electric melting furnace comprising: The midpoint of the straight line connecting the first upper electrode, which is the anode, and the second upper electrode, which is the cathode, coincides with the furnace center, The distance R between the furnace center and the center of either the first upper electrode or the second upper electrode, the radius r of the upper electrode, and the inner diameter d of the furnace at the molten iron surface satisfy 0.05 ≤ (R - r) / d ≤ 0.18 A direct current electric melting furnace satisfying the above relationship.

2. A first upper electrode, a second upper electrode, a third upper electrode, and a fourth upper electrode immersed in slag, A raw material input pipe provided on the side or upper surface of the furnace body for charging a raw material containing a melting raw material having a density smaller than that of molten iron into the furnace, In a direct current electric melting furnace comprising: The first upper electrode and the third upper electrode are anodes, The second upper electrode and the fourth upper electrode are cathodes, In the order of the first upper electrode, the second upper electrode, the third upper electrode, and the fourth upper electrode, the shape formed by connecting the centers of the respective electrodes is a square, and The straight line connecting the first upper electrode and the third upper electrode and the straight line connecting the second upper electrode and the fourth upper electrode intersect at the furnace center, The distance R between the furnace center and the center of any one of the first upper electrode, the second upper electrode, the third upper electrode, or the fourth upper electrode, the radius r of the upper electrode, and the inner diameter d of the furnace at the molten iron surface satisfy 0.125 ≤ (R - r) / d ≤ 0.20 A direct current electric melting furnace satisfying the above relationship.

3. A first upper electrode, a second upper electrode, a third upper electrode, and a fourth upper electrode immersed in slag, A raw material input pipe provided on the side or upper surface of the furnace body for charging a raw material containing a melting raw material having a density smaller than that of molten iron into the furnace, In a direct current electric melting furnace comprising: The first upper electrode and the second upper electrode are anodes, The third upper electrode and the fourth upper electrode are cathodes, In the order of the first upper electrode, the second upper electrode, the third upper electrode, and the fourth upper electrode, the shape formed by connecting the centers of the respective electrodes is a square, and The straight line connecting the first upper electrode and the third upper electrode and the straight line connecting the second upper electrode and the fourth upper electrode intersect at the furnace center, The distance R between the furnace center and the center of any one of the first upper electrode, the second upper electrode, the third upper electrode, or the fourth upper electrode, the radius r of the upper electrode, and the inner diameter d of the furnace at the molten iron surface are 0.125 ≤ (R - r) / d ≤ 0.20 A DC electric melting furnace that satisfies the relationship. **Claim 4** The first upper electrode, the second upper electrode, the third upper electrode, and the fourth upper electrode immersed in the slag, A raw material input pipe provided on the side surface or the upper surface of the furnace body for charging into the furnace a raw material containing a melting raw material having a density smaller than that of the molten iron, In a DC electric melting furnace comprising: The first upper electrode is an anode provided at the furnace center, The second upper electrode, the third upper electrode, and the fourth upper electrode are cathodes provided such that the shape formed by connecting the centers of the respective electrodes is an equilateral triangle and the center of the equilateral triangle coincides with the furnace center, The distance R between the furnace center and the center of any one of the second upper electrode, the third upper electrode, or the fourth upper electrode, the radius r of the upper electrode, and the inner diameter d of the furnace at the molten iron surface are 0.18 ≤ (R - r) / d ≤ 0.30 A DC electric melting furnace that satisfies the relationship.

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