DC arc furnace, and method for dissolving an iron source containing reduced iron using a DC arc furnace.

Abstract

To provide a technique for efficiently dissolving an iron source comprising reduced iron when the iron source is dissolved using a DC arc furnace.SOLUTION: A method for melting an iron source comprising reduced iron using a DC arc furnace comprises: a supply step for supplying the iron source from a supply port into the melting furnace; and a melting step for melting the iron source by generating an arc between an upper electrode and a lower electrode arranged in the melting furnace. The arc is generated between the upper electrode and the lower electrode to generate a downward flow between the upper electrode and the lower electrode for molten iron in the melting furnace, a central flow toward the downward flow is generated on the hot water surface of the molten iron, and the iron source is supplied to the central flow generated on the hot water surface to move toward the downward flow while floating the iron source on the hot water surface.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This application discloses a DC arc furnace and a method for dissolving an iron source containing reduced iron using a DC arc furnace. [Background technology]

[0002] Patent Document 1 discloses a technology for using combustible waste as a heat source when melting and refining scrap using an electric furnace. Patent Document 2 discloses a DC electric furnace for melting and refining scrap by continuously feeding it, wherein a continuous scrap loading inlet is provided in the center of the furnace at an intermediate position between the upper electrodes. Patent Document 3 discloses a furnace body structure for an electric furnace in which the ratio H / D of the molten metal depth (bath depth) H to the molten metal surface diameter (furnace diameter) D is 0.3 or more and 0.45 or less, and discloses a technology for stirring the molten metal at a predetermined flow rate by bottom blowing in the electric furnace. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2004-323873 [Patent Document 2] Japanese Patent Application Publication No. 7-133985 [Patent Document 3] Japanese Patent Application Publication No. 3-274383 [Overview of the project] [Problems that the invention aims to solve]

[0004] When melting and refining iron sources in electric furnaces, iron sources containing reduced iron are sometimes used. In this case, reduced iron has a lower bulk density than molten iron in the electric furnace and floats to the surface of the molten iron. Reduced iron that floats to the surface has a lower heat transfer rate from the molten iron compared to scrap that settles in the molten iron, resulting in a longer melting time. Conventionally, this problem has not been sufficiently studied.

[0005] This application discloses a technique for efficiently melting an iron source containing reduced iron using a DC arc furnace.

Means for Solving the Problems

[0006] As means for solving the above problems, this application discloses the following multiple aspects. (Aspect 1) A method for melting an iron source containing reduced iron using a DC arc furnace, comprising: a supply step of supplying the iron source into the melting furnace from a supply port; and a melting step of generating an arc between an upper electrode and a lower electrode provided in the melting furnace to melt the iron source. Generating the arc between the upper electrode and the lower electrode to generate a downward flow in the molten iron in the melting furnace, generating a central flow toward the downward flow on the surface of the molten iron, and supplying the iron source to the central flow generated on the surface of the molten iron to float the iron source on the surface of the molten iron and move it toward the downward flow. Method. [[ID=XX]](Aspect 2)[[ID=XX]] [[ID=XX]]The method of supplying the iron source is at least one of a method of supplying the iron source through a hole provided in the furnace inner wall or the furnace lid and a method of supplying the iron source by a raw material input chute. [[ID=XX]] [[ID=XX]]The method of Aspect 1. [[ID=XX]] [[ID=XX]](Aspect 3)[[ID=XX]] [[ID=XX]]The arc cross-sectional area S represented by the following formulas (1) to (3) [[ID=XX]] arc [[ID=XX]]is such that power is supplied to the upper electrode and the lower electrode so as to be smaller than the area where the lower electrode contacts the molten iron. [[ID=XX]] [[ID=XX]]The method of Aspect 1 or 2. [[ID=XX]] [[ID=XX]]S [[ID=XX]] arc [[ID=XX]]= πR [[ID=XX]] 2 [[ID=XX]] arc [[ID=XX]]…(1) [[ID=XX]] [[ID=XX]]R [[ID=XX]] arc [[ID=XX]]= R [[ID=XX]] c [[ID=XX]](3.2 - 2.2exp(-z / (5R [[ID=XX]] c [[ID=XX]]))) …(2) [[ID=XX]] [[ID=XX]]R [[ID=XX]] c [[ID=XX]]= (I / (πj [[ID=XX]] c It should be noted that in the original text, there seems to be some formatting or content issues in the formula part (e.g., incomplete expressions). The translation is based on the best understanding of the overall text structure and the provided rules. If there are specific requirements or corrections regarding the formula content, further adjustments may be needed.)) 0.5 …(3) R arc : The radius of the arc at the point in contact with the molten iron (cm) R c : The radius of the arc at the point of contact with the upper electrode (cm) z: Distance (cm) between the upper electrode and the surface of the molten iron I: Current value (kA) j c : Current density of the arc at the point of contact with the upper electrode (kA / cm²) 2 ) (Aspect 4) The depth H of the melting furnace, the furnace diameter D, the distance R from the position between the upper and lower electrodes on the surface of the molten iron to the position where the iron source is supplied, and the furnace radius R0 of the melting furnace satisfy the following relationship (4): Any of the methods described in 1 to 3. R / R0 < 1.24 (H / D) 0.75 …(4) (Appendix 5) A supply port that provides an iron source containing reduced iron, A melting furnace that melts the iron source by generating an arc between the upper electrode and the lower electrode, A power supply unit that supplies power to the upper electrode and the lower electrode, The system includes a control unit that controls either or both of the following: the power supplied from the power supply unit to the upper electrode and the lower electrode, and the supply position of the iron source supplied from the supply port to the molten metal surface in the melting furnace. The control unit is configured to control either or both of the power and the supply position to generate the arc between the upper electrode and the lower electrode, thereby generating a downward flow between the upper electrode and the lower electrode in the molten iron in the melting furnace, generating a central flow toward the downward flow on the surface of the molten iron, and moving the iron source supplied to the central flow generated on the surface of the molten iron toward the downward flow while floating on the surface of the molten iron. DC arc furnace. (Aspect 6) The method of supplying the iron source is at least one of the following: supplying the iron source through a hole provided in the inner wall or lid of the furnace, and supplying the iron source by a raw material input chute. A DC arc furnace according to embodiment 5. (Aspect 7) The control unit controls the arc cross-sectional area S, which is represented by the following equations (1) to (3). arc However, the power is controlled such that the area of ​​the lower electrode in contact with the molten iron is smaller than the area of ​​the lower electrode in contact with the molten iron. A DC arc furnace according to embodiment 5 or 6. S arc = πR 2 arc …(1) R arc = R c (3.2-2.2exp(-z / (5R c ))) …(2) R c = (I / (πj c )) 0.5 …(3) R arc : The radius of the arc at the point in contact with the molten iron (cm) R c : The radius of the arc at the point of contact with the upper electrode (cm) z: Distance (cm) between the upper electrode and the surface of the molten iron I: Current value (kA) j c : Current density of the arc at the point of contact with the upper electrode (kA / cm²) 2 ) (Pattern 8) The depth H of the melting furnace, the furnace diameter D, the distance R from the position between the upper and lower electrodes on the surface of the molten iron to the position where the iron source is supplied, and the furnace radius R0 of the melting furnace satisfy the following relationship (4): A DC arc furnace according to any of embodiments 5 to 7. R / R0 < 1.24 (H / D) 0.75 …(4) (Aspect 9) A supply port that provides an iron source containing reduced iron, A melting furnace that melts the iron source by generating an arc between the upper electrode and the lower electrode, The system includes a power supply unit that supplies power to the upper electrode and the lower electrode, The depth H of the melting furnace, the furnace diameter D, the distance R from the position between the upper and lower electrodes on the surface of the molten iron to the position where the iron source is supplied, and the furnace radius R0 of the melting furnace satisfy the following relationship (4): DC arc furnace. R / R0 < 1.24 (H / D) 0.75 …(4) [Effects of the Invention]

[0007] According to the technology disclosed herein, an iron source containing reduced iron can be efficiently melted using a DC arc furnace. [Brief explanation of the drawing]

[0008] [Figure 1] This diagram schematically shows the configuration of a DC arc furnace according to one embodiment. It primarily shows the internal configuration of the melting furnace. [Figure 2] This diagram outlines one example of a method for supplying iron sources. [Figure 3] This is a schematic diagram illustrating the furnace diameter D, furnace radius R0, and the distance R from the position O between the upper and lower electrodes on the molten iron surface to the position P where the iron source is supplied. [Figure 4] This is a schematic diagram illustrating the depth H of the melting furnace bath and the diameter D of the furnace. [Figure 5] This diagram schematically illustrates the mechanism by which a downward flow occurs between the upper and lower electrodes. (A) shows the electromagnetic force acting on the molten iron, and (B) shows the flow caused by the electromagnetic force. [Figure 6] The results of numerical simulation 1 are shown. (A) shows the case where reduced iron moves towards the upper electrode, and (B) shows the case where reduced iron moves towards the furnace wall. [Figure 7] This diagram schematically illustrates the movement of reduced iron supplied to the molten steel surface. It is based on the results of numerical simulation 1. [Figure 8] This shows the results of Numerical Simulation 2. The vertical axis is R / R0 and the horizontal axis is H / D, with the results of Numerical Simulation 2 ("○" or "×") plotted. [Figure 9] This shows the results of Numerical Simulation 2. The vertical axis is R / R0 and the horizontal axis is H / D, with the results of Numerical Simulation 2 ("○" or "×") plotted. [Figure 10] This shows the results of numerical simulation 2, which confirms the flow velocity distribution of molten steel when the power supplied to the electrodes in a DC arc furnace is changed. [Modes for carrying out the invention]

[0009] 1. DC arc furnace (first embodiment) A DC arc furnace according to the first embodiment of the present disclosure includes a supply port for supplying an iron source containing reduced iron, a melting furnace for generating an arc between an upper electrode and a lower electrode to melt the iron source, a power supply unit for supplying power to the upper electrode and the lower electrode, and a control unit for controlling one or both of the power supplied from the power supply unit to the upper electrode and the lower electrode, and the supply position of the iron source supplied from the supply port to the molten surface in the melting furnace. The DC arc furnace according to the present disclosure is configured such that the control unit controls one or both of the power and the supply position to generate the arc between the upper electrode and the lower electrode, thereby generating a downward flow between the upper electrode and the lower electrode of the molten iron in the melting furnace, generating a central flow toward the downward flow on the surface of the molten iron, and moving the iron source supplied to the central flow generated on the surface of the molten iron toward the downward flow while floating on the surface of the molten iron. The configuration of the DC arc furnace of this disclosure will be described below with reference to the drawings, but the configuration of the DC arc furnace of this disclosure is not limited to the illustrated form.

[0010] As shown in Figure 1, a DC arc furnace 100 according to one embodiment comprises a supply port 10, a melting furnace 20, a power supply unit 30, and a control unit 40. The melting furnace 20 is provided with an upper electrode 21 and a lower electrode 22, and an arc 23 is generated between the electrodes when power is supplied from the power supply unit 30 to the upper electrode 21 and the lower electrode 22. This allows the iron source 5a supplied from the supply port 10 into the melting furnace 20 to melt. Specifically, the iron source 5a is supplied to a predetermined position P on the molten iron surface 5bx of the molten iron 5b. Figure 1 illustrates a configuration in which the power supplied from the power supply unit 30 to the upper electrode 21 and the lower electrode 22 is controlled by the control unit 40, but the control unit 40 may control the supply position P of the iron source 5a supplied from the supply port 10 to the molten iron surface 5bx in the melting furnace 20, or it may control both the power and the supply position P. The iron source 5a supplied to position P floats on the molten surface 5bx and, carried by the central flow described later, moves toward the downward flow directly below the upper electrode 21, that is, gradually approaches position O directly below the upper electrode 21, and eventually melts. The melted iron source 5a forms part of the molten iron 5b in the melting furnace 20.

[0011] 1.1 Iron Source The DC arc furnace 100 of this disclosure can efficiently melt an iron source 5a containing reduced iron. Reduced iron may be obtained, for example, by reducing iron ore using hydrogen, natural gas, or coal. Reduced iron may contain iron oxide, carbon, silicon dioxide, etc. The chemical composition of reduced iron is not particularly limited, but may, for example, contain Fe: 85-100 mass% and C: 0-8 mass%. Whether or not the iron source 5a contains reduced iron can be easily determined by elemental analysis, density measurement, morphological observation, etc. The iron source 5a containing reduced iron has a lower bulk density than the molten iron 5b and floats on the surface of the molten iron 5b. The bulk density of the iron source 5a is, for example, 6500 kg / m³. 3 The following or 6000 kg / m 3The following is also possible: The shape of the iron source 5a is limited to a shape that can be supplied from the supply port 10 to the surface of the molten iron 5b in the melting furnace 20, and may be in various shapes such as powder, granules, or lumps. The shape of the iron source 5a may be, for example, a rectangular parallelepiped or a sphere.

[0012] The iron source 5a may contain components other than reduced iron. Furthermore, scrap metal may be used as the iron source 5a along with reduced iron. When the iron source 5a contains both reduced iron and scrap metal, the reduced iron floats on the molten iron surface 5bx, while the scrap metal may settle in the molten iron 5b. Compared to scrap metal settling in the molten iron 5b, the reduced iron floating on the molten iron surface 5bx receives less heat from the molten iron 5b, resulting in a longer melting time. To solve this problem, in the DC arc furnace 100 of this disclosure, the reduced iron floating on the molten iron surface 5bx is carried by the central flow generated on the molten iron surface 5bx, bringing it closer to position O directly below the upper electrode 21. As it approaches position O, it gets closer to the arc, and the amount of heat transferred to the reduced iron increases, allowing the reduced iron to melt in a short time.

[0013] 1.2 Supply port The supply port 10 is an inlet for supplying the iron source 5a containing reduced iron into the melting furnace 20. The supply port 10 may be located anywhere in the furnace. For example, the supply port 10 may be a hole in the inner wall (side wall) of the furnace, or a hole in the furnace lid. From the viewpoint of supplying the iron source 5a to the surface of the molten iron 5b more easily, it is preferable that the supply port 10 be located above the surface of the molten iron 5b. There may be one supply port 10 or multiple supply ports. The shape, size, orientation, position, and number of supply ports 10 may be determined according to the range of the central flow generated on the surface of the molten iron 5b.

[0014] In the DC arc furnace 100, various methods can be employed for supplying the iron source 5a from the supply port 10. Examples of methods for supplying the iron source 5a include, for example, supplying the iron source 5a through a hole provided in the furnace wall or furnace lid, and supplying the iron source 5a through a raw material input chute. Specifically, examples include supplying the iron source 5a through a hole provided in the furnace wall as shown in Figure 2(A), and supplying the iron source 5a through a hole provided in the furnace lid as shown in Figure 2(B). A raw material input chute or the like may be appropriately adopted depending on the positional relationship between the hole provided in the furnace wall or furnace lid and the supply position P of the iron source 5a at the molten metal surface 5bx. Any known raw material input chute may be used. The iron source 5a may be supplied vertically downward from the supply port 10, or diagonally downward from the supply port 10. In any case, the iron source 5a is preferably supplied directly to position P on the surface of the molten iron 5b where the central flow is occurring. Specifically, the iron source 5a is preferably dropped into position P. If the iron source 5a floating on the surface is located outside the central flow, it is also possible to move the iron source 5a to position P where the central flow is occurring by imparting kinetic energy to it, such as by blowing upward-blowing gas onto it.

[0015] 1.3 Melting furnace The melting furnace 20 is a part that can be defined by the furnace lid, the inner wall of the furnace, and the bottom of the furnace, and is the part in which an upper electrode 21 and a lower electrode 22 are installed, and an arc is generated between the electrodes to melt the iron source 5a. The configuration of the melting furnace 20 itself may be the same as known configurations. The DC arc furnace 100 of this disclosure can efficiently melt the iron source 5a containing reduced iron, regardless of the shape of the furnace lid, the inner wall of the furnace, and the bottom of the furnace.

[0016] The configurations of the upper electrode 21 and lower electrode 22 in the melting furnace 20 are not particularly limited, as long as they can generate the downward flow and central flow described later for the molten iron 5b. In the DC arc furnace 100, the upper electrode 21 is the cathode and the lower electrode 22 is the anode. Therefore, during furnace operation, current flows from the lower electrode 22 through the molten iron 5b to the upper electrode 21. The upper electrode 21 is installed so as to be inserted into the furnace through the furnace lid. The lower electrode 22 is installed at the bottom of the furnace. There is one upper electrode 21 in the melting furnace 20. The positions of the upper electrode 21 and lower electrode 22 in the melting furnace 20 are such that, for example, if the shape of the molten metal surface in the melting furnace 20 is approximately circular in a top view (plan view), the center of the circle coincides with the central axis of the upper electrode 21 and the lower electrode 22.

[0017] In a DC arc furnace 100, it is possible to generate both downward flow and central flow regardless of the planar shape of the melting furnace 20 (the inner circumference defined by the inner wall of the furnace). From the viewpoint of increasing the durability of the furnace, the planar shape of the melting furnace 20 is preferably such that it has a circular section as shown in Figure 3. However, it does not need to be a perfect circle, and it may have protrusions or indentations in part. For example, the melting furnace 20 may have a protrusion 24 as shown in Figure 3, where a tapping port or the like may be located.

[0018] As shown in Figure 4, the melting furnace 20 may have a bath depth H and a furnace diameter D. The bath depth H and furnace diameter D of the melting furnace 20 are not particularly limited. From the viewpoint of making it easier to generate the downward flow and central flow described later, it is preferable that the ratio H / D of the bath depth H to the furnace diameter D of the melting furnace 20 be 0.17 or more and 0.48 or less. In this application, "bath depth H" means the depth from the molten iron surface directly below the upper electrode to the deepest part of the furnace. For example, as shown in Figure 3, the bath depth H may be the distance from the molten iron surface at the center of the furnace to the bottom of the furnace. Also, "furnace diameter D" means the diameter of the molten iron surface. The straight-line distance on the molten iron surface from the molten iron surface position O directly below the upper electrode, through the position P where the iron source 5a is supplied, to the inner wall of the furnace is considered to be the "furnace radius R0", and twice this furnace radius R0 is considered to be the "furnace diameter D".

[0019] 1.4 Molten iron Molten iron 5b is obtained by melting an iron source such as scrap or reduced iron. The DC arc furnace 100 of this disclosure efficiently melts the iron source 5a containing reduced iron when molten iron 5b is present in the melting furnace 20 and an iron source 5a containing reduced iron is further supplied to the molten iron 5b. That is, the molten iron 5b present in the melting furnace 20 before the supply of iron source 5a may be obtained by melting an iron source containing reduced iron, or it may be obtained by melting an iron source that does not contain reduced iron (for example, scrap). Molten iron 5b may contain various elements other than iron. Molten iron 5b may also be molten steel. As described above, the density of molten iron 5b is greater than the bulk density of the iron source 5a containing reduced iron. The density of molten iron 5b is, for example, 6500 kg / m³. 3 Over 6800 kg / m 3 The above is also acceptable. The temperature of the molten iron 5b is not particularly limited.

[0020] 1.5 Power supply In the DC arc furnace 100, power is supplied from the power supply unit 30 to the upper electrode 21 and the lower electrode 22, generating an arc 23 between the upper electrode 21 and the lower electrode 22, thereby creating a downward flow between the upper electrode 21 and the lower electrode 22 of the molten iron 5b in the melting furnace 20. The power supply unit 30 can be a general type that supplies power to the upper electrode 21 and the lower electrode 22. The power supplied from the power supply unit 30 to the electrodes is not particularly limited as long as it can generate an arc between the electrodes.

[0021] 1.6 Control Unit In the DC arc furnace 100, the control unit 40 controls either or both of the following: the power supplied from the power supply unit 30 to the upper electrode 21 and the lower electrode 22, and the supply position P of the iron source 5a supplied from the supply port 10 to the molten surface 5bx in the melting furnace 20. By controlling either or both of the power and the supply position P, the control unit 40 generates an arc 23 between the upper electrode 21 and the lower electrode 22, causing a downward flow between the upper electrode 21 and the lower electrode 22 in the molten iron 5b in the melting furnace 20, generating a central flow toward the downward flow on the molten surface 5bx of the molten iron 5b, and causing the iron source 5a supplied to the central flow generated on the molten surface 5bx to float on the molten surface 5bx and move toward the downward flow.

[0022] The control unit 40 may, for example, control the power supplied from the power supply unit 30 to the upper electrode 21 and the lower electrode 22 so that a central flow is generated at the supply position P of the iron source 5a supplied to the molten surface 5bx. Alternatively, the control unit 40 may, for example, control the supply angle of the iron source 5a so that the iron source 5a is supplied within the range in which a central flow is generated at the molten surface 5bx, thereby controlling the supply position P. Alternatively, the control unit 40 may control both the power and the supply position P. In particular, the form in which the control unit 40 controls the power is simple. The control unit 40 only needs to be capable of performing the above control and may have known configurations for performing such control. For example, the control unit 40 may include a CPU, RAM, ROM, etc.

[0023] 1.7 Flow generated in molten iron by creating an arc between electrodes 1.7.1 Downflow As described above, in the DC arc furnace 100, the upper electrode 21 is the cathode and the lower electrode 22 is the anode, so the main current in the molten iron 5b flows from the bottom of the furnace towards the molten surface 5bx directly below the upper electrode 21. The current density vector in this molten iron 5b is given by J(A / m). 2 Assuming that the magnetic flux density vector is B(T), then as shown in Figure 5(A), there is an electromagnetic force F(N / m) in the molten iron 5b. 3) = J × B is generated. This electromagnetic force F is distributed so as to constrict the molten iron 5b from all sides, and is also called a pinch force. Here, for example, the arc cross-sectional area S at the point where the arc 23 is in contact with the molten iron 5b. arc However, if the area of ​​the lower electrode 22 in contact with the molten iron 5b is smaller, the current density at the molten surface 5bx is greater than the current density near the lower electrode 22, and the pinch force at the molten surface 5bx is greater than the pinch force near the lower electrode 22. Therefore, as shown in Figure 5(B), a downward flow (downward flow) is formed directly below the upper electrode 21.

[0024] More specifically, the downdraft is represented, for example, by the arc cross-sectional area S of equations (1) to (3) below. arc However, this occurs when the area of ​​the lower electrode 22 in contact with the molten iron 5b becomes smaller. In other words, for example, the control unit 40 determines the arc cross-sectional area S, which is represented by the following equations (1) to (3). arc However, the power may be controlled such that the area of ​​the lower electrode 22 in contact with the molten iron 5b is smaller than the area of ​​the lower electrode 22 in contact with the molten iron 5b.

[0025] S arc = πR 2 arc …(1) R arc = R c (3.2-2.2exp(-z / (5R c ))) …(2) R c = (I / (πj c )) 0.5 …(3) R arc : The radius of the arc at the point in contact with the molten iron (cm) R c : The radius of the arc at the point of contact with the upper electrode (cm) z: Distance (cm) between the upper electrode and the surface of the molten iron I: Current value (kA) j c : Current density of the arc at the point of contact with the upper electrode (kA / cm²) 2 )

[0026] In the above equations (1) to (3), z may be, for example, 15 to 50 cm, I may be, for example, 10 to 60 kA, and j c For example, 3.0~4.0 kA / cm 2 This is acceptable. Furthermore, z, I and j c The value of is not limited to this. However, regarding I, there are physical limitations due to the limiting current density and the maximum diameter of the upper electrode, so in reality it is 129 kA or less. Also, from equation (2) above, R arc The maximum value is R c It is approximately 3.2 times that. For example, the limit current density of the upper electrode 21 is 25 A / cm². 2 For the upper electrode 21 with a diameter of φ81 cm (the largest diameter upper electrode existing at the time of this application), R arc Calculating this gives us approximately 11 cm. In this case, the area in contact between the lower electrode 22 and the molten iron 5b is 11 × 11 × π (cm²). 2 If it is greater than ), it can be said that a downward flow can be generated in the molten iron 5b between the upper electrode 21 and the lower electrode 22.

[0027] 1.7.2 Central flow In the DC arc furnace 100, the iron source 5a is supplied to position P where a central flow is occurring on the molten iron surface 5bx of the molten iron 5b. As shown in Figure 5(B), a "central flow" is a flow that forms around at least a portion of the periphery of a downdraft and flows toward the downdraft. Therefore, the position P where the iron source 5a is supplied is located away from position O between the upper electrode 21 and the lower electrode 22. In other words, as shown in Figures 3 and 4, in the melting furnace 20, there is a distance R between position O between the upper electrode 21 and the lower electrode 22 on the molten iron surface 5bx of the molten iron 5b and position P where the iron source 5a is supplied. In the DC arc furnace 100, slag may be present on the molten iron surface 5bx of the molten iron 5b. In this case, whether or not a central flow is occurring can be determined by checking the flow of the slag on the molten surface. One example of a method for determining whether or not a central flow is occurring is to observe the inside of the furnace using a camera, and if it is confirmed that the slag on the surface 5bx of the molten iron 5b is flowing towards position O between the upper electrode 21 and the lower electrode 22, then it can be determined that a central flow is occurring.

[0028] As far as the inventors have confirmed, even if the power supplied to the upper electrode 21 and the lower electrode 22 in a DC arc furnace 100 of the same shape is changed within the range of general power that can generate an arc 23 between the upper electrode 21 and the lower electrode 22, there is no significant change in the range in which a central flow occurs at the molten iron 5b surface 5bx. As far as the inventors have confirmed, the range in which a central flow occurs depends particularly on the shape of the furnace, specifically the depth H of the bath and the diameter D of the furnace. For example, when the depth H of the bath of the melting furnace 20, the diameter D of the furnace, the distance R from the position O between the electrodes of the upper electrode 21 and the lower electrode 22 at the molten iron 5b surface 5bx to the position P where the iron source 5a is supplied, and the furnace radius R0 of the melting furnace 20 satisfy the relationship of equation (4) below, the iron source 5a is easily moved downwards by riding on the central flow generated at the molten iron surface 5bx. The specific value of H / D is not particularly limited, but for example, it may be 0.17 or more and 0.48 or less.

[0029] R / R0 < 1.24 (H / D) 0.75 …(4)

[0030] 1.7.3 Distant current As shown in Figure 5(B), the flow generated by the arc between electrodes in molten iron 5b is not limited to the downward flow or central flow described above. For example, at the surface 5bx of molten iron 5b, a divergent flow may occur outside the central flow. If an iron source 5a is supplied to a location where such a divergent flow is occurring, the iron source 5a will move away from the downward flow towards the lower temperature furnace wall, making it impossible to efficiently melt the iron source 5a. In order to efficiently melt the iron source 5a, as described above, it is effective to supply the iron source 5a to a location P on the surface 5bx of molten iron 5b where the central flow is occurring, and to allow the iron source 5a to float on the surface 5bx of molten iron 5b, ride the central flow, and move toward the downward flow.

[0031] 1.8 Other Configurations In addition to the above configuration, the DC arc furnace of this disclosure may have a configuration that is common to DC arc furnaces. For example, it may be equipped with a lance for supplying top-blowing gas to the molten iron in the melting furnace, various gas passages for bottom-blowing, etc., a slag outlet for slag removal, a tapping outlet for tapping steel, and a cooling device for cooling the furnace body. As other configurations that a DC arc furnace may have are obvious, a detailed explanation is omitted here.

[0032] 2. DC Arc Furnace (Second Embodiment) As described above, in the DC arc furnace 100, when the depth H of the bath of the melting furnace 20, the furnace diameter D, the distance R from the position O between the upper electrode 21 and the lower electrode 22 on the molten iron surface 5bx to the position P where the iron source 5a is supplied, and the furnace radius R0 of the melting furnace 20 satisfy the relationship of equation (4) above, the iron source 5a is easily moved toward the downward flow by being carried by the central flow generated on the molten iron surface 5bx. In other words, the DC arc furnace of this disclosure may have the following configuration.

[0033] In other words, the DC arc furnace according to the second embodiment is A supply port that provides an iron source containing reduced iron, A melting furnace that melts the iron source by generating an arc between the upper electrode and the lower electrode, The system includes a power supply unit that supplies power to the upper electrode and the lower electrode, The depth H of the melting furnace, the furnace diameter D, the distance R from the position between the upper and lower electrodes on the surface of the molten iron to the position where the iron source is supplied, and the furnace radius R0 of the melting furnace satisfy the following equation (4).

[0034] R / R0 < 1.24 (H / D) 0.75 …(4)

[0035] The DC arc furnace according to the second embodiment may also include a control unit, similar to the first embodiment. For example, in the DC arc furnace according to the second embodiment, the control unit controls the arc cross-sectional area S represented by the following formulas (1) to (3). arc However, the power supplied to the upper and lower electrodes may be controlled such that the area of ​​the lower electrode in contact with the molten iron is smaller than the area of ​​the lower electrode in contact with the molten iron.

[0036] S arc = πR 2 arc …(1) R arc = R c (3.2-2.2exp(-z / (5R c ))) …(2) R c = (I / (πj c )) 0.5 …(3) R arc : The radius of the arc at the point in contact with the molten iron (cm) R c : The radius of the arc at the point of contact with the upper electrode (cm) z: Distance (cm) between the upper electrode and the surface of the molten iron I: Current value (kA) j c : Current density of the arc at the point of contact with the upper electrode (kA / cm²) 2 )

[0037] The meaning of the relationship in equation (4) above, and the meanings of equations (1) to (3) above, are as explained in the first embodiment. In the DC arc furnace according to the second embodiment, the basic configuration of the supply port, melting furnace, and power supply unit may be the same as in the first embodiment. In the second embodiment, the same configuration as in the first embodiment will not be explained.

[0038] 3. Method for dissolving an iron source containing reduced iron using a DC arc furnace. In addition to its aspect as a DC arc furnace itself as described above, the technology disclosed herein also has the aspect of a method for melting an iron source containing reduced iron using a DC arc furnace.

[0039] In other words, the method of this disclosure is A method for dissolving an iron source 5a containing reduced iron using a DC arc furnace 100, A supply step involves supplying the iron source 5a into the melting furnace 20 from the supply port 10, The process includes a melting step in which an arc 23 is generated between an upper electrode 21 and a lower electrode 22 provided in the melting furnace 20 to melt the iron source 5a, The arc 23 is generated between the upper electrode 21 and the lower electrode 22, causing a downward flow to be generated between the upper electrode 21 and the lower electrode 22 in the molten iron 5b in the melting furnace 20, and a central flow toward the downward flow is generated on the molten iron surface 5bx of the molten iron 5b, and the iron source 5a is supplied to the central flow generated on the molten iron surface 5bx, causing the iron source 5a to float on the molten iron surface 5bx and move toward the downward flow.

[0040] Details of the supply and melting steps have already been described. In the method of this disclosure, in order to efficiently melt the iron source 5a, the iron source 5a is supplied to a position P where a central flow is occurring on the molten iron surface 5bx of the molten iron 5b, and while the iron source 5a is floating on the molten iron surface 5bx of the molten iron 5b, the iron source 5a is carried on the central flow and moved toward the downward flow. Herein, in the method of this disclosure, in order to directly supply the iron source 5a to the position P where a central flow is occurring on the molten iron surface 5bx, the supply angle of the iron source 5a may be determined according to the position of the supply port 10 and the range where a central flow is occurring on the molten iron surface 5bx. Specifically, if a central flow does not occur at the molten metal surface 5bx directly below the supply port 10, the iron source 5a may be supplied directly to position P by supplying it diagonally downward from the supply port 10 to the molten metal surface 5bx (for example, Figure 2(A)). If a central flow occurs at the molten metal surface 5bx directly below the supply port 10, the iron source 5a may be supplied vertically downward from the supply port 10 to the molten metal surface 5bx (for example, Figure 2(B)).

[0041] The method for supplying the iron source 5a in the present disclosure is not particularly limited. For example, the method for supplying the iron source 5a may be at least one of the following: supplying the iron source 5a through holes provided in the furnace wall or furnace lid, and supplying the iron source 5a by a raw material input chute. Details of the method for supplying the iron source 5a are as described above.

[0042] The method disclosed herein relates to the arc cross-sectional area S represented by the above formulas (1) to (3). arc However, power may be supplied to the upper electrode 21 and the lower electrode 22 in such a way that the area of ​​the lower electrode 22 in contact with the molten iron 5b is smaller. The meaning of equations (1) to (3) is as described above.

[0043] In the method of this disclosure, the depth H of the melting furnace 20, the furnace diameter D, the distance R from the position between the upper electrode 21 and the lower electrode 22 at the molten iron surface 5bx to the position P where the iron source 5a is supplied, and the furnace radius R0 of the melting furnace 20 may satisfy the relationship of equation (4) above. The meaning of equation (4) is as described above. [Examples]

[0044] The present invention will be further described below with reference to examples, but the present invention is not limited to the following examples. The present invention allows for the adoption of various conditions without departing from its gist and insofar as it achieves its objective.

[0045] 1. Numerical Simulation 1 Numerical simulations of the movement of reduced iron in a DC arc furnace were performed using the Discrete Phase Model (DPM) method. Specifically, particles simulating reduced iron were supplied to a steady flow field formed by a molten steel fluid simulation, and their trajectories were tracked. The shape of the DC arc furnace was as shown in Figures 3 and 4. The supplied particles were spherical and had a density of 5500 kg / m³. 3 The diameter is 0.072 m. The diameter is the diameter of a sphere obtained by converting a rectangular parallelepiped of reduced iron with dimensions of 0.04 m × 0.05 m × 0.1 m into a sphere of the same volume. The density of the molten steel is 7000 kg / m³. 3 The reduced iron supplied to the molten steel was assumed to float on the surface of the molten steel. Figures 6(A) and (B) show examples of calculations of the trajectory of reduced iron obtained by the DPM method. Figure 7 shows a schematic diagram of the movement of reduced iron in the furnace. As shown in Figures 6(A) and 7, it can be seen that when reduced iron is supplied to a region where the flow is directed towards the upper electrode, the reduced iron moves toward the upper electrode. On the other hand, as shown in Figures 6(B) and 7, it can be seen that when reduced iron is supplied to a region where the flow is directed toward the furnace wall, the reduced iron moves toward the furnace wall.

[0046] The steady-state flow field formed in molten steel can be described as follows. First, when molten steel is heated by generating an arc between the upper and lower electrodes in a DC arc furnace, the current flowing from the lower electrode to the upper electrode creates an electromagnetic force F(N / m) on the molten steel. 3 A pinch force is generated as follows: Here, the arc cross-sectional area S at the point where the arc contacts the molten steel. arc(See the following formulas (1) to (3)). When it is smaller than the area where the lower electrode contacts the molten steel, the current density on the molten steel surface increases, and the pinch force on the molten steel surface becomes larger than the pinch force near the lower electrode. As a result, directly below the upper electrode, a downward flow (downward current) is formed, and around the downward flow, a central flow toward the downward flow is generated. Further outside the central flow, a separation flow toward the opposite side of the downward flow (the furnace wall side) is generated. In Fig. 6(A), it can be said that the reduced iron is supplied to the position where the central flow occurs, and the reduced iron rides on the central flow and moves toward the downward flow, approaching directly below the upper electrode. On the other hand, in Fig. 6(B), it can be said that the reduced iron is supplied to the position where the separation flow occurs, and the reduced iron rides on the separation flow and approaches the furnace wall.

[0047] S arc = πR 2 arc …(1) R arc = R c (3.2 - 2.2exp(-z / (5R c ))) …(2) R c = (I / (πj c )) 0.5 …(3) R arc : Radius of the arc (cm) at the point where it contacts the molten steel (molten iron) R c : Radius of the arc (cm) at the point where it contacts the upper electrode z: Distance (cm) between the upper electrode and the molten steel surface I: Current value (kA) j c : Arc current density (kA / cm 2 )

[0048] As described above, in order to efficiently melt an iron source containing reduced iron using a DC arc furnace, it is effective to generate an arc between the upper and lower electrodes to create a downward flow between the upper and lower electrodes in the molten iron in the melting furnace, generate a central flow toward the downward flow on the surface of the molten iron, and supply the iron source to the central flow generated on the surface of the molten iron, thereby causing the iron source to float on the surface and move toward the downward flow. For example, by controlling either or both of the power supplied to the upper and lower electrodes, and the supply position of the iron source supplied to the surface of the molten iron in the melting furnace, it is possible to appropriately generate the downward flow and central flow, supply the iron source to an appropriate position on the surface of the molten iron, and cause the iron source to float on the surface and move toward the downward flow.

[0049] 2. Numerical Simulation 2 Numerical fluid simulations were performed using the method described in "HJ Odenthal, A. Kemminger, F. Krause, N. Vogl, AISTech, Iron and Steel Technology Conf., Nashville, USA 2017, 1101.". By changing the simulation conditions, the movement of reduced iron at the molten steel surface in a DC arc furnace was examined.

[0050] Table 1 below shows examples of a 10t DC arc furnace with a power supply of 3MW, a 140t DC arc furnace with a power supply of 42MW, and a 300t DC arc furnace with a power supply of 90MW. The shape of the DC arc furnace was based on the same design as in the preliminary study, and fluid calculations and calculations of reduced iron movement were performed for systems with molten steel volumes of 10t, 140t, and 300t, respectively, for the case where the ratio of bath depth H to furnace diameter D (bath depth / furnace diameter) H / D (bath depth / furnace diameter) was approximately 0.17, approximately 0.25, approximately 0.37, and approximately 0.48, while changing the distance R (reduced iron input position) from the position between the upper and lower electrodes on the molten steel surface to the position where reduced iron is supplied. "○" was used when the reduced iron supplied to the molten steel surface moved towards the area directly below the upper electrode, and "×" was used when it did not move.

[0051] [Table 1]

[0052] Table 2 below shows examples where the power consumption was reduced by 30%. Specifically, the power consumption for 10t, 140t, and 300t DC arc furnaces was set to 2.1MW, 29.4MW, and 63MW, respectively, and fluid dynamics calculations and calculations of reduced iron movement were performed while changing the reduced iron input position.

[0053] [Table 2]

[0054] Table 3 below shows examples where the power consumption was reduced by 15%. Specifically, the power consumption for 10t, 140t, and 300t DC arc furnaces was set to 2.55MW, 35.7MW, and 76.5MW, respectively, and fluid dynamics calculations and calculations of reduced iron movement were performed while changing the reduced iron input position.

[0055] [Table 3]

[0056] Table 4 below shows an example of fluid dynamics calculations and iron reduction movement calculations performed while setting the maximum current value that can flow through the upper electrode and changing the position where reduced iron is introduced. The upper electrode was a carbon electrode. The limiting current density of the carbon electrode is 25 A / cm². 2 In the 300t DC arc furnace, the current value shown in the example in Table 1 was the maximum current value. The power consumption for the 10t and 140t DC arc furnaces was 3.4MW and 52MW, respectively.

[0057] [Table 4]

[0058] Table 5 below shows an example of a similar simulation performed on a DC arc furnace with a spherical shell-shaped furnace bottom. For a 140t DC arc furnace, the power was set to 42MW, and calculations were performed while changing the position of the reduced iron input.

[0059] [Table 5]

[0060] The results shown in Tables 1-5 indicate that when reduced iron is supplied to the molten steel surface in a melting furnace, the reduced iron moves either towards the area directly below the upper electrode or towards the furnace wall, depending on its supply position on the molten surface.

[0061] Figures 8(A) to 8(D) and 8(D) and 8(D) show the results plotted on a graph where the vertical axis represents the ratio R / R0 (iron reduction input position / furnace radius) of the distance R from the position between the upper and lower electrodes on the molten steel surface to the position where reduced iron is supplied, and the horizontal axis represents the ratio H / D (bath depth / furnace diameter) of the melting furnace bath depth H to the furnace diameter D, with the results shown in Tables 1 to 5 ("○" or "×") being plotted. Figure 8(A) corresponds to the results shown in Table 1, Figure 8(B) to Table 2, Figure 8(C) to Table 3, Figure 8(D) to Table 4, and Figure 9 to Table 5.

[0062] From the results shown in Tables 1-5, Figures 8(A)-(D), and Figure 9, it can be seen that the threshold graphs for ○ and × are the same regardless of the shape of the furnace bottom or the magnitude of the supplied power. That is, under the conditions on the upper side of the threshold graph, the reduced iron cannot be moved toward the area directly below the upper electrode ("×"), while under the conditions on the lower side of the graph, the reduced iron can be moved toward the area directly below the upper electrode ("○"). More specifically, when the depth H of the melting furnace bath, the furnace diameter D, the distance R from the position between the upper and lower electrodes on the surface of the molten steel (molten iron) to the position where the reduced iron (iron source) is supplied, and the furnace radius R0 of the melting furnace satisfy the relationship in equation (4) below, it can be seen that the reduced iron (iron source) on the surface of the molten steel (molten iron) can be moved toward the area directly below the upper electrode, and the reduced iron can be efficiently dissolved.

[0063] R / R0 < 1.24(H / D) 0.75 …(4)

[0064] Figures 10(A) to (D) show an example of the flow velocity distribution of molten steel when the power supplied to the electrodes in a DC arc furnace is changed. (A) corresponds to the case where the power is reduced by 30%, (B) corresponds to the case where the power is reduced by 15%, (C) corresponds to the case where the power is not changed, and (D) corresponds to the case where the power is set to the limiting current value. As shown in Figures 10(A) to (D), in a DC arc furnace with the same ratio H / D, in the case where the power is reduced by 30%, the flow velocity of the downward flow becomes the minimum, and in the case where the limiting current value is set, the flow velocity of the downward flow becomes the maximum. On the other hand, the range of the central flow generated on the molten steel surface does not change significantly regardless of the magnitude of the power. That is, it can be seen that although the magnitude of the power affects the absolute value of the flow velocity of the molten steel in the furnace, it has little effect on the range of the central flow generated on the molten steel surface.

[0065] 3. Supplementary In the above embodiments, the form of supplying reduced iron to the molten steel is shown, but the technology of the present disclosure is not limited to this form. The technology of the present disclosure is applicable to the case of supplying an iron source with a small bulk density (an iron source including reduced iron) to the surface of molten iron with a relatively large specific gravity in a DC arc furnace, and there are no particular restrictions on the composition of the molten iron or the composition of the iron source. Also, the method of supplying the iron source is not particularly limited, and for example, a method of supplying the iron source through holes provided in the furnace inner wall, a method of supplying the iron source by a raw material charging chute, or a combination of these methods can be adopted.

[0066] In the above embodiments, examples were given that satisfy the relationship of equation (4) above, but the technology of this disclosure is not limited to this form. Even if the relationship of equation (4) is not satisfied, the DC arc furnace can efficiently dissolve an iron source containing reduced iron by "generating an arc between the upper electrode and the lower electrode, generating a downward flow between the upper electrode and the lower electrode in the molten iron in the melting furnace, generating a central flow toward the downward flow on the surface of the molten iron, and supplying an iron source to the central flow generated on the surface of the molten iron, causing the iron source to float on the surface of the molten iron and move toward the downward flow."

[0067] 4. Conclusion From the results of the above embodiments, it can be said that, by using the following method, when dissolving an iron source containing reduced iron using a DC arc furnace, the iron source containing reduced iron can be efficiently dissolved. Furthermore, it can be said that by configuring the DC arc furnace as shown in (A) and / or (B) below, the iron source containing reduced iron can be efficiently dissolved.

[0068] A method for dissolving an iron source containing reduced iron using a DC arc furnace, A supply step involves supplying the iron source into the melting furnace from the supply port, The process includes a melting step of generating an arc between an upper electrode and a lower electrode provided in the melting furnace to melt the iron source, An arc is generated between the upper electrode and the lower electrode, causing a downward flow to occur between the upper electrode and the lower electrode in the molten iron in the melting furnace, and a central flow is generated on the surface of the molten iron toward the downward flow, and the iron source is supplied to the central flow generated on the surface of the molten iron, causing the iron source to float on the surface of the molten iron and move toward the downward flow. method.

[0069] (A) A supply port that provides an iron source containing reduced iron, A melting furnace that melts the iron source by generating an arc between the upper electrode and the lower electrode, A power supply unit that supplies power to the upper electrode and the lower electrode, A control unit that controls one or both of the following: the power supplied from the power supply unit to the upper electrode and the lower electrode, and the supply position of the iron source supplied from the supply port to the molten metal surface in the melting furnace. Equipped with, The control unit is configured to control either or both of the power and the supply position to generate the arc between the upper electrode and the lower electrode, thereby generating a downward flow between the upper electrode and the lower electrode in the molten iron in the melting furnace, generating a central flow toward the downward flow on the surface of the molten iron, and moving the iron source supplied to the central flow generated on the surface of the molten iron toward the downward flow while floating on the surface of the molten iron. DC arc furnace.

[0070] (B) A supply port that provides an iron source containing reduced iron, A melting furnace that melts the iron source by generating an arc between the upper electrode and the lower electrode, The system includes a power supply unit that supplies power to the upper electrode and the lower electrode, The depth H of the melting furnace, the furnace diameter D, the distance R from the position between the upper and lower electrodes on the surface of the molten iron to the position where the iron source is supplied, and the furnace radius R0 of the melting furnace satisfy the following relationship (4): DC arc furnace. R / R0 < 1.24 (H / D) 0.75 …(4) [Explanation of symbols]

[0071] 5a iron source 5b Molten iron 5bx hot water surface 10 supply ports 20 Melting furnace 21 Upper electrode 22 Lower electrode 23 Arc 30 Power supply section 40 Control Unit

Claims

1. A method for dissolving an iron source containing reduced iron using a DC arc furnace, A supply step involves supplying the iron source into the melting furnace from the supply port, The process includes a melting step of generating an arc between an upper electrode and a lower electrode provided in the melting furnace to melt the iron source, By supplying power to the upper electrode and the lower electrode such that the arc cross-sectional area S arc, represented by the following formulas (1) to (3), is smaller than the area in contact between the lower electrode and the molten iron in the melting furnace, an arc is generated between the upper electrode and the lower electrode, causing a downward flow between the upper electrode and the lower electrode in the molten iron in the melting furnace, and generating a central flow toward the downward flow on the surface of the molten iron. and, The depth H of the melting furnace bath, the furnace diameter D, the distance R from the position between the electrodes of the upper and lower electrodes on the surface of the molten iron to the position where the iron source is supplied, and the furnace radius R0 of the melting furnace satisfy the relationship of equation (4) below, thereby supplying the iron source to the central flow generated on the surface of the molten iron, and moving the iron source toward the downward flow while floating it on the surface of the molten iron. method. S arc = πR 2 arc...(1) R arc = R c (3.2-2.2exp(-z / (5R c )))...(2) R c = (I / (πj c )) 0.5...(3) R arc: The radius (cm) of the arc at the point in contact with the molten iron. R c: Radius of the arc at the point where it contacts the upper electrode (cm) z: Distance (cm) between the upper electrode and the surface of the molten iron. I: Current value (kA) j c: Current density of the arc at the point of contact with the upper electrode (kA / cm²) R / R 0 < 1.24 (H / D) 0.75...(4)

2. The method of supplying the iron source is at least one of the following: supplying the iron source through a hole provided in the inner wall or lid of the furnace, and supplying the iron source by a raw material input chute. The method according to claim 1.

3. A supply port that provides an iron source containing reduced iron, A melting furnace that melts the iron source by generating an arc between the upper electrode and the lower electrode, A power supply unit that supplies power to the upper electrode and the lower electrode, The system includes a control unit that controls either or both of the following: the power supplied from the power supply unit to the upper electrode and the lower electrode, and the supply position of the iron source supplied from the supply port to the molten metal surface in the melting furnace. The control unit controls either or both of the power and the supply position so that the arc cross-sectional area S arc, represented by the following formulas (1) to (3), is smaller than the area in contact between the lower electrode and the molten iron in the melting furnace. The arc is generated between the upper electrode and the lower electrode, causing a downward flow to occur between the upper electrode and the lower electrode in the molten iron in the melting furnace, and also generating a central flow on the surface of the molten iron toward the downward flow, and, The depth H of the melting furnace, the furnace diameter D, the distance R from the position between the upper and lower electrodes on the molten iron surface to the position where the iron source is supplied, and the furnace radius R0 of the melting furnace satisfy the relationship shown in equation (4) below, and the configuration is such that the iron source supplied to the central flow generated on the molten iron surface is moved toward the downward flow while floating on the molten iron surface. DC arc furnace. S arc = πR 2 arc...(1) R arc = R c (3.2-2.2exp(-z / (5R c )))...(2) R c = (I / (πj c )) 0.5...(3) R arc: The radius (cm) of the arc at the point in contact with the molten iron. R c: Radius of the arc at the point where it contacts the upper electrode (cm) z: Distance (cm) between the upper electrode and the surface of the molten iron. I: Current value (kA) j c: Current density of the arc at the point of contact with the upper electrode (kA / cm²) R / R 0 < 1.24 (H / D) 0.75...(4)

4. The method of supplying the iron source is at least one of the following: supplying the iron source through a hole provided in the inner wall or lid of the furnace, and supplying the iron source by a raw material input chute. The DC arc furnace according to claim 3.

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