Method for charging reduced iron and reduced iron charging chute

Abstract

Provided is a method for charging reduced iron (11) into an electric furnace (1) for melting the reduced iron (11) using a reduced iron charging chute (3). When an obstacle with which the reduced iron (11) collides is installed within a range of 200 mm from the outlet of the reduced iron charging chute (3), the obstacle is projected onto the chute outlet surface of the reduced iron charging chute (3), and the maximum inscribed circle of a region through which the reduced iron (11) can pass is defined as the maximum inscribed circle, the ratio d / s between the diameter d [mm] of the maximum inscribed circle and the long diameter s [mm] of the reduced iron falls within a predetermined range with respect to the charging speed k [t / min] of the reduced iron.

Description

Method for Charging Reduced Iron and Shoot for Charging Reduced Iron

[0001] The present invention relates to a method for charging reduced iron and a shoot for charging reduced iron for charging reduced iron into an electric furnace for melting reduced iron.

[0002] In the steelmaking process, the blast furnace method discharges carbon-containing gas when reducing iron ore with coke, while the electric furnace method mainly uses scrap as raw material and thus has the characteristic of low carbon-containing gas discharge.

[0003] In recent years, due to the trend of carbon emission reduction, the steelmaking process is required to shift from the conventional blast furnace method to a manufacturing method using an electric furnace with a lower carbon emission. However, in order to achieve the same production volume as that of a blast furnace by the electric furnace method, it is necessary to increase the size of the electric furnace. In addition, since the amount of scrap raw material generated is limited, it is necessary to use not only scrap but also directly reduced iron as raw material. Therefore, it is important to efficiently melt directly reduced iron in an electric furnace.

[0004] Direct reduced iron is commonly called DRI (Direct Reduced Iron) and is mainly obtained by reducing iron ore or iron ore pellets with gas. Also, the product obtained by hot-compressing DRI is called HBI (Hot Briquetted Iron) and is used as a raw material in an electric furnace. HBI is charged into the electric furnace through a shoot for charging reduced iron (hereinafter simply referred to as "shoot"). It is known that when the charged HBI concentrates at one place in the molten metal of the electric furnace, the HBIs coagulate with each other to form an aggregate with voids, making it difficult to melt. Such coagulation of HBIs with each other is a problem that occurs regardless of the furnace diameter of the electric furnace. Therefore, even in a large electric furnace, in order to efficiently melt HBI, it is effective to disperse HBI over a wide range. In addition, in a large electric furnace, a large amount of HBI is charged to achieve the same production volume as that of a blast furnace, so the risk of shoot clogging is high.

[0005] Patent Document 1 describes a method of dispersing and feeding raw materials by providing a swivel mechanism and a tilting mechanism in the chute. However, applying this to existing equipment would require extensive modifications, and the complex mechanism raises concerns from an equipment maintenance perspective.

[0006] Japanese Patent Publication No. 2014-037913

[0007] Figure 1 shows a schematic diagram of an electric furnace. In the electric furnace 1, an arc is formed between the electrode 2 and the molten steel 12, melting the HBI (hereinafter referred to as "reduced iron 11") fed in from the chute 3 at the top of the electric furnace. It is known that if the reduced iron 11 is concentrated in one place in the molten steel 12, the reduced iron 11 will solidify together, forming aggregates with voids, making it difficult to melt. Therefore, in order to efficiently melt the reduced iron 11 in an electric furnace, it is effective to disperse the reduced iron 11 over a wide area. In addition, in large electric furnaces, a large amount of reduced iron 11 is fed in to achieve the same production volume as a blast furnace, so there is a high risk of chute clogging.

[0008] The present invention aims to provide a method for introducing reduced iron into an electric furnace, and a reduced iron introduction chute, that can further disperse the reduced iron while suppressing chute clogging, even when a large amount of reduced iron is introduced into the chute.

[0009] The present invention provides a method and equipment for introducing reduced iron into an electric furnace, which involves using an obstacle-type chute with an obstacle at the chute outlet, or a convex-shaped type chute with an appropriate convex shape at the chute outlet. This method suppresses chute clogging while introducing reduced iron in a more dispersed manner, thereby enabling more efficient dissolution of reduced iron.

[0010] In other words, the gist of the present invention is as follows: [1] A method for introducing reduced iron into an electric furnace for melting reduced iron using a reduced iron introduction chute, wherein an obstacle into which the reduced iron will collide is placed within 200 mm from the outlet of the reduced iron introduction chute, the maximum inscribed circle of the region through which the reduced iron can pass when the obstacle is projected onto the chute outlet surface of the reduced iron introduction chute is defined as the maximum inscribed circle, and the ratio d / s of the diameter d [mm] of the maximum inscribed circle to the major axis s [mm] of the reduced iron satisfies the following (Equation 1) with respect to the reduced iron introduction rate k [t / min], and also satisfies the following (Equation 2) and (Equation 3). (-0.0021s + 0.2927)k + (0.0024s + 1.7415) < d / s (Equation 1) 30 ≤ s ≤ 126 (Equation 2) 4 ≤ k ≤ 12 (Equation 3)

[0011] [2] A method for introducing reduced iron into an electric furnace for melting reduced iron using a reduced iron introduction chute, wherein the shape of the chute outlet surface of the reduced iron introduction chute is such that a part of the outer circumference is convex inward relative to the shape of the chute inlet surface, the convex shape changes such that the chute cross-sectional area smoothly narrows from a position 1000 mm upstream of the chute outlet, the maximum inscribed circle of the region through which the reduced iron can pass at the chute outlet surface is defined as the maximum inscribed circle, and the ratio d / s of the diameter d [mm] of the maximum inscribed circle to the major axis s [mm] of the reduced iron satisfies the following (Equation 4) with respect to the reduced iron introduction rate k [t / min], and also satisfies the following (Equation 2) and (Equation 3). (-0.0009s + 0.165)k + 1.1367 < d / s (Equation 4) 30 ≤ s ≤ 126 (Equation 2) 4 ≤ k ≤ 12 (Equation 3)

[0012] A method for introducing reduced iron according to [3] [1] or [2], characterized in that the reduced iron introduction chute is used such that the central axis of the reduced iron introduction chute is at an angle of 45° to 90° with respect to the horizontal plane.

[0013] [4] A chute for introducing reduced iron into an electric furnace for melting reduced iron, characterized in that an obstacle to which the reduced iron will collide is installed within 200 mm from the outlet of the chute for introducing reduced iron. [5] A chute for introducing reduced iron into an electric furnace for melting reduced iron, characterized in that the shape of the chute outlet surface of the chute for introducing reduced iron is such that a part of the outer circumference of the chute outlet surface is convex inward, and the convex shape changes such that the cross-sectional area of ​​the chute smoothly narrows from a position 1000 mm upstream of the chute outlet. [6] The chute for introducing reduced iron according to [4] or [5], characterized in that the central axis of the chute for introducing reduced iron is positioned at an angle of 45° to 90° with respect to the horizontal plane.

[0014] This invention makes it possible to disperse reduced iron on the surface of molten steel in an electric furnace while suppressing chute clogging by adjusting the shape of the chute for introducing reduced iron.

[0015] This is a cross-sectional view showing a schematic diagram of an electric furnace. This is a diagram showing the calculation process of a numerical analysis simulation. This is a diagram showing the particle shape of reduced iron (HBI). This is a plan view showing the calculation domain of the numerical analysis simulation. This is a front cross-sectional view showing the calculation domain of the numerical analysis simulation. This is a front view showing an obstacle at the chute outlet (case-a). This is a front view showing an obstacle at the chute outlet (case-b-n). This is a front view showing an obstacle at the chute outlet (case-c). This is a front view showing an obstacle at the chute outlet (case-d). This is a front view showing an obstacle at the chute outlet (case-e). This is a front view showing an obstacle at the chute outlet (case-f). This is a front view showing an obstacle at the chute outlet (case-g-n). This is a diagram showing the convex shape of the chute outlet, where (A1) is a front view and (A2) is a side cross-sectional view, where (A1) is a view along the A1-A1 arrow and (A2) is a cross-sectional view along the A2-A2 arrow. This figure shows the convex shape of the chute outlet, with (B1) being a front view and (B2) being a side cross-sectional view, with (B1) being a view taken along the line B1-B1 and (B2) being a cross-sectional view taken along the line B2-B2. This figure shows the convex shape of the chute outlet, with (C1) being a front view and (C2) being a side cross-sectional view, with (C1) being a view taken along the line C1-C1 and (C2) being a cross-sectional view taken along the line C2-C2. This figure shows the narrowing shape of the chute outlet, with (A1) being a front view and (A2) being a side cross-sectional view. This figure shows the narrowing shape of the chute outlet, with (B1) being a front view and (B2) being a side cross-sectional view. This figure shows the narrowing shape of the chute outlet, with (B1) being a front view and (B2) being a side cross-sectional view. This figure shows the particle distribution on the molten steel surface at the final time of the numerical analysis simulation, and is a comparative example of Case-a. This figure shows the particle distribution on the molten steel surface at the final time of the numerical analysis simulation, and is an example of the invention of Case-b-n (n1=100). This figure shows the relationship between the chute outlet area ratio J and the accumulation rate of reduced iron. This figure shows the relationship between the reduced iron input rate (d / s) and the presence or absence of blockage in the obstacle type, using the reduced iron major axis size indicated above each figure. This figure shows the relationship between the reduced iron input rate (d / s) and the presence or absence of blockage in the obstacle type, using the reduced iron major axis size indicated above each figure. This figure shows the relationship between the reduced iron input rate (d / s) and the presence or absence of blockage in the obstacle type, using the reduced iron major axis size indicated above each figure.This diagram shows the relationship between the input rate of reduced iron (d / s) and the presence or absence of blockage in the obstacle type, using the reduced iron major axis size indicated above each figure. This diagram shows the relationship between the input rate of reduced iron (d / s) and the presence or absence of blockage in the convex shape type, using the reduced iron major axis size indicated above each figure. This diagram shows the relationship between the input rate of reduced iron (d / s) and the presence or absence of blockage in the convex shape type, using the reduced iron major axis size indicated above each figure. This diagram shows the relationship between the input rate of reduced iron (d / s) and the presence or absence of blockage in the convex shape type, using the reduced iron major axis size indicated above each figure. This diagram shows the relationship between the input rate of reduced iron (d / s) and the presence or absence of blockage in the convex shape type, using the reduced iron major axis size indicated above each figure. This is a schematic diagram of the chute input angle (chute angle θ). This is a diagram showing the relationship between the chute angle θ and the number density within a circle with a radius of 1 m. This is a diagram showing the relationship between the convex shape starting position and the accumulation rate in the convex shape type. This is a diagram showing the relationship between the obstacle thickness and the accumulation rate in the obstacle type. This is a schematic diagram showing the case where the exit area of ​​the chute is wider than the inlet area, with (A1) being a front view taken along the line A1-A1 and (A2) being a side cross-sectional view taken along the line A2-A2. This is a schematic diagram showing the case where the exit area of ​​the chute is wider than the inlet area, with (B1) being a front view taken along the line B1-B1 and (B2) being a side cross-sectional view taken along the line B2-B2. This is a front view showing the case where the chute cross-section is rectangular, with (A1) being a front view and (A2) being a side cross-sectional view, with (A1) being a view taken along the line A1-A1 and (A2) being a cross-sectional view taken along the line A2-A2. This is a front view showing the case where the chute cross-section is rectangular, with (B1) being a front view and (B2) being a side cross-sectional view, with (B1) being a view taken along the line B1-B1 and (B2) being a cross-sectional view taken along the line B2-B2. This is a front view showing the case where the chute cross-section is rectangular, with (C1) being a front view and (C2) being a side cross-sectional view, with (C1) being a view taken along the line C1-C1 and (C2) being a cross-sectional view taken along the line C2-C2.

[0016] The present invention aims to provide a method for introducing reduced iron and a reduced iron introduction chute (chute 3) for introducing reduced iron into an electric furnace that does not have a swivel mechanism or tilting mechanism, which can further disperse the reduced iron while suppressing chute clogging even when a large amount of reduced iron is introduced. To achieve this objective, we conceived that by adopting an obstacle type (see Figure 5) in which an obstacle 4 is installed at the chute outlet 7 of the chute 3, or a convex shape type (see Figure 6) in which an appropriate convex shape 5 is given to the shape of the chute outlet 7, it may be possible to introduce reduced iron more dispersively while suppressing chute clogging, and to dissolve the reduced iron more efficiently. The details are described below.

[0017] Since it is difficult to measure the distribution of reduced iron (HBI) introduced into the furnace, evaluation was performed using numerical analysis simulations with commercially available discrete element method software Ansys Rocky 2023R2 (registered trademark) and fluid analysis software Ansys Fluent 2023R2 (registered trademark). The discrete element method (DEM) is a method that models the contact forces between particles and calculates the collision behavior of the particles. The DEM calculation process is shown in Figure 2.

[0018] Ansys Rocky is software that allows you to select a contact force model, specify particle properties, shape parameters, input conditions, and calculation domain, and then calculate the behavior of the particles. It can be coupled with the fluid analysis software Ansys Fluent to perform coupled calculations of particles and fluids.

[0019] When a particle comes into contact with another particle, a contact force acts at the point of contact. This contact force acting on the particle can be decomposed into a normal force and a tangential force. For these models, we used the Linear Spring Dash Pot for the normal force model and the Linear Spring Coulomb Model for the tangential force model.

[0020] For the simulation, the particle density of the reduced iron particles was set to 5500 kg / m³ as the physical property value. ３The Young's modulus was set to 1 GPa, the kinetic and static friction coefficients between particles were set to 0.3, and the kinetic and static friction coefficients between particles and the wall were set to 0.6. The shape of the reduced iron particles was the Briquette shape provided by Rocky. The shape parameters were set to Side Angle 35° and Number of Corners 32.

[0021] The size of reduced iron particles is approximately (48-58) mm × (90-140) mm × (32-34) mm. Figure 3 shows the reduced iron particle shape in DEM calculations. In this calculation, dimensions of 53 mm × 115 mm × 33 mm were used as the standard type, and similar shapes to the standard type were also used. The size of reduced iron is expressed by the major axis s shown in Figure 3. The major axis s of the standard type is 126 mm.

[0022] The coefficient of restitution, a parameter in the contact force model, was set to 0.23. The fluid was assumed to be at rest, and the density of the molten steel was set to 7000 kg / m³ as the physical property of the fluid. ３ The viscosity was set to 0.005 kg / (m·s). Assuming the slag was foamed, the apparent density was set to 750 kg / m³. ３ The viscosity was set to 0.025 kg / (m·s).

[0023] The calculation domain is shown in Figure 4. The molten steel domain 12 has a diameter of 10,000 mm and a depth of 2,900 mm, the slag 13 has a thickness of 600 mm, the chute outlet 7 of chute 3 is 6,500 mm above the slag surface, a typical chute angle θ is 45°, and the height difference between the chute inlet 6 and the chute outlet 7 of chute 3 is 1,974 mm. Here, "chute angle θ" refers to the angle of the central axis of chute 3 with respect to the horizontal plane. The molten steel surface, which is the surface of the molten steel 12 formed by the melting of reduced iron in the electric furnace 1, is a horizontal plane. Therefore, the chute angle θ is the angle of the central axis of chute 3 with respect to the molten steel surface.

[0024] As described above, the present invention is based on the idea that by adopting an obstacle type (see Figure 5) in which an obstacle 4 is installed inside the chute 3, or a convex shape type (see Figure 6) in which an appropriate convex shape 5 is given as the shape of the chute outlet 7, chute clogging can be suppressed, reduced iron can be introduced more widely, and reduced iron can be dissolved more efficiently.

[0025] As an example of an obstacle type, the shape of the obstacle 4 at the chute outlet 7, intended for dispersing reduced iron, is shown in the front view of Figure 5. Figure 5 shows the configuration when the obstacle 4 is projected onto the chute outlet surface 17 of the chute 3. Figure 5A is a comparative example without an obstacle, and Figures 5B to 5G are examples of the present invention with the obstacle 4.

[0026] Figure 6 shows the shape of the chute outlet 7 that was considered as a convex shape type capable of dispersing reduced iron. In Figures 6A to 6C, (A1) to (C1) are front views, and (A2) to (C2) are side cross-sectional views. For example, (A1) is a view taken along the line A1-A1, and (A2) is a cross-sectional view taken along the line A2-A2. The shape of the chute outlet surface 17 of the chute 3 forms a convex shape 5 in the chute with a part of the outer circumference protruding inward relative to the shape of the chute inlet surface 16. The convex shape 5 starts at a position 1000 mm upstream of the chute outlet 7 (convex shape start position 8), and the chute cross-sectional area smoothly narrows from the convex shape start position 8 to the chute outlet 7.

[0027] In the chute outlet surface 17 shown in Figures 5 and 6, the largest circle inscribed within the region through which reduced iron can pass is drawn with a dashed line. Hereafter, this will be referred to as the largest inscribed circle 10. Let the diameter of the largest inscribed circle 10 be d.

[0028] Numerical simulations were performed for each chute shape shown in Figures 5, 6, and 7.

[0029] In the case-b-n condition of Figure 5B, several height levels were calculated for the height n1 shown in the figure. Also, in the case-1-n condition of Figure 6A and case-2-n of Figure 6B, several gap levels were calculated for the gap width n2 shown in the figure. The cross-sectional area of ​​the chute is uniform up to the vicinity of the exit, but when considering the exit shape, as shown in the side views of Figure 6, the convex shape starting position 8 is set 300 mm before the chute exit, and the shape is deformed from the convex shape starting position 8 to form the convex shape 5. The chute diameter was set to 420 mm, but calculations were also performed with a diameter of 520 mm to check the effect of the chute diameter. In that case, the length of the obstacle and the exit shape were changed in proportion to the diameter size. The thickness of the obstacle 4 was set to 50 mm. Here, the thickness of the obstacle 4 refers to the thickness in the depth direction from the chute exit inward.

[0030] The dispersion of the introduced reduced iron was evaluated by calculating the results after introducing the iron for 10 seconds at three different introduction rates k: 4 t / min, 8 t / min, and 12 t / min. Figure 8 shows an example of the calculation results. The center coordinates were determined from the sum average of the coordinates of all the reduced iron after introduction, and a circle 22 with a radius of 1 m was drawn from the center position. The smaller the number density of reduced iron within this circle 22 with a radius of 1 m, the more the reduced iron is dispersed outside of the circle 22, and the wider the range of reduced iron dispersion can be evaluated.

[0031] Figure 8 shows the particle distribution 10 seconds after the end of the input process. Figure 8A is for Case-a of Figure 5A, and Figure 8B is for Case-b-n of Figure 5B with n1 = 100 mm. The number density (particles / m³) of reduced iron introduced into a circle 22 with a radius of 1 m is shown in the figure. ２ The following is described. As can be seen by comparing Figure 8A and Figure 8B, when using chute 3 in Figure 8B, which has an obstacle inside, the amount of reduced iron dispersed outside the circle 22 increases, and the dispersibility is improved compared to when using chute in Figure 8A, which does not have an obstacle inside.

[0032] Case-a in Figure 5A is used as the reference comparative example. The number density of reduced iron particles present within a circle 22 with a radius of 1 m under each condition was divided by the number density of the comparative example in Case-a in Figure 5A, and the resulting value was evaluated as the "accumulation rate (-)".

[0033] After examining several indicators for evaluating the dispersion of reduced iron, it became clear that the size of the region through which reduced iron can pass at the chute exit surface is important. Firstly, the ratio of the diameter d of the maximum inscribed circle 10 defined above to the major axis s of the reduced iron particles was defined as d / s. Here, the major axis s of the reduced iron particles is the maximum length of the straight line connecting any two points on the surface of the particle (see Figure 3). Secondly, the passage area S through which particles can pass at the chute exit surface was divided by the passage area S of each example by the passage area of ​​Case-a in Figure 5A, which is a comparative example, to obtain the exit area ratio J. The evaluation results of the accumulation rate indicating the dispersion of reduced iron are shown in Tables 1 and 2, while displaying the first indicator (d / s) and the second indicator (exit area ratio J). If chute blockage occurred, "blockage" is written in the accumulation rate column of Tables 1 and 2.

[0034]

[0035]

[0036] Table 1 shows the case with an obstacle at the outlet (obstacle type), and Table 2 shows the case with a convex shape at the outlet (convex shape type). The standard shape was used for the reduced iron, and the major axis s of the reduced iron was 126 mm as shown in Figure 3. Both Table 1 and Table 2 use Case-a (Figure 5A) as a comparative example. In all conditions, if no blockage occurred, the accumulation rate was lower than that of the comparative example, resulting in better results than the comparative example. There was a tendency for the effect to decrease as the outlet area ratio J approached 1. Figure 9 shows the relationship between the outlet area ratio J and the accumulation rate shown in Tables 1 and 2. Note that Figure 9 shows the results for Nos. 1-15 and Nos. 21-35 shown in Tables 1 and 2, excluding the comparative examples Nos. 1, 14, 21, and 34. Also, Figure 9 does not show the results when blockage occurred in the chute. The lowest outlet area ratio J is No. The accumulation rate was 0.719 when using 27 chutes (J = 0.664), and the accumulation rate was the highest at 0.985 when using chute No. 2 (J = 0.993), which had the largest outlet area ratio J.

[0037] In the convex shape type, the shape of the chute outlet surface is such that a portion of the outer circumference is convex inward relative to the shape of the chute inlet surface. In contrast, if the shape of the chute outlet differs from that of the chute inlet surface along its entire circumference, it cannot be considered the convex shape of the present invention. For example, as in Case 5 (Figure 7B), when the shape of the chute outlet surface is narrowed in size along its entire circumference relative to that of the chute inlet surface, it is clear that the improvement in the accumulation rate is small, as shown in No. 22 of Table 2.

[0038] Next, to examine the effect of the major axis s of the reduced iron 11, calculations were performed when the reduced iron 11 was isotropically reduced and the major axis s was set to 30 mm, 60 mm, and 80 mm. For the shape of the chute outlet 7, the chute outlet diameter was kept constant at 420 mmφ, and the calculations were performed using the chutes shown in Figure 5B Case-b-n (n1 = 100, 150 mm), Figure 5G Case-g-n (n2 = 60 to 240 mm), Figure 6C Case-3 (triangle 2), and Figure 7A Case-4-n (n2 = 40 to 160 mm).

[0039] The results are shown in Table 3, Table 4, Figure 10, and Figure 11. Table 3 and Figure 10 are for the obstacle type with an obstacle installed at the exit, and Table 4 and Figure 11 are for the convex shape type with a convex shape provided as the exit shape. In Figure 10 and Figure 11, the horizontal axis represents the input speed k, the vertical axis represents d / s, and the non-blocking condition is indicated by ○, and the blocked condition is indicated by ×. From Figure 10 and Figure 11, it can be seen that the smaller the major diameter s, the larger the d / s at which blockage occurs. This is presumably because the number of particles is large and the frictional force increases due to more contact between the particles.

[0040]

[0041]

[0042] In both the obstacle type of Figure 10 and the convex shape type of Figure 11, the smaller the major diameter s, the larger the input speed k, and the smaller the d / s, the easier it is to cause blockage. For example, when comparing No. 62, 69, and 76 with the same input speed k for the case where d / s is the same, it was found that the smaller the major diameter s, the easier it is to cause blockage. Similarly, for example, when comparing No. 61 - 64 with the same input speed k for the case where the major diameter s is the same, it was found that the smaller the d / s, the easier it is to cause blockage. Furthermore, for example, when comparing No. 62 with the same major diameter s and d / s in terms of the input speed, it was found that the larger the input speed k, the easier it is to cause blockage. Also, in the case of the obstacle type with an obstacle installed at the chute exit and the convex shape type where the shape of the exit is changed to a convex shape, the convex shape type was less likely to cause blockage.

[0043] From the above, the conditions for the chute exit not to be blocked are sorted out as follows. In the case of the obstacle type with an obstacle installed, when the relationship between the major diameter s [mm], the input speed k [t / min], and d / s satisfies (-0.0021s + 0.2927)k + (0.0024s + 1.7415) < d / s (Equation 1), it will not be blocked.

[0044] In view of the range where numerical analysis simulations were actually performed, the following limitations of (Equation 2) and (Equation 3) are imposed. 30 ≤ s ≤ 126 (Equation 2) 4 ≤ k ≤ 12 (Equation 3)

[0045] In the case of the convex shape type, blockage does not occur if the relationship between the major axis s [mm], the feeding speed k [t / min], and d / s satisfies (-0.0009s + 0.165)k + 1.1367 < d / s (Equation 4).

[0046] To confirm the effect of the chute 3 insertion angle (chute angle θ), calculations were performed using comparative example, case-b-100, case-2-n (n2 = 280 mm), insertion speed of 4 t / min, and reduced iron major diameter of 126 mm, by changing the chute angle θ, which is the chute central axis and the molten steel surface (the surface of the molten steel 12) shown in Figure 12, to 45°, 65°, and 90°. Here, the chute central axis refers to the central axis of the chute upstream of the convex shape start position 8 (the axis shown by the dashed line in Figure 12) when the chute outlet shape is of the convex type. In this case, the chute length was adjusted so that the height difference for the particles to fall to the outlet was the same, and the results are shown in Figure 13. In Figure 13, the horizontal axis is the chute angle θ, and the vertical axis is the number density of reduced iron particles present in a circle 22 with a radius of 1 m. In the present invention, the number density is maintained at a low level even when the chute angle θ is changed, demonstrating the effectiveness of the present invention. In contrast, in the comparative example, as the chute angle θ increased and chute 3 approached perpendicular to the horizontal plane (molten steel surface), the number density decreased, and the distribution of reduced iron tended to be more dispersed. The reasons for this include: 1) reduced iron is more dispersed within the chute as the input angle approaches perpendicular to the horizontal plane (molten steel surface), 2) the chute becomes shorter, reducing the time the particles are subjected to friction, and 3) friction decreases due to the reduced normal force with the inner wall of the chute. When the time the particles are subjected to friction from the chute decreases, the velocity of the particles is maintained, causing them to collide with each other at higher speeds and travel further, thus improving dispersion.

[0047] Figure 14 shows the results of calculations using the convex-shaped Case-1-n (flat shape) (Figure 6A), n2 = 315 mm, with an input speed k = 4 t / min, reduced iron major axis s = 126 mm, and chute angle θ = 45°, changing the convex shape starting position 8 from 300 mm before the chute outlet 7 used in the above calculation. The horizontal axis is the distance between the chute outlet 7 and the convex shape starting position 8, and the vertical axis is the accumulation rate. When the chute shape begins to change at an early stage, 1) the area of ​​the protrusion increases, which increases the area in which particles contact the chute within the chute, so the velocity decreases due to friction, 2) the rate of change of shape with respect to distance decreases, and 3) the rectification of the raw material within the chute is promoted, resulting in results no different from the comparative example. If the distance between the chute outlet 7 and the convex shape starting position 8 is 1000 mm or less, an improvement effect can be achieved compared to the comparative example, and the shorter the distance between the chute outlet 7 and the convex shape starting position 8, the better the dispersion. Therefore, in this invention, the chute cross-sectional area is designed to smoothly narrow from a position 1000 mm or less upstream of the chute outlet. On the other hand, if the convex shape starts too close to the outlet, the rate of change in shape becomes large, making it prone to blockage, so a position of 300 mm or more is preferable.

[0048] Figure 15 shows the results of calculations performed using Case-f (tooth shape) in Figure 5F, with an input speed k = 4t / min, reduced iron major axis s = 126 mm, and chute angle θ = 45°, and changing the thickness of obstacle 4 from 50 mm to 10 mm and 100 mm. As shown in Figure 15, there was no significant difference in the accumulation rate even when the thickness of obstacle 4 was changed. However, if the obstacle thickness is too thin, there are concerns about strength, and if the obstacle thickness is too thick, installation becomes difficult, so the range of obstacle thickness is preferably 10 mm to 100 mm.

[0049] As shown in Figure 16, the shape of the chute outlet surface 17 is larger than the shape of the chute inlet surface 16. The calculations performed with a chute angle θ = 45°, an input speed k = 4t / min, and a reduced iron diameter s = 126 mm are shown in Table 5. Thus, even a change in shape that increases the chute outlet area is effective.

[0050]

[0051] The shape of the chute outlet in this invention is not limited to a cylindrical shape. As shown in Figure 17, Table 6 shows the results of calculations performed with a rectangular chute shape and obstacles, using a chute angle θ = 45° and an input speed k = 4t / min. Thus, the invention is effective even when the cross-sectional shape of the chute 3 is not cylindrical.

[0052]

[0053] 1. Electric furnace 2. Electrode 3. Chute 4. Obstacle 5. Convex shape 6. Chute entrance 7. Chute exit 8. Starting position of convex shape 10. Maximum inscribed circle 11. Reduced iron 12. Molten steel 13. Slag 14. Arc 16. Chute entrance surface 17. Chute exit surface 18. Widening shape 19. Starting position of widening shape 20. Starting position of narrowing shape 21. Molten metal surface spraying situation 22. Circle with radius 1m

Claims

1. A method for introducing reduced iron into an electric furnace for melting reduced iron, wherein an obstacle into which the reduced iron will collide is placed within 200 mm from the outlet of the reduced iron introduction chute, and when the obstacle is projected onto the chute outlet surface of the reduced iron introduction chute, the maximum inscribed circle of the region through which the reduced iron can pass is defined as the maximum inscribed circle, and the ratio d / s of the diameter d [mm] of the maximum inscribed circle to the major axis s [mm] of the reduced iron satisfies the following equation (Equation 1) with respect to the reduced iron introduction rate k [t / min], and also satisfies the following equations (Equation 2) and (Equation 3). (-0.0021s + 0.2927)k + (0.0024s + 1.7415) < d / s (Equation 1) 30 ≤ s ≤ 126 (Equation 2) 4 ≤ k ≤ 12 (Equation 3) 2. A method for introducing reduced iron into an electric furnace for melting reduced iron using a reduced iron introduction chute, wherein the shape of the chute outlet surface of the reduced iron introduction chute is such that a part of the outer circumference is convex inward relative to the shape of the chute inlet surface, the convex shape changes such that the chute cross-sectional area smoothly narrows from a position 1000 mm upstream of the chute outlet, the maximum inscribed circle of the region through which the reduced iron can pass at the chute outlet surface is defined as the maximum inscribed circle, and the ratio d / s of the diameter d [mm] of the maximum inscribed circle to the major axis s [mm] of the reduced iron satisfies the following equation (Equation 4) with respect to the reduced iron introduction rate k [t / min], and also satisfies the following equations (Equation 2) and (Equation 3). (-0.0009s + 0.165)k + 1.1367 < d / s (Equation 4) 30 ≤ s ≤ 126 (Equation 2) 4 ≤ k ≤ 12 (Equation 3) 3. A method for introducing reduced iron according to claim 1 or claim 2, characterized in that the reduced iron introduction chute is used, wherein the central axis of the reduced iron introduction chute is positioned at an angle of 45° to 90° with respect to the horizontal plane.

4. A chute for introducing reduced iron into an electric furnace for melting reduced iron, characterized in that an obstacle into which the reduced iron will collide is installed within 200 mm from the outlet of the chute for introducing reduced iron.

5. A chute for introducing reduced iron into an electric furnace for melting reduced iron, wherein the shape of the chute outlet surface of the chute for introducing reduced iron is such that a part of the outer circumference is convex inward relative to the shape of the chute inlet surface, and the convex shape changes such that the chute cross-sectional area smoothly narrows from a position 1000 mm upstream of the chute outlet.

6. The reduced iron input chute according to claim 4 or claim 5, characterized in that the central axis of the reduced iron input chute is positioned at an angle of 45° to 90° with respect to the horizontal plane.

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