Method for producing molten steel, and electric arc furnace

Abstract

Disclosed is a method for producing molten steel, which is capable of efficiently generating a target reaction when an oxygen jet is jetted to molten iron in an electric arc furnace and an auxiliary material is supplied. A method for producing molten steel according to the present disclosure is a method for producing molten steel using an electric arc furnace provided with an oxygen supply mechanism and an auxiliary material supply mechanism, the method being characterized by including spraying an oxygen jet from the oxygen supply mechanism to molten steel in the electric arc furnace, and a step for supplying an auxiliary material from the auxiliary material supply mechanism toward a position (P) on the surface of the molten iron, the position (P) being a position on the outside of the surface of impact between the oxygen jet and the molten iron.

Description

TECHNICAL FIELD

[0001] Disclosed is a method for manufacturing molten steel using an electric arc furnace and an electric arc furnace. BACKGROUND

[0002] In Patent Literature 1, disclosed is a technology of making an impregnation lance impregnate in molten iron in an electric arc furnace, blowing carbon material from the impregnation lance, and blowing oxygen into slag generated at the surface of the molten iron. In Patent Literature 1, on the basis of the carbon concentration in the molten iron being increased in the electric arc furnace, the molten iron is discharged from the electric arc furnace, and then, refining is performed in a converter, thereby manufacturing molten steel. In the refining in the converter, for example, CO gas and the like are generated by a decarburization reaction using an oxygen jet, and nitrogen is removed by the CO gas and the like.

[0003] On the other hand, it is also possible to perform the above-described nitrogen removal in the electric arc furnace. For example, it is considered that by simultaneously supplying oxygen and carbon material to the molten iron in the electric arc furnace, the above-described nitrogen removal can be performed. However, regarding the nitrogen removal in the electric arc furnace, the current situation is that sufficient research has not been performed. Further, in the electric arc furnace, sometimes, simultaneous blowing of oxygen and carbon material is performed mainly for the purpose of promoting slag formation and the like. In this case, generally, carbon and oxygen are concentratedly supplied to one place of the molten iron by making the carbon material and the oxygen jet flow together, and CO gas is reliably generated in the slag, and the formation state of the slag is stabilized.

[0004] In addition, it is also possible to simultaneously supply oxygen and an auxiliary material other than carbon material to the molten iron in the electric arc furnace. As the auxiliary material other than carbon material, a Ca-containing material (lime and the like), a Si-containing material (silica sand and the like), an Al-containing material (calcium aluminate and the like), an Mg-containing material (magnesia and the like), and the like can be listed.

[0005] PRIOR ART DOCUMENTS

[0006] PATENT LITERATURE

[0007] Patent Literature 1: Japanese Patent Application Publication No. 2016-145393 SUMMARY

[0008] According to the present inventor's insight, in a case where an auxiliary material is supplied to the molten iron in the electric arc furnace in association with an oxygen jet, the efficiency of a reaction targeted for is likely to decrease. For example, in a case where nitrogen is removed from the molten iron in the electric arc furnace, in a case where carbon material and an oxygen jet are made to flow together, and carbon and oxygen are concentratedly supplied to one place of the molten iron, sufficient nitrogen removal efficiency is not obtained.

[0009] The present application discloses the following multiple modes as one of means for solving the above-described problem.

[0010] <Mode 1>

[0011] A method of manufacturing molten steel, which is a method of manufacturing molten steel using an electric arc furnace provided with an oxygen supply mechanism and an auxiliary raw material supply mechanism,

[0012] The manufacturing method includes a step of jetting an oxygen jet flow from the oxygen supply mechanism toward molten iron in the electric arc furnace, and supplying an auxiliary raw material from the auxiliary raw material supply mechanism toward a position P of a surface of the molten iron,

[0013] The position P is a position outside a collision surface of the oxygen jet flow and the molten iron,

[0014] <Mode 2>

[0015] The method of manufacturing molten steel according to Mode 1,

[0016] The auxiliary raw material is a carbon material.

[0017] <Mode 3>

[0018] The method of manufacturing molten steel according to Mode 1 or 2,

[0019] The following relationship (1) is satisfied,

[0020]

[0021] Here,

[0022] r is a distance (m) from an intersection point O of a central axis of the oxygen jet flow and a surface of the molten iron to the position P,

[0023] W m is a weight (tons (t)) of the molten iron.

[0024] <Mode 4>

[0025] The method of manufacturing molten steel according to any one of Modes 1 to 3,

[0026] includes a step of jetting an oxygen jet flow from the oxygen supply mechanism toward molten iron in the electric arc furnace, and supplying a carbon material from a carbon material supply mechanism that is the auxiliary raw material supply mechanism toward a position P1,

[0027] The oxygen jet flow is inclined with respect to a vertical direction,

[0028] The position P1 is located on a horizontal plane including a still molten iron surface,

[0029] The position P1 is located outside a collision surface of the oxygen jet flow and the horizontal plane,

[0030] A perpendicular line from a top end of the oxygen supply mechanism to the horizontal plane intersects the horizontal plane at an intersection point P2,

[0031] A central axis of the oxygen jet intersects the horizontal plane at an intersection point P3,

[0032] An angle θ1 formed by a line segment P1P3 connecting the position P1 and the intersection point P3 and a line segment P2P3 connecting the intersection point P2 and the intersection point P3 is 0° or more and 90° or less.

[0033] [Mode 5]

[0034] The method of producing molten steel according to Mode 4,

[0035] In the horizontal plane, the position P1 is located inside a semicircle having a radius of 3r1 (r1: short radius of a geometric cusp) centered at the intersection point P3 and having the line segment P2P3 as a symmetric axis.

[0036] [Mode 6]

[0037] An electric arc furnace is an electric arc furnace that handles molten iron, and includes at least one oxygen jet mechanism and at least one auxiliary material supply mechanism,

[0038] The oxygen jet mechanism is configured to jet an oxygen jet toward a surface of the molten iron in the electric arc furnace,

[0039] The auxiliary material supply mechanism is configured to supply an auxiliary material toward a position P of the surface of the molten iron in the electric arc furnace, and is configured such that the position P becomes a position outside a collision surface of the oxygen jet and the molten iron.

[0040] [Mode 7]

[0041] The electric arc furnace according to Mode 6,

[0042] The auxiliary material supply mechanism includes at least one carbon material supply mechanism,

[0043] The oxygen jet mechanism is configured such that a direction of the oxygen jet is inclined with respect to a vertical direction,

[0044] The carbon material supply mechanism is configured to supply a carbon material toward a position P1,

[0045] The oxygen jet mechanism and the carbon material supply mechanism are configured such that:

[0046] The position P1 is located on a horizontal plane including a still molten iron surface,

[0047] The position P1 is located outside a collision surface of the oxygen jet and the horizontal plane,

[0048] A perpendicular line from a top end of the oxygen jet mechanism to the horizontal plane intersects the horizontal plane at an intersection point P2,

[0049] The central axis of the oxygen jet intersects the horizontal plane at an intersection point P3, and

[0050] An angle θ1 formed by a line segment P1P3 connecting the position P1 and the intersection point P3 and a line segment P2P3 connecting the intersection point P2 and the intersection point P3 is 0° or more and 90° or less.

[0051] According to the molten steel manufacturing method and the electric arc furnace of the present disclosure, in a case where an oxygen jet is injected to the molten iron in the electric arc furnace and an auxiliary raw material is supplied, a reaction targeted can be efficiently generated. For example, in a case where an oxygen jet is injected to the molten iron and a carbon material is supplied as an auxiliary raw material, the molten iron can be efficiently denitrified. BRIEF DESCRIPTION OF DRAWINGS

[0052] Figure 1 An example of a positional relationship of each member when the electric arc furnace is viewed from above is schematically shown.

[0053] Figure 2A An example of a positional relationship of the oxygen supply mechanism and the auxiliary raw material supply mechanism when the electric arc furnace is viewed from the side is schematically shown. The upper electrode and the like are omitted.

[0054] Figure 2B An example of a positional relationship of the oxygen supply mechanism and the auxiliary raw material supply mechanism when the electric arc furnace is viewed from the side is schematically shown. The upper electrode and the like are omitted.

[0055] Figure 3 An example of a positional relationship of the oxygen jet and the auxiliary raw material supply position is schematically shown.

[0056] Figure 4 An example of a positional relationship when the electric arc furnace is viewed from above, that is, a positional relationship of a position P1, an intersection point P2, and an intersection point P3 in a horizontal plane including a stationary molten iron surface is schematically shown.

[0057] Figure 5 An example of a positional relationship of the oxygen supply mechanism and the carbon material supply mechanism when the electric arc furnace is viewed from the side is schematically shown. The upper electrode and the like are omitted.

[0058] Figure 6 An example of a shape of the oxygen jet and a shape of a collision surface of the oxygen jet and the horizontal plane including the stationary molten iron surface is schematically shown.

[0059] Figure 7 An example of a direction of a flow induced around the collision surface of the oxygen jet is schematically shown.

[0060] Figure 8 An example of a preferable position of the position P1 in the horizontal plane including the stationary molten iron surface is schematically shown. DETAILED DESCRIPTION

[0061] 1. A method for manufacturing molten steel

[0062] A method for manufacturing molten steel according to the present disclosure will be described with reference to the drawings. However, the method for manufacturing molten steel according to the present disclosure is not limited to the illustrated mode. As shown in FIG. 1, one embodiment of the method for manufacturing molten steel according to the present disclosure is a method for manufacturing molten steel using an electric arc furnace 100 provided with an oxygen supply mechanism 20 and an auxiliary material supply mechanism 30, and the method includes a step of injecting an oxygen jet 21 from the oxygen supply mechanism 20 toward an iron melt 10 in the electric arc furnace 100 and supplying an auxiliary material 31 from the auxiliary material supply mechanism 30 to a position P on the surface of the iron melt 10. Here, the position P is a position outside the impingement surface 21x of the oxygen jet 21 and the iron melt 10. Figures 1-3

[0063] 1.1 Iron melt

[0064] ​The molten iron 10 is obtained by melting an iron source, for example, by generating an electric arc in the electric arc furnace 100. The iron source, for example, can be an iron source containing at least one selected from the group consisting of scrap iron, reduced iron, iron ingot, and granular iron, and a molten iron, a molten steel, or the like produced using other melting furnaces, refining furnaces can also be used. The molten iron 10 can contain various elements other than iron. The composition of the elements other than iron depends on the kind of the iron source. For example, the molten iron 10 before the auxiliary material 31 is supplied can be a molten iron containing 0.02 mass% or more and 3.0 mass% or less of C, can be a molten iron containing 0.005 mass% or more and 0.030 mass% or less of N, and can be a molten iron containing 0.003 mass% or more and 0.1 mass% or less of P. In particular, in the production method of the present disclosure, in the case where the carbon material is supplied as the auxiliary material 31 to the molten iron 10 and the oxygen jet 21 is injected to cause the denitrogenation reaction together with the decarburization, a more significant effect can be obtained in the low-carbon region that becomes a solute carbon movement bottleneck in the decarburization reaction in the molten iron 10. In the production method of the present disclosure, in the case where the carbon material is supplied as the auxiliary material 31 to the molten iron 10, the molten iron 10 before the auxiliary material 31 is supplied can be a molten iron containing 0.02 mass% or more and 3.0 mass% or less of C, can be a molten iron containing 0.005 mass% or more and 0.030 mass% or less of N, and can be a molten iron containing 0.003 mass% or more and 0.1 mass% or less of P. Alternatively, in the production method of the present disclosure, in the case where the auxiliary material other than the carbon material is supplied as the auxiliary material 31 to the molten iron 10, it is preferable to avoid the implementation in the ultra-low-carbon concentration region where the decarburization reaction becomes difficult from a balance standpoint, and for example, the molten iron 10 before the auxiliary material 31 is supplied preferably contains 0.3 mass% or more of C. More specifically, in the production method of the present disclosure, in the case where the auxiliary material other than the carbon material is supplied as the auxiliary material 31 to the molten iron 10, the molten iron 10 before the auxiliary material 31 is supplied can be a molten iron containing 0.3 mass% or more and 3.0 mass% or less of C, can be a molten iron containing 0.010 mass% or more and 0.030 mass% or less of N, and can be a molten iron containing 0.003 mass% or more and 0.1 mass% or less of P. The density of the molten iron 10 can be, for example, 6600 kg / m 3 7000 kg / m 3 or more.

[0065] 1.2 Oxygen supply mechanism

[0066] The electric arc furnace 100 is provided with at least one oxygen supply mechanism 20. The oxygen supply mechanism 20 injects the oxygen jet 21 to the molten iron 10 in the electric arc furnace 100. The oxygen supply mechanism 20 can be a lance. The number of oxygen jets 21 injected from one lance is not particularly limited. For example, the lance can be as shown in FIG. 2 and Figure 3The single-hole lance is shown. Alternatively, the lance can be straight, can have a Laval structure, and can have a coherent burner that injects gas fuel and combustion-supporting gas in a manner that surrounds the oxygen jet. As shown in Figure 1 The oxygen supply mechanism 20 can be at least one of a lance (so-called main lance) that is inserted from a roof of the electric arc furnace 100, a wall lance that is provided to a wall, and a variable lance that is positioned by a robot or the like. As shown in FIGS. 2 and Figure 3 In the electric arc furnace 100, oxygen is blown toward the surface 10x of the molten iron 10 from the oxygen supply mechanism 20. Thereby, various chemical reactions such as a decarburization reaction, a denitrogenation reaction, a dephosphorization reaction, and the like can be generated in the molten iron 10 depending on the kind of the auxiliary raw material 31 described later.

[0067] The shape of the oxygen jet 21 injected from the oxygen supply mechanism 20 depends on the inclination of the oxygen supply mechanism 20, the shape of the injection hole of the oxygen supply mechanism 20, and the like. The direction of the oxygen jet 21 injected from the oxygen supply mechanism 20 can be inclined with respect to the vertical direction. That is, as shown in Figure 3 The direction of the oxygen jet 21 injected from the oxygen supply mechanism 20 can be inclined by an angle θ with respect to the vertical direction. The inclination angle θ can be determined as an angle formed by a central axis of the oxygen supply mechanism 20 and a line parallel to the vertical direction. The inclination angle θ can be, for example, 5° or more and 30° or less. Alternatively, as shown in Figure 3 The oxygen jet 21 can also be injected from the injection hole of the oxygen supply mechanism 20 toward the molten iron 10 with a certain spread angle α. The spread angle α depends on the shape of the injection hole of the oxygen supply mechanism 20 and the like. The spread angle α can be, for example, 10° or more and 13° or less. Alternatively, as shown in Figure 3 A certain height h can be provided from the injection hole of the oxygen supply mechanism 20 to the surface 10x of the molten iron 10. Further, in the case where the oxygen supply mechanism 20 is inclined with respect to the vertical direction, the height h refers to a distance from an upper end of the injection hole of the oxygen supply mechanism 20 to the surface 10x of the molten iron 10. The height h can be, for example, 0.2 m or more and 0.8 m or less. Alternatively, as shown in Figure 3 The oxygen supply mechanism 20 can be an oxygen supply mechanism having an injection hole with a hole diameter d. Further, the hole diameter d refers to an equivalent circular diameter of the injection hole. The hole diameter d can be, for example, 20 mm or more and 100 mm or less.

[0068] The flow rate of the oxygen jet 21 injected from one oxygen supply mechanism 20 is not particularly limited and can be, for example, 1000 Nm 3 / h or more and 4000 Nm 3 / h or less. Further, the flow velocity of the oxygen jet 21 injected from the oxygen supply mechanism 20 (which is the flow velocity in the injection hole of the oxygen supply mechanism 20 and is the flow velocity on the central axis) is not particularly limited and can be, for example, 10 m / s or more and 3000 m / s or less.

[0069] 1.3 Auxiliary raw material supply mechanism

[0070] The electric arc furnace 100 is provided with at least one auxiliary raw material supply mechanism 30. The auxiliary raw material supply mechanism 30 supplies an auxiliary raw material toward a position P of the surface of the molten iron 10 in the electric arc furnace 100. The auxiliary raw material can be supplied into the furnace, for example, via a supply port provided in the electric arc furnace 100. The supply port can be provided in any part of the furnace. For example, the supply port can be a hole provided in the inner wall (side wall) of the furnace, or a hole provided in the furnace cover. As shown in Fig. 2, the supply port can be provided at a position higher than the surface 10x of the molten iron 10. The number of supply ports can be one or a plurality. Figure 3

[0071] The method of supplying the auxiliary raw material by the auxiliary raw material supply mechanism 30 is not particularly limited. For example, the following methods can be cited: a method of supplying the auxiliary raw material 31 via a hole provided in the inner wall of the furnace as shown in Fig. 2(A), and a method of supplying the auxiliary raw material 31 via a hole provided in the furnace cover as shown in Fig. 2(B). A lance, a charging chute, or the like can be appropriately used in accordance with the positional relationship between the hole provided in the inner wall or the furnace cover and the position P of the supply position of the auxiliary raw material 31 in the surface 10x of the molten iron 10, or the like. As the charging chute, a publicly known charging chute can be used. In the case where a lance is used as the auxiliary raw material supply mechanism 30, the auxiliary raw material 31 can be supplied to the molten iron 10 together with the top gas. In this case, the top gas from the auxiliary raw material supply mechanism 30 can be a gas that does not generate a fire point on the surface of the molten iron 10, or a gas that generates a fire point. For example, from the viewpoint of cost, it is preferable to use one or both of air and N2 gas, from the viewpoint of low nitrogenization, it is preferable to use at least one selected from the group consisting of pure oxygen, Ar gas, and CO2 gas, and in the case where the auxiliary raw material is a carbon material, a deoxidizing material, or the like, in order to avoid being consumed in the air before reaching the iron bath, it is preferable to use one or both of Ar gas and CO2 gas, which are less reactive. In this way, the top gas can be selected in accordance with the manufacturing conditions, or can be a gas obtained by mixing at least two or more kinds of gases in a prescribed ratio within the range of these operational constraints. The lance as the oxygen supply mechanism 20 and the lance as the auxiliary raw material supply mechanism 30 are separate from each other.

[0072] ​The auxiliary raw material 31 can be supplied vertically downward with respect to the molten iron 10, or can be supplied obliquely downward. Regardless of this, the auxiliary raw material supply mechanism 30 supplies the auxiliary raw material toward the prescribed position P. Here, the "toward the position P" means that the target position of the supply of the auxiliary raw material 31 is the position P, and a part of the auxiliary raw material 31 can be supplied to a portion other than the position P due to diffusion or the like. For example, a part of the auxiliary raw material 31 can be supplied to the inside of the impingement surface 21x of the oxygen jet 21 with the molten iron 10. In the manufacturing method of the present disclosure, it is good that a majority of the auxiliary raw material 31, for example, 50% by mass or more, 70% by mass or more, or 90% by mass or more, is supplied to the position P outside the impingement surface 21x of the oxygen jet 21 with the molten iron 10.

[0073] The amount of the auxiliary raw material 31 supplied from the auxiliary raw material supply mechanism 30 is not particularly limited. For example, the amount of the auxiliary raw material 31 supplied from one auxiliary raw material supply mechanism 30 can be 10 kg / min or more and 100 kg / min or less.

[0074] The kind of the auxiliary raw material 31 supplied from the auxiliary raw material supply mechanism 30 is not particularly limited. The auxiliary raw material 31 can be, for example, a carbon material, or can be an auxiliary raw material other than the carbon material. Specific examples of the carbon material are described later. The auxiliary raw material other than the carbon material can be at least one selected from a Ca-containing material (lime or the like), a Si-containing material (silica sand or the like), an Al-containing material (calcium aluminate or the like), an Mg-containing material (magnesia or the like), and the like. The shape of the auxiliary raw material 31 can be various shapes such as a powder shape, a granular shape, a block shape, or the like, as long as the auxiliary raw material 31 can be appropriately supplied from the auxiliary raw material supply mechanism 30 to the molten iron 10. In addition, the auxiliary raw material 31 can be a press-formed product. In addition, it can be a substance in which a plurality of auxiliary raw materials 31 are mixed. The auxiliary raw material 31 can have, for example, a particle diameter of 0.1 mm or more and 5 mm or less. In the case where the auxiliary raw material 31 is large, the powder conveying system possessed by a general steelmaking facility is easily clogged, and in addition, since the specific surface area becomes small, the heat transfer property deteriorates, and the time during which the auxiliary raw material 31 remains on the molten iron 10 in an unmelted state becomes long. On the other hand, in the case where the auxiliary raw material 31 is small, the dispersibility in the furnace is high, and the auxiliary raw material 31 is easily sucked into the exhaust system, and the material utilization rate deteriorates.

[0075] In the manufacturing method of the present disclosure, by supplying the auxiliary raw material 31 toward the prescribed position P outside the flame, the auxiliary raw material 31 supplied to the flame is reduced, and the temperature reduction of the flame can be suppressed. Thereby, the reaction targeted can be efficiently generated. In addition, in the manufacturing method of the present disclosure, in the case where the auxiliary raw material 31 is a carbon material, the reduction of the material utilization rate due to the combustion of the carbon material in the oxygen jet 21 can be suppressed, and in addition, by supplying the carbon material toward the prescribed position P outside the flame, the carbon deposition rate to the molten iron 10 is increased, and the nitrogen removal efficiency can be significantly improved.

[0076] 1.4 Position P

[0077] Figure 2 and Figure 3 As shown, the position P is a position outside the collision surface 21x between the oxygen jet 21 and the molten iron 10. Preferably, as shown in FIG2 , the auxiliary raw material 31 does not cross the oxygen jet 21 and is supplied to the position P (in other words, preferably, there is no oxygen jet 21 in the middle of the auxiliary raw material 31 from the auxiliary raw material supply mechanism 30 to the molten iron 10). The "collision surface 21x between the oxygen jet 21 and the molten iron 10" can be geometrically determined based on the aforementioned inclination angle θ, expansion angle α, height h, and aperture d. For example, Figure 3 As shown, the distance z from the intersection O of the central axis of the oxygen supply mechanism 20 and the surface 10x of the molten iron 10 to the outer edge X of the collision surface 21x can be determined as z = (tan (θ + α) - tan θ) h + d / (2cos θ). Figure 1 As shown, if the distance r from the intersection O of the central axis of the oxygen jet 21 and the surface 10x of the molten iron 10 to the position P is greater than the distance z, the position P will be outside the collision surface 21x between the oxygen jet 21 and the molten iron 10. That is, in the manufacturing method of the present disclosure, the distance r from the intersection O of the central axis of the oxygen jet 21 and the surface 10x of the molten iron 10 to the position P can be a distance that satisfies the relationship r>(tan(θ+α)-tanθ)h+d / (2cosθ).

[0078] As described above, the position P can be located outside the collision surface 21x between the oxygen jet 21 and the molten iron 10, and the upper limit of the distance r is not particularly limited. However, in the manufacturing method disclosed herein, by making the distance r shorter than the representative length calculated based on the weight of the molten iron 10, it is believed that the movement of the auxiliary raw material 31 to the ignition point becomes less likely to be delayed, the concentration of the auxiliary raw material near the ignition point is increased, and the target reaction can be generated more efficiently. Consider the case where the auxiliary raw material 31 is a carbon material. In this case, decarburization from the molten iron 10 proceeds by the oxygen jet 21. When the carbon concentration of the molten iron 10 is less than the critical carbon concentration, the rate of consumption of carbon in the molten iron 10 due to the decarburization reaction is greater than the rate of supply of dissolved carbon to the reaction site. Therefore, the ratio of oxygen that contributes to decarburization (decarburization oxygen efficiency) in the oxygen supplied by the oxygen supply gradually decreases, and the rate of CO generation at the ignition point decreases, which may become an unfavorable state for denitrification. Furthermore, there is a risk that the Fe in the molten iron 10 may be excessively oxidized, resulting in a decrease in the iron yield and an increase in the FeO concentration in the slag, leading to wear of the refractory material in the electric arc furnace 100. In contrast, by making the distance r shorter than the representative length calculated based on the weight of the molten iron 10, the dissolved carbon concentration near the ignition point is increased, thereby increasing the activity of dissolved [N], further improving the denitrification efficiency, and suppressing excessive Fe oxidation.

[0079] Based on the above perspective, the position P where the auxiliary raw material 31 is supplied can be determined by referring to the representative length of the iron bath and the stirring power density (stirring power density), calculated based on the weight of the molten iron 10 in each charge. For example, according to the well-known document "Asai et al.: Iron and Steel, 68 (1982), vol. 3, pp. 426-434," the representative flow velocity in the inertia-dominated region of the fluid is proportional to the stirring power density raised to the power of 1 / 3. Therefore, if the distance r from the intersection point O to the position P is sufficiently short relative to this representative flow velocity, the delay in the supply of the auxiliary raw material 31 to the ignition point is mitigated. For example, if the auxiliary raw material 31 is a carbon material, the CO gas generation rate due to the decarburization reaction is maintained high, which is beneficial for denitrification. Specifically, for a furnace where top-blowing and bottom-blowing stirring are dominant, the upper limit of the distance r can be determined so that the following relationship is satisfied.

[0080]

[0081] Among them, L: represents the length (m), ε a : Total stirring power density (W / t), W m : Weight of molten iron (t), ρ l : Density of molten iron (tons / m 3 (t / m 3 )), ε T : Top blowing stirring power density (W / t), ε B : Bottom blowing stirring power density (W / t).

[0082] Furthermore, regarding top blowing and bottom blowing, the stirring power density can be calculated by referring to publicly known documents such as "Kai et al.: Iron and Steel, 69 (1983), vol. 2, pp. 228-237" and "Mori et al.: Iron and Steel, 67 (1981), vol. 6, pp. 672-695," and adopting a linear sum value. The mechanism for imparting stirring is not limited to one based on gas supply; the same treatment can be applied to any mechanism. The stirring power density of stirring mechanisms with different locations and principles does not need to be a linear sum; instead, the values ​​can be treated as mechanisms with independent contribution rates.

[0083] According to the inventors' findings, in the production method disclosed herein, by satisfying the following relationship (1), the movement of the auxiliary raw material 31 to the ignition point is less likely to be delayed, the auxiliary raw material concentration near the ignition point is increased, and the target reaction is more likely to occur more efficiently.

[0084]

[0085] Here,

[0086] r is the distance (m) from the intersection O of the central axis of the oxygen jet 21 and the surface 10x of the molten iron 10 to the position P.

[0087] W m is the weight of the molten iron 10 (t).

[0088] 1.5 Other components of electric arc furnace

[0089] As described above, the electric arc furnace 100 has a melting furnace for melting the iron source. The melting furnace is a portion that can be defined by the furnace cover, the furnace inner wall, and the furnace bottom. The planar shape of the melting furnace is preferably as follows: Figure 1 The melting furnace may have a bath depth and / or a furnace diameter. The bath depth and furnace diameter of the melting furnace are not particularly limited.

[0090] exist Figure 1 In the example, an AC-type arc generating unit using only the upper electrode 40 is illustrated. However, the arc generating unit is not limited to this and may also be a DC-type arc generating unit using both the upper electrode 40 and the lower electrode 50. In the case of a DC-type arc furnace 100, the upper electrode 40 can serve as the cathode, and the lower electrode 50 can serve as the anode. The upper electrode 40 is inserted into the furnace through the furnace roof. The lower electrode 50 is located at the furnace bottom. There is at least one upper electrode 40 and at least one lower electrode 50. The positions of the upper and lower electrodes 40, 50 are not particularly limited. For example, if the liquid surface in the melting furnace is roughly circular in plan view, the center of the circle may coincide with the central axis of one upper electrode 40 and / or one lower electrode 50. Alternatively, multiple upper electrodes 40 and / or multiple lower electrodes 50 may be arranged around the center of the circle in plan view. In the arc furnace 100, for example, power is supplied from a power supply unit (not shown) to the upper electrode 40 and the lower electrode 50, thereby generating an arc between the upper electrode 40 and the lower electrode 50. The power supply unit can be a common power supply unit as a means for supplying power to the upper electrode 40 and the lower electrode 50. The power supplied from the power supply unit to the electrodes is not particularly limited as long as it can generate an arc between the electrodes.

[0091] like Figure 1 As shown, the electric arc furnace 100 may include an iron source loading unit 60 for loading an iron source into the melting furnace. Furthermore, the electric arc furnace 100 may include a slag removal door 70 for removing slag and the like formed on the surface of the molten iron 10. Furthermore, the electric arc furnace 100 may include a liquid outlet 80 for discharging the molten iron 10 or molten steel. These may all employ known configurations.

[0092] The arc furnace 100 can have various control units. The control unit can be, for example, a control unit that controls the supply position P (or a position PI to be described later) of the auxiliary raw material 31 supplied from the auxiliary raw material supply unit 30 to the molten iron 10 in accordance with the position of the oxygen jet 21 jetted from the oxygen supply unit 20 to the molten iron 10, or a control unit that controls the position of the oxygen jet 21 jetted from the oxygen supply unit 20 to the molten iron 10 in accordance with the supply position P (or the position PI to be described later) of the auxiliary raw material 31 supplied from the auxiliary raw material supply unit 30 to the molten iron 10, or a control unit that controls both the position of the oxygen jet 21 jetted from the oxygen supply unit 20 to the molten iron 10 and the supply position P (or the position PI to be described later) of the auxiliary raw material 31 supplied from the auxiliary raw material supply unit 30 to the molten iron 10. The control unit can have a publicly known configuration capable of performing the control described above. For example, the control unit can be a control unit having a CPU, a RAM, a ROM, and the like.

[0093] 1.6 Molten steel

[0094] The composition of the molten steel produced by the method of the present disclosure is not particularly limited. In the production method of the present disclosure, when the molten iron 10 is jetted with the oxygen jet 21 and the auxiliary raw material 31 is supplied as described above, decarburization, denitrification, dephosphorization, and the like of the molten iron 10 can be performed in accordance with the kind of the auxiliary raw material 31. The molten steel produced by the method of the present disclosure can be, for example, a molten steel containing 0.01 mass% or more and 3.0 mass% or less of C, a molten steel containing 0.002 mass% or more and 0.030 mass% or less of N, or a molten steel containing 0.003 mass% or more and 0.1 mass% or less of P. The molten steel in the arc furnace 100 can be tapped, for example, via the tap hole 80. The tapped molten steel can be further refined, or can be supplied as it is to continuous casting or the like.

[0095] 1.7 Application Embodiment

[0096] In the production of the molten steel using the arc furnace 100, when the carbon material is supplied as the auxiliary raw material 31 toward the surface 10x of the molten iron 10 in the arc furnace 100, the carbon material is preferably supplied as described below. Hereinafter, the preferred mode of the method of producing the molten steel when the carbon material is supplied as the auxiliary raw material 31 will be described with reference to Figures 4-8 and Figure 1 .

[0097] As described in Figures 4-8 and Figure 5 , the method of producing the molten steel according to the application embodiment includes a step of jetting the oxygen jet 21 from the oxygen supply unit 20 to the molten iron in the arc furnace 100 and supplying the carbon material toward the position PI from the carbon material supply unit as the auxiliary raw material supply unit 30. As described in Figure 6 andFigure 4 As shown in FIG, the direction of the oxygen jet 21 is inclined relative to the vertical direction. Figure 5 and Figure 4 As shown, the position P1 is located at the horizontal plane 101x including the static iron liquid level. Figure 5 and Figure 4 As shown, the position P1 is located outside the collision surface 102x between the oxygen jet 21 and the horizontal plane 101x. Figure 6 and Figure 4 As shown in FIG. 1 , a vertical line extending from the top of the oxygen supply mechanism 20 to the horizontal plane 101x intersects the horizontal plane 101x at the intersection point P2. Figure 6 and Figure 4 As shown, the central axis of the oxygen jet 21 intersects the horizontal plane 101x at the intersection point P3. Figure 3 As shown, an angle θ1 formed by a line segment P1P3 connecting the position P1 and the intersection point P3 and a line segment P2P3 connecting the intersection point P2 and the intersection point P3 is greater than or equal to 0° and less than or equal to 90°.

[0098] 1.7.1 Molten Iron

[0099] The molten iron 10 is as described above. In the embodiment, the positional relationship between the position P1 in the horizontal plane 101x and the collision surface 102x is determined based on the assumption of a "horizontal plane 101x including the stationary molten iron surface". Here, the "collision surface 102x between the oxygen jet 21 and the horizontal plane 101x" can be said to be the same as the "collision surface 21x between the oxygen jet 21 and the molten iron surface 10x" (see Figure 4 ) are substantially the same.

[0100] 1.7.2 Oxygen delivery mechanism

[0101] The function and type of the oxygen supply mechanism 20 are as described above. In the present embodiment, the direction of the oxygen jet 21 emitted from the oxygen supply mechanism 20 is inclined with respect to the vertical direction. For example, the direction of the oxygen jet 21 emitted from the oxygen supply mechanism 20 can be inclined by an angle θ2 with respect to the vertical direction. The inclination angle θ2 can be determined as the angle formed by the central axis of the oxygen supply mechanism 20 and a line parallel to the vertical direction. The inclination angle θ2 can be, for example, 5° or more and 85° or less, 15° or more and 75° or less, or 25° or more and 65° or less. Further, it is considered that the appropriate inclination angle θ2 differs depending on the operating conditions of the electric arc furnace 100. As long as various reactions other than nitrogen removal are also taken into consideration and an appropriate inclination angle θ2 is determined. In addition, as described above, the oxygen jet 21 can be emitted from the emission hole of the oxygen supply mechanism 20 toward the molten iron 10 with a certain spread angle α, which can be, for example, 10° or more and 13° or less. In addition, a height hi can be provided from the tip end of the oxygen supply mechanism 20 (meaning the "lower end of the emission hole", the same hereinafter) to the horizontal surface 10x. The height hi can be, for example, 0.2 m or more and 1.5 m or less. In addition, as described above, the oxygen supply mechanism 20 can be one having an emission hole with a hole diameter d. The hole diameter d can be, for example, 20 mm or more and 100 mm or less. The flow rate and flow velocity of the oxygen jet 21 emitted from the oxygen supply mechanism 20 are as described above.

[0102] 1.7.3 Carbon material supply mechanism

[0103] In the present embodiment, the electric arc furnace 100 is provided with at least one carbon material supply mechanism as an auxiliary raw material supply mechanism 30. The carbon material supply mechanism supplies a carbon material as an auxiliary raw material 31 toward the position PI of the horizontal surface 101x in the electric arc furnace 100. The carbon material can be supplied into the furnace, for example, via a supply port provided in the electric arc furnace 100. As described above, the supply port can be provided in any part of the furnace. For example, the supply port can be a hole provided in the inner wall (side wall) of the furnace, or a hole provided in the furnace cover. The number of supply ports can be one or a plurality.

[0104] The method of supplying the carbon material by the carbon material supply mechanism is not particularly limited. For example, it can be a method of supplying the carbon material via a hole provided in the inner wall of the furnace, or a method of supplying the carbon material via a hole provided in the furnace cover. A lance, a charging chute, or the like can also be appropriately used in accordance with the positional relationship between the hole provided in the inner wall or the furnace cover and the position PI, or the like. In particular, as described above, the carbon material supply mechanism can be one having an emission hole with a hole diameter d. The hole diameter d can be, for example, 20 mm or more and 100 mm or less. Figure 5 and Figure 4As shown, it is preferred to use a gun to spray the carbon material. When a gun is used to spray the carbon material, for example, it becomes easy to supply the carbon material toward the position P1 where θ1 is 0°, which will be described later. In addition, it is considered that by using a gun to spray the carbon material, it is also possible to induce a flow from the position P1 toward the collision surface 102x. As the input chute, a well-known input chute can be used. When a gun is used as the carbon material supply mechanism, the carbon material can be supplied to the molten iron 10 together with the carrier gas. In this case, the carrier gas from the carbon material supply mechanism can be a carrier gas commonly used in the gas transportation of powders. For example, from the perspective of cost, it is preferred to use one or both of air and N2 gas, and from the perspective of low nitrogenization, it is preferred to use at least one selected from pure oxygen, Ar gas and CO2 gas. In addition, in order to avoid the carbon material being consumed in the air before reaching the iron bath, it is preferred to use one or both of Ar gas and CO2 gas with lower reactivity. In this way, the carrier gas can be selected according to the manufacturing conditions, or it can be a gas obtained by mixing at least two or more gases in a specified proportion within the range of these operating constraints. Furthermore, the lance serving as the oxygen supply mechanism 20 and the lance serving as the carbon material supply mechanism (the auxiliary raw material supply mechanism 30) are separate. The lance serving as the carbon material supply mechanism can be at least one of a lance inserted from the furnace roof of the electric arc furnace 100 (the so-called main lance), a wall lance installed in the furnace wall, and a variable lance positioned by a robot or the like. The tip of the lance serving as the carbon material supply mechanism can be located inside or outside the melting furnace of the electric arc furnace 100.

[0105] In an application embodiment, the carbon material serving as the auxiliary raw material 31 may be supplied vertically downward relative to the molten iron 10, or may be supplied obliquely downward. In any case, the carbon material supply mechanism serving as the auxiliary raw material supply mechanism 30 supplies the carbon material toward a predetermined position P1. Here, the so-called "towards position P1" means that the target position for supplying the carbon material is position P1, and a portion of the carbon material may be supplied to a portion other than position P1 due to diffusion, etc. For example, a portion of the carbon material may be supplied to the inner side of the collision surface 102x of the oxygen jet 21. In an application embodiment, it is preferable that most of the carbon material, for example, more than 50% by mass, more than 70% by mass, or more than 90% by mass, is supplied to position P1 outside the collision surface 102x.

[0106] The amount of carbon material supplied from the carbon material supply unit is not particularly limited. For example, the amount of carbon material supplied from one carbon material supply mechanism may be 10 kg / min or more and 100 kg / min or less.

[0107] The shape of the carbon material can be any shape that can be properly supplied from the carbon material supply mechanism to the molten iron 10, and can be various shapes such as powder, granular, and block. As the carbon material, any carbon material such as bituminous coal, anthracite, pulverized coke, pitch coke, biomass-based carbon material, etc. can be used. In addition, the carbon material can also be a press-formed product. In addition, it can also be a material formed by mixing multiple carbon materials. The carbon material can have a particle size of, for example, 0.1 mm or more and 5 mm or less. In the case of a large carbon material, it is easy to clog the powder conveying system of general steelmaking equipment, and because the specific surface area becomes smaller, the heat transfer performance deteriorates, and the time it stays on the molten iron 10 in an unmelted state will become longer. On the other hand, in the case of a small carbon material, the scattering in the furnace is high, and it is easy to be sucked into the exhaust system, which will deteriorate in material utilization. When a gun is used as the carbon material supply unit, it is preferable to use a carbon material containing 90% by mass or more of powder having a particle size of 0.1 mm to 3 mm in terms of transportability and reactivity in the furnace.

[0108] 1.7.4 Position P1

[0109] like Figure 4 As shown, the position P1 is located outside the collision surface 102x between the oxygen jet 21 and the horizontal plane 101x. Figure 5 and Figure 6 As shown, the carbon material serving as the auxiliary raw material 31 does not cross the oxygen jet 21 and is supplied to the position P1 (in other words, it is preferable that the oxygen jet 21 does not exist between the carbon material supply member and the molten iron 10). The "collision surface 102x between the oxygen jet 21 and the horizontal plane 101x" can be geometrically determined based on the aforementioned inclination angle θ2, expansion angle α, height h, and aperture d. For example, Figure 4 As shown, the distance r2 ( Figure 4 The distance r2) from the intersection point P3 to the point where the outer edge of the collision surface 102x intersects the line segment P2P3 can be determined as r2 = (tanθ2-tan(θ2-α))h+d / (2cosθ2). Figure 8 As shown, if θ1, described later, is between 0° and 90°, and the distance r3 from the intersection P3 of the central axis of the oxygen jet 21 and the horizontal plane 101x to the position P1 is greater than the distance r2 described above, then the position P1 is necessarily outside the collision surface 102x. That is, in an applied embodiment, the distance r3 from the intersection P3 of the central axis of the oxygen jet 21 and the horizontal plane 101x to the position P1 can satisfy the relationship r3 > (tanθ2 - tan(θ2 - α))h + d / (2cosθ2).

[0110] As described above, as long as the position P1 is outside the collision surface 102x and the angle θ1 described later is greater than 0° and less than 90°, the upper limit of the distance r3 is not particularly limited. However, it is believed that when the position P1 is closer to the collision surface 102x, more of the carbon material can contribute to the ignition reaction, and the denitrification efficiency is more significantly improved. According to the present inventors' understanding, when the position P1 is present at Figure 4 The semicircle S shown in H That is, in the horizontal plane 101x, a semicircle S with a radius of 3r1 (r1: the short radius of the geometrical fire point) is assumed with the intersection point P3 as the center and the line segment P2P3 as the symmetry axis. H In the case of H In other words, it is preferred that the distance r3 is greater than the semicircle S H The radius 3r1 is smaller. Furthermore, r1 corresponds to the length from the intersection of a straight line passing through intersection point P3 and perpendicular to line segment P2P3 with the outer edge of collision surface 21x to intersection point P3. Like r2, r1 can be geometrically determined based on the inclination angle θ2, the spread angle α, the height h, and the aperture d.

[0111] As described above, decarburization from the molten iron 10 proceeds through the oxygen jet 21. When the carbon concentration of the molten iron 10 is below the critical carbon concentration, the rate of carbon consumption in the molten iron 10 due to the decarburization reaction exceeds the rate of dissolved carbon supply to the reaction sites. Consequently, the proportion of oxygen supplied by the oxygen supply that contributes to decarburization (decarburization oxygen efficiency) gradually decreases, reducing the rate of CO generation at the flash point, potentially creating an unfavorable situation for denitrification. Furthermore, there is a risk of excessive oxidation of Fe in the molten iron 10, reducing the iron yield, increasing the FeO concentration in the slag, and degrading the refractory material of the electric arc furnace 100. In contrast, it is believed that by shortening the distance r3 relative to the representative length calculated based on the weight of the molten iron 10, the dissolved carbon concentration near the flash point is increased, thereby increasing the activity of dissolved [N], further improving the denitrification efficiency, and suppressing excessive Fe oxidation. From this perspective, the position P1 for supplying the carbon material can be determined by referring to the representative length of the iron bath and the stirring power density calculated based on the weight of the molten iron 10 in each charge. As described above, the representative flow velocity in the inertia-dominated region of the fluid is proportional to the stirring power density raised to the power of 1 / 3. Therefore, if the distance r3 from the intersection point P3 to the position P1 is sufficiently short relative to this representative flow velocity, it is believed that the delay in the supply of carbon material to the ignition point will be further alleviated, and the CO gas generation rate due to the decarburization reaction will be maintained high, which will be beneficial for denitrification. Specifically, for example, in a furnace where top-blowing and bottom-blowing stirring are dominant, the upper limit of the distance r3 can be determined so that the following relationship is satisfied. Regarding the stirring power density, as described above.

[0112] r3≤ (L · ε a ) 1 / 3 / 1.8

[0113] L= (W m / ρ l ) 1 / 3

[0114] ε a =ε T +ε B

[0115] L: represents length (m)

[0116] ε a : total stirring power density (W / t)

[0117] W m : weight of molten iron (t)

[0118] ρ l : density of molten iron (t / m 3 )

[0119] ε T : top blowing stirring power density (W / t)

[0120] ε B : bottom blowing stirring power density (W / t)

[0121] Further, according to the inventor's insight, in the application embodiment, by satisfying the following relationship (1A), movement of carbon material up to the ignition point becomes difficult to delay, the carbon concentration around the ignition point increases, and it is easy to make the target reaction more efficiently occur.

[0122] r3≤0.7×W m 1 / 3 (1A)

[0123] r3: distance from intersection P3 to position PI (m)

[0124] W m : weight of molten iron 10 (t)

[0125] 1.7.5 Angle θ1

[0126] As Figure 7 shown, in the application embodiment, the angle θ1 formed by the line segment PI P3 connecting the position PI and the intersection P3 and the line segment P2P3 connecting the intersection P2 and the intersection P3 is preferably 0° or more and 90° or less. In the case where the orientation of the oxygen jet 21 is inclined with respect to the vertical direction, in the vicinity of the impingement surface 102x of the oxygen jet 21, it is easy to induce a flow having directivity. Specifically, as Figures 1-3As shown, at a position where the angle θ1 exceeds 90°, a flow away from the collision surface 102x is easily induced. On the other hand, at a position where the angle θ1 is greater than 0° and less than 90°, a flow close to the collision surface 102x is easily induced. In the application embodiment, since the carbon material is supplied toward the position P1 where the angle θ1 is greater than 0° and less than 90°, the carbon material is supplied upstream of the flow close to the collision surface 102x, and the carbon material is efficiently supplied to the fire point. That is, most of the carbon material contributes to the fire point reaction, and the denitrification efficiency is significantly improved. In particular, when the angle θ1 is greater than 0° and less than 90°, greater than 0° and less than 80°, greater than 0° and less than 60°, greater than 0° and less than 45°, or greater than 0° and less than 30°, a higher effect is easily obtained.

[0127] 1.7.6 Other matters

[0128] In the applied embodiment, other configurations of the electric arc furnace 100 and the composition of the molten steel are as described above.

[0129] 2. Electric Arc Furnace

[0130] The technology disclosed in this invention has an aspect as an electric arc furnace in addition to the aspect of the method for producing molten steel as described above. Figure 3 As shown, an electric arc furnace 100 according to one embodiment is an electric arc furnace for processing molten iron 10, and is provided with at least one oxygen supply mechanism 20 and at least one auxiliary raw material supply mechanism 30. Here, the oxygen supply mechanism 20 is configured to eject an oxygen jet 21 toward the surface 10x of the molten iron 10 in the electric arc furnace 100. In addition, the auxiliary raw material supply mechanism 30 is configured to supply the auxiliary raw material 31 toward a position P on the surface 10x of the molten iron 10 in the electric arc furnace 100, and is configured so that the position P becomes a position outside the collision surface between the oxygen jet 21 and the molten iron 10. The details of the oxygen supply mechanism 20 and the auxiliary raw material supply mechanism 30 are as described above. The oxygen supply mechanism 20 and the auxiliary raw material supply mechanism 30 can also be controlled by the control unit, for example. That is, the electric arc furnace 100 involved in one embodiment may also be provided with a control unit, which controls one or both of the oxygen supply mechanism 20 and the auxiliary raw material supply mechanism so that the oxygen supply mechanism 20 sprays an oxygen jet 21 toward the molten iron 10 in the electric arc furnace 100, and the auxiliary raw material supply mechanism 30 supplies auxiliary raw material 31 toward a specified position P on the surface of the molten iron 10.

[0131] Further, as described above, in the electric arc furnace 100, the auxiliary raw material supply mechanism 30 can also include at least one carbon material supply mechanism, the oxygen supply mechanism 20 can also be configured so that the direction of the oxygen jet 21 is inclined with respect to the vertical direction, the carbon material supply mechanism can also be configured to supply carbon material toward the position P1, and the oxygen supply mechanism 20 and the carbon material supply mechanism can also be configured so that:

[0132] The position P1 is located on the horizontal plane 101x including the static molten iron surface,

[0133] The position P1 is located on the outside of the collision surface 102x of the oxygen jet 21 and the horizontal plane 101x,

[0134] A perpendicular line from the top end of the oxygen supply mechanism 20 to the horizontal plane 101x intersects the horizontal plane 101x at an intersection point P2,

[0135] The central axis of the oxygen jet 21 intersects the horizontal plane 101x at an intersection point P3, and

[0136] The angle θ1 formed by the line segment P1P3 connecting the position P1 and the intersection point P3 and the line segment P2P3 connecting the intersection point P2 and the intersection point P3 is 0° or more and 90° or less.

[0137] 3. Effects

[0138] Hereinafter, further supplement the effects brought by the molten steel manufacturing method of the present disclosure, focusing on the case where carbon material is used as an auxiliary raw material 31.

[0139] As described above, in the case where carbon material is used as an auxiliary raw material, denitrogenation reaction can be caused together with oxygen supply decarburization. Here, it is believed that factors that generally govern the denitrogenation speed during oxygen supply decarburization include at least:

[0140] (1) CO generation speed in the flame point;

[0141] (2) Temperature of the C-O reaction site in the flame point;

[0142] (3) Gas-liquid reaction interface area between CO bubbles and molten iron.

[0143] In addition, air entrained by the oxygen jet (the amount brought to the flame point increases in soft blowing), the concentration of surface active components in the molten iron (the reaction speed decreases when [S], [O] is high), and the like can also be listed.

[0144] In the past, oxygen jet and carbon material have been simultaneously blown into the electric arc furnace mainly for the purpose of promoting slagging, but in this case, both are blown into the same position on the surface of the molten iron. That is, the carbon material and the oxygen jet are made to flow together, and carbon and oxygen are concentratedly supplied to one place on the surface of the molten iron, thereby reliably generating CO gas in the slag and stabilizing the formation state of the slag. However, in the case where the carbon material and the oxygen are blown into the same position on the surface of the molten iron, from the viewpoint of the denitrogenation reaction,

[0145] (1) Since the C-O reaction sites are dispersed not only in the flame but also in the slag or the air, the CO generation rate in the flame decreases;

[0146] (2) Since the carbon material close to room temperature is directly fed into the flame, the temperature of the C-O reaction sites in the flame also decreases;

[0147] (3) Since the C-O reaction sites are dispersed not only in the flame but also in the slag or the air, the decarburization amount from the molten iron decreases, and the gas-liquid reaction interface area between the CO bubbles and the molten iron also decreases. As described above, in the conventional method, the denitrogenation reaction rate decreases.

[0148] On the other hand, according to the molten steel production method of the present disclosure, in the case where the oxygen jet 21 is injected to the molten iron 10, by supplying the carbon material as the auxiliary material 31 to the position P (or the position Pl) outside the collision surface of the oxygen jet 21 and the molten iron 10 (i.e., outside the flame range),

[0149] (1) The C-O reaction sites are concentrated in the flame, and the CO generation rate in the flame increases;

[0150] (2) The carbon material close to room temperature is fed outside the flame range, and the decrease in the temperature of the C-O reaction sites in the flame is suppressed;

[0151] (3) The C-O reaction sites are concentrated in the flame, and the decarburization amount from the molten iron increases, and the gas-liquid reaction interface area between the CO bubbles and the molten iron also increases. It is considered that this enables the denitrogenation reaction rate to increase. In particular, it is considered that by supplying the carbon material to the position Pl outside the collision surface 102x of the oxygen jet 21 (i.e., outside the flame) and on the upstream side of the flow close to the collision surface 102x (i.e., the flow close to the flame), the denitrogenation reaction rate can be more significantly increased.

[0152] Further, the effect of suppressing the decrease in the flame temperature is exerted regardless of the kind of the auxiliary material 31. That is, according to the production method of the present disclosure, regardless of the kind of the auxiliary material 31, the amount of the auxiliary material 31 directly supplied to the flame can be reduced, the temperature of the flame is difficult to decrease, and the target reaction can be efficiently generated.

[0153] Example

[0154] The present application will be further explained by the following examples, but the present application is not limited by the following examples. The present application can adopt various conditions as long as it does not depart from the gist thereof and achieve the object thereof.

[0155] 1. Study 1

[0156] 1.1 Manufacturing conditions of molten steel

[0157] In the present example, the smelting of molten steel was performed using scrap iron as a cold iron source in an electric arc furnace having the following configurations (1) to (6).

[0158] (1) The diameter of the furnace shell of the melting furnace was 7 m.

[0159] (2) The maximum amount of molten iron that could be treated at one time was 200 t.

[0160] (3) It was a three-phase alternating current type using three upper graphite electrodes.

[0161] (4) It was provided with two oxygen-supplying wall guns and two powder-supplying wall guns fixed to the furnace wall.

[0162] (5) It was provided with a manipulator (movable arm) that could be inserted from the outside of the furnace into the inside of the furnace, and the manipulator was provided with an oxygen-supplying variable gun and a powder-supplying variable gun.

[0163] (6) It was provided with three bottom blow ports at the bottom of the furnace.

[0164] In the present example, an electric arc furnace operation method of a conventional method was adopted. Oxygen supply and supply of auxiliary raw materials were performed from one place each, and the supply amount was 1000 to 4000 Nm 3 / h, 0.01 to 0.10 t / min, and the range of the supply amount and the supply position of the auxiliary raw materials used were appropriately changed.

[0165] Specifically, in each charging, after confirming by visual observation from the slagging port of the furnace body side that the cold iron source charged was completely melted, carbon material as an auxiliary raw material was supplied from a fixed powder gun provided on the inner wall of the furnace, and oxygen was simultaneously supplied from a movable oxygen-supplying gun inserted into the inside of the furnace from the slagging port. The range of the ignition point was changed according to Figure 6The relationship shown in the figure is geometrically derived, and the insertion position and the blowing angle of the movable oxygen lance are adjusted one after another so that the difference Δr of the distance r from the intersection point O of the central axis of the oxygen lance and the surface of the molten iron to the supply target position P of the auxiliary raw material and the distance z from the intersection point O to the outer edge of the flame range becomes a prescribed value. In the case where Δr is positive, the supply target position P is outside the flame range, and in the case where Δr is negative, the supply target position P is inside the flame range. Further, in the present embodiment, the smaller Δr is, the more the movable lance needs to be tilted down (the angle θ is increased), and as a result, there is a tendency that the distance z becomes large. In addition, there is a tendency that the smaller the weight of the molten iron is, the lower the liquid surface is, the larger the height h is, and the larger the distance z is. Sampling is performed before and after the start of oxygen blowing and carbon blowing, and is subjected to chemical analysis, and the evaluation of each level is performed based on the nitrogen concentration change Δ[N] in the same charging material obtained by the analysis. The evaluation index is as follows.

[0166] ◎: Δ[N] ≤ -30 ppm

[0167] O: -30 ppm < Δ[N] ≤ -20 ppm

[0168] Δ: -20 ppm < Δ[N] ≤ -10 ppm

[0169] X: Δ[N] > -10 ppm

[0170] 1.2 Evaluation Results

[0171] The test conditions and the evaluation results of Δ[N] of each of the examples and the comparative examples are shown in Table 1 below. Further, in Table 1 below, "Distance A" is a value obtained by using the following equation using the weight W m (t) of the molten iron.

[0172]

[0173]

[0174] Further, in the present examples and the comparative examples, the auxiliary raw material was blown from the fixed wall lance and the oxygen was supplied from the movable lance inserted from the taphole, but with respect to each level, no superior difference was seen in Δ[N] in the case where the oxygen was supplied from the wall lance and the auxiliary raw material was supplied from the movable lance, and the same results as those shown in Table 1 were obtained. In addition, the amount of the cold iron source inserted was adjusted to change the amount of the molten iron, but in this case, the arrangement of the refractory was changed to adjust so that the geometric positional relationship and the like of the fixed wall lance and the liquid surface did not change.

[0175] In each of the levels, the result of the first sampling was [C] = 0.48 to 0.52%, and the result of the second sampling was [C] = 0.04 to 0.06%, and the decarburization amount from the iron bath was roughly the same. As for [N], the result of the first sampling was [N] = 0.0070 to 0.0075%. In the case where the carbon material was injected as the auxiliary raw material, since the carbon source was continuously supplied from the outside, the desired effect was exerted regardless of the amount of carbon originating from the iron bath. On the other hand, it is considered that in Example 1, Example 2, Comparative Example 1, and Comparative Example 2, since a substance other than the carbon material was used as the auxiliary raw material, the decarburization reaction originating only from the iron bath contributed to the denitrification.

[0176] From the results shown in Table 1, it can be said that, in the case where the oxygen jet was injected from the oxygen injection mechanism toward the molten iron in the furnace, and the auxiliary raw material was supplied from the auxiliary raw material supply mechanism toward the position P of the surface of the molten iron in the electric arc furnace, in the case where the position P was outside the flame point range, i.e., outside the collision surface of the oxygen jet and the molten iron (Examples 1 to 16), compared to the case where the position P was inside (Comparative Examples 1 to 3), it was possible to produce molten steel with a low nitrogen concentration. In addition, from the comparison of Example 1, 2 and Examples 3 to 16, it can be said that, in the case where the auxiliary raw material was the carbon material, it was possible to produce molten steel with a lower nitrogen concentration. Furthermore, from the results of Examples 3 to 16, it can be said that, in the case where the following relationship (1) was satisfied, it was possible to produce molten steel with a lower nitrogen concentration.

[0177]

[0178] Here,

[0179] r is the distance (m) from the intersection O of the central axis of the oxygen jet and the surface of the molten iron to the position P,

[0180] W m is the weight (t) of the molten iron.

[0181] 2. Study 2

[0182] 2.1 Manufacturing conditions of molten steel

[0183] In the electric arc furnace having the following configurations (1) to (7), the smelting of molten steel was performed using scrap iron as the cold iron source.

[0184] (1) The diameter of the shell of the melting furnace was 7 m.

[0185] (2) The maximum amount of molten iron that could be treated at a time was 200 t.

[0186] (3) It was a three-phase alternating current type using three upper graphite electrodes.

[0187] (4) It was provided with two wall guns for oxygen injection and two wall guns for powder injection in a manner fixed to the furnace wall.

[0188] (5) A robot (movable arm) capable of being inserted from the outside to the inside of the furnace is provided, and the robot is provided with a variable lance for oxygen supply and a variable lance for powder supply.

[0189] (6) Three bottom tuyeres are provided at the bottom of the furnace.

[0190] (7) An auxiliary raw material chute is provided at the furnace cover.

[0191] The operation of the electric arc furnace was performed by a conventional method. Oxygen supply and carbon material supply were performed from one place each, and the supply amount of each was 1000 to 4000 Nm 3 / h, 10 to 100 kg / min, and the range of the supply amount of the carbon material was appropriately changed.

[0192] In each charging, it was visually confirmed from the slagging port of the furnace body side that the cold iron source charged was completely melted and formed an iron bath of 180 tons. Then, oxygen jet was sprayed toward the iron bath from the variable lance for oxygen supply inserted from the slagging port to the inside of the furnace or the fixed wall lance for oxygen supply provided on the inner wall of the furnace, and carbon material was charged to the target position Pl in the inside of the furnace from the movable or fixed lance or the chute provided on the furnace cover. The spray direction of the fixed lance was changed by adjusting it before the start of the treatment. The range of the ignition point was geometrically calculated, and the blowing angle was appropriately adjusted so that the horizontal distance r3 from the intersection P3 of the central axis of the oxygen lance and the horizontal plane including the static molten iron surface to the target position Pl of the carbon material supply became a predetermined value. Oxygen supply and carbon material supply were performed for 10 minutes, and sampling of the molten iron was performed before and after the start and end of the oxygen supply and carbon material supply, and was subjected to chemical analysis, and the evaluation of each level was performed based on the nitrogen concentration change Δ[N] in the same charging obtained by the analysis. The evaluation criteria were as follows.

[0193] ◎: Δ[N] ≤ -30 ppm

[0194] O: -30 ppm < Δ[N] ≤ -15 ppm

[0195] Δ: -15 ppm < Δ[N] ≤ -5 ppm

[0196] X: -5 ppm < Δ[N]

[0197] Further, in the present embodiment and the comparative example, the supply of the carbon material was performed by dropping through the auxiliary raw material chute provided on the furnace cover or spraying from the lance using a carrier gas, but regarding each level, no significant difference was seen in Δ[N] when the used supply equipment was changed.

[0198] 2.2 Evaluation Results

[0199] The test conditions and evaluation results of Δ[N] of each of the examples and comparative examples are shown in Table 2 below.

[0200] In Table 2 below, "height h1 (mm)" corresponds to h1 shown in FIG. 1, that is, the height from the tip (lower end) of the lance to the stationary iron liquid surface (horizontal surface 101x). Figure 6

[0201] In Table 2 below, "angle θ2 (°)" corresponds to θ2 shown in FIG. 1, that is, the angle formed by the central axis of the lance and the line parallel to the vertical direction. Figure 4

[0202] In Table 2 below, "r1 (mm)" corresponds to r1 shown in FIG. 1, that is, the length from the intersection of the straight line passing through the intersection P3 and orthogonal to the line segment P2P3 to the intersection P3. "3r1 (mm)" is the value of 3 times r1. Figure 4

[0203] In Table 2 below, "r2 (mm)" corresponds to r2 shown in FIG. 1, that is, the distance from the intersection P3 of the central axis of the lance and the stationary iron liquid surface (horizontal surface 101x) to the point of the outer edge of the impingement surface 102x of the oxygen jet 21 intersecting the line segment P2P3. Figure 4

[0204] In Table 2 below, "r3 (mm)" corresponds to r3 shown in FIG. 1, that is, as described above, the distance from the intersection P3 to the position P1. In the case where r3 is greater than r1, the position P1 is necessarily outside the fire point, on the other hand, in the case where r3 is less than r1, the position P1 can be inside the fire point. In addition, in the case where r3 is greater than 3r1, the position P1 is outside the semicircle S Figure 6 Figure 6 H , on the other hand, in the case where r3 is less than 3r1, the position P1 is included in the semicircle S H Figure 4

[0205] In Table 2 below, "angle θ1 (°)" corresponds to θ1 shown in FIG. 1, that is, the angle formed by the line segment P1P3 connecting the position P1 and the intersection P3 and the line segment P2P3 connecting the intersection P2 and the intersection P3. Figure 7

[0206] The following cases are known from the results shown in Table 2.

[0207]

[0208] ​​​​​​​​​Comparative Example 1A is an example in which the carbon material is supplied into the flame. In this case, Δ[N] is -3 ppm, and sufficient denitrogenation cannot be performed. It is considered that in Comparative Example 1A, by supplying the carbon material into the flame, (1) the C-O reaction sites are dispersed not only into the flame but also into the slag or the air, and thus the CO generation rate in the flame is reduced, (2) the carbon material close to room temperature is directly fed into the flame, and thus the temperature of the C-O reaction sites in the flame is also reduced, and (3) the C-O reaction sites are dispersed not only into the flame but also into the slag or the air, and thus the decarburization amount from the molten iron is reduced, and the gas-liquid reaction interface area between the CO bubbles and the molten iron is also reduced.

[0209] Example 1A is an example in which the carbon material is supplied outside the flame. In this case, Δ[N] is -12 ppm, and the denitrogenation efficiency is improved as compared with Comparative Example 1A. It is considered that in Example 1A, by supplying the carbon material outside the flame, (1) the C-O reaction sites are concentrated in the flame, and the CO generation rate at the flame is increased, (2) the carbon material close to room temperature is fed outside the range of the flame, and the temperature reduction of the C-O reaction sites in the flame is suppressed, and (3) the C-O reaction sites are concentrated in the flame, and the decarburization amount from the molten iron is increased, and the gas-liquid reaction interface area between the CO bubbles and the molten iron is increased.

[0210] Examples 2A to 5A are examples in which the carbon material is supplied to the target position Pl outside the flame and at an angle θ1 of 90° or less. In this case, Δ[N] is -15 ppm or less, and the denitrogenation efficiency is further improved as compared with Example 1A. It is considered that in Examples 2A to 5A, a flow toward the flame is generated at the supply target position Pl of the carbon material (see FIG. 6), and it is considered that the carbon material is efficiently supplied to the flame. As a result, it is considered that in Examples 2A to 5A, the C-O reaction sites are further concentrated in the flame as compared with Example 1A, the CO generation rate in the flame is further increased, the decarburization amount from the molten iron is further increased, and the gas-liquid reaction interface area between the CO bubbles and the molten iron is further increased. ​

[0211] From the results of Examples 2A to 5A, it can be said that in the case of manufacturing the molten steel using the electric arc furnace, the denitrogenation efficiency of the molten iron is further significantly improved when the following conditions A, B and C are satisfied.

[0212] Condition A: the direction of the oxygen jet flow is inclined with respect to the vertical direction;

[0213] Condition B: the position Pl is located outside the collision surface of the oxygen jet flow and the horizontal plane;

[0214] Condition C: the angle θ1 formed by the line segment PlP3 connecting the position Pl and the intersection P3 and the line segment P2P3 connecting the intersection P2 and the intersection P3 is 0° or more and 90° or less. ​

[0215] Furthermore, based on the results of Examples 2A to 5A, it can be seen that when Condition D is satisfied in addition to the above-mentioned Conditions A to C, the denitrification efficiency of the molten iron is further significantly improved.

[0216] Condition D: Assume that a semicircle S with a radius of 3r1 (r1: the short radius of the geometrical fire point) is centered at the intersection point P3 and has a line segment P2P3 as the axis of symmetry. H In the case of H inside.

[0217] Furthermore, in Examples 1A to 5A and Comparative Example 1A, examples are shown in which the height h1, angles θ2, r1, and r2 are each specified. However, the height h1, angles θ2, r1, and r2 do not substantially affect the described effects. In other words, even when the height h1, angles θ2, r1, and r2 differ from those in the examples described, the same effect of improving denitrification efficiency can be achieved by satisfying Conditions A to C (preferably Conditions A to D). Furthermore, in Examples 1A to 5A and Comparative Example 1A, examples are shown in which scrap iron is used as a chill source, but the type of chill source is not particularly limited. When producing molten steel in an electric arc furnace, even when a chill source other than scrap iron (e.g., reduced iron, iron ingots, or granular iron) is used, the same effect of improving denitrification efficiency can be achieved by satisfying Conditions A to C (preferably Conditions A to D).

[0218] Description of Reference Numerals

[0219] 100 Electric Arc Furnace

[0220] 10 molten iron

[0221] 10x Surface of molten iron (liquid surface)

[0222] 20 Oxygen delivery mechanism

[0223] 21 Oxygen Jet

[0224] 21x collision surfaces

[0225] 30 Auxiliary raw material supply mechanism

[0226] 31 Auxiliary raw materials

[0227] 40 Upper electrode

[0228] 50 lower electrode

[0229] 60 Iron source loading mechanism

[0230] 70 Slag removal door

[0231] 80 outlet

[0232] 101x horizontal plane

[0233] 102x impact surface

Claims

1. A method for producing molten steel using an electric arc furnace, wherein the electric arc furnace is equipped with an oxygen supply mechanism and an auxiliary raw material supply mechanism. The manufacturing method includes the steps of injecting an oxygen jet from the oxygen supply mechanism toward the molten iron in the electric arc furnace and supplying an auxiliary raw material from the auxiliary raw material supply mechanism toward a position P on the surface of the molten iron. The position P is a position outside the collision surface between the oxygen jet and the molten iron.

2. The method for producing molten steel according to claim 1, The auxiliary raw material is carbon material.

3. The method for producing molten steel according to claim 1 or 2, Satisfies the following relationship (1), in, r is the distance from the intersection O of the central axis of the oxygen jet and the surface of the molten iron to the position P, in meters, W m is the weight of the molten iron in tons.

4. The method for producing molten steel according to any one of claims 1 to 3, The process includes injecting an oxygen jet from the oxygen supply mechanism toward the molten iron in the electric arc furnace and supplying carbon material from the carbon material supply mechanism as the auxiliary material supply mechanism toward the position P1. The direction of the oxygen jet is inclined relative to the vertical direction. The position P1 is located at a level including the static iron liquid level, The position P1 is located outside the collision surface between the oxygen jet and the horizontal plane. A vertical line from the top of the oxygen supply mechanism to the horizontal plane intersects the horizontal plane at an intersection point P2. The central axis of the oxygen jet intersects the horizontal plane at the intersection point P3. An angle θ1 formed by a line segment P1P3 connecting the position P1 and the intersection point P3 and a line segment P2P3 connecting the intersection point P2 and the intersection point P3 is greater than or equal to 0° and less than or equal to 90°.

5. The method for producing molten steel according to claim 4, In the horizontal plane, assuming a semicircle with a radius of 3r1 centered at the intersection point P3 and with the line segment P2P3 as an axis of symmetry, the position P1 is located inside the semicircle, wherein: The r1 is the geometric short radius of the fire point.

6. An electric arc furnace for processing molten iron, comprising at least one oxygen supply mechanism and at least one auxiliary raw material supply mechanism. The oxygen supply mechanism is configured to spray an oxygen jet toward the surface of the molten iron in the electric arc furnace. The auxiliary material supply mechanism is configured to supply auxiliary material toward a position P on the surface of the molten iron in the electric arc furnace, and is configured so that the position P is outside a collision surface between the oxygen jet and the molten iron.

7. The electric arc furnace according to claim 6, The auxiliary raw material supply mechanism includes at least one carbon material supply mechanism, The oxygen supply mechanism is configured so that the direction of the oxygen jet is inclined relative to the vertical direction. The carbon material supply mechanism is configured to supply the carbon material toward the position P1. The oxygen supply mechanism and the carbon material supply mechanism are configured as follows: The position P1 is located at a level including the static iron liquid level, The position P1 is located outside the collision surface between the oxygen jet and the horizontal plane. A vertical line from the top of the oxygen supply mechanism to the horizontal plane intersects the horizontal plane at an intersection point P2. The central axis of the oxygen jet intersects the horizontal plane at the intersection point P3, and An angle θ1 formed by a line segment P1P3 connecting the position P1 and the intersection point P3 and a line segment P2P3 connecting the intersection point P2 and the intersection point P3 is greater than or equal to 0° and less than or equal to 90°.

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