Method for producing molten steel and arc furnace

Abstract

To provide a method for producing molten steel by which a denitrification reaction can efficiently be caused when an oxygen jet flow is injected to molten iron in an arc furnace and a carbonaceous material is supplied.SOLUTION: A method for producing molten steel according to the present disclosure includes injecting an oxygen jet flow from oxygen feeding means to molten iron in an arc furnace, and supplying a carbonaceous material from carbonaceous material supplying means toward a position P1. The central axis of the oxygen jet flow is inclined with respect to the horizontal plane including the stationary molten iron surface. The position P1 is on the horizontal plane and outside a collision surface between the oxygen jet flow and the horizontal plane. An angle θ1 formed by a line segment P1 P3 connecting the position P1 and an intersection point P3 and a line segment P2 P3 connecting an intersection point P2 and an intersection point P3 is 0° or more and 90° or less. The intersection point P2 is an intersection point between a perpendicular line drawn from the tip of the oxygen feeding means to the horizontal plane and the horizontal plane, and the intersection point P3 is an intersection point between the central axis of the oxygen jet flow and the horizontal plane.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present application discloses a method and an electric arc furnace for producing molten steel. [Background technology]

[0002] Patent Document 1 discloses a technique in which an immersion lance is immersed in molten iron in an arc furnace, carbonaceous material is injected from the immersion lance, and oxygen is injected into slag formed on the surface of the molten iron. In Patent Document 1, the carbon concentration in the molten iron is increased in an arc furnace, the molten iron is tapped from the arc furnace, and then the molten iron is refined in a converter to produce molten steel. In the refining in the converter, for example, CO gas or the like is generated by a decarburization reaction using an oxygen jet, and the CO gas or the like promotes denitrification.

[0003] On the other hand, the above-mentioned denitrification may be performed in an arc furnace. For example, it is considered that the above-mentioned denitrification is possible by simultaneously supplying oxygen and carbonaceous material to the molten iron in the arc furnace. However, the denitrification in the arc furnace has not been fully studied. Due to its structure, the arc furnace is likely to take in outside air, and the nitrogen concentration in the furnace is likely to be high. In other words, the atmosphere in the furnace is likely to be unfavorable to denitrification. In this regard, ingenuity is required to improve the denitrification efficiency of the molten iron in the arc furnace. In addition, in the arc furnace, oxygen and carbonaceous material may be simultaneously injected mainly for the purpose of promoting slag foaming. In this case, it is common to reliably generate CO gas in the slag and stabilize the foaming state of the slag by merging the carbonaceous material with the oxygen jet and supplying carbon and oxygen intensively to one place of the molten iron. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-145393 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the prior art, there is room for improvement in the denitrification efficiency when denitrifying molten iron in an electric arc furnace. [Means for solving the problem]

[0006] The present application discloses the following aspects as one of the means for solving the above problems. <Aspect 1> A method for producing molten steel using an arc furnace equipped with an oxygen supplying means and a carbonaceous material supplying means, The oxygen supplying means injects an oxygen jet into the molten iron in the arc furnace, and the carbonaceous material supplying means injects the oxygen into the molten iron at a position P 1 providing carbonaceous material toward the The direction of the oxygen jet is inclined with respect to the vertical direction, Said position P 1 is in a horizontal plane including the stationary molten iron surface, Said position P 1 is located outside the collision surface between the oxygen jet and the horizontal surface, A perpendicular line drawn from the tip of the oxygen supply means to the horizontal plane intersects with the point P 2 intersects with the horizontal plane at The central axis of the oxygen jet intersects with the intersection point P 3 intersects with the horizontal plane at Said position P 1 and the intersection point P 3 Line segment P connecting 1 P 3 and the intersection point P 2 and the intersection point P 3 Line segment P connecting 2 P 3 The angle θ 1 is between 0° and 90°, A method for producing molten steel. <Aspect 2> A method for producing molten steel according to embodiment 1, comprising the steps of: In the horizontal plane, the intersection point P 3 With the line segment P at the center, 2 P 3with radius 3r as the axis of symmetry 1 (r 1 : the geometrical short radius of the fire point) 1 is inside the semicircle, A method for producing molten steel. <Aspect 3> An electric arc furnace for treating molten iron, comprising at least one oxygen supplying means and at least one carbonaceous material supplying means, The oxygen supplying means is configured to inject an oxygen jet toward the molten iron in the arc furnace, The oxygen supplying means is configured so that the direction of the oxygen jet is inclined with respect to the vertical direction, The carbonaceous material supplying means is at position P 1 The carbonaceous material is supplied to the The oxygen supplying means and the carbonaceous material supplying means are Said position P 1 is in a horizontal plane including the stationary molten iron surface, Said position P 1 is located outside the collision surface between the oxygen jet and the horizontal surface, A perpendicular line drawn from the tip of the oxygen supply means to the horizontal plane intersects with the point P 2 intersects with the horizontal plane at The central axis of the oxygen jet intersects with the intersection point P 3 and intersects the horizontal plane at Said position P 1 and the intersection point P 3 Line segment P connecting 1 P 3 and the intersection point P 2 and the intersection point P 3 Line segment P connecting 2 P 3 The angle θ 1 is between 0° and 90° It is configured as follows: Arc furnace. Effect of the Invention

[0007] According to the method for producing molten steel and the arc furnace of the present disclosure, when an oxygen jet is injected into the molten iron in the arc furnace and a carbonaceous material is supplied, a denitrification reaction can be efficiently caused to occur. [Brief description of the drawings]

[0008] [Figure 1] 2 shows a schematic diagram of an example of the positional relationship of each member when the arc furnace is viewed from above. [Diagram 2] 1 shows a schematic example of the positional relationship between a position P1, an intersection P2, and an intersection P3 on a horizontal plane including the stationary molten iron surface, when the arc furnace is viewed from above. [Diagram 3] 1 is a schematic diagram showing an example of the positional relationship between an oxygen supplying means and a carbonaceous material supplying means when the arc furnace is viewed from the side, with the upper electrode and the like omitted. [Figure 4] 1 shows an example of a shape of an oxygen jet and a shape of a collision surface between the oxygen jet and a horizontal surface including a stationary molten iron surface. [Diagram 5] 1 shows a schematic diagram of an example of the flow direction induced around the impingement surface of an oxygen jet. [Figure 6] 1 shows a schematic example of a preferred position of position P1 in a horizontal plane including the stationary molten iron surface. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] 1. Manufacturing method of molten steel The method for producing molten steel according to the present disclosure will be described with reference to the drawings. However, the method for producing molten steel according to the present disclosure is not limited to the embodiments shown in the drawings.

[0010] As shown in Figs. 1 to 4, a method for producing molten steel according to one embodiment is a method for producing molten steel using an arc furnace 100 equipped with an oxygen supplying means 20 and a carbonaceous material supplying means 30, in which an oxygen jet 21 is sprayed from the oxygen supplying means 20 to the molten iron 10 in the arc furnace 100, and a jet of oxygen 21 is sprayed from the carbonaceous material supplying means 30 to a position P 1 3 and 4, the direction of the oxygen jet 21 is inclined with respect to the vertical direction. 1lies on a horizontal plane 10x including the stationary molten iron surface. As shown in FIGS. 1 is outside the collision surface 21x between the oxygen jet 21 and the horizontal surface 10x. As shown in FIGS. 2 and 4, a perpendicular line drawn from the tip of the oxygen supplying means 20 to the horizontal surface 10x intersects with the intersection point P 2 2 and 4, the central axis of the oxygen jet 21 intersects with the horizontal plane 10x at the intersection point P 3 As shown in FIG. 2, the position P 1 and the intersection point P 3 Line segment P connecting 1 P 3 and the intersection point P 2 and the intersection point P 3 Line segment P connecting 2 P 3 The angle θ 1 is greater than or equal to 0° and less than or equal to 90°.

[0011] 1.1 Molten iron The molten iron 10 is obtained, for example, by generating an arc in an arc furnace 100 to melt an iron source. The iron source may include at least one selected from scrap, reduced iron, pig iron, granulated pig iron, etc., and may be molten iron or molten steel produced in another melting furnace or refining furnace. The molten iron 10 may include various elements other than iron. The composition of the elements other than iron depends on the type of iron source. For example, the molten iron 10 before the carbon material 31 is supplied may include 0.02% by mass to 3.0% by mass of C, 0.005% by mass to 0.030% by mass of N, and 0.003% by mass to 0.1% by mass of P. The density of the molten iron 10 is, for example, 6,600 kg / m 3 More than 7,000kg / m 3 It may be the following.

[0012] 1.2 Oxygen delivery means The arc furnace 100 includes at least one oxygen supplying means 20. The oxygen supplying means 20 injects an oxygen jet 21 into the molten iron 10 in the arc furnace 100. The oxygen supplying means 20 may be, for example, a lance. The number of oxygen jets 21 injected from one lance is not particularly limited. The lance may be a single-hole lance as shown in Figs. 2 to 4. The lance may be straight, may have a Laval structure, or may include a coherent burner in which gaseous fuel and a combustion-supporting gas are injected so as to surround the oxygen jet. As shown in Fig. 1, the oxygen supplying means 20 may be at least one of a lance (so-called main lance) inserted from the furnace cover of the arc furnace 100, a wall lance provided on the furnace wall, and a variable lance positioned by a manipulator or the like. In the arc furnace 100, oxygen is blown upward from the oxygen supplying means 20 toward the molten iron 10. This allows various chemical reactions to occur in the molten iron 10. The tip (lower end) of the oxygen supplying means 20 may be located inside or outside the melting furnace of the arc furnace 100 .

[0013] The shape of the oxygen jet 21 sprayed from the oxygen supplying means 20 depends on the inclination of the oxygen supplying means 20, the shape of the spray hole of the oxygen supplying means 20, etc. As shown in Fig. 4, the direction of the oxygen jet 21 sprayed from the oxygen supplying means 20 is inclined with respect to the vertical direction. For example, the direction of the oxygen jet 21 sprayed from the oxygen supplying means 20 is inclined with respect to the vertical direction at an angle θ 2 The inclination angle θ 2 The inclination angle θ can be specified as the angle between the central axis of the oxygen supplying means 20 and a line parallel to the vertical direction. 2 The inclination angle θ may be, for example, 5° to 85°, 15° to 75°, or 25° to 65°. 2 It is considered that the inclination angle θ varies depending on the operating conditions of the arc furnace 100. Taking into consideration various reactions other than denitrification, an appropriate inclination angle θ 2is determined. As shown in FIG. 4, the oxygen jet 21 may be injected from the injection hole of the oxygen supplying means 20 to 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 supplying means 20. The spread angle α may be, for example, 10° or more and 13° or less. As shown in FIG. 4, a height h may be provided from the tip of the oxygen supplying means 20 (meaning the "lower end of the injection hole" as shown in FIG. 4. The same applies below) to the horizontal plane 10x. The height h may be, for example, 0.2 m or more and 1.5 m or less. As shown in FIG. 4, the oxygen supplying means 20 may have an injection hole with a hole diameter d. The hole diameter d refers to the circle equivalent diameter of the injection hole. The hole diameter d may be, for example, 20 mm or more and 100 mm or less.

[0014] The flow rate of the oxygen jet 21 injected from one oxygen supplying means 20 is not particularly limited, and may be, for example, 1,000 Nm 3 / h or more 4,000Nm 3 / h or less. The flow velocity of the oxygen jet 21 injected from the oxygen supplying means 20 (the flow velocity at the injection hole of the oxygen supplying means 20, that is, the flow velocity at the central axis) is not particularly limited, and may be, for example, 10 m / s or more and 300 m / s or less.

[0015] 1.3 Carbon material supply means The arc furnace 100 includes at least one carbonaceous material supplying means 30. The carbonaceous material supplying means 30 is arranged at a position P 1 The carbonaceous material 31 is supplied toward the furnace. The carbonaceous material 31 can be supplied into the furnace through, for example, a supply port provided in the arc furnace 100. The supply port may be provided in any part of the furnace. For example, the supply port may be a hole provided in the furnace inner wall (side wall) or a hole provided in the furnace cover. The number of supply ports may be one or more.

[0016] There is no particular limitation on the method of supplying the carbonaceous material by the carbonaceous material supplying means 30. For example, the carbonaceous material 31 may be supplied through a hole provided in the inner wall of the furnace, or through a hole provided in the furnace cover. 1 Depending on the positional relationship with the carbonaceous material 31, a lance, a charge chute, or the like may be used as appropriate. In particular, as shown in Figs. 2 and 3, a form in which the carbonaceous material 31 is sprayed using a lance is preferable. When the carbonaceous material 31 is sprayed using a lance, for example, θ 1 Position P where is 0° 1 In addition, by using the lance to blow the carbonaceous material 31, the carbonaceous material 31 can be easily supplied toward the position P 1 It is also possible to induce a flow from the carbonaceous material supply means 30 toward the collision surface 21x (fire point). Any known chute may be used as the supply chute. When a lance is used as the carbonaceous material supply means 30, the carbonaceous material 31 can be supplied to the molten iron 10 together with a carrier gas. In this case, the carrier gas from the carbonaceous material supply means 30 may be one generally used for gas transportation of powder. For example, air and N 2 It is preferable to use one or both of the gases. From the viewpoint of reducing nitrogen, it is preferable to use pure oxygen, Ar gas, and CO 2 It is preferable to use at least one selected from the group consisting of Ar gas and CO gas, which have lower reactivity, in order to prevent the carbonaceous material 31 from being consumed in the air before it reaches the iron bath. 2 It is preferable to use one or both of the gases. Thus, the carrier gas may be selected according to the manufacturing conditions, and may be a mixture of at least two or more types of gases in a predetermined ratio within the range of these operational constraints. The lance as the oxygen supplying means 20 and the lance as the carbonaceous material supplying means 30 are different from each other. The lance as the carbonaceous material supplying means 30 may be at least one of a lance (so-called main lance) inserted from the furnace cover of the arc furnace 100, a wall lance provided on the furnace wall, and a variable lance positioned by a manipulator or the like. The tip of the lance as the carbonaceous material supplying means 30 may be inside or outside the melting furnace of the arc furnace 100.

[0017] The carbonaceous material 31 may be supplied vertically downward or obliquely downward to the molten iron 10. In either case, the carbonaceous material supplying means 30 is arranged at a predetermined position P 1 The carbonaceous material 31 is supplied toward the position P 1 "Towards" means that the target position for supplying the carbon material 31 is position P 1 This means that a part of the carbonaceous material 31 is dispersed at the position P 1 For example, a part of the carbonaceous material 31 may be supplied to the inside of the collision surface 21x of the oxygen jet 21. In the manufacturing method of the present disclosure, most of the carbonaceous material 31, for example, 50 mass % or more, 70 mass % or more, or 90 mass % or more, is supplied to the position P outside the collision surface 21x. 1 It is advisable to provide

[0018] There is no particular limit to the amount of the carbonaceous material 31 supplied from the carbonaceous material supplying means 30. For example, the amount of the carbonaceous material 31 supplied from one carbonaceous material supplying means 30 may be 10 kg / min or more and 100 kg / min or less.

[0019] The shape of the carbonaceous material 31 may be any shape such as powder, granules, or lumps, as long as it can be appropriately supplied from the carbonaceous material supply means 30 to the molten iron 10. As the carbonaceous material 31, any carbonaceous material such as bituminous coal, anthracite, coke powder, pitch coke, or biomass-based carbonaceous material may be used. The carbonaceous material 31 may be a pressure-molded product. It may also be a mixture of multiple types of carbonaceous materials 31. The carbonaceous material 31 may have a particle size of, for example, 0.1 mm or more and 5 mm or less. If the carbonaceous material 31 is large, it is likely to clog the powder conveying system provided in a general steelmaking facility, and the specific surface area is reduced, which deteriorates the heat transfer, and the time that the carbonaceous material 31 remains unmelted on the molten iron 10 may be long. On the other hand, if the carbonaceous material 31 is small, it is likely to scatter in the furnace and is likely to be sucked into the exhaust gas system, which may result in a poor yield. When a lance is used as the carbonaceous material supplying means 30, in consideration of transportability and reactivity in the furnace, it is preferable to use carbonaceous material 31 containing powder having a particle size of 0.1 mm or more and 3 mm or less in an amount of 90 mass % or more.

[0020] 1.4 Position P 1 As shown in FIG. 1 is a position outside the collision surface 21x between the oxygen jet 21 and the horizontal surface 10x. Preferably, as shown in Figs. 2 and 3, the carbonaceous material 31 does not cross the oxygen jet 21 and reaches the position P 1 (In other words, it is preferable that the oxygen jet 21 does not exist between the carbonaceous material 31 and the molten iron 10 from the carbonaceous material supplying means 30.) The "collision surface 21x between the oxygen jet 21 and the horizontal surface 10x" is at the inclination angle θ 2 4, the intersection P of the central axis of the oxygen supplying means 20 and the horizontal plane 10x can be geometrically specified from the spread angle α, the height h, and the hole diameter d. 3 Distance r from the outer edge X of the impact surface 21x 2 (The intersection point P shown in Fig. 2 3 From the above, the point on the outer edge of the collision surface 21x is the line segment P 2 P 3 Distance r to the point of intersection with 2 ) is r 2 =(tanθ 2 -tan(θ 2 -α))h+d / (2cosθ 2 ) as shown in FIG. 1 is 0° or more and 90° or less, and the intersection P 3 From position P 1 Distance to r 3 But the distance r 2 If it is greater than 1 That is, in the manufacturing method of the present disclosure, the intersection point P 3 From position P 1 Distance to r 3 is r 3 >(tanθ 2 -tan(θ 2 -α))h+d / (2cosθ 2 ) may satisfy the relationship:

[0021] As mentioned above, position P 1 is outside the collision surface 21x and is angle θ 1 Any position where the above distance r is greater than or equal to 0° and less than or equal to 90° is acceptable. 3 However, there is no particular upper limit for the position P 1 It is considered that the closer the position P is to the collision surface 21x, the more the carbonaceous material 31 can contribute to the ignition reaction, and the denitrification efficiency is more significantly improved. 1 is the semicircle S shown in Figure 6. H In other words, when the intersection point P 3 With center at, line segment P 2 P 3 with radius 3r as the axis of symmetry 1 (r 1 : Semicircle S of the geometric fire point (minor radius) H Assuming that the position P 1 But semicircle S H In other words, it is preferable that the distance r 3 But the semicircle S H Radius 3r 1 It is preferable that the value is smaller than r 1 is the intersection point P 3 A straight line passing through the line segment P 2 P 3 From the intersection of the line perpendicular to the line and the outer edge of the collision surface 21x, the intersection point P 3 It corresponds to the length up to r 1 is the above r 2 Similarly, the inclination angle θ 2 , can be geometrically specified from the spread angle α, height h, and hole diameter d.

[0022] When the decarburization of the molten iron 10 progresses due to the oxygen jet 21 and the carbon concentration of the molten iron 10 falls below the critical carbon concentration, the consumption rate of carbon in the molten iron 10 by the decarburization reaction exceeds the supply rate of dissolved carbon to the reaction site, so that the ratio of oxygen supplied by the oxygen supply that contributes to decarburization (decarburization efficiency) gradually decreases, the rate of CO generation at the fire point decreases, and a disadvantageous state may be created for denitrification. In addition, Fe in the molten iron 10 may be over-oxidized, reducing the iron yield and increasing the FeO concentration in the slag, which may damage the refractories of the arc furnace 100. In response to this, the above-mentioned distance r 3 It is considered that by shortening the representative length calculated based on the weight of the molten iron 10 and increasing the dissolved carbon concentration near the hot spot, the activity of dissolved [N] increases, the denitrification efficiency is further improved, and the excessive oxidation of Fe is also suppressed. From this point of view, the position P 1 may be determined by referring to the representative length of the iron bath calculated from the weight of the molten iron 10 in each charge and the value of the stirring power density. For example, according to the well-known document "Asai et al.: Tetsu to Hagane, vol. 3, pp. 426-434 (1982)", the representative flow velocity in the inertia-dominated region of the fluid is proportional to the 1 / 3 power of the stirring power density, so that the intersection point P 3 From position P 1 Distance to r 3 If is sufficiently short with respect to this representative flow velocity, the delay in the supply of the carbonaceous material 31 to the hot point is further alleviated, the rate of CO gas generation by the decarburization reaction is maintained high, and it is considered to be advantageous for denitrification. That is, for example, for a furnace in which top and bottom blowing stirring is dominant, the upper limit of the distance r can be determined so as to satisfy the following relationship.

[0023] r 3 ≦(L ε a ) 1 / 3 / 1.8 L=(W m / ρ l ) 1 / 3 ε a =ε T +ε B L: Representative length (m) ε a :Total stirring power density (W / ton) W m : Weight of molten iron (tons) ρ l : Density of molten iron (ton / m 3 ) ε T : Top blowing stirring power density (W / ton) ε B : Bottom blowing stirring power density (W / ton)

[0024] For the stirring power density, a linear sum may be adopted for top blowing, bottom blowing, etc., by referring to known documents such as "Kai et al.: Tetsu-to-Haganen, vol. 69 (1983), pp. 228-237" and "Mori et al.: Tetsu-to-Haganen, vol. 6 (1981), pp. 672-695." The means for providing stirring is not limited to gas supply, and any means may be treated in the same manner, and the stirring power density of stirring means with different positions or principles does not have to be a linear sum, and each may be treated as having an independent contribution rate.

[0025] In addition, according to the findings of the present inventors, in the manufacturing method of the present disclosure, by satisfying the following relationship (1), the movement of the carbonaceous material 31 to the ignition point is less likely to be delayed, the carbon concentration in the vicinity of the ignition point is increased, and the target reaction is more likely to occur efficiently.

[0026] r 3 ≦0.7×W m 1 / 3 (1) r 3 :Intersection P 3 From position P 1 Distance to (m) W m : Weight of 10 molten iron (tons)

[0027] 1.5 Angle θ 1 As shown in FIG. 1 and intersection point P 3 Line segment P connecting 1 P 3 and the intersection point P 2 and intersection point P 3 Line segment P connecting2 P 3 The angle θ 1 is 0° or more and 90° or less. When the direction of the oxygen jet 21 is inclined with respect to the vertical direction, a directional flow is easily induced in the vicinity of the collision surface 21x of the oxygen jet 21. Specifically, as shown in FIG. 1 At a position where the angle θ exceeds 90°, a flow away from the collision surface 21x is easily induced, while 1 In the manufacturing method according to the present disclosure, a flow approaching the collision surface 21x is easily induced at a position where the angle θ is greater than or equal to 0° and less than or equal to 90°. 1 Position P where is between 0° and 90° 1 Since the carbonaceous material 31 is supplied toward the collision surface 21x, the carbonaceous material 31 is supplied upstream of the flow approaching the collision surface 21x, and the carbonaceous material 31 is efficiently supplied to the hot spot. In other words, most of the carbonaceous material 31 contributes to the hot spot reaction, and the denitrification efficiency is significantly improved. In particular, the angle θ 1 However, when the angle is 0° or more and less than 90°, 0° or more and 80° or less, 0° or more and 60° or less, 0° or more and 45° or less, or 0° or more and 30° or less, a higher effect is likely to be obtained.

[0028] 1.6 Other configurations in electric arc furnaces The arc furnace 100 has a melting furnace for melting an iron source. The melting furnace is a portion that may be defined by a furnace cover, an inner wall, and a furnace bottom. The planar shape of the melting furnace may have a circular portion as shown in FIG. 1. The melting furnace may have a constant furnace diameter. The bath depth of the melting furnace may change with the melting of the iron source, etc. The bath depth and furnace diameter of the melting furnace are not particularly limited.

[0029] In FIG. 1, an AC type arc furnace using only the upper electrode 40 is illustrated as an example of a means for generating an arc. However, the means for generating an arc furnace is not limited to this, and may be a DC type arc furnace using the upper electrode 40 and the lower electrode 50. The upper electrode 40 is installed so as to be inserted into the furnace through the furnace cover. The lower electrode 50 is installed at the bottom of the furnace. In the case of a DC type arc furnace, the number of the upper electrode 40 and the lower electrode 50 is at least one. The positions of the upper electrode 40 and the lower electrode 50 are not particularly limited. For example, when the shape of the molten metal surface in the melting furnace is substantially circular when viewed from above (plan view), the center position of the circle may coincide with the central axis of one upper electrode 40 or one lower electrode 50. Alternatively, a plurality of upper electrodes 40 and a plurality of lower electrodes 50 may be arranged around the center position of the circle when viewed from above. In the arc furnace 100, power is supplied from a power supply unit (not shown) to the upper electrode 40 and the lower electrode 50 to generate an arc between the upper electrode 40 and the lower electrode 50. The power supply unit may be a general one that supplies 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.

[0030] As shown in Fig. 1, the arc furnace 100 may include an iron source charging means 60 for charging an iron source into the melting furnace. The arc furnace 100 may also include a slag removal door 70 for discharging slag and the like formed on the surface of the molten iron 10. The arc furnace 100 may also include a tapping port 80 for tapping the molten iron 10 or molten steel. Any of these may be of a known configuration.

[0031] The arc furnace 100 may include various control units. For example, the control unit may adjust the target supply position P of the carbonaceous material 31 supplied from the carbonaceous material supplying means 30 to the molten iron 10 in accordance with the position of the oxygen jet 21 injected from the oxygen supplying means 20 to the molten iron 10. 1 Alternatively, the supply target position P of the carbonaceous material 31 supplied from the carbonaceous material supply means 30 to the molten iron 10 may be controlled. 1Alternatively, the position of the oxygen jet 21 injected from the oxygen supplying means 20 to the molten iron 10 and the supply target position P of the carbonaceous material 31 supplied from the carbonaceous material supplying means 30 to the molten iron 10 may be controlled in accordance with the above. 1 The control unit may control both the above and the above. The control unit may be capable of executing the above control, and may have a known configuration for enabling the execution of the control. For example, the control unit may be equipped with a CPU, a RAM, a ROM, etc.

[0032] 1.7 Molten Steel 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, as described above, the oxygen jet 21 is injected into the molten iron 10, and the carbonaceous material 31 is supplied to cause a denitrification reaction. The molten steel produced by the method of the present disclosure may contain, for example, 0.01 mass% to 3.0 mass% of C, 0.002 mass% to 0.015 mass% of N, or 0.003 mass% to 0.1 mass% of P. The molten steel in the arc furnace 100 may be tapped, for example, through the above-mentioned tapping hole 80. The tapped molten steel may be further refined, or may be directly subjected to continuous casting or the like.

[0033] 2. Arc furnace The technology of the present disclosure has an aspect as an arc furnace in addition to the above-mentioned aspect as a manufacturing method of molten steel. That is, as shown in Figs. 1 to 6, an arc furnace 100 according to one embodiment processes molten iron 10 and includes at least one oxygen supplying means 20 and at least one carbonaceous material supplying means 30. Here, The oxygen supplying means 20 is configured to inject an oxygen jet 21 toward the molten iron 10 in the arc furnace 100, The oxygen supplying means 20 is configured such that the direction of the oxygen jet 21 is inclined with respect to the vertical direction, The carbonaceous material supplying means 30 is at the position P 1 The carbonaceous material 31 is supplied toward the The oxygen supplying means 20 and the carbonaceous material supplying means 30 are Said position P 1 is on a horizontal plane 10x including the stationary molten iron surface, Said position P 1 is located outside the collision surface 21x between the oxygen jet 21 and the horizontal surface 10x, A perpendicular line drawn from the tip of the oxygen supplying means 20 to the horizontal plane 10x intersects with the point P 2 Intersects with the horizontal plane 10x at The central axis of the oxygen jet 21 intersects with the intersection point P 3 Intersects with the horizontal plane 10x at Said position P 1 and the intersection point P 3 Line segment P connecting 1 P 3 and the intersection point P 2 and the intersection point P 3 Line segment P connecting 2 P 3 The angle θ 1 is between 0° and 90° It is configured as follows.

[0034] The types and operations of the oxygen supplying means 20 and the carbonaceous material supplying means 30 are as described above. 1 , intersection P 2 and intersection point P 3 The details of the oxygen supplying means 20 and the carbonaceous material supplying means 30 are also as described above. The oxygen supplying means 20 and the carbonaceous material supplying means 30 may be controlled by, for example, the above-mentioned control unit. That is, the arc furnace 100 according to one embodiment further includes a control unit, and the control unit controls the oxygen supplying means 20 to inject an oxygen jet 21 into the molten iron 10 in the arc furnace 100 and the carbonaceous material supplying means 30 to supply the oxygen to the predetermined position P 1 The control unit may control one or both of the oxygen supplying means 20 and the carbonaceous material supplying means 30 so as to supply the carbonaceous material 31 toward the oxygen supplying means 20. The details of the control unit are as described above.

[0035] 3. Effects The following provides further supplementary information on the effects of the method for producing molten steel according to the present disclosure.

[0036] As described above, by blowing the oxygen jet 21 onto the molten iron 10 and supplying the carbonaceous material 31, it is possible to cause the denitrification reaction together with the oxygen supply decarburization. Here, the factors governing the rate of adsorption and denitrification during general oxygen supply decarburization include at least the following: (1) CO generation rate at the ignition point (2) Temperature of the CO reaction site at the hot spot (3) The gas-liquid reaction interface area between the CO bubbles and the molten iron Other factors include the air entrained by the oxygen jet (soft blowing increases the amount of air entrained to the fire point) and the concentration of surface active components in the molten iron (high [S] and [O] decrease the reaction rate).

[0037] Conventionally, oxygen jets and carbonaceous materials have been simultaneously injected into electric arc furnaces mainly for the purpose of promoting slag foaming, but in this case, both are injected into the same position on the molten iron surface. In other words, by merging the carbonaceous materials with the oxygen jets and intensively supplying carbon and oxygen to one location on the molten iron surface, CO gas is reliably generated in the slag and the foaming state of the slag is stabilized. However, when the carbonaceous materials and oxygen are injected into the same position on the molten iron surface, from the viewpoint of the adsorption and denitrification reaction, (1) The CO reaction site is dispersed not only at the fire point but also in the slag and air, so the rate of CO generation at the fire point decreases, (2) The carbonaceous material, which is close to room temperature, is directly introduced to the fire point, so the temperature of the CO reaction site at the fire point also decreases. (3) The CO reaction sites are dispersed not only at the hot points but also in the slag and air, reducing the amount of decarburization from the molten iron and reducing the gas-liquid reaction interface area between the CO bubbles and the molten iron. As described above, the conventional method leads to a decrease in the denitrification reaction rate.

[0038] In contrast, according to the method for producing molten steel of the present disclosure, when the oxygen jet 21 is injected into the molten iron 10, the oxygen jet 21 is injected from a position P 1By supplying the carbonaceous material 31 toward the fire point, the amount of carbonaceous material 31 supplied to the fire point increases, (1) The CO reaction sites are concentrated at the fire point, increasing the rate of CO generation at the fire point. (2) Charcoal material close to room temperature is added outside the range of the ignition point, suppressing the temperature drop at the CO reaction site at the ignition point. (3) The CO reaction sites are concentrated at the hot points, which increases the amount of decarburization from molten iron and increases the gas-liquid reaction area between the CO bubbles and molten iron, which is believed to increase the denitrification reaction rate. EXAMPLES

[0039] The present invention will be further described below with reference to examples, but the present invention is not limited to the following examples. The present invention can adopt various conditions as long as it does not deviate from the gist of the invention and achieves its object.

[0040] 1. Manufacturing conditions of molten steel In an electric arc furnace having the following configurations (1) to (7), molten steel was produced using scrap as a cold iron source. (1) The diameter of the melting furnace shell is 7 m. (2) The maximum amount of molten iron that can be processed at one time is 200 tons. (3) It is a three-phase AC type that uses three upper graphite electrodes. (4) Two wall lances for supplying oxygen and two wall lances for supplying powder are provided and fixed to the furnace wall. (5) Equipped with a manipulator (movable arm) that can be inserted into the furnace from outside, the manipulator is equipped with a variable lance for supplying oxygen and a variable lance for supplying powder. (6) The hearth is equipped with three bottom-blowing tuyeres. (7) The furnace cover is equipped with a chute for auxiliary materials.

[0041] The arc furnace was operated in the usual manner. Oxygen and carbonaceous materials were fed from one location each, with the amounts fed being 1,000 to 4,000 Nm 3 / h, 10 to 100 kg / min, and the lance used, the supply position of the carbonaceous material, and the range of the supply amount were changed appropriately.

[0042] In each charge, it was visually confirmed through the slag removal port on the side of the furnace that all the cold iron source had melted and an iron bath of 180 tons had been formed. After that, an oxygen jet was sprayed toward the iron bath from a variable oxygen supply lance inserted into the furnace through the slag removal port or a fixed oxygen supply wall lance installed on the furnace inner wall, and oxygen was supplied to the iron bath at the target position P 1 The carbonaceous material was fed into the oxygen supply lance. The injection direction of the fixed lance was adjusted before the start of the treatment. The range of the hot spot was calculated geometrically, and the intersection point P 3 From the target position P for supplying carbon 1 Horizontal distance r to 3 The injection angle was adjusted appropriately so that the specified value was reached. The oxygen and carbonaceous materials were fed for 10 minutes, and samples of the molten iron were taken before and after the oxygen and carbonaceous materials were fed and subjected to chemical analysis. The nitrogen concentration change Δ[N] within the same charge obtained by the analysis was used to evaluate the superiority or inferiority of each level. The evaluation criteria are as follows. ◎:Δ[N]≦-30ppm ○:-30ppm<Δ[N]≦-15ppm △:-15ppm<Δ[N]≦-5ppm ×:-5ppm<Δ[N]

[0043] In this embodiment and the comparative example, the carbonaceous material was supplied by dropping it through a chute for auxiliary raw materials provided on the furnace cover or by spraying it from a lance using carrier gas, but no significant difference in Δ[N] was observed even when the supply equipment used for each level was changed.

[0044] 2. Evaluation results Table 1 below shows the test conditions and the evaluation results related to Δ[N] for each of the examples and comparative examples.

[0045] In Table 1 below, "height h (mm)" corresponds to h shown in FIG. 4, that is, the height from the tip (lower end) of the lance to the stationary molten iron surface (horizontal plane 10x).

[0046] In Table 1 below, "angle θ 2 (°)" refers to the θ 2 i.e., the angle between the central axis of the lance and a line parallel to the vertical direction.

[0047] In Table 1 below, "r 1 (mm)" refers to the r 1 That is, the intersection point P 3 and passes through line segment P 2 P 3 From the intersection of the line perpendicular to the line and the outer edge of the collision surface 21x, the intersection point P 3 The length is up to 3r 1 (mm)" means r 1 This is three times the value.

[0048] In Table 1 below, "r 2 (mm)" refers to the r 2 That is, the intersection point P between the central axis of the lance and the stationary molten iron surface (horizontal plane 10x) 3 From the above, a point on the outer edge of the collision surface 21x of the oxygen jet 21 is a line segment P 2 P 3 is the distance to the point where it intersects with

[0049] In Table 1 below, "r 3 (mm)" refers to the r 3 That is, as mentioned above, the intersection point P 3 From position P 1 is the distance to r 3 is 1 If it is greater than 1 is always outside the fire point, while r 3 is 1 If it is smaller than 1 can be inside the hot spot. Also, r 3 3r 1 If it is greater than 1 is the semicircle S shown in Figure 4. H While it is outside of r 3 3r 1 If it is smaller than1 is the semicircle S shown in Figure 4. H It will be included inside.

[0050] In Table 1 below, "angle θ 1 (°)" refers to the θ 1 That is, at position P 1 and intersection point P 3 Line segment P connecting 1 P 3 and the intersection point P 2 and intersection point P 3 Line segment P connecting 2 P 3 This is the angle between the

[0051] [Table 1]

[0052] The results shown in Table 1 reveal the following:

[0053] Comparative Example 1 is an example in which the carbonaceous material was supplied into the fire point. In this case, Δ[N] was -3 ppm, and sufficient denitrification could not be performed. In Comparative Example 1, it is considered that, by supplying the carbonaceous material into the fire point, (1) the CO reaction site is dispersed not only at the fire point but also in the slag or in the air, so that the CO generation rate at the fire point is reduced, (2) the carbonaceous material, which is close to room temperature, is directly charged into the fire point, so that the temperature of the CO reaction site at the fire point is also reduced, and (3) the amount of decarburization from the molten iron is reduced, and the gas-liquid reaction interface area between the CO bubbles and the molten iron is also reduced, because the CO reaction site is dispersed not only at the fire point but also in the slag or in the air.

[0054] Comparative Example 2 is an example in which the carbonaceous material was supplied outside the fire point. In this case, Δ[N] was -12 ppm, and the denitrification efficiency was improved compared to Comparative Example 1. In Comparative Example 2, it is considered that, by supplying the carbonaceous material outside the fire point, (1) the CO reaction sites were concentrated at the fire point, and the CO generation rate at the fire point increased, (2) the carbonaceous material, which is close to room temperature, was introduced outside the fire point range, and the temperature drop at the CO reaction site at the fire point was suppressed, and (3) the CO reaction sites were concentrated at the fire point, and the amount of decarburization from the molten iron increased, and the gas-liquid reaction interface area between the CO bubbles and the molten iron increased. However, the denitrification efficiency in Comparative Example 2 cannot be said to be sufficient. In Comparative Example 2, the angle θ 1 Since the angle exceeds 90°, the target position for supplying the carbon material P 1 It is thought that a flow away from the fire occurs at the fire point (see Figure 5), and the carbon material may not have been efficiently supplied to the fire point.

[0055] In Examples 1 to 4, the angle θ 1 The target position P is less than 90° 1 In this case, Δ[N] was −15 ppm or less, and the denitrification efficiency was improved compared to Comparative Example 2. In Examples 1 to 4, the carbonaceous material was supplied toward the target position P 1 It is considered that a flow approaching the fire point is generated in the molten iron (see FIG. 5), and the carbonaceous material is efficiently supplied to the fire point. As a result, it is considered that in Examples 1 to 4, compared with Comparative Example 2, the CO reaction sites are further concentrated at the fire point, the CO generation rate at the fire point is further increased, the amount of decarburization 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.

[0056] From the results of Examples 1 to 4 and Comparative Examples 1 and 2, when producing molten steel using an electric arc furnace, Condition A: The direction of the oxygen jet is inclined relative to the vertical. Condition B: Position P 1 is outside the collision surface between the oxygen jet and the horizontal surface; and Condition C: Position P 1 and intersection point P 3 Line segment P connecting 1 P3 and the intersection point P 2 and intersection point P 3 Line segment P connecting 2 P 3 The angle θ 1 is between 0° and 90° When this condition is satisfied, it can be said that the efficiency of denitrification of molten iron is significantly improved.

[0057] Furthermore, from the results of Examples 1 to 4, in addition to the above conditions A to C, Condition D: Intersection P 3 With center at, line segment P 2 P 3 with radius 3r as the axis of symmetry 1 (r 1 : Semicircle S of the geometric fire point (minor radius) H Assuming that the position P 1 But the semicircle S H What is inside When the above condition is satisfied, it can be said that the denitrification efficiency of molten iron is further improved significantly.

[0058] In the above Examples 1 to 4 and Comparative Examples 1 and 2, the height h and the angle θ 2 , r 1 and r 2 Although the example in which each is a predetermined value is shown, the height h and angle θ 2 , r 1 and r 2 does not substantially affect the above-mentioned functions and effects. 2 , r 1 and r 2 Even when the cold iron source is different from the above examples, it can be said that a similar effect of improving denitrification efficiency can be obtained by satisfying the above conditions A to C (preferably the above conditions A to D). Moreover, in the above examples 1 to 4 and comparative examples 1 and 2, the examples in which scrap was used as the cold iron source were shown, but the type of cold iron source is not particularly limited. Even when a cold iron source other than scrap (e.g., reduced iron, pig iron, granulated pig iron, etc.) is used when producing molten steel using an arc furnace, it can be said that a similar effect of improving denitrification efficiency can be obtained by satisfying the above conditions A to C (preferably the above conditions A to D). [Explanation of symbols]

[0059] 100 Arc Furnace 10 Molten Iron 10x horizontal plane including stationary molten iron surface 20 Oxygen delivery means 21 Oxygen jet 21x collision surface 30 Carbon material supply means 31 Charcoal material 40 Upper electrode 50 Lower electrode 60 Iron source charging means 70 Slag removal door 80 Tap hole

Claims

1. A method for producing molten steel using an arc furnace equipped with an oxygen supplying means and a carbonaceous material supplying means, The oxygen supplying means injects an oxygen jet into the molten iron in the arc furnace, and the carbonaceous material supplying means injects the oxygen into the molten iron in the arc furnace at a position P １ providing carbonaceous material toward the The direction of the oxygen jet is inclined with respect to the vertical direction, Said position P １ is in a horizontal plane including the stationary molten iron surface, Said position P １ is located outside the collision surface between the oxygen jet and the horizontal surface, A perpendicular line drawn from the tip of the oxygen supply means to the horizontal plane intersects with the point P ２ intersects with the horizontal plane at The central axis of the oxygen jet intersects with the intersection point P ３ intersects with the horizontal plane at Said position P １ and the intersection point P ３ Line segment P connecting １ P ３ and the intersection point P ２ and the intersection point P ３ Line segment P connecting ２ P ３ The angle θ １ is equal to or greater than 0° and equal to or less than 90°, A method for producing molten steel.

2. The method for producing molten steel according to claim 1, In the horizontal plane, the intersection point P ３ With the line segment P ２ P ３ A symmetric axis of radius 3r １ (r １ : the short radius of the geometric fire point) １ is inside the semicircle, A method for producing molten steel.

3. An electric arc furnace for treating molten iron, comprising at least one oxygen supplying means and at least one carbonaceous material supplying means, The oxygen supplying means is configured to inject an oxygen jet toward the molten iron in the arc furnace, The oxygen supplying means is configured so that the direction of the oxygen jet is inclined with respect to the vertical direction, The carbonaceous material supplying means is at position P １ The carbonaceous material is supplied to the The oxygen supplying means and the carbonaceous material supplying means are Said position P １ is in a horizontal plane including the stationary molten iron surface, Said position P １ is located outside the collision surface between the oxygen jet and the horizontal surface, A perpendicular line drawn from the tip of the oxygen supply means to the horizontal plane intersects with the point P ２ intersects with the horizontal plane at The central axis of the oxygen jet intersects with the intersection point P ３ and intersects the horizontal plane at Said position P １ and the intersection point P ３ Line segment P connecting １ P ３ and the intersection point P ２ and the intersection point P ３ Line segment P connecting ２ P ３ The angle θ １ is between 0° and 90° It is configured as follows: Arc furnace.

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