Method for blowing carbonaceous material in electric furnace and coal feeding lance

Abstract

Provided are a method for manufacturing molten iron by melting a cold iron source in an electric furnace and a coal feeding lance, the method being for blowing a carbonaceous material in the electric furnace and characterized by transporting the carbonaceous material by a carrier gas using the coal feeding lance to supply the carbonaceous material in the furnace under gas blowing conditions in which an angle vertically downward from a blowing direction from the coal feeding lance (blowing angle θ) is smaller than an angle vertically downward from a lance longitudinal direction of the coal feeding lance (lance angle φ), and L / L0 obtained by dividing a recess depth L of slag determined by formula (1) by a reference slag thickness L0 is 1 or greater.　(1): d·v0·cos2θ = 0.007(ρl / ρg)1 / 2(L + h)(L)1 / 2 (where d is the lance outlet diameter, v0 is the carrier gas flow rate, ρl is the slag density, ρg is the carrier gas density, h is the distance between the lance front end and the slag)

Description

Method of injecting carbonaceous material into electric furnace and coal feeding lance

[0001] The present invention relates to a method for injecting carbonaceous material into an electric furnace and a coal feeding lance.

[0002] In electric furnace refining to produce steel, scrap is charged into the electric furnace as the main raw material, and is melted and refined to produce molten steel. Scrap has a carbon content of about 0.05%, which gives it a high melting point. Carburizing the scrap to increase its carbon concentration lowers its melting point, which is expected to promote the melting of the scrap.

[0003] In converter refining using the blast furnace-converter method, molten iron with a high carbon concentration is used as the main raw material, so denitrification proceeds during the decarbonization period in the converter, and the nitrogen concentration can be reduced (N<20 ppm) at the end of the converter refining process. ２ Since it is not possible to lower the partial pressure, the challenge is to reduce the N content of molten steel produced in electric furnaces. If C can be added to the main raw materials charged in an electric furnace, denitrification occurs when CO gas is generated in the molten iron (or at the slag-molten iron interface), making it possible to reduce the N content of molten steel in electric furnaces as well.

[0004] Currently, in electric arc furnaces, scrap is mixed with pig iron (melted in a blast furnace, C = 4.4%) and added. Adding pig iron increases the C concentration in the charged iron source, which lowers the melting point and is expected to promote scrap melting. At the same time, using pig iron has the advantages of being able to supply C directly to the molten iron and being able to control the C addition yield to a certain extent. However, there are issues with using pig iron as a recarburizer, such as the difficulty of using pig iron because it comes from a blast furnace and therefore goes against the direction of carbon neutrality, the issue of impurities such as P and S being mixed in from the pig iron, and the issue that it takes a long time to melt because it is added in lump form.

[0005] Currently, the main source of carbon in the molten metal in an electric furnace is the carbon in the pig iron in addition to the carbon in the scrap. However, instead of pig iron, carbonaceous material is sometimes supplied from a lance during scrap melting and refining in the electric furnace.

[0006] Claim 2 of Patent Document 1 discloses, as a second invention, a method for oxygen blowing in an electric furnace, characterized in that oxygen blowing and carbon powder injection into a steelmaking electric furnace are carried out simultaneously using water-cooled non-consumable lances. It states, "According to the second invention, carbon powder is automatically injected simultaneously with oxygen from the water-cooled non-consumable lance. Therefore, in the early stages of melting, the carbon powder contributes to combustion and is effective in melting the scrap. In addition, in the middle stages of melting and refining, the carbon powder reacts strongly with the molten steel through the direct oxygen blowing flame, providing a foamy slag effect and a carburizing effect."

[0007] Claim 1 of Patent Document 2 discloses a method for operating an electric steelmaking furnace, in which scrap or scrap and molten pig iron are charged into the electric furnace for melting and refining, and a carbon-containing fuel and an oxygen-containing gas are injected into the electric furnace from a vertically movable lance while the electric furnace is energized. It also states that "if the supply rate of the carbon-containing fuel from the lance is increased during scrap melting, a portion of the fuel can enter the steel bath and slag layer without burning, and can contribute to carburization and slag foaming."

[0008] Claim 1 of Patent Document 3 discloses a method for producing molten iron by melting a cold iron source in an electric furnace equipped with a carbonaceous material injection device, in which the carbonaceous material (a) is injected from the center using a carrier gas, and a fuel (b) and a combustion-sustaining gas (c) are injected from the outer periphery, so that the carbonaceous material (a) injected from the center passes through a cylindrical combustion flame formed by a combustion reaction between the fuel (b) and the combustion-sustaining gas (c) and is injected into the molten slag and the molten iron. It also states, "In a method for producing molten iron by melting a cold iron source in an electric furnace equipped with a carbonaceous material injection device, a method is provided in which the carbonaceous material can be efficiently injected into the molten slag and the molten iron without compromising safety."

[0009] In the inventions described in Patent Documents 1 and 2, the carbonaceous material is sprayed together with oxygen gas, so the carbonaceous material burns during injection, resulting in a low rate of carburization of the molten iron. Also, the invention described in Patent Document 3 has a triple-tube lance structure in which fuel and combustion-supporting gas are injected from the outer periphery of the carbonaceous material injection, which results in a complex lance structure, requiring new equipment, and also has the problem of high costs for the combustion-supporting gas.

[0010] In the present invention, the carburization rate refers to the proportion of carbon dissolved in the added carbon material. For example, when adding 0.5% C equivalent to a C concentration to a metal with a C concentration of 0%, and then smelting the metal with a C concentration of 0.05% by oxygen supply, the final carbon material yield is 10%. In this case, when the carburization rate is 100%, the metal immediately after adding the carbon material has a C concentration of 0.5%, which then decreases to 0.05% by oxygen supply. On the other hand, when the carburization rate is 50%, the metal immediately after adding the carbon material has a C concentration of 0.25%, which then decreases to 0.05%. Therefore, even with the same yield, conditions with a high carburization rate result in a high C content in the metal during smelting, which makes it easier for CO gas to be generated, and lower nitrogen can be expected.

[0011] JP-A-6-287624 JP-A-7-26318 International Publication WO2021 / 090654

[0012] "Iron Metallurgical Reaction Engineering" by Kiyoshi Segawa, April 30, 1975, published by Nikkan Kogyo Shimbun, p. 90.

[0013] When carbonaceous material is supplied by spraying it from a lance onto molten iron, there is a layer of molten slag on top of the molten iron. With conventional lance methods, some of the carbonaceous material sprayed onto the molten iron is supplied into the molten iron, but most is absorbed by the slag, and only a small amount of carbon is deposited on the molten iron. Therefore, the main purpose of supplying carbonaceous material from a lance is to foam the slag. By foaming the slag during operation in an electric furnace, it is expected to improve heat transfer efficiency and suppress nitrogen absorption.

[0014] As shown in Figure 1, existing electric furnaces have lances that are primarily divided into two types: lances fixed to the wall (hereafter referred to as "wall lances 5") and lances inserted through the slag discharge door (hereafter referred to as "slag door 3") (hereafter referred to as "door lances 4"). Slag is discharged through the slag door 3, and temperature and sampling probes are inserted and removed. Therefore, the door lance 4 cannot constantly feed coal or oxygen. On the other hand, the wall lance 5 does not have such restrictions, allowing oxygen and coal to be fed at any time. However, because the wall lance 5 is fixed to the wall, it is subject to restrictions such as the inability to adjust the lance angle and the change in the molten metal surface height associated with scrap melting. Because the wall lance 5 is installed on the wall, increasing the blowing angle closer to vertical interferes with the furnace wall or places the furnace wall too close to the hot spot, making it difficult to increase the blowing angle. Currently, the blowing angle is approximately 45°.

[0015] In an existing electric furnace 1, an oxygen supply lance 7 for supplying oxygen and a coal supply lance 6 for supplying carbonaceous material are prepared as separate systems, and the two systems form one set, and it is common for multiple sets to be provided. The oxygen supply lance 7 has a large flow rate, and the target flow rate per oxygen supply lance 7 is 20 to 50 Nm3 so that oxygen penetrates the slag and reaches the molten iron. ３ / (hr·ton), which allows oxygen to be supplied to both the molten slag layer and the molten iron layer below it. On the other hand, the carrier gas flow rate of the coal feeding lance 6 is lower than that of the oxygen feeding lance 7, and the target flow rate per coal feeding lance 6 is 2 to 6 Nm ３ In the case of the existing coal feeding lance 6 provided as the door lance 4 or the wall lance 5, the proportion of the injected carbonaceous material that reaches the molten iron layer is not high, and the carbonaceous material is mainly supplied to the slag.

[0016] The type of carrier gas for the coal feeding lance 6 is preferably a non-oxidizing gas. ２ Air is difficult to use from the viewpoint of nitrogen absorption, and Ar is difficult to use from the viewpoint of cost. ２ may also be used.

[0017] It would be possible to attach a lance to the furnace lid that sprays carbonaceous material at an angle close to perpendicular to the surface of the molten iron, but because the furnace lid is high, the distance between the tip of the lance and the surface of the molten iron becomes large, making it difficult to penetrate the slag and supply the carbonaceous material to the molten iron.The furnace lid of an electric furnace has a swiveling, water-cooled structure, and since the furnace body tilts to discharge slag and tap steel, it is difficult to give the lance a lifting function due to the furnace body structure.

[0018] The door lance 4 is a long lance inserted into the slag door 3 from outside the furnace to feed oxygen and carbon. The height of the slag door 3 is close to the molten iron surface to make it easier to discharge the slag, so when blowing carbon material directly from the door lance 4, the blowing angle must be shallow. On the other hand, unlike fixed lances such as the wall lance 5, the door lance 4 is restricted to moving only within the gap of the slag door 3, but it also has the advantage of being able to change the lance height depending on the scrap melting.

[0019] An object of the present invention is to provide a method for injecting carbonaceous material into an electric furnace and a coal feeding lance that, when using a coal feeding lance 6 provided as a door lance 4 or a wall lance 5 installed in an existing electric furnace, allows the carbonaceous material 24 blown from the coal feeding lance 6 to reach the molten iron layer and efficiently carburize the molten iron.

[0020] That is, the gist of the present invention is as follows: [1] When a cold iron source is melted in an electric furnace to produce molten iron, when carbonaceous material is supplied into the furnace by being transported by a carrier gas through a coal feeding lance, the angle between the blowing direction from the coal feeding lance and the vertical downward direction (blowing angle θ) is smaller than the angle between the lance longitudinal direction of the coal feeding lance and the vertical downward direction (lance angle φ), and the slag recess depth L calculated by the formula (1) is set to the reference slag thickness L ０ L / L divided by ０ A method for injecting carbonaceous material into an electric furnace, characterized in that the carbonaceous material is supplied under gas injection conditions such that d.v is 1 or more. ０ ・cos ２ θ = 0.007(ρ ｌ / ρ ｇ ) １／２ (L + h)(L) １／２ (1) d: Lance outlet diameter (mm) v ０: Carrier gas flow velocity at the tip of the lance (m / s) θ: Spray angle (°) (angle between the spray direction and the vertical downward direction) ρ ｌ : Standard slag density (kg / m ３ ) ρ ｇ : carrier gas density (kg / m ３ ) (standard condition) L: recess depth (mm) L ０ : Reference slag thickness (mm) h: Distance between lance tip and slag surface (mm) Here, the reference slag thickness and reference slag density refer to the slag thickness and slag density when the slag is not foamed. [2] The method for injecting carbonaceous materials into an electric furnace according to [1], characterized in that the carbonaceous materials are injected at a blowing angle θ in the range of 10 to 40°. [3] The method for injecting carbonaceous materials into an electric furnace according to [1] or [2], characterized in that the coal feeding lance makes the blowing angle θ different from the lance angle φ by a deflection member of a deflection nozzle attached to the lance tip, and the Vickers hardness of the material of the deflection member at the portion where the carbonaceous materials collide is 500 or more.

[0021] [4] The method for injecting carbonaceous materials into an electric furnace according to [1] or [2], characterized in that the coal feed lance makes the spray angle θ different from the lance angle φ by a deflection member of a deflection nozzle attached to the tip of the lance, the carbonaceous material collision portion of the deflection member forms a carbonaceous material collision surface, a surface perpendicular to the carbonaceous material collision surface and including the lance center line is defined as a carbonaceous material collision vertical plane, and the direction of the line where the carbonaceous material collision surface and the carbonaceous material collision vertical plane intersect toward the tip of the coal feed lance is defined as the maximum inclination direction, and a shot hole is formed in the lance tip of the coal feed lance in a direction toward the maximum inclination direction, and when the shot hole is viewed from the maximum inclination direction, the circumferential width of the shot hole at the outer periphery of the coal feed lance is equal to or greater than the inner diameter of the coal feed lance, and when the shot hole is viewed from the maximum inclination direction, the cross-sectional area of ​​the shot hole is equal to or less than the cross-sectional area of ​​the inner periphery of the straight pipe part of the coal feed lance. [5] The method for injecting carbonaceous materials into an electric furnace according to [4], characterized in that the Vickers hardness of the material of the portion of the drift member with which the carbonaceous material collides is not less than 500. [6] The method for injecting carbonaceous materials into an electric furnace according to [4] or [5], characterized in that the shape of the outline of the shot holes on the outer periphery of the coal feeding lance when viewed from the maximum inclination direction is a shape other than a circle or an ellipse. [7] The method for injecting carbonaceous materials into an electric furnace according to any one of [4] to [6], characterized in that the circumferential width of the shot holes when viewed from the maximum inclination direction is width W, the height in a direction perpendicular to the circumferential direction is height H, and W / H is in the range of 1 to 4.

[0022] [8] A coal delivery lance used when melting a cold iron source in an electric furnace to produce molten iron, for feeding carbonaceous material into the furnace by transporting it with a carrier gas, wherein the angle between the blowing direction from the coal delivery lance and a vertical downward angle (blowing angle θ) is smaller than the angle between the longitudinal direction of the lance and a vertical downward angle (lance angle φ) of the coal delivery lance. [9] The coal delivery lance according to [8], wherein the blowing angle θ is set in a range of 10 to 40° when feeding carbonaceous material into the furnace by transporting it with a carrier gas.

[10] The coal delivery lance according to [8] or [9], wherein the blowing angle θ is made different from the lance angle φ by a deflection member of a deflection nozzle attached to the tip of the lance, and the Vickers hardness of the material of the deflection member with which the carbonaceous material collides is 500 or more.

[0023]

[11] The coal delivery lance according to [8] or [9], characterized in that the coal delivery lance has a deflection member of a deflection nozzle attached to the tip of the lance that makes the spray angle θ different from the lance angle φ, the carbonaceous material collision portion of the deflection member forms a carbonaceous material collision surface, a surface that is perpendicular to the carbonaceous material collision surface and includes the lance center line is a carbonaceous material collision vertical plane, and the direction toward the tip of the coal delivery lance is the maximum inclination direction in the direction of a line where the carbonaceous material collision surface and the carbonaceous material collision vertical plane intersect, and a spray hole is formed in the lance tip of the coal delivery lance in a direction toward the maximum inclination direction, and when the spray hole is viewed from the maximum inclination direction, the circumferential width of the spray hole at the outer periphery of the coal delivery lance is equal to or greater than the inner diameter of the coal delivery lance, and when the spray hole is viewed from the maximum inclination direction, the cross-sectional area of ​​the spray hole is equal to or less than the cross-sectional area of ​​the inner periphery of the straight pipe part of the coal delivery lance.

[12] The coal feed lance according to

[11] , characterized in that the Vickers hardness of the material of the portion of the drift member with which the carbonaceous material collides is not less than 500.

[13] The method for injecting carbonaceous material into an electric furnace according to

[11] or

[12] , characterized in that the shape of the outline of the shot holes on the outer periphery of the coal feed lance when viewed from the maximum inclination direction is a shape other than a circle or an ellipse.

[14] The coal feed lance according to any one of

[11] to

[13] , characterized in that the circumferential width of the shot holes when viewed from the maximum inclination direction is width W, the height in a direction perpendicular to the circumferential direction is height H, and W / H is in the range of 1 to 4.

[0024] According to the present invention, carbonaceous material can be efficiently supplied to molten iron from an existing coal-feeding lance of an electric furnace, such as a door lance, and the amount of pig iron added can be reduced.

[0025] 1 is a front cross-sectional view showing a schematic of an electric furnace. FIG. 1 is a cross-sectional view showing a depression in the slag caused by the gas flow from the coal feeding lance. FIG. 2 is a partial cross-sectional view showing the nozzle tip of a straight nozzle. FIG. 3 is a partial cross-sectional view showing the nozzle tip of a deviation nozzle. FIG. 4 is a diagram showing the relationship between the carrier gas flow rate, the spray angle θ, and the state of carburization of molten iron. FIG. 5 is a partial cross-sectional view showing the nozzle tip of a deviation nozzle immediately after the start of use. FIG. 6 is a partial cross-sectional view showing the nozzle tip of a deviation nozzle after some time has passed since use. FIG. 7 is a cross-sectional view showing the nozzle tip of a coal feeding lance. FIG. 8 is a cross-sectional view showing the nozzle tip of a coal feeding lance as seen from the arrow B-B. FIG. 9 is a cross-sectional view showing the nozzle tip of a coal feeding lance as seen from the arrow B-B. FIG. 10 is a cross-sectional view showing the nozzle tip of a coal feeding lance as seen from the arrow C-C. FIG. 11 is a diagram showing the cross-sectional shape of the shot hole of the coal feeding lance.

[0026] The electric furnace 1 to which the present invention relates is a melting furnace that produces molten steel using mainly scrap as a raw material. As shown in FIG. 1 , electric energy is supplied from electrodes 2 to melt a cold iron source and heat it up. The electric furnace to which the present invention relates is assumed to be configured such that, for example, in a given channel, scrap (e.g., 105 tons) is added and melted from a seed molten metal (e.g., 65 tons), and once melting and refining are complete, only the scrap supply (e.g., 105 tons) is tapped, and the next channel is operated with the seed molten metal (e.g., 65 tons) remaining. Refining before tapping mainly involves adjusting the molten steel temperature (e.g., >1650°C) and the C concentration (e.g., <0.05%). During the melting process, auxiliary materials (CaO, SiO ２ , MgO, etc.) are added to perform dephosphorization. By supplying oxygen from the oxygen supply lance 7, the Si and Mn in the molten iron are reduced, and part of the molten iron becomes FeO. The processing time is 40 to 60 minutes for the melting period (scrap addition + melting) and approximately 5 to 15 minutes for the temperature rise period. During the melting period, scrap is continuously added to the electric furnace via a belt conveyor.

[0027] As the amount of molten iron 21 increases from 65 tons to 170 tons, the oxygen supply rate per oxygen supply lance 7 is 2500 to 4000 Nm ３ / hr (same for wall lance 5 and door lance 4), and the carrier gas flow rate per coal sending lance 6 is 200 to 600 Nm ３ / hr (same for wall lance 5 and door lance 4), and the coal feed rate is generally fixed at 15 to 25 kg / min, but varies within the range of 10 to 30 kg / min depending on the equipment conditions and the required C concentration.

[0028] The coal supply lances 6 and oxygen supply lances 7 in an existing electric furnace 1 include wall lances 5 (for example, two sets) fixed to the furnace wall and door lances 4 (for example, one set) inserted from the slag door 3, each set having an oxygen supply lance 7 and a coal supply lance 6. For example, if there are two sets of wall lances 5 and one set of door lance 4, there will be three oxygen supply lances 7 and three coal supply lances 6. The door lance 4 is inserted into the electric furnace from the slag door 3 to perform oxygen supply or coal supply. The oxygen supply speed per lance is approximately 20 to 50 Nm ３ / (hr ton), carrier gas during coal delivery (CO ２ ) Flow rate per lance: 2 to 6 Nm ３ / (hr·ton), and the coal feeding rate per lance is approximately 0.059 to 0.462 kg / (min·ton). The door lance 4 has a long straight section and can be inserted from the slag door 3 from a position about 0.5 m away from the furnace wall to near the electrode 2. The lance nozzle has a straight nozzle 9 as shown in Figure 3A, and gas passes through the straight pipe section and is injected linearly from the outlet of the lance tip 30.

[0029] Conventionally, when the door lance 4 was used as the coal feeding lance 6, the rate at which the injected carbonaceous material was added to the molten iron 21 was low. It is presumed that the carrier gas jet from the coal feeding lance 6 was unable to sufficiently break through the slag layer present above the molten iron layer, and most of the carbonaceous material injected together with the carrier gas was absorbed into the slag layer.

[0030] Therefore, the inventors came up with the idea that if the method of blowing the carrier gas from the coal feeding lance 6 is adjusted to concave the slag surface until it reaches the molten iron-slag interface 35, it may be possible to supply the carbonaceous material directly to the molten iron.

[0031] In Non-Patent Document 1, the depression depth L of the molten metal when oxygen gas is blown from an oxygen supply lance into the molten metal in a converter furnace is studied, and the following formula (5.2) is presented: d·v ０= α(L + h)(L) １／２ (A) α=0.015(ρ ｌ / ρ ｇ ) １／２ (B) where d: nozzle diameter (mm), L: recess depth (mm), h: distance from the lance tip to the molten metal surface (mm), v ０ : apparent jet velocity at the nozzle tip (m / s), ρ ｇ : gas density (kg / m ３ ), ρ ｌ : Density of hot water (kg / m ３ ) where α in formula (A) is a coefficient for adjustment and is described in formula (B). When the molten metal is water, the theoretical α calculated by formula (B) is 0.416. According to Non-Patent Document 1, even if conditions such as the type of molten metal, temperature, and type of gas change, the above formulas (A) and (B) can be used as they are, and by modifying the constant on the right-hand side of formula (B) according to the experimental results, it can be used as an empirical formula that is valid in a wide range. Therefore, in the following, a constant β is introduced, and α = β(ρ ｌ / ρ ｇ ) １／２ (B1) will be considered.

[0032] As shown in Figure 2, the horizontal direction from the slag door to the tip of the lance is the X axis (horizontal), the direction rotated at a right angle on the horizontal plane is the Y axis (horizontal), and the vertical direction is the Z axis.

[0033] Here, as shown in Figures 2, 3A, and 3B, a blowing angle θ is introduced with respect to the direction (blowing direction 32) of the jet from the coal feeding lance 6. The blowing angle θ is defined as 0° downward in the vertical direction (Z axis), and refers to the angle between the blowing direction 32 and the vertical downward 34. When the blowing angle θ = 0°, the carbonaceous material is blown from the lance tip 30 toward the vertical downward 34. When the blowing angle θ = 30°, the carbonaceous material is blown in a direction tilted 30° from the vertical downward 34 of the Z axis starting from the lance tip 30. In this case, the lance is basically tilted 30° on the XY plane, which is an extension of the straight portion of the lance, but it may also be tilted on a plane shifted from the XY plane. The formula described in Non-Patent Document 1 above is for the case where the jet from the lance is directed vertically downward, i.e., when the blowing angle θ = 0°. In contrast, in the present invention, the carrier gas and carbonaceous materials ejected from the coal feeding lance 6 are ejected at an angle from vertically downward, i.e., at a finite blowing angle θ. Therefore, here, we investigated how the blowing angle θ affects the depression depth L of the molten metal.

[0034] Here, v on the left side of equation (A) ０ is the carrier gas flow velocity (m / s) at the tip of the lance, assuming a spray angle θ=0°. When the spray angle θ is tilted from the vertical downward 34, it is the vertical component of the velocity that contributes to the depth of the liquid depression 20, and v ０ The vertical component of ０ ・cosθ, so the left side of equation (A) is d・v ０ · cos θ. In addition, on the right side of equation (A), the term (L + h) means the distance from the lance tip 30 to the bottom of the recess 20, and when tilted by the spray angle θ, the distance from the lance tip 30 to the bottom of the recess 20 becomes (L + h) / cos θ (see Figure 2). Then, by introducing the spray angle θ into equation (A) and transforming equation (A), d·v on the left side of equation (A) becomes ０ d.v. ０ ・cosθ, and replace (L + h) on the right side with (L + h) / cosθ. If we combine the cosθ terms on the left side, we get d・v ０ ・cos ２ θ = α(L + h)(L) １／２ (A1) is derived. By substituting the above equation (B1) into equation (A1), d・v０ ・cos ２ θ=β(ρ ｌ / ρ ｇ ) １／２ (L + h)(L) １／２ (C) The formula is derived, where β is a constant that should be determined based on experimental results.

[0035] In Non-Patent Document 1, h refers to the distance between the lance tip and the molten metal surface. In the present invention, since the molten metal being sprayed is molten slag, the distance on the Z axis from the lance tip 30 to the position of the stationary slag surface 31 is defined as the lance tip-slag surface distance h.

[0036] The gas temperature T is proportional to the gas density ρ ｇ The coal feeding lance 6 to which the present invention is applied is water-cooled up to the vicinity of the tip, and it is considered that the temperature of the gas blown out from the lance tip 30 does not increase. Therefore, it is considered that the gas is in a standard state, and the density ρ of the gas is ｇ Calculate.

[0037] Here, we will consider the slag layer formed on the surface of the molten metal in the electric furnace. ３ If the slag thickness (m) is known, the slag thickness (m) can be calculated by the following formula: slag amount (kg) / (slag layer surface area (m ２ ) × slag density (kg / m ３ The density of the slag changes depending on whether or not it is formed, and as a result, the slag thickness also changes. Here, the reference slag thickness L ０ The distance on the Z axis from the surface of the slag in a stationary state without gas blowing and without forming to the surface of the molten iron is defined as the reference slag thickness L ０ The reference slag density ρ when the slag is not formed ｌ If the standard slug thickness L is determined, ０ It is possible to calculate the slug thickness. A comparison with the slug thickness during forming will be described later.

[0038] Here, the recess depth L and the reference slug thickness L ０ The relationship between is assumed as follows:

[0039] In the above, the depth L of the depression of the slag is the depth on the Z axis from the surface 31 of the slag in a stationary state without gas blowing and without forming to the deepest position of the depression 20 formed when gas is blown. ０ In relation to ０ The following parameter is introduced: L / L ０ = 1, the recess depth L is the reference slug thickness L ０ This means that the gas penetrates the slag. ０ If L / L<1, it is estimated that the bottom of the recess 20 does not reach the molten iron-slag interface 35, and the rate of carburization of the molten iron 21 is low. ０ If ≧1, the molten iron 21 is exposed at the bottom of the depression 20, and it is expected that the carburization rate of the molten iron 21 will be high.

[0040] As mentioned above, the slug is actually formed, but in the present invention, the reference slug thickness L obtained without forming is used. ０ and the reference slag density ρ ｌ The calculation is performed using the following formula (C): ｌ ) １／２ (L) １／２ As mentioned above, the value of (slag thickness x slag density) is constant regardless of whether forming is performed or not. ０ When L = 1, the (L + h) term in equation (C) is kept constant regardless of whether forming is performed or not. Therefore, the calculation of equation (C) should yield the same result regardless of whether forming is performed or not, and therefore, in the present invention, the recess depth at the reference time without forming is used.

[0041] With the above preparations, carbonaceous material was sprayed onto the slag layer on the surface of the molten metal from a coal-feeding lance together with carrier gas in an actual electric furnace, and the change in the carbonization rate of the molten metal was evaluated by changing the spraying conditions in various ways. Details of the test conditions are as described in the examples below. 170 tons of molten metal was placed in the electric furnace, and a slag layer was formed on the surface of the molten metal. The slag amount (kg) and the standard slag density ρ when not formed were compared. ｌ From the reference slug thickness L ０As a result of calculating the standard slug thickness L ０ The distance h from the lance tip 30 to the slag surface 31 was 500 mm. The spray angle θ was changed from 0° to 50°, and the carrier gas flow rate was changed from 150 to 450 Nm ３ / hr. In Fig. 4, the horizontal axis represents the carrier gas flow rate, and the vertical axis represents the spray angle θ. In Fig. 4, a carburization rate of 10% or more is indicated by a white circle, and a rate of less than 10% is indicated by an X.

[0042] (C) The apparent injection velocity at the nozzle tip is v ０ (m / s) is the gas density ρ in equation (C) ｇ is the density under standard conditions, the carrier gas flow rate (Nm ３ / hr) / nozzle cross-sectional area (m ２ ) / 3600 (s / hr). Assuming various values ​​for the constant β, the equation (C) is calculated as L / L at the boundary between the white circle and the X mark in the experimental results. ０ In FIG. 4, it was confirmed whether there exists a value of β such that L / L = 1 holds. ０ When the constant β is set to 0.007 instead of 0.015, the L / L ０ It was found that the line where ≈1 can adequately explain the results of the actual machine test in determining whether the carburization rate is good or bad.

[0043] From the above, when the value of L is calculated by the following formula (1) by substituting 0.007 for β in the above formula (C), L / L ０ By selecting the operating conditions such that the value of is greater than 1, the depth L of the slag layer formed by the jet force of the coal feeding lance 6 is equal to the reference slag thickness L ０ Since the molten iron layer is exposed at the bottom of the depression 20, the carbonization rate of the sprayed carbonaceous material can be made to be a good value. ０ ・cos ２ θ = 0.007(ρ ｌ / ρ ｇ ) １／２ (L + h)(L) １／２ (1)

[0044] 3A and 3B, the angle between the lance longitudinal direction 33 of the coal feeding lance 6 and the vertical downward direction 34 is defined as the lance angle φ. The lance longitudinal direction 33 is the direction from the base of the lance toward the lance tip 30. When the lance tip 30 faces the vertical downward direction 34, the lance angle φ is set to 0°. In the existing electric furnace 1, the lance angle φ for the door lance 4 is in the range of approximately 60° to 80°. The lance angle φ for the wall lance 5 is in the range of approximately 40° to 60°. Both the door lance 4 and the wall lance 5 are straight nozzles 9 as shown in FIG. 3A, and the blowing direction 32 of the carbonaceous material 24 is the same as the lance longitudinal direction 33. Therefore, the blowing angle θ = the lance angle φ. Therefore, the blowing angle θ cannot be set to a small angle for either the door lance 4 or the wall lance 5. In addition, the flow rate of the carrier gas of the coal feeding lance 6 in the existing electric furnace is often low. As a result, the value of L calculated by the above formula (1) is ０ In the present invention, when the lance angle φ is in the range of 70° to 80°, the improvement effect of applying the present invention can be preferably enjoyed, and therefore, the carburization rate cannot be improved.

[0045] In the present invention, a method for reducing the blowing angle θ despite a large lance angle φ has been found by machining the tip of the coal feed lance 6 into a drift nozzle 8 as shown in FIG. 3B and providing an angle between the blowing direction 32 and the lance longitudinal direction 33. Here, as shown in FIG. 3B, the angle between the blowing direction 32 and the lance longitudinal direction 33 is defined as the eccentric angle η. By setting the eccentric angle η so that the blowing direction 32 is directed downward, the blowing angle θ = lance angle φ - eccentric angle η, and the blowing angle θ can be reduced despite a large lance angle φ. By reducing the blowing angle θ and blowing the carbonaceous material in a direction closer to vertically downward 34, it is possible to supply the carbonaceous material 24 to the molten iron 21 through the slag 22 even when the carrier gas flow rate of the coal feed lance 6 is low in an existing electric furnace 1. It is preferable to set the eccentric angle η in the range of 20° to 70°. In the drift nozzle 8, the value of d on the left side of equation (1) can be found as the inner diameter of the straight pipe portion of the lance before the nozzle tip where the drift member 10 is attached.

[0046] The present invention can be applied to both the door lance 4 and the wall lance 5, but is more preferably applied to the door lance 4. That is, the door lance 4 allows for adjustment of the distance between the lance tip 30 and the slag surface 31, and the distance between the lance tip 30 and the molten iron-slag interface 35 is closer than that of the wall lance 5. Therefore, the structural formula (1) allows for a wider range of operating conditions for increasing the carburization rate. Furthermore, if the tip of the wall lance 5 is machined, maintenance is difficult (entering the furnace is required only for major repairs). In contrast, if the tip of the door lance 4 is machined, the door lance 4 is removed from the furnace during non-processing times, and therefore, if the tip of the door lance 4 is melted and damaged, maintenance such as replacing only the tip is easy.

[0047] In the case of a conventional straight nozzle 9 for the coal delivery lance 6, the carrier gas passes through the straight body of the lance and is injected linearly from the lance tip outlet in the same direction as the direction of the straight body of the lance (see FIG. 3A). In contrast, in the present invention, the lance is configured such that the blowing angle θ differs from the lance angle φ by bending only the tip portion or by attaching a deflection nozzle 8 to the lance tip (see FIG. 3B). This allows the angle between the blowing direction 32 from the coal delivery lance 6 and the vertical downward direction 34 (the blowing angle θ) to be smaller than the angle between the lance longitudinal direction 33 of the coal delivery lance 6 and the vertical downward direction 34 (the lance angle φ).

[0048] When considering electric furnace operation, equipment durability is a key issue. Equipment replacement frequency is determined by its weakest link.

[0049] When a straight coal feed lance 6 without an eccentric angle η at its tip is used as in the past, there are no obstacles in the direction of travel of the carbonaceous material inside the coal feed lance 6, so lance wear is not an issue, and the frequency of lance replacement is determined by factors other than wear at the lance tip. However, when a flow deflection nozzle 8 with a flow deflection member 10 attached to the tip of the coal feed lance 6 is used as in the present invention, the carbonaceous material transported by the carrier gas collides with the flow deflection member 10. In the present invention, a higher flow velocity of the carrier gas is advantageous because the slag floating above the metal is penetrated. However, because the carbonaceous material is transported by the carrier gas, a higher flow velocity of the carrier gas is disadvantageous in terms of wear of the flow deflection member 10. Therefore, when a coal feed lance 6 using a flow deflection nozzle 8 with a flow deflection member 10 attached is used, wear of the flow deflection member 10 is significant, and a situation arises in which the lance needs to be replaced due to wear.

[0050] There is generally a positive correlation between the wear resistance behavior of a material and its Vickers hardness. Material wear begins when different materials come into contact and exert force on each other. For example, when a hard material wears a soft material, the pressure of the hard material scrapes off fine particles from the surface of the soft material, causing the wear to progress. Therefore, in the present invention, the inventors came up with the idea that by using a wear-resistant material for the flow deflection member 10, the frequency of lance replacement could be reduced compared to materials that have been used traditionally.

[0051] Carbon steel is often used as the material for the coal feeding lance 6 due to its workability and cost. According to commonly used technology, carbon steel is also used for the drift member 10. The Vickers hardness Hv of carbon steel is often about 200 to 300. The Vickers hardness Hv of carbonaceous materials is about 200 to 300, which is about the same as that of carbon steel.

[0052] Although wear behavior varies depending on the particle size of the colliding material, the angle of impact, and the crystalline structure of the material, the hardness of the material significantly affects wear behavior under the same conditions for the shape of the coal delivery lance 6 and the carbonaceous material injected by the carrier gas. Therefore, by using a material with a higher Vickers hardness than conventional carbon steel for the flow deflection member 10, the wear rate of the flow deflection member 10, which is worn by the carbonaceous material, can be reduced, thereby reducing the frequency of lance replacement. The coal delivery lance 6 is used in an electric furnace, and high-temperature slag is present near the tip of the lance 6. Meanwhile, the coal delivery lance 6 has a water-cooled structure, and the carbonaceous material is transported by room-temperature carrier gas through the water-cooled pipe. Since the flow deflection member 10 at the tip of the lance is considered to be cooled by room-temperature carrier gas, the Vickers hardness at room temperature can be used to evaluate the wear properties of the material.

[0053] The lance replacement frequency refers to the frequency with which a deteriorated lance is replaced with a sound lance before the deterioration of the coal feed lance and oxygen feed lance that occurs during operation adversely affects operation. Since lance replacement takes time, a high replacement frequency reduces productivity. As will be made clear in the examples described later, by using a material with a Vickers hardness of 500 or more as the material for the drift member 10 of the drift nozzle 8 attached to the lance tip of the coal feed lance 6, it is possible to reduce wear due to the collision of carbonaceous material and reduce the frequency of lance replacement.

[0054] When a material with a high Vickers hardness is used as the material for the flow deflection member 10 of the flow deflection nozzle 8 attached to the lance tip of the coal feeding lance 6, it is not necessary for the entire flow deflection member 10 to have a high Vickers hardness. At least the portion of the flow deflection member 10 that is hit by the carbonaceous material (carbonaceous material collision portion 11) wears preferentially, so it is sufficient to increase the wear resistance of this portion. If the Vickers hardness of the material of the carbonaceous material collision portion 11 is 500 or more, wear due to the impact of the carbonaceous material can be reduced. The entire flow deflection member 10 may be made of a material with a Vickers hardness of 500 or more.

[0055] The material of the part that the carbonaceous material collides with can be either metal or ceramic. Since the lance body is basically made of carbon steel, the lance tip including the part that the carbonaceous material collides with can be created and welded, or only the part that collides with can be replaced with metal or ceramic.

[0056] When the coal feeding lance 6 of the present invention injects carbonaceous material into the molten metal, CO is used as the carrier gas. ２ It is preferable to use a gas or a non-oxidizing gas. As the non-oxidizing gas, N ２ In the existing electric furnace, the coal feeding lance 6 and the oxygen feeding lance 7 are separately prepared, and the carrier gas for the coal feeding lance 6 is CO ２ The carrier gas is either CO or non-oxidizing gas. ２ If a gas or a non-oxidizing gas is used, the present invention can be implemented with minor modifications to an existing coal feeding lance 6.

[0057] The smaller the blowing angle θ, the larger the value of L calculated from equation (1), which is preferable. A blowing angle θ of 40° or less can provide favorable results. A blowing angle θ in the range of 0° to 12° can provide the most favorable results. On the other hand, if the blowing angle θ is less than 10°, the recess depth L increases, but there is a concern that splashes generated by blowing may directly adhere to the lance tip 30 of the coal feeding lance 6. Therefore, when priority is given to preventing splashes from adhering to the lance tip, it is preferable to set the blowing angle θ to 10° or more.

[0058] The effect of the invention is evaluated by the carburization rate. The carburization rate can be confirmed by performing a mass balance calculation to determine the increase in the C concentration in the molten iron relative to the amount of carbonaceous material added. At this time, a more accurate carbonaceous material addition efficiency can be obtained by performing a test under conditions where no mold iron is added.

[0059] The blowing direction 32 from the coal feed lance 6 can be determined by actually injecting carrier gas from the coal feed lance 6 offline and measuring the blowing direction 32. The blowing direction 32 should be measured when the lance begins to be used, and also as the tip of the lance wears and the blowing direction 32 changes as the lance is used. Therefore, the blowing direction 32 may be measured as needed as the coal feed lance 6 continues to be used. Then, the angle between the blowing direction 32 and the lance longitudinal direction 33 can be evaluated as the eccentric angle η. Once the eccentric angle η is determined, the blowing angle θ can be calculated as θ = φ - η by setting the lance angle φ of the coal feed lance 6.

[0060] In the coal feeding lance 6, as shown in Figures 6A and 6B, a drift member 10 is attached to the lance tip 30 of the coal feeding lance 6 formed of an outer pipe 15 made of a steel pipe, and the blowing holes 14 for blowing the carbonaceous material are sometimes provided on the side of the outer pipe 15. In this case, since the steel pipe is often machined on a lathe, the shape of the blowing holes 14 was assumed to be circular or elliptical. In addition, since a smaller blowing hole area increases the gas flow rate and makes it easier to penetrate the slag, the inner diameter D of the steel pipe is ０ In some cases, the spray holes 14 were drilled with a smaller diameter than the above.

[0061] When using the above-described coal feeding lance 6, wear of the lance tip is an issue because the carbonaceous material being blown is hard, and this wear issue becomes more pronounced as the gas flow velocity increases. Therefore, as described above, wear of the flow deflection member 10 can be prevented by using a material with a Vickers hardness of 500 or more for the part of the flow deflection member that the carbonaceous material collides with. On the other hand, it is difficult to use ceramics around the blast holes 14 opening on the side of the outer tube 15 due to the workability, thermal load, and cost of the lance tip, so it is basically made of a metal that can be welded to the lance body.

[0062] If the outer tube 15 of the lance is made of metal, when carbonaceous material is supplied under conditions favorable for slag penetration, the spray hole 14 will be worn around the spray hole 14, particularly at the wear points 45 on both sides of the spray hole, as shown in Figure 6B.

[0063] Since the carbonaceous material is transported by the gas, in order to prevent wear of the blasting holes 14, it is sufficient to make the outer pipe not be on the flow path through which the gas passes. Specifically, as shown in Figure 7B, the width W of the blasting holes 14 in the circumferential direction 39 is set to be equal to the inner diameter D of the outer pipe 15. ０ The width of the nozzle hole 14 is widened to the above. Instead, in order to avoid reducing the flow rate of the gas ejected from the nozzle hole 14, the height H of the nozzle hole 14 in the direction perpendicular to the circumferential direction 39 is narrowed, thereby reducing the cross-sectional area A of the nozzle hole 14. Generally, even if the outlet shape of the nozzle hole 14 is not circular, the jets ejected from the nozzle hole 14 will coalesce or deform, resulting in a cross-sectional shape approaching a circle. For this reason, the nozzle hole 14 may be elliptical or rectangular, and does not need to be close to a circle. To effectively prevent wear around the nozzle hole, a shape other than a circle or ellipse is preferred. This is because, when ceramics are used as the flow deflection member 10, a nozzle hole 14 with a shape other than a circle or ellipse can simultaneously prevent wear on the outer tube and provide a ceramic coating. Ceramics are less formable and machinable than metals. Therefore, when the nozzle hole shape is circular or elliptical, the ceramic must also have a curved shape at the carbonaceous material collision portion to match the nozzle hole shape. To secure ceramics to the inside of the lance tip, the inner tube must be machined to fit the curved surface. However, machining even metal materials to fit curved surfaces is difficult, time-consuming, and requires processing costs. To secure the ceramics to the inside of the lance tip and reduce manufacturing costs, it is advisable to make the shape of the carbonaceous material collision portion 11 flat. If the carbonaceous material collision portion 11 is made flat and the spray holes are made circular or elliptical, a mismatch will occur between the shape of the carbonaceous material collision portion 11 and the shape of the spray holes 14. That is, if the spray hole diameter is small, wear will occur at the area where the carbonaceous material impacts, while if the spray hole diameter is large, the proportion of the ceramic not covered by the outer tube will increase. While the above is particularly noticeable when the flow deflection member 10 is made of ceramic, the same applies when a metal member is used.

[0064] The procedure for determining the preferred shape of the spray holes 14 will now be described with reference to FIGS.

[0065] As shown in Figure 7A, the carbonaceous material collision portion 11 of the drift member 10 forms a carbonaceous material collision surface 36. A plane perpendicular to this carbonaceous material collision surface 36 and including the lance center line 12 is defined as a carbonaceous material collision vertical plane 37. The carbonaceous material collision vertical plane 37 is parallel to the plane of Figure 7A and does not appear in Figure 7A. Furthermore, the carbonaceous material collision vertical plane 37 is perpendicular to the plane of Figure 7B, and therefore is depicted as a straight line in Figure 7B. The direction of the line where the carbonaceous material collision surface 36 and the carbonaceous material collision vertical plane 37 intersect, toward the tip side of the coal feeding lance 6, is defined as a maximum inclination direction 38 (Figures 7A and 7B).

[0066] A shot hole 14 is formed in the lance tip 30 of the coal feed lance 6 in a direction toward the maximum inclination direction 38. Figure 7B is a view taken along the arrows B-B in Figure 7A, showing the shot hole 14 as viewed from the maximum inclination direction 38. That is, Figure 7B shows the outline of the shot hole 14 at the outer periphery 41 of the coal feed lance 6 (shot hole outer periphery outline 43) and the outline of the shot hole 14 at the inner periphery 42 (shot hole inner periphery outline 44) when the shot hole 14 is viewed from the maximum inclination direction 38. Note that, as shown in Figure 7B, when the carbonaceous material collision surface 36 of the drift member 10 is visible inside the shot hole 14, the carbonaceous material collision surface 36 also constitutes part of the shot hole inner periphery outline 44. In the shot hole outer periphery outline 43 as viewed from the maximum inclination direction 38, the width in the circumferential direction 39 is defined as width W, and the height in the direction perpendicular to the circumferential direction 39 is defined as height H. In this embodiment, the width W is the inner diameter D of the straight pipe portion 40 of the coal feeding lance 6. ０ This is all. This makes it possible to realize a situation where there is no outer pipe on the flow path through which the gas passes, and as a result, wear of the spray hole 14 can be prevented. Furthermore, when the spray hole 14 is viewed from the maximum inclination direction 38, the area of ​​the common part (the dotted hatched part in FIG. 7B) between the part surrounded by the spray hole outer peripheral outline 43 of the spray hole 14 and the part surrounded by the spray hole inner peripheral outline 44 of the spray hole 14 shown in FIG. 7B is defined as the cross-sectional area A of the spray hole 14. The cross-sectional area A of the spray hole 14 is then multiplied by the cross-sectional area A of the inner peripheral part 42 of the straight pipe part 40 of the coal feeding lance 6. ０ This makes it possible to maintain the flow rate of the gas ejected from the spray hole 14 without reducing it. Here, the lance outlet diameter d in equation (1) is more preferably the equivalent diameter of a circle having the same area as the cross-sectional area A of the spray hole 14.

[0067] 7B and 7C, the width in the circumferential direction 39 of the inner peripheral contour 44 of the spray hole is smaller than the width W in the circumferential direction 39 of the outer peripheral contour 43 of the spray hole. ０ By configuring the shot hole 14 in this manner, it is possible to smoothly transition between the contour of the inner peripheral portion 42 of the straight pipe portion 40 of the coal feeding lance 6 and the shot hole inner peripheral portion contour 44 of the shot hole 14. As a result, the width W in the circumferential direction 39 of the shot hole outer peripheral portion contour 43 is equal to the inner diameter D of the straight pipe portion 40. ０ In the present embodiment described above, the gas flow can be stabilized without being disturbed.

[0068] As described above, it is preferable that the shape of the outline of the shot holes 14 in the outer circumferential portion 41 of the coal feeding lance 6 when viewed from the maximum inclination direction 38 be a shape other than a circle or an ellipse.

[0069] As described above, the width in the circumferential direction 39 of the outer peripheral contour 43 of the shot hole as viewed from the maximum inclination direction 38 is defined as width W, and the height in the direction perpendicular to the circumferential direction 39 as height H. In the present invention, it is preferable to set W / H in the range of 1 to 4. Since increasing the gas flow rate is necessary to increase the carburization rate, it is preferable to narrow the area of ​​the shot hole within a range that does not cause clogging with carbonaceous material. When W / H is less than 1, i.e., the shot hole has a shape that extends in the longitudinal direction, the shot hole area increases if W is considered to be the circumferential width W. On the other hand, narrowing the width W so that W / H is less than 1 will cause wear. For this reason, it is preferable that W / H is 1 or greater. On the other hand, when W / H exceeds 4, i.e., the shot hole has a shape that extends in the circumferential direction, the height H becomes smaller, which increases the frequency of collision of carbonaceous material with the base of the shot hole, and wear in this area cannot be ignored. For this reason, it is preferable that W / H is 4 or less.

[0070] Example 1 Using an electric furnace with a molten metal capacity of 170 tons as shown in FIG. 1 , 65 tons of seed metal was placed in the electric furnace. 105 tons of scrap was gradually added over a melting period of 45 to 70 minutes to produce 170 tons of molten steel. During this process, oxygen was fed from the oxygen feeding lance 7 provided as the wall lance 5 and the door lance 4, and coal was fed from the coal feeding lance 6. After the melting period, the furnace was adjusted to a predetermined C concentration and temperature over 5 to 15 minutes, and 105 tons of molten steel was tapped, leaving 65 tons of seed metal in the furnace. At the initial stage of the melting period, slag from the previous channel remained in the furnace with a thickness of approximately 100 mm. After the start of scrap charging, coal feeding and oxygen feeding were performed as necessary, and CaO, SiO, and other elements were removed. ２ Oxides containing MgO and the like were added to the electric furnace as auxiliary raw materials. The rate of addition of carbonaceous material was 15 to 25 kg / min per coal feeding lance, and CO ２ was blown into the furnace as a carrier gas.

[0071] Hereinafter, the slug thickness is the standard slug thickness L ０ That is, the distance on the Z axis from the slag surface 31 in a stationary state without forming to the molten iron-slag interface 35 is used. The distance h from the lance tip 30 to the slag surface 31 is calculated by multiplying the distance from the lance tip 30 to the molten iron-slag interface 35 by the reference slag thickness L ０ can be calculated by subtracting

[0072] In carrying out the present invention, a change in the C concentration in molten steel when carbonaceous material was injected from the coal feeding lance 6 provided as the current door lance 4 was investigated as a base condition (No. 32 in Table 1). The base condition was a condition in which the injection angle θ was 70° (= insertion angle from the slag door (lance angle φ) = 70°), a straight nozzle 9 with no processing at the lance tip (eccentric angle η = 0°), and a carrier gas (CO ２ ) Flow rate is 400 Nm ３ / hr, the distance h between the lance tip and the slag surface is 500 mm, and the standard slag thickness L ０ Since a water-cooled lance is used as the coal feeding lance 6, the carrier gas discharged from the tip of the lance is in a standard state, and the gas density ρ ｇThe standard gas density was used as the gas density. The sequential addition of scrap was temporarily stopped before and after the injection of the carbonaceous material, and molten iron samples were taken to investigate the C concentration in the molten iron. The intervals between molten iron samples were 5 to 10 minutes, during which no pig iron was added and the coal and oxygen supply processes from the wall lance were also stopped, so that the supply of C from sources other than the carbonaceous material and scrap added from the door lance could be ignored.

[0073] In parallel, the change in carbon concentration during carbon injection, determined from the scrap components, scrap addition rate, and carbonaceous material addition amount, was compared with the analyzed carbon concentration value to calculate the carburization rate. Under base conditions, when carbonaceous material was injected from the door lance, the carburization rate was 5% or less, and it is believed that most of the carbonaceous material was captured in the slag. In this case, it was determined that the invention was effective under conditions where 10% or more of the added carbonaceous material could be supplied to the molten iron.

[0074] In the present invention, the lance tip 30 of the coal feeding lance 6 used under the base conditions was processed as shown in Figure 3B, and a flow deflection nozzle 8 to which a flow deflection member 10 was fixed was attached, thereby varying the eccentric angle η from 70° to 20° and the gas blowing direction (blowing angle θ) from 0° to 50°. In addition, the carrier gas flow rate was set to 150 to 450 Nm ３ / hr, and the distance h between the lance tip and the slag surface was changed from 300 to 530 mm. ０ The lance outlet diameter d was 38 mm, and the standard slag density ρ ｌ is the density of the slag in the unformed state: 3000 kg / m ３ , CO gas density ρ ｇ is 1.77 kg / m under standard conditions ３ was treated as such.

[0075]

[0076] Examples are shown in Table 1. Nos. 1 to 17 are examples of the present invention, and Nos. 18 to 32 are comparative examples. ０ In the column, L / L ０ The values ​​less than 1 are underlined. In addition, when the distance between the lance and the slug is 500 mm and the standard slug thickness L ０The results for 100 mm are shown in Figure 4. The dashed line in Figure 4 represents the relationship between L and L in equation (1). ０ The left side of the dashed line in Figure 4 is L / L ０ <1, and the right side is L / L ０ > 1. The area to the right of the broken line is the area where the carrier gas penetrates the slag. The "Effects of the Invention" column in Table 1 and the white circles shown in Figure 4 indicate conditions where the carburization rate was 10% or more and the effects of the invention were observed. On the other hand, the X marks indicate conditions where the carburization rate was less than 10% and the effects of the invention were not observed. In Table 1 and Figure 4, the white circles were obtained when L calculated by equation (1) was less than L ０ It was an area that exceeded this.

[0077] No. 10, No. 13, No. 24, and No. 26 were tested under the same conditions of spray angle, carrier gas flow rate, and distance between the lance tip and the slag surface, with the reference slag thickness L ０ No. 2, No. 5, No. 7, and No. 27 are conditions where the spray angle θ is different under the same conditions of carrier gas flow rate, distance between the lance tip and the slag surface, and standard slag thickness. No. 11, No. 12, No. 24, and No. 25 are conditions where the spray angle, carrier gas flow rate, and standard slag thickness are the same under the same conditions of carrier gas flow rate, distance between the lance tip and the slag surface, and standard slag thickness are different. In all of the conditions where the invention was effective, L calculated by formula (1) was L ０ The conditions were as above.

[0078] From the above, it can be seen that by spraying the carbonaceous material under the conditions specified in the present invention, the addition efficiency of the carbonaceous material sprayed from the door lance can be improved.

[0079] Nos. 1 to 3 and Nos. 18 to 20 are conditions where the spray angle is 0°, but when the spray angle is 0°, the scattered slag adheres to the lance, increasing the maintenance load of the lance. Also, Nos. 17 and 31 are conditions where the spray angle is 50°, but to obtain the effect of the invention, the carrier gas flow rate needs to be 400 Nm ３ / hr greater than 450 Nm ３ / hr, and if the spray angle θ is increased beyond this, a larger flow rate of carrier gas will be required. For this reason, it is desirable that the spray angle θ be in the range of 10° to 40°.

[0080] Example 2 Under the carbonaceous material spraying conditions of No. 5 and No. 7 shown in Table 1 of Example 1, the material of the portion of the flow deflection member 10 on which the carbonaceous material collides (carbonaceous material collision portion 11) was changed, and the frequency of lance replacement when the carbonaceous material was sprayed was investigated. The difference between No. 5 and No. 7 is the eccentric angle η. Because the flow velocity and particle size of the sprayed material have a large effect on wear, when the material of the portion on which the carbonaceous material collides was changed, the same carbonaceous material was sprayed at the same flow velocity.

[0081] 5A and 5B show partial cross-sectional views of the nozzle tip of the drift nozzle 8. Fig. 5A shows the state immediately after the start of use, and Fig. 5B shows the state after some time has passed since use. As shown in Fig. 5A, immediately after the start of use, the carbonaceous material collision portion 11 of the drift member 10 is at a position indicated as carbonaceous material collision portion 11A. As the use of the coal feeding lance 6 progresses, wear of the carbonaceous material collision portion 11 of the drift member 10 progresses, and as shown in Fig. 5B, the carbonaceous material collision portion 11 of the drift member 10 retreats to a position indicated as carbonaceous material collision portion 11B. On the lance center line 12 of the coal feeding lance, the distance between the carbonaceous material collision portion 11A immediately after the start of use and the carbonaceous material collision portion 11B after some time has passed is referred to as a wear allowance 13.

[0082] If wear progresses excessively, the spray angle θ will change and the carbonization rate will also change, so the guideline for lance replacement is set to the timing when the position of the carbonaceous material collision part 11B, which has receded due to wear, has receded by 10 mm or more on the lance center line 12 of the coal supply lance relative to the position of the carbonaceous material collision part 11A at the beginning of use of the drift member 10 (the timing when the wear allowance 13 becomes 10 mm or more).

[0083] The carbonaceous material collision portion 11 of the drift member 10 is made of a base carbon steel, as well as an alloy steel and ceramics with increased Vickers hardness. SKH59 (composition by mass: C: 1.05-1.15, Si: ≦0.70, Mn: ≦0.40, P: ≦0.030, S≦0.030, Cr: 3.5-4.5, Mo: 9.0-10.0, W: 1.2-1.9, V: 0.9-1.3, Co: 7.5-8.5) is used as the alloy steel. Sialon (Si ３ N ４ +Al ２ O ３ , SiO ２ = Si ６－２ Al ２ O ２ N ８－２ The Vickers hardness of each is shown in Table 2.

[0084] The carbonaceous material addition rate was set to 25 kg / min in all cases, and the amount of carbonaceous material added per lance was 700 kg to 1500 kg per ch. The carrier gas flow rate was 250 Nm ３ / hr.

[0085] The lance replacement frequency is shown in Table 2 as a relative value, based on the number of channels until lance replacement in No. 5 when the material of the collision part was carbon steel (5A in Table 2), with the lance replacement frequency at this time set as 1. Note that the eccentric angle changed slightly due to wear until the lance was replaced this time, but no effect on the carburization rate was observed. The results are shown in Table 2.

[0086]

[0087] Under the same eccentric angle of 60° (5A to 5C), when alloy steel with high Vickers hardness was used (5B), the lance replacement frequency improved to 0.2 compared to 5A, which used carbon steel, and when ceramic with even higher Vickers hardness was used (5C), the lance replacement frequency was further reduced to 0.07.

[0088] Under the condition of an eccentric angle of 40° (7A to 7C), compared to 5A, which used carbon steel at an eccentric angle of 60°, the lance replacement frequency when carbon steel was used (7A) was 0.7, when alloy steel was used (7B) it was 0.11, and when ceramics was used (7C) it was 0.04.

[0089] From the above, it can be seen that, regardless of the eccentric angle, it is preferable that the Vickers hardness of the material of the part where the carbonaceous material collides (in the example, the carbonaceous material collision part 11 of the drift member 10) be 500 or more.

[0090] 7A to 7C, carbonaceous material was injected by changing the shape of the injection hole 14 in various ways, and the wear state of the injection hole 14 was compared. The outer diameter (diameter of the outer peripheral part 41) of the outer pipe 15 of the straight pipe part of the coal injection lance 6 was 48 mm, and the inner diameter D ０ The diameter of the inner peripheral portion 42 was 38 mm. ０ is 1133 mm ２ Ceramics was used for the drift member 10, and the angle ψ between the maximum inclination direction 38 of the carbonaceous material collision portion 11 (carbonaceous material collision surface 36) and the lance longitudinal direction 33 was set to 68°. The insertion angle from the slag door (lance angle φ) was 70°, and the spray angle θ was 2°.

[0091] The shape of the spray hole 14 when viewed from the maximum inclination direction 38 was similar to Nos. 1 to 12 in Figure 8. In Figure 8, the common area between the portion surrounded by the outer peripheral contour 43 of the spray hole 14 and the portion surrounded by the inner peripheral contour 44 of the spray hole 14 is indicated by dot hatching. When the carbonaceous material collision surface 36 of the drift member 10 is visible inside the spray hole 14, the carbonaceous material collision surface 36 also constitutes part of the inner peripheral contour 44 of the spray hole. Similarly, for the outer peripheral contour 43 of the spray hole when viewed from the maximum inclination direction 38, the width in the circumferential direction 39 is width W, and the height in the direction perpendicular to the circumferential direction 39 is height H, as shown in Table 3. The numbers in Table 3 correspond to the numbers in Figure 8. The shape of the spray hole 14 shown in Figure 7 is similar to No. 2 in Figure 8.

[0092] The wear index (wear index = width of worn outer pipe / inner diameter of straight pipe section x 100) of the outer pipe 15 of the coal feeding lance 6 when the same amount of carbonaceous material is injected is evaluated. Assuming that the evaluation is performed using the same amount of carbonaceous material used (50 kg / min x 24 min / ch x 10 ch = 12,000 kg), the invention is deemed to be effective if the wear index is less than 10. The results are shown in Table 3.

[0093]

[0094] All of Inventive Examples Nos. 1 to 6 met the preferred conditions of this embodiment, with a wear coefficient of less than 10, effectively preventing wear. Inventive Example No. 5 had a circular spray hole shape, resulting in a higher wear coefficient than the other Inventive Examples (with spray hole shapes other than circular). In addition, Inventive Example No. 6 had a W / H ratio of 4.19, and slight wear marks were observed on the base side of the spray hole.

[0095] On the other hand, in Comparative Examples 7 to 12, the width W of the spray holes was smaller than the inner diameter (38 mm) of the straight pipe portion, and wear was observed when the wear coefficient was 10 or more. ０ It is estimated that the carburization rate is lower than that of Comparative Example No. 10 and the flow rate is lower. ０ It is not considered necessary to make A larger than

[0096] REFERENCE SIGNS LIST 1 electric furnace 2 electrode 3 slag door 4 door lance 5 wall lance 6 coal feeding lance 7 oxygen feeding lance 8 drift nozzle 9 straight nozzle 10 drift member 11 carbonaceous material collision portion 12 lance center line 13 wear margin 14 spray hole 15 outer tube 20 depression 21 molten iron 22 slag 23 discharge flow velocity 24 carbonaceous material 30 lance tip 31 slag surface 32 spray direction 33 lance longitudinal direction 34 vertically downward 35 molten iron-slag interface 36 carbonaceous material collision surface 37 carbonaceous material collision vertical surface 38 maximum inclination direction 39 circumferential direction 40 straight tube portion 41 outer peripheral portion 42 inner peripheral portion 43 outer peripheral portion of spray hole 44 inner peripheral portion of spray hole 45 Wear location

Claims

1. When melting a cold iron source in an electric furnace to produce molten iron, the carbonaceous material is transported into the furnace by a carrier gas through a coal feeding lance. The angle between the blowing direction from the coal feeding lance and the vertical downward direction (blow angle θ) is smaller than the angle between the lance longitudinal direction of the coal feeding lance and the vertical downward direction (lance angle φ), and the slag recess depth L calculated by formula (1) is set to the reference slag thickness L. ０ L / L divided by ０ A method for injecting carbonaceous material into an electric furnace, characterized in that the carbonaceous material is supplied under gas injection conditions such that d.v is 1 or more. ０ ・cos ２ θ = 0.007(ρ ｌ / ρ ｇ ) １／２ (L + h)(L) １／２ (1) d: Lance outlet diameter (mm) v ０ : Carrier gas flow velocity at the tip of the lance (m / s) θ: Spray angle (°) (angle between the spray direction and the vertical downward direction) ρ ｌ : Standard slag density (kg / m ３ ) ρ ｇ : carrier gas density (kg / m ３ ) (standard condition) L: recess depth (mm) L ０ : Reference slag thickness (mm) h: Distance between lance tip and slag surface (mm) Here, the reference slag thickness and reference slag density mean the slag thickness and slag density when the slag is not being formed.

2. The method for injecting carbonaceous material into an electric furnace according to claim 1, characterized in that the carbonaceous material is injected at a blowing angle θ in the range of 10 to 40°.

3. A method for injecting carbonaceous material into an electric furnace as described in claim 1 or claim 2, characterized in that the coal feeding lance makes the spray angle θ different from the lance angle φ by using a deflection member of a deflection nozzle attached to the tip of the lance, and the Vickers hardness of the material of the part of the deflection member with which the carbonaceous material collides is 500 or more.

4. The method of injecting carbonaceous material into an electric furnace as set forth in claim 1 or claim 2, characterized in that the coal delivery lance makes the spray angle θ different from the lance angle φ by a deflection member of a deflection nozzle attached to the tip of the lance, the carbonaceous material collision portion of the deflection member forms a carbonaceous material collision surface, a surface perpendicular to the carbonaceous material collision surface and including the lance center line is defined as the carbonaceous material collision vertical plane, the direction of the line where the carbonaceous material collision surface and the carbonaceous material collision vertical plane intersect toward the tip of the coal delivery lance is defined as the maximum inclination direction, a spray hole is formed at the lance tip of the coal delivery lance in a direction toward the maximum inclination direction, when the spray hole is viewed from the maximum inclination direction, the circumferential width of the spray hole at the outer periphery of the coal delivery lance is equal to or greater than the inner diameter of the coal delivery lance, and when the spray hole is viewed from the maximum inclination direction, the cross-sectional area of ​​the spray hole is equal to or less than the cross-sectional area of ​​the inner periphery of the straight pipe part of the coal delivery lance.

5. A method for injecting carbonaceous material into an electric furnace according to claim 4, characterized in that the Vickers hardness of the material of the portion of the drift member against which the carbonaceous material collides is 500 or more.

6. A method of injecting carbonaceous material into an electric furnace as described in claim 4, characterized in that the shape of the outline of the injection hole on the outer periphery of the coal delivery lance when viewed from the maximum inclination direction is a shape other than a circle or an ellipse.

7. A method of injecting carbonaceous material into an electric furnace as described in claim 4, characterized in that the circumferential width of the injection hole when viewed from the maximum inclination direction is width W, the height perpendicular to the circumferential direction is height H, and W / H is in the range of 1 to 4.

8. A coal feeding lance used when melting a cold iron source in an electric furnace to produce molten iron, for feeding carbonaceous material into the furnace by transporting it with a carrier gas, characterized in that the angle between the blowing direction from the coal feeding lance and the vertical downward direction (blowing angle θ) is smaller than the angle between the longitudinal direction of the lance and the vertical downward direction of the coal feeding lance (lance angle φ).

9. The coal feeding lance according to claim 8, wherein the blowing angle θ is set in the range of 10 to 40° when the coal feeding lance is used to transport the carbonaceous material into the furnace by a carrier gas.

10. A coal delivery lance as described in claim 8 or claim 9, characterized in that the spray angle θ is made different from the lance angle φ by a deflection member of a deflection nozzle attached to the tip of the lance, and the Vickers hardness of the material of the part of the deflection member against which the carbonaceous material collides is 500 or more.

11. The coal delivery lance according to claim 8 or claim 9, characterized in that the coal delivery lance has a blowing angle θ that is different from the lance angle φ by a blowing member of a blowing nozzle attached to the tip of the lance, the carbonaceous material collision portion of the blowing member forms a carbonaceous material collision surface, a surface that is perpendicular to the carbonaceous material collision surface and includes the lance center line is a carbonaceous material collision vertical plane, and the direction of the line where the carbonaceous material collision surface and the carbonaceous material collision vertical plane intersect toward the tip of the coal delivery lance is the maximum inclination direction, and a blowing hole is formed at the lance tip of the coal delivery lance in a direction toward the maximum inclination direction, and when the blowing hole is viewed from the maximum inclination direction, the circumferential width of the blowing hole at the outer periphery of the coal delivery lance is equal to or greater than the inner diameter of the coal delivery lance, and when the blowing hole is viewed from the maximum inclination direction, the cross-sectional area of ​​the blowing hole is equal to or less than the cross-sectional area of ​​the inner periphery of the straight pipe part of the coal delivery lance.

12. A coal feeding lance according to claim 11, wherein the portion of the drift member with which the carbonaceous material collides has a Vickers hardness of 500 or more.

13. A coal feeding lance as described in claim 11, characterized in that the shape of the outline of the spray holes on the outer periphery of the coal feeding lance when viewed from the maximum inclination direction is a shape other than a circle or an ellipse.

14. A coal delivery lance as set forth in claim 11, characterized in that the circumferential width of the spray hole when viewed from the maximum inclination direction is width W, the height in the direction perpendicular to the circumferential direction is height H, and W / H is in the range of 1 to 4.

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