Top-blowing lance for refining and method for refining molten metal

Abstract

To suppress deceleration of a jet blown out from a top-blowing lance provided with a flip-flop nozzle and to suppress spitting in refining of molten metal.SOLUTION: A flip-flop nozzle provided in the top-blowing lance for refining according to one aspect of the present disclosure has dimensions satisfying the following relationship. Here, L1 is the total length (m) of the connecting pipe, L2 is the short side length (m) of the nozzle throat part, L3 is the diameter (m) of a circle having the same area as the opening area in the cross section of the connecting pipe, and L4 is the long side length (m) of the nozzle throat part.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] This application discloses a top-blowing lance for refining and a method for refining molten metal. [Background technology]

[0002] A known method for refining molten metal involves blowing a jet onto the molten metal from a top lance. When a jet is blown onto the molten metal, spitting (molten metal particles flying away from the hot spot) can be a problem. Excessive spitting can cause ingots to adhere to the furnace throat, disrupting operation, and can also cause molten pig iron particles to fly away from the throat, reducing yield. On the other hand, reducing the jet flow rate to suppress spitting can also reduce productivity.

[0003] In order to reduce the spitting, it is effective to perform the blowing while moving the position of the hot point where the jet from the top lance collides with the molten metal. For example, as in Patent Document 1, it is possible to rotate and turn the top lance using a mechanical drive device, or to change the jet direction by changing the flow rate ratio of the bifurcated nozzle, as in Patent Document 2. However, to achieve these, significant modifications to the equipment are required.

[0004] One method for moving a jet without using a driving device is to make the jet self-oscillate. As a means for making the jet self-oscillate, a flip-flop nozzle such as those disclosed in Patent Documents 3 to 5 can be adopted. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 62-130211 [Patent Document 2] Japanese Patent Application Publication No. 2018-179204 [Patent Document 3] Japanese Patent Publication No. 2022-143086 [Patent Document 4] Japanese Patent Application Laid-Open No. 2005-113200 [Patent Document 5] Japanese Patent Application Publication No. 2019-190695 Summary of the Invention [Problem to be solved by the invention]

[0006] According to the inventor's new findings, when a jet is blown toward molten metal from a top-blowing lance having a flip-flop nozzle, the jet may decelerate, resulting in a soft blow. In the prior art, there is room for improvement in suppressing the deceleration of the jet blown from the top-blowing lance and reducing spitting in the refining of molten metal. [Means for solving the problem]

[0007] The present application discloses the following aspects as means for solving the above problems. <Aspect 1> A top-blowing lance for refining having a flip-flop nozzle, The flip-flop nozzle has the following relationship:

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[0008] When molten metal is refining using the top-blowing refining lance of the present disclosure, deceleration of the jet blown out from the lance is suppressed, and spitting is likely to be suppressed. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram showing an example of the positional relationship between a top-blowing lance, molten metal, and a jet in refining molten metal. [Figure 2] 1 is a schematic plan view showing an example of a flow path shape of a flip-flop nozzle provided in a top-blowing lance for refining. [Figure 3] 1 is a three-dimensional diagram illustrating an example of a flow path shape of a flip-flop nozzle provided in a top-blowing lance for refining. [Figure 4] 3 is a schematic and three-dimensional view showing an example of the flow path shape of a flip-flop nozzle provided in a top-blowing lance for refining, and is an enlarged view of a part of FIG. [Figure 5] 10 is a graph showing the relationship between the value of the dimensional parameter P of the flip-flop nozzle and the average maximum jet flow velocity. [Figure 6] 10 is a graph showing the relationship between the value of a dimensional parameter P of a flip-flop nozzle and the spitting occurrence index. [Figure 7] 10 is a graph showing the relationship between the value of the dimension parameter P of the flip-flop nozzle and the rate of decrease in decarbonation efficiency. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, one embodiment of the top-blowing lance for refining and the method for refining molten metal of the present disclosure will be described with reference to the drawings, but the top-blowing lance for refining and the method for refining molten metal of the present disclosure are not limited to this embodiment.

[0011] 1. Top blowing lance for refining 1 shows a schematic diagram of an example of the positional relationship between a top-blowing lance 100, molten metal 20, and a jet 30 in the refining of molten metal. Also, FIGS. 2 to 4 show a schematic diagram of an example of the flow path shape of a flip-flop nozzle 10 provided in the top-blowing lance 100.

[0012] As shown in FIG. 1 , a top-blowing refining lance 100 equipped with a flip-flop nozzle 10 can blow a jet 30 against the surface 20x of the molten metal 20 while self-oscillating during refining of the molten metal 20. By blowing the jet 30 from the top-blowing refining lance 100 while self-oscillating and moving the position of the hot point where the jet 30 impinges on the surface 20x of the molten metal 20, spitting can be reduced. Meanwhile, according to the findings of the present inventors, the self-oscillation frequency of the jet 30 blown from the flip-flop nozzle 10 varies significantly depending on the dimensions of the flip-flop nozzle 10. If the self-oscillation frequency of the jet 30 becomes excessively high, the jet 30 slows down, resulting in soft blowing, and refining efficiency decreases. Thus, when considering application as a top-blowing refining lance 100, it is important that the self-oscillation frequency of the jet 30 blown from the flip-flop nozzle 10 be within a range that can suppress spitting and prevent soft blowing.

[0013] The present inventors have conducted extensive research into nozzle dimensions that can control the self-excited frequency of the jet 30 blown out from the flip-flop nozzle 10 to a range that can suppress spitting and prevent soft blowing. As a result, it has been found that the flip-flop nozzle 10 provided in the refining top-blowing lance 100 satisfies the following relationship:

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[0014] 1.1 Total length of connecting pipe L1 In the above relationship, L1 is the total length (m) of connecting pipe 11. As shown in Fig. 2, total length L1 of connecting pipe 11 is the length connecting the centers (centroids) of the cross-sectional shape of the flow path of connecting pipe 11 (cross-sectional shape in a direction perpendicular to the flow path), and refers to the length from one opening 11a of connecting pipe 11 through connecting pipe 11 to the other opening 11b. Total length L1 of connecting pipe 11 may be, for example, 0.3 m or more and 30 m or less, or 1.0 m or more and 20 m or less.

[0015] 1.2 Short side length L2 and long side length L4 of the nozzle throat In the above relationship, L2 is the length (m) of the short side of the nozzle throat 12, and L4 is the length (m) of the long side of the nozzle throat 12. As shown in FIGS. 2 to 4, the nozzle throat 12 is the portion of the main flow path of the nozzle where the cross-sectional area of ​​the flow path is smallest. As shown in FIGS. 3 and 4, the nozzle throat 12 has a rectangular opening shape in a cross section perpendicular to the gas flow direction. The nozzle throat 12 has a rectangular opening shape with short and long sides, enabling self-excited vibration of the jet 30. The length L2 of the short side of the nozzle throat 12 may be, for example, 0.001 m or more and 0.20 m or less, or 0.002 m or more and 0.15 m or less. The length L4 of the long side of the nozzle throat 12 may be, for example, 0.01 m or more and 1.0 m or less, or 0.02 m or more and 0.75 m or less. In particular, the jet 30 is likely to self-oscillate when the aspect ratio L4 / L1 between the long side and the short side is equal to or greater than 2. There is no particular upper limit to the aspect ratio, but it may be, for example, 20 or less.

[0016] 1.3 Diameter of the connecting pipe equivalent to the cross-sectional area circle L3 In the above relationship, L3 is the diameter (equivalent area diameter) (m) of a circle having the same area as the opening area in the cross section of the connecting pipe 11. The opening area in the cross section of the connecting pipe 11 refers to the area A (see FIG. 4) of the openings 11a and 11b of the connecting pipe 11. As shown in FIGS. 2 to 4, in the flip-flop nozzle 10, one opening 11a and the other opening 11b of the connecting pipe 11 usually have substantially the same area A. The equivalent area diameter L3 may be, for example, 0.01 m or more and 0.2 m or less, or 0.02 m or more and 0.15 m or less. The shape of the openings 11a and 11b may be any shape that allows the jet 30 to self-oscillate, and may be, for example, rectangular. That is, the openings 11a and 11b may have short sides and long sides. The short side length L of the openings 11a and 11b 3x Alternatively, the short side length L of the openings 11a and 11b may be, for example, 0.004 m or more and 0.8 m or less, or 0.008 m or more and 0.6 m or less. 3xThe length L of the long side of the openings 11a and 11b may be two to eight times, or three to five times, the length L2 of the short side of the nozzle throat portion 12. 3y Alternatively, the long side length L of the openings 11a and 11b may be, for example, 0.013 m or more and 2.6 m or less, or 0.026 m or more and 1.95 m or less. 3y The aspect ratio L of the openings 11a and 11b may be 2 times or more and 20 times or less, or 8 times or more and 16 times or less, of the short side length L2 of the nozzle throat portion 12. 3y / L 3x may be, for example, 1 or more and 10 or less, or 3 or more and 5 or less.

[0017] 1.4 Other Configurations 2 to 4, the flip-flop nozzle 10 has vibration side walls 13a, 13b downstream of the nozzle throat 12 and on the two long sides of the nozzle throat 12 to utilize the property of the jet 30 adhering to the side walls (the Coanda effect), and openings 11a, 11b are provided upstream of the vibration side walls 13a, 13b, respectively, and the openings 11a, 11b are connected to each other via the connecting pipe 11, thereby providing the function of causing the jet 30 to self-oscillate. That is, after the jet 30 adheres to one of the vibration side walls 13a due to the Coanda effect, the pressure at the opening 11a on the adhered side decreases, and a flow is generated in the connecting pipe 11 due to the pressure difference, causing the jet 30 to peel off from one of the vibration side walls 13a and adhere to the other vibration side wall 13b, repeating this process. That is, as shown by the white arrow in FIG. 2, the jet 30 ejected from the flip-flop nozzle 10 vibrates self-excited between the two vibrating side walls 13a, 13b on the long side of the nozzle throat portion 12.

[0018] 2 to 4, the flip-flop nozzle 10 may have, in addition to the nozzle throat 12, a terminal portion 14 upstream of the nozzle throat 12, and may have the above-mentioned openings 11a, 11b and vibration side walls 13a, 13b downstream of the nozzle throat 12. The reduction rate of the opening area from upstream to downstream in the terminal portion 14, the flow path length L5, the length L6 of the nozzle throat 12 from upstream to downstream, and the expansion rate and length L7 of the vibration side walls 13a, 13b from upstream to downstream are not particularly limited as long as they can function as a flip-flop nozzle 10. For example, the flow path length L5 of the terminal portion 14 may be 10 mm or more and 1000 mm or less, or 50 mm or more and 500 mm or less, and may be 2 times or more and 100 times or less, or 5 times or more and 50 times or less, of the short side length L2 of the nozzle throat 12. Furthermore, the length L6 of the nozzle throat 12 from upstream to downstream may be 1 mm to 300 mm, or 10 mm to 200 mm, and may be 2 to 30 times, or 5 to 20 times the short-side length L2 of the nozzle throat 12. Furthermore, the length L7 of the vibration side walls 13a, 13b from upstream to downstream may be 4 mm to 800 mm, or 8 mm to 600 mm, and may be 2 to 8 times, or 3 to 6 times the short-side length L2 of the nozzle throat 12.

[0019] 4, the flip-flop nozzle 10 may have a length L8 between the openings 11a, 11b of the connecting pipe 11 and the outlet of the nozzle throat 12. The length L8 may be 0.8 to 3 times, or 1 to 2 times, the length L2 of the short side of the nozzle throat 12.

[0020] As shown in FIGS. 2 to 4, the flip-flop nozzle 10 has a gas outlet 15 at its most downstream side. The opening shape of the gas outlet 15 is, for example, rectangular. That is, the opening shape of the gas outlet 15 may have a short side and a long side. The short side length L9 of the gas outlet 15 may be, for example, 0.004 m or more and 0.80 m or less, or 0.008 m or more and 0.60 m or less. Alternatively, the short side length L9 of the gas outlet 15 may be 2 times or more and 10 times or less, or 3 times or more and 6 times or less, the short side length L2 of the nozzle throat portion 12. The long side length L of the gas outlet 15 10 Alternatively, the long side length L of the gas outlet may be, for example, 0.013 m or more and 2.6 m or less, or 0.026 m or more and 1.95 m or less. 10 The aspect ratio L of the gas outlet 15 may be 2 to 8 times, or 3 to 5 times, the short side length L2 of the nozzle throat portion 12. 10 / L9 may be, for example, 2 or more and 8 or less, or 3 or more and 6 or less.

[0021] When multiple flip-flop nozzles 10 are installed on one refining top-blowing lance 100, the installation locations of the nozzles 10 are naturally restricted due to consideration of the cooling water flow paths and the like in the lance 100. For example, it is impossible to install too many nozzles 10 or to install too large nozzles 10 due to the restrictions on installation of the flip-flop nozzles 10 on the lance 100. In this regard, the shapes and sizes of the connecting pipe 11 and the nozzle throat portion 12 may be set to appropriate sizes so that the above-mentioned dimensional relationships are satisfied, taking into account the restrictions on installation on the lance 100.

[0022] The upper limit of the number of flip-flop nozzles 10 that can be provided in the refining top-blowing lance 100 may be any number that allows the refining top-blowing lance 100 to function as a flip-flop nozzle 10. If there are too many flip-flop nozzles 10, the pressure of the top-blowing gas will be attenuated significantly, and therefore the supply pressure of the top-blowing gas must be made excessively high. Furthermore, due to installation constraints on the lance 100, there is naturally an upper limit to the number of flip-flop nozzles 10 that can be installed in the lance 100. The number of flip-flop nozzles 10 that can be provided in the lance 100 is 1 or more, and may be 2 or more, or 3 or more, or may be 8 or less, 7 or less, or 6 or less.

[0023] The refining top-blowing lance 100 may have the same configuration as a conventional one except for the flip-flop nozzle 10. For example, the overall shape of the lance 100 may be columnar. Specifically, it may be cylindrical, rectangular, or tapered.

[0024] The lower surface of the refining top-blowing lance 100 may have a shape that is convex downward along the central axis of the lance, or may be flat. A specific example of a shape that is convex downward along the central axis of the lance is a cone shape. In this case, the central axis of the cone may coincide with the central axis of the lance. For example, when the lance 100 is cylindrical, the lower surface of the lance 100 may have a cone shape that is convex downward. When the lower surface of the lance 100 is cone-shaped, its apex angle is not particularly limited.

[0025] 2.Method of refining molten metal The technology of the present disclosure also has an aspect as a method for refining molten metal. The method for refining molten metal according to one embodiment includes upward blowing a jet 30 from a refining top lance 100 having a flip-flop nozzle 10 toward a surface 20x of molten metal 20.

[0026] 2.1 Molten metal The type of molten metal 20 to be refined is not particularly limited. The molten metal 20 may be, for example, molten iron, or a molten metal other than molten iron. For example, when the molten metal 20 is molten iron and the jet 30 is an oxygen jet, the refining method according to this embodiment can decarburize the molten iron. The molten iron may be, for example, molten pig iron such as blast furnace molten pig iron, or may be made from other iron sources such as scrap or reduced iron, or may contain these molten pig iron or iron sources. During refining of the molten metal 20, slag or the like may be present on the surface 20x of the molten metal 20.

[0027] 2.2 Jet In the refining method according to this embodiment, a jet 30 is blown upward toward the surface of the molten metal 20. As shown in FIG. 2, in the refining of molten metal, for example, inside a top-blowing lance 100 for refining, top-blown gas flows from a gas supply passage 16 into the distal portion 14 of the flip-flop nozzle 10. The top-blown gas passes through the throat portion 12, openings 11a and 11b, and vibration side walls 13a and 13b, and is ejected as a jet 30 from the nozzle outlet of the lance 100. The jet 30 impinges on the surface 20x of the molten metal 20 in the furnace, generating a hot spot. At this time, the jet 30 blown from the flip-flop nozzle 10 self-oscillates according to the above-described mechanism, causing the position of the hot spot to move over time. The direction in which the jet 30 is ejected from the flip-flop nozzle 10 is not particularly limited.

[0028] In the refining method according to this embodiment, the type of jet 30 is not particularly limited. The jet 30 may be, for example, an oxygen jet or a jet other than an oxygen jet. An oxygen jet refers to a jet containing oxygen.

[0029] In the refining method according to this embodiment, other conditions such as the flow velocity of the jet 30 may be the same as those employed in conventional refining of molten metal. The flow rate and flow velocity of the jet 30 may be such that the jet 30 self-oscillates in the flip-flop nozzle 10 and are suitable for refining. Typically, the flow velocity of the top-blown gas reaches the sonic velocity in the nozzle throat 12 of the flip-flop nozzle 10.

[0030] 2.3 Other In the refining method according to this embodiment, the positional relationship between the refining top-blowing lance 100 and the surface 20x of the molten metal 20 is not particularly limited as long as refining can be performed appropriately. The height from the surface 20x of the molten metal 20 to the nozzle outlet of the refining top-blowing lance 100 (the outlet of the flip-flop nozzle 10) may be the same as the height typically employed in refining molten metal. For example, the height from the surface 20x of the molten metal 20 to the nozzle outlet of the refining top-blowing lance 100 may be 200 mm or more and 5000 mm or less. The lower limit may be 250 mm or more, and the upper limit may be 4000 mm or less, 3000 mm or less, 2000 mm or less, 1000 mm or less, 750 mm or less, 500 mm or less, 400 mm or less, or 350 mm or less.

[0031] The type of refining furnace employed in the refining method according to this embodiment is not particularly limited. An appropriate refining furnace may be selected depending on the type and amount of molten metal 20 to be produced. The refining furnace may be, for example, a converter, an electric furnace, or any other furnace. The converter may be either a top-blown converter or a top-bottom-blown converter.

[0032] 3. Actions and Effects When refining molten metal such as blast furnace hot metal using a refining furnace such as a top-and-bottom blowing converter, it is effective to perform high-speed blowing by increasing the supply of a jet blown onto the molten metal from a top-blowing lance in order to refine the molten metal in a short time. Here, a challenge in high-speed blowing is to suppress spitting, which is a phenomenon in which molten metal particles are scattered when the jet is sprayed onto the molten metal. High-speed blowing intensifies spitting, causing metal to adhere to the throat, hindering operation, and scattering molten metal particles from the throat, reducing yield. On the other hand, reducing the jet flow rate to suppress spitting results in reduced refining efficiency and reduced productivity.

[0033] In contrast, as in the technology disclosed herein, spitting can be reduced by self-oscillating the top-blowing jet and moving the position of the hot spot while performing the blowing. Furthermore, in the top-blowing lance for refining disclosed herein, the flip-flop nozzle has dimensions that satisfy a predetermined relationship, which makes it easier to control the self-oscillation frequency of the jet within a predetermined range, suppressing jet deceleration (soft blowing), and improving refining efficiency. The technology disclosed herein also eliminates the need for a mechanical drive device to move the jet. [Example]

[0034] The effects of the technology of the present disclosure will be described in more detail below with reference to examples, but the technology of the present disclosure is not limited to the following examples.

[0035] 1. Relationship between nozzle dimensions and jet flow velocity We confirmed the relationship between the dimensions of the flip-flop nozzle provided in the top-blowing lance and the flow velocity of the self-oscillated jet. After extensive investigation, we found that the dimensions of the flip-flop nozzle and the self-oscillation frequency of the jet can be organized using the dimension parameter P shown below. In other words, the dimension parameter P is a parameter that has a high correlation with the self-oscillation frequency of the jet. For example, the self-oscillation frequency of a jet blown out from a flip-flop nozzle with a dimension parameter P value of 100 is approximately 100 Hz. Note that when the dimension parameter below is 100, it can be said that the self-oscillation frequency of the jet is approximately 100 Hz, but the converse is not necessarily true.

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[0036] Oxygen was flowed through a single-hole lance with a flip-flop nozzle at the tip, and the jet flow velocity was measured with a hot-wire anemometer. In order to prevent scattered iron particles from entering the nozzle, lances in refining equipment such as converters are generally operated under supersonic conditions where the gas chokes at the throat, and this study also conducted experiments under supersonic conditions.

[0037] The cross-sectional shape of the throat of the flip-flop nozzle used in this example was a rectangle with a long side of 36 mm and a short side of 2.7 mm. Other configurations were based on previously published literature on flip-flop nozzles, and were designed to achieve a supersonic jet velocity that choked at the throat. The connecting pipe shape was adjusted to change the dimensional parameter P. Specifically, the lengths of the connecting pipes of the flip-flop nozzles were 14.2 m for single-hole lance B, 4.0 m for single-hole lance C, 1.5 m for single-hole lance D, 0.58 m for single-hole lance E, 0.33 m for single-hole lance F, and 0.22 m for single-hole lance G. The inner diameters of the connecting pipes (equivalent diameters of the circular area of ​​the opening) were all 32 mm.

[0038] For comparison, the jet flow velocity was also measured for a single-hole lance A having a rectangular nozzle with the same nozzle throat cross-sectional area as the flip-flop nozzle. In other words, the jet ejected from the single-hole lance A does not undergo self-excited vibration. Note that for the single-hole lance A, a connecting pipe cannot be defined, and the above-mentioned dimension parameter P cannot be calculated.

[0039] Table 1 below shows the dimensions of each single-hole lance and the calculation results of the dimension parameter P. [Table 1]

[0040] In the following experiments, the lance front pressure was set to 0.1 MPa or more in gauge pressure so that the jet would reach supersonic speed at the throat. With the above throat shape, the lance front pressure was set to 0.1 MPa or more, and the oxygen flow rate was set to 3.0 Nm 3 Measurements were performed at 1000 kJ / min.

[0041] The flow velocity of the jet ejected from the lance was measured using a hot-wire anemometer. The hot-wire anemometer was installed downstream of the jet on the central axis of the nozzle, 300 mm from the nozzle outlet, in a plane perpendicular to the central axis of the lance, at 10 mm intervals within the range through which the jet passed. The maximum flow velocity of the jet without self-excited vibration (in the case of single-hole lance A) and the maximum flow velocity of the jet whose position was constantly moving due to self-excited vibration (in the case of single-hole lances B to G) were measured, and the time average values ​​were calculated.

[0042] Figure 5 shows the relationship between the average maximum velocity of the jets blown from each of the single-hole lances B to G and the value of the dimension parameter P. The dashed line in Figure 5 also indicates the average maximum velocity of the jet blown from the single-hole lance A. As shown in Figure 5, when the self-oscillating single-hole lances B to G are used, the average maximum velocity of the jets is almost the same as or lower than when the single-hole lance A, which does not self-oscillate, is used. Specifically, when the dimension parameter P is 100 or less, the average maximum velocity is almost the same as when the self-oscillation is not occurring. However, when the dimension parameter P exceeds 100, the average maximum velocity is significantly lower. It is believed that when the dimension parameter exceeds 100, the self-oscillation frequency becomes excessively high, causing the jet to move faster in the vibration direction, weakening the jet's momentum and reducing the flow velocity. From these results, it is considered effective to set the dimension parameter P to 100 or less to prevent the jet from soft-blowing.

[0043] 2. Actual machine testing Below, an example using a 2.5t top and bottom blown converter is shown.

[0044] 2.1 Blowing conditions 2.0 t of molten pig iron was charged into a 2.5 t top-bottom blown converter. After adding flux such as lump quicklime to the molten pig iron, it was blown using a top lance until the carbon concentration reached 0.1 mass%. The height of the top lance during blowing (height from the surface of the molten pig iron to the nozzle outlet of the lance) was 300 mm, and the oxygen flow rate was 3.0 Nm 3The top blowing lances used were the same single-hole lances A to G as those used in the flow rate measurement described above. The lance height and oxygen flow rate were kept constant throughout the investigation.

[0045] 2.2 Spitting evaluation criteria The area around the throat during blowing was filmed with a video camera, and images were extracted from the filmed video every 30 seconds. The number of spitting pixels in the images was counted and the number of spitting pixels during blowing was integrated. The amount of spitting when single-hole lances B to G were used was divided by the amount of spitting when single-hole lance A was used to calculate the spitting occurrence index (%). The results are shown in Figure 6.

[0046] 2.3 Evaluation of decarboxylation efficiency The decarbonation efficiency is the efficiency with which the top-blown oxygen reacts with carbon in the molten iron, and the oxygen that does not react with carbon in the molten iron is used for secondary combustion, etc. In this example, the decarbonation efficiency when single-hole lance A was used was used as the standard, and the extent to which the decarbonation efficiency decreased when single-hole lances B to G were used (decarbonation efficiency decrease rate) was evaluated as an index. Specifically, in the high carbon concentration range of the molten iron, where the carbon concentration in the molten iron was 1.0 mass% or higher, the molten iron was sampled twice using a sublance, and the decarbonation efficiency was calculated from the decrease in the carbon concentration in the molten iron obtained by analysis and the amount of top-blown oxygen during that period, and evaluated as an index as described above. The results are shown in Figure 7.

[0047] 2.4 Evaluation results As shown in Figures 6 and 7, when single-hole lances E to G with flip-flop nozzles were used, spitting was reduced by more than 60% compared to when non-oscillating single-hole lance A was used. However, the self-excited vibration frequency was too high, causing the jet to soften, resulting in a decrease in decarbonation efficiency of more than 5%. In contrast, when single-hole lances B to D were used, spitting was reduced by more than 40% compared to when non-oscillating single-hole lance A was used, and jet deceleration was suppressed, preventing a significant decrease in decarbonation efficiency. From these results, it is considered effective to set the dimension parameter P between 20 and 100 inclusive in order to reduce spitting and avoid soft-blowing of the jet.

[0048] 3. Supplementary Information In the above example, a single-hole lance is used as the top-blowing lance, but the number of nozzles in the top-blowing lance is not limited to 1. Even when the top-blowing lance is a multi-hole lance, it is believed that the same effect as above can be achieved by setting the dimensional parameter P of at least one nozzle to 20 or more and 100 or less.

[0049] In the above embodiment, the decarburization refining of molten pig iron is performed in a top-and-bottom blown converter, but the type of furnace, the type of molten metal, and the type of refining are not limited to this. The technology of the present disclosure can be applied to various refining processes in which a jet is blown from above toward the surface of molten metal.

[0050] 4. Summary From the above results, it can be said that by refining molten metal using a top-blowing refining lance that satisfies the following requirements (1) and (2), it is possible to suppress the deceleration of the jet blown from the lance and reduce spitting. (1) The refining top lance is equipped with a flip-flop nozzle. (2) The flip-flop nozzle has the following relationship:

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[0051] 100 Top blowing lance for refining 10 Flip-Flop Nozzle 11 Connecting pipe 11a, 11b opening 12 Nozzle throat 13a, 13b Vibration side wall 14 End Section 15 Gas outlet 16 Gas supply line 20 Molten Metal 20x hot water surface 30 Jet

Claims

1. A top-blowing lance for refining having a flip-flop nozzle, The flip-flop nozzle has the following relationship: [Equation 1] L １ : Total length of connecting pipe (m) L ２ : Short side length of nozzle throat (m) L ３ : Diameter of a circle having the same area as the opening area of ​​the cross section of the connecting pipe (m) L ４ : Long side length of nozzle throat (m) and having dimensions that satisfy Top blowing lance for refining.

2. A method for refining molten metal, comprising: A jet is blown upward from the refining top-blowing lance according to claim 1 toward the surface of the molten metal; A method for refining molten metal, comprising:

3. 3. The method for refining molten metal according to claim 2, The height from the surface of the molten metal to the nozzle outlet of the refining top lance is 200 mm or more and 5000 mm or less. A method for refining molten metal.

4. The method for refining molten metal according to claim 2 or 3, the molten metal is molten iron, The jet is an oxygen jet. A method for refining molten metal.

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