Top-blowing lance for converter and converter refining method

Abstract

To provide a top-blown lance capable of suppressing spitting upon converter refining.SOLUTION: A converter top-blown lance comprises three or more flip flop nozzles. Each flip flop nozzle has a throat part, each throat part has a rectangular opening shape having a short side and a long side, and the centroid of the opening shape of each throat part is present on the circumference of the same circle with a lance center axis as the center.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present application discloses a top blowing lance for a converter and a converter refining method. [Background technology]

[0002] In converter refining, a technique is known in which an oxygen jet is blown from a top blowing lance onto the molten pig iron in the converter to perform blowing. When an oxygen jet is blown onto the molten pig iron, spitting (the scattering of molten pig iron particles from the hot point) becomes a problem. If there is a lot of spitting, there is a risk that ingots will adhere to the throat and cause problems in operation, and there is also a risk that molten pig iron particles will scatter from the throat and reduce yield. On the other hand, if the oxygen flow rate is reduced to suppress spitting, there is a risk that productivity will decrease.

[0003] As a means to solve the above-mentioned spitting problem, it is possible to perform blowing while moving the hot point where the oxygen jet from the top lance hits the molten iron. For example, it is possible to rotate or turn the top lance using a mechanical drive device, or to change the jet direction by changing the oxygen flow rate ratio of the two-way nozzle. However, in order to realize these methods, a major modification of the equipment is required.

[0004] A method for moving the oxygen jet without using a drive device may be to make the jet self-oscillate, for example by using a flip-flop nozzle as disclosed in US Pat. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2005-113200 A Summary of the Invention [Problem to be solved by the invention]

[0006] A multi-hole lance with multiple nozzles is sometimes used as a top blowing lance for converters. With a single-hole lance, the dynamic pressure of the oxygen jet at the hot point is too high, which tends to cause spitting, whereas a multi-hole lance can reduce the dynamic pressure of the oxygen jet.

[0007] Even when a flip-flop nozzle is applied to a converter top blowing lance, it is considered effective to use a multi-hole lance having multiple flip-flop nozzles. However, according to the inventor's new findings, even if multiple flip-flop nozzles are adopted in a converter top blowing lance, spitting during converter refining may not be sufficiently suppressed. For example, depending on the nozzle arrangement, jets may merge or collide with each other, which may intensify spitting. Thus, there is room for improvement in terms of suppressing spitting with respect to how multiple flip-flop nozzles should be arranged in a converter top blowing lance. [Means for solving the problem]

[0008] As one of the means for solving the above problems, the present application provides: A converter top blowing lance having three or more flip-flop nozzles, Each of the flip-flop nozzles has a throat portion; Each of the throat portions has a rectangular opening shape having short sides and long sides, The centroids of the opening shapes of the throat portions are on the circumference of the same circle centered on the lance central axis. Top blowing lance for converter Disclose.

[0009] In the converter top blowing lance of the present disclosure, the short side of each of the throat portions or the long side of each of the throat portions may be perpendicular to a straight line connecting the centroid and the center of the same circle.

[0010] In the converter top blowing lance of the present disclosure, the short side of each of the throat portions may be perpendicular to a straight line connecting the centroid and the center of the same circle.

[0011] In the converter top blowing lance of the present disclosure, the centroids of the throat portions may be arranged at equal intervals from each other on the circumference of the same circle.

[0012] In the converter top blowing lance of the present disclosure, the aspect ratio of the short side to the long side may be 2 or more.

[0013] The converter top blowing lance of the present disclosure may be cylindrical.

[0014] In the converter top blowing lance of the present disclosure, the lower surface of the lance may be flat or may have a shape that is convex downwardly about the central axis of the lance.

[0015] In the top blowing lance for a converter according to the present disclosure, the direction in which the top blown gas is ejected from the flip-flop nozzle may be perpendicular to the lower surface of the lance.

[0016] As one of the means for solving the above problems, the present application provides: The molten iron in the converter is refined while blowing gas from above using the converter top-blowing lance of the present disclosure. Converter refining method Disclose. Effect of the Invention

[0017] When the throat portions of three or more flip-flop nozzles are arranged on the circumference of the same circle centered on the central axis of the lance, as in the converter top blowing lance disclosed herein, spitting during converter refining is easily suppressed. [Brief description of the drawings]

[0018] [Figure 1]1 is an example of the configuration of a flip-flop nozzle in a top blowing lance for a converter, and shows a schematic configuration of a cross section along the longitudinal direction of the lance. [Diagram 2] 1 is a schematic diagram showing an example of the arrangement of flip-flop nozzles in a converter top blowing lance as viewed from below. [Diagram 3] FIG. 3 shows an example of the configuration of a flip-flop nozzle in a simplified manner, and shows a part of the configuration in a cross section taken along the line III-III in FIGS. [Figure 4] 1 is a schematic diagram showing an example of the arrangement of the throat of a flip-flop nozzle when a converter top blowing lance is viewed from below, with the nozzle shape other than the throat being omitted. [Diagram 5] 1 is a schematic diagram showing another example of the arrangement of the throat of a flip-flop nozzle when the converter top blowing lance is viewed from below, with the nozzle shape other than the throat being omitted. [Figure 6] 1 is a schematic diagram showing the arrangement of a throat portion of a flip-flop nozzle in a converter top blowing lance according to a comparative example, with the nozzle shape other than the throat portion not shown. [Figure 7] 1 is a schematic diagram showing the arrangement of a throat portion of a flip-flop nozzle in a converter top blowing lance according to an embodiment of the present invention, with the nozzle shape other than the throat portion not shown. [Figure 8] 1 is a schematic diagram showing the arrangement of a throat portion of a flip-flop nozzle in a converter top blowing lance according to an embodiment of the present invention, with the nozzle shape other than the throat portion not shown. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] 1. Top Blowing Lance for Converter As shown in Figures 1 and 2, a converter top blowing lance 100 includes three or more flip-flop nozzles 10. As shown in Figures 1 and 3, each flip-flop nozzle 10 has a throat portion 10a. As shown in Figure 4, each throat portion 10a has a rectangular opening shape having short sides and long sides, and the centroids of the opening shapes of each throat portion 10a exist on the circumference of the same circle C centered on the lance central axis X.

[0020] 1.1 Flip-flop nozzle As shown in Figs. 1 to 3, the flip-flop nozzle 10 has a throat portion 10a whose opening shape in a cross section perpendicular to the gas flow direction is rectangular. As shown in Figs. 1 and 3, the flip-flop nozzle 10 has vibration side walls 10d downstream of the throat portion 10a and on the two long sides of the throat portion 10a, for utilizing the property of the jet adhering to the side wall (Coanda effect), and an opening 10c is provided on the upstream side of each vibration side wall 10d, and the openings 10c are connected to each other by a connecting pipe 10g, thereby providing a function of making the jet self-excited vibration. That is, after the jet adheres to one of the two vibration side walls 10d by the Coanda effect, the pressure of the opening 10c on the attached side decreases, and a flow is generated in the connecting pipe 10g due to the pressure difference, so that the jet peels off from one vibration side wall 10d and adheres to the other vibration side wall 10d, and this is repeated. That is, as shown by the white arrows in FIGS. 2 and 3, the jet ejected from the flip-flop nozzle 10 undergoes self-excited vibration between the two vibrating side walls 10d, 10d on the longer sides of the throat portion 10a.

[0021] The structure of the flip-flop nozzle itself is known as disclosed in Patent Document 1 and the like. The lance 100 of the present disclosure may also employ a known flip-flop nozzle. For example, the throat portion 10a of each flip-flop nozzle 10 has a rectangular opening shape having short and long sides, which allows the jet to self-oscillate. In particular, when the aspect ratio between the short side and the long side is 2 or more, the jet is easily made to self-oscillate. The upper limit of the aspect ratio is not particularly limited, but may be, for example, 20 or less. In addition, as described above, since the flip-flop nozzle 10 has a connecting pipe 10g for self-oscillation, when three or more flip-flop nozzles 10 are installed in the lance 100, the installation location of the nozzle is naturally restricted due to the balance with the cooling water flow path 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 the installation of the flip-flop nozzles 10 in the lance 100. In this regard, the size of the throat portion 10a may be set to an appropriate size taking into consideration the constraints on installation on the lance 100.

[0022] As shown in Figs. 1 and 3, the flip-flop nozzle 10 may have a throat portion 10a, a terminal portion 10e upstream of the throat portion 10a, and a divergent portion 10b, an opening 10c, and a vibration side wall 10d downstream of the throat portion 10a. The divergent portion 10b may be omitted as appropriate. The reduction rate of the opening area from upstream to downstream in the terminal portion 10e, the length of the terminal portion 10e, the length of the throat portion 10a, the expansion rate of the opening area from upstream to downstream in the divergent portion 10b, the length of the divergent portion 10b, the size of the opening 10c, the expansion rate from upstream to downstream in the vibration side wall 10d, the length of the vibration side wall 10d, and the like are not particularly limited as long as they can function as a flip-flop nozzle 10. As shown in Figs. 1 to 3, only the short side of the opening shape may be expanded from the throat portion 10a toward the vibration side wall 10d. In other words, the aspect ratio of the opening shape of the throat portion 10a may be smaller than the aspect ratio of the opening shape on the downstream side of the throat portion 10a.

[0023] 1.2 Throat arrangement In the lance 100 of the present disclosure, three or more of the above-mentioned flip-flop nozzles 10 are installed. Here, according to the knowledge of the present inventor, the effect of suppressing spitting during converter refining changes significantly depending on how the throat portions 10a of each flip-flop nozzle 10 are arranged. According to the knowledge of the present inventor, when the lance 100 is viewed from below, if the throat portions 10a are arranged on the same circumference, spitting during converter refining can be suppressed more significantly than if the throat portions 10a are arranged in a straight line.

[0024] That is, as shown in FIG. 4, in the lance 100 of the present disclosure, it is important that each throat portion 10a has a rectangular opening shape having short sides and long sides, and that the centroids of the opening shapes of each throat portion exist on the circumference of the same circle C centered on the lance central axis X. In addition, the "centroid" in this application is the centroid of the opening shape of the throat portion 10a in a cross section perpendicular to the gas flow direction. In addition, the "same circle" allows for error. Specifically, when one circle C1 is assumed, a circle C2 concentric with the circle C1 and having a diameter of 95% to 105% of the diameter of the circle C1 as a reference (100%) is also considered to be the same circle as the circle C1. In addition, the circle C2 may have some positional deviation in the vertical direction with respect to the circle C1. In other words, if the positional deviation in the vertical direction is within 10 mm, it is considered to be within the category of the same circle.

[0025] The orientation of the throat portion 10a (the orientation of the short side and the long side) is not particularly limited. According to the knowledge of the present inventor, the spitting suppression effect is likely to be enhanced when the orientation of the throat portion 10a satisfies the following condition. That is, as shown in FIG. 4 or 5, in the lance 100, when the lance 100 is viewed from below, the short side of each throat portion 10a or the long side of each throat portion 10a may be perpendicular to the straight line L connecting the centroid of the opening shape of the throat portion 10a and the center of the same circle C. In other words, each throat portion 10a may be arranged so that the right-angle bisector of the short side or the long side passes through the center of the same circle C. In particular, as shown in FIG. 4, when the short side of each throat portion 10a is perpendicular to the straight line L connecting the centroid and the center of the same circle C (that is, when the right-angle bisector of the short side passes through the center of the same circle C), the spitting suppression effect is further enhanced. In this application, "orthogonal" allows for some margin of error. Specifically, if the angle between two lines (or surfaces) is 90°±2°, the lines (or surfaces) are considered to be "orthogonal" to each other.

[0026] According to the findings of the present inventor, the spitting suppression effect is improved if the intervals between the throat portions 10a are as uniform as possible. That is, as shown in FIG. 4, in the lance 100 of the present disclosure, the centroids of the throat portions 10a may be arranged at equal intervals on the circumference of the same circle C. Specifically, when n flip-flop nozzles 10 are arranged in the lance 100, the centroids of the opening shapes of the throat portions 10a may exist on n straight lines L that divide the circumference of the same circle C into n equal parts. Note that the term "equally spaced" in the present application allows for some error. Specifically, it allows for a positional deviation of 10 mm or less.

[0027] 1.3 Other configurations As described above, the lance 100 of the present disclosure only needs to have the throat portions 10a of the three or more flip-flop nozzles 10 arranged in the positions described above, and the configuration other than that of the flip-flop nozzles 10 may be the same as that of the conventional lance.

[0028] The overall shape of the lance 100 may be, for example, columnar. Specifically, it may be cylindrical, prismatic, or tapered. In particular, when it is cylindrical, it becomes easier to arrange the throat portion 10a of the flip-flop nozzle 10 at the position described above.

[0029] As described above, in the lance 100, the flip-flop nozzles 10 may be arranged so that the connecting pipes 10g of the respective flip-flop nozzles 10 do not interfere with each other. The size of the concentric circle C may be appropriately determined in consideration of the arrangement of the connecting pipes 10g. The size of the concentric circle C may be, for example, 40% or more, 50% or more, or 90% or less, or 80% or less of the diameter of the lance 100 (the diameter of the circle in the case of a cylindrical shape, or the equivalent circle diameter (equivalent area diameter) in the case of a cylindrical shape other than a cylindrical shape such as a prismatic shape).

[0030] The upper limit of the number of flip-flop nozzles 10 provided in the lance 100 may be any number that allows the lance 100 to function as a flip-flop nozzle 10. For example, it may be 8 or less, 7 or less, or 6 or less. If the number of nozzles is too large, the pressure of the top-blown gas is significantly attenuated, and therefore the supply pressure of the top-blown gas needs to be excessively high. Also, as described above, 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 on the lance 100.

[0031] As shown in FIG. 1, the lower surface 20 of the lance 100 may be in a shape that is convex downward on the lance central axis X, or may be flat. In particular, when the lower surface 20 of the lance 100 is in a shape that is convex downward on the lance central axis X (i.e., when the lower surface 20 has a convex portion 20a that is convex downward on the lance central axis X as shown in FIG. 1), the ejection direction of the upward blown gas from the flip-flop nozzle 10 is obliquely outward with respect to the lance central axis X, and the positions of the fire points of the nozzles 10 can be easily moved away from each other. A specific example of a shape that is convex downward on the lance central axis X is a pyramid shape as shown in FIG. 1. In this case, it is preferable to make the central axis of the pyramid coincide with the lance central axis X. For example, when the lance 100 is cylindrical, the lower surface 20 of the lance 100 may be in a cone shape that is convex downward. When the lower surface 20 of the lance 100 is pyramid, its apex angle is not particularly limited. For example, as shown in FIG. 1, in the side shape of the lance, the angle α between the lower surface 20 of the lance 100 and the horizontal plane may be 10° or more, or 15° or more, and may be 30° or less, or 25° or less.

[0032] As shown in Figs. 1 and 3, in converter refining, inside the lance 100, the top-blown gas flows from the gas supply passage 10f to the end portion 10e of the flip-flop nozzle 10. The top-blown gas passes through the throat portion 10a, the divergent portion 10b, the opening 10c, and the vibration side wall 10d, and is ejected from the bottom surface 20 of the lance 100, and collides with the molten iron in the converter, generating a fire point. At this time, the position of the fire point moves over time as the jet ejected from the flip-flop nozzle 10 self-oscillates by the above-mentioned mechanism. Here, the ejection direction of the top-blown gas from the flip-flop nozzle 10 is not particularly limited. In particular, as shown in Fig. 1, when the ejection direction of the top-blown gas from the flip-flop nozzle 10 is perpendicular to the bottom surface 20 of the lance 100, it is easy to control the direction of the jet and the position of the fire point.

[0033] 2. Converter refining method The technology of the present disclosure also has an aspect as a converter refining method. That is, the converter refining method of the present disclosure is characterized in that the molten iron in the converter is refined while blowing gas from the top using the converter top-blowing lance 100 of the present disclosure. Converter refining can be performed in the same manner as in the past, except for using the lance 100 of the present disclosure. The converter may be the same as in the past. In the converter refining method of the present disclosure, the converter may be either a top-blown converter or a top-bottom blown converter. The flow rate and flow velocity of the top-blown gas (oxygen) during converter refining may be such that the jet vibrates self-excitedly in the flip-flop nozzle 10, and may be suitable for refining. As described above, spitting can be suppressed by performing top blowing using the lance 100 of the present disclosure in converter refining. EXAMPLES

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

[0035] 1.Water model experiment First, a water model experiment was conducted to investigate the relationship between the arrangement of multiple flip-flop nozzles in a lance and the occurrence of spitting. In this example, the throats of the flip-flop nozzles were arranged relative to the lance as shown in any one of Figures 6(A) to (C), Figures 7(A) and (B), and Figures 8(A) and (B). That is, the number of flip-flop nozzles was one (single hole), three, or four (multiple holes), and in all cases the opening shape of the throat was a rectangle with an aspect ratio of 4.0, and the total opening area of ​​the throat was 36 mm under all conditions. 2The shape and size of the multiple flip-flop nozzles installed on one lance are the same. The bottom surface of the lance is flat (α=0° in Fig. 1). The shape of the flip-flop nozzle other than the throat portion was manufactured based on the structure of a conventionally known flip-flop nozzle so that the jet would oscillate stably and self-excitedly, and the jet would oscillate self-excitedly in the direction of the short side of the nozzle (the direction indicated by the white arrow in Figs. 2 and 3).

[0036] 40 L of water was charged as simulated molten iron into a converter-type water model vessel with an inner diameter of 650 mm in the furnace belly, and compressed air was blown in at a flow rate of 60 m from 250 mm above the bath surface using a lance with an outer diameter of 100 mm. 3 / h, and the jet was made to self-oscillate at a frequency of 10 Hz or more. Spitting (scattered water droplets) was collected with an absorbent cloth placed at the furnace mouth of the vessel, and the amount of spitting (amount of collected water droplets) per minute was measured. The lance height (distance from the water bath surface to the tip of the lance) and the compressed air flow rate were all constant during the investigation. The spitting amount of the single-hole lance in Comparative Example 1 was used as the standard, and the spitting amounts of the other lances were divided by the spitting amount of the single-hole lance (spitting amount ratio) to obtain the value. The results are shown in Table 1 below.

[0037] [Table 1]

[0038] The lance according to Comparative Example 1 is a single-hole lance as shown in FIG. 6(A), in which one flip-flop nozzle is disposed at the center of the lower surface of the lance.

[0039] The lance according to Comparative Example 2 is a three-hole lance as shown in Fig. 6(B), in which three flip-flop nozzles are arranged in a straight line in the long side direction. In this case, the jets ejected from each nozzle are close to each other, and may gather and condense into the central jet, so the effect of reducing spitting by making the lance multi-hole was small. Specifically, the amount of spitting was reduced by only 30% compared to the case of the single-hole lance of Comparative Example 1.

[0040] The lance according to Comparative Example 3 is a three-hole lance as shown in Fig. 6(C), in which three flip-flop nozzles are arranged in a straight line in the short side direction. In this case, the jets ejected from each nozzle tend to interfere with each other, and the effect of reducing spitting by making the lance multi-hole was small. Specifically, the amount of spitting was reduced by only 20% compared to the case of the single-hole lance of Comparative Example 1.

[0041] The lance according to the first embodiment is a three-hole lance as shown in FIG. 7(A), in which the centroids of the throats of the three flip-flop nozzles are arranged at equal intervals on the same circumference centered on the central axis of the lance. The long sides of the throats are perpendicular to the line connecting the centroids and the center of the same circle (the central axis of the lance) (i.e., the right-angle bisector of the long sides passes through the center of the concentric circle). In this case, the jets ejected from the nozzles tended to gather and slightly condense in the direction of the central axis of the lance, but the multi-hole lance achieved a high spitting reduction effect. Specifically, the amount of spitting was reduced by 50% compared to the case of the single-hole lance of the first comparative example.

[0042] The lance according to the second embodiment is a four-hole lance as shown in FIG. 7(B), in which the centroids of the throats of the four flip-flop nozzles are arranged at equal intervals on the same circumference centered on the central axis of the lance. The long sides of the throats are perpendicular to the line connecting the centroids and the center of the same circle (the central axis of the lance) (i.e., the right-angle bisector of the long sides passes through the center of the concentric circle). In this case, the jets ejected from the nozzles tended to gather and slightly condense in the direction of the central axis of the lance, but the multi-hole lance achieved a high spitting reduction effect. Specifically, the amount of spitting was reduced by 60% compared to the case of the single-hole lance of the first comparative example.

[0043] The lance according to the third embodiment is a three-hole lance as shown in FIG. 8(A), in which the centroids of the throats of the three flip-flop nozzles are arranged at equal intervals on the same circumference centered on the central axis of the lance. The short sides of the throats are perpendicular to the line connecting the centroids and the center of the same circle (the central axis of the lance) (i.e., the right-angle bisector of the short sides passes through the center of the concentric circle). In this case, the jets ejected from each nozzle vibrate independently without condensation, and a high spitting reduction effect was obtained by making the lance porous. Specifically, the amount of spitting was reduced by 70% compared to the case of the single-hole lance of the first comparative example.

[0044] The lance according to the fourth embodiment is a four-hole lance as shown in FIG. 8(B), in which the centroids of the throats of the four flip-flop nozzles are arranged at equal intervals on the same circumference centered on the central axis of the lance. The short sides of the throats are perpendicular to the line connecting the centroids and the center of the same circle (the central axis of the lance) (i.e., the right-angle bisector of the short sides passes through the center of the concentric circle). In this case, the jets ejected from each nozzle vibrate independently without condensation, and a high spitting reduction effect was obtained by making the lance multi-hole. Specifically, the amount of spitting was reduced by 80% compared to the case of a single-hole lance.

[0045] In addition to the water model experiment under the above conditions, water model experiments were also conducted under various conditions. As a result, it was found that, in order to enhance the spitting reduction effect by making the nozzles multi-hole when multiple flip-flop nozzles are arranged on the underside of the lance, it is important that (1) the centroids of each throat are arranged on the circumference of a circle centered on the central axis of the lance. In addition, (2) the spitting reduction effect is further enhanced when each centroid is arranged at equal intervals on the circumference of the same circle, (3) the spitting reduction effect is further enhanced when the short side or long side of each throat is perpendicular to the line connecting the centroid and the center of the same circle (the right angle bisector of the short side or long side passes through the center of the same circle), and (4) in particular, it was found that spitting can be further significantly reduced when the short side of each throat is perpendicular to the line connecting the centroid and the center of the same circle. It should be noted that the more holes there are, the more spitting is reduced, but there is a limit to the increase in the number of holes from the viewpoint of securing a cooling water flow path in the lance and from the viewpoint of preventing the connecting pipes of the flip-flop nozzles from interfering with each other in the lance. Furthermore, if the number of nozzles is too large, the pressure of the top blown gas is significantly attenuated, and therefore the supply pressure of the top blown gas needs to be excessively high.

[0046] 2. Actual machine testing An actual test was carried out using a 2.5t top and bottom blown converter. First, 2.0t of molten iron was charged into the converter. After that, flux such as lump quicklime was added, and then oxygen was blown at a flow rate of 6.0Nm using a top blowing lance. 3 Oxygen was top-blown into the molten iron at a flow rate of 100 / min and a distance of 450 mm from the lance tip to the molten iron bath surface, until the carbon concentration in the molten iron reached 0.1 mass%. The lance height (the distance from the lance tip to the molten iron bath surface) and oxygen flow rate were kept constant for all conditions.

[0047] In this actual machine test, as in the above water model experiment, the throat of the flip-flop nozzle was arranged relative to the lance as shown in any one of Figures 6(A) to (C), Figures 7(A) and (B), and Figures 8(A) and (B). Specifically, the number of nozzles in the flip-flop nozzle was one (single hole), three, or four (multiple holes), and in all cases, the opening shape of the throat was a rectangle with an aspect ratio of 4.0, and the total opening area of ​​the throat was 100 mm under all conditions. 2 In addition, the shape and size of the multiple flip-flop nozzles installed on one lance are the same.

[0048] The lance was cylindrical with a diameter of 150 mm, and all the nozzles installed on the lance were flip-flop nozzles. The underside of the lance was of two types: a flat surface (Comparative Examples 4 to 6, Examples 5, 8, 9, and 12) and a conical surface (Examples 6, 7, 10, and 11). In the flat surface case, the plane coincided with the horizontal plane (angle α=0° in FIG. 1), and in the conical surface case, the central axis of the cone overlapped with the central axis of the lance, and the conical surface was convex vertically downward, with the angle α between the conical surface and the horizontal plane being 10° or 20°.

[0049] The vicinity of the throat during blowing was photographed with a video camera, and images (field of view 400 mm × 400 mm, total number of pixels 400) were extracted from the photographed video every 30 seconds, the number of spitting pixels in the images was counted, and the number of spitting pixels during blowing was integrated to determine the amount of spitting. The amount of spitting of the single-hole lance of Comparative Example 4 (FIG. 6(A)) was used as the standard, and the amounts of spitting of the other lances were divided by the amount of spitting of the single-hole lance (spitting amount ratio) to obtain the values. The results are shown in Tables 2 to 4 below.

[0050] [Table 2]

[0051] [Table 3]

[0052] [Table 4]

[0053] As is clear from the results shown in Tables 2 to 4 above, the actual machine tests also showed the same tendency as the water model tests. That is, the multi-hole lances of Comparative Examples 5 and 6 had a small spitting reduction effect due to being porous, and the amount of spitting was reduced by only 10 to 20% compared to the single-hole lance of Comparative Example 4. On the other hand, the multi-hole lances of Examples 5 to 12 had a large spitting reduction effect due to being porous, and the amount of spitting was reduced by 30 to 80% compared to the single-hole lance of Comparative Example 4.

[0054] As is clear from the results shown in Tables 3 and 4, it was found that spitting could be reduced even more significantly when the short sides of the throats were perpendicular to the line connecting the centroid and the center of the same circle (Examples 9 to 12). It was also found that spitting could be reduced even more significantly by making the shape of the underside of the lance conical, which allows the jet to be ejected obliquely outward from the central axis of the lance and makes it possible to further separate the positions of the fire points of each nozzle from each other. [Explanation of symbols]

[0055] 10 Flip-flop nozzle 10a Throat 10b Suehirobe 10c opening 10d vibration side wall 10e End part 10f Top blowing gas supply passage in lance 10g connecting tube 20 Lance underside 20a Convex part 100 Converter top blowing lance

Claims

1. A converter refining method in which molten iron in a converter is refined while blowing gas from a converter top lance, comprising the steps of: The converter top blowing lance is provided with three or more flip-flop nozzles, Each of the flip-flop nozzles has a throat portion; Each of the throat portions has a rectangular opening shape having short sides and long sides, The centroids of the opening shapes of the throat portions are arranged at equal intervals on the circumference of the same circle centered on the lance central axis, the short side of each of the throat portions is perpendicular to a straight line connecting the centroid and the center of the same circle, The aspect ratio of the short side to the long side is 4.0 or more. Converter refining method.

2. A converter refining method in which molten iron in a converter is refined while blowing gas from a converter top lance, comprising: The converter top blowing lance is provided with three or more flip-flop nozzles, Each of the flip-flop nozzles has a throat portion; Each of the throat portions has a rectangular opening shape having short sides and long sides, The centroids of the opening shapes of the throat portions are arranged at equal intervals on the circumference of the same circle centered on the lance central axis, the long side of each of the throat portions is perpendicular to a straight line connecting the centroid and the center of the same circle, The aspect ratio of the short side to the long side is 4.0 or more. Converter refining method.

3. The lower surface of the lance is flat or has a shape that is convex downward at the central axis of the lance. The converter refining method according to claim 1 or 2.

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