JP6292019B2 - Top blowing lance for molten metal refining - Google Patents

Description

  The present invention relates to an upper blowing lance for molten metal refining used for blowing a refining gas to molten metal in a steelmaking converter, for example.

  In the operation of obtaining molten steel by decarburization treatment in which oxygen is blown from the top blowing lance to the molten iron in a converter type refining vessel, it is required to increase the oxygen flow rate and perform high-speed treatment in order to improve the treatment efficiency.

  However, when the oxygen flow rate is increased, there is a problem that the grain iron scattering (spitting) during blowing is intensified and the iron yield decreases.

  In order to reduce this spitting, it is effective to make porous lances that can disperse energy when the oxygen gas jet collides with the bath surface. In current steelmaking converters, porous lances are used. Is common.

  Perforated lances are nozzles with two or more holes arranged at equal intervals on the same circumference when the lance is viewed from the lance tip surface side. Normally, the extension of each nozzle axis is on the center axis of the lance. It is inclined to meet at one point.

  In the porous lance, the larger the number of nozzles, the greater the effect of dispersing the collision energy of the jet, which is advantageous in reducing spitting. In the current converter, a porous lance having 4 to 6 holes is used. However, if further high-speed blowing is required in the future, it is desired to make the lance more porous.

  However, the increase in the number of nozzles in the porous lance is naturally limited. That is, if the number of nozzles becomes too large, cavities corresponding to the nozzles (recesses in the bath surface due to jet collision) are overlapped, which facilitates spitting.

  On the other hand, Patent Document 1 discloses that the spitting can be reduced by twisting the direction of the nozzle of the upper blow porous lance and making the ejection direction of each nozzle twisted to each other.

JP 2000-001714 A

  However, as a result of using the top blow porous lance described in Patent Document 1, it has been found that the service life (life) of the tip of the lance decreases as the angle of twisting the nozzle increases. Since the melting damage around the nozzle outlet is more severe than that of a normal lance, the service life is shortened and the frequency of lance replacement is increased. Therefore, the cause of this problem was investigated in detail.

  First, after using a top blown porous lance in which the direction of the nozzle was twisted in an upper bottom blown type converter, the trace of the lance being melted was observed in detail. As a result, the bare metal is attached to a part of the periphery of each nozzle outlet, not to the entire circumference of the outlet, but by twisting the nozzle, it is in a jet direction that is different from the normal lance. A relatively large amount of bullion was attached. Since the place where the metal was attached was near the nozzle outlet in the jetting direction of the jet, it is considered that the pressure in that part is lower than in other places.

  Next, the structure of the top blowing porous lance with the nozzle direction twisted was examined in detail.

  In ordinary porous lances, a large amount of metal is not attached in the jet direction of the jet. Therefore, there is a high possibility that the structure of the upper blow porous lance having the nozzle orientation twisted causes melting at the nozzle outlet. In a normal porous lance, each nozzle center axis is not parallel to the lance center axis, and a tilt angle is given to the outside of the lance so that the jets are ejected radially from the nozzles without being combined. ing.

  If the center axis of the nozzle is not parallel to the center axis of the lance and the tip surface of the lance is a plane perpendicular to the center axis of the lance, the nozzle center axis and the tip surface of the lance do not intersect at right angles. It will disappear. If the nozzle center axis and the lance tip surface do not intersect at right angles, it is considered that the characteristics of the jet jetted may be adversely affected.

  By the way, the nozzle of the top blowing lance of the converter is generally a Laval nozzle. The Laval nozzle is a nozzle in which a narrow nozzle and a wide nozzle are connected. In the case of an upper blowing lance of a converter, a throat straight pipe portion is generally provided between them, and the fine nozzle may be omitted. In any case, the supersonic jet is ejected by expanding the choked gas in the throat straight pipe portion having the smallest flow path cross section in the divergent nozzle.

  If the center axis of the Laval nozzle and the tip of the lance do not intersect at a right angle, the divergent nozzle will be cut obliquely at the tip of the lance, and the gas expansion at the divergent part will be non-uniform. It is considered that the flow velocity, pressure, and temperature distribution of the water will be uneven.

  Therefore, in the porous lance 10 shown in FIG. 1, considering that the nozzle central axis 12d has an inclination angle β, the tip surface 12b of the porous lance 10 has a conical surface so as to intersect the nozzle central axis 12e at a right angle. Generally, it is configured. The general porous lance 10 is designed in such a manner that the nozzle central axis 12e and the front end surface 12b of the porous lance 10 intersect at right angles, and the jet flow velocity, pressure, and temperature distribution on the nozzle outlet surface 12d are not uniform. It is often considered not to become.

  However, in the porous lance 20 having the nozzle orientation shown in FIG. 2, even if the tip surface 22b of the porous lance 20 is designed as a conical surface, the nozzle center axis 22e and the tip surface 22b of the porous lance 20 intersect at right angles. It is not possible. In the upper blow porous lance 20 in which the direction of the Laval nozzle 22a is twisted, in order to intersect the nozzle central axis 22e and the tip end surface 22b of the porous lance 20 at a right angle, a plane perpendicular to each nozzle central axis 22e is formed on the porous lance 20. It is necessary to provide the same number of Laval nozzles 22a on the front end surface 22b. However, in such a case, large irregularities are formed on the front end surface 22b, and it is not only difficult to manufacture the porous lance 20, but it is also possible that the bulge easily adheres to the irregularities during use.

  Therefore, with a porous lance twisted in the direction of the Laval nozzle, it is difficult for the central axis of the Laval nozzle and the lance tip surface to intersect at right angles, and if no other measures are taken, the jet flow velocity at the nozzle exit surface・ Non-uniform pressure and temperature distribution will occur.

  From the above, in the porous lance twisted in the direction of the Laval nozzle, the cause of the large melting damage near the outer periphery of the nozzle exit surface in the jetting direction is that the central axis of the Laval nozzle and the tip surface of the lance do not intersect at a right angle. Since no other measures were taken, it was assumed that the jet flow velocity, pressure, and temperature distribution on the nozzle exit surface were uneven. In addition, the flow analysis shows that the jet pressure (total pressure) around the nozzle exit surface is locally low, and the scattered iron particles are easily attracted here, It is thought that the adhesion and melting damage progressed. That is, the jet passing through the region near the outer periphery of the nozzle exit surface in the jet direction of the jet has a stroke that is more easily expanded than the jet passing through other regions, and as a result, the jet pressure is locally low. A region is formed, and it is considered that a relatively large amount of metal was attached to this region and the lance was melted.

  Therefore, an object of the present invention is to provide an upper blowing lance for refining molten metal that suppresses melting damage around the nozzle outlet in an upper blowing porous lance that is inclined and twisted.

  For porous lances with twisted nozzle orientation, the nozzle shaft and lance tip cannot cross at right angles, so other measures are available to suppress non-uniform jet flow velocity, pressure, and temperature distribution at the nozzle outlet. I thought that it was necessary to take. Therefore, the inventors have made improvements on the boundary between the nozzle throat straight pipe part and the divergent part of the Laval nozzle, and investigated whether it is possible to make the gas expansion uniform on the nozzle outlet surface of the divergent nozzle by performing flow analysis. It was.

  As a result, it has been found that nonuniformity in jet flow velocity, pressure, and temperature distribution on the nozzle exit surface can be suppressed by making the following improvements.

(1) A lance inner pipe serving as a flow path for the oxygen-containing gas, a rubber nozzle having three or more holes extending in communication with the flow path at the tip of the lance inner pipe, and the oxygen-containing gas jets out. An upper blowing lance for molten metal refining provided with a nozzle portion having a lance tip surface,
The Laval nozzles having three or more holes have the same shape, and their central axes are arranged at equal intervals on a concentric circle centered on the central axis of the lance.
In each Laval nozzle, in the xyz orthogonal coordinate system in which the lance center axis of the upper blow lance for molten metal refining is set to the z axis and the center position of the outlet surface of the Laval nozzle is set to the y axis, The angle between the projection of the nozzle center axis and the y axis is the twist angle α (deg), and the angle between the straight line parallel to the z axis passing through the center of the outlet surface of the Laval nozzle and the nozzle center axis is the nozzle tilt angle β (deg ), Α satisfies the equation (1), β satisfies the equation (2),
10 <α <70 (1)
15 ≦ β ≦ 30 (2)
The Laval nozzle has a throat straight pipe portion extending in communication with the flow path, and a divergent portion extending in communication with the throat straight pipe portion, and at one end surface of the divergent portion. An exit surface of the certain Laval nozzle is located at the lance tip surface which is a conical surface having a half apex angle γ (deg) with the lance central axis as an axis, and a boundary surface between the throat straight pipe portion and the divergent portion is An upper blow lance for molten metal refining, wherein the conical surface is located on a virtual conical surface translated in the z-axis direction, and the half apex angle γ satisfies the expression (3).

γ = 90−β (3)
In the present invention, the “boundary surface” represents an imaginary surface partitioned by the boundary portion between the throat straight pipe portion and the divergent portion.

  ADVANTAGE OF THE INVENTION According to this invention, the top blowing lance for molten metal refining which suppresses the fusion | melting loss around a nozzle exit can be provided in the top blowing porous lance which inclined the direction of the nozzle and twisted.

FIG. 1 is a schematic view of the tip of a general porous lance, FIG. 1 (a) is a bottom view, FIG. 1 (b) is a cross-sectional view along aa ′ in FIG. 1 (a), FIG.1 (c) is bb 'sectional drawing of Fig.1 (a). 2 is a schematic view of the tip of the porous lance described in Patent Document 1, FIG. 1 (a) is a bottom view, and FIG. 1 (b) is a cross-sectional view along line aa ′ in FIG. 1 (a). 1C is a cross-sectional view taken along the line bb ′ of FIG. 1A, and FIG. 1D is a cross-sectional view taken along the line cc ′ of FIG. FIG. 3 is a schematic view of the tip of the porous lance according to the present invention, FIG. 1 (a) is a bottom view, and FIG. 1 (b) is a cross-sectional view along line aa ′ of FIG. 1 (a). 1C is a cross-sectional view taken along the line bb ′ of FIG. 1A, and FIG. 1D is a cross-sectional view taken along the line cc ′ of FIG. FIG. 4 is a graph showing the change in the standard deviation value of the static pressure at the nozzle outlet surface when the nozzle twist angle α is changed, comparing the porous lance according to the present invention and the porous lance described in Patent Document 1. is there.

  A mode for carrying out the present invention will be described with reference to the drawings. In the following description, the lance according to the present invention will be described by focusing on one of the three or more Laval nozzles. However, the lance according to the present invention has the same shape of the Laval nozzle with the same center around the center axis of the lance. They are arranged at equal intervals on the top. The following explanations apply to all of the same-shaped Laval nozzles.

1. As shown in FIG. 3, the upper blow lance for molten metal refining (hereinafter simply referred to as “lance”) 30 of the present invention has a lance inner pipe 31 and a nozzle portion 32. The lance inner pipe 31 has a flow path 31a for oxygen-containing gas. The nozzle portion 32 has a Laval nozzle 32 a that extends in communication with the flow path 31 a at the tip of the inner lance tube 31 and a tip surface 32 b of the lance 30.

  In the Laval nozzle 32a, the lance center axis 32c is the z-axis as shown in FIGS. 3B and 3C, and the center of the outlet face 32d of the Laval nozzle 32a as shown in FIGS. 3A and 3C. In the xyz orthogonal coordinate system determined so that the position is on the y-axis, as shown in FIG. 3A, the angle formed by the projection of the nozzle center axis 32e on the xy plane with the y-axis is a twist angle α (deg), As shown in FIG. 3D, when an angle formed by a straight line 32f passing through the center of the outlet surface 32d of the Laval nozzle 32a and a straight line 32f parallel to the z axis and the nozzle center axis 32e is defined as a nozzle inclination angle β (deg), α is ( 1) and β satisfy the formula (2).

10 <α <70 (1)
15 ≦ β ≦ 30 (2)
When the twist angle α is 10 ° or less, since α is small, it is difficult to cause melting damage peculiar to the porous lance twisting the nozzle direction, and it is not necessary to apply the present invention. When α is 70 ° or more, as described in Patent Document 1, the effect of reducing spitting by twisting the nozzle direction is lost, so α needs to be less than 70 °. Further, when the inclination angle β is less than 15 °, mutual interference between jets becomes strong, and when β exceeds 30 °, the decarbonation efficiency decreases greatly. Therefore, the present invention provides a lance having β of 15 ° or more and 30 ° or less. Is targeted.

  When the Laval nozzle 32a has a twist angle α and a nozzle inclination angle β, the top lance for molten metal refining according to the present invention is (1) even when the central axis 32e of the Laval nozzle is not perpendicular to the tip surface 32b. When the equation and the equation (2) are satisfied at the same time, by satisfying the equation (3) described later, the adhesion of the metal can be reduced and the lance can be prevented from being damaged.

  The Laval nozzle 32a has a throat straight pipe portion 32g extending in communication with the flow path 31a and a divergent portion 32h extending in communication with the throat straight pipe portion 32g. The throat straight pipe portion 32g is cylindrical. The throat straight pipe portion 32g and the divergent portion 32h share the boundary surface 32i. The divergent portion 32h has a cross-sectional area that increases from the boundary surface 32i to the distal end surface 32d. That is, the divergent portion 32h has a substantially truncated elliptical cone shape whose bottom surface is the exit surface 32d and whose top surface is the boundary surface 32i. The boundary surface 32i is a virtual conical surface surrounded by a boundary portion 32j between the throat straight pipe portion 32g and the divergent portion 32h.

  The tip surface 32b is a conical surface having a half apex angle γ with the lance center axis 32c as an axis, and the outlet surface 32d of the Laval nozzle 32a is located on this conical surface. As described above, the nozzle center axis 32c does not intersect the tip surface 32b perpendicularly. However, the inventors pay attention to the structure of the Laval nozzle 32a, and the cause of the non-uniform jet flow velocity, pressure, and temperature distribution is the boundary surface 32i between the throat straight pipe portion 32g and the divergent portion 32h of the Laval nozzle 32a. Focused on the orientation. The boundary surface 32i is oriented so as to be positioned on the virtual conical surface 32k obtained by translating the tip surface 32b, which is a conical surface, to the lance inner tube 31 side along the z-axis corresponding to the lance center axis 32c. Furthermore, by making the half apex angle γ (deg) of the conical surface satisfy the expression (3) in relation to the nozzle inclination angle β (deg), the flow velocity and pressure of the jet that could not be achieved conventionally.・ It was possible to suppress uneven temperature distribution.

γ = 90−β (3)
As described above, in the porous lance in which the direction of the Laval nozzle is twisted, the shape in which the above guidelines are incorporated into the design is as shown in FIG. 3, the gas expansion at the divergent portion 32h is made uniform, and the jet at the outlet surface 32d Nonuniformity of flow velocity, pressure, and temperature distribution is suppressed.

  In order to prove the effect of the present invention, the present inventors conducted nozzle flow analysis.

As an example of the flow analysis result, FIG. 4 shows the change in the standard deviation value of the static pressure at the nozzle outlet surface when the nozzle twist angle α is changed, and the porous lance according to the present invention and the porous lance described in Patent Document 1. Is shown in comparison. The standard deviation of the static pressure at the nozzle exit surface was determined from the static pressure at about 100 nodes on the analysis grid at the nozzle exit surface. In FIG. 4, the lance according to the present invention has a nozzle throat diameter (boundary surface diameter) of 56 mm, a nozzle outlet cross-sectional area (outlet surface area) of 75 mm, a nozzle inclination angle β of 18 °, and a half-top. The 5-hole lance is obtained when the angle γ is 72 ° and the nozzle twist angle α is changed in the range of 15 ° to 70 °. On the other hand, according to the present invention, except that the porous lance described in Patent Document 1 is conventional and the angle formed by the boundary surface 32i between the throat straight pipe portion and the divergent portion and the Laval nozzle central axis 32e is not 72 ° but 90 °. The same thing as the porous lance concerning is shown. The standard deviation of the static pressure at the nozzle exit surface when the oxygen flow rate is all blown at 60000 Nm ³ / h is shown in comparison with both.

  In the lance manufactured by the conventional design (lance shown in Fig. 2), the non-uniformity of the jet pressure distribution at the nozzle outlet surface increased as the helix angle increased. In the lance (the lance shown in FIG. 3), the non-uniformity of the jet pressure distribution due to an increase in the twist angle was suppressed.

  As a result, in the upper blown porous lance in which the direction of the Laval nozzle is twisted, the melting damage around the nozzle outlet surface is suppressed, and it can be used up to the same life as a lance that does not give a normal twist.

In addition, for the lance designed by the design method of the present invention, an investigation was also conducted regarding the case where α, β, and γ were not applied to the present invention. The lance is a 5-hole lance with the nozzle twisted as in the previous study, the nozzle throat diameter (boundary surface diameter) is 56 mm, and the equivalent circle diameter of the nozzle outlet cross-sectional area (outlet surface area) is 75 mm. Analysis was performed at 60000 Nm ³ / h. Table 1 shows the conditions of α, β, and γ and the standard deviation of the static pressure at the nozzle exit surface.

  Case 1 is within the scope of the present invention, and the standard deviation of the static pressure at the nozzle outlet surface is kept small compared to a lance with a conventional nozzle twisted, as shown in FIG. In case 2, the twist angle α is as large as 80 °, but the standard deviation of the static pressure at the nozzle outlet surface is suppressed to the same extent as in case 1 by adopting the design method of the present invention. However, since α is 70 ° or more, spitting increases as described above. In case 3, the inclination angle β is as large as 35 °, but the standard deviation of the static pressure at the nozzle outlet surface is suppressed to the same extent as in case 1 by adopting the design method of the invention. However, since β is larger than 30, there arises a problem that the decarbonation efficiency is greatly lowered. In cases 4 and 5, since γ does not satisfy the formula (3), the standard deviation of the static pressure at the nozzle outlet surface is higher than that of case 1, and the nonuniformity of the jet pressure distribution at the nozzle outlet surface is not eliminated. It is thought that the nozzle life is shortened.

2. Hot metal refining method The hot metal refining method according to the present invention uses the lance according to the present invention when refining hot metal by spraying an oxygen-containing gas, which is mainly pure oxygen gas, onto the hot metal charged in the converter. In the hot metal refining method according to the present invention, it does not matter whether the hot metal charged into the converter is pretreated. Further, regardless of the component of the hot metal after refining, the refining may be a so-called hot metal preliminary dephosphorization process, or the molten steel may be produced by refining.

  The lance according to the present invention can be produced by reducing the frequency of lance replacement by suppressing melting damage around the nozzle outlet and extending the life of the nozzle, rather than using a lance with a known nozzle twisted under any operating conditions. It can contribute to the improvement of sex.

  The effect of the present invention was verified by the decarburization blow smelting operation of the dephosphorization furnace in the following bottom blowing converter.

In the top-bottom blow converter, the lance life of a normal porous lance without twisting, a conventional porous lance with twisted nozzle orientation, and a porous lance with twisted nozzle orientation of the present invention were compared. Each lance has 6 nozzles, the nozzle throat diameter is 60 mm, the equivalent circle diameter of the nozzle outlet cross-sectional area is 75 mm, the nozzle inclination angle β is 20 deg, and the lance tip surface is a half apex angle γ with the lance center axis as the axis Was a conical surface of 70 deg. The twist angle α of the porous lance twisted in the nozzle direction was 40 deg. Further, in the developed lance, the connecting portion between the throat straight pipe portion and the divergent portion of the Laval nozzle is set to be on a conical surface having a half apex angle γ with the lance central axis as an axis. Moreover, the hot metal amount was about 300 t, and the oxygen flow rate was blown at a maximum of 70000 Nm ³ / h.

  As a result of prior analysis in the flow analysis, the standard deviation of the jet static pressure on the nozzle outlet surface obtained from the static pressure of about 100 nodes on the analysis grid on the nozzle outlet surface is 2700 Pa for the normal porous lance. The porous lance with a twisted nozzle orientation is 4200 Pa, and the newly developed porous lance with a twisted nozzle orientation is 2900 Pa. The newly developed design suppresses the non-uniformity of jet pressure distribution at the nozzle outlet to a normal lance level. I found out.

  As a result of this verification, when the normal porous lance is divided by the number of times of blowing, the life of the normal porous lance is 1.0, whereas the life of the conventional porous lance twisted in the direction of the nozzle is 0. .7, The life of the porous lance twisted in the direction of the nozzle of this development was 1.0, and the life of the porous lance twisted in the direction of the nozzle was made comparable to that of the normal lance by the effect of this development.

Claims (1)

A lance inner pipe serving as a flow path for the oxygen-containing gas, and a lance front end face from which the oxygen-containing gas is ejected, having a laval nozzle having three or more holes extending in communication with the flow path at the tip of the lance inner pipe A top blow lance for molten metal refining comprising a nozzle part having
The Laval nozzles having three or more holes have the same shape, and their central axes are arranged at equal intervals on a concentric circle centered on the central axis of the lance.
In each of the Laval nozzles, in the xyz orthogonal coordinate system in which the lance center axis of the upper blow lance for molten metal refining is set to the z axis and the center position of the outlet surface of the Laval nozzle is set to the y axis, The angle between the projection of the nozzle center axis and the y axis is the twist angle α (deg), and the angle between the straight line parallel to the z axis passing through the center of the outlet surface of the Laval nozzle and the nozzle center axis is the nozzle tilt angle β (deg ), Α satisfies the equation (1), β satisfies the equation (2),
10 <α <70 (1)
15 ≦ β ≦ 30 (2)
The Laval nozzle has a throat straight pipe portion extending in communication with the flow path, and a divergent portion extending in communication with the throat straight pipe portion, and at one end surface of the divergent portion. An exit surface of the certain Laval nozzle is located at the lance tip surface which is a conical surface having a half apex angle γ (deg) with the lance central axis as an axis, and a boundary surface between the throat straight pipe portion and the divergent portion is An upper blow lance for molten metal refining, wherein the conical surface is located on a virtual conical surface translated in the z-axis direction, and the half apex angle γ satisfies the expression (3).
γ = 90−β (3)

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