JP5332487B2 - Hot metal desiliconization method - Google Patents

Description

  The present invention relates to a hot metal desiliconization method in which an oxygen-containing gas is blown into a hot metal contained in a kneading wheel via an immersion lance, and more specifically, a double pipe structure having four discharge holes on a lower end side surface. The immersion lance is immersed vertically in the molten iron in the kneading car, and oxygen-containing gas is blown from the inner pipe of the double pipe structure, and at the same time, hydrocarbon gas is blown from the gap between the inner pipe and the outer pipe of the double pipe structure. The present invention relates to a hot metal desiliconization method.

  In recent years, hot metal dephosphorization has been widely performed in converters, hot metal pans, or kneading cars (also called “topy cars”) for the purpose of reducing the phosphorus content accompanying the upgrading of steel materials or rationalizing the steel making process. ing. In this dephosphorization process, silicon in the molten iron is also removed, and this silicon inhibits the dephosphorization reaction. Therefore, in order to efficiently perform the dephosphorization process, the silicon in the molten iron is previously removed before the dephosphorization process. Desiliconization treatment to be removed is also performed.

  Silicon in the hot metal is removed by an oxidation reaction. Accordingly, in the hot metal desiliconization process, an oxygen source such as oxygen gas or iron oxide is supplied to the hot metal, and the silicon in the hot metal is oxidized and removed by this oxygen source. At that time, a flux such as quicklime is also added to increase the reaction efficiency or adjust the composition of the slag to be generated.

  In hot metal desiliconization, the method of supplying oxygen-containing gas such as oxygen gas to hot metal is roughly classified into two types. One method is a method of spraying an oxygen-containing gas toward the hot metal bath surface from a non-contact upper blowing lance or the like (referred to as “top blowing acid method”) (for example, see Patent Document 1). . Another method is a method of directly blowing an oxygen-containing gas into hot metal from a dipping lance for gas blowing immersed in hot metal or from a tuyere provided at the bottom of a reaction vessel (referred to as “blow acid feeding method”). (For example, see Patent Document 2).

  Each method has its own characteristics, and in the case of the blow-in acid method, there are advantages such as high addition efficiency of oxygen-containing gas and improved stirring power, while the heat load of the immersion part of the immersion lance Are large (for example, they are more exhausted than a tuyere subjected to a heat load in only one direction), and have a problem that the number of service life is limited. On the other hand, in the case of the top blowing acid method, there is an advantage that the heat load on the top blowing lance is small and it can be used for a long time, but the addition efficiency of the oxygen-containing gas is low, and the stirring power is low. There are problems such as inability to obtain.

  When supplying the oxygen-containing gas, whether to use the top-blowing acid method or the blow-by acid method is determined in consideration of the above characteristics. For example, as in the case of a kneading car, From the shape, the reaction efficiency is poor in the top blowing acid method, and the blowing acid method may be inevitably adopted. In the case of a kneading vehicle, it is difficult to stir and mix due to the shape of the container, and in addition to that, there are few openings for the amount of hot metal accommodated, and the desired reaction efficiency cannot be obtained by the top blowing acid method.

  As described above, the immersion lance used in the blowing acid feeding method has a severe wear of the immersion part, and means for improving this has been proposed. For example, in Patent Document 3, the immersion lance has a double tube structure, an oxygen-containing gas is blown from the inner tube, and a hydrocarbon-based gas is blown from the gap between the inner tube and the outer tube. A technique for cooling the immersion lance using the endothermic heat generated by the above is disclosed, and an industrially beneficial effect is obtained.

  As another technical problem when oxygen-containing gas is blown into the molten iron in the kneading vehicle, the molten metal is ejected from the opening of the kneading vehicle. In particular, when the immersion lance is immersed perpendicularly to the molten iron from the opening of the kneading wheel, the gas blowing part of the immersion lance and the opening of the kneading wheel are close to each other, so that the molten metal is easily ejected. There's a problem. This hot metal jetting may cause equipment troubles, and in order to prevent hot metal jetting, the immersion depth of the immersion lance cannot be made sufficiently deep and it must be shallow. If the immersion depth is shallow, the contact time between the oxygen-containing gas and the hot metal becomes short, which causes a problem that the reaction efficiency decreases.

In order to solve this problem, Patent Document 4 discloses a technique in which an immersion lance is immersed obliquely in the molten iron in the kneading vehicle and the tip of the lance is immersed in the vicinity of the throttle portion on one side of the kneading vehicle. . By immersing the immersion lance obliquely, the gas blowing portion of the immersion lance and the opening of the kneading wheel are separated from each other, and the hot metal jet is suppressed.
JP-A-53-78913 JP-A-56-169716 JP 58-22212 A JP-A-1-306517

  However, Patent Document 4 has the following problems.

  That is, by immersing the immersion lance diagonally, it is possible to reduce hot metal spout from the kneading wheel opening and to increase the immersion depth of the lance, but the lance body receives the buoyancy of the hot metal. The problem is that the lance is easily damaged and the lance is severely damaged. Therefore, Patent Document 4 is not sufficient from the viewpoint of the life of the immersion lance.

  The present invention has been made in view of the above circumstances. The purpose of the present invention is to improve the durability of the immersion lance when degassing the molten iron by blowing an oxygen-containing gas into the molten iron in the kneading vehicle via the immersion lance. It is an object of the present invention to provide a hot metal desiliconization processing method that is high and has a small amount of molten metal ejected from the kneading wheel opening and can be processed with high reaction efficiency.

  The hot metal desiliconization method according to the first aspect of the present invention for solving the above-mentioned problem is the immersion lance when degassing the hot metal by blowing oxygen-containing gas into the hot metal accommodated in the kneading vehicle via the immersion lance. The four discharge holes having a central axis of symmetric and a central angle formed between adjacent discharge holes and having θ1 and θ2 satisfying “θ1 + θ2 = 180 °” and “20 ° ≦ θ1 ≦ θ2” The immersion lance having a double-tube structure consisting of an inner tube and an outer tube, the center angle θ1 side faces the longitudinal direction of the kneading wheel, and the discharge hole faces the direction intersecting the longitudinal direction of the kneading wheel It is immersed in the hot metal vertically, and oxygen-containing gas is blown from the inner tube, and hydrocarbon gas is blown from the gap between the inner tube and the outer tube, and the hot metal is desiliconized. is there.

  The hot metal desiliconization method according to the second invention is characterized in that, in the first invention, the θ1 is in the range of 20 to 65 °.

  The hot metal desiliconization method according to a third aspect of the present invention is the immersion lance according to the first or second aspect, wherein the central position between the adjacent discharge holes faces the longitudinal direction of the kneading wheel with the central angle as θ1. It is characterized by soaking.

  According to the present invention, since the immersion lance has four discharge holes, the energy of the jet flow from the discharge hole is dispersed in the hot metal bath as compared with the two-hole immersion lance, and accordingly, the kneading wheel is opened. It is possible to suppress the hot metal from being ejected from the portion, and the tip of the immersion lance is cooled by the hydrocarbon-based gas blown from the gap between the inner tube and the outer tube, so that the durability of the immersion lance can be improved.

  Hereinafter, the present invention will be specifically described. The inventors of the present invention have a desiliconization method that has high durability of a dipping lance and that can be desiliconized with high reaction efficiency with less hot metal jetting from the kneading wheel opening even when the immersion depth is increased. For the purpose of development, the water model experiment in the water model device simulating a chaotic vehicle and the desiliconization treatment of the hot metal in the actual chaotic vehicle were carried out under various conditions and investigated and examined.

  As a result, it is confirmed that the slanted immersion lance cannot reduce the stress acting on the immersion lance due to the buoyancy of the hot metal and it is difficult to extend the life of the immersion lance beyond the present. It was. Accordingly, the immersion lance of the type that is immersed vertically is targeted. In the immersion lance of the type that immerses vertically, if the immersion depth is the same, the volume of the immersion part is reduced compared to when immersing obliquely, so the stress acting on the immersion lance is reduced, This is because buoyancy acts in the direction of the center axis of the lance and the influence of buoyancy is reduced by making the stress in the circumferential direction of the immersion lance uniform.

  However, in the type of immersion lance that immerses vertically, as described above, jetting of hot metal from the kneading wheel opening becomes a problem. Therefore, the amount of water scattered from the chaotic car opening was evaluated using a water model device with a water volume of 80 liters that imitates a chaotic car. In the water model test, the test was conducted with two discharge holes and four discharge holes.

  In the case of two discharge holes, the immersion lance was immersed so that the discharge holes arranged on the same straight line on both sides of the immersion lance faced the longitudinal direction of the kneading wheel (level 1). When the number of discharge holes is four, a two-level test is performed. In Level 2, the center angles formed by adjacent discharge holes are θ1 (also referred to as “center angle θ1”) and θ2 (also referred to as “center angle θ2”). , So that θ1 and θ2 are all 90 °, and the immersion lance is immersed so that the center position between adjacent discharge holes faces the longitudinal direction of the kneading wheel. Of the center angles formed, θ1 is 60 °, θ2 is 120 °, and the center angle is θ1 (= 60 °), that is, the center position between adjacent ejection holes, that is, the bisector of the angle of the center angle θ1 The dipping lance was dipped so that the direction of the head was in the longitudinal direction of the kneading wheel.

  In order to make the gas discharge speeds from the discharge holes the same, the total value of the cross-sectional areas of the discharge holes was the same for levels 1 to 3. Table 1 shows the experimental conditions, and FIG. 1 shows the measurement results of the water scattering outflow rate. In the figure shown in the column of “Direction of discharge hole” in Table 1, reference numeral 1 indicates an immersion lance, reference numeral 6 indicates a chaotic wheel, and reference numeral 6a indicates an opening of the chaotic wheel. The water scattering outflow rate was obtained by receiving the mass of the ejected water in a container and weighing the outflow amount of water every time.

  As shown in FIG. 1, it has been found that by setting the number of discharge holes to four, the scattering and outflow speed of water can be reduced and the immersion depth of the immersion lance can be further increased. Further, as in level 3 rather than level 2, it is found that the water scattering outflow speed is further reduced by making the central angle θ1 smaller than 90 ° and bringing the direction of the discharge hole closer to the longitudinal direction of the kneading vehicle. It was.

  Based on the knowledge of this water model experiment, a hot metal desiliconization treatment experiment was conducted using an actual mixed car shown in FIG. FIG. 2 is a view showing a state in which the immersion lance 1 is immersed in the molten iron 7 vertically from the opening 6a of the kneading wheel 6 and desiliconized.

  In the experiment, a four-hole immersion lance 1 shown in FIG. 3 and a two-hole immersion lance 1A shown in FIG. 4 were used, and the immersion lances 1 and 1A were vertically immersed in the hot metal 7 from the opening 6a of the kneading wheel 6. It was. The immersion lance 1 shown in FIG. 3 and the immersion lance 1A shown in FIG. 4 both have a double tube structure including an inner tube 2 and an outer tube 3, and a refractory coating layer 4 is provided on the outer periphery and bottom of the outer tube 3. Although it has been constructed, the number of discharge holes 5 is 4 in the immersion lance 1 and 2 in the immersion lance 1A. 3 is a schematic cross-sectional view of the immersion lance used in the present invention, (A) is a side cross-sectional view, (B) is a cross-sectional view of the discharge hole, and FIG. 4 is a comparison in the present invention. It is a schematic sectional drawing of the immersion lance used for, (A) is side sectional drawing, (B) is a cross-sectional view of a discharge hole part.

  In the immersion lance 1, four discharge holes 5 are installed on two straight lines intersecting with the central axis of the immersion lance 1 with the central angles formed by the adjacent discharge holes 5 being the central angle θ1 and the central angle θ2. On the other hand, in the immersion lance 1A, two discharge holes 5 are provided on one straight line. Here, in order to specify the shape of the immersion lance 1, the central angle θ1 is equal to or less than the central angle θ2. Since the discharge holes 5 are arranged on two intersecting straight lines, the sum of the central angle θ1 and the central angle θ2 is naturally 180 °.

  During the desiliconization process, the immersion lance 1A was immersed in the discharge lance 1A so that the direction of the discharge hole 5 was substantially the same as the longitudinal direction of the kneading wheel 6. In contrast, the immersion lance 1 has a central angle θ1 and the center position between adjacent discharge holes, that is, the direction of the bisector of the central angle θ1 is substantially the same as the longitudinal direction of the kneading wheel 6. 1 is immersed, or the central position between adjacent discharge holes with a central angle of θ2, that is, the direction of the bisector of the central angle θ2 is substantially the same as the longitudinal direction of the kneading wheel 6, Changed.

Then, 15 to ³⁰ Nm ³ / min of oxygen gas is blown from the inner pipe 2, and 1.5 to ³ Nm ³ / min of propane gas is blown from the gap between the inner pipe 2 and the outer pipe 3 to perform desiliconization treatment. went. In the present invention, the reason for using the double-tube structure immersion lance 1 composed of the inner tube 2 and the outer tube 3 is that the hydrocarbon-based gas is blown from the gap between the inner tube 2 and the outer tube 3 to This is because the tip portion of 1 is cooled by the decomposition reaction of the hydrocarbon-based gas, and the melting loss of the tip portion of the immersion lance is suppressed.

  As a result of various experiments, the 4-hole immersion lance 1 was generally capable of increasing the immersion depth as compared with the 2-hole immersion lance 1A, and the desiliconization oxygen efficiency was also good. The silicon removal oxygen efficiency is defined by the following equation (1).

Desiliconization oxygen efficiency (%) = (Before treatment [mass% Si]-After treatment [mass% Si]) x 10 ÷ 28 x 22.4 ÷ Oxygen gas intensity (Nm ³ / t-steel)… (1)
Furthermore, when the immersion lance 1 is immersed so that the central position between adjacent discharge holes with the central angle θ1, that is, the direction of the bisector of the central angle θ1 is substantially the same as the longitudinal direction of the kneading wheel 6. It was found that the central angle θ1 needs to be 20 ° or more. When the central angle θ1 was less than 20 °, the molten metal 7 was ejected in the same manner as in the case of the 2-hole lance, and the immersion depth of the lance could not be increased.

  Further, when the immersion lance 1 is immersed so that the central position between the adjacent discharge holes with the central angle θ 2, that is, the direction of the bisector of the central angle θ 2 is substantially the same as the longitudinal direction of the kneading wheel 6. As the central angle θ2 becomes larger than 90 °, the oxygen gas comes into direct contact with the refractory on the inner wall of the kneading vehicle, and the refractory life of the kneading vehicle 6 tends to decrease. Turned out to be undesirable.

  From these results, it was found that the side where the central angle is θ1 needs to face the longitudinal direction of the chaotic wheel 6. That is, it was found that the direction of the discharge hole 5 needs to intersect the longitudinal direction of the kneading wheel 6. When the discharge hole 5 is directed in the longitudinal direction of the kneading wheel 6, the discharge hole 5 adjacent to the discharge hole 5 faces the inner wall of the kneading wheel, and the refractory life of the kneading wheel 6 is reduced. Further, from the viewpoint of effectively suppressing the ejection of the molten iron 7, the immersion lance 1 is immersed so that the center position between the adjacent discharge holes is substantially the same as the longitudinal direction of the kneading wheel 6 with the central angle θ1. I also found it preferable.

  Furthermore, it has been found that the desiliconization oxygen efficiency is highest when the central angle θ1 is in the range of 20 to 65 °. This is presumed to be because the oxygen gas jet from the discharge hole 5 is along the longitudinal direction of the kneading wheel 6 so that the stirring of the hot metal 7 is improved.

  The present invention has been made based on these test results, and the desiliconization method for the hot metal 7 according to the present invention blows oxygen-containing gas into the hot metal 7 accommodated in the kneading wheel 6 through the immersion lance 1. When the hot metal 7 is desiliconized, the central axis of the immersion lance 1 is symmetric, and the central angles formed by the adjacent discharge holes 5 satisfy “θ1 + θ2 = 180 °” and “20 ° ≦ θ1 ≦ θ2”. A double-pipe structure immersion lance 1 having four discharge holes 5 on the lower end portion thereof, which are θ1 and θ2, and having a central angle θ1 on the side of the kneading wheel 6 in the longitudinal direction. The discharge hole 5 is immersed perpendicularly to the hot metal 7 so as to face the direction intersecting the longitudinal direction of the kneading wheel 6, and oxygen-containing gas is blown from the inner tube 2, and the inner tube 2 and the outer tube 3 Hydrocarbon gas is blown from the gap of the metal and the hot metal 7 is desiliconized. It is characterized by a door.

The refractory material constituting the refractory coating layer 4 of the immersion lance 1 may have any composition as long as it has a certain level of durability against melting damage and spalling. Typical refractories include Al ₂ O ₃ —SiO ₂ amorphous refractories containing 10 to 40% by mass of SiO _2, and Al ₂ O ₃ —MgO amorphous refractories containing 5 to 30% by mass of MgO. Things can be used. The thickness of the refractory coating layer 4 is preferably about 25 mm or more in consideration of the lance life. The inner tube 2 and the outer tube 3 can be stainless steel tubes or carbon steel tubes.

  As the oxygen-containing gas blown from the inner pipe 2, oxygen gas (industrial pure oxygen gas), air, oxygen-enriched air, a mixed gas of inert gas and oxygen gas, or the like can be used. The oxygen concentration of the oxygen-containing gas may be appropriately determined from the required amount of oxygen. Further, when the flow rate of the oxygen gas blown from the inner pipe 2 is reduced, an inert gas such as nitrogen gas or Ar gas may be mixed with the oxygen gas to ensure the blown gas flow rate.

As the hydrocarbon gas, propane (C ₃ H ₈ ), methane (CH ₄ ), ethane (C ₂ H ₆ ), butane (C ₄ H ₁₀ ), etc. are thermally decomposed at a relatively low temperature and have a large decomposition endotherm. Therefore, it is easy to use in the steelmaking process. When the flow rate of the hydrocarbon-based gas from the gap between the inner tube 2 and the outer tube 3 is reduced in accordance with the change in the flow rate of the oxygen-containing gas from the inner tube 2, nitrogen gas, Ar gas, etc. The active gas may be mixed with the hydrocarbon gas.

  As described above, according to the present invention, since the immersion lance 1 has the four discharge holes 5, the energy of the jet flow from the discharge hole 5 is higher in the hot metal bath than the two-hole immersion lance 1A. Accordingly, the spout of the molten iron 7 from the opening 6a of the kneading wheel 6 can be suppressed, and the tip end of the immersion lance 1 is caused by the hydrocarbon gas blown from the gap between the inner pipe 2 and the outer pipe 3. Since it is cooled, the durability of the immersion lance 1 can be improved.

  The above-described 4-hole dipping lance shown in FIG. 3 was immersed vertically in the hot metal contained in the approximately 300-ton capacity kneading wheel, and a desiliconization treatment experiment of the hot metal was performed. The immersion lance was immersed so that the direction of the bisector of the central angle θ1 was in the longitudinal direction of the kneading wheel. In some tests, as a comparative example, the two-hole immersion lance shown in FIG. In the case of a two-hole lance, the immersion lance was immersed so that the direction of the discharge hole was in the longitudinal direction of the kneading wheel.

From the inner tube, 15 to ³⁰ Nm ³ / min of oxygen gas was blown, and from the gap between the inner tube and the outer tube, 5 to 10% by volume of propane gas blown from the inner tube was blown. The immersion depth of the lance was made as deep as possible so long as there was not much hot metal jet from the chaotic car opening. The silicon concentration in the hot metal before the desiliconization treatment and after the desiliconization treatment was analyzed, and the desiliconization oxygen efficiency in each test was determined from this analysis value using the above-described equation (1). Test conditions and test results are shown in Table 2.

  FIG. 5 shows the relationship between the immersion depth of the lance and the desiliconization oxygen efficiency. In Comparative Examples 1 to 6 using a two-hole immersion lance, the hot metal spouts from the kneading wheel opening are intense, and the immersion depth of the lance cannot be increased. As a result, as shown in FIG. The efficiency was low. Further, even in Comparative Examples 7 to 12 in which the central angle θ1 is less than 20 °, the hot metal spray is intense from the kneading wheel opening as in Comparative Examples 1 to 6, and the immersion depth of the lance cannot be increased. The oxygen efficiency was low.

  On the other hand, in the example of the present invention, since there was little jet of hot metal from the kneading wheel opening, the immersion depth could be increased, and the desiliconization oxygen efficiency was stable at a high level. Especially, in the present invention examples 1-11 whose center angle (theta) 1 is 20-65 degrees, it turned out that desiliconization oxygen efficiency becomes high stably.

  In this way, by applying the present invention, the immersion lance is immersed perpendicularly to the molten iron in the kneading vehicle, and in the desiliconization process in which oxygen-containing gas is blown from the immersion lance, the injection of molten metal from the kneading vehicle opening is suppressed. Accordingly, the immersion depth of the lance can be increased, and the desiliconization reaction efficiency can be increased. As a result, it is possible to effectively use the heat generated by the desiliconization reaction and to obtain effects such as reduction in manufacturing cost.

It is a figure which shows the measurement result of the scattering outflow speed | rate in a water model test. It is the schematic which shows the chaotic vehicle to which this invention is applied. It is a schematic sectional drawing of the immersion lance used by this invention. It is the schematic sectional drawing used for the comparison. It is a figure which compares and shows the relationship between the immersion depth of a lance, and desiliconization oxygen efficiency.

Explanation of symbols

1 Immersion lance 2 Inner tube 3 Outer tube 4 Refractory coating layer 5 Discharge hole 6 Chaotic wheel 7 Hot metal

Claims (3)

  When degassing the molten iron by blowing an oxygen-containing gas into the molten iron accommodated in the kneading wheel through the immersion lance, the central axis of the immersion lance is symmetrical and the central angle formed by the adjacent discharge holes is “θ1 + θ2 = 180 ° "and four discharge holes with θ1 and θ2 satisfying" 20 ° ≤ θ1 ≤ θ2 "on the side of the lower end thereof, and a double pipe structure immersion lance consisting of an inner pipe and an outer pipe The angle θ1 side faces the longitudinal direction of the kneading wheel, the discharge hole is immersed perpendicularly to the hot metal so as to face the direction crossing the longitudinal direction of the kneading wheel, and an oxygen-containing gas is blown from the inner tube. A hot metal desiliconization method, wherein a hydrocarbon gas is blown from a gap between the outer pipe and the outer pipe to desiliconize the hot metal.   The hot metal desiliconization method according to claim 1, wherein the θ1 is in a range of 20 to 65 °.   3. The hot metal desiliconization according to claim 1, wherein the immersion lance is immersed so that a center position between adjacent discharge holes faces the longitudinal direction of the kneading wheel with the central angle as θ <b> 1. Processing method.

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