JP5223228B2 - Hot metal desiliconization method - Google Patents

Description

  The present invention relates to a hot metal desiliconization method in which gaseous oxygen is blown into a hot metal via an immersion lance, and more specifically, two discharge holes are formed in an inverted T shape on the lower end side surface of the double tube structure immersion lance. The present invention relates to a desiliconization method capable of extending the life of an immersion lance by providing a branch, immersing the lance perpendicularly to the hot metal, and satisfying a predetermined blowing condition for desiliconization.

  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. Moreover, in order to perform this dephosphorization process efficiently, the desiliconization process which removes the silicon in a hot metal beforehand is also performed before the dephosphorization process. Since phosphorus and silicon in the hot metal are removed by an oxidation reaction, the dephosphorization process and desiliconization process of the hot metal supply an oxygen source such as gaseous oxygen or iron oxide to the hot metal, and the phosphorus or silicon in the hot metal is supplied by the oxygen source. Is removed by oxidation. 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.

  Methods for supplying gaseous oxygen to hot metal in hot metal dephosphorization and desiliconization are roughly classified into two types. One method is a method in which gaseous oxygen is sprayed toward the hot metal bath surface from a non-contact upper blowing lance or the like (referred to as “upper blowing acid feeding method”) (see, for example, Patent Document 1). Another method is a method in which gaseous oxygen is directly blown into the hot metal from a soaking lance for gas blowing immersed in the hot metal or a tuyere provided at the bottom of the reaction vessel (referred to as “blow acid feeding method”). Yes (see, for example, Patent Document 2). Each method has its own characteristics, and in the case of the blowing acid method, there are advantages such as high addition efficiency of gaseous oxygen and improved stirring power, while the heat load of the immersion part of the immersion lance is There is a problem that it is large (for example, consumption is severe compared to tuyere that receives a heat load in only one direction) and 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 period of time, but the addition efficiency of gaseous oxygen is low and the stirring power is obtained. There are problems such as inability.

  When supplying gaseous oxygen, whether to use the top blowing method or the blowing method is determined in consideration of the above-mentioned characteristics. For example, as in the case of a kneading vehicle, the shape of the processing vessel Therefore, the top blowing acid method has poor reaction efficiency, and the blowing acid method may have to be 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, in a dipping lance composed of a tip part immersed in molten metal and a holder part holding the tip part, the tip part has a single tube structure, and the entire surface thereof is calorized. Furthermore, a technique is disclosed in which the outer periphery of the immersion lance is covered with a refractory to prevent the tip of the immersion lance from being melted.

Further, Patent Document 4 discloses a tube shaft so that a gap between an inner tube and an outer tube of a double tube structure immersion lance is divided into at least two cooling gas flow paths in a cross section intersecting with the longitudinal direction of the tube shaft. A technique is disclosed in which a partition member along the longitudinal direction is provided, the lance is inclined and immersed in the hot metal, and gaseous oxygen and refining flux are blown from the inner pipe and cooling gas is blown from the outer pipe. In this technique, hydrocarbon-based gas decomposes when heated, and absorbs heat when it is decomposed. By using this heat absorption, the tip of the immersion lance is cooled, and a partition member is provided to prevent melting damage. This technique promotes the cooling of the upper surface side of the inclined dip lance that is significantly inclined.
JP-A-53-78913 JP-A-56-169716 Japanese Utility Model Publication No. 6-6447 JP-A-11-246902

  However, the above Patent Document 3 and Patent Document 4 have the following problems. That is, in blowing gaseous oxygen together with the refining agent into the molten metal, as in Patent Document 3, in the technique of covering the periphery with a refractory as a calorized pipe, iron oxide is used as the oxygen source to be supplied. The upper limit of the ratio of gaseous oxygen to the ratio of gaseous oxygen, that is, the ratio of gaseous oxygen supply to the total oxygen supply (iron oxide (converted to gaseous oxygen) + gaseous oxygen) is 20 to 30%. This is because when the ratio of gaseous oxygen is increased, heat generation is intense and the single tube structure cannot withstand. In order to effectively use the heat generated by the oxidation reaction, the gas oxygen ratio is preferably 100%, but this technique does not have sufficient durability against blowing of gaseous oxygen alone.

  Further, in the method disclosed in Patent Document 4, the tip of the immersion lance is cooled by the decomposition endotherm of the hydrocarbon-based gas, and further, the partition member can promote the cooling of the upper surface side of the immersion lance that is significantly melted, When the flow rate of the blown gas increases, loads such as gas reaction force and buoyancy from the hot metal act on the immersion lance, which increases the lance vibration during processing and causes the refractory coating layer on the outer shell of the immersion lance to increase. There is a problem that physical cracking / peeling damage (spalling) occurs and the device becomes unusable.

  The present invention has been made in view of the above circumstances. The purpose of the present invention is to reduce the damage of the immersion lance when degassing the molten iron by blowing gaseous oxygen into the molten iron through the immersion lance. The present invention is to provide a hot metal desiliconization method that can use a dipping lance many times as compared with the manufacturing cost.

In order to solve the above problems, the hot metal desiliconization method according to the present invention has two discharge holes branched in an inverted T shape on the side surface of the lower end of the immersion lance, and consists of an inner tube and an outer tube. A dipping lance having a double-pipe structure is immersed vertically in the hot metal, and gaseous oxygen is blown from the inner pipe, and hydrocarbon gas is blown from the gap between the inner pipe and the outer pipe, and the flow rate of gaseous oxygen from the inner pipe is 5 to 5. Injecting gaseous oxygen so that the ratio of the flow rate of gaseous oxygen from the inner pipe and the total cross-sectional area of the inner pipe at the discharge hole satisfies the following formula (1): The hot metal is desiliconized. In Equation (1), Q _O2 is the flow rate of gaseous oxygen blown from the inner pipe (Nm ³ / S), and A is the total cross-sectional area (m ² ) of the inner pipe at the discharge hole.

250 ≦ Q _O2 / A ≦ 750 (1)

According to the present invention, the immersion lance having a double-pipe structure consisting of an inner tube and an outer tube is vertically immersed in the hot metal, having a discharge hole having two holes branched in an inverted T shape on the side surface of the lower end portion of the immersion lance. In addition, gaseous oxygen is blown from the inner pipe, and hydrocarbon gas is blown from the gap between the inner pipe and the outer pipe at a flow rate of 5 to 20 vol% of the gaseous oxygen flow rate from the inner pipe. since the ratio of the total cross-sectional area (a) of the inner tube at the Q _O2) and the discharge hole (Q _O2 / a) is adjusted within a range of 250 to 750, erosion of the immersion lance is prevented The immersion lance can be stably extended in life. As a result, a reduction in manufacturing cost is achieved, for example, by effectively utilizing the heat generated by the desiliconization reaction.

  Hereinafter, the present invention will be specifically described.

  In order to solve the above-mentioned problems, the present inventors conducted a water model experiment in a water model apparatus simulating a chaotic vehicle and a desiliconization treatment of hot metal in an actual chaotic vehicle under various conditions, and investigated and examined them. . As a result, the tip of the immersion lance is introduced by introducing a hydrocarbon-based gas such as propane gas as a cooling gas from the gap between the inner tube and the outer tube of the immersion lance having a double tube structure composed of an inner tube and an outer tube. However, if the vibration of the immersion lance itself increases when the gas is blown, the refractory coating layer applied to the outer circumference of the outer tube will cause physical cracking and peeling damage (spoling), which will not be used. It became clear that it would be possible.

  From the above results, the present inventors believe that suppressing the vibration of the immersion lance of the double tube structure immersed in the hot metal leads to the prevention of cracking of the refractory coating layer and the extension of the life of the immersion lance, A method for suppressing the vibration of the immersion lance was studied. The immersion lance during the gas blowing process mainly has (1) reaction force of the blowing gas and (2) buoyancy from the hot metal. When these forces are too large, the vibration becomes large and the refractory coating layer Cracks occur. Therefore, it is necessary to reduce the reaction force of the gas and the buoyancy from the hot metal as much as possible.

  Therefore, in order to reduce the gas reaction force and the buoyancy from the hot metal, the present inventors conventionally have an L-shaped bent portion at the tip portion and one discharge hole at the tip of the bent portion. Immersion lance (referred to as “L-shaped, 1-hole immersion lance”) is immersed perpendicularly to the hot metal bath surface instead of being immersed in the hot metal so that the bent part is substantially horizontal. It was considered to change to the type of immersion lance to be used. It is considered that the buoyancy received from the hot metal is reduced by immersing the immersion lance perpendicularly to the hot metal bath surface. Further, two gas discharge holes are arranged symmetrically in the left and right sides of the lower end of the immersion lance. This is thought to offset the reaction force of the gas. This immersion lance is referred to as an “inverted T-shaped two-hole immersion lance”. In addition, since the kneading vehicle has a narrow opening, in order to widely convey the stirring force generated by gas blowing to the molten iron in the kneading vehicle, it is common to immerse the dipping lance obliquely with respect to the molten metal bath surface. .

  In order to verify whether the above idea is valid, the present inventors conducted an experiment using a water model device simulating a chaotic vehicle. The experiment was carried out on an immersion lance of “inclined immersion type (L-shaped, 1 hole)” shown in FIG. 1 and “vertical immersion type (reverse T-shaped, 2 holes)” shown in FIG. A water model immersion lance 8 is immersed in water 10 accommodated in a container 9, nitrogen gas is blown into the water from the water model immersion lance 8, and the vibration amplitude of the water model immersion lance 8 at that time is measured using a laser displacement meter 11. Measured. The conditions such as the immersion depth and gas flow rate of the water model immersion lance 8 were the same. The experimental conditions and results are shown in Table 1.

  As shown in Table 1, the vibration amplitude of the water model immersion lance was 4.5 to 5.5 mm in the tilted immersion type, whereas it was 1.5 to 2.5 mm in the vertical immersion type, which greatly increased the vibration. It has been clarified that the amplitude of.

  From the results of this water model experiment, it was found that the vibration of the lance can be suppressed in the vertical immersion type (inverted T-shape, two holes).

Therefore, in order to confirm that suppressing the vibration leads to prevention of cracking of the lance refractory and extending its life, a desiliconization treatment experiment was conducted in an actual mixed car as shown in FIG. In the experiment, as shown in FIG. 4, a double-pipe structure comprising an inner tube 2 and an outer tube 3 having two discharge holes 5 branched in an inverted T shape on the side surface of the lower end portion of the immersion lance 1. The immersion lance 1 is immersed vertically in the hot metal 7 accommodated in the kneading wheel 6, gaseous oxygen is 0.5 Nm ³ / s from the inner tube 2, and propane gas is 0. 0 through the gap between the inner tube 2 and the outer tube 3. 05Nm ³ / s blowing level (inverted T-shaped 2 holes / vertical immersion) and L-shaped 1-hole type double pipe structure immersion lance 1A as shown in FIG. 7 is inclined and immersed, and similarly, 0.5 Nm ³ / s of gaseous oxygen is blown from the inner tube 2 and 0.05 Nm ³ / s is blown from the gap between the inner tube 2 and the outer tube 3 (L-shaped). Mold 1 hole / tilted immersion). Table 2 shows the silicon removal treatment conditions and test results. 4 and 5, reference numeral 4 denotes a refractory coating layer.

  As a result of the experiment, in the case of the L-shaped single hole / tilted immersion, the lance vibration is large, resulting in physical damage (spalling) of the lance body, and the average lance life is 3.1 charges (ch) there were. On the other hand, in the case of inverted T-shaped two holes / vertical immersion, the lance vibration was smaller than in the case of L-shaped one hole / tilted immersion, and spalling of the refractory did not occur. However, in the case of the inverted T-shaped two holes / vertical immersion, when the situation around the lance discharge hole after the experiment is observed, the refractory coating layer 4 on the upper side of the discharge hole is melted as shown in FIG. The average lance life was 4.0 ch, and it was not possible to achieve a significant increase in lance life compared to the L-shaped single hole / tilted immersion.

  The present inventors considered that as this factor, the gaseous oxygen flowing out from the discharge hole rises along the periphery of the immersion lance, so that the refractory in the vicinity of the discharge hole melts down. Therefore, the conditions for avoiding the gaseous oxygen from the discharge hole rising along the periphery of the immersion lance were examined again by the water model experiment. As a result, it has been clarified that the gas reaches the position away from the immersion lance and rises as the linear flow velocity in the horizontal direction of the gas from the discharge hole increases. When the linear flow rate was slow, it was confirmed that the gas exiting the discharge hole rose along the circumference of the immersion lance.

Based on this result, in the actual mixed car, the desiliconization process was carried out by changing the horizontal flow velocity of the gaseous oxygen from the discharge hole, and the relationship between the horizontal flow velocity of the gaseous oxygen and the lance life was investigated. . Here, since the gaseous oxygen expands by receiving heat from the hot metal, it is difficult to determine the actual linear velocity of the gaseous oxygen in the discharge hole. Therefore, the gaseous oxygen blowing flow rate ( Q _O2 : Unit “Nm ³ / S”) and the ratio (Q _O2 / A: Unit “m / s”) of the total cross-sectional area (A: Unit “m ² ”) of the inner pipe at the discharge hole The effect of the ratio (Q _O2 / A) on the lance life was investigated.

As a result, when the ratio (Q _O2 / A) is less than 250, the lance life is 3 to 5 ch. However, when the ratio (Q _O2 / A) is 250 or more, the lance life is stably 10 ch or more. I found out. On the other hand, if the ratio (Q _O2 / A) exceeds 750, the linear velocity of gaseous oxygen is too high, the fluctuation of the hot metal in the kneading vehicle becomes intense, and the splash (spattering of molten iron from the container) increases, resulting in operational hindrance I found out. Therefore, it has been found that the ratio (Q _O2 / A) needs to be controlled in the range of 250 to 750.

  Further, the flow rate of the hydrocarbon-based gas blown from the gap between the inner tube and the outer tube also has an appropriate range, and it is understood that it is necessary to blow at a flow rate of 5 to 20 vol% of the flow rate of gaseous oxygen blown from the inner tube. It was. When the flow rate of the hydrocarbon-based gas is less than 5 vol% of the flow rate of gaseous oxygen, the cooling effect of the hydrocarbon-based gas is not sufficient, and the erosion loss at the discharge hole portion becomes severe. On the other hand, when the flow rate of the hydrocarbon-based gas exceeds 20 vol% of the flow rate of gaseous oxygen, the cooling effect of the hydrocarbon-based gas on the refractory coating layer can be sufficiently obtained, but it is cooled to the hot metal and the heat of the hot metal This is not desirable because there is less room.

The present invention has been made on the basis of these test results, and the hot metal desiliconization method according to the present invention is reversed on the side surface of the lower end portion of the immersion lance 1 as shown in FIGS. An immersion lance 1 having a double-pipe structure comprising an inner tube 2 and an outer tube 3 is immersed perpendicularly to the hot metal 7 so that gaseous oxygen is discharged from the inner tube 2. While blowing, hydrocarbon gas is blown from the gap between the inner tube 2 and the outer tube 3 at a flow rate of 5 to 20 vol% of the flow rate of gaseous oxygen from the inner tube 2, and gaseous oxygen is blown from the inner tube 2. Gaseous oxygen was blown into the hot metal 7 so that the ratio (Q _O2 / A) of the flow rate (Q _O2 ) to the total cross-sectional area (A) of the inner pipe at the discharge hole was in the range of 250 to 750. It is characterized by desiliconization treatment.

The refractory material constituting the refractory coating layer 4 of the immersion lance 1 is not particularly required to be specified. Al ₂ O ₃ —SiO ₂ amorphous refractory containing 10 to 40% by mass of SiO ₂ , MgO 5 to An Al ₂ O ₃ —MgO-based amorphous refractory containing 30% by mass 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.

In the present invention, when performing desiliconization treatment of the molten iron 7, oxygen gas is blown from the inner tube 2, and hydrocarbon gas is blown from the gap between the inner tube 2 and the outer tube 3 to perform the desiliconization treatment. In addition, other oxygen gas supply means such as oxygen gas addition by a non-immersion type upper blowing lance may be used in combination. 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, or an oxygen-containing gas such as oxygen-rich air may be used as appropriate. May be. What is necessary is just to determine an oxygen concentration suitably from the amount of oxygen required. An inert gas such as nitrogen gas or Ar gas is used to reduce the flow rate of the hydrocarbon-based gas from the gap between the inner tube 2 and the outer tube 3 in accordance with the change in the flow rate of the oxygen gas blow-in from the inner tube 2. May be mixed in a hydrocarbon-based gas. As 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. Easy to use in steelmaking process.

As described above, according to the present invention, the hydrocarbon-based gas is blown from the gap between the inner tube 2 and the outer tube 3 at a flow rate of 5 to 20 vol% of the gas oxygen flow rate from the inner tube 2, and the inner tube 2 is adjusted so that the ratio (Q _O2 / A) of the flow rate from the nozzle ₂ (Q _O2 ) to the total cross-sectional area (A) of the inner pipe 2 at the discharge hole is in the range of 250 to 750. It is possible to stably extend the life of the lance 1.

  Based on the knowledge obtained in the water model experiment and the actual mixed car experiment described above, in the actual mixed car as shown in FIG. 3 described above, the reverse T-shaped / two-hole type double pipe structure shown in FIG. 4 is immersed. The lance was immersed vertically in the hot metal to conduct a desiliconization treatment experiment, and various investigations were conducted. In some experiments, an experiment using an immersion lance having an L-shaped and one-hole type double tube structure shown in FIG. 5 was also performed as a comparative example. Table 3 shows test conditions and test results.

In Inventive Examples 1 to 9, an immersion lance having an inverted T-shaped double-hole double tube structure is vertically immersed, and oxygen gas is supplied from the inner tube, and propane gas is supplied from the gap between the inner tube and the outer tube to the inner tube gas. Blowing in at a flow rate of 5 to 20 vol% of oxygen, the amount of gaseous oxygen blown from the inner pipe (Q _O2 : [Nm ³ / s]) and the total cross-sectional area of the inner pipe at the discharge hole (A: [m ² ]) As a result of setting the ratio (Q _O2 / A) to 250 to 750, the average lance life exceeded 10 ch, the hot metal temperature increased by about 30 ° C., and there was no problem with the amount of splash generated that hindered operation. .

  On the other hand, as shown in Comparative Example 1, when an immersion lance having an L-shaped / single-hole type double tube structure is immersed in an inclined manner, the lance vibration is large and spalling cracks occur in the lance body. The average lance life was 3.1 ch.

  In Comparative Example 2, an inverted T-shaped two-hole double tube lance was vertically immersed, but the propane gas from the gap between the inner tube and the outer tube had a flow rate of 4 vol% of the inner tube gas oxygen. . In this case, due to insufficient cooling of propane gas, the lance discharge hole was damaged, and as a result, the average lance life was as low as 2.9 ch. In Comparative Example 3, an inverted T-shaped double-hole double-tube lance was immersed vertically, and propane gas was 22 vol% of the inner tube gas oxygen. However, since the cooling effect of propane gas was too strong, An effective rise could not be obtained.

In Comparative Examples 4, 6, and 8, a double-tube lance with an inverted T-shape and two holes was immersed vertically, but the ratio (Q _O2 / A) was smaller than 250, both from the discharge holes The gaseous oxygen increased along the periphery of the immersion lance and the refractory near the upper portion of the discharge hole melted, so the average lance life was as low as 3.2 to 4.6 Ch.

In Comparative Examples 5, 7, and 9, a double-tube lance with an inverted T-shape and two holes was vertically immersed, but the ratio (Q _O2 / A) was larger than 750, and the average lance life was good. However, the linear flow velocity of gaseous oxygen from the discharge hole became too large, and the hot metal in the kneading vehicle fluctuated vigorously, resulting in increased splash and hindered operation.

  Thus, by using the present invention, it is possible to stably extend the life of the immersion lance in the desiliconization process in which gaseous oxygen is blown into the hot metal via the immersion lance, and as a result, the heat generated by the desiliconization reaction is effectively increased. It can be used, and effects such as reduction in manufacturing cost can be obtained.

It is the schematic of an inclination immersion type water model experiment apparatus. It is the schematic of a vertical immersion type water model experimental apparatus. It is a figure which shows the condition which desiliconizes the hot metal accommodated in the kneading vehicle by blowing gaseous oxygen from an immersion lance. It is a schematic sectional drawing of the immersion lance for gaseous oxygen blowing used by this invention. It is a schematic sectional drawing of the immersion lance for gaseous oxygen blowing used for the comparison. It is the schematic which shows the melting damage condition of the immersion lance for gaseous oxygen blowing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Immersion lance 2 Inner pipe 3 Outer pipe 4 Refractory coating layer 5 Discharge hole 6 Chaotic wheel 7 Hot metal 8 Water model immersion lance 9 Container 10 Water 11 Laser displacement meter

Claims (1)

The immersion lance has a double- holed immersion lance consisting of an inner tube and an outer tube, perpendicular to the hot metal contained in the kneading wheel, and has a discharge hole with two holes branched in an inverted T shape on the side of the lower end of the immersion lance. It is immersed, and gaseous oxygen is blown from the inner pipe, and hydrocarbon gas is blown from the gap between the inner pipe and the outer pipe at a flow rate of 5 to 20 vol% of the flow rate of gaseous oxygen from the inner pipe. Gas oxygen is blown so that the ratio of the flow rate of gaseous oxygen to the total cross-sectional area of the inner pipe at the discharge hole satisfies the following formula (1), and desiliconization treatment is applied to the hot metal contained in the kneading car A method for desiliconizing hot metal.
250 ≦ Q _O2 / A ≦ 750 (1)
In Equation (1), Q _O2 is the flow rate of gaseous oxygen blown from the inner pipe (Nm ³ / S), and A is the total cross-sectional area (m ² ) of the inner pipe at the discharge hole.

Images