JP5401938B2 - Hot metal desulfurization method - Google Patents

Description

  The present invention relates to a hot metal desulfurization method using a mechanical stirring desulfurization apparatus.

  The hot metal discharged from the blast furnace contains high concentrations of phosphorus (element symbol P) and sulfur (element symbol S), which adversely affect the quality of steel, and technologies for removing these have been developed. . In today's refining process, prior to decarburization refining in a converter, a method of removing phosphorus and sulfur contained in hot metal, so-called hot metal pretreatment is generally performed. Among these, in the hot metal desulfurization treatment, the hot metal is held in a refining vessel having a substantially circular cross section, and a desulfurizing agent is added onto the hot metal, which is called an impeller (also referred to as “stirring blade” or “stirring blade”). A method (hereinafter referred to as “mechanical stirring type desulfurization method”) in which a rotor having blades is rotated by immersing the rotor in the hot metal and agitating the molten iron and the desulfurizing agent (hereinafter referred to as “mechanical stirring type desulfurization method”) is widely performed.

  In order to increase the desulfurization reaction rate of the hot metal, it has been found that it is preferable to increase the reaction interface area between the hot metal and the desulfurization agent. From this viewpoint, it is desirable that the particle size of the desulfurization agent is fine. However, in the actual mechanical stirring type desulfurization equipment, a method of adding a desulfurizing agent from the upper part of the container holding the hot metal with a charging chute is adopted, and when a fine desulfurizing agent is added, it reaches the hot metal due to scattering. The amount of the desulfurizing agent to be reduced is reduced, and the addition yield of the desulfurizing agent is reduced. For this reason, the problem that reaction efficiency falls arises. Further, the interfacial tension between the CaO powder, which is the main component of the desulfurizing agent, and the molten iron is 1.75 N / m, and the CaO powder has a property that it is difficult to get wet with the molten iron. For this reason, the CaO powder added to the hot metal is agglomerated with each other, and the CaO powder inside the agglomerate remains unreacted, resulting in a problem that the reaction efficiency is lowered. In addition, since the scattered desulfurizing agent is accumulated as dust, there is a problem that the amount of dust processing increases when the production amount increases.

  From these events, in order to promote the desulfurization reaction of hot metal, the addition yield of CaO added as a powder is improved, and aggregation of CaO powder in the hot metal is suppressed to promote dispersion in the hot metal bath. It turns out that is effective.

As a technique for realizing this, Patent Document 1 provides a rectifying body projecting from the side wall of a refining vessel, causing the molten iron stirred and collided with the rectifying body to generate a downward flow, and a desulfurizing agent is generated in the downward flow. There has been proposed a method for entraining. Patent Document 2 proposes a method of desulfurization while blowing a desulfurizing agent into the hot metal from below the rotating impeller shaft. Furthermore, Patent Document 3 discloses that desulfurization is carried out along with a carrier gas through an upper blowing lance at a feed rate of 1.6 kg / min or less of desulfurizing agent per ton of hot metal on a hot metal bath surface stirred by an impeller. It has been proposed to desulfurize by adding a blowing agent.
Japanese Patent Laid-Open No. 51-112416 JP 2005-68506 A JP 2007-247045 A

  However, the above prior art has the following problems.

  That is, when a rectifying body as disclosed in Patent Document 1 is installed, since the rotational stirring force by the impeller is very strong, the rectifying body must have a very strong shape and material. Therefore, there is a problem that much labor and cost are spent on the production and maintenance of the rectifier.

  In the case of powder blowing from under the impeller shaft disclosed in Patent Document 2, the desulfurizing agent powder is supplied into the hot metal together with the carrier gas. When added in this way, the desulfurizing agent powder is trapped in the gas bubbles and rises on the bath surface together with the rising gas bubbles, and as a result, the desulfurizing agent is added above the bath surface. The desulfurization reaction efficiency may not be improved. Furthermore, in order to blow powder from under the impeller shaft, a device for supplying gas and powder into the rotating shaft (for example, a rotary joint) is required, which increases the equipment cost. Also occurs.

  The method disclosed in Patent Document 3 is excellent as a method for adding a powdery desulfurization agent with a high yield, but the hot metal surface of the hot metal being stirred so as to vortex in the container by the impeller is the center. The concave portion has a concave shape in the center so that the inclination angle becomes larger as the portion is larger, and the inventors of the present invention have stated that the desulfurization agent addition yield is where the desulfurization agent is added to the top of the concave shape. We know that it changes greatly depending on the situation. That is, it has been found that the addition rate of the desulfurization agent varies greatly depending on the distance from the center position of the container to the top blowing addition position. In this regard, Patent Document 3 does not disclose anything, and there is a problem that the addition yield cannot be stably increased.

  The present invention has been made in view of the above circumstances. The object of the present invention is to use a relatively simple equipment and to have excellent reactivity when desulfurizing hot metal using a mechanical stirring desulfurization apparatus. To provide a method for efficiently desulfurizing hot metal by adding a fine-grain desulfurizing agent to hot metal with a good yield and promoting dispersion of the desulfurizing agent in the hot metal.

  The hot metal desulfurization method according to the first aspect of the present invention for solving the above-described problem is a hot metal bath surface in a processing vessel that is stirred by forming a vortex on the bath surface thereof by an impeller of a mechanical stirring desulfurization apparatus. In order to desulfurize the hot metal by adding the desulfurization agent from the vertical direction together with the carrier gas through the upper blowing lance, the inclination angle with respect to the horizontal plane is 10 ° to the hot metal bath surface forming the vortex. The desulfurizing agent is blown up at a position of 35 °.

The hot metal desulfurization method according to the second invention is characterized in that, in the first invention, the shape of the hot metal bath surface and the inclination angle with respect to the horizontal surface are obtained by the following equations (1) to (10). is there. In these equations, however, H ₀ is the depth of the recess at the center of the vortex (m), r is the distance (m) from the center of the processing vessel to any position, N is the rotational speed of the impeller (times / minute), and D is Inner diameter (m) of processing vessel, θ is inclination angle (rad) of impeller blade, b is height of impeller blade (m), d is impeller rotational diameter (m), n _P is the number of impeller blades, g is gravitational acceleration (= 9.8 m / sec ² ), Re is the number of lay nozzles (−), ρ is the hot metal density (kg / m ³ ), μ is the hot metal viscosity (Pa · sec), and H is the center of the processing vessel. The bath surface height (m) at a position separated from the processing vessel by r and L is the tangential angle of the hot metal bath surface at a position separated by r from the processing vessel center, that is, the inclination angle (deg) with respect to the horizontal plane.

  The hot metal desulfurization method according to a third invention is characterized in that, in the first or second invention, the impeller has a rotational speed of 80 times / minute to 140 times / minute.

  According to the present invention, the size of the processing vessel to be used, the shape of the impeller, and the number of rotations are used for performing the desulfurization treatment of the hot metal by spraying the desulfurizing agent from the top blowing lance while stirring the hot metal using the mechanical stirring type desulfurization apparatus. Whatever the physical property value of the hot metal, since the desulfurization agent is added at the optimum top position of the desulfurization agent according to these factors, the addition rate of the desulfurization agent is maintained at a high level and is low. The desired desulfurization treatment can be performed with the desulfurization agent. As a result, reduction of the desulfurizing agent basic unit, reduction of the amount of generated slag based on this, and the like, an industrially beneficial effect is brought about.

  Hereinafter, the present invention will be specifically described. First, the background to the present invention will be described.

  In the desulfurization treatment of hot metal using a mechanical stirring type desulfurization apparatus, the present inventors added a fine desulfurization agent having excellent reactivity to the hot metal with a high yield and infiltrated it to disperse the desulfurization agent in the hot metal. Various means for promoting and efficiently desulfurizing the hot metal were studied. As a result, the method of adding the desulfurization agent disclosed in Patent Document 3 by top blowing from the vertical direction significantly improves the addition yield of the fine-grain desulfurization agent compared to the method using the conventional charging chute. It was confirmed to be optimal.

  However, it has been found from the test results in the actual machine that even when the desulfurizing agent is added by top blowing, the addition rate of the desulfurizing agent changes depending on the rotation speed of the impeller and the addition position of the desulfurizing agent. Therefore, various causes were pursued, and as a result, attention was paid to the shape of the hot metal bath surface during stirring by the impeller during addition of top blowing. In other words, the hot metal is stirred by a rotating impeller so as to be swirled in the processing vessel and so that the inclination angle with respect to the horizontal plane becomes larger toward the center, and the shape of the recess on the hot metal bath surface is as follows. From the fact that it varies depending on the amount of hot metal treated, the number of revolutions of the impeller, the shape of the impeller, the size of the processing vessel, etc., it has been thought that the yield of addition depends on the shape of the recess on the hot metal bath surface.

Therefore, we investigated the quantitative determination of the shape of the bath surface during mechanical stirring using a water model experimental device of a mechanical stirring desulfurizer. FIG. 1 shows an outline when a vortex is formed by stirring with a mechanical stirring type desulfurization apparatus. In FIG. 1, reference numeral 2 is a hot metal ladle as a processing vessel, 3 is a hot metal, 4 is an impeller, 9 is a hot water surface of the hot metal, and the hot metal 3 accommodated in the hot metal ladle 2 having an inner diameter D has a rotating diameter. Shows a state in which the hot metal 3 is stirred by immersing the impeller 4 in which d is d, height is b, and blade inclination angle is θ. However, the hot metal surface 9 of the molten iron is at the level of the hot water surface when the impeller 4 is immersed. The hot metal 3 is formed with a vortex centered on the rotation axis of the impeller 4, and the tangential angle of the hot metal bath surface at a position away from the center of the impeller 4 by the distance r, that is, the inclination angle with respect to the horizontal plane, is analyzed as L. doing. The dent center depth (H ₀ ) is analyzed as a distance from the stationary molten metal surface 9, and the impeller immersion depth (h) is analyzed as a distance from the stationary molten metal surface 9.

  As a result of measuring the tangential angle L of the bath surface curve at a position (hereinafter also referred to as “position r”) at an arbitrary distance r from the center of the impeller 4 under various stirring conditions, the bath surface curve at the arbitrary position r is measured. It was found that the tangent angle L can be calculated by using the following formulas (1) to (10).

In these equations, however, H ₀ is the depth of the recess at the center of the vortex (m), r is the distance (m) from the center of the processing vessel to any position, N is the rotational speed of the impeller (times / minute), and D is Inner diameter (m) of processing vessel, θ is inclination angle (rad) of impeller blade, b is height of impeller blade (m), d is impeller rotational diameter (m), n _P is the number of impeller blades, g is gravitational acceleration (= 9.8 m / sec ² ), Re is the number of lay nozzles (−), ρ is the hot metal density (kg / m ³ ), μ is the hot metal viscosity (Pa · sec), and H is the center of the processing vessel. The bath surface height (m) at a position separated from the processing vessel by r and L is the tangential angle of the hot metal bath surface at a position separated by r from the processing vessel center, that is, the inclination angle (deg) with respect to the horizontal plane.

  In the water model experiment, as a result of comparing the tangent angle L of the bath surface curve calculated using the formulas (1) to (10) and the measured value of the tangent angle L of the bath surface curve, both agree well. In the hot metal stirring using the impeller, it was confirmed that the tangent angle L of the bath surface curve at an arbitrary position r can be estimated using the above formula without actually measuring.

  Moreover, it turned out that the penetration | invasion angle with respect to the bath surface of the desulfurization agent added from a top blowing lance is computable from the tangent angle L of the bath surface curve obtained from (10) Formula.

  In addition, in the actual machine, the desulfurization test of the hot metal was carried out by changing the angle between the top blowing lance and the hot metal bath surface calculated using these equations, and the positional relationship between these and the amount of desulfurization agent to be added was scattered. That is, it has been found that there is a great correlation with the desulfurization agent addition yield. This is because the angle between the top blowing lance and the bath surface greatly affects the penetration of the added desulfurizing agent into the bath.

  In the actual machine test, conditions other than the upper blowing lance position are constant, the distance from the impeller center to the upper blowing lance center is changed, that is, the upper blowing lance is set to various positions r, and the upper blowing lance position and the tangent line are set. The scattering situation and desulfurization rate of the desulfurizing agent when the angle L changed were investigated. Here, the desulfurization rate is the difference between the sulfur concentration in the hot metal before and after the treatment, expressed as a percentage of the sulfur concentration in the hot metal before the treatment.

  When the top blowing lance was installed outside the processing vessel, that is, in a range where the tangent angle L of the bath surface was small, the added desulfurizing agent was greatly scattered and the desulfurizing agent addition yield was lowered. In addition, when the top blowing lance was installed in the center of the processing vessel, that is, in a range where the tangent angle L of the bath surface was large, the added desulfurizing agent was greatly scattered, and the desulfurizing agent addition yield was reduced.

  On the other hand, when the top blowing lance is installed at a position where the tangent angle L of the bath surface curve is in the range of 10 ° to 35 °, scattering of the added desulfurizing agent is suppressed, and the desulfurization rate is also extremely low at 92%. It was confirmed that it was high.

  As shown in equations (1) to (10), the angle between the top blowing lance and the hot metal bath surface is determined by the size of the processing vessel, the shape and rotational speed of the impeller, and the physical properties of the hot metal, thereby By adding top blowing at an appropriate position of the required tangential angle L, desulfurization treatment can be performed under optimum conditions.

  The present invention has been made on the basis of these examination results, and a desulfurizing agent is added to the bath surface of the hot metal in the processing vessel through a top blowing lance and a desulfurization agent from the vertical direction through a top blowing lance. In desulfurizing the hot metal, the desulfurizing agent is blown up at a position where the tangential angle of the hot metal bath surface, that is, the inclination angle with respect to the horizontal plane, is 10 ° to 35 ° among the hot metal bath surface forming the vortex. To do.

  Next, specific embodiments of the present invention will be described with reference to the drawings. FIG. 2 is a schematic cross-sectional view showing an example of a mechanical stirring type desulfurization apparatus used in carrying out the present invention, and FIG. 2 shows an example in which a ladle type hot metal ladle is used as a processing container for containing hot metal. Yes. In addition, in this invention, since the bath surface height (H) formed is calculated using the internal diameter (D) of a processing container, the processing container to be used is a container whose horizontal cross-sectional shape is circular or elliptical. It is necessary. However, the inner diameter in the case of an elliptic container is defined as an inner diameter D, which is an average value of the diameter in the oval direction and the diameter in the oval direction. From this point, the ladle type hot metal ladle is optimal as a processing container because the horizontal cross-sectional shape is circular.

  The hot metal 3 discharged from the blast furnace is received by the hot metal pan 2 mounted on the carriage 1 or a topped car, and the received hot metal 3 is conveyed to a mechanical stirring desulfurization apparatus. If it is received by a topped car, it must be transferred to a ladle type processing container prior to the desulfurization treatment. Further, the hot metal 3 to be subjected to the desulfurization treatment according to the present invention may be any component, and for example, desiliconization treatment or dephosphorization treatment may be performed in advance.

  As shown in FIG. 2, the mechanical stirring type desulfurization apparatus includes a refractory impeller 4 that is immersed and buried in the hot metal 3 accommodated in the hot metal ladle 2 and is rotated to stir the hot metal 3. The impeller 4 is moved up and down in a substantially vertical direction by an elevating device (not shown), and is swung around a shaft 4a as a rotating shaft by a rotating device (not shown).

  Further, the mechanical stirring type desulfurization apparatus includes an upper blowing lance 5 for adding the powdered desulfurizing agent 7 to the hot metal 3 in the hot metal ladle from the almost vertical direction, a granular or massive desulfurizing agent, and A charging chute 8 for adding a deoxidizer on the bath surface of the hot metal 3 of the hot metal pan 2 is installed. Further, an exhaust duct port (not shown) connected to a dust collector (not shown) is provided at an upper position of the hot metal ladle 2 so that gas and dust generated during the desulfurization process are discharged. .

The top blowing lance 5 is connected to a dispenser 6 that stores the powdered desulfurizing agent 7, so that the powdered desulfurizing agent 7 can be added from the top blowing lance 5 together with the carrier gas at any timing. It has become. Further, the upper blow lance 5 has a structure in which not only the vertical position but also the horizontal position can be moved to an arbitrary position. An inert gas such as Ar gas or nitrogen gas is used as the carrier gas, and the powdered desulfurization agent 7 is an oxide of CaO powder or CaO such as Al ₂ O ₃ , CaF ₂ , MgO, SiO _2. Use powder mixed with accelerator.

Before starting the desulfurization process, the inner diameter (D) of the hot metal ladle 2, which is a processing container, the inclination angle (θ) of the impeller 4 blades, the height (b) of the impeller 4, the rotational diameter (d) of the impeller 4, The number of impeller 4 blades (n _P ), gravitational acceleration (g), density of molten iron 3 (ρ), viscosity of molten iron 3 (μ), and the planned number of revolutions (N) of the impeller 4 are described above (1 ) To (9) are substituted, the bath surface height (H ₀ ) is calculated with reference to the stationary bath surface, and the tangent angle of the bath surface curve at the position of the upper lance (position r) according to the equation (10) L is calculated.

  The upper blowing lance 5 is moved to a position where the calculated tangent angle L of the bathing surface curve is not less than 10 ° and not more than 35 °, or the rotational speed (N) of the impeller 4 is changed to change the upper blowing lance 5 The rotation speed of the impeller 4 is set so that the tangent angle L of the bath surface curve at the position immediately below is 10 ° or more and 35 ° or less.

  When the stirring conditions are set, the impeller 4 is lowered and immersed in the hot metal 3. In this case, the position of the carriage 1 on which the hot metal ladle 2 is mounted is adjusted in advance so that the position of the impeller 4 is substantially at the center of the hot metal ladle 2. If the impeller 4 is immersed in the hot metal 3, the impeller 4 starts to turn and the speed is increased to a predetermined number of rotations set. When the rotational speed of the impeller 4 reaches a predetermined rotational speed, the powdered desulfurizing agent 7 is sprayed and added to the hot metal bath surface through the top blowing lance 5. In order to accelerate the desulfurization reaction in parallel with the top blowing addition of the powdery desulfurizing agent 7, before or after the top blowing addition, or during the entire period of the desulfurization treatment, a deoxidizing agent such as aluminum dross, It is preferable to supply the hot metal ladle 2 through the charging chute 8.

  Even after the top-blowing addition of the predetermined amount of the powdered desulfurizing agent 7 is completed, the impeller 4 is swirled to continue the desulfurization process, and if the stirring is performed for a predetermined time, the rotational speed of the impeller 4 is decreased. Stop. If the turning of the impeller 4 is stopped, the impeller 4 is raised and waited above the hot metal ladle 2. The generated slag (not shown) floats to cover the hot metal surface, and the desulfurization process of the hot metal 3 is completed in a stationary state. After the desulfurization treatment is completed, the generated slag is discharged from the hot metal ladle 2 and conveyed to the next refining process.

  By performing desulfurization treatment on the hot metal 3 in this way, the size of the hot metal ladle 2 is used regardless of the size of the hot metal ladle 2 to be used, the shape and rotation speed of the impeller 4, and the physical properties of the hot metal 3. The optimum top blowing addition position can be determined according to the shape and rotational speed of the impeller 4 and the physical properties of the hot metal 3. Therefore, the optimum top blowing addition of the powdered desulfurizing agent 7 is possible in any case. In other words, the desulfurization rate can be improved, and the amount of desulfurizing agent used can be reduced and the amount of generated slag can be reduced.

  The result of having performed desulfurization processing of hot metal using CaO powder as a desulfurization agent using the mechanical stirring type desulfurization apparatus shown in FIG. 2 is shown. The impeller used has four blades and the blades are not inclined. The chemical components of the hot metal used were C: 3.5 to 5.0 mass%, Si: 0.1 to 0.3 mass%, S: 0.02 to 0.04 mass%, P: 0.05 to The hot metal temperature was in the range of 1250 to 1350 ° C. at 0.15% by mass. In the desulfurization treatment, a hot metal ladle capable of treating 200 to 350 tons of hot metal was used as a processing container.

  In a hot metal ladle having an inner diameter (D) of 4.0 m and capable of containing 350 tons of hot metal, the distance (r) from the center of the impeller to the top blowing lance is changed with the rotation speed of the impeller being constant. That is, the desulfurization treatment was performed by changing the tangential angle L of the hot metal surface at the position directly below the upper blowing lance. Table 1 shows the tangential angle L and the desulfurization rate at that time. The tangent angle L shown in Table 1 is a calculated value calculated using the equations (1) to (10).

  As shown in Table 1, the desulfurization rate was about 70 to 80% when the top blowing addition position was when the tangent angle L of the bath surface curve was less than 10 ° and greater than 35 °. On the other hand, the desulfurization rate was as high as 90% or more when the top blowing addition position was a tangent angle L of the bath surface curve of 10 ° to 35 °.

It is a figure which shows the outline | summary when stirring with a mechanical stirring type desulfurization apparatus and forming a vortex. It is a schematic sectional drawing which shows an example of the mechanical stirring type desulfurization apparatus used when implementing this invention.

Explanation of symbols

1 Cart 2 Hot metal ladle 3 Hot metal 4 Impeller 5 Top blow lance 6 Dispenser 7 Powdered desulfurization agent 8 Charging chute 9 Stationary hot water surface

Claims (3)

  The desulfurizing agent and the conveying gas are vertically directed through the top blowing lance toward the hot metal bath surface in the processing vessel, which is stirred while forming a vortex on the bath surface by the impeller of the mechanical stirring desulfurization device. When desulfurizing the hot metal by adding up-blowing from above, the desulfurizing agent is blown up at a position where the inclination angle with respect to the horizontal plane is 10 ° to 35 ° in the hot metal bath surface forming the vortex. , Hot metal desulfurization method. 2. The hot metal desulfurization method according to claim 1, wherein the shape of the hot metal bath surface and the inclination angle with respect to the horizontal surface are determined by the following equations (1) to (10):

In these equations, however, H ₀ is the depth of the recess at the center of the vortex (m), r is the distance (m) from the center of the processing vessel to an arbitrary position, N is the number of revolutions of the impeller (times / minute), and D is Inner diameter (m) of processing vessel, θ is inclination angle (rad) of impeller blade, b is height of impeller blade (m), d is impeller rotational diameter (m), n _P is the number of impeller blades, g is gravitational acceleration (= 9.8 m / sec ² ), Re is the number of lay nozzles (-), ρ is the hot metal density (kg / m ³ ), μ is the hot metal viscosity (Pa · sec), and H is the center of the processing vessel. The bath surface height (m) at a position separated from the processing vessel by r and L is the tangential angle of the hot metal bath surface at a position separated by r from the processing vessel center, that is, the inclination angle (deg) with respect to the horizontal plane.   3. The hot metal desulfurization method according to claim 1, wherein the impeller has a rotational speed of 80 times / minute to 140 times / minute.

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