JP5418058B2 - Hot metal desulfurization method - Google Patents

Description

  The present invention relates to a method for desulfurizing hot metal by using a mechanical stirring type desulfurization apparatus equipped with an impeller and adding a desulfurizing agent to the hot metal bath surface stirred by the impeller.

  With the recent increase in low-sulfur steel production, efficient desulfurization treatment at the hot metal stage is essential. Conventionally, hot metal desulfurization treatment is generally performed using a solid lime-based desulfurization agent such as lime (CaO), and an injection lance is used for hot metal contained in a hot metal transfer container such as a topped car or hot metal ladle. An injection desulfurization method in which a lime-based desulfurization agent is blown and added, or an impeller (also called “stirring blade” or “rotary blade”) is immersed in the hot metal in the hot metal transfer container, and the hot metal is stirred by the rotating impeller and the lime type A mechanical stirring desulfurization method in which a desulfurizing agent is added on top has been performed.

  By the way, lime, which is the main component of the lime-based desulfurizing agent, has a specific gravity smaller than that of hot metal and poor wettability with hot metal, so that lime, which is a desulfurizing agent, does not easily penetrate and disperse in hot metal, and the reaction efficiency is high. There is a problem that it is low. Lime floating on the hot metal hardly contributes to the desulfurization reaction. Therefore, several techniques have been proposed for promoting the dispersion of lime in the hot metal and improving the desulfurization reaction efficiency when the hot metal is desulfurized with a mechanical stirring desulfurization apparatus equipped with an impeller.

  For example, Patent Document 1 discloses a hot metal desulfurization method in which an impeller having an impeller blade having a width corresponding to 1/10 to 1/2 of the inner diameter (d) of a refining vessel is immersed in hot metal and rotated to stir the hot metal. In order to increase the stirring strength, the desulfurization method in which the rotation shaft of the impeller is decentered in a region where the distance (L) from the center of the refining vessel is d / 20 or more and the impeller blades do not contact the inner wall of the refining vessel. Is disclosed. According to Patent Document 1, stirring of the hot metal is disturbed to form a turbulent flow, and the desulfurization efficiency is improved.

  In Patent Document 2, in a hot metal desulfurization method using a mechanical stirring desulfurization apparatus, a desulfurizing agent is added together with a carrier gas through an upper blowing lance onto a hot metal bath surface stirred by an impeller. Thus, it is disclosed to perform a desulfurization treatment. According to Patent Document 2, a fine-grain desulfurization agent having excellent reactivity is added together with a carrier gas, so that scattering during addition is reduced, the addition yield of the desulfurization agent is improved, and fine-grain desulfurization is performed. The agent has a large reaction interface area, so that the desulfurization reaction is promoted and the desulfurization rate can be remarkably improved.

  In addition, in Patent Document 3, when adding a component adjusting agent to hot metal during rotary stirring by an impeller, the hot metal is mechanically stirred to form a hot metal flow, and an obstacle is provided in this flow. A method has been proposed in which a component modifier is added to the turbulent flow induced behind the obstacle. According to Patent Document 3, a turbulent flow is formed behind the obstacle, and the alloys or processing agent introduced into this portion are immediately mixed with the molten iron.

JP 2001-262212 A JP 2005-179690 A Japanese Patent Laid-Open No. 61-223115

  However, the above prior art has the following problems.

  As disclosed in Patent Document 1 and Patent Document 3, in the stirring using the impeller, the stirring is improved by disturbing the steady rotating flow generated in the refining vessel. In Patent Document 1 in which the eccentricity is 20 or more, there are restrictions such as a problem of the load of the motor torque and vibration of the equipment, and it is difficult to say that it is a realistic condition. Further, when the impeller is eccentric, the rotational flow is disturbed, and it is considered that the optimum addition position of the desulfurizing agent is determined according to the disturbance of the rotational flow. However, Patent Document 1 does not present the optimum addition position of the desulfurizing agent. . Moreover, in patent document 3, the great force of the hot metal which turns is loaded on an obstruction, the lifetime of an obstruction is very short, and there exists a problem that an obstruction itself will lose | disappear by several desulfurization processes depending on the case. . In other words, the cost associated with the obstacle increases, and there is a risk that the desulfurization processing cost will increase.

  In Patent Document 2, the desulfurizing agent is added by blowing up together with the carrier gas. However, the relationship between the hot metal stirring state and the desulfurizing agent addition position is not clear, and the impeller is decentered to forcibly disturb the rotating flow. The optimum addition position when it is generated cannot be inferred from Patent Document 2.

  The present invention has been made in view of such circumstances, and the object thereof is to use a mechanical stirring type desulfurization apparatus equipped with an impeller, eccentric the impeller with respect to the center of the refining vessel, and When desulfurizing the hot metal while generating forced turbulence, the amount of eccentricity of the impeller to minimize the motor torque load caused by eccentricity while ensuring sufficient forced turbulence in the hot metal rotating flow At the same time, the position of addition of the desulfurizing agent is optimized according to the disturbance of the hot metal rotating flow, and thus the added desulfurizing agent is efficiently dispersed in the hot metal and desulfurized at a higher desulfurization rate than before. It is to provide a hot metal desulfurization method.

  In order to solve the above problems, the hot metal desulfurization method according to the present invention involves immersing an impeller in hot metal contained in a pan-type smelting vessel having a substantially circular flat cross section, and rotating the impeller in a hot metal with the rotation axis thereof being substantially vertical. In the hot metal desulfurization method in which the hot metal is desulfurized by stirring the desulfurizing agent and hot metal added to the hot metal, the rotary shaft has a radius with respect to the center of the refining vessel when the inner diameter of the refining vessel is D In the direction of less than D / 20 in the direction, and the powdered desulfurizing agent is centered on the outer periphery of the impeller blade opposite to the eccentric direction of the impeller, and within a circular range having a radius of D / 4, It is characterized in that the top addition or the top blowing addition is performed together with the carrier gas.

  According to the present invention, since the amount of eccentricity of the impeller is less than 1/20 of the inner diameter of the smelting vessel, it is possible to cause forced turbulence in the rotating flow of the hot metal without significantly increasing the load of the motor torque. In addition, since the powdered desulfurizing agent is added at the optimum position according to this forced disturbance, the added desulfurizing agent is added by the synergistic effect of the forced disturbance of the hot metal rotating flow and the optimal addition position. Efficient dispersion in the hot metal is achieved, and desulfurization treatment is realized at a higher desulfurization rate than conventional. As a result, a reduction in the desulfurization agent basic unit and a reduction in the amount of generated slag associated therewith are realized, and an industrially beneficial effect is brought about.

It is the schematic of the mechanical stirring desulfurization apparatus used by this invention. It is a figure which compares and shows the relationship between a rotation speed and a torque in two levels of the amount of eccentricity zero and 0.045x refinement | purification inner diameter. It is a figure which compares and shows the relationship between a torque and a desulfurization rate in two levels of the amount of eccentricity zero and 0.045 * refinement | purification inner diameter. It is a schematic plan view of the hot metal ladle which shows the addition position of six desulfurization agents in the desulfurization test for investigating desulfurization behavior. It is a figure which compares and shows the desulfurization rate according to the addition position of a desulfurization agent.

  Hereinafter, the present invention will be described in detail.

  In order to clarify the actual eccentric condition of the impeller, the present inventors changed the eccentric amount of the impeller and conducted a desulfurization test in order to clarify the actual eccentric condition of the impeller, using an actual mechanical stirring type desulfurization apparatus having an impeller. Carried out. FIG. 1 shows a schematic diagram of a mechanical stirring desulfurization apparatus used in the desulfurization test.

  In FIG. 1, a hot metal ladle 2 as a pan-type smelting vessel having a substantially circular cross section for containing hot metal 3 discharged from a blast furnace is mounted on a carriage 1 and carried into a mechanical stirring desulfurization apparatus. . The mechanical stirring type desulfurization apparatus is equipped with a refractory impeller 4 that is immersed and buried in a hot metal 3 accommodated in a hot metal ladle 2 and swirls to stir the hot metal 3. The impeller 4 is an elevator device. (Not shown) is moved up and down in a substantially vertical direction, and is rotated about a shaft 4a as a rotation axis by a rotating device (not shown) using an electric motor as a drive source. The impeller 4 only needs to have two or more impeller blades. The outer diameter d of the impeller 4, that is, the width d of the impeller blades is D / 5 to D, where the inner diameter of the hot metal ladle 2 is D. / 2 is sufficient.

  The mechanical stirring type desulfurization apparatus is provided with an upper blowing lance 5 for adding the lime-based desulfurizing agent 7 by blowing it upward toward the hot metal 3 accommodated in the hot metal pan 2. The top blowing lance 5 is connected to a supply device comprising a dispenser 8 containing the powdered lime-based desulfurizing agent 7 and a cutting device 9 for quantitatively cutting out from the dispenser 8. The lime-based desulfurizing agent 7 can be supplied at any timing together with the carrier gas. As the carrier gas, a reducing gas, an inert gas or a non-oxidizing gas is used. In this mechanical stirring type desulfurization apparatus, the lime-based desulfurization agent 7 is added by top blowing from the top blowing lance 5, but the present invention is not limited to the top blowing addition from the top blowing lance 5. The present invention can also be applied to the case where the desulfurizing agent 7 is added over the molten iron 3 from the charging chute.

  Above the hot metal ladle 2, a dust collecting hood 6 is provided to cover the hot metal ladle 2, and exhaust gas and dust during the desulfurization treatment are collected through an exhaust duct (not shown) attached to the dust collecting hood 6 (see FIG. (Not shown). In this case, the shaft 4a and the upper blowing lance 5 of the impeller 4 are configured so as to penetrate the dust collection hood 6 and move up and down.

  The desulfurization treatment of the hot metal 3 in the mechanical stirring desulfurization apparatus configured as described above is performed as follows. That is, the position of the carriage 1 on which the hot metal ladle 2 is mounted is adjusted so that the immersion position of the impeller 4 becomes a predetermined position of the hot metal ladle 2, and the impeller 4 is lowered and immersed in the hot metal 3. If the impeller 4 is immersed in the hot metal 3, the electric motor is driven to start the turning of the impeller 4, and the speed is increased to a predetermined number of revolutions. When the rotational speed of the impeller 4 reaches a predetermined rotational speed, the cutting device 9 is activated and the lime-based desulfurizing agent 7 accommodated in the dispenser 8 is applied to the bath surface of the hot metal 3 via the top blowing lance 5. Add it by spraying it with the carrier gas and desulfurize it. When the addition of a predetermined amount of the lime-based desulfurizing agent 7 is completed and stirring is performed for a predetermined time, the rotation of the impeller 4 is stopped, the impeller 4 is raised, and the desulfurization process is finished.

In the desulfurization test, the radial eccentricity ΔR of the shaft 4a of the impeller 4 with respect to the center of the hot metal ladle 2 is changed within the range of 0.01 × D to 0.20 × D with respect to the inner diameter D of the hot metal ladle 2. After stirring, the torque of the electric motor and the desulfurization behavior of the hot metal 3 were investigated. As the lime-based desulfurizing agent 7, CaO-20 mass% Al ₂ O ₃ having an average particle diameter of 100 μm was used. Table 1 shows the desulfurization treatment conditions.

  Under the condition that the eccentric amount ΔR of the impeller 4 is 0.03 × D or more, compared with the conventional case where the impeller 4 is disposed substantially at the center position of the hot metal ladle 2 (denoted as “center position stirring”), the same rotation speed It was confirmed that the torque in the hot metal 3 increased and the turbulent flow of the hot metal 3 was disturbed.

  However, when the eccentricity ΔR is in the range of 0.05 × D or more, it is 25% or more higher than the torque value that is the standard for maintaining the safety of the equipment, that is, at the time of 120 rpm of the center position stirring that is the standard condition It was found that when the torque was set to the reference value (= 1.0), the torque was 1.25 times or more than that. Even when the rotational speed of the impeller 4 is reduced so that the torque is equivalent to the central position stirring with the eccentricity ΔR being 0.05 × D or more, the equipment is installed at a rate of once per several charges. As a result, the vibration was severe and the stirring was unavoidably stopped. As a result of observation, it was considered that this was caused by the rotating flow of the hot metal 3 generated by the eccentricity having an elliptical shape and the unevenness of the flow resonating with the equipment.

  From these results, it is found that when long-term operation is considered, stable operation is difficult when the amount of eccentricity ΔR is 0.05 × D or more, and the amount of eccentricity ΔR is less than 0.05 × D. I found it necessary. Therefore, the relationship between the torque and the rotational speed, and the torque and the desulfurization behavior was investigated in detail with the eccentricity ΔR as a condition of 0.045 × D.

  FIG. 2 shows the relationship between the rotational speed and torque under the condition that the amount of eccentricity ΔR is zero (center position agitation) and 0.045 × D. As shown in FIG. 2, in the eccentric stirring, the torque at the same rotational speed is higher than in the central position stirring, and the rotational speed dependency is also different. FIG. 3 shows the relationship between torque and desulfurization rate under the condition that the amount of eccentricity ΔR is zero (center position agitation) and 0.045 × D. Here, the desulfurization rate is a percentage of the difference between the sulfur concentration in the hot metal before treatment and the sulfur concentration in the hot metal after treatment to the sulfur concentration in the hot metal before treatment. As shown in FIG. 3, it was found that the desulfurization rate at the same torque is higher in the eccentric stirring than in the center position stirring.

  That is, in the eccentric stirring, the steady rotating flow of the hot metal 3 by the impeller 4 is disturbed, so that the entrainment of the lime-based desulfurizing agent 7 into the hot metal is promoted, which is advantageous for the desulfurization reaction.

  However, since the rotating vortex does not exist at the center of the hot metal ladle 2 in the eccentric stirring, the addition position of the lime-based desulfurizing agent 7 needs to be optimized. Therefore, under the condition that the eccentricity ΔR is 0.045 × D, the installation position of the top blowing lance 5 is changed to the six positions shown in FIG. 4 and the desulfurization behavior when the addition position of the desulfurizing agent is changed. investigated. In this case, a desulfurization test was also conducted in which the top chute lance 5 was not used and the input chute was arranged at six positions shown in FIG. 4 and the lime-based desulfurizing agent 7 was added from the input chute. The basic unit of the lime-based desulfurizing agent 7 was 8 kg / t in all tests.

  The position of 1a shown in FIG. 4 is an intermediate position between the outer periphery of the impeller blade on the side where the impeller 4 is eccentric and the inner wall of the hot metal ladle, and the position of 1b is the position of the outer periphery of the impeller blade on the side where the impeller 4 is eccentric, The position 2a is an intermediate position between the center position of the hot metal ladle 2 opposite to the side where the impeller 4 is eccentric and the inner wall of the hot metal ladle, and the position 2b is an impeller opposite the side where the impeller 4 is eccentric. The position of the blade outer peripheral portion, the position of 3a is an intermediate position between the center of the hot metal ladle and the inner wall of the hot metal ladle on the side orthogonal to the direction in which the impeller 4 is eccentric, and the position of 3b is orthogonal to the direction in which the impeller 4 is eccentric. It is the position of the impeller blade outer peripheral portion on the side.

  The desulfurization rate in each test is shown in FIG. As apparent from FIG. 5, the desulfurization rate is higher in the case of top blowing addition than in the case of top addition, but it has been found that the desulfurization rate varies depending on the addition position. Further, it was found that the optimum addition position of the desulfurizing agent from the viewpoint of the desulfurization rate is near the outer periphery of the impeller blade on the side opposite to the eccentric direction of the impeller 4. However, since a shape change due to melting of the impeller 4 in use also occurs, it is necessary to consider a certain range. As a result of further detailed investigation, the impeller on the side opposite to the eccentric direction of the impeller 4 It was confirmed that a high desulfurization rate could be obtained if it was added within a circular range centered on the outer periphery of the blade and having a radius of D / 4.

  The present invention was made on the basis of the above test results, and the impeller was immersed in hot metal contained in a pan-type smelting vessel having a substantially circular flat cross section, and the impeller was rotated in the hot metal so that the rotation axis thereof was substantially vertical. In the hot metal desulfurization method in which the hot metal is desulfurized by stirring the added desulfurizing agent and hot metal, the rotary shaft is set to D / D in the radial direction with respect to the center of the refining vessel, where D is the inner diameter of the refining vessel. Eccentricity within a range of less than 20 and addition of powdery desulfurization agent in a circular range centering on the outer periphery of the impeller blades opposite to the eccentric direction of the impeller and having a radius of D / 4, or It is characterized by adding top blowing together with the carrier gas.

  A reducing gas, an inert gas, or a non-oxidizing gas is used as a carrier gas when the lime-based desulfurizing agent 7 is blown from the top blowing lance 5. Examples of the reducing gas include hydrocarbon gas, examples of the inert gas include argon gas, and examples of the non-oxidizing gas include nitrogen gas.

As the lime-based desulfurizing agent 7, any substance can be used as long as it contains lime (CaO) as a main component, in other words, contains 50% by mass or more of CaO. For example, quick lime or limestone may be used alone or mixed with Al ₂ O ₃ or CaF ₂ as a hatching accelerator, and dolomite (CaO-MgO) may also be used as a lime-based desulfurizing agent. 7 can be used.

  As described above, according to the present invention, the eccentric amount ΔR of the impeller 4 is set to be less than 1/20 of the inner diameter (D) of the pan-type refining vessel such as the hot metal ladle 2, so that the load of the motor torque is greatly increased. Therefore, forced turbulence can be generated in the rotating flow of the hot metal 3, and the powdery lime-based desulfurization agent 7 is added at an optimum position corresponding to the forced turbulence. Due to the synergistic effect of the forced disturbance of the rotating flow and the optimum addition position, it is possible to efficiently disperse the added lime-based desulfurization agent 7 in the hot metal, and desulfurization treatment can be performed at a higher desulfurization rate than before. Realized.

Using the mechanical stirring type desulfurization apparatus shown in FIG. 1, CaO-20 mass% Al ₂ O ₃ having an average particle diameter of 100 μm is used as a lime-based desulfurization agent, and desulfurization treatment is performed for a long period of time for each of the levels 1 to 4. A test operation (30 charges) was performed. Table 2 shows the operating conditions at each level.

  Level 1 is an operation method in which an impeller is arranged at substantially the center position of the hot metal ladle, and a lime-based desulfurizing agent is added to the middle position between the hot metal ladle and the hot metal ladle side wall through a charging chute. It is the prior art example for comparing with invention.

  Level 2 is that the impeller is decentered as an eccentric amount ΔR = 0.045 × D, and the lime system is placed through a charging chute at an intermediate position between the center position of the hot metal ladle opposite to the eccentric side of the impeller and the inner wall of the hot metal ladle. This is an operation method in which a desulfurizing agent is added on top, and is an example of the present invention. In level 3, the impeller is decentered as an eccentric amount ΔR = 0.045 × D, and a lime-based desulfurizing agent is added to the position of the outer periphery of the impeller blade on the side opposite to the eccentric side of the impeller via a charging chute. This is an operation method and is an example of the present invention.

  In level 4, the impeller is decentered as an eccentric amount ΔR = 0.045 × D, and the lime-based desulfurizing agent is introduced into the nitrogen at the position of the outer periphery of the impeller blade opposite to the eccentric side of the impeller through the top blowing lance. This is an operation method in which top blowing is added together with gas, and is an example of the present invention. Table 3 shows the average value of sulfur concentration in the hot metal before and after the desulfurization treatment and the desulfurizing agent basic unit at each level.

  In level 2, compared with level 1, although the basic unit of the desulfurizing agent was the same, the sulfur concentration in the hot metal after the treatment was greatly reduced. Further, at level 3 where the desulfurizing agent addition position was the most preferable position, low sulfurization equivalent to level 2 was achieved with a small amount of desulfurizing agent basic unit. Furthermore, at level 4, by adding the desulfurization agent by top blowing using the top blowing lance, low sulfidation with a lower desulfurization agent basic unit than level 3 was realized.

1 cart 2 hot metal ladle 3 hot metal 4 impeller 5 top blowing lance 6 dust collecting hood 7 lime-based desulfurizing agent 8 dispenser 9 cutting device

Claims (1)

The impeller is immersed in the hot metal contained in a pan-type smelting vessel having a substantially circular flat cross section, and the impeller is rotated in the hot metal with the rotation axis of the impeller almost vertical, and the desulfurizing agent and hot metal added to the hot metal are stirred to form the hot metal. In the hot metal desulfurization method, when the inner diameter of the refining vessel is D, the rotational axis is in the range of 0.03 × D or more and less than 0.05 × D in the radial direction with respect to the center of the refining vessel. While decentering, the powdered desulfurizing agent is applied to the agitated hot metal bath surface in a circular range having a radius of D / 4 centered on the outer periphery of the impeller blade opposite to the direction of eccentricity of the impeller. The hot metal desulfurization method, wherein the addition is carried out or the top blowing is added together with the conveying gas.

Images