JP5790230B2 - Hot metal desulfurization method - Google Patents

Description

  The present invention relates to a hot metal desulfurization method using a mechanical stirring desulfurization apparatus, and more particularly to a method for efficiently desulfurizing hot metal by promoting a desulfurization reaction.

  The hot metal discharged from the blast furnace contains high concentrations of phosphorus (element symbol: P) and sulfur (element symbol: S), which adversely affect steel quality, and various technologies have been developed to remove them. Has been. For example, in today's steel refining process, a method of previously removing phosphorus and sulfur contained in hot metal prior to decarburization refining in a converter, so-called “hot metal pretreatment” is generally performed. . Among these, the hot metal desulfurization treatment holds the hot metal in a refining vessel having a substantially circular horizontal cross section, adds a desulfurizing agent onto the hot metal, and 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 immersed in hot metal and rotated, and the hot metal and the desulfurizing agent are stirred to perform desulfurization is widely performed. In this mechanical stirring desulfurization method, an inexpensive lime-based desulfurization agent mainly composed of CaO (lime) is used.

  In the desulfurization reaction using this lime-based desulfurization agent, it has been found that increasing the reaction interface area between the hot metal and the desulfurization agent is effective for increasing the desulfurization reaction rate. Desulfurization reaction efficiency can be improved by reducing the particle size of the agent. However, in the mechanical stirring type desulfurization method in an actual machine, it is common to cut out the desulfurization agent from the hopper and add the desulfurization agent over the treatment vessel such as a hot metal ladle installed above the treatment vessel. Yes, adding fine-grained desulfurizing agent in this way increases the amount of desulfurizing agent that scatters and soars in the updraft, reducing the yield of desulfurizing agent addition, and in the end, an efficient desulfurization treatment is obtained. Absent. In addition, the scattered desulfurizing agent accumulates as dust, which causes a problem that dust treatment frequently occurs.

  Moreover, the interfacial tension between CaO powder, which is the main component of the lime-based desulfurizing agent, and molten iron is 1.75 N / m, and CaO has the property of being difficult to wet with molten iron. For this reason, the CaO of the powder added to the hot metal aggregates with each other, and the CaO inside the aggregate remains unreacted, so that there is a problem that the effect of refining the desulfurizing agent cannot be obtained.

  In order to solve this problem, Patent Document 1 discloses, in a hot metal desulfurization method using a mechanical stirring desulfurization apparatus, a desulfurizing agent is placed on the bath surface of the hot metal being stirred by an impeller through an upper blowing lance. It has been proposed to perform desulfurization treatment by adding top blowing with a carrier gas. According to Patent Document 1, a fine-grain desulfurization agent having excellent reactivity is added together with a carrier gas, so that scattering during the 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. Patent Document 1 describes that the addition of the desulfurizing agent from the top chute and the top blowing lance can be used in combination.

  On the other hand, there are many unreacted portions of dust and desulfurization slag generated in the desulfurization treatment, and therefore, a method of reusing them in the desulfurization treatment process has been proposed. For example, Patent Document 2 proposes a technique for reusing dust generated in hot metal pretreatment by a mechanical stirring desulfurization method, and Non-Patent Document 1 discloses mechanical stirring of desulfurized slag generated in a desulfurization process by an injection method. A technique for reusing in the desulfurization method has been proposed. In addition, desulfurization slag is slag which mainly produces | generates a desulfurization agent produced | generated after a desulfurization process.

JP 2005-179690 A JP 2006-291334 A

Sumitomo Metals, vol. 45-3 (1993). p. 52-58

  The present inventors have confirmed that by using the hot metal desulfurization method proposed in Patent Document 1, an efficient desulfurization treatment is possible using a lime-based desulfurization agent. In particular, it has been confirmed that an efficient desulfurization treatment can be achieved by using both desulfurization agent top addition and top blowing addition in combination. In this case, it was confirmed that the desulfurization agent added on top can be sufficiently desulfurized even with dust and desulfurization slag generated in the desulfurization treatment. However, it was confirmed that when the addition of the desulfurization agent and the top blowing addition were used in combination, the desulfurization efficiency deteriorated and the efficient desulfurization treatment could not be obtained if the amount of the desulfurization agent added above was increased. In this regard, Patent Document 1 does not describe anything.

  The present invention has been made in view of the above circumstances, and the object of the present invention is to add the top addition from the charging chute and the top blowing from the top blowing lance to the hot metal being stirred by the mechanical stirring type desulfurization apparatus. When supplying the lime-based desulfurizing agent in combination with the hot metal and desulfurizing the molten iron, even if the amount of the desulfurizing agent added on the top increases, it is possible to allow the desulfurizing agent added to the top blowing to enter the molten iron with a high addition yield. It is possible to provide a hot metal desulfurization method that can stably and efficiently perform desulfurization treatment.

The gist of the present invention for solving the above problems is as follows.
(1) A part of the lime-based desulfurization agent necessary for desulfurizing the hot metal together with the conveying gas is added to the hot metal bath surface being stirred by the impeller, and the remaining lime-based material is added. In the hot metal desulfurization method using the mechanical stirring type desulfurization apparatus, the desulfurization agent is placed on the hot metal bath surface and desulfurized to remove the desulfurization agent from the upper blow lance to the hot metal bath surface of the lime-based desulfurization agent. The hot metal desulfurization method is characterized in that the particle speed at the time of collision of the hot metal is controlled to be equal to or higher than the critical particle speed calculated by the following equation (1) according to the amount of the lime-based desulfurization agent added on top. .
C = −0.000093 × R ² + 0.047 × R + 17 (1)
However, in the formula (1), C is a critical particle velocity (m / sec), R is an addition amount per unit bath area (kg / m ² ) of the lime-based desulfurizing agent added on the hot metal bath surface. ).
(2) The method for desulfurizing hot metal as described in (1) above, wherein a lime-containing substance that is secondarily generated in the iron making process is used as a lime-based desulfurizing agent added on the hot metal bath surface.
(3) The desulfurization slag generated by the desulfurization treatment of the hot metal using the lime-based desulfurization agent in the mechanical stirring desulfurization apparatus is used as the lime-based desulfurization agent to be added on the hot metal bath surface. The hot metal desulfurization method according to (1).
(4) The ratio of the lime-based desulfurizing agent to be added on top is 80% by mass or less of the total lime-based desulfurizing agent to be added, any one of (1) to (3) above The hot metal desulfurization method as described.

  According to the present invention, the amount of the lime-based desulfurizing agent added on top when the hot metal is desulfurized using the mechanically added desulfurization apparatus and the top addition and top blowing addition of the lime-based desulfurization agent is added. The lime-based desulfurizing agent added by top blowing at an optimum speed according to the temperature collides with the hot metal bath surface, so that the desulfurizing agent added by top blowing can stably enter and disperse into the hot metal bath and accelerate the desulfurization reaction. Thus, the desired desulfurization treatment can be performed with a small amount of desulfurization agent. As a result, a reduction in the desulfurization agent basic unit and a reduction in the amount of generated slag associated therewith are achieved, and an industrially beneficial effect is brought about.

It is a schematic diagram which shows the form of the gas jet ejected from a nozzle. It is a schematic diagram which shows the flow velocity distribution of the gas jet ejected from a nozzle. 1 is a schematic side view of a mechanical stirring desulfurization apparatus embodying the present invention. It is a figure which shows the relationship between the particle | grain speed | rate at the time of the collision with the hot metal bath surface of the top blowing desulfurization agent when not adding an upper desulfurization agent, and a desulfurization rate. It is a figure which shows the relationship between the particle velocity at the time of the collision with the hot metal bath surface of a top blowing desulfurization agent when the addition amount of a top desulfurization agent is 74 kg / m < ² >, and a desulfurization rate. It is a figure which shows the relationship between the particle velocity at the time of the collision with the hot metal bath surface of a top blowing desulfurization agent when the addition amount of a top desulfurization agent is 250 kg / m < ² >, and a desulfurization rate. It is a figure which shows the relationship between the addition amount (R) per unit bath area in the hot metal bath surface of the desulfurization agent added on top, and a critical particle velocity (C).

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

  The present inventors have studied various means for efficiently desulfurizing hot metal in hot metal desulfurization treatment using a mechanical stirring desulfurization apparatus. As a result, the desulfurization efficiency can be remarkably improved. Therefore, the desulfurization is performed by combining the addition of the lime-based desulfurization agent from the addition chute and the addition of the upper blowing from the top blowing lance disclosed in Patent Document 1. Confirmed that the method to do is excellent.

  In this case, as the lime-based desulfurization agent, it is possible to use desulfurization slag generated in the desulfurization treatment of hot metal using the lime-based desulfurization agent in a mechanical stirring type desulfurization device. Since it was found that it was most advantageous when comprehensively judged, basically, desulfurization slag was reused as a lime-based desulfurization agent.

  However, from the test results in the actual machine, it was understood that the desulfurization efficiency deteriorates as the desulfurization agent added on top is increased even under the condition that the desulfurization agent added by top blowing is a constant amount. Therefore, as a cause of this, desulfurization slag has more agglomerates than lime (quick lime) that is normally used as a desulfurization agent, and even if the jet flow from the top blowing lance collides, Based on the assumption that the desulfurization slag placed on top prevents the desulfurization agent that is added by top blowing from penetrating and dispersing into the hot metal bath, the top addition and top blowing addition of the lime-based desulfurization agent are performed in the actual machine. When desulfurization was performed in combination, the particle velocity at the time of collision of the desulfurizing agent added by top blowing to the hot metal bath surface was changed, and a test was conducted in which the ease of entering the hot metal bath was changed.

  The particle velocity at the time of collision of the desulfurizing agent added by top blowing through a nozzle such as a Laval nozzle or a straight nozzle installed on the top blowing lance against the hot metal bath surface was calculated using the following method. That is, the particle velocity from the nozzle outlet to the hot metal bath surface at rest using the following equation (8) which is an equation of acceleration applied to particles derived from the following equations (2) to (7-2): The particle velocity at the time of collision of the desulfurizing agent with the hot metal bath surface was obtained by calculating the change in 1 mm.

However, the following assumptions were applied for calculation.
(1) The particle velocity U _Po of the desulfurizing agent at the nozzle outlet of the top blowing lance is equal to the gas flow velocity U _go at the nozzle outlet.
(2) As the particle size d _P of the desulfurizing agent added by top blowing, the mass average diameter of the desulfurizing agent added by top blowing is used.
(3) The gas density ρ _g uses a value of 25 ° C.
(4) The gas viscosity η _g uses a value of 25 ° C.
(5) At the nozzle outlet of the upper blowing lance, as shown in FIG. 1, a region 15 (“" where the flow velocity U _g of the gas jet 14 ejected from the nozzle 13 is maintained at the flow velocity U _go at the nozzle outlet 13a. A potential core ”is formed, and a turbulent region 16 is formed downstream of the potential core 15. The length of the potential core 15 is six times the nozzle outlet diameter (= D) regardless of the nozzle outlet diameter. The gas flow velocity at the potential core 15 is expressed by the equation (7-1), and the gas flow velocity U _g on the lance axis in the turbulent flow region 16 is expressed by the equation (7-2). A schematic diagram of the distribution of the gas flow velocity U _g of the gas jet 14 ejected from the nozzle 13 is shown in FIG.

F = m × a (2)
_{F = m × g-C d} × (π / 4) × d P 2 × (1/2) × ρ g × (U g -U P) 2 ... (3)
C _d = 24 × (1 + 0.125 × Re ^0.72 ) / Re (Re <500) (4-1)
C _d = 0.44 (Re ≧ 500) (4-2)
_{Re = ρ g × (U P} -U g) × d P / η ... (5)
m = (1/6) × π × d _P ³ × ρ _P (6)
U _g = U _go (6D / L ≧ 1) (7-1)
U _g = U _go × (6D / L) (6D / L <1) (7-2)
_{a = g- [C d × (} π / 4) × d P 2 × (1/2) × ρ g × (U g -U P) 2] / m ... (8)
However, in the formulas (2) to (8), F is force (N), m is mass (kg) of desulfurizing agent particles, a is acceleration (m / sec ² ), and g is gravitational acceleration (m / sec ^2). ), C _d is the resistance coefficient (−), π is the circumference, d _P is the particle size (m) of the desulfurizing agent added by top blowing, ρ _g is the gas density (kg / m ³ ), and U _g is the gas flow rate (m / sec), U _P desulfurizing agent particle velocity (m / sec), Re is Reynolds number, eta is the viscosity of the gas (Pa · sec), the density of [rho _P desulfurizing agent particle (kg / m ³⁾ , U _go is the gas flow velocity (m / sec) at the nozzle outlet, D is the nozzle outlet diameter (m) of the upper blowing lance, and L is the distance (m) from the nozzle outlet of the upper blowing lance.

That is, (2) to (7-2) by using the acceleration a which is determined by it (8) based on the equation, calculate the change in particle velocity U _P from the nozzle outlet to the molten iron bath surface at rest in 1mm increments and, the particle velocity U _P calculated in the position corresponding to the lance height L ₀ during operation (L = L _0), obtained as particle velocity at the time of collision of the molten iron bath surface of the desulfurization agent. Here, as shown in FIG. 2, the lance height L ₀ is the distance from the outlet of the nozzle installed on the upper blowing lance to the hot metal bath surface.

As a result of the test, it has been found that the desulfurization rate increases as the particle velocity at the time of collision of the desulfurizing agent with the hot metal bath surface (hereinafter also simply referred to as “particle velocity at the time of collision”) increases. However, when the particle velocity at the time of collision of the desulfurizing agent exceeds a certain value according to the amount of desulfurizing agent added on top, the desulfurization rate is almost saturated, and the particle velocity at the time of collision of the desulfurizing agent is further exceeded. It was found that the desulfurization rate does not become so high even if the slag is increased. In the present invention, the particle velocity at the time of collision when the desulfurization rate is saturated is defined as “critical particle velocity”. From further investigation results, the critical particle velocity is affected by the amount of lime-based desulfurizing agent added on the hot metal bath surface per unit bath area and expressed by the relationship of the following equation (1). I found out.
C = −0.000093 × R ² + 0.047 × R + 17 (1)
However, in the formula (1), C is a critical particle velocity (m / sec), R is an addition amount per unit bath area (kg / m ² ) of the lime-based desulfurizing agent added on the hot metal bath surface. ).

  That is, according to the addition amount (R) per unit bath area on the hot metal bath surface of the lime-based desulfurizing agent added on top, the upper is at a speed equal to or higher than the critical particle speed (C) calculated from the equation (1) It has been found that a high desulfurization rate can be obtained by colliding the desulfurizing agent added by blowing with the hot metal bath surface. This is to increase the particle velocity at the time of collision of the lime-based desulfurizing agent added to the top blowing to a critical particle velocity (C) or higher, so that the top-blown desulfurizing agent penetrates the hot metal by the lime-based desulfurizing agent placed on top. By overcoming the inhibitory action, the penetration and dispersion of the desulfurizing agent blown into the hot metal is activated.

  The present invention is based on these findings, and uses a mechanical stirring type desulfurization apparatus to desulfurize hot metal in combination with the addition of the lime-based desulfurization agent from the top chute and the top blowing lance. In the treatment, the particle speed at the time of collision of the lime-based desulfurizing agent added from the top blowing lance to the hot metal bath surface is determined according to the amount (R) of the lime-based desulfurizing agent added above ( Control is performed so as to be equal to or higher than the critical particle velocity (C) calculated by the equation (1).

  Next, the hot metal desulfurization method according to the present invention will be described with reference to the drawings.

  FIG. 3 is a schematic side view of a mechanical stirring desulfurization apparatus embodying the present invention. In FIG. 3, a hot metal ladle 2 containing hot metal 3 discharged from a blast furnace is mounted on a carriage 1 and is mechanically stirred. It is carried into the desulfurization equipment. 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). Further, in the mechanical stirring type desulfurization apparatus, an upper blowing lance 5 for adding the lime-based desulfurizing agent 6 by blowing it upward toward the hot metal 3 accommodated in the hot metal ladle 2, and the lime-based desulfurizing agent 6 are added. 2 and a charging chute 10 for adding to the hot metal 3 accommodated in the hot metal 3 is installed. The upper blowing lance 5 is installed facing substantially downward in the vertical direction.

  The top blowing lance 5 is connected to a supply device including a dispenser 7 that contains the powdered lime-based desulfurizing agent 6 and a cutting device 8 for quantitatively cutting out from the dispenser 7. The structure is such that the powdery lime-based desulfurization agent 6 can be supplied together with the transfer gas from a nozzle (not shown) such as a Laval nozzle or a straight nozzle that is installed. In the case of injection through a Laval nozzle, the injection speed at the nozzle outlet can be arbitrarily adjusted from a low speed range to a subsonic speed range, and further to a supersonic speed range, so it is preferable to use a Laval nozzle.

  As the carrier gas for the lime-based desulfurizing agent 6, a reducing gas, an inert gas, or a non-oxidizing gas is used. On the other hand, the input chute 10 is connected to a supply device including a hopper 11 containing the powdery or fine lime-based desulfurization agent 6 and a rotary feeder 12 for quantitatively cutting out from the hopper 11. The powdery or fine lime-based desulfurization agent 6 can be supplied at an arbitrary timing. As the lime-based desulfurization agent 6 accommodated in the hopper 11, it is preferable to use desulfurization slag generated by hot metal desulfurization treatment using a lime-based desulfurization agent in a mechanical stirring desulfurization apparatus as described above.

  Further, a dust collection hood 9 that can be moved up and down is provided above the hot metal ladle 2 to cover the hot metal ladle 2, and treatment is performed via an exhaust duct (not shown) attached to the dust collection hood 9. The exhaust gas and dust inside are sucked into a dust collector (not shown). In this case, the shaft 4 a of the impeller 4, the upper blowing lance 5, and the charging chute 10 are configured to penetrate the dust collection hood 9 and move up and down.

  The position of the carriage 1 on which the hot metal ladle 2 is mounted is adjusted so that the position of the impeller 4 is substantially at the center of the hot metal ladle 2, and then the impeller 4 is lowered and immersed in the hot metal 3. 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 rotational speed.

  When the rotational speed of the impeller 4 reaches a predetermined rotational speed, the rotary feeder 12 is activated, and the lime-based desulfurizing agent 6 accommodated in the hopper 11 is placed on the bath surface of the hot metal 3 via the charging chute 10. Add on top. At the same time as or after the start of the charging of the lime-based desulfurizing agent 6 from the charging chute 10, or after the charging of the lime-based desulfurizing agent 6 from the charging chute 10 is completed, the cutting device 8 is activated and stored in the dispenser 7. The lime-based desulfurizing agent 6 is added by spraying from the top blowing lance 5 toward the bath surface of the hot metal 3 together with the carrier gas.

In this case, the input amount of the lime-based desulfurizing agent 6 from the input chute 10 is grasped in advance, and the unit on the hot metal bath surface of the lime-based desulfurizing agent 6 added from the input amount from the input chute 10 is determined. The addition amount per bath area (R: kg / m ² ) is obtained, and the obtained addition amount (R) is substituted into the above equation (1) to calculate the critical particle velocity (C: m / sec). Then, the flow rate of the conveying gas and / or the particle velocity at the time of collision of the lime-based desulfurizing agent 6 sprayed from the top blowing lance 5 on the hot metal bath surface is equal to or higher than the calculated critical particle velocity (C). Adjust pressure. Increasing the flow rate and back pressure of the carrier gas will increase the particle velocity at the time of collision. As described above, the particle velocity at the time of collision of the lime-based desulfurizing agent 6 injected from the top blowing lance 5 with the hot metal bath surface is the hot metal bath at rest from the nozzle outlet using the acceleration a determined by the equation (8). The change in the particle velocity up to the surface is calculated in 1 mm increments, and the particle velocity calculated at the position corresponding to the lance height L ₀ during operation (L = L ₀ ) is applied to the hot metal bath surface of the lime-based desulfurizing agent 6. Determine the particle velocity at impact.

  When the top addition and top blowing addition of a predetermined amount of the lime-based desulfurizing agent 6 are completed and stirring is performed for a predetermined time, the rotation speed of the impeller 4 is decreased and stopped. 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 (referred to as “desulfurization slag”) floats to cover the hot metal surface, and the desulfurization process of the hot metal 3 is finished in a stationary state. After the desulfurization treatment, the generated desulfurization slag is discharged from the hot metal ladle 2 and conveyed to the next refining process. The desulfurized slag is recovered and used as the lime-based desulfurizing agent 6 to be charged from the charging chute 10 in the subsequent desulfurization process.

As the lime-based desulfurizing agent 6 to be added by top blowing, quick lime (CaO), dolomite (MgCO ₃ · CaCO ₃ ), slaked lime (Ca (OH) ₂ ), limestone (CaCO ₃ ) and the like can be used. Further, a mixture of alumina (Al ₂ O ₃ ) or fluorite (CaF ₂ ) that functions as a CaO hatching accelerator can be used. Of course, it is also possible to use them as the lime-based desulfurizing agent 6 to be added on top.

  It is preferable that the lime-based desulfurizing agent 6 added on top is 80% by mass or less of the total lime-based desulfurizing agent added in the desulfurization treatment. This is because if the lime-based desulfurizing agent 6 to be added on top exceeds 80% by mass of the total lime-based desulfurizing agent, the amount of desulfurizing agent added by top blowing decreases and the effect of adding the desulfurizing agent by top blowing decreases. .

  As described above, according to the present invention, when the hot metal 3 is desulfurized using the mechanical stirring type desulfurization apparatus and the top addition and the top blowing addition of the lime-based desulfurization agent 6 are combined, the top addition is performed. Since the lime-based desulfurizing agent 6 added by top blowing is made to collide with the hot metal bath surface at an optimum rate according to the amount of lime-based desulfurizing agent added, the penetration and dispersion of the desulfurized agent added by top blowing into the hot metal bath is prevented. It occurs stably, the desulfurization reaction is accelerated, and the desired desulfurization treatment can be performed with a small amount of desulfurization agent.

  Particle velocity at the time of collision of the desulfurizing agent sprayed from the top blowing lance against the hot metal bath surface using the mechanical stirring type desulfurization apparatus shown in FIG. 3, using quick lime powder as the top blowing desulfurization agent, desulfurization slag as the top desulfurization agent A total of 9 charges of hot metal desulfurization treatment test was conducted.

  Nitrogen gas was used as the carrier gas for the desulfurizing agent to be added by top blowing, and the impeller had four blades and the blades had no inclination. The chemical components of the hot metal used were C: 3.5 to 5.0% by mass, Si: 0.1 to 0.3% by mass, P: 0.02 to 0.15% by mass, S: 0.020 to The hot metal temperature was in the range of 1200 to 1350 ° C. at 0.039 mass%. In the desulfurization treatment, a hot metal ladle capable of treating 200 to 500 tons of hot metal was used as a treatment container, and about 300 tons of hot metal was desulfurized. The desulfurization treatment time was fixed at 15 minutes from the start of the addition of the desulfurizing agent. The desulfurization slag added on top was set at three levels of 0 kg, 1190 kg, and 4000 kg per charge, and the quick-lime added quick lime was fixed at 1000 kg per charge.

  A sample was taken from the hot metal before and after the desulfurization treatment, and the desulfurization rate was investigated. Here, the desulfurization rate is a value defined by the following equation (9).

  Table 1 shows the operating conditions and the desulfurization rate of each desulfurization treatment test. The particle velocity shown in Table 1 is the velocity when colliding with the hot metal bath surface, and the particle velocity = 0 is a condition in which the desulfurizing agent is naturally dropped from the top blowing lance. In the remarks column of Table 1, “Example of the present invention” is displayed for tests within the scope of the present invention, and “Comparative example” is displayed otherwise.

  As shown in Table 1, it was confirmed that the desulfurization rate was increased as the particle velocity increased during the collision of the top blowing desulfurizing agent. The relationship between the desulfurization rate and the particle velocity at the time of collision of the top blowing desulfurizing agent is shown in FIGS. As shown in FIGS. 4 to 6, the desulfurization rate increases as the particle velocity at the time of collision of the top blowing desulfurizing agent increases, but the particle velocity at the time of collision of the top blowing desulfurizing agent with the hot metal bath surface exceeds a certain value. As a result, it was confirmed that the desulfurization rate was saturated and the desulfurization rate was not improved much even if the particle velocity at the time of collision was further increased. As described above, in the present invention, the particle velocity at the time of collision when the desulfurization rate is saturated is defined as the critical particle velocity.

As shown in FIG. 4, when the addition amount (R) per unit bath area on the hot metal bath surface of the desulfurizing agent added above is 0 kg / m ² , the critical particle velocity (C) is 17 m / sec. As shown in FIG. 5, when the addition amount (R) is 74 kg / m ² , the critical particle velocity (C) becomes 20 m / sec, and as shown in FIG. 6, the critical amount velocity (C) becomes critical when the addition amount (R) is 250 kg / m ^2. The particle velocity (C) was found to be 23 m / sec.

  FIG. 7 shows the relationship between the amount of addition (R) per unit bath area on the hot metal bath surface of the desulfurizing agent added on top and the critical particle velocity (C) obtained by FIGS. When the relationship between the addition amount (R) and the critical particle velocity (C) is obtained by a regression equation based on FIG. 7, the above-described equation (1) is determined.

  Therefore, the particle speed at the time of collision of the desulfurizing agent added by top blowing to the hot metal bath surface is determined in accordance with the addition amount (R) per unit bath area of the desulfurizing agent added on the hot metal bath surface. By setting the particle speed (C) or higher, a high desulfurization rate can be stably obtained.

  As shown in FIGS. 4 to 6, the desulfurization rate is high when the particle velocity at the time of collision of the desulfurizing agent is about 50 m / sec. However, if it is excessively fast, the desulfurizing agent added on top is blown off and desulfurized. There is no need to make it too fast, as the rate may drop. Too much speed is not preferable from the viewpoint of energy consumption.

DESCRIPTION OF SYMBOLS 1 Bogie 2 Hot metal ladle 3 Hot metal 4 Impeller 5 Top blowing lance 6 Lime-based desulfurization agent 7 Dispenser 8 Cutting device 9 Dust collection hood 10 Input chute 11 Hopper 12 Rotary feeder 13 Nozzle 14 Gas jet 15 Potential core 16 Turbulence area

Claims (4)

A part of the lime-based desulfurization agent necessary for desulfurizing the hot metal together with the carrier gas is blown over the hot metal bath surface stirred by the impeller, and the remaining lime-based desulfurization agent is added. In the hot metal desulfurization method using a mechanical stirring desulfurization apparatus, the hot metal is added on the hot metal bath surface and desulfurized, and the following (1) wherein the calculated critical particle velocity, to control the particle velocity at the time of collision of the molten iron bath surface lime desulfurization agent which top blowing added from the top lance, above the critical particle velocity was determined using the formula, Hot metal desulfurization method.
C = −0.000093 × R ² + 0.047 × R + 17 (1)
However, in the formula (1), C is a critical particle velocity (m / sec), R is an addition amount per unit bath area (kg / m ² ) of the lime-based desulfurizing agent added on the hot metal bath surface. ).   2. The hot metal desulfurization method according to claim 1, wherein a lime-containing substance that is secondarily generated in the iron making process is used as a lime-based desulfurization agent that is added on the hot metal bath surface. 3.   2. The desulfurization slag generated by desulfurization treatment of hot metal using a lime-based desulfurization agent in a mechanical stirring type desulfurization apparatus is used as the lime-based desulfurization agent added on the hot metal bath surface. The hot metal desulfurization method as described.   The desulfurization of hot metal according to any one of claims 1 to 3, wherein a ratio of the lime-based desulfurizing agent to be added on top is 80% by mass or less of the total lime-based desulfurizing agent to be added. Method.

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