JP6773142B2 - Dephosphorization treatment method - Google Patents

Description

The present invention relates to a dephosphorization treatment method that is particularly suitable for use in melting ultra-low phosphorus hot metal at low cost and with high efficiency while suppressing spitting.

In recent years, the demand for steel materials has become more sophisticated, and the demand for low-phosphorus steel has increased. At present, the dephosphorization treatment of hot metal is widely and generally performed by a method of treating at a low temperature condition of a hot metal stage which is thermodynamically advantageous. An upper bottom blown converter is suitable as a hot metal dephosphorization device. This is because, as an oxidant required for dephosphorization, gaseous oxygen, which has less heat loss than a solid oxidant, can be sprayed onto the hot metal from the top-blown lance at high speed.

Since dephosphorization of hot metal is carried out under low temperature conditions at the hot metal stage, it is important to promote the slag formation of CaO used as a dephosphorizing agent. The use of fluorite (CaF ₂ ) is effective for slagging CaO, which has a very high melting point of 2300 ° C or higher, but when fluorite is used, the slag generated by the slagging of CaO is fluorine (). Since it contains F), it has a great adverse effect such that the reuse destination of slag is significantly restricted. Therefore, a method for promoting CaO slag without using fluorite has been developed.

As a method for that, for example, as a method for efficiently slagging CaO to melt low-phosphorus steel without using fluorite or calcium ferrite, CaO powder, Al ₂ O ₃ powder and Fe ₂ O _{3 are used} from the top-blown lance. A method of spraying a mixed powder containing powder on a hot metal bath surface together with an oxygen gas jet is disclosed (see Patent Document 1). In this method, Al ₂ O ₃ and Fe ₂ O ₃ react with CaO to easily form a low melting point CaO-Al ₂ O _3- FeO melt, and the dephosphorization reaction proceeds extremely efficiently.

However, in this method, the top-blown mixed powder is deeply penetrated into the hot metal bath to increase the dephosphorization utilization efficiency of the CaO-Al ₂ O _3- FeO melt and reduce the [P] in the hot metal to an extremely low concentration. Increasing the dynamic pressure of the blown jet increases spitting, which causes a problem that the amount of metal adhering to the inside of the furnace increases.

Further, a CaO-containing cover slag was formed in the first half of the blowing, and the basicity (weight ratio: CaO / SiO ₂ ) of the cover slag was 0.4 to 1.5, and then CaO powder and Al ₂ O ₃ powder and A hot metal dephosphorization method in which a mixed powder of Fe ₂ O ₃ powder is top-blown is disclosed (see Patent Document 2). According to this method, the amount of spitting can be reduced by forming a cover slag having a low melting point in the first half of dephosphorization.

However, since the first half of hot metal dephosphorization and blowing changes at a low temperature, if the mass CaO is added so that the charge basicity is particularly 1.3 to 1.5, the mass CaO cannot be completely dissolved in the first half of the blowing and dephosphorization. Utilization efficiency will be low. In addition, undissolved CaO remains in the slag even after the hot metal dephosphorization treatment, which causes a problem when the dephosphorized slag is effectively used for roadbed materials and the like. In order to avoid this, when the cover slag is formed by using calcium ferrite having a low melting point, there arises a problem that it is costly.

When the ultra-low phosphorus hot metal is melted while suppressing spitting as described above, the dephosphorization treatment cannot be performed at low cost and with high efficiency.

Japanese Patent No. 3525766 Japanese Patent No. 3678433

In view of the above-mentioned problems, an object of the present invention is to provide a dephosphorization treatment method capable of melting ultra-low phosphorus hot metal at low cost and with high efficiency while suppressing spitting.

In the plume region formed on the melting surface by blowing the bottom blowing gas from the bottom blowing tuyere, the present inventors apply the dynamic pressure of the jet because the mixed powder permeates into the hot metal due to the bubbles of the bottom blowing gas. We focused on the fact that the dephosphorization process can be performed efficiently without raising the amount. Therefore, in completing the present invention, hot metal is charged into a converter having an upper bottom blower, and either CaO powder or CaCO ₃ powder is charged together with oxygen gas from a top blower lance having 4 to 6 nozzles. A mixed powder of both and Al ₂ O ₃ powder was sprayed onto the hot metal bath surface, and gas was blown from the same number of bottom blowing tuyere as the top blowing nozzle, and the in-core metal adhesion behavior and dephosphorization behavior by spitting were investigated. As a result, by properly controlling the geometrical positional relationship between the top-blown jet and the plume region, adhesion of the metal in the furnace due to spitting is avoided and high efficiency, that is, the efficiency of CaO dephosphorization utilization is improved. We have found a dephosphorization treatment device capable of melting ultra-low phosphorus hot metal ([C] ≧ 3.2% by mass, [P] ≦ 0.015% by mass) and a melting method using the device.

The present invention is as follows.
(1) The converter, a top-blowing lance that blows a powder dephosphorizing agent and oxygen gas into the converter, an oxygen supply device that supplies the oxygen gas to the top-blowing lance, and the top-blowing lance. A powder supply device for supplying a powder dephosphorizing agent is provided, and a plurality of nozzles for ejecting the powder dephosphorizing agent and the oxygen gas are arranged on the lower end surface of the top blowing lance, and the furnace of the converter. It is a dephosphorization treatment method using a dephosphorization treatment apparatus in which the same number of bottom blowing tuyere as the nozzles is arranged on the bottom.
The hot metal is held in the converter, and the position U of the intersection of the central axis of the top blowing jet ejected from the nozzle and the bath surface of the hot metal, the straight line drawn vertically upward from the position of the bottom blowing tuyere, and the above. All the sets of nozzle and bottom blowing tuyere that minimize the distance from the position S of the intersection of the hot metal with the bath surface (the length of the line segment SU) satisfy the condition of the following equation (1). Adjust the height of the top blow lance to
In the plume region generated by the bottom blowing gas blown into the hot metal from the bottom blowing tuyere while spreading at 12 ° on one side, the powder dephosphorizing agent is applied from the top blowing lance together with the oxygen gas. A dephosphorization treatment method characterized by spraying.
Length of line segment SU ≤ L ₀・ tan6 ° ・ ・ ・ (1)
Here, L ₀ represents the bath depth (mm) of the hot metal.
(2) The powder dephosphorizing agent is a mixed powder of a powder mainly composed of a CaO source and a powder mainly composed of an Al ₂ O ₃ source, and is _{3 of} CaO, CaCO ₃ and Al ₂ O ₃ . It is a mixed powder having a total mass concentration of 90% or more of the components and (Al ₂ O ₃ mass) / (CaO mass + CaCO ₃ mass × 0.56) of 0.05 to 0.20. The dephosphorization treatment method according to (1) above.
(3) The plurality of nozzles are arranged concentrically with respect to the central axis of the upper blowing lance, and the inclination angle θ between the central axis of the upper blowing lance and the central axis of the nozzle is the same for all nozzles. The dephosphorization treatment method according to (1) or (2) above, which is characterized by the above.
(4) When the position of the intersection between the central axis of the upper blowing lance and the hot metal is O, the length of the line segment OS is 300 mm or more, and the central axis of the upper blowing lance and the central axis of the nozzle. The dephosphorization treatment method according to any one of (1) to (3) above, wherein the inclination angle θ between the two is 25 ° or less.
(5) N ₂ gas as the bottom blowing gas is blown into the hot metal from the bottom blowing tuyere at a flow rate of 0.1 to 0.6 Nm ³ / min / t to stir, and the powder is dephosphorized from the top blowing lance. The agent is sprayed onto the hot metal together with the oxygen gas of 1.0 to 2.5 Nm ³ / min / t to adjust the charge basicity at the end of the treatment to 1.5 to 2.5 (1) to the above. The dephosphorization treatment method according to any one of (4).

According to the present invention, it is possible to provide a dephosphorization treatment method capable of melting ultra-low phosphorus hot metal at low cost and with high efficiency while suppressing spitting.

FIG. 1A is a diagram for explaining the position of the bottom blowing tuyere in the embodiment. FIG. 1B is a diagram for explaining the position of the bottom blowing tuyere in the embodiment. FIG. 2 is a diagram showing the positions of a plurality of fire points and the positions of a plurality of bottom blowing tuyere as viewed from the axial direction of the top blowing lance.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1A and 1B are diagrams for explaining the position of the bottom blowing tuyere in this embodiment. Further, FIG. 2 is a diagram showing the positions of a plurality of fire points and the positions of a plurality of bottom blowing tuyere as viewed from the axial direction of the top blowing lance. The dephosphorization treatment device according to the present embodiment includes a converter, a top blown lance, an oxygen supply device, and a powder supply device, and the bottom of the converter is provided with N ₂ gas, Ar gas, or the like. A plurality of bottom blowing tuyere are provided for blowing an inert gas into the hot metal.

At the lower end of the top blowing lance, 4 to 6 nozzles for ejecting a powder dephosphorizing agent together with oxygen are installed. As a result, hot metal is charged into the converter, the height of the top-blown lance is adjusted so that the lance height becomes H _0, and when a jet is injected from the top-blown lance, the top-blown oxygen gas is bathed in the hot metal bath. A fire point consisting of a high temperature portion of 2000 ° C. or higher is formed on the hot metal bath surface by colliding with the surface. In the example shown in FIG. 2, four nozzles are concentrically installed as a desirable form, and the angle (inclination angle) θ formed by the central axis of these nozzles and the central axis of the top blowing lance is the same. An example is shown, and as shown in FIG. 2, when the jet is injected, the centers U _{1 to} U ₄ of the fire point are formed concentrically. The centers U _{1 to} U ₄ of these fire points are on the x-axis or y-axis so that the distances from the intersection O of the hot metal and the central axis of the top-blown lance are equal by adjusting the height of the top-blown lance. Move on.

In the present embodiment, the bottom of the converter is provided with the same number of bottom blowing tuyere as the number of nozzles, and when adjusting the height of the top blowing lance, the center of the fire point is U _{1 to} U ₄ . , Adjust the lance height H ₀ so that the positions S _{1 to} S ₄ of the bath surface directly above the positions T _{1 to} T ₄ of the bottom blowing tuyere are all within a predetermined distance. That is, in the dephosphorization process, the value of the lance height H ₀ is adjusted by moving the top blow lance up and down so that the centers U _{1 to} U ₄ of the fire point are at the target positions.

Next, the conditions between the position of the bottom blowing tuyere and the center of the fire point will be described. Here, in the examples shown in FIGS. 1A and 1B, a combination of a nozzle having the minimum length of the line segment SU and a bottom blowing tuyere will be described. That is, in FIG. 2, the combination is line segment S ₁ U ₁ , line segment S ₂ U ₂ , line segment S ₃ U ₃ , and line segment S ₄ U ₄ . The bottom-blown gas blown into the hot metal from the bottom-blown tuyere floats while spreading at 12 ° on one side. The region where the bottom-blown gas and the hot metal are mixed is called a plume region. The density in this plume region is low, and the mixture is vigorously stirred and mixed as compared with the surrounding hot metal bath. As shown in FIG. 1B, when the powder dephosphorizer blown from the top-blown lance together with oxygen is blown into this plume region, the powder dephosphorizer can penetrate deeply in the hot metal and is vigorously stirred and mixed. The efficiency of dephosphorization of CaO in the powder dephosphorizer is greatly improved, and the concentration of [P] in the hot metal after the treatment is reduced to an extremely low concentration.

In the dephosphorization treatment apparatus according to the present embodiment, the powder dephosphorizer is sprayed together with oxygen from the top blown lance, and the powder dephosphorizer is mainly composed of a powder mainly composed of CaO source and an Al ₂ O ₃ source. Use a mixed powder with the powder to be used. The powder mainly composed of the CaO source preferably has a total mass concentration of CaO and CaCO ₃ of 90% or more, and more preferably either quicklime (CaO) or limestone (CaCO ₃ ) or a mixed powder. The reason why the total mass concentration of CaO and CaCO ₃ is preferably 90% or more is that if it is less than 90%, a large amount of components other than CaO and CaCO ₃ are mixed, and slag forming becomes excessive during the dephosphorization treatment, resulting in slag. This is because there is an increased risk of overflowing from the furnace mouth or poor dephosphorization. The powder mainly composed of Al ₂ O ₃ source preferably has an Al ₂ O ₃ mass concentration of 50% or more, and in addition to van slab or bauxite, slag or refractory having a high Al ₂ O ₃ mass concentration. Examples of waste materials from. Further, in the mixed powder in which these powders are mixed, the total mass concentration of the three components of CaO, CaCO ₃ and Al ₂ O ₃ is preferably 90% or more. The reason for this is the same as the reason why the total mass concentration of CaO and CaCO ₃ is preferably 90% or more. Further, the maximum particle size of these powders is preferably 0.5 mm or less, more preferably 0.15 mm or less, from the viewpoint of ease of transporting the powders in gas and securing the reaction boundary area in the hot metal. .. The mixing ratio of the powder mainly composed of the CaO source and the powder mainly composed of the Al ₂ O ₃ source will be described later.

The mixed powder is held in the dispenser of the powder feeder, and when the blowing of the dephosphorization process is started, the mixed powder is blown directly from the dispenser to the top blowing lance or via the oxygen gas line. Is supplied to. At this time, oxygen is also supplied from the oxygen supply device to the upper blowing lance, and the mixed powder is sprayed on the hot metal together with oxygen from the upper blowing lance.

Next, the conditions of the dephosphorization treatment apparatus and the melting method such as the range of the length of the line segment SU were confirmed by the experiment of the dephosphorization treatment.
First, hot metal 290t ([C] = 4.4 to 4.5% by mass, [Si] = 0.3 to 0.5% by mass, [P] = 0.100 to 0.120) in the upper bottom blown converter. (Mass%, bath depth L ₀ = approx. 2000 mm) is charged, and N ₂ gas is blown into the hot metal from four bottom blowing tuyere at a flow rate of 0.08 to 0.70 Nm ³ / min / t to stir and powder. As a body dephosphorizing agent, a powder obtained by mixing a powder mainly composed of a CaO source and a powder mainly composed of an Al ₂ O ₃ source (the total mass concentration of the three components of CaO, CaCO ₃ and Al ₂ O ₃ is 90). % Or more and (mixed powder in which (Al ₂ O ₃ mass) / (CaO mass + CaCO ₃ mass × 0.56) is 0.03 to 0.25) has the same number of nozzles as the number of bottom blowing tuyere. From the blowing lance, the lance height H ₀ was set to 2500 to 3500 mm, and the hot metal was sprayed with oxygen gas 0.8 to 2.7 Nm ³ / min / t into a hot metal bath to perform hot metal dephosphorization treatment. The maximum particle size of the powder used was 0.15 mm, the treated hot metal [C] = 3.3 to 3.6% by mass, [P] = 0.004 to 0.023% by mass, and the charged base. The degree (CaO / SiO ₂ mass ratio) was 1.3 to 2.7, and the blowing time was 6 to 10 minutes. The charge basicity is a value calculated by (CaO charge mass) / (SiO _{2 charge} mass + SiO ₂ formation mass due to oxidation of [Si] in hot metal).

At that time, the position of the intersection (center of the fire point) U between the central axis of the jet of top-blown oxygen + mixed powder and the hot metal bath surface, the line drawn vertically upward from the bottom blown tuyere position T, and the hot metal bath surface. Regarding the combination of the top blowing nozzle and the bottom blowing tuyere that minimizes the distance from the intersection position S (the length of the line segment SU), the metal adheres to the vicinity of the furnace mouth by spitting and the hot metal after treatment [ The effect on P] was examined.

The conditions specified in the present invention will be described with reference to Table 1. Regarding the requirements described in Table 1, the angle α: 0 ° between the line segment TS and the line segment TU and the charge basicity at the end of the treatment: 1.8 are based on the experience grasped during the examination process of the present invention. , Top-blown oxygen flow rate: 2.0 Nm ³ / min / t, Bottom-blown gas flow rate: 0.25 Nm ³ / min / t, Top-blown mixed powder (Al ₂ O ₃ mass) / (CaO mass + CaCO ₃ mass x 0) .56): With 0.10 as the basic condition, the effect of changes in various requirements on the P concentration in the hot metal after treatment and the effect of spitting on the amount of metal adhering to the vicinity of the furnace mouth is investigated. did. It should be noted that the adhesion of the bare metal in the hot metal after the treatment [P] shown in Table 1 and in the vicinity of the furnace ostium by spitting is an average value of the results of continuous 10 Chh tests under each condition. As a base condition for confirming the effect according to the present invention, No. 1 in Table 1 is used. “When the four bottom blowing tuyere are α = 5 °, 18 °, 23 °, and 36 °, respectively” shown in 29 was adopted. This base condition is a conventional condition in which the angle (α) formed by the line segment TS and the line segment TU is not particularly concerned. In addition, when the amount of metal deposit at the furnace mouth was about the same as the base condition under each condition, the overall evaluation was set to "Δ". When the amount of [P] in the hot metal after treatment is 0.015% by mass or less and the amount of metal in the furnace mouth is clearly smaller than the base condition and is 70 to 90%, the overall evaluation is "○", which is also remarkable. In the case of less than 60%, the overall evaluation was "◎".

Further, in Table 1, the angle α formed by the line segment TS and the line segment TU represents the angle α shown in FIG. 1A, and the top blowing nozzle and the bottom blowing tuyere that minimize the length of the line segment SU. It represents the maximum angle among the angles in each combination (4 sets) of. However, in this experiment, all the nozzles were arranged concentrically with respect to the central axis of the top blowing lance, and the inclination angle was appropriately selected from the range of 12 ° to 18 ° as the same angle for each lance. In addition, the bottom blowing tuyere is also No. 1-No. In the 28th experiment, they are arranged concentrically with respect to the central axis of the top blowing lance, and by adjusting the height of the top blowing lance, the center U _{1 to} U ₄ of the fire point and the position T of the bottom blowing tuyere It is possible to match the positions S _{1 to} S ₄ of the bath surface directly above _{1 to} T ₄ . Therefore, in this experiment, the angle α formed by the line segment TS and the line segment TU is No. 1-No. In all 28 experiments, the same experiment No. It was the same for all combinations. On the other hand, in the base condition experiment (No. 29), α was disjointed with respect to the four bottom blowing tuyere at the bottom of the furnace.

(1) No. 1 in Table 1. 1-7
By adjusting the center U of the fire point, the effect of the change in α was investigated as the basic condition described above, except that the angle α (deg) formed by the line segment TS and the line segment TU shown in FIG. 1A was changed. As a result, when 0 ° ≤ α ≤ 6 °, the amount of [P] in the hot metal after the treatment was 0.015% by mass or less, and the amount of metal adhered to the vicinity of the furnace mouth by spitting was also small.

As described above, the plume region generated by the bottom blowing gas expands at 12 ° on one side, so if the angle α is 6 ° or less, it means that the top blowing jet collides near the center of the plume region. are doing. Under this condition, the top-blown mixed powder blown into the plume region, which has a low density and is vigorously agitated and mixed as compared with the surrounding hot metal bath, can penetrate deeply and is vigorously agitated and mixed. It is considered that the efficiency of dephosphorization utilization of CaO was greatly improved, and the concentration of [P] in the hot metal after the treatment was reduced to an extremely low concentration. In addition, it is considered that the spitting is reduced because the kinetic energy of the top-blown jet is efficiently consumed in the plume region. As described above, when 0 ° ≤ α ≤ 6 °, the following equation (1) is satisfied. That is, it was confirmed that the effect of the present invention can be obtained when the formula (1) is satisfied.
Line segment SU length ≤ L ₀ tan 6 ° (L ₀ : bath depth) ・ ・ ・ (1)

On the other hand, when α exceeds 6, that is, when the length of the line segment SU> L ₀ tan 6 °, [P] in the hot metal after the treatment exceeds 0.015% by mass. It is considered that this is because the top-blown mixed powder could not penetrate deeply into the hot metal bath and could not enjoy the strong stirring and mixing effect in the plume region.

Here, when the length of the line segment SU> L ₀ tan 6 °, the position of the fire point is an inappropriate position, and if the top blowing lance is adjusted in the vertical direction, the length of the line segment SU is minimized. When all the combinations of the nozzle and the bottom blowing tuyere can be set to the length ≤ L ₀ tan 6 ° of the line segment SU, and even if the lance height H ₀ is changed, the line segment SU There are two possible cases in which it is impossible for all combinations of the nozzle having the minimum length and the bottom blowing tuyere to have the length of the line segment SU ≤ L ₀ tan 6 °.

In the dephosphorization processing apparatus according to the present embodiment, when the center U of the fire point is adjusted to the target position, the nozzle and the bottom blowing tuyere that minimize the length of the line segment SU at the target position are each. All of the combinations satisfy the condition of the equation (1). Therefore, when the dephosphorization treatment is performed using the dephosphorization treatment apparatus according to the present embodiment, if the lance height H ₀ is inappropriate and the center U of the fire point is not the target position, the former is applicable. there's a possibility that. On the other hand, the latter case is, for example, a case where the center U of the fire point is formed concentrically, but the position of the bottom blowing tuyere is irregular. In such a case, even if the lance height H ₀ is adjusted, at least one set of each combination of the nozzle and the bottom blowing tuyere that minimizes the length of the line segment SU is the equation (1). ), Therefore, the effect of the present invention cannot be obtained no matter how the operating conditions are changed.

In addition, when the length of the line segment SU> L ₀ tan 6 °, the amount of metal adhered to the vicinity of the furnace mouth by spitting varied depending on the position of the center U of the fire point. The closer the collision position of the top-blown jet to the hot metal bath surface (center U of the fire point) is the position O of the intersection of the center axis of the top-blown lance and the hot metal, the more the amount of spitting that scatters vertically upward increases. The farther the center U of the fire point was from the position O, the smaller the amount of spitting scattered vertically upward.

As described above, as the center U of the fire point approaches the position O, the amount of spitting scattered vertically upward may increase. Therefore, it is desirable that the length of the line segment OS is 300 mm or more. This is because if there is a bottom blowing tuyere in which the length of the line segment OS is less than 300 mm, the inclination angle θ of the top blowing jet becomes small and the amount of spitting vertically upward increases. Further, it is desirable that the inclination angle θ of the nozzle of the top blowing lance is 25 ° or less. This is because if there is a nozzle with an inclination angle θ that is too large, secondary combustion by the top-blown oxygen jet will increase, and the refractory damage to the converter wall will become severe.

(2) No. in Table 1 8-12
In these experiments, the charge basicity at the end of the treatment was set to 1.3 to 2.7, and the other basic conditions were used. No fine-grained CaO was added before the treatment.
As a result of the experiment, when the charge basicity at the end of the treatment was set to less than 1.5, the dephosphorization ability of the slag became too low, and the [P] in the hot metal after the treatment was reduced to the target value of 0.015% by mass or less. could not.
On the other hand, when the charge basicity at the end of the treatment exceeded 2.5, the [P] in the hot metal after the treatment did not decrease to 0.015% by mass or less. If the charge basicity is excessively increased at the end of the treatment, the fluidity of the bulk slag around the fire point drops sharply, making it difficult for the dephosphorization reaction due to the bulk slag to proceed. It is thought that it has become expensive.
From the above, it was confirmed that the appropriate range of the charge basicity at the end of the treatment was 1.5 to 2.5.

(3) No. in Table 1 13-17
In these experiments, the top-blown oxygen flow rate was 0.8 to 2.7 Nm ³ / min / t, and the other basic conditions were used. When the top-blown oxygen flow rate was less than 1.0 Nm ³ / min / t, the [P] in the hot metal after the treatment did not decrease to 0.015% by mass or less. When the blowing time was set to 6 to 10 minutes, it is considered that the oxygen required to reduce the concentration of [P] in the hot metal after the treatment to 0.015% by mass or less, which is an extremely low concentration, was insufficient.
On the other hand, even when the top-blown oxygen flow rate was increased to more than 2.5 Nm ³ / min / t, the [P] in the hot metal after the treatment did not decrease to 0.015% by mass or less. In this case, the time until the amount of oxygen required for dephosphorization is completed, that is, the blowing time becomes excessively short, and the post-treatment hot metal [P] does not decrease to the target value of 0.015% by mass or less. It is thought that it was.
From the above, it was confirmed that the appropriate range of the top-blown oxygen flow rate was 1.0 to 2.5 Nm ³ / min / t.

(4) No. in Table 1 18-23
In these experiments, the bottom blowing N ₂ flow rate was 0.08 to 0.7 Nm ³ / min / t, and the other basic conditions were used. When the bottom blowing N ₂ flow rate was set to less than 0.1 Nm ³ / min / t, the [P] in the hot metal after the treatment did not decrease to 0.015% by mass or less. In this case, since the mass transfer rate of P in the hot metal was significantly reduced, the mass transfer rate of P in the hot metal after treatment could be reduced to 0.015% by mass or less, which is an extremely low concentration, by short-time blowing for 6 to 10 minutes. It is probable that it was not.
On the other hand, even when the bottom blowing N ₂ flow rate was increased to more than 0.6 Nm ³ / min / t, [P] in the hot metal after the treatment did not decrease to 0.015% by mass or less. In this case, the hot metal and the slag were excessively stirred and mixed, and the FeO concentration in the slag was excessively lowered. Therefore, the [P] in the hot metal after the treatment could not be reduced to the target value of 0.015% by mass or less. It is thought that
From the above, it was confirmed that the appropriate range of the bottom blowing N ₂ flow rate was 0.1 to 0.6 Nm ³ / min / t.

(5) No. in Table 1 24-28
In these experiments, the composition of the top-blown CaO + Al ₂ O ₃ mixed powder was such that the total mass concentration of the three components CaO, CaCO ₃ and Al ₂ O ₃ was 95%, and (Al ₂ O ₃ mass) / (CaO). Mass + CaCO ₃ mass x 0.56) changed the Al ₂ O ₃ concentration from 0.03 to 0.25, and the other conditions were the basic conditions. If (Al ₂ O ₃ mass) / (CaO mass + CaCO ₃ mass x 0.56) in the mixed powder is less than 0.05, the [P] in the hot metal after treatment decreases to the target value of 0.015 mass%. I didn't. It is considered that this is because the CaO content in the mixed powder melted at the fire point and was not sufficiently consumed in the dephosphorization reaction.

At the fire point, Fe in the hot metal is oxidized by top-blown oxygen to generate FeO, and the top-blown powder is melted to form a FeO-CaO-based melt. However, since FeO is reduced by [C] in the hot metal, the FeO concentration in the melt tends to decrease. Then, the melting point of the FeO-CaO melt rises, and the fluid state cannot be maintained, so that the efficiency of dephosphorization utilization of the melt decreases. On the other hand, if the above-mentioned melt contains a small amount of Al ₂ O ₃ , the melting point of the melt is significantly lowered, so that the molten state can be maintained and the dephosphorization utilization efficiency can be maintained high. If the content (Al ₂ O ₃ mass) / (CaO mass + CaCO ₃ mass x 0.56) is less than 0.05, the melting point lowering effect of the melt is small, and it is considered that the dephosphorization efficiency of the melt could not be improved. ..

On the other hand, even when (Al ₂ O ₃ mass) / (CaO mass + CaCO ₃ mass × 0.56) in the mixed powder is increased to more than 0.20, the target value of [P] in the hot metal after treatment is 0. It did not decrease to .015% by mass. In this case, the activity of CaO in the melt generated at the fire point decreased, and the dephosphorization ability of the melt decreased. Therefore, the target value of [P] in the hot metal after treatment was 0.015 mass. It is considered that it did not decrease to%.
From the above results, it was confirmed that the appropriate range of (Al ₂ O ₃ mass) / (CaO mass + CaCO ₃ mass × 0.56) in the mixed powder was 0.05 to 0.20.

Next, the present invention will be further described based on Examples, but the conditions in the Examples are one conditional example adopted for confirming the feasibility and effect of the present invention, and the present invention is the same. It is not limited to the conditional example. In the present invention, various conditions can be adopted as long as the gist of the present invention is not deviated and the object of the present invention is achieved.

(Example 1)
290 tons of hot metal of [C] = 4.4% by mass, [Si] = 0.4% by mass, and [P] = 0.10% by mass was charged into the upper bottom blown converter. The depth L ₀ of the static bath at this time was 2000 mm. Next, N ₂ gas was blown into the hot metal from the four bottom blowing tuyere at a flow rate of 0.25 Nm ³ / min / t to stir, and from the top blowing lance with four nozzles with an inclination angle of 17 °, the lance. When the height H ₀ is 2800 mm, the total mass concentration of the three components CaO, CaCO ₃ and Al ₂ O ₃ is 95% together with the oxygen gas 2.0 Nm ³ / min / t, and (Al ₂ O ₃ mass) / ( A mixed powder having a CaO mass + CaCO ₃ mass × 0.56) of 0.10 and a maximum particle size of 0.15 mm was sprayed to set the charging basicity at the end of the treatment to 1.8.

Distance between the intersection O of the central axis of the top blowing lance and the hot metal bath surface and the position S of the intersection point between the line drawn vertically upward from the position T of the bottom blowing tuyere and the hot metal bath surface (the length of the line segment OS) Was set to 860 mm, which is common to all bottom blowing tuyere. In this case, the line drawn vertically upward from the position of the intersection (center of the fire point) U of the jet of top-blown oxygen + mixed powder and the hot metal bath surface and the position T of the bottom-blown tuyere and the hot metal bath surface. The positions S of the intersections of the above were almost the same at all the fire points. That is, the angle α formed by the line segment TS and the line segment TU was almost 0 °.
As a result of dephosphorization with a blowing time of 7 minutes, the final temperature at the end of blowing was 1342 ° C., [C] in the hot metal after treatment was 3.4% by mass, and [P] was 0.006% by mass. There was almost no adhesion of bare metal near the furnace opening.

(Comparative Example 1)
290 tons of hot metal of [C] = 4.4% by mass, [Si] = 0.4% by mass, and [P] = 0.10% by mass was charged into the upper bottom blown converter. The depth L ₀ of the static bath at this time was 2000 mm. N ₂ gas is blown into the hot metal from four bottom blowing tuyere at a flow rate of 0.25 Nm ³ / min / t to stir, and the lance height is H from the top blowing lance in which four nozzles with an inclination angle of 12 ° are arranged. _{With 0} as 2700 mm, the total mass concentration of the three components CaO, CaCO ₃ and Al ₂ O ₃ is 95% together with oxygen gas 2.0 Nm ³ / min / t, and (Al ₂ O ₃ mass) / (CaO mass + CaCO). A mixed powder having a size of ₃ mass × 0.56) of 0.10 and a maximum particle size of 0.15 mm was sprayed to set the charging basicity at the end of the treatment to 1.8.

Distance between the intersection O of the central axis of the top blowing lance and the hot metal bath surface and the position S of the intersection point between the line drawn vertically upward from the position T of the bottom blowing tuyere and the hot metal bath surface (the length of the line segment OS) Was set to 860 mm, which is common to all bottom blowing tuyere. In this case, the line drawn vertically upward from the position of the intersection (center of the fire point) U and the position T of the bottom blowing tuyere of the jet of top-blown oxygen + mixed powder and the hot metal bath surface and the hot metal bath surface. The positions S of the intersections of the lines did not match, and the angle α formed by the line segment TS and the line segment TU was about 8 ° at the maximum, and the length of the line segment SU was larger than L ₀ tan 6 °. ..
As a result of dephosphorization with a blowing time of 7 minutes, the final temperature at the end of blowing was 1345 ° C., 3.4% by mass of [C] in the hot metal after treatment, and 0.017% by mass of [P]. Furthermore, there was a considerable amount of bare metal adhering to the vicinity of the furnace opening.

According to the present invention, it is possible to provide a dephosphorization treatment apparatus capable of melting ultra-low phosphorus hot metal at low cost and high efficiency while suppressing spitting, and a method for dephosphorizing hot metal using the same. The value is great.

Claims (5)

A converter, a top-blown lance that blows a powder dephosphorizing agent and oxygen gas into the converter, an oxygen supply device that supplies the oxygen gas to the top-blown lance, and powder desorption to the top-blown lance. A powder supply device for supplying a phosphorus agent is provided, and a plurality of nozzles for ejecting the powder dephosphorizer and the oxygen gas are arranged on the lower end surface of the top blowing lance, and the bottom of the converter is provided with a plurality of nozzles. , A dephosphorization treatment method using a dephosphorization treatment apparatus in which the same number of bottom blowing tuyere as the nozzles is arranged.
The hot metal is held in the converter, and the position U of the intersection of the central axis of the top blowing jet ejected from the nozzle and the bath surface of the hot metal, the straight line drawn vertically upward from the position of the bottom blowing tuyere, and the above. All the sets of nozzle and bottom blowing tuyere that minimize the distance from the position S of the intersection of the hot metal with the bath surface (the length of the line segment SU) satisfy the condition of the following equation (1). Adjust the height of the top blow lance to
In the plume region generated by the bottom blowing gas blown into the hot metal from the bottom blowing tuyere while spreading at 12 ° on one side, the powder dephosphorizing agent is applied from the top blowing lance together with the oxygen gas. A dephosphorization treatment method characterized by spraying.
Length of line segment SU ≤ L ₀・ tan6 ° ・ ・ ・ (1)
Here, L ₀ represents the bath depth (mm) of the hot metal. The powder dephosphorizer is a mixed powder of a powder mainly composed of a CaO source and a powder mainly composed of an Al ₂ O ₃ source, and is a total of three components of CaO, CaCO ₃ and Al ₂ O _3. Claim 1 is a mixed powder having a mass concentration of 90% or more and (Al ₂ O ₃ mass) / (CaO mass + CaCO ₃ mass × 0.56) of 0.05 to 0.20. The dephosphorization treatment method described in 1. The plurality of nozzles are arranged concentrically with respect to the central axis of the top blowing lance, and the inclination angle θ between the central axis of the top blowing lance and the central axis of the nozzle is the same for all nozzles. The dephosphorization treatment method according to claim 1 or 2, wherein the method is characterized by. When the position of the intersection of the central axis of the top blowing lance and the hot metal is O, the length of the line segment OS is 300 mm or more, and between the central axis of the top blowing lance and the central axis of the nozzle. The dephosphorization treatment method according to any one of claims 1 to 3, wherein the inclination angle θ is 25 ° or less. N ₂ gas as the bottom blowing gas is blown into the hot metal from the bottom blowing tuyere at a flow rate of 0.1 to 0.6 Nm ³ / min / t and stirred, and the powder dephosphorizing agent is blown from the top blowing lance. Any of claims 1 to 4, wherein the hot metal is sprayed with oxygen gas 1.0 to 2.5 Nm ³ / min / t to set the charging basicity at the end of the treatment to 1.5 to 2.5. The dephosphorization treatment method according to item 1.

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