WO2018150858A1 - Dephosphorization device and dephosphorization method for hot metal using same - Google Patents

Abstract

Nozzles and an equal number of bottom blowing tuyeres are disposed at the bottom of a converter furnace such that, in a state wherein hot metal is charged in the converter furnace at a bath depth L0, and for each pair of nozzle and bottom blowing tuyere where the distance (length of line segment SU) between position U at the intersection of the center axis of an upward jet sprayed from the nozzle and the molten surface of the hot metal and position S at the intersection of a straight line drawn vertically upward from the position of the bottom blowing tuyere and the molten surface of the hot metal is minimized, a top lance is positioned at a height satisfying the condition of line segment SU length ≤ L₀∙tan 6°.

Description

Dephosphorization apparatus and hot metal dephosphorization method using the same

Particularly, the present invention relates to a dephosphorization apparatus suitable for producing ultra-low phosphorus hot metal at low cost and high efficiency while suppressing spitting, and a hot metal dephosphorization method using the same.

In recent years, the demand for steel materials has increased, and the demand for low phosphorus steel has increased. At present, hot metal dephosphorization is widely performed by a method in which the hot metal is treated under low temperature conditions in a hot metal stage, which is thermodynamically advantageous. As the hot metal dephosphorization apparatus, an upper bottom blowing converter is suitable. This is because, as an oxidant necessary for dephosphorization, gaseous oxygen with less heat loss than a solid oxidant can be sprayed from the top blowing lance to the hot metal at high speed.

Since the dephosphorization of hot metal is performed under low temperature conditions in the hot metal stage, it is important to promote the hatching of CaO used as a dephosphorizing agent. The use of fluorite (CaF ₂ ) is effective for hatching CaO, which has a melting point of 2300 ° C. or higher. However, when fluorite is used, the slag generated by the hatching of CaO is fluorine ( Since it contains F), there are significant adverse effects such as greatly restricting the reuse destination of slag. Therefore, CaO hatching promotion methods that do not use fluorite have been developed.

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

However, in this method, the top-blown mixed powder is penetrated deeply into the hot metal bath to increase the dephosphorization utilization efficiency of the CaO—Al ₂ O ₃ —FeO melt and reduce [P] in the hot metal to a very low concentration. When the blowing jet dynamic pressure is increased, spitting increases and the amount of metal adhesion to the furnace increases.

Further, a CaO-containing cover slag is formed in the first half of blowing, and the basicity (weight ratio: CaO / SiO ₂ ) of the cover slag is 0.4 to 1.5, and thereafter, 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 blown up is disclosed (see Patent Document 2). In 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 blowing.

However, since the first half of hot metal dephosphorization changes at a low temperature, the addition of lump CaO so that the charging basicity is particularly 1.3 to 1.5, the lump CaO cannot be completely dissolved in the first half of blowing and dephosphorization. Usage efficiency will be reduced. 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 using calcium ferrite having a low melting point, there arises a problem that costs are increased.

As described above, when producing extremely low phosphorus hot metal while suppressing spitting, dephosphorization cannot be performed at low cost and with high efficiency.

Japanese Patent No. 3525766 Japanese Patent No. 3687433

In view of the above-mentioned problems, the present invention aims to provide a dephosphorization processing apparatus capable of producing an extremely low phosphorus hot metal at a low cost and with high efficiency while suppressing spitting, and a hot metal dephosphorization method using the same. And

In the plume region formed on the molten surface by blowing the bottom blowing gas from the bottom blowing tuyere, the mixed powder penetrates into the hot metal inside by the bubble of the bottom blowing gas. We paid attention to the fact that dephosphorization can be performed efficiently without raising. Therefore, in completing the present invention, molten iron is charged into a converter having an upper bottom blowing, and either one of CaO powder and CaCO ₃ powder together with oxygen gas from an upper blowing lance having 4 to 6 nozzles or The mixed powder of both and Al ₂ O ₃ powder was sprayed onto the hot metal bath surface, and gas was blown from the bottom blowing tuyere of the same number as the top blowing nozzle, and the adhesion behavior and dephosphorization behavior in the furnace by spitting were investigated. As a result, by appropriately controlling the geometric positional relationship between the top blowing jet and the plume region, adhesion of ingots in the furnace due to spitting can be avoided and high efficiency, that is, the dephosphorization efficiency of CaO can be improved. The present inventors have found a dephosphorization processing apparatus capable of melting extremely low phosphorus hot metal ([C] ≧ 3.2 mass%, [P] ≦ 0.015 mass%) and a melting method using the apparatus.

The present invention is as follows.
(1) A dephosphorization apparatus for dephosphorizing hot metal,
A converter,
An upper blowing lance for blowing a powder dephosphorizing agent and oxygen gas into the converter;
An oxygen supply device for supplying the oxygen gas to the upper blowing lance;
A powder supply device for supplying the powder dephosphorizing agent to the upper blowing lance,
A plurality of nozzles for ejecting the powder dephosphorizing agent and the oxygen gas are disposed on the lower end surface of the upper blowing lance,
At the bottom of the converter, the same number of bottom blowing tuyeres as the nozzles are arranged,
With the hot metal having a bath depth L ₀ charged in the converter, 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 and the bottom blowing tuyere In each of the sets of nozzles and bottom blowing tuyere where the distance (the length of the line segment SU) between the straight line drawn vertically upward from the position and the position S of the intersection point of the hot metal bath surface is the following, The dephosphorization processing apparatus, wherein the nozzle and the bottom blowing tuyere are arranged so that the height of the top blowing lance that satisfies the condition of the formula (1) exists.
Length of line segment SU ≦ L ₀・ tan6 ° (1)
(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 includes _{3 of} CaO, CaCO ₃ and Al ₂ O ₃ . the total mass concentration of the components of 90% or more, and characterized in that it is a mixed powder is 0.05 ~ 0.20 (Al ₂ O ₃ by weight) / (CaO mass + CaCO ₃ mass × 0.56) Dephosphorization processing apparatus as described in said (1).
(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 processing apparatus according to (1) or (2) above, wherein
(4) When the position of the intersection between the central axis of the upper blow 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 blow lance and the central axis of the nozzle The dephosphorization processing apparatus according to any one of the above (1) to (3), wherein an inclination angle θ between the first and the second is 25 ° or less.
(5) A hot metal dephosphorization method using the dephosphorization apparatus according to any one of (1) to (4) above,
The molten iron is held in the converter, and N ₂ gas is blown into the molten iron from the bottom blowing tuyere at a flow rate of 0.1 to 0.60 Nm ³ / min / t, and the length of the line segment SU is increased. The height of the upper blowing lance is adjusted so as to satisfy the condition of the formula (1) in all of the nozzle and bottom blowing tuyere that is minimized, and the powder dephosphorizing agent is adjusted from the upper blowing lance. Is sprayed onto the molten iron together with the oxygen gas of 1.0 to 2.5 Nm ³ / min / t, so that the charging basicity at the end of the treatment is 1.5 to 2.5.

According to the present invention, it is possible to provide a dephosphorization processing apparatus capable of producing ultra-low phosphorus hot metal with low cost and high efficiency while suppressing spitting, and a hot metal dephosphorization method using the same.

FIG. 1A is a diagram for explaining the position of a 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 a plurality of fire point positions and a plurality of bottom blowing tuyere positions as seen 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 the present embodiment. Moreover, FIG. 2 is a figure which shows the position of several fire spots and the position of several bottom blowing tuyere seen from the axial direction of the top blowing lance. Dephosphorization processing apparatus according to this embodiment includes a converter, a top-blown lance, an oxygen supply device, and a powder supplying device, the bottom of the converter, such as N ₂ gas or Ar gas A plurality of bottom blowing tuyere for blowing an inert gas into the hot metal is provided.

At the lower end of the upper blowing lance, 4 to 6 nozzles for ejecting a powder dephosphorizing agent together with oxygen are installed. As a result, when the hot metal is charged into the converter, the height of the upper blowing lance is adjusted so that the lance height becomes H _0, and the jet is injected from the upper blowing lance, A hot spot consisting of a high temperature part 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, as a desirable form, four nozzles are concentrically arranged, and the angles (inclination angles) θ formed by the central axes of these nozzles and the central axis of the upper blowing lance are all the same. An example is shown, and as shown in FIG. 2, when jets are injected, the centers U ₁ to U _{4 of the} fire points are formed concentrically. The centers U ₁ to U ₄ of these fire points are adjusted by adjusting the height of the top blowing lance so that the distance from the intersection point O between the center axis of the top blowing lance and the hot metal is equal to the x axis or the y axis. Move up.

In the present embodiment, the bottom blowing tuyere of the same number as the number of nozzles is provided at the bottom of the converter, and when adjusting the height of the top blowing lance, the center of fire point U ₁ to U ₄ and The lance height H ₀ is adjusted so that all the positions S ₁ to S ₄ of the bath surface directly above the bottom blowing tuyere positions T ₁ to T ₄ are equal to or less than a predetermined distance. In other words, in the dephosphorization process, the value of the lance height H ₀ is adjusted by moving the upper blowing lance up and down so that the center U ₁ to U ₄ of the fire point is the target position.

Next, the conditions between the position of the bottom blowing tuyere and the center of the fire point will be described. Here, in the example shown to FIG. 1A and FIG. 1B, it demonstrates as a combination of the nozzle and bottom blowing tuyere which the length of line segment SU becomes the minimum. That is, in FIG. 2, the combination is a line segment S ₁ U ₁ , a line segment S ₂ U ₂ , a line segment S ₃ U ₃ , and a line segment S ₄ U ₄ . The bottom blowing gas blown into the hot metal from the bottom blowing tuyere rises while spreading at 12 ° on one side. The region where the bottom blowing gas and hot metal are mixed is referred to as a plume region. The plume region has a low density and is vigorously stirred and mixed as compared to the surrounding hot metal bath. As shown in FIG. 1B, when the powder dephosphorizing agent blown from the top blowing lance together with oxygen is blown into this plume region, the powder dephosphorizing agent can penetrate deeply into the molten iron and is vigorously stirred and mixed. The dephosphorization utilization efficiency of CaO in the powder dephosphorizing agent is greatly improved, and [P] in the hot metal after the treatment is reduced to a very low concentration.

In the dephosphorization processing apparatus according to the present embodiment, a powder dephosphorizing agent is sprayed together with oxygen from an upper blowing lance. The powder dephosphorizing agent is mainly composed of a powder mainly composed of a CaO source and an Al ₂ O ₃ source. A mixed powder with the powder to be used is 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 is more preferably either quick lime (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 lot of components other than CaO and CaCO ₃ are mixed, and slag forming becomes excessive during the dephosphorization process, resulting in slag. This is because the risk of overflowing from the furnace opening or poor dephosphorization increases. The powder mainly composed of an Al ₂ O ₃ source preferably has an Al ₂ O ₃ mass concentration of 50% or more. In addition to van earth shale or bauxite, slag and refractories having a high Al ₂ O ₃ mass concentration are also available. Examples of such waste materials are exemplified. Moreover, in the mixed powder obtained by mixing these powders, 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 that 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 conveying the powder by gas and securing the reaction interface area in the hot metal. . The mixing ratio between the powder mainly composed of CaO source and the powder mainly composed of Al ₂ O ₃ source will be described later.

The mixed powder is held in the dispenser of the powder supply device. When dephosphorization is started, the mixed powder is directly discharged from the dispenser to the upper blowing lance or via the oxygen gas line. To be supplied. At this time, oxygen is also supplied from the oxygen supply device to the upper blowing lance, and the mixed powder is sprayed onto the molten iron together with oxygen from the upper blowing lance.

Next, the conditions of the dephosphorization processing apparatus and the melting method, such as the range of the length of the line segment SU, were confirmed by an experiment of the dephosphorization process.
First, molten iron 290t ([C] = 4.4 to 4.5 mass%, [Si] = 0.3 to 0.5 mass%, [P] = 0.100 to 0.120) Mass%, bath depth L ₀ = approx. 2000 mm), N ₂ gas was blown into the molten iron from 4 bottom blowing tuyere at a flow rate of 0.08 to 0.70 Nm ³ / min / t, and stirred. As a body dephosphorizing agent, a powder in which a powder mainly composed of a CaO source and a powder mainly composed of an Al ₂ O ₃ source are mixed (total mass concentration of three components of CaO, CaCO ₃ and Al ₂ O ₃ is 90 % And more than (Al ₂ O ₃ mass) / (CaO mass + CaCO ₃ mass × 0.56) is 0.03 to 0.25 mixed powder) From the blow lance, the lance height H ₀ is 2500 to 3500 mm and the oxygen gas is 0.8 to 2.7 Nm ³ / min / t. The hot metal was sprayed on the hot metal bath to perform hot metal dephosphorization. The maximum particle size of the powder used was 0.15 mm, the molten iron after treatment [C] = 3.3 to 3.6% by mass, and [P] = 0.004 to 0.023% by mass. 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 production mass due to oxidation of [Si] in the hot metal).

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

The conditions defined in the present invention will be described based on Table 1. Regarding the various requirements described in Table 1, the angle α formed by the line segment TS and the line segment TU is 0 ° based on the experience grasped in the course of the present invention, and the charging basicity at the end of the process is 1.8. , Top blowing oxygen flow rate: 2.0 Nm ³ / min / t, bottom blowing gas flow rate: 0.25 Nm ³ / min / t, (Al ₂ O ₃ mass) / (CaO mass + CaCO ₃ mass × 0) of the top blowing mixed powder .56): With 0.10 as the basic condition, focusing on this basic condition, the effect of changes in the requirements on the P concentration in the hot metal after treatment and the effect of spitting on the amount of metal in the vicinity of the furnace mouth were investigated. did. In addition, [P] in the hot metal after the treatment described in Table 1 and the adhesion of the metal near the furnace port by spitting are average values of the results of continuous 10 Ch tests under each condition. As a base condition for confirming the effect according to the present invention, No. 1 in Table 1 was obtained. 29, “when four bottom blowing tuyeres are α = 5 °, 18 °, 23 °, and 36 °, respectively” 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 adhesion of the furnace mouth metal in each condition was almost the same as the base condition, the overall evaluation was “△”. If the [P] in the hot metal after treatment is 0.015% by mass or less and the amount of adhesion to the furnace mouth metal is significantly less than the base condition, 70-90%, the overall evaluation is “◯”, and it is also remarkable. In the case of 60% or less, the overall evaluation is “◎”.

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. Among the angles in each combination (4 sets), the maximum angle is represented. However, in this experiment, all the nozzles were concentrically arranged with respect to the central axis of the upper blowing lance, and the inclination angle was appropriately selected from the range of 12 ° to 18 °, with the same angle for each lance. Also, the bottom blowing tuyere is No. 1-No. In 28 experiments, 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 of fire points U ₁ to U ₄ and the position T of the bottom blowing tuyere It was 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. All of the combinations were the same. On the other hand, in the experiment of the base condition (No. 29), α is disjoint with respect to the four bottom blowing tuyere of the furnace bottom.

(1) No. 1 in Table 1 1-7
Except for changing the angle α (deg) between the line segment TS and the line segment TU shown in FIG. 1A by adjusting the center U of the fire point, the influence of the change of α was investigated as the basic condition described above. As a result, in the case of 0 ° ≦ α ≦ 6 °, [P] in the hot metal after treatment was 0.015% by mass or less, and the amount of metal in the vicinity of the furnace port by spitting was small.

As described above, since the plume region generated by the bottom blowing gas spreads at 12 ° on one side, if the angle α is 6 ° or less, it means that the top blowing jet collides with the center of the plume region. is doing. Under this condition, the top blown mixed powder blown into the plume region, which has a low density and is vigorously stirred and mixed as compared to the surrounding hot metal bath, can penetrate deeply and is vigorously stirred and mixed. It is considered that the dephosphorization utilization efficiency of CaO was greatly improved, and [P] in the molten iron after the treatment was reduced to an extremely low concentration. In addition, it is considered that spitting is reduced because the kinetic energy of the top blowing jet is efficiently consumed in the plume region. As described above, when 0 ° ≦ α ≦ 6 °, the following expression (1) is satisfied. That is, it was confirmed that the effect of the present invention can be obtained when the expression (1) is satisfied.
Length of line segment SU ≦ L ₀ tan6 ° (L ₀ : bath depth) (1)

On the other hand, if α exceeds 6, that is, the length of the line segment SU> L ₀ tan 6 °, the amount of [P] in the hot metal after processing exceeds 0.015% by mass. This is presumably because the mixed powder sprayed above could not penetrate deeply into the hot metal bath and could not enjoy the powerful stirring and mixing effects in the plume region.

Here, in the case where the length of the line segment SU> L ₀ tan 6 °, the position of the fire point is an inappropriate position, and if the upper 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 bottom tuyere that can be set to the length of the line segment SU ≦ L ₀ tan 6 °, 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 nozzles and bottom blowing tuyeres having the minimum length 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 hot spot is adjusted to the target position, at the target position, each of the nozzle and the bottom blowing tuyere at which the length of the line segment SU is minimized. All of the combinations satisfy the condition of Equation (1). Therefore, in the case when performing dephosphorization treatment with dephosphorization processing apparatus according to this embodiment, an inadequate lance height H _0, the center U of the fire point is not the position of the aim, it corresponds to the former there's a possibility that. On the other hand, the case corresponding to the latter is, for example, a case where the center U of the fire point is formed concentrically, but the positions of the bottom blowing tuyere are irregular. In such a case, even if the lance height H ₀ is adjusted, at least one of the combinations of the nozzle and the bottom blowing tuyere that minimizes the length of the line segment SU is represented by the formula (1 Therefore, the effect of the present invention cannot be obtained no matter how the operating conditions are changed.

Further, when the length of the line segment SU> L ₀ tan 6 °, the amount of metal adhesion to the vicinity of the furnace port due to spitting varied depending on the position of the center U of the fire point. As the collision position of the top blowing jet on the hot metal bath surface (fire point center U) is closer to the position O of the intersection of the top blowing lance central axis and the hot metal, the amount of spitting scattered upwards increases. As the center U of the hot spot is further away from the position O, the amount of spitting that scatters vertically upward decreases.

Thus, since the amount of spitting scattered vertically upward may increase as the center U of the hot spot approaches the position O, the length of the line segment OS is preferably 300 mm or more. This is because if there is a bottom blowing tuyere whose 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 upward in the vertical direction increases. In addition, it is desirable that the inclination angle θ of the nozzle of the top blowing lance is 25 ° or less. This is because if a nozzle having an excessively large inclination angle θ is present, secondary combustion due to the top blown oxygen jet increases, and refractory damage to the converter furnace wall becomes severe.

(2) No. in Table 1 8-12
In these experiments, the charging basicity at the end of treatment was set to 1.3 to 2.7, and other basic conditions were used. In addition, fine-grain CaO was not added before the process.
As a result of the experiment, when the charge basicity at the end of the treatment is less than 1.5, the dephosphorization ability of the slag becomes too low, and the [P] in the molten iron after the treatment is reduced to a target value of 0.015 mass% or less could not.
On the other hand, when the charge basicity at the end of the treatment exceeded 2.5, [P] in the molten iron after the treatment did not decrease to 0.015% by mass or less. If the charging basicity is excessively increased at the end of the treatment, the fluidity of the bulk slag around the fire point decreases rapidly and the dephosphorization reaction by the bulk slag becomes difficult to proceed. It is thought that it became high.
From the above, it was confirmed that the appropriate range of the charging 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 blowing oxygen flow rate was set to 0.8 to 2.7 Nm ³ / min / t, and other conditions were set as basic conditions. When the top blowing oxygen flow rate was less than 1.0 Nm ³ / min / t, [P] in the hot metal after the treatment did not decrease to 0.015 mass% or less. When the blowing time is 6 to 10 minutes, it is considered that oxygen necessary to make [P] in the molten iron after treatment be 0.015% by mass or less, which is an extremely low concentration, is insufficient.
On the other hand, when the flow rate of the top blown oxygen was increased to more than 2.5 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 time required to finish blowing the amount of oxygen necessary for dephosphorization, that is, the blowing time becomes excessively short, and [P] in the molten iron after treatment does not decrease to a target value of 0.015% by mass or less. It is thought.
From the above, it was confirmed that the appropriate range of the top blowing 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 set to 0.08 to 0.7 Nm ³ / min / t, and other conditions were set as basic conditions. When the bottom blowing N ₂ flow rate was less than 0.1 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, since the mass transfer rate of P in the hot metal was remarkably reduced, [P] in the hot metal after treatment could be reduced to an extremely low concentration of 0.015% by mass or less by short-time blowing of 6 to 10 minutes. Probably not.
On the other hand, when the bottom blown 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 slag were excessively stirred and mixed, and the FeO concentration in the slag was excessively reduced, so that [P] in the hot metal after treatment could not be reduced to the target value of 0.015 mass% or less. It is thought.
From the above, it was confirmed that the appropriate range of the bottom blown N ₂ flow rate was 0.1 to 0.6 Nm ³ / min / t.

(5) No. 1 in Table 1. 24-28
In these experiments, the composition of the top-blown CaO + Al ₂ O ₃ mixed powder is 95% in total mass concentration of three components of CaO, CaCO ₃ and Al ₂ O ₃ , and (Al ₂ O ₃ mass) / (CaO Mass + CaCO ₃ mass × 0.56) was 0.03 to 0.25, and the Al ₂ O ₃ concentration was changed. When (Al ₂ O ₃ mass) / (CaO mass + CaCO ₃ mass × 0.56) in the mixed powder is less than 0.05, the amount of [P] in the molten iron after treatment decreases to 0.015% by mass, which is the target value. I did not. This is considered to be because the CaO content in the mixed powder was 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 the top blowing oxygen to produce FeO, and the top blowing 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 is likely to decrease. As a result, the melting point of the FeO—CaO melt increases and the fluid state cannot be maintained, so that the dephosphorization utilization efficiency of the melt decreases. On the other hand, if the melt contains a small amount of Al ₂ O ₃ , the melting point of the melt will be significantly lowered, so that it should be possible to maintain the molten state and maintain high dephosphorization utilization efficiency. If (Al ₂ O ₃ mass) / (CaO mass + CaCO ₃ mass × 0.56) is less than 0.05, the melting point melting 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, when (Al ₂ O ₃ mass) / (CaO mass + CaCO ₃ mass × 0.56) in the mixed powder is increased to more than 0.20, [P] in the molten iron after treatment is the target value 0 It did not fall to .015 mass%. In this case, the activity of CaO in the melt produced at the hot spot is lowered, and the dephosphorization ability of the melt is lowered. Therefore, [P] in the molten iron after treatment is a target value of 0.015 mass. It is thought that it did not fall 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 example of conditions adopted for confirming the feasibility and effects of the present invention. It is not limited to the example conditions. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

Example 1
The top bottom blowing converter was charged with 290 t of hot metal containing [C] = 4.4 mass%, [Si] = 0.4 mass%, and [P] = 0.10 mass%. The depth L ₀ of the still bath at this time was 2000 mm. Next, N ₂ gas was blown into the molten iron from the four bottom blowing tuyere at a flow rate of 0.25 Nm ³ / min / t and stirred, and from the top blowing lance in which four nozzles having an inclination angle of 17 ° were arranged, The height H ₀ is 2800 mm, the total mass concentration of the three components of 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) / ( 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, and the charging basicity at the end of the treatment was set to 1.8.

The distance between the intersection point O between the center axis of the top blowing lance and the hot metal bath surface and the position S of the hot metal bath surface drawn from the position T of the bottom blowing tuyere vertically (the length of the line segment OS) Was 860 mm, common to all bottom blowing tuyere. In this case, a line drawn vertically upward from the position of the intersection of the central axis of the jet of the top blown oxygen + mixed powder and the hot metal bath surface (center of the fire point) U and the position T of the bottom blow tuyere and the hot metal bath surface The position S of the intersections of these points almost coincided at any of 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 at a blowing time of 7 minutes, the final blowing temperature was 1342 ° C., and [C] in the molten iron after the treatment was 3.4 mass% and [P] was 0.006 mass%. There was almost no metal adhesion near the furnace mouth.

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

The distance between the intersection point O between the center axis of the top blowing lance and the hot metal bath surface and the position S of the hot metal bath surface drawn from the position T of the bottom blowing tuyere vertically (the length of the line segment OS) Was 860 mm, common to all bottom blowing tuyere. In this case, a line drawn vertically upward from the position of the intersection of the central axis of the jet of the top blown oxygen + mixed powder and the hot metal bath surface (center of the fire point) U and the position T of the bottom blow tuyere and the hot metal bath surface None of the positions S of the intersections coincide with each other, the angle α formed by the line segment TS and the line segment TU is about 8 ° at the maximum, and the length of the line segment SU is larger than L ₀ tan6 °. .
As a result of dephosphorization at a blowing time of 7 minutes, the final temperature of blowing was 1345 ° C., and after treatment, [C] was 3.4 mass% and [P] was 0.017 mass%. Furthermore, there was a lot of bullion adhesion near the furnace mouth.

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

Claims (5)

A dephosphorization apparatus for dephosphorizing hot metal,
A converter,
An upper blowing lance for blowing a powder dephosphorizing agent and oxygen gas into the converter;
An oxygen supply device for supplying the oxygen gas to the upper blowing lance;
A powder supply device for supplying the powder dephosphorizing agent to the upper blowing lance,
A plurality of nozzles for ejecting the powder dephosphorizing agent and the oxygen gas are disposed on the lower end surface of the upper blowing lance,
At the bottom of the converter, the same number of bottom blowing tuyeres as the nozzles are arranged,
With the hot metal having a bath depth L ₀ charged in the converter, 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 and the bottom blowing tuyere In each of the sets of nozzles and bottom blowing tuyere where the distance (the length of the line segment SU) between the straight line drawn vertically upward from the position and the position S of the intersection point of the hot metal bath surface is the following, The dephosphorization processing apparatus, wherein the nozzle and the bottom blowing tuyere are arranged so that the height of the top blowing lance that satisfies the condition of the formula (1) exists.
Length of line segment SU ≦ L ₀・ tan6 ° (1) 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 a total of three components of CaO, CaCO ₃ and Al ₂ O _{3. 2.} 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 processing apparatus described in 1. 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 processing apparatus according to claim 1 or 2. 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 between the central axis of the upper blowing lance and the central axis of the nozzle. The dephosphorization processing apparatus according to any one of claims 1 to 3, characterized in that the inclination angle θ of said is not more than 25 °. A hot metal dephosphorization method using the dephosphorization apparatus according to any one of claims 1 to 4,
The molten iron is held in the converter, and N ₂ gas is blown into the molten iron from the bottom blowing tuyere at a flow rate of 0.1 to 0.6 Nm ³ / min / t, and the length of the line segment SU is increased. The height of the upper blowing lance is adjusted so as to satisfy the condition of the formula (1) in all of the nozzle and bottom blowing tuyere that is minimized, and the powder dephosphorizing agent is adjusted from the upper blowing lance. Is sprayed onto the molten iron together with the oxygen gas of 1.0 to 2.5 Nm ³ / min / t, so that the charging basicity at the end of the treatment is 1.5 to 2.5.

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