CN109790590B

CN109790590B - Dephosphorization apparatus and dephosphorization method of molten iron using the same

Info

Publication number: CN109790590B
Application number: CN201880003733.7A
Authority: CN
Inventors: 宫田政树; 浅原纪史
Original assignee: Nippon Steel and Sumitomo Metal Corp
Current assignee: Nippon Steel Corp
Priority date: 2017-02-15
Filing date: 2018-01-29
Publication date: 2021-01-12
Anticipated expiration: 2038-01-29
Also published as: TWI664295B; TW201833336A; KR20190040011A; JP6773142B2; WO2018150858A1; CN109790590A; JPWO2018150858A1; KR102164124B1

Abstract

A dephosphorization apparatus comprising bottom blowing ports arranged at the bottom of a converter in the same number as nozzles, wherein the converter is charged with a bath depth L₀In the molten iron state of (1), in all the groups of the nozzle and the bottom-blowing tuyere in which the distance (the length of the line segment SU) between the position U of the intersection of the central axis of the top-blowing jet stream ejected from the nozzle and the bath surface of the molten iron and the position S of the intersection of the line drawn vertically upward from the position of the bottom-blowing tuyere and the bath surface of the molten iron is the smallest, the length of the line segment SU is less than or equal to L₀The nozzle and the bottom-blowing tuyere are arranged at a height of the top-blowing lance under a condition of tan6 °.

Description

Dephosphorization apparatus and dephosphorization method of molten iron using the same

Technical Field

The present invention relates to an apparatus for dephosphorization used suitably for melting an extremely low-phosphorus molten iron at low cost and with high efficiency while suppressing splashing (spitting), and a method for dephosphorizing a molten iron using the same.

Background

In recent years, demand for steel materials has increased, and demand for low-phosphorous steel has increased. At present, dephosphorization of molten iron is generally conducted by a method of performing treatment under low temperature conditions in a thermodynamically favorable molten iron stage. As the dephosphorization apparatus for the molten iron, a top-and-bottom blowing converter is suitable. This is due to: as an oxidizing agent required for dephosphorization, gaseous oxygen with less heat loss than the solid oxidizing agent can be blown from the top-blowing lance to the molten iron at a high speed.

Because the dephosphorization of the molten iron is carried out under the low-temperature condition of the molten iron stageTherefore, it is important to promote the desulfurization of CaO used as a dephosphorizing agent. Fluorite (CaF) is used for converting CaO dross having a melting point of 2300 ℃ or higher to a very high level₂) Is effective, but has the following disadvantages: in the case of using fluorite, since slag generated by the dross formation of CaO contains fluorine (F), the reuse target of slag is greatly limited. Therefore, a CaO dross promotion method without using fluorite has been developed.

As this method, for example, as a method for melting a low-phosphorus steel by highly digesting CaO without using fluorite or calcium ferrite, a method of melting a low-phosphorus steel by using a top-blowing lance containing CaO powder and Al powder₂O₃Powder and Fe₂O₃A method of blowing a mixed powder of the powder onto a bath surface of molten iron together with an oxygen jet (see patent document 1). In this method, Al₂O₃、Fe₂O₃Readily react with CaO to form CaO-Al having a low melting point₂O₃The dephosphorization reaction proceeds extremely efficiently in the FeO melt.

However, in this method, CaO-Al is used more efficiently if the top-blown mixed powder is allowed to penetrate deeply into the molten iron bath₂O₃Dephosphorization efficiency of FeO melt to remove [ P ] from the iron bath]When the top-blown jet dynamic pressure is increased by lowering the concentration to an extremely low level, there is a problem that the amount of splashes increases and the amount of pig iron accretions in the furnace increases.

Further, there is disclosed a dephosphorization method of molten iron (see patent document 2) in which a cover slag (cover slag) containing CaO is formed in the first half of blowing, and the basicity (weight ratio: CaO/SiO) of the cover slag is determined₂) 0.4 to 1.5, and then adding CaO powder and Al₂O₃Powder and Fe₂O₃The mixed powder of the powders was top-blown. In this method, the amount of splashing can be reduced by forming a mold flux having a low melting point in the first half of dephosphorization blowing.

However, since the hot metal dephosphorization blowing half-time proceeds at a low temperature, if CaO nuggets are added so that the charging basicity becomes particularly 1.3 to 1.5, the CaO nuggets do not completely dissolve in the blowing half-time, and the dephosphorization efficiency by the CaO nuggets is lowered. Further, even after dephosphorization of molten iron, undissolved CaO remains in the slag, which is problematic when the dephosphorized slag is effectively used for road bed materials and the like. In order to avoid this problem, when the mold flux is formed using calcium ferrite having a low melting point, a problem of cost arises.

When the extremely low-phosphorus molten iron is melted while suppressing the splashing as described above, the dephosphorization cannot be efficiently performed at low cost.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 3525766

Patent document 2: japanese patent No. 3687433

Disclosure of Invention

Problems to be solved by the invention

In view of the above-described problems, an object of the present invention is to provide a dephosphorization apparatus capable of melting an extremely low-phosphorus molten iron at low cost and with high efficiency while suppressing splashing, and a dephosphorization method of a molten iron using the same.

Means for solving the problems

The present inventors have focused on: in the plume region formed on the bath surface by blowing the bottom-blowing gas from the bottom-blowing port, the mixed powder permeates into the molten iron by the bubbles of the bottom-blowing gas, and therefore, the dephosphorization can be efficiently performed without increasing the dynamic pressure of the jet flow. Then, in carrying out the present invention, molten iron is charged into a converter having top-bottom blowing, and CaO powder and CaCO are blown together with oxygen from a top-blowing lance having 4 to 6 nozzles₃One or both of the powders and Al₂O₃The mixed powder of the powder was blown onto the surface of the molten iron bath, and gas was blown from the bottom blowing ports, which were the same number as the top blowing nozzles, to investigate the behavior of adhesion of the pig iron to the inside of the furnace and the dephosphorization behavior caused by the splashing. As a result, they have found a dephosphorization apparatus and a smelting method using the same, which can avoid the adhesion of pig iron nuggets in a furnace by sputtering and can improve the utilization efficiency, that is, the utilization efficiency, by properly controlling the geometrical positional relationship between the top-blown jet and the plume regionDephosphorization efficiency of CaO for smelting ultra-low-phosphorus molten iron ([ C ]]Not less than 3.2% by mass and [ P ]]Not more than 0.015% by mass).

The present invention is as follows.

(1) A dephosphorization apparatus for performing dephosphorization of molten iron, comprising:

a converter;

a top-blowing lance for blowing a powder dephosphorizing agent and oxygen into the converter;

an oxygen supply device for supplying the oxygen gas to the top-blowing lance; and

a powder supply device for supplying the powder dephosphorizing agent to the top-blowing lance,

wherein a plurality of nozzles for ejecting the powdery dephosphorizing agent and the oxygen gas are arranged on the lower end surface of the top-blowing lance,

bottom blowing ports of the same number as the nozzles are arranged at the bottom of the converter,

according to the depth of the bath charged into the converter is L₀The nozzle and the bottom-blowing tuyere are arranged in such a manner that the nozzle and the bottom-blowing tuyere are at a height that satisfies the condition of the following formula (1) in all the groups of the nozzle and the bottom-blowing tuyere in which the distance (length of the segment SU) between the position U and the position S is the smallest, the position U being a position of an intersection of a central axis of a top-blowing jet stream ejected from the nozzle and a bath surface of the molten iron, and the position S being a position of an intersection of a straight line drawn vertically upward from the position of the bottom-blowing tuyere and the bath surface of the molten iron.

The length of the line segment SU is less than or equal to L₀·tan6° (1)

(2) The dephosphorization apparatus according to the above (1), wherein said powdery dephosphorization agent is composed of a powdery material mainly containing a CaO source and Al₂O₃A mixed powder of powders mainly composed of CaO and CaCO₃And Al₂O₃The total mass concentration of the 3 components is more than 90%, and (Al)₂O₃mass)/(CaO mass + CaCO₃Mass x 0.56) of 0.05 to 0.20.

(3) The dephosphorization apparatus according to the above (1) or (2), wherein the plurality of nozzles are arranged concentrically with respect to a central axis of the top-blowing lance, and an inclination angle θ between the central axis of the top-blowing lance and the central axis of the nozzle is the same for all the nozzles.

(4) The dephosphorization apparatus according to any one of the above (1) to (3), wherein when a position of an intersection of a central axis of the top-blowing lance and the molten iron is represented by O, a length of the line segment OS is 300mm or more, and an inclination angle θ between the central axis of the top-blowing lance and a central axis of the nozzle is 25 ° or less.

(5) A dephosphorization method of molten iron using the dephosphorization apparatus according to any one of the above (1) to (4),

wherein molten iron is held in the converter and N is blown from the bottom-blowing tuyere₂The gas is supplied in an amount of 0.1 to 0.60Nm³Blowing the molten iron into the molten iron at a flow rate of one minute per ton and stirring the molten iron, adjusting the height of the top-blowing lance so as to satisfy the condition of the formula (1) in all the groups of the nozzle and the bottom-blowing tuyere in which the length of the segment SU is the smallest, and mixing the powdery dephosphorizing agent and the powdery dephosphorizing agent by the top-blowing lance in an amount of 1.0 to 2.5Nm³Blowing the oxygen gas to the molten iron at a rate of one minute per ton, and setting the charging alkalinity at the final stage of the treatment to 1.5 to 2.5.

Effects of the invention

According to the present invention, it is possible to provide a dephosphorization apparatus capable of melting an extremely low-phosphorus molten iron at low cost and with high efficiency while suppressing splashing, and a dephosphorization method of a molten iron using the same.

Drawings

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 view showing positions of a plurality of ignition points and positions of a plurality of bottom-blowing ports as viewed in the axial direction of the top-blowing lance.

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Fig. 1A and 1B are views for explaining the position of the bottom-blowing tuyere in the present embodiment. Fig. 2 is a view showing positions of a plurality of ignition points and positions of a plurality of bottom-blowing ports as viewed in the axial direction of the top-blowing lance. The dephosphorization apparatus according to the present embodiment includes a converter, a top-blowing lance, an oxygen supply device, and a powder supply device, and a plurality of nitrogen injection holes for injecting nitrogen are provided in the bottom of the converter₂And a bottom-blowing tuyere for blowing inert gas such as gas and Ar gas into the molten iron.

4-6 nozzles for spraying the powder dephosphorizing agent and oxygen are arranged at the lower end of the top-blowing spray gun. As a result, when molten iron is charged into the converter, the height of the lance becomes H₀When the height of the top-blowing lance is adjusted and the jet flow is jetted from the top-blowing lance, the top-blown oxygen collides with the molten iron bath surface to form a fire point including a high-temperature portion of 2000 ℃ or higher on the molten iron bath surface. The example shown in fig. 2 shows, as a preferred mode, an example in which 4 nozzles are concentrically arranged and the angles (inclination angles) θ formed by the central axes of these nozzles and the central axis of the top-blowing lance are all the same, and as shown in fig. 2, if a jet is ejected, the center U of the fire is₁～U₄Formed in concentric circles. The centers U of these fires being adjusted by adjusting the height of the top-blowing lances₁～U₄The movement is made on the x-axis or the y-axis so that the distances from the intersection O of the central axis of the top-blowing lance and the molten iron become equal.

In the present embodiment, the bottom blowing ports are provided in the same number as the number of nozzles at the bottom of the converter, and the center U of the fire is adjusted according to the height of the top-blowing lance₁～U₄Position T with bottom blowing tuyere₁～T₄Position S of the bath surface directly above₁～S₄The height H of the spray gun is adjusted to be below a predetermined distance₀. That is, in the dephosphorization treatment, the center U of the fire is determined₁～U₄The top-blowing lance is moved up and down to adjust the lance height H so as to be at the target position₀The value of (c).

Next, the position of the bottom-blowing tuyere and the condition of the center of the ignition point will be described. Here, in the example shown in fig. 1A and 1B, a combination of a nozzle and a bottom-blowing tuyere in which the length of the line segment SU is the smallest is explained. I.e. the line segment S in FIG. 2₁U₁Line segment S₂U₂Line segment S₃U₃Line segment S₄U₄Combinations of (a) and (b). The bottom-blown gas blown into the molten iron from the bottom-blown tuyere gradually floated while spreading at an angle of 12 ° on one side. The region where the bottom-blown gas and the molten iron are mixed is referred to as a plume region. The plume region has a low density and is vigorously stirred and mixed compared to the surrounding molten iron bath. As shown in FIG. 1B, if the powdery dephosphorizing agent blown together with oxygen from the top-blowing lance is blown into the plume region, the powdery dephosphorizing agent can intrude deeply into the molten iron and be vigorously stirred and mixed, so that the efficiency of dephosphorization with CaO in the powdery dephosphorizing agent is greatly improved, and [ P ] in the treated molten iron]Down to very low concentrations.

In the dephosphorization apparatus according to the present embodiment, a powder dephosphorization agent is blown from a top-blowing lance together with oxygen, and the powder dephosphorization agent is composed of a powder mainly containing a CaO source and Al₂O₃A mixed powder of powders mainly composed of a source. The powder mainly containing CaO source is preferably CaO and CaCO₃The total mass concentration of (3) is 90% or more, and is more preferably set to quicklime (CaO) or limestone (CaCO)₃) Any one of them or mixed powder. CaO and CaCO₃The reason why the total mass concentration of (2) is preferably 90% or more is that: if the content is less than 90%, a large amount of CaO and CaCO are removed₃Other components, the following risks increase: in the dephosphorization, the slag formation becomes too large and the slag overflows from the furnace mouth, or the dephosphorization becomes poor. In addition, with Al₂O₃The powder mainly containing the source is preferably Al₂O₃The mass concentration is 50% or more, and Al can be exemplified in addition to alumina shale or bauxite₂O₃Slag and refractory wastes having high mass concentration. Further, a mixed powder obtained by mixing these powdersIn the middle, CaO, CaCO₃And Al₂O₃The total mass concentration of these 3 components is preferably 90% or more. The reason and setting are "CaO and CaCO₃The reason why the total mass concentration of (3) is preferably 90% or more is the same. From the viewpoint of ease of transportation of the powder by gas and securing a reaction interface area in the molten iron, the maximum particle diameter of the powder is preferably 0.5mm or less, and more preferably 0.15mm or less. Further, the powder mainly containing CaO source and Al₂O₃The mixing ratio of the powder mainly composed of the source will be described later.

The mixed powder is held in a distributor (distributor) of the powder supplying apparatus, and if the blowing of the dephosphorization process is started, the mixed powder is directly supplied from the distributor to the top-blowing lance or is supplied to the top-blowing lance via an oxygen line. At this time, oxygen is also supplied from the oxygen supply device to the top-blowing lance, and the mixed powder is blown from the top-blowing lance to the molten iron together with the oxygen.

Next, conditions of the dephosphorization 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.

First, 290 tons of molten iron ([ C ] was charged into a top-bottom converter]4.4 to 4.5 mass% and [ Si ]]0.3 to 0.5 mass% of [ P ]]0.100 to 0.120 mass% and a bath depth L₀About 2000mm), N was blown from 4 bottom blowing ports₂The gas flow rate is 0.08-0.70 Nm³Blowing/min/ton into molten iron, stirring, and adding powder containing CaO source as main component and Al as powder dephosphorizing agent₂O₃Powders (CaO, CaCO) obtained by mixing powders mainly composed of a source₃And Al₂O₃The total mass concentration of the 3 components is more than 90%, and (Al)₂O₃mass)/(CaO mass + CaCO₃Mass x 0.56) of 0.03 to 0.25) from a top-blowing lance having the same number of nozzles as the number of bottom-blowing ports at a lance height H₀Is 2500 to 3500mm and is 0.8 to 2.7Nm³Oxygen gas was blown into the molten iron bath together with oxygen gas per minute per ton, and dephosphorization of the molten iron was performed. The maximum particle diameter of the powder used was 0.15mm, and the iron liquid [ C ] was treated]3.3 to 3.6 mass%, [ P ]]0.004-0.023% by mass percent of the total amount of the raw materials, and filling alkalinity (CaO/SiO)₂Mass ratio) of 1.3 to 2.7, and blowing time of 6 to 10 minutes. The basicity of the charge is defined by (CaO charge mass)/(SiO)₂Charged with mass + from [ Si ] in molten iron]SiO obtained by oxidation₂Generation quality) of the calculated value.

In this case, the influence of [ P ] in the molten iron after the deposition and treatment of the pig iron nugget near the furnace opening due to the splash was examined on the combination of the top-blowing nozzle and the bottom-blowing tuyere where the distance (length of the line segment SU) between the position U (center of fire) at which the center axis of the jet of top-blown oxygen + mixed powder intersects the molten iron bath surface and the position S at which the intersection of the line drawn vertically upward from the bottom-blowing tuyere position T intersects the molten iron bath surface is the smallest.

The conditions specified in the present invention will be described based on table 1. With respect to each requirement described in table 1, based on the experience grasped in the study of the present invention, the angle α formed between the line segment TS and the line segment TU is: 0 °, loading basicity at the end of treatment: 1.8, top-blown oxygen flow: 2.0Nm³Min/ton, bottom-blown gas flow: 0.25Nm³(Al) of mixed powder of one minute per ton and top-blown₂O₃mass)/(CaO mass + CaCO₃Mass × 0.56): 0.10 was set as a basic condition, and the influence of the change in each of the requirements on the P concentration in the treated molten iron and the amount of the pig iron deposited in the vicinity of the taphole due to the splashing was examined with the basic condition as the center. In the treated iron liquid [ P ] shown in Table 1]The pig iron nugget adhesion near the furnace mouth due to the splash was an average of the results obtained by continuously conducting the 10Ch test under each condition. As basic conditions for confirming the effects of the present invention, "the case where the 4 bottom-blowing ports α are 5 °, 18 °, 23 °, and 36 °, respectively" shown in No.29 of table 1 is adopted. The basic condition is a conventional condition that does not particularly concern the angle (α) formed by the line segment TS and the line segment TU. In addition, when the amount of the accretion of the taphole pig iron blocks at the respective conditions was about the same as the basic conditions, the overall evaluation was set to "Δ". In the treated iron bath [ P]The mass ratio is 0.015% or less by mass, and the comprehensive evaluation is "o" when the amount of the pig iron nugget adhered to the furnace mouth is significantly smaller than that of the base condition and is 70 to 90%, and "excellent" when the amount is also significantly smaller than that of the base condition and is 60% or less.

In table 1, the angle α formed by the line segment TS and the line segment TU indicates the angle α shown in fig. 1A, and indicates the largest angle among the angles of the combinations (4 groups) of the top-blowing nozzles and the bottom-blowing ports in which the length of the line segment SU is the smallest. In the present experiment, all the nozzles were arranged concentrically with respect to the central axis of the top-blowing lance, and the inclination angles were set to the same angle for each lance and were appropriately selected from the range of 12 ° to 18 °. In the experiments of nos. 1 to 28, the bottom-blowing tuyere was also arranged concentrically with respect to the center axis of the top-blowing lance, and the height of the top-blowing lance was adjusted to adjust the center U of the ignition point₁～U₄Position T with bottom blowing tuyere₁～T₄Position S of the bath surface directly above₁～S₄And (5) the consistency is achieved. Therefore, in the present experiment, the angle α formed by the segment TS and the segment TU is set to be the same in all combinations in the same experiment nos. 1 to 28. On the other hand, in the experiment of the basic condition (No.29), α is different with respect to 4 bottom-blowing tuyeres of the furnace bottom.

[ Table 1]

(1) Nos. 1 to 7 in Table 1

As a result of setting the above-described basic conditions except that the angle α (degree) formed by the line segment TS and the line segment TU shown in fig. 1A is changed by adjusting the center U of the fire point, and examining the influence of the change in α, when α is 0 ° or more and 6 ° or less, the [ P ] in the molten iron after the treatment becomes 0.015 mass% or less, and the amount of the pig iron nuggets adhered to the vicinity of the furnace mouth due to the spattering is also small.

As described above, since the plume region generated by the bottom-blown gas is expanded at 12 ° on one side, it means: in the case where the angle α is 6 ° or less, the top-blown jet collides with the vicinity of the center of the plume region. It is believed that: under these conditions, the top-blown powder mixture blown into the plume region, which has a low density and is vigorously stirred and mixed with the surrounding molten iron bath, can be deeply introduced and vigorously stirred and mixed, so that the efficiency of dephosphorization by CaO in the powder mixture is greatly improved, and the concentration of [ P ] in the treated molten iron is reduced to an extremely low level. In addition, it is believed that: since the kinetic energy of the top-blown jet is efficiently dissipated in the plume region, the spray is reduced. As described above, in the case of 0 DEG. ltoreq. alpha. ltoreq.6 DEG, the following formula (1) is satisfied. Namely, it was confirmed that: when the formula (1) is satisfied, the effects of the present invention can be obtained.

The length of the line segment SU is less than or equal to L₀tan6°(L₀: bath depth) (1)

On the other hand, if α exceeds 6, the length of segment SU>L₀tan6 DEG, then [ P ] in the iron liquid after treatment]More than 0.015 mass%. This is believed to be due to: the top-blown mixed powder cannot penetrate deeply into the molten iron bath, and cannot enjoy the strong stirring and mixing effect in the plume region.

Here, the length of the line segment SU>L₀In the case of tan6 °, the position of the fire point is inappropriate, and the following two cases are considered: if the top-blowing lance is adjusted in the vertical direction, all combinations of the nozzles and the bottom-blowing ports, in which the length of the segment SU is the smallest, can be set to the length of the segment SU. ltoreq.L₀tan6 °; and even if the lance height H is changed₀All combinations of the nozzle and the bottom-blowing tuyere, in which the length of the segment SU is the smallest, cannot be set to the length of the segment SU. ltoreq.L₀tan6 deg..

In the dephosphorization processing apparatus according to the present embodiment, when the center U of the ignition point is adjusted to the target position, all combinations of the nozzle and the bottom-blowing tuyere in which the length of the segment SU is the smallest satisfy the condition of the formula (1) at the target position. Therefore, when the dephosphorization is performed by using the dephosphorization apparatus according to the present embodiment, the lance height H is set to be high₀Is not exactly rightIf the center U of the fire is not the target position, the former may be satisfied. On the other hand, the case corresponding to the latter is, for example, a case where the center U of the ignition is formed concentrically, but the position of the bottom-blowing tuyere is irregular. In such a case, even if the lance height H is adjusted₀At least 1 group of the combinations of the nozzle and the bottom-blowing tuyere, in which the length of the segment SU is the smallest, does not satisfy the condition of the formula (1), and thus the effect of the present invention is not obtained even if the operation condition is changed.

In addition, the length of the on-line segment SU>L₀In the case of tan6 °, the amount of the pig iron nuggets attached to the vicinity of the furnace opening due to the spattering varies depending on the position of the center U of the fire. The amount of vertically upward splashing increases as the position of collision of the top-blown jet with the molten iron bath surface (the center U of the fire) approaches the position O of the intersection of the central axis of the top-blown lance with the molten iron, and conversely, the amount of vertically upward splashing decreases as the center U of the fire moves away from the position O.

In this manner, since the amount of vertically upward splashing may increase as the center U of the ignition is closer to the position O, the length of each line segment OS is preferably 300mm or more. This is due to: if there is a bottom-blowing tuyere in which the length of the line segment OS becomes less than 300mm, the inclination angle θ of the top-blowing jet becomes small, and the amount of vertically upward splash becomes large. The inclination angles θ of the nozzles of the top-blowing lances are preferably 25 ° or less. This is due to: if the nozzle is inclined at an excessively large angle θ, secondary combustion by the top-blown oxygen jet increases, and the refractory of the furnace wall of the converter is severely damaged.

(2) Nos. 8 to 12 in Table 1

In these experiments, basic conditions were set except that the loading alkalinity at the final stage of the treatment was set to 1.3 to 2.7. Furthermore, no fine-grained CaO was added before the treatment.

As a result of the experiment, if the charging basicity at the final stage of the treatment is set to be less than 1.5, the dephosphorization ability of the slag becomes too low, and [ P ] in the molten iron after the treatment cannot be reduced to the target value, that is, 0.015 mass% or less.

On the other hand, if the charging basicity at the final stage of the treatment exceeds 2.5, [ P ] in the iron melt after the treatment does not decrease to 0.015 mass% or less. It is believed that: if the charging basicity is excessively increased at the final stage of the treatment, the fluidity of the lump slag around the fire point is rapidly decreased, and the dephosphorization reaction by the lump slag becomes difficult to proceed, so that [ P ] in the molten iron after the treatment becomes high.

From the above, it is confirmed that: the appropriate range of the loading alkalinity at the final stage of the treatment is 1.5 to 2.5.

(3) Nos. 13 to 17 in Table 1

In these experiments, the top-blown oxygen flow rate was set to 0.8 to 2.7Nm³Except for the above, the reaction conditions were set as basic conditions. If the top-blown oxygen flow rate is set to less than 1.0Nm³Per minute per ton, [ P ] in the treated iron liquid]Does not fall below 0.015 mass%. This is believed to be due to: setting the blowing time to be 6-10 minutes, and adding [ P ] in the treated molten iron]The oxygen deficiency required for the extremely low concentration, i.e., 0.015 mass% or less.

On the other hand, in increasing the top-blown oxygen flow rate to more than 2.5Nm³In the case of a/minute/ton, P in the iron melt after treatment]Nor decreased to 0.015 mass% or less. It is believed that: in this case, the time required for the completion of dephosphorization by blowing, that is, the blowing time, becomes too short, and [ P ] in the molten iron after the treatment]The content of the polymer particles did not decrease to the target value, i.e., 0.015 mass% or less.

From the above, it is confirmed that: the top-blown oxygen flow rate is suitably in the range of 1.0 to 2.5Nm³Per minute per ton.

(4) Nos. 18 to 23 in Table 1

For these experiments, bottom blowing N₂The flow rate is set to 0.08 to 0.7Nm³Except for the above, the reaction conditions were set as basic conditions. If bottom blowing N₂The flow rate is set to be less than 0.1Nm³Per minute per ton, [ P ] in the treated iron liquid]Does not fall below 0.015 mass%. It is believed that: in this case, since the mass transfer rate of P in the molten iron is significantly reduced, the [ P ] in the treated molten iron cannot be blown into the molten iron in a short time of 6 to 10 minutes]The concentration is reduced to an extremely low concentration, that is, 0.015 mass% or less.

On the other hand, in bottom blowing N₂The flow rate is increased to over 0.6Nm³In the case of a/minute/ton, P in the iron melt after treatment]Nor decreased to 0.015 mass% or less. It is believed that: in this case, the molten iron and the slag are excessively stirred and mixed, and the FeO concentration in the slag is excessively lowered, so that [ P ] in the molten iron after the treatment cannot be adjusted]The amount of the reaction solution was reduced to a target value of 0.015 mass% or less.

From the above, it is confirmed that: bottom blowing N₂The flow rate is properly in the range of 0.1 to 0.6Nm³Per minute per ton.

(5) Nos. 24 to 28 of Table 1

For these experiments, for top blown CaO + Al₂O₃Composition of mixed powder of Al₂O₃Change of concentration into CaO, CaCO₃And Al₂O₃The total mass concentration of these 3 components was 95% (Al)₂O₃mass)/(CaO mass + CaCO₃Mass × 0.56) is 0.03 to 0.25, and other than this, the basic conditions are set. If (Al) is mixed in the powder₂O₃mass)/(CaO mass + CaCO₃Mass x 0.56) is less than 0.05, [ P ] in the treated iron liquid]Does not decrease to the target value, i.e., 0.015 mass%. This is believed to be due to: the CaO component in the mixed powder is melted in the fire point and becomes not sufficiently consumed by the dephosphorization reaction.

In the hot spot, Fe in the molten iron is oxidized by top-blown oxygen to produce FeO, and the top-blown powder is melted to form a FeO-CaO system melt. However, FeO is absorbed by the iron bath [ C ]]Since the FeO concentration in the melt is reduced, the FeO concentration is liable to decrease. As a result, the melting point of the FeO-CaO melt rises and the FeO-CaO melt cannot be kept in a fluidized state, so that the efficiency of dephosphorization by the melt is lowered. In this regard, it is believed that: if Al is contained in a small amount in the above melt₂O₃The melting point of the melt is significantly lowered, so that it should be possible to maintain the molten state to maintain the efficiency of dephosphorization using it at a high level, but (Al) in the mixed powder₂O₃mass)/(CaO mass + CaCO₃Quality x 0.56) below 0.05, the melting point depressing effect of the melt is small, failing to improve the dephosphorization efficiency of the melt completely.

On the other hand, (Al) in the mixed powder₂O₃mass)/(CaO mass + CaCO₃Mass x 0.56) to more than 0.20, P in the treated iron liquid]Nor decreased to the target value, i.e., 0.015 mass%. It is believed that: in this case, the activity of CaO in the melt formed at the ignition point is lowered, and the dephosphorization ability of the melt is lowered, so that [ P ] in the molten iron after the treatment]The content did not decrease to the target value, i.e., 0.015 mass%.

From the above results, it was confirmed that: of mixed powders of (Al)₂O₃mass)/(CaO mass + CaCO₃Mass x 0.56) is 0.05 to 0.20.

Examples

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 applicability and effects of the present invention, and the present invention is not limited to this one example of conditions. Various conditions may be adopted in the present invention as long as the object of the present invention is achieved without departing from the gist of the present invention.

(example 1)

Charging 290t of [ C ] into a top-bottom blowing converter]4.4% by mass or [ Si%]0.4 mass%, [ P ]]0.10 mass% of molten iron. Depth L of the static bath at this time₀Is 2000 mm. Then, N was blown from 4 bottom blowing ports₂Gas at 0.25Nm³Blowing into molten iron at a flow rate of/min/ton and stirring, and blowing from a top-blowing lance equipped with 4 nozzles having an inclination angle of 17 DEG at a lance height of H₀2800mm and 2.0Nm³Blowing CaO, CaCO together with oxygen per minute per ton₃And Al₂O₃The total mass concentration of these 3 components was 95% (Al)₂O₃mass)/(CaO mass + CaCO₃Mass × 0.56) was 0.10 and the maximum particle diameter was 0.15mm, and the charging basicity at the final stage of treatment was set to 1.8.

The distance (length of the line segment OS) between the intersection O of the central axis of the top-blowing lance and the molten iron bath surface and the intersection S of the line drawn vertically upward from the position T of the bottom-blowing tuyere and the molten iron bath surface was set to 860mm common to both bottom-blowing tuyeres. In this case, the position (center of fire) U of the intersection between the central axis of the top-blown oxygen + mixed powder jet and the molten iron bath surface and the position S of the intersection between the line drawn vertically upward from the position T of the bottom-blown tuyere and the molten iron bath surface almost coincide at any fire point. That is, the angle α formed by the line segment TS and the line segment TU is almost 0 °.

Dephosphorization was carried out for 7 minutes at the blowing time, and as a result, the final stage temperature of blowing was 1342 ℃, and [ C ] and [ P ] in the molten iron after the treatment were 3.4 mass% and 0.006 mass%, respectively. There was almost no attachment of pig iron nuggets near the furnace mouth.

Comparative example 1

Charging 290t of [ C ] into a top-bottom blowing converter]4.4% by mass or [ Si%]0.4 mass%, [ P ]]0.10 mass% of molten iron. Depth L of the static bath at this time₀Is 2000 mm. Blowing N from 4 bottom air blowing ports₂Gas at 0.25Nm³Blowing into molten iron at a flow rate of/min/ton, stirring, and blowing at a lance height H from a top-blowing lance equipped with 4 nozzles having an inclination angle of 12 DEG₀2700mm and 2.0Nm³Blowing CaO, CaCO together with oxygen per minute per ton₃And Al₂O₃The total mass concentration of these 3 components was 95% (Al)₂O₃mass)/(CaO mass + CaCO₃Mass × 0.56) was 0.10 and the maximum particle diameter was 0.15mm, and the charging basicity at the final stage of treatment was set to 1.8.

The distance (length of the line segment OS) between the intersection O of the central axis of the top-blowing lance and the molten iron bath surface and the intersection S of the line drawn vertically upward from the position T of the bottom-blowing tuyere and the molten iron bath surface was set to 860mm common to both bottom-blowing tuyeres. In this case, the position U of the intersection point of the central axis of the top-blown oxygen + mixed powder jet and the molten iron bath surface (the center of the fire) and the position S of the intersection point of the line drawn vertically upward from the position T of the bottom-blown tuyere and the molten iron bath surface are not coincident with each other, the angle α formed by the line segment TS and the line segment TU is about 8 DEG at the maximum, and the length of the line segment SU is greater than L₀tan6°。

Dephosphorization was carried out for 7 minutes, and as a result, the final stage temperature of blowing was 1345 ℃, and [ C ] and [ P ] in the molten iron after the treatment were 3.4 mass% and 0.017 mass%, respectively. In addition, a considerable amount of pig iron accretions adhere to the vicinity of the furnace opening.

Industrial applicability

According to the present invention, it is possible to provide a dephosphorization apparatus capable of melting an extremely low-phosphorus molten iron at low cost and with high efficiency while suppressing splashing, and a dephosphorization method of a molten iron using the same, and therefore, the apparatus is industrially valuable.

Claims

1. A dephosphorization apparatus for performing dephosphorization of molten iron, comprising:

a converter;

an oxygen supply device that supplies the oxygen gas into the top-blowing lance; and

wherein a plurality of nozzles for ejecting the powder dephosphorizing agent and the oxygen are arranged on the lower end surface of the top-blowing lance,

bottom blowing ports the number of which is the same as that of the nozzles are arranged at the bottom of the converter,

according to the depth of the bath loaded in the converter to be L₀The nozzle and the bottom-blowing tuyere are arranged in such a manner that the nozzle and the bottom-blowing tuyere are at a height that satisfies the condition of the following formula (1) in all the groups of the nozzle and the bottom-blowing tuyere in which the distance (length of the line segment SU) between the position U and the position S is the smallest, the position U being a position of an intersection of a central axis of a top-blowing jet stream ejected from the nozzle and a bath surface of the molten iron, the position S being a position of an intersection of a straight line drawn vertically upward from the position of the bottom-blowing tuyere and the bath surface of the molten iron,

the length of the line segment SU is less than or equal to L₀·tan6° (1)。

2. The dephosphorization apparatus according to claim 1, wherein said powdery dephosphorization agent is composed of a powdery material mainly containing a CaO source and Al₂O₃A mixed powder of powders mainly composed of CaO and CaCO₃And Al₂O₃The total mass concentration of the 3 components is more than 90%, and (Al)₂O₃mass)/(CaO mass + CaCO₃Mass x 0.56) of 0.05 to 0.20.

3. The dephosphorization apparatus according to claim 1 or 2, wherein said plurality of nozzles are arranged concentrically with respect to a central axis of said top-blowing lance, and an inclination angle θ between the central axis of said top-blowing lance and the central axis of said nozzles is the same in all the nozzles.

4. The dephosphorization apparatus according to claim 1 or 2, wherein when a position of an intersection of a central axis of said top-blowing lance and the molten iron is represented by O, a length of a line segment OS is 300mm or more, and an inclination angle θ between the central axis of said top-blowing lance and a central axis of said nozzle is 25 ° or less.

5. The dephosphorization apparatus according to claim 3, wherein when a position of an intersection of a central axis of said top-blowing lance and the molten iron is O, a length of a line segment OS is 300mm or more, and an inclination angle θ between the central axis of said top-blowing lance and a central axis of said nozzle is 25 ° or less.

6. A dephosphorization method of molten iron, characterized in that the dephosphorization method of molten iron using the dephosphorization apparatus according to any one of claims 1 to 5,

wherein molten iron is held in the converter and N is blown from the bottom-blowing tuyere₂The gas is supplied in an amount of 0.1 to 0.6Nm³Blowing the molten iron into the molten iron at a flow rate of one minute per ton and stirring the molten iron, adjusting the height of the top-blowing lance so as to satisfy the condition of the formula (1) in all the groups of the nozzle and the bottom-blowing tuyere in which the length of the segment SU is the smallest, and mixing the powder dephosphorizing agent and the powder dephosphorizing agent by the top-blowing lance in an amount of 1.0 to 2.5 Nm/m³Per minute per ton of said oxygenBlowing gas to the molten iron, and setting the charging alkalinity at the final treatment stage to be 1.5-2.5.