JP2001040409A - Method for dephosphorizing molten iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dephosphorizing method of molten iron, with which the dephosphorizing reaction is improved and the unit requirement of flux is reduced and the quantity of produced slag can be reduced. SOLUTION: In the dephosphorizing method of the molten iron for dephosphorizing by adding the flux into the molten iron in a pretreating furnace 12, the slag composition produced with the dephosphorization is regulated to 1.5-7.0 basicity, 10-25 wt.% FeO and 5-15 wt.% Al2O3. The molten iron temp. at the completing time of the dephosphorization is desirable to be regulated to 1250-1400 deg.C and Al2O3 in the slag is desirable to be adjusted by adding secondary refining slag into the slag produced with the dephosphorization.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for dephosphorizing hot metal by adding a flux to hot metal for dephosphorization.

[0002]

2. Description of the Related Art Conventionally, molten steel is produced by decarburizing hot metal in a refining furnace such as a converter or an electric furnace and raising the temperature to a predetermined temperature. It is necessary to remove impurities such as silicon and phosphorus from the hot metal in advance, and in a converter or a topped car (pre-treatment furnace), an oxidizing agent or a flux is added and agitated, or the hot metal is mixed with the oxidizing agent and the flux. So-called preliminary treatment of desiliconization and dephosphorization is performed by blowing in from a lance. Furthermore, after a part or all of the slag generated during the desiliconization and dephosphorization treatment is discharged, desulfurization is performed by blowing a desulfurization flux into the hot metal. However, in the method of individually performing desiliconization and dephosphorization, etc., the amount of flux used for desiliconization and dephosphorization increases and the pretreatment cost increases. Furthermore, since the amount of generated slag increases and the slag contains a large amount of CaO, there are problems such as being restricted when used effectively. Therefore, as a measure for preventing an increase in the amount of slag generated, Japanese Patent Application Laid-Open No. 60-218408 discloses that in a vessel in which dephosphorized slag generated by adding and melting lime-based flux and decarburized slag of a converter are mixed. Desiliconization is performed by adding new hot metal. Further, in JP-A-5-5114, only iron oxide and gaseous oxygen are blown into hot metal in a pretreatment furnace to generate a slag having a low melting point and good fluidity, and the slag is being desiliconized or after desiliconization. After removing the pretreatment furnace by tilting it and flowing it out, a lime-based flux is added to perform dephosphorization. Also, in Japanese Patent Application Laid-Open No. 63-18011, hot metal spiked from a blast furnace is fed into a pretreatment furnace in a Fe ₂ O ₃ , CaO
After desiliconization by adding an oxidizing flux having a composition consisting of, for example, the slag generated is removed by a vacuum suction device, and then the hot metal is placed in a transfer vessel such as a hot metal ladle, and the same oxidation as in the desiliconization treatment is performed. Phosphorus is blown in to remove phosphorus by oxidizing it to P ₂ O ₅ , followed by desulfurization with reducing slag.

[0003]

However, in Japanese Patent Application Laid-Open No. 60-218408, although the amount of lime-based flux used for desiliconization and dephosphorization can be reduced, the decarburized slag and desiliconization of the converter can be reduced. The amount of slag generated by melting the dephosphorized lime-based flux increases, the refractory of the pretreatment furnace is worn, and the amount of granular iron mixed into the slag increases. Further, JP-A-5-5114 and JP-A-63-1801.
In the publication No. 1, in order to improve the efficiency of the dephosphorization reaction, a large amount of a slag accelerating agent such as fluorite must be used, which increases the dephosphorization treatment cost and imposes restrictions on effective use. There's a problem.

The present invention has been made in view of the above circumstances, and provides a method for dephosphorizing hot metal in which the dephosphorization reaction can be improved, the basic unit of flux can be reduced, and the amount of slag generated can be reduced. With the goal.

[0005]

According to the present invention, there is provided a method for dephosphorizing hot metal according to the present invention, which comprises adding a flux to hot metal in a pretreatment furnace to remove phosphorus from the hot metal. is the slag composition basicity and 1.5 to 7.0, the FeO 10 to 25 wt%, the Al ₂ O ₃ 5 to 15
% By weight. By this method, the liquid phase ratio of the slag during the dephosphorization reaction can be maintained at a high level, and a decrease in the activity or oxygen potential of CaO, which is a condition for efficiently performing the dephosphorization reaction, can be suppressed. Dephosphorization can be performed with a very small amount of flux. If the basicity (CaO / SiO ₂ ) of the slag at the time of dephosphorization is smaller than 1.5, CaO
And the erosion of the refractory increases. On the other hand, when the basicity exceeds 7.0, the dephosphorization efficiency decreases, the flux unit consumption increases, and the amount of generated slag increases. On the other hand, if FeO is less than 10% by weight, the reaction efficiency is deteriorated due to a decrease in the oxygen potential in the slag. Conversely, if FeO is more than 25% by weight, the reaction with the carbon in the hot metal becomes active, Lapping occurs. Furthermore,
If the content of Al ₂ O ₃ is less than 5% by weight, the liquid phase ratio of the slag becomes poor, and the dephosphorization reaction also decreases. On the other hand, when Al ₂ O ₃ is 1
If it exceeds 5% by weight, the activity of CaO is reduced and the occurrence of slopping occurs.

Here, the hot metal temperature at the end of the dephosphorization is set to 1
It is desirable that the temperature be 250 to 1400 ° C. This makes it possible to efficiently perform dephosphorization by increasing the liquid phase ratio of the slag, so that the workability of subsequent processing and the subsequent refining can be performed at low cost. If the hot metal temperature at the end of the dephosphorization becomes lower than 1250 ° C., the amount of the carbonaceous material for raising the heat in the converter (decarburization refining process) increases, and the refining cost increases.
On the other hand, if the hot metal temperature exceeds 1400 ° C., it becomes difficult to thermodynamically advance the dephosphorization reaction even if the slag composition is adjusted to the above range. Flux unit consumption increases.

Further, a secondary refining slag is added to the slag produced by the dephosphorization, so that Al _{2 in the} slag is removed.
It is preferable to adjust O ₃ . Thereby, high Al ₂
The secondary refining slag (secondary refining slag) containing O ₃ can be reused to promote slagification.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the accompanying drawings to provide an understanding of the present invention. FIG. 1 is an overall view of a hot metal pretreatment apparatus applied to a hot metal dephosphorization method according to one embodiment of the present invention. As shown in FIG. 1, a hot metal pretreatment device 10 used in a hot metal dephosphorization method according to one embodiment of the present invention.
Is a torpedo car (mixed iron wheel) 12 containing hot metal 11 as an example of a pretreatment furnace, a blowing acid lance 14 for blowing oxygen-containing gas from the receiving port 13 of the torpedo car 12 to the hot metal 11, and a dephosphorization An immersion lance 15 for blowing a flux into the hot metal 11 is provided. Note that reference numeral 16
Is a slag formed on the hot metal 11 by melting a flux or the like.

Next, a method for dephosphorizing hot metal according to one embodiment of the present invention will be described. A flux is blown into the hot metal 11 in a state where the hot metal 11 of 250 tons, which has been subjected to desiliconization treatment in advance from the blast furnace, is put in the torpedo car 12. The flux is conveyed by an inert gas or the like from a blow tank (not shown), and is supplied from the immersion lance 15 together with the inert gas at a pressure of 1 to 5 kg / cm ^{2 to} the hot metal 11.
It is blown in. The flux is a mixture of iron oxide, dust dust, and a solid oxygen source (hereinafter referred to as iron oxide) such as mill scale and quicklime powder, and a flux having an amount corresponding to the phosphorus concentration of the hot metal 11 measured in advance is used. A flux of 5 to 10 kg / ton of hot metal is generally used. On the other hand, oxygen is blown onto the surface of the hot metal 11 from a blowing acid lance 14 connected to an oxygen source by a hose or the like, and oxygen is supplied to the hot metal 11 and the slag 16. Then, the phosphorus in the hot metal 11 is oxidized by the sprayed oxygen and the oxygen contained in the flux, and the iron oxide, the quicklime powder and the like in the flux are melted by the hot metal 11 and the slag 16 is formed into a phosphate (P ₂ O). A so-called dephosphorization treatment, which is captured as ₅ ), is performed.

The dephosphorization reaction is represented by the following formula (1). 2P + 5FeO + 3CaO → 3CaO.P ₂ O ₅ + 5Fe (1) In order to efficiently perform the dephosphorization reaction, the liquid phase ratio of the slag 16 must be maintained at a high level, and the activity of CaO must be maintained at a high level. It is important to increase the potential (activity of FeO) in the slag 16. In particular, when the liquid phase ratio of the slag 16 decreases, the contact area between the slag and the metal, which is the effective interface area of the dephosphorization reaction, decreases, and the progress of the dephosphorization reaction deteriorates. Therefore, in order to carry out the dephosphorization reaction quickly and efficiently, it is important to generate slag having good slagging properties.

In view of this, Al in the slag 16 during the dephosphorization treatment
_Two O_Three The concentration is 5 to 15% by weight. This allows
The melting point of the generated slag 16 can be lowered,
As a result, the liquid phase ratio of the slag 16 can be improved. And fluorite
Liquid phase ratio sufficient for dephosphorization without adding slagging accelerators such as
Can be secured. This Al_Two O_Three To adjust the density,
Secondary refining slag (secondary refining
(Slag) to the slag 16
Wear. Secondary smelting slag is Al_Two O_Three Content is high.
CaO, SiO_Two Forming a composite composition with
Has the advantage of dissolving in In addition, the sulfur produced by the dephosphorization
The basicity of the lug 16 is adjusted to 1.5-7.0
And it is easy to slag, and the generated phosphor (P_Two O
_Five ) Can be stably captured by the slag 16. I
If the slag 16 contains excess CaO,
Slag liquid accompanying excessive precipitation of Lee CaO (unreacted CaO)
Deterioration of the dephosphorization reaction due to a decrease in phase ratio, or
Dephosphorization treatment that suppresses deterioration of trapping performance and wear of refractories
It can be carried out. This basicity adjustment is included in the hot metal 11.
To adjust the amount of Si contained, _Two Contains
Can be carried out by adding a substance.

Further, the amount of FeO in the slag 16 is 10-25.
Weight percent. As a result, the potential (activity of FeO) in the slag 16 is increased, and the phosphorous (P
Dephosphorization can be performed efficiently by promoting the production of ₂ O ₅ ). FeO in the slag is supplied from the lance 14 to the hot metal 1
It is supplied into the slag 16 from the oxygen blown to the surface of 1 and the iron oxide in the blown flux, and the FeO concentration can be adjusted to a predetermined range by adjusting the iron oxide content in the flux and the amount of the blown oxygen. it can. Further, the temperature of the hot metal 11 is in the range of 1250 to 1400 ° C.
Stable dephosphorization can be performed by increasing the liquid phase ratio of No. 6 and setting the equilibrium of the phosphorous oxide between the slag and the metal on the side where dephosphorization is easy.

[0013]

Next, an embodiment of a method for dephosphorizing hot metal will be described. 280 tons of hot metal containing 0.1% of phosphorus was put in a torpedo car, and a dephosphorization treatment was performed by blowing flux into the hot metal from an immersion lance and blowing oxygen from another lance. Then, the phosphorus concentration after the dephosphorization treatment, the state of refractory erosion, the decrease in the carbon concentration [C] in the hot metal, the refining agent cost index, and the like were investigated. Table 1 shows the results. Example 1
Is the case where the basic slag is 4.2, the content of FeO is 15.0% by weight, the content of Al ₂ O ₃ is 8.5% by weight, and the secondary smelting slag is used as a flux for adjusting the concentration of Al ₂ O _3. Yes, the phosphorus concentration [P] after treatment can be reduced to 0.015%, there is little erosion of refractories and [C] decrease in hot metal, and the refining agent cost index is 0.65, which is better than the conventional index 1. The overall evaluation was good (良 い). In Example 2, the slag basicity was 5.2, FeO was 16.3% by weight, Al ₂
This is the case where O ₃ is adjusted to 13.4% by weight and secondary smelting slag is used as a flux for adjusting the Al ₂ O ₃ concentration. The [P] concentration after the treatment can be adjusted to 0.013%, and the refractory material is melted. Loss and decrease in [C] in hot metal, refining agent cost index is 0.7
0, which was good, and the overall evaluation was good (良 い). In Example 3, the slag basicity was 3.5 and FeO was 1
1.2 wt%, the Al ₂ O ₃ to 9.7 wt%, Al ₂
This is the case where secondary refining slag is used as a flux for adjusting the O ₃ concentration. The [P] concentration after the treatment can be made 0.021%, and there is little erosion of refractories and [C] drop in hot metal, and refining. The agent cost index was as good as 0.67, and the overall evaluation was good (良 い). In Example 4, the basicity of the slag was set to 7.0, and the [P] concentration after the treatment was set to 0.0.
19%, the erosion of the refractory and the decrease in [C] in the hot metal were small, the refining agent cost index was as good as 0.72, and the overall evaluation was good (○).

In Examples 5 and 6, the slag FeO was added to 10.
0% by weight and 25.0% by weight. The [P] concentration after the treatment can be 0.020% and 0.017%, respectively, and there is little erosion of refractories and [C] drop in hot metal. , And the refining agent cost indices were as good as 0.61 and 0.66, respectively, and the overall evaluation was good (○). Example 7,
No. 8 is a case where the Al ₂ O ₃ of the slag was 5.0% by weight and 15.0% by weight, and the [P] concentration after the treatment was 0.011% and 0.016%, respectively. And the refining agent cost index was good at 0.71 and 0.69, respectively, and the overall evaluation was good (と). Examples 9 and 10 are the cases where the temperature of the hot metal was 1250 ° C. and 1400 ° C., respectively.
The [P] concentrations after the treatment were 0.009% and 0.02%, respectively.
5%, the refractory erosion and the decrease in [C] in the hot metal were small, and the refining agent cost index was good at 0.70 and 0.68, respectively. The overall evaluation was good (良 い). . As described above, good dephosphorization characteristics were obtained in each of the examples, and further, there was no wear of the refractory or increase in the dephosphorization flux, and a good overall evaluation was obtained.

[0015]

[Table 1]

On the other hand, in Comparative Example 1, the slag basicity was 1.4, FeO was 12.3% by weight, and Al ₂ O ₃ was 9.
4 wt%, and secondary refining slag was used as a flux for adjusting the concentration of Al ₂ O _3. Refractory erosion and [C] reduction in hot metal were small, and the refining agent cost index was 0.75.
However, the [P] concentration after the treatment was as high as 0.039%, and the result was poor (x) as the overall evaluation. Comparative Example 2 is a case where the basicity of the slag became 8.4,
The loss of refractory and the decrease in [C] in the hot metal were small, and the refining agent cost index was 0.69, but the [P] concentration after the treatment was as high as 0.042%, which was bad for the overall evaluation ( ×)
The result was. Comparative Example 3 is a case in which the slag FeO was 6.7% by weight, and the refractory erosion and hot metal [C]
Although the decrease was small and the refining agent cost index was 0.71, the [P] concentration after the treatment was as high as 0.041%, and the overall evaluation was poor (x). Comparative Example 4
This is the case where the slag FeO was 28.0% by weight, and the [P] concentration of the hot metal could be as low as 0.007%. However, the erosion of the refractory and the decrease in the [C] in the hot metal increased, and the overall evaluation The result was bad (x). Comparative Example 5 was a case in which alumina flakes were used for adjusting the Al ₂ O ₃ concentration in the slag. Dephosphorization was good, but the refining agent cost index was slightly higher at 0.97. Somewhat bad (△) result.

[0017]

[Table 2]

The embodiment of the present invention has been described above.
The present invention is not limited to the above-described embodiment, and all changes in conditions that do not depart from the gist are within the scope of the present invention. For example, besides secondary refining slag, ladle slag after AL deoxidation can be added to the slag. Further, the dephosphorization of the hot metal can be performed using a container such as a top and bottom blown converter and a hot metal pot in addition to a torpedo car and a converter.

[0019]

The method for dephosphorizing hot metal according to claims 1 to 3,
The slag produced by the dephosphorization has a basicity of 1.5 to 7.0.
And then, the FeO 10 to 25 wt%, the Al ₂ O ₃ 5 to 1
Since it is contained in an amount of 5% by weight, slagification of the slag is promoted, the dephosphorization efficiency is maintained at a high level, the intensity of flux is reduced, and the amount of slag generated can be reduced.
The generated slag can be recycled.

[0020] In particular, the method for dephosphorizing hot metal according to claim 2 comprises:
Since the hot metal temperature at the end of dephosphorization is set to 1250 to 1400 ° C, it is possible to promote the slagging and improve the efficiency of the dephosphorization reaction, reduce the unit flux, and improve the workability of the processing in the post-process. can do. Moreover, refining such as decarburization refining to be performed later can be performed at low cost by using molten iron having a low phosphorus concentration.

According to a third aspect of the present invention, there is provided a method for dephosphorizing hot metal, comprising adding a secondary smelting slag to the dephosphorized slag to remove Al ₂ in the slag.
Since the amount of O ₃ is adjusted, the secondary refining slag, which is waste, can be effectively used, the slag of the slag can be made more favorable, the hot metal can be made low-phosphorus hot metal, and the cost of refining such as dephosphorization can be reduced.

[Brief description of the drawings]

FIG. 1 is an overall view of a hot metal pretreatment apparatus applied to a hot metal dephosphorization method according to an embodiment of the present invention.

[Explanation of symbols]

10: Hot metal pretreatment device: 11: Hot metal: 12: Topped car: 13: Inlet port: 14: Blowing acid lance: 15: Immersion lance: 16: Slag

Claims (3)

[Claims] 1. A method for dephosphorizing hot metal in which a flux is added to hot metal in a pretreatment furnace to remove phosphorus from the hot metal, the slag composition generated by the dephosphorization has a basicity of 1.5 to 7.0,
The FeO 10 to 25 wt%, dephosphorization method molten iron, characterized in that the Al ₂ O ₃ and 5 to 15 wt%. 2. The hot metal dephosphorization method according to claim 1, wherein the hot metal temperature at the end of the dephosphorization is from 1250 to 1400.
C. A method for dephosphorizing hot metal, characterized in that the temperature is set to ° C. 3. The method for dephosphorizing hot metal according to claim 1, wherein a secondary refining slag is added to the slag generated by the dephosphorization to adjust Al ₂ O ₃ in the slag. A method for dephosphorizing hot metal, comprising: