JP4414544B2 - Refining method for converter type hot metal dephosphorization furnace - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hot metal dephosphorization method.
[0002]
[Prior art]
A method of dephosphorizing hot metal using quick lime and an oxidizing agent is widely used. When a topped car that is a transport container is used as a reaction container, since the volume of the upper space (free board) is small, desiliconization treatment is performed in advance in order to suppress slag forming with high basicity and low (T · Fe). Dephosphorization is carried out with a large amount of quicklime unit using the molten iron (for example, iron and steel, Vol. 69, published in 1983, page 1818 and later). In this case, there is a problem that there is a lot of dephosphorization slag because there is a lot of quicklime basic unit although it has been desiliconized in advance, and hatching worsens due to high basicity, such as fluorite and calcium chloride Since it is necessary to use a large amount of halide, there is a problem that the amount of slag increases and the refractory melts severely.
[0003]
Conventionally, attempts have been made to improve the reaction efficiency of hot metal dephosphorization without using a halide.
[0004]
For example, Japanese Patent Application Laid-Open No. 2-11712 discloses a dephosphorization agent obtained by mixing and melting or sintering iron oxide, CaO and SiO ₂ . Japanese Patent Application Laid-Open No. 56-93806 discloses a dephosphorizing agent obtained by sintering a powder raw material containing 2CaO · SiO ₂ by blending basicity (CaO / SiO ₂ ) to be 1.8 to 2.3. ing. In these cases, since the cost required for melting or sintering is high, it has not been put to practical use.
[0005]
JP-A-8-157721 discloses basicity = 1.2 to 2.0, Al ₂ O ₃ = 2 to 16%, (T · Fe) = 7 to 30% in hot metal dephosphorization in a converter. A method is disclosed. In this case, the reaction takes place only by the top slag because of the converter, so the basicity of the top slag is lowered and the dephosphorization ability is greatly increased by adding a large amount of neutral oxide Al ₂ O _3. There is a problem that it drops.
[0006]
On the other hand, hot metal dephosphorization using a decarburizer is disclosed in Japanese Patent Laid-Open No. 63-93913, in which one of two converters is a dephosphorizer and the other is a decarburizer. A method of dephosphorizing with a refining agent mainly composed of furnace lime and quicklime is disclosed. However, although the converter slag (decarburization slag) is in a molten state at the converter blow-off temperature of 1650 ° C., in the case of hot metal dephosphorization, it cannot be easily melted because it is about 1350 ° C. The efficiency is lower than when quicklime is used. Further, the decarburized soot dissolves rapidly when the dephosphorization process proceeds and the temperature and slag composition reach conditions suitable for dissolution. However, since a high concentration of (T · Fe) is contained in the decarburized soot, there is a problem that when the decarburized soot is melted, a decarburization reaction occurs abruptly, so that slopping occurs frequently.
[0007]
On the other hand, as a method for treating hot metal dephosphorization slag, for example, Japanese Patent Application Laid-Open No. 57-179090 discloses (P) in the produced slag by dephosphorizing high phosphorus containing 0.15 to 0.5% of [P]. ₂ O ₅ ) is disclosed as a raw material for phosphate fertilizer with a content of 15% or more, but there is also some knowledge about the concentration of (P ₂ O ₅ ) that can be concentrated in slag under low hot metal [P] conditions. Not.
[0008]
[Problems to be solved by the invention]
The present invention has a problem that the conventional technology has a high basicity and low (T · Fe) treatment in which a large amount of quicklime is required and a large amount of halide is required for hatching. In the dephosphorization agent melted / sintered by mixing CaO and SiO ₂ disclosed in JP-A-1111712 and JP-A-56-93806, the cost required for melting or sintering is high. In the technique disclosed in Japanese Patent Laid-Open No. 63-93913, the method of controlling the top slag composition in the hot metal dephosphorization in the converter disclosed in Japanese Patent No. The dephosphorization efficiency is lower than when quick lime is used, and the decarburization reaction occurs rapidly when the decarburized soot is melted. Raise There is provided a hot metal dephosphorization method capable of reducing the lag emissions.
[0009]
[Means for Solving the Problems]
The gist of the present invention is as follows.
[0010]
(1) In a method of performing hot metal dephosphorization treatment with quicklime and oxygen and / or iron oxide in an upper-bottom blow converter, the hot metal is left with all or part of the dephosphorization slag remaining in the furnace after the dephosphorization treatment is completed. A step of performing a dephosphorization process by charging the hot metal of the next charge while leaving the dephosphorization slag and performing the dephosphorization treatment at least once. Refining method. Here, the dephosphorization process refers to a process of stirring while supplying quicklime and top-blown oxygen and / or iron oxide.
[0011]
(2) In the method (1), the slag basicity at the end of the dephosphorization treatment is 1.5 to 3, wherein the refining method for the converter type hot metal dephosphorization furnace is characterized in that
[0012]
(3) The method for refining a converter type hot metal dephosphorization furnace according to (1) or (2), wherein the [Si] concentration in the molten iron to be charged is 0.3% or less.
[0013]
(4) In the above (1) to (3), the process is repeated in the range where the (P) concentration in the slag amount after dephosphorization is 35% or less. Phosphorus furnace refining method.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is based on the fact that the slag produced by the dephosphorization process has an additional dephosphorization capability.
[0015]
Hot metal dephosphorization is a non-equilibrium process that occurs between a slag phase with a high (T · Fe) and high oxygen activity and molten iron with a low oxygen activity close to carbon saturation, and the dephosphorization rate is ( 1) It is represented by the formula.
[0016]
−d [% P] / dt = (A · k / W) {[% P] −a _PO2.5 / L} (1)
[0017]
Where [% P] is the phosphorus concentration in the hot metal, t is the time (s), A is the reaction interfacial area (cm ² ), k is the overall mass transfer coefficient (cm / s), and W is the hot metal amount (t). , A _PO2.5 is the activity in the slag (PO _2.5 ), L is the equilibrium distribution ratio at the interface, and is expressed by the equation (2) according to the interface concentration indicated by ^* . The concentration (%) means mass percent (the same shall apply hereinafter).
[0018]
L = a _PO2.5 ^* / [% P] ^* = K × a _O ^{* 2.5} (2)
[0019]
Here, K is an equilibrium constant, and _aO ^* is an interfacial oxygen activity.
[0020]
If, a _PO2.5 is proportional to the concentration in the slag (PO _2.5), and, if L is not large enough, with an increase in the slag (PO _2.5) Concentration (1) of a _PO2.5 Since / L increases, the dephosphorization rate decreases.
[0021]
However, according to a detailed study by the present inventors, in the case of hot metal dephosphorized slag, even if the (PO _2.5 ) concentration in the slag changes, a _PO2.5 / L in the formula (1) is hardly affected. I found out. This is due to the following two factors.
[0022]
1) The contact interface between hot metal and slag where the reaction takes place is not the interface between bulk hot metal and slag, but mainly the surface of molten iron particles suspended in the slag with the energy of top blowing or bottom blowing. The amount is close to a value almost in equilibrium with (T · Fe) on the slag side, and is sufficiently large. Therefore, as can be seen from equation (2), L is sufficiently large so that a _PO2.5 / L is always small enough to be ignored even if the (PO _2.5 ) concentration in the slag changes.
[0023]
2) Even if the concentration of slag (PO _2.5 ) changes, as long as the slag is two-phase saturated of 2CaO · SiO ₂ and 3CaO · P ₂ O ₅ , a _PO2.5 is constant. Therefore, a _PO2.5 / L does not change at all even if the concentration in slag (PO _2.5 ) changes.
[0024]
This is the principle that even though (PO _2.5 ) is contained in the slag after dephosphorization, dephosphorization is possible even if it is reused.
[0025]
Furthermore, (PO _2.5 ) contained in dephosphorization has a function of suppressing the nucleation of CO bubbles accompanying decarburization because it is a surface active component, and suppresses decarburization during dephosphorization and hardens (T · Fe). Can keep. Accordingly, the dephosphorization treatment using the dephosphorization soot containing (PO _2.5 ) has less decarburization and can greatly increase the heat tolerance in the converter as the next step.
[0026]
The invention according to the above (1) utilizes this, and in the method of performing hot metal dephosphorization treatment with quicklime and oxygen and / or iron oxide in an upper bottom blowing converter, the dephosphorization treatment is performed in the furnace after completion of the dephosphorization treatment. The step of removing the hot metal while leaving all or part of the phosphorous slag and then charging the molten iron with the next charge while leaving the dephosphorized slag is performed at least once. Is.
[0027]
The dephosphorization slag remaining in the furnace is desirably 10 kg / t or more in order to sufficiently exhibit the effects of 1) and 2). Moreover, if the said process is implemented once or more, in order to fully show the effect of 1) and 2), an upper limit in particular is not prescribed | regulated. If the amount of slag increases, iron loss to the slag and a decrease in heat tolerance will occur, but if only a part of the slag amount is eliminated and the slag amount is maintained within the range of 30 to 150 kg / t, it will be repeated any number of times. Is possible.
[0028]
Here, the reason for the top-bottom blowing converter is that the contact interface between the hot metal and slag where the reaction occurs is not the interface between the bulk hot metal and slag, but the molten iron particles suspended in the slag with the energy of top blowing and bottom blowing. This is because the surface is mainly used. In order to promote the generation of granular iron by top blowing, the top blowing acid rate is preferably 0.5 to 2.5 Nm ³ / min / t, and as the bottom blowing gas flow rate to promote the generation of granular iron by bottom blowing. 0.03 to 0.2 Nm ³ / min / t is desirable. When the top blowing acid rate is less than 0.5 Nm ³ / min / t, the reaction interface area with high oxygen activity decreases because of the generation of granular iron, so the effect of (PO _2.5 ) concentration in the slag is reduced. On the contrary, when it is larger than 2.5 Nm ³ / min / t, the generation of granular iron due to top blowing is too intense, and a lot of splash is generated, which tends to hinder the operation. When the bottom blowing gas flow rate is smaller than 0.03 Nm ³ / min / t, the reaction interface area with high oxygen activity decreases because of the generation of granular iron, which is affected by the (PO _2.5 ) concentration in the slag. On the other hand, if it is greater than 0.2 Nm ³ / min / t, the generation of granular iron due to bottom blowing is so intense that a large amount of splash is generated and the operation tends to be hindered. The amount of dephosphorization slag remaining in the furnace is not particularly defined, but is preferably 150 kg / t or less for the above-mentioned reasons.
[0029]
The invention according to (2) defines the slag basicity (CaO / SiO ₂ ) at the end of the dephosphorization treatment, and the basicity is 1.5 to 3. Since basicity is slag CaO · SiO ₂ saturation is lower than 1.5, because the slag does not satisfy the condition that a two-phase saturation of 2CaO · SiO ₂ and 3CaO · P ₂ O ₅ a _{PO2 .5} increases, conversely, because the basicity is slag 3CaO · SiO ₂ saturation is higher than 3, that slag is two-phase saturation of 2CaO · SiO ₂ and 3CaO · P ₂ O ₅ Since the condition is not satisfied, _aPO2.5 increases, and as shown in FIG. 1, the dephosphorization efficiency is greatly reduced in any case. Here, the dephosphorization efficiency (K) is defined by equation (3).
[0030]
K = {ln (before treatment [% P] / after treatment [% P])} / lime unit (kg / t) (3)
[0031]
The invention according to (3) defines the hot metal composition charged into the dephosphorization furnace, and the [Si] concentration in the hot metal charged is 0.3% or less. When the [Si] concentration is higher than 0.3%, it is necessary to add quick lime repeatedly in order to secure basicity for dephosphorization, which is not economical. The lower limit is not particularly specified, but it is preferably 0.1% or more in consideration of the load during desiliconization work.
[0032]
The invention according to the above (4) defines the upper limit in the case of repeated execution, and the process is repeated in the range where the (P) concentration in the slag amount after dephosphorization is 35% or less. is there. If (P) concentration in the slag amount in the after dephosphorization refining is higher than 35%, the slag does not satisfy the condition that a two-phase saturation of 2CaO · SiO ₂ and 3CaO · P ₂ O ₅ a _{PO2 .5} increases, and the dephosphorization ability is greatly reduced as shown in FIG.
[0033]
【Example】
The examples were carried out using a 6-ton scale top-bottom blow converter. A 4-hole lance of 7 mmφ was used as the top blowing lance, and the oxygen supply rate was 350 Nm ³ / h. The bottom blowing was a small diameter collecting tube tuyere, and nitrogen was supplied at 22 Nm ³ / h.
[0034]
Melted in another melting furnace, C: 4.15%, Si: 0.21%, Mn: 0.23%, P: 0.095%, S: 0.012%, and the temperature was 1330 ° C. About 6 tons of hot metal was charged into the converter and dephosphorization was performed for 7 minutes. During the dephosphorization, quick lime 9.3 kg / t and iron ore 16.4 kg / t were introduced from the upper bunker. After the treatment, C: 3.84%, Si: 0.02%, Mn: 0.08%, P: 0.021%, S: 0.015%, and the temperature was 1365 ° C. The composition of the generated dephosphorization slag was as follows: T · Fe: 9.25%, CaO: 47.3%, SiO ₂ : 25.5%, PO _2.5 : 8.65%, MnO: 5.55%, Al ₂ O ₃ : 2.32%, MgO: 3.13%, the basicity was 1.85, and the amount was about 20 kg / t. The dephosphorization efficiency was 0.163.
[0035]
After the above treatment, the hot metal is discharged, and then C: 4.11%, Si: 0.18%, Mn: 0.20%, P: 0.11%, with all the dephosphorization slag remaining in the furnace. S: About 6 tons of hot metal having a temperature of 0.014% and 1320 ° C. was charged into a converter, and dephosphorization was performed for 7 minutes. During dephosphorization, quick lime was 5.7 kg / t, iron ore was 14.5 kg / t, and the upper bunker was used. After the treatment, C: 3.95%, Si: 0.02%, Mn: 0.095%, P: 0.012%, S: 0.016%, and the temperature was 1370 ° C. The composition of the generated dephosphorization slag was as follows: T · Fe: 13.75%, CaO: 45.3%, SiO ₂ : 26.5%, PO _2.5 : 12.1%, MnO: 6.55%, Al ₂ O _{3 was} 2.84%, MgO was 3.53%, the basicity was 1.71, and the amount was about 35 kg / t. The dephosphorization efficiency was as extremely high as 0.389.
[0036]
[Comparative example]
In the comparative example, an injection dephosphorization test using a 6-ton scale hot metal ladle was performed. A 7-mmφ 2-hole nozzle was provided at the tip of the injection lance, the carrier gas was supplied as nitrogen at 10 Nm ³ / h, and quick lime and iron ore were blown at a rate of about 2 kg / min / t.
[0037]
Melted in another melting furnace, C: 4.25%, Si: 0.10%, Mn: 0.21%, P: 0.11%, S: 0.011% and the temperature was 1340 ° C. About 6 tons of hot metal was placed in a hot metal ladle and dephosphorized for 15 minutes. During dephosphorization, 19.5 kg / t of quicklime and 43.4 kg / t of iron ore were injected. After the treatment, C: 4.14%, Si: 0.02%, Mn: 0.18%, P: 0.023%, S: 0.008%, and the temperature was 1325 ° C. The composition of the generated dephosphorization slag was as follows: T · Fe: 4.05%, CaO: 59.3%, SiO ₂ : 14.65%, PO _2.5 : 7.75%, MnO: 4.15%, Al ₂ O ₃ : 3.53%, MgO: 2.85%, basicity was 4.08, and the amount was about 34 kg / t. The dephosphorization efficiency was 0.08.
[0038]
After the above treatment, the hot metal is poured out, and then C: 4.15%, Si: 0.12%, Mn: 0.25%, P: 0.11%, leaving all the dephosphorization slag in the pan. S: About 6 tons of hot metal having a temperature of 0.014% and a temperature of 1365 ° C. was charged, and dephosphorization was performed for 15 minutes. During the dephosphorization, 17.7 kg / t of quicklime and 42.5 kg / t of iron ore were injected. After the treatment, C: 4.05%, Si: 0.02%, Mn: 0.15%, P: 0.042%, S: 0.011%, and the temperature is 1345 ° C. could not. The dephosphorization efficiency was as extremely low as 0.054.
[0039]
【The invention's effect】
According to the present invention, it is possible to carry out hot metal dephosphorization treatment by reusing dephosphorization slag without using a quick lime basic unit and using a halide represented by fluorite.
[Brief description of the drawings]
FIG. 1 is a diagram showing the relationship between basicity and dephosphorization efficiency in a dephosphorization process.
FIG. 2 is a graph showing the relationship between the (P) concentration in the amount of slag after dephosphorization and the dephosphorization efficiency.

Claims (4)

In a method of performing hot metal dephosphorization treatment with quicklime and oxygen and / or iron oxide in a top-bottom blowing converter, hot metal is poured out with all or part of the dephosphorization slag remaining in the furnace after the dephosphorization treatment. Next, a refining method for a converter type hot metal dephosphorization furnace, wherein the dephosphorization treatment is performed at least once by charging the molten iron of the next charge while leaving the dephosphorization slag. 2. The refining method for a converter type hot metal dephosphorization furnace according to claim 1, wherein the slag basicity at the end of the dephosphorization process is 1.5 to 3. The refining method for a converter type hot metal dephosphorization furnace according to claim 1 or 2, wherein the [Si] concentration in the hot metal charged is 0.3% or less. Refining method. In the refining method of the converter type hot metal dephosphorization furnace according to any one of claims 1 to 3, the step is repeatedly performed in a range where the (P) concentration in the slag amount after dephosphorization is 35% or less. A refining method for a converter type hot metal dephosphorization furnace characterized by the above.

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