JP2001234223A - Method for refining converter type molten pig iron dephosphorization furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To execute a molten pig iron dephosphorization treatment with a little quicklime unit requirement and without using halide. SOLUTION: In the method for executing the molten pig iron dephosphrization treatment by the quicklime and oxygen and/or iron oxide in a top and bottom blown converter, a stage of tapping the molten pig iron while allowing dephosphorization slag to remain wholly or partly in the furnace after the end of the dephosphorization treatment, then charging the molten pig iron of the next charge into the furnace in the state of allowing the dephosphorization slag to remain and subjecting the molten pig iron to the dephosphorization is executed at least >=1 times. The slag basicity at the end of the dephosphorization treatment is preferably regulated to 1.5 to 3 and the [Si] concentration in the molten pig iron to be charged to <=0.3%. The stages described above may be repetitively executed in a range where the (P) concentration in the slag amount after the dephosphorization refining is <=35%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a hot metal dephosphorization method.

[0002]

2. Description of the Related Art A method for dephosphorizing hot metal using quick lime and an oxidizing agent is widely used. When a topped car, which is a transport container, is used as a reaction container, the volume of the upper space (free board) is small, so that it has a high basicity and a low (T ·
In order to suppress slag forming as Fe), dephosphorization is performed in a large amount of quick lime by using hot metal that has been desiliconized in advance (for example, iron and steel, Vol. 69, 1).
983, pp. 1818). In this case,
Although desiliconization has been performed in advance, there is a problem that the amount of dephosphorized slag is large due to the large amount of quicklime, and the slagification is poor due to the high basicity, and a large amount of halides such as fluorite and calcium chloride are used. Since it is necessary to use the slag, there arises a problem that the amount of slag increases and erosion of the refractory becomes severe.

[0003] Conventionally, attempts have been made to improve the reaction efficiency of hot metal dephosphorization without using a halide.

For example, Japanese Patent Application Laid-Open No. Hei 2-11712 discloses a dephosphorizing agent obtained by mixing iron oxide, CaO and SiO ₂ and melting or sintering them. JP-A-56-938
No. 06 discloses a basicity (CaO / SiO ₂ ) of 1.8.
A dephosphorizing agent is disclosed, which is obtained by sintering a powdery raw material which becomes 2CaO.SiO ₂ by being blended so as to be 2.3 to 2.3. In these cases, the cost required for melting or sintering is high, so that they have not been put to practical use.

Japanese Patent Application Laid-Open No. 8-157921 discloses that in dephosphorization of hot metal in a converter, the basicity is 1.2 to 2.0,
A method is disclosed in which ₂ O ₃ = 2 to 16% and (T · Fe) = 7 to 30%. In this case, since the reaction takes place only by the top slag due to the converter, the basicity of the top slag is reduced, 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 decreases.

On the other hand, hot metal dephosphorization using decarburized slag is disclosed in Japanese Unexamined Patent Publication No. 63-93813 by using one of two converters as a dephosphorizing furnace and the other as a decarburizing furnace. There is disclosed a method of dephosphorizing the generated converter slag and a refining agent mainly containing quicklime. However, although the converter slag (decarburized 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 melted easily because it is about 1350 ° C. Efficiency is lower than with quicklime. Furthermore, the decarburized slag rapidly dissolves when the dephosphorization process proceeds and the temperature and the slag composition reach conditions suitable for dissolution. However, since the decarburized slag contains a high concentration of (T.Fe), there is a problem that when the decarburized slag is melted, a decarburizing reaction occurs rapidly, so that slopping frequently occurs.

On the other hand, as a method for treating hot metal dephosphorization slag,
For example, Japanese Patent Application Laid-Open No. 57-179090 discloses a phosphate fertilizer in which (P ₂ O ₅ ) in the produced slag is reduced to 15% or more by dephosphorizing high-phosphorus iron containing 0.15 to 0.5% of [P]. Although a method using the raw material is disclosed, there is no knowledge about the (P ₂ O ₅ ) concentration that can be concentrated in the slag under the condition that the hot metal [P] is low.

[0008]

SUMMARY OF THE INVENTION The present invention requires a large amount of quicklime and a large amount of halide for slagging in the case of high basicity and low (T.Fe) treatment of the prior art. and a problem that there is, in the dephosphorization agent by mixing the disclosed CaO and SiO ₂ was melted / sintered in JP-a 2-11712 and JP 56-93806, JP-required melting or sintering The problem of high cost,
In the technique disclosed in Japanese Patent Application Laid-Open No. 63-93813, the method of controlling the top slag composition in hot metal dephosphorization in a converter disclosed in Japanese Patent No. 7921 significantly reduces the dephosphorization ability. The dephosphorization efficiency is lower than when using quick lime, and when the decarburization slag is melted, the decarburization reaction occurs abruptly, which solves the problem of frequent slopping.The dephosphorization reaction efficiency is reduced without using halide. An object of the present invention is to provide a hot metal dephosphorization method capable of raising the slag generation amount by lowering.

[0009]

The gist of the present invention is as follows.

(1) In a method of performing hot metal dephosphorization treatment with quick lime and oxygen and / or iron oxide in a top and bottom blown converter, the whole or a part of the dephosphorization slag is left in the furnace after completion of the dephosphorization treatment. A step of performing dephosphorization treatment at least once by charging hot metal while leaving the dephosphorized slag and then charging the next charge of hot metal while leaving the dephosphorized slag. Refining method of phosphorus furnace. Here, the dephosphorization treatment refers to a treatment of stirring while supplying quicklime and top-blown oxygen and / or iron oxide.

(2) The method for refining a converter type hot metal dephosphorization furnace according to (1), wherein the slag basicity at the end of the dephosphorization treatment is 1.5 to 3.

(3) In the above (1) or (2),
A refining method for a converter type hot metal dephosphorization furnace, wherein the [Si] concentration in the hot metal charged is 0.3% or less.

(4) The converter according to any one of (1) to (3), wherein the step (P) in the slag after the dephosphorizing refining is repeated within a range of 35% or less. Refining method for hot metal dephosphorization furnace.

[0014]

DETAILED DESCRIPTION OF THE INVENTION The invention is based on the fact that the slag produced in the dephosphorization process has an additional dephosphorization capacity.

The hot metal dephosphorization treatment is a non-equilibrium system process that occurs between a slag phase having a high (T.Fe) and a high oxygen activity and a molten iron having a low oxygen activity close to carbon saturation. The speed is expressed by equation (1).

−d [% P] / dt = (A · k / W) {[% P] −a _PO2.5 / L} (1)

Here, [% P] is the phosphorus concentration in the hot metal, t is time (s), A is the reaction interface area (cm ² ), and k is the overall mass transfer coefficient.
(cm / s), W is the amount of hot metal (t), a _PO2.5 is the activity in (PO _2.5 ) in slag, L is the equilibrium distribution ratio at the interface, and the interface concentration indicated by ^* is given by equation (2). expressed. The concentration (%) means percent by mass (the same applies to the following).

[0018] ^{_{L = a PO2.5 * / [%}} P] * = K × a O * 2.5 ··· ... (2)

Here, K is an equilibrium constant, and _aO ^* is an interfacial oxygen activity.

[0020] If, in proportion to the concentration of a _PO2.5 is slag (PO _2.5), and, if L is not large enough, the slag
As the (PO _2.5 ) concentration increases, a _PO2.5 / L in equation (1) increases, so that the dephosphorization rate decreases.

However, according to a detailed study by the present inventors, in the case of hot metal dephosphorization slag, even if the (PO _2.5 ) concentration in the slag changes, a _PO2.5 / L in the equation (1) is hardly affected. I did not receive it. This is due to the following two factors.

1) The contact interface between the hot metal and the slag at which the reaction takes place is not the interface between the bulk hot metal and the slag, but is mainly the surface of the molten iron particles suspended in the slag by the energy of top blowing or bottom blowing. Oxygen activity of the slag side
It is close to a value that balances with (T.Fe) and is sufficiently large. Therefore, as can be seen from equation (2), L is sufficiently large, so that a _{PO 2.5} / L is always negligibly small even if the (PO _2.5 ) concentration in the slag changes.

2) Even if the (PO _2.5 ) concentration in the slag changes, a _PO2.5 is constant as long as the slag is two-phase saturated with 2CaO · SiO ₂ and 3CaO · P ₂ O ₅ . Therefore, a _PO2.5 / L does not change at all even if the (PO _2.5 ) concentration in the slag changes.

This means that (P)
O _2.5 ) is included, but the principle is that dephosphorization is possible even if reused.

Further, (PO _2.5 ) contained in the dephosphorization slag has a function of suppressing the nucleation of CO bubbles due to decarburization because it is a surface active component. ) Can be kept firm. Therefore, in the dephosphorization treatment using the dephosphorization slag containing (PO _2.5 ), decarburization is small, and the heat tolerance in the converter, which is the next step, can be greatly increased.

The invention according to the above (1) utilizes this, and in the method of performing hot metal dephosphorization treatment with quick lime and oxygen and / or iron oxide in a top and bottom blown converter, the furnace is provided after the dephosphorization treatment is completed. A step of discharging hot metal while leaving the whole or a part of the dephosphorized slag inside, and then performing a dephosphorization treatment by charging hot metal of the next charge while leaving the dephosphorized slag, at least once The above is to be implemented.

The dephosphorized slag remaining in the furnace is 1), 2).
Is preferably 10 kg / t or more in order to sufficiently exhibit the effect of the present invention. In addition, if this step is performed one or more times, the effects of 1) and 2) are sufficiently exhibited, so the upper limit is not particularly defined. If the amount of slag increases, iron loss to the slag and decrease in heat tolerance will occur.However, if only a part of the slag is discharged and the slag amount is maintained in the range of 30 to 150 kg / t, it will be carried out any number of times. It is possible to

Here, the reason for using the top-bottom blow converter is that the contact interface between the hot metal and the slag where the reaction takes place is suspended not in the interface between the bulk hot metal and the slag but in the slag with the energy of the top blow and the bottom blow. This is because the surface of the molten iron particles is mainly used. In order to promote the generation of granular iron by top blowing, the top blowing acid transfer rate is preferably 0.5 to 2.5 Nm ³ / min / t, and 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 transfer rate is less than 0.5 Nm ³ / min / t, the influence of the (PO _2.5 ) concentration in the slag is small because the reaction area of the high oxygen activity is small due to the small generation of iron particles. On the other hand, when it is larger than 2.5 Nm ³ / min / t, the generation of granular iron by top blowing is too severe, and a large amount of splash is generated, which tends to hinder the operation. When the bottom blown gas flow rate is less than 0.03 Nm ³ / min / t, the reaction interface area of the high oxygen activity is reduced due to the small generation of iron particles, so the influence of the (PO _2.5 ) concentration in the slag is affected. On the other hand, when it is larger than 0.2 Nm ³ / min / t, the generation of granular iron due to bottom blowing is too severe, and a large amount of splash is generated, which tends to hinder the operation. The amount of dephosphorized slag remaining in the furnace is not particularly limited, but is desirably 150 kg / t or less for the above-mentioned reason.

In the invention according to the above (2), the slag basicity (CaO / SiO ₂ ) at the end of the dephosphorization treatment is specified, and the basicity is 1.5 to 3. Basicity is 1.
If it is lower than 5, the slag becomes saturated with CaO.SiO ₂ , and the slag does not satisfy the condition of two-phase saturation of 2CaO.SiO ₂ and 3CaO.P ₂ O ₅ , so that _aPO2.5 increases. on the contrary, since the basicity is slag 3CaO · SiO ₂ saturation is higher than 3, the slag is 2CaO · SiO ₂ and 3CaO · P ₂ O _{5 2}
Since the condition of phase saturation is not satisfied, a _{PO 2.5}
, And as shown in FIG. 1, the dephosphorization efficiency is greatly reduced in each case. Here, the dephosphorization efficiency (K) is defined by equation (3).

K = {ln (before treatment [% P] / after treatment [% P])} / quick lime basic unit (kg / t) (3)

In the invention according to the above (3), the composition of the hot metal charged into the dephosphorization furnace is specified, and the [Si] concentration in the hot metal charged is set to 0.3% or less. . [S
i] When the concentration is higher than 0.3%, it is necessary to repeatedly add quicklime to secure basicity for dephosphorization, which is not economical. The lower limit is not particularly defined, but is preferably 0.1% or more in consideration of the load during the desiliconization work.

In the invention according to the above (4), the upper limit in the case of repeating the process is specified, and the process is repeatedly performed when the (P) concentration in the slag after dephosphorization refining is 35% or less. Is what you do. When the (P) concentration in the slag after dephosphorization refining is higher than 35%, the slag is 2Ca
O · SiO ₂ and 3CaO · P ₂ O a _PO2.5 for not satisfy the condition that a two-phase saturation ₅ increases, the dephosphorization capacity as shown in FIG. 2 significantly reduced.

[0033]

EXAMPLES The examples were carried out using a 6 ton scale top and bottom blown converter. A 4-mm lance having a diameter of 7 mm was used as the upper blowing lance, and the oxygen supply rate was 350 Nm ³ / h. The bottom was blown with a small diameter collecting pipe tuyere, and nitrogen was supplied at 22 Nm ³ / h.

C: 4.15% melted in another melting furnace,
Si: 0.21%, Mn: 0.23%, P: 0.095
%, S: 0.012%, about 6 tons of hot metal at a temperature of 1330 ° C. was charged into a converter, and dephosphorization refining was performed for 7 minutes. During dephosphorization, 9.3 kg / t of quicklime and 16.4 kg / t of iron ore were fed from the upper bunker. After treatment: C: 3.84%, S
i: 0.02%, Mn: 0.08%, P: 0.021%,
S: 0.015% and the temperature was 1365 ° C. The composition of the resulting dephosphorized slag was T.Fe: 9.25%, CaO: 47.
3%, SiO ₂ : 25.5%, PO _2.5 : 8.65%, MnO: 5.5
_{55%, Al 2 O 3:} 2.32%, MgO: 3.13% basicity was an amount of about 20 kg / t 1.85. Dephosphorization efficiency is 0.
163.

After the above treatment, the hot metal is discharged, and
C: 4.11%, S with all phosphorus slag remaining in the furnace
i: 0.18%, Mn: 0.20%, P: 0.11%,
S: about 6 tons of solution at 0.014% at a temperature of 1320 ° C
The iron was charged into the converter, and dephosphorization refining was performed for 7 minutes. During dephosphorization
Is 5.7kg / t for quicklime, 14.5kg / t for iron ore, upper bun
I put it in the car. After the treatment, C: 3.95%, Si: 0.2.
02%, Mn: 0.095%, P: 0.012%, S:
The temperature was 1370 ° C at 0.016%. Generated
The composition of the phosphorus slag is T.Fe: 13.75%, CaO: 45.3
%, SiO_Two: 26.5%, PO _2.5: 12.1%, MnO: 6.5
5%, Al_TwoO_Three: 2.84%, MgO: 3.53%, basicity is
At 1.71, it was about 35 kg / t. Dephosphorization efficiency is 0.3
It was extremely high at 89.

[0036]

Comparative Example In a comparative example, an injection dephosphorization test using a 6-ton scale hot metal pot was conducted. A 7 mmφ two-hole nozzle was provided at the tip of the injection lance. 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.

Melted in another melting furnace, C: 4.25%,
Si: 0.10%, Mn: 0.21%, P: 0.11%,
S: About 6 tons of hot metal at a temperature of 1340 ° C. at 0.011% was charged into a hot metal pot, and dephosphorization refining was performed for 15 minutes. During the dephosphorization, 19.5 kg / t of quicklime and 43.4 kg / t of iron ore were injected. After the treatment, C: 4.14%, Si: 0.1.
02%, Mn: 0.18%, P: 0.023%, S: 0.1%
At 008% the temperature was 1325 ° C. The composition of the resulting dephosphorized slag is 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 4.0
8 was about 34 kg / t. The dephosphorization efficiency was 0.08.

After the above treatment, the hot metal is discharged, and subsequently, while the entire amount of dephosphorized slag remains in the pot, C: 4.15%, S
i: 0.12%, Mn: 0.25%, P: 0.11%,
About 6 tons of hot metal having a S of 0.014% and a temperature of 1365 ° C. was charged, and the dephosphorization refining was performed for 15 minutes. During dephosphorization, 17.7 kg / t of quicklime and 42.5 kg / t of iron ore were injected. After the treatment, C: 4.0%, Si: 0.02%,
Mn: 0.15%, P: 0.042%, S: 0.011%
And the temperature was 1345 ° C., and the phosphorous could not be sufficiently removed. The dephosphorization efficiency was extremely low at 0.054.

[0039]

According to the present invention, it is possible to carry out hot metal dephosphorization treatment with a small amount of quicklime and without using a halide represented by fluorite by recycling dephosphorized slag. Become.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between basicity and dephosphorization efficiency in dephosphorization treatment.

FIG. 2 is a diagram showing the relationship between the (P) concentration in the slag amount after dephosphorization refining and the dephosphorization efficiency.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Yoji Demoto 20-1 Shintomi, Futtsu Nippon Steel Corporation Technology Development Division F term (reference) 4K002 AB04 AC07 AC09 AD05 AE00 AE02 4K014 AA03 AB03 AB04 AC16 AD00

Claims (4)

[Claims] 1. A method for performing hot metal dephosphorization treatment with quick lime and oxygen and / or iron oxide in a top and bottom blown converter, wherein all or part of the dephosphorization slag is left in the furnace after the dephosphorization treatment is completed. A converter-type hot metal dephosphorization method characterized by performing at least one or more steps of removing hot metal as it is, and then performing a dephosphorization treatment by charging hot metal of a next charge while the dephosphorized slag is left. Furnace refining method. 2. A refining method for a converter type hot metal dephosphorization furnace according to claim 1, wherein the slag basicity at the end of the dephosphorization treatment is 1.5.
A refining method for a converter type hot metal dephosphorization furnace, characterized in that: 3. The method for refining a converter type hot metal dephosphorization furnace according to claim 1, wherein the [Si] concentration in the hot metal charged is 0.3% or less. Refining method for hot metal dephosphorization furnace. 4. The method for refining a converter type hot metal dephosphorization furnace according to claim 1, wherein the (P) concentration in the slag after dephosphorization refining is within a range of 35% or less. The method for refining a converter-type hot metal dephosphorization furnace, wherein the method is repeated.