JP2000160220A - Method for restraining slag foaming - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the method for more restraining slag foaming and reducing the lowered of molten iron temp. in the case of pre-treating the molten iron. SOLUTION: When the molten iron 2 is dephosphorized by blowing oxygen source and dephosphorizing agent 4 into the molten iron 2 held in a refining vessel through a lance, a top-blown lance 6 is provided separately from the lance for blowing the dephosphorizing agent 4, and a foaming depressant 8 is blown onto the surface of the slag 5 through the top-blown lance 6 by using oxidizing gas containing >=20 vol.% the air or the oxygen as the carrier gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for suppressing slag forming, and more particularly, to a method of blowing a flux such as iron oxide, oxygen gas or quick lime into hot metal to remove slag from the hot metal. Is a technique for suppressing foaming and expansion (called forming).

[0002]

2. Description of the Related Art In refining a molten metal, when a gas is blown into a slag having a low basicity (for example, CaO / SiO ₂ ), the gas stays in the slag, and the volume of the slag is remarkably increased to form a so-called bubble. It is known that a slag forming phenomenon occurs.

[0003] In recent years, in the steelmaking industry, when molten iron is blasted with oxygen in a converter to form molten steel, in order to reduce the refining load in the converter, oxygen is added to the molten iron before charging the converter. In many cases, a source (iron oxide and oxygen gas) and a dephosphorizing agent such as lime are blown to dephosphorize hot metal in advance. At this time, Si existing in the hot metal is oxidized before the dephosphorization reaction occurs, and the slag having a low basicity is generated. In addition, prior to the dephosphorization treatment, during the tapping of the blast furnace, desiliconization may be performed in a tapping gutter, and if slag generated at this time is accompanied by hot metal to be dephosphorized, it is generated during the dephosphorization treatment. The basicity of the slag decreases. When the dephosphorization treatment is performed under the condition that such a low basicity slag is present, the slag is transported for blowing CO gas or a dephosphorizer generated by a decarburization reaction that proceeds in parallel with the dephosphorization reaction. Gas is included, and the above-described forming phenomenon occurs.

[0004] The reaction vessel used in the pretreatment process of the hot metal (the hot metal is processed before charging the converter, so called as such) is often a topped car or a hot metal pot. Since these vessels have a smaller free board (space in the vessel above the charge) compared to the converter, the slag may flow out of the reaction vessel when the slag is formed. As a result, the hot metal processing is interrupted or the iron yield is reduced, which is not preferable for performing the hot metal processing.

Conventionally, the following three methods have been adopted as measures against such a slag forming phenomenon.

(1) Decrease or stop the supply rate of oxygen source, dephosphorizing agent, etc. (interruption of processing) (2) Sludge treatment (3) Injection of forming inhibitor

[0007] Among them, the method (1) is a method for mainly reducing the supply rate of the oxygen source when slag flows out of the reaction vessel. If the slag flows out severely, the process may be interrupted. This method prolongs the hot metal processing time and lowers the hot metal temperature, which adversely affects the next process.

The method (2) is a method in which measures are taken in advance so that the slag may flow out (for example, pits for the slag flowing out around the reaction vessel), and the hot metal treatment is performed while the slag is flowing out. . In this method, the outflow slag usually contains about 10% by weight of iron, so that the iron yield decreases. In addition, the cost of placing the pits is high, and new work such as unloading slag is increasing.
Not a good measure.

The method (3) sprays an inhibitor on the formed slag to calm down the forming.
For example, Japanese Patent Publication No. 6-084521 discloses that an inert gas (a gaseous suppressant) is sprayed from a side surface of a powder injection lance to a vicinity of a slag / metal interface to agitate the slag or to provide a large number of openings communicating with the atmosphere. It discloses a method of making gas easily released from slag by making. However, this method has a problem that the effect of suppressing the forming is extremely insufficient. Also, Japanese Patent Application Laid-Open No. 4-180507
The publication discloses that 5 to 100 kg of carbonaceous material is added to slag through a powder spraying lance or an addition-only lance adjacent to the lance.
A method of spraying at a rate of / min was proposed. However, in this method, although there is a forming suppressing effect as compared with the gas blowing method described above, it was not possible to sufficiently suppress the forming. Further, Japanese Patent Application Laid-Open No. H08-049004 discloses a method in which CaCO ₃ is sprayed on slag using an inert gas as a carrier gas to suppress forming. However, CaC
O ₃ is decomposed by an endothermic reaction at 898 ° C. or higher as shown in the following formula, so that CaCO ₃ → CaO + CO ₂ lowers the hot metal temperature and limits the amount of the dephosphorizing agent,
There is a problem that a desired amount of dephosphorization cannot be obtained, or a heating agent is required in a converter in the next step, which leads to an increase in cost. There is also a technique for separately blowing oxygen gas through a lance to prevent a temperature drop. The above-mentioned carbonaceous materials, CaCO 3
_In addition to ₃ , there are powders such as expensive metals such as Al and alumina.

[0010]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides a method for suppressing slag forming in which the forming of hot metal can be more effectively suppressed and the amount of drop in the temperature of hot metal is reduced in the pretreatment of hot metal. It is intended to be.

[0011]

Means for Solving the Problems In order to achieve the above object, the inventor has found that it is possible to suppress slag forming by reviewing the conventional control method and devising a method of spraying the suppressant. It was embodied in the present invention.

That is, according to the present invention, an oxygen source and a dephosphorizer are blown into a hot metal held in a refining vessel through a lance,
When dephosphorizing the hot metal, an upper blowing lance is provided separately from the lance into which the dephosphorizing agent is blown, and forming is suppressed through the upper blowing lance using an oxidizing gas containing at least 20% by volume of air or oxygen as a carrier gas. This is a method for suppressing slag forming, characterized by spraying an agent onto the surface of slag.

[0013] In the present invention, the angle of the inhibitor blowing hole of the upper blowing lance may be 5 to 70 ° with respect to the vertical.
This is a method for suppressing slag forming, which comprises spraying a forming inhibitor on the surface of slag.

Furthermore, the present invention is also a method for suppressing slag forming, wherein the forming inhibitor is CaCO ₃ .

In the present invention, since the oxidizing gas is blown at the same time as the forming inhibitor, the presence of the oxidizing gas in the blowing portion of the inhibitor causes a local rise in temperature in that portion, and the viscosity of the slag is increased. And gas is easily released. Further, secondary combustion of the CO gas also occurs simultaneously with the oxidizing gas, and the temperature effect of the hot metal is suppressed.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention applied to dephosphorization of hot metal using a topped car as a reaction vessel will be described below with reference to the drawings.

As shown in FIG. 1, a dephosphorizing treatment of hot metal is performed by immersing a lance 3 for dephosphorization through an opening in hot metal 2 held in a torpedo car 1 through an opening. This is performed by blowing a source (iron oxide, oxygen gas) and a dephosphorizing agent 4. At this time, a decarburization reaction occurs at the same time, and CO gas is generated. The CO gas and the carrier gas of the dephosphorizing agent are trapped in the slag 5 and contained therein, and the volume of the slag increases. That is, the slag foams, and a so-called forming phenomenon occurs.

In the present invention, an upper blowing lance 6 separate from the dephosphorizing lance 3 is separately provided at the opening of the toped car 1. The upper blowing lance 6 is connected to a storage tank 7 for forming inhibitor. And the upper blowing lance 6
An oxidizing gas containing air or oxygen in an amount of 20% or more as a carrier gas is blown out from the blowout hole as a carrier gas, and blown onto the slag surface being formed. As a result, it was possible to obtain a more excellent suppressing effect of forming than the conventional method in which the forming agent and the oxygen for secondary combustion were independently blown, and it was possible to reduce the drop amount of the hot metal temperature. Further, by reducing the drop amount of the hot metal temperature, inexpensive CaCO ₃ can be used as an inhibitor, and the refining cost can be reduced.

The reason why the suppression effect has increased is that air or acid
Oxidizing gas and CO gas react to form high-temperature part in slag
Is formed, the viscosity of the slag decreases, and Ca
CO _ThreeDecomposes to form a CO gas passage in the slag
Therefore, it is assumed that a large loophole can be easily formed in the slag.
I have decided.

In the present invention, it is desirable that the angle θ of the inhibitor blowing hole of the upper blowing lance is in the range of 5 to 60 °. The reason is that if this θ is less than 5 °, the amount of the loss of the inhibitor outside the furnace port of the torpedo car in the early stage of spraying increases, and if θ is more than 70 °, the spraying area of the inhibitor decreases. This is because, in each case, the effect of suppressing the forming is reduced.

[0021]

EXAMPLES 200 tons of hot metal per charge (ch) was dephosphorized by a topped car, and the above-described forming suppressing method according to the present invention was applied. Further, in order to compare the effects, a conventional suppression method in which oxygen gas for secondary combustion was separately blown with the suppressant was also implemented.

The results are shown in FIG. 2 in terms of the number of forming occurrences per charge process. In the case of the conventional method,
Although forming was performed at an average of 2.4 times / ch, when the present invention is applied, the forming becomes about 0.4 times / ch, which is about 17%.
Decreased to. Further, the present invention (deterrent agent = CaCO ₃ , carrier gas = air and O ₂ : N ₂ = 60: 40, 100: 0)
FIG. 3 shows the amount of drop in hot metal temperature obtained in the implementation of Comparative Example (inhibitor = CaCO ₃ , carrier gas = nitrogen). If the oxygen concentration in the carrier gas is less than 20% by volume, the hot metal temperature during the dephosphorization treatment is reduced by 10 ° C. or more as compared with the case where the suppressant spraying is not performed, which indicates that there is a problem in operation. Therefore, based on this result, in the present invention, the oxygen concentration of the oxidizing gas blown at the same time is limited to 20% by volume.

[0023]

As described above, according to the present invention, slag forming can be suppressed without reducing the hot metal temperature during the dephosphorization treatment of the hot metal. As a result, the input speed of iron oxide required for dephosphorization is increased, and the hot metal can be efficiently dephosphorized, and the industrial effect is very large. Further, the time required for the dephosphorization treatment was shortened, and the shortened time could be used for the desulfurization treatment.

[Brief description of the drawings]

FIG. 1 is a diagram showing a situation in which a method for suppressing slag forming according to the present invention is carried out on a topped car.

FIG. 2 is a diagram showing the effect of implementing the slag forming suppression method according to the present invention.

FIG. 3 is a diagram showing the relationship between the drop amount of the hot metal temperature and the oxygen concentration in the carrier gas in the slag forming suppression method according to the present invention.

[Description of Signs] 1 Topeed car 2 Hot metal 3 Lance for dephosphorization 4 Dephosphorizer 5 Slag 6 Top blowing lance for spraying inhibitor 7 Storage tank of forming inhibitor 8 Forming inhibitor

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shuji Takeuchi 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Prefecture Within the Technical Research Institute of Kawasaki Steel Co., Ltd. (72) Kenichi Sorimachi 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki (72) Inventor Mamoru Suda 1-chome, Mizushima-Kawasaki-dori, Kurashiki-shi (No address) Kawasaki Steel Corporation Mizushima Works F-term (reference) 4K014 AA03 AB03 AB04 AB12 AC16 AD01 AD27

Claims (3)

[Claims] 1. An oxygen source and a dephosphorizer are blown into a hot metal held in a refining vessel via a lance, and when dephosphorizing from the hot metal, an upper blowing lance is provided separately from the lance for blowing the dephosphorizer. A method for suppressing slag foaming, comprising blowing a forming inhibitor onto the surface of the slag through the upper blowing lance using an oxidizing gas containing at least 20% by volume of air or oxygen as a carrier gas. 2. The slag forming apparatus according to claim 1, wherein the angle of the inhibitor blowing hole of the upper blowing lance is set to 5 to 70 ° with respect to the vertical, and the forming inhibitor is sprayed on the surface of the slag. How to control. 3. The method according to claim 2, wherein the forming inhibitor is CaCO _3.
The slag according to claim 1 or 2,
Forming suppression method.