JP2004323959A - Method for removing slag in converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for removing slag which leaves only a small amount of slag in a converter while restraining the flow-out of molten iron when pre-dephosphorization of the molten iron is performed with the converter and only the slag is removed by tilting the converter in a state the molten iron is remaining in the converter after performing the dephosphorizing treatment. <P>SOLUTION: When the pre-dephosphorizing treatment of molten iron is performed with the converter and only the slag is removed by tilting the converter in the state the molten iron is remaining in the converter after performing the dephosphorizing treatment, the slag is removed by adjusting the slag composition so that (CaO)/(SiO<SB>2</SB>)≥1.0 and (Al<SB>2</SB>O<SB>3</SB>)=2 to 10 mass%. As the Al<SB>2</SB>O<SB>3</SB>source used in the adjustment into the slag composition, the slag produced in a steelmaking secondary refining process is used. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００２７】
表１に示すように、従来のスラグ組成（水準１）では排滓率が４５％であるのに対し、本発明の範囲のスラグ組成（水準２〜４）では、７０％以上の排滓率が得られ、排滓性が大幅に向上している。さらに、スラグの脱りん能の指標となる（ＣａＯ）／（ＳｉＯ_２）がほぼ等しい水準１〜３を比較すると、排滓が良好であった水準２、３では脱炭吹錬後のりん濃度（＝［Ｐ］）が低位となった。また、本発明の範囲を逸脱するスラグ組成（水準５〜７）では、いずれも脱りん処理中に過剰なフォーミングやスロッピングが生じており、さらに、その鎮静に時間を要したため、排滓に十分な角度まで転炉が横転できずに、排滓率が低下した。
【００２８】
【発明の効果】
転炉にて溶銑の予備脱りんを行い、脱りん処理後に溶銑を転炉内に残したまま、転炉を横転させてスラグを排滓する際に、溶銑の流出を抑制しつつ、残留スラグの量が少ない排滓が可能となり、脱炭吹錬時における仕上げ脱りん処理のための生石灰等の造滓剤が削減されるとともに、造滓剤の投入による温度降下が減少した。さらに、排滓率の変動による吹止時の溶鋼中りん濃度の変動が減少し、低位で安定する。
【図面の簡単な説明】
【図１】スラグ組成とフォーミング高さの関係を示す図。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for discharging waste from a converter.
[0002]
[Prior art]
BACKGROUND ART In iron and steel refining, in order to improve dephosphorization reaction efficiency, preliminary hot metal dephosphorization in which dephosphorization and decarburization are divided and hot metal before decarburization is dephosphorized is widely performed. The method of preliminarily dephosphorizing hot metal is broadly classified into a method using a hot metal transport container such as a torpedo car and a pan, and a method using a converter. 1) The container has a large internal volume, and there are few problems such as operation failure due to forming (= slag foaming phenomenon) and slopping (= slag or molten iron overflowing from the container), 2) High-speed dephosphorization treatment is possible because gas oxygen can be sent at a high speed. 3) Dephosphorization treatment with low basicity is possible because of a large amount of oxygen supply, and reduction of quicklime for refining and effective use of slag. It is possible to reduce free CaO, which is a problem in use. 4) For the above-mentioned reason, it is not necessary to perform a preliminary desiliconization treatment before the dephosphorization treatment, and desiliconization and dephosphorization can be performed simultaneously. 5) Solid oxygen (= Iron oxide, etc.) 6) It is easy to re-use the pre-charged decarburized slag as a dephosphorizing slag in a converter vessel, and it is easy to hot reuse in the converter vessel. There are advantages. Furthermore, if the idle converter or the existing converter can be used, the amount of new capital investment is small, and the method is highly advantageous in terms of resource saving and energy saving.
[0003]
Among the pre-phosphorus dephosphorization treatment methods using a converter, the converter is rolled over to remove only the dephosphorized slag while leaving the hot metal in the converter after the dephosphorization treatment, and then removed in the same converter. There is a method of performing coal blowing (for example, see Patent Document 1), and a method of using two or more converters as dedicated furnaces for dephosphorization and decarburization (for example, see Patent Document 2). Compared to the latter, 1) there is no tapping / charging process after dephosphorization, so the non-operating time of the converter is short, and 2) there is no hot metal transfer process. And 3) it is easy to leave the decarburized slag in the furnace and use it as a dephosphorizing slag agent.
[0004]
On the other hand, in the former method, since the converter is rolled over and the dephosphorized slag is discharged while leaving the hot metal in the converter, the outflow of the hot metal is suppressed, and only the slag is discharged with high efficiency. However, there is a problem that slag remaining in the furnace without slag is rephosphorized during decarburization blowing. Therefore, various proposals have been made as follows as an efficient waste disposal method.
[0005]
First, a method in which gas is blown from a plurality of tuyeres provided on the furnace belly and the furnace bottom to move slag to the furnace port side and discharge the waste (for example, see Patent Document 1), slag forming by blowing an oxidizing gas (For example, see Patent Document 3) has been proposed. However, in these methods, it is necessary to remodel the converter to install tuyeres on the belly of the furnace, In the converter where the loss has progressed, the slag position changes due to the change in the internal volume, the tuyere position deviates from the optimal position, and it is necessary to constantly blow gas to prevent tuyere clogging during blowing. There is a problem that the cost of gas that is originally unnecessary increases.
[0006]
Further, a method of selectively discharging only slag using electromagnetic force (for example, see Patent Document 4) has been proposed. However, capital investment costs are high, and a high temperature and severe environment with severe vibration are proposed. There is a problem such as an increase in maintenance costs below.
[0007]
Further, a method has been proposed in which the position of the hot metal is detected by electrical conduction or an optical fiber to determine the optimum tilting position of the converter for the waste and to discharge the waste (for example, see Patent Documents 5 and 6). Although these methods can detect the position of the hot metal and determine the optimum tilting position of the converter, they are insufficient for promoting the waste.
[0008]
In addition, it is conceivable to apply a method of scraping slag by a waste plate used as a method of discharging torpedo cars or pans (for example, see Patent Document 7) to the converter, but considering the capacity of the converter, However, the facilities are too large to be realistic.
[0009]
[Patent Document 1]
Patent No. 2582692 [Patent Document 2]
Patent No. 1761646 [Patent Document 3]
JP 05-279721 A [Patent Document 4]
JP 05-247514 A [Patent Document 5]
Japanese Patent Application Laid-Open No. 05-288479 [Patent Document 6]
JP 06-235016 A [Patent Document 7]
JP-A-59-130909
[Problems to be solved by the invention]
Preliminary dephosphorization of the hot metal in the converter, and while the hot metal remains in the converter after the dephosphorization treatment, when the converter is rolled over and the slag is discharged, while controlling the outflow of the hot metal, It is an object of the present invention to provide a waste disposal method having a small amount of waste.
[0011]
[Means for Solving the Problems]
The present invention performs preliminary dephosphorization of hot metal in a converter, and promotes slag forming by promoting slag forming when the converter is rolled over and discharged while leaving the hot metal in the converter after the dephosphorization treatment. By increasing the bulk volume, the discharge of the hot metal is suppressed and the waste is promoted, and as a means for controlling the slag physical properties, the slag composition is adjusted to an appropriate range.
[0012]
That is, the gist of the present invention is as follows.
[0013]
1) Preliminary dephosphorization of hot metal is performed in a converter, and after the dephosphorization process, while leaving the hot metal in the converter, the converter is turned over to discharge slag, and the slag composition is (1). A converter waste method comprising adjusting the slag composition so as to fall within the range of the expression (2) and discharging the waste.
[0014]
(CaO) / (SiO ₂ ) ≧ 1.0 (1)
(Al ₂ O ₃ ) = 2 to 10 (2)
Here, (CaO), (SiO ₂ ), and (Al ₂ O ₃ ) represent CaO, SiO ₂ , and Al ₂ O ₃ concentrations (mass%) in the slag, respectively.
[0015]
2) A converter slag method characterized by using slag generated in a steelmaking secondary refining process as an Al ₂ O ₃ source used when adjusting the slag composition according to the above item 1.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described below.
[0017]
The slag forming is caused by the gas staying in the slag phase, and the forming height is determined by the amount of gas staying in the slag. That is, when the rising speed of the gas in the slag and the bursting speed of the bubbles are both low, and when the generation speed of the gas generated by decarburization or the like is high, the amount of retained gas increases and the forming height increases. The rate at which the gas in the slag rises is determined by the viscosity and density of the slag and the bubble diameter in the slag, and the burst rate of the bubbles is determined by the surface tension of the slag. Therefore, it is considered that forming can be controlled by changing the slag composition and setting the slag physical properties in an appropriate range.
[0018]
Then, the present inventors examined the relationship between the slag composition, the physical properties, and the forming height for the purpose of controlling the forming height to an appropriate range for waste. FIG. 1 shows the relationship between the slag composition and the forming height estimated based on the experimental results in a small furnace, and it is empirical that in the actual converter, the waste is most promoted when the forming height is 4 to 8 m. Therefore, it was found that the waste was most promoted when the slag composition was in the range of (CaO) / (SiO ₂ ) ≧ 1.0 and (Al ₂ O ₃ ) = _{2 to} 10 mass%. Also, if the slag composition is out of this range, the forming height is too low to perform the waste efficiently, or excessive forming or slopping occurs during the dephosphorization treatment, thereby causing an operation failure, Not desirable. When (CaO) / (SiO ₂ ) is too low, the slag dephosphorizing ability is adversely affected.
[0019]
On the other hand, the slag physical properties are also affected by the temperature, but it was also found that the above-mentioned slag composition was most appropriate in the temperature range (= 1250 to 1400 ° C.) of the normal preliminary dephosphorization treatment.
[0020]
As a method of adjusting the slag composition, in order to secure the basicity and the amount of slag necessary for dephosphorization, the production of quicklime or silica stone is appropriately performed according to the amount of Si in the hot metal and the residual amount of the pre-charged decarburized slag. A slag is charged and an Al ₂ O ₃ source is charged several minutes before the end of the dephosphorization treatment. Furthermore, the use of the slag generated in the steelmaking secondary refining step as Al ₂ O ₃ source, it is possible to effectively utilize the steelmaking byproducts.
[0021]
【Example】
The dephosphorization test by the waste disposal method of the present invention will be described.
[0022]
The test was performed in a 370t converter. After charging the scrap and hot metal, according to the amount of Si in the hot metal, etc., a slag-making agent such as quicklime or silica is charged so as to have a predetermined basicity and a slag amount, and the hot metal is preliminarily dephosphorized. Further, 1 to 3 minutes before the end of the dephosphorization treatment, slag composition was added as a source of Al ₂ O ₃ to adjust the slag composition so as to have a predetermined Al ₂ O ₃ concentration. After the dephosphorization treatment, temperature measurement and sampling were performed, the converter was turned over, and slag was discharged from the furnace port for about 5 minutes. The temperature after the dephosphorization treatment was in the range of 1300 to 1350 ° C. Thereafter, the converter was set upright, a predetermined amount of a slag-making agent was charged, and decarburization blowing was performed.
[0023]
Regarding the slag, the slag remaining in the furnace after the dephosphorization treatment based on the equations (3) and (4) based on the phosphorus balance in the molten iron and slag before and after the preliminary dephosphorization and decarburization blowing and the balance of CaO. Was calculated and evaluated by the waste rate defined by the equation (5).
[0024]
1000 × [P] ₁ + _{Wr, 1} × (P) ₁ = 1000 × [P] ₂ + Ws _{, 2} × (P) ₂ (3)
W _{s, 2} = {W _{r, 1} × (CaO) ₁ + I _{CaO, 2} × 100} / (CaO) ₂ (4)
η = {(Ws _{, 1−} Wr _{, 1} ) × 100} / Ws _{, 1} (5)
here,
W _{s, 1} , W _{s, 2} : Slag amount after dephosphorization and decarburization treatment (kg / t-steel), respectively
W _{r, 1} : Amount of slag remaining in the furnace after waste (kg / t-steel)
I _{CaO, 2} : CaO input during decarburization treatment (kg / t-steel)
[P] ₁ , [P] ₂ : phosphorus concentration in molten iron after dephosphorization and decarburization treatment (mass%), respectively
(P) ₁ , (P) ₂ : phosphorus concentration in slag after dephosphorization and decarburization treatment, respectively (mass%)
(CaO) ₁ , (CaO) ₂ : CaO concentration (mass%) in slag after dephosphorization and decarburization treatment, respectively
η: Waste rate (%).
[0025]
Table 1 shows the test levels and test results. Level 1 is a comparative example based on the conventional slag composition, Levels 2 to 4 are invention examples in which the slag composition is in the range described in the present patent, and Levels 5 and 6 are outside the range described in the present patent and have excessive (Al ₂ O ₃ ). Comparative Example, Level 7 is a comparison in which (CaO) / (SiO ₂ ) is low outside the range described in the patent of the present application.
[0026]
[Table 1]

[0027]
As shown in Table 1, the waste rate is 45% in the conventional slag composition (level 1), whereas the waste rate in the range of the present invention (levels 2 to 4) is 70% or more. Is obtained, and the waste property is greatly improved. Furthermore, comparing levels 1 to 3 in which (CaO) / (SiO ₂ ), which are indicators of the dephosphorizing ability of slag, are almost equal, the levels of phosphorus after decarburization blowing were found in levels 2 and 3 where the waste was good. (= [P]) was low. In addition, in any slag composition (levels 5 to 7) that deviates from the scope of the present invention, excessive forming and slopping occurred during the dephosphorization treatment, and furthermore, it took time to calm down the slag. The converter could not roll over to a sufficient angle, and the waste rate decreased.
[0028]
【The invention's effect】
Preliminary dephosphorization of the hot metal in the converter, and while the hot metal remains in the converter after the dephosphorization treatment, when the converter is rolled over and the slag is discharged, while controlling the outflow of the hot metal, The amount of slag is reduced, the amount of slag-forming agent such as quicklime used for finishing dephosphorization during decarburization blowing is reduced, and the temperature drop due to the introduction of the slag-forming agent is reduced. Further, the fluctuation of the phosphorus concentration in the molten steel at the time of blow-off due to the fluctuation of the waste rate is reduced, and is stabilized at a low level.
[Brief description of the drawings]
FIG. 1 is a view showing a relationship between a slag composition and a forming height.

Claims (2)

When the hot metal is preliminarily dephosphorized in the converter and the hot metal is left in the converter after the dephosphorization, the converter is overturned to discharge the slag, and the slag composition is (1), (2). A converter waste method comprising adjusting the slag composition so as to fall within the range of the expression (1) and discharging the waste.
(CaO) / (SiO ₂ ) ≧ 1.0 (1)
(Al ₂ O ₃ ) = 2 to 10 (2)
Here, (CaO), (SiO ₂ ), and (Al ₂ O ₃ ) represent CaO, SiO ₂ , and Al ₂ O ₃ concentrations (mass%) in the slag, respectively. As Al ₂ O ₃ source used in adjusting the slag composition of claim 1 wherein, BOF Haikasu method which comprises using a slag generated in the steelmaking secondary refining process.

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