JP2003253315A - Method for desulfurizing molten pig iron with mechanical stirring - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for efficiently desulfurizing molten pig iron with mechanical stirring, in order to deal with an increasing tendency for smelting a steel having lower sulfur concentration. <P>SOLUTION: This desulfurization method comprises, when desulfurizing molten pig iron with mechanical stirring, using a refining agent containing FeO of 0.02-0.07 pts.wt. added to CaO of 1 pts.wt., and controlling the value of (CaO /SiO<SB>2</SB>) at the end of desulfurization treatment to 3.5 or higher. The above refining agent includes one or two out of Na<SB>2</SB>O and Al<SB>2</SB>O<SB>3</SB>, wherein 0.02-0.10 pts.wt. in terms of Na<SB>2</SB>O and 0.02-0.20 pts.wt. in terms of Al<SB>2</SB>O<SB>3</SB>, in order to realize the higher desulfurization efficiency. In the above method, preferably, converter slag is used for the FeO source, secondary refining slag for the Al<SB>2</SB>O<SB>3</SB>source, and soda glass scrap, glass cullet, or sodium metasilicate for the Na<SB>2</SB>O source; and the Al source is charged into the molten pig iron to adjust Al concentration after desulfurization treatment to 0.01% (mass%) or higher, in order to more stably obtain the high desulfurization efficiency. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to CaF ₂
The present invention relates to a technique for effectively carrying out desulfurization and refining of hot metal without using.

[0002]

2. Description of the Related Art In the steel industry, CaO is used for desulfurizing hot metal by a powder injection method or a mechanical stirring method.
Is used as a main component, and in order to improve the reaction characteristics,
CaF ₂ disclosed in Japanese Patent Publication No. 5-51402 and Japanese Examined Patent Publication No. 61
Al ₂ O ₃ according to -24491, JP-A No. 8-20
It is carried out under a strongly reducing condition using a refining agent added with a substance having a large effect of melting CaO, such as soda lime glass presented in Japanese Patent No. 9212. On the other hand, from the viewpoint of global environment protection and effective utilization of industrial waste, the use of fluorite as a CaF ₂ source that has been generally used until now is limited, and the refining agent to be used has a wide latitude as a desulfurization method. Mechanical agitation is being used.

However, in the mechanical stirring method, even if a refining agent having a high desulfurizing ability is used aimlessly as described above,
High desulfurization efficiency cannot be realized. That is, in the mechanical stirring method, the requirements for the refining agent are to maintain a high desulfurizing ability and to easily wind the refining agent into the hot metal by mechanical stirring. The technology disclosed so far is concerned with the presentation of refining agents having a high desulfurization ability and the hardware such as the shape of the immersion rotary vane and the number of revolutions for promoting the entrainment (for example, Japanese Patent Application Laid-open No.
No. 000-212621, JP 2001-247910 A), there is no presentation of a technique focusing on the difficulty of granulating and rolling up the refining agent due to the difference in refining agent composition.

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The present invention proposes a technique for achieving high desulfurization efficiency by mechanical stirring in the melting of steel with a lower sulfur concentration without using F ₂ .

[0005]

That is, the gist of the present invention is that when carrying out the desulfurization treatment of hot metal by a mechanical stirring method, quick lime is used as a main raw material, and a FeO source is added to this to obtain CaO 1 FeO content is 0.02 to weight part.
The refining agent added in 0.07 parts by weight was used to react with the hot metal, and the value of (CaO / SiO ₂ ) at the end of the treatment was 3.5.
In order to achieve higher desulfurization efficiency, one or two kinds of Na ₂ O and Al ₂ O ₃ are further added, and Na ₂ O content is added to 1 part by weight of CaO. 0.02 to 0.10 parts by weight, Al ₂ O ₃ minutes 0.02 to
It is characterized by using a refining agent added with 0.20 parts by weight. At this time, converter slag and calcium shale ferrite were used as FeO sources, secondary refining slag was used as an Al ₂ O ₃ source, and Na ₂ O.
Use soda / glass scrap, glass / cullet or sodium metasilicate as a source. Further, in order to obtain a higher desulfurization efficiency, an Al source is added to the hot metal to adjust the [Al] concentration after desulfurization treatment to 0.01 (mass%) or more.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION FIG. 4 shows a conceptual diagram of a mechanical stirring method (KR method) for carrying out the present invention. The basic concept of the present invention is to granulate the refining agent charged in the part A into an appropriate size,
This is a desulfurization method of hot metal in which the granulated refining agent is rolled up from the dented portion B into the hot metal through a rotary stirring blade, and the refining agent grains that have been rolled up react with [S] in the hot metal to perform desulfurization. .

The desulfurization treatment of hot metal using a refining agent mainly containing quick lime (CaO) proceeds by the reaction of the following equation (1), and the desulfurization rate is described by the equation (2). In order to achieve high desulfurization efficiency, it is necessary to reduce the oxygen potential of the reaction system as much as possible and increase the contact area A between the slag and the hot metal. CaO + [S] + [Fe] = CaS + (FeO) (1) -d [S] / dt = (S / V) .ks. ([S]-[S] equi.) (2) S: Slag and Area of contact interface with hot metal, V: hot metal volume [S] equi .: equilibrium sulfur concentration of reaction, ks: desulfurization rate constant

However, in the mechanical stirring system using rotary blades such as KR, in addition to the desulfurizing ability of the refining agent, the composition of the refining agent charged, the composition of the blast furnace slag that inevitably remains in the hot metal ladle, and the hot metal temperature are determined. The refining agent "difficulty of granulation" greatly affects the desulfurization efficiency. That is, in general, the desulfurizing agent is a powder, and in this state, even if the refining agent and the hot metal are rotationally agitated by mechanical agitation, it is difficult to efficiently involve the powder in the hot metal. Is also extremely small.

The present inventors have studied various conditions for efficiently injecting the introduced refining agent into the hot metal, and as a result, mixed an iron oxide source with the refining agent to add an appropriate liquid phase ratio. By doing so, it was found that the refining agent was granulated by the rotary motion of the rotor, and the granulated particles were efficiently wound into the hot metal by the rotary blade, and the desulfurization efficiency was improved (Fig. 1). At this time, the FeO content was 0.0 parts by weight with respect to 1.0 part by weight of CaO.
The condition is 2 to 0.07 parts by weight. That is,
When the FeO content is small, the liquid phase ratio is too small, granulation of the refining agent is delayed, and sufficient desulfurization does not proceed in the hot metal refining treatment for a fixed time. On the other hand, if the FeO content is too large, the desulfurization efficiency is impaired for the following reason. The liquid phase ratio becomes large, granulation proceeds, the diameter becomes too large, and the contact area S with the hot metal decreases even if it is rolled up in the hot metal, and the desulfurization rate decreases. The FeO component is also a strong oxidation source and increases the oxygen potential during the desulfurization reaction represented by the formula (1) and reduces the ability of sulfur to be absorbed by slag. That is, excess F
The presence of the eO component is disadvantageous for the desulfurization of hot metal. Therefore, the proper FeO content is 0.02 parts by weight with respect to 1.0 part by weight of CaO.
Limited to ~ 0.07 parts by weight.

Here, the FeO content means iron oxide (Fe _X O _Y )
Fe was converted to FeO and MnO was 0.8 · Fe
It is the sum of the values converted as O. That is, MnO is also Fe
Similar to O, it has the effect of increasing the liquid phase ratio and at the same time increases the oxygen potential. The effect is that of FeO.
It is about 8 times. Therefore, according to the above definition, MnO is
Manage as eO minutes.

At this time, the slag basicity (CaO /
If the value of (SiO ₂ : weight ratio) is small, the adverse effect of FeO becomes apparent. In order to suppress the desulfurization reaction inhibitory effect of FeO as much as possible and to realize a stable desulfurization efficiency, it is essential that the slag be saturated with CaO, and the slag (CaO
The value of / SiO ₂ ) must be 3.5 or more.

It has been known for a long time that CaO containing a small amount of Na ₂ O greatly increases the desulfurization ability. However, Na ₂ O itself is extremely active and has a strong hygroscopic property, and is generally used in the form of Na ₂ CO ₃ .
However, when Na ₂ CO ₃ is in high temperature and comes into contact with hot metal having a high concentration of [C], it is vaporized and lost in the reaction of the following formula (3), and it is not economical to use a large amount. Therefore, Na ₂ CO ₃
When the amount of Na ₂ O added is in the range of 0.02 to 0.10 parts by weight, it works most effectively. Na ₂ O + [C] = 2Na (g) + CO Na ₂ CO ₃ +3 [C] = 2Na + 3CO (3)

On the other hand, alumina (Al₂O₃) Addition
Has a relatively large effect of lowering the melting point of CaO.
It is known. However, when coexisting with CaO and melting, acid
Acts as a sex component to reduce the ability of sulfur to absorb slag
Let Therefore, Al₂O₃The amount added is 0.02-0.2
Prescribe to 0 parts by weight. Al₂O₃And Na₂The combination of O is as follows
It is more effective for the reason. Al₂O₃Use of Ca
Helps to melt O, Na ₂Al by adding O₂O₃By use
The effect of improving desulfurization efficiency can be compensated for by the decrease in desulfurization capacity.
Can enjoy. FeO, Na mentioned above₂O and Al₂O
₃The following substances are sources of effective use of waste.
From the viewpoint, it is extremely effective in carrying out the present invention.

[FeO source] Converter slag (decarburizing slag), calcium-ferrite: FeO
At the same time as being used as a source, it has a large value of (CaO / SiO ₂ ) and can be used as a CaO source. Table 1 shows typical compositions of converter slag (decarburizing slag) and calcium-ferrite used in the present invention. Unlike the iron ore and mill scale, the FeO source has a liquid phase ratio of about 30 (mass%) or more in the hot metal treatment temperature range, is not only advantageous for granulation of refining agents, but also melts once. Since it coexists with CaO after passing through the state, its oxidizing power is weaker than that of iron ore and mill scale, and it acts favorably for desulfurization.

[Al ₂ O ₃ source] Secondary refining slag: The value of (Al ₂ O ₃ ) concentration is large, and (CaO
The value of / SiO ₂ ) is also large. Therefore, it can be utilized as a CaO source at the same time as an Al ₂ O ₃ source. Table 1 shows a representative composition of the secondary refining slag used in the present invention. Further, the effect is the same even if alumina brick scraps or alumina rough stones are used.

[Na ₂ O Source] Soda / glass scraps (glass cullet) and sodium metasilicate Na ₂ O are strongly basic oxides, and when they coexist with SiO ₂ , their activity is greatly reduced and they become hot metal. It is extremely stable even when contacted. That is, when Na ₂ O is protected by SiO ₂ and melts with CaO when it comes into contact with molten iron and melts, its desulfurizing ability is exhibited. Soda, glass scraps (glass cullet), and sodium metasilicate are easily available, and are stable even when they come into contact with hot metal at high temperatures, so they are extremely useful. Table 2 shows typical compositions of soda and glass scraps (glass cullet, sodium metasilicate) used in the present invention.

In carrying out the present invention, it is extremely important to lower the oxygen potential of the reaction system. The desulfurization reaction between the granulated refining agent and the hot metal proceeds according to the above formula (1). That is, the smaller the value of the oxygen potential of the reaction system, the easier the desulfurization is, and the addition of Al is effective for promoting desulfurization (FIG. 3). If the addition amount of Al is small, the effect cannot be exhibited,
The more the added amount of Al is, the more advantageous it is. However, practically, the lower limit of the [Al] concentration is 0.010 (mass%),
(Mass%) is the upper limit. As the Al source, it is possible to utilize Al ash discharged in the Al manufacturing process, and Al ₂ O ₃ contained in Al ash can also be utilized. Table 3 shows A used in the present invention.
1 shows a typical composition of 1 ash.

[0018]

[Example] [Example 1] [S] concentration was 0.035 to 0.0
The desulfurization treatment of the hot metal was carried out in a mechanical stirring desulfurization facility (RK desulfurization facility) using 100 tons of hot metal having a temperature of 40 (mass%) and a temperature range of 1320 ° C to 1370 ° C. As a desulfurizing agent, C
A powder was used in which the mixing amount of FeO was changed with respect to 1 part by weight of aO. The FeO source used was iron ore powder, mill scale, converter slag (or calcium ferrite), the basic unit of desulfurization agent was 6.0 (kg / ton), and the value of (CaO / SiO ₂ ) after refining Is 3.9 or higher. The rotation number of the stirring rotor is 110 to 115 (rpm), and the desulfurization treatment time is 12 to 13 (min). Before the treatment, residual blast furnace slag in the refining vessel was excluded so that its thickness was in the range of 10 to 15 mm. The effect of this level of residual amount of blast furnace slag on the desulfurization rate is minor.

FIG. 1 shows the relationship between the desulfurization rate η _[S] and the value of the FeO content mixed parts by weight. The value of η _[S] is 0.02 to 0.07.
A large value was obtained in the case of FeO parts by weight, and highly efficient desulfurization treatment could be performed. Among them, the desulfurization rate of the refining agent using the converter slag was the highest among the mixed FeO sources, followed by the iron ore powder and the mill scale, which were almost the same.
As a comparative example, η _[S] of the refining agent containing CaF ₂ mixed at 5 mass% is also shown. The method of the present invention, without using CaF _2, or approximately the same as the case of using CaF _2, or more desulfurizing effect can be stably obtained. However, the desulfurization rate η _[S] is a value calculated by the equation (4). η _[S] = ([S] ₀ − [S] _end ) / [S] _end (4) [S] ₀ : Hot metal sulfur concentration before desulfurization treatment (mass%) [S] _end : Hot metal sulfur concentration after desulfurization treatment (Mass%)

[Example 2] The [S] concentration was 0.035 to 0.
Desulfurization treatment of hot metal was carried out in a mechanical stirring desulfurization equipment (RK desulfurization equipment) using 100 tons of hot metal having a temperature of 040 (mass%) and 1330 ° C to 1360 ° C. The number of rotations of the stirring rotor is 110 to 115 (rpm), and the desulfurization treatment time is 12
(Min). Before the treatment, residual blast furnace slag in the refining vessel was excluded so that its thickness was in the range of 10 to 15 mm. As a standard desulfurizing agent, 1 part by weight of CaO was mixed with a converter slag as a source of FeO to prepare 0.03 to 0.03 part by weight of FeO.
The average η _[S] of each of the 15 channels desulfurized using the desulfurizing agent adjusted to 6 is shown in a bar graph in FIG. A desulfurization rate of about 0.82 is obtained.

Case-1 uses a standard desulfurizing agent as a source of Al ₂ O _{3 such} as alumina brick scraps and rough alumina (Al ₂ O ₃ content of 50 ma.
ss% or more) and secondary refining slag are mixed, and the average η _[S] of each 15 ch when using a desulfurizing agent in which Al ₂ O ₃ parts by weight is adjusted to 0.05 to 0.20 parts by weight. . In case-2, a standard desulfurizing agent was mixed with soda glass scrap and Na ₂ CO ₃ as a Na ₂ O source, respectively, and a desulfurizing agent having a Na ₂ O weight part adjusted to 0.02 to 0.10 was used. The average η _[S] of each 15 ch is shown. case-3
Is a standard desulfurizing agent mixed with a secondary refining slag as an Al ₂ O ₃ source to make Al ₂ O ₃ parts by weight of 0.05 to 0.10 parts by weight, and at the same time mixed with soda glass scrap as a Na ₂ O source. , Na ₂ O weight parts with average eta _[S] of each 15ch when using desulfurization agent was adjusted to 0.02 to 0.10, said Al ₂ O ₃ source and simultaneously Na ₂ O source as Na ₂ CO ₃ are mixed, Al ₂ O ₃ weight part is 0.05 to 0.10 weight part, and Na ₂ O weight part is 0.0 weight part.
The average η _[S] of each 15 ch when the desulfurizing agent adjusted to 2 to 0.10 was used is shown for comparison. After desulfurization treatment (CaO / S
The values of iO ₂ ) are all 3.5 or more. In each case, a large desulfurization rate was obtained as compared with the standard desulfurizing agent, and efficient desulfurization could be carried out.

[Embodiment 3] [S] concentration is 0.035 to 0.
The hot metal desulfurization treatment was carried out in a mechanical stirring desulfurization facility (RK desulfurization facility) using 100 tons of hot metal having a temperature of 040 (mass%) and 1320 ° C to 1390 ° C. The rotation speed of the stirring rotor is 110 to 115 (rpm), and the desulfurization treatment time is 12 (m
in). Prior to the desulfurization treatment, metallic Al was added to adjust the Al concentration value in the hot metal. Before the treatment, residual blast furnace slag in the refining vessel was excluded so that its thickness was in the range of 10 to 15 mm.

The desulfurizing agent used was such that an iron oxide source was added to 1 part by weight of CaO so that the FeO content was 0.0.
A refining agent added with 2 to 0.07 parts by weight (iron oxide source: converter slag, calcium ferrite, iron ore, mill scale alone or a mixture thereof). Na as the refining agent
₂ O and one or two kinds of Al ₂ O ₃ are added, and 0.02 to 0.10 part by weight of Na ₂ O and 0.02 to 0 of Al ₂ O ₃ are added with respect to 1 part by weight of CaO. A refining agent containing 20 parts by weight (secondary refining slag or alumina brick scrap as an Al ₂ O ₃ source, soda / glass scrap, glass cullet or sodium metasilicate alone or a mixture thereof as a Na ₂ O source) . The values of (CaO / SiO ₂ ) after desulfurization are all 3.5 or more.

FIG. 3 shows the relationship between the desulfurization rate ratio and the [Al] concentration. However, the desulfurization rate ratio is the value calculated by equation (5),
When the desulfurization ratio is larger than 1, it is an index showing that the addition of Al is effective in promoting desulfurization. Desulfurization ratio = (desulfurization ratio when Al is added) / (desulfurization ratio when Al is not added) (5) In any case, the desulfurization ratio increases as the [Al] concentration increases, but The concentration is [Al] ≧ 0.01 (mass
%). The upper limit of the [Al] concentration is 0.
10 (mass%) is appropriate. Here, the desulfurization rate when Al ash was mixed with the refining agent as a substitute for metallic Al is also shown.
The effect is the same even if Al ash is mixed with the refining agent as a substitute for metallic Al.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

[Table 3]

[0028]

The method of the present invention enables efficient desulfurization and refining of hot metal in harmony with the environment without using fluorspar (CaF ₂ ).

[Brief description of drawings]

FIG. 1 is a drawing showing the relationship between the desulfurization rate of hot metal after desulfurization treatment and the FeO mixed part by weight.

FIG. 2 is a drawing comparing the relationship between the desulfurization rate of hot metal after desulfurization treatment and the desulfurizing agent used.

FIG. 3 is a drawing showing the relationship between the desulfurization rate ratio of hot metal after desulfurization treatment and the [Al] concentration.

FIG. 4 is a drawing showing an outline of a mechanical stirring desulfurization facility for carrying out the method of the present invention.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takenori Taniguchi             1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel shares             Company Kimitsu Works (72) Inventor Masahiro Toki             1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel shares             Company Kimitsu Works F-term (reference) 4K014 AA02 AB02 AB03 AB04 AB21                       AC08

Claims (4)

[Claims] 1. A refining agent containing quick lime as a main raw material,
In carrying out the desulfurization treatment of the hot metal by the mechanical stirring method, C
To 1 part by weight of aO, an iron oxide source was added to this, and F
Using a refining agent mixed with 0.02 to 0.07 parts by weight as the eO content, the slag basicity (CaO / Si
A method for desulfurizing hot metal, wherein the value of O ₂ ) is 3.5 or more. 2. The method according to claim 1, wherein Na ₂ O is used.
And one or two of Al ₂ O ₃ are added, and the content of Na ₂ O is 0.02 to 0.10 with respect to 1 part by weight of CaO.
A method for desulfurizing hot metal, characterized in that a refining agent containing 0.02 to 0.20 parts by weight of Al ₂ O ₃ is added. 3. The method according to claim 1, wherein F
As a source of eO, converter slag and calcium-ferrite
Secondary refining slag and alumina brick scrap were added as Na ₂ O ₃ source
_{2 A} method for desulfurizing hot metal, characterized by using soda / glass scrap, glass / cullet or sodium metasilicate as an O ₂ source. 4. The method according to claim 1, wherein an Al source is added to the hot metal to be desulfurized to adjust the [Al] concentration after desulfurization treatment to 0.01 (mass%) or more. Item desulfurization method.