JP2002206109A - Desulfurizing agent for molten iron and desulfurization method for molten iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow desulfurization for molten iron by which molten iron can be desulfurized with high efficiency and high operability, and the molten iron can rapidly be fed to a converter in the following stage. SOLUTION: The desulfurizing agent for molten iron has a composition containing 5 to 30% metal Mg powder, 50 to 90% CaO and 4 to 10% calcium aluminate, and the balance inevitable impurities, and in which CaO and calcium aluminate are blended in the ratio of 3 to 15. Further, in the desulfurization method for molten iron, the desulfurizing agent is blown so that the feed rate of the metal Mg powder therein is controlled to 5 to 25 kg/min by using a laddle for separating molten slag, on blowing-off of molten iron after the treatment, the laddle is decanted so that the molten iron is discharged from a blow- off port of molten iron, and on blowing-off of desulfurized slag, the laddle is decanted so that the slag is discharged from a slag discharge port provided in the opposite direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a desulfurizing agent for efficiently and quickly desulfurizing hot metal and a method for desulfurizing hot metal using the same.

[0002]

2. Description of the Related Art Conventionally, in the case of producing low sulfur steel having a sulfur concentration of 30 ppm or less in steel, first, 30 ppm in a hot metal stage.
In general, the desulfurization treatment is performed as follows, and the finish desulfurization treatment is performed in the secondary refining process. In this case, it is difficult to perform a rapid desulfurization treatment in the secondary refining process in which the oxygen concentration is high and the desulfurization efficiency tends to be low. Therefore, desulfurization is desirably performed to the lowest possible sulfur concentration in the hot metal stage.

[0003] As a desulfurizing agent for hot metal, most commonly,
Lime, calcium carbide, soda ash, etc. are selected. Each of these has advantages and disadvantages, for example, lime is the cheapest, but the processing time is long because the main component is solid at the hot metal temperature. Calcium carbide has environmental problems because P contained as an impurity generates harmful phosphine. In addition, soda ash generates a large amount of white smoke during processing due to its high vapor pressure, and significantly lowers the hot metal temperature. Also, when the latter two are used, it is difficult to recycle the generated slag, and there is also a problem in slag treatment.

[0004] For these reasons, magnesium-based desulfurizing agents have recently been attracting attention as an alternative to the above. Magnesium has a strong deoxidizing and desulfurizing power, but is extremely reactive and has a high vapor pressure at the temperature of the hot metal, so it is practically difficult to put it alone into the hot metal. Mg alloyed with components such as Al, Mn and Al
Various methods have been proposed for use as alloys or, in special cases, impregnating coke with Mg. In addition, a mixture of an appropriate flux and metallic Mg may be used, and a method of injecting these magnesium-based desulfurizing agents into hot metal using a carrier gas has been proposed.

[0005] In carrying out these hot metal desulfurization treatments, the most commonly used processing vessels include a torpedo car for transporting hot metal from a blast furnace to a steelmaking plant and a pouring pot for charging hot metal into a converter. Used. When a torpedo car is used, desulfurization treatment and desulfurization slag removal are performed during the transportation of hot metal. Desulfurization can be performed in the high hot metal temperature range just after tapping, and the heat retention after the treatment is good, so the desulfurization efficiency is excellent. On the other hand, when a pouring ladle is used, the converter can be charged immediately after the desulfurization treatment and deslagging of desulfurized slag are completed, so that the temperature loss after the treatment is small.

[0006] However, the desulfurization slag removing method for both uses manual scraping or mechanical scraping. However, these methods require a lot of time and labor to separate the desulfurized slag and use a desulfurizing agent. If the amount is large,
Of course, the amount of desulfurized slag generated also increases, and the time required for removing slag increases. As a result, the treatment time plus the slag removal time becomes longer, which causes a problem of lowering the hot metal temperature and matching with the converter operating time.

[0007]

SUMMARY OF THE INVENTION Under the above-mentioned background, the present invention can perform desulfurization of hot metal more efficiently and operability than conventionally proposed, and can quickly perform the next step. It is an object of the present invention to develop a hot metal desulfurization method capable of supplying hot metal to a converter.

[0008]

According to the present invention, in a hot metal desulfurization method in which a desulfurizing agent is introduced into a bath of hot metal to perform desulfurization, a desulfurizing agent containing metallic Mg is added to the hot metal by using an immersion lance. And a method for desulfurizing hot metal, characterized in that the time for desulfurization treatment can be shortened by injection and the time for deslagging of desulfurized slag using a ladle for slag separation is reduced. In the method of the present invention, a slag separation ladle for accommodating hot metal, a tilting device for the slag separation ladle, a pouring ladle for receiving hot metal, a slag pan for receiving desulfurized slag, and an outlet are immersed in the hot metal. And a dipping lance for injection of a desulfurizing agent.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 schematically shows equipment for implementing the present invention. According to the present invention, the hot metal 2 in the slag separation ladle 1 is desulfurized. After the desulfurization treatment using the immersion lance 3, the tilting device 11 is used to perform desulfurization processing. Tapping is performed by tilting the pot 1 toward the pouring pot 9 and then desulfurized slag is discharged by tilting the pot 1 toward the slag pot 10 provided on the opposite side.

The immersion lance 3 has a blow-out port 4 at the tip of a tubular body protected by a refractory, and in the example shown in the figure, the blow-out port 4 is formed laterally in a body near the tip. Therefore, when the immersion lance 3 is immersed vertically,
The powdery desulfurizing agent 5 is injected along with the carrier gas 6 laterally in the deep part of the bath from the outlet 4.

The injection of the powdery desulfurizing agent 5 is as follows:
The transfer is performed by the carrier gas 6, but the use of an oxygen-containing gas as the carrier gas 6 is avoided. In order to accelerate the desulfurization reaction, it is effective to lower the oxygen partial pressure as much as possible, and it is possible to use nitrogen gas or other oxygen-free gas.

As the powdery desulfurizing agent 5, a premixed calcium aluminate is preferable, and a powder obtained by post-mixing these powders may be used. As the component ratio, by weight, metal Mg powder: 5 to 30%, CaO: 5
0 to 90%, calcium aluminate: 4 to 23%, others: unavoidable impurities, CaO / calcium aluminate: 3 to 15. Soda ash and calcium carbide are preferably avoided for the reasons described above.

In the method of the present invention, the main components of the desulfurizing agent are metallic Mg and CaO, and calcium aluminate is a slag-making agent for preventing outflow of desulfurized slag during tapping. Calcium aluminate has a low melting point of 12CaO.Al ₂
It is preferable that O ₃ be the main component. Ca in the form of fine powder
This is for adhering to the surface of O and coagulating fine powder CaO. Here, the mixing ratio of each component is defined as described above.

The desulfurization reaction and oxidation reaction by Mg are (1)-
It is expressed by equation (2). MgS generated by desulfurization with Mg is unstable in the atmosphere, and reacts with oxygen in the atmosphere to cause resulfurization according to the formula (3). In order to prevent resulfurization according to the formula (4), it is preferable to simultaneously supply CaO. Mg + [S] = MgS (1) Mg + [O] = MgO (2) MgS + O = MgO + S (3) MgS + CaO = MgO + CaS (4) The mixing ratio of metallic Mg is 5 to 30%. The reasons specified in the above are as follows. If the content of metallic Mg is less than 5%, sufficient (1)
In order to obtain the desulfurization reaction of the formula, a considerable amount of a desulfurizing agent is used, which results in an unnecessary increase in the amount of slag. Metallic Mg 3
If it exceeds 0%, the remaining amount of CaO becomes relatively short,
The reaction of the formula (4) cannot be sufficiently obtained, and the resulfurization reaction cannot be prevented.

It is preferable to mix calcium aluminate, which is a slag-making agent, with CaO / calcium aluminate: 3 to 15 as compared with CaO. The reason for defining the CaO / calcium aluminate to be 3 or more is as follows. In other words, if it is smaller than this, the melting point of the desulfurized slag becomes too low, and when the processing pot is tilted and tapping, it is mixed into the pouring pot simultaneously with the hot metal,
Since the desulfurized slag is brought into the converter to cause resulfurization, the effect in the desulfurization treatment is not satisfied. On the other hand, the reason why the content of CaO / calcium aluminate is specified to be 15 or less is that if it is larger than this value, CaO slag or coagulation becomes insufficient, and the CaO remains in a fine powder state even after the treatment. This is because desulfurized slag is brought into the pouring ladle.

When the desulfurizing agent of the present invention is injected into hot metal, the maximum effect is obtained by controlling the blowing rate of the desulfurizing agent to 5 to 25 kg / min in terms of the supply rate of the pure metal Mg. can get. Since Mg is very reactive, the upper limit of the supply rate is restricted from the viewpoint of safety. On the other hand, if the supply speed is less than 5 kg / min, the processing time becomes longer, and the characteristics of the present invention cannot be fully utilized in terms of production efficiency and cost.

The maximum effect can be obtained by desulfurizing the slag separating ladle using the desulfurizing agent of the present invention. As described above, a torpedo car or a pouring pot is generally used for the desulfurization treatment container. When the desulfurizing agent of the present invention is injected in these treatment vessels, the desulfurizing effect is confirmed as in the case of using the ladle for slag separation.
However, if the desulfurized slag is not scraped manually or mechanically before being charged into the converter, resulfurization in the converter occurs. In order to prevent resulfurization, much time and effort must be spent to sufficiently separate the desulfurized slag.

On the other hand, when a lime-based desulfurization treatment is performed using a ladle for slag separation, there are the following advantages and disadvantages.
As described above, lime is the cheapest, but since the main component is solid at the hot metal temperature, the melting time of ultra-low sulfur steel increases the processing time and the unit unit of desulfurizing agent used. Even if the separation time of hot metal-desulfurization slag can be reduced by using a ladle for slag separation, the processing time cannot be reduced,
Difficulties arise in matching with the next step.

As described above, in the ladle for slag separation, the premixed or postmixed Mg-CaO-calcium aluminate is subjected to the desulfurization treatment to thereby obtain the treatment time and the hot metal-desulfurization slag separation time. Can be shortened as much as possible, and the effects of the present invention can be maximized in terms of production efficiency and cost.

[0020]

EXAMPLES (Example 1) In a ladle for slag separation of 180 tons, a desulfurization experiment was conducted using hot metal shown in Table 1.

[0021]

【table 1】

As a desulfurizing agent, metal Mg powder is 10% by weight,
A mixed powder in which CaO powder was mixed at 75% by weight and calcium aluminate powder at 15% by weight was used. The blowing speed of the desulfurizing agent can be adjusted by adjusting the differential pressure (tank pressure-blowing pressure) to 13
Adjusted to 0 kg / min. At this time, the supply rate of pure Mg is 1
Equivalent to 3 kg / min. A ladle for slag separation was used as a processing vessel. Table 2 summarizes the processing conditions.

[0023]

[Table 2]

FIG. 2 shows the change over time in the sulfur concentration in the hot metal. Eventually, it dropped to 13 ppm. Table 3 summarizes the results of final component analysis and the like. Incidentally, the average desulfurization rate (min ^-1 ) in Table 3 is based on the assumption that the desulfurization reaction proceeds in the primary reaction, and -d [S] / dt = K ([S]-
[S] _i ), where [S]: initial sulfur concentration (pp
m), [S] _i : reached sulfur concentration (ppm)). Tapping was completed in 5 minutes by tilting the ladle for slag separation, and was immediately ready for the converter. In addition, since desulfurization slag was prevented from being brought into the converter, resulfurization was not observed.

[0025]

[Table 3]

Comparative Example 1 A desulfurization experiment was performed using the same hot metal as in Example 1. Here, a desulfurizing agent having a small amount of metallic Mg and a large CaO / calcium aluminate ratio was used. That is, a mixed powder in which 3% by weight of metallic Mg powder, 96% by weight of CaO powder, and 1% by weight of calcium aluminate powder were used. The blowing rate of the desulfurizing agent was adjusted to 80 kg / min. Mg at this time
The net feed rate corresponds to 2.4 kg / min. A pouring pot was used as a processing vessel. Table 2 summarizes the processing conditions. FIG. 3 shows the change over time in the sulfur concentration in the hot metal. Eventually it dropped to 67 ppm. Table 3 summarizes the results of final component analysis and the like. After the treatment in the pouring ladle, the slag was removed using a slag dragger, and the slag was supplied to a converter. It took 15 minutes from the treatment to charging the converter. Also,
Desulfurization occurred due to dropping of the desulfurized slag by the dragger.

Comparative Example 2 A desulfurization experiment was carried out using the same hot metal as in Example 1. Here, as a desulfurizing agent, Ca
Those having a small O / calcium aluminate ratio were used.
That is, a mixed powder was used in which 20% by weight of metallic Mg powder, 55% by weight of CaO powder and 25% by weight of calcium aluminate powder were used. Desulfurizer blowing rate is 80kg
/ Min. At this time, the supply rate of pure Mg is 16 kg.
/ Min. A ladle for slag separation was used as a processing vessel. Table 2 summarizes the processing conditions. Finally one
It dropped to 7 ppm. Table 3 summarizes the results of final component analysis and the like. After the desulfurization treatment, tapping was possible in 5 minutes by tilting the ladle for slag separation, but the slag was in a molten state, and a considerable amount of slag was carried into the pouring ladle. Since the desulfurized slag was carried into the converter, resulfurization occurred.

[0028]

According to the present invention, in a hot metal desulfurization method in which a desulfurizing agent is introduced into a bath of hot metal to perform desulfurization, a desulfurizing agent containing metallic Mg is injected into the hot metal using an immersion lance. In addition to shortening the processing time, it has become possible to reduce the time required for desulfurization slag deslagging using a clay bottle type processing vessel.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of equipment for implementing the method of the present invention.

FIG. 2 is a graph showing the change over time in the S concentration in hot metal when the method of the present invention (Example 1) is performed.

FIG. 3 is a graph showing the change over time in the S concentration in hot metal when Comparative Example 1 described in the text is performed.

[Explanation of symbols]

 1. Ladle for slag separation 2. Hot metal 3. Immersion lance 4. 4. outlet of immersion lance 5. Powdery desulfurizing agent Carrier gas 7. 7. Hot metal tap hole 8. Outlet side of desulfurization slag Pouring ladle 10. Slag pan 11. Tilt device

Claims (2)

[Claims] 1. Metal Mg powder: 5-30%, CaO: 50-
90%, calcium aluminate: 4 to 23%, balance consisting of unavoidable impurities, and CaO / calcium aluminate: 3 to 15; 2. A molten ladle for molten metal is blown into the molten iron desulfurizing agent according to claim 1 at a supply rate of 5 to 25 kg / min using a ladle for separating molten metal. A hot metal desulfurization method characterized in that the hot metal is tilted so as to tap hot metal from a mouth, and when the desulfurization slag is dispensed, the hot metal is tilted so as to discharge from a discharge port provided in an opposite direction.