JP2001348607A - Method for desulfurizing molten iron using closed type free board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for desulfurizing molten iron by using a closed type free board for effectively performing the desulfurizing treatment of the molten iron. SOLUTION: In the treatment for performing the desulfurization of the molten iron by dipping the closed type free board into the molten iron in a molten iron ladle and blowing flux from the tip part of an injection lance nozzle dipped into the molten iron, the lateral cross sectional area of the inner surface of the dipped free board is secured to be >50% of the cross sectional area of the inner surface of the molten iron ladle to restrain the lowering of the desulfurizing efficiency caused by oxygen from the peripheral atmosphere. Further, the closed type free board for blowing a carrier gas from the nozzle is used under the condition satisfying the following formula (1) so that whole blown desulfurizing agent is floated up in the free board: 0.5A<=L<=0.9A... (1), wherein L is the arrival distance of the carrier gas bubbles from the center of the injection lance, and A is the radius of the inner surface of the free board.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot metal desulfurization method using a closed type freeboard for efficiently performing a hot metal desulfurization treatment.

[0002]

2. Description of the Related Art In a refining process performed in a converter or the like, prior to the refining process, a hot metal pretreatment corresponding to a blast furnace hot metal component or a component composition of a molten steel type is generally performed. The main purpose of such hot metal pretreatment is to efficiently perform desiliconization, dephosphorization, and desulfurization. Among them, the content of phosphorus and sulfur has been decreasing as demand for high-grade steel production has increased in recent years. Has been strongly desired.

[0003] Many patents have been disclosed for the desulfurization technology.
No. 172314 has been proposed. To summarize, a process of immersing a closed freeboard in hot metal in a hot metal pot, blowing CaO-based flux into the hot metal from the tip of a lance immersed in the hot metal, and performing dephosphorization and desulfurization of the hot metal In the method, a CaO-based and / or Na ₂ CO ₃ -based desulfurizing agent is charged from above into the freeboard filled with CO gas during the dephosphorization / desulfurization treatment to remove phosphorus from the hot metal.
A method for desulfurization, wherein the cross-sectional area of the inner surface of the freeboard is 20 to 50% of the cross-sectional area of the hot metal ladle, and the lance immersion depth is 50% or more of the bath depth.

According to the present invention, however, the dephosphorization and desulfurization of hot metal can be performed efficiently, so that the unit of dephosphorization and desulfurization flux can be reduced and, at the same time, extremely low phosphorus and low sulfur steel can be easily produced. Because it is possible, great effects can be obtained in both cost and quality.

[0005]

However, in the processing method proposed above, since the cross-sectional area ratio of the freeboard to the hot metal ladle is suppressed to 50%, an increase in the oxygen content in the hot metal affects the efficiency reduction. In the treatment method aimed at the following, the ratio of the hot metal surface contained in the freeboard, which is easy to dissolve oxygen into the hot metal from the atmosphere outside the freeboard and the reducing atmosphere that is favorable for desulfurization, is There was a possibility that the effect of oxygen could not be suppressed because it was not sufficient, and that the inside of the freeboard was not sufficiently reduced, so that the desulfurization efficiency might be lowered or resulfurization might occur.

[0006] In addition, since appropriate conditions have not been set with respect to the blowing conditions (including the amount of powder carrier gas), the desulfurizing agent (powder) may fall outside the freeboard depending on the processing conditions. I sometimes saw the emergence of the situation. This has led to a decrease in desulfurization efficiency due to reaction with oxygen in the surrounding atmosphere. Further, when the jet generated by the carrier gas containing the desulfurizing agent blown from the injection lance reaches the inner wall of the freeboard, the side wall of the hot metal ladle, and the like, the refractory in the portion concerned is significantly promoted.

[0007] Even if the desulfurizing agent does not flow out of the freeboard, sufficient desulfurization efficiency cannot be obtained unless proper lance immersion and blowing conditions are set. In hot metal ladle desulfurization using a freeboard, high-speed injection with suppressed oscillation of hot metal is possible,
Since high-speed desulfurization becomes impossible due to the above-mentioned efficiency decrease, if the appropriate free board and blowing conditions are not satisfied,
The above-described problem occurs. Particularly, in a steel plant having two or more converters, one desulfurization station cannot cope with the desulfurization of a plurality of converters, and thus has the disadvantage of having to provide a plurality of facilities. It was in a situation that had to be forced.

Accordingly, the present invention proposes a hot metal treatment process with good desulfurization efficiency by properly defining freeboard and blowing conditions, and provides a method for reducing the desulfurizing agent cost and realizing high-speed desulfurization treatment. The purpose is to do so.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems in the conventional method, and its gist lies in the following means. (1) In a treatment method in which a closed freeboard is immersed in hot metal in a hot metal pot and a flux is blown from the tip of an injection lance nozzle immersed in hot metal to desulfurize hot metal, the desulfurization efficiency is reduced by oxygen from the surrounding atmosphere. The following formula (1) must be satisfied so that the cross-sectional area of the inner surface of the immersion freeboard is more than 50% of the cross-sectional area of the inner surface of the hot metal ladle in order to suppress the flow, and that the blown desulfurizing agent all floats in the freeboard. A hot metal desulfurization method using a closed freeboard in which a carrier gas is blown from the nozzle under the conditions. 0.5A ≦ L ≦ 0.9A (1) Where, L: Carrier gas bubble arrival distance from the center of the injection lance A: Free board inner surface radius

(2) A method of desulfurizing hot metal using a closed freeboard as set forth in (1), wherein the lance immersion depth is at least 0.5 times the hot metal depth in the hot metal pot. (3) In the case of using a soda ash desulfurizing agent as the flux in (1) or (2), use a sealed freeboard that satisfies the condition of 0.5 kg / min · t-pig or less as the soda ash blowing speed. Hot metal desulfurization method.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors of the present invention have conducted various studies and studies on a hot metal desulfurization method using a closed free board in order to solve the above-mentioned problems, and as a result, have immersed a desulfurizing agent injection method. It was found that efficient desulfurization can be achieved by changing the injection method from a lance and selecting the appropriate free board size and injection conditions.

It has been found that when the desulfurizing agent is added into the freeboard from above, only the entrapment of the desulfurizing agent occurs in the raised portion of the hot metal on the upper surface of the freeboard, and the whole cannot be efficiently desulfurized. Therefore, it was considered that the desulfurizing agent was distributed to the entire hot metal by injecting it from the lance deeply immersed in the hot metal pot. In addition, immersion free board, when the distance between the top of the hot metal pot and the hot metal surface can not be secured, and there is a concern that outflow due to the rise of hot metal, etc.,
This equipment is indispensable to suppress the swing of hot metal caused by the injection of desulfurizing agent.

FIG. 1 shows a desulfurization equipment used in the present invention, in which a free board 2 is immersed in a hot metal ladle 1 containing treated hot metal P, and an injection lance for blowing a desulfurizing agent from the upper part of the free board 2. 3 is the hot metal P in the hot metal ladle 1.
Immerse in it. Reference numeral 5 denotes a carrier gas (bubbles) containing a desulfurizing agent injected from the nozzle 4 at the tip of the injection lance 3. Freeboard has a remarkable effect in blocking oxygen and hot metal in the atmosphere and suppressing the decrease in desulfurization efficiency due to oxygen. Therefore, with respect to desulfurization, it is advantageous that the immersion free board is large for the reasons described above.

The present inventors have found from many test results that a freeboard having a cross-sectional area of more than 50% on the inner surface of the hot metal ladle as shown in FIG. 2 is required. FIG. 2 shows the relationship between the ratio of the cross-sectional area of the immersion free board to the cross-sectional area of the hot metal ladle and the desulfurization rate. Also, if the desulfurizing agent (powder) blown from the injection lance flows out of the above-mentioned freeboard and floats, the desulfurization efficiency decreases due to atmospheric oxygen, resulfurization occurs, and white smoke is generated during processing. It is necessary to cause a desulfurizing agent to float in the interior to cause a desulfurization reaction.

The present inventors have conducted many experiments on the reach of bubbles containing the desulfurizing agent injected from the injection lance nozzle in the free board, and obtained the results shown in FIGS. 3 and 4. FIG.
Fig. 4 shows the relationship between the reach of air bubbles in the freeboard (L in Fig. 1) and the desulfurization rate, and Fig. 4 shows the reach of air bubbles in the freeboard and the refractory erosion index on the freeboard side wall surface ( The relationship between the distance between L and A shown in FIG. 1 was normalized with the refractory erosion rate when L = A as 100). As is clear from these figures, the desulfurizing agent must be injected so that the reach distance of the bubbles is kept constant.

From these results, the following equation (1) was derived as an experimental equation. 0.5A ≦ L ≦ 0.9A (1) where: L: Carrier gas bubble reaching distance from the center of the injection lance A: Free board inner surface radius Therefore, desulfurization under conditions satisfying the above formula (1) The agent must be injected.

The upper and lower limits in the above equation (1) are set based on the following concept. That is, when L (FIG. 1) is small, the desulfurization efficiency is reduced due to insufficient stirring in the hot metal bath. In addition, when L is large, stirring of the hot metal is sufficiently obtained, but the jet generated by the carrier gas from the injection lance hits the inner wall of the immersion free board (in some cases, the side wall of the hot metal ladle), and the refractory at the portion is markedly reduced. It will melt away. Therefore, the lower limit is set to L ≧ 0.5 A from the evaluation of desulfurization efficiency, and the upper limit is set to L
≦ 0.9A.

The above L is represented as follows. L = L1 + R L1: Carrier gas bubble reaching distance from the tip of the injection lance nozzle R: Distance from the center of the lance to the tip of the nozzle Here, L1 may be one introduced in several documents. The following formula is used, and the conditions include the lance immersion depth and the blowing (gas) speed. (Source: Iron and Steel 61 (1975) N
o. 4 S111)

L1 / d _o = 1.6 Fr ' ^1/3 Fr' = Fr (d _o / H _o ) Fr = (p _g / p ₁ ) ・ (u _ON ² / (d _o · g)) d _o : lance feather diameter (cm) H _o: lance immersion depth (cm) ρ _g: carrier gas density _{^{(g / Ncm 3) ρ 1}} : liquid density (g / cm ³⁾ g: gravitational acceleration, 980cm / s ² Fr : Fluid number Fr ': Corrected fluid number

When the above condition is satisfied,
Furthermore, keeping the lance immersion depth, which indicates the depth from the injection lance nozzle tip to the hot metal surface, sufficiently large, ensures the desulfurizing agent floating distance in the injection method where the contribution of the reaction during powder levitation is high. This greatly contributes to improving the desulfurization efficiency (improving the probability that the desulfurizing agent encounters and reacts with sulfur in the hot metal).

When the evaluation was made by the experiments of the present inventors, the results shown in FIG. 5 were obtained. FIG. 5 shows the relationship between the ratio of the lance immersion depth to the hot metal bath depth and the desulfurization rate. That is, it was found from the figure that it was necessary to satisfy the condition of (lance immersion depth) ≧ (hot metal depth in hot metal pot) × 0.5. This indicates that desulfurization can be efficiently performed in a short time by securing a long floating time of the blowing desulfurizing agent.

Soda ash (Na ₂ CO ₃ ), which has a particularly high desulfurization ability and is a cheaper desulfurizing agent than Mg and CaC ₂
Can desulfurize in a short time by high-speed blowing under the above conditions, but in this case also, there are appropriate conditions as shown in FIG. That is, FIG. 6 shows the relationship between the soda ash (powder) blowing speed (kg / min · t-pig) and the desulfurization rate. The soda ash blowing speed is important for securing the desulfurizing agent (powder) floating time. Is a matter
(Soda ash blowing speed) ≤ 0.5 kg / min-tp
ig.

As can be seen from FIG. 6, even if the amount exceeds 0.5, the improvement of the desulfurization efficiency by soda ash is not recognized, and the desulfurizing agent is wasted unnecessarily. Here, the lower limit of the blowing speed should be separately considered depending on the allowable processing time and processing equipment capacity.
In order to reduce the soda ash blowing speed, there is simply a method of mechanically lowering the blowing speed.In this case, however, in order to prevent soda ash having insufficient fluidity from being clogged in the piping, an appropriate method is used. It is not recommended for efficient small-volume blowing because it must have a large pipe diameter and blowing equipment.

On the other hand, if the amount of soda ash is reduced by mixing with quick lime or the like, the amount of soda ash can be reduced to a small amount depending on the blending ratio with quick lime even if the blowing speed of the entire treatment agent is increased. Since it can be placed, even if the blowing speed is increased, the blowing speed of only soda ash can be kept low, and good fluidity can be ensured by the mixed quicklime, which is preferable.

[0025]

Embodiments of the present invention will be described below. 1. Reaction vessel and equipment used Using hot metal pot 1 (inner diameter: 4.5 m), immersion freeboard 2 and injection lance 3 shown in FIG.
The hot metal was desulfurized. 2. Hot metal component before desulfurization treatment [C] = 4.1-4.6%, [Si] = 0.20-0.
60%, [Mn] = 0.15 to 0.40%, [P] =
0.092-0.155%, [S] = 0.018-0.
035%

3. Converter slag representative component CaO = 45 to 55%, SiO ₂ = 15 to 20%, Mn
O = 6 to 12%, MgO = 4 to 7%, P ₂ O ₅ = 2.5
３3%, T.Fe = 12〜19% 4. Hot metal volume and hot metal bath depth Hot metal volume; 350 t; hot metal bath depth; 3.5 m Operating conditions and results Table 1 shows the examples of the present invention and Table 2 shows the comparative examples.

[0027]

[Table 1]

[0028]

[Table 2]

As can be seen from Table 1, according to the embodiment of the present invention, the desulfurization rate is maintained at 60% or more because the above conditions are set within the appropriate ranges so as to satisfy the various conditions. Have been done. However, Example 10 of the present invention did not satisfy the condition of the lance immersion depth described in claim 2, and the desulfurization rate was 62%, which was lower than the condition of Example 6 of the present invention.

In Example 11 of the present invention, the soda ash blowing speed described in claim 3 was low, and the desulfurization rate was 60.9%, which was lower than that of Examples 1 and 4. Further, in Example 12 of the present invention, since both the lance immersion depth and the soda ash blowing speed were small,
The desulfurization rate was 60.1%, which was lower than Examples 1, 4, and 11 of the present invention.

Next, in Comparative Examples shown in Table 2, in Comparative Examples 1 and 2, since the cross-sectional area of the freeboard was out of the proper range, the desulfurization rates were only 56.3% and 56.0%. . Conversely, in Comparative Examples 3 and 4, the reach of the bubbles containing the desulfurizing agent was short, and the desulfurization rates were reduced to 54.2% and 52.4%.
Further, in Comparative Example 5, although the reach of the bubble containing the desulfurizing agent was long and the desulfurization rate was good, the refractory erosion index was remarkably high at 76, which adversely affected the refractory.

[0032]

As described above, by using the immersion free board and blowing conditions as in the present invention, efficient desulfurization treatment can be performed while reducing the flux and avoiding the adverse effect on the hot metal refractory. It is possible. Further, the use of the immersion free board suppresses the swinging of the hot metal, so that the desulfurization treatment by high-speed blowing can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing an outline of a desulfurization facility used in an embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the ratio of the hot metal ladle cross-sectional area to the immersion freeboard cross-sectional area and the desulfurization rate.

FIG. 3 is a diagram showing a relationship between a reaching distance of bubbles in a free board and a desulfurization rate.

FIG. 4 is a graph showing the relationship between the reach of air bubbles in a freeboard and the refractory erosion index on the side wall surface of the freeboard.

FIG. 5 is a diagram showing a relationship between a ratio of a lance immersion depth to a hot metal bath depth and a desulfurization rate.

FIG. 6 is a diagram showing a relationship between a soda ash powder blowing speed and a desulfurization rate.

[Explanation of symbols]

 1: Hot metal pot 2: Free board 3: Injection lance 4: Injection nozzle 5: Air bubbles P: Hot metal

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Toshiyuki Kaneko Oita, Oita-shi, 1 Nishinosu, Nippon Steel Corporation Oita Works (72) Inventor Keisuke Okuhara, 1 Oita, Oita-shi, Oita, Oita 4K014 AA02 AB02 AB03 AB04 AB13 AC08 AC14 AC16 AD23 AD27

Claims (3)

[Claims] 1. A method for desulfurizing hot metal by dipping a sealed freeboard in hot metal in a hot metal pot, blowing a flux from the tip of an injection lance nozzle dipped in hot metal, and desulfurizing the hot metal by oxygen from the surrounding atmosphere. The following formula (1) is used to ensure that the cross-sectional area of the inner surface of the immersion free board is more than 50% of the cross-sectional area of the inner surface of the hot metal ladle in order to suppress the reduction in efficiency, and that the blown desulfurizing agent all floats in the free board. A hot metal desulfurization method using a closed freeboard, wherein a carrier gas is blown from the nozzle under satisfactory conditions. 0.5A ≦ L ≦ 0.9A (1) Where, L: Carrier gas bubble arrival distance from the center of the injection lance A: Free board inner surface radius 2. The hot metal desulfurization method using a closed freeboard according to claim 1, wherein the lance immersion depth is at least 0.5 times the hot metal depth in the hot metal ladle. 3. The method according to claim 1, wherein the soda ash desulfurizing agent is used as a flux, and the soda ash blowing rate satisfies the condition of 0.5 kg / min · t-pig or less. Hot metal desulfurization method using closed freeboard.