JP2005146335A - Method for dephosphorizing molten pig iron - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for effectively dephosphorizing molten pig iron for obtaining a large dispersing action of dephosphorizing agent into the molten pig iron and a high dephosphorizing efficiency because the effective elimination of a dead zone is obtained with the large stirring force of the molten pig iron in a mixer car. <P>SOLUTION: In the method for dephosphorizing the molten pig iron, by which the dephosphorization is applied by blowing oxygen gas and the dephosphorizing agent composed of iron oxide, CaO-base flux, etc., together with carrier gas through immersion lances into the molten pig iron filled up in the mixer car, this dephosphorizing method to the molten pig iron is performed, with which two pieces of immersion lances inserted by directing the longitudinal direction in the pig iron ladle car, are dipped into the molten pig iron so as to be mutually faced, and the blowing of the dephosphorizing agent is performed under conditions satisfying the following (1)-(3) formulas from these lances. In the (1) formula, 0.5H<HL<0.9H, in the (2) formula, 50≤Qp/Qg and in the (3) formula, 0.10L≤W≤0.50L. In these formulas, HL: lance immersion depth (m) from statical molten metal surface, H: molten pig iron bath depth (m), Qp: solid dephosphorizing agent blowing velocity (kg/min), Qg: carrier gas flowing rate (m<SP>3</SP>(standard condition)/min), W: distance (m) between the tip parts of two immersion lances, L: the maximum distance (m) in the longitudinal direction of torpedo car. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a hot metal dephosphorization method improved to increase the reaction efficiency of a dephosphorizing agent blown into a kneading vehicle.

  In the ironmaking and steelmaking processes at steelworks, hot metal preliminary treatment is performed to remove silicon, phosphorus, sulfur (Si, P, S), etc. contained in the hot metal in advance before decarburization blowing in the converter. ing. The hot metal dephosphorization treatment in the hot metal pretreatment is oxidative refining, and oxygen (oxygen gas, iron oxide), basic flux (CaO system, etc.), etc. are used as the dephosphorizing agent. There are various types of oxidation refining methods, and they are mainly classified into converter type processing, hot metal ladle type processing, and kneading car type processing (hereinafter also referred to as “topped processing”). Among these, the toped process has the advantage that the reaction efficiency of the dephosphorizing agent is high and the processing cost is low compared to the processing method using a converter, but the oxygen supply rate is small and the de-P rate is small because the free board is small. There was a problem of being bad.

Moreover, in the above-mentioned topped treatment, a dipping lance is used for blowing a dephosphorizing agent. The method of using it is, for example, related to hot metal desulfurization, but disclosed in Patent Document 1 and Patent Document 2 and the like. is there. Moreover, there is a proposal in Patent Document 3 as an example of the hot metal dephosphorization method. Furthermore, Patent Document 4, Patent Document 5, and Patent Document 6 can be cited as proposals for giving the immersion lance insertion position flexibility. Patent Document 7 also discloses a method of operating while discharging low basicity slag generated in the initial de-Si reaction from a kneading vehicle (hereinafter also referred to as “toped car”) in the topped hot metal treatment.
Japanese Patent Laid-Open No. 54-40216 JP-A-53-477441 JP 20002-69519 A Japanese Unexamined Patent Publication No. 64-7256 JP-A 64-7257 Japanese Patent Laid-Open No. 05-5144

A method using a plurality of lances is known in the hot metal preliminary processing by the above-mentioned topped car. The purpose of this method is (1) Dispersing promotion action of refining agent in hot metal (Patent Document 1, Patent Document 2), (2) Increase action of stirring force in topped car, Dead zone elimination action (Patent Document 3) As a technology developed as. However, the method (2) has a problem that stirring is insufficient because the shape of the container of the topped car is oval.
In general, what is important in the hot metal dephosphorization treatment by the topped car is how to improve the dephosphorization rate. That is, in order to increase the reaction efficiency of the dephosphorizing agent at the same time while avoiding the blowout of the molten iron in the treatment with the conventional topped car with a small free board, the dephosphorizing agent supply rate is increased and the dephosphorizing rate is increased. It is necessary to raise However, in the case of the conventional blowing technique using a plurality of lances, the dephosphorization reaction is not considered from such a viewpoint. Further, Patent Document 7 discloses a method in which low basicity slag generated by the de-Si reaction is discharged out of the system and operated, but the preliminary treatment can be performed without reducing the blowing rate of the dephosphorizing agent. It does not disclose how to rationally discharge only slag.

  Accordingly, an object of the present invention is to provide a hot metal mixture that has a large stirring force and is effective in eliminating the dead zone, has a large dispersion action of the dephosphorizing agent in the molten iron, and is effective in obtaining high dephosphorization efficiency. It is to propose a dephosphorization method.

  Therefore, as a result of earnest research on the method for solving the above-mentioned problems of the prior art, the present invention devised a means for stirring hot metal using two immersion lances, The present invention was completed by obtaining the knowledge that it was effective to use constant conditions for the relationship between the lance immersion depth, the control of the gas flow rate ratio relative to the dephosphorization agent, and the distance adjustment of the lance tip.

The present invention developed under such a concept is that a dephosphorizing agent composed of oxygen gas, iron oxide, CaO-based flux, etc. is blown together with a carrier gas into a hot metal filled in a kneading vehicle through an immersion lance. In the dephosphorization method of the hot metal to be dephosphorized, the above-mentioned two immersion lances inserted in the longitudinal direction in the kneading vehicle are immersed in the hot metal in opposite directions, and from these lances, the following ( A hot metal dephosphorization method, wherein the dephosphorization agent is blown under conditions satisfying the formulas (1) to (3).
0.5H <HL <0.9H (1)
50 ≦ Qp / Qg (2)
0.10L ≦ W ≦ 0.50L (3)
HL: Lance immersion depth from stationary hot water surface (m)
H: Hot metal bath depth (m)
Qp: Solid dephosphorizing agent blowing speed (kg / min)
Qg: Carrier gas flow rate (m ³ (standard state) / min)
W: Distance between two immersion lance tips (m)
L: Maximum distance in the longitudinal direction of the topped car (m)

  In the present invention, it is preferable that the kneading wheel is tilted 3 to 10 degrees around the rotation axis thereof, and the dephosphorizing agent is blown while the low basicity slag generated during the de-Si treatment is discharged.

  In the present invention, when the dephosphorization of the hot metal in the topped car is performed using two dipping lances having different dipping (insertion) directions from the toped mouth, the dephosphorizing agent is blown in the blowing conditions described above. Compared with the conventional method of dephosphorizing a single immersion lance, high-efficiency and high-speed processing becomes possible. Moreover, in the dephosphorization method of the present invention, the temperature drop of the hot metal during the treatment is small, and it can be expected that the treatment capacity is improved by reducing the cost and shortening the treatment time.

  In the hot metal dephosphorization treatment with a topped car, a treatment is required to blow a dephosphorizing agent mainly composed of oxygen oxide or CaO as an oxygen source into the hot metal in the topped car through an immersion lance together with a carrier gas. Since the dephosphorization reaction that occurs in this treatment is an oxidation reaction as shown in the following formula (1), it also competes with the oxidation reaction of carbon or manganese (C, Mn) in the hot metal. In particular, since hot metal is saturated with carbon, the decarburization reaction easily proceeds during the dephosphorization reaction.

The hot metal dephosphorization reaction is carried out by reacting the metal / slag as shown in the following formula (1).
2 [P] +5 [O] +3 (CaO) = 3CaO.P2O ₅ (1)
Where [P]: phosphorus in hot metal, [O]: oxygen in hot metal (from oxygen gas or iron oxide) (P ₂ O ₅ ), (CaO): P ₂ O ₅ in slag, slag or flux Medium CaO

  In the dephosphorization treatment of hot metal having the above-described reaction characteristics, it is considered effective to increase the blowing rate of the dephosphorizing agent in order to increase the dephosphorization rate. However, in this case, since the gas (mainly CO gas) will increase locally, the hot metal-dephosphorizing agent due to the outflow (blowing) of hot metal from the toped mouth and the aggregation of the dephosphorizing agent in the hot metal. There is a problem in that dephosphorization oxygen efficiency is lowered due to a decrease in the reaction interface.

  On the other hand, it is considered effective to increase the lance immersion depth in order to increase the stirring power of hot metal in the topped car and increase the reaction interfacial area of the dephosphorizing agent (dephosphorizing agent dispersion action). The buoyancy due to the dephosphorization carrier gas and the CO gas bubbles generated by the decarburization reaction is increased, and the molten iron outflow from the toped port is promoted.

  On the other hand, in order to increase the reaction interface area (= contact area) between the dephosphorizing agent and the hot metal, it is effective to promote the penetration of the dephosphorizing agent into the hot metal. In general, it is known that the dephosphorizing agent blown into the hot metal together with the carrier gas is surrounded by the carrier gas expanded near the outlet of the lance, and part of the degassing gas leaves and enters the hot metal. It has been. Therefore, in the present invention, by increasing the ratio of the carrier gas to the solid dephosphorizing agent, the release of the solid dephosphorizing agent from the gas bubbles is promoted, thereby promoting the penetration of the dephosphorizing agent into the hot metal. The conclusion is reached that this is effective.

Under such a concept, the inventors use two immersion lances having different immersion (insertion) methods, and the optimum dephosphorizing agent blowing conditions, lances that maximize the dephosphorization oxygen efficiency and the dephosphorization rate. Experiments were conducted on the insertion position. Hereinafter, the examination result will be described.
In this experiment, a 400 t topped car was used, and the CaO powder blown into the hot metal was generated from the hot metal (Si) in the initial stage of the treatment in the form shown in Fig. 1 under the conditions shown in Table 1 (hot metal and dephosphorizing agent). Blowing was performed until the weight ratio of SiO ₂ was doubled (slag basicity 2.0 target), and then only sintered powder was blown. In this experiment, first, a dephosphorization treatment experiment using a single immersion lance was performed in order to find out appropriate blowing conditions of the sintered powder. The experimental levels are shown in Table 2. In any conditions, the CaO supply rate was constant.

In experiment level 1, an experiment was conducted in which the lance immersion depth was changed under the condition that the sintered powder supply rate was constant at 1.0 kg / min / t. As a result of the experiment, FIG. 2 shows the relationship between the lance immersion depth and the de-P oxygen efficiency. As shown in this figure, dephosphorization oxygen efficiency is highly stabilized by setting the lance immersion depth to 50% or more of the hot metal depth H in a stationary state. In particular, dephosphorization oxygen efficiency is substantially constant at 60% or more. Met. However, when the lance immersion depth (lance immersion depth HLm from the stationary hot water surface) exceeds 90% of the hot metal depth (bath depth) H, refractory erosion damage at the bottom of the topped car became prominent. Accordingly, it was found that the bath depth H of 0.5 to 0.9 is preferable as the lance immersion depth.
That is, the relationship of the above equation (1) is established, 0.5H <HL <0.9H.

Next, in Experiment Level 2, when the lance immersion depth is 60% in the bath depth, the sintered powder is fixed at 1.25 kg / mim / t, which is a critical condition that does not cause hot metal blow-out from the topped port, and the carrier gas An experiment was carried out to reduce this. The results are shown in FIG. 3. In this case, the deoxygenation oxygen efficiency (%) is expressed as follows: solid-gas ratio (dephosphorization agent blowing speed Qp (kg / min) and carrier gas flow rate Qg (m ³ (standard state) / It was found that by setting the ratio to min) to 50 (kg / m ³ (standard state)) or more, it was stabilized at a high level.
That is, the relationship of the above equation (2) is established, 50 ≦ Qp / Qg.
Here, the upper limit of the solid-gas ratio is about 120 kg / min / m ³ (standard state) as a condition that enables powder transport at the experimental powder supply rate of 1.25 kg / min / t. Met. The upper limit of the solid-gas ratio varies depending on various factors such as the supply speed of the sintered powder, the powder transport pipe, and the pressure. However, an increase in the upper limit of the solid-gas ratio due to an increase in the supply rate of the sintered powder promotes the aggregation of the sintered powder in the hot metal and reduces the reaction interface area, so about 1.25 kg / min / t is appropriate. .

Next, as an experiment level 3, an experiment was carried out using a facility as shown in FIG. 4 and dephosphorizing using two immersion lances in different immersion states. The blowing form is shown in FIG. That is, this experiment is for examining the influence of the distance in the longitudinal direction of the topped car at the tip of the immersion lance. As shown in FIG. 5, when the distance (m) between the two immersion lance tips is 0.1 or less in the maximum distance L (m) in the longitudinal direction of the topped car, the dephosphorizing agent is removed by hot metal blowing from the toped port. Insufflation became difficult. On the other hand, the dephosphorization oxygen efficiency decreased under the condition of the distance between the immersion lance tips W> 0.5L. This is presumably because the volume of the container decreases as the structure of the topped car approaches both ends, and the loss of energy becomes significant because the injection position approaches the wall of the surrounding refractory. Therefore, a relational expression based on the above expression (3), 0.10 L ≦ W ≦ 0.50 L, was obtained.
FIG. 5 also shows the experimental results with one lance (level 3). As shown in FIG. 5, the P oxygen removal efficiency is clearer when two immersion lances are blown (level 4) than when one immersion lance is used regardless of the distance between the lance tips. It is good. Moreover, as long as it is performed at level 4 (two lances), the same effect can be obtained in any range where the distance between the lance tips is ≦ 0.7 L. This is believed to be due to the mixing characteristics of the shape of the elongated topped car.

  In this case, the immersion depths of the two lances are basically the same, but the immersion depths of the two lances vary from 0 to 0.2H with respect to the hot metal depth (bath depth) H in a stationary state. You may let them. The insertion angle (θ) of the lance inserted from the topped car of the topped car can be adjusted in the range of 0 to 30 °.

As the dephosphorizing agent used in the present invention, that is, as an oxidizing component such as iron oxide to be added to the hot metal, ash-containing sintered ore, dust, or a material mainly composed of iron oxide such as a rolling scale is used. it can. Further, as the CaO source, it is possible to use recycled products such as converters and cast slag. As the carrier gas, an inert gas such as nitrogen or argon, which is mixed with an oxidizing gas such as compressed air, oxygen gas or CO ₂ gas can be used.

  FIG. 6 is a schematic diagram of an experiment in which the topped container is tilted and slag is discharged during the operation of blowing the dephosphorizing agent. This experiment was performed by the level 4 method using the above-described two lances, and FIG. 7 shows the relationship between the torpedo inclination angle and the de-P oxygen efficiency. From FIG. 7, it can be seen that the tilt angle of the topped car is preferably 3 to 10 ° in order to realize stable discharge of slag without blowing out of molten iron and to prevent molten iron outflow from the toped opening. In the first place, the significance of discharging the slag simultaneously with the dephosphorization treatment is to remove the low basicity slag generated inside the topped car.

In general, in the early stage of the torpedo treatment, the de-Si reaction proceeds preferentially over the dephosphorization reaction, and this de-Si reaction generates SiO ₂ -rich slag, and the torpedo is already contained inside before the dephosphorization treatment. Low basicity slag mixed with existing blast furnace slag and cast-bed de-Si slag (both are rich in SiO ₂ ) is produced. However, since the dephosphorization reaction is generally promoted as the basicity increases, it is advantageous to cause the low basicity slag to flow out of the topped car in advance. On the other hand, if there is a hot metal outflow at this time, it is necessary to avoid it because the iron yield decreases. Therefore, in the present invention, in order to satisfy both requirements, the above-mentioned preferred range of the tilted angle of the topped car is determined as described above.

The implementation conditions employed in this example were a treatment time of 30 minutes, and the amount of hot metal and the initial hot metal component were as shown in Table 1.
(1) Table 3 is an example for verifying the level A (lance immersion depth). In the table, the lance immersion depths of the comparative examples were 0.4H and 0.9H, and the lance immersion depths of the present invention examples were 0.5H and 0.6H. The results of this example are shown in Table 4. When the lance immersion depth suitable for the method of the present invention was 0.5H and 0.6H, a low [% P] was obtained after the treatment.
(2) Table 5 is an example for verifying the level B (solid-gas ratio). In this example, a solid-gas ratio of 30 kg / m ³ (standard state) is used as a comparative example, and examples of the present invention are 50 kg / m ³ (standard state), 60 kg / m ³ (standard state), 100 kg / m ³ (standard state) was used. The results are shown in Table 6, and it was found that [% P] decreased after the treatment when the solid-gas ratio> 50 kg / m ³ (standard state) compatible with the method of the present invention.
(3) Table 7 shows an example for verifying level C (two lances). In this example, as Comparative Example 1, when one lance was blown at the same sintered powder blowing speed, as Comparative Example 2, when the distance between lances was 0.05 L with two lances, as Comparative Example 3 The distance between the two lances was 0.6L. On the other hand, as an example of the present invention, a lance having a distance between lances of 0.1 L and 0.5 L was used. The results are shown in Table 8. It was found that when the distance between the lances was set to 0.1 L to 0.5 L with two lances, [% P] decreased after the treatment.
(4) Table 9 shows an example for verifying the level D (tilt angle). In this example, Comparative Example 1 is an example in which there is no inclination, Comparative Example 2 is an example in which the inclination is 12 °, while the method of the present invention is executed with an inclination of 5 °. The results are shown in Table 10. According to the method of the present invention, there was no hot metal outflow during blowing of the dephosphorization agent, and low basicity slag was discharged by tilting flow drought, thereby increasing the slag basicity after treatment. As a result, [% P] decreased after the treatment. In particular, by making the blowing conditions appropriate with two lances, the supply speed of the sintered powder can be increased without generating hot metal blowing and with high reaction efficiency, and the processing speed is increased. Furthermore, it was also found that slag discharge due to topped tilting increases the basicity of slag and promotes the reaction.

  The present invention can be applied to molten iron production technology in an ironworks.

It is sectional drawing which shows the example of the dephosphorization agent blowing apparatus by one lance. It is a graph which shows the relationship between lance immersion depth and de-P oxygen efficiency. It is a graph which shows the relationship between solid-gas ratio and de-P oxygen efficiency. It is sectional drawing which shows the example of the dephosphorizing agent blowing apparatus according to this invention method. It is a graph which shows the relationship between the distance between lance front-end | tips, and de-P oxygen efficiency. It is a schematic diagram explaining the slag outflow method by topped inclination. It is a graph which shows the relationship between a topped inclination angle and de-P oxygen efficiency.

Explanation of symbols

1, 1 'lance for blowing 2 topped car 3 hot metal 4 slag 5 dephosphorizing agent 6 carrier gas

Claims (2)

In the hot metal dephosphorization method of dephosphorizing hot metal, which is dephosphorized by blowing a dephosphorizing agent composed of oxygen gas, iron oxide, CaO flux, etc. with carrier gas into the hot metal filled in the chaotic vehicle. The two above-mentioned immersion lances inserted in the longitudinal direction are immersed in the hot metal in opposite directions, and from these lances, the following conditions (1) to (3) are satisfied: A hot metal dephosphorization method comprising blowing the dephosphorizing agent.
0.5H <HL <0.9H (1)
50 ≦ Qp / Qg (2)
0.10L ≦ W ≦ 0.50L (3)
HL: Lance immersion depth from stationary hot water surface (m)
H: Hot metal bath depth (m)
Qp: Solid dephosphorizing agent blowing speed (kg / min)
Qg: Carrier gas flow rate (m ³ (standard state) / min)
W: Distance between two immersion lance tips (m)
L: Maximum distance in the longitudinal direction of the topped car (m) 2. The low basicity slag generated during de-Si treatment is caused to flow out by tilting the kneading wheel 3 to 10 ° about the rotation axis when blowing the dephosphorizing agent by the immersion lance. How to remove phosphorus from hot metal.

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