JP2011202200A - Slopping prevention method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a slopping prevention method by which slopping can be prevented without reducing oxygen feeding speed even under high speed feeding of oxygen, and an amount of use of carboneceous material can be reduced and an inexpensive facility cost is actualized.SOLUTION: By using a top-bottom blowing type converter, the top-blowing oxygen is blown for 4-8 min toward molten iron at a top-blowing oxygen flow rate of 2.0-4.0 Nm/min/ton, and iron oxide of Mkg (10≤M≤30) per ton of the molten iron is charged in a lump or intermittently into the converter during elapse of 1-4 min from the blowing start of the top-blowing oxygen, and slag basicity (CaO%/SiO%) and T. Fe concentration at the blowing-finish time of the blowing oxygen are controlled to 2.0-2.5 and 5-15%, respectively and thus, a dephosphorizing treatment of the molten iron is performed. Then, the carbonaceous material of 0.4-1.0 Kg per ton of the molten iron is blown into a slag layer through a sub-lance layer at a speed of 0.4-1.0 Kg/min from the point of time when time T (T≥0) calculated by using {26/(M-1.4)-1.0}≤T≤{26/(M-1.4)} has passed after the charging completion time of the iron oxide. Thereby, the slopping during the dephosphorizing treatment is prevented.

Description

  TECHNICAL FIELD The present invention relates to a method for preventing slopping, and specifically, using a converter-type smelting vessel, and without using fluorite, the use of gaseous oxygen or solid oxygen to simultaneously perform desiliconization and dephosphorization. The present invention relates to a method for preventing slopping in preliminary processing.

  In recent years, when steel is produced by decarburizing hot metal, a hot metal pretreatment for performing treatments such as desiliconization, dephosphorization, and desulfurization has been performed in advance for the purpose of reducing production costs and improving quality. In particular, using a converter-type smelting vessel capable of top-bottom blowing, a hot metal preliminary treatment is performed in which desiliconization and dephosphorization are performed simultaneously.

Since Si in the hot metal is oxidized to SiO ₂ by desiliconization, the basicity (CaO / SiO ₂ ), which is the ratio between the CaO mass concentration and the SiO ₂ mass concentration in the slag, is reduced, and the melting point of the slag is reduced. descend. Further, FeO in slag necessary for the dephosphorization reaction similarly lowers the melting point of slag.

  As a result, a molten slag is formed, and the oxygen source input at the same time oxidizes carbon in the hot metal to generate gas. At this time, when the slag forms (foams) and becomes more than the free board of the smelting vessel, the slag is blown over and slopping occurs. The occurrence of slopping not only lowers the iron yield, but also may cause operational troubles such as temporary suspension of operation.

  In Patent Document 1, a lime compound or coke is introduced into the hot metal in a torpedo car, and the criticality of slopping using the solid oxide and gaseous oxygen as an index and the slag basicity as indices are obtained, and the oxygen input is controlled. Thus, an invention for suppressing slopping is disclosed.

  Patent Document 2 discloses an invention for preventing slopping by subduing slag forming after dephosphorization blowing by blowing a carbonaceous material into slag using a sublance in dephosphorization pretreatment using a converter ( Slag forming prevention method) is disclosed.

Japanese Patent Laid-Open No. 10-195515 JP 2000-160222 A

  The invention disclosed by Patent Document 1 is intended for a torpedo type reaction vessel, and cannot be applied as it is to a converter type reaction vessel, and also reduces the amount of oxygen input in the slopping generation region. The dephosphorization process cannot be performed.

  Since the invention disclosed by Patent Document 2 aims at forming calming after the end of blowing, no consideration is given to the relationship with the input of iron oxide (iron ore or scale) as a refining agent that promotes dephosphorization. Furthermore, when dephosphorization is performed for a short time with high-speed acid supply, the prevention of slopping during acid supply becomes a major issue. Patent Document 2 discloses a method for solving such slopping accompanying high-speed acid supply. Not.

An object of the present invention is to provide a method for preventing slopping, which is a problem when performing hot metal dephosphorization processing at high speed and high efficiency using a top-bottom blown converter, more specifically. Under the condition that the flow rate of the top blown oxygen is 2.0 to 4.0 Nm ³ / min / ton, the supply time of the top blown oxygen is 4 to 8 minutes without causing slopping that causes an operational problem. Is to provide a method for stably obtaining a dephosphorization rate of 80% or more.

There are two possible causes of slopping.
One is oxygen supply conditions, and the CO gas generated by the reaction of oxygen source such as scale or iron ore, which is introduced into the converter as top blown oxygen or auxiliary material, with C in the hot metal is in the slag layer. The amount of gas and the state of dispersion of bubbles when rising. These are related to the occurrence of slopping.

  The other is slag generation conditions, such as the composition, temperature, and slag amount of slag present in the converter when the CO gas rises in the slag layer. These are related to the difficulty of detaching CO gas from the slag layer and the spillability of slag outside the furnace.

  Of these two causes of slopping, the slag generation condition is not considered in the present invention. An object of the present invention is to prevent slopping caused by performing a high-speed and high-efficiency hot metal dephosphorization method. Therefore, in order to reduce the amount of slag or change the slag composition, high-speed and high-efficiency hot metal desorption This is because it is necessary to consider the phosphorus method itself. For example, if the amount of Si brought in from the hot metal or scrap charged in the converter can be adjusted, the amount of slag can be reduced, so that the occurrence of slopping can be suppressed, but the desiliconization treatment and removal of the desiliconized slag, etc. This requires time and labor to solve the problem, and means and solutions for the solution are separately required. As a result, the hot metal dephosphorization method will be examined as a whole. In addition, the slag component after the dephosphorization treatment is considerably restricted to achieve the basic purpose of achieving a high efficiency and a dephosphorization rate of the hot metal of 80% or more, and can be adjusted to prevent the occurrence of slopping. There is little room.

Further, regarding the generation state of the CO gas, since the present invention is premised on performing hot metal dephosphorization at a high speed, the flow rate of top blown oxygen is set to 2.0 Nm ³ / min / ton or more and 4.0 Nm ³ / min. Basically, it should be blown as high as possible. For this reason, there is little room for adjusting the flow rate of the top blown oxygen.

  The present inventors have intensively studied conditions that can be adjusted to prevent slopping in hot metal dephosphorization treatment under such constraint conditions. As a result, the hot metal dephosphorization treatment is scaled as an auxiliary material (oxidant). It was found that iron oxide sources such as iron ore are always used, and that the method of using the iron oxide source affects the occurrence of slopping during hot metal dephosphorization.

  In addition, the present inventors can also use the technique described in Patent Documents 1 and 2 for blowing carbonaceous materials such as coke powder into slag to calm down slag forming in order to prevent slopping. I found out.

The present invention has been made based on these novel findings.
In the present invention, top blown oxygen is blown at a flow rate of 2.0 to 4.0 Nm ³ / min / ton toward hot metal contained in a top bottom blown type converter for 4 to 8 minutes. In 1 to 4 minutes from the start of spraying, Mkg of iron oxide per ton of molten iron is charged all at once or intermittently into this converter, and the slag basicity (CaO mass% at the end of spraying of top-blown oxygen) / SiO ₂ % by mass) is set to 2.0 to 2.5 and T.I. When the hot metal is dephosphorized at an Fe concentration of 5 to 15% by mass, from the time when the time T (min) calculated using the following equation (1) has elapsed since the completion of the iron oxide addition, A slopping prevention method characterized by blowing 0.4 to 1.0 kg of carbonaceous material into a slag layer at a rate of 0.4 to 1.0 kg / min.
{26 / (M-1.4) -1.0} ≦ T ≦ {26 / (M-1.4)} (1)
However, 10 ≦ M ≦ 30 and T ≧ 0.

  In the present invention, it is desirable to blow the carbon material into the slag layer through the sub lance.

  According to the present invention, slapping can be prevented without lowering the acid feeding rate even under high-speed acid feeding. Further, according to the present invention, the amount of carbonaceous material used can be reduced, and the use of a sub lance can prevent slopping at a low equipment cost.

FIG. 1 is a graph showing the relationship between the amount of iron oxide input and the slapping start time (the time from the completion of scale injection to the occurrence of slopping). FIG. 2 is a graph showing the relationship between the charcoal charging speed and the slipping occurrence index. FIG. 3 is an explanatory view schematically showing an outline of the hot metal pretreatment in the embodiment.

Hereinafter, modes for carrying out the present invention will be described.
First, the relationship between the occurrence of slopping and the use conditions of the iron oxide source will be described.
The occurrence of slopping is closely related to the hot metal treatment conditions. Therefore, as shown in Table 1, conditions such as the amount of hot metal, the hot metal component before and after the dephosphorization treatment, the acid feed rate from the main lance, the type and amount of the dephosphorizing agent used, the slag component after the dephosphorization treatment, etc. The relationship between the occurrence of slopping and the use of iron oxide sources (scale, iron ore) was investigated.

The range of the slag composition targeted in the present invention is such that the basicity of slag at the end of dephosphorization treatment (ratio of CaO mass concentration to SiO ₂ mass concentration in slag: (CaO% / SiO ₂ %)) is 2. The iron oxide mass concentration in the slag (T.Fe% as a representative value) is 5% or more and 15% or less.

  When the basicity of the slag exceeds 2.5, the slag forming does not cause much problem. Instead, the increase in the input unit of quick lime and the undehydrated CaO concentration in the treated slag are problematic. Because it becomes. On the other hand, when the basicity of the slag is low, such as less than 2.0, T.I. Even if the Fe concentration is 5 to 15%, it may not be possible to achieve the hot metal dephosphorization rate of 80% or more in a short time of 4 to 8 minutes, so the basicity of the slag is 2.0 or more. And

  Here, the timing of supplying the iron oxide source is such that the duration of acid transported over the dephosphorization treatment according to the present invention is 4 minutes or more and 8 minutes or less in total. Since the addition is scheduled, iron oxide is charged from the furnace bunker all at once or intermittently into the hot metal in the converter for 1 minute or more and 4 minutes or less from the start of top blowing acid.

  As a result of this investigation, there is a relationship that the time from the completion of iron oxide input to the occurrence of slapping (referred to as “slipping start time” in this specification) becomes shorter as the amount of iron oxide input increases. I understood.

FIG. 1 is a graph showing the relationship between the amount of iron oxide input and the slapping start time (the time from the completion of scale injection to the occurrence of slopping).
Under the conditions shown in Table 1, the input amount M (kg / ton) of iron oxide and the slopping start time T ′ (min) are in the relationship shown by the equation (2) as shown in the graph of FIG. I know that there is.
{26 / (M−1.4) −0.5} ≦ T ′ ≦ {26 / (M−1.4) +0.5} (2)
However, in the formula (2), 10 ≦ M ≦ 30.

In addition, as for the influence of the kind of iron oxide, a significant difference was not confirmed in the tested range, whether the iron oxide was a scale or an iron ore (particle size of 10 mm or less).
Next, the relationship between the prevention of slopping and the charging conditions of the carbonaceous material will be described.

  In order to prevent the occurrence of slopping, the charging of the charcoal must be started before the slopping begins. Even if charcoal is added after slopping has started, the suppression effect due to the charging is not immediate, and if the charcoal that has been injected spills out of the converter together with the slag, the stability of the input itself It is also lacking.

On the other hand, even if carbon material is input even though the slag is not formed, it is not appropriate to input the carbon material, and the cost to input is increased.
Here, as described above, the start time of slopping can be obtained from the input amount M (kg / ton) of iron oxide by calculation according to the equation (2). The addition effect of the carbon material was investigated as starting the addition of the carbon material from 0.5 to 1 minute before.

That is, as shown by the above equation (2), since the slapping starts within {26 / (M-1.4) ± 0.5} minutes from the completion of the iron oxide charging, the iron oxide charging The time T from the time of completion to the start of charging of the carbonaceous material may be according to equation (1).
{26 / (M-1.4) -1.0} ≦ T ≦ {26 / (M-1.4)} (1)
However, 10 ≦ M ≦ 30 and T ≧ 0.

  In the formula (1), there is a selection range of 0 to 1 minute with respect to a numerical value that can be calculated from the input amount M of iron oxide. The material input start time T may be determined as appropriate.

FIG. 2 is a graph showing the relationship between the carbon material charging speed and the slipping occurrence index when the carbon material is charged in this way.
The results shown in the graph of FIG. 2 are the same as the investigation of the results shown in the graph of FIG. 1 and the blowing conditions, and the coke powder is 0.05 to 1.0 kg / min as the carbon material from the time point obtained by the equation (1). The carbon material was changed in the range of / ton and blown into the slag layer for 1 minute or more using nitrogen as a carrier gas from the tip of the sub lance.

  In the graph shown in FIG. 2, the index of occurrence of slopping is: index 0: no sign of occurrence of slopping, index 20: occurrence of small amount of slag adhering to the furnace port, index 40: in the slag to the furnace port Occurrence of quantity adhesion, index 100: state where blowing cannot be continued, respectively.

  In the graph shown in FIG. 2, since the slipping occurrence index of 40 or less is required for stable operation, the carbon material charging speed is 0.4 kg / min / ton or more and 1.0 kg / min / ton or less. I understood.

  It is sufficient that the carbon material is blown for one minute at a charging speed of 0.4 to 1.0 kg / min / ton. If the effect does not appear even if one minute is blown, the blowing is continued further. But it was almost useless. For this reason, the required amount of carbonaceous material is 0.4 kg / ton or more, and 1.0 kg / ton or less is sufficient. This is because if the input amount of the carbon material is increased, not only the cost of the carbon material is increased, but also iron oxide in the slag is excessively reduced, resulting in a decrease in temperature and poor dephosphorization.

  In addition, when the charging speed of the carbonaceous material is as fast as 0.4 kg / min / ton or more, 0.4 kg / min / ton is continued for 1 minute when the amount of carbonaceous material blown becomes 0.4 kg / ton. It has been separately confirmed that the same effect of suppressing slopping as that obtained can be obtained.

FIG. 3 is an explanatory view showing an outline of the hot metal preliminary process in the embodiment.
As shown in FIG. 3, with respect to the hot metal 2 accommodated in the top-bottom blown converter 1, the amount of the hot metal 2, the components of the hot metal 2 before and after the dephosphorization treatment, the acid feed rate by the main lance 3, the use desorption The effect of the present invention can be achieved by dephosphorizing the hot metal 2 by determining the type and amount of the phosphorus agent and the conditions such as the four components of the slag after the treatment as shown in Table 1 except for the following. confirmed. In addition, the code | symbol 5 in FIG. 3 is a sub lance, and the code | symbol 6 is a bottom blow plug.

(Example of the present invention)
For hot metal 280 ton of hot metal before treatment [Si] = 0.40 mass%, hot metal before treatment [P] = 0.103 mass%, acid feed rate by main lance 3 = 2.4 Nm ³ / min / ton, upper In the treatment of blowing oxygen blowing time = 4.6 minutes, 20 kg / ton of iron oxide was intermittently added during the lapse of 1.5 to 2.0 minutes from the start of blowing of the top blowing oxygen.

Then, carbon dioxide (coke) is blown into the slag layer from sub lance 5 for 0.8 minutes using N ₂ as a carrier gas at a rate of 0.9 kg / min / ton after 0.8 minutes have elapsed after the completion of iron oxide charging. It is.

No slipping occurred during the dephosphorization process. After treatment, the slag basicity is 2.2, and slag T.I. Fe was 11% and hot metal [P] was 0.014%.
(Conventional method)
For hot metal 280 ton of hot metal before treatment [Si] = 0.38% by mass and hot metal [P] = 0.098% by mass, acid feed rate by main lance 3 = 2.4 Nm ³ / min / ton, upper In the treatment of blowing oxygen blowing time = 4.9 minutes, 15 kg / ton of iron oxide was intermittently added during the lapse of 1.5 to 1.9 minutes from the start of blowing the upper blowing oxygen.

Carbon material was not blown in.
Slipping occurred when 2.1 minutes had elapsed since the addition of iron oxide. After treatment, the slag basicity is 2.2, and slag T.I. Fe was 10% and hot metal [P] was 0.018%.

(Comparative example)
For hot metal 280 ton of hot metal before treatment [Si] = 0.36% by mass and hot metal [P] = 0.100% by mass, acid feed rate by main lance 3 = 2.4 Nm ³ / min / ton, upper In the treatment with blowing oxygen blowing time = 4.4 minutes, 13 kg / ton of iron oxide was intermittently added during the lapse of 1.4 to 1.9 minutes from the start of blowing of the upper blowing oxygen. Then, after 0.3 minutes after the completion of the iron oxide charging, carbon material (coke) was blown into the slag layer from the sublance 5 for 0.8 minutes using N ₂ as a carrier gas at a rate of 0.9 kg / min / ton. Slipping occurred 2.0 minutes after the iron oxide was charged.

  After the treatment, the slag basicity is 2.3 and the slag T.P. Fe was 11% and hot metal [P] was 0.015%.

Claims (2)

Top blowing oxygen is sprayed at a flow rate of 2.0 to 4.0 Nm ³ / min / ton toward the hot metal contained in the top bottom blowing type converter for 4 to 8 minutes, and from the start of blowing the top blowing oxygen During 1 to 4 minutes, Mkg of iron oxide per ton of molten iron was charged all at once or intermittently into the converter, and the slag basicity (CaO mass% / SiO ₂ mass%) is set to 2.0 to 2.5 and T.I. When the hot metal is dephosphorized with an Fe concentration of 5 to 15% by mass,
From the time when the time T (min) calculated using the following equation (1) has elapsed since the completion of the iron oxide charging, 0.4 to 1.0 kg of carbonaceous material per ton of hot metal was 0.4 per ton of hot metal. An anti-slipping method characterized by blowing into the slag layer at a speed of ˜1.0 kg / min.
{26 / (M-1.4) -1.0} ≦ T ≦ {26 / (M-1.4)} (1)
However, 10 ≦ M ≦ 30 and T ≧ 0.   The method according to claim 1, wherein the carbonaceous material is blown into the slag layer through a sub lance.

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