JP4779464B2 - Method for producing low phosphorus hot metal - Google Patents

Description

  The present invention relates to a method for efficiently producing a low phosphorus hot metal by a dephosphorization process performed as a hot metal pretreatment.

  Instead of the conventional blast furnace-converter method, a treatment method in which a hot metal pretreatment for performing a dephosphorization treatment and a desulfurization treatment at the hot metal stage has been widely used. Initially, these pretreatments were carried out for steels that required low sulfidation and low phosphatization due to the quality of the steel materials. However, in recent years, productivity improvement in converters and reduction of Mn ore in converters As a means of reducing the total cost of the steelmaking process in a steelmaking integrated steelworks, desulfurization and dephosphorization treatments have been applied to almost all the hot metal that is produced. It was.

Among these, the dephosphorization treatment is performed by supplying a gaseous oxygen source such as oxygen gas or a solid oxygen source such as iron ore as a dephosphorizing agent while stirring the hot metal and adding a dephosphorizing flux such as quick lime. In this method, phosphorus is oxidized with such an oxygen source, and the resulting phosphorus oxide is absorbed and fixed in a dephosphorization flux such as quick lime to remove phosphorus from the hot metal. In this case, since the phosphorous oxide is not absorbed unless the dephosphorization flux is hatched, it is widely performed to add fluorite (CaF ₂ ) in order to promote the hatching of the dephosphorization flux. A torpedo car, a hot metal ladle, a converter-type refining furnace, or the like is used as the processing vessel.

In order to promote this dephosphorization reaction, various means have been conventionally proposed. For example, Patent Document 1 discloses a dephosphorization treatment method in which a solid oxygen source and quicklime are blown into hot metal contained in a torpedo car, and air or inert gas is blown as a carrier gas, and oxygen gas is blown into hot metal. Is disclosed. Patent Document 2 discloses a dephosphorization processing method in which a solid oxygen source, quicklime, and fluorite are blown into the hot metal while oxygen gas or a solid oxygen source is continuously supplied from above while blowing oxygen gas as a carrier gas. It is disclosed. Further, Patent Document 3 discloses a dephosphorization processing method in which calcium oxide powder is blown onto the hot metal together with oxygen gas from an upper blowing lance while stirring and blowing the gas into the hot metal accommodated in the converter type refining furnace. It is disclosed.
JP-A-6-279825 JP-A-6-287616 JP-A-8-311523

  The hot metal dephosphorization reaction is promoted by the reaction between the supplied oxygen source and the phosphorus in the hot metal to form a phosphor oxide, which is absorbed and fixed by a dephosphorization flux such as quicklime. Therefore, in order to promote the dephosphorization reaction, it is necessary to make the conditions such that the generated phosphor oxide is immediately absorbed by the dephosphorization flux. In addition, since the rate of formation of phosphorus oxides depends on the phosphorus concentration in the hot metal, the molten iron with low phosphorus concentration must be renewed as soon as possible from the vicinity of the oxygen source to be supplied and renewed with high phosphorus concentration. I must. By doing in this way, it becomes possible to dephosphorize efficiently with few dephosphorization fluxes. That is, the addition position of the dephosphorization flux such as quick lime needs to be around the addition position of the oxygen source, and the dephosphorization efficiency does not increase even if it is simply blown into the hot metal. In addition, when the hot metal is stirred by blowing a stirring gas, a position where the stirring is vigorous and a position where the stirring is not intense occur. However, in order to increase the efficiency of the dephosphorization reaction, it is necessary to proceed the dephosphorization reaction at a position where the stirring is intense. is there.

  If the above prior arts are examined from such a viewpoint, it can be said that any of the techniques still has a high room for improvement. In other words, efficient dephosphorization with a small amount of dephosphorization flux is not yet sufficient, and there is enough room for further improvement.

  By the way, in recent years, with regard to the addition of fluorite to promote the hatching of lime-based dephosphorization flux such as quick lime, the amount of fluorite used in steel refining has been reduced in consideration of the effect of fluorine on the environment. Reduction as much as possible is required, and there is a limit to improving the dephosphorization efficiency by adding fluorite.

  The present invention has been made in view of such circumstances, and its object is to produce a low phosphorus hot metal by dephosphorizing the hot metal without using a large amount of fluorite and reducing the amount of lime. It is an object of the present invention to provide a method for producing a low phosphorus hot metal, which can be efficiently dephosphorized with a flux for dephosphorization, thereby reducing the amount of slag generated as much as possible.

  The present inventors have intensively studied and studied to solve the above problems. As a result, the lime-based dephosphorization flux such as quick lime is sprayed on the hot metal bath surface together with oxygen gas from the top blowing lance, and at the same time the hatching of the lime-based dephosphorization flux is promoted by the large amount of FeO produced. It was confirmed that the phosphorous oxide produced by the reaction with oxygen gas was immediately absorbed by the lime-based dephosphorization flux, so that the dephosphorization reaction was promoted. Further, in this state, by increasing the stirring strength in the vicinity of the fire point formed by the oxygen gas supplied from the top blowing lance, the hot metal in the vicinity of the fire point, that is, the dephosphorization reaction interface is renewed, and the dephosphorization reaction becomes more efficient. I got the knowledge that it was carried out.

The present invention has been made on the basis of the above knowledge, and the method for producing low phosphorus hot metal according to the first invention comprises a container containing hot metal, an oxygen source and a lime-based dephosphorization containing no alumina. In the method for producing a low phosphorus hot metal by adding a working flux and dephosphorizing the hot metal, oxygen gas and at least a part of the lime-based dephosphorizing flux are passed through an upper blowing lance . While spraying on the hot spot which arises on the hot metal bath surface by spraying , the solid oxygen source blown in hot metal with the carrier gas is supplied to the vicinity of the hot spot.

The method for producing low phosphorus hot metal according to the second invention is characterized in that, in the first invention, the blowing rate of the solid oxygen source blown into the hot metal together with the carrier gas is 0.03 to 1 kg / min · hot metal ton. It is what.

According to a third aspect of the present invention, there is provided a method for producing a low phosphorus hot metal, wherein in the first or second invention , 10 mass% or more of the solid oxygen source added in the dephosphorization treatment is blown into the hot metal and added. It is a feature.

The method for producing low phosphorus hot metal according to the fourth invention is characterized in that, in any one of the first to third inventions, dephosphorization treatment is performed on the hot metal having a silicon content of 0.40% by mass or less. It is what.

According to a fifth aspect of the present invention, there is provided a method for producing low phosphorus hot metal in any one of the first to fourth inventions, wherein a hot pot holding vessel is a pan-type or torpedo car type vessel, and at least oxygen gas is passed through an upper blowing lance. A part of the lime-based dephosphorization flux is sprayed on the hot metal bath surface, and a solid oxygen source is blown together with a carrier gas through an injection lance or a blowing tuyere.

  According to the present invention, an efficient dephosphorization process can be performed without adding a large amount of fluorite and using a small amount of lime-based dephosphorization flux, thereby reducing the amount of slag generation as much as possible. It becomes possible.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic cross-sectional view of a dephosphorization treatment facility used when carrying out a dephosphorization treatment according to the present invention.

  In FIG. 1, a hot metal ladle 2 containing hot metal 16 discharged from a blast furnace (not shown) is mounted on a carriage 3 and carried into a dephosphorization treatment facility 1. An upper blowing lance 4 and an injection lance 5 are installed in the dephosphorization processing equipment 1, and the upper blowing lance 4 and the injection lance 5 can move up and down in the hot metal ladle 2.

  An oxygen gas pipe 7 is connected to the upper blowing lance 4, and oxygen gas as a gaseous oxygen source is supplied from the upper blowing lance 4 into the hot metal ladle 2 through the oxygen gas pipe 7 at an arbitrary flow rate. It has become so. Further, the oxygen gas pipe 7 is branched, and the branched oxygen gas pipe 7A is connected to a storage tank 6 containing a powdery lime-based dephosphorization flux 17, and the storage tank 6 includes A flux transfer pipe 8 connected to the blowing lance 4 is connected. That is, the oxygen gas supplied to the storage tank 6 functions as a conveying gas for the lime-based dephosphorization flux 17 accommodated in the storage tank 6, and from the tip of the upper blowing lance 4 via the flux transfer pipe 8. The lime-based dephosphorization flux 17 can be supplied by spraying on the bath surface of the hot metal 16 accommodated in the hot metal pan 2. The oxygen gas pipe 7 is provided with a shut-off valve 9, and the oxygen gas pipe 7 A is provided with a shut-off valve 10, so that oxygen gas can be supplied directly from the top blowing lance 4, Supplying via can also be adjusted arbitrarily.

  As the lime-based dephosphorization flux 17, quick lime powder can be used. Alumina powder or the like may be added to the quicklime powder as a hatching accelerator, but in the present invention, the lime-based dephosphorization flux 17 is added by spraying on the hot metal bath surface. Thus, it is possible to sufficiently remove phosphorus without using a hatching accelerator such as alumina powder. In particular, from the viewpoint of protecting the environment by suppressing the amount of fluorine eluted from the produced slag 21, it is preferable not to use a fluorine-containing substance such as fluorite as a hatching accelerator. However, a substance in which fluorine is inevitably mixed as an impurity component may be used.

  The oxygen gas blown from the top blowing lance 4 as a dephosphorizing agent is industrial pure oxygen, and may contain impurities such as nitrogen gas in a volume percentage of several percent. By using oxygen gas as the dephosphorizing agent, the temperature of the hot metal 16 is increased by the heat of oxidation. Oxygen-containing gases such as air and oxygen-enriched air can also be used as a gaseous oxygen source, but it is preferable to use oxygen gas because of its high dephosphorization reaction rate.

  The injection lance 5 is connected to a storage tank 11, and a powdered solid oxygen source 18 made of iron oxide such as iron ore accommodated in the storage tank 11 is passed through a non-oxidizing gas such as nitrogen gas or Ar gas or a non-oxidizing gas. The active gas can be blown and added to the hot metal 16 as a carrier gas. The solid oxygen source 18 functions as a dephosphorizing agent similarly to the oxygen gas. However, although the heat of oxidation is generated by adding the solid oxygen source 18, the temperature of the hot metal 16 decreases due to the sensible heat and latent heat of the solid oxygen source 18. From the injection lance 5, only the non-oxidizing gas or inert gas such as nitrogen gas or Ar gas can be blown to stir the hot metal 16.

  Further, the dephosphorization processing facility 1 is provided with a raw material supply facility including a hopper 12 and a hopper 13, a raw material transfer device 14, and a chute 15, and is accommodated in the hopper 12 using this raw material supply facility. The granular or massive solid oxygen source 19 and the granular or massive lime-based dephosphorization flux 20 accommodated in the hopper 13 can be added on top of the hot metal ladle 2. The granular or massive solid oxygen source 19 functions as a dephosphorizing agent in the same way as the powdered solid oxygen source 18, and the granular or massive lime-based dephosphorization flux 20 is composed of phosphorous oxide produced by the dephosphorization reaction. The reaction is to fix the phosphor oxide to the slag 21. As the solid oxygen sources 18 and 19, iron ore, sintered ore, mill scale, dust collection dust, or the like can be used. In the present invention, since the powdery lime-based dephosphorization flux 17 is mainly used as the lime-based dephosphorization flux, the massive lime-based dephosphorization flux 20 is not necessarily required. In the case where the lime-based dephosphorization flux 20 is added, the hatching of the lime-based dephosphorization flux 20 is slow. Instead of the dephosphorization flux 20, another flux may be accommodated.

  Using the dephosphorization processing equipment 1 having such a configuration, the dephosphorization processing according to the present invention is performed as follows.

  The injection lance 5 is immersed in the hot metal 16, and the solid oxygen source 18 is continuously blown from the injection lance 5 using nitrogen gas, Ar gas or the like as a carrier gas, and the lime-based dephosphorization flux 17 is blown up together with the oxygen gas. 4 is continuously sprayed onto the bath surface of the hot metal 16 to perform dephosphorization of the hot metal 16. The oxygen gas blown through the upper blowing lance 4 collides with the bath surface of the hot metal 16 to form a so-called “fire point”. In FIG. 1, the fire point is indicated by R. The fire point R is recessed from the surroundings, and the slag 21 is pushed around the fire point R.

  At that time, the discharge angle and position of the injection lance 5 and the flow rate of the conveying gas are adjusted so that the solid oxygen source 18 blown from the injection lance 5 is supplied in the vicinity of the fire point R. This can be carried out without problems by conducting a preliminary test or the like in advance. In this case, instead of the injection lance 5, a tuyere (not shown) may be provided on the bottom or side wall of the hot metal ladle 2, and the solid oxygen source 18 may be blown from the tuyere. If the position of the tuyere is a position directly below the upper blowing lance 4, the solid oxygen source 18 blown from the tuyere is inevitably supplied in the vicinity of the fire point R.

When oxygen gas is blown onto the hot metal bath surface through the upper blowing lance 4, a large amount of FeO is generated at the fire point R by the oxygen gas colliding with the bath surface. As a result, the fire point R becomes an advantageous condition for hatching of the lime-based dephosphorization flux 17, and the lime-based dephosphorization flux 17 is directly supplied to the region where a large amount of FeO is generated through the top blowing lance 4. When the CaO of the lime-based dephosphorization flux 17 comes into contact with the generated FeO, the lime-based dephosphorization flux 17 forms a CaO—FeO-based melt on the surface thereof. That is, the surface of the lime-based dephosphorization flux 17 is in a hatched state. Phosphorus oxide (P ₂ O ₅ ) produced by reaction with oxygen gas is taken into this CaO—FeO melt and forms a stable solid phase of 3CaO · P ₂ O ₅ . The lime-based dephosphorization flux 17 that forms a stable solid phase of 3CaO · P ₂ O ₅ is pushed out around the fire point R as the slag 21 as the dephosphorization process proceeds.

  In addition, due to the stirring effect of the solid oxygen source 18 blown into the hot metal 16, the reacted hot metal with a low phosphorus concentration is immediately eliminated from the vicinity of the hot spot R, and the vicinity of the hot spot R is equivalent to the bulk of the hot metal 16. Since the concentration is maintained, the reaction rate between the supplied oxygen gas and phosphorus in the hot metal can be maintained at a high level for dephosphorization. That is, the dephosphorization rate can be increased.

  In this way, a direct dephosphorization reaction occurs in the region centered on the fire point R, and the slag 21 pushed out of the fire point R exists in a solid-phase state, so that a small amount of lime-based dephosphorization occurs. Efficient dephosphorization can be performed with the amount of flux 17 and 20 used.

  Therefore, in the present invention, at least a part of the lime-based dephosphorization flux is sprayed to the fire point R. If possible, it is preferable to spray the entire amount of lime-based dephosphorization flux required on the hot spot R. When the total amount of lime-based dephosphorization flux required can be added from the top blowing lance 4, it is not necessary to add the lime-based dephosphorization flux 20 added on top.

  In order to maintain the stirring strength of the hot metal 16 at the fire point R, the solid oxygen source 18 is blown from the injection lance 5 until the end of the dephosphorization process. By blowing the solid oxygen source 18, a larger stirring force can be obtained as compared with the case of blowing only the stirring gas. The blowing rate of the solid oxygen source 18 is preferably 0.03 to 1 kg / min · molten ton. When the blowing speed is less than 0.03 kg / min · molten ton, the stirring force is insufficient. On the other hand, even if the blowing speed exceeds 1 kg / min · molten ton, the effect of increasing the stirring force is small, and the blowing equipment This is not preferable because the equipment cost increases. The solid oxygen source 18 is blown at a blowing speed in this range, and if a solid oxygen source is required, the solid oxygen source 19 is added on top. In this case, in order to ensure the stirring power, it is preferable to adjust the blowing speed so that at least 10% by mass or more of the solid oxygen source used in the dephosphorization treatment is blown into the hot metal and added.

  The ratio between the oxygen gas supplied as the oxygen source and the solid oxygen source is set from the temperature balance according to the temperature and components of the hot metal before and after the treatment. As described above, the temperature increases when oxygen gas is used, and the temperature decreases when a solid oxygen source is used. The temperature of the hot metal 16 at the end of the dephosphorization process may be 1250 ° C to 1400 ° C, preferably 1250 ° C to 1350 ° C.

  Although the stirring power increases even when lime-based dephosphorization flux is blown from the injection lance 5, the ratio of the lime-based dephosphorization flux blown into the hot metal 16 to the hot point R where the FeO concentration is high is the ratio for lime-based dephosphorization. Compared to the case where the flux is directly sprayed on the fire point R, the amount is reduced. In order to efficiently perform the dephosphorization reaction with a small amount of lime-based dephosphorization flux, it is necessary to spray the lime-based dephosphorization flux on the hot spot R which is a dephosphorization reaction site. Accordingly, in the present invention, the lime-based dephosphorization flux is not supplied from the injection lance 5. The amount of the lime-based dephosphorization fluxes 17 and 20 is changed according to the silicon concentration and the phosphorus concentration of the hot metal 16, but it is sufficient if it is about 40 kg / molten ton. The lance height need not be particularly limited, and may be set in consideration of the amount of slag 21 generated.

  After the dephosphorization treatment, the hot metal ladle 2 containing the hot metal 16 is transported to the waste disposal site, and the slag 21 is discharged from the hot metal ladle 2 using a dragger or the like, and then transported to the next step.

The hot metal 16 targeted by the dephosphorization treatment of the present invention can be treated with any composition, and may be subjected to desulfurization treatment or desiliconization treatment before the dephosphorization treatment. The desiliconization process is a process in which iron oxide such as oxygen gas or mill scale is added to the hot metal 16 to mainly remove silicon from the hot metal 16. Incidentally, the main chemical components of the hot metal 16 before the dephosphorization treatment are carbon: 3.8 to 5.0% by mass, silicon: 0.2% by mass or less, sulfur: 0.05% by mass or less, phosphorus: 0.00%. It is about 08-0.2 mass%. However, since the dephosphorization efficiency decreases as the amount of slag 21 generated in the dephosphorization process increases, in order to increase the dephosphorization efficiency by reducing the amount of slag 21 generated, the hot metal 16 is preliminarily treated by desiliconization process or the like. It is preferable to reduce the silicon content to 0.4% by mass or less. Silicon in the hot metal is preferentially oxidized in the dephosphorization process to form SiO ₂ . Moreover, if the hot metal temperature is in the range of 1250 to 1350 ° C., dephosphorization can be performed without any problem.

  As described above, in the present invention, the lime-based dephosphorization flux 17 is added by spraying toward the bath surface of the hot metal 16 together with the oxygen gas, and the solid oxygen source 18 blown into the hot metal is set to a fire point R. Since it is supplied to the vicinity, hatching of the lime-based dephosphorization flux 17 is sufficiently advanced without using a fluorine source such as fluorite, and efficient dephosphorization with a small amount of lime-based dephosphorization flux used. It is possible to perform processing, thereby reducing the amount of slag generated.

  In the above description, the hot metal ladle 2 has been described as an example of the processing container. However, in carrying out the present invention, the processing container is not limited to the hot metal ladle 2, and even a torpedo car or a charging pan, Furthermore, even if it is a converter type | mold refining furnace, this invention can be implemented along the above.

The hot metal discharged from the blast furnace was received by a hot metal ladle having a capacity of 200 tons and conveyed to a dephosphorization treatment facility shown in FIG. The hot metal components before dephosphorization were silicon concentration: 0.05 to 0.30 mass% and phosphorus concentration: 0.08 to 0.12 mass%. Dust generated at the iron ore sintering plant using lime-based dephosphorization flux as a lime-based dephosphorization flux along with oxygen gas on the hot metal bath surface through the top blowing lance and nitrogen gas from the injection lance as a carrier gas Was blown at a blowing rate of 0.05 to 0.5 kg / min. All the required quicklime was sprayed and added from the top blowing lance. The amount of quicklime to be added was set according to the silicon concentration in the hot metal before the treatment. The oxygen source basic unit was 7 to 9 Nm ³ / molten iron ton in terms of oxygen gas, excluding oxygen required for desiliconization.

  As a result of the dephosphorization treatment under these conditions, the amount of quicklime used as the lime-based dephosphorization flux is 5.5 kg / molten iron ton, and the amount of quicklime required in the conventional case where the amount of dephosphorization is equivalent is about 7.2 kg / Compared with hot metal ton, the amount used could be greatly reduced.

It is a schematic sectional drawing of the dephosphorization processing equipment used when implementing the dephosphorization process by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Dephosphorization processing equipment 2 Hot metal ladle 3 Carriage 4 Top blowing lance 5 Injection lance 6 Storage tank 7 Oxygen gas piping 8 Flux transfer piping 9 Shut-off valve 10 Shut-off valve 11 Storage tank 12 Hopper 13 Hopper 14 Raw material conveyance device 15 Chute 16 Hot metal 17 Lime-based dephosphorization flux 18 Solid oxygen source 19 Solid oxygen source 20 Lime-based dephosphorization flux 21 Slag R Hot point

Claims (5)

In a method of producing a low phosphorus hot metal by adding an oxygen source and a lime-based dephosphorization flux not containing alumina into a container holding hot metal, oxygen gas and at least a portion of the lime-based flux for dephosphorization, the oxygen with blown onto the fire spot occurring in molten iron bath surface by blowing of gas, the solid oxygen source the fire spot blown into molten iron together with a carrier gas through A method for producing a low phosphorus hot metal, characterized by being supplied to the vicinity. The method for producing low phosphorus hot metal according to claim 1, wherein the solid oxygen source blown into the hot metal together with the carrier gas has a blowing speed of 0.03 to 1 kg / min · hot metal ton. The method for producing a low phosphorus hot metal according to claim 1 or 2 , wherein 10 mass% or more of the solid oxygen source added in the dephosphorization treatment is blown into the hot metal and added. The method for producing a low phosphorus hot metal according to any one of claims 1 to 3 , wherein the dephosphorization treatment is performed on the hot metal having a silicon content of 0.40 mass% or less. A pan-type or torpedo-car type container is used as a container for holding the hot metal, and oxygen gas and at least a part of the lime-based dephosphorization flux are sprayed on the hot metal bath surface through the top blowing lance, and through the injection lance or blowing tuyere. The method for producing a low phosphorus hot metal according to any one of claims 1 to 4, wherein a solid oxygen source is blown together with the carrier gas.

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