JP3332010B2 - Manufacturing method of low phosphorus hot metal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dephosphorization treatment performed as a pretreatment of hot metal,
The present invention relates to a method for producing low-phosphorus hot metal capable of performing efficient dephosphorization even when a CaO-based solvent containing no F source is used.

[0002]

2. Description of the Related Art Heretofore, a hot metal pretreatment method has been developed in which preliminary dephosphorization is performed at a hot metal stage, P in the hot metal is removed to some extent, and then converter decarburization blowing is performed. This preliminary dephosphorization treatment is performed in equipment such as a torpedo, a hot metal pot, and a converter, and is performed by adding a CaO-based solvent and an oxygen source such as gaseous oxygen or a solid oxygen source. In order to transfer P efficiently from the hot metal to the slag side during the dephosphorization treatment, control of the slag composition and the slag amount is an important factor. In particular, by adding CaF ₂ to the solvent medium, 1) the meltability of the slag is improved, 2)
It has been pointed out that the following effects can be obtained: the SiO ₂ network is divided to increase Ca ions, 3) the activity of FeO is increased, and the like. CaF ₂ is used widely.

[0003] For example, Japanese Patent Publication No.
Is the weight ratio of CaO to oxygen O other than CaO / O
[CaF₂+ Al₂O₃] / CaO and Al₂O₃
/ CaF ₂Is defined, and CaF₂Desorption by addition
Techniques for improving phosphorus efficiency have been disclosed. However,
Recently, from the viewpoint of environmental protection, regulation of the amount of F released from slag
Standards have tended to be strengthened, and as a result
There is a need to lower the F concentration to the limit.

[0004] For this reason, there is a strong demand for the development of a dephosphorization treatment technique that does not use an F source such as CaF _2. However, at present, slag is made to have a low basicity to carry out an operation with an extremely large amount of slag, In fact, there are only effective measures, such as performing processing. However, the extreme increase in the amount of dephosphorized slag, as in the former case, goes against the need to reduce the amount of slag, which is strongly demanded from the viewpoint of environmental protection. Doing so raises the problem of increasing the production cost of molten steel, and therefore these cannot be a drastic measure.

[0005]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art, and to efficiently perform hot metal dephosphorization even when a medium solvent not containing an F source such as CaF ₂ is used. An object of the present invention is to provide a method for producing low-phosphorus hot metal that can be performed.

[0006]

Means for Solving the Problems The present inventors have proposed CaF ₂
Various experiments and examinations were conducted using a converter type vessel in order to find a hot metal pretreatment method capable of efficiently performing a dephosphorization treatment without using an F source such as (fluorite). As described above, CaF ₂ plays an important role in ensuring the meltability of the slag, and in the experiments of the present inventors, when CaF ₂ was not added, the added medium solvent (CaO 2) was used. Source) did not appear to be slag, and the dephosphorization reaction efficiency was reduced. However, as a result of various experiments, the following facts were found.

(1) From the results of experiments conducted under various conditions of charging the CaO source and the oxygen source, it was found that if the initial slag could be melted, the efficiency of the dephosphorization reaction would increase dramatically.
It has also been found that such initial melting of slag can be achieved by supplying an oxygen source to the hot metal before the addition of the initial CaO source to actively generate iron oxide (FeO). That is, conventionally, it has been considered that it is necessary to add a CaO source at an early stage to carry out acidification in order to make slagging of a CaO source as early as possible. Prior to adding the source, first, only the oxygen source is supplied to the hot metal to generate FeO to increase the concentration of iron oxide in the slag, and then add the CaO source (preferably, divided addition). Gives Ca
Region to fully melt in CaO-FeO slag containing no F source, such as F ₂ is generated, dephosphorization reaction efficiency was found to dramatically improve.

[0008]

(2) From the results of experiments conducted under various conditions of charging the solid oxygen source and the medium solvent, it was found that adding a solid oxygen source and a medium solvent preheated to a predetermined temperature or higher to hot metal
dissolution of aO is promoted effectively, dephosphorization reaction efficiency even when a medium solvent mainly containing CaO which do not contain F source, such as CaF ₂ was found to dramatically improve. In addition, since the solid oxygen source has a lower melting point than the medium solvent, it has been found that it is advantageous to preheat the solid oxygen source in order to more effectively promote the dissolution of CaO.

(3) From the results of an experiment conducted to investigate the effect of the exhaust gas generated by the dephosphorization on the efficiency of the dephosphorization reaction, it was found that the exhaust gas generated by the dephosphorization was secondary to improve the efficiency of the dephosphorization reaction. Combustion is effective, and by controlling the secondary combustion rate of exhaust gas to a certain appropriate range, CaF
It has been found that the efficiency of the dephosphorization reaction is drastically improved even when a medium solvent mainly containing CaO which does not contain the F source such as No. ₂ is used. This is because the heat generated by the secondary combustion of the exhaust gas heats the slag and effectively promotes the dissolution of CaO.

(4) From the results of experiments conducted under various conditions of supply of gaseous oxygen, it is effective to optimize the acid supply conditions from the top blowing lance to improve the dephosphorization reaction efficiency. By controlling the pit depth of the hot metal bath surface formed by the acid supply from the lance and the acid supply rate from the top blowing lance to a certain range, and optimizing the FeO concentration in the slag,
Dephosphorization reaction efficiency even when a medium solvent mainly containing CaO which do not contain F source, such as CaF ₂ was found to dramatically improve.

The present invention has been made on the basis of such knowledge, and the characteristic configuration thereof is as follows. [1] In the dephosphorization treatment performed as a hot metal pretreatment, the concentration of iron oxide in the slag is increased by supplying gaseous oxygen before adding a medium solvent that is a CaO source to the hot metal, and then the CaO source A method for producing low-phosphorus hot metal, comprising adding a medium solvent as described above. [2] The method of the above-mentioned [1], further comprising a solid oxygen source
Is supplied before adding a solvent to the hot metal.

[3] The method for producing low-phosphorus molten iron according to the above-mentioned [1] or [2], wherein the medium solvent is added in plural portions. [4] In the production method according to any one of the above [1] to [3], before adding a medium solvent that is a CaO source to the hot metal, an amount of gaseous oxygen or gaseous oxygen satisfying the following expression (1) is satisfied. A method for producing low-phosphorus hot metal, comprising supplying a source . 0.010 ≦ B / A ≦ 0.50 (1) where A: the total amount of CaO in the solvent required for the dephosphorization treatment [k
g / T] B: Oxygen supply amount in terms of gas [Nm ³ / T]

[5] The method according to any one of the above [1] to [4], wherein the gaseous oxygen or the gaseous oxygen and the solid before the addition of the medium solvent are added.
The amount of decarburized hot metal was determined from the gas analysis value of the exhaust gas when the oxygen source was supplied, and the decarbonized amount and gaseous oxygen or gaseous oxygen and solidified
The iron oxide concentration in the slag is calculated based on the supply amount of the body oxygen source , and gaseous oxygen or gas
A method for producing low-phosphorus hot metal, comprising controlling supply conditions of oxygen and a solid oxygen source .

[6] In the dephosphorization treatment performed as a hot metal pretreatment, a solid oxygen source and / or a medium solvent is preheated to a temperature of 200 ° C. or more and less than 1000 ° C., and then added to the hot metal. Manufacturing method of hot metal. [7] In the dephosphorization treatment performed as a hot metal pretreatment, the dephosphorization treatment is performed under operating conditions such that the concentrations of CO and CO _{2 in} the exhaust gas discharged from the dephosphorization treatment container satisfy the following expression (2). A method for producing low-phosphorus hot metal, comprising: 0.10 ≦ [CO ₂ ] / ([CO ₂ ] + [CO]) ≦ 0.35 (2) where [CO ₂ ]: CO ₂ concentration in exhaust gas [wt%] [CO]: In exhaust gas CO concentration [wt%]

[8] In the dephosphorization treatment performed as a hot metal pretreatment, gas oxygen is blown upward from the upper blowing lance to the hot metal, and a pit on the hot metal bath surface formed by the kinetic energy of the gas oxygen blown upward. The ratio L / Lo of the depth L (m) to the hot metal bath depth Lo (m) and the acid feed rate F (Nm ³ / min / T) from the top blowing lance are expressed by the following equations (3) and (4). A method for producing low-phosphorus molten iron, comprising performing a dephosphorization treatment under conditions that satisfy the following conditions. 0.02 ≦ L / Lo ≦ 0.10 (3) 0.25 ≦ F ≦ 1.50 (4)

[9] The method for producing low-phosphorus hot metal according to any one of [1] to [8] , wherein the hot metal having a Si concentration of 0.10% by weight or less is dephosphorized. [10] In the manufacturing method of the above [9] , the Si concentration is 0.10
A method for producing low-phosphorus hot metal, comprising desiliconizing a hot metal exceeding 0.1% by weight to a Si concentration of 0.10% by weight or less, and then dephosphorizing. [11] The method according to any one of [1] to [10] , wherein
A method for producing low-phosphorus hot metal, comprising using a medium solvent mainly containing CaO that does not contain a source.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the first invention of the present application will be described. Method for producing low phosphorus hot metal of the present invention (phosphorus removal method)
In this method, the concentration of iron oxide (FeO) in slag is increased by supplying an oxygen source before adding a medium solvent as a CaO source to hot metal, and then a medium solvent as a CaO source is added. Thus, the efficiency of the dephosphorization reaction can be dramatically increased without adding an F source such as CaF ₂ . This is because FeO is sufficiently generated by adding an oxygen source to hot metal before the addition of a medium solvent, an initial slag having a high iron oxide concentration is melted, and a CaO source is contained in the initial slag having a high iron oxide concentration. Is directly added, the slagging proceeds in a form in which CaO having a high melting point is incorporated into FeO generated at a high concentration, and slagging by the reaction of CaO + FeO is drastically promoted. Conceivable.

On the other hand, when the CaO source is supplied at an early stage to supply the oxygen source as in the prior art,
Contrary to the above-described operation of the present invention, since slagging proceeds in a form in which FeO generated by supply of an oxygen source is incorporated into unslagged CaO, slagging due to the reaction of CaO + FeO does not rapidly progress. it is conceivable that.

In the present invention, the oxygen source supplied to the hot metal before the addition of the medium solvent may be gaseous oxygen or solid oxygen source as long as it generates FeO, but the temperature of the slag-metal interface is increased. Gaseous oxygen is more preferred in that it can be used. Further, gaseous oxygen and a solid oxygen source may be used in combination. The gaseous oxygen used may be either a pure oxygen gas or an oxygen-containing gas, and iron oxide or mill scale can be used as a solid oxygen source. Note that the dephosphorization treatment of the present invention is characterized in that an oxygen source is supplied to hot metal before the addition of a medium solvent as a CaO source. A source (a source of gaseous oxygen and / or solid oxygen) is provided.

In the method for producing low-phosphorus hot metal according to the present invention,
It is important to secure the initial amount of FeO generated by the supply of the oxygen source before the addition of the medium solvent, but on the other hand, the supply of the oxygen source also promotes the decarburization of the hot metal, When the source is supplied, the amount of oxygen becomes insufficient in the supply of the oxygen source after the addition of the medium solvent. Therefore, it is necessary to optimize the oxygen supply amount before the addition of the medium solvent. That is,
It is preferable that the amount of oxygen supplied before adding the medium solvent as the CaO source satisfies the following expression (1) from the viewpoint of securing a necessary and sufficient amount of FeO generated. 0.010 ≦ B / A ≦ 0.50 (1) where A: the total amount of CaO in the solvent required for the dephosphorization treatment [k
g / T] (T: hot metal ton, the same applies hereinafter) B: Oxygen supply amount in terms of gas [Nm ³ / T]

Here, when B / A <0.010, it is not possible to secure a sufficient amount of FeO before the addition of the medium solvent, whereas when B / A> 0.50, the oxygen source after the addition of the medium solvent is not obtained. There is a risk that the amount of oxygen in the supply of iron may be insufficient and a desired dephosphorization rate may not be secured, and the amount of decarburization of the hot metal is also increased. In addition, a particularly preferable range of B / A from such a viewpoint is 0.05 to 0.20. After supplying an oxygen source as described above to generate FeO at a predetermined concentration, a medium solvent serving as a CaO source is added, and an amount of FeO necessary for slagging is added when the medium solvent is added. For,
It is preferable to add the solvent in a plurality of times. For the same reason, the medium solvent may be added little by little continuously or intermittently.

In carrying out the present invention, the following method can be employed as a method for appropriately controlling the supply amount of the oxygen source before adding the medium solvent. In other words, when the oxygen source is supplied before the addition of the medium solvent, the gas analysis of the exhaust gas discharged from the dephosphorization vessel (analysis of the C concentration in the exhaust gas) is performed online, whereby the decarburized amount of the hot metal can be obtained,
Based on the decarburization amount and the supply amount of the oxygen source, and further considering the desiliconization amount of the hot metal and the amount of secondary combustion determined from the exhaust gas analysis as necessary, it was accumulated in the dephosphorization vessel. The amount of oxygen can be determined, and from this the amount of FeO in the slag can be calculated. Therefore, the decarburization amount of the hot metal is determined from the gas analysis value of the exhaust gas, the iron oxide concentration in the slag is calculated based on the decarburization amount and the supply amount of the oxygen source, and the oxygen concentration is calculated based on the calculated value of the iron oxide concentration. By controlling the supply conditions of the source (for example, the amount of acid supply, the rate of acid supply, etc.), the concentration of iron oxide can be easily controlled by supplying the oxygen source before adding the solvent medium.

Further, the effect of the present invention is different depending on the Si concentration of the hot metal before the dephosphorization treatment, and when the method of the present invention is carried out on the hot metal having the Si concentration before the dephosphorization treatment of 0.10 wt% or less. It was found that particularly remarkable dephosphorization efficiency was obtained. In general, when the Si concentration of the hot metal before the dephosphorization treatment is high, the generated SiO ₂ increases, and as a result, not only the amount of slag increases, but also the amount of CaO for adjusting the basicity increases. Therefore, from such a viewpoint, it is preferable that the Si concentration of the hot metal before the dephosphorization treatment is low. On the other hand, if the Si concentration of the hot metal before the dephosphorization treatment is low, the SiO ₂ content in the slag is low.
Since the concentration is reduced, the melting property of CaO is further deteriorated, and the dephosphorization reaction efficiency is reduced.

However, when the present inventors carried out the method of the present invention on hot metal having various Si concentrations, contrary to the above prediction, the Si concentration before the dephosphorization treatment was 0.10 watts.
It has been found that when the method of the present invention is carried out on hot metal of not more than t%, particularly remarkable dephosphorization reaction efficiency can be obtained. The reason is considered as follows. First, as a first reason, when the Si concentration in the hot metal is low, a small percentage of the oxygen source supplied before the addition of the medium solvent is consumed by the reaction with Si in the hot metal to generate SiO _2. Therefore, it is conceivable that the production amount of FeO is increased by that much, and the slagging of CaO is more effectively promoted.

The following is a second and larger reason. That is, P is 3Ca in the dephosphorization reaction.
It is fixed in the slag in the form of O.P ₂ O ₅ or 4CaO.P ₂ O ₅ . Therefore, SiO ₂ in the slag is a slag component that is not directly necessary for dephosphorization, and
A part of O ₂ reacts with a part of CaO that has been slagged,
CaO reacted with O ₂ will not contribute to the dephosphorization reaction. Therefore, when the Si concentration of the hot metal is low and the amount of generated SiO ₂ is small, the amount of CaO that does not contribute to the dephosphorization reaction by reacting with SiO ₂ is reduced, and CaO that can contribute to the dephosphorization reaction is reduced.
Although the amount is relatively increased, particularly in the case of the method of the present invention, since CaO slagging ability is extremely high, low Si
The effect of the slag composition (increase in the amount of CaO that can contribute to the dephosphorization reaction) due to the concentration appears remarkably, and as a result, the dephosphorization reaction efficiency is considered to be improved. Si concentration in hot metal before treatment: 0.10 wt%
It is considered that it becomes obvious in the following low Si concentration region. In the conventional method with respect to this, even if the amount of CaO is increased relatively to contribute to the dephosphorization reaction by less SiO ₂ generation amount lower Si concentration of the molten iron, originally it has low grounds of ability of CaO, It is considered that the effect of reducing the Si concentration of the hot metal as described above does not appear.

As described above, the method of the present invention for producing a low-phosphorus hot metal is particularly effective when applied to hot metal having an Si concentration of 0.10 wt% or less. If the content exceeds 10 wt%, desiliconization (usually performed by adding oxygen such as a solid oxygen source or gaseous oxygen to the hot metal) is performed in a blast furnace cast bed or hot metal pot, etc. It is preferable to perform the dephosphorization treatment after setting the Si concentration to 0.10 wt% or less.

As the container in which the dephosphorization treatment of the present invention is carried out, a converter type container is most preferable in that a sufficient free board can be secured, but any other container such as a hot metal pot or torpedo may be used. Can be used. Also,
There is no particular restriction on the supply method of the oxygen source (supply method before and after the addition of the medium solvent), and in the case of gaseous oxygen, any method such as top blowing with a lance, injection into hot metal, or bottom blowing. Acid supply can be performed, and in the case of a solid oxygen source, supply into the hot metal can be performed by any method such as injection or overhead charging. When gaseous oxygen is supplied, the dephosphorization treatment is performed by upward blowing with a lance when the dephosphorization is performed using a converter type vessel or hot metal pot, and when the dephosphorization is performed using a torpedo, Injection is common.

Further, in order to further improve the dephosphorization efficiency, it is preferable to stir the hot metal with gas. This gas stirring is performed by blowing an inert gas such as a nitrogen gas or an argon gas into the hot metal through an injection lance, a bottom blowing nozzle, or the like. The supply amount of such a stirring gas is set at 0.1 to obtain a sufficient bath stirring property.
0.3 Nm ³ / min / T. Since the rate of C reduction in the hot metal from the produced FeO is too high if the bath is stirred too strongly, the rate is 0.3 Nm ³ / min / T.
It is preferable to set the following.

[0030] The dephosphorization treatment of the present invention is carried out by removing F such as CaF _2.
The biggest feature is that a high dephosphorization reaction efficiency can be obtained only by using a medium solvent mainly containing CaO that does not contain a source, but this does not exclude the addition of an F source such as CaF ₂ .
For example, it does not prevent the addition of an F source, such as CaF ₂ , to an acceptable limit in order to further promote slagging of the CaO source. In the case of using only a medium mainly composed of CaO that does not contain an F source such as CaF ₂ in the dephosphorization treatment of the present invention, the fact that the medium does not contain the F source means that the F source is not substantially contained. Therefore, it does not prevent that a small amount of the F source is contained in the medium solvent as, for example, unavoidable impurities.

[0031]

[0032]

[0033]

[0034]

[0035]

[0036]

[0037]

[0038]

[0039]

Next, the second invention of the present application will be described. In the manufacturing method of the low phosphorus hot metal according to the present invention, the solid oxygen source and / or medium solvent 200 ° C. or higher, was preheated to a temperature below 1000 ° C., is intended to be added to the molten iron, thereby F, such as CaF ₂ The efficiency of the dephosphorization reaction can be drastically increased without adding a medium solvent containing a source. This is because the addition of a solid oxygen source or a medium solvent preheated to an appropriate temperature to the hot metal effectively promotes the dissolution of CaO.

If the preheating temperature of the solid oxygen source and / or the solvent is less than 200 ° C., the dissolution of CaO cannot be sufficiently promoted, so that the efficiency of the dephosphorization reaction cannot be effectively increased. On the other hand, the preheating temperature of the solid oxygen source and / or the medium solvent is 1000
C. or more is not preferred because the cost for maintaining and repairing the heating / holding portion of the solid oxygen source and the solvent and the like increases. In the present invention, the solid oxygen source to be added to the hot metal, one or both of the medium solvent can be preheated,
Since the melting point of the solid oxygen source is lower than that of the medium solvent, the dissolution of CaO by preheating is more effectively promoted. Therefore, it is preferable to preheat at least the solid oxygen source.

There is no particular limitation on the type of solid oxygen source used in the dephosphorization treatment of the present invention, but iron oxide or mill scale is usually used as the solid oxygen source. Further, gaseous oxygen (pure oxygen gas or oxygen-containing gas) may be used in combination as an oxygen source to be supplied to the hot metal. Further, Ca is used as a medium solvent.
An O source is added, and a medium mainly composed of CaO that does not contain an F source such as CaF ₂ can be used as described later.

Further, the effect of the present invention is different depending on the Si concentration of the hot metal before the dephosphorization treatment, and when the method of the present invention is performed on the hot metal having the Si concentration of 0.10 wt% or less before the dephosphorization treatment. It was found that particularly remarkable dephosphorization efficiency was obtained. In general, when the Si concentration of the hot metal before the dephosphorization treatment is high, the generated SiO ₂ increases, and as a result, not only the amount of slag increases, but also the amount of CaO for adjusting the basicity increases. Therefore, from such a viewpoint, it is preferable that the Si concentration of the hot metal before the dephosphorization treatment is low. On the other hand, if the Si concentration of the hot metal before the dephosphorization treatment is low, the SiO ₂ content in the slag is low.
Since the concentration is reduced, the melting property of CaO is further deteriorated, and the dephosphorization reaction efficiency is reduced.

However, when the present inventors carried out the method of the present invention on hot metal having various Si concentrations, contrary to the above-mentioned prediction, the Si concentration before the dephosphorization treatment was 0.10 watts.
It has been found that when the method of the present invention is carried out on hot metal of not more than t%, particularly remarkable dephosphorization reaction efficiency can be obtained. The reason for this is that when the Si concentration before the dephosphorization treatment is 0.10 wt% or less, the amount of slag generated is small, and thus the heating of the slag from the preheated solid oxygen source and / or medium solvent to the unit slag It is thought to be due to the increase per weight. In addition, when a preheated solid oxygen source and / or a medium solvent is added to the hot metal, the forming of SiO ₂ is promoted to increase the slopping, which tends to hinder stable operability. The concentration is 0.10wt%
In the following cases, no problematic slopping occurs and the stable operability is not impaired.

As described above, the method of the present invention for producing low-phosphorus hot metal is particularly effective when applied to hot metal having a Si concentration of 0.10% by weight or less. If the content exceeds 10 wt%, desiliconization (usually performed by adding oxygen such as a solid oxygen source or gaseous oxygen to the hot metal) is performed in a blast furnace cast bed or hot metal pot, etc. It is preferable to perform the dephosphorization treatment after setting the Si concentration to 0.10 wt% or less.

As a container in which the dephosphorization treatment of the present invention is carried out, a converter type container is most preferable from the viewpoint that a sufficient free board can be secured, but other containers such as a hot metal pot, a torpedo, etc. may be used. Can be used. In addition, there is no special restriction on the supply method of the oxygen source, and in the case of gaseous oxygen, the upper lance is injected by lance or injected into hot metal,
Alternatively, the acid can be fed by any method such as bottom blowing, and in the case of a solid oxygen source, it can be fed into the hot metal by any method such as injection or overhead charging. When gaseous oxygen is supplied, the dephosphorization treatment is performed by upward blowing with a lance when the dephosphorization is performed using a converter type vessel or a hot metal ladle, or when the dephosphorization is performed using a torpedo. Injection is common.

Further, in order to further improve the dephosphorization reaction efficiency, it is preferable to stir the hot metal with gas. This gas stirring is performed by blowing an inert gas such as a nitrogen gas or an argon gas into the hot metal through an injection lance, a bottom blowing nozzle, or the like. The supply amount of such a stirring gas is set to 0.02 Nm ³ / min / T or more in order to obtain a sufficient bath stirring property, and if the stirring of the bath is too strong, the C in the hot metal reduces the generated FeO. 0.3 Nm ³ / min.
/ T or less.

The dephosphorization process of this invention, F, such as CaF ₂
The biggest feature is that a high dephosphorization reaction efficiency can be obtained only by using a medium solvent mainly containing CaO that does not contain a source, but this does not exclude the addition of an F source such as CaF ₂ .
For example, it does not prevent the addition of an F source, such as CaF ₂ , to an acceptable limit in order to further promote slagging of the CaO source. In the case of using only a medium mainly composed of CaO that does not contain an F source such as CaF ₂ in the dephosphorization treatment of the present invention, the fact that the medium does not contain the F source means that the F source is not substantially contained. Therefore, it does not prevent that a small amount of the F source is contained in the medium solvent as, for example, unavoidable impurities.

Next, the third invention of the present application will be described. In the manufacturing method of the low phosphorus hot metal according to the present invention, in which the concentration of CO and CO ₂ in the exhaust gas discharged from the dephosphorization container perform dephosphorization in such operating conditions as to satisfy the following formula (2) This makes it possible to dramatically increase the dephosphorization reaction efficiency without adding an F source such as CaF ₂ . 0.10 ≦ [CO ₂ ] / ([CO ₂ ] + [CO]) ≦ 0.35 (2) where [CO ₂ ]: CO ₂ concentration in exhaust gas [wt%] [CO]: In exhaust gas CO concentration [wt%]

This is because the heat generated by the secondary combustion of the exhaust gas heats the slag, and the dissolution of CaO is effectively promoted. [CO ₂ ] / ([CO ₂ ] + [CO]) of the exhaust gas discharged from the dephosphorization treatment vessel is 0.10
If it is less than 2, the secondary combustion rate is too low and the heat on the slag is insufficient, so that the dissolution of CaO is not sufficiently promoted. For this reason, the efficiency of the dephosphorization reaction does not improve much. On the other hand, [CO
_{If 2} ] / ([CO ₂ ] + [CO]) exceeds 0.35, the excess heat generated by the secondary combustion undesirably accelerates the erosion of the refractory in the dephosphorization vessel.

[C] of the exhaust gas discharged from the dephosphorization treatment vessel
O ₂ ] / ([CO ₂ ] + [CO]) can be easily adjusted by controlling the acid feeding speed and the lance height, for example, when acid feeding to hot metal is performed from the top blowing lance. it can. When performing the dephosphorization treatment of the present invention, the gas composition of the exhaust gas discharged from the dephosphorization treatment vessel is analyzed,
If the above control is performed based on the gas composition analysis value, [CO ₂ ] / ([CO ₂ ] + [CO]) of the exhaust gas can be easily controlled online.

Further, the effect of the present invention is different depending on the Si concentration of the hot metal before the dephosphorization treatment. When the method of the present invention is carried out on the hot metal having the Si concentration before the dephosphorization treatment of 0.10 wt% or less. It was found that particularly remarkable dephosphorization efficiency was obtained. In general, when the Si concentration of the hot metal before the dephosphorization treatment is high, the generated SiO ₂ increases, and as a result, not only the amount of slag increases, but also the amount of CaO for adjusting the basicity increases. Therefore, from such a viewpoint, it is preferable that the Si concentration of the hot metal before the dephosphorization treatment is low. On the other hand, if the Si concentration of the hot metal before the dephosphorization treatment is low, the SiO ₂ content in the slag is low.
Since the concentration is reduced, the melting property of CaO is further deteriorated, and the dephosphorization reaction efficiency is reduced.

However, when the present inventors carried out the method of the present invention on hot metal having various Si concentrations, contrary to the above-mentioned prediction, the Si concentration before the dephosphorization treatment was 0.10 watts.
It has been found that when the method of the present invention is carried out on hot metal of not more than t%, particularly remarkable dephosphorization reaction efficiency can be obtained. The reason for this is that when the Si concentration before the dephosphorization treatment is 0.10 wt% or less, the amount of slag generated is small, so that the heat on the slag by secondary combustion increases per unit slag weight. it is conceivable that.

As described above, the method for producing low-phosphorus hot metal of the present invention is particularly effective when applied to hot metal having a Si concentration of 0.10 wt% or less. If the content exceeds 10 wt%, desiliconization (usually performed by adding oxygen such as a solid oxygen source or gaseous oxygen to the hot metal) is performed in a blast furnace cast bed or hot metal pot, etc. It is preferable to perform the dephosphorization treatment after setting the Si concentration to 0.10 wt% or less.

The oxygen source supplied in the dephosphorization treatment of the present invention may be either gaseous oxygen or solid oxygen source, or both may be used in combination. The gaseous oxygen used is pure oxygen gas,
Any oxygen-containing gas may be used, and iron oxide or mill scale may be used as a solid oxygen source.
As the container in which the dephosphorization treatment of the present invention is performed, a converter type container is most preferable from the viewpoint that a free board can be sufficiently secured, but any other container such as a hot metal pot or a torpedo may be used. it can.

There is no particular limitation on the method of supplying the oxygen source. In the case of gaseous oxygen, the acid can be fed by any method such as top blowing with a lance, injection into hot metal, or bottom blowing. In the case of a solid oxygen source, it can be supplied into the hot metal by any method such as injection or overhead charging. When gaseous oxygen is supplied, the dephosphorization treatment is performed by upward blowing with a lance when the dephosphorization is performed using a converter type vessel or a hot metal ladle, or when the dephosphorization is performed using a torpedo. Injection is common.

Further, in order to further improve the dephosphorization reaction efficiency, it is preferable to agitate the hot metal with gas. This gas stirring is performed by blowing an inert gas such as a nitrogen gas or an argon gas into the hot metal through an injection lance, a bottom blowing nozzle, or the like. The supply amount of such a stirring gas is set to 0.02 Nm ³ / min / T or more in order to obtain a sufficient bath stirring property, and if the stirring of the bath is too strong, the C in the hot metal reduces the generated FeO. 0.3 Nm ³ / min.
/ T or less.

The dephosphorization treatment of the present invention is carried out by removing F such as CaF _2.
The biggest feature is that a high dephosphorization reaction efficiency can be obtained only by using a medium solvent mainly containing CaO that does not contain a source, but this does not exclude the addition of an F source such as CaF ₂ .
For example, it does not prevent the addition of an F source, such as CaF ₂ , to an acceptable limit in order to further promote slagging of the CaO source. In the case of using only a medium mainly composed of CaO that does not contain an F source such as CaF ₂ in the dephosphorization treatment of the present invention, the fact that the medium does not contain the F source means that the F source is not substantially contained. Therefore, it does not prevent that a small amount of the F source is contained in the medium solvent as, for example, unavoidable impurities.

Next, the fourth invention of the present application will be described. In the method for producing a low-phosphorus hot metal of the present invention, gas oxygen is blown upward from the top blowing lance onto the hot metal, and the pit depth L (m) of the hot metal bath surface formed by the kinetic energy of the gas oxygen blown upward. Ratio L of hot metal bath depth Lo (m)
/ Lo and the acid feed rate F from the top blowing lance (Nm ³ / mi
(n / T) is such that the dephosphorization treatment is performed under the conditions satisfying the following formulas (3) and (4) , whereby the dephosphorization can be performed without adding a medium solvent containing an F source such as CaF _2. Phosphorus reaction efficiency can be dramatically increased. 0.02 ≦ L / Lo ≦ 0.10 (3) 0.25 ≦ F ≦ 1.50 (4) This is because the depth of the pit of the hot metal bath formed by the acid supply from the top blowing lance is This is because the FeO concentration in the slag can be optimized by controlling the acid feed rate from the blowing lance within the above range.

The hot metal component is C: 4.0-4.7 wt%, S
i: tr to 0.20 wt%, S: tr to 0.030 wt%
%, P: 0.10 to 0.15 wt%, hot metal temperature is 127
The hot metal at 0 to 1330 ° C was subjected to dephosphorization using a ladle-type refining vessel as shown in FIG. 6 and a converter-type refining vessel as shown in FIG. In this dephosphorization treatment, nitrogen as a stirring gas was blown into the hot metal within a range of 0.02 to 0.3 Nm ³ / min / T, and a quicklime or a medium solvent mainly containing quicklime was added. In the dephosphorization treatment using the ladle shown in FIG. 6, a medium solvent was blown into the hot metal together with the stirring gas using an injection lance, and the acid was fed from the upper blow lance. In the dephosphorization treatment using the converter type refining vessel shown in FIG. 7, while stirring gas was blown from the bottom, acid was fed from the top blowing lance, and the solvent was placed above the furnace hopper and charged.

In this test, the acid was fed from the top blowing lance under various conditions, and the transition of the P concentration and C concentration in the hot metal and the composition of the slag formed by the medium solvent were investigated while stirring the hot metal with gas. , Tried to organize. At that time, in order to consider the energy when the oxygen gas blown from the top blowing lance collides with the hot metal bath surface, the pit depth of the hot metal surface obtained from the following formulas (5) and (6) is considered. L (m) and hot metal bath depth L
The ratio L / Lo of o (m) was used as an index. The hot metal bath depth Lo is the distance from the bottom of the refining vessel to the hot metal bath surface.

(Equation 1)

L / Lo under various operating conditions is determined,
The relationship between the acid supply speed F and L / Lo from the top blowing lance and the operation index was summarized. As the operation index, the P concentration in the hot metal [P] after carrying out the acid supply for 12 minutes in the case of the ladle type refining vessel, and the carrying out of the acid supply for 10 minutes in the case of the converter type refining vessel, and decarburization by dephosphorization The quantity ΔC was used. Acid transfer rate F and L / Lo
FIG. 3 shows that the P concentration [P] in the hot metal after the dephosphorization treatment is arranged to be 0.020% by weight or less and more than 0.020% by weight. According to this, L / Lo> 0.1
In the case of 0, L / Lo <0.02, and the acid feed rate F <0.25, the P concentration [P] in the hot metal exceeds 0.020 wt%, and efficient dephosphorization has not been performed. You can see that.

Here, when L / Lo> 0.10, the bath surface is greatly disturbed, and it is difficult for oxygen and FeO generated on the bath surface to react and fuse with CaO in the medium solvent existing near the flash point. Therefore, the reaction efficiency with phosphorus in the hot metal decreases, and the decarburization reaction is likely to occur preferentially, so that the dephosphorization hardly proceeds. on the other hand,
When L / Lo <0.02, the amount of oxygen reaching the bath surface is small, so that a sufficient amount of FeO cannot be generated, and the reaction melting of CaO and FeO in the medium solvent does not easily progress. Therefore, the dephosphorization reaction is delayed.
Further, when the acid supply rate F <0.25, the amount of oxygen supplied to the bath surface is small, so that the production of FeO is delayed, and the reaction and melting of CaO and FeO in the solvent become difficult to proceed, and the dephosphorization reaction Will be delayed.

Next, FIG. 4 shows the relationship between the acid supply rate F and L / Lo when the decarburization amount ΔC is less than 1.2 wt% and 1.2 wt% or more. The decarburization amount ΔC was 1.
It has been empirically known that if the content is less than 2 wt%, stable operation can be performed without performing carburizing in the preceding step or the subsequent step. According to FIG. 4, when the acid feed rate F> 1.50, ΔC becomes 1.2 wt% or more, and the amount of decarburization becomes excessive, which is not desirable in operation. This is because the oxygen supplied to the bath surface is abundant and the generation of FeO is sufficient,
This is because the decarburization proceeds with the progress of dephosphorization, and the decarburization amount becomes excessive.

From the results of FIG. 3 and FIG. 4, the dephosphorization can be carried out efficiently while suppressing the decarburization by optimizing the acid feeding conditions from the upper blowing lance.
It was found that / Lo and F were within the ranges defined by the above equations (3) and (4) . This proper range is shown in FIG.

Further, the effect of the present invention differs depending on the Si concentration of the hot metal before the dephosphorization treatment. When the method of the present invention is carried out on the hot metal having the Si concentration before the dephosphorization treatment of 0.10 wt% or less. It was found that particularly remarkable dephosphorization efficiency was obtained. In general, when the Si concentration of the hot metal before the dephosphorization treatment is high, the generated SiO ₂ increases, and as a result, not only the amount of slag increases, but also the amount of CaO for adjusting the basicity increases. Therefore, from such a viewpoint, it is preferable that the Si concentration of the hot metal before the dephosphorization treatment is low. On the other hand, if the Si concentration of the hot metal before the dephosphorization treatment is low, the SiO ₂ content in the slag is low.
Since the concentration is reduced, the melting property of CaO is further deteriorated, and the dephosphorization reaction efficiency is reduced.

However, when the present inventors carried out the method of the present invention on hot metal having various Si concentrations, contrary to the above-mentioned prediction, the Si concentration before the dephosphorization treatment was 0.10 watts.
It has been found that when the method of the present invention is carried out on hot metal of not more than t%, particularly remarkable dephosphorization reaction efficiency can be obtained. The reason may be as follows. That, P is in the dephosphorization reaction 3CaO _· P 2 _{O 5} or 4CaO · _P 2 O
It is fixed in the slag in the form of ₅ . Therefore, SiO ₂ in the slag is a slag component that is not directly required for dephosphorization, and a part of this SiO ₂ reacts with a part of CaO that has been turned into slag, and the CaO that has reacted with this SiO ₂ is removed. It will not contribute to the phosphorus reaction. Therefore, when the Si concentration of the hot metal is low and the amount of generated SiO ₂ is small, the amount of CaO that does not contribute to the dephosphorization reaction by reacting with SiO ₂ decreases, and the amount of CaO that can contribute to the dephosphorization reaction relatively increases. In particular, in the case of the method of the present invention, the slag forming ability of CaO becomes extremely high by optimizing the FeO concentration in the slag, so that the slag composition (which can contribute to the dephosphorization reaction) caused by the low Si concentration of the hot metal. The increase in the amount of CaO) is conspicuous, and as a result, the efficiency of the dephosphorization reaction is considered to be improved.
Such an effect is due to the Si concentration in the hot metal before the dephosphorization treatment: 0.1
It is considered that it becomes apparent in a low Si concentration region of 0 wt% or less. In the conventional method with respect to this, even if the amount of CaO is increased relatively to contribute to the dephosphorization reaction by less SiO ₂ generation amount lower Si concentration of the molten iron, is low slag formation ability per se of CaO, above It is considered that the effect of lowering the concentration of Si in the hot metal does not appear.

As described above, the method of the present invention for producing a low-phosphorus hot metal is particularly effective when applied to hot metal having a Si concentration of 0.10 wt% or less. If the content exceeds 10 wt%, desiliconization (usually performed by adding oxygen such as a solid oxygen source or gaseous oxygen to the hot metal) is performed in a blast furnace cast bed or hot metal pot, etc. It is preferable to perform the dephosphorization treatment after setting the Si concentration to 0.10 wt% or less.

The gaseous oxygen used in the dephosphorization treatment of the present invention may be either a pure oxygen gas or an oxygen-containing gas.
As the container in which the dephosphorization treatment of the present invention is carried out, a converter type container is most preferable in that a free board can be sufficiently secured, but in addition, a ladle type container such as a hot metal pot,
Any container such as torpedo can be used. However, these containers need to be equipped with a top blowing lance. There is no restriction on the hole diameter or the number of holes of the upper blowing lance, so that the acid feeding conditions within the condition range of the present invention can be obtained.
The hole diameter and the number of holes are selected.

In the dephosphorization treatment of the present invention, the supply of oxygen to the hot metal requires the supply of acid from the top blow lance, but a solid oxygen source may be added together with the supply of oxygen. Usually, iron oxide or mill scale is used as a solid oxygen source. The supply of the solid oxygen source to the hot metal can be performed by an arbitrary method such as placing it on an upper hopper or the like and blowing it through an injection lance. Also, the supply of the solvent to the hot metal can be carried out by an arbitrary method such as overhead charging (batch charging or split charging) from an upper hopper or the like, or blowing through an injection lance. The supply amount of the medium solvent is determined according to the concentrations of Si, S, and P in the hot metal, but is preferably 20 kg / T or less from the viewpoint of reducing the amount of slag generated.

Further, in order to further improve the dephosphorization reaction efficiency, it is preferable to agitate the hot metal with gas. This gas stirring is performed by blowing an inert gas such as a nitrogen gas or an argon gas into the hot metal through an injection lance, a bottom blowing nozzle, or the like. The supply amount of such a stirring gas is set to 0.02 Nm ³ / min / T or more in order to obtain a sufficient bath stirring property, and if the stirring of the bath is too strong, the C in the hot metal reduces the generated FeO. 0.3 Nm ³ / min.
/ T or less.

The dephosphorization treatment of the present invention is performed by removing F such as CaF _2.
The biggest feature is that a high dephosphorization reaction efficiency can be obtained only by using a medium solvent mainly containing CaO that does not contain a source, but this does not exclude the addition of an F source such as CaF ₂ .
For example, it does not prevent the addition of an F source, such as CaF ₂ , to an acceptable limit in order to further promote slagging of the CaO source. In the case of using only a medium mainly composed of CaO that does not contain an F source such as CaF ₂ in the dephosphorization treatment of the present invention, the fact that the medium does not contain the F source means that the F source is not substantially contained. Therefore, it does not prevent that a small amount of the F source is contained in the medium solvent as, for example, unavoidable impurities.

[0073]

[Example 1- (1)] Hot metal spouted from a blast furnace was desiliconized in a blast furnace casting bed and a hot metal pot, then desulfurized in a hot metal pot using mechanical stirring, and then 300 ton rolling. Dephosphorization was performed in the furnace. In this example, the hot metal temperature before and after the dephosphorization treatment was 1280 to 1320 ° C., and only CaO-based calcined lime containing no CaF ₂ was used as a medium solvent for dephosphorization. The basic unit of CaO was 8 to 12 kg / T.

The supply of gaseous oxygen is carried out by a top blowing lance, and a solid oxygen source mainly composed of iron ore is also added. The total oxygen consumption is 8 to 10 Nm ³ / T in terms of gaseous O _2.
And Acid supply rate is 15000-25000Nm ³ / h
r, the lance height is 1.5 to 2.5 m, and the blowing time (total blowing time) is 9-1 to supply a predetermined amount of gaseous oxygen.
One minute. In the present example, the dephosphorization treatments of the present invention example and the comparative example were performed on hot metal having a P concentration of approximately 0.1 wt%, which was almost constant, and various Si concentrations.

In the example of the present invention, gaseous oxygen was supplied to the hot metal prior to the addition of the medium solvent, and then the medium solvent was dividedly added in about 2 to 6 times every about 30 seconds. The blowing time before the addition of the solvent is 15 seconds to 4 minutes, the total CaO amount A [kg / T] in the solvent required for the dephosphorization treatment and the oxygen supply amount B [Nm ³ / T] in gaseous form. Ratio B / A of 0.010
It was set to be within the range of 0.50. On the other hand, in the comparative example, the acid supply was started simultaneously with the addition of the initial solvent, without performing the acid supply before the addition of the solvent as in the present invention.

FIG. 1 shows the relationship between the P concentration in the hot metal after the dephosphorization treatment and the Si concentration in the hot metal before the dephosphorization treatment. According to this, in the present invention example, irrespective of the Si concentration in the hot metal before the dephosphorization treatment, extremely high dephosphorization reaction efficiency was obtained as compared with the comparative example, and the target P concentration of 0.020 wt% or less was obtained. Has been achieved. In addition, the Si concentration in the hot metal before the dephosphorization treatment is 0.1.
[P] ≦ 0.015 wt% or less is achieved at 15 wt% or less, and especially when the Si concentration in the hot metal before the dephosphorization treatment is 0.10 wt% or less, [P] ≦ 0.0 of the low P standard is satisfied.
10 wt% is stably achieved. Further, among the examples of the present invention, B / A ≦ 0.20 (however, B / A ≧ 0.0
In the case of 5), higher dephosphorization reaction efficiency is obtained.

[Example 1- (2)] In the same manner as in Example 1, the hot metal poured from the blast furnace was desiliconized in the blast furnace casting bed and the hot metal pot, and then desulfurized in the hot metal pot using mechanical stirring. After the treatment, a dephosphorization treatment was performed in a 300-ton converter. The hot metal temperature before and after the dephosphorization treatment was set to 1280 to 1320 ° C., and only CaO-based calcined lime containing no CaF ₂ was used as a medium solvent for dephosphorization.

In this embodiment, gaseous oxygen or gaseous oxygen and a solid oxygen source (mill
Scale) was supplied to the hot metal. The supply of gaseous oxygen is performed by an upper blowing lance, and the blowing time is 15 seconds or more.
4 minutes. The supply of the mill scale, which is a solid oxygen source, was performed by continuous top-loading. The addition of the solvent
This was carried out by a method of adding the solution in two to six portions at intervals of about 30 seconds or a method of adding the entire amount of the solvent at once. After the addition of the solvent, gaseous oxygen is supplied by the top blowing lance, and a solid oxygen source mainly composed of iron ore is also added. It was set to 8 to 10 Nm ³ / T in terms of O ₂ .

In the acid feeding using the top blowing lance, the acid feeding speed is set to 15,000 to 25000 Nm ³ / hr, the lance height is set to 1.5 to 2.5 m, and the blowing time for supplying a predetermined amount of gaseous oxygen is set. (Total blowing time) was 9 to 11 minutes. In this embodiment, the P content is almost constant at 0.1 wt% and the Si concentration is variously different, and the total CaO amount A [kg / T] in the medium solvent required for the dephosphorization treatment is supplied before the addition of the medium solvent. The dephosphorization treatment was carried out by variously changing the ratio B / A with respect to the supplied oxygen supply amount B [Nm ³ / T] of the oxygen source.

Tables 1 and 2 show the hot metal components and the ratio B / A before and after the dephosphorization treatment in this example. According to this, the ratio B /
It can be seen that by setting A in the range of 0.010 to 0.50, a high dephosphorization reaction efficiency can be obtained. Also, the ratio B / A:
B / A among 0.050 to 0.50 is 0.05 to
In the range of 0.20, particularly good dephosphorization reaction efficiency is obtained.

[0081]

[Table 1]

[0082]

[Table 2]

[0083]

[0084]

[0085]

[0086]

[Example 2 ] Hot metal spouted from a blast furnace was desiliconized in a blast furnace casting bed and a hot metal pot, and then desulfurized in a hot metal pot using mechanical stirring, and then dephosphorized in a 300 ton converter. Processing was performed. The hot metal temperature before and after the dephosphorization treatment was set to 1250 to 1330 ° C., and only the calcined lime mainly containing CaO containing no CaF ₂ was used as the dephosphorization medium solvent, and the basic unit of CaO was set to 9 to 11 kg / T.
As the oxygen source, the supply of gaseous oxygen through the top blowing lance and the supply of a solid oxygen source mainly composed of iron ore were used together, and the total oxygen consumption was 8 to 10 Nm ³ / T. The addition amount of the solid oxygen source was 1 to 4 Nm ³ / T in terms of gaseous oxygen. As the supply condition of the gaseous oxygen, the acid supply rate is set to 1500
0-25000 Nm ³ / hr, lance height 1.5-
2.5 m, blowing time for supplying a predetermined amount of oxygen is 8
-10 minutes.

In supplying the solid oxygen source to the hot metal, the solid oxygen source is preheated to various temperatures in a heating furnace (no preheating in some comparative examples), and this is immediately passed through an injection lance using nitrogen as a carrier gas to convert the hot metal into hot metal. Injected inside. In each of the examples, the P concentration in the hot metal before the dephosphorization treatment was approximately constant at about 0.10 wt%, and the target P concentration after the dephosphorization treatment was 0.015 wt% or less. The desiliconization treatment of the blast furnace cast floor and the hot metal pot was controlled to adjust the Si concentration in the hot metal before the dephosphorization treatment.

FIG. 2 shows the P concentrations after the dephosphorization treatment of the present invention example and the comparative example. In the present invention example in which a solid oxygen source preheated to a temperature of 200 ° C. or more was supplied into the hot metal, the Si concentration of the hot metal was Regardless, the target P concentration of [P] ≦ 0.015 wt% is achieved, and particularly, the Si concentration in the hot metal is 0.10 wt%.
[P] ≦ 0.010wt% which is low P standard in the following cases
Has been achieved stably. On the other hand, in the comparative example in which the solid oxygen source having a preheating temperature of less than 200 ° C. was supplied into the hot metal with or without preheating, the target P concentration of [P] ≦ 0.015 wt% was achieved. Not.

[Example 3 ] Hot metal spouted from a blast furnace was desiliconized in a blast furnace casting bed and a hot metal pot, and then desulfurized in a hot metal pot using mechanical stirring, and then desulfurized in a 300 ton converter. A phosphorus treatment was performed. The hot metal temperature before and after the dephosphorization treatment was set to 1280 to 1320 ° C., and only the calcined lime mainly containing CaO containing no CaF ₂ was used as the dephosphorization medium solvent, and the basic unit of CaO was set to 9 to 11 kg / T.

The solvent is supplied through an injection lance.
Inject into the hot metal with nitrogen as carrier gas
Was. The oxygen source is gaseous acid
Combination of elemental supply and supply of solid oxygen source mainly iron ore
And the total oxygen intensity is 8 to 10 Nm³/ T. Also,
The added amount of solid oxygen source is 1-4 Nm in gaseous oxygen equivalent.³/ T
And As the oxygen supply conditions for gaseous oxygen, the acid supply rate is set to 15
000-25000Nm ³/ Hr, lance height 1.5
~ 2.5m, the blowing time to supply the specified amount of oxygen is
9-11 minutes. In each of the examples, the P
The concentration is almost constant at around 0.10wt%, and after dephosphorization
Was set to 0.015 wt% or less. Also high
By controlling the desiliconization of the furnace cast iron and hot metal pot,
The Si concentration in the hot metal was adjusted.

[CO ₂ ] / ([CO ₂ ] + [CO]) in the exhaust gas discharged from the converter, which is a dephosphorization treatment vessel, is obtained by adjusting the acid supply conditions and the height of the lance, and It was controlled by changing the burn rate. Therefore, the gas composition of the exhaust gas discharged from the converter was analyzed as needed, and [CO ₂ ] / ([CO ₂ ] + [CO]) was controlled based on the gas analysis value. The melting of the furnace body was evaluated by visually observing the inside of the furnace during tapping.

The P concentration and the Si concentration in the hot metal before and after the dephosphorization treatment in each example and the degree of furnace erosion were determined by the [C
O _{2] /} it is shown <br/> in Table 3 together with the _{([CO 2] + [CO} ]). According to Table 3 , [CO ₂ ] / ([C
In the example of the present invention in which (O ₂ ] + [CO]) is controlled to 0.10 to 0.35, the target P concentration [P] ≦ 0.015 wt% is achieved irrespective of the Si concentration of the hot metal. Particularly, when the Si concentration in the hot metal is 0.1 wt% or less, [P] ≦ 0.01 wt%, which is a low P standard, is stably achieved.

On the other hand, [CO ₂ ] /
In the comparative example in which ([CO ₂ ] + [CO]) is less than 0.10, the target P concentration [P] ≦ 0.015 wt% is achieved even when the Si concentration in the hot metal is 0.10 wt% or less. It has not been. [[CO ₂ ] / [CO ₂ ] + [CO])
In a comparative example in which exceeds 0.35, the furnace body is melted due to excessive secondary combustion.

[0095]

[Table 3]

Example 4- (1) The hot metal was dephosphorized using a ladle-type refining vessel (150 ton) as shown in FIG. Calcined lime was used as a medium solvent, and this was blown into hot metal from an injection lance using nitrogen as a carrier gas. The components, temperature, and acid supply time of the hot metal were kept as constant as possible, and care was taken to set the charging standard according to the Si concentration in the hot metal before the dephosphorization treatment. Table 4 shows the main dephosphorization conditions.

In each of the examples, the target P concentration of the hot metal after the dephosphorization treatment was set to 0.020 wt% or less, and the decarburization amount ΔC was set to less than 1.20 wt%. The P concentration in the hot metal after the dephosphorization treatment and the decarburization amount ΔC by the dephosphorization treatment were obtained from the analysis values of the components of the hot metal and slag before and after the start of the acid supply. P concentration in hot metal after dephosphorization treatment in each example (end point [P] concentration)
And the decarburization amount ΔC by the dephosphorization treatment are shown in Table 5 together with the hot metal temperature, the acid feed rate F, and L / Lo.

According to Table 5 , 0.02 ≦ L / Lo ≦ 0.
In the example of the present invention which satisfies 0.25 ≦ F ≦ 1.50 and the target P concentration, [P] ≦ 0.020 wt% and ΔC <1.20 wt% are achieved. On the other hand, in the comparative examples in which L / Lo and F do not satisfy the above conditions of the present invention, at least [P] ≦ 0.020 wt% and ΔC <
Any of 1.20 wt% has not been achieved.

[0099]

[Table 4]

[0100]

[Table 5]

Example 4- (2) The hot metal was dephosphorized using a converter type refining vessel (350 ton) as shown in FIG. Calcined lime was used as a medium solvent, and was supplied to the hot metal by batch charging or split charging from the upper hopper. The components, temperature, and acid supply time of the hot metal were kept as constant as possible, and care was taken to set the charging standard according to the Si concentration in the hot metal before the dephosphorization treatment.
Table 6 shows the main dephosphorization conditions.

In each of the examples, the target P concentration of the hot metal after the dephosphorization treatment was 0.020 wt% or less, and the decarburization amount ΔC was less than 1.20 wt%. The P concentration in the hot metal after the dephosphorization treatment and the decarburization amount ΔC by the dephosphorization treatment were obtained from the analysis values of the components of the hot metal and slag before and after the start of the acid supply. P concentration in hot metal after dephosphorization treatment in each example (end point [P] concentration)
And the decarburization amount ΔC by the dephosphorization treatment are shown in Tables 7 and 8 together with the hot metal temperature, the acid supply rate F, L / Lo, and the like.

According to Tables 7 and 8 , 0.02 ≦ L / L
In the example of the present invention in which o ≦ 0.10 and 0.25 ≦ F ≦ 1.50, the target P concentration [P] ≦ 0.020 w
t% and ΔC <1.2 wt% have been achieved. On the other hand, in the comparative examples in which L / Lo and F do not satisfy the above conditions of the present invention, at least [P] ≦ 0.020 wt%,
Any of ΔC <1.20 wt% has not been achieved.

[0104]

[Table 6]

[0105]

[Table 7]

[0106]

[Table 8]

[0107]

As described above, according to the method of the present invention, C
dephosphorization of the hot metal with excellent dephosphorization efficiency without using any medium solvent containing F source, such as aF ₂ can be performed.

[Brief description of the drawings]

FIG. 1 is a graph showing the P concentration in hot metal after dephosphorization in relation to the Si concentration in hot metal before dephosphorization in Example 1- (1).

FIG. 2 is a graph showing the relationship between the preheating temperature of the solid oxygen source used in the dephosphorization treatment and the P concentration in the hot metal after the dephosphorization treatment in Example 2 .

FIG. 3 shows the relationship between L / Lo and the acid feed rate F in the dephosphorization treatment performed using a ladle type refining vessel and a converter type refining vessel, respectively, based on the P concentration in the hot metal after the dephosphorization treatment. Graph shown

FIG. 4 is a graph showing the relationship between L / Lo and the acid transfer rate F in the dephosphorization treatment performed using the ladle-type refining vessel and the converter-type refining vessel, respectively, based on the decarburization amount ΔC by the dephosphorization treatment. The graph shown

FIG. 5 is a graph showing an appropriate range of L / Lo and an acid feed rate F.

FIG. 6 is an explanatory view showing an example of an embodiment of the present invention using a ladle-type refining vessel.

FIG. 7 is an explanatory view showing an example of an embodiment of the present invention using a converter type refining vessel.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Hidekazu Tanaka, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Shinichi Akai 1-1-2, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Inside (72) Inventor Yoshiteru Kikuchi 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Inventor Yoshiaki Tabata 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. ( 72) Inventor Satoshi Kodaira 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Examiner, Nippon Kokan Co., Ltd.Koichi Kimura (56) References JP-A-62-109910 (JP, A) JP-A-9-20914 ( JP, A) JP-A-63-57712 (JP, A) JP-A-11-172313 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C21C 1/02 110

Claims (11)

(57) [Claims] 1. In a dephosphorization treatment performed as a hot metal pretreatment, a gaseous solvent as a CaO source is added to hot metal before adding a solvent.
A method for producing low-phosphorus hot metal, characterized by increasing the iron oxide concentration in slag by supplying body oxygen , and then adding a medium solvent as a CaO source. 2. Further, a solid oxygen source and a medium solvent in the hot metal
2. The method according to claim 1, wherein the supply is performed before the addition.
Production method of low phosphorus hot metal. 3. The method for producing low-phosphorus hot metal according to claim 1, wherein the medium solvent is added in plural times. 4. An amount of gaseous oxygen or gaseous oxygen satisfying the following expression (1) before adding a medium solvent as a CaO source to hot metal:
And supplying a solid oxygen source.
Or the method for producing low-phosphorus hot metal according to 3. 0.010 ≦ B / A ≦ 0.50 (1) where A: the total amount of CaO in the solvent required for the dephosphorization treatment [k
g / T] B: Oxygen supply amount in terms of gas [Nm ³ / T] 5. Gaseous oxygen or gaseous oxygen before addition of a solvent
And determine the decarburization of molten iron from the gas analysis value of the exhaust gas at the time of supply of the solid oxygen source, dehydration coal quantity and the gaseous oxygen or gaseous acid
Based on the supplied amount of iodine and the solid oxygen source to calculate the iron oxide concentration in the slag, gaseous oxygen and based on the iron oxide concentration value
5. The method for producing low-phosphorus hot metal according to claim 1, wherein the step of controlling the supply conditions of the gaseous oxygen and the solid oxygen source . 6. In the dephosphorization treatment performed as a hot metal pretreatment, a solid oxygen source and / or a medium solvent is heated to 200 ° C. or more.
A method for producing low-phosphorus hot metal, comprising adding to hot metal after preheating to a temperature of less than 1000 ° C. 7. In the dephosphorization treatment performed as a hot metal pretreatment, the dephosphorization treatment is performed under operating conditions such that the concentrations of CO and CO _{2 in} the exhaust gas discharged from the dephosphorization treatment container satisfy the following expression (2). A method for producing low-phosphorus molten iron. 0.10 ≦ [CO ₂ ] / ([CO ₂ ] + [CO]) ≦ 0.35 (2) where [CO ₂ ]: CO ₂ concentration in exhaust gas [wt%] [CO]: In exhaust gas CO concentration [wt%] 8. In a dephosphorization treatment performed as a hot metal pretreatment, gas oxygen is blown upward from a top blowing lance to hot metal, and a pit depth of a hot metal bath surface formed by the kinetic energy of the gas oxygen blown upward. The ratio L / Lo of the length L (m) to the hot metal bath depth Lo (m) and the acid feed rate F (Nm ³ / min / T) from the top blowing lance are calculated by the following equations (3) and (4). A method for producing low-phosphorus molten iron, comprising performing a dephosphorization treatment under satisfactory conditions. 0.02 ≦ L / Lo ≦ 0.10 (3) 0.25 ≦ F ≦ 1.50 (4) 9. The method according to claim 1, wherein the hot metal having a Si concentration of 0.10 wt% or less is dephosphorized.
The method for producing a low-phosphorus hot metal according to 5, 6, 7, or 8. 10. The low-phosphorus hot metal according to claim 9, wherein the hot metal having a Si concentration exceeding 0.10 wt% is desiliconized to a Si concentration of 0.10 wt% or less and then dephosphorized. Production method. 11. A method according to claim 1, wherein a solvent mainly containing CaO containing no F source is used.
The method for producing low-phosphorus molten iron according to 5, 6, 7, 8, 9 or 10.