JP2002212616A - Method for controlling desulfurization in molten iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for dephosphorizing molten iron with which the phosphorus concentration in the molten iron after treating can stably be controlled to a suitable concentration without using a halide. SOLUTION: In the method for dephosphorizing the molten iron by using lime and oxidizing gas or the lime, gaseous oxygen and iron oxide in a refining apparatus having top-bottom combined blowing function, a unit requirement of the oxygen for refining is defined with a corrective unit requirement of the oxygen (O: m3(Normal)/t) calculated with a target phosphorus concentration (Pf: mass%) in the molten iron after dephosphorizing treatment, a silicon concentration (Si: mass%) in the molten iron before dephosphorizing treatment, a unit requirement of top blown gaseous oxygen (G: m3(Normal)/t), a unit requirement of oxygen (S: m3(Normal)/t) in the iron oxide and an effective realizing ratio (η) of the gaseous oxygen.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling dephosphorization in a converter-type hot metal pretreatment of hot metal that has not been subjected to desiliconization beforehand, and particularly to a method for controlling the phosphorus concentration in hot metal after treatment without using a halide. The present invention relates to a method for controlling hot metal dephosphorization for stably controlling the concentration of hot metal.

[0002]

2. Description of the Related Art Conventionally, a method of dephosphorizing hot metal using lime and an oxidizing agent has been widely used. Particularly, a method using a refining furnace having a top-bottom blowing function is disclosed in JP-A-58-16007, in which a high melting point slag having a basicity of 2 or more and iron oxide of 15% is produced. A large amount of stone is used to promote slagification. In addition, Japanese Unexamined Patent Publication
In the method using two converter type furnaces disclosed in Japanese Patent Application Laid-Open No. 3-93813, "refining agents used in a dephosphorization furnace include iron oxide and fluorite in addition to the converter slag and quicklime. And fluorite are also used in the examples. In these cases, the fluorite contains halogen, which has a problem of having a great adverse effect on refractories.

[0003] Conventionally, attempts have been made to improve the reaction efficiency of hot metal dephosphorization without using a halide such as fluorite.

For example, Japanese Patent Application Laid-Open No. 2-11712 discloses a dephosphorizing agent obtained by mixing iron oxide, CaO, and SiO ₂ and melting or sintering the mixture. JP-A-56-93
No. 806 discloses a dephosphorizing agent obtained by mixing CaO / SiO ₂ so that the basicity is 1.8 to 2.3, and sintering a powder material to be 2CaO · SiO ₂ . In these cases, the cost required for melting or sintering is high, so that they have not been put to practical use. Further, JP-A-7-70626 discloses that the slag basicity is 0.6 to 2.5,
(Hereinafter referred to as T.Fe) at a temperature of from 10 to 30% by weight and a temperature of from 1200 to 1450 ° C., and fluorite is not used in Examples. Further, Japanese Patent Application Laid-Open No. Hei 8-157921 discloses that in dephosphorization of hot metal in a converter containing converter slag and iron oxide as main components, the basicity is from 1.2 to 1.2.
2.0, Al ₂ O ₃ = 2 to 16%, T · Fe in slag = 7
A method of reducing the content by 30% is disclosed. In this case, the relationship between the fluorine content in the slag and the refractory erosion index is described, but the effect of Al ₂ O ₃ is not described. In general, when a large amount of Al ₂ O ₃ is added, there is a problem that the solubility of MgO in the slag increases and the refractory is more damaged than when fluorite is used.

[0005] It is generally known that decarburized slag in a decarburizing furnace also has a dephosphorizing ability. Therefore, the concentration of phosphorus in the hot metal after dephosphorization (hereinafter referred to as [P]) should be treated at a higher concentration than [P] required after decarburization in consideration of the dephosphorization rate in the decarburization furnace. Termination is advantageous in terms of cost. In other words, only when the dephosphorization load is properly shared between two vessels (two furnaces) of a dephosphorization furnace and a decarburization furnace, both of which have dephosphorization capacity, the amount of slag generated is reduced and the required quicklime unit consumption is reduced. Also decrease. On the other hand, when dephosphorization is performed only by a decarburization furnace without a dephosphorization furnace (that is, 1
Furnace), the amount of slag generated, and the amount of quick lime used are large. This is a major reason for industrializing the hot metal pretreatment process. On the other hand, reducing [P] after dephosphorization to the same level as [P] after decarburization means that dephosphorization is performed only in the dephosphorization furnace and the decarburization furnace is not used for dephosphorization. I do. Therefore, from the viewpoint of dephosphorization, it is equivalent to the one-furnace method, and there is a problem that a large amount of slag is generated and a unit of quicklime is large. According to the inventor's detailed calculation, the optimum [P] after dephosphorization is 0.020% to 0. 0% depending on the temperature of the blow stopper and the carbon concentration which govern the dephosphorization ability in the decarburization furnace.
Since it greatly changes to 040%, a technique for appropriately controlling [P] after dephosphorization is required.

[0006] However, in the above-mentioned known documents, oxygen gas and iron oxide basic units are determined according to the silicon concentration in the hot metal before treatment (hereinafter referred to as [Si]) and the target after treatment [P]. No technical idea of controlling is disclosed. For example, [P] after dephosphorization described in Examples of JP-A-8-157921 is as low as 0.010%. In the example of JP-A-7-70626, [P] after dephosphorization is reduced to the same level as [P] after decarburization. These indicate that [P] is not properly controlled after the treatment in the dephosphorization furnace.

[0007]

SUMMARY OF THE INVENTION The present invention relates to Japanese Patent Application Laid-Open
JP-A-16007 and JP-A-63-93813 disclose the problem of refractory erosion caused by the use of fluorite.
No. 712 and Japanese Patent Application Laid-Open No. 56-93806 disclose the problem of high cost required for melting or sintering.
The purpose of the present invention is to solve the problem that the [P] cannot be properly controlled after the treatment in a dephosphorization furnace disclosed in Japanese Patent Application Laid-Open No. 0626 or JP-A-8-157921, and after the treatment without using a halide [ P] can be controlled appropriately and stably.

[0008]

SUMMARY OF THE INVENTION Accordingly, the gist of the present invention is to provide (1) a refining apparatus having a top-bottom blowing function, which removes hot metal by using lime and oxidizing gas or lime, oxygen gas and iron oxide. In the phosphorus method, the target phosphorus concentration in the hot metal after the dephosphorization treatment (Pf; mass%), the hot metal silicon concentration before the dephosphorization treatment (Si; mass%), the unit oxygen consumption of the top blown gas (G: Nm ³ / t), Basic unit of oxygen in iron oxide (S: Nm ³
/ T) and a corrected oxygen consumption unit (O: Nm ³ / t) calculated by the effective utilization rate of oxygen gas (η) to determine the oxygen consumption unit for refining,
(2) The Pf and the Si of the molten iron to be dephosphorized
And the range of O is represented by the formula 1;

[0009]

(Equation 3)

Wherein α is 6.5 to 9.0, and the range of O is expressed by the following formula:

[0011]

(Equation 4)

The control method according to claim 1, wherein said G and said S are determined such that O represented by (where η is 0.4 to 0.6) is suitable. A dephosphorizing agent composed of lime, iron oxide or oxygen gas, or a dephosphorization mixture of lime, iron oxide or oxygen gas and one or more selected from the group consisting of SiO ₂ , Al ₂ O ₃ and MgO The control method according to (1) or (2), wherein an agent is used and no halide is used.

(4) The slag after hot metal dephosphorization treatment has a basicity (% by mass CaO /% by mass SiO 2) of 1.2 to 1.9, and the total Fe in the slag is 5 to 20% by mass.
The control method according to any one of (1) to (3). It is. Here, the unit Nm ³ indicates the volume of gas at normal temperature and normal pressure, and is similarly used hereinafter.

[0014]

Embodiments of the present invention will be described below in detail.

The present invention relates to a method for dephosphorizing hot metal using quick lime and oxygen gas or quick lime and oxygen gas and iron oxide using a refining device having a top and bottom blowing function, wherein the dephosphorization rate is corrected. Based on being proportional to speed.

In general, the dephosphorization rate of hot metal is expressed by equation (3).

[0017]

(Equation 5)

Here, kP 'is a dephosphorization rate (mass% / m
in), A is reaction area (m ² ), k is overall mass transfer constant (m / min), V is hot metal volume (m ³ ), t is time (min), and [P] e is equilibrium phosphorus concentration (mass%)
It is.

Assuming that [P] e is smaller than the phosphorus concentration during the treatment, the dephosphorization rate (kP ') is expressed by equation (4).

[0020]

(Equation 6)

However, the present inventors have found that the actual dephosphorization rate (kP ') does not become a function of [P] as in the equation (5).

[0022]

(Equation 7)

Since there is no erroneous chemical determination that the phosphorus removal reaction is the rate of mass transfer of phosphorus in slag or metal, Equation 3 holds as an elementary reaction. However, in the hot metal dephosphorization method using quick lime and oxygen gas or quick lime, oxygen gas and iron oxide using a refining device having a top and bottom blowing function, the term (Ak / V) is inversely proportional to [P]. Therefore, Expression 5 is apparently established as a result.

The reason will be described below.

1) In the hot metal dephosphorization method of the present invention, (A)
k / V) is affected by the stirring of the slag by the CO gas generated by the decarburization reaction that occurs simultaneously with the dephosphorization.

2) CO gas capable of effectively stirring slag is CO gas generated by a reaction between iron oxide (hereinafter, referred to as (FeO)) in slag and carbon in hot metal (hereinafter, referred to as [C]). Yes, the CO gas directly generated by the reaction with the top blown oxygen does not contribute. Therefore, oxygen supplied in the form of oxygen gas has a lower effective contribution to slag agitation than oxygen supplied in the form of iron oxide.

3) Generated by the supplied oxygen (F
eO) is consumed for the generation of CO gas and the dephosphorization reaction,
As the dephosphorization proceeds, the dephosphorization rate decreases according to the principle of Equation 3, and conversely, the generation rate of the CO gas increases and the slag stirring rate increases.

4) As a result of experimental arrangement, (Ak / V)
Generation rate (Q; m ³ (Normal) / min / t) of the CO gas generated by the reaction of the compound (FeO) with [C]
Is shown as a proportional relationship, and Q was found to be inversely proportional to [P]. Therefore, (Ak / V) is inversely proportional to [P], and as a result, Expression 5 is established.

As a result, Expression 5 is expressed as Expression 6, and the phosphorus concentration (P) after the processing is expressed by Expression 7 when the phosphorus concentration before the processing is P ₀ and the processing time is tt (min). Is shown.

[0030]

(Equation 8)

(Here, b 'is a constant.) Next, CO generated by the reaction between (FeO) and [C]
The gas generation rate (Q; Nm ³ / min / t) will be described in detail.

I) Oxygen consumed in the oxidation of [Si] contained in the hot metal before treatment does not contribute to the generation of CO gas. Therefore, stoichiometrically according to the reaction of [Si] + O ₂ = SiO ₂ in slag. Subtract the calculated amount of oxygen.

II) As described above, since the CO gas directly generated by the reaction with the top-blown oxygen does not contribute to the slag stirring, the oxygen supplied in the form of oxygen gas has an effective contribution to the slag stirring of iron oxide. Lower than the oxygen supplied in the form. The effective contribution rate of the oxygen gas is defined as an oxygen gas effective utilization rate (η).

Here, since Q is proportional to the oxygen supply rate (F; Nm ³ / min / t) in consideration of the effective contribution ratio of oxygen gas, Equation 7 is expressed as Equation 8.

[0035]

(Equation 9)

(Here, a and b are constants.) Therefore, the invention described in the above (1) is based on the above findings, and uses a refining device having an upper and lower blowing function. In a hot metal dephosphorization method using quicklime and oxygen gas, or quicklime, oxygen gas and iron oxide, the target phosphorus concentration in hot metal after dephosphorization (Pf; mass%) and the hot metal silicon concentration before dephosphorization (Si; Mass%), top blowing oxygen gas basic unit (G: Nm ³ / t), iron oxide oxygen basic unit (S: Nm ³
/ T) and the corrected oxygen intensity (O: Nm ³ / t) calculated from the effective utilization rate of oxygen gas (η). is there. Here, refining oxygen is oxygen gas and / or
Or, it indicates oxygen in iron oxide, and decarburized slag,
It also includes oxygen in iron oxide contained in dephosphorized slag, desiliconized slag, dust, mill scale, and the like. That is, the oxygen unit for refining is the hot metal 1 of the total amount of oxygen for refining.
It is a supply amount per ton. For oxygen gas, a value converted from the molecular weight of oxygen gas by mass is used. As a method for supplying such refining oxygen, any of injection, top blowing, and top addition may be used.

The reason for using the refining device having the top-bottom blowing function in the present invention is that (Ak / V) is decarburized simultaneously with dephosphorization only when the metal side is sufficiently stirred by bottom-blowing stirring. This is because conditions that are affected by slag agitation by the CO gas generated by the reaction are satisfied.
Further, since oxygen gas by bottom blowing does not contribute to the generation of (FeO) at all, it is necessary to supply oxygen by top blowing.
It should be noted that although iron oxide alone can be used without using top blowing, the operation can be performed in principle, but the operation cannot be practically performed due to a large temperature drop.

As the furnace for the refining apparatus, an upper-bottom blow converter is desirable, but a ladle shape may be used as long as the furnace has an internal volume that does not overflow the slag. The top blown gas is desirably pure oxygen, and the bottom blown gas is desirably oxygen, inert gas or hydrocarbon gas.

The reason for using lime and oxygen gas or lime, oxygen gas and iron oxide in the hot metal dephosphorization method of the present invention is as follows. Since the dephosphorization reaction is an oxidation reaction, both or both of oxygen and iron oxide are required as an oxidizing agent. In addition, a basic oxide is needed to reduce the activity of the generated phosphoric acid, where the cheapest lime is advantageous. Examples of the lime include quick lime and limestone, and also includes a case where CaO contained in decarburized slag and dephosphorized slag is reused.

In the present invention, the oxygen unit for refining is defined as a target phosphorus concentration (Pf; mass%) in hot metal after the dephosphorization treatment.
Hot metal silicon concentration before dephosphorization treatment (Si; mass%), top blowing oxygen gas basic unit (G: Nm ³ / t), oxygen basic unit in iron oxide (S: Nm ³ / t) and effective utilization rate of oxygen gas ( By determining the corrected oxygen intensity (O: Nm ³ / t) calculated by η), it is possible to accurately control P to an appropriate value.

Next, the invention described in the above (2) defines specific control indices, and the range of the corrected oxygen consumption unit O obtained by the expression 1 is within the range of the corrected oxygen consumption unit O obtained by the expression 2. This is a method for controlling hot metal dephosphorization, wherein G and S are determined so that O is contained.

[0042]

(Equation 10)

(Here, α is 6.5 to 9.0.)

[0044]

[Equation 11]

(Here, η is 0.4 to 0.6.) As described above, P is represented by O as shown in Expression 8.
From an industrial point of view, it is more meaningful to express as in Equation 1. That is,
First, the optimum phosphorus concentration after dephosphorization determined from the type of symmetric steel to be treated is defined as Pf, and O for obtaining the Pf is calculated. Next, O is the hot metal silicon concentration before dephosphorization (Si; mass%), which can be known as the hot metal composition before the processing.
It can be calculated from the top blown oxygen gas basic unit (G: Nm ³ / t), the iron oxide basic unit (S: Nm ³ / t), and the oxygen gas effective utilization rate (η). The blowing unit conditions can be determined by calculating the unit oxygen consumption (G: Nm ³ / t) and the unit oxygen consumption in iron oxide (S: Nm ³ / t). Here, G and S are not independent variables, and decarburization, desiliconization and desiliconization by top-blown oxygen are performed based on the amount of scrap used in the treatment, the hot metal temperature before the treatment, and the like so that the temperature after the treatment becomes appropriate. Considering the calorific value associated with each reaction of phosphorus, the calorific value or endothermic amount associated with each of the reactions of decarburization, desiliconization and dephosphorization by iron oxide, and the sensible heat of dephosphorizing agents such as quicklime and iron oxide, etc. It is preferable to calculate the balance and determine the ratio so that the hot metal temperature after the treatment becomes a target value.

FIG. 1 shows the relationship between P and O. It can be seen that the relationship can be well organized within the range of Expression 1. Equation 1
Is larger than 9.0, P decreases excessively from the optimum value (Pf) because oxygen is supplied excessively. On the other hand, if α is smaller than 6.5, It is not preferable because blowing is terminated before P does not decrease to the optimum value due to insufficient supply.

On the other hand, when G / (S + G) is the gas-acid ratio, when the gas-acid ratio exceeds 90%, and when the gas-acid ratio is 10%
In the dephosphorization treatment in the case of less than, the effective utilization efficiency of oxygen gas can be estimated from the relationship between the oxygen consumption rate and the phosphorus concentration after the treatment. From the test results in FIG. In this case, it can be seen that a larger gas-acid ratio requires more oxygen unit consumption, and that oxygen gas has a lower effective contribution to the dephosphorization reaction. Based on this result, for example, the post-treatment phosphorus concentration is set to 0.03%.
When the gas-acid ratio exceeds 90%, the oxygen basic unit is about twice that in the case where the gas-acid ratio is less than 10%, and the effective contribution rate of oxygen gas is estimated to be about 0.5. . As a result of calculation using such a method, η is determined to be 0.4 to 0.6. Here, when η is smaller than 0.4, the contribution ratio of oxygen gas is estimated to be too small. , Causing excessive dephosphorization. On the other hand, when η is larger than 0.6, the contribution ratio of the oxygen gas is overestimated too much, so that the blowing is terminated before Pf does not decrease to the optimum value, which is not preferable.

Table 1 shows the experimental results when α and η were properly adjusted according to the present invention.

[0049]

[Table 1]

The invention described in the above (3) specifies an appropriate dephosphorizing agent composition. According to the present invention, since it is not necessary to dephosphorize to an excessively low phosphorus concentration, it is not necessary to use a halide, and therefore, a dephosphorizing agent composed of lime, iron oxide or oxygen gas, or lime, iron oxide or SiO ₂ , Al ₂ O ₃ and M together with oxygen gas
It is preferable to use a dephosphorizing agent obtained by mixing one or more selected from the group consisting of gO. SiO ₂ , A
An example of one or a mixture of two or more selected from the group consisting of l ₂ O ₃ and MgO is recycled decarburized slag. Here, SiO ₂ , Al ₂ O ₃ and MgO
Is preferably not more than 15% of the total dephosphorizing agent in order not to reduce the dephosphorizing ability of the dephosphorizing slag.
Further, when a halide is used, the melting point of the slag is unnecessarily lowered and the solubility of MgO in the slag is increased, so that the refractory erosion is increased, which is not preferable.

The invention described in the above (4) specifies an appropriate dephosphorization slag composition. In order to convert Equation 3 to Equation 4, it is necessary to use a slag composition that can make [P] e extremely small. Further, in order to satisfy Equation 6, the derinsed slag needs to have sufficient fluidity. As a composition satisfying both, the basicity of the slag after the hot metal dephosphorization treatment is 1.2 to 1.9, and the total Fe (hereinafter, referred to as T.Fe) is 5 to 20% by mass. is necessary. The basicity of slag is C in slag
mass ratio of aO and SiO ₂ (% by mass CaO /% by mass S
iO ₂ ). If this value is lower than 1.2, the dephosphorizing ability of the slag is reduced, and if it is higher than 1.9, the fluidity of the slag is undesirably impaired. Also, T
-If Fe is less than 5%, the dephosphorizing ability of the slag decreases,
If it is more than 20% by mass, slopping occurs and the operation becomes difficult, which is not preferable. The basicity of the slag is controlled by the concentration of silicon in the hot metal before treatment, the composition and amount of the dephosphorizing agent, and T / Fe is controlled by the oxygen supply rate, the oxygen consumption rate, the stirring power, and the gas-acid ratio.

[0052]

EXAMPLE This example was implemented using a 300 ton scale top-bottom blow converter. Composition: C: 4.1-4.5%, S
i: 0.25 to 0.85%, P: 0.098 to 0.10
5%, S: 0.025 to 0.032%, and a temperature of 1
Dephosphorization refining was carried out by charging hot metal at 340 to 1380 ° C. and scrap. During the dephosphorization treatment, oxygen is supplied from the top blowing lance to 0.8 to 2.5 m ³ (Normal) / m.
spraying at a rate of in / t for about 5 to 10 minutes, and about 10 to 15 kg / t of quicklime and about 10 to 15 k of iron ore.
g / t was added. Here, no halide such as fluorite was added. The components after the treatment are C: 3.8 to 4.0%, S
i: 0.01% or less, P: 0.016 to 0.038%, temperature is 1340 to 1370 ° C, slag basicity is 1.3 to 1.6, and T · Fe is 11 to 18%. Met.

Target phosphorus concentration in hot metal after treatment (Pf)
As a result of controlling the oxygen gas basic unit (G) and the iron oxide basic unit (S) in consideration of the silicon concentration (Si) in the hot metal before the treatment, the variation of the phosphorus concentration in the hot metal after the treatment with respect to Pf is as follows. ± 0.007%. Furthermore, by making α and η appropriate as shown in Table 1, ± 0.003%
It became.

<Comparative Example> In comparison with the embodiment, the oxygen gas intensity unit (G) and the oxidation were considered without considering the target phosphorus concentration in the hot metal after treatment (Pf) and the silicon concentration in the hot metal before treatment (Si). As a result of blowing the iron basic unit (S) at a constant value, the variation was ±
It was extremely large at 0.015%.

[0055]

According to the present invention, the phosphorus concentration after treatment can be stably controlled to an appropriate concentration without using a halide, and the lime consumption rate and the amount of slag generated can be reduced.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the concentration of phosphorus in hot metal after treatment and the corrected oxygen intensity.

FIG. 2 is a graph showing a relationship between an oxygen consumption rate and a phosphorus concentration in hot metal after treatment.

Claims (4)

[Claims] 1. A method for dephosphorizing hot metal by using lime and oxidizing gas or lime, oxygen gas and iron oxide in a refining apparatus having a top and bottom blowing function, the target phosphorus concentration in the hot metal after the dephosphorization treatment ( Pf; mass%), hot metal silicon concentration before dephosphorization (Si; mass%), top blowing oxygen gas basic unit (G: Nm ³ / t), iron oxide oxygen basic unit (S:
Nm ³ / t) and the oxygen gas effective utilization rate (eta) by calculated the corrected oxygen consumption rate (O: Nm ³ / t) in the control method of hot metal dephosphorization, characterized in that defining the refining oxygen consumption rate. 2. Based on the Pf and the Si of the molten iron subjected to the dephosphorization treatment, the range of the O is represented by the following formula 1: Where α is 6.5-9.0,
In the range of O, the formula 2; The G and the S are determined so that O represented by (where η is 0.4 to 0.6) is suitable.
The control method described in 1. 3. A dephosphorizing agent comprising lime, iron oxide or oxygen gas, or one or more members selected from the group consisting of SiO ₂ , Al ₂ O ₃ and MgO together with lime, iron oxide or oxygen gas. The control method according to claim 1, wherein a dephosphorizing agent mixed with a compound is used without using a halide. 4. The slag after hot metal dephosphorization treatment has a basicity (% by mass CaO /% by mass SiO ₂ ) of 1.2 to 1.9, and the total Fe in the slag is 5 to 20% by mass. The control method according to any one of Items 1 to 3.