JP2002173707A - Method for dephosphorizing molten iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for dephosphorizing molten iron for restraining sticking and growth of slag on the inner surface of a refractory at a free board in a vessel, in the method for dephosphorizing the molten iron held in the vessel by utilizing converter slag as a dephosphorizing agent. SOLUTION: Gaseous oxygen is blown into the vessel from the upper-space of the molten iron at >=20 deg. nozzle angle to the vertical downward direction. Then, at least one item among an outlet diameter of the nozzle for blowing the gaseous oxygen, pressure of the gaseous oxygen at the outlet of the nozzle and vertical distance from the outlet of the nozzle to the molten iron surface, is changed so that collision pressure of the gaseous oxygen in the vertical direction onto the molten iron surface becomes not less than a prescribed value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a hot metal dephosphorization method for removing P (phosphorus) contained in hot metal produced in a blast furnace by hot metal pretreatment before charging the converter. In particular, the present invention relates to a method for suppressing the attachment and growth of slag to the ceiling of a pretreatment furnace.

[0002]

2. Description of the Related Art Hot metal pretreatment for removing [Si] and [P] components in a hot metal stage has recently become widespread. De-phosphorus reaction among them is carried out in the 4CaO + [P] + 5FeO → 4CaO · P 2 O 5 + 5Fe. Conventionally, for the removal of phosphorus in hot metal, a method of adding a large amount of quicklime in a converter to remove phosphorus has been widely used, but refining in a converter is usually performed at a high temperature of about 1650 ° C. Converter scouring is not an advantageous method for dephosphorization where low temperature processing is suitable. In contrast, hot metal pretreatment is
Since it is performed at about 1300 ° C at a lower temperature than converter scouring, it is a more effective method in terms of dephosphorization. In addition, when performing dephosphorization by hot metal pretreatment, there are cases where desiliconization is performed in advance in pretreatment and after that, and cases where dephosphorization is performed by directly adding a dephosphorizing agent to hot metal that has been tapped from a blast furnace . And
When the hot metal after hot metal dephosphorization is blown in a converter, if the amount of [P] in the hot metal is reduced to below the product specification, dephosphorization is no longer necessary. Blowing without any slag (slagless) significantly increases dust loss to exhaust gas, so a small amount is usually used for covering hot metal during blowing. Quicklime is added. On the other hand, if the [P] of the hot metal is not reduced below the product specification, some dephosphorization is required even in the converter blowing process, so quick lime is added according to the [P] content in the hot metal. . That is, even if the hot metal dephosphorization is performed in advance, as described above, it is indispensable to add a small amount of the auxiliary material in the converter blowing process, and as a result, 2 to 2 when the unphosphorized untreated hot metal is used. About 30% of converter slag is generated. On the other hand, the refining temperature of the converter is as high as about 1650 ° C.
Therefore, the phosphorus concentration in the converter slag generated at the time of refining becomes low. In particular, the converter slag using hot metal that has been subjected to hot metal dephosphorization has a very low phosphorus concentration, about 0.4 to 0.8% by mass, and usually 50% by mass, because [P] in the hot metal is low. % CaO. Therefore, it has been confirmed that if this converter slag is used as a dephosphorizing agent at the time of hot metal dephosphorization, it will exhibit the dephosphorizing ability again. The phosphorus concentration in the pretreated slag after hot metal dephosphorization is usually 2
44% by mass, so if converter slag with low phosphorus concentration is used as hot metal dephosphorizer, phosphorus can be effectively taken into pretreatment slag and concentrated, and it is used as a dephosphorizer. The amount of quicklime used can be greatly reduced. As an example of such a hot metal dephosphorization process using converter slag, hot metal that has been tapped from a blast furnace facility is subjected to hot metal pretreatment in the process of being transferred by a mixed iron wheel, and then blown in a converter. Here, conventionally, pretreatment slag and converter slag generated by hot metal pretreatment and converter blowing are carried out of the system,
Although it was used as a cement raw material or as a roadbed material, in the above-mentioned process using converter slag, all or part of the converter slag generated from the converter is returned to the hot metal pretreatment process to be used as a hot metal dephosphorizer. Only the generated pretreatment slag is carried out of the system. The usual general converter slag composition (% by mass) when adopting this process is as follows.

[0003] _{CaO: 45~53, SiO 2: 12~18} , MgO: 6~8, Fe
_{O: 10~12, Fe 2 O 3} : 4~5, MnO: 3~10, P 2 O 5: 1.0~1.8.

As a reaction vessel in which the hot metal dephosphorization treatment is performed, a ladle, a converter type dephosphorization furnace or the like is used in addition to a mixed iron wheel, and in any case, a by-product is produced in a converter blowing process. By using the converter slag as a dephosphorizing agent, the amount of quicklime used can be greatly reduced, and a great cost reduction can be achieved.
Such reuse of converter slag as a dephosphorizing agent is described, for example, in Japanese Patent Publication No. 55-30042 and Japanese Patent Laid-Open No. 4-333506.
This is a technique described in Japanese Patent Publication No.

[0005]

The converter slag is used as a dephosphorizing agent.
For hot metal dephosphorization in a reaction vessel such as a mixed-iron car.
One of the major operational problems that arises when
The space above the so-called freeboard to the inner surface of the refractory
This is the phenomenon of pretreatment slag adhesion. This deposit is
Growing with repeated phosphorus treatment, dephosphorizing about 200 times
At the time of the treatment, the thickness of the deposit can reach about 1 m.
In some cases. Fire resistance of the mixed iron car ceiling (free board)
Identification of the mineral phase of the deposits formed on the inner surface of the object by X-ray diffraction
As a result, β-2CaO ・ SiO_TwoPhase and 2C
aO ・ SiO_Two・ Al_TwoO_ThreeThe presence of a phase was confirmed. Light the slag
Observation of the structure with a microscopic reflection microscope showed that β-2CaO_TwoPhase
2CaO ・ SiO between_Two・ Al_TwoO_ThreeIt turned out that the phase was filling. Sa
The slag is melted at 1400 ° C and quenched.
As a result of observation, β-2CaO ・ SiO_Two2CaO ・ SiO around phase_Two・ A
l_TwoO_ThreePhase dendrites were identified. From now on, hot metal processing
2CaO ・ SiO with high melting point at processing temperature_TwoPhase and liquid phase with low melting point coexist
And 2CaO ・ SiO_Two・ Al_TwoO_ThreePhase precipitated from liquid phase during cooling
It turns out to be something. Therefore, the low melting liquid phase
High melting point 2CaO ・ SiO _TwoActs as a phase binder
It became clear that. Refractory inner surface of free board
The causes of increased pretreatment slag adhesion to
Can be considered. Fig. 5 shows how much CaO in the dephosphorizer
An indicator of whether or not it has been replaced with converter slag (converter of dephosphorizer
Slag replacement ratio) and the concentration of free lime in pretreated slag.
It shows the person in charge. Here the converter slag storage of the dephosphorizer
The conversion rate was determined by the following equation (1).

[0006] Converter slag replacement ratio of dephosphorizing agent (%) = (CaO content in converter slag) / (total CaO content of dephosphorizing agent) × 100 (1) Shall include an oxidizing agent such as iron ore powder (however, excluding oxygen gas blown) (the same shall apply hereinafter).

The calculated f-CaO concentration in FIG. 5 is the free lime concentration in the pre-treated slag calculated on the assumption that all of the quicklime in the dephosphorizing agent was converted to free lime. As shown in FIG. 5, the converter slag replacement ratio of the dephosphorizing agent is 0.
%, That is, in the conventional dephosphorization treatment using a lime-based dephosphorizing agent, the concentration of free lime in the pretreated slag after the treatment is 0.1%.
It varies widely from 1% to 28%. However, when the converter slag replacement ratio of the dephosphorizing agent is 25% or more, the free lime concentration in the pre-treated slag after the treatment is greatly reduced. There are two forms of free lime in the slag: fossilized lime and crystallized lime.As a result of observing the conversion rate of the converter slag = 0%, ie, the pretreatment slag of the conventional dephosphorization treatment,
It was confirmed that a large amount of unslagged lime was present. on the other hand,
In the case of the dephosphorization treatment using converter slag as a dephosphorizing agent, no uncalcified lime was found in the pretreated slag. In other words, quicklime has a high melting point of 2570 ° C, so it does not react with other oxides, and it is difficult to generate a low-melting phase, so it does not serve as a binder between the high-melting mineral phases. Since slag is a pre-melt product cooled and solidified after melting, a liquid phase is easily generated in a short time, and a low melting point mineral is easily generated. This is considered to be a cause of an increase in the adhesion of the pretreatment slag to the ceiling of a reaction vessel such as a mixed iron wheel by using an increased amount of converter slag as a dephosphorizing agent. In the dephosphorization treatment, iron ore powder and oxygen gas supplied as oxidizing agents for dephosphorization react with [C] in the hot metal, and dephosphorization proceeds with generation of CO gas. For this reason, CO gas is trapped in the pretreatment slag, and the slag forms. When the foaming is severe, the pretreatment slag overflows from the furnace port of the reaction vessel, causing so-called slopping. Since slopping causes serious troubles such as burnout of tracks and peripheral equipment, it is important to suppress the occurrence of slopping to a low level in the dephosphorization treatment. In order to suppress the occurrence of slopping, it is necessary to secure a sufficient space on the hot metal surface in a reaction vessel such as a mixed iron car, so-called free board part.However, when converter slag is used as a dephosphorizer, In addition, the slag adhered remarkably to the inner surface of the refractory of the free board portion, and the free board portion became small, and slopping was easily induced. For this reason, in order to secure a free board part in the reaction vessel, the amount of hot metal received in the vessel must be reduced, and the dephosphorization treatment capacity is reduced and the refractory cost of the vessel per unit mass of hot metal is reduced accordingly. Had problems such as rising. In other words, by using converter slag as a dephosphorizing agent, quicklime for dephosphorization can be significantly reduced and dephosphorization cost can be significantly reduced, while pretreatment slag adheres to the free board part, It had a problem of growing, and had been a major obstacle in reusing converter slag as a dephosphorizer.

[0008] As a method for removing the deposits in the mixed iron car, coke is charged in advance on a mixture of slag and metal which has been attached to the bottom of the vessel, and oxygen is blown from the top blowing lance toward the mixture to dissolve and remove. Japanese Patent Laid-Open No. 5-2728
No. 79 is described. However, although this method is effective for removing deposits on the bottom of a mixed iron vehicle, it is not effective for removing deposits on the inner surface of a refractory of a freeboard portion of a mixed iron vehicle. Furthermore, since the operation for removing the deposits is performed after the dephosphorized hot metal is discharged from the mixed iron wheel, there is a problem that an extra mixed iron wheel is required as a substitute.

In Japanese Patent Application Laid-Open No. 2-200714, a lance for supplying gaseous oxygen at the end of pretreatment of molten iron is raised without stopping the supply of oxygen to dissolve and remove the metal adhering to the furnace port. A method is described. However, this method also has a problem that productivity is deteriorated because extra time is required to dissolve the metal in addition to the time required for ordinary hot metal dephosphorization. In addition, since the top blown oxygen is continued to be blown even after the normal dephosphorization treatment, oxygen more than the amount of oxygen necessary for the original dephosphorization treatment is blown to the hot metal, and [C] in the hot metal decreases, and There is also a problem that heat is insufficient during furnace blowing.

Accordingly, the present invention has been made to solve the above problems, and an object of the present invention is to suppress the adhesion and growth of pretreated slag to the inner surface of a freeboard refractory in a container. It is intended to provide a hot metal dephosphorization method.

[0011]

In order to achieve the above-mentioned object, the invention of claim 1 is to remove hot metal contained in a container by adding a dephosphorizing agent partially substituted with converter slag. A hot metal dephosphorization method characterized by blowing oxygen gas at a nozzle angle of 20 ° or more with respect to a vertically downward direction from a space above the hot metal in the vessel during the phosphorus treatment. By blowing the oxygen gas at a predetermined angle or more, the exhaust gas spreads to the inside of the container, so that slag adhesion and growth on the inner wall of the refractory of the freeboard portion can be suppressed.

According to a second aspect of the present invention, when the horizontal distance from the tip of the nozzle into which the oxygen gas is blown to the inner surface of the container is not constant, the oxygen gas flows in a direction longer than the average of the horizontal distances. The hot metal dephosphorization method according to claim 1, wherein the hot metal is blown. In the case of containers with an elongated horizontal cross-section, such as
By blowing the oxygen gas in the longitudinal direction, the exhaust gas reaches the interior of the vessel in the longitudinal direction, so that the slag can be prevented from adhering to the inner wall of the freeboard refractory and growing.

According to a third aspect of the present invention, there is provided an outlet diameter D of a nozzle for blowing the oxygen gas so that a vertical collision pressure of the oxygen gas against the hot metal surface is equal to or more than a predetermined value. 2. The method according to claim 1, wherein at least one of an oxygen gas pressure P ₀ (X ^* = 0) and a vertical distance X ₁ from the nozzle outlet to the hot metal surface is changed.
Or the hot metal dephosphorization method described in 2 (see FIG. 4).

[0014] A fourth aspect of the present invention, together with the collision pressure is calculated P _S by the following equation (2), wherein the predetermined value
The hot metal dephosphorization method according to claim 3, wherein the pressure is set to 1700 Pa (see FIG. 4).

Formula P _S = C (X ^* −X ₀ ^* ) ⁿ × [P ₀ (x ^* = 15) −P _atm ] × cos θ (2) where X ₀ ^* = 1.2434 M ² −0.5458 M + 2.1558, C = - 26.344 M 2 + 11.815 M + 162.79, n = - 2, X * = X / D, X = X 1 / cosθ, P 0 (x * = 15) = (0.2512 M 2 - 1.0567 M +1.4281) ×
P ₀ (x ^* = 0), M = [2 / (γ-1) × [(P ₀ (x ^* = 0) / P _atm )
^{(γ-1) / γ} -1]] ^1/2 , P _S is the vertical collision pressure of oxygen gas on the hot metal surface, θ
Is the oxygen gas blowing angle with respect to the vertical downward direction, P ₀
(x ^* = 0) the oxygen gas pressure at the nozzle exit, P _atm is the atmospheric pressure, D is the nozzle outlet diameter, the vertical distance X ₁ from the nozzle outlet to the hot metal surfaces, and γ is the specific heat ratio of the oxygen gas.

The invention according to claim 5 is characterized in that the predetermined value 1700Pa
Instead be a predetermined value 3993 · [(Q _O2 + Q
_DP · y _DP ) / Q _O2 ] ^{-1 / 1.01} .

Here, Q _O2 is the flow rate of the top-blown oxygen [m ³ (standard state) / min], and Q _DP is the blowing rate of the dephosphorizing agent [kg / mi].
n] and y _DP are the amount of O ₂ as an oxidizing agent contained per unit mass of the dephosphorizing agent [m ³ (standard state) / kg]. Here, the amount of O ₂ as the oxidizing agent refers to the iron oxide components (FeO, F) contained in converter slag, iron ore powder, etc. used as a dephosphorizing agent.
It refers to amount of O ₂ e ₂ O _3, etc.) in.

By setting the collision pressure of the oxygen gas to the surface of the hot metal in the vertical direction to a predetermined value or more, the reaction rate to the secondary combustion by the oxygen gas can be adjusted, and the _PCO /
Since P _CO2 can be maintained at a predetermined value or more, FeO is not generated and melting of the refractory in the freeboard portion can be prevented.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors increased the ambient temperature of the freeboard portion during the dephosphorization treatment and melted the low-melting-point phase serving as a binder for deposits, thereby refractory material in the freeboard portion. It was thought that the formation of deposits on the inner surface could be suppressed. That is, since the slag drops from the inner surface of the refractory by melting the low melting point phase in the deposit to lower the viscosity of the slag, the deposit is removed or growth is suppressed. We, deposits taken from the free board section refractory inner surface of the actual machine torpedo car (chemical composition [wt%]: CaO: 45.75, SiO 2: 28.65, MgO: 2.95, T.Fe:
1.57, MnO: 2.70, P ₂ O ₅ : 1.73) molded into a Zegel cone and gradually heated and heated in an inert gas atmosphere.
A lab test was conducted to investigate the relationship between the ambient temperature and the molten state of the deposit. FIG. 6 shows the relationship between the ambient temperature and the appearance of the attached matter. From FIG. 6, the hot metal processing temperature of 13
At 00 ° C., the deposits remained in a solid state, but when the temperature was increased to 1350 ° C., the deposits were softened and flowed out (not shown), and at 1400 ° C., they were found to flow almost completely.
From this investigation result, it was clarified that the adhesion can be suppressed by raising the ambient temperature of the free board part to about 1350 ° C. during the dephosphorization treatment.

If the temperature of the hot metal is increased from about 1300 ° C. to about 1350 ° C. to increase the ambient temperature of the free board to about 1350 ° C., the dephosphorization reaction that favors low-temperature treatment is hindered, and the required amount of the dephosphorizing agent is reduced. Will increase. Therefore, the hot metal temperature is about
Keep the ambient temperature of the free board at about 13
As a method of raising the temperature to 50 ° C, we focused on the use of secondary combustion of CO gas in the furnace with top-blown oxygen.

In the dephosphorization treatment, iron oxide or oxygen gas is used as an oxidizing agent for [P] in the hot metal. The iron oxide or oxygen gas may be added from above the hot metal, or may be injected from a lance immersed in the hot metal. In any case, the addition of these oxidizing agents oxidizes a large amount of [C] present in the hot metal, resulting in the generation of a large amount of CO gas by the decarburization reaction represented by the formula (3).

O + [C] = CO (3) When oxygen gas is blown onto the hot metal from above the hot metal via a lance, part of the oxygen gas does not react with [C] or [P] in the hot metal. , As shown in equation (4),
It is known to be used for combustion of CO gas, and this reaction is called secondary combustion. This reaction is a large exothermic reaction, which increases the temperature of the exhaust gas. Thus, the reaction can be used to raise the ambient temperature.

O ₂ + 2CO = 2CO ₂ (4) However, in order to effectively use the secondary combustion heat to prevent slag from adhering to the entire inner surface of the refractory of the freeboard portion, the exhaust gas having a raised temperature must be used. It is necessary to flow deep into the mixed iron car. Therefore, the inventors thought that by setting the oxygen blowing angle of the upper-blown oxygen lance at a certain angle or more with respect to the vertical downward direction, the exhaust gas could flow deep into the mixed-iron car. A 1/10 size three-dimensional cold model (made of transparent acrylic resin) is filled with a predetermined amount of water simulating hot metal, and the gas is blown by changing the angle of the gas injection nozzle at the tip of the lance in various ways. The effect of gas on exhaust gas flow was investigated. The blowing gas used was air at room temperature, and smoke was added to visualize the gas flow.
One example of the result is shown in FIG. As is evident from FIG. 1, when the nozzle angle is small with respect to the vertical downward direction, most of the exhaust gas does not flow into the interior of the mixed iron wheel and flows out of the furnace as it is. In contrast, when the nozzle angle is increased with respect to the vertical downward direction,
The exhaust gas will reach the interior of the pig iron wheel. From the experimental results, it is recommended that the nozzle angle be set to 20 ° or more, preferably 25 ° or more, and more preferably 30 ° or more in order to spread exhaust gas to the depth of the pig iron wheel.

On the other hand, if the amount of the secondary combustion is too large, the following problem may occur. That is, if the amount of the secondary combustion is increased, the CO ₂ concentration in the exhaust gas increases, and this CO ₂ gas is contained in the deposit on the inner surface of the freeboard portion of the refractory of the mixed iron wheel in an amount of about 20 to 30% by mass. Is oxidized to generate FeO (see equation (5)), which causes the refractory of the freeboard portion to be melted. The metallic iron is derived from the slag and the like scattered together with the pretreated slag.

Fe + CO ₂ → FeO + CO (5) In order to prevent the above-mentioned problem from occurring, the expression (5)
It is effective to control the amount of secondary combustion to maintain the value of P _CO / P _CO2 in the exhaust gas higher than the equilibrium value so that the reaction does not proceed. FIG. 3 is an equilibrium diagram relating to the reaction of the formula (5). In the region above the curve a, the metal iron (Fe) is stable, and the reaction of the formula (5) does not proceed and no FeO is generated. Represents. Therefore, 1350 ° C where the deposits melt
Area of the shaded portion of FIG. 3 in order not to generate FeO at a temperature above, i.e. P _CO / P _CO2 in the exhaust gas may be approximately 3.5 or more. However, considering the variation of the refractory surface temperature, it is desirable that P _CO / P _CO2 is about 4 or more so that FeO is not generated even when the refractory surface temperature is 1400 ° C. Exhaust gas is generated by CO + generated from dephosphorizer (converter slag, iron ore powder, etc.) and CO + generated by top blowing oxygen gas.
Since CO ₂ gas is obtained by mixing, given the amount of supply of the feed rate and the top-blown oxygen gas dephosphorization agent, on blowing oxygen gas for the P _CO / P _CO2 in the exhaust gas with a predetermined value The reaction rate PC _TOP to the secondary combustion (hereinafter, also simply referred to as the reaction rate PC _TOP ) is obtained. Here, the reaction rate PC _TOP is defined by the following equation (6).

The reaction rate PC _TOP (%) of the top-blown oxygen gas to the secondary combustion = (the amount of the top-blown oxygen gas used for the secondary combustion) / (the total amount of the top-blown oxygen gas) × 100 = (secondary Top blowing oxygen gas used for combustion) / [(top blowing oxygen gas used for secondary combustion) + (top blowing oxygen gas used for decarburization reaction)] x 100 ... (6) Normal dephosphorization agent in dephosphorization processing performed in the range of the top-blown oxygen gas supply amount, about the P _CO / P _CO2 in the exhaust gas
The reaction rate PC _{TOP for achieving} 4 or more may be about 40% or less. The reaction rate PC _TOP is the vertical collision pressure P _S of the top-blown oxygen gas on the hot metal surface (hereinafter simply referred to as collision pressure).
It can be controlled by adjusting a collision pressure P _S, the nozzle angle theta, the nozzle outlet diameter D, the nozzle outlet oxygen gas pressure
P ₀ (X ^* = 0) and the distance from the nozzle outlet to the hot metal surface (hereinafter referred to as the lance height) X ₁ have, for example, a relationship represented by Expression (2). In the equation (2), various parameters were variously changed by a cold experiment using the nozzle angle θ, the nozzle outlet diameter D, the nozzle outlet gas pressure P ₀ (X ^* = 0), and the lance height X ₁ as parameters. Is an empirical formula obtained by measuring the collision pressure P _S using a pitot tube and performing statistical processing. This experiment was performed when the Mach number M in the equation (2) was in the range of 1.4 ≦ M ≦ 2.5.

P _S = C (X ^* −X ₀ ^* ) ⁿ × [P ₀ (x ^* = 15) −P _atm ] × cos θ (2) [Reprinted] Here, X ₀ ^* = 1.2434 M ² − 0.5458 M + 2.1558, C = -26.344 M ² + 11.815 M + 162.79, n =-2, X ^* = X / D, X = X ₁ / cosθ, P ₀ (x ^* = 15) = (0.2512 M ^2- 1.0567 M + 1.4281) ×
P ₀ (x ^* = 0), M = [2 / (γ-1) × [(P ₀ (x ^* = 0) / P _atm )
^{(γ-1) / γ} -1]] ^1/2 , P _S is the vertical collision pressure of oxygen gas on the hot metal surface, θ
Is the oxygen gas blowing angle with respect to the vertical downward direction, P ₀
(x ^* = 0) oxygen gas pressure at the nozzle outlet, P _atm is the atmospheric pressure, D is the nozzle outlet diameter (vertical distance = the nozzle outlet to the hot metal surface) X ₁ is lance height, and γ is an oxygen gas Is the specific heat ratio.

Therefore, the range of the nozzle angle (θ ≧ 20) capable of spreading the exhaust gas to the depth of the mixed iron wheel described above.
°) nozzle angle set properly, the nozzle outlet diameter, the collision pressure P _S by changing at least one of the nozzle outlet oxygen gas pressure, and the lance height (distance from the nozzle outlet to the hot metal surface) is It can be adjusted to a predetermined value.

Furthermore, to be able to control the reaction rate PC _TOP by adjusting the collision pressure P _S, it was confirmed by the following actual experiments. In other words, using an actual 300t class
Dephosphorization is performed by variously changing the lance nozzle angle, nozzle outlet diameter, nozzle outlet oxygen gas pressure, and lance height.
Exhaust gas was collected for each condition and P _CO / P _CO2 was measured. This P
From _CO / P _CO2, in view of the dephosphorization agent and the oxygen gas supply amount as described above obtains a reaction rate PC _TOP, whereas, to calculate the collision pressure P _S in the above equation (2), the collision pressure P _S And reaction rate PC
Fig. 2 shows the relationship with _TOP . According to FIG. 2, the collision pressure P _{S is set} to 170 to reduce the reaction rate PC _{TOP of} 40% or less at which FeO is not generated.
It is understood that the pressure should be 0 Pa or more.

On the other hand, if the flow rate of the top-blown oxygen gas decreases, even if the reaction rate PC _TOP increases, the amount of CO ₂ gas generated is small.
P _CO / P _{CO 2} does not fall below 4 and no FeO is generated. In addition,
P _CO / P _CO2 is defined by the following equation (7).

P _CO / P _CO2 = [(CO generation rate by top blowing oxygen gas) + (CO generation rate by dephosphorizing agent) − (CO ₂ generation rate by top blowing oxygen gas)] / (top blowing oxygen gas CO ₂ evolution rate) ... according to (7) here, (CO generation rate due to the top-blown oxygen _{gas) = 2 Q O2 · (1} -
PC _TOP / 100), (CO generation rate by dephosphorization _{agent) = 2 Q DP · y DP} , (CO 2 generation rate due to the top-blown oxygen gas) = 2 Q _O2 · PC _TOP
/ 100, Q _O2 is the flow rate of top-blown oxygen [m ³ (standard condition) / min], Q _DP
Is the blowing rate of the dephosphorizing agent [kg / min], and y _DP is O ₂ [m ³ (standard condition) / kg] as the oxidizing agent contained per unit mass of the dephosphorizing agent.

Further, the reaction rate PC _TOP and collision pressure P _S is a relationship of the following expression from Fig. 2 (8).

PC _TOP = 72311 · P _S ^-1.01 (8) Therefore, in order to ^satisfy P _CO / P _CO2 ≧ 4, P _CO / P
In _CO2 ≧ 4, to organize for P _S by substituting the equations (7) and _{(8), P S ≧ [} (1/72311) · (100 / (2 + 4)) · (Q O2 + Q DP _{· y DP) / Q O2]} -1/1 .01 = 3993 · [(Q O2 + Q DP · y DP) / Q O2] may be set to ^{-1 / 1.01.}

Therefore, in the dephosphorization treatment, for example, the conditions for blowing the upper-blown oxygen gas may be determined according to the following procedure. First, the nozzle angle is 20 ° or more, preferably 25 °
Above, more preferably, an appropriate nozzle angle is selected within the range of 30 ° or more, and then the upper blowing oxygen gas supply rate calculated from the total amount of upper blowing oxygen gas required for the dephosphorization treatment and the target dephosphorization time is obtained. determining an oxygen gas pressure in the number and the nozzle outlet diameter and the nozzle outlet of the nozzle to be, finally lance adjust the height to collide pressure P _S to 1700 Pa or more, or 399
3. [(Q _O2 + Q _DP · y _DP ) / Q _O2 ] ^{-1 / 1.01} or more. In addition, the amount of O ₂ as an oxidizing agent contained per unit mass of the dephosphorizing agent y _DP is, when a plurality of dephosphorizing agents are used, the component (Fe ₂ O ₃ , FeO, etc.) of each dephosphorizing agent. ) And the amount of blowing may be obtained by a weighted average. As a result, the nozzle angle is set so that the exhaust gas reaches the far end of the mixed iron wheel, so that no slag adheres to the inner surface of the refractory of the freeboard part, and the reaction rate PC _TOP is 40% or less. As a result,
Since _PCO / _PCO2 of 4 or more is obtained and no FeO is generated, dephosphorization treatment with less damage to refractories can be performed. The number of nozzles is usually two, so that the exhaust gas goes in both longitudinal directions because the wheel is long and narrow.However, the number of nozzles is not limited to this. It can be appropriately changed according to the blowing oxygen gas supply speed or the like. The lance height is the above condition (collision pressure P _S ≧ 1700 Pa)
The lance height is not particularly limited as long as it satisfies, but it is desirable that the lance height should be equal to or higher than a certain height in order to avoid the adhesion of slag or metal scattered from the bath to the nozzle outlet. After determining the height, the collision pressure P _S ≧ 17
The nozzle outlet diameter at 00 Pa and the oxygen gas pressure at the nozzle outlet may be determined.

In order to confirm the operation and effect of the present invention, the actual machine 30
Using a 0 t class mixed iron wheel, the dephosphorization treatment was performed with the nozzle angle and nozzle outlet diameter of the top-blown oxygen gas lance varied, and the other conditions were kept constant. The following results were obtained.

[0036]

EXAMPLES (Example 1) A specific mixed iron wheel was subjected to dephosphorization treatment 200 times by the following dephosphorization method. Desiliconization is performed on the blast furnace cast floor, and the desiliconized hot metal is 280 to 320 t
In the range of. After removing the desiliconized slag generated by the treatment with a slag dragger, 15 to 25 kg of converter slag powder, 7 to 13 kg of quicklime powder per ton of hot metal,
A mixture of 0.9 to 1.5 kg of fluorite powder and 20 to 40 kg of iron ore powder was blown from a lance dipped in hot metal together with nitrogen gas at 10 m ³ (standard state) / min to remove phosphorus. During the dephosphorization process, the nozzle angle was 25 ° and the nozzle outlet diameter was 27 mm.
Oxygen gas of 0.5 to 3.0 m ³ per ton of hot metal (standard condition) was sprayed onto the hot metal from a water-cooled lance in a hole (arranged so that the blown oxygen gas goes in both longitudinal directions of the mixed iron wheel). The lance height at this time is 1450 mm, the oxygen gas flow rate is 50 to 60 m ³ (standard condition) / min, and the collision pressure P _S calculated by the equation (2) is used.
Ranged from 2663 to 3554 Pa. The mixed-iron car is as described in 2 above.
Even after the dephosphorization process was performed 00 times, no slag was attached to the inner surface of the refractory around the receiving port, and about 1/2 of that of Comparative Example 1 was applied to the inner wall of the refractory of the other freeboard portions. Only the thick slag was attached, and no erosion of these refractories was observed. The composition range (% by mass) of the pretreated slag was as follows. CaO: 38.9-49.7, Si
_{O 2: 12.7~15.7, MgO: 1.8~4.3} , T.Fe: 10.7~15.2, MnO:
_{2.3~4.6, P 2 O 5: 2.90~4.96} .

(Embodiment 2) Regarding a specific mixed iron wheel different from that of Embodiment 1, the nozzle angle and the nozzle outlet diameter are different from those of Embodiment 1, the nozzle angle is 35 °, the nozzle outlet diameter is 22 mm, and two holes The dephosphorization treatment was carried out under the same conditions except that the lance was arranged so that the oxygen gas was directed in both longitudinal directions of the mixed iron wheel. Collision pressure P _S which is calculated by the equation (2) at that time was in the range of 2329~ 3053 Pa. The mixed pig wheel is
Even after the completion of the 200 dephosphorization treatments, almost no slag adhered to the inner surface of the refractory in the freeboard portion, and no melting of the refractory was observed.

(Comparative Example 1) With respect to a specific mixed iron wheel different from Examples 1 and 2, the nozzle angle and the nozzle exit diameter are different from those of Examples 1 and 2, the nozzle angle is 15 °, and the nozzle exit diameter is 30.7 m.
The dephosphorization treatment was carried out using a lance with m, 2 holes (arranged so that the blown-out oxygen gas goes in both longitudinal directions of the mixed iron wheel), and the other conditions were exactly the same. Collision pressure P _S which is calculated by the equation (2) at that time was in the range of 2853 ~ 3836 Pa. After the dephosphorization treatment was completed 200 times, no erosion of the refractory in the freeboard portion was observed, but slag with a thickness of about 1 m was observed on the inner wall of the refractory material in the freeboard portion.

Comparative Example 2 Examples 1 and 2 and Comparative Example 1
The nozzle angle and the nozzle outlet diameter are different from those of Examples 1 and 2 and Comparative Example 1. The nozzle angle is 45 °, the nozzle outlet diameter is 25.7 mm, and two holes are used. The dephosphorization treatment was carried out under the same conditions except for using a lance arranged in both longitudinal directions. At this time, the collision pressure P _S calculated by the equation (2) is 1275
161686 Pa. Although no slag adhered to the freeboard part of the refractory inner wall, no abnormal erosion was observed on the freeboard part refractory inner surface after 73 dephosphorization treatments from the start of use of the mixed pig wheel. Was.

[0040]

As described above, according to the first and second aspects of the present invention, the angle of the nozzle in the container from the upper space of the hot metal accommodated in the container to the vertical downward direction is not less than 20 °. By blowing oxygen gas, the exhaust gas spreads to the inside of the container, so that slag adhesion to the freeboard part refractory inner wall, which had been a problem when using converter slag for dephosphorization, can be suppressed. Was. As a result, the amount of hot metal received in the container increases, and the dephosphorization treatment capacity increases,
As a result, the cost of refractories per unit mass of hot metal was significantly reduced. In addition, the operation of removing the deposits became unnecessary, and the maintenance cost was reduced.

According to the third to fifth aspects of the present invention, in addition to the effects of the first aspect, the outlet diameter of the nozzle into which the oxygen gas is blown, the pressure of the oxygen gas at the nozzle outlet, and the nozzle outlet By changing at least one of the vertical distances from the hot metal surface to the hot metal surface, by making the vertical collision pressure of the oxygen gas on the hot metal surface equal to or more than a predetermined value, the secondary combustion of the oxygen gas is started. the possible reaction rate is adjusted, since the P _CO / P _{C O2} in the exhaust gas can be maintained above a predetermined value, melting of the free board section a refractory without generation FeO was prevented. As a result, the life of the refractory can be extended, the cost of the refractory can be reduced, and the maintenance cost for repairing the refractory can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the nozzle angle of an upper-blown oxygen gas lance and the flow of exhaust gas in a mixed iron vehicle.

Fig. 2 Impact pressure P _S and reaction rate of top-blown oxygen to secondary combustion
It is a figure showing the relation with PC _TOP .

FIG. 3 is an equilibrium diagram in an Fe—FeO—CO—CO ₂ system.

FIG. 4 is a view for explaining a state in which a top-blown oxygen gas is blown into a mixed-iron car to perform a dephosphorization treatment.

FIG. 5 is a diagram showing a relationship between a converter slag replacement ratio of a dephosphorizing agent and a concentration of free lime in pretreated slag.

FIG. 6 is a diagram illustrating a molten state of an attached matter.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshiya Miyake 1-5-5 Takatsukadai, Nishi-ku, Kobe City, Hyogo Prefecture Inside Kobe Research Institute, Kobe Steel Works, Ltd. (72) Inventor Taiichi Ueyama Kanazawa, Kakogawa City, Hyogo Prefecture No. 1 Kobe Steel Works Kakogawa Works (72) Inventor Koji Nakanishi 1 Kanazawacho, Kakogawa City, Hyogo Prefecture Kobe Steel Works Kakogawa Works F-term (reference) 4K014 AA03 AB00 AB03 AB04 AB16 AC14 AC16 AD01 AD23 AD27

Claims (5)

[Claims] When a dephosphorizing treatment is performed by adding a dephosphorizing agent partially replaced with converter slag to hot metal stored in a container, dephosphorization is performed in a vertically downward direction from a space above the hot metal in the container. A hot metal dephosphorization method, characterized by blowing oxygen gas at a nozzle angle of 20 ° or more to the hot metal. 2. When the horizontal distance from the tip of the nozzle for blowing the oxygen gas to the inner surface of the container is not constant, the oxygen gas is blown in a direction in which the horizontal distance is longer than the average of the horizontal distances. The hot metal dephosphorization method according to claim 1, wherein 3. An outlet diameter of a nozzle for blowing the oxygen gas, a pressure of the oxygen gas at the nozzle outlet, and a pressure of the oxygen gas so that a vertical collision pressure of the oxygen gas against the hot metal surface is equal to or more than a predetermined value. The hot metal dephosphorization method according to claim 1, wherein at least one of a vertical distance from the nozzle outlet to the hot metal surface is changed. 4. The method according to claim 1, wherein the collision pressure is calculated by the following equation.
_S and the predetermined value The hot metal dephosphorization method according to claim 3, wherein the pressure is 1700Pa. Formula P _S = C (X ^* -X ₀ ^* ) ⁿ × [P ₀ (x ^* = 15)-P _atm ] ×
cos [theta] ^{_{Here, X 0 * = 1.2434 M 2}} - 0.5458 M + 2.1558, C = - 26.344 M 2 + 11.815 M + 162.79, n = - 2, X * = X / D, X = X 1 / cosθ, P 0 ^{(x * = 15) = (} 0.2512 M 2 - 1.0567 M + 1.4281) ×
P ₀ (x ^* = 0), M = [2 / (γ-1) × [(P ₀ (x ^* = 0) / P _atm )
^{(γ-1) / γ} -1]] ^1/2 , P _S is the vertical collision pressure of oxygen gas on the hot metal surface, θ is the angle of the oxygen gas blowing nozzle with respect to the vertical downward direction, P ₀ (x ^* = 0) is the oxygen gas pressure at the nozzle outlet, P _atm is the atmospheric pressure, D is the nozzle outlet diameter, X ₁ is the vertical distance from the nozzle outlet to the hot metal surface, and γ is the specific heat ratio of oxygen gas. 5. The predetermined value The instead be 1700Pa, the predetermined value _{3993 · [(Q O2 + Q} DP · y DP) / Q
_O2 ]. Here, Q _O2 is the flow rate of top-blown oxygen [m ³ (standard state) / min], Q _DP is the blowing rate of dephosphorizer [kg / min], and y _DP is contained per unit mass of dephosphorizer. O ₂ as an oxidizing agent [m ³ (standard state) / kg].