JPH09202912A - Method for dephosphorizing molten iron under condition excellent in scrap melting capacity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dephosphorizing method of molten iron which has high melting capacity of scrap, related to the dephosphorizing treatment of the molten iron in a converter. SOLUTION: In the dephosphorizing refining of the molten iron used to a refining apparatus, in which oxygen is supplied from a top-blown lance 2 and the molten steel 5 is stirred by gas, carbonaceous material having <=3mm grain diameter from the center of the top-blown lance 2 to vertically downward is blown together with gaseous nitrogen and also, oxygen is supplied toward the furnace wall direction at 14-20 deg. angle to the vertical downward line, and the carbonaceous quantity W (ton/Hr) to the oxygen blowing quantity F (Nm<3> /Hr) is made to 0.2-0.6 as W/F. Further, a ratio LN/H of the depth LN of recessed part formed on the surface of the molten iron 5 with the gaseous nitrogen to the surface of the molten iron 5 with the gaseous nitrogen to the molten iron depth H is made to 0.65-0.85, and a ratio L0/H of the depth L0 of recessed part formed on the surface of the molten iron with the gaseous oxygen to the molten iron depth H is made to 0.15-0.55.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for dephosphorizing hot metal having a high scrap melting capacity.

[0002]

2. Description of the Related Art Regarding the minimization of the total cost of steelmaking and the stable melting of low-phosphorus steel, the conventional method for dephosphorizing hot metal has been
(1) A method for performing pre-phosphorization by injecting a flux for dephosphorization (iron oxide, quick lime, etc.) on the hot metal in the tope car, (2) Injecting a flux for dephosphorization on the hot metal in a ladle, Alternatively, a method of spraying and performing preliminary dephosphorization is used.

However, since these methods use iron oxide represented by iron ore and scale powder as an oxidant for promoting the dephosphorization reaction, the hot metal temperature decreases during the treatment,
There is a problem that scrap consumption in the converter, which is the next step, is reduced and molten steel production is reduced.

When oxygen gas is used instead of iron oxide in this method, when the oxygen gas is injected, agitation becomes excessive and (T.Fe) becomes extremely low so that dephosphorization does not proceed, and it is simply sprayed from above. In that case, there was a problem that the (T · Fe) of the slag was high and the slag slopped.

A method in which two converters are used to perform dephosphorization on the one hand and decarburization on the other hand (for example, JP-A-63-1).
No. 95210) is used. In this method, oxygen gas is used as the oxidizer, and scrap can be used to control the temperature during the dephosphorization treatment, but heat loss occurs because the hot metal after dephosphorization is tapped and charged into the decarburization furnace. Occurs, the scrap consumption is reduced, the molten steel production is reduced, and there is a problem that capital investment is large because two converters are used.

On the other hand, as disclosed in Japanese Patent Application No. 6-011027, subsequent to the hot metal dephosphorization process using a converter, the process of tilting the furnace to discharge the produced dephosphorization slag, the furnace Upright, supplying oxygen from the top blowing lance to decarburize, degassing only the molten steel without discharging the decarburizing slag generated during decarburization, and leaving the decarburizing slag in the furnace. In the method of continuously performing the hot metal of the next charge, the capital investment is small because there is only one converter used, and since there is no dephosphorization hot metal tapping process, heat loss is small and scrap consumption Is characterized by not decreasing.

However, even with this method, the amount of scrap melted is limited because scrap melting only utilizes the sensible heat and latent heat of the hot metal. Also, in the converter, a method of supplying carbonaceous material from a top-blown lance is known, but the heat deposition efficiency is not always high, and if this is applied to hot metal dephosphorization, (T ・ Fe) in the slag is lowered. There is a problem that the dephosphorization efficiency is lowered.

[0008]

DISCLOSURE OF THE INVENTION The present invention solves the problem in the prior art that the amount of scrap melted is limited because the scrap melt only utilizes the sensible heat and latent heat of the hot metal. It is what

[0009]

Means for Solving the Problems Even when the carbonaceous material is sprayed in the hot metal dephosphorization in the converter, the inventors of the present invention have realized that the nitrogen gas jet flow, which is the carrier gas of the carbonaceous material, is improved by optimizing the lance structure. , The oxygen gas jet is not united, and the nitrogen gas jet flow velocity is high (hard blow) to allow the carbonaceous material to sufficiently penetrate into the molten iron to promote carburization, while the oxygen gas jet surface It was found that the carbonaceous material can be supplied without inhibiting or reducing the dephosphorization reaction by reducing the reaching flow rate (soft blow) and maintaining high (T · Fe) in the slag to promote dephosphorization. .

The present invention has been made on the basis of this finding, and the gist thereof is as follows. (1) Using a refining device that supplies oxygen from an upper blowing lance and stirs a steel bath with gas, a stirring energy density E (kW /
ton) is 1 to 3 and the hot metal temperature at the time of dephosphorization refining blowing stop is 1
250 to 1450 ° C., the carbon concentration in the hot metal is 2.5 to 3.
In the dephosphorization method under the condition of 5%, carbonaceous material having a grain size of 3 mm or less was blown together with nitrogen gas onto the steel bath surface vertically downward from the center of the upper blowing lance, and 14 Oxygen is supplied to another position on the steel bath surface at an angle of ~ 20 degrees, and the amount of carbonaceous material W (ton / Hr) is changed to the amount of oxygen F (Nm ³
/ Hr) is 0.2 as W / F with respect to the oxygen amount F (Nm ³ / Hr)
It is a hot metal dephosphorization method excellent in scrap dissolving ability, characterized in that (2) In the above item (1), the ratio of the depth LN of the depression formed on the surface of the molten iron by the nitrogen gas to the bath depth H of the molten iron is LN / H.
65 to 0.85, and at the same time, the ratio of another recess depth LO formed on the molten iron surface by oxygen gas and the bath depth H of molten iron is set to 0.15 to 0.55 in LO / H. It is a hot metal dephosphorization method with excellent scrap dissolving ability.

(3) Subsequent to the hot metal dephosphorization method (step 1) described in (1) or (2) above, a step of tilting the furnace to discharge the produced dephosphorization slag (step 2), the furnace is erected. A step of supplying oxygen from the upper blowing lance to decarburize (step 3),
The step of tapping only the molten steel without discharging the decarburized slag generated during decarburization (step 4) and the step of receiving the hot metal of the next charge with the decarburized slag left in the furnace (step 5) It is a hot metal dephosphorization method having high productivity and excellent scrap dissolving ability, which is characterized by being continuously and repeatedly carried out.

Here, the stirring energy-density E (kW / ton)
Is the bottom blowing gas flow rate Q (Nm ³ / s), temperature T (K), molten iron amount W (t
on), static pressure P (Pa) at the bottom blowing tuyere position, and atmospheric pressure P ₀ (Pa) are expressed by the equation (1).

[0013]

[Equation 1]

The depression depth LN (mm) formed on the molten iron surface by the nitrogen gas is calculated by the equation (2), and the depression depth L0 (mm) formed by the oxygen gas on the molten iron surface is calculated by the equation (3). It

[0015]

[Equation 2]

H is the distance from the tip of the lance to the molten iron surface (m
m) and d are lance nozzle diameters (mm), n is the number of nozzles,
FN is the top-blown nitrogen gas flow rate (Nm ³ / Hr), and FO is the top-blown oxygen gas flow rate (Nm ³ / Hr). The molten iron surface and the bath depth H were calculated geometrically with the specific gravity of the molten iron being 7 g / cm ³ .

[0017]

1 shows an example of an embodiment of the present invention. Hot metal dephosphorization step (step 1), step of tilting the converter 1 to discharge the dephosphorization slag 6 generated in step 1 (step 2), standing the converter 1 upright and supplying oxygen from the upper blowing lance 2 to remove it. The step of carbonizing (step 3), the step of tapping only the molten steel 5 without discharging the decarburized slag 4 generated during decarburization (step 4), and the next charging with the decarburized slag 4 left in the furnace. Process of receiving hot metal 5 (process 5)
It consists of

In the dephosphorization step shown in step 1 of FIG. 1, oxygen is supplied from a top blowing lance 2 and oxygen and LPG are supplied from a bottom blowing tuyere 3 of a double tube provided in the furnace bottom. Gas stir the bath. Here, there is no problem even if Ar or CO ₂ or N ₂ is supplied from the bottom blowing tuyere 3 and stirred.

About 30 kg / ton of pre-charged decarburizing slag 4
Scrap 7 is 150-250 kg / t with the remaining state.
After charging, a predetermined amount of hot metal is charged and refining is started. The stirring energy density E (kW / ton) during refining is 1 to 3, and the hot metal temperature at the end of dephosphorization refining (blowing stop) is 1250 to 145.
Dephosphorization treatment is carried out at 0 ° C. under the condition that the carbon concentration in the hot metal is 2.5 to 3.5%.

When the hot metal temperature at the time of blowing off the dephosphorization refining is lower than 1250 ° C., the slag is poorly slagged and the dephosphorization rate is lowered, and the slag rate in the step 2 is lowered to 1450.
When the temperature is higher than ° C, the dephosphorization rate decreases due to the chemical equilibrium relationship.

Further, when the carbon concentration in the hot metal is lower than 2.5%, the heat at the decarburization stage of the process 3 is insufficient, so the temperature at the end of the decarburization should meet the requirements of the continuous casting process. No
If it is higher than 3.5%, the heat during the decarburization period becomes excessive, so a cold material is required, and the rate of dissolution of the carbonaceous material supplied from the top-blowing lance into the molten iron decreases and the carbonaceous material particles However, since (T · Fe) in the slag is lowered because of mixing with the slag, dephosphorization becomes worse.

When the stirring energy density E is lower than 1 (kW / ton), the dephosphorization reaction is slow, and the scrap dissolution rate is small, so that a sufficient refining effect cannot be obtained, so that it is higher than 3 (kW / ton). When it is large, the iron oxide in the slag is reduced by the carbon in the hot metal, so that the oxidizing power cannot be maintained and the dephosphorization rate decreases.

FIG. 2 shows an example of the upper blowing lance used in the present invention. In FIG. 2, the lance 9 has four main hole system nozzles 10 and one sub hole system nozzle 11. The main hole system and the sub hole system can independently control the gas species and the flow rate. The sub-hole type nozzle 11 has a structure for ejecting gas vertically downward, and the main hole system nozzle 10 has a structure for ejecting gas toward the furnace wall at an angle of 14 to 20 degrees from vertically downward.

A carbonaceous material having a particle size of 3 mm or less is sprayed from the auxiliary pore system using nitrogen as a carrier gas, and oxygen is supplied from the main pore system. When the angle θ from the vertically lower side of the main hole system nozzle 10 is smaller than 14 degrees, the carbonaceous material and oxygen discharged from the subhole system nozzle 11 are combined in the space, and the carbonaceous material is burned in the jet flow to heat the heat. Is extremely deteriorated, and when θ is larger than 20 degrees, a problem occurs that the furnace wall is melted and damaged by the oxygen jet flow.

When the particle size of the carbonaceous material supplied from the sub-hole type nozzle is larger than 3 mm, it takes a long time to dissolve the carbonaceous material into the molten iron, so that undissolved carbonaceous material particles are mixed in the slag. As a result, the problem of dephosphorization becomes worse.

The amount of carbonaceous material W (ton / Hr) must be 0.2 to 0.6 as W / F with respect to the amount of oxygen F (Nm ³ / Hr). W
When / F is larger than 0.6, an excess amount of carbonaceous material is supplied compared to the amount of decarburization of molten iron due to oxygen, so that undissolved carbonaceous material particles are mixed in the slag and dephosphorization deteriorates. When the ratio is less than 0.2, the effect of increasing the scrap dissolving ability by adding the carbonaceous material is small and not practical.

Further, by optimizing the distance h (mm) from the tip of the lance to the molten iron surface and the diameter d (mm) of the lance nozzle of the main hole and the auxiliary hole, the depth of the recess formed on the molten iron surface by nitrogen gas The ratio of LN to the molten depth H of molten iron is LN / H of 0.65
0.85, and the ratio of the depth L0 of the recess formed on the surface of the molten iron by the oxygen gas to the bath depth H of the molten iron is 0.15 as LO / H.
When it is set to 0.55, a higher scrap dissolving ability is exhibited.

When LN / H is less than 0.65, undissolved carbonaceous material particles are generated due to insufficient penetration of carbonaceous material particles into molten iron. Wear of refractories occurs. If LO / H is smaller than 0.15, sloping occurs, and if it is larger than 0.55, hard blow occurs, so that (T · Fe) decreases and the dephosphorization rate decreases.

Although the present invention is effective in continuously carrying out the steps shown in FIG. 1, it is also effective when the hot metal dephosphorization in step 1 and the decarburization in step 3 are carried out in different converters. . In FIG. 1, hot metal dephosphorization step (step 1) and decarburization step (step 3)
Is different from the conditions of temperature and slag composition suitable for dephosphorization, and the conditions of temperature and slag composition suitable for decarburization,
This is because the cost of the auxiliary material typified by quick lime is lower when the steps are performed separately.

Further, when the dephosphorization slag 6 is carried over to the decarburization step, phosphorus in the slag returns to molten iron, so-called recondensation occurs, so that an intermediate slag (step 2) is required between steps 1 and 3. . The middle slag is shortest and the slag ratio is high. It is desirable to tilt the converter to discharge the slag.

Subsequent to the decarburization step (step 3), a step of tapping only the molten steel 5 without discharging the decarburization slag 4 generated during decarburization (step 4), and leaving the decarburization slag 4 in the furnace The process (process 5) of receiving the hot metal 5 of the next charge is continued as it is. Here, the reason why the decarburized slag is left is that the decarburized slag has a dephosphorization ability when the temperature is lowered, and therefore the cost of quick lime and iron oxide can be reduced by reusing the decarburized slag in the step 1. Is.

[0032]

EXAMPLE The experiment was conducted in the same process as in FIG. 1 using a 6 ton scale converter. Nitrogen gas or oxygen gas and tuyere cooling gas was used as the bottom blowing gas, and oxygen gas was blown from the main hole of the top blowing lance, and nitrogen gas and carbonaceous material were blown from the auxiliary hole.
The main operating conditions are shown below.

Bath depth (after melting scrap) About 0.5 m Top-blown oxygen flow rate 1200-1800 Nm ³ / Hr Top-blown nitrogen flow rate 250-350 Nm ³ / Hr Top-blown carbonaceous material feed rate 60-120 kg / Hr Bottom-blown gas flow rate 100 ~ 150Nm ³ / Hr Quick lime basic unit 15 ~ 20kg / ton Slag amount 35 ~ 45kg / ton (CaO / SiO ₂ ) 1.8 ~ 2.2 Scrap usage amount 175 ~ 225kg / ton Lance / molten iron surface distance 800 ~ 1200mm The lance has the shape shown in FIG. 2, the nozzle diameter of the main hole is 10 to 15 mm, and the nozzle diameter of the auxiliary hole is 4.5 to 6.5 mm.
And

In Table 1, carbonaceous material having a particle size of 3 mm or less is sprayed together with nitrogen gas, and the spread angle of the main holes is 17
It is a test result when a degree lance is used. In the present invention, there was no undissolved scrap after dephosphorization refining, the heat deposition efficiency shown by the following formula was 90% or more, and the dephosphorization rate was also good.

[0035]

(Equation 3)

However, even if the experimental conditions are the same as those in Table 1, when a lance having a main hole divergence angle of 12 degrees is used, unmelting of scrap after dephosphorization refining occurs, and the heat transfer efficiency is 65.
It suddenly deteriorated to%.

FIG. 3 shows the depth LN of the recess formed on the surface of molten iron by nitrogen gas when nozzles of various diameters are used.
The results of experiments on the relationship between the ratio of molten iron bath depth H (LN / H) and the dephosphorization rate are shown below. When LN / H is less than 0.65, the dephosphorization rate decreases.

FIG. 4 shows the experimental results on the relationship between the dephosphorization rate and the ratio (LO / H) of the dent depth LO formed on the surface of molten iron by oxygen gas and the bath depth H of molten iron. When H is larger than 0.55, the dephosphorization rate decreases.

[0039]

[Table 1]

[0040]

According to the present invention, scrap of 150 kg / t can be obtained.
It has become possible to dephosphorize the hot metal after using more than on.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of an implementation process of the present invention.

FIG. 2 is a diagram showing an example of an upper blowing lance used in the present invention.

FIG. 3 is a diagram showing experimental results on the relationship between the ratio of the depression depth LN formed on the surface of molten iron by nitrogen gas to the bath depth H of molten iron (LN / H) and the dephosphorization rate.

FIG. 4 is a diagram showing experimental results on a relationship between a ratio (LO / H) of a depression depth LO formed on the surface of molten iron by oxygen gas and a bath depth H of molten iron and a dephosphorization rate.

[Explanation of symbols]

1 converter, 2 top blowing lance, 3 bottom blowing tuyere, 4 decarburizing slag, 5 hot metal or molten steel,
6 dephosphorization slag, 7 scrap, 9 lance,
10 main hole type nozzles, 11 sub hole type nozzles.

Claims (3)

[Claims] 1. A refining apparatus that supplies oxygen from a top-blowing lance and stirs a steel bath with a gas, and has a stirring energy density E (kW / ton) of 1 to 3 and a hot metal temperature when dephosphorization refining is stopped. In the dephosphorization method under the conditions of 1250 to 1450 ° C. and the carbon concentration in the hot metal of 2.5 to 3.5%, the grain size is 3 mm on the steel bath surface vertically downward from the center of the upper blowing lance.
The following carbonaceous materials are blown together with nitrogen gas, and oxygen is supplied to another position on the steel bath surface at an angle of 14 to 20 degrees from the vertically downward direction toward the furnace wall, and the carbonaceous material amount W (ton / Hr) Is 0.2 to 0.6 as W / F with respect to the oxygen amount F (Nm ³ / Hr)
A hot metal dephosphorization method having excellent scrap dissolving ability, characterized by: 2. The ratio between the depth LN of the depression formed on the surface of the molten iron by nitrogen gas and the bath depth H of the molten iron is LN according to claim 1.
/ H is set to 0.65 to 0.85, and at the same time, the ratio of another dent depth LO formed on the molten iron surface by oxygen gas to the bath depth H of molten iron is set to 0.15 to 0.55. A hot metal dephosphorization method having excellent scrap dissolving ability, characterized by: 3. A method of tilting the furnace to discharge the generated dephosphorization slag (step 2) subsequent to the hot metal dephosphorization method (step 1) according to claim 1 or 2, wherein the furnace is erected upright and oxygen is supplied from an upper blowing lance. To decarburize (step 3), to discharge only the molten steel without discharging the decarburized slag generated during decarburization (step 4), and to leave the decarburized slag in the furnace as the next step. A hot metal dephosphorization method having high productivity and excellent scrap dissolving ability, characterized in that the step of receiving hot metal of charge (step 5) is continuously and repeatedly performed.