JPH0873915A - Method for dephosphorizing and desulfurizing molten iron - Google Patents

Abstract

PURPOSE: To provide an effective dephosphorizing and desulfurizing method of molten iron which can progress the desulfurization during dephosphorizing without bringing about the lowering of scrap consumption, related to the dephos phorizing treatment of the molten iron by using top-blowing gaseous oxygen. CONSTITUTION: In a refining apparatus by supplying the oxygen from a top- blowing lance and gas-stirring the molten steel, the ratio L/Lo of the recessed depth L (mm) on the molten iron surface by the gas spouted from the top- blowing lance and the molten iron depth Lo (mm) is made to be 0.3-0.7, the oxygen supplying rate (Nm<3> /min.ton) is made to be 0.3-0.9 and the stirring energy density (kW/ton) is made to be 1.5-4, and further, the ratio C/O of lime consumption C (kg/ton) and the oxygen consumption 0 (Nm<3> /ton) is made to be 1.5-3.5 and the ratio CF/C of fluorspar consumption CF (kg/ton) and the lime consumption C is made to be 0.05-0.3. Further, the lime or the mixed material of the lime and the fluorspar is supplied from the top-blowing lance or a stirring gas blowing hole.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for dephosphorization and desulfurization refining of hot metal with a small temperature drop.

[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) Method of pre-dephosphorization by injecting flux for dephosphorization (iron oxide, quick lime, etc.) to hot metal in tope car, (2) Injecting flux for dephosphorization to hot metal in ladle Alternatively, a method of performing preliminary dephosphorization by spraying or (3) a method of performing dephosphorization on one side and decarburization on the other side by using two converters (for example, Japanese Patent Laid-Open No. 63- 195210) is used.

However, the above methods (1) and (2) use slag having a low (T.Fe) and a high (CaO / SiO ₂ ), and therefore has an advantage that the desulfurization reaction proceeds simultaneously with the dephosphorization. However, since iron oxide represented by iron ore and scale powder is used as an oxidizer, the temperature decreases during processing, and the scrap consumption in the converter, which is the next process, decreases, resulting in a molten steel production amount. There is a problem of reduction. When oxygen gas is used instead of iron oxide in this method, if the oxygen gas is injected, agitation becomes excessive (T.
Fe) becomes extremely low and dephosphorization does not proceed. In addition, in the case of simply spraying from above, the slag (TF
There is a problem that desulfurization deteriorates because e) becomes high.

On the other hand, in the above method (3), although oxygen gas is used as the oxidizer and scrap can be used for temperature control during the dephosphorization treatment, the scrap consumption does not decrease, but Since a converter is used, there is a problem that the flow rate of top-blown oxygen gas is high, (T.Fe) is high, and desulfurization does not proceed during dephosphorization. By the way, a converter is a typical refining device that supplies oxygen from an upper blowing lance and stirs a steel bath with gas. As hot metal dephosphorization treatment using a converter, iron and steel, Vol. 76, No. 11, 1817
Techniques described on pages ff and iron and steel, Vol. 76, No. 11,
Although the techniques described on and after page 1801 are known, the oxygen supply rate F is as large as 1 or more, and the stirring energy density E is also 1 or more, but the ratio L / L of the depression depth of the hot metal surface to the bath depth is L / L. _There is no description about ₀ . Further, the ratio C / O of the amount of quick lime used to the amount of oxygen used is smaller than 1.5, and desulfurization during dephosphorization hardly progresses.

On the other hand, hot metal dephosphorization using a tope car or a hot metal ladle is not carried out by only blowing oxygen gas,
Be sure to inject iron oxide powder. In this case, as described in Iron and Steel, Vol. 76, No. 11, p. 1801, the oxygen supply rate F is smaller than 1,
Although the stirring energy density E is 1 or more, the ratio C / O of the amount of quick lime used and the amount of oxygen used is larger than 1.5, so desulfurization proceeds during the dephosphorization.

That is, in the prior art, when the iron oxide powder is not injected and only oxygen gas top blowing is performed, the oxygen supply rate F increases, so the ratio C of the amount of quick lime used to the amount of oxygen used C There is a problem that / O becomes small and desulfurization does not proceed during dephosphorization. Further, by simply lowering the oxygen supply rate F by this method, the desulfurization reaction during dephosphorization does not proceed. Further, the method of injecting iron oxide powder using a tope car or a hot metal ladle has a problem that the temperature decrease during processing is remarkable because the reaction between iron oxide and carbon is an endothermic reaction, and the scrap consumption is significantly reduced. .

[0007]

SUMMARY OF THE INVENTION In the prior art, when oxygen gas is used as the oxidant in the upper blowing in order to prevent the reduction of the scrap consumption, the (T.Fe) is high and the desulfurization occurs during the dephosphorization. It tries to solve the problem of not progressing.

[0008]

The inventors of the present invention have found that in order to control (T.Fe) low when oxygen gas is blown upward,
We have found that it is important to consider the collision energy of the top-blown gas on the steel bath surface. The present invention has been made based on this finding, and the gist thereof is as follows.

(1) In a refining apparatus that supplies oxygen from a top blowing lance and stirs a steel bath with gas, the depth L (mm) of the hot metal surface depression and the bath depth due to the kinetic energy of the gas discharged from the top blowing lance. The ratio L / L ₀ of L ₀ (mm) is 0.3 or more and 0.7 or less, and the oxygen supply rate F (Nm ³ / (m
in • ton)) is 0.3 or more and 0.9 or less, and the stirring energy density E (kW / ton) is 1.5 or more and 4 or less, and the quick lime use amount C (kg / ton) and oxygen use amount O
The ratio C / O of (Nm ³ / ton) is 1.5 or more and 3.5 or less, and the amount fluorite used CF (kg / ton) is CF / C of 0.
The method for dephosphorization and desulfurization refining of hot metal is characterized in that the content is from 05 to 0.3.

(2) Dephosphorization and desulfurization of hot metal according to item (1)
In the smelting method, quicklime powder or quicklime powder and fluorspar powder
Of the mixture with a top-blown lance or a top-blown gas.
Stirring gas injection hole installed in the projection plane of the point surface onto the furnace bottom
Desulfurization and refining refining method of hot metal characterized by being supplied from
Law. Here, the stirring energy density E (kW / ton)
Is the bottom blowing gas flow rate Q (Nm ³/ S), temperature T (K),
Molten steel amount W (ton), static pressure P (P
a), atmospheric pressure P₀If it is (Pa), it is expressed by the following equation.

E = {371 / (1000 · W)} × Q ×
T × {ln (P / P ₀ ) +0.06 (1-298 /
T)} Further, the cavity depth L (m) due to the top-blown gas is the nozzle diameter d (mm), the distance h (m) between the lance and the steel bath surface.
m) and the number of nozzles n, it is calculated by the following equation. L = {L _h × exp (−0.78 × h / L _h )} / 10
0 L _h = 63 × (F × W × 60 / (n × d)) ^2/3 Further, the fire point surface due to the upper blowing gas is a conical shape in which the jet from the lance nozzle has a spread of 12 degrees on one side. Is calculated as the cut portion by the hot metal surface of this cone.

[0012]

The present invention can be applied when any one of a tope car, a hot metal ladle and a converter is used as a reaction vessel. When it is carried out in a converter type container, the upper blowing lance has an L / L ₀ within an appropriate range, and therefore, it is necessary to use a lance having a smaller number of nozzles and a smaller nozzle diameter than a normal converter decarburizing lance. . For example, if it is carried out in a 350 ton converter,
With three holes, a proper nozzle diameter is about 20 to 30 mm. Moreover, the top blowing lance when it is carried out in a tope car type or a hot metal ladle type container has a lower lance height, so it has a larger porosity or a larger diameter than the converter type, for example, it is carried out in a 350 ton tope car. In case of 4 holes 2
Nozzle diameter of 0 to 30 mm is 40 to 50 mm with 2 holes
The appropriate nozzle diameter is the proper structure.

FIG. 1 shows the relationship between L / L ₀ and the dephosphorization rate and the desulfurization rate. When L / L ₀ is smaller than 0.3, (T.Fe) becomes high. Therefore, the desulfurization rate deteriorates,
Than 0.7. In the case of the threshold, (T.Fe) becomes low, so that the dephosphorization rate is deteriorated. Therefore, the proper range of L / L ₀ is 0.3 or more and 0.7 or less. Even if L / L ₀ is in the proper range, the oxygen supply rate is 0.3 (Nm ³ / (m
in.ton)), the oxygen supply becomes insufficient and (T.Fe) becomes low, so the dephosphorization rate decreases,
When it is larger than 0.9 (Nm ³ / (min · ton)), the oxygen supply is excessive and (T.Fe) becomes too high, so that the desulfurization rate decreases.

Further, the stirring energy density is 1.5 (k
If it is lower than W / ton), the reaction rate is slow, and both the dephosphorization rate and the desulfurization rate are poor, and if it is higher than 4 (kW / ton), in the hot metal of (T.Fe) of the slag. The dephosphorization rate decreases because the rate of reduction by carbon increases (T.Fe) decreases. In addition to this, when the ratio C / O of the amount of quicklime used C and the amount of oxygen used O is smaller than 1.5 (kg / Nm ³ ), the amount of quicklime as a dephosphorization / desulfurization agent is less than that of slag. Basicity ((Ca
O) / (SiO ₂ )) is too low, resulting in poor dephosphorization rate and desulfurization rate. When C / O is more than 3.5 (kg / Nm ³ ), a large amount of unsintered lime is produced. However, the refining cost is not realistic.

Fluorite has the effect of improving the fluidity of slag and increasing the reaction rate, but in the present invention, the amount of quicklime used C
If the ratio (CF / C) of (kg / ton) to CF (kg / ton) used is less than 0.05, the reaction rate decreases, and if greater than 0.3, it is a refractory material. The problem of great wear occurred. Furthermore, in the present invention,
Dephosphorization and desulfurization by supplying quick lime powder or a mixture of quick lime powder and fluorspar powder from a top blowing lance or a stirring gas blowing hole installed in the projection surface of the fire point surface on the furnace bottom by top blowing gas Both will be more efficient. this is,
If L / L ₀ is within an appropriate range, a high-temperature hot spot of 2000 ° C. or higher is generated at the hot spot where the oxygen jet collides with the hot metal surface, and the powder is supplied to the hot spot to rapidly melt the molten slag. Is realized.

In the present invention, the amount of oxygen accumulated in the slag as (T.Fe) is small, so the oxygen unit consumption is small. Therefore, even if all the oxygen is supplied as oxygen gas, the temperature rises to only about 1400 ° C. No adverse effect on dephosphorization. Moreover, the temperature can be lowered to about 1350 ° C. by using an appropriate amount of scrap in the dephosphorization refining furnace.

[0017]

EXAMPLE Example 1 was carried out using a 350 ton top and bottom blowing converter. Nitrogen gas or oxygen gas and tuyere cooling gas were used as the bottom blowing gas, and oxygen gas was blown from the top blowing lance. The basic unit of quick lime is 15 to 20 kg / ton, and the quick lumps of lump calcium from the top together with fluorite are 0.07 in F / C.
It was input in the range of 0.27. The post-treatment temperature was set to 1350 to 1450 ° C. by adding scrap. As the lance, a 2-hole lance having a nozzle with a diameter of 24 mm was mainly used, and the lance height was variously changed, and in some experiments, the nozzle diameter was also changed to adjust L / L ₀ .

Experiment numbers 1 to 11 shown in Table 1 are examples of the present invention. As a result of the treatment for about 15 to 20 minutes, high values of both the dephosphorization rate and the desulfurization rate were obtained. On the other hand, as shown in Experiment Nos. 12 to 19, L / L ₀ , oxygen supply rate F, stirring energy density E, ratio C / O of the amount of quicklime used C and oxygen used O, and the amount of quicklime used C and fluorite Usage C
When either of the ratios CF / C of F is out of the range of the present invention,
Either the dephosphorization rate or the desulfurization rate is greatly reduced.

[0019]

[Table 1]

Further, the following experiment was carried out using a 350 ton toped car. The stirring gas was nitrogen gas blown from the injection lance, and oxygen gas was blown from the top blowing lance. In this case, the quicklime basic unit is 15 to 20k.
It was g / ton, and powdered quicklime was blown together with fluorspar from the injection lance. The temperature after treatment was set to 1350 to 1450 ° C. by introducing small scrap.
The lance used was a 4-hole lance with a nozzle having a diameter of 24 mm. Adjusting the lance height to L / L ₀ of 0.5, oxygen supply rate F of 0.5 Nm ³ / (min · ton), stirring energy density E of 2.1 kW / ton, and using quicklime The ratio C / O (kg / Nm ³ ) of the amount C and the amount O of oxygen used was 2, and the ratio CF / C of the amount C of quicklime used and the amount CF of fluorite used was 0.15. As a result, the dephosphorization rate was 84%. , Desulfurization rate is 53%
The same result as in Example 1 was obtained.

Example 2 is a result obtained by using a 350 ton top and bottom blowing converter. Nitrogen gas was used as the bottom blowing gas, and oxygen gas was blown from the top blowing lance. Quicklime basic unit is 1
5 to 20 kg / ton, and the post-treatment temperature is 1350 to
It was 1450 ° C. The lance has 2 nozzles with a diameter of 24 mm.
The hole lance was mainly used. In addition, L / L was used for all experiments.
₀ is 0.5 and the oxygen supply rate F is 0.6 Nm ³ / (min
・ Ton), stirring energy density E is 2.5 kW / to
Then, the ratio C of quicklime use C and oxygen use C /
O (kg / Nm ³ ) was set to 2.

Experiment Nos. 20 to 22 shown in Table 2 are the cases in which quick lime powder, or quick lime powder and fluorspar powder were mixed and sprayed to the top-blown oxygen gas jet. In addition, experiment numbers 23-2
No. 5 is a case where quick lime powder, or quick lime powder and fluorite powder were mixed and sprayed to the bottom blowing nitrogen gas jet. Here, the stirring gas blowing hole is a case where the stirring gas blowing hole is installed in the projection surface of the recessed portion (cavity) of the hot metal surface onto the furnace bottom by the top blowing gas. Specifically, the fire point is 0.2 to 0.5 from the center of the furnace cross section.
Since it spreads at a radius of m, the bottom blowing nozzle for supplying the powder was installed within a radius of 0.2 to 0.5 m from the center of the furnace bottom. On the other hand, Experiment No. 26 is a case in which quick lime powder and fluorspar powder were mixed and sprayed into a nitrogen gas jet for agitation, but tuyere was provided on the furnace wall to blow the gas onto the furnace bottom of the cavity. This is the case where the stirring gas blowing hole is not installed in the projection plane.
Specifically, as described above, the fire point projection plane is 0.
Since it is within a radius of 2 to 0.5 m, the powder-supplying bottom-blowing nozzle in this case was installed at a position separated by 0.6 m or more from the furnace bottom center. From this, it can be seen that both the dephosphorization rate and the desulfurization rate are higher than those of Experiment Nos. 1 to 10 shown in Example 1. However, Experiment No. 26, in which the stirring gas injection holes were not installed in the projection surface of the cavity onto the furnace bottom by the top-blown gas, had only the same dephosphorization rate and desulfurization rate as Experiment Nos. 1-10. I understand.

[0023]

[Table 2]

[0024]

EFFECTS OF THE INVENTION By using the present invention, it is possible to perform hot metal refining at a low (T.Fe) level using top-blown oxygen gas, and to desulfurize during dephosphorization without reducing scrap consumption. It has become possible to proceed.

[Brief description of drawings]

FIG. 1 is a diagram showing the effect of L / L _{0 on} the dephosphorization rate and the desulfurization rate.

Claims (2)

[Claims] 1. In a refining device for supplying oxygen from a top blowing lance and stirring a steel bath with gas, the depth L (mm) and the bath depth L of the hot metal surface are caused by the kinetic energy of the gas discharged from the top blowing lance. The ratio L / L ₀ of ₀ (mm) is set to 0.
3 or more and 0.7 or less, oxygen supply rate F (Nm ³ / (min
・ Ton)) is 0.3 or more and 0.9 or less, and stirring energy density E (kW / ton) is 1.5 or more and 4 or less, and then quicklime use amount C (kg / ton) and oxygen use amount O
The ratio C / O of (Nm ³ / ton) is 1.5 or more and 3.5 or less, and the amount fluorite used CF (kg / ton) is CF / C of 0.
The method for dephosphorization and desulfurization refining of hot metal is characterized in that the content is from 05 to 0.3. 2. The hot metal dephosphorization and desulfurization refining method according to claim 1, wherein quick lime powder or a mixture of quick lime powder and fluorspar powder is top-blown lance or a projection surface of a fire point surface onto the furnace bottom by top-blown gas. A method for dephosphorization and desulfurization refining of hot metal, which is characterized in that the gas is supplied from a stirring gas blowing hole installed inside.