JP2011001585A - Method for dephosphorization of molten iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a means for improving slag formation rate and dephosphorization rate of flux in a method for dephosphorization of molten iron using a converter, by increasing interference rate of a flux powder and oxygen jet.SOLUTION: A lance having three or more concyclic pores (peripheral pores) located at equal intervals and a center pore is used for top-blowing an oxygen-containing gas from the peripheral pores and top-blowing a CaO-containing powder and an inert gas from the center pore. For each of the peripheral pores, α and β, which are defined as angles formed by Z-axis and projections of the peripheral pore on the yz plane and the xz plane in an xyz rectangular coordinate system wherein the z-axis is a lance central axis and the x-axis is a pore outlet position of the peripheral pore, satisfy the relation: 0<tanα/tanβ<2.75, and the pressure of the inert gas emitted from the center pore (i.e. the pressure when the CaO-containing powder is not top-blown) is smaller than the pressure of the oxygen-containing gas emitted from the peripheral pore.

Description

  The present invention relates to a hot metal dephosphorization method in which a refining flux powder and a gas are sprayed onto a hot metal bath surface in a converter.

In recent years, the demand for low phosphorus steel has increased, and it is customary to perform dephosphorization by hot metal pretreatment prior to decarburization and refining by a converter. The purpose of this technique is to perform dephosphorization efficiently from a thermodynamic advantage by performing dephosphorization reaction with hot metal at a lower temperature than decarburization refining. However, it is necessary to lower the melting point of the slag under the condition of low temperature and keep its molten state well. In addition to the flux for refining, specifically dephosphorizing flux such as massive quicklime, as a melting point depressant for slag A method of adding an alkali metal or alkaline earth metal fluoride or chloride such as fluorite (the main component is CaF ₂ ) has been adopted.

However, in order to reduce the total cost of refining, it is necessary to reduce the amount of slag generated and effectively use the slag. For effective use of slag, it is not preferable to use a fluorine source such as CaF ₂ for environmental protection. Therefore, it is necessary to minimize the use of CaF ₂ as much as possible.

That is, there is a need for a method for promoting the dephosphorization reaction by hatching CaO without using fluorite in hot metal dephosphorization.
One of the prior arts proposed to achieve this object is a method using an alumina-containing material instead of fluorite (Patent Document 1).

However, since the hatching promoting effect of alumina was not as strong as that of fluorite, there was a problem that the hatching rate and dephosphorization rate of massive quicklime varied.
Then, the method of making powder and using it for hot metal dephosphorization was examined so that fluxes, such as quick lime, may hatch more easily.

  However, when added from a scrap chute or a furnace hopper, the flux powder scatters to the outside of the hot metal bath without being captured or captured on the hot metal bath surface, which significantly reduces the flux yield and the dephosphorization rate. have done.

Japanese Patent No. 3321536 Japanese Patent No. 3396522 JP 60-165313 A

  As a result of extensive studies, the powder powder was sprayed from the center hole of the lance together with the inert gas onto the hot metal bath surface in the top-bottom blowing converter, and at equal intervals around the center hole on the same circumference. The present inventors have conceived a method in which oxygen gas is blown from a plurality of holes arranged to perform hot metal dephosphorization.

In this method, most of the flux powder can be landed and captured on the hot metal bath surface, so that the scattering loss can be greatly reduced.
However, this method has the following problems.

That is, if CaO-based flux powder is sprayed on the collision part (fire point) between the oxygen gas-containing jet and hot metal, the high-temperature (Fe _t O) generated at the fire point and CaO powder contact and react, very high CaO · Fe _t O melt the dephosphorization capacity is generated.

In that case, almost all of the CaO-based flux powder blown up rapidly hatched, and as a result, the ratio between the actual basicity (CaO mass concentration in slag (excluding un-enriched CaO content) and SiO ₂ mass concentration). That is, a slag having a high (% CaO) / (% SiO ₂ )) is formed, and a high dephosphorization rate is obtained.

  However, as described above, when CaO-based flux powder is sprayed together with an inert gas from the center hole of the lance and oxygen gas is sprayed from a plurality of holes arranged at equal intervals around the center hole, CaO It was clarified that the actual basicity does not increase due to the fact that the flux powder does not interfere with the oxygen jet so much that it cannot be hatched at the fire point.

Since slag having high actual basicity is not formed as described above, the dephosphorization rate is also low in this method.
Against this background, the present invention states that "flux powder is sprayed together with an inert gas from the center hole of the lance onto the hot metal bath surface in the top-bottom blowing converter, and on the same circumference around the center hole. In the `` method of spraying hot metal dephosphorization by blowing oxygen gas from a plurality of holes arranged at equal intervals '', means for improving the hatching rate and dephosphorization rate of the flux by increasing the interference rate between the flux powder and the oxygen jet The purpose is to provide.

  In order to solve the above-mentioned problem, an upper blow lance for molten metal refining (hereinafter referred to as “twist lance”) that can smooth the flow velocity distribution of the jet without complicating the shape of the tip of the lance disclosed in Patent Document 2 by the present applicant. The lance structure is also referred to as a “twisted structure”).

  That is, in order to cause the jet of flux powder and inert gas ejected from the central hole to interfere with the oxygen jet ejected from a plurality of surrounding holes, three or more holes arranged at equal intervals on the same circumference We thought that it was effective to twist the peripheral hole, which is a hole.

  FIG. 1 shows a lance having a twist described in Patent Document 2. Reference numeral 1 in FIG. 1 is a lance, and 2 is a nozzle based on a peripheral hole. In the torsion lance 1, the directions of the nozzles 2 are twisted relative to each other.

  Patent Document 2 investigates the dynamic pressure distribution of the jet in the radial direction from the center axis of the lance in the six-hole torsion lance 1, the direction in which the dynamic pressure is the maximum when viewed from the center of the lance, and the adjoining by 30 ° Torsional lances such that the peak dynamic pressure value in each azimuth is the close value (the dynamic pressure fluctuation in the circumferential direction is small) in the azimuth corresponding to the boundary with the nozzle 2 (the azimuth with the smallest dynamic pressure). 1 (specifies the range of the twist degree δ) is disclosed.

  However, Patent Document 2 does not disclose any interference between a jet from the central hole and jets from a plurality of surrounding holes. Therefore, the present inventors have studied this point, and twisting a peripheral hole, which is a plurality of holes around the central hole, that is, three or more holes arranged at equal intervals on the same circumference, from the central hole. If the jet consisting of the ejected flux powder and inert gas interferes with the oxygen jet ejected from the surrounding holes (peripheral holes), the interference rate between the flux powder and the oxygen jet is increased, and the flux It came to the idea that hatching rate and dephosphorization rate could be improved. Based on this idea, the present inventors have further studied and completed the present invention as follows.

(1) In the hot metal dephosphorization method using a converter, oxygen is contained from the peripheral hole using a lance having a peripheral hole and a central hole that are three or more holes arranged at equal intervals on the same circumference. When the gas is blown up and the CaO-containing powder and the inert gas are blown up from the center hole, for each of the peripheral holes, the lance center axis is on the z axis and the outlet position of the peripheral hole is on the x axis. In the defined xyz orthogonal coordinate system, α and β satisfy the following formula (1), where α and β are angles formed by the projection of the hole axis of the peripheral hole on the yz plane and the xz plane, respectively, with the z axis. And the dephosphorization of hot metal, wherein the pressure of the inert gas ejected from the central hole (pressure when the CaO-containing powder is not blown up) is smaller than the pressure of the oxygen-containing gas ejected from the peripheral hole Method.
0 <tan α / tan β <2.75 (1)

  In the hot metal dephosphorization process in which the oxygen-containing gas and the refining flux powder are sprayed onto the hot metal bath surface, the use of the lance of the present invention increases the landing and capture efficiency of the CaO-based flux powder on the hot metal bath surface. The hatching rate at the point increases, the actual basicity of the slag improves, and the phosphorus concentration in the hot metal after the treatment can be reduced.

FIG. 1A is a schematic diagram showing a tip portion of a normal porous lance, and FIG. 1B is a schematic diagram showing a tip portion of a torsion lance disclosed in Patent Document 2. As shown in FIG. It is a schematic diagram which shows the example of 6 hole lances of the upper blowing lance tip part which has a twist lance structure concerning the present invention, the figure (a) is a top view and the figure (b) is B- of the figure (a). FIG. 7C is a projection view of the B section on the yz plane, and FIG. 10C is a projection view of the CC section of FIG. For ease of explanation, only the nozzle A in FIG. 1A is shown in FIG. It is a schematic diagram which shows the geometrical positional relationship of one nozzle and the corresponding fire point in the case of using the top blowing lance for molten metal refining which concerns on this invention in a molten metal refining furnace.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the accompanying drawings.
1. FIG. 2 is a schematic view showing an example of a tip portion of an upper blowing lance 1 for molten metal refining according to the present invention, where FIG. 2 (a) is a plan view and FIG. 2 (b) is the same drawing (a). FIG. 4C is a projection view of the BB plane of FIG. 4B on the yz plane, and FIG. 4C is a projection view of the CC section of FIG. For ease of explanation, only the nozzle A in FIG. 1A is shown in FIG. That is, in FIG. 2, the lance center axis is the z-axis, and the xyz orthogonal coordinate system in which the outlet position of the nozzle A, which is three or more holes (peripheral holes) arranged at equal intervals on the same circumference, is on the x-axis. Will be described.

  The lance 1 corresponds to an angle α (hereinafter referred to as “nozzle turning angle”) formed by the projection of the nozzle axis onto the yz plane and the z axis, which corresponds to the twist of the nozzle, and the inclination in the outer direction of the nozzle. Six nozzles 2 (of which one hole on the x-axis is referred to as “nozzle A”) having an angle β (hereinafter referred to as “nozzle inclination angle”) formed by projection of the nozzle axis onto the xz plane and the z-axis. Are arranged on the axis object at equal intervals around the lance axis.

  When a normal porous lance in which the nozzle axis intersects at one point on the z-axis (such as the lance disclosed in Patent Document 3) is applied to the angle shown in the figure, α is 0 °. Yes, β corresponds to the angle of the nozzle in a normal lance (ie a lance that does not have a twisted structure).

FIG. 3 is a schematic diagram showing the geometric positional relationship between the nozzle 2 and the corresponding fire point 5 when the torsion lance is used in a molten metal refining furnace.
Only one nozzle is shown in the figure. As shown in the figure, the angle formed by the projection on the xy plane of the perpendicular drawn from the center of the hot spot 5 (the position where the extension of the nozzle axis intersects the molten metal bath surface 4) to the z axis and the x axis is a twist degree. δ, α, β, the distance H ₀ between the torsion lance 1 and the bath surface 4, and the distance D (see FIG. 2) between the hole outlet position of the nozzle 2 and the lance central axis, The relationship is obtained.
tan δ = H ₀ tan α / (H ₀ tan β + D) (2)

Here, in Equation (2), if D is sufficiently smaller than H ₀ , the relationship of Equation (3) is approximately obtained for δ.
δ = tan ⁻¹ (tan α / tan β) (3)

The distance R between the center of the hot spot 5 on the bath surface and the lance center axis position is given by the equation (4).
R = H ₀ · (tan ² α + tan ² β) ^1/2 (4)

Regarding the torsion lance 1, Patent Document 2 discloses Formula (5) as an appropriate range for reducing spitting.
0 <tan α / tan β <2.75 (5)

2. Test using torsion lance About 250 tons of molten iron was charged into the top bottom blowing converter, CaO powder was sprayed together with nitrogen gas from the center hole of the top blowing lance 1 having the above twisted structure to the hot metal bath surface. The hot metal dephosphorization blowing was performed by blowing oxygen gas from the nozzle 2 forming 6 holes arranged at equal intervals around the hole, that is, the peripheral hole, to the hot metal bath surface.

CaO powder was blown up together with nitrogen gas from the center hole of the lance, and oxygen gas was blown up from a plurality of holes (peripheral holes) around the center hole.
As an example of hot metal dephosphorization blowing under the above conditions, nozzle inclination angle, lance height, and diameter of the center hole were examined. The results are shown below.

  As shown in the examples described later, when the twist degree δ of the nozzle 2 obtained by the above equation (3) is 70 ° or more, the swirling flow velocity of the jet becomes too large, and the CaO-based powder is scattered and detached. The proportion that does not contribute to the phosphorus reaction increases. Therefore, when the twist degree δ is less than 70 °, the landing / capturing efficiency of the CaO-based flux powder on the hot metal bath surface 4 is increased, the hatching rate at the hot spot 5 is increased, and the actual basicity of the slag is increased. Improving and reducing the phosphorus concentration in the hot metal after treatment is realized.

Since the suitable twist degree δ is less than 70 °, from the above equation (3), 0 ° <tan ⁻¹ (tan α / tan β) <70 °. Therefore, a preferable relationship between α and β is 0 <tan α / tan β <2.75.

  That is, by setting α and β so as to satisfy the above 0 <tan α / tan β <2.75 for each of the nozzles constituting the torsion lance 1, the jets ejected from the nozzles on the hot metal bath surface 4 Make a swirl flow. Since the CaO-based flux powder is supplied to the center of the swirling flow, the CaO-based flux powder is prevented from scattering outside the furnace, the hatching rate at the hot spot 5 is increased, and the hot metal dephosphorization reaction. Can be efficiently advanced. From the viewpoint of appropriately forming this swirl flow, it is preferable that the variation in tan α / tan β of the entire nozzle is small, and at least in design it is preferable that tan α / tan β be the same for all nozzles. Note that the allowable range of this variation is influenced by the number of nozzles, the flow rate of oxygen supplied from the nozzles, the mass and shape of the CaO-based flux powder, and may be set appropriately in consideration of these.

Here, the distance H ₀ between the torsion lance 1 and the liquid level 4 will be described. If H ₀ is made too small, the lance 1 is likely to be melted or thermally deformed due to hot metal scattering, and the lance life is shortened. On the other hand, if H ₀ is too large, the spread of the jet becomes large, and problems such as secondary combustion of CO gas and refractory wear occur as in the case where the nozzle inclination angle is excessively increased. Further, the landing / supplement rate of CaO powder ejected from the lance center hole to the hot metal bath surface 4 is lowered. Therefore, it is desirable that H ₀ in the hot metal dephosphorization operation is about 2000 to 4000 mm.

  In the lance 1 according to the present invention, the number of nozzles 2 (peripheral holes) excluding the central hole is set to 3 or more. This is because if the number of installations is 2 or less, the symmetry of the reaction in the converter is lost. Although the upper limit of the number of twisted nozzles 2 is not set, if the number of twisted nozzles 2 is excessive, the structure of the tip of the lance 1 becomes complicated, and the momentum of the jet per nozzle 2 becomes excessively small. 10 or less is desirable.

  The diameter of the lance center hole may be appropriately determined so that the pressure of the inert gas ejected from the center hole (in the state where powder is not supplied) does not exceed the pressure of the oxygen gas ejected from a plurality of holes around the center hole. .

  As a result, the diameter of the nozzle 2 (or the breakage of the center hole), which is a plurality of holes (peripheral holes) arranged at equal intervals around the center hole diameter and the periphery, based on the oxygen gas flow rate and the inert gas flow rate. The relationship between the area and the total cross-sectional area of the surrounding holes) is determined.

In addition, what is necessary is just to use the value measured in either of the piping from a valve station exit to a lance for the pressure of each gas.
When the pressure of the inert gas ejected from the central hole is higher, the jet from the central hole is strong, and thus it is difficult to interfere with oxygen jets ejected from a plurality of surrounding holes.

  As a result, not so much (FeO) is generated in the vicinity of the hot metal bath surface 4 on which the CaO-based flux powder has landed, and the CaO-based flux powder remains in the slag without being unhulled. And dephosphorization rate will get worse.

The present invention will be described more specifically with reference to examples.
・ About 250 tons of hot metal (Si concentration: about 0.3% by mass, P concentration: about 0.1% by mass) is charged into the top-bottom blowing converter, and about 1 CaO powder is placed from the center hole of the top blowing lance. It was sprayed on the hot metal bath surface with nitrogen gas 0.2Nm ³ / min / t at a rate of 4-1.8 kg / min / t. In addition, oxygen gas is supplied from 1.6 holes to 6 holes or 5 holes arranged at equal intervals around the center hole (for some lances, these holes are twisted as described above). It sprayed on the hot metal bath surface at 2.1 Nm < ³ > / min / t. Further, N ₂ gas was blown from the bottom blowing tuyere at 0.35 to 0.4 Nm ³ / min / t, and lance height was set to 2.5 to 2.6 m to perform hot metal dephosphorization blowing.

  The lance is a conventional lance without twisting or the direction of each nozzle is twisted relative to each other, the twist δ is 10 ° to 70 ° and has a central hole, and the pressure of the inert gas ejected from the central hole (powder is supplied) The difference between the state of not being carried out and the value being absolute pressure) and the pressure of oxygen gas ejected from 6 or 5 holes around the central hole was changed. In addition, α, β, and δ of 6 holes or 5 holes around the center hole in each lance were the same.

The C concentration in the hot metal after treatment was 3.4 to 3.6 mass%, the temperature in the pan after treatment was 1351 to 1380 ° C., and the charging basicity (the mass concentration ratio of CaO / SiO ₂ ) was 2.6.
The actual basicity of the slag after the treatment (the value obtained by subtracting the unoxidized CaO mass concentration from the CaO mass concentration of the collected slag by the SiO ₂ mass concentration, that is, {(% CaO) − (% f-CaO )} / (% SiO ₂ )) and [P] (phosphorus concentration, unit: mass%) in the hot metal after the treatment.

Table 1 shows the actual basicity of the treated slag during operation using the lances of the present invention and the comparative example and [P] in the treated hot metal.
These values are average values when 10-20 Ch of each lance is used.

  Comprehensive evaluation is effective only when the basicity is 2.4 or more and the [P] after treatment reaches a desired value (0.0020% by mass or less) based on Comparative Example 1 (Table) Middle, “○”).

Regarding the experimental results, first, Comparative Examples 1 and 2 will be described.
When the torsion δ is based on a lance with 0 °, if the torsion δ is increased to 70 °, the whirling flow of the jet becomes too strong and the scattering loss of the CaO-based flux powder increases and the actual basicity decreases. After the treatment, [P] was as high as 0.025 to 0.027% by mass.

  In Comparative Example 3, since the pressure of nitrogen blown up from the center hole was as low as 0.2 MPa even when the twist degree δ was 30 °, landing / supplemental efficiency of CaO powder blown up from the center hole on the hot metal bath surface The basicity was low. For this reason, [P] after processing was as high as 0.028 mass%.

  In Comparative Examples 4 and 5, even when the twist degree δ was set to 30 °, the pressure of nitrogen blown up from the center hole was equal to or higher than the pressure of oxygen gas ejected from the six holes around the center hole. The momentum of the jet erupted from is very large. For this reason, the interference between the jet ejected from the central hole and the oxygen jet ejected from the surrounding six holes was weakened, the hatching rate of the CaO-based flux powder was lowered, and the actual basicity was lowered.

Subsequently, Examples 1 to 4 will be described. When the pressure of nitrogen blown up from the center hole is lower than the pressure of oxygen gas ejected from the six holes around the center hole, the CaO powder ejected from the center hole is adjusted by setting the twist δ of the lance to 10 to 60 °. Is considered to have collided with the hot metal bath surface while contacting and mixing with the oxygen gas jet ejected from the surrounding 6 or 5 holes. For this reason, the high temperature (Fe _t O) generated at the collision part (fire point) of the oxygen gas-containing jet and hot metal contacts and reacts with the CaO powder, so that the CaO · Fe _t O melt with extremely high dephosphorization ability is obtained. A body was produced, and after the treatment, [P] was reduced to 0.017 to 0.019% by mass.

1 Lance 2 Nozzle 3 Center hole 4 Bath surface 5 Fire point α Nozzle turning angle β Nozzle tilt angle δ Twist degree D Nozzle outlet and lance center distance H ₀ Lance and bath surface distance

Claims (1)

In the hot metal dephosphorization method using a converter, the oxygen-containing gas is increased from the peripheral hole by using a lance having a peripheral hole and a central hole which are three or more holes arranged at equal intervals on the same circumference. When blowing and blowing CaO-containing powder and inert gas from the center hole,
For each of the peripheral holes, projection of the hole axis of the peripheral hole onto the yz plane and the xz plane in an xyz orthogonal coordinate system in which the lance center axis is the z axis and the outlet position of the peripheral hole is on the x axis Α and β satisfy the following formula (1), and the pressure of the inert gas ejected from the center hole (when the CaO-containing powder is not blown up) The hot metal dephosphorization method is characterized in that the pressure is smaller than the pressure of the oxygen-containing gas ejected from the peripheral hole.
0 <tan α / tan β <2.75 (1)

Images