JP2000001714A - Top-blown lance for refining molten metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain the spitting under high speed blowing condition by specifying the relation of angles formed between (z) axis and the projected lines of the nozzle axis to a (yz) plane and a (xz) plane, in the (xyz) orthogonal coordinate system defined so that the center axis of a lance having three or more of nozzles arranged at the same interval on the same circumference is regarded as the (z) axis and the outlet position of the nozzle is regarded as the (x) axis. SOLUTION: In the plan figure (a) of the six-hole lance 1, the projection figure (b) to the (xz) plane of the B-B cross section of the figure (a) and the projection figure (c) to the (xz) plane of the C-C cross section of the figure (a), the small diameter nozzle 3 is set at the center. In the (xyz) orthogonal coordinate system defined so that the lance center axis is regarded as the (z) axis and the outlet position of the nozzle is regarded as the (x) axis, the nozzles 2, in which the angle α formed between the (z) axis and the projected line of the nozzle axis to the (yz) plane corresponding to the twist of the nozzle and the angle β formed between the (z) axis and the projected line of the nozzle axis to the (xz) plane corresponding to the inclination in the outside direction of the nozzle, satisfy 0<tanα/tanβ<2.75, are arranged at the same interval around the same circumference in the symmetry with respect to the lance center axis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a top blowing lance used for blowing a refining gas to a molten metal in a steelmaking converter, for example.

[0002]

2. Description of the Related Art In recent years, the predominant role of a converter has been only decarburization due to the spread of hot metal pretreatment facilities such as Si removal and P removal. For this reason, in a steelmaking plant having these facilities, less slag blowing with little added auxiliary material is often performed.

[0003] In order to improve the productivity in the steelmaking process, it is an issue how to shorten the converter decarburization process for all molten steel. That is, it is important to increase the acid supply rate and shorten the blowing time.

[0004] As described above, in today's popular slag blowing, the problem at high speed blowing is spitting rather than slag forming.

An increase in the amount of spitting causes a decrease in yield due to an increase in dust generation, a reduction in equipment capacity due to dust accumulation in ducts, equipment damage, and a hindrance to operation due to sticking of metal to the furnace opening.

[0006] In order to reduce this spitting,
It is effective to make the lance porous, which can disperse the energy when the oxygen gas jet collides with the bath surface, and a porous lance is generally used in the current steelmaking converter.

[0007] A porous lance is one in which three or more nozzles are arranged at equal intervals on the same circumference, and is usually inclined so that the extension of each nozzle axis intersects at one point on the center axis of the lance. ing.

In a porous lance, as the number of nozzles increases, the effect of dispersing the collision energy of the jet increases, which is advantageous in reducing spitting. In the current converter, a 4 to 6 hole porous lance is used. However, if further high-speed blowing is required in the future, it is desired to make the lance more porous.

[0009] However, there is naturally a limit to the increase in the number of nozzles in a porous lance. That is, it has been pointed out that if the number of nozzles is too large, cavities (dents in the bath surface due to jet collision) corresponding to the nozzles overlap, which promotes spitting.

As means for solving this problem, Japanese Patent Application Laid-Open No.
In the publication No. 0-165313, the diameter D of the cavity
And the overlap ratio δ (= d / D), which is the ratio of the distance d between two cavities on a straight line connecting the centers of adjacent cavities, is used as an index to increase the nozzle inclination angle θ. Methods have been proposed to reduce tee overlap.

From the geometrical viewpoint, it is necessary to increase θ as the number of nozzles increases. In this case, however, the decarbonation efficiency (reaction efficiency between top-blown oxygen and carbon in molten steel) decreases. Extension of blowing time and T. during slag. Fe (Total F
e, that is, the total iron content), and the rate of wear of the furnace wall refractories increases due to an increase in the secondary combustion rate. In other words, although increasing the θ is effective in reducing the overlapping of the cavities and reducing spitting, it cannot be said to be an effective means for improving the productivity of the steelmaking process, which is the original purpose.

If the number of nozzles is too large, the flow rate of oxygen gas at the nozzle outlet decreases, and the scattered granular iron enters the nozzles, causing nozzle clogging and lance melting.

As a method of reducing spitting without increasing the number of nozzles, Japanese Patent Application Laid-Open No. 8-269530 discloses a method in which a plurality of sub-ejection holes are provided on the inner surface of the outlet of a main ejection hole.
A method of reducing spitting by smoothing the jet flow velocity distribution is disclosed.

The inventors of the present invention have confirmed that the smoothing of the jet flow distribution is effective for reducing spitting, as described later. However, the method disclosed in Japanese Patent Application Laid-Open No.
There is a problem that it is necessary to increase the number of oxygen flow paths in the lance, and the manufacturing cost of the lance increases because the tip shape of the lance becomes complicated.

[0015]

SUMMARY OF THE INVENTION An object of the present invention is to provide an upper blowing lance for refining molten metal which can suppress spitting under high-speed blowing conditions.

[0016]

The present inventors have studied lances of various shapes for the purpose of reducing spitting, and as a result,
The following findings were obtained.

(A) The flow velocity distribution or dynamic pressure distribution (proportional to the square of the flow velocity) when the jetted jet collides with the steel bath surface becomes maximum on the central axis of the nozzle. There is a positive correlation with the amount of occurrence of ting.

(B) It is effective for reducing spitting that the flow velocity distribution when the jet collides with the steel bath surface is as smooth as possible.

(C) FIG. 1 is a schematic view showing the tip of a porous lance. FIG. 1 (a) shows a conventional lance, and FIG. 1 (b) shows a twisted lance according to the present invention. Reference numeral 1 denotes a lance, and 2 denotes a nozzle. In the case of FIG. 3A, the central axis of each nozzle intersects at one point on the central axis of the lance, but in the case of FIG. 3B, the directions of the nozzles are mutually twisted.

In order to obtain a smooth flow velocity distribution, as shown in FIG. 1 (b), the nozzles should be arranged so that the ejection directions of the nozzles are in a mutually twisted positional relationship.

(D) However, if the cavities of the steel bath surface formed by the nozzles interfere with each other, spitting increases. Therefore, the range in which the cavities of the steel bath surface do not interfere with each other, that is, the size of the cavity of the steel bath surface and the ignition point Must be smoothed without changing the position. Under these constraints,
In order to increase the torsion of the nozzle, it is necessary to increase the twist of the nozzle at the tip of the lance and to reduce the inclination angle of the nozzle in the outward direction. As a result, jets approach each other, and cavities interfere with each other on the steel bath surface, and spitting increases. Therefore,
An appropriate relationship must be maintained between nozzle twist and nozzle tilt.

The gist of the present invention based on the above findings is as follows.

In an upper blowing lance for metal refining having three or more nozzles arranged at equal intervals on the same circumference, the center axis of the lance is set on the z-axis, and the outlet position of the nozzle is set on the x-axis. In the xyz rectangular coordinate system, when angles formed by the projection of the nozzle axis on the yz plane and the xz plane with the z axis are α and β, respectively, α and β satisfy the following expression (1). Lance for refining molten metal.

0 <tanα / tanβ <2.75 (1)

[0025]

FIG. 2 is a schematic view showing an example of a six-hole lance at the tip of an upper blowing lance according to the present invention, wherein FIG. 2 (a) is a plan view and FIG. ) Is a projection view of the BB section on the yz plane, and FIG. 2C is a projection view of the CC section on the xz plane of FIG. In the figure, the same parts as those in FIG. 1 are represented by the same reference numerals. In FIG. 2, reference numeral 3 denotes a small-diameter nozzle disposed at the center.

In FIG. 2, a description will be given using an xyz rectangular coordinate system in which the lance center axis is on the z-axis and the exit position of the nozzle is on the x-axis. The lance 1 has y corresponding to the twist of the nozzle.
An angle α (hereinafter, referred to as a projection) of the nozzle axis on the z plane and the z axis
A nozzle 2 having a nozzle swivel angle) and an angle β (hereinafter referred to as a nozzle tilt angle) between the projection of the nozzle axis on the xz plane corresponding to the outward tilt of the nozzle and the z axis.
Are symmetrically arranged around the lance axis at equal intervals.

When a normal porous lance where the nozzle axis intersects at one point on the z-axis (for example, disclosed in Japanese Patent Application Laid-Open No. 60-165313) is applied to the angle shown in FIG.
And β corresponds to the angle of inclination of the nozzle in a normal lance.

FIG. 3 is a schematic diagram showing the geometric positional relationship between the nozzle 2 and the corresponding fire point 5 when the lance of the present invention is used in a molten metal refining furnace. In the figure, nozzle 1
Only the main part is shown. As shown in the figure, the angle between the projection of the perpendicular drawn from the center of the fire point (the position where the extension of the nozzle axis intersects the molten metal bath surface 4) to the z-axis and the x-axis and the x-axis is defined as the degree of twist δ. Δ, α, β, lance-bath surface distance H ₀ , distance D between the nozzle exit position and the lance center axis
(See FIG. 2) and the relationship of equation (2) is obtained. tan δ = H ₀ tan α / (H ₀ tan β + D) (2).

Assuming that D is sufficiently smaller than H ₀ in equation (2), δ is approximately given by equation (3). δ = tan ^-1 (tan α / tan β) (3).

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

The present inventors have investigated the effect of the nozzle twist degree δ on the droplet scattering speed by a water model experiment.

FIG. 4 is a schematic diagram showing a water model experiment apparatus at a scale of 1/10. Reference numeral 6 denotes a scattered droplet, and reference numeral 7 denotes a water absorbing paper for measurement. In the lance 1 shown in the figure, six holes lances A to F shown in Table 1 were prepared, and an experiment was performed for each.

[0033]

[Table 1]

The lance A in Table 1 is a lance corresponding to the conventional type, in which the center axis of each nozzle intersects at one point on the z-axis, and α = 0 ° β = 20 °.

On the other hand, lances B, C, D, E, and F are lances in which the directions of the respective nozzles according to the present invention are in a twisted relationship with each other. Constant at 98 mm, and the torsion degree δ in equation (3) is 10
Α, β are determined so as to be °, 30 °, 60 °, 70 °, and 90 °.

In FIG. 4, the distance between the lance 1 and the water surface 4 was set to 270 mm, and compressed air was blown upward from the lance 1 at a flow rate of 1000 Nl / min for a certain period of time. Meanwhile, water surface 4
The water-absorbing paper 7 was attached 800 mm above the sample, and the scattering speed of the droplets 6 was calculated from the weight change before and after that. The droplet 6 assumes spitting in a converter.

Under the same conditions, the flow velocity distribution of the jet on a plane corresponding to the water surface was measured by a dynamic pressure distribution by a pitot tube.

FIG. 5 shows the droplet scattering speed (corresponding to the amount of spitting) of various lances in the water model experiment, and the degree of twist was 0 °.
It is the graph which indexed and made the value of the lance A of 1 into 1 and compared.

As can be seen from FIG.
The amounts of spitting of the lances B to E at the angles of 30 °, 30 °, and 60 ° were smaller than those of the lance A, and were stable about 0.4 to 0.5 times. On the other hand, in the lances having δ of 70 ° and 90 °, the spitting amount was larger than that of the conventional lance, and the amount was about 1.2 times and 1.5 times.

6 to 8 are graphs showing the dynamic pressure distribution of the jet in the radial direction from the center axis of the conventional lance having a twist degree δ of 0 ° and the 6-hole lances having 30 ° and 70 °. 6 to 8, the azimuth at which the dynamic pressure takes the maximum value when viewed from the center of the lance and the azimuth corresponding to the boundary with the adjacent nozzle, which is shifted by 30 ° therefrom (the azimuth at which the dynamic pressure becomes the smallest).
Only shown.

As shown in FIG. 6, the maximum value of the dynamic pressure in the conventional lance was about twice as large as the peak value in the azimuth where the dynamic pressure was the smallest.

On the other hand, as shown in FIG. 7, in a lance having a degree of twist of 30 °, the maximum value of the dynamic pressure is 1.3 times the peak value of the azimuth where the dynamic pressure is smallest. Met.

Also, as shown in FIG.
At the lance of 0 °, there was no clear difference in the dynamic pressure distribution for each direction, and the maximum value of the dynamic pressure was found at a position closer to the lance central axis than the conventional lance A.

From the above results, δ is larger than 0 ° and 70
If it is less than 0 °, the dynamic pressure distribution becomes smoother and the droplet scattering speed decreases as a result. However, if it is 70 ° or more, coalescence due to mutual interference between jets proceeds, and conversely, the droplet scattering It turned out to increase the speed.

Next, as an example, the lance of the present invention is blown at 270 ton / ch at an acid feed rate of 60,000 Nm ³ / hr in a converter having an inner diameter of 7 m. Describe how to determine.

As will be described in the following embodiments, if the nozzle twist degree δ obtained from the equation (3) is 70 ° or more, spitting increases. This is because interference coalescence between jets is strengthened and the effect of smoothing the dynamic pressure distribution is reduced. Therefore, the degree of twist δ is determined to be less than 70 °. That is, the relationship between δ, α, and β is 0 ° <δ = tan ⁻¹
(Tan α / tan β) <70 °, that is, 0 <tan α /
tan β <2.75.

Next, the distance R between the geometric center of the fire point and the center axis of the lance will be described. As is clear from FIG. 3, the smaller R is, the more the jet enters the bath surface at an angle close to the vertical, and as a result, scatters at an angle close to the vertical direction. Problematic spitting increases.

On the other hand, although the spitting decreases as R increases, the blowing time increases due to a decrease in the decarbonation efficiency and the T.C. Problems such as an increase in Fe and an increase in the rate of refractory erosion due to an increase in the secondary combustion rate of CO gas occur.

Thus, in an actual converter, the distance R between the center of the fire point and the center axis of the lance is 500 mm or more and 15 mm or more.
It is desirable that it is not more than 00 mm.

Next, the distance between the lance and the liquid surface describes H _0. If H ₀ is too small, lance melting and thermal deformation due to molten steel scattering are likely to occur, and the lance life will be shortened.

On the other hand, if H ₀ is too large, the spread of the jet becomes large, causing problems of secondary combustion of CO gas and wear of refractories as in the case where the nozzle inclination angle is too large.

Thus, in an actual converter, it is desirable that H ₀ is not less than 2200 mm and not more than 3000 mm.

In the lance of the present invention, the number of nozzles is three or more. When the number of nozzles is 2 or less, the symmetry of the reaction in the converter is lost. Although the upper limit is not particularly defined, it is preferable to set the upper limit to 10 or less, because if the number of nozzles is too large, the structure of the tip of the lance becomes complicated, and the momentum of the jet per nozzle becomes too small.

In the lance of the present invention, in order to prevent the adhesion of granular iron to the central portion of the lance, a small-hole nozzle (FIG. 2) which generates a weak jet which hardly interferes with jets from other nozzles. Reference numeral 3) can be arranged at the center of the lance.

The lance of the present invention is preferably used for a steelmaking process using a top-bottom blow converter, but is not limited thereto, and a steelmaking process using only a top-blowing lance, and other AODs
It is applicable to any metal smelting process that supplies smelting gas from a top blowing lance such as a furnace or a copper smelting furnace.

[0056]

EXAMPLE In a top-bottom blowing converter with a molten steel amount of 270 ton / ch, low carbon steel was melted using the top blowing lance of the present invention, and the amount of spitting loss was investigated.

[0057] blowing is a Resusuragu blowing using all dephosphorization pig iron (slag amount of molten steel ton per 30~35kg), top-blown oxygen flow rate 55000Nm ³ / hr, bottom-blown gas is CO ₂ 2000Nm ³ / hr, The lance height was constant at about 2.7 m. The end point [C] is about 0.05
%.

The lance is a conventional porous lance where the center axis of each nozzle intersects at one point on the center axis of the lance (Comparative Example 1,
2, 3) and a lance (Comparative Example 4 and Invention Examples 1 to 3) in which the directions of the nozzles are mutually twisted, the twist degree δ of the nozzle in the latter is 10 °, 30 °.
°, 50 °, and 70 °.

The lance of Comparative Example 2 was an 8-hole lance having the same total nozzle cross-sectional area as the 6-hole lance of Comparative Example 1, and β was set to 15 ° which was the same as that of Comparative Example 1.

The lance of Comparative Example 3 was an 8-hole lance having the same total nozzle cross-sectional area as the 6-hole lance of Comparative Example 1, and β was set to 20 ° so that adjacent cavities did not overlap.

In Comparative Example 3 and Example having the same number of holes and the same nozzle diameter as Comparative Example 1, the distance R from the center of the geometrical fire point and the lance center axis position on the bath surface was determined. Α and β were determined to be the same as

Further, in all the lances, a nozzle having a diameter of 20 mm was arranged at the center of the lance in order to prevent the adhesion of granular iron to the center of the lance.

Table 2 shows the spitting loss during the operation using the lances of the present invention and comparative examples, and the T.T. The Fe concentration and the total Fe loss are shown in comparison. These values are the average values when each lance is used for 10 to 20 ch. Spitting loss, T. in slag Fe and the total Fe loss were expressed in terms of% by weight based on Comparative Example 1.

[0064]

[Table 2]

First, lances of Comparative Examples 1, 2, and 3 having a nozzle at δ = 0 ° will be described.

Comparative Example 2 is a lance in which β is set to 15 ° as in Comparative Example 1 and the number of nozzles is increased to eight. In this lance, the spitting loss is large because the overlap of the fire points corresponding to the nozzles is large, and the T.C. Fe was also slightly higher.

Comparative Example 3 is an eight-hole lance similarly to Comparative Example 2, except that β is increased to 20 ° in order to avoid overlapping of flash points. In this lance, since there is no overlap of the fire points, the effect of the porosity is directly reflected and the spitting loss is reduced. However, at the same time, the decarboxylation efficiency also decreases, so that T.C. Fe concentration increases,
The total iron loss was not much different from Comparative Example 1.

Next, lances with α> 0 ° (Comparative Example 4,
Examples 1, 2, 3) will be compared. In the lances of Examples 1, 2, and 3 in which the degree of twist δ is less than 70 °, the spitting loss is reduced by 0.45 to 0.48% with respect to the reference value, and the T.S. Fe is also ±
The value was almost the same as 0.5%, and the total iron loss was greatly reduced.

On the other hand, the twist degree δ of Comparative Example 4 was 70
° lance in the slag. Fe decreased by 1.0%, indicating improvement in decarbonation efficiency, but spitting loss increased by 1.22%.

This is, as seen in the water model experiment,
When the nozzle twist degree δ is less than 70 °, the dynamic pressure distribution becomes smoother and spitting decreases, but when it exceeds 70 °, coalescence due to mutual interference between jets proceeds rapidly, and conversely spitting. It is considered that this would increase the

That is, it has been found that the twisting degree δ of the lance needs to be less than 70 ° in order to reduce the spitting loss.

From the above results, it has been found that the lance of the present invention is an optimal lance in terms of reduction of spitting loss, reduction of iron loss to slag, and suppression of refractory erosion.

[0073]

EFFECT OF THE INVENTION In the refining process in which the refining gas is blown onto the molten metal bath surface, the use of the lance of the present invention significantly reduces spitting without reducing the reaction efficiency between the refining gas and the molten metal. can do.

As a result, it is possible to improve the refining yield and to avoid operational troubles such as sticking of metal at the furnace mouth, thereby improving productivity.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a tip portion of a porous lance, and FIG.
FIG. 3B shows a conventional lance, and FIG. 3B shows a twisted lance according to the present invention.

FIG. 2 is a schematic view showing an example of a 6-hole lance at the tip of the upper blowing lance of the present invention, wherein FIG. 2 (a) is a plan view and FIG. 2 (b) is a cross-sectional view taken along the line BB of FIG. FIG. 3C is a projection view on the yz plane, and FIG. 3C is a projection view on the xz plane of the C-C cross section in FIG.

FIG. 3 is a schematic diagram showing a geometrical positional relationship between a nozzle of a lance of the present invention and a corresponding fire point.

FIG. 4 is a schematic diagram showing a water model experiment device.

FIG. 5 is a graph comparing the droplet scattering speeds (spitting amounts) of various lances in a water model experiment.

FIG. 6 is a graph showing a dynamic pressure distribution of a conventional lance having a twist degree δ of 0 °.

FIG. 7 is a graph showing a radial dynamic pressure distribution of a lance having a degree of twist δ of 30 °.

FIG. 8 is a graph showing a dynamic pressure distribution in a radial direction of a lance having a torsion degree δ of 70 °.

[Explanation of symbols]

1: Lance 2: Nozzle 3: Small-diameter nozzle 4: Bath surface 5: Fire point 6: Droplet 7: Water-absorbing paper α: Nozzle swivel angle β: Nozzle inclination angle δ: Twist degree D: Distance between nozzle outlet and lance center H ₀ : Distance between lance and bath surface R: Distance between center of fire point on bath surface and center axis position of lance

Claims (2)

[Claims] 1. An upper blowing lance for metal refining having three or more nozzles arranged at equal intervals on the same circumference,
In an xyz orthogonal coordinate system in which the lance center axis is set on the z-axis and the exit position of the nozzle is on the x-axis, the angles of the projection of the nozzle axis on the yz plane and the xz plane with the z axis are α and β, respectively. Wherein α and β satisfy the following formula (1). 0 <tanα / tan β <2.75 (1) (2)