EP2470678B1 - Device for degassing molten steel with an improved discharge nozzle - Google Patents

Description

The present invention relates to a device for degassing a molten steel with an improved spout. In particular, the present invention relates to a particular form of spout for avoiding dead water regions in a steel ladle. The present invention further relates to a method of degassing the liquid steel with the improved spout.

The process for degassing liquid steel is an RH process (Ruhrstahl-Heraeus process). In the RH process, the liquid steel is conveyed from a ladle in a riser to an evacuation vessel. A conveying gas, in particular argon, is introduced into the riser above the steel bath level. The injected into the riser through several nozzles argon stream breaks down into a variety of argon bubbles that rise in the immediate vicinity of the wall. The conveyance of the liquid steel is made possible by the volume increase by argon in the riser and by the pressure difference between the external air pressure and the negative pressure in the evacuation vessel. The argon bubbles entrain the melt and ensure a uniform melt circulation. The partial pressure is lowered at the same time and the decarburization reaction is accelerated. The steel sucked into the evacuation vessel is sprayed. This results in a strong increase in surface area and good degassing of the liquid steel.

Oxygen, which is simultaneously introduced throughout the treatment period and replenished, among other things, from the slag, leads to the formation of carbon monoxide (CO). CO gas in the vacuum vessel, resulting in the desired decarburization is reached. The fine decarburization can be optimized to the lowest possible values by additionally injected oxygen. A high rotational speed of the melt and thus an increase in the flow of carrier gas and an increase in the diameter of the bowl of the vacuum system lead to a faster decarburization process.

Out DE 19511640 C1 is a trunk for a degassing vessel with a refractory lining and arranged therein a gas purging device with multiple channels known. The channels are distributed over the circumference of the trunk and extend, based on the central longitudinal axis of the trunk, through the refractory lining in the radial direction. The channels can be connected to at least one gas supply line on the outside.

The channels are circumferentially arranged to form a nearly continuous gas curtain along the inner wall of the trunk in close succession. A steady stream of liquid steel is reached into the vacuum vessel. The distributed over the entire circumference, preferably fine-bubble gas supply allows a particularly fine distribution of the treatment gas at the same time greatly increased reaction volume between the treatment gas and molten steel. In this way, a higher and faster decarburization performance can be achieved, so that smaller amounts of reduction media are necessary.

Out JP 6299227 A For example, there is known a method of producing very low carbon steel with a degassing apparatus, wherein the inlet trunk is positioned so that the distance between the axis of the inlet trunk and the axis of the metal bath is at least 10% of the inner diameter of the metal bath.

Out JP 1198418 A a device and a method for the vacuum degassing of molten steel is known, wherein both introduced into the inlet and outlet spout gas and alternately the function of the trunk can be changed.

Out JP 57200514 A A method for degassing molten steel is known, wherein the degassing effect is improved by degassing in an RH vacuum apparatus in which an inert gas is injected into a steel melting vessel from the bottom.

Out JP 3271315 A is a RH vacuum decarburization of stainless steel known, the degassing and decarburization is achieved in a short time and the loss of chromium is reduced. The result is achieved by using low silicon steel and repeated degassing and decarburization with an RH vacuum vessel.

Out JP 2173204 A For example, a vacuum vessel for an RH degassing apparatus is known wherein an ultrasonic oscillator is installed at a contact point with the liquid steel in the vacuum vessel to destroy bubbles generated by the gas injection and to improve the reaction surface on the phase reaction.

Out JP 11158536 A For example, a method of smelting very low carbon steel is known wherein inert gas is injected through the inlet tube under the added aluminum into the vessel at the spout for circulation after decarburization.

Out JP 3107412 A discloses a method of producing very low carbon steel, wherein argon is injected at the same time during decarburization into both the inlet and outlet tubes.

Furthermore, from the JP 05214426 another degassing known, in which at least one bore for a propellant gas line is introduced laterally in a riser and in an outlet pipe.

In the JP 01275715 a degassing device is described, in whose outlet pipe gas supply openings are provided, by means of which an inert gas in the Molten steel can be blown in order to prevent the ingress of slag into the molten steel.

It has been shown and proved by numerical simulations that form in the steel ladle of an RH plant local flow areas, so-called dead water areas, which mix relatively late, after about two minutes with the rest of the melt.

The devices and methods known in the prior art have the disadvantage that dead water areas in the steel ladle form by which the homogenization time of the melt is increased.

A dead water area is usually formed between the spout and the refractory wall of the ladle. Due to the downward stream of melt from the spout little material from the immediate vicinity is sucked in around the spout. As a result, the overall carbon concentration remains high due to the delayed homogenization. The dead water area mixes poorly with the rest of the melt because the average flow rate is low. Because of the low mass, momentum and energy exchange between the high carbon concentration dead water zone and the remainder of the low carbon concentration melt, the ladle melt often has to be recirculated until the desired final carbon content is achieved. Since the ladle melt has to circulate frequently, the treatment time is high.

The invention has for its object to provide an apparatus for degassing a molten steel with an improved spout, which reduces the formation of dead water areas.

The invention has for its object to provide an improved and reliable method for degassing and / or decarburization of molten steel, wherein the formation of dead water areas is reduced.

The object of the present invention is achieved by a device comprising at least one degassing vessel, a Stahlgießpfanne, an inlet trunk and a gas purging device arranged therein and a spout. The spout has at least one bore at the lower edge in the radial direction, relative to the central longitudinal axis of the spout, for sucking a carbonaceous melt from a dead water zone between the spout and the socket delivery and directing it into the downflow of the spout.

The device is preferably an RH plant.

As a result of a self-adjusting Venturi effect, the carbonaceous melt is drawn in from the dead water zone between the spout and the pan feed and directed into the downflow of the spout.

The size and number of holes at the bottom of the spout are dependent on the RH method and must be adjusted accordingly. The main parameters are the geometry and immersion depth of the inlet and outlet probes and the negative pressure in the RH vacuum vessel.

It must be prevented that not too much melt from outside is transported into the spout and thus possibly sucking up-floating slag from the free surface of the steel ladle with.

The inventive device, in particular the new shape of the spout, the local dead water area is reduced in size. The treatment and circulation time of the melt can be advantageously shortened. This leads to the advantageous reduction of argon consumption and further cost reduction. The productivity of the RH plant is increased.

A preferred embodiment of the invention is an outlet spout having a plurality of bores within a radius of 360 °. The outlet trunk particularly preferably has several holes within a radius of 180 ° in the direction of the refractory wall the ladle. Due to the inventive design of the spout, the local dead water areas are effectively reduced.

The size and number of holes depends on the geometry and immersion depth of the spout and the vacuum in the evacuation vessel.

Another preferred embodiment of the invention is a spout, wherein the holes have a diameter of 10 mm to 50 mm, preferably 25 mm to 35 mm. With these diameters for the holes good results are achieved in the Totwasserreduzierung.

A further preferred embodiment of the invention is a spout whose immersion depth in the molten steel of the ladle is from 300 mm to 1200 mm, preferably 400 mm to 1000 mm. In this range for the immersion depth good results are achieved in the Totwasserreduzierung.

A further preferred embodiment of the invention is a spout, wherein one or more holes 50 mm to 900 mm, preferably 100 mm to 700 mm, are arranged above the lower edge of the spout. As a result, the vertical distance between the holes and the ladle slag is as large as possible. It is prevented that ladle slag is sucked into the spout.

A further preferred embodiment of the invention is a spout, wherein holes in a row of holes or in several superposed rows of holes are on the spout. Preference is given to one or two superimposed rows of holes on the outlet trunk.

1. a) ein Fördergas, insbesondere Argon, über dem Stahlbadspiegel in einen Einlaufrüssel eingeleitet wird,
2. b) flüssiger Stahl aus einer Gießpfanne in den Einlaufrüssel gesogen wird
3. c) flüssiger Stahl aus dem Einlaufrüssel in ein darüber befindliches Evakuierungsgefäß befördert wird,
4. d) flüssiger Stahl entgast und entkohlt wird und
5. e) flüssiger Stahl über einen Auslaufrüssel in die Gießpfanne befördert wird,

wobei der Auslaufrüssel an der Unterkante in radialer Richtung, bezogen auf die Mittenlängsachse des Auslaufrüssels, mindestens eine Bohrung aufweist, durch welche eine kohlenstoffhaltige Schmelze aus einem Totwassergebiet zwischen dem Auslaufrüssel und der Pfannenzustellung angesaugt und in den Abwärtsstrom des Auslaufrüssels geleiten wird.The object of the present invention is achieved by a method for degassing a molten steel, wherein

1. a) a conveying gas, in particular argon, above the Stahlbadspiegel in a Inflow trunk is initiated
2. b) sucking liquid steel from a ladle into the inlet spout
3. c) transporting liquid steel from the inlet trunk into an evacuation vessel above it,
4. d) degassing and decarburizing liquid steel, and
5. e) transporting liquid steel through a spout into the ladle,

wherein the spout at the lower edge in the radial direction, relative to the central longitudinal axis of the spout, has at least one bore through which a carbonaceous melt is sucked from a Totwassergebiet between the spout and the Pfannenzustellung and directed in the downward flow of the spout.

The object of the present invention is further achieved by the use of the spout according to the invention in a RH plant for reducing local dead water areas in a ladle. By using the spout according to the invention local dead water areas are effectively reduced.

The invention will be explained in more detail with reference to a drawing. In the drawing, an embodiment of the invention is shown.

• Fig. 1 einen Querschnitt durch eine RH-Anlage nach dem Stand der Technik ohne Bohrungen im Auslaufrüssel und mit einem lokalen Totwassergebiet zwischen dem Auslaufrüssel und der Feuerfestwand der Gießpfanne,
• Fig. 2 einen Querschnitt durch eine erfindungsgemäße RH-Anlage mit Bohrungen im Auslaufrüssel und mit reduziertem lokalen Totwassergebiet zwischen dem Auslaufrüssel und der Feuerfestwand der Gießpfanne,
• Fig. 3 einen Querschnitt durch eine erfindungsgemäße RH-Anlage im Ruhezustand und
• Fig. 4 einen Querschnitt durch eine erfindungsgemäße RH-Anlage im Betriebszustand.

Show it:

• Fig. 1 a cross section through a prior art RH plant without holes in the spout and with a local Totwassergebiet between the spout and the refractory wall of the ladle,
• Fig. 2 a cross section through an inventive RH plant with holes in the spout and reduced local Totwassergebiet between the spout and the refractory wall of the ladle,
• Fig. 3 a cross section through an inventive RH plant at rest and
• Fig. 4 a cross section through an RH plant according to the invention in the operating state.

In the Fig. 1 shown RH plant I has a steel cistern 3 with a volume of 200 t. The immersion depth of the spout 1 and the inlet trunk 4 was 600 mm. The process time was 85 s. The following process steps were carried out in the RH plant. Argon 5 was introduced over the mirror of the steel bath 10 into the inlet trunk 4. The liquid steel 10 was sucked from the ladle 3 into the inlet trunk 4. The liquid steel 10 was conveyed from the inlet trunk 4 into the evacuation vessel 2 located above. The liquid steel 10 was degassed in the evacuation vessel 2. The liquid steel 10 was conveyed via the spout 1 back into the ladle 3. A local Totwassergebiet 9 formed between the spout 4 and the refractory wall 8 of the ladle 3 from. Due to the downwardly directed melt stream from the spout 4 little molten steel 10 was sucked in from the immediate vicinity of the spout 1 ago. As a result, the carbon concentration in the dead water area 9 remained high at a high level due to the delayed homogenization. The dead water area 9 mixed poorly with the remainder of the melt 10 because the average flow rate was low. The duration of the proceedings was high.

Fig. 2 shows a cross section through an inventive RH plant I with holes 7 in the spout 1 and with greatly reduced local Totwassergebiet 9 between the spout 1 and refractory wall 8 of the ladle 3. The procedure was as in the example in Fig. 1 with the following differences. The spout 1 had several holes 7 in the radial direction, based on the central longitudinal axis 6 of the spout 1 on the side towards the refractory wall 8 of the ladle 3. The holes 7 were 150 mm above the lower edge of the spout 1 is arranged. The immersion _{depth of the spout} H _snorkel was 400 mm. Molten steel 10 was sucked in from the immediate vicinity around the spout 1 ago. The homogenization in the molten steel 10 was faster. Consequently, the carbon concentration in the dead water region 9 dropped. The process time was thereby greatly reduced.

FIGS. 3 and 4 illustrate the following example. First, the geometry of an RH plant in Table 1 and the physical quantities in Table 2 are explained. Table 1 Geometry of the RH plant Measurement unit H _melt Distance from the lower edge of the degassing vessel to the gas inlet 1350 meter D ₁ Diameter of the degassing vessel 2200 meter D _2a Outer diameter of the inlet spout and the spout 1294 meter D _2i Inner diameter of the inlet spout and the spout 0650 meter D ₃ Diameter of the ladle 3396 meter H _snorkel Immersion depth of the spout 0.6 meter h _nozzel Distance of the hole from the lower edge of the spout 0275 meter Physical sizes Measurement unit P ₀ Pressure in the ladle at rest 100000 Pa P _RH Pressure in the degassing vessel 200 Pa r _ho Density of the melt 6930 - 7050 Kg / m ³ T Temperature of the melt 1600 ° C

The negative pressure in the RH vessel is gradually reduced, for example, from initially 250 mbar down to 2 mbar within about 6 min. The pressure of 2 mbar is then also the lowest pressure in the RH vessel, in particular directly above the melt surface in the RH vessel.

The cycle time in an RH plant is about 10 minutes to 50 minutes. The homogenization time in the melt at a spout without holes about 90 s to 480 s. The homogenization time in the melt is approximately 85 s to 456 s for a spout with holes. This means a reduction in the cycle time of about 5%.

The number n of holes is preferably 3 to 9. The number is preferably odd, since central hole should lie on the axis, therefore in the narrowest gap between Pfannenausmauerung and proboscis.

The angle α between the holes depends on the number n of holes. For up to 3 holes, α = 10 ° to 20 °. This results in a targeted extraction of the dead water from the area between Pfannenzustellung and trunk wall. For up to 9 holes, α = 7.5 ° - 11.25 °. This then corresponds to a covered area of 60 ° to 90 °.

The preferred bore diameter is 10 mm to 50 mm.

With a standard immersion _{depth of} the outlet _spout of H _snorkel = 600 m, the _{row of holes} should be positioned no more than 300 mm above the exit _{opening of the spout} . The row of holes in the vertical direction should not be closer than 300 mm below the melt surface in the steel ladle, otherwise there is a risk that slag will be sucked in from the surface.

For immersion depths greater than 600 mm, alternatively, two or more rows of holes can be arranged one above the other, see Table 2.

Also advantageous is a single vertical row of holes in the space between the trunk outer wall and refractory lining of the pan. In this way, the whole Dead space material, which collects mainly here, very specifically sucked into the trunk.

Furthermore, the holes in the spout can also be arranged between the two trunks, as it also collects in this area calmed melting material.

Characteristic parameters with variation of the immersion depth of the spout on the example of the trunk inner diameter D _i = 650 mm and the negative pressure in the RH vessel 2 mbar are shown in Table 3. Table 3 Immersion depth ^E) Number ^A) Distance ^V) Number ^B) Angle ^W) Bore diameter ^D) H _snorkel in mm m H in mm N α in ° D in mm 400 1 100 3 10 30 600 1 300 5 15 30 800 2 200 3 10 30 500 5 15 100 3 10 1000 2 400 5 10 30 700 5 15 ^E) Immersion depth of the spout
^A) Number of superimposed rows of holes at the spout
^V) Vertical distance between the trunk lower edge and the rows of holes
^B) Number of holes
^W) Angle between the holes
^D) bore diameter

LIST OF REFERENCE NUMBERS

I

RH degasser

1

Discontinued trunk

2

Evacuation vessel / vacuum vessel

3

Ladle / ladle / crucible

4

Inlet trunk / riser

5

Gas purifier / inert gas / argon

6

central longitudinal axis

7

drilling

8th

Refractory wall

9

dead water

10

molten steel

P ₀

Pressure in the ladle at rest

P _RH

Pressure in the degassing vessel

H _melt

Distance from the lower edge of the degassing vessel to the gas inlet

D ₁

Diameter of the degassing vessel

D _2a

Outer diameter of the inlet spout and the spout

D _2i

Inner diameter of the inlet spout and the spout

D ₃

Diameter of the ladle

rho

Density of the melt

H _snorkel

Immersion depth of the spout

h _nozzel

Distance of the hole from the lower edge of the spout

H

Distance from the lower edge of the degassing vessel and melting mirror

Z ₁

Rise of the melt

Az

Distance from the lower edge of the degassing vessel and gas inlet

T

Temperature of the melt

Claims (13)

1. Device for degassing a steel melt, comprising an evacuation vessel (2), a casting ladle (3), an inlet nozzle (4) with a gas flushing device (5) arranged therein and an outlet nozzle (1), wherein the outlet nozzle (1) has at the lower edge in radial direction referred to the centre longitudinal axis (6) of the outlet nozzle (1) at least one bore (7) so as to suck up melt with carbon content from a deadwater region (9) between the outlet nozzle (1) and the ladle infeed and to conduct it into the downward flow of the outlet nozzle (1).
2. Device according to claim 1, wherein the outlet nozzle (1) has a plurality of bores (7).
3. Device according to claim 1 or 2, wherein the outlet nozzle (1) has a plurality of bores (7) in the surrounding area of 360°.
4. Device according to any one of claims 1 to 3, wherein the outlet nozzle (1) has a plurality of bores (7) in the surrounding area of 180° in the direction of the refractory wall (9) of the casting ladle (3).
5. Device according to any one of claims 1 to 4, wherein the bores (7) have a diameter of 10 millimetres to 50 millimetres.
6. Device according to claim 5, wherein the bores (7) have a diameter of 25 millimetres to 35 millimetres.
7. Device according to any one of claims 1 to 6, wherein the immersion depth of the outlet nozzle (7) in the steel melt (10) in the casting ladle (3) is from 300 millimetres to 1200 millimetres.
8. Device according to claim 7, wherein the immersion depth of the outlet nozzle (7) in the steel melt (10) in the casting ladle (3) is from 400 millimetres to 1000 millimetres.
9. Device according to any one of claims 1 to 8, wherein one or more bores (7) are arranged 50 millimetres to 900 millimetres above the lower edge of the outlet nozzle (1).
10. Device according to claim 9, wherein one or more bores (7) are arranged 100 millimetres to 700 millimetres above the lower edge of the outlet nozzle (1).
11. Device according to any one of claims 1 to 10, wherein bores (7) are disposed in a bore row or in a plurality of bore rows, which lie one above the other, at the outlet nozzle (1).
12. Method for degassing a steel melt, wherein

    a) a conveying gas, particularly argon, is introduced above the surface of the steel bath in an inlet nozzle (4),

    b) liquid steel (10) is conducted from a casting ladle (3) into the inlet nozzle (4),

    c) liquid steel (10) is conveyed from the inlet nozzle (4) into an evacuation vessel (2) disposed thereabove,

    d) liquid steel (10) is degassed and

    e) liquid steel (10) is conveyed by way of an outlet nozzle (1) into the casting ladle (3), wherein the outlet nozzle (1) has at the lower edge in radial direction referred to the centre longitudinal axis (6) of the outlet nozzle (1) at least one bore (7) through which a melt with carbon content is sucked up from a deadwater region (9) between the outlet nozzle (1) and the ladle infeed and conducted into the downward flow of the outlet nozzle (1).
13. Use of an outlet nozzle according to any one of claims 1 to 11 in an RH plant for reduction of local deadwater regions (9) in a casting ladle (3).

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