EP0305319B1 - Device and method for reducing slag carry-over with a minimal amount of steel remaining in the converter - Google Patents

Abstract

When converters are tapped, steel also runs out with the slag towards the end of the tapping. With a minimal amount of steel remaining in the converter, the proportion of slag also running out must be minimised in order to improve the accuracy of analytical sampling, the degree of purity and the output. The cause of slag also running out is essentially the formation of a vortex and a lowered channel above the tap hole, when the level falls below the critical steel bath level. According to the invention, a depression is therefore created around the tap hole, the depth of the depression being greater than the critical bath height for vortex formation and, to prevent the latter, the depression being provided with weirs, feeds for inert gas and/or coils for generating flows in the steel bath and measuring instruments to detect the slag also running out. The process provides that the depression is uniformly filled until the end of tapping, the stiffness of the slag is increased by means of lime if necessary and/or the melt is perturbed by pulsed introduction of inert gas and/or the vortex flow is perturbed by electromagnetic fields. By means of the novel device and the process, formation of the vortex is very largely prevented and therefore has the advantage of improving the accuracy of analytical sampling, the degree of purity and the output of steel in the tapping of converters. <IMAGE>

Description

The invention relates to a device and a method for reducing the proportion of accompanying slag when tapping converters for steel production.

When refining pig iron to steel in converters, for example by means of the oxygen blowing process, undesirable accompanying elements, e.g. Phosphorus, separated in the slag during casting (tapping) with the best possible effectiveness, the proportion of slag that runs with the steel is kept as low as possible. This increases the accuracy of the analysis, the degree of purity and the output of steel.

The running of slag essentially occurs - at a critical minimum height of the liquid steel above the tap opening - through the formation of a vortex or a channel sink into which slag is drawn. Experience has shown that the critical height is 200 to 300 mm above the tap opening.

A suggestion for increasing the bath depth when pouring the steel out of a converter can be found in AT-258 986.

The described brick converter interior has a converter belly, which is formed from truncated cone-shaped upper and lower converter halves, the base of which is elliptically shaped in each case.

The tap hole is located in the converter belly at the apex of the smallest ellipse arc.

For emptying, the converter is tilted so that the tap hole is at the lowest converter point.

Due to the large converter dimensions, however, an uneconomical large remaining amount remains in the converter when the pouring is stopped at the bath height critical for the running of slag.

From theoretical considerations (Arch. Eisenhüttenwesen 54, 1983, No. 5, pages 187-194) and model tests with simulated pans it is known that the vortex is composed of a central vertebra and a concentric potential flow.

• in der Nähe des Ausgußeinlaufes radial angeordnete mechanische Hindernisse (US-PS 40 79 868),
• in die Wirbelsenke eingetauchter feuerfester Stab (DE-OS 31 26 559),
• Eintauchen eines Rohres in das Bad und kontinuierliches Blasen von Inertgas dicht über dem Ausguß (DE-OS 26 07 070).

Despite the good theoretical description of the vortex formation, it was not possible to provide a prediction for the point in time of the slag running that is necessary for practice. Therefore, only a few general constructive tips for reducing the vertebrae in pans could be recommended:

• mechanical obstacles arranged radially near the pouring spout (US Pat. No. 4,079,868),
• refractory rod immersed in the vertebra (DE-OS 31 26 559),
• Immersion of a tube in the bath and continuous blowing of inert gas close to the spout (DE-OS 26 07 070).

• den Auftrieb der Schlacke durch Verflüssigen mit CaO zu erhöhen,
• den Ausströmwirbel zu behindern,
• die Sogwirkung des Ausströmwirbels zu mindern und
• den Ausströmvorgang vor dem Schlackedurchschlupf zu drosseln bzw. zu unterbrechen.

Dazu werden einige allgemeine Hinweise gegeben wie
"Erhöhung der Mindestüberdeckung über der Ausströmöffnung (Gefäß neigen, günstigere Bodengestaltung mit Schräge oder Vertiefung)" sowie "Gasblasen nahe der Ausströmachse" und "Einflußnahme auf die Zuströmung zur Ausströmachse",
Die Umsetzung in konstruktive Maßnahmen wurde in diesen Fällen nicht spezifiziert.In a later publication on the same subject (Stahl und Eisen 105, 1985, No. 14/15, pages 765 - 769), the purge gas treatment carried out in the center of the spout (analogous to DE-PS 26 39 712) is described as an incomplete method because the stirring effect in the vortex is split.
There is further recommended for pans (bottom of metallurgical vessels):

• increase the buoyancy of the slag by liquefying it with CaO,
• to obstruct the outflow vortex,
• reduce the suction effect of the outflow vortex and
• to restrict or interrupt the outflow process before slag slippage.

Some general information is given such as
"Increasing the minimum coverage above the outflow opening (tilting the vessel, cheaper bottom design with a slope or recess)", "gas bubbles near the outflow axis" and "influencing the inflow to the outflow axis",
The implementation in constructive measures was not specified in these cases.

The representation of simplified ladle models helps to solve the problem of preventing the residual slag from running along from converters, only indirectly, as a further publication (Ironmaking and Steelmaking, 1984, Vol. 11, No. 6, pages 332 - 339) uses the example of converter attempts shows. There it is established that in steel converters the initial flow - responsible for the potential field around the vertebral sink - can result from the converter tilting or oxygen bubbles. Remaining currents before The beginning of tapping is unknown.
For pans, it is recommended to stir electromagnetically or to place radial obstacles on the spout. For converters, gas blowing with argon through porous stones around the spout, which is obviously designed to be exchangeable, brought some advantages in reducing slag flow. In a 300 t converter, argon was injected at 200 l per minute; the amount of slag that came along was 100 kg. Contrary to the publications cited at the beginning, the measures such as "non-centric spouts, floating or fixed disks and balls over the spout and occasional closing of the tap hole" are only allowed to have a minor influence on the problem solution.

Furthermore, it is known from DE-OS 34 41 324 to generate a gas bubble curtain made of inert gas around a ladle tap hole in that a perforated brick that can be used from the inside of the ladle contains highly porous, tubular or annular refractory elements through which gas is blown from the bottom.

Finally, DE-OS 14 33 511 discloses a converter which has a component flanged in front of an opening in the converter wall with a refractory brick funnel and tap hole. This arrangement is intended to serve the same purpose as the bleed hole on conventional converters.

DE-PS 26 39 712 shows a ratio pyrometer for detecting slag running with the cast jet and then swiveling in a tap hole closure.

DE-OS 31 26 559 shows a field coil that detects the cast jet, with which slag can be located in the cast jet. It is also shown that a converter is only pivoted very slightly about its 90-degree tilt position from the start of tapping until the critical bath height (steel and slag) of 600 mm is reached.

The converter should then be rotated continuously in an upright position while immersing and guiding an immersion body via a linkage, with no slag being able to run out from around 73 degrees.

In order to prevent slag from moving through the immersion body, appropriate devices, rods, drives, etc. are necessary, which could only be used with considerable effort in steel mill operation, especially on the converter, since the tilting movement of the converter and the guidance of the immersion body are coordinated have to. The observation of the pouring jet enables the tapping to be terminated when slag is carried along, but on the one hand a considerable amount of slag has already run off, and on the other hand a relatively large amount of liquid steel is still present in the converter.

The invention is therefore based on the object of shifting the running of slag as far as possible to the end of the tapping process without great design effort for immersion bodies, guide rods, etc., when only a small residual amount of steel is present in the converter.

The running of slag is caused by a flow of steel generated due to the tilting movement and the shape of the converter. This gradually forms when the steel runs out through the tap hole.

The above-mentioned object is consequently achieved in that the formation of the biaxial flow, in particular the circulating or vortex flow (flow with a tangential component) in the potential field around the tap hole, is largely delayed by a special design of the surroundings of the tap hole and the amount of residual steel when vortex formation occurs is minimized.

For this purpose, a device according to claim 1 or a method according to claim 15 is provided.

This size has proven to be favorable experimentally, on the one hand to obtain economical tap currents and on the other hand to minimize the amount of residual steel in the converter for a largely slag-free tap.

The trough depth is determined depending on the converter dimensions and the amount of steel or slag as well as the tap hole diameter in accordance with the resulting critical steel bath height at which the vortex formation would start.

Weirs can also be installed in the trough, which further impede the eddy flow. The trough can furthermore have an overlap within the trough in the area of the vertebral sink forming in the converter content, which creates a slag-free zone on the steel bath in the trough. With regard to the introduction of lumpy scrap and pig iron, the overlap should not protrude over the edge of the trough and could form a unit made of refractory mass with the weirs.

The trough can be designed as a recess from the brick lining, as an additional brick lining or as a bulge of the converter jacket with a brick lining.

A supplementary measure to largely prevent flows with a tangential component is the intermittent introduction of inert gas next to the tapping tube. Gas bubbles rise through the melt located above the tapping tube, which interferes with the formation of a potential flow.

The intermittent supply of argon or nitrogen or other gas which is as cheap as possible but inert has three advantages. Compared to a constant gas supply, this process lowers the costs. In addition, the vortex disturbance is intense if there is no quasi-steady state of flow in the converter content. In addition, in contrast to the continuous supply of gas, the slag is prevented from forming an emulsion with the steel and in this way prevents the slag from running in unintentionally. The gas supply can be designed in the form of individual bores with tubes around the tap hole, but also as an annular gap around the tap hole. The annular gap is preferably formed by a sheet metal jacket around the tap hole, which is customarily designed as a perforated brick which is open to the inside of the converter and has a gas connection to the outside. The porous refractory materials usually used do not allow a sufficient impact with an inert gas. Since the tap hole is about ten times more worn than the converter lining, the tap tube and gas duct can be replaced several times as a pre-assembled unit during a converging trip.

Furthermore, the trough itself or the trough with built-in weirs and / or the cover over the tap hole can be replaced as a structural unit. In the ideal form, the trough and its internals, including the tapping tube and gas supply, form an assembly unit.

As a further additional measure, the steel melt can be induced by electromagnetic fields, which are generated by coils embedded in the trough, a flow which either points in the direction of the axis of the tapping tube or acts against an existing tangential component of the flow.
By designing the trough, the stirring effect can be limited to the relevant steel bath volume.

As a further function, the trough serves as a delimited volume filled with liquid steel during which the occurrence of slag with a decreasing steel bath level can be determined using suitable measuring techniques (e.g. resistance measurement, induction measurement).

The measuring devices can be designed to determine the occurrence of slag in the region of the trough or in the region of the tap hole. As soon as these devices detect slag in the region of the trough or the tap hole by means of appropriate measuring methods, the slag can be prevented from entering the pan, for example, by pivoting a stopper into the pouring opening.

A prerequisite for the effect of this device according to the invention is the control of the tilting movement of the converter, through which a uniform filling of the trough with steel is achieved during the entire tapping. Known setpoint indicators can be used to show the trough position that cannot be viewed relative to the converter position for the helmsman.

A further increase in the effectiveness of the device according to the invention for reducing the amount of slag running along can be achieved by stiffening the slag, for example with coarse lime, which only melts through subsequent introduction and thus forms bonding bridges without a metallurgical reaction produce.

Fig. 1

einen Querschnitt eines Konverters mit einer Mulde als Ausbauchung,

Fig. 2

einen Querschnitt eines Konverters mit einer Mulde als zusätzliche Ausmauerung,

Fig. 3

einen Ausschnitt eines Konverters in der Umgebung des Abstichloches mit einer Mulde als Ausnehmung der Ausmauerung.

The schematic representations show three special exemplary embodiments of the device for carrying out the method according to the invention. Show it

Fig. 1

a cross section of a converter with a trough as a bulge,

Fig. 2

a cross section of a converter with a trough as an additional lining,

Fig. 3

a section of a converter in the vicinity of the tap hole with a trough as a recess of the lining.

Fig. 1 shows a cross section through a converter 1 with a trough 21, which is designed as a bulge 5 around the tap hole 7. The trough 21 formed by the bulge 5 of the converter jacket 11 and the lining 41 has a height H which is greater than the critical height for the formation of eddies in the converter content. The cross-sectional area perpendicular to the axis of the tap hole 7 of the trough 21 is approximately 10 to 100 times larger than the cross-sectional area of the tap hole 7. With the converter standing vertically, the tap hole 7 is preferably inclined at an angle α with respect to the horizontal. Weirs 31 are provided in the trough 21 to prevent a rotationally symmetrical flow.

Fig. 2 shows a cross section through a converter 1 with a trough 22, which is designed as a cavity of the special lining 42 around the tap hole 7. The trough 22 formed by the lining 42 has a height H which is greater than the critical height for the vortex formation. The cross-sectional area perpendicular to the axis of the tap hole 7 of the trough 22 is approximately 10 to 100 times larger than the cross-sectional area of the tapping hole 7. Weirs 32 are provided in the trough 22 to prevent a rotationally symmetrical flow.

FIG. 3 shows a section of a converter with a depression 23, which is designed as a recess in the lining 43 around the tap hole 7. The trough 23 formed by the recess has a height H which is greater than the critical height for the vortex formation. The cross-sectional area perpendicular to the axis of the tap hole 7 of the trough 23 is approximately 10 to 100 times larger than the cross-sectional area of the tap hole 7. Weirs 33 are provided in the trough 23 to prevent a rotationally symmetrical flow.

There is a refractory filling compound 45 between the tap hole 8, which is connected to the converter jacket 11, and the tap hole stones 44. In the refractory filling compound 45, inert gas feeds 6 are introduced, which start as individual pipes 6 and form an annular gap in the region below the depression 23 a sheet metal jacket 47 around the tap holes 44 can be executed. The inert gas supply 6 can be guided through the end face 46 of the refractory filling compound 45 or through the tapping tube 8 or through the converter jacket 11.

Claims (19)

1. Device for reducing a portion of slag, which passes through a discharge aperture towards the end of a discharge process of a converter, which is provided with a wall lining, the wall lining of the converter being shaped, at the discharge aperture, to form a trough (21, 22, 23), the depth of which is substantially identical to or greater than the critical height for the formation of a vortex in the converter contents, the projection area of said trough, in the plane vertically relative to the axis of the discharge aperture (7), being at least substantially ten times the cross-sectional area of the discharge aperture, but being substantially smaller than the projection area, formed by the longitudinal and transverse configurations of the converter, in accordance with AT-258 986, and the cross-section of said trough - relative to the axis of the discharge aperture (7) - not being rotationally symmetrical.
2. Device according to claim 1, characterised in that the cross-section of the trough (21, 22, 23) is substantially rectangular.
3. Device according to claim 1 or 2, characterised in that blocking means (31, 32, 33), which interrupt a tangential flow around the discharge aperture (7), are disposed in the trough (21, 22, 23).
4. Device according to one of claims 1 to 3, characterised in that a covering is installed in the trough (21, 22, 23) over the discharge aperture (7).
5. Device according to one of claims 1 to 4, characterised in that the trough (21) is formed by a bulge portion (5) comprising converter casing (11) and wall lining (41).
6. Device according to one of claims 1 to 4, characterised in that the trough (22) is formed by a wall lining (42), which is situated in the interior of the converter.
7. Device according to one of claims 1 to 4, characterised in that the trough (23) is formed by a recess in the wall lining (43) at the discharge aperture.
8. Device according to one of claims 1 to 7, characterised in that at least one tubular gas supply pipe (6), which extends into the lower portion of the trough, is disposed laterally of the discharge aperture.
9. Device according to claim 8, characterised in that at least some cylindrical perforated blocks (44), which are arranged in rows relative to one discharge aperture, are surrounded by a sheet metal tubular casing (47) for the gas supply pipe, which casing is open towards the interior of the converter.
10. Device according to one of claims 1 to 9, characterised in that the perforated blocks (44) and the sheet metal tubular casing (47) form an interchangeable unit.
11. Device according to one of claims 1 to 10, characterised in that at least one portion of the trough (21, 22, 23) is an independent assembly unit.
12. Device according to one of claims 1 to 11, characterised in that the trough (21, 22, 23), the perforated blocks (44) and the sheet metal tubular casing (47) are an independent assembly unit.
13. Device according to one or more of claims 1 to 12, characterised in that coils are installed in the wall lining (41, 42, 43) of the trough (21, 22, 23) to produce electromagnetic fields.
14. Device according to one of claims 1 to 13, characterised in that measuring means are provided in the wall lining (41, 42, 43) at the discharge aperture (7) to determine the entry of slag into the trough (21, 22, 23) and/or into the discharge pipe (8).
15. Method of reducing a portion of slag, which passes through a discharge aperture (7) towards the end of a discharge process of a wall-lined converter, by utilisation of devices according to one or more of claims 1 to 14, characterised in that the pivotal movement of the converter (1) is so controlled that, during the discharge, the level of the steel bath above and in the trough (21, 22, 23), and more especially above the discharge aperture (7), remains as long as possible above the height critical for the formation of a vortex.
16. Method according to claim 15, characterised in that means for increasing the viscosity of the slag are applied to the slag substantially above the trough (21, 22, 23).
17. Method according to claim 16, characterised in that lime is scattered over the slag.
18. Method according to one of claims 15 to 17, more especially utilising a device according to claim 8, characterised in that an inert gas, which rises through the steel bath in the trough (21, 22, 23) to the slag, is injected intermittently at one or a plurality of locations adjacent the discharge aperture (7).
19. Method according to one of claims 15 to 18, more especially utilising a device according to claim 13, characterised in that electromagnetic fields are so produced that flows in the converter contents are counteracted with tangential components around the axis of the discharge aperture (7).

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