EP0270520B1 - Plasma arc igniting method - Google Patents

Plasma arc igniting method Download PDF

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Publication number
EP0270520B1
EP0270520B1 EP87890271A EP87890271A EP0270520B1 EP 0270520 B1 EP0270520 B1 EP 0270520B1 EP 87890271 A EP87890271 A EP 87890271A EP 87890271 A EP87890271 A EP 87890271A EP 0270520 B1 EP0270520 B1 EP 0270520B1
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EP
European Patent Office
Prior art keywords
auxiliary
plasma
burner
melting stock
circuit
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EP87890271A
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German (de)
French (fr)
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EP0270520A3 (en
EP0270520A2 (en
Inventor
Heinz Dipl.-Ing. Dr. techn. Müller
Reinhard Dipl.-Ing. Buzzi
Gerhard Dipl.-Ing. Scheiblhofer
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Primetals Technologies Austria GmbH
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Voest Alpine Industrienlagenbau GmbH
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B7/00—Heating by electric discharge
    • H05B7/005—Electrical diagrams
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H1/00—Generating plasma; Handling plasma
    • H05H1/24—Generating plasma
    • H05H1/26—Plasma torches
    • H05H1/32—Plasma torches using an arc
    • H05H1/34—Details, e.g. electrodes, nozzles
    • H05H1/36—Circuit arrangements

Definitions

  • an auxiliary plasma arc being ignited when the main circuit is already connected to the plasma torch between the electrode of the plasma torch and a torch jacket surrounding the electrode and blown by adding gas to a length of about 10 cm, whereupon the plasma torch is brought closer to the melting material placed in the furnace vessel until the main plasma arc ignites. The plasma torch is then moved back to the desired position.
  • the invention aims to avoid these disadvantages and difficulties and has as its object to provide a method for igniting a plasma arc and a device for carrying out the method, which ensure high and uniform burner service lives, particularly in high-performance furnaces.
  • This object is achieved in a method of the type described in the introduction in that, with the main circuit switched off, the electrode of the plasma torch and the melt material charged in the furnace vessel are placed on the auxiliary circuit and an auxiliary plasma arc is ignited between the plasma torch and the melt material, whereupon the plasma torch is separated from the melt material is moved back with the extension of the auxiliary plasma arc and then the main circuit is connected to the plasma torch and the melting material and the plasma arc is ignited.
  • the plasma arc is only ignited when the plasma torch is at a safe distance from the melting material, splashes occurring during the ignition process can no longer reach the plasma torch. While the auxiliary plasma arc is ignited, touching the torch with the melted material is irrelevant, since the current flowing through the auxiliary circuit does not destroy the electrode of the plasma torch or the torch jacket. Since the plasma arc is only ignited when the plasma torch is far away from the melting material, there can be none even if the slag cover is poorly conductive or the furnace atmosphere is cold - i.e. with short ignition intervals Damage to the electrode of the plasma torch or the torch jacket.
  • auxiliary plasma arc that is burning between the melting material and the plasma torch between the electrode of the plasma torch and the torch jacket surrounding the electrode and connected to the auxiliary circuit, which is preferably at the same potential as the melting material is, an auxiliary plasma arc ignited with the aid of the auxiliary circuit, whereupon the plasma torch is brought closer to the melting material until this auxiliary plasma arc overturns on the melting material.
  • the burner jacket is preferably separated from the auxiliary circuit.
  • the current of the auxiliary circuit flowing over the melting material is advantageously measured and a switching device which switches off the burner jacket from the auxiliary circuit is actuated as a function of the measured current of the auxiliary circuit, as a result of which the thermal load on the burner can be kept very low and time and energy savings result.
  • the switching device is advantageously actuated when a partial current flows. Furthermore, the burner does not need to be moved any closer to the melting material than is absolutely necessary. This process step also enables fully automatic control of the ignition process.
  • the voltage of the auxiliary circuit is advantageously measured after the ignition of the auxiliary plasma arc between the plasma torch and the melting material the connection of the main circuit depending on the measured voltage.
  • the plasma arc is switched on automatically, without having to take distance measurements between the burner and the melting material or having to observe this distance. This also saves time and energy.
  • a device for carrying out the method with a metallurgical furnace vessel having a plasma torch which plasma torch can be connected to a main circuit and to an auxiliary circuit and can be moved to different heights by means of an actuator relative to the bottom of the furnace vessel, is characterized in that the auxiliary circuit has a Switching device having line is connected to the melting material in terms of lines.
  • the auxiliary circuit can be connected to the burner jacket with a line branching from the line leading to the melting material and equipped with a switching device.
  • a current measuring device is advantageously provided in the line leading to the melting material and is connected via a control line to the switching device provided in the line leading to the burner jacket.
  • a voltage measuring device is expediently provided in the auxiliary circuit and is connected to a switching device provided in the main circuit by means of a control line.
  • FIG. 1 a vertical section through an oven vessel and FIG. 2 a Show circuit diagram for performing the ignition process according to the invention.
  • 3 shows a schematic diagram of a circuit diagram for a three-phase plasma torch.
  • a plasma furnace 1 has a furnace vessel 3 provided with a refractory lining 2 and is covered by a cover 4. An opening 5 is provided centrally in the cover 4, through which a plasma torch 6 projects.
  • the plasma torch 6 can be raised and lowered by means of an actuator 7, so that it can be approached or removed from the melting material 9 charged in the furnace interior 8.
  • a bottom electrode 11 is arranged centrally and opposite the plasma torch 6.
  • the plasma torch 6 is formed by a central electrode 12 and a torch jacket 13, which is preferably water-cooled and surrounds the electrode.
  • the plasma torch 6 and the bottom electrode 11 (and thus the melting material 9) can be connected to an auxiliary circuit 14 and / or to a main circuit 15.
  • the current source of the auxiliary circuit 14 is designated 16. It is via a main switching device 17, a transformer 18 and a rectifier 19 by means of a line 20 connected to the negative potential with the electrode 12 of the plasma torch 6 and by means of a line 21 connected to the positive potential with the melting material 9 via the bottom electrode 11 connected.
  • Controllable switching devices 22 are provided both in the line 20 leading to the electrode 12 and in the line 21 leading to the melt 9.
  • a series resistor 23 is also provided in the line 20 leading to the electrode 12 of the plasma torch 6 for current limitation and determination of the operating point.
  • the same is effected by a choke inserted between the transformer 18 and the rectifier 19.
  • a voltmeter 29 is connected, which is connected by means of a control line 30 to a switching device 31 which is provided in the main circuit 15.
  • the main circuit 15 is connected to a main power source 32 via a transformer 33 and a rectifier 34.
  • a DC choke 35 is provided between the switching device 31 of the main circuit 15 and the connection to the electrode 12 of the plasma torch 6.
  • the function of the facility is as follows: To ignite the plasma arc, when the main circuit 15 is switched off, the switching devices 22 provided in the lines 20, 21 to the electrode 12 of the plasma torch 6 and to the bottom electrode 11 are first closed, but the switching device 28 remains open. The switching device 25 provided in the line 24, which is connected to the burner jacket 13, and the main switching device 17 of the auxiliary circuit 14 are then closed. The burner jacket 13 and the melting material 9 is not yet at the same potential.
  • auxiliary plasma arc is then ignited between the burner electrode 12 and the burner jacket 13 with the aid of an auxiliary igniter 36.
  • the plasma burner 6 is still at a greater distance 37 from the melt material 9 (or the bath surface).
  • the plasma torch is brought closer to the melting material 9 by means of the actuator 7, and so on. until an auxiliary plasma arc ignites between the melt 9 and the burner electrode 12 or the auxiliary plasma arc ignited first between the burner jacket 13 and the electrode 12 of the plasma torch 6 overlaps the melt 9 due to the lower voltage drop.
  • the ammeter 27 is used to determine this flashover. As soon as it registers a certain minimum value, the burner jacket 13 is separated from the auxiliary circuit 14, and so on. by opening the switching device 25 arranged in the line 24 leading to the burner jacket 13. This is accomplished via a control line 38 which connects this switching device 25 to the ammeter 27. The entire current of the auxiliary circuit 14 is thus conducted via the bottom electrode 11.
  • the plasma torch 6 is moved back from the melt 9, whereby the auxiliary plasma arc burning between the burner electrode 12 and the melt 9 is extended.
  • a predetermined extent which depends, among other things, on the distance of the plasma torch 6 from the melt material 9, which is determined by means of the voltmeter 29, is carried out via the from the voltmeter 29 to the switching device 31 of the main circuit 15 leading control line 30 of the main circuit 15 is placed on the melt 9 and the burner electrode 12, whereby the plasma arc ignites instantaneously.
  • a distance 37 of the plasma torch 6 from the melting material of approximately 30 cm Thereupon the auxiliary circuit 14 is separated both from the melting material 9 and from the burner electrode 12, etc. by opening switchgear 17, 22 and 28.
  • the invention is not limited to the exemplary embodiment shown, but can be modified in various ways. It can be implemented not only in direct current circuits, but also in alternating current circuits.
  • a basic circuit for three-phase plasma torches is shown in FIG. 3, the ignition devices 39 shown there with broken lines each comprising the circuit parts which are enclosed in the rectangle 40 formed by broken lines in FIG. 2.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Vertical, Hearth, Or Arc Furnaces (AREA)
  • Gasification And Melting Of Waste (AREA)
  • Furnace Details (AREA)
  • Plasma Technology (AREA)

Description

Die Erfindung betrifft ein Verfahren zum Zünden eines von einem Hauptstromkreis gespeisten Plasmabogens eines in einem metallurgischen Ofengefäß vorgesehenen Plasmabrenners mit Hilfe eines von einem Hilfsstromkreis gespeisten Hilfsplasmabogens, sowie eine Einrichtung zur Durchführung des Verfahrens.The invention relates to a method for igniting a plasma arc fed by a main circuit of a plasma torch provided in a metallurgical furnace vessel with the aid of an auxiliary plasma arc fed by an auxiliary circuit, and a device for carrying out the method.

Es ist intern bekannt, den Plasmabrenner mit Hilfe eines Hilfsbogens zu zünden, wobei bei bereits am Plasmabrenner anliegendem Hauptstromkreis zwischen der Elektrode des Plasmabrenners und einem die Elektrode umgebenden Brennermantel ein Hilfsplasmabogen gezündet und durch Gaszugabe auf eine Länge von ca. 10 cm geblasen wird, worauf der Plasmabrenner an das im Ofengefäß eingebrachte Schmelzgut angenähert wird, bis der Haupt-Plasmabogen zündet. Danach wird der Plasmabrenner in die gewünschte Position zurückbewegt.It is known internally to ignite the plasma torch with the aid of an auxiliary arc, an auxiliary plasma arc being ignited when the main circuit is already connected to the plasma torch between the electrode of the plasma torch and a torch jacket surrounding the electrode and blown by adding gas to a length of about 10 cm, whereupon the plasma torch is brought closer to the melting material placed in the furnace vessel until the main plasma arc ignites. The plasma torch is then moved back to the desired position.

Hierbei ist nachteilig, daß es - kommt es zu einer Berührung zwischen dem Schmelzgut und dem Brennermantel - zu einem Fließen eines Stromes mit hoher Stromstärke zwischen der Elektrode und dem Brennermantel kommen kann, wodurch sich ein sogenannter Nebenbogen bildet. Dieser Nebenbogen kann infolge der hohen Stromstärke zur Zerstörung des Brennermantels führen.It is disadvantageous here that there is a flow of a current with a high current between the electrode and the burner jacket, resulting in a so-called secondary arc. This secondary arc can lead to the destruction of the burner jacket due to the high current.

Weiters kann es dazu kommen, daß Schmelzgutspritzer, die gerade beim Zünden auftreten, den Brennermantel bzw. die Elektrode des Plasmabrenners treffen können, was zu starken Abtragungen an denselben führt. Hierdurch ergibt sich eine empfindliche Verkürzung der Brennerstandzeiten bei gleichzeitig starker Streuung der Brennerstandzeiten, wodurch die Zuverlässigkeit und Wirtschaftlichkeit eines Plasmaofens schwer beeinträchtigt wird: Die starke Streuung der Brennerstandzeiten verhindert einen noch wirtschaftlich vertretbaren vorbeugenden Brennerwechsel. Ein solcher vorbeugender Brennerwechsel ist jedoch notwendig, weil ein Brennerwechsel während des Schmelzens einer Charge Komplikationen verursacht.Furthermore, it can happen that molten metal splashes that occur during ignition can hit the burner jacket or the electrode of the plasma torch, which leads to severe abrasion of the same. This results in a noticeable reduction in the burner service life with a wide spread of burner service life, which severely affects the reliability and economy of a plasma furnace: The large spread of burner service life still prevents you economically justifiable preventive burner change. However, such a preventive burner change is necessary because changing the burner causes complications during the melting of a batch.

Die Erfindung bezweckt die Vermeidung dieser Nachteile und Schwierigkeiten und stellt sich die Aufgabe, ein Verfahren zum Zünden eines Plasmabogens sowie eine Einrichtung zur Durchführung des Verfahrens zu schaffen, welche hohe und gleichmäßige Brennerstandzeiten sicherstellen, insbesondere bei Öfen mit hoher Leistung.The invention aims to avoid these disadvantages and difficulties and has as its object to provide a method for igniting a plasma arc and a device for carrying out the method, which ensure high and uniform burner service lives, particularly in high-performance furnaces.

Diese Aufgabe wird bei einem Verfahren der eingangs beschriebenen Art erfindungsgemäß dadurch gelöst, daß bei abgeschaltetem Hauptstromkreis die Elektrode des Plasmabrenners und das im Ofengefäß chargierte Schmelzgut an den Hilfsstromkreis gelegt werden und zwischen dem Plasmabrenner und dem Schmelzgut ein Hilfsplasmabogen gezündet wird, worauf der Plasmabrenner vom Schmelzgut unter Verlängerung des Hilfsplasmabogens zurückbewegt wird und anschließend der Hauptstromkreis an den Plasmabrenner und das Schmelzgut gelegt und der Plasmabogen gezündet werden.This object is achieved in a method of the type described in the introduction in that, with the main circuit switched off, the electrode of the plasma torch and the melt material charged in the furnace vessel are placed on the auxiliary circuit and an auxiliary plasma arc is ignited between the plasma torch and the melt material, whereupon the plasma torch is separated from the melt material is moved back with the extension of the auxiliary plasma arc and then the main circuit is connected to the plasma torch and the melting material and the plasma arc is ignited.

Da der Plasmabogen erst gezündet wird, wenn sich der Plasmabrenner in sicherer Entfernung vom Schmelzgut befindet, können beim Zündvorgang auftretende Spritzer den Plasmabrenner nicht mehr erreichen. Während des Zündens des Hilfsplasmabogens spielt eine Berührung des Brenners mit dem Schmelzgut keine Rolle, da der hierbei fließende Strom des Hilfsstromkreises weder eine Zerstörung der Elektrode des Plasmabrenners noch des Brennermantels hervorruft. Da der Plasmabogen erst bei großer Entfernung des Plasmabrenners vom Schmelzgut gezündet wird, kann es selbst bei schlecht leitender Schlackendecke oder kalter Ofenatmosphäre - also bei kurzen Zündabständen - zu keiner Beschädigung der Elektrode des Plasmabrenners bzw. des Brennermantels kommen.Since the plasma arc is only ignited when the plasma torch is at a safe distance from the melting material, splashes occurring during the ignition process can no longer reach the plasma torch. While the auxiliary plasma arc is ignited, touching the torch with the melted material is irrelevant, since the current flowing through the auxiliary circuit does not destroy the electrode of the plasma torch or the torch jacket. Since the plasma arc is only ignited when the plasma torch is far away from the melting material, there can be none even if the slag cover is poorly conductive or the furnace atmosphere is cold - i.e. with short ignition intervals Damage to the electrode of the plasma torch or the torch jacket.

Um eine Berührung zwischen Schmelzgut und Plasmabrenner prinzipiell vermeiden zu können, wird vorzugsweise vor Zünden des zwischen dem Schmelzgut und dem Plasmabrenner brennenden Hilfsplasmabogens zwischen der Elektrode des Plasmabrenners und dem die Elektrode umgebenden und an den Hilfsstromkreis gelegten Brennermantel, der vorzugsweise am selben Potential wie das Schmelzgut liegt, ein Hilfsplasmabogen mit Hilfe des Hilfsstromkreises gezündet, worauf der Plasmabrenner dem Schmelzgut so weit genähert wird, bis dieser Hilfsplasmabogen auf das Schmelzgut überschlägt.In order to be able to avoid contact between the melting material and the plasma torch in principle, it is preferable to ignite the auxiliary plasma arc that is burning between the melting material and the plasma torch between the electrode of the plasma torch and the torch jacket surrounding the electrode and connected to the auxiliary circuit, which is preferably at the same potential as the melting material is, an auxiliary plasma arc ignited with the aid of the auxiliary circuit, whereupon the plasma torch is brought closer to the melting material until this auxiliary plasma arc overturns on the melting material.

Vorzugsweise wird nach Fließen zumindest eines Teilstromes des zwischen dem Schmelzgut und der Elektrode des Plasmabrenners brennenden Hilfsbogens der Brennermantel vom Hilfsstromkreis getrennt.After at least a partial flow of the auxiliary arc burning between the melting material and the electrode of the plasma torch, the burner jacket is preferably separated from the auxiliary circuit.

Vorteilhaft wird der über das Schmelzgut fließende Strom des Hilfsstromkreises gemessen und ein den Brennermantel vom Hilfsstromkreis abschaltendes Schaltgerät in Abhängigkeit des gemessenen Stromes des Hilfsstromkreises betätigt, wodurch die thermische Belastung des Brenners sehr gering gehalten werden kann und sich Zeit- und Energieeinsparungen ergeben. Das Schaltgerät wird vorteilhaft bereits bei Fließen eines Teilstromes betätigt. Weiters braucht der Brenner zum Zünden dem Schmelzgut nicht weiter genähert zu werden als unbedingt notwendig. Dieser Verfahrensschritt ermöglicht auch eine vollautomatische Steuerung des Zündvorganges.The current of the auxiliary circuit flowing over the melting material is advantageously measured and a switching device which switches off the burner jacket from the auxiliary circuit is actuated as a function of the measured current of the auxiliary circuit, as a result of which the thermal load on the burner can be kept very low and time and energy savings result. The switching device is advantageously actuated when a partial current flows. Furthermore, the burner does not need to be moved any closer to the melting material than is absolutely necessary. This process step also enables fully automatic control of the ignition process.

Weiters wird vorteilhaft nach dem Zünden des Plasmahilfsbogens zwischen dem Plasmabrenner und dem Schmelzgut die Spannung des Hilfsstromkreises gemessen und die Zuschaltung des Hauptstromkreises in Abhängigkeit von der gemessenen Spannung vorgenommen. Hierdurch erfolgt das Einschalten des Plasmabogens automatisch, ohne Entfernungsmessungen zwischen Brenner und Schmelzgut vornehmen zu müssen bzw. diese Entfernung beobachten zu müssen. Es ergeben sich hierdurch auch Zeit- und Energieeinsparungen.Furthermore, the voltage of the auxiliary circuit is advantageously measured after the ignition of the auxiliary plasma arc between the plasma torch and the melting material the connection of the main circuit depending on the measured voltage. As a result, the plasma arc is switched on automatically, without having to take distance measurements between the burner and the melting material or having to observe this distance. This also saves time and energy.

Eine Einrichtung zur Durchführung des Verfahrens mit einem einen Plasmabrenner aufweisenden metallurgischen Ofengefäß, welcher Plasmabrenner an einen Hauptstromkreis und an einen Hilfsstromkreis anschließbar ist und mittels eines Stellantriebes gegenüber dem Boden des Ofengefäßes in unterschiedliche Höhenlagen bewegbar ist, ist dadurch gekennzeichnet, daß der Hilfsstromkreis mit einer ein Schaltgerät aufweisenden Leitung mit dem Schmelzgut leitungsmäßig verbunden ist.A device for carrying out the method with a metallurgical furnace vessel having a plasma torch, which plasma torch can be connected to a main circuit and to an auxiliary circuit and can be moved to different heights by means of an actuator relative to the bottom of the furnace vessel, is characterized in that the auxiliary circuit has a Switching device having line is connected to the melting material in terms of lines.

Gemäß einer bevorzugten Ausführungsform ist der Hilfsstromkreis mit einer von der zum Schmelzgut führenden Leitung abzweigenden Leitung, die mit einem Schaltgerät ausgestattet ist, an den Brennermantel anschließbar.According to a preferred embodiment, the auxiliary circuit can be connected to the burner jacket with a line branching from the line leading to the melting material and equipped with a switching device.

Vorteilhaft ist in der zum Schmelzgut führenden Leitung ein Stromstärkenmeßgerät vorgesehen, welches über eine Steuerleitung mit dem in der zum Brennermantel führenden Leitung vorgesehenen Schaltgerät verbunden ist.A current measuring device is advantageously provided in the line leading to the melting material and is connected via a control line to the switching device provided in the line leading to the burner jacket.

Zweckmäßig ist in dem Hilfsstromkreis ein Spannungsmeßgerät vorgesehen, das mittels einer Steuerleitung mit einem im Hauptstromkreis vorgesehenen Schaltgerät verbunden ist.A voltage measuring device is expediently provided in the auxiliary circuit and is connected to a switching device provided in the main circuit by means of a control line.

Die Erfindung ist nachfolgend anhand der Zeichnung an zwei Ausführungsbeispielen näher erläutert, wobei Fig. 1 einen Vertikalschnitt durch ein Ofengefäß und Fig. 2 ein Schaltschema zur Durchführung des erfindungsgemäßen Zündvorganges zeigen. In Fig. 3 ist in schematischer Darstellung ein Schaltschema für einen Drehstromplasmabrenner veranschaulicht.The invention is explained in more detail below with the aid of two exemplary embodiments, with FIG. 1 a vertical section through an oven vessel and FIG. 2 a Show circuit diagram for performing the ignition process according to the invention. 3 shows a schematic diagram of a circuit diagram for a three-phase plasma torch.

Ein Plasmaofen 1 weist ein mit einer feuerfesten Auskleidung 2 versehenes Ofengefäß 3 auf und ist von einem Deckel 4 bedeckt. Im Deckel 4 ist zentral eine Öffnung 5 vorgesehen, durch die ein Plasmabrenner 6 ragt. Der Plasmabrenner 6 ist mittels eines Stellantriebes 7 heb- und senkbar, so daß er gegen das im Ofeninnenraum 8 chargierte Schmelzgut 9 annäherbar bzw. von diesem entfernbar ist. Im Boden 10 des Ofengefäßes 3 ist zentral und dem Plasmabrenner 6 gegenüberliegend eine Bodenelektrode 11 angeordnet.A plasma furnace 1 has a furnace vessel 3 provided with a refractory lining 2 and is covered by a cover 4. An opening 5 is provided centrally in the cover 4, through which a plasma torch 6 projects. The plasma torch 6 can be raised and lowered by means of an actuator 7, so that it can be approached or removed from the melting material 9 charged in the furnace interior 8. In the bottom 10 of the furnace vessel 3, a bottom electrode 11 is arranged centrally and opposite the plasma torch 6.

Der Plasmabrenner 6 ist von einer zentralen Elektrode 12 und einem vorzugsweise wassergekühlten und die Elektrode umgebenden Brennermantel 13 gebildet. Der Plasmabrenner 6 und die Bodenelektrode 11 (und damit das Schmelzgut 9) sind an einen Hilfsstromkreis 14 und/oder an einen Hauptstromkreis 15 anschließbar.The plasma torch 6 is formed by a central electrode 12 and a torch jacket 13, which is preferably water-cooled and surrounds the electrode. The plasma torch 6 and the bottom electrode 11 (and thus the melting material 9) can be connected to an auxiliary circuit 14 and / or to a main circuit 15.

Die Stromquelle des Hilfsstromkreises 14 ist mit 16 bezeichnet. Sie ist über ein Hauptschaltgerät 17, über einen Transformator 18 und über einen Gleichrichter 19 mittels einer an das negative Potential angeschlossenen Leitung 20 mit der Elektrode 12 des Plasmabrenners 6 und mittels einer an das positive Potential gelegten Leitung 21 mit dem Schmelzgut 9 über die Bodenelektrode 11 verbunden. Sowohl in der zur Elektrode 12 führenden Leitung 20 als auch in der zum Schmelzgut 9 führenden Leitung 21 sind gemeinsam steuerbare Schaltgeräte 22 vorhanden. In der zur Elektrode 12 des Plasmabrenners 6 führenden Leitung 20 ist weiters ein Vorwiderstand 23 zur Strombegrenzung und Arbeitspunktbestimmung vorgesehen.The current source of the auxiliary circuit 14 is designated 16. It is via a main switching device 17, a transformer 18 and a rectifier 19 by means of a line 20 connected to the negative potential with the electrode 12 of the plasma torch 6 and by means of a line 21 connected to the positive potential with the melting material 9 via the bottom electrode 11 connected. Controllable switching devices 22 are provided both in the line 20 leading to the electrode 12 and in the line 21 leading to the melt 9. A series resistor 23 is also provided in the line 20 leading to the electrode 12 of the plasma torch 6 for current limitation and determination of the operating point.

Gleiches bewirkt eine zwischen dem Transformator 18 und dem Gleichrichter 19 eingefügte Drossel.The same is effected by a choke inserted between the transformer 18 and the rectifier 19.

Von der zum Schmelzgut 9 führenden Leitung 21 zweigt eine an den Mantel 13 des Plasmabrenners 6 gelegte Leitung 24 ab, in der ein Schaltgerät 25 zum wahlweisen Anschluß des Mantels 13 an den Hilfsstromkreis 14 vorgesehen ist. Zwischen der Abzweigung 26 der zum Mantel 13 führenden Leitung 24 und dem Anschluß an die Bodenelektrode 11 ist ein Amperemeter 27 und zwischen diesem Amperemeter 27 und dem Anschluß an die Bodenelektrode 11 ein weiteres Schaltgerät 28 angeordnet.From the line 21 leading to the melt material 9 branches off a line 24 placed on the jacket 13 of the plasma torch 6, in which a switching device 25 is provided for the optional connection of the jacket 13 to the auxiliary circuit 14. An ammeter 27 is arranged between the branch 26 of the line 24 leading to the jacket 13 and the connection to the bottom electrode 11, and a further switching device 28 is arranged between this ammeter 27 and the connection to the bottom electrode 11.

Zwischen der zur Elektrode 12 des Plasmabrenners 6 führenden Leitung 20 und der zur Bodenelektrode 11 führenden Leitung 21 ist ein Voltmeter 29 gelegt, welches mittels einer Steuerleitung 30 mit einem Schaltgerät 31 verbunden ist, das im Hauptstromkreis 15 vorgesehen ist. Der Hauptstromkreis 15 ist an eine Hauptstromquelle 32 über einen Transformator 33 und einen Gleichrichter 34 angeschlossen. Zum Glätten von Spannungsschwankungen ist zwischen dem Schaltgerät 31 des Hauptstromkreises 15 und dem Anschluß an die Elektrode 12 des Plasmabrenners 6 eine Gleichstromdrossel 35 vorgesehen.Between the line 20 leading to the electrode 12 of the plasma torch 6 and the line 21 leading to the bottom electrode 11, a voltmeter 29 is connected, which is connected by means of a control line 30 to a switching device 31 which is provided in the main circuit 15. The main circuit 15 is connected to a main power source 32 via a transformer 33 and a rectifier 34. To smooth voltage fluctuations, a DC choke 35 is provided between the switching device 31 of the main circuit 15 and the connection to the electrode 12 of the plasma torch 6.

Die Funktion der Einrichtung ist folgende:
Zum Zünden des Plasmabogens werden bei abgeschaltetem Hauptstromkreis 15 zunächst die in den Leitungen 20, 21 zur Elektrode 12 des Plasmabrenners 6 und zur Bodenelektrode 11 vorgesehenen Schaltgeräte 22 geschlossen, wobei jedoch das Schaltgerät 28 geöffnet bleibt. Hierauf werden das in der Leitung 24, die an den Brennermantel 13 angeschlossen ist, vorgesehene Schaltgerät 25 und das Hauptschaltgerät 17 des Hilfsstromkreises 14 geschlossen. Der Brennermantel 13 und das Schmelzgut 9 befinden sich noch nicht auf gleichem Potential.The function of the facility is as follows:
To ignite the plasma arc, when the main circuit 15 is switched off, the switching devices 22 provided in the lines 20, 21 to the electrode 12 of the plasma torch 6 and to the bottom electrode 11 are first closed, but the switching device 28 remains open. The switching device 25 provided in the line 24, which is connected to the burner jacket 13, and the main switching device 17 of the auxiliary circuit 14 are then closed. The burner jacket 13 and the melting material 9 is not yet at the same potential.

Danach erfolgt die Zündung eines Hilfsplasmabogens zwischen der Brenner-Elektrode 12 und dem Brennermantel 13 mit Hilfe eines Hilfs-Zündgerätes 36. Hierbei befindet sich der Plasmabrenner 6 noch in größerer Entfernung 37 zum Schmelzgut 9 (bzw. zur Badoberfläche).An auxiliary plasma arc is then ignited between the burner electrode 12 and the burner jacket 13 with the aid of an auxiliary igniter 36. Here, the plasma burner 6 is still at a greater distance 37 from the melt material 9 (or the bath surface).

Nach Schließen des zwischen dem Amperemeter 27 und der Bodenelektrode 11 vorgesehenen Schaltgerätes 28 wird der Plasmabrenner mittels des Stellantriebes 7 an das Schmelzgut 9 genähert, u.zw. so weit, bis ein Hilfsplasmabogen zwischen dem Schmelzgut 9 und der Brenner-Elektrode 12 zündet bzw. der zwischen dem Brennermantel 13 und der Elektrode 12 des Plasmabrenners 6 zuerst gezündete Hilfsplasmabogen auf das Schmelzgut 9 aufgrund des geringeren Spannungsabfalles überschlägt. Zur Feststellung dieses Überschlages dient das Amperemeter 27. Sobald dieses einen bestimmten Mindestwert registriert, wird der Brennermantel 13 vom Hilfsstromkreis 14 getrennt, u.zw. durch Öffnen des in der zum Brennermantel 13 führenden Leitung 24 angeordneten Schaltgerätes 25. Dies wird über eine Steuerleitung 38 bewerkstelligt, die dieses Schaltgerät 25 mit dem Amperemeter 27 verbindet. Damit wird der gesamte Strom des Hilfsstromkreises 14 über die Bodenelektrode 11 geleitet.After the switching device 28 provided between the ammeter 27 and the bottom electrode 11 is closed, the plasma torch is brought closer to the melting material 9 by means of the actuator 7, and so on. until an auxiliary plasma arc ignites between the melt 9 and the burner electrode 12 or the auxiliary plasma arc ignited first between the burner jacket 13 and the electrode 12 of the plasma torch 6 overlaps the melt 9 due to the lower voltage drop. The ammeter 27 is used to determine this flashover. As soon as it registers a certain minimum value, the burner jacket 13 is separated from the auxiliary circuit 14, and so on. by opening the switching device 25 arranged in the line 24 leading to the burner jacket 13. This is accomplished via a control line 38 which connects this switching device 25 to the ammeter 27. The entire current of the auxiliary circuit 14 is thus conducted via the bottom electrode 11.

Danach wird der Plasmabrenner 6 vom Schmelzgut 9 zurückbewegt, wodurch der zwischen der Brenner-Elektrode 12 und dem Schmelzgut 9 brennende Hilfsplasmabogen verlängert wird. Sobald die Spannung des zwischen dem Schmelzgut 9 und der Brenner-Elektrode 12 fließenden Stromes ein vorbestimmtes Ausmaß, das u.a. vom Abstand des Plasmabrenners 6 vom Schmelzgut 9 abhängt, übersteigt, was mittels des Voltmeters 29 festgestellt wird, wird über die vom Voltmeter 29 zum Schaltgerät 31 des Hauptstromkreises 15 führende Steuerleitung 30 der Hauptstromkreis 15 an das Schmelzgut 9 und die Brenner-Elektrode 12 gelegt, wodurch der Plasmabogen augenblicklich zündet. Dies geschieht zweckmäßig in einer Entfernung 37 des Plasmabrenners 6 vom Schmelzgut von etwa 30 cm. Hierauf wird der Hilfsstromkreis 14 sowohl vom Schmelzgut 9 als auch von der Brenner-Elektrode 12 getrennt, u.zw. durch Öffnen der Schaltgeräte 17, 22 und 28.Thereafter, the plasma torch 6 is moved back from the melt 9, whereby the auxiliary plasma arc burning between the burner electrode 12 and the melt 9 is extended. As soon as the voltage of the current flowing between the melt material 9 and the burner electrode 12 exceeds a predetermined extent, which depends, among other things, on the distance of the plasma torch 6 from the melt material 9, which is determined by means of the voltmeter 29, is carried out via the from the voltmeter 29 to the switching device 31 of the main circuit 15 leading control line 30 of the main circuit 15 is placed on the melt 9 and the burner electrode 12, whereby the plasma arc ignites instantaneously. This is conveniently done at a distance 37 of the plasma torch 6 from the melting material of approximately 30 cm. Thereupon the auxiliary circuit 14 is separated both from the melting material 9 and from the burner electrode 12, etc. by opening switchgear 17, 22 and 28.

Die Erfindung beschränkt sich nicht auf das dargestellte Ausführungsbeispiel, sondern ist in verschiedener Hinsicht modifizierbar. Sie kann nicht nur bei Gleichstromkreisen, sondern auch bei Wechselstromkreisen verwirklicht werden. Eine Prinzipschaltung für Drehstromplasmabrenner ist in Fig. 3 gezeigt, wobei die dort mit strichlierten Linien dargestellten Zündeinrichtungen 39 jeweils die Schaltungsteile umfassen, die in Fig. 2 in dem von strichlierten Linien gebildeten Rechteck 40 eingefaßt sind.The invention is not limited to the exemplary embodiment shown, but can be modified in various ways. It can be implemented not only in direct current circuits, but also in alternating current circuits. A basic circuit for three-phase plasma torches is shown in FIG. 3, the ignition devices 39 shown there with broken lines each comprising the circuit parts which are enclosed in the rectangle 40 formed by broken lines in FIG. 2.

Claims (9)

  1. A method of igniting a plasma arc fed by a main circuit (15), of a plasma burner (6) provided within a metallurgical furnace vessel (3), by aid of an auxiliary plasma arc fed by an auxiliary circuit (14), characterized in that, with the main circuit (15) switched off, the electrode (12) of the plasma burner (6) and the melting stock charged into the furnace vessel (3) are applied to the auxiliary circuit and an auxiliary plasma arc is ignited between the plasma burner (6) and the melting stock, whereupon the plasma burner (6) is moved back from the melting stock (9), thus extending the auxiliary plasma arc, and subsequently the main circuit (15) is applied to the plasma burner (6) and the melting stock (9) and the plasma arc is ignited.
  2. A method according to claim 1, characterized in that, prior to igniting the auxiliary plasma arc burning between the melting stock (9) and the plasma burner (6), an auxiliary plasma arc is ignited between the electrode (12) of the plasma burner and the burner jacket (13) surrounding the electrode (12) and laid at the auxiliary circuit (14), which preferably lies at the same potential as the melting stock, whereupon the plasma burner (6) is approached to the melting stock until this auxiliary plasma arc sparks over to the melting stock (9).
  3. A method according to claim 2, characterized in that the burner jacket (13) is separated from the auxiliary circuit (14) after the flow of at least a partial current of the auxiliary plasma arc burning between the melting stock (9) and the electrode (12) of the plasma burner (6).
  4. A method according to claim 3, characterized in that the current of the auxiliary circuit (14) flowing over the melting stock (9) is measured and a switching device (15) switching the burner jacket (13) off the auxiliary circuit (14) is actuated as a function of the current of the auxiliary cirucit (14) measured.
  5. A method according to one or several of claims 1 to 4, characterized in that the voltage of the auxiliary circuit (14) is measured after ignition of the plasma auxiliary arc between the plasma burner (6) and the melting stock (9) and the switching in of the main circuit is effected as a function of the voltage measured.
  6. An arrangement for carrying out the method according to one or several of claims 1 to 5, comprising a metallurgical furnace vessel (3) incorporating a plasma burner (6) capable of being switched to a main circuit (15) and to an auxiliary circuit (14) and movable to different height levels by means of an adjustment drive (7) relative to the bottom (10) of the furnace vessel (3), characterized in that the auxiliary circuit (14) is electrically connected with the melting stock by a conduit (21) including a switching device (28).
  7. An arrangement according to claim 6, characterized in that the auxiliary circuit (14) is connectable to the burner jacket (13) by a conduit (24) branching off the conduit (21) that leads to the melting stock (9) and equipped with a switching device (25).
  8. An arrangement according to claim 7, characterized in that a current-intensity measuring means (27) is provided in the conduit (21) leading to the melting stock (9), which means is connected with the switching device (25) provided in the conduit (24) leading to the burner jacket (13), by a control conduit (38).
  9. An arrangement according to one or several of claims 6 to 8, characterized in that a current-intensity measuring means (29) is provided in the auxiliary circuit (14), which is connected with a switching device (31) provided in the main current by a control conduit (30).
EP87890271A 1986-12-01 1987-11-26 Plasma arc igniting method Expired - Lifetime EP0270520B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AT3194/86 1986-12-01
AT0319486A AT386717B (en) 1986-12-01 1986-12-01 METHOD FOR ENDING A PLASMA BOW

Publications (3)

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EP0270520A2 EP0270520A2 (en) 1988-06-08
EP0270520A3 EP0270520A3 (en) 1989-02-01
EP0270520B1 true EP0270520B1 (en) 1993-01-13

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Application Number Title Priority Date Filing Date
EP87890271A Expired - Lifetime EP0270520B1 (en) 1986-12-01 1987-11-26 Plasma arc igniting method

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US (1) US4764208A (en)
EP (1) EP0270520B1 (en)
JP (1) JPS63148600A (en)
AT (1) AT386717B (en)
DD (1) DD269741A5 (en)
DE (1) DE3783586D1 (en)
FI (1) FI875211A (en)
NO (1) NO169690C (en)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5444208A (en) * 1993-03-29 1995-08-22 Fmc Corporation Multiple source plasma generation and injection device

Family Cites Families (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2119179A6 (en) * 1970-12-23 1972-08-04 Anvar
BE809746A (en) * 1974-01-15 1974-05-02 ELECTRICAL CURRENT SUPPLY (CONTINUOUS AND ALTERNATIVE) FOR PLASMAS SYSTEMS AT HIGH TEMPERATURES.
AT331434B (en) * 1974-05-28 1976-08-25 Ver Edelstahlwerke Ag PROCEDURE FOR REMOVING UNWANTED ELEMENTS, IN PARTICULAR H2 AND O2 DURING ELECTRIC SLAG REMOVAL AND ARRANGEMENT FOR CARRYING OUT THE PROCEDURE
DD122908A1 (en) * 1975-12-19 1976-11-05
CA1173784A (en) * 1981-07-30 1984-09-04 William H. Gauvin Transferred-arc plasma reactor for chemical and metallurgical applications
AT372977B (en) * 1982-01-19 1983-12-12 Voest Alpine Ag METHOD AND DEVICE FOR REDUCING OXIDE-CONTAINING FINE-PARTED ORES
EP0118655B1 (en) * 1982-12-22 1988-03-02 VOEST-ALPINE Aktiengesellschaft Method of carrying out metallurgical or chemical processes, and a low-shaft furnace
US4580029A (en) * 1983-10-27 1986-04-01 Union Carbide Corporation Plasma arc power supply and method
AT388271B (en) * 1984-09-26 1989-05-26 Voest Alpine Ag CONTROL DEVICE FOR A HIGH-PERFORMANCE PLASMA TORCH, IN PARTICULAR FOR A MELTING STOVE
CA1278431C (en) * 1985-09-26 1991-01-02 Nicholas Adrian Barcza Thermal production of magnesium

Also Published As

Publication number Publication date
FI875211A (en) 1988-06-02
US4764208A (en) 1988-08-16
EP0270520A3 (en) 1989-02-01
NO169690B (en) 1992-04-13
NO874991L (en) 1988-06-02
AT386717B (en) 1988-10-10
JPS63148600A (en) 1988-06-21
DE3783586D1 (en) 1993-02-25
DD269741A5 (en) 1989-07-05
NO169690C (en) 1992-07-22
FI875211A0 (en) 1987-11-25
ATA319486A (en) 1988-02-15
NO874991D0 (en) 1987-11-30
EP0270520A2 (en) 1988-06-08

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