EP0778354A1 - Process for supplying controlled atmosphere gases into a heat treatment furnace and heat treatment plant - Google Patents

Process for supplying controlled atmosphere gases into a heat treatment furnace and heat treatment plant Download PDF

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EP0778354A1
EP0778354A1 EP96119651A EP96119651A EP0778354A1 EP 0778354 A1 EP0778354 A1 EP 0778354A1 EP 96119651 A EP96119651 A EP 96119651A EP 96119651 A EP96119651 A EP 96119651A EP 0778354 A1 EP0778354 A1 EP 0778354A1
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gas
oxygen
heat treatment
furnace
zone
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German (de)
French (fr)
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EP0778354B1 (en
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Reinhard Dipl.-Ing. Strigl
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Linde Gas AG
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Linde GmbH
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
    • C21D1/76—Adjusting the composition of the atmosphere
    • C21D1/763—Adjusting the composition of the atmosphere using a catalyst
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04521—Coupling of the air fractionation unit to an air gas-consuming unit, so-called integrated processes
    • F25J3/04527—Integration with an oxygen consuming unit, e.g. glass facility, waste incineration or oxygen based processes in general
    • F25J3/04539—Integration with an oxygen consuming unit, e.g. glass facility, waste incineration or oxygen based processes in general for the H2/CO synthesis by partial oxidation or oxygen consuming reforming processes of fuels
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04521—Coupling of the air fractionation unit to an air gas-consuming unit, so-called integrated processes
    • F25J3/04563—Integration with a nitrogen consuming unit, e.g. for purging, inerting, cooling or heating

Definitions

  • the invention relates to a method for supplying protective gas to a heat treatment furnace with several zones, in particular an inlet and outlet zone and a heating zone, in which the protective gas is obtained using starting gas which is generated by an on-site air separation plant.
  • the invention also relates to a corresponding heat treatment system.
  • CO and H 2 -containing protective or reaction gases for heat treatments from air and a hydrocarbon gas (KW gas), in particular natural gas, and by means of catalytic conversion of the reactive components, namely oxygen and, for example, methane.
  • KW gas hydrocarbon gas
  • This reaction is usually accomplished with a gas generator arranged next to the one or more heat treatment furnaces and consisting of a catalyst in the core, and the so-called endogas formed in the generator is usually fed to the associated heat treatment system without further treatment. It is also known to implement the same starting gas mixture in a catalyst retort which is arranged in an oven and is thus already set to a higher temperature level, and either to let the product gas flow directly into the oven or to draw it off and to distribute it (see, for example, DE 39 42 810 A1.
  • the object is achieved in that the starting gas fraction usually obtained with such an air separation and containing predominantly nitrogen is introduced as protective gas into the inlet and, if appropriate, the outlet zone of the furnace without further oxygen removal and that further protective gas suitable for the heating zone is obtained by mixing at least part of the oxygen-rich fraction likewise produced by the separation plant with a hydrocarbon gas, preferably methane or natural gas, this mixture catalytically with the addition of heat to a - besides nitrogen - mainly carbon monoxide and hydrogen-containing gas mixture is reacted, and this gas mixture is supplied to the heating zone (heat zone) of the furnace as a protective gas.
  • a hydrocarbon gas preferably methane or natural gas
  • the oxygen-contaminated nitrogen obtained from the dismantling plant directly that is to say without post-purification, as a protective gas, specifically in furnace zones in which the oxygen content of the protective gas is less critical.
  • these are generally the colder supply and removal tunnels in front of the heating chamber (prechamber) or, in the case of continuous systems, the inlet area in front of the heating zone or treatment chamber (inlet chamber with subsequent zone) and the cooling zone or cooling chamber of the system on the outlet side.
  • the nitrogen shielding gas not warmed up according to the invention also acts as a particularly effective cooling gas.
  • the proportion of oxygen to be converted in this gas fraction is very high - namely at least about 25% - so that an effective conversion reaction between the oxygen of the said product gas and a correspondingly admixed KW gas is appropriate 1.5 O 2 + 3.5 N 2 + 3 CH 4 ⁇ 3 CO + 6 H 2 + 3.5 N 2 can take place. Since the starting gas used here has a relatively low nitrogen content, the unnecessarily heated gas content is relatively low compared to the above-mentioned post-purification of impure nitrogen, and the formation of protective gas is therefore comparatively energy-efficient.
  • the predominantly nitrogen-containing fraction is produced with a purity of at least 98.5% and the oxygen-rich starting gas fraction with 25 to 35% oxygen.
  • a particularly favorable embodiment of the procedure according to the invention is characterized in that the oxygen-rich starting gas is reacted with a catalyst retort arranged in the heat treatment furnace, the retort and the reactants being heated to a temperature of over 500 ° C, preferably over 800 ° C, for which purpose If necessary, the retort is additionally heated.
  • a heat treatment furnace initially generally has a protective gas supply which comprises an air separation device (1) and a conversion unit (2) for oxygen with a hydrocarbon gas, and is characterized in particular by that the product gas outlet of the air separation plant, which supplies the predominantly nitrogen-containing gas fraction, is connected to the inlet and possibly the outlet zone (3, 7) of the heat treatment furnace by gas supply lines, and that, on the other hand, the product gas outlet of the air separation plant, which supplies the oxygen-rich fraction, is connected to the conversion unit (2) via further lines (8, 6), the conversion unit also being connected to a hydrocarbon gas source (CnHm) and, on the other hand, delivering or forwarding its product gas to the heating zone (5) of the furnace (which contain gas lines) of course the necessary valves and actuators).
  • a protective gas supply which comprises an air separation device (1) and a conversion unit (2) for oxygen with a hydrocarbon gas, and is characterized in particular by that the product gas outlet of the air separation plant, which supplies the predominantly nitrogen-containing gas fraction, is connected to the inlet and possibly the outlet zone
  • the figure shows an elongated continuous furnace D with an inlet zone 3, a central heating and treatment zone 5 and a cooling zone 7.
  • a catalyst retort 2 inside the furnace, that is to say an aggregate containing a catalyst material and having gas outlet openings at its head end , arranged, which is connected via gas lines 6 and 8 on the one hand to a membrane-based, ie permeate air separation plant 1 and its oxygen outlet O 2+ and on the other hand is connected via lines 6 and 10 to a hydrocarbon source CnHm, eg natural gas.
  • a hydrocarbon source CnHm eg natural gas.
  • At the interface of lines 8 and 10 there is also a mixing and setting unit 9 for the inflowing gases.
  • the second product gas outlet N 2 of the air separator 1 that is to say the one which supplies a nitrogen-rich gas, is finally connected directly to the heat treatment furnace via lines 11, 12 and 14, the gas feed line, however, specifically into the furnace inlet zone 3 - line 12 - and into the furnace outlet zone 7 - Line 14 - done.
  • the middle part of the heat treatment plant is not supplied with any gas which does not come from the nitrogen outlet of the air separation plant and is not further treated.
  • the shielding gas requirement of the continuous furnace shown can be, for example, 150 m 3 / h.
  • the permeation air separation plant 1 shown is now set so that approximately 110 m 3 of nitrogen gas with 99% purity are made available per hour.
  • This nitrogen gas, the so-called retentate is fed to the inlet zone 3 and the outlet zone 7 of the furnace shown in a quantity of 55 m 3 / h in each case, without removing further oxygen therefrom.
  • the still necessary for the heating zone 5, 40 m 3 / h of very low-oxygen protective gas are obtained according to the invention from the oxygen-rich gas, the so-called permeate, which also occurs in larger quantities in the operation of the air separation plant 1 described.
  • this is done by mixing 15.6 m 3 of this permeate, which contains about 31% oxygen and 69% nitrogen, in mixer 9 with 7 m 3 / h of natural gas (methane) and catalytically gas mixture obtained in catalyst retort 2 is converted to a protective gas containing about 24% CO, 48% H 2 and 28% N 2 and is released as such into the heating zone 5 of the furnace.
  • the catalyst 2 which is preferably a nickel catalyst, must be set to temperatures above 800 ° C., preferably 900 to 1050 ° C.
  • a large part of the heat supply for maintaining this temperature level is already guaranteed by the heating in the heating zone 5 of the continuous furnace D, which is heated to, for example, 800 to 900 ° C.
  • the protective gas quantity of 40 m 3 / h required for the heating zone is obtained.
  • Excesses of oxygen-rich permeate are installed in the gas line 8 Outlet A is emitted to the environment or advantageously fed as O 2 -enriched air to the other jet pipes instead of air as an oxygen carrier for heating the jet pipes.
  • the shielding gas supplied in the middle part of the furnace represents a shielding gas consisting essentially of CO, H 2 and N 2 , while the shielding gas supplied on the inlet and outlet sides consists of almost pure nitrogen, the nitrogen purity for the complete avoidance of metallurgically disadvantageous effects at least about 99 % should be.
  • the supply of differently composed protective gases according to the invention also results in a protective gas composition that varies somewhat over the length of the furnace, which leads to an equally locally varying gas reactivity, which has its peak in particular in the heating zone of the furnace and which decreases towards the furnace ends.
  • an atmosphere with about 12% CO, 24% H 2 and 64% N 2 is usually established in the heating zone at the described conditions, which gives an atmosphere which is particularly advantageous for many annealing treatments, which is somewhat reducing and in terms of the carburizing effect has almost neutral properties for many materials.
  • the supply of the cold nitrogen shielding gas in the outlet area of the continuous furnace achieves an improved cooling performance compared to other annealing processes.
  • the method according to the invention thus has advantages such as the improved economy and the increased cooling capacity compared to methods in which only the nitrogen product of an on-site air separator is used for protective gas production, and thus represents an advantageous alternative to these methods.

Abstract

A protective gas for a heat treatment furnace with several zones is generated from the exit gas from an air separation unit. The gas fraction containing mainly nitrogen is passed into the intake zone and if necessary the exit zone of the furnace without further removal of oxygen. The protective gas used in the heating or treatment zone is obtained from at least a part of the oxygen rich gas fraction from the air separation unit mixed with natural gas or propane by heating and catalytic conversion to mainly carbon monoxide and hydrogen. Also claimed is a heat treatment furnace with a protective gas generating plant that includes an air separation unit (1) and a unit (2) for reacting O2 with a hydrocarbon gas as described above.

Description

Die Erfindung betrifft ein Verfahren zur Schutzgasversorgung eines Wärmebehandlungsofens mit mehreren Zonen, insbesondere einer Einlauf- und Auslaufzone sowie einer Heizzone, bei dem das Schutzgas unter Verwendung von Ausgangsgas gewonnen wird, das mit einer vor Ort arbeitenden Luftzerlegungsanlage erzeugt wird. Ebenso bezieht sich die Erfindung auf eine entsprechende Wärmebehandlungsanlage.The invention relates to a method for supplying protective gas to a heat treatment furnace with several zones, in particular an inlet and outlet zone and a heating zone, in which the protective gas is obtained using starting gas which is generated by an on-site air separation plant. The invention also relates to a corresponding heat treatment system.

Grundsätzlich ist es bekannt, CO- und H2-haltige Schutz- oder Reaktionsgase für Wärmebehandlungen aus Luft und einem Kohlenwasserstoffgas (KW-Gas), insbesondere Erdgas, und mittels katalytischer Umsetzung der reaktiven Bestandteile, nämlich Sauerstoff und beispielsweise Methan, zu bilden. Die typische Bildungsreaktion, die eine unvollständige Verbrennung des KW-Gases darstellt, lautet hierbei wie folgt:

        (O2 + 4 N2) + 2 CH4 → 2 CO + 4 H2 + 4 N2 = Luft

Basically, it is known to form CO and H 2 -containing protective or reaction gases for heat treatments from air and a hydrocarbon gas (KW gas), in particular natural gas, and by means of catalytic conversion of the reactive components, namely oxygen and, for example, methane. The typical formation reaction, which represents incomplete combustion of the KW gas, is as follows:

(O 2 + 4 N 2 ) + 2 CH 4 → 2 CO + 4 H 2 + 4 N 2 = air

Diese Reaktion wird üblicherweise mit einem neben dem oder den Wärmebehandlungsöfen angeordneten, im Kernstück aus einem Katalysator bestehenden Gasgenerator bewerkstelligt, und das im Generator gebildete, sogenannte Endogas wird im Regelfall ohne weitere Behandlung der zughörigen Wärmebehandlungsanlage zugeführt. Ebenso ist es bekannt, das gleiche Ausgangsgasgemisch in einer in einem Ofen angeordneten und auf diese Weise bereits auf ein höheres Temperaturniveau versetzten Katalysatorretorte umzusetzen und das Produktgas entweder direkt in den Ofen einfließen zu lassen oder auch abzuziehen und zu verteilen (siehe z.B. DE 39 42 810 A1.This reaction is usually accomplished with a gas generator arranged next to the one or more heat treatment furnaces and consisting of a catalyst in the core, and the so-called endogas formed in the generator is usually fed to the associated heat treatment system without further treatment. It is also known to implement the same starting gas mixture in a catalyst retort which is arranged in an oven and is thus already set to a higher temperature level, and either to let the product gas flow directly into the oven or to draw it off and to distribute it (see, for example, DE 39 42 810 A1.

Außerdem ist es auch bekannt, sogenannten kommerziellen Stickstoff, also Stickstoff der noch mit erheblichen Anteilen Sauerstoff (1% und mehr) verunreinigt ist auf diese Weise zu einer sauerstofffreien und somit brauchbaren Wärmebehandlungsatmophäre für metallisches Gut umzuwandeln (Fachartikel "Commercial Nitrogen - The Basis For A Universal Controlled Atmophere" aus Metal Science and Heat Treatment 1978, Heft 5/6, Seiten 377 - 381).In addition, it is also known to convert so-called commercial nitrogen, that is to say nitrogen which is still contaminated with considerable amounts of oxygen (1% and more), into an oxygen-free and therefore usable heat treatment atmosphere for metallic material (technical article "Commercial Nitrogen - The Basis For A Universal Controlled Atmophere "from Metal Science and Heat Treatment 1978, No. 5/6, pages 377 - 381).

In jüngerer Zeit ist mehrfach vorgeschlagen worden, einen kommerziellen Stickstoff mit etwa 0,5 bis 5 % Sauerstoff vor Ort bei Wärmebehandlungen mit Hilfe von nunmehr entsprechend weit entwickelten adsorptiven oder permeativen Luftzerlegungseinheiten bereitzustellen und daraus wiederum - wie beschrieben - ein nahezu sauerstofffreies Schutzgas herzustellen (siehe z.B. US-PS 5 242 509 = EP 0 482 992 (von 1990) oder DE-PS 42 12 307 (1992)). Mit den geschilderten Verfahren wird jeweils ein nahezu sauerstofffreies, CO, H2 und N2 enthaltendes Behandlungsgas erhalten, das für verschiedenste Wärmebehandlungen geeignet ist.In recent times, it has been proposed several times to provide a commercial nitrogen with about 0.5 to 5% oxygen on site during heat treatments with the aid of now appropriately developed adsorptive or permeative air separation units and, in turn, to produce an almost oxygen-free protective gas as described (see e.g. US Pat. No. 5,242,509 = EP 0 482 992 (from 1990) or DE-PS 42 12 307 (1992)). With the described processes, an almost oxygen-free treatment gas containing CO, H 2 and N 2 is obtained, which is suitable for a wide variety of heat treatments.

Nachteilig bei den letztgenannten Verfahren unter Einsatz einer Luttzerlegung vor Ort ist jedoch, daß zur Nachreinigung des Unrein-Stickstoffs beträchtliche Mengen an Energie erforderlich sind, da ja die Gesamtmenge an Unreinstickstoff auf die zur katalytischen Umsetzung des Restsauerstoffs erforderliche Temperatur zu erwärmen ist, um die sauerstoffentfernende Reaktion auszulösen. Im Ergebnis wird zwar ein ausgezeichnetes Behandlungsgas erhalten, jedoch stellt sich die Frage, ob nicht beispielsweise mit angeliefertem Reinstickstoff in Kombination mit einer der bekannten Endogaserzeugungsmethoden identische Schutzgase ähnlich ökonomisch hergestellt werden können, wobei hierbei auf die Luttzerlegung vor Ort vollständig verzichtet werden kann.A disadvantage of the latter methods using on-site luttage decomposition, however, is that considerable amounts of energy are required to purify the impure nitrogen, since the total amount of impure nitrogen has to be heated to the temperature required for the catalytic conversion of the residual oxygen in order to remove the oxygen Trigger reaction. As a result, an excellent treatment gas is obtained, but the question arises whether, for example, with the pure nitrogen supplied in combination with one of the known endogas production methods, it is possible to produce identical shielding gases in a similar economical manner, with the fact that the waste separation on site can be completely dispensed with.

Die Anmelderin hat sich vor diesem Hintergrund nunmehr speziell die Aufgabe gestellt, insbesondere die Ökonomie der Verfahren, die auf Basis der Luttzerlegung vor Ort arbeiten, zu verbessern.Against this background, the applicant has now specifically set itself the task of improving , in particular, the economy of the processes which work on the basis of the Lutt decomposition on site.

Die Aufgabe wird erfindungsgemäß dadurch gelöst, daß die mit einer solchen Luftzerlegung üblicherweise erhaltene, überwiegend Stickstoff enthaltende Ausgangsgas-Fraktion ohne weitere Sauerstoffentfernung in die Einlauf- und gegebenenfalls die Auslaufzone des Ofens als Schutzgas eingeleitet wird
und daß weiteres, für die Heizzone taugliches Schutzgas dadurch gewonnen wird, daß zumindest ein Teil der von der Zerlegungsanlage ebenfalls erzeugten sauerstoffreichen Fraktion mit einem Kohlenwasserstoffgas, vorzugsweise Methan oder Erdgas, vermischt wird, dieses Gemisch unter Wärmezufuhr katalytisch zu einem - neben Stickstoff - hauptsächlich Kohlenmonoxid und Wasserstoff enthaltenden Gasgemisch umgesetzt wird, und dieses Gasgemisch der Heizzone (Hitzezone) des Ofens als Schutzgas zugeführt wird.The object is achieved in that the starting gas fraction usually obtained with such an air separation and containing predominantly nitrogen is introduced as protective gas into the inlet and, if appropriate, the outlet zone of the furnace without further oxygen removal
and that further protective gas suitable for the heating zone is obtained by mixing at least part of the oxygen-rich fraction likewise produced by the separation plant with a hydrocarbon gas, preferably methane or natural gas, this mixture catalytically with the addition of heat to a - besides nitrogen - mainly carbon monoxide and hydrogen-containing gas mixture is reacted, and this gas mixture is supplied to the heating zone (heat zone) of the furnace as a protective gas.

Es wird also vorgeschlagen, den von der Zerlegungsanlage erhaltenen, sauerstoffverunreinigten Stickstoff unmittelbar, d.h. ohne Nachreinigung, als Schutzgas anzuwenden, und zwar in Ofenzonen, in denen der Sauerstoffgehalt des Schutzgases weniger kritisch ist. Dies sind im allgemeinen bei nicht kontinuierlichen Öfen der kältere, vor der Heizkammer liegende Zufuhr- und Entnahmetunnel (Vorkammer) oder bei Durchlaufanlagen der vor der Heizzone oder Behandlungskammer liegende Einlaufbereich (Eintrittkammer mit nachfolgender Zone) sowie die ausgangsseitig liegende Kühlzone oder Abkühlkammer der Anlage. In der Kühlzone wirkt das erfindungsgemäß nicht angewärmte Stickstoffschutzgas außerdem auch als besonders effektives Kühlgas. In der auf Behandlungstemperatur zu haltenden Zone oder Kammer eines Ofens ist jedoch die Anwendung des Unrein-Stickstoffs als Schutz- oder Behandlungsgas nicht möglich. Daher ist hier ein anderes Schutzgas anzuwenden, das erfindungsgemäß aus dem zweiten, insbesondere bei permeativen und adsorptiven Luftzerlegern anfallenden, sauerstoffreichen Produktgas wiederum durch katalytische Umsetzung mit einem Kohlenwasserstoffgas erzeugt wird. Hierbei ist als erstes anzumerken, daß - da lediglich noch die Heizzone mit Schutzgas zu versorgen ist - zunächst nur noch eine geringere Gasmenge erforderlich ist, die etwa die Hälfte bis 1/4 des Gesamtbedarfs eines Ofens umfaßt. Zudem ist in dieser Gasfraktion der umzusetzende Sauerstoffanteil sehr hoch - nämlich wenigstens etwa 25 % - so daß eine effektive Umsetzungsreaktion zwischen dem Sauerstoff des besagten Produktgases und einem entsprechend zuzumischenden KW-Gas gemäß

        1,5 O2 + 3,5 N2 + 3 CH4 → 3 CO + 6 H2 + 3,5 N2

stattfinden kann. Da bei dem hier angewandten Ausgangsgas ein relativ niedriger Stickstoffanteil vorliegt, ist der unnötig erhitzte Gasanteil im Vergleich zur oben angesprochenen Nachreinigung von Unrein-Stickstoff relativ niedrig und somit die Schutzgasbildung vergleichsweise energieökonomisch.It is therefore proposed to use the oxygen-contaminated nitrogen obtained from the dismantling plant directly, that is to say without post-purification, as a protective gas, specifically in furnace zones in which the oxygen content of the protective gas is less critical. In the case of non-continuous furnaces, these are generally the colder supply and removal tunnels in front of the heating chamber (prechamber) or, in the case of continuous systems, the inlet area in front of the heating zone or treatment chamber (inlet chamber with subsequent zone) and the cooling zone or cooling chamber of the system on the outlet side. In the cooling zone, the nitrogen shielding gas not warmed up according to the invention also acts as a particularly effective cooling gas. In the zone or chamber of a furnace to be kept at the treatment temperature, however, the use of the impure nitrogen as a protective or treatment gas is not possible. Therefore, another protective gas is to be used here, which, according to the invention, is in turn generated from the second, oxygen-rich product gas, which occurs in particular in the case of permeative and adsorptive air separators, by catalytic reaction with a hydrocarbon gas. First of all, it should be noted that - since only the heating zone is to be supplied with protective gas - initially only a smaller amount of gas is required, which comprises about half to 1/4 of the total requirement of a furnace. In addition, the proportion of oxygen to be converted in this gas fraction is very high - namely at least about 25% - so that an effective conversion reaction between the oxygen of the said product gas and a correspondingly admixed KW gas is appropriate

1.5 O 2 + 3.5 N 2 + 3 CH 4 → 3 CO + 6 H 2 + 3.5 N 2

can take place. Since the starting gas used here has a relatively low nitrogen content, the unnecessarily heated gas content is relatively low compared to the above-mentioned post-purification of impure nitrogen, and the formation of protective gas is therefore comparatively energy-efficient.

Hinsichtlich des zu erbringenden Aufwands ergibt sich ein Vorteil, wenn die Luftzerlegung vor Ort nicht kryogen, d.h. nicht nach der Tieftemperaturmethode, sondern permeativ oder adsorptiv ausgeführt wird.With regard to the effort to be achieved, there is an advantage if the air separation on site is not carried out cryogenically, ie not using the low-temperature method, but rather permeatively or adsorptively.

Für ein vorteilhattes Funktionieren der Erfindung ist es ferner vorteilhaft, wenn die überwiegend Stickstoff enthaltende Fraktion mit einer Reinheit von wenigstens 98,5% und die sauerstoffreiche Ausgangsgas-Fraktion mit 25 bis 35 % Sauerstoff hergestellt wird.For an advantageous functioning of the invention, it is also advantageous if the predominantly nitrogen-containing fraction is produced with a purity of at least 98.5% and the oxygen-rich starting gas fraction with 25 to 35% oxygen.

Eine besonders günstige Ausgestaltung des erfindungsgemäßen Vorgehens ist dadurch gekennzeichnet, daß das sauerstoffreiche Ausgangsgas mit einer im Wärmebehandlungsofen angeordneten Katalysatorretorte umgesetzt wird, wobei die Retorte und die Reaktionspartner auf eine Temperatur von über 500 °C, vorzugsweise über 800 °C, aufgeheizt werden, wozu die Retorte gegebenenfalls zusätzlich beheizt wird .A particularly favorable embodiment of the procedure according to the invention is characterized in that the oxygen-rich starting gas is reacted with a catalyst retort arranged in the heat treatment furnace, the retort and the reactants being heated to a temperature of over 500 ° C, preferably over 800 ° C, for which purpose If necessary, the retort is additionally heated.

Ein erfindungsgemäßer Wärmebehandlungsofen weist zunächst im generellen eine Schutzgasversorgung auf, die eine Luftzerlegungseinrichtung (1) und ein Umsetzungsaggregat (2) für Sauerstoff mit einem Kohlenwasserstoffgas umfaßt, und ist im speziellen dadurch gekennzeichnet,
daß der Produktgasausgang der Luftzerlegungsanlage, der die überwiegend Stickstoff enthaltende Gas-Fraktion liefert, mit der Einlauf- und gegebenfalls der Auslaufzone (3,7) des Wärmebehandlungsofens durch Gasversorgungsleitungen verbunden ist, und daß andererseits der Produktgasausgang der Luftzerlegungsanlage, der die sauerstoffreiche Fraktion liefert, mit dem Umsetzungsaggregat (2) über weitere Leitungen (8,6) in Verbindung steht, wobei das Umsetzungsaggregat zudem mit einer Kohlenwasserstoffgasquelle (CnHm) verbunden ist und andererseits ihr Produktgas an die Heizzone (5) des Ofens abgibt bzw. weiterleitet (die Gasleitungen enthalten selbstverständlich auch die notwendigen Ventile und Stellglieder).A heat treatment furnace according to the invention initially generally has a protective gas supply which comprises an air separation device (1) and a conversion unit (2) for oxygen with a hydrocarbon gas, and is characterized in particular by
that the product gas outlet of the air separation plant, which supplies the predominantly nitrogen-containing gas fraction, is connected to the inlet and possibly the outlet zone (3, 7) of the heat treatment furnace by gas supply lines, and that, on the other hand, the product gas outlet of the air separation plant, which supplies the oxygen-rich fraction, is connected to the conversion unit (2) via further lines (8, 6), the conversion unit also being connected to a hydrocarbon gas source (CnHm) and, on the other hand, delivering or forwarding its product gas to the heating zone (5) of the furnace (which contain gas lines) of course the necessary valves and actuators).

Anhand der anliegenden Figur wird im folgenden ein Ausführungsbeispiel der Erfindung näher beschrieben.An exemplary embodiment of the invention is described in more detail below with reference to the attached figure.

Die Figur zeigt einen länglich ausgebildeten Durchlaufofen D mit einer Eintrittszone 3, einer mittig liegenden Heiz- und Behandlungszone 5 und einer Kühlzone 7. In der Heizzone 5 ist im Ofeninneren eine Katalysatorretorte 2, also ein ein Katalysatormaterial enthaltendes Aggregat, das an seinem Kopfende Gasauslaßöffnungen aufweist, angeordnet, das über Gasleitungen 6 und 8 einerseits mit einer auf Membranbasis, also permeativ arbeitenden Luftzerlegungsanlage 1 und dessen Sauerstoffausgang O 2+ in Verbindung steht und andererseits über Leitungen 6 und 10 mit einer Kohlenwasserstoffquelle CnHm, z.B. Erdgas, verbunden ist. An der Schnittstelle der Leitungen 8 und 10 ist ferner eine Misch- und Einstelleinheit 9 für die zufließenden Gase vorhanden. Der zweite Produktgasausgang N2 des Luftzerlegers 1, also derjenige der ein stickstoffreiches Gas liefert, ist schließlich über Leitungen 11, 12 und 14 direkt mit dem Wärmebehandlungsofen verbunden, wobei die Gaszuleitung jedoch spezifisch in die Ofeneinlaufzone 3 - Leitung 12 - und in die Ofenauslaufzone 7 - Leitung 14 - erfolgt. Dem Mittelteil der Wärmebehandlungsanlage wird kein, unmittelbar vom Stickstoffausgang der Luftzerlegungsanlage stammendes, nicht weiterbehandeltes Gas zugeführt.The figure shows an elongated continuous furnace D with an inlet zone 3, a central heating and treatment zone 5 and a cooling zone 7. In the heating zone 5 there is a catalyst retort 2 inside the furnace, that is to say an aggregate containing a catalyst material and having gas outlet openings at its head end , arranged, which is connected via gas lines 6 and 8 on the one hand to a membrane-based, ie permeate air separation plant 1 and its oxygen outlet O 2+ and on the other hand is connected via lines 6 and 10 to a hydrocarbon source CnHm, eg natural gas. At the interface of lines 8 and 10 there is also a mixing and setting unit 9 for the inflowing gases. The second product gas outlet N 2 of the air separator 1, that is to say the one which supplies a nitrogen-rich gas, is finally connected directly to the heat treatment furnace via lines 11, 12 and 14, the gas feed line, however, specifically into the furnace inlet zone 3 - line 12 - and into the furnace outlet zone 7 - Line 14 - done. The middle part of the heat treatment plant is not supplied with any gas which does not come from the nitrogen outlet of the air separation plant and is not further treated.

Ein erfindungsgemäßer Betrieb der gezeigten Anlage verläuft nunmehr wie folgt:Operation of the system shown according to the invention now proceeds as follows:

Der Schutzgasbedarf des gezeigten Durchlaufofens kann beispielsweise 150 m3/h betragen. Erfindungsgemäß wird nun die gezeigte, permeativ arbeitende Luftzerlegungsanlage 1 so eingestellt, daß etwa 110 m3 Stickstoffgas mit 99 %-iger Reinheit in der Stunde zur Verfügung gestellt werden. Dieses Stickstoffgas, das sogenannte Retentat, wird, ohne daraus weiteren Sauerstoff zu entfernen, in einer Quantität von jeweils 55 m3/h der Einlaufzone 3 und der Auslaufzone 7 des gezeigten Ofens zugeleitet. Die für die Heizzone 5 noch notwendigen, 40 m3/h an sehr sauerstoffarmem Schutzgas werden gemäß der Erfindung aus dem sauerstoffreichen Gas, dem sogenannten Permeat, gewonnen, das ebenfalls bei dem geschilderten Betrieb der Luftzerlegungsanlage 1 in größerer Menge anfällt. Im einzelnen erfolgt dies dadurch, daß 15,6 m3 dieses Permeats, das etwa 31 % Sauerstoff und 69 % Stickstoff enthält, im Mischer 9 mit 7 m3/h Erdgas (Methan) gemischt werden und das erhaltene Gasgemisch in der Katalysatorretorte 2 katalytisch zu einem etwa 24 % CO, 48 % H2 und 28 % N2 enthaltenden Schutzgas umgesetzt wird und als solches in die Heizzone 5 des Ofens entlassen wird. Hierbei ist - um die saubere Umsetzung der Ausgangsgase zu gewährleisten - der Katalysator 2, der vorzugsweise ein Nickelkatalysator ist, auf Temperaturen von oberhalb 800 C, vorzugsweise 900 bis 1050° C einzustellen.The shielding gas requirement of the continuous furnace shown can be, for example, 150 m 3 / h. According to the invention, the permeation air separation plant 1 shown is now set so that approximately 110 m 3 of nitrogen gas with 99% purity are made available per hour. This nitrogen gas, the so-called retentate, is fed to the inlet zone 3 and the outlet zone 7 of the furnace shown in a quantity of 55 m 3 / h in each case, without removing further oxygen therefrom. The still necessary for the heating zone 5, 40 m 3 / h of very low-oxygen protective gas are obtained according to the invention from the oxygen-rich gas, the so-called permeate, which also occurs in larger quantities in the operation of the air separation plant 1 described. In particular, this is done by mixing 15.6 m 3 of this permeate, which contains about 31% oxygen and 69% nitrogen, in mixer 9 with 7 m 3 / h of natural gas (methane) and catalytically gas mixture obtained in catalyst retort 2 is converted to a protective gas containing about 24% CO, 48% H 2 and 28% N 2 and is released as such into the heating zone 5 of the furnace. In order to ensure the clean conversion of the starting gases, the catalyst 2, which is preferably a nickel catalyst, must be set to temperatures above 800 ° C., preferably 900 to 1050 ° C.

Durch die durch nicht gezeigte Heizeinrichtungen auf beispielsweise 800 bis 900 C aufgeheizte Atmosphäre in der Heizzone 5 des Durchlaufofens D wird bereits ein Großteil der Wärmezufuhr zur Aufrechterhaltung dieses Temperaturniveaus gewährleistet. Eine zusätzlich Wärmemenge Qzu kann gegebenenfalls durch eine in die Katalysatorretorte 2 integrierte Heizung aufgebracht werden. Durch thermokatalytische Umsetzung der obengenannten Ausgangsmengen an Erdgas und sauerstoffreichem Gas wird also die für die Heizzone erforderliche Schutzgasmenge von 40 m3/h erhalten. Überschüsse an sauerstoffreichem Permeat werden dabei über einen in der Gasleitung 8 installierten Auslaß A an die Umgebung abgegeben oder als O2-angereicherte Luft den übrigen Strahlrohren statt Luft als Sauerstoffträger zur Beheizung der Strahlrohre vorteilhaft zugeleitet.A large part of the heat supply for maintaining this temperature level is already guaranteed by the heating in the heating zone 5 of the continuous furnace D, which is heated to, for example, 800 to 900 ° C. An additional quantity of heat Q to be optionally applied by an integrated in the catalyst retort 2 heating. By thermocatalytic conversion of the above-mentioned initial quantities of natural gas and oxygen-rich gas, the protective gas quantity of 40 m 3 / h required for the heating zone is obtained. Excesses of oxygen-rich permeate are installed in the gas line 8 Outlet A is emitted to the environment or advantageously fed as O 2 -enriched air to the other jet pipes instead of air as an oxygen carrier for heating the jet pipes.

Insgesamt werden auf diese Weise dem Durchlaufofen D also 150 m3 Schutzgas/h zugeführt, wobei jeweils 55 m3 auf die Einlauf- bzw. Auslaufzone entfallen und der mittig im Ofen liegenden Heizzone die verbleibenden 40 m3 zugeführt werden. Das im Mittelteil des Ofens zugeführte Schutzgas stellt dabei ein im wesentlichen aus CO, H2 und N2 bestehendes Schutzgas dar, während das eingangs- und ausgangsseitig zugeführte Schutzgas aus nahezu reinem Stickstoff besteht, wobei die Stickstoffreinheit zur gänzlichen Vermeidung metallurgisch nachteiliger Effekte wenigstens etwa 99 % betragen sollte.In this way, a total of 150 m 3 of protective gas / h are fed to the continuous furnace D, 55 m 3 each being in the inlet and outlet zones and the remaining 40 m 3 being supplied to the central heating zone in the furnace. The shielding gas supplied in the middle part of the furnace represents a shielding gas consisting essentially of CO, H 2 and N 2 , while the shielding gas supplied on the inlet and outlet sides consists of almost pure nitrogen, the nitrogen purity for the complete avoidance of metallurgically disadvantageous effects at least about 99 % should be.

Durch die erfindungsgemäße Zuleitung unterschiedlich zusammengesetzter Schutzgase ergibt sich im übrigen eine über die Ofenlänge hinweg etwas variierende Schutzgaszusammensetzung, die zu einer ebenso örtlich variierenden Gasreaktivität führt, welche insbesondere in der Heizzone des Ofens ihre Spitze besitzt und die zu den Ofenenden hin abnimmt. Bei den beschriebenen Verhältnissen stellt sich nach Erfahrungen der Anmelderin in der Heizzone im Regelfall eine Atmosphäre mit etwa 12 % CO, 24 % H2 und 64 % N2 ein, womit eine für viele Glühbehandlungen besonders vorteilhafte Atmosphäre gegeben ist, die etwas reduzierende und hinsichtlich der Kohlungswirkung für viele Werkstoffe nahezu neutrale Eigenschaften aufweist. Im übrigen wird durch die Zufuhr des kalten Stickstoffschutzgases im Auslaufbereich des Durchlaufofens eine im Vergleich zu anderen Glühverfahren verbesserte Kühlleistung erzielt. Das erfindungsgemäße Verfahren weist also im Vergleich zu Verfahren, bei denen lediglich das Stickstoffprodukt eines vor Ort betriebenen Luftzerlegers zur Schutzgaserzeugung eingesetzt wird, Vorteile wie die verbesserte Ökonomie und die erhöhte Kühlleistung auf und stellt somit eine vorteilhafte Alternative zu diesen Verfahren dar.The supply of differently composed protective gases according to the invention also results in a protective gas composition that varies somewhat over the length of the furnace, which leads to an equally locally varying gas reactivity, which has its peak in particular in the heating zone of the furnace and which decreases towards the furnace ends. According to the experience of the applicant, an atmosphere with about 12% CO, 24% H 2 and 64% N 2 is usually established in the heating zone at the described conditions, which gives an atmosphere which is particularly advantageous for many annealing treatments, which is somewhat reducing and in terms of the carburizing effect has almost neutral properties for many materials. Incidentally, the supply of the cold nitrogen shielding gas in the outlet area of the continuous furnace achieves an improved cooling performance compared to other annealing processes. The method according to the invention thus has advantages such as the improved economy and the increased cooling capacity compared to methods in which only the nitrogen product of an on-site air separator is used for protective gas production, and thus represents an advantageous alternative to these methods.

Claims (6)

Verfahren zur Schutzgasversorgung eines Wärmebehandlungsofens mit mehreren Zonen, insbesondere einer Einlauf- und Auslaufzone sowie einer Heizzone,
   bei dem das Schutzgas unter Verwendung von Ausgangsgas gewonnen wird, das mit einer vor Ort arbeitenden Luftzerlegungsanlage erzeugt wird,
dadurch gekennzeichnet,
daß die mit der Zerlegungsanlage erhaltene, überwiegend Stickstoff enthaltende Ausgangsgas-Fraktion ohne weitere Sauerstoffentfernung in die Einlauf- und gegebenenfalls die Auslaufzone des Ofens als Schutzgas eingeleitet wird
und daß ein für die Heiz- oder Behandlungszone taugliches Schutzgas dadurch gewonnen wird, daß zumindest ein Teil der von der Zerlegungsanlage ebenfalls erzeugten sauerstoffreichen Fraktion mit einem Kohlenwasserstoffgas, vorzugsweise Erdgas oder Propan, vermischt wird, dieses Gemisch unter Wärmezufuhr katalytisch zu einem - neben Stickstoff - hauptsächlich Kohlenmonoxid und Wasserstoff enthaltenden Gasgemisch umgesetzt wird,
und dieses Gasgemisch der Heizzone (Hitzezone) des Ofens als Schutzgas zugeführt wird.Process for the protective gas supply of a heat treatment furnace with several zones, in particular an inlet and outlet zone as well as a heating zone,
in which the protective gas is obtained using source gas which is generated by an on-site air separation plant,
characterized,
that the starting gas fraction obtained with the separation plant, which contains predominantly nitrogen, is introduced as protective gas into the inlet and possibly the outlet zone of the furnace without further oxygen removal
and that a protective gas suitable for the heating or treatment zone is obtained by mixing at least part of the oxygen-rich fraction likewise produced by the decomposition system with a hydrocarbon gas, preferably natural gas or propane, catalytically adding this mixture to a - in addition to nitrogen - mainly gas mixture containing carbon monoxide and hydrogen is reacted,
and this gas mixture is supplied to the heating zone (heat zone) of the furnace as a protective gas. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß die Luftzerlegung vor Ort permeativ oder adsorptiv ausgeführt wird.A method according to claim 1, characterized in that the air separation is carried out on site permeatively or adsorptively. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß die überwiegend Stickstoff enthaltende Fraktion mit einer Reinheit von wenigstens 98,5 % hergestellt wird.A method according to claim 1 or 2, characterized in that the fraction containing predominantly nitrogen is produced with a purity of at least 98.5%. Verfahren nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, daß eine sauerstoffreiche Ausgangsgas-Fraktion mit 25 bis 35 % Sauerstoff hergestellt wird.Method according to one of claims 1 to 3, characterized in that an oxygen-rich starting gas fraction is produced with 25 to 35% oxygen. Verfahren nach einem der Ansprüche 1 bis 4, dadurch gekennzeichnet, daß das sauerstoffreiche Ausgangsgas mit einem Kohlenwasserstoffgas und mit einer im Wärmebehandlungsofen angeordneten Katalysatorretorte umgesetzt wird, wobei die Retorte und die Reaktionspartner auf eine Temperatur über 500 °C, vorzugsweise über 800 °C, aufgeheizt werden, wozu die Retorte gegebenenfalls zusätzlich beheizt wird.Method according to one of claims 1 to 4, characterized in that the oxygen-rich starting gas is reacted with a hydrocarbon gas and with a catalyst retort arranged in the heat treatment furnace, the retort and the reactants being heated to a temperature above 500 ° C, preferably above 800 ° C are, for which purpose the retort may be additionally heated. Wärmebehandlungsofen mit einer Schutzgasversorgung, die eine Luftzerlegungseinrichtung (1) und ein Umsetzungsaggregat (2) für Sauerstoff mit einem Kohlenwasserstoffgas umfaßt, dadurch gekennzeichnet,
daß der Produktgasausgang der Luftzerlegungsanlage (1), der die überwiegend Stickstoff enthaltende Gas-Fraktion liefert (N2), mit der Einlauf- und gegebenfalls der Auslaufzone (3,7) des Wärmebehandlungsofens durch Gasversorgungsleitungen (11, 12,14) verbunden ist,
daß andererseits der Produktgasausgang (O2+)der Luftzerlegungsanlage, der die sauerstoffreiche Fraktion liefert, mit dem Umsetzungsaggregat (2) über Leitungen (8,6) in Verbindung steht, wobei das Umsetzungsaggregat zudem mit einer Kohlenwasserstoffgasquelle (CnHm) verbunden ist und andererseits ihr Produktgas an die Heizzone (5) des Ofens abgibt bzw. weiterleitet.Heat treatment furnace with a protective gas supply, which comprises an air separation device (1) and a conversion unit (2) for oxygen with a hydrocarbon gas, characterized in that
that the product gas outlet of the air separation plant (1), which supplies the predominantly nitrogen-containing gas fraction (N 2 ), is connected to the inlet and optionally the outlet zone (3,7) of the heat treatment furnace by gas supply lines (11, 12, 14),
that, on the other hand, the product gas outlet (O 2+ ) of the air separation plant, which supplies the oxygen-rich fraction, is connected to the conversion unit (2) via lines (8, 6), the conversion unit also being connected to a hydrocarbon gas source (CnHm) and, on the other hand, to it Dispenses or transfers product gas to the heating zone (5) of the furnace.
EP96119651A 1995-12-07 1996-12-06 Process for supplying controlled atmosphere gases into a heat treatment furnace and heat treatment plant Expired - Lifetime EP0778354B1 (en)

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ATE200307T1 (en) 2001-04-15

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