EP0992597A1 - Deoxidation of copper melt by gas poling with hydrogen-nitrogen mixture - Google Patents

Abstract

Copper poling process employs a deoxidizing gas mixture of hydrogen and inert gas. Copper poling is carried out using a deoxidizing gas mixture of inert gas (preferably nitrogen) and 35-90 (especially 60-72) volume % hydrogen.

Description

The invention relates to a process for polishing (deoxidizing) copper in molten liquid State in which a gaseous deoxidizer is passed into the melt becomes.

The use of hydrogen gas and natural gas to deoxidize copper is - besides of wood or materials derived from it - known (cf. DE-PS 34 27 435).

Introductory consideration for the reduction of liquid copper

In the refining process for the production of anode copper, the last process step before casting is a reduction in the molten copper bath. The technical term for this process stage is Poland. The reducing agent used (various feedstocks) primarily has the task of reducing the oxygen content to a certain final size and expelling sulfur dioxide in the copper bath. The technology currently used provides for the use of hardwood trunks that are pressed into the liquid copper bath using a crane. The very intensive reactions of the wood with the melt that occur bring about a reduction in the oxygen component and - if present - the sulfur dioxide component. It is always of the utmost importance that the most important, harmful additives have been slagged before the reduction process begins and that the surface of the bath has been removed cleanly. Otherwise, the metal oxides in the slag which float on the copper bath are reduced to metals, appear as metal impurities in the anode copper and sometimes interfere with further processing by wet metallurgy. For the entire reduction process of 3-4 hours, approx. 7- 8 fm trunks with bound indoor crane and crane driver are required. The process is discontinuous because new logs have to be made available after the imported wood has burned down.
The part of the wood that is not immersed in the copper bath burns outside the melt or the flame furnace and further reduces the overall efficiency to a total of approx. 35%. As a result of the length dimension of the pole rods, it is also impossible to completely avoid that exhaust gases are emitted into the furnace hall. The high level of heat at the work gate puts a great strain on the employees working there (crane operators, 1st and 2nd refiners).

Use of hydrogen for poling

As is known, the pole process has already been carried out with a wide variety of reducing agents. In addition to the original method with logs, crude oil of the HT-B type with a sulfur content of less than 2% was used for anode production in the 1980s. Attempts were made almost simultaneously to design the reduction phase with CH ₄ .
The first-mentioned oiling, however, posed major environmental problems if the resulting carbon in the exhaust gas did not undergo any aftertreatment and filtering.

Polishing with CH ₄ in anode operation was and is problematic because a very important requirement, the high starting temperature of the oxidized anode copper, can only be achieved with great effort.
However, natural gas poling could often be introduced at least as a partial process, particularly in the remelting work for the production of wire bars.
Because the leading material was of cathode quality, the temperatures of approx. 1,250 ° C were reached even without major energy losses, which then allowed natural gas poling with two lances economically. The technological conditions provided, with an oxygen content of approximately 800-1,000 ppm, to continue the pole process with logs until the end, because the O ₂ removal at these contents is quick and the sampling and O ₂ determinations did not cumulate .

Since the reducing agent in the examples mentioned cannot react directly with the oxygen in the copper, it must first be broken down into reactive constituents (CO / H ₂ ), which, however, can only be achieved by supplying energy. Therefore, the considerations were made to use a gas as a reducing agent, which is already a reducing agent and supplies the process with energy through its "combustion". The use of hydrogen for this purpose has therefore already been proposed.

Example of hydrogen polarity

One was in the flame furnace of an anode plant in a former copper smelter Hydrogen polarization performed. The flame furnace is stationary; the delivery exists made of CM material inside and fireclay outside and this is off in the range the 2nd layer down. The furnace rack is on the front compared to the two permanently installed natural gas / oxygen burners. The exhaust gas leaves the furnace chamber via an underground duct system to the furnace filter and through the work gate via the auxiliary hood filter system. The oven is over two vault openings cold-charged and has a capacity of approx. 155 t total use with an anode output of around 135 - 140 t per batch.

Further furnace data:

Batch time

= 28 - 30 hours

Natural gas consumption

= 105 m ³ / t an.

O2 consumption

= 185 m ³ / t an.

Slag waste

= 10% of Vorlf.

Anode copper

= 99.2% Cu

Copper bath surface

= approx. 24 - 26 m ²

Injection device or pole for H ₂ addition: 3/4 "gas pipe was used as the outer jacket, into which an approx. 3/8" pipe was inserted. Since the gas flow should flow through the inner pipe, both gas pipes were welded to the threaded head piece. The pipe length of the pollanze was 3 m. The lower part was thermally protected from plastic fabric combined with fireclay mortar and soda water glass. A pulpy mixture was produced from both components and pulled evenly, spirally over the outer tube via a spindle with a roller seat for the absorption of the tissue. The lance was covered at the lower end with a length of approx. 1.5 m.

• Hohe Standzeit durch mechanische Stabilität (Doppelrohr) und Feuerfestschutz durch das Aufbringen der Isolation in Selbstherstellung.
• Dichte Verbindung durch Verschraubung am Lanzenende mit einem flexiblen Metallschlauch mit Kugelhahn.
• Gute Ausströmgeschwindigkeit am ´Übergang mit Lanze zu Flüssigkupfer bei einem konstant eingestellten Druck.
• Einfache Herstellung; unkomplizierte Handhabung beim Wechsel und während des Polprozesses; geringe Fertigungskosten.

The overall design of such a pollanze thus met the following factors:

• Long service life due to mechanical stability (double pipe) and fire protection through the application of insulation in self-production.
• Tight connection by screwing at the end of the lance with a flexible metal hose with ball valve.
• Good outflow speed at the transition from lance to liquid copper at a constant pressure.
• Easy manufacture; uncomplicated handling when changing and during the pole process; low manufacturing costs.

Procedure:

• Initiation of the pole process: Before the pole process, the pipe system is flushed with nitrogen: flushing time 2 min.
• Pole process with hydrogen: Poles with hydrogen entry via the described pole lance immersed in the Cu melt or also several pole lances.
• Final nitrogen purge.

• die Pollanzen unterliegen einem relativ hohen Verschleiß;
• insbesondere gegen Ende der Desoxidationsprozesses langer Zeitbedarf bis Desoxidationsziel erreicht ist.

However, using hydrogen gas for deoxidation has the following disadvantages:

• the pollanzes are subject to relatively high wear;
• especially towards the end of the deoxidation process, it takes a long time until the deoxidation target is reached.

The present invention is therefore based on the task, a simple feasible, functional and also effective deoxidation process based on to specify gaseous treatment agents.

According to the invention, this is achieved in that a hydrogen is used as the deoxidation gas and a gas mixture containing 35 to 90% by volume, preferably nitrogen, Hydrogen is applied. According to the invention, a deoxidation gas is preferably used Hydrogen-nitrogen mixture with 60 to 72 vol% hydrogen is applied. Further Design variants can be found in the appended subclaims.

Surprisingly, it was found that the use of an H ₂ / N ₂ mixture shortened the effective pole time compared to poling with natural gas, and reduced wear on the pollances could be achieved. The H ₂ / N ₂ mixture acts not only as a reducing agent but also as an energy source due to the exothermic reactions in the copper melt.

• Eintauchen der Eindüsungslanze in die Cu-Schmelze,
• Schließen der Hauptabsperrung für Wasserstoff und der Absperrung sowie der Hauptabsperrung für Stickstoff aus dem Tank,
• Öffnen de Strangabsperrung für Wasserstoff,
• Öffnen des angeschlossenen Stickstoff-Bündels,
• Öffnen der Hauptabsperrung für Stickstoff - Spüldauer 2 min.

An exemplary embodiment of the invention is described below:
A poling process with an oven and with an injection device as described above is presented. Before the pole process, the piping system is flushed with nitrogen. The following operating steps are carried out:

• Immersing the injection lance in the Cu melt,
• Closing the main barrier for hydrogen and the barrier as well as the main barrier for nitrogen from the tank,
• Opening the line shut-off for hydrogen,
• Opening the connected nitrogen bundle,
• Opening the main shut-off for nitrogen purging time 2 min.

For Poland:

• Closing the connected nitrogen bundle,
• Closing the main nitrogen barrier,
• Opening the main barrier for hydrogen and a barrier as well as the Main shut-off for nitrogen from the tank,
• Poland under hydrogen nitrogen entry.

End of the pole process:

• Die Eindüsenlanzen verbleiben in der Cu-Schmelze,
• Schließen de Hauptabsperrung für Wasserstoff,
• Öffnen des angeschlossenen Stickstoff-Bündels,
• Öffnen der Hauptabsperrung für Stickstoff,
• Spüldauer 2 min.,
• Schließen des angeschlossenen Stickstoff-Bündels,
• Schließen der Hauptabsperrung für Stickstoff,
• Schließen der Strangabsperrung für Wasserstoff und der Absperrung sowie der Hauptabsperrung für Stickstoff aus dem Tank,
• Herausziehen der Eindüsungslanzen aus der Cu-Schmelze
• Druckentlastung des Leitungssystems durch kurzzeitiges Öffnen einer Strangabsperrung für Wasserstoff.

To end the pole process, the power system is flushed again with nitrogen. Operating steps:

• The nozzle lances remain in the Cu melt,
• Closing the main barrier to hydrogen,
• Opening the connected nitrogen bundle,
• Opening the main nitrogen barrier,
• Rinsing time 2 min.,
• Closing the connected nitrogen bundle,
• Closing the main nitrogen barrier,
• Closing the string shut-off for hydrogen and the shut-off as well as the main shut-off for nitrogen from the tank,
• Pull the injection lances out of the Cu melt
• Relief of pressure in the pipeline system by briefly opening a line shut-off for hydrogen.

Result of the described H ₂ / N ₂ polarity:

• H₂ = 8,474 m³ N / t Anoden
• N₂ = 4,45 m³ N / t Anoden.

The wear of the pollanzas is significantly reduced compared to the procedure with pure hydrogen. The pollanzas could be reused for up to 3 batches.
The volume fraction of H ₂ in the H ₂ / N ₂ mixture is particularly advantageously in the range from 60 to 72% by volume.
Average H ₂ / N ₂ consumption based on the test period:

• H ₂ = 8.474 m ³ N / t anodes
• N ₂ = 4.45 m ³ N / t anodes.

The flow rate per lance (H ₂ / N ₂ mixture) is advantageously in the range from 200 to 350 m ³ N / h and lance. Favorable results were achieved with blowing pressures of 10 bar in front of the lance and a lance outlet cross section of 1.2265 * 10 ^-4 m ² (d _i = 12.5 mm).

In order to determine the optimal delivery of the pollanzas, it could be determined - based on the existing conditions - that with the increase in the supply pressure and the associated smaller outlet cross-sections d = 10 mm and increasing outlet speed beyond 12 bar, the reduction could not be intensified. A disadvantage of these tests with blowing pressures up to 15 bar was the higher wear of the pole ends. The maximum period of use per lance was only one batch.
With the chosen lance construction, exit speeds equal to the speed of sound have been achieved. The overpressures at the outlet cross section are estimated to be around 2 - 3 bar.
When using nozzles, based on the pre-pressure of 10 bar, higher dynamic pressures at the outlet of the lances result in about 5 - 6 bar. As a result, higher exit speeds are also achieved, which under certain circumstances can lead to a further intensification of the reduction.

Energetic efficiency

• Holz (sog. Polstangen)
• Heizöl, L u. M (Steinkohleheizöl) und
• Erdgas, H

geht der Trend bei der Herstellung von Kupferanoden hin zum Gaspolen mit der Verwendung von Erdgas der Gruppe H.
Obwohl für einen Vergleich des Nutzungsgrades die jeweilige Ofentype, das Chargengewicht und die eingesetzten kupferhaltigen Vorlaufmaterialien von Einfluß sind, kann doch - bezogen auf einen Sauerstoffgehalt im Bad von ≤ 1 % - eine Vergleichbarkeit zu den in der entsprechenden Fachliteratur für angegebene spezifische Verbräuche bei der Herstellung von Kupfer-Anoden zur Bewertung des Nutzungsgrades angenommen werden.
Der Produktionslauf zur Herstellung der Kupferanoden im Chargenregime mit der Untergliederung der Prozeßstufen ist:

• Einsetzen,
• Einschmelzen,
• Oxidieren,
• Polen,
• Vergießen und
• Vorbereiten.

Of the previously known methods for reducing copper melts with the use of

• Wood (so-called pole poles)
• Heating oil, L u. M (hard coal heating oil) and
• Natural gas, H

the trend in the production of copper anodes is towards gas poling with the use of natural gas from group H.
Although the respective type of furnace, the batch weight and the copper-containing pre-run materials used have an influence on a comparison of the degree of utilization, a comparison with the specific consumption stated in the relevant technical literature for the specific consumption in the bath can - based on an oxygen content in the bath of ≤ 1% of copper anodes to assess the degree of utilization.
The production run for the production of copper anodes in the batch regime with the breakdown of the process stages is:

• Deploy,
• Melting,
• Oxidize,
• Poland,
• Shedding and
• To prepare.

Based on the batch regime, an average of around 10% the time needed. To evaluate the degree of utilization can in a first approximation the average oxygen quantity to be reduced with 9 kg / t anodes be placed. This corresponds to a degree of utilization = 1.

The following applies:

H ₂ requirement per t: 9 32 22.4 * 0.5 = 12.6 m 3rd N / t anodes

Compilation of the actual Polgas consumption and the theoretically required hydrogen consumption quantities: Batch number Batch weight H ₂ -is consumption m ³ N / batch N ₂ -Is consumption M ³ N / batch H ₂ / N ₂ ratio Theoretical H ₂ consumption m ³ N / batch 39 133.3 1,003 900 40 134.4 1,240 300 41 145.7 1,028 400 71.98 / 28.02 1,285 44 139.3 1,058 600 63.8 / 36.2 1,073 45 140.5 1,086 650 62.55 / 37.45 1,261 46 129.8 1,086 250 - - (finished polish with wood) 47 140.3 1,396 750 65.05 / 34.95 1,604 50 139.4 1,168 450 72.19 / 27.81 1,550 51 134.7 1,304 750 63.48 / 36.52 1,371 52 126 1,040 650 61.54 / 38.46 1,177 55 135.7 1,222 600 67/33 1,581 56 144.8 912 600 60.32 / 39.68 1,521 57 144.5 1,049 650 61.74 / 38.26 987 58 139 1,360 650 66.77 / 33.23 1,332 61 139 1,587 1,000 61.34 / 38.66 1,230

The ratio of the amount of hydrogen in m ³ N / batch of theoretical consumption to actual consumption results in utilization rates from 077 to greater than 1 (!). Due to this fact, it is likely that the swirling up of the copper bath in the immersion area of the pollanzes by the flame gases of the natural gas / oxygen furnace will result in a further, noteworthy reduction .
In the example cases, an air ratio of λ ≥ 0 6 was observed for furnace heating. Compared to Poland with natural gas, the use of H ₂ / N ₂ mixture> 60/40 vol.% And the described atmospheric conditions increases the degree of energy efficiency by a factor of two.

The use of hydrogen and nitrogen in the specified proportions and their introduction - advantageously at an immersion angle of greater than 30 to 90 ° - with a defined volume flow and with a defined supply pressure, as well as by maintaining a reducing furnace atmosphere, results in particularly advantageous conditions when poling . Particularly good results were achieved in particular by firing the refinery with natural gas / oxygen.
The swirling up of the copper bath at the pollanzas by the reducing agent on the one hand and by the flame gases on the other hand obviously creates extremely favorable reduction conditions with a noteworthy reduction also above the melt bath, where the temperature is between 1300 and 1400 ° C. The air ratio of the heating burners is advantageously between 0.5 and 0.8, preferably in the range from 0.6 to 0.7.

also einem Verfahren zur Desoxidation von Kupferschmelzen in einen Raffinierofen mit direkter Flammbeheizung und mit Einblasen eines brennbaren, gasförmigen Reduktionsmittels in die Schmelze, das dadurch gekennzeichnet ist,
daß als Reduktionsmittel ein Gemisch aus Wasserstoff und Stickstoff in einem Volumenverhältnis von 60 zu 40 bis 72 zu 28 eingesetzt wird und
daß im Ofenraum eine desoxidierende Atmosphäre durch entsprechende Einstellung der Ofenbeheizung, d.h. der Heizbrenner, auf eine Lufverhältniszahl von 0,5 bis 0,8 eingehalten wird,

ein hochwirksames, schnelles und gut praktikables Verfahren zur Desoxidation und Raffination von Kupfer.

Overall, with the described method,

a process for deoxidizing copper melts in a refining furnace with direct flame heating and with blowing a combustible, gaseous reducing agent into the melt, which is characterized in that
that a mixture of hydrogen and nitrogen in a volume ratio of 60 to 40 to 72 to 28 is used as the reducing agent and
that a deoxidizing atmosphere in the furnace space is maintained by an appropriate setting of the furnace heating, ie the heating burner, to an air ratio of 0.5 to 0.8,

a highly effective, fast and well practicable process for the deoxidation and refining of copper.

Claims (7)

Process for polishing (deoxidizing) copper in the molten state, in which a gaseous deoxidizing agent is passed into the melt,
characterized in that a gas mixture containing hydrogen and inert gas, preferably nitrogen, containing 35 to 90% by volume of hydrogen is used as the deoxidation gas. Process according to Claim 1, characterized in that a hydrogen-nitrogen mixture containing 50 to 75% by volume, preferably 60 to 72% by volume, of hydrogen is used as the deoxidation gas. A method according to claim 1 or 2, characterized in that a deoxidizing atmosphere is generated over the melt. Method according to one of claims 1 to 3, characterized in that the deoxidizing atmosphere is generated above the melt by appropriate adjustment of the heating burner. Method according to one of claims 1 to 3, characterized in that the gaseous deoxidizing agent is passed into and onto the melt and thus at least part of the reducing atmosphere is generated above the melt. Method according to one of claims 1 to 5, characterized in that in the case of pipe lances, the deoxidizing gas is introduced into the melt at admission pressures of 5 to 15 bar, preferably 8 to 12 bar. A method according to claim 6, characterized in that in the case of tubular lances, the flow rate per lance (H ₂ / N ₂ mixture) is set in the range from 200 to 350 m ³ N / h, lance outlet cross sections from 1 to 1.5 * 10 ^-4 m ² (= cm ² ) are observed.