Distillation Processes for Magnesium Winning and Recycling

André Ditze et al.: Distillation Processes for Magnesium Winning and Recycling
Distillation Processes for Magnesium Winning
and Recycling
André Ditze, Christiane Scharf
The low melting and boiling temperature of magnesium
allows distillation processes for winning and recycling.
Fundamentals for the distillation under vacuum show high
distillation rates if molecular distillation is assumed. In
practical application, the distillation processes are carried
out in the high vacuum region and therefore inert gases are
present. – The increasing use of magnesium alloys results
in increasing scrap quantities. Starting from the scrap classification post consumer scrap and residues come into consideration for distillation processes, because the removal of
impurities from magnesium is very limited by conventional
refining. The winning processes for magnesium using distillation are shortly described and their qualification for the
addition of magnesium scrap is discussed. – Distillation of
magnesium scrap has been done already in the past. These
processes and actual work are reviewed. The results are
compared with each other, and the distillation rates are
calculated. It is evident that the distillation rates in these
processes are much lower than expected from molecular
distillation. Based on that, possible arrangements are presented and the production rate and energy consumption
are estimated.
Keywords:
Distillation – Magnesium – Magnesium scrap – Energy
consumption – Costs – Recycling
Destillationsprozesse zur Gewinnung von Magnesiummetall und zur Aufbereitung von Magnesiumschrott
Wegen der geringen Schmelz- und Siedetemperatur von
Magnesium kann das Verfahren der Destillation sowohl
zur Gewinnung von Magnesiummetall als auch zur Aufbereitung von Magnesiumschrott genutzt werden. Aus
Grundlagenuntersuchungen zur Vakuumdestillation von
Magnesium ergeben sich durch Annahme der Molekulardestillation hohe Destillationsraten. In der Praxis werden solche Prozesse im Hochvakuum durchgeführt. – Der
steigende Einsatz von Magnesiumlegierungen führt zu
einem steigenden Schrottaufkommen. Ausgehend von der
Schrottklassifizierung kommen vor allem post consumer
scrap (PCS) und Rückstände aus dem Recyclingprozess
als Ausgangsmaterial für die Destillation infrage, da die
Entfernung von Verunreinigungen aus Magnesium auf
konventionellem Wege beschränkt ist. Zunächst werden
Destillationsprozesse zur Gewinnung von Magnesium-
metall beschrieben, um schließlich deren Einsatz für Magnesiumschrotte zu diskutieren. – Die Destillation von
Magnesiumschrotten wurde bereits in der Vergangenheit
praktiziert. Diese und derzeitig eingesetzte Verfahren
werden aufgeführt und hinsichtlich ihrer erzielten Ergebnisse und der berechneten Destillationsraten verglichen.
Es zeigt sich, dass die Destillationsraten der genannten
Prozesse kleiner sind, als dies von der Berechnung der
Molekulardestillation zu erwarten wäre. Davon ausgehend
werden Auslegungen für praktisch einsetzbare Anlagen
vorgeschlagen, wobei die Produktionsraten, der Energieverbrauch und die Kosten kalkuliert werden.
Schlüsselwörter:
Destillation – Magnesium – Magnesiumschrott – Energieverbrauch – Kosten – Recycling
Procédés de distillation pour obtenir du magnésium métallique et pour le recyclage de la mitraille de magnésium
Procesos de destilado para ganancia y reciclado de magnesio
Paper presented on the occasion of the European Metallurgical Conference Emc 2003, September 16 to 19, 2003, in
Hannover.
1
Fundamentals
Already at temperatures below the melting temperature
of magnesium (650 °C) the vapour pressure even enables
sublimation of magnesium. The vapour pressure of pure
magnesium compared to that of pure zinc is shown in
Figure 1.
The vapour pressure of zinc exceeds the vapour pressure of
magnesium. Remembering most magnesium alloys contain
zinc, some contamination of the distillate with zinc has to
be expected.
World of Metallurgy – ERZMETALL 57 (2004) No. 5
The distillation of metals can be done at ambient pressure
or under vacuum. In the case of vacuum distillation the
temperature can be lower than the boiling temperature,
which is 1090 °C of pure magnesium. On the other hand
extra expenses are necessary for the vacuum equipment.
The rate determining steps at the vacuum distillation are:
•
•
•
•
Heat and materials transport in the liquid metal
Evaporation
Materials transport in the gas
Condensation
251
Petra Zapp et al.: Long Term Supply of Aluminium to the European Automotive Industry
Long Term Supply of Aluminium
to the European Automotive Industry
Petra Zapp, Wilhelm Kuckshinrichs, Georg Rombach
The paper discusses various long-term developments of
the use of aluminium in the automotive sector and their
possible impact on the European aluminium industry in
view with both primary aluminium industry and the use
of scrap, up to 2040. Using a scenario, the differences between the increased use of aluminium in conventional and
aluminium-intensive vehicles (AIV) are shown. A variety
of parameters influences the availability of old and new
scrap and also the demand of primary or recycled metal.
Investigated are market developments of new automobiles
and collection behaviour for end of live vehicles (ELV) in
general. To illustrate the impacts on the different car concepts, the automotive aluminium is classified in casting or
wrought alloys, which have to be distinguished with regard
to recycling aspects.
Keywords:
Aluminium use in cars – Car market – Scenario calculation
– Supply of wrought and cast alloys – Primary production
and recycling – System sensitivity
Langfristige Aluminiumversorgung der Europäischen Automobilindustrie
Der Beitrag diskutiert verschiedene langfristige Entwicklungen des Einsatzes von Aluminium im Verkehrssektor
und ihre möglichen Auswirkungen auf die europäische
Aluminiumindustrie im Hinblick auf die Produktion von
Primäraluminium und die Nutzung von Schrotten. Mit Hilfe von Szenariotechniken werden die Unterschiede eines
steigenden Einsatzes von Aluminium in konventionellen
Fahrzeugkonzepten im Gegensatz zu aluminium-intensiven Fahrzeugen (AIV) bis zum Jahr 2040 aufgezeigt. Eine
Vielzahl von Parametern beeinflusst dabei die Verfügbarkeit von Alt- und Neuschrotten sowie die Nachfrage nach
Primär- bzw. Recyclingmetall. Unabhängig vom Einsatz
des Aluminiums im Automobil werden die Marktentwick-
lung von Neufahrzeugen sowie die Erfassung von „End of
life“-Fahrzeugen (ELV) als wichtige Parameter bestimmt.
Zur besseren Darstellung der Bedarfsentwicklung bei unterschiedlichen Fahrzeugkonzepten werden die verwendeten Werkstoffe in Guss- und Knetlegierungen eingeteilt,
um insbesondere den verschiedenen Recyclingaspekten
Rechnung zu tragen.
Schlüsselwörter:
Aluminium im Automobil – PKW-Markt – Szenariorechnung – Versorgung mit Guss- und Knetlegierungen – Primärproduktion und Recycling – Sensitivitäten
Approvisionnement en aluminium à long terme à l’industrie automobile européenne
Abastecimiento a largo plazo de aluminio a la industria europea del automóvil
Paper presented on the occasion of the European Metallurgical Conference Emc 2003, September 16 to 19, 2003,
in Hannover
1
Introduction
The growth of aluminium and the automotive sector are
closely connected. The transport sector was the biggest
end use sector of the European aluminium industry in 2000
accounting for 29 % of demand. And it will become even
more important. The entire European aluminium industry
is affected by these developments. Within the transport sector car production plays the dominating role. Using more
and more extrusions and rolled products beside castings,
the automotive sector covers the variety of production
paths. On the other hand, the availability of primary and
recycled aluminium is strongly influenced by the car industry being the biggest old scrap-producing sector and the
biggest user of new and old scrap at the same time.
258
During the last two to three years, a lot of changes in the
overall aluminium system and in certain parameters of the
metal flows have taken place which are worthwhile to be
investigated and which show former studies in a new light
[1]. Especially the availability of aluminium scrap has been
matter of lively discussions in different committees like
GARC (Global Aluminium Recycling Committee), and
working groups of OEA, EAA, and their members. Additionally, the need became obvious to expand the system
boundaries from a national to an European or even to a
global level due to several reasons. First of all, the international scrap trade makes the determination of recycling
quotas and recycled contents of a certain region or country
nearly impossible. Here the global approach of GARC
will hopefully create better knowledge in the near future.
World of Metallurgy – ERZMETALL 57 (2004) No. 5
Udo Boin et al.: Measuring – Modelling: Understanding the Al Scrap Melting Processes Inside a Rotary Furnace
Measuring – Modelling:
Understanding the Al Scrap Melting Processes
Inside a Rotary Furnace
Udo Boin, Markus A. Reuter, Thomas Probst
Karl Konzelmann Metallschmelzwerke GmbH and the
Institute of Resources Engineering of Delft University of
Technology agreed upon a joint measuring and modelling
program for a standard-type rotary furnace. The fundamental processes inside rotary furnaces as a function of
various operating parameters are in fact not yet widely
known. For example the economically decisive metal yield
is predominantly controlled by the metal burn-off rate
inside the furnace. However, this burn-off rate is neither
measurable nor deducible from data so far routinely recorded at refiner plant operations. An aluminium refiner
is rather interested in a feed forward control than in a retrospective explanation of past metallurgical errors. Therefore an extensive measuring program was carried out at
Konzelmann’s plant in Hannover during which meaningful
data were registered or recorded and then methodically
evaluated by interconnected mass- and energy balances.
The output of such a combined computer model was compared with actual operating results. Essential parameters
were altered until actual furnace and model results were
in acceptable conformity. As one final result, burn-off rates
specific for different scrap categories were calculated from
a total of 26 furnace cycles.
Keywords:
Aluminium recycling – Data reconciliation – Energy and
mass balance model – Burn-off rates – Feed forward control
Messen – Modellieren: Zum Verständnis der Schmelzprozesse von Al-Schrott im Drehrohrofen
In einem gemeinsamen Mess- und Simulationsprojekt der
Konzelmann Metallschmelzwerke GmbH und des Institute für Resources Engineering der Delft Universität der
Technologie wurde ein Drehrohrofen auf verschiedene
bisher zum Teil ungemessene Parameter untersucht. Ökonomisch entscheidend für einen Betrieb ist die Minimierung des Metallverlusts durch Aluminiummetallabbrand.
In diesem Artikel wird beschrieben, wie die unmessbaren
Abbrandraten für Schrotte durch Verwendung eines entwickelten Massen- und Energiebilanzmodells bestimmt
wurden, das durch gemessene Industriedaten kalibriert
wurde unter Berücksichtigung von Datenausgleichsrech-
nungen und deren statistischen Eigenschaften. Durch eine
iterative Ausgleichsrechnung konnten aus 26 Ofenreisen
die Abbrandraten für verschiedene Schrottkategorien bestimmt werden. Dieses Modell ermöglicht eine vorwärts
gekoppelte Steuerung des Ofens in Bezug auf den Schrotteinkauf, den Ofenbetrieb und die Minimierung der Metallverluste.
Schlüsselwörter:
Aluminiumrecycling – Datenausgleichrechnung – Energie- und Massenbilanzmodell – Abbrandraten – Vorwärts
gekoppelte Steuerung
Mesurage – Modelage: Comprendre le processus de fusion des mitrailles d‘aluminium dans un four tournant
Medición – Modelado: Comprender el proceso de la fusión de chatarra de aluminio en un horno rotatorio
Paper presented on the occasion of the European Metallurgical Conference Emc 2003, September 16 to 19, 2003,
in Hannover.
1
Introduction
A rotary furnace is the preferred melting device at aluminium refiners when processing contaminated mixed scrap.
The prevailing fraction of this scrap category is collected
old scrap. With regard to the increasing aluminium alloy inventory in European automobiles the tonnage of collected
aluminium scrap from this sector will in the foreseeable
future sizeably grow.
266
In view of the outstanding economic importance of the
European automobile industry and its obligation to make
at least 85 % of its cars recyclable by 2006 – and 95 % by
2015 – an efficient processing of collected aluminium scrap
is as well imperative as indispensable.
Due to contemporary automobile design collected scrap
from old cars – customary after passing a shredder and a
sink-float plant – contains inorganic and organic impurities
as well.
World of Metallurgy – ERZMETALL 57 (2004) No. 5
Martin Iffert et al.: „9-Box-Control“ zur Optimierung der Aluminium Schmelzflusselektrolyse
„9-Box-Control“ zur Optimierung der
Aluminium-Schmelzflusselektrolyse
Martin Iffert, Andreas Heime
Die Erzeugung von Reinaluminium als wichtigstem Leichtmetall steht weltweit unter dem starken Druck steigender
Energiekosten, insbesondere in Mitteleuropa. Daher steht
die Verminderung des Energieeinsatzes im Fokus der Erzeuger von Primäraluminium. TRIMET Aluminium AG
und Heraeus Electro-Nite haben gemeinsam die Liquidusmesstechnik zur industriereifen Anwendung in Zellen
der Aluminium-Schmelzflusselektrolyse weiterentwickelt.
Auf dieser Basis wurde ein Algorithmus konzipiert, der
eine optimierte Steuerung der Energie- und Massenbilanz von Elektrolysezellen ermöglicht. Kern dieser neuen
Strategie ist die direkte und gleichzeitige Messung von
Badtemperatur, Liquidustemperatur und somit auch Superheat. Weitere Messungen dienen u.a. zur Analyse des
Kathodenzustandes. Die so ermittelten Daten bestimmen
die Lage des Ofens im Zustandsraum, welcher in neun
Bereiche (Boxen) unterteilt ist. Abhängig von der Box
werden Spannung und/oder AlF3-Zufuhr geregelt. Durch
Anwendung dieses Systems ist es möglich die Prozessvariationen zu vermindern und den Energieverbrauch zu optimieren. TRIMET betreibt seit Mitte 2003 alle 360 Zellen
seiner 155 000 t/a produzierenden Aluminiumelektrolyse
in Essen mit dieser sog. 9-Box-Control. Die Ergebnisse aus
dem ersten Jahr sind vielversprechend, es wird ein spezifischer Energieverbrauch von unter 14 kWh/kg Aluminium
und eine Stromausbeute von über 94 % als dauerhaft erreichbar angesehen.
Schlüsselwörter:
Aluminiumelektrolyse – Superheat – 9-Box-Control –
Energiebilanz – Massenbilanz
“9-Box-Control” for an Optimised Aluminium Smelting Process
TRIMET Aluminium AG operates an aluminium reduction plant in Essen at the heart of the industrial Ruhr area
of Germany. The smelter was commissioned between 1971
and 1973. The pots are produced in line with the latest Alusuisse technology, with end-to-end cells having pre-baked
anodes. They are equipped with point feeders and modern
computer pot controllers. With amperages between 158
and 165 kA, the 360 pots in three pot-lines achieve an annual output of 155,000 t of high-grade primary aluminium.
Reduction of specific energy consumption is a core target
for aluminium smelters worldwide. In the past 30 years, the
introduction of point-feeders, computer pot-controllers
and subsequent development of sophisticated algorithms
to control the alumina concentration in a narrow band,
have decreased the specific energy consumption by about
2 kWh per kg of aluminium. Further savings are feasible by
reducing the process variations associated with energy and
mass-balance disturbances. These balances are strongly linked to the mass of solid and liquid bath in the pot. Liquid
baths consist of cryolite that is modified with additions of
aluminium fluoride, calcium fluoride and alumina, in order
to reduce the liquidus temperature from 1010°C to 950 °C
and, at the same time, decrease metal solubility. The side
crust (ledge) consists of pure cryolite and hence, melting
or freezing of side ledge will, respectively, decrease or
increase the aluminium fluoride concentration in the bath.
Hence, changes in pot energy balance will affect the mass
balance and vice versa. Therefore, it is necessary to distin272
guish between energy and mass-balance induced disturbances in order to come to the right decisions. Superheat
(the difference between bath and liquidus temperature)
measurements provide the necessary information to overcome this problem. TRIMET Aluminium AG and Heraeus
Electro-Nite have jointly developed a new control algorithm to optimise energy and mass balance in aluminium
reduction cells. Central to this new strategy is the direct and
combined measurement of bath temperature, liquidus temperature, and hence superheat. Additional measurements
are used to monitor cathode voltage drop and sodium impurities in the alumina. These received data determine the
state of the pot in the 9-box scheme. Setup of the nine boxes
is done by dividing the bath temperature (x-axis) and liquidus temperature (y-axis) into three sectors each. This will
divide the space of a two-dimensional diagram into nine
boxes. A set of linguistic rules describes the control action
in each of the nine boxes. Additions are determined according to the box number, voltage and/or aluminium fluoride.
The application of this system reduces process variations
and hence leads to optimised energy consumptions. – Prior
to the start of this system, it is important to determine the
impact of process operations, measurement location and
modifications of voltage, as well as aluminium fluoride
additions. At this stage, detailed measurements are done
while manipulating individual pots. After completing these
tests, the routine measurement schedule is clearly set up
and individual rules for all boxes are defined. – TRIMET
World of Metallurgy – ERZMETALL 57 (2004) No. 5
Rudolf P. Pawlek: Bauxite and Alumina Activities at the Turn of the Year 2003 / 2004
Bauxite and Alumina Activities
at the Turn of the Year 2003 / 2004
Report by Rudolf P. Pawlek
This review covers the period January 2003 to July 2004.
Key events were:
Alcan acquired Aluminium Pechiney, paying ¥ 4 bn.
Alcan has decided to expand its Gove alumina refinery
in northern Australia from 2 mill t/a to 3.5 mill t/a using
proprietary Alcan technology.
Comalco and Hydro Aluminium signed one of the largest
alumina supply contracts in the history of the aluminium
industry. Under the agreement, starting with a volume of
300,000 t/a in 2005, Comalco will supply Hydro Aluminium
with 500,000 t/a from 2006 through to 2030.
Alcoa will increase the capacity of its alumina refinery in
Suriname by 200,000 t/a and at its Australian alumina refinery at Pinjarra by 600,000 t/a. Alcoa expanded the capacity of its Jamaican alumina refinery by 250,000 t/a and of its
US-based refinery at Point Comfort by 300,000 t/a.
Kaiser Aluminum’s sale of its aluminium upstream activities became a saga which rebounded surprisingly at several
stages.
Brazil’s Alunorte project kicked off its second expansion
phase, increasing capacity by 2.4 mill t/a.
Hydro Aluminium sold its 50 % stake in Aluminium Oxid
Stade to Dadco.
1
Africa
1.1
Guinea
In December 2002, Russian Aluminium (RusAl) acquired
a majority interest in Africa’s only alumina refinery at
Friguia in Guinea. Rusal bought the stake in Guinean
Investment Co Ltd (GIC) from Cayman Islands-based
trading company Manro Haydan Overseas. Although
further details were not disclosed, the price is rumoured to
have been as much as US$ 75 mill. GIC together with the
government of Guinea owns the Alumina Co of Guinea
(ACG), which has a 23-year lease on the assets of the Friguia alumina refinery. During 2002 the refinery achieved its
700,000 t/a capacity the first time during its 40-year history.
A group of ex-Reynolds Metals Co executives installed by
Manro Hayden at ACG is credited with turning around the
performance of the refinery and increasing its efficiency.
Despite this improvement the plant still needs further investment to achieve its planned expansion. RusAl officials
in Guinea struck a partnership deal with Randy Reynolds
to raise production at the refinery to 1.2 mill t/a. According
World of Metallurgy – ERZMETALL 57 (2004) No. 5
to preliminary estimates the project will cost US$ 250 to
300 mill. RusAl has a 25-year contract to manage Guinea’s
Cie des Bauxites de Kindia bauxite mine and a concession
to develop another bauxite mine Dian-Dian. Guinea has
30 % of the world’s known reserves of high quality bauxite
for refining into alumina.
In February 2004, RusAl announced the commencement
of a detailed feasibility study on the expansion and modernization of its Friguia Alumina Refinery in Guinea. The
Canadian engineering company Hatch Associates will conduct the feasibility study in collaboration with RusAl-owned
VAMI. The plant’s capacity will increase from 700,000 t/a
to about 1.4 mill t/a within three years of the project’s
completion. Modernisation will improve alumina quality,
improve environmental performance and reduce operating costs. The feasibility study is expected to be complete
by the end of 2004 and the engineering, procurement and
construction stages of the project will begin in early 2005.
The estimated cost of the project is about US$ 350 mill. The
Hatch Group, which incorporated both Kaiser Engineers
and BHP Engineers, is a world-renowned engineering and
construction organization, which has provided industry
and government with management and technical services
for more than 80 years.
In January 2003, Guinea Aluminium Products (from May
2004 onwards Global Aluminium Products Co) (Gapco),
through its wholly-owned subsidiary Boké Alumina Co
(BAG), was planning to build a 2.6 mill t/a alumina refinery
in the west African country, and shortlisted US investment
bank Salomon Smith Barney to arrange financing for the
US$ 2.2 bn project. The Sangarédi bauxite mine is operated by Cie des Bauxite de Guinée (CBG), a joint venture
49 %-owned by the government of Guinea and 51 % by
Halco Mining, a consortium formed by Alcan and Alcoa.
Halco is not involved in the Gapco project as its members
have existing refinery capacity of their own, but BAG has
been granted a concession to mine bauxite in Boké, which
has estimated reserves of 6 bn t. This project could be one
of the lowest cost producers in the world. The lifespan of
the project is potentially 100 years. The bauxite at Boké is
particularly abundant, with an alumina content recorded
as high as 69 %. Gapco is a consortium whose members
include Mitsubishi and Marubeni, two of Japan’s largest
trading companies, and western venture capital providers.
New York-based Herakles is one of two leading developers
in Boké, and has raised most of the private investor capital.
The other is Karalco, a London-based concern with experi281