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The standard practice with such large preheaters
is to have two right-hand shafts and two
left-hand shafts, with only one shaft being
motor-driven and the other three shafts being
driven by toothed gears. “For Emal, the shaft
driven by toothed gears is identical in construction
to the motor-driven shaft. Although this
requires more design effort, as well as more
material, it reduces the spares that have to be
kept in stock should a fault occur. Therefore
only one right-hand shaft and one left-hand
shaft are needed for all three units.”
Mr Ginster points out that the largest machines
available have always been supplied by
Köllemann. For example, there is a preheater
with a capacity of 50 tonnes an hour at Alcoa
Mosjøen in Norway. Köllemann
also recently supplied a 60t/hunit
to an anode plant in China
– the largest preheater currently
available on the market.
Köllemann preheaters have
a number of distinguishing features.
Small mixing paddles are
attached to the outside of the
shaft to better loosen and mix
the product, and ensure that the
kneader can thoroughly wet the
petcoke with pitch without difficulty;
this results in optimal, homogenous
mixing of the petcoke
and avoids hot spots.
The preheaters are designed
so that they are very easy to
service: all parts of the unit are
readily accessible to maintain
the shaft exits and the sealing
elements. Furthermore, the seals
where the shafts exit the machine
housing can be removed
completely from the top without
having to dismantle the whole
console. The worm itself does
not require any maintenance
and is characterised by a long
service life, measured in terms
of decades.
The bearings, too, have been
specially designed. “I have seen
competitive products which
have the riskiest designs of bearing
possible,” says Mr Ginster.
“However, at the ends we use
maintenance-free high-temperature
bearings made from special
graphite; these allow the shaft
to be swivelled slightly and to
move freely along its length. This
means thermal expansion does
not exert any stress on the shaft,
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which thus increases its service life. We also
use a double bearing so that the toothed gears
mesh accurately, which is also very maintenance-friendly.”
The preheaters are also characterised by
very good insulation and thanks to which
there are hardly any heat losses. The thick
insulation does not only ensure high energy
efficiency though: above all it is important for
occupational safety. “Our preheaters are only
lukewarm on the outside even though there
is thermal oil at 300 °C flowing through the
shafts. We thus conform to the latest machinery
directive even though the preheaters are
used in countries where such requirements do
not apply.”
The leading Mixing Technology
for Anode Pastes
The insulation (rock wool) is also of modular
design and can be removed and installed again
without damage. It is cassette-type insulation
with clips holding the cassettes together.
fit for the future
Köllemann is already undertaking development
work for a new generation of preheaters
in order to be well prepared when hightemperature
pitch is increasingly used in a few
years’ time; such pitch does not melt until it
reaches 300 °C, in contrast to the 180 °C that
is the case with the standard pitch commonly
used today. The reason for this change is
that a new environmental directive that forbids
For over 50 years BUSS KE and CP series Kneaders have been
the benchmark for reliable, cost-effective compounding of
anode pastes. Now we go one step further.
ALUMINIUM · 9/2013