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TECHNOLOGY
Low-energy air-cooled electromagnetic stirring systems
A. Peel, Altek
The benefits of metal circulation in aluminium
reverberatory furnaces have been
very well documented over the years, especially
the higher productivity, reduced
fuel consumption and reduced dross
generation, along with excellent alloy and
temperature homogeneity. One popular
method to achieve circulation is electromagnetic
stirring. That said, this technology
has traditionally had certain drawbacks
which limited its wider acceptance.
Financial drawbacks included high capital
and operating costs (especially power
consumption and maintenance of water
cooling systems). Technical drawbacks included
customers’ reluctance to use water
in close proximity to molten metal – in
the basement under the furnace hearth,
and in some cases the system was unable
to operate through full-thickness refractory
hearths. There have also been cases
where existing systems did not work in an
effective way through the side wall.
This article describes a technology
which amounts to a reinvention of the
traditional electromagnetic stirring device,
effectively addressing all of the
above negative aspects of traditional systems.
This article also discusses some of
these aspects and results in more detail.
The application of electromagnetic (EM) stirring,
which was initially introduced into the
aluminium industry in the 1960s, has grown
significantly since the late 1990s. Fig. 1 shows
the huge growth in application of different
types of EM stirring or pumping technologies
to circulate liquid aluminium in furnaces.
This was reported some years ago, but the
market has continued to grow significantly as
customers recognise the huge benefits to be
gained from stirring metal.
There are many different types of stirrers
available today, as the above graph shows, and
all will have more or less the same operational
benefits within the furnace. However, the big
difference between these devices is how they
achieve that result from the point of view of
installation, reliability and operational cost.
Water-cooled stirrers have predominated
until now, as there had not been a credible
alternative. Over the past three to four years
Altek’s air-cooled electromagnetic stirring
technology, Siber Force, has become increasingly
accepted in many of the world’s leading
aluminium operations as a credible alternative
to water-cooled EM stirring. Users include
Hydro, Constellium, Novelis, Hulamin, Sapa,
Kaiser Aluminum, Rusal, Nichols Aluminum,
Bridgenorth Aluminium, Carcano, China Steel
Aluminium, etc.
The Altek Siber Force technology ensures
that the stirrer has no direct contact with the
aluminium. There are no slots, channels, hollow
copper water tubing or water pipes, and
there is no risk or effect from the aluminium
bath content on the stirrer operation. The stirrer
can be started and stopped as required
without any risk to the stirrer operation or any
risk of blocking or plugging of dross into any
tubes or channels. It is a highly reliable piece
of equipment.
The technology – originally developed in
the MHD Centre in Krasnoyarsk in the 1990s
and then implemented widely throughout
Rusal – has been totally transformed by Altek
to meet the stringent requirements of international
aluminium operations. The technology
today is 100% designed and manufactured in
the UK and incorporates the very latest manufacturing
and control system techniques. It
has been progressively introduced into various
aluminium
operations,
each with different
operating
characteristics
and installation
requirements, and has been thoroughly tested
and proven. Several key factors have driven
its growing acceptance as an alternative to the
traditional water-cooled EM technology.
Low energy consumption operation: Traditional
water-cooled stirring devices consumed
quite large amounts of electrical energy because
their designs were quite inefficient in
view of energy consumption. Comparisons
with the new air-cooled technology discussed
in this article have shown the savings could
run into many hundred’s of thousands of euros
per year. Over five years this can add up to a
significant sum.
Air-cooling: It has become increasingly
apparent that customers are more and more
nervous of having water circulating systems
within the basement areas under the furnace
hearth. There have been one or two accidents
where a furnace has leaked aluminium into
the pit (due to a premature refractory failure
for instance), and having water under the
hearth in these situations increases the risk of
a catastrophic explosion. It is also not uncommon
to encounter flooded basements / pools
of water due to a water leak on a coil or water
feed hose.
EM stirrer design
To achieve the above differentiating points,
the design of the Altek Siber Force electromagnetic
stirrer features several fundamentally
different aspects and we will discuss each of
these in turn below.
Cooling medium: The inductor coils are
made from solid copper bar (not hollow tubing)
of certain dimensions and configured in a
special way around the laminated Fe core, so
as to reduce the resistance heating effect of
the electrical current as it passes through the
copper coils. In conventional devices this current
generates a lot of heat, and the water cooling
must remove this large I 2 R loss.
The cooling medium serves to remove the
heat that is generated by the electrical current
passing through the copper inductor. The Al-
Fig. 1: The application of electromagnetic stirring and pumping devices has grown
hugely since the late 1990s
Fig. 2: A solid
copper inductor
dissipates less heat
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