K INTERVIEW
Internet-PDF from “Casting Plant & Technology “ 02 / 2012, pages 6 – 7
© Giesserei-Verlag, Düsseldorf
Cutting costs by charging with iron
residues
The price of input materials plays a major role in the foundry sector, with its intensive use of
raw materials and energy. Substantial cost savings in foundries can be achieved by using iron
residues instead of scrap in cupola furnaces, according to Dr. Michael Lemperle, Technical Consultant and former Vice President of shaft melting furnaces at the plant constructor Küttner in
Essen, Germany
We carried out successful trials with
residues in hot blast cupolas. In addition, we have already constructed shaft
melting furnaces for the steel industry
that are specially designed for charging
with residues.
How can the iron-bearing residues be
used in cupola furnaces?
Dr. Michael Lemperle studied physics and graduated in metallography at
RWTH Aachen in Germany. The expert for shaft furnaces was vice president
for this business segment at Küttner most recently, where he is still working
as a technical advisor (Photos: Küttner)
The advantage is purely financial. The
iron in the residues is always cheaper than scrap. There may be a further
advantage if the residues come from
steelworks. Because then they do not
have any undesirable elements.
Apart from the steel industry, the residues can also come from other industries. What is important, however, is that ferric oxide is left over as
a residue. This is the case, for example, when one roasts ores containing
zinc. Residues containing iron occur
in steelworks in large quantities, because the big smelters operate dust extraction systems that provide a lot of
dust and sludge containing ferric oxide.
Where else can those residues come
from?
What were your experiences with
iron residues at Küttner?
Dr. Lemperle. You say that iron resi­
dues are a reasonably priced alter­
native to scrap for the production of
molten iron in cupola furnaces. What
is the advantage of using residues?
Casting Plant & Technology 2/ 2012
This is possible if ferric oxide, lime
and other slaggable materials are
mixed with carbon and processed
to produce so-called self-reducing
bricks. Calculations of how much
carbon is needed to reduce the ferric oxide are made in advance. This
is generally 10 to 12 % carbon. The
mixture is then used in a normal
brick press for road construction.
With cement as a binder, the bricks
must harden for three days and can
then be used to charge the furnace.
Specialized brick producers are already providing bricks to the steel industry. Something similar is also possible in the foundry industry.
How much money can one save on
the melting process by using this
method?
The bricks contain about 40 to 45 %
iron in the form of ferric oxide. The
proportion of the oxide is over 60 %.
So 450 kg of iron can be obtained from
one tonne of bricks. One thus needs
about twice the amount of bricks compared to scrap. At the end of the day,
between 50 and 100 Euros can be saved
per tonne of molten iron.
Can shaft and cupola furnaces also be
completely charged with these bricks?
This is, unfortunately, not possible because one cannot fully utilize the melting performance of, say, a 20 tonne furnace if one only uses bricks. Compared
to scrap, one needs twice the amount
of bricks for the required amount of
molten iron. So you come up against
the capacity limits. Moreover, most
large plants now have dry gas cleaning.
Here the dirty gas is first burnt then
cooled and then goes into the filter. If
you now use bricks that also contain
carbon, the quantity of gas and the
CO content in the gas will increase. If
this is also supposed to be burnt in the
combustion chamber you end up with
a gas quantity that exceeds the capacity of the filter. With normal plants,
however, one can replace 20 to 30 % of
the scrap with bricks.
Has Küttner already sold furnaces
that specialize in melting bricks?
Self-reducing brick and possible sources of iron residues
Yes, for the first time in the steel industry we constructed such a furnace for
the German steel producer Thyssen.
Then another two in Japan and three in
China. The Japanese haven’t yet melted any bricks. They have limited themselves to scrap. The Chinese, however,
are running two lines. One line with
normal steelworks residues, like at
Thyssen, and the other line with residues from stainless steel production.
In this way, chromium and nickel are
reclaimed. Tisko Taiyuan has a reference plant in China that is also at an
advanced project stage. These plants
have wet gas cleaning, whereby only a
small amount of the gas is burnt to generate a hot blast. Most of it is used in
a power station to generate electricity.
This is, of course, particularly efficient.
www.kuettner.com
Casting Plant & Technology 2/2012