CPT International 04/2016

cuit for the electrical equipment uses
only one pump of the same rating.
The water recooling system is controlled
by the furnace PLC via a remote
substation.
The extra hardware to be fitted for
the SRC system consisted only of
the variable frequency drive units
for the two furnace-circuit pumps, a
few temperature sensors, and some
small accessories. This was in addition,
needless to say, to the new
smart software developed for the application.
This software ensures that
the cooling water flow rate is adapted
at once when the cooling water
demand changes suddenly, e.g., because
the furnace is set to full power
by the operator or the load shedding
system. A simple control scheme
based on water temperatures alone
had been found inadequate. Figure
2 shows a typical screen menu, albeit
for a solution based on a water-to-water
cooler.
A water-to-water cooler fed from
the municipal water supply is fitted
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in the electrical equipment cooling
circuit for the event that the air temperature
exceeds 30 °C and the water-to-air
cooler can no longer adequately
cool the more heat-sensitive
converter assembly. For heat recovery,
a plate-type heat exchanger is integrated
into the circuit.
By now the two Monomelt systems
have been in operation for five
months, and a first comparison between
the traditional and new water
recooling systems can be made.
Considering the different service
conditions of the two furnace systems
it can be said that the variable-frequency
drive units of the
cooling water pumps save a lot of
energy. Thanks to the use of the SRC
the energy consumption of the water
recooling system could be reduced
by more than 30 %.
Thomas Wagner of KSB AG’s Pegnitz-based
foundry production engineering
unit had this comment:
“The scheme using VFD-controlled
pumps in the cooling circuit has
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proved a full success at our site. In the
five months since the melting system
was commissioned, we have benefited
from a trouble-free operation and
substantial energy savings. In our
production conditions, we save so
much power that the extra cost of
frequency-controlling the cooling
pumps will be recovered within just
about one year. KSB AG now plans to
retrofit the second coreless induction
furnace, which does not yet feature
frequency control of the cooling water
pumps, to this new technology.”
Moreover, the new system has led to
higher and more constant water temperatures,
which augurs well for the
intended installation of a waste heat
recovery system.
Conclusion
The smart SRC system has successfully
proven itself in practice and the
specified targets were achieved. The
use of this control scheme clearly increases
the energy efficiency of a water
recooling system, apart from delivering
a constant temperature that
facilitates energy recovery. Further
benefits include a rapid adjustment
to the melting furnace’s operating regime
plus an extended service life of
cooling system components. In all,
the economic benefits yield a short
payback period. These advantages
are confirmed by the fact that KSB
AG now aims to convert its second
melting furnace to this technology
as well.
It remains to be noted that a conversion
of existing water recooling
circuits to the new system can take
place at short notice and with little
installation effort. Work is now
ongoing to realize this system for
Duomelt applications as well (two
furnaces, one frequency converter)
and a solution for controlling the
fans of the air cooler or evaporative
cooler is in preparation. The system
is also suitable for use on other water-cooled
thermoprocessing equipment.
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Casting Plant & Technology 4/2016 19