CPT International 01/2018

heated exhaust gas flow is directed to a
heat exchanger via a suitable pipe system”,
continues Sauke.
The primary air side (hot gas side),
which is prefixed to the heat exchanger,
requires additional components: for
example, a control unit that directs the
exhaust gas flow to the heat exchanger
according to the requirement, and additional
measuring points that ensure
safe process management. In the event
of failure of the heat exchanger or any
of the components, the control unit
must direct the exhaust flow through a
bypass function, past the heat exchanger,
directly into the secondary system to
protect the heat exchanger and its components.
In the heat exchanger, the energy
is released to the secondary air side
(burner air) – the cooled exhaust gas is
discharged in the other system either
directly into the atmosphere or for preheating
the melting material in a corresponding
chamber.
The burner air fan conveys cold
burner air from the environment into
the heat exchanger, which is heated
there in the ZPF smelting systems
to about 200 °C. The pipe system after
the heat exchanger is insulated and
equipped with appropriate butterfly
valves, measuring instruments and displays.
An air collector installed directly
after the heat exchanger helps distribute
the heated medium evenly across
the piping to the entire burner system.
Thus, the flame temperature increases
significantly, resulting in a higher energy
input and lower gas consumption.
“In this way, not only are operating
and energy costs reduced, it also
allows for a careful handling of the
valuable resource of gas,” says Sauke.
“The efficiency of the entire system is
increased, and the pollutant emissions
are reduced.” This heat exchanger variant
is suitable for all ZPF gas-fired aluminum
smelting and heating furnaces,
which have a connected load of more
than 300 kW and a high smelting ratio
over the entire operating time of the
furnace. However, the specified limit
temperatures for the refractory lining
of the kilns must be strictly adhered to.
In burner air preheating by means of a heat exchanger, the warm exhaust gas volume
gas consumption
“Burner air preheating not only saves on
operating and energy costs, it also makes
it possible to use the valuable resource of
system will be increased, and pollutant
emissions will decrease,” explains Sven-
Olaf Sauke, head of R & D at ZPF
Burner air preheating by
means of heat exchanger as
ing
systems
The extension of the energy-efficient
burner air preheating with an integrated
heat exchanger can also be carried out
with an existing smelting system, but requires
some changes, according to Sauke:
“When upgrading existing ZPF systems,
in addition to the heat exchanger, a hot
gas withdrawal point, suitable piping
and temperature-resistant control and
butterfly valves must be integrated. The
adjustments with regard to the control
as well as the user interface must also be
observed. “All electrically operated components,
for example the control valves
and the measuring technology, are integrated
in the control and in the control
cabinet in order to simplify the operation
of the system.
All modifications and retrofits of
the system are done by ZPF directly
at the customer’s premises - before
this, a comprehensive inventory, consultative
discussions and an in-depth
conception will take place. In closing,
Sauke explains: “The need for pipes,
routes and insulation material must
be calculated on a project-specific basis.
The advantage of the developed
system lies in the fact that all components
are installed directly at the plant
and thus no further space requirement
arises in the smelting system. “In addition,
ZPF is working intensively on further
measures to improve the efficiency
of the aluminum smelting systems.
www.zpf-gmbh.de
Casting Plant & Technology 1 / 2018 19