The Comparison, Measuring & Labelling of Energy-efficient Textile Machinery
be integrated into the exhaust air
system. The fresh air for the drying
process is therefore preheated here,
usually resulting in a heat recovery
efficiency of about 30%.
Air/water heat exchangers are even
more efficient because they have a
better heat transfer with the associated
benefits. A prerequisite for this solution
is of course a corresponding demand
for the hot water generated by the
exchanger. As a further measure, the
energy loss is minimized over the
surface of the dryer by an insulating
layer and specific design measures to
reduce the thermal bridges.
Example: CalenderCalender
nonwovens, this involves dry bonding
which dispenses with the use of
aqueous binders. This process requires
less energy consumption.
Electrical energyElectrical energy
The electrical energy required is mainly
composed of the following variables :The electrical energy required is mainly
composed of the following variables :
-The drive of the calender rollers
-Additional drives (reversing rollers,
gap adjustment, etc.)
Thermal energy
The thermal energy required is mainly
determined by the heating of the
calender rollers.
Calender heating
The calender rollers are heated by
thermal oil. The thermal oil can be
heated by either electrical energy or
fossil fuels (e.g. natural gas). Heat
generation by electricity makes sense
only in the minority of cases.
Features of an energy-efficient
machine concept
An essential part of the loss of thermal
energy is caused by the unused
surface of the heated calender rollers.
The losses can be reduced by
approximately 30 % by insulating this
area.
Example : Belt oven for the
thermal bonding of nonwovens
Unlike the chemical process of bonding-Generating the air flow which
passes through the product
-Generation of the exhaust air flow
-Generation of the fresh air flow
-Drive for the main transport system
(conveyor belts)
Here too, generating the air flow passing
through the product – as in the drying
processes – represents the main
electrical energy consumption. The
pressure loss created by the products
themselves can be regarded as a
constant. In essence, the pressure
loss (equivalent to electrical energy)
is determined by the circulation of the
internal air flow.
Thermal energy
The thermal energy required is mainly
composed of the following variables :
-Heating the product
-Heating the conveyor belts
-Water evaporation exhaust air/fresh
air exchange
-Heat loss on the surfaces
The thermal energy needed for heating
the material depends mainly on the
NCM-APRIL 2020
56fibre-specific properties (specific heat
capacity) of the product and can be
regarded as a constant. This also
applies to the water evaporation even
though the residual moisture of the
fibres is already very low. A major
influence on energy demand, however,
is the exhaust air that is withdrawn from
the system. This mainly involves the
discharge of the resulting vapour
production (avivages), flue gases (use
of fossil fuels for the heating system)
and the evaporated water from the
thermo bonding process. The system
is fed with fresh air in order to maintain
a constant air balance. Another relevant
factor is the conveyor belts used as
the product must be cooled to “freezing
temperature” after heating. All heat
losses arising on the surfaces depend
on the design of the insulation and
existing thermal bridges.
Features of an energy efficient
machine concept
Potential savings in the electrical
energy are provided by a machine
design with an optimized flow profile
and resulting low pressure losses. With
regard to thermal energy, the exhaust
and fresh air management is the
significant influencing factor. In
addition, heat recovery to heat the fresh
air can further reduce energy demand
– as does the use of lightweight
conveyor belts. The mass per unit area
of each conveyor belt type ranges from
approximately 5.4 kg/m2 (steel) to 0.5
kg/m2 (PTFe glass mesh). The specific
heat capacity of each type also varies.