Paper Technology Journal 17 - Voith

than 5% organic content. In Austria this
ruling has been effective since 01.01.
2004.
The “export” of rejects for disposal in
countries with lower standards involves
tremendous transport costs, and is only
possible to a very small extent because
of regulations on waste shipment. As a
result, rejects from recycled fiber operations
must generally be incinerated and
only the combustion residues can be
landfilled.
What are the consequences of incineration?
The rejects have to meet certain
quality requirements. What at first seems
to be a paradox is going to become a
major design criterion for recycled fiber
plants:
● Inspection of the incoming raw
material will become more and more
important
● With baled material the dewiring
efficiency will influence the required
technology for rejects handling
Fiber Systems
Fig. 1: Automatic container loading station.
Fig. 2: Lightweight coarse rejects after
compacting.
Fig. 3: Heavyweight fine rejects from the
cleaners.
2 3
● Removal of incombustible, inert
material such as metal, glass or sand
from the rejects is essential
● The metal fraction should be as clean
as possible to facilitate its recycling,
instead of disposal
● Rejects dry content has a decisive
influence on suitability for incineration
and on the transport costs involved.
The main objective is still to get rid of the
rejects. Immediately, wherever and whenever
they arise.
What exactly are rejects composed of?
First of all, there is a basic difference between
rejects and sludge. Sludge is homogeneous,
like for instance the residue
from deinking cells, from micro-flotation
or from primary clarification.
Rejects, however are not homogeneous.
They consist of coarse and fine rejects.
Coarse rejects are found in pulping and
coarse screening, fine rejects in the subsequent
process stages of cleaning and
fine screening as well as in the approach
flow system.
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Heavy coarse rejects are all kinds of metal
of different shapes and sizes, stones,
wet strength waste paper that has not
disintegrated, wires etc.
Light coarse rejects (Fig. 2) consist of
bits of plastic, plastic foils, CDs, etc.
The composition of the coarse rejects depends
mainly on the type of pulping system:
here one can distinguish between
systems that discharge heavy- and lightweight
coarse rejects separately (e.g.
TwinPulp System) or systems where
these are removed together. With the increasing
use of drum pulpers the focus is
more and more on the latter option.
With fine rejects one distinguishes between
light- and heavyweight, too.
Heavy fine rejects mainly consist of sand,
glass, staples and other metallic office
waste as removed by HD and LD cleaners,
as well as via the heavy junk traps of
combined screening and cleaning equipment
(Fig. 3).
Light fine rejects from slot screening or
lightweight cleaning contain fiber debris,
stickies, wax, fillers, etc.
And now back to the main concern: how
can we ensure that all these types of rejects
are got rid of at all times and in all
places?
To answer this question we have to go
back and look at the available options for
disposal. Here we again come face to
face with the increasingly exacting standards
set by legislation and with the requirements
for rejects quality.
17/04