Paper Technology Journal 17 - Voith

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Fig. 1: Previous AK design.
Fig. 2: New CompactPulper design.
Fig. 3: 3D presentation of the new Compact-
Pulper.
Fig. 4: Chest widths: comparison between
conventional and new design.
At sheet breaks the broke pulper must
reach full operating speed from start-up
in the shortest possible time. The procedure
is as follows:
As soon as a sheet break is detected, the
sheet is diverted directly into the broke
pulper located ahead of the sheet break.
At the same time the showers open, and
the sheet is wetted and pulled down with
the water flow. In the meantime, the
pulper rotors have reached full speed,
generating enough circulation energy to
draw in the sheet, which is then rapidly
pulped down and pumped off through the
pulper screenplate.
Based on Voith’s long experience, with
over 375 AK series pulpers delivered
since 1990, the objective of this development
project was to further increase
broke pulper efficiency whilst at the same
time reducing investment costs.
Slushing conditions in the broke pulper
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seem simple at first sight, but a closer
look quickly reveals just how many
boundary conditions have to be simultaneously
taken into account in order to ensure
reliable operation:
● Paper machine width and speed
● Paper grade, basis weight and location
of the sheet break in the machine
● Pulping intensity and suspension level
● Dwelltime
● Broke removal rate through the pulper
screenplate.
Additionally, the pulping consistency has
to keep within certain limits to ensure a
reliable sheet draw-in, good pulping and
stable pump operation.
The development project was carried out
on two levels due to the complexity of the
process and also the need for field trials:
● A full-size trial pulper, incorporating
the new optimized geometry of the
CompactPulper, was tested in Voith
Paper’s Technology Center. This
enabled intensive investigation of
machine parameters which usually
cannot be changed in mill operation
● Extensive mill trials and comparison
with the Technology Center’s trial
results.
Figs. 1 and 2 show the differences
between the conventional broke pulper
design and the new CompactPulper.
The trials clearly showed that a large part
of broke pulping energy is used for moving
the stock round. Compared with
pulpers for slushing recovered paper or
virgin fiber pulp, in broke pulpers the
sheet is brought into the pulper in a
clearly defined way. It has already been
thoroughly wetted on both sides by the
showers. This means that pulper dwelltime
is reduced by the time otherwise required
for breaking down and wetting the
paper when presented in bale form.The
pulper chest can therefore be much
smaller, as confirmed by the trial results.