Paper Technology Journal - Voith

Experience with PM 5 led to the decision
to carry out trials in the Voith Sulzer
Paper Technology pilot plant facilities in
Ravensburg in order to improve stock
quality for the tissue machines PM 4 and
PM 7 as well. The basis for this was the
existing stock preparation plant PM 4/7,
but with the following changes:
■ The perforation of the hole screen
stage was reduced from 1.6 mm
to 1.2 mm.
■ A complete new MC slot screening
stage was installed.
■ The slot width of the LC slot screening
stage was reduced from 0.25 mm to
0.15 mm.
It was gratifying to have the results
obtained with PM 5 confirmed by these
trials. A reduction in stickies area of
74% was achieved in Voith Sulzer’s pilot
plant with the MC screening stages
(Fig. 11).
Further considerable reductions of 70%
and 67% respectively were achieved with
the low-consistency screening and dispersion
stages, the latter with a specific
energy consumption of approx. 90 kWh/t.
In all, a stickies area reduction of 97.5%
was achieved, compared with 88% with
the PM 4/7 plant.
The decision to change the plant concept
was made on the basis of these trial
results (Fig. 12). The upgrade has since
been completed and put into operation.
The detailed changes were:
Stock Preparation
HC pulping system
HD cleaning
MC screening B 1.2 mm
MC screening // 0.20 mm
Flotation
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Fig. 12: PM 4/7 stock preparation plant following
upgrading.
Loop I PM loop
HW cleaning
LC screening // 0.15 mm
LW cleaning
■ The perforation of the hole screening
stage was reduced from 1.6 mm to
1.2 mm.
■ A complete new MC slot screening
stage with a slot width of 0.20 mm
was installed.
■ The slot width of the LC slot screening
stage was reduced from 0.25 mm to
0.15 mm.
■ A new washer was installed for
improved reduction of ash and fines.
Latest measurements from the PM 4/7
plant confirm the expectations:
■ The MC screening stages reduce the
stickies area by 70%,
■ LC slot screening by a further 70%
and
■ dispersion by 67%.
In all, a reduction in stickies area of 97%
was achieved.
Washing
HC thickening
Dispersion
Reductive bleaching
Storage tower
HW cleaning
LC screening B 1.6 mm
PM 4/7
Conclusions
Analyses of the stock preparation under
investigation, experience from another
plant in the mill and trials in the machine
supplier’s pilot plant led to an upgrade of
the stock preparation plant.
The objective was an improvement in
product quality, advantages in converting
and a reduction in cleaning work on the
paper machines. To achieve this, the perforation
of the hole screening stage and
the slot width of the LC screening stage
were reduced, an MC slot screening
stage was installed and the washer was
replaced by a new one.
The stickies problem was significantly
reduced by these measures. The reduction
in stickies increased from 88% to
97% and, consequently, the stickies
content in the finished stock was reduced
by 75%.
Our expectations for the upgrade have
been completely fulfilled.
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