Paper Technology International 2020 - Journal - Page 56

PAPERTECHNOLOGYINTERNATIONAL
After an accurate assessment, our technicians proposed
a brand-new, customized solution starting from the forming board,
followed by an hydrofoil, three modulated flat boxes, two vacuumfoil
boxes, a duoflow and a bivac case tailed by a trivac box.
Further on, in the high-vacuum area after the wet line, the
installation of bivac and trivac boxes creates different zones of
progressively increasing vacuum in the flow direction towards the
machine, so to prevent the sheet from being subject to atmospheric
pressure again as it passes from one vacuum
zone to the next with greater vacuum.
To guarantee the vacuum efficiency,
each vacuum zone is equipped with an airwater separator installed on the drain pipe and
it can also take advantage of an automatic
VRV-AF valve to perform a more accurate
vacuum adjustment of each chamber.
This process allows for energy savings
and a significant improvement in the final sheet
dryness percentage.
By carefully monitoring drainage
values and vacuum analysis and optimization,
the customer’s needs were finally met: higher
speed and improved formation were achieved
while saving energy.
Figure 3: Fourdrinier machine functioning.
To further improve dewatering performances, it was also
suggested to install ceramic covers in aluminium oxide and plastic
deckles on modulated flat boxes.
Starting from the formation area, in fact, the modulated
flat boxes are ideal for creating the optimal pulp slurry activity on
the basis of speed and grammage produced: taking advantage
of vacuum, the wire is pulled into
depressions created by plastic elements
installed at a lower height than the
ceramic ones; the intensity of this kind of
activity may be varied by adjusting the
vacuum level.
This box comes with false
air valve and vacuum gauge, so to
guarantee the optimization of the
drainage and the formation frequency
and it was also equipped with an
additional VRV-AF valve to adjust the
vacuum level inside the box in an even
more accurate way.
Figure 4: Trivac connection to vacuum system.
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