Paper Technology International 2020 - Journal - Page 40

PAPERTECHNOLOGYINTERNATIONAL
CASE: Dryer section rebuild reduced web breaks
Paper machine A targeted improved runnability and
enhanced production. During breaks, the time tail threading took
was causing production losses.
Traditional runnability control with an increased draw not
only reduces sheet strength and quality but easily causes breaks
in the dryer section. A high draw difference means additional raw
material costs, as more chemical pulp is required to improve sheet
strength.
Reducing the draw provides the potential to increase
machine speed and optimize furnish. The RunPro EasyOne web
stabilizer optimizes the web release with a special high-vacuum
system during the critical sheet release between the upper cylinder
and the vacuum roll. It prevents the web from following the upper
cylinder, resulting in fewer breaks and defects.
Runtech Systems conducted a study at the mill and
proposed several improvements for the process. The dryer section
rebuild included a new vacuum Press Run roll, EasyOne stabilizers
for the 1st dryer, TailVac drilling for the 2nd group and Gardner
Sheet moisture profile survey
A sheet moisture profile survey aims to improve quality by
pinpointing where existing moisture profile problems are generated.
It analyzes machine and cross-directional measurements, sheet
moisture profile measurements, cylinder surface temperature profile
measurements, cylinder surface cleanliness, pocket humidity and
temperature profile measurements as well as evenness of the zero
level.
Hood air balance / zero level
Hood zero level describes the over pressure versus under
pressure inside the hood. The top part of the hood is always in an
overpressure state, and the lower part and basement of the hood is
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Denver compressors. In addition, tail threading was converted to be
ropeless for the single- and double-felted sections. A Runshooter F
was installed to bypass the Yankee cylinder.
At paper mill A, with the installation of EasyOne stabilizers,
the draw reduction between the press and dryer section decreased
about 30%. After the rebuild, break frequency was fewer than 1 per
week. In addition, the mill has been able to reduce the share of long
fibers by approximately 8–10%.
Ropeless tail threading improves operator safety significantly
while also shortening tail threading time during web breaks by up to
80% to increase production. In many cases, the technology enables
mills to increase machine speed. The tail threading time over the
modified area is under 60 seconds – from press to after dryer – and
it is possible to run at full speed. Earlier, a speed reduction of 200 m/
min during tail threading was necessary in some situations.
in an underpressure state. Therefore, humid air tends to exhaust out
from the hood through the upper part, while leakage air enters the
hood from the basement.
The height in which the pressure is in balance, in other
words, the even pressure between the machine hall and inside the
hood, is called zero level. The level should be located where the
largest openings are in the hood construction, for example, where
the paper web enters and exits the hood. Typically, it is at about
a 2-meter height from the operation level. The zero level is set by
adjusting the hood exhaust and supply air ratio. When exhaust air
increases or supply air decreases, the zero level rises.

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