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56<br />
Fig. 1: Pulsation<br />
example.<br />
Line Pressure 11.20 psi<br />
Peak to Peak 3.11 psi<br />
Overall Variation 27.7%<br />
Fig. 2: Approach Flow<br />
problems.<br />
Fig. 3: Approach Flow<br />
modification.<br />
2 3<br />
<strong>17</strong>/04<br />
Peak List for Frequencies Comments<br />
0.379 psi at 8.375 Hz => 1x Fan Pump<br />
0.167 psi at 9.000 Hz => 2x Screens<br />
0.279 psi at 29.750 Hz => 2x Secondary Fan Pump<br />
0.137 psi at 58.250 Hz => 7x Fan Pump<br />
Pressure Variation (psi)<br />
0.70<br />
0.60<br />
0.50<br />
0.40<br />
0.30<br />
0.20<br />
0.10<br />
0.00<br />
and found a problem we did not even<br />
know existed. We were able to reduce<br />
draw by <strong>17</strong> feet and got incredible<br />
runnability on the machine.”<br />
Stock Approach Flow System<br />
A large LWC machine was experiencing<br />
severe machine directions and cross-ma-<br />
0 10 20 30 40 50 60 70 80 90 100<br />
Frequency<br />
chine-direction basis weight swings. The<br />
problem left the machine unable to meet<br />
customer specifications for the mill’s<br />
most important product at an acceptable<br />
machine efficiency rate.<br />
The <strong>Voith</strong> Process Solutions team conducted<br />
a complete analysis of the stock<br />
approach flow system including a pulsation<br />
study, engineering review of the pip-<br />
1 ing flow characteristics, Tapio/TSO analysis,<br />
and headbox mapping. One of<br />
Process Solutions’ <strong>Paper</strong> Process Engineers<br />
performed the pulsation study utilizing<br />
a multi-channel spectrum analyzer<br />
to assess the pressure variations at various<br />
points in the stock system (Fig. 1).<br />
This type of analysis can identify mixing<br />
problems, cavitation, and pulsations induced<br />
by rotating machinery as well as<br />
other flow related issues. <strong>Voith</strong>’s paper<br />
testing laboratory tested finished paper<br />
samples to identify periodic variations in<br />
the sheet and fiber orientation. The study<br />
identified several areas in the approach<br />
flow system that were contributing to the<br />
basis weight instability being experienced<br />
on the machine (Fig. 2).<br />
The outcome of the analysis was a two<br />
stage approach that included changes to<br />
the existing approach flow piping system<br />
for short-term improvements as well as a<br />
redesign of the entire piping system as a<br />
capital project that would allow the<br />
machine to fully reach its expectations<br />
(Fig. 3).<br />
By implementing <strong>Voith</strong>’s recommendations<br />
the mill was able to improve basis<br />
weight control significantly. This improvement<br />
allowed a reduction of 2 lbs.<br />
per 3300 sq. ft. in the basis weight<br />
target. Improved operational efficiency<br />
has resulted in additional savings for the<br />
mill.
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