Paper Technology International 2024 - Journal - Page 140
PAPERTECHNOLOGYINTERNATIONAL
Figure 8: Left side is the same as Fig 7 . Right side
of chart shows control achieved with ECHOWISE.®
Figure 9: (below) Statistical analysis of production
rate before and after ECHOWISE® closed loop
control was established.
Figure 8 shows the same graphic but with the period
after control is initiated added to the right-hand side. As shown
in the graphic, all wet end drainage indicators become more
stable once control is established and entrained air no longer
varies. Of note in this graphic is a period when Auto-slice
Vacuum varies without an associated entrained air change. This
is an example of another drainage driver external to entrained
air. This is an important point to discuss: Entrained air control
will not remove all drainage variability drivers, but it will remove
one of the most dominant drivers and will allow the papermaker
to uncover others more easily.
Now that a link between entrained air and drainage is
established, a papermaking operation would need to be able to
attach a concrete value to removing this variability. One example
of this value can be seen in Figure 9. This 昀椀gure shows statistical
analysis that was done on production rate data from a paper
machine before and after ECHOWISE closed loop control was
established. As shown in this graphic, the overall production rate
increased by 0.7 ton/hour, a 1.4% improvement. What is not shown
in this graphic is that the overall defoamer consumption decreased
by 40.2%. While this defoamer consumption reduction was
remarkable, its value is minute when compared to the value of the
production increase.
Sheet Quality
Figure 10 is a fortunate example that was captured of
the impact entrained air can have on sheet quality. ECHOWISE
units had been installed for several months on a 2-ply paperboard
machine. During the period following installation there had not been
much observed entrained air variability and the move to closed loop
control had been delayed. The 昀椀gure below captures a period when
the machine experienced an upset and began rejecting paper due
to smoothness and print test falling out of range. In a review of the
entrained air data, it was noted that the entrained air had moved well
beyond the values seen in the preceding months. An effort began
to institute closed loop control. Figure 10 captures this conversion
period. In this graphic the entrained air, in gray, starts out at greater
than 0.5%. In the preceding months the entrained air value had
hovered continuously around 0.15%. As can be seen, during this
elevated period of entrained air Parker
Print and Smoothness test values (orange
and blue) were falling outside of target
and paper was being rejected. There is a
period in the middle of the graphic where
defoamer dose (yellow) was extremely high
and variable, but the controls were able to
bring levels down to the point where sheet
quality returned to spec. It can also be seen
how the controls began working smoothly
once the system had been tuned to handle
the upset by adding more defoamer pump
capacity. Finally, the graphic shows that the
defoamer speed returned to minimum after
the upset had passed.
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Additive Cost
Another important point can be taken from Figure 10 there
had been no entrained air upset like the one in this graphic for
months prior to this episode. So, after rejecting hours of production,
it was noted that entrained air was high and defoamer dosage
was increased tremendously to overcome the issue. In this case,
ECHOWISE control was initiated during the upset, but what would
the scenario look like without ECHOWISE control? The defoamer
dosage would likely remain very high following the upset without
some way to know it had passed. Figure 10 is a visual example
of how ECHOWISE with closed loop control can eliminate wasted
defoamer spending.
Closed Loop Control Using ECHOWISE®
As discussed, the presence of foam in a paper machine
system can be a problem. But the presence of foam can be
an indicator of the much more costly problem of entrained air.
ECHOWISE provides real-time visibility into this problem and sheds
light on how it can negatively impact papermaking operations. More
importantly, ECHOWISE used with closed loop control provides a
means to eliminate these negative impacts.
Figure 10: (below) ECHOWISE® was monitoring but not set
for closed loop control when an entrained air upset happened
(gray); ECHOWISE® was switched to control during the upset,
and it regained control.
