Paper Technology International 2024 - Journal - Page 139
PAPERTECHNOLOGYINTERNATIONAL
Figure 5:(left) Variation reduction with the
ECHOWISE® closed loop control process.
Figure 6:(below) Typical entrained air data
monitored by ECHOWISE® but not yet being
controlled by it.
After Control is Established – Additional Learnings
Once ECHOWISE has been installed and the subsequent
move has been made to use closed loop control, much of the
variability and waste due to manual defoamer dosing have been
eliminated. An additional step is to 昀椀nd the optimum air setpoint
for the speci昀椀c paper machine. For many years there have been
industry targets used for wet end entrained air. These targets
might be anywhere from 0.3 – 1.0% based on grade and furnish.
These targets were established through use of manual testers
that were single point in time measurements. The targets had to
be set arti昀椀cially low so that they could account for variation to
higher levels in between test sample collection. Figure 5 is a visual
representation of each stage of the ECHOWISE Closed Loop
Control process. ECHOWISE enables modern air targets to be
established and is providing insight that each paper machine can
have a different entrained air threshold. Closed loop control with
targeted air setpoints allows the papermaking operation to 昀椀nd the
optimal setpoint for a speci昀椀c paper machine and hold entrained
air at that level. This setpoint will minimize additive waste while
also minimizing the impact of entrained air on the papermaking
operation. In many instances, this target will be higher than the
historical standards.
What are the Bene昀椀ts of ECHOWISE Entrained Air Control
The impacts of entrained air can be varied across different
types of paper machines and different grades produced. These
bene昀椀ts are typically isolated to a few different groups: machine
performance in speed or break frequency, sheet quality, and additive
cost and defoamer spend. Following are some graphic examples of
how ECHOWISE closed loop air control can positively impact paper
machine operations.
Machine Performance
The impact of entrained air on machine performance is
almost entirely based in the impact of entrained air on wet end
drainage. When the forming section drainage rate is slow or
variable, this will drive the subsequent moisture pro昀椀le down the
machine. As discussed, this can drive draw variation, high steam
consumption, defects, and breaks. Figure 6 shows an example
of typical entrained air data collected once an ECHOWISE unit is
installed. This is a period of data collection where the air is not being
controlled, only monitored. As can be seen in the graphic, the air
varies throughout the period based on incoming defoamer demand
variability.
Figure 7:(above) Entrained air data plus some wet end drainage
indicators.
Figure 7 shows this entrained air data paired with some of
the wet end drainage indicators. For simplicity, the focus here will
be on entrained air (green) and Auto-slice Vacuum (Blue). Higher
Auto-slice Vacuum is indicative of a wetter sheet coming to the top
former section of the paper machine. As can be seen in the 昀椀gure,
when entrained air increases, Auto-slice Vacuum increases. Also
seen in the graphic are the Gamma gauge consistencies in yellow.
These consistencies con昀椀rm what is seen in the Auto-slice Vacuum.
This type of entrained air / drainage rate relationship has been seen
repeatedly in ECHOWISE installations. So then, what happens to
these drainage indicators when closed loop entrained air control is
established?
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