Paper Technology International 2024 - Journal - Page 138
PAPERTECHNOLOGYINTERNATIONAL
Figure 3: ECHOWISE® 360
The ECHOWISE 360, shown in Figure 3 can be installed
around existing process pipe to gather entrained air information
anywhere in the process that is needed. ECHOWISE has no moving
parts, the equipment will not plug, and it has a long service life.
The equipment uses sonar to gather information that is converted
into entrained air data. Both types of ECHOWISE equipment
provide entrained air readings once every 1.5 seconds generating
continuous, real-time information for the paper machine operation.
The equipment uses basic 120 VAC or 20VDC power and can be
mounted in the most severe environments. The entrained air data
collected can be accessed in several ways as the ECHOWISE is
equipped with MODBUS, HART, USB, and 2 X 4-20mA outputs.
All the considerations embedded into the ECHOWISE equipment
provide for a reliable, 昀氀exible tool that can provide the paper
machine crew the feedback it needs to proactively control entrained
air to the proper level 100% of the time. It then becomes important
to determine the most effective way to use this tool.
The goal of installing and using the ECHOWISE equipment
is to locate an installation point that will provide information that is
relevant to the location in the process that suffers due to entrained
air and eventual foam. Most of the time for paper machines this
location is the headbox jet. When installing on paper machines the
ECHOWISE equipment will typically be installed on the immediate
stock approach to the headbox or on the headbox recirculation
system. This will provide entrained air information at a location and a
frequency relevant to what the headbox is experiencing in real-time.
The next step is to now decide how to best use this information.
Entrained Air Monitoring Versus Control
Now that a tool has been established to collect continuous
entrained air information, it must be decided how best to use this
new data. One option is to send this information to the paper
machine control room so that operators can see current entrained air
level and make defoamer dosage changes as needed. However, this
option still relies on manual intervention and continuous monitoring
by the operator. Another option is to establish closed loop control
of the defoamer dosing. This method requires that a 4-20mA signal
be sent from the ECHOWISE equipment to the paper machine
DCS or to a Buckman supplied controller. This signal is then used
to establish a PID control loop that continuously adjusts the speed
of the defoamer pump to control entrained air values to a target
setpoint. Figure 4 shows an example Buckman controller for use in
closed loop control.
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Closed loop control of defoamer dosing
is where the true value of ECHOWISE can be
realized in papermaking operations. Paper
machine additives, furnish, and machine
conditions change very rapidly. If a goal
of the operation is to minimize variability,
continuous control is necessary to eliminate
the negative effects of constantly changing
conditions. Closed loop control of defoamer
dosing using ECHOWISE will hold the paper
machine entrained air at a constant level while
continuously adjusting defoamer dosage rather
than allow entrained air to vary while defoamer
dose remains constant. By holding entrained air
constant, its impact to paper machine drainage
will be reduced or removed. This will be seen in stabilized wet end
vacuums, more stable draws, and potentially reduced sheet breaks.
An additional bene昀椀t to closed loop defoamer control is a reduction
in defoamer chemistry spend. Without continuous visibility into the
state of entrained air and foam potential, a paper machine operator
must dose defoaming chemistry for worst case conditions. This
means that the dosage is held at a level that the operator feels
will prevent any issue that might occur, and issues do occur as
defoamer demand is constantly changing. However, if an operator
is dosing to control an issue that happens 5% of the time, then
defoamer is being wasted 95% of the time. Continuous closed loop
defoamer control will eliminate this wasted spend. This waste can
mean hundreds of thousands of dollars in unnecessary spending.
Figure 4:Controller for closed loop control of
defoamer dosing.
