The Sugar Cane Growers Cooperative of
Florida is a 54-member sugar farmers’ cooperative that
provides its members assistance with agricultural
administration and processing operations for their more than
70,000 acres of sugarcane. At its Belle Glade plant, 24,000
tons of sugar cane is ground daily, producing 350,000 tons of
raw sugar annually, on average. During the October through
April harvest season, the plant operates 24 hours a day, seven
days a week. Because sugar cane must be processed within a day
of harvest, high throughput is essential.
Key components in the multi-step process of
converting cane into raw sugar are the sugar centrifuges,
which separate crystals of sugar from sugar syrups. As the
centrifuge spins at a rate of 45 to 1,200 RPM, the syrup
(molasses) is forced out through perforations in the
centrifuge wall, and raw sugar is left. The centrifuge’s
drive controls the speed of the machine, ensuring maximum
moisture is extracted.
After the 2003 harvest, the Sugar Cane
Growers Cooperative decided to replace the drive control on a
centrifuge, which has a 450 hp motor, one of the operation’s
two largest centrifuges. The existing drive was outdated and
was subject to frequent and expensive repairs, resulting in
shutdowns that reduced production capacity. Because space was
at a premium, they wanted a drive system with a compact
footprint that would work with the existing OEM-supplied
control configuration.
"Our previous unit failed at least
once or twice a year, costing us thousands of dollars in
replacement parts. Plus, when the centrifuge went down, it
crippled the entire production line," explains Jose Mena,
chief electrical engineer at the Belle Glade plant. "We
needed a drive system that was reliable, in addition to a
drive that could re-harness the power lost when the centrifuge
recycled."
The solution: a stand-alone industrial
low-voltage drive for speed and torque control—the first of
its kind installed in a sugar-processing facility. "We
retrofitted with this drive, because it offered the Sugar Cane
Growers processing plant everything they needed—a compact
drive footprint, regenerative capability, and exact motor
sizing," says Chris Visage, an ABB Low-Voltage Drives
territory manager at Hummel Industrial Sales (Ft. Lauderdale),
the company commissioned to perform the retrofit. "The
resulting improvement in cycle time will increase throughput
and eliminate bottlenecks at the centrifuge, without adding a
new larger motor," he noted.
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Shortened Cycle Time
Means Increased Production
The drive provides precise, rapid motor-speed response based
on exact variations of the centrifuge load—and this direct
torque control immediately accelerated the centrifuge cycle
time from 44 to 32 seconds, a 20 percent savings over the
previous drive. Direct torque control enables the drive to
calculate the torque and flux of the motor 40,000 times per
second, quickly slowing the load down at end of cycle, saving
seconds in unload/reload operations. Additional time and
energy savings are realized, as the energy from the spinning
centrifuge, which turns the motor into a generator, is
recovered and transferred via the drive to an adjacent
centrifuge. (This energy is dissipated as heat, in
installations that do not utilize regenerative drives.)
Stable Ride
Through Unstable Conditions
The industrial low-voltage drive also enables motors to run at
full power at full motor voltage in 80 percent brownout
conditions. This ride-through ability means that, even when
there’s a dramatic short-term reduction in voltage, the
drive sustains full power for uninterrupted operation. In
operating conditions where line voltage from a utility varies,
this benefit helps ensure constant, optimum throughput. The
industrial low-voltage drive employs an insulated gate bipolar
transistor (IGBT) active front end, which is far more robust
than traditional silicon-controlled rectifier (SCR) front
ends. (SCR front ends are susceptible to inversion faults,
which occur when the line power fails during a regenerative
stop at the end of the spin cycle. It is not uncommon for such
inversion faults to cause extended down times.) The IGBT front
end, in conjunction with the microprocessor control of the
industrial low-voltage drive, can be shut down safely, to
prevent damage to the drive, should a power failure occur
during a regenerative stop. The technology advance makes
catastrophic inversion faults a thing of the past.
A Perfect Match to
Existing Equipment
Because uptime is paramount during harvest, it was crucial to
complete the retrofit installation before the season began.
"We were able to install and test this system in five
working days time, meeting the co-op’s deadline with a month
to spare," Visage says.
Installation time was shortened because ABB
matched the existing control system from the OEM without using
any relays, outside control interfaces, or power logic
controllers (PLCs). "Our regenerative line was able to
drive the motor and match the input power supply precisely,
eliminating any additional spikes or fluctuations,"
Visage says. "Because the throughput has increased, the
co-op will be able to use the existing motor to the fullest,
instead of dissipating much of the energy, which was the case
with their prior drive."
The drive cabinet is in a confined area, so
a compact footprint was vital. The modular design provided a
40 percent savings in floor space over the previous unit, and
the modular construction of the drive makes maintenance and
repairs easier.
Software Aids Ease
of Operation
Keypads and software designs facilitate smooth and accurate
operation and maintenance, because they offer the capability
to store programming within the removable keypad. This
eliminates guesswork when the drive is reprogrammed after
service. Parameters are simply downloaded from a unique
user-saved position. In addition, exact run times are easily
accessible by keypad, which promotes systematic maintenance
scheduling and fewer secondary failures such as clogged
filters.
"ABB has provided us a reliable
product and an excellent service team," Mena says.
"Because we have other ABB products at the plant, we knew
the reliability factor and anticipated no downtime with the
retrofit."
Local Support /
Local Service
Sugar Cane Growers Cooperative worked closely with Miller
Bearings, Inc., an industrial distributor for ABB products in
Florida (http://www.millerbearings.com). Because the
distributorship is factory certified DSS (Drive Service
Station), providing maintenance and service for drive
installations like these also is available, if needed.
Throughout the project for Sugar Cane Growers Cooperative, a
team consisting of Miller Bearings, ABB engineers and sales
managers collaborated from start to finish, to size the drive,
plan the installation, and commission the drive, ensuring
total customer satisfaction. For further information about the
products used in this project: see http://www.abb-drives.com.
Ken Graber is the marketing
communications manager for ABB Inc., Low Voltage Drives,
New Berlin. He joined ABB in 2002 as a marketing
specialist, and supported ABB drives in an agency
capacity for eight years prior to joining the company. |
