Chemical Engineering January 2012 - 19

Newsfront
SAY GOOD-BYE TO
OLD-SCHOOL CENTRIFUGES
More modern equipment
provides increased efficiency,
flexibility and safety
M
any chemical processes in
the U.S. that use centrifuges
were established between
the 1950s and the 1980s.
As a result, most of these machines
employ technology that was outdated
literally generations ago. In addition,
many processes have changed since
installation, and doing more with less
is now a key method of survival in
today's global economy. At the same
time, regulatory and environmental
issues have become more important.
This combination of outdated equipment,
the advent of more modern processes,
a tighter economy and bumped
up compliance creates challenges for
chemical processors using old-school
centrifuges. Fortunately, more modern
equipment is available to bring these
processes into the 21st century.
" Processors are working to optimize
product throughput,
product yields
and separation efficiency while keeping
an eye on energy costs, " says Chad
Mendelsohn, sales manager of chemical
centrifuges with TEMA Systems
(Cincinnati, Ohio). " In our applications,
the largest energy costs are often in the
downstream-process thermal dryers -
where for every 1% of extra moisture removal
through mechanical separation
of a solid, a dramatic longterm savings
is produced. Lower discharge moistures
can also increase the potential throughput
of a whole process line. "
Mendelsohn adds that as plants try
to keep up with demand for their products
with less and less staff available,
processors look to maximize production
up time while limiting operator
interface requirements and the need
for maintenance. Certain applications
also have environmental reasons to
FIGURE 1. Thickened sludge is discharged efficiently
with the THK Series's Hydraulic Assist Technology, so
the process of centrifugal thickening offers a low-cost
and smaller footprint approach to reduce volume while
increasing digesting capacity and performance
Heinkel USA
minimize personnel interaction with
the process equipment.
All these challenges lead to one
thing: The need for modern equipment
that is highly efficient and flexible, as
well as safer and more automated.
Higher efficiencies
Chemical processors are looking for
higher recoveries and higher captures
from their centrifuges, says Victor
Norton, vice president of sales with
Andritz Separation (Arlington, Tex.).
In addition, they want dryer cake discharges
and less moisture so downstream
drying costs are reduced, he
says. This demands more efficiency
and effectiveness out of the machines.
One of the ways this is accomplished,
says Norton, is by improving
the internals of the centrifuge. A typical
decanter centrifuge has a bowl and
scroll or conveyor within the bowl to
move the settled solids. There are different
pitches on the blades of the conveyor
and differing numbers of leads
(usually single, double, triple or more).
" The variations here have the ability
to provide a dryer cake discharge and
more capacity, and we are improving
the internals all the time, " says
Norton. " Years ago a 40-in.-dia. machine
on a PVC line would process 7
ton/h. Now the same size machine can
FIGURE 2. The inverting filter centrifuge
technology allows difficult-to-filter
material that traditionally could not be
processed on a centrifuge to be turned
into a dry powder
handle up to 15 or 20 ton/h due to the
speed of the machine and new designs
on the pitch of conveyors. "
He adds that materials of construction
for the bowl and type of drive
used also increase the speed of the
machine. Stainless steel was previously
the typical material of choice,
but now heavier strength alloys like
duplex steel are needed for corrosion
resistance and strength. New controls,
too, such as variable frequency drives
(VFDs), which allow soft starts that
don't consume as much horsepower
as an across-the-line start and move
things along at a faster, more consistent
rate, are also being employed.
" Scroll drives can be VFD, which
CHEMICAL ENGINEERING WWW.CHE.COM JANUARY 2012 19
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Chemical Engineering January 2012

Table of Contents for the Digital Edition of Chemical Engineering January 2012
