Chemical Engineering August 2014 - 64

Solids Processing
screening may be required to segregate
materials into manageable
size ranges prior to gravity separation.
Where significant variations in
shape are found to be detrimental to
separation efficiency, size reduction
may be added to the process to reduce
the range of variation. These factors
become more important as the densities
of the materials to be separated
become closer.
In operation, the material is fed
onto the narrow side of a flat porous
deck, sloped in two directions and
vibrated with a straight-line reciprocating
motion. Low-pressure air,
blown upward through the deck,
fluidizes and stratifies the material
according to differences in the
terminal velocity of the particles.
Heavy particles sink to the bottom
of the stratified bed and are conveyed
upward toward the high or
" heavy " side by the deck's vibration.
Light particles, lifted by the fluidizing
air, flow downslope toward the
light-end discharge. Particles with
intermediate characteristics form
a mixture between the light and
heavy fractions and may be drawn
off for retreatment. Affected by both
the vibration and airflow, the material
bed thins as the deck broadens
toward the discharge face. Here, the
material is arrayed from heaviest
to lightest in a thin layer than can
be precisely and easily divided into
multiple fractions. Adjustable cutting
fingers, positioned to make the
final selection between separated
fractions, direct each fraction to a
separate discharge spout.
Gravity separators are generally
available in two basic designs: rectangular-deck
models and the more
common trapezoidal-deck models.
Rectangular-deck separators are
recommended strictly for light-end
separations where the objective is
to separate a clean, light tailing
from a larger amount of heavy material,
like removing trash or sticks
from grains or seeds. Conversely,
trapezoidal-deck separators are
recommended for heavy-end separations,
requiring the removal of a
relatively small amount of heavy
material, such as removing small
rocks in a material stream.
FIGURE 4. Processing a chopped power cable to recover its copper content is an
example of a gravity separation where the " heavy " fraction (in this case, copper)
must be isolated from the " light " fraction
Today, some manufacturers
offer both the original pressurestyle
gravity separator and the
vacuum version, which instead of
blowing air up through the unit,
uses a vacuum to suck the air
down across the face of the deck.
A pressure-style gravity separator
can be tuned for a more precise air
distribution or separation than the
vacuum style. And while the pressure-style
machine has fewer seal
points that require maintenance,
the vacuum style of gravity separator
is more sanitary and easier
to clean. The vacuum style runs
considerably quieter at the operator's
station and requires only one
blower on dusty material.
While technology has made the
controls aspect of the specific gravity
separator simpler, fundamentally,
the operation is the same as
it was at the turn of the century.
Going forward, gravity separators,
as well as air classifiers and
screening equipment will continue
to be crucial to any industrial application
that must handle dry
bulk-solid materials.
■
Edited by Mary Page Bailey
References
1. A History of Innovation and Custom Engineering,
www.sssdynamics.com/about/history
64 ChemiCal engineering www.Che.Com august 2014
Acknowledgements
The authors would like to acknowledge
that some of the text and photography
for this article were taken
from notes and documents of the
archives of Triple/S Dynamics.
Authors
Matt Mayo is a product
manager for Triple/S Dynamics,
Inc. (1031 S. Haskell
Avenue, Dallas, Tex. 75223;
Phone: 214-828-8600; Email:
mmayo@sssdynamics.com).
He has over 25 years of experience
in testing and specifying
dry-material handling
equipment including gravity
separators. Mayo holds a mechanical
engineering degree
from the University of Texas at Arlington. He is
a licensed professional engineer (P.E.).
Chris Meadows is a market
development specialist
at Triple/S Dynamics, Inc.
(Same address as above;
Email: cmeadows@sssdynamics.com).
Meadows has over
20 years of experience in the
dry-solids processing industry.Prior
to joining Triple/S
Dynamics, Meadows served
17 years as vice president of
sales and marketing for Progressive
Industries. Meadows was educated at
the University of Alabama, where he majored in
marketing.
Celie A. Reid is a sales
and marketing manager at
Triple/S Dynamics, Inc. (Same
address as above; Email:
creid@sssdynamics.com). She
has over 25 years experience
in marketing and advertising,
including beginning her
career at Bozell, a full-service
agency in Houston. Reid has
been with Triple/S Dynamics
for over ten years.
http://www.ics.com http://www.sssdynamics.com/about/history http://www.Che.Com
Chemical Engineering August 2014

Table of Contents for the Digital Edition of Chemical Engineering August 2014
