Chemical Engineering October 2017 - 49

an enclosure over the pan. Actual flowrates
for a given material will be influenced by particle
size, cohesive strength, wall friction and
a variety of other factors. Depending on the
material, additional testing may be required
to ensure proper feeding and control.
Louvered feeders. A louvered feeder attaches
directly to an outlet and uses a series
of internal louvers (or slats) that gently
vibrate to discharge material. The louvers will
be spaced and angled such that when not
vibrating, material will find its angle of repose
and not discharge. A vibratory drive attached
to the outer housing of the enclosed louvers
provides discharge. Beneath the louvers is a
chute that directs the material stream to the
desired outlet.
The housing of the feeder is supported by
cables attached to the bin. The feeder has a
flexible skirt to seal and isolate the bin from
vibrations (Figure 9b).
Circle feeders. A circle feeder is a unique
table-style feeder that uses a rotating vane
to push material to an outer perimeter and
one or more discharge points. It consists of
a slow rotating vane, an enclosed housing,
discharge ports, and a driving mechanism
(Figure 9c). The feeder mounts directly on
the outlet and uses a number of flat blades
spaced equidistantly, making up the vane, to
work material to an outer-perimeter chamber
and then to outlet ports. These feeders have
excellent precision and work well with a large
variety of materials.
Cone-bottom or auger-type unloaders. A
cone-bottom or auger-type unloader consists
of an internal auger that sweeps around
the cone bottom of a bin. The auger undercuts
material in the bin, feeding it to the center
outlet. The auger drive is located outside
of the hopper, keeping it out of the material
stream and accessible. These types of feeders
are ideal for feeding difficult-flowing or
very cohesive materials that might otherwise
bridge over the outlet (Figure 9d).
Gravimetric feeder types
A gravimetric feeder allows for material to
be fed on a weight-per-time basis (rather
than volume-per-time). Gravimetric feeders
achieve a greater degree of accuracy than
volumetric feeders. If a system or process
requires accuracy closer than ±5%, a gravimetric
feeder will be able to achieve 0.25
to 0.5% accuracy. Unlike volumetric feeders,
gravimetric feeders will allow for density
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OCTOBER 2017
49
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Chemical Engineering October 2017

Table of Contents for the Digital Edition of Chemical Engineering October 2017
