Tecweigh - Powder and Bulk Engineering Magazine

20 Powder and Bulk Engineering, February 1995
Case history
Feeders
reliably add
chemicals to
kaolin clay
I
compounds
A
company called E.C.C. International,
Sandersville, Ga., supplies
clay compounds used in the
ceramics, paper, plastic, paint, pharmaceutical,
and chemical industries. E.C.C.
also owns and operates the mining operation
that supplies materials to the company’s
plants.
Kaolin clay is mined from pits as far as
100 miles away and either mixed to a
slurry on site and pumped to the plant or
moved in solid form to the plant in trucks.
Slurry is stored in tanks at the plant,
while solid clay is stored in sheds and
later moved by front-end loaders to a
slurry mixer. The plant’s slurry mixers
When feeders designed in-house
by a kaolin clay plant failed to
reliably deliver chemical
additives, the plant installed
feeders that eliminated the
problem.
A M er at the kaolin clay plant uses a flexible hopper wifh massaging paddles
to consisten+ deliver the desired amount of chemical addihes.

each use a 100- to 200-horsepower motor
that drives a shaft bearing disc-mounted
blades.
The slurry is next pumped through several
stages of high-speed centrifugal
classification, known as degritting. Magnets
then remove any metallic impurities
before vacuum drum filters dewater the
slurry to raise its solids level from about
30 percent to about 50 percent. Pumps
then move the slurry to a spray dryer’s
top and through an atomizing nozzle that
sprays a fine mist into the dryer’s heating
chamber, which dries the slurry to bead
form.
Screw, belt, or pneumatic conveyors
move the dried clay through the rest of
the process, which begins in a calciner
that heats the clay, changing its chemical
properties. At various process stages,
feeders add different amounts of various
chemicals to form clay compounds with
properties needed by end users. The
chemicals vary from powders to granules
and can be corrosive or abrasive. Dried
clay compounds are finally shipped out
in railcars or bags. The compounds can
also be remixed with water and shipped
in slurry form.
High-maintenance feeders unreliably
deliver chemical additives
In the past, E.C.C. added chemicals to its
clay compounds using dry product feeders
with hard sides and no flow agitation.
But the feeders were unreliable, often
created a material bridging problem,
were difficult to control, and required
high maintenance. Each feeder was developed
on-site and used a DC drive
motor with sprockets and chains. A
straight-sided sheet metal container
served as the feeder hopper, and a screw
at the hopper’s bottom fed material.
However, fabricating the feeders was expensive
and a local fabricator had to CUStom-make
the feed screws.
The feeders also needed frequent maintenance
and replacement of items such as
bearings and chains. In addition, the
feeders were large and bulky to move and
required 440-volt power to operate. A
broken feeder required an electrician because
the plant couldn’t get safety-approved
quick disconnect plugs for
440-volt power. The electrician might
not arrive for up to 3 hours.
Even when the feeders were operating,
the feedrate fluctuated considerably. “A
Powder and Bulk Engineering, February 1995 21
feeder operator could check the system
every 2 hours and get a different reading
each time,” said calcine plant process engineer
Gregg Brantley. Then, the operator
would try to adjust the feedrate and
possibly overadjust if a bridged feeder
suddenly started feeding. “It was a nightmare
as far as process control was concerned,”
Brantley said.
Material in the feeder often bridged or
ratholed, and the feeder would run for
hours without delivering material. Although
the feeder hopper appeared full,
the resulting kaolin clay compound
was out of spec according to laboratory
results.
“Then we had to rework the material by
running it back through the system,
which reduced production,” Brantley
said. A bridged feeder could result in
anywhere from 50 to 400 tons of rework,
which was very costly. In some cases,
shipments had to be delivered out of spec
when customers were waiting for the material.
This kept customers supplied with
clay, but reduced the plant’s quality credibility.
Plant considers new feeders
Brantley then read an ad in a trade magazine
describing a feeder with a flexible
hopper and agitation paddles. He was
concerned a flexible hopper might wear
too easily from the corrosive and abrasive
materials. “We wouldn’t want to
bust a hopper and let the material get
down in the motor and sprockets and
everything,” Brantley said.
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Frequent maintenance of a kaolin
plant‘s previous feeders required up to
a 3-hour wait for an electrician. Quickdisconnect
plugs on the plant’s new
feeders permit changing out an entire
feeder in 3 to 4 minutes.
An extended hopper on his feeder provides additional capcity

24 Powder and Bulk Engineering, February 1995
After considering a variety of flexiblehopper
feeders, Brantley chose to further
investigate the one that had the fewest
moving parts from a manufacturer who
appeared very willing to work with the
plant’s maintenance and engineering
staff to come up with a working solution.
An equipment sales representative then
stopped at the plant to demonstrate some
feeder options.
In early 199 1, the plant tested a Tecweigh
Series E5 volumetric feeder with a Flex
Feed hopper and standard digital control.
A demonstration was scheduled using a
variety of end product ingredients and
the company’s system process. Over several
months, the company witnessed the
unit’s reliability, elimination of product
bridging, and ease of maintenance.
Durable feeders use adiustable
agitation paddles
The feeder’s polyurethane hopper has a
0.4-cubic-foot nominal capacity. Dual
external paddles press in on the flexible
hopper’s sides with a massaging action
that conditions the material into a uniform
bulk density to fill each flight of the
unit’s feed auger. The amplitude of paddle
actuation adjusts to various materials
for optimal consistency and minimal
hopper wear. The stainless steel agitation
paddles don’t rust, pit, or damage the
flexible hopper.
A %-horsepower motor turns the feeder’s
auger through a feed tube, delivering material
at 0.0003 to 6.0 ft3/h. The feeder
drive train and cabinet are sealed to
protect the motor and all internal components
from water and dust. A hopperto-drive-shaft
seal protects against
leakage of even abrasive materials into
the feeder cabinet to prevent breakdowns.
An automatic chain tensioner
eliminates manual adjustment for chain
stretch. The feeder disassembles quickly,
and a twist and pull removes both the
feed tube and the auger. The flexible hopper
lifts out of the feeder cabinet, and the
entire chassis and motor drive remove for
repairs.
z
Feeders reliab deliier chemicals to
claycompoun s
The kaolin plant has installed eight of the
feeders. The feeders consistently deliver
a controllable flow of chemical additives
that’s repeatable to k2 grams. Some have
operated continuously for nearly 4 years
with no maintenance. Some are controlled
by computers and others use standard
digital controls for very constant
processes. E.C.C. has noticed reduced
labor and maintenance and increased
product quality, while experiencing almost
no system downtime.
The kaolin clay plant keeps spare feeders
on hand to swap in quickly and reduce
downtime when maintenance is required.
Each feeder has a 1 IO-volt quick-disconnect
plug from the feeder to the controller,
which workers can disconnect
without an electrician present. “That aspect
has helped us a lot,” Brantley said.
“We can change out a feeder in 3 to 4
minutes, compared with the hour or more
it used to take.” The quick-disconnect
plugs are different for each size feeder
drive to prevent any potential miswiring.
The plant has worn out only one flexible
hopper, which wasn’t due to material
wear, but rather to an improperly adjusted
agitation paddle that eventually
wore through the hopper. The plant readjusted
the paddle and has since had no
hopper wear problems.
The feeder manufacturer has worked
with the kaolin plant to ensure continued
success. In one case, a connecting spring
between a feeder’s auger and drive shaft
pushed into a seal and wore it over time.
The manufacturer then put in several
Teflon bushings, installed a different type
of bearing, and reengineered the drive
shaft coupling to take the pressure off the
seal. The changes eliminated the seal
wear problem. In another case, the auger
flights weren’t sufficiently tapered,
which packed material against a bearing.
The manufacturer then worked with the
plant to redesign the screw flights and
solve the problem.
Regarding the feeder manufacturer,
Brantley said, “I wish every company
was like them because they’ve been willing
to take criticism and put that criticism
on the drawing board as many times as it
takes until it’s right.”
PBE
Tecnetics Industries, St. Paul, MN
6 1 217774780 #350
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