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Maker
of plastic color concentrates
cleans and recirculates
dust-laden air, cuts AC
load and summer electric
bills more than half
When you're in the business
of formulating specialty
colors for plastics using
fine pigment powders, you
must invest in systems
that ensure consistency
in processing. To meet
that objective, a leader
in plastic colorants, whose
raw materials include powdered
pigments, invested in a
source-capture dust collection
system at its new North
Carolina processing facility.
Designed by Kirk & Blum,
Cincinnati, the system
not only cleans and recirculates
plant air, but it also
reduces the AC equipment
requirement by more than
half, cutting summer electric
bills by approximately
$3800/month. The system
also provides recycled-air
quality that's "cleaner
than fresh air" during
pollen season, according
to customer reports.
The processing plant is
a business unit of a publicly
held, $1.7-billion-per-year
specialty chemicals company.
It produces about 270 million
pounds per year of custom
colorants for use in most
plastics to produce eye-catching
toys, housewares, packaging
and auto parts.
Powdered pigment is the
chief raw material handled
at the company's 12 plants
across the U.S. And handled
it is: weighed precisely,
blended and mixed with
natural plastic resin;
conveyed in tote bins;
distributed through feeders;
and finally processed into
pellets.
The company's forte is
quick turnaround of custom
colorants for in less-than-truckload
lots. The company has a
palette of more than 46,000
color formulations. "Operating
24 hours per day, with
30-40 color changes per
shift, we'd have a rainbow
colored plant in one afternoon,
without efficient dust
control," according
to the client.
The 44,000-sq-ft newly
completed plant is fairly
typical of the company's
operations. Plastic resins
that the company processes
include low density polyethylene,
ABS, polypropylene and
styrenics. These resins
arrive by tanker truck
in pelletized form and
are stored in silos. Pigments,
arriving from all over
the world in bags, drums
and boxes, come as a talc-fine
powder, averaging about
half-micron particle size.
Production begins with
hand-weighing of pigment,
according to formula, into
a batch container. The
container is moved to one
of six high-speed dispersers
where the contents are
discharged, mixed, and
then mixed again after
resin is added. The batch
is bottom-discharged into
tote bins, which are transported
to a mezzanine where six
starve-feed metering systems
supply six special twin-screw
compounding extruders that
mix the formulation into
a pelletized color concentrate.
The color concentrate is
classified, packaged appropriately,
and shipped to a plastic
processor for part production,
or to a plastics compounder
for further processing.
"Pigment particles
are classified as a nuisance
for OSHA purposes," the
customer says, "but
they are a nuisance we
don't want circulating
in our plants."
With the opportunity to
integrate a dust collection
system into a new plant's
construction, rather than
add a system on after the
fact, the customer put
the job out for bid. "We
sought high value and functionality," the
customer emphasized. "Our
selection of Kirk & Blum's
Greensboro office was based
on turnkey design/build
experience, and the ability
to work flexibly with our
crews and other contractors."
More
than a collector and flex
hose
According to Dale Tompkins,
K&B's (Greensboro,
NC office) project engineer
on the job, the key to
success at the new facility
was hood design and sizing
of ductwork. "You
can have the best fans
and collectors in the world,
but if you cannot get the
particulate to the filter
media, you've wasted your
money," he explains. "People
who think they can get
by with some flex hose
or plastic collection pipe
as ductwork only end up
cheating themselves."
Hood design was based
on a study of what had
worked best at similar
color concentrate plants,
including this customer's
other facilities, as well
as application of K&B's
experience in hundreds
of foundries, die casting,
machining and woodworking
operations. "It's
important to study an operation
in action, to see the workers'
needs and where the particulate
moves," says Tompkins. "For
this type of particulate,
we design for a specific
face velocity for each
style of hood, and a duct
velocity of 4000 FPM, while
making our hoods as operator-
and process-friendly as
possible."
Taking the layout of the
customer's process into
account, the ductwork was
designed in the general
shape of a loop, with a
return air duct from the
collectors coming up the
middle of the loop. Discharge
of the return air creates
a flow across the plant,
back to the collection
hoods, and improves the
dispersion of air from
the plant's tempered air
system. The 72" x
36" return air duct
was designed large to keep
velocity—hence, noise—at
an OSHA-recommended level.
"We justified the
recirculation system after
an engineering study of
the plant's air conditioning
load, with and without
recirculation," the
customer reports. "To
air condition this plant
without recirculation would
have required almost 160
tons of refrigeration,
and we've done it with
just 28. In addition to
reducing our HVAC equipment
cost, we projected a savings
of $3800/month in our summer
utility bills."
The final system uses
two cartridge-type collectors
that handle a total of
36,000+ cfm. Total system
static pressure is 12" w.g.
The fans discharge into
HEPA filters which polish
the air before it is ducted
back into the plant. "We
included the HEPA filters
as insurance, in case of
a cartridge failure, or
in the event the plant
someday handles a heavy
metal," says the client
concludes. "Air passed
through the HEPA filters
is 99.97 percent free of
particulate, actually cleaner
than outdoor air during
pollen season."
The collection system
captures approximately
800 pounds of pigment per
month, much of which the
company recycles—minus
the "green."
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