Product category:
Air handling: Dust + Fume extraction
News Release from: Kirk & Blum Duct | Subject: Plastic colour plant
Edited by the Processingtalk Editorial
Team on 16 February 2007
Dust extraction and air recirculation
saves money
With help from Kirk and Blum Duct, a maker of plastic colour concentrates extracts and cleans dust-laden air, and recirculates the filtered air, reducing AC load and summer electric bills by half
When you're in the business of formulating specialty colours for plastics using fine pigment powders, you must invest in systems that ensure consistency in processing To meet that objective, a leader in plastic colourants, whose raw materials include powdered pigments, invested in a source-capture dust collection system at its new North Carolina processing facility
This article was originally published on Processingtalk on 12 Feb 2007 at 8.00am (UK)
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Designed by Kirk and Blum, Cincinnati, the system not only cleans and recirculates plant air, but as a result reduces the AC equipment and power requirement by more than half, cutting summer electric bills by approximately USD3800/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, USD1.7-billion-per-year specialty chemicals company.
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It produces about 270 million pounds per year of custom colourants 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 USA.
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 forte is quick turnaround of custom colourants for in less-than-truckload lots.
The company has a palette of more than 46,000 colour formulations.
"Operating 24 hours per day, with 30-40 colour changes per shift, we'd have a rainbow coloured plant in one afternoon, without efficient dust control," according to the client.
The 44,000-sq-ft newly completed plant is fairly typical of their operations.
Plastic resins that the company processes include low density polyethylene, ABS, polypropylene and styrenics.
These resins arrive by tanker truck in pelletised 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 a 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 pelletised colour concentrate.
The colour 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 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 the Kirk and Blum Greensboro office was based on turnkey design/build experience, and the ability to work flexibly with our crews and other contractors".
According to Dale Tompkins, the Kirk and Blum 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 colour concentrate plants, including this customer's other facilities, as well as application of the Kirk and Blum 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 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 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 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 project savings of USD3800/month in our summer utility bills".
The final system uses two cartridge-type collectors that handle a total of 36,000cfm.
Total system static pressure is 12'' wg.
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 that the plant someday handles a heavy metal," 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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