The DeDuster® –
Where Do Fines Come From and Why Is Cleaning So Important?
Some dust and contaminants occur naturally in products like minerals, food, tablets and other bulk solids, while others are caused by the way the products are handled. Impurities in plastic pellets, both fines (dust) and angel hair (streamers), are generated by the friction in conveying lines. Dilute phase systems create large amounts of dust and streamers; the higher the velocity, the larger the amount of impurities. Pipe elbows also cause friction and result in the creation of more dust and streamers. The high pressure in dense phase, or slow motion systems, creates very fine dust due to wall friction and friction between pellets. Temperature, pellet shape and product characteristics can also contribute to the creation of dust.
Cleaning bulk solids is important for several reasons. Food and pharmaceutical bulk solids are cleaned for hygienic reasons and to improve the quality of the finished, packaged product. Minerals are cleaned primarily to avoid environmental and health problems. The plastics industry cleans pellets to improve the quality of both the pellets and the finished plastic product.
How it works
The Pelletron DeDuster® was developed as a result of Demands for high quality standards in the plastics industry, but the technology can be used for all kinds of granular bulk materials. The list of requirements for a new, universal dedusting machine was long:
- Remove dust and streamers with one machine
- Separate and remove electro-statically charged dust particles
- Fit on injection molding machines
- Offer low construction height
- Fit on top of extruders and under silos
- Reduce remaining dust level after cleaning to < 50PPM
How it works
To address this list of requirements, Pelletron developed a cleaning machine that combines a variety of air wash principles, plus the revolutionary electro-static flux field feature, and built it with the lowest possible construction height. When electrostatically charged particles enter into the Magnetic Flux Field, the resulting “Lorentz Force” weakens the electro-static bond between fine dust and plastic pellets. This weakening, in combination with the air flow, allows the micro fine particles attracted to the pellet surfaces to be removed.
Dust and streamer (angel hair) problems in the plastics industry
Production of high quality end products requires clean plastic pellets. Dust and streamers in plastic pellets cause many problems for the plastics processing industry:
- High “scrap” rates from fines burning in mold
- Blurry surfaces resulting from vaporized dust particles
- Weak spots in fibers
- Flaws in wire insulation
- Gels in films
- Housekeeping problems caused by dust and streamers
- Crusting of feed throat of screw
- Reduced mold and screw life resulting from carbonization of dust
- Mold vents clogged by dust
- Equipment and machines clogged by streamers
- Dust accumulation on silo walls, roofs and hopper walls
Dust problems in other industries
Pelletron has developed several solutions to address unique customer applications. Besides the cleaning of plastic pellets, the DeDuster® can be used for cleaning dry bulk solids in the food, mineral and pharmaceutical industries. Some examples for materials that require cleaning are:
- Rice, corn, peanuts, coffee beans
- Iron ore, special sand, wood pellets
- Tablets, pills
- And many more…
Applications
System Configurations
Open Loop
An open loop system is recommended for processes with frequent product changes or for lines with frequent color changes in order to avoid cross contamination. Filtered fresh air is pushed from a wash air fan into the DeDuster® supplying the cleaning air. A second exhaust air fan pulls the dusty air into a cyclone or baghouse dust collector. The dust is separated in a dust collector and dropped into the dust container. The cleaned air is then released into the atmosphere.
Closed Loop
A closed loop system is recommended for standard operations with the same or similar product grades or for inert gas applications. A push/pull wash air fan supplies the wash air and pushes it into the DeDuster®. The dust is separated by the baghouse dust collector and dropped into a dust container. The cleaned air is returned to the fan.
As an alternative to a baghouse, there are also Compact Cyclonic DeDuster® (CCD) systems available, a closed loop application solution with a cyclone and an inline filter. The dust is separated by the cyclone and dropped into a dust container. Remaining fine particles are separated using an inline filter. The cleaned air is returned to the fan.
DeDuster® systems are available in open loop and closed loop versions, as well as in configurations for air tight systems with inert gas or clean room applications. Wash down versions for wet cleaning are also available upon request.
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