For high-volume pneumatic conveying in plastics resin and compounding plants, the standard today is dense-phase conveying, whereby the resin moves in “plugs” with low velocity and high pressure. This approach creates high wall friction, which generates fine resin dust that carries static charge, making it stick to pellets and silo walls and roofs, causing periodic “dust surges.” Friction also causes wear on piping, and the vibrations caused by plug movement require special pipe supports and additional steel structures.
These drawbacks can be avoided with the new Strandphase conveying approach from Pelletron Corp., Lancaster, Pa. It is intermediate between dense-phase conveying and the dilute-phase conveying that is typical in manufacturing plants. Strandphase uses an intermediate air velocity (15 to 25 m/sec, or 3000 to 5000 ft/min), intermediate conveying pressure (up to 2 bar or 28 psi), and intermediate product-to-air ratio. Its merits are said to be less dust generation, reduced maintenance costs, and around 25% lower installation costs due to elimination of special pipe supports and ability to use smaller pipe diameters as well as lower-pressure roots-type blowers instead of compressors. These factors compensate for higher air volume used in Strandphase vs. dense-phase conveying.
Pelletron combines this new conveying approach with two of its existing technologies in an overall system concept it calls Pellcon3. This includes aerodynamically designed Pellbows (pipe elbows) to prevent formation of “streamers” and DeDusters to remove the moderate amount of dust formed in conveying.