PVC powder is harder to handle than plastic pellets for three reasons. First the particle size: PVC powder has a high fine fraction, and in pneumatic conveying the fines are carried into the duct and the dust collector, so a cyclone has to recover them without the air being so violent that it disperses the bed. Second the melting window is narrow: PVC softens at a moderate temperature, and a slightly loose temperature control leads to wall build-up and caking, which is exactly what the seconds-long heating of a flash dryer keeps to a minimum. Third, static and hygroscopicity: once PVC powder takes on moisture it cakes in the screw and the hopper. Our configuration is a flash airflow line with cyclone separation.
PVC powder is harder to handle than plastic pellets for three reasons. First the particle size: PVC powder has a high fine fraction, and in pneumatic conveying the fines are carried into the duct and the dust collector, so a cyclone has to recover them without the air being so violent that it disperses the bed. Second the melting window is narrow: PVC softens at a moderate temperature, and a slightly loose temperature control leads to wall build-up and caking, which is exactly what the seconds-long heating of a flash dryer keeps to a minimum. Third, static and hygroscopicity: once PVC powder takes on moisture it cakes in the screw and the hopper, which hurts downstream processing. Our configuration is a flash airflow line with cyclone separation: the main separator splits the product from the coarse fraction and the fines are captured separately, either returned to the line or sold as a different grade. In other words the dust collection here is not only an environmental requirement, it also does the classification and protects the yield. We have run a case taking moisture from 25 points down to 1 point, at which level the material goes straight into processing without a second pass.