Classification Characteristics of a Cyclone Type Classifier with Improved Collection Boxes for Separating Particles near the Wall Surface

摘要

Cyclone separators are used in many processes to remove powders for collection in a wide range of diameters. When the cyclone separator is used as a classification device that requires high effectiveness, the 50% cut-off size (D-p50) is restricted to less than several microns owing to the strong centrifugal force. We developed a cyclone-type classifier to effectively classify coarse particles collected by the normal cyclone, as discussed in our previous study. The classifier comprises inner and outer collection boxes with a sloping channel region between the upper sections. The sloping channel could derive the additional air, called blow-up flow, from the tangent nozzle established in the outer box. The blow-up flow becomes confluent with the main swirling flow of the cyclone. In the channel, the fine particles affected by the drag of the blow-up flow were collected in the inner box. Additionally, the coarse particles affected by the centrifugal force induced by the swirling flow were collected in the outer box. The previous study, regarding a classifier with a channel length of 6 mm, demonstrated that D-p50 and the effectiveness of the classification K, which is the ratio of the 25% cut-off size to the 75% cut-off size (D-p25/D-p75), increase linearly with the increase in blow-up flow rate (Delta q). In this study, we increased the channel length from 6 to 23 mm. This resulted in the following beneficial characteristics for separating acrylic particles having a size distribution of 15-35 mu m. Unlike the previous study, D-p50 depended on the main flow rate at the entrance regardless of Delta q since the increase in Delta q increases the centrifugal force, which acts simultaneously on the D-p50 particles, and the drag force. Meanwhile, K increased significantly with the increase in Delta q. The classifier classified the particles with high effectiveness (K ranging from 0.75 to 0.92).