Performance Recovery of Scale Reduced Cyclone Particle Separators using a Rotating Classifier
Abstract
Cyclone particle separators are often used to collect particles that are of value or environmental concern. These devices achieve high Total Collection Efficiency (TCE) with steady pressure drop. Increasing the height of the cyclone improves both TCE and pressure drop. However, due to the height of the cyclone, these devices are often forced to be placed outside, which can lead to decreased performance over time. The research examines the outcome of scale reducing a cyclone. This is achieved by (i) how the scale reduction changes the flow field, (ii) identifying what flow aspects contribute to the reduction in TCE and (iii) how the TCE can be recovered using a rotating classifier. The scale reduction of the cyclone is performed in two stages: first, the barrel length is reduced in height by a factor of two (Intermediate), then the cone height is reduced by a factor of two (Truncated). Thus, the Truncated cyclone is half the overall height as the initial Full-size cyclone. Experimental and Computational Fluid Dynamics (CFD) with Discrete Phase Modeling (DPM) methods were used, with a newly developed injection method (A-STERP), which has the accuracy of a fully random transient injection and reduces the computational time from over six months to an hour. The experiments served as a validation tool for the flow fields predicted by CFD and for tuning the drag model of a non-spherical particle used in the DPM.
Examination of the flow fields showed that shortcutting in the Truncated cyclone increased from 20% to 36% and, as such, was considered a contributor to the 20% decrease in the TCE. Adding a classifier that rotates at 4000 rpm increased the TCE by 3% in the Truncated cyclone but reduced it by an additional 20% when rotating at 6000 rpm. The drop in TCE at high rotational speeds resulted from particle re-entrainment from the Collection Hopper (CH). Increasing the diameter of the CH or adding a vortex stabilizer will eliminate re-entrainment. Thus, a Truncated cyclone with a vortex stabilizer and a classifier rotating at 6000 rpm can achieve a similar TCE as a Full-size cyclone.