Doctor of Philosophy
Mechanical and Materials Engineering
Straatman, Anthony G.
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.
Summary for Lay Audience
A cyclone particle separator is a device used to filter particles out of air. The cyclone archives this filtration using a tornado-like flow to throw the particles out of the air. The particles then fall to the bottom of the device and are stored in the collection hopper of the cyclone. For a cyclone to be able to collect most of the particles, it needs to be tall. This project focused on how a cyclone of half the height could achieve a similar ability to collect particles as a cyclone of typical height. This is accomplished by using experiments and simulations to examine what about the flow results in the high collection and changes with a decrease in height.
A new method that allowed for the accurate injection of simulated particles into the computer-modelled flow was developed, which resulted in the time to simulate the particles taking several months to only an hour. This new method was validated against more comprehensive methods on three different particle filtering devices, with the third device being a cyclone particle separator. Using the new method of injecting particles, it was found that reducing the height of a cyclone by half significantly decreased the short cyclone’s ability to remove particles from the airflow. The reduction in the cyclone height increased the amount of flow that prematurely exited the short cyclone, and this was identified as a significant contributor to the decrease in the ability to collect particles. Rotating blades were added inside the cyclone to prevent the flow from prematurely leaving the cyclone. The rotation of the blades forced the air that was prematurely leaving away from the exit and created a strong tornado-like flow in the cyclone. The flow, however, becomes so strong that it pulls particles out of the collection hopper and further decreases the short cyclone’s ability to collect particles. Lastly, the collection hopper was altered by increasing its size or adding a blockage to ensure particles that enter cannot escape, thus allowing the short cyclone with rotating blades to collect most of the particles.
Parker, Mark J., "Performance Recovery of Scale Reduced Cyclone Particle Separators using a Rotating Classifier" (2023). Electronic Thesis and Dissertation Repository. 9859.