(89a) Single Particle Collection Efficiency of Tangential Versus Volute Inlet Style Cyclones

Proper cyclone design is essential to minimizing solids loss in a fluidized bed system. Dr. Fred Zenz, a pioneer in fluidization and cyclone design, published a set of empirical correlations, known as the single particle (zero-loading) collection efficiency curves, for volute and tangential inlet cyclones. These design curves are a fundamental step of Zenz’s cyclone design methodology. The Zenz data suggest that volute inlet cyclones are less efficient than tangential inlet cyclones, which directly contradicts recent cyclone efficiency studies at PSRI. Furthermore, the Zenz curves tend to underpredict cyclone efficiency, likely due to the fact that they do not take into account the clumping phenomena typically characteristic of fine, cohesive powders. Powder clumping and its effects on cyclone collection efficiency have not been systematically studied. The aim of this research is to revisit Zenz’ fundamental cyclone curves to (1) determine the difference, if any, between efficiency for volute and tangential inlet cyclones, and (2) incorporate clumping behavior into cyclone design methodology for more accurate and reliable cyclone evaluation. To conduct this research, material was injected at “single particle loading” (1 grain solids/ft³ suspending gas) into a 21-in (53-cm) diameter cyclone, and the overflow and underflow streams were collected to determine the overall collection efficiency and fractional collection efficiency. Tests were conducted with both a tangential and 180° full scroll volute inlet cyclone. The test materials include a wide variety of extremely fine (dp₅₀<44um), cohesive powders. PSRI has developed correlations for effective clump sizes as they relate to entrainment in fluidized beds; the aim of this research is to provide a similar correlation that incorporates a critical clump diameter into cyclone efficiency calculations.