Abstract
A three-dimensional particle dynamic analyzer (3D-PDA) was employed to measure the gas-solid two-phase flow in a lab-scale square cyclone
separator with downward gas-exit. Several cases of different inlet velocity and particle concentration were studied. The particle used in the test
was glass bead of mean diameter 30-40 p,m. Discussion was given on the distribution of flow vector, mean velocity, turbulent intensity and kinetic
energy of both gas and particles of different diameter at different position in the separator. It was found that the center of the flow field deviated
from the geometric center of the cyclone. The flow fields had the feature of Rankine eddy, i.e., strongly swirling region in the central part and
pseudo-free eddy region of weak swirling intensity near the cyclone wall. Local vortex existed at the corners where the flow changed its direction
sharply. When the cyclone wall was heated and the suspension temperature was elevated, the flow field became more uniform than that under
room-temperature condition. The local vortexes at the corners were weakened and the swirling intensity became poorer which led to decreased total
mean separation efficiency from about 81 % to 76.5%. The right-side wall facing the suspension inlet gave the major contribution to the separation
efficiency, where the largest downward velocity was measured. Back-flow (upward velocity) was found around the center of the separator above
the gas-exit. The quasi-laminar motion of particles enhanced the turbulent motion at the corners due to particle-particle or particle-wall collision,
which led to the local peak value of the turbulent kinetic energy and turbulent intensity. The corner was one of the major regions to cause pressure
drop and was found to be beneficial to particle separation mainly because the strong fluctuating flow consumed much of the kinetic energy of both
the particle and gas.
⑥2006 Elsevier B.V. All rights reserved.
Keywords: Square-shaped cyclone separator; Circulating fluidized bed; Turbulent flow; Three-dimensional particle dynamic analyzer (3D-PDA)