LOCAL INTERACTIVE PATTERNS OF DISPERSED AND SWARM PARTICLES IN A CIRCULATING FLUIDIZED-BED RISER

Motion of glass beads of 0.4 mm mean diameter is observed in the centr al region of a circulating fluidized-bed (CFB) riser by coupling a ref lective-type particle image scope (RPIS) with a highspeed video system of 3000 frames s(-1) recording rate. Transient changes in the particl e velocity are measured under both dilute and dense conditions. The ob served speed of ascending particles ranges from 0 to 3.0 m s(-1) at a superficial gas velocity of 6.0 m s(-1). Descending particles are also observed, and their speed ranges from 0 to 1.6 m s(-1) The structure and motion of particle swarms are analyzed with a special emphasis on particle collision. It is confirmed that the speed, moving direction, and packed density of the particle swarms are subjected to persistent time variations. Various patterns of particle motions are identified i n the CFB riser, induced by a diversity of collision mechanisms. These include momentum transfer from a colliding particle to other particle s being contacted, grazing followed by particle rotation, roundabout m otion of a particle around another, simultaneous collision involving m ore than three particles, and successive particle collisions.