Axial gas dispersion in a fluidized bed of polyethylene particles

Gas mixing behavior was investigated in a residence time distribution exper iment in a bubbling fluidized bed of 0.07 m ID and 0.80 m high. Linear low density polyethylene (LLDPE) particles having a mean diameter of 772 mu m a nd a particle size range of 200-1,500 mu m were employed as the bed materia l. The stimulus-response technique with CO2 as a tracer gas was performed f or the RTD study. The effects of gas velocity, aspect ratio (H-0/D) and sca le-up on the axial gas dispersion were determined from the unsteady-state d ispersion model, and the residence time distributions of gas in the fluidiz ed bed were compared with the ideal reactors. It was found that axial dispe rsion depends on the gas velocity and aspect ratio of the bed. The dimensio nless dispersion coefficient was correlated with Reynolds number and aspect ratio.