Hydrodynamics in downflow fluidized beds (2): Particle velocity and solids flux profiles

In a 9.3 m high and 0.10 m i.d. gas-solids downflow fluidized bed (downer), the radial distributions of the local particle velocities along the downer column were measured so as to study the hydrodynamics of the gas-solids flow, using a fiber-optic particle velocity probe. Local solids fluxes were also calculated from the local particle velocities and solids hold-ups. Results show that the radial distributions of particle velocity and solids flux in a downer reactor are very uniform compared to those in a riser although they vary significantly with the operating conditions. For most of the conditions tested, the particle velocity profile reaches its fully developed state within 3-8 m from the top entrance of the downer. On the other hand, particles are normally fully accelerated within 1-4 m, although the development zone and/or the acceleration section under certain conditions can extend to as long as the downer itself. (C) 2000 Elsevier Science Ltd. All rights reserved.