Gas–solid structure in the vicinity of a sparger nozzle in a fluidized bed

A new experimental approach is proposed to investigate the gas–solid structure in the vicinity of a sparger nozzle in a fluidized bed. The approach consists in performing an injection velocity sweep with a fiber-optic probe located at a fixed distance downstream the sparger nozzle. Following this approach, the local gas–solid structure was investigated for different nozzle orientations (downward, horizontal and upward) and measurement distances. For a given fluidized media (FCC catalyst, Geldart A) and superficial gas velocity (0.9 m/s), the local gas–solid structure depended upon the measurement distance, sparger nozzle orientation and injection velocity. Four distinct impact zones were identified from the average local solid holdup, with the boundaries corresponding to the characteristic jet lengths (Lmin, Lmax and Lb). Locally, the major hydrodynamic parameters of the gas–solid structure (e.g. average holdup, phase holdup, phase fraction, and phase changeover frequency) showed nearly linear dependence with the injection velocity, allowing for an easy estimation of the gas–solid structure. Dynamic aspects of the gas–solid structure were investigated. A simple analysis suggests that the frequency of the pulsating jet (between Lmin and Lmax) was in the order of 1 and 1.5 Hz. Comparison of the collected data with existing correlations indicated that none of the correlations are capable of adequately predicting the penetration lengths, under the present test conditions. This is especially true for the upward and horizontal sparger nozzles, for which correlations have mostly been developed using Geldart B and D particles and operated at superficial velocities at or near the minimum fluidization velocity.