(140b) Effect of Baffles on the Flow Regime, Transition Velocities and Void Characteristics in a 6 in. Diameter Fluidized Bed

Fluidized beds are often fitted with internals that come in various shapes and arrangements. Internals such as sheds are used to improve flow behavior of solids, by distributing the bubbles across the column diameter. This study highlights the importance and advantages of fluid bed operation with baffles on the hydrodynamics of the bed. Cross hatched sheds were used as internals that were mounted inside a 6 in (15 cm) diameter fluidized bed. The unit was operated under ambient conditions with Geldart Group A FCC catalyst. An optical fiber probe was used to characterize the bubble and slug rise velocities. The identification of flow regimes was accomplished through high frequency differential pressure transmitters that were mounted across a 3ft section of the dense bed. The bed hydrodynamics were then compared and contrasted to an open bed at superficial gas velocities ranging from 1 ft/s to 6 fts/s. The sheds reduced the bed transition velocity (U_c) to the turbulent regime and bypassed the slugging regime that was dominant in an open bed. The pressure fluctuations were orders of magnitude lesser in the bed with internals suggesting their role in promoting uniform fluidization. Finally, the slug rise velocities in an open bed were widely different from the bubble rise velocities with the internals at the same bed superficial gas velocity. This is an important parameter for fast catalytic reactions that are mass transfer limited. The gas solids contacting time in various fluidization regimes can largely differ, affecting the yield of the reaction, hence care must be taken during scaleup where a pilot plant may operate in a different regime than a commercial reactor. The experimental data was then compared with previous literature studies to see if the correlations can be used to predict the bed hydrodynamics