Behavior of fluidized beds with variable gas velocity

The objective of this study was to investigate how gas generating within a fluidized bed affects the bed behavior. A special experimental system was designed and constructed for this investigation. The system was a simple modification of a two-dimensional fluidized bed used previously by numerous researchers. The gas generation was simulated by introducing uniformly an air stream throughout the back wall of the bed. Trends and characteristics of fluidized beds with gas generation were identified. A relationship between the overall bed void fraction and gas generation rate was found to be linear. This linear relationship was experimentally verified only in the range in which the ratio of Lf/Lp^f was less than 1.20. Above this range the bed was too turbulent to measure the void fraction accurately. A correlation between bubble size and bubble velocity with and without generation was derived. The scattering of the data was large such that both a linear and parabolic relationship would be acceptable. It was observed that as gas generation increased, the bubble size slightly increased, and this in turn resulted in a slight increase in bubble velocity. Three simplified, idealized cases were examined to explain the observed bed expansion and bubble velocities: a) All generated gas passes through the bed in the form of new bubbles of equal size identical to that of the existing bubbles, b) All generated gas penetrates existing bubbles and passes through the bed. c) All generated gas passes through the bed in the emulsion phase while the existing bubbles remain unaffected. The model most consistent with experimental data was that the generation gas penetrates the existing bubbles and passes through the bed.