(657c) Expansion and Fluidization of Pelletized Activated Carbon Columns: Effects of Column Diameter and Glass Bead Retention Layer

There is always a desire to process as much gas as possible in the smallest bed as possible in a pressure swing adsorption (PSA) process. This necessarily leads to higher velocities, especially during pressure changing steps that may exceed the particle fluidization velocity in a traditional packed bed. To combat the possibility of bed expansion and fluidization, bed retention systems are usually employed that consist of a layer of dense stone or glass beads at the top of the bed. The beds may also be spring loaded to prevent movement, but this presents an engineering challenge depending on the scale of the bed.

To study bed expansion and fluidization phenomena, in support of a PSA pilot plant currently in operation in the field, several clear plastic, full scale columns in height (80 inches) with different diameters were fabricated for operation at ambient and elevated pressures. The bed contained a carbon-based material with glass beads sometimes on top. The packed bed is subjected to increasing flow rates until fluidization is observed while keeping the bed exit pressure constant. The diameters varied from 2.4 inches to 8 inches. The tested beds contained different heights of the adsorbent, with and without different amounts of glass beads. The bed pressures are also varied. A camera and a light sensor were positioned right above the packed bed surface to detect movement of the bed.

The objective is to characterize each bed with increasing diameter in terms of bed pressure drop coupled with static force balances to compare the onset of fluidization predicted via modeling using a modified Janssen equation and wall friction effects to that observed experimentally. The supposition is that wall effects play a critical role in preventing movement in the bed, with the wall effect being more prominent in smaller diameter beds. This presentation will present the latest results obtained from this study.