(366a) Analysis of Fluidization of Pelletized Activated Carbon Columns: Effects of Glass Bead Retention Layer

In pressure swing adsorption (PSA) processes there is always a desire to process as much gas as possible in the smallest beds possible. This necessarily leads to velocities that, especially during pressure-changing steps, may exceed the adsorbent particle fluidization velocity within the bed. To prevent the possibility of bed expansion and fluidization bed retention systems are usually employed at the top of the bed in the form of dense beads. When a layer of glass beads was placed on top of the adsorbent, fluidization of the bed occurred only at velocities several times higher than those predicted by Archimedes' balance.

To investigate bed expansion and fluidization, the bed consisted of a carbon-based material with the possibility of adding a layer of glass beads on top. It was exposed to progressively increasing flow rates until fluidization occurred, while maintaining a constant bed exit pressure. Parameters investigated included adsorbent height (0.24, 0.48, 0.73, 0.97 and 1.58 m), glass bead weight (0, 100 and 200 g), and bed pressure (20, 30, 40, 50 and 60 psia). The experimental results indicated that the minimum fluidization velocity increased with the weight of glass beads. Conversely, an increase in bed pressure and height led to a reduction in the minimum fluidization velocity. A modified form of Janssen’s equation, tailored to the experimental system, was developed to account for the frictional wall effects. This modification enabled the model to successfully capture the influence of the glass bead weight, bed height and outlet pressure.