Particle motion in packed/ebullated beds by CT and CARPT

Abstract

Computed tomography (CT) and computer‐automated radioactive particle tracking (CARPT) were used to study the gas distribution and incipient particle motion in a packed/ebullated bed in which gas and liquid are in cocurrent upflow. CT scans were performed to evaluate the gas–liquid distributor and gas sparger for the experiments. Using a perforated plate gas–liquid distributor (with 96 1‐mm holes, open area of 0.1%) and a gas sparger (cross‐shaped, with 16 3‐mm holes), the cross‐sectional gas holdup distribution in the packed/ebullated bed was relatively uniform, with gas holdup of about 0.11 in the center and 0.09 near the wall of the bed at superficial gas and liquid velocities of 2 and 0.3 cm/s, respectively. The cross‐sectional averaged gas holdup was 0.095. CARPT experiments were utilized in an air–water–ethanol– (10 wt. %) solids system to identify the operating conditions at which solid particles first start to move in the bed. At a superficial gas velocity of 1.7 cm/s and superficial liquid velocity of 0.3 cm/s, solids particles in the bed started to move and travel long distances in the axial direction. CARPT experiments in the same system at superficial gas velocity of 2.0 cm/s and superficial liquid velocity of 0.3 cm/s showed that the solid particles in the bed were moving significantly throughout the column, generating a recirculation pattern with upflow in the center and downflow near the wall of the column. The time‐averaged maximum upward and downward velocity of the tracer particle was about 0.47 and 0.57 mm/s, respectively.