Particle motion in packed/ebullated beds by CT and CARPT

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 far 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. Ar 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.