Tracer Fast Ascending Velocities in a Bubble Column Inferred from CARPT - Calibration Experiments

S. Fraguío1, M. C. Cassanello1, M. A. Cardona2, D. Hojman2 and H. Somacal2,3

1PINMATE, Dep. Industrias, FCEyN, Universidad de Buenos Aires, Int. Güiraldes 2620, Buenos Aires,

Argentina, C1428BGA, Email: solfraguio@yahoo.com.ar

2TANDAR, Comisión Nacional de Energía Atómica (CNEA), Centro Atómico Constituyentes, Buenos Aires, Argentina

3ECyT, Universidad Nacional de San Martín, San Martín, Argentina

ABSTRACT

The numerous applications of bubble columns (BC) in diverse fields of the chemical, petrochemical, biochemical and mineral industries are well known. In addition, the ability of the Computer Automated Radioactive Particle Tracking (CARPT) technique to get features of the liquid and/or the solid motion in BC and slurry BC has been thoroughly demonstrated (Degaleesan et al., 2001; Devanathan et al., 1990). Furthermore, fast ascending velocities of the tracer found during the prolonged tracking periods have been associated to its motion while entrapped into the wake of passing large bubbles, pursuing the inference of information of the gas phase dynamics (Cassanello et al., 2001; Larachi et al., 1996). For other type of contactors (gas-solid risers and fluidized beds), fast tracer velocities have been related to solid clusters (Mostoufi and Chaouki, 2004; Bhusarapu et al., 2006). Therefore, present work pursues to point out, through calibration experiments, if differences between the actual tracer velocities and the velocities calculated from the reconstructed tracer positions during fast ascending/descending paths are acceptable. With this purpose, the motion of a radioactive tracer attached to a rod moving upwards/downwards, driven by a pneumatic system, is reconstructed from the combined response of eight NaI(Tl) scintillation detectors. The tracer is a PVC particle containing scandium oxide, activated by neutron bombardment to around 30 ?Ci. The rod is moved at different velocities in the range of 0.1 to 1 m/s and it travels 0.2 m upwards and downwards close to the column centre. A mini-pilot scale BC, 0.1m inner diameter and 1.2m high, is used with batch liquid, tap water, and flowing air at different gas velocities within the homogeneous and the heterogeneous flow regimes. Tracer positions are reconstructed every 0.03 s. Fast velocities are calculated from continuously ascending/descending paths and they are compare to the tracer velocity.

Keywords Radioactive Particle Tracking, solid tracers, bubble columns