APPLICATION OF GAMMA-RAY ATTENUATION FOR MEASUREMENT OF GAS HOLDUPS AND FLOW REGIME TRANSITIONS IN BUBBLE-COLUMNS

In this study a gamma-ray densitometry was used to measure radial and axial volume fraction distributions in a 0.21 m diameter bubble column , and flow regime transitions in a 0.05 m and 0.21 m diameter bubble c olumns. Experiments were conducted with two- and three-phase systems ( nitrogen-Fischer-Tropsch derived waxes-iron oxide or silica particles) in both batch and continuous modes of operation at 265 degrees C and ambient pressure. Average radial gas holdups in the large diameter col umn showed the existence of a maximum at the center of the column, in both two- and three-phase systems. The maximum was more pronounced at higher superficial gas velocities (churn-turbulent flow regime). The a xial and average gas holdup measurements in two-phase systems were in good agreement with results obtained by a conventional method (pressur e measurements along the column height). An independent treatment of a ll three phases did not yield satisfactory results, due to large impac t of small experimental errors on calculated holdups. Alternative meth ods based on measured values of solids concentration in the slurry yie lded satisfactory results. Instantaneous signals from the nuclear dens ity gauges were used successfully to determine transitions from homoge neous flow regime to slug flow (small diameter column) or churn-turbul ent flow regime (large diameter column) in two-phase systems.