Db. Bukur et al., APPLICATION OF GAMMA-RAY ATTENUATION FOR MEASUREMENT OF GAS HOLDUPS AND FLOW REGIME TRANSITIONS IN BUBBLE-COLUMNS, Industrial & engineering chemistry research, 35(1), 1996, pp. 70-80
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.