Regime Transition and Holdup in Pulsed Sieve-Plate and Pulsed Disc-and-Doughnut Columns: A Comparative Study

ABSTRACT

This study reports a detailed comparison of dispersed-phase holdup and onset of different operating regimes in PSPC (pulsed sieve-plate column) and PDDC (pulsed disc-and-doughnut column) for 3 N nitric acid–30% tributyl phosphate (TBP) in dodecane system. Experiments are performed in a 3-inch glass column with SS internals for aqueous-continuous mode of operation keeping O/A ratio at 1:3. The effects of column throughput (0.0097–0.0219 m/s) and pulsing velocity (0.011–0.039 m/s) on holdup and onset of operating regimes are studied and compared. Holdup in PDDC is found to be consistently more than that in PSPC. Onset of dispersion regime is found to be delayed in PDDC in comparison to PSPC. Insights into the movement of a typical dispersed-phase drop under pulsatile flow in PSPC have been provided. Additionally, a sensitivity analysis of the effect of pulsing velocity on holdup in PDDC and PSPC is reported. For the phase system and O/A ratio used in the experiments, holdup in PSPC is observed to be more sensitive to variation in pulsing velocity as compared to PDDC. Efficacy of several previously reported correlations to predict dispersed-phase holdup in PSPC and PDDC is evaluated using the experimental data generated in this study.

KEYWORDS:

• Pulsed column
• PSPC
• PDDC
• holdup
• operating regime
• two-phase flow

Notations

 Amplitude of pulsation [m]

 Frequency of pulsation [Hz]

 Pulsing velocity [m/s]

 Dispersed-phase velocity [m/s]

 Continuous-phase velocity [m/s]

Slip velocity [m/s]

S Sensitivity of dispersed-phase holdup [-]

Greek letters

 Interfacial tension [N/m]

 Viscosity [kg/m.s]

 Dispersed-phase holdup [-]

ϕ_avg Average of dispersed-phase holdup values [-]

ϕ_SD Standard deviation of dispersed-phase holdup values [-]

 Density [kg/m³]