Hydrodynamic Characteristics of a Horizontal Pulsed Solvent Extraction Column
A horizontal configuration for a pulsed solvent extraction contactor has been recognized as having a great potential in replacing standard vertical pulsed column (VPC) in the separation of heavy elements in the reprocessing of spend nuclear fuel. Published work examining the performance of the horizontal pulsed column (HPC) has been sparse to date, thus preventing the design of large-scale units.
The hydrodynamic studies were conducted in a 0.072-m by 1-m long column with a perforated-plate cartridge arrangement using a 30% tributyl phosphate +70% Isopar M -2.0 mol/L nitric acid system. The hydrodynamic behaviour was characterized in terms of throughput capacity, dispersed phase holdup, axial mixing of both phases and power dissipation. Emphasis in this study was given to the effects of the major operating variables that include: aqueous and organic flowrates, and pulse amplitude and frequency, on the key hydrodynamic factors. The effects of physical properties for liquid-liquid systems and plate geometry were also examined for selected hydrodynamic factors.
The variation of throughput capacity with the operating variables was found to be similar to that reported for the VPC when presented on standard flooding diagrams. The flooding behaviour of the HPC was strongly dependent on both pulse amplitude and frequency, as well as on the coupled pulse effect represented by pulse velocity. A procedure for constructing flooding diagrams from correlations derived from experimental results was demonstrated. Mechanisms to determine the onset of flooding and flooding anomalies were investigated and the results compared with experimental data.
A detailed analysis of the dispersed (aqueous phase holdup was made. The aqueous holdup did not vary significantly along the column, however, local radial variations are reported. Correlations based on experimental data for the average holdup for the HPC indicated the effect of the major operating variables is similar to that reported for the VPC in the mixer-settler region of the operation. However, the range of the aqueous holdup observed for the HPC (0.15 - .50) is several times larger than that typically reported for the VPC.
Axial mixing, as determined by a two-point tracer method of measurement, was well represented by a backflow model. Axial mixing of the dispersed (aqueous) phase was found to be insignificant. The organic phase axial mixing was significant with backflow conditions as large as 25.4 (dispersion coefficient of 18. 2 cm^2/s) were observed. The effects of the major operating variables on the organic phase axial mixing in the HPC were consistent with similar data reported for the VPC.
Power dissipation studies, by the force-displacement method, revealed a pronounced dependency on the pulse amplitude-frequency product. Individual phas flowrates were found to have a minimal effect on the time-averaged power dissipation. Experimental results were in good agreement with a quasi-steady state model commonly used for the VPC.
A comparison of the major hydrodynamic factors for the HPC with the VPC suggested that the HPC can be a viable alternative where space and portability factors are critical.