Axial dispersion in pulsed-, perforated-plate extraction columns



Continuous-phase backmixing coefficients have been determined by continuous tracer injection for pulsed-plate extraction columns of 72-, 152- and 300-mm-diameter. Both single-phase water and two-phase kerosene-water were studied in all three columns, together with four other solvent-water systems in the smallest column; in all cases, water was the continuous phase. Evidence of maldistribution of the phases was obtained in the largest column. The backmixing coefficient was found to increase with column diameter in single-phase operation, but was diameter-independent in the two-phase case. Alternative correlations of the data were based on dimensional analysis and on a physical model, respectively. The influence of different systems was accounted for in the latter in terms of droplet size and terminal velocity, dispersed phase holdup, and density difference. Qualitative color tracer tests on the dispersed phase gave no evidence of backmixing of this phase, although strong forward dispersion was observed in the emulsion regime.