HYDRODYNAMICS AND AXIAL MIXING IN A THREE-PHASE BUBBLE COLUMN

The aim of this experimental study was to provide a better understanding of the current state of the field of the multiphase hydrodynamic and mixing characteristics. The fluid dynamics of three-phase cocurrent flow in a 15.2 cm diameter by 335 cm long bubble column were studied. Behavior of gas liquid and solids holdups, slurry-phase axial mixing and flow regime transition in gas-liquid-solid systems were investigated by varying a number of parameters such as particle size (10-70 microns), solids concentration (10-40%, by weight), superficial gas velocity (3-30 cm/sec), and superficial slurry velocity (0-10 cm/sec). Data for gas holdup were analyzed by the hydrostatic-head-technique from the pressures measured by a series of "u" tube manometers at different axial locations. To determine the solid and liquid holdups in the three-phase mixtures, solid-liquid samples, collected at several locations along the length of the column, were used. The solids concentration in the sampled slurry was measured gravimetrically. Temperature profiles were obtained during the continuous addition of heat as a tracer under steady-state conditions. This data were analyzed by the one-dimensional axial dispersion model. Gas holdup was found to increase with the increasing gas velocity, but decreased with liquid velocity, solids content and particle size. Liquid holdup decreased with increasing gas velocity and solids content, but it increased with increasing slurry velocity and particle size. Similar behavior was observed for solids holdup. The heat dispersion coefficients were found to increase with gas velocity, to be independent of solids concentration. They decreased with both increasing slurry velocity and increasing size of the solids over the ranges studied. Comparison of the heat dispersion coefficients with the mass dispersion coefficients indicated that the dispersion coefficients for both heat and mass were equivalent. Flow regime maps were also determined by relating drift flux and gas holdup. Most of the present data fell in the turbulent bubbling or transition region. The effects of solids concentration, particle size, and slurry velocity on the prevailing flow regimes were found to be significant. An increase in values of all these parameters caused an earlier deviation from bubble flow regime. The experimental data for flow regimes, gas holdup and dispersion coefficient were empirically correlated and frequently compared with the existing data and correlations, found in the literature.