Study of axial mixing, holdup and slip velocity of dispersed phase in a pulsed sieve plate extraction column using radiotracer technique.
Axial mixing, holdup and slip velocity of dispersed phase which are parameters of fundamental importance in the design and operation of liquid-liquid extraction pulsed sieve plate columns have been investigated. Experiments for residence time distribution (RTD) analysis have been carried out for a range of pulsation frequency and amplitude in a liquid-liquid extraction pulsed sieve plate column with water as dispersed and kerosene as continuous phase using radiotracer technique. The column was operated in emulsion region and (99m)Tc in the form of sodium pertechnetate eluted from a (99)Mo/(99m)Tc generator was used to trace the dispersed phase. Axial dispersed plug flow model with open-open boundary condition and two points measurement method was used to simulate the hydrodynamics of dispersed phase. It has been observed that the axial mixing and holdup of dispersed phase increases with increase in pulsation frequency and amplitude until a maximum value is achieved while slip velocity decreases with increase in pulsation frequency and amplitude until it approaches a minimum value. Short lived and low energy radiotracer (99m)Tc in the form of sodium pertechnetate was found to be a good water tracer to study the hydrodynamics of a liquid-liquid extraction pulsed sieve plate column operating with two immiscible liquids, water and kerosene. Axial dispersed plug flow model with open-open boundary condition was found to be a suitable model to describe the hydrodynamics of dispersed phase in the pulsed sieve plate extraction column.
Measurement of liquid holdup and axial dispersion in trickle bed reactors using radiotracer technique
The holdup and axial dispersion of aqueous phase has been measured in trickle bed reactors as a function of liquid and gas flow rates using radioisotope tracer technique. Experiments were carried out in a glass column of inner diameter of 15.2× 10 -2 m column for air-water system using three different types of packings i.e. non-porous glass beads, porous catalysts of tablet and extrudate shape. The range of liquid and gas flow rates used were 8.3× 10 -5 -3.3× 10 -4 m 3 /s and 0-6.67× 10 -4 m 3 /s, respectively. Residence time distributions of liquid phase were measured and mean residence times were determined. The values of liquid holdup were calculated from the measured mean residence times. It was observed that the liquid holdup increases with increase in liquid flow rates and was independent of increase in gas flow rates used in the study. Two-parameter axial dispersion model was used to simulate measured residence time distribution data and values of mean residence time and Peclet number were obtained. It was observed that the values of Peclet number increases with increase in liquid flow rate for glass beads and tablets and remains almost constant for extrudates. The values of mean residence time obtained from model simulation were found to be in good agreement with the values measured experimentally.
Longitudinal dispersion in pulsed perforated-plate columns
Experimental measurements have been performed for pulsed perforated-plate columns of different sizes and geometry to obtain longitudinal dispersion coefficients for continuous and dispersed phases and size and holdup of liquid droplets dispersed in the columns. These quantities are correlated with operating conditions and column design, including the data published by different authors. Longitudinal dispersion coefficients for the continuous phase are shown to follow the backflow model. A superficial number of stages in series in each compartment is shown to come from inherent instability of fluid motion in the compartment. The longitudinal dispersion coefficient of the dispersed phase approaches that of the continuous phase with increasing pulse velocity. Holdup and mean size of droplets are correlated mainly on the basis of the rate of energy dissipation in the column fluid. Inclusion of dispersed-phase viscosity is shown to correlate the holdup data successfully for different liquid-liquid systems.