Liquid holdup and flow dispersion in zeolite packed beds

A simple tracing method, based on residence time distribution measurements, is presented for the evaluation of the liquid holdup and dispersion in zeolite packed beds. Two tracers and two different materials, one porous (zeolite clinoptilolite) and one non-porous (SiC), were used in experiments on seven packed beds of different dimensions, operating under downflow or upflow condition, in the range of superficial velocities from 0.04 to 0.61 × 10^-2 m/s. The corresponding superficial Reynolds number is between 0.6 and 8.50. Drainage and tracing methods are experimentally compared. The tracing techniques tested are reliable and applicable for the determination of liquid holdup and dispersion in clinoptilolite beds. Liquid holdup, as % of void volume of the bed, is 90 ± 10% for upflow condition, independent of the superficial velocity. For downflow condition it reaches 80% for superficial velocities greater than 0.4 × 10^-2 m/s. Peclet numbers were determined, giving different trends for upflow and downflow conditions. For superficial velocity near 0.4 × 10^-2 m/s (Reynolds number near 4) and greater, Peclet numbers are identical and in the vicinity of 0.12. A discussion is conducted in order to clarify this observation. Approximate correlations are proposed for liquid holdup and Peclet number in zeolite packed beds.