Improved Mass-Transfer Model for Distillation in a Pilot-Scale Concentric Ring Rotating Bed as a Rotating Packed Bed

Abstract

To make a further investigation into the masstransfer mechanism of distillation in rotating packed beds (RPBs), an improved mass-transfer model based on liquid-droplet flight, liquid-droplet impingement, and gas turbulence in a pilot-scale concentric ring rotating bed (CRRB) is developed from Li's masstransfer model of distillation. The CCRB belongs to a type of RPB. Total reflux distillation experiments are carried out in a pilot-scale CCRB using the ethanol−water system. With the improved model and experimental data, radial distributions of liquid-droplet flying and impinging mass-transfer coefficients, local liquid-and gas-side mass-transfer coefficients, and overall volumetric gas-side masstransfer coefficient in the rotor and casing are obtained. The improved model can accurately describe the actual mass transfer occurring in the pilot-scale CRRB. It is found that the liquid-droplet flying mass transfer has a significant contribution to the liquidside mass transfer, and there exist gas-side end zones with excellent mass-transfer efficiency at the inner periphery of the rotor and in the casing. The total reflux distillation of the pilot-scale CRRB is basically gas-side-controlled. Also, experiments of measuring liquid distribution at the outer periphery of the pilot-scale CCRB rotor are conducted by capturing liquid trajectories on paperboards. Results show that a good and uniform liquid distribution exists at the outer periphery of the rotor, which results from the existence of the tangential slip velocity of liquid on the inner wall of the concentric ring in the pilot-scale CRRB. The improved mass-transfer model that reveals the mass-transfer mechanism of RPB distillation will significantly facilitate the industrial application of RPB in distillation.

Comprehensive Analysis of Pressure Drop Phenomena in Rotating Packed Bed Distillation: An In-Depth Investigation

“…A study by Burns et al extensively researched the factors affecting liquid holdup and validated their model with experimental results . Consequently, the study was widely utilized by other researchers. , Other studies have also pointed out the importance of liquid holdup in RPBs, demonstrating its influence on micromixing efficiency, mass transfer rates, and overall system performance. ,− …”

“… 31 , 39 Other studies have also pointed out the importance of liquid holdup in RPBs, demonstrating its influence on micromixing efficiency, mass transfer rates, and overall system performance. 23 , 40 − 42 …”