Performance of a Multistage Fluidized-Bed Ion-Exchange Contractor with Fluid-Diode Downcomers

Abstract

<p>A study was carried out on the operational and mass-transfer performance of a multistage fluidized-bed continuous countercurrent ion-exchange contractor with fluid-diode downcomers. For the mass-transfer study, the ion-exchange system Na+/H+ with Dowex-50W-x8 resin was used. The total solution concentration used was 0.06 meq/ml.</p> <p>The fluid-diode downcomer design significantly reduces the bypassing of liquid up the downcomer. Easy start-up and shut-down were observed and the resin was evenly distributed on each mass-transfer stage. The effects of fluid-diode lateral displacement, weir height, weir shape and resin particle size on the operational performance (in terms of liquid-bypassing and resin fluidization) of the solid-liquid contactor were investigated.</p> <p>A one-quarter replicate of a factorial experimental design to 7 factors at 2 levels successfully and efficiently revealed the main factors and interactions which significantly affect the overall stage efficiency of the ion-exchange column operation. The significant main factors are resin feed-rate, process solution flow-rate, weir length and weir height. The significant interactions are between resin feed-rate and weir length, process solution flow-rate and weir length, and weir height and weir length.</p> <p>The mass-transfer study has shown that the solid-liquid contact time in the contactor determines the overall stage efficiency. The composition dependence of the mass-transfer coefficients in both the solid and liquid sides also plays a role in affecting the overall mass-transfer.</p> <p>The relative specific volumes calculated from the experimental results justify further development of the present contactor in the consideration from industrial scale applications. The present type of contactor is simple in design and requires simple control strategy, providing operational stability, and large solid and liquid handling capacity.</p>