Gas-Phase Mass Transfer in a Centrifugal Gas-Liquid Contactor with a Stack of Flexible Disks as Packing

Abstract

Rotating packed beds have been proposed for carrying out distillation and absorption as an alternative to conventional columns. It had been claimed that the mass transfer rates are one to two orders of magnitude higher than for conventional columns, permitting a volume reduction of a similar order of magnitude. However, we found that the gas undergoes ‘solid-body’ like rotation, implying that there should be no enhancement of the gas-side transfer coefficient. To verify this contention, mass transfer studies were carried out on the absorption of SO2 from air into an NaOH solution using wire-mesh packing. The volumetric mass-transfer coefficient was in the range of that for conventional packed beds. The gas-side mass-transfer coefficient was far lower. With a view to promote tangential slip and thereby enhance the transfer rate, we used a stack of flexible disks of cloth with a spacing of 1.5 mm as packing. Studies were carried out on gas-phase pressure drop and mass transfer. From the total pressure drop, the local friction factor in the rotor was deduced. The gas-side transfer coefficient was much lower than for conventional beds, but in close agreement with those reported for flow through stationary annular disks. The experimental values for gas-side mass transfer coefficient were an order-of-magnitude lower than those estimated from theory considering the flow to be laminar. This discrepancy was attributed to severe liquid maldistribution.