Gas-liquid-solid Operation of a Vortex-ingesting Stirred Tank Reactor

The vortex-ingesting stirred tank reactor uses a combination of a helical screw impeller and concentric draft-tube to entrain and recycle headspace gas and disperse it as bubbles in a liquid reaction solvent. This study presents an experimental characterisation of a 0.29 m diameter vortex-ingesting gas-liquid stirred reactor, operated with solids mass fractions from 0 to 25%, over a range of specific power inputs up to 3 W/kg and for a variety of tank geometries. As was found in previous studies the most important geometric variable is the draft-tube top clearance, since this has the most direct effect on the gas ingestion rate. The presence of low solids fractions causes a significant increase in the minimum speed required for vortex ingestion of the gas. At low impeller speeds and low solids mass fractions, accumulation of particles in the annulus surrounding the draft-tube reduces the pumping capacity of the impeller. This mechanism also reduces the gas holdup and gas-liquid mass transfer coefficient, although not always in a monotonic fashion. In this design of reactor, aeration results in only a small decrease in the specific power input and so the just-suspended condition is not much affected by the presence of gas.