Investigation of a swirling flow nozzle for a fluidised bed gas distributor

Abstract

This paper relates to a multi-orifice distributor for a gas-fluidised bed, using many upward-facing nozzles, equally spaced in a horizontal plate. Each orifice contained a removable helical coil, which made the gas swirl as it entered the bed. For a single orifice in such a distributor, ultra-fast magnetic resonance imaging (MRI) and pressure measurements were applied to study: (i) the formation of jets and bubbles and (ii) the orifice pressure drop. Results from MRI show that the swirling flow induced by the helix significantly improves the fluidisation quality compared to a plain nozzle without spiral. The helix gives rise to secondary flow which increases pressure drop across the nozzle, the measured values of which are predicted satisfactorily by using a friction factor correlation for helical coils.