A review of pulsed flow fluidisation; the effects of intermittent gas flow on fluidised gas-solid bed behaviour

Pulsed flow fluidisation involves the use of either a relocating or intermittent gas stream flowing through a bed of particles, and produces a range of fluidisation effects dependent on the type and frequency of the pulsation. Pulsed flow has been shown in a range of studies to improve mixing and heat transfer, and reduce agglomeration. However these effects are dependent on the pulsation frequency, particle characteristics and other process conditions. Research into pulsed flow fluidised beds has demonstrated a pattern for an improvement in heat and mass transfer rates, specifically in Group A and B particles, reduced slugging and channelling in wet or cohesive particles, and an improvement in the fluidisation of hard to fluidise materials such as Group C powders. In addition, reduced energy consumption from lower minimum fluidisation rates under pulsed flow further indicates a potentially significant efficiency improvement. These findings, however, highlight needs for correlations to be drawn between the effects studied and the pulsation method and frequencies applied. Here, we present a comparison of continuous and pulsed flow fluidisation, and discuss effects such as minimum fluidisation velocity, bubble characteristics and bed expansion. Areas for future research have been identified in order to build a better picture of how pulsed flow frequencies and particle characteristics interact, aiding the development of this technology within industry. (C) 2016 Published by Elsevier B.V.