Application of Small Swirling Jets in Fluidised Beds

This thesis provides an analysis of the effects of introducing a novel flow regime into fluidised beds, where swirling structures interact with particles of a similar scale. The motivation behind the work is to investigate the potential of increasing the efficiency of a widespread industrial process by a system that is readily scaled up and possible to retrofit. It begins by providing a review of the scientific literature around swirl flows and fluidised beds, explaining the reasoning behind the research hypothesis and the flow mechanisms in the inventive principle. This covers the background and utilisation of swirling and helical flow structures, followed by the principles of fluidised beds. The research hypothesis was tested empirically on a specially constructed pilot scale rig designed to provide a range of different flow regimes. The apparatus required advanced manufacturing methods and design was guided by Finite Element Analysis to ensure the desired flow regimes were achieved. The empirical studies with the apparatus were backed up through numerical modelling of the pseudo one dimensional fluidised bed, that is, the interaction between one jet and one particle. The empirical studies indicate a significant change in the behaviour of the fluidised bed between the novel flow regime and the standard design control. It was found that the novel flow resulted in improved gas distribution and the creation of smaller bubbles, improving the gas-solid interaction demonstrated by 2% lower bed expansion, 18% shorter drying times, 29% increased bubble frequency and minimal difference in total bubble volume. The numerical model shows change in the direction of momentum transfer and reduced heat transfer rate as the intensity of novel flow conditioning increases. This results in the particle being drawn towards an individual jet by a recirculation zone and a more even spread of heat throughout the gaseous phase. The evidence presented shows that by the introduction of a novel flow conditioning to fluidised beds results in significantly improved gas distribution across the system, leading to improved mixing between the gas and solid phases and resultantly a more efficient process.