The Influence of Fluidising Gas Density and Viscosity on Segregation in a Cylindrical Fluidised Bed Separator

This study investigates the segregation behaviour of a fluidised bed separator by assessing the effects of density and viscosity of the fluidising agent. Segregation can be desirable for some applications, such as for the continuous removal of one type of product or for classification of particles. In particular, their impact on the bed composition, bubble formation, pressure fluctuation, and superficial gas velocity are discussed. The particle distribution profile along with the bed height and pressure drop are measured, together with the pressure fluctuation profile and mixing index. The results show that varying the ratio of solid to gas density has a negligible impact on segregation for superficial gas velocities between 1.2 (minimum fluidisation velocity) and 3.5 . The gas viscosity has a significant impact on segregation for a superficial gas velocity of between 1.2 and 1.5 , but its impact reduces as the superficial gas velocity and bed composition are increased. The high gas viscosity case was found to lead a suppression of the bubble formation and pressure fluctuation, thus resulting in low segregation. Pressure fluctuations further demonstrate the inhibitory effect of high gas viscosity on bubble formation, and the experiments discovered that high gas viscosity promotes fluidised bed stability. It is noteworthy that although the present experiments were carried out in a lab-scale fluidised bed at ambient temperature, the particle density ratio and the particle to gas density ratio are based on the dimensionless scaling numbers that can provide a guide to the segregation in the gasification system using sand and char. The large range of gas viscosities examined in the experiments also can assist with the control of high viscosity steam gasification system.