Turbulent fluidization and transition velocity of Geldart B granules in a spout–fluidized bed reactor

A spout–fluidized bed reactor (SFBR) is a promising process intensification device used in energy chemical processes, such as combustion, gasification, powder preparation and chemical reaction. The reaction performance primarily depends on the flow behaviour of gas-solid in the reactor. This study examined the transition of flow regimes for Geldart B granules through spectral analysis of pressure drop fluctuations and visual observation, and the transition velocity of turbulent fluidization was analysed using the standard deviation of pressure gradient. An empirical model was proposed to predict the transition velocity. Eight types of regimes are identified, and the transition of flow regimes is dominated by the coalescing and breaking up of bubbles formed around the air distributor and spout. The turbulent fluidization in a SFBR has no obvious jet flow but cluster is formed, and the flows both in spout and anulus zone reach a superficial homogeneity. Owing to the spouted gas, the turbulent regime can be transformed from spout-fluidization at a high spouted gas velocity or slugging fluidization at a low spouted gas velocity. The turbulent fluidization does not occur simultaneously, the lower the bed region is, the higher the transition velocity will be. The spouted gas has an optimal inlet condition that can minimize the transition velocity. The transition velocity increases with the static bed height or granule size owing to the more inhomogeneous.