Simultaneous Observation of Gas Properties' Effect on Emulsion Phase Voidage and Bubble Size in Fluidized Catalyst Beds

Many correlations have been proposed for bubble size in fluidized beds, mainly for Geldart B particles. For particles with physical properties suitable for fluidized catalyst beds, the bubble size is significantly affected by gas properties. However, there are no correlations that take into account the effect of the properties of fluidizing gases. Reactor models are necessary for the appropriate design and operation of fluidized bed reactors, and bubble size is one of the important parameters in determining the mass transfer coefficient between the bubble phase and emulsion phase in the model. Various gases are used in industrial reaction processes, making it important to correctly consider the influence of gas properties on bubble size. In this study, Geldart A particles were fluidized in a two-dimensional fluidized bed using several fluidizing gases, and the behavior of bubbles and emulsion phase voidage was simultaneously observed. Color movies were created to visually observe the emulsion phase voidage, and the average bubble size under each condition was determined from the images. We confirmed that the bubble size decreases as the emulsion phase voidage increases. The effects of particle size, particle density, gas viscosity, and gas density on bubble size were explained using a previously proposed correlation for apparent viscosity. We emphasized the importance of considering the effects of gas properties in fluidized catalyst beds.