Eulerian simulations of bubbling and jetting regimes in a fluidized bed

Abstract

The mode of gas-injection is known to influence the local bubbling and jetting behavior in gas–solid fluidized beds. The resultant bubbling behavior influences the mixing and distribution of the gas and solid phases, which in turn can influence heat and mass transfer, and reaction performance in large-scale gas–solid fluidized beds. In the present work, we simulated unary gas–solid flow of particles differing in density, fluidized using uniform and two-jet distributors at different UG. The predictions are validated using the measured local gas-phase area fraction fluctuations, bubble size distribution, and bubble rise velocity. The effect of the models used for calculation of gas–solid drag (βgs), solids frictional pressure (Ps,f), and specularity coefficient (φ) on the bubbling characteristics under dense and dilute flow conditions are analysed. Under dense bed condition (UG = 1.1 Umf), an increase in the Ps,f and φ led to an increase in solids viscosity, which in turn led to a decrease in the bubble rise velocity and size. In the case of the two-jet distributor, an increase in βgs predicted merging of the larger jets and formation of larger bubbles. Further, to predict the different jetting regimes (isolated jets, breakage/merging of jets, and generation of larger bubbles) at different UG correctly, we show that different βgs models are required. Whereas, in the case of gas–solid flows comprised of particles of different density fluidized with the uniform distributor, a single βgs model predicted the bubbling characteristics reasonably well with measurements.