Experimental and numerical study of the swirling fluidized bed hydrodynamics

Abstract

Process intensification (PI) is a design strategy that pursues novel solutions to improve energy efficiency, cost-effectiveness, and enhance other qualities. PI in the gas-solid field involves enhancing mass, momentum, and heat transfer rates, thereby maximizing production capacity per size of installation. Gas-solid processes are commonly conducted in conventional fluidized beds for different industrial applications and processes, such as heating, drying, separation, or reactions. This work involves a swirling fluidized bed (SFB), which is a variation of the fluidized bed where the fluidization fluid introduces a swirling motion to particles and generates a centrifugal bed. The SFB achieves a more uniform bed, higher transfer rate, and shorter processing time than the conventional fluidized bed. The SFB performance is related to its hydrodynamics. This research studies the hydrodynamics of SFBs through experiments and numerical simulations. First, a literature overview of SFBs was performed to support experimental and numerical procedures. Second, an experimental study of an SFB was conducted to characterize its hydrodynamic behavior. The experimental study measured the bed pressure drop and the tangential velocity of solids using pressure gauges and particle image velocimetry (PIV). The experimental study was conducted with varying bed mass over a wide air volumetric flow rate range. Besides, the study includes two gas distributor configurations to corroborate the SFB behavior. The numerical study was performed using a computational fluid dynamic (CFD) simulation. The CFD simulation was computed in the open-source software OpenFoam V10 using the multiphaseEulerFoam solver. The CFD simulation was validated using the mean bed solids velocity obtained via PIV. The validation process includes the test of different combinations of specularity coefficients. A grid converge index study was also performed to check the field's convergence. The grid convergence study was conducted for solid azimuthal velocity fields. Finally, a CFD-based analysis was performed to gain insights into the influence of the inner wall height on bed hydrodynamics and proposed a design recommendation regarding bed uniformity. The experimental results include the minimum fluidization velocity, identification of SFB flow regimes and bed solids velocity, and testing of a previously proposed angular momentum model. The experimental results reveal a plausible alternative to locate the minimum fluidization velocity and the SFBs flow regimes using the standard deviation of the bed pressure drop signal, which is made in conventional fluidized beds. The SFB flow regimes were identified and showed good agreement with previous studies. Besides, the angular momentum model shows promising results for future works.