A computational fluid dynamics study of gas–solid distribution of Geldart Group B particles in a swirling fluidized bed

Abstract

The study's main goal, as reported in this research paper, was to investigate the gas–solid flow behaviors in a twin cyclonic fluidized-bed combustor (T-FBC) in swirling mode under a range of operating conditions. Silica sand in three size ranges, 300–500 μm, 500–710 μm, and 710–1000 μm, with 1700 kg/m3 solid density was used as the bed material in the study's experimental tests and its computer simulations. The Eulerian–Eulerian approach for two-phase fluid flows was selected to investigate the cold hydrodynamic characteristics of gas–solid particles, at a constant ambient temperature, in the fluidized-bed combustor. The three different turbulence models; the standard k-ε model, the renormalization group (RNG) k-ε model, and the Reynolds Stress Models (RSM) were studied in order to select the most appropriate model. Finally, the RNG k-ε turbulence model was applied in all simulations for both phases of our work. The computational simulations were performed using the same parameters and operating conditions as in the experimental tests, with the validity of the computational simulations thus experimentally verified. In the simulation results, it was shown that the increasing size of the bed particles, the solid hold-up tended to decrease, the time duration for initializing full-bed fluidization increased, and the bed fluctuation frequency decreased. When increasing excess air (EA), the simulation results showed the opposite trend. The secondary to total air ratio (S/T) had substantial effects on time duration to initialize bed fluidization and the bed fluctuation frequency in the swirling fluidized bed; however, it had slightly effects on the radial solid hold-up and radial solid velocity in the dense bed region.