Hydrodynamics of air–sand flow in a conical swirling fluidized bed: A comparative study between tangential and axial air entries

Hydrodynamic regimes and characteristics of air–sand flow were studied in a cone-shape swirling fluidized bed for two types of air entry, or swirl generator: through a four-nozzle system (tangential entry) and using an annular-spiral air distributor (axial entry). Quartz sand of four particle sizes, 180–300, 300–500, 500–600 and 850–1180 μm, was used as the bed material in experimental tests on a cold model of a conical swirling fluidized bed combustor. During each test run, the pressure drop across the bed (Δp) was measured versus superficial velocity at the lower bed basis (u) for three static bed heights (20, 30 and 40 cm). Four regimes were found in the bed behavior for both swirl generators. The Δp–u diagrams were compared between tangential and axial air entries for different operating conditions. Mathematical models for predicting major hydrodynamic characteristics, the minimum fluidization velocity (umf) and corresponding pressure drop across the bed (Δpmf), were empirically developed. The dimensionless dependency of Δp/Δpmf on u/umf showed the apparent common trends and similarity for most of the test trials. For the two air injection systems, a Nomograph for assessment of Δp at any arbitrary superficial velocity and bed height was proposed as well.