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

Abstract

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 (Δ p) 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 Δ p– 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 ( u mf) and corresponding pressure drop across the bed (Δ p mf), were empirically developed. The dimensionless dependency of Δ p/Δ p mf on u/ u mf showed the apparent common trends and similarity for most of the test trials. For the two air injection systems, a Nomograph for assessment of Δ p at any arbitrary superficial velocity and bed height was proposed as well.