Abstract
Hydrodynamic characteristics in a wind-box and bubbling fluidized-bed (BFB) gasifier zone of a dual fluidized-bed (DFB) were investigated by a two-phase three-dimensional computational fluid dynamics (CFD) model. The gas and solid phases were treated by an Eulerian–Eulerian two-fluid model, coupled with the realizable k–epsilon turbulence model and the kinetic theory of granular flow (KTGF) describing the random motion of solid particles. Pressure drops obtained from the cold-rig CFD simulation were validated with experimental data which were measured in a pilot-scale BFB using air as a fluidization agent and sand as heat carrier particles at an operating temperature of 800°C. Hydrodynamics of the fluidized-bed with a uniform gas distributor (Ideal case) and a nozzle-type gas distributor (Real case) were evaluated in terms of the pressure drop, solid volume fraction (SVF), uniformity index (UI), and solid stack volume (SSV) for three inlet air flow rates (low, medium and high). Similar behaviors were shown for both the two cases in pressure drop along the gasifier height. However, significant differences were observed in SVF, UI, and SSV. A threshold changing the slope of SSV to the air flow rate was found at a fluidization index (u/umf) of 2.9.
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