Hydrodynamics Study on Wind-Box and Gasifier Zone of Dual Fluidized-Beds By CFD Simulation

The hydrodynamic characteristics in a wind-box and gasifier zone of dual fluidized-bed (DFB) are investigated by a computational fluid dynamics (CFD) model to find a stable flow rate zone of fluidizing gas in a pilot-scale biomass gasification process. The gas and granular phases are treated by an Eulerian-Eulerian two-fluid model, coupling with the k-epsilon realizable turbulent model. The random motion of solid particles in the granular phase is represented with the help of the kinetic theory of granular flow (KTGF). A time-step adaptation procedure is implemented to provide the solution stability in the wide range of turbulence and to achieve the numerical solution efficiency for the huge number of mesh elements. The three-dimensional CFD model is used to identify hydrodynamics of bubbling fluidization using air as the fluidization agent and sand as the heat carrier particles in the pilot-scale DFB at an operating temperature of 800 ^oC. The simulation results provide detailed information of gas and solid flow regimes, pressure drops, temperature and particles distribution, and bubble behaviors. Effects of different air flow rates on hydrodynamics of the bubbling gasification zone are examined and the stable air flow rate zone is proposed.