Inlet boundary conditions for the simulation of fluid dynamics in gas-solid fluidized beds

The interaction between a fluidized bed and the air-supply system is studied numerically in a cold circulating fluidized bed unit. The bed was operated with Group B solids and with an air-distributor pressure-drop similar to that often applied under industrial conditions. The simulations and experiments are compared through power spectral density distributions of pressure fluctuations in the bed and air plenum. This work focuses on the inlet boundary conditions of the numerical simulations, i.e., the purpose is to include a representation of fluctuations in pressure and flow in the air-supply system. The fluctuations are computed and coupled with the simulations of the flow field in the bed and the air plenum, based on an Eulerian approach. Parametric models are employed for spectral estimates as the time consumption for the three-dimensional simulation limits the length of the pressure time series. The simulations provide satisfactory agreement with experiments, and it is seen that, under certain conditions, there is a strong interaction between the fluidized bed and the air-supply system in the form of pressure waves, as well as pressure and flow pulsations from the air-supply system, which propagate through the entire system. It is demonstrated that for such a system, the assumption of a uniform inlet gas flow over the air distributor, assumed in most previous fluidized-bed studies, is not appropriate. This study demonstrates the importance of further development of numerical models for simulating the hydrodynamics of fluidized beds, in particular for industrially sized units.