Through the analysis of the effects of secondary air ratio,secondary air distribution,and swirl number on the gas velocity distribution and particle phase flow field,the strong vortexing effect on the flow characteristic of rice husk in the freeboard of annular vortexing fluidized bed(AV-FB)were understood.Results showed that the backflow area in the freeboard of AV-FB reflect the backflow intensity in that region,and backflow intensity increases with the increases of swirl number.When S＜1,the influence on tangential velocity is relatively small,but it has a significant impact between 1.6 and 2.5.Compared with secondary air distribution equally,secondary air distribution unequally is more beneficial to improve the vortexing flow in the freeboard.Particle suspension layers are observed between the near secondary-air inlets.Solid mass flow rate along the radial direction decreases firstly,then increases with increasing r/R at different h/R,and the maximum value of mass flow rate appears near the freeboard wall,but it decreases with the increase of h/R at different r/R.Applied to the combustion of fine particles in fluidized bed combustor,combustion optimization and pollutant control can be achieved through gas-solid flow characteristics.
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