Entrainment of solids in an internally circulating fluidized bed with draft tube

The effects of gas velocity and particle size d(p) on the transport disengaging height (TDH) and solid entrainment rate E along the freeboard height were determined in a fluidized bed (0.3 m internal diameter by 2.6 m height) with or without a draft tube (0.1 m internal diameter by 0.3 m height). The entrainment rates of sand (d(p) = 210-610 mu m) and PVC ((d(p)) over bar = 130 mu m) particles along the axial height of the bed were measured by an isokinetic sampling probe. The entrainment rate in the freeboard region decreases exponentially with the freeboard height and the value at the bed surface increases sharply with increasing excess gas velocity (U-U-mf) in the beds with or without a draft tube. The entrainment rate at the bed surface with a draft tube can be predicted by a correlation for conventional fluidized beds. The exponential decay coefficients a in the present and previous studies were correlated in terms of the Froude number and the ratio of gas velocities U-t/U. Also, the TDH values in the beds with and without a draft tube can be determined by TDH=(1/a)In(E-0/0.003). (C) 1997 Elsevier Science S.A.