Axial voidage profiles and identification of flow regimes in the riser of a circulating fluidized bed

The hydrodynamics and flow regimes identification in fast-fluidized bed for single systems consisting of FCC, sand, coal, iron ore and mixed systems of FCC–sand and coal–iron ore were investigated in a perspex column (0.1016 m ID × 5.62 m high). The real voidage profiles have been found out by incorporating gas and solid friction factor and shear stress at the wall of column in the momentum balance equation. To study the flow regimes, the transport velocity (Utr) was determined from the (ΔPL/L)–Ug–Gs relationship. The gas velocity at which solid hold-up in the upper dilute region exhibits a maximum value is defined as the fast transition velocity (UTF) and the transition velocity to pneumatic transport as UFD. In the present work, two correlations have been proposed for both the transition velocities. It has been found that the proposed correlation is in good agreement with experimental values of axial voidage.