Effect of riser exit geometry on bed hydrodynamics and heat transfer in a circulating fluidized bed riser column

This paper reports the variation of suspension density along the riser colu mn and the effect of riser exit geometry on bed hydrodynamics and heat tran sfer in the upper region of a circulating fluidized bed (CFB) riser column. The experiments are conducted in a CFB riser column which is 102 mm x 102 mm in bed cross-section (square), 5.25 m height, with a return leg of the s ame dimension. The unit is made up of interchangeable plexiglass columns. T he superficial primary air velocity is varied between 4.2 and 6.4 m/s. The suspension density profile along the riser height is influenced by the exit geometry. With a 90 degrees riser exit geometry, the suspension density pr ofile in the upper region of the CFB riser column increases towards the ris er exit. This particular trend has been observed for about 2 m length in th e top region of the riser. The change in suspension density profile in the top region influences the variation of heat transfer coefficient. With a 90 degrees riser exit geometry, the suspension density increases towards the riser exit, which in turn increases the heat transfer coefficient. The effe ct of riser exit geometry on hydrodynamics and heat transfer is significant for about 2 m length in the upper region of the riser column. Copyright (C ) 2001 John Wiley & Sons, Ltd.