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Keywords:

  • binary mixture;
  • continuous particle size distribution;
  • Geldart Group B;
  • circulating fluidized bed riser;
  • elutriation;
  • entrainment;
  • species segregation

Experiments in a dilute, gas-solids circulating fluidized bed have been conducted, with an emphasis on the impact of polydispersity on elutriation and species segregation. Two categories of polydispersity were studied: binary mixtures with various compositions and continuous particle size distributions (PSDs) with various widths. Qualitative differences between the two include (i) total elutriation flux of binary mixtures increases with the composition of fines (Ut < Us) but not so for continuous PSDs and (ii) elutriation flux of coarse particles (Ut > Us) depends non-monotonically on fines composition for binary mixtures but monotonically for continuous PSDs. These differences are explained by the increasing size disparity of continuous PSDs as distribution width increases, while the size disparity remains constant in binary mixtures of varying compositions. A third qualitative difference is the monotonic decrease in mass % of coarse particles with riser height observed for continuous PSDs, and a nonmonotonic behavior for binary mixtures. © 2012 American Institute of Chemical Engineers AIChE J, 59: 84–95, 2013