Factors affecting solids segregation in circulating fluidized-bed riser



Axial and radial segregation effects due to differences in particle sizes and solids densities were studied in a 0.2-m-dia. riser at gas velocities between 3.5 and 7 m/s and solids circulation rates between 8 and 40 kg/(m2·s). Two bed materials (a quartz sand/iron powder mixture and a quartz sand with a broad size distribution) with identical terminal velocity distributions were used. Local mean particle sizes and local mass fractions of the iron powder (for the mixture) decreased with height. Measurements of the solids streams revealed that the downflowing solids consist preferentially of large and/or heavy particles, while the reverse happens in the upward solids flow. The single particle terminal velocity is the decisive parameter affecting solids segregation. The comparison of both bed materials indicates that two bed materials will exhibit the same segregation patterns only if the distributions of the particles' terminal velocities in both materials are the same.