FACTORS AFFECTING SOLIDS SEGREGATION IN CIRCULATING FLUIDIZED-BED RISER

Axial and radial segregation effects due to differences in particle si zes and solids densities were studied in a 0.2-m-dia. riser at gas vel ocities between 3.5 and 7 m/s and solids circulation rates between 8 a nd 40 kg/(m(2).s). Two bed materials (a quartz sand/iron powder mixtur e and a quartz sand with a broad size distribution) with identical ter minal velocity distributions were used. Local mean particle sizes and local mass fractions of the iron powder (for the mixture) decreased wi th height. Measurements of the solids streams revealed that the downfl owing solids consist preferentially of large and/or heavy particles, w hile the reverse happens in the upward solids flow. The single particl e terminal velocity is the decisive parameter affecting solids segrega tion. The comparison of both bed materials indicates that two bed mate rials will exhibit the same segregation patterns only if the distribut ions of the particles' terminal velocities in both materials are the s ame.