CHARACTERIZING NONUNIFORMITIES IN GAS-PARTICLE FLOW IN THE RISER OF A CIRCULATING FLUIDIZED-BED

A sampling probe operating in a non-isokinetic manner was used to measure variations of local solids mass flux with radial, angular and axial position and time in the 152 mm i.d. riser of a circulating fluidized bed cold model. Time-averaged solids flux profiles exhibit a typically flattened parabolic shape with a region of downward flow adjacent to the riser wall. These profiles do not generally exhibit axial symmetry and a minimum of six radial profiles measurements are found to be necessary to describe the flow pattern adequately. These angular non-uniformities are reproducible, difficult to eliminate and although their form is probably system dependent, it is thought that such non-uniformities are likely to exist in all such gas-particle flow systems to a greater or lesser extent. Detail of the nature of the flowing suspension near to the riser wall has been delineated by analysis of variations in local solids flux with time measured using an adaptation of the same sampling probe.