RADIAL AND AXIAL VOIDAGE DISTRIBUTIONS IN CIRCULATING FLUIDIZED-BED WITH RING-TYPE INTERNALS

Non-uniform radial and axial flow structures are characteristic of cir culating fluidized beds (CPB). As a result, gas solids contact is stil l relatively poor in the riser although much better than in the bubbli ng bed. In this study, the influence of ring-type internals on the red uction of nonuniformity in a riser of 7.5 cm in diameter and 3 m in he ight was investigated. Three ring internals with open areas of 70%, 90 % and 95% were installed in five axial positions in the riser. Measure ment results for solids hold-up distribution of sand particles obtaine d using a fibre optic probe indicate that the internals can reduce rad ial nonuniformity and evenly redistribute solids in the radial directi on. Under high superficial gas velocities and low solids circulation s ales, reversed radial solids distribution profiles with more dilute fl ow in the wall region than in the core region were also observed. A de tailed study on the radial solids distributions around the ring intern als shows the formation of a denser region above the 70% opening ring as compared to above the 90% and 95% opening internals and a more dilu te region below all three rings. Results of the axial voidage distribu tion with the presence of internals show the formation of a zigzag typ e axial profile instead of the regular S-shape profile.