FLUIDIZATION REGIMES AND TRANSITIONS FROM FIXED-BED TO DILUTE TRANSPORT FLOW

Characterization by means of Kolmogorov entropy shows that the dynamic s of the bottom bed in small size circulating fluidized bed risers are significantly different from the dynamics of the dense bottom bed in large size risers and, as a consequence, two types of circulating regi mes are introduced: the exploding bubble bed for large risers and the circulating 'slugging' bed for small risers, the latter at high superf icial gas velocities. In a pictorial fluidization diagram ten gas-soli d fluidization regimes are given, seven of which are experimentally id entified with the Kolmogorov entropy by varying the superficial gas ve locity, riser solids holdup and diameter (or width) of the riser: bubb ling bed, slugging bed, exploding bubble bed, intermediate turbulent b ed, circulating 'slugging' bed, intermediate dilute flow, and dilute t ransport flow. No transition could be identified between the exploding bubble bed at captive conditions and the exploding bubble bed at circ ulating conditions in the dense bottom bed of the two largest faciliti es in this study. This suggests that the dense bottom bed in large siz e risers can be considered as a bubbling bed. A turbulent bed was foun d in none of the facilities of this study with the Geldart B solids us ed. As well as by the Kolmogorov entropy ( chaos analysis), the hydrod ynamics have been characterized by amplitude of pressure fluctuations, while a solids distribution analysis has also been carried out. The s tudy has been made in four (circulating) fluidize beds of different si ze and design, all operated with 0.30 mm silica sand. The dimensions o f the fluidized bed risers are 1.47 x 1.42 x 13.5 m, 0.70 x 0.12 x 8.5 m, 0.12 m i.d. x 5.8 m, and 0.083 m i.d. x 4.0 m. (C) 1998 Elsevier S cience S.A.