Gas and solids between dynamic bubble and emulsion in gas-fluidized beds

The gas and solid distributions of the dynamic two-phase structure in fluidized beds were studied by statistic analysis of experimental results from an optical fiber probe. The FCC (Geldart A) and irregular sand particles (Geldart B) were used as bed materials, respectively. Such two types of particle led to extremely different dynamic flow structures in the bed. However, for both particles, the dynamic flow structure exhibited the continuous double-peak probability density functions of the local voidages from epsilon (mf) to 1, one peak for the emulsion and another for the bubbles. A probability model was thus proposed to describe and simulate such dynamic gas-solid distribution and its complex evolution from bubbling to turbulent regimes. The gas and solid distributions in the two phases were further investigated and were found to depend strongly on gas velocity, bed position and particle properties. Both gas and solid distributions in the emulsion decrease, whereas those in the bubble phase increase with increasing superficial gas velocity. The ratio of gas distributions in the two phases is heterogeneous over the cross section of the column and exhibits a core-annulus structure, which is considerably different for the FCC and sand particles. The bubbles contain more solids while closer to the bed centre and at higher gas velocity. Compared to the sand, for the FCC, more particles distribute into the bubble phase. (C) 2001 Elsevier Science B.V. All rights reserved.