EULERIAN SIMULATIONS OF BUBBLING BEHAVIOR IN GAS-SOLID FLUIDIZED-BEDS

In literature little attempt has been made to verify experimentally Eu lerian-Eulerian gas-solid model simulations of bubbling fluidised beds with existing correlations for bubble size or bubble velocity. In the present study, a CFD model for a free bubbling fluidised bed was impl emented in the commercial code CFX of AEA Technology. This CFD model i s based on a two fluid model including the kinetic theory of granular flow. Simulations of the bubble behaviour in fluidised beds at differe nt superficial gas velocities and at different column diameters are co mpared to the Darton et al. (1977) equation for the bubble diameter ve rsus the height in the column and to the Hilligardt and Werther (1986) equation, corrected for the two dimensional geometry using the bubble rise velocity correlation of Pyle and Harrison (1967). It is shown th at the predicted bubble sizes are in agreement with the Darton et al. (1977) bubble size equation. Comparison of the predicted bubble veloci ty with the Hilligardt and Werther (1986) equation shows a deviation f or the velocity of smaller bubbles. To explain this, the predicted bub bles are divided into two bubble classes : bubbles that have either co alesced, broken-up or have touched the wall, and bubbles without these occurrences. The bubbles of this second class are in agreement with t he Hilligardt and Werther (1986) equation. Fit parameters of Hilligard t and Werther (1986) are compared to the fit parameters obtained in th is work. It is shown that coalescence, break-up, and direct wall inter actions are very important effects, often dominating the dynamic bubbl e behaviour, but these effects are not accounted for by the Hilligardt and Werther (1986) equation. (C) 1998 Elsevier Science Ltd. All right s reserved.