PREDICTION OF THE MINIMUM FLUIDIZATION VELOCITY FOR FINE PARTICLES OF VARIOUS DEGREES OF COHESIVENESS

Abstract

Based on the well-known Ergun equation and the force balance of a particle bed under fluidization bringing into account the interparticle forces, a new correlation for prediction of the minimum fluidization velocity (u_mf ) for fine particles of various degrees of cohesiveness has been derived. For the first time, a general correlation of the minimum fluidization voidage (ϵ_mf ) versus particle size is obtained from various sets of experimental data. The newly derived u_mf correlation combined with the one for ϵ_mf proves to be superior to the traditional ones proposed by Leva (1959) and Wen and Yu (1966), especially for the cases where very fine or very large particles are employed in fluidization. The correlations of Leva (1959) and Wen and Yu (1966), both disregarding the cohesive-force effect and the effect of particle size on ϵ_mf , result in noticeable errors in u_mf prediction for very fine (Geldart groups C and C/A) and very large (Geldart group D) particles, although they work satisfactorily for small-to-medium size particles (Geldart groups B and A). In contrast, the prediction with the new correlation shows good agreement with the experimental data for various types of particles ranging from Geldart group C to group D.

Keywords:

• Fine particles
• Interparticle forces
• Minimum fluidization velocity
• Minimum fluidization voidage
• Modeling
• New correlations

Acknowledgments

The authors are grateful to the Ontario Research and Development Challenge Fund for supporting this study, through a Research Chair Program awarded to Jesse Zhu.

Notes

^a Volume-weighted mean diameter by laser diffraction (Malvern Mastersizer 2000).

^b Soda lime silica glass bead samples of spherical shape and narrow size distribution.

^a Fluidization in ambient air (293 K) without vibration; settled bed height: L ₀ = 0.07 – 0.2 m.

^a Fluidization carried out in ambient air at room temperature without vibration.