A review on multi-solids fluidized beds

Multi-solids fluidized bed (MSFB) is one particular type of fluidized bed with binary particles, comprising a dense fluidized bed of coarse particles mixed with fine powder percolating through and a dilute freeboard region of fine powder. Due to its enhanced mass and heat transfer and the ability to control fine powder residence time, emerging applications of MSFB, such as catalytic reaction processes, gasification and combustion of solid fuels, pollutant gas removal, and sorption enhanced reaction processes, call for a comprehensive understanding of the fundamentals and developments of the MSFB. In this review, unique transition velocities are defined and correlated for the fluidized bed of coarse-fine mixtures. Complex hydrodynamic behavior, including solids holdup, entrainment and elutriation rates, bed turnover time and residence time of fine particles, pressure drop, pressure fluctuations, and gas dispersion of the binary particle fluidized bed are reviewed. Experimental data suggest that multi-solids fluidized bed can assist in the distribution and fluidization of fine particles with the presence of coarse particles. Heat transfer rate is improved in MSFB by increased heat capacity and inter-particle convective heat transfer, whilst enhanced gas-solid contact in MSFB leads to the improved mass transfer efficiency. Correlations for mass and heat transfer coefficients in MSFB are compared and suitable correlations are recommended. Performance of typical chemical processes that use MSFBs reported in the literature is evaluated.

Automated summary

This review paper provides a comprehensive understanding of the fundamentals and developments of multi-solids fluidized bed (MSFB) and discusses its hydrodynamic behavior, heat and mass transfer efficiency. The performance of MSFB in typical chemical processes is also evaluated.