Bubbling to turbulent bed regime transition of ternary particles in a gas–solid fluidized bed

• Gas–solid fluidized beds; flow regime transitions of solids mixture of wide particle size distributions
• The bubbling to turbulent fluidization transition is significantly influenced by particle size distribution (PSD).
• The Uc transition velocity decreased with the widening of the PSD for a given mean particle diameter.
• A new Uc correlation that accounts for the effect of PSD has been proposed.

The transition from bubbling to turbulent flow regime of a wide particle size distribution (PSD) powder was investigated in a circulating fluidized bed riser with an internal diameter and a height of 0.1 and 3.7 m, respectively. Iron ore and limestone particles were used as the wide PSD powder. To study the effect of particle size distribution on the flow regime transition, five types of mono size glass bead were used. Binary and ternary mixtures were made from the mixture of mono size glass beads. The regime transition of the wide PSD powder was studied by means of overall pressure drop and pressure fluctuation analysis. By gradually increasing the superficial gas velocity, a bed of a wide PSD powder changed from a fixed bed state to partial fluidization and then to complete fluidization. The transition from bubbling to turbulent fluidization occurred in the complete fluidization state. The effects of fine particle concentration, coarse particle size, and particle size distribution on bubbling-to-turbulent regime transition velocity were also studied. A correlation expressed in terms of Rec, Ar, and standard deviation of particle size distribution (σp) was proposed to predict the transition velocity (Uc). The predicted Uc values were in close agreement with the experimental data of mono, binary, and ternary mixtures.

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