Turbulent Fluidization

Abstrakt

In the flow regime of turbulent fluidization, pockets of gas (bubbles or slugs) no longer appear distinct. Clusters and strands of fine particles as well as voids of elongated and distorted shapes move rapidly in a zigzag manner through the bed. The solids hold-up is quite high (25 - 35 % by volume) and at the indistinct bed surface, aggregates of particles are continuously ejected into the freeboard. Turbulent fluidization is often employed in industrial fluidized-bed reactors because of efficient gas-solid contact, rapid heat and mass transfer and limited axial mixing of gas. Although it accounts for most commercial applications of gas-solid fluidization, the turbulent fluidization has received far less attention than the adjacent flow regimes of bubbling (or slugging) and fast fluidization. A number of empirical correlations are presented for prediction of the range of turbulent fluidization. Turbulent beds exhibit non-uniform distributions of voidage/solids hold-up in both axial and radial directions. Some reactor models treat the turbulent bed as a single-phase homogeneous system, others assume the existence of two phases. Such aspects as energy dissipation, turbulence and chaos need to be explored to improve the knowledge of this turbulent fluidization regime.