(103b) Fluidization Regimes in High Flux-High Velocity CFB Risers

Circulating fluidized beds (CFBs) have applications in gas-solids reaction and gas-phase catalytic reaction processes, predominantly in fluidized bed coal combustion and fluid catalytic cracking (FCC) of crude oil and to a lesser extent in calcination. CFBs use is also expanding to other areas such as dehydrogenation and chemical looping. There is, therefore, still need for continued study of CFB riser hydrodynamics, especially as it applies to fast reactions processes. That calls for studies at high superficial gas velocities and solids fluxes, and to be more relevant to industry, conducted in large-scale CFB systems. Additionally, computational fluid dynamics (CFD) modelling is increasingly being adopted by industry. Experimental data are needed for validation of the CFD models. Tests were conducted in this study with FCC catalyst particles in a 0.3-m diameter CFB riser operating at a superficial gas velocity of 12 m/s and solids fluxes of about 300 to 700 kg/sm². Fluidization behavior in the riser, assessed from axial voidage profiles, local solids fluxes and high-speed video imaging, suggested a co-existence of the dense suspension upflow regime (Grace, 2000) and dilute pneumatic transport regime. There was no solids refluxing at the wall.

References:

John R Grace (2000), Reflections on turbulent fluidization and dense suspension upflow, Powder Technology, 113 (3), 242-248.