Detailed hydrodynamics of high flux gas–solid flow in a circulating turbulent fluidized bed

Hydrodynamics of gas–solid flow were experimentally studied in depth in a circulating turbulent fluidized bed (CTFB) using FCC particles of 76 μm at a wide range of air velocities (0.5–5.0 m/s) and solids circulation rates from 0 to 420 kg/m2 s. A high density macro-flow structure, corresponding to homogeneous axial profiles with cross-sectional average solids holdup of higher than 0.25 and parabolic radial profiles of solids holdup from 0.15 to 0.50, was easily obtained throughout the entire CTFB. Using Moment Consistency Data Processing Method and Divided Phase Cross-Correlation Method, solids holdups of the dense and dilute phases and dense phase fraction, local net solids flux and apparent particle velocity were predicted from the solids holdup signals. The results demonstrated that CTFB was characterized by dilute dominating flow in the center and dense phase dominating flow in the annular region, different from dense phase dominating flow in bubbling fluidized bed and dilute phase dominating flow in fast fluidized bed. The results also displayed that the local net solids flux and the local apparent particle velocity were proportional to the measured solids circulation rates.

► A new fluidization regime, circulating turbulent fluidized bed (CTFB), was experimentally confirmed. ► CTFB is shown to have high-density (>25% solids holdup) throughout the bed. ► Macro- and micro-flow structures of CTFB were studied in terms of solids holdups in the dilute and dense phases. ► CTFB had a different flow structure from either bubbling or fast fluidized beds.