Hydrodynamic and solid residence time distribution in a circulating fluidized bed: Experimental and 3D computational study

Vertical profiles of local pressure, horizontal profiles of net vertical solid mass flux, and residence time distributions (RTD) of the solid phase are experimentally assessed in the riser of a small scale cold circulating fluidized bed of 9 m high having a square cross section of 11 cm × 11 cm. Air (density 1.2 kg/m3, dynamic viscosity 1.8 × 10−5 Pa s) and typical FCC particles (density 1400 kg/m3, mean diameter 70 μm) are used. The superficial gas velocity is kept constant at 7 m/s while the solid mass flux ranges from 46 to 133 kg/m2 s. The axial dispersion of the solid phase is found to decrease when increasing the solid mass flux. Simultaneously, 3D transient CFD simulations are performed to conclude on the usability of the eulerian-eulerian approach for the prediction of the solid phase mixing in the riser. The numerical investigation of the solid mixing is deferred until later since the near-wall region where the solid phase downflow and mixing are predominant is not well predicted in spite of well-predicted vertical profiles of pressure.