Investigation on local solid concentration of coarse particles in circulating fluidized bed risers

To investigate the flow behaviors of coarse particles in CFB, the local solid concentrations of sands in a Φ 100 mm×10 m CFB riser were systematically measured by an improved fiber-optic probe. The results show that compared with fine particles (FCC), the coarse particles (sands) have quite different distributions in both radial and axial directions due to the significant effect of gravity. For coarse particles, no clear similarities for the radial distributions of normalized solids holdup are found along the axial direction, and the core-annulus flow structures are also changed greatly, with the core region extending to the vicinity of the riser wall. The analyses of the flow behaviors of gas-solid indicate that the intermittency indexes decrease with increasing height of riser section and become more uniformly distributed in radial direction. It is also found that for various conditions with the same values of G_s^1.2/G_g^2.0, the radial distributions of intermittency index become similar on a given cross-section of riser.