Catalytic ozone decomposition in high density gas-solids circulating fluidized bed riser and downer reactors

Detailed measurements of axial and radial ozone concentration in a CFB riser (76 mm i.d., 10.0 m in height) and two downers (76 mm i.d., 5.8 m in height and 50 mm i.d., 4.9 m in height) were conducted in this study. Experiments were carried out under various superficial gas velocities and solids circulation rates up to 1000 kg/m²s in the riser and 700 kg/m²s in the downers, using spent FCC particles impregnated with ferric nitrate as the catalyst for the ozone decomposition reaction. Results show that radial distributions of ozone concentration in the two downers are more uniform than that in the riser reactor. Both axial and radial distribution profiles of the ozone concentration are consistent with the corresponding profiles of the solids concentration in CFB reactors. The conversion of ozone in the entrance section accounts for most of the overall conversion. Compared to the riser reactor where the overall conversion is even less reactant conversion than the continuous stirred-tank reactor, overall conversion in both downers is less than but very close to that in the ideal plug flow reactor indicating a good reactor performance because of the nearly "ideal" hydrodynamics in downer reactors.