Performance evaluation of high density riser and downer: Experimental study using ozone decomposition

Reactor performance of high density circulating fluidized bed (CFB) riser and downer is studied with superficial gas velocities of 3-9 m/s and solids circulation rates of 100-700 kg/m(2) s using ozone decomposition reaction. Results show that the reactant conversion in the riser and downer is closely related to the hydrodynamics, with solids holdup being the most influential parameter on ozone decomposition. Both axial and radial distribution profiles of the ozone concentration and the solids holdup in the downer are more uniform than that in the riser. Overall ozone conversion increases with the increase of solids circulation rate and/or the decrease of superficial gas velocity in both reactors. Compared to the riser reactor where the overall conversion is even less than the reactant conversion in stirred-tank reactor, overall conversion in the downer is less than but very close to that in ideal plug flow reactor. Contact efficiency is higher in the downer than in the riser indicating that gas-solids contacting in the downer is better due to the uniform solids flow structure and the reactant concentration. (C) 2014 Elsevier B.V. All rights reserved.