Axial solids flow structure in a high density gas-solids circulating fluidized bed downer

Axial flow behaviors are investigated with an optical fiber probe using FCC particles at extremely high solids circulation rates up to 700 kg/m(2)s and superficial gas velocity ranging from 3-7 m/s in a laboratory-scale downer system. Results show that axial distributions of particle velocity and solids holdup are significantly affected by the operating conditions. Superficial gas velocity is the predominance for particle velocity distribution while solids circulation rate plays a key role in solids holdup distribution. Development of solids flow can be accelerated by increasing superficial gas velocity and/or decreasing solids circulation rate. High solids holdup, higher than 0.06, can be achieved in the entire downer with relatively uniform axial profiles at solids circulation rate of 700 kg/m(2)s indicating a preferential flow with reduced backmixing in the downer. (C) 2014 Elsevier B.V. All rights reserved.