FLOW OF DILUTE GAS-PARTICLE SUSPENSIONS

A semi-empirical model of the radial segregation of solids in upward flow of dilute gas-particle suspensions in riser systems is presented on the basis of a reduced form of the fundamental two-phase flow governing equations and experimental evidence concerning the solids concentration at the wall. The following simple expression for the radial solids concentration profile is obtained: 1-epsilon/1-epsilonBAR=2(r/R)2 and is in agreement with experimental data over a wide range of operating conditions: superficial gas velocity from 1.4 to 15.3 m/s, riser diameter from 0. 032 to 0. 40 m, imposed solids flux from 6.60 to 207 kg/m2 . s, mean particle size from 32 to 120 mum and particle density from 1,000 to 3,500 kg/m3. The model confirms the existence of the core-annulus flow structure in gas-particle suspensions reported in riser reactors, circulating fluidized beds, and the freeboard of bubbling fluidized beds.