FLOW CHARACTERISTICS OF COAL ASH IN A CIRCULATING FLUIDIZED-BED

Solids flow characteristics of coal ash are investigated with the meas urement of the local solids flux, local solids concentration, and spat ial distribution of particle size. Two sets of the solids sampling pro be are used to quantify the local solids flux at different radial and axial locations. The macroscopic flow structure is presented by analyz ing the radial profiles of solids flux and the local particle size dis tributions, while the mesoscale flow structure is illustrated on the b asis of probability density function of instantaneous solids concentra tion, the intermittency index, and the cluster frequency. It is found that both macroscopic and mesoscopic structures of gas-solid flow of c oal ash are different from those of commonly studied fluid catalytic c racking and sand particles. The differences include higher upward and downward solids fluxes in the lower dense region, significant particle segregation, and more uniform annular flow. Furthermore, a semiempiri cal model taking into consideration the higher slip velocity between g as and solids is developed to account for the radial profiles of the s olids flux in the upper dilute region of the riser.