TRANSPORT PHENOMENA IN MULTIPARTICLE SYSTEMS .4. HEAT-TRANSFER TO A LARGE FREELY MOVING PARTICLE IN GAS-FLUIDIZED BED OF SMALLER PARTICLES

In fluidized-bed combustion, relatively few larger and lighter coal particles are fluidized along with more dense and smaller sulphur-sorbent bed particles. Predictions for drying, ignition and devolatilization, as well as particle temperatures during char combustion, require knowledge of the external heat transfer coefficients. Several studies have dealt with mass transfer to freely moving 'active' particles. Heat transfer to fixed immersed objects in fluidized beds has also received wide research attention. Very few studies have addressed heat transfer to freely moving 'active' spheres. This paper proposes a mechanistic model for heat transfer with the effect of 'active' particle motion taken into account. The average heat transfer coefficients calculated from the model compare well with experimental data in the literature. The model predictions are also compared with available empirical correlations. The implications of the model predictions for modelling fluidized-bed combustion are also discussed.