Canadian Journal of Chemical Engineering, Vol.87, No.2, 308-317, 2009
A DISCRETE ELEMENT STUDY OF WET PARTICLE-PARTICLE INTERACTION DURING GRANULATION IN A SPOUT FLUIDIZED BED
In this article we study the effect of the inter-particle interaction on the bed dynamics, by considering a variable restitution coefficient. The restitution coefficient is varied in time and space depending on the moisture content due to the particle-droplet interaction and evaporation. This study is done computation ally, by using an extended discrete element model (DEM). The examined flow regimes comprise the intermediate/spoutfluidization regime (B1), spouting-with-aeration regime (B2) and the jet-in-fluidized-bed regime (B3). For all flow regimes, the averaged bed height increases with decreasing restitution coefficient. Moreover, the averaged bed height for a variable restitution coefficient is larger for all flow regimes compared to a case with a constant restitution coefficient, indicating that the distribution of the restitution coefficient influences the bed dynamics. The effect of evaporation on the distribution of the restitution coefficient is only observed for the jet-in-fluidized-bed regime (B3), where the background velocity is relatively high leading to enhanced evaporation from the particles in the annulus region. This is reflected in the averaged bed height for the evaporation test case, which is larger compared to a test case without evaporation. A larger bed height for cases with variable restitution coefficient is due to the pressure build up in the spout region caused by the longer closing period of the spout channel. This is confirmed by the recorded pressure fluctuation signal and its root mean square which are larger for the cases with the variable restitution coefficient.