Spout fluidized beds find widespread application in the process industry in granulation processes, in which efficient contacting between large particles, droplets and gas is of paramount importance. However, detailed understanding of the complex behavior of these systems is lacking. In this paper we study the effect of the inter-particle interaction on the bed dynamics, by investigating the bed height, pressure drop and vertical particle velocity as function of the restitution coefficient. In addition, the amplitude of the fluctuations of these quantities is displayed in terms of the root mean square (RMS). This is done computationally, by using the discrete element model (DEM) which describes the dynamics of the continuous gas-phase and the discrete particles. The objective of this work is to gain insight in the effect of the restitution coefficient on the flow behavior of spout fluidized beds at different flow regimes using DEM. The three flow regimes comprise the intermediate / spout-fluidization regime (B1), spouting-with-aeration regime (B2) and the jet-in-fluidized-bed regime (B3). The pressure drop and the vertical particle velocity are compared to experimental data obtained by Link et al. (2007). The computed results with en = 0.97 show the same resemblance with the experiments as reported by Link et al. (2007). It is shown that if the restitution coefficient decreases, more bubbles are present causing more pronounced heterogeneity (instability) in the overall flow structure of the bed, in more or less extent dependent on the flow regime. The particle velocity and RMS profiles confirm the effect on the stability of the bed and show that the spout channel for cases B1 (intermediate/spout-fluidization regime) and B3 (jet-in-fluidized-bed regime) becomes unstable when the restitution coefficient decreases. For case B2, a transition occurs from the spouting-with-aeration to the intermediate/spout-fluidization regime at low restitution coefficient. These findings show the great importance of the influence of the restitution coefficient on the dynamics of the bed. During the granulation process, when the particles contain different moisture contents, regions in the bed exist that contain particles with different restitution coefficients. These regions thus experience different dynamics, resulting in varying performance. In future work we intend to improve the discrete element model, by giving each particle its own restitution coefficient dependent on its moisture content.
|Number of pages||9|
|Publication status||Published - 9 Jul 2007|
|Event||6th International Conference on Multiphase Flow, ICMF 2007 - Leipzig, Germany|
Duration: 9 Jul 2007 → 13 Jul 2007
Conference number: 6
|Conference||6th International Conference on Multiphase Flow, ICMF 2007|
|Period||9/07/07 → 13/07/07|
- Discrete element modeling
- Spout fluidized beds
- Restitution coefficient
van Buijtenen, M. S., Deen, N. G., Heinrich, S., Antonyuk, S., & Kuipers, J. A. M. (2007). Improvement of the discrete element model for the study of granulation in a spout fluidized bed. Paper presented at 6th International Conference on Multiphase Flow, ICMF 2007, Leipzig, Germany.