Modeling of particle velocities in an apparatus with a draft tube operating in a fast circulating dilute spout-fluid bed regime

Abstract

The objective of this paper was to verify the applicability of the EE (Euler-Euler) model for the description of hydrodynamics of particle flow in an apparatus with circulating dilute spout-fluid bed, as well as to test the impact of the model parameters, such as interphase momentum coefficient, restitution coefficient and packing limit on the velocity results of the dispersed phase.It was found that the inter-phase momentum exchange coefficient has the greatest impact on the particle velocities in the specific hydrodynamic conditions in the tested apparatus (high velocity of particle circulation, very low volume fraction of the dispersed phase in all zones). It was established that the value of the restitution coefficient considerably affects the granular temperature and the remaining parameters that are relative to it. This, in turn, results in the variations in the determined particle velocities, which are discernible only in the zone of the draft tube. The packing limit affects the value of the radial distribution function, and the increase of its value leads to the increase of the particle velocities. For the optimum set of model parameters (packing limit 0.55, restitution coefficient 0.9, inter-phase momentum exchange model by Gidaspow), the mean calculation error regarding the particle velocities for all initial bed heights was equal to maximum 9% in the zone of the draft tube and 19% in the annulus. The research confirmed the applicability of the EE model for the description of the gas-solid flow in the spout-fluid system with an original design applied for dry coating. The developed model will serve for the future description of the dry coating process.