A Lagrangian-Eulerian hybrid model for the simulation of industrial-scale gas-solid cyclones

Abstract

We present a generalization of the Lagrangian-Eulerian hybrid model for the numerical assessment of poly-disperse gas-solid flows (Pirker and Kahrimanovic, Acta Mechanica 204, 2009) [1] to industrial-scale cyclones. The main idea of this hybrid model is to use a combination of a Lagrangian discrete phase model (DPM) and a two-fluid model (TFM) to take advantage of the benefits of those two different formulations. On the one hand, the local distribution of the different particle diameters, which is required for the gas-solid drag force, can be obtained by tracking statistically representative particle trajectories for each particle diameter class. On the other hand, the contribution from the inter-particle stresses, i.e. inter-particle collisions, can be deduced from the TFM solution. These then appear as additional body force in the force balance of the tracer particles. Furthermore, we apply sub-grid modifications to the TFM to account for the small unresolved scales in the case of coarse grids required for industrial-scale applications. The numerical model is applied to an industrial-scale gas-solid cyclone separator, where the impact of an apex cone is studied. Furthermore, we investigate the effect of agglomeration on the separation efficiency of the cyclone. The results show (i) that the apex cone increases the separation efficiency of the sub-micrometer particles but yields an considerable increase of the cyclone's pressure drop and (ii) an adequate modeling of agglomeration is required to correctly predict the separation efficiency of the sub-micrometer particles. Finally, the presented model requires considerably less computational resources compared to multi-fluid models, where each particle diameter class is represented by its own transport equations.