Keynote Talk: Evaluation of Coarse Graining Strategy and Degree in DEM-CFD Simulations of Cyclone Flow

Circulating fluidized beds are used in a variety of energy, chemical and petrochemical applications. Recent developments based on this configuration have been proposed in gas-phase reactors for the polymer industry, like the MZCRreactor technology [1], which already reached the commercial stage for polypropylene and polyethylene. Simulations are being increasingly used to provide insight and further improve scale-up and design of advanced multiphase process units and reactors. However, due to their prohibitive computational cost for medium- to large-scale systems, numerical models based on the DEM-CFD approach cannot be used, with their enormous predictive potential remaining unusable. In the recent years, methods that scale particle size by lumping smaller particles into representative parcelshave been proposed [2], in an attempt to reduce the number of elements to consider and possibly increase the time-step. The concept behind the approach is simple and the derivation relatively rudimentary but these methods have been shown to provide highly powerful means to overcome computational limitations. A lot remains to be understood and characterized, however, such as the extent to which the predictive capability of the model is preserved.

In the present work, simulations of the two-phase flow in complex gas-solid cyclones are investigated at different gas and solid loadings. In particular, the attention is focused on the effect that the coarse graining strategy and degree exert on the replicability of the results as compared to pure DEM-CFD simulations and experimental data. A standard high-efficiency cyclone design is considered for simplicity, although more complex geometries do not introduce particular limitations. The number of particles represented by a parceland the scaling of properties is examined both in terms of the macroscopic performance indicators, like separation efficiency and gas pressure drop, and the local distribution of the gas and solid flows inside the cyclone, including vortex formation, solids sliding, number of turns and particle entrainment.

References

[1] Covezzi, M., Mei, G. (2001). The multizone circulating reactor technology. Chemical Engineering Science,56, 4059–4067.

[2] Hilton, J.E., Cleary, P.W. (2014) Comparison of non-cohesive resolved and coarse grain DEM models for gas flow through particle beds. Applied Mathematical Modelling, 38, 4197-4214