Investigation of proper modeling of very dense granular flows in the recirculation system of CFBs--颗粒学报PARTICUOLOGY

Nikolopoulos, A., Nikolopoulos, N., Varveris, N., Karellas, S., Grammelis, P., & Kakaras, E. (2012). Investigation of proper modeling of very dense granular flows in the recirculation system of CFBs. Particuology, 10(6), 699–709. https://doi.org/10.1016/j.partic.2012.09.001

Investigation of proper modeling of very dense granular flows in the recirculation system of CFBs

Aristeidis Nikolopoulos ^{a b *}, Nikos Nikolopoulos ^b, Nikos Varveris ^a, Sotirios Karellas ^a, Panagiotis Grammelis ^b, Emmanuel Kakaras ^{a b}

a Laboratory of Steam Boilers and Thermal Plants, Thermal Engineering Sector, School of Mechanical Engineering, NTUA, Athens, Greece
b Centre for Research and Technology Hellas, Institute for Solid Fuels Technology and Applications, Athens Gr-15310, Greece

10.1016/j.partic.2012.09.001

Volume 10, Issue 6, December 2012, Pages 699-709

Received 15 February 2012, Revised 15 April 2012, Accepted 10 June 2012, Available online 25 October 2012.

E-mail: a.nikolopoulos@certh.gr

Highlights

► A new stress model for inter-particle friction forces is developed for TFM simulations.

► The model, adopting an alternative yield criterion, is validated via a repose experiment.

► The model can be applied in pneumatic valves (full-loop modeling) where the flow is dense.

Abstract

The aim of this paper is the development of new models and/or the improvement of existing numerical models, used for simulating granular flow in CFB (circulating fluidized bed) recirculation systems. Most recent models follow the TFM (two-fluid model) methodology, but they cannot effectively simulate the inter-particle friction forces in the recirculation system, because the respective stress tensor does not incorporate compressibility of flow due to change of effective particle density. As a consequence, the induced normal and shear stresses are not modeled appropriately during the flow of the granular phase in the CFB recirculation system. The failure of conventional models, such as that of von Mises/Coulomb, is mainly caused by false approximation of the yield criterion which is not applicable to the CFB recirculation system. The present work adopts an alternative yield function, used for the first time in TFM Eulerian modeling. The proposed model is based on the Pitman–Schaeffer–Gray–Stiles yield criterion. Both the temporal deformation of the solid granular phase and the repose angle that the granular phase forms are more accurately simulated by this model. The numerical results of the proposed model agree well with experimental data, implying that frictional forces are efficiently simulated by the new model.

Graphical abstract

Keywords

Euler–Euler; CFB; Repose angle; Full-loop simulation; Granular viscosity; Yield criterion

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