Full-Loop CPFD Simulation on the Multi-Scale Gas-Solids Flow Characteristics of a Pressurized Circulating Fluidized Bed

Complete
understandings of the gas-solids flow hydrodynamic characteristics are
necessary for the design and optimization of the pressurized circulating
fluidized bed (PCFB). However, few researches on the PCFB hydrodynamic behaviors
based on CFD simulation have been reported in the literature. In this research,
three-dimensional full-loop computational particle fluid dynamic (CPFD)
simulation combined with pressure measurement was
presented to improve the understandings of the multi-scale hydrodynamic
behaviors of an industrial-scale cold PCFB test rig.  

To
investigate the drag models effects on the simulation accuracy, the
conventional homogeneous drag model (i.e. Wen-Yu model)
and two schemes of sub-grid drag models, namely, the empirical scaling model
(i.e. 0.6*Wen-Yu model) and the EMMS drag model,
are implemented in the CPFD simulation respectively. The gas-solids flow
behaviors predicted by those three drag models were compared and evaluated by
the measurement results based on pressure transducers. In addition, a series of operating pressure conditions were
investigated to address the pressure effects on the PCFB hydrodynamic
behaviors. Detailed CPFD simulation results are given and analyzed.

The results show that EMMS
drag model not only predicts the most accurate macro-scale flow
behaviors of the pressure distribution,
particles volume fraction distribution and circulation flux with the experiment results, but also performs well in
capturing the meso-scale coalescence and breakage of the
particles clusters than the other two drag models. By contrast, Wen-Yu drag model heavily over-predicts the particles expansion and
circulation flux, and 0.6*Wen-Yu drag model alleviates the
over-prediction to some degree. The hydrodynamic
behaviors of PCFB are enhanced with the increase of operating pressure, by means of the more homogeneous particles
distribution, higher particles velocity and larger circulation flux.