CPFD study of a full-loop three-dimensional pilot-scale circulating fluidized bed based on EMMS drag model

Abstract

For the purpose of process optimization and scale-up, coupling energy-minimization multi-scale (EMMS) drag model with computational particle fluid dynamics (CPFD) is a good option for large scale three dimensional full-loop circulating fluidized bed (CFB) simulation. In this study, such integration is applied for a complex CFB with six cyclones, based on Barracuda platform, to investigate the gas-solids flow dynamic characteristics in scaled-up system, especially in the dense flow region, and to characterize different fluidization regimes. The simulation results are compared with those obtained from Wen-Yu model, in terms of axial pressure distribution, solid volume fraction, particle recirculation, etc., and are evaluated against available measurement data. The result demonstrates that EMMS drag model can predict the axial pressure distribution well, especially in the dense region, which gives an S-shape solid volume fraction in the axial direction and two-core-annulus structures (‘M’ shape) in the radial direction. Meanwhile, EMMS drag model provides smaller drag force between the gas phase and the solids that the particle recirculation fluxes inside and outside the riser is relatively smaller. With the increase of superficial gas velocity, three different fluidization regimes, including multiple bubble regime, exploding bubble regime and turbulent fluidization regime, are identified based on EMMS drag model. The results show that the dense region is clear at the multiple and exploding bubble regimes; while the particle volume fraction and mass flow rate in the riser top are larger than those in the middle at the turbulent fluidization regime, which gives a guidance that the riser height is limited that particles do not have enough space to distribute.