Numerical investigation on scale-up rule of circulating fluidized bed
Circulating fluidized beds have been widely used in industry,and scaling laws have been proposed during research and development from lab-scale units to industry plants.The particle diameter ratio has to be changed to keep the scale-up ratio,which may change the particle classification from Geldart A to Geldart B and even change the fluidization regime,thus limiting the utilization of these scale-up rules.A new scale-up rule,which can keep material properties or operating conditions unchanged,is thus proposed based on the Shi scale-up rule applicable for the same circulating fluidized bed and the Horio scale-up rule suitable for different circulating fluidized beds.The Euler-Lagrange model coupled with the EMMS drag coefficient was used to simulate the flow behavior in a circulating fluidized bed,and the rationality of the Shi scale-up rule was further verified by these simulations.The new scale-up rule proposed was then validated under the conditions of fixed superficial gas velocity,fixed superficial particle diameter and unrestricted combination of the gas velocity and the particle diameter in different circulating fluidized beds.The simulation results showed that the proposed scale-up rule can maintain similarities in the axial solid concentration,radial solid concentration and radial dimensionless velocity distribution.The mesoscopic characteristic distributions were further discussed through the analysis of pressure fluctuations in the time domain and frequency domain.The results showed that the mesoscopic characteristics were different to some extent,which meant that more work should be done to keep the similarities when considering heat and mass transfer in circulating fluidized beds.
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