CFD SIMULATIONS OF LATERAL SOLID MIXING IN FLUIDIZED BEDS
Lateral solid mixing is crucial in the design and operation of large-scale fluidized bed reactors.To quantify the rate at which solids mix laterally, researchers often resort to a lateral dispersion coefficient (Dsr).To determine Dsr several empirical correlations have been developed in the literature through different approaches;however, they lack general validity.In this work we used a computational model, based on the Eulerian-Eulerian modeling approach, to calculate Dsr.Following the usual approach used in the literature, we defined Dsr using an equation analogous to Ficks law of diffusion.To estimate Dsr we fitted the void-free solid volume fraction radial profiles obtained numerically with those obtained analytically by solving Ficks law.The profiles match very well.The values of Dsr obtained numerically are larger than the experimental ones, but the two do have the same order of magnitude.We believe that the overestimation is due to how we modeled the frictional solid stress;we used the kinetic theory of granular flow (KTGF) model for the frictional solid pressure and the model of Schaeffer (1987) for the frictional solid viscosity.To investigate how sensitive the numerical results are on the constitutive model used for the frictional stress, we ran the simulations again using different frictional stress models and changing the solid volume fraction at which the bed is assumed to enter the frictional flow regime (φmin).We observed from the results that Dsr is quite sensitive to φmin.This is because the latter influences the size and behavior of the bubbles in the bed.We obtained the best predictions for Dsr when φmin is 0.50.The results show that accurate prediction of lateral solid dispersion in fluidized beds depends on adequate understanding of the frictional flow regime, and accurate modeling of the parameters that characterize the latter, in particular the frictional pressure.
Oyebanjo Oke Paola Lettieri Piero Salatino Luca Mazzei
Department of Chemical Engineering,University College London,WC1E 7JE,London,UK Dipartimento di Ingegneria Chimica-Università degli Studi di Napoli Federico Ⅱ,P.le Tecchio,Napoli,I
国际会议
The 11th International Conference on Fluidized Bed Technology(CFB-11)(第十一届流化床技术国际会议)
北京
英文
287-292
2014-05-14（万方平台首次上网日期，不代表论文的发表时间）