THE ROLE OF FINES IN THE TRANSPORT OF GAS-SOLID SUSPENSIONS

摘要

In many transport processes involving gas and solids flow, the solid phase has a nonuniform particle size distribution (PSD). This nonuniformity may be due to attrition, an initial nonuniform size distribution, or particle size change due to chemical reaction. To date, however, fundamental models for gas-solid flow which treat the particle phase as a continuum have only considered a monodisperse particle phase. In this work we consider a bimodal solids suspension which consists of larger particles which engage in particle-particle and particle-wall collisions and smaller particles or fines which closely follow the gas streamlines. Such a bimodal system is representative of many chemical processes which occur in circulating fluidized beds, for example. The fluctuating motion of the smaller particles is considered as a fraction of gas phase fluctuations. A low Reynolds number k-e closure is used to model the gas phase turbulence and includes the effects of suppression and enhancement of gas phase turbulence due to the two different sized particles. The prediction from this bimodal PSD model indicates the addition of fines to a monodisperse system of larger particles results in a significant decrease in the pressure drop required to convey a given solids flux; this result is consistent with what is commonly observed in practice.