Size distribution in gas vibration bed and its application on grain drying

By putting the binary mixture in vibration bed (u = 0), the large particles usually rise to the bed top, resulting “Brazil Nut” separation. Reversely, the large and heavy particles sink to the bed bottom in fluidized bed (u > umf), resulting “Reverse Brazil Nut” separation. In this paper, a gas flow, which velocity is less than the minimum fluidized velocity (u < umf), is introduced into a vibration bed from its perforated bottom. By analyzing the effects of gas velocity, vibration acceleration, size ratio and density ratio on size distribution of binary mixture, we have reached the conclusion that the “Brazil Nut” separation is strengthen by increasing the size ratio or decreasing the density ratio. The mixture could separate from “Brazil Nut” effect to its reverse with increasing the gas velocity or the vibration acceleration. Those conclusions are successfully applied on grain drying to solve the problems induced by the diameter differences between large grains and small ones. And an amended process is present in which much more energy can be saved than the traditional gas fluidized process.

With increasing the gas velocity introduced into a vibration bed, the bed presents three states. The large particles rise to the bed top at the vibration state (a) and sink to the bottom at the fluidized state (c). At the vibration fluidized state (b), the mixture is difficult to separate completely because of the particle convection.Figure optionsDownload as PowerPoint slide