Developing pneumatic conveying classification diagram for powders

Abstract

Accurate prediction of flow mode in pneumatic conveying can be beneficial for design of a reliable pneumatic conveying system. The existing popular powder classification diagrams use particle or loose poured bulk density and average particle diameter. An evaluation carried out with powder characterization and conveying data of 58 powders reveals that all the existing classification diagrams have some overlapping zones between fluidized dense- and dilute-phase. Such uncertainty significantly limits the use of existing classification diagrams. A new classification diagram has been developed using the powder characterization and conveying data of 58 powders for fluidized dense to dilute-phase regime using a modified particle Froude number term (based on loose poured bulk density) and particle size distribution. The novelty of this classification diagram is that it uses coarse to fine ratio (instead of average particle size) and a loose poured bulk density based Froude number term which uses both loose poured bulk density and median size. Hence, the classification diagram considers larger number of particle and bulk properties: loose poured bulk density and different particle size terms (such as d10, d50, d90, instead of only d50). The new characterization diagram quantitatively marks an uncertain zone in the classification diagram, which in the zone the powders can be transported in either dense-phase or dilute-phase, as there is no certainty on the expected nature of flow for powders falling in these zones and hence these powders must be tested in a pilot plant for conveyability.