Material properties and flow modes in pneumatic conveying

When bulk solid materials are transported in conventional pneumatic conveyi ng systems, three flow modes have been observed. These are: (i) smooth tran sition from dilute- to fluidised dense-phase, (ii) dilute-phase, unstable-z one and slug-flow and (iii) dilute-phase only. The flow mode for a bulk sol id material is totally dependant on material properties, in particular, tho se properties which involve particle/air interaction (e.g., permeability, a ir retention and de-aeration). Usually, the particle/air interaction charac teristics are a function of basic particle properties, such as particle siz e, size distribution, density and shape. Loose-poured bulk density also is a function of these basic particle properties. Therefore, there should be a relationship between the loose-poured bulk density and the particle/air in teraction characteristics. Based on experimental results and theoretical an alysis, a new flow mode diagram is developed for the purpose of selecting s uitable flow mode for a particular material. Based on the developed flow mo de diagram, the bulk solid materials can be classified into three groups (P C1, PC2 and PC3), characterised simply by loose poured bulk density and med ian particle diameter. Materials in,group PCI can be transported smoothly a nd gently from dilute- to fluidised dense-phase. Materials in group PC2 can be transported in dilute-phase, unstable zone or slug-flow and materials i n group PC3 are conveyed in dilute-phase only. A good accuracy is achieved when many test results with the observed flow modes are superimposed on the developed flow mode diagram. (C) 1999 Published by Elsevier Science S.A. A ll rights reserved.