Air-Float Conveying Of Particulate Bulk Solids

In almost any situation where particulate or granular bulk solids have to be conveyed, whether for a distance of a few metres or for many hundreds of metres, a pneumatic conveying system may be considered. Conveying by pipeline is convenient and clean, but running costs may be substantial because of the heavy air consumption and the trend has therefore been towards dense-phase transport in which the ratio of conveyed solids to conveying air is kept high. This paper concentrates on air-float conveying, which can be regarded as an extreme form of dense-phase conveying where the bulk solid is fluidised in a channel and then caused to flow, either by inclining the channel or creating a pressure gradient along 'it. Various designs of air-float conveyor for upward, horizontal and down- ward transport of powders are discussed, with special emphasis on the latter case. In situations where a continuous downward slope can be provided, the combination of air-fluidisation and gravity flow results in a conveying system that, for many kinds of bulk particulate solid, would be hard to better in terms of convenience, reliability and economy. The paper is concluded with a discussion of design features and performance of practical air-gravity conveyors, involving the handling of various bulk particulate solids, both in research and in full-scale industria1 applications.