Pneumatic Conveying

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Pneumatic conveying involves the transport of particulate materials by air or other gases. It is generally suitable for the transport of particles in the size range 20m m to 50mm. Finer particles cause problems arising from their tendency to adhere together and to the walls of the pipe and ancillary equipment. Sticky and moist powders are the worst of all. Large particles may exceed excessively high velocities in order to maintain them in suspension or to lift them from the bottom of the pipe in horizontal systems.

The successful operation of a pneumatic conveyor may well depend much more on the need to achieve reliable operation, by removing the risks of blockage and of damage by erosion, than on achieving conditions which optimize the performance of the straight sections of the pipeline. It is important to keep changes in direction of flow as gradual as possible, to use suitable materials of construction (polyurethane lining is frequently employed) and to use velocities of flow sufficiently high to keep the particles moving, but not so high as to cause serious erosion.

In hydraulic conveying the densities of the solids and the fluid are of the same order of magnitude, with the solids usually having a somewhat higher density than the liquid. Practical flow velocities are commonly in the range of 1 to 5 m/sec.

In pneumatic transport, the solids may have a density two to three orders of magnitude greater than the gas and velocities will be considerably greater - up to 20-30 m/sec.