Influence of entry duct bends on the performance of return-flow cyclone dust collectors

Major changes in cyclone collection efficiency are found with different upstream bends in the feed pipe, under otherwise the same cyclone design and conditions. These effects are shown for a number of plant-sized cyclones, and for a laboratory-scale cyclone, for bends up-flow to horizontal, down-flow to horizontal, and bending towards the barrel and away from it. It is expected that this behaviour occurs wherever solids inertia is important, such as with strong large aggregate formation (the example studied here was wood pulp) or with high solids loading (milled coal suspension). The efficiency changes are explained by stronger or weaker radial penetration of the cyclone vortex by the incoming coherent solids stream. This same idea, after allowing for the properties of strand conveying in the inlet duct, could also give a new reason for the generally observed increase in efficiency with solids loading, and other cyclone behaviour.