Effects of the gas outlet duct length and shape on the performance of cyclone separators

• The gas outlet duct may influence the performance of cyclone separators.
• The relationship between the outlet duct length and pressure drop is assessed.
• The relationship between cut off diameter and duct length is not trivial.
• The use of a short gas outlet duct in a LES simulation will affect the results.

In most published studies regarding the numerical simulation of cyclone separators, the gas outlet duct is usually treated as a short straight duct, differing considerably from the experimental apparatus, in which a relatively long duct followed by a curve, or vice versa, is generally used. This work focuses on the influence of length and shape of the outlet duct on the grade efficiency and pressure drop inside a small cyclone separator. The results are obtained through Large Eddy Simulation of the fluid flow inside the separator, coupled with a concomitant Lagrangian description-based on Newton’s second law-of the dispersed phase. More than thirty different outlet duct configurations, including different lengths, curves, curves positions and curvature radii were simulated. The results show that the cyclone gas outlet duct may affect the cyclone performance: the pressure drop initially decreases with duct length until a minimum is reached, and from this point on it monotonically increases with duct length. As for the cut off diameter, the relation showed itself much more complex.