Defoaming Capabilities of the Mueller KLS Helical Coil Separator

Swirling flow plays a central role in process intensification and is the basis for the operation of foam-breaking or “defoaming”. Foam breaking occurs in three stages: draining of the cellular liquid that makes up the walls, breakage of the foam walls, and diffusion of the gas out of the foam cells.

Defoaming chemicals are widely used in industrial applications but requires the user to install and maintain a special chemical injection system and the ongoing purchase of chemicals which can be expensive. It has been found that one of the most effective ways of breaking many types of foams is by using centrifugal force. Foam breaking through centrifugal force can often significantly reduce, if not eliminate, the dependency of such chemicals (Hoffmann, et al., 2007).


Generally speaking, when a fluid mixture enters into the helical coil separator, the light phase (gas) is displaced inward toward the axis due to the heavy phase (liquid, solids, or both) being pushed to the outer wall by the centrifugal force. If the fluid mixture contains foam, the gas bubbles will tend to migrate toward the central axis of the KLS. As the foam concentrates toward the axis, the shear stresses within the KLS will distort the cellular structure of the foam.

The combination of the centrifugal force and the shear separates the incoming foam into its component vapor and liquid phases so that only the gas remains at the center and the liquid is pushed to the wall (Hoffmann, et al., 2007).
As one can imagine, the defoaming benefits of mechanical separators is proportional to the centrifugal force that they create. In the case of the KLS, the helical coil element is designed in such a way that it creates a high G swirl region between the helical element and the clean gas tube. This region has been shown to generate over 10,000 Gs at high gas flows (10.967 lb/min) and just over 200 Gs at low gas flows (1.567 lb/min).

Another advantage of the KLS is the high tangential flow region just outside of the vortex core. The motion in this region is almost purely tangential further aiding in the removal of the liquid after the foam structure has broken. Further analysis by Hoffman et al indicates that the low pressure core of the vortex allows the dissolved gas to be liberated from the foam structure. The gas bubbles that have been liberated can then be separated from the liquid phase.

Works Cited
Hoffmann, A.C. and Stein, L.E. 2007. Gas Cyclones and Swirl Tubes. New York : Springer-Verlag, 2007.


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