Gravity-induced separation, emulsion

The chapter by Urdahl, Wayth, Fordedal, Williams, and Bailey begins by discussing droplet break-up processes under both laminar and turbulent flow conditions and in electrostatic fields. The authors then discuss the droplet coalescence process under normal Brownian motion, under gravity sedimentation, and in laminar shear, including turbulent collisions as well as collisions due to electrostatic forces. The remainder of the chapter is devoted to electrostatic-induced separation of the water-in-oil emulsions and emerging technologies. 

Induced Gas Flotation. Mechanically induced gas dotation (IGF) is employed extensively to remove suspended solids, oil, and other organic matter from oil-field and refinery wastewaters. Consequently, these IGF units are particularly suited to the treatment of oil-in-water or reverse emulsions. Such units generally follow gravity oil-water separation units such as FWKOs, gun barrels, and skim tanks in oil-field-produced water-treatment schemes, and also handle the oily water streams generated from all treaters in a specific produced-fiuid treatment plant. 

The main mechanisms of instability that are involved in leading to complete phase separation of emulsions are creaming [64], flocculation [65,66], coalescence [67], and Ostwald ripening [68,69]. However, nano-emulsions do not cream (or sediment) because the Brownian motion is larger than the small creaming rate induced by gravity. Practically, the creaming of droplets smaller than 1 im is stopped by their faster diffusion rate. 

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