Flotation

Fact Sheet - Flotation

   
 
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This fact sheet describes flotation technologies. It complements other fact sheets highlighting physical and chemical separation methods that remove oil and other organics from produced water. Flotation technologies introduce bubbles of air or other gas into the bottom of a sealed tank. As the bubbles rise, they lift oil droplets and solids particles to the surface where they can be skimmed off.

In the course of preparing the national offshore discharge standards for produced water, the U.S. Environmental Protection Agency (EPA) published a detailed and informative Development Document (EPA 1993). The Development Document describes different technologies used at offshore platforms, including flotation technologies.

  Schematic drawing of induced gas flotation unit.Schematic of induced gas flotation unit; Source: EPA Development Document.

Gas flotation technology is subdivided into dissolved gas flotation (DGF) and induced gas flotation (IGF). The two technologies differ by the method used to generate gas bubbles and the resultant bubble sizes. In DGF units, gas (usually air) is fed into the flotation chamber, which is filled with a fully saturated solution. Inside the chamber, the gas is released by applying a vacuum or by creating a rapid pressure drop. IGF technology uses mechanical shear or propellers to create bubbles that are introduced into the bottom of the flotation chamber.

DGF units create smaller gas bubbles than IGF systems. However, they require more space than IGF systems and more operational and maintenance oversight. Because space and weight are at a premium on offshore platforms, IGF systems are used at most offshore facilities. In the past few years, some new types of pumps have been introduced that generate a large number of small bubbles in an IGF system to improve performance (Broussard 2003).

  Photo of flotation unit on offshore platform.Flotation unit on offshore platform; Source: J. Veil, Argonne National Laboratory.

Many IGF systems use multiple cells in series to enhance the hydraulic characteristics and improve oil and solids removal. Chemicals are often added to aid the flotation process. They can break emulsions, improve aggregation of particles, and serve other functions.

Cline (2000) offers a useful overview of flotation technology. The author discusses advantages and disadvantages of different types of flotation equipment offered by various vendors.

References 
Broussard, P.C., 2003, "Continued Success of the Monosep Flotation Pump," presented at the 13th Produced Water Seminar, Houston, TX, Jan. 15-17.

Cline, J.T., 2000, "Survey of Gas Flotation Technologies for Treatment of Oil & Grease," presented at the 10th Produced Water Seminar, Houston, TX, Jan. 19-21.

EPA, 1993, "Development Document for Effluent Limitations Guidelines and New Source Performance Standards for the Offshore Subcategory of the Oil and Gas Extraction Point Source Category," EPA 821-R-93-003, U.S. Environmental Protection Agency, Jan.

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