Flotation units have been widely used for the treatment of produced water both onshore and offshore. They have, however, exhibited numerous operational and performance limitations. Over the past several years, new designs for the treatment of produced water by flotation have been developed. These have resulted from years of intensive research in both the laboratory and at oil production facilities. These new designs utilize features which improve the performance and reduce the operating problems associated with conventional designs.
The first design discussed is the pressurized IGF. This unit provides highly efficient removal of oil and suspended solids. Its operation improves safety because it eliminates any emission of volatile organic compounds, natural gas or hydrogen sulfide gas. The IGF resolves traditional flotation unit operating problems. These include the inability to operate under pressure, the production of large amounts of oily waste skimmings which require additional treatment, and the inability to operate on floating production facilities or tension leg platforms.
The recently developed and patented design includes several features which provide improved performance. These include the use of a cylindrical pressure vessel, the incorporation of floating skimmers for oil and suspended solids removal and a unique stator assembly for the dispersion of the gas into the liquid phase. Effluent from the IGF is suitable for discharge into surface waters or subsequent treatment prior to reinjection. The unit's design does not require motor driven skimmers. Its use can eliminate the need for additional pumps thereby decreasing the energy requirements of the water treatment equipment train.
A second new design which will be discussed is based on modification of an existing hydraulic induced gas flotation cell to operate as a dissolved gas flotation unit. The gas bubbles are formed by reducing the pressure of a gas saturated produced water stream. This produces a fine bubble dispersion which has been shown to remove smaller oil droplets than does conventional equipment. This patented process, called Hybrid Gas Flotation, allows for increased throughputs and improved effluent quality.
The protection of the environment has become an increasingly important consideration in the production of oil and natural gas. Discharge of produced water containing residual oil and oil coated solids has come under intense scrutiny by regulatory agencies.