The significance of interfacial chemistry for the oil removal efficiency during flotation was demonstrated in a series of laboratory flotation and pilot-scale compact flotation unit (CFU) tests. Three crude oils with different physicochemical properties were used in the investigations. The differences in drop size distributions and densities of the oils could not fully account for the observed oil removal. However, taking the time for drainage and rupture (i.e., induction time) of the thin aqueous film separating the drops and bubbles into consideration resulted in good agreement with the oil removal. Moreover, it was demonstrated in a modified CFU setup that water-soluble hydrocarbons adsorbed onto the bubbles and reduced the oil removal. This was most likely as a result of increased induction times caused by the adsorbed components.

No abstract

Produced water is a major byproduct in oil production and the largest waste stream generated in the petroleum industry. At the Norwegian Continental Shelf, produced water is still mostly discharged to the sea, but some installations re-inject produced water into the reservoir for pressure support or disposal. Gas flotation is a separation technology widely used both onshore and offshore that generally reduces the oil concentration to <25 ppmv. It is also a promising technology for subsea water treatment. The aim of this review is to give an overview and provide a link between the industrial use and the fundamental aspects of gas flotation. The industrial analysis examines the development and design of gas flotation technologies: induced, dissolved, and compact flotation units. Several aspects of subsea water separation are also discussed. The fundamental aspects are dedicated to the fluid dynamics of bubble−droplet collisions and the phenomena involved after their encounter, i.e., film drainage, forces involved in this process, and spreading of oil on the surface of gas bubbles. Moreover, a detailed analysis of parameters that can affect gas flotation, like gas bubble and oil droplet sizes, droplet−bubble attachment mechanisms, interfacial properties, water composition, oil and gas properties, pressure, and temperature, is provided.

Produced water (PW) is the major byproduct and the largest waste stream in petroleum production. Handling this water is a major issue in the oil industry. Gas flotation has proven to be an effective topside separation technology, and it is currently pursued for subsea produced water treatment. The combined effect of pressure and temperature on gas flotation has not been thoroughly investigated. In this study, we used a gas flotation rig to study the oil removal efficiency at elevated pressures and temperatures. Gas flotation experiments were performed up to 80 bar and 80 °C determining the oil removal at three different retention times. Gravity separation experiments at ambient temperature and elevated pressure conditions were used as a reference. The best oil removal was found at 80 °C in combination with high pressure. The temperature had the most significant impact on enhancing the separation, due to improved oil drop–gas bubble, gas bubble–gas bubble, and oil drop–oil drop coalescence due to the increased film thinning rates caused by lowered viscosity of the water, all leading to enhanced creaming. The pressure effect was attributed to more and smaller bubbles with increased pressures at a given temperature, increasing the available area for drop-bubble attachments. Finally, a first-order kinetic model described the gas flotation well.