Induced Gas Flotation (IGF) is a rapid physical-chemical separation process used offshore and in refineries to treat oily produced water before ocean disposal or reinjection. Produced water passes through 3 to 4 sequential chambers. In each chamber, an eductor jet or high-speed self-inducing impeller draws blanket gas (natural gas or nitrogen) into the water stream, shearing it into billions of microbubbles (30 to 90 μm). Microbubbles collide with and adhere to suspended oil droplets, forming low-density oil-gas aggregates that rise rapidly to the water surface where rotating skim paddles push the oily froth into a collection trough.

In conventional API gravity separators or skim tanks, tiny oil droplets (10 to 30 μm) settle upward very slowly under pure gravity (Stokes rise velocity <0.1 mm/s), requiring hours of residence time. In an IGF, attachment of multiple gas bubbles reduces the aggregate density from ~850 kg/m³ to under 300 kg/m³, while doubling the effective diameter. According to Stokes law, rise velocity scales with diameter squared and density difference, boosting rise rates by 20 to 50 times (up to 3 to 10 mm/s) and reducing required residence time to just 3 to 5 minutes.

International maritime conventions strictly regulate overboard oil discharge. Under OSPAR (North Sea and Northeast Atlantic), the performance standard for dispersed oil-in-water is 30 mg/L (ppm). In the US Gulf of Mexico, EPA NPDES permits enforce a 29 mg/L monthly average and 42 mg/L daily maximum. In sensitive marine zones (Mediterranean or Middle East), local standards often mandate <15 mg/L. Unscheduled spikes above discharge thresholds trigger automated shut-in of overboard dump valves, forcing production throttling.

If produced water is transferred to the flotation unit using high-shear centrifugal pumps, or throttled across high pressure drop control valves, turbulent shear breaks 40–80 μm oil droplets down into sub-10 μm micro-emulsions. Because collision efficiency with gas bubbles scales with droplet diameter squared (η_coll ∝ d_drop²), flotation kinetics collapse. Offshore facilities must use low-shear progressive cavity pumps, screw pumps, or gentle diaphragm pumps upstream of flotation units.

Natural surfactants, naphthenic acids, and asphaltenes in crude oil impart a negative electrostatic zeta potential (-20 to -50 mV) on suspended droplets, causing them to repel each other and resist gas bubble adhesion. Dosing 2 to 15 ppm of cationic water clarifiers (polyamine or poly-DADMAC coagulants) neutralizes surface charges, destabilizes the emulsion, and dramatically increases bubble-droplet attachment efficiency from ~15% to over 85%.