Induced (IGF) and dissolved (DGF) gas flotation — the secondary stage that floats dispersed oil droplets too small for gravity separation.
Produced-Water Deoiling — in depth
After gravity removes free oil, dispersed oil droplets of 10–100 microns remain. Induced and dissolved gas flotation generate fine gas bubbles that attach to these droplets and float them to a skimmed layer — often with a coagulant to aid attachment — cutting oil-in-water to tens of mg/L.
What matters in practice
Induced or dissolved gas creates the bubble cloud.
Bubbles lift dispersed oil to the surface.
Coagulant/flocculant boosts capture.
Oily float removed continuously.
| Type | Bubble source | Outlet oil |
|---|---|---|
| IGF | Mechanical/eductor | 20–40 mg/L |
| DGF | Dissolved gas release | 10–25 mg/L |
| Stage | Secondary | After separators |
| Droplet | 10–100 µm | Dispersed oil |
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Fundamentals, design drivers and practical guidance
Induced (IGF) and dissolved (DGF) gas flotation — the secondary stage that floats dispersed oil droplets too small for gravity separation.
The treatment train follows droplet size. Bulk gravity and plate separators (API/CPI) take out free oil and coarse droplets; hydrocyclones use centrifugal force to remove finer dispersed oil compactly, ideal for the weight and footprint constraints offshore; induced or dissolved gas flotation attaches micro-bubbles to smaller droplets to float them out; and polishing media such as walnut-shell filters or adsorption capture the residual to meet tight discharge limits.
Emulsions are the hard case — chemically or mechanically stabilised oil-in-water that will not separate by gravity — and need demulsifier chemistry, pH adjustment or thermal/electrostatic treatment to break before the physical stages can work. For reinjection, the spec flips toward solids and particle-size control to protect formation permeability, so the train is tuned to the disposal route rather than a generic standard.
Reynolds & Bauhm designs produced-water trains stage by stage against the governing discharge or reinjection spec — selecting separators, hydrocyclones, flotation and polishing media, and the demulsification chemistry that makes the physical stages perform.
What our engineers assess on every scope of this type
| Parameter | Typical basis | Why it matters |
|---|---|---|
| Dispersed oil | Hydrocyclones | Compact, high-G separation |
| Fine droplets | Gas flotation (IGF/DGF) | Floats out small droplets |
| Residual | Walnut-shell / adsorption | Polishes to discharge limit |
| Emulsions | Demulsifier / heat / electro | Breaks stabilised oil |
| Limit | OSPAR 30 mg/l / EPA ELG | Sets the train target |
| Free oil | API/CPI separators | Removes coarse droplets first |
Common questions on produced-water treatment
It depends on the route: offshore discharge typically targets the OSPAR 30 mg/l dispersed-oil standard, US operations follow EPA effluent limitation guidelines, and reinjection is governed instead by solids and particle-size limits to protect the formation.
Reinjection shifts the priority from oil concentration to suspended-solids and particle-size control, because plugging solids damage formation permeability. Induced & Dissolved Gas Flotation is then tuned around filtration and solids removal rather than de-oiling alone.
Because free, dispersed and emulsified oil behave differently and no single device removes all three economically. Induced & Dissolved Gas Flotation sits within a sequence sized by droplet size, from bulk separation through to fine polishing.
Deoiling hydrocyclones remove fine dispersed oil using centrifugal force in a compact, static device with no moving parts — ideal for the weight and footprint limits of an offshore platform where settling tanks are impractical.
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