Induced gas flotation is the workhorse polishing step in produced water treatment, and it does something gravity alone cannot: it removes tiny dispersed oil droplets that are too small and too slow to float on their own. It works by generating clouds of fine gas bubbles inside the water, letting those bubbles attach to oil droplets and carry them up to a froth layer that is skimmed off the top. This guide explains the flotation mechanism, the difference between eductor and mechanical flotation cells, and how the level, recycle rate, and skimmer cycles are monitored in the field.
Induced Gas Flotation in one line: Induced gas flotation is a produced water treatment process that removes small dispersed oil droplets by dispersing fine gas bubbles into the water; the bubbles attach to the oil, reducing its effective density so it rises quickly to the surface as a froth that is skimmed away, polishing water that gravity separation left behind.
The oil that survives gravity separation is present as very small droplets, often only a few microns across, which rise so slowly that no practical tank could remove them by settling alone. Flotation solves this by introducing a large number of fine gas bubbles into the water. Because oil is hydrophobic and gas bubbles carry a similar surface character, oil droplets preferentially attach to the bubbles. A droplet with a bubble stuck to it has a dramatically lower effective density than water, so instead of drifting up over hours it races to the surface in seconds, where it accumulates as an oily froth.
A flocculant or coalescing chemical is often injected upstream to help small droplets stick together and to bridge them onto the bubbles, which sharply improves removal efficiency. The gas used is typically the facility's own natural gas or nitrogen rather than air, because introducing oxygen into a hydrocarbon stream creates corrosion and safety problems. This is why the term of art in oil and gas is usually induced gas flotation rather than the induced air flotation used in municipal water plants.
There are two common ways to make the bubbles. In a hydraulic or eductor-type unit, a stream of water is recirculated at high pressure through eductors that draw gas from the vapor space and shear it into fine bubbles as it re-enters the cell. There are no moving parts inside the water, which makes these units simple and low-maintenance, and the recycle rate through the eductors becomes the main lever an operator has over bubble generation. Dissolved gas flotation is a related hydraulic variant where gas is dissolved into pressurized water that is then released to atmospheric pressure, precipitating a fog of very fine bubbles.
In a mechanical or dispersed-gas cell, a motor-driven rotor and stator in each of several chambers whips gas into the water, creating a dense curtain of bubbles as the water passes from cell to cell. Mechanical units handle a wider range of inlet oil concentrations and are common on larger facilities, but they add rotating equipment that must be maintained. In both designs the water passes through the cell or cell train, the froth is skimmed off the top continuously or on a cycle, and clarified water exits from below the froth layer for filtration or disposal.
A flotation unit lives or dies on three variables an operator watches constantly: the liquid level in each cell, which fixes how thick the skimmable froth layer sits above the water outlet; the recycle or gas induction rate, which sets how many bubbles are being made; and the skimmer cycle, which decides how often the froth is paddled or overflowed off the surface. Too little skimming lets froth build until oil re-entrains into the outlet water; too much skimming carries clean water off with the oil and overloads the recovered-oil handling.
In an instrumented plant, level transmitters, recycle-pump flow and pressure, chemical injection rate, and skimmer motor status feed a PLC that runs the cell as an automated loop. Merobix, as a cloud SCADA, reads those digitized tags from the site controller over a standard protocol rather than connecting to any field sensor directly. From that data a remote operator can trend inlet oil load against outlet quality, confirm the recycle rate is holding, watch each cell's level band, and get an alarm when a skimmer stalls or froth level runs high. Because the flotation cell is often the last active treatment before an oil-in-water analyzer and the disposal pumps, keeping that visibility is central to staying inside a discharge or injection limit.
Induced gas flotation shears gas into fine bubbles mechanically or through eductors right inside the cell. Dissolved gas flotation first dissolves gas into pressurized water and then drops the pressure, so the gas comes out of solution as a fog of very fine bubbles. Dissolved gas flotation tends to make smaller bubbles, while induced gas flotation is simpler and handles higher oil loads.
Introducing air means introducing oxygen into a hydrocarbon and produced water stream, which accelerates corrosion and can create an explosive atmosphere. Facilities instead use their own natural gas or nitrogen, keeping the system oxygen-free. That is why the process is called induced gas flotation rather than the induced air flotation used for municipal wastewater.
Flotation is a polishing step that comes after bulk gravity separation in skim tanks or plate packs and usually before media filtration. Gravity separation removes the easy free oil, and flotation captures the small dispersed droplets that will not settle. The result is water clean enough to filter and then inject or discharge within limits.
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