Mechanical Induced Gas Flotation (IGF)

In this apparatus froth flotation occurs, which is the selective separation of solids and free oil based on the degree of surface hydrophobicity. The addition of cationic or anionic polyelectrolytes to the system causes particles to be selectively adsorbed. This will render one particle type hydrophobic while the other stays hydrophilic.

Hydrophobic particles will attach to small air bubbles added into a mixture of oil, fine solids and water, and will float to the surface as a froth and are skimmed into a launder. The introduction of air is performed by a mechanical device or agitator that creates and distributes fine air or gas bubbles.

The intensity of agitation required will determine the results of the separation. AutoFlot™ agitators are designed to impose the ideal intensity to each chamber, making these units highly efficient. This process of creating and dispersing bubbles is called mechanical induction.

The AutoFlot™ tank is constructed to provide a total water retention time of four minutes. The total volume of the tank is divided into four chambers, or cells; therefore, the hydraulic retention time is expressed as one minute per cell. The AutoFlot™ unit includes inlet and outlet chambers.

The AutoFlot™ unit is a horizontal vessel. Each cell and outlet box is separated by a diaphragm. The diaphragms are metal plates welded to the sides of the vessel and are open across the bottom and top for free water passage across the bottom and air/gas across the top. Positioned on each side of the vessel is a skimming compartment, also referred to as launder.

Mounted on top of and inside each cell is the rotating air induction mechanism. The mechanism's main components are a draft tube, shroud, and shaft with a specially constructed impeller. The entire mechanism assembly is bolted and sealed to the top of the vessel. Standard metallurgy is 316/316L stainless steel. Veolia Water Solutions & Technologies possess the flexibility to accommodate any special requirement; for example, VWS has also built mechanisms in monel. Each mechanism is belt driven by its own electrical motor.

Mounted within each of the launders is a skimming shaft that runs the full length of the vessel. On each shaft and at each cell are a series of adjustable skimming paddles. Typically, there will be six paddles in the first cell and four in each of the three remaining cells. Externally mounted electrical motors drive the skimming mechanisms. Each cell and the outlet box are equipped with a pair of fast opening doors. These doors can be opened to offer visual observance of the flotation and skimming operation. External to the vessel the flotation system may include piping, associated valves, instrumentation, control panel, and a chemical (polymer) feed system.

The AutoFlot™ separator may be a self-contained system with its own controls, or it could be equipped with transmitters to send signals to a control panel that oversees a complete treatment system.