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Optimizing dissolved air flotation design system

Author(s): Féris L.A. | Gallina S.C.W. | Rodrigues R.T. | Rubio J.

Journal: Brazilian Journal of Chemical Engineering
ISSN 0104-6632

Volume: 17;
Issue: 4-7;
Start page: 549;
Date: 2000;
Original page

Keywords: flotation | precipitate | air saturation system | surfactant

Dissolved Air (Pressure) Flotation-DAF, is a well-established separation process that employs micro-bubbles as a carrier phase. This work shows results concerning bubble generation at low working pressures in modified DAF-units to improve the collection of fragile coagula by bubbles. DAF of Fe (OH)3 (as model) was studied as a function of saturation pressure in the absence and presence of surfactants in the saturator. DAF was possible at 2 atm by lowering the air/water surface tension. This fact, which leads to substantial energy savings, was explained in terms of decreasing the "minimum" energy required for bubble nucleation and cavity in the nozzle. More, bubbles-fragile coagula attachment was improved by dividing the recycling water into two: 1) the inclined inlet to the cell (traditional) and 2) inside the separation tank through a water flow inlet situated below the floating bed using a "mushroom" type diffuser. Because of the reduction observed in the degree of turbulence in the conventional collection zone, DAF performance improved yielding high precipitate recoveries.
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