Control build-up of foam in aeration and settling basins, mixing vessels and below weirs and spillways
Foam is a dispersion of gas (typically air) in a liquid. Air can be entrained via agitation at the surface, such as a spinning impeller partially out of the liquid or a stream entering the free surface of a liquid (e.g., where a waterfall meets the pool at its base).
Foam is undesirable because it can overflow vessels, create slippery and unsafe working conditions, interfere with processing, damage materials, and cause tanks to drain and dry slowly.
Controlling foam can be accomplished by spraying liquid onto the surface of the pool. The sprayed liquid may be recirculated from the pool or added fresh. The droplets of the spray impact the foam bubbles causing them to break. If the droplets have too little momentum they will bounce off the bubble surface with no effect. Similarly, if the droplets have too much momentum they will crash through the bubble and impact the liquid below, causing more foam to be generated.
Typical Areas of Use
Foam control is often required in aeration and settling basins, mixing vessels and below weirs and spillways. Pulp and paper processing plants and waste water treatment plants (WWTP) are common industries that experience foam buildup.
Nozzle Selection Guidelines
Nozzle operating pressure can range from 3 to 20 psi (0.2-1 bar). Spray angles are wide, typically 120°, to cover the maximum amount of area. For stationary tanks, Full Cone nozzles are used, often in an array or at strategic locations. If the contents of the tank are rotating, a line of nozzles from the center of the tank to the edge can be used as the entire surface of the tank will pass under the line of nozzles after a complete rotation.
Typical operating conditions for this application are listed for each nozzle