Antifoaming / defoaming agents for foam control.
Foaming is a physical incorporation of a gas in a liquid. Foam is stabilised by solids, hydrocarbons, heat stable salts and other contaminants. Process chemicals with surfactant properties stabilise the foam too. Corrosion inhibitors, dispersants and emulsion breakers have surfactant characteristics. Foam formation may cause health and safety issues. Excessive foaming may lead to pump cavitation, pump failure and loss of process control.
The liquid film surrounds the gas creating a bubble. The bubble wall or film is a dynamic system, constantly stretching and contracting. After stretching is has a high surface tension. The thinner film section contains less liquid. Immediate action is required to prevent or destabilise the foam. Based on definition antifoams prevent foam formation. Defoamers break existing foam.
Powerful antifoam additives are intended to act with defoaming and antifoam properties. Antifoaming agent programmes increase the elasticity of the formed film layer. The antifoam provides a surfactant diffusion. It creates a film with a built-in weakness to become unstable. The defoaming agent properties destroy the foam formation immediately and prevent a new formation of foam.
Typical antifoaming agent applications are:
- Crude distillation tower and vacuum tower
- Delayed coker and visbreaker
- thermal cracker and bitumen (asphalt) plants
- Lube oil extraction and propane deasphalting
- Caustic scrubber, sour water strippers and amine units
Delayed cokers and amine units are process units, where antifoams are steadily used. Foam carry-over from the coke drum must be avoided. Otherwise, that could results in an unexpected shutdown. PDMS based antifoams are mainly used at delayed cokers. They are the preferred products because of the high thermal stability. A suitable PDMS antifoam thermally decomposes, but the fragments still have antifoam properties. Silicone is a catalyst poison, why the dosing must be done carefully.
Foaming in amine units is an omnipresent threat. The addition of liquid hydrocarbons to amine solutions is a primary cause for foaming. Foam carry-over in the absorber should be avoided. In amine units, PDMS antifoams show very good foam control results. Polyol based antifoams are often used as well.
Kurita provides highly efficient antifoaming agent programmes. Defoaming agents immediately displace the foam stabiliser and locally burst bubbles. This reduces the wall viscosity and lowers the electrostatic surface potential. Defoaming agent characteristics are, that they are non-toxic and not harmful to products. Chemically non-reactive properties are required. The antifoam should be easy to feed with non-volatile characteristics.
Types of antifoams are based on hydrocarbons, silicone or organic chemistry. Organic antifoams are polyols, fatty alcohols and esters. Silicone antifoams are very efficient antifoaming agent types. Many types of silicones are available like silicone fluids, emulsions, hydrophobised or substituted fluids.
Kurita ´s defoaming agent formulations contain:
- Oil-free components
- Natural oils or Mineral oils
- Silicone containing or silicone-free active substances
- Polydimethylsiloxane (PDMS)
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