Anti-foaming and anti-priming agents are mixtures of surfactants that modify the surface tension of liquids, eliminate foaming and prevent the priming of fine water particles in steam.
The phenomenon of foaming in boiler water is characterized by the contamination of steam by solids present in the water. Bubbles or foam are created on the surface of the boiler water and rise with the steam. Foaming is created by high concentrations of solids in boiler water. However, specific substances such as alkalis, oils, fats, greases, certain types of organic matter and suspended solids are particularly favorable to foam formation.
Priming is characterized by the presence of large quantities of water droplets in the steam. As a result, the energy yield of the steam is reduced, leading to salt crystal deposits on heat exchangers and turbines. Priming can be caused by poor boiler construction, excessive revs, or sudden fluctuations in steam demand. Priming is sometimes aggravated by impurities in boiler water.
The most common measure to prevent foaming and priming is to keep the solids concentration in the boiler water at reasonably low levels. To achieve this, excessive loads and sudden changes in load should be avoided, and condensate should be temporarily rejected until the source of contamination is found and eliminated.
On the other hand, the use of chemical anti-foaming and anti-squeezing agents, mixtures of surfactants, eliminates foaming and prevents contamination of the steam by fine particles. Chemical treatments remain highly effective, preventing priming due to high concentrations of impurities in boiler water.