Iron oxide is a widespread, but often neglected, boiler problem. Commonly called “red iron rust,” iron oxide is formed by the reaction of iron (steel) and oxygen.
It forms on boiler tubes and tube sheets from dissolved oxygen coming in with the feedwater. Iron oxide forms a deposit layer on the tubes and inhibits heat transfer. This reduces the overall efficiency of the boiler and causes more fuel to be used.
Iron can also enter the boiler in the form of dissolved iron in the feedwater (from well water high in iron or from return condensate high in iron).
When this type of iron oxide mixes with highly alkaline boiler water, it reacts with hydroxide to form iron hydroxide. This gelatinous precipitate can stick onto boiler tubes and when it cools, it can badly damage the tubes and lead to costly equipment downtime.
How can you prevent such problems? Proper blowdown is critical for removing iron sludge from the boiler. Using an oxygen scavenger formulated with sodium sulfite will remove oxygen and prevent the chemical reaction that produces iron oxide.
A boiler system dispersant can also be highly effective. It will prevent the iron oxide from sticking to boiler tubes. It lifts and suspends iron oxide, mud and silt so that they can be removed during normal blowdown.