Ammonia and Amine Adjuncts

The FW oxygen scavengers mentioned earlier are volatile and can therefore provide additional protection against post-boiler section corrosion induced or enhanced by oxygen in-leakage. These particular scavengers also break down under pressure to produce some level of volatile ammonia, which can neutralize any carbon dioxide found in the steam-condensate system. 

NOTE The C02 itself may result from several possible sources, such as low levels of bicarbonates in the FW, air in-leakage, or even from thermal disintegration of the oxygen scavenger used as part of the treatment program. 

Whether ammonia arises from its use as a FW pH level adjuster or from adventitious provision as a result of DO scavenger breakdown, it should be recognized that any excess ammonia will clearly end up in the steam-condensate system. Although the benefit of carbon dioxide neutralization may be legitimately claimed, unfortunately, excess ammonia also may permit the corrosion of copper and its alloys, especially if some oxygen persists. 

The question, therefore, of whether to tolerate ammonia in a boiler, either directly or indirectly, is not necessarily easy to answer, despite its benefits of being a low-cost material and highly basic in nature. When it is used, normally it is as a component of AVT programs in high-puri-ty boiler systems. 

In lower pressure commercial and industrial boilers, handling and safety are issues of more concern than relative chemical effectiveness, and the fact is that because of such problems, ammonia simply is not used in these smaller plants. Caustic generally provides the necessary FW alkalinity and amines are then employed to overcome the problems of carbonic acid corrosion in the steam-condensate system. 

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