Introduction
"Condensate" or "(boiler) return condensate" is condensed steam
which is returned to the boiler.
Condensing steam or steam condensate is in principle relatively pure
water (at least, in the absence of water treatment chemicals). The
condensate water differs from distilled water in level of contamination.
Although the steam condensate of a properly controlled boiler should
be pure and non-corrosive, in most practical systems it contains a
number of impurities (e.g., dissolved iron, oxygen, carbon dioxide
and/or entrained caustic, sodium carbonates, chlorides, silica).
Therefore, steam condensates can be fairly aggressive to a number of
metals due to a high content of carbon dioxide or oxygen or both. This
oxygen may result from the partial decomposition of superheated steam.
The impurities and their concentrations may differ from those
present in the makeup water. The presence of iron is normally due to
corrosion. Oxygen may arise directly from ingress in the condensate
return system or may originate from improper deaeration of the boiler
feed water. Carbon dioxide can result from a makeup with high
bicarbonate content. Silica is quite volatile and may be carried over in
the steam cycle (especially in high-pressure steam systems).
Treatment
Boiler return condensate may also be treated ("polished") by
filtration and ion exchange to prevent accumulation of iron or other
salts in the system.
Good quality return condensate should have a conductivity of at most
50 micro-mho.
Water Treatment and Corrosion Control
If necessary, corrosion in steam condensate systems is usually
controlled through additions of neutralizing or filming amines (e.g.,
morpholine, octadecylamine, )
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