I need to know a bit more about your case. Is the water meant for use in a boiler ? If so, where is the (caustic ?)corrosion observed, in the boiler or further on in the system. Are any other chemicals added ? Do you know anything about the quality of the return condensate?
To be honest, I am a bit surprised to find corrosion caused by phosphate. In all power plants in my country that use phosphate, no significant corrosion caused by phosphate is found.
There are a lot of alternatives available (just ask Drew, Betz or Nalco) but these are on an organic basis. Under the circumstances in a boiler (high p/T), these compounds decompose to water and CO2 with several organic acids as intermediate products. These acids are dissolved in the steam. At the point in the turbine where the first condensate is formed, these acids have a strong preference for the liquid phase, thus creating an acidic environment on the turbine blades even though the steam is conditioned on a pH of around 10 by ammonia.
This phenomenum is called acid enrichment and is widely studied by ABB and KEMA. If the system is constantly operated on full capacity, the acid enrichment will always take place on the same place in the turbine.
To be honest, I could talk all day about the subject. You can contact me if you like so we can talk more specific about the case. I am familiar with both water conditioning and corrosion. Edwin Muller
KEMA Power Generation & Sustainables
Arnhem, The Netherlands
E-mail e.f.muller@kema.nl
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