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Posted by Tony Conner on January 25, 2002 at 06:45:29:
In Reply to: Re: Corrosion in Deaerator & Feed Tank posted by Ramesh R on January 25, 2002 at 05:51:57:
The water must go directly from the pre-treatment equipment (softener, dealkalizer, etc.) directly to the DA.
The actual DA mechanism has to strip almost all of the dissolved oxygen out of the water before it goes to the storage section. No DA is 100% effective, so it's necessary to add an oxygen scavenger like sulphite to the storage section. The typical sulphite residual is 30 - 50 PPM. If you test regularly, and find this level of sulphite, then you're pretty much assured there is no dissolved oxygen present.
If I understand your arrangement correctly, you're heating un-deaerated water in a carbon steel tank with steam coils. The oxygen corrosion level in tanks like this is huge, not to mention that all of the products of this corrosion (dissolved iron) is getting sent to your boiler. If you need to carry on with (what I believe) is your current arrangement, you'll need to go with a stainless steel tank, and coil assembly.