"material selection for evaporator/crystallizer"

Question:

"I am looking for any material/references, which would be helpful in determining suitable materials for an Evaporator/Crystallizer, which will be seeing effluent from a supercritical water oxidation unit. I’m also interested in your recommendations for this application (suitable material for the associated tanks, valves, and piping). 316 SS and Teflon are the leading candidates now, based on plant life (less than 2 years) and costs. The major materials expected to precipitate from the processing of the brine are sodium sulfate and disodium hydrogen phosphate. pH will be adjusted by caustic addition (NaOH) from 6 to 9.5pH. Temperatures will be as high as 250 deg F at less than 20 psig.

Major constituents in the brine are:
Sulfate 74,000 mg/l
Sodium 150,000 mg/l
Nitrate Nitrogen 550 mg/l
Nitrite Nitrogen 500 mg/l
Total Sulfur 20,700 mg/l
Calcium 9,300 mg/l
Ortho-Phosphate Phosphorus 4,400 mg/l
Total Phosphorus 78,000 mg/l
Chloride <12,000 mg/l

Solids derived from this brine are:
Na2HPO4.7h30 41.82%
Na2HPO4 13.16%
Na2SO4.10h3O 18.56%
Na2SO4 25.78%
NaCl <1.0% for this and the remainder below:
NaNO3
NaNO2
K2SO4
CaH(PO4)
SiO2
(NH4)2SO4
CaF2
TiO2
TiO2
BaSO4
Zn(OH)2"

Answer:

I am careful about addressing specific materials of construction recommendations for process applications based on the normally limited information available in discussion forum formats. Corrosion issues are more complicated than can be properly addressed here. However, as a comment, I am concerned with the use of 316SS in your stated application, due to the potential for pitting corrosion and/or chloride stress corrosion cracking, based on your elevated temperatures and high chloride content.

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