Seeking advice on materials for MVR high-salinity wastewater concentration equipment
Thread Content
Media: Anionic chlorides and sulfates are common; others include nitrate ions, fluoride ions, organic acid ions, etc； The cations are mainly chromium, nickel, zinc, iron, copper, aluminum, etc. Temperature: Different media have different boiling temperature increases; the evaporation temperature for MVR is generally between 90 and 110°C. Pressure: There is a vacuum of about 20 kPa in front of the compressor, and a positive pressure of about 20 kPa behind it. It generally gets concentrated to the point of crystallization, and scaling occurs on the wall surfaces; therefore, the concentration is at the saturated level. I would like to ask what kind of materials or anti-corrosion methods should be used for such equipment?
It’s impossible to prevent corrosion. Use 2205
Dual-phase stainless steel will do; those starting with S2. Austenitic stainless steels starting with S3, such as S31603 and S30408, cannot be used.
The chloride concentration in saturated conditions can exceed 30 percent; can 2205 be used under such conditions?
At saturation concentration, the chloride concentration may exceed 30 percent; is duplex steel suitable as well? Also, can high-purity ferritic steel be used under these conditions?
It is recommended to use graphite evaporation tanks and graphite condensers; using graphite-based equipment under these operating conditions is the best choice. --
Thank you for the suggestion. But graphite requires too much investment, and the heat exchange tubes often get clogged
It is recommended to use 2205 duplex steel; if you need samples for testing, please contact me
The price of graphite heat exchangers is higher than that of carbon steel heat exchangers, lower than that of titanium heat exchangers, and similar to that of some stainless steel heat exchangers. Whether blockage will occur depends mainly on the sulfate concentration and the concentrations of calcium and magnesium ions in the wastewater.
As the temperature rises, the corrosiveness of chloride ions increases; therefore, it is recommended to use TA2 material for heat exchangers. This is the case for many wastewater streams with similar components in our company； For example, at 90 degrees, when the chloride concentration is 10*-6 (ppm), 316 stainless steel will definitely corrode if the value exceeds 105, while alloys 20, 18, and 6* will definitely corrode if the value exceeds 1100; at 100 degrees, these values are 85 and 740 respectively. Therefore, the material selection is closely related to both your evaporation temperature and ion content