Heat exchanger material selection
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I have a difficult question: For a solution in the tube side of a heat exchanger that contains 15% *AO acid and 3% hydrofluoric acid, what material should be used?
The conditions aren’t complete; the key is to know what your temperature is as well
PFA heat exchangers; other materials are not resistant to HF
Stainless steels containing molybdenum have lower corrosion resistance than those without it; in boiling 68%*ao acid, 316L exhibits a corrosion rate of up to 0.35 mm per year, which is almost twice as high as that of 304L! 304L stainless steel can resist acid corrosion at levels below 65% *ao in normal-pressure boiling conditions; zirconium and tantalum can withstand acids at 70% *ao under pressure, with a corrosion rate of less than 0.13 mm/year at a temperature of 250 degrees
Although the temperature details are not complete, I personally estimate that Hastelloy or silicon carbide heat exchangers might be more suitable for you; the heat transfer coefficient of silicon carbide is three times that of steel, and it does not cause contamination of the fluid due to its cleanliness. The only minor drawback is that the price is a bit high, but it’s still much lower than using Hastelloy. For detailed consultation, please inform me of your specific operating conditions.
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Graphite: Our graphite heat exchangers can fully meet your requirements
The commonly used form of HF acid has a relative density of 1.128 (at 40% concentration) and possesses an irritating odor. In concentrated solutions, hydrogen fluoride undergoes polymerization to form H2F2 molecules, which then dissociate into H2F2 = H+HF2-. This substance is extremely corrosive; it can corrode glass and silicates to produce gaseous silicon tetrafluoride, which is highly volatile. It may be worthwhile to consider whether enamel or graphite materials could be used as alternatives.