Sulfuric Acid dilution, H-X material of construction?
Sulfuric Acid dilution, H-X material of construction?
(OP)
I'm looking for a heat exchanger that can handle 78% sulfuric acid at 320oF. I am diluting 98% acid to 78%, therefore generating a great deal of heat. I've looked into several options inlcuding: Hastelloy B, C and D, teflon/graphite, fluoropolymer, etc. Does anyone have experience with these materials - expected life, durability, etc.?





RE: Sulfuric Acid dilution, H-X material of construction?
http://www.alleghenytechnologies.com/wahchang/pages/pro...
I have had HXers made by Astro Cosmos http://www.astrocosmos.com/ and
Titan Metal Fabricators http://www.titanmf.com/
Both have chemical resistance data for various materials on their sites.
RE: Sulfuric Acid dilution, H-X material of construction?
Metals Handbook, 9th/10th Edn., vol. 13 Corrosion, pages 1148-1152 has information on materials for handling sulfuric acid:
PTFE, PFA or glass coatings should work. Graphite can be used if impregnated with PTFE.
Corrosion curves for most of the metals used with sulfuric do not extend to 300oF; there are some cast alloys such as Alloy 55 (Ni-Cr-Fe-Co-Si) and Illium B (Ni-Cr-Mo-Cu) which look pretty good (data extend to 284oF) but may not be available as HXers.
Anodic protection is commonly used for HXers in sulfuric service. It is also mentioned that a wrought, Si-containing SS alloy A-611 “has useful corrosion resistance in 99% H2SO4 up to 120oC (250oF) without anodic protection” [p. 1151], so presumably anodic protection would extend its range.
RE: Sulfuric Acid dilution, H-X material of construction?
The problem is the dilution. Conc sulphuric can be handled by a variety of materials, but the range of dilution may eliminate many from consideration. I have no experience with the electrochemical protection methods so can't comment- perhaps somebody in the acid plant business could.
RE: Sulfuric Acid dilution, H-X material of construction?
Another option may be Ametek exchangers that have Teflon based tubes. Does anyone have experience with these? Apparently, they have replaced many metal based acid coolers.
RE: Sulfuric Acid dilution, H-X material of construction?
RE: Sulfuric Acid dilution, H-X material of construction?
500 F is an absolute maximum service temperature for PTFE and PFA- both materials become soft and creep readily at these temperatures unless they are entrapped. Most people use 450 F as a safe upper temperature for PTFE as a material of construction (even in well entrapped service)- PFA may perhaps be stretched the extra 50 F depending on who you talk to.
I personally would be very hesitant to use an exchanger with PFA tubes at these temperatures, unless there was a way to ensure that the shell and tube side pressures were well matched all the time so that the tubes experienced very little pressure driving force to creep. The tubes must also be very thoroughly mechanically supported, and there was a thorough plan in place to handle leakage when it occurs. Perhaps at the larger sizes there's a way to use PFA-sleeved metal tubes to provide better support, but I can't see how such an exchanger could be fabricated in a way that I'd personally trust.
And I'm assuming shell and tube, which are the only fluoropolymer units I've seen- perhaps another design like a plate coil can be fitted with a thick and durable liner. Perhaps a fluoropolymer exchanger manufacturer could comment.
This is of course assuming that the relatively poor thermal conductivity of the PFA itself does not render the exchanger too large for your liking.
RE: Sulfuric Acid dilution, H-X material of construction?
http://www.process-heating.com/CDA/ArticleInformation/c...
http://preview.ametek.com/content-manager/files/HAV/040...
Alfa Laval's HXer page
http://www.alfalaval.com/scripts/WebObjects.dll/ecore.w...
specifically mentions "Cooling of concentrated sulfuric acid..."
so definitely contact them.
RE: Sulfuric Acid dilution, H-X material of construction?
http://www.ptfe-lining.com/usa/flurosicusa.htm
Thanks!
RE: Sulfuric Acid dilution, H-X material of construction?
RE: Sulfuric Acid dilution, H-X material of construction?
Is silicon carbide an option? From a corrosion standpoint, I believe so. It's not cheap (we were quoted $400 US for a small thermowell tube, and small magdrive pump bushings are usually $250 or so, so I'd hate to see what a SiC exchanger would cost...). Even the best grades are sensitive to thermal shock, particularly to rapid cooling- it is a ceramic after all. The tubes can have quite high thermal conductivities, and the material is surprisingly strong- but the thermal shock and brittle fracture concerns tend to require that the tubes be made quite thick. Thermal resistance includes both thickness AND thermal conductivity, so you may not get the area reduction you want. And I have no idea how the tubes are mated to a tubesheet- if it's with fluoropolymer ferrules, you'll be in the same boat as you would be with the fluoropolymer exchanger.
You might get away with a lower alloy exchanger with anodic protection, but this method is for corrosion mitigation and control rather than elimination. Do it wrong and the unit may dissolve, rapidly. The same goes for spray-applied thin fluoropolymer coatings etc.- a pinhole through the coating will rapidly mean a pinhole through the metal.
The only metal I know will survive these conditions is tantalum. It's used for the tubes which add acid into hydrometallurgical autoclaves (i.e. units which dissolve metals like nickel and chromium...). Very, very expensive- 1/4"- 0.035" wall tubing is hundreds of dollars per foot. But also thermally conductive, metallic (i.e. not brittle), and possible to build an exchanger out of which will withstand 100 psig at these conditions. It can also be applied as a vapour deposited coating on other metals- with the same problems as other coatings wrt pinholes and scratches etc.
I think you either have to compromise on pressure handling, max temperature, size and/or cost. You're up against some hard physical limitations here...If you can compromise on your pressure and/or temperature a bit, you might get away with the Ametek unit- but make sure you baby the thing, because the fluoropolymer tubes will be like cooked spaghetti at these temperatures. The key is to find out what the expected temperature of the tubes themselves will be- they'll be somewhere between the shell and tubeside temperatures, and just where they end up will depend on the heat transfer conditions on each side. Careful design may yield an exchanger which, during normal operating conditions, keeps the tubes cool enough to be safe- but an upset may rupture the spaghetti, resulting in an acid-water dilution event that nobody will enjoy...
Agree that the Nickel Development Institute is a good place to go for advice in selecting a nickel superalloy for this service. I also suggest you speak with somebody in the acid plant business to see what they recommend- they have lots of contacts in various industries and they have a pretty good idea what works and what doesn't- plus their advice is generally free.
RE: Sulfuric Acid dilution, H-X material of construction?
RE: Sulfuric Acid dilution, H-X material of construction?
What material is suitable for 70% Conc Sulphuric Acid.Pump(Impeller) and Piping.
Temp is 40°C.
Suction is from road tanker(open to atomosphere), it is to be transferred to storage tank of about 10 Mts Height.
Thanks in advance
RE: Sulfuric Acid dilution, H-X material of construction?
Never choose a corrosion-resistant material when a corrosion-IMMUNE material is suitable for the service AND cheaper!
RE: Sulfuric Acid dilution, H-X material of construction?
I am interested what material selection you finally made for this problem and what your experiences are so far...we are concentrating sulphuric acid up to 78%, so we do not have this heat development problem..nevertheless it is an aggressive corrosion environment and the material selection is limited ..we use graphite/epoxy heat exchangers with mixed success/ a few years lifetime...always looking for improvements !
thanks in advance
RE: Sulfuric Acid dilution, H-X material of construction?
What is the heat of solution in diluting 98% sulfuric acid to 10% sulfuric acid at 25 °C.
Also let me know the suitable material of construction for this process
Regds,
Bharathi
RE: Sulfuric Acid dilution, H-X material of construction?
It is better to start a new thread for a question like this, but OK.
Resistoflex has all the info you need.
http://www.resistoflex.com/sulfuric.htm