Low-cost heat exchanger
Low-cost heat exchanger
(OP)
Hi all, I'm looking at material selection for an ammonia and salt water heat exchanger application. The working temperatures are relatively ambient with a low approach (temperature difference is less than 10 degrees C), and the pressures don't go above 13 bar (188 psi). I was thinking, therefore, that plastics might be an alternative except for their low thermal conductivity (anyone know of some newer plastics manufacturers that are ramping up production of improved heat exchangers?). I was also looking at aluminum, but I don’t know how it performs relative to steels. Steels are probably not as ideal as titanium because of their general higher susceptibility to corrosion effects, however, I'm not familiar with all steels relative to titanium and a cost per performance analysis might be in order. Copper alloys or aluminum-copper alloys seem to be out because of coppers reactivity with ammonia. However, I don’t want to rule out any ideas, these are just my initial thoughts. Again, cost relative to titanium is the biggest issue at this point since titanium is otherwise somewhat ideal. Any help would be greatly appreciated!





RE: Low-cost heat exchanger
I wonder if there's a possibility of considering Titanium cladding!
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RE: Low-cost heat exchanger
Low cost is a pretty relative term. However for your combination of materials, I would strongly consider a titanium plate and frame exchanger for the following reasons:
1. Titanium is the preferred material in contact with salt water.
2. PHE's have a high heat transfer coefficient compared to other types of exchangers (but they don't use fouling factors either).
3. PHE's are normally capable of close approach temperatures. The flow rates of the two fluids should be more-or-less ballanced, however for best performance.
Regards,
speco (www.stoneprocess.com)
RE: Low-cost heat exchanger
Ti is the traditional material for these. Not hte only choice, but PHE builders have not been agressive about using high performance stainless alloys.
S&T will be larger and heavier, but you have more material choices. You could use superferritic stainless tubes, which offer excellent corrosion resistance and are a lot less expensive than Ti.
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RE: Low-cost heat exchanger
The issue then would be lifetime and increased surface area requirements. If the cost savings are significant, though, I would definitely consider plastic PHE's.
ddot
RE: Low-cost heat exchanger
Has anyone heard of titanium cladding on steel at these thicknesses?
RE: Low-cost heat exchanger
You actually mean due their thinness !
When you think Titanium-clad-Steel, it is the Steel that matters for thickness, not the cladding material. You'll have to adopt base material of suitable thickness, with a thin Ti cladding.
Btw, I was not thinking PHE in particular when I posted my point. It is interesting to note that both speco and EdStainless seem to recommend PHE over ST in your case.
RE: Low-cost heat exchanger
Im not a materials person - but maybe this can be used for your combination? Dont know if is cheaper though!
Best regards
Morten
RE: Low-cost heat exchanger
Asif Raza
RE: Low-cost heat exchanger
ddot
RE: Low-cost heat exchanger
Just a thought.
RE: Low-cost heat exchanger
dott
RE: Low-cost heat exchanger
RE: Low-cost heat exchanger
I am not aware of any manufacturers of plate heat exchangers who make any kind of titanium clad plates. The normal thickness for ti plates is around .4 to .5 mm. There is an industry standard, but don't have the actual thickness handy.
In your intitial posting you said that you were looking for an inexpensive heat exchanger. While titanium is not cheap, the glass-lined exchangers with silicon carbide tubes are REALLY expensive. I believe that you find that the graphite phe is also way up there in price.
I would suggest concentrating on finding a phe manufacturer who can provide this exchanger. There are many out there to choose from. Some of the lesser-known names (example: Sondex in Louisville, KY) might be worth checking out.
Regards,
speco (www.stoneprocess.com)
RE: Low-cost heat exchanger
At this point, I'm contacting a number of manufacturers (probably the hardest thing to do is getting someone on the phone who knows what they are talking about).
Thanks for the Sondex name, I'll check them out.
ddot
RE: Low-cost heat exchanger
they are currently in prototype semi-commercial production of a seawater cooling system using PE bundles submerged in a seawater bath for hot (90 degrees C) process water cooling in a steel mill.
RE: Low-cost heat exchanger
RE: Low-cost heat exchanger
There are lots of tube in tube manufacturers who build "vent space" between dissimilar tube materials for just this type of application, in some case "vent space" becomes a fill of its own, like an alcohol solution....The S & T manufacturers would go either sacraficial containment or titanium tube, and if you are dealing with multiple high capacity units, the cost effectiveness can get pretty good...
Won't beat a P & F for compactness though they are all pre-designed based on equivalent passages, largely; and you are looking at a sizeable volumetric change on the condensing side.
RE: Low-cost heat exchanger
Thermcool,
I actually did hear about HDPE (high-density PE) as an option for tube heat exchangers. I'm actually very interested in hearing about your PE tube application. Do you have any problems with bio-fouling or shortened lifecycles? I read about PE used as downhole heat exchangers for geothermal applications (similarly mineral rich liquids at low temps/pressures) and would really like to dig deeper in that direction since cost savings may be substantial.
As I said, however, size is still a limitation to some degree. A substantial cost savings in material, though, could warrant the increased area. Please let me know more!
Sterl,
These heat exchangers have a pretty big duty. Other than the manufacturer that I've already established for the current titanium PHE's, most manufacturers I've contacted have said they aren't prepared to meet the duty that I'm looking at based on the standardized PHE's they have available. What I'm looking for, really, is something modular rather than one large heat exchanger. Of course, the bigger each module the better.
I really do need to limit the floor area required (it can go larger than titanium PHE but I don't know about switching to S&T). I'm really curious to know what the size difference is in thermcools application though. It would be great to cut cost on this project.
Again, thanks much for you valuable input!
ddot
RE: Low-cost heat exchanger
RE: Low-cost heat exchanger
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RE: Low-cost heat exchanger
Any more details about the conditions that you're working under would be great (temperatures, pressures, etc). Otherwise, thanks very much!
ddot
RE: Low-cost heat exchanger
When it comes to transferring heat to/from a toxic medium like ammonia, metals are the way to go. Be thankful that you have, in this case, a relatively large selection of metals to choose from! Titanium isn't the only metallic option at your disposal if seawater and anhydrous ammonia at modest temperatures are the only corrodents.
RE: Low-cost heat exchanger
RE: Low-cost heat exchanger
RE: Low-cost heat exchanger
RE: Low-cost heat exchanger
Forget about glass coil in shell, SiC tubed, glass-lined, graphite etc. This is not a severe enough corrosive service to warrant these expensive options. Unfortunately, I would also forget about solid polymer tubed or plate-type exchangers if anhydrous ammonia under significant pressure is involved. There's no fancy polymer I'm aware of which will eliminate the hazards associated with that approach completely, and if you go too fancy on the polymer you've lost your cost advantage anyway.
An option worth considering might be a gasketed plate-type exchanger with plates of a lower grade of stainless steel with a thin polymeric or metallic coating only on the seawater side. While the coating will impair heat transfer somewhat, it may provide sufficient resistance to prevent pitting of the stainless steel. Depending on the coating, this may be cheaper than a titanium plate exchanger or a shell/tube exchanger with titanium tubeside materials (i.e. seawater in the tubes- providing cheaper construction in return for some difficulty in maintenance). How effectively a coated plate type unit would work would depend on the quality, type and thickness of the coating and on the temperatures the metal would encounter. Just as ammonia may diffuse through a polymeric plate or tube, chloride may diffuse through an intact polymeric coating and may lead to SCC etc., and this tendency would increase with the expected coating and metal temperatures. Another issue to consider with this approach is the significant area of, you guessed it, polymeric gasketing that would represent another potential leakage or permeation risk for ammonia.
RE: Low-cost heat exchanger
RE: Low-cost heat exchanger
there is another option for material on this, as far you are in low temperatures you can use duplex stainless s31803 tubing and ss T316 tubesheet, the plate and frame heat exchangers are the most efficient in size and are but they are not the most practical for sea water use because the marine life becames a problem on this type of ammonia condensers on boats
RE: Low-cost heat exchanger
Anyway, unless I'm mistaken, I hear from many people in industry that S316 does not have the same level of corrosion resistance necessary for marine applications. What is the problem with plate exchangers that is not encountered by tubesheets?
RE: Low-cost heat exchanger
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Rust never sleeps
Neither should your protection
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RE: Low-cost heat exchanger
I mentioned one of the superferritics as a solution for a heat transfer problem based on better HTC and presence of chlorides and their reaction wasn't so much that it wouldn't work than it was "not invented here".
So, if the SF's can be pressed into the PHE plate form, it should be an excellent PHE material with respect to both corrosion and HTC.
rmw
RE: Low-cost heat exchanger
ddot
RE: Low-cost heat exchanger
Wade in here EdStainless and bale me out.
rmw
RE: Low-cost heat exchanger
Sea-Cure is considered equal to S44660 thus a visit to
www.copperweld.com/pdfs/S44660_Brochure.pdf
www
thread330-150259
may be of help.
RE: Low-cost heat exchanger
That said, both of these alloys are regularly fromed into deaply convoluted shapes. They are used in the HX of high efficency furnaces.
You do have to be very careful when you form these grades, but it has been done.
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Rust never sleeps
Neither should your protection
http://www.trent-tube.com/contact/Tech_Assist.cfm
RE: Low-cost heat exchanger
I was told by DJ while on a plant tour at Plymouth that there was a specific and particular part of the tube mfg process that gave S44660 material the corrosion resistant characteristic and that any variations in that particular process or part of the process would sacrifice the great corrosion resistance that SeaCure has.
I just don't know if I would be giving up a trade secret to say what that was, but I can say that it is something that I would consider difficult to do (control) in a plate forming process as opposed to a tube forming process.
I may need to ask you the question via e mail.
rmw
RE: Low-cost heat exchanger
If you buy S44660 sheet and you want to use it as sheet, with the best corrosion resistance possible, you are going to need to do some work with the supplier. Often the strip supplied to tube mills is under annealed and over pickled. The steel mill knows that the tuber will be processing it further so it doesn't matter.
If I were buying strip for this application I would require ductility tests in L and T, NDTT, and corrosion tests on the as shipped surface (G48D).
The forming of these alloys will be slower than with 3XX grades. You need to make sure that you don't have any sharp corners or edges. You need to use low strain rates.
One advantage is that there is no need for anneal or stress relief after forming. The material will not CSCC.
= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection
http://www.trent-tube.com/contact/Tech_Assist.cfm