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Low-cost heat exchanger
2

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!

.

RE: Low-cost heat exchanger

ddot,

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

You will get closer approach temps in PHE than S&T.
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.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection
http://www.trent-tube.com/contact/Tech_Assist.cfm

RE: Low-cost heat exchanger

(OP)
Thanks very much for the input! PHE's do seem to be the way to  go.  However, I do still wonder about materials options.  One of the problems with titanium is the long wait on availability.  Contacing a firm or two I found a long wait list over a year for titanium PHE's due to the large quantity that I require.  Does anyone have any experience with seawater and plastic S&T or PHE's?  I would really like to consider a cheaper alternative to titanium (with better availability).

  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

(OP)
Thanks Panduru for suggesting this idea of cladding.  I don't really know that titanium cladding could work for PHE's due to their thickness (for titanium, plate thickness is probably below 2mm thick for my application).

Has anyone heard of titanium cladding on steel at these thicknesses?

RE: Low-cost heat exchanger

@ddot:

You actually mean due their thinness ! bigsmile

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

Alfa laval makes graphite PHEs

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

You might want to explore the possibility of glass lined Heat Exchanegrs. They use silicon carbide tubes and the shell is lined with glass. They can be used up to 200 deg C and offer excellent Heat Transfer coefficient. The recommended manufatures are De-Dietrich, Estrella etc.

Asif Raza

RE: Low-cost heat exchanger

(OP)
Thank you all for the suggestions.  I hadn't explored glass-lined heat exchangers, though if they are not used in plate applications, I doubt they would fit in the area I have allocated.  Definitely will look into that though.  I hear that graphite PHEs are pretty pricy, so I'd have to check that out.  We'll see.  If anyone has any other suggetions, let me know!

ddot

RE: Low-cost heat exchanger

What about using a secondary cooling fluid on your exchangers, say cooling water.  Then you have two types of exchangers.  Ammonia and cooling water  then cooling water and salt water.   You could isolate your need for titanium to one larger exchanger and make the rest of them out of carbon steel shell and tubes.

Just a thought.

RE: Low-cost heat exchanger

(OP)
Thanks very much for the fluid change suggestion, but the setup doesn't allow me to change the fluids that I'm using.  It would be nice, though.  I've been playing with the idea of using a composite material like the titanium-cladding that panduru mentioned.  However, I don't know who I would contact for that kind of manufacturing if it is even possible.

dott

RE: Low-cost heat exchanger

Just a remark with graphite HE. They are quite nice and compact, but be sure the temperatures that you are working with will not go below the freezing point of the sea water or the boiling point of the ammonia. Graphite HEs are quite fragile when the fluid changes physical state. I know this because I recently had a graphite HE that it was broken due to water freezing inside it. And the only repair is a full replacement of the interior module.

RE: Low-cost heat exchanger

ddot,

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

(OP)
Thanks for the advice on the graphite PHEs and on the lack of titanium clad plate manufacturers.  It appears that you are both correct unless I am missing something.  A number of sources have cited graphite HE as more expensive than even titanium while I have yet to find a website for titanium clad plate manufacturers or an HE manufacturer with these plates as part of their production.  

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

Check out FAFCO.COM and contact a fella there by the name Freeman Ford, he's the best bet for info relative to it,
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

As a cheaper option you may also give a try to polyethylene material for the heat exchanger. Due to the low thermal conductivity of the plastic material you will need more tube bundles but the PE material is relatively cheaper option for the HE. We have use these kind of heat exchangers with salt water as the heat transfer medium. This is particular good also due to their low reactivity and resistance against corrosion. As long as you dont have any space limitations, you can end up with relatively low cost heat exchanger using PE tubes.

RE: Low-cost heat exchanger

How big are these heat exchangers?

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

(OP)
Thank you for new suggestions!

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

We had use these heat exchanger without any substantial problems. Actually, with stagnant flow or very low flow rates for highly saturated salt mixture sometime deposition of the salt takes place in these tubes but it is very easy to clear the pipes by periodic increasing the flow. As i said such a deposition only occured when the flow was stangnant for longer time period like more than a week or so. PE tubes are relatively smooth and does not pose any of the issues as faced by the metal heat exchanger with bulk saturated fluid. we had use very small diameter PE tubes for sampling solar pond salinity trends as well as extraction of the heat from the ponds. Also, we have use these kind of heat exchanger for aquaculature using solar ponds.


RE: Low-cost heat exchanger

(OP)
Thanks very much Thermcool, for you suggestions.  Did you go to a particular manufacturer for your particular exchangers?  I contacted wastech myself and haven't yet heard back from georgefischer, but the wastech guys said they didn't have what I was looking for.  I'll make sure to consider teflon as well.

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

With miles of polyethylene tubing, you'll probably be losing a fair bit of pressurized ammonia by permeation through the tubing into the seawater.  As I said in the other thread where you posted this question, the low thermal conductivity of polyethylene will probably require an enormous heat transfer area in comparison to that required for a metallic plate exchanger, which of course means a larger area available for permeation losses. You may (doubtfully) save on the first cost of the exchanger, but you'll be paying for it in lost ammonia, risk of ammonia release in future etc.

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

(OP)
moltenmetal, thanks for your critical points!  I think you've safely ruled out PE tubing.  If there is another plastic available with a higher thermal conductivity, then I would definitely consider it.  It sounds like you are correct in pointing out the permeation problem with PE.  Do you happen to know anything about the permeation of ammonia through other types of polymers?  I don't want to give up on polymers yet because if they are an alternative to titanium, they might be the only alternative of significantly lower cost that can provide similar corrosion resistance.  I've been trying to find some, and I may have interesting leads if they check out. We'll see.  Otherwise it looks like titanium is the winner out of the available metals.

RE: Low-cost heat exchanger

Give me metal (that doesnt cost a bomb,) anyday. Nothing can beat metal when it comes to heat transfer apps.

RE: Low-cost heat exchanger

Glass (not glass lined) may be an option.  I know you can buy glass S&T exchangers.

RE: Low-cost heat exchanger

Yes, it would be really nice to have corrosion immunity rather than accepting mere corrosion resistance, so I see why you're after polymers.  In an exchanger with modest temperature seawater on one side and modest temperature anhydrous ammonia on the other, I would guess that titanium would give you excellent service.  But couldn't you also get away with 2205 duplex or perhaps a 6-moly stainless steel?  Cheaper than titanium I would imagine, in return for some added but manageable risk of corrosion damage over the long term.

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

I don't know about the ammonia side of the equation, but on the seawater side I can say that a number of PHE suppliers delivering for SW/FW cooling service in the shipbuilding market have been offering Hastelloy C22 and similar instead of the normally used titanium (due to long lead times on titanium).

RE: Low-cost heat exchanger

Have you solve your need?
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

(OP)
Thank you all for your input.  I have not found a viable replacement for titanium.  In the end, I began to evaluate plastics in terms of their structural properties as well as their permeation issues.  I essentially assumed nearly any plastic would do the job on the seawater side.  It just seems that plastics don't cut it (unless someone invents a plastic with stiffness that can rival metals...).

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

Will any of the P&F guys work with superferritic stainless?  Both SEA-CURE and AL-29 4C have been used extensivly in seawater.  They have good heat transfer, excellent corrosion resistance, high strength, and they cost a heck of a lot less than Ti.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection
http://www.trent-tube.com/contact/Tech_Assist.cfm

RE: Low-cost heat exchanger

EdStainless,

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

(OP)
As far as their website advertises, SEA-CURE has been used as heat exchange tubing, but not for P&F designs.  There is a significant amount of cold-working that will go on, so ductility may be an issue.  However, I'm sure it could be overcome with enough money thrown at it.  Steels and aluminum alloys seem to be the near term replacements for titanium given the large development costs of getting new exchangers designed and tested.

ddot

RE: Low-cost heat exchanger

I don't know that EdStainless was advocating Sea-Cure and/or AL-29 4C specifically as much as he was extolling the virtues of superferritics in general.  Sea-Cure is the trade name of a tubular product I think, not an alloy and part of its properties that give it good corrosion resistance is determined by certain steps (I don't know if I am allowed to say which one) of the tube fabrication process which I have a hard time visualizing being done to strip or a stamped plate.

Wade in here EdStainless and bale me out.

rmw

RE: Low-cost heat exchanger

Sea-Cure is the tradename for S44660 made by Plymouth tube. The tradename applies to the alloy, not the product form. The guys at Plymouth are the only people out there with tube experience in these grades.

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.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection
http://www.trent-tube.com/contact/Tech_Assist.cfm

RE: Low-cost heat exchanger

EdStainless,

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

Wellllllll, sort of.
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

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