Joining Titanium tubes to teflon tubesheet.

  • #1
rollingstein
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What would be the possible options to join Titanium Heat Exchanger tubes to a PTFE / Teflon tubesheet? These are 38 mm tubes, 2 mm thick. 6 m total length. Seamless tubes.

Is this a reasonable design decision? Full titanium tubesheet would be excessively expensive & isn't needed since only the tube-side fluid needs Ti because of corrosive nature.

The other options might be Ti clad Stainless tubesheets or an SS tubesheet with an epoxy coating. But not sure if joining those to Titanium tubes is any easier?
 

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  • #2
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What sort of pressure, and what sort of fluid in contact with the teflon?
 
  • #3
rollingstein
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What sort of pressure, and what sort of fluid in contact with the teflon?
Tubeside pressure 2 barg max. Shellside is steam at 2 barg max. i.e. 135 C.

The teflon tubesheet will contact steam on one side & on the other a saturated salt (NaCl / Na2SO4) solution at approx. 105 C.

The high chloride conc. & high T motivate Titanium tubes. The unit is fairly small capacity, approx. 20 m2.

PS. If you'd suggest any alternative design decisions, I'd love to hear.
 
  • #4
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Unknown in Ti. Two barg steam in the shell. Close the shell with Teflon. Saturated brine other side of tube sheet from shell --- also at 2 barg?
 
  • #5
rollingstein
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Unknown in Ti. Two barg steam in the shell. Close the shell with Teflon. Saturated brine other side of tube sheet from shell --- also at 2 barg?
Yes. Both sides at 2 barg.

Hot NaCl brine on tube side.
Steam on shell side.

PS. Did I misunderstand what you asked for?
 
  • #6
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The teflon tubesheet will contact steam on one side & on the other a saturated salt (NaCl / Na2SO4) solution at approx. 105 C.
I keep hearing you say you're separating three streams from one another, and Teflon is a working seal between two of them.
 
  • #7
rollingstein
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I keep hearing you say you're separating three streams from one another, and Teflon is a working seal between two of them.
Ok, sorry. That's not what I meant. There's only two streams.

Perhaps this diagram clarifies things:

V8IrK45.jpg
 
  • #8
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Okay, so the Teflon is dealing with steam pressure versus atmosphere. You are going to have to support it with some sort of plate, in which case you might want to look at packed glands through a plate. That kicks expenses up, but the creep rate for Teflon at that temperature is going to be an endless headache. Can you just run the process tubing as sleeves through a longer tube shell? Or, is that too much loss in heat transfer efficiency?


Edit:

And, this does nothing but move the problem --- you've still got to come up with something for a tube sheet.

Second Edit:

Actually if the Ti cost is the constraint, steam jacket that length of Ti tubing, and forget the tube and shell configuration.
 
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