HCBN,H2O,H2 Prodect Cooler (in hydroteater plant)

[JohnCal]

This will be an air cooled heat exchanger (Inconel 625 tubing and header boxes). Inlet vapor weight fraction is 0.85 while outelet vapor fraction is 0.25. When it was designed with 2 tube passes (1" tubing, 6 tube rows, 3 rows/pass), the velocity in first/second tube pass is about 16.5/12.5 ft/s. HTRI ACE gave a warning message "potencial phase separation in header". To prevent the possible phase separation, the air cooler may be designed with one tube row per pass e.g. use 1.5" tubing, but it will be very expensive. Please advise:
(1)is the phase separation possible?
(2)actual experience with multiple tube rows per pass in similar service,
(3)any flow distribution device at inlet header,

 

[speco]

Dear stheatexchanger,

1. Is phase separation possible? Yes. There are two places where this can happen. Once at the inlet header wher you have three rows of tubes being fed. And once more at the return header where the condensed liquid will also tend to go to the bottom row(s) of tubes.

2. Actual experience with multiple tube rows per pass in similar service? I have designed and buily air-coolers in similar services with multiple rows per pass. However, I don't have any operational experience with this, but never heard any problems from my customer about performance.

3. Any flow distribution device at inlet header? If phase separation is really a concern, your best alternative is to make the design one pass per row. However, to do this, you would have to use much larger diameter tubes to keep the pressure drop in the same range. This may not be a practical solution, since the largest practical tube diameter for a cooler is 1.5" OD.

Regards,

SPECO (

http://www.stoneprocess.com)

 

[25362]

I've heard of inserts for turbulence enhancement to avoid phase separation along horizontal tubes of partial condensers while improving heat transfer. This effect could reduce the number of tubes per pass and further diminish the chances of potential phase segregation.
I suggest a web search on tubular inserts to learn more about this subject.

 

[JohnCal]

speco and 25362,

Thank you very much for your information. Per literatures, the phase separation in floating head of a S&T exchanger will not affect heat transfer significantly, but the temperature profile (hence LMTD). Based on this, I designed this air cooler with 6 tube rows and 2 tube passes (each pass has three tube rows). The 2nd tube pass was sloped to assist the drainage of condensate so that the temperature profile will not be significantly affected by the condensate build-up. However, I do not have operation data in similar case to confirm my design.

 

[speco]

Stheatexchanger,

I suspect that the reason for the warning in the HTRI program is because it makes an assumption of evenly distributed flow throughout the exchanger. Having multiple rows per pass will obviously result in a situation where more of the liquid goes to the lower tubes of each pass, hence the warning. However, the big question is whether you will get sufficient cooling. If you have used the right properties of the fluids and included sufficient fouling factors for safety (and uncertainty), I don't think there should be a problem with heat transfer.

Another factor to keep in mind is that the pressure drop will automatically balance between the various tubes or rows in the same pass.

If you would like me to check the design using my software please let me know.

Regards,

Speco (

http://www.stoneprocess.com)