Hot Oil Expansion Tank: N2 Blanketing 1

[ColourfulFigsnDiags]

Hi all, I was hoping someone could explain a little more clearly what the use of a "Cold Seal Trap" is in then following paracgraph (from Therminol's manual):

An effective way of minimizing fluid oxidation is to blanket the system with an inert gas (e.g. nitrogen) as shown in figure A. When using a nitrogen blanket, moisture should be driven off from the fluid before the gas pressure is set. If this is not practical, air contact can be minimized by a cold seal trap arrangement as shown in figure B. Low boilers and moisture can collect in the cold seal trap, so the fluid in the trap should be discarded periodically.

Figure A:

Figure B:

From Therminol "Liquid phase systems design guide"

Any other hints or tips in this area would be appreciated! Thanks!

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[StoneCold]

The cold seal trap is used to stop the exchange of air and moisture above the expansion tank.
The most important part of the cold seal trap is that the vent from the expansion tank ends below the liquid level in the trap.
I have used the nitrogen purge option but not the cold seal trap. But nitrogen is readily available at my facility.

Regards
StoneCold

 

[ColourfulFigsnDiags]

Thanks Stonecold! I understood that part (and probably did not make it clear enough what I meant) ... it was this part in particular that was a bit confusing "moisture should be driven off from the fluid before the gas pressure is set. If this is not practical ..." ... What fluid should the moisture be driven off from, what gas pressure are they talking about and "If what" is not practical, Nitrogen purging or driving the moisture off?

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[StoneCold]

They are talking about the heat transfer fluid containing moisture. Sometimes there is water in the system left over from hydrotesting. This needs to be removed when the system is commissioned. During the startup the oil is heated to say 120C and nitrogen is swept through the vapor space in the expansion tank. This sweeps the moisture out the vent. Moisture in the system can cause problems when it flashes into steam or when it sits on the bottom as descrete water or freezes.

If you don't have nitrogen to purge the system then the best you can do is go with a high liquid level in the expansion tank at startup and drive the water off simply by vapor displacement through the vent line.

Does that clear it up a little?

Regards
StoneCold

 

[ColourfulFigsnDiags]

Bullseye, thank you, that makes perfect sense!

Any other tips about these systems?

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