Nitrogen Blanket on Dowtherm A

[Dave872]

Is it worth it to put a nitrogen blanket on an expansion tank of Dowtherm A? I am worried about oxidation of the thermal fluid if it comes into contact with air.

Are there any other benefits which would come from this?

 

[LittleInch]

Temperature of the oil in contact with air / gas?

What does the manufacturer say?

If you're worried, then do it - not much cost involved. No other significant benefits I can see.

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Also: If you get a response it's polite to respond to it.

 

[Latexman]

Look at the Design Guides of Dow, Therminol, Duratherm, etc. Inerting excludes O2 and reduces oxidation tremendously. It also excludes moisture (H2O). Both extends the life of a very expensive product. There's also a very good chance you are operating above the flash point of Dowtherm A (236^oF). Seems like a no-brainer to me. Do it.

Good Luck,
Latexman

 

[LittleInch]

But if the expansion tank is not a breather type, then an oxidation would be very limited no?

Also temperature in the expansion tank is normally a lot lower than the main stream.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[pierreick]

Hi,
Definitely a good option to add N2 pad on your system .Contact your hot oil supplier for advices and periodic monitoring of Hot oil .
My 2 cents
Pierre

 

[Latexman]

The Therminol design, which we have in a couple plants, allows oil to circulate through the expansion tank at full flow, reduced flow, or essentially no flow. "Lights" and other contaminants are slowly formed in the hot oil. Full circulation to the expansion tank vents the lights off, thus removing those contaminants and prolonging the service life of the oil.

Good Luck,
Latexman

 

[LittleInch]

Full or partial flow sounds more like a degassing vessel / drum??

That will make a big difference to the story instead of an "expansion vessel".

But the question was "Is it worth it"? Almost certainly.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

Well, you've got to have some gas makeup to maintain pressure / release pressure in the drum as level rises and drops. Level will rise and drop as drum temperature swings with plant heat demand. Degassing of the HTF upon return the drum will almost certainly be required also, which implies pressure release.

What would you use otherwise ? It has to be chemically inert and moisture free. Contact with O2 in dry air will cause polymerisation and gunking of the HTF.
If you want to minimise the use of N2, keep a wide gap between the setpoint of the inbreathing PIC-PCV and that of the outbreathing PIC-PCV. The wider the gap, the less N2 demand from N2 source. You can calculate what the gap should be, given the change in head space volume between LAL and LAH settings for the drum.

If you are considering inert gas produced from an inert gas generation unit (PSA type), N2 purity may be some 95% v/v. Talk to HTF supplier if this is acceptable. Compressed air feed to the PSA unit will have to be from oilfree screw compressors, else there is a high risk of lube oil vapor contamination / deactivation of the PSA carbon bed material.

 

[pierreick]

HI,
To add to my previous reply:

https://www.process-heating.com/articles/84799-tips-hot-oil-systems

Good luck
Pierre