Hot Oil vs Glycol/water as heating medium

[Trond]

I tried posting this in the Chemical Plant Design forum, but perhaps this is a better place. Apologies for cross-posting. My question was as follows:

We are looking at a new offshore oil & gas facility where we want to install a heating medium system. The heat will come from several WHRU on gas turbin outlets. Operating temperature of the system will be around 170°C (340°F), and the proposal is to go for a glycol/water mixture. I have done some work with hot oil systems before, and would have thought that would have been better suited, but naturally I am biased here smile

I have done some searching on the web, and some sources indicate that 170°C is too high for a glycol/water system. Others claim it is OK.

The way I see it, hot oil is less prone to fouling/degrading, can be operated at lower pressures, is inherently inert and hence less likely to cause corrosion. On the down side, it is flammable and more expensive to purchase than glycol/water. Then again,I would presume a glycol/water system would be more labour intensive in terms of operation?

 

[IRstuff]

It's obviously above the boiling point of water/glycol, so the system would have to be pressurized, which is a cost factor unto itself. But, the heat capacity ought to be better.

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[EdStainless]

Either system would need to be closed, so you need and expansion tank with high pressure relief and inert gas blanket.
Yes, the pressure for water glycol will be higher.
Flammability may be the biggest thing in favor, though the high heat capacity will also allow a smaller system.
Both systems will require some monitoring and addition of corrosion inhibitors, though a lot less with oil.

You might look around, there are other aqueous systems other than glycol that might be a better fit at this temp.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[willard3]

Specific heat of water/glycol will be higher than oil meaning your pumping costs will be lower.

 

[davefitz]

Offshore, a fire hazard has a really negative value. Revisit the tragedies of the north sea oil rigs of the 1960's- 1970's. The water/glycol has much better heat transfer properties, no fire hazard, less environmental issues and the equipment would be sized smaller ( due to better heat transfer).

One can also produce power for working fluids at 170 C- there is now available compact power systems using supercritical CO2 as the working fluid, designed for use aboard a ship. And there is o fire hazard with CO2, but it will cause asphyxia if it leaks from an indoor system.

"Whom the gods would destroy, they first make mad "

 

[IRstuff]

Since there doesn't appear to be a freeze problem, you could consider using propylene glycol, which does not have the same level of hazardous material handling.

TTFN
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