Seal for supercritical C02 1

[simaonobrega]

Hello everyone,

I am currently working on the connection of two cylindrical vessels that requires a sealing in-between.
The environment is filled with super-critical CO2 (environment at 100bar and 65C with a pressure differential between the sealing of 0.01 bar), meaning that rubbers aren't allowed.

When removing the vessels from the main chamber, they must be decoupled. This implies that the seal connection will be opened three times per day.
As a solution, my initial thought is to use a dovetail groove (since the connection is opened often) with a PTFE teflon o-ring. Since the pressure differential is small, do you advise a simpler solution like the use of a gasket?
Any other recommendation?

Thank you very much for your time in advance!

Regards

 

[Tuckabag]

Unless you replace the PTFE o-ring everytime I think you'll have issues with it re-sealing repeatably once it has been compressed.
I assume elastomers are not allowed due to RGD issues?
Would an RGD resistant elastomer be acceptable?
If so, I'd use that in the same dove tail o-ring groove, just keep the squish pretty tight as you've got bugger dP there to energise the o-ring.

 

[simaonobrega]

Hello Tuckabag,

Thank you your feedback.
You are right, I have double checked and PTFE o-rings are not indicated for active coupling/decoupling due to their lack of elasticity.
Elastomers cannot be used since this application uses CO2 at 100 bar. At the end of the process, before opening the vessel, pressure returns to atmospheric causing the CO2 to expand. This is the expansion that destroys the rubber o-rings.

 

[Tuckabag]

Yes, this is Rapid Gas Decompression (RGD) damage.
I would talk to one of the elastomer manufacturers.
The majority of them produce compounds that are designed to reduce/prevent RGD damage.
I have used polymers that are Norsok M-710 compliant for high CO2 content streams at high pressure (~150bar) and high temperature (+95deg C). They worked very well in both static and dynamic applications where a lot of other elastomers had failed.

 

[simaonobrega]

That is great! Do you recall which polymer you have used for that high pressure/temperature application?
I have also checked spring energized options and they might be an alternative solution, much probably at the expense of a higher price.

 

[Tuckabag]

I've used Precision Polymer's V91J compound as well as TRP's F226 compound on the same application.
The elastomers are not cheap, but they certainly do the job.

 

[simaonobrega]

Thank you Tuckabag.
I will check with the supplier then!