HELP SEALS BIOGAS

[Mac001]

Hi !!

I'm working at an BIOGAS receiver.
The BIOGAS came from WASTE and does not have any zootechnical origin)
I have looked at the "general" BIOGAS specs and I have found these components:
1) H2S Hydrogen SOLFIDE
2) Ammonia
3) CH4 Methane (of course)
4) Carbonic acid (also called areal acid)
5) Hidrogen (< 1%)
6) CO2

Are they correct, in you experience ?
For the cilinder material I have selected AISI 304

Now I must select the material for the seals near the condensate exit...
what kind of seal would you suggest ... ( the section required is a diameter of 18 mm) ? Does viton or neoprene have some possibility of survive in such enviroment?

 

[gr2vessels]

Mac001,
The gases listed, including the hydrogen, are quite dangerous for handling and containing them with rubber seals. Perhaps you would consider welded connections instead of flanged connections and where flanges are unavoidable, use appropriate gaskets, not rubber seals, to contain the hydrogen and to prevent the blow-up of your plant. You cannot have low enough pressure to contain the gases mixed with hydrogen and all you need is a very small, invisible hydrogen fuelled flame to melt your seal and blow-up the plant..
For the corrosion side, check with NACE MR0175, but the 304 sounds quite suitable for your application.

 

[Mac001]

Other data:
Temperature 30°C
Pressure from 0.5 Bar to 1 Bar
the vapor content is max 10%

The trouble is which kind of gasket shall I use !!

It's difficult to find a polimer which works well with all those materials !!

 

[gr2vessels]

Mac001,
Your service doesn't qualify for a full "hydrogen service" as specified on many standards, codes, etc (look up for hydrogen service on google). However, the practice of containing the sneaky hydrogen should be followed. Please read it again;- don't use any soft or hard rubber seal, use only the gasket recommended by your local supplier for flanges ASME B16.5, Class 150#, RF type. Don't use screwed connections. Don't use reinforcing pads on the vessel and get the design done by an experienced designer for vessels operating in hydrogen service (minimum nozzles/flanges, welded connections, etc..). Also, he will take care of the wet sour service requirements and all that horrible acidic combination you might gather in your system.
Cheers
gr2vessels

 

[Mac001]

Thank you for the advice !!