[Digestion] Photosythetically Conditioned Biogas Compression

[David]

Jacob,

Take 2,


On 10/29/2013 11:08 AM, Jacob Douenias wrote:
> Hi all!
>
> Excited to join this group. I am a researcher working at carnegie 
> mellon university in pittsburgh.I am working on a startup where we 
> are making biogas at home and biologically purifying this gas.
>
> Our gas composition at the end of our system is comprised of about 
> 80% methane and 20% oxygen. We are concerned about the storage and 
> possible compression of this gas due to the presence of oxygen in 
> the gas. I know that 80% methane is well above the upper explosive 
> limit of methane (our working conditions are 15-20psi for final gas 
> compression and 60-80 degrees farenheight). I know it is bad 
> practice to have oxygen mixed with combustible gas but at our 
> composition should we worry about safely compressing this mixture to 
> a low pressure (15-20psi) and storing it in gas cylinder? I would 
> really love to hear what you think as I am just an architect who 
> happens to read a lot about biochem. 


The upper limit of flammability for methane in air is of course about 
15%. I took a bit of time between tasks to look it up, and in pure 
oxygen, the upper limit is 61%. (The lower limit is about the same in 
either case: ~5%.) There is a formula proposed by Zabetakis which 
indicates-- if I've done my figgers correct-- that at 20 PSI it should 
increase to perhaps 63% methane in oxygen. But note: that is an 
extrapolation, not a test result. And I would not call 80% "well 
above" that extrapolated limit.

I have to say, that particularly if I had children in the house-- you 
did say "biogas at home", and you did say "we"-- I would not want to 
take any implied risks. In the case of the information I have just 
given you, for example, maybe it's true, maybe I made a mistake. Maybe 
you didn't measure the gas ratio correctly and maybe it will change, 
if the presumed algae get frisky. Maybe, maybe.

If it were me, I would have a tendency to look at the gas cylinder and 
wonder whether I was unintentionally planning on making a bomb with 
its own built-in shrapnel, and then I would begin to wonder how I 
might store the gas some other way, such that if the marginally 
unthinkable did happen, nobody would be likely to be nearby, and 
nothing sharp and glittering would be hurled hither and thither as a 
result.





d.
-- 
David William House
"The Complete Biogas Handbook" |www.completebiogas.com|
/Vahid Biogas/, an alternative energy consultancy |www.vahidbiogas.com

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