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I'd dismissed this one as a stupid idea...
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dpack



Joined: 02 Jul 2005
Posts: 32879
Location: yes
PostPosted: Tue Dec 13, 16 2:07 pm    Post subject:  Reply with quote    

fingers in ears

ctrl methane will pull up 5 rather relevant bits. as a mixture it needs a little bit of a poke to set it off but not much of a poke even at cryogenic temps and the mix range for a surprise is fairly broad.

JUST DON'T . if you do let us know so i can sandbag the windows

Hairyloon



Joined: 20 Nov 2008
Posts: 14799
Location: Today I are mostly being in Yorkshire.
PostPosted: Tue Dec 13, 16 2:19 pm    Post subject: Reply with quote    

dpack wrote:
JUST DON'T . if you do let us know so i can sandbag the windows

I've already told you that I don't have a cowshed...

dpack



Joined: 02 Jul 2005
Posts: 32879
Location: yes
PostPosted: Tue Dec 13, 16 2:46 pm    Post subject: Reply with quote    

true but you do have a bucket of fermenting stuff and could probably find a lot of fermenting stuff.

like shane said compression and cryogenics have some complex issues,many of which can surprise the neighbours.

i wonder if there are chemical means to concentrate low levels of methane into a convenient space for later use ? .
adsorbsion or compounding might be a way to go, a bit like dissolving acetylene in acetone on pugging for gas axe bottles or using carbide for caving lamps.

maybe not for direct use but as a means of separation from a low concentration in air.

Hairyloon



Joined: 20 Nov 2008
Posts: 14799
Location: Today I are mostly being in Yorkshire.
PostPosted: Tue Dec 13, 16 2:56 pm    Post subject: Reply with quote    

dpack wrote:
true but you do have a bucket of fermenting stuff and could probably find a lot of fermenting stuff.

Actually I've upgrade the bucket to a barrel, but it leaks so I've not had any successful gas production from that.
But, while it may want refining, I don't think it wants doing by fractional distillation: more likely a bucket of lime to take out the CO2, but it did burn well enough straight out of the bucket so I think that is unnecessary.
How to store and regulate the gas flow are the only real questions I have on that count.

dpack



Joined: 02 Jul 2005
Posts: 32879
Location: yes
PostPosted: Tue Dec 13, 16 5:28 pm    Post subject: Reply with quote    

the old " tin can floating over water " gasometers seemed to work pretty well.

low tech and reasonably safe they also provide a positive pressure for the feed to use pipe.

Hairyloon



Joined: 20 Nov 2008
Posts: 14799
Location: Today I are mostly being in Yorkshire.
PostPosted: Tue Dec 13, 16 11:15 pm    Post subject: Reply with quote    

dpack wrote:
the old " tin can floating over water " gasometers seemed to work pretty well...

Yes, but I'm not convinced that they scale down that well.

dpack



Joined: 02 Jul 2005
Posts: 32879
Location: yes
PostPosted: Wed Dec 14, 16 12:05 am    Post subject: Reply with quote    

how many litres of lp methane do you get from a barrel of ferment?

i recon scrapheap challenge ( and some bath sealant ) should give the materials to test the principle on a backyard scale

iirc methane isnt very soluble in water and unless there is a big surface area of water exposed re gassification to atmostphere should be minimal but any leaks from any cause would be a hazard as well as a loss of product

a simple bubble trap in an inverted bottle on a small batch of ferment should give some idea of the size of gasometer required and solubility issues.

a gasometer is just two vessels that fit one inside the other with the lower one full of water, the top one rises ( between some guide poles is optional ) as it fills . seems pretty easy to make.

super simple picture

a lot safer than compression and cryogenics but still rather iffy unless you can gnt there is not enough air to give an explosive mixture.

numbers indicate methane isnt as bad as some things but anything with a 10% window of surprise needs reasonable caution.

Hairyloon



Joined: 20 Nov 2008
Posts: 14799
Location: Today I are mostly being in Yorkshire.
PostPosted: Wed Dec 14, 16 12:20 am    Post subject: Reply with quote    

dpack wrote:
a gasometer is just two vessels that fit one inside the other with the lower one full of water, the top one rises ( between some guide poles is optional ) as it fills . seems pretty easy to make...

Yes, that is basically what I had as the first test, but the top barrel would need enough weight to provide proper pressure for the gas appliances. I only did it to check the principles: I didn't do any measuring.

But I suspect that an increase in pressure is likely to repress the fermentation reactions, so I'm thinking the store wants to be separated from the reactor...

dpack



Joined: 02 Jul 2005
Posts: 32879
Location: yes
PostPosted: Wed Dec 14, 16 12:26 am    Post subject: Reply with quote    

if the top vessel is only heavy enough to give say 1.5 atm i cant imagine it would retard the ferment much (i have opened bottles with far higher pressures from fermentations) but it would make for a non mechanical rig that works with no pumps etc .

a mix of floats and weights could be the way to go re getting a working pressure for ferment and use .

what point of use pressure is the feed to a standard gas ring ? that might be a number to work towards .

dpack



Joined: 02 Jul 2005
Posts: 32879
Location: yes
PostPosted: Wed Dec 14, 16 12:29 am    Post subject: Reply with quote    

getting an anerobic system seems important for the ferment and to avoid any surprises so that needs designing in.

Hairyloon



Joined: 20 Nov 2008
Posts: 14799
Location: Today I are mostly being in Yorkshire.
PostPosted: Wed Dec 14, 16 12:50 am    Post subject: Reply with quote    

dpack wrote:
getting an anerobic system seems important for the ferment and to avoid any surprises so that needs designing in.

Well that is easy enough: a bucket full of water upside down in a bucket full of water·..
You do need the right bacteria though. I had assumed there would be some naturally in some of the anaerobic sludge I had accumulated about the place, but I had no sign of any production until I seeded it from another source...

Shane



Joined: 31 Oct 2005
Posts: 3035
Location: Doha. Is hot.
PostPosted: Wed Dec 14, 16 4:10 am    Post subject: Reply with quote    

Hairyloon wrote:
Shane wrote:
I would recommend that you never put a liquid nitrogen generator in a shed

Where else should I keep it when it's not in use? Is too big to go in the basement.

Okay, smarty pants - let me rephrase it to say "don't operate it in a confined space". The reasons why should be obvious, I would hope.

Hairyloon wrote:
But thinking on, if you're gradually chilling air 'till it liquefies, then isn't the methane going to drop out first, followed by the oxygen...


From Wikipedia, typical biogas concentrations are:

Methane 50–75%
Carbon dioxide 25–50%
Nitrogen 0–10%
Hydrogen 0–1%
Hydrogen sulphide 0–3%
Oxygen 0%

I'd be surprised if that was all that was in it, and any impurities can become problematic for cryogenics. Oh - and 3% H2S will kill you, instantly, so you'll need to find a way to remove and dispose of that, as it will condense before the methane (which means you'll have a very strong concentration of H2S in your initial condensate).

The liquid nitrogen generator looks like a bit of fun, but I'd seriously stay away from liquefying flammable gases at home.

As for methane storage - here's one I made earlier :


Mistress Rose



Joined: 21 Jul 2011
Posts: 8723

PostPosted: Wed Dec 14, 16 7:03 am    Post subject: Reply with quote    

Well I hope Hairyloon isn't going for one that size Shane. We would blow up the whole of Yorkshire and a bit more with one of them.

Hairyloon, if you take this project very far, do remember that air and methane can make an explosive mixture. A friends house was damaged rather badly from a natural gas leak in the early days. Her mother got some burns, but luckily wasn't too badly hurt, and the rest of the family got away with it because the lounge to kitchen door blew off its hinges so the main blast hit the wall.

dpack



Joined: 02 Jul 2005
Posts: 32879
Location: yes
PostPosted: Wed Dec 14, 16 1:02 pm    Post subject: Reply with quote    

h2s is about as toxic as hcn but has the added advantage of a very wide concentration of surprise range, more explosive than methane is a good way to think of it.

a sniff of 3% would be a very bad idea and iirc 4% is the lower limit of concentration of surprise in air.

if you wanted to remove it at lp running the gas stream via a chemical collector system ( trapping as fes using wire wool or filings is a possible answer) might work for small scale (cost is an issue) but in bulk flare it off is the option but that has a big environmental downside as you will mostly make so2 (and water so sulphurous acid is the main pollutant). ether way there are some rather trick pollution issues.

looking at the digester product gas if you run it strait to a burner same chemistry for the h2s applies ( ie so2[ aq ] as vapour ) which might not be wise to breathe but a gas leak in the kitchen would be seriously toxic from the h2s and smothering from the co2.
"natural" ie fossil gas is usually a lot cleaner from the ground than that biogas recipe and gets some hard core purification if it isnt.

my overall opinion is biogas might be green on the surface but there is some rather nasty chemistry to overcome if you look a bit more closely before domestic use is sensible.

Nick



Joined: 02 Nov 2004
Posts: 33659
Location: Hereford
PostPosted: Wed Dec 14, 16 1:17 pm    Post subject: Reply with quote    

Keeping the right bugs happy is the challenge in digesters. With a fixed food source hats not too hard but with mixed feed it's a nightmare. But the Product isn't purified before being pushed into the grid.

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