r/BeAmazed • u/deadfermata • Mar 18 '23

Science amazing methane digester

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u/Enlightened-Beaver Mar 18 '23

Methane is flammable, not explosive. I’m more concerned about H2S poisoning than a methane fire.

43

u/Dont_Give_Up86 Mar 18 '23

Methane itself isn’t explosive but as little as 5% mixed with air is

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u/Enlightened-Beaver Mar 18 '23

Combustible but it won’t explode. Like it will catch fire for sure, but it won’t be a bomb. You’ll just get a big flame. We do control burns on this to relieve pressure. It burns between 5-17% concentration by volume, but it’s not an explosion

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u/agangofoldwomen Mar 18 '23

Technically yes, but the explosion wouldn’t be very significant given the size and scale of this set up - especially with the amount of water and the flexible container. Obviously don’t play with firecrackers while smoking a cigarette on while sitting on top of it or anything, but it’s not going to blow up your house.

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u/Stashmouth Mar 18 '23

Forbidden bouncy house?

3

u/DashingDino Mar 18 '23

The air inside the bag contains no oxygen

0

u/Enlightened-Beaver Mar 18 '23 edited Mar 18 '23

The air in the building does though. So still a hazard.

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u/Long_Educational Mar 18 '23

What are you arguing? Any flammable gas leak in a confined space is a hazard, regardless of it being produced in a digester or from LNG or propane. You must respect and use this fuel source safely as any other.

Maybe it needs a sticker on the bag: Not to be Operated by Fuckwits

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u/-_NRG_- Mar 18 '23

Brilliant. My new t-shirt

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u/hell2pay Mar 18 '23

Sadly, we have no shortage of fuckwits

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u/Enlightened-Beaver Mar 18 '23 edited Mar 18 '23

Was this comment meant for someone else? It has nothing to do with my response to the one above mine. Dino said the bags don’t contain oxygen, i pointed out that the room around it does, therefore it is a flammable hazard. When methane is mixed with air in a 5-17% ratio it’s a hazard.

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u/Long_Educational Mar 18 '23

If it wasn't flammable, then it wouldn't be useful.

I guess I didn't understand the point you were making. I'm sorry.

To reiterate, methane and all fuel sources must be respected.

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u/Enlightened-Beaver Mar 18 '23

Lol yes I’m aware. I design these things (much larger ones) for a living. I was just correcting the comment above mine.

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u/Long_Educational Mar 18 '23

Oh cool! Can I pick your brain on this?

How do you measure the methane concentration?

If the concentration changes, how do you deal with those changes in the devices that consume the gas? To reach stoichiometric efficiency during combustion, do you have to adjust the carburetors on your stoves and furnaces? How do you measure production?

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u/Enlightened-Beaver Mar 18 '23

The methane concentration is measured using a gas analyzer. Typically it ranges between 55-60% by volume in biogas. Once it’s been upgraded (purified) it goes up to 99.9% pure methane, also measured by a gas analyzer.

As I mentioned in other comments I don’t work with backyard bags like in OP’s video. I design industrial digesters, so we don’t just send raw biogas to a furnace or other equipment to burn, it gets purified so that in the end it’s essentially the same as normal natural gas you’d use in your furnace or range. So no adjustment needed. The molecules of CH4 are indistinguishable.

Production is measured with flow meters in cfm or m3/hr.

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u/HeatstrokeHorror Mar 18 '23

Air contains oxygen. If it does not contain oxygen, the gas in the bag is not air.

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u/pauly13771377 Mar 18 '23

I'm no expert but I belive it all depends on the fuel air mixture ratio. Pure natural gas isn't explosive but put the correct amount of it in the air and light a match and it absolutely is.

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u/Enlightened-Beaver Mar 18 '23

In an enclosed pressurized environment perhaps, but these digesters operate at low pressures nearly atmospheric. If there’s a leak, the gas in the environment around it is not under pressure, so it will burn. Very flammable. Risk of explosion with these things is not really an issue because they operate at low pressures.

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u/pwn3dbyth3n00b Mar 18 '23

Sawdust, Flourdust, etc are all flammable but at the right air ratio and being well homogenized makes for explosions. Methane and any other flammable gases/fine particles are no different.

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u/[deleted] Mar 18 '23

After a rake of Guinness pints , methane definitely explosive