Going to start a small digester project. Input welcome.

OK I have decided to start a project over the summer to experiment with some of this methane digestion. After some clarification from some of you folks and doing a lot of reading and you tube watching I want to try this on a small scale and see how it goes.

I happen to have two plastic barrels in the 55 gal size range that fit one in the other. SO I am going to build a digester to run my gas BBQ grill with. The grill is outside on the back porch so carbon monoxide should not be an issue.

This will tell me a few things like...

How much of a pain in the butt is it to run such a system for home cooking.
What its like to run an actual appliance with it.
The smell factor
How sanitary can such a system be run
Is it really a cost/time effective system

As we all know there are a lot of things that look good on paper that become a real headache in real life application and different people have different tolerances for such headache. This small scale experiment will give me a good idea as to whether this would be a good system for me down the road.

I pretty much have the design worked out using bungees for compression (pulling down on the floating barrel) to create pressure.
My first question for you guys is this.

Will I have to get a different regulator for my propane grill or will I be able just hook to the current regulator and run it? Are there any mods to the burner system that I will have to make?

Ray

Methane is "natural gas" more-or-less.

It will not burn properly in a propane appliance. IF (less and less common these days) the appliance is "convertible" it may be possible to convert it to run on methane. This is a matter of jet (orifice) size and pressure, since they use a different ratio of gas to air for a proper burn. With a low-pressure source you probably don't need a regulator as such for the methane, as you probably won't have much pressure on it.

Word of caution - methane digesters are hard to downscale. The smaller they get, the harder it is to keep them warm without wasting some other form of heat. Big ones easily heat themselves, and provide excess gas for other uses (depending on the other use, it may provide heat that the digester can use as a byproduct, so more gas can be sent to it.)

I recall one successful "small" system that was written up decades ago (I don't recall which magazine) where the digesters were buried in a compost pile for the heat and insulation. It was a fairly large/work intensive "small" system, I recall thinking at the time. Used tractor tire innertubes for gas storage (and possibly also as the digesters, but I can't recall how that was supposed to work.)

Another word of caution - methane is essentially odorless. I don't know how "odorless" it will be coming out of a digester, but...
The "smell of gas" is added to it commercially. If it smells like anything, it won't be what you are used to thinking of as "gas".

Ray, that's great man... please keep us updated with the results. I'm considering the same project on my end. What I considered is getting a hold of one of those latex weather balloon to collect the gas from a barrel. However, that bungee idea of yours is brilliant.

Agh! Just when I think I have a basic understanding along comes another peice of information that reintroduces confusion.

Now you say that methane is basically natural gas. Yet others have said that methane is too dangerous a gas for indoor devices like water heaters. I have used a natural gas water heater for years without incident and the boiler that my radiant heat runs from is also natural gas. So if they are basically the same thing why is one acceptable ( and widely used ) for such uses and the other one too dangerous?

I can think of a few reasons, though I can certainly think of more dangerous gasses, too.

Not that NG (despite your comfort with it) is hazard free...

The big ones: No smell or wrong smell (cow-manure-is or sewerish rather than "GAS LEAK!")

Oh man, who farted, that's awful, let's light a candle...FOOM!

Possibility of the gas generated being mixed with oxygen/air in a small digester system especially whenever started up or opened to feed - which means the gas lines could have a flammable mixture in them rather than pure gas, which won't ignite inside the pipes.

Smaller issues: troubles with inconsistent or wet gas ruining your NG appliances.

Troubles with sue-happy readers - the "don't try this at home, folks" approach. By the way, don't try this at home

Also, kiss your house insurance goodbye, probably. The gas company is a known entity that works to a certain standard. Insurance companies are OK wih that standard. Homebrew gas system connected to the house will probably get your coverage voided even if it has nothing to do with any claim you need to make (or if the insurance company finds out about it they may cancel you before you need to make a claim.)


...aaaand finally, I wonder if you are confusing biogas (methane, digester gas) with "biomass gasification" gasifier, wood-gas, producer gas which IS one of those "much more dangerous" gasses, as it has a lot of carbon monoxide, which makes it phenomenally dangerous indoors as compared to methane/natural gas.

L. Jones wrote:I can think of a few reasons, though I can certainly think of more dangerous gasses, too.

Not that NG (despite your comfort with it) is hazard free...

The big ones: No smell or wrong smell (cow-manure-is or sewerish rather than "GAS LEAK!")

Oh man, who farted, that's awful, let's light a candle...FOOM!

Possibility of the gas generated being mixed with oxygen/air in a small digester system especially whenever started up or opened to feed - which means the gas lines could have a flammable mixture in them rather than pure gas, which won't ignite inside the pipes.

Smaller issues: troubles with inconsistent or wet gas ruining your NG appliances.

Troubles with sue-happy readers - the "don't try this at home, folks" approach. By the way, don't try this at home

Also, kiss your house insurance goodbye, probably. The gas company is a known entity that works to a certain standard. Insurance companies are OK wih that standard. Homebrew gas system connected to the house will probably get your coverage voided even if it has nothing to do with any claim you need to make (or if the insurance company finds out about it they may cancel you before you need to make a claim.)


...aaaand finally, I wonder if you are confusing biogas (methane, digester gas) with "biomass gasification" gasifier, wood-gas, producer gas which IS one of those "much more dangerous" gasses, as it has a lot of carbon monoxide, which makes it phenomenally dangerous indoors as compared to methane/natural gas.

That makes sense and you may be correct I may be getting my gasses mixed up. That is very possible. I thought that gas made form a wood or biomas gassifier was called syngas and that methane was made out of garbage/biomass in a digester. This is new ground for me. I very well may have my wires crossed.

Ray Cover wrote:That makes sense and you may be correct I may be getting my gasses mixed up. That is very possible. I thought that gas made form a wood or biomas gassifier was called syngas and that methane was made out of garbage/biomass in a digester. This is new ground for me. I very well may have my wires crossed.

You're right. Methane is generated from the digester. It's about 50-60% methane, and the remainder is mainlly carbon dioxide.

Wood gas (also called producer gas or syngas) is primarily nitrogen when generated by forcing air through a gasifier. The fuel gases are carbon monoxide, hydrogen, and small amounts of methane. There's a bit of carbon dioxide also.

I see no reason to worry about oxygen building up in a digester. First of all, free oxgyen is the first thing consumed in a digester. Second, the system operates at a positive pressure that would prevent air from entering during operation. The main problem is developing a system that works well with the feedstock that most people have readily available (like grass clippings and food waste). I am totally convinced that it can be done and work well.

I think I am going to go ahead and give it a try. I mean we can talk theory back and forth all day but the only way I am going to get my questions answered is to actually act upon it and actually do it.

Here is how I look at it. The burners on my grill are already burned out and need to be changed anyway. I already have everything I need in my shed except for the parts to refit the grill so if it doesn't work I haven't sunk a lot of money into it. I have a good friend who is a very experienced appliance repair man who can help me make the correct alterations to the grill. The actual knowing is worth the little money I will lose if it doesn't fly.

So I figure what the heck. If it doesn't work it doesn't work. If it does then AWESOME!!!

Ray

Ray: Did you ever build your biogas project?

So...
whats the prognosis? did it work?