onboard methane digester for the cook stove

[Grid Runner Adventures]

Hey all, just wanted to start a thread on some plans im working up to build an onboard methane digester to generate fuel for my cook stove. filling up with some cow manure even every month of hard use would not be as bad as buying propane!

speaking of propane I am picking up a couple spent bottles today to turn one of them into my digester and the other will be my storage tank
on the tongue of the trailer they will look nice and natural.

I will post some more as im working on it. have any of you guys thought of doing this.

[Dale M.]

I think from what I have seen, the physical size is going to take up more space in you trailer than practical for amount of fuel it will produce over the cost of propane..... But I keep watching thread in case I am wrong...

Dale

[dh]

I remember learning about these in college. Are you going to produce at home and fill your tank, or haul around dung when you camp? You may be on to something.

[eamarquardt]

Do you have a link to plans that you are using. Also, it seems to me, that there might be "alternatives" to cow manure that are always "close at hand" if you know what I mean. Cow manure isn't exactly growing on trees here in my neighborhood (although we have a fair amout of horse manure). Could these alternative "raw materials" be used or do you get more "bang for the buck" so to speak from cow manure?

Always thinking.

Angry, no. Dissatisfied, yes.

Cheers,

Gus

[Ageless]

Any organic material will feed a digester, wood chips, grass clippings, etc. What you want to produce is hydrocarbons (methane). Manure already has the bacterial activity going that gives it a head start on the process.

Digesters have been a boon to 3rd world countries where fuel is at a premium.

[Grid Runner Adventures]

I will be toting the whole system around with me. the digester is an old propane tank. I will be cutting a 4 in hole in the top around the exiting hookups, and welding a 4in diameter pipe to it few inches tall, this will be my feeding tube. I am building a closed system batch load digester.

an 4in O ring stuffed up inside an end cap i'll make to fit over the pipe will give me a air/gas tight seal when i torque it down.

inside this tank I will fashion a rebar paddle to mix the contents. welded to a length of bar stock and a pressure through fitting to allow it to spin without loosing pressure in the tank.

exiting the tank will be a line that goes to an adjoining propane tank that will be used for storage.

now normally people are storing methane in plastic bags or in a 1psi environment of sorts.

talking with people i've found a properly running digester produces abut 1psi which is enough to run a cook stove with proper jetting.

problem is a fixed sided storage tank has drastically different psi depending on volume you want a soft sided storage tank

that is the part of the design i am on right now.
so far I am thinking of putting a weather balloon inside the propane tank that is hooked to a through wall fitting and piped to the inside of the camper, all that is in the balloon is air
inside the camper is a pvc pipe with a end cap on the bottom and a rod through the center and a plug that rides up and down the rod freely, i figure that as gas is produced it fills up the propane tank and causes the weather balloon to decrease in size forcing the plug to rise up in the pvc pipe contraption in the camper, when im ready to cook i can set a weight depending on what psi the cook stove needs to operate on over the plug
it will pressurize the gas line without use of power!

and presto I have gas flowing to the cook stove.
so all in all i think in my head at least
that I can produce gas and store it all on my camper to run my cook stove, all i need is enough gas per run to boil water.
on the outside it will look just like any other camper with two propane bottles on the tongue.

what do you guys think.

one issue methane becomes explosive i believe when 70% mixed with air. if the weather balloon springs a leak it would introduce air into the system, maybe I should run something else inside the pressure system i've developed?

[Dale M.]

I will be toting the whole system around with me. the digester is an old propane tank. I will be cutting a 4 in hole in the top around the exiting hookups, and welding a 4in diameter pipe to it few inches tall, this will be my feeding tube. I am building a closed system batch load digester.

You ever weld on a propane tank?

Dale

[Grid Runner Adventures]

I havnt but i m having a friend do it who has.

[Rock]

Just talking out my arse here but I see the storage tank as a serious limitation. I think that using a variable size tank with a weight to maintain consistent pressure is a good idea. I just think that it won't hold enough gas at 1 PSI to do much.

I mean the gas effectively won't be compressed at all at 1 PSI, so the volume of the tank is how many cubic feet of gas you'll have. Not to discourage you - it's a very cool concept. You'd just have to look at the BTUs in 1 cubic foot of methane, the BTUs/hour your intended stove burns (at 1 PSI supply) to see how long it will actually run on a tank. Not long enough to boil water for a cup of coffee I bet.

Hopefully you prove me wrong. If so I'm going to look at building one just for fun.

Eric

[bobhenry]

http://www.motherearthnews.com/Renewable-Energy/1973-03-01/Modest-Experiment-in-Methane-Gas-Production.aspx

And ya got somewhere to empty the porta potty !

Pheeewww !

[Grid Runner Adventures]

ya thats where the experimenting comes in at. will be interesting. i was told the stove can operate at .2 psi

[dreadcptflint]

It's so mad max that I want to see it in action. Go for it.

[eamarquardt]

I saw a TV program with the two English blokes who travel around England solving energy issues with "green" solutions. They did a segment on a "poo" (as Mike Rowe calls it) digester. They had a huge storage contraption that floated in a big pool of water. It was a huge production and took a couple of weeks or so to work as I recall (but my memory is sometimes not entirely accurate).

I think you gotta do some more homework, maybe.

I have PERSONALLY welded on a propane tank. I obtained two roughly 25 gallon tanks with rusted bottoms, cut the bottom off of one of them, the top off the other, welded them together to make a big air receiver.

I've heard rumor that propane, diesel, and propane will seep into the pores of the metal, be released with the heat of welding, and go BOOM to the detriment of one's health. Maybe gas and diesel but I find it hard to belive with propane. Two ways to solve the issue. Keep flushing the tank with fresh air while welding so you can't reach a combustable mixture or fill the tank with a non combustable substance as in water, argon, or CO2. Me, I cut the tank open with a saber saw flooding the cut with water and after opening the tanks up let them sit a day or so in the sun just to be safe. Then welded them up with no problem.

I frequent a local recycling yard and often see SS water tanks from solar water heating systems that were sold in the early 80s. Most of the heater was plastic and didn't hold up to the sun/weather but the tanks were as good as new. Maybe you could scrounge around and find some of them.

Cheers,

Gus

[Dale M.]

I saw a TV program with the two English blokes who travel around England solving energy issues with "green" solutions. They did a segment on a "poo" (as Mike Rowe calls it) digester. They had a huge storage contraption that floated in a big pool of water. It was a huge production and took a couple of weeks or so to work as I recall (but my memory is sometimes not entirely accurate).

I think you gotta do some more homework, maybe.

I have PERSONALLY welded on a propane tank. I obtained two roughly 25 gallon tanks with rusted bottoms, cut the bottom off of one of them, the top off the other, welded them together to make a big air receiver.

I've heard rumor that propane, diesel, and propane will seep into the pores of the metal, be released with the heat of welding, and go BOOM to the detriment of one's health. Maybe gas and diesel but I find it hard to belive with propane. Two ways to solve the issue. Keep flushing the tank with fresh air while welding so you can't reach a combustable mixture or fill the tank with a non combustable substance as in water, argon, or CO2. Me, I cut the tank open with a saber saw flooding the cut with water and after opening the tanks up let them sit a day or so in the sun just to be safe. Then welded them up with no problem.

I frequent a local recycling yard and often see SS water tanks from solar water heating systems that were sold in the early 80s. Most of the heater was plastic and didn't hold up to the sun/weather but the tanks were as good as new. Maybe you could scrounge around and find some of them.

Cheers,

Gus

Saw same show on science channel.... The contraption was very large very inefficient and had to may steps to accomplish what they were trying to do.... And they did a lot of things in very awkward ways, but yes it worked....

To have enough volume (of fuel) to heat more than a cup of water I think one is going to need a compressor and a high pressure storage vessel to store enough volume to make it effective.... In the end it I'll bet it takes more energy to run compressor and space for additional storage than the comparable cost of commercial propane.....

Gus also makes my point about welding safety...

Dale

[Grid Runner Adventures]

i think the btu on methane is similar to natural gas?
1 cubic ft of natural gas has 1000btu to it
there are a few cubic feet in a propane tank's volume.
water at 60 degree's 1 gallon-8lbs to reach boiling would take 1200 btu to get to 212 degree's

I wont be boiling a gallon of water any time soon for cooking pastas and such
im not sure but i think it might be able to let me cook some stuff every day.