Methane Digester Experiments
Experiment by Tony T (from WoodGas)
A small methane digester that we ran off of chicken manure. It was a very small digester built out of a one gallon pickle jar (glass). As a storage device I used a 12 inch bicycle inner tube.
The fist couple of days the digester is getting rid of the air in the digester and producing CO2, alot of it. After about 3 days CO2 production stops as the bacteria deplete the oxygen and die. After a lull of a couple of days the anaerobic bacteria kick in and start producing methane. I have allowed the system to fill my storage device with CO2 and then I empty it every day (and squeeze out every bit of CO2 by rolling the tube up). By the time it produces methane there is only a very tiny bit of CO2 left in the tube. As I burned the gas for the first few days the fuel quality starts to come up as the rest of the CO2 is "flushed" out of the system with the gas.
This little inner tube would hold enough gas to run my 8hp lawn tractor for about 7 minutes at full throttle. I would hold the tube and squeeze it with my hand to keep the pressure up.
I know that during WWII they would use gas bags and apply a weight to it to keep the pressure up so I assume we can do this with other gases. The only reason I see for compressing the gas is to put more in less space and get longer run times which is more practical than a gas bag/inner tube. If you need a quick easy way to store gas the bag/inner tube would work (IMHO).
The manure I used was just scooped up from the bottom of my chicken house. The litter would get packed down and mixed with all the manure, I'd just clean out the house and use whatever I scooped up. I would fill the gallon jar about a quarter of the way up with manure/litter and add enough water to make a thin slurry --- that's it. I'm sorry I really didn't messure anything I just guessed and mixed it until it looked right.
I'd bring the digester into the utility closet where my water heater sits because it's warmer in there than anywhere else in my house (somewhere around 75 to 80 degrees). By the next morning the inner tube would be filled with CO2 to the point where it was about to pop. I would take the unit outside and open the valve to relieve the pressure. I'd sqeeze the tube until all the gas was out and then close the valve and put it back into the closet, I repeated this everyday. After 4 or 5 days it would stop making any kind of gas and it would sit there for a couple of days.
Slowly the tube would start to fill again and it would take a few days to fill the tube with gas (methane and CO2) very weak gas. I had a little burner I made out of copper tubing and steel wool so I'd take the unit outside and try to light the gas. It would make a flame and go out several times then it would make a very tiny flame for a few minutes. The quality of gas would get much better over the next couple of days and the volume would come up also. The inner tube would start filling up once a day for a month or so and then it would slack off and stop. You could shake the jar a bit to mix the slurry and it would make a little more gas and then die yet again.
