Methane Biodigestor Experiences

by Mike Anderson
(Taranaki, N.Z.)

Hi Folks, I have been researching these Methane bio-digestors and playing around here on our little life style block in NZ (6 Acres). We run three horses which my wife Ingrid shows, events and trains in dressage equestrian discipline. We pick up the pooh off the pasture everyday and have copius quantaties of the stuff which we need to do "something" with. Trying our best to be organic as possible we have moved to Seaweed based pasture fertilizer, water based lime products and low endophitic pasture grasses. Further to that we hard feed to provide all the supplements an Equine athlete needs consequently the pooh is very rich. We have been collecting the pooh in a worm farm and use the vermicast to spread back on the pasture.

The big one was to make methane enough to
a. run the BBQ then
b. run the tractor.
OK first we had to mix the pooh with water in a concrete mixer to get a slurry.
Next we poured it into a 200litre drum with a 150mm pipe suspended about 120mm from the bottom of the drum and filled it to about 80%.
Off the top a clear plastic 13mm tube was fitted and sealed which was directed to the second 200litre drum which was about 40% filled with water and was elevated so the top of the fluid in the first drum equaled the top of the fluid in the second drum.
We found a Sulpher scrubber was required otherwise the methane burnt very smelly and toxic (this was simply a small disposable tube - 40mm pipe - filled with steel wool, sealed and in line with the tube).
What was on top of the second drum was cleanish methane.
To pressurize we added another drum with about 25% water in it again elevated which became pressurized with methane after about 22 days.
The test allowed enough gas to run the BBQ for about 5 meals and the gas was a bit smelly.
This was a batch Methane bio digestor.
Lessons learnt:
A. Seal everything up double tight - no losses = higher output.
B. You can do it but in this case the input did not equal the output.
C. BioD Methane is smelly to burn - too bad for the BBQer's.
D. Small batch bio methane units are a poor substitute for whipping down the road and buying LPG for $20/9kg and BBQing for months on it.

Comment: The true use of BioD Methane must be in generating electricity for clean power use away from smelly source material and process.
So the next trial is using a 10,000litre tank with two linings and an expanding rubberized gas collector with a pressure pump filling cylinders to be installed on a diesel generator with new injectors for Diesel start and Methane change over injection regulator.
There is a group in Auckland called EN Technologies who specialize in Bio-digestor Methane / diesel generator conversions.
Catch you later with that test results and more.
All the best
Mike Anderson
Alternative Energy Systems & White Light Electrical
Taranaki
New Zealand

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