Tuesday, April 6, 2010

Welding oil drums to make a biogas digestor

  Our Masai mechanic friend Stephen taught Hanna and me how to arc weld today so that we could create a different kind of biodigester today more suited to local materials and the budget of the Masai (average salary for those employed in tourism is 13 dollars a day). Turns out plastic tanks are prohibitively expensive but discarded oil drums are everywhere. The trick is welding them together to be gas-tight, and it ain't easy!

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Thomas Henry CulhaneWhen I first tried to learn welding in Egypt (arc and torch) the folks showing me were doing it barefoot in the rain. At least here we wear rubber shoes and do it when it is dry! :)
Poverty forces all sorts of compromises -- but they get the job done. So far no burns!

Our new system is based on a sketch in an old FAO manual they used to give to the peace corps, modified to accomodate the new info about kitchen garbage outperforming dung by about 400 times.The problem is lots of micro leaks. We will see if brazing can help tomorrow morning, we will also apply bitumen tar and wrap with rubber inner tube strips.
By the way, we have also been inspecting an adsorption chiller fridge (used to use kerosene) and are videotaping the piping so we can youtube it for you. Still can't see what is going on on the inside, but everyone agrees it could run on biogas. Unforntunately we leave before first flammability. How is your system in Seattle going? Heard from Al? Before I left he was about to flame test but had had no results. Peace core manual predicts over a month particularly in low temps...

Peter Foxon Miller
Watch for UV burns on those fore arms too! I remember getting the worst "Sun burn" of my life on a little exposed patch on my neck after arc welding for a couple of hours. Man did that hurt!
April 7 at 1:06pm · 
Thomas Henry Culhane
Thomas Henry Culhane
Could it be the UV that caused all of our eyes to itch so terribly last night Peter? Me, Hanna and the Masai mechanic Stephen who worked on the project all suffered a sleepless night because of it. Stephen is experienced but the number of hours we had to spend patching holes made it an extreme job. Definitely need better goggles; the shield they had was too dark so we had to keep glancing at our welds.
April 7 at 9:55pm · 
Thomas Henry Culhane
Thomas Henry Culhane
Sybille, we solved the leakage problem by lathering bitumen on the welds, covering them with black electrical tape to smooth out the rough edges and then cutting rings out of old innertubes and stretch fitting them over the tanks where they were joined and lathering more bitumen on. Now we have a functional system. Don't know how long it will hold before leaking, but that is what this research is all about, right? Will be interesting to consult with Dirk when we get back to Germany and he is back from his travels.
April 7 at 9:58pm · 
Peter Foxon Miller
Peter Foxon Miller
I assume UV will affect your cornea and conjuntiva as much, if not more, than your skin. Could also be gases and ash. Iron oxide is pretty harsh stuff. Regarding the leaks, you might try to improve the welds by adding a band of metal (cut from another barrel) on each side I'd the weld, then bridge it with a second weld. Happy travels, and looking forward to seeing you soon!
April 7 at 10:04pm · 
Thomas Henry Culhane
Thomas Henry Culhane
Thanks for the tip Pete! If we build another of these type of oil drum systems in Tanzania next week we will employ your suggestion about the band of metal (assuming they have proper metal cutters, called "snips here; we had to remove the bottoms of the barrels here using hammers and chisels.
Look forward to singing with you at Sanders soon too!
April 7 at 10:09pm ·
Peter Foxon Miller
Peter Foxon Miller
Or... Cut one barrel at the point where it's flared, to increase the amount of overlap at the weld. Thin metal, edge to edge, is one of the hardest welds to do.
April 7 at 10:10pm ·
Thomas Henry Culhane
Thomas Henry Culhane
That's an even better suggestion! Wow! Glad you are online Pete! We've welded flare to flare (or rim to rim), but you are right; if we can find a way to insert a rimless barrel into the other barrel we can weld down... we'll try that. If the barrels don't slide in each other to overlap, might we then put nip and tuck snips into the metal, the way your Mom might sew costume pieces and join them, to get the metal to fit in?
April 7 at 10:14pm · 
Peter Foxon Miller
Peter Foxon Miller
The nips would certainly make a stronger joint, but I think it might make it more challenging to make a water tight joint..
April 7 at 11:24pm · 
Peter Foxon Miller
Peter Foxon Miller
Another thought. If the metal is thin, and it sounds like it is, you can flare an end by hammering the metal (against something hard, think anvil) working your way around. You'll be surprised how quickly you'll gain diameter! You only need to increase the circumference by 1/3.14 of the thickness of the metal. Pi is your friend in this case. Don't forget to protect your ears! Otherwise we'll need to sing in the key of your tinitus next month.
April 7 at 11:33pm · 
Peter Foxon Miller
Peter Foxon Miller
Oops. Got that ratio exactly backwards, but it's still much!
April 8 at 1:01pm · 
Marcel Lenormand
Marcel Lenormand
Seems like quite a mission. How many you sticking together?
April 14 at 10:57pm · 
Thomas Henry Culhane
Thomas Henry Culhane
3 drums, Marcel, based on a couple of sketches in an old Food and Agriculture Manual called "Biogas I and II" that I bought from knowledgepublications.com that we modified to accomodate waste food as the feedstock instead of manure. Our goal is to try and build at least one of every design in the literature so we have a diverse toolkit to deploy in every circumstance.

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