Thursday, September 10, 2009
Running a small engine on household biogas (Biogas untuk limbah dapur) using "bricking' for gas pressure
A hearty thanks to British engineer Marcel Lenormand for prodding us to finish a project a long time overdue with a well timed blog comment: "Does 'bricking' the digester's floating dome produce insufficient pressure to feed the engine?".
We'd wondered the same thing but since we hadn't built a cage to hold the floating dome in place we couldn't test our intuition that the simple act of "bricking" would actually work because every time we put bricks on the gas filled dome it would tip over.
In India we had observed that some of the ARTI Urban Biogas systems families had built had various "cages" to keep the dome level as it fills but, swamped as we've been, we hadn't put in the time, effort or money to complete our own digester. Like many of the urban poor we engage in what the literature calls "Incremental Housing" and "bricolage" (putting things together in a hodge podge fashion using whatever materials are available or lying around).
But the day after we had done our first engine conversion trial and met with success using a hand-drill water pump for pressure we got so excited to see if mere "brickage" with the "bricolage" would do the trick we ran off to Bauhaus and bought the cheapest materials we could think of to make a cage to enable us to allow us to experiment with "bricking" -- a bunch of plastic plumbing pipes, elbows and fittings. Still it wasn't cheap -- 35 Euro for everything (this explains why so few people bother -- bricking isn't necessary for using the gas for cooking so the extra expense isn't needed if you aren't running a generator).
The results shown in the video above prove that 4 3.5 Kg bricks (so 14 kg) is enough to keep the generator going when the pressure regulator primer is depressed (this indicates that without the regulator it would work just fine at that pressure), while the addition of two more 4.5 kg bricks, bringing our total to 23 kg (about the max weight of a full suitcase on an airline) provided enough pressure to keep the engine running and producing electricity with the regulator attached without keeping the primer depressed.
We could adjust the regulator to allow more gas in under the 14 kg pressure but for now we want to keep it set the way it came from http://www.propane-generators.com/a-c_kits.htm so that if we need to use a standard CNG bottle we can. The idea is to be able to use our biogas when we have it but also be able to run the household using the most climate friendly fuels available on the days when sunshine is not enough here in cloudy Germany.
(A note to our critics and to fossil fuel and nuclear industry shills and lobbyists: we concede that home-made biogas electricity generation and cooking fuel from garbage , do-it-yourself solar hot water, and self-wired PV systems may not be "economical". Thus we will try to build our own backyard nuclear power plant, rooftop oil refinery and basement coal gasifier next and see how they pencil out. We hear Ahmadinejad has some extra centrifuges; anybody got the other feedstocks?)