[permaculture] More on BIOGAS for household use. Attn: Jenny

Lawrence F. London, Jr. venaurafarm at bellsouth.net
Sun Feb 7 13:27:11 EST 2010

David wrote:

 > On 2/5/2010 7:27 PM, Lawrence F. London, Jr. wrote:

> This is about fuel for cooking and heating water in Haiti as part of 
> relief projects helping to normalize the lives of the people there....
> I think the humanure/methane conversion units could be quickly built 
> in an array of sites covering the country.
> 1) modified porta-potties on a large platform covering
> 2) a large humanure collection/digestion tank(s) (drop from toilet 
> directly into tank(s)) just like an outhouse, into a pit
> 3) gas collection apparatus/filtration unit/pump would be able to fill 
> pressurized cylinders for distribution to households...
> Invent a gas burning "rocket stove" that can burn butane, propane 
> (kinda nasty fumes) and methane. 

With regard to biogas, you should note that without supplementing with
food or other material, the wastes from one person will not generate
enough biogas to cook their own meals. This is because the feces and
urine from one person will, on average, produce one cubic foot of biogas
per day, which in turn is enough to run a one burner stove for about 10
minutes. (On my stove, it takes 12-15 minutes to heat enough water for
three large cups of coffee, and cooking rice takes about 40-50 minutes.)

That means, in essence, that a community toilet facility which connects
to a digester-- again, without supplementation with other wastes-- will
most certainly not produce enough biogas to support pressurization of
cylinders to distribute to anything except a small fraction of those who
"contribute". (And it will take a good deal of the energy from the
biogas to run the pump.) Further, it is wasteful to compress raw biogas,
since it's about half carbon dioxide, and it is functionally impossible
to liquefy it using low-cost pumps.

Again, though, where food or other digestible wastes are added to such a
digester, then it could produce more (and perhaps far more) biogas.

You should also know that anaerobic digestion will not destroy some of
the more persistent pathogens until the wastes have been allowed to
remain anaerobic for 6 or more months. Where fresh material is mixed in,
the clock must be restarted. Thus a community wastes digester must deal
both with the issue of what to do with the effluent, and how to insure
it is safe.

Propane, on burning, does /not/ produce fumes that are any nastier or
more dangerous than butane or methane. And finally, butane, methane and
propane all require different-sized holes in the burner, so that one
stove cannot be designed to efficiently burn any of the three. The issue
of designing efficient stoves is indeed very important, but it has as
much to do with the design of the pots that go on the stove as it does
the stove itself. Quite good biogas stoves have been designed and are
being sold, but I am not aware of any that have taken the step of
designing pots that contribute to the capture of the heat produced.

David William House
"The Complete Biogas Handbook" |www.completebiogas.com|
/Vahid Biogas/, an alternative energy consultancy |www.vahidbiogas.com

"Make no search for water.       But find thirst,
And water from the very ground will burst."
(Rumi, a Persian mystic poet, quoted in /Delight of Hearts/, p. 77)


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