Re: DIG-L: Residential digester

[Paul Harris <Paul.Harris@adelaide.edu.au>]

G'day Dave,

Welcome to the list! 

Remember there are no ridiculous (or stupid) questions, just dumb
mistakes made by people who did not know enough to ask questions! Also
it is MUCH easier to answer a stupid question than fix a dumb mistake!

Try the "Beginners Tour of Biogas",
http://www.roseworthy.adelaide.edu.au/~pharris/biogas/beginners.html for
some basic information.

Your idea is wonderful - it is done in many places like Columbia,
Vietnam, India, China, Nepal and Cambodia to name a few. A poly digester
is a good, cheap way to start but the idea can be made with more robust
materials if needed.

I am attaching an Excel spreadsheet to help you with your size
calculations (it is mentioned in the "Beginners Tour").

May I make a few suggestions? 

You will see from the model that you actually get more methane from the
longer retention times needed at lower temperatures because of the
larger digester volume needed, but I am fairly sure the Total Cost of
Ownership will be less as you have a bigger tank to buy but no
heating/stirring equipment to buy or maintain. The longer retention
times also mean you can go to longer intervals between feeding the
digester - you need a dynamic model to check that, a bit more difficult.

It would also be better if each dairy had a group of houses it supplied
directly to avoid double handling of manure. A possible setup would be a
contractor who visited the dairy (or dairies if necessary) each day and
collected the manure, which he then delivered to the households. During
delivery he would mix the slurry, collect the outflow and check the
digester. A contractor would have enough runs to give him a full time
job (or at least the income that he/she wanted), may be 5 runs for once
a week feeding so you only need one digester per house. The digested
effluent could then be delivered to a user who would also pay for the
fertiliser, so the contracor may be paid by the dairy operator, the
households and the end user.

Good luck with your project, let us know how you get on,
HOOROO

JDAVIDERICKSON@cs.com wrote:
> 
> Hello,
> I am new to the list and new to biogas, so forgive me if I ask
> ridiculous questions!
> 
> I live in an agricultural area (Sonoma County, CA, USA), and became
> interested in the potential for harvesting methane from livestock
> waste from the many dairies in the area.
> 
> Although biogas plants have been built on dairies to generate
> electricity, I was curious about the potential to use biogas as a
> natural gas or liquid propane replacement for residential cooking and
> heating use.
> 
> The question for the list I had was this:
> Suppose one could build a low cost digester that would have enough
> capacity to generate sufficient biogas for cooking and heating for a
> typical residential household, using livestock manure slurry.  (I'm
> sure it's possible to easily calculate the required digester capacity,
> but I don't have the background to know how. Could someone point me to
> a reference on how to do this?)
> 
> I'm envisioning possibly a fiberglass digester tank with a motorized
> stirring system driven by a small photovoltaic array. The biogas would
> be used to heat the digester, so the whole thing could be completely
> self-contained, once it was up and running. It would have two chambers
> to allow continuous gas production. The digester could be buried and
> connected to the house's gas line.
> 
> The livestock waste from the dairies would be collected at a central
> point, where it would be turned into slurry, and stored  in tanks.
> Tank trucks would then take the slurry around to the residential
> digesters and charge them on an as-needed basis. The trucks could also
> collect the digested effluent.
> 
> Is a scheme like this totally far-fetched? Does it seem
> practical/economical? Is anyone doing anything like this?
> 
> Thank you for any input.
> 
> Dave Erickson

-- 
Mr. Paul Harris
Faculty of Sciences
The  University of Adelaide, Roseworthy Campus, AUSTRALIA 5371
Ph    : +61 8 8303 7880
Fax   : +61 8 8303 7979
mailto:paul.harris@adelaide.edu.au
http://www.roseworthy.adelaide.edu.au/~pharris

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