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[welshboy]

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[dhaslam]

Are you using dry cow dung or will the source be from a slatted system?  The drier  the source material  the less space you will need and the better efficiency will be.  If you could source waste from hens it would be better again, up to 60% dry matter. Cattle slurry is about 12% dry matter and produces about 25 cu metres of biogas per tonne  but broiler manure would be two to four times more efficient.  Something like half of the energy  goes heating the dung and there will be additional losses if the dung is not fresh.    The work involved must be quite substantial because you are working in tonnes of fairly unpleasant material. 

[KenB]

List,

I don't think that the cowdung digester would be practical for supplying enough gas for home heating.  Cooking and possibly water heating (to augment solar might just be within its capability).

Have a look at the ARTI design to see just what volume of gas is available per m3 capacity on a daily basis. Remember that many parts of India are at 35 to 40 C ambient temperature - which greatly improves the gas production.

Even with my modest winter gas consumption, I'm still using about 80kwh or 7m3 per day.  If you derate to allow for the CO2 content, it would appear that you would need to be adding 1 tonne of cow slurry every 3 days just to keep up with this demand.

Research in India proved that cow slurry was not the best starting point as an efficient gas generator - afterall, it's had most of it's energy content removed by the cow!   Grass cuttings, over ripe fruit, waste starches, flour and other carbohydrates are a much better feedstock.

Do not underestimate the energy that can flow through a 22mm gas pipe 



Ken

[KenB]

Welshboy,

I had an idea regarding the scaling of the IBC based grass cutting digester - see my other post.

It appears that in the ARTI system the bulk of the volume of the vessel is used for the accumulated gas storage, whilst the actual volume of feedstock and water per day is really quite manageable.

You might wish to look here

http://www.habmigern2003.info/biogas/Baron-digester/Baron-digester.htm

and here is a report on lab experimental grass cutting biogas production.

http://cigr-ejournal.tamu.edu/submissions/volume7/EE%2005%20010%20Maehnert%20final%2020Dec2005.pdf

It suggests that up to 0.86 m3 of gas could be produced per kilo of (assumed dry) grass cuttings.

Starchy materials such as potato peelings and stale bread are good feedstocks.   Contact your greengrocer for damaged fruit?



Ken