[Stoves] RE Drying of wood

[Crispin Pemberton-Pigott]

Dear AD

One of informed compliments we received at the Transkei Appropriate 
Technology Unit was for the fact that we didn't have a biogas digester.  It 
is so cold there in winter, actually for about 4 or 5 months of the year, 
they they are very unproductive, they get sick, they need love and attention 
and daily care.

There was a farmer even higher up in the MacLear area who had a massive 
digester only 1.5 metres deep fuelled with pig manure. He ran 12" diameter 
steel pipes horizontally through the mash and burned a fair portion of the 
gas inside them to heat the whole thing.

I believe he produces 1/10th of a cubic metre of gas per square meter of 
digester per day, something like that. It was on the verge of being 
pointless.

He could easily have dried the dung in that clear Maluti Mountain air and 
burned it with a fan-assisted boiled.

Regards
Crispin

PS Many people don't know that the normal biogas digester was invented by a 
(different) South African farmer.

----- Original Message ----- 
Sent: Saturday, January 06, 2007 10:36 AM
Subject: [Stoves] Drying of wood


This topic reminded me of a discussion that I participated in last year in
Germany. I had suggested  that dung should be burned directly instead of
converting it into methane, because one loses more than 75 percent of the
total energy in the dung during the process of producing methane. Drying
dung is not a problem in India, one just spreads out the dung cakes on the
ground and the sun dries them. I was therefore quite surprised when my
counterparts in Germany pointed out to me that they would have to spend a
lot of energy just to get the dung sufficiently dry for direct combustion,
and that they therefore prefered to convert the dung into methane. However,
I found out later, that even the biogas fermenters have to be heated in
Northern Europe, because the methanogenic bacteria do not work well if the
temperature is lower than about 30 degrees Celsius. It seems that our hot
climate, though uncomfortable to humans who have to work in such weather, is
not always a disadvantage.
Yours
A.D.Karve