[Stoves] RE Drying of wood

[Richard Stanley]

Crisin,
Ref the biodigester and heat loss,

You say that he had a "massive digester only 1.5 meters deep...  
Optimum is to minimalise the surface area to volume ratio, defaulting  
to deeper, rather than larger diameter--if in ground heat retention  
is your concern. The last thing I should think, is that you want is a  
large top surface exposure to air as this is where most of the heat  
will go.
Richard Stanley

On Jan 8, 2007, at 08:06, Crispin Pemberton-Pigott wrote:

> 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
>
>
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