[Terrapreta] Economics of biochar

[andrew]

On Monday 31 December 2007 13:08, andrew wrote:
> I have collected a sample by
> scraping and 3kg wet has reduced to kg air dry, I'll carbonise
> this and then ash it just to see what the energy balances look
> like with inevitable soil contamination.

I mistyped that, the sample oven dried to 1.5kg but there was a lot 
of soil as fines. I've just attempted a simple top down charring 
experiment with the 3kg and though it started well it soon went bad. 
I've had this result before and the appearance of a blue smoke from 
the flare, which normally runs very clean, normally means that 
somewhere in the middle of the column the flame front has changed 
from a steady downward pyrolysis from to simple updraught 
combustion. It often happens is a sample where a burning piece is 
able to drop down through the unburnt material. I've quenched the 
experiment and will try again with a simple retort method.

I'm still fairly optimistic that the energy available is enough to 
cope with the contamination even when harvested in a wet period.

AJH