[Terrapreta] medium-size charcoal making - the tools?

[andrew]

On Saturday 22 December 2007 21:45, Gerald Van Koeverden wrote:
> Is there any open-source do-it-
> yourself technology  that is ready to be made and used locally by
>   communities on the medium level scale?

This all depends on what your resource is and how much it costs. If 
you are going to add the char to the soil then soil contamination is 
not an issue. You note that offgas can be polluting and the most 
straightforward way to do this is to flare it, effectively losing 
half the energy in the wood. Flaring is easy if the biomass is dry.

I've successfully made a lot of char in a short period (8m3 bulk in 
2hrs using a mechanical loader) in UK using forest waste (lop and 
top) using both a ring kiln and a simple pit. The technique was used 
in Tudor times but is quite wasteful compared with traditional 
methods.

Firstly the resource needs to be small diameter and having dried out 
substantially. Waste from a hardwood thinning is <50mm diameter and 
if winter felled in UK is dry enough by mid May.

Find a container or dig a trench wide enough for your needs and long 
enough for the branches. Build a small fire at the bottom and slowly 
add small branches whilst maintaining a good flame. Keep adding 
branches such that there is always sufficient offgas to flare and 
prevent any oxygen getting to the pyrolysing wood. If you can see 
white surface on the sticks then the char has started to oxidise and 
either the wood is not dry enough or you have not added enough. 
Heavy smoke indicates too much wood or too much moisture.

Once the trench has filled with char and the flare is dying cover the 
trench and seal with earth and consider dowsing it with water.

AJH