Re: GAS-L: Re: SIMPLE CHARCOAL MAKER...

[AJH <andrew.heggie@dtn.ntl.com>]

Xposted to stoves
On Mon, 16 Sep 2002 09:13:31 +1200, "renertech" <renertech@xtra.co.nz>
wrote:

>Folks,   there s an even simpler method of making charcoal than all those
>pretty pictures. It is called the "Tongan Drum" method. All you need is one
>old drum (Barrel)  with a 9" wide slot cut out of the side, and the full
>length of the drum.   You start with the drum lying on its side and  the
>slot at the  9 O'clock position.   Once you have a  good  fire going  you
>wait till the smoke diminishes before adding more wood and waiting  for that
>too to burn off  the volatiles.
>When the drum is  full of hot charcoal to the edge of the slot  you simply
>roll the drum
>over until the slot is at 11am.  and keep adding wood.   When the slot is
>vertical  and the drum is full of redhot embers, you just roll the drum
>quickly right over,  to p ut the slot at the bottom, and  shovel dirt around
>the edges to block off the air.  And next day you have a full drum of
>charcoal.   Back on the  beautiful island of Tonga , one man could operate
>about 16 of these drums at once to run a complete commercial charcoal
>operation  with supplies of  mangrove wood, supply the BBQ  market with a
>very high quality  charcoal.  Ken Calvert.

Good stuff Ken, this is the boy scout way of making charcoal. It does
scale up really well and then lends itself to mechanical loading, on
this scale I refer to it as the modified pit method (I have used both
ring kilns and a 3000 litre tank) and the output per man can be
amazing (I think I estimated 2 tonne in 3 hrs on an attempt 3 years
ago). On the large scale cooling becomes a big issue.

It works well with dryish material of small cross section. I believe
this is because the only feedback path to maintain pyrolysis
temperatures is radiative from the flame and thence conductive through
the wood. It is similar to adding fresh would to an idd stove in char
making mode. The pyrolysis has to complete at the same rate as the
flare.

There is nothing new in the technique it is described in Evelyn's
sylva c1760. He suggests digging a pit and lighting a fire in it, then
throwing in bavins (loose bundles of coppice material) until each
succeeding layer is carbonised, when full the pit is covered and
allowed to cool for many days. A similar technique was exported to
Africa, here a btd6 sized dozer would carve out the pit and then cover
it at end of burn.

If the flare is clean then this may not have a lot of pollution,
however the fact remains that 70% of the available energy in the wood
is lost to entropy heaven.

AJH

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