[Stoves] Biochar retort
crispinpigott at gmail.com
Tue Oct 29 20:03:41 MDT 2013
All things considered, I think I would prefer a retort like the ones made by
Chris Adam. The reason is that the fuel does not burn will in the first
place and because of the dense packing, it will be difficult to properly
supply at least a little air to the centre of the bundle.
The retorts work by sealing the material into a metal or concrete shell and
heating the metal bottom with some other fuel (anything). Once the gas
production is going well, the gases are ignited in the same flame as the
external fire. Then it becomes a self-heating retort. There are industrial
versions of this with multiple retorts but the system works fine with a
Because the bales will stack very tightly, it is worth making the kiln to
suit the fuel size. It needs to be very air tight to prevent any burning
inside. It is only heated by exothermic reactions started off and supported
by heating the plate under one end (or the whole thing depending on how you
construct it). The method produces very little smoke and you can in theory
fire bricks or something with the excess heat.
If I were trying to char bales of straw I would start with a kiln that
tumbles, like an industrial dryer.
If you tumbled the bales in a cage the straw would fall out to the bottom of
the kiln as it chars.
I charred a square bale (actually rectangular) of wheat straw in my barbecue
cooker once. I replaced the bale strings with wire and the whole bale cooked
to char and stayed together. It stunk up the place.
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