South Africa: Create Biochar with a Trans-Portable Kiln Method
Vuthisa Technologies in South Africa have been working on improving the Portable Metal Kiln Charcoal Making Method and using a retort design to reduce emissions and improve efficiency making charcoal.
They have a great description with lots of detail on their web site: http://vuthisa.com/biochar/
as well as a Google Group:
In short the system is composted of an outer drum, often fabricated of sheet steel enclosing an inner set of 30 gallon drums.
To produce biochar, the Trans-Portable Biochar Kiln can be constructed from either one and a half (Smaller unit) or two (Larger unit) standard (2.350 x 1.225 metres) mild steel sheets. In the case of the larger unit, each sheet is cut in half to produce 2 sheets measuring 1.175 metre (L) x 1.225 metre (H). Sixteen holes are laser cut in both ends, then ‘cold rolled’ to a preset radius. The ends (35 mm) are then bent outward (± 90°) with a bending machine at the required angle to make the ‘flanges’. When all 4 sheets are brought together the kiln diameter should be 1.406 metres.
They've found that closed drum system with slightly thicker gauge steel has resulted in dramatically reduced emissions, and longer retort life.
Plans for their 3 barreled retort can be purchase from: http://vuthisa.com/biochar/portable-kiln-order-page/
( Vuthisa is a Zulu word meaning "to set on fire".)