The Prototype Downdraft Sawdust Carboniser
Elsen Karstad July 3/98
Chardust, Nairobi, Kenya
(Note firebox at base of chimney).
I've yet to weigh the carbonised sawdust, but conversion looks good. The volatiles seem to burn O.K. in the firebox, but not as continuously as I'd like. This should be improved with the controllable secondary air vent
I'm installing tomorrow. This vent can be used as a re-ignition point if necessary as well. Interestingly, weight loss in air/sun drying fresh sawdust was 39%. I doubt very much if it's possible to carbonise fresh material in this kiln.
Indications are that with a bit of practice, over 300 kg sawdust can be
carbonised in this small (120 cm dia. X 1.5 m. deep) kiln within 8 hours.
I doubt if 300 kg of raw sawdust would fit into the chamber- pyrolysis begins with only 15 cm or so at the bottom, and layers of sawdust are added onto the surface at pyrolysis proceeds.
At the end of the shift, the carbonised sawdust is extinguished either by wetting or by transferring to a sealable drum.
I'm leaving a fellow in charge of operating the kiln in my absence ('till the 26th July), and all going according to plan, will scale this up substantially using an earthen pit instead of an metal kiln.
The drying racks for extruded charcoal made from waste powder collected from charcoal vendors in Nairobi.
Mechanical extrusion using a geared electric motor and a modified meat mincer.