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One example of making charcoal from crop residue is https://practicalaction.org/fuel-from-the-fields-charcoal-from-agricultural-waste which is based on work done in Haiti by D-Lab based at MIT. It is a very simple approach using an old oil drum as a kiln.
One example of briquetting sawdust with a binding agent in Malaysia first carbonised the sawdust
then uses starch as a binder. The starch paste is made in a separate cooking tank.
Charcoal = 73%
Starch
= 5%
Calcium carbonate = 2%
Water = 20%.
These charcoal briquettes can be made with a
low-pressure mould.
There is some research by Chardust Ltd, based in Kenya, into making charcoal briquettes from various crop wastes including sisal waste. One report concluded that carbonising sisal was technically quite difficult in respect to regulating the temperature resulting in non-homogenous carbonisation but once the sisal waste had been carbonised it was relatively easy to produce briquettes. These were made by producing a paste of carbon dust and water which is then combined with 15% clay.
Experience in Gambia and elsewhere has shown that residue and charcoal briquettes may not burn well in existing stoves (see Boiling Point special Edition on Briquettes 1989/90).
Most waste materials can be burnt directly without being briquetted beforehand. Sawdust stoves and rice husk stoves are relatively common; see the Stoves for Rice Husk and Other Fine Residues technical brief. https://practicalaction.org/stoves-for-rice-husk-and-other-fine-residues