Because wood will be mixed species, the groups will have to be kept separate as they require different cooking temperatures to make charcoal and will act differently in the silicon furnace.
In CSIRO tests, carbon content is said to range 85-95% (the company says they are aiming for 80-85% fixed carbon), compared to Jarrah 95%. Carbon content should be as high as possible for the silicon plant.
An alternative to timber use is coal. Coal carbon content 45-55%, but needs grinding and washing, and the technology to rebind is not ready yet. If this technology becomes available, coal may replace wood as coal supplies are closer to the Lithgow silicon plant).
The tree species to be harvested as suitable for charcoal making comprise three basic groups that will have to be kept separate to be fed into a retort:-
a) Most preferred – denser red wood – Ironbark, Woollybutt, Bloodwood, Grey Box.
b) Less preferred – Spotted Gum
c) Least preferred – Blackbutt, Silvertop Ash, Stringybarks, Monkey Gum, etc.
They will not use species not taken for sawlogs eg Angophora Costata, Peppermints, etc.
Mature wood is preferred (ie larger, older trees with greater habitat and food resource value for wildlife).