Wood chips Drying: Equipment Selection

Wood chips are the same material as sawdust in a different form: at the front of the line they are flakes or chips, and at the back the job is to have them as a granular sawdust, so the drying requirement changes from drying the whole piece to drying the surface enough to be milled. That difference decides the machine: chips hold a lot of water and are barely permeable, so the surface has to be dry enough to be milled first, and after milling the material has to be dried again to take the water out properly. Our approach is to string the milling and the drying together, with the two steps buffering each other.

Wood chips are the same material as sawdust in a different form: at the front of the line they are flakes or chips, and at the back the job is to have them as a granular sawdust, so the drying requirement changes from drying the whole piece to drying the surface enough to be milled. That difference decides the machine: chips hold a lot of water and are barely permeable, so the surface has to be dry enough to be milled first, and after milling the material has to be dried again to take the water out properly. Our approach is to string the milling and the drying together, with the dryer feeding the mill directly, or the mill feeding the dryer, so the two steps buffer each other and a blockage in one does not stop the other. The rotary route has a second advantage here: the lift height the flights create stays within a controllable range, so the chips are not shattered and the fibre length is preserved, which gives a more uniform product after milling. Biomass is the main heat source here as well, and the ash must be settled separately and kept out of the drum.

How should milling and drying be arranged?
Both orders work, and the point is to let them buffer each other: the dryer feeding the mill directly, or the mill feeding the dryer. Then a blockage in one stage does not stop the other. Where there is a flake stage upstream, the material usually has to be dried enough to be milled first and then dried again after milling to take the water out properly.

Does the flight pattern affect the fibre length of wood chips?
It does. The advantage of the rotary route is that the lift height the flights create stays within a controllable range, so the chips are not shattered and the fibre length is preserved, which gives a more uniform product after milling. Flights that lift too high and drop too far break the fibre more than it needs to be broken.

How is the heat source chosen for wood chips?
Biomass is the natural choice, with fuel easy to get and a low cost per tonne of water. But as with sawdust, the ash has to be settled separately and kept out of the drum, because ash in the wood chips contaminates the product.