Woodchips are small to medium sized pieces of wood formed by cutting or chipping larger pieces of wood such as trees, branches, logging residues, stumps, roots, and wood waste.
Woodchips may be used as a biomass solid fuel and are raw material for producing wood pulp. They may also be used as an organic mulch in gardening, landscaping, restoration ecology, bioreactors for denitrification and as a substrate for mushroom cultivation.
The process of making woodchips is called wood chipping and is done using a wood chipper. The types of woodchips formed following chipping is dependent on the type of wood chipper used and the material from which they are made. Woodchip varieties include: forest chips (from forested areas), wood residue chips (from untreated wood residues, recycled wood and off-cuts), sawing residue chips (from sawmill residues), and short rotation forestry chips (from energy crops.)
Types of wood chippers
Disk: a disk wood chipper features a flywheel made of steel and chopping blades with slotted disks. The blades slice through the wood as the material is fed through the chute. Knives located in the throat of the chipper cuts the wood in the opposite direction. The design is not as energy efficient as other styles but produces consistent shapes and sizes of woodchips.
Drum: a drum wood chipper has a rotating parallel-sided drum attached to the engine with reinforced steel blades attached in a horizontal direction. Wood is drawn into the chute by gravity and the rotation of the drum where it is broken up by the steel blades. The drum type is noisy and creates large uneven chips but are more energy efficient than the disk type.
Screw-type: a screw-type wood chipper contains a conical, screw-shaped blade. The blade rotation is set parallel to the opening so wood is pulled into the chipper by the spiral motion. Screw-type, also called high-torque rollers, are popular for residential use due to being quiet, easy to use and safer than disk and drum types.
Waste and emissions
Automated handling of solid fuel
Micro combined heat and power
Comparison to other fuels