Wood Pellets
Wood pellets are made from dry sawdust compressed under high pressure and extruded through a die. They may include a low level of added binder, such as starch, but many use nothing other than steam.
They come in a range of sizes: for domestic and relatively small scale systems 6 or 8 mm is typical, while for larger systems 10 or 12 mm are common.
Wood pellets should be dry, clean, mechanically robust and have an ash content defined by the appropriate standard (see below) to which they have been made, which may also define other contaminants such as chlorine content.
They should also flow freely and can be delivered via a pneumatic system.
Standards Wood pellets
Wood pellets are only as good as the standard to which they are manufactured. Poor quality pellets may display inferior mechanical robustness, and will tend to disintegrate into sawdust more readily than those of better quality. They may also have lower energy density, higher levels of ash or contaminants such as heavy metals, chlorides or sulphur or higher moisture content.
Chippers & Hammer Mills
Some pellet plants start their process by putting large pieces of wood through a chipping machine for processing. These are only necessary for mills that accept this non-uniform feed stock. There are many different configurations to pellet manufacturing plants depending on their raw material source. While they all don't have chippers, almost all of them have a hammer mill at the beginning of their milling process. These machines take sawdust and wood chips and break them down into a consistent smaller size, making drying and pressing through the pellet die quick and consistent.