To reduce the size of wood chips and other suitably sized biomass raw materials to the correct particle size, a hammer mills is used. A hammer mill works on the principle of attrition. A rotating centre with a collection of flailing hammers impact at high speeds, shattering the material into particles. A screen with the desired particle size ensures the correct particle size is produced.
Post Particle Size Reduction and Cyclone Separation
Once particle size reduction has taken place, a fan is used to extract the particles from the based of the hammer mill. However the particles are now mixed in the air stream, and need to be separated. To separate the particles from the air stream, a cyclone separator is used.
The cyclone has a vertical position, and the air stream and particles are injected into the top of the cyclone. The gas stream, due to the shape of the cyclone is sent into a spiral. During the spiral action, the particles are separated from the air stream and leave the based of the cyclone. The separated air then leaves the cyclone through a central pipe through the top. The particles are now a suitable size for briquette or pellet compression, depending they have a suitable moisture content of around 12% for briquette compression, and 15% for the pellet mill.