No matter what kind of raw material you intend to use to make biomass pellets, you need to pulverize them into uniform powder size. One vital principle you need to keep in mind is that the size of raw material particle should be smaller than the hole of the pellet mill die. There are different kinds of pulverizing equipments designed to process with materials with different characteristics. Sometimes you just need one machines, but sometimes it may require two machines.
Chipper and shredder are applicable for dealing with the raw material with large diameter such as logs, branches and other biomass waste with a diameter over 1 inch.
Chippers: The conventional chipper is a rotating disk with several blades attached to the surface. As the material comes into the chipper, the blades on the disk will keep shaving off the large bulk of raw material into small sections until they become powder.
Shredders: Shredders push the material against a rotating roller with teeth. The teeth eat into the material and drag it against a screen. The size of the holes in the screen decides the particle size.
Hammer mill is recommended to further grind the raw material with the diameter smaller than 1 inch such as wood chip, wheat straw and grass. Hammer is comprised of many small flailing blades which is used to reduce the raw material finely. The pulverized particle has a size ranges from 1mm to over 10mm after getting through the small hole in the screen. Hammer mill can produce the particle with different size, so it is widely used in the large pellet mill plant.