Due to the different characteristics of various raw materials, the pellet quality is unequal. To improve the pellet quality or maximize production capacity, you can add binder to help the lignin-lacked material to compress into pellets much easier.
Whether producing a single material pellet or a mixed material pellet, material consistency is crucial to efficient pelletization. Batch mixers are used after the material has been milled and dried (if required). Through mixing the material, a more consistent material blend is fed into the pellet mill . Mixing may occur before or after conditioning.
Inconsistent material: Inconsistent material could be due to significant changes in moisture content, sections of material with poor binding properties and changes in material density. All of these factors affect the pellet mill’s ability to create quality pellets.
The pellet mill has certain tolerances with regards to a maximum and minimum percentage of moisture to create a pellet. The maximum and minimum tolerances are not the same for every material. When the material moisture percentage goes above or below the pellet mill’s abilities this will either lead to the pellets not forming, to poor quality pellets or, worst case scenario, blockage of the pellet mill die.
Consistent material: Sourcing material, which is consistent throughout the batch, or mixing the material to create consistent quality, is crucial for pellet production. If the material’s moisture content consistently falls within the mill’s pelleting capabilities the result is more successful pellet production, with higher quality pellets and less blockage.
Not all materials require mixing; some materials may already have consistent quality. Other materials have a low density and bind well due to their oily characteristics—for instance, rape cake. To increase consistency, mixing equipment is available for small-scale production. For large-scale operations, there are industrial rolling drums and agitators.
Binders for agricultural materials
The binding properties of warm season grasses or oat hull pellets are often weak because of the low protein and starch content of the biomass. Some binding agents that can improve binding and durability include corn stalks and wheat bran.
Production of switchgrass and oat hull pellets without binders can be successfully achieved but requires several basic conditions to achieve high density and high durability pellets. Binders are typically not needed for the pelletization of wood sawdust.