For the manufacture of wood fuel pellets, as a rule, the following production processes are required.
1) Primary treatment of wood waste. In order to process wood waste into pellets, certain requirements must be met. For example, the product must have a certain particle-size composition and humidity of 11-14%. Wood waste that does not meet these requirements must be subjected to primary treatment. For example, large pieces of wood should be fined and additionally dried with insufficient humidity. Then the chips and sawdust are crushed in a hammermill to obtain a homogeneous structure.
2) Air conditioning. During conditioning, steam and/or water must be inserted into the wood waste that has undergone primary treatment. As a result, the binding properties of the lignin contained in the wood are improved. During crushing in a hammermill, the adhesion forces in a wood fuel pellet can be significantly increased if lignin decomposition has already occurred in the raw material due to long-term storage.
3) Press. The process of pressing wood waste takes place in the so-called matrix molding presses. They can have a circular or a flat construction. At the same time, steel rolls push the product through the holes of the matrix. The resulting cylindrical bundles are cut off to the required length.
4) Cooling. After pressing, the pellets are soft, moist and very hot (as a rule, their temperature is 90-120 ° C). In order to transport and store wood fuel pellets, they need to be cooled and dried. During cooling, heat and moisture leave the pellets. When the temperature decreases, the wood fuel pellets are stabilized and become solid.
5) Screening. The separation of the fine fraction is carried out by screening the cooled pellets. The remains are fed back into the plant for the production of wood fuel pellets.