Production stages of biomass pellets. Part 1: For treatment of biomass

The pellets (pellets) are produced from raw material of wood-products industries (eg sawmills), residues from logging and special sustainable short rotation forestry crops. Furthermore, there is the possibility of producing agropellets derived from agricultural residues (e.g., straw) or pruning crops. The agropellets disadvantage as to the pellets of wood due to the significantly higher ash content.
There are 7 different stages in the production process of biomass pellets:

1) Storage of raw materials
2) Purification of raw materials from impurities Pretreatment
3) Drying biomass Biomass
4) Grinding-cutting biomass
5) Pelletisation
6) Cooling and sifting of pellets Production
7) Storage of pellets Pellets

Storage of raw materials
A good system of storage of raw materials necessary for maintaining the biomass from impurities and to protect from rain, which can increase the humidity to such a degree that it is unprofitable drying (and hence the use of in the production process). The automated supply of raw material from storage to production site (eg via a conveyor belt or screw) is often preferred for the reduction of labor costs.

Cleaning of raw materials from impurities
ΤThis stage is essential in particular when used or recycled raw wood (eg pallets) as feedstock. So many units use sorting mechanisms timber of inert material such as stones or magnetic separators to capture metal objects such as nails and tacks. The presence of even the slightest quantity of such impurities in the final product is unacceptable while they can cause serious damage to the equipment of the production process, e.g. the hammer mill and press.

Drying biomass
The majority of the materials used for the production of pellets requires drying to produce a satisfactory product quality. Only a few materials collected dry as straw, can bypass this stage of the production process. Drying of the biomass at a level between 10 and 15% is necessary. Dryers biomass used are for the most part type rotatable drum (drum dryers), although there are several reports on belt dryers (belt dryers). The fuel used for drying the biomass is either natural gas or part of the same biomass, the second option is preferred for environmental, technical and economic reasons. Note that this step is the most energy intensive production process and contribute to the fullest extent the operating costs of the unit. Consequently, the majority of research efforts and innovations in production of pellets located in the successful drying of the feedstock.

Cutting-Grinding biomass
Before the introduction of the press pelletisation is necessary biomass have acquired the appropriate homogeneity and grain size. These characteristics are achieved by using different kinds of cutting machines and grinding the raw material, such as hammer mills. The size of shredded biomass to be introduced in the press is not random: the particles must not be large enough to be able to enter through the holes of the mold punch. On the other hand, however, if very fine-grained material is less than the conversion efficiency of biomass into pellets as it is more difficult to agglomeration.