Grinding unit is the second largest electricity consumer in pellet production (pel­let mill is the maximum electricity consumer) [34]. The whole process of pellet production is divided into: raw material, general investment, drying, grinding, pel­letization, cooling, storage, peripheral equipment, and personnel. If the raw material is wet, grinding cost is 3 % of the whole cost, and if the raw material is dry, the grinding cost is 2 % of the whole cost. It should be considered that sawdust is the base raw material [34]. A hammer mill cost ranges between 62,000 € (with a ca­pacity of about 2.5-3 t (d. b.)/h) and 168,000 € (two large hammer mills with a total capacity of about 9 t(d. b.)/h) depending on the plant size and the equipment used. The maintenance cost is 18 % of the investment costs per year. Scale of operation can impact overall costs, for example the overall cost of pellet production is lower in Sweden because of their larger capacity plants and lower electricity price.

One step of grinding is sufficient for material preparation for the traditional pellet production using sawdust and shaving as feedstock. When the feedstock sources change from sawdust and shaving to other mill residues (e. g., logging residues, thinning materials, agricultural residues, and short rotational trees), two or more steps of size reduction is needed to prepare the material for pelletization. Two stages of size reduction using a coarse grinder and a hammer mill were used for the pellet production of short rotation trees [35].