Short rotation woody crops and forest biomass sawdust mixture pellet quality

Abstract

Global pellet production has been growing steadily, and it was higher in 2021 by approximately 6.8% compared with 2020, with EU production increasing by 9%. In consequence, the demand for sawdust is growing while its availability is increasingly limited, and the prices are increasing. This is why woody biomass from short-rotation woody crops (SRWC) may have to be used to satisfy the demand for this raw material. Therefore, the aim of this study was to determine the thermophysical properties and elemental composition of pellets produced from forest wood (pine, birch) sawdust and biomass from SRWC (black locust, poplar and willow) and from their mixtures. Moreover, the study also seeks to demonstrate which types of pellets met the parameters laid down in selected standards which categorize pellets into various classes. A total of 23 types of pellets were produced – two from forest-derived biomass, three from SRWC biomass and 18 from mixtures of forest-derived and SRWC biomass. The lower heating value of all pellet types met the strict criteria for class A1 pellets (≥16.5 MJ kg–1). Furthermore, only three pellet types: those obtained from Scots pine and mixed pellets from 75% of Scots pine biomass and 25% willow or poplar biomass, met the strict criteria for class A1 and Grade 1 with respect to all the analyzed parameters. The quality of pellets from biomass mixtures decreased with increasing portions of SRWC biomass relative to pure sawdust from forest wood, especially due to the increasing content of ash, nitrogen, sulfur and chlorine.