Influence of chipping device and storage method on the quality of SRC poplar biomass

Wood chips need to fulfill specific quality parameters in order to be used as fuel for industrial or residential use. Moisture content and chip size distribution are recognized as the main physical characteristics affecting energy conversion efficiency. Objective of the study was to evaluate the effects of harvesting mode on the quality of wood chips, under the typical conditions offered by SRC poplar grown in Central Italy. Single-pass and two-pass harvesting were compared. Standing stems and cut windrowed stems were harvested using two modified foragers alternately equipped with a drum or a disc chipper, allowing a further comparison of different chipping devices. Data were obtained from 3 fields in Central Italy and allowed analyzing the drying process occurring when stems are felled and stored in the field as windrows. The mean water content at the time of cutting was 59% (wH2O)(wH2O), which was reduced below 30% after about 100 days of storage in the windrows. Regression analysis of storage duration and moisture content showed that air temperature is the main driver of the drying process, under the typical conditions of a Mediterranean climate. Harvest mode (single-pass or two-pass) and chipping device (drum or disc) have a significant effect on particle-size distribution. The incidence of accept particle was higher when chipping windrowed stems or using the drum chipper. The paper discusses the advantages of two-pass harvesting and emphasizes the importance of flexibility when choosing harvest mode and chipper type