Fuel quality of whole-tree chips from freshly felled and summer dried Norway spruce on a poor sandy soil and a rich loamy soil

Abstract

Chipping of summer dried trees compared with chipping of freshly felled trees is considered to improve the fuel quality, and to be a more environmentally benign method. An experiment was established in Western Denmark in 1995 to determine effects of chipping methods on whole-tree chip quality and nutrient removal from two stands of Norway spruce ( Picea abies (L.) Karst.): a poor sandy site and a site with rich loamy soil. Fuel chip quality was expressed as size distribution, moisture content, and net calorific value. In each stand samples were taken from both freshly felled and summer dried trees. When freshly felled trees were chipped, the loss of plant essential nutrients (Calcium, Magnesium, Potassium and Nitrogen) was significantly larger compared to the removal of nutrients, when the summer dried trees were chipped. The size distribution of the chips was significantly improved when the trees were left for summer drying. The fine fraction (dust) was reduced, and the amount of chunk and acceptable output increased, i.e., the chips from summer dried trees were more homogeneous. The moisture content dropped significantly from an average in the two trials of 57% of total weight to 42% of total weight after summer drying. The net calorific value based on total weight ( Q p,net,m) increased significantly in the chips of summer dried wood. Net calorific value based on dry weight ( Q p,net,d) was slightly reduced during the drying period. This resulted from a loss of energy rich extractives. Chipping of summer dried trees improves fuel quality in regard to size distribution, moisture content, and net calorific value of moist wood ( Q p,net,m). The summer drying ensures reduction in the loss of plant essential nutrients caused by the removal of biomass from the stand.