Quality variation in comminuted forest fuels delivered during the winter in north Sweden

Abstract

Swedish legislation stipulates the precision required for estimates of parameters used to determine the value of various forest fuels. The net energy value of fuel, as it is received, is often used to set the trade price. The estimate of energy content is based on the moisture content of samples taken from each truckload and the weight of the biomass; the ash content and net calorific value are measured a few times each year. Hence, it is necessary to know the variation in moisture content to ensure that a sufficient number of samples are taken, a number based on the allowed variation and precision of estimates, as defined in the legalization. In this study, the variation in moisture content was measured by taking samples from 18 truckloads of comminuted forest fuels during the winter. The results showed that the current sampling regime, i.e., manually taking four samples from each truckload, is sufficient for deliveries with 10 truckloads for logging residue chips and 4 for stem wood chips. The number of samples should be increased to 12–43, 8–21, and, 17–82 depending on assortment for what the measuring act defines as large deliveries (>=50 tonnes; >=3 truckloads), medium-sized deliveries (<50 – >25 tonnes; 2 truckloads) and single truck deliveries (<= 25 tonnes; 1 truckload), respectively. Current research into fast online sampling and analysis methods could resolve this issue for small deliveries.