Continuous weighing of a pile of poplar wood chips – A comparison of methods to determine the dry matter losses during storage

The measurement of dry matter (DM) losses occurring during the storage of wood chips is of crucial importance for understanding the efficiency of bioenergy supply chains. When obtaining representative measurements of a whole storage heap, it is necessary to distribute a large number of samples over cross sections of the pile. The recovery of these samples can be very labour-intensive, and can lead to major disturbances in the pile. Accordingly, this method is not suitable for periodic examinations of storage heaps. In this study, two 100 m³ piles (P1 and P2) of fine wood chips from poplar were investigated over a period of 228 days of storage. The P1 pile was used to compare the different methods in which to determine the moisture content (MC) changes and DM losses during storage. The results generated by the balance bag method (M1) were compared with three alternative methods. These alternative methods (M2–M4) involved the analysis of MC and mass changes in balance bags within measuring columns located within the heap (M2), MC and mass changes occurring in the entire pile (M3), and from changes in ash contents of samples in balance bags within the measuring columns (M4). DM losses of 23.3% and 22.7% were determined using methods M1 and M2, respectively. The DM losses calculated using M3 and M4 were considerably lower at 13.9% and 16.6%, respectively. The M2 method proved to be the most suitable for periodic determination of storage losses in a similar experimental design. - Highlights: • Storage losses of poplar wood chips were investigated with 4 different methods. • Representative moisture contents take top priority when determining dry matter losses. • Measuring columns are suitable as aids for simple periodic sampling. • A large number of samples is necessary to determine ash contents. • Determining dry matter losses by weighing a whole pile provides only indicative results.