Johanna Ruotsalainen

Precision measurement of forest harvesting residue moisture change and dry matter losses by constant weight monitoring

The moisture content of forest-wood chips is one of the most important quality factors for the rapidly growing bioenergy sector. Rising transportation costs and increased use of forest biomass for energy are forcing biomass suppliers towards better moisture-content management in the supply chain. In the literature, numerous studies on natural drying of forest biomass have been conducted based on traditional sampling of piles or weighing. The latest methodology for moisture-change monitoring has been constant weighing of piles in racks built on load cells. In this study, seven piles of logging residues were monitored for between 35 and 85 weeks in Finnish climatic conditions. In addition, two small piles which imitated drying in stand conditions were monitored for 6 weeks. After 8 months of drying, a remarkable dry-matter loss was observed in the logging residue piles.

Weather based moisture content modelling of harvesting residues in the stand

Harvesting residues collected from the final cuttings of boreal forests are an important source of solid biofuel for energy production in Finland and Sweden. In the Finnish supply chain, the measurement of residues is performed by scales integrated in forwarders. The mass of residues is converted to volume by conversion factors. In this study, weather based models for defining the moisture content of residues were developed and validated. Models were also compared with the currently used fixed tables of conversion factors. The change of the moisture content of residues is complex, and an exact estimation was challenging. However, the model predicting moisture change for three hour periods was found to be the most accurate. The main improvement compared to fixed tables was the lack of a systematic error. It can be assumed that weather based models will give more reliable estimates for the moisture in varying climate conditions and the further development of models should be focused on obtaining more appropriate data from varying drying conditions in different geographical and microclimatological locations.