Bioenergy from Swedish forests : A Study of extraction methods, quality and effects for forest owners

Abstract: The forest constitutes a very important element of renewable natural resources and makes a significant contribution to the Swedish bioeconomy. Biofuels are Sweden’s largest source of energy; of all the energy we use, 32% comes from biofuels, and of this approximately 85% comes from the forest and the forestry sector. In spite of this, logging residues constitute only a small component, compared to for example byproducts from sawmills and pulpindustry, and there is considered to be great potential for increasing their use.In 2019 the Swedish Forestry Agency issued new recommendations for logging residue harvest and ash recycling. This was a further development of the 2008 recommendations, which formed the foundation for how forest fuel producers work today, and were based on several decades of research into, for example, the impact on forest productivity and technological development of machinery. This practice of logging residue harvest aims to yield a dry and defoliated fuel where the needles are left at the clear felled area.However, if we are to increase the use of green renewable energy from forestry, it is very important to understand how different procurement systems affect the handling and storability of fuels from a quality perspective. It is also of great importance to understand, from the forest owners’ perspective, how removal of additional products from forestry influences nutritional balance and long-term productivity. If harvesting of logging residues does not affect long-term productivity, it is up to small-scale private forest owners to decide if removal of logging residues will be performed on their land. This thesis addresses some of these issues regarding removal of logging residues from the point of tree harvest up to the point of delivery to the energy conversion industry when the fuel chips are measured.Regarding different methods of handling of logging residues, the traditional method – dry-stacking – was compared with the, fresh-stacking method. The logging residues investigated came from stands that mainly consisted of Norway spruce (Picea abies (L.) Karst). The loads investigated in Paper 3 also came from logging of spruce-dominated forests. Both methods aim to dry the logging residues to an acceptable moisture content for delivery to the energyconversion industry. For the later part in the supply chain, moisture content measurements of logging residues were compared during a winter and summer season.The results of the studies indicate that the two methods do not create results that differ from what is allowed by the Swedish Forestry Agency and that they are quite similar with respect to dry mass- and nutrient removal from the clearfelled area. The results also show that similar yields and distributions of material are obtained from the logging residues with different stacking methods; in addition, the final felling itself, combined with the work performed by the forwarder operator, has a greater impact on the result than the method chosen for residue stacking of the logging residues. For the individual clear-felled area and the individual forest owner the increased removal associated with freshstacked logging residue has no major impact, however from a national perspective this small increase in removed logging residues may yield a supplement of between 0.5 – 1 TWh of green energy annually.Regardless of treatment, the studies indicated that the delivered fuel chips will have similar characteristics. The moisture content measurement techniques currently in use are sufficiently accurate and reliable. However, if the forest owner is unlucky and an error in measurement occurs or comminution and delivery happens during an especially wet period they may suffer a significant financial loss; indeed, it is generally not under the individual forest owners’ control when the logging residues are comminuted and delivered.