To reduce the use of fossil fuels, it is important to increase the use of renewable alternatives such as fuel pellets. Fuel pellets in Sweden are primary produced from various residual products from spruce and pine. Before the production of fuel pellets, the pine sawdust needs some storage time to achieve the right pelletizing properties. During the storing process self-ignition may occur, which is a known and common problem. The purpose of this work was to increase the knowledge about how pine shavings change during laboratory storage, and to demonstrate whether it is the sapwood or heartwood that causes self-ignition. Further, it investigates the differences between pine sapwood and heartwood when it is run through a mechanical dewatering process. This in order to increase the knowledge to industries that handle and stores pine-sawdust, about how and why the problem of self-heating occurs and in the long run can be counteracted. The aim was to prove, by temperature measurements, if the cause of self-ignition is greater in the sapwood or heartwood of the pine. The study will also show how the pine shavings changes during storage through color-, moisture- and NIR-analyses. A checkpoint in the study is to show if the organic compounds, the moisture content and the compression energy are different in the sapwood and heartwood, due to a dewatering process.  It was not possible to show if it is a certain part in the pinewood that causes self-ignition through temperature measurements, but during the storage process both color- and moisture differences occurred. The NIR-analyses showed that during both anaerobic and aerobic storage the content of extractives and other compounds in the pine shavings was reduced. The dewatering process did not show big differences between the organic compounds in the sapwood and heartwood. But the process where able to decrease the moisture levels in the shavings even if the heartwood needed more compression energy.  To sum up, the study showed that it occurs changes in pine shavings during a storage process even though there was not possible to prove if it is the sapwood or heartwood that causes self-ignition.

Idag när den globala uppvärmningen är ett faktum behöver en omställning ske ifrån fossila energikällor till förnybara energikällor. Biomassa kan ersätta fossila bränslen såsom kol och olja vid förbränningsprocesser. Ett sätt att hantera biomassa är genom pelletering till pellets. Pellets produceras till största del av sågspån som är en rest ifrån sågverk. Ett problem för producenter av pellets idag är att det finns svårigheter med att pelletera sågspån av olika träslag eller färskhet i samma utrustning.En annan rest ifrån sågverk och annan trähantering är en mix av avbarkningsrester. Användningsområdet för denna mix av rester är idag begränsat och eldas för det mesta upp. Mixen kan på grund av sin kemiska komposition potentiellt användas som inblandning vid pelletering.Studien syftar till att lösa svårigheterna med att pelletera sågspån av olika färskhet genom att utöka kunskapen kring pelleteringsegenskaper hos avbarkningsrester. Det huvudsakliga målet med studien är att en blandning av lagrat furuspån och avbarkningsmixen ska kunna pelleteras i samma matris som färskt furuspån med en pelletskvalité som uppfyller 97,5% hållfasthet. Även pelletens hårdhet ska utvärderas i huvudmålet. Som delmål ska pelleteringsegenskaperna kompressionsenergi, backpressure och friktionsenergi kartläggas vid olika fukthalter hos mixen, mixens olika barksorter samt lagrat och färskt furuspån, dessutom ska studien utvärdera om backpressure och friktionsenergi fungerar som uppskalningsparametrar från singelpellet press till labbpress.Studien genomfördes i två delar där den första delen bestod i att pelletera furubark, björkbark, granbark, mix av avbarkningsrester, färskt furuspån och lagrat furuspån vid olika fukthalter i en enpetarpress. Under pelleteringen mättes kompressionsenergi, backpressure och friktionsenergi. I andra delen utformades två testmatriser utifrån första delens resultat som sen testades i en labbpress. Pelletskvalitén hos pressade pellets i båda delarna utvärderades genom att testa hållfasthet och hårdhet.Resultaten av studien visar att mixen av avbarkningsrester kan blandas med lagrat furuspån och pelleteras i samma matris som färskt furuspån. Enligt enpetartesterna hade mixen låg kompressionsenergi, backpressure och friktionsenergi i förhållande till mixens beståndsdelar separat. Enpetartesterna visade också att den största skillnaden mellan färskt och lagrat furuspån ligger i kompressionsenergin. Vidare studier rekommenderas där användandet av kompressionsenergi som uppskalningsparameter från enpetarpress undersöks. 30% inblandning av mix resulterade i 95,5% hållfasthet vilket var högre än vid 20 och 40% inblandning som hade 77,3% respektive 94,7%.Backpressure fungerade inte som en uppskalningsparameter mellan enpetarpress och labbpress. Friktionsenergi fungerade som en uppskalningsparameter i den här studien men behöver verifieras av vidare studier. Ingen av de testade blandningarna av avbarkningsrester och lagrat furuspån uppnådde hållfasthets kravet på 97,5% men de kunde pelleteras i samma matris som färskt furuspån. / Today, when global warming is a fact, a shift needs to take place from fossil-based energy sources towards renewable energy sources. Biomass can replace fossil fuels such as coal and oil in combustion processes. One way to handle biomass is by pelletizing it into pellets. Pellets are mostly produced from sawdust, which is a residue from sawmills. A problem for pellet producers today is that there are difficulties in pelletizing sawdust of different types of wood or age of sawdust in the same equipment.Another residue from sawmills and other wood handling is a mix of debarking residues. The area of use for this mix of residues is today limited and is most often burnt to produce heat. Due to its chemical composition, the mix can potentially be used as an additive when pelletizing.The study aims to solve the difficulties of pelletizing sawdust of different freshness by expanding the knowledge about pelletizing properties of debarking residues. The main goal of the study is that a mixture of stored pine shavings and the debarking mix should be able to be pelletized in the same matrix as fresh pine shavings with a pellet quality that meets 97.5% strength. The hardness of the pellet will also be evaluated in the main target. As a sub-goal, the pelletizing properties compression energy, backpressure and friction energy will be mapped at different moisture contents of the mix, the mix's different bark types and stored and fresh pine shavings, in addition the study will evaluate whether backpressure and friction energy function as upscaling parameters from single pellet press to labpress.The study was carried out in two parts where the first part consisted of pelletizing pine bark, birch bark, spruce bark, mix of debarking residues, fresh pine shavings and stored pine shavings at different moisture contents in a single-press. During the pelletization, compression energy, backpressure and friction energy were measured. In the second part, two test matrices were designed based on the results of the first part, which were then tested in a lab press with the same die. The pellet quality of pressed pellets in both parts was evaluated by testing strength and hardness.The results of the study show that the mix of debarking residues can be mixed with stored pine shavings and pelleted in the same die as fresh pine shavings.According to the single-press tests, the mix of debarking residues had low compression energy, backpressure and frictional energy in relation to the components of the mix separately. The single-press tests also showed that the biggest difference between fresh and stored pine shavings lies in the compression energy. Further studies are recommended where the use of compression energy as a scaling parameter from a single-press is investigated. A blend with 30% mix resulted in 95.5% strength which was higher than with 20 and 40% mix which had 77.3% and 94.7% respectively.Backpressure did not work as an upscaling parameter. Friction energy served as an upscaling parameter in this study but needs to be verified by further studies. None of the tested mixtures of debarking residues and stored pine shavings achieved the strength requirement of 97.5%, but they could be pelletized in the same die as fresh pine shavings.