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.