Effect of raw material composition in woody biomass pellets on combustion characteristics

Char yield, char combustion time and char combustion rate of pellets made from different tree parts of Norway spruce and industrially made stem wood pellets of Norway spruce and Scots pine were studied. The pellets were incinerated in a laboratory scale oven at various temperatures, gas flows and oxygen concentrations. It was found that the combustion time for a single pellet mostly depended on the raw material composition and to a minor extent on the density. Pellets made of bark had up to a 50% longer char combustion time compared to that of stem wood pellets, due to differences in char yield. Industrially made stem wood pellets of pine and spruce sawdust were found to have small differences in combustion characteristics. The variations in combustion characteristics of pellets are discussed in relation to composition of raw material.