Particulate Matter Production of Small Heat Source Depending on the Bark Content in Wood Pellets

Wood pellets as biofuel are more and more used in small heat sources in Europe. Standard wood pellets are produced from wood sawdust without bark. The paper deals about the impact of bark in wood pellets on their properties and combustion process. Special attention in this work is paid to production of particulate matter during combustion of wood pellets depending on bark content. There were experimentally produced spruce wood pellet samples with 0, 1, 2, 5, 10, and 20% content of bark. The density, moisture content, calorific value, ash content, and ash fusion temperature were detected on produced samples. Then, the combustion took place in a small heat source which was tested on an experimental device designed for the measuring of heat output and emission production. Based on the achieved results, we can conclude that bark content in pellets has a significant impact not only on wood pellet properties but also on performance and environmental characteristics of pellets. The results showed that growing bark content has negative impact on wood pellet properties, mainly decrease calorific value and ash fusion temperature, and increase ash content. Growing bark content in wood pellets also decreased heat output of heat source and increased gas emissions and particulate matter production.