Processing Pellets Towards Low Emissions.

Fuel pellets are usually produced from raw materials with high lignocellulosic content like bio-mass from wood, straw etc. with a huge variety of the raw material quality grades. While high calorific value is the most desired end-product property, other product characteristics are also of interest. Gas emissions could be crucial for the subjective acceptance of pellets as "green product" and could lead to higher indoor concentrations of unwanted volatile substances if the pellets are stored inside the premises.VOC (volatile organic compounds) emissions from pellets produced from pine and spruce were evaluated at the early stages of the product lifecycle - from wood shredding through transport and storage of the freshly produced pellets. It was found out that the VOC emission profile depends on wood type and lifecycle stage. The emitted VOC belonged exclusively to the substance classes of terpenes and aldehydes. The observations showed that spruce- and pinewood based pellets differentiated mainly in their aldehyde emissions whereby pinewood based pellets emitted substantially more aldehydes. The treatment of pinewood chips with the blue stain fungus Ceratocystis coerulescens for four weeks led to a reduction in aldehyde emissions of the produced pellets with more than 80%. Thus the profile of the VOC emissions of treated pinewood based pellets was much more similar to that of spruce based pellets.