Effects of microwave drying on biomass fatty acid composition and fuel pellet quality

Drying of biomass for fuel pellet production is a time- and energy-consuming process. The objective of this study was to investigate not only whether microwave drying could be an alternative drying method but also whether the microwave treatment brings beneficial chemical properties into the biomass feedstock in terms of, for example, fatty acid composition and, further, whether this could be advantageous in the production of wood pellets. Microwave drying tests were conducted using fresh sawdust from pinewood as a biomass model. In these tests sawdust was dried from weight-based moisture content 0.47 to final moisture contents in the interval 0.08-0.14. The chemical composition, pellet-making and mechanical properties of the pellets were then investigated. It was shown that 0.5 kg sawdust could be dried within 40 min of microwave exposure. The effects of microwave treatment on the fatty and resin acid composition indicated that some changes occurred, but the total amounts were not significantly different from those in oven-dried samples. However, the microwave treatment of sawdust significantly improved pellet density and pellet strength. These results indicate new possibilities to alter fatty and resin acid composition and to improve particle bonding within fuel pellets.