Influence of blending and hot water extraction on the quality of wood pellets

In order to meet the projected demand for biomass feedstocks, multiple sources will be needed. Biomass feedstocks are often have a high degree of variability with regards to important properties such as ash, moisture, and energy content. The efficiency of conversion processes may be sensitive to this variability; thus, strategies are needed to ensure that consistent and reliable feedstocks are produced that meet end-user specifications. The objective of this study was to examine the effect of source, blending and hot water extraction (HWE) on the quality of wood pellets. Debarked maple biomass was blended at various rates with whole stem harvested willow, HWE willow, and HWE maple biomass, made into pellets and then compared to existing ISO (17225) pellet standards. Untreated willow pellets were unable to consistently meet key specifications such as ash and moisture. However, pellets blended with either HWE willow, maple or HWE maple at rates between 20 and 50 percent willow still met the most stringent requirements. HWE decreased the ash content of willow below 1% and was on par with untreated maple. HWE increased the energy content of pellets in this study approximately 1 MJ kg⁻¹. Blending and HWE have the potential to decrease variation in feedstock for pellet production and expand the range of material that can be used while still meeting standards for quality. Technologies for rapidly assessing feedstock properties at the front or back end will be needed to maximize the benefits of these two strategies when more variable feedstocks are used.