Experimentally determined storage and handling properties of fuel pellets made from torrefied whole-tree pine chips, logging residues and beech stem wood

Torrefaction is currently of interest for the production of a new generation of fuel pellets suitable for increasing co-firing rates at pulverised-coal power plants. However, few results have been reported on properties of pellets which can currently be produced from torrefied materials. This data is required in order to evaluate the suitability of this fuel for its primary application.The objective of this study was to obtain measured results on storage and handling properties of pellets made of torrefied pine, logging residues (with and without wheat flour binder) and beech. Experimental methods, most of which adhere to standard procedures, are described. The measured properties include calorific value, bulk density, durability, hardness and equilibrium moisture content (EMC). Additionally, EMC isotherms of torrefied beech wood are presented. The results are analysed and their influence on the feasibility of large-scale pellet production is discussed. The measured and derived values presented will be of use in determining feasibility of torrefied pellet production in offsetting the use of fossil coal.From the results the following statements can be made regarding produced pellet samples:• Feedstock choice has a strongly influence on properties of torrefied pellets.• Durability of torrefied pellets is problematic compared to wood pellets.• Outdoor heap storage of torrefied pellets is not recommended.• Logging residues do not seem to be an optimal feedstock choice for torrefied pellets.• Wheat flour does not appear suitable as binder for torrefied pellets production due to water absorption.• Pelletising using high die temperature (above 170 °C) should be investigated.