Simultaneous Thermal Analysis of Norway Spruce Wood Pellets with Digestate Additive: A DSC and TGA Study

Abstract

Wood pellets represent one of the most important solid biofuels produced from renewable lignocellulosic biomass, yet the thermal behaviour of pellets containing alternative additives such as digestate from biogas plants remains insufficiently characterised. This study provides a dataset from simultaneous differential scanning calorimetry and thermogravimetric analysis for four wood pellet samples: three commercial Norway spruce pellets of different geographical origin and quality classes, and one experimental sample prepared as a one-to-one mass mixture of spruce sawdust and solid digestate from an agricultural biogas plant. Measurements were performed in an oxidative atmosphere from 30 to 700 degrees Celsius at a heating rate of 20 degrees Celsius per minute. The three commercial pellets exhibited consistent thermal behaviour, with decomposition onset temperatures falling within narrow ranges. The experimental sample showed substantially different behaviour, including a downward shift in the decomposition onset temperatures of hemicellulose and cellulose by 23 and 41 degrees Celsius, respectively, an elevated endothermic peak temperature consistent with stronger moisture binding, and a residual mass of 10 percent, which was six to ten times higher than that of the commercial pellets. These findings document that incorporating digestate fundamentally alters the thermal behaviour of wood pellets.