Thermal properties of native and densified hardwood, softwoods, and agricultural residue

Abstract

Biomass, a significant renewable resource for bioenergy and carbon-based chemicals, sees its product yield and quality highly influenced by feedstock quality and treatment conditions. Accurate prediction of thermal properties and behavior under various conditions, such as feedstock density and particle size, is essential in thermochemical treatments conducted at high temperatures. Due to the highly variable nature of biomass feedstock, specialized thermal properties measurement techniques must be identified or developed to match specific feedstock and treatment conditions. In this study, a novel measurement technique was developed to assess the thermal properties of various biomass (e.g., corn stover, alpine fir, ponderosa pine, oak) under different conditions: un-densified (as-received), loosely compacted, and densely compacted. Thermal properties were measured using the transient plane source (TPS) technique, which indicated average geometric thermal conductivities of 0.14, 0.19, and 0.23 Wm⁻¹K⁻¹ for alpine fir, ponderosa pine, and oak, respectively, with diffusivities of 0.11, 0.096, and 0.097 mm²/s. The new technique prepared the feedstock at various particle sizes (2, 6, and 25 mm) and densities (180–1032 kg/m³). Thermal conductivity measurements ranged from 0.071 to 0.259 Wm⁻¹K⁻¹, showing no dependency on particle size but a positive linear relationship with density. Additionally, heat cycling revealed an increase in oak pellet conductivity from 0.146 to 0.359 Wm⁻¹K⁻¹ as temperature rose from 25 to 330 °C. This study demonstrates that biomass feedstock can be reformatted to obtain reliable thermal property data which can further enhance the bioprocessing simulations.