Development and experimental validation of a local thermal non-equilibrium drying model for biomass packed beds

Drying is an energy-intensive pretreatment process for producing bioenergy from biomass through thermo-chemical conversion. Efficient drying is important for the cost and sustainability of bioenergy. The objective of this study is to develop and experimentally validate a local thermal non-equilibrium drying model for biomass packed beds. To inform the model with essential effective parameters, namely, the volumetric heat transfer coefficient ( h v ) and effective thermal conductivities for solid and gas phases, an experimental facility was designed. The study was carried out on wood pellets and wood chips of various moisture contents. The numerical model was implemented in the Porous Material Analysis Toolbox based on OpenFOAM (PATO). Effective parameter identification was carried out by using the local optimization method NL2SOL. The experimental–numerical inverse analysis showed that reducing moisture from 6.2% to 0.4% increased h v by 20.2% for wood pellets, and from 9.1% to 0.4% increased h v by 11.9% for wood chips, at a Reynolds number of 61 and temperatures below 347 K. Furthermore, two new correlations for the Nusselt number as a function of moisture content have been proposed and validated under the conditions of our experiment: N u ( M C ) p = 2 + ( 0 . 545 − 1 . 2 M C ) R e 0 . 6 P r 1 / 3 for wood pellets and N u ( M C ) c = 2 + ( 0 . 524 − 0 . 9 M C ) R e 0 . 6 P r 1 / 3 for wood chips. These moisture-dependent correlations extend classical packed bed heat transfer models and can be directly integrated into reactor scale simulations for drying and thermochemical conversion processes.