Hydrothermal flow-through treatment of wheat straw: Coupled heat and mass transfer modeling with changing bed properties

Abstract

Fixed-bed processes handling lignocellulose pose several challenges for reactor modeling. The fluid and solid material as well as the complete fixed-bed show varying properties with temperature, composition and advancing reaction progress. For this reason, biomass-specific reaction kinetics need to be combined with detailed heat and mass transfer, varying material properties and the filling process. In the present work, a detailed reactor model for hydrothermal flow-through pretreatment of pelletized wheat straw at 3L scale is developed. For the first time, this model not only considers reaction kinetics and simple mass transfer equations but also heat transfer, non-ideal flow and varying fixed-bed properties during the filling process as well as the extraction phase. The influence of different levels of detail is discussed and the final model is validated at 185–215°C with prediction accuracies between 0.013 and 0.02kg/kg for hemicellulose oligomers and 0.0008 and 0.004kg/kg for monomers.