Process modeling for torrefaction of birch branches

This work presents a complete biomass torrefaction model for Norwegian birch branches. The model can provide detailed distribution of both the main and by-products from the torrefaction process. Reduction in mass and energy yields as well as increase in heating value of the torrefied biomass with increasing torrefaction temperature are observed. Simulation results show good agreement with available experimental data in the literature. Furthermore, the overall energy consumption and the process energy efficiency can be also estimated, which is essential for process up-scaling. It reveals that drying accounts for 76-81% of the total heat demand. More importantly, the process energy efficiency reduces with increasing temperature thus torrefaction at high temperatures is not advisable. The information obtained from the model is important for industrialization and commercialization of the torrefaction process.