Mass and Energy Balances for Wet Torrefaction of Lignocellulosic Biomass


hermal pretreatment of diverse lignocellulosic biomass feedstocks converts them into an energy dense homogeneous solid, a step necessary for subsequent thermochemical conversion. In this work, loblolly pine was treated by wet torrefaction (hot compressed water, 200–260°C) and dry torrefaction (nitrogen, 250–300°C), with a mass yield of solid product ranging between 57% and 89%, and energy densification ranging from 108% to 136% of the original feedstock. The solid product characterization includes proximate analysis, fiber analysis, ultimate analysis, and equilibrium moisture. In both dry and wet torrefaction, increasing temperature results in decreased mass yield and increased energy densification, and also results in a solid with increased carbon content, decreased oxygen content, and decreased volatiles. The biomass is transformed into a fuel similar to a low-rank coal. Generally, the wet torrefaction process produces a solid with greater energy density than dry torrefaction, with the same mass yield. The fiber analysis indicates that hemicellulose is quickly removed during wet torrefaction, and the solid product contains substantial quantities of aqueous soluble compounds. The equilibrium moisture content of solids produced by both processes is somewhat decreased from that of the biomass feedstock, indicating a hydrophobic solid suitable for storage and transportation.

Hamburg, Germany