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Torrefaction is a process to convert diverse lignocellulosic biomass feedstocks into an energy dense homogeneous solid, a pretreatment for subsequent thermochemical conversion. Loblolly pine was treated by wet torrefaction (hot compressed water, 200-2608C) and dry torrefaction (nitrogen, 250-3008C), with mass yield of solid product ranging between 57 and 89%, and energy densification to 108-136% of the original feedstock. The solid product has been characterized, including 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 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.

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Solid handling of diverse lignocellulosic biomass feedstock is very challenging for thermochemical conversion to renewable fuels. Wet torrefaction is a pretreatment process to convert biomass to energy-dense solid fuel, with relatively uniform handling characteristics. The fuel value of the produced solid may be as much as 36% higher than that of the original biomass. In the process, biomass is reacted with hot compressed water at the temperature of 200−260 °C. The mass and energy balance in wet torrefaction were established for these conditions. Products include pretreated solid, precipitates (simple sugars and sugar derivatives), volatile acids, and gases (carbon dioxide). With increasing temperature, the mass of the solid decreases, the fuel value of the solid increases, and the quantity of gas increases. The heat of reaction for each temperature was estimated from an energy balance. The uncertainty analysis also showed that the temperature slightly affected the heat of reaction, which is very close to zero.