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Pelletization of biochar from hydrothermally carbonized wood



Hydrothermal carbonization (HTC) is a pretreatment process for making a homogenized, carbon rich, and energy dense solid fuel, called biochar, from underutilized lignocellulosic biomass. Compared to raw biomass, HTC biochar is both more hydrophobic for better storage and more friable for better processing. In this pretreatment method, the biomass is treated with hot compressed water in the temperature range of 200–260°C. Hemicelluloses and water extractives react very quickly compared to cellulose. Lignin is relatively inert, resulting in a biochar with increased lignin content. Lignin acts as a binder for pelletization of pretreated lignocellulosic biomass. A hydraulic press with a controllable heated die was used for pelletization studies. The materials used to make pellets were raw loblolly pine and pine pretreated at different temperatures. The presence of solid bridges was observed in both raw pine pellets and HTC biochar pellets. Pellets made from HTC biochar exhibit favorable properties, including increased hydrophobicity, abrasion resistance, energy density, and mass density compared to pellets produced from raw pine or from dry torrefied pine. Pellets produced from biomass pretreated at 260°C have a volumetric fuel value 70% greater than pellets produced from untreated pine (38.8 MJ/m3 vs. 22.8 GJ/m3), a mass density of 1468 kg/m3, and a higher heating value of 26.4 MJ/kg. © 2012 American Institute of Chemical Engineers Environ Prog, 2012