Optimum Torrefaction Range for Macaw Husks Aiming Its Use as a Solid Biofuel

Abstract

Abstract Biomass feedstock is broadly available in many countries, and a significant amount of residual biomass comes from agriculture and forest crops. This study aims to identify a consistent criteria for optimize Macaw husks torrefaction process maximizing the energy content and minimizing the mass loss. The optimization criteria is based on the severity factor (SF), HHVTorrefied, and ηSolid-Yield. The energy density (ρEnergy) does not provide consistent and indisputable evidence as an optimization criteria; the same applies to energy-mass co-benefit index (EMCI) and ηEnergy-Yield. This investigation combined few temperatures (180 °C, 220 °C, and 260 °C) with different residence times (20, 40, and 60 min) and found that the optimum torrefaction range for Macaw husk is 220 < T (°C) < 240 and 10 < t (min) < 40. The best experimental result was 220-40 (dry torrefaction at T = 220 °C and t = 40 min) corresponding to SF ∼ 5.14 and HHVTorrefied ∼ 21.71 MJ/kg (ηSolid-Yield ∼ 0.86 and HHVRatio ∼ 1.14). As the raw material has small ρBulk or ρEnergy, the authors suggest the use of a densification process previously to torrefaction. The obtained solid final product had high-quality biofuel following properties: FCdb, H/C, and O/C ratios, high heating value (HHV). The gain and loss optimization method seems promising to identify the optimum torrefaction parameters for any biomass species and the obtained optimum temperature is not far from the ones available as waste heat in industrial processes.