Identification of differences and comparison of fuel characteristics of torrefied agro-byproducts under oxidative conditions

Torrefaction is a pretreatment method for upgrading biomass into solid fuels. This study aimed to investigate the properties of agro-byproducts pretreated under different oxidative conditions at temperatures of 210–290 °C for 1 h to determine optimal operating conditions for upgrading biomass. The mass yields of lignocellulosic and herbaceous biomass were 90.27–42.20% and 92.00–45.50% and 85.71–27.23% and 88.09–41.58% under oxidative and reductive conditions, respectively. The calorific value of lignocellulosic and herbaceous biomass under oxidative conditions increased by approximately 0.14–9.60% and 3.98–20.02%, respectively. Energy yield of lignocellulosic and herbaceous biomass showed 63.78–96.93% and 90.77–44.39% showed 88.09–41.58% and 92.38–27.23% under oxygen-rich and deficit conditions. A decrease in oxygen and an increase in carbon dioxide and carbon monoxide were confirmed through gas measurements. Torrefaction evaluations were conducted using energy–mass co-benefit index (EMCI). Decreases of ΔEMCI were observed under certain conditions. Both oxidative and reductive conditions can be employed for pepper stems, wood pellets, and pruned apple branches. Based on standards, the optimal temperatures for pepper stems, wood pellets, and pruned apple branches in oxidative conditions were 250, 270, and 250 °C, respectively.