Flue Gas Torrefaction of Corn Stover-Densified Fuel: Impacts on Physicochemical Properties and Combustion Performance

Abstract Corn stover pellets were torrefied under a simulated flue gas atmosphere (220 °C–300 °C, 15–25 min) to evaluate physicochemical and combustion modifications. Analyses revealed that increasing torrefaction severity significantly reduced the volatile matter, hydrogen, and oxygen contents, while enriching the fixed carbon and ash fractions. Consequently, the higher heating value increased by up to 33.41%, peaking at an energy density of 1.33, albeit at the expense of a sharp decline in mass yield. Thermogravimetric analysis revealed that increasing torrefaction severity elevated the ignition temperatures while reducing burnout temperatures. Mild torrefaction (220–240 °C, 15–20 min) maintained optimal combustion stability; conversely, severe conditions (>260 °C, >20 min) significantly deteriorated the combustion kinetics, as evidenced by a marked reduction in both the maximum combustion rate and the comprehensive combustion characteristic index.