Upgrading biomass waste to bio-coking coal by pressurized torrefaction: Synergistic effect between corncob and lignin

Gas-pressurized torrefaction is efficient for upgrading biomass to substitute metallurgical coke. Herein, the ef-fects of pressure and temperature on corncob torrefied products as well as the synergistic mechanism were investigated. The results indicated pressure facilitated secondary reactions that converted volatiles to fixed carbon. As the temperature increased to 280 degrees C from 180 degrees C under 3 MPa, the volatile content decreased from 82.72% to 48.71%, and the HHV improved from 16.14 MJ/kg to 28.60 MJ/kg, which were close to the quality of bituminous coal. Lignin was mixed with corncob to further improve the property of torrefied products. The fixed carbon of mixture semi-char increased by 11.28% compared to the theoretical value, the O/C and H/C ratios decreased to 0.18 and 0.74 respectively, reaching the quality of coking coal. The blending of lignin promoted the formation of water under subcritical conditions, accelerating biomass decomposition. Cross-interaction reactions among volatiles intensified the deoxygenation and more acetic acid was produced that promoted carbonization reactions, causing the removal of oxygen in the form of gas and a higher fixed carbon in the semi-char. The finding promoted biomass application in low-carbon iron production significantly by obtaining bio-coking coal.