Physicochemical characteristics of biomass‐coal blend char: The role of co‐pyrolysis synergy

Co‐pyrolysis synergy between cornstalk and bituminous coal was investigated based on the physicochemical properties of the char. The char was prepared by directly putting the individual or blended materials into a heated resistance furnace at 600°C or 800°C. The performance of surface morphology and mineral matters was not notably changed by co‐pyrolysis, indicated by scanning electron microscope and X‐ray diffraction. However, N2 and CO2 adsorption‐desorption isotherms confirmed that surface area and pore structure were strongly influenced, particularly in large micropores and mesopores. Ultimate analysis and inductively coupled plasma optical emission spectrometer measurement revealed excessive depositions of carbon, alkali, and alkaline‐earth metal species in co‐pyrolysis char. Energy‐dispersive X‐ray spectrometer analysis examined the elemental surface distribution, suggesting that co‐pyrolysis under moderate temperature strongly favored inhibiting potassium release. The non‐isothermal thermogravimetry‐differential scanning calorimeter experiments under air atmosphere were conducted for char combustion reactivity, which was expected to be instructive for deeper understanding about co‐pyrolysis synergy and reutilization of the char. The thermal behaviors during combustion of co‐pyrolysis char clearly resembled a single fuel, which completely varied from those of the char blends. Besides, co‐pyrolysis chars and char blends were superior in total heat release compared with the simple addition of calculated values from individual char. Based on these observations, key factors of the synergy were supposed to have consisted of free radical reaction, secondary char formation, and the migration of alkali and alkaline‐earth metal species.