Char characteristics from the pyrolysis of straw, wood and coal at high temperatures

The effects of raw material type and pyrolysis temperature on the microstructure, chemical composition and combustion reactivity of biomass char produced by pyrolysis are investigated in the presented work. The properties of biomass char and coal char (C-char) are compared based on characterization using BET surface area analysis, scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Results show that the BET surface area and porous volume of C-char increase as the pyrolysis temperature increases, whereas those of wood char (W-char) insignificantly change from 600 °C to 1000 °C. Straw char (S-char) has the largest surface area and pore volume at 800 °C because sintering occurs at higher temperatures. As the pyrolysis temperature increases, the C content of char increases, whereas its H and O contents decrease, a finding that agrees with the previous statistical formula. EDS and XRD results show that no chlorine species is found in residual biomass char at 1000 °C. The combustion reactivity of S-char is higher than that of W-char and C-char. The increase in O₂ concentration improves the combustion reactivity of C-char more significantly than that of biomass char. As the pyrolysis temperature increases, the combustion reactivity of W-char and C-char decreases. S-char exhibits the highest combustion reactivity at 800 °C.