Further study on biomass ash characteristics at elevated ashing temperatures: The evolution of K, Cl, S and the ash fusion characteristics

► Inorganic S is released in the form of SO2 by the silicate of K2SO4 above 1000°C. ► K is mainly reduced by the evaporation of KCl and K2SO4 aerosols. ► Cl disappears at 815°C in the form of HCl due to the aluminosilicate of sylvite. ► Biomass AFC is mainly dependent on the high-temperature molten material. ► High-temperature molten material is built up by SiO2, K3FeO2 and silicates. Based on the ash-related problems during biomass combustion, the evolution of element S, Cl, K and chemical components and ash fusion characteristics of capsicum stalks, cotton stalks and wheat stalks ashed at 1000, 1200 and 1400°C are further studied by XRF and XRD. Cl disappears at 815°C in the form of HCl due to the aluminosilicate of sylvite. Above 1000°C, inorganic S is released in the form of SO2 by the silicate of K2SO4, which is the main reason that ashing ratio decreases at high temperature. Except of the evaporation of KCl and K2SO4 aerosol which cause the release of K, Cl and S, K may be also reduced by the organic decomposition and the releases of metal K and KOH. The ash fusion characteristics of biomass are mainly dependent on the high-temperature molten material built up by quartz, potassium iron oxide and silicates.