High-Temperature Ash Behavior of Biomass: A Comparative Study of Corn and Wheat Straw
The high-temperature behavior of biomass ash critically influences gasifier operational efficiency. This study investigates the differential high-temperature behaviors of corn straw ash (CSA) and wheat straw ash (WSA) using an intelligent ash fusion analyzer, high-temperature rotating viscometer, X-ray diffraction (XRD), SEM-EDS, and FactSage thermodynamic simulations. Both ashes contain high K2O (>30%) and exhibit flow temperatures below 1300 °C. Despite higher K2O and lower SiO2, CSA exhibits a higher flow temperature (1241 °C) than WSA, attributed to elevated CaO (10.39%) and MgO (7.33%) that promote formation of high-melting silicates (K2MgSiO4, K2Ca2Si2O7, CaSiO3). In contrast, WSA with lower CaO (4.92%) and MgO (2.82%) tends to form low-melting potassium silicates. At high temperatures, both slags are typical crystalline slags, with viscosity rising sharply below a critical temperature. For CSA, rapid nucleation and coarsening of silicate crystals (e.g., KAlSiO4 grain size increases from 20.5 nm at 1350 °C to 192.9 nm at 1050 °C) cause abrupt viscosity increase. For WSA, a high P2O5 content (10.05%) induces a 'chemical dilution effect', leading to persistent KAlSiO4 during cooling and elevated viscosity, especially at the final cooling stage. This study elucidates how ash chemical composition governs high-temperature phase equilibrium and non-equilibrium kinetics, thereby macroscopically affecting ash fusion and rheological behavior, providing a theoretical basis for deeper understanding of biomass ash high-temperature characteristics.