Microscopic structural characteristics of Na and Ca in CaONa2O-Al2O3-SiO2-SO3 system slag: Molecular dynamics simulation and experimental study

Abstract

To enhance the resource utilization of industrial byproducts, such as coal ash, and to mitigate slagging and fouling on boiler heating surfaces, this study investigates the structural characteristics of CaONa₂O-Al₂O₃-SiO₂-SO₃ slag, a significant component of high-alkali coal ash. Using molecular dynamics (MD) simulations and combining the actual deposited ash at 660MW utility boiler, we analyzed the diffusion behaviors, viscosity, and surface tension of the slag to understand its interactions during combustion. The results show that Na atom exhibits the highest mobility and promote the dissociation of the slag network, while Ca atom moves more slowly and contribute to ash deposition by forming viscous surface materials. Temperature sensitivity analysis reveals that Na and Si are most responsive to thermal changes, whereas Ca and S are less affected. Radial distribution analysis indicates strong binding of Ca with S and O, leading to calcium sulfate formation, while Na more readily binds with Si and Al, forming sodium aluminosilicate. These findings offer valuable insights for optimizing combustion processes to minimize slagging and fouling, while enhancing the reuse of coal ash in ecological industrial development.