A molecular dynamic simulation on the factors influencing the fluidity of molten coke ash during alkalization with K2O and Na2O

Abstract Molecular dynamics (MD) simulations were carried out to determine the influence of alkalis (K2O and Na2O; up to 10%) on the local structural order, bonding networks and fluidity of molten Al2O3-CaO-SiO2 system (2223 K). The behavior of these aluminosilicates, present as mineral matter in cokes/coals, can have a significant influence on the strength and the reactivity of cokes in high temperature regions of a blast furnace. Experimental results on the system indicate an increasing viscosity in the presence of K2O and a decreasing trend for Na2O. Attributing these differences to local distortions and the sizes of K+ and Na+ ions, theoretical investigations on these systems have predicted a reduction in viscosity for both alkalis. Our simulation results have shown that there were only marginal differences in the local structural order and bond lengths in aluminosilicates in the presence of Na2O and K2O; no specific trends were recorded. Significant differences were however observed in the location of these ions in the oxygen bonding networks. While Na+ ions were preferentially located in the bridging/non-bridging oxygen networks, K+ ions tended to be present in various oxygen tri-clusters. With increasing alkali concentrations, the total diffusion coefficients DTotal of Na2O-bearing system were found to increase, while an opposite trend was observed for K2O-bearing systems. Opposite trends observed in total diffusion coefficients of various ions in Na2O-bearing and K2O-bearing systems are expected to result in opposite trends in the viscosity as well. In addition to reproducing experimental trends, these simulations have helped identify key factors influencing the viscosities of aluminosilicates in the presence of alkalis.