Molecular Dynamics Investigation on Coke Ash Behavior in the High-Temperature Zones of a Blast Furnace: Influence of Alkalis

With specific focus on local structural order, bonding networks, transport properties, and viscosity of the molten ash oxides, we report molecular dynamics simulations on the influence of alkalis (Na₂O and K₂O) on coke behavior within a blast furnace. Atomistic simulations were carried out on the Al₂O₃–SiO₂–CaO–K₂O–Na₂O system at 2223 K for a range and relative proportions of Na₂O and K₂O. Alkalis were seen to have a strong effect on the oxygen bonding networks; the relative proportions of bridging and nonbridging oxygen showed a sharp increase, while significant reductions were observed for tricluster oxygens. Total diffusion coefficients and viscosity showed a highly nonlinear dependence on the relative proportions of two alkalis with large changes observed in the simultaneous presence of alkalis as compared to their individual presence. Our studies have shown that the combined influence of alkalis on the viscosity of molten ash, and associated coke degradation within a blast furnace, is likely to be much smaller than previously perceived and could even be negligible for some alkali concentrations

ReaxFF Molecular Dynamics Simulation for the Graphitization of Amorphous Carbon: A Parametric Study

A parametric study of ReaxFF for molecular dynamics simulation of graphitization of amorphous carbon was conducted. The responses to different initial amorphous carbon configurations, simulation time steps, simulated temperatures, and ReaxFF parameter sets were investigated. The results showed that a time step shorter than 0.2 fs is sufficient for the ReaxFF simulation of carbon using both Chenoweth 2008 and Srinivasan 2015 parameter sets. The amorphous carbon networks produced using both parameter sets at 300 K are similar to each other, with the first peak positions of pair distribution function curves located between the graphite sp² bond peak position and the diamond sp³ bond peak position. In the graphitization process, the graphene fragment size increases and the orientation of graphene layers transforms to be parallel with each other with the increase of temperature and annealing time. This parallel graphene structure is close to the crystalline graphite. Associated with this graphitization is the presence of small voids and pores which arise because of the more efficient atomic packing relative to a disordered structure. For all initial densities, both potential parameter sets exhibit the expected behavior in which the sp² fraction increases significantly over time. The sp² fraction increases with increasing temperature. The differences of sp² fraction at different temperatures are more obvious in lower density at 1.4 g/cm³. When density is increased, the gap caused by different temperatures becomes small. This study indicates that both Chenoweth 2008 and Srinivasan 2015 potential sets are appropriate for molecular dynamics simulations in which the growth of graphitic structures is investigated