Silicon-monoxide flames: the nucleation and condensation of silica fume

Abstract

Silica fume is a valuable by-product from the silicon and ferrosilicon production. It is therefore important to understand the impact on the silica fume quality when converting the furnace feed from fossil-based to renewable reduction materials. Using self-consistent numerical simulations of the nucleation and condensation process, we present a detailed study of the silica fume formation process. It is found that the most critical physical effect that determines the final particle size distribution is coalescence due to Brownian motion. Furthermore, it is crucial to use appropriate thermophysical parameters in order to reproduce reliable particle size distributions. Contrary to what has been done in previous studies on the same topic, this is now done by using reasonable expressions for surface energy, saturation pressure and the nucleation pre-exponential factor. It is also found that under conditions relevant to furnaces, the liberation of latent heat leads to an explosive chain reaction of particle nucleation and condensation when the first particles nucleate and start growing due to condensation. This process continues until the relative saturation pressure of silicon dioxide is reduced to unity. Finally, it is found that the Lagrangian approach for particle tracking is more flexible and accurate, and also more CPU efficient, than the Eulerian approach.