A significant negative correlation was found between the SSA of PM and the concentration of H 2O and SO 2 in the off-gas, while a significant positive correlation was found between the SSA and the temperature of the off-gas, the concentration of dust in the off-gas, and the NO X generation during the process. The SSA was measured for the sampled PM and correlated to a selection of operational parameters. Silica fume samples were collected during several tapping cycles with varying flue gas recirculation (FGR) rates. Using a pilot-scale setup, the combustion gas for the silicon process was altered by recirculating different ratios of flue gas back to the furnace hood. Condensation products were only found when replacing O 2 with CO, where brown PM was formed through SiO reacting with SiO 2, SiC, and Si. PM formed at a holding temperature of 1650 ☌ was found to have a significantly higher SSA of 32.9 m 2/g compared to the SSA of 22.3 m 2/g formed at 1700 ☌ with the same gas mixtures. No significant difference between the particulate matter (PM) formed was found when replacing O 2 with CO 2 using a holding temperature of 1700 ☌, when measuring the specific surface area (SSA), particle size distribution, or carbon content. In the small-scale experiments, SiO gas was formed and reacted with four mixtures of nitrogen fixed at 79 vol %, oxygen, carbon dioxide, and carbon monoxide.
In this work, the effect of different combustion gas atmospheres on the properties of silica fume has been investigated through small-scale experiments and a pilot-scale experiment. Silica fume is an important byproduct from the silicon production process, with mainly concrete and refractory applications.
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