Migration mechanisms of sodium during high-sodium coal gasification

The formation of ultrafine particles containing Na is believed to be the primary cause of ash deposition during highsodium coal gasification. In this study, the migration and transformation of Na in various forms within high-sodium coal were investigated using a flat-flame reactor and thermodynamic calculations. The results indicate that Na primarily migrates into $P M_{0.1}$ via nucleation-condensation-collision mechanisms, whereas the distribution of residual Na within the $PM_{0.1-10}$ is governed by char fragmentation. Notably, Na accumulates predominantly at $0.0536 \mu \mathrm{m}$ and $0.0308 \mu \mathrm{m}$ under $15 \%$ and $30 \%$ water vapor conditions, suggesting that the accumulation of Na onto larger particles is inhibited as water vapor concentration increases. In the gas phase, Na primarily exists as NaCl, Na atom, and NaOH, accounting for 60.97% to 72.25%, 23.80% to $35.79 \%$, and $3.20 \%$ to $3.89 \%$, respectively. As water vapor concentrations rise, the concentrations of NaCl and NaOH decrease, while that of Na atoms increases. These insightful results offer crucial information for the mitigation of deposition and the control of pollutants.