Effect of H₂O(g) and SO₂(g) on the volatilization and transformation of sodium during Xinjiang high-sodium coal combustion

Combustion experiment of Xinjiang coal with high sodium content was carried out in a horizontal tube furnace at 400-1 100℃. The occurrence of sodium in coal and ash was analyzed by sequential extraction method to study the release and transformation characteristics of sodium, especially the effect of H₂O(g) and SO₂(g) at 700℃ and 1 100℃. The results show that, the release ratio of sodium in coal increases gradually with the increase of temperature. The sodium in organic form vaporizes first, followed by water-soluble inorganic sodium, while the inorganic sodium in the form of aluminosilicate is difficult to vaporize due to high thermal stability. At lower temperature (700℃), H₂O(g) has a negative effect on the volatilization of sodium, while at higher temperature (1 100℃), the reductive atmosphere formed by the reaction of char and H₂O(g) promotes the volatilization of sodium. When the proportion of H₂O(g) is larger than 20% in inlet gas, the promotion effect of H₂O(g) is weakened. SO₂ can inhibit sodium volatilization, while the inhibiting effect of SO₂ becomes less significant as the temperature increases from 700℃ to 1 100℃. In the presence of both H₂O(g) and SO₂, the sodium volatilization at 700℃ is inhibited. The combination effect of H₂O(g) and SO₂ at 1 100℃ depends on its concentration. Under the atmosphere containing 20%H₂O and 2.0×10^-3 SO₂ the total volatilization ratio of sodium increases from 86% to 87.1%.